The International GPS Network for Charting the Evolving Global Reference Frame

NASA Technical Reports Server (NTRS)

Zumberge, J. F.; Heflin, M. B.; Lindqwister, U. J.; Neilan, R. E.; Watkins, M. M.

1995-01-01

The Telecommunications and Engineering Division of Caltech's Jet Propulsion Laboratory is funded by the National Aeronautics and Space Administration to play a variety of roles in applying the Global Positioning System (GPS) to geodesy and geodynamics. Among these are the operation of dozens of globally-distributed, permanently-operating Earth fixed GPS stations. This, and other applications are described.

Accuracy of Single Frequency GPS Observations Processing In Near Real-time With Use of Code Predicted Products

NASA Astrophysics Data System (ADS)

Wielgosz, P. A.

In this year, the system of active geodetic GPS permanent stations is going to be estab- lished in Poland. This system should provide GPS observations for a wide spectrum of users, especially it will be a great opportunity for surveyors. Many of surveyors still use cheaper, single frequency receivers. This paper focuses on processing of single frequency GPS observations only. During processing of such observations the iono- sphere plays an important role, so we concentrated on the influence of the ionosphere on the positional coordinates. Twenty consecutive days of GPS data from 2001 year were processed to analyze the accuracy of a derived three-dimensional relative vec- tor position between GPS stations. Observations from two Polish EPN/IGS stations: BOGO and JOZE were used. In addition to, a new test station - IGIK was created. In this paper, the results of single frequency GPS observations processing in near real- time are presented. Baselines of 15, 27 and 42 kilometers and sessions of 1, 2, 3, 4, and 6 hours long were processed. While processing we used CODE (Centre for Orbit De- termination in Europe, Bern, Switzerland) predicted products: orbits and ionosphere info. These products are available in real-time and enable near real-time processing. Software Bernese v. 4.2 for Linux and BPE (Bernese Processing Engine) mode were used. These results are shown with a reference to dual frequency weekly solution (the best solution). Obtained GPS positional time and GPS baseline length dependency accuracy is presented for single frequency GPS observations.

Integrating Continuous GPS Time Series and Geodetic Leveling Data to Estimate Secular Vertical Velocity of Taiwan

NASA Astrophysics Data System (ADS)

LAI, Y. R.; Hsu, Y. J.; You, R. J.

2017-12-01

GPS technique services as the most powerful method in monitoring crustal deformation owing to its advantage of temporal continuity. Geodetic leveling is also widely used not only in engineering but also in geophysics applicants due to its high precision in vertical datum determination and spatial continuity advantages. As widely known, the reference frames of GPS and geodetic leveling are different- the former refers to the reference ellipsoid (WGS84 ellipsoid) and the latter refers to the geoid. In order to combine vertical velocity fields from different datums, we decide to examine discrepancy between these two data sets. Moreover, GPS stations and benchmarks always do not locate at the same places. In place of using a spatial reduced function (Ching et.al, JGR, 2011) to find the discrepancy between them, we focused on comparing termporal variation of GPS vertical motions and geodetic leveling displacements. In this study, we analyzed the vertical velocity field from 238 GPS stations and 1634 benchmarks, including the time-period (2000 to 2015) influenced by postseismiceffects from 1999 Chi-Chi earthquake (Mw 7.6), 2003 Chengkung earthquake (Mw 6.8), and so on. After we thoroughly examined all the process and considered coseismic and postseismic deformation of significant earthquakes, we found that the discrepancy of vertical velocity of the GPS station and its nearby benchmarks is about 1 - 2 mm/yr, including several source of errors in data processing. We suggest that this discrepancy of vertical velocity field can be ignored as tolerable error, and two heterogeneous fields can be integrated together without any mathematical presumptions of spatial regression. The result shows that the western coast is suffering sever subsidence with rates up to 40 mm/yr; the Central Range of Taiwan is uplifting with rates about +10 mm/yr and active landslides with significant subsidence of 5-10 mm/yr in local area. A huge velocity contrast of 30 mm;/yr indicating east over west thrusting is shown across the Longitudinal Valley Fault. Estimation of vertical velocity from 2000 to 2015 is consistent with velocities from 2008 to 2015, indicating our modification process is not affected by the Chi-Chi earthquake (Mw 7.6).

Multi-geodetic characterization of the seasonal signal at the CERGA geodetic reference station, France

NASA Astrophysics Data System (ADS)

Mémin, Anthony; Viswanathan, Vishnu; Fienga, Agnes; Santamarìa-Gómez, Alvaro; Boy, Jean-Paul; Cavalié, Olivier; Deleflie, Florent; Exertier, Pierre; Bernard, Jean-Daniel; Hinderer, Jacques

2017-04-01

Crustal deformations due to surface-mass loading account for a significant part of the variability in geodetic time series. A perfect understanding of the loading signal observed by geodetic techniques should help in improving terrestrial reference frame (TRF) realizations. Yet, discrepancies between crustal motion estimates from models of surface-mass loading and observations are still too large so that no model is currently recommended by the IERS for reducing the observations. We investigate the discrepancy observed in the seasonal variations of the position at the CERGA station, South of France. We characterize the seasonal motions of the reference geodetic station CERGA from GNSS, SLR, LLR and InSAR. We investigate the consistency between the station motions deduced from these geodetic techniques and compare the observed station motion with that estimated using models of surface-mass change. In that regard, we compute atmospheric loading effects using surface pressure fields from ECMWF, assuming an ocean response according to the classical inverted barometer (IB) assumption, considered to be valid for periods typically exceeding a week. We also used general circulation ocean models (ECCO and GLORYS) forced by wind, heat and fresh water fluxes. The continental water storage is described using GLDAS/Noah and MERRA-land models. Using the surface-mass models, we estimate that the seasonal signal due to loading deformation at the CERGA station is about 8-9, 1-2 and 1-2 mm peak-to-peak in Up, North and East component, respectively. There is a very good correlation between GPS observations and non-tidal loading predicted deformation due to atmosphere, ocean and hydrology which is the main driver of seasonal signal at CERGA. Despite large error bars, LLR observations agree reasonably well with GPS and non-tidal loading predictions in Up component. Local deformation as observed by InSAR is very well correlated with GPS observations corrected for non-tidal loading. Finally, we estimate local mass changes using the absolute gravity measurement campaigns available at the station and the global models of surface-mass change. We compute the induced station motion that we compare with the local deformation observed by InSAR and GPS.

CGPS Implementation and Lidar/Laser Altimeter Experiences at l'Estartit, Ibiza and Barcelona Harbours for Sea Level Monitoring

NASA Astrophysics Data System (ADS)

Martinez-Benjamin, J.; Schutz, B.; Urban, T.; Ortiz Castellon, M.; Martinez-Garcia, M.; Ruiz, A.; Perez, B.; Rodriguez-Velasco, G.

2008-12-01

In the framework of a Spanish Space Project, the instrumentation of sea level measurements has been improved by providing the Barcelona site with a radar tide gauge and with a continuous GPS station nearby. The radar tide gauge is a Datamar 3000C device and a Thales Navigation Internet-Enabled GPS Continuous Geodetic Reference Station (iCGRS) with a choke ring antenna. It is intended that the overall system will constitute a CGPS Station of the ESEAS (European Sea Level) and TIGA (GPS Tide Gauge Benchmark Monitoring) networks. Puertos del Estado (Spanish Harbours) installed the tide gauge station at Ibiza harbour in January 2003. The station belongs to the REDMAR network, composed at this moment by 21 stations distributed along the whole Spanish waters, including also the Canary islands. The tide gauge also belongs to the ESEAS (European Sea Level) network. At the Barcelona harbour they have installed a radar tide gauge near a GPS station belonging to Puerto de Barcelona. L'Estartit floating tide gauge was set up in 1990. Data are taken in graphics registers from each two hours the mean value is recorded in an electronic support. L'Estartit tide gauge series provides good quality information about the changes in the sea heights at centimeter level, that is the magnitude of the common tides in the Mediterranean. Two airborne calibration campaigns carrying an Optech Lidar ALTM-3025 (ICC) were made on June 16, 2007 with a Partenavia P-68 and October 12, 2007, with a Cessna Caravan 208B flying along two ICESat target tracks including crossover near l'Estartit. The validation of this new technology LIDAR may be useful to fill coastal areas where satellite radar altimeters are not measuring due to the large footprint and the resulting gaps of about 15-30 km within the coastline. Measurements with a GPS Buoy at l'Estartit harbour were made during the June experience and a GPS reference station was installed in Aiguablava. On October 12, 2007, another LIDAR campaign was made at night at the same time of the ICESat overflying. A description of the actual geodetic CGPS infrastructures at Ibiza, l'Estartit and Barcelona is presented as their applications to sea level monitoring and altimeter calibration.

Navigation system and method

NASA Technical Reports Server (NTRS)

Taylor, R. E.; Sennott, J. W. (Inventor)

1984-01-01

In a global positioning system (GPS), such as the NAVSTAR/GPS system, wherein the position coordinates of user terminals are obtained by processing multiple signals transmitted by a constellation of orbiting satellites, an acquisition-aiding signal generated by an earth-based control station is relayed to user terminals via a geostationary satellite to simplify user equipment. The aiding signal is FSK modulated on a reference channel slightly offset from the standard GPS channel. The aiding signal identifies satellites in view having best geometry and includes Doppler prediction data as well as GPS satellite coordinates and identification data associated with user terminals within an area being served by the control station and relay satellite. The aiding signal significantly reduces user equipment by simplifying spread spectrum signal demodulation and reducing data processing functions previously carried out at the user terminals.

Geocenter Coordinates from a Combined Processing of LEO and Ground-based GPS Observations

NASA Astrophysics Data System (ADS)

Männel, Benjamin; Rothacher, Markus

2017-04-01

The GPS observations provided by the global IGS (International GNSS Service) tracking network play an important role for the realization of a unique terrestrial reference frame that is accurate enough to allow the monitoring of the Earth's system. Combining these ground-based data with GPS observations tracked by high-quality dual-frequency receivers on-board Low Earth Orbiters (LEO) might help to further improve the realization of the terrestrial reference frame and the estimation of the geocenter coordinates, GPS satellite orbits and Earth rotation parameters (ERP). To assess the scope of improvement, we processed a network of 50 globally distributed and stable IGS-stations together with four LEOs (GRACE-A, GRACE-B, OSTM/Jason-2 and GOCE) over a time interval of three years (2010-2012). To ensure fully consistent solutions the zero-difference phase observations of the ground stations and LEOs were processed in a common least-square adjustment, estimating GPS orbits, LEO orbits, station coordinates, ERPs, site-specific tropospheric delays, satellite and receiver clocks and ambiguities. We present the significant impact of the individual LEOs and a combination of all four LEOs on geocenter coordinates derived by using a translational approach (also called network shift approach). In addition, we present geocenter coordinates derived from the same set of GPS observations by using a unified approach. This approach combines the translational and the degree-one approach by estimating translations and surface deformations simultaneously. Based on comparisons against each other and against geocenter time series derived by other techniques the effect of the selected approach is assessed.

The UNAVCO Real-time GPS Data Processing System and Community Reference Data Sets

NASA Astrophysics Data System (ADS)

Sievers, C.; Mencin, D.; Berglund, H. T.; Blume, F.; Meertens, C. M.; Mattioli, G. S.

2013-12-01

UNAVCO has constructed a real-time GPS (RT-GPS) network of 420 GPS stations. The majority of the streaming stations come from the EarthScope Plate Boundary Observatory (PBO) through an NSF-ARRA funded Cascadia Upgrade Initiative that upgraded 100 backbone stations throughout the PBO footprint and 282 stations focused in the Pacific Northwest. Additional contributions from NOAA (~30 stations in Southern California) and the USGS (8 stations at Yellowstone) account for the other real-time stations. Based on community based outcomes of a workshop focused on real-time GPS position data products and formats hosted by UNAVCO in Spring of 2011, UNAVCO now provides real-time PPP positions for all 420 stations using Trimble's PIVOT software and for 50 stations using TrackRT at the volcanic centers located at Yellowstone (Figure 1 shows an example ensemble of TrackRT networks used in processing the Yellowstone data), Mt St Helens, and Montserrat. The UNAVCO real-time system has the potential to enhance our understanding of earthquakes, seismic wave propagation, volcanic eruptions, magmatic intrusions, movement of ice, landslides, and the dynamics of the atmosphere. Beyond its increasing uses for science and engineering, RT-GPS has the potential to provide early warning of hazards to emergency managers, utilities, other infrastructure managers, first responders and others. With the goal of characterizing stability and improving software and higher level products based on real-time GPS time series, UNAVCO is developing an open community standard data set where data processors can provide solutions based on common sets of RT-GPS data which simulate real world scenarios and events. UNAVCO is generating standard data sets for playback that include not only real and synthetic events but also background noise, antenna movement (e.g., steps, linear trends, sine waves, and realistic earthquake-like motions), receiver drop out and online return, interruption of communications (such as, bulk regional failures due to specific carriers during an actual event), satellites rising and setting, various constellation outages and differences in performance between real-time and simulated (retroactive) real-time. We present an overview of the UNAVCO RT-GPS system, a comparison of the UNAVCO generated real-time data products, and an overview of available common data sets.

Mapping the Coastline Limits of the Mexican State Sinaloa Using GPS

NASA Astrophysics Data System (ADS)

Vazquez, G. E.

2007-12-01

This research work presents the delimitation of the coastline limits of Sinaloa (one of the richest states of northwestern Mexico). In order to achieve this big task, it was required to use GPS (Global Positioning System) together with leveling spirit measurements. Based on the appropriate selection of the cited measurement techniques, the objective was to map the Sinaloa's state coastline to have the cartography of approximate 1600 km of littoral. The GPS measurements were performed and referred with respect to a GPS network located across the state. This GPS network consists of at least one first-order-site at each of the sixteen counties that constitute the state, and three to four second-order-sites of the ten counties of the state surrounded by sea. The leveling spirit measurements were referred to local benchmarks pre-established by the Mexican agency SEMARNAT (SEcretaría Del Medio Ambiente y Recursos NATurales). Within the main specifications of the GPS measurements and equipment, we used geodetic-dual-frequency GPS receivers in kinematic mode for both base stations (first and second order sites of the GPS state network) and rover stations (points forming the state littoral) with 5-sec log-rate interval and 10 deg cut-off angle. The GPS data processing was performed using the commercial software Trimble Geomatics Office (TGO) with Double Differences (DD) in post-processing mode. To this point, the field measurements had been totally covered including the cartography (scale 1:1000) and this includes the specifications and appropriate labeling according to the Mexican norm NOM-146-SEMARNAT-2005.

Quality assessment of DInSAR deformation measurements in volcanic areas by comparing GPS and SBAS results

NASA Astrophysics Data System (ADS)

Bonforte, A.; Casu, F.; de Martino, P.; Guglielmino, F.; Lanari, R.; Manzo, M.; Obrizzo, F.; Puglisi, G.; Sansosti, E.; Tammaro, U.

2009-04-01

Differential Synthetic Aperture Radar Interferometry (DInSAR) is a methodology able to measure ground deformation rates and time series of relatively large areas. Several different approaches have been developed over the past few years: they all have in common the capability to measure deformations on a relatively wide area (say 100 km by 100 km) with a high density of the measuring points. For these reasons, DInSAR represents a very useful tool for investigating geophysical phenomena, with particular reference to volcanic areas. As for any measuring technique, the knowledge of the attainable accuracy is of fundamental importance. In the case of DInSAR technology, we have several error sources, such as orbital inaccuracies, phase unwrapping errors, atmospheric artifacts, effects related to the reference point selection, thus making very difficult to define a theoretical error model. A practical way to obtain assess the accuracy is to compare DInSAR results with independent measurements, such as GPS or levelling. Here we present an in-deep comparison between the deformation measurement obtained by exploiting the DInSAR technique referred to as Small BAseline Subset (SBAS) algorithm and by continuous GPS stations. The selected volcanic test-sites are Etna, Vesuvio and Campi Flegrei, in Italy. From continuous GPS data, solutions are computed at the same days SAR data are acquired for direct comparison. Moreover, three dimensional GPS displacement vectors are projected along the radar line of sight of both ascending and descending acquisition orbits. GPS data are then compared with the coherent DInSAR pixels closest to the GPS station. Relevant statistics of the differences between the two measurements are computed and correlated to some scene parameter that may affect DInSAR accuracy (altitude, terrain slope, etc.).

Accurate Realization of GPS Vertical Global Reference Frame

NASA Technical Reports Server (NTRS)

Elosegui, Pedro

2005-01-01

The goal of this project is to improve our current understanding of GPS error sources associated with estimates of radial velocities at global scales. An improvement in the accuracy of radial global velocities would have a very positive impact on a large number of geophysical studies of current general interest such as global sea-level and climate change, coastal hazards, glacial isostatic adjustment, atmospheric and oceanic loading, glaciology and ice mass variability, tectonic deformation and volcanic inflation, and geoid variability. A set of GPS error sources relevant to this project are those related to the combination of the positions and velocities of a set of globally distributed stations as determined &om the analysis of GPS data, including possible methods of combining and defining terrestrial reference frames. This is were our research activities during this reporting period have concentrated. During this reporting period, we have researched two topics: (1) The effect of errors on the GPS satellite antenna models (or lack thereof) on global GPS vertical position and velocity estimates; (2) The effect of reference W e definition and practice on estimates of the geocenter variations.

Rigidity of Major Plates and Microplates Estimated From GPS Solution GPS2006.0

NASA Astrophysics Data System (ADS)

Kogan, M. G.; Steblov, G. M.

2006-05-01

Here we analyze the rigidity of eight major lithospheric plates using our global GPS solution GPS2006.0. We included all daily observations in interval 1995.0 to 2006.0 collected at IGS stations, as well as observations at many important stations not included in IGS. Loose multiyear solution GPS2006.0 is based on daily solutions by GAMIT software, performed at SOPAC and at Columbia University; those daily solutions were combined by Kalman filter (GLOBK software) into a loose multiyear solution. The constrained solution for station positions and velocities was obtained without a conventional reference frame; instead, we applied translation and rotation in order to best fit the zero velocities of 76 stations in stable plate cores excluding the regions of postglacial rebound. Simultaneously, we estimated relative plate rotation vectors (RV) and the origin translation rate (OTR), and then corrected station velocities for it. Therefore, the velocities in GPS2006.0 are unaffected by the OTR error of ITRF2000 conventionally used to constrain a loose solution. The 1-sigma plate-residual velocity in a stable plate core is less than 1 mm/yr for the plates: Eurasia, Pacific, North and South Americas, Nubia, Australia, and Antarctica; it is 1.4 mm/yr for the Indian plate, most probably because of poorer data quality. Plate-residuals at other established plates (Arabia, Nazca, Caribbean, Philippine) were not assessed for lack of observations. From our analysis, an upper bound for the mobility of the plate inner area is 1 mm/yr. Plate- residual GPS velocities for several hypothesized microplates in east Asia, such as Okhotsk, Amuria, South China, are 3-4 times higher; corresponding strain rates for these microplates are an order of magnitude higher than for Eurasia, North America, and other large plates.

Lessons Learned from Two Years of On-Orbit Global Positioning System Experience on International Space Station

NASA Technical Reports Server (NTRS)

Gomez, Susan F.; Lammers, Michael L.

2004-01-01

The Global Positioning System Subsystem (GPS) for International Space Station (ISS) was activated April 12,2002 following the installation of the SO truss segment that included the GPS antennas on Shuttle mission STS-110. The ISS GPS receiver became the primary source for position, velocity, and attitude information for ISS two days after activation. The GPS receiver also provides a time reference for manual control of ISS time, and will be used for automatic time updates after problems are resolved with the output from the receiver. After two years of on-orbit experience, the GPS continues to be used as the primary navigation source for ISS; however, enough problems have surfaced that the firmware in the GPS attitude code has had to be totally rewritten and new algorithms developed, the firmware that processed the time output from the GPS receiver had to be rewritten, while the GPS navigation code has had minor revisions. The factors contributing to the delivery of a GPS receiver for use on ISS that requires extensive operator intervention to function are discussed. Observations from two years worth of GPS solutions will also be discussed. The technical solutions to the anomalous GPS receiver behavior will be discussed.

Inferring Large-Scale Terrestrial Water Storage Through GRACE and GPS Data Fusion in Cloud Computing Environments

NASA Astrophysics Data System (ADS)

Rude, C. M.; Li, J. D.; Gowanlock, M.; Herring, T.; Pankratius, V.

2016-12-01

Surface subsidence due to depletion of groundwater can lead to permanent compaction of aquifers and damaged infrastructure. However, studies of such effects on a large scale are challenging and compute intensive because they involve fusing a variety of data sets beyond direct measurements from groundwater wells, such as gravity change measurements from the Gravity Recovery and Climate Experiment (GRACE) or surface displacements measured by GPS receivers. Our work therefore leverages Amazon cloud computing to enable these types of analyses spanning the entire continental US. Changes in groundwater storage are inferred from surface displacements measured by GPS receivers stationed throughout the country. Receivers located on bedrock are anti-correlated with changes in water levels from elastic deformation due to loading, while stations on aquifers correlate with groundwater changes due to poroelastic expansion and compaction. Correlating linearly detrended equivalent water thickness measurements from GRACE with linearly detrended and Kalman filtered vertical displacements of GPS stations located throughout the United States helps compensate for the spatial and temporal limitations of GRACE. Our results show that the majority of GPS stations are negatively correlated with GRACE in a statistically relevant way, as most GPS stations are located on bedrock in order to provide stable reference locations and measure geophysical processes such as tectonic deformations. Additionally, stations located on the Central Valley California aquifer show statistically significant positive correlations. Through the identification of positive and negative correlations, deformation phenomena can be classified as loading or poroelastic expansion due to changes in groundwater. This method facilitates further studies of terrestrial water storage on a global scale. This work is supported by NASA AIST-NNX15AG84G (PI: V. Pankratius) and Amazon.

Compact Integration of a GSM-19 Magnetic Sensor with High-Precision Positioning using VRS GNSS Technology

PubMed Central

Martín, Angel; Padín, Jorge; Anquela, Ana Belén; Sánchez, Juán; Belda, Santiago

2009-01-01

Magnetic data consists of a sequence of collected points with spatial coordinates and magnetic information. The spatial location of these points needs to be as exact as possible in order to develop a precise interpretation of magnetic anomalies. GPS is a valuable tool for accomplishing this objective, especially if the RTK approach is used. In this paper the VRS (Virtual Reference Station) technique is introduced as a new approach for real-time positioning of magnetic sensors. The main advantages of the VRS approach are, firstly, that only a single GPS receiver is needed (no base station is necessary), reducing field work and equipment costs. Secondly, VRS can operate at distances separated 50–70 km from the reference stations without degrading accuracy. A compact integration of a GSM-19 magnetometer sensor with a geodetic GPS antenna is presented; this integration does not diminish the operational flexibility of the original magnetometer and can work with the VRS approach. The coupled devices were tested in marshlands around Gandia, a city located approximately 100 km South of Valencia (Spain), thought to be the site of a Roman cemetery. The results obtained show adequate geometry and high-precision positioning for the structures to be studied (a comparison with the original low precision GPS of the magnetometer is presented). Finally, the results of the magnetic survey are of great interest for archaeological purposes. PMID:22574055

Progress in SLR-GPS co-location at San Juan (Argentina) station

NASA Astrophysics Data System (ADS)

Luis, Hernan; Rojas, Alvis; Adarvez, Sonia; Quinteros, Johana; Cobos, Pablo; Aracena, Andrés; Pacheco, Ana M.; Podestá, Ricardo; Actis, Eloy V.; Li, Jinzeng; Yin, Zhiqiang; Wang, Rui; Huang, Dongping; Márquez, Raúl

2012-08-01

From February, 2006, performing a Cooperation Agreement with National Astronomical Observatories of China (NAOC) of the Chinese Academy of Sciences (CAS), Observatorio Astronómico Félix Aguilar (OAFA) of Universidad Nacional de San Juan (UNSJ) is operating a SLR System (ILRS 7406 Station). From the beginning of 2012 a GPS Aztech - Micro Z CGRS is operative at the same place, which made the SLR - GPS co - location possible. The prior objective is to reach co - location between both techniques, so the Station became of 1st order in ITRF net. For that we study and adopt an appropriate strategy to select and place Survey Control Points that ensures higher precision in determination of 3D vectors between the selected reference point s. Afterwards we perform translocation tasks of receptor and antenna checking that the GPS verifies builder standards. Then we design and compensate survey control network, by means of software of our own draught. We expect to obtain definitive local ties with precision better than 3 mm, as suggested by IERS for co - located stations. There are very few stations with co - located spatial techniques in the Southern Hemisphere, so it is of great importance to have one in Argentina for improve our participation in IERS on the new realizations of ITRF from now on.

Evaluation of Integration Degree of the ASG-EUPOS Polish Reference Networks With Ukrainian GeoTerrace Network Stations in the Border Area

NASA Astrophysics Data System (ADS)

Siejka, Zbigniew

2017-09-01

GNSS systems are currently the basic tools for determination of the highest precision station coordinates (e.g. basic control network stations or stations used in the networks for geodynamic studies) as well as for land, maritime and air navigation. All of these tasks are carried out using active, large scale, satellite geodetic networks which are complex, intelligent teleinformatic systems offering post processing services along with corrections delivered in real-time for kinematic measurements. Many countries in the world, also in Europe, have built their own multifunctional networks and enhance them with their own GNSS augmentation systems. Nowadays however, in the era of international integration, there is a necessity to consider collective actions in order to build a unified system, covering e.g. the whole Europe or at least some of its regions. Such actions have already been undertaken in many regions of the world. In Europe such an example is the development for EUPOS which consists of active national networks built in central eastern European countries. So far experience and research show, that the critical areas for connecting these networks are border areas, in which the positioning accuracy decreases (Krzeszowski and Bosy, 2011). This study attempts to evaluate the border area compatibility of Polish ASG-EUPOS (European Position Determination System) reference stations and Ukrainian GeoTerrace system reference stations in the context of their future incorporation into the EUPOS. The two networks analyzed in work feature similar hardware parameters. In the ASG-EUPOS reference stations network, during the analyzed period, 2 stations (WLDW and CHEL) used only one system (GPS), while, in the GeoTerrace network, all the stations were equipped with both GPS and GLONASS receivers. The ASG EUPOS reference station network (95.6%) has its average completeness greater by about 6% when compared to the GeoTerrace network (89.8%).

An accurate Kriging-based regional ionospheric model using combined GPS/BeiDou observations

NASA Astrophysics Data System (ADS)

Abdelazeem, Mohamed; Çelik, Rahmi N.; El-Rabbany, Ahmed

2018-01-01

In this study, we propose a regional ionospheric model (RIM) based on both of the GPS-only and the combined GPS/BeiDou observations for single-frequency precise point positioning (SF-PPP) users in Europe. GPS/BeiDou observations from 16 reference stations are processed in the zero-difference mode. A least-squares algorithm is developed to determine the vertical total electron content (VTEC) bi-linear function parameters for a 15-minute time interval. The Kriging interpolation method is used to estimate the VTEC values at a 1 ° × 1 ° grid. The resulting RIMs are validated for PPP applications using GNSS observations from another set of stations. The SF-PPP accuracy and convergence time obtained through the proposed RIMs are computed and compared with those obtained through the international GNSS service global ionospheric maps (IGS-GIM). The results show that the RIMs speed up the convergence time and enhance the overall positioning accuracy in comparison with the IGS-GIM model, particularly the combined GPS/BeiDou-based model.

Integration Of Low-Cost Single-Frequency GPS Stations Using 'Spider' Technology Within Existing Dual-Frequency GPS Network at Soufrière Hills Volcano, Montserrat (West Indies): Processing And Results

NASA Astrophysics Data System (ADS)

Pascal, K.; Palamartchouk, K.; Lahusen, R. G.; Young, K.; Voight, B.

2015-12-01

Twenty years ago, began the eruption of the explosive Soufrière Hills Volcano, dominating the southern part of the island of Montserrat, West Indies. Five phases of effusive activity have now occurred, characterized by dome building and collapse, causing numerous evacuations and the emigration of half of the population. Over the years, the volcano monitoring network has greatly expanded. The GPS network, started from few geodetic markers, now consists of 14 continuous dual frequency GPS stations, distributed on and around the edifice, where topography and vegetation allow. The continuous GPS time series have given invaluable insight into the volcano behavior, notably revealing deflation/inflation cycles corresponding to phases and pauses of effusive activity, respectively. In 2014, collaboration of the CALIPSO Project (Penn State; NSF) with the Montserrat Volcano Observatory enriched the GPS and seismic monitoring networks with six 'spider' stations. The 'spiders', developed by R. Lahusen at Cascades Volcano Observatory, are designed to be deployed easily in rough areas and combine a low cost seismic station and a L1-only GPS station. To date, three 'spiders' have been deployed on Soufrière Hills Volcano, the closest at ~1 km from the volcanic conduit, adjacent to a lava lobe on the dome. Here we present the details of GPS data processing in a network consisting of both dual and single frequency receivers ('spiders') using GAMIT/GLOBK software. Processing together single and dual frequency data allowed their representation in a common reference frame, and a meaningful geophysical interpretation of all the available data. We also present the 'spiders' time series along with the results from the rest of the network and examine if any significant deformation, correlating with other manifestations of volcanic activity, has been recorded by the 'spiders' since deployment. Our results demonstrate that low cost GNSS equipment can serve as valuable components in volcano deformation monitoring networks.

A Precision, Low-Cost GPS-Based Transmitter Synchronization Scheme for Improved AM Reception

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, Stephen Fulton; Moore, Anthony

2009-01-01

This paper describes a highly accurate carrier-frequency synchronization scheme for actively, automatically locking multiple, remotely located AM broadcast transmitters to a common frequency/timing reference source such as GPS. The extremely tight frequency lock (to {approx}1 part in 10{sup 9} or better) permits the effective elimination of audible and even sub-audible beats between the local (desired) station's carrier signal and the distant stations carriers, usually received via skywave propagation during the evening and nighttime hours. These carrier-beat components cause annoying modulations of the desired station's audio at the receiver and concurrent distortion of the audio modulation from the distant station(s) andmore » often cause listeners to ldquotune outrdquo due to the low reception quality. Significant reduction or elimination of the beats and related effects will greatly enlarge the effective (interference-limited) listening area of the desired station (from 4 to 10 times as indicated in our tests) and simultaneously reduce the corresponding interference of the local transmitter to the distant stations as well. In addition, AM stereo (CQUAM) reception will be particularly improved by minimizing the phase shifts induced by co-channel interfering signals; hybrid digital (HD) signals will also benefit via reduction in beats from analog signals. The automatic frequency-control hardware described is inexpensive ($1000-$2000), requires no periodic recalibration, has essentially zero long-term drift, and could employ alternate wide-area frequency references of suitable accuracy, including broadcasts from WWVB, LORAN-C, and equivalent sources. The basic configuration of the GPS-disciplined oscillator which solves this problem is extremely simple. The main oscillator is a conventional high-stability quartz-crystal type. To counter long- term drifts, the oscillator is slightly adjusted to track a high-precision source of standard frequency obtained from a specialized GPS receiver (or other source), usually at 10.000 MHz. This very stable local reference frequency is then used as a clock for a standard digitally implemented frequency synthesizer, which is programmed to generate the specific carrier frequency desired. The stability of the disciplining source, typically {approx}1 part in 10{sup 9} to 10{sup 11}, is thus transferred to the final AM transmitter carrier output frequency.« less

A Contribution For The Understanding of The Deformation Pattern Across The Terceira Axis

NASA Astrophysics Data System (ADS)

Navarro, A.; Catalão, J.; Miranda, J. M.

In spite of several geodynamics studies performed in the Azores region, little is known about the deformation pattern of the tectonically more active sector around the Ter- ceira Axis. GPS campaigns performed in the area, in the last few years, were mainly concerned to the study of the relative motions between the Eurasian, African and North-American plates. This study, developed in the scope of the STAMINA project, has as main purpose the establishment of a dense GPS network to study the crustal deformation pattern in the area between the North Hirondelle basin and the East Gra- ciosa basin. The GPS network consists of 20 stations uniformly distributed throughout the island. The first GPS survey was carried out during days 90 to 98 of 2001. TERC and TCAT stations were used as reference stations, recording continuously throughout the survey. All the other stations were occupied for at least three sessions, except for cases of receiver malfunction, each session has a duration of 12 to 24 hours. The GPS data processing approach consisted of three main steps: (1) first, all sessions were processed separately using GAMIT in order to obtain a daily solution for two local sites (TERC and TCAT) and six global tracking stations (CCV3, RABT, SAV1, SFER, STJO and WSRT) using precise orbits from the IGS; (2) then, all stations of the local network are processed together and (3) finally, all station, including the global tracking ones, are reprocessed again. Precise orbits from the IGS were used in the processing. In each step a compensation program was used to compute a least squares network adjusted solution for the campaign, where all sessions are combined to yield estimates of improved station coordinates. The final solution achieved with the described methodology is documented in this paper. Further geodetic observations are needed in order to estimate the stations ve- locities and displacements and consequently to determine the rate of deformation of the island.

GPS IPW as a Meteorological Parameter and Climate Global Change Indicator

NASA Astrophysics Data System (ADS)

Kruczyk, M.; Liwosz, T.

2011-12-01

Paper focuses on comprehensive investigation of the GPS derived IPW (Integrated Precipitable Water, also IWV) as a geophysical tool. GPS meteorology is now widely acknowledged indirect method of atmosphere sensing. First we demonstrate GPS IPW quality. Most thorough inter-technique comparisons of directly measured IPW are attainable only for some observatories (note modest percentage of GPS stations equipped with meteorological devices). Nonetheless we have managed to compare IPW series derived from GPS tropospheric solutions (ZTD mostly from IGS and EPN solutions) and some independent techniques. IPW values from meteorological sources we used are: radiosoundings, sun photometer and input fields of numerical weather prediction model. We can treat operational NWP models as meteorological database within which we can calculate IWV for all GPS stations independently from network of direct measurements (COSMO-LM model maintained by Polish Institute of Meteorology and Water Management was tried). Sunphotometer (CIMEL-318, Central Geophysical Observatory IGF PAS, Belsk, Poland) data seems the most genuine source - so we decided for direct collocation of GPS measurements and sunphotometer placing permanent GPS receiver on the roof of Belsk Observatory. Next we analyse IPW as geophysical parameter: IPW demonstrates some physical effects evoked by station location (height and series correlation coefficient as a function of distance) and weather patterns like dominant wind directions (in case of neighbouring stations). Deficiency of surface humidity data to model IPW is presented for different climates. This inadequacy and poor humidity data representation in NWP model extremely encourages investigating information exchange potential between Numerical Model and GPS network. The second and most important aspect of this study concerns long series of IPW (daily averaged) which can serve as climatological information indicator (water vapour role in climate system is hard to exaggerate). Especially intriguing are relatively unique shape of such series in different climates. Long lasting changes in weather conditions: 'dry' and 'wet' years are also visible. The longer and more uniform our series are the better chance to estimate the magnitude of climatological IWV changes. Homogenous ZTD solution during long period is great concern in this approach (problems with GPS strategy and reference system changes). In case of continental network (EUREF Permanent Network) reliable data we get only after reprocessing. Simple sinusoidal model has been adjusted to the IPW series (LS method) for selected stations (mainly Europe but also other continents - IGS stations), every year separately. Not only amplitudes but also phases of annual signal differ from year to year. Longer IPW series (up to 14 years) searched for some climatological signal sometimes reveal weak steady trend. Large number of GPS permanent stations, relative easiness of IPW derivation (only and surface meteo data needed apart from GPS solution) and water vapour significance in water cycle and global climate make this GPS IPW promising element of global environmental change monitoring.

Detecting Tsunami Genesis and Scales Directly from Coastal GPS Stations

NASA Astrophysics Data System (ADS)

Song, Y. Tony

2013-04-01

Different from the conventional approach to tsunami warnings that rely on earthquake magnitude estimates, we have found that coastal GPS stations are able to detect continental slope displacements of faulting due to big earthquakes, and that the detected seafloor displacements are able to determine tsunami source energy and scales instantaneously. This method has successfully replicated several historical tsunamis caused by the 2004 Sumatra earthquake, the 2005 Nias earthquake, the 2010 Chilean earthquake, and the 2011 Tohoku-Oki earthquake, respectively, and has been compared favorably with the conventional seismic solutions that usually take hours or days to get through inverting seismographs (reference listed). Because many coastal GPS stations are already in operation for measuring ground motions in real time as often as once every few seconds, this study suggests a practical way of identifying tsunamigenic earthquakes for early warnings and reducing false alarms. Reference Song, Y. T., 2007: Detecting tsunami genesis and scales directly from coastal GPS stations, Geophys. Res. Lett., 34, L19602, doi:10.1029/2007GL031681. Song, Y. T., L.-L. Fu, V. Zlotnicki, C. Ji, V. Hjorleifsdottir, C.K. Shum, and Y. Yi, 2008: The role of horizontal impulses of the faulting continental slope in generating the 26 December 2004 Tsunami, Ocean Modelling, doi:10.1016/j.ocemod.2007.10.007. Song, Y. T. and S.C. Han, 2011: Satellite observations defying the long-held tsunami genesis theory, D.L. Tang (ed.), Remote Sensing of the Changing Oceans, DOI 10.1007/978-3-642-16541-2, Springer-Verlag Berlin Heidelberg. Song, Y. T., I. Fukumori, C. K. Shum, and Y. Yi, 2012: Merging tsunamis of the 2011 Tohoku-Oki earthquake detected over the open ocean, Geophys. Res. Lett., doi:10.1029/2011GL050767 (Nature Highlights, March 8, 2012).

Geocenter variations derived from a combined processing of LEO- and ground-based GPS observations

NASA Astrophysics Data System (ADS)

Männel, Benjamin; Rothacher, Markus

2017-08-01

GNSS observations provided by the global tracking network of the International GNSS Service (IGS, Dow et al. in J Geod 83(3):191-198, 2009) play an important role in the realization of a unique terrestrial reference frame that is accurate enough to allow a detailed monitoring of the Earth's system. Combining these ground-based data with GPS observations tracked by high-quality dual-frequency receivers on-board low earth orbiters (LEOs) is a promising way to further improve the realization of the terrestrial reference frame and the estimation of geocenter coordinates, GPS satellite orbits and Earth rotation parameters. To assess the scope of the improvement on the geocenter coordinates, we processed a network of 53 globally distributed and stable IGS stations together with four LEOs (GRACE-A, GRACE-B, OSTM/Jason-2 and GOCE) over a time interval of 3 years (2010-2012). To ensure fully consistent solutions, the zero-difference phase observations of the ground stations and LEOs were processed in a common least-squares adjustment, estimating all the relevant parameters such as GPS and LEO orbits, station coordinates, Earth rotation parameters and geocenter motion. We present the significant impact of the individual LEO and a combination of all four LEOs on the geocenter coordinates. The formal errors are reduced by around 20% due to the inclusion of one LEO into the ground-only solution, while in a solution with four LEOs LEO-specific characteristics are significantly reduced. We compare the derived geocenter coordinates w.r.t. LAGEOS results and external solutions based on GPS and SLR data. We found good agreement in the amplitudes of all components; however, the phases in x- and z-direction do not agree well.

Correction of clock errors in seismic data using noise cross-correlations

NASA Astrophysics Data System (ADS)

Hable, Sarah; Sigloch, Karin; Barruol, Guilhem; Hadziioannou, Céline

2017-04-01

Correct and verifiable timing of seismic records is crucial for most seismological applications. For seismic land stations, frequent synchronization of the internal station clock with a GPS signal should ensure accurate timing, but loss of GPS synchronization is a common occurrence, especially for remote, temporary stations. In such cases, retrieval of clock timing has been a long-standing problem. The same timing problem applies to Ocean Bottom Seismometers (OBS), where no GPS signal can be received during deployment and only two GPS synchronizations can be attempted upon deployment and recovery. If successful, a skew correction is usually applied, where the final timing deviation is interpolated linearly across the entire operation period. If GPS synchronization upon recovery fails, then even this simple and unverified, first-order correction is not possible. In recent years, the usage of cross-correlation functions (CCFs) of ambient seismic noise has been demonstrated as a clock-correction method for certain network geometries. We demonstrate the great potential of this technique for island stations and OBS that were installed in the course of the Réunion Hotspot and Upper Mantle - Réunions Unterer Mantel (RHUM-RUM) project in the western Indian Ocean. Four stations on the island La Réunion were affected by clock errors of up to several minutes due to a missing GPS signal. CCFs are calculated for each day and compared with a reference cross-correlation function (RCF), which is usually the average of all CCFs. The clock error of each day is then determined from the measured shift between the daily CCFs and the RCF. To improve the accuracy of the method, CCFs are computed for several land stations and all three seismic components. Averaging over these station pairs and their 9 component pairs reduces the standard deviation of the clock errors by a factor of 4 (from 80 ms to 20 ms). This procedure permits a continuous monitoring of clock errors where small clock drifts (1 ms/day) as well as large clock jumps (6 min) are identified. The same method is applied to records of five OBS stations deployed within a radius of 150 km around La Réunion. The assumption of a linear clock drift is verified by correlating OBS for which GPS-based skew corrections were available with land stations. For two OBS stations without skew estimates, we find clock drifts of 0.9 ms/day and 0.4 ms/day. This study salvages expensive seismic records from remote regions that would be otherwise lost for seismicity or tomography studies.

Study on common seasonal signals in GPS time series and environmental loadings using Multichannel Singular Spectrum Analysis

NASA Astrophysics Data System (ADS)

Gruszczynska, Marta; Rosat, Severine; Klos, Anna; Bogusz, Janusz

2017-04-01

Seasonal oscillations in the GPS position time series can arise from real geophysical effects and numerical artefacts. According to Dong et al. (2002) environmental loading effects can account for approximately 40% of the total variance of the annual signals in GPS time series, however using generally acknowledged methods (e.g. Least Squares Estimation, Wavelet Decomposition, Singular Spectrum Analysis) to model seasonal signals we are not able to separate real from spurious signals (effects of mismodelling aliased into annual period as well as draconitic). Therefore, we propose to use Multichannel Singular Spectrum Analysis (MSSA) to determine seasonal oscillations (with annual and semi-annual periods) from GPS position time series and environmental loading displacement models. The MSSA approach is an extension of the classical Karhunen-Loève method and it is a special case of SSA for multivariate time series. The main advantage of MSSA is the possibility to extract common seasonal signals for stations from selected area and to investigate the causality between a set of time series as well. In this research, we explored the ability of MSSA application to separate real geophysical effects from spurious effects in GPS time series. For this purpose, we used GPS position changes and environmental loading models. We analysed the topocentric time series from 250 selected stations located worldwide, delivered from Network Solution obtained by the International GNSS Service (IGS) as a contribution to the latest realization of the International Terrestrial Reference System (namely ITRF2014, Rebishung et al., 2016). We also researched atmospheric, hydrological and non-tidal oceanic loading models provided by the EOST/IPGS Loading Service in the Centre-of-Figure (CF) reference frame. The analysed displacements were estimated from ERA-Interim (surface pressure), MERRA-land (soil moisture and snow) as well as ECCO2 ocean bottom pressure. We used Multichannel Singular Spectrum Analysis to determine common seasonal signals in two case studies with adopted a 3-years lag-window as the optimal window size. We also inferred the statistical significance of oscillations through the Monte Carlo MSSA method (Allen and Robertson, 1996). In the first case study, we investigated the common spatio-temporal seasonal signals for all stations. For this purpose, we divided selected stations with respect to the continents. For instance, for stations located in Europe, seasonal oscillations accounts for approximately 45% of the GPS-derived data variance. Much higher variance of seasonal signals is explained by hydrological loadings of about 92%, while the non-tidal oceanic loading accounted for 31% of total variance. In the second case study, we analysed the capability of the MSSA method to establish a causality between several time series. Each of estimated Principal Component represents pattern of the common signal for all analysed data. For ZIMM station (Zimmerwald, Switzerland), the 1st, 2nd and 9th, 10th Principal Components, which accounts for 35% of the variance, corresponds to the annual and semi-annual signals. In this part, we applied the non-parametric MSSA approach to extract the common seasonal signals for GPS time series and environmental loadings for each of the 250 stations with clear statement, that some part of seasonal signal reflects the real geophysical effects. REFERENCES: 1. Allen, M. and Robertson, A.: 1996, Distinguishing modulated oscillations from coloured noise in multivariate datasets. Climate Dynamics, 12, No. 11, 775-784. DOI: 10.1007/s003820050142. 2. Dong, D., Fang, P., Bock, Y., Cheng, M.K. and Miyazaki, S.: 2002, Anatomy of apparent seasonal variations from GPS-derived site position time series. Journal of Geophysical Research, 107, No. B4, 2075. DOI: 10.1029/2001JB000573. 3. Rebischung, P., Altamimi, Z., Ray, J. and Garayt, B.: 2016, The IGS contribution to ITRF2014. Journal of Geodesy, 90, No. 7, 611-630. DOI:10.1007/s00190-016-0897-6.

The Terceira island (Azores) crustal deformations from GPS data

NASA Astrophysics Data System (ADS)

Navarro, A.; Catalão, J.; Fernandes, R.; Miranda, M.; Bastos, L.

2003-04-01

Several GPS campaigns performed, for the last few years, in the Azores region have proved the utility of GPS data in the evaluation of the relative motion among the Eurasian, North-American and African plates. The study here presented was developed in the scope of the STAMINA project. This project main intention is the study of the deformation pattern of the area along the Terceira Axis, which is considered nowadays as the most active tectonic area of the Azores region. To achieve that, a dense GPS network was implemented on the Terceira Island in October 2000. The network has 23 stations spread uniformly throughout the island, ten of which had already been implemented on 1999 (1 in 1988) in the scope of the TANGO project. These 10 stations were observed for the first time in 1999 and re-observed in 2000 and 2001. The complete network was observed for the first time in March/April of 2001. GPS data from 2 epochs, 1999 and 2001, were used to evaluate the horizontal deformation of the Island for a period of one and a half year. Both campaigns last for 9 days, each station being observed for at least 3 sessions of 12 to 24 hours. One of the stations, located at the Terceira Astronomic Observatory (TERC), was continuously measured during both campaigns. The data processing was performed using the GAMIT and FONDA software. Data from six IGS/EUREF permanent stations were considered to link the local network to the ITRF97 reference system. Precise orbits from the IGS were used in the GPS data processing. The results exhibit repeatabilities of about 3 mm and 2 mm for both components of the horizontal position, respectively for 1999 and 2001. The resulting estimation of the main strain rates for the Island indicates N, NNE and NE directions for the extension of the Island. However, these results are not yet conclusive due to the poor geometry of the 10 stations network and to the short interval of observation. To establish a more reliable deformation pattern for the Island, the 23 stations network are intended to be re-observed during 2003.

Dtection of Sea Level Rise within the Arabian Gulf Using Space Based GNSS Measurements and Insitu Tide Gauge data

NASA Astrophysics Data System (ADS)

Alothman, Abdulaziz; Ayhan, Mehmet

In the 21st century, sea level rise is expected to be about 30 cm or even more (up to 60 cm). Saudi Arabia has very long coasts of about 3400 km and hundreds of islands. Therefore, sea level monitoring may be important in particular along coastal low lands on Red Sea and Arabian Gulf coasts. Arabian Gulf is connected to Indian Ocean and lying along a parallel course in the south-west of the Zagros Trust Belt. We expect vertical land motion within the area due to both tectonic structures of the Arabian Peninsula and oil production activities. Global Navigation Satellite System (GNSS) Continues observations were used to estimate the vertical crustal motion. Bahrain International GPS Service (IGS-GPS) station is the only continuous GPS station accessible in the region, and it is close to the Mina Sulman tide gauge station in Bahrain. The weekly GPS time series of vertical component at Bahrain IGS-GPS station referring to the ITRF97 from 1999.2 to 2008.6 are used in the computation. We fitted a linear trend with an annual signal and a break to the GPS vertical time series and found a vertical land motion rate of 0.46 0.11 mm/yr. To investigate sea level variation within the west of Arabian Gulf, monthly means of sea level at 13 tide gauges along the coast of Saudi Arabia and Bahrain, available in the database of the Permanent Service for Mean Sea Level (PSMSL), are studied. We analyzed separately the monthly mean sea level measurements at each station, and estimated secular sea level rate by a robust linear trend fitting. We computed the average relative sea level rise rate of 1.96 0.21 mm/yr within the west of Arabian Gulf based on 4 stations spanning longer than 19 years. Sea level rates at the stations are first corrected for vertical land motion contamination using the ICE-5G v1.2 VM4 Glacial Isostatic Adjustment (GIA) model, and the average sea level rate is found 2.27 0.21 mm/yr. Assuming the vertical rate at Bahrain IGS-GPS station represents the vertical rate at each of the other tide gauge stations studied here in the region, we computed average sea level rise rate of 2.42 0.21 mm/yr within the west of Arabian Gulf.

Global and regional kinematics with GPS

NASA Technical Reports Server (NTRS)

King, Robert W.

1994-01-01

The inherent precision of the doubly differenced phase measurement and the low cost of instrumentation made GPS the space geodetic technique of choice for regional surveys as soon as the constellation reached acceptable geometry in the area of interest: 1985 in western North America, the early 1990's in most of the world. Instrument and site-related errors for horizontal positioning are usually less than 3 mm, so that the dominant source of error is uncertainty in the reference frame defined by the satellites orbits and the tracking stations used to determine them. Prior to about 1992, when the tracking network for most experiments was globally sparse, the number of fiducial sites or the level at which they could be tied to an SLR or VLBI reference frame usually, set the accuracy limit. Recently, with a global network of over 30 stations, the limit is set more often by deficiencies in models for non-gravitational forces acting on the satellites. For regional networks in the northern hemisphere, reference frame errors are currently about 3 parts per billion (ppb) in horizontal position, allowing centimeter-level accuracies over intercontinental distances and less than 1 mm for a 100 km baseline. The accuracy of GPS measurements for monitoring height variations is generally 2-3 times worse than for horizontal motions. As for VLBI, the primary source of error is unmodeled fluctuations in atmospheric water vapor, but both reference frame uncertainties and some instrument errors are more serious for vertical than horizontal measurements. Under good conditions, daily repeatabilities at the level of 10 mm rms were achieved. This paper will summarize the current accuracy of GPS measurements and their implication for the use of SLR to study regional kinematics.

International GPS Service 2001 - 2002 Technical Reports

NASA Technical Reports Server (NTRS)

Gowey, Ken (Editor); Neilan, Ruth (Editor); Moore, Angelyn (Editor)

2004-01-01

Applications of the Global Positioning System (GPS) to Earth Science are numerous. The International GPS Service (IGS), a federation of government agencies and universities, plays an increasingly critical role in support of GPS-related research and engineering activities. Contributions from the IGS Governing Board and Central Bureau, analysis and data centers, station operators, and others constitute the 2001 / 2002 Technical Reports. Hard copies of each volume can be obtained by contacting the IGS Central Bureau at the Jet Propulsion Laboratory. This report is published in black and white. To view graphs or plots that use color to represent data trends or information, please refer to the online PDF version at http://igscb.jpl.nasa.gov/overview/pubs.html.

GPS/REFSAT definition study report for low-cost terminals

NASA Technical Reports Server (NTRS)

1980-01-01

A relay transponder, located either on a satellite in geostationary orbit or on a local tower to relay acquisition-aiding data, ephemerides, etc, from a ground-based remote control station to a GPS civil user terminal located on a ship or land-transportation vehicle is described. Termed REFSAT (Reference Satellite), this concept reduces the circuit complexity and cost of user terminals. The various systems needed to implement the REFSAT concept for low-cost, GPS civil terminals are defined. The GPS/REFSAT system compatible with the NAVSTAR GPS system consists of a geostationary relay satellite, civil user terminals, and the central facility which performs operations common to all users for relay via the space segment. A GPS/REFSAT system utilizing a local tower for the relay transponder is described, results of a study of civil user requirements are presented, and specifications for the GPS/REFSAT system and its individual segments are included.

Subsidence and Fault Displacement Along the Long Point Fault Derived from Continuous GPS Observations (2012-2017)

NASA Astrophysics Data System (ADS)

Tsibanos, V.; Wang, G.

2017-12-01

The Long Point Fault located in Houston Texas is a complex system of normal faults which causes significant damage to urban infrastructure on both private and public property. This case study focuses on the 20-km long fault using high accuracy continuously operating global positioning satellite (GPS) stations to delineate fault movement over five years (2012 - 2017). The Long Point Fault is the longest active fault in the greater Houston area that damages roads, buried pipes, concrete structures and buildings and creates a financial burden for the city of Houston and the residents who live in close vicinity to the fault trace. In order to monitor fault displacement along the surface 11 permanent and continuously operating GPS stations were installed 6 on the hanging wall and 5 on the footwall. This study is an overview of the GPS observations from 2013 to 2017. GPS positions were processed with both relative (double differencing) and absolute Precise Point Positioning (PPP) techniques. The PPP solutions that are referred to IGS08 reference frame were transformed to the Stable Houston Reference Frame (SHRF16). Our results show no considerable horizontal displacements across the fault, but do show uneven vertical displacement attributed to regional subsidence in the range of (5 - 10 mm/yr). This subsidence can be associated to compaction of silty clays in the Chicot and Evangeline aquifers whose water depths are approximately 50m and 80m below the land surface (bls). These levels are below the regional pre-consolidation head that is about 30 to 40m bls. Recent research indicates subsidence will continue to occur until the aquifer levels reach the pre-consolidation head. With further GPS observations both the Long Point Fault and regional land subsidence can be monitored providing important geological data to the Houston community.

NGEE Arctic Plant Traits: Vegetation Plot Locations, Ecotypes, and Photos, Kougarok Road Mile Marker 64, Seward Peninsula, Alaska, 2016

DOE Office of Scientific and Technical Information (OSTI.GOV)

Colleen Iversen; Amy Breen; Verity Salmon

Data includes GPS waypoints for intensive plots, reference points, vegetation plots, and soil temperature/moisture monitoring stations that were established in July 2016 at the Kougarok hill slope located at Kougarok Road, Mile Marker 64. Photographs of all intensive plots and reference points are also included.

Ideas for Future GPS Timing Improvements

NASA Technical Reports Server (NTRS)

Hutsell, Steven T.

1996-01-01

Having recently met stringent criteria for full operational capability (FOC) certification, the Global Positioning System (GPS) now has higher customer expectations than ever before. In order to maintain customer satisfaction, and the meet the even high customer demands of the future, the GPS Master Control Station (MCS) must play a critical role in the process of carefully refining the performance and integrity of the GPS constellation, particularly in the area of timing. This paper will present an operational perspective on several ideas for improving timing in GPS. These ideas include the desire for improving MCS - US Naval Observatory (USNO) data connectivity, an improved GPS-Coordinated Universal Time (UTC) prediction algorithm, a more robust Kalman Filter, and more features in the GPS reference time algorithm (the GPS composite clock), including frequency step resolution, a more explicit use of the basic time scale equation, and dynamic clock weighting. Current MCS software meets the exceptional challenge of managing an extremely complex constellation of 24 navigation satellites. The GPS community will, however, always seek to improve upon this performance and integrity.

Accuracy of velocities from repeated GPS surveys: relative positioning is concerned

NASA Astrophysics Data System (ADS)

Duman, Huseyin; Ugur Sanli, D.

2016-04-01

Over more than a decade, researchers have been interested in studying the accuracy of GPS positioning solutions. Recently, reporting the accuracy of GPS velocities has been added to this. Researchers studying landslide motion, tectonic motion, uplift, sea level rise, and subsidence still report results from GPS experiments in which repeated GPS measurements from short sessions are used. This motivated some other researchers to study the accuracy of GPS deformation rates/velocities from various repeated GPS surveys. In one of the efforts, the velocity accuracy was derived from repeated GPS static surveys using short observation sessions and Precise Point Positioning mode of GPS software. Velocities from short GPS sessions were compared with the velocities from 24 h sessions. The accuracy of velocities was obtained using statistical hypothesis testing and quantifying the accuracy of least squares estimation models. The results reveal that 45-60 % of the horizontal and none of the vertical solutions comply with the results from 24 h solutions. We argue that this case in which the data was evaluated using PPP should also apply to the case in which the data belonging to long GPS base lengths is processed using fundamental relative point positioning. To test this idea we chose the two IGS stations ANKR and NICO and derive their velocities from the reference stations held fixed in the stable EURASIAN plate. The University of Bern's GNSS software BERNESE was used to produce relative positioning solutions, and the results are compared with those of GIPSY/OASIS II PPP results. First impressions indicate that it is worth designing a global experiment and test these ideas in detail.

Three decades of harnessing the GPS data explosion for geophysics (Vening Meinesz Medal Lecture)

NASA Astrophysics Data System (ADS)

Blewitt, Geoffrey

2015-04-01

In this presentation, I attempt to convey the immensity of the task that faced the geodesy community three decades ago, and continues to challenge us, to harness all potentially valuable GPS data available in the world for geophysical science. It would be fair to see that three decades ago, we were struggling with controlled tests just to get GPS geodesy working, and had little time to imagine the flood of data today. Yet the geodesy community has succeeded in meeting this challenge. Today, for example, the Nevada Geodetic Laboratory produces and makes publicly available coordinate time series for over 12,000 geodetic GPS station around the globe with various data intervals, latencies, and reference frames. About 8,000 stations have their daily time series updated every week, with 4,000 being updated the next day with coordinates at daily and 5 minute intervals. About 2,000 stations have their time series updated every hour with coordinates at 5 minute intervals. I will show examples of how these time series are being used by NGL and many other scientists to study a wide variety of geophysical topics, including plate tectonics, earthquake modeling, seismic and tsunami hazard, volcanic deformation, water resources, mountain growth, terrestrial reference frame realization, glacial isostatic adjustment, ice sheet melting, sea level rise and coastal subsidence, and even fundamental physics, using GPS atomic clocks to probe the nature of dark matter in the universe. The explosion in GPS data has challenged us to invent new data processing algorithms and develop robust automation in order to keep up with the flood. This explosion has been exponential, and therefore it can be said that it is not a recent phenomena, but rather that it began in the earliest years of GPS geodesy, and has always posed a challenge to us. Over the course of my post-doctoral career starting in late 1985, I have had the good fortune to witness the key developments that have taken place since the early years of geodetic GPS and over the course of three decades. These developments continue today as strongly as ever. Essential innovations have included, for example, automation of GPS cycle slip detection and mitigation, carrier phase ambiguity resolution, the birth and operation of the IGS for reliable orbit and clock estimation, the invention of algorithms that scale linearly with the number of stations, and the deep integration of GPS solutions into the ITRF, providing measures of accuracy, precision, and stability. As a recent example of automation, I show a new non-parametric algorithm to estimate station velocities quickly and robustly, without need to detect and correct for outliers, seasonal signals, and discontinuities in the time series steps that commonly occur due to equipment changes. The complete automation from data collection to production of station velocities (and, now, velocity time series) allows us to process all potentially valuable data, and to focus more on discovery and analysis of the results for geophysical applications, often with great redundancy in the data leading to high statistical significance and more robust scientific conclusions. I show by example that another benefit of this capability to process all data in a robust turn-key fashion is to enhance the opportunity for making discoveries, without necessarily planning all of the steps that can lead us to discovery's door.

GPS Monitor Station Upgrade Program at the Naval Research Laboratory

NASA Technical Reports Server (NTRS)

Galysh, Ivan J.; Craig, Dwin M.

1996-01-01

One of the measurements made by the Global Positioning System (GPS) monitor stations is to measure the continuous pseudo-range of all the passing GPS satellites. The pseudo-range contains GPS and monitor station clock errors as well as GPS satellite navigation errors. Currently the time at the GPS monitor station is obtained from the GPS constellation and has an inherent inaccuracy as a result. Improved timing accuracy at the GPS monitoring stations will improve GPS performance. The US Naval Research Laboratory (NRL) is developing hardware and software for the GPS monitor station upgrade program to improve the monitor station clock accuracy. This upgrade will allow a method independent of the GPS satellite constellation of measuring and correcting monitor station time to US Naval Observatory (USNO) time. THe hardware consists of a high performance atomic cesium frequency standard (CFS) and a computer which is used to ensemble the CFS with the two CFS's currently located at the monitor station by use of a dual-mixer system. The dual-mixer system achieves phase measurements between the high-performance CFS and the existing monitor station CFS's to within 400 femtoseconds. Time transfer between USNO and a given monitor station is achieved via a two way satellite time transfer modem. The computer at the monitor station disciplines the CFS based on a comparison of one pulse per second sent from the master site at USNO. The monitor station computer is also used to perform housekeeping functions, as well as recording the health status of all three CFS's. This information is sent to the USNO through the time transfer modem. Laboratory time synchronization results in the sub nanosecond range have been observed and the ability to maintain the monitor station CFS frequency to within 3.0 x 10 (sup minus 14) of the master site at USNO.

A Demonstration of GPS Landslide Monitoring Using Online Positioning User Service (OPUS)

NASA Astrophysics Data System (ADS)

Wang, G.

2011-12-01

Global Positioning System (GPS) technologies have been frequently applied to landslide study, both as a complement, and as an alternative to conventional surveying methods. However, most applications of GPS for landslide monitoring have been limited to the academic community for research purposes. High-accuracy GPS has not been widely equipped in geotechnical companies and used by technicians. The main issue that limits the applications of GPS in the practice of high-accuracy landslide monitoring is the complexity of GPS data processing. This study demonstrated an approach using the Online Positioning User Service (OPUS) (http://www.ngs.noaa.gov/OPUS) provided by the National Geodetic Survey (NGS) of National Oceanic and Atmospheric Administration (NOAA) to process GPS data and conduct long-term landslide monitoring in the Puerto Rico and Virgin Islands Region. Continuous GPS data collected at a creeping landslide site during two years were used to evaluate different scenarios for landslide surveying: continuous or campaign, long duration or short duration, morning or afternoon (different weather conditions). OPUS uses Continuously Operating Reference Station (CORS) managed by NGS (http://www.ngs.noaa.giv/CORS/) as references and user data as a rover to solve a position. There are 19 CORS permanent GPS stations in the Puerto Rico and Virgin Islands region. The dense GPS network provides a precise and reliable reference frame for subcentimeter-accuracy landslide monitoring in this region. Our criterion for the accuracy was the root-mean-square (RMS) of OPUS solutions over a 2-year period with respect to true landslide displacement time series overt the same period. The true landslide displacements were derived from a single-baseline (130 m) GPS processing by using 24-hour continuous data. If continuous GPS surveying is performed in the field, then OPUS static processing can provide 0.6 cm horizontal and 1.1 cm vertical precision with few outliers. If repeated campaign-style surveying is performed in the field, then the choice of observation time window and duration are very important. In order to detect a suspected sliding mass and track the kinematics of a creeping landslide, sub-centimeter horizontal accuracy is often required. OPUS static solutions for sessions of 4 hours or longer and OPUS rapid-static solutions for sessions as short as 15 minutes can achieve accuracy at this level if data collection during extreme weather conditions is avoided, such as rainfall and storm time. This study also indicated that rainfall events can seriously degrade the performance of high-accuracy GPS. Field GPS landslide surveying should avoid rainfall time that is usually accompanied by thunderstorms and the passage of weather fronts.

Strategic planning of INA-CORS development for public service and tectonic deformation study

NASA Astrophysics Data System (ADS)

Syetiawan, Agung; Gaol, Yustisi Ardhitasari Lumban; Safi'i, Ayu Nur

2017-07-01

GPS technology can be applied for surveying, mapping and research purposes. The simplicity of GPS technology for positioning make it become the first choice for survey compared with another positioning method. GPS can measure a position with various accuracy level based on the measurement method. In order to facilitate the GPS positioning, many organizations are establishing permanent GPS station. National Geodetic Survey (NGS) called it as Continuously Operating Reference Stations (CORS). Those devices continuously collect and record GPS data to be used by users. CORS has been built by several government agencies for particular purposes and scattered throughout Indonesia. Geospatial Information Agency (BIG) as a geospatial information providers begin to compile a grand design of Indonesia CORS (INA-CORS) that can be used for public service such as Real Time Kinematic (RTK), RINEX data request, or post-processing service and for tectonic deformation study to determine the deformation models of Indonesia and to evaluate the national geospatial reference system. This study aims to review the ideal location to develop CORS network distribution. The method was used is to perform spatial analysis on the data distribution of BIG and BPN CORS overlayed with Seismotectonic Map of Indonesia and land cover. The ideal condition to be achieved is that CORS will be available on each radius of 50 km. The result showed that CORS distribution in Java and Nusa Tenggara are already tight while on Sumatra, Celebes and Moluccas are still need to be more tighten. Meanwhile, the development of CORS in Papua will encounter obstacles toward road access and networking. This analysis result can be used as consideration for determining the priorities of CORS development in Indonesia.

Automated daily processing of more than 1000 ground-based GPS receivers for studying intense ionospheric storms

NASA Astrophysics Data System (ADS)

Komjathy, Attila; Sparks, Lawrence; Wilson, Brian D.; Mannucci, Anthony J.

2005-12-01

As the number of ground-based and space-based receivers tracking the Global Positioning System (GPS) satellites steadily increases, it is becoming possible to monitor changes in the ionosphere continuously and on a global scale with unprecedented accuracy and reliability. As of August 2005, there are more than 1000 globally distributed dual-frequency GPS receivers available using publicly accessible networks including, for example, the International GPS Service and the continuously operating reference stations. To take advantage of the vast amount of GPS data, researchers use a number of techniques to estimate satellite and receiver interfrequency biases and the total electron content (TEC) of the ionosphere. Most techniques estimate vertical ionospheric structure and, simultaneously, hardware-related biases treated as nuisance parameters. These methods often are limited to 200 GPS receivers and use a sequential least squares or Kalman filter approach. The biases are later removed from the measurements to obtain unbiased TEC. In our approach to calibrating GPS receiver and transmitter interfrequency biases we take advantage of all available GPS receivers using a new processing algorithm based on the Global Ionospheric Mapping (GIM) software developed at the Jet Propulsion Laboratory. This new capability is designed to estimate receiver biases for all stations. We solve for the instrumental biases by modeling the ionospheric delay and removing it from the observation equation using precomputed GIM maps. The precomputed GIM maps rely on 200 globally distributed GPS receivers to establish the "background" used to model the ionosphere at the remaining 800 GPS sites.

The application of GPS precise point positioning technology in aerial triangulation

NASA Astrophysics Data System (ADS)

Yuan, Xiuxiao; Fu, Jianhong; Sun, Hongxing; Toth, Charles

In traditional GPS-supported aerotriangulation, differential GPS (DGPS) positioning technology is used to determine the 3-dimensional coordinates of the perspective centers at exposure time with an accuracy of centimeter to decimeter level. This method can significantly reduce the number of ground control points (GCPs). However, the establishment of GPS reference stations for DGPS positioning is not only labor-intensive and costly, but also increases the implementation difficulty of aerial photography. This paper proposes aerial triangulation supported with GPS precise point positioning (PPP) as a way to avoid the use of the GPS reference stations and simplify the work of aerial photography. Firstly, we present the algorithm for GPS PPP in aerial triangulation applications. Secondly, the error law of the coordinate of perspective centers determined using GPS PPP is analyzed. Thirdly, based on GPS PPP and aerial triangulation software self-developed by the authors, four sets of actual aerial images taken from surveying and mapping projects, different in both terrain and photographic scale, are given as experimental models. The four sets of actual data were taken over a flat region at a scale of 1:2500, a mountainous region at a scale of 1:3000, a high mountainous region at a scale of 1:32000 and an upland region at a scale of 1:60000 respectively. In these experiments, the GPS PPP results were compared with results obtained through DGPS positioning and traditional bundle block adjustment. In this way, the empirical positioning accuracy of GPS PPP in aerial triangulation can be estimated. Finally, the results of bundle block adjustment with airborne GPS controls from GPS PPP are analyzed in detail. The empirical results show that GPS PPP applied in aerial triangulation has a systematic error of half-meter level and a stochastic error within a few decimeters. However, if a suitable adjustment solution is adopted, the systematic error can be eliminated in GPS-supported bundle block adjustment. When four full GCPs are emplaced in the corners of the adjustment block, then the systematic error is compensated using a set of independent unknown parameters for each strip, the final result of the bundle block adjustment with airborne GPS controls from PPP is the same as that of bundle block adjustment with airborne GPS controls from DGPS. Although the accuracy of the former is a little lower than that of traditional bundle block adjustment with dense GCPs, it can still satisfy the accuracy requirement of photogrammetric point determination for topographic mapping at many scales.

The Navstar GPS master control station's Kalman filter experience

NASA Technical Reports Server (NTRS)

Scardera, Michael P.

1990-01-01

The Navstar Global Positioning System (GPS) is a highly accurate space based navigation system providing all weather, 24 hour a day service to both military and civilian users. The system provides a Gaussian position solution with four satellites, each providing its ephemeris and clock offset with respect to GPS time. The GPS Master Clock Station (MCS) is charged with tracking each Navstar spacecraft and precisely defining the ephemeris and clock parameters for upload into the vehicle's navigation message. Briefly described here are the Navstar system and the Kalman filter estimation process used by MCS to determine, predict, and ensure quality control for each of the satellite's ephemeris and clock states. Routine performance is shown. Kalman filter reaction and response is discussed for anomalous clock behavior and trajectory perturbations. Particular attention is given to MCS efforts to improve orbital adjust modeling. The satellite out of service time due to orbital maneuvering has been reduced in the past year from four days to under twelve hours. The planning, reference trajectory model, and Kalman filter management improvements are explained.

Link calibration against receiver calibration: an assessment of GPS time transfer uncertainties

NASA Astrophysics Data System (ADS)

Rovera, G. D.; Torre, J.-M.; Sherwood, R.; Abgrall, M.; Courde, C.; Laas-Bourez, M.; Uhrich, P.

2014-10-01

We present a direct comparison between two different techniques for the relative calibration of time transfer between remote time scales when using the signals transmitted by the Global Positioning System (GPS). Relative calibration estimates the delay of equipment or the delay of a time transfer link with respect to reference equipment. It is based on the circulation of some travelling GPS equipment between the stations in the network, against which the local equipment is measured. Two techniques can be considered: first a station calibration by the computation of the hardware delays of the local GPS equipment; second the computation of a global hardware delay offset for the time transfer between the reference points of two remote time scales. This last technique is called a ‘link’ calibration, with respect to the other one, which is a ‘receiver’ calibration. The two techniques require different measurements on site, which change the uncertainty budgets, and we discuss this and related issues. We report on one calibration campaign organized during Autumn 2013 between Observatoire de Paris (OP), Paris, France, Observatoire de la Côte d'Azur (OCA), Calern, France, and NERC Space Geodesy Facility (SGF), Herstmonceux, United Kingdom. The travelling equipment comprised two GPS receivers of different types, along with the required signal generator and distribution amplifier, and one time interval counter. We show the different ways to compute uncertainty budgets, leading to improvement factors of 1.2 to 1.5 on the hardware delay uncertainties when comparing the relative link calibration to the relative receiver calibration.

Study of Ground Subsidence in North West Houston using GPS, LiDAR and InSAR techniques

NASA Astrophysics Data System (ADS)

Karacay, A.; Khan, S. D.

2012-12-01

Land subsidence can be caused by natural or human activities, such as carbonate dissolution, extraction of material from mines, soil compaction and fluid withdrawal. This phenomenon affects many cities around the world, such as Nagoya-Japan, Venice-Italy, San Joaquin Valley and Long Beach in California. Recent work by Engelkemeir et al, (2010), suggested that subsidence occurred as high as 5.6 cm/year in northwest Houston. The processes that may contribute to land subsidence in the Houston-Galveston area includes faulting, soil compaction, salt tectonic, water pumping and hydrocarbon extraction. This study aims to assess the possible role of water pumping on subsidence. Northwest Houston has two aquifer systems, the Evangeline and Chicot aquifers that dip in the southeast direction. The effect of water pumping on subsidence from these two aquifers was monitored using InSAR, GPS and LiDAR data. The data from eleven GPS stations were processed using Online Positioning User Service (OPUS) of National Geodetic Survey (NGS). Three of these GPS stations are Continuously Operating Reference Stations (CORS) and eight are Port-A-Measure (PAM) sites. All the GPS data were obtained from Harris-Galveston Subsidence District (HGSD). CORS sites were used as reference stations for processing GPS data from the PAM stations. GPS data show that subsidence rate in northwest Houston decreased to approximately 2 cm/year. In addition, the surface deformation is also estimated using Light Detection and Ranging (LiDAR) technique. For this purpose, raw LiDAR (LAS-Long ASCII Standart) files of 2001 and 2008 were processed. The subsidence rate near the Hockley Fault was calculated by applying zonal statistics method on LiDAR data which shows about 10 cm of subsidence in nine years. This result is supported by processed GPS data from PAM site 48 that show subsidence rate of 1.3 cm/yr. For the InSAR (Interferometric Synthetic Aperture Radar) technique, an image pair of PALSAR (The Phased Array type L-band Synthetic Aperture Radar) for 2008 was processed using Sarscape ENVI. The result demonstrates both uplift (approximately 5 mm near the Tomball salt dome) and subsidence (approximately 5.3 mm on the west part of Tomball region). In order to improve results, other image pairs from PALSAR, ERS1/2 and ENVISAT are being processed to monitor surface changes before and after 2000. Changes of groundwater level in the study area were observed, in order to distinguish the amount of land subsidence caused by groundwater withdrawal. The groundwater historical observation data were taken from The USGS National Water Information System (NWIS). The results of the groundwater level between 1990 and 2011 show approximately 0.5 m per year of water decline in the study area. Results of these complementary techniques will help in assessing the possible role of the water pumping from the subsurface on the subsidence in the area.

Analysis of meteorological variables in the Australasian region using ground- and space-based GPS techniques

NASA Astrophysics Data System (ADS)

Kuleshov, Yuriy; Choy, Suelynn; Fu, Erjiang Frank; Chane-Ming, Fabrice; Liou, Yuei-An; Pavelyev, Alexander G.

2016-07-01

Results of analysis of meteorological variables (temperature and moisture) in the Australasian region using the global positioning system (GPS) radio occultation (RO) and GPS ground-based observations verified with in situ radiosonde (RS) data are presented. The potential of using ground-based GPS observations for retrieving column integrated precipitable water vapour (PWV) over the Australian continent has been demonstrated using the Australian ground-based GPS reference stations network. Using data from the 15 ground-based GPS stations, the state of the atmosphere over Victoria during a significant weather event, the March 2010 Melbourne storm, has been investigated, and it has been shown that the GPS observations has potential for monitoring the movement of a weather front that has sharp moisture contrast. Temperature and moisture variability in the atmosphere over various climatic regions (the Indian and the Pacific Oceans, the Antarctic and Australia) has been examined using satellite-based GPS RO and in situ RS observations. Investigating recent atmospheric temperature trends over Antarctica, the time series of the collocated GPS RO and RS data were examined, and strong cooling in the lower stratosphere and warming through the troposphere over Antarctica has been identified, in agreement with outputs of climate models. With further expansion of the Global Navigation Satellite Systems (GNSS) system, it is expected that GNSS satellite- and ground-based measurements would be able to provide an order of magnitude larger amount of data which in turn could significantly advance weather forecasting services, climate monitoring and analysis in the Australasian region.

Earth Rotation Parameter Solutions using BDS and GPS Data from MEGX Network

NASA Astrophysics Data System (ADS)

Xu, Tianhe; Yu, Sumei; Li, Jiajing; He, Kaifei

2014-05-01

Earth rotation parameters (ERPs) are necessary parameters to achieve mutual transformation of the celestial reference frame and earth-fix reference frame. They are very important for satellite precise orbit determination (POD), high-precision space navigation and positioning. In this paper, the determination of ERPs including polar motion (PM), polar motion rate (PMR) and length of day (LOD) are presented using BDS and GPS data of June 2013 from MEGX network based on least square (LS) estimation with constraint condition. BDS and GPS data of 16 co-location stations from MEGX network are the first time used to estimate the ERPs. The results show that the RMSs of x and y component errors of PM and PM rate are about 0.9 mas, 1.0 mas, 0.2 mas/d and 0.3 mas/d respectively using BDS data. The RMS of LOD is about 0.03 ms/d using BDS data. The RMSs of x and y component errors of PM and PM rate are about 0.2 mas, 0.2 mas/d respectively using GPS data. The RMS of LOD is about 0.02 ms/d using GPS data. The optimal relative weight is determined by using variance component estimation when combining BDS and GPS data. The accuracy improvements of adding BDS data is between 8% to 20% for PM and PM rate. There is no obvious improvement in LOD when BDS data is involved. System biases between BDS and GPS are also resolved per station. They are very stable from day to day with the average accuracy of about 20 cm. Keywords: Earth rotation parameter; International GNSS Service; polar motion; length of day; least square with constraint condition Acknowledgments: This work was supported by Natural Science Foundation of China (41174008) and the Foundation for the Author of National Excellent Doctoral Dissertation of China (2007B51) .

Reduction of ZTD outliers through improved GNSS data processing and screening strategies

NASA Astrophysics Data System (ADS)

Stepniak, Katarzyna; Bock, Olivier; Wielgosz, Pawel

2018-03-01

Though Global Navigation Satellite System (GNSS) data processing has been significantly improved over the years, it is still commonly observed that zenith tropospheric delay (ZTD) estimates contain many outliers which are detrimental to meteorological and climatological applications. In this paper, we show that ZTD outliers in double-difference processing are mostly caused by sub-daily data gaps at reference stations, which cause disconnections of clusters of stations from the reference network and common mode biases due to the strong correlation between stations in short baselines. They can reach a few centimetres in ZTD and usually coincide with a jump in formal errors. The magnitude and sign of these biases are impossible to predict because they depend on different errors in the observations and on the geometry of the baselines. We elaborate and test a new baseline strategy which solves this problem and significantly reduces the number of outliers compared to the standard strategy commonly used for positioning (e.g. determination of national reference frame) in which the pre-defined network is composed of a skeleton of reference stations to which secondary stations are connected in a star-like structure. The new strategy is also shown to perform better than the widely used strategy maximizing the number of observations available in many GNSS programs. The reason is that observations are maximized before processing, whereas the final number of used observations can be dramatically lower because of data rejection (screening) during the processing. The study relies on the analysis of 1 year of GPS (Global Positioning System) data from a regional network of 136 GNSS stations processed using Bernese GNSS Software v.5.2. A post-processing screening procedure is also proposed to detect and remove a few outliers which may still remain due to short data gaps. It is based on a combination of range checks and outlier checks of ZTD and formal errors. The accuracy of the final screened GPS ZTD estimates is assessed by comparison to ERA-Interim reanalysis.

Terrestrial Reference Frame from GPS and SLR

NASA Astrophysics Data System (ADS)

Weiss, Jan; Bertiger, Willy; Desai, Shailen; Haines, Bruce; Sibois, Aurore

2015-04-01

We present strategies for realizing the terrestrial reference frame (TRF) using tracking data from terrestrial GPS receivers alone and in tandem with the GRACE and LAGEOS satellites. We generate solutions without apriori ties to the International Terrestrial Reference Frame (ITRF). Our approach relies on processing multi-day orbit arcs to take advantage of the satellite dynamics, GPS receiver and transmitter calibrations derived from low-Earth orbiter (LEO) data, and estimation strategies tuned for realizing a stable and accurate TRF. We furthermore take advantage of the geometric diversity provided by GPS tracking from GRACE, and explore the impacts of including ground-based satellite laser range (SLR) measurements to LAGEOS-1 and -2 with local ties relating the two geodetic techniques. We process data from 2003-2014 and compute Helmert transformations relative to ITRF/IGb08. With GPS alone we achieve a 3D origin offset and rate of <7 mm and <1 mm/yr, and reduce the offset to <4 mm when GRACE is included in the global solutions. Scale bias and rate are 3.1 ppb and 0.01 ppb/yr in either solution. Including SLR tracking from 11 ground stations to the LAGEOS satellites from 2012-2014 yields a reduction in scale bias of 0.5-1.0 ppb depending on the weight assigned to the SLR measurements. However, scatter is increased due to the relatively sparse SLR tracking network. We conclude with approaches for improving the TRF realized from GPS and SLR combined at the measurement level.

Evaluating Pseudorange Multipath at CGPS Stations Spanning Mexico

NASA Astrophysics Data System (ADS)

Vazquez, G.; Bennett, R. A.; Spinler, J. C.

2013-12-01

A research study was conducted in order to quantify and analyze the amount of pseudorange multipath at continuous Global Positioning System (CGPS) stations spanning Mexico. These CGPS stations are administered by a variety of organizations, including government agencies and public universities, and thus serve a wide range of positioning needs. Despite the diversity of the networks and their intended audiences, a core function of all of the networks is to provide a stable framework for high-precision positioning in support of diverse commercial and scientific applications. CGPS data from a large number of publicly available networks located in Mexico were studied. These include the RGNA (National Active Geodetic Network) administered by INEGI (National Institute of Statistics and Geography), the PBO network (Plate Boundary Observatory) funded by the National Science Foundation (NSF) and operated by UNAVCO (University NAVstar Consortium), the Southern California Integrated GPS Network (SCIGN), which is a collaboration effort of the United States Geological Survey (USGS), Scripps Institution of Oceanography and the Jet Propulsion Laboratory (JPL), the UNAM network, operated by the National Seismological System (SSN) and the Institute of Geophysics of the National Autonomous University of Mexico (UNAM), the Suominet Geodetic Network (SNG) and the CORS (Continuously Operating Reference Station) network, operated by the Federal Aviation Administration (FAA). A total of 54 CGPS stations were evaluated, where dual-frequency geodetic-grade receivers collected GPS data continuously during the period from 1994 to 2013. It is usually assumed that despite carefully selected locations, all CGPS stations are to some extent, affected by the presence of signal multipath. In addition, the geographic distribution of stations provides a nation-wide access to the International Terrestrial Reference Frame (ITRF). For real-time kinematic (RTK) and rapid static applications that depend on the pseudo-range observable, the accuracy with which a roaming user may locate their assets with respect to the ITRF may be limited by site-specific multipath. The issue is particularly critical for users depending on pseudorange measurements for 'real-time' (or 'near-real-time') kinematic GPS positioning, where ambiguity resolution is a critical step. Therefore, to identify the most and the least affected GPS stations we analyzed the averaged daily root mean square pseudorange multipath variations (MP1-RMS and MP2-RMS) for all feasible satellites tracked by the CGPS networks. We investigated the sources of multipath, including changes associated with hardware replacement (i.e., receiver and antenna type) and receiver firmware upgrades.

Detection test of wireless network signal strength and GPS positioning signal in underground pipeline

NASA Astrophysics Data System (ADS)

Li, Li; Zhang, Yunwei; Chen, Ling

2018-03-01

In order to solve the problem of selecting positioning technology for inspection robot in underground pipeline environment, the wireless network signal strength and GPS positioning signal testing are carried out in the actual underground pipeline environment. Firstly, the strength variation of the 3G wireless network signal and Wi-Fi wireless signal provided by China Telecom and China Unicom ground base stations are tested, and the attenuation law of these wireless signals along the pipeline is analyzed quantitatively and described. Then, the receiving data of the GPS satellite signal in the pipeline are tested, and the attenuation of GPS satellite signal under underground pipeline is analyzed. The testing results may be reference for other related research which need to consider positioning in pipeline.

Implementation of CGPS at Estartit, Ibiza and Barcelona harbours for sea level monitoring

NASA Astrophysics Data System (ADS)

Martinez-Benjamin, J. J.; Ortiz Castellon, M.; Martinez-Garcia, M.; Perez, B.; Bosch, E.; Termens, A.; Martinez de Oses, X.

2009-12-01

The determination of global and regional mean sea level variations with accura-cies better than 1 mm/yr is a critical problem, the resolution of which is central to the current debate on climate change and its impact on the environment. Highly accurate time series from both satellite altimetry and tide gauges are needed. Measuring the sea surface height with in-situ tide gauges and GPS receivers pro-vides an efficient way to control the long term stability of the radar altimeters and other applications as the vertical land motion and studies of sea level change. L’Estartit tide gauge is a classical floating tide gauge set up in l’Estartit harbour (NE Spain) in 1990. Data are taken in graphics registers from which each two hours the mean value is recorded in an electronic support and delivered to the Permanent Service for Mean Sea level (PSMSL). Periodic surveying campaigns along the year are carried out for monitoring possible vertical movement of the geodetic benchmark adjacent to the tide gauge. Puertos del Estado (Spanish Harbours) installed the tide gauge station at Ibiza har-bour in January 2003 and a near GPS reference station. The station belongs to the REDMAR network, composed at this moment by 21 stations distributed along the whole Spanish waters, including also the Canary islands (http://www.puertos.es). The tide gauge also belongs to the ESEAS (European Sea Level) network. A description of the actual infrastructure at Ibiza, Barcelona and l’Estartit har-bours is presented.The main objective is the implementation of these harbours as a precise geodetic areas for sea level monitoring and altimeter calibration. Actually is a CGPS with a radar tide gauge from Puertos del Estado and a GPS belonging to Puerto de Barcelona. A precise levelling has been made by the Cartographic Insti-tute of Catalonia, ICC. The instrumentation of sea level measurements has been improved by providing the Barcelona site with a radar tide gauge Datamar 3000C device and a Thales Navigation Internet-Enabled GPS Continuous Geodetic Ref-erence Station (iCGRS) with a choke ring antenna, located at the EPSEB of the Technical University of Catalonia, UPC. It is intended that the overall system will constitute a CGPS Station of the ESEAS and TIGA networks.

India plate angular velocity and contemporary deformation rates from continuous GPS measurements from 1996 to 2015.

PubMed

Jade, Sridevi; Shrungeshwara, T S; Kumar, Kireet; Choudhury, Pallabee; Dumka, Rakesh K; Bhu, Harsh

2017-09-12

We estimate a new angular velocity for the India plate and contemporary deformation rates in the plate interior and along its seismically active margins from Global Positioning System (GPS) measurements from 1996 to 2015 at 70 continuous and 3 episodic stations. A new India-ITRF2008 angular velocity is estimated from 30 GPS sites, which include stations from western and eastern regions of the plate interior that were unrepresented or only sparsely sampled in previous studies. Our newly estimated India-ITRF2008 Euler pole is located significantly closer to the plate with ~3% higher angular velocity than all previous estimates and thus predicts more rapid variations in rates and directions along the plate boundaries. The 30 India plate GPS site velocities are well fit by the new angular velocity, with north and east RMS misfits of only 0.8 and 0.9 mm/yr, respectively. India fixed velocities suggest an approximate of 1-2 mm/yr intra-plate deformation that might be concentrated along regional dislocations, faults in Peninsular India, Kachchh and Indo-Gangetic plain. Relative to our newly-defined India plate frame of reference, the newly estimated velocities for 43 other GPS sites along the plate margins give insights into active deformation along India's seismically active northern and eastern boundaries.

Deformation analysis of Aceh April 11{sup th} 2012 earthquake using GPS observation data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maulida, Putra, E-mail: putra.maulida@gmail.com; Meilano, Irwan; Sarsito, Dina A.

This research tries to estimate the co-seismic deformation of intraplate earthquake occurred off northern Sumatra coast which is about 100-200 km southwest of Sumatrasubduction zone. The earthquake mechanism was strike-slip with magnitude 8.6 and triggering aftershock with magnitude 8.2 two hours later. We estimated the co-seismic deformation by using the GPS (Global Positioning System) continuous data along western Sumatra coast. The GPS observation derived from Sumatran GPS Array (SuGAr) and Geospatial Information Agency (BIG). For data processing we used GPS Analyze at Massachusetts Institute of Technology (GAMIT) software and Global Kalman Filter (GLOBK) to estimate the co-seismic deformation. From themore » GPS daily solution, the result shows that the earthquake caused displacement for the GPS stations in Sumatra. GPS stations in northern Sumatra showed the displacement to the northeast with the average displacement was 15 cm. The biggest displacement was found at station BSIM which is located at Simeuleu Island off north west Sumatra coast. GPS station in middle part of Sumatra, the displacement was northwest. The earthquake also caused subsidence for stations in northern Sumatra, but from the time series there was not sign of subsidence was found at middle part of Sumatra. In addition, the effect of the earthquake was worldwide and affected the other GPS Stations around Hindia oceanic.« less

Analysis of Vlbi, Slr and GPS Site Position Time Series

NASA Astrophysics Data System (ADS)

Angermann, D.; Krügel, M.; Meisel, B.; Müller, H.; Tesmer, V.

Conventionally the IERS terrestrial reference frame (ITRF) is realized by the adoption of a set of epoch coordinates and linear velocities for a set of global tracking stations. Due to the remarkable progress of the space geodetic observation techniques (e.g. VLBI, SLR, GPS) the accuracy and consistency of the ITRF increased continuously. The accuracy achieved today is mainly limited by technique-related systematic errors, which are often poorly characterized or quantified. Therefore it is essential to analyze the individual techniques' solutions with respect to systematic differences, models, parameters, datum definition, etc. Main subject of this presentation is the analysis of GPS, SLR and VLBI time series of site positions. The investigations are based on SLR and VLBI solutions computed at DGFI with the software systems DOGS (SLR) and OCCAM (VLBI). The GPS time series are based on weekly IGS station coordinates solutions. We analyze the time series with respect to the issues mentioned above. In particular we characterize the noise in the time series, identify periodic signals, and investigate non-linear effects that complicate the assignment of linear velocities for global tracking sites. One important aspect is the comparison of results obtained by different techniques at colocation sites.

Precise orbit determination of the Sentinel-3A altimetry satellite using ambiguity-fixed GPS carrier phase observations

NASA Astrophysics Data System (ADS)

Montenbruck, Oliver; Hackel, Stefan; Jäggi, Adrian

2017-11-01

The Sentinel-3 mission takes routine measurements of sea surface heights and depends crucially on accurate and precise knowledge of the spacecraft. Orbit determination with a targeted uncertainty of less than 2 cm in radial direction is supported through an onboard Global Positioning System (GPS) receiver, a Doppler Orbitography and Radiopositioning Integrated by Satellite instrument, and a complementary laser retroreflector for satellite laser ranging. Within this study, the potential of ambiguity fixing for GPS-only precise orbit determination (POD) of the Sentinel-3 spacecraft is assessed. A refined strategy for carrier phase generation out of low-level measurements is employed to cope with half-cycle ambiguities in the tracking of the Sentinel-3 GPS receiver that have so far inhibited ambiguity-fixed POD solutions. Rather than explicitly fixing double-difference phase ambiguities with respect to a network of terrestrial reference stations, a single-receiver ambiguity resolution concept is employed that builds on dedicated GPS orbit, clock, and wide-lane bias products provided by the CNES/CLS (Centre National d'Études Spatiales/Collecte Localisation Satellites) analysis center of the International GNSS Service. Compared to float ambiguity solutions, a notably improved precision can be inferred from laser ranging residuals. These decrease from roughly 9 mm down to 5 mm standard deviation for high-grade stations on average over low and high elevations. Furthermore, the ambiguity-fixed orbits offer a substantially improved cross-track accuracy and help to identify lateral offsets in the GPS antenna or center-of-mass (CoM) location. With respect to altimetry, the improved orbit precision also benefits the global consistency of sea surface measurements. However, modeling of the absolute height continues to rely on proper dynamical models for the spacecraft motion as well as ground calibrations for the relative position of the altimeter reference point and the CoM.

IGS 1996 Analysis Center Workshop

NASA Technical Reports Server (NTRS)

Neilan, R. E. (Editor); VanScoy, P. A. (Editor); Zumberge, J. F. (Editor)

1996-01-01

Components of the IGS[International GPS (Global Positioning System) Service for geodynamics], have operated a GPS tracking system for several years. The network now contains more than 100 stations and has produced a combined GPS ephemeris that has become the standard for geodesists and geophysicists worldwide. IGS data and products are freely available to all thanks to the cooperation and participation of all the IGS members. The IGS has initiated development of several new products, and technical issues permitting greater accuracy of IGS products have been identified. The IGS convened a workshop on March 1996 in Silver Spring, Maryland, USA, to coordinate these developments and to examine technical problems and solutions. The following topics were addressed: orbit/clock combination; Earth orientation; antenna calibration; SINEX and densification of the International Terrestrial Reference Frame (ITRF) using the GPS; receiver standards and performance; and atmospheric topics.

GNSS station displacement analysis

NASA Astrophysics Data System (ADS)

Haritonova, Diana; Balodis, Janis; Janpaule, Inese; Normand, Madara

2013-04-01

Time series of GNSS station results of both the EUPOS®-Riga and LatPos networks have been developed at the Institute of Geodesy and Geoinformation (University of Latvia). The reference stations from EUREF Permanent Network (EPN) in surroundings of Latvia have been used and Bernese GPS Software, Version 5.0, in both static and kinematic modes was applied. The standard data sets were taken from IGS data base. The results of time series have been analysed and distinctive behaviour of daily and subdaily movements of EUPOS®-Riga and LatPos stations was identified. The reasons of dependence of GNSS station coordinate distribution on possible external factors such as seismic activity of some areas of Latvia and periodic processes were given.

A single-station empirical model for TEC over the Antarctic Peninsula using GPS-TEC data

NASA Astrophysics Data System (ADS)

Feng, Jiandi; Wang, Zhengtao; Jiang, Weiping; Zhao, Zhenzhen; Zhang, Bingbing

2017-02-01

Compared with regional or global total electron content (TEC) empirical models, single-station TEC empirical models may exhibit higher accuracy in describing TEC spatial and temporal variations for a single station. In this paper, a new single-station empirical total electron content (TEC) model, called SSM-month, for the O'Higgins Station in the Antarctic Peninsula is proposed by using Global Positioning System (GPS)-TEC data from 01 January 2004 to 30 June 2015. The diurnal variation of TEC in the O'Higgins Station may have changing features in different months, sometimes even in opposite forms, because of ionospheric phenomena, such as the Mid-latitude Summer Nighttime Anomaly (MSNA). To avoid the influence of different diurnal variations, the concept of monthly modeling is proposed in this study. The SSM-month model, which is established by month (including 12 submodels that correspond to the 12 months), can effectively describe the diurnal variation of TEC in different months. Each submodel of the SSM-month model exhibits good agreement with GPS-TEC input data. Overall, the SSM-month model fits the input data with a bias of 0.03 TECU (total electron content unit, 1 TECU = 1016 el m-2) and a standard deviation of 2.78 TECU. This model, which benefits from the modeling method, can effectively describe the MSNA phenomenon without implementing any modeling correction. TEC data derived from Center for Orbit Determination in Europe global ionosphere maps (CODE GIMs), International Reference Ionosphere 2012 (IRI2012), and NeQuick are compared with the SSM-month model in the years of 2001 and 2015-2016. Result shows that the SSM-month model exhibits good consistency with CODE GIMs, which is better than that of IRI2012 and NeQuick, in the O'Higgins Station on the test days.

Present day geodynamics in Iceland monitored by a permanent network of continuous GPS stations

NASA Astrophysics Data System (ADS)

Völksen, Christof; Árnadóttir, Thóra; Geirsson, Halldór; Valsson, Guðmundur

2009-12-01

Iceland is located on the Mid-Atlantic Ridge and thereby offers a rare opportunity to study crustal movements at a divergent plate boundary. Iceland is not only characterized by the divergence of the Eurasian and North American Plates, as several active volcanoes are located on the island. Moderate size earthquakes occur in the transform zones, causing measurable crustal deformation. In 1999 the installation of a permanent network of continuous GPS stations (ISGPS) was initiated in order to observe deformation due to unrest in the Hengill volcanic system and at the Katla volcano. The ISGPS network has been enlarged over the years and consists today of more than 25 CGPS stations. Most of the stations are located along the plate boundary, where most of the active deformation takes place. Uplift due to post-glacial rebound due to the melting of the largest glacier in Europe, Vatnajökull, is also detected by the ISGPS network. This study presents results from analysis of 9 years of data from the ISGPS network, in the global reference frame PDR05, which has been evaluated by the Potsdam-Dresden-Reprocessing group with reprocessed GPS data only. We thus determine subsidence or land uplift in a global frame. The horizontal station velocities clearly show spreading across the plate boundary of about 20 mm/a. Stations in the vicinity of the glacier Vatnajökull indicate uplift in the range of 12 mm/a, while a station in the central part of Iceland shows uplift rates of about 25 mm/a. Tide gauge readings in Reykjavik and current subsidence rates observed with CGPS agree also quite well.

Laser, GPS and absolute gravimetry vertical positioning time series comparison at the OCA observatory, France

NASA Astrophysics Data System (ADS)

Nicolas, J.; Nocquet, J.; van Camp, M.; Coulot, D.

2003-12-01

Time-dependent displacements of stations usually have magnitude close to the accuracy of each individual technique, and it still remains difficult to separate the true geophysical motion from possible artifacts inherent to each space geodetic technique. The Observatoire de la C“te d'Azur (OCA), located at Grasse, France benefits from the collocation of several geodetic instruments and techniques (3 laser ranging stations, and a permanent GPS) what allows us to do a direct comparison of the time series. Moreover, absolute gravimetry measurement campaigns have also been regularly performed since 1997, first by the "Ecole et Observatoire des Sciences de la Terre (EOST) of Strasbourg, France, and more recently by the Royal Observatory of Belgium. This study presents a comparison between the positioning time series of the vertical component derived from the SLR and GPS analysis with the gravimetric results from 1997 to 2003. The laser station coordinates are based on a LAGEOS -1 and -2 combined solution using reference 10-day arc orbits, the ITRF2000 reference frame, and the IERS96 conventions. Different GPS weekly global solutions provided from several IGS are combined and compared to the SLR results. The absolute gravimetry measurements are converted into vertical displacements with a classical gradient. The laser time series indicate a strong annual signal at the level of about 3-4 cm peak to peak amplitude on the vertical component. Absolute gravimetry data agrees with the SLR results. GPS positioning solutions also indicate a significant annual term, but with a magnitude of only 50% of the one shown by the SLR solution and by the gravimetry measurements. Similar annual terms are also observed on other SLR sites we processed, but usually with! lower and various amplitudes. These annual signals are also compared to vertical positioning variations corresponding to an atmospheric loading model. We present the level of agreement between the different techniques and we discuss possible explanations for the discrepancy noted between the signals. At last, we expose explanations for the large annual term at Grasse: These annual variations could be partly due to an hydrological loading effect on the karstic massif on which the observatory is located.

Intrasite motions and monument instabilities at Medicina ITRF co-location site

NASA Astrophysics Data System (ADS)

Sarti, Pierguido; Abbondanza, Claudio; Legrand, Juliette; Bruyninx, Carine; Vittuari, Luca; Ray, Jim

2013-03-01

We process the total-station surveys performed at the ITRF co-location site Medicina (Northern Italy) over the decade (2001-2010) with the purpose of determining the extent of local intrasite motions and relating them to local geophysical processes, the geological setting and the design of the ground pillars. In addition, continuous observations acquired by two co-located GPS stations (MEDI and MSEL separated by ≈27 m) are analysed and their relative motion is cross-checked with the total-station results. The local ground control network extends over a small area (<100 × 100 m) but the results demonstrate significant anisotropic deformations with rates up to 1.6 mm a-1, primarily horizontal, a value comparable to intraplate tectonic deformations. The results derived from GPS and total-station observations are consistent and point to the presence of horizontal intrasite motions over very short distances possibly associated with varying environmental conditions in a very unfavourable local geological setting and unsuitable monument design, these latter being crucial aspects of the realization and maintenance of global permanent geodetic networks and the global terrestrial reference frame.

Helicopter flight test demonstration of differential GPS

NASA Technical Reports Server (NTRS)

Denaro, R. P.; Beser, J.

1985-01-01

An off-line post-mission processing facility is being established by NASA Ames Research Center to analyze differential GPS flight tests. The current and future differential systems are described, comprising an airborne segment in an SH-3 helicopter, a GPS ground reference station, and a tracking system. The post-mission processing system provides for extensive measurement analysis and differential computation. Both differential range residual corrections and navigation corrections are possible. Some preliminary flight tests were conducted in a landing approach scenario and statically. Initial findings indicate the possible need for filter matching between airborne and ground systems (if used in a navigation correction technique), the advisability of correction smoothing before airborne incorporation, and the insensitivity of accuracy to either of the differential techniques or to update rates.

Comparison between multi-constellation ambiguity-fixed PPP and RTK for maritime precise navigation

NASA Astrophysics Data System (ADS)

Tegedor, Javier; Liu, Xianglin; Ørpen, Ole; Treffers, Niels; Goode, Matthew; Øvstedal, Ola

2015-06-01

In order to achieve high-accuracy positioning, either Real-Time Kinematic (RTK) or Precise Point Positioning (PPP) techniques can be used. While RTK normally delivers higher accuracy with shorter convergence times, PPP has been an attractive technology for maritime applications, as it delivers uniform positioning performance without the direct need of a nearby reference station. Traditional PPP has been based on ambiguity-­float solutions using GPS and Glonass constellations. However, the addition of new satellite systems, such as Galileo and BeiDou, and the possibility of fixing integer carrier-phase ambiguities (PPP-AR) allow to increase PPP accuracy. In this article, a performance assessment has been done between RTK, PPP and PPP-AR, using GNSS data collected from two antennas installed on a ferry navigating in Oslo (Norway). RTK solutions have been generated using short, medium and long baselines (up to 290 km). For the generation of PPP-AR solutions, Uncalibrated Hardware Delays (UHDs) for GPS, Galileo and BeiDou have been estimated using reference stations in Oslo and Onsala. The performance of RTK and multi-­constellation PPP and PPP-AR are presented.

Monitoring of GPS Water Vapor Variability During ENSO Events Over the Sulawesi

NASA Astrophysics Data System (ADS)

Arief, S.; Heki, K.

2017-12-01

The purpose of this study is to see the El Niño phenomenon that occurs on the island of Sulawesi. By analyzing the measurements of wet troposphere delay from 3 stations inaCORS (Indonesia Continous Operating Reference Station) namely CBIT, PALP and CMAK and radiosonde data 3 locations of sulawesi region ie WAMM, WAML and WAAA. This paper describes the ways and analysis results of PWV measurements as an effort to monitor El Niño events in 2015 - 2016.

Real-time estimation of ionospheric delay using GPS measurements

NASA Astrophysics Data System (ADS)

Lin, Lao-Sheng

1997-12-01

When radio waves such as the GPS signals propagate through the ionosphere, they experience an extra time delay. The ionospheric delay can be eliminated (to the first order) through a linear combination of L1 and L2 observations from dual-frequency GPS receivers. Taking advantage of this dispersive principle, one or more dual- frequency GPS receivers can be used to determine a model of the ionospheric delay across a region of interest and, if implemented in real-time, can support single-frequency GPS positioning and navigation applications. The research objectives of this thesis were: (1) to develop algorithms to obtain accurate absolute Total Electron Content (TEC) estimates from dual-frequency GPS observables, and (2) to develop an algorithm to improve the accuracy of real-time ionosphere modelling. In order to fulfil these objectives, four algorithms have been proposed in this thesis. A 'multi-day multipath template technique' is proposed to mitigate the pseudo-range multipath effects at static GPS reference stations. This technique is based on the assumption that the multipath disturbance at a static station will be constant if the physical environment remains unchanged from day to day. The multipath template, either single-day or multi-day, can be generated from the previous days' GPS data. A 'real-time failure detection and repair algorithm' is proposed to detect and repair the GPS carrier phase 'failures', such as the occurrence of cycle slips. The proposed algorithm uses two procedures: (1) application of a statistical test on the state difference estimated from robust and conventional Kalman filters in order to detect and identify the carrier phase failure, and (2) application of a Kalman filter algorithm to repair the 'identified carrier phase failure'. A 'L1/L2 differential delay estimation algorithm' is proposed to estimate GPS satellite transmitter and receiver L1/L2 differential delays. This algorithm, based on the single-site modelling technique, is able to estimate the sum of the satellite and receiver L1/L2 differential delay for each tracked GPS satellite. A 'UNSW grid-based algorithm' is proposed to improve the accuracy of real-time ionosphere modelling. The proposed algorithm is similar to the conventional grid-based algorithm. However, two modifications were made to the algorithm: (1) an 'exponential function' is adopted as the weighting function, and (2) the 'grid-based ionosphere model' estimated from the previous day is used to predict the ionospheric delay ratios between the grid point and reference points. (Abstract shortened by UMI.)

Rapid Modeling of and Response to Large Earthquakes Using Real-Time GPS Networks (Invited)

NASA Astrophysics Data System (ADS)

Crowell, B. W.; Bock, Y.; Squibb, M. B.

2010-12-01

Real-time GPS networks have the advantage of capturing motions throughout the entire earthquake cycle (interseismic, seismic, coseismic, postseismic), and because of this, are ideal for real-time monitoring of fault slip in the region. Real-time GPS networks provide the perfect supplement to seismic networks, which operate with lower noise and higher sampling rates than GPS networks, but only measure accelerations or velocities, putting them at a supreme disadvantage for ascertaining the full extent of slip during a large earthquake in real-time. Here we report on two examples of rapid modeling of recent large earthquakes near large regional real-time GPS networks. The first utilizes Japan’s GEONET consisting of about 1200 stations during the 2003 Mw 8.3 Tokachi-Oki earthquake about 100 km offshore Hokkaido Island and the second investigates the 2010 Mw 7.2 El Mayor-Cucapah earthquake recorded by more than 100 stations in the California Real Time Network. The principal components of strain were computed throughout the networks and utilized as a trigger to initiate earthquake modeling. Total displacement waveforms were then computed in a simulated real-time fashion using a real-time network adjustment algorithm that fixes a station far away from the rupture to obtain a stable reference frame. Initial peak ground displacement measurements can then be used to obtain an initial size through scaling relationships. Finally, a full coseismic model of the event can be run minutes after the event, given predefined fault geometries, allowing emergency first responders and researchers to pinpoint the regions of highest damage. Furthermore, we are also investigating using total displacement waveforms for real-time moment tensor inversions to look at spatiotemporal variations in slip.

Temporal Stability of GPS Transmitter Group Delay Variations.

PubMed

Beer, Susanne; Wanninger, Lambert

2018-05-29

The code observable of global navigation satellite systems (GNSS) is influenced by group delay variations (GDV) of transmitter and receiver antennas. For the Global Positioning System (GPS), the variations can sum up to 1 m in the ionosphere-free linear combination and thus can significantly affect precise code applications. The contribution of the GPS transmitters can amount to 0.8 m peak-to-peak over the entire nadir angle range. To verify the assumption of their time-invariance, we determined daily individual satellite GDV for GPS transmitter antennas over a period of more than two years. Dual-frequency observations of globally distributed reference stations and their multipath combination form the basis for our analysis. The resulting GPS GDV are stable on the level of a few centimeters for C1, P2, and for the ionosphere-free linear combination. Our study reveals that the inconsistencies of the GDV of space vehicle number (SVN) 55 with respect to earlier studies are not caused by temporal instabilities, but are rather related to receiver properties.

Study of the active deformation of Mitidja (Tell Atlas, Algeria) by GPS

NASA Astrophysics Data System (ADS)

Bacha, Wahab; Masson, Frederic; Yelles-Chaouche, Abdelkrim; Lammali, Kamel; Bellik, Amar; Hamai, Lamine

2013-04-01

A network was created in the Mitidja region around the capital Algiers (Algeria). It has been established to study the deformation of the region and the slow operation of flaws in it. The network was installed by a distribution of GPS stations according to structural domains existing in the region. Twelve bases spread across the study area, have been installed. The measurements were acquired by performing four measurement campaigns in 2006, 2007, 2009 and 2010, with sessions over a month of action. This work allowed the installation of a geodetic network of regional monitoring by methodology GPS in the zone of Mitidja (Tellian Atlas, Algeria). Four observation campaigns were carried out on this area with session's superiors in one month of measurements. The treatment was carried out with software GAMIT-GLOBK, the network is attached to several world stations IGS treated between 2000-2010, indexed in a precise frame of reference ITRF05. The results presented in this memory show a deformation in shortening ≤ 0.5 mm/an in the plain of Mitidja and the surrounding Solid masses.

Variations of total electron content in the equatorial anomaly region in Thailand

NASA Astrophysics Data System (ADS)

Chowdhary, V. Rajesh; Tripathi, N. K.; Arunpold, Sanit; Raju, Durairaju Kumaran

2015-01-01

This paper presents the first results of total electron content (TEC), derived by analyzing dual frequency Novatel GSV4004 GPS receiver's data which were installed by the SCINDA project, located at the Asian Institute of Technology, Bangkok (AITB, 14.079N, 100.612E) and Chiang Mai University, Chiang Mai (CHGM, 18.480N, 98.570E) with magnetic latitude of 4.13°N and 8.61°N respectively in Thailand, for the year 2011. These two stations are separated by 657 km in the equatorial anomaly region. The highest TEC values occurred from 1500 to 1900 LT throughout the study period. The diurnal, monthly and seasonal GPS-TEC have been plotted and analyzed. The diurnal peaks in GPS-TEC is observed to be maximum during equinoctial months (March, April, September and October) and minimum in solstice months (January, February, June, July and December). These high TEC values have been attributed to the solar extreme ultra-violet ionization coupled with the upward vertical E × B drift. A comparison of both station's TEC has been carried out and found that CHGM station experiences higher values of TEC than AITB station, due to formation of ionization crest over the CHGM station. Also, TEC values have shown increasing trend due to approaching solar maximum. These results from both stations were also compared with the TEC derived from the International Reference Ionosphere's (IRI) recently released, IRI-2012 model. Results have shown positive correlation with IRI-2012 model. Although, IRI-model does not show any response to geomagnetic activity, the IRI model normally remains smooth and underestimates TEC during a storm.

Towards better GNSS observations at the new IGS reference station BRUX: multipath mitigation and individual antenna calibration

NASA Astrophysics Data System (ADS)

Aerts, W.; Baire, Q.; Bruyninx, C.; Legrand, J.; Pottiaux, E.

2012-12-01

A new multi-GNSS IGS reference station, BRUX, has been installed at Brussels. It replaces the former IGS reference station BRUS, which had to be dismantled because of construction works. The antenna of BRUX is sited on top of a telescope dome. Although this might be an unfortunate choice from an electromagnetic point of view, the siting is very convenient for other reasons. Being close to the time lab hosting the atomic clocks, the cable length is within acceptable and affordable limits, both for cost and signal loss reasons. Moreover, the site offers open sky view, which can indeed be expected from a former telescope siting. The dome is entirely metal, hence shielding of the dome was required in order to mitigate multipath propagation. This was achieved using a metal shield topped with RF absorbing material and respecting a certain antenna-to-absorber spacing in order not to alter the antenna phase center offset (PCO) and variations (PCVs) too much. This would otherwise render the individual calibration of the antenna, in an anechoic chamber in the case of BRUX, invalid. But even taking all precautions, the PCO and PCVs of the calibration do not exactly equal those after installation. Moreover, different calibrations, in an anechoic chamber and by an outdoor robot, of the same antenna have shown to result in PCO and PCVs that differ up to several mm at certain azimuths and elevations. A test set-up with 6 such redundantly calibrated GNSS antennas revealed that the calibration differences can reach 8 mm on the ionosphere-free frequency, which amplifies the calibration differences by a factor three compared to L1 and L2 only. The use of different receiver antenna calibration models can impact position at almost the centimeter level. In an attempt to align the historical time series for BRUS with the (future) data for BRUX, the tie between the new station BRUX and the old IGS station BRUS was determined using terrestrial measurements as well as GPS. In the case of GPS, several L1, L2 and ionosphere-free baseline measurements were performed using state-of-the-art type-mean receiver antenna calibrations as well as individual calibrations. Differences between the different GPS measurements are several mm, while the differences between the terrestrial tie and the GPS ties reaches almost the cm-level. One contribution to the error budget is the absence of an individual calibration for the BRUS antenna, another one is the difference in PCO and PCVs on site, as opposed to at calibration, as already mentioned.

A Precision, Low-Cost GPS-Based Synchronization Scheme for Improved AM Reception.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, Stephen Fulton; Moore, Anthony

2009-01-01

This paper describes a highly accurate carrier-frequency synchronization scheme for actively, automatically locking multiple, remotely located AM broadcast transmitters to a common frequency/timing reference source such as GPS. The extremely tight frequency lock (to ~1 part in 109 or better) permits the effective elimination of audible and even sub-audible beats between the local (desired) station s carrier signal and the distant stations carriers, usually received via skywave propagation during the evening and nighttime hours. These carrier-beat components cause annoying modulations of the desired station s audio at the receiver and concurrent distortion of the audio modulation from the distant station(s)more » and often cause listeners to tune out due to the poor reception quality. Significant reduction or elimination of the beats and related effects will greatly enlarge the effective (interference-limited) listening area of the desired station (from 4 to 10 times as indicated in our tests) and simultaneously reduce the corresponding interference of the local transmitter to the distant stations as well. In addition, AM stereo (CQUAM) reception will be particularly improved by minimizing the phase shifts induced by co-channel interfering signals; HD will also benefit via reduction in beats from analog signals. The automatic frequency-control hardware described is inexpensive ($1-2K), requires no periodic recalibration, has essentially zero long-term drift, and could employ alternate wide-area frequency references of suitable accuracy, including broadcasts from WWVB, LORAN-C, and equivalent sources. The basic configuration of the GPS-disciplined oscillator which solves this problem is extremely simple. The main oscillator is a conventional high-stability quartz-crystal type. To counter long-term drifts, the oscillator is slightly adjusted to track a high-precision source of standard frequency obtained from a specialized GPS receiver (or other source), usually at 10.000 MHz. This very stable local reference frequency is then used as a clock for a standard digitally implemented frequency synthesizer, which is programmed to generate the specific (AM broadcast) transmitter carrier frequency desired. The stability of the disciplining source, typically ~ 1 part in 109 to 1011, is thus transferred to the final AM transmitter carrier output frequency. Generally, an AM radio listener during the evening and nighttime hours, and to a lesser extent in the early morning, receives undesired skywave signals from several distant stations as well as the desired local (groundwave) signal. If all of these signals are within about 0.01-0.001 Hz of each other, any resulting carrier beats will be of such long periods that the beats will be effectively suppressed by the action of the receiver s AGC circuitry and thus be unnoticeable to the listener. Many modern, synthesizer-based transmitters can directly lock to the precision disciplined 10-MHz source, while older units usually require references at either1 e, 2 e, or 4 e the final frequency. In these latter cases, the existing transmitter crystal can usually be satisfactorily pulled via injection locking. The effectiveness of the synchronization concept to reduce interference effects was demonstrated in a laboratory test setup. Many hours of careful subjective listening were conducted, with the two interfering units both precisely on-frequency with the main unit (synchronous operation) and with the two interferers at various frequency offsets, from below 1 Hz to above 10 Hz.« less

NoWMex: Continuous GNSS Sites in Northwest Mexico

NASA Astrophysics Data System (ADS)

Gonzalez-Garcia, J. J.; Gonzalez-Ortega, J. A.

2008-05-01

Nowadays GPS has become part of daily life activities. In the near future, with the GPS modernization and the use of Glonass and Galileo as a Global Navigation Satellite System will give relative location precision from decimeters to millimeters in near real time applications. In order to realize this, we need a global array of continuously operating GNSS stations built to meet the standards of the geophysical communities and linked with gravimetric local measurements to discern the vertical component of our active Earth. Trying to follow this revolution, CICESE has been working with GPS since 1985. The GPS site CICE was built as an IGS reference station in 1995. Afterward we built 5 more continuous GPS sites in Northwest Mexico with the support of SCIGN. The CGPS NoWMex network is currently made up of six sites: CIC1, SPMX, CORX, GUAX, USMX and YESX (sopac.ucsd.edu). Recently, we implemented an experimental GPS processing lab as part of the Geodesy and Geodynamics Laboratory in the Seismology Department at CICESE. 30 stations are now currently processed from the network Red Geodesica Nacional Activa (RGNA-INEGI), NoWMex, and sites in neighbor countries. Fiducials solutions in ITRF2000 are obtained using GAMIT/GLOBK 10.31 with final igs orbits, every month since 2006. In order to make a contribution to densification of ITRF and support NAREF, SIRGAS and SNARF issues related to scientific and geomatics results; we are looking for internal (Mexican) and external colleagues as well as funding for maintenance and increase the number of CGNSS in NoWMeX including southern Basin and Ranger (Sonora, Chihuahua, Sinaloa and Durango), Gulf of California islands, Peninsular Californias, Nayarit, Jalisco, Colima and the Mexican Pacific islands: Guadalupe (2 more sites), Cedros, Socorro (DORIS site), Clarion and Tres Marias. We must to build more and free available CGNSS sites in and around Mexico to contribute to sea level rise and global change studies.

A theoretical study on the bottlenecks of GPS phase ambiguity resolution in a CORS RTK Network

NASA Astrophysics Data System (ADS)

Odijk, D.; Teunissen, P.

2011-01-01

Crucial to the performance of GPS Network RTK positioning is that a user receives and applies correction information from a CORS Network. These corrections are necessary for the user to account for the atmospheric (ionospheric and tropospheric) delays and possibly orbit errors between his approximate location and the locations of the CORS Network stations. In order to provide the most precise corrections to users, the CORS Network processing should be based on integer resolution of the carrier phase ambiguities between the network's CORS stations. One of the main challenges is to reduce the convergence time, thus being able to quickly resolve the integer carrier phase ambiguities between the network's reference stations. Ideally, the network ambiguity resolution should be conducted within one single observation epoch, thus truly in real time. Unfortunately, single-epoch CORS Network RTK ambiguity resolution is currently not feasible and in the present contribution we study the bottlenecks preventing this. For current dual-frequency GPS the primary cause of these CORS Network integer ambiguity initialization times is the lack of a sufficiently large number of visible satellites. Although an increase in satellite number shortens the ambiguity convergence times, instantaneous CORS Network RTK ambiguity resolution is not feasible even with 14 satellites. It is further shown that increasing the number of stations within the CORS Network itself does not help ambiguity resolution much, since every new station introduces new ambiguities. The problem with CORS Network RTK ambiguity resolution is the presence of the atmospheric (mainly ionospheric) delays themselves and the fact that there are no external corrections that are sufficiently precise. We also show that external satellite clock corrections hardly contribute to CORS Network RTK ambiguity resolution, despite their quality, since the network satellite clock parameters and the ambiguities are almost completely uncorrelated. One positive is that the foreseen modernized GPS will have a very beneficial effect on CORS ambiguity resolution, because of an additional frequency with improved code precision.

Predicting present-day rates of glacial isostatic adjustment using a smoothed GPS velocity field for the reconciliation of NAD83 reference frames in Canada

NASA Astrophysics Data System (ADS)

Craymer, M. R.; Henton, J. A.; Piraszewski, M.

2008-12-01

Glacial isostatic adjustment following the last glacial period is the dominant source of crustal deformation in Canada east of the Rocky Mountains. The present-day vertical component of motion associated with this process may exceed 1 cm/y and is being directly measured with the Global Positioning System (GPS). A consequence of this steady deformation is that high accuracy coordinates at one epoch may not be compatible with those at another epoch. For example, modern precise point positioning (PPP) methods provide coordinates at the epoch of observation while NAD83, the officially adopted reference frame in Canada and the U.S., is expressed at some past reference epoch. The PPP positions are therefore incompatible with coordinates in such a realization of the reference frame and need to be propagated back to the frame's reference epoch. Moreover, the realizations of NAD83 adopted by the provincial geodetic agencies in Canada are referenced to different coordinate epochs; either 1997.0 or 2002.0. Proper comparison of coordinates between provinces therefore requires propagating them from one reference epoch to another. In an effort to reconcile PPP results and different realizations of NAD83, we empirically represent crustal deformation throughout Canada using a velocity field based solely on high accuracy continuous and episodic GPS observations. The continuous observations from 2001 to 2007 were obtained from nearly 100 permanent GPS stations, predominately operated by Natural Resources Canada (NRCan) and provincial geodetic agencies. Many of these sites are part of the International GNSS Service (IGS) global network. Episodic observations from 1994 to 2006 were obtained from repeated occupations of the Canadian Base Network (CBN), which consists of approximately 160 stable pillar-type monuments across the entire country. The CBN enables a much denser spatial sampling of crustal motions although coverage in the far north is still rather sparse. NRCan solutions of the continuous GPS data were combined with those from other agencies as part of the North American Reference Frame (NAREF) effort to improve the reliability of the results. This NAREF solution has then been combined with our CBN results to obtain a denser velocity sampling for fitting different types of surfaces in a first attempt to determine a continuous GPS velocity field for the entire country. Expressing this velocity field as a grid enables users to interpolate to any location in Canada, allowing for the propagation of coordinates to any desired reference epoch. We examine the accuracy and limitations of this GPS velocity field by comparing it to other published GPS velocity solutions (which are all based on less data) as well as to GIA models, including versions of ICE-3G, ICE-5G and the recent Stable North America Reference Frame (SNARF) model. Of course, the accuracy of the GPS velocity field depends directly on the density of the GPS coverage. Consequently, the GPS velocity field is unable to fully represent the actual GIA motion in the far north and tends to smooth out the signal due to the spatially sparse coverage. On the other hand, the model performs quite well in the southern parts of the country where there is a much greater spatial density of GPS measurements.

Real-time GPS seismology using a single receiver: method comparison, error analysis and precision validation

NASA Astrophysics Data System (ADS)

Li, Xingxing

2014-05-01

Earthquake monitoring and early warning system for hazard assessment and mitigation has traditional been based on seismic instruments. However, for large seismic events, it is difficult for traditional seismic instruments to produce accurate and reliable displacements because of the saturation of broadband seismometers and problematic integration of strong-motion data. Compared with the traditional seismic instruments, GPS can measure arbitrarily large dynamic displacements without saturation, making them particularly valuable in case of large earthquakes and tsunamis. GPS relative positioning approach is usually adopted to estimate seismic displacements since centimeter-level accuracy can be achieved in real-time by processing double-differenced carrier-phase observables. However, relative positioning method requires a local reference station, which might itself be displaced during a large seismic event, resulting in misleading GPS analysis results. Meanwhile, the relative/network approach is time-consuming, particularly difficult for the simultaneous and real-time analysis of GPS data from hundreds or thousands of ground stations. In recent years, several single-receiver approaches for real-time GPS seismology, which can overcome the reference station problem of the relative positioning approach, have been successfully developed and applied to GPS seismology. One available method is real-time precise point positioning (PPP) relied on precise satellite orbit and clock products. However, real-time PPP needs a long (re)convergence period, of about thirty minutes, to resolve integer phase ambiguities and achieve centimeter-level accuracy. In comparison with PPP, Colosimo et al. (2011) proposed a variometric approach to determine the change of position between two adjacent epochs, and then displacements are obtained by a single integration of the delta positions. This approach does not suffer from convergence process, but the single integration from delta positions to displacements is accompanied by a drift due to the potential uncompensated errors. Li et al. (2013) presented a temporal point positioning (TPP) method to quickly capture coseismic displacements with a single GPS receiver in real-time. The TPP approach can overcome the convergence problem of precise point positioning (PPP), and also avoids the integration and de-trending process of the variometric approach. The performance of TPP is demonstrated to be at few centimeters level of displacement accuracy for even twenty minutes interval with real-time precise orbit and clock products. In this study, we firstly present and compare the observation models and processing strategies of the current existing single-receiver methods for real-time GPS seismology. Furthermore, we propose several refinements to the variometric approach in order to eliminate the drift trend in the integrated coseismic displacements. The mathematical relationship between these methods is discussed in detail and their equivalence is also proved. The impact of error components such as satellite ephemeris, ionospheric delay, tropospheric delay, and geometry change on the retrieved displacements are carefully analyzed and investigated. Finally, the performance of these single-receiver approaches for real-time GPS seismology is validated using 1 Hz GPS data collected during the Tohoku-Oki earthquake (Mw 9.0, March 11, 2011) in Japan. It is shown that few centimeters accuracy of coseismic displacements is achievable. Keywords: High-rate GPS; real-time GPS seismology; a single receiver; PPP; variometric approach; temporal point positioning; error analysis; coseismic displacement; fault slip inversion;

Tightly-coupled real-time analysis of GPS and accelerometer data for translational and rotational ground motions and application to earthquake and tsunami early warning

NASA Astrophysics Data System (ADS)

Geng, J.; Bock, Y.; Melgar, D.; Hasse, J.; Crowell, B. W.

2013-12-01

High-rate GPS can play an important role in earthquake early warning (EEW) systems for large (>M6) events by providing permanent displacements immediately as they are achieved, to be used in source inversions that can be repeatedly updated as more information becomes available. This is most valuable to implement at a site very near the potential source rupture, where broadband seismometers are likely to clip, and accelerometer data cannot be objectively integrated to produce reliable displacements in real time. At present, more than 525 real-time GPS stations have been established in western North America, which are being integrated into EEW systems. Our analysis technique relies on a tightly-coupled combination of GPS and accelerometer data, an extension of precise point positioning with ambiguity resolution (PPP-AR). We operate a PPP service based on North American stations available through the IGS and UNAVCO/PBO. The service provides real-time satellite clock and fractional-cycle bias products that allow us to position individual client stations in the zone of deformation. The service reference stations are chosen to be further than 200 km from the primary zones of tectonic deformation in the western U.S. to avoid contamination of the satellite products during a large seismic event. At client stations, accelerometer data are applied as tight constraints on the positions between epochs in PPP-AR, which improves cycle-slip repair and rapid ambiguity resolution after GPS outages. Furthermore, we estimate site displacements, seismic velocities, and coseismic ground tilts to facilitate the analysis of ground motion characteristics and the inversion for source mechanisms. The seismogeodetic displacement and velocity waveforms preserves the detection of P wave arrivals, and provides P-wave arrival displacement that is key new information for EEW. Our innovative solution method for coseismic tilts mitigates an error source that has continually plagued strong motion data analysis, and has a resolution of about 0.01 degrees. At present, there are few collocations of GPS and accelerometers in western North America (the exception being the BARD network in northern California) so we have developed a cost-effective way to upgrade existing real-time GPS stations with low-cost MEMS accelerometers; fifteen PBO and SCIGN stations in southern California have already been upgraded. We demonstrate our method of recovering broadband displacement and tilt waveforms using 13 experiments from the single-axis George E. Brown Jr. Network for Earthquake Engineering Simulation Large High-Performance Outdoor Shake Table at the University of California San Diego. Then we apply the method to data from the 2010 Mw 7.2 El Mayor-Cucapah earthquake and the 2011 Mw 9.0 Tohoku-oki earthquake to illustrate the improvement over standard base-line correction acceleration techniques and to demonstrate the order of magnitude of tilt errors present in typical observations.

Assessment of second- and third-order ionospheric effects on regional networks: case study in China with longer CMONOC GPS coordinate time series

NASA Astrophysics Data System (ADS)

Deng, Liansheng; Jiang, Weiping; Li, Zhao; Chen, Hua; Wang, Kaihua; Ma, Yifang

2017-02-01

Higher-order ionospheric (HOI) delays are one of the principal technique-specific error sources in precise global positioning system analysis and have been proposed to become a standard part of precise GPS data processing. In this research, we apply HOI delay corrections to the Crustal Movement Observation Network of China's (CMONOC) data processing (from January 2000 to December 2013) and furnish quantitative results for the effects of HOI on CMONOC coordinate time series. The results for both a regional reference frame and global reference frame are analyzed and compared to clarify the HOI effects on the CMONOC network. We find that HOI corrections can effectively reduce the semi-annual signals in the northern and vertical components. For sites with lower semi-annual amplitudes, the average decrease in magnitude can reach 30 and 10 % for the northern and vertical components, respectively. The noise amplitudes with HOI corrections and those without HOI corrections are not significantly different. Generally, the HOI effects on CMONOC networks in a global reference frame are less obvious than the results in the regional reference frame, probably because the HOI-induced errors are smaller in comparison to the higher noise levels seen when using a global reference frame. Furthermore, we investigate the combined contributions of environmental loading and HOI effects on the CMONOC stations. The largest loading effects on the vertical displacement are found in the mid- to high-latitude areas. The weighted root mean square differences between the corrected and original weekly GPS height time series of the loading model indicate that the mass loading adequately reduced the scatter on the CMONOC height time series, whereas the results in the global reference frame showed better agreements between the GPS coordinate time series and the environmental loading. When combining the effects of environmental loading and HOI corrections, the results with the HOI corrections reduced the scatter on the observed GPS height coordinates better than the height when estimated without HOI corrections, and the combined solutions in the regional reference frame indicate more preferred improvements. Therefore, regional reference frames are recommended to investigate the HOI effects on regional networks.

4D computerized ionospheric tomography by using GPS measurements and IRI-Plas model

NASA Astrophysics Data System (ADS)

Tuna, Hakan; Arikan, Feza; Arikan, Orhan

2016-07-01

Ionospheric imaging is an important subject in ionospheric studies. GPS based TEC measurements provide very accurate information about the electron density values in the ionosphere. However, since the measurements are generally very sparse and non-uniformly distributed, computation of 3D electron density estimation from measurements alone is an ill-defined problem. Model based 3D electron density estimations provide physically feasible distributions. However, they are not generally compliant with the TEC measurements obtained from GPS receivers. In this study, GPS based TEC measurements and an ionosphere model known as International Reference Ionosphere Extended to Plasmasphere (IRI-Plas) are employed together in order to obtain a physically accurate 3D electron density distribution which is compliant with the real measurements obtained from a GPS satellite - receiver network. Ionospheric parameters input to the IRI-Plas model are perturbed in the region of interest by using parametric perturbation models such that the synthetic TEC measurements calculated from the resultant 3D electron density distribution fit to the real TEC measurements. The problem is considered as an optimization problem where the optimization parameters are the parameters of the parametric perturbation models. Proposed technique is applied over Turkey, on both calm and storm days of the ionosphere. Results show that the proposed technique produces 3D electron density distributions which are compliant with IRI-Plas model, GPS TEC measurements and ionosonde measurements. The effect of the GPS receiver station number on the performance of the proposed technique is investigated. Results showed that 7 GPS receiver stations in a region as large as Turkey is sufficient for both calm and storm days of the ionosphere. Since the ionization levels in the ionosphere are highly correlated in time, the proposed technique is extended to the time domain by applying Kalman based tracking and smoothing approaches onto the obtained results. Combining Kalman methods with the proposed 3D CIT technique creates a robust 4D ionospheric electron density estimation model, and has the advantage of decreasing the computational cost of the proposed method. Results applied on both calm and storm days of the ionosphere show that, new technique produces more robust solutions especially when the number of GPS receiver stations in the region is small. This study is supported by TUBITAK 114E541, 115E915 and Joint TUBITAK 114E092 and AS CR 14/001 projects.

Accurate Realization of GPS Vertical Global Reference Frame

NASA Technical Reports Server (NTRS)

Elosegui, Pedro

2004-01-01

The few millimeter per year level accuracy of radial global velocity estimates with the Global Positioning System (GPS) is at least an order of magnitude poorer than the accuracy of horizontal global motions. An improvement in the accuracy of radial global velocities would have a very positive impact on a number of geophysical studies of current general interest such as global sea-level and climate change, coastal hazards, glacial isostatic adjustment, atmospheric and oceanic loading, glaciology and ice mass variability, tectonic deformation and volcanic inflation, and geoid variability. The goal of this project is to improve our current understanding of GPS error sources associated with estimates of radial velocities at global scales. GPS error sources relevant to this project can be classified in two broad categories: (1) those related to the analysis of the GPS phase observable, and (2) those related to the combination of the positions and velocities of a set of globally distributed stations as determined from the analysis of GPS data important aspect in the first category include the effect on vertical rate estimates due to standard analysis choices, such as orbit modeling, network geometry, ambiguity resolution, as well as errors in models (or simply the lack of models) for clocks, multipath, phase-center variations, atmosphere, and solid-Earth tides. The second category includes the possible methods of combining and defining terrestrial reference flames for determining vertical velocities in a global scale. The latter has been the subject of our research activities during this reporting period.

A strawman SLR program plan for the 1990s

NASA Technical Reports Server (NTRS)

Degnan, John J.

1994-01-01

A series of programmatic and technical goals for the satellite laser ranging (SLR) network are presented. They are: (1) standardize the performance of the global SLR network; (2) improve the geographic distribution of stations; (3) reduce costs of field operations and data processing; (4) expand the 24 hour temporal coverage to better serve the growing constellation of satellites; (5) improve absolute range accuracy to 2 mm at key stations; (6) improve satellite force, radiative propagation, and station motion models and investigate alternative geodetic analysis techniques; (7) support technical intercomparison and the Terrestrial Reference Frame through global collocations; (8) investigate potential synergisms between GPS and SLR.

The Plate Boundary Observatory Cascadia Network: Development and Installation of a Large Scale Real-time GPS Network

NASA Astrophysics Data System (ADS)

Austin, K. E.; Blume, F.; Berglund, H. T.; Feaux, K.; Gallaher, W. W.; Hodgkinson, K. M.; Mattioli, G. S.; Mencin, D.

2014-12-01

The EarthScope Plate Boundary Observatory (PBO), through a NSF-ARRA supplement, has enhanced the geophysical infrastructure in in the Pacific Northwest by upgrading a total of 282 Plate Boundary Observatory GPS stations to allow the collection and distribution of high-rate (1 Hz), low-latency (<1 s) data streams (RT-GPS). These upgraded stations supplemented the original 100 RT-GPS stations in the PBO GPS network. The addition of the new RT-GPS sites in Cascadia should spur new volcano and earthquake research opportunities in an area of great scientific interest and high geophysical hazard. Streaming RT-GPS data will enable researchers to detect and investigate strong ground motion during large geophysical events, including a possible plate-interface earthquake, which has implications for earthquake hazard mitigation. A Mw 6.9 earthquake occurred on March 10, 2014, off the coast of northern California. As a response, UNAVCO downloaded high-rate GPS data from Plate Boundary Observatory stations within 500 km of the epicenter of the event, providing a good test of network performance.In addition to the 282 stations upgraded to real-time, 22 new meteorological instruments were added to existing PBO stations. Extensive testing of BGAN satellite communications systems has been conducted to support the Cascadia RT-GPS upgrades and the installation of three BGAN satellite fail over systems along the Cascadia margin will allow for the continuation of data flow in the event of a loss of primary communications during in a large geophysical event or other interruptions in commercial cellular networks. In summary, with these additional upgrades in the Cascadia region, the PBO RT-GPS network will increase to 420 stations. Upgrades to the UNAVCO data infrastructure included evaluation and purchase of the Trimble Pivot Platform, servers, and additional hardware for archiving the high rate data, as well as testing and implementation of GLONASS and Trimble RTX positioning on the receivers. UNAVCO staff is working closely with the UNAVCO community to develop data standards, protocols, and a science plan for the use of RT-GPS data.

Temporal–Spatial Surface Seasonal Mass Changes and Vertical Crustal Deformation in South China Block from GPS and GRACE Measurements

PubMed Central

He, Meilin; Shen, Wenbin; Chen, Ruizhi; Ding, Hao; Guo, Guangyi

2017-01-01

The solid Earth deforms elastically in response to variations of surface atmosphere, hydrology, and ice/glacier mass loads. Continuous geodetic observations by Global Positioning System (CGPS) stations and Gravity Recovery and Climate Experiment (GRACE) record such deformations to estimate seasonal and secular mass changes. In this paper, we present the seasonal variation of the surface mass changes and the crustal vertical deformation in the South China Block (SCB) identified by GPS and GRACE observations with records spanning from 1999 to 2016. We used 33 CGPS stations to construct a time series of coordinate changes, which are decomposed by empirical orthogonal functions (EOFs) in SCB. The average weighted root-mean-square (WRMS) reduction is 38% when we subtract GRACE-modeled vertical displacements from GPS time series. The first common mode shows clear seasonal changes, indicating seasonal surface mass re-distribution in and around the South China Block. The correlation between GRACE and GPS time series is analyzed which provides a reference for further improvement of the seasonal variation of CGPS time series. The results of the GRACE observations inversion are the surface deformations caused by the surface mass change load at a rate of about −0.4 to −0.8 mm/year, which is used to improve the long-term trend of non-tectonic loads of the GPS vertical velocity field to further explain the crustal tectonic movement in the SCB and surroundings. PMID:29301236

Multichannel Singular Spectrum Analysis in the Estimates of Common Environmental Effects Affecting GPS Observations

NASA Astrophysics Data System (ADS)

Gruszczynska, Marta; Rosat, Severine; Klos, Anna; Gruszczynski, Maciej; Bogusz, Janusz

2018-03-01

We described a spatio-temporal analysis of environmental loading models: atmospheric, continental hydrology, and non-tidal ocean changes, based on multichannel singular spectrum analysis (MSSA). We extracted the common annual signal for 16 different sections related to climate zones: equatorial, arid, warm, snow, polar and continents. We used the loading models estimated for a set of 229 ITRF2014 (International Terrestrial Reference Frame) International GNSS Service (IGS) stations and discussed the amount of variance explained by individual modes, proving that the common annual signal accounts for 16, 24 and 68% of the total variance of non-tidal ocean, atmospheric and hydrological loading models, respectively. Having removed the common environmental MSSA seasonal curve from the corresponding GPS position time series, we found that the residual station-specific annual curve modelled with the least-squares estimation has the amplitude of maximum 2 mm. This means that the environmental loading models underestimate the seasonalities observed by the GPS system. The remaining signal present in the seasonal frequency band arises from the systematic errors which are not of common environmental or geophysical origin. Using common mode error (CME) estimates, we showed that the direct removal of environmental loading models from the GPS series causes an artificial loss in the CME power spectra between 10 and 80 cycles per year. When environmental effect is removed from GPS series with MSSA curves, no influence on the character of spectra of CME estimates was noticed.

Multichannel Singular Spectrum Analysis in the Estimates of Common Environmental Effects Affecting GPS Observations

NASA Astrophysics Data System (ADS)

Gruszczynska, Marta; Rosat, Severine; Klos, Anna; Gruszczynski, Maciej; Bogusz, Janusz

2018-05-01

We described a spatio-temporal analysis of environmental loading models: atmospheric, continental hydrology, and non-tidal ocean changes, based on multichannel singular spectrum analysis (MSSA). We extracted the common annual signal for 16 different sections related to climate zones: equatorial, arid, warm, snow, polar and continents. We used the loading models estimated for a set of 229 ITRF2014 (International Terrestrial Reference Frame) International GNSS Service (IGS) stations and discussed the amount of variance explained by individual modes, proving that the common annual signal accounts for 16, 24 and 68% of the total variance of non-tidal ocean, atmospheric and hydrological loading models, respectively. Having removed the common environmental MSSA seasonal curve from the corresponding GPS position time series, we found that the residual station-specific annual curve modelled with the least-squares estimation has the amplitude of maximum 2 mm. This means that the environmental loading models underestimate the seasonalities observed by the GPS system. The remaining signal present in the seasonal frequency band arises from the systematic errors which are not of common environmental or geophysical origin. Using common mode error (CME) estimates, we showed that the direct removal of environmental loading models from the GPS series causes an artificial loss in the CME power spectra between 10 and 80 cycles per year. When environmental effect is removed from GPS series with MSSA curves, no influence on the character of spectra of CME estimates was noticed.

Integration of the Plate Boundary Observatory and Existing GPS Networks in Southern California: A Multi Use Geodetic Network

NASA Astrophysics Data System (ADS)

Walls, C.; Blume, F.; Meertens, C.; Arnitz, E.; Lawrence, S.; Miller, S.; Bradley, W.; Jackson, M.; Feaux, K.

2007-12-01

The ultra-stable GPS monument design developed by Southern California Geodetic Network (SCIGN) in the late 1990s demonstrates sub-millimeter errors on long time series where there are a high percentage of observations and low multipath. Following SCIGN, other networks such as PANGA and BARGEN have adopted the monument design for both deep drilled braced monuments (DDBM = 5 legs grouted 10.7 meters into bedrock/stratigraphy) and short drilled braced monuments (SDBM = 4 legs epoxied 2 meters into bedrock). A Plate Boundary Observatory (PBO) GPS station consists of a "SCIGN" style monument and state of the art NetRS receiver and IP based communications. Between the years 2003-2008 875 permanent PBO GPS stations are being built throughout the United States. Concomitant with construction of the PBO the majority of pre-existing GPS stations that meet stability specifications are being upgraded with Trimble NetRS and IP based communications to PBO standards under the EarthScope PBO Nucleus project. In 2008, with completed construction of the Plate Boundary Observatory, more than 1100 GPS stations will share common design specifications and have identical receivers with common communications making it the most homogenous geodetic network in the World. Of the 875 total Plate Boundary Observatory GPS stations, 211 proposed sites are distributed throughout the Southern California region. As of August 2007 the production status is: 174 stations built (81 short braced monuments, 93 deep drilled braced monuments), 181 permits signed, 211 permits submitted and 211 station reconnaissance reports. The balance of 37 stations (19 SDBM and 18 DDBM) will be built over the next year from Long Valley to the Mexico border in order of priority as recommended by the PBO Transform, Extension and Magmatic working groups. Fifteen second data is archived for each station and 1 Hz as well as 5 Hz data is buffered to be triggered for download in the event of an earthquake. Communications equipment includes CDMA Proxicast modems, Hughes Vsat, Intuicom 900 MHz Ethernet bridge radios and several "real-time" sites use 2.4 GHz Wilan radios. Ultimately, 125 of the existing former-SCIGN GPS stations will be integrated into the So Cal region of PBO, of which 25 have real-time data streams. At the time of this publication the total combined Southern California region has over 40 stations streaming real-time data using both radios and CDMA modems. The real-time GPS sites provide specific benefits beyond the standard GPS station: they can provide a live correction for local surveyors and can be used to trigger an alarm if large displacements are recorded. The cross fault spatial distribution of these 336 GPS stations in the seismically active southern California region has the grand potential of augmenting a strong motion earthquake early warning system.

Crustal deformation rates in Central and Eastern U.S. inferred from GPS

USGS Publications Warehouse

Gan, Weijun; Prescott, W.H.

2001-01-01

Analysis of continuous GPS observations between 1996 and 2000 at 62 stations distributed throughout the central and eastern United States suggests that the area is generally stable. Seven of the 62 stations show anomalous velocities, but there is reason to suspect their monument stability. Assuming the remaining 55 stations are stable with respect to interior North America, we have found the North America-ITRF97 Euler vector (-1.88o ± 1.04oN, 77.67o ± 0.39oW, 0.201o ± 0.004o Myr-1) that minimizes the RMS station velocity. Referred to fixed North America, all of these velocities are less than 3.2 mm yr-1. Motion of several stations suggests the Mississippi embayment may be moving southward away from the rest of the continent at a rate of 1.7±0.9 mm yr-1. The motion of the embayment produces a large gradient in velocity which, in turn, implies the highest seismic moment accumulation rate that we found. Although the highest rate is only marginally significant, the fact that it occurs near New Madrid, where earthquake risk is thought to be high, argues that the anomaly may be real. Nevertheless, the identification of the anomaly remains tentative.

Present day crustal deformation of the Italian peninsula observed by permanent GPS stations

NASA Astrophysics Data System (ADS)

Devoti, Roberto; Esposito, Alessandra; Galvani, Alessandro; Pietrantonio, Grazia; Pisani, Anna Rita; Riguzzi, Federica; Sepe, Vincenzo

2010-05-01

Italian penisula is a crucial area in the Mediterranean region to understand the active deformation processes along Nubia-Eurasia plate boundary. We present the velocity and strain rate fields of the Italian area derived from continuous GPS observations of more than 300 sites in the time span 1998-2009. The GPS networks were installed and managed by different institutions and for different purposes; altogether they cover the whole country with a mean inter-site distance of about 50 km and provide a valuable source of data to map the present day kinematics of the region. The data processing is performed by BERNESE software ver. 5.0, adopting a distributed session approach, with more than 10 clusters, sharing common stations, each of them consisting of about 40 stations. Daily loosely constrained solutions are routinely produced for each cluster and then combined into a network daily loose solution. Subsequently daily solutions are transformed on the chosen reference frame and the constrained time series are fitted using the complete covariance matrix, simultaneously estimating site velocities together with annual signals and sporadic offsets at epochs of instrumental changes. In this work we provide an updated detailed picture of the horizontal and vertical kinematics (velocity maps) and deformation pattern (strain rate maps) of the Italian area. The results show several crustal domains characterized by different velocity rates and styles of deformation.

The quasi-biennial vertical oscillations at global GPS stations: identification by ensemble empirical mode decomposition.

PubMed

Pan, Yuanjin; Shen, Wen-Bin; Ding, Hao; Hwang, Cheinway; Li, Jin; Zhang, Tengxu

2015-10-14

Modeling nonlinear vertical components of a GPS time series is critical to separating sources contributing to mass displacements. Improved vertical precision in GPS positioning at stations for velocity fields is key to resolving the mechanism of certain geophysical phenomena. In this paper, we use ensemble empirical mode decomposition (EEMD) to analyze the daily GPS time series at 89 continuous GPS stations, spanning from 2002 to 2013. EEMD decomposes a GPS time series into different intrinsic mode functions (IMFs), which are used to identify different kinds of signals and secular terms. Our study suggests that the GPS records contain not only the well-known signals (such as semi-annual and annual signals) but also the seldom-noted quasi-biennial oscillations (QBS). The quasi-biennial signals are explained by modeled loadings of atmosphere, non-tidal and hydrology that deform the surface around the GPS stations. In addition, the loadings derived from GRACE gravity changes are also consistent with the quasi-biennial deformations derived from the GPS observations. By removing the modeled components, the weighted root-mean-square (WRMS) variation of the GPS time series is reduced by 7.1% to 42.3%, and especially, after removing the seasonal and QBO signals, the average improvement percentages for seasonal and QBO signals are 25.6% and 7.5%, respectively, suggesting that it is significant to consider the QBS signals in the GPS records to improve the observed vertical deformations.

The Quasi-Biennial Vertical Oscillations at Global GPS Stations: Identification by Ensemble Empirical Mode Decomposition

PubMed Central

Pan, Yuanjin; Shen, Wen-Bin; Ding, Hao; Hwang, Cheinway; Li, Jin; Zhang, Tengxu

2015-01-01

Modeling nonlinear vertical components of a GPS time series is critical to separating sources contributing to mass displacements. Improved vertical precision in GPS positioning at stations for velocity fields is key to resolving the mechanism of certain geophysical phenomena. In this paper, we use ensemble empirical mode decomposition (EEMD) to analyze the daily GPS time series at 89 continuous GPS stations, spanning from 2002 to 2013. EEMD decomposes a GPS time series into different intrinsic mode functions (IMFs), which are used to identify different kinds of signals and secular terms. Our study suggests that the GPS records contain not only the well-known signals (such as semi-annual and annual signals) but also the seldom-noted quasi-biennial oscillations (QBS). The quasi-biennial signals are explained by modeled loadings of atmosphere, non-tidal and hydrology that deform the surface around the GPS stations. In addition, the loadings derived from GRACE gravity changes are also consistent with the quasi-biennial deformations derived from the GPS observations. By removing the modeled components, the weighted root-mean-square (WRMS) variation of the GPS time series is reduced by 7.1% to 42.3%, and especially, after removing the seasonal and QBO signals, the average improvement percentages for seasonal and QBO signals are 25.6% and 7.5%, respectively, suggesting that it is significant to consider the QBS signals in the GPS records to improve the observed vertical deformations. PMID:26473882

Geodetic positioning of the Aerospace Electronics Research Lab (ERL) Osborne Time Transfer Receiver (TTR) using the GPS NAVSTAR Block I satellites

NASA Technical Reports Server (NTRS)

Liu, Anthony S.

1990-01-01

Aerospace has routinely processed the Osborne Time Transfer Receiver (TTR) data for the purpose of monitoring the performance of ground and GPS atomic clocks in near real-time with on-line residual displays and characterizing clock stability with Allan Variance calculations. Recently, Aerospace added the ability to estimate the TTR's location by differentially correcting the TTR's location in the WGS84 reference system. This new feature is exercised on a set of TTR clock phase data and Sub-meter accurate station location estimates of the TTR at the Aerospace Electronic Research Lab (ERL) are obtained.

Ionospheric Modelling using GPS to Calibrate the MWA. I: Comparison of First Order Ionospheric Effects between GPS Models and MWA Observations

NASA Astrophysics Data System (ADS)

Arora, B. S.; Morgan, J.; Ord, S. M.; Tingay, S. J.; Hurley-Walker, N.; Bell, M.; Bernardi, G.; Bhat, N. D. R.; Briggs, F.; Callingham, J. R.; Deshpande, A. A.; Dwarakanath, K. S.; Ewall-Wice, A.; Feng, L.; For, B.-Q.; Hancock, P.; Hazelton, B. J.; Hindson, L.; Jacobs, D.; Johnston-Hollitt, M.; Kapińska, A. D.; Kudryavtseva, N.; Lenc, E.; McKinley, B.; Mitchell, D.; Oberoi, D.; Offringa, A. R.; Pindor, B.; Procopio, P.; Riding, J.; Staveley-Smith, L.; Wayth, R. B.; Wu, C.; Zheng, Q.; Bowman, J. D.; Cappallo, R. J.; Corey, B. E.; Emrich, D.; Goeke, R.; Greenhill, L. J.; Kaplan, D. L.; Kasper, J. C.; Kratzenberg, E.; Lonsdale, C. J.; Lynch, M. J.; McWhirter, S. R.; Morales, M. F.; Morgan, E.; Prabu, T.; Rogers, A. E. E.; Roshi, A.; Shankar, N. Udaya; Srivani, K. S.; Subrahmanyan, R.; Waterson, M.; Webster, R. L.; Whitney, A. R.; Williams, A.; Williams, C. L.

2015-08-01

We compare first-order (refractive) ionospheric effects seen by the MWA with the ionosphere as inferred from GPS data. The first-order ionosphere manifests itself as a bulk position shift of the observed sources across an MWA field of view. These effects can be computed from global ionosphere maps provided by GPS analysis centres, namely the CODE. However, for precision radio astronomy applications, data from local GPS networks needs to be incorporated into ionospheric modelling. For GPS observations, the ionospheric parameters are biased by GPS receiver instrument delays, among other effects, also known as receiver DCBs. The receiver DCBs need to be estimated for any non-CODE GPS station used for ionosphere modelling. In this work, single GPS station-based ionospheric modelling is performed at a time resolution of 10 min. Also the receiver DCBs are estimated for selected Geoscience Australia GPS receivers, located at Murchison Radio Observatory, Yarragadee, Mount Magnet and Wiluna. The ionospheric gradients estimated from GPS are compared with that inferred from MWA. The ionospheric gradients at all the GPS stations show a correlation with the gradients observed with the MWA. The ionosphere estimates obtained using GPS measurements show promise in terms of providing calibration information for the MWA.

Real-time source deformation modeling through GNSS permanent stations at Merapi volcano (Indonesia

NASA Astrophysics Data System (ADS)

Beauducel, F.; Nurnaning, A.; Iguchi, M.; Fahmi, A. A.; Nandaka, M. A.; Sumarti, S.; Subandriyo, S.; Metaxian, J. P.

2014-12-01

Mt. Merapi (Java, Indonesia) is one of the most active and dangerous volcano in the world. A first GPS repetition network was setup and periodically measured since 1993, allowing detecting a deep magma reservoir, quantifying magma flux in conduit and identifying shallow discontinuities around the former crater (Beauducel and Cornet, 1999;Beauducel et al., 2000, 2006). After the 2010 centennial eruption, when this network was almost completely destroyed, Indonesian and Japanese teams installed a new continuous GPS network for monitoring purpose (Iguchi et al., 2011), consisting of 3 stations located at the volcano flanks, plus a reference station at the Yogyakarta Observatory (BPPTKG).In the framework of DOMERAPI project (2013-2016) we have completed this network with 5 additional stations, which are located on the summit area and volcano surrounding. The new stations are 1-Hz sampling, GNSS (GPS + GLONASS) receivers, and near real-time data streaming to the Observatory. An automatic processing has been developed and included in the WEBOBS system (Beauducel et al., 2010) based on GIPSY software computing precise daily moving solutions every hour, and for different time scales (2 months, 1 and 5 years), time series and velocity vectors. A real-time source modeling estimation has also been implemented. It uses the depth-varying point source solution (Mogi, 1958; Williams and Wadge, 1998) in a systematic inverse problem model exploration that displays location, volume variation and 3-D probability map.The operational system should be able to better detect and estimate the location and volume variations of possible magma sources, and to follow magma transfer towards the surface. This should help monitoring and contribute to decision making during future unrest or eruption.

Combining Real-time Seismic and Geodetic Data to Improve Rapid Earthquake Information

NASA Astrophysics Data System (ADS)

Murray, M. H.; Neuhauser, D. S.; Gee, L. S.; Dreger, D. S.; Basset, A.; Romanowicz, B.

2002-12-01

The Berkeley Seismological Laboratory operates seismic and geodetic stations in the San Francisco Bay area and northern California for earthquake and deformation monitoring. The seismic systems, part of the Berkeley Digital Seismic Network (BDSN), include strong motion and broadband sensors, and 24-bit dataloggers. The data from 20 GPS stations, part of the Bay Area Regional Deformation (BARD) network of more than 70 stations in northern California, are acquired in real-time. We have developed methods to acquire GPS data at 12 stations that are collocated with the seismic systems using the seismic dataloggers, which have large on-site data buffer and storage capabilities, merge it with the seismic data stream in MiniSeed format, and continuously stream both data types using reliable frame relay and/or radio modem telemetry. Currently, the seismic data are incorporated into the Rapid Earthquake Data Integration (REDI) project to provide notification of earthquake magnitude, location, moment tensor, and strong motion information for hazard mitigation and emergency response activities. The geodetic measurements can provide complementary constraints on earthquake faulting, including the location and extent of the rupture plane, unambiguous resolution of the nodal plane, and distribution of slip on the fault plane, which can be used, for example, to refine strong motion shake maps. We are developing methods to rapidly process the geodetic data to monitor transient deformation, such as coseismic station displacements, and for combining this information with the seismic observations to improve finite-fault characterization of large earthquakes. The GPS data are currently processed at hourly intervals with 2-cm precision in horizontal position, and we are beginning a pilot project in the Bay Area in collaboration with the California Spatial Reference Center to do epoch-by-epoch processing with greater precision.

GPS Lessons Learned from the International Space Station, Space Shuttle and X-38

NASA Technical Reports Server (NTRS)

Goodman, John L.

2005-01-01

This document is a collection of writings concerning the application of Global Positioning System (GPS) technology to the International Space Station (ISS), Space Shuttle, and X-38 vehicles. An overview of how GPS technology was applied is given for each vehicle, including rationale behind the integration architecture, and rationale governing the use (or non-use) of GPS data during flight.

Gnss Geodetic Monitoring as Support of Geodynamics Research in Colombia, South America

NASA Astrophysics Data System (ADS)

Mora-Paez, H.; Acero-Patino, N.; Rodriguez-Zuluaga, J. S.; Diederix, H.; Bohorquez-Orozco, O. P.; Martinez-Diaz, G. P.; Diaz-Mila, F.; Giraldo-Londono, L. S.; Cardozo-Giraldo, S.; Vasquez-Ospina, A. F.; Lizarazo, S. C.

2013-05-01

To support the geodynamics research at the northwestern corner of South America, GEORED, the acronym for "Geodesia: Red de Estudios de Deformación" has been adopted for the Project "Implementation of the National GNSS Network for Geodynamics" carried out by the Colombian Geological Survey, (SGC), formerly INGEOMINAS. Beginning in 2007, discussions within the GEORED group led to a master plan for the distribution of the base permanent GPS/GNSS station array and specific areas of interest for campaign site construction. The use of previously identified active faults as preferred structures along which stresses are transferred through the deformational area led to the idea of segmentation of the North Andes within Colombia into 20 tectonic sub-blocks. Each of the 20 sub-blocks is expected to have, at least, three-four permanent GPS/GNSS stations within the block along with construction of campaign sites along the boundaries. Currently, the GEORED Network is managing 46 continuously including: 40 GEORED GPS/GNSS continuously operating stations; 4 GNSS continuously operating stations provided by the COCONet (Continuously Operating Caribbean GPS Observational Network) Project; the Bogotá IGS GPS station (BOGT), installed in 1994 under the agreement between JPL-NASA and the SGC; and the San Andres Island station, installed in 2007 under the MOU between UCAR and the SGC. In addition to the permanent installations, more than 230 GPS campaign sites have been constructed and are being occupied one time per year. The Authority of the Panama Canal and the Escuela Politecnica de Quito have also provided data of 4 and 5 GPS/GNSS stations respectively. The GPS data are processed using the GIPSY-OASIS II software, and the GPS time series of daily station positions give fundamental information for both regional and local geodynamics studies. Until now, we have obtained 100 quality vector velocities for Colombia, 23 of them as part of the permanent network. The GPS/GNSS stations are located on the three major plates that interact within the Wide Plate Margin Deformation Zone including existing permanent installations on IGS Galapagos and Malpelo Islands on the Nazca Plate, and San Andres Island on the Caribbean plate. The velocity vectors confirm the oblique subduction of the Nazca Plate and Carnegie aseismic ridge collision processes at the Colombia-Ecuador trench which are assumed to be the mechanism for the transpressional deformation and the "escape" of the North Andes Block (NAB). The northernmost vectors in Colombia are indicative of the ongoing collision of the Panama Arc with northwestern Colombia. Planned for the year 2013 is the installation of 10 additional GNSS continuously operating stations, and construction of 20 GPS campaign sites.

Calibration of Envisat radar altimeter over Lake Issykkul

NASA Astrophysics Data System (ADS)

Crétaux, J.-F.; Bergé-Nguyen, M.; Calmant, S.; Romanovski, V. V.; Meyssignac, B.; Perosanz, F.; Tashbaeva, S.; Arsen, A.; Fund, F.; Martignago, N.; Bonnefond, P.; Laurain, O.; Morrow, R.; Maisongrande, P.

2013-04-01

This study presents the results of calibration/validation (C/V) of Envisat satellite radar altimeter over Lake Issykkul located in Kyrgyzstan, which was chosen as a dedicated radar altimetry C/V site in 2004. The objectives are to estimate the absolute altimeter bias of Envisat and its orbit based on cross-over analysis with TOPEX/Poseidon (T/P), Jason-1 and Jason-2 over the ocean. We have used a new method of GPS data processing in a kinematic mode, developed at the Groupe de Recherche de Geodesie Spatiale (GRGS), which allows us to calculate the position of the GPS antenna without needing a GPS reference station. The C/V is conducted using various equipments: a local GPS network, a moving GPS antenna along the satellites tracks over Lake Issykkul, In Situ level gauges and weather stations. The absolute bias obtained for Envisat from field campaigns conducted in 2009 and 2010 is between 62.1 and 63.4 ± 3.7 cm, using the Ice-1 retracking algorithm, and between 46.9 and 51.2 cm with the ocean retracking algorithm. These results differ by about 10 cm from previous studies, principally due to improvement of the C/V procedure. Apart from the new algorithm for GPS data processing and the orbit error reduction, more attention has been paid to the GPS antenna height calculation, and we have reduced the errors induced by seiche over Lake Issykkul. This has been assured using cruise data along the Envisat satellite track at the exact date of the pass of the satellite for the two campaigns. The calculation of the Envisat radar altimeter bias with respect to the GPS levelling is essential to allow the continuity of multi-mission data on the same orbit, with the expected launch of SARAL/Altika mission in 2012. Implications for hydrology in particular, will be to produce long term homogeneous and reliable time series of lake levels worldwide.

Using Airborne Lidar Data from IcePod to Measure Annual and Seasonal Ice Changes Over Greenland

NASA Astrophysics Data System (ADS)

Frearson, N.; Bertinato, C.; Das, I.

2014-12-01

The IcePod is a multi-sensor airborne science platform that supports a wide suite of instruments, including a Riegl VQ-580 infrared scanning laser, GPS-inertial positioning system, shallow and deep-ice radars, visible-wave and infrared cameras, and upward-looking pyrometer. These instruments allow us to image the ice from top to bottom, including the surface of melt-water plumes that originate at the ice-ocean boundary. In collaboration with the New York Air National Guard 109th Airlift Wing, the IcePod is flown on LC-130 aircraft, which presents the unique opportunity to routinely image the Greenland ice sheet several times within a season. This is particularly important for mass balance studies, as we can measure elevation changes during the melt season. During the 2014 summer, laser data was collected via IcePod over the Greenland ice sheet, including Russell Glacier, Jakobshavn Glacier, Eqip Glacier, and Summit Camp. The Icepod will also be routinely operated in Antarctica. We present the initial testing, calibration, and error estimates from the first set of laser data that were collected on IcePod. At a survey altitude of 1000 m, the laser swath covers ~ 1000 m. A Northrop-Grumman LN-200 tactical grade IMU is rigidly attached to the laser scanner to provide attitude data at a rate of 200 Hz. Several methods were used to determine the lever arm between the IMU center of navigation and GPS antenna phase center, terrestrial scanning laser, total station survey, and optimal estimation. Additionally, initial bore sight calibration flights yielded misalignment angles within an accuracy of ±4 cm. We also performed routine passes over the airport ramp in Kangerlussuaq, Greenland, comparing the airborne GPS and Lidar data to a reference GPS-based ground survey across the ramp, spot GPS points on the ramp and a nearby GPS base station. Positioning errors can severely impact the accuracy of a laser altimeter when flying over remote regions such as across the ice sheets. Setting up GPS base stations along the flight track can prove to be logistically challenging. We have processed the GPS-inertial data using both DGPS and PPP and present the comparison of those results here. Finally, we discuss our processing, calibration and error estimation methods and compare our results to previously flown IceBridge lines.

Towards a Refined Realisation of the Terrestrial Reference System

NASA Astrophysics Data System (ADS)

Angermann, D.; Drewes, H.; Meisel, B.; Kruegel, M.; Tesmer, V.

2004-12-01

Global reference frames provide the framework for scientific investigations of the Earth's system (e.g. plate tectonics, sea level change, seasonal and secular loading signals, atmosphere dynamics, Earth orientation excitation), as well as for many practical applications (e.g. surveying and navigation). Today, space geodetic techniques allow to determine geodetic parameters (e.g. station positions, Earth rotation) with a precision of a few millimeters (or even better). However, this high accuracy is not reflected by current realisations of the terrestrial reference system. To fully exploit the potential of the space geodetic observations for investigations of various global and regional, short-term, seasonal and secular phenomena of the Earth's system, the reference frame must be realised with the highest accuracy, spatial and temporal consistency and stability over decades. Furthermore, future progress in Earth sciences will fundamentally depend on understanding the Earth as a system, into which the three areas of geodetic research (geometry/deformation, Earth rotation, gravity) are to be integrated. The presentation focusses on various aspects that must be considered for a refined realisation of the terrestrial reference system, such as the development of suitable methods for the combination of the contributing space geodetic observations, the realisation of the TRF datum and the parameterisation of site motions. For this purpose we investigated time series of station positions and datum parameters obtained from VLBI, SLR, GPS and DORIS solutions, and compared the results at co-location sites and with other studies. Furthermore, we present results obtained from a TRS realisation based on epoch (weekly/daily) normal equations with station positions and daily Earth Orientation Parameters (EOP) using five years (1999-2004) of VLBI, SLR, GPS and DORIS data. This refined approach has major advantages compared to past TRF realisations based on multi-year solutions with station positions at a given epoch and constant velocities, as for instance non-linear effects of site positions and datum parameters can be considered, and consistency between TRF and EOPs can be achieved. First results of this new approach are promising.

New PBO GPS Station Construction: Eastern Region Network Enhancements and Multiple-Monument Stability Comparisons

NASA Astrophysics Data System (ADS)

Dittmann, S. T.; Austin, K. E.; Berglund, H. T.; Blume, F.; Feaux, K.; Mann, D.; Mattioli, G. S.; Walls, C. P.

2013-12-01

The Plate Boundary Observatory (PBO) network consists of 1100 continuously operating, permanent GPS stations throughout the United States. The majority of this network was constructed using NSF-MREFC funding as part of the EarthScope Project during FY2003-FY2008. Since FY2009, UNAVCO has operated and maintained PBO through a Cooperative Agreement (CA) with NSF. Construction of new, permanent GPS monuments in the PBO network was the result of two change orders to the original PBO O&M CA. Change Order 33 (CO33) allocated funds to construct additional GPS stations at six locations in the Eastern Region of PBO. Three of these locations were designed to replace poorly performing existing GPS monuments in Georgia, Texas and New York. The remaining three new locations were selected to fill in gaps in network coverage in Pennsylvania, Wisconsin and North Dakota. Construction of all six new sites was completed in September 2013. Important scientific goals for CO33 include improvement of the stable North American reference frame, measurement of the vertical signal associated with the Glacial Isostatic Adjustment, and improved constraints on surface deformation and possible earthquakes, which occur in the low-strain tectonic setting of the eastern North American Plate. Change Order 35 (CO35) allocated funds to construct two additional geodetic monuments at five existing PBO stations in order to test and compare the long-term stability of various monument designs under near-identical geologic conditions. Sites were chosen to yield a variety of geographic, hydrologic and geologic conditions, including both fine-grained alluvium and crystalline bedrock. At each location, three different monuments (deep drill braced, short drill braced/driven-braced, mast/pillar) were built with 10 meter spacing, with shared power systems and data telemetry infrastructure. Construction of these multi-monument test locations began in October 2012 and finished in September 2013. See G010- Berglund, H., Blume, F., et al... 'PBO Monument Stability Experiment Analysis' for the initial results of the data quality comparison from these locations.

The effect of observing session duration on OPUS-RS results

NASA Astrophysics Data System (ADS)

Dincer Dogru, A.; Ugur Sanli, D.; Hayal, Adem G.; Berber, Mustafa

2016-04-01

Online GPS positioning software has now a widespread interest among practitioners and researchers. Researchers rescently use online software to monitor natural hazards such as landslides. The fact that this software usually employs continuously operating GPS stations of the International GNSS Service (IGS) as reference stations in the processing, the community of world-wide users is growing day by day. In the monitoring of landslides, rapid static mode of a GPS surveying is usually preferred because it is possible to have wider field coverage with only a few minutes of data and low cost ground markers. Results comparable to static positioning can be obtained with careful network design and processing strategies. Some online software such as OPUS-RS developed by the National Geodetic Survey (NGS) of the USA provides rapid static positioning engine that processes GPS data from sessions of only a few minutes. 15-minute is the recommended/standard observing session duration for OPUS-RS processing. In this study, using the CORS data operating in the US, we carried out some tests in which the observing session duration is changed from 8 through 118 minutes, and observed the accuracy change on the OPUS-RS solutions. Then we compared the results with the accuracy levels given for 15-min solutions by the NGS. We determined that there is the effect of changing observing session duration on the obtained results, and we report them in this study.

Velocity Noise in Space Shuttle and ISS GPS from the Ionosphere

NASA Technical Reports Server (NTRS)

Kramer, Leonard

2004-01-01

A viewgraph presentation on the noise velocity effects on the Space Shuttle and International Space Station (ISS) Global Positioning System (GPS) from the ionosphere is shown. The topics include: Scintillation in MAGR/S GPS used for Shuttle; 2) Geographic Distribution of Scintillation; 3) Diurnal Variability; 4) Feynman's interpretation of interference; 5) Angle between line of sight and S/C velocity; and 6) Space Station GPS

Analysis of ionosphere variability over low-latitude GNSS stations during 24th solar maximum period

NASA Astrophysics Data System (ADS)

Venkata Ratnam, D.; Sivavaraprasad, G.; Latha Devi, N. S. M. P.

2017-07-01

Global Positioning System (GPS) is a remote sensing tool of space weather and ionospheric variations. However, the interplanetary space-dependent drifts in the ionospheric irregularities cause predominant ranging errors in the GPS signals. The dynamic variability of the low-latitude ionosphere is an imperative threat to the satellite-based radio communication and navigation ranging systems. The study of temporal and spatial variations in the ionosphere has triggered new investigations in modelling, nowcasting and forecasting the ionospheric variations. Hence, in this paper, the dynamism in the day-to-day, month-to-month and seasonal variability of the ionospheric Total Electron Content (TEC) has been explored during the solar maximum period, January-December 2013, of the 24th solar cycle. The spatial and temporal variations of the ionosphere are analysed using the TEC values derived from three Indian low-latitude GPS stations, namely, Bengaluru, Guntur and Hyderabad, separated by 13-18° in latitude and 77-81° in longitude. The observed regional GPS-TEC variations are compared with the predicted TEC values of the International Reference Ionosphere (IRI-2012 and 2007) models. Ionospheric parameters such as Vertical TEC (VTEC), relative TEC deviation index and monthly variations in the grand-mean of ionosphere TEC and TEC intensity, along with the upper and lower quartiles, are adopted to investigate the ionosphere TEC variability during quiet and disturbed days. The maximum ionospheric TEC variability is found during March and September equinoxes, followed by December solstice while the minimum variability is observed during June solstice. IRI models are in reasonable agreement with GPS TEC but are overestimating during dawn hours (01:00-06:00 LT) as compared to the dusk hours. Higher percentage deviations are observed during equinoctial months than summer over EIA stations, Guntur and Hyderabad. GPS TEC variations are overestimated during dawn hours for all the seasons over Bengaluru. It has also been observed that positive storm effect (enhancement of TEC) is observed during the main phase of the March storm, 2013 (March 16-18, 2013) while both positive and negative storm effects (depletion of TEC) are registered during the main phase of the June storm, 2013 (June 28-30, 2013) at Bengaluru and Guntur, respectively. IRI-2012 model has slightly large discrepancies with the GPS-VTEC compared with the IRI-2007 model during the June storm, 2013 over Guntur station. This analysis highlights the importance of upgrading the IRI models due to their discrepancies during quiet and disturbed states of the ionosphere and developing an early warning forecast system to alert about ionosphere variability.

Crustal Deformation of the Central Walker Lane from GPS velocities: Block Rotations and Slip Rates

NASA Astrophysics Data System (ADS)

Bormann, J. M.; Hammond, W. C.; Kreemer, C. W.; Blewitt, G.; Wesnousky, S. G.

2010-12-01

The Walker Lane is a complex zone of active intracontinental transtension between the Sierra Nevada/Great Valley (SNGV) microplate and the Basin and Range in the western United States. Collectively, this ~100 km wide zone accommodates ~20% of the Pacific-North American relative plate motion. The Central Walker Lane (CWL) extends from the southern boundary of the Mina Deflection (~38.0°N) to the latitude of Lake Tahoe (~39.5°N) and encompasses the transition from Basin and Range style faulting in the east to the stable block motion of the SNGV microplate in the West. We combine GPS data from the Mobile Array of GPS for Nevada Transtension (MAGNET, http://geodesy.unr.edu/networks) with continuous observations from the EarthScope Plate Boundary Observatory to solve for rates of crustal deformation in the CWL through a block modeling approach. The GPS coordinate time series are derived in this region as part of a 7000-station global network solution using the latest JPL reanalysis of GPS orbits, and the latest antenna models for stations and satellites. The data were processed by precise point positioning using JPL's GIPSY OASIS II software followed by our custom Ambizap3 software, to produce a globally-consistent, ambiguity-resolved network solution. GPS time series in the western United States are rotated into a North America-fixed reference frame and are spatially filtered with respect to the secular motions of reference stations that demonstrate long-term secular stability. In the study region, we use 130 GPS velocities that are corrected for viscoelastic postseismic relaxation following 19th and 20th century earthquakes in the Central Nevada Seismic Belt to constrain rates of long-term fault slip and block rotation. The spatial density and precision of our velocity field (average station spacing of ~20 km with uncertainties well below 1 mm/yr) allow us to compare geodetically estimated slip rates with geologic observations as well as address specific questions about how shear is transferred from the Southern Walker Lane through the Mina Deflection and evaluate along-strike variation of the slip rate on the Sierra Nevada range front fault. Preliminary results confirm a pattern of deformation consistent with geological observations. Deformation zones are characterized by 1) left-lateral slip on east-northeast trending faults and clockwise block rotations in the Mina Deflection, 2) right-lateral slip on northwest trending faults along the eastern margin of the CWL, 3) east-west extension along north trending faults in the western portion of the CWL with right lateral slip increasing toward the SNGV microplate boundary, 4) clockwise rotation of blocks in the Carson Domain, and 5) northwest directed extension in the Basin and Range. Estimates of fault slip rates along the eastern boundary of the SNGV block find that slip is oblique with preliminary rates ranging between 0.4-0.8(±0.1) mm/yr horizontal extension and 0.9-1.5(±0.1) mm/yr right lateral.

Time Transfer by Laser Link T2L2: First Results of the 2010 Campaign

DTIC Science & Technology

2010-11-01

stations are also equipped by GPS and TWSTFT devices, this campaign should allow the performance comparisons between these systems operating with...Europe and Asia, GPS and TWSTFT links, and cold atomic fountains. Objectives of this second international campaign go from the comparison between T2L2...configuration in the ground setup (the time and frequency distribution has been changed, such as the two laser stations, the GPS receiver, the TWSTFT station

A comparison of annual vertical crustal displacements from GPS and Gravity Recovery and Climate Experiment (GRACE) over Europe

NASA Astrophysics Data System (ADS)

van Dam, T.; Wahr, J.; LavalléE, David

2007-03-01

We compare approximately 3 years of GPS height residuals (with respect to the International Terrestrial Reference Frame) with predictions of vertical surface displacements derived from the Gravity Recovery and Climate Experiment (GRACE) gravity fields for stations in Europe. An annual signal fit to the residual monthly heights, corrected for atmospheric pressure and barotropic ocean loading effects, should primarily represent surface displacements due to long-wavelength variations in water storage. A comparison of the annual height signal from GPS and GRACE over Europe indicates that at most sites, the annual signals do not agree in amplitude or phase. We find that unlike the annual signal predicted from GRACE, the annual signal in the GPS heights is not coherent over the region, displaying significant variability from site to site. Confidence in the GRACE data and the unlikely possibility of large-amplitude small-scale features in the load field not captured by the GRACE data leads us to conclude that some of the discrepancy between the GPS and GRACE observations is due to technique errors in the GPS data processing. This is evidenced by the fact that the disagreement between GPS and GRACE is largest at coastal sites, where mismodeling of the semidiurnal ocean tidal loading signal can result in spurious annual signals.

The Brave New World of Real-time GPS for Hazards Mitigation

NASA Astrophysics Data System (ADS)

Melbourne, T. I.; Szeliga, W. M.; Santillan, V. M.; Scrivner, C. W.

2015-12-01

Over 600 continuously-operating, real-time telemetered GPS receivers operate throughout California, Oregon, Washington and Alaska. These receivers straddle active crustal faults, volcanoes and landslides, the magnitude-9 Cascadia and northeastern Alaskan subduction zones and their attendant tsunamigenic regions along the Pacific coast. Around the circum-Pacific, there are hundreds more and the number is growing steadily as real-time networks proliferate. Despite offering the potential for sub-cm positioning accuracy in real-time useful for a broad array of hazards mitigation, these GPS stations are only now being incorporated into routine seismic, tsunami, volcanic, land-slide, space-weather, or meterologic monitoring. We will discuss NASA's READI (Real-time Earthquake Analysis for DIsasters) initiative. This effort is focussed on developing all aspects of real-time GPS for hazards mitigation, from establishing international data-sharing agreements to improving basic positioning algorithms. READI's long-term goal is to expand real-time GPS monitoring throughout the circum-Pacific as overseas data become freely available, so that it may be adopted by NOAA, USGS and other operational agencies responsible for natural hazards monitoring. Currently ~100 stations are being jointly processed by CWU and Scripps Inst. of Oceanography for algorithm comparison and downstream merging purposes. The resultant solution streams include point-position estimates in a global reference frame every second with centimeter accuracy, ionospheric total electron content and tropospheric zenith water content. These solutions are freely available to third-party agencies over several streaming protocols to enable their incorporation and use in hazards monitoring. This number will ramp up to ~400 stations over the next year. We will also discuss technical efforts underway to develop a variety of downstream applications of the real-time position streams, including the ability to broadcast solutions to thousands of users in real time, earthquake finite-fault and tsunami excitation estimations, and several user interfaces, both stand-alone client and browser-based, that allow interaction with both real-time position streams and their derived products.

Time aspects of the European Complement to GPS: Continental and transatlantic experimental phases

NASA Technical Reports Server (NTRS)

Uhrich, Pierre J. M.; Juompan, B.; Tourde, R.; Brunet, M.; Dutrey, J.-F.

1995-01-01

The CNES project of a European Complement to GPS (CE-GPS) is conceived to fulfill the needs of Civil Aviation for a non-precise approach phase with GPS as sole navigation means. This generates two missions: a monitoring mission - alarm of failure - ,and a navigation mission - generating a GPS-like signal on board the geostationary satellites. The host satellites will be the Inmarsat constellation. The CE-GPS missions lead to some time requirements, mainly the accuracy of GPS time restitution and of monitoring clock synchronization. To demonstrate that the requirements of the CE-GPS could be achieved, including the time aspects, an experiment has been scheduled over the Last two years, using a part of the Inmarsat II F-2 payload and specially designed ground stations based on 10 channels GPS receivers. This paper presents a review of the results obtained during the continental phase of the CE-GPS experiment with two stations in France, along with some experimental results obtained during the transatlantic phase (three stations in France, French Guyana, and South Africa). It describes the synchronization of the monitoring clocks using the GPS Common-view or the C- to L-Band transponder of the Inmarsat satellite, with an estimated accuracy better than 10 ns (1 sigma).

NChina16: A stable geodetic reference frame for geological hazard studies in North China

NASA Astrophysics Data System (ADS)

Wang, Guoquan; Bao, Yan; Gan, Weijun; Geng, Jianghui; Xiao, Gengru; Shen, Jack S.

2018-04-01

We have developed a stable North China Reference Frame 2016 (NChina16) using five years of continuous GPS observations (2011.8-2016.8) from 12 continuously operating reference stations (CORS) fixed to the North China Craton. Applications of NChina16 in landslide and subsidence studies are illustrated in this article. A method for realizing a regional geodetic reference frame is introduced. The primary result of this study is the seven parameters for transforming Cartesian ECEF (Earth-Centered, Earth-Fixed) coordinates X, Y, and Z from the International GNSS Service Reference Frame 2008 (IGS08) to NChina16. The seven parameters include the epoch that is used to align the regional reference frame to IGS08 and the time derivatives of three translations and three rotations. The GIPSY-OASIS (V6.4) software package was used to obtain the precise point positioning (PPP) daily solutions with respect to IGS08. The frame stability of NChina16 is approximately 0.5 mm/year in both horizontal and vertical directions. This study also developed a regional model for correcting seasonal motions superimposed into the vertical component of the GPS-derived displacement time series. Long-term GPS observations (1999-2016) from five CORS in North China were used to develop the seasonal model. According to this study, the PPP daily solutions with respect to NChina16 could achieve 2-3 mm horizontal accuracy and 4-5 mm vertical accuracy after being modified by the regional model. NChina16 will be critical to study geodynamic problems in North China, such as earthquakes, faulting, subsidence, and landslides. The regional reference frame will be periodically updated every few years to mitigate degradation of the frame with time and be synchronized with the update of IGS reference frame.

Further characterization of the time transfer capabilities of precise point positioning (PPP): the Sliding Batch Procedure.

PubMed

Guyennon, Nicolas; Cerretto, Giancarlo; Tavella, Patrizia; Lahaye, François

2009-08-01

In recent years, many national timing laboratories have installed geodetic Global Positioning System receivers together with their traditional GPS/GLONASS Common View receivers and Two Way Satellite Time and Frequency Transfer equipment. Many of these geodetic receivers operate continuously within the International GNSS Service (IGS), and their data are regularly processed by IGS Analysis Centers. From its global network of over 350 stations and its Analysis Centers, the IGS generates precise combined GPS ephemeredes and station and satellite clock time series referred to the IGS Time Scale. A processing method called Precise Point Positioning (PPP) is in use in the geodetic community allowing precise recovery of GPS antenna position, clock phase, and atmospheric delays by taking advantage of these IGS precise products. Previous assessments, carried out at Istituto Nazionale di Ricerca Metrologica (INRiM; formerly IEN) with a PPP implementation developed at Natural Resources Canada (NRCan), showed PPP clock solutions have better stability over short/medium term than GPS CV and GPS P3 methods and significantly reduce the day-boundary discontinuities when used in multi-day continuous processing, allowing time-limited, campaign-style time-transfer experiments. This paper reports on follow-on work performed at INRiM and NRCan to further characterize and develop the PPP method for time transfer applications, using data from some of the National Metrology Institutes. We develop a processing procedure that takes advantage of the improved stability of the phase-connected multi-day PPP solutions while allowing the generation of continuous clock time series, more applicable to continuous operation/monitoring of timing equipment.

Helicopter precision approach capability using the Global Positioning System

NASA Technical Reports Server (NTRS)

Kaufmann, David N.

1992-01-01

The period between 1 July and 31 December, 1992, was spent developing a research plan as well as a navigation system document and flight test plan to investigate helicopter precision approach capability using the Global Positioning System (GPS). In addition, all hardware and software required for the research was acquired, developed, installed, and verified on both the test aircraft and the ground-based reference station.

An update to the analysis of the Canadian Spatial Reference System

NASA Astrophysics Data System (ADS)

Ferland, R.; Piraszewski, M.; Craymer, M.

2015-12-01

The primary objective of the Canadian Spatial Reference System (CSRS) is to provide users access to a consistent geo-referencing infrastructure over the Canadian landmass. Global Navigation Satellite System (GNSS) positioning accuracy requirements ranges from meter level to mm level (e.g.: crustal deformation). The highest level of the Canadian infrastructure consist of a network of continually operating GPS and GNSS receivers, referred to as active control stations. The network includes all Canadian public active control stations, some bordering US CORS and Alaska stations, Greenland active control stations, as well as a selection of IGS reference frame stations. The Bernese analysis software is used for the daily processing and the combination into weekly solutions which form the basis for this analysis. IGS weekly final orbit, Earth Rotation parameters (ERP's) and coordinates products are used in the processing. For the more demanding users, the time dependant changes of station coordinates is often more important.All station coordinate estimates and related covariance information is used in this analysis. For each input solution, variance factor, translation, rotation and scale (and if needed their rates) or subsets of these are estimated. In the combination of these weekly solutions, station positions and velocities are estimated. Since the time series from the stations in these networks often experience changes in behavior, new (or reuse of) parameters are generally used in these situations. As is often the case with real data, unrealistic coordinates may occur. Automatic detection and removal of outliers is used in these cases. For the transformation, position and velocity parameters loose apriori estimates and uncertainties are provided. Alignment using the usual Helmert transformation to the latest IGb08 realization of ITRF is also performed during the adjustment.

GPS Time Series Analysis of Southern California Associated with the 2010 M7.2 El Mayor/Cucapah Earthquake

NASA Technical Reports Server (NTRS)

Granat, Robert; Donnellan, Andrea

2011-01-01

The Magnitude 7.2 El-Mayor/Cucapah earthquake the occurred in Mexico on April 4, 2012 was well instrumented with continuous GPS stations in California. Large Offsets were observed at the GPS stations as a result of deformation from the earthquake providing information about the co-seismic fault slip as well as fault slip from large aftershocks. Information can also be obtained from the position time series at each station.

Mapping experiment with space station

NASA Technical Reports Server (NTRS)

Wu, Sherman S. C.

1987-01-01

Mapping the earth from space stations can be approached in two areas. One is to collect gravity data for defining a new topographic datum using the earth's gravitational field in terms of spherical harmonics. The other, which should be considered as a very significant contribution of the Space Station, is to search and explore techniques of mapping the earth's topography using either optical or radar images with or without references to ground control points. Geodetic position of ground control points can be predetermined by the Global Positioning System (GPS) for the mapping experiment with the Space Station. It is proposed to establish four ground control points in North America or Africa (including the Sahara Desert). If this experiment should be successfully accomplished, it may also be applied to the defense charting service.

Performance Analysis of Several GPS/Galileo Precise Point Positioning Models

PubMed Central

Afifi, Akram; El-Rabbany, Ahmed

2015-01-01

This paper examines the performance of several precise point positioning (PPP) models, which combine dual-frequency GPS/Galileo observations in the un-differenced and between-satellite single-difference (BSSD) modes. These include the traditional un-differenced model, the decoupled clock model, the semi-decoupled clock model, and the between-satellite single-difference model. We take advantage of the IGS-MGEX network products to correct for the satellite differential code biases and the orbital and satellite clock errors. Natural Resources Canada’s GPSPace PPP software is modified to handle the various GPS/Galileo PPP models. A total of six data sets of GPS and Galileo observations at six IGS stations are processed to examine the performance of the various PPP models. It is shown that the traditional un-differenced GPS/Galileo PPP model, the GPS decoupled clock model, and the semi-decoupled clock GPS/Galileo PPP model improve the convergence time by about 25% in comparison with the un-differenced GPS-only model. In addition, the semi-decoupled GPS/Galileo PPP model improves the solution precision by about 25% compared to the traditional un-differenced GPS/Galileo PPP model. Moreover, the BSSD GPS/Galileo PPP model improves the solution convergence time by about 50%, in comparison with the un-differenced GPS PPP model, regardless of the type of BSSD combination used. As well, the BSSD model improves the precision of the estimated parameters by about 50% and 25% when the loose and the tight combinations are used, respectively, in comparison with the un-differenced GPS-only model. Comparable results are obtained through the tight combination when either a GPS or a Galileo satellite is selected as a reference. PMID:26102495

Performance Analysis of Several GPS/Galileo Precise Point Positioning Models.

PubMed

Afifi, Akram; El-Rabbany, Ahmed

2015-06-19

This paper examines the performance of several precise point positioning (PPP) models, which combine dual-frequency GPS/Galileo observations in the un-differenced and between-satellite single-difference (BSSD) modes. These include the traditional un-differenced model, the decoupled clock model, the semi-decoupled clock model, and the between-satellite single-difference model. We take advantage of the IGS-MGEX network products to correct for the satellite differential code biases and the orbital and satellite clock errors. Natural Resources Canada's GPSPace PPP software is modified to handle the various GPS/Galileo PPP models. A total of six data sets of GPS and Galileo observations at six IGS stations are processed to examine the performance of the various PPP models. It is shown that the traditional un-differenced GPS/Galileo PPP model, the GPS decoupled clock model, and the semi-decoupled clock GPS/Galileo PPP model improve the convergence time by about 25% in comparison with the un-differenced GPS-only model. In addition, the semi-decoupled GPS/Galileo PPP model improves the solution precision by about 25% compared to the traditional un-differenced GPS/Galileo PPP model. Moreover, the BSSD GPS/Galileo PPP model improves the solution convergence time by about 50%, in comparison with the un-differenced GPS PPP model, regardless of the type of BSSD combination used. As well, the BSSD model improves the precision of the estimated parameters by about 50% and 25% when the loose and the tight combinations are used, respectively, in comparison with the un-differenced GPS-only model. Comparable results are obtained through the tight combination when either a GPS or a Galileo satellite is selected as a reference.

Study of movement of the western and central belts of Peninsular Malaysia using GPS data analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ramli, Siti Hafizah; Samsudin, Abdul Rahim

Since the large earthquakes in Sumatera and Nias, there were some tremors incidents at Bukit Tinggi. Therefore, a study on the earth’s crust movement and the effects of the earthquake in Indonesia on the tectonic blocks of Peninsular Malaysia have been carried out using GPS data analysis. GPS data from five MyRTKnet stations within Peninsular Malaysia have been analyzed to monitor the movement of two major tectonic blocks of Peninsular Malaysia which are the western belt represented by the Behrang (BEHR) and UPM Serdang (UPMS) stations and the central belt represented by Bentong (BENT), Jerantut (JRNT) and Temerloh (TLOH) stations.more » GPS data recorded from 2005 to 2010 were analysed based on horizontal and vertical displacements of the respective stations by using Trimble Business Centre (TBC) software. Based on the results of accumulated displacements of recorded GPS data from January 2006 to December 2013, it shows that the western belt which represented by UPMS has shifted 0.096m towards northwest with changes of ellipsoidal height of +0.030m while the central belt which represented by TLOH has shifted 0.080m towards northwest with changes of ellipsoidal height of −0.015m. Meanwhile, BENT station which is located on the Bentong-Raub suture zone turns to its original position as well as JRNT station. However, BEHR station which are located in western belt do not show any movements. All of these movements may be due to the influence of reactive faults in the stations area stimulated by several large earthquakes that occurred in 2005 to 2010. Study on using the GPS data analysis and combine with integrated geophysical methods are necessary to understand in detail about the tectonic evolution of Peninsular Malaysia.« less

Improving the Quality of Low-Cost GPS Receiver Data for Monitoring Using Spatial Correlations

NASA Astrophysics Data System (ADS)

Zhang, Li; Schwieger, Volker

2016-06-01

The investigations on low-cost single frequency GPS receivers at the Institute of Engineering Geodesy (IIGS) show that u-blox LEA-6T GPS receivers combined with Trimble Bullet III GPS antennas containing self-constructed L1-optimized choke rings can already obtain an accuracy in the range of millimeters which meets the requirements of geodetic precise monitoring applications (see [27]). However, the quality (accuracy and reliability) of low-cost GPS receiver data, particularly in shadowing environment, should still be improved, since the multipath effects are the major error for the short baselines. For this purpose, several adjoined stations with low-cost GPS receivers and antennas were set up next to the metal wall on the roof of the IIGS building and measured statically for several days. The time series of three-dimensional coordinates of the GPS receivers were analyzed. Spatial correlations between the adjoined stations, possibly caused by multipath effect, will be taken into account. The coordinates of one station can be corrected using the spatial correlations of the adjoined stations, so that the quality of the GPS measurements is improved. The developed algorithms are based on the coordinates and the results will be delivered in near-real-time (in about 30 minutes), so that they are suitable for structural health monitoring applications.

COCONet enhancements to circum-Caribbean tsunami warning, tidal, and sea-level monitoring: update on tide gauge installations

NASA Astrophysics Data System (ADS)

Dausz, K.; Dittmann, S. T.; Feaux, K.; von Hillebrandt-Andrade, C.; Mattioli, G. S.; Normandeau, J.

2014-12-01

The Continually Operating Caribbean GPS Observational Network (COCONet) is a National Science Foundation (NSF) funded multi-hazard geodetic and meteorological network distributed throughout the Caribbean, which provides infrastructure and capacity building for a broad range of earth science questions. The network is a multi-national collaboration consisting of 46 newly constructed continuous Global Positioning Systems (cGPS) and 21 refurbished existing GPS stations, all co-located with meteorological sensors. One recommendation of the COCONet working group was to improve the vertical reference frame for long-term sea level monitoring. A COCONet supplement was awarded by the NSF to further address this particular objective through the co-location of GPS and tide gauges. This COCOnet infrastructure, along with the new tide gauges, will have broad scientific implications for hazards mitigation, solid earth, and atmospheric science research. UNAVCO engineers have meet with members of the Caribbean tide gauge community to establish target locations and design station layout. Allocated NSF funds allow for the construction of two complete new tide gauge systems each with two complimentary cGPS. Following the recommendations of NOAA and the sea level monitoring community, the two "new" locales will be Port Royal, Jamaica and Puerto Morelos, Mexico. Both locations had previously existing, but currently non-operational tide gauges. UNAVCO engineers will install a Sutron Radar Level Recorder and a backup pressure sensor tide gauge with GOES satellite telemetry. Tide data will be freely available by the Intergovernmental Oceanographic Commission (www.ioc-sealevelmonitoring.org). The NSF supplement also provided funds for adding cGPS to two additional locations where currently functioning tide gauge systems exist. Proposed locations for this additional infrastructure are Barahona, Dominican Republic and Bocas del Toro, Panama. All four locations will feature two standard COCONet cGPS systems consisting of a Trimble Choke Ring GNSS antenna, Trimble NetR9 GPS receiver, and a Vaisala meteorological sensor. All GPS data will be collected, processed and distributed via standard COCONet archiving and processing along with raw meteorological data at coconet.unavco.org.

Estimation of satellite position, clock and phase bias corrections

NASA Astrophysics Data System (ADS)

Henkel, Patrick; Psychas, Dimitrios; Günther, Christoph; Hugentobler, Urs

2018-05-01

Precise point positioning with integer ambiguity resolution requires precise knowledge of satellite position, clock and phase bias corrections. In this paper, a method for the estimation of these parameters with a global network of reference stations is presented. The method processes uncombined and undifferenced measurements of an arbitrary number of frequencies such that the obtained satellite position, clock and bias corrections can be used for any type of differenced and/or combined measurements. We perform a clustering of reference stations. The clustering enables a common satellite visibility within each cluster and an efficient fixing of the double difference ambiguities within each cluster. Additionally, the double difference ambiguities between the reference stations of different clusters are fixed. We use an integer decorrelation for ambiguity fixing in dense global networks. The performance of the proposed method is analysed with both simulated Galileo measurements on E1 and E5a and real GPS measurements of the IGS network. We defined 16 clusters and obtained satellite position, clock and phase bias corrections with a precision of better than 2 cm.

Land motion estimates from GPS at tide gauges: a geophysical evaluation

NASA Astrophysics Data System (ADS)

Bouin, M. N.; Wöppelmann, G.

2010-01-01

Space geodesy applications have mainly been limited to horizontal deformations due to a number of restrictions on the vertical component accuracy. Monitoring vertical land motion is nonetheless of crucial interest in observations of long-term sea level change or postglacial rebound measurements. Here, we present a global vertical velocity field obtained with more than 200 permanent GPS stations, most of them colocated with tide gauges (TGs). We used a state of the art, homogeneous processing strategy to ensure that the reference frame was stable throughout the observation period of almost 10 yr. We associate realistic uncertainties to our vertical rates, taking into account the time-correlation noise in the time-series. The results are compared with two independent geophysical vertical velocity fields: (1) vertical velocity estimates using long-term TG records and (2) postglacial model predictions from the ICE-5G (VM2) adjustment. The quantitative agreement of the GPS vertical velocities with the `internal estimates' of vertical displacements using the TG record is very good, with a mean difference of -0.13 +/- 1.64 mm yr-1 on more than 100 sites. For 84 per cent of the GPS stations considered, the vertical velocity is confirmed by the TG estimate to within 2 mm yr-1. The overall agreement with the glacial isostatic adjustment (GIA) model is good, with discrepancy patterns related either to a local misfit of the model or to active tectonics. For 72 per cent of the sites considered, the predictions of the GIA model agree with the GPS results to within two standard deviations. Most of the GPS velocities showing discrepancies with respect to the predictions of the GIA model are, however, consistent with previously published space geodesy results. We, in turn, confirm the value of 1.8 +/- 0.5 mm yr-1 for the 20th century average global sea level rise, and conclude that GPS is now a robust tool for vertical land motion monitoring which is accurate at least at 1 mm yr-1.

GPS Estimates of Integrated Precipitable Water Aid Weather Forecasters

NASA Technical Reports Server (NTRS)

Moore, Angelyn W.; Gutman, Seth I.; Holub, Kirk; Bock, Yehuda; Danielson, David; Laber, Jayme; Small, Ivory

2013-01-01

Global Positioning System (GPS) meteorology provides enhanced density, low-latency (30-min resolution), integrated precipitable water (IPW) estimates to NOAA NWS (National Oceanic and Atmospheric Adminis tration Nat ional Weather Service) Weather Forecast Offices (WFOs) to provide improved model and satellite data verification capability and more accurate forecasts of extreme weather such as flooding. An early activity of this project was to increase the number of stations contributing to the NOAA Earth System Research Laboratory (ESRL) GPS meteorology observing network in Southern California by about 27 stations. Following this, the Los Angeles/Oxnard and San Diego WFOs began using the enhanced GPS-based IPW measurements provided by ESRL in the 2012 and 2013 monsoon seasons. Forecasters found GPS IPW to be an effective tool in evaluating model performance, and in monitoring monsoon development between weather model runs for improved flood forecasting. GPS stations are multi-purpose, and routine processing for position solutions also yields estimates of tropospheric zenith delays, which can be converted into mm-accuracy PWV (precipitable water vapor) using in situ pressure and temperature measurements, the basis for GPS meteorology. NOAA ESRL has implemented this concept with a nationwide distribution of more than 300 "GPSMet" stations providing IPW estimates at sub-hourly resolution currently used in operational weather models in the U.S.

High-resolution station-based diurnal ionospheric total electron content (TEC) from dual-frequency GPS observations

NASA Astrophysics Data System (ADS)

ćepni, Murat S.; Potts, Laramie V.; Miima, John B.

2013-09-01

electron content (TEC) estimates derived from Global Navigation Satellite System (GNSS) signal delays provide a rich source of information about the Earth's ionosphere. Networks of Global Positioning System (GPS) receivers data can be used to represent the ionosphere by a Global Ionospheric Map (GIM). Data input for GIMs is dual-frequency GNSS-only or a mixture of GNSS and altimetry observations. Parameterization of GNSS-only GIMs approaches the ionosphere as a single-layer model (SLM) to determine GPS TEC models over a region. Limitations in GNSS-only GIM TEC are due largely to the nonhomogenous global distribution of GPS tracking stations with large data gaps over the oceans. The utility of slant GPS ionospheric-induced path delays for high temporal resolution from a single-station data rate offers better representation of TEC over a small region. A station-based vertical TEC (TECV) approach modifies the traditional single-layer model (SLM) GPS TEC method by introducing a zenith angle weighting (ZAW) filter to capture signal delays from mostly near-zenith satellite passes. Comparison with GIMs shows the station-dependent TEC (SD-TEC) model exhibits robust performance under variable space weather conditions. The SD-TEC model was applied to investigate ionospheric TEC variability during the geomagnetic storm event of 9 March 2012 at midlatitude station NJJJ located in New Jersey, USA. The high temporal resolution TEC results suggest TEC production and loss rate differences before, during, and after the storm.

TIGA Tide Gauge Data Reprocessing at GFZ

NASA Astrophysics Data System (ADS)

Deng, Zhiguo; Schöne, Tilo; Gendt, Gerd

2014-05-01

To analyse the tide gauge measurements for the purpose of global long-term sea level change research a well-defined absolute reference frame is required by oceanographic community. To create such frame the data from a global GNSS network located at or near tide gauges are processed. For analyzing the GNSS data on a preferably continuous basis the International GNSS Service (IGS) Tide Gauge Benchmark Monitoring Working Group (TIGA-WG) is responsible. As one of the TIGA Analysis Centers the German Research Centre for Geosciences (GFZ) is contributing to the IGS TIGA Reprocessing Campaign. The solutions of the TIGA Reprocessing Campaign will also contribute to 2nd IGS Data Reprocessing Campaign with GFZ IGS reprocessing solution. After the first IGS reprocessing finished in 2010 some improvements were implemented into the latest GFZ software version EPOS.P8: reference frame IGb08 based on ITRF2008, antenna calibration igs08.atx, geopotential model (EGM2008), higher-order ionospheric effects, new a priori meteorological model (GPT2), VMF mapping function, and other minor improvements. GPS data of the globally distributed tracking network of 794 stations for the time span from 1994 until end of 2012 are used for the TIGA reprocessing. To handle such large network a new processing strategy is developed and described in detail. In the TIGA reprocessing the GPS@TIGA data are processed in precise point positioning (PPP) mode to clean data using the IGS reprocessing orbit and clock products. To validate the quality of the PPP coordinate results the rates of 80 GPS@TIGA station vertical movement are estimated from the PPP results using Maximum Likelihood Estimation (MLE) method. The rates are compared with the solution of University of LaRochelle Consortium (ULR) (named ULR5). 56 of the 80 stations have a difference of the vertical velocities below 1 mm/yr. The error bars of PPP rates are significant larger than those of ULR5, which indicates large time correlated noise in the PPP solutions.

Comparison of Ground Deformation Measurements and Atmospheric Artifacts Using Insar Cosmo-Skymed and GPS Data

NASA Astrophysics Data System (ADS)

Zerbini, S.; Prati, C.; Errico, M.; Novali, F.; Santi, E.

2012-12-01

Integrating and exploiting the synergetic combination of the InSAR and GPS techniques allows overcoming the limitations inherent in the use of each technique alone. GPS-based estimates of tropospheric delays may contribute in obtaining better corrections of the wet tropospheric path delay in InSAR signals. This will enhance the coherence and will allow the application of InSAR in a wider range of applications. The test area chosen for the comparison between InSAR and GPS data is in northeastern Italy, in particular, in the city of Bologna (urbanized area) and in the surroundings of Medicina (agricultural area). In these sites, two permanent GPS stations (EUREF EPN sites) of the University of Bologna are operational since mid 1999 (BOLG) and 1996 (MSEL) respectively. The InSAR data used are the COSMO-SkyMed (CSK) images made available by the Italian Space Agency (ASI). The Permanent Scatterers (PS) technique was applied to a number of repeated CSK strip map SAR images acquired over a 40x40 square km area encompassing the two towns mentioned above. The results of this work demonstrate, on the one hand, the CSK capabilities to operate in a repeated interferometric survey mode for measuring ground deformation with millimeter accuracy in different environments. On the other, the comparison of the differential height between the two stations derived with the GPS and the InSAR data, using both acquisition geometries, is satisfactory. Elevation, ground deformation and atmospheric artifacts were estimated in correspondence of the identified PS and compared with the GPS measurements carried out at the same acquisition time by the permanent stations at Bologna and Medicina. The comparison of the differential height between the two stations shows the sensitivity of the GPS height solution to the length of the observation interval. The vertical dispersion achieved by GPS is higher than that achieved by PS InSAR, as expected; however, a similar linear trend appears in the results of both techniques. For the comparison of differential tropospheric delays, two GPS solutions derived with different session length and data acquisition rate were considered. The InSAR results are those relevant to two PSs located at very close distance from the GPS stations. These are representative of the majority of PSs identified around the two stations. A similar behavior is present in the results achieved by both GPS and PS-InSAR techniques, despite of expected differences due to the almost instantaneous nature of the PS-InSAR estimates compared to the GPS 5-minute averaged results.

Observing crustal deformation and atmospheric signals from COSMO-SKYMED and GPS data

NASA Astrophysics Data System (ADS)

Zerbini, S.; Prati, C.; Cappello, G.; Errico, M.; Novali, F.

2012-04-01

The combined use of InSAR and GPS allows for the full exploitation of the complementary aspects of the two techniques by overcoming the limitations inherent in the use of each technique alone. Additionally, GPS-based estimates of tropospheric delays may contribute in obtaining better corrections of the wet tropospheric path delay in InSAR signals. This will enhance the coherence and will allow the application of InSAR in a wider range of applications. We have compared the InSAR and GPS data at Bologna (urbanized area) and Medicina (agricultural area), in northeastern Italy, where two permanent GPS stations of the University of Bologna are operational since mid 1999 and 1996 respectively. The InSAR data used are the COSMO-SkyMed (CSK) images made available by the Italian Space Agency (ASI) in the framework of the research contract AO-1140. The Permanent Scatterers (PS) technique was applied to a number of repeated CSK strip map SAR images acquired over a 40x40 square km area encompassing the two towns mentioned above. The results of this work demonstrate on the one hand the CSK capabilities to operate in a repeated interferometric survey mode for measuring ground deformation with millimeter accuracy in different environments. On the other, the comparison of the differential height between the two stations derived with the GPS and the InSAR data, using both acquisition geometries, is satisfactory. Elevation, ground deformation and atmospheric artifacts were estimated in correspondence of the identified PS and compared with the GPS measurements carried out at the same acquisition time by the permanent stations at Bologna and Medicina. The comparison of the differential height between the two stations shows the sensitivity of the GPS height solution to the length of the observation interval. The vertical dispersion achieved by GPS is higher than that achieved by PS InSAR, as expected; however, a similar linear trend appears in the results of both techniques. The comparison of differential tropospheric delays has been carried out. Two GPS solutions derived with different session length and data acquisition rate were considered. The InSAR results were those relevant to two PS located at a very close distance from the GPS stations. These are representative of the majority of PSs identified around the two stations. A similar behavior is present in the results achieved by both GPS and PS-InSAR techniques, despite of expected differences due to the almost instantaneous nature of the PS-InSAR estimates compared to the GPS 5-min averaged results.

Precise Point Positioning Using Triple GNSS Constellations in Various Modes

PubMed Central

Afifi, Akram; El-Rabbany, Ahmed

2016-01-01

This paper introduces a new dual-frequency precise point positioning (PPP) model, which combines the observations from three different global navigation satellite system (GNSS) constellations, namely GPS, Galileo, and BeiDou. Combining measurements from different GNSS systems introduces additional biases, including inter-system bias and hardware delays, which require rigorous modelling. Our model is based on the un-differenced and between-satellite single-difference (BSSD) linear combinations. BSSD linear combination cancels out some receiver-related biases, including receiver clock error and non-zero initial phase bias of the receiver oscillator. Forming the BSSD linear combination requires a reference satellite, which can be selected from any of the GPS, Galileo, and BeiDou systems. In this paper three BSSD scenarios are tested; each considers a reference satellite from a different GNSS constellation. Natural Resources Canada’s GPSPace PPP software is modified to enable a combined GPS, Galileo, and BeiDou PPP solution and to handle the newly introduced biases. A total of four data sets collected at four different IGS stations are processed to verify the developed PPP model. Precise satellite orbit and clock products from the International GNSS Service Multi-GNSS Experiment (IGS-MGEX) network are used to correct the GPS, Galileo, and BeiDou measurements in the post-processing PPP mode. A real-time PPP solution is also obtained, which is referred to as RT-PPP in the sequel, through the use of the IGS real-time service (RTS) for satellite orbit and clock corrections. However, only GPS and Galileo observations are used for the RT-PPP solution, as the RTS-IGS satellite products are not presently available for BeiDou system. All post-processed and real-time PPP solutions are compared with the traditional un-differenced GPS-only counterparts. It is shown that combining the GPS, Galileo, and BeiDou observations in the post-processing mode improves the PPP convergence time by 25% compared with the GPS-only counterpart, regardless of the linear combination used. The use of BSSD linear combination improves the precision of the estimated positioning parameters by about 25% in comparison with the GPS-only PPP solution. Additionally, the solution convergence time is reduced to 10 minutes for the BSSD model, which represents about 50% reduction, in comparison with the GPS-only PPP solution. The GNSS RT-PPP solution, on the other hand, shows a similar convergence time and precision to the GPS-only counterpart. PMID:27240376

Precise Point Positioning Using Triple GNSS Constellations in Various Modes.

PubMed

Afifi, Akram; El-Rabbany, Ahmed

2016-05-28

This paper introduces a new dual-frequency precise point positioning (PPP) model, which combines the observations from three different global navigation satellite system (GNSS) constellations, namely GPS, Galileo, and BeiDou. Combining measurements from different GNSS systems introduces additional biases, including inter-system bias and hardware delays, which require rigorous modelling. Our model is based on the un-differenced and between-satellite single-difference (BSSD) linear combinations. BSSD linear combination cancels out some receiver-related biases, including receiver clock error and non-zero initial phase bias of the receiver oscillator. Forming the BSSD linear combination requires a reference satellite, which can be selected from any of the GPS, Galileo, and BeiDou systems. In this paper three BSSD scenarios are tested; each considers a reference satellite from a different GNSS constellation. Natural Resources Canada's GPSPace PPP software is modified to enable a combined GPS, Galileo, and BeiDou PPP solution and to handle the newly introduced biases. A total of four data sets collected at four different IGS stations are processed to verify the developed PPP model. Precise satellite orbit and clock products from the International GNSS Service Multi-GNSS Experiment (IGS-MGEX) network are used to correct the GPS, Galileo, and BeiDou measurements in the post-processing PPP mode. A real-time PPP solution is also obtained, which is referred to as RT-PPP in the sequel, through the use of the IGS real-time service (RTS) for satellite orbit and clock corrections. However, only GPS and Galileo observations are used for the RT-PPP solution, as the RTS-IGS satellite products are not presently available for BeiDou system. All post-processed and real-time PPP solutions are compared with the traditional un-differenced GPS-only counterparts. It is shown that combining the GPS, Galileo, and BeiDou observations in the post-processing mode improves the PPP convergence time by 25% compared with the GPS-only counterpart, regardless of the linear combination used. The use of BSSD linear combination improves the precision of the estimated positioning parameters by about 25% in comparison with the GPS-only PPP solution. Additionally, the solution convergence time is reduced to 10 minutes for the BSSD model, which represents about 50% reduction, in comparison with the GPS-only PPP solution. The GNSS RT-PPP solution, on the other hand, shows a similar convergence time and precision to the GPS-only counterpart.

Going Up. A GPS Receiver Adapts to Space

NASA Technical Reports Server (NTRS)

Lightsey, E. Glenn; Simpson, James E.

2000-01-01

Current plans for the space station call for the GPS receiver to be installed on the U.S. lab module of the station in early 2001 (ISS Assembly Flight SA), followed by the attachment of the antenna array in late 2001 (Flight 8A). At that point the U.S. ISS guidance and control system will be operational. The flight of SIGI on the space station represents a "coming of age" for GPS technology on spacecraft. For at least a decade, the promise of using GPS receivers to automate spacecraft operations, simplify satellite design, and reduce mission costs has enticed satellite designers. Integration of this technology onto spacecraft has been slower than some originally anticipated. However, given the complexity of the GPS sensor, and the importance of the functions it performs, its incorporation into mainstream satellite design has probably occurred at a very reasonable pace. Going from providing experimental payloads on small, unmanned satellites to performing critical operational functions on manned vehicles has been a major evolution. If all goes as planned in the next few months, GPS receivers will soon provide those critical functions on one of the most complex spacecraft in history, the International Space Station.

Decadal GPS Time Series and Velocity Fields Spanning the North American Continent and Beyond: New Data Products, Cyberinfrastructure and Case Studies from the EarthScope Plate Boundary Observatory (PBO) and Other Regional Networks

NASA Astrophysics Data System (ADS)

Phillips, D. A.; Herring, T.; Melbourne, T. I.; Murray, M. H.; Szeliga, W. M.; Floyd, M.; Puskas, C. M.; King, R. W.; Boler, F. M.; Meertens, C. M.; Mattioli, G. S.

2017-12-01

The Geodesy Advancing Geosciences and EarthScope (GAGE) Facility, operated by UNAVCO, provides a diverse suite of geodetic data, derived products and cyberinfrastructure services to support community Earth science research and education. GPS data and products including decadal station position time series and velocities are provided for 2000+ continuous GPS stations from the Plate Boundary Observatory (PBO) and other networks distributed throughout the high Arctic, North America, and Caribbean regions. The position time series contain a multitude of signals in addition to the secular motions, including coseismic and postseismic displacements, interseismic strain accumulation, and transient signals associated with hydrologic and other processes. We present our latest velocity field solutions, new time series offset estimate products, and new time series examples associated with various phenomena. Position time series, and the signals they contain, are inherently dependent upon analysis parameters such as network scaling and reference frame realization. The estimation of scale changes for example, a common practice, has large impacts on vertical motion estimates. GAGE/PBO velocities and time series are currently provided in IGS (IGb08) and North America (NAM08, IGb08 rotated to a fixed North America Plate) reference frames. We are reprocessing all data (1996 to present) as part of the transition from IGb08 to IGS14 that began in 2017. New NAM14 and IGS14 data products are discussed. GAGE/PBO GPS data products are currently generated using onsite computing clusters. As part of an NSF funded EarthCube Building Blocks project called "Deploying MultiFacility Cyberinfrastructure in Commercial and Private Cloud-based Systems (GeoSciCloud)", we are investigating performance, cost, and efficiency differences between local computing resources and cloud based resources. Test environments include a commercial cloud provider (Amazon/AWS), NSF cloud-like infrastructures within XSEDE (TACC, the Texas Advanced Computing Center), and in-house cyberinfrastructures. Preliminary findings from this effort are presented. Web services developed by UNAVCO to facilitate the discovery, customization and dissemination of GPS data and products are also presented.

Production and Uses of Multi-Decade Geodetic Earth Science Data Records

NASA Astrophysics Data System (ADS)

Bock, Y.; Kedar, S.; Moore, A. W.; Fang, P.; Liu, Z.; Sullivan, A.; Argus, D. F.; Jiang, S.; Marshall, S. T.

2017-12-01

The Solid Earth Science ESDR System (SESES) project funded under the NASA MEaSUREs program produces and disseminates mature, long-term, calibrated and validated, GNSS based Earth Science Data Records (ESDRs) that encompass multiple diverse areas of interest in Earth Science, such as tectonic motion, transient slip and earthquake dynamics, as well as meteorology, climate, and hydrology. The ESDRs now span twenty-five years for the earliest stations and today are available for thousands of global and regional stations. Using a unified metadata database and a combination of GNSS solutions generated by two independent analysis centers, the project currently produces four long-term ESDR's: Geodetic Displacement Time Series: Daily, combined, cleaned and filtered, GIPSY and GAMIT long-term time series of continuous GPS station positions (global and regional) in the latest version of ITRF, automatically updated weekly. Geodetic Velocities: Weekly updated velocity field + velocity field histories in various reference frames; compendium of all model parameters including earthquake catalog, coseismic offsets, and postseismic model parameters (exponential or logarithmic). Troposphere Delay Time Series: Long-term time series of troposphere delay (30-min resolution) at geodetic stations, necessarily estimated during position time series production and automatically updated weekly. Seismogeodetic records for historic earthquakes: High-rate broadband displacement and seismic velocity time series combining 1 Hz GPS displacements and 100 Hz accelerometer data for select large earthquakes and collocated cGPS and seismic instruments from regional networks. We present several recent notable examples of the ESDR's usage: A transient slip study that uses the combined position time series to unravel "tremor-less" slow tectonic transient events. Fault geometry determination from geodetic slip rates. Changes in water resources across California's physiographic provinces at a spatial resolution of 75 km. Retrospective study of a southern California summer monsoon event.

Current Trends and Challenges in Satellite Laser Ranging

NASA Astrophysics Data System (ADS)

Appleby, Graham M.; Bianco, Giuseppe; Noll, Carey E.; Pavlis, Erricos C.; Pearlman, Michael R.

2016-12-01

Satellite Laser Ranging (SLR) is used to measure accurately the distance from ground stations to retro-reflectors on satellites and on the Moon. SLR is one of the fundamental space-geodetic techniques that define the International Terrestrial Reference Frame (ITRF), which is the basis upon which many aspects of global change over space, time, and evolving technology are measured; with VLBI the two techniques define the scale of the ITRF; alone the SLR technique defines its origin (geocenter). The importance of the reference frame has recently been recognized at the inter-governmental level through the United Nations, which adopted in February 2015 the Resolution "Global Geodetic Reference Frame for Sustainable Development." Laser Ranging provides precision orbit determination and instrument calibration and validation for satellite-borne altimeters for the better understanding of sea level change, ocean dynamics, ice mass-balance, and terrestrial topography. It is also a tool to study the dynamics of the Moon and fundamental constants and theories. With the exception of the currently in-orbit GPS constellation, all GNSS satellites now carry retro-reflectors for improved orbit determination, harmonization of reference frames, and in-orbit co-location and system performance validation; the next generation of GPS satellites due for launch from 2019 onwards will also carry retro-reflectors. The ILRS delivers weekly realizations that are accumulated sequentially to extend the ITRF and the Earth Orientation Parameter series with a daily resolution. SLR technology continues to evolve towards the next-generation laser ranging systems and it is expected to successfully meet the challenges of the GGOS2020 program for a future Global Space Geodetic Network. Ranging precision is improving as higher repetition rate, narrower pulse lasers, and faster detectors are implemented within the network. Automation and pass interleaving at some stations is expanding temporal coverage and greatly enhancing efficiency. Discussions are ongoing with some missions that will allow the SLR network stations to provide crucial, but energy-safe, range measurements to optically vulnerable satellites. New retro-reflector designs are improving the signal link and enable daylight ranging that is now the norm for many stations. We discuss many of these laser ranging activities and some of the tough challenges that the SLR network currently faces.

Transition of NOAA's GPS-Met Data Acquisition and Processing System to the Commercial Sector

NASA Astrophysics Data System (ADS)

Jackson, M. E.; Holub, K.; Callahan, W.; Blatt, S.

2014-12-01

In April of 2014, NOAA/OAR/ESRL Global Systems Division (GSD) and Trimble, in collaboration with Earth Networks, Inc. (ENI) signed a Cooperative Research and Development Agreement (CRADA) to transfer the existing NOAA GPS-Met Data Acquisition and Processing System (GPS-Met DAPS) technology to a commercial Trimble/ENI partnership. NOAA's GPS-Met DAPS is currently operated in a pseudo-operational mode but has proven highly reliable and running at over 95% uptime. The DAPS uses the GAMIT software to ingest dual frequency carrier phase GPS/GNSS observations and ancillary information such as real-time satellite orbits to estimate the zenith-scaled tropospheric (ZTD) signal delays and, where surface MET data are available, retrieve integrated precipitable water vapor (PWV). The NOAA data and products are made available to end users in near real-time. The Trimble/ENI partnership will use the Trimble Pivot™ software with the Atmosphere App to calculate zenith tropospheric (ZTD), tropospheric slant delay, and integrated precipitable water vapor (PWV). Evaluation of the Trimble software is underway starting with a comparison of ZTD and PWV values determined from GPS stations located near NOAA Radiosonde Observation (Upper-Air Observation) launch sites. A success metric was established that requires Trimble's PWV estimates to match ESRL/GSD's to within 1.5 mm 95% of the time, which corresponds to a ZTD uncertainty of less than 10 mm 95% of the time. Initial results indicate that Trimble/ENI data meet and exceed the ZTD metric, but for some stations PWV estimates are out of specification. These discrepancies are primarily due to how offsets between MET and GPS stations are handled and are easily resolved. Additional test networks are proposed that include low terrain/high moisture variability stations, high terrain/low moisture variability stations, as well as high terrain/high moisture variability stations. We will present results from further testing along with a timeline for the transition of the GPS-Met DAPS to an operational commercial service.

Water vapor over Europe obtained from remote sensors and compared with a hydrostatic NWP model

NASA Astrophysics Data System (ADS)

Johnsen, K.-P.; Kidder, S. Q.

Due to its high-variability water vapor is a crucial parameter in short-term numerical weather prediction. Integrated water vapor (IWV) data obtained from a network of groundbased Global Positioning System (GPS) receivers mainly over Germany and passive microwave measurements of the Advanced Microwave Sounding Unit (AMSU-A) are compared with the high-resolution regional weather forecast model HRM of the Deutscher Wetterdienst (DWD). Time series of the IWV at 74 GPS stations obtained during the first complete year of the GFZ/GPS network between May 2000 and April 2001 are applied together with colocated forecasts of the HRM model. The low bias (0.08 kg/m 2) between the HRM model and the GPS data can mainly be explained by the bias between the ECMWF analysis data used to initilize the HRM model and the GPS data. The IWV standard deviation between the HRM model and the GPS data during that time is about 2.47 kg/ m2. GPS stations equipped with surface pressure sensors show about 0.29 kg/ m2 lower standard deviation compared with GPS stations with interpolated surface pressure from synoptic stations. The NOAA/NESDIS Total Precipitable Water algorithm is applied to obtain the IWV and to validate the model above the sea. While the mean IWV obtained from the HRM model is about 2.1 kg/ m2 larger than from the AMSU-A data, the standard deviations are 2.46 kg/ m2 (NOAA-15) and 2.29 kg/ m2 (NOAA-16) similar to the IWV standard deviation between HRM and GPS data.

Deployment of Autonomous GPS Stations in Marie Byrd Land, Antartica

NASA Technical Reports Server (NTRS)

Donnellan, A.; Luyendyk, B.; Smith, M.; Dace, G.

1999-01-01

During the 1998-1999 Antarctic field season, we installed three autonomous GPS stations in Marie Byrd Land, West Antarctica to measure glacio-isostatic rebound and rates of spreading across the West Antartic Rift System.

High-rate real-time GPS network at Parkfield: Utility for detecting fault slip and seismic displacements

USGS Publications Warehouse

Langbein, J.; Bock, Y.

2004-01-01

A network of 13 continuous GPS stations near Parkfield, California has been converted from 30 second to 1 second sampling with positions of the stations estimated in real-time relative to a master station. Most stations are near the trace of the San Andreas fault, which exhibits creep. The noise spectra of the instantaneous 1 Hz positions show flicker noise at high frequencies and change to frequency independence at low frequencies; the change in character occurs between 6 to 8 hours. Our analysis indicates that 1-second sampled GPS can estimate horizontal displacements of order 6 mm at the 99% confidence level from a few seconds to a few hours. High frequency GPS can augment existing measurements in capturing large creep events and postseismic slip that would exceed the range of existing creepmeters, and can detect large seismic displacements. Copyright 2004 by the American Geophysical Union.

Relating the Hadamard Variance to MCS Kalman Filter Clock Estimation

NASA Technical Reports Server (NTRS)

Hutsell, Steven T.

1996-01-01

The Global Positioning System (GPS) Master Control Station (MCS) currently makes significant use of the Allan Variance. This two-sample variance equation has proven excellent as a handy, understandable tool, both for time domain analysis of GPS cesium frequency standards, and for fine tuning the MCS's state estimation of these atomic clocks. The Allan Variance does not explicitly converge for the nose types of alpha less than or equal to minus 3 and can be greatly affected by frequency drift. Because GPS rubidium frequency standards exhibit non-trivial aging and aging noise characteristics, the basic Allan Variance analysis must be augmented in order to (a) compensate for a dynamic frequency drift, and (b) characterize two additional noise types, specifically alpha = minus 3, and alpha = minus 4. As the GPS program progresses, we will utilize a larger percentage of rubidium frequency standards than ever before. Hence, GPS rubidium clock characterization will require more attention than ever before. The three sample variance, commonly referred to as a renormalized Hadamard Variance, is unaffected by linear frequency drift, converges for alpha is greater than minus 5, and thus has utility for modeling noise in GPS rubidium frequency standards. This paper demonstrates the potential of Hadamard Variance analysis in GPS operations, and presents an equation that relates the Hadamard Variance to the MCS's Kalman filter process noises.

Ionospheric scintillation detection based on GPS observations, a case study over Iran

NASA Astrophysics Data System (ADS)

Sobhkhiz Miandehi, Sahar; Alizadeh Elizei, M. Mahdi; Schuh, Harald

2017-04-01

Global Positioning System (GPS) which is used extensively for various purposes such as navigation, surveying, remote sensing and telecommunication, is strongly affected by the earth's upper atmosphere, the ionosphere. Ionosphere is a highly variable region with complex physical characteristics in which the density of free electrons are large enough to have considerable effects on signals' propagation travelling through this dispersive medium. As GPS signals travel through the ionosphere, they may experience rapid amplitude fluctuations or unexpected phase changes. This is referred to as ionospheric scintillation. Ionospheric scintillation which is caused by small scale irregularities in the electron density, is one of the dominant propagation disturbances at radio frequency signals. These irregularities severely affect the accuracy and reliability of GPS measurements. Therefore it is necessary to investigate ionospheric scintillation and its effects on GPS observations. The focus of this paper is to detect ionospheric scintillations over Iran's region, during different periods of solar activity and to investigate these effects on GPS observations in more detail. Furthermore the effects of these irregularities on regional modeling of ionosphere over Iran is also investigated. The results show that effectiveness of this phenomenon depends on geographic location, local time and global geomagnetic storm index (kp index). The required data for this investigation are ground based measurements of permanent GPS stations over Iran, established by the National Cartographic Center of Iran (NCC).

Regional model-based computerized ionospheric tomography using GPS measurements: IONOLAB-CIT

NASA Astrophysics Data System (ADS)

Tuna, Hakan; Arikan, Orhan; Arikan, Feza

2015-10-01

Three-dimensional imaging of the electron density distribution in the ionosphere is a crucial task for investigating the ionospheric effects. Dual-frequency Global Positioning System (GPS) satellite signals can be used to estimate the slant total electron content (STEC) along the propagation path between a GPS satellite and ground-based receiver station. However, the estimated GPS-STEC is very sparse and highly nonuniformly distributed for obtaining reliable 3-D electron density distributions derived from the measurements alone. Standard tomographic reconstruction techniques are not accurate or reliable enough to represent the full complexity of variable ionosphere. On the other hand, model-based electron density distributions are produced according to the general trends of ionosphere, and these distributions do not agree with measurements, especially for geomagnetically active hours. In this study, a regional 3-D electron density distribution reconstruction method, namely, IONOLAB-CIT, is proposed to assimilate GPS-STEC into physical ionospheric models. The proposed method is based on an iterative optimization framework that tracks the deviations from the ionospheric model in terms of F2 layer critical frequency and maximum ionization height resulting from the comparison of International Reference Ionosphere extended to Plasmasphere (IRI-Plas) model-generated STEC and GPS-STEC. The suggested tomography algorithm is applied successfully for the reconstruction of electron density profiles over Turkey, during quiet and disturbed hours of ionosphere using Turkish National Permanent GPS Network.

Ionospheric threats to the integrity of airborne GPS users

NASA Astrophysics Data System (ADS)

Datta-Barua, Seebany

The Global Positioning System (GPS) has both revolutionized and entwined the worlds of aviation and atmospheric science. As the largest and most unpredictable source of GPS positioning error, the ionospheric layer of the atmosphere, if left unchecked, can endanger the safety, or "integrity," of the single frequency airborne user. An augmentation system is a differential-GPS-based navigation system that provides integrity through independent ionospheric monitoring by reference stations. However, the monitor stations are not in general colocated with the user's GPS receiver. The augmentation system must protect users from possible ionosphere density variations occurring between its measurements and the user's. This study analyzes observations from ionospherically active periods to identify what types of ionospheric disturbances may cause threats to user safety if left unmitigated. This work identifies when such disturbances may occur using a geomagnetic measure of activity and then considers two disturbances as case studies. The first case study indicates the need for a non-trivial threat model for the Federal Aviation Administration's Local Area Augmentation System (LAAS) that was not known prior to the work. The second case study uses ground- and space-based data to model an ionospheric disturbance of interest to the Federal Aviation Administration's Wide Area Augmentation System (WAAS). This work is a step in the justification for, and possible future refinement of, one of the WAAS integrity algorithms. For both WAAS and LAAS, integrity threats are basically caused by events that may be occurring but are unobservable. Prior to the data available in this solar cycle, events of such magnitude were not known to be possible. This work serves as evidence that the ionospheric threat models developed for WARS and LAAS are warranted and that they are sufficiently conservative to maintain user integrity even under extreme ionospheric behavior.

Simulating Future GPS Clock Scenarios with Two Composite Clock Algorithms

NASA Technical Reports Server (NTRS)

Suess, Matthias; Matsakis, Demetrios; Greenhall, Charles A.

2010-01-01

Using the GPS Toolkit, the GPS constellation is simulated using 31 satellites (SV) and a ground network of 17 monitor stations (MS). At every 15-minutes measurement epoch, the monitor stations measure the time signals of all satellites above a parameterized elevation angle. Once a day, the satellite clock estimates the station and satellite clocks. The first composite clock (B) is based on the Brown algorithm, and is now used by GPS. The second one (G) is based on the Greenhall algorithm. The composite clock of G and B performance are investigated using three ground-clock models. Model C simulates the current GPS configuration, in which all stations are equipped with cesium clocks, except for masers at USNO and Alternate Master Clock (AMC) sites. Model M is an improved situation in which every station is equipped with active hydrogen masers. Finally, Models F and O are future scenarios in which the USNO and AMC stations are equipped with fountain clocks instead of masers. Model F is a rubidium fountain, while Model O is more precise but futuristic Optical Fountain. Each model is evaluated using three performance metrics. The timing-related user range error having all satellites available is the first performance index (PI1). The second performance index (PI2) relates to the stability of the broadcast GPS system time itself. The third performance index (PI3) evaluates the stability of the time scales computed by the two composite clocks. A distinction is made between the "Signal-in-Space" accuracy and that available through a GNSS receiver.

Benefits Derived From Laser Ranging Measurements for Orbit Determination of the GPS Satellite Orbit

NASA Technical Reports Server (NTRS)

Welch, Bryan W.

2007-01-01

While navigation systems for the determination of the orbit of the Global Position System (GPS) have proven to be very effective, the current research is examining methods to lower the error in the GPS satellite ephemerides below their current level. Two GPS satellites that are currently in orbit carry retro-reflectors onboard. One notion to reduce the error in the satellite ephemerides is to utilize the retro-reflectors via laser ranging measurements taken from multiple Earth ground stations. Analysis has been performed to determine the level of reduction in the semi-major axis covariance of the GPS satellites, when laser ranging measurements are supplemented to the radiometric station keeping, which the satellites undergo. Six ground tracking systems are studied to estimate the performance of the satellite. The first system is the baseline current system approach which provides pseudo-range and integrated Doppler measurements from six ground stations. The remaining five ground tracking systems utilize all measurements from the current system and laser ranging measurements from the additional ground stations utilized within those systems. Station locations for the additional ground sites were taken from a listing of laser ranging ground stations from the International Laser Ranging Service. Results show reductions in state covariance estimates when utilizing laser ranging measurements to solve for the satellite s position component of the state vector. Results also show dependency on the number of ground stations providing laser ranging measurements, orientation of the satellite to the ground stations, and the initial covariance of the satellite's state vector.

A mobile mapping system for spatial information based on DGPS/EGIS

NASA Astrophysics Data System (ADS)

Pei, Ling; Wang, Qing; Gu, Juan

2007-11-01

With the rapid developments of mobile device and wireless communication, it brings a new challenge for acquiring the spatial information. A mobile mapping system based on differential global position system (DGPS) integrated with embedded geographic information system (EGIS) is designed. A mobile terminal adapts to various GPS differential environments such as single base mode and network GPS mode like Virtual Reference Station (VRS) and Master- Auxiliary Concept (MAC) by the mobile communication technology. The spatial information collected through DGPS is organized in an EGIS running in the embedded device. A set of mobile terminal in real-time DGPS based on GPRS adopting multithreading technique of serial port in manner of simulating overlapped I/O operating is developed, further more, the GPS message analysis and checkout based on Strategy Pattern for various receivers are included in the process of development. A mobile terminal accesses to the GPS network successfully by NTRIP (Networked Transport of RTCM via Internet Protocol) compliance. Finally, the accuracy and reliability of the mobile mapping system are proved by a lot of testing in 9 provinces all over the country.

GRACE-Based Estimates of GPS Satellite Antenna Phase Variations: Impact on Determining the Scale of the Terrestrial Reference Frame

NASA Astrophysics Data System (ADS)

Haines, B. J.; Bar-Sever, Y. E.; Bertiger, W.; Desai, S.; Owen, S.; Sibois, A.; Webb, F.

2007-12-01

Treating the GRACE tandem mission as an orbiting fiducial laboratory, we have developed new estimates of the phase and group-delay variations of the GPS transmitter antennas. Application of these antenna phase variation (APV) maps have shown great promise in reducing previously unexplained errors in our realization of GPS measurements from the TOPEX/POSEIDON (T/P; 1992--2005) and Jason-1 (2001--) missions. In particular, a 56 mm vertical offset in the solved-for position of the T/P receiver antenna is reduced to insignificance (less than 1 mm). For Jason-1, a spurious long-term (4-yr) drift in the daily antenna offset estimates is reduced from +3.7 to +0.1 mm/yr. Prior ground-based results, based on precise point positioning, also hint at the potential of the GRACE-based APV maps for scale determination, reducing the spurious scale rate by one half. In this paper, we report on the latest APV estimates from GRACE, and provide a further assessment of the impact of the APV maps on realizing the scale of the terrestrial reference frame (TRF) from GPS alone. To address this, we re-analyze over five years of data from a global (40+ station) ground network in a fiducial-free approach, using the new APV maps. A specialized multi-day GPS satellite orbit determination (OD) strategy is employed to better capitalize on dynamical constraints. The resulting estimates of TRF scale are compared to ITRF2005 in order to assess the quality of the solutions.

IGS Directory

NASA Technical Reports Server (NTRS)

1997-01-01

The International GPS (Global Positioning System) Service for Geodynamics (IGS) supports and helps coordinate GPS data production and parameters useful for generating more accurate data products. The IGS has operated a GPS tracking system for several years. It contains more than 100 stations worldwide and has produced a combined GPS ephemeris that has become the standard for geodesists and geophysicists worldwide. IGS data and products are freely available to all, thanks to the cooperation and participation of all the IGS members. This directory provides data on the stations and provides names and contact information with personnel involved with the IGS.

Feature Orientation and Positional Accuracy Assessment of Digital Orthophoto and Line Map for Large Scale Mapping: the Case Study on Bahir Dar Town, Ethiopia

NASA Astrophysics Data System (ADS)

Sisay, Z. G.; Besha, T.; Gessesse, B.

2017-05-01

This study used in-situ GPS data to validate the accuracy of horizontal coordinates and orientation of linear features of orthophoto and line map for Bahir Dar city. GPS data is processed using GAMIT/GLOBK and Lieca GeoOfice (LGO) in a least square sense with a tie to local and regional GPS reference stations to predict horizontal coordinates at five checkpoints. Real-Time-Kinematic GPS measurement technique is used to collect the coordinates of road centerline to test the accuracy associated with the orientation of the photogrammetric line map. The accuracy of orthophoto was evaluated by comparing with in-situ GPS coordinates and it is in a good agreement with a root mean square error (RMSE) of 12.45 cm in x- and 13.97 cm in y-coordinates, on the other hand, 6.06 cm with 95 % confidence level - GPS coordinates from GAMIT/GLOBK. Whereas, the horizontal coordinates of the orthophoto are in agreement with in-situ GPS coordinates at an accuracy of 16.71 cm and 18.98 cm in x and y-directions respectively and 11.07 cm with 95 % confidence level - GPS data is processed by LGO and a tie to local GPS network. Similarly, the accuracy of linear feature is in a good fit with in-situ GPS measurement. The GPS coordinates of the road centerline deviates from the corresponding coordinates of line map by a mean value of 9.18 cm in x- direction and -14.96 cm in y-direction. Therefore, it can be concluded that, the accuracy of the orthophoto and line map is within the national standard of error budget ( 25 cm).

The Foundation GPS Water Vapor Inversion and its Application Research

NASA Astrophysics Data System (ADS)

Liu, R.; Lee, T.; Lv, H.; Fan, C.; Liu, Q.

2018-04-01

Using GPS technology to retrieve atmospheric water vapor is a new water vapor detection method, which can effectively compensate for the shortcomings of conventional water vapor detection methods, to provide high-precision, large-capacity, near real-time water vapor information. In-depth study of ground-based GPS detection of atmospheric water vapor technology aims to further improve the accuracy and practicability of GPS inversion of water vapor and to explore its ability to detect atmospheric water vapor information to better serve the meteorological services. In this paper, the influence of the setting parameters of initial station coordinates, satellite ephemeris and solution observation on the total delay accuracy of the tropospheric zenith is discussed based on the observed data. In this paper, the observations obtained from the observation network consisting of 8 IGS stations in China in June 2013 are used to inverse the water vapor data of the 8 stations. The data of Wuhan station is further selected and compared with the data of Nanhu Sounding Station in Wuhan The error between the two data was between -6mm-6mm, and the trend of the two was almost the same, the correlation reached 95.8 %. The experimental results also verify the reliability of ground-based GPS inversion of water vapor technology.

USGS Menlo Park GPS Data Processing Techniques and Derived North America Velocity Field (Invited)

NASA Astrophysics Data System (ADS)

Svarc, J. L.; Murray-Moraleda, J. R.; Langbein, J. O.

2010-12-01

The U.S. Geological Survey in Menlo Park routinely conducts repeated GPS surveys of geodetic markers throughout the western United States using dual-frequency geodetic GPS receivers. We combine campaign, continuous, and semi-permanent data to present a North America fixed velocity field for regions in the western United States. Mobile campaign-based surveys require less up-front investment than permanently monumented and telemetered GPS systems, and hence have achieved a broad and dense spatial coverage. The greater flexibility and mobility comes at the cost of greater uncertainties in individual daily position solutions. We also routinely process continuous GPS data collected at PBO stations operated by UNAVCO along with data from other continuous GPS networks such as BARD, PANGA, and CORS operated by other agencies. We have broken the Western US into several subnetworks containing approximately 150-250 stations each. The data are processed using JPL’s GIPSY-OASIS II release 5.0 software using a modified precise positioning strategy (Zumberge and others, 1997). We use the “ambizap” code provided by Geoff Blewitt (Blewitt, 2008) to fix phase ambiguities in continuous networks. To mitigate the effect of common mode noise we use the positions of stations in the network with very long, clean time series (i.e. those with no large outliers or offsets) to transform all position estimates into “regionally filtered” results following the approach of Hammond and Thatcher (2007). Velocity uncertainties from continuously operated GPS stations tend to be about 3 times smaller than those from campaign data. Langbein (2004) presents a maximum likelihood method for fitting a time series employing a variety of temporal noise models. We assume that GPS observations are contaminated by a combination of white, flicker, and random walk noise. For continuous and semi-permanent time series longer than 2 years we estimate these values, otherwise we fix the amplitudes of these processes to 0.85 mm, 1.7 mm/yr1/4, and 0.4 mm/yr1/2 respectively for the north components, 0.84 mm, 1.4 mm/yr1/4, and 0.6 mm/yr1/2 respectively for the east components and 3.2 mm, 6.4 mm/yr1/4, and 0.0 mm/yr1/2 respectively for the vertical. We have also deployed “semi-permanent” stations in selected regions of California. Semi-permanent stations have the advantage of increasing the density of coverage without the high cost of monumentation and telemetry associated with continuous GPS stations. Also, because of the increased temporal coverage of these stations, accurate estimates of station velocities can be achieved in a far shorter time period than from campaign mode surveys.

TLALOCNet: A Continuous GPS-Met Array in Mexico for Seismotectonic and Atmospheric Research

NASA Astrophysics Data System (ADS)

Cabral-Cano, E.; Salazar-Tlaczani, L.; Galetzka, J.; DeMets, C.; Serra, Y. L.; Feaux, K.; Mattioli, G. S.; Miller, M. M.

2015-12-01

TLALOCNet is a network of continuous Global Positioning System (cGPS) and meteorology stations in Mexico for the interrogation of the earthquake cycle, tectonic processes, land subsidence, and atmospheric processes of Mexico. Once completed, TLALOCNet will span all of Mexico and will link existing GPS infrastructure in North America and the Caribbean aiming towards creating a continuous, federated network of networks in the Americas. Phase 1 (2014-2015), funded by NSF and UNAM, is building and upgrading 30+ cGPS-Met sites to the high standard of the EarthScope Plate Boundary Observatory (PBO). Phase 2 (2016) will add ~25 more cGPS-Met stations to be funded through CONACyT. TLALOCNet provides open and freely available raw GPS data, GPS-PWV, surface meteorology measurements, time series of daily positions, as well as a station velocity field to support a broad range of geoscience investigations. This is accomplished through the development of the TLALOCNet data center (http://tlalocnet.udg.mx) that serves as a collection and distribution point. This data center is based on UNAVCO's Dataworks-GSAC software and can work as part of UNAVCO's seamless archive for discovery, sharing, and access to data.The TLALOCNet data center also contains contributed data from several regional networks in Mexico. By using the same protocols and structure as the UNAVCO and other COCONet regional data centers, the geodetic community has the capability of accessing data from a large number of scientific and academically operated Mexican GPS sites. This archive provides a fully querable and scriptable GPS and Meteorological data retrieval point. Additionally Real-time 1Hz streams from selected TLALOCNet stations are available in BINEX, RTCM 2.3 and RTCM 3.1 formats via the Networked Transport of RTCM via Internet Protocol (NTRIP).

Accuracy of Snow Water Equivalent Estimated From GPS Vertical Displacements: A Synthetic Loading Case Study for Western U.S. Mountains

NASA Astrophysics Data System (ADS)

Enzminger, Thomas L.; Small, Eric E.; Borsa, Adrian A.

2018-01-01

GPS monitoring of solid Earth deformation due to surface loading is an independent approach for estimating seasonal changes in terrestrial water storage (TWS). In western United States (WUSA) mountain ranges, snow water equivalent (SWE) is the dominant component of TWS and an essential water resource. While several studies have estimated SWE from GPS-measured vertical displacements, the error associated with this method remains poorly constrained. We examine the accuracy of SWE estimated from synthetic displacements at 1,395 continuous GPS station locations in the WUSA. Displacement at each station is calculated from the predicted elastic response to variations in SWE from SNODAS and soil moisture from the NLDAS-2 Noah model. We invert synthetic displacements for TWS, showing that both seasonal accumulation and melt as well as year-to-year fluctuations in peak SWE can be estimated from data recorded by the existing GPS network. Because we impose a smoothness constraint in the inversion, recovered TWS exhibits mass leakage from mountain ranges to surrounding areas. This leakage bias is removed via linear rescaling in which the magnitude of the gain factor depends on station distribution and TWS anomaly patterns. The synthetic GPS-derived estimates reproduce approximately half of the spatial variability (unbiased root mean square error ˜50%) of TWS loading within mountain ranges, a considerable improvement over GRACE. The inclusion of additional simulated GPS stations improves representation of spatial variations. GPS data can be used to estimate mountain-range-scale SWE, but effects of soil moisture and other TWS components must first be subtracted from the GPS-derived load estimates.

Preparations for the IGS realization of ITRF2014

NASA Astrophysics Data System (ADS)

Rebischung, Paul; Schmid, Ralf

2016-04-01

The International GNSS Service (IGS) currently prepares its own realization, called IGS14, of the latest release of the International Terrestrial Reference Frame (ITRF2014). This preparation involves: - a selection of the most suitable reference frame (RF) stations from the complete set of GNSS stations in ITRF2014; - the design of a well-distributed core network of RF stations for the purpose of aligning global GNSS solutions; - a re-evaluation of the GPS and GLONASS satellite antenna phase center offsets (PCOs), based on the SINEX files provided by the IGS Analysis Centers (ACs) in the frame of the second IGS reprocessing campaign repro2. This presentation will first cover the criteria used for the selection of the IGS14 and IGS14 core RF stations as well as preliminary station selection results. We will then use the preliminary IGS14 RF to re-align the daily IGS combined repro2 SINEX solutions and study the impact of the RF change on GNSS-derived geodetic parameter time series. In a second part, we will focus on the re-evaluation of the GNSS satellite antenna PCOs. A re-evaluation of at least their radial (z) components is indeed required, despite the negligible scale difference between ITRF2008 and ITRF2014, because of modeling changes recently introduced within the IGS which affect the scale of GNSS terrestrial frames (Earth radiation pressure, antenna thrust). Moreover, the 13 GPS and GLONASS satellites launched since September 2012 are currently assigned preliminary block-specific mean PCO values which need to be updated. From the daily AC repro2 SINEX files, we will therefore derive time series of satellite z-PCO estimates and analyze the resulting time series. Since several ACs provided all three components of the satellite PCOs in their SINEX files, we will additionally derive similar x- and y-PCO time series and discuss the relevance of their potential re-evaluation.

Robust Real-Time Wide-Area Differential GPS Navigation

NASA Technical Reports Server (NTRS)

Yunck, Thomas P. (Inventor); Bertiger, William I. (Inventor); Lichten, Stephen M. (Inventor); Mannucci, Anthony J. (Inventor); Muellerschoen, Ronald J. (Inventor); Wu, Sien-Chong (Inventor)

1998-01-01

The present invention provides a method and a device for providing superior differential GPS positioning data. The system includes a group of GPS receiving ground stations covering a wide area of the Earth's surface. Unlike other differential GPS systems wherein the known position of each ground station is used to geometrically compute an ephemeris for each GPS satellite. the present system utilizes real-time computation of satellite orbits based on GPS data received from fixed ground stations through a Kalman-type filter/smoother whose output adjusts a real-time orbital model. ne orbital model produces and outputs orbital corrections allowing satellite ephemerides to be known with considerable greater accuracy than from die GPS system broadcasts. The modeled orbits are propagated ahead in time and differenced with actual pseudorange data to compute clock offsets at rapid intervals to compensate for SA clock dither. The orbital and dock calculations are based on dual frequency GPS data which allow computation of estimated signal delay at each ionospheric point. These delay data are used in real-time to construct and update an ionospheric shell map of total electron content which is output as part of the orbital correction data. thereby allowing single frequency users to estimate ionospheric delay with an accuracy approaching that of dual frequency users.

TIGO: a geodetic observatory for the improvement of the global reference frame

NASA Astrophysics Data System (ADS)

Schlueter, Wolfgang; Hase, Hayo; Boeer, Armin

1999-12-01

The Bundesamt fuer Kartographie und Geodaesie (BKG) will provide a major contribution to the improvement and maintenance of the global reference frames: ICRF (International Celestial Reference Frame), ITRF (International Terrestrial Reference Frame) with the operation of TIGO (Transportable Integrated Geodetic Observatory). TIGO is designed as a transportable geodetic observatory which consists of all relevant geodetic space techniques for a fundamental station (including VLBI, SLR, GPS). The transportability of the observatory enables to fill up gaps in the International Space Geodetic Network and to optimize the contribution to the global reference frames. TIGO should operate for a period of 2 to 3 years (at minimum) at one location. BKG is looking for a cooperation with countries willing to contribute to the ITRF and to support the operation of TIGO.

Analysis of orbital configurations for geocenter determination with GPS and low-Earth orbiters

NASA Astrophysics Data System (ADS)

Kuang, Da; Bar-Sever, Yoaz; Haines, Bruce

2015-05-01

We use a series of simulated scenarios to characterize the observability of geocenter location with GPS tracking data. We examine in particular the improvement realized when a GPS receiver in low Earth orbit (LEO) augments the ground network. Various orbital configurations for the LEO are considered and the observability of geocenter location based on GPS tracking is compared to that based on satellite laser ranging (SLR). The distance between a satellite and a ground tracking-site is the primary measurement, and Earth rotation plays important role in determining the geocenter location. Compared to SLR, which directly and unambiguously measures this distance, terrestrial GPS observations provide a weaker (relative) measurement for geocenter location determination. The estimation of GPS transmitter and receiver clock errors, which is equivalent to double differencing four simultaneous range measurements, removes much of this absolute distance information. We show that when ground GPS tracking data are augmented with precise measurements from a GPS receiver onboard a LEO satellite, the sensitivity of the data to geocenter location increases by more than a factor of two for Z-component. The geometric diversity underlying the varying baselines between the LEO and ground stations promotes improved global observability, and renders the GPS technique comparable to SLR in terms of information content for geocenter location determination. We assess a variety of LEO orbital configurations, including the proposed orbit for the geodetic reference antenna in space mission concept. The results suggest that a retrograde LEO with altitude near 3,000 km is favorable for geocenter determination.

TLALOCNet continuous GPS-Met Array in Mexico supporting the 2017 NAM GPS Hydrometeorological Network.

NASA Astrophysics Data System (ADS)

Cabral-Cano, E.; Salazar-Tlaczani, L.; Adams, D. K.; Vivoni, E. R.; Grutter, M.; Serra, Y. L.; DeMets, C.; Galetzka, J.; Feaux, K.; Mattioli, G. S.; Miller, M. M.

2017-12-01

TLALOCNet is a network of continuous GPS and meteorology stations in Mexico to study atmospheric and solid earth processes. This recently completed network spans most of Mexico with a strong coverage emphasis on southern and western Mexico. This network, funded by NSF, CONACyT and UNAM, recently built 40 cGPS-Met sites to EarthScope Plate Boundary Observatory standards and upgraded 25 additional GPS stations. TLALOCNet provides open and freely available raw GPS data, and high frequency surface meteorology measurements, and time series of daily positions. This is accomplished through the development of the TLALOCNet data center (http://tlalocnet.udg.mx) that serves as a collection and distribution point. This data center is based on UNAVCO's Dataworks-GSAC software and also works as part of UNAVCO's seamless archive for discovery, sharing, and access to GPS data. The TLALOCNet data center also contains contributed data from several regional GPS networks in Mexico for a total of 100+ stations. By using the same protocols and structure as the UNAVCO and other COCONet regional data centers, the scientific community has the capability of accessing data from the largest Mexican GPS network. This archive provides a fully queryable and scriptable GPS and Meteorological data retrieval point. In addition, real-time 1Hz streams from selected TLALOCNet stations are available in BINEX, RTCM 2.3 and RTCM 3.1 formats via the Networked Transport of RTCM via Internet Protocol (NTRIP) for real-time seismic and weather forecasting applications. TLALOCNet served as a GPS-Met backbone for the binational Mexico-US North American Monsoon GPS Hydrometeorological Network 2017 campaign experiment. This innovative experiment attempts to address water vapor source regions and land-surface water vapor flux contributions to precipitation (i.e., moisture recycling) during the 2017 North American Monsoon in Baja California, Sonora, Chihuahua, and Arizona. Models suggest that moisture recycling is a large contributor to summer rainfall. This experiment represents a first attempt to quantify the surface water vapor flux contribution to GPS-derived precipitable water vapor. Preliminary results from this campaign are presented.

Crustal Deformation in the India-Eurasia Collision Zone From 25 Years of GPS Measurements

NASA Astrophysics Data System (ADS)

Zheng, Gang; Wang, Hua; Wright, Tim J.; Lou, Yidong; Zhang, Rui; Zhang, Weixing; Shi, Chuang; Huang, Jinfang; Wei, Na

2017-11-01

The India-Eurasia collision zone is the largest deforming region on the planet; direct measurements of present-day deformation from Global Positioning System (GPS) have the potential to discriminate between competing models of continental tectonics. But the increasing spatial resolution and accuracy of observations have only led to increasingly complex realizations of competing models. Here we present the most complete, accurate, and up-to-date velocity field for India-Eurasia available, comprising 2576 velocities measured during 1991-2015. The core of our velocity field is from the Crustal Movement Observation Network of China-I/II: 27 continuous stations observed since 1999; 56 campaign stations observed annually during 1998-2007; 1000 campaign stations observed in 1999, 2001, 2004, and 2007; 260 continuous stations operating since late 2010; and 2000 campaign stations observed in 2009, 2011, 2013, and 2015. We process these data and combine the solutions in a consistent reference frame with stations from the Global Strain Rate Model compilation, then invert for continuous velocity and strain rate fields. We update geodetic slip rates for the major faults (some vary along strike), and find that those along the major Tibetan strike-slip faults are in good agreement with recent geological estimates. The velocity field shows several large undeforming areas, strain focused around some major faults, areas of diffuse strain, and dilation of the high plateau. We suggest that a new generation of dynamic models incorporating strength variations and strain-weakening mechanisms is required to explain the key observations. Seismic hazard in much of the region is elevated, not just near the major faults.

Comparison of GPS-TEC variation during quiet and disturbed period using the Holt-Winter method and IRI-2012 model over Malaysia

NASA Astrophysics Data System (ADS)

Ahmed Ismail, Nouf Abd Emunim; Abdullah, Mardina; Hasbi, Alina Marie

2016-07-01

Total Electron Content (TEC) is the main parameter in the ionosphere that has significant effects on radio wave; it changes the speed and direction of the signal propagation, causing the delay of the Global Positioning System (GPS) signals. Therefore, it is crucial to validate the performance of the ionospheric model to reveal the variety of ionospheric behaviour during quiet and disturbed period. This research presents the performance evaluation of the statistical Holt-Winter method and IRI-2012 model using three topside electron density options: IRI-2001, IRI01-corr and NeQuick with the observed GPS-TEC during quiet and disturbed period. The GPS-TEC data were derived from the dual frequency GPS receiver at JUPEM (Department of Survey and Mapping Malaysia), from the UUMK station (north Peninsular Malaysia) at geographic coordinates of 6.46°N-100.50°E and geomagnetic coordinates of 3.32°S-172.99°E and TGPG station (south Peninsular Malaysia) at geographic coordinates of 1.36°N-104.10°E and geomagnetic coordinates of 8.43°S -176.53°E, during March of 2013. The maximum value of the GPS-TEC was at the post noon time at 17:00 LT and the minimum was in the early morning from 6:00-7:00 LT. During the quiet period, the maximum GPS-TEC at the UUMK station was 52 TECU while at the TGPG station, it was 60 TECU. During the disturbed period, when intense geomagnetic storm occurred on 17 March 2013, the maximum GPS-TEC recorded was 58 TECU and 65 TECU in UUMK and TGPG station, respectively. The diurnal hourly variation during the quiet period indicated that IRI-2001, IRI01-corr, and NeQuick had overestimation agreement during the day hours except for the time between 11:00-19:00 LT when IRI01-corr and NeQuick showed underestimation, while during 13:00-20:00 LT, IRI-2001 showed slight underestimation whereas the Holt-Winter method showed good agreement with GPS-TEC. During the disturbed period, IRI-2001 showed overestimation agreement for all hours, while the IRI01-corr and NeQuick model did not show any changes during the geomagnetic storm event. The Holt-Winter method showed better agreement with the GPS-TEC for both the UUMK and TGPG stations. The correlation between the observed and modeled GPS-TEC during the quiet and disturbed period for the UUMK station showed a slightly better correlation compared to the TGPG station. The Holt-Winter method showed good correlation of around 0.98 during the quiet period and 0.95 during the disturbed period, while IRI-2001, IRI01-corr, and NeQuick had comparatively lower correlation of around ≈ 0.8 during the quiet period and ≈ 0.7 during the disturbed period. Overall, this research concludes that the Holt-Winter method effectively the GPS-TEC with good correlation during the quiet and disturbed period in the equatorial region over Malaysia.

PBO Southwest Region: Baja Earthquake Response and Network Operations

NASA Astrophysics Data System (ADS)

Walls, C. P.; Basset, A.; Mann, D.; Lawrence, S.; Jarvis, C.; Feaux, K.; Jackson, M. E.

2011-12-01

The SW region of the Plate Boundary Observatory consists of 455 continuously operating GPS stations located principally along the transform system of the San Andreas fault and Eastern California Shear Zone. In the past year network uptime exceeded an average of 97% with greater than 99% data acquisition. Communications range from CDMA modem (307), radio (92), Vsat (30), DSL/T1/other (25) to manual downloads (1). Sixty-three stations stream 1 Hz data over the VRS3Net typically with <0.5 second latency. Over 620 maintenance activities were performed during 316 onsite visits out of approximately 368 engineer field days. Within the past year there have been 7 incidences of minor (attempted theft) to moderate vandalism (solar panel stolen) with one total loss of receiver and communications gear. Security was enhanced at these sites through fencing and more secure station configurations. In the past 12 months, 4 new stations were installed to replace removed stations or to augment the network at strategic locations. Following the M7.2 El Mayor-Cucapah earthquake CGPS station P796, a deep-drilled braced monument, was constructed in San Luis, AZ along the border within 5 weeks of the event. In addition, UNAVCO participated in a successful University of Arizona-led RAPID proposal for the installation of six continuous GPS stations for post-seismic observations. Six stations are installed and telemetered through a UNAM relay at the Sierra San Pedro Martir. Four of these stations have Vaisala WXT520 meteorological sensors. An additional site in the Sierra Cucapah (PTAX) that was built by CICESE, an Associate UNAVCO Member institution in Mexico, and Caltech has been integrated into PBO dataflow. The stations will be maintained as part of the PBO network in coordination with CICESE. UNAVCO is working with NOAA to upgrade PBO stations with WXT520 meteorological sensors and communications systems capable of streaming real-time GPS and met data. The real-time GPS and meteorological sensor data streaming support watershed and flood analyses for regional early-warning systems related to NOAA's work with California Department of Water Resources. Currently 19 stations are online and streaming with 7 more in preparation. In 2008 PBO became the steward of 209 existing network stations of which 140 are in the SW region that included SCIGN, BARD, BARGEN stations. Due to the mix of incompatible equipment used between PBO and existing network stations a project was undertaken to standardize existing network GPS stations to PBO specifications by upgrading power systems and enclosures. To date 96 stations have been upgraded. UNAVCO is currently funded through a USGS ARRA grant to construct 8 new GPS stations in the San Francisco Bay Area capable of streaming high rate data. At present 6 stations are built with 2 permits outstanding.

The Plate Boundary Observatory Student Field Assistant Program in Southern California

NASA Astrophysics Data System (ADS)

Seider, E. L.

2007-12-01

Each summer, UNAVCO hires students as part of the Plate Boundary Observatory (PBO) Student Field Assistant Program. PBO, the geodetic component of the NSF-funded EarthScope project, involves the reconnaissance, permitting, installation, documentation, and maintenance of 880 permanent GPS stations in five years. During the summer 2007, nine students from around the US and Puerto Rico were hired to assist PBO engineers during the busy summer field season. From June to September, students worked closely with PBO field engineers to install and maintain permanent GPS stations in all regions of PBO, including Alaska. The PBO Student Field Assistant Program provides students with professional hands-on field experience as well as continuing education in the geosciences. It also gives students a glimpse into the increasing technologies available to the science community, the scope of geophysical research utilizing these technologies, and the field techniques necessary to complete this research. Students in the PBO Field Assistant Program are involved in all aspects of GPS support, including in-warehouse preparation and in-field installations and maintenance. Students are taught practical skills such as drilling, wiring, welding, hardware configuration, documentation, and proper field safety procedures needed to construct permanent GPS stations. These real world experiences provide the students with technical and professional skills that are not always available to them in a classroom, and will benefit them greatly in their future studies and careers. The 2007 summer field season in Southern California consisted of over 35 GPS permanent station installations. To date, the Southern California region of PBO has installed over 190 GPS stations. This poster presentation will highlight the experiences gained by the Southern California student field assistants, while supporting PBO- Southern California GPS installations in the Mohave Desert and the Inyo National Forest.

Deformation Along the Rio Grande Rift: Investigating the Spatial and Temporal Distribution of Strain Using GPS

NASA Astrophysics Data System (ADS)

Murray, K. D.; Murray, M. H.; Sheehan, A. F.; Nerem, R. S.

2014-12-01

Low velocity (<1 mm/yr) extensional environments, such as the Rio Grande rift (RGR) in Colorado and New Mexico, are complex but can provide insights into continental dynamics, tectonic processes, and seismic hazards. We use eight years of measurements from 26 continuous GPS stations across the RGR installed as part of a collaborative EarthScope experiment. We combine this data with regional Plate Boundary Observatory (PBO) and National Geodetic Survey (NGS) CORS GPS stations, and survey-mode data collected on NGS benchmarks to investigate how deformation is distributed across a broad area from the Great Plains to the Colorado Plateau. The data from over 150 stations are processed using GAMIT/GLOBK, and time series, velocities, strain rates are estimated with respect to realizations of a stable North America reference frame, such as NA12. This study extends our previous analysis, based on 4 years of data, which found an approximately uniform 1.2 nanostrain/yr east-west extensional strain rate across the entire region that was not concentrated on the narrow surface expression of the rift. We expand on this previous work by using a denser network of GPS stations and analyzing longer time series, which reduce horizontal velocity uncertainties to approximately 0.15 mm/yr. We also improve the accuracy of the estimated velocity uncertainties by robustly characterizing time-correlated noise. The noise models indicate that both power-law and flicker noise are present in the time series along with white noise. On average, power law noise constitutes about 90% of the total noise in the vertical component and 60% in the horizontal components for the RGR sites. We use the time series, and velocity and strain-rate estimates to constrain spatial and temporal variations in the deformation field in order to locate possible regions of strain localization and detect transient deformation signals, and to address some of the kinematic and dynamic issues raised by the observation that a broad, low seismic velocity zone underlies the narrow geologic surface expression of the RGR defined by normal fault bounded basins.

Preliminary study of GPS orbit determination accuracy achievable from worldwide tracking data

NASA Technical Reports Server (NTRS)

Larden, D. R.; Bender, P. L.

1982-01-01

The improvement in the orbit accuracy if high accuracy tracking data from a substantially larger number of ground stations is available was investigated. Observations from 20 ground stations indicate that 20 cm or better accuracy can be achieved for the horizontal coordinates of the GPS satellites. With this accuracy, the contribution to the error budget for determining 1000 km baselines by GPS geodetic receivers would be only about 1 cm.

Variation of GPS-TEC in a low latitude Indian region during the year 2012 and 2013

NASA Astrophysics Data System (ADS)

Patel, Nilesh C.; Karia, Sheetal P.; Pathak, Kamlesh N.

2018-05-01

The paper is based on the ionospheric variations in terms of vertical total electron content (VTEC) for the period from January 2012 to December 2013 based on the analysis of dual frequency signals from the Global Positioning System (GPS) satellites recorded at ground stations Surat (21.16°N, 72.78°E Geog.), situated under the northern crest of the equatorial ionization anomaly region (EIA) and other three International GNSS Service (IGS) stations Bangalore (13.02°N, 77.57°E Geog.), Hyderabad (17.25°N, 78.30°E Geog.), and Lucknow (26.91°N, 80.95°E Geog.) in India. We describe the diurnal and seasonal characteristics. It was observed that GPS-TEC reaches its maximum value between 12:00 and 16:00 IST. Further, Seasonal variations of GPS-TEC is categorized into four seasons, i.e., March equinox (February, March, and April), June solstice (May, June, and July), September equinox (August, September, and October) and December solstice (November, December and January). The forenoon rate of production in Lucknow (beyond EIA crest) is faster than Bangalore, Hyderabad and Surat station. It is found that September equinox shows GPS-TEC slightly higher than the March equinox, followed by June solstice and the lowest GPS-TEC are in winter solstice at four stations. The equinoctial asymmetry clearly observed in the current study. Also GPS-TEC shows a semiannual variation.

Surface Temperature and Precipitation Affecting GPS Signals Before the 2009 L'Aquila Earthquake (Central Italy).

NASA Astrophysics Data System (ADS)

Crescentini, L.; Amoruso, A.; Chiaraluce, L.

2017-12-01

This work focuses on GPS time series recorded before the Mw 6.1 earthquake which struck Central Italy in April 2009. It shows how environmental noise effects may be subtle and relevant when investigating relatively small strain signals and how the availability of data from weather stations and water level sensors co-located with GPS stations may provide critical information which must be taken into consideration while dealing with deformation signals.The preparatory phase of a large earthquake may include both seismic (foreshocks) and aseismic (slow slip event, SSE) deforming episodes but, unlike afterslip, no slow event has yet been recorded before moderate earthquakes, even when they occurred close to high-sensitivity strain meters. An exception to this seems to be represented by the 2009 earthquake. The main shock was preceded by a foreshock sequence lasting 6 months; it has been claimed that an analysis of continuous GPS data shows that during the foreshock sequence a 5.9 Mw SSE occurred along a decollement located beneath the reactivated normal fault system. This hypothesized SSE, that started in the middle of February 2009 and lasted for almost two weeks, would have eventually loaded the largest foreshock and the main shock.We show that the strain signal that the SSE would have generated at two laser strainmeters operating at about 20 km NE from the SSE source was essentially undetected. On the contrary, a transient signal is present in temperature and precipitation time series recorded close to the GPS station, MTTO, that has largest signal referred to the SSE, implying that these contaminated the GPS record. This interpretation is corroborated by the strong similarity, during the coldest winter months, between the displacement data of MTTO and a linear combination of filtered temperature and precipitation data, mimicking simple heat conduction and snow accumulation/removal processes. Such a correlation between displacement and environmental data is missing during the other seasons, when it neither snows nor freezes. This lack of correlation seems to exclude simple thermal expansion of the bedrock or the pillar monument itself as a local source of deformation. We hypothesize that thermal effects might be caused by ground freezing and consequent water expansion (about 9%) when liquid water is converted into ice.

Effect of removing the common mode errors on linear regression analysis of noise amplitudes in position time series of a regional GPS network & a case study of GPS stations in Southern California

NASA Astrophysics Data System (ADS)

Jiang, Weiping; Ma, Jun; Li, Zhao; Zhou, Xiaohui; Zhou, Boye

2018-05-01

The analysis of the correlations between the noise in different components of GPS stations has positive significance to those trying to obtain more accurate uncertainty of velocity with respect to station motion. Previous research into noise in GPS position time series focused mainly on single component evaluation, which affects the acquisition of precise station positions, the velocity field, and its uncertainty. In this study, before and after removing the common-mode error (CME), we performed one-dimensional linear regression analysis of the noise amplitude vectors in different components of 126 GPS stations with a combination of white noise, flicker noise, and random walking noise in Southern California. The results show that, on the one hand, there are above-moderate degrees of correlation between the white noise amplitude vectors in all components of the stations before and after removal of the CME, while the correlations between flicker noise amplitude vectors in horizontal and vertical components are enhanced from un-correlated to moderately correlated by removing the CME. On the other hand, the significance tests show that, all of the obtained linear regression equations, which represent a unique function of the noise amplitude in any two components, are of practical value after removing the CME. According to the noise amplitude estimates in two components and the linear regression equations, more accurate noise amplitudes can be acquired in the two components.

GPS Modeling and Analysis. Summary of Research: GPS Satellite Axial Ratio Predictions

NASA Technical Reports Server (NTRS)

Axelrad, Penina; Reeh, Lisa

2002-01-01

This report outlines the algorithms developed at the Colorado Center for Astrodynamics Research to model yaw and predict the axial ratio as measured from a ground station. The algorithms are implemented in a collection of Matlab functions and scripts that read certain user input, such as ground station coordinates, the UTC time, and the desired GPS (Global Positioning System) satellites, and compute the above-mentioned parameters. The position information for the GPS satellites is obtained from Yuma almanac files corresponding to the prescribed date. The results are displayed graphically through time histories and azimuth-elevation plots.

A Geodetic Strain Rate Model for the Pacific-North American Plate Boundary, western United States

NASA Astrophysics Data System (ADS)

Kreemer, C.; Hammond, W. C.; Blewitt, G.; Holland, A. A.; Bennett, R. A.

2012-04-01

We present a model of crustal strain rates derived from GPS measurements of horizontal station velocities in the Pacific-North American plate boundary in the western United States. The model reflects a best estimate of present-day deformation from the San Andreas fault system in the west to the Basin and Range province in the east. Of the total 2,846 GPS velocities used in the model, 1,197 are derived by ourselves, and 1,649 are taken from (mostly) published results. The velocities derived by ourselves (the "UNR solution") are estimated from GPS position time-series of continuous and semi-continuous stations for which data are publicly available. We estimated ITRF2005 positions from 2002-2011.5 using JPL's GIPSY-OASIS II software with ambiguity resolution applied using our custom Ambizap software. Only stations with time-series that span at least 2.25 years are considered. We removed from the time-series continental-scale common-mode errors using a spatially-varying filtering technique. Velocity uncertainties (typically 0.1-0.3 mm/yr) assume that the time-series contain flicker plus white noise. We used a subset of stations on the stable parts of the Pacific and North American plates to estimate the Pacific-North American pole of rotation. This pole is applied as a boundary condition to the model and the North American - ITRF2005 pole is used to rotate our velocities into a North America fixed reference frame. We do not include parts of the time-series that show curvature due to post-seismic deformation after major earthquakes and we also exclude stations whose time-series display a significant unexplained non-linearity or that are near volcanic centers. Transient effects longer than the observation period (i.e., slow viscoelastic relaxation) are left in the data. We added to the UNR solution velocities from 12 other studies. The velocities are transformed onto the UNR solution's reference frame by estimating and applying a translation and rotation that minimizes the velocities at collocated stations. We removed obvious outliers and velocities in areas that we identified to undergo subsidence likely due to excessive water pumping. For the strain rate calculations we excluded GPS stations with anomalous vertical motion or annual horizontal periodicity, which are indicators of local site instability. First, we used the stations from the UNR solution to create a Delaunay triangulation and estimated the horizontal strain rate components (and rigid body rotation) for each triangle in a linear least-squares inversion using the horizontal velocities as input. Some level of spatial damping was applied to minimize unnecessary spatial variation in the model parameters. The strain rates estimates were then used as a priori strain rate variances in a method that fits continuous bi-cubic Bessel spline functions through the velocity gradient field while minimizing the weighted misfit to all velocities. A minimal level of spatial smoothing of the variances was applied. The strain rate tensor model is shown by contours of the second invariant of the tensor, which is a measure of the amplitude that is coordinate frame independent. We also show a map of the tensor style and of the signal-to-noise ratio of the model.

Fusion of Location Fingerprinting and Trilateration Based on the Example of Differential Wi-Fi Positioning

NASA Astrophysics Data System (ADS)

Retscher, G.

2017-09-01

Positioning of mobile users in indoor environments with Wireless Fidelity (Wi-Fi) has become very popular whereby location fingerprinting and trilateration are the most commonly employed methods. In both the received signal strength (RSS) of the surrounding access points (APs) are scanned and used to estimate the user's position. Within the scope of this study the advantageous qualities of both methods are identified and selected to benefit their combination. By a fusion of these technologies a higher performance for Wi-Fi positioning is achievable. For that purpose, a novel approach based on the well-known Differential GPS (DGPS) principle of operation is developed and applied. This approach for user localization and tracking is termed Differential Wi-Fi (DWi-Fi) by analogy with DGPS. From reference stations deployed in the area of interest differential measurement corrections are derived and applied at the mobile user side. Hence, range or coordinate corrections can be estimated from a network of reference station observations as it is done in common CORS GNSS networks. A low-cost realization with Raspberry Pi units is employed for these reference stations. These units serve at the same time as APs broadcasting Wi-Fi signals as well as reference stations scanning the receivable Wi-Fi signals of the surrounding APs. As the RSS measurements are carried out continuously at the reference stations dynamically changing maps of RSS distributions, so-called radio maps, are derived. Similar as in location fingerprinting this radio maps represent the RSS fingerprints at certain locations. From the areal modelling of the correction parameters in combination with the dynamically updated radio maps the location of the user can be estimated in real-time. The novel approach is presented and its performance demonstrated in this paper.

GPS Imaging of Global Vertical Land Motion for Sea Level Studies

NASA Astrophysics Data System (ADS)

Hammond, W. C.; Blewitt, G.; Hamlington, B. D.

2015-12-01

Coastal vertical land motion contributes to the signal of local relative sea level change. Moreover, understanding global sea level change requires understanding local sea level rise at many locations around Earth. It is therefore essential to understand the regional secular vertical land motion attributable to mantle flow, tectonic deformation, glacial isostatic adjustment, postseismic viscoelastic relaxation, groundwater basin subsidence, elastic rebound from groundwater unloading or other processes that can change the geocentric height of tide gauges anchored to the land. These changes can affect inferences of global sea level rise and should be taken into account for global projections. We present new results of GPS imaging of vertical land motion across most of Earth's continents including its ice-free coastlines around North and South America, Europe, Australia, Japan, parts of Africa and Indonesia. These images are based on data from many independent open access globally distributed continuously recording GPS networks including over 13,500 stations. The data are processed in our system to obtain solutions aligned to the International Terrestrial Reference Frame (ITRF08). To generate images of vertical rate we apply the Median Interannual Difference Adjusted for Skewness (MIDAS) algorithm to the vertical times series to obtain robust non-parametric estimates with realistic uncertainties. We estimate the vertical land motion at the location of 1420 tide gauges locations using Delaunay-based geographic interpolation with an empirically derived distance weighting function and median spatial filtering. The resulting image is insensitive to outliers and steps in the GPS time series, omits short wavelength features attributable to unstable stations or unrepresentative rates, and emphasizes long-wavelength mantle-driven vertical rates.

Real-Time GPS Monitoring for Earthquake Rapid Assessment in the San Francisco Bay Area

NASA Astrophysics Data System (ADS)

Guillemot, C.; Langbein, J. O.; Murray, J. R.

2012-12-01

The U.S. Geological Survey Earthquake Science Center has deployed a network of eight real-time Global Positioning System (GPS) stations in the San Francisco Bay area and is implementing software applications to continuously evaluate the status of the deformation within the network. Real-time monitoring of the station positions is expected to provide valuable information for rapidly estimating source parameters should a large earthquake occur in the San Francisco Bay area. Because earthquake response applications require robust data access, as a first step we have developed a suite of web-based applications which are now routinely used to monitor the network's operational status and data streaming performance. The web tools provide continuously updated displays of important telemetry parameters such as data latency and receive rates, as well as source voltage and temperature information within each instrument enclosure. Automated software on the backend uses the streaming performance data to mitigate the impact of outages, radio interference and bandwidth congestion on deformation monitoring operations. A separate set of software applications manages the recovery of lost data due to faulty communication links. Displacement estimates are computed in real-time for various combinations of USGS, Plate Boundary Observatory (PBO) and Bay Area Regional Deformation (BARD) network stations. We are currently comparing results from two software packages (one commercial and one open-source) used to process 1-Hz data on the fly and produce estimates of differential positions. The continuous monitoring of telemetry makes it possible to tune the network to minimize the impact of transient interruptions of the data flow, from one or more stations, on the estimated positions. Ongoing work is focused on using data streaming performance history to optimize the quality of the position, reduce drift and outliers by switching to the best set of stations within the network, and automatically select the "next best" station to use as reference. We are also working towards minimizing the loss of streamed data during concurrent data downloads by improving file management on the GPS receivers.

"GP Psych Opinion": evaluation of a psychiatric consultation service.

PubMed

Simpson, Alex E; Emmerson, W Brett; Frost, Aaron D J; Powell, Jacinta L

2005-07-18

To evaluate a hospital-based psychiatric consultation service for patients referred by general practitioners (GPs), and the effect on its use of a focused marketing strategy aimed at GPs. Postal survey of GPs in the catchment area (inner north Brisbane, Queensland), September to November 2003; and assessment of referrals, March to August 2003. Patient referrals, satisfaction among GPs who had referred, and awareness and opinions of the service among GPs who had not referred, compared with results of a similar survey conducted before marketing. In the 6 months after marketing, 43 patients were referred by 23 GPs, an average of 7.2 patients per month, compared with 2.5 per month in the first 12 months of the service. Survey responses were received from 13 of 36 GPs who had referred patients and 97 of 282 GPs who had not (response rate, 35%). Satisfaction among GPs who had referred remained high, and 12/13 felt the service should continue. Among GPs who had not referred, 76% were aware of the service, up from 26% in the previous survey, and 99% liked the concept of the service. Given the ongoing low utilisation of this service, we question whether this model is accepted by most GPs in our district. Possibly, they prefer more traditional models, where treatment is taken over by psychiatrists in the public or private system. We believe there is a need to increase the capacity and scope of publicly funded services to treat mental health problems.

Establishment of Karadeniz Technical University Permanent GNSS Station as Reactivated of TRAB IGS Station

NASA Astrophysics Data System (ADS)

Kazancı, Selma Zengin; Kayıkçı, Emine Tanır

2017-12-01

In recent years, Global Navigation Satellite Systems (GNSS) have gained great importance in terms of the benefi ts it provides such as precise geodetic point positioning, determining crustal deformations, navigation, vehicle monitoring systems and meteorological applications etc. As in Turkey, for this purpose, each country has set up its own GNSS station networks like Turkish National Permanent RTK Network analyzed precise station coordinates and velocities together with the International GNSS Service, Turkish National Fundamental GPS Network and Turkish National Permanent GNSS Network (TNPGN) stations not only are utilized as precise positioning but also GNSS meteorology studies so total number of stations are increased. This work is related to the reactivated of the TRAB IGS station which was established in Karadeniz Technical University, Department of Geomatics Engineering. Within the COST ES1206 Action (GNSS4SWEC) KTU analysis center was established and Trop-NET system developed by Geodetic Observatory Pecny (GOP, RIGTC) in order to troposphere monitoring. The project titled "Using Regional GNSS Networks to Strengthen Severe Weather Prediction" was accepted to the scientifi c and technological research council of Turkey (TUBITAK). With this project, we will design 2 new constructed GNSS reference station network. Using observation data of network, we will compare water vapor distribution derived by GNSS Meteorology and GNSS Tomography. At this time, KTU AC was accepted as E-GVAP Analysis Centre in December 2016. KTU reference station is aimed to be a member of the EUREF network with these studies.

Global Positioning System data collection, processing, and analysis conducted by the U.S. Geological Survey Earthquake Hazards Program

USGS Publications Warehouse

Murray, Jessica R.; Svarc, Jerry L.

2017-01-01

The U.S. Geological Survey Earthquake Science Center collects and processes Global Positioning System (GPS) data throughout the western United States to measure crustal deformation related to earthquakes and tectonic processes as part of a long‐term program of research and monitoring. Here, we outline data collection procedures and present the GPS dataset built through repeated temporary deployments since 1992. This dataset consists of observations at ∼1950 locations. In addition, this article details our data processing and analysis procedures, which consist of the following. We process the raw data collected through temporary deployments, in addition to data from continuously operating western U.S. GPS stations operated by multiple agencies, using the GIPSY software package to obtain position time series. Subsequently, we align the positions to a common reference frame, determine the optimal parameters for a temporally correlated noise model, and apply this noise model when carrying out time‐series analysis to derive deformation measures, including constant interseismic velocities, coseismic offsets, and transient postseismic motion.

Precise regional baseline estimation using a priori orbital information

NASA Technical Reports Server (NTRS)

Lindqwister, Ulf J.; Lichten, Stephen M.; Blewitt, Geoffrey

1990-01-01

A solution using GPS measurements acquired during the CASA Uno campaign has resulted in 3-4 mm horizontal daily baseline repeatability and 13 mm vertical repeatability for a 729 km baseline, located in North America. The agreement with VLBI is at the level of 10-20 mm for all components. The results were obtained with the GIPSY orbit determination and baseline estimation software and are based on five single-day data arcs spanning the 20, 21, 25, 26, and 27 of January, 1988. The estimation strategy included resolving the carrier phase integer ambiguities, utilizing an optial set of fixed reference stations, and constraining GPS orbit parameters by applying a priori information. A multiday GPS orbit and baseline solution has yielded similar 2-4 mm horizontal daily repeatabilities for the same baseline, consistent with the constrained single-day arc solutions. The application of weak constraints to the orbital state for single-day data arcs produces solutions which approach the precise orbits obtained with unconstrained multiday arc solutions.

Strain Variation along Cimandiri Fault, West Java Based on Continuous and Campaign GPS Observation From 2006-2016

NASA Astrophysics Data System (ADS)

Safitri, A. A.; Meilano, I.; Gunawan, E.; Abidin, H. Z.; Efendi, J.; Kriswati, E.

2018-03-01

The Cimandiri fault which is running in the direction from Pelabuhan Ratu to Padalarang is the longest fault in West Java with several previous shallow earthquakes in the last 20 years. By using continues and campaign GPS observation from 2006-2016, we obtain the deformation pattern along the fault through the variation of strain tensor. We use the velocity vector of GPS station which is fixed in stable International Terrestrial Reference Frame 2008 to calculate horizontal strain tensor. Least Square Collocation is applied to produce widely dense distributed velocity vector and optimum scale factor for the Least Square Weighting matrix. We find that the strain tensor tend to change from dominantly contraction in the west to dominantly extension to the east of fault. Both the maximum shear strain and dilatation show positive value along the fault and increasing from the west to the east. The findings of strain tensor variation along Cimandiri Fault indicate the post seismic effect of the 2006 Java Earthquake.

An EarthScope Plate Boundary Observatory Progress Report

NASA Astrophysics Data System (ADS)

Jackson, M.; Anderson, G.; Blume, F.; Walls, C.; Coyle, B.; Feaux, K.; Friesen, B.; Phillips, D.; Hafner, K.; Johnson, W.; Mencin, D.; Pauk, B.; Dittmann, T.

2007-12-01

UNAVCO is building and operating the Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project to understand the structure, dynamics, and evolution of the North American continent. When complete in October 2008, the 875 GPS, 103 strain and seismic, and 28 tiltmeters stations will comprise the largest integrated geodetic and seismic network in United States and the second largest in the world. Data from the PBO network will facilitate research into plate boundary deformation with unprecedented scope and detail. As of 1 September 2007, UNAVCO had completed 680 PBO GPS stations and had upgraded 89% of the planned PBO Nucleus stations. Highlights of the past year's work include the expansion of the Alaska subnetwork to 95 continuously-operating stations, including coverage of Akutan and Augustine volcanoes and reconnaissance for future installations on Unimak Island; the installation of nine new stations on Mt. St. Helens; and the arrival of 33 permits for station installations on BLM land in Nevada. The Augustine network provided critical data on magmatic and volcanic processes associated with the 2005-2006 volcanic crisis, and has expanded to a total of 11 stations. Please visit http://pboweb.unavco.org/?pageid=3 for further information on PBO GPS network construction activities. As of September 2007, 41 PBO borehole stations had been installed and three laser strainmeter stations were operating, with a total of 60 borehole stations and 4 laser strainmeters expected by October 2007. In response to direction from the EarthScope community, UNAVCO installed a dense network of six stations along the San Jacinto Fault near Anza, California; installed three of four planned borehole strainmeter stations on Mt. St. Helens; and has densified coverage of the Parkfield area. Please visit http://pboweb.unavco.org/?pageid=8 for more information on PBO strainmeter network construction progress. The combined PBO/Nucleus GPS network provides 350 GB of raw standard rate data, with special downloads of more than 250 GB of high-rate GPS data following large earthquakes in Russia, Tonga, and Peru, as well as for community requests. The standard rate GPS data are processed routinely to generate data products including station position time series, velocity vectors, and related information, and all data products are available from the UNAVCO Facility archive. The PBO seismic network seismic network has provided 201 GB of raw data, which are available via Antelope and Earthworm from PBO and via the IRIS Data Management Center (DMC); we provide data to seismic networks operated from Caltech, UCSD, UCSB, University of Washington, and the Pacific Geosciences Center in Sidney, BC. The PBO strainmeter network has provided 93 GB of raw data, available in both raw native format and SEED format from the Northern California Earthquake Data Center and the IRIS DMC, along with higher-level products such as cleaned strain time series and related information. Please visit http://pboweb.unavco.org/gps_data and http://pboweb.unavco.org/strain_data for more information on PBO GPS and strainmeter/seismic data products, respectively.

Analysis of Site Position Time Series Derived From Space Geodetic Solutions

NASA Astrophysics Data System (ADS)

Angermann, D.; Meisel, B.; Kruegel, M.; Tesmer, V.; Miller, R.; Drewes, H.

2003-12-01

This presentation deals with the analysis of station coordinate time series obtained from VLBI, SLR, GPS and DORIS solutions. We also present time series for the origin and scale derived from these solutions and discuss their contribution to the realization of the terrestrial reference frame. For these investigations we used SLR and VLBI solutions computed at DGFI with the software systems DOGS (SLR) and OCCAM (VLBI). The GPS and DORIS time series were obtained from weekly station coordinates solutions provided by the IGS, and from the joint DORIS analysis center (IGN-JPL). We analysed the time series with respect to various aspects, such as non-linear motions, periodic signals and systematic differences (biases). A major focus is on a comparison of the results at co-location sites in order to identify technique- and/or solution related problems. This may also help to separate and quantify possible effects, and to understand the origin of still existing discrepancies. Technique-related systematic effects (biases) should be reduced to the highest possible extent, before using the space geodetic solutions for a geophysical interpretation of seasonal signals in site position time series.

Height Accuracy Based on Different Rtk GPS Method for Ultralight Aircraft Images

NASA Astrophysics Data System (ADS)

Tahar, K. N.

2015-08-01

Height accuracy is one of the important elements in surveying work especially for control point's establishment which requires an accurate measurement. There are many methods can be used to acquire height value such as tacheometry, leveling and Global Positioning System (GPS). This study has investigated the effect on height accuracy based on different observations which are single based and network based GPS methods. The GPS network is acquired from the local network namely Iskandar network. This network has been setup to provide real-time correction data to rover GPS station while the single network is based on the known GPS station. Nine ground control points were established evenly at the study area. Each ground control points were observed about two and ten minutes. It was found that, the height accuracy give the different result for each observation.

Introduction to the High-Rate GPS Network of Puerto Rico and the U.S. Virgin Islands

NASA Astrophysics Data System (ADS)

Wang, G.; Hillebrandt, C. V.; Martinez, J. M.; Huerfano, V.; Schellekens, J.

2008-12-01

The Puerto Rico Seismic Network at the University of Puerto Rico at Mayagüez is a regional earthquake and tsunami monitoring institute. One of its primary objective is to provide timely and reliable earthquake and tsunami information and warning to the state (Puerto Rico) and local governments, the US and British Virgin Islands, as well as to the general public. In the past five years, it has been expanding its operations for the establishment of a Caribbean Tsunami Warning Center. With funding of the Puerto Rico government and NOAA, it is operated 24 hours per day and 7 days per week. Broadband seismometers are generally unable to capture the full bandwidth of long period ground motions following very large earthquakes. As a result, it is difficult to rapidly estimate the true magnitudes of large earthquakes using only seismic data. High-rate GPS has been justified as a very useful tool in recording long-period and permanent earthquake ground motions. Estimation of the true magnitude (and therefore tsunami potential) of large earthquakes may be determined more accurately in a timely manner (minutes after the quake) using high rate GPS observations. With the major aim of improving the ability of the PRSN in rapidly and precisely monitoring large earthquakes, NSF funded a Major Research Instrumentation (MRI) project, Acquisition of 9 High-rate GPS Units for Developing a Broadband Earthquake Observation System in Puerto Rico and the U.S. Virgin Islands (EAR-0722540, August 1, 2007-July 31, 2009). The major purpose of this project is to build a high-rate GPS network in Puerto Rico and the U.S. Virgin Islands. The GPS network includes 3 campaign and 6 permanent GPS stations. These campaign stations were designed to use in emergency response after large earthquakes to get co-seismic and post-seismic displacement. These six permanent stations were designed to complement current seismic observation system of Puerto Rico and U.S. Virgin Islands. We have installed three permanent GPS stations in May, 2008. They locate in Arecibo Observatory, Bayamon Science Park, and Caja de Muertos Island. We will install the other three stations in October, 2008. They will be located in Mona, Culebra, and St. Thomas islands. All of these permanent GPS stations are colocated with seismic stations operated by the Puerto Rico Seismic Network and the Puerto Rico Strong Motion Program. They are also very-closely spaced to the Tide Gauge stations operated by PRSN and NOAA. Therefore they will also complement the tide gauge sea-level observation system to get accurate absolute sea-level changes after large earthquakes. The integrated velocitymeter-accelerometer- GPS earthquake observation system will advance knowledge of seismic wave propagation, the kinematics and dynamics of fault rupture process, pre-seismic, co-seismic and post-seismic deformation, and is also likely to be useful for improving building and critical structure designs. It will support earthquake and tsunami hazards research and mitigation in Puerto Rico and the surrounding region. High-rate GPS observations can also be used for real time tropospheric water vapor tomography which is useful for weather prediction, including improved hurricane track forecasting. Raw GPS data are freely available through the UNAVCO archive. As a result, a large number of researchers can potentially benefit from the data for research and applications ranging from neotectonics to atmospheric science to civil engineering.

Preliminary study of GPS orbit determination accuracy achievable from worldwide tracking data

NASA Technical Reports Server (NTRS)

Larden, D. R.; Bender, P. L.

1983-01-01

The improvement in the orbit accuracy if high accuracy tracking data from a substantially larger number of ground stations is available was investigated. Observations from 20 ground stations indicate that 20 cm or better accuracy can be achieved for the horizontal coordinates of the GPS satellites. With this accuracy, the contribution to the error budget for determining 1000 km baselines by GPS geodetic receivers would be only about 1 cm. Previously announced in STAR as N83-14605

The ionospheric eclipse factor method (IEFM) and its application to determining the ionospheric delay for GPS

NASA Astrophysics Data System (ADS)

Yuan, Y.; Tscherning, C. C.; Knudsen, P.; Xu, G.; Ou, J.

2008-01-01

A new method for modeling the ionospheric delay using global positioning system (GPS) data is proposed, called the ionospheric eclipse factor method (IEFM). It is based on establishing a concept referred to as the ionospheric eclipse factor (IEF) λ of the ionospheric pierce point (IPP) and the IEF’s influence factor (IFF) bar{λ}. The IEF can be used to make a relatively precise distinction between ionospheric daytime and nighttime, whereas the IFF is advantageous for describing the IEF’s variations with day, month, season and year, associated with seasonal variations of total electron content (TEC) of the ionosphere. By combining λ and bar{λ} with the local time t of IPP, the IEFM has the ability to precisely distinguish between ionospheric daytime and nighttime, as well as efficiently combine them during different seasons or months over a year at the IPP. The IEFM-based ionospheric delay estimates are validated by combining an absolute positioning mode with several ionospheric delay correction models or algorithms, using GPS data at an international Global Navigation Satellite System (GNSS) service (IGS) station (WTZR). Our results indicate that the IEFM may further improve ionospheric delay modeling using GPS data.

International GPS Service for Geodynamics

NASA Technical Reports Server (NTRS)

Zumberge, J. F. (Editor); Urban, M. P. (Editor); Liu, R. (Editor); Neilan, R. E. (Editor)

1996-01-01

This 1995 annual report of the IGS International GPS (Global Positioning System) Service for Geodynamics - describes the second operational year of the service. It provides the many IGS contributing agencies and the rapidly growing user community with essential information on current organizational and technical matters promoting the IGS standards and products (including organizational framework, data processing strategies, and statistics showing the remarkable expansion of the GPS monitoring network, the improvement of IGS performance, and product quality). It also introduces important practical concepts for network densification by integration of regional stations and the combination of station coordinate solutions. There are groups of articles describing general aspects of the IGS, the Associate Analysis Centers (AACs), Data Centers, and IGS stations.

Vertical deformation at western part of Sumatra

DOE Office of Scientific and Technical Information (OSTI.GOV)

Febriyani, Caroline, E-mail: caroline.fanuel@students.itb.ac.id; Prijatna, Kosasih, E-mail: prijatna@gd.itb.ac.id; Meilano, Irwan, E-mail: irwan.meilano@gd.itb.ac.id

2015-04-24

This research tries to make advancement in GPS signal processing to estimate the interseismic vertical deformation field at western part of Sumatra Island. The data derived by Continuous Global Positioning System (CGPS) from Badan Informasi Geospasial (BIG) between 2010 and 2012. GPS Analyze at Massachusetts Institute of Technology (GAMIT) software and Global Kalman Filter (GLOBK) software are used to process the GPS signal to estimate the vertical velocities of the CGPS station. In order to minimize noise due to atmospheric delay, Vienna Mapping Function 1 (VMF1) is used as atmospheric parameter model and include daily IONEX file provided by themore » Center for Orbit Determination in Europe (CODE) as well. It improves GAMIT daily position accuracy up to 0.8 mm. In a second step of processing, the GLOBK is used in order to estimate site positions and velocities in the ITRF08 reference frame. The result shows that the uncertainties of estimated displacement velocity at all CGPS stations are smaller than 1.5 mm/yr. The subsided deformation patterns are seen at the northern and southern part of west Sumatra. The vertical deformation at northern part of west Sumatra indicates postseismic phase associated with the 2010 and 2012 Northern Sumatra earthquakes and also the long-term postseismic associated with the 2004 and 2005 Northern Sumatra earthquakes. The uplifted deformation patterns are seen from Bukit Tinggi to Seblat which indicate a long-term interseismic phase after the 2007 Bengkulu earthquake and 2010 Mentawai earthquake. GANO station shows a subsidence at rate 12.25 mm/yr, indicating the overriding Indo-Australia Plate which is dragged down by the subducting Southeast Asian Plate.« less

Determination of recent horizontal crustal movements and deformations of African and Eurasian plates in western Mediterranean region using geodetic-GPS computations extended to 2006 (from 1997) related to NAFREF and AFREF frames.

NASA Astrophysics Data System (ADS)

Azzouzi, R.

2009-04-01

Determination of recent horizontal crustal movements and deformations of African and Eurasian plates in western Mediterranean region using geodetic-GPS computations extended to 2006 (from 1997) related to NAFREF and AFREF frames. By: R. Azzouzi*, M. Ettarid*, El H. Semlali*, et A. Rimi+ * Filière de Formation en Topographie Institut Agronomique et Vétérinaire Hassan II B.P. 6202 Rabat-Instituts MAROC + Département de la Physique du Globe Université Mohammed V Rabat MAROC This study focus on the use of the geodetic spatial technique GPS for geodynamic purposes generally in the Western Mediterranean area and particularly in Morocco. It aims to exploit this technique first to determine the geodetic coordinates on some western Mediterranean sites. And also this technique is used to detect and to determine movements cross the boundary line between the two African and Eurasian crustal plates on some well chosen GPS-Geodynamics sites. It will allow us also to estimate crustal dynamic parameters of tension that results. These parameters are linked to deformations of terrestrial crust in the region. They are also associated with tectonic constraints of the study area. The usefulness of repeated measurements of these elements, the estimate of displacements and the determination of their temporal rates is indisputable. Indeed, sismo-tectonique studies allow a good knowledge of the of earthquake processes, their frequency their amplitude and even of their prediction in the world in general and in Moroccan area especially. They allow also contributing to guarantee more security for all most important management projects, as projects of building great works (dams, bridges, nuclear centrals). And also as preliminary study, for the most important joint-project between Europe and Africa through the Strait of Gibraltar. For our application, 23 GPS monitoring stations under the ITRF2000 reference frame are chosen in Eurasian and African plates. The sites are located around the Western Mediterranean and especially on Morocco. Exploiting parameters of positions and dispersions of these stations within the 1997-2003 period, the motion and the interaction types of interaction between African and Eurasian tectonic plates can be estimated. Similarly, the crustal dynamic parameters of tension of these sites will be computed. The time occupation on repeated observations sites is at least 72 hours. The measurements are continuous on permanent stations. The precise ephemerides are used in GPS computations. The post-treatments are done using commercial and scientific softwares. The coordinates obtained for two consecutive periods to and t within a period of 8 years will be used by programs established for this purpose to estimate crustal dynamic parameters of tension as well as to evaluate the appropriate movements. Even crustal dynamic parameters will be determined on each sites of the GPS-Geodynamics network, whose interest of seismic investigations is very important. This will allow best knowledge of substantial seismic activities of the surrounding zones. It can be deduced by measuring the motions and their parameter tensions using GPS. These estimations will contribute on the earthquake prediction by supervising the strain accumulation and its release in the active areas. For the geodetically aspect the GPS-Geodynamics sites computed in the ITRF frame can be used with other similar ounces' of Africa country and some well selected and convenient IGS, EUREF stations..to determine first the NAFREF and the AFRER frames.

GPS/GLONASS Combined Precise Point Positioning with Receiver Clock Modeling

PubMed Central

Wang, Fuhong; Chen, Xinghan; Guo, Fei

2015-01-01

Research has demonstrated that receiver clock modeling can reduce the correlation coefficients among the parameters of receiver clock bias, station height and zenith tropospheric delay. This paper introduces the receiver clock modeling to GPS/GLONASS combined precise point positioning (PPP), aiming to better separate the receiver clock bias and station coordinates and therefore improve positioning accuracy. Firstly, the basic mathematic models including the GPS/GLONASS observation equations, stochastic model, and receiver clock model are briefly introduced. Then datasets from several IGS stations equipped with high-stability atomic clocks are used for kinematic PPP tests. To investigate the performance of PPP, including the positioning accuracy and convergence time, a week of (1–7 January 2014) GPS/GLONASS data retrieved from these IGS stations are processed with different schemes. The results indicate that the positioning accuracy as well as convergence time can benefit from the receiver clock modeling. This is particularly pronounced for the vertical component. Statistic RMSs show that the average improvement of three-dimensional positioning accuracy reaches up to 30%–40%. Sometimes, it even reaches over 60% for specific stations. Compared to the GPS-only PPP, solutions of the GPS/GLONASS combined PPP are much better no matter if the receiver clock offsets are modeled or not, indicating that the positioning accuracy and reliability are significantly improved with the additional GLONASS satellites in the case of insufficient number of GPS satellites or poor geometry conditions. In addition to the receiver clock modeling, the impacts of different inter-system timing bias (ISB) models are investigated. For the case of a sufficient number of satellites with fairly good geometry, the PPP performances are not seriously affected by the ISB model due to the low correlation between the ISB and the other parameters. However, the refinement of ISB model weakens the correlation between coordinates and ISB estimates and finally enhance the PPP performance in the case of poor observation conditions. PMID:26134106

Inventory of anthropogenic surface deformation measured by InSAR in the western U.S./Mexico and possible impacts on GPS measurements

NASA Astrophysics Data System (ADS)

Semple, A.; Pritchard, M. E.; Taylor, H.

2014-12-01

The western US and Mexico are deforming at several spatial scales that can be measured by ground and satellite observations like GPS and Interferometric Synthetic Aperture Radar (InSAR). Many GPS stations have been installed throughout this area to monitor ground deformation caused by large scale tectonic processes; however, several studies have noted that the data recorded at a GPS station can be contaminated by local, non-tectonic ground deformation. In this study, we use InSAR to examine deformation from various sources in the western US and Mexico. We chose this method due to the spatially large study area and the availability and temporal coverage of SAR imagery. We use SAR images acquired by the satellites Envisat, ERS-1 and ERS-2 over a time period from 1992-2010 to create several time series. Data from the ALOS satellite between 2006-2011 are also used in some areas. We use these time series analysis along with previously published results to observe and catalogue various sources of surface deformation in the western US and Mexico - from groundwater pumping, geothermal activity, mining, hydrocarbon production, and other sources. We then use these results to identify GPS stations that have potentially been contaminated by non-tectonic deformation signals. We document more than 150 distinct regions of non-tectonic and likely anthropogenic deformation. We have located 82 GPS stations within 20km of the center of at least one of the non-tectonic deformation signals we have identified. It is likely that the data from these 82 GPS stations have been contaminated by local anthropogenic deformation. Some examples of previously unpublished non-tectonic deformation we have seen in this study include but are not limited to, subsidence due to groundwater extraction in Jesus Garcia, Mexico, both uplift and subsidence due to natural gas extraction at Jonah Field in Sublette County, WY, and uplift due to a water recharge project in Tonopah, AZ.

Atmospheric pressure loading effects on Global Positioning System coordinate determinations

NASA Technical Reports Server (NTRS)

Vandam, Tonie M.; Blewitt, Geoffrey; Heflin, Michael B.

1994-01-01

Earth deformation signals caused by atmospheric pressure loading are detected in vertical position estimates at Global Positioning System (GPS) stations. Surface displacements due to changes in atmospheric pressure account for up to 24% of the total variance in the GPS height estimates. The detected loading signals are larger at higher latitudes where pressure variations are greatest; the largest effect is observed at Fairbanks, Alaska (latitude 65 deg), with a signal root mean square (RMS) of 5 mm. Out of 19 continuously operating GPS sites (with a mean of 281 daily solutions per site), 18 show a positive correlation between the GPS vertical estimates and the modeled loading displacements. Accounting for loading reduces the variance of the vertical station positions on 12 of the 19 sites investigated. Removing the modeled pressure loading from GPS determinations of baseline length for baselines longer than 6000 km reduces the variance on 73 of the 117 baselines investigated. The slight increase in variance for some of the sites and baselines is consistent with expected statistical fluctuations. The results from most stations are consistent with approximately 65% of the modeled pressure load being found in the GPS vertical position measurements. Removing an annual signal from both the measured heights and the modeled load time series leaves this value unchanged. The source of the remaining discrepancy between the modeled and observed loading signal may be the result of (1) anisotropic effects in the Earth's loading response, (2) errors in GPS estimates of tropospheric delay, (3) errors in the surface pressure data, or (4) annual signals in the time series of loading and station heights. In addition, we find that using site dependent coefficients, determined by fitting local pressure to the modeled radial displacements, reduces the variance of the measured station heights as well as or better than using the global convolution sum.

Navstar Global Positioning System (GPS) clock program: Present and future

NASA Technical Reports Server (NTRS)

Tennant, D. M.

1981-01-01

Global Positioning System (GPS) program status are discussed and plans for ensuring the long term continuation of the program are presented. Performance of GPS clocks is presented in terms of on orbit data as portrayed by GPS master control station kalman filter processing. The GPS Clock reliability program is reviewed in depth and future plans fo the overall clock program are published.

Review of current GPS methodologies for producing accurate time series and their error sources

NASA Astrophysics Data System (ADS)

He, Xiaoxing; Montillet, Jean-Philippe; Fernandes, Rui; Bos, Machiel; Yu, Kegen; Hua, Xianghong; Jiang, Weiping

2017-05-01

The Global Positioning System (GPS) is an important tool to observe and model geodynamic processes such as plate tectonics and post-glacial rebound. In the last three decades, GPS has seen tremendous advances in the precision of the measurements, which allow researchers to study geophysical signals through a careful analysis of daily time series of GPS receiver coordinates. However, the GPS observations contain errors and the time series can be described as the sum of a real signal and noise. The signal itself can again be divided into station displacements due to geophysical causes and to disturbing factors. Examples of the latter are errors in the realization and stability of the reference frame and corrections due to ionospheric and tropospheric delays and GPS satellite orbit errors. There is an increasing demand on detecting millimeter to sub-millimeter level ground displacement signals in order to further understand regional scale geodetic phenomena hence requiring further improvements in the sensitivity of the GPS solutions. This paper provides a review spanning over 25 years of advances in processing strategies, error mitigation methods and noise modeling for the processing and analysis of GPS daily position time series. The processing of the observations is described step-by-step and mainly with three different strategies in order to explain the weaknesses and strengths of the existing methodologies. In particular, we focus on the choice of the stochastic model in the GPS time series, which directly affects the estimation of the functional model including, for example, tectonic rates, seasonal signals and co-seismic offsets. Moreover, the geodetic community continues to develop computational methods to fully automatize all phases from analysis of GPS time series. This idea is greatly motivated by the large number of GPS receivers installed around the world for diverse applications ranging from surveying small deformations of civil engineering structures (e.g., subsidence of the highway bridge) to the detection of particular geophysical signals.

Performance evaluation of ionospheric time delay forecasting models using GPS observations at a low-latitude station

NASA Astrophysics Data System (ADS)

Sivavaraprasad, G.; Venkata Ratnam, D.

2017-07-01

Ionospheric delay is one of the major atmospheric effects on the performance of satellite-based radio navigation systems. It limits the accuracy and availability of Global Positioning System (GPS) measurements, related to critical societal and safety applications. The temporal and spatial gradients of ionospheric total electron content (TEC) are driven by several unknown priori geophysical conditions and solar-terrestrial phenomena. Thereby, the prediction of ionospheric delay is challenging especially over Indian sub-continent. Therefore, an appropriate short/long-term ionospheric delay forecasting model is necessary. Hence, the intent of this paper is to forecast ionospheric delays by considering day to day, monthly and seasonal ionospheric TEC variations. GPS-TEC data (January 2013-December 2013) is extracted from a multi frequency GPS receiver established at K L University, Vaddeswaram, Guntur station (geographic: 16.37°N, 80.37°E; geomagnetic: 7.44°N, 153.75°E), India. An evaluation, in terms of forecasting capabilities, of three ionospheric time delay models - an Auto Regressive Moving Average (ARMA) model, Auto Regressive Integrated Moving Average (ARIMA) model, and a Holt-Winter's model is presented. The performances of these models are evaluated through error measurement analysis during both geomagnetic quiet and disturbed days. It is found that, ARMA model is effectively forecasting the ionospheric delay with an accuracy of 82-94%, which is 10% more superior to ARIMA and Holt-Winter's models. Moreover, the modeled VTEC derived from International Reference Ionosphere, IRI (IRI-2012) model and new global TEC model, Neustrelitz TEC Model (NTCM-GL) have compared with forecasted VTEC values of ARMA, ARIMA and Holt-Winter's models during geomagnetic quiet days. The forecast results are indicating that ARMA model would be useful to set up an early warning system for ionospheric disturbances at low latitude regions.

Collision-induced rotation in an arc-continent collision: Constrained by continuous GPS observations in Mindoro, Philippines

NASA Astrophysics Data System (ADS)

Rau, R.; Hung, H.; Yang, C.; Tsai, M.; Ching, K.; Bacolcol, T.; Solidum, R.; Chang, W.

2012-12-01

The Mindoro Island, situated at the southern end of the Manila trench, is a modern arc-continent collision. Seismic activity in Mindoro concentrates mainly in the northern segment of the island as part of the Manila subduction processes; in contrast, seismicity in the middle and the southern parts of the island is rather diffuse. Although the Mindoro Island has been experiencing intense seismic activities and is a type example of arc-continent collision, the modern mode of deformation of the Mindoro collision remains unclear. We have installed eight dual-frequency continuous GPS stations in the island since May 2010. The questions we want to address by using continuous GPS observations are (1) if there are still compressions within the Mindoro collision? Have they ceased as seen by the diffuse seismicity, or are the thrust faults locked? (2) What is the mode of deformation in the Mindoro collision and what are the roles of thrust and strike-slip faults playing in the collision? (3) How does the Mindoro collision compare with the other collision, such as the Taiwan orogen? Do they share similar characteristics for the subduction-collision transition zone? For the results of the first two years GPS measurements, if we take the Sablayan site near the southern end of the Manila trench as the reference station, a large counterclockwise rotation from south to north, with horizontal velocities of 1.9-31.1 mm/yr from 165 to 277 degrees, are found in the island. The deformation of the Mindoro is similar to the pattern of the transition zone from collision to subduction in northeastern Taiwan. This result suggests that collision-induced rotation is occurring in the Mindoro Island and the Mindoro arc-continent collision is still active.

GPS, BDS and Galileo ionospheric correction models: An evaluation in range delay and position domain

NASA Astrophysics Data System (ADS)

Wang, Ningbo; Li, Zishen; Li, Min; Yuan, Yunbin; Huo, Xingliang

2018-05-01

The performance of GPS Klobuchar (GPSKlob), BDS Klobuchar (BDSKlob) and NeQuick Galileo (NeQuickG) ionospheric correction models are evaluated in the range delay and position domains over China. The post-processed Klobuchar-style (CODKlob) coefficients provided by the Center for Orbit Determination in Europe (CODE) and our own fitted NeQuick coefficients (NeQuickC) are also included for comparison. In the range delay domain, BDS total electrons contents (TEC) derived from 20 international GNSS Monitoring and Assessment System (iGMAS) stations and GPS TEC obtained from 35 Crust Movement Observation Network of China (CMONC) stations are used as references. Compared to BDS TEC during the short period (doy 010-020, 2015), GPSKlob, BDSKlob and NeQuickG can correct 58.4, 66.7 and 54.7% of the ionospheric delay. Compared to GPS TEC for the long period (doy 001-180, 2015), the three ionospheric models can mitigate the ionospheric delay by 64.8, 65.4 and 68.1%, respectively. For the two comparison cases, CODKlob shows the worst performance, which only reduces 57.9% of the ionospheric range errors. NeQuickC exhibits the best performance, which outperforms GPSKlob, BDSKlob and NeQuickG by 6.7, 2.1 and 6.9%, respectively. In the position domain, single-frequency stand point positioning (SPP) was conducted at the selected 35 CMONC sites using GPS C/A pseudorange with and without ionospheric corrections. The vertical position error of the uncorrected case drops significantly from 10.3 m to 4.8, 4.6, 4.4 and 4.2 m for GPSKlob, CODKlob, BDSKlob and NeQuickG, however, the horizontal position error (3.2) merely decreases to 3.1, 2.7, 2.4 and 2.3 m, respectively. NeQuickG outperforms GPSKlob and BDSKlob by 5.8 and 1.9% in vertical component, and by 25.0 and 3.2% in horizontal component.

Integrating stations from the North America Gravity Database into a local GPS-based land gravity survey

USGS Publications Warehouse

Shoberg, Thomas G.; Stoddard, Paul R.

2013-01-01

The ability to augment local gravity surveys with additional gravity stations from easily accessible national databases can greatly increase the areal coverage and spatial resolution of a survey. It is, however, necessary to integrate such data seamlessly with the local survey. One challenge to overcome in integrating data from national databases is that these data are typically of unknown quality. This study presents a procedure for the evaluation and seamless integration of gravity data of unknown quality from a national database with data from a local Global Positioning System (GPS)-based survey. The starting components include the latitude, longitude, elevation and observed gravity at each station location. Interpolated surfaces of the complete Bouguer anomaly are used as a means of quality control and comparison. The result is an integrated dataset of varying quality with many stations having GPS accuracy and other reliable stations of unknown origin, yielding a wider coverage and greater spatial resolution than either survey alone.

Research in Application of Geodetic GPS Receivers in Time Synchronization

NASA Astrophysics Data System (ADS)

Zhang, Q.; Zhang, P.; Sun, Z.; Wang, F.; Wang, X.

2018-04-01

In recent years, with the development of satellite orbit and clock parameters accurately determining technology and the popularity of geodetic GPS receivers, Common-View (CV) which proposed in 1980 by Allan has gained widespread application and achieved higher accuracy time synchronization results. GPS Common View (GPS CV) is the technology that based on multi-channel geodetic GPS receivers located in different place and under the same common-view schedule to receiving same GPS satellite signal at the same time, and then calculating the time difference between respective local receiver time and GPST by weighted theory, we will obtain the difference between above local time of receivers that installed in different station with external atomic clock. Multi-channel geodetic GPS receivers have significant advantages such as higher stability, higher accuracy and more common-view satellites in long baseline time synchronization application over the single-channel geodetic GPS receivers. At present, receiver hardware delay and surrounding environment influence are main error factors that affect the accuracy of GPS common-view result. But most error factors will be suppressed by observation data smoothing and using of observation data from different satellites in multi-channel geodetic GPS receiver. After the SA (Selective Availability) cancellation, using a combination of precise satellite ephemeris, ionospheric-free dual-frequency P-code observations and accurately measuring of receiver hardware delay, we can achieve time synchronization result on the order of nanoseconds (ns). In this paper, 6 days observation data of two IGS core stations with external atomic clock (PTB, USNO distance of two stations about 6000 km) were used to verify the GPS common-view theory. Through GPS observation data analysis, there are at least 2-4 common-view satellites and 5 satellites in a few tracking periods between two stations when the elevation angle is 15°, even there will be at least 2 common-view satellites for each tracking period when the elevation angle is 30°. Data processing used precise GPS satellite ephemeris, double-frequency P-code combination observations without ionosphere effects and the correction of the Black troposphere Delay Model. the weighted average of all common-viewed GPS satellites in the same tracking period is taken by weighting the root-mean-square error of each satellite, finally a time comparison data between two stations is obtained, and then the time synchronization result between the two stations (PTB and USNO) is obtained. It can be seen from the analysis of time synchronization result that the root mean square error of REFSV (the difference between the local frequency standard at the mid-point of the actual tracking length and the tracked satellite time in unit of 0.1 ns) shows a linear change within one day, However the jump occurs when jumping over the day which is mainly caused by satellites position being changed due to the interpolation of two-day precise satellite ephemeris across the day. the overall trend of time synchronization result is declining and tends to be stable within a week-long time. We compared the time synchronization results (without considering the hardware delay correction) with those published by the International Bureau of Weights and Measures (BIPM), and the comparing result from a week earlier shows that the trend is same but there is a systematic bias which was mainly caused by hardware delays of geodetic GPS receiver. Regardless of the hardware delay, the comparing result is about between 102 ns and 106 ns. the vast majority of the difference within 2 ns but the difference of individual moment does not exceed 4ns when taking into account the systemic bias which mainly caused by hardware delay. Therefore, it is feasible to use the geodetic GPS receiver to achieve the time synchronization result in nanosecond order between two stations which separated by thousands kilometers, and multi-channel geodetic GPS receivers have obvious advantages over single-channel geodetic GPS receivers in the number of common-viewing satellites. In order to obtain higher precision (e.g sub-nanosecond order) time synchronization results, we shall take account into carrier phase observations, hardware delay ,and more error-influencing factors should be considered such as troposphere delay correction, multipath effects, and hardware delays changes due to temperature changes.

Physical applications of GPS geodesy: a review.

PubMed

Bock, Yehuda; Melgar, Diego

2016-10-01

Geodesy, the oldest science, has become an important discipline in the geosciences, in large part by enhancing Global Positioning System (GPS) capabilities over the last 35 years well beyond the satellite constellation's original design. The ability of GPS geodesy to estimate 3D positions with millimeter-level precision with respect to a global terrestrial reference frame has contributed to significant advances in geophysics, seismology, atmospheric science, hydrology, and natural hazard science. Monitoring the changes in the positions or trajectories of GPS instruments on the Earth's land and water surfaces, in the atmosphere, or in space, is important for both theory and applications, from an improved understanding of tectonic and magmatic processes to developing systems for mitigating the impact of natural hazards on society and the environment. Besides accurate positioning, all disturbances in the propagation of the transmitted GPS radio signals from satellite to receiver are mined for information, from troposphere and ionosphere delays for weather, climate, and natural hazard applications, to disturbances in the signals due to multipath reflections from the solid ground, water, and ice for environmental applications. We review the relevant concepts of geodetic theory, data analysis, and physical modeling for a myriad of processes at multiple spatial and temporal scales, and discuss the extensive global infrastructure that has been built to support GPS geodesy consisting of thousands of continuously operating stations. We also discuss the integration of heterogeneous and complementary data sets from geodesy, seismology, and geology, focusing on crustal deformation applications and early warning systems for natural hazards.

Time Transfer by Laser Link - T2L2: Results of the First Year of Operation

DTIC Science & Technology

2009-11-01

transportable laser ranging system (FTLRS) based at Paris (Syrte). The availability on these sites of both a GPS and a TWSTFT station will allow a direct...on these two sites, of both a GPS and a TWSTFT station will also allow a direct comparison of T2L2 with RF time transfer techniques. T2L2...calibration of various existing radiofrequency time and frequency transfer systems like GPS or TWSTFT , and comparisons of cold-atom clocks at a level

Determinations of ionosphere and plasmasphere electron content for an African chain of GPS stations

NASA Astrophysics Data System (ADS)

Mazzella, Andrew J., Jr.; Bosco Habarulema, John; Yizengaw, Endawoke

2017-05-01

The confluence of recent instrumentation deployments in Africa with developments for the determination of plasmasphere electron content using Global Positioning System (GPS) receivers has provided new opportunities for investigations in that region. This investigation, using a selected chain of GPS stations, extends the method (SCORPION) previously applied to a chain of GPS stations in North America in order to separate the ionosphere and plasmasphere contributions to the total electron content (TEC) during a day (24 July) in 2011. The results span latitudes from the southern tip of Africa, across the Equator, to the southern Arabian Peninsula, providing a continuous latitudinal profile for both the ionosphere and plasmasphere during this day.The peak diurnal vertical ionosphere electron content (IEC) increases from about 14 TEC units (1 TEC unit = 1016 electrons m-2) at the southernmost station to about 32 TEC units near the geographic equator, then decreases to about 28 TEC units at the Arabian Peninsula. The peak diurnal slant plasmasphere electron content (PEC) varies between about 4 and 7 TEC units among the stations, with a local latitudinal profile that is significantly influenced by the viewing geometry at the station location, relative to the magnetic field configuration. In contrast, the peak vertical PEC varies between about 1 and 6 TEC units among the stations, with a more uniform latitudinal variation.Comparisons to other GPS data analyses are also presented for TEC, indicating the influence of the PEC on the determination of latitudinal TEC variations and also on the absolute TEC levels, by inducing an overestimate of the receiver bias. The derived TEC latitudinal profiles, in comparison to global map profiles, tend to differ from the map results only about as much as the map results differ among themselves. A combination of ionosonde IEC and alternative GPS TEC measurements, which in principle permits a PEC determination through their difference, was compared to the composite and separate ionosphere and plasmasphere contributions derived solely by the SCORPION method for one station. Although there is considerably more scatter in the PEC values derived from the difference of the GPS TEC and ionosonde IEC measurements compared to the PEC values derived by the SCORPION method, the average overhead values for this day are comparable for the two methods, near 2 TEC units, at the South African site examined.This initial investigation provides a basis for day-to-day TEC monitoring for Africa, with separate ionosphere and plasmasphere electron content determinations.

The 2001 January 13th M {W}7.7 and February 13th M {W}6.6 El Salvador Earthquakes: Deformation and Stress Triggering

NASA Astrophysics Data System (ADS)

Hreinsdóttir, S.; Freymueller, J. T.

2001-12-01

On the 13th of January 2001, an M {W} 7.7 normal fault earthquake occurred offshore El Salvador. The earthquake occurred in the subducting Cocos plate and was followed by high seismic activity and several earthquakes exceeding magnitude 5. On the 13th of February, an M {W} 6.6 strike slip earthquake occurred in the overriding Caribbean plate, about 75 km NNW from the epicenter of the large January earthquake. Deformation due to these earthquakes was observed at six continuous CORS GPS stations in Central America. In the M {W} 7.7 earthquake about 10 mm displacement was measured at GPS stations in El Salvador and Honduras. A smaller but significant dispacement was also observed at GPS stations in Nicaragua, more then 200 km from the earthquake's epicenter. In the M {W} 6.6 earthquake 41+/- 1 mm displacement in direction N111oE was measured at the GPS station in San Salvador, El Salvador. Other CORS GPS stations were not affected by that earthquake. A postsesmic signal is detectable at the San Salvador GPS station, strongest right after the earthquake and then decays. On average we see 0.3 +/- 0.1 mm/day of SSW motion of the station in the first twenty days following the earthquake. Using seismic and geodetic data, we calculated Coulomb stress changes following the January 13th, M {W} 7.7 earthquake. Of special interest were six 5.4 <= {M} {W}<=5.8 thrust events that presumably occurred on the interface between the Caribean and Cocos plate, and the M {W} 6.6 strike slip earthquake that occurred in the overriding Caribean plate. The location and focal mechanism of these earthquakes correlate with areas of calculated increase in static stress thus indicating stress triggering. The thrust events occurred 2 to 20 days after the M {W} 7.7 earthquake, in increasing distance from the M {W} 7.7 event with time.

Earth's Surface Displacements from the GPS Time Series

NASA Astrophysics Data System (ADS)

Haritonova, D.; Balodis, J.; Janpaule, I.; Morozova, K.

2015-11-01

The GPS observations of both Latvian permanent GNSS networks - EUPOS®-Riga and LatPos, have been collected for a period of 8 years - from 2007 to 2014. Local surface displacements have been derived from the obtained coordinate time series eliminating different impact sources. The Bernese software is used for data processing. The EUREF Permanent Network (EPN) stations in the surroundings of Latvia are selected as fiducial stations. The results have shown a positive tendency of vertical displacements in the western part of Latvia - station heights are increasing, and negative velocities are observed in the central and eastern parts. Station vertical velocities are ranging in diapason of 4 mm/year. In the case of horizontal displacements, site velocities are up to 1 mm/year and mostly oriented to the south. The comparison of the obtained results with data from the deformation model NKG_RF03vel has been made. Additionally, the purpose of this study is to analyse GPS time series obtained using two different data processing strategies: Precise Point Positioning (PPP) and estimation of station coordinates relatively to the positions of fiducial stations also known as Differential GNSS.

GPS Water Vapor Tomography Based on Accurate Estimations of the GPS Tropospheric Parameters

NASA Astrophysics Data System (ADS)

Champollion, C.; Masson, F.; Bock, O.; Bouin, M.; Walpersdorf, A.; Doerflinger, E.; van Baelen, J.; Brenot, H.

2003-12-01

The Global Positioning System (GPS) is now a common technique for the retrieval of zenithal integrated water vapor (IWV). Further applications in meteorology need also slant integrated water vapor (SIWV) which allow to precisely define the high variability of tropospheric water vapor at different temporal and spatial scales. Only precise estimations of IWV and horizontal gradients allow the estimation of accurate SIWV. We present studies developed to improve the estimation of tropospheric water vapor from GPS data. Results are obtained from several field experiments (MAP, ESCOMPTE, OHM-CV, IHOP, .). First IWV are estimated using different GPS processing strategies and results are compared to radiosondes. The role of the reference frame and the a priori constraints on the coordinates of the fiducial and local stations is generally underestimated. It seems to be of first order in the estimation of the IWV. Second we validate the estimated horizontal gradients comparing zenith delay gradients and single site gradients. IWV, gradients and post-fit residuals are used to construct slant integrated water delays. Validation of the SIWV is under progress comparing GPS SIWV, Lidar measurements and high resolution meteorological models (Meso-NH). A careful analysis of the post-fit residuals is needed to separate tropospheric signal from multipaths. The slant tropospheric delays are used to study the 3D heterogeneity of the troposphere. We develop a tomographic software to model the three-dimensional distribution of the tropospheric water vapor from GPS data. The software is applied to the ESCOMPTE field experiment, a dense network of 17 dual frequency GPS receivers operated in southern France. Three inversions have been successfully compared to three successive radiosonde launches. Good resolution is obtained up to heights of 3000 m.

Tectonic movements along the Anegada Passage derived from GPS Observations (2008-2017)

NASA Astrophysics Data System (ADS)

Liu, H.; Wang, G.

2017-12-01

The Anegada Passage system, mainly includes the Virgin Islands Basin (VIB), Anegada Gap, and the Sombrero Basin, are located within the tectonically complex plate boundary zone between the North America and Caribbean plates. It separated the Puerto Rico and Northern Virgin Islands (PRNVI) block from St. Croix and Anguilla. Long-term seismic observations indicated that this region still faces high risk from earthquakes. This study used current GPS geodesy infrastructure in the Northeastern Caribbean region, which includes high densely GPS stations on PRNVI block and northern Lesser Antilles and a stable PRNVI reference frame (SPRNVIRF). Current GPS geodesy infrastructure in the PRVI region makes it possible to precisely delineate minor tectonic motions (1 to 2 mm/year) within the northeastern Caribbean region. The carrier phase Double-Difference (DD) and Precise Point Positioning (PPP) post-processing methods are both used to processing GPS data. Over ten years of GPS observations indicate that the St. Croix Island is moving away from the PRVI block toward southeast with a velocity of 1.8 ± 0.2 mm/year; there is not considerable relative motions between the Saint Martin Island and the PRVI block. The Saint Martin Island is located at the south side of the Anegada Gap. The GPS and seismic observations along the two sides of the Anegada passage suggest that the west segment (VIB) of the passage retains active, while the east segment is presently inactive. The Virgin Islands basin presently experiences left-lateral motion in a nearly east-west direction with a velocity of about 1.2 mm/year and an extension in a nearly north-south direction with a velocity of about 1.3 mm/year. The quantitative measurements derived from GPS observations would improve seismic hazard assessment in the Anegada Passage region.

Kinematic GPS solutions for aircraft trajectories: Identifying and minimizing systematic height errors associated with atmospheric propagation delays

USGS Publications Warehouse

Shan, S.; Bevis, M.; Kendrick, E.; Mader, G.L.; Raleigh, D.; Hudnut, K.; Sartori, M.; Phillips, D.

2007-01-01

When kinematic GPS processing software is used to estimate the trajectory of an aircraft, unless the delays imposed on the GPS signals by the atmosphere are either estimated or calibrated via external observations, then vertical height errors of decimeters can occur. This problem is clearly manifested when the aircraft is positioned against multiple base stations in areas of pronounced topography because the aircraft height solutions obtained using different base stations will tend to be mutually offset, or biased, in proportion to the elevation differences between the base stations. When performing kinematic surveys in areas with significant topography it should be standard procedure to use multiple base stations, and to separate them vertically to the maximum extent possible, since it will then be much easier to detect mis-modeling of the atmosphere. Copyright 2007 by the American Geophysical Union.

A New Technique to Observe ENSO Activity via Ground-Based GPS Receivers

NASA Astrophysics Data System (ADS)

Suparta, Wayan; Iskandar, Ahmad; Singh, Mandeep Singh Jit

In an attempt to study the effects of global climate change in the tropics for improving global climate model, this paper aims to detect the ENSO events, especially El Nino phase by using ground-based GPS receivers. Precipitable water vapor (PWV) obtained from the Global Positioning System (GPS) Meteorology measurements in line with the sea surface temperature anomaly (SSTa) are used to connect their response to El Niño activity. The data gathered from four selected stations over the Southeast Asia, namely PIMO (Philippines), KUAL (Malaysia), NTUS (Singapore) and BAKO (Indonesia) for the year of 2009/2010 were processed. A strong correlation was observed for PIMO station with a correlation coefficient of -0.90, significantly at the 99 % confidence level. In general, the relationship between GPS PWV and SSTa at all stations on a weekly basis showed with a negative correlation. The negative correlation indicates that during the El Niño event, the PWV variation was in decreased trend. Decreased trend of PWV value is caused by a dry season that affected the GPS signals in the ocean-atmospheric coupling. Based on these promising results, we can propose that the ground-based GPS receiver is capable used to monitor ENSO activity and this is a new prospective method that previously unexplored.

Geodetic point positioning with GPS (Global Positioning System) carrier beat phase data from the CASA (Central and South America) Uno experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malys, S.; Jensen, P.A.

1990-04-01

The Global Positioning System (GPS) carrier beat phase data collected by the TI4100 GPS receiver has been successfully utilized by the US Defense Mapping Agency in an algorithm which is designed to estimate individual absolute geodetic point positions from data collected over a few hours. The algorithm uses differenced data from one station and two to four GPS satellites at a series of epochs separated by 30 second intervals. The precise GPS ephemerides and satellite clock states, held fixed in the estimation process, are those estimated by the Naval Surface Warfare Center (NSWC). Broadcast ephemerides and clock states are alsomore » utilized for comparative purposes. An outline of the data corrections applied, the mathematical model and the estimation algorithm are presented. Point positioning results and statistics are presented for a globally-distributed set of stations which contributed to the CASA Uno experiment. Statistical assessment of 114 GPS point positions at 11 CASA Uno stations indicates that the overall standard deviation of a point position component, estimated from a few hours of data, is 73 centimeters. Solution of the long line geodetic inverse problem using repeated point positions such as these can potentially offer a new tool for those studying geodynamics on a global scale.« less

Global Positioning Svstem (GPS) on International Space Station (ISS) and Crew Return Vehicle (CRV)

NASA Technical Reports Server (NTRS)

Gomez, Susan F.

2002-01-01

Both the International Space Station and Crew Return Vehicle desired to have GPS on their vehicles due to improve state determination over traditional ground tracking techniques used in the past for space vehicles. Both also opted to use GPS for attitude determination to save the expense of a star tracker. Both vehicles have stringent pointing requirements for roll, pitch, and heading, making a sun or earth sensor not a viable option since the heading is undetermined. This paper discusses the technical challenges associated with the implementation of GPS on both of these vehicles. ISS and CRY use the same GPS receiver, but have faced different challenges since the mission of each is di fferent. ISS will be discussed first, then CRY. The flight experiments flown on the Space Shuttle in support of these efforts is also discussed.

Joint Inversion of GPS and Teleseismic Data for the Source Model of the 2016 Meinong, Taiwan Earthquake

NASA Astrophysics Data System (ADS)

Lai, Y. P.; Ching, K. E.; Chuang, R.; Wen, Y. Y.; Chen, C. L.

2016-12-01

The ML 6.6 Meinong earthquake occurred in SW Taiwan, which is located at 22.92°N, 120.54°E, and depth of 14.6 km, at 03:57:26.1 (UTC+8) on February 6th 2016 in SW Taiwan. To understand the kinematics and geodynamics of this earthquake event, we select 43 continuous GPS (CGPS) stations, installed by the CGS, CWB, IES and NCKU, 94 campaign-mode GPS (RGPS) stations and 4 precise leveling routes, surveyed by the CGS from 2002 to 2016. The GPS coordinate daily solution is calculated using the software Bernese v.5.0 under the ITRF2008 as the velocity and coseismic displacement fields are relative to the station KMNM at the Chinese continental margin. To verify the reliability of the velocity inferred from the RGPS stations, we first consider the misfit value which is highly correlated to the quality of the time series. The misfit values from 67 stations are smaller than 20 mm and the misfit values from the other 27 stations are larger than 20 mm. We then interpolated the velocities from 43 CGPS stations into 67 RGPS stations, and compared the residuals between the observed velocities and the interpolated velocities with three standard deviation of the observation. All of the 67 RGPS stations meet the standard so we interpolated the velocity from 43 CGPS stations and 67 RGPS stations into the rest 27 RGPS stations, and then checked the value of residuals between the observed velocity and the interpolated velocity divided by the observed velocity. Finally, 19 RGPS stations are rejected, and the remaining stations are believe to increase the constraint of modeling. By using CGPS data, we correct the coseismic displacement fields of the RGPS stations and the precise leveling route by removing the postseismic effect. The horizontal coseismic displacement fields show a spreading trend start from the epicenter to the SW, west and NW while the horizontal velocity fields show only westward in the interseismic period. The vertical coseismic displacement fields are mainly uplift at the west of the epicenter while subsidence at the east of the epicenter. The maximum vertical coseismic displacement area is slightly north of the area that has the highest uplift velocity from precise leveling during the interseismic period. Joint inversion of the GPS and teleseismic data will soon be processed for the spatial and temporal distribution of earthquake slip.

Retrieval and Validation of Zenith and Slant Path Delays From the Irish GPS Network

NASA Astrophysics Data System (ADS)

Hanafin, Jennifer; Jennings, S. Gerard; O'Dowd, Colin; McGrath, Ray; Whelan, Eoin

2010-05-01

Retrieval of atmospheric integrated water vapour (IWV) from ground-based GPS receivers and provision of this data product for meteorological applications has been the focus of a number of Europe-wide networks and projects, most recently the EUMETNET GPS water vapour programme. The results presented here are from a project to provide such information about the state of the atmosphere around Ireland for climate monitoring and improved numerical weather prediction. Two geodetic reference GPS receivers have been deployed at Valentia Observatory in Co. Kerry and Mace Head Atmospheric Research Station in Co. Galway, Ireland. These two receivers supplement the existing Ordnance Survey Ireland active network of 17 permanent ground-based receivers. A system to retrieve column-integrated atmospheric water vapour from the data provided by this network has been developed, based on the GPS Analysis at MIT (GAMIT) software package. The data quality of the zenith retrievals has been assessed using co-located radiosondes at the Valentia site and observations from a microwave profiling radiometer at the Mace Head site. Validation of the slant path retrievals requires a numerical weather prediction model and HIRLAM (High-Resolution Limited Area Model) version 7.2, the current operational forecast model in use at Met Éireann for the region, has been used for this validation work. Results from the data processing and comparisons with the independent observations and model will be presented.

Development of the TLALOCNet GPS-Met Network in Northwestern Mexico: Supporting Continuous Water Vapor Observations of the North American Monsoon

NASA Astrophysics Data System (ADS)

Galetzka, J.; Feaux, K.; Cabral, E.; Salazar-Tlaczani, L.; Adams, D. K.; Serra, Y. L.; Mattioli, G. S.; Miller, M. M.

2014-12-01

TLALOCNet is a combined atmospheric and tectonic cGPS-Met network in Mexico designed for the investigation of climate, atmospheric processes, the earthquake cycle, and tectonics. While EarthScope-Plate Boundary Observatory (conterminous US, Alaska, Puerto Rico) is among the networks poised to become a nucleus for hemisphere-scale GPS observations, the completion of TLALOCNet at the end of 2015 will close a gap between PBO and other Latin American GPS networks that include COCONet (Central America, Caribbean, and Northern South America), CAnTO, CAP, and IGS extending from Alaska to Patagonia. The National Science Foundation funded the construction and operation of TLALOCNet, with significant matching funds and resources provided by the Universidad Nacional Autónoma de México (UNAM). The project will involve the construction or refurbishment of 38 cGPS-Met stations in Mexico built to PBO standards. The first three TLALOCNet stations were installed in the northern Mexican states of Sonora and Chihuahua in July 2014, following the North American Monsoon GPS Transect Experiment 2013. Together these observations better characterize critical components of water transport in the region. Data from these stations are now available through the UNAVCO data archive and can be downloaded from http://facility.unavco.org/data/dai2/app/dai2.html#. By the end of 2014, TLALOCNet data, together with complementary data from other regional cGPS networks in Mexico, will also be openly available through a Mexico-based data center. We will present the status of the project to date, including an overview of the station hardware, data communications, data flow, construction schedule, and science objectives. We will also present some of the challenges encountered, including regional logistics, shipping and importation, site security, and other issues associated with the construction and operation of a large continuous GPS network.

Investigation of Noises in GPS Time Series: Case Study on Epn Weekly Solutions

NASA Astrophysics Data System (ADS)

Klos, Anna; Bogusz, Janusz; Figurski, Mariusz; Kosek, Wieslaw; Gruszczynski, Maciej

2014-05-01

The noises in GPS time series are stated to be described the best by the combination of white (Gaussian) and power-law processes. They are mainly the effect of mismodelled satellite orbits, Earth orientation parameters, atmospheric effects, antennae phase centre effects, or of monument instability. Due to the fact, that velocities of permanent stations define the kinematic reference frame, they have to fulfil the requirement of being stable at 0.1 mm/yr. The previously performed researches showed, that the wrong assumption of noise model leads to the underestimation of velocities and their uncertainties from 2 up to even 11, especially in the Up direction. This presentation focuses on more than 200 EPN (EUREF Permanent Network) stations from the area of Europe with various monument types (concrete pillars, buildings, metal masts, with or without domes, placed on the ground or on the rock) and coordinates of weekly changes (GPS weeks 0834-1459). The topocentric components (North, East, Up) in ITRF2005 which come from the EPN Re-Processing made by the Military University of Technology Local Analysis Centre (MUT LAC) were processed with Maximum Likelihood Estimation (MLE) using CATS software. We have assumed the existence of few combinations of noise models (these are: white, flicker and random walk noise with integer spectral indices and power-law noise models with fractional spectral indices) and investigated which of them EPN weekly time series are likely to follow. The results show, that noises in GPS time series are described the best by the combination of white and flicker noise model. It is strictly related to the so-called common mode error (CME) that is spatially correlated error being one of the dominant error source in GPS solutions. We have assumed CME as spatially uniform, what was a good approximation for stations located hundreds of kilometres one to another. Its removal with spatial filtering reduces the amplitudes of white and flicker noise by a factor of 2 or 3. The assumption of white plus flicker plus random-walk noise (which is considered to be the effect of badly monumented stations) resulted in the random-walk amplitudes at the level of single millimetres for some of the stations, while for the majority of them no random-walk was detected, due to the fact that flicker noise prevails in GPS time series. The removal of CME caused the decrease in flicker noise amplitudes leading at the same time to greater random-walk amplitudes. The assumed combination of white plus power-law noise showed that the spectral indices for the best fitted noise model are unevenly distributed around -1 what also indicates the flicker noise existence in EPN weekly time series. The poster will present all of the assumed noise model combinations with the comparison of noise amplitudes before and after spatial filtering. Additionally, we will discuss over the latitude and longitude noise dependencies for the area of Europe to indicate any similarities between noise amplitudes and the location of stations. Finally, we will focus on the velocities with their uncertainties that were determined from EPN weekly solutions and show how the wrong assumption of noise model changes both of them.

The contribution of engineering surveys by means of GPS to the determination of crustal movements in Istanbul

NASA Astrophysics Data System (ADS)

Özyaşar, M.; Özlüdemir, M. T.

2011-06-01

Global Navigation Satellite Systems (GNSS) are space based positioning techniques and widely used in geodetic applications. Geodetic networking accomplished by engineering surveys constitutes one of these tasks. Geodetic networks are used as the base of all kinds of geodetic implementations, Co from the cadastral plans to the relevant surveying processes during the realization of engineering applications. Geodetic networks consist of control points positioned in a defined reference frame. In fact, such positional information could be useful for other studies as well. One of such fields is geodynamic studies that use the changes of positions of control stations within a network in a certain time period to understand the characteristics of tectonic movements. In Turkey, which is located in tectonically active zones and struck by major earthquakes quite frequently, the positional information obtained in engineering surveys could be very useful for earthquake related studies. For this purpose, a GPS (Global Positioning System) network of 650 stations distributed over Istanbul (Istanbul GPS Triangulation Network; abbreviated IGNA) covering the northern part of the North Anatolian Fault Zone (NAFZ) was established in 1997 and measured in 1999. From 1998 to 2004, the IGNA network was extended to 1888 stations covering an area of about 6000 km2, the whole administration area of Istanbul. All 1888 stations within the IGNA network were remeasured in 2005. In these two campaigns there existed 452 common points, and between these two campaigns two major earthquakes took place, on 17 August and 12 November 1999 with a Richter scale magnitude of 7.4 and 7.2, respectively. Several studies conducted for estimating the horizontal and vertical displacements as a result of these earthquakes on NAFZ are discussed in this paper. In geodynamic projects carried out before the earthquakes in 1999, an annual average velocity of 2-2.5 cm for the stations along the NAFZ were estimated. Studies carried out using GPS observations in the same area after these earthquakes indicated that point displacements vary depending on their distance to the epicentres of the earthquakes. But the directions of point displacements are similar. The results obtained through the analysis of the IGNA network also show that there is a common trend in the directions of point displacements in the study area. In this paper, the past studies about the tectonics of Marmara region are summarised and the results of the displacement analysis on the IGNA network are discussed.

Fixing a Reference Frame to a Moving and Deforming Continent

NASA Astrophysics Data System (ADS)

Blewitt, G.; Kreemer, C.; Hammond, W. C.

2016-12-01

The U.S. National Spatial Reference System will be modernized in 2022. A foundational component will be a geocentric reference frame fixed to the North America tectonic plate. Here we address challenges of fixing a reference frame to a moving and deforming continent. Scientific applications motivate that we fix the frame with a scale consistent with the SI system, an origin that coincides with the Earth system's center of mass, and with axes attached to the rigidly rotating interior of the North America plate. Realizing the scale and origin is now achieved to < 0.5 mm/yr by combining space-geodetic techniques (SLR, VLBI, GPS, and DORIS) in the global system, ITRS. To realize the no-net rotation condition, the complexity of plate boundary deformation demands that we only select GPS stations far from plate boundaries. Another problem is that velocity uncertainties in models of glacial isostatic adjustment (GIA) are significant compared to uncertainties in observed velocities. GIA models generally agree that far-field horizontal velocities tend to be directed toward/away from Hudson Bay, depending on mantle viscosity, with uncertain sign and magnitude of velocity. Also in the far field, strain rates tend to be small beyond the peripheral bulge ( US-Canada border). Thus the Earth's crust in the US east of the Rockies may appear to be rigid, even if this region moves relative to plate motion. This can affect Euler vector estimation, with implications (pros and cons) on scientific interpretation. Our previous approach [ref. 1] in defining the NA12 frame was to select a core set of 30 stations east of the Rockies and south of the U.S.-Canada border that satisfy strict criteria on position time series quality. The resulting horizontal velocities have an RMS of 0.3 mm/yr, quantifying a combination of plate rigidity and accuracy. However, this does not rule out possible common-mode motion arising from GIA. For the development of new frame NA16, we consider approaches to this problem. We also apply new techniques including the MIDAS robust velocity estimator [ref. 2] and "GPS Imaging" of vertical motions and strain rates (Fig. 1), which together could assist in better defining "stable North America".[1] Blewitt et al. (2013). J. Geodyn. 72, 11-24, doi:10.1016/j.jog.2013.08.004[2] Blewitt et al. (2016). JGR 121, doi:10.1002/2015JB012552

GNSS strain rate patterns and their application to investigate geodynamical credibility of the GNSS velocities

NASA Astrophysics Data System (ADS)

Araszkiewicz, Andrzej; Figurski, Mariusz

2015-04-01

The potential that lies in the use of GNSS measurements for crustal deformation studies have already noticed in the beginning of the first of such a system (GPS). Today thanks to the development of satellite positioning techniques it is possible to detect displacement on the Earth surface with an accuracy less than 1 cm. With long-term observations we can determine the velocities even more accurately. Growing demand in the last years for GNSS applications, both for scientific and civil use, meant that new networks of the reference stations were created. Such a dense GNSS networks allow to conduct research in the field of crust deformation at a higher spatial resolution than before. In Europe most of the research focuses on Mediterranean regions, where we can monitor events resulting from the tectonic plates collision. But even in Central Europe we can see effect of Africa push. In our research we focused on Polish territory, where in the past 5 years a nearly 300 reference stations were established. With minimal movements that have been observed in Poland, a key issue in this type of research is to determine the geodynamic reliability of the estimated stations velocities. While the long-term observations enable us to determine the very accurate velocities, it hard to indicate how reliably they reflect actual tectonic movements is. In this paper we proposed a method for testing the reliability of stations velocities based on the strain rate field analysis. The method is based on the analysis of the distribution of the rate of deformation tensor components obtained for triangular elements built on the basis of assessed station. The paper presents the results of numerical simulations and initial use of the method for the Polish network of reference stations: ASG-EUPOS

2001 GPS and Classical Survey at Medicina Observatory: Local Tie and VLBI Antenna's Reference Point Determination

NASA Astrophysics Data System (ADS)

Vittuari, Luca; Sarti, Pierguido; Tomasi, Paolo

2001-12-01

During a 6 days campaign in June 2001, we have performed a local survey at Medicina Observatory using classical geodesy and GPS techniques in order to determine the effects of an undergone track repair. We have determined the position of the reference point P within a local and ITRF2000 (epoch 1997.0) reference frames using trilateration and triangulation: Pclas_{loc}^{2001}=(21.580pm0.001,45.536pm0.001,17.699pm0.001) Pclas_{loc}^{2001}=(21.580pm0.001,45.536pm0.001,17.699pm0.001) Pclas_{ITRF2000}^{1997.0}=(4461369.982pm0.001,919596.818pm0.001,4449559.207pm0.001) Kinematic GPS has also given interesting results:

Mass balance assessment using GPS

NASA Technical Reports Server (NTRS)

Hulbe, Christina L.

1993-01-01

Mass balance is an integral part of any comprehensive glaciological investigation. Unfortunately, it is hard to determine at remote locations where there is no fixed reference. The Global Positioning System (GPS) offers a solution. Simultaneous GPS observations at a known location and the remote field site, processed differentially, will accurately position the camp site. From there, a monument planted in the firn atop the ice can also be accurately positioned. Change in the monument's vertical position is a direct indicator of ice thickness change. Because the monument is not connected to the ice, its motion is due to both mass balance change and to the settling of firn as it densifies into ice. Observations of relative position change between the monument and anchors at various depths within the firn are used to remove the settling effect. An experiment to test this method has begun at Byrd Station on the West Antarctic Ice Sheet and the first epoch of observations was made. Analysis indicates that positioning errors will be very small. It appears likely that the largest errors involved with this technique will arise from ancillary data needed to determine firn settling.

On-orbit frequency stability analysis of the GPS NAVSTAR-1 quartz clock and the NAVSTARs-6 and -8 rubidium clocks

NASA Technical Reports Server (NTRS)

Mccaskill, T. B.; Buisson, J. A.; Reid, W. G.

1984-01-01

An on-orbit frequency stability performance analysis of the GPS NAVSTAR-1 quartz clock and the NAVSTARs-6 and -8 rubidium clocks is presented. The clock offsets were obtained from measurements taken at the GPS monitor stations which use high performance cesium standards as a reference. Clock performance is characterized through the use of the Allan variance, which is evaluated for sample times of 15 minutes to two hours, and from one day to 10 days. The quartz and rubidium clocks' offsets were corrected for aging rate before computing the frequency stability. The effect of small errors in aging rate is presented for the NAVSTAR-8 rubidium clock's stability analysis. The analysis includes presentation of time and frequency residuals with respect to linear and quadratic models, which aid in obtaining aging rate values and identifying systematic and random effects. The frequency stability values were further processed with a time domain noise process analysis, which is used to classify random noise process and modulation type.

Recent GPS Results at SLAC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Behrend, Dirk; Imfeld, Hans L.; /SLAC

2005-08-17

The Alignment Engineering Group (AEG) makes use of GPS technology for fulfilling part of its above ground surveying tasks at SLAC since early 2002. A base station (SLAC M40) has been set up at a central location of the SLAC campus serving both as master station for real-time kinematic (RTK) operations and as datum point for local GPS campaigns. The Leica RS500 system is running continuously and the GPS data are collected both externally (logging PC) and internally (receiver flashcard). The external logging is facilitated by a serial to Ethernet converter and an Ethernet connection at the station. Internal loggingmore » (ring buffer) is done for data security purposes. The weatherproof boxes for the instrumentation are excellent shelters against rain and wind, but do heat up considerably in sun light. Whereas the GPS receiver showed no problems, the Pacific Crest PDL 35 radio shut down several times due to overheating disrupting the RTK operations. In order to prevent heat-induced shutdowns, a protection against direct sun exposure (shading) and a constant air circulation system (ventilation) were installed. As no further shutdowns have occurred so far, it appears that the two measures successfully mended the heat problem.« less

Clustering of velocities in a GPS network spanning the Sierra Nevada Block, the Northern Walker Lane Belt, and the Central Nevada Seismic Belt, California-Nevada

NASA Astrophysics Data System (ADS)

Savage, J. C.; Simpson, R. W.

2013-09-01

The deformation across the Sierra Nevada Block, the Walker Lane Belt, and the Central Nevada Seismic Belt (CNSB) between 38.5°N and 40.5°N has been analyzed by clustering GPS velocities to identify coherent blocks. Cluster analysis determines the number of clusters required and assigns the GPS stations to the proper clusters. The clusters are shown on a fault map by symbols located at the positions of the GPS stations, each symbol representing the cluster to which the velocity of that GPS station belongs. Fault systems that separate the clusters are readily identified on such a map. Four significant clusters are identified. Those clusters are strips separated by (from west to east) the Mohawk Valley-Genoa fault system, the Pyramid Lake-Wassuk fault system, and the Central Nevada Seismic Belt. The strain rates within the westernmost three clusters approximate simple right-lateral shear (~13 nstrain/a) across vertical planes roughly parallel to the cluster boundaries. Clustering does not recognize the longitudinal segmentation of the Walker Lane Belt into domains dominated by either northwesterly trending, right-lateral faults or northeasterly trending, left-lateral faults.

Clustering of velocities in a GPS network spanning the Sierra Nevada Block, the northern Walker Lane Belt, and the Central Nevada Seismic Belt, California-Nevada

USGS Publications Warehouse

Savage, James C.; Simpson, Robert W.

2013-01-01

The deformation across the Sierra Nevada Block, the Walker Lane Belt, and the Central Nevada Seismic Belt (CNSB) between 38.5°N and 40.5°N has been analyzed by clustering GPS velocities to identify coherent blocks. Cluster analysis determines the number of clusters required and assigns the GPS stations to the proper clusters. The clusters are shown on a fault map by symbols located at the positions of the GPS stations, each symbol representing the cluster to which the velocity of that GPS station belongs. Fault systems that separate the clusters are readily identified on such a map. Four significant clusters are identified. Those clusters are strips separated by (from west to east) the Mohawk Valley-Genoa fault system, the Pyramid Lake-Wassuk fault system, and the Central Nevada Seismic Belt. The strain rates within the westernmost three clusters approximate simple right-lateral shear (~13 nstrain/a) across vertical planes roughly parallel to the cluster boundaries. Clustering does not recognize the longitudinal segmentation of the Walker Lane Belt into domains dominated by either northwesterly trending, right-lateral faults or northeasterly trending, left-lateral faults.

Impact of continuing medical education in cancer diagnosis on GP knowledge, attitude and readiness to investigate - a before-after study.

PubMed

Toftegaard, Berit Skjødeberg; Bro, Flemming; Falborg, Alina Zalounina; Vedsted, Peter

2016-07-26

Continuing medical education (CME) in earlier cancer diagnosis was launched in Denmark in 2012 as part of the Danish National Cancer Plan. The CME programme was introduced to improve the recognition among general practitioners (GPs) of symptoms suggestive of cancer and improve the selection of patients requiring urgent investigation. This study aims to explore the effect of CME on GP knowledge about cancer diagnosis, attitude towards own role in cancer detection, self-assessed readiness to investigate and cancer risk assessment of urgently referred patients. We conducted a before-after study in the Central Denmark Region including 831 GPs assigned to one of eight geographical clusters. All GPs were invited to participate in the CME at three-week intervals between clusters. A questionnaire focusing on knowledge, attitude and clinical vignettes was sent to each GP one month before and seven months after the CME. The GPs were also asked to assess the risk of cancer in patients urgently referred to a fast-track cancer pathway during an eight-month period. CME-participating GPs were compared with reference (non-participating) GPs by analysing before-after differences. One quarter of all GPs participated in the CME. 202 GPs (24.3 %) completed both the baseline and the follow-up questionnaires. 532 GPs (64.0 %) assessed the risk of cancer before the CME and 524 GPs (63.1 %) assessed the risk of cancer after the CME in urgently referred consecutive patients. Compared to the reference group, CME-participating GPs statistically significantly improved their understanding of a rational probability of diagnosing cancer among patients urgently referred for suspected cancer, increased their knowledge of cancer likelihood in a 50-year-old referred patient and lowered the assessed risk of cancer in urgently referred patients. The standardised CME lowered the GP-assessed cancer risk of urgently referred patients, whereas the effect on knowledge about cancer diagnosis and attitude towards own role in cancer detection was limited. No effect was found on the GPs' readiness to investigate. CME may be effective for optimising the interpretation of cancer symptoms and thereby improve the selection of patients for urgent cancer referral. NCT02069470 on ClinicalTrials.gov. Retrospectively registered, 1/29/2014.

GPS determined eastward Sundaland motion with respect to Eurasia confirmed by earthquakes slip vectors at Sunda and Philippine trenches

NASA Astrophysics Data System (ADS)

Chamot-Rooke, N.; Le Pichon, X.

1999-12-01

GPS measurements acquired over Southeast Asia in 1994 and 1996 in the framework of the GEODYSSEA program revealed that a large piece of continental lithosphere comprising the Indochina Peninsula, Sunda shelf and part of Indonesia behaves as a rigid `Sundaland' platelet. A direct adjustment of velocity vectors obtained in a Eurasian frame of reference shows that Sundaland block is rotating clockwise with respect to Eurasia around a pole of rotation located south of Australia. We present here an additional check of Sundaland motion that uses earthquakes slip vectors at Sunda and Philippine trenches. Seven sites of the GEODYSSEA network are close to the trenches and not separated from them by large active faults (two at Sumatra Trench, three at Java Trench and two at the Philippine Trench). The difference between the vector at the station and the adjacent subducting plate vector defines the relative subduction motion and should thus be aligned with the subduction earthquake slip vectors. We first derive a frame-free solution that minimizes the upper plate (or Sundaland) motion. When corrected for Australia-Eurasia and Philippines-Eurasia NUVEL1-A motion, the misfit between GPS and slip vectors azimuths is significant at 95% confidence, indicating that the upper plate does not belong to Eurasia. We then examine the range of solutions compatible with the slip vectors azimuths and conclude that the minimum velocity of Sundaland is a uniform 7-10 mm/a eastward velocity. However, introducing the additional constraint of the fit of the GEODYSSEA sites with the Australian IGS reference ones, or tie with the NTUS Singapore station, leads to a much narrower range of solutions. We conclude that Sundaland has an eastward velocity of about 10 mm/a on its southern boundary increasing to 16-18 mm/a on its northern boundary.

Multi-GNSS Opportunities and Challenges

NASA Astrophysics Data System (ADS)

Al-Shaery, A.; Zhang, S.; Lim, S.; Rizos, C.

2012-04-01

The multi-GNSS era has began attracting more attention with the declaration of full operational capability of GLONASS , with a 24 satellites being set to 'healthy' on December 8th 2011 (IAC, 2011). This means that GPS is no longer the only GNSS that provides global positioning coverage. This status brings benefits for GNSS users in areas (e.g. 'urban canyon' environments or in deep open cut mines) where the number of visible satellites is limited because of shadowing effects. In such areas adding more functioning satellites, which is one of the aiding solutions, becomes easier, at no extra cost. The inclusion of GLONASS observations in positioning solutions will increase the available number of satellites and thus positioning accuracy may improve as a result of enhanced overall satellite geometry. Such an aiding solution is increasingly attractive due to the successful revitalisation of GLONASS. Another motivation is the availability of improved GLONASS orbits from the IGS and individual analysis centres of the IGS. The increasing availability of receivers with GPS/GLONASS tracking capability on the market is an additional motive. Consequently, most networks of continuously operating reference stations (CORS) are now equipped with receivers that can track both GPS and GLONASS satellite signals, and therefore network-based positioning with combined GPS and GLONASS observations is possible. However, adding GLONASS observations to GPS is not a straight forward process. This is attributable to a few system differences in reference frames for time and coordinates, and in signal structures. The first two differences are easy to deal with using well-defined conversion and transformation parameters (El-Mowafy, 2001). However, signal structure differences have some implications. The mathematical modelling of combined GPS/GLONASS observations is not performed as in the case of GPS-alone. Special care should be paid to such integration. Not only is the software part affected but also the hardware. Recent research has identified one of the challenges users may face if precise positioning is sought (Takac, 2009, Yamada et al., 2010, Wanninger, 2011). A user of heterogeneous receiver pairs will experience ambiguity fixing challenges due to inter-channel bias which cannot be cancelled by differencing GLONASS observations, pseudorange or carrier-phase. This paper outlines the opportunities and challenges of combining two currently fully operational GNSS systems (GPS and GLONASS) for precise positioning solutions. Discussion and analysis considering mathematical modelling challenges and users' selection of hardware constraints will be performed.

Cross-cultural differences in GPs' attitudes towards complementary and alternative medicine: a survey comparing regions of the UK and Germany.

PubMed

Schmidt, K; Jacobs, P A; Barton, A

2002-09-01

To investigate whether there is a difference in general practitioners' attitudes towards CAM in the UK and Germany. A descriptive questionnaire was developed and sent to 97 GPs in the UK and 99 GPs in Germany. The overall response rate was 68%. German GPs showed a (non-significant) overall more positive attitude towards CAM than did British GPs. British GPs made more referrals to complementary practitioners. The most popular CAM therapies that UK GPs referred their patients to were chiropractic treatment, acupuncture and osteopathy. German GPs referred their patients mainly to acupuncture treatment, chiropractic treatment and herbal medicine. A significantly higher number of German GPs reported having practised as a CAM practitioner before and having personally used CAM themselves. Seventy percent of British GPs and 76% of German GPs thought it is safe to prescribe complementary medicine and therapies to patients. There are small national differences in referring patients to various CAM modalities. Both nations have an overall positive attitude toward and a high interest in CAM. Lack of scientific evidence and information on training opportunities were important points that were continuously raised by GPs in both countries.

Rigidity and definition of Caribbean plate motion from COCONet and campaign GPS observations

NASA Astrophysics Data System (ADS)

Mattioli, G. S.; Miller, J. A.; DeMets, C.; Jansma, P. E.

2015-12-01

The kinematic model of the Caribbean plate presented by DeMets et al. (2007) is based on velocities from 6 continuous and 14 campaign GPS sites. COCONet is a multi-hazard GPS-Met observatory, which extends the existing infrastructure of the PBO in North America into the Caribbean basin. In 2010, UNAVCO in collaboration with UCAR, was funded by NSF to design, build, and initially maintain a network of 50 new cGPS/Met sites and include data from another 50 existing sites in the Caribbean region. The COCONet siting plan is for 46 new stations, 21 refurbished stations, and 77 existing stations across 26 nations in the Caribbean region. Data from all COCONet sites flow into the UNAVCO archive and are processed by the PBO analysis centers and are also processed independently by the UTA Geodesy Lab using GIPSY-OASISII (v.6.3) using an APP strategy and final, precise orbits, clocks, and EOP from JPL in the IGS08r frame. We present a refined estimate of Caribbean plate motion by evaluating data from an expanded number of stations with an improved spatial distribution. In order to better constrain the eastern margin of the plate near the Lesser Antilles subduction interface, campaign GPS observations have been collected on the island of Dominica over the last decade. These are combined with additional campaign observations from the western Caribbean, specifically from Honduras and Nicaragua. We have analyzed a total of 117 sites from the Caribbean region, including campaign data and the data from the cGPS stations that comprise COCONet. An updated velocity field for the Caribbean plate is presented and an inversion of the velocities for 24 sites yields a plate angular velocity that differs from previously published models. Our best fitting inversion to GPS velocities from these 24 sites suggests that 2-plate model for the Caribbean is required to fit the GPS observations, which implies that the Caribbean is undergoing modest (1-3 mm/yr) deformation within its interior. Some sites in the western Caribbean included in our analysis may be biased by small, but significant coseismic deformation, which has not been removed from the site velocities used in our inversion to define Caribbean motion and rigidity. Scenarios for possible east-west deformation accommodated across the Lower Nicaraguan Rise and Beata Ridge will be presented.

Assessment of the Water Levels and Currents at the Mississippi Bight During Hurricane Katrina.

NASA Astrophysics Data System (ADS)

Nwankwo, U. C.; Howden, S. D.; Dodd, D.; Wells, D. E.

2017-12-01

In an effort to extend the length of GPS baselines further offshore, the Hydrographic Science Research Center at the University of Southern Mississippi deployed a buoy which had a survey grade GPS receiver, an ADPC and a motion sensor unit in the Mississippi Bight in late 2004. The GPS data were initially processed using the Post Processed Kinematic technique with data from a nearby GPS base station on Horn Island. This processing technique discontinued when the storm (Hurricane Katrina) destroyed the base station in late August of 2005. However, since then a stand-alone positioning technique termed Precise Point Positioning (PPP) matured and allowed for the reprocessing of the buoy GPS data throughout Katrina. The processed GPS data were corrected for buoy angular motions using Tait Bryan transformation model. Tidal datums (Epoch 1983-2001) were transferred from the National Oceanic and Atmospheric Administration (NOAA) National Water Level at Waveland, Mississippi (Station ID 8747766) to the buoy using the Modified Range Ratio method. The maximum water level during the storm was found to be about 3.578m, relative to the transferred Mean Sea Level datum. The storm surge built over more than 24 hours, but fell back to normal levels in less than 3 hours. The maximum speed of the current with respect to the seafloor was recorded to be about 4knots towards the southeast as the storm surge moved back offshore.

Real-time GPS integration for prototype earthquake early warning and near-field imaging of the earthquake rupture process

NASA Astrophysics Data System (ADS)

Hudnut, K. W.; Given, D.; King, N. E.; Lisowski, M.; Langbein, J. O.; Murray-Moraleda, J. R.; Gomberg, J. S.

2011-12-01

Over the past several years, USGS has developed the infrastructure for integrating real-time GPS with seismic data in order to improve our ability to respond to earthquakes and volcanic activity. As part of this effort, we have tested real-time GPS processing software components , and identified the most robust and scalable options. Simultaneously, additional near-field monitoring stations have been built using a new station design that combines dual-frequency GPS with high quality strong-motion sensors and dataloggers. Several existing stations have been upgraded in this way, using USGS Multi-Hazards Demonstration Project and American Recovery and Reinvestment Act funds in southern California. In particular, existing seismic stations have been augmented by the addition of GPS and vice versa. The focus of new instrumentation as well as datalogger and telemetry upgrades to date has been along the southern San Andreas fault in hopes of 1) capturing a large and potentially damaging rupture in progress and augmenting inputs to earthquake early warning systems, and 2) recovering high quality recordings on scale of large dynamic displacement waveforms, static displacements and immediate and long-term post-seismic transient deformation. Obtaining definitive records of large ground motions close to a large San Andreas or Cascadia rupture (or volcanic activity) would be a fundamentally important contribution to understanding near-source large ground motions and the physics of earthquakes, including the rupture process and friction associated with crack propagation and healing. Soon, telemetry upgrades will be completed in Cascadia and throughout the Plate Boundary Observatory as well. By collaborating with other groups on open-source automation system development, we will be ready to process the newly available real-time GPS data streams and to fold these data in with existing strong-motion and other seismic data. Data from these same stations will also serve the very practical purpose of enabling earthquake early warning and greatly improving rapid finite-fault source modeling. Multiple uses of the effectively very broad-band data obtained by these stations, for operational and research purposes, are bound to occur especially because all data will be freely, openly and instantly available.

Fine tuning GPS clock estimation in the MCS

NASA Technical Reports Server (NTRS)

Hutsell, Steven T.

1995-01-01

With the completion of a 24 operational satellite constellation, GPS is fast approaching the critical milestone, Full Operational Capability (FOC). Although GPS is well capable of providing the timing accuracy and stability figures required by system specifications, the GPS community will continue to strive for further improvements in performance. The GPS Master Control Station (MCS) recently demonstrated that timing improvements are always composite Clock, and hence, Kalman Filter state estimation, providing a small improvement to user accuracy.

Analyzing the Impact of Different Pcv Calibration Models on Height Determination Using Gps/Glonass Observations from Asg-Eupos Network

NASA Astrophysics Data System (ADS)

Dawidowicz, Karol

2014-12-01

The integration of GPS with GLONASS is very important in satellite-based positioning because it can clearly improve reliability and availability. However, unlike GPS, GLONASS satellites transmit signals at different frequencies. This results in significant difficulties in modeling and ambiguity resolution for integrated GNSS positioning. There are also some difficulties related to the antenna Phase Center Variations (PCV) problem because, as is well known, the PCV is dependent on the received signal frequency dependent. Thus, processing simultaneous observations from different positioning systems, e.g. GPS and GLONASS, we can expect complications resulting from the different structure of signals and differences in satellite constellations. The ASG-EUPOS multifunctional system for precise satellite positioning is a part of the EUPOS project involving countries of Central and Eastern Europe. The number of its users is increasing rapidly. Currently 31 of 101 reference stations are equipped with GPS/GLONASS receivers and the number is still increasing. The aim of this paper is to study the height solution differences caused by using different PCV calibration models in integrated GPS/GLONASS observation processing. Studies were conducted based on the datasets from the ASG-EUPOS network. Since the study was intended to evaluate the impact on height determination from the users' point of view, a so-called "commercial" software was chosen for post-processing. The analysis was done in a baseline mode: 3 days of GNSS data collected with three different receivers and antennas were used. For the purposes of research the daily observations were divided into different sessions with a session length of one hour. The results show that switching between relative and absolute PCV models may cause an obvious effect on height determination. This issue is particularly important when mixed GPS/GLONASS observations are post-processed.

Multi-technique combination of space geodesy observations: Impact of the Jason-2 satellite on the GPS satellite orbits estimation

NASA Astrophysics Data System (ADS)

Zoulida, Myriam; Pollet, Arnaud; Coulot, David; Perosanz, Félix; Loyer, Sylvain; Biancale, Richard; Rebischung, Paul

2016-10-01

In order to improve the Precise Orbit Determination (POD) of the GPS constellation and the Jason-2 Low Earth Orbiter (LEO), we carry out a simultaneous estimation of GPS satellite orbits along with Jason-2 orbits, using GINS software. Along with GPS station observations, we use Jason-2 GPS, SLR and DORIS observations, over a data span of 6 months (28/05/2011-03/12/2011). We use the Geophysical Data Records-D (GDR-D) orbit estimation standards for the Jason-2 satellite. A GPS-only solution is computed as well, where only the GPS station observations are used. It appears that adding the LEO GPS observations results in an increase of about 0.7% of ambiguities fixed, with respect to the GPS-only solution. The resulting GPS orbits from both solutions are of equivalent quality, agreeing with each other at about 7 mm on Root Mean Square (RMS). Comparisons of the resulting GPS orbits to the International GNSS Service (IGS) final orbits show the same level of agreement for both the GPS-only orbits, at 1.38 cm in RMS, and the GPS + Jason2 orbits at 1.33 cm in RMS. We also compare the resulting Jason-2 orbits with the 3-technique Segment Sol multi-missions d'ALTimétrie, d'orbitographie et de localisation précise (SSALTO) POD products. The orbits show good agreement, with 2.02 cm of orbit differences global RMS, and 0.98 cm of orbit differences RMS on the radial component.

Continuous GPS observations in Tohoku University and recovery effort after the 2011 off the Pacific coast of Tohoku Earthquake

NASA Astrophysics Data System (ADS)

Demachi, T.; Miura, S.; Ohta, Y.; Tachibana, K.; Ueki, S.; Sato, T.; Ohzono, M.; Umino, N.

2012-04-01

The nation-wide GPS observation network which is named GPS Earth Observation Network System (GEONET) has been established by the Geospatial Information Authority of Japan (GSI) (Miyazaki et al., 1997). The network composed more than 1,200 stations with baseline length is about 20-25 km. Tohoku University has also conducted continuous GPS observations since 1987 in the Tohoku district, Northeastern Japan (Miura et al., 1993). Recently, to investigate short-length crustal deformations such as volcanic deformation, co- and post-seismic deformation of M6-7 class earthquakes and inter-seismic deformations, we have deployed continuous GPS observation stations to complement the location of GEONET stations (Miura et al. 2000, 2002, and 2004). We installed GPS receiver, PC for data logging (ALIX series, PC Engines GmbH) and re-booter (e.g., WATCH BOOT nino, Meikyo Electric Co., Ltd.) in each station. We have secure and stable online access to each station from our university (Sendai city, Japan) using IP-VPN over fixed telephone lines (FLET'S Office service, Nippon Telegraph and Telephone East Corp.). Through this network, the data are transferred to our university and we can restart the devices if the devices hang up. Since 2010, we have tried to use on-line system through internet by prepaid mobile data-communication (b-mobile3G and b-mobileSIM U300, Japan Communications Inc.) in eight observation stations. Compared with the FLET'S Office service, we can conveniently and inexpensively establish wherever the mobile phone service is provided. The two stations are located in volcanoes, we activate the network system for an hour in every day using motor time switch, because of these devices are operated by limited DC power supplies through solar cell. In other six stations, we can use commercial AC power supplies, so that data connections are always available. On March 11, 2011, the 2011 off the Pacific coast of Tohoku Earthquake (Mw 9.0) occurred and a huge tsunami caused more than 19,000 dead and missing. After the main shock, the electricity failure and communication failure occurred in almost entire the Tohoku district. We obtained the GPS data of co-seismic and immediately after the main shock in only about 10% of our stations. Our observations resumed automatically in inland area as the electricity supply was resumed, while near the Pacific coastal area, recovery efforts were needed on site for resuming the observations. We carried out recovery effort in this area after March 20 when the essential utilities were almost repaired in Sendai city except tsunami-hit area. We used DC power supplies through solar cell and batteries and the prepaid mobile data-communication to operate GPS receivers and transfer data. This system is very useful in the area where fixed telephone and electric wires aren't reconstructed, because of the service of mobile phone is restored faster than fixed telephone service. We could resume the observations in almost all of our stations by April 1. Currently, we have been constructing redundant system of power supply using batteries to avoid data missing owing to electricity failure. We need to construct redundant network system in future.

Low-latency high-rate GPS data streams from the EarthScope Plate Boundary Observatory

NASA Astrophysics Data System (ADS)

Anderson, G.; Borsa, A.; Jackson, M.; Stark, K.

2008-05-01

Real-time processing of high rate GPS data can give precise (e.g., 5-10 mm for data recorded once per second) recordings of rapid volcanic and seismic deformation. These time series now provide an emerging tool for seismic, volcanic, and tsunami geodesy and early warning applications. UNAVCO, as part of the EarthScope Plate Boundary Observatory project, has developed the UStream system to provide streaming GPS data from some PBO and other UNAVCO-operated GPS stations. UStream is based on the Ntrip standard, a widely used protocol for streaming GNSS data over the Internet. Remote GPS stations provide a stream of BINEX data at 1 sample/sec to an Ntrip server at UNAVCO's Boulder offices, while simultaneously recording data locally in the event of communications failure. Once in Boulder, the data fork into three output streams: BINEX files stored at UNAVCO and streams of data in BINEX and RTCM 2.3 format. These streams flow to an Ntrip broadcaster that distributes data to Ntrip clients, which can be anything from low-latency processing systems to external data archiving systems. Current development efforts are geared toward providing data in RTCM 3.x format. This system is now operating in a public beta test mode, with data available from over 55 PBO and Nucleus GPS stations across the western United States. Data latencies from stations operating on mobile telephone communications are under 1.1 seconds at 95% confidence, and data completeness is typically more than 95% barring transient communications disruptions. Data from the system are available under the terms of the draft UNAVCO streaming data usage policy. For further information, please visit http://rtgps.unavco.org or send e-mail to rtgps@unavco.org.

Subnanosecond GPS-based clock synchronization and precision deep-space tracking

NASA Technical Reports Server (NTRS)

Dunn, C. E.; Lichten, S. M.; Jefferson, D. C.; Border, J. S.

1992-01-01

Interferometric spacecraft tracking is accomplished by the Deep Space Network (DSN) by comparing the arrival time of electromagnetic spacecraft signals at ground antennas separated by baselines on the order of 8000 km. Clock synchronization errors within and between DSN stations directly impact the attainable tracking accuracy, with a 0.3-nsec error in clock synchronization resulting in an 11-nrad angular position error. This level of synchronization is currently achieved by observing a quasar which is angularly close to the spacecraft just after the spacecraft observations. By determining the differential arrival times of the random quasar signal at the stations, clock offsets and propagation delays within the atmosphere and within the DSN stations are calibrated. Recent developments in time transfer techniques may allow medium accuracy (50-100 nrad) spacecraft tracking without near-simultaneous quasar-based calibrations. Solutions are presented for a worldwide network of Global Positioning System (GPS) receivers in which the formal errors for DSN clock offset parameters are less than 0.5 nsec. Comparisons of clock rate offsets derived from GPS measurements and from very long baseline interferometry (VLBI), as well as the examination of clock closure, suggest that these formal errors are a realistic measure of GPS-based clock offset precision and accuracy. Incorporating GPS-based clock synchronization measurements into a spacecraft differential ranging system would allow tracking without near-simultaneous quasar observations. The impact on individual spacecraft navigation-error sources due to elimination of quasar-based calibrations is presented. System implementation, including calibration of station electronic delays, is discussed.

Noise analysis of GPS time series in Taiwan

NASA Astrophysics Data System (ADS)

Lee, You-Chia; Chang, Wu-Lung

2017-04-01

Global positioning system (GPS) usually used for researches of plate tectonics and crustal deformation. In most studies, GPS time series considered only time-independent noises (white noise), but time-dependent noises (flicker noise, random walk noise) which were found by nearly twenty years are also important to the precision of data. The rate uncertainties of stations will be underestimated if the GPS time series are assumed only time-independent noise. Therefore studying the noise properties of GPS time series is necessary in order to realize the precision and reliability of velocity estimates. The lengths of our GPS time series are from over 500 stations around Taiwan with time spans longer than 2.5 years up to 20 years. The GPS stations include different monument types such as deep drill braced, roof, metal tripod, and concrete pier, and the most common type in Taiwan is the metal tripod. We investigated the noise properties of continuous GPS time series by using the spectral index and amplitude of the power law noise. During the process we first remove the data outliers, and then estimate linear trend, size of offsets, and seasonal signals, and finally the amplitudes of the power-law and white noise are estimated simultaneously. Our preliminary results show that the noise amplitudes of the north component are smaller than that of the other two components, and the largest amplitudes are in the vertical. We also find that the amplitudes of white noise and power-law noises are positively correlated in three components. Comparisons of noise amplitudes of different monument types in Taiwan reveal that the deep drill braced monuments have smaller data uncertainties and therefore are more stable than other monuments.

Using Meteosat-10 and GPS ZWD measurements for creating regional water vapor maps.

NASA Astrophysics Data System (ADS)

Leontiev, Anton; Reuveni, Yuval

2017-04-01

Water vapor (WV) is one of the greenhouse gases, which plays a crucial role in global warming. It's investigation is of great importance for climate and global warming studies. One of the main difficulties of such studies is that WV varies constantly across the lower part of the atmosphere. Currently, most of studies provides WV estimations using only one technique such as tropospheric GPS path delays [Duan et al.] or multi-spectral reflected measurements from different meteorological satellites such as the Meteosat series [Schroedter et al.]. Constructing WV maps using only interpolated GPS zenith wet delay (ZWD) estimations has a main disadvantage - it doesn't take in account clouds which are located outside the integrated GPS paths. Using our previous work [Leontiev, Reuveni, in review] we were able to estimate Meteosat-10 7.3 μm WV pixel values by extracting the mathematical dependency between the WV amount calculated using GPS ZWD and the Meteosat-10 data. Here, we present a new strategy which combines these two approaches for WV estimation by using the mathematical dependency between GPS-ZWD and Meteosat-10 in order to evaluate the WV amount at cloudy conditions when preforming the interpolation between adjusted GPS station inside our network. This approach increases the accuracy of the estimated regional water vapor maps. References: Duan, J. et al. (1996), GPS Meteorology: Direct Estimation of the Absolute Value of Precipitable Water, J. Appl. Meteorol., 35(6), 830-838, doi:10.1175/15200450(1996)035<0830:GMDEOT>2.0.CO;2. Leontiev, A., Reuveni, Y.: Combining METEOSAT-10 satellite image data with GPS tropospheric path delays to estimate regional Integrated Water Vapor (IWV) distribution, Atmos. Meas. Tech. Discuss, doi:10.5194/amt-2016-217, in review, 2016. Schroedter-Homscheidt, M., A. Drews, and S. Heise (2008), Total water vapor column retrieval from MSG-SEVIRI split window measurements exploiting the daily cycle of land surface temperatures, Remote Sens. Environ., 112(1), 249-258, doi:10.1016/j.rse.2007.05.006

Present day vertical deformation of Pico and Faial islands revealed by merged INSAR and GPS data

NASA Astrophysics Data System (ADS)

Catalao, Joao; Nico, Giovanni; Catita, Cristina

2010-05-01

In this paper we investigate the problem of the integration of repeated GPS geodetic measurements and interferometric Synthetic Aperture Radar (SAR) observations for the determination of high resolution vertical deformation maps. The Faial and Pico islands in the Azores archipelago were chosen as study area. These islands are characterized by a intense volcanic and seismic activity. Both islands are covered by huge vegetation and have very unstable atmospheric conditions which negatively influence the interferometric processing. In this work, we apply the advanced interferometric SAR processing based on Persistent Scatterers. However, the small number of man made structures reduces the density of Persistent Scatterers. Furthermore, the different ascending and descending acquisition geometries give different sets of Persistent Scatterers, with complementary spatial coverage, and different line-of-sight velocities. The estimated velocities are relative to the master image (different from ascending and descending) and must be referred to an absolute velocity (in the sense of referred to a geodetic reference frame). The strategy used to overcome the aforementioned problems is based on the combination of sparse GPS 3D-velocities with two sets of Persistent Scatterers determined from ascending and descending passes. The input data are: a set of GPS - 3D velocities relative to ITRF05 (18 Stations) and two sets of Persistent Scatterers corresponding to the descending and ascending orbits. A dataset of 60 interferometric repeat-pass ASAR/ENVISAT images were acquired over the Faial and Pico islands, from 2006 to 2008, along ascending and descending passes. Each interferogram obtained by this dataset was corrected for atmospheric artefacts using a Weather Forecasting model. Initially, the horizontal velocity component (east and north) is assigned to each PS from interpolation of available GPS observations. Then, the vertical component of the velocity is determined from the SAR line-of-sight velocity and the GPS horizontal velocity component. Later, the vertical velocity offsets are numerically determined by comparison between GPS (ITRF velocities) and PS (the two ascending and descending sets) measurements. These values are then used to create the vertical deformation map of Faial and Pico islands with considerably better resolution and accuracy than using a single set of observations. The vertical deformation map has identified a large continuous area of subsidence on the west of Faial island, on the flank of Capelinhos eruption cone, with a maximum subsidence range of 10 mm/yr. It has also revealed the subsidence of the summit crater of Pico island (9 mm/yr) and a large area of subsidence on the west of the island, corresponding mostly to creep movement. Key words: SAR Interferometry, GPS-INSAR integration, Volcano, subsidence

High Frequency Fluctuations of Polar Motion During IGS'92 Campaign

NASA Astrophysics Data System (ADS)

Huang, Chengli; Jin, Wenjin; Liao, Dechun; Zhu, Wenyao; Wang, Jiexian

1994-09-01

During IGS'92 Campaign seven PM(Polar Motion) series provided by GPS Processing Centers are analysed in this paper. Some similar high frequency fluctuations in these PM series are detected by using spectra! analyses, least square adjustment and F-test as follows: there are short periodic fluctuations of 27.0, 16.5, 13.4, 10.4 day in X direction; and of 10.0, 20.5, 15.8 day in Y direction. And there are similar systematic deviations derived from the comparison of each series with EOP(IERS) 92 C 04. The inain cause of these systematic deviations is that the rotation between the reference frames of these series and ITRF91 exists. As for the reason, the coordinates of stations are not fixed (or partly fixed only) when solving X and Y with GPS data. The high frequency fluctuations of polar motion are explained to some extent by the excitation of atmospheric angular momentum.

Anomalous tidal loading signals in South-West England and Brittany

NASA Astrophysics Data System (ADS)

Keshin, M.; Penna, N. T.; Clarke, P. J.; Bos, M. S.; Baker, T. F.

2010-05-01

The tidal deformation of the Earth, including ocean tide loading (OTL), sheds light on the Earth's internal structure. Uncertainties in the knowledge of this deformation may be a source of both direct and propagated periodic errors in GPS geodesy. The increasing number of global GPS stations with long histories of observations, as well as recent developments in precise GPS geodesy such as the availability of reprocessed satellite orbits, enables further study of these geophysical and geodetic phenomena. There are more than 10 worldwide regions where OTL displacement amplitudes exceed 25mm. In our work we considered one such region covering South-West England and stretching southward along the coasts of France, Spain and Portugal. Estimates of three-dimensional harmonic site motion at each of the principal diurnal (K1, O1, P1, Q1) and semi-diurnal (K2, M2, N2, S2) frequencies were obtained for 40 European stations with at least 2 year observation span, using the GIPSY-OASIS II software package with reprocessed precise satellite orbits from JPL. All GPS data available from 2002.0 to 2010.0 were considered. 34 stations were situated close to the Atlantic coast; a further 6 inland stations at similar latitudes were processed as a check on solid Earth tide models. Inter-model OTL displacement differences are small, especially for the inland sites; the problematic Bristol Channel area of South-West England was excluded. We validated the quality of our GPS estimates by using and comparing three different analysis strategies: (1) Harmonic estimation of total tidal displacement in 24-hour Precise Point Positioning (PPP) batch solutions: harmonic displacements are estimated per coordinate component for each of the eight principal tidal constituents. OTL is not modelled a priori, and nodal corrections are applied in post-processing after combination of the daily results; (2) Harmonic estimation of residual tidal displacement in 24-hour PPP batch solutions: OTL is modelled a priori using the FES2004 model in the reference frame of the whole Earth system (CM); the residual harmonic displacements are estimated per component per principal tidal constituent. Minor tidal harmonics are removed a priori using the routine "hardisp" by D. Agnew. Because of this, post-processing nodal corrections are not applied; (3) Amplitude and phase from kinematic PPP processing: kinematic GPS processing with a priori OTL modelling using FES2004 and hardisp as in (2); amplitude spectra are later estimated from the entire coordinate time series using the Lomb-Scargle periodogram method. We typically obtain excellent (0.3-0.7mm except for the K1 and K2 constituents) phasor agreement between all three strategies, comparable to the inter-model agreement between computed OTL displacements and suggesting that the GPS analysis strategy robustly detects actual tidal displacements. For sites in inland Europe where computed OTL displacements are less than 10mm with inter-model differences of less than 0.2mm, residual harmonic amplitudes are also at the 0.3-0.7mm level, confirming that solid Earth tides are modelled to at least this accuracy. For GPS stations located in South-West England and Brittany, onshore of the continental shelf, anomalous residual tidal signals were detected of about 2-3mm magnitude for the vertical M2 OTL constituent (10% of the expected signal). In contrast, sites in the Iberian Peninsula, with similar expected OTL magnitudes, have residuals at the expected 0.3-0.7mm level. Sites near to the Bay of Biscay show transitional behaviour between these regimes. Therefore at these locations, the different modern ocean tide models that agree very well must all either be systematically in error, or the difference in behaviour may be caused by errors in the displacement Green's functions applicable to loads on the nearby continental shelf.

Improved vertical displacements induced by a refined thermal expansion model and its quantitative analysis in GPS height time series

NASA Astrophysics Data System (ADS)

Wang, Kaihua; Chen, Hua; Jiang, Weiping; Li, Zhao; Ma, Yifang; Deng, Liansheng

2018-04-01

There are apparent seasonal variations in GPS height time series, and thermal expansion is considered to be one of the potential geophysical contributors. The displacements introduced by thermal expansion are usually derived without considering the annex height and underground part of the monument (e.g. located on roof or top of the buildings), which may bias the geophysical explanation of the seasonal oscillation. In this paper, the improved vertical displacements are derived by a refined thermal expansion model where the annex height and underground depth of the monument are taken into account, and then 560 IGS stations are adopted to validate the modeled thermal expansion (MTE) displacements. In order to evaluate the impact of thermal expansion on GPS heights, the MTE displacements of 80 IGS stations with less data discontinuities are selected to compare with their observed GPS vertical (OGV) displacements with the modeled surface loading (MSL) displacements removed in advance. Quantitative analysis results show the maximum annual and semiannual amplitudes of the MTE are 6.65 mm (NOVJ) and 0.51 mm (IISC), respectively, and the maximum peak-to-peak oscillation of the MTE displacements can be 19.4 mm. The average annual amplitude reductions are 0.75 mm and 1.05 mm respectively after removing the MTE and MSL displacements from the OGV, indicating the seasonal oscillation induced by thermal expansion is equivalent to >75% of the impact of surface loadings. However, there are rarely significant reductions for the semiannual amplitude. Given the result in this study that thermal expansion can explain 17.3% of the annual amplitude in GPS heights on average, it must be precisely modeled both in GPS precise data processing and GPS time series analysis, especially for those stations located in the middle and high latitudes with larger annual temperature oscillation, or stations with higher monument.

Horizontal Displacement Vector Analysis in Ujong Muloh GPS Station (UMLH) Sumatra Island on March 27 – April 25, 2012

NASA Astrophysics Data System (ADS)

Pamungkas, S. S.; Koesuma, S.; Legowo, Budi

2018-03-01

Sumatra Island is an area that has high tectonic activities. This is because the island of Sumatra is located in two major plates of the world, the Indo-Australian plate and the Eurasia plate. The subduction zone causes Sumatra to deform from time to time. The deformation of Sumatra Island can be observed by continuous recording coordinates using the GPS Station. Continous-GPS (C-GPS) in Sumatra Island is named Sumatran GPS Array (SuGAr), one of them named UMLH. The UMLH GPS station used to observe the displacement in the Aceh City of Sumatra Island, is located in Ujung Muloh. The changes of GPS coordinate recording data can represent the deformation pattern that occurred in Sumatra. On April 11, 2012, according to USGS data, there had been an earthquake in the city of Aceh about 8.6 at coordinates of 2.433°N, 93.072°E. The purpose of this research is to analyze the horizontal displacement due to the occurrence of the earthquake. Data processing is carried out using software GAMIT/GLOBK. The magnitude of the displacement of Sumatra Island before the earthquake, during the earthquake, and after the quake on component X were respectively: 0.04 mm/day, 56.63 mm/day, and 8.28 mm/day; while on component Y were respectively: 0.03 mm/day, 23.78 mm/day, and 1.22 mm/day. The direction of displacement was 253.8° towards Southwest with the assumption that 0° was in the North.

Application of Seasonal Trend Loess to GPS data in Cascadia

NASA Astrophysics Data System (ADS)

Bal, A.; Bartlow, N. M.

2016-12-01

Plate Boundary Observatory GPS stations provide crucial data for the study of slow slip events and volcanic hazards in the Cascadia region. However, these GPS stations also record seasonal changes in deformation caused by hydrologic, atmospheric, and other seasonal loading. Removing these signals is necessary for accurately modeling the tectonic sources of deformation. Traditionally, seasonal trends in data been accounted for by fitting and removing sine curves from the data. However, not all seasonal trends follow a sinusoidal shape. Seasonal Trend Loess, or STL, is a filtering procedure for a decomposing a time series into trend, seasonal, and remainder components (Cleveland et. al, Journal of Official Statistics, 1990). STL has a simple design that consists of a sequence of applications of the loess smoother which allows for fast computation of large amounts of trend and seasonal smoothing. STL allows for non-sinusoidal shapes in seasonal deformation signals, and allows for evolution of seasonal signals over time. We applied Seasonal Trend Loess to GPS data from the Cascadia region. We compared our results to a traditional sine wave fit for seasonal removal at selected stations, including stations with slow slip event and volcanic signals. We hope that the STL method may be able to more accurately differentiate seasonal and tectonic deformation signals.

A study of El Niño-Southern oscillation impacts to the South China Sea region using ground-based GPS receiver

NASA Astrophysics Data System (ADS)

Suparta, Wayan; Iskandar, Ahmad; Singh Jit Singh, Mandeep; Alauddin Mohd Ali, Mohd; Yatim, Baharudin; Tangang, Fredolin

2013-04-01

We observe an ENSO activity by using ground-based GPS receiver as an effort to study the effects of global warming and climate change in the tropical region. The precipitable water vapor (PWV) derived from Global Positioning System (GPS) meteorology in line with the sea surface temperature anomaly (SSTa) is used to indicate their response on ENSO activities. The PWV data used in this study was taken from the station at Universiti Malaysia Sabah, Kota Kinabalu (UMSK) over 2011, together with NTUS station (in the Singapore), PIMO (in Philippines) and BAKO (in Indonesia) are also compared. The relationship between PWV and SSTa at all stations on weekly basis exhibited modest with correlation coefficients between -0.30 and -0.78 significantly at the 99% confidence level. The negative correlation indicates that during a La Niña phase, the PWV is increased when the sea surface temperatures getting cold causes warm air mass in the central Pacific moved to west Pacific. The increased of PWV causes the GPS signals will be getting slower.

SURMODERR: A MATLAB toolbox for estimation of velocity uncertainties of a non-permanent GPS station

NASA Astrophysics Data System (ADS)

Teza, Giordano; Pesci, Arianna; Casula, Giuseppe

2010-08-01

SURMODERR is a MATLAB toolbox intended for the estimation of reliable velocity uncertainties of a non-permanent GPS station (NPS), i.e. a GPS receiver used in campaign-style measurements. The implemented method is based on the subsampling of daily coordinate time series of one or more continuous GPS stations located inside or close to the area where the NPSs are installed. The continuous time series are subsampled according to real or planned occupation tables and random errors occurring in antenna replacement on different surveys are taken into account. In order to overcome the uncertainty underestimation that typically characterizes short duration GPS time series, statistical analysis of the simulated data is performed to estimate the velocity uncertainties of this real NPS. The basic hypotheses required are: (i) the signal must be a long-term linear trend plus seasonal and colored noise for each coordinate; (ii) the standard data processing should have already been performed to provide daily data series; and (iii) if the method is applied to survey planning, the future behavior should not be significantly different from the past behavior. In order to show the strength of the approach, two case studies with real data are presented and discussed (Central Apennine and Panarea Island, Italy).

Subsidence at the Fairport Harbor Water Level Gauge

NASA Astrophysics Data System (ADS)

Conner, D. A.

2014-12-01

SUBSIDENCE AT THE FAIRPORT HARBOR WATER LEVEL GAUGE I will provide information on methods being used to monitor Lake Erie water levels and earth movement at Fairport Harbor, Ohio. Glacial Isostatic Adjustment (GIA) is responsible for vertical movement throughout the Great Lakes region. Fairport Harbor is also experiencing vertical movement due to salt mining, so the nearby water level gauge operated by the National Oceanic and Atmospheric Administration (NOAA) is affected by both GIA and mining. NOAA's National Geodetic Survey (NGS) defines and maintains the National Spatial Reference System (NSRS). The NSRS includes a network of permanently marked points; a consistent, accurate, and up-to-date national shoreline; a network of Continuously Operating Reference Stations (CORS) which supports three-dimensional positioning activities; and a set of accurate models describing dynamic, geophysical processes that affect spatial measurements. The NSRS provides the spatial reference foundation for transportation, mapping, charting and a multitude of scientific and engineering applications. Fundamental elements of geodetic infrastructure include GPS CORS (3-D), water level and tide gauges (height) and a system of vertical bench marks (height). When two or more of these elements converge they may provide an independent determination of position and vertical stability as is the case here at the Fairport Harbor water level gauge. Analysis of GPS, leveling and water level data reveal that this gauge is subsiding at about 2-3 mm/year, independent of the effects of GIA. Analysis of data from the nearby OHLA GPS CORS shows it subsiding at about 4 mm/yr, four times faster than expected due to GIA alone. A long history of salt mine activity in the area is known to geologists but it came as a surprise to other scientists.

A New Global Geodetic Strain Rate Model

NASA Astrophysics Data System (ADS)

Kreemer, C.; Blewitt, G.; Klein, E. C.; Shen, Z.; Wang, M.; Estey, L.; Wier, S.

2013-12-01

As part of the Global Earthquake Model (GEM) effort to improve global seismic hazard models, we present a new global geodetic strain rate model. This model (GSRM v. 2) is a vast improvement on the previous model from 2004 (v. 1.2). The model is still based on a finite-element type approach and has deforming cells in between the assumed rigid plates. The new model contains ~144,700 cells of 0.25° by 0.2° dimension. We redefined the geometries of the deforming zones based on the definitions of Bird (2003) and Chamot-Rooke and Rabaute (2006). We made some adjustments to the grid geometry at places where seismicity and/or GPS velocities suggested either the presence of deforming areas or a rigid block where those previous studies did not. GSRM v.2 includes 50 plates and blocks, including many not considered by Bird (2003). The new GSRM model is based on over 20,700 horizontal geodetic velocities at over 17,000 unique locations. The GPS velocity field consists of a 1) Over 6500 velocities derived by the University of Nevada, Reno, for CGPS stations for which >2.5 years of RINEX data are available until April 2013, 2) ~1200 velocities for China from a new analysis of all data from the Crustal Movement Network of China (CMONOC), and 3) about 13,000 velocities from 212 studies published in the literature or made otherwise available to us. Velocities from all studies were combined into the same reference frame by a 6-parameter transformation using velocities at collocated stations. We model co-seismic jumps while estimating velocities, ignore periods of post-seismic deformation, and exclude time-series that reflect magmatic and anthropogenic activity. GPS velocities were used to estimate angular velocities for 36 of the 50 rigid plates and blocks (the rest being taken from the literature), and these were used as boundary conditions in the strain rate calculations. For the strain rate calculations we used the method of Haines and Holt. In order to fit the data equally well in slowly and rapidly deforming areas, we first calculated a very smooth model by setting the a priori variances of the strain rate components very low. We then used this model as a proxy for the a priori standard deviations of the final model, at least for the areas that are well constrained by the GPS data. We will show examples of the strain rate and velocity field results. We will also highlight how and where the results can be viewed and accessed through a dedicated webportal (gsrm2.unavco.org). New GPS velocities (in any reference frame) can be uploaded to a new tool and displayed together with velocities used in GSRM v.2 in 53 reference frames (http://facility.unavco.org/data/maps/GPSVelocityViewer/GSRMViewer.html) .

Transition of NOAA's GPS-Met Data Acquisition and Processing System to the Commercial Sector: Inital Results

NASA Astrophysics Data System (ADS)

Jackson, Michael; Blatt, Stephan; Holub, Kirk

2015-04-01

In April of 2014, NOAA/OAR/ESRL Global Systems Division (GSD) and Trimble, in collaboration with Earth Networks, Inc. (ENI) signed a Cooperative Research and Development Agreement (CRADA) to transfer the existing NOAA GPS-Met Data Acquisition and Processing System (GPS-Met DAPS) technology to a commercial Trimble/ENI partnership. NOAA's GPS-Met DAPS is currently operated in a pseudo-operational mode but has proven highly reliable and running at over 95% uptime. The DAPS uses the GAMIT software to ingest dual frequency carrier phase GPS/GNSS observations and ancillary information such as real-time satellite orbits to estimate the zenith-scaled tropospheric (ZTD) signal delays and, where surface MET data are available, retrieve integrated precipitable water vapor (PWV). The NOAA data and products are made available to end users in near real-time. The Trimble/ENI partnership will use the Trimble Pivot™ software with the Atmosphere App to calculate zenith tropospheric (ZTD), tropospheric slant delay, and integrated precipitable water vapor (PWV). Evaluation of the Trimble software is underway starting with a comparison of ZTD and PWV values determined from four sub networks of GPS stations located 1. near NOAA Radiosonde Observation (Upper-Air Observation) launch sites; 2. Stations with low terrain/high moisture variability (Gulf Coast); 3. Stations with high terrain/low moisture variability (Southern California); and 4. Stations with high terrain/high moisture variability (high terrain variability elev. > 1000m). For each network GSD and T/ENI run the same stations for 30 days, compare results, and perform an evaluation of the long-term solution accuracy, precision and reliability. Metrics for success include T/ENI PWV estimates within 1.5 mm of ESRL/GSD's estimates 95% of the time (ZTD uncertainty of less than 10 mm 95% of the time). The threshold for allowable variations in ZTD between NOAA GPS-Met and T/ENI processing are 10mm. The CRADA 1&2 Trimble processing show a variation of 4±2mm and 3±8mm respectively. The threshold for allowable variations in PWV between NOAA GPS-Met and T/ENI processing are 15mm. The CRADA 1&2 Trimble processing show a variation of 2±4mm and 10±13 respectively. The T/ENI PWV and ZTD values meet and exceed the requirements outlined in the CRADA for the first two networks processed. T/ENI Partnership brings a footprint of GNSS and meteorological stations that could significantly enhance the latency, temporal, and geographic density of ZTD and PWV over the US and Europe. We will provide a brief overview of the Trimble Pivot™ software and the Atmosphere App and present results from further testing along with a timeline for the transition of the GPS-Met DAPS to an operational commercial service.

Benchmarking the Algorithms to Detect Seasonal Signals Under Different Noise Conditions

NASA Astrophysics Data System (ADS)

Klos, A.; Bogusz, J.; Bos, M. S.

2017-12-01

Global Positioning System (GPS) position time series contain seasonal signals. Among the others, annual and semi-annual are the most powerful. Widely, these oscillations are modelled as curves with constant amplitudes, using the Weighted Least-Squares (WLS) algorithm. However, in reality, the seasonal signatures vary over time, as their geophysical causes are not constant. Different algorithms have been already used to cover this time-variability, as Wavelet Decomposition (WD), Singular Spectrum Analysis (SSA), Chebyshev Polynomial (CP) or Kalman Filter (KF). In this research, we employed 376 globally distributed GPS stations which time series contributed to the newest International Terrestrial Reference Frame (ITRF2014). We show that for c.a. 20% of stations the amplitudes of seasonal signal varies over time of more than 1.0 mm. Then, we compare the WD, SSA, CP and KF algorithms for a set of synthetic time series to quantify them under different noise conditions. We show that when variations of seasonal signals are ignored, the power-law character is biased towards flicker noise. The most reliable estimates of the variations were found to be given by SSA and KF. These methods also perform the best for other noise levels while WD, and to a lesser extend also CP, have trouble in separating the seasonal signal from the noise which leads to an underestimation in the spectral index of power-law noise of around 0.1. For real ITRF2014 GPS data we discovered, that SSA and KF are capable to model 49-84% and 77-90% of the variance of the true varying seasonal signals, respectively.

Effects of non-tidal atmospheric loading on a Kalman filter-based terrestrial reference frame

NASA Astrophysics Data System (ADS)

Abbondanza, C.; Altamimi, Z.; Chin, T. M.; Collilieux, X.; Dach, R.; Heflin, M. B.; Gross, R. S.; König, R.; Lemoine, F. G.; MacMillan, D. S.; Parker, J. W.; van Dam, T. M.; Wu, X.

2013-12-01

The International Terrestrial Reference Frame (ITRF) adopts a piece-wise linear model to parameterize regularized station positions and velocities. The space-geodetic (SG) solutions from VLBI, SLR, GPS and DORIS global networks used as input in the ITRF combination process account for tidal loading deformations, but ignore the non-tidal part. As a result, the non-linear signal observed in the time series of SG-derived station positions in part reflects non-tidal loading displacements not introduced in the SG data reduction. In this analysis, the effect of non-tidal atmospheric loading (NTAL) corrections on the TRF is assessed adopting a Remove/Restore approach: (i) Focusing on the a-posteriori approach, the NTAL model derived from the National Center for Environmental Prediction (NCEP) surface pressure is removed from the SINEX files of the SG solutions used as inputs to the TRF determinations. (ii) Adopting a Kalman-filter based approach, a linear TRF is estimated combining the 4 SG solutions free from NTAL displacements. (iii) Linear fits to the NTAL displacements removed at step (i) are restored to the linear reference frame estimated at (ii). The velocity fields of the (standard) linear reference frame in which the NTAL model has not been removed and the one in which the model has been removed/restored are compared and discussed.

The March 1985 demonstration of the fiducial network concept for GPS geodesy: A preliminary report

NASA Technical Reports Server (NTRS)

Davidson, J. M.; Thornton, C. L.; Dixon, T. H.; Vegos, C. J.; Young, L. E.; Yunck, T. P.

1986-01-01

The first field tests in preparation for the NASA Global Positioning System (GPS) Caribbean Initiative were conducted in late March and Early April of 1985. The GPS receivers were located at the POLARIS Very Long Base Interferometry (VLBI) stations at Westford, Massachusetts; Richmond, Florida; and Ft. Davis, Texas; and at the Mojave, Owens Valley, and Hat Creek VLBI stations in California. Other mobile receivers were placed near Mammoth Lakes, California; Pt. Mugu, California; Austin, Texas; and Dahlgren, Virginia. These sites were equipped with a combination of GPS receiver types, including SERIES-X, TI-4100 and AFGL dual frequency receivers. The principal objectives of these tests were the demonstration of the fiducial network concept for precise GPS geodesy, the performance assessment of the participating GPS receiver types, and to conduct the first in a series of experiments to monitor ground deformation in the Mammoth Lakes-Long Valley caldera region in California. Other objectives included the testing of the water vapor radiometers for the calibration of GPS data, the development of efficient procedures for planning and coordinating GPS field exercise, the establishment of institutional interfaces for future cooperating ventures, the testing of the GPS Data Analysis Software (GIPSY, for GPS Inferred Positioning SYstem), and the establishment of a set of calibration baselines in California. Preliminary reports of the success of the field tests, including receiver performance and data quality, and on the status of the data analysis software are given.

Comparative analysis of positioning and zenith total delay retrieval using GPS-, GLONASS-only, and GPS/GLONASS combined precise point positioning

NASA Astrophysics Data System (ADS)

Zhou, Feng; Li, Xingxing; Cai, Miaomiao; Chen, Wen; Dong, Danan; Schuh, Harald

2017-04-01

Since October 2011, the Russian GLONASS has been revitalized and is now fully operational with 24 satellites in orbit. It is critical to assess the benefits and problems of using GLONASS observations (i.e. GLONASS-only or combined GPS/GLONASS) for precise positioning and zenith total delay (ZTD) retrieval on a global scale using the precise point positioning (PPP) technique. In this contribution, extensive evaluations are conducted with GNSS data sets collected from 251 globally distributed stations of the International GNSS Service (IGS) network in July 2016. The stations are divided into 30 groups by antenna/radome types to investigate whether there are antenna/radome-dependent biases in position and ZTD results derived from GLONASS-only PPP. The positioning results do not show obvious antenna/radome-dependent biases except the stations with JAV_RINGANT_G3T/NONE. The averaged biases of the stations with JAV_RINGANT_G3T/NONE in horizontal component especially in north component can even achieve -9.0 mm. The standard deviation (STD) and root mean square (RMS) are used as indicators of positioning repeatability and accuracy, respectively. Compared with GPS-only PPP, smaller averaged STD and RMS values of GLONASS-only PPP are achieved in horizontal component, while larger ones in vertical component. Furthermore, the STD and RMS values of GPS/GLONASS combined PPP solutions are the smallest in horizontal and vertical components, indicating that adding GLONASS observations can achieve better positioning performance than GPS-only PPP. Meanwhile, better positioning repeatability and accuracy are found in north component than that in east component, which may be caused by the configuration of GNSS satellite orbit. With respect to GPS-only PPP-derived ZTD, the ZTD biases, accuracy, and correlation derived from GLONASS-only and GPS/GLONASS PPP solutions are antenna/radome-independent, while the biases and accuracy are slightly latitude- or Geometric Dilution of Precisions (GDOP)-dependent, as well as the ZTD correlation are highly latitude- or GDOP-dependent. We also studied the impact of the chosen elevation cutoff angles on the positioning and ZTD retrieval. GLONASS-only PPP is found more sensitive with the elevation cutoff angles than GPS-only PPP.

Estimation and filtering techniques for high-accuracy GPS applications

NASA Technical Reports Server (NTRS)

Lichten, S. M.

1989-01-01

Techniques for determination of very precise orbits for satellites of the Global Positioning System (GPS) are currently being studied and demonstrated. These techniques can be used to make cm-accurate measurements of station locations relative to the geocenter, monitor earth orientation over timescales of hours, and provide tropospheric and clock delay calibrations during observations made with deep space radio antennas at sites where the GPS receivers have been collocated. For high-earth orbiters, meter-level knowledge of position will be available from GPS, while at low altitudes, sub-decimeter accuracy will be possible. Estimation of satellite orbits and other parameters such as ground station positions is carried out with a multi-satellite batch sequential pseudo-epoch state process noise filter. Both square-root information filtering (SRIF) and UD-factorized covariance filtering formulations are implemented in the software.

PTB’s Time and Frequency Activities in 2008 and 2009

DTIC Science & Technology

2009-11-01

techniques (C/A code, P3, carrier phase, PPP). Two-way satellite time and fre- quency transfer ( TWSTFT ) is made routinely with several stations in...and frequency transfer ( TWSTFT ) is routinely per- formed with several European and US stations. PTB provides services to disseminate time and...years 2008 and 2009 are pre- sented. TWSTT AND GPS ACTIVITIES PTB uses TWSTFT and GPS Time Transfer to compare the local time scale UTC (PTB

Identification of nutrition communication styles and strategies: a qualitative study among Dutch GPs.

PubMed

van Dillen, Sonja M E; Hiddink, Gerrit J; Koelen, Maria A; de Graaf, Cees; van Woerkum, Cees M J

2006-10-01

The objectives of this study were to identify nutrition communication styles of Dutch GPs, their strategies regarding nutrition communication and nutrition information seeking behaviours. Another aim is to provide a hypothetical model for nutrition communication style, including psycho-social and socio-demographic variables. Nine focus groups with 81 GPs were used to obtain GPs' perceptions of nutrition communication. Data were analysed with the computer software program NUD*IST. Five nutrition communication styles were identified, namely informational, reference, motivational, confrontational and holistic style. Referring to a dietician, providing advice according to Dietary Guidelines, and offering written education materials were mentioned as strategies regarding nutrition communication. GPs sought nutrition information in scientific studies, specialist literature, and postgraduate training courses. The informational style of nutrition communication was dominant among Dutch GPs. GPs hardly provided maintenance advice for nutrition behaviour. Many GPs referred patients to dieticians, who were viewed as colleagues. GPs tried to get basic information about nutrition by scanning the literature, but they were seldom actively involved in seeking specific nutrition information. Although GPs felt that patients expect expert nutrition information, they perceived their nutrition knowledge as restricted. We advise to raise self-efficacy of GPs regarding nutrition communication and to build good collaboration with dieticians.

NChina16: A stable geodetic reference frame for geological hazard studies in north China

NASA Astrophysics Data System (ADS)

Wang, G.; Yan, B.; Gan, W.; Geng, J.

2017-12-01

This study established a stable North China Reference Frame 2016 (NChina16) using five years of continuous GPS observations (2011.8 to 2016.8) from 12 continuously operating reference stations (CORS) fixed to the stable interior of the North China Craton. Applications of NChina16 in landslide, subsidence, and post-seismic displacement studies are illustrated. The primary result of this study is the seven parameters for transforming Cartesian ECEF (Earth-Centered, Earth-Fixed) coordinates X, Y, and Z from the International GNSS Service Reference Frame 2008 (IGS08) to NChina16. The seven parameters include the epoch that is used to tie the regional reference frame to IGS08 and the time derivatives of three translations and three rotations. A method for developing a regional geodetic reference frame is introduced in detail. The GIPSY-OASIS (V6.4) software package was used to obtain the precise point positioning (PPP) time series with respect to IGS08. The stability (accuracy) of NChina16 is about 0.5 mm/year in both vertical and horizontal directions. This study also developed a regional seasonal model for correcting vertical displacement time series data derived from the PPP solutions. Long-term GPS observations (1999-2016) from five CORS in north China were used to develop the seasonal model. According to this study, the PPP daily solutions with respect to NChina16 could achieve 2-3 mm horizontal accuracy and 4-5 mm vertical accuracy after being modified by the regional model. NChina16 will be critical to the long-term landslide, subsidence, fault, and structural monitoring in north China and for ongoing post-seismic crustal deformation studies in Japan. NChina16 will be incrementally improved and synchronized with the IGS reference frame update.

Navigating the Return Trip from the Moon Using Earth-Based Ground Tracking and GPS

NASA Technical Reports Server (NTRS)

Berry, Kevin; Carpenter, Russell; Moreau, Michael C.; Lee, Taesul; Holt, Gregg N.

2009-01-01

NASA s Constellation Program is planning a human return to the Moon late in the next decade. From a navigation perspective, one of the most critical phases of a lunar mission is the series of burns performed to leave lunar orbit, insert onto a trans-Earth trajectory, and target a precise re-entry corridor in the Earth s atmosphere. A study was conducted to examine sensitivity of the navigation performance during this phase of the mission to the type and availability of tracking data from Earth-based ground stations, and the sensitivity to key error sources. This study also investigated whether GPS measurements could be used to augment Earth-based tracking data, and how far from the Earth GPS measurements would be useful. The ability to track and utilize weak GPS signals transmitted across the limb of the Earth is highly dependent on the configuration and sensitivity of the GPS receiver being used. For this study three GPS configurations were considered: a "standard" GPS receiver with zero dB antenna gain, a "weak signal" GPS receiver with zero dB antenna gain, and a "weak signal" GPS receiver with an Earth-pointing direction antenna (providing 10 dB additional gain). The analysis indicates that with proper selection and configuration of the GPS receiver on the Orion spacecraft, GPS can potentially improve navigation performance during the critical final phases of flight prior to Earth atmospheric entry interface, and may reduce reliance on two-way range tracking from Earth-based ground stations.

Multi-instrumental Study of Storm-induced Ionospheric Irregularities at Midlatitudes

NASA Astrophysics Data System (ADS)

Cherniak, I.; Zakharenkova, I.; Sokolovskiy, S. V.

2017-12-01

We present multi-instrumental analysis of the unusually intense plasma density irregularities occurred over European midlatitudes during geomagnetic storm of 22-23 June 2015. We combine GPS/GLONASS observations derived from the dense ground-based networks ( 1500 stations) with in situ plasma density onboard Swarm and DMSP satellites and COSMIC Radio Occultation (RO) ionospheric electron density profiles. During this geomagnetic storm, the strong ionospheric irregularities of auroral origin were registered over the Northern Europe sub-auroral and midlatitudes. Meanwhile, another kind of ionospheric irregularities of equatorial origin reached European midlatitudes from the south. The prompt penetration electric fields caused the occurrence of plasma bite-outs in the post-sunset sector over the Western Africa low latitudes and extension of the large-scale plasma bubbles toward Europe. Using GPS/GLONASS observations, the plasma bubble signatures were mapped in Europe. They were observed for more than 8 h (20-04 UT) and covered a broad area within 30o-40o N and 20o W-10o E. In this region, the steep plasma gradients, as large as 5-10 TECU/degree, and numerous embedded deep plasma depletions were developed on the background of high plasma density. For low latitude region, the bite-out signature was recognized in the form of the significantly modified shape of the COSMIC-derived ionospheric electron density profiles. These unique results were confirmed by the in situ density and upward-looking GPS data onboard the Swarm satellites at 500 km altitude, in situ density measured by DMSP and ground-based absolute TEC observations. It was found that close similarity between in situ Ne and Swarm-derived topside vertical TEC suggests that plasma density enhancements and depletions are developed in the topside ionosphere (>500 km). The intensity of plasma gradients at different altitudes was also estimated by COSMIC-based measurements of GPS signal intensity and phase fluctuations as well as by rate of TEC changes on COSMIC-GPS links. Occurrence of the plasma bubbles in Europe affected GNSS measurements over number of reference stations and led to performance degradation of SBAS EGNOS.

Development of a Real-Time GPS/Seismic Displacement Meter: GPS Component

NASA Astrophysics Data System (ADS)

Bock, Y.; Canas, J.; Andrew, A.; Vernon, F.

2002-12-01

We report on the status of the Orange County Real-Time GPS Network (OCRTN), an upgrade of the SCIGN sites in Orange County and Catalina Island to low latency (1 sec), high-rate (1 Hz) data streaming, analysis, and dissemination. The project is a collaborative effort of the California Spatial Reference Center (CSRC) and the Orange County Dept. of Geomatics, with partners from the geophysical community (SCIGN), local and state government, and the private sector. As part of Phase 1 of the project, nine sites are streaming data by dedicated, point-to-point radio modems to a central data server located in Santa Ana. Instantaneous positions are computed for each site. Data are converted from 1 Hz Ashtech binary MBEN format to (1) 1 Hz RTCM format, and (2) decimated (15 sec) RINEX format. A second computer outside a firewall and located in another building at the Orange County's Computer Center is a TCP-based client of RTCM data (messages 18, 19, 3, and 22) from the data server, as well as a TCP-based server of RTCM data to the outside world. An external computer can access the RTCM data from all active sites through an IP socket connection. Data latency, in the best case, is less than 1 sec from real-time. Once a day, the decimated RINEX data are transferred by ftp from the data server to the SOPAC-CSRC archive at Scripps. Data recovery is typically 99-100%. As part of the second phase of the project, the RTCM server provides data to field receivers to perform RTK surveying. On connection to the RTCM server the user gets a list of active stations, and can then choose from which site to retrieve RTCM data. This site then plays the role of the RTK base station and a CDPD-based wireless Internet device plays the role of the normal RTK radio link. If an Internet connection is available, we will demonstrate how the system operates. This system will serve as a prototype for the GPS component of the GPS/seismic displacement meter.

Supporting EarthScope Cyber-Infrastructure with a Modern GPS Science Data System

NASA Astrophysics Data System (ADS)

Webb, F. H.; Bock, Y.; Kedar, S.; Jamason, P.; Fang, P.; Dong, D.; Owen, S. E.; Prawirodirjo, L.; Squibb, M.

2008-12-01

Building on NASA's investment in the measurement of crustal deformation from continuous GPS, we are developing and implementing a Science Data System (SDS) that will provide mature, long-term Earth Science Data Records (ESDR's). This effort supports NASA's Earth Surface and Interiors (ESI) focus area and provide NASA's component to the EarthScope PBO. This multi-year development is sponsored by NASA's Making Earth System data records for Use in Research Environments (MEaSUREs) program. The SDS integrates the generation of ESDRs with data analysis and exploration, product generation, and modeling tools based on daily GPS data that include GPS networks in western North America and a component of NASA's Global GPS Network (GGN) for terrestrial reference frame definition. The system is expandable to multiple regional and global networks. The SDS builds upon mature data production, exploration, and analysis algorithms developed under NASA's REASoN, ACCESS, and SENH programs. This SDS provides access to positions, time series, velocity fields, and strain measurements derived from continuous GPS data obtained at tracking stations in both the Plate Boundary Observatory and other regional Western North America GPS networks, dating back to 1995. The SDS leverages the IT and Web Services developments carried out under the SCIGN/REASoN and ACCESS projects, which have streamlined access to data products for researchers and modelers, and which have created a prototype an on-the-fly interactive research environment through a modern data portal, GPS Explorer. This IT system has been designed using modern IT tools and principles in order to be extensible to any geographic location, scale, natural hazard, and combination of geophysical sensor and related data. We have built upon open GIS standards, particularly those of the OGC, and have used the principles of Web Service-based Service Oriented Architectures to provide scalability and extensibility to new services and capabilities.

3D-RTK Capability of Single Gnss Receivers

NASA Astrophysics Data System (ADS)

Stempfhuber, W.

2013-08-01

Small, aerial objects are now being utilised in many areas of civil object capture and monitoring. As a rule, the standard application of a simple GPS receiver with code solutions serves the 3D-positioning of the trajectories or recording positions. Without GPS correction information, these can be calculated at an accuracy of 10-20 metres. Corrected code solutions (DGPS) generally lie in the metre range. A precise 3D-positioning of the UAV (unmanned aerial vehicle) trajectories in the centimetre range provides significant improvements. In addition, the recording time of each sensor can be synchronized with the exact time stamp of the GNSS low-cost system. In recent years, increasing works on positioning from L1 GPS raw data have been published. Along with this, the carrier phase measurements with the established evaluation algorithms are analysed in the post processing method to centimetre-exact positions or to high-precision 3D trajectories [e.g. Schwieger and Gläser, 2005 or Korth and Hofmann 20011]. The use of reference information from local reference stations or a reference network serves the purpose of carrier phase ambiguity resolution. Furthermore, there are many activities worldwide in the area of PPP techniques (Precise Point Positioning). However, dual frequency receivers are primarily used in this instance. Moreover, very long initialisation times must be scheduled for this. A research project on the subject of low-cost RTK GNSS was developed for real-time applications at the Beuth Hochschule für Technik Berlin University of Applied Sciences [Stempfhuber 2012]. The overall system developed for the purpose of real-time applications with centimetre accuracy is modularly constructed and can be used for various applications (http://prof.beuthhochschule.de/stempfhuber/seite-publikation/). With hardware costing a few hundred Euro and a total weight of 500-800 g (including the battery), this system is ideally suited for UAV applications. In addition, the GNSS data processed with the RTK method can be provided in standardised NMEA format. Through the reduced shadowing effects of the aerial objects, GNSS external factors such as multipath cause few problems. With L1 carrier phase analysis, the baseline computation must nevertheless remain limited at the range of a few kilometres. With distances of more than 5 kilometres between the reference station and the rover station position, mistakes arise in the decimetre area. The overall modular system consists of a low-cost, single-frequency receiver (e.g. uBlox LEA4T or 6T receiver), a L1 antenna (e.g. the Trimble Bullet III), a developed data logger including an integrated WLAN communication module for storage and securing of the raw data as well as a power supply. Optimisation of the L1 antenna has shown that, in this instance, many problems relating to signal reception can be reduced. A calibration of the choke-ring adaptors for various antenna calibration facilities results in good and homogeneous antenna parameters. In this situation, the real-time algorithm from the Open Source project RTKLib [Takasu, 2010] generally runs on a small computer at the reference station. In this case, the data transfer from the L1 receiver to the PC is realisable through a serial cable. The rover station can transfer the raw data to the computing algorithm over a WLAN network or through a data radio. Of course, this computational algorithm can also be adapted to an integrated computing module for L1 carrier phase resolutions. The average time to first fix (TTFF) amounts to a few minutes depending on the satellite constellation. Different test series in movement simulators and in moving objects have shown that a stable, fixed solution is achieved with a normal satellite constellation. A test series with a Microdrones quadrocopter could also be conducted. In comparison of the RTK positions with a geodetic dual frequency receiver, differences are in millimetre ranges. In addition, reference systems (based on total stations) are present for the precise examination of the kinematically captured positioning [Eisenbeiss et al. 2009].

Spatio-temporal filtering for determination of common mode error in regional GNSS networks

NASA Astrophysics Data System (ADS)

Bogusz, Janusz; Gruszczynski, Maciej; Figurski, Mariusz; Klos, Anna

2015-04-01

The spatial correlation between different stations for individual components in the regional GNSS networks seems to be significant. The mismodelling in satellite orbits, the Earth orientation parameters (EOP), largescale atmospheric effects or satellite antenna phase centre corrections can all cause the regionally correlated errors. This kind of GPS time series errors are referred to as common mode errors (CMEs). They are usually estimated with the regional spatial filtering, such as the "stacking". In this paper, we show the stacking approach for the set of ASG-EUPOS permanent stations, assuming that spatial distribution of the CME is uniform over the whole region of Poland (more than 600 km extent). The ASG-EUPOS is a multifunctional precise positioning system based on the reference network designed for Poland. We used a 5- year span time series (2008-2012) of daily solutions in the ITRF2008 from Bernese 5.0 processed by the Military University of Technology EPN Local Analysis Centre (MUT LAC). At the beginning of our analyses concerning spatial dependencies, the correlation coefficients between each pair of the stations in the GNSS network were calculated. This analysis shows that spatio-temporal behaviour of the GPS-derived time series is not purely random, but there is the evident uniform spatial response. In order to quantify the influence of filtering using CME, the norms L1 and L2 were determined. The values of these norms were calculated for the North, East and Up components twice: before performing the filtration and after stacking. The observed reduction of the L1 and L2 norms was up to 30% depending on the dimension of the network. However, the question how to define an optimal size of CME-analysed subnetwork remains unanswered in this research, due to the fact that our network is not extended enough.

The Influence of Volcanic Processes on the Distribution of Seismic Velocity Changes at Piton de la Fournaise Volcano (La Reunion)

NASA Astrophysics Data System (ADS)

Sens-Schönfelder, Christoph; Pomponi, Eraldo

2014-05-01

The velocity of seismic waves propagating in the edifice of Piton de la Fournaise volcano (La Reunion) is known to change in response to volcanic eruptions. Here we present a detailed investigation of a the period from end of 2009 until end of 2011 that contains eruptions, non-eruptive intrusions and periods of relaxation and perform a detailed comparison of the associated velocity signals. We use data from by 21 seismograph stations of the IPGP/OVPF seismic network installed on Piton de la Fournaise volcano within the UnderVolc project. Seismic noise of vertical and horizontal components of all possible station pairs is cross-correlated in chunks of 24 hours to obtain daily approximations of Green's functions in order to monitor tiny changes in therein that are related to changes of the elastic properties in the volcano. Velocity changes are measured as apparent stretching of the coda. For some station pairs the apparent velocity changes exceed 1% and a decorrelation of waveforms is observed at the time of volcanic activity. This distorts monitoring results if changes are measured with respect to a global reference. To overcome this we present a method to estimate changes using multiple references that stabilizes the quality of estimated velocity changes. We observe abrupt changes that occur coincident with volcanic events as well as long term transient signals. Using a simple assumption about the spatial sensitivity of our measurements we can map the spatial distribution of velocity changes for selected periods. Comparing these signals with volcanic activity and GPS derived surface displacement we can identify patterns of the velocity changes that appear characteristic for the different types of volcanic activity. We can differentiate intrusive processes associated with inflation and increased seismic activity, periods of relaxation without seismicity and eruptions solely based on the velocity signal. This information can help to assess the processes acting in the volcano by offering an alternative observable to GPS, seismicity and tilt.

Rigidity and definition of Caribbean plate motion from COCONet and campaign GPS observations

NASA Astrophysics Data System (ADS)

Mattioli, Glen; Miller, Jamie; DeMets, Charles; Jansma, Pamela

2014-05-01

The currently accepted kinematic model of the Caribbean plate presented by DeMets et al. (2007) is based on velocities from 6 continuous and 14 campaign GPS sites. COCONet is a multi-hazard GPS-Met observatory, which extends the existing infrastructure of the Plate Boundary Observatory in North America into the Caribbean basin. In 2010, UNAVCO in collaboration with UCAR, was funded by NSF to design, build, and initially maintain a network of 50 new cGPS/Met sites and include data from another 50 existing sites in the Caribbean region. The current COCONet siting plan calls for 46 new stations, 21 refurbished stations, and 77 existing stations across 26 nations in the Caribbean region. Data from all COCONet sites flow into the UNAVCO archive and are processed by the PBO analysis centers and are also processed independently by the UTA Geodesy Lab using GIPSY-OASISII (v.6.2) using an absolute point positioning strategy and final, precise orbits, clocks, and Earth orientation parameters from JPL in the IGS08 frame. We present here our refined estimate of Caribbean plate motion by evaluating data from an expanded number of stations with an improved spatial distribution. In order to better constrain the eastern margin of the plate near the Lesser Antilles subduction interface, campaign GPS observations have been collected on the island of Dominica over the last decade. These are combined with additional campaign observations from the western Caribbean, specifically from Honduras and Nicaragua. We have analyzed a total of 117 sites from the Caribbean region, including campaign data and the data from the cGPS stations that comprise COCONet. An updated velocity field for the Caribbean plate is presented and an inversion of the velocities for 24 sites yields a plate angular velocity that differs from previously published models. Our best fitting inversion to GPS velocities from these 24 sites suggests that 2-plate model for the Caribbean is required to fit the GPS observations, which implies that the Caribbean is undergoing modest (1-3 mm/yr) deformation within its interior. Some sites in the western Caribbean included in our analysis may be biased by small, but significant coseismic deformation, which has not been removed from the site velocities used in our inversion to define Caribbean motion and rigidity. Scenarios for possible east-west deformation accommodated across the Lower Nicaraguan Rise and Beata Ridge will be presented.

Topo-Iberia GPS network: installation complete

NASA Astrophysics Data System (ADS)

Khazaradze, G.

2009-04-01

As part of the project, titled "Geociencias en Iberia: Estudios integrados de topografía y evolución 4D: Topo-Iberia", we have established a network of 26 continuous GPS stations, covering the Spanish part of the Iberian Peninsula (22 stations) and Morocco (4 stations). A major objective behind the establishment of this array is to monitor millimeter level deformation of the crust due to the collision of African and Eurasian (including Iberian) tectonic plates. More specific goals of the project include the identification of the areas and/or specific seismic faults which exhibit higher deformation rates, which could imply an increased seismic hazard in these specific areas. The network has been designed as two X-shaped transects crossing the peninsula from NE to SW and NW to SE, with relatively coarse distribution of the stations, superimposed with denser coverage in the seismically active areas of the Betics, Pyrenees and Cantabrian chains. The majority of the built monuments consist of 1.5-1.8 m tall concrete pillars of 40 cm in diameter anchored to the bedrock using iron rebars. One station in Huesca was built according the UNAVCO's short drilled braced monument (SDBM) specifications. All the monuments were equipped with the SCIGN leveling mounts to ensure the precise antenna alignment and re-alignment in case of the antenna replacement, as well as, tamper resistance of the monument mark. In places were the snow accumulation was possible the antennas were covered with plastic radomes. The instrumentation used is Trimble NetRS dual-frequency receivers with choke-ring antennas. The communication is mainly via cellular telephone system. As of December 2008, the network installation has been competed and all the stations are fully operational. Here we report the milestones of the installation of the network and, as well as, present the first preliminary results of the analysis of the data. Besides the newly established Topo-Iberia CGPS stations, we have included in our daily analysis the data from the selected IGS and EUREF stations located within the region of our interest. In our analysis we also include data from the regional GPS network in Spain: CATNET in Catalonia, ERVA in Valencia, RAP in Andalucía and several other stations from Rioja, Basque country and Castilla León. The GPS data were analyzed using GAMIT/GLOBK software from MIT employing a network mode, where all the stations (including IGS continuous GPS sites) are analyzed simultaneously, followed by carrier phase ambiguity resolution. The work has been supported by the Spanish Ministry of Science and Innovation project: Topo-Iberia (CSD2006-00041).

Development of a System to Generate Near Real Time Tropospheric Delay and Precipitable Water Vapor in situ at Geodetic GPS Stations, to Improve Forecasting of Severe Weather Events

NASA Astrophysics Data System (ADS)

Moore, A. W.; Bock, Y.; Geng, J.; Gutman, S. I.; Laber, J. L.; Morris, T.; Offield, D. G.; Small, I.; Squibb, M. B.

2012-12-01

We describe a system under development for generating ultra-low latency tropospheric delay and precipitable water vapor (PWV) estimates in situ at a prototype network of geodetic GPS sites in southern California, and demonstrating their utility in forecasting severe storms commonly associated with flooding and debris flow events along the west coast of North America through infusion of this meteorological data at NOAA National Weather Service (NWS) Forecast Offices and the NOAA Earth System Research Laboratory (ESRL). The first continuous geodetic GPS network was established in southern California in the early 1990s and much of it was converted to real-time (latency <1s) high-rate (1Hz) mode over the following decades. GPS stations are multi-purpose and can also provide estimates of tropospheric zenith delays, which can be converted into mm-accuracy PWV using collocated pressure and temperature measurements, the basis for GPS meteorology (Bevis et al. 1992, 1994; Duan et al. 1996) as implemented by NOAA with a nationwide distribution of about 300 GPS-Met stations providing PW estimates at subhourly resolution currently used in operational weather forecasting in the U.S. We improve upon the current paradigm of transmitting large quantities of raw data back to a central facility for processing into higher-order products. By operating semi-autonomously, each station will provide low-latency, high-fidelity and compact data products within the constraints of the narrow communications bandwidth that often occurs in the aftermath of natural disasters. The onsite ambiguity-resolved precise point positioning solutions are enabled by a power-efficient, low-cost, plug-in Geodetic Module for fusion of data from in situ sensors including GPS and a low-cost MEMS meteorological sensor package. The decreased latency (~5 minutes) PW estimates will provide the detailed knowledge of the distribution and magnitude of PW that NWS forecasters require to monitor and predict severe winter storms, landfalling atmospheric rivers, and summer thunderstorms associated with the North American monsoon. On the national level, the ESRL will evaluate the utility of ultra-low resolution GNSS observations to improve NOAA's warning and forecast capabilities. The overall objective is to better forecast, assess, and mitigate natural hazards through the flow of information from multiple geodetic stations to scientists, mission planners, decision makers, and first responders.

Tomography Reconstruction of Ionospheric Electron Density with Empirical Orthonormal Functions Using Korea GNSS Network

NASA Astrophysics Data System (ADS)

Hong, Junseok; Kim, Yong Ha; Chung, Jong-Kyun; Ssessanga, Nicholas; Kwak, Young-Sil

2017-03-01

In South Korea, there are about 80 Global Positioning System (GPS) monitoring stations providing total electron content (TEC) every 10 min, which can be accessed through Korea Astronomy and Space Science Institute (KASI) for scientific use. We applied the computerized ionospheric tomography (CIT) algorithm to the TEC dataset from this GPS network for monitoring the regional ionosphere over South Korea. The algorithm utilizes multiplicative algebraic reconstruction technique (MART) with an initial condition of the latest International Reference Ionosphere-2016 model (IRI-2016). In order to reduce the number of unknown variables, the vertical profiles of electron density are expressed with a linear combination of empirical orthonormal functions (EOFs) that were derived from the IRI empirical profiles. Although the number of receiver sites is much smaller than that of Japan, the CIT algorithm yielded reasonable structure of the ionosphere over South Korea. We verified the CIT results with NmF2 from ionosondes in Icheon and Jeju and also with GPS TEC at the center of South Korea. In addition, the total time required for CIT calculation was only about 5 min, enabling the exploration of the vertical ionospheric structure in near real time.

May tropospheric noise in satellite radar data affect decision making results?

NASA Astrophysics Data System (ADS)

Bloutsos, Aristeidis; Bekri, Eleni; Moschas, Fanis; Saltogianni, Vasso; Stiros, Stathis; Yannopoulos, Panayotis

2015-04-01

Meteorological and air pollution conditions affect the satellite positioning signals. To investigate the uncertainty introduced in these signals in various meteorological and air pollution conditions, an array of GPS/GNSS stations and another of meteorological and air pollution stations has been established. The study area is expanded next to Patraikos and Corinth Gulf (NW Peloponnisos, Greece), which is characterized by high variability sequences from hot to cold weather, low to high relative humidity and clear to cloudy or/and Sahara dusty atmosphere, as a result of the particular geographical and topographical features of the study area. The GNSS recordings from several stations with very high vertical separation (with altitude up to 1600m and with a gradient of up to 20%) are analyzed in order to control in some extend both the vertical and the horizontal variability of the atmospheric effects, as well as the noise of geodetic recordings. Then, the GPS results will be combined with meteorological and atmospheric pollution data, as well as satellite radar data, in order to evaluate the enhanced troposphere noise in satellite radar and to estimate the magnitude of uncertainty that may cause alterations to decision making results in the management of water and other natural resources. This project takes advantage of GPS stations established in wider study area in the framework of the Corinth Rift Laboratory (http://crlab.eu/) in conjunction to the air pollution and meteorological monitoring stations of the Environmental Engineering Laboratory of the Department of Civil Engineering of the University of Patras. Regarding GPS stations, the project has been partly funded by the PLATO Project of the Greek Secretariat for Research and Technology.

Analysis of South Atlantic Anomaly perturbations on Sentinel-3A Ultra Stable Oscillator. Impact on DORIS phase measurement and DORIS station positioning

NASA Astrophysics Data System (ADS)

Jalabert, Eva; Mercier, Flavien

2018-07-01

DORIS measurements rely on the precise knowledge of the embedded oscillator which is called the Ultra Stable Oscillator (DORIS USO). The important radiations in the South Atlantic Anomaly (SAA) perturb the USO behavior by causing rapid frequency variations when the satellite is flying through the SAA. These variations are not taken into account in standard DORIS processing, since the USO is modelled as a third degree polynomial over 7-10 days. Therefore, there are systematic measurements errors when the satellite passes through SAA. In standard GNSS processing, the clock is directly estimated at each epoch. On Sentinel-3A, the GPS receiver and the DORIS receiver use the same USO. It is thus possible to estimate the behavior of the USO using GPS measurements. This estimated USO behavior can be used in the DORIS processing, instead of the third degree polynomial, hence allowing an estimation of the orbit sensitivity to these USO anomalies. This study shows two main results. First, the SAA effect on the DORIS USO is observed well using GPS measurements. Second, the USO behavior observed with GPS can be used to mitigate the SAA effect. Indeed, when used in Sentinel-3A processing, the resulting DORIS orbit shows improved phase measurements and station positioning for stations inside the SAA (Arequipa and Cachoeira). The phase measurements residuals are improved by up to 10 cm, and station vertical positioning (i.e. on the estimated Up component in the North-East-Up station frame) is improved by up to a few centimeters. However, the orbit itself is not sensitive to the correction because only two stations (out of almost 60) are SAA-sensitive on Sentinel-3A.

Constraining Puerto Rico - Virgin Islands microplate internal deformation with two decades of GPS observations

NASA Astrophysics Data System (ADS)

Lopez, A. M.; Jansma, P. E.; Mattioli, G. S.; James, S. A.; Ihemedu, D.; Quintana, S. M.; Salazar, J. S.

2011-12-01

The Puerto Rico - Virgin Island microplate, a crustal block within the deformation region of the Northern Caribbean Plate Boundary Zone has been monitored with campaign and permanent Global Positioning System stations for almost 20 years. Within this time period a total of 37 sites have been used to describe and quantify internal deformation of the plate and estimate elastic strain accumulation along the key geological bounding features. In June 2011, 12 of the 20 sites that comprise the campaign GPS network in Puerto Rico were re-occupied and their results were merged with at least three years of continuous GPS data from the Puerto Rico - Virgin Islands cGPS network. The remaining 8 in PR sites will be reoccupied soon, while sites from the Virgin Islands were last reoccupied in 2007. All data were processed with v5 of GOAII using an APP strategy. Here we present the latest results of the newly computed velocity field of our mixed network in both North America and Caribbean fixed frames employing the latest IGS05 reference frame and updated satellite orbits, earth orientation, and xfiles from JPL. Of particular importance in this study are the results of a three station transect across the Lajas Valley, the most seismically active area on southwestern Puerto Rico. Relative to a fixed velocity for a campaign site on Isla Magueyes in La Parguera, the southernmost site in the Lajas Valley has a residual motion of -4.38±1.39 and 2.41±2.10 mm/yr in the north and east components, respectively. This suggests that there is SSE-directed shortening across a structure located between these two sites. In contrast, sites near Mayagüez are moving toward SW at ˜2 mm/yr relative to La Parguera. These results demonstrate the PRVI block shows small internal deformation in addition to its generally westward rigid block translation relative the stable interior of the Caribbean plate.

Inflation of Long Valley Caldera from 1 year of continuous GPS observations

NASA Technical Reports Server (NTRS)

Webb, Frank H.; Bursik, Marcus; Dixon, Timothy; Farina, Frederic; Marshall, Grant; Stein, Ross S.

1995-01-01

A permanent Global Positioning System (GPS) receiver at Casa Diablo Hot Springs, Long Valley Caldera, California was installed in January, 1993, and has operated almost continuously since then. The data have been transmitted daily to the Jet Propulsion Laboratory (JPL) for routine analysis with data from the Fiducial Laboratories for an International Natural sciences Network (FLINN) by the JPL FLINN analysis center. Results from these analyses have been used to interpret the on going deformation at Long Valley, with data excluded from periods when the antenna was covered under 2.5 meters of snow and from some periods when Anti Spoofing was enforced on the GPS signal. The remaining time series suggests that uplift of the resurgent dome of Long Valley Caldera during 1993 has been 2.5 +/- 1.1 cm/yr and horizontal motion has been 3.0 +/- 0.7 cm/yr at S53W in a no-net-rotation global reference frame, or 1.5 +/- 0.7 cm/yr at S14W relative to the Sierra Nevada block. These rates are consistent with uplift predicted from frequent horizontal strain measurements. Spectral analysis of the observations suggests that tidal forcing of the magma chamber is not a source of the variability in the 3 dimensional station location. These results suggest that remotely operated, continuously recording GPS receivers could prove to be a reliable tool for volcanic monitoring throughout the world.

Detection of Seismic Precursors Using Distance Metrics Between GPS-TEC and IRI-Plas

NASA Astrophysics Data System (ADS)

Necat Deviren, M.; Gulyaeva, Tamara; Sezen, Umut; Arikan, Feza; Arikan, Orhan

Ionosphere is an important layer of atmosphere that varies under solar, geomagnetic, gravitational and seismic activities. Total Electron Content (TEC) is one of the main observables of ionosphere. International Reference Ionosphere Extended to Plasmasphere (IRI-Plas) is accepted by International Organization for Standardization (ISO) as the standard climatic model. IRI-Plas provides TEC up to GPS satellite height. TEC can be estimated using Global Positioning System (GPS) Networks. In this study, TEC is computed using both IRI-Plas and Turkish National Permanent GPS Network as IONOLAB-TEC. In order to detect seismic precursors, three different distance metrics, namely Symmetric Kullback-Liebler Distance (SKLD), Cross-Correlation Coefficient (CC), and L2-Norm (L2N), are implemented between IONOLAB-TEC and IRI-Plas-TEC values. SKLD is also computed between IONOLAB-TEC Maps and IRI-Plas-TEC Maps over Turkey. Between May 2009 and September 2012, it is observed that SKLD metric indicates a disturbance within the period prior to 10 days of earthquake day. The disturbance in SKLD increases for the range of stations in the neighborhood of the epicenter. For strong earthquakes all of the three distance metrics indicate a disturbance before the earthquake, yet SKLD behaves as a more sensitive precursor for earthquakes larger than magnitude 4. This study is supported by the joint grant of TUBITAK 112E568 and RFBR 13-02-91370-CT_a.

A Terrestrial Reference Frame realised on the observation level using a GPS-LEO satellite constellation

NASA Astrophysics Data System (ADS)

Koenig, Daniel

2018-02-01

Applying a one-step integrated process, i.e. by simultaneously processing all data and determining all satellite orbits involved, a Terrestrial Reference Frame (TRF) consisting of a geometric as well as a dynamic part has been determined at the observation level using the EPOS-OC software of Deutsches GeoForschungsZentrum. The satellite systems involved comprise the Global Positioning System (GPS) as well as the twin GRACE spacecrafts. Applying a novel approach, the inherent datum defect has been overcome empirically. In order not to rely on theoretical assumptions this is done by carrying out the TRF estimation based on simulated observations and using the associated satellite orbits as background truth. The datum defect is identified here as the total of all three translations as well as the rotation about the z-axis of the ground station network leading to a rank-deficient estimation problem. To rectify this singularity, datum constraints comprising no-net translation (NNT) conditions in x, y, and z as well as a no-net rotation (NNR) condition about the z-axis are imposed. Thus minimally constrained, the TRF solution covers a time span of roughly a year with daily resolution. For the geometric part the focus is put on Helmert transformations between the a priori and the estimated sets of ground station positions, and the dynamic part is represented by gravity field coefficients of degree one and two. The results of a reference solution reveal the TRF parameters to be estimated reliably with high precision. Moreover, carrying out a comparable two-step approach using the same data and models leads to parameters and observational residuals of worse quality. A validation w.r.t. external sources shows the dynamic origin to coincide at a level of 5 mm or better in x and y, and mostly better than 15 mm in z. Comparing the derived GPS orbits to IGS final orbits as well as analysing the SLR residuals for the GRACE satellites reveals an orbit quality on the few cm level. Additional TRF test solutions demonstrate that K-Band Range-Rate observations between both GRACE spacecrafts are crucial for accurately estimating the dynamic frame's orientation, and reveal the importance of the NNT- and NNR-conditions imposed for estimating the components of the dynamic geocenter.

A processing centre for the CNES CE-GPS experimentation

NASA Technical Reports Server (NTRS)

Suard, Norbert; Durand, Jean-Claude

1994-01-01

CNES is involved in a GPS (Global Positioning System) geostationary overlay experimentation. The purpose of this experimentation is to test various new techniques in order to select the optimal station synchronization method, as well as the geostationary spacecraft orbitography method. These new techniques are needed to develop the Ranging GPS Integrity Channel services. The CNES experimentation includes three transmitting/receiving ground stations (manufactured by IN-SNEC), one INMARSAT 2 C/L band transponder and a processing center named STE (Station de Traitements de l'Experimentation). Not all the techniques to be tested are implemented, but the experimental system has to include several functions; part of the future system simulation functions, such as a servo-loop function, and in particular a data collection function providing for rapid monitoring of system operation, analysis of existing ground station processes, and several weeks of data coverage for other scientific studies. This paper discusses system architecture and some criteria used in its design, as well as the monitoring function, the approach used to develop a low-cost and short-life processing center in collaboration with a CNES sub-contractor (ATTDATAID), and some results.

Studies on Anthropogenic Impact on Water Quality in Hilo (Hawaii) Bay and Mapping the Study Stations Using Geospatial Technologies

NASA Astrophysics Data System (ADS)

Cartier, A. J.; Williams, M. S.; Adolf, J.; Sriharan, S.

2015-12-01

Hilo Bay has uncharacteristically brown waters compared to other waters found in Hawai'i. The majority of the freshwater entering Hilo Bay is from storm and surface water runoff. The anthropogenic impact on water quality at Hilo Bay is due to sediment entrance, cesspools (Bacteria), and invasive species (Albizia). This poster presentation will focus on the water quality and phytoplankton collected on a weekly basis at a buoy positioned one meter from the shore of Hilo Bay, preserving the phytoplankton intact, concentrating and dehydrating the sample with ethanol, and viewing the phytoplankton with a scanning electron microscope (Hitachi S-3400NII). The GPS (Global Positioning System) points were collected at the sampling stations. Three transects on three separate dates were performed in Hilo Bay with salinity, percent dissolved oxygen, turbidity, secchi depth, temperature, and chlorophyll fluorescence data collected at each sampling station. A consistent trend observed in all transects was as distance from the river increased turbidity decreased and salinity increased. The GPS data on June 30, 2015 showed a major correlation between stations and their distance from shore. There is a decrease in the turbidity but not the temperature for these stations. The GPS points collected on July 7, 2015 at thirteen stations starting with station one being at the shore to the water, showed that the salinity concentration fluctuate noticeably at the first 6 stations. As we proceed further away from the shore, the salinity concentration increases from stations seven through thirteen. The water temperature shows little variation throughout the thirteen stations. The turbidity level was high at the shore and shows a noticeable drop at station thirteen.

UNAVCO-PBO Southwest Region Network Operations

NASA Astrophysics Data System (ADS)

Walls, C. P.; Mann, D.; Basset, A.; Sklar, J.; Jarvis, C.; Pitcher, T.; Lawrence, S.; Greathouse, M.; Feaux, K.

2012-12-01

The UNAVCO Southwest region of the Plate Boundary Observatory manages 470 continuously operating GPS stations located principally along the transform system of the San Andreas Fault, Eastern California Shear Zone and the northern Baja peninsula. In the past year, network uptime averaged 98% with greater than 99% data acquisition. Communications range from CDMA modem (314), radio (100), Vsat (30), DSL/T1/other (25) to manual download (1). Thirty-four stations have WXT520 metpacks. Sixty-four stations stream 1 Hz data over the VRS3Net typically with <0.5 second latency. Over 650 maintenance activities were performed during 341 onsite visits out of approximately 346 engineer field days. Within the past year there have been 7 incidences of minor (attempted theft) to moderate vandalism (solar panel stolen) with one total loss of receiver and communications gear. Security was enhanced at these sites through fencing and more secure station configurations. UNAVCO is working with NOAA to stream real-time GPS and met data from PBO stations with WXT520 meteorological sensors and high rate data communications. These streams support watershed and flood analyses for regional early-warning systems related to NOAA's work with California Department of Water Resources. Network-wide NOAA receives a total of 54 streams including stations in Cascadia. In 2008 PBO became the steward of 209 existing network stations ("Nucleus stations") of which 140 are in the SW region that included SCIGN, BARD, BARGEN stations. Due to the mix of incompatible equipment used between PBO and existing network stations a project was undertaken to standardize existing network GPS stations to PBO specifications by upgrading antenna cabling, power systems and enclosures. In 2012 the Nucleus upgrade project was completed.

GPS-PWV Estimation and Analysis for CGPS Sites Operating in Mexico

NASA Astrophysics Data System (ADS)

Gutierrez, O.; Vazquez, G. E.; Bennett, R. A.; Adams, D. K.

2014-12-01

Eighty permanent Global Positioning System (GPS) tracking stations that belong to several networks spanning Mexico intended for diverse purposes and applications were used to estimate precipitable water vapor (PWV) using measurement series covering the period of 2000-2014. We extracted the GPS-PWV from the ionosphere-free double-difference carrier phase observations, processed using the GAMIT software. The GPS data were processed with a 30 s sampling rate, 15-degree cutoff angle, and precise GPS orbits disseminated by IGS. The time-varying part of the zenith wet delay was estimated using the Global Mapping Function (GMF), while the constant part is evaluated using the Neil tropospheric model. The data reduction to compute the zenith wet delay follows the step piecewise linear strategy, which is subsequently transformed to PWV estimated every 2-hr. Although there exist previous isolated studies for estimating PWV in Mexico, this study is an attempt to perform a more complete and comprehensive analysis of PWV estimation throughout the Mexican territory. Our resulting GPS-based PWV were compared to available PWV values for 30 stations that operate in Mexico and report the PWV to Suominet. This comparison revealed differences of 1 to 2 mm between the GPS-PWV solution and the PWV reported by Suominet. Accurate values of GPS-PWV will help enhance Mexico ability to investigate water vapor advection, convective and frontal rainfall and long-term climate variability.

How and Why to Do VLBI on GPS

NASA Technical Reports Server (NTRS)

Dickey, J. M.

2010-01-01

In order to establish the position of the center of mass of the Earth in the International Celestial Reference Frame, observations of the Global Positioning Satellite (GPS) constellation using the IVS network are important. With a good frame-tie between the coordinates of the IVS telescopes and nearby GPS receivers, plus a common local oscillator reference signal, it should be possible to observe and record simultaneously signals from the astrometric calibration sources and the GPS satellites. The standard IVS solution would give the atmospheric delay and clock offsets to use in analysis of the GPS data. Correlation of the GPS signals would then give accurate orbital parameters of the satellites in the ICRF reference frame, i.e., relative to the positions of the astrometric sources. This is particularly needed to determine motion of the center of mass of the earth along the rotation axis.

DPOD2005: An extension of ITRF2005 for Precise Orbit Determination

NASA Astrophysics Data System (ADS)

Willis, P.; Ries, J. C.; Zelensky, N. P.; Soudarin, L.; Fagard, H.; Pavlis, E. C.; Lemoine, F. G.

2009-09-01

For Precise Orbit Determination of altimetry missions, we have computed a data set of DORIS station coordinates defined for specific time intervals called DPOD2005. This terrestrial reference set is an extension of ITRF2005. However, it includes all new DORIS stations and is more reliable, as we disregard stations with large velocity formal errors as they could contaminate POD computations in the near future. About 1/4 of the station coordinates need to be defined as they do not appear in the original ITRF2005 realization. These results were verified with available DORIS and GPS results, as the integrity of DPOD2005 is almost as critical as its accuracy. Besides station coordinates and velocities, we also provide additional information such as periods for which DORIS data should be disregarded for specific DORIS stations, and epochs of coordinate and velocity discontinuities (related to either geophysical events, equipment problem or human intervention). The DPOD model was tested for orbit determination for TOPEX/Poseidon (T/P), Jason-1 and Jason-2. Test results show DPOD2005 offers improvement over the original ITRF2005, improvement that rapidly and significantly increases after 2005. Improvement is also significant for the early T/P cycles indicating improved station velocities in the DPOD2005 model and a more complete station set. Following 2005 the radial accuracy and centering of the ITRF2005-original orbits rapidly degrades due to station loss.

Three Years of Global Positioning System Experience on International Space Station

NASA Technical Reports Server (NTRS)

Gomez, Susan

2005-01-01

The International Space Station global positioning systems (GPS) receiver was activated in April 2002. Since that time, numerous software anomalies surfaced that had to be worked around. Some of the software problems required waivers, such as the time function, while others required extensive operator intervention, such as numerous power cycles. Eventually, enough anomalies surfaced that the three pieces of code included in the GPS unit have been re-written and the GPS units were upgraded. The technical aspects of the problems are discussed, as well as the underlying causes that led to the delivery of a product that has had numerous problems. The technical aspects of the problems included physical phenomena that were not well understood, such as the affect that the ionosphere would have on the GPS measurements. The underlying causes were traced to inappropriate use of legacy software, changing requirements, inadequate software processes, unrealistic schedules, incorrect contract type, and unclear ownership responsibilities.

Three Years of Global Positioning System Experience on International Space Station

NASA Technical Reports Server (NTRS)

Gomez, Susan

2006-01-01

The International Space Station global positioning system (GPS) receiver was activated in April 2002. Since that time, numerous software anomalies surfaced that had to be worked around. Some of the software problems required waivers, such as the time function, while others required extensive operator intervention, such as numerous power cycles. Eventually enough anomalies surfaced that the three pieces of code included in the GPS unit have been re-written and the GPS units upgraded. The technical aspects of the problems are discussed, as well as the underlying causes that led to the delivery of a product that has had so many problems. The technical aspects of the problems included physical phenomena that were not well understood, such as the affect that the ionosphere would have on the GPS measurements. The underlying causes were traced to inappropriate use of legacy software, changing requirements, inadequate software processes, unrealistic schedules, incorrect contract type, and unclear ownership responsibilities..

Accuracy and coverage of the modernized Polish Maritime differential GPS system

NASA Astrophysics Data System (ADS)

Specht, Cezary

2011-01-01

The DGPS navigation service augments The NAVSTAR Global Positioning System by providing localized pseudorange correction factors and ancillary information which are broadcast over selected marine reference stations. The DGPS service position and integrity information satisfy requirements in coastal navigation and hydrographic surveys. Polish Maritime DGPS system has been established in 1994 and modernized (in 2009) to meet the requirements set out in IMO resolution for a future GNSS, but also to preserve backward signal compatibility of user equipment. Having finalized installation of the new technology L1, L2 reference equipment performance tests were performed.The paper presents results of the coverage modeling and accuracy measuring campaign based on long-term signal analyses of the DGPS reference station Rozewie, which was performed for 26 days in July 2009. Final results allowed to verify the coverage area of the differential signal from reference station and calculated repeatable and absolute accuracy of the system, after the technical modernization. Obtained field strength level area and position statistics (215,000 fixes) were compared to past measurements performed in 2002 (coverage) and 2005 (accuracy), when previous system infrastructure was in operation.So far, no campaigns were performed on differential Galileo. However, as signals, signal processing and receiver techniques are comparable to those know from DGPS. Because all satellite differential GNSS systems use the same transmission standard (RTCM), maritime DGPS Radiobeacons are standardized in all radio communication aspects (frequency, binary rate, modulation), then the accuracy results of differential Galileo can be expected as a similar to DGPS.Coverage of the reference station was calculated based on unique software, which calculate the signal strength level based on transmitter parameters or field signal strength measurement campaign, done in the representative points. The software works based on Baltic sea vector map, ground electric parameters and models atmospheric noise level in the transmission band.

Status and Future Developments of SIRGAS

NASA Astrophysics Data System (ADS)

Fortes, L.; Lauría, E.; Brunini, C.; Amaya, W.; Sanchez, L.; Drewes, H.

2007-05-01

This paper presents the status and future developments of the SIRGAS (Geocentric Reference System for the Americas) project. Since its creation, in 1993, SIRGAS has coordinated two continental GPS campaigns in 1995 an 2000, responsible for the establishment of a very accurate 3D reference frame in the region. First focusing on South America, the project has expanded its scope to Latin America since 2001. Currently the maintenance of the SIRGAS reference frame is carried out through more than 80 continuous operating GNSS (Global Navigation Satellite System) stations available in the region, whose data is officially processed by the International GNSS Service (IGS) Regional Network Associate Analysis Centre for SIRGAS (IGS RNACC-SIR), functioning at the DGFI (Deutsches Geodatisches Forschungsinstitut), in Munich, to generate weekly coordinates and velocity information of each continuous GNSS station. Since October 2006, five additional experimental processing centers - located at the Brazilian Institute of Geography and Statistics (IBGE), National Institute of Statistics, Geography and Informatics of Mexico (INEGI), Military Geographic Institute of Argentina (IGM), University of La Plata (UNLP), Argentina, and Geographic Institute Agustín Codazzi, Colombia (IGAC) - have also been processing data from those stations in order to assume the official processing responsibility in near future. Many Latin American countries have already adopted SIRGAS as their new official reference system. Besides, efforts have been carried out in order to have the national geodetic networks of Central American countries connected to the SIRGAS reference frame, which will be accomplished by a GNSS campaign scheduled for the first semester of 2007. In terms of vertical datum, SIRGAS continues to coordinate with each member country all the necessary efforts towards making the geodetic leveling data available together with gravity information in order to support the computation of geopotential numbers, to be unified in a continental adjustment.

Innovative Navigation Systems to Support Digital Geophysical Mapping

DTIC Science & Technology

2004-02-01

9 Figure 8. Blackhawk/ Applanix GPS/INS System.................................................................10 Figure 9. Figure-Eight Traverse...Vulcan/LaserStation Line-of-sight laser Parsons Trimble INS/GPS DGPS and inertia guidance Blackhawk Applanix INS/GPS DGPS and inertia guidance...The Applanix Positioning and Orientation System for Land Survey (POS/LS) was used for the Phase I work. The system is similar to the Parsons

High Altitude Platforms for Disaster Recovery: Capabilities, Strategies, and Techniques for Providing Emergency Telecommunications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Juan D. Deaton

2008-05-01

Natural disasters and terrorist acts have significant potential to disrupt emergency communication systems. These emergency communication networks include first-responder, cellular, landline, and emergency answering services such as 911, 112, or 999. Without these essential emergency communications capabilities, search, rescue, and recovery operations during a catastrophic event will be severely debilitated. High altitude platforms could be fitted with telecommunications equipment and used to support these critical communications missions once the catastrophic event occurs. With the ability to be continuously on station, HAPs provide excellent options for providing emergency coverage over high-risk areas before catastrophic incidents occur. HAPs could also provide enhancedmore » 911 capabilities using either GPS or reference stations. This paper proposes potential emergency communications architecture and presents a method for estimating emergency communications systems traffic patterns for a catastrophic event.« less

Calibration of Galileo signals for time metrology.

PubMed

Defraigne, Pascale; Aerts, Wim; Cerretto, Giancarlo; Cantoni, Elena; Sleewaegen, Jean-Marie

2014-12-01

Using global navigation satellite system (GNSS) signals for accurate timing and time transfer requires the knowledge of all electric delays of the signals inside the receiving system. GNSS stations dedicated to timing or time transfer are classically calibrated only for Global Positioning System (GPS) signals. This paper proposes a procedure to determine the hardware delays of a GNSS receiving station for Galileo signals, once the delays of the GPS signals are known. This approach makes use of the broadcast satellite inter-signal biases, and is based on the ionospheric delay measured from dual-frequency combinations of GPS and Galileo signals. The uncertainty on the so-determined hardware delays is estimated to 3.7 ns for each isolated code in the L5 frequency band, and 4.2 ns for the ionosphere-free combination of E1 with a code of the L5 frequency band. For the calibration of a time transfer link between two stations, another approach can be used, based on the difference between the common-view time transfer results obtained with calibrated GPS data and with uncalibrated Galileo data. It is shown that the results obtained with this approach or with the ionospheric method are equivalent.

Plate Boundary Observatory GPS Network Status in California

NASA Astrophysics Data System (ADS)

Walls, C. P.; Austin, K. E.; Dittman, T.; Mann, D.; Basset, A.; Turner, R.; Lawrence, S.; Woolace, A. C.; Kasmer, D.; Hodgkinson, K. M.; Feaux, K.; Mattioli, G. S.

2015-12-01

The EarthScope PBO GPS network, funded by the NSF and operated by UNAVCO, is comprised of 599 permanent GPS stations spanning three principal tectonic regimes and is administered by separate management regions (Subduction - Pacific Northwest [91 sites], Extension - East [41 sites], Transform - Southwest [467 sites]). Since the close of construction in September 2008 various enhancements have been implemented through additional funding by the NSF, NOAA, and NASA and in collaboration with stakeholders such as Caltrans, Scripps, and the USGS. Initially, the majority of stations used first generation IP based cellular modems and radios capable of ~10KB/s data rates. The bandwidth limitation was a challenge for regional high-rate data downloads for GPS-seismology and airborne LiDAR surveys, and real-time data flow. Today, only 13 of the original cell modems remain with 297 upgraded cell modems providing 3G/4G/LTE data communications with transfer rates ranging from 80-400 KB/s. Ongoing radio network expansion and upgrades continue to harden communications. 32 VSAT and one manual download site remain. In CA, the network capabilities for 1Hz and 5Hz downloads or real-time streaming are ~95%, ~80% and ~65%, respectively. During the past year, uptime ranged from 94-99% with data return for 15 s data exceeding 99%. Real-time (1 Hz) data from 204 sites are distributed in BINEX and RTCM 2.3/3.1 formats with an average latency of 0.5 s and completion of 86%. A variety of geophysical sensors are co-located with the GPS stations and include: 21 MEMS accelerometers, 31 strong motion and broadband seismometers, 9 borehole strainmeters and 1 long baseline strainmeter. Vaisala meteorological instruments are located at 60 sites of which 38 stream GPS/Met data. In an effort to modernize the network, Trimble NetRS receivers are gradually being replaced with GNSS-capable/enabled receivers and antennas. Today, 11 stations are GLONASS enabled and 84 are GNSS capable.

Re-investigation of slip rate along the southern part of the Sumatran Fault Zone using SuMo GPS network

NASA Astrophysics Data System (ADS)

Hermawan, I.; Lubis, A. M.; Sahputra, R.; Hill, E.; Sieh, K.; Feng, L.; Salman, R.; Hananto, N.

2015-12-01

The Sumatran Fault Zone (SFZ) accommodates a significant component of the strike-slip motion of oblique convergence along the Sumatra subduction zone. Previous studies have suggested that the slip rates of the SFZ increase from south to north. However, recent work shows that the slip rates may not vary along the SFZ [Bradley et al., 2015]. New data are needed to help confirm these results, and to assess slip-rate variability and fault segmentation in more detail. This information is vital for seismic hazard assessment for the region. We have therefore installed and operated the SuMo (Sumatran Fault Monitoring) network, a dense GPS campaign network focused around the SFZ. From 2013-2015 we selected and installed 32 GPS monuments over the southern part of the SFZ. The network comprises of three transects. The first transect is around the location of the great 1900 earthquake, at the Musi segment. Two transects cover the Manna segment, which saw its last great earthquake in 1893, and the Kumering segment, which saw two great earthquakes in 1933 (M 7.5) and 1994 (M 7.0). We have now conducted three GPS campaign surveys for these stations (3-4 days of measurement for each occupation site), and established 5 semi-permanent cGPS stations in the area. The processed data show that the campaigns sites are still too premature to be used for estimating slip rates, but from the preliminary results for the semi-permanent stations we may see our first signal of deformation. More data from future survey campaigns will help us to estimated revised slip rates. In addition to the science goals for our project, we are this year starting a project called "SuMo Goes to School," which will aim to disseminate information on our science to the schools that house the SuMo GPS stations. The SuMo project also achieves capacity building by training students from Bengkulu University in geodesy and campaign GPS survey techniques.

GNSS Monitoring of Deformation within heavy civil infrastructure

NASA Astrophysics Data System (ADS)

Montillet, Jean-Philippe; Melbourne, Timothy; Szeliga, Walter; Schrock, Gavin

2015-04-01

The steady increase in precision simultaneous with the decreasing of continuous GPS monitoring has enabled the deployment of receivers for a host of new activities. Here we discuss the precision obtained from several multi-station installations operated over a five-year period on several heavy civil-engineered structures, including two earthen-fill dams and subsiding highway overpass damaged by seismic shaking. In the past 5 years, the Cascadia Hazards Institute (Pacific Northwest Geodetic Array) at Central Washington University together with the Washington department of public utilities (Land Survey) have been monitoring several structures around Seattle area including two dams (Howard Hansen and Tolt). One aim of this study is to test the use of continuous GNSS in order to detect any deformations due to rapid pool level rises or to monitor the safety of a structure when an Earthquake strikes it. In this study, data is processed using Real Time Kinematic GPS with short baseline (d < 500 m) and GPS daily position (PPP). However, multipath is the most limiting factor on accuracy for very precise positioning applications with GPS. It is very often present indoors and outdoors, especially in narrow valleys with a limited view of the sky. As a result, multipath can amount to an error of a few centimetres. Unfortunately, the accuracy requirements of precision deformation monitoring are generally at the sub centimetre level, which is presently a big challenge on an epoch-by-epoch basis with regular, carrier phase techniques. Thus, it needs to be properly mitigated. In this study, several stations are set up on the dams (4 stations on the Tolt reservoir and 10 stations on the Howard Hansen dam), and spatial filtering can then be used to mitigate multipath. In addition, several signal processing techniques are also investigated (i.e. Empirical mode decomposition, sidereal filtering, adaptive filtering). RTK GPS should allow to monitor rapid deformations, whereas GPS daily position is used to detect long-term deformations such as the pool level rises due to the melting of ice cap on surrounding mountains. Note that RTK measurements are processed with the MIT software TRACK and the GPS daily positions estimated with GAMIT-GLOBK.

Seasonal Water Storage Variations as Impacted by Water Abstractions: Comparing the Output of a Global Hydrological Model with GRACE and GPS Observations

NASA Astrophysics Data System (ADS)

Döll, Petra; Fritsche, Mathias; Eicker, Annette; Müller Schmied, Hannes

2014-11-01

Better quantification of continental water storage variations is expected to improve our understanding of water flows, including evapotranspiration, runoff and river discharge as well as human water abstractions. For the first time, total water storage (TWS) on the land area of the globe as computed by the global water model WaterGAP (Water Global Assessment and Prognosis) was compared to both gravity recovery and climate experiment (GRACE) and global positioning system (GPS) observations. The GRACE satellites sense the effect of TWS on the dynamic gravity field of the Earth. GPS reference points are displaced due to crustal deformation caused by time-varying TWS. Unfortunately, the worldwide coverage of the GPS tracking network is irregular, while GRACE provides global coverage albeit with low spatial resolution. Detrended TWS time series were analyzed by determining scaling factors for mean annual amplitude ( f GRACE) and time series of monthly TWS ( f GPS). Both GRACE and GPS indicate that WaterGAP underestimates seasonal variations of TWS on most of the land area of the globe. In addition, seasonal maximum TWS occurs 1 month earlier according to WaterGAP than according to GRACE on most land areas. While WaterGAP TWS is sensitive to the applied climate input data, none of the two data sets result in a clearly better fit to the observations. Due to the low number of GPS sites, GPS observations are less useful for validating global hydrological models than GRACE observations, but they serve to support the validity of GRACE TWS as observational target for hydrological modeling. For unknown reasons, WaterGAP appears to fit better to GPS than to GRACE. Both GPS and GRACE data, however, are rather uncertain due to a number of reasons, in particular in dry regions. It is not possible to benefit from either GPS or GRACE observations to monitor and quantify human water abstractions if only detrended (seasonal) TWS variations are considered. Regarding GRACE, this is mainly caused by the attenuation of the TWS differences between water abstraction variants due to the filtering required for GRACE TWS. Regarding GPS, station density is too low. Only if water abstractions lead to long-term changes in TWS by depletion or restoration of water storage in groundwater or large surface water bodies, GRACE may be used to support the quantification of human water abstractions.

Rapid bedrock uplift in the Antarctic Peninsula explained by viscoelastic response to recent ice unloading

NASA Astrophysics Data System (ADS)

Nield, Grace A.; Barletta, Valentina R.; Bordoni, Andrea; King, Matt A.; Whitehouse, Pippa L.; Clarke, Peter J.; Domack, Eugene; Scambos, Ted A.; Berthier, Etienne

2014-07-01

Since 1995 several ice shelves in the Northern Antarctic Peninsula have collapsed and triggered ice-mass unloading, invoking a solid Earth response that has been recorded at continuous GPS (cGPS) stations. A previous attempt to model the observation of rapid uplift following the 2002 breakup of Larsen B Ice Shelf was limited by incomplete knowledge of the pattern of ice unloading and possibly the assumption of an elastic-only mechanism. We make use of a new high resolution dataset of ice elevation change that captures ice-mass loss north of 66°S to first show that non-linear uplift of the Palmer cGPS station since 2002 cannot be explained by elastic deformation alone. We apply a viscoelastic model with linear Maxwell rheology to predict uplift since 1995 and test the fit to the Palmer cGPS time series, finding a well constrained upper mantle viscosity but less sensitivity to lithospheric thickness. We further constrain the best fitting Earth model by including six cGPS stations deployed after 2009 (the LARISSA network), with vertical velocities in the range 1.7 to 14.9 mm/yr. This results in a best fitting Earth model with lithospheric thickness of 100-140 km and upper mantle viscosity of 6×1017-2×1018 Pa s - much lower than previously suggested for this region. Combining the LARISSA time series with the Palmer cGPS time series offers a rare opportunity to study the time-evolution of the low-viscosity solid Earth response to a well-captured ice unloading event.

An Introduction to the Tibet cGPS pilot project: TigiCAS

NASA Astrophysics Data System (ADS)

Zhang, Z.; Liu, J.; Galetzka, J.; Avouac, J.; Tapponnier, P.; Zeng, L.; Gan, W.; Shen, Z.; Wang, M.

2007-12-01

The convergence between India and Eurasia is the¡¡prototype of continental collision in action. Compared¡¡to geological history and fault kinematics studies, the present-day, regional pattern of strain-partitioning¡¡is still inadequately known. Among limited geodetic¡¡efforts in the past decade or two, most have been focused¡¡on refining measurements of the current crustal¡¡shortening rate across the Himalaya. The vast region¡¡immediately to the north is sparsely instrumented, with only one continuous GPS station (Lhasa) within¡¡the plateau proper. Campaign stations are few and¡¡ill-positioned, mostly along major roads, providing¡¡poor constraints on present-day slip-rates on individual¡¡active faults. The extant GPS network configuration is thus still insufficient to discriminate between block vs continuum deformation. In November 2006, the¡¡Chinese Academy of Sciences led a pilot program and¡¡installed 6 continuous GPS stations in southern Tibet, crossing the NS-trending normal fault systems and¡¡complementing the Nepal cGPS profiles. We present¡¡here the new sites, preliminary data processing results, and the spatial relationship with ongoing or planned¡¡continuous GPS sites from a couple of other projects. Together with such projects, TigiCAS will provide¡¡a substantial increase in geodetic data in the¡¡Himalayan-Tibet convergent belt in the next few¡¡years, and lead to a better understanding of¡¡contemporary deformation of the region.

Nanosecond-level time synchronization of autonomous radio detector stations for extensive air showers

NASA Astrophysics Data System (ADS)

The Pierre Auger Collaboration

2016-01-01

To exploit the full potential of radio measurements of cosmic-ray air showers at MHz frequencies, a detector timing synchronization within 1 ns is needed. Large distributed radio detector arrays such as the Auger Engineering Radio Array (AERA) rely on timing via the Global Positioning System (GPS) for the synchronization of individual detector station clocks. Unfortunately, GPS timing is expected to have an accuracy no better than about 5 ns. In practice, in particular in AERA, the GPS clocks exhibit drifts on the order of tens of ns. We developed a technique to correct for the GPS drifts, and an independent method is used to cross-check that indeed we reach a nanosecond-scale timing accuracy by this correction. First, we operate a ``beacon transmitter'' which emits defined sine waves detected by AERA antennas recorded within the physics data. The relative phasing of these sine waves can be used to correct for GPS clock drifts. In addition to this, we observe radio pulses emitted by commercial airplanes, the position of which we determine in real time from Automatic Dependent Surveillance Broadcasts intercepted with a software-defined radio. From the known source location and the measured arrival times of the pulses we determine relative timing offsets between radio detector stations. We demonstrate with a combined analysis that the two methods give a consistent timing calibration with an accuracy of 2 ns or better. Consequently, the beacon method alone can be used in the future to continuously determine and correct for GPS clock drifts in each individual event measured by AERA.

Nanosecond-level time synchronization of autonomous radio detector stations for extensive air showers

DOE PAGES

Aab, Alexander

2016-01-29

To exploit the full potential of radio measurements of cosmic-ray air showers at MHz frequencies, a detector timing synchronization within 1 ns is needed. Large distributed radio detector arrays such as the Auger Engineering Radio Array (AERA) rely on timing via the Global Positioning System (GPS) for the synchronization of individual detector station clocks. Unfortunately, GPS timing is expected to have an accuracy no better than about 5 ns. In practice, in particular in AERA, the GPS clocks exhibit drifts on the order of tens of ns. We developed a technique to correct for the GPS drifts, and an independentmore » method used for cross-checks that indeed we reach nanosecond-scale timing accuracy by this correction. First, we operate a “beacon transmitter” which emits defined sine waves detected by AERA antennas recorded within the physics data. The relative phasing of these sine waves can be used to correct for GPS clock drifts. In addition to this, we observe radio pulses emitted by commercial airplanes, the position of which we determine in real time from Automatic Dependent Surveillance Broadcasts intercepted with a software-defined radio. From the known source location and the measured arrival times of the pulses we determine relative timing offsets between radio detector stations. We demonstrate with a combined analysis that the two methods give a consistent timing calibration with an accuracy of 2 ns or better. Consequently, the beacon method alone can be used in the future to continuously determine and correct for GPS clock drifts in each individual event measured by AERA.« less

Station Coordinates Combination Status and Contribution to ITRF2005

NASA Astrophysics Data System (ADS)

Ferland, R.

2007-12-01

Under the auspices of the International GNSS Service (IGS), the Reference Frame Working Group combines at Natural Resources Canada (NRCan) an accurate and consistent set of station coordinates, velocities and Earth Rotation Parameters (ERP) that are updated weekly. The consistency of these parameters is ensured by simultaneously combining them using their full variance-covariance information. The IGS Analysis Centers (ACs) (cod, emr, esa, gfz, jpl, mit, ngs, sio) provide the solutions used in the IGS weekly combination. The Global Network Associates Analysis Centers (GNAAC) (mit, ncl) also generate weekly combined solutions that include consistent station coordinates and ERPs. Those GNAAC solutions are used for comparisons and quality control of the IGS weekly solution. In recent weeks each AC has been contributing between about 50 and 250 station coordinates estimates. The combined product currently approaches 300 stations. Of those, between 40 and 110 are used for the current IGS reference frame realization of the ITRF2005 in each AC solution. The quality of the AC station coordinates solutions has improved significantly since they have started contributing in early 1996. This is due to the densification of the network of stations along with gradual improvements in station hardware and processing software. For recent solutions, the estimated noise (std. dev.) level between the AC weekly solutions and the different combined solutions varies between 1-3mm horizontally and 2-10mm vertically. More details about the statistics, their evolution and differences between the ACs will be presented. IGS weekly station coordinates and ERP combined products have also been contributed to the ITRF2005. Those weekly solutions were all recombined from the original AC contributions, going back to the beginning of 1996. The recombined solutions were edited for known problems (e.g. incorrect antenna heights and outliers). Several stations with short time span were also removed. A list of station coordinates discontinuities was also prepared, in collaboration with several individuals and contributed to the IERS. Since November 5, 2006 (GPS week 1400), the IGS has implemented a realization of ITRF2005. It includes mainly the change from relative to absolute antenna phase centers and an update of the selected reference frame stations for the new realization. An expected change of scale from about 3 ppb to -0.7 ppb caused by the phase center shift was observed.

High-precision coseismic displacement estimation with a single-frequency GPS receiver

NASA Astrophysics Data System (ADS)

Guo, Bofeng; Zhang, Xiaohong; Ren, Xiaodong; Li, Xingxing

2015-07-01

To improve the performance of Global Positioning System (GPS) in the earthquake/tsunami early warning and rapid response applications, minimizing the blind zone and increasing the stability and accuracy of both the rapid source and rupture inversion, the density of existing GPS networks must be increased in the areas at risk. For economic reasons, low-cost single-frequency receivers would be preferable to make the sparse dual-frequency GPS networks denser. When using single-frequency GPS receivers, the main problem that must be solved is the ionospheric delay, which is a critical factor when determining accurate coseismic displacements. In this study, we introduce a modified Satellite-specific Epoch-differenced Ionospheric Delay (MSEID) model to compensate for the effect of ionospheric error on single-frequency GPS receivers. In the MSEID model, the time-differenced ionospheric delays observed from a regional dual-frequency GPS network to a common satellite are fitted to a plane rather than part of a sphere, and the parameters of this plane are determined by using the coordinates of the stations. When the parameters are known, time-differenced ionospheric delays for a single-frequency GPS receiver could be derived from the observations of those dual-frequency receivers. Using these ionospheric delay corrections, coseismic displacements of a single-frequency GPS receiver can be accurately calculated based on time-differenced carrier-phase measurements in real time. The performance of the proposed approach is validated using 5 Hz GPS data collected during the 2012 Nicoya Peninsula Earthquake (Mw 7.6, 2012 September 5) in Costa Rica. This shows that the proposed approach improves the accuracy of the displacement of a single-frequency GPS station, and coseismic displacements with an accuracy of a few centimetres are achieved over a 10-min interval.

GPS PPP-derived precipitable water vapor retrieval based on Tm/Ps from multiple sources of meteorological data sets in China

NASA Astrophysics Data System (ADS)

Zhang, Hongxing; Yuan, Yunbin; Li, Wei; Ou, Jikun; Li, Ying; Zhang, Baocheng

2017-04-01

Weighted mean temperature (Tm) and pressure (Ps) are two parameters of great relevance to precipitable water vapor (PWV) retrieval from global positioning system (GPS) data. However, information about the Tm and Ps cannot be available for those GPS stations that are not colocated with meteorological sensors. To investigate the optimal GPS-PWV retrieval method for China, two enhanced Tm models, GM-Tm (temperature dependent) and GH-Tm (temperature independent), are developed. Additionally, the potentials of the Ps data from the two reanalysis data sets, the National Centers for Environmental Prediction (NCEP)-Department of Energy (DOE) Reanalysis II (NCEP II) and ERA-Interim, and from the empirical model GPT2w for GPS-PWV retrieval are investigated over China. To evaluate the performances of multisources Tm and Ps data for GPS-PWV retrieval, GPS data (2011-2013) collected from 22 stations of the Crustal Movement Observation Network of China (CMONOC) were processed by using the precise point positioning (PPP) technique, estimating the zenith tropospheric delay (ZTD) so as to be subsequently converted to GPS-PWV. The retrieved GPS-PWVs are compared with their counterparts derived from NCEP II and radiosonde data over China. The results show that (1) the GM-Tm model consistently shows the highest accuracy (with root mean square error of 2.3 K), and the GH-Tm model should be selected when temperature observations are not available, and that (2) the performances of Ps from NCEP II and ERA-Interim differ marginally for GPS-PWV retrieval, and significant seasonal variations are found in the agreement between the GPS-PWVs and the PWVs derived from NCEP II and radiosonde data over China.

Forecasting Space Weather-Induced GPS Performance Degradation Using Random Forest

NASA Astrophysics Data System (ADS)

Filjar, R.; Filic, M.; Milinkovic, F.

2017-12-01

Space weather and ionospheric dynamics have a profound effect on positioning performance of the Global Satellite Navigation System (GNSS). However, the quantification of that effect is still the subject of scientific activities around the world. In the latest contribution to the understanding of the space weather and ionospheric effects on satellite-based positioning performance, we conducted a study of several candidates for forecasting method for space weather-induced GPS positioning performance deterioration. First, a 5-days set of experimentally collected data was established, encompassing the space weather and ionospheric activity indices (including: the readings of the Sudden Ionospheric Disturbance (SID) monitors, components of geomagnetic field strength, global Kp index, Dst index, GPS-derived Total Electron Content (TEC) samples, standard deviation of TEC samples, and sunspot number) and observations of GPS positioning error components (northing, easting, and height positioning error) derived from the Adriatic Sea IGS reference stations' RINEX raw pseudorange files in quiet space weather periods. This data set was split into the training and test sub-sets. Then, a selected set of supervised machine learning methods based on Random Forest was applied to the experimentally collected data set in order to establish the appropriate regional (the Adriatic Sea) forecasting models for space weather-induced GPS positioning performance deterioration. The forecasting models were developed in the R/rattle statistical programming environment. The forecasting quality of the regional forecasting models developed was assessed, and the conclusions drawn on the advantages and shortcomings of the regional forecasting models for space weather-caused GNSS positioning performance deterioration.

Proceedings of the Symposium on GPS Applications in Space (2nd) Held in Bedford, Massachusetts on 10-11 October 1989. Volume 1

DTIC Science & Technology

1990-02-13

Freedom GPS Implementation Plans - An Overview, Penny E. Saunders . . . . . .................. 95 Recent Results In High-Precision GPS Orbit Determination...Upperstages" 7. Penny Saunders (NASA Johnson Space Center): "Space Station GPS Implementation Plans and Overview" 12:00 - 13:30 LUNCH NCO Club vii 13...and design. In this phase we plan to do a ground demon- stration to determine experimentally what sort of attitude accuracy we can get from this

BRAD BRDY and BRD1 GPS Station RINEX Files 09-17-2015

DOE Data Explorer

Corne Kreemer

2015-09-17

CSV files with links to RINEX data for stations BRAD and BRDY for all days after those reported previous (i.e., since 21-JAN-2015) Links to websites that show the position time-series of both stations.

UTC Time Transfer for High Frequency Trading Using IS-95 CDMA Base Station Transmissions and IEEE-1588 Precision Time Protocol

DTIC Science & Technology

2010-11-01

CDMA base stations are each synchronized by GPS receivers, they provide an indirect link to GPS system time and UTC time . The major stock...antenna synchronizes the Local Area Network (LAN) to within 10 microseconds of UTC using the IEEE-1588 Precision Time Protocol (PTP). This is an...activities. Understanding and measuring latency on the LAN is key to the success of HFTs. Without precise time synchronization below 1 millisecond

Contemporary Deformation within the Snake River Plain and Northern Basin and Range Province, USA

NASA Astrophysics Data System (ADS)

Payne, S. J.; McCaffrey, R.; King, R. W.

2007-05-01

GPS velocities, earthquakes, faults, and volcanic features are used to evaluate contemporary deformation within the Snake River Plain (SRP) and surrounding northern Basin and Range Province. The SRP is a prominent low- relief physiographic feature that extends from eastern Oregon through southern Idaho and into northwestern Wyoming, USA. The Eastern Snake River Plain (ESRP) is a 400-km long, NE-trending volcanic province that is characterized by bimodal volcanism, which represents the track of the Yellowstone Hotspot currently located in Wyoming. The Western Snake River Plain (WSRP) is a 300-km long, NW-trending graben that extends into eastern Oregon. The WSRP is an extensional basin that formed adjacent to an earlier position of the Yellowstone Hotspot in southern Idaho. Previous geodetic investigations suggest the ESRP and, perhaps the WSRP, have GPS velocities indicative of rigid block motion of the SRP along its physiographic boundaries. GPS data compiled for this study are used to test this hypothesis. Several institutions including the National Geodetic Survey, Idaho National Laboratory, Rensselaer Polytechnic Institute, and University of Utah observed GPS stations from 1994 to 2006 within the SRP and surrounding region. Horizontal velocities show generally consistent N110°W orientations with an average rate of 1.5 ± 0.3 mm/yr (for 11 stations) along most of the ESRP and adjacent northwest Basin and Range, although some Basin and Range velocities are less and may be influenced by post viscoelastic relaxation following the 1983 Mw 6.9 normal-faulting Borah Peak, Idaho earthquake. GPS velocities with an average rate of 1.9 ± 0.3 mm/yr (for 5 stations) change orientation to N95°W at a distance of 190 km from the Yellowstone Hotspot within the southern region of the ESRP and adjacent Basin and Range. Within the WSRP, GPS velocities have an average rate of 2.0 ± 0.5 mm/yr (for 7 stations) and change orientation to N40°W. These GPS velocities are more consistent with those in eastern Oregon, a region that is rotating clockwise relative to North America. To assess possible rotations and strain rates, we invert GPS horizontal velocities, geologic fault slip rates, earthquake-derived fault slip vector azimuths, and volcanic dike extension rates. We interpret GPS velocities to describe the relative motions of coherent regions of consistent strain within the SRP and surrounding Basin and Range Province.

Persistent summit subsidence at Volcán de Colima, México, 1982 1999: strong evidence against Mogi deflation

NASA Astrophysics Data System (ADS)

Murray, John B.; Wooller, Luke K.

2002-09-01

This paper re-examines recent ground-deformation measurements at Volcán de Colima, Mexico, to test the hypothesis that the observed movements are in response to pressure changes within a sub-volcanic magma chamber, as suggested for other volcanoes by [Mogi (1958) Earthq. Res. Inst. 36, 99-134]. Measurements of vertical ground deformation across the summit dome complex of Volcán de Colima from a precise levelling network between 1982 and 1999, together with vertical and horizontal displacements derived from dual-frequency GPS measurements in 1994 and 1997, show continuous subsidence. The deformation pattern derived from the levelling shows that subsidence increases towards the summit. The closest stations to the summit (1.1 km distant) show a mean subsidence rate of 5 mm per year compared to the reference station at 2.3 km distance, which may be subsiding itself. Vertical displacements of individual stations since 1982 show that the subsidence has been fairly continuous. The GPS stations, which are distributed more widely and include some close to the edge of the active dome, confirm summit subsidence. The largest measured value, a decrease of 280 mm, or 93 mm subsidence per year, was obtained at the edge of the dome. Horizontal displacements measured during 1994-1997 also show the largest values at the summit, but these are much smaller than the vertical displacements, with the maximum rate of 23 mm per year recorded close to the dome. It is conclusively shown that these measured movements cannot be due to deflation of a buried Mogi source, as vertical and horizontal displacements for some stations are in contrary directions to those predicted by the model, and there is no consistent pattern to the horizontal movements. We attribute the measured deformation to downslope creep, settling and compaction of the edifice, gravitational spreading, or a combination of these processes.

Strain rate orientations near the Coso Geothermal Field

NASA Astrophysics Data System (ADS)

Ogasa, N. T.; Kaven, J. O.; Barbour, A. J.; von Huene, R.

2016-12-01

Many geothermal reservoirs derive their sustained capacity for heat exchange in large part due to continuous deformation of preexisting faults and fractures that permit permeability to be maintained. Similarly, enhanced geothermal systems rely on the creation of suitable permeability from fracture and faults networks to be viable. Stress measurements from boreholes or earthquake source mechanisms are commonly used to infer the tectonic conditions that drive deformation, but here we show that geodetic data can also be used. Specifically, we quantify variations in the horizontal strain rate tensor in the area surrounding the Coso Geothermal Field (CGF) by analyzing more than two decades of high accuracy differential GPS data from a network of 14 stations from the University of Nevada Reno Geodetic Laboratory. To handle offsets in the data, from equipment changes and coseismic deformation, we segment the data, perform a piecewise linear fit and take the average of each segment's strain rate to determine secular velocities at each station. With respect to North America, all stations tend to travel northwest at velocities ranging from 1 to 10 mm/yr. The nearest station to CGF shows anomalous motion compared to regional stations, which otherwise show a coherent increase in network velocity from the northeast to the southwest. We determine strain rates via linear approximation using GPS velocities in Cartesian reference frame due to the small area of our network. Principal strain rate components derived from this inversion show maximum extensional strain rates of 30 nanostrain/a occur at N87W with compressional strain rates of 37nanostrain/a at N3E. These results generally align with previous stress measurements from borehole breakouts, which indicate the least compressive horizontal principal stress is east-west oriented, and indicative of the basin and range tectonic setting. Our results suggest that the CGF represents an anomaly in the crustal deformation field, which may be influenced by the hydrothermal anomaly and possibly by the geothermal reservoir operations as well.

Contemporary Rigidity of Precambrian and Paleosoic Platform on the Area of Poland on the Base of GPS Data

NASA Astrophysics Data System (ADS)

Kontny, B.; Grzempowski, P.; Bogusz, J.; Jarosinski, M.; Klos, A.

2012-12-01

Now it became obvious in the world literature that Cenozoic intraplate deformations of the Northwestern Eurasia were connected with the Alpine plate collision. However, relations of the Cenozoic intraplate deformations with the contemporary spreading in the north and transcontinental shears along the Tornquist line and Urals must be taken into account as well. On the contrary, in East Europe, periods of the activity being coincident with those in the Caucasus and the phases of the Red Sea opening. It is also evidence that the southern East European craton belongs to the Periarabian collision area. A compression axis orientation was sub latitudinal there, this allows suggestion that the deformations were originated under pressure of the adjacent Urals. According to some authors the present view of unity and rigidity of the Cenozoic Eurasian plate is correct only at the first approximation. In reality, the Eurasian plate represented a time varying kaleidoscope of sub plates that moved at different velocities from the Atlantic-Arctic spreading axis. Contemporary image of the intraplate deformation can be verified on the basis of observations of permanent stations GPS at present. Density the IGS and EPN station on the North-East Eurasian area isn't sufficient to the credible estimation of geokinematics parameters of every sub plates (platforms). But national networks of the GBAS stations, as for example a Polish network ASG-EUPOS, are ensuring the much higher density of measuring stations (average distance between stations of the c 70 km). Stations are located on both sides of the Teisseyre - Tornquist zone, both on East-European Precambrian platform (East European Craton) as well as on West-European Paleozoic platform. Three-year period of permanent GPS observation on ASG-EUPOS stations enabled the estimation of the velocities of the stations with the sufficing accuracy for the geodynamic purposes. It gave the possibility of the evaluation of contemporary rigidity of both of these platforms in the area of the reach the Polish ASG-EPOS network. The authors used CATREF to combine weekly SINEX (Solution Independent Exchange Format) files (results of GNSS data processing of the ASG-EUPOS network in BERNESE 5.0 software) with variance-covariance matrices in order to determine the cumulative solution (by means of coordinates and velocities). Estimated values of the horizontal velocities of the ASG-EUPOS stations in the ITRF2005 reference frame do not differ from the generally known model of the EURA plate movement. Differences with respect to other published results are seen at the level of the intraplate velocities and intraplate deformations. Compression deformations on the area of the Precambrian platform are reaching much considerable values than in the area of the Paleozoic platform. Also a distribution of directions of the maximum compressions is different. At the work an attempt of preliminary interpretation of these results was made.

High rate GPS positioning , JASON altimetry and marine gravimetry : monitoring the Antarctic Circumpolar Current (ACC) through the DRAKE campaigns.

NASA Astrophysics Data System (ADS)

Melachroinos, S. A.; Biancale, R.; Menard, Y.; Sarrailh, M.

2008-12-01

The Drake campaign which took place from Jan 14, 2006 - 08 Feb, 2006 has been a very successful mission in collecting a wide range of GPS and marine gravity data all along JASON altimetry ground track n° 104. The same campaign will be repeated in 2009 along 028 and 104 JASON-2 ground track. The Drake Passage (DP) chokepoint is not only well suited geographically, as the Antarctic Circumpolar Current (ACC) is constricted to its narrowest extent of 700 km, but observations and models suggest that dynamical balances are particular effective in this area. Furthermore the space geodesy observations and their products provided from several altimetry missions (currently operating ENVISAT, JASON 1 and 2, GFO, ERS and other plannified for the future such as Altika, SWOT) require the cross comparison with independent geodetic techniques at the DP. The current experiment comprises a kinematic GPS and marine gravimetry Cal/Val geodetic approach and it aims to : validate with respect to altimetry data and surface models such a kinematic high frequency GPS technique for measuring sea state and sea surface height (SSH), compare the GPS SSH profiles with altimetry mean dynamic topography (MDT) and mean sea surface (MSS) models, give recommendations for future "offshore" Cal/Val activities on the ground tracks of altimeter satellites such as JASON-2, GFO, Altika using the GNSS technology etc. The GPS observations are collected from GPS antennas installed on a wave-rider buoy , aboard the R/V "Polarstern" and from continuous geodetic reference stations in the proximity. We also analyse problems related to the ship's attitude variations in roll, pitch and yaw and a way to correct them. We also give emphasis on the impact of the ship's acceleration profiles on the so called "squat effect" and ways to deal with it. The project will in particular benefit the GOCE mission by proposing to integrate GOCE in the ocean circulation study and validate GOCE products with our independent geodetic data set. The high rate GPS SSH solutions are derived using two different GPS kinematic software, GINS (CNES) and TRACK (MIT).

An Observational Study of Tropical Cyclone Spin-Up in Supertyphoon Jangmi and Hurricane Georges

DTIC Science & Technology

2011-12-01

Reconnaissance Squadron stationed at Keesler Air Force Base in Biloxi, Mississippi, and the National Oceanic and Atmospheric Administration (NOAA) Aircraft...implementation of the National Center for Atmospheric Research (NCAR) Global Positioning System (GPS) dropsonde in specialized boundary-layer...transiting the western Pacific, Gulf of Mexico, and Atlantic Ocean basins. 107 APPENDIX A: NCAR GPS DROPSONDES The Global Positioning System (GPS

Reliability of calculation of the lithosphere deformations in tectonically stable area of Poland based on the GPS measurements

NASA Astrophysics Data System (ADS)

Araszkiewicz, Andrzej; Jarosiński, Marek

2013-04-01

In this research we aimed to check if the GPS observations can be used for calculation of a reliable deformation pattern of the intracontinental lithosphere in seismically inactive areas, such as territory of Poland. For this purpose we have used data mainly from the ASG-EUPOS permanent network and the solutions developed by the MUT CAG team (Military University of Technology: Centre of Applied Geomatics). From the 128 analyzed stations almost 100 are mounted on buildings. Daily observations were processed in the Bernese 5.0 software and next the weekly solutions were used to determine the station velocities expressed in ETRF2000. The strain rates were determined for almost 200 triangles with GPS stations in their corners plotted used Delaunay triangulation. The obtained scattered directions of deformations and highly changeable values of strain rates point to insufficient antennas' stabilization as for geodynamical studies. In order to depict badly stabilized stations we carried out a benchmark test to show what might be the effect of one station drift on deformations in contacting triangles. Based on the benchmark results, from our network we have eliminated the stations which showed deformation pattern characteristic for instable station. After several rounds of strain rate calculations and eliminations of dubious points we have reduced the number of stations down to 60. The refined network revealed more consistent deformation pattern across Poland. Deformations compared with the recent stress field of the study area disclosed good correlation in some places and significant discrepancies in the others, which will be the subject of future research.

A unified analysis of crustal motion in Southern California, 1970-2004: The SCEC crustal motion map

NASA Astrophysics Data System (ADS)

Shen, Z.-K.; King, R. W.; Agnew, D. C.; Wang, M.; Herring, T. A.; Dong, D.; Fang, P.

2011-11-01

To determine crustal motions in and around southern California, we have processed and combined trilateration data collected from 1970 to 1992, VLBI data from 1979 to 1992, and GPS data from 1986 to 2004: a long temporal coverage required in part by the occurrence of several large earthquakes in this region. From a series of solutions for station positions, we have estimated interseismic velocities, coseismic displacements, and postseismic motions. Within the region from 31°N to 38°N. and east to 114°W, the final product includes estimated horizontal velocities for 1009 GPS, 190 trilateration, and 16 VLBI points, with ties between some of these used to stabilize the solution. All motions are relative to the Stable North American Reference Frame (SNARF) as realized through the velocities of 20 GPS stations. This provides a relatively dense set of horizontal velocity estimates, with well-tested errors, for the past quarter century over the plate boundary from 31°N to 36.5°N. These velocities agree well with those from the Plate Boundary Observatory, which apply to a later time period. We also estimated vertical velocities, 533 of which have errors below 2 mm/yr. Most of these velocities are less than 1 mm/yr, but they show 2-4 mm/yr subsidence in the Ventura and Los Angeles basins and in the Salton Trough. Our analysis also included estimates of coseismic and postseismic motions related to the 1992 Landers, 1994 Northridge, 1999 Hector Mine, and 2003 San Simeon earthquakes. Postseismic motions increase logarithmically over time with a time constant of about 10 days, and generally mimic the direction and relative amplitude of the coseismic offsets.

Rapid Ice Loss at Vatnajokull,Iceland Since Late 1990s Constrained by Synthetic Aperture Radar Interferometry

NASA Astrophysics Data System (ADS)

Zhao, W.; Amelung, F.; Dixon, T. H.; Wdowinski, S.

2012-12-01

Synthetic aperture radar interferometry time series is applied over Vatnajokull, Iceland by using 15 years ERS data. Ice loss at Vatnajokull accelerates since late 1990s especially after 21th century. Clear uplift signal due to ice mass loss is detected. The rebound signal is generally linear and increases a little bit after 2000. The relative annual velocity (GPS station 7485 as reference) is about 12 mm/yr at the ice cap edge, which matches the previous studies using GPS. The standard deviation compared to 11 GPS stations in this area is about 2 mm/yr. A relative-value modeling method ignoring the effect of viscous flow is chosen assuming elastic half space earth. The final ice loss estimation - 83 cm/yr - matches the climatology model with ground observations. Small Baseline Subsets is applied for time series analysis. Orbit error coupling with long wavelength phase trend due to horizontal plate motion is removed based on a second polynomial model. For simplicity, we do not consider atmospheric delay in this area because of no complex topography and small-scale turbulence is eliminated well after long-term average when calculating the annual mean velocity. Some unwrapping error still exits because of low coherence. Other uncertainties can be the basic assumption of ice loss pattern and spatial variation of the elastic parameters. It is the first time we apply InSAR time series for ice mass balance study and provide detailed error and uncertainty analysis. The successful of this application proves InSAR as an option for mass balance study and it is also important for validation of different ice loss estimation techniques.

Implementation and testing of the gridded Vienna Mapping Function 1 (VMF1)

NASA Astrophysics Data System (ADS)

Kouba, J.

2008-04-01

The new gridded Vienna Mapping Function (VMF1) was implemented and compared to the well-established site-dependent VMF1, directly and by using precise point positioning (PPP) with International GNSS Service (IGS) Final orbits/clocks for a 1.5-year GPS data set of 11 globally distributed IGS stations. The gridded VMF1 data can be interpolated for any location and for any time after 1994, whereas the site-dependent VMF1 data are only available at selected IGS stations and only after 2004. Both gridded and site-dependent VMF1 PPP solutions agree within 1 and 2 mm for the horizontal and vertical position components, respectively, provided that respective VMF1 hydrostatic zenith path delays (ZPD) are used for hydrostatic ZPD mapping to slant delays. The total ZPD of the gridded and site-dependent VMF1 data agree with PPP ZPD solutions with RMS of 1.5 and 1.8 cm, respectively. Such precise total ZPDs could provide useful initial a priori ZPD estimates for kinematic PPP and regional static GPS solutions. The hydrostatic ZPDs of the gridded VMF1 compare with the site-dependent VMF1 ZPDs with RMS of 0.3 cm, subject to some biases and discontinuities of up to 4 cm, which are likely due to different strategies used in the generation of the site-dependent VMF1 data. The precision of gridded hydrostatic ZPD should be sufficient for accurate a priori hydrostatic ZPD mapping in all precise GPS and very long baseline interferometry (VLBI) solutions. Conversely, precise and globally distributed geodetic solutions of total ZPDs, which need to be linked to VLBI to control biases and stability, should also provide a consistent and stable reference frame for long-term and state-of-the-art numerical weather modeling.

How well can online GPS PPP post-processing services be used to establish geodetic survey control networks?

NASA Astrophysics Data System (ADS)

Ebner, R.; Featherstone, W. E.

2008-09-01

Establishing geodetic control networks for subsequent surveys can be a costly business, even when using GPS. Multiple stations should be occupied simultaneously and post-processed with scientific software. However, the free availability of online GPS precise point positioning (PPP) post-processing services offer the opportunity to establish a whole geodetic control network with just one dual-frequency receiver and one field crew. To test this idea, we compared coordinates from a moderate-sized (~550 km by ~440 km) geodetic network of 46 points over part of south-western Western Australia, which were processed both with the Bernese v5 scientific software and with the CSRS (Canadian Spatial Reference System) PPP free online service. After rejection of five stations where the antenna type was not recognised by CSRS, the PPP solutions agreed on average with the Bernese solutions to 3.3 mm in east, 4.8 mm in north and 11.8 mm in height. The average standard deviations of the Bernese solutions were 1.0 mm in east, 1.2 mm in north and 6.2 mm in height, whereas for CSRS they were 3.9 mm in east, 1.9 mm in north and 7.8 mm in height, reflecting the inherently lower precision of PPP. However, at the 99% confidence level, only one CSRS solution was statistically different to the Bernese solution in the north component, due to a data interruption at that site. Nevertheless, PPP can still be used to establish geodetic survey control, albeit with a slightly lower quality because of the larger standard deviations. This approach may be of particular benefit in developing countries or remote regions, where geodetic infrastructure is sparse and would not normally be established without this approach.

Development and testing of a new ray-tracing approach to GNSS carrier-phase multipath modelling

NASA Astrophysics Data System (ADS)

Lau, Lawrence; Cross, Paul

2007-11-01

Multipath is one of the most important error sources in Global Navigation Satellite System (GNSS) carrier-phase-based precise relative positioning. Its theoretical maximum is a quarter of the carrier wavelength (about 4.8 cm for the Global Positioning System (GPS) L1 carrier) and, although it rarely reaches this size, it must clearly be mitigated if millimetre-accuracy positioning is to be achieved. In most static applications, this may be accomplished by averaging over a sufficiently long period of observation, but in kinematic applications, a modelling approach must be used. This paper is concerned with one such approach: the use of ray-tracing to reconstruct the error and therefore remove it. In order to apply such an approach, it is necessary to have a detailed understanding of the signal transmitted from the satellite, the reflection process, the antenna characteristics and the way that the reflected and direct signal are processed within the receiver. This paper reviews all of these and introduces a formal ray-tracing method for multipath estimation based on precise knowledge of the satellite reflector antenna geometry and of the reflector material and antenna characteristics. It is validated experimentally using GPS signals reflected from metal, water and a brick building, and is shown to be able to model most of the main multipath characteristics. The method will have important practical applications for correcting for multipath in well-constrained environments (such as at base stations for local area GPS networks, at International GNSS Service (IGS) reference stations, and on spacecraft), and it can be used to simulate realistic multipath errors for various performance analyses in high-precision positioning.

Intercontinental time and frequency transfer using a global positioning system timing receiver

NASA Technical Reports Server (NTRS)

Clements, P. A.

1983-01-01

The Deep Space Network (DSN) has a requirement to maintain knowledge of the frequency offset between DSN stations within 3 x 10 to the -13th power and time offset within 10 microseconds. It is further anticipated that in the 1987-1990 era the requirement for knowledge of time offset between DSN stations will be less than 10 nanoseconds. The Jet Propulsion Laboratory (JPL) is using the Global Positioning System (GPS) Space Vehicles, as a development project, to transfer time and frequency over intercontinental distances between stations of the DSN and between the DSN and other agencies. JPL has installed GPS timing receivers at its tracking station near Barstow, California and at its tracking station near Madrid, Spain. The details of the experiment and the data are reported. There is a discussion of the ultimate capabilities of these techniques for meeting the functional requirements of the DSN.

Software Defined GPS Receiver for International Space Station

NASA Technical Reports Server (NTRS)

Duncan, Courtney B.; Robison, David E.; Koelewyn, Cynthia Lee

2011-01-01

JPL is providing a software defined radio (SDR) that will fly on the International Space Station (ISS) as part of the CoNNeCT project under NASA's SCaN program. The SDR consists of several modules including a Baseband Processor Module (BPM) and a GPS Module (GPSM). The BPM executes applications (waveforms) consisting of software components for the embedded SPARC processor and logic for two Virtex II Field Programmable Gate Arrays (FPGAs) that operate on data received from the GPSM. GPS waveforms on the SDR are enabled by an L-Band antenna, low noise amplifier (LNA), and the GPSM that performs quadrature downconversion at L1, L2, and L5. The GPS waveform for the JPL SDR will acquire and track L1 C/A, L2C, and L5 GPS signals from a CoNNeCT platform on ISS, providing the best GPS-based positioning of ISS achieved to date, the first use of multiple frequency GPS on ISS, and potentially the first L5 signal tracking from space. The system will also enable various radiometric investigations on ISS such as local multipath or ISS dynamic behavior characterization. In following the software-defined model, this work will create a highly portable GPS software and firmware package that can be adapted to another platform with the necessary processor and FPGA capability. This paper also describes ISS applications for the JPL CoNNeCT SDR GPS waveform, possibilities for future global navigation satellite system (GNSS) tracking development, and the applicability of the waveform components to other space navigation applications.

Regional biases in absolute sea-level estimates from tide gauge data due to residual unmodeled vertical land movement

NASA Astrophysics Data System (ADS)

King, Matt A.; Keshin, Maxim; Whitehouse, Pippa L.; Thomas, Ian D.; Milne, Glenn; Riva, Riccardo E. M.

2012-07-01

The only vertical land movement signal routinely corrected for when estimating absolute sea-level change from tide gauge data is that due to glacial isostatic adjustment (GIA). We compare modeled GIA uplift (ICE-5G + VM2) with vertical land movement at ˜300 GPS stations located near to a global set of tide gauges, and find regionally coherent differences of commonly ±0.5-2 mm/yr. Reference frame differences and signal due to present-day mass trends cannot reconcile these differences. We examine sensitivity to the GIA Earth model by fitting to a subset of the GPS velocities and find substantial regional sensitivity, but no single Earth model is able to reduce the disagreement in all regions. We suggest errors in ice history and neglected lateral Earth structure dominate model-data differences, and urge caution in the use of modeled GIA uplift alone when interpreting regional- and global- scale absolute (geocentric) sea level from tide gauge data.

Regional application of multi-layer artificial neural networks in 3-D ionosphere tomography

NASA Astrophysics Data System (ADS)

Ghaffari Razin, Mir Reza; Voosoghi, Behzad

2016-08-01

Tomography is a very cost-effective method to study physical properties of the ionosphere. In this paper, residual minimization training neural network (RMTNN) is used in voxel-based tomography to reconstruct of 3-D ionosphere electron density with high spatial resolution. For numerical experiments, observations collected at 37 GPS stations from Iranian permanent GPS network (IPGN) are used. A smoothed TEC approach was used for absolute STEC recovery. To improve the vertical resolution, empirical orthogonal functions (EOFs) obtained from international reference ionosphere 2012 (IRI-2012) used as object function in training neural network. Ionosonde observations is used for validate reliability of the proposed method. Minimum relative error for RMTNN is 1.64% and maximum relative error is 15.61%. Also root mean square error (RMSE) of 0.17 × 1011 (electrons/m3) is computed for RMTNN which is less than RMSE of IRI2012. The results show that RMTNN has higher accuracy and compiles speed than other ionosphere reconstruction methods.

Time Distribution Using SpaceWire in the SCaN Testbed on ISS

NASA Technical Reports Server (NTRS)

Lux, James P.

2012-01-01

A paper describes an approach for timekeeping and time transfer among the devices on the CoNNeCT project s SCaN Testbed. It also describes how the clocks may be synchronized with an external time reference; e.g., time tags from the International Space Station (ISS) or RF signals received by a radio (TDRSS time service or GPS). All the units have some sort of counter that is fed by an oscillator at some convenient frequency. The basic problem in timekeeping is relating the counter value to some external time standard such as UTC. With SpaceWire, there are two approaches possible: one is to just use SpaceWire to send a message, and use an external wire for the sync signal. This is much the same as with the RS- 232 messages and l pps line from a GPS receiver. However, SpaceWire has an additional capability that was added to make it easier - it can insert and receive a special "timecode" word in the data stream.

CORS911:Real-Time Subsidence Monitoring of the Napoleonville Salt Dome Sinkhole Using GPS

NASA Astrophysics Data System (ADS)

Kent, J. D.

2013-12-01

The sinkhole associated with the Napoleonville salt dome in Assumption Parish, Louisiana, threatens the stability of Highway 70 - a state maintained route. To mitigate the potential damaging effects to the highway and address issues of public safety, a program of research and decision support has been implemented to provide long-term measurements of the surface stability using continuous operating GPS reference stations (CORS). Four CORS sites were installed in the vicinity of the sinkhole to measure the horizontal and vertical motions of each site relative to each other and a fixed location outside the study area. Differential motions measured by a integrity monitoring software are summarized for response agencies tasked with ensuring public safety and stability of the Highway, a designated hurricane evacuation route. Implementation experience and intermediate findings will be shared and discussed. Strategies for monitoring random and systematic biases detected in the system are presented. Figure depicting the location of CORS sites used to monitor surface stability along Highway 70 near the Bayou Corne Sinkhole.

IGS14/igs14.atx: a new Framework for the IGS Products

NASA Astrophysics Data System (ADS)

Rebischung, P.; Schmid, R.

2016-12-01

The International GNSS Service (IGS) is about to switch to a new reference frame (IGS14), based on the latest release of the International Terrestrial Reference Frame (ITRF2014), as the basis for its products. An updated set of satellite and ground antenna calibrations (igs14.atx) will become effective at the same time. IGS14 and igs14.atx will then replace the previous IGS08/igs08.atx framework in use since GPS week 1632 (17 April 2011) and in the second IGS reprocessing campaign (repro2). Despite the negligible scale difference between ITRF2008 and ITRF2014 (0.02 ppb), the radial components of all GPS and GLONASS satellite antenna phase center offsets (z-PCOs) had to be updated in igs14.atx, because of modeling changes recently introduced within the IGS that affect the scale of the IGS products. This was achieved by deriving and averaging time series of satellite z-PCO estimates, consistent with the ITRF2014 scale, from the daily repro2 and latest operational SINEX solutions of seven IGS Analysis Centers (ACs). Compared to igs08.atx, igs14.atx includes robot calibrations for 16 additional ground antenna types, so that the percentage of stations with absolute calibrations in the IGS network will reach 90% after the switch. 19 type-mean robot calibrations were also updated thanks to the availability of calibration results for additional antenna samples. IGS14 is basically an extract of well-suited reference frame stations (i.e., with long and stable position time series) from ITRF2014. However, to make the IGS14 station coordinates consistent with the new igs14.atx ground antenna calibrations, position offsets due to the switch from igs08.atx to igs14.atx were derived for all IGS14 stations affected by ground antenna calibration updates and applied to their ITRF2014 coordinates. This presentation will first detail the different steps of the elaboration of IGS14 and igs14.atx. The impact of the switch on GNSS-derived geodetic parameter time series will then be assessed by re-aligning the daily repro2 and latest operational IGS combined SINEX solutions to IGS14/igs14.atx. A particular focus will finally be given to the biases and trends present in the satellite z-PCO time series derived from the daily AC SINEX solutions, and to their interpretation in terms of scale and scale rate of the terrestrial frame.

Sub-nanosecond clock synchronization and precision deep space tracking

NASA Technical Reports Server (NTRS)

Dunn, Charles; Lichten, Stephen; Jefferson, David; Border, James S.

1992-01-01

Interferometric spacecraft tracking is accomplished at the NASA Deep Space Network (DSN) by comparing the arrival time of electromagnetic spacecraft signals to ground antennas separated by baselines on the order of 8000 km. Clock synchronization errors within and between DSN stations directly impact the attainable tracking accuracy, with a 0.3 ns error in clock synchronization resulting in an 11 nrad angular position error. This level of synchronization is currently achieved by observing a quasar which is angularly close to the spacecraft just after the spacecraft observations. By determining the differential arrival times of the random quasar signal at the stations, clock synchronization and propagation delays within the atmosphere and within the DSN stations are calibrated. Recent developments in time transfer techniques may allow medium accuracy (50-100 nrad) spacecraft observations without near-simultaneous quasar-based calibrations. Solutions are presented for a global network of GPS receivers in which the formal errors in clock offset parameters are less than 0.5 ns. Comparisons of clock rate offsets derived from GPS measurements and from very long baseline interferometry and the examination of clock closure suggest that these formal errors are a realistic measure of GPS-based clock offset precision and accuracy. Incorporating GPS-based clock synchronization measurements into a spacecraft differential ranging system would allow tracking without near-simultaneous quasar observations. The impact on individual spacecraft navigation error sources due to elimination of quasar-based calibrations is presented. System implementation, including calibration of station electronic delays, is discussed.

A province-scale block model of Walker Lane and western Basin and Range crustal deformation constrained by GPS observations (Invited)

NASA Astrophysics Data System (ADS)

Hammond, W. C.; Bormann, J.; Blewitt, G.; Kreemer, C.

2013-12-01

The Walker Lane in the western Great Basin of the western United States is an 800 km long and 100 km wide zone of active intracontinental transtension that absorbs ~10 mm/yr, about 20% of the Pacific/North America plate boundary relative motion. Lying west of the Sierra Nevada/Great Valley microplate (SNGV) and adjoining the Basin and Range Province to the east, deformation is predominantly shear strain overprinted with a minor component of extension. The Walker Lane responds with faulting, block rotations, structural step-overs, and has distinct and varying partitioned domains of shear and extension. Resolving these complex deformation patterns requires a long term observation strategy with a dense network of GPS stations (spacing ~20 km). The University of Nevada, Reno operates the 373 station Mobile Array of GPS for Nevada transtension (MAGNET) semi-continuous network that supplements coverage by other networks such as EarthScope's Plate Boundary Observatory, which alone has insufficient density to resolve the deformation patterns. Uniform processing of data from these GPS mega-networks provides a synoptic view and new insights into the kinematics and mechanics of Walker Lane tectonics. We present velocities for thousands of stations with time series between 3 to 17 years in duration aligned to our new GPS-based North America fixed reference frame NA12. The velocity field shows a rate budget across the southern Walker Lane of ~10 mm/yr, decreasing northward to ~7 mm/yr at the latitude of the Mohawk Valley and Pyramid Lake. We model the data with a new block model that estimates rotations and slip rates of known active faults between the Mojave Desert and northern Nevada and northeast California. The density of active faults in the region requires including a relatively large number of blocks in the model to accurately estimate deformation patterns. With 49 blocks, our the model captures structural detail not represented in previous province-scale models, and improves our ability to compare results to geologic fault slip rates. Modeling the kinematics on this scale has the advantages of 1) reducing the impact of poorly constrained boundaries on small geographically limited models, 2) consistent modeling of rotations across major structural step-overs near the Mina deflection and Carson domain, 3) tracking the kinematics of the south-to-north varying budget of Walker Lane deformation by solving for extension in the Basin and Range to the east, and 4) using a contiguous SNGV as a uniform western kinematic boundary condition. We compare contemporary deformation to geologic slip rates and longer term rotation rates estimated from rock paleomagnetism. GPS-derived block rotation rates are somewhat dependent on model regularization, but are generally within 1° per million years, and tend to be slower than published paleomagnetic rotations rates. GPS data, together with neotectonic and rock paleomagnetism studies provide evidence that the relative importance of Walker Lane block rotations and fault slip continues to evolve, giving way to a more through-going system with slower rotation rates and higher slip rates on individual faults.

Monitoring Sea Level At L'Estartit, Spain

NASA Astrophysics Data System (ADS)

Martinez-Benjamin, J.; Ortiz Castellon, M.; Martinez-Garcia, M.; Talaya, J.; Rodriguez Velasco, G.; Perez, B.

2007-12-01

Sea level is an environmental variable which is widely recognised as being important in many scientific disciplines as a control parameter for coastal dynamical processes or climate processes in the coupled atmosphere-ocean systems, as well as engineering applications. A major source of sea-level data are the national networks of coastal tide gauges, in Spain belonging to different institutions as the Instituto Geográfico Nacional (IGN), Puertos del Estado (PE), Instituto Hidrográfico de la Marina (IHM), Ports de la Generalitat, etc. Three Begur Cape experiences on radar altimeter calibration and marine geoid mapping made on 1999, 2000 and 2002 are overviewed. The marine geoid has been used to relate the coastal tide gauge data from l'Estartit harbour to off-shore altimetric data. The necessity to validate and calibrate the satellite's altimeter due to increasing needs in accuracy and long term integrity implies establishing calibration sites with enhanced ground based methods for sea level monitoring. A technical Spanish contribution to the calibration experience has been the design of GPS buoys and GPS catamaran taking in account the University of Colorado at Boulder and Senetosa/Capraia designs. Altimeter calibration is essential to obtain an absolute measure of sea level, as are knowing the instrument's drifts and bias. Specially designed tidegauges are necessary to improve the quality of altimetric data, preferably near the satellite track. Further, due to systematic differences a month instruments onboard different satellites, several in-situ calibrations are essentials to tie their systematic differences. L'Estartit tide gauge is a classical floating tide gauge set up in l'Estartit harbour (NE Spain) in 1990. It provides good quality information about the changes in the sea heights at centimetre level, that is the magnitude of the common tides in theMediterranean. In the framework of a Spanish Space Project, ref:ESP2001- 4534-PE, the instrumentation of sea level measurements as been improved by providing this site with a radar tide gauge and with a continuous GPS station nearby. This will have a significant incidence in the satellite altimeter calibration activities. The radar tide gauge with data recorder and transmitter is a Datamar 3000C with 26 GHz frequency, 1mm resolution, 8º beam width incorporating a GPS receiver for automatic clock synchronization and a Thales Navigation Internet-Enabled GPS Continuous Geodetic Reference Station (iCGRS) with a choke ring antenna. It is intended that the overall system will constitute a CGPS Station of the ESEAS (European Sea Level) and TIGA (GPS Tide Gauge Benchmark Monitoring) networks. A Partenavia P-68 airborne LIDAR campaign carrying an Optech Lidar ALT-3025 has been made in June 2007 to test the potential of Lidar to connect sea level measurements from tide gauges at the coast with satellite (as Jason-1 or Envisat) altimetry measurements offshore. The calibrated airborne Lidar can then be used over ocean to detect the sea surface height. In consequence, the objective is to check that the coastal sea level can be observed with GPS buoys and may be Lidar campaigns for get detailed regional geoid and sea surface topography models for referencing satellite altimeter measurements.

Development of TEC fluctuations in northern and southern hemispheres on the base of GPS observations

NASA Astrophysics Data System (ADS)

Shagimuratov, Irk; Krankowski, Andrzej; Sieradzki, Rafal; Ephishov, I. I.

GPS technique is widely used to study the global structure and dynamics of the ionosphere. In this paper GPS observations carried out at Arctic and Antarctic stations belonging to the IGS network were used to study TEC fluctuations in the high-latitude ionosphere during the ionospheric storms. Dual-frequency GPS phase measurements along individual satellite passes served as raw data. It was shown that ionospheric irregularities of a different scale were devel-oped in the auroral and polar ionosphere. It is a common phenomenon caused phase fluctuations of GPS signals. In November 2009, West Department of IZMIRAN in Kaliningrad (Russia) and University of Warmia and Mazury in Olsztyn (Poland) established computer server for automatic monitoring of these irregularities. The rate of TEC index (ROTI) expressed in TECU/min was used as a measure of TEC fluctuations. During its operation TEC variations related to ionospheric structures of a spatial scale more than 200-300 km were detected. Large-scale ionospheric structures cause an increase in horizontal gradients and difficulties with the carrier phase ambiguity resolution in GPS positioning. In turn, the phase fluctuations can cause cycle-slip effects. At the polar stations, ionospheric structures with TEC enhanced by a factor of 3-5 relative to the background were detected, whereas TEC increased to 5-8 TECU in about 10-15 min. These structures were observed during a storm, as well as during a moderate geomagnetic activity. It can be probably attributed to the polar cap patches. In this study are presented the extended and more detailed analyses of TEC fluctuations in both the northern and southern hemispheres and compare the winter and summer events (November and July 2004 storms). A special attention is given to the features related to TEC fluctuations occur-rence in both hemispheres for conjugated GPS stations. The temporal development of both storms was rather similar. During storms the intensity of irregularities essentially increases and its location expands to equator. Maximal activity of TEC fluctuations took place when IMF Bz component was negative. Storm-time development of TEC fluctuations caused by ionospheric irregularities was controlled by UT. At polar stations TEC fluctuations were more expressed at southern (winter) hemisphere. Over auroral stations the difference of TEC fluctuations oc-currence was less expressed. During storm the strong TEC fluctuations can be registered at subauroral ionosphere (on latitudes lower than 55 CGL). The seasonal effect in this area also took place. Differences and similarities of these storms occurrence of TEC fluctuations with dependence on season are discussed.

Breadth of Scientific Activities and Network Station Specifications in the International GPS Service (IGS)

NASA Technical Reports Server (NTRS)

Moore, A. W.; Neilan, R. E.; Springer, T. A.; Reigber, Ch.

2000-01-01

A strong multipurpose aspect of the International GPS Service (IGS) is revealed by a glance at the titles of current projects and working groups within the IGS: IGS/BIPM Time Transfer Project; Ionosphere Working Group; Troposphere Working Group; International GLONASS Experiment; Working Group on Low-Earth Orbiter Missions; and Tide Gauges, CGPS, and the IGS. The IGS network infrastructure, in large part originally commissioned for geodynamical investigations, has proved to be a valuable asset in developing application-oriented subnetworks whose requirements overlap the characteristics of existing IGS stations and future station upgrades. Issues encountered thus far in the development of multipurpose or multitechnique IGS projects as well as future possibilities will be reviewed.

Establishment of a high accuracy geoid correction model and geodata edge match

NASA Astrophysics Data System (ADS)

Xi, Ruifeng

This research has developed a theoretical and practical methodology for efficiently and accurately determining sub-decimeter level regional geoids and centimeter level local geoids to meet regional surveying and local engineering requirements. This research also provides a highly accurate static DGPS network data pre-processing, post-processing and adjustment method and a procedure for a large GPS network like the state level HRAN project. The research also developed an efficient and accurate methodology to join soil coverages in GIS ARE/INFO. A total of 181 GPS stations has been pre-processed and post-processed to obtain an absolute accuracy better than 1.5cm at 95% of the stations, and at all stations having a 0.5 ppm average relative accuracy. A total of 167 GPS stations in Iowa and around Iowa have been included in the adjustment. After evaluating GEOID96 and GEOID99, a more accurate and suitable geoid model has been established in Iowa. This new Iowa regional geoid model improved the accuracy from a sub-decimeter 10˜20 centimeter to 5˜10 centimeter. The local kinematic geoid model, developed using Kalman filtering, gives results better than third order leveling accuracy requirement with 1.5 cm standard deviation.

NRT Atmospheric Water Vapour Retrieval on the Area of Poland at IGG WUELS AC

NASA Astrophysics Data System (ADS)

Kaplon, Jan; Bosy, Jaroslaw; Sierny, Jan; Hadas, Tomasz; Rohm, Witold; Wilgan, Karina; Ryczywolski, Marcin; Oruba, Artur; Kroszczynski, Krzysztof

2013-04-01

Global Navigation Satellite Systems (GNSS) are designed for positioning, navigation and amongst other possible applications it can also be used to derive information about the state of the atmosphere. Continuous observations from GNSS receivers provide an excellent tool for studying the neutral atmosphere, currently in near real-time. The Near Real-Time (NRT) neutral atmosphere and water vapour distribution models are currently obtained with high resolution from Ground Base Augmentation Systems (GBAS), where reference stations are equipped with GNSS and meteorological sensors. The Poland territory is covered by dense network of GNSS stations in the frame of GBAS system called ASG-EUPOS (www.asgeupos.pl). This system was established in year 2008 by the Head Office of Geodesy and Cartography in the frame of the EUPOS project (www.eupos.org) for providing positioning services. The GNSS data are available from 130 reference stations located in Poland and neighbour countries. The ground meteorological observations in the area of Poland and neighbour countries are available from ASG-EUPOS stations included in EUREF Permanent Network (EPN) stations, airports meteorological stations (METAR messages stations), and stations managed by national Institute of Meteorology and Water Management (SYNOP messages stations). Institute of Geodesy and Geoinformatics (IGG) of Wroclaw University of Environmental and Life Sciences had created permanent NRT service of ZTD (Zenith Total Delay) estimation for the area of Poland from GPS observations called IGGHZG. The first part of the paper presents the methodology of NRT GNSS data processing for ASG-EUPOS stations for ZTD estimation and its comparison to the results coming from EPN ACs and Military University of Technology in Warsaw AC (MUT AC). Second part covers the procedure of IWV (atmospheric Integrated Water Vapour content) estimation at IGG from IGGHZG product and ZHD (Zenith Hydrostatic Delay) derived from Saastamoinen formula (1972) and meteorological observations from ASG-EUPOS stations, SYNOP (synoptic stations network) and METAR (airport meteorological stations). Paper presents comparison of IWV with the results from NWP (Numerical Weather Prediction) models HIRLAM (via EGVAPII - http://egvap.dmi.dk) and COAMPS (via MUT AC) as well.

An Initial Investigation of Ionospheric Gradients for Detection of Ionospheric Disturbances over Turkey

NASA Astrophysics Data System (ADS)

Koroglu, Meltem; Arikan, Feza; Koroglu, Ozan

2015-04-01

Ionosphere is an ionized layer of earth's atmosphere which affect the propagation of radio signals due to highly varying electron density structure. Total Electron Content (TEC) and Slant Total Electron Content (STEC) are convenient measures of total electron density along a ray path. STEC model is given by the line integral of the electron density between the receiver and GPS satellite. TEC and STEC can be estimated by observing the difference between the two GPS signal time delays that have different frequencies L1 (1575 MHz) and L2 (1227 MHz). During extreme ionospheric storms ionospheric gradients becomes larger than those of quiet days since time delays of the radio signals becomes anomalous. Ionosphere gradients can be modeled as a linear semi-infinite wave front with constant propagation speed. One way of computing the ionospheric gradients is to compare the STEC values estimated between two neighbouring GPS stations. In this so-called station-pair method, ionospheric gradients are defined by dividing the difference of the time delays of two receivers, that see the same satellite at the same time period. In this study, ionospheric gradients over Turkey are computed using the Turkish National Permanent GPS Network (TNPGN-Active) between May 2009 and September 2012. The GPS receivers are paired in east-west and north-south directions with distances less than 150 km. GPS-STEC for each station are calculated using IONOLAB-TEC and IONOLAB-BIAS softwares (www.ionolab.org). Ionospheric delays are calculated for each paired station for both L1 and L2 frequencies and for each satellite in view with 30 s time resolution. During the investigation period, different types of geomagnetic storms, Travelling Ionospheric Disturbances (TID), Sudden Ionospheric Disturbances (SID) and various earthquakes with magnitudes between 3 to 7.4 have occured. Significant variations in the structure of station-pair gradients have been observed depending on location of station-pairs, the path of the satellites, strength of the geomagnetic storms and type, depth and magnitude of the earthquakes. For a typical geomagnetic storm the gradients can get as high as 30 mm/km. For the earthquakes, both the magnitude and the structure of the ionospheric delay gradients exhibit strong variability. This study forms a basis for a comprehensive understanding of ionospheric variability for midlatitude GBAS and SBAS systems. This study is supported by a joint grant of TUBITAK 112E568 and RFBR 13-02-91370-CT_a.

Annual variations of monsoon and drought detected by GPS: A case study in Yunnan, China.

PubMed

Jiang, Weiping; Yuan, Peng; Chen, Hua; Cai, Jianqing; Li, Zhao; Chao, Nengfang; Sneeuw, Nico

2017-07-19

The Global Positioning System (GPS) records monsoonal precipitable water vapor (PWV) and vertical crustal displacement (VCD) due to hydrological loading, and can thus be applied jointly to diagnose meteorological and hydrological droughts. We have analyzed the PWV and VCD observations during 2007.0-2015.0 at 26 continuous GPS stations located in Yunnan province, China. We also obtained equivalent water height (EWH) derived from the Gravity Recovery And Climate Experiment (GRACE) and precipitation at these stations with the same period. Then, we quantified the annual variations of PWV, precipitation, EWH and VCD and provided empirical relationships between them. We found that GPS-derived PWV and VCD (positive means downward movement) are in phase with precipitation and GRACE-derived EWH, respectively. The annual signals of VCD and PWV show linearly correlated amplitudes and a two-month phase lag. Furthermore, the results indicate that PWV and VCD anomalies can also be used to explore drought, such as the heavy drought during winter/spring 2010. Our analysis results verify the capability of GPS to monitor monsoon variations and drought in Yunnan and show that a more comprehensive understanding of the characteristics of regional monsoon and drought can be achieved by integrating GPS-derived PWV and VCD with precipitation and GRACE-derived EWH.

Crustal deformations in the Central Mediterranean derived from the WHAT A CAT GPS project.

NASA Astrophysics Data System (ADS)

Kaniuth, K.; Drewes, H.; Stuber, K.; Tremel, H.; Kahler, H.-G.; Peter, Y.; Zerbini, S.; Tonti, G.; Veis, G.; Fagard, H.

1999-03-01

The West Hellenic Arc Tectonics and Calabrian Arc Tectonics (WHAT A CAT) project aimes at monitoring crustal deformations in the Central Mediterranean by repeated GPS campaigns. The data set acquired so far is rather heterogeneous in terms of availability of GPS satellites, performance of the involved receiver systems and quality of the satellites' orbits. The paper presents the velocity estimates achieved using a modified version of the Bernese GPS software. Main characteristic of the solution strategy is the definition of station velocity parameters already on theobservation equation level.

Precision GPS orbit determination strategies for an earth orbiter and geodetic tracking system

NASA Technical Reports Server (NTRS)

Lichten, Stephen M.; Bertiger, Willy I.; Border, James S.

1988-01-01

Data from two 1985 GPS field tests were processed and precise GPS orbits were determined. With a combined carrier phase and pseudorange, the 1314-km repeatability improves substantially to 5 parts in 10 to the 9th (0.6 cm) in the north and 2 parts in 10 to the 8th (2-3 cm) in the other components. To achieve these levels of repeatability and accuracy, it is necessary to fine-tune the GPS solar radiation coefficients and ground station zenith tropospheric delays.

ERP-Variations on Time Scales Between Hours and Months Derived From GNSS Observations

NASA Astrophysics Data System (ADS)

Weber, R.; Englich, S.; Mendes Cerveira, P.

2007-05-01

Current observations gained by the space geodetic techniques, especially VLBI, GPS and SLR, allow for the determination of Earth Rotation Parameters (ERPs - polar motion, UT1/LOD) with unprecedented accuracy and temporal resolution. This presentation focuses on contributions to the ERP recovery provided by satellite navigation systems (primarily GPS). The IGS (International GNSS Service), for example, currently provides daily polar motion with an accuracy of less than 0.1mas and LOD estimates with an accuracy of a few microseconds. To study more rapid variations in polar motion and LOD we established in a first step a high resolution (hourly resolution) ERP-time series from GPS observation data of the IGS network covering the year 2005. The calculations were carried out by means of the Bernese GPS Software V5.0 considering observations from a subset of 113 fairly stable stations out of the IGS05 reference frame sites. From these ERP time series the amplitudes of the major diurnal and semidiurnal variations caused by ocean tides are estimated. After correcting the series for ocean tides the remaining geodetic observed excitation is compared with variations of atmospheric excitation (AAM). To study the sensitivity of the estimates with respect to the applied mapping function we applied both the widely used NMF (Niell Mapping Function) and the VMF1 (Vienna Mapping Function 1). In addition, based on computations covering two months in 2005, the potential improvement due to the use of additional GLONASS data will be discussed.

Microwave-based navigation of femtosatellites using on-off keying

NASA Astrophysics Data System (ADS)

Kamte, Namrata Jagdish

The objective of this research is to validate that a custom-built microchip-scale satellite transmitting a signal modulated with a Pseudo Random Noise code using On-Off Keying, can be tracked. The weak GPS satellite signal is modulated with a Pseudo Random Noise (PRN) code that provides a mathematical gain. Our signal is modulated with the same PRN code using On-Off Keying (OOK) unlike Phase Shift Keying used in GPS satellites. Our goal is to obtain timing and positioning information from the microchip-scale satellite via a ground station using the concepts of PRN encoding and the OOK modulation technique. Decimeter scale satellites, with a mass of 2--6 kilograms, referred to as picosatellites, have been tracked successfully by ground stations. The microchip-scale satellite, called the femtosatellite is smaller with even less mass, at most 100 grams. At this size the satellite can take advantage of small-scale physics to perform maneuver, such as solar pressure, which only slightly perturb large spacecraft. Additionally, the reduced size decreases the cost of launch as compared to the picosatellites. A swarm of such femtosatellites can serve as environmental probes, interplanetary chemists or in-orbit inspectors of the parent spacecraft. In May 2011, NASA's last space shuttle mission STS-134 carried femtosatellites developed by Cornell researchers called "Sprites". The sprites were deployed from the International Space Station but ground stations on Earth failed to track them. In an effort to develop an alternative femtosatellite design, we have built our own femtosatellite prototype. Our femtosatellite prototype contains the AVR microcontroller on an Arduino board. This assembly is connected to a radio transmitter and a custom antenna transmitting a 433 Mhz radio frequency signal. The prototype transmits a PRN code modulated onto the signal using OOK. Our ground station consists of a Universal Software Radio Peripheral (USRP) with a custom antenna for reception of the 433 MHz signal. The USRP is driven by an open source software-defined radio application called GNU Radio. The required components of the signal are extracted from GNU Radio and processed in order to plot the received data. Benchtop testing of these OOK signals has yielded a reception sensitivity of upto 1 microsecond, which translates into a ranging capability similar to that of GPS satellites. We have correlated the received and replica PRN sequences and demonstrated that they match. The correlation can be used to obtain the identity and position of the femtosatellite prototype. This demonstrates the ability to track a femtosatellite signal that is lower than ambient noise, just like the signals broadcast from GPS satellites. Further, we have performed a system analysis and recognized key system behavioral problems. Thus we have determinately developed an optimum femtosatellite prototype and designed a novel positioning signal, providing a stepping- stone in the journey of successful femtosatellite communication.

New advantages of the combined GPS and GLONASS observations for high-latitude ionospheric irregularities monitoring: case study of June 2015 geomagnetic storm

NASA Astrophysics Data System (ADS)

Cherniak, Iurii; Zakharenkova, Irina

2017-05-01

Monitoring, tracking and nowcasting of the ionospheric plasma density disturbances using dual-frequency measurements of the Global Positioning System (GPS) signals are effectively carried out during several decades. Recent rapid growth and modernization of the ground-based segment gives an opportunity to establish a great database consisting of more than 6000 stations worldwide which provide GPS signals measurements with an open access. Apart of the GPS signals, at least two-third of these stations receive simultaneously signals transmitted by another Global Navigation Satellite System (GNSS)—the Russian system GLONASS. Today, GLONASS signal measurements are mainly used in navigation and geodesy only and very rarely for ionosphere research. We present the first results demonstrating advantages of using several independent but compatible GNSS systems like GPS and GLONASS for improvement of the permanent monitoring of the high-latitude ionospheric irregularities. For the first time, the high-resolution two-dimensional maps of ROTI perturbation were made using not only GPS but also GLONASS measurements. We extend the use of the ROTI maps for analyzing ionospheric irregularities distribution. We demonstrate that the meridional slices of the ROTI maps can be effectively used to study the occurrence and temporal evolution of the ionospheric irregularities. The meridional slices of the geographical sectors with a high density of the GPS and GLONASS measurements can represent spatio-temporal dynamics of the intense ionospheric plasma density irregularities with very high resolution, and they can be effectively used for detailed study of the space weather drivers on the processes of the ionospheric irregularities generation, development and their lifetimes. Using a representative database of 5800 ground-based GNSS stations located worldwide, we have investigated the occurrence of the high-latitude ionospheric plasma density irregularities during the geomagnetic storm of June 22-23, 2015.[Figure not available: see fulltext.

Temperature anomalies in the plumes of the August, 18 and August, 29, 2000 eruptions of Miyake Jima volcano (Japan) inferred from delays of GPS waves crossing them.

NASA Astrophysics Data System (ADS)

Houlié, N.; Nercessian, A.; Briole, P.; Murakami, M.

2003-12-01

Using the GAMIT software we processed seventy days of GPS data (30s sampling rate) collected by the GSI at four sites on Miyake Jima volcanic island (Japan) between June 27, 2000 and September 5, 2000. This period includes a large seismic swarm (June 27, 2000 - July 8, 2000) followed by several major paroxysms at the volcano crater (July 9, 10, 14, 15, August 29) producing a 1 km wide caldera. The medium term velocity of the stations coordinates, already published elsewhere, is maximum during the seismic swarm and corresponds to a large dyke intrusion mostly offshore west of the volcano. No anomalies are observed in the time series of the daily GPS coordinates for the days of the paroxysms. An epoch by epoch processing of those days, using a kinematic software shows that there is no deformation during the paroxysms themselves. We then examined epoch by epoch the path delay residuals of the GPS phases at each GPS station during the events. Those delays exceed 200 mm in some cases. As they cannot be explained by a temporal change of the stations coordinates, we conclude that the cause of these delays is the presence of the hot volcanic plume not modeled by the GPS data processing which assumes a homogenous troposphere. We used a classical seismic tomography algorithm (modified to handle 3D + time) to map the path delay anomaly in the plume as a function of time. We interpret the anomalous delays as temperature anomalies in the plume, assuming a normal pressure and a plume saturated in humidity. The maximum average temperature anomaly is 20° , a low value compared to what is currently proposed in the literature. Higher temperature should exist in the inner part of the plume, but the horizontal extension of this hot zone cannot be more than 50-100 m, otherwise the GPS data would detect it.

Semipermanent GPS (SPGPS) as a volcano monitoring tool: Rationale, method, and applications

USGS Publications Warehouse

Dzurisin, Daniel; Lisowski, Michael; Wicks, Charles W.

2017-01-01

Semipermanent GPS (SPGPS) is an alternative to conventional campaign or survey-mode GPS (SGPS) and to continuous GPS (CGPS) that offers several advantages for monitoring ground deformation. Unlike CGPS installations, SPGPS stations can be deployed quickly in response to changing volcanic conditions or earthquake activity such as a swarm or aftershock sequence. SPGPS networks can be more focused or more extensive than CGPS installations, because SPGPS equipment can be moved from station to station quickly to increase the total number of stations observed in a given time period. SPGPS networks are less intrusive on the landscape than CGPS installations, which makes it easier to satisfy land-use restrictions in ecologically sensitive areas. SPGPS observations are preferred over SGPS measurements because they provide better precision with only a modest increase in the amount of time, equipment, and personnel required in the field. We describe three applications of the SPGPS method that demonstrate its utility and flexibility. At the Yellowstone caldera, Wyoming, a 9-station SPGPS network serves to densify larger preexisting networks of CGPS and SGPS stations. At the Three Sisters volcanic center, Oregon, a 14-station SPGPS network complements an SGPS network and extends the geographic coverage provided by 3 CGPS stations permitted under wilderness land-use restrictions. In the Basin and Range province in northwest Nevada, a 6-station SPGPS network has been established in response to a prolonged earthquake swarm in an area with only sparse preexisting geodetic coverage. At Three Sisters, the estimated precision of station velocities based on annual ~ 3 month summertime SPGPS occupations from 2009 to 2015 is approximately half that for nearby CGPS stations. Conversely, SPGPS-derived station velocities are about twice as precise as those based on annual ~ 1 week SGPS measurements. After 5 years of SPGPS observations at Three Sisters, the precision of velocity determinations is estimated to be 0.5 mm/yr in longitude, 0.6 mm/yr in latitude, and 0.8 mm/yr in height. We conclude that an optimal approach to monitoring volcano deformation includes complementary CGPS and SPGPS networks, periodic InSAR observations, and measurements from in situ borehole sensors such as tiltmeters or strainmeters. This comprehensive approach provides the spatial and temporal detail necessary to adequately characterize a complex and evolving deformation pattern. Such information is essential to multi-parameter models of magmatic or tectonic processes that can help to guide research efforts, and also to inform hazards assessments and land-use planning decisions.

Semipermanent GPS (SPGPS) as a volcano monitoring tool: Rationale, method, and applications

NASA Astrophysics Data System (ADS)

Dzurisin, Daniel; Lisowski, Michael; Wicks, Charles W.

2017-09-01

Semipermanent GPS (SPGPS) is an alternative to conventional campaign or survey-mode GPS (SGPS) and to continuous GPS (CGPS) that offers several advantages for monitoring ground deformation. Unlike CGPS installations, SPGPS stations can be deployed quickly in response to changing volcanic conditions or earthquake activity such as a swarm or aftershock sequence. SPGPS networks can be more focused or more extensive than CGPS installations, because SPGPS equipment can be moved from station to station quickly to increase the total number of stations observed in a given time period. SPGPS networks are less intrusive on the landscape than CGPS installations, which makes it easier to satisfy land-use restrictions in ecologically sensitive areas. SPGPS observations are preferred over SGPS measurements because they provide better precision with only a modest increase in the amount of time, equipment, and personnel required in the field. We describe three applications of the SPGPS method that demonstrate its utility and flexibility. At the Yellowstone caldera, Wyoming, a 9-station SPGPS network serves to densify larger preexisting networks of CGPS and SGPS stations. At the Three Sisters volcanic center, Oregon, a 14-station SPGPS network complements an SGPS network and extends the geographic coverage provided by 3 CGPS stations permitted under wilderness land-use restrictions. In the Basin and Range province in northwest Nevada, a 6-station SPGPS network has been established in response to a prolonged earthquake swarm in an area with only sparse preexisting geodetic coverage. At Three Sisters, the estimated precision of station velocities based on annual 3 month summertime SPGPS occupations from 2009 to 2015 is approximately half that for nearby CGPS stations. Conversely, SPGPS-derived station velocities are about twice as precise as those based on annual 1 week SGPS measurements. After 5 years of SPGPS observations at Three Sisters, the precision of velocity determinations is estimated to be 0.5 mm/yr in longitude, 0.6 mm/yr in latitude, and 0.8 mm/yr in height. We conclude that an optimal approach to monitoring volcano deformation includes complementary CGPS and SPGPS networks, periodic InSAR observations, and measurements from in situ borehole sensors such as tiltmeters or strainmeters. This comprehensive approach provides the spatial and temporal detail necessary to adequately characterize a complex and evolving deformation pattern. Such information is essential to multi-parameter models of magmatic or tectonic processes that can help to guide research efforts, and also to inform hazards assessments and land-use planning decisions.

Is Nubia plate rigid? A geodetic study of the relative motion of different cratonic areas within Africa.

NASA Astrophysics Data System (ADS)

Njoroge, M. W.; Malservisi, R.; Hugentobler, U.; Mokhtari, M.; Voytenko, D.

2014-12-01

Plate rigidity is one of the main paradigms of plate tectonics and a fundamental assumption in the definition of a global reference frame as ITRF. Although still far for optimal, the increased GPS instrumentation of the African region can allow us to understand how rigid one of the major plate can be. The presence of diffused band of seismicity, the Cameroon volcanic line, Pan African Kalahari orogenic belt and East Africa Rift suggest the possibility of relative motion among the different regions within the Nubia. The study focuses on the rigidity of Nubia plate. We divide the plate into three regions: Western (West Africa craton plus Nigeria), Central (approximately the region of the Congo craton) and Southern (Kalahari craton plus South Africa) and we utilize Euler Vector formulation to study internal rigidity and eventual relative motion. Developing five different reference frames with different combinations of the 3 regions, we try to understand the presence of the relative motion between the 3 cratons thus the stability of the Nubia plate as a whole. All available GPS stations from the regions are used separately or combined in creation of the reference frames. We utilize continuous stations with at least 2.5 years of data between 1994 and 2014. Given the small relative velocity, it is important to eliminate eventual biases in the analysis and to have a good estimation in the uncertainties of the observed velocities. For this reason we perform our analysis using both Bernese and Gipsy-oasis codes to generate time series for each station. Velocities and relative uncertainties are analyzed using the Allan variance of rate technique, taking in account for colored noise. An analysis of the color of the noise as function of latitude and climatic region is also performed to each time series. Preliminary results indicate a slight counter clockwise motion of West Africa craton with respect to South Africa Kalahari, and South Africa Kalahari-Congo Cratons. In addition, a possible counter clockwise rotation of the South African Kalahari craton with respect to the Nubian plate caused by southward propagation of the East Africa Rift is compatible with the observations. However, the results are at the limit of the statistical significance and within the current velocity uncertainties the Nubia plate appears as single- rigid plate.

Assessing the impact of non-tidal atmospheric loading on a Kalman filter-based terrestrial reference frame

NASA Astrophysics Data System (ADS)

Abbondanza, Claudio; Altamimi, Zuheir; Chin, Toshio; Collilieux, Xavier; Dach, Rolf; Gross, Richard; Heflin, Michael; König, Rolf; Lemoine, Frank; Macmillan, Dan; Parker, Jay; van Dam, Tonie; Wu, Xiaoping

2014-05-01

The International Terrestrial Reference Frame (ITRF) adopts a piece-wise linear model to parameterize regularized station positions and velocities. The space-geodetic (SG) solutions from VLBI, SLR, GPS and DORIS used as input in the ITRF combination process account for tidal loading deformations, but ignore the non-tidal part. As a result, the non-linear signal observed in the time series of SG-derived station positions in part reflects non-tidal loading displacements not introduced in the SG data reduction. In this analysis, we assess the impact of non-tidal atmospheric loading (NTAL) corrections on the TRF computation. Focusing on the a-posteriori approach, (i) the NTAL model derived from the National Centre for Environmental Prediction (NCEP) surface pressure is removed from the SINEX files of the SG solutions used as inputs to the TRF determinations; (ii) adopting a Kalman-filter based approach, two distinct linear TRFs are estimated combining the 4 SG solutions with (corrected TRF solution) and without the NTAL displacements (standard TRF solution). Linear fits (offset and atmospheric velocity) of the NTAL displacements removed during step (i) are estimated accounting for the station position discontinuities introduced in the SG solutions and adopting different weighting strategies. The NTAL-derived (atmospheric) velocity fields are compared to those obtained from the TRF reductions during step (ii). The consistency between the atmospheric and the TRF-derived velocity fields is examined. We show how the presence of station position discontinuities in SG solutions degrades the agreement between the velocity fields and compare the effect of different weighting structure adopted while estimating the linear fits to the NTAL displacements. Finally, we evaluate the effect of restoring the atmospheric velocities determined through the linear fits of the NTAL displacements to the single-technique linear reference frames obtained by stacking the standard SG SINEX files. Differences between the velocity fields obtained restoring the NTAL displacements and the standard stacked linear reference frames are discussed.

The Contribution of the IGS to a Globally Integrated Geodetic Observing System

NASA Astrophysics Data System (ADS)

WEBER, R.

2002-05-01

The dedicated goal of the International GPS Service (IGS) is 'to provide a service to support geodetic and geophysical research activities through GPS data and data products'. To accomplish its mission IGS began routine operations in Jan 1994. Nowadays operations are based on a large number of components like a globally distributed tracking network of about 200 stations, local and regional data centers as well as eight analysis centers. This presentation summarizes the measurement principles of the GPS and GLONASS microwave satellite navigation systems. An overview of current IGS-products will be given and factors limiting the accuracy of these products are discussed. Moreover IGS serves as one of the technique center of the IERS and therefore the delivered products follow designated IERS standards as close as possible. It can be anticipated that the IGS will also play an important role within the framework of an upcoming Globally Integrated Geodetic Observing System. Even today there are a number of scientific crosslinks to other space geodetic techniques and services e.g. to the ILRS in the determination of the geocentre or to the IVS in questions of a temporal and spatial densification of the reference frame. The above-mentioned initiative will strengthen further the cooperation and increase the scientific outcome.

Atmospheric processes in reaction of Northern Sumatra Earthquake sequence Dec 2004-Apr 2005

NASA Astrophysics Data System (ADS)

Ouzounov, D.; Pulinets, S.; Cervone, G.; Singh, R.; Taylor, P.

2005-05-01

This work describes our first results in analyzing data from different and independent sources ûemitted long-wavelength radiation (OLR), surface latent heat flux (SHLF) and GPS Total Electron Content (TEC) collected from ground based (GPS) and satellite TIR (thermal infra-red) data sources (NOAA/AVHRR, MODIS). We found atmosphere and ionosphere anomalies one week prior to both the Sumatra-Andaman Islands earthquake (Dec 26, 2004) and M 8.7 - Northern Sumatra, March 28, 2005. We analyzed 118 days of data from December 1, 2004 through April 1, 2005 for the area (0°-10°,north latitude and 90°-100° east longitude) which included 125 earthquakes with M>5.5. Recent analysis of the continuous OLR from the Earth surface indicates anomalous variations (on top of the atmosphere) prior to a number of medium to large earthquakes. In the case of M 9.0 - Sumatra-Andaman Islands event, compared to the reference fields for the months of December between 2001 and 2004, we found strongly OLR anomalous +80 W/m2 signals (two sigma) along the epicentral area on Dec 21, 2004 five days before the event. In the case of M8.7 March 28, 2005 anomalues signatures over the epicenter appears on March 26 is much weaker (only +20W/m2) and have a different topology. Anomalous values of SHLF associated with M9.0 - Sumatra-Andaman Islands were found on Dec 22, 2005 (SLHF +280Wm2) and less intensity on Mar 23, 2005 (SLHF +180Wm2). Ionospheric variations (GPS/TEC) associated with the Northern Sumatra events were determine by five Regional GPS network stations (COCO, BAKO, NTUS, HYDE and BAST2). For every station time series of the vertical TEC (VTEC) were computed together with correlation with the Dst index. On December 22, four days prior to the M9.0 quake GPS/TEC data reach the monthly maximum for COCO with minor DST activity. For the M 8.7-March 28 event, the increased values of GPS/TEC were observed during four days (March 22-25) in quiet geomagnetic background. Our results need additional validation and the could be explained within the framework of a model of Lithosphere-Atmosphere-Ionosphere coupling, supporting the hypothesis of a relationship between a thermodynamic processes produced by increasing tectonic stresses in the Earth's crust and attendant electro-chemical interactions between the crust and the atmosphere/ionosphere.

Validation of GPS atmospheric water vapor with WVR data in satellite tracking mode

NASA Astrophysics Data System (ADS)

Shangguan, M.; Heise, S.; Bender, M.; Dick, G.; Ramatschi, M.; Wickert, J.

2015-01-01

Slant-integrated water vapor (SIWV) data derived from GPS STDs (slant total delays), which provide the spatial information on tropospheric water vapor, have a high potential for assimilation to weather models or for nowcasting or reconstruction of the 3-D humidity field with tomographic techniques. Therefore, the accuracy of GPS STD is important, and independent observations are needed to estimate the quality of GPS STD. In 2012 the GFZ (German Research Centre for Geosciences) started to operate a microwave radiometer in the vicinity of the Potsdam GPS station. The water vapor content along the line of sight between a ground station and a GPS satellite can be derived from GPS data and directly measured by a water vapor radiometer (WVR) at the same time. In this study we present the validation results of SIWV observed by a ground-based GPS receiver and a WVR. The validation covers 184 days of data with dry and wet humidity conditions. SIWV data from GPS and WVR generally show good agreement with a mean bias of -0.4 kg m-2 and an rms (root mean square) of 3.15 kg m-2. The differences in SIWV show an elevation dependent on an rms of 7.13 kg m-2 below 15° but of 1.76 kg m-2 above 15°. Nevertheless, this elevation dependence is not observed regarding relative deviations. The relation between the differences and possible influencing factors (elevation angles, pressure, temperature and relative humidity) are analyzed in this study. Besides the elevation, dependencies between the atmospheric humidity conditions, temperature and the differences in SIWV are found.

Assessing the Performance of GPS Precise Point Positioning Under Different Geomagnetic Storm Conditions during Solar Cycle 24.

PubMed

Luo, Xiaomin; Gu, Shengfeng; Lou, Yidong; Xiong, Chao; Chen, Biyan; Jin, Xueyuan

2018-06-01

The geomagnetic storm, which is an abnormal space weather phenomenon, can sometimes severely affect GPS signal propagation, thereby impacting the performance of GPS precise point positioning (PPP). However, the investigation of GPS PPP accuracy over the global scale under different geomagnetic storm conditions is very limited. This paper for the first time presents the performance of GPS dual-frequency (DF) and single-frequency (SF) PPP under moderate, intense, and super storms conditions during solar cycle 24 using a large data set collected from about 500 international GNSS services (IGS) stations. The global root mean square (RMS) maps of GPS PPP results show that stations with degraded performance are mainly distributed at high-latitude, and the degradation level generally depends on the storm intensity. The three-dimensional (3D) RMS of GPS DF PPP for high-latitude during moderate, intense, and super storms are 0.393 m, 0.680 m and 1.051 m, respectively, with respect to only 0.163 m on quiet day. RMS errors of mid- and low-latitudes show less dependence on the storm intensities, with values less than 0.320 m, compared to 0.153 m on quiet day. Compared with DF PPP, the performance of GPS SF PPP is inferior regardless of quiet or disturbed conditions. The degraded performance of GPS positioning during geomagnetic storms is attributed to the increased ionospheric disturbances, which have been confirmed by our global rate of TEC index (ROTI) maps. Ionospheric disturbances not only lead to the deteriorated ionospheric correction but also to the frequent cycle-slip occurrence. Statistical results show that, compared with that on quiet day, the increased cycle-slip occurrence are 13.04%, 56.52%, and 69.57% under moderate, intense, and super storms conditions, respectively.

Performance assessment of multi-GNSS real-time PPP over Iran

NASA Astrophysics Data System (ADS)

Abdi, Naser; Ardalan, Alireza A.; Karimi, Roohollah; Rezvani, Mohammad-Hadi

2017-06-01

With the advent of multi-GNSS constellations and thanks to providing the real-time precise products by IGS, multi-GNSS Real-Time PPP has been of special interest to the geodetic community. These products stream in the form of RTCM-SSR through NTRIP broadcaster. In this contribution, we aim at assessing the convergence time and positioning accuracy of Real-Time PPP over Iran by means of GPS, GPS + GLONASS, GPS + BeiDou, and GPS + GLONASS + BeiDou configurations. To this end, RINEX observations of six GNSS stations, within Iranian Permanent GNSS Network (IPGN), over consecutive sixteen days were processed via BKG NTRIP Client (BNC, v 2.12). In the processing steps, the IGS-MGEX broadcast ephemerides (BRDM, provided by TUM/DLR) and the pre-saved CLK93 broadcast corrections stream (provided by CNES) have been used as the satellites known information. The numerical results were compared against the station coordinates obtained from the double-difference solutions by Bernese GPS Software v 5.0. Accordingly, we have found that GPS + BeiDou combination can reduce the convergence time by 27%, 16% and 10% and improve the positioning accuracy by 22%, 18% and 2%, in the north, east and up components, respectively, as compared with the GPS PPP. Additionally, in comparison to the GPS + GLONASS results, GPS + GLONASS + BeiDou combination speeds up the convergence time by 9%, 8% and 9% and enhance the positioning accuracy by 8%, 5% and 6%, in the north, east and up components, respectively. Overall, thanks to the availability of the current BeiDou constellation observations, the considerable decrease in the convergence time on one hand, and the improvement in the positioning accuracy on the other, can verify the efficiency of utilizing multi-GNSS PPP for real-time applications over Iran.

Relative navigation and attitude determination using a GPS/INS integrated system near the International Space Station

NASA Astrophysics Data System (ADS)

Um, Jaeyong

2001-08-01

The Space Integrated GPS/INS (SIGI) sensor is the primary navigation and attitude determination source for the International Space Station (ISS). The SIGI was successfully demonstrated on-orbit for the first time in the SIGI Orbital Attitude Readiness (SOAR) demonstration on the Space Shuttle Atlantis in May 2000. Numerous proximity operations near the ISS have been and will be performed over the lifetime of the Station. The development of an autonomous relative navigation system is needed to improve the safety and efficiency of vehicle operations near the ISS. A hardware simulation study was performed for the GPS-based relative navigation using the state vector difference approach and the interferometric approach in the absence of multipath. The interferometric approach, where the relative states are estimated directly, showed comparable results for a 1 km baseline. One of the most pressing current technical issues is the design of an autonomous relative navigation system in the proximity of the ISS, where GPS signals are blocked and maneuvers happen frequently. An integrated GPS/INS system is investigated for the possibility of a fully autonomous relative navigation system. Another application of GPS measurements is determination of the vehicle's orientation in space. This study used the SOAR experiment data to characterize the SICI's on-orbit performance for attitude determination. A cold start initialization algorithm was developed for integer ambiguity resolution in any initial orientation. The original algorithm that was used in the SIGI had an operational limitation in the integer ambiguity resolution, which was developed for terrestrial applications, and limited its effectiveness in space. The new algorithm was tested using the SOAR data and has been incorporated in the current SIGI flight software. The attitude estimation performance was examined using two different GPS/INS integration algorithms. The GPS/INS attitude solution using the SOAR data was as accurate as 0.06 deg (RMS) in 3-axis with multipath mitigation. Other improvements to the attitude determination algorithm were the development of a faster integer ambiguity resolution method and the incorporation of line bias modeling.

Absolute GPS Positioning Using Genetic Algorithms

NASA Astrophysics Data System (ADS)

Ramillien, G.

A new inverse approach for restoring the absolute coordinates of a ground -based station from three or four observed GPS pseudo-ranges is proposed. This stochastic method is based on simulations of natural evolution named genetic algorithms (GA). These iterative procedures provide fairly good and robust estimates of the absolute positions in the Earth's geocentric reference system. For comparison/validation, GA results are compared to the ones obtained using the classical linearized least-square scheme for the determination of the XYZ location proposed by Bancroft (1985) which is strongly limited by the number of available observations (i.e. here, the number of input pseudo-ranges must be four). The r.m.s. accuracy of the non -linear cost function reached by this latter method is typically ~10-4 m2 corresponding to ~300-500-m accuracies for each geocentric coordinate. However, GA can provide more acceptable solutions (r.m.s. errors < 10-5 m2), even when only three instantaneous pseudo-ranges are used, such as a lost of lock during a GPS survey. Tuned GA parameters used in different simulations are N=1000 starting individuals, as well as Pc=60-70% and Pm=30-40% for the crossover probability and mutation rate, respectively. Statistical tests on the ability of GA to recover acceptable coordinates in presence of important levels of noise are made simulating nearly 3000 random samples of erroneous pseudo-ranges. Here, two main sources of measurement errors are considered in the inversion: (1) typical satellite-clock errors and/or 300-metre variance atmospheric delays, and (2) Geometrical Dilution of Precision (GDOP) due to the particular GPS satellite configuration at the time of acquisition. Extracting valuable information and even from low-quality starting range observations, GA offer an interesting alternative for high -precision GPS positioning.

Predicted Surface Displacements for Scenario Earthquakes in the San Francisco Bay Region

USGS Publications Warehouse

Murray-Moraleda, Jessica R.

2008-01-01

In the immediate aftermath of a major earthquake, the U.S. Geological Survey (USGS) will be called upon to provide information on the characteristics of the event to emergency responders and the media. One such piece of information is the expected surface displacement due to the earthquake. In conducting probabilistic hazard analyses for the San Francisco Bay Region, the Working Group on California Earthquake Probabilities (WGCEP) identified a series of scenario earthquakes involving the major faults of the region, and these were used in their 2003 report (hereafter referred to as WG03) and the recently released 2008 Uniform California Earthquake Rupture Forecast (UCERF). Here I present a collection of maps depicting the expected surface displacement resulting from those scenario earthquakes. The USGS has conducted frequent Global Positioning System (GPS) surveys throughout northern California for nearly two decades, generating a solid baseline of interseismic measurements. Following an earthquake, temporary GPS deployments at these sites will be important to augment the spatial coverage provided by continuous GPS sites for recording postseismic deformation, as will the acquisition of Interferometric Synthetic Aperture Radar (InSAR) scenes. The information provided in this report allows one to anticipate, for a given event, where the largest displacements are likely to occur. This information is valuable both for assessing the need for further spatial densification of GPS coverage before an event and prioritizing sites to resurvey and InSAR data to acquire in the immediate aftermath of the earthquake. In addition, these maps are envisioned to be a resource for scientists in communicating with emergency responders and members of the press, particularly during the time immediately after a major earthquake before displacements recorded by continuous GPS stations are available.

Precise point positioning with the BeiDou navigation satellite system.

PubMed

Li, Min; Qu, Lizhong; Zhao, Qile; Guo, Jing; Su, Xing; Li, Xiaotao

2014-01-08

By the end of 2012, China had launched 16 BeiDou-2 navigation satellites that include six GEOs, five IGSOs and five MEOs. This has provided initial navigation and precise pointing services ability in the Asia-Pacific regions. In order to assess the navigation and positioning performance of the BeiDou-2 system, Wuhan University has built up a network of BeiDou Experimental Tracking Stations (BETS) around the World. The Position and Navigation Data Analyst (PANDA) software was modified to determine the orbits of BeiDou satellites and provide precise orbit and satellite clock bias products from the BeiDou satellite system for user applications. This article uses the BeiDou/GPS observations of the BeiDou Experimental Tracking Stations to realize the BeiDou and BeiDou/GPS static and kinematic precise point positioning (PPP). The result indicates that the precision of BeiDou static and kinematic PPP reaches centimeter level. The precision of BeiDou/GPS kinematic PPP solutions is improved significantly compared to that of BeiDou-only or GPS-only kinematic PPP solutions. The PPP convergence time also decreases with the use of combined BeiDou/GPS systems.

Precise Point Positioning with the BeiDou Navigation Satellite System

PubMed Central

Li, Min; Qu, Lizhong; Zhao, Qile; Guo, Jing; Su, Xing; Li, Xiaotao

2014-01-01

By the end of 2012, China had launched 16 BeiDou-2 navigation satellites that include six GEOs, five IGSOs and five MEOs. This has provided initial navigation and precise pointing services ability in the Asia-Pacific regions. In order to assess the navigation and positioning performance of the BeiDou-2 system, Wuhan University has built up a network of BeiDou Experimental Tracking Stations (BETS) around the World. The Position and Navigation Data Analyst (PANDA) software was modified to determine the orbits of BeiDou satellites and provide precise orbit and satellite clock bias products from the BeiDou satellite system for user applications. This article uses the BeiDou/GPS observations of the BeiDou Experimental Tracking Stations to realize the BeiDou and BeiDou/GPS static and kinematic precise point positioning (PPP). The result indicates that the precision of BeiDou static and kinematic PPP reaches centimeter level. The precision of BeiDou/GPS kinematic PPP solutions is improved significantly compared to that of BeiDou-only or GPS-only kinematic PPP solutions. The PPP convergence time also decreases with the use of combined BeiDou/GPS systems. PMID:24406856

GPS coordinate time series measurements in Ontario and Quebec, Canada

NASA Astrophysics Data System (ADS)

Samadi Alinia, Hadis; Tiampo, Kristy F.; James, Thomas S.

2017-06-01

New precise network solutions for continuous GPS (cGPS) stations distributed in eastern Ontario and western Québec provide constraints on the regional three-dimensional crustal velocity field. Five years of continuous observations at fourteen cGPS sites were analyzed using Bernese GPS processing software. Several different sub-networks were chosen from these stations, and the data were processed and compared to in order to select the optimal configuration to accurately estimate the vertical and horizontal station velocities and minimize the associated errors. The coordinate time series were then compared to the crustal motions from global solutions and the optimized solution is presented here. A noise analysis model with power-law and white noise, which best describes the noise characteristics of all three components, was employed for the GPS time series analysis. The linear trend, associated uncertainties, and the spectral index of the power-law noise were calculated using a maximum likelihood estimation approach. The residual horizontal velocities, after removal of rigid plate motion, have a magnitude consistent with expected glacial isostatic adjustment (GIA). The vertical velocities increase from subsidence of almost 1.9 mm/year south of the Great Lakes to uplift near Hudson Bay, where the highest rate is approximately 10.9 mm/year. The residual horizontal velocities range from approximately 0.5 mm/year, oriented south-southeastward, at the Great Lakes to nearly 1.5 mm/year directed toward the interior of Hudson Bay at stations adjacent to its shoreline. Here, the velocity uncertainties are estimated at less than 0.6 mm/year for the horizontal component and 1.1 mm/year for the vertical component. A comparison between the observed velocities and GIA model predictions, for a limited range of Earth models, shows a better fit to the observations for the Earth model with the smallest upper mantle viscosity and the largest lower mantle viscosity. However, the pattern of horizontal deformation is not well explained in the north, along Hudson Bay, suggesting that revisions to the ice thickness history are needed to improve the fit to observations.

Comparison with IRI-PLUS and IRI-2012-TEC values of GPS-TEC values

NASA Astrophysics Data System (ADS)

Atıcı, Ramazan; Saǧır, Selçuk

2016-07-01

This study presents a comparison with IRI-PLUS and IRI-2012 Total Electron Content (TEC) values of Total Electron Content (TEC) values obtained from Ankara station (39,7 N; 32,76 E) of Global Position System (GPS) of Turkey on equinox and solstice days of 2009 year. For all days, it is observed that GPS-TEC values are greater than IRI-2012-TEC values, while IRI-PLUS-TEC values are very close to GPS-TEC values. When GPS-TEC values for both equinoxes are compared, it is seen that TEC values on September equinox are greater than one on March equinox. However, it is observed that GPS-TEC values on June solstice are greater than one on December solstice. Also, the relationship between GPS-TEC values and geomagnetic indexes is investigated.

Two laboratory methods for the calibration of GPS speed meters

NASA Astrophysics Data System (ADS)

Bai, Yin; Sun, Qiao; Du, Lei; Yu, Mei; Bai, Jie

2015-01-01

The set-ups of two calibration systems are presented to investigate calibration methods of GPS speed meters. The GPS speed meter calibrated is a special type of high accuracy speed meter for vehicles which uses Doppler demodulation of GPS signals to calculate the measured speed of a moving target. Three experiments are performed: including simulated calibration, field-test signal replay calibration, and in-field test comparison with an optical speed meter. The experiments are conducted at specific speeds in the range of 40-180 km h-1 with the same GPS speed meter as the device under calibration. The evaluation of measurement results validates both methods for calibrating GPS speed meters. The relative deviations between the measurement results of the GPS-based high accuracy speed meter and those of the optical speed meter are analyzed, and the equivalent uncertainty of the comparison is evaluated. The comparison results justify the utilization of GPS speed meters as reference equipment if no fewer than seven satellites are available. This study contributes to the widespread use of GPS-based high accuracy speed meters as legal reference equipment in traffic speed metrology.

InSAR tropospheric delay mitigation by GPS observations: A case study in Tokyo area

NASA Astrophysics Data System (ADS)

Xu, Caijun; Wang, Hua; Ge, Linlin; Yonezawa, Chinatsu; Cheng, Pu

2006-03-01

Like other space geodetic techniques, interferometric synthetic aperture radar (InSAR) is limited by the variations of tropospheric delay noise. In this paper, we analyze the double-difference (DD) feature of tropospheric delay noise in SAR interferogram. By processing the ERS-2 radar pair, we find some tropospheric delay fringes, which have similar patterns with the GMS-5 visible-channel images acquired at almost the same epoch. Thirty-five continuous GPS (CGPS) stations are distributed in the radar scene. We analyze the GPS data by GIPSY-OASIS (II) software and extract the wet zenith delay (WZD) parameters at each station at the same epoch with the master and the slave image, respectively. A cosine mapping function is applied to transform the WZD to wet slant delay (WSD) in line-of-sight direction. Based on the DD WSD parameters, we establish a two-dimensional (2D) semi-variogram model, with the parameters 35.2, 3.6 and 0.88. Then we predict the DD WSD parameters by the kriging algorithm for each pixel of the interferogram, and subtract it from the unwrapped phase. Comparisons between CGPS and InSAR range changes in LOS direction show that the root of mean squares (RMS) decreased from 1.33 cm before correction to 0.87 cm after correction. From the result, we can conclude that GPS WZD parameters can be effectively used to identify and mitigate the large-scale InSAR tropospheric delay noise if the spatial resolution of GPS stations is dense enough.

Operational GPS Imaging System at Multiple Scales for Earth Science and Monitoring of Geohazards

NASA Astrophysics Data System (ADS)

Blewitt, Geoffrey; Hammond, William; Kreemer, Corné

2016-04-01

Toward scientific targets that range from slow deep Earth processes to geohazard rapid response, our operational GPS data analysis system produces smooth, yet detailed maps of 3-dimensional land motion with respect to our Earth's center of mass at multiple spatio-temporal scales with various latencies. "GPS Imaging" is implemented operationally as a back-end processor to our GPS data processing facility, which uses JPL's GIPSY OASIS II software to produce positions from 14,000 GPS stations in ITRF every 5 minutes, with coordinate precision that gradually improves as latency increases upward from 1 hour to 2 weeks. Our GPS Imaging system then applies sophisticated signal processing and image filtering techniques to generate images of land motion covering our Earth's continents with high levels of robustness, accuracy, spatial resolution, and temporal resolution. Techniques employed by our GPS Imaging system include: (1) similarity transformation of polyhedron coordinates to ITRF with optional common-mode filtering to enhance local transient signal to noise ratio, (2) a comprehensive database of ~100,000 potential step events based on earthquake catalogs and equipment logs, (3) an automatic, robust, and accurate non-parametric estimator of station velocity that is insensitive to prevalent step discontinuities, outliers, seasonality, and heteroscedasticity; (4) a realistic estimator of velocity error bars based on subsampling statistics; (5) image processing to create a map of land motion that is based on median spatial filtering on the Delauney triangulation, which is effective at despeckling the data while faithfully preserving edge features; (6) a velocity time series estimator to assist identification of transient behavior, such as unloading caused by drought, and (7) a method of integrating InSAR and GPS for fine-scale seamless imaging in ITRF. Our system is being used to address three main scientific focus areas, including (1) deep Earth processes, (2) anthropogenic lithospheric processes, and (3) dynamic solid Earth events. Our prototype images show that the striking, first-order signal in North America and Europe is large scale uplift and subsidence from mantle flow driven by Glacial Isostatic Adjustment. At regional scales, the images reveal that anthropogenic lithospheric processes can dominate vertical land motion in extended regions, such as the rapid subsidence of California's Central Valley (CV) exacerbated by drought. The Earth's crust is observed to rebound elastically as evidenced by uplift of surrounding mountain ranges. Images also reveal natural uplift of mountains, mantle relaxation associated with earthquakes over the last century, and uplift at plate boundaries driven by interseismic locking. Using the high-rate positions at low latency, earthquake events can be rapidly imaged, modeled, and monitored for afterslip, potential aftershocks, and subsequent deeper relaxation. Thus we are imaging deep Earth processes with unprecedented scope, resolution and accuracy. In addition to supporting these scientific focus areas, the data products are also being used to support the global reference frame (ITRF), and show potential to enhance missions such as GRACE and NISAR by providing complementary information on Earth processes.

GPS Array as a Sensor of Lithosphere, Troposphere and Ionosphere

NASA Astrophysics Data System (ADS)

Heki, K.

2011-12-01

The Japanese dense array of GPS receivers (GEONET) started operation in 1993, and is currently composed of ~1200 stations. GPS (or GNSS in general) receivers can be compared to a Swiss army knife: it could be used not only for positioning (a knife) but also for various purposes, e.g. remote sensing of tropospheric water vapor or ionospheric electrons (screw driver, tin opener etc). Dense GPS arrays have been found extremely useful for variety of geophysical studies. In this lecture, I briefly review their historical achievements, recent highlights, and future perspectives. In Japan, first generation GPS stations were implemented in 1993 (the Kanto-Tokai region) and 1994 (nationwide) by GSI, Japan. Shortly after the launch, they successfully caught coseismic crustal movement of several major earthquakes, the 1994 October Shikotan (Mw8.3), the 1994 December Sanriku (Mw7.6), and the 1995 January Kobe (Mw7.0) earthquakes. These earthquakes accelerated the densification of the GPS network, achieving 1000 in the number of stations within the following 2-3 years. In addition to coseismic jumps, important discoveries continued in 1990s, e.g. large-scale afterslip of interplate thrust earthquakes and slow slip events (SSE). Later it was shown that tilt- and strainmeter can better observe short-term SSEs, and InSAR can draw more detailed maps of coseismic crustal movements. Now GPS array is recognized as a good tool to measure crustal movement with high temporal resolution and stability and with moderate sensitivity and spatial resolution. GPS data are also useful to study hydrosphere. Seasonal crustal movements in Japan mainly reflect changes in hydrological loads. Multipath signatures in GPS data also provide useful information on the environment around the antenna, e.g. soil moisture, snow depth and vegetation. I will compare the snow depth record over a winter inferred by analyzing GPS multipath signatures, and observed by a conventional apparatus. GPS can also measure precipitable water vapor (PWV) of troposphere. After intense feasibility studies of GPS meteorology in 1990s, PWV information from GEONET has been routinely assimilated in the operational mesoscale model of the Japan Meteorological Agency since 2009. It is found useful in predicting localized heavy rainfalls that often attack Japan in summer. It is fairly easy to measure ionospheric total electron content (TEC) by using phase differences between L1 and L2 carriers from GPS satellites. Applications of GPS for upper atmospheric studies started for ionospheric disturbances of space weather origins. In 2003, clear coseismic ionospheric disturbances of the Tokachi-Oki earthquake were found, and the GPS-TEC technique has been extensively used to study ionospheric disturbances of solid earth origins, e.g. earthquakes and volcanic eruptions. There are also several recent examples of artificial ionospheric disturbances caused by rocket launches and passage of ballistic missiles from North Korea above NE Japan. In the last part of the lecture, I summarize what the GPS array saw before, during and after the 2011 Tohoku-Oki earthquake. The topic covers not only pre-, co- and postseismic crustal movements, but also results of high-rate sampling, and possible detection of precursory changes in ionospheric TEC immediately before the earthquake.

Seasonal and Surface Hydrologic Loading Signals at GPS Stations Processed by the GAGE Facility

NASA Astrophysics Data System (ADS)

Puskas, C. M.; Meertens, C. M.; Phillips, D.

2017-12-01

UNAVCO is now producing hydrologic displacement model time series at GPS station coordinates in the Geodesy Advancing Geosciences and EarthScope (GAGE) Facility, including the Plate Boundary Observatory (PBO). The surface loads are obtained from global and national land data assimilation systems (GLDAS and NLDAS, respectively) land surface models produced by the Goddard Earth Sciences Data and Information Services Center (GES DISC). The land surface models are available as monthly files of environmental parameters documenting water, pressure, temperature, and other measures mass/energy transfer on a grid at the Earth's surface. Grids are 1º for the global GLDAS models and 0.125º for the NLDAS models in the conterminous US. UNAVCO extracts the soil moisture, snowpack, and water stored in vegetation parameters and calculates displacements in an elastic half-space at selected points, i.e., GPS station locations. UNAVCO has recently upgraded its hydrologic data products from GLDAS version 1 to version 2 and added NLDAS-based models, and the new data products are now available from the UNAVCO ftp server (ftp://data-out.unavco.org/pub/products/hydro) and will soon be available through web services. The GLDAS v2 models supersede those based on v1, which will no longer be updated. UNAVCO updates its hydrologic products on a quarterly basis. Seasonal signals in the GAGE GPS position time series have amplitudes on the order of several millimeters, which vary across the PBO network depending on local climate and geology. The signals are thought to be a combination of elastic displacement from surface loading and poroelastic displacement from groundwater depletion and recharge. We present a description of the hydrologic displacement modeling and provide examples of loading and resulting displacement. The GLDAS and NLDAS models are compared with each other and with GPS position time series at selected stations in different geographic regions.

Calibration of GPS based high accuracy speed meter for vehicles

NASA Astrophysics Data System (ADS)

Bai, Yin; Sun, Qiao; Du, Lei; Yu, Mei; Bai, Jie

2015-02-01

GPS based high accuracy speed meter for vehicles is a special type of GPS speed meter which uses Doppler Demodulation of GPS signals to calculate the speed of a moving target. It is increasingly used as reference equipment in the field of traffic speed measurement, but acknowledged standard calibration methods are still lacking. To solve this problem, this paper presents the set-ups of simulated calibration, field test signal replay calibration, and in-field test comparison with an optical sensor based non-contact speed meter. All the experiments were carried out on particular speed values in the range of (40-180) km/h with the same GPS speed meter. The speed measurement errors of simulated calibration fall in the range of +/-0.1 km/h or +/-0.1%, with uncertainties smaller than 0.02% (k=2). The errors of replay calibration fall in the range of +/-0.1% with uncertainties smaller than 0.10% (k=2). The calibration results justify the effectiveness of the two methods. The relative deviations of the GPS speed meter from the optical sensor based noncontact speed meter fall in the range of +/-0.3%, which validates the use of GPS speed meter as reference instruments. The results of this research can provide technical basis for the establishment of internationally standard calibration methods of GPS speed meters, and thus ensures the legal status of GPS speed meters as reference equipment in the field of traffic speed metrology.

Variations of TEC near the Indian Equatorial Ionospheric anomaly (EIA) stations by GPS measurements during descending phase of solar activity (2005 -2009)

NASA Astrophysics Data System (ADS)

Kumar, Sanjay; Singh, Abhay Kumar

The dual frequency Global Positioning System (GPS) data recorded at Varanasi (geographic latitude 250, 16 N longitude 820, 59 E) and Kanpur (geographic latitude 260, 30 N longitude 800, 12 E) stations, near the equatorial ionosphere anomaly (EIA) in India, have been analyzed to retrieve total electron content (TEC). The daily peak value of vertical total electron content (VTEC) has been utilized to study the variability of EIA. Present paper studied monthly, seasonal and annual variations as well as solar and geomagnetic effects on EIA. It has been found that EIA yield their maximum values during the equinox months and minimum during summer and winter. The correlations of EIA with solar as well as geomagnetic indices have been also discussed. Key words: Total electron contents (TECs), EIA, GPS.

VLBI and GPS-based Time-Transfer Using CONT08 Data

NASA Technical Reports Server (NTRS)

Rieck, Carsten; Haas, Ruediger; Jaldehag, Kenneth; Jahansson, Jan

2010-01-01

One important prerequisite for geodetic Very Long Baseline Interferometry (VLBI) is the use of frequency standards with excellent short term stability. This makes VLBI stations, which are often co-located with Global Navigation Satellite System (GNSS) receiving stations, interesting for studies of time- and frequency-transfer techniques. We present an assessment of VLBI time-transfer based on the data of the two week long consecutive IVS CONT08 VLBI campaign by using GPS Carrier Phase (GPSCP). CONT08 was a 15 day long campaign in August 2008 that involved eleven VLBI stations on five continents. For CONT08 we estimated the worst case VLBI frequency link stability between the stations of Onsala and Wettzell to 1e-15 at one day. Comparisons with GPSCP confirm the VLBI results. We also identify time-transfer related challenges of the VLBI technique as used today.

Analysis of High Precision GPS Time Series and Strain Rates for the Geothermal Play Fairway Analysis of Washington State Prospects Project

DOE Data Explorer

Michael Swyer

2015-02-22

Global Positioning System (GPS) time series from the National Science Foundation (NSF) Earthscope’s Plate Boundary Observatory (PBO) and Central Washington University’s Pacific Northwest Geodetic Array (PANGA). GPS station velocities were used to infer strain rates using the ‘splines in tension’ method. Strain rates were derived separately for subduction zone locking at depth and block rotation near the surface within crustal block boundaries.

Verification of the modelling of the main ionospheric trough by the Electron Density Assimilative Model (EDAM)

NASA Astrophysics Data System (ADS)

Parker, James; Pryse, Eleri; Jackson-Booth, Natasha

2017-04-01

The main ionospheric trough is a large-scale spatial depletion in the ionospheric electron density that commonly separates the auroral and mid-latitude regions. The feature covers several degrees in latitude and is extended in longitude. It exhibits substantial day-to-day variability in both the location of its minimum ionisation density and in its latitudinal structure. Observations from the UK have shown the trough to be a night-time feature, appearing in early evening to the north of the mainland and progressing equatorward during the course of the night. At dawn, photoionisation fills in the feature. Under increasing levels of geomagnetic activity, the trough moves progressively to lower latitudes. Steep gradients on the trough walls and their variability can cause problems for radio applications. EDAM can be used to model the ionosphere at the trough latitudes by assimilating ionospheric observations from this region into the International Reference Ionosphere (IRI). In this study troughs modelled by EDAM, assimilating data for a period from September to December 2002, are presented and are verified by comparisons with independent observations. Measurements of slant total electron content (sTEC) between GPS satellites and forty ground receivers in Europe were assimilated into EDAM to model the ionospheric electron density. The Vertical Total Electron Content (VTEC) was then calculated through the model, with the values at the longitude of 0.0E considered to obtain statistical characteristics of identified troughs parameters. Comparisons of the parameters with those obtained previously, using transmissions from the satellites of NIMS (Navy Ionospheric Monitoring System) orbiting at altitudes lower than GPS, revealed consistent results. Further support for the EDAM trough was obtained by comparisons of the model with independent GPS measurements. For this a GPS ground station not used in the assimilation was used to observe the sTEC to this "truth" station. Comparisons of these independent truth data with sTEC calculated through the model were used to determine the accuracy of EDAM in the vicinity of the trough.

Comparison of Ionospheric TEC Derived from GPS and IRI 2012 Model during Geomagnetic Storms at Indonesia

NASA Astrophysics Data System (ADS)

Marlia, Dessi; Wu, Falin

2016-07-01

This paper investigates the variations of vertical Total Electron Content (VTEC) at Manado, Indonesia (geographic coordinates : lat 1.34 ° S and long 124.82 ° E) for period 2013. The GPS measured TEC is compared with the TEC derived from the IRI (International Reference Ionosphere) 2012 model. Vertical TEC measurements obtained from dual frequency GPS receiver that is GISTM (GPS Ionospheric Scintillations and TEC monitor). Variation of TEC validate to IRI 2012 model at Manado station has been compared with the model for three different topside of electron density namely NeQuick, IRI-01-Corr and IRI2001.There is a need to investigation on diurnal, seasonal variations, solar activity dependence of TEC and including effects of space weather related events to TEC and modeling of TEC. In this paper, diurnal and seasonal variations of VTEC and the effect of VTEC due to space weather events like Geomagnetic storms are analyzed. The result show that the TEC prediction using IRI-2001 model overestimated the GPS TEC measurements, while IRI-NeQuick and IRI-01-corr show a tendency to underestimates the observed TEC during the day time particularly in low latitude region in the maximum solar activity period (2013). The variations of VTEC during 17th March, 2013, 29th June, 2013 storms are analyzed. During 17th March,2013 storm enhancement in VTEC with Kp value 6 and Disturbance storm index (DST) -132 nT. During 29th June, 2013 storm VTEC depletion with value 7 and DST -98 nT. Significant deviations in VTEC during the main phase of the storms are observed. It is found that the response of ionospheric TEC consist of effects of both enhancement and depletions in ionospheric structures (positive and negative storm). Keywords: TEC ionosphere, GPS, GISTM, IRI 2012 model, solar activity, geomagnetic storm

SIRGAS: ITRF densification in Latin America and the Caribbean

NASA Astrophysics Data System (ADS)

Brunini, C.; Costa, S.; Mackern, V.; Martínez, W.; Sánchez, L.; Seemüller, W.; da Silva, A.

2009-04-01

The continental reference frame of SIRGAS (Sistema de Referencia Geocéntrico para las Américas) is at present realized by the SIRGAS Continuously Operating Network (SIRGAS-CON) composed by about 200 stations distributed over all Latin America and the Caribbean. SIRGAS member countries are qualifying their national reference frames by installing continuously operating GNSS stations, which have to be consistently integrated into the continental network. As the number of these stations is rapidly increasing, the processing strategy of the SIRGAS-CON network was redefined during the SIRGAS 2008 General Meeting in May 2008. The new strategy relies upon the definition of two hierarchy levels: a) A core network (SIRGAS-CON-C) with homogeneous continental coverage and stabile site locations ensures the long-term stability of the reference frame and provides the primary link to the ITRS. Stations belonging to this network have been selected so that each country contributes with a number of stations defined according to its surface and guarantying that the selected stations are the best in operability, continuity, reliability, and geographical coverage. b) Several densification sub-networks (SIRGAS-CON-D) improve the accessibility to the reference frame. The SIRGAS-CON-D sub-networks shall correspond to the national reference frames, i.e., as an optimum there shall be as many sub-networks as countries in the region. The goal is that each country processes its own continuously stations following the SIRGAS processing guidelines, which are defined in accordance with the IERS and IGS standards and conventions. Since at present not all of the countries are operating a processing centre, the existing stations are classified in three densification networks (a Northern, a middle, and a Southern one), which are processed by three local processing centres until new ones are installed. As SIRGAS is defined as a densification of the ITRS, stations included in the core network, as well as in the densification sub-networks match the requirements, characteristics, and processing performance of the ITRF. The SIRGAS-CON-C network is processed by DGFI (Deutsches Geodätisches Forschungsinstitut, Germany) as the IGS-RNAAC-SIR. The Local Processing Centres are for the Northern sub-network IGAC (Instituto Geográfico Augustín Codazzi, Colombia), for the middle sub-network IBGE (Instituto Brasileiro de Geografia e Estátistica, Brazil), and for the Southern sub-network IGG-CIMA (Instituto de Geodesia y Geodinámica, Universidad Nacional de Cuyo, Argentina). These four Processing Centres deliver loosely constrained weekly solutions for station coordinates (i.e., satellite orbits, satellite clock offsets, and Earth orientation parameters are fixed to the final weekly IGS solutions and coordinates for all sites are constrained to 1 m). The individual contributions are integrated in a unified solution by the SIRGAS Combination Centres (DGFI and IBGE) according to the following strategy: 1) Individual solutions are reviewed/corrected for possible format problems, data inconsistencies, etc. 2) Constraints imposed in the delivered normal equations are removed. 3) Sub-networks are individually aligned to the IGS05 reference frame by applying the No Net Rotation (NNR) and No Net Translation (NNT) conditions. 4) Coordinates obtained in (3) for each sub-network are compared to IGS05 values and to each other in order to identify possible outliers. 5) Stations with large residuals (more than 10 mm in the N-E component, and more than 20 mm in the Up component) are reduced from the normal equations. Steps (3), (4), and (5) are done iteratively. 6) Since at present the four Analysis Centres are processing GPS observations only and all of them use the Bernese Software for computing weekly solutions, relative weighting factors are not applied in the combination. 7) Individual normal equations are accumulated and solved for computing a loosely constrained weekly solution for station coordinates (i.e., coordinates for all stations are constrained to 1 m). This solution in SINEX format is submitted to IGS for the global polyhedron. 8) Combination obtained in (7) is constrained by applying NNR+NNT conditions with respect to the IGS05 stations included the SIRGAS region to provide constrained coordinates for all SIRGAS-CON (core + densification) stations. The applied IGS05 reference coordinates correspond to the weekly IGS solution for the global network, i.e., coordinates included in the igsYYPwwww.snx files. This constrained solution provides the final weekly SIRGAS-CON coordinates for practical applications. The DGFI (i.e. IGS RNAAC SIR) weekly combinations are delivered to the IGS Data Centres for combination in the global polyhedron, and made available for users as official SIRGAS products, respectively. The IBGE weekly combinations provide control and back-up. The above described analysis strategy is applied since GPS week 1495. Before (since June 1996 to August 2008), the SIRGAS-CON network was totally processed by DGFI. Until now, results show a very good agreement with previous computations; however, the present sub-networks distribution has two main disadvantages: 1) Not all SIRGAS-CON stations are included in the same number of individual solutions, i.e., they are unequally weighted in the weekly combinations, and 2) since there are not enough Local Processing Centres, the required redundancy (each station processed by at least three processing centres) is not fulfilled. Therefore, efforts are being made to install additional Local Processing Centres in Latin American countries as Argentina, Ecuador, Mexico, Peru, Uruguay, and Venezuela.

Clustering of GPS velocities in the Mojave Block, southeastern California

USGS Publications Warehouse

Savage, James C.; Simpson, Robert W.

2013-01-01

We find subdivisions within the Mojave Block using cluster analysis to identify groupings in the velocities observed at GPS stations there. The clusters are represented on a fault map by symbols located at the positions of the GPS stations, each symbol representing the cluster to which the velocity of that GPS station belongs. Fault systems that separate the clusters are readily identified on such a map. The most significant representation as judged by the gap test involves 4 clusters within the Mojave Block. The fault systems bounding the clusters from east to west are 1) the faults defining the eastern boundary of the Northeast Mojave Domain extended southward to connect to the Hector Mine rupture, 2) the Calico-Paradise fault system, 3) the Landers-Blackwater fault system, and 4) the Helendale-Lockhart fault system. This division of the Mojave Block is very similar to that proposed by Meade and Hager. However, no cluster boundary coincides with the Garlock Fault, the northern boundary of the Mojave Block. Rather, the clusters appear to continue without interruption from the Mojave Block north into the southern Walker Lane Belt, similar to the continuity across the Garlock Fault of the shear zone along the Blackwater-Little Lake fault system observed by Peltzer et al. Mapped traces of individual faults in the Mojave Block terminate within the block and do not continue across the Garlock Fault [Dokka and Travis, ].

Response of nighttime equatorial and low latitude F-region to the geomagnetic storm of August 18, 2003, in the Brazilian sector

NASA Astrophysics Data System (ADS)

Sahai, Y.; Becker-Guedes, F.; Fagundes, P. R.; Lima, W. L. C.; Otsuka, Y.; Huang, C.-S.; Espinoza, E. S.; Pi, X.; de Abreu, A. J.; Bolzan, M. J. A.; Pillat, V. G.; Abalde, J. R.; Pimenta, A. A.; Bittencourt, J. A.

This paper presents an investigation of geomagnetic storm effects in the equatorial and low latitude F-region in the Brazilian sector during the intense geomagnetic storm on 18 August, 2003 (SSC 14:21 UT on 17/08; ΣKp = 52+; Ap = 108; ∣Dst∣ max = 168 at 1600 UT on 18/08). Simultaneous ionospheric sounding measurements from two stations, viz., Palmas (10.2°S, 48.2°W; dip latitude 5.7°S) and Sao Jose dos Campos (23.2°S, 45.9°W; dip latitude 17.6°S), Brazil, are presented for the nights of 16-17, 17-18 and 18-19 August, 2003 (quiet, disturbed and recovery phases). Both stations are equipped with the Canadian Advanced Digital Ionosonde (CADI). Quiet and disturbed conditions of the F-region ionosphere are compared using data collected from the two stations. The relationship between magnetospheric disturbance and low-latitude ionospheric dynamics, and generation of ionospheric irregularities are discussed. On the disturbed nights (17-18 and 18-19 August), the low latitude station S. J. Campos showed strong enhancements in the F-region critical frequency (foF2), whereas the near equatorial station Palmas showed strong uplifting of the F-layer about 1 h earlier. Normally during the June solstice months (May-August) in the Brazilian sector, large-scale ionospheric irregularities in form of plasma bubbles are rarely observed. On the night of 17-18 August, ionsospheric sounding observations at Palmas showed the presence of bottomside spread-F, whereas on the night of 18-19 August, the observations at Palmas and S. J. Campos showed the presence of plasma bubbles when the storm recovery phase had just started. The complementary GPS data available from several stations in the "Rede Brasileira de Monitoramento Continuo de GPS (Brazilian Network for Continuous GPS Monitoring)" are used to obtain the vertical total electron content (VTEC) and the rate of change of TEC per minute on UT days 18 and 19 August, 2003 and presented. Also, several global ionospheric TEC maps from the worldwide network of GPS receivers are presented, showing widespread latitudinal and longitudinal TEC changes during the different phases of the storm. All the observations (local ionospheric sounding and GPS network measurements, and global GPS measurements) presented in this investigation related to the geomagnetic storm on 18 August indicate that the equatorial and low latitude region in the Brazilian sector had much stronger effect during the recovery phase compared with the main phase. A comparison of the observed disturbance drifts with the Fejer-Scherliess storm-time model drifts indicate that the modeled drifts are not consistent with the present observations.

GPS and GLONASS 1 Hz phase rate observations to study high latitudes ionospheric irregularities

NASA Astrophysics Data System (ADS)

Ghoddousi-Fard, R.; Prikryl, P.; Jacobsen, K. S.; Lahaye, F.

2016-12-01

It has been shown that dual frequency 1 Hz GPS phase rate observations can serve as a promising proxy for phase scintillation over high latitudes (see e.g. Ghoddousi-Fard et al., 2013, 2015). However signals from other GNSS constellations including GLONASS have been available and widely used for positioning applications. Usage of additional GNSS constellations should allow improved sampling of the ionosphere, a critical advantage to study small scale ionospheric irregularities over high latitudes. Migration of global GPS networks to multi-GNSS are now underway such as International GNSS Service (IGS) Multi-GNSS Experiment (MGEX) and other national, public and private sector networks. In this presentation, GPS and GLONASS observations from high latitude MGEX stations as well as a dense regional network over Norway are used to map high latitude ionospheric irregularities by means of standard deviation of phase rate variations. Occurrence of GPS phase irregularities as a function of magnetic latitude and local time are compared with those from both GPS and GLONASS. By including 1 Hz GLONASS measurements at about 185 stations over Norway during geomagnetic storm of March 17-18, 2015, this study complements a recently submitted paper that examined the GPS phase scintillation occurrence in the context of solar wind coupling to the magnetosphere-ionosphere system and auroral electrojet currents (Prikryl et al., 2016). Ghoddousi-Fard et al. (2013). GPS phase difference variation statistics: A comparison between phase scintillation index and proxy indices. Adv. Space Res., 52, 1397-1405, doi: 10.1016/j.asr.2013.06.035. Ghoddousi-Fard et al. (2015). Analysis of GPS phase rate variations in response to geomagnetic field perturbations over the Canadian auroral region. Adv. Space Res., 55, 1372-1381, doi: 10.1016/j.asr.2014.12.021. Prikryl et al. (2016). GPS phase scintillation at high latitudes during the geomagnetic storm of March 17-18, 2015, submitted to J. Geophys. Res. ESS contribution number: 20160112

Precision assessment of the orthometric heights determination in northern part of Algeria by combining the GPS data and the local geoid model

NASA Astrophysics Data System (ADS)

Benahmed Daho, Sid Ahmed

2010-02-01

The main purpose of this article is to discuss the use of GPS positioning together with a gravimetrically determined geoid, for deriving orthometric heights in the North of Algeria, for which a limited number of GPS stations with known orthometric heights are available, and to check, by the same opportunity, the possibility of substituting the classical spirit levelling. For this work, 247 GPS stations which are homogeneously distributed and collected from the international TYRGEONET project, as well as the local GPS/Levelling surveys, have been used. The GPS/Levelling geoidal heights are obtained by connecting the points to the levelling network while gravimetric geoidal heights were interpolated from the geoid model computed by the Geodetic Laboratory of the National Centre of Spatial Techniques from gravity data supplied by BGI. However, and in order to minimise the discordances, systematic errors and datum inconsistencies between the available height data sets, we have tested two parametric models of corrector surface: a four parameter transformation and a third polynomial model are used to find the adequate functional representation of the correction that should be applied to the gravimetric geoid. The comparisons based on these GPS campaigns prove that a good fit between the geoid model and GPS/levelling data has been reached when the third order polynomial was used as corrector surface and that the orthometric heights can be deducted from GPS observations with an accuracy acceptable for the low order levelling network densification. In addition, the adopted methodology has been also applied for the altimetric auscultation of a storage reservoir situated at 40 km from the town of Oran. The comparison between the computed orthometric heights and observed ones allowed us to affirm that the alternative of levelling by GPS is attractive for this auscultation.

Precipitable Water Vapor Characterization In The Gulf Of Cadiz Region (Southwestern Spain) Based On Sun Photometer, GPS And Radiosonde Data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Torres, B.; Cachorro, V. E.; Toledano, C.

2010-09-16

Column integrated water vapor (IWV) data in the Gulf of Cádiz area (Southwestern Spain) are analyzed during the period 2001 to 2005 with two aims: 1) to establish the climatology over this area using three different techniques, such as Sun-Photometer (SP), Global Position System (GPS) and Radiosondes, and 2) to take advantage of this comparative process to assess the quality of radiometric IWV data collected at the RIMA-AERONET station. The 5 years of climatological series gives a mean value of about 2 cm (STD=0.72) and a clear seasonal behavior as a general feature, with the highest values in summer andmore » the lowest in winter. In the multi-annual monthly means basis, the highest values are reached in August-September, with a mean value of 2.5-2.6 cm, whereas the lowest are obtained in January-February, with an average of 1.4-24 1.5. However the most relevant results for this area is the observed local minimum in July, occurring during the maximum of desert dust intrusions in the southern Iberian Peninsula. A comparison process allows us to evaluate the agreement of IWV data sets between these three different techniques at different temporal scales because of different time sampling. On a daily basis and taking GPS as the reference value we have a bias or difference between Radiosonde and GPS measurements for the entire data base of 0.07 cm (relative bias of 3%) and RMSE of 0.33. For SP-GPS we have a bias of 0.14 cm (about 7%) and RMSE of 0.37. On a monthly basis the differences between Radiosonde and GPS values varies from summer with 2% to winter with -8% and between SP and GPS values from 3% in summer to -14% in winter. The observed bias between GPS and SP varies during each SP operational period, with lower values at the beginning of the measurements and increasing until the end of its measurement term and with the bias values being quite dependent on each individual SP. The observed differences highlight the importance of drift in each Sun-Photometer, because of filter aging or other calibration problems. Hence the comparison with GPS appears to be a powerful tool to assess the quality of Sun-Photometer for IWV retrieval.« less

Application of the Undifferenced GNSS Precise Positioning in Determining Coordinates in National Reference Frames

NASA Astrophysics Data System (ADS)

Krzan, Grzegorz; Stępniak, Katarzyna

2017-09-01

In high-accuracy positioning using GNSS, the most common solution is still relative positioning using double-difference observations of dual-frequency measurements. An increasingly popular alternative to relative positioning are undifferenced approaches, which are designed to make full use of modern satellite systems and signals. Positions referenced to global International Terrestrial Reference Frame (ITRF2008) obtained from Precise Point Positioning (PPP) or Undifferenced (UD) network solutions have to be transformed to national (regional) reference frame, which introduces additional bases related to the transformation process. In this paper, satellite observations from two test networks using different observation time series were processed. The first test concerns the positioning accuracy from processing one year of dual-frequency GPS observations from 14 EUREF Permanent Network (EPN) stations using NAPEOS 3.3.1 software. The results were transformed into a national reference frame (PL-ETRF2000) and compared to positions from an EPN cumulative solution, which was adopted as the true coordinates. Daily observations were processed using PPP and UD multi-station solutions to determine the final accuracy resulting from satellite positioning, the transformation to national coordinate systems and Eurasian intraplate plate velocities. The second numerical test involved similar processing strategies of post-processing carried out using different observation time series (30 min., 1 hour, 2 hours, daily) and different classes of GNSS receivers. The centimeter accuracy of results presented in the national coordinate system satisfies the requirements of many surveying and engineering applications.

Comparison of observed and modeled seasonal crustal vertical displacements derived from multi-institution GPS and GRACE solutions

NASA Astrophysics Data System (ADS)

Gu, Yanchao; Fan, Dongming; You, Wei

2017-07-01

Eleven GPS crustal vertical displacement (CVD) solutions for 110 IGS08/IGS14 core stations provided by the International Global Navigation Satellite Systems Service Analysis Centers are compared with seven Gravity Recovery and Climate Experiment (GRACE)-modeled CVD solutions. The results of the internal comparison of the GPS solutions from multiple institutions imply large uncertainty in the GPS postprocessing. There is also evidence that GRACE solutions from both different institutions and different processing approaches (mascon and traditional spherical harmonic coefficients) show similar results, suggesting that GRACE can provide CVD results of good internal consistency. When the uncertainty of the GPS data is accounted for, the GRACE data can explain as much as 50% of the actual signals and more than 80% of the GPS annual signals. Our study strongly indicates that GRACE data have great potential to correct the nontidal loading in GPS time series.

Comparison of GPS derived TEC with the TEC predicted by IRI 2012 model in the southern Equatorial Ionization Anomaly crest within the Eastern Africa region

NASA Astrophysics Data System (ADS)

Sulungu, Emmanuel D.; Uiso, Christian B. S.; Sibanda, Patrick

2018-04-01

We have compared the TEC obtained from the IRI-2012 model with the GPS derived TEC data recorded within southern crest of the EIA in the Eastern Africa region using the monthly means of the 5 international quiet days for equinoxes and solstices months for the period of 2012 - 2013. GPS-derived TEC data have been obtained from the Africa array and IGS network of ground based dual-frequency GPS receivers from four stations (Kigali (1.95°S, 30.09°E; Geom. Lat. 11.63°S), Malindi (2.99°S, 40.19°E; Geom. Lat. 12.42°S), Mbarara (0.60°S, 30.74°E; Geom. Lat. 10.22°S) and Nairobi (1.22°S, 36.89°E; Geom. Lat. 10.69°S)) located within the EIA crest in this region. All the three options for topside Ne of IRI-2012 model and ABT-2009 for bottomside thickness have been used to compute the IRI TEC. Also URSI coefficients were considered in this study. These results are compared with the TEC estimated from GPS measurements. Correlation Coefficients between the two sets of data, the Root-Mean Square Errors (RMSE) of the IRI-TEC from the GPS-TEC, and the percentage RMSE of the IRI-TEC from the GPS-TEC have been computed. Our general results show that IRI-2012 model with all three options overestimates the GPS-TEC for all seasons and at all stations, and IRI-2001 overestimates GPS-TEC more compared with other options. IRI-Neq and IRI-01-corr are closely matching in most of the time. The observation also shows that, GPS TEC are underestimated by TEC from IRI model during noon hours, especially during equinoctial months. Further, GPS-TEC values and IRI-TEC values using all the three topside Ne options show very good correlation (above 0.8). On the other hand, the TEC using IRI-Neq and IRI-01- corr had smaller deviations from the GPS-TEC compared to the IRI-2001.

Egnos Limitations over Central and Eastern Poland - Results of Preliminary Tests of Egnos-Eupos Integration Project

NASA Astrophysics Data System (ADS)

Jaworski, Leszek; Swiatek, Anna; Zdunek, Ryszard

2013-09-01

The problem of insufficient accuracy of EGNOS correction for the territory of Poland, located at the edge of EGNOS range is well known. The EEI PECS project (EGNOS EUPOS Integration) assumes improving the EGNOS correction by using the GPS observations from Polish ASG-EUPOS stations. One of the EEI project tasks was the identification of EGNOS performance limitations over Poland and services for EGNOSS-EUPOS combination. The two sets of data were used for those goals: statistical, theoretical data obtained using the SBAS simulator software, real data obtained during the measurements. The real measurements were managed as two types of measurements: static and dynamic. Static measurements are continuously managing using Septentrio PolaRx2 receiver. The SRC permanent station works in IMAGE/PERFECT project. Dynamic measurements were managed using the Mobile GPS Laboratory (MGL). Receivers (geodetic and navigation) were working in two modes: determining navigation position from standalone GPS, determining navigation position from GPS plus EGNOS correction. The paper presents results of measurements' analyses and conclusions based on which the next tasks in EEI project are completed

GPS Installation Progress in the Northern California Region of the Plate Boundary Observatory Coyle, B., Basset, A., Williams, T., Enders, M., Feaux, K., Jackson, M.

NASA Astrophysics Data System (ADS)

Coyle, B.; Basset, A.; Enders, M.; Williams, T.; Feaux, K.; Jackson, M.

2005-12-01

The Plate Boundary Observatory (PBO) is the geodetic component of the NSF funded EarthScope Project . The final PBO GPS network will comprise 875 continuously operating GPS stations installed throughout the Western US and Alaska. There are 435 stations planned for California with 229 of these in Northern California (NCA). This poster will present the past year's progress of GPS installations in NCA. At the end of the first year of the Project, PBO NCA installed 12 stations. During the second year, another 56 were installed for a total of 68 stations including 18 SDBM, and 50 DDBM. We have sited 128 stations, submitted 112 permit applications and received 73 permits. A particularly important statistic for planning our schedules is the time lag between reconnaissance and permit accepted; our average thus far is 137 days. We have been particularly successful locating stations on Caltrans Rights of Way with 20 Stations built, 3 sites permitted and 5 permits pending. Other land use partners include: East Bay Regional Parks - 8 Stations built and 2 sites permitted, Bureau of Land Management - 5 Stations built, 3 permits pending, Water Municipalities - 4 Stations built, 3 sites permitted and 4 permits pending, and Airports - 4 Stations built and 3 permits pending. Highlights from last year: On September 28, 2004 a Mw 6.0 earthquake occurred on the San Andreas Fault seven miles southeast of the town of Parkfield, CA. Field crews from the Northern and Southern California offices of PBO began the site reconnaissance and permitting process the day after the earthquake and installation of the first Station was begun within 36 hours and completed the following day. In total, 5 Stations were installed by the first week of November. On June 14, 2045 a Mw 7.1 earthquake occurred on the Gorda Plate, approximately 100 miles NW of Eureka. PBO stations, P158, P162, P169 and P170, recorded coseismic deformation associated with this event. We plan to have 127 stations built by the end of the current project year. In order to meet this goal we intend to focus our efforts on two areas, National Forests (NF) sites in the Coast Ranges, and sites in the area around Hollister and San Juan Bautista. We expect the recon-to-permit period to be somewhat longer for the NF sites, possibly up to one year, so we have already submitted applications for our sites in the Mendocino and Shasta-Trinity NF. This should enable us to begin these installations next summer. We will submit permit applications for the remaining NF by the end of next year. By end of the year we hope to have permit applications submitted for all 229 of our proposed sites, so we can then focus our efforts on installations and revisiting "problem" sites.

PTTI applications at the limits of GPS

NASA Technical Reports Server (NTRS)

Douglas, Rob J.; Popelar, J.

1995-01-01

Canadian plans for precise time and time interval services are examined in the light of GPS capabilities developed for geodesy. We present our experience in establishing and operating a geodetic type GPS station in a time laboratory setting, and show sub-nanosecond residuals for time transfer between geodetic sites. We present our approach to establishing realistic standard uncertainties for short-term frequency calibration services over time intervals of hours, and for longer-term frequency dissemination at better than the 10(exp -15) level of accuracy.

Integrated Water Vapour Retrieval From Irish GPS Network: Results From Validation With Radiosondes And Microwave Profiler And Assimilation Into HIRLAM 7.2 Operational Forecasting Model

NASA Astrophysics Data System (ADS)

Hanafin, J. A.; Whelan, E.; McGrath, R.; Jennings, S. G.; O'Dowd, C.

2009-12-01

Retrieval of atmospheric integrated water vapour (IWV) from ground-based GPS receivers and provision of this data product for meteorological applications is the focus of the European EUMETNET GPS water vapour programme. The results presented here are the first from a project to provide such information about the state of the atmosphere around Ireland for climate monitoring and improved numerical weather prediction. Two geodetic reference GPS receivers have been deployed at Valentia Observatory in Co. Kerry and Mace Head Atmospheric Research Station in Co. Galway, Ireland. A system to retrieve column-integrated atmospheric water vapour from the data they provide has been developed. Data quality has been assessed using co-located radiosondes at Valentia and observations from a microwave profiling radiometer at Mace Head. Results from the data processing and comparisons with independent observations will be presented. Water vapour retrievals from such sensors can provide good quality observations at hourly intervals of this essential climate variable for assimilation into numerical nowcast and forecast systems. Previous studies have shown that using these data to constrain initial model conditions can improve the accuracy of precipitation forecasts, particularly for heavy rainfall. The current operational forecast model in use at Met Éireann for the region is the new version 7.2 HIRLAM (High-Resolution Limited Area Model). The effects on the forecast for Ireland have been evaluated by assimilating the data into 48-hour forecast runs of this model and results of this study will also be presented.

GPS measurements of strain accumulation across the Imperial Valley, California: 1986-1989

NASA Technical Reports Server (NTRS)

Larsen, Shawn; Reilinger, Robert

1989-01-01

The Global Positioning System (GPS) data collected in southern California from 1986 to 1989 indicate considerable strain accumulation across the Imperial Valley. Displacements are computed at 29 stations in and near the valley from 1986 to 1988, and at 11 sites from 1988 to 1989. The earlier measurements indicate 5.9 +/- 1.0 cm/yr right-lateral differential velocity across the valley, although the data are heavily influenced by the 1987 Superstition Hills earthquake sequence. Some measurements, especially the east-trending displacements, are suspects for large errors. The 1988 to 1989 GPS displacements are best modeled by 5.2 +/- 0.9 cm/yr of valley crossing deformation, but rates calculated from conventional geodetic measurements (3.4 to 4.3 cm/yr) fit the data nearly as well. There is evidence from GPS and Very Long Base Interferometry (VLBI) observations that the present slip rate along the southern San Andreas fault is smaller than the long-term geologic estimate, suggesting a lower earthquake potential than is currently assumed. Correspondingly, a higher earthquake potential is indicated for the San Jacinto fault. The Imperial Valley GPS sites form part of a 183 station network in southern California and northern Baja California, which spans a cross-section of the North American-Pacific plate boundary.

Status of DORIS stations in Antarctica for precise geodesy

NASA Technical Reports Server (NTRS)

Willis, P.; Amalvict, M.; Shibuya, K.

2005-01-01

In Antarctica, besides the quite numerous GPS stations, four DORIS stations are permanently operating. In addition to the permanent DORIS stations, episodic campaigns took place at DomeC/Conccordia and on Sorsdal and Lambert glaciers. In this paper, we first collect general information concerning the stations and the campaigns (location, start of measurements, etc). We then present the results of observations of the permanent stations keeping in mind that we are primarily interested here in the vertical component, which is the most uncertain component.

Dietitian-general practitioner interface: a pilot study on what influences the provision of effective nutrition management.

PubMed

Nicholas, Lisa G; Pond, C Dimity; Roberts, David C K

2003-04-01

Effective patient nutrition management can both improve people's health and reduce the cost of health care. In Australia, general practitioners (GPs) and dietitians are in a position to provide this service. However, there is a lack of information available on what influences the provision of the service. The objective was to determine qualitative factors that influence nutrition management by GPs and dietitians. A convenience sample of GPs and dietitians was surveyed using a qualitative questionnaire. The questionnaire related to issues including influences on the GP's decision to initiate nutrition management, barriers to providing nutrition counseling, influences on the GP's decision to refer to a dietitian, and barriers to referral. Fourteen of 20 GPs and 15 of 30 dietitians responded with usable data. The primary influence on a GP's decision to initiate nutrition management (GPs' and dietitians' responses) was the presentation of a patient who required nutrition advice. Barriers to providing nutrition counseling were time and knowledge (GP response), whereas dietitians saw time and lack of patient interest as issues. The primary influence on the GP's decision to refer to a dietitian was a patient presenting with complicated nutrition requirements (GP response), whereas dietitians considered a patient seeking nutrition knowledge as the key influencer. GPs identified cost to the patient as the main barrier to referring to a dietitian, whereas dietitians saw lack of knowledge of where to refer as the key issue. The differing responses suggest that more research is required to understand what influences patient nutrition management by GPs and dietitians in Australia.

Long range geoid control through the European GPS traverse: Final results

NASA Technical Reports Server (NTRS)

Torge, W.; Basic, T.; Denker, H.; Doliff, J.; Wenzel, H.-G.

1989-01-01

The European north-south Global Positioning System (GPS)-traverse proposed by IAG SSG 3.88, should control and improve the European geoid. This traverse follows first order leveling lines, included in the United European Leveling Network. From May to August 1986 and in July 1987, the central and northern part of this traverse (approx. 3000 km) was observed using up to four TI 4100 receivers, covering Austria, Federal Republic of Germany, Denmark, Sweden and Norway. Both traverse parts contain 71 stations with distances of about 50 km. In addition, 8 stations have been occupied for overlapping connections, and traverse links were established for connecting the fundamental stations Wettzell (VLBI and SLR) and Onsala (VLBI). Final results show a GPS observation precision of a few cm for loops of some 100 km circumference. After transformation of the GPS results to geoid heights using the leveled heights, comparisons with different existing gravimetric geoid determinations including geopotential models were performed. In addition, new geopotential models complete to degree and order 360 tailored to gravity data in Europe, and gravimetric geoid solutions using 6 x 10' mean gravity anomalies were investigated. The comparison with GPS and leveling yields rms discrepancies of + or - 0.1...0.2 m over 1000 km traverse sections for the best solutions, but a strong slope is existing in Sweden and southern Norway in almost all solutions, which is probably caused by systematic errors in the available gravity data for Scandinavia. This is confirmed by a new geoid computation at the Danish Geodetic Institute where the slope has disappeared. If this new solution is taken for the northern traverse section and the best solution for the central part, the rms discrepancy reduces to approximately + or - 0.2 m over 3000 km. Thus, a + or - 10 (exp 7) relative height accuracy seems to be achievable over long distances with the GPS/leveling and the gravimetric geoid calculation techniques, applied in this experiment.

Demonstration of precise estimation of polar motion parameters with the global positioning system: Initial results

NASA Technical Reports Server (NTRS)

Lichten, S. M.

1991-01-01

Data from the Global Positioning System (GPS) were used to determine precise polar motion estimates. Conservatively calculated formal errors of the GPS least squares solution are approx. 10 cm. The GPS estimates agree with independently determined polar motion values from very long baseline interferometry (VLBI) at the 5 cm level. The data were obtained from a partial constellation of GPS satellites and from a sparse worldwide distribution of ground stations. The accuracy of the GPS estimates should continue to improve as more satellites and ground receivers become operational, and eventually a near real time GPS capability should be available. Because the GPS data are obtained and processed independently from the large radio antennas at the Deep Space Network (DSN), GPS estimation could provide very precise measurements of Earth orientation for calibration of deep space tracking data and could significantly relieve the ever growing burden on the DSN radio telescopes to provide Earth platform calibrations.

Evaluation of a regional real-time precise positioning system based on GPS/BeiDou observations in Australia

NASA Astrophysics Data System (ADS)

Ding, Wenwu; Tan, Bingfeng; Chen, Yongchang; Teferle, Felix Norman; Yuan, Yunbin

2018-02-01

The performance of real-time (RT) precise positioning can be improved by utilizing observations from multiple Global Navigation Satellite Systems (GNSS) instead of one particular system. Since the end of 2012, BeiDou, independently established by China, began to provide operational services for users in the Asia-Pacific regions. In this study, a regional RT precise positioning system is developed to evaluate the performance of GPS/BeiDou observations in Australia in providing high precision positioning services for users. Fixing three hourly updated satellite orbits, RT correction messages are generated and broadcasted by processing RT observation/navigation data streams from the national network of GNSS Continuously Operating Reference Stations in Australia (AUSCORS) at the server side. At the user side, RT PPP is realized by processing RT data streams and the RT correction messages received. RT clock offsets, for which the accuracy reached 0.07 and 0.28 ns for GPS and BeiDou, respectively, can be determined. Based on these corrections, an accuracy of 12.2, 30.0 and 45.6 cm in the North, East and Up directions was achieved for the BeiDou-only solution after 30 min while the GPS-only solution reached 5.1, 15.3 and 15.5 cm for the same components at the same time. A further improvement of 43.7, 36.9 and 45.0 percent in the three directions, respectively, was achieved for the combined GPS/BeiDou solution. After the initialization process, the North, East and Up positioning accuracies were 5.2, 8.1 and 17.8 cm, respectively, for the BeiDou-only solution, while 1.5, 3.0, and 4.7 cm for the GPS-only solution. However, we only noticed a 20.9% improvement in the East direction was obtained for the GPS/BeiDou solution, while no improvements in the other directions were detected. It is expected that such improvements may become bigger with the increasing accuracy of the BeiDou-only solution.

Effect of tropospheric models on derived precipitable water vapor over Southeast Asia

NASA Astrophysics Data System (ADS)

Rahimi, Zhoobin; Mohd Shafri, Helmi Zulhaidi; Othman, Faridah; Norman, Masayu

2017-05-01

An interesting subject in the field of GPS technology is estimating variation of precipitable water vapor (PWV). This estimation can be used as a data source to assess and monitor rapid changes in meteorological conditions. So far, numerous GPS stations are distributed across the world and the number of GPS networks is increasing. Despite these developments, a challenging aspect of estimating PWV through GPS networks is the need of tropospheric parameters such as temperature, pressure, and relative humidity (Liu et al., 2015). To estimate the tropospheric parameters, global pressure temperature (GPT) model developed by Boehm et al. (2007) is widely used in geodetic analysis for GPS observations. To improve the accuracy, Lagler et al. (2013) introduced GPT2 model by adding annual and semi-annual variation effects to GPT model. Furthermore, Boehm et al. (2015) proposed the GPT2 wet (GPT2w) model which uses water vapor pressure to improve the calculations. The global accuracy of GPT2 and GPT2w models has been evaluated by previous researches (Fund et al., 2011; Munekane and Boehm, 2010); however, investigations to assess the accuracy of global tropospheric models in tropical regions such as Southeast Asia is not sufficient. This study tests and examines the accuracy of GPT2w as one of the most recent versions of tropospheric models (Boehm et al., 2015). We developed a new regional model called Malaysian Pressure Temperature (MPT) model, and compared this model with GPT2w model. The compared results at one international GNSS service (IGS) station located in the south of Peninsula Malaysia shows that MPT model has a better performance than GPT2w model to produce PWV during monsoon season. According to the results, MPT has improved the accuracy of estimated pressure and temperature by 30% and 10%, respectively, in comparison with GPT2w model. These results indicate that MPT model can be a good alternative tool in the absence of meteorological sensors at GPS stations in Peninsula Malaysia. Therefore, for GPS-based studies, we recommend MPT model to be used as a complementary tool for the Malaysia Real-Time Kinematic Network to develop a real-time PWV monitoring system.

Characteristics of equatorial plasma bubble zonal drift velocity and tilt based on Hong Kong GPS CORS network: From 2001 to 2012

NASA Astrophysics Data System (ADS)

Ji, Shengyue; Chen, Wu; Weng, Duojie; Wang, Zhenjie

2015-08-01

Hong Kong (22.3°N, 114.2°E, dip: 30.5°N; geomagnetic 15.7°N, 173.4°W, declination: 2.7°W) is a low-latitude area, and the Hong Kong Continuously Operating Reference Station (CORS) network has been developed and maintained by Lands Department of Hong Kong government since 2001. Based on the collected GPS observations of a whole solar cycle from 2001 to 2012, a method is proposed to estimate the zonal drift velocity as well as the tilt of the observed plasma bubbles, and the estimated results are statistically analyzed. It is found that although the plasma bubbles are basically vertical within the equatorial plane, the tilt can be as big as more than 60° eastward or westward sometimes. And, the tilt and the zonal drift velocity are correlated. When the velocity is large, the tilt is also large generally. Another finding is that large velocity and tilt generally occur in spring and autumn and in solar active years.

Flight Test Results from Real-Time Relative Global Positioning System Flight Experiment on STS-69

NASA Technical Reports Server (NTRS)

Park, Young W.; Brazzel, Jack P., Jr.; Carpenter, J. Russell; Hinkel, Heather D.; Newman, James H.

1996-01-01

A real-time global positioning system (GPS) Kalman filter has been developed to support automated rendezvous with the International Space Station (ISS). The filter is integrated with existing Shuttle rendezvous software running on a 486 laptop computer under Windows. In this work, we present real-time and postflight results achieved with the filter on STS-69. The experiment used GPS data from an Osborne/Jet propulsion Laboratory TurboRouge receiver carried on the Wake Shield Facility (WSF) free flyer and a Rockwell Collins 3M receiver carried on the Orbiter. Real time filter results, processed onboard the Shuttle and replayed in near-time on the ground, are based on single vehicle mode operation and on 5 to 20 minute snapshots of telemetry provided by WSF for dual-vehicle mode operation. The Orbiter and WSF state vectors calculated using our filter compare favorably with precise reference orbits determined by the University of Texas Center for Space Research. The lessons learned from this experiment will be used in conjunction with future experiments to mitigate the technology risk posed by automated rendezvous and docking to the ISS.

Continuous GPS observations of postseismic deformation following the 16 October 1999 Hector Mine, California, earthquake (Mw 7.1)

USGS Publications Warehouse

Hudnutt, K.W.; King, N.E.; Galetzka, J.E.; Stark, K.F.; Behr, J.A.; Aspiotes, A.; van, Wyk S.; Moffitt, R.; Dockter, S.; Wyatt, F.

2002-01-01

Rapid field deployment of a new type of continuously operating Global Positioning System (GPS) network and data from Southern California Integrated GPS Network (SCIGN) stations that had recently begun operating in the area allow unique observations of the postseismic deformation associated with the 1999 Hector Mine earthquake. Innovative solutions in fieldcraft, devised for the 11 new GPS stations, provide high-quality observations with 1-year time histories on stable monuments at remote sites. We report on our results from processing the postseismic GPS data available from these sites, as well as 8 other SCIGN stations within 80 km of the event (a total of 19 sites). From these data, we analyze the temporal character and spatial pattern of the postseismic transients. Data from some sites display statistically significant time variation in their velocities. Although this is less certain, the spatial pattern of change in the postseismic velocity field also appears to have changed. The pattern now is similar to the pre-Landers (pre-1992) secular field, but laterally shifted and locally at twice the rate. We speculate that a 30 km ?? 50 km portion of crust (near Twentynine Palms), which was moving at nearly the North American plate rate (to within 3.5 mm/yr of that rate) prior to the 1992 Landers sequence, now is moving along with the crust to the west of it, as though it has been entrained in flow along with the Pacific Plate as a result of the Landers and Hector Mine earthquake sequence. The inboard axis of right-lateral shear deformation (at lower crustal to upper mantle depth) may have jumped 30 km farther into the continental crust at this fault junction that comprises the southern end of the eastern California shear zone.

Combining various space geodetic techniques for regional modeling of ionospheric electron density over Iran

NASA Astrophysics Data System (ADS)

Zare, Saeed; Alizadeh, M. Mahdi; Schuh, Harald

2017-04-01

Ionosphere is a layer of the upper atmosphere, between the thermosphere and the exosphere, distinguished because it is ionized by solar radiation. As an important part of human living environment, ionosphere affects our modern society in many ways. International broadcasters use this medium to reflect radio signals back toward the Earth. Ionosphere provides long range capabilities for commercial ship-to-shore communications, for trans-oceanic aircraft links, and for military communication and surveillance systems. Space geodetic techniques have turned into a capable tool for studying the ionosphere in the last decades. Up to now, two dimensional (2-D) models of vertical TEC (VTEC) have been widely developed and used by different communities; however, due to the fact that these models provide information about the integral of the whole electron content along the vertical or slant ray path, these maps are not useful when information about the ionosphere at different altitude is required. The aim of this study is to develop three dimensional (3-D) regional model of electron density by using combination of various space geodetic techniques. B-Spline basis functions are used for longitude and latitude variations of the electron density and Chapman profile function for altitude variations. The National Cartographic Center of Iran (NCC) has established a network of one hundred GPS stations: The Iranian Permanent GPS Network for Geodynamics (IPGN). The main task of the GPS stations is to collect and store raw GPS data and send it to Tehran processing center on a daily basis for final processing. The required data for our investigation are ground based measurements of permanent GPS stations over Iran and radio occultation data from Formosat-3/Cosmic for region of interest. We expect to increase accuracy and reliability of final model by integrating different observation techniques.

Hydrological signals in height and gravity in northeastern Italy inferred from principal components analysis

NASA Astrophysics Data System (ADS)

Zerbini, S.; Raicich, F.; Richter, B.; Gorini, V.; Errico, M.

2010-04-01

This work describes a study of GPS heights, gravity and hydrological time series collected by stations located in northeastern Italy. During the last 12 years, changes in the long-term behaviors of the GPS heights and gravity time series are observed. In particular, starting in 2004-2005, a height increase is observed over the whole area. The temporal and spatial variability of these parameters has been studied as well as those of key hydrological variables, namely precipitation, hydrological balance and water table by using the Empirical Orthogonal Functions (EOF) analysis. The coupled variability between the GPS heights and the hydrological balance and precipitation data has been investigated by means of the Singular Value Decomposition (SVD) approach. Significant common patterns in the spatial and temporal variability of these parameters have been recognized. In particular, hydrology-induced variations are clearly observable starting in 2002-2003 in the southern part of the Po Plain for the longest time series, and from 2004-2005 over the whole area. These findings, obtained by means of purely mathematical approaches, are supported by sound physical interpretation suggesting that the climate-related fluctuations in the regional/local hydrological regime are one of the main contributors to the observed variations. A regional scale signal has been identified in the GPS station heights; it is characterized by the opposite behavior of the southern and northern stations in response to the hydrological forcing. At Medicina, in the southern Po Plain, the EOF analysis has shown a marked common signal between the GPS heights and the Superconducting Gravimeter (SG) data both over the long and the short period.

Transient Volcano Deformation Event Detection over Variable Spatial Scales in Alaska

NASA Astrophysics Data System (ADS)

Li, J. D.; Rude, C. M.; Gowanlock, M.; Herring, T.; Pankratius, V.

2016-12-01

Transient deformation events driven by volcanic activity can be monitored using increasingly dense networks of continuous Global Positioning System (GPS) ground stations. The wide spatial extent of GPS networks, the large number of GPS stations, and the spatially and temporally varying scale of deformation events result in the mixing of signals from multiple sources. Typical analysis then necessitates manual identification of times and regions of volcanic activity for further study and the careful tuning of algorithmic parameters to extract possible transient events. Here we present a computer-aided discovery system that facilitates the discovery of potential transient deformation events at volcanoes by providing a framework for selecting varying spatial regions of interest and for tuning the analysis parameters. This site specification step in the framework reduces the spatial mixing of signals from different volcanic sources before applying filters to remove interfering signals originating from other geophysical processes. We analyze GPS data recorded by the Plate Boundary Observatory network and volcanic activity logs from the Alaska Volcano Observatory to search for and characterize transient inflation events in Alaska. We find 3 transient inflation events between 2008 and 2015 at the Akutan, Westdahl, and Shishaldin volcanoes in the Aleutian Islands. The inflation event detected in the first half of 2008 at Akutan is validated other studies, while the inflation events observed in early 2011 at Westdahl and in early 2013 at Shishaldin are previously unreported. Our analysis framework also incorporates modelling of the transient inflation events and enables a comparison of different magma chamber inversion models. Here, we also estimate the magma sources that best describe the deformation observed by the GPS stations at Akutan, Westdahl, and Shishaldin. We acknowledge support from NASA AIST-NNX15AG84G (PI: V. Pankratius).

Geodetic antenna calibration test in the Antarctic environment

USGS Publications Warehouse

Grejner-Brzezinska, A.; Vazquez, E.; Hothem, L.

2006-01-01

TransAntarctic Mountain DEFormation (TAMDEF) Monitoring Network is the NSF-sponsored OSU and USGS project, aimed at measuring crustal motion in the Transantarctic Mountains of Victoria Land using GPS carrier phase measurements. Station monumentation, antenna mounts, antenna types, and data processing strategies were optimized to achieve mm-level estimates for the rates of motion. These data contributes also to regional Antarctic frame definition. Significant amount of data collected over several years allow the investigation of unique aspects of GPS geodesy in Antarctica, to determine how the error spectrum compares to the mid-latitude regions, and to identify the optimum measurement and data processing schemes for Antarctic conditions, in order to test the predicted rates of motion (mm-level w.r.t. time). The data collection for the TAMDEF project was initiated in 1996. The primary antenna used has been the Ashtech L1/L2 Dorne Margolin (D/M) choke ring. A few occupations involved the use of a Trimble D/M choke ring. The data were processed using the antenna calibration data available from the National Geodetic Survey (NGS). The recent developments in new antenna designs that are lighter in weight and lower in cost are being considered as a possible alternative to the bulkier and more expensive D/M choke ring design. In November 2003, in situ testing of three alternative models of L1/L2 antennas was conducted at a site located in the vicinity of McMurdo Station, Antarctica (S77.87, E166.56). The antenna models used in this test were: Ashtech D/M choke ring, Trimble D/M choke ring, Trimble Zephyr, and the NovAtel GPS-702. Two stations, spaced within 30 meters, were used in the test. Both had the characteristics similar to the stations of the TAMDEF network, i.e., the UNAVCO fixed-height, force-centered level mounts with a constant antenna offset were used, ensuring extreme stability of the antenna/ mount/pin set up. During each of the four 3-day test data collection sessions, a reference station was occupied continuously with the Ashtech D/M choke ring antenna, while the second station was occupied by the tested antennas, one 3-day session for each antenna type. The coordinate differences were produced using software optimized for the analysis of data collected over short baselines. Each solution incorporated the NGS antenna calibration data appropriate for each antenna model. Hourly and 24-hour solutions were analyzed for repeatability and compared to the standard baseline coordinate differences. No significant variation was observed when comparing the same type of antennas and when switching antennas at the test site using daily solutions. An mm-level scatter can be observed comparing different antennas over the 1-hour solutions; it is smaller for the horizontal components, as compared to the vertical direction. At this point, it can be concluded that the standard antenna calibration models from NGS used for each antenna involved in this test did not result in any significant variation in the daily results, but with some in the hourly results. Thus, based on this fact, the antenna types tested here could be used in the future TAMDEF campaigns, where 24-hour solutions are normally used for deformation monitoring. These results can serve as good guidance to any future use of GPS equipment in Antarctica.

Reliable positioning in a sparse GPS network, eastern Ontario

NASA Astrophysics Data System (ADS)

Samadi Alinia, H.; Tiampo, K.; Atkinson, G. M.

2013-12-01

Canada hosts two regions that are prone to large earthquakes: western British Columbia, and the St. Lawrence River region in eastern Canada. Although eastern Ontario is not as seismically active as other areas of eastern Canada, such as the Charlevoix/Ottawa Valley seismic zone, it experiences ongoing moderate seismicity. In historic times, potentially damaging events have occurred in New York State (Attica, 1929, M=5.7; Plattsburg, 2002, M=5.0), north-central Ontario (Temiskaming, 1935, M=6.2; North Bay, 2000, M=5.0), eastern Ontario (Cornwall, 1944, M=5.8), Georgian Bay (2005, MN=4.3), and western Quebec (Val-Des-Bois,2010, M=5.0, MN=5.8). In eastern Canada, the analysis of detailed, high-precision measurements of surface deformation is a key component in our efforts to better characterize the associated seismic hazard. The data from precise, continuous GPS stations is necessary to adequately characterize surface velocities from which patterns and rates of stress accumulation on faults can be estimated (Mazzotti and Adams, 2005; Mazzotti et al., 2005). Monitoring of these displacements requires employing high accuracy GPS positioning techniques. Detailed strain measurements can determine whether the regional strain everywhere is commensurate with a large event occurring every few hundred years anywhere within this general area or whether large earthquakes are limited to specific areas (Adams and Halchuck, 2003; Mazzotti and Adams, 2005). In many parts of southeastern Ontario and western Québec, GPS stations are distributed quite sparsely, with spacings of approximately 100 km or more. The challenge is to provide accurate solutions for these sparse networks with an approach that is capable of achieving high-accuracy positioning. Here, various reduction techniques are applied to a sparse network installed with the Southern Ontario Seismic Network in eastern Ontario. Recent developments include the implementation of precise point positioning processing on acquired GPS raw data. These are based on precise GPS orbit and clock data products with centimeter accuracy computed beforehand. Here, the analysis of 1Hz GPS data is conducted in order to find the most reliable regional network from eight stations (STCO, TYNO, ACTO, INUQ, IVKQ, KLBO, MATQ and ALGO) that cover the study area in eastern Ontario. In this way, the estimated parameters are the total number of ambiguities and resolved ambiguities, posteriori rms of each baseline and the coordinates for each station and their differences with the known coordinates. The positioning accuracy, the corrections and the accuracy of interpolated corrections, and the initialization time required for precise positioning are presented for the various applications.

Optical Tracking Data Validation and Orbit Estimation for Sparse Observations of Satellites by the OWL-Net.

PubMed

Choi, Jin; Jo, Jung Hyun; Yim, Hong-Suh; Choi, Eun-Jung; Cho, Sungki; Park, Jang-Hyun

2018-06-07

An Optical Wide-field patroL-Network (OWL-Net) has been developed for maintaining Korean low Earth orbit (LEO) satellites' orbital ephemeris. The OWL-Net consists of five optical tracking stations. Brightness signals of reflected sunlight of the targets were detected by a charged coupled device (CCD). A chopper system was adopted for fast astrometric data sampling, maximum 50 Hz, within a short observation time. The astrometric accuracy of the optical observation data was validated with precise orbital ephemeris such as Consolidated Prediction File (CPF) data and precise orbit determination result with onboard Global Positioning System (GPS) data from the target satellite. In the optical observation simulation of the OWL-Net for 2017, an average observation span for a single arc of 11 LEO observation targets was about 5 min, while an average optical observation separation time was 5 h. We estimated the position and velocity with an atmospheric drag coefficient of LEO observation targets using a sequential-batch orbit estimation technique after multi-arc batch orbit estimation. Post-fit residuals for the multi-arc batch orbit estimation and sequential-batch orbit estimation were analyzed for the optical measurements and reference orbit (CPF and GPS data). The post-fit residuals with reference show few tens-of-meters errors for in-track direction for multi-arc batch and sequential-batch orbit estimation results.

EarthScope's Plate Boundary Observatory in Alaska: Building on Existing Infrastructure to Provide a Platform for Integrated Research and Hazard-monitoring Efforts

NASA Astrophysics Data System (ADS)

Boyce, E. S.; Bierma, R. M.; Willoughby, H.; Feaux, K.; Mattioli, G. S.; Enders, M.; Busby, R. W.

2014-12-01

EarthScope's geodetic component in Alaska, the UNAVCO-operated Plate Boundary Observatory (PBO) network, includes 139 continuous GPS sites and 41 supporting telemetry relays. These are spread across a vast area, from northern AK to the Aleutians. Forty-five of these stations were installed or have been upgraded in cooperation with various partner agencies and currently provide data collection and transmission for more than one group. Leveraging existing infrastructure normally has multiple benefits, such as easier permitting requirements and costs savings through reduced overall construction and maintenance expenses. At some sites, PBO-AK power and communications systems have additional capacity beyond that which is needed for reliable acquisition of GPS data. Where permits allow, such stations could serve as platforms for additional instrumentation or real-time observing needs. With the expansion of the Transportable Array (TA) into Alaska, there is increased interest to leverage existing EarthScope resources for station co-location and telemetry integration. Because of the complexity and difficulty of long-term O&M at PBO sites, however, actual integration of GPS and seismic equipment must be considered on a case-by-case basis. UNAVCO currently operates two integrated GPS/seismic stations in collaboration with the Alaska Earthquake Center, and three with the Alaska Volcano Observatory. By the end of 2014, PBO and TA plan to install another four integrated and/or co-located geodetic and seismic systems. While three of these are designed around existing PBO stations, one will be a completely new TA installation, providing PBO with an opportunity to expand geodetic data collection in Alaska within the limited operations and maintenance phase of the project. We will present some of the design considerations, outcomes, and lessons learned from past and ongoing projects to integrate seismometers and other instrumentation at PBO-Alaska stations. Developing the PBO network as a platform for ongoing research and hazard monitoring equipment may also continue to serve the needs of the research community and the public beyond the sun-setting and completion of EarthScope science plan in 2018.

The International GPS Service (IGS) as a Continuous Reference System for Precise GPS Positioning

NASA Technical Reports Server (NTRS)

Neilan, Ruth; Heflin, Michael; Watkins, Michael; Zumberge, James

1996-01-01

The International GPS Service for Geodynamics (IGS) is an organization which operates under the auspices of the International Association of Geodesy (IAG) and has been operational since January 1994. The primary objective of the IGS is to provide precise GPS data and data products to support geodetic and geophysical research activities.

DORIS and GNSS processing at CNES/CLS for the contribution to the next ITRF2013

NASA Astrophysics Data System (ADS)

Loyer, Sylvain; Capdeville, Hugues; Soudarin, Laurent; Mezerette, Adrien; Lemoine, Jean-Michel; Mercier, Flavien; Perosanz, Felix

2014-05-01

CNES serves as Analysis Center in the International DORIS Service (IDS) and the International GNSS Service (IGS). DORIS and GNSS data are processed by its subsidiary CLS with the GRGS package software GINS/DYNAMO. For the contribution to the next release of the International Terrestrial Reference Frame planned this year (ITRF2013), two decades of data were analyzed (1993-2013 for DORIS, 1998-2013 for GPS, and 2009-2013 for GLONASS). In this context, the CNES/CLS Analysis Centers provided SINEX solutions to the IDS and IGS Combination Centers, respectively multi-satellite weekly solutions and daily solutions. Normal equations derived from this analysis are also made available to the GRGS Combination Center for the combination at the observation level of the geodetic parameters measured by DORIS, GPS, SLR and VLBI techniques. The purpose of this presentation is to point out how the overall quality of the DORIS and GNSS data processing benefits from the use of the same software and a common basis of models. Here, we present the modeling standards, the networks and the processing strategies. Assessments of some models are also discussed. The quality and the homogeneity of the products (orbits, station coordinates and Earth Orientation Parameters) over the complete period are shown, as well as the temporal variations of some parameters (dynamical parameters, orbit residuals, internal orbit overlaps ...). Some examples of time series of DORIS and GNSS station positions at collocated sites complete this presentation.

A new GPS velocity field in the south-western Balkans: insights for continental dynamics

NASA Astrophysics Data System (ADS)

D'Agostino, N.; Avallone, A.; Duni, L.; Ganas, A.; Georgiev, I.; Jouanne, F.; Koci, R.; Kuka, N.; Metois, M.

2017-12-01

The Balkans peninsula is an area of active distributed deformation located at the southern boundary of the Eurasian plate. Relatively low strain rates and logistical reasons have so far limited the characterization and definition of the active tectonics and crustal kinematics. The increasing number of GNSS stations belonging to national networks deployed for scientific and cadastral purposes, now provides the opportunity to improve the knowledge of the crustal kinematics in this area and to define a cross-national velocity field that illuminates the active tectonic deformation. In this work we homogeneously processed the data from the south western Balkans and neighbouring regions using available rinex files from scientific and cadastral networks (ALBPOS, EUREF, HemusNET, ITALPOS, KOPOS, MAKPOS, METRICA, NETGEO, RING, TGREF). In order to analyze and interpret station velocities relative to the Eurasia plate and to reduce the common mode signal, we updated the Eurasian terrestrial reference frame described in Métois et al. 2015. Starting from this dataset we present a new GPS velocity field covering the south western part of the Balkan Peninsula. Using this new velocity field, we derive the strain rate tensor to analyze the regional style of the deformation. Our results (1) improve the picture of the general southward flow of the crust characterizing the south western Balkans behind the contractional belt at the boundary with Adriatic and (2) provide new key elements for the understanding of continental dynamics in this part of the Eurasian plate boundary.

Global Positioning System (GPS) civil signal monitoring (CSM) trade study report

DOT National Transportation Integrated Search

2014-03-07

This GPS Civil Signal Monitoring (CSM) Trade Study has been performed at the direction of DOT/FAA Navigation Programs as the agency of reference for consolidating civil monitoring requirements on the Global Positioning System (GPS). The objective of ...

Why do GPs hesitate to refer diabetes patients to a self-management education program: a qualitative study.

PubMed

Sunaert, Patricia; Vandekerckhove, Marie; Bastiaens, Hilde; Feyen, Luc; Bussche, Piet Vanden; De Maeseneer, Jan; De Sutter, An; Willems, Sara

2011-09-08

Self-management support is seen as a cornerstone of good diabetes care and many countries are currently engaged in initiatives to integrate self-management support in primary care. Concerning the organisation of these programs, evidence is growing that engagement of health care professionals, in particular of GPs, is critical for successful application. This paper reports on a study exploring why a substantial number of GPs was (initially) reluctant to refer patients to a self-management education program in Belgium. Qualitative analysis of semi-structured face-to-face interviews with a purposive sample of 20 GPs who were not regular users of the service. The Greenhalgh diffusion of innovation framework was used as background and organising framework. Several barriers, linked to different components of the Greenhalgh model, emerged from the interview data. One of the most striking ones was the limited readiness for innovation among GPs. Feelings of fear of further fragmentation of diabetes care and frustration and insecurity regarding their own role in diabetes care prevented them from engaging in the innovation process. GPs needed time to be reassured that the program respects their role and has an added value to usual care. Once GPs considered referring patients, it was not clear enough which of their patients would benefit from the program. Some GPs expressed the need for training in motivational skills, so that they could better motivate their patients to participate. A practical but often mentioned barrier was the distance to the centre where the program was delivered. Further, uncertainty about continuity interfered with the uptake of the offer. The study results contribute to a better understanding of the reasons why GPs hesitate to refer patients to a self-management education program. First of all, the role of GPs and other health care providers in diabetes care needs to be clarified before introducing new functions. Feelings of security and a basic trust of providers in the health system are a prerequisite for participation in care innovation. Moreover, some important lessons regarding the implementation of an education program in primary care have been learned from the study.

Why do GPs hesitate to refer diabetes patients to a self-management education program: a qualitative study

PubMed Central

2011-01-01

Background Self-management support is seen as a cornerstone of good diabetes care and many countries are currently engaged in initiatives to integrate self-management support in primary care. Concerning the organisation of these programs, evidence is growing that engagement of health care professionals, in particular of GPs, is critical for successful application. This paper reports on a study exploring why a substantial number of GPs was (initially) reluctant to refer patients to a self-management education program in Belgium. Methods Qualitative analysis of semi-structured face-to-face interviews with a purposive sample of 20 GPs who were not regular users of the service. The Greenhalgh diffusion of innovation framework was used as background and organising framework. Results Several barriers, linked to different components of the Greenhalgh model, emerged from the interview data. One of the most striking ones was the limited readiness for innovation among GPs. Feelings of fear of further fragmentation of diabetes care and frustration and insecurity regarding their own role in diabetes care prevented them from engaging in the innovation process. GPs needed time to be reassured that the program respects their role and has an added value to usual care. Once GPs considered referring patients, it was not clear enough which of their patients would benefit from the program. Some GPs expressed the need for training in motivational skills, so that they could better motivate their patients to participate. A practical but often mentioned barrier was the distance to the centre where the program was delivered. Further, uncertainty about continuity interfered with the uptake of the offer. Conclusions The study results contribute to a better understanding of the reasons why GPs hesitate to refer patients to a self-management education program. First of all, the role of GPs and other health care providers in diabetes care needs to be clarified before introducing new functions. Feelings of security and a basic trust of providers in the health system are a prerequisite for participation in care innovation. Moreover, some important lessons regarding the implementation of an education program in primary care have been learned from the study. PMID:21902832

The role of general practitioners in the pre hospital setting, as experienced by emergency medicine technicians: a qualitative study

PubMed Central

2014-01-01

Background Together with the ambulances staffed with emergency medical technicians (EMTs), general practitioners (GPs) on call are the primary resources for handling emergencies outside hospitals in Norway. The benefit of the GP accompanying the ambulance to pre-hospital calls is a matter of controversy in Norway. The purpose of the present study was to gain better insight into the EMT’s experiences with the role of the GPs in the care for critically ill patients in the pre-hospital setting. Methods We conducted four focus group interviews with EMTs at four different ambulance stations in Norway. Three of the stations were located at least 2 hours driving distance from the nearest hospital. The interviews were transcribed and analyzed using systematic text condensation. Results The EMTs described increasing confidence in emergency medicine during the last few years. However, they felt the need for GP participation in the ambulance when responding to a critically ill patient. The presence of GPs made the EMTs feel more confident, especially in unclear and difficult cases that did not fit into EMT guidelines. The main contributions of the GPs were described as diagnosis and decision-making. Bringing the physician to the patient shortened transportation time to the hospital and important medication could be started earlier. Several examples of sub-optimal treatment in the absence of the GP were given. The EMTs described discomfort with GPs not responding to the calls. They also experienced GPs responding to calls that did not function in the pre-hospital emergency setting. The EMTs reported a need for professional requirements for GPs taking part in out-of-hours work and mandatory interdisciplinary training on a regular basis. Conclusions EMTs want GPs to be present in challenging pre-hospital emergency settings. The presence of GPs is perceived as improving patient care. However, professional requirements are needed for GPs taking part in out-of-hours work, and the informants suggested a formalized area for training between EMTs and GPs on call. PMID:25145390

Testing of the International Space Station and X-38 Crew Return Vehicle GPS Receiver

NASA Technical Reports Server (NTRS)

Simpson, James; Campbell, Chip; Carpenter, Russell; Davis, Ed; Kizhner, Semion; Lightsey, E. Glenn; Davis, George; Jackson, Larry

1999-01-01

This paper discusses the process and results of the performance testing of the GPS receiver planned for use on the International Space Station (ISS) and the X-38 Crew Return Vehicle (CRV). The receiver is a Force-19 unit manufactured by Trimble Navigation and modified in software by the NASA Goddard Space Flight Center (GSFC) to perform navigation and attitude determination in space. The receiver is the primary source of navigation and attitude information for ISS and CRV. Engineers at GSFC have developed and tested the new receiver with a Global Simulation Systems Ltd (GSS) GPS Signal Generator (GPSSG). This paper documents the unique aspects of ground testing a GPS receiver that is designed for use in space. A discussion of the design of tests using the GPSSG, documentation, data capture, data analysis, and lessons learned will precede an overview of the performance of the new receiver. A description of the challenges that were overcome during this testing exercise will be presented. Results from testing show that the receiver will be within or near the specifications for ISS attitude and navigation performance. The process for verifying other requirements such as Time to First Fix, Time to First Attitude, selection/deselection of a specific GPS satellite vehicles (SV), minimum signal strength while still obtaining attitude and navigation, navigation and attitude output coverage, GPS week rollover, and Y2K requirements are also given in this paper.

Testing of the International Space Station and X-38 Crew Return Vehicle GPS Receiver

NASA Technical Reports Server (NTRS)

Simpson, James; Campbell, Chip; Carpenter, Russell; Davis, Ed; Kizhner, Semion; Lightsey, E. Glenn; Davis, George; Jackson, Larry

1999-01-01

This paper discusses the process and results of the performance testing of the GPS receiver planned for use on the International Space Station (ISS) and the X-38 Crew Return Vehicle (CRV). The receiver is a Force-19 unit manufactured by Trimble Navigation and Modified in software by the NASA Goddard Space Flight Center (GSFC) to perform navigation and attitude determination in space. The receiver is the primary source of navigation and attitude information for ISS and CRV. Engineers at GSFC have developed and tested the new receiver with a Global Simulation Systems Ltd (GSS) GPS Signal Generator (GPSSG). This paper documents the unique aspects of ground testing a GPS receiver that is designed for use in space. A discussion of the design and tests using the GPSSG, documentation, data capture, data analysis, and lessons learned will precede an overview of the performance of the new receiver. A description of the challenges of that were overcome during this testing exercise will be presented. Results from testing show that the receiver will be within or near the specifications for ISS attitude and navigation performance. The process for verifying other requirements such as Time to First Fix, Time to First Attitude, selection/deselection of a specific GPS satellite vehicles (SV), minimum signal strength while still obtaining attitude and navigation, navigation and attitude output coverage, GPS week rollover, and Y2K requirements are also given in this paper.

Testing of the International Space Station and X-38 Crew Return Vehicle GPS Receiver

NASA Technical Reports Server (NTRS)

Simpson, James; Lightsey, Glenn; Campbell, Chip; Carpenter, Russell; Davis, George; Jackson, Larry; Davis, Ed; Kizhner, Semion

1999-01-01

This paper discusses the process and results of the performance testing of the GPS receiver planned for use on the International Space Station (ISS) and the X- 38CrewReturnVehicle(CRV). The receiver is a Force-19 unit manufactured by Trimble Navigation and modified in software by NASA:s Goddard Space Flight Center (GSFC) to perform navigation and attitude determination in space. The receiver is the primary source of navigation and attitude information for ISS and CRV. Engineers at GSFC have developed and tested the new receiver with a Global Simulation Systems Ltd (GSS) GPS Signal Generator (GPSSG). This paper documents the unique aspects of ground testing a GPS receiver that is designed for use in space. A discussion of the design of tests using the GPSSG, documentation, data capture, data analysis, and lessons learned will precede an overview of the performance of the new receiver. A description of the challenges that were overcome during this testing exercise will be presented. Results from testing show that the receiver will be within or near the specifications for ISS attitude and navigation performance. The process for verifying other requirements such as Time to First Fix, Time to First Attitude, selection/deselection of a specific GPS satellite vehicles (SV), minimum signal strength while still obtaining attitude and navigation, navigation and attitude output coverage, GPS week rollover, and Y2K requirements are also given in this paper.

Positional and Dimensional Accuracy Assessment of Drone Images Geo-referenced with Three Different GPSs

NASA Astrophysics Data System (ADS)

Cao, C.; Lee, X.; Xu, J.

2017-12-01

Unmanned Aerial Vehicles (UAVs) or drones have been widely used in environmental, ecological and engineering applications in recent years. These applications require assessment of positional and dimensional accuracy. In this study, positional accuracy refers to the accuracy of the latitudinal and longitudinal coordinates of locations on the mosaicked image in reference to the coordinates of the same locations measured by a Global Positioning System (GPS) in a ground survey, and dimensional accuracy refers to length and height of a ground target. Here, we investigate the effects of the number of Ground Control Points (GCPs) and the accuracy of the GPS used to measure the GCPs on positional and dimensional accuracy of a drone 3D model. Results show that using on-board GPS and a hand-held GPS produce a positional accuracy on the order of 2-9 meters. In comparison, using a differential GPS with high accuracy (30 cm) improves the positional accuracy of the drone model by about 40 %. Increasing the number of GCPs can compensate for the uncertainty brought by the GPS equipment with low accuracy. In terms of the dimensional accuracy of the drone model, even with the use of a low resolution GPS onboard the vehicle, the mean absolute errors are only 0.04 m for height and 0.10 m for length, which are well suited for some applications in precision agriculture and in land survey studies.

GPS Measurements of Crustal Deformation in Lebanon: Implication for Current Kinematics of the Sinaï Plate.

NASA Astrophysics Data System (ADS)

Vergnolle, M.; Jomaa, R.; Brax, M.; Menut, J. L.; Sursock, A.; Elias, A. R.; Mariscal, A.; Vidal, M.; Cotte, N.

2016-12-01

The Levant fault is a major strike-slip fault bounding the Arabia and the Sinaï plates. Its kinematics, although understood in its main characteristics, remains partly unresolved in its quantification, especially in the Lebanese restraining bend. We present a GPS velocity field based on survey GPS data acquired in Lebanon (1999, 2002, 2010) and on continuous GPS data publicly available in the Levant area. To complete the measurements along the Levant fault, we combine our velocity field with previously published velocity fields. First, from our velocity field, we derive two velocity profiles, across the Lebanese fault system, which we analyze in terms of elastic strain accumulation. Despite the uncertainty on the locking depth of the main strand of the Levant fault, small lateral fault slip rates (2-4mm/yr) are detected on each profile, with a slight slip rate decrease (<1mm/yr) from south to north. The latter is consistent with published results south and north of Lebanon. Small compression (<0.5mm/yr), with most part of it located across Mount Lebanon, is also suggested. Second, we analyze the combined GPS velocity field in the Sinaï tectonic framework. We evaluate how well the Sinaï plate motion is described with an Euler pole. Due to heterogeneous velocity errors (5 times smaller for cGPS velocities wrt sGPS velocities), a unique pole estimation using all the data provides good statistical results. However, the residuals show systematic deviations at central and northern sGPS stations. Using only the velocities at these stations, the estimated pole is significantly different from the unique pole at 95% confidence level. This analysis highlights the difficulty to robustly resolve the rigid Sinaï plate motion while the uncertainties on the velocities are heterogeneous. New sGPS measurements on existing sites should improve the solution and help to conclude.

A Teachable Moment in Earth Deformation: An Undergraduate Strain Module Incorporating GPS Measurement of the August 24, 2014 M6.0 South Napa Earthquake

NASA Astrophysics Data System (ADS)

Resor, P. G.; Cronin, V. S.; Hammond, W. C.; Pratt-Sitaula, B.; Olds, S. E.

2014-12-01

The August 24, 2014 M 6.0 South Napa Earthquake was the largest earthquake to occur in the San Francisco Bay Area, home to more than 7 million people, in almost 25 years. The event occurred within an area of dense GPS instrumentation including continuous stations from the EarthScope Plate Boundary Observatory, Bay Area Regional Deformation Network and other networks. Coseismic displacements of up to 3 cm were rapidly estimated within one day after the event, providing a map of Earth shape change at over one hundred stations around the epicenter. The earthquake thus presets as an excellent "teachable moment" to introduce students to basic geoscience concepts, modern geophysical methods, and the state of knowledge in earthquake science. We have developed an example exercise that uses GPS-derived interseismic velocities and coseismic offsets to explore deformation in the vicinity of the earthquake rupture. This exercise builds on the UNAVCO education resource "Infinitesimal Strain Analysis Using GPS Data" (http://www.unavco.org/education/resources/educational-resources/lesson/majors-gps-strain/majors-gps-strain.html), a module designed to introduce undergraduate geoscience majors to concepts of crustal deformation using GPS velocity data. In the module students build their intuition about infinitesimal strain through manipulation of physical models, apply this intuition to interpret maps of GPS velocity vectors, and ultimately calculate the instantaneous deformation rate of triangles on the Earth's surface defined by three GPS sites. The South Napa data sets provide an example with clear societal relevance that can be used to explore the basic concepts of deformation, but may also be extended to explore topics such as strain accumulation, release, and transfer associated with the earthquake cycle. The UNAVCO module could be similarly extended to create additional exercises in response to future events with clear geodetic signals.

Present-Day Strain and Rotation in the Lebanese Restraining Bend of the Dead Sea Fault System Based on Analysis of GPS Velocities

NASA Astrophysics Data System (ADS)

Gomez, F.; Jaafar, R.; Abdallah, C.; Karam, G.

2012-12-01

The Lebanese Restraining Bend (LRB) is a ~200-km-long bend in the central part of the Dead Sea Fault system (DSFS). As with other large restraining bends, this part of the transform is characterized by more complicated structure than other parts. Additionally, results from recent GPS studies have documented slower velocities north of the LRB than are observed along the southern DSFS to the south. In an effort to understand how strain is transferred through the LRB, this study analyzes improved GPS velocities within the central DSFS based on new data and additional stations. Despite relatively modest rates of seismicity, the Dead Sea Fault system (DSFS) has a historically documented record of producing large and devastating earthquakes. Hence, geodetic measurements of crustal deformation may provide key constraints on processes of strain accumulation that may not be evident in instrumentally recorded seismicity. Within the LRB, the transform splays into two prominent strike-slip faults: The through-going Yammouneh fault and the Serghaya fault. The latter appears to terminate in the Anti-Lebanon Mountains. Additionally, some oblique plate motion is accommodated by thrusting along the coast of Lebanon. This study used GPS observations from survey-mode GPS sites, as well as continuous GPS stations in the region. In total, 22 GPS survey sites have been measured in Lebanon between 2002 and 2010, along with GPS data from the adjacent area. Elastic models are used for initial assessment of fault slip rates. Incorporating two major strike-slip faults, as well as an offshore thrust fault, this modeling suggests left-lateral slip rates of 3.8 mm/yr and 1.1 mm/yr for the Yammouneh and Serghaya faults, respectively. The GPS survey network has sufficient density for analyzing velocity gradients in an effort to quantify tectonic strains and rotations. The velocity gradients suggest that differential rotations play a role in accommodating some plate motion.

The first geocenter estimation results using GPS measurements

NASA Technical Reports Server (NTRS)

Malla, R. P.; Wu, S. C.

1990-01-01

The center of mass of the Earth is the natural and unambiguous origin of a geocentric satellite dynamical system. A geocentric reference frame assumes that the origin of its coordinate axes is at the geocenter, in which all relevant observations and results can be referred and in which geodynamic theories or models for the dynamic behavior of Earth can be formulated. In practice, however, a kinematically obtained terrestrial reference frame may assume an origin other than the geocenter. A fast and accurate method of determining origin offset from the geocenter is highly desirable. Global Positioning System (GPS) measurements, because of their abundance and broad distribution, provide a powerful tool to obtain this origin offset in a short period of time. Two effective strategies have been devised. Data from the first Central and South America (Casa Uno) global GPS experiment were studied to demonstrate the ability of recovering the geocenter location with present-day GPS satellites and receivers.

ProSEDS Telemetry System Utilization of GPS Position Data for Transmitter Cycling

NASA Technical Reports Server (NTRS)

Kennedy, Paul; Sims, Herb

2000-01-01

NASA Marshall Space Flight Center will launch the Propulsive Small Expendable Deployer System (ProSEDS) space experiment in late 2000. ProSEDS will demonstrate the use of an electrodynamic tether propulsion system and will utilize a conducting wire tether to generate limited spacecraft power. This paper will provide an overview of the ProSEDS mission and will discuss the design, development and test of the spacecraft telemetry system which utilizes a custom designed GPS subsystem to determine spacecraft position relative to ground station location and to control transmitter on/off cycling based on spacecraft state vector and ground station visibility.

Independent Assessment of ITRF Site Velocities using GPS Imaging

NASA Astrophysics Data System (ADS)

Blewitt, G.; Hammond, W. C.; Kreemer, C.; Altamimi, Z.

2015-12-01

The long-term stability of ITRF is critical to the most challenging scientific applications such as the slow variation of sea level, and of ice sheet loading in Greenland and Antarctica. In 2010, the National Research Council recommended aiming for stability at the level of 1 mm/decade in the ITRF origin and scale. This requires that the ITRF include many globally-distributed sites with motions that are predictable to within a few mm/decade, with a significant number of sites having collocated stations of multiple techniques. Quantifying the stability of ITRF stations can be useful to understand stability of ITRF parameters, and to help the selection and weighting of ITRF stations. Here we apply a new suite of techniques for an independent assessment of ITRF site velocities. Our "GPS Imaging" suite is founded on the principle that, for the case of large numbers of data, the trend can be estimated objectively, automatically, robustly, and accurately by applying non-parametric techniques, which use quantile statistics (e.g., the median). At the foundation of GPS Imaging is the estimator "MIDAS" (Median Interannual Difference Adjusted for Skewness). MIDAS estimates the velocity with a realistic error bar based on sub-sampling the coordinate time series. MIDAS is robust to step discontinuities, outliers, seasonality, and heteroscedasticity. Common-mode noise filters enhance regional- to continental-scale precision in MIDAS estimates, just as they do for standard estimation techniques. Secondly, in regions where there is sufficient spatial sampling, GPS Imaging uses MIDAS velocity estimates to generate a regionally-representative velocity map. For this we apply a median spatial filter to despeckle the maps. We use GPS Imaging to address two questions: (1) How well do the ITRF site velocities derived by parametric estimation agree with non-parametric techniques? (2) Are ITRF site velocities regionally representative? These questions aim to get a handle on (1) the accuracy of ITRF site velocities as a function of characteristics of contributing station data, such as number of step parameters and total time span; and (2) evidence of local processes affecting site velocity, which may impact site stability. Such quantification can be used to rank stations in terms the risk that they may pose to the stability of ITRF.

Station-Keeping Strategies for Lead-Trail Formation Flying

NASA Astrophysics Data System (ADS)

Martinot, V.; Rozanes, P.

Numerous projects in the Science and Observation domains involve the use of formation flying to ensure the mission performance. The formation flying configurations proposed in some of them are quite complex with several satellites in different planes generating relative differential motions between the satellites like in case of circular projected formation-flying. However, more simple designs consisting of two satellites in a lead-trail formation appear to be sufficient for a wide range of applications (interferometry, geodesy,...). This article concentrates on the station- keeping phase of such formations in Low-Earth Orbits The station-keeping criterion for such formations can be expressed for example in terms of difference in argument of latitude between both satellites and at the altitudes considered, it evolves mainly under the differential effect of the atmospheric drag between the trailing and leading satellites. In the present paper, this differential effect is supposed to originate from the difference in the area-to-mass ratio between the satellites due to their different designs. A preliminary estimation of the navigation performance is first given assuming that on-board GPS receiver are mounted on each satellite of the formation to acquire pseudo-range measurements between the LEO satellites and the MEO GPS constellation. The distance between both satellites of the formation is derived from independent orbit restitution performed for each LEO satellite in a ground master control station processing the GPS measurements. A strategy for controlling the satellite formation disturbed by the differential effect of the drag is then proposed. Simulations are performed to assess the feasibility of the station-keeping with different types of engines. As by-products, the propellant budget and the frequency of the station-keeping manoeuvres are also given. A case study inspired from the ESA project Acechem/Metop is used for the simulations.

Data Access and Web Services at the EarthScope Plate Boundary Observatory

NASA Astrophysics Data System (ADS)

Matykiewicz, J.; Anderson, G.; Henderson, D.; Hodgkinson, K.; Hoyt, B.; Lee, E.; Persson, E.; Torrez, D.; Smith, J.; Wright, J.; Jackson, M.

2007-12-01

The EarthScope Plate Boundary Observatory (PBO) at UNAVCO, Inc., part of the NSF-funded EarthScope project, is designed to study the three-dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, PBO will install 880 continuous GPS stations, 103 borehole strainmeter stations, and five laser strainmeters, as well as manage data for 209 previously existing continuous GPS stations and one previously existing laser strainmeter. UNAVCO provides access to data products from these stations, as well as general information about the PBO project, via the PBO web site (http://pboweb.unavco.org). GPS and strainmeter data products can be found using a variety of access methods, incuding map searches, text searches, and station specific data retrieval. In addition, the PBO construction status is available via multiple mapping interfaces, including custom web based map widgets and Google Earth. Additional construction details can be accessed from PBO operational pages and station specific home pages. The current state of health for the PBO network is available with the statistical snap-shot, full map interfaces, tabular web based reports, and automatic data mining and alerts. UNAVCO is currently working to enhance the community access to this information by developing a web service framework for the discovery of data products, interfacing with operational engineers, and exposing data services to third party participants. In addition, UNAVCO, through the PBO project, provides advanced data management and monitoring systems for use by the community in operating geodetic networks in the United States and beyond. We will demonstrate these systems during the AGU meeting, and we welcome inquiries from the community at any time.

The Plate Boundary Observatory: Community Focused Web Services

NASA Astrophysics Data System (ADS)

Matykiewicz, J.; Anderson, G.; Lee, E.; Hoyt, B.; Hodgkinson, K.; Persson, E.; Wright, J.; Torrez, D.; Jackson, M.

2006-12-01

The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, is designed to study the three-dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, PBO will install 852 continuous GPS stations, 103 borehole strainmeter stations, 28 tiltmeters, and five laser strainmeters, as well as manage data for 209 previously existing continuous GPS stations. UNAVCO provides access to data products from these stations, as well as general information about the PBO project, via the PBO web site (http://pboweb.unavco.org). GPS and strainmeter data products can be found using a variety of channels, including map searches, text searches, and station specific data retrieval. In addition, the PBO construction status is available via multiple mapping interfaces, including custom web based map widgets and Google Earth. Additional construction details can be accessed from PBO operational pages and station specific home pages. The current state of health for the PBO network is available with the statistical snap-shot, full map interfaces, tabular web based reports, and automatic data mining and alerts. UNAVCO is currently working to enhance the community access to this information by developing a web service framework for the discovery of data products, interfacing with operational engineers, and exposing data services to third party participants. In addition, UNAVCO, through the PBO project, provides advanced data management and monitoring systems for use by the community in operating geodetic networks in the United States and beyond. We will demonstrate these systems during the AGU meeting, and we welcome inquiries from the community at any time.

Clustering of GPS velocities in the Mojave Block, southeastern California

NASA Astrophysics Data System (ADS)

Savage, J. C.; Simpson, R. W.

2013-04-01

find subdivisions within the Mojave Block using cluster analysis to identify groupings in the velocities observed at GPS stations there. The clusters are represented on a fault map by symbols located at the positions of the GPS stations, each symbol representing the cluster to which the velocity of that GPS station belongs. Fault systems that separate the clusters are readily identified on such a map. The most significant representation as judged by the gap test involves 4 clusters within the Mojave Block. The fault systems bounding the clusters from east to west are 1) the faults defining the eastern boundary of the Northeast Mojave Domain extended southward to connect to the Hector Mine rupture, 2) the Calico-Paradise fault system, 3) the Landers-Blackwater fault system, and 4) the Helendale-Lockhart fault system. This division of the Mojave Block is very similar to that proposed by Meade and Hager []. However, no cluster boundary coincides with the Garlock Fault, the northern boundary of the Mojave Block. Rather, the clusters appear to continue without interruption from the Mojave Block north into the southern Walker Lane Belt, similar to the continuity across the Garlock Fault of the shear zone along the Blackwater-Little Lake fault system observed by Peltzer et al. []. Mapped traces of individual faults in the Mojave Block terminate within the block and do not continue across the Garlock Fault [Dokka and Travis, ].

GPS measurements of deformation associated with the 1987 Superstition Hills earthquake: Evidence for conjugate faulting

NASA Technical Reports Server (NTRS)

Larsen, Shawn; Reilinger, Robert; Neugebauer, Helen; Strange, William

1991-01-01

Large station displacements observed from Imperial Valley Global Positioning System (GPS) campaigns are attributed to the November 24, 1987 Superstition Hills earthquake sequence. Thirty sites from a 42 station GPS network established in 1986 were reoccupied during 1988 and/or 1990. Displacements at three sites within 3 kilometers of the surface rupture approach 0.5 m. Eight additional stations within 20 km of the seismic zone are displaced at least 10 cm. This is the first occurrence of a large earthquake (M(sub S) 6.6) within a preexisting GPS network. Best-fitting uniform slip models of rectangular dislocations in an elastic half-space indicate 130 + or - 8 cm right-lateral displacement along the northwest-trending Superstition Hills fault and 30 + or - 10 cm left-lateral displacement along the conjugate northeast-trending Elmore Ranch fault. The geodetic moments are 9.4 x 10(exp 25) dyne-cm and 2.3 x 10(exp 25) dyne-cm for the Superstition Hills and Elmore Ranch faults, respectively, consistent with teleseismic source parameters. The data also suggest the post seismic slip along the Superstition Hills fault is concentrated at shallow depths. Distributed slip solutions using Singular Value Decomposition indicate near uniform displacement along the Elmore Ranch fault and concentrated slip to the northwest and southeast along the Superstition Hills fault. A significant component of non-seismic displacement is observed across the Imperial Valley, which is attributed in part to interseismic plate-boundary deformation.

Convergence rate across the Nepal Himalaya and interseismic coupling on the Main Himalayan Thrust, implications for seismic hazard

NASA Astrophysics Data System (ADS)

Ader, T. J.; Avouac, J.; Bollinger, L.; Lyon-Caen, H.; Chanard, K. D.; Galetzka, J. E.; Genrich, J. F.; Sapkota, S. N.

2011-12-01

We use 24 continuous GPS stations installed by Caltech throughout Nepal, in addition to previously published campaign GPS points and leveling data collected along the road Birganj-Katmandu-Kodari to propose a detailed pattern of coupling on the MHT. The continuous GPS time series are processed modeling the noise on the daily positions by a combination of white and flicker noise, in order to infer secular velocities at the stations with consistent error bars. We then locate the pole of rotation of the Indian plate in the ITRF 2005 reference frame at longitude = 3.6o ± 2.6o, latitude = 51.52o ± 0.26o with an angular velocity of Ω = 0.518 ± 0.008o/Myr. The pattern of coupling on the MHT is computed with a backslip model on a fault dipping 10o to the North and whose strike roughly follows the foothills of the Himalayan chain. The model indicates that the MHT is locked from the surface to a distance of approximately 100 km along dip, corresponding to a depth of 15 to 20 km where the temperature reaches 350oC. In map view, the transition locked/creeping seems to be at the most a few tens of kilometers wide and overlaps with the belt of midcrustal microseismicity underneath the Himalayas. The convergence of the Indian plate underneath the Tibetan plateau proceeds at a rate of 18.1 ± 0.5~mm/yr in central and eastern Nepal and 19.9 ± 0.7~mm/yr in western Nepal. The moment deficit accrues at a rate of 6.7 ± 1019 Nm/yr on the MHT. This rate exceeds by far the moment released by the seismicity in the past 500 years, indicating that the risk for a large M > 8 earthquake to happen in Nepal is real.

Russian State Time and Earth Rotation Service: Observations, Eop Series, Prediction

NASA Astrophysics Data System (ADS)

Kaufman, M.; Pasynok, S.

2010-01-01

Russian State Time, Frequency and Earth Rotation Service provides the official EOP data and time for use in scientific, technical and metrological works in Russia. The observations of GLONASS and GPS on 30 stations in Russia, and also the Russian and worldwide observations data of VLBI (35 stations) and SLR (20 stations) are used now. To these three series of EOP the data calculated in two other Russian analysis centers are added: IAA (VLBI, GPS and SLR series) and MCC (SLR). Joint processing of these 7 series is carried out every day (the operational EOP data for the last day and the predicted values for 50 days). The EOP values are weekly refined and systematic errors of every individual series are corrected. The combined results become accessible on the VNIIFTRI server (ftp.imvp.ru) approximately at 6h UT daily.

The BDS iGMAS RIOS station at Observatório Nacional, Rio de Janeiro

NASA Astrophysics Data System (ADS)

Humberto Andrei, Alexandre; Song, Shuli; Junqueira, Selma; Beauvalet, Laurene

2016-07-01

GNSS navigation satellites are currently being developed by all major players in the science and technology scene, to compete with the GPS system. Because their applications span many different areas, from traffic and cargo control, to geodesy and seismic monitoring, it is required to assess the coherence between the different constellations. BDS is the GNSS system currently developed in China. Its first generation of satellites consisted of 3 geostationnary satellites allowing geolocalisation in China only. In addition to these satellites, other satellites have been launched in geostationnary and geosynchronous orbits, as well as satellites orbiting with a classical GNSS semi-major axis. With these additions, the BDS system possesses 19 operating satellites, and though the system is mostly efficient for geolocalisation in Asia, the satellites are also visible in other parts of the globe. In parallel to the development of the BDS constellation, China has launched the iGMAS (International GNSS Monitoring and Assessment Service) project to develop a global tracking network of multi-GNSS geodetic receivers. One of the goals of this project is to evaluate the efficiency of the BDS constellation as well as the efficiency of the receivers developed by the Chinese laboratories. As part of the Brazilian program COSBAN leaded by the Foreign Affairs Ministry to foster up the science and technology partnership with China, materialized by the collaboration between the Shanghai Astronomical Observatory/CAS and the Observatório Nacional/MCTI, in Rio de Janeiro. Through it the RIOS-iGMAS station was installed at Observatório Nacional, where the RJEP GNSS station already operates as part of the Brazilian reference system. Thus at the Observatório Nacional can be observed satellites from any constellation with both systems of reception, leading to a direct, efficient way to compare the results obtained for each network. In this communication we focus on the determination of the position of the satellites by analyzing the pseudo-ranges obtained by C1W code for GPS, and C7I code for BDS. Using the Allan variation a crucial result is obtained. It is shown that the BDS system can perform at the level of the GPS system, provided equal satellite coverage. On the other hand at the Observatório Nacional it is detected a near constant bias of about 35m between the ranges simultaneously derived from the RIOS (iGMAS) and RJEP (GNSS) stations, no matter the observed satellite, or constellation. Both results are presented and discussed. We also present the current status of the installation of a second BDS iGMAS station, in a northern, equatorial location in Brazil. The operational and scientific perspectives are disclosed.

New approach to detect seismic surface waves in 1Hz-sampled GPS time series

PubMed Central

Houlié, N.; Occhipinti, G.; Blanchard, T.; Shapiro, N.; Lognonné, P.; Murakami, M.

2011-01-01

Recently, co-seismic seismic source characterization based on GPS measurements has been completed in near- and far-field with remarkable results. However, the accuracy of the ground displacement measurement inferred from GPS phase residuals is still depending of the distribution of satellites in the sky. We test here a method, based on the double difference (DD) computations of Line of Sight (LOS), that allows detecting 3D co-seismic ground shaking. The DD method is a quasi-analytically free of most of intrinsic errors affecting GPS measurements. The seismic waves presented in this study produced DD amplitudes 4 and 7 times stronger than the background noise. The method is benchmarked using the GEONET GPS stations recording the Hokkaido Earthquake (2003 September 25th, Mw = 8.3). PMID:22355563

Microwave radiometer observations of interannual water vapor variability and vertical structure over a tropical station

NASA Astrophysics Data System (ADS)

Renju, R.; Suresh Raju, C.; Mathew, Nizy; Antony, Tinu; Krishna Moorthy, K.

2015-05-01

The intraseasonal and interannual characteristics and the vertical distribution of atmospheric water vapor from the tropical coastal station Thiruvananthapuram (TVM) located in the southwestern region of the Indian Peninsula are examined from continuous multiyear, multifrequency microwave radiometer profiler (MRP) measurements. The accuracy of MRP for precipitable water vapor (PWV) estimation, particularly during a prolonged monsoon period, has been demonstrated by comparing with the PWV derived from collocated GPS measurements based on regression model between PWV and GPS wet delay component which has been developed for TVM station. Large diurnal and intraseasonal variations of PWV are observed during winter and premonsoon seasons. There is large interannual PWV variability during premonsoon, owing to frequent local convection and summer thunderstorms. During monsoon period, low interannual PWV variability is attributed to the persistent wind from the ocean which brings moisture to this coastal station. However, significant interannual humidity variability is seen at 2 to 6 km altitude, which is linked to the monsoon strength over the station. Prior to monsoon onset over the station, the specific humidity increases up to 5-10 g/kg in the altitude region above 5 km and remains consistently so throughout the active spells.

PBO Facility Construction: Basin and Range and Rocky Mountain Regions Status

NASA Astrophysics Data System (ADS)

Friesen, B.; Jenkins, F.; Kasmer, D.; Feaux, K.

2007-12-01

The Plate Boundary Observatory (PBO), part of the larger NSF-funded EarthScope project, will study the three- dimensional strain field resulting from active plate boundary deformation across the western United States. PBO is a large construction project involving the reconnaissance, permitting, installation, documentation, and maintenance of 875 permanent GPS stations in five years. 163 of these stations lie within the Basin and Range and Rocky Mountain Regions consisting of the states of Montana, Idaho, Nevada, Utah, Wyoming, Colorado, New Mexico, and Arizona. During the fourth year of the project, the Basin and Range and Rocky Mountain regions of PBO completed reconnaissance and nearly all permitting activities, and maintained a fast pace of station installations. The fall of 2006 and spring of 2007 were devoted to the construction of a large push of 50 stations, most located on Bureau of Land Management controlled public lands in Nevada. This transect is located along Highway 50 and will profile the extension of the Basin and Range province. The Yellowstone area, including surrounding National Parks and Forests was the target of summer 2007, during which time 10 remote stations with difficult logistics were installed. To date, construction is complete for 135 of 163 GPS stations.

The influence of grounding on GPS receiver differential code biases

NASA Astrophysics Data System (ADS)

Choi, Byung-Kyu; Lee, Sang Jeong

2018-07-01

The Global Positioning System (GPS) has become an effective tool for estimating ionospheric total electron content (TEC). One of the critical factors affecting ionospheric TEC estimation from GPS data is the differential code biases (DCBs) inherent in both GPS receivers and satellites. To investigate the factor that affects the receiver DCB, we consider the relationship between the receiver DCB and the grounding of an antenna. GPS data from 9 stations in South Korea from three periods (the years 2009, 2014, and 2017) were used in the analysis. It was found that a significant jump (∼8-13 ns, or ∼ 23-37 TECU) in hourly DCB time series occurred simultaneously at the two different sites when an antenna is changed from a grounded to the non-grounded state. Thus, our study clearly identifies that the grounding of GPS equipment is a factor of the receiver DCB changes.

Computation of Estonian CORS data using Bernese 5.2 and Gipsy 6.4 softwares

NASA Astrophysics Data System (ADS)

Kollo, Karin; Kall, Tarmo; Liibusk, Aive

2017-04-01

GNSS permanent station network in Estonia (ESTREF) was established already in 2007. In 2014-15 extensive reconstruction of ESTREF was carried out, including the establishment of 18 new stations, change of the hardware in CORS stations as well as establishing GNSS-RTK service for the whole Estonia. For GNSS-RTK service one needs precise coordinates in well-defined reference frame, i.e., ETRS89. For long time stability of stations and time-series analysis the re-processing of Estonian CORS data is ongoing. We re-process data from 2007 until 2015 with program Bernese GNSS 5.2 (Dach, 2015). For the set of ESTREF stations established in 2007, we perform as well computations with GIPSY 6.4 software (Ries et al., 2015). In the computations daily GPS-only solution was used. For precise orbits, final products from CODE (CODE analysis centre at the Astronomical Institute of the University of Bern) and JPL (Jet Propulsion Laboratory) for Bernese and GIPSY solutions were used, respectively. The cut-off angle was set to 10 degrees in order to avoid near-field multipath influence. In GIPSY, precise point positioning method with fixing ambiguities was used. Bernese calculations were performed based on double difference processing. Antenna phase centers were modelled based on igs08.atx and epnc_08.atx files. Vienna mapping function was used for mapping tropospheric delays. For the GIPSY solution, the higher order ionospheric term was modelled based on IRI-2012b model. For the Bernese solution higher order ionospheric term was neglected. FES2004 ocean tide loading model was used for the both computation strategies. As a result, two solutions using different scientific GNSS computation programs were obtained. The results from Bernese and GIPSY solutions were compared, using station repeatability values, RMS and coordinate differences. KEYWORDS: GNSS reference station network, Bernese GNSS 5.2, Gipsy 6.4, Estonia. References: Dach, R., S. Lutz, P. Walser, P. Fridez (Eds); 2015: Bernese GNSS Software Version 5.2. User manual, Astronomical Institute, Universtiy of Bern, Bern Open Publishing. DOI: 10.7892/boris.72297; ISBN: 978-3-906813-05-9. Paul Ries, Willy Bertiger, Shailen, Shailen Desai, & Kevin Miller. (2015). GIPSY 6.4 Release Notes. Jet Propulsion Laboratory, California Institute of Technology. Retrieved from https://gipsy-oasis.jpl.nasa.gov/docs/index.php

Repeated Seafloor Geodetic Observation west off Miyake-jima volcanic island

NASA Astrophysics Data System (ADS)

Mochizuki, M.; Sato, M.; Fujita, M.; Katayama, M.; Yoshida, Z.; Yabuki, T.; Asada, A.

2003-12-01

An intensive earthquake swarm started under Miyake-jima island, 180 km south off Japan main island, on June 26, 2000. The earthquake swarm migrated towards northwest off Miyake-jima island, where numerous earthquakes, more than 100,000, were detected within about two months and an extensive crustal deformation was observed by on-land geodetic observations. Inst. of Industrial Science, Univ. of Tokyo and Hydrographic and Oceanographic Dept, Japan Coast Guard deployed three seafloor geodetic reference stations (St.A, St.B & St.C) in triangle area surrounded by three islands, Miyake-jima, Nii-jima and Kouzu-jima islands, in November and December, 2000, and have been conducting observations using these three stations to monitor seafloor deformation for the better understandings of underground magmatic activities. The observations have been conducted thirteen times until present. Fast and quickly varying ocean current in this area prevented us from stable observation. The surface current makes the pole, which connects the GPS antenna and the ship-board transducer, bend. This bending of the pole gave uncertainty to the analyses of locating the positions of the seafloor geodetic reference stations. The pole was replaced new, more rigid pole to overcome the problem in August 2002. The first observation with this new system was conducted at the reference station in the Sagami-bay. Smaller amount of bending with the new pole than that with the old one against both roll and pitch components could be seen in the data from this observation. This shows that the replacement of the pole provided stability to the observation system. We started to adopt the new system to the observation at the three stations west-off Miyake-jima island area, too. Station C, that is located nearest one to the Miyake-jima island, is one where we had most frequent observation after improvement of the system. The observations with the new system have been conducted four times in September, December 2002, April and August 2003 there. We have been processing and analyzing the data from these four observations at Station C. More stable analyses have been done with the data from the observations which the new system was employed than with ones observed by the old system. In this poster, we will present the repeatability of the observation system with the new pole, as well as discuss the preliminary results from them.

Ionospheric Modelling using GPS to Calibrate the MWA. II: Regional Ionospheric Modelling using GPS and GLONASS to Estimate Ionospheric Gradients

NASA Astrophysics Data System (ADS)

Arora, B. S.; Morgan, J.; Ord, S. M.; Tingay, S. J.; Bell, M.; Callingham, J. R.; Dwarakanath, K. S.; For, B.-Q.; Hancock, P.; Hindson, L.; Hurley-Walker, N.; Johnston-Hollitt, M.; Kapińska, A. D.; Lenc, E.; McKinley, B.; Offringa, A. R.; Procopio, P.; Staveley-Smith, L.; Wayth, R. B.; Wu, C.; Zheng, Q.

2016-07-01

We estimate spatial gradients in the ionosphere using the Global Positioning System and GLONASS (Russian global navigation system) observations, utilising data from multiple Global Positioning System stations in the vicinity of Murchison Radio-astronomy Observatory. In previous work, the ionosphere was characterised using a single-station to model the ionosphere as a single layer of fixed height and this was compared with ionospheric data derived from radio astronomy observations obtained from the Murchison Widefield Array. Having made improvements to our data quality (via cycle slip detection and repair) and incorporating data from the GLONASS system, we now present a multi-station approach. These two developments significantly improve our modelling of the ionosphere. We also explore the effects of a variable-height model. We conclude that modelling the small-scale features in the ionosphere that have been observed with the MWA will require a much denser network of Global Navigation Satellite System stations than is currently available at the Murchison Radio-astronomy Observatory.

Space geodetic observation of expansion of the San Gabriel Valley, California, aquifer system, during heavy rainfall in winter 2004-2005

USGS Publications Warehouse

King, N.E.; Argus, D.; Langbein, J.; Agnew, D.C.; Bawden, G.; Dollar, R.S.; Liu, Z.; Galloway, D.; Reichard, E.; Yong, A.; Webb, F.H.; Bock, Y.; Stark, K.; Barseghian, D.

2007-01-01

Starting early in 2005, the positions of GPS stations in the San Gabriel valley region of southern California showed statistically significant departures from their previous behavior. Station LONG moved up by about 47 mm, and nearby stations moved away from LONG by about 10 mm. These changes began during an extremely rainy season in southern California and coincided with a 16-m increase in water level at a nearby well in Baldwin Park and a regional uplift detected by interferometric synthetic aperture radar. No equivalent signals were seen in GPS station position time series elsewhere in southern California. Our preferred explanation, supported by the timing and by a hydrologic simulation, is deformation due to recharging of aquifers after near-record rainfall in 2004-2005. We cannot rule out an aseismic slip event, but we consider such an event unlikely because it requires slip on multiple faults and predicts other signals that are not observed. Copyright 2007 by the American Geophysical Union.

Real-time Kinematics Base Station and Survey Unit Setup Method for the Synchronous Impulse Reconstruction (SIRE) Radar

DTIC Science & Technology

2012-12-01

GPS receiver, the Ashtech ProMark 500; a 3.4-GHz radio modem, the FreeWave 3400-SMR; a display unit, the Magellan MobileMapper CX; a 12-V battery pack...Figure 8. Bottom view of the ProMark 500. 3.1 Survey Unit RTK GPS Setup The following are the procedures for setting up...the RTK GPS Survey Unit: 1. Connect the radio modem to the ProMark 500 with serial cable #7 and #8. Display Screen Scroll Button Power LED Log

Rail inspection system based on iGPS

NASA Astrophysics Data System (ADS)

Fu, Xiaoyan; Wang, Mulan; Wen, Xiuping

2018-05-01

Track parameters include gauge, super elevation, cross level and so on, which could be calculated through the three-dimensional coordinates of the track. The rail inspection system based on iGPS (indoor/infrared GPS) was composed of base station, receiver, rail inspection frame, wireless communication unit, display and control unit and data processing unit. With the continuous movement of the inspection frame, the system could accurately inspect the coordinates of rail; realize the intelligent detection and precision measurement. According to principle of angle intersection measurement, the inspection model was structured, and detection process was given.

Global positioning system network analysis with phase ambiguity resolution applied to crustal deformation studies in California

NASA Technical Reports Server (NTRS)

Dong, Da-Nan; Bock, Yehuda

1989-01-01

An efficient algorithm is developed for multisession adjustment of GPS data with simultaneous orbit determination and ambiguity resolution. Application of the algorithm to the analysis of data from a five-year campaign in progress in southern and central California to monitor tectonic motions using observations by GPS satellites, demonstrates improvements in estimates of station position and satellite orbits when the phase ambiguities are resolved. Most of the phase ambiguities in the GPS network were resolved, particularly for all the baselines of geophysical interest in California.

METAS New Time Scale Generation System - A Progress Report

DTIC Science & Technology

2007-01-01

and a TWSTFT station are used for remote T&F comparisons. The GPS TAI link is driven by one of the atomic clocks defined as the REF clock...UTC(CH.P) paper clock TA(CH.P) paper clock TWSTFT link GPS link CH00 WAB1 H-maser 1-PPS H-maser 1-PPS REF 1-PPS 5-MHz from all clocks UTC(CH.R) 1-PPS...lost, the only consequence would be a transient of UTC (CH.P), which can be corrected by a subsequent steering. The GPS and TWSTFT links can be

Strategies for high-precision Global Positioning System orbit determination

NASA Technical Reports Server (NTRS)

Lichten, Stephen M.; Border, James S.

1987-01-01

Various strategies for the high-precision orbit determination of the GPS satellites are explored using data from the 1985 GPS field test. Several refinements to the orbit determination strategies were found to be crucial for achieving high levels of repeatability and accuracy. These include the fine tuning of the GPS solar radiation coefficients and the ground station zenith tropospheric delays. Multiday arcs of 3-6 days provided better orbits and baselines than the 8-hr arcs from single-day passes. Highest-quality orbits and baselines were obtained with combined carrier phase and pseudorange solutions.

GPS Imaging of Time-Dependent Seasonal Strain in Central California

NASA Astrophysics Data System (ADS)

Kraner, M.; Hammond, W. C.; Kreemer, C.; Borsa, A. A.; Blewitt, G.

2016-12-01

Recently, studies are suggesting that crustal deformation can be time-dependent and nontectonic. Continuous global positioning system (cGPS) measurements are now showing how steady long-term deformation can be influenced by factors such as fluctuations in loading and temperature variations. Here we model the seasonal time-dependent dilatational and shear strain in Central California, specifically surrounding the Parkfield region and try to uncover the sources of these deformation patterns. We use 8 years of cGPS data (2008 - 2016) processed by the Nevada Geodetic Laboratory and carefully select the cGPS stations for our analysis based on the vertical position of cGPS time series during the drought period. In building our strain model, we first detrend the selected station time series using a set of velocities from the robust MIDAS trend estimator. This estimation algorithm is a robust approach that is insensitive to common problems such as step discontinuities, outliers, and seasonality. We use these detrended time series to estimate the median cGPS positions for each month of the 8-year period and filter displacement differences between these monthly median positions using a filtering technique called "GPS Imaging." This technique improves the overall robustness and spatial resolution of the input displacements for the strain model. We then model our dilatational and shear strain field for each month of time series. We also test a variety of a priori constraints, which controls the style of faulting within the strain model. Upon examining our strain maps, we find that a seasonal strain signal exists in Central California. We investigate how this signal compares to thermoelastic, hydrologic, and atmospheric loading models during the 8-year period. We additionally determine whether the drought played a role in influencing the seasonal signal.

A combined method to calculate co-seismic displacements through strong motion acceleration baseline correction

NASA Astrophysics Data System (ADS)

Zhan, W.; Sun, Y.

2015-12-01

High frequency strong motion data, especially near field acceleration data, have been recorded widely through different observation station systems among the world. Due to tilting and a lot other reasons, recordings from these seismometers usually have baseline drift problems when big earthquake happens. It is hard to obtain a reasonable and precision co-seismic displacement through simply double integration. Here presents a combined method using wavelet transform and several simple liner procedures. Owning to the lack of dense high rate GNSS data in most of region of the world, we did not contain GNSS data in this method first but consider it as an evaluating mark of our results. This semi-automatic method unpacks a raw signal into two portions, a summation of high ranks and a low ranks summation using a cubic B-spline wavelet decomposition procedure. Independent liner treatments are processed against these two summations, which are then composed together to recover useable and reasonable result. We use data of 2008 Wenchuan earthquake and choose stations with a near GPS recording to validate this method. Nearly all of them have compatible co-seismic displacements when compared with GPS stations or field survey. Since seismometer stations and GNSS stations from observation systems in China are sometimes quite far from each other, we also test this method with some other earthquakes (1999 Chi-Chi earthquake and 2011 Tohoku earthquake). And for 2011 Tohoku earthquake, we will introduce GPS recordings to this combined method since the existence of a dense GNSS systems in Japan.

SLR tracking of GPS-35

NASA Technical Reports Server (NTRS)

Pavlis, Erricos C.

1994-01-01

An experiment was designed to launch a corner cube retroreflector array on one of the Global Positioning Satellites (GPS). The launch on Aug. 31, 1993 ushered in the era of SLR tracking of GPS spacecraft. Once the space operations group finished the check-out procedures for the new satellite, the agreed upon SLR sites were allowed to track it. The first site to acquire GPS-35 was the Russian system at Maidanak and closely after the MLRS system at McDonald Observatory, Texas. The laser tracking network is currently tracking the GPS spacecraft known as GPS-35 or PRN 5 with great success. From the NASA side there are five stations that contribute data regularly and nearly as many from the international partners. Upcoming modifications to the ground receivers will allow for a further increase in the tracking capabilities of several additional sites and add some desperately needed southern hemisphere tracking. We are analyzing the data and are comparing SLR-derived orbits to those determined on the basis of GPS radiometric data.

Local effects of redundant terrestrial and GPS-based tie vectors in ITRF-like combinations

NASA Astrophysics Data System (ADS)

Abbondanza, Claudio; Altamimi, Zuheir; Sarti, Pierguido; Negusini, Monia; Vittuari, Luca

2009-11-01

Tie vectors (TVs) between co-located space geodetic instruments are essential for combining terrestrial reference frames (TRFs) realised using different techniques. They provide relative positioning between instrumental reference points (RPs) which are part of a global geodetic network such as the international terrestrial reference frame (ITRF). This paper gathers the set of very long baseline interferometry (VLBI)-global positioning system (GPS) local ties performed at the observatory of Medicina (Northern Italy) during the years 2001-2006 and discusses some important aspects related to the usage of co-location ties in the combinations of TRFs. Two measurement approaches of local survey are considered here: a GPS-based approach and a classical approach based on terrestrial observations (i.e. angles, distances and height differences). The behaviour of terrestrial local ties, which routinely join combinations of space geodetic solutions, is compared to that of GPS-based local ties. In particular, we have performed and analysed different combinations of satellite laser ranging (SLR), VLBI and GPS long term solutions in order to (i) evaluate the local effects of the insertion of the series of TVs computed at Medicina, (ii) investigate the consistency of GPS-based TVs with respect to space geodetic solutions, (iii) discuss the effects of an imprecise alignment of TVs from a local to a global reference frame. Results of ITRF-like combinations show that terrestrial TVs originate the smallest residuals in all the three components. In most cases, GPS-based TVs fit space geodetic solutions very well, especially in the horizontal components (N, E). On the contrary, the estimation of the VLBI RP Up component through GPS technique appears to be awkward, since the corresponding post fit residuals are considerably larger. Besides, combination tests including multi-temporal TVs display local effects of residual redistribution, when compared to those solutions where Medicina TVs are added one at a time. Finally, the combination of TRFs turns out to be sensitive to the orientation of the local tie into the global frame.

Precise orbit determination of Multi-GNSS constellation including GPS GLONASS BDS and GALIEO

NASA Astrophysics Data System (ADS)

Dai, Xiaolei

2014-05-01

In addition to the existing American global positioning system (GPS) and the Russian global navigation satellite system (GLONASS), the new generation of GNSS is emerging and developing, such as the Chinese BeiDou satellite navigation system (BDS) and the European GALILEO system. Multi-constellation is expected to contribute to more accurate and reliable positioning and navigation service. However, the application of multi-constellation challenges the traditional precise orbit determination (POD) strategy that was designed usually for single constellation. In this contribution, we exploit a more rigorous multi-constellation POD strategy for the ongoing IGS multi-GNSS experiment (MGEX) where the common parameters are identical for each system, and the frequency- and system-specified parameters are employed to account for the inter-frequency and inter-system biases. Since the authorized BDS attitude model is not yet released, different BDS attitude model are implemented and their impact on orbit accuracy are studied. The proposed POD strategy was implemented in the PANDA (Position and Navigation Data Analyst) software and can process observations from GPS, GLONASS, BDS and GALILEO together. The strategy is evaluated with the multi-constellation observations from about 90 MGEX stations and BDS observations from the BeiDou experimental tracking network (BETN) of Wuhan University (WHU). Of all the MGEX stations, 28 stations record BDS observation, and about 80 stations record GALILEO observations. All these data were processed together in our software, resulting in the multi-constellation POD solutions. We assessed the orbit accuracy for GPS and GLONASS by comparing our solutions with the IGS final orbit, and for BDS and GALILEO by overlapping our daily orbit solution. The stability of inter-frequency bias of GLONASS and inter-system biases w.r.t. GPS for GLONASS, BDS and GALILEO were investigated. At last, we carried out precise point positioning (PPP) using the multi-constellation POD orbit and clock products, and analyzed the contribution of these POD products to PPP. Keywords: Multi-GNSS, Precise Orbit Determination, Inter-frequency bias, Inter-system bias, Precise Point Positioning

Monitoring of seafloor crustal deformation using GPS/Acoustic technique along the Nankai Trough, Japan

NASA Astrophysics Data System (ADS)

Yasuda, K.; Tadokoro, K.; Ikuta, R.; Watanabe, T.; Fujii, C.; Matsuhiro, K.; Sayanagi, K.

2014-12-01

Seafloor crustal deformation is crucial for estimating the interplate locking at the shallow subduction zone and has been carried out at subduction margins in Japan, e.g., Japan Trench and Nankai Trough [Sato et al., 2011; Tadokoro et al., 2012]. Iinuma et al. [2012] derived slip distributions during the 2011 Tohoku-Oki earthquake using GPS/Acoustic data and on-land GPS data. The result showed that maximum slip is more than 85 m near the trench axis. The focal area along the Nankai trough extended to the trough axis affected this earthquake by cabinet office, government of Japan. 　We monitored seafloor crustal deformation along the Nankai trough, Japan. Observation regions are at the eastern end of Nankai trough (named Suruga trough) and at the central Nankai trough. We established and monitored by two sites across the trough at each region. In the Suruga trough region, we repeatedly observed from 2005 to 2013. We observed 13 and 14 times at a foot wall side (SNE) and at a hanging wall side (SNW), respectively. We estimated the displacement velocities with relative to the Amurian plate from the result of repeated observation. The estimated displacement velocity vectors at SNE and SNW are 42±8 mm/y to N94±3˚W direction and 39±11 mm/y to N84±9˚W direction, respectively. The directions are the same as those measured at the on-land GPS stations. The magnitudes of velocity vector indicate significant shortening by approximately 4 mm/y between SNW and on-land GPS stations at hanging wall side of the Suruga Trough. This result shows that the plate interface at the northernmost Suruga trough is strongly locked. In the central Nankai trough region, we established new two stations across the central Nankai trough (Both stations are about 15km distance from trough) and observed only three times, August 2013, January 2014, and June 2014. We report the results of monitoring performed in this year.

Latitudinal dependence of diurnal and seasonal variations in the tropospheric zenith delay observed from GPS measurements within the longitudinal sector of 50oE to 130oE.

NASA Astrophysics Data System (ADS)

Raju, Suresh; Saha, Korak; Anupama, K.; Parameswaran, Krishnaswamy

Ground based GPS finds potential applications in many atmospheric studies such as the spatial distribution of columnar water vapor as well as tidal oscillations in the atmosphere. As the zenith tropospheric delay (ZTD) derived from GPS data is a function of atmospheric pressure, temperature and watervapor, the effect of atmospheric oscillations could reflect more promi-nently in its temporal variations. The GPS data with very high temporal resolution (5 min.) from thirteen IGS stations in the longitudinal sector of 50o-130oE are used to establish its potential for studying the atmospheric tidal, intra-seasonal and planetary oscillations. Very prominent tidal (diurnal and semi-diurnal) oscillations observed at all these stations, with am-plitude of the diurnal variation as ˜0.5-12+0.5 mm and that of the semi-diurnal variation in the range ˜0.1-5+0.2 mm. Although 90% of the delay is contributed by the dry atmospheric pressure (which shows prominent semi-diurnal oscillations) the tidal oscillations in the ZTD is dominated by the diurnal component. This effect could be attributed to the temporal variations of atmospheric water vapor in a diurnal scale. The amplitude of these variations in general is largest near the equator and decreases with increase in latitude. Interestingly, this latitudinal trend matches very well with the latitude variation of the precipitable water vapor (as well as the actual precipitation) in this longitudinal region. Though the values of ZTD at stations very close to equator stations do not show any prominent seasonal variation, as the latitude increases the annual variation in ZTD becomes more distinct. A prominent peak in ZTD is observed during the July-August period, which matches well with the annual variation of atmospheric water vapor. This shows that the diurnal and seasonal variation of ZTD is mainly governed by the corresponding variations in atmospheric water vapor, even though its contribution to the total delay is around 10%. Keywords: GPS, Tropospheric delay, Atmospheric oscillations # Dr. K. Parameswaran is supported by CSIR through Emeritus Scientist Scheme. * corresponding author: koraksaha@gmail.com

Near Real-Time Processing and Archiving of GPS Surveys for Crustal Motion Monitoring

NASA Astrophysics Data System (ADS)

Crowell, B. W.; Bock, Y.

2008-12-01

We present an inverse instantaneous RTK method for rapidly processing and archiving GPS data for crustal motion surveys that gives positional accuracy similar to traditional post-processing methods. We first stream 1 Hz data from GPS receivers over Bluetooth to Verizon XV6700 smartphones equipped with Geodetics, Inc. RTD Rover software. The smartphone transmits raw receiver data to a real-time server at the Scripps Orbit and Permanent Array Center (SOPAC) running RTD Pro. At the server, instantaneous positions are computed every second relative to the three closest base stations in the California Real Time Network (CRTN), using ultra-rapid orbits produced by SOPAC, the NOAATrop real-time tropospheric delay model, and ITRF2005 coordinates computed by SOPAC for the CRTN stations. The raw data are converted on-the-fly to RINEX format at the server. Data in both formats are stored on the server along with a file of instantaneous positions, computed independently at each observation epoch. The single-epoch instantaneous positions are continuously transmitted back to the field surveyor's smartphone, where RTD Rover computes a median position and interquartile range for each new epoch of observation. The best-fit solution is the last median position and is available as soon as the survey is completed. We describe how we used this method to process 1 Hz data from the February, 2008 Imperial Valley GPS survey of 38 geodetic monuments established by Imperial College, London in the 1970's, and previously measured by SOPAC using rapid-static GPS methods in 1993, 1999 and 2000, as well as 14 National Geodetic Survey (NGS) monuments. For redundancy, each monument was surveyed for about 15 minutes at least twice and at staggered intervals using two survey teams operating autonomously. Archiving of data and the overall project at SOPAC is performed using the PGM software, developed by the California Spatial Reference Center (CSRC) for the National Geodetic Survey (NGS). The importation of raw receiver data, site metadata and antenna height information is performed using PGM client software running on the same PDA running RTD Rover or laptop, and uploaded to the PGM server where the raw data are converted to RINEX format. The campaign information is then published online, where all of the campaign information can be accessed such as start and stop times, equipment information, RINEX and solution SINEX files, observer information and baseline information for network adjustments.

Implementation of Barcelona, L'estartit and Ibiza Sites for Altimeter Calibration

NASA Astrophysics Data System (ADS)

Martinez-Benjamin, J. J.; Gili, J.; Lopez, R.; Tapia, A.; Bosch, E.; Perez, B.; Pros, F.

2012-12-01

A marine campaign to compute the sea surface data along the Spanish Mediterranean coastline and Balearic Islands is being prepared for 2013. Jason-2 (period ~10 days) and Saral/AltiKa (period of 35 days and expected launch in 2012) altimetric data and on-board GPS data will be used. Many GPS Buoy sessions along the ship route will be performed.Sea height estimates (instantaneous and mean sea levels) will be compared. Recently some geodetic improvements has been made in specific coastal spanish sites in the NW Mediterranean Sea for monitoring sea level. The goal is to maintain and improve the quality of the observation of the sea level change in the three sites. The information is coming from Puertos del Estado www.puertos.es L'Estartit tide gauge has been co-located with geodetic techniques (GPS measurements of XU, Utilitary Network, and XdA, Levelling Network,) and it is tied to the SPGIC (Integrated Geodetic Positioning System of Catalonia) project of the Cartographic Institute of Catalunya (ICC). In the past three calibration campaigns for Topex/Poseidon and Jason-1 in March 1999, August 2000 and July 2002 near Cape of Begur. At Barcelona harbour there is one MIROS radar tide gauge belonging to Puertos del Estado (Spanish Harbours).The radar sensor is over the water surface, on a L-shaped structure which elevates it a few meters above the quay shelf. 1-min data are transmitted to the ENAGAS Control Center by cable and then sent each 1 min to Puertos del Estado by e-mail. The information includes wave forescast (mean period, significant wave height, sea level, etc.This sensor also measures agitation and sends wave parameters each 20 min. There is a GPS station Leica Geosystems GRX1200 GG Pro and antenna 1202. Bathymetric campaigns inside the harbour have been made. At Ibiza site new measurements and levelling between the GPS reference station and a Radar MIROS, both from Puertos del Estado, has been made recently. A calibration campaign for Jason-1 was made in June 2003 in the Ibiza area, main calibration site. The presentation is directed to the description of the actual situation of the geodetic infrastructure of Barcelona, l'Estartit sites for sea level determination and complementing Ibiza site for a new altimeter calibration campaign of Jason-2 and Saral/AltiKa satellites to be made in 2013. Specifications of the new marine calibration campaign will be presented.

GPS data exploration for seismologists and geodesists

NASA Astrophysics Data System (ADS)

Webb, F.; Bock, Y.; Kedar, S.; Dong, D.; Jamason, P.; Chang, R.; Prawirodirdjo, L.; MacLeod, I.; Wadsworth, G.

2007-12-01

Over the past decade, GPS and seismic networks spanning the western US plate boundaries have produced vast amounts of data that need to be made accessible to both the geodesy and seismology communities. Unlike seismic data, raw geodetic data requires significant processing before geophysical interpretations can be made. This requires the generation of data-products (time series, velocities and strain maps) and dissemination strategies to bridge these differences and assure efficient use of data across traditionally separate communities. "GPS DATA PRODUCTS FOR SOLID EARTH SCIENCE" (GDPSES) is a multi-year NASA funded project, designed to produce and deliver high quality GPS time series, velocities, and strain fields, derived from multiple GPS networks along the western US plate boundary, and to make these products easily accessible to geophysicists. Our GPS product dissemination is through modern web-based IT methodology. Product browsing is facilitated through a web tool known as GPS Explorer and continuous streams of GPS time series are provided using web services to the seismic archive, where it can be accessed by seismologists using traditional seismic data viewing and manipulation tools. GPS-Explorer enables users to efficiently browse several layers of data products from raw data through time series, velocities and strain by providing the user with a web interface, which seamlessly interacts with a continuously updated database of these data products through the use of web-services. The current archive contains GDPSES data products beginning in 1995, and includes observations from GPS stations in EarthScope's Plate Boundary Observatory (PBO), as well as from real-time real-time CGPS stations. The generic, standards-based approach used in this project enables GDPSES to seamlessly expand indefinitely to include other space-time-dependent data products from additional GPS networks. The prototype GPS-Explorer provides users with a personalized working environment in which the user may zoom in and access subsets of the data via web services. It provides users with a variety of interactive web tools interconnected in a portlet environment to explore and save datasets of interest to return to at a later date. At the same time the GPS time series are also made available through the seismic data archive, where the GPS networks are treated as regular seismic networks, whose data is made available in data formats used by seismic utilities such as SEED readers and SAC. A key challenge, stemming from the fundamental differences between seismic and geodetic time series, is the representation of reprocessed of GPS data in the seismic archive. As GPS processing algorithms evolve and their accuracy increases, a periodic complete recreation of the the GPS time series archive is necessary.

Ionospheric response to the 2006 sudden stratospheric warming event over the equatorial and low latitudes in the Brazilian sector using GPS observations

NASA Astrophysics Data System (ADS)

de Jesus, R.; Batista, I. S.; Fagundes, P. R.; Venkatesh, K.; de Abreu, A. J.

2017-02-01

The main purpose of this paper is to study the response of the ionospheric F-region using GPS-TEC measurements at equatorial and low latitude regions over the Brazilian sector during an sudden stratospheric warming (SSW) event in the year 2006. In this work, we present vertical total electron content (VTEC) and phase fluctuations derived from GPS network in Brazil. The continuous wavelet transform (CWT) was employed to check the periodicities of the ΔVTEC during the SSW event. The results show a strong decrease in VTEC and ΔVTEC values in the afternoon over low latitudes from DOY 05-39 (during the SSW event) mainly after the second SSW temperature peak. The ionospheric ΔVTEC pattern over Brazilian sector shows diurnal and semidiurnal oscillations during the 2006 SSW event. In addition, for the first time, variations in ΔVTEC (low latitude stations) with periods of about 02-08 day have been reported during an SSW event. Using GPS stations located in the Brazilian sector, it is reported for the first time that equatorial ionospheric irregularities were not suppressed by the SSW event.

Seasonal Mass Changes and Crustal Vertical Deformations Constrained by GPS and GRACE in Northeastern Tibet

PubMed Central

Pan, Yuanjin; Shen, Wen-Bin; Hwang, Cheinway; Liao, Chaoming; Zhang, Tengxu; Zhang, Guoqing

2016-01-01

Surface vertical deformation includes the Earth’s elastic response to mass loading on or near the surface. Continuous Global Positioning System (CGPS) stations record such deformations to estimate seasonal and secular mass changes. We used 41 CGPS stations to construct a time series of coordinate changes, which are decomposed by empirical orthogonal functions (EOFs), in northeastern Tibet. The first common mode shows clear seasonal changes, indicating seasonal surface mass re-distribution around northeastern Tibet. The GPS-derived result is then assessed in terms of the mass changes observed in northeastern Tibet. The GPS-derived common mode vertical change and the stacked Gravity Recovery and Climate Experiment (GRACE) mass change are consistent, suggesting that the seasonal surface mass variation is caused by changes in the hydrological, atmospheric and non-tidal ocean loads. The annual peak-to-peak surface mass changes derived from GPS and GRACE results show seasonal oscillations in mass loads, and the corresponding amplitudes are between 3 and 35 mm/year. There is an apparent gradually increasing gravity between 0.1 and 0.9 μGal/year in northeast Tibet. Crustal vertical deformation is determined after eliminating the surface load effects from GRACE, without considering Glacial Isostatic Adjustment (GIA) contribution. It reveals crustal uplift around northeastern Tibet from the corrected GPS vertical velocity. The unusual uplift of the Longmen Shan fault indicates tectonically sophisticated processes in northeastern Tibet. PMID:27490550

Vertical land motion along the coast of Louisiana: Integrating satellite altimetry, tide gauge and GPS

NASA Astrophysics Data System (ADS)

Dixon, T. H.; A Karegar, M.; Uebbing, B.; Kusche, J.; Fenoglio-Marc, L.

2017-12-01

Coastal Louisiana is experiencing the highest rate of relative sea-level rise in North America due to the combination of sea-level rise and subsidence of the deltaic plain. The land subsidence in this region is studied using various techniques, with continuous GPS site providing high temporal resolution. Here, we use high resolution tide-gauge data and advanced processing of satellite altimetry to derive vertical displacements time series at NOAA tide-gauge stations along the coast (Figure 1). We apply state-of-the-art retracking techniques to process raw altimetry data, allowing high accuracy on range measurements close to the coast. Data from Jason-1, -2 and -3, Envisat, Saral and Cryosat-2 are used, corrected for solid Earth tide, pole tide and tidal ocean loading, using background models consistent with the GPS processing technique. We reprocess the available GPS data using precise point positioning and estimate the rate uncertainty accounting for correlated noise. The displacement time series are derived by directly subtracting tide-gauge data from the altimetry sea-level anomaly data. The quality of the derived displacement rates is evaluated in Grand Isle, Amerada Pass and Shell Beach where GPS data are available adjacent to the tide gauges. We use this technique to infer vertical displacement at tide gauges in New Orleans (New Canal Station) and Port Fourchon and Southwest Pass along the coastline.

GPS Tomography: Water Vapour Monitoring for Germany

NASA Astrophysics Data System (ADS)

Bender, Michael; Dick, Galina; Wickert, Jens; Raabe, Armin

2010-05-01

Ground based GPS atmosphere sounding provides numerous atmospheric quantities with a high temporal resolution for all weather conditions. The spatial resolution of the GPS observations is mainly given by the number of GNSS satellites and GPS ground stations. The latter could considerably be increased in the last few years leading to more reliable and better resolved GPS products. New techniques such as the GPS water vapour tomography gain increased significance as data from large and dense GPS networks become available. The GPS tomography has the potential to provide spatially resolved fields of different quantities operationally, i. e. the humidity or wet refractivity as required for meteorological applications or the refraction index which is important for several space based observations or for precise positioning. The number of German GPS stations operationally processed by the GFZ in Potsdam was recently enlarged to more than 300. About 28000 IWV observations and more than 1.4 millions of slant total delay data are now available per day with a temporal resolution of 15 min and 2.5 min, respectively. The extended network leads not only to a higher spatial resolution of the tomographically reconstructed 3D fields but also to a much higher stability of the inversion process and with that to an increased quality of the results. Under these improved conditions the GPS tomography can operate continuously over several days or weeks without applying too tight constraints. Time series of tomographically reconstructed humidity fields will be shown and different initialisation strategies will be discussed: Initialisation with a simple exponential profile, with a 3D humidity field extrapolated from synoptic observations and with the result of the preceeding reconstruction. The results are compared to tomographic reconstructions initialised with COSMO-DE analyses and to the corresponding model fields. The inversion can be further stabilised by making use of independent adequately weighted observations, such as synoptic observations or IWV data. The impact of such observations on the quality of the tomographic reconstruction will be discussed together with different alternatives for weighting different types of observations.

Critical aspects of integrated monitoring systems for landslides risk management: strategies for a reliable approach

NASA Astrophysics Data System (ADS)

Castagnetti, C.; Bertacchini, E.; Capra, A.; Corsini, A.

2012-04-01

The use of advanced technologies for remotely monitor surface processes is a successful way for improving the knowledge of phenomena evolution. In addition, the integration of various techniques is becoming more and more common in order to implement early warning systems that can monitor the evolution of landslides in time and prevent emergencies. The reliability of those systems plays a key role when Public Administrations have to plan actions in case of disasters or for preventing an incoming emergency. To have confidence in the information given by the system is an essential condition for a successful policy aiming to protect the population. The research deals with the major critical aspects to be taken into account when implementing a reliable monitoring system for unstable slopes. The importance of those aspects is often neglected, unlike the effects of a not careful implementation and management of the system can lead to erroneous interpretations of the phenomenon itself. The case study which ruled the research and highlighted the actual need of guidelines for setting up a reliable monitoring system is the Valoria landslide, located in the Northern Italy. The system is based on the integration of an automatic Total Station (TS) measuring 45 reflectors and a master GPS, acting as the reference station for three rovers placed within the landslide. In order to monitor local disturbing effects, a bi-dimensional clinometer has been applied on the TS pillar. Topographic measurements have been also integrated with geotechnical sensors (inclinometers and piezometers) in a GIS for landslide risk management. At the very beginning, periodic measurements were carried out, while the system is now performing continuously since 2008. The system permitted to evaluate movements from few millimeter till some meters per day in most dangerous areas. A more spatially continuous description has been also provided by LiDAR and terrestrial SAR interferometry. Some of the most interesting and critical aspects that will be deeper described and analyzed are: - strategy for planning a successful integrated system for continuous monitoring. - Choice of the reference frame: local coordinate system or georeferenced one. - Stability of the site for the master unit positioning: GPS time series analysis for controlling the effective stability. Thanks to the GPS master station that are operating for over three years, atmospheric disturbances affecting the signal may be removed in order to carefully verify the stability of the area and to establish whether the site is geologically stable, as originally suggested, or not. In the latter case, the magnitude of movements may also be computed for providing corrections to TS observations. - Stability of the monumentation, both for reference points and TS pillar. This is an essential aspect for avoiding misinterpretations when analyzing displacements of prisms placed within the landslide. The results of experiences carried out by Authors over last years about different landslides will be presented in order to propose guidelines for a sort of procedure aiming to increase the reliability of the information provided by the system and the usefulness for local Agencies.

LONG-TERM STABILITY OF THE LOCAL GROUND CONTROL NETWORK AT THE CO-LOCATION SITE OF MEDICINA

NASA Astrophysics Data System (ADS)

Abbondanza, C.; Sarti, P.; Legrand, J.

2009-12-01

ITRF combinations rely on the availability of accurate tie vectors linking reference points of space geodetic techniques. Co-located instruments are assumed to move consistently and no local relative motion is taken into account. Instabilities may degrade the quality of the co-location itself and perturb the result of ITRF combinations. This work aims to determine the stability of the local ground control network at Medicina (Italy) with independent surveying methods. The observatory hosts a co-location between a VLBI telescope and two GPS antennas, MEDI and MSEL. It is located in the Po Plain where thick layers of clays are the prevalent soil characteristics. Hence, provision of long term stability of geodetic monuments is a challenge and monitoring their stability is an issue. MEDI and the VLBI station regularly contribute to the determination of ITRF, while MSEL is part of the EUREF network. A set of five tie vectors observations linking the VLBI and MEDI reference points was acquired between 2001 and 2007. It is our main tool for performing local deformation analysis. Additionally, the GPS time series of MEDI and MSEL were used to cross check and confirm the local instability detected by terrestrial methods. To achieve a rigorous and reliable investigation of the local stability, multi-epoch terrestrial observations were homogeneously processed according to common parameterizations in a consistent reference frame. Similarly, continuous GPS observations from MEDI and MSEL were analysed according to the new EPN reprocessing strategy in order to monitor the short baseline between MEDI and MSEL; to spotlight any change in its length. Both approaches confirm differential motions at the site which can be related to monument instabilities originated by the particularly unfavourable local geological setting and the inapt design of the monuments foundation. The monuments move non homogeneously at rates reaching up to 1.6 mm/year, this value being comparable to intra-plate tectonic deformations. Evidences of relative motion between MEDI and MSEL are found: an annual signal with amplitude ≈1.3 mm is detected along the East component and an 80 weeks signal with amplitude ≈1.1 mm is found along the vertical component of the baseline. The combination of the two independent observing techniques confirms the importance of repeatedly performed terrestrial surveys and the presence of intra-technique co-locations at geodetic sites. Although available, VLBI observations were not considered since we are interested in detecting local relative motions in a very restricted area (100m x 100m) avoiding problems of datum consistencies between different space geodetic techniques. In fact, the combination of technique-specific frames might originate local inconsistencies on station positions due to misalignments of tie vectors in the global reference frame. These inconsistencies might degrade the accuracy of the displacement analysis and can be difficult to deal with.

Modeling environmental bias and computing velocity field from data of Terra Nova Bay GPS network in Antarctica by means of a quasi-observation processing approach

USGS Publications Warehouse

Casula, Giuseppe; Dubbini, Marco; Galeandro, Angelo

2007-01-01

A semi-permanent GPS network of about 30 vertices has been installed at Terra Nova Bay (TNB) near Ross Sea in Antarctica. A permanent GPS station TNB1 based on an Ashtech Z-XII dual frequency P-code GPS receiver with ASH700936D_M Choke Ring Antenna has been mounted on a reinforced concrete pillar built on bedrock since October 1998 and has recorded continuously up to the present. The semi-permanent network has been routinely surveyed every summer using high quality dual frequency GPS receivers with 24 hour sessions at 15 sec rate; data, metadata and solutions will be available to the scientific community at (http://www.geodant.unimore.it). We present the results of a distributed session approach applied to processing GPS data of the TNB GPS network, and based on Gamit/Globk 10.2-3 GPS analysis software. The results are in good agreement with other authors' computations and with many of the theoretical models.

The Performance Analysis of a Real-Time Integrated INS/GPS Vehicle Navigation System with Abnormal GPS Measurement Elimination

PubMed Central

Chiang, Kai-Wei; Duong, Thanh Trung; Liao, Jhen-Kai

2013-01-01

The integration of an Inertial Navigation System (INS) and the Global Positioning System (GPS) is common in mobile mapping and navigation applications to seamlessly determine the position, velocity, and orientation of the mobile platform. In most INS/GPS integrated architectures, the GPS is considered to be an accurate reference with which to correct for the systematic errors of the inertial sensors, which are composed of biases, scale factors and drift. However, the GPS receiver may produce abnormal pseudo-range errors mainly caused by ionospheric delay, tropospheric delay and the multipath effect. These errors degrade the overall position accuracy of an integrated system that uses conventional INS/GPS integration strategies such as loosely coupled (LC) and tightly coupled (TC) schemes. Conventional tightly coupled INS/GPS integration schemes apply the Klobuchar model and the Hopfield model to reduce pseudo-range delays caused by ionospheric delay and tropospheric delay, respectively, but do not address the multipath problem. However, the multipath effect (from reflected GPS signals) affects the position error far more significantly in a consumer-grade GPS receiver than in an expensive, geodetic-grade GPS receiver. To avoid this problem, a new integrated INS/GPS architecture is proposed. The proposed method is described and applied in a real-time integrated system with two integration strategies, namely, loosely coupled and tightly coupled schemes, respectively. To verify the effectiveness of the proposed method, field tests with various scenarios are conducted and the results are compared with a reliable reference system. PMID:23955434

Changes in Sea Levels around the British Isles Revisited (Invited)

NASA Astrophysics Data System (ADS)

Teferle, F. N.; Hansen, D. N.; Bingley, R. M.; Williams, S. D.; Woodworth, P. L.; Gehrels, W. R.; Bradley, S. L.; Stocchi, P.

2009-12-01

Recently a number of new and/or updated sources for estimates of vertical land movements for the British Isles have become available allowing the relative and average changes in sea levels for this region to be revisited. The geodetic data set stems from a combination of re-processed continuous Global Positioning System (GPS) measurements from stations in the British Isles and from a global reference frame network, and absolute gravity (AG) measurements from two stations in the British Isles. The geologic data set of late Holocene sea level indicators has recently been updated, now applying corrections for the 20th century sea level rise, syphoning effect and late Holocene global ice melt, and expanded to Northern Ireland and Ireland. Several new model predictions of the glacial isostatic adjustment (GIA) process active in this region form the modelling data set of vertical land movements for the British Isles. Correcting the updated revised local reference (RLR) trends from the Permanent Service for Mean Sea Level (PSMSL) with these vertical land movement data sets, regional and averaged changes in sea levels around the British Isles have been investigated. Special focus is thereby also given to the coastal areas that have recently been identified within the UK Climate Projections 2009.

Army AL&T, October-December 2008

DTIC Science & Technology

2008-12-01

during the WIN-T technology demonstration Nov. 8, 2007, at Naval Air Engineering Station , Lakehurst, NJ. (U.S. Army photo by Russ Messeroll.) 16 OCTOBER...worldwide communications architecture, enabling connectivity from the global backbone to regional networks to posts/camps/ stations , and, lastly, to...Force Tracker. • Tacticomp™ wireless and Global Positioning System(GPS)-enabled hand-held computer. • One Station Remote Video Terminal. • Counter

Extending permanent volcano monitoring networks into Iceland's ice caps

NASA Astrophysics Data System (ADS)

Vogfjörd, Kristín S.; Bergsson, Bergur H.; Kjartansson, Vilhjálmur; Jónsson, Thorsteinn; Ófeigsson, Benedikt G.; Roberts, Matthew J.; Jóhannesson, Tómas; Pálsson, Finnur; Magnússon, Eyjólfur; Erlendsson, Pálmi; Ingvarsson, Thorgils; Pálssson, Sighvatur K.

2015-04-01

The goals of the FUTUREVOLC project are the establishment of a volcano Supersite in Iceland to enable access to volcanological data from the country's many volcanoes and the development of a multiparametric volcano monitoring and early warning system. However, the location of some of Iceland's most active volcanoes inside the country's largest ice cap, Vatnajökull, makes these goals difficult to achieve as it hinders access and proper monitoring of seismic and deformation signals from the volcanoes. To overcome these obstacles, one of the developments in the project involves experimenting with extending the permanent real-time networks into the ice cap, including installation of stations in the glacier ice. At the onset of the project, only one permanent seismic and GPS site existed within Vatnajökull, on the caldera rim of the Grímsvötn volcano. Two years into the project both seismic and GPS stations have been successfully installed and operated inside the glacier; on rock outcrops as well as on the glacier surface. The specific problems to overcome are (i) harsh weather conditions requiring sturdy and resilient equipment and site installations, (ii) darkness during winter months shutting down power generation for several weeks, (iii) high snow accumulation burying the instruments, solar panels and communication and GPS antennae, and in some locations (iv) extreme icing conditions blocking transmission signals and connection to GPS satellites, as well as excluding the possibility of power generation by wind generators. In 2013, two permanent seismic stations and one GPS station were installed on rock outcrops within the ice cap in locations with 3G connections and powered by solar panels and enough battery storage to sustain operation during the darkest winter months. These sites have successfully operated for over a year with mostly regular maintenance requirements, transmitting data in real-time to IMO for analysis. Preparations for two permanent seismic sites in the ice started in early 2014, with the installation of windmills, solar panels and web camera to monitor snow accumulation and icing. The site locations were constrained by the availability of communication and locations of ice-divides to avoid significant lateral motion of the stations. At the onset of the Bárdarbunga dyke intrusion in August 2014, these sites were temporarily instrumented and transmitted real-time seismic data, important for tracking the dyke intrusion. In late 2014, a specially designed vault was installed at one of the sites and a Güralp broadband glacier seismometer installed. Since 2013, three GPS stations powered by solar energy have been operated on the ice, to monitor the movement of the glacier during an expected subglacial flood, when accumulated melt water at the Eastern Skaftá cauldron sub-glacial geothermal area will drain. One of the sites, located in the depression above the subglacial lake to monitor the onset of the flood, transmits the data to a repeater just outside the depression, from where the signal is transmitted by 3G to IMO. Maintaining the transmission through the winter months has required considerable maintenance. The experience gained through this operation proved crucial for the successful installation and operation of a real-time transmitting GPS and strong motion seismometer inside the Bárdarbunga cauldron in October 2014 to monitor the ongoing caldera subsidence.

Improvement of Klobuchar model for GNSS single-frequency ionospheric delay corrections

NASA Astrophysics Data System (ADS)

Wang, Ningbo; Yuan, Yunbin; Li, Zishen; Huo, Xingliang

2016-04-01

Broadcast ionospheric model is currently an effective approach to mitigate the ionospheric time delay for real-time Global Navigation Satellite System (GNSS) single-frequency users. Klobuchar coefficients transmitted in Global Positioning System (GPS) navigation message have been widely used in various GNSS positioning and navigation applications; however, this model can only reduce the ionospheric error by approximately 50% in mid-latitudes. With the emerging BeiDou and Galileo, as well as the modernization of GPS and GLONASS, more precise ionospheric correction models or algorithms are required by GNSS single-frequency users. Numerical analysis of the initial phase and nighttime term in Klobuchar algorithm demonstrates that more parameters should be introduced to better describe the variation of nighttime ionospheric total electron content (TEC). In view of this, several schemes are proposed for the improvement of Klobuchar algorithm. Performance of these improved Klobuchar-like models are validated over the continental and oceanic regions during high (2002) and low (2006) levels of solar activities, respectively. Over the continental region, GPS TEC generated from 35 International GNSS Service (IGS) and the Crust Movement Observation Network of China (CMONOC) stations are used as references. Over the oceanic region, TEC data from TOPEX/Poseidon and JASON-1 altimeters are used for comparison. A ten-parameter Klobuchar-like model, which describes the nighttime term as a linear function of geomagnetic latitude, is finally proposed for GNSS single-frequency ionospheric corrections. Compared to GPS TEC, while GPS broadcast model can correct for 55.0% and 49.5% of the ionospheric delay for the year 2002 and 2006, respectively, the proposed ten-parameter Klobuchar-like model can reduce the ionospheric error by 68.4% and 64.7% for the same period. Compared to TOPEX/Poseidon and JASON-1 TEC, the improved ten-parameter Klobuchar-like model can mitigate the ionospheric delay by 61.1% and 64.3% in 2002 and 2006, respectively.

Continuous monitoring of surface deformation at Long Valley Caldera, California, with GPS

USGS Publications Warehouse

Dixon, T.H.; Mao, A.; Bursik, M.; Heflin, M.; Langbein, J.; Stein, R.; Webb, F.

1997-01-01

Continuous Global Positioning System (GPS) measurements at Long Valley Caldera, an active volcanic region in east central California, have been made on the south side of the resurgent dome since early 1993. A site on the north side of the dome was added in late 1994. Special adaptations for autonomous operation in remote regions and enhanced vertical precision were made. The data record ongoing volcanic deformation consistent with uplift and expansion of the surface above a shallow magma chamber. Measurement precisions (1 standard error) for "absolute" position coordinates, i.e., relative to a global reference frame, are 3-4 mm (north), 5-6 mm (east), and 10-12 mm (vertical) using 24 hour solutions. Corresponding velocity uncertainties for a 12 month period are about 2 mm/yr in the horizontal components and 3-4 mm/yr in the vertical component. High precision can also be achieved for relative position coordinates on short (<10 km) baselines using broadcast ephemerides and observing times as short as 3 hours, even when data are processed rapidly on site. Comparison of baseline length changes across the resurgent dome between the two GPS sites and corresponding two-color electronic distance measurements indicates similar extension rates within error (???2 mm/yr) once we account for a random walk noise component in both systems that may reflect spurious monument motion. Both data sets suggest a pause in deformation for a 3.5 month period in mid-1995, when the extension rate across the dome decreased essentially to zero. Three dimensional positioning data from the two GPS stations suggest a depth (5.8??1.6 km) and location (west side of the resurgent dome) of a major inflation center, in agreement with other geodetic techniques, near the top of a magma chamber inferred from seismic data. GPS systems similar to those installed at Long Valley can provide a practical method for near real-time monitoring and hazard assessment on many active volcanoes.

High Frequency Variations in Earth Orientation Derived From GNSS Observations

NASA Astrophysics Data System (ADS)

Weber, R.; Englich, S.; Snajdrova, K.; Boehm, J.

2006-12-01

Current observations gained by the space geodetic techniques, especially VLBI, GPS and SLR, allow for the determination of Earth Orientation Parameters (EOPs - polar motion, UT1/LOD, nutation offsets) with unprecedented accuracy and temporal resolution. This presentation focuses on contributions to the EOP recovery provided by satellite navigation systems (primarily GPS). The IGS (International GNSS Service), for example, currently provides daily polar motion with an accuracy of less than 0.1mas and LOD estimates with an accuracy of a few microseconds. To study more rapid variations in polar motion and LOD we established in a first step a high resolution (hourly resolution) ERP-time series from GPS observation data of the IGS network covering the period from begin of 2005 till March 2006. The calculations were carried out by means of the Bernese GPS Software V5.0 considering observations from a subset of 79 fairly stable stations out of the IGb00 reference frame sites. From these ERP time series the amplitudes of the major diurnal and semidiurnal variations caused by ocean tides are estimated. After correcting the series for ocean tides the remaining geodetic observed excitation is compared with variations of atmospheric excitation (AAM). To study the sensitivity of the estimates with respect to the applied mapping function we applied both the widely used NMF (Niell Mapping Function) and the VMF1 (Vienna Mapping Function 1). In addition, based on computations covering two months in 2005, the potential improvement due to the use of additional GLONASS data will be discussed. Finally, satellite techniques are also able to provide nutation offset rates with respect to the most recent nutation model. Based on GPS observations from 2005 we established nutation rate time series and subsequently derived the amplitudes of several nutation waves with periods less than 30 days. The results are compared to VLBI estimates processed by means of the OCCAM 6.1 software.

Analysis of Seasonal Signal in GPS Short-Baseline Time Series

NASA Astrophysics Data System (ADS)

Wang, Kaihua; Jiang, Weiping; Chen, Hua; An, Xiangdong; Zhou, Xiaohui; Yuan, Peng; Chen, Qusen

2018-04-01

Proper modeling of seasonal signals and their quantitative analysis are of interest in geoscience applications, which are based on position time series of permanent GPS stations. Seasonal signals in GPS short-baseline (< 2 km) time series, if they exist, are mainly related to site-specific effects, such as thermal expansion of the monument (TEM). However, only part of the seasonal signal can be explained by known factors due to the limited data span, the GPS processing strategy and/or the adoption of an imperfect TEM model. In this paper, to better understand the seasonal signal in GPS short-baseline time series, we adopted and processed six different short-baselines with data span that varies from 2 to 14 years and baseline length that varies from 6 to 1100 m. To avoid seasonal signals that are overwhelmed by noise, each of the station pairs is chosen with significant differences in their height (> 5 m) or type of the monument. For comparison, we also processed an approximately zero baseline with a distance of < 1 m and identical monuments. The daily solutions show that there are apparent annual signals with annual amplitude of 1 mm (maximum amplitude of 1.86 ± 0.17 mm) on almost all of the components, which are consistent with the results from previous studies. Semi-annual signal with a maximum amplitude of 0.97 ± 0.25 mm is also present. The analysis of time-correlated noise indicates that instead of flicker (FL) or random walk (RW) noise, band-pass-filtered (BP) noise is valid for approximately 40% of the baseline components, and another 20% of the components can be best modeled by a combination of the first-order Gauss-Markov (FOGM) process plus white noise (WN). The TEM displacements are then modeled by considering the monument height of the building structure beneath the GPS antenna. The median contributions of TEM to the annual amplitude in the vertical direction are 84% and 46% with and without additional parts of the monument, respectively. Obvious annual signals with amplitude > 0.4 mm in the horizontal direction are observed in five short-baselines, and the amplitudes exceed 1 mm in four of them. These horizontal seasonal signals are likely related to the propagation of daily/sub-daily TEM displacement or other signals related to the site environment. Mismodeling of the tropospheric delay may also introduce spurious seasonal signals with annual amplitudes of 5 and 2 mm, respectively, for two short-baselines with elevation differences greater than 100 m. The results suggest that the monument height of the additional part of a typical GPS station should be considered when estimating the TEM displacement and that the tropospheric delay should be modeled cautiously, especially with station pairs with apparent elevation differences. The scheme adopted in this paper is expected to explicate more seasonal signals in GPS coordinate time series, particularly in the vertical direction.

Nutation determination using the Global Positioning System

NASA Astrophysics Data System (ADS)

Yao, Kunliang; Capitaine, Nicole; Umnig, Elke; Weber, Robert

2012-08-01

VLBI observation of extragalactic radio sources is the only technique that allows high accuracy determination of nutation on a regular basis. However, this is limited to periods of nutation greater than about 30 days due to the current resolution of VL BI estimation. It is there fore important to use another technique to improve nutation at shorter periods. It has been shown by Rothacher et al. (1999) and Weber & Rothacher (2001) that GPS is a potential technique for the determination of the short period terms of nutation. The met hod, which is based on the estimation of nutation rates with respect to an a priori model, is limited to nutation terms in the higher frequency range (with periods up to about 21 days) due to deficiencies in the modeling of the satellite orbits. The high accuracy and high time resolution of the GPS observations that are now achieved give us the possibility to estimate the nutation variations with respect to the IAU2000A nutation, with an expected precision of 10 microarcseconds (μas ). The purpose of our study is to use recent GPS observations obtained by 140 IGS stations (IGS08 Core Reference Frame sites included) to estimate the short period nutations. Two methods are applied: one is to investigate the retrograde diurnal term of polar motion with nutation fixed to the IAU 2006/2000 precession - nutation, using CNES/GRGS software GINS/DYNAMO at Observatoire de Paris; another one is to investigate the nutation time derivative, with polar motion fixed, using Bernese GPS software at University of Technology in Vienna. In this poster, we report on our preliminary results with data set covering a period of 3 years (2009 - 2011), with appropriate time resolutions and on the comparison between the two approaches.

New Radiosonde Temperature Bias Adjustments for Potential NWP Applications Based on GPS RO Data

NASA Astrophysics Data System (ADS)

Sun, B.; Reale, A.; Ballish, B.; Seidel, D. J.

2014-12-01

Conventional radiosonde observations (RAOBs), along with satellite and other in situ data, are assimilated in numerical weather prediction (NWP) models to generate a forecast. Radiosonde temperature observations, however, have solar and thermal radiation induced biases (typically a warm daytime bias from sunlight heating the sensor and a cold bias at night as the sensor emits longwave radiation). Radiation corrections made at stations based on algorithms provided by radiosonde manufacturers or national meteorological agencies may not be adequate, so biases remain. To adjust these biases, NWP centers may make additional adjustments to radiosonde data. However, the radiation correction (RADCOR) schemes used in the NOAA NCEP data assimilation and forecasting system is outdated and does not cover several widely-used contemporary radiosonde types. This study focuses on work whose objective is to improve these corrections and test their impacts on the NWP forecasting and analysis. GPS Radio Occultation (RO) dry temperature (Tdry) is considered to be highly accurate in the upper troposphere and low stratosphere where atmospheric water vapor is negligible. This study uses GPS RO Tdry from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) as the reference to quantify the radiation induced RAOB temperature errors by analyzing ~ 3-yr collocated RAOB and COSMIC GPS RO data compile by the NOAA Products Validation System (NPROVS). The new radiation adjustments are developed for different solar angle categories and for all common sonde types flown in the WMO global operational upper air network. Results for global and several commonly used sondes are presented in the context of NCEP Global Forecast System observation-minus-background analysis, indicating projected impacts in reducing forecast error. Dedicated NWP impact studies to quantify the impact of the new RADCOR schemes on the NCEP analyses and forecast are under consideration.

Flight evaluation of differential GPS aided inertial navigation systems

NASA Technical Reports Server (NTRS)

Mcnally, B. David; Paielli, Russell A.; Bach, Ralph E., Jr.; Warner, David N., Jr.

1992-01-01

Algorithms are described for integration of Differential Global Positioning System (DGPS) data with Inertial Navigation System (INS) data to provide an integrated DGPS/INS navigation system. The objective is to establish the benefits that can be achieved through various levels of integration of DGPS with INS for precision navigation. An eight state Kalman filter integration was implemented in real-time on a twin turbo-prop transport aircraft to evaluate system performance during terminal approach and landing operations. A fully integrated DGPS/INS system is also presented which models accelerometer and rate-gyro measurement errors plus position, velocity, and attitude errors. The fully integrated system was implemented off-line using range-domain (seventeen-state) and position domain (fifteen-state) Kalman filters. Both filter integration approaches were evaluated using data collected during the flight test. Flight-test data consisted of measurements from a 5 channel Precision Code GPS receiver, a strap-down Inertial Navigation Unit (INU), and GPS satellite differential range corrections from a ground reference station. The aircraft was laser tracked to determine its true position. Results indicate that there is no significant improvement in positioning accuracy with the higher levels of DGPS/INS integration. All three systems provided high-frequency (e.g., 20 Hz) estimates of position and velocity. The fully integrated system provided estimates of inertial sensor errors which may be used to improve INS navigation accuracy should GPS become unavailable, and improved estimates of acceleration, attitude, and body rates which can be used for guidance and control. Precision Code DGPS/INS positioning accuracy (root-mean-square) was 1.0 m cross-track and 3.0 m vertical. (This AGARDograph was sponsored by the Guidance and Control Panel.)

A new global grid model for the determination of atmospheric weighted mean temperature in GPS precipitable water vapor

NASA Astrophysics Data System (ADS)

Huang, Liangke; Jiang, Weiping; Liu, Lilong; Chen, Hua; Ye, Shirong

2018-05-01

In ground-based global positioning system (GPS) meteorology, atmospheric weighted mean temperature, T_m , plays a very important role in the progress of retrieving precipitable water vapor (PWV) from the zenith wet delay of the GPS. Generally, most of the existing T_m models only take either latitude or altitude into account in modeling. However, a great number of studies have shown that T_m is highly correlated with both latitude and altitude. In this study, a new global grid empirical T_m model, named as GGTm, was established by a sliding window algorithm using global gridded T_m data over an 8-year period from 2007 to 2014 provided by TU Vienna, where both latitude and altitude variations are considered in modeling. And the performance of GGTm was assessed by comparing with the Bevis formula and the GPT2w model, where the high-precision global gridded T_m data as provided by TU Vienna and the radiosonde data from 2015 are used as reference values. The results show the significant performance of the new GGTm model against other models when compared with gridded T_m data and radiosonde data, especially in the areas with great undulating terrain. Additionally, GGTm has the global mean RMS_{PWV} and RMS_{PWV} /PWV values of 0.26 mm and 1.28%, respectively. The GGTm model, fed only by the day of the year and the station coordinates, could provide a reliable and accurate T_m value, which shows the possible potential application in real-time GPS meteorology, especially for the application of low-latitude areas and western China.

Compaction of Aquifer at Different Depths: Observations from a Vertical GPS Array in the Coastal Center of the University of Houston, Texas

NASA Astrophysics Data System (ADS)

Lee, D.; Kearns, T.; Yang, L.; Wang, G.

2014-12-01

Houston and the surrounding Harris County have experienced the detrimental effects of subsidence even prior to World War II, to the extent that the land along Galveston Bay had sunk as much as 20 feet since 1906. One dramatic example is the Brownwood subdivision, a coastal community in Baytown where continuous flooding due to subsidence forced the area to be deemed unlivable and consequently abandoned. Thus, Houston's changes in groundwater and compaction of its aquifers are of relatively high concern to those in the public (infrastructure), private (oil & gas), and international (Port of Houston Authority) sectors. One of the key questions related to the subsidence issue in Houston area is what are the contributions of sediments at different depths, and what particularly is the contribution from shallow sediments? To address these questions, University of Houston has installed a vertical GPS array in the UH Coastal Center in March 2014. The GPS array includes four permanent GPS stations with the antenna pole foundations anchored at different depths below ground surface (-10 m, -7m, -4m, 0 m). A special, double-pipe GPS antenna monument was designed for GPS stations with the array. This project was funded by an NSF grant and a UH internal grant. Five groundwater wells with the depths ranging from 2 m to 100 m below the ground surface were also installed at the UH Coastal Center site. This study will investigate continuous GPS and groundwater level measurements (March-November, 2014) at the UHCC site. It is expected that the GPS array will provide total information on subsidence as well as compaction of aquifers within different depth ranges (0 to -4m, -4 to -7 m, -7 to -10m, and below -10 m). Correlation of land subsidence and groundwater fluctuation will also be investigated.

UNAVCO GPS High-Rate and Real-Time Products and Services: Building a next generation geodetic network.

NASA Astrophysics Data System (ADS)

Mencin, David; Meertens, Charles; Mattioli, Glen; Feaux, Karl; Looney, Sara; Sievers, Charles; Austin, Ken

2013-04-01

Recent advances in GPS technology and data processing are providing position estimates with centimeter-level precision at high-rate (1-5 Hz) and low latency (<1 s). Broad community interest in these data is growing rapidly because these data will have the potential to improve our understanding in diverse areas of geophysics including properties of seismic, volcanic, magmatic and tsunami deformation sources, and moreover profoundly transforming rapid event characterization, early warning, as well as hazard mitigation and response. Other scientific and operational applications for high-rate GPS also include glacier and ice sheet motions, tropospheric modeling, and better constraints on the dynamics of space weather. UNAVCO, through community input and the recent Plate Boundary Observatory (PBO) NSF-ARRA Cascadia initiative, has nearly completed the process of upgrading a total of 373 PBO GPS sites to real-time high-rate capability and these streams are now being archived in the UNAVCO data center. Further, through the UNAVCO core proposal (GAGE), currently under review at NSF, UNAVCO has proposed upgrading a significant portion of the ~1100 GPS stations that PBO currently operates to real-time high-rate capability to address community science and operational needs. In addition, in collaboration with NOAA, 74 of these stations will provide meteorological data in real-time, primarily to support watershed and flood analyses for regional early-warning systems related to NOAA's work with California Department of Water Resources. In preparation for this increased emphasis on high-rate GPS data, UNAVCO hosted an NSF funded workshop in Boulder, CO on March 26-28, 2012, which brought together 70 participants representing a spectrum of research fields with a goal to develop a community plan for the use of real-time GPS data products within the UNAVCO and EarthScope communities. These data products are expected to improve and expand the use of real-time, high-rate GPS data over the next decade.

47 CFR 87.171 - Class of station symbols.

Code of Federal Regulations, 2014 CFR

2014-10-01

... systems AXO—Aeronautical operational fixed DGP—Differential GPS DLT—Aircraft data link land test FA...—Radionavigation land test RLW—Microwave landing system RNV—Radio Navigation Land/DME RPC—Ramp Control TJ—Aircraft earth station in the Aeronautical Mobile-Satellite Service UAT—Universal Access Transceiver [53 FR 28940...

The GPS Topex/Poseidon precise orbit determination experiment - Implications for design of GPS global networks

NASA Technical Reports Server (NTRS)

Lindqwister, Ulf J.; Lichten, Stephen M.; Davis, Edgar S.; Theiss, Harold L.

1993-01-01

Topex/Poseidon, a cooperative satellite mission between United States and France, aims to determine global ocean circulation patterns and to study their influence on world climate through precise measurements of sea surface height above the geoid with an on-board altimeter. To achieve the mission science aims, a goal of 13-cm orbit altitude accuracy was set. Topex/Poseidon includes a Global Positioning System (GPS) precise orbit determination (POD) system that has now demonstrated altitude accuracy better than 5 cm. The GPS POD system includes an on-board GPS receiver and a 6-station GPS global tracking network. This paper reviews early GPS results and discusses multi-mission capabilities available from a future enhanced global GPS network, which would provide ground-based geodetic and atmospheric calibrations needed for NASA deep space missions while also supplying tracking data for future low Earth orbiters. Benefits of the enhanced global GPS network include lower operations costs for deep space tracking and many scientific and societal benefits from the low Earth orbiter missions, including improved understanding of ocean circulation, ocean-weather interactions, the El Nino effect, the Earth thermal balance, and weather forecasting.

Is Active Tectonics on Madagascar Consistent with Somalian Plate Kinematics?

NASA Astrophysics Data System (ADS)

Stamps, D. S.; Kreemer, C.; Rajaonarison, T. A.

2017-12-01

The East African Rift System (EARS) actively breaks apart the Nubian and Somalian tectonic plates. Madagascar finds itself at the easternmost boundary of the EARS, between the Rovuma block, Lwandle plate, and the Somalian plate. Earthquake focal mechanisms and N-S oriented fault structures on the continental island suggest that Madagascar is experiencing east-west oriented extension. However, some previous plate kinematic studies indicate minor compressional strains across Madagascar. This inconsistency may be due to uncertainties in Somalian plate rotation. Past estimates of the rotation of the Somalian plate suffered from a poor coverage of GPS stations, but some important new stations are now available for a re-evaluation. In this work, we revise the kinematics of the Somalian plate. We first calculate a new GPS velocity solution and perform block kinematic modeling to evaluate the Somalian plate rotation. We then estimate new Somalia-Rovuma and Somalia-Lwandle relative motions across Madagascar and evaluate whether they are consistent with GPS measurements made on the island itself, as well as with other kinematic indicators.

Joint Geodetic and Seismic Analysis of the effects of Englacial and Subglacial Hydraulics on Surface Crevassing near a Seasonal, Glacier-Dammed Lake on Gornergletscher, Switzerland

NASA Astrophysics Data System (ADS)

Garcia, L.; Luttrell, K. M.; Kilb, D. L.; Walter, F.

2017-12-01

Glacial outburst floods are difficult to predict and threaten human life and property near glaciated regions. These events are characterized by rapid draining of glacier-dammed lakes via the sub/englacial hydraulic network to the proglacial stream. The glacier-dammed lake on Gornergletscher in Switzerland, which fills and drains each summer, provides an opportunity to study this hazard. For three drainages (2004, 2006, and 2007), we track icequakes (IQ) and on-ice GPS movement. Our seasonal seismic networks had 8 - 24 three component stations and apertures of about 300 - 400 m on the glacier surface. The seasonal GPS arrays contained 4 - 8 GPS antennae on the glacier surface. Using Rayleigh wave coherence surface IQ location, we located 2924, 7822 and 3782 IQs, in 2004, 2006 and 2007, respectively. The GPS data were smoothed using a nonparametric protocol, with average station velocities of 10 - 90 mm/day. In 2006, strains were calculated using five stations within 500 m of the lake, co-located with the seismic network. IQ productivity increased substantially during lake drainage only in 2004, which was the only year when the lake drainage was rapid ( 6 days) and primarily subglacial. In 2006, there was no obvious increase in GPS speeds with slow ( 21 days), supraglacial lake drainage. However, when drainage was subglacial as in 2004 and 2007 (sub/englacial over 11 days), GPS speed increased up to 160%. This speed increase is evidence for basal sliding induced by subglacial drainage. In general, we find that when the strain increase on the principle extension axis aligns with the crevasse opening direction, IQ are more prolific. We also observe a diurnal signal in both IQ occurrence and surface strain, with peak strain occurring in the mid- to late-afternoon (15:00 - 19:00 local) across the study area in 2006. We interpret this time-shift in strain and spatiotemporal dependence of IQs to be caused by diurnal variations in melt-induced sliding. Our analysis sheds light on crevasse formation on short time scales where glacier flow is controlled by sliding variations in response to water input into the subglacial drainage system. Coupled seismic and GPS monitoring can thus make a key contribution to our understanding of brittle deformation and crevassing of glacier ice.

Exploring methods of cGPS transient detections for the Chilean cGPS network in conjunction with displacement predictions from seismic catalogues: To what extent can we detect seismic and aseismic motion in the cGPS network?

NASA Astrophysics Data System (ADS)

Bedford, J. R.; Moreno, M.; Oncken, O.; Li, S.; Schurr, B.; Metzger, S.; Baez, J. C.; Deng, Z.; Melnick, D.

2016-12-01

Various algorithms for the detection of transient deformation in cGPS networks are under currently being developed to relieve us of by-eye detection, which is an error prone and time-expensive activity. Such algorithms aim to separate the time series into secular, seasonal, and transient components. Additional white and coloured noise, as well as common-mode (network correlated) noise, may remain in the separated transient component of the signal, depending on the processing flow before the separation step. The a-priori knowledge of regional seismicity can assist in the recognition of steps in the data, which are generally corrected for if they are above the noise-floor. Sometimes, the cumulative displacement caused by small earthquakes can create a seemingly continuous transient signal in the cGPS leading to confusion as to whether to attribute this transient motion as seismic or aseismic. Here we demonstrate the efficacy of various transient detection algorithms for subsets of the Chilean cGPS network and present the optimal processing flow for teasing out the transients. We present a step-detection and removal algorithm and estimate the seismic efficiency of any detected transient signals by forward modelling the surface displacements of the earthquakes and comparing to the recovered transient signals. A major challenge in separating signals in the Chilean cGPS network is the overlapping of postseismic effects at adjacent segments: For example, a Mw 9 earthquake will produce a postseismic viscoelastic relaxation that is sustained over decades and several hundreds of kilometres. Additionally, it has been observed in Chile and Japan that following moderately large earthquakes (e.g. Mw > 8) the secular velocities of adjacent segments in the subduction margin suddenly change and remain changed: this effect may be related to a change in speed of slab subduction rather than viscoelastic relaxation, and therefore the signal separation algorithms that assume a time-independent secular velocity at each station may need to be revised to account for this effect. Accordingly, we categorize the recovered separated secular and transient signals of a particular station in terms of the seismic cycle in both its own and adjacent segments and discuss the appropriate modelling strategy for this station given its category.

Coseismic deformation of the 2001 El Salvador and 2002 Denali fault earthquakes from GPS geodetic measurements

NASA Astrophysics Data System (ADS)

Hreinsdottir, Sigrun

2005-07-01

GPS geodetic measurements are used to study two major earthquakes, the 2001 MW 7.7 El Salvador and 2002 MW 7.9 Denali Fault earthquakes. The 2001 MW 7.7 earthquake was a normal fault event in the subducting Cocos plate offshore El Salvador. Coseismic displacements of up to 15 mm were measured at permanent GPS stations in Central America. The GPS data were used to constrain the location of and slip on the normal fault. One month later a MW 6.6 strike-slip earthquake occurred in the overriding Caribbean plate. Coulomb stress changes estimated from the M W 7.7 earthquake suggest that it triggered the MW 6.6 earthquake. Coseismic displacement from the MW 6.6 earthquake, about 40 mm at a GPS station in El Salvador, indicates that the earthquake triggered additional slip on a fault close to the GPS station. The MW 6.6 earthquake further changed the stress field in the overriding Caribbean plate, with triggered seismic activity occurring west and possibly also to the east of the rupture in the days to months following the earthquake. The MW 7.9 Denali Fault earthquake ruptured three faults in the interior of Alaska. It initiated with a thrust motion on the Susitna Glacier fault but then ruptured the Denali and Totschunda faults with predominantly right-lateral strike-slip motion unilaterally from west to east. GPS data measured in the two weeks following the earthquake suggest a complex coseismic rupture along the faults with two main regions of moment release along the Denali fault. A large amount of additional data were collected in the year following the earthquake which greatly improved the resolution on the fault, revealing more details of the slip distribution. We estimate a total moment release of 6.81 x 1020 Nm in the earthquake with a M W 7.2 thrust subevent on Susitna Glacier fault. The slip on the Denali fault is highly variable, with 4 main pulses of moment release. The largest moment pulse corresponds to a MW 7.5 subevent, about 40 km west of the Denali-Totschunda fault junction. We estimate relatively low and shallow slip on the Totschunda fault.

Homeopathy in rural Australian primary health care: a survey of general practitioner referral and practice in rural and regional New South Wales, Australia.

PubMed

Wardle, J; Adams, J; Sibbritt, D

2013-07-01

Homeopathy has attracted considerable recent attention from the Australian conventional medical community. However, despite such increased attention there has been little exploration of the interface between homeopathy and Australian conventional medical practice. This article addresses this research gap by exploring homeopathic practice and referral by rural and regional Australian general practitioners (GPs). A 27-item questionnaire was sent to all 1486 GPs currently practising in rural and regional New South Wales, Australia (response rate 40.7%). Few GPs in this study utilised homeopathy in their personal practice, with only 0.5% of GPs prescribing homeopathy in the past 12 months, and 8.5% referring patients for homeopathic treatment at least a few times over the past 12 months. Nearly two-thirds of GPs (63.9%) reported that they would not refer for homeopathy under any circumstances. Being in a remote location, receiving patient requests for homeopathy, observing positive responses from homeopathy previously, using complementary and alternative medicine (CAM) practitioners as information sources, higher levels of knowledge of homeopathy, and being interested in increasing CAM knowledge were all independently predictive of increased referral to homeopathy amongst GPs in this study. GPs in this study were less likely to refer to homeopathy if they used peer-reviewed literature as the major source of their information on CAM. Homeopathy is not integrated significantly in rural general practice either via GP utilisation or referral. There is significant opposition to homeopathy referral amongst rural and regional GPs, though some level of interaction with homeopathic providers exists. Copyright © 2013 The Faculty of Homeopathy. Published by Elsevier Ltd. All rights reserved.

Comparison of GPS TEC variations with Holt-Winter method and IRI-2012 over Langkawi, Malaysia

NASA Astrophysics Data System (ADS)

Elmunim, N. A.; Abdullah, M.; Hasbi, A. M.; Bahari, S. A.

2017-07-01

The Total Electron Content (TEC) is the ionospheric parameter that has the main effect on radio wave propagation. Therefore, it is crucial to evaluate the performance of the TEC models for the further improvement of the ionospheric modelling in equatorial regions. This work presents an analysis of the TEC, derived from the GPS Ionospheric Scintillation and TEC Monitor (GISTM) receiver at the Langkawi station, Malaysia, located at the geographic coordinates of 6.19°N, 99.51°E and the geomagnetic coordinates of 3.39°S, 172.42°E. The diurnal, monthly and seasonal variations in 2014 of the observed GPS-TEC were compared with the statistical Holt-Winter method and a recent version of the International Reference Ionosphere model (IRI-2012), using three different topside options of an electron density, which are the IRI-2001, IRI01-corr and NeQuick. The maximum peaks of the GPS-TEC were observed in the post-noon time and the minimum was observed during the early morning time. In addition, in monthly variations the Holt-Winter and the IRI-2012 topside options showed an underestimation that was in agreement with the GPS-TEC, except for the IRI-2001 model which showed an overestimation in June, July and August. Regarding the seasonal variation of the GPS-TEC, the lowest values were observed during summer and it reached its maximum value during the equinox season. The IRI-2001 showed the highest value of percentage deviation compared to the IRI01-corr, NeQuick and Holt-Winter method. Therefore, the accuracy of the models was found to be approximately 95% in the Holt-Winter method, 75% in the IRI01-corr, 73% in the NeQuick and 66% in the IRI-2001 model. Hence, it can be inferred that the Holt-Winter method showed a higher performance and better estimates of the TEC compared to the IRI01-corr and NeQuick, while the IRI-2001 showed a poor predictive performance in the equatorial region over Malaysia.

Contribution of Multi-GNSS Constellation to SLR-Derived Terrestrial Reference Frame

NASA Astrophysics Data System (ADS)

Sośnica, K.; Bury, G.; Zajdel, R.

2018-03-01

All satellites of new Global Navigation Satellite Systems (GNSS) are equipped with laser retroreflectors dedicated to Satellite Laser Ranging (SLR). This paper demonstrates the contribution of SLR tracking of multi-GNSS constellations to the improved SLR-derived reference frame and scientific products. We show a solution strategy with estimating satellite orbits, SLR station coordinates, geocenter coordinates, and Earth rotation parameters using SLR observations to 2 Laser Geodynamics Satellites (LAGEOS) and 55 GNSS satellites: 1 GPS, 31 Globalnaya Navigatsionnaya Sputnikovaya Sistema, 18 Galileo, 3 BeiDou Inclined Geosynchronous Orbit, 1 BeiDou Medium Earth Orbit, and 1 Quasi-Zenith Satellite System satellite for the period 2014.0-2017.4. Due to a substantial number of GNSS observations, the number of weekly solutions for some SLR stations, for example, Arkhyz, Komsomolsk, Altay, and Brasilia, is larger up to 41% in the combined LAGEOS + GNSS solution when compared to the LAGEOS-only solution. The SLR observations to GNSS can transfer the orientation of the reference frame from GNSS to SLR solutions. As a result, the SLR-derived pole coordinates and length-of-day estimates become more consistent with GNSS microwave-based results. The root-mean-square errors of length-of-day are reduced from 122.5 μs/d to 43.0 μs/d, whereas mean offsets are reduced from -81.6 μs/d to 0.5 μs/d in LAGEOS only and in the combined LAGEOS + GNSS solutions, respectively.

Directional Networking in GPS Denied Environments - Time Synchronization

DTIC Science & Technology

2016-03-14

RF-based measurements to synchronize time and measure node range.  Satellite Doppler: Using Doppler measurements from multiple satellites along...with satellite catalog data to determine time and position.  LTE : Use existing LTE base-stations for time and position.  Differential GPS: A...Opportunistic Signals: Opportunistically take advantage of existing RF signals (i.e., FM radio, DTV, LTE , etc.) transmitted from known locations

Augmenting Onshore GPS Displacements with Offshore Observations to Improve Slip Characterization for Cascadia Subduction Earthquakes

NASA Astrophysics Data System (ADS)

Saunders, J. K.; Haase, J. S.

2017-12-01

The rupture location of a Mw 8 megathrust earthquake can dramatically change the near-source tsunami impact, where a shallow earthquake can produce a disproportionally large tsunami for its magnitude. Because the locking pattern of the shallow Cascadia megathrust is unconstrained due to the lack of widespread seafloor geodetic observations, near-source tsunami early warning systems need to be able to identify shallow, near-trench earthquakes. Onshore GPS displacements provide low frequency ground motions and coseismic offsets for characterizing tsunamigenic earthquakes, however the one-sided distribution of data may not be able to uniquely determine the rupture region. We examine how augmenting the current real-time GPS network in Cascadia with different offshore station configurations improves static slip inversion solutions for Mw 8 earthquakes at different rupture depths. Two offshore coseismic data types are tested in this study: vertical-only, which would be available using existing technology for bottom pressure sensors, and all-component, which could be achieved by combining pressure sensors with real-time GPS-Acoustic observations. We find that both types of offshore data better constrain the rupture region for a shallow earthquake compared to onshore data alone when offshore stations are located above the rupture. However, inversions using vertical-only offshore data tend to underestimate the amount of slip for a shallow rupture, which we show underestimates the tsunami impact. Including offshore horizontal coseismic data into the inversions improves the slip solutions for a given offshore station configuration, especially in terms of maximum slip. This suggests that while real-time GPS-Acoustic sensors may have a long development timeline, they will have more impact for inversion-based tsunami early warning systems than bottom pressure sensors. We also conduct sensitivity studies using kinematic models with varying rupture speeds and rise times as a proxy for expected rigidity changes with depth along the megathrust. We find distinguishing features in displacement waveforms that can be used to infer primary rupture region. We discuss how kinematic inversion methods that use these characteristics in high-rate GPS data could be applied to the Cascadia subduction zone.

Using GPS to Detect Imminent Tsunamis

NASA Technical Reports Server (NTRS)

Song, Y. Tony

2009-01-01

A promising method of detecting imminent tsunamis and estimating their destructive potential involves the use of Global Positioning System (GPS) data in addition to seismic data. Application of the method is expected to increase the reliability of global tsunami-warning systems, making it possible to save lives while reducing the incidence of false alarms. Tsunamis kill people every year. The 2004 Indian Ocean tsunami killed about 230,000 people. The magnitude of an earthquake is not always a reliable indication of the destructive potential of a tsunami. The 2004 Indian Ocean quake generated a huge tsunami, while the 2005 Nias (Indonesia) quake did not, even though both were initially estimated to be of the similar magnitude. Between 2005 and 2007, five false tsunami alarms were issued worldwide. Such alarms result in negative societal and economic effects. GPS stations can detect ground motions of earthquakes in real time, as frequently as every few seconds. In the present method, the epicenter of an earthquake is located by use of data from seismometers, then data from coastal GPS stations near the epicenter are used to infer sea-floor displacements that precede a tsunami. The displacement data are used in conjunction with local topographical data and an advanced theory to quantify the destructive potential of a tsunami on a new tsunami scale, based on the GPS-derived tsunami energy, much like the Richter Scale used for earthquakes. An important element of the derivation of the advanced theory was recognition that horizontal sea-floor motions contribute much more to generation of tsunamis than previously believed. The method produces a reliable estimate of the destructive potential of a tsunami within minutes typically, well before the tsunami reaches coastal areas. The viability of the method was demonstrated in computational tests in which the method yielded accurate representations of three historical tsunamis for which well-documented ground-motion measurements were available. Development of a global tsunami-warning system utilizing an expanded network of coastal GPS stations was under consideration at the time of reporting the information for this article.

Evaluation of 14 global GIA forward models using a novel GPS dataset and GRACE

NASA Astrophysics Data System (ADS)

Bamber, J. L.; Schumacher, M.; Sha, Z.; Rougier, J.; King, M. A.; Khan, S. A.; Shum, C. K.; Luthcke, S. B.

2017-12-01

Observed mass movement from GRACE and vertical land motion from a global network of permanent GPS stations are used in a data driven approach to estimate GIA signals without introducing any assumptions about Earth structure nor ice loading history. Satellite data and in-situ observations are combined using a multivariate spatiotemporal model within a Bayesian Hierarchical Modelling (BHM) framework. In this study, the GPS data set of the Nevada Geodetic Laboratory (NGL) is used as the starting point for providing an observational estimate of global GIA uplift rates. A novel fully automatic post-processing strategy is developed to correct for non-GIA artifacts, including: (i) outlier detection (e.g. due to icing of Choke Ring Antennas or the antenna being buried in snow); (ii) automatic removal of reported and unreported jumps due to geophysical and hardware issues (a refinement of the jump database provided by NGL); and (iii) filtering for GPS stations that observe primarily the GIA signal rather than unwanted local effects (e.g., unmodelled loading effects from land hydrology, atmosphere, or tides). In order to accurately account for the elastic response of the Earth's crust over Antarctica and Greenland, uplift rates in these regions were corrected for the contemporary ice mass loading impact on elastic deformation using high-resolution ice mass balance time series. The novel global GPS data set shows a clean GIA signal at all post-processed stations and is therefore suitable to investigate the behavior of global GIA forward models. In addition, NASA's GSFC GRACE global mascon solutions are employed. The equal area 1x1 degree gridded mascons are spatially aggregated for larger regions to account for their spatial error correlations. Both the GPS and GRACE datasets are combined with prior information about spatial wavelengths of GIA signals obtained from the ICE-6G model within the BHM framework to solve for GIA. The results are compared with 14 global GIA forward model solutions to identify statistically significant deviations between the forward and inverse solutions, which may be due to either uncertain mantle rheology and/or ice loading history/magnitude.

Modelling of The Dyke Emplacement Leading To The Etna July 2001 Eruption Through Continuous Tilt and GPS Data

NASA Astrophysics Data System (ADS)

Bonaccorso, A.; Aloisi, M.; Mattia, A.

During the June 2001 eruption of Mt. Etna the continuous ground deformation mon- itoring have been recorded through tilt (9 stations) and GPS (11 stations) permanent networks. The evolution of the July crisis preceding and leading to the eruption has been monitored through the tilt and GPS continuous measurements, which constrained in time the final intrusion and inferred the position and geometry of the uprising dyke. The tilt signals, which record 48 samples/day, fixed the time action of the intrusion, whose main effects are recorded during 13-15 July in concomitance with the first days of the seismic crisis. In particular, the high precision long-base mercury tiltmeter, in- stalled at Pizzi Deneri observatory in the high north-eastern flank close to the crater area, showed very well the continuous deformation during the dyke emplacement. The deformation pattern, at the entire volcano scale, was well characterised by the daily measurement sessions recorded at the GPS permanent network. The variations recorded at the permanent GPS stations started from July 13 and, in agreement with tilt recordings, were mainly cumulated in the following two days. The GPS measurements showed horizontal displacement vectors much bigger than vertical changes. The defor- mation pattern indicates the response to a tensile mechanisms that appears compatible with an intrusion in the volcano edifice along a ca. N-S direction. In this poster we show the modelling of the marked ground deformation changes recorded in the days before the eruption starting. The first results show that a tensile crack with an opening dislocation of ~3 m. and crossing the entire edifice, south-west to the crater area, can explain the recorded deformation pattern. The location of the modelled tensile source fits the seismogenetic zone characterized by epicenters aligned in a ca. N-S direction with the foci clustered in the last shallow kilometers. The ground deformation pat- tern associated with the final uprising and its modelling suggest a dyke emplacement which appears different, both in terms of velocity and source position, with respect to the sources modelled for the other lateral eruptions in the previous twenty years.

Report On Fiducial Points At The Space Geodesy Based Cagliari Astronomical Observatory

NASA Astrophysics Data System (ADS)

Banni, A.; Buffa, F.; Falchi, E.; Sanna, G.

At the present time two research groups are engaged to space-geodesy activities in Sardinia: a staff belonging to the Stazione Astronomica of Cagliari (SAC) and the To- pography Section of the Dipartimento di Ingegneria Strutturale (DIST) of the Cagliari University. The two groups have a share in international campaigns and services. The local structure, consists of permanent stations of satellite observation both on radio and laser techniques. Particularly in the Cagliari Observatory a Satellite Laser Ranging system runs with nearly daily, low, medium and high orbit satellite tracking capability (e. g. Topex, Ajisai, Lageos1/2, Glonass); up to this time the Cagliari laser station has contributed towards the following international campaigns/organizations. Besides in the Observatory's site a fixed GPS system, belonging the Italian Space Agency GPS- Network and to the IGS-Network; and a GPS+GLONASS system, acquired by DIST and belonging to the IGLOS are installed and managed. All the above stations are furnished with meteorological sensors with RINEX format data dissemination avail- ability. Moreover a new 64 meters dish radio telescope (Sardinian Radio Telescope), geodetic VLBI equipped, is under construction not long away from the Observatory. The poster fully shows the facilities and furnishes a complete report on the mark- ers eccentricities, allowing co-location of the different space techniques operating in Sardinia.

Recovery of a geocentric reference frame using the present-day GPS system

NASA Technical Reports Server (NTRS)

Malla, Rajendra P.; Wu, Sien-Chong

1990-01-01

A geocentric reference frame adopts the center of mass of the earth as the origin of the coordinate axes. The center of mass of the earth is the natural and unambiguous origin of a geocentric satellite dynamical system. But in practice a kinematically obtained terrestrial reference frame may assume an origin other than the geocenter. The establishment of a geocentric reference frame, to which all relevant observations and results can be referred and in which geodynamic theories or models for the dynamic behavior of earth can be formulated, requires the ability to accurately recover a given coordinate frame origin offset from the geocenter. GPS measurements, because of their abundance and broad distribution, provide a powerful tool to obtain this origin offset in a short period of time. Two effective strategies have been devised. Data from the First Central And South America (Casa Uno) geodynamics experiment has been studied, in order to demonstrate the ability of recovering the geocenter location with present day GPS satellites and receivers.

The PBO Nucleus: Integration of the Existing Continuous GPS Networks in the Western U.S.

NASA Astrophysics Data System (ADS)

Blume, F.; Anderson, G.; Freymueller, J. T.; Herring, T. A.; Melbourne, T. I.; Murray, M. H.; Prescott, W. H.; Smith, R. B.; Wernicke, B.

2004-12-01

Tectonic and earthquake research in the US has experienced a quiet revolution over the last decade precipitated by the recognition that slow-motion faulting events can both trigger and be triggered by regular earthquakes. Transient motion has now been found in essentially all tectonic environments, and the detection and analysis of such events is the first-order science target of the EarthScope Project. Because of this and a host of other fundamental tectonics questions that can be answered only with long-duration geodetic time series, the incipient 1400-station EarthScope Plate Boundary Observatory (PBO) network has been designed to leverage 432 existing continuous GPS stations whose measurements extend back over a decade. The irreplaceable recording history of these stations will accelerate EarthScope scientific return by providing the highest possible resolution. This resolution will be used to detect and understand transients, to determine the three-dimensional velocity field (particularly vertical motion), and to improve measurement precision by understanding the complex noise sources inherent in GPS. The PBO Nucleus Project is designed operate, maintain and upgrade a subset of six western U.S. geodetic networks: the Alaska Deformation Array (AKDA), Bay Area Regional Deformation network (BARD), the Basin and Range Geodetic Network (BARGEN), the Eastern Basin and Range/Yellowstone network (EBRY), the Pacific Northwest Geodetic Array (PANGA), and the Southern California Integrated Geodetic Network (SCIGN), until they are subsumed by PBO in 2008. Uninterrupted data flow from these stations will effectively double the time-series length of PBO over the expected life of EarthScope, and create, for the first time, a single GPS-based geodetic network in the US. Other existing sites will remain in operation under support from non-NSF sources (e.g. the USGS), and EarthScope will benefit from their continued operation. On the grounds of relevance to EarthScope science goals, geographic distribution and data quality, 209 of the 432 existing stations have been selected as the nucleus upon which to build PBO. We have begun converting these stations to a PBO-compatible mode of operation; data now flow directly to PBO archives and processing centers while maintenance, operations, and meta-data requirements are currently under upgrade to PBO standards.

Impact of different NWM-derived mapping functions on VLBI and GPS analysis

NASA Astrophysics Data System (ADS)

Nikolaidou, Thalia; Balidakis, Kyriakos; Nievinski, Felipe; Santos, Marcelo; Schuh, Harald

2018-06-01

In recent years, numerical weather models have shown the potential to provide a good representation of the electrically neutral atmosphere. This fact has been exploited for the modeling of space geodetic observations. The Vienna Mapping Functions 1 (VMF1) are the NWM-based model recommended by the latest IERS Conventions. The VMF1 are being produced 6 hourly based on the European Centre for Medium-Range Weather Forecasts operational model. UNB-VMF1 provide meteorological parameters aiding neutral atmosphere modeling for VLBI and GNSS, based on the same concept but utilizing the Canadian Meteorological Centre model. This study presents comparisons between the VMF1 and the UNB-VMF1 in both delay and position domains, using global networks of VLBI and GPS stations. It is shown that the zenith delays agree better than 3.5 mm (hydrostatic) and 20 mm (wet) which implies an equivalent predicted height error of less than 2 mm. In the position domain and VLBI analysis, comparison of the weighted root-mean-square error (wrms) of the height component showed a maximum difference of 1.7 mm. For 48% of the stations, the use of VMF1 reduced the height wrms of the stations by 2.6% on average compared to a respective reduction of 1.7% for 41% of the stations employing the UNB-VMF1. For the subset of VLBI stations participating in a large number of sessions, neither mapping function outranked the other. GPS analysis using Precise Point Positioning had a sub-mm respective difference, while the wrms of the individual solutions had a maximum value of 12 mm for the 1-year-long analysis. A clear advantage of one NWM over the other was not shown, and the statistics proved that the two mapping functions yield equal results in geodetic analysis.

Reactivation of a Deep Seated Gravitational Slope Deformation observed during the recent seismic events in Central Italy.

NASA Astrophysics Data System (ADS)

Amato, Gabriele; Aringoli, Domenico; Devoti, Roberto; Fubelli, Giandomenico; Galvani, Alessandro; Pambianchi, Gilberto; Sepe, Vincenzo

2017-04-01

Deep-Seated Gravitational Slope Deformations (DSGSDs) represent an important geomorphological feature of the European mountain chains and several cases from Central Apennine (Italy) are accurately described in literature. These phenomena generally present evident geomorphological markers (e.g. double ridges, trenches, counterslopes) and low activity rates (i.e. mm to cm per year), which can be triggered by many different means (e.g. seismic activity, erosional processes, rainfall, post-glacial debuttressing). To understand which is the most influential factor in DSGSDs' activity is rarely an easy task because this can vary from case to case. This work illustrates the outcomes provided by a monitoring activity conducted along the Mt. Frascare slope (Fiastra Lake, Marche region, Italy). The monitoring system is composed by 4 low cost GPS stations, based on single-frequency receivers, and 2 double-frequency GPS stations, aimed to cross-check the surface deformations measured by the two types of monitoring stations. The 6 GPS stations have been operated in place starting from October 2014 grounded on the base of a geomorphological field survey of the investigated phenomenon. Two stations have been equipped with both receiver types in order to facilitate the comparison of the results. The Fiastra DSGSD affects a marly limestone bedrock throughout a >5km2 area and along a slope against which a dam for hydroelectric power leans. Our monitoring system allowed to measure the Fiastra DSGSD's seismically induced relative displacements on the order of two mean steps of about 10 cm, due to the recent seismic sequence occurred in Central Italy in 2016, which resulted considerably higher than the observed mean annual velocity (≈5mm/y).

Relation of decorrelated transionospheric GPS signal fluctuations from two stations in the northern anomaly crest region with equatorial ionospheric dynamics

NASA Astrophysics Data System (ADS)

Paul, K. S.; Paul, A.

2017-05-01

The ionosphere around the northern crest of the equatorial ionization anomaly (EIA) and beyond exhibits rapid temporal as well as spatial development of ionization density irregularities during postsunset hours. A GPS campaign was conducted during September 2012 and April 2013 from the Institute of Radio Physics and Electronics, Calcutta (22.58°N, 88.38°E geographic; magnetic dip: 32°N), and North Bengal University (NBU), Siliguri (26.72°N, 88.39°E geographic, magnetic dip: 39.49°N) in India in order to assess and quantify differences, if any, in the nature of carrier to noise ratio (C/N0) fluctuations observed on the same satellite link around the same time interval from these stations. Significant decorrelation of the received signals was found when tracking the same satellite vehicle (SV) link from these stations during periods of scintillations. Low values of correlation coefficient of C/N0 at L1 frequency recorded on the same SV link at these two stations were found to correspond with high irregularity characteristic velocities. North-south spatial displacement rates of the impact of ionospheric irregularities were calculated based on coordinated GPS observations which followed an increasing trend with irregularity characteristic velocities measured at VHF. Values of characteristic velocities in excess of 36 m/s were also found to result in large receiver position deviations 3.5-4.0 m during periods of scintillations. Information related to time lag associated with occurrence of scintillations on the same SV link observed from two stations could be useful for improving performance of transionospheric satellite-based position determination techniques.

Continuous Estimates of Precipitable Water Vapor Within and Around Hurricane Systems

NASA Astrophysics Data System (ADS)

Braun, J. J.; Iwabuchi, T.; van Hove, T.

2008-12-01

This study investigates how estimates of precipitable water vapor (PW) from Global Positioning System (GPS) stations can be used to quantify how atmospheric moisture influences the intensity of tropical storms and hurricanes. The motivation for this study is based on the fact that hurricanes derive their strength through water vapor that is both evaporated from warm ocean surfaces and the existing moisture in the surrounding atmospheric environment. Observationally, there are relatively few instruments that can accurately measure water vapor in the presence of clouds and rain. Retrievals of PW using GPS stations may be the most reliable way to continuously monitor column integrated water vapor. Using storm information from the National Hurricane Center (www.nhc.noaa.gov), we have compared storm intensity to PW estimates for all tropical storms and hurricanes making landfall within 100-km of a GPS station between 2003 and 2008. We find that PW is inversely correlated (r**2 < -0.7) to the drop in surface pressure observed at that station. We have also begun to relate atmospheric PW at a station to the local sea surface temperature (SST). This comparison can be used to measure how strongly atmospheric water vapor and SST are coupled. It can also be used to measure how quickly the atmosphere responds to changes in SST. Finally we have compared the estimated PW to the Global Forecast System (GFS) analysis fields that are used to initialize numerical weather prediction models. This comparison indicates that the GFS analysis fields have significantly larger errors in atmospheric moisture in the Caribbean and Gulf of Mexico when compared to differences over the continental United States. These results illustrate that estimates of PW are an important data set for atmospheric scientists and forecasters attempting to improve the prediction of hurricane intensity.

Multi-parameter observations in the Ibero-Moghrebian region: the Western Mediterranean seismic network (WM) and ROA GPS geodynamic network

NASA Astrophysics Data System (ADS)

Pazos, Antonio; Martín Davila, José; Buforn, Elisa; Gárate Pasquín, Jorge; Catalán Morollón, Manuel; Hanka, Winfried; Udías, Agustín.; Benzzeghoud, Mourad; Harnafi, Mimoun

2010-05-01

The plate boundary between Eurasia and Africa plates crosses the called "Ibero-Maghrebian" region from the San Vicente Cape (SW Portugal) to Tunisia including the South of Iberia, Alboran Sea, and northern Morocco and Algeria. In this area, the convergence, with a low rate, is accommodated over a wide and diffuse deformation zone, characterized by a significant and widespread moderate seismic activity [Buforn et al., 1995], and the occurrence of large earthquakes is separated by long time intervals. Since more than hundred years ago San Fernando Naval Observatory (ROA), in collaboration with other Institutes, has deployed different geophysical and geodetic equipment in the Southern Spain - North-western Africa area in order to study this broad deformation zone. Currently a Broad Band seismic net (Western Mediterranean, WM net) is deployed, in collaboration with other institutions, around the Gulf of Cádiz and the Alboran sea, with stations in the South of Iberia and in North Africa (at Spanish places and Morocco), together with the seismic stations a permanent geodetic GPS net is co-installed at the same sites. Also, other geophysical instruments have been installed: a Satellite Laser Ranging (SLR) station at San Fernando Observatory Headquarter, a Geomagnetic Observatory in Cádiz bay area and some meteorological stations. These networks have been recently improved with the deployment of a new submarine and on-land geophysical observatory in the Alboran island (ALBO Observatory), where a permanent GPS, a meteorological station were installed on land and a permanent submarine observatory in 50 meters depth was also deploy in last October (with a broad band seismic sensor, a 3 C accelerometer and a DPG). This work shows the present status and the future plans of these networks and some results.

A directional model of tropospheric horizontal gradients in Global Positioning System and its application for particular weather scenarios

NASA Astrophysics Data System (ADS)

Masoumi, Salim; McClusky, Simon; Koulali, Achraf; Tregoning, Paul

2017-04-01

Improper modeling of horizontal tropospheric gradients in GPS analysis induces errors in estimated parameters, with the largest impact on heights and tropospheric zenith delays. The conventional two-axis tilted plane model of horizontal gradients fails to provide an accurate representation of tropospheric gradients under weather conditions with asymmetric horizontal changes of refractivity. A new parametrization of tropospheric gradients whereby an arbitrary number of gradients are estimated as discrete directional wedges is shown via simulations to significantly improve the accuracy of recovered tropospheric zenith delays in asymmetric gradient scenarios. In a case study of an extreme rain event that occurred in September 2002 in southern France, the new directional parametrization is able to isolate the strong gradients in particular azimuths around the GPS stations consistent with the "V" shape spatial pattern of the observed precipitation. In another study of a network of GPS stations in the Sierra Nevada region where highly asymmetric tropospheric gradients are known to exist, the new directional model significantly improves the repeatabilities of the stations in asymmetric gradient situations while causing slightly degraded repeatabilities for the stations in normal symmetric gradient conditions. The average improvement over the entire network is ˜31%, while the improvement for one of the worst affected sites P631 is ˜49% (from 8.5 mm to 4.3 mm) in terms of weighted root-mean-square (WRMS) error and ˜82% (from -1.1 to -0.2) in terms of skewness. At the same station, the use of the directional model changes the estimates of zenith wet delay by 15 mm (˜25%).

Analysis of surface deformation during the eruptive process of El Hierro Island (Canary Islands, Spain): Detection, Evolution and Forecasting.

NASA Astrophysics Data System (ADS)

Berrocoso, M.; Fernandez-Ros, A.; Prates, G.; Martin, M.; Hurtado, R.; Pereda, J.; Garcia, M. J.; Garcia-Cañada, L.; Ortiz, R.; Garcia, A.

2012-04-01

The surface deformation has been an essential parameter for the onset and evolution of the eruptive process of the island of El Hierro (October 2011) as well as for forecasting changes in seismic and volcanic activity during the crisis period. From GNSS-GPS observations the reactivation is early detected by analizing the change in the deformation of the El Hierro Island regional geodynamics. It is found that the surface deformation changes are detected before the occurrence of seismic activity using the station FRON (GRAFCAN). The evolution of the process has been studied by the analysis of time series of topocentric coordinates and the variation of the distance between stations on the island of El Hierro (GRAFCAN station;IGN network; and UCA-CSIC points) and LPAL-IGS station on the island of La Palma. In this work the main methodologies and their results are shown: •The location (and its changes) of the litospheric pressure source obtained by applying the Mogi model. •Kalman filtering technique for high frequency time series, used to make the forecasts issued for volcanic emergency management. •Correlations between deformation of the different GPS stations and their relationship with seismovolcanic settings.

The ionospheric impact on GPS performance in southern polar region

USGS Publications Warehouse

Hong, C.-K.; Grejner-Brzezinska, D. A.; Arslan, N.; Willis, M.; Hothem, L.

2006-01-01

The primary objective of this paper is to present the results of the study of the effects of varying ionospheric conditions on the GPS signal tracking in the southern polar region. In the first stage of this study, the data collected by the OSU/USGS team in October-November 2003 within the TAMDEF (Transantarctic Mountains Deformation) network were used together with some IGS Antarctic stations to study the effect of severe ionospheric storms on GPS hardware. Note that TAMDEF is a joint USGS/OSU project with the primary objective of measuring crustal motion in the Transantarctic Mountains of Southern Victoria Land using GPS techniques. This study included ten Antarctic stations equipped with different dual-frequency GPS hardware, and the data were evaluated for two 24-hour periods of severe ionospheric storm (2003/10/29) and moderate ionospheric conditions (minor storm of 2003/11/11). The results of this study were presented at the LAG Assembly in Cairns, Australia (Grejner-Brzezinska et al., 2005). Additional tests, in a more controlled environment, were carried out at the US Antarctic station, McMurdo, between January 10 and February 6, 2006, under varying ionospheric conditions, where several different types of receivers were connected to the same antenna located on the rooftop of the Crary Laboratory (the primary test site). In this scenario, each antenna was subject to identical ionospheric effects during each day of the test, and no spatial decorrelation effects were present, as seen in the previous study, due to the spatial separation of the receivers tested. It should be noted, however, that no moderate or severe ionospheric storms occurred during the experiment, so, unfortunately, this type of conditions was not tested here. The test was repeated with different receivers connected to different antenna types; a total of four 5-day sessions were carried out. The following receiver types were used at the primary site: Trimble 5700, Ashtech Z-Surveyor, JNS Euro-80 and Novatel DL-4, with the following antennas: Trimble Zephyr Geodetic, Ashtech D/M and Ashtech E/M chokering. In addition, data collected by the MCM4 IGS station, MCMD UNAVCO station, and CRAR USGS station, all located within 300 m from the primary test site, were used in the analyses. These stations were equipped with the following receiver/antenna combinations: ADA SNR-12/AOAD/MJT chokering (MCM4), Trimble NETRS/AOAD/MJT chokering (MCMD), and TPS ODYSEY_E/JPSREGANT_DD_E (CRAR). The UNAVCO TEQC software was used to carry out the analyses. Depending on the data sampling rate and the mask angle, the expected numbers of observations per receiver/satellite were compared to the actual number of measurements collected during the ionospheric events, with a special emphasis on L2 data. A total number of cycle slips and losses of lock were computed and compared among the hardware types. The results presented here indicate that there is no significant effects on the GPS receivers during minor ionospheric storms (Kp<5). However, the results reported in ibid, indicate significant differences in the hardware performance under severe ionospheric storms. Thus, careful hardware selection is needed to assure data quality/continuity when observations may be affected by severe ionospheric disturbances, while under calm to minor ionospheric activity level there is no significant difference in performance among the hardware tested here.