Automated time activity classification based on global positioning system (GPS) tracking data.

PubMed

Wu, Jun; Jiang, Chengsheng; Houston, Douglas; Baker, Dean; Delfino, Ralph

2011-11-14

Air pollution epidemiological studies are increasingly using global positioning system (GPS) to collect time-location data because they offer continuous tracking, high temporal resolution, and minimum reporting burden for participants. However, substantial uncertainties in the processing and classifying of raw GPS data create challenges for reliably characterizing time activity patterns. We developed and evaluated models to classify people's major time activity patterns from continuous GPS tracking data. We developed and evaluated two automated models to classify major time activity patterns (i.e., indoor, outdoor static, outdoor walking, and in-vehicle travel) based on GPS time activity data collected under free living conditions for 47 participants (N = 131 person-days) from the Harbor Communities Time Location Study (HCTLS) in 2008 and supplemental GPS data collected from three UC-Irvine research staff (N = 21 person-days) in 2010. Time activity patterns used for model development were manually classified by research staff using information from participant GPS recordings, activity logs, and follow-up interviews. We evaluated two models: (a) a rule-based model that developed user-defined rules based on time, speed, and spatial location, and (b) a random forest decision tree model. Indoor, outdoor static, outdoor walking and in-vehicle travel activities accounted for 82.7%, 6.1%, 3.2% and 7.2% of manually-classified time activities in the HCTLS dataset, respectively. The rule-based model classified indoor and in-vehicle travel periods reasonably well (Indoor: sensitivity > 91%, specificity > 80%, and precision > 96%; in-vehicle travel: sensitivity > 71%, specificity > 99%, and precision > 88%), but the performance was moderate for outdoor static and outdoor walking predictions. No striking differences in performance were observed between the rule-based and the random forest models. The random forest model was fast and easy to execute, but was likely less robust than the rule-based model under the condition of biased or poor quality training data. Our models can successfully identify indoor and in-vehicle travel points from the raw GPS data, but challenges remain in developing models to distinguish outdoor static points and walking. Accurate training data are essential in developing reliable models in classifying time-activity patterns.

Comparison of global positioning system (GPS) tracking and parent-report diaries to characterize children's time-location patterns.

PubMed

Elgethun, Kai; Yost, Michael G; Fitzpatrick, Cole T E; Nyerges, Timothy L; Fenske, Richard A

2007-03-01

Respondent error, low resolution, and study participant burden are known limitations of diary timelines used in exposure studies such as the National Human Exposure Assessment Survey (NHEXAS). Recent advances in global positioning system (GPS) technology have produced tracking devices sufficiently portable, functional and affordable to utilize in exposure assessment science. In this study, a differentially corrected GPS (dGPS) tracking device was compared to the NHEXAS diary timeline. The study also explored how GPS can be used to evaluate and improve such diary timelines by determining which location categories and which respondents are least likely to record "correct" time-location responses. A total of 31 children ages 3-5 years old wore a dGPS device for all waking hours on a weekend day while their parents completed the NHEXAS diary timeline to document the child's time-location pattern. Parents misclassified child time-location approximately 48% of the time using the NHEXAS timeline in comparison to dGPS. Overall concordance between methods was marginal (kappa=0.33-0.35). The dGPS device found that on average, children spent 76% of the 24-h study period in the home. The diary underestimated time the child spent in the home by 17%, while overestimating time spent inside other locations, outside at home, outside in other locations, and time spent in transit. Diary data for time spent outside at home and time in transit had the lowest response concordance with dGPS. The diaries of stay-at-home mothers and mothers working unskilled labor jobs had lower concordance with dGPS than did those of the other participants. The ability of dGPS tracking to collect continuous rather than categorical (ordinal) data was also demonstrated. It is concluded that automated GPS tracking measurements can improve the quality and collection efficiency of time-location data in exposure assessment studies, albeit for small cohorts.

GPS/GLONASS Time Transfer with 20-Channel Dual GNSS Receiver

NASA Technical Reports Server (NTRS)

Daly, P.; Riley, S.

1996-01-01

One of the world's two global navigation systems, the Global Positioning System (GPS), is already fully operational (April 1994) and the other, the Global Navigation Satellite System (GLONASS) will become operational by the end of 1995 or early 1996. Each will offer, independently of the other, precise location and time transfer continuously anywhere in the world and indeed in space itself. Many potential users, in particular the civil aviation community, are keenly interested in a joint GPS/GLONASS operation since it would offer substantial advantages in defining and maintaining the integrity of the navigation aid. Results are presented on the characterization of GPS/GLONASS time comparison using a 20-channel dual receiver developed and constructed at the University of Leeds, UK.

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.

The use of the AOA TTR-4P GPS receiver in operation at the BIPM for real-time restitution of GPS time

NASA Technical Reports Server (NTRS)

Thomas, Claudine

1994-01-01

The Global Positioning System is an outstanding tool for the dissemination of time. Using mono-channel C/A-code GPS time receivers, the restitution of GPS time through the satellite constellation presents a peak-to-peak discrepancy of several tens of nanoseconds without SA but may be as high as several hundreds of nanoseconds with SA. As a consequence, civil users are more and more interested in implementing hardware and software methods for efficient restitution of GPS time, especially in the framework of the project of a real-time prediction of UTC (UTCp) which could be available in the form of time differences (UTCp - GPS time). Previous work, for improving the real-time restitution of GPS time with SA, to the level obtained without SA, focused on the implementation of a Kalman filter based on past data and updated at each new observation. An alternative solution relies upon the statistical features of the noise brought about by SA; it has already been shown that the SA noise is efficiently reduced by averaging data from numerous satellites observed simultaneously over a sufficiently long time. This method was successfully applied to data from a GPS time receiver, model AOA TTR-4P, connected to the cesium clock kept at the BIPM. This device, a multi-channel, dual frequency, P-code GPS time receiver, is one of the first TTR-4P units in operation in a civil laboratory. Preliminary comparative studies of this new equipment with conventional GPS time receivers are described in this paper. The results of an experimental restitution of GPS time, obtained in June 1993, are also detailed: 3 to 6 satellites were observed simultaneously with a sample interval of 15 s, an efficient smoothing of SA noise was realized by averaging data on all observed satellites over more than 1 hour. When the GPS system is complete in 1994, 8 satellites will be observable continuously from anywhere in the world and the same level of uncertainty will be obtained using a shorter averaging time.

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

Near real-time monitoring of volcanic surface deformation from GPS measurements at Long Valley Caldera, California

USGS Publications Warehouse

Ji, Kang Hyeun; Herring, Thomas A.; Llenos, Andrea L.

2013-01-01

Long Valley Caldera in eastern California is an active volcanic area and has shown continued unrest in the last three decades. We have monitored surface deformation from Global Positioning System (GPS) data by using a projection method that we call Targeted Projection Operator (TPO). TPO projects residual time series with secular rates and periodic terms removed onto a predefined spatial pattern. We used the 2009–2010 slow deflation as a target spatial pattern. The resulting TPO time series shows a detailed deformation history including the 2007–2009 inflation, the 2009–2010 deflation, and a recent inflation that started in late-2011 and is continuing at the present time (November 2012). The recent inflation event is about four times faster than the previous 2007–2009 event. A Mogi source of the recent event is located beneath the resurgent dome at about 6.6 km depth at a rate of 0.009 km3/yr volume change. TPO is simple and fast and can provide a near real-time continuous monitoring tool without directly looking at all the data from many GPS sites in this potentially eruptive volcanic system.

Assessment of GPS carrier-phase stability for time-transfer applications.

PubMed

Larson, K M; Levine, J; Nelson, L M; Parker, T E

2000-01-01

We have conducted global positioning system (GPS) carrier-phase time-transfer experiments between the master clock (MC) at the U.S. Naval Observatory (USNO) in Washington, DC and the alternate master clock (AMC) at Schriever Air Force Base near Colorado Springs, Colorado. These clocks are also monitored on an hourly basis with two-way satellite time-transfer (TWSTT) measurements. We compared the performance of the GPS carrier phase and TWSTT systems over a 236-d period. Because of power problems and data outages during the carrier-phase experiment, the longest continuous time span is 96 d. The data from this period show agreement with TWSTT within +/-1 ns, apart from an overall constant time offset (caused by unknown delays in the GPS hardware at both ends). For averaging times of a day, the carrier-phase and TWSTT systems have a frequency uncertainty of 2.5 and 5.5 parts in 10(15), respectively.

Characters of Vertical Variability with Geodetic Satellites and Ground-based Continuous GPS in Taiwan

NASA Astrophysics Data System (ADS)

Yang, C.-C.; Wu, Y.-H.; Chao, B. F.; Yu, S.-B.

2009-04-01

Present-day GPS network have been extensively used to monitor crustal deformation due to various geodynamic mechanisms. Situated among the Pacific Ring of Fire on the suture zone of Eurasian and Philippine Sea Plates, the island of Taiwan with a dense continuous GPS network since ~1996 and now over 300 stations sees plenty of geophysical phenomena including particularly prominent crustal motions. We assessed daily solution of each station's coordinate time series, and made the routine corrections, such as orbital, EOP, atmospheric and tidal corrections, using GAMIT/GLOBK software (with ITRF05). We then employ the Quasi-Observation Combination Analysis (QOCA) package to obtain the variability and trend after removing occasional earthquake "disruptions". Preliminary results show strong seasonal variations. We then utilize the numerical method of Empirical Orthogonal Function (EOF) to analysis the geophysical signals from the continuous and dense GPS vertical crustal motion observations. We wish to be able to characterize both the seasonal and non-seasonal variability in the vertical crustal motion, in terms of the EOF modes in the spatial domain over Taiwan (plus a few offshore islets) with time evolution spanning the entire period of time. Corraborating with time-variable gravity data from the geodetic satellite mission GRACE, we can further obtain vertical components of both mass-induced loading with respect to the precipitation minus evaporation and the crustal motion caused by the active tectonic processes on Taiwan.

Using Global Positioning Systems (GPS) and temperature data to generate time-activity classifications for estimating personal exposure in air monitoring studies: an automated method.

PubMed

Nethery, Elizabeth; Mallach, Gary; Rainham, Daniel; Goldberg, Mark S; Wheeler, Amanda J

2014-05-08

Personal exposure studies of air pollution generally use self-reported diaries to capture individuals' time-activity data. Enhancements in the accuracy, size, memory and battery life of personal Global Positioning Systems (GPS) units have allowed for higher resolution tracking of study participants' locations. Improved time-activity classifications combined with personal continuous air pollution sampling can improve assessments of location-related air pollution exposures for health studies. Data was collected using a GPS and personal temperature from 54 children with asthma living in Montreal, Canada, who participated in a 10-day personal air pollution exposure study. A method was developed that incorporated personal temperature data and then matched a participant's position against available spatial data (i.e., road networks) to generate time-activity categories. The diary-based and GPS-generated time-activity categories were compared and combined with continuous personal PM2.5 data to assess the impact of exposure misclassification when using diary-based methods. There was good agreement between the automated method and the diary method; however, the automated method (means: outdoors = 5.1%, indoors other =9.8%) estimated less time spent in some locations compared to the diary method (outdoors = 6.7%, indoors other = 14.4%). Agreement statistics (AC1 = 0.778) suggest 'good' agreement between methods over all location categories. However, location categories (Outdoors and Transit) where less time is spent show greater disagreement: e.g., mean time "Indoors Other" using the time-activity diary was 14.4% compared to 9.8% using the automated method. While mean daily time "In Transit" was relatively consistent between the methods, the mean daily exposure to PM2.5 while "In Transit" was 15.9 μg/m3 using the automated method compared to 6.8 μg/m3 using the daily diary. Mean times spent in different locations as categorized by a GPS-based method were comparable to those from a time-activity diary, but there were differences in estimates of exposure to PM2.5 from the two methods. An automated GPS-based time-activity method will reduce participant burden, potentially providing more accurate and unbiased assessments of location. Combined with continuous air measurements, the higher resolution GPS data could present a different and more accurate picture of personal exposures to air pollution.

Using Global Positioning Systems (GPS) and temperature data to generate time-activity classifications for estimating personal exposure in air monitoring studies: an automated method

PubMed Central

2014-01-01

Background Personal exposure studies of air pollution generally use self-reported diaries to capture individuals’ time-activity data. Enhancements in the accuracy, size, memory and battery life of personal Global Positioning Systems (GPS) units have allowed for higher resolution tracking of study participants’ locations. Improved time-activity classifications combined with personal continuous air pollution sampling can improve assessments of location-related air pollution exposures for health studies. Methods Data was collected using a GPS and personal temperature from 54 children with asthma living in Montreal, Canada, who participated in a 10-day personal air pollution exposure study. A method was developed that incorporated personal temperature data and then matched a participant’s position against available spatial data (i.e., road networks) to generate time-activity categories. The diary-based and GPS-generated time-activity categories were compared and combined with continuous personal PM2.5 data to assess the impact of exposure misclassification when using diary-based methods. Results There was good agreement between the automated method and the diary method; however, the automated method (means: outdoors = 5.1%, indoors other =9.8%) estimated less time spent in some locations compared to the diary method (outdoors = 6.7%, indoors other = 14.4%). Agreement statistics (AC1 = 0.778) suggest ‘good’ agreement between methods over all location categories. However, location categories (Outdoors and Transit) where less time is spent show greater disagreement: e.g., mean time “Indoors Other” using the time-activity diary was 14.4% compared to 9.8% using the automated method. While mean daily time “In Transit” was relatively consistent between the methods, the mean daily exposure to PM2.5 while “In Transit” was 15.9 μg/m3 using the automated method compared to 6.8 μg/m3 using the daily diary. Conclusions Mean times spent in different locations as categorized by a GPS-based method were comparable to those from a time-activity diary, but there were differences in estimates of exposure to PM2.5 from the two methods. An automated GPS-based time-activity method will reduce participant burden, potentially providing more accurate and unbiased assessments of location. Combined with continuous air measurements, the higher resolution GPS data could present a different and more accurate picture of personal exposures to air pollution. PMID:24885722

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).

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.

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.

Global Ionosphere Perturbations Monitored by the Worldwide GPS Network

NASA Technical Reports Server (NTRS)

Ho, C. M.; Manucci, A. T.; Lindqwister, U. J.; Pi, X.

1996-01-01

For the first time, measurements from the Global Positioning System (GPS) worldwide network are employed to study the global ionospheric total electron content(TEC) changes during a magnetic storm (November 26, 1994). These measurements are obtained from more than 60 world-wide GPS stations which continuously receive dual-frequency signals. Based on the delays of the signals, we have generated high resolution global ionospheric maps (GIM) of TEC at 15 minute intervals. Using a differential method comparing storm time maps with quiet time maps, we find that significant TEC increases (the positive effect ) are the major feature in the winter hemisphere during this storm (the maximum percent change relative to quiet times is about 150 percent).

Continental-scale water fluxes from continuous GPS observations of Earth surface loading

NASA Astrophysics Data System (ADS)

Borsa, A. A.; Agnew, D. C.; Cayan, D. R.

2015-12-01

After more than a decade of observing annual oscillations of Earth's surface from seasonal snow and water loading, continuous GPS is now being used to model time-varying terrestrial water fluxes on the local and regional scale. Although the largest signal is typically due to the seasonal hydrological cycle, GPS can also measure subtle surface deformation caused by sustained wet and dry periods, and to estimate the spatial distribution of the underlying terrestrial water storage changes. The next frontier is expanding this analysis to the continental scale and paving the way for incorporating GPS models into the National Climate Assessment and into the observational infrastructure for national water resource management. This will require reconciling GPS observations with predictions from hydrological models and with remote sensing observations from a suite of satellite instruments (e.g. GRACE, SMAP, SWOT). The elastic Earth response which transforms surface loads into vertical and horizontal displacements is also responsible for the contamination of loading observations by tectonic and anthropogenic transients, and we discuss these and other challenges to this new application of GPS.

Reprocessing Multiyear GPS Data from Continuously Operating Reference Stations on Cloud Computing Platform

NASA Astrophysics Data System (ADS)

Yoon, S.

2016-12-01

To define geodetic reference frame using GPS data collected by Continuously Operating Reference Stations (CORS) network, historical GPS data needs to be reprocessed regularly. Reprocessing GPS data collected by upto 2000 CORS sites for the last two decades requires a lot of computational resource. At National Geodetic Survey (NGS), there has been one completed reprocessing in 2011, and currently, the second reprocessing is undergoing. For the first reprocessing effort, in-house computing resource was utilized. In the current second reprocessing effort, outsourced cloud computing platform is being utilized. In this presentation, the outline of data processing strategy at NGS is described as well as the effort to parallelize the data processing procedure in order to maximize the benefit of the cloud computing. The time and cost savings realized by utilizing cloud computing approach will also be 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.

Kalman filter implementation for small satellites using constraint GPS data

NASA Astrophysics Data System (ADS)

Wesam, Elmahy M.; Zhang, Xiang; Lu, Zhengliang; Liao, Wenhe

2017-06-01

Due to the increased need for autonomy, an Extended Kalman Filter (EKF) has been designed to autonomously estimate the orbit using GPS data. A propagation step models the satellite dynamics as a two body with J2 (second zonal effect) perturbations being suitable for orbits in altitudes higher than 600 km. An onboard GPS receiver provides continuous measurement inputs. The continuity of measurements decreases the errors of the orbit determination algorithm. Power restrictions are imposed on small satellites in general and nanosatellites in particular. In cubesats, the GPS is forced to be shut down most of the mission’s life time. GPS is turned on when experiments like atmospheric ones are carried out and meter level accuracy for positioning is required. This accuracy can’t be obtained by other autonomous sensors like magnetometer and sun sensor as they provide kilometer level accuracy. Through simulation using Matlab and satellite tool kit (STK) the position accuracy is analyzed after imposing constrained conditions suitable for small satellites and a very tight one suitable for nanosatellite missions.

Pressure during decision making of continuous sedation in end-of-life situations in Dutch general practice

PubMed Central

2012-01-01

Background Little is known about pressure from patients or relatives on physician’s decision making of continuous palliative sedation. We aim to describe experienced pressure by general practitioners (GPs) in cases of continuous sedation after the introduction of the Dutch practice guideline, using a questionnaire survey. Methods A sample of 918 Dutch GPs were invited to fill out a questionnaire about their last patient under continuous sedation. Cases in which GPs experienced pressure from the patient, relatives or other persons were compared to those without pressure. Results 399 of 918 invite GPs (43%) returned the questionnaire and 250 provided detailed information about their most recent case of continuous sedation. Forty-one GPs (16%) indicated to have experienced pressure from the patient, relatives or colleagues. In GPs younger than 50, guideline knowledge was not related to experienced pressure, whereas in older GPs, 15% with and 36% without guideline knowledge reported pressure. GPs experienced pressure more often when patients had psychological symptoms (compared to physical symptoms only) and when patients had a longer estimated life expectancy. A euthanasia request of the patient coincided with a higher prevalence of pressure for GPs without, but not for GPs with previous experience with euthanasia. GPs who experienced pressure had consulted a palliative consultation team more often than GPs who did not experience pressure. Conclusion One in six GPs felt pressure from patients or relatives to start sedation. This pressure was related to guideline knowledge, especially in older GPs, longer life expectancy and the presence of a euthanasia request, especially for GPs without previous experience of euthanasia. PMID:22759834

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.

Analysis of continuous GPS measurements from southern Victoria Land, Antarctica

USGS Publications Warehouse

Willis, Michael J.

2007-01-01

Several years of continuous data have been collected at remote bedrock Global Positioning System (GPS) sites in southern Victoria Land, Antarctica. Annual to sub-annual variations are observed in the position time-series. An atmospheric pressure loading (APL) effect is calculated from pressure field anomalies supplied by the European Centre for Medium-Range Weather Forecasts (ECMWF) model loading an elastic Earth model. The predicted APL signal has a moderate correlation with the vertical position time-series at McMurdo, Ross Island (International Global Navigation Satellite System Service (IGS) station MCM4), produced using a global solution. In contrast, a local solution in which MCM4 is the fiducial site generates a vertical time series for a remote site in Victoria Land (Cape Roberts, ROB4) which exhibits a low, inverse correlation with the predicted atmospheric pressure loading signal. If, in the future, known and well modeled geophysical loads can be separated from the time-series, then local hydrological loading, of interest for glaciological and climate applications, can potentially be extracted from the GPS time-series.

A comparison of hydrological deformation using GPS and global hydrological model for the Eurasian plate

NASA Astrophysics Data System (ADS)

Li, Zhen; Yue, Jianping; Li, Wang; Lu, Dekai; Li, Xiaogen

2017-08-01

The 0.5° × 0.5° gridded hydrological loading from Global Land Surface Discharge Model (LSDM) mass distributions is adopted for 32 GPS sites on the Eurasian plate from January 2010 to January 2014. When the heights of these sites that have been corrected for the effects of non-tidal atmospheric and ocean loading are adjusted by the hydrological loading deformation, more than one third of the root-mean-square (RMS) values of the GPS height variability become larger. After analyzing the results by continuous wavelet transform (CWT) and wavelet transform coherence (WTC), we confirm that hydrological loading primarily contributes to the annual variations in GPS heights. Further, the cross wavelet transform (XWT) is used to investigate the relative phase between the time series of GPS heights and hydrological deformation, and it is indicated that the annual oscillations in the two time series are physically related for some sites; other geophysical effect, GPS systematic errors and hydrological modeling errors could result in the phase asynchrony between GPS and hydrological loading signals for the other sites. Consequently, the phase asynchrony confirms that the annual fluctuations in GPS observations result from a combination of geophysical signals and systematic errors.

Tracking magma volume recovery at okmok volcano using GPS and an unscented kalman filter

USGS Publications Warehouse

Fournier, T.; Freymueller, Jeffrey T.; Cervelli, Peter

2009-01-01

Changes beneath a volcano can be observed through position changes in a GPS network, but distinguishing the source of site motion is not always straightforward. The records of continuous GPS sites provide a favorable data set for tracking magma migration. Dense campaign observations usually provide a better spatial picture of the overall deformation field, at the expense of an episodic temporal record. Combining these observations provides the best of both worlds. A Kalman filter provides a means for integrating discrete and continuous measurements and for interpreting subtle signals. The unscented Kalman filter (UKF) is a nonlinear method for time-dependent observations. We demonstrate the application of this technique to deformation data by applying it to GPS data collected at Okmok volcano. Seven years of GPS observations at Okmok are analyzed using a Mogi source model and the UKF. The deformation source at Okmok is relatively stable at 2.5 km depth below sea level, located beneath the center of the caldera, which means the surface deformation is caused by changes in the strength of the source. During the 7 years of GPS observations more than 0.5 m of uplift has occurred, a majority of that during the time period January 2003 to July 2004. The total volume recovery at Okmok since the last eruption in 1997 is ??60-80%. The UKF allows us to solve simultaneously for the time-dependence of the source strength and for the location without a priori information about the source. ?? 2009 by the American Geophysical Union.

Evaluation of High-Precision Sensors in Structural Monitoring

PubMed Central

Erol, Bihter

2010-01-01

One of the most intricate branches of metrology involves the monitoring of displacements and deformations of natural and anthropogenic structures under environmental forces, such as tidal or tectonic phenomena, or ground water level changes. Technological progress has changed the measurement process, and steadily increasing accuracy requirements have led to the continued development of new measuring instruments. The adoption of an appropriate measurement strategy, with proper instruments suited for the characteristics of the observed structure and its environmental conditions, is of high priority in the planning of deformation monitoring processes. This paper describes the use of precise digital inclination sensors in continuous monitoring of structural deformations. The topic is treated from two viewpoints: (i) evaluation of the performance of inclination sensors by comparing them to static and continuous GPS observations in deformation monitoring and (ii) providing a strategy for analyzing the structural deformations. The movements of two case study objects, a tall building and a geodetic monument in Istanbul, were separately monitored using dual-axes micro-radian precision inclination sensors (inclinometers) and GPS. The time series of continuous deformation observations were analyzed using the Least Squares Spectral Analysis Technique (LSSA). Overall, the inclinometers showed good performance for continuous monitoring of structural displacements, even at the sub-millimeter level. Static GPS observations remained insufficient for resolving the deformations to the sub-centimeter level due to the errors that affect GPS signals. With the accuracy advantage of inclination sensors, their use with GPS provides more detailed investigation of deformation phenomena. Using inclinometers and GPS is helpful to be able to identify the components of structural responses to the natural forces as static, quasi-static, or resonant. PMID:22163499

Crustal Movements and Gravity Variations in the Southeastern Po Plain, Italy

NASA Astrophysics Data System (ADS)

Zerbini, S.; Bruni, S.; Errico, M.; Santi, E.; Wilmes, H.; Wziontek, H.

2014-12-01

At the Medicina observatory, in the southeastern Po Plain, in Italy, we have started a project of continuous GPS and gravity observations in mid 1996. The experiment, focused on a comparison between height and gravity variations, is still ongoing; these uninterrupted time series certainly constitute a most important data base to observe and estimate reliably long-period behaviors but also to derive deeper insights on the nature of the crustal deformation. Almost two decades of continuous GPS observations from two closely located receivers have shown that the coordinate time series are characterized by linear and non-linear variations as well as by sudden jumps. Both over long- and short-period time scales, the GPS height series show signals induced by different phenomena, for example, those related to mass transport in the Earth system. Seasonal effects are clearly recognizable and are mainly associated with the water table seasonal behavior. To understand and separate the contribution of different forcings is not an easy task; to this end, the information provided by the superconducting gravimeter observations and also by absolute gravity measurements offers a most important means to detect and understand mass contributions. In addition to GPS and gravity data, at Medicina, a number of environmental parameters time series are also regularly acquired, among them water table levels. We present the results of study investigating correlations between height, gravity and environmental parameters time series.

minSKIN does a multifaceted intervention improve the competence in the diagnosis of skin cancer by general practitioners? Study protocol for a randomised controlled trial.

PubMed

Badertscher, Nina; Rosemann, Thomas; Tandjung, Ryan; Braun, Ralph P

2011-06-30

In Switzerland, skin cancer is one of the most common neoplasms. Melanoma is the most aggressive one and can be lethal if not detected and removed on time. Nonmelanoma skin cancer is more frequent as melanoma; it is seldom lethal but can disfigure patients in advanced stages. General practitioners (GPs) are often faced with suspicious skin lesions of their patients. Randomised controlled trial (RCT). 60 GPs, randomised into intervention group and control group. GPs get a Lumio loupe, a digital camera and continuous feedback based on pictures of skin lesions they send to the Dermatologist. Competence in the diagnosis of skin cancer by GPs, measured as the percentage of correctly classified pictures of skin lesions. At baseline, and prior to any intervention (T0), GPs will be asked to rate 36 pictures of skin lesions according to their likelihood of malignancy on a visual analogue scale (VAS). After a full day training course with both groups (T1) and after one year of continuous feedback (T2) with the intervention group, we will repeat the picture scoring session with both groups, using new pictures. We want to determine whether a multifaceted intervention (including technical equipment and a continuous feedback on skin lesions) leads to an improved competence in the diagnosis of skin cancer by GPs. This study addresses the hypothesis that an additional feedback loop, based on pictures performed in daily practice by GPs is superior to a simple educational intervention regarding diagnostic competence. We expect an improvement of the competence in skin cancer diagnosis by GPs in both groups after the full day training course. Beside this immediate effect, we also expect a long term effect in the intervention group because of the continuous problem based feedback. ISRCTN29854485.

Interferometric investigations with the S1 constellation: an application to the Vesuvius/Campi Flegrei volcanic test site

NASA Astrophysics Data System (ADS)

Borgstrom, Sven; Del Gaudio, Carlo; De Martino, Prospero; Siniscalchi, Valeria; Prats-Iraola, Pau; Nannini, Matteo; Yague-Martinez, Nestor; Pinheiro, Muriel; Kim, Jun-Su; Vecchioli, Francesco; Minati, Federico; Costantini, Mario; Foumelis, Michael; Desnos, Yves-Louis

2017-04-01

The contribution focuses on the current status of the ESA study entitled "INSARAP Sentinel-1 Constellation Study" and investigates the interferometric performance of the S1A/S1B units. In particular, we refer to the Vesuvius/Campi Flegrei (Southern Italy) volcanic test site, where the continuous inflation (about 35 cm from 2011 to date) and the huge availability of ground-based geodetic data (continuous GPS - cGPS - leveling, tiltmetric, gravimetric, etc.) from the INGV-Osservatorio Vesuviano monitoring networks have allowed to get a clear deformation signal, besides the comparison between S1A/S1B and geodetic data. In this regard, the integration between InSAR and geodetic measurements is crucial for a continuous and extended monitoring of such an active volcanic area, as InSAR investigations allow to get an information on wide areas, whereas permanent networks (e.g., cGPS), allow to provide a continuous information complementing InSAR, which is limited by its revisiting time. Comparisons between S1 constellation data and geodetic measurements, with a particular focus on cGPS, will be presented, exploiting both LOS and inverted (E-W and vertical inversion) InSAR data starting from October, 2014. In addition, as a next step we are planning to model the deformation source of the area by exploiting the S1 time series results. Ultimately, very encouraging results suggest for a continuation of this activity also for the future, showing the great potential of S1 constellation data for monitoring active volcanic areas and, in general, to retrieve a very high quality deformation signal.

Earthquake cycle deformation in Mexico and Central America constrained by GPS: Implications for coseismic, postseismic, and slow slip

NASA Astrophysics Data System (ADS)

Graham, Shannon E.

Using surface deformation measured by GPS stations within Mexico and Central America, I model coseismic slip, Coulomb stress changes, postseismic afterslip, and slow slip events in order to increase our knowledge of the earthquake deformation cycle in seismically hazardous regions. In Chapter 1, I use GPS data to estimate coseismic slip due to the May 28, 2009 Swan Islands fault earthquake off the coast of Honduras and then use the slip distribution to calculate Coulomb stress changes for the earthquake. Coulomb stress change calculations resolve stress transfer to the seismically hazardous Motagua fault and further show an unclamping of normal faults in northern Honduras. In Chapter 2, the focus shifts to southern Mexico, where continuous GPS measurements since the mid-1990s are revolutionizing our understanding of the flatly subducting Cocos plate. I perform a time-dependent inversion of continuous GPS observations of the 2011-2012 slow slip event (SSE) to estimate the location and magnitude of slow slip preceding the March 20, 2012 Ometepec earthquake. Coulomb stress changes as a result of slip during the SSE are consistent with the hypothesis that the SSE triggered the Ometepec earthquake. Chapter 3 describes inversions for slip both during and after the Ometepec earthquake. Time-dependent modeling of the first six months of postseismic deformation reveals that fault afterslip extended ˜250 km inland to depths of ˜50 km along the Cocos plate subduction. The postseismic afterslip and previous SSEs in southern Mexico occur at similar depths down-dip from the seismogenic zone, indicating that transitional areas of the subduction interface underlie much of southern Mexico. Finally, I perform the first time-dependent modeling of SSEs below Mexico and the first to exploit all available continuous GPS stations in southern and central Mexico. The results provide a more complete and consistent catalog of modeled SSE for the Mexico subduction zone (MSZ) than is currently available and add to our understanding of how SSEs on the subduction interface evolve in time, migrate in space, and possibly interact. I find that slow slip along the MSZ migrates across the gap between the Guerrero and Oaxaca regions, contrary to previous results.

Covert checks by standardised patients of general practitioners' delivery of new periodic health examinations: clustered cross-sectional study from a consumer organisation

PubMed Central

Thaler, Kylie; Harris, Mark F

2012-01-01

Objective To assess if data collected by a consumer organisation are valid for a health service research study on physicians' performance in preventive care. To report first results of the analysis of physicians performance like consultation time and guideline adherence in history taking. Design Secondary data analysis of a clustered cross-sectional direct observation survey. Setting General practitioners (GPs) in Vienna, Austria, visited unannounced by mystery shoppers (incognito standardised patients (ISPs)). Participants 21 randomly selected GPs were visited by two different ISPs each. 40 observation protocols were realised. Main outcome measures Robustness of sampling and data collection by the consumer organisation. GPs consultation and waiting times, guideline adherence in history taking. Results The double stratified random sampling method was robust and representative for the private and contracted GPs mix of Vienna. The clinical scenarios presented by the ISPs were valid and believable, and no GP realised the ISPs were not genuine patients. The average consultation time was 46 min (95% CI 37 to 54 min). Waiting times differed more than consultation times between private and contracted GPs. No differences between private and contracted GPs in terms of adherence to the evidence-based guidelines regarding history taking including questions regarding alcohol use were found. According to the analysis, 20% of the GPs took a perfect history (95% CI 9% to 39%). Conclusions The analysis of secondary data collected by a consumer organisation was a valid method for drawing conclusions about GPs preventive practice. Initial results, like consultation times longer than anticipated, and the moderate quality of history taking encourage continuing the analysis on available clinical data. PMID:22872721

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.

Sea level rise within the west of Arabian Gulf using tide gauge and continuous GPS measurements

NASA Astrophysics Data System (ADS)

Ayhan, M. E.; Alothman, A.

2009-04-01

Arabian Gulf is connected to Indian Ocean and located in the south-west of the Zagros Trust Belt. To investigate sea level variations 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 individually the monthly means 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. Vertical land motions are included into the relative sea level measurements at the tide gauges. Therefore sea level rates at the stations are corrected for vertical land motions using the ICE-5G v1.2 VM4 Glacial Isostatic Adjustment (GIA) model then we found the average sea level rise rate of 2.27 mm/yr. Bahrain International GPS Service (IGS) GPS station, which is close to the Mina Sulman tide gauge station in Bahrain, is the only continuous GPS station accessible in the region. The weekly GPS time series of vertical component at Bahrain IGS-GPS station referring to the ITRF97 from 1999.2 to 2008.6 are downloaded from http://www-gps.mit.edu/~tah/. We fitted a linear trend with an annual signal and one break to the GPS vertical time series and found a vertical land motion rate of 0.48 ± 0.11 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 2.44 ± 0.21 mm/yr within the west of Arabian Gulf.

A new algorithm for automatic Outlier Detection in GPS Time Series

NASA Astrophysics Data System (ADS)

Cannavo', Flavio; Mattia, Mario; Rossi, Massimo; Palano, Mimmo; Bruno, Valentina

2010-05-01

Nowadays continuous GPS time series are considered a crucial product of GPS permanent networks, useful in many geo-science fields, such as active tectonics, seismology, crustal deformation and volcano monitoring (Altamimi et al. 2002, Elósegui et al. 2006, Aloisi et al. 2009). Although the GPS data elaboration software has increased in reliability, the time series are still affected by different kind of noise, from the intrinsic noise (e.g. thropospheric delay) to the un-modeled noise (e.g. cycle slips, satellite faults, parameters changing). Typically GPS Time Series present characteristic noise that is a linear combination of white noise and correlated colored noise, and this characteristic is fractal in the sense that is evident for every considered time scale or sampling rate. The un-modeled noise sources result in spikes, outliers and steps. These kind of errors can appreciably influence the estimation of velocities of the monitored sites. The outlier detection in generic time series is a widely treated problem in literature (Wei, 2005), while is not fully developed for the specific kind of GPS series. We propose a robust automatic procedure for cleaning the GPS time series from the outliers and, especially for long daily series, steps due to strong seismic or volcanic events or merely instrumentation changing such as antenna and receiver upgrades. The procedure is basically divided in two steps: a first step for the colored noise reduction and a second step for outlier detection through adaptive series segmentation. Both algorithms present novel ideas and are nearly unsupervised. In particular, we propose an algorithm to estimate an autoregressive model for colored noise in GPS time series in order to subtract the effect of non Gaussian noise on the series. This step is useful for the subsequent step (i.e. adaptive segmentation) which requires the hypothesis of Gaussian noise. The proposed algorithms are tested in a benchmark case study and the results confirm that the algorithms are effective and reasonable. Bibliography - Aloisi M., A. Bonaccorso, F. Cannavò, S. Gambino, M. Mattia, G. Puglisi, E. Boschi, A new dyke intrusion style for the Mount Etna May 2008 eruption modelled through continuous tilt and GPS data, Terra Nova, Volume 21 Issue 4 , Pages 316 - 321, doi: 10.1111/j.1365-3121.2009.00889.x (August 2009) - Altamimi Z., Sillard P., Boucher C., ITRF2000: A new release of the International Terrestrial Reference frame for earth science applications, J Geophys Res-Solid Earth, 107 (B10): art. no.-2214, (Oct 2002) - Elósegui, P., J. L. Davis, D. Oberlander, R. Baena, and G. Ekström , Accuracy of high-rate GPS for seismology, Geophys. Res. Lett., 33, L11308, doi:10.1029/2006GL026065 (2006) - Wei W. S., Time Series Analysis: Univariate and Multivariate Methods, Addison Wesley (2 edition), ISBN-10: 0321322169 (July, 2005)

Prescribing and deprescribing antihypertensive medication in older people by Dutch general practitioners: a qualitative study

PubMed Central

van Middelaar, Tessa; Ivens, Sophie D; van Peet, Petra G; Poortvliet, Rosalinde K E; Richard, Edo; Pols, A Jeannette; Moll van Charante, Eric P.

2018-01-01

Objectives To explore general practitioners’ (GPs) routines and considerations on (de)prescribing antihypertensive medication (AHM) in older patients, their judgement on usability of the current guideline and needs for future support. Design Semistructured interviews. Setting Dutch general practice. Participants Fifteen GPs were purposively sampled based on level of experience and practice characteristics until saturation was reached. Results GPs appeared reluctant to start AHM, especially in patient >80 years. High systolic blood pressure and history of cardiovascular disease or diabetes were enablers to start or intensify treatment. Reasons to refrain from this were frailty and patient preference. GPs described a tendency to continue AHM regimens unchanged, influenced by daily time constraints, automated prescription routines and anticipating discomfort when disturbing patients’ delicate balance. GPs were only inclined to deprescribe AHM in terminally ill patients or after prolonged achievement of target levels in combination with side effects or patient preference. Deprescription was facilitated when GPs had experience with patients showing increased quality of life after deprescription and was withheld by anticipated regret (ie, GPs’ fear of a stroke after deprescribing). GPs felt insufficient guidance from current guidelines, especially on deprescription. Conclusions GPs are reluctant to start or deprescribe AHM in older people and have a propensity to continue AHM within a daily routine that insufficiently supports critical medication review. (De)prescription is influenced by patient preferences and anticipated regret and current guidelines provide insufficient guidance. PMID:29678989

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

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.

Orbit determination performances using single- and double-differenced methods: SAC-C and KOMPSAT-2

NASA Astrophysics Data System (ADS)

Hwang, Yoola; Lee, Byoung-Sun; Kim, Haedong; Kim, Jaehoon

2011-01-01

In this paper, Global Positioning System-based (GPS) Orbit Determination (OD) for the KOrea-Multi-Purpose-SATellite (KOMPSAT)-2 using single- and double-differenced methods is studied. The requirement of KOMPSAT-2 orbit accuracy is to allow 1 m positioning error to generate 1-m panchromatic images. KOMPSAT-2 OD is computed using real on-board GPS data. However, the local time of the KOMPSAT-2 GPS receiver is not synchronized with the zero fractional seconds of the GPS time internally, and it continuously drifts according to the pseudorange epochs. In order to resolve this problem, an OD based on single-differenced GPS data from the KOMPSAT-2 uses the tagged time of the GPS receiver, and the accuracy of the OD result is assessed using the overlapping orbit solution between two adjacent days. The clock error of the GPS satellites in the KOMPSAT-2 single-differenced method is corrected using International GNSS Service (IGS) clock information at 5-min intervals. KOMPSAT-2 OD using both double- and single-differenced methods satisfies the requirement of 1-m accuracy in overlapping three dimensional orbit solutions. The results of the SAC-C OD compared with JPL’s POE (Precise Orbit Ephemeris) are also illustrated to demonstrate the implementation of the single- and double-differenced methods using a satellite that has independent orbit information available for validation.

Assessing the precision of a time-sampling-based study among GPs: balancing sample size and measurement frequency.

PubMed

van Hassel, Daniël; van der Velden, Lud; de Bakker, Dinny; van der Hoek, Lucas; Batenburg, Ronald

2017-12-04

Our research is based on a technique for time sampling, an innovative method for measuring the working hours of Dutch general practitioners (GPs), which was deployed in an earlier study. In this study, 1051 GPs were questioned about their activities in real time by sending them one SMS text message every 3 h during 1 week. The required sample size for this study is important for health workforce planners to know if they want to apply this method to target groups who are hard to reach or if fewer resources are available. In this time-sampling method, however, standard power analyses is not sufficient for calculating the required sample size as this accounts only for sample fluctuation and not for the fluctuation of measurements taken from every participant. We investigated the impact of the number of participants and frequency of measurements per participant upon the confidence intervals (CIs) for the hours worked per week. Statistical analyses of the time-use data we obtained from GPs were performed. Ninety-five percent CIs were calculated, using equations and simulation techniques, for various different numbers of GPs included in the dataset and for various frequencies of measurements per participant. Our results showed that the one-tailed CI, including sample and measurement fluctuation, decreased from 21 until 3 h between one and 50 GPs. As a result of the formulas to calculate CIs, the increase of the precision continued and was lower with the same additional number of GPs. Likewise, the analyses showed how the number of participants required decreased if more measurements per participant were taken. For example, one measurement per 3-h time slot during the week requires 300 GPs to achieve a CI of 1 h, while one measurement per hour requires 100 GPs to obtain the same result. The sample size needed for time-use research based on a time-sampling technique depends on the design and aim of the study. In this paper, we showed how the precision of the measurement of hours worked each week by GPs strongly varied according to the number of GPs included and the frequency of measurements per GP during the week measured. The best balance between both dimensions will depend upon different circumstances, such as the target group and the budget available.

Satellite Geodetic Constraints On Earthquake Processes: Implications of the 1999 Turkish Earthquakes for Fault Mechanics and Seismic Hazards on the San Andreas Fault

NASA Technical Reports Server (NTRS)

Reilinger, Robert

2005-01-01

Our principal activities during the initial phase of this project include: 1) Continued monitoring of postseismic deformation for the 1999 Izmit and Duzce, Turkey earthquakes from repeated GPS survey measurements and expansion of the Marmara Continuous GPS Network (MAGNET), 2) Establishing three North Anatolian fault crossing profiles (10 sitedprofile) at locations that experienced major surface-fault earthquakes at different times in the past to examine strain accumulation as a function of time in the earthquake cycle (2004), 3) Repeat observations of selected sites in the fault-crossing profiles (2005), 4) Repeat surveys of the Marmara GPS network to continue to monitor postseismic deformation, 5) Refining block models for the Marmara Sea seismic gap area to better understand earthquake hazards in the Greater Istanbul area, 6) Continuing development of models for afterslip and distributed viscoelastic deformation for the earthquake cycle. We are keeping close contact with MIT colleagues (Brad Hager, and Eric Hetland) who are developing models for S. California and for the earthquake cycle in general (Hetland, 2006). In addition, our Turkish partners at the Marmara Research Center have undertaken repeat, micro-gravity measurements at the MAGNET sites and have provided us estimates of gravity change during the period 2003 - 2005.

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.

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.

Tracking down a solution: exploring the acceptability and value of wearable GPS devices for older persons, individuals with a disability and their support persons.

PubMed

Williamson, Brittany; Aplin, Tammy; de Jonge, Desleigh; Goyne, Matthew

2017-11-01

To explore the acceptability and value of three wearable GPS devices for older persons and individuals with a disability and safety concerns when accessing the community. This pilot study explored six wearers' and their support persons' experience of using three different wearable GPS devices (a pendant, watch, and mini GPS phone), each for a two-week period. Participants identified safety as the main value of using a wearable GPS device. The acceptability and value of these devices was strongly influenced by device features, ease of use, cost, appearance, the reliability of the GPS coordinates, the wearer's health condition and the users familiarity with technology. Overall, participants indicated that they preferred the pendant. Wearable GPS devices are potentially useful in providing individuals who have safety concerns with reassurance and access to assistance as required. To ensure successful utilization, future device design and device selection should consider the user's familiarity with technology and their health condition. This study also revealed that not all wearable GPS devices provide continuous location tracking. It is therefore critical to ensure that the device's location tracking functions address the wearer's requirements and reason for using the device. Implications for Rehabilitation The acceptability and usability of wearable GPS devices is strongly influenced by the device features, ease of use, cost, appearance, the reliability of the device to provide accurate and timely GPS coordinates, as well as the health condition of the wearer and their familiarity with technology. Wearable GPS devices need to be simple to use and support and training is essential to ensure they are successfully utilized. Not all wearable GPS devices provide continuous location tracking and accuracy of location is impacted by line of sight to satellites. Therefore, care needs to be taken when choosing a suitable device, to ensure that the device's location tracking features are based on the wearer's requirements and value behind using the device.

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.

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).

An accuracy assessment of realtime GNSS time series toward semi- real time seafloor geodetic observation

NASA Astrophysics Data System (ADS)

Osada, Y.; Ohta, Y.; Demachi, T.; Kido, M.; Fujimoto, H.; Azuma, R.; Hino, R.

2013-12-01

Large interplate earthquake repeatedly occurred in Japan Trench. Recently, the detail crustal deformation revealed by the nation-wide inland GPS network called as GEONET by GSI. However, the maximum displacement region for interplate earthquake is mainly located offshore region. GPS/Acoustic seafloor geodetic observation (hereafter GPS/A) is quite important and useful for understanding of shallower part of the interplate coupling between subducting and overriding plates. We typically conduct GPS/A in specific ocean area based on repeated campaign style using research vessel or buoy. Therefore, we cannot monitor the temporal variation of seafloor crustal deformation in real time. The one of technical issue on real time observation is kinematic GPS analysis because kinematic GPS analysis based on reference and rover data. If the precise kinematic GPS analysis will be possible in the offshore region, it should be promising method for real time GPS/A with USV (Unmanned Surface Vehicle) and a moored buoy. We assessed stability, precision and accuracy of StarFireTM global satellites based augmentation system. We primarily tested for StarFire in the static condition. In order to assess coordinate precision and accuracy, we compared 1Hz StarFire time series and post-processed precise point positioning (PPP) 1Hz time series by GIPSY-OASIS II processing software Ver. 6.1.2 with three difference product types (ultra-rapid, rapid, and final orbits). We also used difference interval clock information (30 and 300 seconds) for the post-processed PPP processing. The standard deviation of real time StarFire time series is less than 30 mm (horizontal components) and 60 mm (vertical component) based on 1 month continuous processing. We also assessed noise spectrum of the estimated time series by StarFire and post-processed GIPSY PPP results. We found that the noise spectrum of StarFire time series is similar pattern with GIPSY-OASIS II processing result based on JPL rapid orbit products with 300 seconds interval clock information. And we report stability, precision and accuracy of StarFire in the moving conditon.

Soliciting additional concerns in the primary care consultation and the utility of a brief communication intervention to aid solicitation: A qualitative study.

PubMed

Summers, Rachael H; Moore, Michael; Ekberg, Stuart; Chew-Graham, Carolyn A; Little, Paul; Stevenson, Fiona; Brindle, Lucy; Leydon, Geraldine M

2016-05-01

To investigate the perspectives of general practitioners (GPs) on the practice of soliciting additional concerns (ACs) and the acceptability and utility of two brief interventions (prompts) designed to aid the solicitation. Eighteen GPs participating in a feasibility randomised controlled trial were interviewed. Interviews were semi-structured and audio-recorded. Data were analysed using a Framework Approach. Participants perceived eliciting ACs as important for: reducing the need for multiple visits, identifying serious illness early, and increasing patient and GP satisfaction. GPs found the prompts easy to use and some continued their use after the study had ended to aid time management. Others noted similarities between the intervention and their usual practice. Nevertheless, soliciting ACs in every consultation was not unanimously supported. The prompts were acceptable to GPs within a trial context, but there was disagreement as to whether ACs should be solicited routinely. Some GPs considered the intervention to aid their prioritisation efficiency within consultations. Some GPs will find prompts which encourage ACs to be solicited early in the consultation enable them to better organise priorities and manage time-limited consultations more effectively. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

3-component time-dependent crustal deformation in Southern California from Sentinel-1 and GPS

NASA Astrophysics Data System (ADS)

Tymofyeyeva, E.; Fialko, Y. A.

2017-12-01

We combine data from the Sentinel-1 InSAR mission collected between 2014-2017 with continuous GPS measurements to calculate the three components of the interseismic surface velocity field in Southern California at the resolution of InSAR data ( 100 m). We use overlapping InSAR tracks with two different look geometries (descending tracks 71, 173, and 144, and ascending tracks 64 and 166) to obtain the 3 orthogonal components of surface motion. Because of the under-determined nature of the problem, we use the local azimuth of the horizontal velocity vector as an additional constraint. The spatially variable azimuths of the horizontal velocity are obtained by interpolating data from the continuous GPS network. We estimate both secular velocities and displacement time series. The latter are obtained by combining InSAR time series from different lines of sight with time-dependent azimuths computed using continuous GPS time series at every InSAR epoch. We use the CANDIS method [Tymofyeyeva and Fialko, 2015], a technique based on iterative common point stacking, to correct the InSAR data for tropospheric and ionospheric artifacts when calculating secular velocities and time series, and to isolate low-amplitude deformation signals in our study region. The obtained horizontal (East and North) components of secular velocity exhibit long-wavelength patterns consistent with strain accumulation on major faults of the Pacific-North America plate boundary. The vertical component of velocity reveals a number of localized uplift and subsidence anomalies, most likely related to hydrologic effects and anthropogenic activity. In particular, in the Los Angeles basin we observe localized uplift of about 10-15mm/yr near Anaheim, Long Beach, and Redondo Beach, as well as areas of rapid subsidence near Irvine and Santa Monica, which are likely caused by the injection of water in the oil fields, and the pumping and recharge cycles of the aquifers in the basin.

Availability of Dutch General Practitioners for After-Hours Palliative Care.

PubMed

Plat, Fredrik M; Peters, Yvonne A S; Giesen, Paul; Smits, Marleen

2018-01-01

Continuity of care is important for palliative patients in their end of life. In the Netherlands, after-hours primary care for palliative patients is either provided by large-scale general practitioner (GP) cooperatives or GPs choose to give palliative care by themselves while they are not on duty. To examine the availability of, perceived problems by, and attitude of Dutch GPs regarding providing palliative care for their own patients outside office hours. Cross-sectional observational study among 1772 GPs from 10 Dutch regions. Online questionnaire among GPs affiliated with 10 GP cooperatives. Five hundred twenty-four (29.6%) eligible questionnaires were returned. Of the GPs, 60.8% were personally available outside office hours for their own palliative patients on their own private cell phone and performed home visits if needed. In 33.0%, GPs were willing to make home visits in private time instigated by the GP cooperative and 26.8% were only accessible for telephone consultation by the GP cooperative. In 12.2%, the GP delegated after-hours palliative care completely to the GP cooperative. The GPs predominantly reported "time pressure" problems (17.3%) as a barrier and 61.7% stated that after-hours palliative care is the responsibility of the own GP. The large majority of Dutch GPs is personally available for telephone consultation and/or willing to provide palliative care for their own patients outside office hours. For the future, it is important to maintain the willingness of GPs to remain personally available for their palliative patients.

High-precision GPS autonomous platforms for sea ice dynamics and physical oceanography

NASA Astrophysics Data System (ADS)

Elosegui, P.; Wilkinson, J.; Olsson, M.; Rodwell, S.; James, A.; Hagan, B.; Hwang, B.; Forsberg, R.; Gerdes, R.; Johannessen, J.; Wadhams, P.; Nettles, M.; Padman, L.

2012-12-01

Project "Arctic Ocean sea ice and ocean circulation using satellite methods" (SATICE), is the first high-rate, high-precision, continuous GPS positioning experiment on sea ice in the Arctic Ocean. The SATICE systems collect continuous, dual-frequency carrier-phase GPS data while drifting on sea ice. Additional geophysical measurements also collected include ocean water pressure, ocean surface salinity, atmospheric pressure, snow-depth, air-ice-ocean temperature profiles, photographic imagery, and others, enabling sea ice drift, freeboard, weather, ice mass balance, and sea-level height determination. Relatively large volumes of data from each buoy are streamed over a satellite link to a central computer on the Internet in near real time, where they are processed to estimate the time-varying buoy positions. SATICE system obtains continuous GPS data at sub-minute intervals with a positioning precision of a few centimetres in all three dimensions. Although monitoring of sea ice motions goes back to the early days of satellite observations, these autonomous platforms bring out a level of spatio-temporal detail that has never been seen before, especially in the vertical axis. These high-resolution data allows us to address new polar science questions and challenge our present understanding of both sea ice dynamics and Arctic oceanography. We will describe the technology behind this new autonomous platform, which could also be adapted to other applications that require high resolution positioning information with sustained operations and observations in the polar marine environment, and present results pertaining to sea ice dynamics and physical oceanography.

Application of GPS radio occultation to the assessment of temperature profile retrievals from microwave and infrared sounders

NASA Astrophysics Data System (ADS)

Feltz, M.; Knuteson, R.; Ackerman, S.; Revercomb, H.

2014-05-01

Comparisons of satellite temperature profile products from GPS radio occultation (RO) and hyperspectral infrared (IR)/microwave (MW) sounders are made using a previously developed matchup technique. The profile matchup technique matches GPS RO and IR/MW sounder profiles temporally, within 1 h, and spatially, taking into account the unique RO profile geometry and theoretical spatial resolution by calculating a ray-path averaged sounder profile. The comparisons use the GPS RO dry temperature product. Sounder minus GPS RO differences are computed and used to calculate bias and RMS profile statistics, which are created for global and 30° latitude zones for selected time periods. These statistics are created from various combinations of temperature profile data from the Constellation Observing System for Meteorology, Ionosphere & Climate (COSMIC) network, Global Navigation Satellite System Receiver for Atmospheric Sounding (GRAS) instrument, and the Atmospheric Infrared Sounder (AIRS)/Advanced Microwave Sounding Unit (AMSU), Infrared Atmospheric Sounding Interferometer (IASI)/AMSU, and Crosstrack Infrared Sounder (CrIS)/Advanced Technology Microwave Sounder (ATMS) sounding systems. By overlaying combinations of these matchup statistics for similar time and space domains, comparisons of different sounders' products, sounder product versions, and GPS RO products can be made. The COSMIC GPS RO network has the spatial coverage, time continuity, and stability to provide a common reference for comparison of the sounder profile products. The results of this study demonstrate that GPS RO has potential to act as a common temperature reference and can help facilitate inter-comparison of sounding retrieval methods and also highlight differences among sensor product versions.

Application of GPS radio occultation to the assessment of temperature profile retrievals from microwave and infrared sounders

NASA Astrophysics Data System (ADS)

Feltz, M.; Knuteson, R.; Ackerman, S.; Revercomb, H.

2014-11-01

Comparisons of satellite temperature profile products from GPS radio occultation (RO) and hyperspectral infrared (IR)/microwave (MW) sounders are made using a previously developed matchup technique. The profile matchup technique matches GPS RO and IR/MW sounder profiles temporally, within 1 h, and spatially, taking into account the unique RO profile geometry and theoretical spatial resolution by calculating a ray-path averaged sounder profile. The comparisons use the GPS RO dry temperature product. Sounder minus GPS RO differences are computed and used to calculate bias and rms profile statistics, which are created for global and 30° latitude zones for selected time periods. These statistics are created from various combinations of temperature profile data from the Constellation Observing System for Meteorology, Ionosphere & Climate (COSMIC) network, Global Navigation Satellite System Receiver for Atmospheric Sounding (GRAS) instrument, and the Atmospheric Infrared Sounder (AIRS)/Advanced Microwave Sounding Unit (AMSU), Infrared Atmospheric Sounding Interferometer (IASI)/AMSU, and Crosstrack Infrared Sounder (CrIS)/Advanced Technology Microwave Sounder (ATMS) sounding systems. By overlaying combinations of these matchup statistics for similar time and space domains, comparisons of different sounders' products, sounder product versions, and GPS RO products can be made. The COSMIC GPS RO network has the spatial coverage, time continuity, and stability to provide a common reference for comparison of the sounder profile products. The results of this study demonstrate that GPS RO has potential to act as a common temperature reference and can help facilitate inter-comparison of sounding retrieval methods and also highlight differences among sensor product versions.

Perceived future career prospects in general practice: quantitative results from questionnaire surveys of UK doctors

PubMed Central

Lambert, Trevor W; Smith, Fay; Goldacre, Michael J

2016-01-01

Background There are more studies of current job satisfaction among GPs than of their views about their future career prospects, although both are relevant to commitment to careers in general practice. Aim To report on the views of GPs compared with clinicians in other specialties about their future career prospects. Design and setting Questionnaire surveys were sent to UK medical doctors who graduated in selected years between 1974 and 2008. Method Questionnaires were sent to the doctors at different times after graduation, ranging from 3 to 24 years. Results Based on the latest survey of each graduation year of the 20 940 responders, 66.2% of GPs and 74.2% of hospital doctors were positive about their prospects and 9.7% and 8.3%, respectively, were negative. However, with increasing time since graduation and increasing levels of seniority, GPs became less positive about their prospects; by contrast, over time, surgeons became more positive. Three to 5 years after graduation, 86.3% of those training in general practice were positive about their prospects compared with 52.9% of surgical trainees: in surveys conducted 12–24 years after graduation, 60.2% of GPs and 76.6% of surgeons were positive about their prospects. Conclusion GPs held broadly positive views of their career prospects, as did other doctors. However, there was an increase in negativity with increasing time since graduation that was not seen in hospital doctors. Research into the causes of this negativity and policy measures to ameliorate it would contribute to the continued commitment of GPs and may help to reduce attrition. PMID:27578813

Ionospheric corrections to precise time transfer using GPS

NASA Technical Reports Server (NTRS)

Snow, Robert W.; Osborne, Allen W., III; Klobuchar, John A.; Doherty, Patricia H.

1994-01-01

The free electrons in the earth's ionosphere can retard the time of reception of GPS signals received at a ground station, compared to their time in free space, by many tens of nanoseconds, thus limiting the accuracy of time transfer by GPS. The amount of the ionospheric time delay is proportional to the total number of electrons encountered by the wave on its path from each GPS satellite to a receiver. This integrated number of electrons is called Total Electron Content, or TEC. Dual frequency GPS receivers designed by Allen Osborne Associates, Inc. (AOA) directly measure both the ionospheric differential group delay and the differential carrier phase advance for the two GPS frequencies and derive from this the TEC between the receiver and each GPS satellite in track. The group delay information is mainly used to provide an absolute calibration to the relative differential carrier phase, which is an extremely precise measure of relative TEC. The AOA Mini-Rogue ICS-4Z and the AOA TurboRogue ICS-4000Z receivers normally operate using the GPS P code, when available, and switch to cross-correlation signal processing when the GPS satellites are in the Anti-Spoofing (A-S) mode and the P code is encrypted. An AOA ICS-Z receiver has been operated continuously for over a year at Hanscom AFB, MA to determine the statistics of the variability of the TEC parameter using signals from up to four different directions simultaneously. The 4-channel ICS-4Z and the 8-channel ICS-4000Z, have proven capabilities to make precise, well calibrated, measurements of the ionosphere in several directions simultaneously. In addition to providing ionospheric corrections for precise time transfer via satellite, this dual frequency design allows full code and automatic codeless operation of both the differential group delay and differential carrier phase for numerous ionospheric experiments being conducted. Statistical results of the data collected from the ICS-4Z during the initial year of ionospheric time delay in the northeastern U.S., and initial results with the ICS-4000Z, will be presented.

'Two sides of the coin'--the value of personal continuity to GPs: a qualitative interview study.

PubMed

Ridd, Matthew; Shaw, Alison; Salisbury, Chris

2006-08-01

Continuity is thought to be important to GPs but the values behind this are unknown. To explore the values that doctors working in general practice attach to continuity of patient care and to outline how these values are applied in practice. In-depth qualitative interview with 24 GPs in England. Participants were purposefully sampled according to personal and practice characteristics. Analysis was thematic, drawing on the constant comparative method. The majority of doctors valued doctor-patient, or personal, continuity in their everyday work. It was most valued in patients with serious, complex or psychological problems. GPs believed that through their personal knowledge of the patient and the doctor-patient relationship, personal continuity enabled them to provide higher quality care. However, the benefits of personal continuity were balanced against problems, and GPs identified personal, professional and external constraints that limited its provision. GPs seemed to have resolved the tension between the benefits, limits and constraints they described by accepting an increased reliance on continuity being provided within teams. Personal continuity may offer important benefits to doctors and patients, but we do not know how unique its values are. In particular, it is not clear whether the same benefits can be achieved within teams, the level at which continuity is increasingly being provided. The relative advantages and limits of the different means of delivering continuity need to be better understood, before further policy changes that affect personal continuity are introduced.

Networked differential GPS system

NASA Technical Reports Server (NTRS)

Sheynblat, Leonid (Inventor); Kalafus, Rudolph M. (Inventor); Loomis, Peter V. W. (Inventor); Mueller, K. Tysen (Inventor)

1994-01-01

An embodiment of the present invention relates to a worldwide network of differential GPS reference stations (NDGPS) that continually track the entire GPS satellite constellation and provide interpolations of reference station corrections tailored for particular user locations between the reference stations Each reference station takes real-time ionospheric measurements with codeless cross-correlating dual-frequency carrier GPS receivers and computes real-time orbit ephemerides independently. An absolute pseudorange correction (PRC) is defined for each satellite as a function of a particular user's location. A map of the function is constructed, with iso-PRC contours. The network measures the PRCs at a few points, so-called reference stations and constructs an iso-PRC map for each satellite. Corrections are interpolated for each user's site on a subscription basis. The data bandwidths are kept to a minimum by transmitting information that cannot be obtained directly by the user and by updating information by classes and according to how quickly each class of data goes stale given the realities of the GPS system. Sub-decimeter-level kinematic accuracy over a given area is accomplished by establishing a mini-fiducial network.

Saving Space and Time: The Tractor That Einstein Built

NASA Technical Reports Server (NTRS)

2006-01-01

In 1984, NASA initiated the Gravity Probe B (GP-B) program to test two unverified predictions of Albert Einstein s theory of general relativity, hypotheses about the ways space, time, light, and gravity relate to each other. To test these predictions, the Space Agency and researchers at Stanford University developed an experiment that would check, with extreme precision, tiny changes in the spin direction of four gyroscopes contained in an Earth satellite orbiting at a 400-mile altitude directly over the Earth s poles. When the program first began, the researchers assessed using Global Positioning System (GPS) technology to control the attitude of the GP-B spacecraft accurately. At that time, the best GPS receivers could only provide accuracy to nearly 1 meter, but the GP-B spacecraft required a system 100 times more accurate. To address this concern, researchers at Stanford designed high-performance, attitude-determining hardware that used GPS signals, perfecting a high-precision form of GPS called Carrier-Phase Differential GPS that could provide continuous real-time position, velocity, time, and attitude sensor information for all axes of a vehicle. The researchers came to the realization that controlling the GP-B spacecraft with this new system was essentially no different than controlling an airplane. Their thinking took a new direction: If this technology proved successful, the airlines and the Federal Aviation Administration (FAA) were ready commercial markets. They set out to test the new technology, the "Integrity Beacon Landing System," using it to automatically land a commercial Boeing 737 over 100 times successfully through Real-Time Kinematic (RTK) GPS technology. The thinking of the researchers shifted again, from automatically landing aircraft, to automating precision farming and construction equipment.

Determining Sea-Level Rise and Coastal Subsidence in the Canadian Arctic Using a Dense GPS Velocity Field for North America

NASA Astrophysics Data System (ADS)

Craymer, M.; Forbes, D.; Henton, J.; Lapelle, E.; Piraszewski, M.; Solomon, S.

2005-12-01

With observed climate warming in the western Canadian Arctic and potential increases in regional sea level, we anticipate expansion of the coastal region subject to rising relative sea level and increased flooding risk. This is a concern for coastal communities such as Tuktoyaktuk and Sachs Harbour and for the design and safety of hydrocarbon production facilities on the Mackenzie Delta. To provide a framework in which to monitor these changes, a consistent velocity field has been determined from GPS observations throughout North America, including the Canadian Arctic Archipelago and the Mackenzie Delta region. An expanded network of continuous GPS sites and multi-epoch (episodic) sites has enabled an increased density that enhances the application to geophysical studies including the discrimination of crustal motion, other components of coastal subsidence, and sea-level rise. To obtain a dense velocity field consistent at all scales, we have combined weekly solutions of continuous GPS sites from different agencies in Canada and the USA, together with the global reference frame under the North American Reference Frame initiative. Although there is already a high density of continuous GPS sites in the conterminous United States, there are many fewer such sites in Canada. To make up for this lack of density, we have incorporated high-accuracy episodic GPS observations on stable monuments distributed throughout Canada. By combining up to ten years of repeated, episodic GPS observations at such sites, together with weekly solutions from the continuous sites, we have obtained a highly consistent velocity field with a significantly increased spatial sampling of crustal deformation throughout Canada. This exhibits a spatially coherent pattern of uplift and subsidence in Canada that is consistent with the expected rates of glacial isostatic adjustment. To determine the contribution of vertical motion to sea-level rise under climate warming in the Canadian Arctic, we have established co-located tide gauges and continuous GPS at a number of sites across the Canadian Arctic, including Tuktoyaktuk on the eastern side of the Mackenzie Delta. We are also investigating additional sources of subsidence in the delta, including sediment loading, compaction of unfrozen and discontinuously ice-bonded sediments, and anticipated subsidence resulting from future natural gas production. Further densification of the velocity field, including the addition of new sites in the delta, and regular reoccupation of episodic sites will assist in determining local rates of motion. Strategies for discriminating the various components of subsidence in this large delta include episodic GPS on monuments and borehole casing penetrating to various depths and supporting InSAR analysis and geological data. Coastal flooding hazards will be evaluated using digital elevation models derived from real-time kinematic GPS, airborne LiDAR surveys, and synthetic aperture radar flood mapping.

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.

Toward Continuous GPS Carrier-Phase Time Transfer: Eliminating the Time Discontinuity at an Anomaly

PubMed Central

Yao, Jian; Levine, Judah; Weiss, Marc

2015-01-01

The wide application of Global Positioning System (GPS) carrier-phase (CP) time transfer is limited by the problem of boundary discontinuity (BD). The discontinuity has two categories. One is “day boundary discontinuity,” which has been studied extensively and can be solved by multiple methods [1–8]. The other category of discontinuity, called “anomaly boundary discontinuity (anomaly-BD),” comes from a GPS data anomaly. The anomaly can be a data gap (i.e., missing data), a GPS measurement error (i.e., bad data), or a cycle slip. Initial study of the anomaly-BD shows that we can fix the discontinuity if the anomaly lasts no more than 20 min, using the polynomial curve-fitting strategy to repair the anomaly [9]. However, sometimes, the data anomaly lasts longer than 20 min. Thus, a better curve-fitting strategy is in need. Besides, a cycle slip, as another type of data anomaly, can occur and lead to an anomaly-BD. To solve these problems, this paper proposes a new strategy, i.e., the satellite-clock-aided curve fitting strategy with the function of cycle slip detection. Basically, this new strategy applies the satellite clock correction to the GPS data. After that, we do the polynomial curve fitting for the code and phase data, as before. Our study shows that the phase-data residual is only ~3 mm for all GPS satellites. The new strategy also detects and finds the number of cycle slips by searching the minimum curve-fitting residual. Extensive examples show that this new strategy enables us to repair up to a 40-min GPS data anomaly, regardless of whether the anomaly is due to a data gap, a cycle slip, or a combination of the two. We also find that interference of the GPS signal, known as “jamming”, can possibly lead to a time-transfer error, and that this new strategy can compensate for jamming outages. Thus, the new strategy can eliminate the impact of jamming on time transfer. As a whole, we greatly improve the robustness of the GPS CP time transfer. PMID:26958451

Accuracy and reliability of multi-GNSS real-time precise positioning: GPS, GLONASS, BeiDou, and Galileo

NASA Astrophysics Data System (ADS)

Li, Xingxing; Ge, Maorong; Dai, Xiaolei; Ren, Xiaodong; Fritsche, Mathias; Wickert, Jens; Schuh, Harald

2015-06-01

In this contribution, we present a GPS+GLONASS+BeiDou+Galileo four-system model to fully exploit the observations of all these four navigation satellite systems for real-time precise orbit determination, clock estimation and positioning. A rigorous multi-GNSS analysis is performed to achieve the best possible consistency by processing the observations from different GNSS together in one common parameter estimation procedure. Meanwhile, an efficient multi-GNSS real-time precise positioning service system is designed and demonstrated by using the multi-GNSS Experiment, BeiDou Experimental Tracking Network, and International GNSS Service networks including stations all over the world. The statistical analysis of the 6-h predicted orbits show that the radial and cross root mean square (RMS) values are smaller than 10 cm for BeiDou and Galileo, and smaller than 5 cm for both GLONASS and GPS satellites, respectively. The RMS values of the clock differences between real-time and batch-processed solutions for GPS satellites are about 0.10 ns, while the RMS values for BeiDou, Galileo and GLONASS are 0.13, 0.13 and 0.14 ns, respectively. The addition of the BeiDou, Galileo and GLONASS systems to the standard GPS-only processing, reduces the convergence time almost by 70 %, while the positioning accuracy is improved by about 25 %. Some outliers in the GPS-only solutions vanish when multi-GNSS observations are processed simultaneous. The availability and reliability of GPS precise positioning decrease dramatically as the elevation cutoff increases. However, the accuracy of multi-GNSS precise point positioning (PPP) is hardly decreased and few centimeter are still achievable in the horizontal components even with 40 elevation cutoff. At 30 and 40 elevation cutoffs, the availability rates of GPS-only solution drop significantly to only around 70 and 40 %, respectively. However, multi-GNSS PPP can provide precise position estimates continuously (availability rate is more than 99.5 %) even up to 40 elevation cutoff (e.g., in urban canyons).

Reconciling GRACE and GPS estimates of long-term load deformation in southern Greenland

NASA Astrophysics Data System (ADS)

Wang, Song-Yun; Chen, J. L.; Wilson, Clark R.; Li, Jin; Hu, Xiaogong

2018-02-01

We examine vertical load deformation at four continuous Global Positioning System (GPS) sites in southern Greenland relative to Gravity Recovery and Climate Experiment (GRACE) predictions of vertical deformation over the period 2002-2016. With limited spatial resolution, GRACE predictions require adjustment before they can be compared with GPS height time series. Without adjustment, both GRACE spherical harmonic (SH) and mascon solutions predict significant vertical displacement rate differences relative to GPS. We use a scaling factor method to adjust GRACE results, based on a long-term mass rate model derived from GRACE measurements, glacial geography, and ice flow data. Adjusted GRACE estimates show significantly improved agreement with GPS, both in terms of long-term rates and interannual variations. A deceleration of mass loss is observed in southern Greenland since early 2013. The success at reconciling GPS and GRACE observations with a more detailed mass rate model demonstrates the high sensitivity to load distribution in regions surrounding GPS stations. Conversely, the value of GPS observations in constraining mass changes in surrounding regions is also demonstrated. In addition, our results are consistent with recent estimates of GIA uplift (˜4.4 mm yr-1) at the KULU site.

GPS meteorology - Remote sensing of atmospheric water vapor using the Global Positioning System

NASA Technical Reports Server (NTRS)

Bevis, Michael; Businger, Steven; Herring, Thomas A.; Rocken, Christian; Anthes, Richard A.; Ware, Randolph H.

1992-01-01

We present a new approach to remote sensing of water vapor based on the Global Positioning System (GPS). Geodesists and geophysicists have devised methods for estimating the extent to which signals propagating from GPS satellites to ground-based GPS receivers are delayed by atmospheric water vapor. This delay is parameterized in terms of a time-varying zenith wet delay (ZWD) which is retrieved by stochastic filtering of the GPS data. Given surface temperature and pressure readings at the GPS receiver, the retrieved ZWD can be transformed with very little additional uncertainty into an estimate of the integrated water vapor (IWV) overlying that receiver. Networks of continuously operating GPS receivers are being constructed by geodesists, geophysicists, and government and military agencies, in order to implement a wide range of positioning capabilities. These emerging GPS networks offer the possibility of observing the horizontal distribution of IWV or, equivalently, precipitate water with unprecedented coverage and a temporal resolution of the order of 10 min. These measurements could be utilized in operational weather forecasting and in fundamental research into atmospheric storm systems, the hydrologic cycle, atmospheric chemistry, and global climate change.

Improvement of tsunami detection in timeseries data of GPS buoys with the Continuous Wavelet Transform

NASA Astrophysics Data System (ADS)

Chida, Y.; Takagawa, T.

2017-12-01

The observation data of GPS buoys which are installed in the offshore of Japan are used for monitoring not only waves but also tsunamis in Japan. The real-time data was successfully used to upgrade the tsunami warnings just after the 2011 Tohoku earthquake. Huge tsunamis can be easily detected because the signal-noise ratio is high enough, but moderate tsunami is not. GPS data sometimes include the error waveforms like tsunamis because of changing accuracy by the number and the position of GPS satellites. To distinguish the true tsunami waveforms from pseudo-tsunami ones is important for tsunami detection. In this research, a method to reduce misdetections of tsunami in the observation data of GPS buoys and to increase the efficiency of tsunami detection was developed.Firstly, the error waveforms were extracted by using the indexes of position dilution of precision, reliability of GPS satellite positioning and satellite number for calculation. Then, the output from this procedure was used for the Continuous Wavelet Transform (CWT) to analyze the time-frequency characteristics of error waveforms and real tsunami waveforms.We found that the error waveforms tended to appear when the accuracy of GPS buoys positioning was low. By extracting these waveforms, it was possible to decrease about 43% error waveforms without the reduction of the tsunami detection rate. Moreover, we found that the amplitudes of power spectra obtained from the error waveforms and real tsunamis were similar in the component of long period (4-65 minutes), on the other hand, the amplitude in the component of short period (< 1 minute) obtained from the error waveforms was significantly larger than that of the real tsunami waveforms. By thresholding of the short-period component, further extraction of error waveforms became possible without a significant reduction of tsunami detection rate.

The 2014 Mw 6.0 Napa Earthquake, California: Observations from Real-time GPS-enhanced Earthquake Early Warning

NASA Astrophysics Data System (ADS)

Johanson, I. A.; Grapenthin, R.; Allen, R. M.

2014-12-01

Recently, progress has been made to demonstrate feasibility and benefits of including real-time GPS (rtGPS) in earthquake early warning and rapid response systems. While most concepts have yet to be integrated into operational environments, the Berkeley Seismological Laboratory is currently running an rtGPS based finite fault inversion scheme in true real-time, which is triggered by the seismic-based ShakeAlert system and then sends updated earthquake alerts to a test receiver. The Geodetic Alarm System (G-larmS) was online and responded to the 2014 Mw6.0 South Napa earthquake in California. We review G-larmS' performance during this event and for 13 aftershocks, and we present rtGPS observations and real-time modeling results for the main shock. The first distributed slip model and a magnitude estimate of Mw5.5 were available 24 s after the event origin time, which could be reduced to 14 s after a bug fix (~8 s S-wave travel time, ~6 s data latency). The system continued to re-estimate the magnitude once every second: it increased to Mw5.9 3 s after the first alert and stabilized at Mw5.8 after 15 s. G-larmS' solutions for the subsequent small magnitude aftershocks demonstrate that Mw~6.0 is the current limit for alert updates to contribute back to the seismic-based early warning system.

General practitioners' psychosocial resources, distress, and sickness absence: a study comparing the UK and Finland.

PubMed

Heponiemi, Tarja; Elovainio, Marko; Presseau, Justin; Eccles, Martin P

2014-06-01

Many countries, including the UK and Finland, face difficulties in recruiting GPs and one reason for these difficulties may be due to negative psychosocial work environments. To compare psychosocial resources (job control and participative safety), distress and sickness absences between GPs from the UK and those from Finland. We also examined differences in how psychosocial resources are associated with distress and sickness absence and how distress is associated with sickness absence for both countries. Two independent cross-sectional surveys conducted in general practice in the UK and Finland. Analyses of covariance were used for continuous outcome variables and logistic regression for dichotomized variable (sickness absence) adjusted for gender, qualification year and response format. UK GPs reported more opportunities to control their work and had higher levels of participative safety but were more distressed than Finnish GPs. Finnish GPs were 2.3 (95% confidence interval = 1.8-3.1) times more likely to report sickness absence spells than UK GPs. Among Finnish GPs, job control opportunities and high participative safety were associated with lower levels of distress, but not among UK GPs. Among UK GPs, higher distress was associated with 2.1 (95% confidence interval = 1.3-3.6) times higher likelihood of sickness absence spells, but among Finnish GPs there were no such association. In Finland, primary health care organizations should try to improve participative safety and increase control opportunities of physicians to decrease GP distress, whereas in the UK, other work or private life factors may be more important. © The Author 2014. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Monitoring and Prediction of Precipitable Water Vapor using GPS data in Turkey

NASA Astrophysics Data System (ADS)

Ansari, Kutubuddin; Althuwaynee, Omar F.; Corumluoglu, Ozsen

2016-12-01

Although Global Positioning System (GPS) primarily provide accurate estimates of position, velocity and time of the receiver, as the signals pass through the atmoshphere carrying its signatures, thus offers opportunities for atmoshpheric applications. Precipitable water vapor (PWV) is a vital component of the atmosphere and significantly influences atmospheric processes like rainfall and atmospheric temperature. The developing networks of continuously operating GPS can be used to efficiently estimate PWV. The Turkish Permanent GPS Network (TPGN) is employed to monitor PWV information in Turkey. This work primarily aims to derive long-term data of PWV by using atmospheric path delays observed through continuously operating TPGN from November 2014 to October 2015. A least square mathematical approach was then applied to establish the relation of the observed PWV to rainfall and temperature. The modeled PWV was correlated with PWV estimated from GPS data, with an average correlation of 67.10 %-88.60 %. The estimated root mean square error (RMSE) varied from 2.840 to 6.380, with an average of 4.697. Finally, data of TPGN, rainfall, and temperature were obtained for less than 2 months (November 2015 to December 2015) and assessed to validate the mathematical model. This study provides a basis for determining PWV by using rainfall and temperature data.

Study of seasonal and long-term vertical deformation in Nepal based on GPS and GRACE observations

NASA Astrophysics Data System (ADS)

Zhang, Tengxu; Shen, WenBin; Pan, Yuanjin; Luan, Wei

2018-02-01

Lithospheric deformation signal can be detected by combining data from continuous global positioning system (CGPS) and satellite observations from the Gravity Recovery and Climate Experiment (GRACE). In this paper, we use 2.5- to 19-year-long time series from 35 CGPS stations to estimate vertical deformation rates in Nepal, which is located in the southern side of the Himalaya. GPS results were compared with GRACE observations. Principal component analysis was conducted to decompose the time series into three-dimensional principal components (PCs) and spatial eigenvectors. The top three high-order PCs were calculated to correct common mode errors. Both GPS and GRACE observations showed significant seasonal variations. The observed seasonal GPS vertical variations are in good agreement with those from the GRACE-derived results, particularly for changes in surface pressure, non-tidal oceanic mass loading, and hydrologic loading. The GPS-observed rates of vertical deformation obtained for the region suggest both tectonic impact and mass decrease. The rates of vertical crustal deformation were estimated by removing the GRACE-derived hydrological vertical rates from the GPS measurements. Most of the sites located in the southern part of the Main Himalayan Thrust subsided, whereas the northern part mostly showed an uplift. These results may contribute to the understanding of secular vertical crustal deformation in Nepal.

A Recommendation on SLR Ranging to Future Global Navigation Satellite Systems

NASA Astrophysics Data System (ADS)

Labrecque, J. L.; Miller, J. J.; Pearlman, M.

2008-12-01

The multi-agency US Geodetic Requirements Working Group has recommended that Satellite Laser Retro- reflectors be installed on GPS III satellites as a principal component of the Positioning, Navigation, and Timing mandate of the Global Positioning System. The Working Group, which includes NASA, NGA, NOAA, NRL, USGS, and the USNO, echoes the Global Geodetic Observing System recommendation that SLR retro- reflectors be installed on all GNSS satellites. It is further recommended that the retro-reflectors conform to and hopefully exceed the minimum standard of the International Laser Ranging Service for retro-reflector cross sections of 100 million square meters for the HEO GNSS satellites to insure sufficiently accurate ranging by the global network of satellite laser ranging systems. The objective of this recommendation is to contribute to the improvement in the International Terrestrial Reference Frame, and its derivative the WGS84 reference frame, through continuing improvements in the characterization of the GPS orbits and clocks. Another objective is to provide an independent means of assessing the interoperability and accuracy of the GNSS systems and regional augmentation systems. The ranging to GNSS-mounted retro-reflectors will constitute a significant new means of space-based collocation to constrain the tie between the GPS and SLR networks that constitute over 50% of the data from which the ITRF is derived. The recommendation for the installation of SLR retro-reflectors aboard future GPS satellites is one of a number of efforts aimed at improving the accuracy and stability of ITRF. These steps are being coordinated with and supportive of the efforts of the GGOS and its services such at the VLBI2010 initiative, developing a next generation geodetic network, near real-time GPS positioning and EOP determination, and numerous efforts in the improvement of geodetic algorithms for GPS, SLR, VLBI, DORIS, and the determination of the ITRF. If past is prologue, the requirements of accuracy placed upon GNSS systems will continue to evolve at a factor of ten per decade for the lifetime of the GPS III, extending to 2025 and beyond. Global societal priorities such as sea level change measurement already require a factor of ten or more improvement in the accuracy and stability of the ITRF. Increasing accuracy requirements by civilian users for precision positioning and time keeping will certainly continue to grow at an exponential rate. The PNT accuracy of our GNSS systems will keep pace with these societal needs only if we equip the GNSS systems with the capability to identify and further reduce systematic errors.

Development of a GPS buoy system for monitoring tsunami, sea waves, ocean bottom crustal deformation and atmospheric water vapor

NASA Astrophysics Data System (ADS)

Kato, Teruyuki; Terada, Yukihiro; Nagai, Toshihiko; Koshimura, Shun'ichi

2010-05-01

We have developed a GPS buoy system for monitoring tsunami for over 12 years. The idea was that a buoy equipped with a GPS antenna and placed offshore may be an effective way of monitoring tsunami before its arrival to the coast and to give warning to the coastal residents. The key technology for the system is real-time kinematic (RTK) GPS technology. We have successfully developed the system; we have detected tsunamis of about 10cm in height for three large earthquakes, namely, the 23 June 2001 Peru earthquake (Mw8.4), the 26 September 2003 Tokachi earthquake (Mw8.3) and the 5 September 2004 earthquake (Mw7.4). The developed GPS buoy system is also capable of monitoring sea waves that are mainly caused by winds. Only the difference between tsunami and sea waves is their frequency range and can be segregated each other by a simple filtering technique. Given the success of GPS buoy experiments, the system has been adopted as a part of the Nationwide Ocean Wave information system for Port and HArborS (NOWPHAS) by the Ministry of Land, Infrastructure, Transport and Tourism of Japan. They have established more than eight GPS buoys along the Japanese coasts and the system has been operated by the Port and Airport Research Institute. As a future scope, we are now planning to implement some other additional facilities for the GPS buoy system. The first application is a so-called GPS/Acoustic system for monitoring ocean bottom crustal deformation. The system requires acoustic waves to detect ocean bottom reference position, which is the geometrical center of an array of transponders, by measuring distances between a position at the sea surface (vessel) and ocean bottom equipments to return the received sonic wave. The position of the vessel is measured using GPS. The system was first proposed by a research group at the Scripps Institution of Oceanography in early 1980's. The system was extensively developed by Japanese researchers and is now capable of detecting ocean bottom positions with a few centimeters in accuracy. The system is now operational for more than ten sites along the Japanese coasts. Currently, however, the measurements are not continuous but have been done once to several times a year using a boat. If a GPS and acoustic system is placed on a buoy, ocean bottom position could be monitored in near real-time and continuous manner. This will allow us to monitor more detailed and short term crustal deformations at the sea bottom. Another application plan is for an atmospheric research. Previous researchers have shown that GPS is capable of measuring atmospheric water vapor through estimating tropospheric zenith delay measurements of GPS at the sea surface. Information of water vapor content and its temporal variation over sea surface will much contribute to weather forecast on land which has mostly been conducted only by land observations. Considering that the atmospheric mass moves from west to east in general in and around Japanese islands, information of water vapor together with other atmospheric data from an array of GPS buoy placed in the west of Japanese Islands, will much improve weather forecast. We try to examine if this is also feasible. As a conclusion of a series of GPS buoy experiments, we could assert that GPS buoy system will be a powerful tool to monitor ocean surface and much contribute to provide safe and secure life of people.

January 30, 1997 eruptive event on Kilauea Volcano, Hawaii, as monitored by continuous GPS

USGS Publications Warehouse

Owen, S.; Segall, P.; Lisowski, M.; Miklius, Asta; Murray, M.; Bevis, M.; Foster, J.

2000-01-01

A continuous Global Positioning System (GPS) network on Kilauea Volcano captured the most recent fissure eruption in Kilauea's East Rift Zone (ERZ) in unprecedented spatial and temporal detail. The short eruption drained the lava pond at Pu'u O' o, leading to a two month long pause in its on-going eruption. Models of the GPS data indicate that the intrusion's bottom edge extended to only 2.4 km. Continuous GPS data reveal rift opening 8 hours prior to the eruption. Absence of precursory summit inflation rules out magma storage overpressurization as the eruption's cause. We infer that stresses in the shallow rift created by the continued deep rift dilation and slip on the south flank decollement caused the rift intrusion.

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

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.

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

Constraints on dike propagation from continuous GPS measurements

USGS Publications Warehouse

Segall, P.; Cervelli, Peter; Owen, S.; Lisowski, M.; Miklius, Asta

2001-01-01

The January 1997 East Rift Zone eruption on Kilauea volcano, Hawaii, occurred within a network of continuous Global Positioning System (GPS) receivers. The GPS measurements reveal the temporal history of deformation during dike intrusion, beginning ??? 8 hours prior to the onset of the eruption. The dike volume as a function of time, estimated from the GPS data using elastic Green's functions for a homogeneous half-space, shows that only two thirds of the final dike volume accumulated prior to the eruption and the rate of volume change decreased with time. These observations are inconsistent with simple models of dike propagation, which predict accelerating dike volume up to the time of the eruption and little or no change thereafter. Deflationary tilt changes at Kilauea summit mirror the inferred dike volume history, suggesting that the rate of dike propagation is limited by flow of magma into the dike. A simple, lumped parameter model of a coupled dike magma chamber system shows that the tendency for a dike to end in an eruption (rather than intrusion) is favored by high initial dike pressures, compressional stress states, large, compressible magma reservoirs, and highly conductive conduits linking the dike and source reservoirs. Comparison of model predictions to the observed dike volume history, the ratio of erupted to intruded magma, and the deflationary history of the summit magma chamber suggest that most of the magma supplied to the growing dike came from sources near to the eruption through highly conductive conduits. Interpretation is complicated by the presence of multiple source reservoirs, magma vesiculation and cooling, as well as spatial variations in dike-normal stress. Reinflation of the summit magma chamber following the eruption was measured by GPS and accompanied a rise in the level of the Pu'u O'o lava lake. For a spheroidal chamber these data imply a summit magma chamber volume of ??? 20 km3, consistent with recent estimates from seismic tomography. Continuous deformation measurements can be used to image the spatiotemporal evolution of propagating dikes and to reveal quantitative information about the volcanic plumbing systems. Copyright 2001 by the American Geophysical Union.

Constraints on dike propagation from continuous GPS measurements

NASA Astrophysics Data System (ADS)

Segall, Paul; Cervelli, Peter; Owen, Susan; Lisowski, Mike; Miklius, Asta

2001-09-01

The January 1997 East Rift Zone eruption on Kilauea volcano, Hawaii, occurred within a network of continuous Global Positioning System (GPS) receivers. The GPS measurements reveal the temporal history of deformation during dike intrusion, beginning ˜8 hours prior to the onset of the eruption. The dike volume as a function of time, estimated from the GPS data using elastic Green's functions for a homogeneous half-space, shows that only two thirds of the final dike volume accumulated prior to the eruption and the rate of volume change decreased with time. These observations are inconsistent with simple models of dike propagation, which predict accelerating dike volume up to the time of the eruption and little or no change thereafter. Deflationary tilt changes at Kilauea summit mirror the inferred dike volume history, suggesting that the rate of dike propagation is limited by flow of magma into the dike. A simple, lumped parameter model of a coupled dike magma chamber system shows that the tendency for a dike to end in an eruption (rather than intrusion) is favored by high initial dike pressures, compressional stress states, large, compressible magma reservoirs, and highly conductive conduits linking the dike and source reservoirs. Comparison of model predictions to the observed dike volume history, the ratio of erupted to intruded magma, and the deflationary history of the summit magma chamber suggest that most of the magma supplied to the growing dike came from sources near to the eruption through highly conductive conduits. Interpretation is complicated by the presence of multiple source reservoirs, magma vesiculation and cooling, as well as spatial variations in dike-normal stress. Reinflation of the summit magma chamber following the eruption was measured by GPS and accompanied a rise in the level of the Pu'u O'o lava lake. For a spheroidal chamber these data imply a summit magma chamber volume of ˜20 km3, consistent with recent estimates from seismic tomography. Continuous deformation measurements can be used to image the spatiotemporal evolution of propagating dikes and to reveal quantitative information about the volcanic plumbing systems.

GPS net­work operations for the International GPS Geodynamics Service

USGS Publications Warehouse

Neilan, Ruth E.

1993-01-01

As GPS technology comes of age in the 1990’s, it is evident that an internationally sponsored GPS tracking system is called for to provide consistent, timely ground tracking data and data products to the geophysical community. The planning group for the International GPS Geodynamics Service (IGS), sponsored by the International Association of Geodesy (IAG), is addressing all elements of the end-to-end tracking system, ranging from data collection to data analysis and distribution of products (Mueller, 1992). Part of the planning process is to formulate how these various elements work together to create the common infrastructure needed to support a wide variety of GPS investigations. A key element for any permanent satellite tracking system is certainly the acquisition segment; the reliability and robustness of the ground network operations directly determine the fates and limitations of final products. The IGS planning group therefore included a committee tasked to develop and establish standards governing data acquisition and site-specific characteristics deemed necessary to ensure the collection of a high quality, continuous data set.

Keeping primary care "in the loop": General practitioners want better communication with specialists and hospitals when caring for people diagnosed with cancer.

PubMed

Lizama, Natalia; Johnson, Claire E; Ghosh, Manonita; Garg, Neeraj; Emery, Jonathan D; Saunders, Christobel

2015-06-01

To investigate general practitioners' (GP) perceptions about communication when providing cancer care. A self-report survey, which included an open response section, was mailed to a random sample of 1969 eligible Australian GPs. Content analysis of open response comments pertaining to communication was undertaken in order to ascertain GPs' views about communication issues in the provision of cancer care. Of the 648 GPs who completed the survey, 68 (10%) included open response comments about interprofessional communication. Participants who commented on communication were a median age of 50 years and worked 33 h/week; 28% were male and 59% practiced in the metropolitan area. Comments pertaining to communication were coded using five non-mutually exclusive categories: being kept in the loop; continuity of care; relationships with specialists; positive communication experiences; and strategies for improving communication.GPs repeatedly noted the importance of receiving detailed and timely communication from specialists and hospitals, particularly in relation to patients' treatment regimes and follow-up care. Several GPs remarked that they were left out of "the information loop" and that patients were "lost" or "dumped" after referral. While many GPs are currently involved in some aspects of cancer management, detailed and timely communication between specialists and GPs is imperative to support shared care and ensure optimal patient outcomes. This research highlights the need for established channels of communication between specialist and primary care medicine to support greater involvement by GPs in cancer care. © 2015 Wiley Publishing Asia Pty Ltd.

Searching for the Signature of Wastewater Injection in continuous GPS Data from The Geysers Geothermal Field

NASA Astrophysics Data System (ADS)

Terry, R. L.; Funning, G.; Floyd, M.

2017-12-01

The Geysers geothermal field in California, which provides a large portion of northern California's power, has seen declining steam pressures over the past three decades, accompanied by surface subsidence. Together, these two phenomena are likely the result of the exploitation of the reservoir without adequate time for natural restoration. To combat the decline in steam pressures, The Geysers began injecting imported wastewater into the geothermal reservoir in 1997 and expanded injection in 2003. In 2012 and 2013, we installed three continuously recording GPS stations in The Geysers to closely monitor crustal deformation due to both the extraction of steam and the injection of wastewater. To assess the impact of the current injection and extraction activities on the geothermal reservoir, we analyze the position time-series from these GPS stations alongside wastewater injection and steam extraction data. We use common-mode filtering to remove any regionally-correlated noise from our GPS time series, and also estimate and subtract any seasonal signals present. To predict the effect of injection and production on surface movement, we summed the monthly time series of well data within a rectangular grid framework. We then use an array of Mogi sources based on each grid cell's total volume change to calculate the expected surface deformation due to these volume changes at depth. The temporal resolution provided by GPS allows us to characterize more accurately the properties of the subsurface geothermal reservoir related to forcing. For example, based on a similar spatiotemporal relationship between injection and seismicity, we hypothesize that there may be a delayed deformation response following injection, related to the permeability of the reservoir, and are undertaking detailed comparisons between our time series data to identify this response. Overall changes in the sense and rate of vertical motion in the field due to injection over time are also expected. We anticipate that the impact of discovering a relationship between injection and surface deformation will be of great importance in maintaining and managing geothermal resources in the future.

GPS Imaging suggests links between climate, magmatism, seismicity, and tectonics in the Sierra Nevada-Long Valley Caldera-Walker Lane system, western United States

NASA Astrophysics Data System (ADS)

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

2017-12-01

The Walker Lane is a region of complex active crustal transtension in the western Great Basin of the western United States, accommodating about 20% of the 50 mm/yr relative motion between the Pacific and North American plates. The Long Valley caldera lies in the central Walker Lane in eastern California, adjacent to the eastern boundary of the Sierra Nevada/Great Valley microplate, and experiences intermittent inflation, uplift, and volcanic unrest from the magma chamber that resides at middle crustal depths. Normal and transform faults accommodating regional tectonic transtension pass by and through the caldera, complicating the interpretation of the GPS-measured strain rate field, estimates of fault slip rates, and seismic hazard. Several dozen continuously recording GPS stations measure strain and uplift in the area with mm precision. They observe that the most recent episode of uplift at Long Valley began in mid-2011, continuing until late 2016, raising the surface by 100 mm in 6 years. The timing of the initiation of uplift coincides with the beginning of severe drought in California. Furthermore, the timing of a recent pause in uplift coincides with the very wet 2016-2017 winter, which saw approximately double normal snow pack. In prior studies, we showed that the timing of changes in geodetically measured uplift rate of the Sierra Nevada coincides with the timing of drought conditions in California, suggesting a link between hydrological loading and Sierra Nevada elevation. Here we take the analysis three steps further to show that changes in Sierra Nevada uplift rate coincide in time with 1) enhanced inflation at the Long Valley caldera, 2) shifts in the patterns and rates of horizontal tensor strain rate, and 3) seismicity patterns in the central Walker Lane. We use GPS solutions from the Nevada Geodetic Laboratory and the new GPS Imaging technique to produce robust animations of the time variable strain and uplift fields. The goals of this work are to document links between climate, Sierra Nevada uplift rates, response of the magmatic system, and seismicity in the Central Walker Lane, and to explore the physical mechanisms that may be behind these correlations.

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.

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.

Continued study of NAVSTAR/GPS for general aviation

NASA Technical Reports Server (NTRS)

Alberts, R. D.; Ruedger, W. H.

1979-01-01

A conceptual approach for examining the full potential of Global Positioning Systems (GPS) for the general aviation community is presented. Aspects of an experimental program to demonstrate these concepts are discussed. The report concludes with the observation that the true potential of GPS can only be exploited by utilization in concert with a data link. The capability afforded by the combination of position location and reporting stimulates the concept of GPS providing the auxiliary functions of collision avoidance, and approach and landing guidance. A series of general recommendations for future NASA and civil community efforts in order to continue to support GPS for general aviation are included.

Current and planned use of the Navstar Global Positioning System by NASA

NASA Technical Reports Server (NTRS)

Theiss, Harold L.

1993-01-01

NASA was quick to realize the potential that the Global Positioning System (GPS) had to offer for its many diverse vehicles, experiments and platforms. Soon after the first Block 1 GPS satellites were launched, NASA began to use the tremendous capabilities that they had to offer. Even with a partial GPS constellation in place, important results have been obtained about the shape, orientation and rotation of the earth and calibration of the ionosphere and troposphere. These calibrations enhance geophysical science and facilitate the navigation of interplanetary spacecraft. Some very important results have been obtained in the continuing NASA program for aircraft terminal area operations. Currently, a large amount of activity is being concentrated on real time kinematic carrier phase tracking which has the potential to revolutionize aircraft navigation. This year marks the launch of the first GPS receiver equipped earth-orbiting NASA spacecraft: the Extreme Ultraviolet Explorer and the Ocean Topography Experiment (TOPEX/Poseidon). This paper describes a cross section of GPS-based research at NASA.

Survey of Irish general practitioners' preferences for continuing professional development.

PubMed

Maher, B; O'Neill, R; Faruqui, A; Bergin, C; Horgan, M; Bennett, D; O'Tuathaigh, C M P

2018-01-01

Doctors' continuing professional development (CPD) training needs are known to be strongly influenced by national and local contextual characteristics. Given the changing national demographic profile and government-mandated changes to primary care health care provision, this study aimed to investigate Irish General Practitioners' (GPs) perceptions of, and preferences for, current and future CPD programmes. A cross-sectional questionnaire, using closed- and open-ended questions, was administered to Irish GPs, focusing on training needs analysis; CPD course content; preferred format and the learning environment. The response rate was 719/1000 (71.9%). GPs identified doctor-patient communication as the most important and best-performed GP skill. Discrepancies between perceived importance (high) and current performance (low) emerged for time/workload management, practice finance and business skills. GPs identified clinically-relevant primary care topics and non-clinical topics (stress management, business skills, practice management) as preferences for future CPD. Flexible methods for CPD delivery were important. Gender and practice location (urban or rural) significantly influenced CPD participation and future course preference. The increasing diversity of services offered in the Irish primary care setting, in both clinical and non-clinical areas, should be tailored based to include GP practice location and structure.

Time Transfer by Laser Link - T2L2: An Opportunity to Calibrate RF Links

DTIC Science & Technology

2008-12-01

GNSS and TWSTFT , with an improvement of at least one order of magnitude as compared to the best calibrations performed so far (about 1 ns exactitude...frequency transfer systems like GPS or TWSTFT , and comparisons of cold atomic clocks at a level never reached before. Continuous comparison of T2L2 and...Station reattachment to local UTC Ground to Space Transfer : 30 Ground to Ground Transfer : 43 Common view TWSTFT GPS Laser ranging

Detection of Geomagnetic Pulsations of the Earth Using GPS-TEC Data

NASA Astrophysics Data System (ADS)

Koroglu, Ozan; Arikan, Feza; Köroǧlu, Meltem; Sabri Ozkazanc, Yakup

2016-07-01

The magnetosphere of the Earth is made up of both magnetic fields and plasma. In this layer, plasma waves propagate as Ultra Low Frequency (ULF) waves having mHz scale frequencies. ULF waves are produced due to complicated solar-geomagnetic interactions. In the literature, these ULF waves are defined as pulsations. The geomagnetic pulsations are classified into main two groups as continuous pulsations (Pc) and irregular pulsations (Pi). These pulsations can be determined by ionospheric parameters due to the complex lithosphere-ionosphere-magnetosphere coupling processes. Total Electron Content (TEC) is one of the most important parameters for investigating the variability of ionosphere. Global Positioning System (GPS) provides a cost-effective means for estimating TEC from GPS satellite orbital height of 20,000 km to the ground based receivers. Therefore, the time series of GPS-TEC inherently contains the above mentioned ULF waves. In this study, time series analysis of GPS-TEC is carried out by applying periodogram method to the mid-latitude annual TEC data. After the analysis of GPS-TEC data obtained for GPS stations located in Central Europe and Turkey for 2011, it is observed that some of the fundamental frequencies that are indicators of Pc waves, diurnal and semi-diurnal periodicity and earth-free oscillations can be identified. These results will be used in determination of low frequency trend structure of magnetosphere and ionosphere. Further investigation of remaining relatively low magnitude frequencies, all Pi and Pc can be identified by using time and frequency domain techniques such as wavelet analysis. This study is supported by the joint TUBITAK 115E915 and joint TUBITAK114E092 and AS CR 14/001 projects.

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.).

West-Coast Wide Expansion and Testing of the Geodetic Alarm System (G-larmS)

NASA Astrophysics Data System (ADS)

Ruhl, C. J.; Grapenthin, R.; Melgar, D.; Aranha, M. A.; Allen, R. M.

2016-12-01

The Geodetic Alarm System (G-larmS) was developed in collaboration between the Berkeley Seismological Laboratory (BSL) and New Mexico Tech for real-time Earthquake Early Warning (EEW). G-larmS has been in continuous operation at the BSL since 2014 using event triggers from the ShakeAlert EEW system and real-time position time series from a fully triangulated network consisting of BARD, PBO and USGS stations across northern California (CA). G-larmS has been extended to include southern CA and Cascadia, providing continuous west-coast wide coverage. G-larmS currently uses high rate (1 Hz), low latency (< 5 s), accurate positioning (cm level) time series data from a regional GPS network and P-wave event triggers from the ShakeAlert EEW system. It extracts static offsets from real-time GPS time series upon S-wave arrival and performs a least squares inversion on these offsets to determine slip on a finite fault. A key issue with geodetic EEW approaches is that unlike seismology-based algorithms that are routinely tested using frequent small-magnitude events, geodetic systems are not regularly exercised. Scenario ruptures are therefore important for testing the performance of G-larmS. We discuss results from scenario events on several large faults (capable of M>6.5) in CA and Cascadia built from realistic 3D geometries. Synthetic long-period 1Hz displacement waveforms were obtained from a new stochastic kinematic slip distribution generation method. Waveforms are validated by direct comparison to peak P-wave displacement scaling laws and to PGD GMPEs obtained from high-rate GPS observations of large events worldwide. We run the scenarios on real-time streams to systematically test the recovery of slip and magnitude by G-larmS. In addition to presenting these results, we will discuss new capabilities, such as implementing 2D geometry and the applicability of these results to GPS enhanced tsunami warning systems.

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

The Continuous Generation of Equatorial Plasma Bubbles during the Passage of the Solar Terminator, Observed with a Densely-Clustered Network of GPS Receivers in Southeast Asia.

NASA Astrophysics Data System (ADS)

Buhari, S. M.; Tsunoda, R. T.; Abdullah, M.; Hasbi, A. M.; Otsuka, Y.; Yokoyama, T.; Nishioka, M.; Tsugawa, T.

2014-12-01

Equatorial plasma bubbles (EPBs) are three-dimensional structures of depleted plasma density that are often observed in the nighttime equatorial ionosphere. They are initiated near the magnetic dip equator, in the bottomside of the F layer, and develop with time, upward in altitude and poleward in latitude (into both hemispheres), taking the form of longitudinally-narrow, vertically-extended wedges that penetrate deep into the topside of the F layer. Moreover, these structures drift zonally as they evolve in time. Much of what is not yet known about EPBs stems from our inability (1) to capture spatial descriptions of these structures, and (2) to monitor their evolution as a function of time. An objective of this presentation is to report the existence and availability of total electron content (TEC) data from densely-clustered networks of GPS receivers that are capable of providing time-continuous descriptions of EPBs with both high spatial resolution and broad geographical coverage. The networks include the Malaysia Real-Time Kinematics GNSS Network (MyRTKnet), Sumatera GPS Array (SUGAR) network and International GNSS Service (IGS) located in Southeast Asia (SEA). These networks contain 127 GPS receivers with average spacing of about 50 to 100 km. With the ability to resolve space-time ambiguities, we are able to follow the temporal evolution of EPB structures over an extended longitude sector (90 to 120 degrees, East longitude). We will present results from a case study (April 5, 2011) in which 16 EPBs were detected in longitude and tracked in time. We show, for the first time, that the births of 10 out of 16 observed EPBs coincided with the time of passage of the solar terminator across the longitude of birth. The distance between birth locations varied between 100 and 550 km with 10-minute interval. These EPBs were found to persist for 50 minutes to 7 hours, while drifting eastward at a speed of 92 to 150 ms-1. The finding that as many as 16 EPBs can be generated in a continuous sequence over 30 degree of longitude is new. The implications of these findings in terms of seeding and amplification will be discussed.

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.

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.

Worldwide differential GPS for Space Shuttle landing operations

NASA Technical Reports Server (NTRS)

Loomis, Peter V. W.; Denaro, Robert P.; Saunders, Penny

1990-01-01

Worldwide differential Global Positioning System (WWDGPS) is viewed as an effective method of offering continuous high-quality navigation worldwide. The concept utilizes a network with as few as 33 ground stations to observe most of the error sources of GPS and provide error corrections to users on a worldwide basis. The WWDGPS real-time GPS tracking concept promises a threefold or fourfold improvement in accuracy for authorized dual-frequency users, and in addition maintains an accurate and current ionosphere model for single-frequency users. A real-time global tracking network also has the potential to reverse declarations of poor health on marginal satellites, increasing the number of satellites in the constellation and lessening the probability of GPS navigation outage. For Space Shuttle operations, the use of WWDGPS-aided P-code equipment promises performance equal to or better than other current landing guidance systems in terms of accuracy and reliability. This performance comes at significantly less cost to NASA, which will participate as a customer in a system designed as a commercial operation serving the global civil navigation community.

System Proposal for Mass Transit Service Quality Control Based on GPS Data

PubMed Central

Padrón, Gabino; Cristóbal, Teresa; Alayón, Francisco; Quesada-Arencibia, Alexis; García, Carmelo R.

2017-01-01

Quality is an essential aspect of public transport. In the case of regular public passenger transport by road, punctuality and regularity are criteria used to assess quality of service. Calculating metrics related to these criteria continuously over time and comprehensively across the entire transport network requires the handling of large amounts of data. This article describes a system for continuously and comprehensively monitoring punctuality and regularity. The system uses location data acquired continuously in the vehicles and automatically transferred for analysis. These data are processed intelligently by elements that are commonly used by transport operators: GPS-based tracking system, onboard computer and wireless networks for mobile data communications. The system was tested on a transport company, for which we measured the punctuality of one of the routes that it operates; the results are presented in this article. PMID:28621745

System Proposal for Mass Transit Service Quality Control Based on GPS Data.

PubMed

Padrón, Gabino; Cristóbal, Teresa; Alayón, Francisco; Quesada-Arencibia, Alexis; García, Carmelo R

2017-06-16

Quality is an essential aspect of public transport. In the case of regular public passenger transport by road, punctuality and regularity are criteria used to assess quality of service. Calculating metrics related to these criteria continuously over time and comprehensively across the entire transport network requires the handling of large amounts of data. This article describes a system for continuously and comprehensively monitoring punctuality and regularity. The system uses location data acquired continuously in the vehicles and automatically transferred for analysis. These data are processed intelligently by elements that are commonly used by transport operators: GPS-based tracking system, onboard computer and wireless networks for mobile data communications. The system was tested on a transport company, for which we measured the punctuality of one of the routes that it operates; the results are presented in this article.

EarthScope: Cyberinfrastructure to access Plate Boundary Observatory data products and services

NASA Astrophysics Data System (ADS)

Meertens, C. M.; Mattioli, G. S.; Miller, M.; Boler, F. M.; Crosby, C. J.; Mencin, D.; Phillips, D. A.; Snett, L.

2013-12-01

The wealth of data from geodetic observing systems, especially the Plate Boundary Observatory (PBO), presents major data management challenges. The challenges are driven by ingenious new uses of Global Positioning System (GPS) data, demands for higher-rate, lower latency data, the need for continued access and long term preservation of archival data, the expansion of data users into other science, engineering and commercial arenas, and the growth of enhanced products that expand the utility of the data. To meet these challenges, UNAVCO has established a comprehensive suite of data services encompassing sensor network data operations, data product generation (through the activities of partners at Massachusetts Institute of Technology, Central Washington University, New Mexico Institute of Mining and Technology, and the University of California, San Diego - UCSD), data management, access and archiving, and advanced cyberinfrastructure. PBO sensor systems include 1,100 continuously operating GPS stations, 79 borehole geophysical sites (with a combination of strainmeters, tiltmeters, seismometers, pore pressure gauges, and meteorological sensors), and 6 long baseline strainmeters. Imaging data acquired for EarthScope include large volumes of satellite synthetic aperture radar (SAR) and airborne LiDAR data. Core data products such as daily GPS position time series and derived crustal motion velocities have been augmented with real-time data streams and positions calculated every second from 367 PBO stations. Higher rate (5 Hz) data files are available for applications such as GPS seismology. Efforts are underway with UCSD to integrate GPS and accelerometers at a subset of PBO sites to increase the reliability and capability of the observations. These observations have utility for research and hazards mitigation. Ingenious methods of GPS data analysis, developed by the University of Colorado and the University Corporation for Atmospheric Research, measure snow depth, near surface soil moisture, and vegetation. Along with atmospheric water vapor estimates, these products are expanding the utility of the data into atmospheric, environmental, ecological and soil sciences. Another new PBO product, hydrologic loading models derived from the NASA Global Land Data Assimilation System, is available for correcting GPS time series and hydrologic studies. To facilitate discovery and access of these extensive, diverse, and distributed data collections, UNAVCO has led collaborative efforts to develop web services and federated query capabilities for GPS, LiDAR and SAR. These services form the foundations for global integration projects such as EarthCube, GEO Geohazard Supersites and Natural Laboratories, and COOPEUS. In order to further curation and enhance access and processing capabilities, UNAVCO is exploring cloud computing and storage with UCSD and Amazon that will increase capacity over the next five years. Finally, with the rich set of data and services offered from PBO comes the need to help users better understand data techniques, observations, and quality. To serve this need, UNAVCO is enhancing online resources and, with its community partners, will continue to develop technical short courses and workshops.

[Exploring the prospects for general practitioners over 55 years old from three counties of western France].

PubMed

Robino, Stéphane; Buis, Hélène; Delansorne, Fanny; Tomas, Josiane; Huez, Jean-François; La Combe, Antoine; Fanello, Serge

2009-01-01

Medical demography and the practice of medicine will be influenced by the personal plans of GPs and their decisions to stop practicing in the coming years. This study aims to understand the events that could potentially worsen the medical demography in terms of shortages of GPs for primary care in the short term. 455 GPs (all aged over 55 years) practicing in three districts of western France were selected to participate in this prospective study. 258 valid and complete questionnaires (56%) were received. With the use of a special programme, SPSS version 1.5, an overall comprehensive analysis and one by geographical sub-regional groups were performed. When queried about their plans or wishes for their practice between the present time and their age of 65, of the responding physicians, 27% wanted to continue working under the same conditions, 10% were undecided, and 63% wanted to stop or adjust their professional activity before age 65. The main reasons and factors motivating these plans were their current time constraints, the workload related to administrative tasks and the continuity of care; moreover, GPs noted the demands and expectations of patients, professional burnout and difficulties in obtaining a healthy work-life balance as factors contributing to these plans. Physicians who wanted to stop practicing (30%) were the least satisfied with their work and seem to have anticipated this plan of action given that they reduced their number of hours in the office and on-call. Those who wish to adapt their work time (33%) are for the most part satisfied even if they work more, but 70% want to reduce their work hours. The impact of these projects is a potentially heavy one, especially since two of the counties concerned have a low medical density and high rate of practicing physicians. Government measures currently proposed do not seem to respond to the evolution of private practice expected by GPs over 55 years.

Mapping stream habitats with a global positioning system: Accuracy, precision, and comparison with traditional methods

USGS Publications Warehouse

Dauwalter, D.C.; Fisher, W.L.; Belt, K.C.

2006-01-01

We tested the precision and accuracy of the Trimble GeoXT??? global positioning system (GPS) handheld receiver on point and area features and compared estimates of stream habitat dimensions (e.g., lengths and areas of riffles and pools) that were made in three different Oklahoma streams using the GPS receiver and a tape measure. The precision of differentially corrected GPS (DGPS) points was not affected by the number of GPS position fixes (i.e., geographic location estimates) averaged per DGPS point. Horizontal error of points ranged from 0.03 to 2.77 m and did not differ with the number of position fixes per point. The error of area measurements ranged from 0.1% to 110.1% but decreased as the area increased. Again, error was independent of the number of position fixes averaged per polygon corner. The estimates of habitat lengths, widths, and areas did not differ when measured using two methods of data collection (GPS and a tape measure), nor did the differences among methods change at three stream sites with contrasting morphologies. Measuring features with a GPS receiver was up to 3.3 times faster on average than using a tape measure, although signal interference from high streambanks or overhanging vegetation occasionally limited satellite signal availability and prolonged measurements with a GPS receiver. There were also no differences in precision of habitat dimensions when mapped using a continuous versus a position fix average GPS data collection method. Despite there being some disadvantages to using the GPS in stream habitat studies, measuring stream habitats with a GPS resulted in spatially referenced data that allowed the assessment of relative habitat position and changes in habitats over time, and was often faster than using a tape measure. For most spatial scales of interest, the precision and accuracy of DGPS data are adequate and have logistical advantages when compared to traditional methods of measurement. ?? 2006 Springer Science+Business Media, Inc.

Surface deformation analysis over Vrancea seismogenic area through radar and GPS geospatial data

NASA Astrophysics Data System (ADS)

Zoran, Maria A.; Savastru, Roxana S.; Savastru, Dan M.; Serban, Florin S.; Teleaga, Delia M.; Mateciuc, Doru N.

2017-10-01

Time series analysis of GPS (Global Positioning Systems) and InSAR (Interferometric Synthetic Aperture Radar) data are important tools for Earth's surface deformation assessment, which can result from a wide range of geological phenomena like as earthquakes, landslides or ground water level changes. The aim of this paper was to identify several types of earthquake precursors that might be observed from geospatial data in Vrancea seismogenic region in Romania. Continuous GPS Romanian network stations and few field campaigns data recorded between 2005-2012 years revealed a displacement of about 5 or 6 millimeters per year in horizontal direction relative motion, and a few millimeters per year in vertical direction. In order to assess possible deformations due to earthquakes and respectively for possible slow deformations, have been used also time series Sentinel 1 satellite data available for Vrancea zone during October 2014 till October 2016 to generate two types of interferograms (short-term and medium- term). During investigated period were not recorded medium or strong earthquakes, so interferograms over test area revealed small displacements on vertical direction (subsidence or uplifts) of 5-10 millimeters per year. Based on GPS continuous network data and satellite Sentinel 1 results, different possible tectonic scenarios were developed. The localization of horizontal and vertical motions, fault slip, and surface deformation of the continental blocks provides new information, in support of different geodynamic models for Vrancea tectonic active region in Romania and Europe.

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.

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.

Differentiation of Secular and Postseismic Deformation in the Mojave Shear Zone in Southern California and Inference of Lithospheric Rheology

NASA Astrophysics Data System (ADS)

Shen, Z.; Liu, S.; Burgmann, R.

2015-12-01

The 1992 Mw 7.3 Landers and 1999 Mw7.1 Hector Mine earthquakes struck the Eastern California Shear Zone (ECSZ) in the Mojave Desert, Southern California. Coseismic and postseismic deformation from these events affect efforts to use Global Positioning System (GPS) observations collected since these events to establish a secular surface velocity field, especially in the near field of the coseismic ruptures. We devise block motion models constrained by both historical pre-Landers triangulation and trilateration observations and post-Landers GPS measurements to recover the secular deformation field and differentiate the postseismic transients in the Mojave region. Postseismic transients are found to remain in various "interseismic" GPS velocity solutions in the form of 2-3 mm/yr excess right-lateral shear across the Landers and Hector Mine coseismic ruptures [Liu et al., 2015 JGR]. Postseismic GPS time series differentiated from the secular velocity field reveal enduring late-stage transient motions in the near field of the coseismic ruptures. Using the postseismic time series data as model constraints, we develop postseismic deformation model invoking afterlip on faults and viscoelastic relaxation in the lower crust and upper mantle. A Burgers body material and a Maxwell material are assumed for the lower crust and upper mantle respectively. Our preliminary modeling result, constrained using GPS time series data from the SCEC Crustal Motion Map 4.0 (covering the time period of 1992-2004), reveals that both the long-term viscosities for the lower crust and upper mantle are on the order of e+19 Pa-s. This finding differs significantly from the "Crème Brulee" model predictions about the rheological structure of the lower crust and upper mantle, in which the lower crust has a substantially higher viscosity. We are incorporating more GPS time series data into our model, particularly the ones from continuous sites of the Plate Boundary Observatory network with post-2004 time span, and the modeling result will be presented at the meeting.

Whole-system evaluation research of a scheme to support inner city recruitment and retention of GPs.

PubMed

Bellman, Loretta

2002-12-01

The GP Assistant/Research Associate scheme developed in the Guy's, King's and St Thomas' School of Medicine, London, aims to attract and recruit young GPs (GP Assistants) and develop their commitment to work in local inner city practices. Continuing professional development for both young and established GPs is a key feature of the scheme. The objectives of the whole-system evaluation research were to explore the perspectives of 34 stakeholders in the academic department, the practices and the PCGs, and to investigate the experiences of 19 GP Assistants who have participated in the scheme. Qualitative methods included semi-structured interviews, non-participant observations in the practices, audio-taped meetings and personal journals. Data collection also included reviewing documentation of the scheme, i.e. the previous quantitative evaluation report, publications and e-mails. The multi-method approach enabled individual, group and team perspectives of the scheme and triangulation of the data through comparing dialogue with observations and documentary evidence. Thematic analysis was undertaken to elicit the complex experiences of the GP Assistants. Wide-ranging findings included enthusiastic support for the continuation of the scheme. The GP Assistants' personal and professional development was clearly evident from the themes 'eye opener', new knowledge, managing multiple roles, feeling vulnerable, time constraints and empowering processes. Seven of the GP Assistants have become partners and ten chose to remain working in local practices. Significant challenges for managing and leading the scheme were apparent. Greater co-operation and collaborative working between the academic department and the practices is required. The scheme provides a highly valued visible means of support for GPs and could act as a model for a career pathway aimed at enhancing recruitment and retention of GPs. The scheme is also at the forefront of national initiatives aimed at supporting single-handed practices and helping GPs with their continuing professional development. An integrated approach to change, education, research and development is advocated to enable recruitment and retention of GPs, their academic development, and to underpin the evolution of PCTs as learning organizations.

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.

Collaboration between general practitioners (GPs) and mental healthcare professionals within the context of reforms in Quebec

PubMed Central

2012-01-01

Background In the context of the high prevalence and impact of mental disorders worldwide, and less than optimal utilisation of services and adequacy of care, strengthening primary mental healthcare should be a leading priority. This article assesses the state of collaboration among general practitioners (GPs), psychiatrists and psychosocial mental healthcare professionals, factors that enable and hinder shared care, and GPs’ perceptions of best practices in the management of mental disorders. A collaboration model is also developed. Methods The study employs a mixed-method approach, with emphasis on qualitative investigation. Drawing from a previous survey representative of the Quebec GP population, 60 GPs were selected for further investigation. Results Globally, GPs managed mental healthcare patients in solo practice in parallel or sequential follow-up with mental healthcare professionals. GPs cited psychologists and psychiatrists as their main partners. Numerous hindering factors associated with shared care were found: lack of resources (either professionals or services); long waiting times; lack of training, time and incentives for collaboration; and inappropriate GP payment modes. The ideal practice model includes GPs working in multidisciplinary group practice in their own settings. GPs recommended expanding psychosocial services and shared care to increase overall access and quality of care for these patients. Conclusion As increasing attention is devoted worldwide to the development of optimal integrated primary care, this article contributes to the discussion on mental healthcare service planning. A culture of collaboration has to be encouraged as comprehensive services and continuity of care are key recovery factors of patients with mental disorders. PMID:23730332

23 October 2011 (Mw=7.2) Van Earthquake (Turkey): Revised Coseismic and Postseismic Models from New GPS Observations

NASA Astrophysics Data System (ADS)

Dogan, U.; Demir, D. O.; Cakir, Z.; Ergintav, S.; Cetin, S.; Ozdemir, A.; Reilinger, R. E.

2017-12-01

The 23 October 2011, Mw=7.2 Van Earthquake occurred in eastern Turkey on a thrust fault trending NE-SW and dipping to the north. We use GPS time series from the survey and continuous stations to determine coseismic deformation and to identify spatial and temporal changes in the near and far field due to postseismic processes (2011-2017). The coseismic deformation in the near field is derived from GPS data collected at 25 cadastral GPS survey sites. The coseismic horizontal displacements reach nearly 50 cm close to the surface trace of the fault that ruptured at depth during the earthquake. The density and distribution of the GPS sites allow us to better constrain the extent of the coseismic rupture using elastic dislocations on triangular faults embedded in a homogeneous, elastic half space. Modeling studies suggest that the coseismic rupture stopped west of the Erçek Lake before veering to the north. Estimated seismic moment is in good agreement with the seismologically and geodetically estimated seismic moment, estimated from the finite-fault model. Our preferred coseismic model consists of a simple elliptical slip patch centered at around 8 km depth with a maximum slip of about 2.5 m, consistent with the previous estimates based on InSAR measurements. The postseismic deformation field is derived from far field continuous GPS observations (10.2011 - 11.2017) and near field GPS campaigns (10.2011 - 09.2015). The postseismic time-series are fit better with a logarithmic than an exponential function, suggesting that the postseismic deformation is due to afterslip. Then, we modified our published postseismic model, using the coseismic model and data sets, extended until the end of 2017. The results show that during 6 years following the earthquake, after slip of up to 65 cm occurred at relatively shallow (< 10 km) depths, mostly above the deep coseismic slip that reaches depths > 15 km. New interpretations of the shallow afterslip, also, adds further evidence that the surface break observed after the earthquake was caused by coseismic stress changes rather than representing the coseismic fault. (This study is supported by TUBITAK no: 112Y109 project). Keywords: Van earthquake, GPS, coseismic, postseismic, deformation, elastic modeling

Geoscience Australia Continuous Global Positioning System (CGPS) Station Field Campaign Report

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

Ruddick, R.; Twilley, B.

2016-03-01

This station formed part of the Australian Regional GPS Network (ARGN) and South Pacific Regional GPS Network (SPRGN), which is a network of continuous GPS stations operating within Australia and its Territories (including Antarctica) and the Pacific. These networks support a number of different science applications including maintenance of the Geospatial Reference Frame, both national and international, continental and tectonic plate motions, sea level rise, and global warming.

Ionospheric earthquake effects detection based on Total Electron Content (TEC) GPS Correlation

NASA Astrophysics Data System (ADS)

Sunardi, Bambang; Muslim, Buldan; Eka Sakya, Andi; Rohadi, Supriyanto; Sulastri; Murjaya, Jaya

2018-03-01

Advances in science and technology showed that ground-based GPS receiver was able to detect ionospheric Total Electron Content (TEC) disturbances caused by various natural phenomena such as earthquakes. One study of Tohoku (Japan) earthquake, March 11, 2011, magnitude M 9.0 showed TEC fluctuations observed from GPS observation network spread around the disaster area. This paper discussed the ionospheric earthquake effects detection using TEC GPS data. The case studies taken were Kebumen earthquake, January 25, 2014, magnitude M 6.2, Sumba earthquake, February 12, 2016, M 6.2 and Halmahera earthquake, February 17, 2016, M 6.1. TEC-GIM (Global Ionosphere Map) correlation methods for 31 days were used to monitor TEC anomaly in ionosphere. To ensure the geomagnetic disturbances due to solar activity, we also compare with Dst index in the same time window. The results showed anomalous ratio of correlation coefficient deviation to its standard deviation upon occurrences of Kebumen and Sumba earthquake, but not detected a similar anomaly for the Halmahera earthquake. It was needed a continous monitoring of TEC GPS data to detect the earthquake effects in ionosphere. This study giving hope in strengthening the earthquake effect early warning system using TEC GPS data. The method development of continuous TEC GPS observation derived from GPS observation network that already exists in Indonesia is needed to support earthquake effects early warning systems.

Coseismic slip distributions of the 26 December 2004 Sumatra-Andaman and 28 March 2005 Nias earthquakes from GPS static offsets

USGS Publications Warehouse

Banerjee, P.; Pollitz, F.; Nagarajan, B.; Burgmann, R.

2007-01-01

Static offsets produced by the 26 December 2004 M ???9 Sumatra-Andaman earthquake as measured by Global Positioning System (GPS) reveal a large amount of slip along the entire ???1300 km-long rupture. Most seismic slip inversions place little slip on the Andaman segment. whereas both near-field and far-field GPS offsets demand large slip on the Andaman segment. We compile available datasets of the static offset to render a more detailed picture of the static-slip distribution. We construct geodetic offsets such that postearthquake positions of continuous GPS sites are reckoned to a time 1 day after the earthquake and campaign GPS sites are similarly corrected for postseismic motions. The newly revised slip distribution (Mw 9.22) reveals substantial segmentation of slip along the Andaman Islands, with the southern quarter slipping ???15 m in unison with the adjacent Nicobar and northern Sumatran segments of length ???700 km. We infer a small excess of geodetic moment relative to the seismic moment. A similar compilation of GPS offsets from the 28 March 2005 Nias earthquake is well explained with dip slip averaging several meters (Mw = 8.66) distributed primarily at depths greater than 20 km.

Permanent GPS Geodetic Array in Southern California (PGGA) and GPS observations in Indonesia

NASA Technical Reports Server (NTRS)

Bock, Yehuds

1994-01-01

The Permanent GPS Geodetic Array (PGGA) is a network of permanent monitoring GPS stations in southern California devoted to the continuous measurement of crustal deformation in near real-time. The PGGA plays a unique role in studies of the kinematics of crustal deformation and the earthquake cycle in southern California because it is also providing temporally dense geodetic measurements of crustal motion over periods of minutes to variations in regional crustal strain. As it expands and matures the PGGA will play an increasingly important role in the study of active tectonics of southern California by bridging the frequency range between seismology, observatory geodesy, paleoseismology, and geology. In Indonesia GPS data is used for measurement of a large scale crustal deformation, extending from north China to the Indonesian archipelago. Indonesia offers a tremendous laboratory to study some of the processes that build continents, and mountains are active there. We began GPS observations in August 1989 on mainland Sumatra and the Mentawai Islands to study the phenomena of oblique plate convergence. We have analyzed the Indonesian data in conjunction with data collected on Christmas and Cocos Islands and at Darwin, Australia, and with the triangulation data in Sumatra.

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.

Linking the global positioning system (GPS) to a personal digital assistant (PDA) to support tuberculosis control in South Africa: a pilot study

PubMed Central

Dwolatzky, Barry; Trengove, Estelle; Struthers, Helen; McIntyre, James A; Martinson, Neil A

2006-01-01

Background Tuberculosis (TB) is the leading clinical manifestation of HIV infection and caseloads continue to increase in high HIV prevalence settings. TB treatment is prolonged and treatment interruption has serious individual and public health consequences. We assessed the feasibility of using a handheld computing device programmed with customised software and linked to a GPS receiver, to assist TB control programmes to trace patients who interrupt treatment in areas without useful street maps. In this proof of concept study, we compared the time taken to re-find a home comparing given residential addresses with a customised personalised digital assistant linked to a global positioning system (PDA/GPS) device. Additionally, we assessed the feasibility of using aerial photographs to locate homes. Results The study took place in two communities in Greater Johannesburg, South Africa: Wheillers Farm, a relatively sparsely populated informal settlement, and a portion of Alexandra, an urban township with densely populated informal settlements. Ten participants in each community were asked to locate their homes on aerial photographs. Nine from Wheillers Farm and six from Alexandra were able to identify their homes. The total time taken by a research assistant, unfamiliar with the area, to locate 10 homes in each community using the given addresses was compared with the total time taken by a community volunteer with half an hour of training to locate the same homes using the device. Time taken to locate the ten households was reduced by 20% and 50% in each community respectively using the PDA/GPS device. Conclusion In this pilot study we show that it is feasible to use a simple PDA/GPS device to locate the homes of patients. We found that in densely populated informal settlements, GPS technology is more accurate than aerial photos in identifying homes and more efficient than addresses provided by participants. Research assessing issues of, confidentiality and cost effectiveness would have to be undertaken before implementing PDA/GPS – based technology for this application. However, this PDA/GPS device could be used to reduce part of the burden on TB control programs. PMID:16911806

Continuous GPS : pilot applications - Phase II

DOT National Transportation Integrated Search

2003-08-01

The primary objective of this research was to evaluate the feasibility of applying Global Positioning System (GPS) technology in the study of geotechnical phenomenon by developing, integrating, and test deploying a GPS-based instrumentation package u...

GPS interferometric reflectometry for ground-based remote sensing of snow depth and density

NASA Astrophysics Data System (ADS)

Nievinski, F. G.; Larson, K. M.; Gutmann, E. D.; Zavorotny, V.; Williams, M. W.

2011-12-01

GPS interferometric reflectometry (GPS-IR) is a method that exploits multipath for ground-based remote sensing in the surroundings of a GPS antenna. It operates on L-band, leveraging hundreds of conventional GPS sites existing in the U.S., with a typical footprint of 30-meter radius. Multipath is the coherent interference of line-of-sight and reflected signals; as the two go in and out of phase, the power recorded by a GPS interferometer goes through peaks and troughs that can be related to land surface characteristics, such as soil moisture and snow depth. GPS-IR has been demonstrated to be capable of retrieving snow depth during extended periods at various locations, as validated by comparisons with a continuously-operating terrestrial scanning laser, an airborne LIDAR campaign, manual stake surveys, and ultrasonic depth sensors. Here we explore the possibility of retrieving snow density, too. This will determine the feasibility and limitations of GPS-IR for monitoring of snow water equivalent (SWE). Data were collected at Niwot Ridge LTER in Colorado, at a 3,500-m altitude alpine tundra site. Niwot receives around 1,000 mm of precipitation per year and has a mean annual air temperature of -3.8°C. Snow density and temperature is measured in 10-cm vertical increments at snowpits dug approximately every week. A continuously-operating GPS system established in 2009 allows for measurement of the snowpack several times a day at multiple azimuths as satellites rise and set. The typical peak snow depth at the GPS site is 1.5 m, with a peak depth during the study period of 1.7 m in 2009/2010 and 2.5 m in 2010/2011; density ranged 200-600 kg/m3. We employ a forward/inverse model originally developed for snow depth and recently extended to account for layering to study both synthetic and real observations. We present comparisons of density estimates obtained using GPS-IR observations to snowpit field data, focusing initially on dry snow. In addition, we explore the sensitivity of the model to roughness, density, snow depth, and random noise. Synthetic observations derived from the forward model based on realistic snow profiles are utilized in the inverse model to quantify both the formal uncertainty and the expected error in parameter retrievals.

How GPs learn.

PubMed

MacLeod, Sheona

2009-07-01

As the requirements for the revalidation of general practitioners (GPs) unfold, there is an increasing emphasis on demonstrating effective continued medical education (CME) based on identified learning needs. This qualitative study aimed to promote understanding of how GPs currently approach their learning. The behaviour of one group of GPs was studied to explore how they assessed and met individual learning needs. The GPs studied showed a pragmatic approach, valuing learning that gave them practical advice and instant access to information for patient-specific problems. The main driver for the GPs' learning was discomfort during their daily work if a possible lack of knowledge or skills was perceived. However, some learning benchmarked current good practice or ensured continued expertise. Learning purely for interest was also described. The GPs in this study all demonstrated a commitment to personal learning, although they were not yet thinking about demonstrating the effectiveness of this for revalidation. The GPs prioritised their learning needs and were beginning to use some objective assessment methods to do this and the GP appraisal process was found to have a mainly positive effect on learning.

Different deformation patterns using GPS in the volcanic process of El Hierro (Canary Island) 2011-2013

NASA Astrophysics Data System (ADS)

García-Cañada, Laura; José García-Arias, María; Pereda de Pablo, Jorge; Lamolda, Héctor; López, Carmen

2014-05-01

Ground deformation is one of the most important parameter in volcano monitoring. The detected deformations in volcanic areas can be precursors of a volcanic activity and contribute with useful information to study the evolution of an unrest, eruption or any volcanic process. GPS is the most common technique used to measure volcano deformations. It can be used to detect slow displacement rates or much larger and faster deformations associated with any volcanic process. In volcanoes the deformation is expected to be a mixed of nature; during periods of quiescence it will be slow or not present, while increased activity slow displacement rates can be detected or much larger and faster deformations can be measure due to magma intrusion, for example in the hours to days prior a eruption beginning. In response to the anomalous seismicity detected at El Hierro in July 2011, the Instituto Geográfico Nacional (IGN) improved its volcano monitoring network in the island with continuous GPS that had been used to measure the ground deformation associated with the precursory unrest since summer 2011, submarine eruption (October 2011-March 2012) and the following unrest periods (2012-2013). The continuous GPS time series, together with other techniques, had been used to evaluate the activity and to detect changes in the process. We investigate changes in the direction and module of the deformation obtained by GPS and they show different patterns in every unrest period, very close to the seismicity locations and migrations.

Handling cycle slips in GPS data during ionospheric plasma bubble events

NASA Astrophysics Data System (ADS)

Banville, S.; Langley, R. B.; Saito, S.; Yoshihara, T.

2010-12-01

During disturbed ionospheric conditions such as the occurrence of plasma bubbles, the phase and amplitude of the electromagnetic waves transmitted by GPS satellites undergo rapid fluctuations called scintillation. When this phenomenon is observed, GPS receivers are more prone to signal tracking interruptions, which prevent continuous measurement of the total electron content (TEC) between a satellite and the receiver. In order to improve TEC monitoring, a study was conducted with the goal of reducing the effects of signal tracking interruptions by correcting for "cycle slips," an integer number of carrier wavelengths not measured by the receiver during a loss of signal lock. In this paper, we review existing cycle-slip correction methods, showing that the characteristics associated with ionospheric plasma bubbles (rapid ionospheric delay fluctuations, data gaps, increased noise, etc.) prevent reliable correction of cycle slips. Then, a reformulation of the "geometry-free" model conventionally used for ionospheric studies with GPS is presented. Geometric information is used to obtain single-frequency estimates of TEC variations during momentary L2 signal interruptions, which also provides instantaneous cycle-slip correction capabilities. The performance of this approach is assessed using data collected on Okinawa Island in Japan during a plasma bubble event that occurred on 23 March 2004. While an improvement in the continuity of TEC time series is obtained, we question the reliability of any cycle-slip correction technique when discontinuities on both GPS legacy frequencies occur simultaneously for more than a few seconds.

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.

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.

Consistent Long-Time Series of GPS Satellite Antenna Phase Center Corrections

NASA Astrophysics Data System (ADS)

Steigenberger, P.; Schmid, R.; Rothacher, M.

2004-12-01

The current IGS processing strategy disregards satellite antenna phase center variations (pcvs) depending on the nadir angle and applies block-specific phase center offsets only. However, the transition from relative to absolute receiver antenna corrections presently under discussion necessitates the consideration of satellite antenna pcvs. Moreover, studies of several groups have shown that the offsets are not homogeneous within a satellite block. Manufacturer specifications seem to confirm this assumption. In order to get best possible antenna corrections, consistent ten-year time series (1994-2004) of satellite-specific pcvs and offsets were generated. This challenging effort became possible as part of the reprocessing of a global GPS network currently performed by the Technical Universities of Munich and Dresden. The data of about 160 stations since the official start of the IGS in 1994 have been reprocessed, as today's GPS time series are mostly inhomogeneous and inconsistent due to continuous improvements in the processing strategies and modeling of global GPS solutions. An analysis of the signals contained in the time series of the phase center offsets demonstrates amplitudes on the decimeter level, at least one order of magnitude worse than the desired accuracy. The periods partly arise from the GPS orbit configuration, as the orientation of the orbit planes with regard to the inertial system repeats after about 350 days due to the rotation of the ascending nodes. In addition, the rms values of the X- and Y-offsets show a high correlation with the angle between the orbit plane and the direction to the sun. The time series of the pcvs mainly point at the correlation with the global terrestrial scale. Solutions with relative and absolute phase center corrections, with block- and satellite-specific satellite antenna corrections demonstrate the effect of this parameter group on other global GPS parameters such as the terrestrial scale, station velocities, the geocenter position or the tropospheric delays. Thus, deeper insight into the so-called `Bermuda triangle' of several highly correlated parameters is given.

A GPS-based Real-time Road Traffic Monitoring System

NASA Astrophysics Data System (ADS)

Tanti, Kamal Kumar

In recent years, monitoring systems are astonishingly inclined towards ever more automatic; reliably interconnected, distributed and autonomous operation. Specifically, the measurement, logging, data processing and interpretation activities may be carried out by separate units at different locations in near real-time. The recent evolution of mobile communication devices and communication technologies has fostered a growing interest in the GIS & GPS-based location-aware systems and services. This paper describes a real-time road traffic monitoring system based on integrated mobile field devices (GPS/GSM/IOs) working in tandem with advanced GIS-based application software providing on-the-fly authentications for real-time monitoring and security enhancement. The described system is developed as a fully automated, continuous, real-time monitoring system that employs GPS sensors and Ethernet and/or serial port communication techniques are used to transfer data between GPS receivers at target points and a central processing computer. The data can be processed locally or remotely based on the requirements of client’s satisfaction. Due to the modular architecture of the system, other sensor types may be supported with minimal effort. Data on the distributed network & measurements are transmitted via cellular SIM cards to a Control Unit, which provides for post-processing and network management. The Control Unit may be remotely accessed via an Internet connection. The new system will not only provide more consistent data about the road traffic conditions but also will provide methods for integrating with other Intelligent Transportation Systems (ITS). For communication between the mobile device and central monitoring service GSM technology is used. The resulting system is characterized by autonomy, reliability and a high degree of automation.

Exploring the training and scope of practice of GPs in England, Germany and Spain.

PubMed

Glonti, Ketevan; Struckmann, Verena; Alconada, Alvaro; Pettigrew, Luisa M; Hernandez-Santiago, Virginia; Minue, Sergio; Risso-Gill, Isabelle; McKee, Martin; Legido-Quigley, Helena

2018-03-22

To explore general practitioner (GP) training, continuing professional development, scope of practice, ethical issues and challenges in the working environment in three European countries. Qualitative study of 35 GPs from England, Germany and Spain working in urban primary care practices. Participants were recruited using convenience and snowball sampling techniques. Semi-structured interviews were recorded, transcribed and analysed by four independent researchers adopting a thematic approach. Entrance to and length of GP training differ between the three countries, while continuing professional development is required in all three, although with different characteristics. Key variations in the scope of practice include whether there is a gatekeeping role, whether GPs work in multidisciplinary teams or singlehandedly, the existence of appraisal processes, and the balance between administrative and clinical tasks. However, similar challenges, including the need to adapt to an ageing population, end-of-life care, ethical dilemmas, the impact of austerity measures, limited time for patients and gaps in coordination between primary and secondary care are experienced by GPs in all three countries. Primary health care variations have strong historical roots, derived from the different national experiences and the range of clinical services delivered by GPs. There is a need for an accessible source of information for GPs themselves and those responsible for safety and quality standards of the healthcare workforce. This paper maps out the current situation before Brexit is being implemented in the UK which could see many of the current EU arrangements and legislation to assure professional mobility between the UK and the rest of Europe dismantled. Copyright © 2017. Publicado por Elsevier España, S.L.U.

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.

Drought-induced uplift in the western United States as observed by the EarthScope Plate Boundary Observatory GPS network

NASA Astrophysics Data System (ADS)

Borsa, A. A.; Agnew, D. C.; Cayan, D. R.

2014-12-01

The western United States (WUS) has been experiencing severe drought since 2013. The solid earth response to the accompanying loss of surface and near-surface water mass should be a broad region of uplift. We use seasonally-adjusted time series from continuously operating GPS stations in the EarthScope Plate Boundary Observatory and several smaller networks to measure this uplift, which reaches 15 mm in the California Coastal Ranges and Sierra Nevada and has a median value of 4 mm over the entire WUS. The pattern of mass loss due to the drought, which we recover from an inversion of uplift observations, ranges up to 50 cm of water equivalent and is consistent with observed decreases in precipitation and streamflow. We estimate the total deficit to be 240 Gt, equivalent to a uniform 10 cm layer of water over the entire region, or the magnitude of the current annual mass loss from the Greenland Ice Sheet. In the WUS, interannual changes in crustal loading are driven by changes in cool-season precipitation, which cause variations in surface water, snowpack, soil moisture, and groundwater. The results here demonstrate that the existing network of continuous GPS stations can be used to recover loading changes due to both wet and dry climate patterns. This suggests a new role for GPS networks such as that of the Plate Boundary Observatory. The exceptional stability of the GPS monumentation means that this network is also capable of monitoring the long-term effects of regional climate change. Surface displacement observations from GPS have the potential to expand the capabilities of the current hydrological observing network for monitoring current and future hydrological changes, with obvious social and economic benefits.

Unwrapping the diagnosis of tuberculosis in primary care: a qualitative study.

PubMed

Metcalf, Elizabeth P; Davies, Joanne C; Wood, Fiona; Butler, Christopher C

2007-02-01

Although tuberculosis (TB) is relatively rare in the UK, its diagnosis is important because diagnostic delays can result in worse outcomes for patients and expose others to the risk of infection. Atypical presentations may be common, and patients' help-seeking behaviour may influence the diagnostic process in primary care. Little is known about the process of diagnosing TB in primary care in developed countries. To understand the process of diagnosing TB in UK primary care. Qualitative inductive study with paired semi-structured interviews. Communities and general practices in south-east Wales. Interviews were conducted with 17 patients diagnosed with TB in the previous 6 months and 16 GPs involved with their care. Data were analysed thematically. In response to expected classical features, GPs generally ordered specific tests. Both GPs and patients reported atypical presentations, and then the diagnostic and referral net was appropriately widened in most cases. Identified barriers to prompt diagnosis included atypical presentations and low clinical suspicion of TB, lack of continuity of care, workload demands that limit time with patients, and suboptimal clinician-patient communication. GPs recognised the growing problem of TB nationally and the need for improved education among health professionals. GPs' and patients' accounts about the process of diagnosing TB suggest that delays can occur, although they are not typical. Where diagnosis is clear, GPs generally test specifically and refer appropriately; where diagnosis is less clear, the diagnostic net is cast further. It is only when certain core values of general practice are not applied (including continuity of care, considering context appropriately, and eliciting and responding appropriately to patients' explanatory models) that clinicians and patients identify a suboptimal diagnostic process.

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.

Carrier-phase time transfer.

PubMed

Larson, K M; Levine, J

1999-01-01

We have conducted several time-transfer experiments using the phase of the GPS carrier rather than the code, as is done in current GPS-based time-transfer systems. Atomic clocks were connected to geodetic GPS receivers; we then used the GPS carrier-phase observations to estimate relative clock behavior at 6-minute intervals. GPS carrier-phase time transfer is more than an order of magnitude more precise than GPS common view time transfer and agrees, within the experimental uncertainty, with two-way satellite time-transfer measurements for a 2400 km baseline. GPS carrier-phase time transfer has a stability of 100 ps, which translates into a frequency uncertainty of about two parts in 10(-15) for an average time of 1 day.

GPS timing products - Naval Oceanography Portal

Science.gov Websites

section Advanced Search... Sections Home Time Earth Orientation Astronomy Meteorology Oceanography Ice You are here: Home › USNO › Precise Time › GPS USNO Logo USNO Navigation Master Clock GPS Display Clocks TWSTT Telephone Time NTP Info GPS timing products USNO monitors the GPS constellation and provides

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.

Tightly-Coupled Integration of Multi-GNSS Single-Frequency RTK and MEMS-IMU for Enhanced Positioning Performance

PubMed Central

Li, Tuan; Zhang, Hongping; Niu, Xiaoji; Gao, Zhouzheng

2017-01-01

Dual-frequency Global Positioning System (GPS) Real-time Kinematics (RTK) has been proven in the past few years to be a reliable and efficient technique to obtain high accuracy positioning. However, there are still challenges for GPS single-frequency RTK, such as low reliability and ambiguity resolution (AR) success rate, especially in kinematic environments. Recently, multi-Global Navigation Satellite System (multi-GNSS) has been applied to enhance the RTK performance in terms of availability and reliability of AR. In order to further enhance the multi-GNSS single-frequency RTK performance in terms of reliability, continuity and accuracy, a low-cost micro-electro-mechanical system (MEMS) inertial measurement unit (IMU) is adopted in this contribution. We tightly integrate the single-frequency GPS/BeiDou/GLONASS and MEMS-IMU through the extended Kalman filter (EKF), which directly fuses the ambiguity-fixed double-differenced (DD) carrier phase observables and IMU data. A field vehicular test was carried out to evaluate the impacts of the multi-GNSS and IMU on the AR and positioning performance in different system configurations. Test results indicate that the empirical success rate of single-epoch AR for the tightly-coupled single-frequency multi-GNSS RTK/INS integration is over 99% even at an elevation cut-off angle of 40°, and the corresponding position time series is much more stable in comparison with the GPS solution. Besides, GNSS outage simulations show that continuous positioning with certain accuracy is possible due to the INS bridging capability when GNSS positioning is not available. PMID:29077070

Tightly-Coupled Integration of Multi-GNSS Single-Frequency RTK and MEMS-IMU for Enhanced Positioning Performance.

PubMed

Li, Tuan; Zhang, Hongping; Niu, Xiaoji; Gao, Zhouzheng

2017-10-27

Dual-frequency Global Positioning System (GPS) Real-time Kinematics (RTK) has been proven in the past few years to be a reliable and efficient technique to obtain high accuracy positioning. However, there are still challenges for GPS single-frequency RTK, such as low reliability and ambiguity resolution (AR) success rate, especially in kinematic environments. Recently, multi-Global Navigation Satellite System (multi-GNSS) has been applied to enhance the RTK performance in terms of availability and reliability of AR. In order to further enhance the multi-GNSS single-frequency RTK performance in terms of reliability, continuity and accuracy, a low-cost micro-electro-mechanical system (MEMS) inertial measurement unit (IMU) is adopted in this contribution. We tightly integrate the single-frequency GPS/BeiDou/GLONASS and MEMS-IMU through the extended Kalman filter (EKF), which directly fuses the ambiguity-fixed double-differenced (DD) carrier phase observables and IMU data. A field vehicular test was carried out to evaluate the impacts of the multi-GNSS and IMU on the AR and positioning performance in different system configurations. Test results indicate that the empirical success rate of single-epoch AR for the tightly-coupled single-frequency multi-GNSS RTK/INS integration is over 99% even at an elevation cut-off angle of 40°, and the corresponding position time series is much more stable in comparison with the GPS solution. Besides, GNSS outage simulations show that continuous positioning with certain accuracy is possible due to the INS bridging capability when GNSS positioning is not available.

Evaluation of Advanced Access in the National Primary Care Collaborative

PubMed Central

Pickin, Mark; O'Cathain, Alicia; Sampson, Fiona C; Dixon, Simon

2004-01-01

Background: An aim of the National Primary Care Collaborative is to improve quality and access for patients in primary care using principles of Advanced Access. Aims: To determine whether Advanced Access led to improved availability of appointments with general practitioners (GPs) and to examine GPs' views of the process. Design: Observational study. Setting: Four hundred and sixty-two general practices in England participating in four waves of the collaborative during 2000 and 2001. Method: Regression analysis of the collaborative's monthly data on the availability of GP appointments for the 352 practices in waves 1–3, and a postal survey of lead GPs in all four waves. The main outcome measures were the change in mean time to the third available appointment with GPs, and the proportion of GPs thinking it worthwhile participating in the collaborative. Results: The time to the third available appointment improved from a mean of 3.6 to 1.9 days, difference = 1.7 days, 95% confidence interval (CI) = 1.4 to 2.0 days. It improved in two-thirds of practices (66% [219/331]), remained the same in 16% (53/331), and worsened in 18% (59/331). The majority of GPs in all four waves, 83% (308/371, 95% CI = 79 to 87), felt that it was worthwhile participating in the collaborative, although one in 12 practices would not recommend it. One-fifth of GPs cited a lack of resources as a constraint, and some expressed concerns about the trade-off between immediate access and continuity of care. Conclusion: Advanced Access helped practices to improve availability of GP appointments, and was well received by the majority of practices. PMID:15113514

GPS determination of diurnal and semidiurnal variations in earth rotation parameters and the geocenter

NASA Astrophysics Data System (ADS)

Nam, Young-Sun

One year of GPS data collected from the dense, global network of the International GPS Service for Geodynamics (IGS) stations are processed to generate a continuous time series of Earth Rotation Parameters (ERP: Polar Motion and UT1) and Geocenter (GC) with a time resolution of one hour. The spectral analysis of the time series shows that the high-frequency variations in ERP are dominated by the tidal terms at nearly diurnal and semidiurnal frequencies due to ocean tides. The amplitudes and phases of ERP variations at the 8 major diurnal and semidiurnal tidal frequencies (Q 1, O1, P1, K1, N2, M 2, S2 and K2) are estimated and compared with the results from GPS, VLBI, SLR and ocean tide models. The agreement between GPS results from this study and others is about 20 muas for PM and 2 mus for UT1. However, the. GPS results show substantial discrepancies at or near the orbit period, K2 and S2 , and less substantial but considerable discrepancies at or near twice the orbit period, K1 and P 1. The impacts of three different force models---ROCK, RTN and RPR---on the HF-ERP estimation are evaluated. The RTN and RPR model improves the orbit repeatability and accuracy of the HF-ERP/GC estimation. Diurnal and semidiurnal ERP coefficients from the RTN model augmented by the RPR model in semidiurnal retrograde PM is presented as the best GPS HF-ERP model. One year of IGS data with the currently available force models could not successfully determine HF-GC. The annual or semiannual variations in the force parameters as the function of the attitude of the satellite to the Sun are identified. Anomalies in Y-bias during eclipsing season are explained by the effects of noon-turns.

Improving Ambiguity Resolution for Medium Baselines Using Combined GPS and BDS Dual/Triple-Frequency Observations.

PubMed

Gao, Wang; Gao, Chengfa; Pan, Shuguo; Wang, Denghui; Deng, Jiadong

2015-10-30

The regional constellation of the BeiDou navigation satellite system (BDS) has been providing continuous positioning, navigation and timing services since 27 December 2012, covering China and the surrounding area. Real-time kinematic (RTK) positioning with combined BDS and GPS observations is feasible. Besides, all satellites of BDS can transmit triple-frequency signals. Using the advantages of multi-pseudorange and carrier observations from multi-systems and multi-frequencies is expected to be of much benefit for ambiguity resolution (AR). We propose an integrated AR strategy for medium baselines by using the combined GPS and BDS dual/triple-frequency observations. In the method, firstly the extra-wide-lane (EWL) ambiguities of triple-frequency system, i.e., BDS, are determined first. Then the dual-frequency WL ambiguities of BDS and GPS were resolved with the geometry-based model by using the BDS ambiguity-fixed EWL observations. After that, basic (i.e., L1/L2 or B1/B2) ambiguities of BDS and GPS are estimated together with the so-called ionosphere-constrained model, where the ambiguity-fixed WL observations are added to enhance the model strength. During both of the WL and basic AR, a partial ambiguity fixing (PAF) strategy is adopted to weaken the negative influence of new-rising or low-elevation satellites. Experiments were conducted and presented, in which the GPS/BDS dual/triple-frequency data were collected in Nanjing and Zhengzhou of China, with the baseline distance varying from about 28.6 to 51.9 km. The results indicate that, compared to the single triple-frequency BDS system, the combined system can significantly enhance the AR model strength, and thus improve AR performance for medium baselines with a 75.7% reduction of initialization time on average. Besides, more accurate and stable positioning results can also be derived by using the combined GPS/BDS system.

Improving Ambiguity Resolution for Medium Baselines Using Combined GPS and BDS Dual/Triple-Frequency Observations

PubMed Central

Gao, Wang; Gao, Chengfa; Pan, Shuguo; Wang, Denghui; Deng, Jiadong

2015-01-01

The regional constellation of the BeiDou navigation satellite system (BDS) has been providing continuous positioning, navigation and timing services since 27 December 2012, covering China and the surrounding area. Real-time kinematic (RTK) positioning with combined BDS and GPS observations is feasible. Besides, all satellites of BDS can transmit triple-frequency signals. Using the advantages of multi-pseudorange and carrier observations from multi-systems and multi-frequencies is expected to be of much benefit for ambiguity resolution (AR). We propose an integrated AR strategy for medium baselines by using the combined GPS and BDS dual/triple-frequency observations. In the method, firstly the extra-wide-lane (EWL) ambiguities of triple-frequency system, i.e., BDS, are determined first. Then the dual-frequency WL ambiguities of BDS and GPS were resolved with the geometry-based model by using the BDS ambiguity-fixed EWL observations. After that, basic (i.e., L1/L2 or B1/B2) ambiguities of BDS and GPS are estimated together with the so-called ionosphere-constrained model, where the ambiguity-fixed WL observations are added to enhance the model strength. During both of the WL and basic AR, a partial ambiguity fixing (PAF) strategy is adopted to weaken the negative influence of new-rising or low-elevation satellites. Experiments were conducted and presented, in which the GPS/BDS dual/triple-frequency data were collected in Nanjing and Zhengzhou of China, with the baseline distance varying from about 28.6 to 51.9 km. The results indicate that, compared to the single triple-frequency BDS system, the combined system can significantly enhance the AR model strength, and thus improve AR performance for medium baselines with a 75.7% reduction of initialization time on average. Besides, more accurate and stable positioning results can also be derived by using the combined GPS/BDS system. PMID:26528977

What to give the patient who has everything? A qualitative study of prescribing for multimorbidity in primary care.

PubMed

Sinnott, Carol; Hugh, Sheena Mc; Boyce, Maria B; Bradley, Colin P

2015-03-01

Using clinical guidelines in the management of patients with multimorbidity can lead to the prescription of multiple and sometimes conflicting medications. To explore how GPs make decisions when prescribing for multimorbid patients, with a view to informing intervention design. In-depth qualitative interviews incorporating chart-stimulated recall with purposively sampled GPs in the Republic of Ireland. Grounded theory analysis with iterative theory development. Twenty GPs were interviewed about 51 multimorbid cases. In these cases, GPs integrated information from multiple sources including the patient, specialists, and evidence-based medicine. Difficulties arose when recommendations or preferences conflicted, to which GPs responded by 'satisficing': accepting care that they deemed satisfactory and sufficient for a particular patient. Satisficing was manifest as relaxing targets for disease control, negotiating compromise with the patient, or making 'best guesses' about the most appropriate course of action to take. In multimorbid patients perceived as stable, GPs preferred to 'maintain the status quo' rather than rationalise medications, even in cases with significant polypharmacy. Proactive changes in medications were facilitated by continuity of care, sufficient consultation time, and open lines of communication with the patient, other healthcare professionals, and other GPs. GPs respond to conflicts in the management of multimorbid patients by making compromises between patient-centred and evidence-based care. These findings will be used to inform interventions that aim to care in multimorbidity. © British Journal of General Practice 2015.

[The information about discharge medication: what do general practitioners need?].

PubMed

Adam, Henning; Niebling, Wilhelm-Bernhard; Schott, Gisela

2015-04-01

The information about the patient's discharge medication (DM) in the discharge letter guarantees the subsequent pharmacotherapy at the interface between tertiary to primary care. International data however shows that general practitioners (GPs) receive discharge letters with a delay and relevant information about DM is lacking. The aim of this study was to assess the point of view of German GPs concerning the information about DM, since no recent data about this topic is available. In a postal survey 516 GPs in the city of Berlin were contacted and asked about the transit of discharge letters and the information about DM. Results | 117 GPs answered the questionnaire (23 %). Most frequently, the patient himself handed over the information about DM to the GP on the day of his first visit in the practice after discharge. However, more than two third of GPs wished to receive the information before the patient's first consultation (73 %). Therefore, the majority preferred the electronic communication via fax (46 %) or email (9 %). Almost half of the GPs stated that discharge letters were lacking information about changes in medication and reasons for these changes. At the same time, nearly all GPs thought that these informational aspects were important. GPs wish an early and electronic transit of the DM with information concerning changes in medication and reasons. If these wishes were considered, a continuous and thus safer pharmacotherapy at the interface could be guaranteed. © Georg Thieme Verlag KG Stuttgart · New York.

Achieving and Validating the 1-centimeter Orbit: JASON-1 Precision Orbit Determination Using GPS, SLR, DORIS and Altimeter data

NASA Technical Reports Server (NTRS)

Luthcke, Scott B.; Zelensky, Nikita P.; Rowlands, David D.; Lemoine, Frank G.; Williams, Teresa A.

2003-01-01

Jason-1, launched on December 7, 2001, is continuing the time series of centimeter level ocean topography observations as the follow-on to the highly successful TOPEX/POSEIDON (T/P) radar altimeter satellite. The precision orbit determination (POD) is a critical component to meeting the ocean topography goals of the mission. Jason-1 is no exception and has set a 1 cm radial orbit accuracy goal, which represents a factor of two improvement over what is currently being achieved for T/P. The challenge to precision orbit determination (POD) is both achieving the 1 cm radial orbit accuracy and evaluating and validating the performance of the 1 cm orbit. Fortunately, Jason-1 POD can rely on four independent tracking data types including near continuous tracking data from the dual frequency codeless BlackJack GPS receiver. In addition, to the enhanced GPS receiver, Jason-1 carries significantly improved SLR and DORIS tracking systems along with the altimeter itself. We demonstrate the 1 cm radial orbit accuracy goal has been achieved using GPS data alone in a reduced dynamic solution. It is also shown that adding SLR data to the GPS-based solutions improves the orbits even further. In order to assess the performance of these orbits it is necessary to process all of the available tracking data (GPS, SLR, DORIS and altimeter crossover differences) as either dependent or independent of the orbit solutions. It was also necessary to compute orbit solutions using various combinations of the four available tracking data in order to independently assess the orbit performance. Towards this end, we have greatly improved orbits determined solely from SLR+DORIS data by applying the reduced dynamic solution strategy. In addition, we have computed reduced dynamic orbits based on SLR, DORIS and crossover data that are a significant improvement over the SLR and DORIS based dynamic solutions. These solutions provide the best performing orbits for independent validation of the GPS-based reduced dynamic orbits.

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.

Time dependent deformation of Kilauea Volcano, Hawaii

NASA Astrophysics Data System (ADS)

Montgomery-Brown, Emily Kvietka Desmarais

In 1997 the continuous Global Positioning System (GPS) network was completed on Kilauea, providing the first network of daily position measurements during eruptions and earthquakes on Kilauea. Kilauea has been studied for many decades with continuous seismic and tilt instruments. Other geodetic data (e.g., campaign GPS, leveling, electronic distance measurements) are also available although they contain only sparse data. Data analysis methods used here include inverting multiple data sets for optimal source parameters and the spatio-temporal distribution of magma volume and fault slip, and combining GPS and seismic observations to understand flank tectonics. The field area for this study, Kilauea Volcano, was chosen because of its frequent activity and potential hazards. The 1997 East Rift Zone eruption (Episode 54) was the first major event to occur after the completion of the continuous GPS network. The event lasted 2 days, but transient deformation continued for six months. This long-duration transient allowed the first spatio-temporal study of transient dike deformation on Kilauea from daily GPS positions. Slow-slip events were discovered on Kilauea during which the southern flank of the volcano would accelerate seaward for approximately 2 days. The discovery was made possible because of the continuously operating GPS network. These slip events were also observed to correlate with small swarms of microearthquakes found to follow temporal pattern consistent with them being co- and aftershocks of the slow-slip event (Segall, 2006). Half-space models of geodetic data favor a shallow fault plane (˜ 5 km), which is much too shallow to have increased the Coulomb stress at the depths of the co- and aftershocks. However, optimizations for the slow-slip source parameters including a layered elastic structure and a topographic correction favor deeper models within the range of the co- and aftershocks. Additionally, the spatial distribution of seaward fault slip, fixed to a decollement structure 8 km under the south flank, and the locations of the microearthquakes suggest that both occur on the same structure. In 2007, Episode 56 of the Pu'u 'O'o-Kupianaha eruption occurred. This episode was exciting both because it was the largest intrusion in the last decade, and because it occurred concurrently with a flank slow-slip event. The intrusion started on Father's day (June 17th), 2007 with increased seismicity and abrupt tilts at the summit and rift zones. Quasi-static models of the total deformation determined from GPS, tilt, and InSAR indicate that the intrusion occurred on two en echelon dike segments in the upper East Rift Zone along with deformation consistent with slow-slip in the same areas of previous events. The ˜ 2 m maximum opening occurred on the eastern segment near Makaopui crater. Unlike previous intrusions in 1997, 1999, and 2000, the dike model was not sufficient to explain deformation on the western flank. Additionally, a coastal tiltmeter installed in anticipation of a slow-slip event recorded tilts consistent with those observed during the 2005 slow-slip event. These observations led to the conclusion that a concurrent slow-slip event occurred. Geodetic models indicate a similar amount of decollement slip occurred as in previous slow-slip events. Sub-daily GPS positions were used to study the spatio-temporal distribution of the dike intrusion. The time-dependent intrusion model shows that the intrusion began on the western en echelon segment before jumping to the eastern segment, which accumulated the majority of the 2 m of opening. Sub-daily GPS positions limit the number of stations available since there are very few continuous stations north of the East Rift Zone, where coverage is critical for separating the intrusion from the slow-slip. However, an ENVISAT interferogram at 08:22 on June 18, 2007 provides additional spatial coverage of deformation up to that point. Combining this image with the GPS and tilt data up to that point, we perform a quasi-static inversion for the intrusion source. The residual deformation indicates that slow-slip had not significantly progressed by the ENVISAT image. The slow-slip event occurred therefore at least 20 hours after the initiation of the dike intrusion. (Abstract shortened by UMI.)

GPs' perceptions of workload in England: a qualitative interview study.

PubMed

Croxson, Caroline Hd; Ashdown, Helen F; Hobbs, Fd Richard

2017-02-01

GPs report the lowest levels of morale among doctors, job satisfaction is low, and the GP workforce is diminishing. Workload is frequently cited as negatively impacting on commitment to a career in general practice, and many GPs report that their workload is unmanageable. To gather an in-depth understanding of GPs' perceptions and attitudes towards workload. All GPs working within NHS England were eligible. Advertisements were circulated via regional GP e-mail lists and national social media networks in June 2015. Of those GPs who responded, a maximum-variation sample was selected until data saturation was reached. Semi-structured, qualitative interviews were conducted. Data were analysed thematically. In total, 171 GPs responded, and 34 were included in this study. GPs described an increase in workload over recent years, with current working days being long and intense, raising concerns over the wellbeing of GPs and patients. Full-time partnership was generally not considered to be possible, and many participants felt workload was unsustainable, particularly given the diminishing workforce. Four major themes emerged to explain increased workload: increased patient needs and expectations; a changing relationship between primary and secondary care; bureaucracy and resources; and the balance of workload within a practice. Continuity of care was perceived as being eroded by changes in contracts and working patterns to deal with workload. This study highlights the urgent need to address perceived lack of investment and clinical capacity in general practice, and suggests that managing patient expectations around what primary care can deliver, and reducing bureaucracy, have become key issues, at least until capacity issues are resolved. © British Journal of General Practice 2017.

New Estimates of Crustal Velocity in the Solomon Islands

NASA Astrophysics Data System (ADS)

Phillips, D. A.; Bevis, M.; Taylor, F. W.; Papabatu, A. K.; Basi, S.; Kendrick, E.

2002-12-01

We present crustal velocity estimates derived from a dense GPS network in the western Solomon Islands. Initial crustal motion estimates reported by Tregoning et al. (1998) showed convergence between the Australian Plate and the Solomon Arc at the San Cristobal Trench. Active deformation between the Pacific Plate and the Solomon Arc block was also detected. In 1997, we established a continuous GPS (CGPS) site on Guadalcanal and five rover GPS sites in the New Georgia Group. The Guadalcanal site was short-lived due to vandalism so we established a new CGPS site in the New Georgia Group in 1999. The original rover sites were re-occupied in 1999 and 2001. We have analyzed this four-year time series using GAMIT/GLOBK software. Our measurements show convergence with the Australian Plate as well as motion between the Solomon Arc and the Pacific Plate. Possible intra-arc deformation is also observed. Regional tectonic interpretations based upon our GPS measurements and other data will be discussed.

GPS in pioneering dynamic monitoring of long-period structures

USGS Publications Warehouse

Celebi, M.; Sanli, A.

2002-01-01

Global Positioning System (GPS) technology with 10-20-Hz sampling rates allows scientifically justified dynamic measurements of relative displacements of long-period structures. The displacement response of a simulated tall building in real time and permanent deployment of GPS units at the roof of a building are described. To the authors' best knowledge, this is the first permanent deployment of GPS units (in the world) for continuous dynamic monitoring of a tall building. Data recorded from the building during a windy day is analyzed to determine the structural characteristics. When recorded during extreme motions caused by earthquakes and strong winds, such measurements can be used to compute average drift ratios and changes in dynamic characteristics, and therefore can be used by engineers and building owners or managers to assess the structural integrity and performance by establishing pre-established thresholds. Such information can be used to secure public safety and/or take steps to improve the performance of the building.

A low-cost GPS/INS integrated vehicle heading angle measurement system

NASA Astrophysics Data System (ADS)

Wu, Ye; Gao, Tongyue; Ding, Yi

2018-04-01

GPS can provide continuous heading information, but the accuracy is easily affected by the velocity and shelter from buildings or trees. For vehicle systems, we propose a low-cost heading angle update algorithm. Based on the GPS/INS integrated navigation kalman filter, we add the GPS heading angle to the measurement vector, and establish its error model. The experiment results show that this algorithm can effectively improve the accuracy of GPS heading angle.

Comprehensive seismic monitoring of the Cascadia megathrust with real-time GPS

NASA Astrophysics Data System (ADS)

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

2013-12-01

We have developed a comprehensive real-time GPS-based seismic monitoring system for the Cascadia subduction zone based on 1- and 5-second point position estimates computed within the ITRF08 reference frame. A Kalman filter stream editor that uses a geometry-free combination of phase and range observables to speed convergence while also producing independent estimation of carrier phase biases and ionosphere delay pre-cleans raw satellite measurements. These are then analyzed with GIPSY-OASIS using satellite clock and orbit corrections streamed continuously from the International GNSS Service (IGS) and the German Aerospace Center (DLR). The resulting RMS position scatter is less than 3 cm, and typical latencies are under 2 seconds. Currently 31 coastal Washington, Oregon, and northern California stations from the combined PANGA and PBO networks are analyzed. We are now ramping up to include all of the remaining 400+ stations currently operating throughout the Cascadia subduction zone, all of which are high-rate and telemetered in real-time to CWU. These receivers span the M9 megathrust, M7 crustal faults beneath population centers, several active Cascades volcanoes, and a host of other hazard sources. To use the point position streams for seismic monitoring, we have developed an inter-process client communication package that captures, buffers and re-broadcasts real-time positions and covariances to a variety of seismic estimation routines running on distributed hardware. An aggregator ingests, re-streams and can rebroadcast up to 24 hours of point-positions and resultant seismic estimates derived from the point positions to application clients distributed across web. A suite of seismic monitoring applications has also been written, which includes position time series analysis, instantaneous displacement vectors, and peak ground displacement contouring and mapping. We have also implemented a continuous estimation of finite-fault slip along the Cascadia megathrust using a NIF-type approach. This currently operates on the terrestrial GPS data streams, but could readily be expanded to use real-time offshore geodetic measurements as well. The continuous slip distributions are used in turn to compute tsunami excitation and, when convolved with pre-computed, hydrodynamic Green functions calculated using the COMCOT tsunami modeling software, run-up estimates for the entire Cascadia coastal margin. Finally, a suite of data visualization tools has been written to allow interaction with the real-time position streams and seismic estimates based on them, including time series plotting, instantaneous offset vectors, peak ground deformation contouring, finite-fault inversions, and tsunami run-up. This suite is currently bundled within a single client written in JAVA, called ';GPS Cockpit,' which is available for download.

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.

Short-term variations of Icelandic ice cap mass inferred from cGPS coordinate time series

NASA Astrophysics Data System (ADS)

Compton, Kathleen; Bennett, Richard A.; Hreinsdóttir, Sigrún; van Dam, Tonie; Bordoni, Andrea; Barletta, Valentina; Spada, Giorgio

2017-06-01

As the global climate changes, understanding short-term variations in water storage is increasingly important. Continuously operating Global Positioning System (cGPS) stations in Iceland record annual periodic motion—the elastic response to winter accumulation and spring melt seasons—with peak-to-peak vertical amplitudes over 20 mm for those sites in the Central Highlands. Here for the first time for Iceland, we demonstrate the utility of these cGPS-measured displacements for estimating seasonal and shorter-term ice cap mass changes. We calculate unit responses to each of the five largest ice caps in central Iceland at each of the 62 cGPS locations using an elastic half-space model and estimate ice mass variations from the cGPS time series using a simple least squares inversion scheme. We utilize all three components of motion, taking advantage of the seasonal motion recorded in the horizontal. We remove secular velocities and accelerations and explore the impact that seasonal motions due to atmospheric, hydrologic, and nontidal ocean loading have on our inversion results. Our results match available summer and winter mass balance measurements well, and we reproduce the seasonal stake-based observations of loading and melting within the 1σ confidence bounds of the inversion. We identify nonperiodic ice mass changes associated with interannual variability in precipitation and other processes such as increased melting due to reduced ice surface albedo or decreased melting due to ice cap insulation in response to tephra deposition following volcanic eruptions, processes that are not resolved with once or twice-yearly stake measurements.

Toward shared care for people with cancer: developing the model with patients and GPs.

PubMed

Hall, Susan J; Samuel, Leslie M; Murchie, Peter

2011-10-01

The number of people surviving cancer for extended periods is increasing. Consequently, due to workload and quality issues, there is considerable interest in alternatives to traditional secondary care-led cancer follow-up. To explore the views of potential recipients of shared follow-up of cancer. To conduct a modelling exercise for shared follow-up and to explore the opinions and experiences of both the patients and GPs involved. Semi-structured audio-taped telephone or face-to-face interviews were conducted with 18 patients with a range of cancers currently attending for structured follow-up in secondary care. Six GPs and five patients (four with melanoma and one with stable metastatic colorectal cancer) took part in a shared follow-up modelling exercise. During the modelling exercise, the GPs attended 4 review meetings, which included brief training seminars, and at the conclusion 10 individuals took part in semi-structured audio-taped telephone or face-to-face interviews. Many rural patients, and some urban patients, would appreciate follow-up being available nearer to home with the associated benefits of time saved and easier parking and continuity of care. Patients have concerns related to the level of extra training received by the GP and loss of contact with their consultant. GPs have concerns about gaining and maintaining the clinical skills needed to conduct follow-up, especially if the numbers of patients seen are small. They also have concerns about lack of support from other GPs, and some administrative and organizational issues. Many patients would be willing to have GPs share their cancer follow-up with the caveat that they had received extra training and were appropriately supported by secondary care specialists. Patients attending shared care clinics appreciated a local service and longer appointment times. GPs stress the importance of maintaining their own clinical skills and reliable clinical and administrative support from secondary care.

Assessing the performance of the generalized propensity score for estimating the effect of quantitative or continuous exposures on binary outcomes.

PubMed

Austin, Peter C

2018-05-20

Propensity score methods are increasingly being used to estimate the effects of treatments and exposures when using observational data. The propensity score was initially developed for use with binary exposures. The generalized propensity score (GPS) is an extension of the propensity score for use with quantitative or continuous exposures (eg, dose or quantity of medication, income, or years of education). We used Monte Carlo simulations to examine the performance of different methods of using the GPS to estimate the effect of continuous exposures on binary outcomes. We examined covariate adjustment using the GPS and weighting using weights based on the inverse of the GPS. We examined both the use of ordinary least squares to estimate the propensity function and the use of the covariate balancing propensity score algorithm. The use of methods based on the GPS was compared with the use of G-computation. All methods resulted in essentially unbiased estimation of the population dose-response function. However, GPS-based weighting tended to result in estimates that displayed greater variability and had higher mean squared error when the magnitude of confounding was strong. Of the methods based on the GPS, covariate adjustment using the GPS tended to result in estimates with lower variability and mean squared error when the magnitude of confounding was strong. We illustrate the application of these methods by estimating the effect of average neighborhood income on the probability of death within 1 year of hospitalization for an acute myocardial infarction. © 2018 The Authors. Statistics in Medicine published by John Wiley & Sons Ltd.

[Development of an embedded mobile terminal for real-time remote monitoring of out-of-hospital cardiac patients].

PubMed

Xu, Zhi-min; Fang, Zu-Xiang; Lai, Da-Kun; Song, Hai-Lang

2007-05-01

A kind of real-time remote monitoring embedded terminal which is combined with mobile communication technology and GPS localization technology, has been developed. The results of preliminary experiments show that the terminal can transmit ECG signals and localization information in real time and continuously, supply a real-time monitoring of out-of-hospital cardiac patients and trace the patients.

Landslide monitoring using Geocubes, a wireless network of low-cost GPS receivers

NASA Astrophysics Data System (ADS)

Benoit, Lionel; Thom, Christian; Martin, Olivier

2013-04-01

Many geophysical structures such as landslides, glaciers or even volcanoes are features characterized by small extend area and deformation rate in the order of 1 to 10cm per day. Their study needs ever more accurate positioning data with an increased space and time resolution. Using an ublox LEA-6T GPS receiver, the French national mapping agency IGN developed its own wireless multi-sensor geo-monitoring system named Geocube. The basic device is equipped with a GPS and a wireless communication media and can be completed with various sensor modules such as meteorological sensors, ground humidity and pressure or seismograph. Due to the low cost of each receiver, spatial dense surveying networks are deployed. Data are then continuously collected and transmitted to a processing computer in real-time as well as saved in situ on a Micro-SD card. Among them, raw GPS carrier phase data give access to real-time accurate relative positioning on all mesh nodes if small baselines are used. In order to achieve a high accuracy, a dedicated GPS data processing method based on a Kalman filter is proposed. It allows an epoch by epoch positioning providing a high time resolution. Special attention is paid on two points : adaptation to wireless networks of low-cost GPS and real-time ability. A first test of Geocubes usability under field conditions was carried out during summer 2012. A fifteen receivers network was deployed on the landslide of Super-Sauze (French Alps) for a two months trial. The experimental area, the deployed network and the acquisition protocol are presented. Position time series with a 30 seconds sampling rate are then derived from raw data for 10 mobile receivers on a forty days session. A sub-centimetric accuracy on an epoch by epoch positioning is reached despite difficult field conditions due to a 40° elevation mask in the south direction. Then, the measured deformations are compared with in situ rainfall measurements collected by a dedicated sensor added to a Geocube on a network's node.

Landslide monitoring using Geocubes, a wireless network of low-cost GPS receivers.

NASA Astrophysics Data System (ADS)

Benoit, Lionel; Thom, Christian; Martin, Olivier

2013-04-01

Many geophysical structures such as landslides, glaciers or even volcanoes are features characterized by small extend area and deformation rate in the order of 1 to 10cm per day. Their study needs ever more accurate positioning data with an increased space and time resolution. Using an Ublox LEA-6T GPS receiver, the French national mapping agency IGN developed its own wireless multi-sensor geo-monitoring system named Geocube. The basic device is equipped with a GPS and a wireless communication media and can be completed with various sensor modules such as meteorological sensors, ground humidity and pressure or seismograph. Due to the low cost of each receiver, spatial dense surveying networks are deployed. Data are then continuously collected and transmitted to a processing computer in real-time as well as saved in situ on a Micro-SD card. Among them, raw GPS carrier phase data give access to real-time accurate relative positioning on all mesh nodes if small baselines are used. In order to achieve a high accuracy, a dedicated GPS data processing method based on a Kalman filter is proposed. It allows an epoch by epoch positioning providing a high time resolution. Special attention is paid on two points : adaptation to wireless networks of low-cost GPS and real-time ability. A first test of Geocubes usability under field conditions was carried out during summer 2012. A fifteen receivers network was deployed on the landslide of Super-Sauze (French Alps) for a two months trial. The experimental area, the deployed network and the acquisition protocol are presented. Position time series with a 30 seconds sampling rate are then derived from raw data for 10 mobile receivers on a forty days session. A sub-centimetric accuracy on an epoch by epoch positioning is reached despite difficult field conditions due to a 40° elevation mask in the south direction. Then, the measured deformations are compared with in situ rainfall measurements collected by a dedicated sensor added to a Geocube on a network's node.

Analysis of five years of continuous GPS recording at Piton de La Fournaise (R

NASA Astrophysics Data System (ADS)

Peltier, A.; Staudacher, T.; Boissier, P.; Lauret, F.; Kowalski, P.

2009-04-01

A network of twelve permanent GPS stations has been implemented since 2004 at Piton de La Fournaise (hot spot basaltic volcano of La Réunion Island, Indian Ocean) to follow the ground deformation associated with its high eruptive activity. During the period covered by the continuous GPS recording, 12 eruptions occurred. The compilation of the data recorded between 2004 and 2008 allows us to define two time scales of ground deformation systematically associated with this eruptive activity: (1) Large short-term displacements, reaching up to 14 mm/min, monitored a few min to hours prior each eruption during magma injections toward the surface (co-eruptive deformation); (2) But also, small long-term ground displacements recorded during inter-eruptive periods. Between 2 weeks and 5 months before each eruption a slight summit inflation occurs (0.4-0.7 mm/day); whereas a post-eruptive summit deflation lasting 1 to 3 months is only recorded after the largest distal eruptions (0.3 - 1.3 mm/day). These two time scales ground deformation precursors allowed us to forecast all eruptions up to five months in advance. And the follow up of the large short-term displacement in real-time allowed us to evaluated the approximate location of the eruptive fissure a few min to hours before its opening (i.e. inside the summit crater, northern flank or southern flank). The large short-term ground displacements have been attributed to the dyke propagation toward the surface, whereas the long-term ground displacements, which were also recorded by the extensometer network since 2000, have been attributed to a continuous over pressurization of the shallow magma reservoir located at about 2300m depth. The continuous over-pressurization of the shallow magma reservoir would explain the high eruptive activity observed since 1998; 27 eruptions in 10 years.

GPS Position Time Series @ JPL

NASA Technical Reports Server (NTRS)

Owen, Susan; Moore, Angelyn; Kedar, Sharon; Liu, Zhen; Webb, Frank; Heflin, Mike; Desai, Shailen

2013-01-01

Different flavors of GPS time series analysis at JPL - Use same GPS Precise Point Positioning Analysis raw time series - Variations in time series analysis/post-processing driven by different users. center dot JPL Global Time Series/Velocities - researchers studying reference frame, combining with VLBI/SLR/DORIS center dot JPL/SOPAC Combined Time Series/Velocities - crustal deformation for tectonic, volcanic, ground water studies center dot ARIA Time Series/Coseismic Data Products - Hazard monitoring and response focused center dot ARIA data system designed to integrate GPS and InSAR - GPS tropospheric delay used for correcting InSAR - Caltech's GIANT time series analysis uses GPS to correct orbital errors in InSAR - Zhen Liu's talking tomorrow on InSAR Time Series analysis

Non-GPS full position and angular orientation onboard sensors for moving and stationary platforms

NASA Astrophysics Data System (ADS)

Dhadwal, Harbans S.; Rastegar, Jahangir; Feng, Dake; Kwok, Philip; Pereira, Carlos M.

2016-05-01

Angular orientation of both mobile and stationary objects continues to be an ongoing topic of interest for guidance and control as well as for non-GPS based solutions for geolocations of assets in any environment. Currently available sensors, which include inertia devices such as accelerometers and gyros; magnetometers; surface mounted antennas; radars; GPS; and optical line of sight devices, do not provide an acceptable solution for many applications, particularly for gun-fired munitions and for all-weather and all environment scenarios. A robust onboard full angular orientation sensor solution, based on a scanning polarized reference source and a polarized geometrical cavity orientation sensor, is presented. The full position of the object, in the reference source coordinate system, is determined by combining range data obtained using established time-of-flight techniques, with the angular orientation information.

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.

Seafloor horizontal positioning from a continuously operating buoy-based GPS-acoustic array

NASA Astrophysics Data System (ADS)

Chadwell, C. D.; Brown, K. M.; Tryon, M. D.; Send, U.

2009-12-01

Seafloor horizontal positions in a global frame were estimated daily from an autonomous buoy operating continuously over several months. The buoy (GEOCE) was moored offshore San Diego in 100-m-deep waters above an array of 4 seafloor transponders. Dual-frequency GPS data were collected at 1-Hz at a main antenna on the buoy and at 3 shore stations to provide continuous 2-3 cm positions of the buoy main antenna. Two single-frequency antennas on the buoy along with the main antenna were used to estimate the buoy attitude and short-term velocity. At one minute intervals the two-way acoustic travel time was measured between the buoy and transponders. During this few second span when transmitting and receiving acoustic signals, 10-Hz attitude and velocity were collected to locate the position of the transducer mounted approximately 2 m below the water line. The GPS and acoustic data were recorded internally and transmitted to shore over a cell-phone link and/or a wireless Ethernet. GPS data were combined with the acoustic data to estimate the array location at 1 minute intervals. The 1-minute positions are combined to provide a daily estimate of the array position. The buoy is autonomous, solar-powered and in addition to the GPS and acoustic data collects air pressure, temperature, wind speed/direction as well as water level at the surface and conductivity and temperature along the mooring line from near the sea surface to just above the sea floor. Here we report results from the horizontal positioning effort from Phase I of the project in shallow waters. The project also includes a vertical deformation sensor and physical oceanographic monitoring. A deep water (nominally 1000 m) test is planned for 2010. This work is supported by NSF-OCE-0551363 of the Ocean Technology and Interdisciplinary Coordination Program.

Real-Time Detection of Tsunami Ionospheric Disturbances with a Stand-Alone GNSS Receiver: An Integration of GPS and Galileo Systems

NASA Astrophysics Data System (ADS)

Savastano, Giorgio; Komjathy, Attila; Verkhoglyadova, Olga; Wei, Yong; Mazzoni, Augusto; Crespi, Mattia

2017-04-01

Tsunamis can produce gravity waves that propagate up to the ionosphere generating disturbed electron densities in the E and F regions. These ionospheric disturbances are studied in detail using ionospheric total electron content (TEC) measurements collected by continuously operating ground-based receivers from the Global Navigation Satellite Systems (GNSS). Here, we present results using a new approach, named VARION (Variometric Approach for Real-Time Ionosphere Observation), and for the first time, we estimate slant TEC (sTEC) variations in a real-time scenario from GPS and Galileo constellations. Specifically, we study the 2016 New Zealand tsunami event using GNSS receivers with multi-constellation tracking capabilities located in the Pacific region. We compare sTEC estimates obtained using GPS and Galileo constellations. The efficiency of the real-time sTEC estimation using the VARION algorithm has been demonstrated for the 2012 Haida Gwaii tsunami event. TEC variations induced by the tsunami event are computed using 56 GPS receivers in Hawai'i. We observe TEC perturbations with amplitudes up to 0.25 TEC units and traveling ionospheric disturbances moving away from the epicenter at a speed of about 316 m/s. We present comparisons with the real-time tsunami model MOST (Method of Splitting Tsunami) provided by the NOAA Center for Tsunami Research. We observe variations in TEC that correlate well in time and space with the propagating tsunami waves. We conclude that the integration of different satellite constellations is a crucial step forward to increasing the reliability of real-time tsunami detection systems using ground-based GNSS receivers as an augmentation to existing tsunami early warning systems.

Integrity Analysis of Real-Time Ppp Technique with Igs-Rts Service for Maritime Navigation

NASA Astrophysics Data System (ADS)

El-Diasty, M.

2017-10-01

Open sea and inland waterways are the most widely used mode for transporting goods worldwide. It is the International Maritime Organization (IMO) that defines the requirements for position fixing equipment for a worldwide radio-navigation system, in terms of accuracy, integrity, continuity, availability and coverage for the various phases of navigation. Satellite positioning systems can contribute to meet these requirements, as well as optimize marine transportation. Marine navigation usually consists of three major phases identified as Ocean/Coastal/Port approach/Inland waterway, in port navigation and automatic docking with alert limit ranges from 25 m to 0.25 m. GPS positioning is widely used for many applications and is currently recognized by IMO for a future maritime navigation. With the advancement in autonomous GPS positioning techniques such as Precise Point Positioning (PPP) and with the advent of new real-time GNSS correction services such as IGS-Real-Time-Service (RTS), it is necessary to investigate the integrity of the PPP-based positioning technique along with IGS-RTS service in terms of availability and reliability for safe navigation in maritime application. This paper monitors the integrity of an autonomous real-time PPP-based GPS positioning system using the IGS real-time service (RTS) for maritime applications that require minimum availability of integrity of 99.8 % to fulfil the IMO integrity standards. To examine the integrity of the real-time IGS-RTS PPP-based technique for maritime applications, kinematic data from a dual frequency GPS receiver is collected onboard a vessel and investigated with the real-time IGS-RTS PPP-based GPS positioning technique. It is shown that the availability of integrity of the real-time IGS-RTS PPP-based GPS solution is 100 % for all navigation phases and therefore fulfil the IMO integrity standards (99.8 % availability) immediately (after 1 second), after 2 minutes and after 42 minutes of convergence time for Ocean/Coastal/Port approach/Inland waterway, in port navigation and automatic docking, respectively. Moreover, the misleading information is about 2 % for all navigation phases that is considered less safe is not in immediate danger because the horizontal position error is less than the navigation alert limits.

GPS Observations of Postseismic Deformation Associated With the 1994 Northridge Earthquake

NASA Technical Reports Server (NTRS)

Donnellan, A.

1995-01-01

Measurement of postseismic deformation following the 1994 M 6.7 Northridge earthquake indicates continued shortening of the region since the earthquake with motion slowing over a an exponential time scale of 3 years. Afterslip best explains the data, but that is still being tested.

Advancing Technology: GPS and GIS Outreach Training for Agricultural Producers

ERIC Educational Resources Information Center

Flynn, Allison; Arnold, Shannon

2010-01-01

The use of the Global Positioning System (GPS) and Global Information Systems (GIS) has made significant impacts on agricultural production practices. However, constant changes in the technologies require continuing educational updates. The outreach program described here introduces the operation, use, and applications of GPS receivers and GIS…

47 CFR 87.151 - Special requirements for differential GPS receivers.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 47 Telecommunication 5 2011-10-01 2011-10-01 false Special requirements for differential GPS receivers. 87.151 Section 87.151 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND... differential GPS receivers. (a) The receiver shall achieve a message failure rate less than or equal to one...

International developments in revenues and incomes of general practitioners from 2000 to 2010

PubMed Central

2013-01-01

Background The remuneration system of General Practitioners (GPs) has changed in several countries in the past decade. The aim of our study was: to establish the effect of these changes on the revenues and income of GPs in the first decade of the 21st century. Methods Annual GP revenue and practice costs were collected from national institutes in the eight countries included in our study (Belgium, Denmark, Finland, France, Germany, The Netherlands, Sweden, The United Kingdom (UK)) from 2000–2010. The data were corrected for inflation and purchasing power. Data on the remuneration systems and changes herein were collected from the European Observatory Health Systems Reviews and country experts. Results Comprehensive changes in the remuneration system of GPs were associated with considerable changes in GP income. Incremental changes mainly coincided with a gradual increase in income after correction for inflation. Average GP income was higher in countries with a strong primary care structure. Conclusions The gap between the countries where GPs have a lower income (Belgium, Sweden, France and Finland) and the countries where GPs have a higher income (Netherlands, Germany and the UK) continues to exist over time and appeared to be related to dimensions of primary care, such as governance and access. New payment forms, such as integrated care payment systems, and new health care professionals that are working for GPs, increasingly blur the line between practice costs and income, making it more and more important to clearly define expenditures on GPs, to remain sight on the actual income of GPs. PMID:24152337

Analysis of afterslip and viscoelastic relaxation following the 2004 Sumatra-Andaman earthquake from GPS observations in northern Sumatra

NASA Astrophysics Data System (ADS)

Gunawan, E.; Sagiya, T.; Ito, T.; Kimata, F.; Tabei, T.; Ohta, Y.; Meilano, I.; Abidin, H. Z.; Agustan, A.; Nurdin, I.; Sugiyanto, D.

2013-12-01

Global Positioning System (GPS) data in northern Sumatra, Andaman Islands and Thailand provides an opportunity to understand the postseismic deformation associated with the 2004 Sumatra-Andaman earthquake. Previous study of postseismic deformation after the 2004 earthquake reached different conclusions, which attributed to different assumption on the postseismic deformation mechanisms. Also, previous studies use only a certain part (e.g. Andaman Islands only) of observations without investigating postseismic deformation data in northern Sumatra, which is close to the largest coseismic slip rupture of 2004 SAE. In this study, we tackle this problem by taking GPS data in northern Sumatra, Aceh GPS Network for Sumatran Fault System (AGNeSS), into account. AGNeSS data are important because of the following reasons: (1) The network is located in the near-field of the main slip patch of the 2004 SAE. (2) GPS measurements started a few months after the main shock, providing information of early postseismic deformation after the 2004 SAE. (3) Continuous GPS measurements provide a good control on both horizontal and vertical components. (4) GPS data have never been used in analyzing postseismic deformation. The continuous GPS data in northern Sumatra suggest that there are multiple physical mechanisms controls the postseismic deformation, that is afterslip and viscoelastic relaxation. In the first step, we search for the optimum rheology model by fitting vertical component with viscoelastic relaxation model, and consider residual is caused by an afterslip. Using the estimated rheology model, we calculate 'afterslip' displacements by subtracting predicted viscoelastic displacements from observed GPS data, and with these 'afterslip' displacements, we estimate afterslip distribution on the plate interface. Since in the first estimation of the rheology model analyzed displacement data contain afterslip effects, we then correct the afterslip contribution from the original deformation data and estimate the rheology model again. We iterate this calculation process until we obtain the optimum model. By using this strategy, we can calculate joint mechanisms of viscoelastic relaxation and afterslip simultaneously. For viscoelastic relaxation, our best solution yields a rheological structure with elastic layer depth of 65×5 km and a Maxwell viscosity of 8.0×1 x 1e18 Pa s, respectively. The afterslip inversion results shows that major afterslip occurred during two years after the 2004 Sumatra-Andaman earthquake where the maximum slip was approximately 0.9 m occurred between 20 to 40 km depth. Our afterslip patch result showed that it is consistent with the idea of afterslip is driven by the stress change due to the mainshock. We also find that the dominance of viscoelastic relaxation significantly increased, as the afterslip continuously decreased during the four years time periods between 2005.91~2009.87. Finally, our results suggest that our model satisfied observation data in northern Sumatra, however, it poorly fit GPS data in Thailand, respectively.

Feasibility of Construction of the Continuously Operating Geodetic GPS Network of Sinaloa, Mexico

NASA Astrophysics Data System (ADS)

Vazquez, G. E.; Jacobo, C.

2011-12-01

This research is based on the study and analysis of feasibility for the construction of the geodetic network for GPS continuous operation for Sinaloa, hereafter called (RGOCSIN). A GPS network of continuous operation is defined as that materialized structure physically through permanent monuments where measurements to the systems of Global Positioning (GPS) is performed continuously throughout a region. The GPS measurements in this network are measurements of accuracy according to international standards to define its coordinates, thus constituting the basic structure of geodetic referencing for a country. In this context is that in the near future the RGOCSIN constitutes a system state only accurate and reliable georeferencing in real-time (continuous and permanent operation) and will be used for different purposes; i.e., in addition to being fundamental basis for any lifting topographic or geodetic survey, and other areas such as: (1) Different construction processes (control and monitoring of engineering works); (2) Studies of deformation of the Earth's crust (before and after a seismic event); (3) GPS meteorology (weather forecasting); (4) Demarcation projects (natural and political); (5) Establishment of bases to generate mapping (necessary for the economic and social development of the state); (6) Precision agriculture (optimization of economic resources to the various crops); (7) Geographic information systems (Organization and planning activities associated with the design and construction of public services); (8) Urban growth (possible settlements in the appropriate form and taking care of the environmental aspect), among others. However there are criteria and regulations according to the INEGI (Instituto Nacional de Estadística y Geografía, http://www.inegi.org.mx/) that must be met; even for this stage of feasibility of construction that sees this project as a first phase. The fundamental criterion to be taken into account according to INEGI is a geometric distribution appropriate to ensure the state coverage, so the radius of coverage is found in the 10 to 15 Km. station. Likewise INEGI recommends the implementation of GPS measurements a priori in the vertices where at the end of such measurements generate a report by station containing details of the conditions of visibility, the GPS equipment used, the methodology of measurement and field data processing mode and is intended to build the RGOCSIN. Based on the results of the final report for each one of the measures beforehand, it will be or not feasible to determine if it meets these specifications to be finally considered as part of the RGOCSIN. It should be noted that the selection of the potential places where is intended to carry out the study and analysis of feasibility for the construction of the RGOCSIN will be some of the weather stations of the Centro de Investigación en Alimentación y Desarrollo (CIAD) Culiacán (http://www.ciad.edu.mx/clima/pc.asp). These weather stations have some technical infrastructure which would be used in the future; In addition to providing meteorological information which will ensure success in the solution of scientific and technological problems in various sectors requiring our state.

Three Strategies for Delivering Continuing Medical Education in Geriatrics to General Practitioners

ERIC Educational Resources Information Center

Rikkert, Marcel G. M.; Rigaud, Anne-Sophie

2004-01-01

General practitioners (GPs) need advanced skills in geriatric assessment to be competent to treat the increasing number of elderly patients. Continuing medical education in geriatrics for GPs is heterogeneous, and not assessed for effectiveness. In this study we compared the educational effects of three geriatric post-graduate training methods on…

Is participation in research as an investigator an effective form of continuing medical education?

PubMed Central

Huas, D; Wallace, P

2000-01-01

Continuing medical education and research are a daily necessity for general practitioners (GPs). This study investigated the possibility that participation in research is an effective form of continuing medical education. Although there was an indication that some modification of GPs' knowledge and skills had occurred, it was not possible to conclude that this was entirely due to participation in research. PMID:11224971

Precise time dissemination via portable atomic clocks

NASA Technical Reports Server (NTRS)

Putkovich, K.

1982-01-01

The most precise operational method of time dissemination over long distances presently available to the Precise Time and Time Interval (PTTI) community of users is by means of portable atomic clocks. The Global Positioning System (GPS), the latest system showing promise of replacing portable clocks for global PTTI dissemination, was evaluated. Although GPS has the technical capability of providing superior world-wide dissemination, the question of present cost and future accessibility may require a continued reliance on portable clocks for a number of years. For these reasons a study of portable clock operations as they are carried out today was made. The portable clock system that was utilized by the U.S. Naval Observatory (NAVOBSY) in the global synchronization of clocks over the past 17 years is described and the concepts on which it is based are explained. Some of its capabilities and limitations are also discussed.

Does burnout among doctors affect their involvement in patients' mental health problems? A study of videotaped consultations.

PubMed

Zantinge, Else M; Verhaak, Peter F M; de Bakker, Dinny H; van der Meer, Klaas; Bensing, Jozien M

2009-08-26

General practitioners' (GPs') feelings of burnout or dissatisfaction may affect their patient care negatively, but it is unknown if these negative feelings also affect their mental health care. GPs' available time, together with specific communication tools, are important conditions for providing mental health care. We investigated if GPs who feel burnt out or dissatisfied with the time available for their patients, are less inclined to encourage their patients to disclose their distress, and have shorter consultations, in order to gain time and energy. This may result in less psychological evaluations of patients' complaints. We used 1890 videotaped consultations from a nationally representative sample of 126 Dutch GPs to analyse GPs' communication and the duration of their consultations. Burnout was subdivided into emotional exhaustion, depersonalisation and reduced accomplishment. Multilevel regression analyses were used to investigate which subgroups of GPs differed significantly. GPs with feelings of exhaustion or dissatisfaction with the available time have longer consultations compared to GPs without these feelings. Exhausted GPs, and GPs with feelings of depersonalisation, talk more about psychological or social topics in their consultations. GPs with feelings of reduced accomplishment are an exception: they communicate less affectively, are less patient-centred and have less eye contact with their patients compared to GPs without reduced accomplishment.We found no relationship between GPs' feelings of burnout or dissatisfaction with the available time and their psychological evaluations of patients' problems. GPs' feelings of burnout or dissatisfaction with the time available for their patients do not obstruct their diagnosis and awareness of patients' psychological problems. On the contrary, GPs with high levels of exhaustion or depersonalisation, and GPs who are dissatisfied with the available time, sometimes provide more opportunities to discuss mental health problems. This increases the chance that appropriate care will be found for patients with mental health problems. On the other hand, these GPs are themselves more likely to retire, or risk burnout, because of their dissatisfaction. Therefore these GPs may benefit from training or personal coaching to decrease the chance that the process of burnout will get out of hand.

Combined cGPS and InSAR time series for observing subsidence in the southern Central Valley due to groundwater exploitation

NASA Astrophysics Data System (ADS)

Neely, W.; Borsa, A. A.; Silverii, F.

2017-12-01

Recent droughts have increased reliance on groundwater for agricultural production in California's Central Valley. Using Interferometric Synthetic Aperture Radar (InSAR), we observe upwards of 25 cm/yr of subsidence from November 2014 to February 2017 due to intense pumping. However, these observations are contaminated by atmospheric noise and orbital errors. We present a novel method for correcting long wavelength errors in InSAR deformation estimates using time series from continuous Global Positioning System (cGPS) stations within the SAR footprint, which we apply to C-band data from the Sentinel mission. We test our method using 49 SAR acquisitions from the Sentinel 1 satellites and 107 cGPS times series from the Geodesy Advancing Geoscience and EarthScope (GAGE) network in southern Central Valley. We correct each interferogram separately, implementing an intermittent Small Baseline Subset (ISBAS) technique to produce a time series of line-of-sight surface motion from 276 InSAR pairs. To estimate the vertical component of this motion, we remove horizontal tectonic displacements predicted by the Southern California Earthquake Center's (SCEC) Community Geodetic Model. We validate our method by comparing the corrected InSAR results with independent cGPS data and find a marked improvement in agreement between the two data sets, particularly in the deformation rates. Using this technique, we characterize the time evolution of surface vertical deformation in the southern Central Valley related to human exploitation of local groundwater resources. This methodology is applicable to data from other SAR satellites, including ALOS-2 and the upcoming US-India NISAR mission.

Airborne Laser Altimetric Monitoring of the Rapid Evolution of Topography in the Long Valley, CA, Caldera

NASA Technical Reports Server (NTRS)

Rundle, John

1998-01-01

A consortium of investigators from several universities and Government agencies have conducted a series of aircraft topographic surveys over the Long Valley caldera, California. The region has a geologic history of extensive volcanism, and its central dome has recently been undergoing resurgent uplift episodes of up to 4 cm per year, a deformation rate that is still continuing. These surveys were conducted from the NASA WFF T39 jet aircraft, outfitted with a nadir-profiling altimetric laser (ATLAS), a GPS guidance system for in-flight precision navigation, two P-code GPS receivers, a Litton LTN92 inertial unit for attitude determination, and both video and still-frame aerial cameras. In addition, two base-station GPS receivers were deployed for post-flight differential navigation, complementing the permanent GPS station operated on the resurgent dome by JPL, and a kinematic automobile survey of roads crossing the area was conducted, thereby complementing the JPL kinematic GPS surveys of some of the same roads. Precision flying yielded multiple profiles along nearly identical paths, including crossing profiles over selected locations within the caidera and calibration flights over Mono Lake, and Lake Crowley. Data from the most recent survey in 1995 are at this time still being reduced, but the standard error of the mean is very low (< 3 mm), due to the high number of crossover points. We thus intend to evaluate the technique for measuring systematic changes in the dome height over time.

Monitoring Location-Specific Physical Activity via Integration of Accelerometry and Geotechnology Within Patients With or At Risk of Diabetic Foot Ulcers: A Technological Report.

PubMed

Crews, Ryan T; Yalla, Sai V; Dhatt, Navdeep; Burdi, Drew; Hwang, Sungsoon

2017-09-01

Physical activity variability is a risk factor for diabetic foot ulcers (DFU). Geographic context may influence variability. This study developed initial methods for monitoring location-specific physical activity in this population. Secondarily, preliminary comparisons in location-specific physical activity were made between patients at risk versus patients with active DFU. Five at-risk and 5 actively ulcerated patients were monitored continuously for 72 hours with physical activity and GPS monitors. A custom algorithm time synchronized the 2 devices' data. On average for all 10 subjects, 1.5 ± 2.1% of activity lacked a corresponding GPS location. 80 ± 11% of self-reported activity events per subject had a GPS identified location. The GPS identified locations were in agreement with the self-reported locations 98 ± 6% of the time. DFU participants' weight-bearing activity was 188% higher at home than away from home. At-risk participants showed similar weight-bearing activity at home as active DFU participants, however, at-risk participants had 132% more weight-bearing activity away-from-home. Objectively monitoring location-specific physical activity proved feasible. Future studies using such methodology may enhance understanding of pathomechanics and treatment of DFU.

Robust GPS autonomous signal quality monitoring

NASA Astrophysics Data System (ADS)

Ndili, Awele Nnaemeka

The Global Positioning System (GPS), introduced by the U.S. Department of Defense in 1973, provides unprecedented world-wide navigation capabilities through a constellation of 24 satellites in global orbit, each emitting a low-power radio-frequency signal for ranging. GPS receivers track these transmitted signals, computing position to within 30 meters from range measurements made to four satellites. GPS has a wide range of applications, including aircraft, marine and land vehicle navigation. Each application places demands on GPS for various levels of accuracy, integrity, system availability and continuity of service. Radio frequency interference (RFI), which results from natural sources such as TV/FM harmonics, radar or Mobile Satellite Systems (MSS), presents a challenge in the use of GPS, by posing a threat to the accuracy, integrity and availability of the GPS navigation solution. In order to use GPS for integrity-sensitive applications, it is therefore necessary to monitor the quality of the received signal, with the objective of promptly detecting the presence of RFI, and thus provide a timely warning of degradation of system accuracy. This presents a challenge, since the myriad kinds of RFI affect the GPS receiver in different ways. What is required then, is a robust method of detecting GPS accuracy degradation, which is effective regardless of the origin of the threat. This dissertation presents a new method of robust signal quality monitoring for GPS. Algorithms for receiver autonomous interference detection and integrity monitoring are demonstrated. Candidate test statistics are derived from fundamental receiver measurements of in-phase and quadrature correlation outputs, and the gain of the Active Gain Controller (AGC). Performance of selected test statistics are evaluated in the presence of RFI: broadband interference, pulsed and non-pulsed interference, coherent CW at different frequencies; and non-RFI: GPS signal fading due to physical blockage and multipath. Results are presented which verify the effectiveness of these proposed methods. The benefits of pseudolites in reducing service outages due to interference are demonstrated. Pseudolites also enhance the geometry of the GPS constellation, improving overall system accuracy. Designs for pseudolites signals, to reduce the near-far problem associated with pseudolite use, are also presented.

Retirement intentions of general practitioners aged 45-65 years.

PubMed

Brett, Thomas D; Arnold-Reed, Diane E; Hince, Dana A; Wood, Ian K; Moorhead, Robert G

2009-07-20

To ascertain the retirement intentions of a cohort of Australian general practitioners. Postal questionnaire survey of members of four Divisions of General Practice in Western Australia, sent out November 2007 - January 2008. A sample of 178 GPs aged 45-65 years. Intention to work in general practice until retirement; reasons for retiring before age 65 years; factors that might encourage working beyond chosen retirement age; and perceived obstacles to working in general practice. 63% of GPs intended to work to at least age 65 years, with men more likely to retire early. Of 63 GPs intending to retire early, 46% gave pressure of work, exhaustion and burnout as reasons for early retirement. Better remuneration, better staffing levels and more general support were incentives to continue working for 46% of the 64 GPs who responded to the question about incentives, and more flexible working hours, part-time work and reduced workload for 41%. Of 169 participants, 65% gave increasing bureaucracy, poor job satisfaction and disillusionment with the medical system or Medicare as obstacles to working in general practice in Australia, whereas workforce shortage, increasing patient demands and diminishing lifestyle through overwork were obstacles named by 48%. Many GPs are planning to retire early, reflecting an emerging trend among professionals and society generally. Declining job satisfaction, falling workforce numbers, excessive workload and increasing bureaucracy were recurrent concerns of older WA GPs considering premature retirement.

GPS for structural health monitoring - case study on the Basarab overpass cable-stayed bridge

NASA Astrophysics Data System (ADS)

Lepadatu, Alexandru; Tiberius, Christian

2014-04-01

The Basarab cable-stayed bridge is a newly built structure in Bucharest, Romania, which was inaugurated in June 2011. Before the oficial opening, in order to assure its qualification for trafic, it had to pass several loading tests with convoys of trucks and trams. For this, besides a priori evaluation using the Finite Element Method (FEM), levelling and acceleration measurements were made to identify vertical displacements, as well as vibration frequencies of the bridge. The three-day loading trial of the bridge represented a good opportunity for setting-up a GPS campaign for structural monitoring of the Basarab bridge. Taking advantage of the redundancy obtained via simultaneous multi-sensor measurements, it was possible to compare and validate the GPS estimated displacements with both FEM and levelling. Moreover, the dynamic behaviour of the bridge during a dynamic loading test was evaluated using a 20 Hz GPS observation rate and validated afterwards with vibration frequency estimates from acceleration time series. Along with simulations (FEM) and laboratory tests, the in situ monitoring of a structure has a particular importance in establishing the safety of a newly-built structure. Furthermore, in some cases permanent monitoring is needed for safety and economic reasons, especially for strategic structures such as dams and bridges. GPS technology can satisfy this request due to its real-time processing capability and thus it can be looked upon as a new and promising tool for dynamic evaluation of engineering structures. In this contribution we have also assessed the performance of GPS with regard to accuracy and false alarm probability demands for the continuous monitoring of the Basarab cable-stayed bridge.

Characterizing the spatial and temporal activities of free-ranging cows from GPS data

USDA-ARS?s Scientific Manuscript database

Electronic tracking provides a unique way to document animal behavior on a continuous basis. This manuscript describes how uncorrected 1 s GPS fixes can be used to characterize the rate of cow travel (m·s-1) into stationary, foraging and walking activities. Cows instrumented with GPS devices were ...

GPS-UTC Time Synchronization

DTIC Science & Technology

1989-11-01

GPS-UTC TIME SYNCHRONIZATION C. H. MCKENZIE W. A. FEESS R, H. LUCAS H. HOLTZ A. L. SATIN The Aerospace Corporation El Segundo, California...Abstract Two automatic algorithms for synchronizing the GPS time standard to the UTC time standard are evaluated. Both algorithms control GPS-UTC...is required to synchronize its broadcast time standard to within one microsecond o f the time standard maintained by the US Naval Observatory

Test results of the STI GPS time transfer receiver

NASA Technical Reports Server (NTRS)

Hall, D. L.; Handlan, J.; Wheeler, P.

1983-01-01

Global time transfer, or synchronization, between a user clock and USNO UTC time can be performed using the Global Positioning System (GPS), and commercially available time transfer receivers. This paper presents the test results of time transfer using the GPS system and a Stanford Telecommunications, Inc. (STI) Time Transfer System (TTS) Model 502. Tests at the GPS Master Control Site (MCS) in Vandenburg, California and at the United States Naval Observatory (USNO) in Washington, D.C. are described. An overview of GPS, and the STI TTS 502 is presented. A discussion of the time transfer process and test concepts is included.

The work hours of GPs: survey of English GPs.

PubMed

Gravelle, Hugh; Hole, Arne Risa

2007-02-01

There is no current information about the hours worked by English GPs. To compare the reported hours worked by GPs with that of other professions and to explain the variation in GP hours worked and on call. National postal survey of 1871 GPs in February 2004. English general practice. Multiple regression analyses of part-time versus full-time status, hours worked, and hours on call. Full-time male GPs report more hours worked (49.6; 95% CI [confidence interval] = 48.9 to 50.2) than males in other professional occupations (47.9; 95% CI = 47.6 to 48.1) and male managers (49.1; 95% CI = 48.8 to 49.5). Full-time female GPs report fewer hours (43.2; 95% CI = 42.0 to 44.3) than females in other professional occupations (44.7; 95% CI = 44.4 to 45.0) and female managers (44.1; 95% CI = 43.7 to 44.5). The number of hours worked decreased with practice list size, and increased with the number of patients per GP. GPs work longer hours in practices with older patients and with a higher proportion of patients in nursing homes. Fewer hours are worked in practices with higher 'additional needs' payments. Having children under 18 years of age increased the probability that female GPs work part-time but has no effect on the probability of male GPs working part-time. Given full-time/part-time status, having children under 18 years of age reduces the hours of male and female GPs. Male English GPs report longer hours worked than other professional groups and managers. The sex differences between GPs in hours worked are mostly attributable to the differential impact of family circumstances, particularly the number of children they have. Perversely, 'additional needs' payments are higher in practices where GPs work fewer hours.

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.

Calibrating GPS With TWSTFT For Accurate Time Transfer

DTIC Science & Technology

2008-12-01

40th Annual Precise Time and Time Interval (PTTI) Meeting 577 CALIBRATING GPS WITH TWSTFT FOR ACCURATE TIME TRANSFER Z. Jiang1 and...primary time transfer techniques are GPS and TWSTFT (Two-Way Satellite Time and Frequency Transfer, TW for short). 83% of UTC time links are...Calibrating GPS With TWSTFT For Accurate Time Transfer 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT

Present-Day Kinematics of the Central Mediterranean Plate Boundary Region from Large GPS Network Analysis Using the Ambizap Algorithm

NASA Astrophysics Data System (ADS)

D'Anastasio, E.; D'Agostino, N.; Avallone, A.; Blewitt, G.

2008-12-01

The large, recent increase of continuous GPS (CGPS) stations in the Central Mediterranean plate boundary zone offers the opportunity to study in detail the present-day kinematics of this actively deforming region. CGPS data from scientific and commercial networks in the Italian region is now available from more than 350 stations, including more than 130 from the RING network deployed by the Istituto Nazionale di Geofisica e Vulcanologia. The RING stations all have high quality GPS monuments and are co- located with broadband or very broadband seismometers and strong motion sensors. The analysis presented here also uses far-field data to provide reference frame control, bringing the total to over 580 CGPS stations. GPS ambiguity resolution of such a large amount of data presents a serious challenge in terms of processing time. Many scientific GPS data processing software packages address this problem by dividing the network into several clusters. In contrast, this analysis uses the new Ambizap GPS processing algorithm (Blewitt, 2008) to obtain unique, self-consistent daily ambiguity-fixed solutions for the entire network. Ambizap allows for a rapid and multiple reanalysis of large regional networks such the one presented in this work. Tests show that Ambizap reproduces solutions from time-prohibitive full-network ambiguity resolution to much less than 1 mm. Single station GPS data are first processed with the GIPSY-OASIS II software by the precise point positioning (PPP) strategy (Zumberge et al., 1997) using JPL products from ftp://sideshow.jpl.nasa.gov. Integer ambiguity resolution is then applied using Ambizap. The resulting daily solutions are aligned to the ITRF2005 reference frame. Then, using the CATS software (Williams, 2007), time series are cleaned to remove outliers and are analyzed for their noise properties, linear velocities, periodic signals and antenna jumps. Stable plate reference frames are realized by minimizing the horizontal velocities at more than 70 and 20 sites on the Eurasia and Nubia plates, respectively. The daily RMS scatter for the east coordinates (derived from PPP) in this frame is typically in the range 2-4 mm before applying Ambizap, and 1-2 mm after applying Ambizap. The solutions are then evaluated with regard to the numerous scientific motivations behind this project, ranging from the definition of strain distribution and microplate kinematics within the plate boundary, to the evaluation of tectonic strain accumulation on active faults. References: Blewitt, G. (2008), Fixed-point theorems of GPS carrier phase ambiguity resolution and their application to massive network processing: 'Ambizap', J. Geophys. Res., doi:10.1029/2008JB005736, in press. Williams, S.D.P. (2007), CATS: GPS coordinate time series analysis software, GPS solut., doi:10.1007/s10291-007-0086-4 Zumberge, J. F., M. B. Heflin, D. C. Jefferson, M. M. Watkins, and F. H. Webb (1997), Precise point positioning for the efficient and robust analysis of GPS data from large networks, J. Geophys. Res., 102, 5005-501

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.

First results of geodetic deformation monitoring after commencement of CO2 injection at the Aquistore underground CO2 storage site

NASA Astrophysics Data System (ADS)

Craymer, M.; White, D.; Piraszewski, M.; Zhao, Y.; Henton, J.; Silliker, J.; Samsonov, S.

2015-12-01

Aquistore is a demonstration project for the underground storage of CO2 at a depth of ~3350 m near Estevan, Saskatchewan, Canada. An objective of the project is to design, adapt, and test non-seismic monitoring methods that have not been systematically utilized to date for monitoring CO2 storage projects, and to integrate the data from these various monitoring tools to obtain quantitative estimates of the change in subsurface fluid distributions, pressure changes and associated surface deformation. Monitoring methods being applied include satellite-, surface- and wellbore-based monitoring systems and comprise natural- and controlled-source electromagnetic methods, gravity monitoring, continuous GPS, synthetic aperture radar interferometry (InSAR), tiltmeter array analysis, and chemical tracer studies. Here we focus on the GPS, InSAR and gravity monitoring. Five monitoring sites were installed in 2012 and another six in 2013, each including GPS and InSAR corner reflector monuments (some collocated on the same monument). The continuous GPS data from these stations have been processed on a daily basis in both baseline processing mode using the Bernese GPS Software and precise point positioning mode using CSRS-PPP. Gravity measurements at each site have also been performed in fall 2013, spring 2014 and fall 2015, and at two sites in fall 2014. InSAR measurements of deformation have been obtained for a 5 m footprint at each site as well as at the corner reflector point sources. Here we present the first results of this geodetic deformation monitoring after commencement of CO2 injection on April 14, 2015. The time series of these sites are examined, compared and analyzed with respect to monument stability, seasonal signals, longer term trends, and any changes in motion and mass since CO2 injection.

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.

Quake clamps down on slow slip

NASA Astrophysics Data System (ADS)

Wallace, Laura M.; Bartlow, Noel; Hamling, Ian; Fry, Bill

2014-12-01

Using continuous GPS (cGPS) data from the Hikurangi subduction zone in New Zealand, we show for the first time that stress changes induced by a local earthquake can arrest an ongoing slow slip event (SSE). The cGPS data show that the slip rate in the northern portion of the 2013/2014 Kapiti SSE decreased abruptly following a nearby intraslab earthquake. We suggest that deceleration of the Kapiti SSE in early 2014 occurred due to a tenfold increase in the normal stress relative to shear stress in the SSE source, induced by the nearby Mw 6.3 earthquake, consistent with expectations of rate and state friction. Our observation of an abrupt halting/slowing of the SSE in response to stress changes imposed by a local earthquake has implications for the strength of fault zones hosting SSEs and supports the premise that static stress changes are an important ingredient in triggering (or delaying) fault slip.

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.

Continuity of care through medical records--an explorative study on GPs' management considerations.

PubMed

Schers, Henk; van den Hoogen, Henk; Grol, Richard; van den Bosch, Wil

2006-06-01

The growing complexity of care with more professionals involved is a threat to the delivery of coherent and consistent care. Excellent exchange of information between professionals may be a way to maintain continuity of care. Relevant information to be passed over includes thoughts about future management for individual patients. To explore the nature of GPs' thoughts about future management, and to determine the extent to which such thoughts are actually recorded in medical records. Cross-sectional study of 5741 consultations. Thirty GPs from 17 practices in a region in the eastern part of The Netherlands. The GPs responded to an electronic questionnaire, directly after 200 successive consultations. The questionnaire included items on management considerations, consultation characteristics and personal continuity. We compared the data from the questionnaire to the actual recording of management considerations in the patient records. The GPs had management considerations in 66.4% of the consultations, involving mainly considerations about additional testing (15.5%), adjustment of medication (22.5%), alternative treatment plans (18.6%), possible referral (11.8%) and coping behaviour (18.0%). These considerations were seldom recorded in the electronic patient record; additional testing (3.0%) adjustment of medication (2.9%) and alternative treatment plans (4.1%). Surprisingly however, GPs rarely found that management considerations from earlier consultations were lacking in the medical record. GPs often have thoughts on how to deal with this patient, but hardly ever record such considerations. We recommend the development of tools that facilitate the recording of management considerations in electronic patient records.

Assessing the performance of the generalized propensity score for estimating the effect of quantitative or continuous exposures on binary outcomes

PubMed Central

2018-01-01

Propensity score methods are increasingly being used to estimate the effects of treatments and exposures when using observational data. The propensity score was initially developed for use with binary exposures. The generalized propensity score (GPS) is an extension of the propensity score for use with quantitative or continuous exposures (eg, dose or quantity of medication, income, or years of education). We used Monte Carlo simulations to examine the performance of different methods of using the GPS to estimate the effect of continuous exposures on binary outcomes. We examined covariate adjustment using the GPS and weighting using weights based on the inverse of the GPS. We examined both the use of ordinary least squares to estimate the propensity function and the use of the covariate balancing propensity score algorithm. The use of methods based on the GPS was compared with the use of G‐computation. All methods resulted in essentially unbiased estimation of the population dose‐response function. However, GPS‐based weighting tended to result in estimates that displayed greater variability and had higher mean squared error when the magnitude of confounding was strong. Of the methods based on the GPS, covariate adjustment using the GPS tended to result in estimates with lower variability and mean squared error when the magnitude of confounding was strong. We illustrate the application of these methods by estimating the effect of average neighborhood income on the probability of death within 1 year of hospitalization for an acute myocardial infarction. PMID:29508424

General practitioners' management of mental disorders: a rewarding practice with considerable obstacles.

PubMed

Fleury, Marie-Josée; Imboua, Armelle; Aubé, Denise; Farand, Lambert; Lambert, Yves

2012-03-16

Primary care improvement is the cornerstone of current reforms. Mental disorders (MDs) are a leading cause of morbidity worldwide and widespread in industrialised countries. MDs are treated mainly in primary care by general practitioners (GPs), even though the latter ability to detect, diagnose, and treat patients with MDs is often considered unsatisfactory. This article examines GPs' management of MDs in an effort to acquire more information regarding means by which GPs deal with MD cases, impact of such cases on their practices, factors that enable or hinder MD management, and patient-management strategies. This study employs a mixed-method approach with emphasis on qualitative investigation. Based on a previous survey of 398 GPs in Quebec, Canada, 60 GPs representing a variety of practice settings were selected for further study. A 10-minute-long questionnaire comprising 27 items was administered, and 70-minute-long interviews were conducted. Quantitative (SPSS) and qualitative (NVivo) analyses were performed. At least 20% of GP visits were MD-related. GPs were comfortable managing common MDs, but not serious MDs. GPs' based their treatment of MDs on pharmacotherapy, support therapy, and psycho-education. They used clinical intuition with few clinical tools, and closely followed their patients with MDs. Practice features (salary or hourly fees payment; psycho-social teams on-site; strong informal networks), and GPs' individual characteristics (continuing medical education; exposure and interest in MDs; traits like empathy) favoured MD management. Collaboration with psychologists and psychiatrists was considered key to good MD management. Limited access to specialists, system fragmentation, and underdeveloped group practice and shared-care models were impediments. MD management was seen as burdensome because it required more time, flexibility, and emotional investment. Strategies exist to reduce the burden (one-problem-per-visit rule; longer time slots). GPs found MD practice rewarding as patients were seen as grateful and more complying with medical recommendations compared to other patients, generally leading to positive outcomes. To improve MD management, this study highlights the importance of extending multidisciplinary GP practice settings with salary or hourly fee payment; access to psychotherapeutic and psychiatric expertise; and case-discussion training involving local networks of GPs and MD specialists that encourage both knowledge transfer and shared care.

General practitioners' management of mental disorders: A rewarding practice with considerable obstacles

PubMed Central

2012-01-01

Background Primary care improvement is the cornerstone of current reforms. Mental disorders (MDs) are a leading cause of morbidity worldwide and widespread in industrialised countries. MDs are treated mainly in primary care by general practitioners (GPs), even though the latter ability to detect, diagnose, and treat patients with MDs is often considered unsatisfactory. This article examines GPs' management of MDs in an effort to acquire more information regarding means by which GPs deal with MD cases, impact of such cases on their practices, factors that enable or hinder MD management, and patient-management strategies. Methods This study employs a mixed-method approach with emphasis on qualitative investigation. Based on a previous survey of 398 GPs in Quebec, Canada, 60 GPs representing a variety of practice settings were selected for further study. A 10-minute-long questionnaire comprising 27 items was administered, and 70-minute-long interviews were conducted. Quantitative (SPSS) and qualitative (NVivo) analyses were performed. Results At least 20% of GP visits were MD-related. GPs were comfortable managing common MDs, but not serious MDs. GPs' based their treatment of MDs on pharmacotherapy, support therapy, and psycho-education. They used clinical intuition with few clinical tools, and closely followed their patients with MDs. Practice features (salary or hourly fees payment; psycho-social teams on-site; strong informal networks), and GPs' individual characteristics (continuing medical education; exposure and interest in MDs; traits like empathy) favoured MD management. Collaboration with psychologists and psychiatrists was considered key to good MD management. Limited access to specialists, system fragmentation, and underdeveloped group practice and shared-care models were impediments. MD management was seen as burdensome because it required more time, flexibility, and emotional investment. Strategies exist to reduce the burden (one-problem-per-visit rule; longer time slots). GPs found MD practice rewarding as patients were seen as grateful and more complying with medical recommendations compared to other patients, generally leading to positive outcomes. Conclusions To improve MD management, this study highlights the importance of extending multidisciplinary GP practice settings with salary or hourly fee payment; access to psychotherapeutic and psychiatric expertise; and case-discussion training involving local networks of GPs and MD specialists that encourage both knowledge transfer and shared care. PMID:22423592

GPS and InSAR Observations of Active Mountain Growth Across the Sierra Nevada/Great Basin Transition

NASA Astrophysics Data System (ADS)

Hammond, W. C.; Blewitt, G.; Li, Z.; Kreemer, C. W.; Plag, H.

2010-12-01

Topographic relief across the Sierra Nevada Mountains and Great Basin of the western United States is dominated by mountain ranges and valleys that are the product of active tectonic deformation. The contemporary rate of uplift of the Sierra Nevada via slip on range front faults and/or tilting of the Sierra Nevada/Great Valley microplate (SNGV) has been the subject of controversy. For example, geologic estimates of the age of the modern range topography vary by one order of magnitude, from 3 to 30 million years. With present elevations near 3 km, the more rapid of these implied rates is large enough to be detected by the most precise GPS measurements. We use GPS vertical and horizontal components, and InSAR time series analysis to address these long standing questions about the rates of Sierran uplift. The data are from western U.S. high precision GPS networks including the EarthScope Plate Boundary Observatory, its nucleus networks, the University of Nevada Mobile Array of GPS for Nevada Transtension, and from integrated InSAR+GPS time series analysis of ERS and ENVISAT scenes acquired between 1992 and 2010 from the GeoEarthScope and WinSAR data archives. GPS data are processed using the GIPSY OASIS II software, with ambiguities resolved, ocean tidal loading, latest GMF troposphere model and antenna calibrations applied. InSAR time series analysis results provide enhanced geographic resolution, improving our ability to locate the boundary of SNGV block-like behavior. Vertical velocities from long-running continuous stations in eastern Nevada are very similar to one another, averaging -0.1 mm/yr, with standard deviation of 0.27 mm/yr, placing an upper bound on the uncertainty in vertical rates. We find agreement between the results of InSAR time series analysis aligned to GPS and GPS line of site rates at the level of 0.35 mm/yr, placing an upper bound on the uncertainty of InSAR time series results. Because we seek to infer long-term uplift rates, applicable over millions of years, we correct the geodetic velocity field for postseismic transients from earthquakes that can cause long-wavelength distortions of the GPS velocity field. The signal of viscoelastic relaxation from historic earthquakes in Central Nevada is clearly visible in the data. We remove this transient relaxation by subtracting the predictions from a published model, although the effect on SNGV vertical motion is negligible. There is general agreement among stations on the west slope of the Sierra Nevada, near the central and southern Sierra between latitude 36° and 39°, that the rates are between 0.8 and 1.6 mm/yr upward with respect to eastern Nevada. These rates are in broad agreement with normal slip rates on the range front faults along the eastern edge of the SNGV estimated using block models constrained by horizontal GPS measurements. Thus our results agree with models that call for a Sierra Nevada uplift rate near 1 mm/yr, and a younger Sierra Nevada whose age is on the order of 3 Ma.

The association between general practitioner participation in joint teleconsultations and rates of referral: a discrete choice experiment.

PubMed

Cravo Oliveira, Tiago; Barlow, James; Bayer, Steffen

2015-04-21

Joint consultations - such as teleconsultations - provide opportunities for continuing education of general practitioners (GPs). It has been reported this form of interactive case-based learning may lead to fewer GP referrals, yet these studies have relied on expert opinion and simple frequencies, without accounting for other factors known to influence referrals. We use a survey-based discrete choice experiment of GPs' referral preferences to estimate how referral rates are associated with participation in joint teleconsultations, explicitly controlling for a number of potentially confounding variables. We distributed questionnaires at two meetings of the Portuguese Association of General Practice. GPs were presented with descriptions of patients with dermatological lesions and asked whether they would refer based on the waiting time, the distance to appointment, and pressure from patients for a referral. We analysed GPs' responses to multiple combinations of these factors, coupled with information on GP and practice characteristics, using a binary logit model. We estimated the probabilities of referral of different lesions using marginal effects. Questionnaires were returned by 44 GPs, giving a total of 721 referral choices. The average referral rate for the 11 GPs (25%) who had participated in teleconsultations was 68.1% (range 53-88%), compared to 74.4% (range 47-100%) for the remaining physicians. Participation in teleconsultations was associated with reductions in the probabilities of referral of 17.6% for patients presenting with keratosis (p = 0.02), 42.3% for psoriasis (p < 0.001), 8.4% for melanoma (p = 0.14), and 5.4% for naevus (p = 0.19). The results indicate that GP participation in teleconsultations is associated with overall reductions in referral rates and in variation across GPs, and that these effects are robust to the inclusion of other factors known to influence referrals. The reduction in range, coupled with different effects for different clinical presentations, may suggest an educational effect. However, more research is needed to establish whether there are causal relationships between participation in teleconsultations, continuing education, and referral rates.

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.

Results of an Internet-Based Dual-Frequency Global Differential GPS System

NASA Technical Reports Server (NTRS)

Muellerschoen, R.; Bertiger, W.; Lough, M.

2000-01-01

Observables from a global network of 18 GPS receivers are returned in real-time to JPL over the open Internet. 30 - 40 cm RSS global GPS orbits and precise dual-frequency GPS clocks are computed in real-time with JPL's Real Time Gipsy (RTG) software.

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.

Research on the impact factors of GRACE precise orbit determination by dynamic method

NASA Astrophysics Data System (ADS)

Guo, Nan-nan; Zhou, Xu-hua; Li, Kai; Wu, Bin

2018-07-01

With the successful use of GPS-only-based POD (precise orbit determination), more and more satellites carry onboard GPS receivers to support their orbit accuracy requirements. It provides continuous GPS observations in high precision, and becomes an indispensable way to obtain the orbit of LEO satellites. Precise orbit determination of LEO satellites plays an important role for the application of LEO satellites. Numerous factors should be considered in the POD processing. In this paper, several factors that impact precise orbit determination are analyzed, namely the satellite altitude, the time-variable earth's gravity field, the GPS satellite clock error and accelerometer observation. The GRACE satellites provide ideal platform to study the performance of factors for precise orbit determination using zero-difference GPS data. These factors are quantitatively analyzed on affecting the accuracy of dynamic orbit using GRACE observations from 2005 to 2011 by SHORDE software. The study indicates that: (1) with the altitude of the GRACE satellite is lowered from 480 km to 460 km in seven years, the 3D (three-dimension) position accuracy of GRACE satellite orbit is about 3˜4 cm based on long spans data; (2) the accelerometer data improves the 3D position accuracy of GRACE in about 1 cm; (3) the accuracy of zero-difference dynamic orbit is about 6 cm with the GPS satellite clock error products in 5 min sampling interval and can be raised to 4 cm, if the GPS satellite clock error products with 30 s sampling interval can be adopted. (4) the time-variable part of earth gravity field model improves the 3D position accuracy of GRACE in about 0.5˜1.5 cm. Based on this study, we quantitatively analyze the factors that affect precise orbit determination of LEO satellites. This study plays an important role to improve the accuracy of LEO satellites orbit determination.

The Plate Boundary Observatory: Current status and plans for the next five years

NASA Astrophysics Data System (ADS)

Mattioli, G. S.; Feaux, K.; Meertens, C. M.; Mencin, D.; Miller, M.

2013-12-01

UNAVCO currently operates and maintains the NSF-funded Plate Boundary Observatory (PBO), which is the geodetic facility of EarthScope. PBO was designed and built from 2003 to 2008 with $100M investment from the NSF Major Research Equipment and Facilities Construction (MREFC) Program. UNAVCO operated and maintained PBO under a Cooperative Agreement (CA) with NSF from 2008 to 2013 and will continue PBO O&M for the next five years as part of the new Geodesy Advancing Geosciences and EarthScope (GAGE) Facility. PBO is largest continuous GPS and borehole geophysical network in the Americas, with 1100 continuous Global Positioning System (cGPS) sites, including several with multiple monuments, 79 boreholes, with 75 tensor strainmeters, 78 short-period, 3-component seismometers, and pore pressure sensors at 23 sites. PBO also includes 26 tiltmeters deployed at volcanoes in Alaska, Mt St Helens, and Yellowstone caldera and 6 long-baseline laser strainmeters. Surface meteorological sensors are collocated at 154 GPS sites. UNAVCO provides high-rate (1 Hz), low-latency (<1 s) GPS data streams (RT-GPS) from 382 stations in PBO. UNAVCO has delivered over 62 Tb of geodetic data to the EarthScope community since its PBO's inception in 2004. Over the past year, data return for the cGPS component of PBO is 98%, well above the data return metric of 85% set by the NSF, a result of efforts to upgrade power systems and communications infrastructure. In addition, PBO has set the standard for the design, construction, and operation of other multi-hazard networks across the Americas, including COCONet in the Caribbean region and TLALOCNet in Mexico. Funding to support ongoing PBO O&M has declined from FY2012 CA levels under the new GAGE Facility. The implications for data return and data quality metrics as well as replacement of aging PBO GPS instruments with GNSS-compatible systems are as yet unknown. A process to assess the cost of specific PBO components, data rates, enhanced capabilities, and method of delivery (i.e. continuous streams vs. archived files) relative to their scientific value will be proposed. In addition, options to partner with other federal mission-oriented agencies and possible commercial ventures also will be discussed. 1100 station PBO continuous GPS Network.

Investigation of correlation of the variations in land subsidence (detected by continuous GPS measurements) and methodological data in the surrounding areas of Lake Urmia

NASA Astrophysics Data System (ADS)

Moghtased-Azar, K.; Mirzaei, A.; Nankali, H. R.; Tavakoli, F.

2012-11-01

Lake Urmia, a salt lake in the north-west of Iran, plays a valuable role in the environment, wildlife and economy of Iran and the region, but now faces great challenges for survival. The Lake is in immediate and great danger and is rapidly going to become barren desert. As a result, the increasing demands upon groundwater resources due to expanding metropolitan and agricultural areas are a serious challenge in the surrounding regions of Lake Urmia. The continuous GPS measurements around the lake illustrate significant subsidence rate between 2005 and 2009. The objective of this study was to detect and specify the non-linear correlation of land subsidence and temperature activities in the region from 2005 to 2009. For this purpose, the cross wavelet transform (XWT) was carried out between the two types of time series, namely vertical components of GPS measurements and daily temperature time series. The significant common patterns are illustrated in the high period bands from 180-218 days band (~6-7 months) from September 2007 to February 2009. Consequently, the satellite altimetry data confirmed that the maximum rate of linear trend of water variation in the lake from 2005 to 2009, is associated with time interval from September 2007 to February 2009. This event was detected by XWT as a critical interval to be holding the strong correlation between the land subsidence phenomena and surface temperature. Eventually the analysis can be used for modeling and prediction purposes and probably stave off the damage from subsidence phenomena.

Investigating Atmospheric Rivers using GPS PW from Ocean Transits

NASA Astrophysics Data System (ADS)

Almanza, V.; Foster, J. H.; Businger, S.

2014-12-01

Atmospheric Rivers (AR) can be described as a long narrow feature within a warm conveyor belt where anomalous precipitable water (PW) is transported from low to high latitudes. Close monitoring of ARs is heavily reliant on satellites, which are limited both in space and time, to capture the fluctuations PW particularly over the ocean. Ship-based Global Positioning System (GPS) receivers have been successful in obtaining millimeter PW accuracy within 100 km from the nearest ground-based reference receiver at a 30 second sampling rate. We extended this capability with a field experiment using ship-based GPS PW on board a cargo ship to traverse over the Eastern Pacific Ocean. In one 14-day cruise cycle, between the periods of February 3-16, 2014, the ship-based GPS captured PW spikes >50 mm during the early development of two ARs, which lead to moderate to heavy rainfall events for Hawaii and flood conditions along the West Coast of the United States. Comparisons between PW solutions processed using different GPS reference sites at distances 100-2000 km provided an internal validation for the ship-based GPS PW with errors typically less than 5 mm. Land-based observations provided an external validation and are in good agreement with ship-based GPS PW at distances <100 km from the coast, a zone heavily trafficked by cargo containers and a challenge area for satellite retrievals. From these preliminary results, commercial ship-based GPS receivers offer an extremely cost-effective approach for acquiring continuous meteorological observations over the oceans, which can provide important calibration/validation data for satellite retrieval algorithms. Ship-based systems could be particularly useful for augmenting our meteorological observing networks to improve weather prediction and nowcasting, which in turn provide critical support for hazard response and mitigation efforts in coastal regions.

Detection of Natural Hazards Generated TEC Perturbations and Related New Applications

NASA Astrophysics Data System (ADS)

Komjathy, A.; Yang, Y.; Langley, R. B.

2013-12-01

Natural hazards, including earthquakes, volcanic eruptions, and tsunamis, have been significant threats to humans throughout recorded history. The Global Positioning System satellites have become primary sensors to measure signatures associated with such natural hazards. These signatures typically include GPS-derived seismic deformation measurements, co-seismic vertical displacements, and real-time GPS-derived ocean buoy positioning estimates. Another way to use GPS observables is to compute the ionospheric total electron content (TEC) to measure and monitor post-seismic ionospheric disturbances caused by earthquakes, volcanic eruptions, and tsunamis. Research at the University of New Brunswick (UNB) laid the foundations to model the three-dimensional ionosphere at NASA's Jet Propulsion Laboratory by ingesting ground- and space-based GPS measurements into the state-of-the-art Global Assimilative Ionosphere Modeling (GAIM) software. As an outcome of the UNB and NASA research, new and innovative GPS applications have been invented including the use of ionospheric measurements to detect tiny fluctuations in the GPS signals between the spacecraft and GPS receivers caused by natural hazards occurring on or near the Earth's surface. This continuing research is expected to provide early warning for tsunamis, earthquakes, volcanic eruptions, and meteor impacts, for example, using GPS and other global navigation satellite systems. We will demonstrate new and upcoming applications including recent natural hazards and artificial explosions that generated TEC perturbations to perform state-of-the-art imaging and modeling of earthquakes, tsunamis and meteor impacts. By studying the propagation properties of ionospheric perturbations generated by natural hazards along with applying sophisticated first-principles physics-based modeling, we are on track to develop new technologies that can potentially save human lives and minimize property damage.

A survey of the assessment and management of gout in general practitioners and medical officers within the Illawarra Network, Australia.

PubMed

Terrill, Matthew; Riordan, John

2017-08-01

To review the assessment and management of gout by general practitioners (GPs) and medical officers (MOs) within the Illawarra Network, Australia. A survey was sent to GPs and MOs within the Illawarra Network. Of 110 GPs, 45 responded. Of 129 MOs, 42 responded. The overall response was 32.6%. On analysis, 65.1% felt their knowledge of gout to be adequate and 61.6% thought they had been educated well. In acute assessment, 59.1% of GPs responded that the diagnosis of gout best be confirmed with a joint aspiration and 36.4% clinical suspicion. Differing, 85.7% of MOs chose a joint aspiration. In acute management, if colchicine were used, 59.1% of GPs would give 1 mg followed by 0.5 mg an hour later, then 0.5 mg twice daily, compared to 9.5% of MOs, while 20.5% of GPs would use 1 mg twice daily. Chronic management was answered poorly. After an acute attack, urate lowering therapy (ULT) would be started 14 days after by 47.7% of GPs, compared to 69.0% of MOs. GPs were more likely to start ULT within 7 days (52.3% vs. 31.0%). With dosing of ULT, 45.3% would treat to target, while 46.5% would dose to the creatinine clearance. Prophylactic therapy with ULT would be started by 81.8%, although only 17.4% would continue it for 3-6 months. There is poor adherence to recommended practice for dosing of colchicine in acute gout. Also in the management of chronic gout, in particular, the timing of starting ULT and the use of prophylaxis when initiating ULT. © 2016 Asia Pacific League of Associations for Rheumatology and John Wiley & Sons Australia, Ltd.

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.

An Analysis Of The Gps R and D Program As A Case Study Illustrating Dod R and D And Its Associated Successes To Justify The Continued Investments Into And Sustainment Of Dod R and D Budgets

DTIC Science & Technology

2016-09-01

Global Positioning System (GPS). • DOD R&D budget analysis • GPS case study analysis These research areas will support the thesis on the defense... CASE STUDY ANALYSIS As successful as GPS has been on both the battlefield and in worldwide civilian life, the end state wasn’t realized when the...NAVAL POSTGRADUATE SCHOOL MONTEREY, CALIFORNIA JOINT APPLIED PROJECT AN ANALYSIS OF THE GPS R&D PROGRAM AS A CASE STUDY

Quantifying movement demands of AFL football using GPS tracking.

PubMed

Wisbey, Ben; Montgomery, Paul G; Pyne, David B; Rattray, Ben

2010-09-01

Global positioning system (GPS) monitoring of movement patterns is widespread in elite football including the Australian Football League (AFL). However documented analysis of this activity is lacking. We quantified the movement patterns of AFL football and differences between nomadic (midfield), forward and defender playing positions, and determined whether the physical demands have increased over a four season period. Selected premiership games were monitored during the 2005 (n=80 game files), 2006 (n=244), 2007 (n=632) and 2008 (n=793) AFL seasons. Players were fitted with a shoulder harness containing a GPS unit. GPS data were downloaded after games and the following measures extracted: total distance (km), time in various speed zones, maximum speed, number of surges, accelerations, longest continuous efforts and a derived exertion index representing playing intensity. In 2008 nomadic players covered per game 3.4% more total distance (km), had 4.8% less playing time (min), a 17% higher exertion index (per min), and 23% more time running >18kmh(-1) than forwards and defenders (all p<0.05). Physical demands were substantially higher in the 2008 season compared with 2005: an 8.4% increase in mean speed, a 14% increase in intensity (exertion index) and a 9.0% decrease in playing time (all p<0.05). Nomadic players in AFL work substantially harder than forwards and defenders in covering more ground and at higher running intensities. Increases in the physical demands of AFL football were evident between 2005 and 2008. The increasing speed of the game has implications for game authorities, players and coaching staff.

General practitioners’ experiences using cognitive behavioural therapy in general practice: A qualitative study

PubMed Central

Aschim, Bente; Lundevall, Sverre; Martinsen, Egil W.; Frich, Jan C.

2011-01-01

Objective To explore GPs’ experiences using cognitive behavioural therapy (CBT), with a focus on factors that promote or limit the use of CBT in general practice. Design Qualitative study using data from written evaluation reports and focus-group interviews. Setting Norwegian general practice. Subjects GPs who participated in a longitudinal CBT course in the continuous medical education (CME) programme for GPs in Norway, of whom 19 filled in evaluation forms and 15 participated in focus-group interviews. Main outcome measures Experiences with the use of CBT in general practice. Results GPs used CBT mainly in the treatment of patients with anxiety disorders and depression. Factors that promoted the use of CBT in general practice were structured supervision and group counselling, receiving feedback on individual video-recorded consultations, and experiencing that one mastered the therapeutic techniques. Limiting factors were that it took some time before one mastered the techniques, lack of eligible patients, constraints related to attending group supervision during office hours, and the lack of financial incentives to use CBT in general practice. Conclusion Tailored training programmes in CBT for GPs may contribute to more frequent use of CBT in general practice. A formal recognition of CBT in the reimbursement scheme for GPs might counter limiting factors to an increased use of CBT in general practice. PMID:21861599

Evaluation of the Time and Frequency Transfer Capabilities of a Network of GNSS Receivers Located in Timing Laboratories

DTIC Science & Technology

2009-11-01

metrology, different techniques are used for time and frequency transfer, basically TWSTFT (Two-Way Satellite Time and Frequency Transfer), GPS CV (Common...traditional GPS/GLONASS CV/AV receivers and TWSTFT equipment. Time and frequency transfer using GPS code and carrier-phase is an important...or mixing GPS geodetic results with other independent techniques, such as the TWSTFT . 41 st Annual Precise Time and Time Interval (PTTI

Quality improvement competency gaps in primary care in Albanian, polish and slovenian contexts: a study protocol.

PubMed

Czabanowska, Katarzyna; Burazeri, Genc; Klemenc-Ketis, Zalika; Kijowska, Violetta; Tomasik, Tomasz; Brand, Helmut

2012-12-01

Nowadays, general practitioners (GPs) and family doctors (FDs) face increasing demands, as a consequence of complex patients' expectations, developments in science and technology, and limitations within healthcare systems which can result in competency gaps. Therefore, there is a need to identify which competencies in quality improvement (QI) are most important for GPs and FDs to possess in order to meet the demands of contemporary health care practice. To date, however, little information is available on the self-assessment of competencies related to QI among GPs and FDs. To deal with these issues, a project on QI in continuous medical education was launched in 2011. The project aims to broaden the GPs'/ FDs' continuous education offer, its quality and attractiveness, as well as provide them with opportunities for vocational advancement and enable the development of common, European frame of reference for GPs'/FDs' occupational competencies. The third work package of the project consists of the validation research of the questionnaire developed on the basis of the competency framework in QI for GPs/FDs in Europe. A cross-sectional study will be carried out using the self-assessment QI questionnaire which was originally developed in English and subsequently it was cross-culturally adapted in Slovenian, Albanian and Polish settings by use of a pilot study on a conveniently selected group of FDs/GPs (N=10) in each participating country. The final version of the questionnaire will be administered to large samples in each country involved in the survey. Two weeks after the first administration of the questionnaire, a second round, with the same procedure and including the same group of respondents, will follow. Psychometric tests will be conducted including internal consistency (after the initial and subsequent application of the instrument) and stability over time (two-week test-retest reliability). This self-assessment study will demonstrate the complex environment in which general practice/family medicine operates and, eventually, this gap analysis will set out strategically important areas for collaborative efforts related to QI in primary care. The authors consider that the study should be extended to other European countries to help identify most required competencies that GPs/FDs should possess in Europe and thus stir system and educational debate around QI curricula and training for primary care in Europe.

UK GPs' and practice nurses' views of continuity of care for patients with type 2 diabetes.

PubMed

Alazri, Mohammed H; Heywood, Philip; Neal, Richard D; Leese, Brenda

2007-04-01

Continuity of care is widely regarded as a core value of primary care. Type 2 diabetes is a common chronic disease with major health, social and economic impacts. Primary health care professionals in many countries are involved in the management of patients with type 2 diabetes, but their perspectives on continuity remain neglected in research. To explore UK GPs' and nurses' experiences of continuity of care for patients with type 2 diabetes in primary care settings. Semi-structured individual interviews were conducted with 16 GPs and 18 practice nurses who manage patients with type 2 diabetes recruited from 20 practices with various organizational structures in Leeds, UK. Three types of continuities were identified: relational continuity from the same health care professional, team continuity from a group of health care professionals and cross-boundary continuity across primary-secondary care settings. Relational continuity was influenced by the quality of the patient-health care professional relationship, policy of the National Health Service (NHS) in the UK (new General Medical Services contract), walk-in centres, the behaviour of receptionists and the structure and systems of the practice. Team and cross-boundary continuities were influenced by the relationship between team members and by effective communication. Relational continuity contributed to more 'personal care', but the usual health care professional might know less about diabetes. Team continuity was important in providing 'physical care', but patients could be confused by conflicting advice from different professionals. Cross-boundary continuity helps to provide 'expert advice', but is dependent upon effective communication. GPs and practice nurses dealing with patients with type 2 diabetes identified three types of continuities, each influenced by several factors. Relational continuity deals better with psychosocial care while team continuity promotes better physical care; therefore, imposing one type of continuity may inhibit good diabetic care. Cross-boundary continuity between primary and secondary care is fundamental to contemporary diabetic services and ways should be found to achieve more effective communication.

Children's GPS-determined versus self-reported transport in leisure time and associations with parental perceptions of the neighborhood environment.

PubMed

Vanwolleghem, Griet; Schipperijn, Jasper; Gheysen, Freja; Cardon, Greet; De Bourdeaudhuij, Ilse; Van Dyck, Delfien

2016-05-05

This study aimed to examine both GPS-determined and self-reported walking, cycling and passive transport in leisure time during week- and weekend-days among 10 to 12-year old children. Comparisons between GPS-determined and self-reported transport in leisure time were investigated. Second, associations between parental perceptions of the neighborhood environment and GPS-determined walking, cycling and passive transport in leisure time were studied. Children (10 to 12-years old; n = 126) wore a GPS device and an accelerometer for 7 consecutive days to assess objectively measured transport in leisure time and filled out a diary to assess self-reported transport in leisure time. Parents completed a questionnaire to assess parental perceptions of the neighborhood environment. Pearson correlations and t-tests were used to test for concurrent validity and differences between GPS-determined and self-reported transport in leisure time. Generalized linear models were used to determine the associations between the parental perceptions of the neighborhood environment and GPS-determined transport in leisure time. Overall, children under-reported their walking and cycling in leisure time, compared to GPS-determined measures (all p values <0.001). However, children reported their passive transport in leisure time during weekend days quite accurate. GPS-determined measures revealed that children walked most during weekdays (M = 3.96 trips/day; 26.10 min/day) and used passive transport more frequently during weekend days (M = 2.12 trips/day; 31.39 min/day). Only a few parental perceived environmental attributes of the neighborhood (i.e. residential density, land use mix access, quality and availability of walking and cycling facilities, and aesthetics) were significantly associated with children's GPS-determined walking, cycling or passive transport in leisure time. To accurately assess children's active transport in leisure time, GPS measures are recommended over self-reports. More research using GPS with a focus on children's transport in leisure time and investigating the associations with parental perceptions of the neighborhood environment is needed to confirm the results of the present study.

Localization Based on Magnetic Markers for an All-Wheel Steering Vehicle

PubMed Central

Byun, Yeun Sub; Kim, Young Chol

2016-01-01

Real-time continuous localization is a key technology in the development of intelligent transportation systems. In these systems, it is very important to have accurate information about the position and heading angle of the vehicle at all times. The most widely implemented methods for positioning are the global positioning system (GPS), vision-based system, and magnetic marker system. Among these methods, the magnetic marker system is less vulnerable to indoor and outdoor environment conditions; moreover, it requires minimal maintenance expenses. In this paper, we present a position estimation scheme based on magnetic markers and odometry sensors for an all-wheel-steering vehicle. The heading angle of the vehicle is determined by using the position coordinates of the last two detected magnetic markers and odometer data. The instant position and heading angle of the vehicle are integrated with an extended Kalman filter to estimate the continuous position. GPS data with the real-time kinematics mode was obtained to evaluate the performance of the proposed position estimation system. The test results show that the performance of the proposed localization algorithm is accurate (mean error: 3 cm; max error: 9 cm) and reliable under unexpected missing markers or incorrect markers. PMID:27916827

Barriers and facilitators to using a web-based tool for diagnosis and monitoring of patients with depression: a qualitative study among Danish general practitioners.

PubMed

Krog, Mette Daugbjerg; Nielsen, Marie Germund; Le, Jette Videbæk; Bro, Flemming; Christensen, Kaj Sparle; Mygind, Anna

2018-06-27

Depression constitutes a significant part of the global burden of diseases. General practice plays a central role in diagnosing and monitoring depression. A telemedicine solution comprising a web-based psychometric tool may reduce number of visits to general practice and increase patient empowerment. However, the current use of telemedicine solutions in the field of general practice is limited. This study aims to explore barriers and facilitators to using a web-based version of the Major Depression Inventory (eMDI) for psychometric testing of potentially depressive patients in general practice. Semi-structured individual interviews were conducted with nine general practitioners (GPs) from eight general practices in the Central Denmark Region. All interviewees had previous experience in using the eMDI in general practice. Determinants for using the eMDI were identified in relation to the GPs' capability, opportunity and motivation to change clinical behaviour (the COM-B system). Our results indicate that the main barriers for using the eMDI are related to limitations in the GPs' opportunity in regards to having the time it takes to introduce change. Further, the use of the eMDI seems to be hampered by the time-consuming login process. Facilitating factors included behavioural aspects of capability, opportunity and motivation. The implementation of the eMDI was facilitated by the interviewees' previous familiarity with the paper-based version of the tool. Continued use of the eMDI was facilitated by a time-saving documentation process and motivational factors associated with clinical core values. These factors included perceptions of improved consultation quality and services for patients, improved possibilities for GPs to prioritise their patients and improved possibilities for disease monitoring. Furthermore, the flexible nature of the eMDI allowed the GPs to use the paper-based MDI for patients whom the eMDI was not considered appropriate. Implementation of a telemedicine intervention in general practice can be facilitated by resemblance between the intervention and already existing tools as well as the perception among GPs that the intervention is time-saving and improves quality of care for the patients.

Real-time, autonomous precise satellite orbit determination using the global positioning system

NASA Astrophysics Data System (ADS)

Goldstein, David Ben

2000-10-01

The desire for autonomously generated, rapidly available, and highly accurate satellite ephemeris is growing with the proliferation of constellations of satellites and the cost and overhead of ground tracking resources. Autonomous Orbit Determination (OD) may be done on the ground in a post-processing mode or in real-time on board a satellite and may be accomplished days, hours or immediately after observations are processed. The Global Positioning System (GPS) is now widely used as an alternative to ground tracking resources to supply observation data for satellite positioning and navigation. GPS is accurate, inexpensive, provides continuous coverage, and is an excellent choice for autonomous systems. In an effort to estimate precise satellite ephemeris in real-time on board a satellite, the Goddard Space Flight Center (GSFC) created the GPS Enhanced OD Experiment (GEODE) flight navigation software. This dissertation offers alternative methods and improvements to GEODE to increase on board autonomy and real-time total position accuracy and precision without increasing computational burden. First, GEODE is modified to include a Gravity Acceleration Approximation Function (GAAF) to replace the traditional spherical harmonic representation of the gravity field. Next, an ionospheric correction method called Differenced Range Versus Integrated Doppler (DRVID) is applied to correct for ionospheric errors in the GPS measurements used in GEODE. Then, Dynamic Model Compensation (DMC) is added to estimate unmodeled and/or mismodeled forces in the dynamic model and to provide an alternative process noise variance-covariance formulation. Finally, a Genetic Algorithm (GA) is implemented in the form of Genetic Model Compensation (GMC) to optimize DMC forcing noise parameters. Application of GAAF, DRVID and DMC improved GEODE's position estimates by 28.3% when applied to GPS/MET data collected in the presence of Selective Availability (SA), 17.5% when SA is removed from the GPS/MET data and 10.8% on SA free TOPEX data. Position estimates with RSS errors below I meter are now achieved using SA free TOPEX data. DRVID causes an increase in computational burden while GAAF and DMC reduce computational burden. The net effect of applying GAAF, DRVID and DMC is an improvement in GEODE's accuracy/precision without an increase in computational burden.

Precise estimation of tropospheric path delays with GPS techniques

NASA Technical Reports Server (NTRS)

Lichten, S. M.

1990-01-01

Tropospheric path delays are a major source of error in deep space tracking. However, the tropospheric-induced delay at tracking sites can be calibrated using measurements of Global Positioning System (GPS) satellites. A series of experiments has demonstrated the high sensitivity of GPS to tropospheric delays. A variety of tests and comparisons indicates that current accuracy of the GPS zenith tropospheric delay estimates is better than 1-cm root-mean-square over many hours, sampled continuously at intervals of six minutes. These results are consistent with expectations from covariance analyses. The covariance analyses also indicate that by the mid-1990s, when the GPS constellation is complete and the Deep Space Network is equipped with advanced GPS receivers, zenith tropospheric delay accuracy with GPS will improve further to 0.5 cm or better.

Comparison of GPS and GRACE hydrological loading signatures in Myanmar, India, Bangladesh, and Bhutan

NASA Astrophysics Data System (ADS)

Materna, K.; Feng, L.; Lindsey, E. O.; Hill, E.; Burgmann, R.

2017-12-01

The elastic response of the lithosphere to surface mass redistributions produces significant deformation that can be observed in geodetic time series. This deformation is especially pronounced in Southeast Asia, where the annual monsoon produces large-amplitude hydrological loads. The MIBB network of 20 continuous GPS stations in Myanmar, India, Bangladesh, and Bhutan, operational since 2012, provides an opportunity to study the earth's response to these loads. In this study, we use GRACE gravity products as an estimate of surface water distribution, and input these estimates into an elastic loading calculation. We compare the predicted deformation with that observed with GPS. We find that elastic loading from the GRACE gravity field is able to explain the phase and the peak-to-peak amplitude (typically 2-3 cm) of the vertical GPS oscillations in northeast India and central Myanmar. GRACE-based corrections reduce the RMS scatter of the GPS data by 30%-45% in these regions. However, this approach does not capture all of the variation in central Bangladesh and southern Myanmar. Local hydrological effects, non-tidal ocean loads, poroelastic deformation, or differences in elastic properties may explain discrepancies between the GPS and GRACE signals in these places. The results of our calculations have practical implications for campaign GPS measurements in Myanmar, which make up the majority of geodetic measurements at this point. We may be able to reduce errors in campaign measurements and increase the accuracy of velocity estimates by correcting for hydrologic signals with GRACE data. The results also have potential implications for crustal rheology in Southeast Asia.

Capturing Postseismic Processes of the 2016 Mw 7.1 Kumamoto Earthquake, Japan, Using Dense, Continuous GPS and Short-repeat Time ALOS-2 InSAR Data: Implications for the Shallow Slip Deficit Problem

NASA Astrophysics Data System (ADS)

Milliner, C. W. D.; Burgmann, R.; Wang, T.; Inbal, A.; Bekaert, D. P.; Liang, C.; Fielding, E. J.

2017-12-01

Separating the contribution of shallow coseismic slip from rapidly decaying, postseismic afterslip in surface rupturing events has been difficult to resolve due to the typically sparse configuration of GPS networks and long-repeat time of InSAR acquisitions. Whether shallow fault motion along surface ruptures is a result of coseismic slip, or largely a product of rapid afterslip occurring within the first minutes to days, has significant implications for our understanding of the mechanics and frictional behavior of faulting in the shallow crust. To test this behavior in the case of a major surface rupturing event, we attempt to quantify the co- and postseismic slip of the 2016 Mw 7.1 Kumamoto earthquake sequence using a dense and continuous GPS network ( 10 km spacing), with short-repeat time, ALOS-2 InSAR data. Using the Network Inversion Filter method, we jointly invert the GPS and InSAR data to obtain a time history of afterslip in the first minutes to months following the mainshock. From our initial results, we find no clear evidence of significant shallow afterslip (i.e., no observable slip > 30 cm at depths of < 3 km, a minimum resolvable value), that could account for the 1 m of coseismic deficit of shallow slip inferred from our static finite-fault inversion. Our results show, aside from significant volumetric changes related to poroelastic processes, the majority of shallow fault slip was largely complete after rupture cessation. We also attempt to improve our coseismic slip model by implementing a method that inverts changes in seismicity rates for coseismic slip, helping constrain parts of the model space at depth where geodetic data loses resolving power. The use of geodetic data with the ability to resolve near-field, coseismic deformation and rapidly decaying postseismic processes will aid in our understanding of the frictional properties of shallow faulting, giving more reliable predictions for ground motion simulations and seismic hazard assessments.

InSAR and GPS Time Series Analysis in Areas with Large Scale Hydrological Deformation: Separating Signal From Noise at Varying Length Scales in the San Joaquin Valley

NASA Astrophysics Data System (ADS)

Murray, K. D.; Lohman, R.

2017-12-01

Areas of large-scale subsidence are observed over much of the San Joaquin Valley of California due to the extraction of groundwater and hydrocarbons from the subsurface.These signals span regions with spatial extents of up to 100 km and have rates of up to 45 cm/yr or more. InSAR and GPS are complementary methods commonly used to measure such ground displacements and can provide important constraints on crustal deformation models, support groundwater studies, and inform water resource management efforts. However, current standard methods for processing these data sets and creating displacement time series are suboptimal for the deformation observed in areas like the San Joaquin Valley because (1) the ground surface properties are constantly changing due largely to agricultural activity, resulting in low coherence in half or more of a SAR frame, and (2) the deformation signals are distributed throughout the SAR frames, and are comparable to the size of the frames themselves. Therefore, referencing areas of deformation to non-deforming areas and correcting for long wavelength signals (e.g. atmospheric delays, orbital errors) is particularly difficult. We address these challenges by exploiting pixels that are stable in space and time, and use them for weighted spatial averaging and selective filtering before unwrapping. We then compare a range of methods for both long wavelength corrections and referencing via automatic partitioning of non-deforming areas, then benchmark results against continuous GPS measurements. Our final time series consist of nearly 15 years of displacement measurements from continuous GPS data, and Envisat, ALOS-1, Sentinel SAR data, and show significant temporal and spatial variations. We find that the choice of reference and long wavelength corrections can significantly bias long-term rate and seasonal amplitude estimates, causing variations of as much as 100% of the mean estimate. As we enter an era with free and open data access and regular observations plans from missions such as NISAR and the Sentinel constellation, our approach will help users evaluate the significance of observed deformation at a range of spatial scales and in areas with challenging surface properties.

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.

New insights into the kinematics and seismotectonics of the Adria-Eurasia boundary in the eastern Alps from geodetic and seismic data

NASA Astrophysics Data System (ADS)

Serpelloni, Enrico; Vannucci, Gianfranco; Bennett, Richard A.; Anderlini, Letizia; Cavaliere, Adriano

2015-04-01

In this work we describe a new kinematic and seismotectonic model of the eastern Alps, at the boundary between Italy, Austria, Slovenia and Croatia, obtained from the analysis of geodetic (GPS) and seismological data. We use a dense GPS velocity field, obtained from integration of continuous, semi-continuous and survey-mode networks (~200 GPS stations between longitude 10°E and 17°E and latitude 44.5°N and 47.5°N) and an updated seismic and focal mechanisms catalogue, with uniformly calibrated moment magnitudes from ~1000 B.C.. Improved accuracies and precisions of GPS motion rates have been obtained by filtering displacement time-series for the spatially correlated common mode errors. The eastern Alps mark the boundary between the Adriatic microplate and the Eurasian plate through a wide zone of distributed deformation. Geodetic deformation and seismic release are more localized, and characterized by larger earthquakes, along the southeastern Alps fold-and-thrust belt, which accommodates the large part of the ~N-S Adria-Eurasia convergence, and in Slovenia, where a transition from ~N-S shortening to the eastward escape of the Pannonian Basin units occurs through a complex pattern of crustal deformation. GPS velocities well describe the overall kinematics, with a transition from NNW-ward to NE-ward motion trends (in a Eurasian frame) across Slovenia and Austria, but also show small but significant crustal deformation far from the major blocks boundaries. This may suggest internal continuous deformation or a more complex configuration of interacting tectonic blocks in the eastern Alps. This second hypothesis is taken into account and tested in this work. We use seismic moment release rate maps, active faults databases and inspections of GPS velocities in different local frames to define the geometry of a kinematic block model, constrained by GPS horizontal velocities, in order to estimate blocks rotations and elastic strain at blocks bounding faults. The improved GPS velocity field highlights significant strain accumulation off the main thrust fault segments in the southeastern Alps, in regions stroke by large (M>6.5) historical earthquakes (e.g., the 1117 Verona and the 1695 Asolo events). This is evident in the Venetian plain, where GPS highlights significant shortening in areas that are tens of km southward of the south Alpine mountain front. In the Italian southeastern Alps results from the block model, constrained by a denser GPS velocity field (e.g., around the Montello fault), put new lights on i) the way the Adria-Eurasia convergence is partitioned across the southeast Alpine mountain range, ii) about interseismic coupling along the main thrust faults and iii) the way N-S shortening is transferred, through right-lateral shear across the Dinaric system, to shortening across the Sava folds in Slovenia. In the end, a comparison of the estimated seismic moment release rates and the seismic moment accumulation rates, estimated from the model velocities, provide new insights into the seismic potential of the study region.

Air traffic management system design using satellite based geo-positioning and communications assets

NASA Technical Reports Server (NTRS)

Horkin, Phil

1995-01-01

The current FAA and ICAO FANS vision of Air Traffic Management will transition the functions of Communications, Navigation, and Surveillance to satellite based assets in the 21st century. Fundamental to widespread acceptance of this vision is a geo-positioning system that can provide worldwide access with best case differential GPS performance, but without the associated problems. A robust communications capability linking-up aircraft and towers to meet the voice and data requirements is also essential. The current GPS constellation does not provide continuous global coverage with a sufficient number of satellites to meet the precision landing requirements as set by the world community. Periodic loss of the minimum number of satellites in view creates an integrity problem, which prevents GPS from becoming the primary system for navigation. Furthermore, there is reluctance on the part of many countries to depend on assets like GPS and GLONASS which are controlled by military communities. This paper addresses these concerns and provides a system solving the key issues associated with navigation, automatic dependent surveillance, and flexible communications. It contains an independent GPS-like navigation system with 27 satellites providing global coverage with a minimum of six in view at all times. Robust communications is provided by a network of TDMA/FDMA communications payloads contained on these satellites. This network can support simultaneous communications for up to 30,000 links, nearly enough to simultaneously support three times the current global fleet of jumbo air passenger aircraft. All of the required hardware is directly traceable to existing designs.

DOTD standards for GPS data collection accuracy : research project capsule.

DOT National Transportation Integrated Search

2013-12-01

Global Navigational Satellite Systems (GNSS), which includes GPS technologies : maintained by the United States, are used extensively throughout government : and industry. These technologies continue to revolutionize positional data : collection acti...

Using continuous GPS and absolute gravity to separate vertical land movements and changes in sea-level at tide-gauges in the UK.

PubMed

Teferle, F N; Bingley, R M; Williams, S D P; Baker, T F; Dodson, A H

2006-04-15

Researchers investigating climate change have used historical tide-gauge measurements from all over the world to investigate the changes in sea-level that have occurred over the last century or so. However, such estimates are a combination of any true sea-level variations and any vertical movements of the land at the specific tide-gauge. For a tide- gauge record to be used to determine the climate related component of changes in sea-level, it is therefore necessary to correct for the vertical land movement component of the observed change in sea-level.In 1990, the Institute of Engineering Surveying and Space Geodesy and Proudman Oceanographic Laboratory started developing techniques based on the Global Positioning System (GPS) for measuring vertical land movements (VLM) at tide-gauges in the UK. This paper provides brief details of these early developments and shows how they led to the establishment of continuous GPS (CGPS) stations at a number of tide-gauges. The paper then goes on to discuss the use of absolute gravity (AG), as an independent technique for measuring VLM at tide-gauges. The most recent results, from CGPS time-series dating back to 1997 and AG time-series dating back to 1995/1996, are then used to demonstrate the complementarity of these two techniques and their potential for providing site-specific estimates of VLM at tide-gauges in the UK.

GPS Data Analysis for Earth Orientation at the Jet Propulsion Laboratory

NASA Technical Reports Server (NTRS)

Zumberge, J.; Webb, F.; Lindqwister, U.; Lichten, S.; Jefferson, D.; Ibanez-Meier, R.; Heflin, M.; Freedman, A.; Blewitt, G.

1994-01-01

Beginning June 1992 and continuing indefinitely as part of our contribution to FLINN (Fiducial Laboratories for an International Natural Science Network), DOSE (NASA's Dynamics of the Solid Earth Program), and the IGS (International GPS Geodynamics Service), analysts at the Jet Propulsion Laboratory (JPL) have routinely been reducing data from a globally-distributed network of Rogue Global Positioning System (GPS) receivers.

Ageing of the baby boomer generation: how demographic change will impact on city and rural GP and nursing workforce.

PubMed

Schofield, D J; Page, S L; Lyle, D M; Walker, T J

2006-01-01

To compare the impact of ageing on the GP and nursing rural and city workforce. Cohort analysis of Australian Bureau of Statistics census data. The data was used to examine the age distribution of the city and rural GP and nursing workforce; patterns of attrition for those 50 years and over; and the impact of changes in working hours. The rural GP and nursing workforce is significantly older than their city counterparts (p<0.001) with the 'baby boomer' generation making up 52% of city GPs but 59% of rural GPs in 2001. While a large proportion of city and rural GPs continued to work past the age of 65 years, rural GPs left the workforce at a significantly younger age than city doctors (p<0.001). Rural nurses are older than their city peers (p<0.001) but retire at an older age than city nurses (p<0.001). In 1986, a significantly higher proportion of rural GPs in all age cohorts worked more than 41 hours per week compared with their city counterparts (p<0.001). By 2001, rural 'generation X' GPs were no more likely to work long hours than those in the city (p<0.001). However, significantly more rural than city 'baby boomers' continued to work long hours. Rural GPs are retiring faster than city GPs and strategies to attract rural GPs and nurses will be critical to ensure adequate rural health care and that current rural workforce shortage do not worsen.

Principle component analysis to separate deformation signals from multiple sources during a 2015 intrusive sequence at Kīlauea Volcano

NASA Astrophysics Data System (ADS)

Johanson, I. A.; Miklius, A.; Poland, M. P.

2016-12-01

A sequence of magmatic events in April-May 2015 at Kīlauea Volcano produced a complex deformation pattern that can be described by multiple deforming sources, active simultaneously. The 2015 intrusive sequence began with inflation in the volcano's summit caldera near Halema`uma`u (HMM) Crater, which continued over a few weeks, followed by rapid deflation of the HMM source and inflation of a source in the south caldera region during the next few days. In Kīlauea Volcano's summit area, multiple deformation centers are active at varying times, and all contribute to the overall pattern observed with GPS, tiltmeters, and InSAR. Isolating the contribution of different signals related to each source is a challenge and complicates the determination of optimal source geometry for the underlying magma bodies. We used principle component analysis of continuous GPS time series from the 2015 intrusion sequence to determine three basis vectors which together account for 83% of the variance in the data set. The three basis vectors are non-orthogonal and not strictly the principle components of the data set. In addition to separating deformation sources in the continuous GPS data, the basis vectors provide a means to scale the contribution of each source in a given interferogram. This provides an additional constraint in a joint model of GPS and InSAR data (COSMO-SkyMed and Sentinel-1A) to determine source geometry. The first basis vector corresponds with inflation in the south caldera region, an area long recognized as the location of a long-term storage reservoir. The second vector represents deformation of the HMM source, which is in the same location as a previously modeled shallow reservoir, however InSAR data suggest a more complicated source. Preliminary modeling of the deformation attributed to the third basis vector shows that it is consistent with inflation of a steeply dipping ellipsoid centered below Keanakāko`i crater, southeast of HMM. Keanakāko`i crater is the locus of a known, intermittently active deformation source, which was not previously recognized to have been active during the 2015 event.

Multiscale GPS tomography during COPS: validation and applications

NASA Astrophysics Data System (ADS)

Champollion, Cédric; Flamant, Cyrille; Masson, Frédéric; Gégout, Pascal; Boniface, Karen; Richard, Evelyne

2010-05-01

Accurate 3D description of the water vapour field is of interest for process studies such as convection initiation. None of the current techniques (LIDAR, satellite, radio soundings, GPS) can provide an all weather continuous 3D field of moisture. The combination of GPS tomography with radio-soundings (and/or LIDAR) has been used for such process studies using both advantages of vertically resolved soundings and high temporal density of GPS measurements. GPS tomography has been used at short scale (10 km horizontal resolution but in a 50 km² area) for process studies such as the ESCOMPTE experiment (Bastin et al., 2005) and at larger scale (50 km horizontal resolution) during IHOP_2002. But no extensive statistical validation has been done so far. The overarching goal of the COPS field experiment is to advance the quality of forecasts of orographically induced convective precipitation by four-dimensional observations and modeling of its life cycle for identifying the physical and chemical processes responsible for deficiencies in QPF over low-mountain regions. During the COPS field experiment, a GPS network of about 100 GPS stations has been continuously operating during three months in an area of 500 km² in the East of France (Vosges Mountains) and West of Germany (Black Forest). If the mean spacing between the GPS is about 50 km, an East-West GPS profile with a density of about 10 km is dedicated to high resolution tomography. One major goal of the GPS COPS experiment is to validate the GPS tomography with different spatial resolutions. Validation is based on additional radio-soundings and airborne / ground-based LIDAR measurement. The number and the high quality of vertically resolved water vapor observations give an unique data set for GPS tomography validation. Numerous tests have been done on real data to show the type water vapor structures that can be imaging by GPS tomography depending of the assimilation of additional data (radio soundings), the resolution of the tomography grid and the density of GPS network. Finally some applications to different cases studies will be shortly presented.

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).

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.

GPS Radio Occultation as Part of the Global Observing System for Atmosphere

NASA Technical Reports Server (NTRS)

Mannucci, Anthony J.; Ao, C. O.; Iijima, B. A.; Wilson, B. D.; Yunck, T. P.; Kursinski, E. R.

2008-01-01

Topics include: The Measurement (Physical retrievals based on time standards), GPS Retrieval Products, Retrievals and Radiances: CLARREO Mission, GPS RO and AIRS, GPS RO and Microwave, GPS RO and Radiosondes, GPS/GNSS Science, and Conclusions.

Does the proportion of pay linked to performance affect the job satisfaction of general practitioners?

PubMed

Allen, Thomas; Whittaker, William; Sutton, Matt

2017-01-01

There is concern that pay-for-performance (P4P) can negatively affect general practitioners (GPs) by reducing their autonomy, increasing their wage dispersion or eroding their intrinsic motivation. This is especially a concern for the Quality and Outcomes Framework (QOF), a highly powered P4P scheme for UK GPs. The QOF affected all GPs but the exposure of their income to P4P varied. GPs did not know their level of exposure before the QOF was introduced and could not choose or manage it. We examine whether changes in GPs' job satisfaction before and after the introduction of the QOF in 2004 were correlated with the proportion of their income that became exposed to P4P. We use data on 1920 GPs observed at three time points spanning the introduction of the QOF; 2004, 2005 and 2008. We estimate the effect of exposure to P4P using a continuous difference-in-differences model. We find no significant effects of P4P exposure on overall job satisfaction or 12 additional measures of working lives in either the short or longer term. The level of exposure to P4P does not harm job satisfaction or other aspects of working lives. Policies influencing the exposure of income to P4P are unlikely to alter GP job satisfaction subject to final income remaining constant. Copyright © 2016 Elsevier Ltd. All rights reserved.

Ionospheric Remote Sensing using GPS Radio Occultation and Ultraviolet Photometry aboard the ISS

NASA Astrophysics Data System (ADS)

Budzien, S. A.; Powell, S. P.; O'Hanlon, B.; Humphreys, T.; Bishop, R. L.; Stephan, A. W.; Gross, J.; Chakrabarti, S.

2017-12-01

The GPS Radio Occultation and Ultraviolet Photometer Co-located (GROUP-C) experiment launched to the International Space Station (ISS) on February 19, 2017 as part of the Space Test Program Houston #5 payload (STP-H5). After early orbit testing, GROUP-C began routine science operations in late April. GROUP-C includes a high-sensitivity far-ultraviolet photometer measuring horizontal nighttime ionospheric gradients and an advanced software-defined GPS receiver providing ionospheric electron density profiles, scintillation measurements, and lower atmosphere profiles. GROUP-C and a companion experiment, the Limb-Imaging Ionospheric and Thermospheric Extreme-Ultraviolet Spectrograph (LITES), offer a unique capability to study spatial and temporal variability of the thermosphere and ionosphere using multi-sensor approaches, including ionospheric tomography. Data are collected continuously across low- and mid-latitudes as the ISS orbit precesses through all local times every 60 days. The GROUP-C GPS sensor routinely collects dual-frequency GPS occultations, makes targeted raw signal captures of GPS and Galileo occultations, and includes multiple antennas to characterize multipath in the ISS environment. The UV photometer measures the 135.6 nm ionospheric recombination airglow emision along the nightside orbital track. We present the first analysis of ionospheric observations, discuss the challenges and opportunities of remote sensing from the ISS platform, and explore how these new data help address questions regarding the complex and dynamic features of the low and middle latitude ionosphere-thermosphere relevant to the upcoming GOLD and ICON missions.

Near-Field Postseismic Deformation Measurements from the Andaman and Nicobar Islands

NASA Astrophysics Data System (ADS)

Freymueller, J. T.; Rajendran, C.; Rajendran, K.; Rajamani, A.

2006-12-01

Since the December 26, 2004 Sumatra-Andaman Islands earthquake, we have carried out campaign GPS measurements at several sites in the Andaman and Nicobar Islands (India) and installed three continuous GPS sites in the region. Most of these sites had pre-earthquake measurements, which showed slow westward motion relative to the Indian plate. Postseismic measurements, on the other hand, show average westward velocities of several cm/yr to a few decimeters per year relative to the Indian plate. The motion of all sites is strongly non-linear in time, and is not uniform in space. We use a combination of continuous site time series and nearby campaign site time series to construct the most complete possible postseismic displacement records. Postseismic deformation from large earthquakes is likely to be dominated by a combination of afterslip on the deeper subduction interface, and viscoelastic relaxation of the mantle. Afterslip following the (similar magnitude) 1964 Alaska earthquake amounted to 20-50% of the magnitude of the coseismic slip, and smaller subduction zone earthquakes have exhibited the same or even larger proportion of afterslip to coseismic slip. We compare the time decay and spatial pattern of the observed postseismic displacement to postseismic deformation models and to observations from the Alaska earthquake.

Monitoring beach changes using GPS surveying techniques

USGS Publications Warehouse

Morton, Robert; Leach, Mark P.; Paine, Jeffrey G.; Cardoza, Michael A.

1993-01-01

The adaptation of Global Positioning System (GPS) surveying techniques to beach monitoring activities is a promising response to this challenge. An experiment that employed both GPS and conventional beach surveying was conducted, and a new beach monitoring method employing kinematic GPS surveys was devised. This new method involves the collection of precise shore-parallel and shore-normal GPS positions from a moving vehicle so that an accurate two-dimensional beach surface can be generated. Results show that the GPS measurements agree with conventional shore-normal surveys at the 1 cm level, and repeated GPS measurements employing the moving vehicle demonstrate a precision of better than 1 cm. In addition, the nearly continuous sampling and increased resolution provided by the GPS surveying technique reveals alongshore changes in beach morphology that are undetected by conventional shore-normal profiles. The application of GPS surveying techniques combined with the refinement of appropriate methods for data collection and analysis provides a better understanding of beach changes, sediment transport, and storm impacts.

Combined GPS/GLONASS Precise Point Positioning with Fixed GPS Ambiguities

PubMed Central

Pan, Lin; Cai, Changsheng; Santerre, Rock; Zhu, Jianjun

2014-01-01

Precise point positioning (PPP) technology is mostly implemented with an ambiguity-float solution. Its performance may be further improved by performing ambiguity-fixed resolution. Currently, the PPP integer ambiguity resolutions (IARs) are mainly based on GPS-only measurements. The integration of GPS and GLONASS can speed up the convergence and increase the accuracy of float ambiguity estimates, which contributes to enhancing the success rate and reliability of fixing ambiguities. This paper presents an approach of combined GPS/GLONASS PPP with fixed GPS ambiguities (GGPPP-FGA) in which GPS ambiguities are fixed into integers, while all GLONASS ambiguities are kept as float values. An improved minimum constellation method (MCM) is proposed to enhance the efficiency of GPS ambiguity fixing. Datasets from 20 globally distributed stations on two consecutive days are employed to investigate the performance of the GGPPP-FGA, including the positioning accuracy, convergence time and the time to first fix (TTFF). All datasets are processed for a time span of three hours in three scenarios, i.e., the GPS ambiguity-float solution, the GPS ambiguity-fixed resolution and the GGPPP-FGA resolution. The results indicate that the performance of the GPS ambiguity-fixed resolutions is significantly better than that of the GPS ambiguity-float solutions. In addition, the GGPPP-FGA improves the positioning accuracy by 38%, 25% and 44% and reduces the convergence time by 36%, 36% and 29% in the east, north and up coordinate components over the GPS-only ambiguity-fixed resolutions, respectively. Moreover, the TTFF is reduced by 27% after adding GLONASS observations. Wilcoxon rank sum tests and chi-square two-sample tests are made to examine the significance of the improvement on the positioning accuracy, convergence time and TTFF. PMID:25237901

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.

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.

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.

Strategies for Near Real Time Estimates of Precipitable Water Vapor from GPS Ground Receivers

NASA Technical Reports Server (NTRS)

Y., Bar-Sever; Runge, T.; Kroger, P.

1995-01-01

GPS-based estimates of precipitable water vapor (PWV) may be useful in numerical weather models to improve short-term weather predictions. To be effective in numerical weather prediction models, GPS PWV estimates must be produced with sufficient accuracy in near real time. Several estimation strategies for the near real time processing of GPS data are investigated.

Calibration of the BEV GPS Receiver by Using TWSTFT

DTIC Science & Technology

2008-12-01

40th Annual Precise Time and Time Interval (PTTI) Meeting 543 CALIBRATION OF THE BEV GPS RECEIVER BY USING TWSTFT A. Niessner1, W...a calibration of the BEV reference GPS time receiver by using Two-way Satellite Time and Frequency Transfer ( TWSTFT ). Due to antenna changes, a new...calibration of the BEV receiver was necessary. This receiver is the first GPS receiver with calibration through TWSTFT and used for UTC computation

Estimating secular velocities from GPS data contaminated by postseismic motion at sites with limited pre-earthquake data

NASA Astrophysics Data System (ADS)

Murray, J. R.; Svarc, J. L.

2016-12-01

Constant secular velocities estimated from Global Positioning System (GPS)-derived position time series are a central input for modeling interseismic deformation in seismically active regions. Both postseismic motion and temporally correlated noise produce long-period signals that are difficult to separate from secular motion and can bias velocity estimates. For GPS sites installed post-earthquake it is especially challenging to uniquely estimate velocities and postseismic signals and to determine when the postseismic transient has decayed sufficiently to enable use of subsequent data for estimating secular rates. Within 60 km of the 2003 M6.5 San Simeon and 2004 M6 Parkfield earthquakes in California, 16 continuous GPS sites (group 1) were established prior to mid-2001, and 52 stations (group 2) were installed following the events. We use group 1 data to investigate how early in the post-earthquake time period one may reliably begin using group 2 data to estimate velocities. For each group 1 time series, we obtain eight velocity estimates using observation time windows with successively later start dates (2006 - 2013) and a parameterization that includes constant velocity, annual, and semi-annual terms but no postseismic decay. We compare these to velocities estimated using only pre-San Simeon data to find when the pre- and post-earthquake velocities match within uncertainties. To obtain realistic velocity uncertainties, for each time series we optimize a temporally correlated noise model consisting of white, flicker, random walk, and, in some cases, band-pass filtered noise contributions. Preliminary results suggest velocities can be reliably estimated using data from 2011 to the present. Ongoing work will assess velocity bias as a function of epicentral distance and length of post-earthquake time series as well as explore spatio-temporal filtering of detrended group 1 time series to provide empirical corrections for postseismic motion in group 2 time series.

Progress of BeiDou time transfer at NTSC

NASA Astrophysics Data System (ADS)

Guang, Wei; Dong, Shaowu; Wu, Wenjun; Zhang, Jihai; Yuan, Haibo; Zhang, Shougang

2018-04-01

Time transfer using global navigation satellite system (GNSS) is a primary method of remote atomic clock comparisons. As of today, there are four operational GNSS systems, namely GPS, GLONASS, Galileo and BeiDou Navigation Satellite System (BDS or BeiDou). All of them can continuously provide position, navigation and time services. This paper mainly focuses on the progress of BeiDou time transfer at the National Time Service Center, Chinese Academy of Sciences (NTSC). In order to realize the BeiDou common view (CV) time comparison, we developed the Rinex2CGGTTS software according to the guidelines of the Common GNSS Generic Time Transfer Standard, Version 2E (CGGTTS V2E). By comparing the solutions of the Rinex2CGGTTS software to the solutions of the sbf2cggtts software provided by the manufacturer of our multi-GNSS receiver, we found the sbf2cggtts (version 1.0.5) solutions contained biases in measurements to different BeiDou satellites. The biases are most likely caused by sbf2cggtts’ timing group delay corrections in data processing. The noise of the observation data is analyzed by code multipath and common clock difference. Finally, the BeiDou CV results are compared to the GPS/GLONASS/Galileo CV results between NTSC and three European UTC(k) laboratories, including Royal Observatory of Belgium (ORB), Real Institute y Observatory de la Armada (ROA), Research Institutes of Sweden (RISE or SP). For the comparisons of each baseline, we aligned the BeiDou/Galileo/GLONASS links to the calibrated GPS link with the double-difference method. The results show that the performance of BeiDou CV is correlated to the number of BeiDou satellites available in common view. With the current BeiDou constellation, the standard deviation of the differences between all BeiDou CV satellites averaging result and the GPS PPP result is 2.03 ns, 2.90 ns and 4.06 ns for ORB-NTSC, SP-NTSC and ROA-NTSC links respectively.

A new analytical method for the classification of time-location data obtained from the global positioning system (GPS).

PubMed

Kim, Taehyun; Lee, Kiyoung; Yang, Wonho; Yu, Seung Do

2012-08-01

Although the global positioning system (GPS) has been suggested as an alternative way to determine time-location patterns, its use has been limited. The purpose of this study was to evaluate a new analytical method of classifying time-location data obtained by GPS. A field technician carried a GPS device while simulating various scripted activities and recorded all movements by the second in an activity diary. The GPS device recorded geological data once every 15 s. The daily monitoring was repeated 18 times. The time-location data obtained by the GPS were compared with the activity diary to determine selection criteria for the classification of the GPS data. The GPS data were classified into four microenvironments (residential indoors, other indoors, transit, and walking outdoors); the selection criteria used were used number of satellites (used-NSAT), speed, and distance from residence. The GPS data were classified as indoors when the used-NSAT was below 9. Data classified as indoors were further classified as residential indoors when the distance from the residence was less than 40 m; otherwise, they were classified as other indoors. Data classified as outdoors were further classified as being in transit when the speed exceeded 2.5 m s(-1); otherwise, they were classified as walking outdoors. The average simple percentage agreement between the time-location classifications and the activity diary was 84.3 ± 12.4%, and the kappa coefficient was 0.71. The average differences between the time diary and the GPS results were 1.6 ± 2.3 h for the time spent in residential indoors, 0.9 ± 1.7 h for the time spent in other indoors, 0.4 ± 0.4 h for the time spent in transit, and 0.8 ± 0.5 h for the time spent walking outdoors. This method can be used to determine time-activity patterns in exposure-science studies.

Signal existence verification (SEV) for GPS low received power signal detection using the time-frequency approach.

PubMed

Jan, Shau-Shiun; Sun, Chih-Cheng

2010-01-01

The detection of low received power of global positioning system (GPS) signals in the signal acquisition process is an important issue for GPS applications. Improving the miss-detection problem of low received power signal is crucial, especially for urban or indoor environments. This paper proposes a signal existence verification (SEV) process to detect and subsequently verify low received power GPS signals. The SEV process is based on the time-frequency representation of GPS signal, and it can capture the characteristic of GPS signal in the time-frequency plane to enhance the GPS signal acquisition performance. Several simulations and experiments are conducted to show the effectiveness of the proposed method for low received power signal detection. The contribution of this work is that the SEV process is an additional scheme to assist the GPS signal acquisition process in low received power signal detection, without changing the original signal acquisition or tracking algorithms.

Current state of active-fault monitoring in Taiwan

NASA Astrophysics Data System (ADS)

Hou, C.; Lin, C.; Chen, Y.; Liu, H.; Chen, C.; Lin, Y.; Chen, C.

2008-12-01

The earthquake is one of the major hazard sources in Taiwan where an arc-continent collision is on-going. For the purpose of seismic hazard mitigation, to understand current situation of each already-known active fault is urgently needed. After the 1999 Chi-chi earthquake shocked Taiwan, the Central Geological Survey (CGS) of Taiwan aggressively promoted the tasks on studying the activities of active faults. One of them is the deployment of miscellaneous monitoring networks to cover all the target areas, where the earthquake occurrence potentials on active faults are eager to be answered. Up to the end of 2007, CGS has already deployed over 1000 GPS campaign sites, 44 GPS stations in continuous mode, and 42 leveling transects across the major active faults with a total ground distance of 974 km. The campaign sites and leveling tasks have to be measured once a year. The resulted crustal deformation will be relied on to derive the fault slip model. The time series analysis on continuous mode of GPS can further help understand the details of the fault behavior. In addition, 12 down-hole strain meters, five stations for liquid flux and geochemical proxies, and two for water table monitoring have been also installed to seek possible anomalies related to the earthquake activities. It may help discover reliable earthquake precursors.

Postseismic Deformation following the 1995 Kobe, Japan, Earthquake Detected by Space Geodesy

NASA Astrophysics Data System (ADS)

Hashimoto, Manabu; Ozawa, Taku; Nishimura, Takuya; Munekane, Hiroshi; Tobita, Mikio

2017-04-01

A Mw 6.8 earthquake hit the city of Kobe, southwest Japan, and its surrounding area on January 17, 1995, and claimed more than 6,400 fatalities. The source faults, trending in the NE-SW direction, are estimated beneath the foothill of the Rokko Mountains, which are located north of the city and the highest peak is 931 m high, but it has a dominant right lateral strike slip components. The Rokko Mountains may have been built by the motion of active faults, but the uplift during the 1995 earthquake may not be enough. Therefore there is a possibility that postseismic deformation contributes to the building of the Rokko Mountains. In order to study the postseismic deformation following the Kobe earthquake, we collected all available space geodetic data during about 20 years, including ERS-1/2, Envisat, JERS-1, ALOS/PALSAR and ALOS-2/PALSAR-2 images and continuous GPS data, and reanalyzed them. Especially, temporal continuous GPS observation made by the Geographical Survey Institute (present the Geospatial Information Authority), Japan in and around the Kobe area is important. We recalculated coordinates of these continuous GPS stations with recent PPP procedure using reanalyzed orbits and clocks of satellites. We made DInSAR and PSInSAR analyses of SAR images using ASTER-GDEM ver.2 or GSI DEM. Time series analysis of JERS-1 images revealed line-of-sight (LOS) decrease of the Rokko Mountains. PS-InSAR results of ALOS/PALSAR also revealed slight uplift north of the Rokko Mountains that uplifted by 20 cm coseismically. These observations suggest that the Rokko Mountains might have uplifted during the postseismic period. LOS increase in a wedge shaped region between two active faults east of the Rokko Mountains in the vicinity of the NE terminus of the source fault of the Kobe earthquake. The LOS increase is also confirmed by ERS-1/2, Envisat and ALOS/PALSAR images. These facts indicate that the subsidence between these two faults continued up to 2010. Continuous GPS observation during the first two years of the postseismic period shows north-south extension with right lateral motion between these two faults. These observations suggest that the Rokko Mountains may have uplift till 2010. On the other hand, active faults near the NE terminus continued to slip with the formation of graben-like structure, due to coseismically loaded stress.

Did the new French pay-for-performance system modify benzodiazepine prescribing practices?

PubMed

Rat, Cédric; Penhouet, Gaëlle; Gaultier, Aurélie; Chaslerie, Anicet; Pivette, Jacques; Nguyen, Jean Michel; Victorri-Vigneau, Caroline

2014-07-11

French general practitioners (GPs) were enrolled in a new payment system in January 2012. As part of a national agreement with the French National Ministry of Health, GPs were asked to decrease the proportion of patients who continued their benzodiazepine treatment 12 weeks after its initiation and to decrease the proportion of patients older than 65 who were prescribed long half-life benzodiazepines. In return, GPs could expect an extra payment of up to 490 euros per year. This study reports the evolution of the corresponding prescribing practices of French GPs during that period regarding patients who were prescribed a benzodiazepine for the first time. The national healthcare system's administrative database was used to report the longitudinal follow-up of two historical cohorts of French patients from the Pays de la Loire area. The "2011" and "2012" cohorts included all patients who initiated benzodiazepine regimens from April 1 to June 30 in 2011 and 2012, respectively.The primary outcomes were the proportion of those study patients who continued benzodiazepine treatment after 12 weeks and the proportion of study patients >65 years who were prescribed long half-life benzodiazepines.Analyses were performed using a multi-level regression. In total, 41,436 and 42,042 patients initiated benzodiazepine treatment in 2011 and 2012, respectively. A total of 18.97% of patients continued treatment for more than 12 weeks in 2012, compared with 18.18% in 2011. In all, 27.43% and 28.06% of patients >65 years continued treatment beyond 12 weeks in 2011 and 2012, respectively. The proportion of patients >65 years who were prescribed long half-life benzodiazepines decreased from 53.5% to 48.8% (p < 0.005) due to an increase in short half-life benzodiazepine prescriptions. Patients >65 years who were prescribed short half-life benzodiazepines were more likely to continue treatment after 12 weeks (p < 0.005). Despite the pay-for-performance strategy, the number of short half-life benzodiazepine prescriptions increased between 2011 and 2012, and the number of long half-life benzodiazepine initiations remained unchanged. Reducing the proportion of long half-life benzodiazepine prescriptions might be counterproductive because prescribing short half-life benzodiazepines was associated with higher rates of continuation beyond the recommended duration.

Real-Time Earthquake Monitoring with Spatio-Temporal Fields

NASA Astrophysics Data System (ADS)

Whittier, J. C.; Nittel, S.; Subasinghe, I.

2017-10-01

With live streaming sensors and sensor networks, increasingly large numbers of individual sensors are deployed in physical space. Sensor data streams are a fundamentally novel mechanism to deliver observations to information systems. They enable us to represent spatio-temporal continuous phenomena such as radiation accidents, toxic plumes, or earthquakes almost as instantaneously as they happen in the real world. Sensor data streams discretely sample an earthquake, while the earthquake is continuous over space and time. Programmers attempting to integrate many streams to analyze earthquake activity and scope need to write code to integrate potentially very large sets of asynchronously sampled, concurrent streams in tedious application code. In previous work, we proposed the field stream data model (Liang et al., 2016) for data stream engines. Abstracting the stream of an individual sensor as a temporal field, the field represents the Earth's movement at the sensor position as continuous. This simplifies analysis across many sensors significantly. In this paper, we undertake a feasibility study of using the field stream model and the open source Data Stream Engine (DSE) Apache Spark(Apache Spark, 2017) to implement a real-time earthquake event detection with a subset of the 250 GPS sensor data streams of the Southern California Integrated GPS Network (SCIGN). The field-based real-time stream queries compute maximum displacement values over the latest query window of each stream, and related spatially neighboring streams to identify earthquake events and their extent. Further, we correlated the detected events with an USGS earthquake event feed. The query results are visualized in real-time.

Lectin Affinity Plasmapheresis for Middle East Respiratory Syndrome-Coronavirus and Marburg Virus Glycoprotein Elimination.

PubMed

Koch, Benjamin; Schult-Dietrich, Patricia; Büttner, Stefan; Dilmaghani, Bijan; Lohmann, Dario; Baer, Patrick C; Dietrich, Ursula; Geiger, Helmut

2018-04-26

Middle East respiratory syndrome coronavirus (MERS-CoV) and Marburg virus (MARV) are among the World Health Organization's top 8 emerging pathogens. Both zoonoses share nonspecific early symptoms, a high lethality rate, and a reduced number of specific treatment options. Therefore, we evaluated extracorporeal virus and glycoprotein (GP) elimination by lectin affinity plasmapheresis (LAP). For both MERS-CoV (pseudovirus) as well as MARV (GPs), 4 LAP devices (Mini Hemopurifiers, Aethlon Medical, San Diego, CA, USA) and 4 negative controls were tested. Samples were collected every 30 min and analyzed for reduction in virus infectivity by a flow cytometry-based infectivity assay (MERS-CoV) and in soluble GP content (MARV) by an immunoassay. The experiments show a time-dependent clearance of MERS-CoV of up to 80% within 3 h (pseudovirus). Up to 70% of MARV-soluble GPs were eliminated at the same time. Substantial saturation of the binding resins was detected within the first treatment hour. MERS-CoV (pseudovirus) and MARV soluble GPs are eliminated by LAP in vitro. Considering the high lethality and missing established treatment options, LAP should be evaluated in vivo. Especially early initiation, continuous therapy, and timed cartridge exchanges could be of importance. The Author(s). Published by S. Karger AG, Basel.

Highlights of Recent Developments in the International GPS Service and Perspectives for Future Directions

NASA Technical Reports Server (NTRS)

Neilan, R.; Reigber, C.; Springer, T.; Beutler, G.; Kouba, J.

1999-01-01

In December 1998, the IGS Governing Board officially changed the name of this IAG service from 'International GPS Service for Geodynamics to simply the 'International GPS Service'. This change of name reflects the fact that today the IGS supports numerous scientific projects outside the traditional geodetic and geodynamic disciplines. A number of IGS projects and working groups have been established, each concentrating on a particular science application, such as the ionosphere, atmosphere, reference frame, precise time transfer, etc. These activities are enabled and simulated by the IGS and directly contribute to the continuing development of the service. The IGS is currently poised to respond to evolving user requirements that focus on timeliness and reliability of data and products, particularly in support of a slate of Low Earth Orbiter missions over the next decade. Perspectives on the future of the IGS will be developed based on current directions as well as anticipated external influences, such as GPS satellite modernization, GLONASS, availability of global communications, and plans for the European GALILEO (Global Navigation Satellite System - GNSS). We will address development of user friendly interfaces and IGS product tutorials.

Gps-Denied Geo-Localisation Using Visual Odometry

NASA Astrophysics Data System (ADS)

Gupta, Ashish; Chang, Huan; Yilmaz, Alper

2016-06-01

The primary method for geo-localization is based on GPS which has issues of localization accuracy, power consumption, and unavailability. This paper proposes a novel approach to geo-localization in a GPS-denied environment for a mobile platform. Our approach has two principal components: public domain transport network data available in GIS databases or OpenStreetMap; and a trajectory of a mobile platform. This trajectory is estimated using visual odometry and 3D view geometry. The transport map information is abstracted as a graph data structure, where various types of roads are modelled as graph edges and typically intersections are modelled as graph nodes. A search for the trajectory in real time in the graph yields the geo-location of the mobile platform. Our approach uses a simple visual sensor and it has a low memory and computational footprint. In this paper, we demonstrate our method for trajectory estimation and provide examples of geolocalization using public-domain map data. With the rapid proliferation of visual sensors as part of automated driving technology and continuous growth in public domain map data, our approach has the potential to completely augment, or even supplant, GPS based navigation since it functions in all environments.

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.

Slip rate of the Húsavík-Flatey Fault, North Iceland, derived from GPS and InSAR Time Series

NASA Astrophysics Data System (ADS)

Metzger, S.; Jonsson, S.

2010-12-01

The Húsavík-Flatey fault is one of mainly two parallel fault zones within the Tjörnes Fracture Zone (TFZ), North Iceland. The TFZ is a transform zone and a 120km-offset between two segments of the Mid-Atlantic Ridge, accommodating the 18.2mm/year spreading motion between the North American and the Eurasian Plate at this latitude (NUVEL 1A). Geodetic research mostly concentrates on a relatively short 20km onshore portion of the Húsavík-Flatey fault, as the rest of the whole transform zone, including the Grímsey lineament to the Northeast, is located offshore. The fact that a coastal town with 2300 inhabitants has been built directly at the fault surface trace increases the importance of studying this area. No major earthquake has occurred in the vicinity of the town since two M6.3 earthquakes took place in 1872. Hence, there is a compelling need to estimate the fault slip rate, slip deficit and finally, the seismic risk to which this town is exposed to, as the interseismic part of the current earthquake cycle may be drawing to a close. We use geodetic data, both continuous GPS and satellite radar interferograms (InSAR) to determine the interseismic deformation field around the on-land portion of the Húsavík-Flatey fault. The continuous GPS stations have been recording data since 2006 or longer at 14 sites within the TFZ. In addition, we use time-series analysis of ERS radar interferograms from 1992 to 2000 to derive interseismic velocities across the fault. We simulate the resulting deformation field with an interseismic back-slip model consisting of planar dislocations in an elastic half space and constrain the associated model parameters using a non-linear optimization approach. It has earlier been estimated that only 40% of the total motion is concentrated on the Húsavík-Flatey fault, while the larger 60% is taken up by the Grímsey lineament. This estimate however, was based on only three continuous GPS stations. Including more GPS data, we find that the partial motion on the Húsavík-Flatey fault is even less, closer to 30% and that the locking depth is relatively shallow. The exact parameter values, however, depend significantly on the modeling assumptions. Still, the results show that if moment has been accumulating on the Húsavík-Flatey fault at the current rate since 1872, then the total accumulated moment corresponds to an earthquake of magnitude just below 7.

MINOS Timing and GPS Precise Point Positioning

DTIC Science & Technology

2012-01-01

Minos Timing Spec • Neutrinos created in bunches separated by 19 ns • ~ 1 neutrino/day detected in Soudan Mine – 2 milliseconds travel time...calibration – No low-cost Fermilab to Soudan Mine connections known – Not yet tested for operational time transfer Clock Options • High-Performance... UNDERGROUND LABORATORY •;, ~ (((ft.F ~’: · GPS PRECISE POINT POSITIONING A Brief Overview What is GPS PPP? • GPS PPP is a way to use precise ephemerides

Addressing the problems associated with general practitioners' workload in nursing and residential homes: findings from a qualitative study.

PubMed Central

Jacobs, Sally

2003-01-01

BACKGROUND: Caring for older people in residential and nursing homes makes major demands on general practitioners (GPs). AIM: To investigate the perceptions and experiences of home managers and GPs of the provision of general medical services for older residents. DESIGN OF STUDY: In-depth qualitative study. SETTING: Forty-two nursing and residential homes in five locations in England, interviewing home managers and eight of their residents' GPs. METHOD: Semi-structured face-to-face and telephone interviews. RESULTS: Most homes endorse principles of continuity of care and patient choice. Although many homes therefore deal with a large number of GPs, with the inherent difficulties of coordinating care and duplication of GP effort, limitations in residents' choice of GP result in the majority of residents in many homes being registered with only one or two practices. Contracts between homes and GPs may provide opportunities for improving medical care but do not guarantee additional services and have implications for patient choice and residents' fees. Visits on request form the bulk of GPs' workload in homes but can be hard to obtain for residents and may not be appropriate. Regular weekly surgeries are preferred by many homes but may have additional workload implications for GPs. CONCLUSION: The assumption that patient choice and continuity in medical care are paramount for older people in nursing and residential homes is questioned. While recognition of the additional workload for GPs working in these settings is necessary, this should be accompanied by additional NHS remuneration. Further research is urgently required to identify which models of GP provision would most benefit both residents and GPs. PMID:12817356

GPs’ perceptions of workload in England: a qualitative interview study

PubMed Central

Croxson, Caroline HD; Ashdown, Helen F; Hobbs, FD Richard

2017-01-01

Background GPs report the lowest levels of morale among doctors, job satisfaction is low, and the GP workforce is diminishing. Workload is frequently cited as negatively impacting on commitment to a career in general practice, and many GPs report that their workload is unmanageable. Aim To gather an in-depth understanding of GPs’ perceptions and attitudes towards workload. Design and setting All GPs working within NHS England were eligible. Advertisements were circulated via regional GP e-mail lists and national social media networks in June 2015. Of those GPs who responded, a maximum-variation sample was selected until data saturation was reached. Method Semi-structured, qualitative interviews were conducted. Data were analysed thematically. Results In total, 171 GPs responded, and 34 were included in this study. GPs described an increase in workload over recent years, with current working days being long and intense, raising concerns over the wellbeing of GPs and patients. Full-time partnership was generally not considered to be possible, and many participants felt workload was unsustainable, particularly given the diminishing workforce. Four major themes emerged to explain increased workload: increased patient needs and expectations; a changing relationship between primary and secondary care; bureaucracy and resources; and the balance of workload within a practice. Continuity of care was perceived as being eroded by changes in contracts and working patterns to deal with workload. Conclusion This study highlights the urgent need to address perceived lack of investment and clinical capacity in general practice, and suggests that managing patient expectations around what primary care can deliver, and reducing bureaucracy, have become key issues, at least until capacity issues are resolved. PMID:28093422

Single-Receiver GPS Phase Bias Resolution

NASA Technical Reports Server (NTRS)

Bertiger, William I.; Haines, Bruce J.; Weiss, Jan P.; Harvey, Nathaniel E.

2010-01-01

Existing software has been modified to yield the benefits of integer fixed double-differenced GPS-phased ambiguities when processing data from a single GPS receiver with no access to any other GPS receiver data. When the double-differenced combination of phase biases can be fixed reliably, a significant improvement in solution accuracy is obtained. This innovation uses a large global set of GPS receivers (40 to 80 receivers) to solve for the GPS satellite orbits and clocks (along with any other parameters). In this process, integer ambiguities are fixed and information on the ambiguity constraints is saved. For each GPS transmitter/receiver pair, the process saves the arc start and stop times, the wide-lane average value for the arc, the standard deviation of the wide lane, and the dual-frequency phase bias after bias fixing for the arc. The second step of the process uses the orbit and clock information, the bias information from the global solution, and only data from the single receiver to resolve double-differenced phase combinations. It is called "resolved" instead of "fixed" because constraints are introduced into the problem with a finite data weight to better account for possible errors. A receiver in orbit has much shorter continuous passes of data than a receiver fixed to the Earth. The method has parameters to account for this. In particular, differences in drifting wide-lane values must be handled differently. The first step of the process is automated, using two JPL software sets, Longarc and Gipsy-Oasis. The resulting orbit/clock and bias information files are posted on anonymous ftp for use by any licensed Gipsy-Oasis user. The second step is implemented in the Gipsy-Oasis executable, gd2p.pl, which automates the entire process, including fetching the information from anonymous ftp

NASA's global differential GPS system and the TDRSS augmentation service for satellites

NASA Technical Reports Server (NTRS)

Bar-Sever, Yoaz; Young, Larry; Stocklin, Frank; Rush, John

2004-01-01

NASA is planning to launch a new service for Earth satellites providing them with precise GPS differential corrections and other ancillary information enabling decimeter level orbit determination accuracy, and nanosecond time-transfer accuracy, onboard, in real-time. The TDRSS Augmentation Service for Satellites (TASS) will broadcast its message on the S-band multiple access channel of NASA's Tracking and Data Relay Satellite System (TDRSS). The satellite's phase array antenna has been configured to provide a wide beam, extending coverage up to 1000 km altitude over the poles. Global coverage will be ensured with broadcast from three or more TDRSS satellites. The GPS differential corrections are provided by the NASA Global Differential GPS (GDGPS) System, developed and operated by NASA's Jet Propulsion Laboratory. The GDGPS System employs a global ground network of more than 70 GPS receivers to monitor the GPS constellation in real time. The system provides real-time estimates of the GPS satellite states, as well as many other real-time products such as differential corrections, global ionospheric maps, and integrity monitoring. The unique multiply redundant architecture of the GDGPS System ensures very high reliability, with 99.999% demonstrated since the inception of the system in Early 2000. The estimated real time GPS orbit and clock states provided by the GDGPS system are accurate to better than 20 cm 3D RMS, and have been demonstrated to support sub-decimeter real time positioning and orbit determination for a variety of terrestrial, airborne, and spaceborne applications. In addition to the GPS differential corrections, TASS will provide real-time Earth orientation and solar flux information that enable precise onboard knowledge of the Earth-fixed position of the spacecraft, and precise orbit prediction and planning capabilities. TASS will also provide 5 seconds alarms for GPS integrity failures based on the unique GPS integrity monitoring service of the GDGPS System.

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.

The need for GPS standardization

NASA Technical Reports Server (NTRS)

Lewandowski, Wlodzimierz W.; Petit, Gerard; Thomas, Claudine

1992-01-01

A desirable and necessary step for improvement of the accuracy of Global Positioning System (GPS) time comparisons is the establishment of common GPS standards. For this reason, the CCDS proposed the creation of a special group of experts with the objective of recommending procedures and models for operational time transfer by GPS common-view method. Since the announcement of the implementation of Selective Availability at the end of last spring, action has become much more urgent and this CCDS Group on GPS Time Transfer Standards has now been set up. It operates under the auspices of the permanent CCDS Working Group on TAI and works in close cooperation with the Sub-Committee on Time of the Civil GPS Service Interface Committee (CGSIC). Taking as an example the implementation of SA during the first week of July 1991, this paper illustrates the need to develop urgently at least two standardized procedures in GPS receiver software: monitoring GPS tracks with a common time scale and retaining broadcast ephemeris parameters throughout the duration of a track. Other matters requiring action are the adoption of common models for atmospheric delay, a common approach to hardware design and agreement about short-term data processing. Several examples of such deficiencies in standardization are presented.

General practitioners' knowledge of ageing and attitudes towards older people in China.

PubMed

Yang, Yanni; Xiao, Lily Dongxia; Ullah, Shahid; Deng, Lanlan

2015-06-01

To explore general practitioners (GPs)knowledge of ageing, attitudes towards older people and factors affecting their knowledge and attitudes in a Chinese context. Four hundred GPs were surveyed using the Chinese version of the Aging Semantic Differential (CASD) and the Chinese version of the Facts on Aging Quiz (CFAQ1) scale. The CASD scores indicated that GPs had a neutral attitude towards older people. The CFAQ1 scores indicated a low level of knowledge about ageing. GPs' awareness of the mental and social facts of ageing was poorer compared to that of physical facts. Male GPs had a significantly higher negative bias score than female GPs. No other variables had a statistically significant influence on knowledge and attitudes. The findings suggest the need for education interventions for GPs regarding knowledge of ageing and also provide evidence to guide future development of continuing medical programs for this group of medical doctors. © 2013 ACOTA.

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

A Low Cost Automated Monitoring System for Landslides Using Dual Frequency GPS

NASA Astrophysics Data System (ADS)

Mills, H.; Edwards, S.

2006-12-01

Landslides are an existing and permanent threat to societies across the globe, generating financial and human losses whenever and wherever they occur. Drawing together the strands of science that provide increased understanding of landslide triggers through accurate modelling is therefore vital for the development of mitigation and management strategies. Together with climatic and geomorphological data a key input here is information on the precise location and timing of landslide events. However, the detailed monitoring of landslides and precursor movements is generally limited to episodic campaigns where limiting factors include equipment and mobilisation costs, time constraints and spatial resolution. This research has developed a geodetic tool of benefit to scientists involved in the development of closely coupled models that seek to explain trigger mechanisms such as rainfall duration and intensity and changes in groundwater pressure to actual real land movements. A fully automated low cost dual frequency GPS station for the continuous in-situ monitoring of landslide sites has been developed. System configuration combines a dual frequency GPS receiver, PC board with a GPRS modem and power supply to deliver 24hr/365day operation capability. Individual components have been chosen to provide the highest accuracies while minimising power consumption resulting in a system around half that of equivalent commercial systems. Measurement point-costs can be further reduced through the use of antenna switching and multi antenna arrays. Continuous data is delivered via mobile phone uplink and processed automatically using geodetic software. The developed system has been extensively tested on a purpose built platform capable of simulating ground movements. Co-mounted antennas have allowed direct comparisons with more expensive geodetic GPS receivers. The system is capable of delivering precise 3D coordinates with a 9 mm rms. The system can be up-scaled resulting in the increased spatial density of monitoring and yielding more detailed information on landslide movements for improved downstream modelling and monitoring.

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.

Global Positioning System III (GPS III)

DTIC Science & Technology

2013-12-01

Galileo satellite navigation system signal, E1. L1C is also compatible with those signals planned for broadcast on Japan’s Quazi-Zenith Satellite...and Galileo constellations, further increasing the accuracy and availability of civil PNT solutions. GPS III December 2013 SAR April 16, 2014...vehicle- level core mate. The overall program continues to make progress on the GPS III Non-Flight Satellite Testbed (GNST), on SV01 development, and

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.

The new versatile general purpose surface-muon instrument (GPS) based on silicon photomultipliers for μSR measurements on a continuous-wave beam

NASA Astrophysics Data System (ADS)

Amato, A.; Luetkens, H.; Sedlak, K.; Stoykov, A.; Scheuermann, R.; Elender, M.; Raselli, A.; Graf, D.

2017-09-01

We report on the design and commissioning of a new spectrometer for muon-spin relaxation/rotation studies installed at the Swiss Muon Source (SμS) of the Paul Scherrer Institute (PSI, Switzerland). This new instrument is essentially a new design and replaces the old general-purpose surface-muon (GPS) instrument that has been for long the workhorse of the μSR user facility at PSI. By making use of muon and positron detectors made of plastic scintillators read out by silicon photomultipliers, a time resolution of the complete instrument of about 160 ps (standard deviation) could be achieved. In addition, the absence of light guides, which are needed in traditionally built μSR instrument to deliver the scintillation light to photomultiplier tubes located outside magnetic fields applied, allowed us to design a compact instrument with a detector set covering an increased solid angle compared with the old GPS.

Observations on the Reliability of Rubidium Frequency Standards on Block 2/2A GPS Satellites

NASA Technical Reports Server (NTRS)

Dieter, Gary L.

1996-01-01

Currently, the block 2/2A Global Positioning System (GPS) satellites are equipped with two rubidium frequency standards. These frequency standards were originally intended to serve as the back-ups to two cesium frequency standards. As the constellation ages, the master Control Station is forced to initialize and increasing number or rubidium frequency standards. Unfortunately the operational use of these frequency standards has not lived up to initial expectations. Although the performance of these rubidium frequency standards has met and even exceeded GPS requirements, their reliability has not. The number of unscheduled outage times and the short operational lifetimes of the rubidium frequency standards compare poorly to the track record of the cesium frequency standards. Only a small number of rubidium frequency standards have actually been made operational. Of these, a large percentage have exhibited poor reliability. If this trend continues, it is unlikely that the rubidium frequency standards will help contribute to the navigation payload meeting program specification.

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.

Crustal Deformation During the 2011 Volanic Crisis of El Hierro, Canary Islands, Revealed by Continuous GPS Observation

NASA Astrophysics Data System (ADS)

Sagiya, T.; Barrancos Martinez, J.; Calvo, D.; Padron, E.; Hernandez, G. H.; Hernández, P. A.; Perez Rodriguez, N.; Suárez, J. M. P.

2012-04-01

Seismo-volcnic activity of El Hierro started in the middle of July of 2011 and resulted in the active submarine eruption after October 12 south off La Restinga, the southern tip of the island. We have been operating one continuous GPS site on the island since 2004. Responding to the activity, we quickly installed 5 more GPS sites. Including another site operated by the Canary Islands Cartograhical Service (GRAFCAN) for a cartographic purpose, we have been monitoring 7 GPS sites equipped with dual-frequency receivers. We present the result of our crustal deformation monitoring and the magmatic activity inferred from the deformation data. In accordance with the deformation pattern, we divide the volcanic activity in 2011 into 4 stages. The first stage is from the middle of July to middle of September, during which steady magmatic inflation is estimated at the center of the island. The inflated volume of the first stage is estimated to be about 1.3 X 107 m3 at the depth of about 5km. The second stage, which continued until the first submarine eruption on October 12, is characterized by the accelerated deformation due to the upward as well as southward migration of magma. Additional inflation of about 2.1 X 107 m3 occurred in the depth range of 1-2km. The third stage continued for about 3 weeks after the first submarine eruption. During this stage, submarine eruption continues while no significant surface deformation is observed. It is considered magma supply from a deeper magma chamber continued during this 3 weeks period. Therefore, the total inflation volume during the first two stages gives the minimum estimate for the total magma volume. Since the beginning of November 2011, many GPS sites started subsiding. However, this deflation pattern is quite different from those in the shallow inflation stages. Horizontal deformation during this 4th stage is not significant, implying that deflation is occurring below the moho.

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.

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

An internet based approach to improve general practitioners' knowledge and practices: the development and pilot testing of the "ABC's of vitamin D" program.

PubMed

Bonevski, B; Magin, P; Horton, G; Bryant, J; Randell, M; Kimlin, M G

2015-06-01

Online continuing medical education (CME) offers a number of advantages for physicians including flexibility with regards to location and timing of use. In order to effect physician practices and improve patient outcomes, it is important that the development of online CME is theory and evidence-based. This paper aims to describe the development of an online CME program for practising general practitioners (GPs) on vitamin D and sun health called "The ABC's of Vitamin D for GPs" using elements of design principles for physician-education web sites as a framework. The paper will also report the program's usability and acceptability pilot test results. The ABC's of Vitamin D program was developed following nine principles: needs assessment; evidence-based content development; multimodal program and modularisation; clinical cases; tailoring and interactivity; audit and feedback; credibility of the web site host; patient education materials; ease of use and navigation. Among the 20 GPs invited, acceptability and useability was tested with 12 GPs (60%) who agreed to participate and were interviewed following use of the program. The study was conducted between 2011 and 2013. An online CME program consisting of eight modules was constructed. Of the 12 participating GPs, most (n=11) reported that the program was clear and easy to understand, logical, easy to navigate, and took a reasonable amount of time (estimated between 1 and 3h) to complete. Eleven of 12 participants said they would use the program as an accredited CME activity and all participants indicated that the program was 'very or somewhat' likely to lead to changes in the advice patients are given. This study found that a theory and evidence based approach for the development of an online CME program for GPs was acceptable to users. Further research is needed to examine whether the online CME program is effective at changing GP practices and improving patient outcomes. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

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.

GPS or travel diary: Comparing spatial and temporal characteristics of visits to fast food restaurants and supermarkets

PubMed Central

Vernez Moudon, Anne; Hurvitz, Philip M.; Aggarwal, Anju; Drewnowski, Adam

2017-01-01

To assess differences between GPS and self-reported measures of location, we examined visits to fast food restaurants and supermarkets using a spatiotemporal framework. Data came from 446 participants who responded to a survey, filled out travel diaries of places visited, and wore a GPS receiver for seven consecutive days. Provided by Public Health Seattle King County, addresses from food permit data were matched to King County tax assessor parcels in a GIS. A three-step process was used to verify travel-diary reported visits using GPS records: (1) GPS records were temporally matched if their timestamps were within the time window created by the arrival and departure times reported in the travel diary; (2) the temporally matched GPS records were then spatially matched if they were located in a food establishment parcel of the same type reported in the diary; (3) the travel diary visit was then GPS-sensed if the name of food establishment in the parcel matched the one reported in the travel diary. To account for errors in reporting arrival and departure times, GPS records were temporally matched to three time windows: the exact time, +/- 10 minutes, and +/- 30 minutes. One third of the participants reported 273 visits to fast food restaurants; 88% reported 1,102 visits to supermarkets. Of these, 77.3 percent of the fast food and 78.6 percent supermarket visits were GPS-sensed using the +/-10-minute time window. At this time window, the mean travel-diary reported fast food visit duration was 14.5 minutes (SD 20.2), 1.7 minutes longer than the GPS-sensed visit. For supermarkets, the reported visit duration was 23.7 minutes (SD 18.9), 3.4 minutes longer than the GPS-sensed visit. Travel diaries provide reasonably accurate information on the locations and brand names of fast food restaurants and supermarkets participants report visiting. PMID:28388619

GPS or travel diary: Comparing spatial and temporal characteristics of visits to fast food restaurants and supermarkets.

PubMed

Scully, Jason Y; Vernez Moudon, Anne; Hurvitz, Philip M; Aggarwal, Anju; Drewnowski, Adam

2017-01-01

To assess differences between GPS and self-reported measures of location, we examined visits to fast food restaurants and supermarkets using a spatiotemporal framework. Data came from 446 participants who responded to a survey, filled out travel diaries of places visited, and wore a GPS receiver for seven consecutive days. Provided by Public Health Seattle King County, addresses from food permit data were matched to King County tax assessor parcels in a GIS. A three-step process was used to verify travel-diary reported visits using GPS records: (1) GPS records were temporally matched if their timestamps were within the time window created by the arrival and departure times reported in the travel diary; (2) the temporally matched GPS records were then spatially matched if they were located in a food establishment parcel of the same type reported in the diary; (3) the travel diary visit was then GPS-sensed if the name of food establishment in the parcel matched the one reported in the travel diary. To account for errors in reporting arrival and departure times, GPS records were temporally matched to three time windows: the exact time, +/- 10 minutes, and +/- 30 minutes. One third of the participants reported 273 visits to fast food restaurants; 88% reported 1,102 visits to supermarkets. Of these, 77.3 percent of the fast food and 78.6 percent supermarket visits were GPS-sensed using the +/-10-minute time window. At this time window, the mean travel-diary reported fast food visit duration was 14.5 minutes (SD 20.2), 1.7 minutes longer than the GPS-sensed visit. For supermarkets, the reported visit duration was 23.7 minutes (SD 18.9), 3.4 minutes longer than the GPS-sensed visit. Travel diaries provide reasonably accurate information on the locations and brand names of fast food restaurants and supermarkets participants report visiting.

CORRELATION OF CHANDRA PHOTONS WITH THE RADIO GIANT PULSES FROM THE CRAB PULSAR

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

Bilous, A. V.; McLaughlin, M. A.; Kondratiev, V. I.

2012-04-10

No apparent correlation was found between giant pulses (GPs) and X-ray photons from the Crab pulsar during 5.4 hr of simultaneous observations with the Green Bank Telescope at 1.5 GHz and Chandra X-Ray Observatory primarily in the energy range of 1.5-4.5 keV. During the Crab pulsar periods with GPs, the X-ray flux in radio emission phase windows does not change more than by {+-}10% for main pulse (MP) GPs and {+-}30% for interpulse (IP) GPs. During GPs themselves, the X-ray flux does not change by more than two times for MP GPs and five times for IP GPs. All limitsmore » quoted are compatible with 2{sigma} fluctuations of the X-ray flux around the sets of false GPs with random arrival times. The results speak in favor of changes in plasma coherence as the origin of GPs. However, the results do not rule out variations in the rate of particle creation if the particles that emit coherent radio emission are mostly at the lowest Landau level.« less

GPS Availability for Aviation Applications : How Good Does it Need to Be?

DOT National Transportation Integrated Search

2000-09-19

The availability of GPS for airborne applications is driven by the accuracy, integrity, and continuity of the system. The International Civil Aviation Organization (ICAO) Standards and Recommended Practices (SARPS) for GNSS spells out all of these re...

A Hybrid-Cloud Science Data System Enabling Advanced Rapid Imaging & Analysis for Monitoring Hazards

NASA Astrophysics Data System (ADS)

Hua, H.; Owen, S. E.; Yun, S.; Lundgren, P.; Moore, A. W.; Fielding, E. J.; Radulescu, C.; Sacco, G.; Stough, T. M.; Mattmann, C. A.; Cervelli, P. F.; Poland, M. P.; Cruz, J.

2012-12-01

Volcanic eruptions, landslides, and levee failures are some examples of hazards that can be more accurately forecasted with sufficient monitoring of precursory ground deformation, such as the high-resolution measurements from GPS and InSAR. In addition, coherence and reflectivity change maps can be used to detect surface change due to lava flows, mudslides, tornadoes, floods, and other natural and man-made disasters. However, it is difficult for many volcano observatories and other monitoring agencies to process GPS and InSAR products in an automated scenario needed for continual monitoring of events. Additionally, numerous interoperability barriers exist in multi-sensor observation data access, preparation, and fusion to create actionable products. Combining high spatial resolution InSAR products with high temporal resolution GPS products--and automating this data preparation & processing across global-scale areas of interests--present an untapped science and monitoring opportunity. The global coverage offered by satellite-based SAR observations, and the rapidly expanding GPS networks, can provide orders of magnitude more data on these hazardous events if we have a data system that can efficiently and effectively analyze the voluminous raw data, and provide users the tools to access data from their regions of interest. Currently, combined GPS & InSAR time series are primarily generated for specific research applications, and are not implemented to run on large-scale continuous data sets and delivered to decision-making communities. We are developing an advanced service-oriented architecture for hazard monitoring leveraging NASA-funded algorithms and data management to enable both science and decision-making communities to monitor areas of interests via seamless data preparation, processing, and distribution. Our objectives: * Enable high-volume and low-latency automatic generation of NASA Solid Earth science data products (InSAR and GPS) to support hazards monitoring. * Facilitate NASA-USGS collaborations to share NASA InSAR and GPS data products, which are difficult to process in high-volume and low-latency, for decision-support. * Enable interoperable discovery, access, and sharing of NASA observations and derived actionable products, and between the observation and decision-making communities. * Enable their improved understanding through visualization, mining, and cross-agency sharing. Existing InSAR & GPS processing packages and other software are integrated for generating geodetic decision support monitoring products. We employ semantic and cloud-based data management and processing techniques for handling large data volumes, reducing end product latency, codifying data system information with semantics, and deploying interoperable services for actionable products to decision-making communities.

Incorporating GPS geodetic data into the undergraduate classroom to improve data and information literacy

NASA Astrophysics Data System (ADS)

Jansma, P. E.; Mattioli, G. S.

2002-12-01

As part of an NSF-funded project, we are incorporating Global Positioning System (GPS) geodesy into the classroom to improve data and information literacy among undergraduate students. Our objectives are: to introduce statistical concepts essential for the interpretation of large datasets; to promote communication skills; to enhance critical thinking; and to build teamwork. GPS geodesy is ideal for illustrating data literacy concepts. Data precision and accuracy depend upon several factors, including type of equipment, environmental conditions, length of occupations, monument design, site location, configuration of the geodetic network, and processing strategies. All of these can be varied, allowing the students to learn the trade-offs among cost, time, and quality and to determine the most efficient methodology for specific problems. In addition, precision, accuracy, and errors govern the interpretations that can be made and the potential to distinguish among competing models. Our focus is a semester-long course that uses GPS geodesy in real-world applications and also requires integration of GPS data into oral presentations and written reports. Students work in teams on "cases" that pose hypotheses for testing. The cases are derived from our on-going research projects and take advantage of on-line continuous GPS (CGPS) data as well as our archived campaign data. The case studies are: 1) Microplate tectonics in the northeastern Caribbean; 2) Inflation/deflation cycles of the Soufriere Hills volcano, Montserrat; and 3) Contribution of monument instability to the overall error in geodetic data from the New Madrid Seismic Zone. All course materials will be on-line and available for the community.

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.

Continued Rapid Uplift at Laguna del Maule Volcanic Field (Chile) from 2007 through 2014

NASA Astrophysics Data System (ADS)

Le Mével, H.; Feigl, K. L.; Cordova, L.; DeMets, C.; Lundgren, P.

2014-12-01

The current rate of uplift at Laguna del Maule (LdM) volcanic field in Chile is among the highest ever observed geodetically for a volcano that is not actively erupting. Using data from interferometric synthetic aperture radar (InSAR) and the Global Positioning System (GPS) recorded at five continuously operating stations, we measure the deformation field with dense sampling in time (1/day) and space (1/hectare). These data track the temporal evolution of the current unrest episode from its inception (sometime between 2004 and 2007) to vertical velocities faster than 200 mm/yr that continue through (at least) July 2014. Building on our previous work, we evaluate the temporal evolution by analyzing data from InSAR (ALOS, TerraSAR-X, TanDEM-X) and GPS [http://dx.doi.org/ 10.1093/gji/ggt438]. In addition, we consider InSAR data from (ERS, ENVISAT, COSMO-Skymed, and UAVSAR), as well as constraints from magneto-telluric (MT), seismic, and gravity surveys. The goal is to test the hypothesis that a recent magma intrusion is feeding a large, existing magma reservoir. What will happen next? To address this question, we analyze the temporal evolution of deformation at other large silicic systems such as Yellowstone, Long Valley, and Three Sisters, during well-studied episodes of unrest. We consider several parameterizations, including piecewise linear, parabolic, and Gaussian functions of time. By choosing the best-fitting model, we expect to constrain the time scales of such episodes and elucidate the processes driving them.

Triggering of tremors and slow slip event in Guerrero, Mexico, by the 2010 Mw 8.8 Maule, Chile, earthquake

NASA Astrophysics Data System (ADS)

Zigone, Dimitri; Rivet, Diane; Radiguet, Mathilde; Campillo, Michel; Voisin, Christophe; Cotte, Nathalie; Walpersdorf, Andrea; Shapiro, Nikolai M.; Cougoulat, Glenn; Roux, Philippe; Kostoglodov, Vladimir; Husker, Allen; Payero, Juan S.

2012-09-01

We investigate the triggering of seismic tremor and slow slip event in Guerrero (Mexico) by the February 27, 2010 Maule earthquake (Mw 8.8). Triggered tremors start with the arrival of S wave generated by the Maule earthquake, and keep occurring during the passing of ScS, SS, Love and Rayleigh waves. The Rayleigh wave dispersion curve footprints the high frequency energy envelope of the triggered tremor, indicating a strong modulation of the source of tremors by the passing surface wave. This correlation and modulation by the passing waves is progressively lost with time over a few hours. The tremor activity continues during the weeks/months after the earthquake. GPS time series suggest that the second sub-event of the 2009-2010 SSE in Guerrero is actually triggered by the Maule earthquake. The southward displacement of the GPS stations starts coincidently with the earthquake and tremors. The long duration of tremors indicate a continuing deformation process at depth, which we propose to be the second sub-event of the 2009-2010 SSE. We show a quasi-systematic correlation between surface displacement rate measured by GPS and tremor activity, suggesting that the NVT are controlled by the variations in the slip history of the SSE. This study shows that two types of tremors emerge: (1) Those directly triggered by the passing waves and (2) those triggered by the stress variations associated with slow slip. This indicates the prominent role of aseismic creep in the Mexican subduction zone response to a large teleseismic earthquake, possibly leading to large-scale stress redistribution.

Real-time bus location monitoring using Arduino

NASA Astrophysics Data System (ADS)

Ibrahim, Mohammad Y. M.; Audah, Lukman

2017-09-01

The Internet of Things (IoT) is the network of objects, such as a vehicles, mobile devices, and buildings that have electronic components, software, and network connectivity that enable them to collect data, run commands, and be controlled through the Internet. Controlling physical items from the Internet will increase efficiency and save time. The growing number of devices used by people increases the practicality of having IoT devices on the market. The IoT is also an opportunity to develop products that can save money and time and increase work efficiency. Initially, they need more efficiency for real-time bus location systems, especially in university campuses. This system can easily find the accurate locations of and distances between each bus stop and the estimated time to reach a new location. This system has been separated into two parts, which are the hardware and the software. The hardware parts are the Arduino Uno and the Global Positioning System (GPS), while Google Earth and GpsGate are the software parts. The GPS continuously takes input data from the satellite and stores the latitude and longitude values in the Arduino Uno. If we want to track the vehicle, we need to send the longitude and latitude as a message to the Google Earth software to convert these into maps for navigation. Once the Arduino Uno is activated, it takes the last received latitude and longitude positions' values from GpsGate and sends a message to Google Earth. Once the message has been sent to Google Earth, the current location will be shown, and navigation will be activated automatically. Then it will be broadcast using ManyCam, Google+ Hangouts, and YouTube, as well as Facebook, and appear to users. The additional features use Google Forms for determining problems faced by students, who can also take immediate action against the responsible department. Then after several successful simulations, the results will be shown in real time on a map.

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.

Wakeshield WSF-02 GPS Experiment

NASA Technical Reports Server (NTRS)

Schutz, B. E.; Abusali, P. A. M.; Schroeder, Christine; Tapley, Byron; Exner, Michael; Mccloskey, rick; Carpenter, Russell; Cooke, Michael; Mcdonald, samantha; Combs, Nick;

Novel Hybrid of LS-SVM and Kalman Filter for GPS/INS Integration

NASA Astrophysics Data System (ADS)

Xu, Zhenkai; Li, Yong; Rizos, Chris; Xu, Xiaosu

Integration of Global Positioning System (GPS) and Inertial Navigation System (INS) technologies can overcome the drawbacks of the individual systems. One of the advantages is that the integrated solution can provide continuous navigation capability even during GPS outages. However, bridging the GPS outages is still a challenge when Micro-Electro-Mechanical System (MEMS) inertial sensors are used. Methods being currently explored by the research community include applying vehicle motion constraints, optimal smoother, and artificial intelligence (AI) techniques. In the research area of AI, the neural network (NN) approach has been extensively utilised up to the present. In an NN-based integrated system, a Kalman filter (KF) estimates position, velocity and attitude errors, as well as the inertial sensor errors, to output navigation solutions while GPS signals are available. At the same time, an NN is trained to map the vehicle dynamics with corresponding KF states, and to correct INS measurements when GPS measurements are unavailable. To achieve good performance it is critical to select suitable quality and an optimal number of samples for the NN. This is sometimes too rigorous a requirement which limits real world application of NN-based methods.The support vector machine (SVM) approach is based on the structural risk minimisation principle, instead of the minimised empirical error principle that is commonly implemented in an NN. The SVM can avoid local minimisation and over-fitting problems in an NN, and therefore potentially can achieve a higher level of global performance. This paper focuses on the least squares support vector machine (LS-SVM), which can solve highly nonlinear and noisy black-box modelling problems. This paper explores the application of the LS-SVM to aid the GPS/INS integrated system, especially during GPS outages. The paper describes the principles of the LS-SVM and of the KF hybrid method, and introduces the LS-SVM regression algorithm. Field test data is processed to evaluate the performance of the proposed approach.

Program for Continued Development and Use of Ocean Acoustic/GPS Geodetic Techniques

NASA Technical Reports Server (NTRS)

Spiess, Fred N.

1997-01-01

Under prior NASA grants our group, with collaboration from scientists at the CalTech Jet Propulsion Lab (JPL), visualized and carried out the initial development of a combined GPS and underwater acoustic (GPS/A) method for determining the location of points on the deep sea floor with accuracy relevant to studies of crustal deformation. Under an immediately preceding grant we built, installed and surveyed a set of the necessary seafloor marker precision transponders just seaward of the Cascadia Subduction Zone off British Columbia. The JPL group carried out processing of the GPS data.

Age-related differences in working hours among male and female GPs: an SMS-based time use study.

PubMed

van Hassel, Daniël; van der Velden, Lud; de Bakker, Dinny; Batenburg, Ronald

2017-12-19

In several countries, the number of hours worked by general practitioners (GPs) has decreased, raising concern about current and impending workforce shortages. This shorter working week has been ascribed both to the feminisation of the workforce and to a younger generation of GPs who prefer more flexible working arrangements. There is, however, limited insight into how the impact of these determinants interact. We investigated the relative importance of differences in GPs' working hours in relation to gender, age, and employment position. An analysis was performed on real-time monitoring data collected by sending SMS text messages to 1051 Dutch GPs, who participated during a 1-week time use study. We used descriptive statistics, independent sample t-tests, and one-way ANOVA analysis to compare the working time of different GP groups. A path analysis was conducted to examine the difference in working time by gender, age, employment position, and their combinations. Female GPs worked significantly fewer hours than their male peers. GPs in their 50s worked the highest number of hours, followed by GPs age 60 and older. GPs younger than 40 worked the lowest number of hours. This relationship between working hours and age was not significantly different for women and men. As shown by path analysis, female GPs consistently worked fewer hours than their male counterparts, regardless of their age and employment position. The relationship between age and working hours was largely influenced by gender and employment position. The variation in working hours among GPs can be explained by the combination of gender, age, and employment position. Gender appears to be the most important predictor as the largest part of the variation in working hours is explained by a direct effect of this variable. It has previously been reported that the difference in working hours between male and female GPs had decreased over time. However, our findings suggest that gender remains a critical factor for variation in time use and for policy instruments such as health workforce planning.

Evolution of offshore wind waves tracked by surface drifters with a point-positioning GPS sensor

NASA Astrophysics Data System (ADS)

Komatsu, K.

2009-12-01

Wind-generated waves have been recognized as one of the most important factors of the sea surface roughness which plays crucial roles in various air-sea interactions such as energy, momentum, heat and gas exchanges. At the same time, wind waves with extreme wave heights representatively called as freak or rogue waves have been a matter of great concern for many people involved in shipping, fishing, constracting, surfing and other marine activities, because such extreme waves frequently affect on the marine activities and sometimes cause serious disasters. Nevertheless, investigations of actual conditions for the evolution of wind waves in the offshore region are less and sparse in contrast to dense monitoring networks in the coastal regions because of difficulty of offshore observation with high accuracy. Recently accurate in situ observation of offshore wind waves is getting possible at low cost owing to a wave height and direction sensor developed by Harigae et al. (2004) by installing a point-positioning GPS receiver on a surface drifting buoy. The point-positioning GPS sensor can extract three dimensional movements of the buoy excited by ocean waves with minimizing effects of GPS point-positioning errors through the use of a high-pass filter. Two drifting buoys equipped with the GPS-based wave sensor charged by solar cells were drifted in the western North Pacific and one of them continued to observe wind waves during 16 months from Sep. 2007. The RMSE of the GPS-based wave sensor was less than 10cm in significant wave height and about 1s in significant wave period in comparison with other sensors, i.e. accelerometers installed on drifting buoys of Japan Meteorological Agency, ultrasonic sensors placed at the Hiratsuka observation station of the University of Tokyo and altimeter of the JASON-1. The GPS-based wave buoys enabled us to detect freak waves defined as waves whose height is more than twice the significant wave height. The observation conducted by the wave buoys in 2007-2008 indicated a little more frequent occurrence of freak waves comparing with Forristall’s (1978) empirical formula and Naess’s (1985) distribution for a narrow-band Gaussian sea. Fig.1. Time series of the ratio of the significant wave height to the maximum wave height in 20 minutes sampling period observed by a drifting buoy with a GPS sensor

An improved grey model for the prediction of real-time GPS satellite clock bias

NASA Astrophysics Data System (ADS)

Zheng, Z. Y.; Chen, Y. Q.; Lu, X. S.

2008-07-01

In real-time GPS precise point positioning (PPP), real-time and reliable satellite clock bias (SCB) prediction is a key to implement real-time GPS PPP. It is difficult to hold the nuisance and inenarrable performance of space-borne GPS satellite atomic clock because of its high-frequency, sensitivity and impressionable, it accords with the property of grey model (GM) theory, i. e. we can look on the variable process of SCB as grey system. Firstly, based on limits of quadratic polynomial (QP) and traditional GM to predict SCB, a modified GM (1,1) is put forward to predict GPS SCB in this paper; and then, taking GPS SCB data for example, we analyzed clock bias prediction with different sample interval, the relationship between GM exponent and prediction accuracy, precision comparison of GM to QP, and concluded the general rule of different type SCB and GM exponent; finally, to test the reliability and validation of the modified GM what we put forward, taking IGS clock bias ephemeris product as reference, we analyzed the prediction precision with the modified GM, It is showed that the modified GM is reliable and validation to predict GPS SCB and can offer high precise SCB prediction for real-time GPS PPP.

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.

USNO GPS program

NASA Technical Reports Server (NTRS)

Putkovich, K.

1981-01-01

Initial test results indicated that the Global Positioning System/Time Transfer Unit (GPS/TTU) performed well within the + or - 100 nanosecond range required by the original system specification. Subsequent testing involved the verification of GPS time at the master control site via portable clocks and the acquisition and tracking of as many passes of the space vehicles currently in operation as possible. A description and discussion of the testing, system modifications, test results obtained, and an evaluation of both GPS and the GPS/TTU are presented.

47 CFR 87.151 - Special requirements for differential GPS receivers.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 47 Telecommunication 5 2010-10-01 2010-10-01 false Special requirements for differential GPS receivers. 87.151 Section 87.151 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES AVIATION SERVICES Technical Requirements § 87.151 Special requirements for...

Model based Computerized Ionospheric Tomography in space and time

NASA Astrophysics Data System (ADS)

Tuna, Hakan; Arikan, Orhan; Arikan, Feza

2018-04-01

Reconstruction of the ionospheric electron density distribution in space and time not only provide basis for better understanding the physical nature of the ionosphere, but also provide improvements in various applications including HF communication. Recently developed IONOLAB-CIT technique provides physically admissible 3D model of the ionosphere by using both Slant Total Electron Content (STEC) measurements obtained from a GPS satellite - receiver network and IRI-Plas model. IONOLAB-CIT technique optimizes IRI-Plas model parameters in the region of interest such that the synthetic STEC computations obtained from the IRI-Plas model are in accordance with the actual STEC measurements. In this work, the IONOLAB-CIT technique is extended to provide reconstructions both in space and time. This extension exploits the temporal continuity of the ionosphere to provide more reliable reconstructions with a reduced computational load. The proposed 4D-IONOLAB-CIT technique is validated on real measurement data obtained from TNPGN-Active GPS receiver network in Turkey.

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.

Continuous professional development for GPs: experience from Denmark.

PubMed

Kjaer, N K; Steenstrup, A P; Pedersen, L B; Halling, A

2014-07-01

Continuous professional development (CPD) for Danish general practitioners (GPs) is voluntary and based on funded accredited activities. There is an ongoing discussion on how to improve this current system by introducing mandatory elements. To inform this debate, we set out to identify GPs' current use of CPD and to explore the motives behind their choices. A mixed-methods study with a combined qualitative and quantitative approach was used. In 2012, two focus group interviews were conducted, followed up the same year by an online questionnaire sent to 1079 randomly chosen Danish GPs. Focus groups: CPD activities are chosen based on personal needs analysis, and in order to be professionally updated, to meet engaged colleagues and to prevent burnout. GPs also attend CPD to assess their own pre-existing level of competence. CPD activities need to be experienced as being both meaningful and relevant in order to have an impact. Questionnaire: The response rate was 686/1079 (63%). GPs spend on average 10.5 days per year on accredited, voluntary CPD activities. Workplace-related CPD activities and practice-based small group learning played a significant role. The main motivation for choice of CPD activities included academic interest, experience of patient-related problems in their own surgeries and medical topics where the GPs felt insufficiently confident. Danish GPs are frequent users of voluntary accredited CPD. Their CPD choices are motivated by topics strengthening their professional capacity and preventing burnout. There would seem to be no need for a mandatory system. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

The lesser evil? Initiating a benzodiazepine prescription in general practice: a qualitative study on GPs' perspectives.

PubMed

Anthierens, Sibyl; Habraken, Hilde; Petrovic, Mirko; Christiaens, Thierry

2007-12-01

Chronic benzodiazepine (BZD) use is widespread and linked with adverse effects. There is consensus concerning the importance of initiating BZD as a crucial moment. Nevertheless specific research in this field is lacking. This paper addresses the views of GPs on why they start prescribing BZDs to first-time users. Qualitative study with five focus groups analysed using a systematic content analysis. Regions of Ghent and Brussels in Belgium. A total of 35 general practitioners. The GPs' perspective on their initiating of BZD prescribing. GPs reported that they are cautious in initiating BZD usage. At the same time, GPs feel overwhelmed by the psychosocial problems of their patients. They show empathy by prescribing. They feel in certain situations there are no other solutions and they experience BZDs as the lesser evil. They admit to resorting to BZDs because of time restraint and lack of alternatives. GPs do not perceive the addictive nature of BZD consumption as a problem with first-time users. GPs do not specifically mention patients' demand as an element for starting. The main concern of GPs is to help the patient. GPs should be aware of the addictive nature of BZD even in low doses and a non-pharmacological approach should be seen as the best first approach. If GPs decide to prescribe a BZD they should make plain to the patient that the medication is only a "temporary" solution with clear agreements with regard to medication withdrawal.

Time Transfer from Combined Analysis of GPS and TWSTFT Data

DTIC Science & Technology

2008-12-01

40th Annual Precise Time and Time Interval (PTTI) Meeting 565 TIME TRANSFER FROM COMBINED ANALYSIS OF GPS AND TWSTFT DATA...bipm.org Abstract This paper presents the time transfer results obtained from the combination of GPS data and TWSTFT data. Two different methods...view, constrained by TWSTFT data. Using the Vondrak-Cepek algorithm, the second approach (named PPP+TW) combines the TWSTFT time transfer data with

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.

GPS: Public Utility or Software Platform

DTIC Science & Technology

2016-09-01

major occurrences that could interrupt GPS’s operation for an extended period of time . Despite these safeguards, the U.S. government has...in the event of a GPS interruption .178 2. GPS Infrastructure is designed to Prevent and Minimize Disruption Like a public utility, GPS is designed ...production and distribution while at the same time minimizing the likelihood of signal interruptions . Each of GPS’s operational satellites are

The Integration of TLS and Continuous GPS to Study Landslide Deformation: A Case Study at the El Yunque National Forest, Puerto Rico

NASA Astrophysics Data System (ADS)

Phillips, D. A.; Wang, G.; Joyce, J.; Rivera, F. O.; Galan, G.; Meertens, C. M.

2010-12-01

Terrestrial Laser Scanning (TLS) and Global Positioning System (GPS) technologies provide comprehensive information of landslide deformation in the both spatial and temporal domains, which are critical to study the dynamics and kinematics of landslides. TLS allows the generation of a precise 3D model of a landslide surface by deriving spatial deformation from consecutive TLS campaigns. Continuous GPS (CGPS) monitoring allows the generation of the displacement time series of single points. Integrated TLS and CGPS datasets were collected at the base of a 500-600 meter long landslide on a steep mountain slope in the El Yunque National Rainforest in Puerto Rico. Major movements of this landslide in 2004 and 2005 caused the closing of one of three remaining access roads to the national forest. A retaining wall was constructed to restrain the landslide and allow the road reopen. Prior to termination of the wall a significant portion of the northwest end of the wall failed. This portion was repaired but prior to final termination in August 2009 significant soil displacements behind the failed section thwarted final grading efforts. Geologic investigation indicated that the landslide extended much further upslope than indicated and involved bedrock as well as overlying residual soils. Striations along flank escarpments indicated displacement of the entire landslide to the northwest but active displacement could only be certified in the lower most portions behind the retaining wall. The northwest portion of the wall continued to show flexural deformation until it finally burst in July 2010. The size and displacement magnitude of the presently moving mass has become a major focus of investigation. To precisely identify the present boundaries and displacement magnitude of the lower portions of the landslide, we performed two TLS campaigns at the landslide site in May and August 2010. A continuous GPS array consisting of 3 stations was also installed at the site, one of which was located outside of the landslide as a stable reference point. Topcon GB-1000 dual frequency receivers and PG-A1 antennas were used to collect the GPS data. GPS data were processed using Topcon software. A Riegl VZ-400 laser scanner, provided by UNAVCO, was used to collect the TLS data. This scanner provides high resolution, high-speed data acquisition using a narrow infrared laser beam and a fast scanning mechanism. Centimeter-level scans from 12 scan positions were performed during each TLS campaign. TLS data acquisition and global registration were performed using RIEGL RiSCAN-PRO software. The Generic Mapping Tools (GMT, http://gmt.soest.hawaii.edu), a software package widely utilized in the geophysical community, was used for data post processing and map plotting. Our TLS and GPS results have clearly identified the boundaries, the rate and direction of displacement, and the volume change of the lower portions of presently sliding mass. Rainfall data from a local USGS weather station were also integrated to this study. Our results indicate close correlation between landslide movements and rainfall.

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.

Applicability of the theory of planned behavior in explaining the general practitioners eLearning use in continuing medical education.

PubMed

Hadadgar, Arash; Changiz, Tahereh; Masiello, Italo; Dehghani, Zahra; Mirshahzadeh, Nahidossadat; Zary, Nabil

2016-08-22

General practitioners (GP) update their knowledge and skills by participating in continuing medical education (CME) programs either in a traditional or an e-Learning format. GPs' beliefs about electronic format of CME have been studied but without an explicit theoretical framework which makes the findings difficult to interpret. In other health disciplines, researchers used theory of planned behavior (TPB) to predict user's behavior. In this study, an instrument was developed to investigate GPs' intention to use e-Learning in CME based on TPB. The goodness of fit of TPB was measured using confirmatory factor analysis and the relationship between latent variables was assessed using structural equation modeling. A total of 148 GPs participated in the study. Most of the items in the questionnaire related well to the TPB theoretical constructs, and the model had good fitness. The perceived behavioral control and attitudinal constructs were included, and the subjective norms construct was excluded from the structural model. The developed questionnaire could explain 66 % of the GPs' intention variance. The TPB could be used as a model to construct instruments that investigate GPs' intention to participate in e-Learning programs in CME. The findings from the study will encourage CME managers and researchers to explore the developed instrument as a mean to explain and improve the GPs' intentions to use eLearning in CME.

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.

Preliminary Comparison of Two-Way Satellite Time and Frequency Transfer and GPS Common-View Time Transfer During the INTELSAT Field Trial

NASA Technical Reports Server (NTRS)

Davis, John A.; Lewandowski, W.; DeYoung, James A.; Kirchner, Dieter; Hetzel, Peter; deJong, Gerrit; Soering, A.; Baumont, F.; Klepczynski, William; McKinley, Angela Davis;

Contemporary Surface Seasonal Oscillation and Vertical Deformation in Tibetan Plateau and Nepal Derived from the GPS, Leveling and GRACE Data

NASA Astrophysics Data System (ADS)

Shen, W.; Pan, Y.; Hwang, C.; Ding, H.

2015-12-01

We use 168 Continuous Global Positioning System (CGPS) stations distributed in the Tibetan Plateau (TP) and Nepal from lengths of 2.5 to 14 years to estimate the present-day velocity field in this area, including the horizontal and vertical deformations under the frame ITRF2008. We estimate and remove common mode errors in regional GPS time series using the principal component analysis (PCA), obtaining a time series with high signal to noise ratio. Following the maximum estimation analysis, a power law plus white noise stochastic model are adopted to estimate the velocity field. The highlight of Tibetan region is the crust vertical deformation. GPS vertical time series present seasonal oscillations caused by temporal mass loads, hence GRACE data from CSR are used to study the mass loads change. After removing the mass load deformations from GPS vertical rates, the results are improved. Leveling data about 48 years in this region are also used to estimate the rates of vertical movements. Our study suggests that the boundary of south Nepal is still sinking due to the fact that the India plate is crashing into the Eurasian plate. The uplift rates from south to north of TP reduce gradually. Himalayas region and north Nepal uplift around 6 mm/yr in average. The uplift rate along East TP in Qinhai is around 2.7 mm/yr in average. In contrast, the southeast of Tibetan Plateau, south Yunnan and Tarim in Xinjiang sink with different magnitudes. Our observation results suggest complicated mechanism of the mass migration in TP. This study is supported by National 973 Project China (grant Nos. 2013CB733302 and 2013CB733305), NSFC (grant Nos. 41174011, 41429401, 41210006, 41128003, 41021061).

Improving access and continuity of care for homeless people: how could general practitioners effectively contribute? Results from a mixed study

PubMed Central

Grassineau, Dominique; Balique, Hubert; Loundou, Anderson; Sambuc, Roland; Daguzan, Alexandre; Gentile, Gaetan; Gentile, Stéphanie

2016-01-01

Objectives To analyse the views of general practitioners (GPs) about how they can provide care to homeless people (HP) and to explore which measures could influence their views. Design Mixed-methods design (qualitative –> quantitative (cross-sectional observational) → qualitative). Qualitative data were collected through semistructured interviews and through questionnaires with closed questions. Quantitative data were analysed with descriptive statistical analyses on SPPS; a content analysis was applied on qualitative data. Setting Primary care; views of urban GPs working in a deprived area in Marseille were explored by questionnaires and/or semistructured interview. Participants 19 GPs involved in HP's healthcare were recruited for phase 1 (qualitative); for phase 2 (quantitative), 150 GPs who provide routine healthcare (‘standard’ GPs) were randomised, 144 met the inclusion criteria and 105 responded to the questionnaire; for phase 3 (qualitative), data were explored on 14 ‘standard’ GPs. Results In the quantitative phase, 79% of the 105 GPs already treated HP. Most of the difficulties they encountered while treating HP concerned social matters (mean level of perceived difficulties=3.95/5, IC 95 (3.74 to 4.17)), lack of medical information (mn=3.78/5, IC 95 (3.55 to 4.01)) patient's compliance (mn=3.67/5, IC 95 (3.45 to 3.89)), loneliness in practice (mn=3.45/5, IC 95 (3.18 to 3.72)) and time required for the doctor (mn=3.25, IC 95 (3 to 3.5)). From qualitative analysis we understood that maintaining a stable follow-up was a major condition for GPs to contribute effectively to the care of HP. Acting on health system organisation, developing a medical and psychosocial approach with closer relation with social workers and enhancing the collaboration between tailored and non-tailored programmes were also other key answers. Conclusions If we adapt the conditions of GPs practice, they could contribute to the improvement of HP's health. These results will enable the construction of a new model of primary care organisation aiming to improve access to healthcare for HP. PMID:27903566

Evaluation of GPS Coverage for the X-33 Michael-6 Trajectory

NASA Technical Reports Server (NTRS)

Lundberg, John B.

1998-01-01

The onboard navigational system for the X-33 test flights will be based on the use of measurements collected from the Embedded Global Positioning System (GPS)/INS system. Some of the factors which will affect the quality of the GPS contribution to the navigational solution will be the number of pseudorange measurements collected at any instant in time, the distribution of the GPS satellites within the field of view, and the inherent noise level of the GPS receiver. The distribution of GPS satellites within the field of view of the receiver's antenna will depend on the receiver's position, the time of day, pointing direction of the antenna, and the effective cone angle of the antenna. The number of pseudorange measurements collected will depend upon these factors as well as the time required to lock onto a GPS satellite signal once the GPS satellite comes into the field of view of the antenna and the number of available receiver channels. The objective of this study is to evaluate the GPS coverage resulting from the proposed antenna pointing directions, the proposed antenna cone angles, and the effects due to the time of day for the X-33 Michael-6 trajectory from launch at Edwards AFB, California, to the start of the Terminal Area Energy Management (TAEM) phase on approach to Michael AAF, Utah.

General practitioners' attitudes toward reporting and learning from adverse events: results from a survey.

PubMed

Mikkelsen, Thorbjørn H; Sokolowski, Ineta; Olesen, Frede

2006-03-01

To investigate GPs' attitudes to and willingness to report and learn from adverse events and to study how a reporting system should function. Survey. General practice in Denmark. GPs' attitudes to exchange of experience with colleagues and others, and circumstances under which such exchange is accepted. A structured questionnaire sent to 1198 GPs of whom 61% responded. RESULTS. GPs had a positive attitude towards discussing adverse events in the clinic with colleagues and staff and in their continuing medical education groups. The GPs had a positive attitude to reporting adverse events to a database if the system granted legal and administrative immunity to reporters. The majority preferred a reporting system located at a research institute. GPs have a very positive attitude towards discussing and reporting adverse events. This project encourages further research and pilot projects testing concrete reporting systems.

Comparative Analysis of Volcanic Inflation—Deflation Cycles

NASA Astrophysics Data System (ADS)

Walwer, D.; Ghil, M.; Calais, E.

2016-12-01

GPS geodetic data together with INSAR images are often used to formulate kinematic models of the sources of volcanic deformations. The increasing amount of data now available allows one to produce time series that are several years long and thus capture continuously the history of volcanic deformations, in particular their nonlinear behavior. This information is highly valuable in helping understand the dynamics of volcanic systems.Nonlinear deformation signals are, however, difficult to extract from the background noise inherent in the GPS time series. It is also arduous to unravel the signal of interest from other nonlinear signals, such as the seasonal oscillations associated with mass variations in the atmosphere, the ocean, and the hydrological reservoirs. Here we use Multichannel Singular Spectrum Analysis (M-SSA) — an advanced, data-adaptive method for time series analysis that exploits simultaneously the temporal and spatial correlations of geophysical fields — to extract such deformation signals.We apply M-SSA to GPS data sets from four volcanoes: Akutan, Alaska; Okmok, Alaska; Westdahl, Alaska; and Piton de la Fournaise, La Reunion. Our analyses show that all four volcanoes share similar features in their deformation history, suggesting similarities in the dynamics that generate the inflation-deflation cycles. In particular, all four volcanic systems exhibit sawtooth-shaped oscillations with slow inflations followed by slower deflations, with time scales that vary from 6 months to 4 years. This relation of dynamical similarity is further highlighted by the phase portrait reconstruction of the four systems in the plane of deformation vs. rate-of-deformation, as obtained from the deformation signals extracted from the GPS time series using M-SSA.The inflating phase of these oscillations is followed by eruptions at Okmok volcano and at Piton de la Fournaise. These analysis results suggest that these volcanic inflation—deflation cycles are associated with the destabilization of a volcanic system and may lead to the identification of premonitory signals for an eruptive regime.

Comparison of GPS and GLONASS common-view time transfers

NASA Technical Reports Server (NTRS)

Lewandowski, W.; Petit, G.; Thomas, C.; Cherenkov, G. T.; Koshelyaevsky, N. B.; Pushkin, S. B.

1993-01-01

It was already shown than even with a simple daily averaging of GLONASS data at each site, continental GLONASS time transfer can be achieved at a level of several tens of nanoseconds. A further step is to carry out observations of GLONASS satellites by the common-view method. A comparison of GPS and GLONASS common-view time transfers between Russia and Western Europe are reported. At each site, a GPS receiver and a GLONASS receiver are connected to the same atomic clock. Both GPS receivers are of NBS type and the GLONASS receivers are of type A-724. As GPS common-view time transfer between Sevres and Mendeleevo is accomplished at a level of a few nanoseconds in precision, it gives an excellent reference with which to evaluate the performance of GLONASS common-view time transfer.

Regional Phenomena of Vertical Deformation in Southern Part of Indonesia

NASA Astrophysics Data System (ADS)

Sarsito, D. A.; Susilo; Andreas, H.; Pradipta, D.; Gumilar, I.

2018-02-01

Distribution of present-day horizontal and vertical deformation across the Southern Part of Indonesia at Java, Bali and Nusa Tenggara now days can be determined from continuous and campaign types of GNSS GPS data monitoring. For vertical deformation in this case we use the continuous types since they are give better quality of data consistency compare to campaign type. Continuous Global Positioning System (CGPS) are maintaining by Geospatial Information Agency for more than a decade. The vertical displacements or velocity rates are estimated from time series analysis after multi-baseline GPS processing using GAMIT-GLOBK software with respect to the latest International Terrestrial Reference Frame. The result shows some interesting phenomena where the northern part of research area majority have negative value that may indicate land subsidence with or without tectonic subsidence combination. In the middle part, the uplift phenomena are clearly shown and in the southern part show combine pattern between uplift and subsidence. The impacts of those phenomena would be discuss also in this paper since many population and infrastructure are located in the areas that will need more protection planning to reduce the negative impact such as earthquake and flooding.

Reduced variability and execution time to reach a target with a needle GPS system: Comparison between physicians, residents and nurse anaesthetists.

PubMed

Fevre, Marie-Cécile; Vincent, Caroline; Picard, Julien; Vighetti, Arnaud; Chapuis, Claire; Detavernier, Maxime; Allenet, Benoît; Payen, Jean-François; Bosson, Jean-Luc; Albaladejo, Pierre

2018-02-01

Ultrasound (US) guided needle positioning is safer than anatomical landmark techniques for central venous access. Hand-eye coordination and execution time depend on the professional's ability, previous training and personal skills. Needle guidance positioning systems (GPS) may theoretically reduce execution time and facilitate needle positioning in specific targets, thus improving patient comfort and safety. Three groups of healthcare professionals (41 anaesthesiologists and intensivists, 41 residents in anaesthesiology and intensive care, 39 nurse anaesthetists) were included and required to perform 3 tasks (positioning the tip of a needle in three different targets in a silicon phantom) by using successively a conventional US-guided needle positioning and a needle GPS. We measured execution times to perform the tasks, hand-eye coordination and the number of repositioning occurrences or errors in handling the needle or the probe. Without the GPS system, we observed a significant inter-individual difference for execution time (P<0.05), hand-eye coordination and the number of errors/needle repositioning between physicians, residents and nurse anaesthetists. US training and video gaming were found to be independent factors associated with a shorter execution time. Use of GPS attenuated the inter-individual and group variability. We observed a reduced execution time and improved hand-eye coordination in all groups as compared to US without GPS. Neither US training, video gaming nor demographic personal or professional factors were found to be significantly associated with reduced execution time when GPS was used. US associated with GPS systems may improve safety and decrease execution time by reducing inter-individual variability between professionals for needle-handling procedures. Copyright © 2016 Société française d'anesthésie et de réanimation (Sfar). Published by Elsevier Masson SAS. All rights reserved.

Integration of GRACE and GNET GPS in modeling the deglaciation of Greenland

NASA Astrophysics Data System (ADS)

Knudsen, P.; Madsen, F. B.; Khan, S. A.; Bevis, M. G.; van Dam, T. M.

2017-12-01

The use the monthly gravity fields from the Gravity Recovery and Climate Experiment (GRACE) has become essential when assessing and modeling the mass changes of the ice sheets. The recent degradation of the current mission, however, has hampered the continuous monitoring of ice sheet masses, at least until GRACE Follow-On mission will become operational. Through the recent years it has been demonstrated that mass changes can be observed by GPS receivers mounted on the adjacent bedrock. Especially, the Greenland GPS Network (GNET) has proven that GPS is a valuable technique for detecting mass changes through the Earths elastic response. An integration of GNET with other observations of the Greenland ice sheet, e.g. satellite altimetry and GRACE, has made studies of GIA progressing significantly. In this study, we aim at improving the monitoring of the ice sheet mass by utilizing the redundancy for reducing the influence of errors and to fill in at data voids and, not at least to bridge the gap between GRACE and GRACE FO. Initial analyses are carried out to link GRACE and GNET time series empirically. EOF analyses are carried out to extract the main part of the variability and to isolate errors. Subsequently, empirical covariance functions are derived and used in the integration. Preliminary results are derived and inter-compared.

GPS Data Filtration Method for Drive Cycle Analysis Applications

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

Duran, A.; Earleywine, M.

2013-02-01

When employing GPS data acquisition systems to capture vehicle drive-cycle information, a number of errors often appear in the raw data samples, such as sudden signal loss, extraneous or outlying data points, speed drifting, and signal white noise, all of which limit the quality of field data for use in downstream applications. Unaddressed, these errors significantly impact the reliability of source data and limit the effectiveness of traditional drive-cycle analysis approaches and vehicle simulation software. Without reliable speed and time information, the validity of derived metrics for drive cycles, such as acceleration, power, and distance, become questionable. This study exploresmore » some of the common sources of error present in raw onboard GPS data and presents a detailed filtering process designed to correct for these issues. Test data from both light and medium/heavy duty applications are examined to illustrate the effectiveness of the proposed filtration process across the range of vehicle vocations. Graphical comparisons of raw and filtered cycles are presented, and statistical analyses are performed to determine the effects of the proposed filtration process on raw data. Finally, an evaluation of the overall benefits of data filtration on raw GPS data and present potential areas for continued research is presented.« less

Computer Assisted Chronic Disease Management: Does It Work? A Pilot Study Using Mixed Methods

PubMed Central

Jones, Kay M.; Biezen, Ruby; Piterman, Leon

2013-01-01

Background. Key factors for the effective chronic disease management (CDM) include the availability of practical and effective computer tools and continuing professional development/education. This study tested the effectiveness of a computer assisted chronic disease management tool, a broadband-based service known as cdmNet in increasing the development of care plans for patients with chronic disease in general practice. Methodology. Mixed methods are the breakthrough series methodology (workshops and plan-do-study-act cycles) and semistructured interviews. Results. Throughout the intervention period a pattern emerged suggesting GPs use of cdmNet initially increased, then plateaued practice nurses' and practice managers' roles expanded as they became more involved in using cdmNet. Seven main messages emerged from the GP interviews. Discussion. The overall use of cdmNet by participating GPs varied from “no change” to “significant change and developing many the GPMPs (general practice management plans) using cdmNet.” The variation may be due to several factors, not the least, allowing GPs adequate time to familiarise themselves with the software and recognising the benefit of the team approach. Conclusion. The breakthrough series methodology facilitated upskilling GPs' management of patients diagnosed with a chronic disease and learning how to use the broadband-based service cdmNet. PMID:24959576

Removing Hydrology Signals to Determine Ground Motion at the Apache Point Lunar Laser Ranging Site, New Mexico

NASA Astrophysics Data System (ADS)

Crossley, D. J.; Borsa, A. A.; Murphy, T.

2017-12-01

We continue the analysis of superconducting gravimeter (SG) and GPS data at Apache Point Observatory (APO) as part of the astrophysical effort to reduce LLR errors to the mm level. With 8 years of data accumulated, the main impediment to getting benefit from the SG data is the assessment of the hydrology signal that arises mainly from the attraction of local water masses close to the site. Traditional SG processing attempts to remove as much signal as possible from the loading and attraction contributions, but we are limited at APO because here is no hydrology ground truth. Nevertheless, we produce a gravity residual that corresponds to some extent with the rather noisy vertical GPS data from Plate Boundary Site PB07 close to Sunspot observatory 2 km from APO. The main goal of this paper, apart from updating the gravity and GPS correction using recent models, is to construct simulated SG and GPS time series from the synthetic source functions - ground uplift, hydrology attraction and loading - and to perform an inversion to see what can be recovered of the vertical ground motion. The simulation will also include a first look at the effect of this synthetic local data on the current Planetary Ephemeris Program solution for the lunar distance.

Comparison of GLONASS and GPS Time Transfers Between Two West European Time Laboratories and VNIIFTRI

DTIC Science & Technology

1991-12-01

COMPARISON OF GLONASS AND GPS TIME TRANSFERS BETWEEN TWO WEST EUROPEAN TIME LABORATORIES AND VNIIFTRI P. Daly Department of Electronic and...Radiotechnical Measurements - VNIIFTRI Mendeleevo, Moscow region, 141570, USSR and W. Lewandowski, G. Petit, C. Thomas Bureau International des Poids et...00-1991 to 00-00-1991 4. TITLE AND SUBTITLE Comparison of GLONASS and GPS Time Transfers Between Two West European Time Laboratories and VNIIFTRI

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.

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.

Near-Real Time Monitoring of TEC Over Japan at NICT (RWC Tokyo OF ISES)

NASA Astrophysics Data System (ADS)

Miyake, W.; Jin, H.

2010-05-01

The world wide use of global navigation satellite systems such as GPS offers unique opportunities for a permanent monitoring of the total electron content (TEC) of the ionosphere. We have developed a system of the rapid derivation of TEC from GEONET (a dense GPS receiver network in Japan). In addition to a previous plot of TEC temporal variation over Japan, we have recently developed a near-real-time two-dimensional TEC map and have used it for the daily operation of Space Weather Forecast Center at NICT (Regional Warning Center Tokyo of International Space Environment Service). The TEC map can be used to continuously monitor the ionospheric disturbances over Japan, including spatial and temporal development of ionospheric storms, large-amplitude traveling ionospheric disturbances, and plasma bubbles intruding over Japan, with high time resolution. The development of the real-time monitoring system of TEC enables us to monitor large ionospheric disturbances, ranging from global- to small-scale disturbances, expected in the next solar maximum. The plot and maps are open to the public and are available on http://wdc.nict.go.jp/IONO/index_E.html.

Searching for geodetic transient slip signals along the Parkfield segment of the San Andreas Fault

NASA Astrophysics Data System (ADS)

Rousset, B.; Burgmann, R.

2017-12-01

The Parkfield section of the San Andreas fault is at the transition between a segment locked since the 1857 Mw 7.9 Fort Tejon earthquake to its south and a creeping segment to the north. It is particularly well instrumented since it is the many previous studies have focused on studying the coseismic and postseismic phases of the two most recent earthquake cycles, the interseismic phase is exhibiting interesting dynamics at the down-dip edge of the seismogenic zone, characterized by a very large number of low frequency earthquakes (LFE) with different behaviors depending on location. Interseismic fault creep rates appear to vary over a wide range of spatial and temporal scales, from the Earth's surface to the base of crust. In this study, we take advantage of the dense Global Positioning System (GPS) network, with 77 continuous stations located within a circle of radius 80 km centered on Parkfield. We correct these time series for the co- and postseismic signals of the 2003 Mw 6.3 San Simeon and 2004 Mw 6.0 Parkfield earthquakes. We then cross-correlate the residual time series with synthetic slow-slip templates following the approach of Rousset et al. (2017). Synthetic tests with transient events contained in GPS time series with realistic noise show the limit of detection of the method. In the application with real GPS time series, the highest correlation amplitudes are compared with micro-seismicity rates, as well as tremor and LFE observations.

Ionospheric Sensor Developments for the Year-2000 Solar Maximum

DTIC Science & Technology

2000-10-23

locations, work during the year enhanced and exploited several diagnostic instruments deployed for the High frequency Active Aurora Research Program ( HAARP ...Under HAARP , measurements employing both GPS and coherent VHF-UHF signals transmitted from satellites in low-earth polar orbit resulted in time...histories and latitudinal scans of absolute TEC over Maska, and enhanced operation of the HAARP classic riometer resulted in essentially continuous

An introduction to the global positioning system and some geological applications

NASA Technical Reports Server (NTRS)

Dixon, T. H.

1991-01-01

The fundamental principles of the global positioning system (GPS) are reviewed, with consideration given to geological and geophysical applications and related accuracy requirements. Recent improvements are emphasized which relate to areas such as equipment cost, limitations in the GPS satellite constellation, data analysis, uncertainties in satellite orbits and propagation delays, and problems in resolving carrier phase cycle ambiguities. Earthquake processes and near-fault crustal deformation monitoring have been facilitated by advances in GPS data acquisition and analysis. Horizontal positioning capability has been improved by new satellite constellation, better models, and global tracking networks. New classes of tectonic problems may now be studied through GPS, such as kinematic descriptions of crustal deformation and the measurement of relative plate motion at convergent boundaries. Continued improvements in the GPS are foreseen.

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.

Applications of GPS technologies to field sports.

PubMed

Aughey, Robert J

2011-09-01

Global positioning system (GPS) technology was made possible after the invention of the atomic clock. The first suggestion that GPS could be used to assess the physical activity of humans followed some 40 y later. There was a rapid uptake of GPS technology, with the literature concentrating on validation studies and the measurement of steady-state movement. The first attempts were made to validate GPS for field sport applications in 2006. While GPS has been validated for applications for team sports, some doubts continue to exist on the appropriateness of GPS for measuring short high-velocity movements. Thus, GPS has been applied extensively in Australian football, cricket, hockey, rugby union and league, and soccer. There is extensive information on the activity profile of athletes from field sports in the literature stemming from GPS, and this includes total distance covered by players and distance in velocity bands. Global positioning systems have also been applied to detect fatigue in matches, identify periods of most intense play, different activity profiles by position, competition level, and sport. More recent research has integrated GPS data with the physical capacity or fitness test score of athletes, game-specific tasks, or tactical or strategic information. The future of GPS analysis will involve further miniaturization of devices, longer battery life, and integration of other inertial sensor data to more effectively quantify the effort of athletes.

How can general practitioners establish 'place attachment' in Australia's Northern Territory? Adjustment trumps adaptation.

PubMed

Auer, K; Carson, D

2010-01-01

Retention of GPs in the more remote parts of Australia remains an important issue in workforce planning. The Northern Territory of Australia experiences very high rates of staff turnover. This research examined how the process of forming 'place attachment' between GP and practice location might influence prospects for retention. It examines whether GPs use 'adjustment' (short term trade-offs between work and lifestyle ambitions) or 'adaptation' (attempts to change themselves and their environment to fulfil lifestyle ambitions) strategies to cope with the move to new locations. 19 semi-structured interviews were conducted mostly with GPs who had been in the Northern Territory for less than 3 years. Participants were asked about the strategies they used in an attempt to establish place attachment. Strategies could be structural (work related), personal, social or environmental. There were strong structural motivators for GPs to move to the Northern Territory. These factors were seen as sufficiently attractive to permit the setting aside of other lifestyle ambitions for a short period of time. Respondents found the environmental aspects of life in remote areas to be the most satisfying outside work. Social networks were temporary and the need to re-establish previous networks was the primary driver of out migration. GPs primarily use adjustment strategies to temporarily secure their position within their practice community. There were few examples of adaptation strategies that would facilitate a longer term match between the GPs' overall life ambitions and the characteristics of the community. While this suggests that lengths of stay will continue to be short, better adjustment skills might increase the potential for repeat service and limit the volume of unplanned early exits.

Repeated anaesthesia with isoflurane and medetomidine-midazolam-fentanyl in guinea pigs and its influence on physiological parameters

PubMed Central

Tacke, Sabine; Guth, Brian; Henke, Julia

2017-01-01

Repeated anaesthesia may be required in experimental protocols and in daily veterinary practice, but anaesthesia is known to alter physiological parameters in GPs (Cavia porcellus, GPs). This study investigated the effects of repeated anaesthesia with either medetomidine-midazolam-fentanyl (MMF) or isoflurane (Iso) on physiological parameters in the GP. Twelve GPs were repeatedly administered with MMF or Iso in two anaesthesia sets. One set consisted of six 40-min anaesthesias, performed over 3 weeks (2 per week); the anaesthetic used first was randomized. Prior to Iso anaesthesia, atropine was injected. MMF anaesthesia was antagonized with AFN (atipamezole-flumazenil-naloxone). Abdominally implanted radio-telemetry devices recorded the mean arterial blood pressure (MAP), heart rate (HR) and core body temperature continuously. Additionally, respiratory rate, blood glucose and body weight were assessed. An operable state could be achieved and maintained for 40 min in all GPs. During the surgical tolerance with MMF, the GPs showed a large MAP range between the individuals. In the MMF wake- up phase, the time was shortened until the righting reflex (RR) returned and that occurred at lower MAP and HR values. Repeated Iso anaesthesia led to an increasing HR during induction (anaesthesias 2–6), non-surgical tolerance (anaesthesias 3–6) and surgical tolerance (anaesthesias 4, 6). Both anaesthetics may be used repeatedly, as repeating the anaesthesias resulted in only slightly different physiological parameters, compared to those seen with single anaesthesias. The regular atropine premedication induced HR increases and repeated MMF anaesthesia resulted in a metabolism increase which led to the faster return of RR. Nevertheless, Iso’s anaesthesia effects of strong respiratory depression and severe hypotension remained. Based on this increased anaesthesia risk with Iso, MMF anaesthesia is preferable for repeated use in GPs. PMID:28328950

Repeated anaesthesia with isoflurane and medetomidine-midazolam-fentanyl in guinea pigs and its influence on physiological parameters.

PubMed

Schmitz, Sabrina; Tacke, Sabine; Guth, Brian; Henke, Julia

2017-01-01

Repeated anaesthesia may be required in experimental protocols and in daily veterinary practice, but anaesthesia is known to alter physiological parameters in GPs (Cavia porcellus, GPs). This study investigated the effects of repeated anaesthesia with either medetomidine-midazolam-fentanyl (MMF) or isoflurane (Iso) on physiological parameters in the GP. Twelve GPs were repeatedly administered with MMF or Iso in two anaesthesia sets. One set consisted of six 40-min anaesthesias, performed over 3 weeks (2 per week); the anaesthetic used first was randomized. Prior to Iso anaesthesia, atropine was injected. MMF anaesthesia was antagonized with AFN (atipamezole-flumazenil-naloxone). Abdominally implanted radio-telemetry devices recorded the mean arterial blood pressure (MAP), heart rate (HR) and core body temperature continuously. Additionally, respiratory rate, blood glucose and body weight were assessed. An operable state could be achieved and maintained for 40 min in all GPs. During the surgical tolerance with MMF, the GPs showed a large MAP range between the individuals. In the MMF wake- up phase, the time was shortened until the righting reflex (RR) returned and that occurred at lower MAP and HR values. Repeated Iso anaesthesia led to an increasing HR during induction (anaesthesias 2-6), non-surgical tolerance (anaesthesias 3-6) and surgical tolerance (anaesthesias 4, 6). Both anaesthetics may be used repeatedly, as repeating the anaesthesias resulted in only slightly different physiological parameters, compared to those seen with single anaesthesias. The regular atropine premedication induced HR increases and repeated MMF anaesthesia resulted in a metabolism increase which led to the faster return of RR. Nevertheless, Iso's anaesthesia effects of strong respiratory depression and severe hypotension remained. Based on this increased anaesthesia risk with Iso, MMF anaesthesia is preferable for repeated use in GPs.

Development of GPS survey data management protocols/policy.

DOT National Transportation Integrated Search

2010-08-01

This project developed a statewide policy and criteria for collecting, analyzing, and managing global position system (GPS) survey data. The research project determined the needs of the Department in adopting the GPS real time kinetic (GPS RTK) stake...

SCIGN; new Southern California GPS network advances the study of earthquakes

USGS Publications Warehouse

Hudnut, Ken; King, Nancy

2001-01-01

Southern California is a giant jigsaw puzzle, and scientists are now using GPS satellites to track the pieces. These puzzle pieces are continuously moving, slowly straining the faults in between. That strain is then eventually released in earthquakes. The innovative Southern California Integrated GPS Network (SCIGN) tracks the motions of these pieces over most of southern California with unprecedented precision. This new network greatly improves the ability to assess seismic hazards and quickly measure the larger displacements that occur during and immediatelyafter earthquakes.

Airborne Pseudolites in a Global Positioning System (GPS) Degraded Environment

DTIC Science & Technology

2011-03-01

continuously two types of encoded pseudo-random noise (PRN) signals via using two center frequencies 4 in the L- band , namely L1 (1575.42 MHz) and L2...Jovanevic, Aleksandar, Nikhil Bhaita, Joseph Noronha, Brijesh Sirpatil, Michael Kirchner, and Deepak Saxena. “ Piercing the Veil ”. GPS World, 30–37, March...difficulties in receiver design. • Pseudolites can operate either at GPS L1, L2 and L5, or any other available frequency band . Similarly, other parameters to

Volcano monitoring using the Global Positioning System: Filtering strategies

USGS Publications Warehouse

Larson, K.M.; Cervelli, Peter; Lisowski, M.; Miklius, Asta; Segall, P.; Owen, S.

2001-01-01

Permanent Global Positioning System (GPS) networks are routinely used for producing improved orbits and monitoring secular tectonic deformation. For these applications, data are transferred to an analysis center each day and routinely processed in 24-hour segments. To use GPS for monitoring volcanic events, which may last only a few hours, real-time or near real-time data processing and subdaily position estimates are valuable. Strategies have been researched for obtaining station coordinates every 15 min using a Kalman filter; these strategies have been tested on data collected by a GPS network on Kilauea Volcano. Data from this network are tracked continuously, recorded every 30 s, and telemetered hourly to the Hawaiian Volcano Observatory. A white noise model is heavily impacted by data outages and poor satellite geometry, but a properly constrained random walk model fits the data well. Using a borehole tiltmeter at Kilauea's summit as ground-truth, solutions using different random walk constraints were compared. This study indicates that signals on the order of 5 mm/h are resolvable using a random walk standard deviation of 0.45 cm/???h. Values lower than this suppress small signals, and values greater than this have significantly higher noise at periods of 1-6 hours. Copyright 2001 by the American Geophysical Union.

Performances of different global positioning system devices for time-location tracking in air pollution epidemiological studies.

PubMed

Wu, Jun; Jiang, Chengsheng; Liu, Zhen; Houston, Douglas; Jaimes, Guillermo; McConnell, Rob

2010-11-23

People's time-location patterns are important in air pollution exposure assessment because pollution levels may vary considerably by location. A growing number of studies are using global positioning systems (GPS) to track people's time-location patterns. Many portable GPS units that archive location are commercially available at a cost that makes their use feasible for epidemiological studies. We evaluated the performance of five portable GPS data loggers and two GPS cell phones by examining positional accuracy in typical locations (indoor, outdoor, in-vehicle) and factors that influence satellite reception (building material, building type), acquisition time (cold and warm start), battery life, and adequacy of memory for data storage. We examined stationary locations (eg, indoor, outdoor) and mobile environments (eg, walking, traveling by vehicle or bus) and compared GPS locations to highly-resolved US Geological Survey (USGS) and Digital Orthophoto Quarter Quadrangle (DOQQ) maps. The battery life of our tested instruments ranged from <9 hours to 48 hours. The acquisition of location time after startup ranged from a few seconds to >20 minutes and varied significantly by building structure type and by cold or warm start. No GPS device was found to have consistently superior performance with regard to spatial accuracy and signal loss. At fixed outdoor locations, 65%-95% of GPS points fell within 20-m of the corresponding DOQQ locations for all the devices. At fixed indoor locations, 50%-80% of GPS points fell within 20-m of the corresponding DOQQ locations for all the devices except one. Most of the GPS devices performed well during commuting on a freeway, with >80% of points within 10-m of the DOQQ route, but the performance was significantly impacted by surrounding structures on surface streets in highly urbanized areas. All the tested GPS devices had limitations, but we identified several devices which showed promising performance for tracking subjects' time location patterns in epidemiological studies.

Performances of Different Global Positioning System Devices for Time-Location Tracking in Air Pollution Epidemiological Studies

PubMed Central

Wu, Jun; Jiang, Chengsheng; Liu, Zhen; Houston, Douglas; Jaimes, Guillermo; McConnell, Rob

2010-01-01

Background: People’s time-location patterns are important in air pollution exposure assessment because pollution levels may vary considerably by location. A growing number of studies are using global positioning systems (GPS) to track people’s time-location patterns. Many portable GPS units that archive location are commercially available at a cost that makes their use feasible for epidemiological studies. Methods: We evaluated the performance of five portable GPS data loggers and two GPS cell phones by examining positional accuracy in typical locations (indoor, outdoor, in-vehicle) and factors that influence satellite reception (building material, building type), acquisition time (cold and warm start), battery life, and adequacy of memory for data storage. We examined stationary locations (eg, indoor, outdoor) and mobile environments (eg, walking, traveling by vehicle or bus) and compared GPS locations to highly-resolved US Geological Survey (USGS) and Digital Orthophoto Quarter Quadrangle (DOQQ) maps. Results: The battery life of our tested instruments ranged from <9 hours to 48 hours. The acquisition of location time after startup ranged from a few seconds to >20 minutes and varied significantly by building structure type and by cold or warm start. No GPS device was found to have consistently superior performance with regard to spatial accuracy and signal loss. At fixed outdoor locations, 65%–95% of GPS points fell within 20-m of the corresponding DOQQ locations for all the devices. At fixed indoor locations, 50%–80% of GPS points fell within 20-m of the corresponding DOQQ locations for all the devices except one. Most of the GPS devices performed well during commuting on a freeway, with >80% of points within 10-m of the DOQQ route, but the performance was significantly impacted by surrounding structures on surface streets in highly urbanized areas. Conclusions: All the tested GPS devices had limitations, but we identified several devices which showed promising performance for tracking subjects’ time location patterns in epidemiological studies. PMID:21151593

Global Positioning System (GPS): Current status and possible nursery uses

Treesearch

Dick Karsky

2002-01-01

The GPS (Global Positioning System) is a worldwide satellite-positioning system that was funded, installed, and continues to be operated by the U.S. Department of Defense. The navigation signals are provided free and can be used by anyone who has the equipment necessary to receive them.

The use of precise ephemerides, ionospheric data, and corrected antenna coordinates in a long-distance GPS time transfer

NASA Technical Reports Server (NTRS)

Lewandowski, Wlodzimierz W.; Petit, Gerard; Thomas, Claudine; Weiss, Marc A.

1990-01-01

Over intercontinental distances, the accuracy of The Global Positioning System (GPS) time transfers ranges from 10 to 20 ns. The principal error sources are the broadcast ionospheric model, the broadcast ephemerides and the local antenna coordinates. For the first time, the three major error sources for GPS time transfer can be reduced simultaneously for a particular time link. Ionospheric measurement systems of the National Institute of Standards and Technology (NIST) type are now operating on a regular basis at the National Institute of Standards and Technology in Boulder and at the Paris Observatory in Paris. Broadcast ephemerides are currently recorded for time-transfer tracks between these sites, this being necessary for using precise ephemerides. At last, corrected local GPS antenna coordinates are now introduced in GPS receivers at both sites. Shown here is the improvement in precision for this long-distance time comparison resulting from the reduction of these three error sources.

A web-based GPS system for displacement monitoring and failure mechanism analysis of reservoir landslide.

PubMed

Li, Yuanyao; Huang, Jinsong; Jiang, Shui-Hua; Huang, Faming; Chang, Zhilu

2017-12-07

It is important to monitor the displacement time series and to explore the failure mechanism of reservoir landslide for early warning. Traditionally, it is a challenge to monitor the landslide displacements real-timely and automatically. Globe Position System (GPS) is considered as the best real-time monitoring technology, however, the accuracies of the landslide displacements monitored by GPS are not assessed effectively. A web-based GPS system is developed to monitor the landslide displacements real-timely and automatically in this study. And the discrete wavelet transform (DWT) is proposed to assess the accuracy of the GPS monitoring displacements. Wangmiao landslide in Three Gorges Reservoir area in China is used as case study. The results show that the web-based GPS system has advantages of high precision, real-time, remote control and automation for landslide monitoring; the Root Mean Square Errors of the monitoring landslide displacements are less than 5 mm. Meanwhile, the results also show that a rapidly falling reservoir water level can trigger the reactivation of Wangmiao landslide. Heavy rainfall is also an important factor, but not a crucial component.

Airborne Antenna System for Minimum-Cycle-Slip GPS Reception

NASA Technical Reports Server (NTRS)

Wright, C. Wayne

2009-01-01

A system that includes a Global Positioning System (GPS) antenna and associated apparatus for keeping the antenna aimed upward has been developed for use aboard a remote-sensing-survey airplane. The purpose served by the system is to enable minimum- cycle-slip reception of GPS signals used in precise computation of the trajectory of the airplane, without having to restrict the airplane to maneuvers that increase the flight time needed to perform a survey. Cycle slip signifies loss of continuous track of the phase of a signal. Minimum-cycle-slip reception is desirable because maintaining constant track of the phase of the carrier signal from each available GPS satellite is necessary for surveying to centimeter or subcentimeter precision. Even a loss of signal for as short a time as a nanosecond can cause cycle slip. Cycle slips degrade the quality and precision of survey data acquired during a flight. The two principal causes of cycle slip are weakness of signals and multipath propagation. Heretofore, it has been standard practice to mount a GPS antenna rigidly on top of an airplane, and the radiation pattern of the antenna is typically hemispherical, so that all GPS satellites above the horizon are viewed by the antenna during level flight. When the airplane must be banked for a turn or other maneuver, the reception hemisphere becomes correspondingly tilted; hence, the antenna no longer views satellites that may still be above the Earth horizon but are now below the equatorial plane of the tilted reception hemisphere. Moreover, part of the reception hemisphere (typically, on the inside of a turn) becomes pointed toward ground, with a consequent increase in received noise and, therefore, degradation of GPS measurements. To minimize the likelihood of loss of signal and cycle slip, bank angles of remote-sensing survey airplanes have generally been limited to 10 or less, resulting in skidding or slipping uncoordinated turns. An airplane must be banked in order to make a coordinated turn. For small-radius, short-time coordinated turns, it is necessary to employ banks as steep as 45 , and turns involving such banks are times and for confining airplanes as closely as possible to areas to be surveyed. The idea underlying the design is that if the antenna can be kept properly aimed, then the incidence of cycle slips caused by loss or weakness of signals can be minimized. The system includes an articulating GPS antenna and associated electronic circuitry mounted under a radome atop an airplane. The electronic circuitry includes a microprocessor-based interface-circuit-and-data-translation module. The system receives data on the current attitude of the airplane from the inertial navigation system of the airplane. The microprocessor decodes the attitude data and uses them to compute commands for the GPS-antenna-articulating mechanism to tilt the antenna, relative to the airplane, in opposition to the roll or bank of the airplane to keep the antenna pointed toward the zenith. The system was tested aboard the hurricane- hunting airplane of the National Oceanic and Atmospheric Administration (NOAA) [see figure] during an 11-hour flight to observe the landfall of Hurricane Bret in late summer of 1999. No bank-angle restrictions were imposed during the flight. Post-flight analysis of the GPS trajectory data revealed that no cycle slip had occurred.considered normal maneuvers. These steep banks are highly desirable for minimizing flight

Building a mechanistic understanding of predation with GPS-based movement data.

PubMed

Merrill, Evelyn; Sand, Håkan; Zimmermann, Barbara; McPhee, Heather; Webb, Nathan; Hebblewhite, Mark; Wabakken, Petter; Frair, Jacqueline L

2010-07-27

Quantifying kill rates and sources of variation in kill rates remains an important challenge in linking predators to their prey. We address current approaches to using global positioning system (GPS)-based movement data for quantifying key predation components of large carnivores. We review approaches to identify kill sites from GPS movement data as a means to estimate kill rates and address advantages of using GPS-based data over past approaches. Despite considerable progress, modelling the probability that a cluster of GPS points is a kill site is no substitute for field visits, but can guide our field efforts. Once kill sites are identified, time spent at a kill site (handling time) and time between kills (killing time) can be determined. We show how statistical models can be used to investigate the influence of factors such as animal characteristics (e.g. age, sex, group size) and landscape features on either handling time or killing efficiency. If we know the prey densities along paths to a kill, we can quantify the 'attack success' parameter in functional response models directly. Problems remain in incorporating the behavioural complexity derived from GPS movement paths into functional response models, particularly in multi-prey systems, but we believe that exploring the details of GPS movement data has put us on the right path.

A Real-Time Capable Software-Defined Receiver Using GPU for Adaptive Anti-Jam GPS Sensors

PubMed Central

Seo, Jiwon; Chen, Yu-Hsuan; De Lorenzo, David S.; Lo, Sherman; Enge, Per; Akos, Dennis; Lee, Jiyun

2011-01-01

Due to their weak received signal power, Global Positioning System (GPS) signals are vulnerable to radio frequency interference. Adaptive beam and null steering of the gain pattern of a GPS antenna array can significantly increase the resistance of GPS sensors to signal interference and jamming. Since adaptive array processing requires intensive computational power, beamsteering GPS receivers were usually implemented using hardware such as field-programmable gate arrays (FPGAs). However, a software implementation using general-purpose processors is much more desirable because of its flexibility and cost effectiveness. This paper presents a GPS software-defined radio (SDR) with adaptive beamsteering capability for anti-jam applications. The GPS SDR design is based on an optimized desktop parallel processing architecture using a quad-core Central Processing Unit (CPU) coupled with a new generation Graphics Processing Unit (GPU) having massively parallel processors. This GPS SDR demonstrates sufficient computational capability to support a four-element antenna array and future GPS L5 signal processing in real time. After providing the details of our design and optimization schemes for future GPU-based GPS SDR developments, the jamming resistance of our GPS SDR under synthetic wideband jamming is presented. Since the GPS SDR uses commercial-off-the-shelf hardware and processors, it can be easily adopted in civil GPS applications requiring anti-jam capabilities. PMID:22164116

A real-time capable software-defined receiver using GPU for adaptive anti-jam GPS sensors.

PubMed

Seo, Jiwon; Chen, Yu-Hsuan; De Lorenzo, David S; Lo, Sherman; Enge, Per; Akos, Dennis; Lee, Jiyun

2011-01-01

Due to their weak received signal power, Global Positioning System (GPS) signals are vulnerable to radio frequency interference. Adaptive beam and null steering of the gain pattern of a GPS antenna array can significantly increase the resistance of GPS sensors to signal interference and jamming. Since adaptive array processing requires intensive computational power, beamsteering GPS receivers were usually implemented using hardware such as field-programmable gate arrays (FPGAs). However, a software implementation using general-purpose processors is much more desirable because of its flexibility and cost effectiveness. This paper presents a GPS software-defined radio (SDR) with adaptive beamsteering capability for anti-jam applications. The GPS SDR design is based on an optimized desktop parallel processing architecture using a quad-core Central Processing Unit (CPU) coupled with a new generation Graphics Processing Unit (GPU) having massively parallel processors. This GPS SDR demonstrates sufficient computational capability to support a four-element antenna array and future GPS L5 signal processing in real time. After providing the details of our design and optimization schemes for future GPU-based GPS SDR developments, the jamming resistance of our GPS SDR under synthetic wideband jamming is presented. Since the GPS SDR uses commercial-off-the-shelf hardware and processors, it can be easily adopted in civil GPS applications requiring anti-jam capabilities.

Contribution of various microenvironments to the daily personal exposure to ultrafine particles: Personal monitoring coupled with GPS tracking

NASA Astrophysics Data System (ADS)

Bekö, Gabriel; Kjeldsen, Birthe Uldahl; Olsen, Yulia; Schipperijn, Jasper; Wierzbicka, Aneta; Karottki, Dorina Gabriela; Toftum, Jørn; Loft, Steffen; Clausen, Geo

2015-06-01

Exposure to ultrafine particles (UFP) may have adverse health effects. Central monitoring stations do not represent the personal exposure to UFP accurately. Few studies have previously focused on personal exposure to UFP. Sixty non-smoking residents living in Copenhagen, Denmark were asked to carry a backpack equipped with a portable monitor, continuously recording particle number concentrations (PN), in order to measure the real-time individual exposure over a period of ˜48 h. A GPS logger was carried along with the particle monitor and allowed us to estimate the contribution of UFP exposure occurring in various microenvironments (residence, during active and passive transport, other indoor and outdoor environments) to the total daily exposure. On average, the fractional contribution of each microenvironment to the daily integrated personal exposure roughly corresponded to the fractions of the day the subjects spent in each microenvironment. The home environment accounted for 50% of the daily personal exposure. Indoor environments other than home or vehicles contributed with ˜40%. The highest median UFP concentration was obtained during passive transport (vehicles). However, being in transit or outdoors contributed 5% or less to the daily exposure. Additionally, the subjects recorded in a diary the periods when they were at home. With this approach, 66% of the total daily exposure was attributable to the home environment. The subjects spent 28% more time at home according to the diary, compared to the GPS. These results may indicate limitations of using diaries, but also possible inaccuracy and miss-classification in the GPS data.

Match-play demands of elite youth Gaelic football using global positioning system tracking.

PubMed

Reilly, Brian; Akubat, Ibrahim; Lyons, Mark; Collins, D Kieran

2015-04-01

Global positioning systems (GPS) technology has made athlete-tracking a convenient and accepted technique to specify movement patterns and physical demands in sport. The purpose of this study was to examine positional demands of elite youth Gaelic football match-play using portable GPS technology to examine movement patterns and heart rates across match periods. Fifty-six elite youth male Gaelic footballers (age, 15 ± 0.66 years) fitted with portable 4-Hz GPS units were observed during 6 competitive matches (60 minutes). Data provided from the GPS unit included total distance, high-intensity (≥17·km·h(-1)) distance, sprint (≥22 km·h(-1)) distance, and total number of sprints. Heart rate was monitored continuously throughout the games. Players covered a mean distance of 5732 ± 1047 m, and the mean intensity of match-play was 85% of the peak heart rate. There was a significant (p = 0.028) drop in the total distance covered in the second half (2783 ± 599 m) compared with the first half (2948 ± 580 m). In particular, there is a noticeable drop in the distance covered in the third quarter of the game (after half-time), which has implications for re-warming up at the end of the half-time interval. There was a highly significant (p < .001) difference in the distance traveled across the 5 positional groups with midfielders covering the greatest total distance (6740 ± 384 m). The significant differences found with respect to positional groups support the implementation of individual, position-specific strength and conditioning programs.

Laser Calibration Experiment for Small Objects in Space

NASA Technical Reports Server (NTRS)

Campbell, Jonathan; Ayers, K.; Carreras, R.; Carruth, R.; Freestone, T.; Sharp, J.; Rawleigh, A.; Brewer, J.; Schrock, K.; Bell, L.;

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.

Application of Global Positioning Measurements to Continental Collision in the Pamir-Tien Shan Region, Central Asia and GPS Survey of the Western Tien Shan

NASA Technical Reports Server (NTRS)

Hamburger, Michael W.; Reilinger, Robert E.; Hager, Bradford H.; Molnar, Peter

1997-01-01

In this report, we summarize what we have accomplished with five years of funding from NASA under its DOSE program, and with a comparable level of funding from NSF. We describe the development of a GPS network in the Tien Shan of Kyrgyzstan and Kazakhstan of the former Soviet Union, the analysis of data, and the main results. This discussion presents the state of the current network, which has grown significantly since the termination of our DOSE grants, with continued support both from NSF through its continental dynamics program and from NASA's SENH program. Although grants from NASA's DOSE program did not support this growth not directly, it did so indirectly by building the infrastructure that has enabled further expansion in an area where otherwise there would be only a small GPS presence. We note how the network has grown over time, but the emphasis of this discussion is on the quantity and quality of measurements that we have made.

The 2010 Eyjafjallajökull and 2011 Grimsvötn ash plumes as seen by GPS

NASA Astrophysics Data System (ADS)

Grapenthin, R.; Hreinsdottir, S.; Gudmundsson, M. T.

2015-12-01

The injection of a volcanic plume introduces a dynamic, localized, short-term heterogeneity in the atmosphere. Satellite-imagery based remote sensing techniques provide good spatial coverage for the detection of such plumes, but slow satellite repeat times (>30 minutes) and cloud cover can delay, if not entirely prevent, the detection. GPS, in turn, provides excellent temporal coverage, but requires favorable satellite-station-geometry such that the signal propagates through the plume if it is to be used for plume detection and analysis. Two methods exist to detect / analyze ash plumes with GPS: (a) Ash-heavy plumes result in signal dispersion and hence a lowered signal-to-noise ratio (SNR). A lowered SNR, recorded by some receivers, can provide useful information about the plume, such as location and velocity of ascent. These data can be evaluated directly as they are recorded by the receiver; without the need of solving for a receiver's position. (b) Wet plumes refract the GPS signals piercing the plume and hence induce a propagation delay. When solving for a receiver position GPS analysis tools do not model this localized phase delay effect and solutions for plume-piercing satellites do not fit the data well. This can be exploited for plume analysis such as the estimation of changes to the atmospheric refractivity index. We analyze GPS data of the ~2 month 2010 Eyafjallajökull erption and the week-long 2011 Grímsvötn eruption to infer a first order estimate of plume geometry and its progression. Using SNR and phase delay information, we evaluate the evolution of the partitioning of wet versus dry parts of the plume. During the GPS processing we iteratively solve for phase-delay and position and fix other parameters, hence reducing the mapping of least-squares misfit into position estimates and other parameters. Nearly continuous webcam imagery provides independent observations of first-order plume characteristics for the Eyafjallajökull event.

Pre-Flight Testing of Spaceborne GPS Receivers using a GPS Constellation Simulator

NASA Technical Reports Server (NTRS)

Kizhner, Semion; Davis, Edward; Alonso, R.

1999-01-01

The NASA Goddard Space Flight Center (GSFC) Global Positioning System (GPS) applications test facility has been established within the GSFC Guidance Navigation and Control Center. The GPS test facility is currently housing the Global Simulation Systems Inc. (GSSI) STR2760 GPS satellite 40-channel attitude simulator and a STR4760 12-channel navigation simulator. The facility also contains a few other resources such as an atomic time standard test bed, a rooftop antenna platform and a radome. It provides a new capability for high dynamics GPS simulations of space flight that is unique within the aerospace community. The GPS facility provides a critical element for the development and testing of GPS based technologies i.e. position, attitude and precise time determination used on-board a spacecraft, suborbital rocket balloon. The GPS simulation system is configured in a transportable rack and is available for GPS component development as well as for component, spacecraft subsystem and system level testing at spacecraft integration and tests sites. The GPS facility has been operational since early 1996 and has utilized by space flight projects carrying GPS experiments, such as the OrbView-2 and the Argentine SAC-A spacecrafts. The SAC-A pre-flight test data obtained by using the STR2760 simulator and the comparison with preliminary analysis of the GPS data from SAC-A telemetry are summarized. This paper describes pre-flight tests and simulations used to support a unique spaceborne GPS experiment. The GPS experiment mission objectives and the test program are described, as well as the GPS test facility configuration needed to verify experiment feasibility. Some operational and critical issues inherent in GPS receiver pre-flight tests and simulations using this GPS simulation, and test methodology are described. Simulation and flight data are presented. A complete program of pre-flight testing of spaceborne GPS receivers using a GPS constellation simulator is detailed.

Pre-Flight Testing of Spaceborne GPS Receivers Using a GPS Constellation Simulator

NASA Technical Reports Server (NTRS)

Kizhner, Semion; Davis, Edward; Alonso, Roberto

1999-01-01

The NASA Goddard Space Flight Center (GSFC) Global Positioning System (GPS) applications test facility has been established within the GSFC Guidance Navigation and Control Center. The GPS test facility is currently housing the Global Simulation Systems Inc. (GSSI) STR2760 GPS satellite 40-channel attitude simulator and a STR4760 12-channel navigation simulator. The facility also contains a few other resources such as an atomic time standard test bed, a rooftop antenna platform and a radome. It provides a new capability for high dynamics GPS simulations of space flight that is unique within the aerospace community. The GPS facility provides a critical element for the development and testing of GPS based technologies i.e. position, attitude and precise time determination used on-board a spacecraft, suborbital rocket or balloon. The GPS simulator system is configured in a transportable rack and is available for GPS component development as well as for component, spacecraft subsystem and system level testing at spacecraft integration and test sites. The GPS facility has been operational since early 1996 and has been utilized by space flight projects carrying GPS experiments, such as the OrbView-2 and the Argentine SAC-A spacecrafts. The SAC-A pre-flight test data obtained by using the STR2760 simulator and the comparison with preliminary analysis of the GPS data from SAC-A telemetry are summarized. This paper describes pre-flight tests and simulations used to support a unique spaceborne GPS experiment. The GPS experiment mission objectives and the test program are described, as well as the GPS test facility configuration needed to verify experiment feasibility. Some operational and critical issues inherent in GPS receiver pre-flight tests and simulations using this GPS simulator, and test methodology are described. Simulation and flight data are presented. A complete program of pre-flight testing of spaceborne GPS receivers using a GPS constellation simulator is detailed.

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.

Characterizing and minimizing the effects of noise in tide gauge time series: relative and geocentric sea level rise around Australia

NASA Astrophysics Data System (ADS)

Burgette, Reed J.; Watson, Christopher S.; Church, John A.; White, Neil J.; Tregoning, Paul; Coleman, Richard

2013-08-01

We quantify the rate of sea level rise around the Australian continent from an analysis of tide gauge and Global Positioning System (GPS) data sets. To estimate the underlying linear rates of sea level change in the presence of significant interannual and decadal variability (treated here as noise), we adopt and extend a novel network adjustment approach. We simultaneously estimate time-correlated noise as well as linear model parameters and realistic uncertainties from sea level time series at individual gauges, as well as from time-series differences computed between pairs of gauges. The noise content at individual gauges is consistent with a combination of white and time-correlated noise. We find that the noise in time series from the western coast of Australia is best described by a first-order Gauss-Markov model, whereas east coast stations generally exhibit lower levels of time-correlated noise that is better described by a power-law process. These findings suggest several decades of monthly tide gauge data are needed to reduce rate uncertainties to <0.5 mm yr-1 for undifferenced single site time series with typical noise characteristics. Our subsequent adjustment strategy exploits the more precise differential rates estimated from differenced time series from pairs of tide gauges to estimate rates among the network of 43 tide gauges that passed a stability analysis. We estimate relative sea level rates over three temporal windows (1900-2011, 1966-2011 and 1993-2011), accounting for covariance between time series. The resultant adjustment reduces the rate uncertainty across individual gauges, and partially mitigates the need for century-scale time series at all sites in the network. Our adjustment reveals a spatially coherent pattern of sea level rise around the coastline, with the highest rates in northern Australia. Over the time periods beginning in 1900, 1966 and 1993, we find weighted average rates of sea level rise of 1.4 ± 0.6, 1.7 ± 0.6 and 4.6 ± 0.8 mm yr-1, respectively. While the temporal pattern of the rate estimates is consistent with acceleration in sea level rise, it may not be significant, as the uncertainties for the shorter analysis periods may not capture the full range of temporal variation. Analysis of the available continuous GPS records that have been collected within 80 km of Australian tide gauges suggests that rates of vertical crustal motion are generally low, with the majority of sites showing motion statistically insignificant from zero. A notable exception is the significant component of vertical land motion that contributes to the rapid rate of relative sea level change (>4 mm yr-1) at the Hillarys site in the Perth area. This corresponds to crustal subsidence that we estimate in our GPS analysis at a rate of -3.1 ± 0.7 mm yr-1, and appears linked to groundwater withdrawal. Uncertainties on the rates of vertical displacement at GPS sites collected over a decade are similar to what we measure in several decades of tide gauge data. Our results motivate continued observations of relative sea level using tide gauges, maintained with high-accuracy terrestrial and continuous co-located satellite-based surveying.

A Report on GPS and Galileo Time Offset Coordination Efforts

DTIC Science & Technology

2007-01-01

broadcast as part of the GPS and Galileo navigation message and determined by: Two-way Satellite Time and Frequency Transfer ( TWSTFT ); Common...navigation message • use of TWSTFT and GPS Common View The overall goal is to verify the GGTO performance budget for the IOV Phase (detailed budget

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.

Consulting room computers and their effect on general practitioner-patient communication.

PubMed

Noordman, Janneke; Verhaak, Peter; van Beljouw, Ilse; van Dulmen, Sandra

2010-12-01

in the western medical world, computers form part of the standard equipment in the consulting rooms of most GPs. As the use of a computer requires time and attention from GPs, this may well interfere with the communication process. Yet, the information accessed on the computer may also enhance communication. the present study affords insight into the relationship between computer use and GP-patient communication recorded by the same GPs over two periods. videotaped GP consultations collected in 2001 and 2008 were used to observe computer use and GP-patient communication. In addition, patients questionnaires about their experiences with communication by the GP were analysed using multilevel models with patients (Level 1) nested within GPs (Level 2). both in 2008 and in 2001, GPs used their computer in almost every consultation. Still, our study showed a change in computer use by the GPs over time. In addition, the results indicate that computer use is negatively related to some communication aspects: the patient-directed gaze of the GP and the amount of information given by GPs. There is also a negative association between computer use and the body posture of the GP. Computer use by GPs is not associated with other (analysed) non-verbal and verbal behaviour of GPs and patients. Moreover, computer use is scarcely related to patients' experiences with the communication behaviour of the GP. GPs show greater reluctance to use computers in 2008 compared to 2001. Computer use can indeed affect the communication between GPs and patients. Therefore, GPs ought to remain aware of their computer use during consultations and at the same time keep the interaction with the patient alive.

The views and experiences of female GPs on professional practice and career support.

PubMed

Wedderburn, Clare; Scallan, Samantha; Whittle, Clare; Curtis, Anthony

2013-09-01

National GP demographic data demonstrate an increasing 'feminisation' of the workforce. With female GP specialty trainees continuing to outnumber males, this trend is set to continue. The changing composition of the workforce presents challenges in terms of how best to support the long-term career and educational development needs of this sector of the workforce in an evolving healthcare context. The aim of this work was to capture female GPs' experiences of working in general practice and their expectations concerning their career and educational development. Participants were surveyed and completed a semi-structured questionnaire, which generated qualitative and quantitative data. The sample comprised GP registrars, principals and sessionals. This study has generated an important dataset on working patterns, educational experiences and long-term career intentions of female GPs. Despite increased representation in the GP workforce, female GPs (particularly those with young children) appear less likely to be involved in education and training than their male counterparts, and even less likely to be involved in roles linked to primary care trusts, medico-political issues, hospital service delivery, special clinical interests or deanery education management. younger GPs reported significantly more difficulties in managing their childcare needs than older colleagues. Marital status, number of children and employment status did not moderate the effect of these difficulties. Female GPs reported working more hours with increasing age, but were not necessarily represented in a range of educational and/or training posts as a consequence.

Positioning performance of the NTCM model driven by GPS Klobuchar model parameters

NASA Astrophysics Data System (ADS)

Hoque, Mohammed Mainul; Jakowski, Norbert; Berdermann, Jens

2018-03-01

Users of the Global Positioning System (GPS) utilize the Ionospheric Correction Algorithm (ICA) also known as Klobuchar model for correcting ionospheric signal delay or range error. Recently, we developed an ionosphere correction algorithm called NTCM-Klobpar model for single frequency GNSS applications. The model is driven by a parameter computed from GPS Klobuchar model and consecutively can be used instead of the GPS Klobuchar model for ionospheric corrections. In the presented work we compare the positioning solutions obtained using NTCM-Klobpar with those using the Klobuchar model. Our investigation using worldwide ground GPS data from a quiet and a perturbed ionospheric and geomagnetic activity period of 17 days each shows that the 24-hour prediction performance of the NTCM-Klobpar is better than the GPS Klobuchar model in global average. The root mean squared deviation of the 3D position errors are found to be about 0.24 and 0.45 m less for the NTCM-Klobpar compared to the GPS Klobuchar model during quiet and perturbed condition, respectively. The presented algorithm has the potential to continuously improve the accuracy of GPS single frequency mass market devices with only little software modification.

Contribution to defining a geodetic reference frame for Africa (AFREF): Geodynamics implications

NASA Astrophysics Data System (ADS)

Saria, Elifuraha E.

African Reference Frame (AFREF) is the proposed regional three-dimensional standard frame, which will be used to reference positions and velocities for geodetic sites in Africa and surrounding. This frame will play a crucial role in scientific application for example plate motion and crustal deformation studies, and also in mapping when it involves for example national boundary surveying, remote sensing, GIS, engineering projects and other development programs in Africa. To contribute to the definition of geodetic reference frame for Africa and provide the first continent-wide position/velocity solution for Africa, we processed and analyzed 16 years of GPS and 17 years of DORIS data at 133 GPS sites and 9 DORIS sites continuously operating geodetic sites in Africa and surroundings to describe the present-day kinematics of the Nubian and Somalian plates and constrain relative motions across the East African Rift. We use the resulting horizontal velocities to determine the level of rigidity of Nubia and updated a plate motion model for the East African Rift and revise the counter clockwise rotation of the Victoria plate and clockwise rotation of the Rovuma plate with respect to Nubia. The vertical velocity ranges from -2 to +2 mm/yr, close to their uncertainties with no clear geographical pattern. This study provides the first continent-wide position/velocity solution for Africa, expressed in International Terrestrial Reference Frame (ITRF2008), a contribution to the upcoming African Reference Frame (AFREF). In the next step we used the substantial increase in the geologic, geophysical and geodetic data in Africa to improve our understanding of the rift geometry and the block kinematics of the EAR. We determined the best-fit fault structure of the rift in terms of the locking depth and dip angle and use a block modeling approach where observed velocities are described as the contribution of rigid block rotation and strain accumulation on locked faults. Our results show a better fit with three sub-plates (Victoria, Rovuma and Lwandle) between the major plates Nubia and Somalia. We show that the earthquake slip vectors provide information that is consistent with the GPS velocities and significantly help reduce the uncertainties in plate angular velocity estimates. However, we find that 3.16 My average spreading rates along the Southwest Indian Ridge (SWIR) from MORVEL model are systematically faster than GPS-derived motions across that ridge, possibly reflecting the need to revise the MORVEL outward displacement correction. In the final step, we attempt to understand the hydrological loading in Africa, which may affect our geodetic estimates, particularly the uplift rates. In this work, we analyze 10 years (2002 - 2012) of continuous GPS measurements operating in Africa, and compare with the modeled hydrological loading deformation inferred from the Gravity Recovery and Climate Experiment (GRACE) at the same GPS location and for the same time period. We estimated hydrological loading deformation based on the Equivalent Water Height (EWH) derived from the 10-days interval reprocessed GRACE solution second release (RL02). We took in to account in both GPS and GRACE the systematic errors from atmospheric pressure and non-tidal ocean loading effects and model the Earth as perfect elastic and compute the deformation using appropriate Greens function. We analyze the strength of association between the observation (GPS) and the model (GRACE) in terms of annual amplitude and phase as well as the original data (time-series). We find a good correlation mainly in regions associated with strong seasonal hydrological variations. To improve the correlation between the two solutions, we subtract the GRACE-derived vertical displacement from GPS-observed time series and determine the variance reduction. Our solution shows average variance between the model and the observation reduced to ~40%. (Abstract shortened by UMI.)

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.

GPS Ocean Reflection Experiment (GORE) Wind Explorer (WindEx) Instrument Design and Development

NASA Astrophysics Data System (ADS)

Ganoe, G.

2004-12-01

This paper describes the design and development of the WindEx instrument, and the technology implemented by it. The important design trades will be covered along with the justification for the options selected. An evaluation of the operation of the instrument, and plans for continued development and enhancements will also be given. The WindEx instrument consists of a processor that receives data from an included GPS Surface reflection receiver, and computes ocean surface wind speeds in real time utilizing an algorithm developed at LaRC by Dr. Stephen J. Katzberg. The WindEx performs a windspeed server function as well as acting as a repository for the client moving map applications, and providing a web page with instructions on the installation and use of the WindEx system. The server receives the GPS reflection data produced by the receiver, performs wind speed processing, then makes the wind speed data available as a moving map display to requesting client processors on the aircraft network. The client processors are existing systems used by the research personnel onboard. They can be configured to be WINDEX clients by downloading the Java client application from the WINDEX server. The client application provides a graphical display of a moving map that shows the aircraft position along with the position of the reflection point from the surface of the ocean where the wind speed is being estimated, and any coastlines within the field of view. Information associated with the reflection point includes the estimated wind speed, and a confidence factor that gives the researcher an idea about the reliability of the wind speed measurement. The instrument has been installed on one of NOAA's Hurricane Hunters, a Gulfstream IV, whose nickname is "Gonzo". Based at MacDill AFB, Florida, "Gonzo" flies around the periphery of the storm deploying GPS-based dropsondes which measure local winds. The dropsondes are the "gold-standard" for determining surface winds, but can only be deployed sparingly. The GPS WindEx system allows for a continuous map between dropsonde releases as well as monitoring the ocean surface for suspicious areas. The GPS technique is insensitive to clouds or rain and can give information concerning surface conditions not available to the flight crew.

QUALITY IMPROVEMENT COMPETENCY GAPS IN PRIMARY CARE IN ALBANIAN, POLISH AND SLOVENIAN CONTEXTS: A STUDY PROTOCOL

PubMed Central

Czabanowska, Katarzyna; Burazeri, Genc; Klemenc-Ketis, Zalika; Kijowska, Violetta; Tomasik, Tomasz; Brand, Helmut

2012-01-01

Background: Nowadays, general practitioners (GPs) and family doctors (FDs) face increasing demands, as a consequence of complex patients’ expectations, developments in science and technology, and limitations within healthcare systems which can result in competency gaps. Therefore, there is a need to identify which competencies in quality improvement (QI) are most important for GPs and FDs to possess in order to meet the demands of contemporary health care practice. To date, however, little information is available on the self-assessment of competencies related to QI among GPs and FDs. To deal with these issues, a project on QI in continuous medical education was launched in 2011. The project aims to broaden the GPs’/ FDs’ continuous education offer, its quality and attractiveness, as well as provide them with opportunities for vocational advancement and enable the development of common, European frame of reference for GPs’/FDs’ occupational competencies. The third work package of the project consists of the validation research of the questionnaire developed on the basis of the competency framework in QI for GPs/FDs in Europe. Methods: A cross-sectional study will be carried out using the self-assessment QI questionnaire which was originally developed in English and subsequently it was cross-culturally adapted in Slovenian, Albanian and Polish settings by use of a pilot study on a conveniently selected group of FDs/GPs (N=10) in each participating country. The final version of the questionnaire will be administered to large samples in each country involved in the survey. Two weeks after the first administration of the questionnaire, a second round, with the same procedure and including the same group of respondents, will follow. Psychometric tests will be conducted including internal consistency (after the initial and subsequent application of the instrument) and stability over time (two-week test-retest reliability). Discussion: This self-assessment study will demonstrate the complex environment in which general practice/family medicine operates and, eventually, this gap analysis will set out strategically important areas for collaborative efforts related to QI in primary care. The authors consider that the study should be extended to other European countries to help identify most required competencies that GPs/FDs should possess in Europe and thus stir system and educational debate around QI curricula and training for primary care in Europe. PMID:23378694

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.

Terrestrial water storage variations and surface vertical deformation derived from GPS and GRACE observations in Nepal and Himalayas

NASA Astrophysics Data System (ADS)

Pan, Y.; Shen, W.; Hwang, C.

2015-12-01

As an elastic Earth, the surface vertical deformation is in response to hydrological mass change on or near Earth's surface. The continuous GPS (CGPS) records show surface vertical deformations which are significant information to estimate the variation of terrestrial water storage. We compute the loading deformations at GPS stations based on synthetic models of seasonal water load distribution and then invert the synthetic GPS data for surface mass distribution. We use GRACE gravity observations and hydrology models to evaluate seasonal water storage variability in Nepal and Himalayas. The coherence among GPS inversion results, GRACE and hydrology models indicate that GPS can provide quantitative estimates of terrestrial water storage variations by inverting the surface deformation observations. The annual peak-to-peak surface mass change derived from GPS and GRACE results reveal seasonal loads oscillations of water, snow and ice. Meanwhile, the present uplifting of Nepal and Himalayas indicates the hydrology mass loss. This study is supported by National 973 Project China (grant Nos. 2013CB733302 and 2013CB733305), NSFC (grant Nos. 41174011, 41429401, 41210006, 41128003, 41021061).

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.

High accurate time system of the Low Latitude Meridian Circle.

NASA Astrophysics Data System (ADS)

Yang, Jing; Wang, Feng; Li, Zhiming

In order to obtain the high accurate time signal for the Low Latitude Meridian Circle (LLMC), a new GPS accurate time system is developed which include GPS, 1 MC frequency source and self-made clock system. The second signal of GPS is synchronously used in the clock system and information can be collected by a computer automatically. The difficulty of the cancellation of the time keeper can be overcomed by using this system.

Prescribing tamoxifen in primary care for the prevention of breast cancer: a national online survey of GPs' attitudes.

PubMed

Smith, Samuel G; Foy, Robbie; McGowan, Jennifer A; Kobayashi, Lindsay C; DeCensi, Andrea; Brown, Karen; Side, Lucy; Cuzick, Jack

2017-06-01

The cancer strategy for England (2015-2020) recommends GPs prescribe tamoxifen for breast cancer primary prevention among women at increased risk. To investigate GPs' attitudes towards prescribing tamoxifen. In an online survey, GPs in England, Northern Ireland, and Wales ( n = 928) were randomised using a 2 × 2 between-subjects design to read one of four vignettes describing a healthy patient seeking a tamoxifen prescription. In the vignette, the hypothetical patient's breast cancer risk (moderate versus high) and the clinician initiating the prescription (GP prescriber versus secondary care clinician [SCC] prescriber) were manipulated in a 1:1:1:1 ratio. Outcomes were willingness to prescribe, comfort discussing harms and benefits, comfort managing the patient, factors affecting the prescribing decision, and awareness of tamoxifen and the National Institute for Health and Care Excellence (NICE) guideline CG164. Half (51.7%) of the GPs knew tamoxifen can reduce breast cancer risk, and one-quarter (24.1%) were aware of NICE guideline CG164. Responders asked to initiate prescribing (GP prescriber) were less willing to prescribe tamoxifen than those continuing a prescription initiated in secondary care (SCC prescriber) (68.9% versus 84.6%, P <0.001). The GP prescribers reported less comfort discussing tamoxifen (53.4% versus 62.5%, P = 0.01). GPs willing to prescribe were more likely to be aware of the NICE guideline ( P = 0.039) and to have acknowledged the benefits of tamoxifen ( P <0.001), and were less likely to have considered its off-licence status ( P <0.001). Initiating tamoxifen prescriptions for preventive therapy in secondary care before asking GPs to continue the patient's care may overcome some prescribing barriers. © British Journal of General Practice 2017.

Successful implantation of an abdominal aortic blood pressure transducer and radio-telemetry transmitter in guinea pigs - Anaesthesia, analgesic management and surgical methods, and their influence on hemodynamic parameters and body temperature.

PubMed

Schmitz, Sabrina; Henke, Julia; Tacke, Sabine; Guth, Brian

2016-01-01

Guinea pigs (GPs) are a valuable cardiovascular pharmacology model. Implantation of a radio-telemetry system into GPs is, however, challenging and has been associated with a high failure rate in the past. We provide information on a novel procedure for implanting telemetry devices into GPs and we have measured the hemodynamics (arterial blood pressure, BP and heart rate, HR) and core body temperature (BT) in the 24h after surgery. Male Hartley GPs (Crl:HA, 350-400g, 6.5weeks, n=16) were implanted with a radio transmitter abdominally and were then monitored continuously (HR, BP and BT) for 24h after surgery. 13 of 16 GPs (81%) survived the surgery. Surgery duration was 94min (min) (range: 76-112min) and anaesthesia duration was 131min (range: 107-158min). GPs lost body weight until 2days after surgery and then regained weight. Mean arterial BP increased from 33.7mmHg directly after surgery to 59.1mmHg after 24h. HR increased from 206bpm directly after surgery to 286bpm at 8h and fell to 251bpm at 24h after implantation. BT was 36°C directly after surgery, fell to 35.4°C until regaining of the righting reflex and then stabilized at 38.5°C after 24h. A high survival rate in telemetered GPs is possible. We achieved this through a procedure with minimal stress through habituation and planning, continuous warming during anaesthesia, an optimal anaesthetic and analgesic management, efficient surgical techniques and vitamin C supplementation. Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.

A tailored educational intervention improves doctor's performance in managing depression: a randomized controlled trial.

PubMed

Shirazi, Mandana; Lonka, Kirsti; Parikh, Sagar V; Ristner, Gunilla; Alaeddini, Farshid; Sadeghi, Majid; Wahlstrom, Rolf

2013-02-01

To assess the effects of a tailored and activating educational intervention, based on a three-stage modified Prochaska model of readiness-to-change, on the performance of general physicians in primary care (GPs) regarding management of depressive disorders. Parallel group, randomized control trial. Primary hypothesis was that performance would improve by 20 percentage units in the intervention arm. The setting was primary care in southern Tehran. The participants were 192 GPs stratified on stage of readiness-to-change, sex, age and work experience. The intervention was a 2-day interactive workshop for a small group of GPs' at a higher stage of readiness-to-change ('intention') and a 2-day interactive large group meeting for those with lower propensity to change ('attitude') at the pre-assessment. GPs in the control arm participated in a standard educational programme on the same topic. The main outcome measures were validated tools to assess GPs' performance by unannounced standardized patients, regarding diagnosis and treatment of depressive disorders. The assessments were made 2 months before and 2 months after the intervention. GPs in the intervention arm significantly improved their overall mean scores for performance regarding both diagnosis, with an intervention effect of 14 percentage units (P = 0.007), and treatment and referral, with an intervention effect of 20 percentage units (P < 0.0001). The largest improvement after the intervention appeared in the small group: 30 percentage units for diagnosis (P = 0.027) and 29 percentage units for treatment and referral (P < 0.0001). Activating learning methods, tailored according to the participants' readiness to change, improved clinical performance of GPs in continuing medical education and can be recommended for continuing professional development. © 2011 Blackwell Publishing Ltd.

"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.

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.

Mobility assessment of a rural population in the Netherlands using GPS measurements.

PubMed

Klous, Gijs; Smit, Lidwien A M; Borlée, Floor; Coutinho, Roel A; Kretzschmar, Mirjam E E; Heederik, Dick J J; Huss, Anke

2017-08-09

The home address is a common spatial proxy for exposure assessment in epidemiological studies but mobility may introduce exposure misclassification. Mobility can be assessed using self-reports or objectively measured using GPS logging but self-reports may not assess the same information as measured mobility. We aimed to assess mobility patterns of a rural population in the Netherlands using GPS measurements and self-reports and to compare GPS measured to self-reported data, and to evaluate correlates of differences in mobility patterns. In total 870 participants filled in a questionnaire regarding their transport modes and carried a GPS-logger for 7 consecutive days. Transport modes were assigned to GPS-tracks based on speed patterns. Correlates of measured mobility data were evaluated using multiple linear regression. We calculated walking, biking and motorised transport durations based on GPS and self-reported data and compared outcomes. We used Cohen's kappa analyses to compare categorised self-reported and GPS measured data for time spent outdoors. Self-reported time spent walking and biking was strongly overestimated when compared to GPS measurements. Participants estimated their time spent in motorised transport accurately. Several variables were associated with differences in mobility patterns, we found for instance that obese people (BMI > 30 kg/m 2 ) spent less time in non-motorised transport (GMR 0.69-0.74) and people with COPD tended to travel longer distances from home in motorised transport (GMR 1.42-1.51). If time spent walking outdoors and biking is relevant for the exposure to environmental factors, then relying on the home address as a proxy for exposure location may introduce misclassification. In addition, this misclassification is potentially differential, and specific groups of people will show stronger misclassification of exposure than others. Performing GPS measurements and identifying explanatory factors of mobility patterns may assist in regression calibration of self-reports in other studies.

Performance Analysis on Carrier Phase-Based Tightly-Coupled GPS/BDS/INS Integration in GNSS Degraded and Denied Environments

PubMed Central

Han, Houzeng; Wang, Jian; Wang, Jinling; Tan, Xinglong

2015-01-01

The integration of Global Navigation Satellite Systems (GNSS) carrier phases with Inertial Navigation System (INS) measurements is essential to provide accurate and continuous position, velocity and attitude information, however it is necessary to fix ambiguities rapidly and reliably to obtain high accuracy navigation solutions. In this paper, we present the notion of combining the Global Positioning System (GPS), the BeiDou Navigation Satellite System (BDS) and low-cost micro-electro-mechanical sensors (MEMS) inertial systems for reliable navigation. An adaptive multipath factor-based tightly-coupled (TC) GPS/BDS/INS integration algorithm is presented and the overall performance of the integrated system is illustrated. A twenty seven states TC GPS/BDS/INS model is adopted with an extended Kalman filter (EKF), which is carried out by directly fusing ambiguity fixed double-difference (DD) carrier phase measurements with the INS predicted pseudoranges to estimate the error states. The INS-aided integer ambiguity resolution (AR) strategy is developed by using a dynamic model, a two-step estimation procedure is applied with adaptively estimated covariance matrix to further improve the AR performance. A field vehicular test was carried out to demonstrate the positioning performance of the combined system. The results show the TC GPS/BDS/INS system significantly improves the single-epoch AR reliability as compared to that of GPS/BDS-only or single satellite navigation system integrated strategy, especially for high cut-off elevations. The AR performance is also significantly improved for the combined system with adaptive covariance matrix in the presence of low elevation multipath related to the GNSS-only case. A total of fifteen simulated outage tests also show that the time to relock of the GPS/BDS signals is shortened, which improves the system availability. The results also indicate that TC integration system achieves a few centimeters accuracy in positioning based on the comparison analysis and covariance analysis, even in harsh environments (e.g., in urban canyons), thus we can see the advantage of positioning at high cut-off elevations that the combined GPS/BDS brings. PMID:25875191

Performance analysis on carrier phase-based tightly-coupled GPS/BDS/INS integration in GNSS degraded and denied environments.

PubMed

Han, Houzeng; Wang, Jian; Wang, Jinling; Tan, Xinglong

2015-04-14

The integration of Global Navigation Satellite Systems (GNSS) carrier phases with Inertial Navigation System (INS) measurements is essential to provide accurate and continuous position, velocity and attitude information, however it is necessary to fix ambiguities rapidly and reliably to obtain high accuracy navigation solutions. In this paper, we present the notion of combining the Global Positioning System (GPS), the BeiDou Navigation Satellite System (BDS) and low-cost micro-electro-mechanical sensors (MEMS) inertial systems for reliable navigation. An adaptive multipath factor-based tightly-coupled (TC) GPS/BDS/INS integration algorithm is presented and the overall performance of the integrated system is illustrated. A twenty seven states TC GPS/BDS/INS model is adopted with an extended Kalman filter (EKF), which is carried out by directly fusing ambiguity fixed double-difference (DD) carrier phase measurements with the INS predicted pseudoranges to estimate the error states. The INS-aided integer ambiguity resolution (AR) strategy is developed by using a dynamic model, a two-step estimation procedure is applied with adaptively estimated covariance matrix to further improve the AR performance. A field vehicular test was carried out to demonstrate the positioning performance of the combined system. The results show the TC GPS/BDS/INS system significantly improves the single-epoch AR reliability as compared to that of GPS/BDS-only or single satellite navigation system integrated strategy, especially for high cut-off elevations. The AR performance is also significantly improved for the combined system with adaptive covariance matrix in the presence of low elevation multipath related to the GNSS-only case. A total of fifteen simulated outage tests also show that the time to relock of the GPS/BDS signals is shortened, which improves the system availability. The results also indicate that TC integration system achieves a few centimeters accuracy in positioning based on the comparison analysis and covariance analysis, even in harsh environments (e.g., in urban canyons), thus we can see the advantage of positioning at high cut-off elevations that the combined GPS/BDS brings.

General practitioner workforce planning: assessment of four policy directions.

PubMed

Teljeur, Conor; Thomas, Stephen; O'Kelly, Fergus D; O'Dowd, Tom

2010-06-02

Estimating the supply of GPs into the future is important in forecasting shortages. The lengthy training process for medicine means that adjusting supply to meet demand in a timely fashion is problematic. This study uses Ireland as a case study to determine the future demand and supply of GPs and to assess the potential impact of several possible interventions to address future shortages. Demand was estimated by applying GP visit rates by age and sex to national population projections. Supply was modelled using a range of parameters derived from two national surveys of GPs. A stochastic modelling approach was adopted to determine the probable future supply of GPs. Four policy interventions were tested: increasing vocational training places; recruiting GPs from abroad; incentivising later retirement; increasing nurse substitution to enable practice nurses to deliver more services. Relative to most other European countries, Ireland has few GPs per capita. Ireland has an ageing population and demand is estimated to increase by 19% by 2021. Without intervention, the supply of GPs will be 5.7% less than required in 2021. Increasing training places will enable supply to meet demand but only after 2019. Recruiting GPs from overseas will enable supply to meet demand continuously if the number recruited is approximately 0.8 per cent of the current workforce per annum. Later retirement has only a short-term impact. Nurse substitution can enable supply to meet demand but only if large numbers of practice nurses are recruited and allowed to deliver a wide range of GP services. A significant shortfall in GP supply is predicted for Ireland unless recruitment is increased. The shortfall will have numerous knock-on effects including price increases, longer waiting lists and an increased burden on hospitals. Increasing training places will not provide an adequate response to future shortages. Foreign recruitment has ethical considerations but may provide a rapid and effective response. Increased nurse substitution appears to offer the best long-term prospects of addressing GP shortages and presents the opportunity to reshape general practice to meet the demands of the future.

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.

Comparison of two-way satellite time transfer and GPS common-view time transfer between OCA and TUG

NASA Technical Reports Server (NTRS)

Kirchner, Dieter; Thyr, U.; Ressler, H.; Robnik, R.; Grudler, P.; Baumont, Francoise S.; Veillet, Christian; Lewandowski, Wlodzimierz W.; Hanson, W.; Clements, A.

1992-01-01

For about one year the time scales UTC(OCA) and UTC(TUG) were compared by means of GPS and two-way satellite time transfer. At the end of the experiment both links were independently 'calibrated' by measuring the differential delays of the GPS receivers and of the satellite earth stations by transportation of a GPS receiver and of one of the satellite terminals. The results obtained by both methods differ by about 3 ns, but reveal a seasonal variation of about 8 ns peak-to-peak which is likely the result of a temperature-dependence of the delays of the GPS receivers used. For the comparison of both methods the stabilities of the timescales are of great importance. Unfortunately, during the last three months of the experiment a less stable clock had to be used for the generation of UTC(TUG).

Power and powerlessness: GPs' narratives about lifestyle counselling.

PubMed

Abildsnes, Eirik; Walseth, Liv Tveit; Flottorp, Signe A; Stensland, Per S

2012-03-01

Power in doctor-patient relationships is asymmetrically distributed. The doctor holds resources the patient needs and has a mandate to promote healthy living. Power may benefit or harm the patients' health, and the doctor-patient relationship. To identify aspects of power and powerlessness in GPs' narratives about lifestyle counselling. A qualitative study using focus groups from peer-group meetings of Norwegian GPs attending continuing medical education. GPs discussed case stories about lifestyle counselling in focus groups. The discussions were transcribed and the text analysed using systematic text condensation. Aspects of power concerning the framework of the consultation and the GPs' professional role were found. Also identified were: power expressed by opportunistic approaches to change patients' lifestyle; rhetoric communication; paternalism; and disclosure. GPs reported powerlessness in complex communication, when there were difficulties reaching goals, and when patients resisted or ignored their proposals. Case-study discussions in peer groups disclose several aspects of power and powerlessness that occur in consultations. Consciousness about aspects of power may facilitate counselling that benefits the patient and the doctor-patient relationship.

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.

Coordinate Time and Proper Time in the GPS

ERIC Educational Resources Information Center

Matolcsi, T.; Matolcsi, M.

2008-01-01

The global positioning system (GPS) provides an excellent educational example of how the theory of general relativity is put into practice and becomes part of our everyday life. This paper gives a short and instructive derivation of an important formula used in the GPS, and is aimed at graduate students and general physicists. The authors…

Timing Comparisons for GLEs and High-energy Proton Events using GPS Proton Measurements

NASA Astrophysics Data System (ADS)

Bernstein, V.; Winter, L. M.; Carver, M.; Morley, S.

2017-12-01

The newly released LANL GPS particle sensor data offers a unique snapshot of access of relativistic particles into the geomagnetic field. Currently, 23 of the 31 operational GPS satellites host energetic particle detectors which can detect the arrival of high-energy solar protons associated with Ground Level Enhancements (GLEs). We compare the timing profiles of solar energetic proton detections from GPS satellites as well as from ground-based Neutron Monitors and GOES spacecraft at geostationary orbit in order to understand how high-energy protons from the Sun enter the geomagnetic field and investigate potential differences in arrival time of energetic protons at GPS satellites as a function of location. Previous studies could only use one or two spacecraft at a similar altitude to track the arrival of energetic particles. With GPS data, we can now test whether the particles arrive isotropically, as assumed, or whether there exist differences in the timing and energetics viewed by each of the individual satellites. Extensions of this work could lead to improvements in space weather forecasting that predict more localized risk estimates for space-based technology.

Aseismic Deformation Associated with an Earthquake Swarm in the Northern Apennines (Italy)

NASA Astrophysics Data System (ADS)

Gualandi, A.; Nichele, C.; Serpelloni, E.; Chiaraluce, L.; Anderlini, L.; Latorre, D.; Belardinelli, M. E.; Avouac, J. P.

2017-12-01

Analyzing the displacement time series from continuous GPS (cGPS) with an Independent Component Analysis (ICA) we detect a transient deformation signal that correlates both in space and time with a seismic swarm activity (maximum Mw = 3.69 ± 0.09) occurred in the hanging wall of the Altotiberina normal fault (Northern Apennines, Italy) in 2013-2014. The geodetic transient lasted ˜6 months and produced a NW-SE trending extension of ˜ 5.3 mm, consistent with the regional tectonic regime. The seismicity and the geodetic signal are consistent with slip on two splay faults in the ATF hanging wall. Comparing the seismic moment associated with the geodetic transient and the seismic events, we observe that seismicity accounts for only a fraction of the measured geodetic deformation. The combined seismic and aseismic slip decreased the Coulomb stress on the locked shallow portion of the ATF, while the transition region to the creeping section has been loaded.

Identification of AR(I)MA processes for modelling temporal correlations of GPS observations

NASA Astrophysics Data System (ADS)

Luo, X.; Mayer, M.; Heck, B.

2009-04-01

In many geodetic applications observations of the Global Positioning System (GPS) are routinely processed by means of the least-squares method. However, this algorithm delivers reliable estimates of unknown parameters und realistic accuracy measures only if both the functional and stochastic models are appropriately defined within GPS data processing. One deficiency of the stochastic model used in many GPS software products consists in neglecting temporal correlations of GPS observations. In practice the knowledge of the temporal stochastic behaviour of GPS observations can be improved by analysing time series of residuals resulting from the least-squares evaluation. This paper presents an approach based on the theory of autoregressive (integrated) moving average (AR(I)MA) processes to model temporal correlations of GPS observations using time series of observation residuals. A practicable integration of AR(I)MA models in GPS data processing requires the determination of the order parameters of AR(I)MA processes at first. In case of GPS, the identification of AR(I)MA processes could be affected by various factors impacting GPS positioning results, e.g. baseline length, multipath effects, observation weighting, or weather variations. The influences of these factors on AR(I)MA identification are empirically analysed based on a large amount of representative residual time series resulting from differential GPS post-processing using 1-Hz observation data collected within the permanent SAPOS® (Satellite Positioning Service of the German State Survey) network. Both short and long time series are modelled by means of AR(I)MA processes. The final order parameters are determined based on the whole residual database; the corresponding empirical distribution functions illustrate that multipath and weather variations seem to affect the identification of AR(I)MA processes much more significantly than baseline length and observation weighting. Additionally, the modelling results of temporal correlations using high-order AR(I)MA processes are compared with those by means of first order autoregressive (AR(1)) processes and empirically estimated autocorrelation functions.

Large-Strain Monitoring Above a Longwall Coal Mine With GPS and Seismic Measurements

NASA Astrophysics Data System (ADS)

Swanson, P. L.; Andreatta, V.; Meertens, C. M.; Krahenbuhl, T.; Kenner, B.

2001-12-01

As part of an effort to evaluate continuous GPS measurements for use in mine safety studies, a joint GPS-seismic experiment was conducted at an underground longwall coal mine near Paonia, Colorado in June, 2001. Seismic and deformation signals were measured using prototype low-cost monitoring systems as a longwall panel was excavated 150 m beneath the site. Data from both seismic and GPS instruments were logged onto low-power PC-104 Linux computers which were networked using a wireless LAN. The seismic system under development at NIOSH/SRL is based on multiple distributed 8-channel 24-bit A/D converters. The GPS system uses a serial single-frequency (L1) receiver and UNAVCO's "Jstream" Java data logging software. For this experiment, a continuously operating dual-frequency GPS receiver was installed 2.4 km away to serve as a reference site. In addition to the continuously operating sites, 10 benchmarks were surveyed daily with short "rapid-static" occupations in order to provide greater spatial sampling. Two single-frequency sites were located 35 meters apart on a relatively steep north-facing slope. As mining progressed from the east, net displacements of 1.2 meters to the north and 1.65 meters of subsidence were observed over a period of 6 days. The east component exhibited up to 0.45 meters of eastward displacement (toward the excavation) followed by reverse movement to the west. This cycle, observed approximately two days earlier at the eastern L1 site, is consistent with a change in surface strain from tension to compression as the excavation front passed underneath. As this strain "wave" propagated across the field site, surface deformation underwent a cycle of tension crack nucleation, crack opening (up to 15 cm normal displacements), subsequent crack closure, and production of low-angle-thrust compressional deformation features. Analysis of seismic results, surface deformation, and additional survey results are presented.

PBO Nucleus Project Summary: The Successful Integration of 209 Existing GPS Sions in the Plate Boundary Observatory

NASA Astrophysics Data System (ADS)

Blume, F.; Miller, M.; Boyce, E.; Borsa, A.; Eriksson, S.

2008-12-01

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 1100-station EarthScope Plate Boundary Observatory (PBO) network was designed to leverage 445 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 supports the operation, maintenance and hardware upgrades of a subset of the six western U.S. geodetic networks until they are subsumed by PBO. Uninterrupted data flow from these stations will effectively double the time-series length of PBO over the expected life of EarthScope, and has created, for the first time, a single GPS-based geodetic network in the US. The other existing sites remain in operation under support from non-NSF sources (e.g. the USGS), and EarthScope continues to 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 were selected as the nucleus upon which to build PBO. Conversion of these stations to a PBO-compatible mode of operation was begun under previous funding, and as a result data now flow directly to PBO archives and processing centers while maintenance, operations, and meta-data requirements are continue to be upgraded to PBO standards. At the end of this project all 209 stations have been fully incorporated into PBO, meeting all standards for new PBO construction including data communications and land use permits. Funds for operation of these stations have been included in approved budgets for PBO's Operations and Maintenance phase. The data from these stations serve a much larger audience than just the few people who work to keep them operating. This project is now collecting the data that will be used by the next generation of solid-earth researchers for at least two decades. Educational modules are being developed by a team of researchers, educators, and curriculum development professionals, and are being disseminated through regional and national workshops. An interactive website provides the newest developments in tectonics research to K-16 classrooms. class="ab'>

Physicians' characteristics associated with exploring suicide risk among patients with depression: a French panel survey of general practitioners.

PubMed

Bocquier, Aurélie; Pambrun, Elodie; Dumesnil, Hélène; Villani, Patrick; Verdoux, Hélène; Verger, Pierre

2013-01-01

General practitioners (GPs) have a key role to play in suicide prevention, but the rates at which they question patients with depression about suicidal thoughts and plans are rather low. Little is known about GPs' characteristics associated with such inquiries. Our objectives were to describe GPs' attitudes, perceived barriers, and self-reported practices in this questioning of these patients and to analyze factors associated with these practices. This cross-sectional survey was conducted among participants in a panel of randomly selected French GPs (1249/1431 participated: 87.3%). GPs were interviewed with a standardized questionnaire covering their professional and personal characteristics, attitudes, and practices in exploring the suicide risk of their patients with depression. We built a suicide inquiry score by summing the responses to 5 items and used a multiple linear regression analysis to explore the characteristics associated with this score. Most GPs reported inquiring about the presence of suicidal ideation often or very often; less than 30% reported that they frequently explored signs of a specific suicide plan. The mean suicide inquiry score was 12.4 (SD, 2.9; range, 5-20). False ideas, such as thinking that patients who report suicidal ideas do not often commit suicide, were frequent (42.3%). Previous continuing medical education on suicide, participation in a formal mental health network, and patients who committed suicide in the past 5 years were associated with a higher score. Reluctance to question patients about suicide and perception of insufficient skill were associated with a lower score. This study showed great variability in French GPs' practices in exploring suicide risk in patients with depression. Interventions aiming at improving GPs' initial training and continuing medical education in suicide and/or depression, and their collaboration with mental health specialists should be developed, and their impacts assessed.

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.

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.

Physicians' Characteristics Associated with Exploring Suicide Risk among Patients with Depression: A French Panel Survey of General Practitioners

PubMed Central

Bocquier, Aurélie; Pambrun, Elodie; Dumesnil, Hélène; Villani, Patrick; Verdoux, Hélène; Verger, Pierre

2013-01-01

Background General practitioners (GPs) have a key role to play in suicide prevention, but the rates at which they question patients with depression about suicidal thoughts and plans are rather low. Little is known about GPs' characteristics associated with such inquiries. Our objectives were to describe GPs' attitudes, perceived barriers, and self-reported practices in this questioning of these patients and to analyze factors associated with these practices. Methodology This cross-sectional survey was conducted among participants in a panel of randomly selected French GPs (1249/1431 participated: 87.3%). GPs were interviewed with a standardized questionnaire covering their professional and personal characteristics, attitudes, and practices in exploring the suicide risk of their patients with depression. We built a suicide inquiry score by summing the responses to 5 items and used a multiple linear regression analysis to explore the characteristics associated with this score. Principal Findings Most GPs reported inquiring about the presence of suicidal ideation often or very often; less than 30% reported that they frequently explored signs of a specific suicide plan. The mean suicide inquiry score was 12.4 (SD, 2.9; range, 5–20). False ideas, such as thinking that patients who report suicidal ideas do not often commit suicide, were frequent (42.3%). Previous continuing medical education on suicide, participation in a formal mental health network, and patients who committed suicide in the past 5 years were associated with a higher score. Reluctance to question patients about suicide and perception of insufficient skill were associated with a lower score. Conclusions/Significance This study showed great variability in French GPs' practices in exploring suicide risk in patients with depression. Interventions aiming at improving GPs' initial training and continuing medical education in suicide and/or depression, and their collaboration with mental health specialists should be developed, and their impacts assessed. PMID:24339883

Time series evaluation of an intervention to increase statin tablet splitting by general practitioners.

PubMed

Polinski, Jennifer M; Schneeweiss, Sebastian; Maclure, Malcolm; Marshall, Blair; Ramsden, Samuel; Dormuth, Colin

2011-02-01

Tablet splitting, in which a higher-dose tablet is split to get 2 doses, reduces patients' drug costs. Statins can be split safely. General practitioners (GPs) may not direct their patients to split statins because of safety concerns or unawareness of costs. Medical chart inserts provide cost-effective education to physicians. The aim of this study was to assess whether providing GPs with statin-splitting chart inserts would increase splitting rates, and to identify predictors of splitting. In 2005 and 2006, we faxed a statin chart insert to British Columbia GPs with a request for a telephone interview. Consenting GPs were mailed 3 statin chart inserts and interviewed by phone (the intervention). In an interrupted time series, we compared monthly rates of statin-splitting prescriptions among intervention and nonintervention GPs before, during, and after the intervention. In multivariate logistic regressions accounting for patient clustering, predictors of splitting included physician and patient demographics and the specific statin prescribed. Of 5051 GPs reached, 282 (6%) agreed to the intervention. Before the intervention, GPs' splitting rate was 2.6%; after intervention, GPs' splitting rate was 7.5%. The rate for the nonintervention GPs was 4.4%. Intervention GPs were 1.68 (95% CI, 1.12-2.53) times more likely to prescribe splitting after the intervention than were nonintervention GPs. Other predictors were a patient's female sex (odds ratio [OR] = 1.26; 95% CI, 1.18-1.34), lower patient income (OR = 1.33; 95% CI, 1.18-1.34), and a lack of drug insurance (OR = 1.89; 95% CI, 1.69-2.04). An inexpensive intervention was effective in producing a sustained increase in GPs' splitting rate during 22 months of observed follow-up. Expanding statin-splitting education to all GPs might reduce prescription costs for many patients and payors. Copyright © 2011 Elsevier HS Journals, Inc. All rights reserved.

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.

Non-dynamic decimeter tracking of earth satellites using the Global Positioning System

NASA Technical Reports Server (NTRS)

Yunck, T. P.; Wu, S. C.

1986-01-01

A technique is described for employing the Global Positioning System (GPS) to determine the position of a low earth orbiter with decimeter accuracy without the need for user dynamic models. A differential observing strategy is used requiring a GPS receiver on the user vehicle and a network of six ground receivers. The technique uses the continuous record of position change obtained from GPS carrier phase to smooth position measurements made with pseudo-range. The result is a computationally efficient technique that can deliver decimeter accuracy down to the lowest altitude orbits.

GP Practices as a One-Stop Shop: How Do Patients Perceive the Quality of Care? A Cross-Sectional Study in Thirty-Four Countries.

PubMed

Schäfer, Willemijn L A; Boerma, Wienke G W; Schellevis, François G; Groenewegen, Peter P

2017-12-29

To contribute to the current knowledge on how a broad range of services offered by general practitioners (GPs) may contribute to the patient perceived quality and, hence, the potential benefits of primary care. Between 2011 and 2013, primary care data were collected among GPs and their patients in 31 European countries, plus Australia, Canada, and New Zealand. In these countries, GPs are the main providers of primary care, mostly specialized in family medicine and working in the ambulatory setting. In this cross-sectional study, questionnaires were completed by 7,183 GPs and 61,931 visiting patients. Moreover, 7,270 patients answered questions about what they find important (their values). In the analyses of patient experiences, we adjusted for patients' values in each country to measure patient perceived quality. Perceived quality was measured regarding five areas: accessibility and continuity of care, doctor-patient communication, patient involvement in decision making, and comprehensiveness of care. The range of GP services was measured in relation to four areas: (1) to what extent they are the first contact to the health care system for patients in need of care, (2) their involvement in treatment and follow-up of acute and chronic conditions, in other words treatment of diseases, (3) their involvement in minor technical procedures, and (4) their involvement in preventive treatments. Data of the patients were linked to the data of the GPs. Multilevel modeling was used to construct scale scores for the experiences of patients in the five areas of quality and the range of services of GPs. In these four-level models, items were nested within patients, nested in GP practices, nested in countries. The relationship between the range of services and the experiences of patients was analyzed in three-level multilevel models, also taking into account the values of patients. In countries where GPs offer a broader range of services patients perceive better accessibility, continuity, and comprehensiveness of care, and more involvement in decision making. No associations were found between the range of services and the patient perceived communication with their GP. The range of GP services mostly explained the variation between countries in the areas of patient perceived accessibility and continuity of care. This study showed that in countries where GP practices serve as a "one-stop shop," patients perceive better quality of care, especially in the areas of accessibility and continuity of care. Therefore, primary care in a country is expected to benefit from investments in a broader range of services of GPs or other primary care physicians. © Health Research and Educational Trust.

GPs asking patients to self-rate their health: a qualitative study

PubMed Central

Waller, Göran; Hamberg, Katarina; Forssén, Annika

2015-01-01

Background In epidemiological research, self-rated health is an independent predictor of mortality, cardiovascular diseases, and other critical outcomes. It is recommended for clinical use, but research is lacking. Aim To investigate what happens in consultations when the question ‘How would you assess your general health compared with others your own age?’ is posed. Design and setting Authentic consultations with GPs at health centres in Sweden. Method Thirty-three planned visits concerning diabetes, pain, or undiagnosed symptoms were voice-recorded. Dialogue regarding self-rated health was transcribed verbatim and analysed using a systematic text condensation method. Speaking time of patients and doctors was measured and the doctors’ assessment of the value of the question was documented in a short questionnaire. Results Two overarching themes are used to describe patients’ responses to the question. First, there was an immediate reaction, often expressing strong emotions, setting the tone of the dialogue and influencing the continued conversation. This was followed by reflection regarding their functional ability, management of illnesses and risks, and/or situation in life. The GPs maintained an attitude of active listening. They sometimes reported a slight increase in consultation time or feeling disturbed by the question, but mostly judged it as valuable, shedding additional light on the patients’ situation and making it easier to discuss difficulties and resources. The patients’ speaking time increased noticeably during this part of the consultation. Conclusion Asking patients to comparatively self-rate their health is an effective tool in general practice. PMID:26324500

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.

Recent Developments in Balloon Support Instrumentation at TIFR Balloon Facility, Hyderabad.

NASA Astrophysics Data System (ADS)

Vasudevan, Rajagopalan

2012-07-01

The Balloon Facility of Tata Institute of Fundamental Research has been conducting stratospheric balloon flights regularly for various experiments in Space Astronomy and Atmospheric Sciences. A continuous improvement in Balloon flight Support instrumentation by the Control Instrumentation Group to keep in space with the growing complexities of the scientific payloads have contributed to the total success of balloon flights conducted recently. Recent improvements in display of Balloon position during balloon flight by showing on real time the balloon GPS position against Google TM maps is of immense help in selecting the right spot for payload landing and safe recovery . For further speeding up the payload recovery process, a new GPS-GSM payload system has been developed which gives SMS of the payload position information to the recovery team on their cell phones. On parallel footing, a new GPS- VHF system has been developed using GPS and Radio Modems for Balloon Tracking and also for obtaining the payload impact point. On the Telecommand side, a single board Telecommand/ Timer weighing less than 2 Kg has been specially developed for use in the mesosphere balloon test flight. The interference on the existing Short Range Telemetry System has been eliminated by introducing a Band Pass Filter and LNA in the Receiving system of the modules, thereby enhancing its reliability. In this paper , we present the details of the above mentioned developments.

PBO Nucleus Project Status: Integration of 209 Existing GPS Stations into the Plate Boundary Observatory

NASA Astrophysics Data System (ADS)

Blume, F.; Meertens, C.; Anderson, G.; Eriksson, S.; Boyce, E.

2007-12-01

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 1100-station EarthScope Plate Boundary Observatory (PBO) network has been designed to leverage 445 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 supports the operation, maintenance and hardware upgrades of a subset of the six western U.S. geodetic networks until they are subsumed by PBO. Uninterrupted data flow from these stations will effectively double the time-series length of PBO over the expected life of EarthScope, and has created, for the first time, a single GPS-based geodetic network in the US. The other existing sites remain in operation under support from non-NSF sources (e.g. the USGS), and EarthScope continues to 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 were selected as the nucleus upon which to build PBO. Conversion of these stations to a PBO-compatible mode of operation was begun under previous funding, and as a result data now flow directly to PBO archives and processing centers while maintenance, operations, and meta-data requirements are continue to be upgraded to PBO standards. At the end of this project all 209 stations will be fully incorporated into PBO, meeting all standards for new PBO construction including data communications and land use permits. Funds for operation of these stations have been included in planned budgets for PBO after the construction phase ends and PBO begins an operational phase in 2008. At this time work on the project is apporixmately 80% complete, with over 90% of the stations having been upgraded. The data from these stations serve a much larger audience than just the few people who work to keep them operating. This project is now collecting the data that will be used by the next generation of solid-earth researchers for at least two decades. Educational modules are being developed by a team of researchers, educators, and curriculum development professionals, and are being disseminated through regional and national workshops. An interactive website provides the newest developments in tectonics research to K-16 classrooms.

Travel patterns during pregnancy: comparison between Global Positioning System (GPS) tracking and questionnaire data.

PubMed

Wu, Jun; Jiang, Chengsheng; Jaimes, Guillermo; Bartell, Scott; Dang, Andy; Baker, Dean; Delfino, Ralph J

2013-10-09

Maternal exposures to traffic-related air pollution have been associated with adverse pregnancy outcomes. Exposures to traffic-related air pollutants are strongly influenced by time spent near traffic. However, little is known about women's travel activities during pregnancy and whether questionnaire-based data can provide reliable information on travel patterns during pregnancy. Examine women's in-vehicle travel behavior during pregnancy and examine the difference in travel data collected by questionnaire and global positioning system (GPS) and their potential for exposure error. We measured work-related travel patterns in 56 pregnant women using a questionnaire and one-week GPS tracking three times during pregnancy (<20 weeks, 20-30 weeks, and >30 weeks of gestation). We compared self-reported activities with GPS-derived trip distance and duration, and examined potentially influential factors that may contribute to differences. We also described in-vehicle travel behavior by pregnancy periods and influences of demographic and personal factors on daily travel times. Finally, we estimated personal exposure to particle-bound polycyclic aromatic hydrocarbon (PB-PAH) and examined the magnitude of exposure misclassification using self-reported vs. GPS travel data. Subjects overestimated both trip duration and trip distance compared to the GPS data. We observed moderately high correlations between self-reported and GPS-recorded travel distance (home to work trips: r = 0.88; work to home trips: r = 0.80). Better agreement was observed between the GPS and the self-reported travel time for home to work trips (r = 0.77) than work to home trips (r = 0.64). The subjects on average spent 69 and 93 minutes traveling in vehicles daily based on the GPS and self-reported data, respectively. Longer daily travel time was observed among participants in early pregnancy, and during certain pregnancy periods in women with higher education attainment, higher income, and no children. When comparing self-reported vs. GPS data, we found that estimated personal exposure to PB-PAH did not differ remarkably at the population level, but the difference was large at an individual level. Self-reported home-to-work data overestimated both trip duration and trip distance compared to GPS data. Significant differences in PAH exposure estimates were observed at individual level using self-reported vs. GPS data, which has important implications in air pollution epidemiological studies.

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;

Special Issue on Time Scale Algorithms

DTIC Science & Technology

2008-01-01

are currently Two Way Satellite Time and Frequency Transfer ( TWSTFT ) and GPS carrier phase time transfer. The interest in time scale algorithms and...laboratory-specific innovations and practices, GNSS applications, UTC generation, TWSTFT applications, GPS applications, small-ensemble applications

The lesser evil? Initiating a benzodiazepine prescription in general practice

PubMed Central

Anthierens, Sibyl; Habraken, Hilde; Petrovic, Mirko; Christiaens, Thierry

2007-01-01

Objective Chronic benzodiazepine (BZD) use is widespread and linked with adverse effects. There is consensus concerning the importance of initiating BZD as a crucial moment. Nevertheless specific research in this field is lacking. This paper addresses the views of GPs on why they start prescribing BZDs to first-time users. Design Qualitative study with five focus groups analysed using a systematic content analysis. Setting Regions of Ghent and Brussels in Belgium. Subjects A total of 35 general practitioners. Main outcome measure The GPs’ perspective on their initiating of BZD prescribing. Results GPs reported that they are cautious in initiating BZD usage. At the same time, GPs feel overwhelmed by the psychosocial problems of their patients. They show empathy by prescribing. They feel in certain situations there are no other solutions and they experience BZDs as the lesser evil. They admit to resorting to BZDs because of time restraint and lack of alternatives. GPs do not perceive the addictive nature of BZD consumption as a problem with first-time users. GPs do not specifically mention patients’ demand as an element for starting. Conclusion The main concern of GPs is to help the patient. GPs should be aware of the addictive nature of BZD even in low doses and a non-pharmacological approach should be seen as the best first approach. If GPs decide to prescribe a BZD they should make plain to the patient that the medication is only a “temporary” solution with clear agreements with regard to medication withdrawal. PMID:18041658

Awareness of the role of general practitioners in primary care among outpatient populations: evidence from a cross-sectional survey of tertiary hospitals in China.

PubMed

Liu, Xiaojun; Tan, Anran; Towne, Samuel D; Hou, Zhaoxun; Mao, Zongfu

2018-03-16

General practitioners (GPs) are highly underutilised in China with many patients going directly to hospitals when seeking routine care. Multiple countries around the world have successfully used GPs in routine care, and as such, China may benefit from the use of GPs. This study examines the status of, and factors associated with, knowledge related to GPs among outpatient populations from China's tertiary hospitals. This is a cross-sectional survey study. The questionnaires were completed by 565 outpatients from four tertiary hospitals in China during 2016. Convenience sampling on different floors and throughout the outpatient building was carried out. We used the logistic regression models to identify GP-related knowledge among different populations. Overall, 50.27% of respondents said they had never heard of GPs. This was also true among females (adjusted OR (AOR)=1.57, 95% CI 1.43 to 2.71), older adults (AOR 46-65 =1.61, 95% CI 1.39 to 2.98; AOR >65 =2.01, 95% CI 1.62 to 3.59), those with lower education level (AOR Bachelor's degree =0.61, 95% CI 0.20 to 0.81; AOR ≥Master's degree =0.49, 95% CI 0.23 to 0.76), rural residents (AOR=1.51, 95% CI 1.35 to 2.82) and those with chronic disease (AOR without chronic disease =0.61, 95% CI 0.22 to 0.71). What is more, less than one-in-ten (9.03%) outpatients were able to accurately describe what a GP was, with less than 30% accurately describing a GP among those receiving GPs' services. Outpatients who could have received less costly health services from GPs in primary medical institutions were more likely to choose costlier specialist physicians in tertiary hospitals, which is likely linked to limited knowledge about GPs. Policy makers should invest in outreach efforts to improve public awareness of GPs, while at the same time conducting continued surveillance of these efforts to evaluate progress towards this goal. © Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2018. All rights reserved. No commercial use is permitted unless otherwise expressly granted.

Management of childhood gastroenteritis in the community.

PubMed

Rahman, S; Aszkenasy, O M

2001-07-01

Good evidence-based research exists for the management of gastroenteritis. However, we encountered local anecdotal evidence of wide variations in the management of gastroenteritis. In order to assess the prevailing practice in gastroenteritis management in primary care, in the Tees Health region, an anonymous questionnaire study involving general practitioners (GPs) and health visitors (HVs) was performed. Three case scenarios were presented in the questionnaire, involving a breast-fed infant, a formula-fed infant and a four-y-old child all with diarrhoea and vomiting, but able to tolerate oral fluids and not ill enough to need hospital admission. Most GPs (78.6%) and HVs (80.5%) advised continuation of breast-feeding, though the practice of giving advice to stop breast-feeding, starve the child and substitute inappropriate fluids such as flat coke, was still common. For infants who were bottle-fed, this inappropriate advice was given much more commonly (only 25.6% and 52.8% of GPs and HVs, respectively gave advice to continue bottle-feeding). This was even more true for the four-y-old, for whom advice to continue with a normal diet was very much the exception (7.7% of GPs and 19.5% of HVs). Advice given to parents of children with gastroenteritis was inconsistent and, in many cases, inappropriate. This has implications for clinical governance. There is an urgent need for the development and implementation of local guidelines.

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, ].

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.

Improved Data Access From the Northern California Earthquake Data Center

NASA Astrophysics Data System (ADS)

Neuhauser, D.; Oppenheimer, D.; Zuzlewski, S.; Klein, F.; Jensen, E.; Gee, L.; Murray, M.; Romanowicz, B.

2002-12-01

The NCEDC is a joint project of the UC Berkeley Seismological Laboratory and the USGS Menlo Park to provide a long-term archive and distribution center for geophysical data for northern California. Most data are available via the Web at http://quake.geo.berkeley.edu and research accounts are available for access to specialized datasets. Current efforts continue to expand the available datasets, enhance distribution methods, and to provide rapid access to all datasets. The NCEDC archives continuous and event-based seismic and geophysical time-series data from the BDSN, the USGS NCSN, the UNR Seismic Network, the Parkfield HRSN, and the Calpine/Unocal Geysers network. In collaboration with the USGS, the NCEDC has archived a total of 887 channels from 139 sites of the "USGS low-frequency" geophysical network (UL), including data from strainmeters, creep meters, magnetometers, water well levels, and tiltmeters. There are 336 active continuous data channels that are updated at the NCEDC on a daily basis. Geodetic data from the BARD network of over 40 continuously recording GPS sites are archived at the NCEDC in both raw and RINEX format. The NCEDC is the primary archive for survey-mode GPS and other geodetic data collected in northern California by the USGS, universities, and other agencies. All of the BARD data and GPS data archived from USGS Menlo Park surveys are now available through the GPS Seamless Archive Centers (GSAC), and by FTP directly from the NCEDC. Virtually all time-series data at the NCEDC are now available in SEED with complete instrument responses. Assembling, verifying, and maintaining the response information for these networks is a huge task, and is accomplished through the collaborative efforts of the NCEDC and the contributing agencies. Until recently, the NCSN waveform data were available only through research accounts and special request methods due to incomplete instrument responses. In the last year, the USGS compiled the necessary descriptions for for both historic and current NCSN instrumentation. The NCEDC and USGS jointly developed a procedure to create and maintain the hardware attributes and instrument responses at the NCEDC for the 3500 NCSN channels. As a result, the NCSN waveform data can now be distributed in SEED format. The NCEDC provides access to waveform data through Web forms, email requests, and programming interfaces. The SeismiQuery Web interface provides information about data holdings. NetDC allows users to retrieve inventory information, instrument responses, and waveforms in SEED format. STP provides both a Web and programming interface to retrieve data in SEED or other user-friendly formats. Through the newly formed California Integrated Seismic Network, we are working with the SCEDC to provide unified access to California earthquake data.

Determining GPS average performance metrics

NASA Technical Reports Server (NTRS)

Moore, G. V.

1995-01-01

Analytic and semi-analytic methods are used to show that users of the GPS constellation can expect performance variations based on their location. Specifically, performance is shown to be a function of both altitude and latitude. These results stem from the fact that the GPS constellation is itself non-uniform. For example, GPS satellites are over four times as likely to be directly over Tierra del Fuego than over Hawaii or Singapore. Inevitable performance variations due to user location occur for ground, sea, air and space GPS users. These performance variations can be studied in an average relative sense. A semi-analytic tool which symmetrically allocates GPS satellite latitude belt dwell times among longitude points is used to compute average performance metrics. These metrics include average number of GPS vehicles visible, relative average accuracies in the radial, intrack and crosstrack (or radial, north/south, east/west) directions, and relative average PDOP or GDOP. The tool can be quickly changed to incorporate various user antenna obscuration models and various GPS constellation designs. Among other applications, tool results can be used in studies to: predict locations and geometries of best/worst case performance, design GPS constellations, determine optimal user antenna location and understand performance trends among various users.

GPs' attitudes, beliefs and behaviours regarding exercise for chronic knee pain: a questionnaire survey.

PubMed

Cottrell, Elizabeth; Foster, Nadine E; Porcheret, Mark; Rathod, Trishna; Roddy, Edward

2017-06-17

The aim of this study was to investigate general practitioners' (GPs) attitudes, beliefs and behaviours regarding the use of exercise for patients with chronic knee pain (CKP) attributable to osteoarthritis. Primary care GPs in the UK. 5000 GPs, randomly selected from Binley's database, were mailed a cross-sectional questionnaire survey. GPs' attitudes and beliefs were investigated using attitude statements, and reported behaviours were identified using vignette-based questions. GPs were invited to report barriers experienced when initiating exercise with patients with CKP RESULTS: 835 (17%) GPs responded. Overall, GPs were positive about general exercise for CKP. 729 (87%) reported using exercise, of which, 538 (74%) reported that they would use both general and local (lower limb) exercises. However, only 92 (11% of all responding) GPs reported initiating exercise in ways aligning with best-evidence recommendations. 815 (98%) GPs reported barriers in using exercise for patients with CKP, most commonly, insufficient time in consultations (n=419; 51%) and insufficient expertise (n=337; 41%). While GPs' attitudes and beliefs regarding exercise for CKP were generally positive, initiation of exercise was often poorly aligned with current recommendations, and barriers and uncertainties were reported. GPs' use of exercise may be improved by addressing the key barriers of time and expertise, by developing a pragmatic approach that supports GPs to initiate individualised exercise, and/or by other professionals taking on this role. © Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2017. All rights reserved. No commercial use is permitted unless otherwise expressly granted.

GPs' prescription routines and cooperation with other healthcare personnel before and after implementation of multidose drug dispensing.

PubMed

Wekre, Liv Johanne; Bakken, Kjersti; Garåsen, Helge; Grimsmo, Anders

2012-08-01

This study addresses GPs' attitudes towards multidose drug dispensing before and after implementation and their perceived experience of how multidose drug dispensing affects prescription and communication routines for patients in the home care services. This study contributes to a method triangulation with two other studies on the introduction of multidose drug dispensing in Trondheim. A controlled before-and-after study carried out in Trondheim (intervention) and Tromsø (control). A questionnaire was distributed to all GPs in the two towns in 2005 with a follow-up questionnaire in 2008. The GPs in Trondheim showed a positive attitude to multidose drug dispensing both before and after the implementation. Increased workload was reported, but still the GPs wanted the system to be continued. Most of the GPs reported a better overview of the patients' medication and a supposed reduction in medication errors. The GPs' prescription- and communication routines were changed only for the multidose drug users and not for the other patients in the home care services. The study supports the results presented in two previous publications according to GPs' positive attitude towards multidose drug dispensing, their better overview of the patients' medications, and improved cooperation with the pharmacy. This study adds to our understanding of prescription routines among GPs and the use of the medication module in the electronic health record.

Real-Time In-Situ Measurements for Earthquake Early Warning and Space-Borne Deformation Measurement Mission Support

NASA Astrophysics Data System (ADS)

Kedar, S.; Bock, Y.; Webb, F.; Clayton, R. W.; Owen, S. E.; Moore, A. W.; Yu, E.; Dong, D.; Fang, P.; Jamason, P.; Squibb, M. B.; Crowell, B. W.

2010-12-01

In situ geodetic networks for observing crustal motion have proliferated over the last two decades and are now recognized as indispensable tools in geophysical research, along side more traditional seismic networks. The 2007 National Research Council’s Decadal Survey recognizes that space-borne and in situ observations, such as Interferometric Synthetic Aperture Radar (InSAR) and ground-based continuous GPS (CGPS) are complementary in forecasting, in assessing, and in mitigating natural hazards. However, the information content and timeliness of in situ geodetic observations have not been fully exploited, particularly at higher frequencies than traditional daily CGPS position time series. Nor have scientists taken full advantage of the complementary natures of geodetic and seismic data, as well as those of space-based and in situ observations. To address these deficits we are developing real-time CGPS data products for earthquake early warning and for space-borne deformation measurement mission support. Our primary mission objective is in situ verification and validation for DESDynI, but our work is also applicable to other international missions (Sentinel 1a/1b, SAOCOM, ALOS 2). Our project is developing new capabilities to continuously observe and mitigate earthquake-related hazards (direct seismic damage, tsunamis, landslides, volcanoes) in near real-time with high spatial-temporal resolution, to improve the planning and accuracy of space-borne observations. We also are using GPS estimates of tropospheric zenith delay combined with water vapor data from weather models to generate tropospheric calibration maps for mitigating the largest source of error, atmospheric artifacts, in InSAR interferograms. These functions will be fully integrated into a Geophysical Resource Web Services and interactive GPS Explorer data portal environment being developed as part of an ongoing MEaSUREs project and NASA’s contribution to the EarthScope project. GPS Explorer, originally designed for web-based dissemination of long-term Solid Earth Science Data Records (ESDR’s) such as deformation time series, tectonic velocity vectors, and strain maps, provides the framework for seamless inclusion of the high rate data products. Detection and preliminary modeling of interesting signals by dense real-time high-rate ground networks will allow mission planners and decision makers to fully exploit the less-frequent but higher resolution InSAR observations. Fusion of in situ elements into an advanced observation system will significantly improve the scientific value of extensive surface displacement data, provide scientists with improved access to modern software tools to manipulate and model these data, increase the data’s accuracy and timeliness at higher frequencies than available from space-based observations, and increase the accuracy of space-based observations through calibration of atmospheric and other systematic errors.

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.

Exploring the General Practitioner-pharmacist relationship in the community setting in Ireland.

PubMed

Moore, Thomas; Kennedy, Julia; McCarthy, Suzanne

2014-10-01

To explore the General Practitioner (GP)-pharmacist relationship, to gain insight into communication between the professions and evaluate opinion on extension of the role of the community pharmacist. A postal questionnaire sent to 500 GPs and 335 community pharmacists with work addresses in the counties of Cork, Kerry, Tipperary, Waterford and Limerick, Ireland. An overall response rate of 56% was achieved. Clear differences of opinion exist between GPs and pharmacists on the extension of the role of the community pharmacist; pharmacist provision of vaccinations (12% of GPs in favour versus 78% of pharmacists), pharmacists prescribing the oral contraceptive pill (18% GP versus 88% pharmacist) and increasing the prescribing power of the pharmacist (37% GP versus 95% pharmacist). Fifty-four percent of GPs and 97% of pharmacists were in favour of pharmacists providing screening services, while 82% of GPs and 96% of pharmacists were in favour of pharmacists dealing with minor ailments. Seventy-three percent of GPs and 43% of pharmacists agreed that communication between the professions was very good. This study identifies a clear difference of opinion on the extension of the role of the community pharmacist and recognises problems in communication between the professions. This comes on the background of continued calls from the Pharmaceutical Society of Ireland for an extension of pharmacist roles and continued opposition from the Irish Medical Organisation to such moves. This study highlights the need for increased dialogue between representative organisations and a commitment for professional agendas to be set aside in the best interests of patients. © 2014 Royal Pharmaceutical Society.

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

The Glasgow Prognostic Score at the Time of Palliative Esophageal Stent Insertion is a Predictive Factor of 30-Day Mortality and Overall Survival.

PubMed

Driver, Robert J; Handforth, Catherine; Radhakrishna, Ganesh; Bennett, Michael I; Ford, Alexander C; Everett, Simon M

2018-03-01

Optimizing the timing of esophageal stent insertion is a challenge, partly due to difficulty predicting survival in advanced malignancy. The Glasgow prognostic score (GPS) is a validated tool for predicting survival in a number of cancers. To assess the utility of the GPS in predicting 30-day mortality and overall survival postesophageal stent insertion. Patients at a tertiary referral center who had received an esophageal stent for palliation of dysphagia were included if they had a measurement of albumin and C-reactive protein (CRP) in the week preceding the procedure (n=209). Patients with both an elevated CRP (>10 mg/L) and hypoalbuminemia (<35 g/L) were given a GPS score of 2 (GPS2). Patients with only one of these abnormalities were assigned as GPS1 and those with normal CRP and albumin were assigned as GPS0. Clinical and pathologic parameters were also collected to assess for potential confounding factors in the survival analysis. Increasing GPS was associated with 30-day mortality; for patients with GPS0, 30-day mortality was 5% (2/43), for GPS1 it was 23% (26/114), and for GPS2 it was 33% (17/52). The adjusted hazard ratio for overall poststent mortality was 1.6 (95% confidence interval, 1.1-2.4; P=0.02) for GPS1 and 2.4 (95% confidence interval, 1.5-3.8; P<0.001) for GPS2 patients compared with GPS0. GPS is an independent prognostic factor of 30-day mortality and overall survival after esophageal stent insertion. It is a potential adjunct to clinical assessment in identifying those patients at high-risk of short-term mortality poststent.

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.

Using surface displacement derived from GRACE to constrain the water loading signal in cGPS measurements in the Amazon Basin

NASA Astrophysics Data System (ADS)

Jose, L.; Bennett, R. A.; Harig, C.

2017-12-01

Currently, cGPS data is well suited to track vertical changes in the Earth's surface. However, there are annual, semi-annual, and interannual signals within cGPS time series that are not well constrained. We hypothesize that these signals are primarily due to water loading. If this is the case, the conventional method of modeling cGPS data as an annual or semiannual sinusoid falls short, as such models cannot accurately capture all variations in surface displacement, especially those due to extreme hydrologic events. We believe that we can better correct the cGPS time series with another method we are developing wherein we use a time series of surface displacement derived from the GRACE geopotential field instead of a sinusoidal model to correct the data. Currently, our analysis is constrained to the Amazon Basin, where the signal due to water loading is large enough to appear in both the GRACE and cGPS measurements. The vertical signal from cGPS stations across the Amazon Basin show an apparent spatial correlation, which further supports our idea that these signals are due to a regional water loading signal. In our preliminary research, we used tsview for Matlab to find that the WRMS of the corrected cGPS time series can be reduced as much as 30% from the model corrected data to the GRACE corrected data. The Amazon, like many places around the world, has experienced extreme drought, in 2005, 2010, and recently in 2015. In addition to making the cGPS vertical signal more robust, the method we are developing has the potential to help us understand the effects of these weather events and track trends in water loading.

Cesium and Rubidium Frequency Standards Status and Performance on the GPS Program

NASA Technical Reports Server (NTRS)

VanMelle, M. J.

1996-01-01

This paper is an update of the on-orbit operational performance of the frequency standards on the last Block 1 Navstar satellite (GPS-10), the complete Block 2 Navstar satellites (GPS-13 to 21) and the Block 2A Navstar (GPS-22 to 40) satellites. Since the status of the GPS constellation is now at full operational capability (FOC), a minimum of twenty-four satellites are in position with all the necessary tests successfully completed. The evolution of frequency standards on board the GPS vehicles will be presented with corresponding results. Various methods and techniques will be presented to show on-orbit life time, down time, state of health telemetry, on-orbit trending and characterization of all the frequency standards. Other topics such as reliability, stability, clock quirks and idiosyncrasies of each vehicle will be covered.

Placebo use in the UK: a qualitative study exploring GPs' views on placebo effects in clinical practice.

PubMed

Bishop, Felicity L; Howick, Jeremy; Heneghan, Carl; Stevens, Sarah; Hobbs, F D Richard; Lewith, George

2014-06-01

Surveys show GPs use placebos in clinical practice and reported prevalence rates vary widely. To explore GPs' perspectives on clinical uses of placebos. A web-based survey of 783 UK GPs' use of placebos in clinical practice. Qualitative descriptive analysis of written responses ('comments') to three open-ended questions. Comments were classified into three categories: (i) defining placebos and their effects in general practice; (ii) ethical, societal and regulatory issues faced by doctors and (iii) reasons why a doctor might use placebos and placebo effects in clinical practice. GPs typically defined placebos as lacking something, be that adverse or beneficial effects, known mechanism of action and/or scientific evidence. Some GPs defined placebos positively as having potential to benefit patients, primarily through psychological mechanisms. GPs described a broad array of possible harms and benefits of placebo prescribing, reflecting fundamental bioethical principles, at the level of the individual, the doctor-patient relationship, the National Health Service and society. While some GPs were adamant that there was no place for placebos in clinical practice, others focused on the clinically beneficial effects of placebos in primary care. This study has elucidated specific costs, benefits and ethical barriers to placebo use as perceived by a large sample of UK GPs. Stand-alone qualitative work would provide a more in-depth understanding of GPs' views. Continuing education and professional guidance could help GPs update and contextualize their understanding of placebos and their clinical effects. © The Author 2014. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Development of a Real-Time GPS/Seismic Displacement Meter: Applications to Civilian Infrastructure in Orange and Western Riverside Counties, California

NASA Technical Reports Server (NTRS)

Bock, Yehuda

2005-01-01

We propose a three-year applications project that will develop an Integrated Real-Time GPS/Seismic System and deploy it in Orange and Western Riverside Counties, spanning three major strike-slip faults in southern California (San Andreas, San Jacinto, and Elsinore) and significant populations and civilian infrastructure. The system relying on existing GPS and seismic networks will collect and analyze GPS and seismic data for the purpose of estimating and disseminating real-time positions and total ground displacements (dynamic, as well as static) during all phases of the seismic cycle, from fractions of seconds to years. Besides its intrinsic scientific use as a real-time displacement meter (transducer), the GPS/Seismic System will be a powerful tool for local and state decision makers for risk mitigation, disaster management, and structural monitoring (dams, bridges, and buildings). Furthermore, the GPS/Seismic System will become an integral part of California's spatial referencing and positioning infrastructure, which is complicated by tectonic motion, seismic displacements, and land subsidence. Finally, the GPS/Seismic system will also be applicable to navigation in any environment (land, sea, or air) by combining precise real-time instantaneous GPS positioning with inertial navigation systems. This development will take place under the umbrella of the California Spatial Reference Center, in partnership with local (Counties, Riverside County Flood and Water Conservation District, Metropolitan Water District), state (Caltrans), and Federal agencies (NGS, NASA, USGS), the geophysics community (SCIGN/SCEC2), and the private sector (RBF Consulting). The project will leverage considerable funding, resources, and R&D from SCIGN, CSRC and two NSF-funded IT projects at UCSD and SDSU: RoadNet (Real-Time Observatories, Applications and Data Management Network) and the High Performance Wireless Research and Education Network (HPWREN). These two projects are funded to develop both the wireless networks and the integrated, seamless, and transparent information management system that will deliver seismic, geodetic, oceanographic, hydrological, ecological, and physical data to a variety of end users in real-time in the San Diego region. CSRC is interested in providing users access to real-time, accurate GPS data for a wide variety of applications including RTK surveying/GIS and positioning of moving platforms such as aircraft and emergency vehicles. SCIGN is interested in upgrading sites to high-frequency real-time operations for rapid earthquake response and GPS seismology. The successful outcome of the project will allow the implementation of similar systems elsewhere, particularly in plate boundary zones with significant populations and civilian infrastructure. CSRC would like to deploy the GPS/Seismic System in other parts of California, in particular San Diego, Los Angeles County and the San Francisco Bay Area.

The Ionosphere and Ocean Altimetry

NASA Technical Reports Server (NTRS)

Lindqwister, Ulf J.

1999-01-01

The accuracy of satellite-based single-frequency radar ocean altimeters benefits from calibration of the total electron content (TEC) of the ionosphere below the satellite. Data from the global network of Global Positioning System (GPS) receivers provides timely, continuous, and globally well-distributed measurements of ionospheric electron content. We have created a daily automated process called Daily Global Ionospheric Map (Daily-GIM) whose primary purpose is to use global GPS data to provide ionospheric calibration data for the Geosat Follow-On (GFO) ocean altimeter. This process also produces an hourly time-series of global maps of the electron content of the ionosphere. This system is designed to deliver "quick-look" ionospheric calibrations within 24 hours with 90+% reliability and with a root-mean-square accuracy of 2 cm at 13.6 GHz. In addition we produce a second product within 72 hours which takes advantage of additional GPS data which were not available in time for the first process. The diagram shows an example of a comparison between TEC data from the Topographic Experiment (TOPEX) ocean altimeter and Daily-GIM. TEC are displayed in TEC units, TECU, where 5 TECU is 1 cm at 13.6 GHz. Data from a single TOPEX track is shown. Also shown is the Bent climatological model TEC for the track. Although the GFO satellite is not yet in its operational mode, we have been running Daily-GIM reliably (much better than 90%) with better than 2-cm accuracy (based on comparisons against TOPEX) for several months. When timely ephemeris files for the European Remote Sensing Satellite 2 (ERS-2) are available, daily ERS-2 altimeter ionospheric calibration files are produced. When GFO ephemeris files are made available to us, we produce GFO ionosphere calibration files. Users of these GFO ionosphere calibration files find they are a great improvement over the alternative International Reference Ionosphere 1995 (IRI-95) climatological model. In addition, the TOPEX orbit determination team at JPL has been using the global ionospheric maps to calibrate the single frequency GPS data from the TOPEX receiver, and report highly significant improvements in the ephemeris. The global ionospheric maps are delivered daily to the International GPS Service (IGS), making them available to the scientific community. Additional information is contained in the original.

Paperless migrants and Norwegian general practitioners.

PubMed

Aarseth, Svein; Kongshavn, Trygve; Maartmann-Moe, Kjell; Hjortdahl, Per

2016-06-01

In Norway, the rights of paperless migrants are restricted. We wished to investigate the extent to which Norwegian general practitioners give treatment to this group and their grounds for doing so, as well as to identify the health problems that were presented. In 2010, an online questionnaire was distributed to 3 994 general practitioners who were members of the Norwegian Medical Association. Altogether 1 027 GPs responded. Of these, 237 (23 %) reported to have treated paperless migrants. Mental problems, pregnancy-related issues and respiratory ailments were the most frequently reported reasons for contact. Of the 237 GPs who reported to have treated paperless migrants, altogether 166 (70 %) stated that they would continue to receive these patients. The fact that most of the GPs who had treated paperless migrants would continue to receive this patient group and thus provide health services beyond this group’s entitlements, we regard as a wish to comply with the Code of Ethics for Norwegian doctors.

Establishment of a Subsidence Superstation in the Mississippi Delta: Integrating sediment core, SET, GPS and vertical strainmeter data to understand subsidence

NASA Astrophysics Data System (ADS)

Steckler, M. S.; Allison, M. A.; Bridgeman, J.; Dixon, T. H.; Hatfield, W.; A Karegar, M.; Tornqvist, T. E.; Zumberge, M. A.; Wyatt, F. K.

2017-12-01

There is a great need for coordinated efforts to monitor and better understand subsidence rates in low-elevation coastal zones by integrating different, complementary techniques at carefully selected sites. We present recent efforts to establish a subsidence superstation in the Mississippi Delta. The site is 2 km from the river near Myrtle Grove, Louisiana, at a CRMS (Coastwide Reference Monitoring System) site. The CRMS site consists of a surface elevation table (SET) and marker horizon established in 2008. The surface elevation relative to a rod driven to refusal (26 m) and the sedimentation above the marker horizon is measured semiannually. Adjacent to this site we have added three borehole optical fiber strainmeters that have been providing continuous records of displacement between the near-surface and depths of 10, 26, and 42 m. The instruments provide unprecedented resolution for compaction studies (see Hatfield et al. abstract). We regularly record teleseismic events with amplitudes <1 μm. The records also show a number of days-long compaction and rebound events of less than 1 mm, resulting from changes in the weather and water level. We have attached GPS to each of the wells. For the deepest well, the GPS is anchored to the bottom of the well with the base of the optical strainmeter. For the other two wells, the GPS is anchored to the upper casing of the well. While drilling the wells, a 5" diameter continuous core was collected reaching the Pleistocene boundary at 37 m depth (see Bridgeman et al. abstract). The silty uppermost 10 m, comprised of proximal overbank deposits, reveal up to 5-6 m of subsidence over the past 3000 years. In contrast, the surficial sediments ( 70 cm) are almost entirely organic matter and show little subsidence. The SET shows only 0.4 mm/yr for a 7.4 yr time window. Over the first year, the strainmeters show no long-term compaction or extension greater than ± 0.5 mm. Precise processing of the available GPS data indicates the sites subside at subtly different rates, but a longer time series will be required to confirm this result. The current low-density organic deposition is not driving significant compaction, but this may change when the planned nearby Mid-Barataria diversion becomes operational. We may see significant change in compaction once clastic sediment fluxes increase after the diversion.

General practitioners' clinical expertise in managing suicidal young people: implications for continued education.

PubMed

Michail, Maria; Tait, Lynda; Churchill, Dick

2017-09-01

Aim To examine general practitioners' (GPs) clinical expertise in assessing, communicating with, and managing suicidal young people aged 14-25 to inform the development of an educational intervention for GPs on youth suicide prevention. Suicide is the second leading cause of death for young people worldwide. GPs are ideally suited to facilitate early identification and assessment of suicide risk. However, GPs' levels of competence, knowledge, and attitudes towards suicidal young people have not yet been explored. A cross-sectional survey on GPs' levels of confidence in assessing and managing young people at risk of suicide; knowledge of risk factors and warning signs of suicide in young people; attitudes towards young suicidal people; and training preferences on managing suicide risk. Findings Seventy GPs completed the survey (30 males). The majority of GPs reported high levels of confidence in assessing and managing suicidality in young people. Experienced GPs demonstrated high levels of knowledge of suicide risk factors in young people but low levels of knowledge of warning signs that might indicate heightened risk. Although 48% of GPs disagreed that maintaining compassionate care is difficult with those who deliberately self-harm, GPs perceived communication with young people to be difficult, with one-third reporting frustration in managing those at risk of suicide. A total of 75% of GPs said they would be interested in receiving further training on assessing and managing young people at risk of suicide. The study has important implications for providing specialist training to support GPs in assessing and managing youth suicide risk and facilitating attitudinal change. GP education on youth suicide risk assessment and management should promote a holistic understanding and assessment of risk and its individual, social and contextual influences in line with clinical recommendations to facilitate therapeutic engagement and communication with young people.

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.

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.

Assessment of the SonixGPS system for its application in real-time ultrasonography navigation-guided percutaneous nephrolithotomy for the treatment of complex kidney stones.

PubMed

Li, Xiang; Long, Qingzhi; Chen, Xingfa; He, Dalin; He, Hui

2017-04-01

SonixGPS is a novel real-time ultrasonography navigation technology, which has been demonstrated to promote accuracy of puncture in surgical operations. The aim of this study is to evaluate its application in guiding the puncture during percutaneous nephrolithotomy (PCNL). We retrospectively reviewed our experience in treating a total of 74 patients with complex kidney stones with PCNL, in which puncture in 37 cases were guided by SonixGPS system, while the other 37 by conventional ultrasound. The effectiveness of operation was evaluated in terms of stone clearance rate, operation time, time to successful puncture, number of attempts for successful puncture and hospital stay. The safety of operation was examined by evaluating postoperative complications. Our retrospective review showed that although there were no significant differences in stone clearance rates between the groups, SonixGPS guidance resulted in more puncture accuracy with shorter puncture time and higher successful puncture rate. Under the help of SonixGPS, most patients (92 %) had no or just mild complications, compared to that (73 %) in conventional ultrasound group. Post-operative decrease of hemoglobin in SonixGPS group was 13.79 (7-33) mg/dl, significantly lower than that 20.97 (8-41) mg/dl in conventional ultrasound group. Our experience demonstrates that SonixGPS is superior to conventional ultrasound in guiding the puncture in PCNL for the treatment of complex kidney stone.

Common mode error in Antarctic GPS coordinate time series on its effect on bedrock-uplift estimates

NASA Astrophysics Data System (ADS)

Liu, Bin; King, Matt; Dai, Wujiao

2018-05-01

Spatially-correlated common mode error always exists in regional, or-larger, GPS networks. We applied independent component analysis (ICA) to GPS vertical coordinate time series in Antarctica from 2010 to 2014 and made a comparison with the principal component analysis (PCA). Using PCA/ICA, the time series can be decomposed into a set of temporal components and their spatial responses. We assume the components with common spatial responses are common mode error (CME). An average reduction of ˜40% about the RMS values was achieved in both PCA and ICA filtering. However, the common mode components obtained from the two approaches have different spatial and temporal features. ICA time series present interesting correlations with modeled atmospheric and non-tidal ocean loading displacements. A white noise (WN) plus power law noise (PL) model was adopted in the GPS velocity estimation using maximum likelihood estimation (MLE) analysis, with ˜55% reduction of the velocity uncertainties after filtering using ICA. Meanwhile, spatiotemporal filtering reduces the amplitude of PL and periodic terms in the GPS time series. Finally, we compare the GPS uplift velocities, after correction for elastic effects, with recent models of glacial isostatic adjustment (GIA). The agreements of the GPS observed velocities and four GIA models are generally improved after the spatiotemporal filtering, with a mean reduction of ˜0.9 mm/yr of the WRMS values, possibly allowing for more confident separation of various GIA model predictions.

Application of GPS attitude determination to gravity gradient stabilized spacecraft

NASA Technical Reports Server (NTRS)

Lightsey, E. G.; Cohen, Clark E.; Parkinson, Bradford W.

1993-01-01

Recent advances in the Global Positioning System (GPS) technology have initiated a new era in aerospace navigation and control. GPS receivers have become increasingly compact and affordable, and new developments have made attitude determination using subcentimeter positioning among two or more antennas feasible for real-time applications. GPS-based attitude control systems will become highly portable packages which provide time, navigation, and attitude information of sufficient accuracy for many aerospace needs. A typical spacecraft application of GPS attitude determination is a gravity gradient stabilized satellite in low Earth orbit that employs a GPS receiver and four body mounted patch antennas. The coupled, linearized equations of motion enable complete position and attitude information to be extracted from only two antennas. A discussion of the various error sources for spaceborne GPS attitude measurement systems is included. Attitude determination of better than 0.3 degrees is possible for 1 meter antenna separation. Suggestions are provided to improve the accuracy of the attitude solution.

Structured functional assessments in general practice increased the use of part-time sick leave: a cluster randomised controlled trial.

PubMed

Osterås, Nina; Gulbrandsen, Pål; Kann, Inger Cathrine; Brage, Søren

2010-03-01

A method for structured functional assessments of persons with long-term sick leave was implemented in a cluster randomised controlled trial in general practice. The aim was to analyse intervention effects on general practitioner (GP) sick-listing practice and patient sick leave. 57 GPs were randomly assigned to an intervention or a control group. The intervention group GPs learned the method at a 1-day workshop including teamwork and role-playing. The control group GPs were requested to assess functional ability as usual during the 8 months intervention period in 2005. Outcome measures included duration of patient sick leave episodes, GP prescription of part-time sick leave, active sick leave, and vocational rehabilitation. This data was extracted from a national register. The GPs in the intervention group prescribed part-time sick leave more often (p < 0.01) and active sick leave less often (p = 0.04) than the control group GPs during the intervention period. There was no intervention effect on duration of patient sick leave episodes or on GP prescription of vocational rehabilitation. Implementing structured functional assessments in general practice made the GPs capable to assess functional ability of persons with long-term sick leave in a standardised and explicit manner. The intervention GPs' sick-listing practice was changed as they prescribed more part-time and less active sick leave compared to the control group GPs. As a result, more intervention GP patients returned to part-time work compared to control GP patients. No intervention effect was seen on duration of patient sick leave episodes or on prescription of vocational rehabilitation.

Comparison of methods to estimate water access: a pilot study of a GPS-based approach in low resource settings.

PubMed

Pearson, Amber L

2016-09-20

Most water access studies involve self-reported measures such as time spent or simple spatial measures such as Euclidean distance from home to source. GPS-based measures of access are often considered actual access and have shown little correlation with self-reported measures. One main obstacle to widespread use of GPS-based measurement of access to water has been technological limitations (e.g., battery life). As such, GPS-based measures have been limited by time and in sample size. The aim of this pilot study was to develop and test a novel GPS unit, (≤4-week battery life, waterproof) to measure access to water. The GPS-based method was pilot-tested to estimate number of trips per day, time spent and distance traveled to source for all water collected over a 3-day period in five households in south-western Uganda. This method was then compared to self-reported measures and commonly used spatial measures of access for the same households. Time spent collecting water was significantly overestimated using a self-reported measure, compared to GPS-based (p < 0.05). In contrast, both the GIS Euclidean distances to nearest and actual primary source significantly underestimated distances traveled, compared to the GPS-based measurement of actual travel paths to water source (p < 0.05). Households did not consistently collect water from the source nearest their home. Comparisons between the GPS-based measure and self-reported meters traveled were not made, as respondents did not feel that they could accurately estimate distance. However, there was complete agreement between self-reported primary source and GPS-based. Reliance on cross-sectional self-reported or simple GIS measures leads to misclassification in water access measurement. This new method offers reductions in such errors and may aid in understanding dynamic measures of access to water for health studies.

Modeling Geodetic Processes with Levy α-Stable Distribution and FARIMA

NASA Astrophysics Data System (ADS)

Montillet, Jean-Philippe; Yu, Kegen

2015-04-01

Over the last years the scientific community has been using the auto regressive moving average (ARMA) model in the modeling of the noise in global positioning system (GPS) time series (daily solution). This work starts with the investigation of the limit of the ARMA model which is widely used in signal processing when the measurement noise is white. Since a typical GPS time series consists of geophysical signals (e.g., seasonal signal) and stochastic processes (e.g., coloured and white noise), the ARMA model may be inappropriate. Therefore, the application of the fractional auto-regressive integrated moving average (FARIMA) model is investigated. The simulation results using simulated time series as well as real GPS time series from a few selected stations around Australia show that the FARIMA model fits the time series better than other models when the coloured noise is larger than the white noise. The second fold of this work focuses on fitting the GPS time series with the family of Levy α-stable distributions. Using this distribution, a hypothesis test is developed to eliminate effectively coarse outliers from GPS time series, achieving better performance than using the rule of thumb of n standard deviations (with n chosen empirically).

Possible Time Dependent Deformation over Socorro Magma Body from GPS and InSAR

NASA Astrophysics Data System (ADS)

Havazli, E.; Wdowinski, S.; Amelug, F.

2015-12-01

The Socorro Magma Body (SMB) is one of the largest, currently active magma intrusions in the Earth's continental crust. The area of Socorro is a segment of the Rio Grande Rift that display a broad seismic anomaly and ground deformation. The seismic reflector is imaged at 19 km depth coinciding with the occurrence of numerous small earthquake swarms. Broad crustal uplift was also observed above this reflector and led to the hypothesis of the presence of a large mid-crustal sill-like magma body. Previous geodetic studies over the area reveal ground deformation at the rate of 2-3 mm/yr from 1992 to 2006. The magma body was modeled as a penny-shaped crack of 21 km radius at 19 km depth based on InSAR results [Finnegan et. al., 2009]. In this study we expand the uplift measurement period over the SMB to two decades by using additional InSAR and GPS observations. We extended the InSAR observation record by analyzing 27 Envisat scenes acquired during the years 2006-2010. Continuous GPS observation acquired by the SC01 station since 2001 and three more recent Plate Boundary Observatory stations, which were installed between 2005 and 2011, provide high temporal record of uplift over the past decade and a half. We analyzed the InSAR data using ROI_PAC software package and calculated the temporal evolution of the vertical displacement using time series analysis. Preliminary results of 2006-2010 Envisat data show no significant deformation above the 1-2 mm noise level, which disagree with the previous ERS-1/2 results; 2-3 mm/yr during 1992-2006. This disagreement suggests a time dependent uplift of the SMB, which is also supported by GPS observations. The average uplift rate of the SC01 station is 0.9±0.02 mm/yr for 2001-2015 and 0.6±0.08 mm/yr for 2006-2010. Furthermore the SC01 time series exhibits episodic uplift events. The observed time dependent uplift suggests that magma supply in the middle crust may also occur episodically, as in shallow magmatic systems.

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.

Slow slip events in Guerrero, Mexico, and consequences on strain accumulation over the past 15 years.

NASA Astrophysics Data System (ADS)

Radiguet, M.; Cotton, F.; Cavalié, O.; Pathier, E.; Kostoglodov, V.; Vergnolle, M.; Campillo, M.; Walpersdorf, A.; Cotte, N.; Santiago, J.; Franco, S.

2012-12-01

Continuous Global Positioning System (cGPS) time series in Guerrero, Mexico, reveal the widespread existence of large Slow Slip Events (SSEs) at the boundary between the Cocos and North American plates. The existence of these SSEs asks the question of how seismic and aseismic slips complement each other in subduction zones. We examined the last three SSEs that occurred in 2001/2002, 2006 and 2009/2010, and their impact on the strain accumulation along the Guerrero subduction margin. We use continuous cGPS time series and InSAR images to evaluate the surface displacement during SSEs and inter-SSE periods. The slip distributions on the plate interface associated with each SSE, as well as the inter-SSE (short-term) coupling rates are evaluated by inverting these surface displacements. Our results reveal that the three analyzed SSEs have equivalent moment magnitudes of around 7.5 and their lateral extension is variable.The slip distributions for the three SSEs show that in the Guerrero gap area, the slow slip occurs at shallower depth (updip limit around 15-20 km) than in surrounding regions. The InSAR data provide additional information for the 2006 SSE. The joint inversion of InSAR and cGPS data confirms the lateral variation of the slip distribution along the trench, with shallower slip in the Guerrero seismic gap, west of Acapulco, and deeper slip further east. Inversion of inter-SSE displacement rates reveal that during the inter-SSE time intervals, the interplate coupling is high in the area where the slow slip subsequently occurs. Over a 12 year period, corresponding to three cycles of SSEs, our results reveal that the accumulated slip deficit in the Guerrero gap area is only ¼ of the slip deficit accumulated on both sides of the gap. Moreover, the regions of large slip deficit coincide with the rupture areas of recent large earthquakes. We conclude that the SSEs account for a major portion of the overall moment release budget in the Guerrero gap. If large subduction thrust earthquakes occur in the Guerrero gap, their recurrence time is probably increased compared to adjacent regions.

Precise Point Positioning Based on BDS and GPS Observations

NASA Astrophysics Data System (ADS)

Gao, ZhouZheng; Zhang, Hongping; Shen, Wenbin

2014-05-01

BeiDou Navigation Satellite System (BDS) has obtained the ability applying initial navigation and precise point services for the Asian-Pacific regions at the end of 2012 with the constellation of 5 Geostationary Earth Orbit (GEO), 5 Inclined Geosynchronous Orbit (IGSO) and 4 Medium Earth Orbit (MEO). Till 2020, it will consist with 5 GEO, 3 IGSO and 27 MEO, and apply global navigation service similar to GPS and GLONASS. As we known, GPS precise point positioning (PPP) is a powerful tool for crustal deformation monitoring, GPS meteorology, orbit determination of low earth orbit satellites, high accuracy kinematic positioning et al. However, it accuracy and convergence time are influenced by the quality of pseudo-range observations and the observing geometry between user and Global navigation satellites system (GNSS) satellites. Usually, it takes more than 30 minutes even hours to obtain centimeter level position accuracy for PPP while using GPS dual-frequency observations only. In recent years, many researches have been done to solve this problem. One of the approaches is smooth pseudo-range by carrier-phase observations to improve pseudo-range accuracy. By which can improve PPP initial position accuracy and shorten PPP convergence time. Another sachems is to change position dilution of precision (PDOP) with multi-GNSS observations. Now, BDS has the ability to service whole Asian-Pacific regions, which make it possible to use GPS and BDS for precise positioning. In addition, according to researches on GNSS PDOP distribution, BDS can improve PDOP obviously. Therefore, it necessary to do some researches on PPP performance using both GPS observations and BDS observations, especially in Asian-Pacific regions currently. In this paper, we focus on the influences of BDS to GPS PPP mainly in three terms including BDS PPP accuracy, PDOP improvement and convergence time of PPP based on GPS and BDS observations. Here, the GPS and BDS two-constellation data are collected from BeiDou experimental tracking stations (BETS) built by Wuhan University. And BDS precise orbit and precise clock products are applied by GNSS center, Wuhan University. After an introduction about GPS+BDS PPP mathematical and the error correction modes, we analyze the influence of BDS to GPS PPP carefully with calculating results. The statistics results show that BDS PPP can reach centimeter level and BDS can improve PDOP obviously. Moreover, the convergence time and position stability of GPS+BDS PPP is better than that of GPS PPP.

GPS common-view time transfer

NASA Technical Reports Server (NTRS)

Lewandowski, W.

1994-01-01

The introduction of the GPS common-view method at the beginning of the 1980's led to an immediate and dramatic improvement of international time comparisons. Since then, further progress brought the precision and accuracy of GPS common-view intercontinental time transfer from tens of nanoseconds to a few nanoseconds, even with SA activated. This achievement was made possible by the use of the following: ultra-precise ground antenna coordinates, post-processed precise ephemerides, double-frequency measurements of ionosphere, and appropriate international coordination and standardization. This paper reviews developments and applications of the GPS common-view method during the last decade and comments on possible future improvements whose objective is to attain sub-nanosecond uncertainty.

Global Positioning System Time Transfer Receiver (GPS/TTR) prototype design and initial test evaluation

NASA Technical Reports Server (NTRS)

Oaks, J.; Frank, A.; Falvey, S.; Lister, M.; Buisson, J.; Wardrip, C.; Warren, H.

1982-01-01

Time transfer equipment and techniques used with the Navigation Technology Satellites were modified and extended for use with the Global Positioning System (GPS) satellites. A prototype receiver was built and field tested. The receiver uses the GPS L1 link at 1575 MHz with C/A code only to resolve a measured range to the satellite. A theoretical range is computed from the satellite ephemeris transmitted in the data message and the user's coordinates. Results of user offset from GPS time are obtained by differencing the measured and theoretical ranges and applying calibration corrections. Results of the first field test evaluation of the receiver are presented.

New Zealand rural primary health care workforce in 2005: more than just a doctor shortage.

PubMed

Goodyear-Smith, Felicity; Janes, Ron

2008-02-01

To obtain a 2005 snapshot of New Zealand (NZ) rural primary health care workforce, specifically GPs, general practice nurses and community pharmacists. Postal questionnaires, November 2005. NZ-wide rural general practices and community pharmacies. Rural general practice managers, GPs, nurses, community pharmacy managers and pharmacists. Self-reported data: demographics, country of training, years in practice, business ownership, hours worked including on-call, intention to leave rural practice. General practices: response rate 95% (206/217); 70% GP-owned, practice size ranged from one GP/one nurse to 12 GPs/nine nurses. PHARMACIES: Response rate 90% (147/163). Majority had one (33%) or two (32%) pharmacists; <10% had more than three pharmacists. GPs: response rate 64% (358/559), 71% male, 73% aged >40, 61% full-time, 79% provide on-call, 57% overseas-trained, 78% male and 57% female GPs aged >40; more full-time male GPs (76%) than female (37%) . Nurses: response rate 65% (445/685), 97% female, 72% aged >40, 31% full-time, 28% provide on-call, 84% NZ-trained, 45% consulted independently in 'nurse-clinics' within practice setting. Pharmacists: response rate 96% (248/258), 52% male, 66% aged >40, 71% full-time, 33% provide on-call, 92% NZ-trained, 55% sole/partner pharmacy owners. Many intend to leave NZ rural practice within 5 years: GPs (34%), nurses (25%) and pharmacists (47%). This is the first NZ-wide rural workforce survey to include a range of rural primary health care providers (GPs, nurses and pharmacists). Ageing rural primary health care workforce and intentions to leave herald worsening workforce shortages.

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

Integrating GPS, GYRO, vehicle speed sensor, and digital map to provide accurate and real-time position in an intelligent navigation system

NASA Astrophysics Data System (ADS)

Li, Qingquan; Fang, Zhixiang; Li, Hanwu; Xiao, Hui

2005-10-01

The global positioning system (GPS) has become the most extensively used positioning and navigation tool in the world. Applications of GPS abound in surveying, mapping, transportation, agriculture, military planning, GIS, and the geosciences. However, the positional and elevation accuracy of any given GPS location is prone to error, due to a number of factors. The applications of Global Positioning System (GPS) positioning is more and more popular, especially the intelligent navigation system which relies on GPS and Dead Reckoning technology is developing quickly for future huge market in China. In this paper a practical combined positioning model of GPS/DR/MM is put forward, which integrates GPS, Gyro, Vehicle Speed Sensor (VSS) and digital navigation maps to provide accurate and real-time position for intelligent navigation system. This model is designed for automotive navigation system making use of Kalman filter to improve position and map matching veracity by means of filtering raw GPS and DR signals, and then map-matching technology is used to provide map coordinates for map displaying. In practical examples, for illustrating the validity of the model, several experiments and their results of integrated GPS/DR positioning in intelligent navigation system will be shown for the conclusion that Kalman Filter based GPS/DR integrating position approach is necessary, feasible and efficient for intelligent navigation application. Certainly, this combined positioning model, similar to other model, can not resolve all situation issues. Finally, some suggestions are given for further improving integrated GPS/DR/MM application.

Practice variation in surgical procedures and IUD-insertions among general practitioners in Norway - a longitudinal study.

PubMed

Pahle, Andreas Saxlund; Sørli, Daniel; Kristiansen, Ivar Sønbø; Deraas, Trygve S; Halvorsen, Peder A

2017-01-21

Studies of Primary Health Care (PHC) reveal considerable practice variations in terms of the range of services provided. In Norway, general practitioners (GPs) are traditionally expected to perform IUD-insertions and several surgical procedures as a part of comprehensive PHC. We aimed to investigate variation in the provision of surgical procedures and IUD-insertions across GPs and over time and explore determinants of such variation. Retrospective registry study of Norwegian GPs. From a comprehensive database of GPs' reimbursement claims, we obtained procedure codes and GP characteristics such as age, gender, list size and municipality characteristics from 2006 through 2013. Multivariable logistic regression models were fitted to explore determinants of practice variation. We extracted data from 4,828 GPs. In 2013, 91.0, 76.1 and 74.8% were reimbursed at least once for minor and major surgical procedures and IUD-insertion, respectively. Female GPs had lower odds for performing major surgical procedures (OR 0.38, 95% CI 0.32-0.45) and higher odds for performing IUD-insertions (OR 6.28, 95% CI 4.47-8.82) than male GPs. Older GPs and GPs with shorter patient lists were less likely to perform surgical procedures. GPs with longer patient lists had higher odds for performing IUD-insertions. The proportion of GPs performing surgical procedures increased over time, while the proportion decreased for IUD-insertions. The number of IUD-insertions in specialist care increased from 12,575 in 2011 to 15 216 (+21.0%) in 2014. We observed a large variation in the provision of surgical procedures and IUD-insertions amongst GPs in Norway. The GPs' age, gender, list size and size of municipality were associated with performing the procedures. Our findings suggest a shift of IUD-insertions from primary to specialist care.

Comparison of GPS/SAC-C and MIPAS/ENVISAT temperature profiles and its implementation for EOS AURA-MLS observations

NASA Technical Reports Server (NTRS)

Jiang, Jonathan H.; Wang, Ding-Yi; Romans, Larry J.; Ao, Chi O.; Schwartz, Michael J.; Stiller, Gabriele P.; von Clarmann, Thomas; Lopez-Puertas, Manuel; Funke, Bernd; Gil-Lopez, Sergio;

Power and powerlessness: GPs' narratives about lifestyle counselling

PubMed Central

Abildsnes, Eirik; Walseth, Liv Tveit; Flottorp, Signe A; Stensland, Per S

2012-01-01

Background Power in doctor–patient relationships is asymmetrically distributed. The doctor holds resources the patient needs and has a mandate to promote healthy living. Power may benefit or harm the patients' health, and the doctor–patient relationship. Aim To identify aspects of power and powerlessness in GPs' narratives about lifestyle counselling. Design and setting A qualitative study using focus groups from peer-group meetings of Norwegian GPs attending continuing medical education. Method GPs discussed case stories about lifestyle counselling in focus groups. The discussions were transcribed and the text analysed using systematic text condensation. Results Aspects of power concerning the framework of the consultation and the GPs' professional role were found. Also identified were: power expressed by opportunistic approaches to change patients' lifestyle; rhetoric communication; paternalism; and disclosure. GPs reported powerlessness in complex communication, when there were difficulties reaching goals, and when patients resisted or ignored their proposals. Conclusion Case-study discussions in peer groups disclose several aspects of power and powerlessness that occur in consultations. Consciousness about aspects of power may facilitate counselling that benefits the patient and the doctor–patient relationship. PMID:22429431

General practitioners knowledge about use of topical corticosteroids in paediatric atopic dermatitis in Australia.

PubMed

Smith, Saxon D; Harris, Victoria; Lee, Andrew; Blaszczynski, Alex; Fischer, Gayle

2017-01-01

Topical corticosteroids are the standard of care in paediatric atopic dermatitis (pAD). However, messages that overstress possible side effects can have a negative impact on perceptions of safety and contribute to treatment non-adherence. The aim of this study was to assess general practitioners' (GPs') perception of the safety of topical corticosteroids in pAD treatment. Australian GPs participating in continuing professional development programs were assessed before an education session on pAD. Responses were recorded via an electronic survey. A total of 257 GPs were surveyed. More than one-third (40.7%) of the GPs instructed parents to apply topical corticosteroids for two weeks or less. Nearly half (47.7%) instructed parents to apply topical corticosteroids sparingly or with the smallest amount possible. Furthermore, nearly one-third (30.2%) reported skin atrophy as the most common side effect of topical corticosteroids. Advice to patients given by Australian GPs may carry unintentional risk messages contributing to treatment non‑adherence. Evidence-based information on the safety of topical corticosteroids is needed to empower GPs to improve treatment outcomes in pAD.

Volcano monitoring using GPS: Developing data analysis strategies based on the June 2007 Kīlauea Volcano intrusion and eruption

USGS Publications Warehouse

Larson, Kristine M.; Poland, Michael; Miklius, Asta

2010-01-01

The global positioning system (GPS) is one of the most common techniques, and the current state of the art, used to monitor volcano deformation. In addition to slow (several centimeters per year) displacement rates, GPS can be used to study eruptions and intrusions that result in much larger (tens of centimeters over hours-days) displacements. It is challenging to resolve precise positions using GPS at subdaily time intervals because of error sources such as multipath and atmospheric refraction. In this paper, the impact of errors due to multipath and atmospheric refraction at subdaily periods is examined using data from the GPS network on Kīlauea Volcano, Hawai'i. Methods for filtering position estimates to enhance precision are both simulated and tested on data collected during the June 2007 intrusion and eruption. Comparisons with tiltmeter records show that GPS instruments can precisely recover the timing of the activity.

A Mobile GPS Application: Mosque Tracking with Prayer Time Synchronization

NASA Astrophysics Data System (ADS)

Hashim, Rathiah; Ikhmatiar, Mohammad Sibghotulloh; Surip, Miswan; Karmin, Masiri; Herawan, Tutut

Global Positioning System (GPS) is a popular technology applied in many areas and embedded in many devices, facilitating end-users to navigate effectively to user's intended destination via the best calculated route. The ability of GPS to track precisely according to coordinates of specific locations can be utilized to assist a Muslim traveler visiting or passing an unfamiliar place to find the nearest mosque in order to perform his prayer. However, not many techniques have been proposed for Mosque tracking. This paper presents the development of GPS technology in tracking the nearest mosque using mobile application software embedded with the prayer time's synchronization system on a mobile application. The prototype GPS system developed has been successfully incorporated with a map and several mosque locations.

Characterization of a Strain Rate Transient Along the San Andreas and San Jacinto Faults Following the October 1999 Hector Mine Earthquake.

NASA Astrophysics Data System (ADS)

Hernandez, D.; Holt, W. E.; Bennett, R. A.; Dimitrova, L.; Haines, A. J.

2006-12-01

We are continuing work on developing and refining a tool for recognizing strain rate transients as well as for quantifying the magnitude and style of their temporal and spatial variations. We determined time-averaged velocity values in 0.05 year epochs using time-varying velocity estimates for continuous GPS station data from the Southern California Integrated GPS Network (SCIGN) for the time period between October 1999 and February 2004 [Li et al., 2005]. A self-consistent model velocity gradient tensor field solution is determined for each epoch by fitting bi-cubic Bessel interpolation to the GPS velocity vectors and we determine model dilatation strain rates, shear strain rates, and the rotation rates. Departures of the time dependent model strain rate and velocity fields from a master solution, obtained from a time-averaged solution for the period 1999-2004, with imposed plate motion constraints and Quaternary fault data, are evaluated in order to best characterize the time dependent strain rate field. A particular problem in determining the transient strain rate fields is the level of smoothing or damping that is applied. Our current approach is to choose a damping that both maximizes the departure of the transient strain rate field from the long-term master solution and achieves a reduced chi-squared value between model and observed GPS velocities of around 1.0 for all time epochs. We observe several noteworthy time-dependent changes. First, in the Eastern California Shear Zone (ECSZ) region, immediately following the October 1999 Hector Mine earthquake, there occurs a significant spatial increase of relatively high shear strain rate, which encompasses a significant portion of the ECSZ. Second, also following the Hector Mine event, there is a strain rate corridor that extends through the Pinto Mt. fault connecting the ECSZ to the San Andreas fault segment in the Salton Trough region. As this signal slowly decays, shear strain rates on segments of the San Andreas fault, just east of Palm Springs, and the San Jacinto fault increase during 2001-2004. During this period shear strain rates increase by roughly 20 nanostrain per year on the San Andreas fault and 20-30 nanostrain per year on the San Jacinto fault (over a zone approximately 20 km wide). Lastly, a further investigation into this strain rate recovery reveals a power law flow mechanism during the first six months after the earthquake for the Anza segment, after which strain rates appear to reach a steady state for the remainder of the data. Moreover, seismicity rates increase along these segments following the period of shear strain rate increase. These results quantify the spatial coverage of the strain rate changes and provide some bounds on their magnitude and confidence, as well as constraints on the associated regional rheology and interseismic cycle strain rate pattern. The compiled epoch solution "movies" may be viewed at the additional resources site.

Use of global positioning system measurements to determine geocentric coordinates and variations in Earth orientation

NASA Technical Reports Server (NTRS)

Malla, R. P.; Wu, S.-C.; Lichten, S. M.

1993-01-01

Geocentric tracking station coordinates and short-period Earth-orientation variations can be measured with Global Positioning System (GPS) measurements. Unless calibrated, geocentric coordinate errors and changes in Earth orientation can lead to significant deep-space tracking errors. Ground-based GPS estimates of daily and subdaily changes in Earth orientation presently show centimeter-level precision. Comparison between GPS-estimated Earth-rotation variations, which are the differences between Universal Time 1 and Universal Coordinated Time (UT1-UTC), and those calculated from ocean tide models suggests that observed subdaily variations in Earth rotation are dominated by oceanic tidal effects. Preliminary GPS estimates for the geocenter location (from a 3-week experiment) agree with independent satellite laser-ranging estimates to better than 10 cm. Covariance analysis predicts that temporal resolution of GPS estimates for Earth orientation and geocenter improves significantly when data collected from low Earth-orbiting satellites as well as from ground sites are combined. The low Earth GPS tracking data enhance the accuracy and resolution for measuring high-frequency global geodynamical signals over time scales of less than 1 day.

Wildlife tracking data management: a new vision.

PubMed

Urbano, Ferdinando; Cagnacci, Francesca; Calenge, Clément; Dettki, Holger; Cameron, Alison; Neteler, Markus

2010-07-27

To date, the processing of wildlife location data has relied on a diversity of software and file formats. Data management and the following spatial and statistical analyses were undertaken in multiple steps, involving many time-consuming importing/exporting phases. Recent technological advancements in tracking systems have made large, continuous, high-frequency datasets of wildlife behavioural data available, such as those derived from the global positioning system (GPS) and other animal-attached sensor devices. These data can be further complemented by a wide range of other information about the animals' environment. Management of these large and diverse datasets for modelling animal behaviour and ecology can prove challenging, slowing down analysis and increasing the probability of mistakes in data handling. We address these issues by critically evaluating the requirements for good management of GPS data for wildlife biology. We highlight that dedicated data management tools and expertise are needed. We explore current research in wildlife data management. We suggest a general direction of development, based on a modular software architecture with a spatial database at its core, where interoperability, data model design and integration with remote-sensing data sources play an important role in successful GPS data handling.

Wildlife tracking data management: a new vision

PubMed Central

Urbano, Ferdinando; Cagnacci, Francesca; Calenge, Clément; Dettki, Holger; Cameron, Alison; Neteler, Markus

2010-01-01

To date, the processing of wildlife location data has relied on a diversity of software and file formats. Data management and the following spatial and statistical analyses were undertaken in multiple steps, involving many time-consuming importing/exporting phases. Recent technological advancements in tracking systems have made large, continuous, high-frequency datasets of wildlife behavioural data available, such as those derived from the global positioning system (GPS) and other animal-attached sensor devices. These data can be further complemented by a wide range of other information about the animals' environment. Management of these large and diverse datasets for modelling animal behaviour and ecology can prove challenging, slowing down analysis and increasing the probability of mistakes in data handling. We address these issues by critically evaluating the requirements for good management of GPS data for wildlife biology. We highlight that dedicated data management tools and expertise are needed. We explore current research in wildlife data management. We suggest a general direction of development, based on a modular software architecture with a spatial database at its core, where interoperability, data model design and integration with remote-sensing data sources play an important role in successful GPS data handling. PMID:20566495

Precise GPS ephemerides from DMA and NGS tested by time transfer

NASA Technical Reports Server (NTRS)

Lewandowski, Wlodzimierz W.; Petit, Gerard; Thomas, Claudine

1992-01-01

It was shown that the use of the Defense Mapping Agency's (DMA) precise ephemerides brings a significant improvement to the accuracy of GPS time transfer. At present a new set of precise ephemerides produced by the National Geodetic Survey (NGS) has been made available to the timing community. This study demonstrates that both types of precise ephemerides improve long-distance GPS time transfer and remove the effects of Selective Availability (SA) degradation of broadcast ephemerides. The issue of overcoming SA is also discussed in terms of the routine availability of precise ephemerides.

Relative Navigation of Formation-Flying Satellites

NASA Technical Reports Server (NTRS)

Long, Anne; Kelbel, David; Lee, Taesul; Leung, Dominic; Carpenter, J. Russell; Grambling, Cheryl

2002-01-01

This paper compares autonomous relative navigation performance for formations in eccentric, medium and high-altitude Earth orbits using Global Positioning System (GPS) Standard Positioning Service (SPS), crosslink, and celestial object measurements. For close formations, the relative navigation accuracy is highly dependent on the magnitude of the uncorrelated measurement errors. A relative navigation position accuracy of better than 10 centimeters root-mean-square (RMS) can be achieved for medium-altitude formations that can continuously track at least one GPS signal. A relative navigation position accuracy of better than 15 meters RMS can be achieved for high-altitude formations that have sparse tracking of the GPS signals. The addition of crosslink measurements can significantly improve relative navigation accuracy for formations that use sparse GPS tracking or celestial object measurements for absolute navigation.

Demonstration of an Enhanced Vertical Magnetic Gradient System for UXO

DTIC Science & Technology

2008-04-01

flights were conducted and results evaluated. The cesium magnetometers , GPS systems (positioning and attitude), fluxgate magnetometers , data...makes a measurement and when it is time-stamped and recorded. This applies to the magnetometers , fluxgate and the GPS. Accurate positioning...requires a correction for this lag. Time lags between the magnetometers , fluxgate and GPS signals were measured by a proprietary utility. This utility

GPS Timing Performance

DTIC Science & Technology

2014-01-01

termed the Galileo -GPS Time Offset (GGTO), and it will be Type 35 in the GPS CNAV message. Knowledge of the GGTO makes it possible for a properly...U.S. Naval Observatory (USNO) [1]. Interoperability with Galileo , and perhaps someday with other Global Navigation Satellite Systems (GNSS), is to...Interoperability with Galileo , and perhaps someday with other Global Navigation Satellite Systems (GNSS), is to be established through transmission of the

Interseismic Coupling on the Quito Fault System in Ecuador Using New GPS and InSAR Data and Its Implication on Seismic Hazard Assessment.

NASA Astrophysics Data System (ADS)

Mariniere, J.; Champenois, J.; Nocquet, J. M.; Beauval, C. M.; Audin, L.; Baize, S.; Alvarado, A. P.; Yepes, H. A.; Jomard, H.

2017-12-01

Quito, the capital of Ecuador hosting two million inhabitants lies on an active reverse fault system within the Andes. Regular moderate size earthquakes (M 5) occur on these faults, widely felt within the city and its surrounding. Despite a relatively small magnitude of Mw 5.1, the 2014 August 12 earthquake triggered landslides that killed 4 people, cut off one of the main highways for several weeks and caused the temporary shutdown of the airport. Quantifying the seismic potential of the Quito fault system is therefore crucial for a better preparation and mitigation to seismic risk. Previous work using a limited GPS data set found that the Quito fault accommodates 4 mm/yr of EW shortening (Alvarado et al., 2014) at shallow locking depths (3-7 km). We combine GPS and new InSAR data to extend the previous analysis and better quantify the spatial distribution of locking of the Quito fault. GPS dataset includes new continuous sites operating since 2013. 18 ERS SAR scenes, spanning the 1993-2000 time period and covering an area of 85 km by 30 km, were processed using a Permanent Scatter strategy. We perform a joint inversion of both data set (GPS and InSAR) to infer a new and better-constrained kinematic model of the fault to determine both the slip rate and the locking distribution at depth. We find a highly variable level of locking which changes along strike. At some segments, sharp displacement gradients observed both for GPS and InSAR suggest that the fault is creeping up to the surface, while shallow locking is found for other segments. Previous Probabilistic Seismic Hazard Assessment studies have shown that the Quito fault fully controls the hazard in Quito city (Beauval et al. 2014). The results will be used to improve the forecast of earthquakes on the Quito fault system for PSHA studies.

Travel patterns during pregnancy: comparison between Global Positioning System (GPS) tracking and questionnaire data

PubMed Central

2013-01-01

Background Maternal exposures to traffic-related air pollution have been associated with adverse pregnancy outcomes. Exposures to traffic-related air pollutants are strongly influenced by time spent near traffic. However, little is known about women’s travel activities during pregnancy and whether questionnaire-based data can provide reliable information on travel patterns during pregnancy. Objectives Examine women’s in-vehicle travel behavior during pregnancy and examine the difference in travel data collected by questionnaire and global positioning system (GPS) and their potential for exposure error. Methods We measured work-related travel patterns in 56 pregnant women using a questionnaire and one-week GPS tracking three times during pregnancy (<20 weeks, 20–30 weeks, and >30 weeks of gestation). We compared self-reported activities with GPS-derived trip distance and duration, and examined potentially influential factors that may contribute to differences. We also described in-vehicle travel behavior by pregnancy periods and influences of demographic and personal factors on daily travel times. Finally, we estimated personal exposure to particle-bound polycyclic aromatic hydrocarbon (PB-PAH) and examined the magnitude of exposure misclassification using self-reported vs. GPS travel data. Results Subjects overestimated both trip duration and trip distance compared to the GPS data. We observed moderately high correlations between self-reported and GPS-recorded travel distance (home to work trips: r = 0.88; work to home trips: r = 0.80). Better agreement was observed between the GPS and the self-reported travel time for home to work trips (r = 0.77) than work to home trips (r = 0.64). The subjects on average spent 69 and 93 minutes traveling in vehicles daily based on the GPS and self-reported data, respectively. Longer daily travel time was observed among participants in early pregnancy, and during certain pregnancy periods in women with higher education attainment, higher income, and no children. When comparing self-reported vs. GPS data, we found that estimated personal exposure to PB-PAH did not differ remarkably at the population level, but the difference was large at an individual level. Conclusion Self-reported home-to-work data overestimated both trip duration and trip distance compared to GPS data. Significant differences in PAH exposure estimates were observed at individual level using self-reported vs. GPS data, which has important implications in air pollution epidemiological studies. PMID:24107241

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

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.)

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.

At the dawn of delegation? Experiences and attitudes of general practitioners in Germany - a questionnaire survey.

PubMed

Goetz, Katja; Kornitzky, Anna; Mahnkopf, Janis; Steinhäuser, Jost

2017-12-19

In the future, 'delegation' as task shifting from general practitioners (GPs) to non-physicians will be important in primary care. Therefore, the aim of this study was to evaluate the attitudes towards the concept of task shifting and to identify predictors of a positive attitude towards task shifting from the perspective of GPs. This cross-sectional questionnaire study analysed attitudes towards the concept of task shifting and delegated tasks from the perspective of GPs who were recruited in the German federal state of Schleswig-Holstein. Descriptive statistics and binary regression analyses were computed to identify potential predictors of a positive attitude towards task shifting. Out of 1538 questionnaires distributed, 577 GP questionnaires were returned (response rate: 37.5%). A total of 53.2% of the respondents were male, and 37.3% were female. A positive attitude regarding task shifting was shown by 49% of the participating GPs. The highest level of agreement (95.2%) was found for time savings with task shifting, and a lower agreement (39%) was found regarding the lack of clarity concerning the responsibilities and legal aspects with regards to task shifting. The most frequently delegated tasks were recording electrocardiograms and measuring blood glucose levels. A positive attitude towards task shifting was positively associated with higher job satisfaction and a need for qualified staff. Our sample of GPs for this study was very open-minded towards the concept of task shifting. Germany is just beginning this delegation, but the implementation of task shifting depends on different aspects, such as legal requirements, adequate payment and qualified staff. Finally, there is a need for continuing professional development in primary care teams, especially for non-clinical practice staff.

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).

Support of EarthScope GPS Campaigns at the UNAVCO Facility

NASA Astrophysics Data System (ADS)

Boyce, E.; Blume, F.; Normandeau, J.

2008-12-01

In order to support portable GPS deployments funded by the NSF's EarthScope Science panel, PBO has purchased 100 campaign GPS systems. Based Topcon GB-1000 equipment, the systems have been designed for stand-alone temporary or semi-permanent deployment that will be used for densifying areas not sufficiently covered by continuous GPS, and responding to volcanic and tectonic crises. UNAVCO provides support for all aspects of these projects, including proposal and budget development, project planning, equipment design, field support, and data archiving. Ten of the 100 systems have been equipped with real-time kinematic (RTK) capability requiring additional radio and data logging equipment. RTK systems can be used to rapidly map fault traces and profile fault escarpments and collect precise position information for GIS based geologic mapping. Each portable self-contained campaign systems include 18 Ah batteries, a regulated 32 watt solar charging system, and a low-power dual frequency GPS receiver and antenna in a waterproof case with security enhancements. The receivers have redundant memory sufficient for storing over a year's worth of data as well as IP and serial communications capabilities for longer-term deployments. Monumentation options are determined on a project-by-project basis, with options including Tech2000 masts, low-profile spike mounts, and traditional tripods and optical tribrachs. Drilled-braced monuments or masts can be installed for "semi- permanent" style occupations. The systems have been used to support several projects to date, including the University of Washington's 30-unit deployment to monitor the Episodic Tremor and Slip event in November, 2005 and the ongoing Rio Grande Rift experiment, run by the Universities of Colorado, Utah State, and New Mexico, which has seen the construction of 25 permanent monuments in 2006 and 2007 and a 26-site campaign reoccupation in 2008.

Support of EarthScope GPS Campaigns at the UNAVCO Facility

NASA Astrophysics Data System (ADS)

Boyce, E.; Blume, F.; Normandeau, J.

2007-12-01

In order to support portable GPS deployments funded by the NSF's EarthScope Science panel, PBO has purchased 100 campaign GPS systems. Based Topcon GB-1000 equipment, the systems have been designed for stand-alone temporary or semi-permanent deployment that will be used for densifying areas not sufficiently covered by continuous GPS, and responding to volcanic and tectonic crises. UNAVCO provides support for all aspects of these projects, including proposal and budget development, project planning, equipment design, field support, and data archiving. Ten of the 100 systems will be purchased with real-time kinematic (RTK) capability requiring additional radio and data logging equipment. RTK systems can be used to rapidly map fault traces and profile fault escarpments and collect precise position information for GIS based geologic mapping. Each portable self-contained campaign systems include 18 Ah batteries, a regulated 32 watt solar charging system, and a low-power dual frequency GPS receiver and antenna in a waterproof case with security enhancements. The receivers have redundant memory sufficient for storing over a year's worth of data as well as IP and serial communications capabilities for longer-term deployments. Monumentation options are determined on a project-by-project basis, with options including Tech2000 masts, low-profile spike mounts, and traditional tripods and optical tribrachs. Drilled-braced monuments or masts can be installed for "semi-permanent" style occupations. The systems have been used to support several projects to date, including the University of Washington's 30- unit deployment to monitor the Episodic Tremor and Slip event in November, 2005 and the ongoing Rio Grande Rift experiment, run by the Universities of Colorado, Utah State, and New Mexico, which has seen the construction of 25 permanent monuments in 2006 and 2007.

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.

GPS test range mission planning

NASA Astrophysics Data System (ADS)

Roberts, Iris P.; Hancock, Thomas P.

The principal features of the Test Range User Mission Planner (TRUMP), a PC-resident tool designed to aid in deploying and utilizing GPS-based test range assets, are reviewed. TRUMP features time history plots of time-space-position information (TSPI); performance based on a dynamic GPS/inertial system simulation; time history plots of TSPI data link connectivity; digital terrain elevation data maps with user-defined cultural features; and two-dimensional coverage plots of ground-based test range assets. Some functions to be added during the next development phase are discussed.

Sex of the GP--20 years on.

PubMed

Harrison, Christopher M; Britt, Helena C; Charles, Janice

2011-08-15

Previous research with the Australian Morbidity and Treatment Survey (1990-1991) showed significant differences in general practitioner characteristics and patient mix of male and female GPs. Even after adjusting for these, it was seen that male and female GPs managed different types of medical conditions. The proportion of female GPs increased from 19.6% in 1990-1991 to 37.1% in 2009-2010. This study investigates whether differences remain two decades later. Analysis of 2009-2010 Bettering the Evaluation and Care of Health (BEACH) data examining GP characteristics, patient encounter characteristics, patient reasons for encounter (RFE), problem types managed and management methods used, by GP sex. Whether GP sex was an independent predictor of problem types being managed, or management methods used, was tested using multiple logistic regressions and Poisson regression. 988 GPs recorded 98 800 GP-patient encounters. Adjusted differences in clinical activity of male and female GPs. After adjustment, compared with male GPs, females recorded more RFEs about general and unspecified issues and endocrine, female genital, pregnancy and family planning problems; and fewer concerning the musculoskeletal, respiratory, skin and male genital systems. Female GPs managed more general and unspecified, digestive, circulatory, psychological, endocrine, female genital and social problems; recorded nearly 20% more clinical treatments and referrals; recorded nearly 10% more imaging and pathology tests; and 4.3% fewer medications. After two decades, even with increased numbers of female GPs, the differences in problems managed by male and female GPs remain, and will probably continue. Female GPs use more resources per encounter, but may not use more resources in terms of annual patient care.

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.

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.

Usefulness of commercially available GPS data-loggers for tracking human movement and exposure to dengue virus

PubMed Central

2009-01-01

Background Our understanding of the effects of human movement on dengue virus spread remains limited in part due to the lack of precise tools to monitor the time-dependent location of individuals. We determined the utility of a new, commercially available, GPS data-logger for long-term tracking of human movements in Iquitos, Peru. We conducted a series of evaluations focused on GPS device attributes key to reliable use and accuracy. GPS observations from two participants were later compared with semi-structured interview data to assess the usefulness of GPS technology to track individual mobility patterns. Results Positional point and line accuracy were 4.4 and 10.3 m, respectively. GPS wearing mode increased spatial point error by 6.9 m. Units were worn on a neck-strap by a carpenter and a moto-taxi driver for 14-16 days. The application of a clustering algorithm (I-cluster) to the raw GPS positional data allowed the identification of locations visited by each participant together with the frequency and duration of each visit. The carpenter moved less and spent more time in more fixed locations than the moto-taxi driver, who visited more locations for a shorter period of time. GPS and participants' interviews concordantly identified 6 common locations, whereas GPS alone identified 4 locations and participants alone identified 10 locations. Most (80%) of the locations identified by participants alone were places reported as visited for less than 30 minutes. Conclusion The present study demonstrates the feasibility of a novel, commercially available GPS data-logger for long-term tracking of humans and shows the potential of these units to quantify mobility patterns in relationship with dengue virus transmission risk in a tropical urban environment. Cost, battery life, size, programmability and ease of wear are unprecedented from previously tested units, proving the usefulness of GPS-dataloggers for linking movement of individuals and transmission risk of dengue virus and other infectious agents, particularly in resource-poor settings. PMID:19948034

Usefulness of commercially available GPS data-loggers for tracking human movement and exposure to dengue virus.

PubMed

Vazquez-Prokopec, Gonzalo M; Stoddard, Steven T; Paz-Soldan, Valerie; Morrison, Amy C; Elder, John P; Kochel, Tadeusz J; Scott, Thomas W; Kitron, Uriel

2009-11-30

Our understanding of the effects of human movement on dengue virus spread remains limited in part due to the lack of precise tools to monitor the time-dependent location of individuals. We determined the utility of a new, commercially available, GPS data-logger for long-term tracking of human movements in Iquitos, Peru. We conducted a series of evaluations focused on GPS device attributes key to reliable use and accuracy. GPS observations from two participants were later compared with semi-structured interview data to assess the usefulness of GPS technology to track individual mobility patterns. Positional point and line accuracy were 4.4 and 10.3 m, respectively. GPS wearing mode increased spatial point error by 6.9 m. Units were worn on a neck-strap by a carpenter and a moto-taxi driver for 14-16 days. The application of a clustering algorithm (I-cluster) to the raw GPS positional data allowed the identification of locations visited by each participant together with the frequency and duration of each visit. The carpenter moved less and spent more time in more fixed locations than the moto-taxi driver, who visited more locations for a shorter period of time. GPS and participants' interviews concordantly identified 6 common locations, whereas GPS alone identified 4 locations and participants alone identified 10 locations. Most (80%) of the locations identified by participants alone were places reported as visited for less than 30 minutes. The present study demonstrates the feasibility of a novel, commercially available GPS data-logger for long-term tracking of humans and shows the potential of these units to quantify mobility patterns in relationship with dengue virus transmission risk in a tropical urban environment. Cost, battery life, size, programmability and ease of wear are unprecedented from previously tested units, proving the usefulness of GPS-dataloggers for linking movement of individuals and transmission risk of dengue virus and other infectious agents, particularly in resource-poor settings.

Home visits - central to primary care, tradition or an obligation? A qualitative study

PubMed Central

2011-01-01

Background Home visits are claimed to be a central element of primary care. However, the frequency with which home visits are made is declining both internationally and in Germany despite the increase in the number of chronically ill elderly patients. Given this, the question arises as to how to ensure sufficient primary health care for this vulnerable patient group. The aim of this study was to explore German general practitioners' (GPs) attitudes with regard to the feasibility, burden and outlook of continued home visits in German primary care. Methods Qualitative semi-structured interviews were carried out with 24 GPs from the city of Hannover, Germany, and its rural surroundings. Data was analysed using qualitative content analysis. Results The GPs indicated that they frequently conduct home visits, but not all of them were convinced of their benefit. Most were not really motivated to undertake home visits but some felt obliged to. The basic conditions covering home visits were described as unsatisfactory, in particular with respect to reimbursement and time constraints. House calls for vulnerable, elderly people remained undisputed, whereas visits of a social nature were mostly deleted. Urgent house calls were increasingly delegated to the emergency services. Visits to nursing homes were portrayed as being emotionally distressing. GPs considered good cooperation with nursing staff the key factor to ensure a successful nursing home visit. The GPs wanted to ease their work load while still ensuring quality home care but were unable to suggest how this might be achieved. Better financial compensation was proposed most often. The involvement of specially trained nurses was considered possible, but viewed with resentment. Conclusions Home visits are still an integral aspect of primary care in Germany and impose a considerable workload on many practices. Though the existing situation was generally perceived as unsatisfactory, German GPs could not envisage alternatives if asked to consider whether the current arrangements were sustainable in the future. To guarantee an unaltered quality of primary home care, German GPs and health care policy makers should actively initiate a debate on the need for and nature of home visits in the future. PMID:21513534

Characteristics of offshore extreme wind-waves detected by surface drifters with a low-cost GPS wave sensor

NASA Astrophysics Data System (ADS)

Komatsu, Kosei

Wind-generated waves have been recognized as one of the most important factors of the sea surface roughness which plays crucial roles in various air-sea interactions such as energy, mo-mentum, heat and gas exchanges. At the same time, wind waves with extreme wave heights representatively called as freak or rogue waves have been a matter of great concern for many people involved in shipping, fishing, constracting, surfing and other marine activities, because such extreme waves frequently affect on the marine activities and sometimes cause serious dis-asters. Nevertheless, investigations of actual conditions for the evolution of wind waves in the offshore region are less and sparse in contrast to dense monitoring networks in the coastal re-gions because of difficulty of offshore observation with high accuracy. Recently accurate in situ observation of offshore wind waves is getting possible at low cost owing to a wave height and di-rection sensor developed by Harigae et al. (2004) by installing a point-positioning GPS receiver on a surface drifting buoy. The point-positioning GPS sensor can extract three dimensional movements of the buoy excited by ocean waves with minimizing effects of GPS point-positioning errors through the use of a high-pass filter. Two drifting buoys equipped with the GPS-based wave sensor charged by solar cells were drifted in the western North Pacific and one of them continued to observe wind waves during 16 months from Sep. 2007. The RMSE of the GPS-based wave sensor was less than 10cm in significant wave height and about 1s in significant wave period in comparison with other sensors, i.e. accelerometers installed on drifting buoys of Japan Meteorological Agency, ultrasonic sensors placed at the Hiratsuka observation station of the University of Tokyo and altimeter of the JASON-1. The GPS-based wave buoys enabled us to detect freak waves defined as waves whose height is more than twice the significant wave height. The observation conducted by the wave buoys in 2007-2008 indicated a little more frequent occurrence of freak waves comparing with Forristall's (1978) empirical formula and Naess's (1985) distribution for a narrow-band Gaussian sea.

Orbiter global positioning system design and Ku-band problem investigations, exhibit B, revision 1

NASA Technical Reports Server (NTRS)

Lindsey, W. C.

1983-01-01

The hardware, software, and interface between them was investigated for a low dynamics, nonhostile environment, low cost GPS receiver (GPS Z set). The set is basically a three dimensional geodetic and way point navigator with GPS time, ground speed, and ground track as possible outputs in addition to the usual GPS receiver set outputs. Each functional module comprising the GPS set is described, enumerating its functional inputs and outputs, leading to the interface between hardware and software of the set.

SEXTANT - Station Explorer for X-Ray Timing and Navigation Technology

NASA Technical Reports Server (NTRS)

Mitchell, Jason; Hasouneh, Monther; Winternitz, Luke; Valdez, Jennifer; Price, Sam; Semper, Sean; Yu, Wayne; Gaebler, John; Ray, Paul; Wood, Kent;

Are "part-time" general practitioners workforce idlers or committed professionals?

PubMed

Dwan, Kathryn M; Douglas, Kirsty A; Forrest, Laura E

2014-09-19

The traditional view of general practice holds that only general practitioners (GPs) in full-time clinical practice can provide quality patient care. Nevertheless, increasing numbers of GPs are choosing to work sessionally, that is, ostensibly "part-time". There are concerns about the health workforce's ability to meet demand and also fears that patient care may be compromised. We sought answers to a) what activities do GPs undertake when not consulting patients, b) why do they choose to work sessionally, and c) does sessional general practice reflect a lack of commitment to patients and the profession? Semi-structured interviews were conducted with GPs who worked sessionally, (i.e. six or fewer sessions a week in clinical general practice, where a session comprises four consecutive hours of patient care). These data were analysed qualitatively and saturation was reached. The majority of participants were in full-time paid employment, while part-time in clinical general practice. They reported that consultations increasingly required the management of patients with complex, chronic conditions who also required psychological management. Coupled with unrealistic patient expectations, these factors led GPs to be concerned about maintaining the quality patient care they considered professionally desirable. Many diversified their work activities to ensure that they retained their professional standards. "Part-time" general practice is a misnomer that masks the contribution these GPs make as part of the health workforce. Sessional practice more accurately describes the nature of our participants' clinical work. Their choice of sessional work is a professional response to the increasing demands within the consultation. It enables GPs to maintain their commitment to quality patient care and their profession, while attenuating the challenges of demanding consultations. Sessional general practitioners demonstrate strong commitment to their patients and the profession.

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.

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.

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, ].