Science.gov

Sample records for satellite laser altimetry

  1. Sand dune tracking from satellite laser altimetry

    NASA Astrophysics Data System (ADS)

    Dabboor, Mohammed

    Substantial problems arise from sand movement in arid and semi-arid countries. Sand poses a threat to infrastructure, agricultural and urban areas. These issues are caused by the encroachment of sand on roads and railway tracks, farmland, towns and villages, and airports, to name a few. Sand movement highly depends on geomorphology including vegetation cover, shape and height of the terrain, and grain size of the sand. However, wind direction and speed are the most important factors that affect efficient sand movement. The direction of the movement depends on the main direction of the wind, but it has been shown that a minimum wind speed is required, e.g. wind gusts, to initiate sand transport. This fact prevents a simple calculation of sand transport from conventional wind data as wind records rarely contain sub-minute intervals masking out any wind gusts. An alternative of predicting sand transport is the direct observation of sand advance by in situ measurements or via satellite. Until recently, satellite imagery was the only means to compare dune shape and position for predicting dune migration over several years. In 2003, the NASA laser altimetry mission ICESat became operational and monitors elevations over all surface types including sand dunes with an accuracy of about 10-20 cm. In this study, ICESat observations from repeat tracks (tracks overlapping eachother within 50 m) are used to derive sand dune advance and direction. The method employs a correlation of the elevation profiles over several dunes and was sucessfully validated with synthetic data. The accuracy of this method is 5 meters of dune advance. One of the most active areas exhibiting sand and dune movement is the area of the Arabian Peninsula. Approximately one-third of the Arabian Peninsula is covered by sand dunes. Different wind regimes (Shamal, Kaus) cause sand dune movement in the selected study area in the eastern part of the Arabian Peninsula between 20-25 degrees North and 45-55 degrees

  2. Assessment of long-range kinematic GPS positioning errors by comparison with airborne laser altimetry and satellite altimetry

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaohong; Forsberg, Rene

    2007-03-01

    Long-range airborne laser altimetry and laser scanning (LIDAR) or airborne gravity surveys in, for example, polar or oceanic areas require airborne kinematic GPS baselines of many hundreds of kilometers in length. In such instances, with the complications of ionospheric biases, it can be a real challenge for traditional differential kinematic GPS software to obtain reasonable solutions. In this paper, we will describe attempts to validate an implementation of the precise point positioning (PPP) technique on an aircraft without the use of a local GPS reference station. We will compare PPP solutions with other conventional GPS solutions, as well as with independent data by comparison of airborne laser data with “ground truth” heights. The comparisons involve two flights: A July 5, 2003, airborne laser flight line across the North Atlantic from Iceland to Scotland, and a May 24, 2004, flight in an area of the Arctic Ocean north of Greenland, near-coincident in time and space with the ICESat satellite laser altimeter. Both of these flights were more than 800 km long. Comparisons between different GPS methods and four different software packages do not suggest a clear preference for any one, with the heights generally showing decimeter-level agreement. For the comparison with the independent ICESat- and LIDAR-derived “ground truth” of ocean or sea-ice heights, the statistics of comparison show a typical fit of around 10 cm RMS in the North Atlantic, and 30 cm in the sea-ice region north of Greenland. Part of the latter 30 cm error is likely due to errors in the airborne LIDAR measurement and calibration, as well as errors in the “ground truth” ocean surfaces due to drifting sea-ice. Nevertheless, the potential of the PPP method for generating 10 cm level kinematic height positioning over long baselines is illustrated.

  3. An Alternative Approach for Registration of High-Resolution Satellite Optical Imagery and ICESat Laser Altimetry Data.

    PubMed

    Liu, Shijie; Lv, Yi; Tong, Xiaohua; Xie, Huan; Liu, Jun; Chen, Lei

    2016-11-27

    Satellite optical images and altimetry data are two major data sources used in Antarctic research. The integration use of these two datasets is expected to provide more accurate and higher quality products, during which data registration is the first issue that needs to be solved. This paper presents an alternative approach for the registration of high-resolution satellite optical images and ICESat (Ice, Cloud, and land Elevation Satellite) laser altimetry data. Due to the sparse distribution characteristic of the ICESat laser point data, it is difficult and even impossible to find same-type conjugate features between ICESat data and satellite optical images. The method is implemented in a direct way to correct the point-to-line inconsistency in image space through 2D transformation between the projected terrain feature points and the corresponding 2D image lines, which is simpler than discrepancy correction in object space that requires stereo images for 3D model construction, and easier than the indirect way of image orientation correction via photogrammetric bundle adjustment. The correction parameters are further incorporated into imaging model through RPCs (Rational Polynomial Coefficients) generation/regeneration for the convenience of photogrammetric applications. The experimental results by using the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) images and ZY-3 (Ziyuan-3 satellite) images for registration with ICESat data showed that sub-pixel level registration accuracies were achieved after registration, which have validated the feasibility and effectiveness of the presented approach.

  4. An Alternative Approach for Registration of High-Resolution Satellite Optical Imagery and ICESat Laser Altimetry Data

    PubMed Central

    Liu, Shijie; Lv, Yi; Tong, Xiaohua; Xie, Huan; Liu, Jun; Chen, Lei

    2016-01-01

    Satellite optical images and altimetry data are two major data sources used in Antarctic research. The integration use of these two datasets is expected to provide more accurate and higher quality products, during which data registration is the first issue that needs to be solved. This paper presents an alternative approach for the registration of high-resolution satellite optical images and ICESat (Ice, Cloud, and land Elevation Satellite) laser altimetry data. Due to the sparse distribution characteristic of the ICESat laser point data, it is difficult and even impossible to find same-type conjugate features between ICESat data and satellite optical images. The method is implemented in a direct way to correct the point-to-line inconsistency in image space through 2D transformation between the projected terrain feature points and the corresponding 2D image lines, which is simpler than discrepancy correction in object space that requires stereo images for 3D model construction, and easier than the indirect way of image orientation correction via photogrammetric bundle adjustment. The correction parameters are further incorporated into imaging model through RPCs (Rational Polynomial Coefficients) generation/regeneration for the convenience of photogrammetric applications. The experimental results by using the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) images and ZY-3 (Ziyuan-3 satellite) images for registration with ICESat data showed that sub-pixel level registration accuracies were achieved after registration, which have validated the feasibility and effectiveness of the presented approach. PMID:27898048

  5. Estimation of Sea Ice Thickness Distributions through the Combination of Snow Depth and Satellite Laser Altimetry Data

    NASA Technical Reports Server (NTRS)

    Kurtz, Nathan T.; Markus, Thorsten; Cavalieri, Donald J.; Sparling, Lynn C.; Krabill, William B.; Gasiewski, Albin J.; Sonntag, John G.

    2009-01-01

    Combinations of sea ice freeboard and snow depth measurements from satellite data have the potential to provide a means to derive global sea ice thickness values. However, large differences in spatial coverage and resolution between the measurements lead to uncertainties when combining the data. High resolution airborne laser altimeter retrievals of snow-ice freeboard and passive microwave retrievals of snow depth taken in March 2006 provide insight into the spatial variability of these quantities as well as optimal methods for combining high resolution satellite altimeter measurements with low resolution snow depth data. The aircraft measurements show a relationship between freeboard and snow depth for thin ice allowing the development of a method for estimating sea ice thickness from satellite laser altimetry data at their full spatial resolution. This method is used to estimate snow and ice thicknesses for the Arctic basin through the combination of freeboard data from ICESat, snow depth data over first-year ice from AMSR-E, and snow depth over multiyear ice from climatological data. Due to the non-linear dependence of heat flux on ice thickness, the impact on heat flux calculations when maintaining the full resolution of the ICESat data for ice thickness estimates is explored for typical winter conditions. Calculations of the basin-wide mean heat flux and ice growth rate using snow and ice thickness values at the 70 m spatial resolution of ICESat are found to be approximately one-third higher than those calculated from 25 km mean ice thickness values.

  6. Resolving Seamounts in Satellite Altimetry

    NASA Astrophysics Data System (ADS)

    Marks, K. M.; Smith, W. H.

    2006-12-01

    We have examined three factors influencing the use of satellite altimeter data to map seamounts and guyots in the deep ocean: (1) the resolution of seamount and guyot gravity anomalies by altimetry; (2) the non-linearity of the relationship between gravity and bathymetry; and (3) the homogeneity of the mass density within the seamount or guyot. When altimeter data are used to model the marine gravity anomaly field the result may have limited resolution due to noise levels in the altimeter data, track spacing of the satellite profiles, inclination angles of the orbits, and filters used to combine and interpolate the data (Sandwell and Smith, JGR, 1997). We compared the peak-to-trough amplitude of gravity anomalies in Sandwell and Smith`'s version 15.1 field to peak-to-trough amplitudes measured by gravimeters on board ships. The satellite gravity field amplitudes match ship measurements well over seamounts and guyots having volumes exceeding ~2000 km3. Over smaller volume seamounts, where the anomalies have most of their power at quite short wavelengths, the satellite field under-estimates the anomaly amplitude. If less filtering could be done, or a new mission with a lower noise level were flown, more of the anomalies associated with small seamounts might be resolved. Smith and Sandwell (Science, 1997) predicted seafloor topography from altimetric gravity assuming that the density of seafloor topography is nearly constant over ~100 km distances, and that the relationship between gravity and topography may be approximated by a liner filter over those distances. In fact, the true theoretical relationship is non-linear (Parker, Geophys. J. R. astr. Soc, 1972); it can be expressed as an N-th order expansion, with the N=1 term representing a linear filter and the N>1 terms accounting for higher-order corrections. We find that N=2 is a sufficient approximation at both seamounts and guyots. Constant density models of large volume guyots do not fit the observed gravity

  7. Interdisciplinary Earth Science Applications Using Satellite Radar Altimetry

    NASA Astrophysics Data System (ADS)

    Kuo, C.; Shum, C.; Lee, H.; Dai, C.; Yi, Y.

    2012-12-01

    Satellite altimetry was conceived as a space geodetic concept for ocean surface topography mapping in the NASA-sponsored 1969 Williamstown, MA Conference, and was tested as part of the passive and active radar payload (S192), along with a radiometer and a scatterometer, on Skylab-1 in May 14, 1973. Since then, numerous radar and laser satellite altimetry missions orbiting/flying-by the Earth, Mars, Mercury, Titan and the Moon have been launched, evolving from the original scientific objective of marine gravity field mapping to a geodetic tool to address interdisciplinary Earth and planetary sciences. The accuracy of the radar altimeter has improved from 0.9 m RMS for the S-192 Skylab Ku-band compressed-pulse altimeter, to 2 cm RMS (2 second average) for the dual-frequency pulse-limited radar altimetry and associated sensors onboard TOPEX/POSEIDON. Satellite altimetry has evolved into a unique cross-disciplinary geodetic tool in addressing contemporary Earth science problems including sea-level rise, large-scale general ocean circulation, ice-sheet mass balance, terrestrial hydrology, and bathymetry. Here we provide a concise review and describe specific results on the additional recent innovative and unconventional applications of interdisciplinary science research using satellite radar altimetry, including geodynamics, land subsidence, snow depth, wetland and cold region hydrology.

  8. Observing storm surges from satellite altimetry

    NASA Astrophysics Data System (ADS)

    Han, Guoqi

    2016-07-01

    Storm surges can cause catastrophic damage to properties and loss of life in coastal communities. Thus it is important to enhance our capabilities of observing and forecasting storm surges for mitigating damage and loss. In this presentation we show examples of observing storm surges around the world using nadir satellite altimetry, during Hurricane Sandy, Igor, and Isaac, as well as other cyclone events. The satellite observations are evaluated against tide-gauge observations and discussed for dynamic mechanisms. We also show the potential of a new wide-swath altimetry mission, the Surface Water and Ocean Topography (SWOT), for observing storm surges.

  9. Geophysical applications of satellite altimetry

    SciTech Connect

    Sandwell, D.T. )

    1991-01-01

    Publications related to geophysical applications of Seasat and Geosat altimetry are reviewed for the period 1987-1990. Problems discussed include geoid and gravity errors, regional geoid heights and gravity anomalies, local gravity field/flexure, plate tectonics, and gridded geoid heights/gravity anomalies. 99 refs.

  10. Geoid Determination At Coastal Areas From Satellite and Airborne Altimetry

    NASA Astrophysics Data System (ADS)

    Leite, F. B.; Bastos, L.; Fernandes, M. J.

    During the last ten years, the data from various satellite altimetry missions had a great impact in the definition of the sea surface topography and the Earth gravity field. How- ever, despite of its continuity, global covering and increasing accuracy, the use of satel- lite altimetry is mainly maximised in the open oceans. In the coastal and islands zones, where tidal dynamics and oceans currents have a special interest for several regional studies, the lower accuracy of these data limits the potentialities and applications of this technique. Although significant data recovery and accuracy improvement can be obtained in satellite data by applying appropriate filtering and interpolation methods, at these land/ocean transition zones, satellite altimetry information can benefit from the complementary information given by airborne altimetry/gravimetry data. As a consequence of the recent advances in GPS/INS integration for positioning and orientation of airborne sensors, it is now possible to obtain good quality airborne al- timetry data in coastal and island areas. Merging this information with satellite al- timetry, and also with existing marine gravity data, allows an accurate definition of the geoid in zones where satellite data are unavailable or are poor in quality and accu- racy. This study aims at the determination of a high accuracy regional geoid using free air anomalies derived by inversion of satellite and airborne altimetry data. The data sets used were ERS and TOPEX/POSEIDON altimeter data and airborne laser altimeter measurements collected during an observation campaign that took place in the Azores region, in 1997, in the scope of the European project AGMASCO. This paper outlines the evaluation and the impact of the results obtained and points out the main limitations and possibilities for further improvements in the use of satellite and airborne altimeter data for regional geoid mapping in coastal and island regions.

  11. A photogrammetric DEM of Greenland based on 1978-1987 aerial photos: validation and integration with laser altimetry and satellite-derived DEMs

    NASA Astrophysics Data System (ADS)

    Korsgaard, N. J.; Kjaer, K. H.; Nuth, C.; Khan, S. A.

    2014-12-01

    Here we present a DEM of Greenland covering all ice-free terrain and the margins of the GrIS and local glaciers and ice caps. The DEM is based on the 3534 photos used in the aero-triangulation which were recorded by the Danish Geodata Agency (then the Geodetic Institute) in survey campaigns spanning the period 1978-1987. The GrIS is covered tens of kilometers into the interior due to the large footprints of the photos (30 x 30 km) and control provided by the aero-triangulation. Thus, the data are ideal for providing information for analysis of ice marginal elevation change and also control for satellite-derived DEMs.The results of the validation, error assessments and predicted uncertainties are presented. We test the DEM using Airborne Topographic Mapper (IceBridge ATM) as reference data; evaluate the a posteriori covariance matrix from the aero-triangulation; and co-register DEM blocks of 50 x 50 km to ICESat laser altimetry in order to evaluate the coherency.We complement the aero-photogrammetric DEM with modern laser altimetry and DEMs derived from stereoscopic satellite imagery (AST14DMO) to examine the mass variability of the Northeast Greenland Ice Stream (NEGIS). Our analysis suggests that dynamically-induced mass loss started around 2003 and continued throughout 2014.

  12. Mapping lake level changes using ICESat/GLAS satellite laser altimetry data: a case study in arid regions of central Asia

    NASA Astrophysics Data System (ADS)

    Li, JunLi; Fang, Hui; Yang, Liao

    2011-12-01

    Lakes in arid regions of Central Asia act as essential components of regional water cycles, providing sparse but valuable water resource for the fragile ecological environments and human lives. Lakes in Central Asia are sensitive to climate change and human activities, and great changes have been found since 1960s. Mapping and monitoring these inland lakes would improve our understanding of mechanism of lake dynamics and climatic impacts. ICESat/GLAS satellite laser altimetry provides an efficient tool of continuously measuring lake levels in these poorly surveyed remote areas. An automated mapping scheme of lake level changes is developed based on GLAS altimetry products, and the spatial and temporal characteristics of 9 typical lakes in Central Asia are analyzed to validate the level accuracies. The results show that ICESat/GLAS has a good performance of lake level monitoring, whose patterns of level changes are the same as those of field observation, and the max differences between GLAS and field data is 3cm. Based on the results, it is obvious that alpine lakes are increasing greatly in lake levels during 2003-2009 due to climate change, while open lakes with dams and plain endorheic lakes decrease dramatically in water levels due to human activities, which reveals the overexploitation of water resource in Central Asia.

  13. Spaceborne Laser Altimetry On Icesat

    NASA Astrophysics Data System (ADS)

    Schutz, B.

    The Geoscience Laser Altimeter System (GLAS) is planned for launch on ICESat in 2002, into a 600 km altitude, near polar orbit from Vandenberg, California. The sys- tem is designed to operate up to five years in orbit. GLAS is under development by NASA Goddard and it will be delivered to the spacecraft contractor, Ball Aerospace, for mating and testing with the spacecraft bus. The GLAS instrument will transmit both near infrared (1064 nm) and green (532 nm) pulses using a diode-pumped, Q- switched Nd:YAG laser. The 1064 wavelength will be used for surface altimetry, in- cluding dense clouds, and the 532 wavelength will be used for atmospheric backscat- ter measurements. The altitude measurement will produce elevation time series of the Greenland and Antarctic ice sheets, which will enable determination of present-day elevation change and mass balance. Other applications of the altimetry channel in- clude precise measurements of land topography and vegetation canopy heights, sea ice roughness and thickness, and ocean surface elevations. The atmospheric channel will provide information on the vertical distribution of clouds and aerosols. The laser pulse energy at 1064 nm is about 75 mJ with a width of about 5 ns and the pulse has a divergence of about 0.11 mrad, which illuminates a spot on the surface with a 66 m diameter. Three lasers are available (two are required for lifetime requirements and the third provides redundancy). The pulse echo is captured with a 1 m telescope mounted on the rigid GLAS optical bench. A Si analog detector receives the return pulse and an A/D converter digitizes the pulse with a 1 GHz sampling rate. Two detectors and two digitizers are available for redundancy. Unlike wide pulse radar altimeters, accurate knowledge of the laser beam direction is required for the laser altimeter. The pointing will be determined with the assistance of an innovative system of CCD cameras that will measure the direction of each laser pulse with respect to

  14. Land subsidence measured by satellite radar altimetry

    NASA Technical Reports Server (NTRS)

    Krabill, W. B.; Brooks, R. L.

    1981-01-01

    Radar altimeter measurements from the GEOS-3 and SEASAT satellites are being evaluated to assess their potential contribution to terrain mapping. The primary evaluation area is the San Joaquin Valley of southern California; 40,000/sq km of the Valley have been mapped at a contour interval of 10 m from the satellite altimeter measurements. The accuracy of the altimeter derived terrain elevations is being assessed by comparison with 1:24,000 and digitized 1:250,000 maps and by intercomparisons at the crossover altimeter intersections. Comparisons of the altimeter derived elevations with historical maps archived at the U.S. Geological Survey confirms the USGS 1926-1972 subsidence contours for this area. Preliminary results from a similar analysis in the Houston-Galveston area of subsidence also demonstrates a capability of measuring land subsidence by satellite altimetry.

  15. Application of satellite altimetry for fisheries investigation

    NASA Astrophysics Data System (ADS)

    Sirota, A. M.; Lebedev, S. A.; Burykin, S. N.; Timokhin, E. N.; Chernyshkov, P. P.

    Satellite altimetry data provide good possibility to reveal the zones of high dynamic activity e g oceanic currents and fronts mesoscale features etc The four oceanic region were considered Irminger Sea Mid Atlantic Ridge North Atlantic Canary Upwelling Region Eastern Central Atlantic and Southeastern Pacific Both satellite altimetry data TOPEX Poseidon ERS -1 2 and in situ measurements oceanographic surveys demonstrated good correlation between these two different types of data in revealing of dynamic features at the ocean surface The main dynamic features in the regions are Sub-Polar Front and North Atlantic Current Irminger Sea and Mid Atlantic Ridge Canary Current and coastal upwelling Eastern Central Atlantic Sub-Tropical Front and South Pacific Current Southeastern Pacific Analysis of distribution abundance and biological state of various fish species revealed the links between organisms and their dynamic environmental conditions in the considered regions Variability of the distribution and abundance of rock grenadier over Mid Atlantic Ridge is closely connected to variations of Sub-Polar Front location Distribution of fishery grounds in the Irminger Sea coincides with dynamic heterogeneities at the sea surface elevation field Distribution of small pelagic fish in Canary Upwelling Region is influenced by mesoscale features of Canary Current and coastal upwelling Sub-Tropical Front meandering and eddies in Southeast Pacific influence significantly horse mackerel distribution Thus the peculiarities of dynamic features of the ocean

  16. Satellite Altimetry for Rivers : Review and Perspectives

    NASA Astrophysics Data System (ADS)

    Calmant, S.

    2013-05-01

    Pioneer works using satellite altimetry over rivers started two decades ago. Next decade, we should have SWOT, the first mission to monitor all the water bodies on Earth larger than (250 m x 250 m). Over these three decades, radar altimetry for hydrology will have evolved significantly. In the past decade, ESA's ENVISAT has turned to be the most useful altimetry mission for hydrology. The major improvement brought by ENVISAT has been to propose various estimates of the radar "range" (the distance between the sensor and reflecting surface) in the raw data distributed. Owing to this choice in ranges, typical rms error for series computed with the ice-1 algorithm for the ENVISAT or Jason-2 data is in the range of 20-40 cm, which is a factor 2 to 4 better than it was previously with the standard -ocean- tracking algorithm, with the T/P mission for instance. Before ENVISAT, it has long been considered that altimetry could work only over wide rivers or large lakes. When the contrast in backscatter between the river surface and the surrounding ground was favorable, valuable time series have been recovered over reaches as narrow as a few tens of meters. All the past missions, including ENVISAT, were working in the Ku band in Low Resolution mode (LR), in opposite to the delay Doppler (DD), SAR, mode, which should be the most common technology in the near-future missions. SAR mode is currently tested with Cryosat-2, launched in2010. With AltiKa, to be launched in February this year, a new band will be tested, the Ka band. In 2014, ESA should launch Sentinel-3A, the first of a series of four SAR satellites. Thus, in the middle of the decade, we should have the most favorable situation ever encountered, with 2 to 3 SAR altimeters (Sentinel-3A from 2014, Sentinel-3B from 2016, Jason-CS from 2017), and in LR mode (Jason 2 & 3 and AltiKa). Next decade, SWOT will embark a Ka band wide swath (120 km) interferometric altimeter. It will cover the Earth continents twice every 22 days

  17. Laser Altimetry Sampling Strategies over Sea Ice

    NASA Technical Reports Server (NTRS)

    Farrell, Sinead L.; Markus, Thorsten; Kwok, Ron; Connor, Laurence

    2011-01-01

    With the conclusion of the science phase of the Ice, Cloud and land Elevation Satellite (ICESat) mission in late 2009, and the planned launch of ICESat-2 in late 2015, NASA has recently established the IceBridge program to provide continuity between missions. A major goal of IceBridge is to obtain a sea-ice thickness time series via airborne surveys over the Arctic and Southern Oceans. Typically two laser altimeters, the Airborne Topographic Mapper (ATM) and the Land, Vegetation and Ice Sensor (LVIS), are utilized during IceBridge flights. Using laser altimetry simulations of conventional analogue systems such as ICESat, LVIS and ATM, with the multi-beam system proposed for ICESat-2, we investigate differences in measurements gathered at varying spatial resolutions and the impact on sea-ice freeboard. We assess the ability of each system to reproduce the elevation distributions of two seaice models and discuss potential biases in lead detection and sea-surface elevation, arising from variable footprint size and spacing. The conventional systems accurately reproduce mean freeboard over 25km length scales, while ICESat-2 offers considerable improvements over its predecessor ICESat. In particular, its dense along-track sampling of the surface will allow flexibility in the algorithmic approaches taken to optimize the signal-to-noise ratio for accurate and precise freeboard retrieval.

  18. An observational philosophy for GEOS-C satellite altimetry

    NASA Technical Reports Server (NTRS)

    Weiffenbach, G. C.

    1972-01-01

    The parameters necessary for obtaining a 10 cm accuracy for GEOS-C satellite altimetry are outlined. These data include oceanographic parameters, instrument calibration, pulse propagation, sea surface effects, and optimum design.

  19. Arctic geodynamics: Arctic science and ERS-1 satellite altimetry

    NASA Technical Reports Server (NTRS)

    Anderson, Allen Joel; Sandwell, David T.

    1994-01-01

    A detailed gravity field map of the mid Arctic Ocean, spreading ridge system was produced on the basis of ERS-1 satellite altimetry data. Areas of special concern, the Barents and Kara Seas, and areas surrounding the islands of Svalbard, Frans Josef Land and Novoya Zemlya are reviewed. ERS-1 altimetry covers unique Arctic and Antarctic latitudes above 72 degrees. Before ERS-1 it was not possible to study these areas with satellite altimetry. Gravity field solutions for the Barents Sea, portions of the Arctic Ocean and the Norwegian sea are shown. The largest gravity anomalies occur along the Greenland fracture zone as well as along transform faults near Svalbard.

  20. Tracking the PRIME eddy using satellite altimetry

    NASA Astrophysics Data System (ADS)

    Wade, Ian P.; Heywood, Karen J.

    The PRIME cruise to the North Atlantic during June/July 1996 surveyed and sampled an extremely vigorous and deep-reaching eddy with a significant barotropic component. Although it exhibited anticyclonic flow and featured a warm core at depth, it had been capped at some point during its lifetime, so appeared as a cold feature in the upper 500 m. Satellite-derived sea-surface temperatures (SST) showed it to have moved little during the few weeks prior to the cruise. In this paper we discuss the origin of the PRIME eddy including where and when it is likely to have formed. Consistently large amounts of cloud cover restrict the use of SST imagery to track such features. Altimetry provides a better method to trace this eddy back in time and space since microwave radiation is not significantly affected by cloud cover. Sea-level anomaly (SLA) data from the TOPEX/POSEIDON and European Remote Sensing (ERS) satellites were used. Results show that the eddy remained almost stationary in the Iceland Basin since first being detected in late 1995 and that it almost certainly formed locally, probably as a result of an instability in the current flow around the northwest of the Hatton Bank. Comparisons between satellite SLAs and hydrographic estimates of sea-surface elevation confirm that the eddy had a substantial barotropic flow. Both the altimeter data and the sea-surface height derived from the acoustic Doppler current profiler agree that the PRIME eddy had a sea-surface elevation of about 20 cm and that its diameter was about 120 km.

  1. Application of Satellite Altimetry for Fisheries Research

    NASA Astrophysics Data System (ADS)

    Sirota, A.; Lebedev, S.; Burykin, S.; Timokhin, E.; Chernyshkov, P.

    2006-07-01

    The three oceanic regions were considered: Mid Atlantic Ridge (North Atlantic), Canary Upwelling Region (Eastern Central Atlantic), and Southeastern Pacific. Both satellite altimetry data (TOPEX/Poseidon, ERS -1, 2) and in situ measurements (oceanographic surveys) demonstrated good correlation between these two different types of data in revealing of dynamic features at the ocean surface. The main dynamic features in the regions are: Sub-Polar Front and North Atlantic Current (Mid Atlantic Ridge), Canary Current and coastal upwelling (Eastern Central Atlantic), Sub- Tropical Front and South Pacific Current (Southeastern Pacific). Analysis of distribution, abundance and biological state of various fish species revealed the links between organisms and their dynamic environmental conditions in the considered regions. Variability of the distribution and abundance of rock grenadier over Mid Atlantic Ridge is closely connected to variations of Sub- Polar Front location. Distribution of small pelagic fish in Canary Upwelling Region is influenced by mesoscale features of Canary Current and coastal upwelling. Sub- Tropical Front meandering and eddies in Southeast Pacific influence significantly horse mackerel distribution.

  2. Satellite Altimetry, Ocean Circulation, and Data Assimilation

    NASA Technical Reports Server (NTRS)

    Fu, Lee-Lueng

    1999-01-01

    Ocean circulation is a critical factor in determining the Earth's climate. Satellite altimetry has been proven a powerful technique for measuring the height of the sea surface for the study of global ocean circulation dynamics. A major objective of my research is to investigate the utility of altimeter data for ocean circulation studies. The 6 years' data record of TOPEX/POSEIDON have been analyzed to study the spatial and temporal characteristics of large-scale ocean variability. A major result obtained in 1998 is the discovery of large-scale oscillations in sea level with a period of 25 days in the Argentine Basin of the South Atlantic Ocean (see diagram). They exhibit a dipole pattern with counterclockwise rotational propagation around the Zapiola Rise (centered at 45S and 317E), a small seamount in the abyssal plain of the basin. The peak-to-trough amplitude is about 10 cm over a distance of 500-1000 km. The amplitude of these oscillations has large seasonal-to-interannual variations. The period and rotational characteristics of these oscillations are remarkably similar to the observations made by two current meters deployed near the ocean bottom in the region. What TOPEX/POSEIDON has detected apparently are manifestations of the movement of the entire water column (barotropic motion). The resultant transport variation is estimated to be about 50 x 10(exp 6) cubic M/S, which is about 50% of the total water transport in the region. Preliminary calculations suggest that these oscillations are topographically trapped waves. A numerical model of the South Atlantic is used to investigate the nature of and causes for these waves. A very important property of sea surface height is that it is directly related to the surface geostrophic velocity, which is related to deep ocean circulation through the density field. Therefore altimetry observations are not only useful for determining the surface circulation but also for revealing information about the deep ocean. Another

  3. Laser Altimetry for Earth and Planetary Science

    NASA Technical Reports Server (NTRS)

    Smith, David E.; Zuber, Maria T.

    2001-01-01

    Laser altimeters are presently operating on spacecraft at Mars (MOLA), at the asteroid 433 Eros (NLR), and an earlier system operated at the Moon (Clementine) several years ago. These systems have all advanced our understanding of the evolution of the primary body and several more laser altimeter systems will be launched in the next several years around Earth and other planets to address a wide range of scientific problems. Laser technology for precision altimetry and atmospheric lidar is still in its infancy but the promise of the technology and its demonstrated results already show that laser altimetry/lidar will play an important role in future space observations. To date, lasers have mapped the Moon, Mars, and an asteroid but in a short while they will help measure the planetary librations of Mercury, the tidal distortions of Europa, and tree heights, upper atmosphere winds and the icecaps of planet Earth. Major areas of interest for the immediate future are the development of long-life lasers that can withstand the rigors of long planetary missions in extreme thermal and radiation environments and continue to operate successfully for many years.

  4. Satellite Laser Ranging operations

    NASA Technical Reports Server (NTRS)

    Pearlman, Michael R.

    1994-01-01

    Satellite Laser Ranging (SLR) is currently providing precision orbit determination for measurements of: 1) Ocean surface topography from satellite borne radar altimetry, 2) Spatial and temporal variations of the gravity field, 3) Earth and ocean tides, 4) Plate tectonic and regional deformation, 5) Post-glacial uplift and subsidence, 6) Variations in the Earth's center-of-mass, and 7) Variations in Earth rotation. SLR also supports specialized programs in time transfer and classical geodetic positioning, and will soon provide precision ranging to support experiments in relativity.

  5. Efficient Swath Mapping Laser Altimetry Demonstration Instrument Incubator Program

    NASA Technical Reports Server (NTRS)

    Yu, Anthony W.; Krainak, Michael A,; Harding, David J.; Abshire, James B.; Sun, Xiaoli; Cavanaugh, John; Valett, Susan

    2010-01-01

    In this paper we will discuss our eighteen-month progress of a three-year Instrument Incubator Program (IIP) funded by NASA Earth Science Technology Office (ESTO) on swath mapping laser altimetry system. This paper will discuss the system approach, enabling technologies and instrument concept for the swath mapping laser altimetry.

  6. Arctic Sea Level During the Satellite Altimetry Era

    NASA Astrophysics Data System (ADS)

    Carret, A.; Johannessen, J. A.; Andersen, O. B.; Ablain, M.; Prandi, P.; Blazquez, A.; Cazenave, A.

    2016-11-01

    Results of the sea-level budget in the high latitudes (up to 80°N) and the Arctic Ocean during the satellite altimetry era. We investigate the closure of the sea-level budget since 2002 using two altimetry sea-level datasets based on the Envisat waveform retracking: temperature and salinity data from the ORAP5 reanalysis, and Gravity Recovery And Climate Experiment (GRACE) space gravimetry data to estimate the steric and mass components. Regional sea-level trends seen in the altimetry map, in particular over the Beaufort Gyre and along the eastern coast of Greenland, are of halosteric origin. However, in terms of regional average over the region ranging from 66°N to 80°N, the steric component contributes little to the observed sea-level trend, suggesting a dominant mass contribution in the Arctic region. This is confirmed by GRACE-based ocean mass time series that agree well with the altimetry-based sea-level time series. Direct estimate of the mass component is not possible prior to GRACE. Thus, we estimated the mass contribution from the difference between the altimetry-based sea level and the steric component. We also investigate the coastal sea level with tide gauge records. Twenty coupled climate models from the CMIP5 project are also used. The models lead us to the same conclusions concerning the halosteric origin of the trend patterns.

  7. Arctic Sea Level During the Satellite Altimetry Era

    NASA Astrophysics Data System (ADS)

    Carret, A.; Johannessen, J. A.; Andersen, O. B.; Ablain, M.; Prandi, P.; Blazquez, A.; Cazenave, A.

    2017-01-01

    Results of the sea-level budget in the high latitudes (up to 80°N) and the Arctic Ocean during the satellite altimetry era. We investigate the closure of the sea-level budget since 2002 using two altimetry sea-level datasets based on the Envisat waveform retracking: temperature and salinity data from the ORAP5 reanalysis, and Gravity Recovery And Climate Experiment (GRACE) space gravimetry data to estimate the steric and mass components. Regional sea-level trends seen in the altimetry map, in particular over the Beaufort Gyre and along the eastern coast of Greenland, are of halosteric origin. However, in terms of regional average over the region ranging from 66°N to 80°N, the steric component contributes little to the observed sea-level trend, suggesting a dominant mass contribution in the Arctic region. This is confirmed by GRACE-based ocean mass time series that agree well with the altimetry-based sea-level time series. Direct estimate of the mass component is not possible prior to GRACE. Thus, we estimated the mass contribution from the difference between the altimetry-based sea level and the steric component. We also investigate the coastal sea level with tide gauge records. Twenty coupled climate models from the CMIP5 project are also used. The models lead us to the same conclusions concerning the halosteric origin of the trend patterns.

  8. Using satellite altimetry and tide gauges for storm surge warning

    NASA Astrophysics Data System (ADS)

    Andersen, O. B.; Cheng, Y.; Deng, X.; Steward, M.; Gharineiat, Z.

    2015-03-01

    The combination of the coarse temporal sampling by satellite altimeters in the deep ocean with the high temporal sampling at sparsely located tide gauges along the coast has been used to improve the forecast of high water for the North Sea along the Danish Coast and for the northeast coast of Australia. For both locations we have tried to investigate the possibilities and limitations of the use of satellite altimetry to capture high frequency signals (surges) using data from the past 20 years. The two regions are chosen to represent extra-tropical and tropical storm surge conditions. We have selected several representative high water events on the two continents based on tide gauge recordings and investigated the capability of satellite altimetry to capture these events in the sea surface height data. Due to the lack of recent surges in the North Sea we focused on general high water level and found that in the presence of two or more satellites we could capture more than 90% of the high water sea level events. In the Great Barrier Reef section of the northeast Australian coast, we have investigated several large tropical cyclones; one of these being Cyclone Larry, which hit the Queensland coast in March 2006 and caused both loss of lives as well as huge devastation. Here we demonstrate the importance of integrating tide gauges with satellite altimetry for forecasting high water at the city of Townsville in northeast Australia.

  9. The role of satellite altimetry in climate studies

    NASA Technical Reports Server (NTRS)

    Parsons, C. L.

    1980-01-01

    The results of three generations of satellite-borne radar altimetry experiments are summarized. The diverse measurements possible from this instrument are shown to be directly applicable to studies of the importance of the oceans in climate. The radar altimeter has unique value for investigations seeking knowledge of the interconnections between ocean dynamics, heat and momentum transfer across the air-sea interface, sea ice extent, and polar ice sheet thickness.

  10. Malvinas Current variability as observed by satellite altimetry data

    NASA Astrophysics Data System (ADS)

    Saraceno, Martin; Artana, Camila; Bodichon, Renaud; Provost, Christine

    The Malvinas Current (MC) is the northernmost extension of the Antarctic Circumpolar Current that carries cold and nutrient-rich waters. The MC is thought to be a major source of nutrients to the SW South Atlantic. The interaction of the MC with the sloping bottom is presumably responsible for sustaining upwelling along the shelf-break. Numerical and analytical models indicate that the upwelling intensity and mean transport along the Patagonian continental shelf is modulated by the MC transport. Apart from its regional influence, the MC contributes to regulate the climate since it helps the exchange of heat and salt as is a crucial component of the Meridional Overturning Circulation. Satellite altimetry data in conjunction with in-situ data allowed monitoring the transport of the MC at 41ºS. A CNES founded program will repeat those measures and will measure at the same time currents over the continental shelf under a satellite altimetry track. First deployment of instruments will occur in November 2014. In this work we use satellite altimetry data to explore the relationship between the MC and continental shelf transports and the correspondence between the variability of the MC and the mesoscale activity in the SW South Atlantic. Results suggest that (i) the large decreases of the MC transport are associated to eddies that interact with the MC and (ii) the first mode associated to the variability of the transport over the Patagonian continental shelf is significantly correlated to the first mode of variability of the MC transport.

  11. Laser altimetry of Mercury, Moon, and Mars

    NASA Astrophysics Data System (ADS)

    Neumann, G. A.; Mazarico, E.; Smith, D. E.; Zuber, M. T.; Torrence, M. H.; Barnouin, O. S.; Solomon, S. C.

    2011-12-01

    Since March 29 of this year, the Mercury Laser Altimeter (MLA) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft has been ranging twice daily to the surface of Mercury from orbit, collecting more than 1 million ranges each month. Mercury joins Earth, Moon, and Mars as a planetary body mapped precisely by laser altimetry from orbit. Ranging covers nearly all of the northern hemisphere. The southern hemisphere largely lies beyond the 1800-km range of MLA from MESSENGER's eccentric orbit, but the 10-cm-precision MLA data will eventually be complemented by less precise radio occultation and limb profiling measurements by the MESSENGER spacecraft, as well as by digital topographic models produced by stereo photogrammetry. Mercury topography is distinguished from its larger and smaller counterparts by a relatively low (<10 km) dynamic range, less than half that of Earth, Moon, and Mars, and two-thirds that of its nearest neighbor, Venus. There are ample indications from the topography of Mercury impact structures as well as from its low-degree shape that Mercury's thermal evolution was complex and differed from those of other terrestrial planets. Central to the thermal history are the extensive contractional tectonic features for which altimetry quantifies accommodated strain. As well, MLA profiles of extensional graben within more than two dozen impact craters and basins, together with topographic and gravity field observations, will constrain the evolution of Mercury's upper crust and lithosphere. Lidar topographic data provide a wealth of geological contextual information regarding impact crater formation and modification, tectonics, volcanism, lithospheric strength, thermal evolution, and internal structure. Topography is essential for orthorectification of images and calibration of reflectance data. Geodetic topography, referenced to the center of mass, in conjunction with gravity, allows an assessment of the distribution of

  12. On the unification of geodetic leveling datums using satellite altimetry

    NASA Technical Reports Server (NTRS)

    Mather, R. S.; Rizos, C.; Morrison, T.

    1978-01-01

    Techniques are described for determining the height of Mean Sea Level (MSL) at coastal sites from satellite altimetry. Such information is of value in the adjustment of continental leveling networks. Numerical results are obtained from the 1977 GEOS-3 altimetry data bank at Goddard Space Flight Center using the Bermuda calibration of the altimeter. Estimates are made of the heights of MSL at the leveling datums for Australia and a hypothetical Galveston datum for central North America. The results obtained are in reasonable agreement with oceanographic estimates obtained by extrapolation. It is concluded that all gravity data in the Australian bank AUSGAD 76 and in the Rapp data file for central North America refer to the GEOS-3 altimeter geoid for 1976.0 with uncertainties which do not exceed + or - 0.1 mGal.

  13. Ice sheet topography by satellite altimetry

    NASA Technical Reports Server (NTRS)

    Brooks, R. L.; Campbell, W. J.; Ramseier, R. O.; Stanley, H. R.; Zwally, H. J.

    1978-01-01

    The measured time between the transmission and rzturn of 13.9 GHz radar pulses from the GEOS 3 satellite (at a mean altitude of 844.5 km and an inclination of 114 deg 52 min) is used to determine the thickness of the Greenland ice cap, with an accuracy in surface elevation on the order of 2 m. Attention is given to changes in ice thickness as an indicator of climatic change in general, and change in mean sea level in particular. Each elevation data point obtained by the satellite represents an average along 0.67 km of ground track, and three-dimensional maps are presented to illustrate the data.

  14. Ice sheet topography by satellite altimetry

    USGS Publications Warehouse

    Brooks, R.L.; Campbell, W.J.; Ramseier, R.O.; Stanley, H.R.; Zwally, H.J.

    1978-01-01

    The surface elevation of the southern Greenland ice sheet and surface features of the ice flow are obtained from the radar altimeter on the GEOS 3 satellite. The achieved accuracy in surface elevation is ???2 m. As changes in surface elevation are indicative of changes in ice volume, the mass balance of the present ice sheets could be determined by repetitive mapping of the surface elevation and the surface could be monitored to detect surging or significant changes in ice flow. ?? 1978 Nature Publishing Group.

  15. Detection of uncharted seamounts using satellite altimetry

    SciTech Connect

    Lazarewicz, A.P.; Schwank, D.C.

    1982-04-01

    The topography of the marine geoid (and corresponding sea surface) contains characteristic local features caused by sediments. These features can be successfully detected and located using matched filters to process single tracks of satellite altimeter data. Comparison of detected seamount features with the SNYBAPS and Scripps bathymetric data bases can reveal uncharted seamounts. This technique has been applied to 33 Seasat tracks in a region of the western Pacific bounded by 0 to 15 degrees North and 160 and 165 degrees East. From this analysis, we find three uncharted seamounts in this region. In all three cases, a detailed examination of the bathymetry shows no known bathymetric feature consistent with the detected signature. The method used to estimate the size and location of these uncharted seamounts is discussed.

  16. 3-D modelling of seamount topography from satellite altimetry

    SciTech Connect

    Baudry, N. ); Calmant, S. )

    1991-06-01

    The authors develop a complete set of algorithms to perform 3D modelling of seamount bathymetry from satellite altimetry. The first stage of the data processing consists in gridding the geoid: to account for the long wavelength errors geoid heights are first bias-adjusted at cross-overs. Then a collocation on a regular grid is performed, accounting for the altimeter errors. In a second stage, geoid heights are converted into bathymetry. No simplifying assumption on the shape and location of the bathymetry highs is necessary. Bathymetric uncertainties due to the data sampling and the parameters of the mechanical and crustal models are evaluated.

  17. New estimates of oceanic tidal energy dissipation from satellite altimetry

    NASA Technical Reports Server (NTRS)

    Cartwright, David E.; Ray, Richard D.

    1989-01-01

    As a novel approach to computing the flux of tidal power into shelf areas, tidal maps of an oceanic area near the Patagonian Shelf are derived from 11 months of altimetry records from the GEOSAT satellite. Power fluxes are computed from the maps through Laplace's tidal equations. Flux vectors for M2 clearly show a convergence on to the southern portion of the shelf sea and their total is nearly twice the loss computed by Miller for that area. A decrease of 'quality factor' with frequency from M2 to S2 is in keeping with Webb's hypothesis of shelf resonances at frequencies a little higher than the tidal band.

  18. Impact of improved models for precise orbits of altimetry satellites on the orbit accuracy and regional mean sea level trends

    NASA Astrophysics Data System (ADS)

    Rudenko, Sergei; Esselborn, Saskia; Dettmering, Denise; Schöne, Tilo; Neumayer, Karl-Hans

    2015-04-01

    Precise orbits of altimetry satellites are a prerequisite for investigations of global and regional sea level changes. We show a significant progress obtained in the recent decades in modeling and determination of the orbits of altimetry satellites. This progress was reached due to the improved knowledge of the Earth gravity field obtained by using CHAMP (CHAllenging Mini-Satellite Payload), GRACE (Gravity Recovery and Climate Experiment) and GOCE (Gravity field and Ocean Circulation Explorer) data, improved realizations of the terrestrial and celestial reference frames and transformations between these reference frames, improved modeling of ocean and solid Earth tides, improved accuracy of observations and other effects. New precise orbits of altimetry satellites ERS-1 (1991-1996), TOPEX/Poseidon (1992-2005), ERS-2 (1995-2006), Envisat (2002-2012) and Jason-1 (2002-2012) have been recently derived at the time intervals given within the DFG UHR-GravDat project and the ESA Climate Change Initiative Sea Level project using satellite laser ranging (SLR), Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), Precise Range And Range-Rate Equipment (PRARE) and altimetry single-satellite crossover data (various observation types were used for various satellites). We show the current state of the orbit accuracy and the improvements obtained in the recent years. In particular, we demonstrate the impact of recently developed time-variable Earth gravity field models, improved tropospheric refraction models for DORIS observations, latest release 05 of the atmosphere-ocean dealiasing product (AOD1B) and some other models on the orbit accuracy of these altimetry satellites and regional mean sea level trends computed using these new orbit solutions.

  19. ICESat laser altimetry over small mountain glaciers

    NASA Astrophysics Data System (ADS)

    Treichler, Désirée; Kääb, Andreas

    2016-09-01

    Using sparsely glaciated southern Norway as a case study, we assess the potential and limitations of ICESat laser altimetry for analysing regional glacier elevation change in rough mountain terrain. Differences between ICESat GLAS elevations and reference elevation data are plotted over time to derive a glacier surface elevation trend for the ICESat acquisition period 2003-2008. We find spatially varying biases between ICESat and three tested digital elevation models (DEMs): the Norwegian national DEM, SRTM DEM, and a high-resolution lidar DEM. For regional glacier elevation change, the spatial inconsistency of reference DEMs - a result of spatio-temporal merging - has the potential to significantly affect or dilute trends. Elevation uncertainties of all three tested DEMs exceed ICESat elevation uncertainty by an order of magnitude, and are thus limiting the accuracy of the method, rather than ICESat uncertainty. ICESat matches glacier size distribution of the study area well and measures small ice patches not commonly monitored in situ. The sample is large enough for spatial and thematic subsetting. Vertical offsets to ICESat elevations vary for different glaciers in southern Norway due to spatially inconsistent reference DEM age. We introduce a per-glacier correction that removes these spatially varying offsets, and considerably increases trend significance. Only after application of this correction do individual campaigns fit observed in situ glacier mass balance. Our correction also has the potential to improve glacier trend significance for other causes of spatially varying vertical offsets, for instance due to radar penetration into ice and snow for the SRTM DEM or as a consequence of mosaicking and merging that is common for national or global DEMs. After correction of reference elevation bias, we find that ICESat provides a robust and realistic estimate of a moderately negative glacier mass balance of around -0.36 ± 0.07 m ice per year. This regional

  20. The ICESat-2 Laser Altimetry Mission

    NASA Technical Reports Server (NTRS)

    Abdalati, Waleed; Zwally, H. Jay; Bindschadler, Robert; Csatho, Bea; Farrell, Sinead Louise; Fricker, Helen Amanda; Harding, David; Kwok, Ronald; Lefsky, Michael; Markus, Thorsten; Marshak, Alexander; Neumann, Thomas; Palm, Stephen; Schutz, Bob; Smith, Ben; Spinhirne, James; Webb, Charles

    2010-01-01

    Satellite and aircraft observations have revealed that remarkable changes in the Earth s polar ice cover have occurred in the last decade. The impacts of these changes, which include dramatic ice loss from ice sheets and rapid declines in Arctic sea ice, could be quite large in terms of sea level rise and global climate. NASA's Ice, Cloud and Land Elevation Satellite-2 (ICESat-2), currently planned for launch in 2015, is specifically intended to quantify the amount of change in ice sheets and sea ice and provide key insights into their behavior. It will achieve these objectives through the use of precise laser measurements of surface elevation, building on the groundbreaking capabilities of its predecessor, the Ice Cloud and Land Elevation Satellite (ICESat). In particular, ICESat-2 will measure the temporal and spatial character of ice sheet elevation change to enable assessment of ice sheet mass balance and examination of the underlying mechanisms that control it. The precision of ICESat-2's elevation measurement will also allow for accurate measurements of sea ice freeboard height, from which sea ice thickness and its temporal changes can be estimated. ICESat-2 will provide important information on other components of the Earth System as well, most notably large-scale vegetation biomass estimates through the measurement of vegetation canopy height. When combined with the original ICESat observations, ICESat-2 will provide ice change measurements across more than a 15-year time span. Its significantly improved laser system will also provide observations with much greater spatial resolution, temporal resolution, and accuracy than has ever been possible before.

  1. Fusion of Laser Altimetry Data with Dems Derived from Stereo Imaging Systems

    NASA Astrophysics Data System (ADS)

    Schenk, T.; Csatho, B. M.; Duncan, K.

    2016-06-01

    During the last two decades surface elevation data have been gathered over the Greenland Ice Sheet (GrIS) from a variety of different sensors including spaceborne and airborne laser altimetry, such as NASA's Ice Cloud and land Elevation Satellite (ICESat), Airborne Topographic Mapper (ATM) and Laser Vegetation Imaging Sensor (LVIS), as well as from stereo satellite imaging systems, most notably from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Worldview. The spatio-temporal resolution, the accuracy, and the spatial coverage of all these data differ widely. For example, laser altimetry systems are much more accurate than DEMs derived by correlation from imaging systems. On the other hand, DEMs usually have a superior spatial resolution and extended spatial coverage. We present in this paper an overview of the SERAC (Surface Elevation Reconstruction And Change detection) system, designed to cope with the data complexity and the computation of elevation change histories. SERAC simultaneously determines the ice sheet surface shape and the time-series of elevation changes for surface patches whose size depends on the ruggedness of the surface and the point distribution of the sensors involved. By incorporating different sensors, SERAC is a true fusion system that generates the best plausible result (time series of elevation changes) a result that is better than the sum of its individual parts. We follow this up with an example of the Helmheim gacier, involving ICESat, ATM and LVIS laser altimetry data, together with ASTER DEMs.

  2. An efficient algorithm for computing the crossovers in satellite altimetry

    NASA Technical Reports Server (NTRS)

    Tai, Chang-Kou

    1988-01-01

    An efficient algorithm has been devised to compute the crossovers in satellite altimetry. The significance of the crossovers is twofold. First, they are needed to perform the crossover adjustment to remove the orbit error. Secondly, they yield important insight into oceanic variability. Nevertheless, there is no published algorithm to make this very time consuming task easier, which is the goal of this report. The success of the algorithm is predicated on the ability to predict (by analytical means) the crossover coordinates to within 6 km and 1 sec of the true values. Hence, only one interpolation/extrapolation step on the data is needed to derive the crossover coordinates in contrast to the many interpolation/extrapolation operations usually needed to arrive at the same accuracy level if deprived of this information.

  3. Revisiting the pole tide for and from satellite altimetry

    NASA Astrophysics Data System (ADS)

    Desai, Shailen; Wahr, John; Beckley, Brian

    2015-12-01

    Satellite altimeter sea surface height observations include the geocentric displacements caused by the pole tide, namely the response of the solid Earth and oceans to polar motion. Most users of these data remove these effects using a model that was developed more than 20 years ago. We describe two improvements to the pole tide model for satellite altimeter measurements. Firstly, we recommend an approach that improves the model for the response of the oceans by including the effects of self-gravitation, loading, and mass conservation. Our recommended approach also specifically includes the previously ignored displacement of the solid Earth due to the load of the ocean response, and includes the effects of geocenter motion. Altogether, this improvement amplifies the modeled geocentric pole tide by 15 %, or up to 2 mm of sea surface height displacement. We validate this improvement using two decades of satellite altimeter measurements. Secondly, we recommend that the altimetry pole tide model exclude geocentric sea surface displacements resulting from the long-term drift in polar motion. The response to this particular component of polar motion requires a more rigorous approach than is used by conventional models. We show that erroneously including the response to this component of polar motion in the pole tide model impacts interpretation of regional sea level rise by ± 0.25 mm/year.

  4. Monitoring drying up of Urmia lake with satellite altimetry

    NASA Astrophysics Data System (ADS)

    Roohi, Shirzad; Sneeuw, Nico

    2013-04-01

    Urmia lake is a UNESCO protected area with more than a hundred small rocky islands. It is home to several species of birds and animals. Located in northwestern Iran, it is the largest lake in the Middle East and the third largest salty water lake on earth. It has a surface area of approximately 5200 km², and an average depth of 16 m. Unfortunately during the recently years Urmia lake has been shrinking. If the drought process continues at the current rate it would be disappear in the near future. The main factors that speeds up the drought rate of the lake, are dam construction on the main rivers which feeds the lake, evaporation and lack of precipitation during recent years as well as irrigation. The construction of a causeway in the middle of the lake also affects the natural ecosystem of the lake. The case of Urmia lake and similar cases in other parts of the word emphasize the role of new technology such as satellite altimetry in better management of water resource and monitoring such critical situations. In this research we show the current situation and recent past of the lake from processing 10 years of Envisat satellite radar altimetry data. For internal validation of the result, water level time series were built from ascending and descending tracks separately and for external validation in-situ gauge measurements were used. Internal and external comparisons indicates the result are consistent, i.e there is no bias and systematic error in Envisat data. The RMSE between ascending and descending tracks is several centimeters and between satellite and gauge data is 1m. Water level time series analysis shows that there is a declining rate of 0.3 m/year in the water level but after 2005 it seems to have accelerated. This rate increases the salinity of lake and expands receding shoreline rapidly so the lake bed will reveal fast because the lake is shallow especially in the south part. Following this research we are investigating to find the best re-tracker in

  5. Arctic Ocean Gravity Field Derived From ERS-1 Satellite Altimetry.

    PubMed

    Laxon, S; McAdoo, D

    1994-07-29

    The derivation of a marine gravity field from satellite altimetry over permanently ice-covered regions of the Arctic Ocean provides much new geophysical information about the structure and development of the Arctic sea floor. The Arctic Ocean, because of its remote location and perpetual ice cover, remains from a tectonic point of view the most poorly understood ocean basin on Earth. A gravity field has been derived with data from the ERS-1 radar altimeter, including permanently ice-covered regions. The gravity field described here clearly delineates sections of the Arctic Basin margin along with the tips of the Lomonosov and Arctic mid-ocean ridges. Several important tectonic features of the Amerasia Basin are clearly expressed in this gravity field. These include the Mendeleev Ridge; the Northwind Ridge; details of the Chukchi Borderland; and a north-south trending, linear feature in the middle of the Canada Basin that apparently represents an extinct spreading center that "died" in the Mesozoic. Some tectonic models of the Canada Basin have proposed such a failed spreading center, but its actual existence and location were heretofore unknown.

  6. Equilibrium wave spectrum and sea state bias in satellite altimetry

    NASA Technical Reports Server (NTRS)

    Glazman, Roman E.; Srokosz, Meric A.

    1991-01-01

    For a well-developed sea at equilibrium with a constant wind, the energy-containing range of the wavenumber spectrum for wind-generated gravity waves is approximated by a generalized power law involving the angular spread function and mu, interpreted as a fractal codimension of a small surface patch. Dependence of mu on the wave age is estimated, and the 'Phillips constant', beta, along with the low-wavenumber boundary, k0, of the inertial subrange are analyzed on the basis of the wave action and energy conservation principles. The resulting expressions are employed to evaluate various non-Gaussian statistics of a weakly nonlinear sea surface, which determine the sea state bias in satellite altimetry. The locally accelerated decay of the spectral density function in a high-wavenumber dissipation subrange is pointed out as an important factor of wave dynamics and the geometrical optics treatment of the sea state bias. The analysis is carried out in the approximation of a unidirectional wave field and confined to the case of a well-developed sea.

  7. Detailed gravity anomalies from Geos 3 satellite altimetry data

    NASA Technical Reports Server (NTRS)

    Gopalapillai, G. S.; Mourad, A. G.

    1979-01-01

    Detailed gravity anomalies are computed from a combination of Geos 3 satellite altimeter and terrestrial gravity data using least-squares principles. The mathematical model used is based on the Stokes' equation modified for a nonglobal solution. Using Geos 3 data in the calibration area, the effects of several anomaly parameter configurations and data densities/distributions on the anomalies and their accuracy estimates are studied. The accuracy estimates for 1 deg x 1 deg mean anomalies from low density altimetry data are of the order of 4 mgal. Comparison of these anomalies with the terrestrial data and also with Rapp's data derived using collocation techniques show rms differences of 7.2 and 4.9 mgal, respectively. Indications are that the anomaly accuracies can be improved to about 2 mgal with high density data. Estimation of 30 in. x 30 in. mean anomalies indicates accuracies of the order of 5 mgal. Proper verification of these results will be possible only when accurate ground truth data become available.

  8. Global gravity field to degree and order 30 from Geos 3 satellite altimetry and other data

    NASA Technical Reports Server (NTRS)

    Gaposchkin, E. M.

    1980-01-01

    A model of the geopotential field in spherical harmonics to degree and order 30 is obtained from Geos 3 satellite to sea surface altimetry data, terrestrial gravity measurements and satellite perturbation analysis. A general perturbation solution is employed for the calculation of the orbits of 10 satellites based on satellite laser ranging data, and 1 deg x 1 deg surface gravity data are used to compute 550 km x 550 km block anomalies by means of autocovariance analysis. Altimeter-determined sea-surface heights, which are taken as the geoid, are averaged for each 1 deg x 1 deg ocean surface area and treated by autocovariance analysis to obtain 550 x 550 km block undulations. Observation and normal equations are formed from the altimeter and surface gravity data, which together cover 1635 out of 1654 possible surface elements, and are combined with the available satellite-derived normal equations to obtain a solution for the spherical harmonics coefficients. In addition, a value of 6,378,138.23 + or - 1.3 m is obtained for the earth's semimajor axis.

  9. Accuracy assessment of satellite altimetry over central East Antarctica by kinematic GNSS and crossover analysis

    NASA Astrophysics Data System (ADS)

    Schröder, Ludwig; Richter, Andreas; Fedorov, Denis; Knöfel, Christoph; Ewert, Heiko; Dietrich, Reinhard; Matveev, Aleksey Yu.; Scheinert, Mirko; Lukin, Valery

    2014-05-01

    Satellite altimetry is a unique technique to observe the contribution of the Antarctic ice sheet to global sea-level change. To fulfill the high quality requirements for its application, the respective products need to be validated against independent data like ground-based measurements. Kinematic GNSS provides a powerful method to acquire precise height information along the track of a vehicle. Within a collaboration of TU Dresden and Russian partners during the Russian Antarctic Expeditions in the seasons from 2001 to 2013 we recorded several such profiles in the region of the subglacial Lake Vostok, East Antarctica. After 2006 these datasets also include observations along seven continental traverses with a length of about 1600km each between the Antarctic coast and the Russian research station Vostok (78° 28' S, 106° 50' E). After discussing some special issues concerning the processing of the kinematic GNSS profiles under the very special conditions of the interior of the Antarctic ice sheet, we will show their application for the validation of NASA's laser altimeter satellite mission ICESat and of ESA's ice mission CryoSat-2. Analysing the height differences at crossover points, we can get clear insights into the height regime at the subglacial Lake Vostok. Thus, these profiles as well as the remarkably flat lake surface itself can be used to investigate the accuracy and possible error influences of these missions. We will show how the transmit-pulse reference selection correction (Gaussian vs. centroid, G-C) released in January 2013 helped to further improve the release R633 ICESat data and discuss the height offsets and other effects of the CryoSat-2 radar data. In conclusion we show that only a combination of laser and radar altimetry can provide both, a high precision and a good spatial coverage. An independent validation with ground-based observations is crucial for a thorough accuracy assessment.

  10. Detailed gravity anomalies from GEOS-3 satellite altimetry data

    NASA Technical Reports Server (NTRS)

    Gopalapillai, G. S.; Mourad, A. G.

    1978-01-01

    A technique for deriving mean gravity anomalies from dense altimetry data was developed. A combination of both deterministic and statistical techniques was used. The basic mathematical model was based on the Stokes' equation which describes the analytical relationship between mean gravity anomalies and geoid undulations at a point; this undulation is a linear function of the altimetry data at that point. The overdetermined problem resulting from the excessive altimetry data available was solved using Least-Squares principles. These principles enable the simultaneous estimation of the associated standard deviations reflecting the internal consistency based on the accuracy estimates provided for the altimetry data as well as for the terrestrial anomaly data. Several test computations were made of the anomalies and their accuracy estimates using GOES-3 data.

  11. Feasibility of Estimating Snow Depth in Complex Terrain Using Satellite Lidar Altimetry

    NASA Technical Reports Server (NTRS)

    Jasinski, Michael F.; Stoll, Jeremy

    2012-01-01

    Satellite retrievals of snow depth and water equivalent (SWE) are critical for monitoring watershed scale processes around the world. However, the problem is especially challenging in mountainous regions where complex heterogeneities limit the utility of low resolution satellite sensors. The Geoscience Laser Altimeter Sensor (GLAS) aboard the Ice, Cloud, and land Elevation Satellite (ICESat) collected surface elevation data along near-repeat reference transects over land areas from 2003-2009. Although intended for monitoring ice caps and sea ice, the seven year global GLAS data base has provided unprecedented opportunity to test the capability of satellite lidar technology for estimating snow depth over land. GLAS single track and low repeat frequency does not provide data sufficient for operational estimates. However, its comparatively small footprint size of -65 m and its database of seasonal repeat observations during both snow and no-snow conditions have been sufficient to evaluate the potential of spacebased lidar altimetry for estimating snow depth. Recent analysis of ICESat elevations in the Uinta Mountains in NE Utah provide encouraging results for watershed scale estimates of snow depth. Research reported here focuses on the sensitivity of several versions of an ICESat snow depth algorithm to a range of landscape types defined by vegetation cover, slope and roughness. Results are compared to available SNOTEL data.

  12. Subglacial water transport throughout Antarctica from ICESAT laser altimetry

    NASA Astrophysics Data System (ADS)

    Smith, B. E.; Joughin, I. R.; Fricker, H. A.; Tulaczyk, S.

    2007-12-01

    A survey of the Antarctic ice sheet using satellite laser altimetry has detected 46 small regions of surface uplift or drawdown in twelve different glacier drainages around Antarctica. Surface displacements are measured relative to the best-fitting plane passing through multiple (5-11) elevation measurements on the same repeat-track, allowing correction for across-track slopes. Volume displacements are derived by interpolating displacements from multiple tracks to a common grid. These ECAs (Elevation Change Anomalies) range from less than four km to more than 60 km across, with vertical displacements ranging from a few decimeters to over ten meters. Typical volume displacements are on the order of 0.05 cubic kilometers over the three-year survey, and the largest displacement is more than 1.4 cubic kilometers. Although the majority of the ECAs are within the Filchner- Ronne catchment, others (including those discussed by Fricker and others, 2007), are found in the Ross Embayment, in the drainages of Byrd Glacier and Lambert Glaciera, and in the interior of Wilkes Land. As have other researchers who have observed ECAs, we take these features to result from water motion at the bed. In all cases where the ice sheet velocity structure is known, the ECAs are in regions of ice stream or tributary flow, which implies that they are associated with melting bed conditions. Some of the ECAs appear to be downstream of linear features in the ice sheet surface, suggesting that they are associated with local minima in the hydraulic potential at the bed. Others have no clear association with surface topography. The relatively small number of ECAs precludes drawing strong conclusions about spatial and temporal correlations between filling and drainage events. However, a few conclusions are clear: Because adjacent ECAs are more likely to have correlated filling or drainage rates than to have anticorrelated filling or drainage rates, it does not appear that water is conserved among

  13. Studies of oceanic tectonics based on GEOS-3 satellite altimetry

    NASA Technical Reports Server (NTRS)

    Poehls, K. A.; Kaula, W. M.; Schubert, G.; Sandwell, D.

    1979-01-01

    Using statistical analysis, geoidal admittance (the relationship between the ocean geoid and seafloor topography) obtained from GEOS-3 altimetry was compared to various model admittances. Analysis of several altimetry tracks in the Pacific Ocean demonstrated a low coherence between altimetry and seafloor topography except where the track crosses active or recent tectonic features. However, global statistical studies using the much larger data base of all available gravimetry showed a positive correlation of oceanic gravity with topography. The oceanic lithosphere was modeled by simultaneously inverting surface wave dispersion, topography, and gravity data. Efforts to incorporate geoid data into the inversion showed that the base of the subchannel can be better resolved with geoid rather than gravity data. Thermomechanical models of seafloor spreading taking into account differing plate velocities, heat source distributions, and rock rheologies were discussed.

  14. Airborne laser altimetry survey of Glaciar Tyndall, Patagonia

    NASA Astrophysics Data System (ADS)

    Keller, Kristian; Casassa, Gino; Rivera, Andrés; Forsberg, Rene; Gundestrup, Niels

    2007-10-01

    The first airborne laser altimetry measurements of a glacier in South America are presented. Data were collected in November of 2001 over Glaciar Tyndall, Torres del Paine National Park, Chilean Patagonia, onboard a Twin Otter airplane of the Chilean Air Force. A laser scanner with a rotating polygon-mirror system together with an Inertial Navigation System (INS) were fixed to the floor of the aircraft, and used in combination with two dual-frequency GPS receivers. Together, the laser-INS-GPS system had a nominal accuracy of 30 cm after data processing. On November 23rd, a total of 235 km were flown over the ablation area of Glaciar Tyndall, with 5 longitudinal tracks with a mean swath width of 300 m, which results in a point spacing of approximately 2 m both along and across track. A digital elevation model (DEM) generated using the laser altimetry data was compared with a DEM produced from a 1975 map (1:50,000 scale — Instituto Geográfico Militar (IGM), Chile). A mean thinning of - 3.1 ± 1.0 m a - 1 was calculated for the ablation area of Glaciar Tyndall, with a maximum value of - 7.7 ± 1.0 m a - 1 at the calving front at 50 m a.s.l. and minimum values of between - 1.0 and - 2.0 ± 1.0 m a - 1 at altitudes close to the equilibrium line altitude (900 m a.s.l.). The thinning rates derived from the airborne survey were similar to the results obtained by means of ground survey carried out at ˜ 600 m of altitude on Glaciar Tyndall between 1975 and 2002, yielding a mean thinning of - 3.2 m a - 1 [Raymond, C., Neumann, T.A., Rignot, E., Echelmeyer, K.A., Rivera, A., Casassa, G., 2005. Retreat of Tyndall Glacier, Patagonia, over the last half century. Journal of Glaciology 173 (51), 239-247.]. A good agreement was also found between ice elevation changes measured with laser data and previous results obtained with Shuttle Radar Topography Mission (SRTM) data. We conclude that airborne laser altimetry is an effective means for accurately detecting glacier elevation

  15. Evaluation of Aster Gdem v3 Using Icesat Laser Altimetry

    NASA Astrophysics Data System (ADS)

    Carabajal, C. C.; Boy, J.-P.

    2016-06-01

    We have used a set of Ground Control Points (GCPs) derived from altimetry measurements from the Ice, Cloud and land Elevation Satellite (ICESat) to evaluate the quality of the 30 m posting ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) Global Digital Elevation Model (GDEM) V3 elevation products produced by NASA/METI for Greenland and Antarctica. These data represent the highest quality globally distributed altimetry measurements that can be used for geodetic ground control, selected by applying rigorous editing criteria, useful at high latitudes, where other topographic control is scarce. Even if large outliers still remain in all ASTER GDEM V3 data for both, Greenland and Antarctica, they are significantly reduced when editing ASTER by number of scenes (N≥5) included in the elevation processing. For 667,354 GCPs in Greenland, differences show a mean of 13.74 m, a median of -6.37 m, with an RMSE of 109.65 m. For Antarctica, 6,976,703 GCPs show a mean of 0.41 m, with a median of -4.66 m, and a 54.85 m RMSE, displaying smaller means, similar medians, and less scatter than GDEM V2. Mean and median differences between ASTER and ICESat are lower than 10 m, and RMSEs lower than 10 m for Greenland, and 20 m for Antarctica when only 9 to 31 scenes are included.

  16. Water resource monitoring in Iran using satellite altimetry and satellite gravimetry (GRACE)

    NASA Astrophysics Data System (ADS)

    Khaki, Mehdi; Sneeuw, Nico

    2015-04-01

    Human civilization has always been in evolution by having direct access to water resources throughout history. Water, with its qualitative and quantitative effects, plays an important role in economic and social developments. Iran with an arid and semi-arid geographic specification is located in Southwest Asia. Water crisis has appeared in Iran as a serious problem. In this study we're going to use various data sources including satellite radar altimetry and satellite gravimetry to monitor and investigate water resources in Iran. Radar altimeters are an invaluable tool to retrieve from space vital hydrological information such as water level, volume and discharge, in particular from regions where the in situ data collection is difficult. Besides, Gravity Recovery and Climate Experiment (GRACE) provide global high resolution observations of the time variable gravity field of the Earth. This information is used to derive spatio-temporal changes of the terrestrial water storage body. This study isolates the anthropogenic perturbations to available water supplies in order to quantify human water use as compared to available resources. Long-term monitor of water resources in Iran is contain of observing freshwaters, lakes and rivers as well as exploring ground water bodies. For these purposes, several algorithms are developed to quantitatively monitor the water resources in Iran. The algorithms contain preprocessing on datasets, eliminating biases and atmospheric corrections, establishing water level time series and estimating terrestrial water storage considering impacts of biases and leakage on GRACE data. Our primary goal in this effort is to use the combination of satellite radar altimetry and GRACE data to study on water resources as well as methods to dealing with error sources include cross over errors and atmospheric impacts.

  17. Monitoring Sea Level in the Coastal Zone with Satellite Altimetry and Tide Gauges

    NASA Astrophysics Data System (ADS)

    Cipollini, Paolo; Calafat, Francisco M.; Jevrejeva, Svetlana; Melet, Angelique; Prandi, Pierre

    2017-01-01

    We examine the issue of sustained measurements of sea level in the coastal zone, first by summarizing the long-term observations from tide gauges, then showing how those are now complemented by improved satellite altimetry products in the coastal ocean. We present some of the progresses in coastal altimetry, both from dedicated reprocessing of the radar waveforms and from the development of improved corrections for the atmospheric effects. This trend towards better altimetric data at the coast comes also from technological innovations such as Ka-band altimetry and SAR altimetry, and we discuss the advantages deriving from the AltiKa Ka-band altimeter and the SIRAL altimeter on CryoSat-2 that can be operated in SAR mode. A case study along the UK coast demonstrates the good agreement between coastal altimetry and tide gauge observations, with root mean square differences as low as 4 cm at many stations, allowing the characterization of the annual cycle of sea level along the UK coasts. Finally, we examine the evolution of the sea level trend from the open to the coastal ocean along the western coast of Africa, comparing standard and coastally improved products. Different products give different sea level trend profiles, so the recommendation is that additional efforts are needed to study sea level trends in the coastal zone from past and present satellite altimeters. Further improvements are expected from more refined processing and screening of data, but in particular from the constant improvements in the geophysical corrections.

  18. Recent Advances in Satellite and Airborne Altimetry over Arctic Sea Ice

    NASA Astrophysics Data System (ADS)

    Farrell, S. L.; Newman, T.; Richter-Menge, J.; Haas, C.; Petty, A.; McAdoo, D. C.; Connor, L. N.

    2014-12-01

    Over the last two decades altimeters on satellite and aircraft platforms have revolutionized our understanding of Arctic sea ice mass balance. Satellite laser and radar altimeters provide unique measurements of sea ice elevation, from which ice thickness may be derived, across basin scales and interdecadal time periods. Meanwhile airborne altimetry, together with high-resolution digital imagery, provides a range of novel observations that describe key features of the ice pack including its snow cover, surface morphology and deformation characteristics. We provide an update on current Arctic sea ice thickness conditions based on IceBridge measurements, discussing these in the context of previously observed decadal change. Fundamental to the goal of understanding interannual variability, and monitoring long-term trends in sea ice volume, is the accurate characterization of measurement uncertainty. This is particularly true when linking observations from different sensors. We discuss recent advances in tracking and quantifying the major components of the altimetric sea ice thickness error budget. We pay particular attention to two major components of the error: freeboard and snow loading uncertainty. We describe novel measurement techniques that are helping to reduce measurement uncertainty and allowing, for the first time, quantification of errors with respect to ice type.

  19. Topography over South America from ERS altimetry

    NASA Technical Reports Server (NTRS)

    Brenner, Anita; Frey, Herb; DiMarzio, John; Tsaoussi, Lucia

    1997-01-01

    The results of the surface topography mapping of South America during the ERS-1 geodetic mission are presented. The altimeter waveforms, the range measurement, and the internal and Doppler range corrections were obtained. The atmospheric corrections and solid tides were calculated. Comparisons between Shuttle laser altimetry and ERS-1 altimetry grid showed good agreement. Satellite radar altimetry data can be used to improve the topographic knowledge of regions for which only poor elevation data currently exist.

  20. Requirements for a marine geoid compatible with geoid deducible from satellite altimetry

    NASA Technical Reports Server (NTRS)

    Fubara, D. M. J.; Mourad, A. G.

    1972-01-01

    Theory deficiencies, data, and potential computational procedures that make the physical determination of the ocean geoid with true scale, shape, and absolute orientation of an elusive target are outlined. Satellite altimetry potential, in combination with adequate ground support and sea truth to resolve accurate global marine geoid and other peripheral benefits associated with ocean physics, are stated. Results are given in tabular form.

  1. A digital elevation model of the Greenland Ice Sheet derived from combined laser and radar altimetry data

    NASA Astrophysics Data System (ADS)

    Fredenslund Levinsen, Joanna; Smith, Ben; Sørensen, Louise S.; Forsberg, René

    2014-05-01

    When estimating elevation changes of ice-covered surfaces from radar altimetry, it is important to correct for slope-induced errors. They cause the reflecting point of the pulse to move up-slope and thus return estimates in the wrong coordinates. Slope-induced errors can be corrected for by introducing a Digital Elevation Model (DEM). In this work, such a DEM is developed for the Greenland Ice Sheet using a combination of Envisat radar and ICESat laser altimetry. If time permits, CryoSat radar altimetry will be included as well. The reference year is 2010 and the spatial resolution 2.5 x 2.5 km. This is in accordance with the results obtained in the ESA Ice Sheets CCI project showing that a 5 x 5 km grid spacing is reasonable for ice sheet-wide change detection (Levinsen et al., 2013). Separate DEMs will be created for the given data sets, and the geostatistical spatial interpolation method collocation will be used to merge them, thus adjusting for potential inter-satellite biases. The final DEM is validated with temporally and spatially agreeing airborne lidar data acquired in the NASA IceBridge and ESA CryoVex campaigns. The motivation for developing a new DEM is based on 1) large surface changes presently being observed, and mainly in margin regions, hence necessitating updated topography maps for accurately deriving and correcting surface elevation changes, and 2) although radar altimetry is subject to surface penetration of the signal into the snowpack, data is acquired continuously in time. This is not the case with e.g. ICESat, where laser altimetry data were obtained in periods of active lasers, i.e. three times a year with a 35-day repeat track. Previous DEMs e.g. have 2007 as the nominal reference year, or they are built merely from ICESat data. These have elevation errors as small as 10 cm, which is lower than for Envisat and CryoSat. The advantage of an updated DEM consisting of combined radar and laser altimetry therefore is the possibility of

  2. Impact of Atmospheric and Oceanic De-aliasing Level-1B (AOD1B) products on precise orbits of altimetry satellites and altimetry results

    NASA Astrophysics Data System (ADS)

    Rudenko, Sergei; Dettmering, Denise; Esselborn, Saskia; Fagiolini, Elisa; Schöne, Tilo

    2016-03-01

    We have extended backwards from 2001 to 1979 the current release 05 (RL05) of the Gravity Recovery and Climate Experiment (GRACE) Atmospheric and Oceanic De-aliasing Level-1B (AOD1B) product and studied the impact of this and a previous release 04 (RL04) of the AOD1B product on precise orbits of five altimetry satellites (ERS-1, ERS-2, TOPEX/Poseidon, Envisat and Jason-1) for the time span 1991-2012, as compared to the case when no AOD1B product is used. We have found that using AOD1B RL05 product reduces root mean square (RMS) fits of satellite laser ranging (SLR) observations by about 1.0-6.4 per cent, 2-d arc overlaps in radial, cross-track and along-track directions by about 1.3-12.0, 0.3-10.0 and 2.0-10.0 per cent, respectively, for various satellites tested, as compared to the case without AOD1B product. Using AOD1B RL05 product instead of RL04 one reduces SLR RMS fits by 0.1-0.7 per cent, 2-d arc overlaps in radial, cross-track and along-track directions by 0.1-0.6, 0.1-1.3 and 0.2-1.2 per cent, respectively, for the satellite orbits tested. The multi-mission crossover analysis shows that the application of an AOD1B product reduces the scatter of radial errors by 0.4-2.8 per cent for the satellite missions studied. At the regions with the most pronounced changes the use of the AOD1B products improves the consistency between the sea level as measured by the TOPEX and ERS-2 missions and by the Jason-1 and Envisat missions by 5 to 10 per cent (globally by about 2 per cent). The results of our study show that extended AOD1B RL05 product performs better than the AOD1B RL04 and improves orbits of altimetry satellites and consistency of sea level products.

  3. Measuring water storage fluctuations in lake Dongting, China, by Topex/Poseidon satellite altimetry.

    PubMed

    Zhang, Jiqun; Xu, Kaiqin; Yang, Yonghui; Qi, Lianhui; Hayashi, Seiji; Watanabe, Masataka

    2006-04-01

    Although satellite radar altimetry was developed and optimized for open oceans, it has been used to monitor variations in the level of inland water-bodies such as lakes and rivers. Here, for the first time, we have further used the altimetry-derived variation of water level for estimating the fluctuation of water storage as an addition to the present in situ water storage estimation systems to be used in remote areas and in emergency situation such as in the events flooding monitoring and for studying the effect of climate change. Lake Dongting, the second largest lake in China, influenced frequently by flooding, was, therefore, chosen to demonstrate the potential of the technique. By using the concept of an "assumed reference point", we converted Topex/Poseidon satellite altimetry data on water level variations in Lake Dongting to "water level" data. The "water level" time-series data and in situ water storage were used to establish a rating curve. From the rating curve, we converted data on "water level" derived from seven years (1993-1999) of Topex/Poseidon data to actual water storage in Lake Dongting. The result reveals that the seasonal and annual fluctuations of water storage occurred during the 1990s with a more frequent flooding at the late 1990s' especially the flooding in whole catchment level in 1998 and 1999. The study supports the usefulness of satellite altimetry for dense and continuous monitoring of the temporal variations in water dynamic in moderate to large lakes.

  4. Arctic geodynamics: Continental shelf and deep ocean geophysics. ERS-1 satellite altimetry: A first look

    NASA Technical Reports Server (NTRS)

    Anderson, Allen Joel; Sandwell, David T.; Marquart, Gabriele; Scherneck, Hans-Georg

    1993-01-01

    An overall review of the Arctic Geodynamics project is presented. A composite gravity field model of the region based upon altimetry data from ERS-1, Geosat, and Seasat is made. ERS-1 altimetry covers unique Arctic and Antarctic latitudes above 72 deg. Both areas contain large continental shelf areas, passive margins, as well as recently formed deep ocean areas. Until ERS-1 it was not possible to study these areas with satellite altimetry. Gravity field solutions for the Barents sea, portions of the Arctic ocean, and the Norwegian sea north of Iceland are shown. The gravity anomalies around Svalbard (Spitsbergen) and Bear island are particularly large, indicating large isostatic anomalies which remain from the recent breakup of Greenland from Scandinavian. Recently released gravity data from the Armed Forces Topographic Service of Russia cover a portion of the Barents and Kara seas. A comparison of this data with the ERS-1 produced gravity field is shown.

  5. Laser satellite power systems

    SciTech Connect

    Walbridge, E.W.

    1980-01-01

    A laser satellite power system (SPS) converts solar power captured by earth-orbiting satellites into electrical power on the earth's surface, the satellite-to-ground transmission of power being effected by laser beam. The laser SPS may be an alternative to the microwave SPS. Microwaves easily penetrate clouds while laser radiation does not. Although there is this major disadvantage to a laser SPS, that system has four important advantages over the microwave alternative: (1) land requirements are much less, (2) radiation levels are low outside the laser ground stations, (3) laser beam sidelobes are not expected to interfere with electromagnetic systems, and (4) the laser system lends itself to small-scale demonstration. After describing lasers and how they work, the report discusses the five lasers that are candidates for application in a laser SPS: electric discharge lasers, direct and indirect solar pumped lasers, free electron lasers, and closed-cycle chemical lasers. The Lockheed laser SPS is examined in some detail. To determine whether a laser SPS will be worthy of future deployment, its capabilities need to be better understood and its attractiveness relative to other electric power options better assessed. First priority should be given to potential program stoppers, e.g., beam attenuation by clouds. If investigation shows these potential program stoppers to be resolvable, further research should investigate lasers that are particularly promising for SPS application.

  6. Analysis of lake level changes in Nam Co in central Tibet utilizing synergistic satellite altimetry and optical imagery

    NASA Astrophysics Data System (ADS)

    Kropáček, Jan; Braun, Andreas; Kang, Shichang; Feng, Chen; Ye, Qinghua; Hochschild, Volker

    2012-07-01

    The fluctuations of closed basin lakes on the Tibetan Plateau are a valuable record of climate change induced water balance alterations within the catchments. Since these basins are remote and hard to access, multisensoral remote sensing is a valuable method to gather the necessary water budget components with appropriate spatial coverage and with high temporal resolutions. Thus the lake level elevation changes of the central Tibetan lake Nam Co were examined in example by a comparison of satellite altimetry (RA-2/ENVISAT, GFO radar altimeters and GLAS/ICESat laser altimeter for the period 2000-2009) and the evaluation of a time series of optical satellite data dating back to 1976 (Landsat) and 1965 (Corona) in order to validate hydrological water budget modelling results. The combination of all three altimeters revealed a rising trend of lake level on average by 0.31 m/year in the period 2000-2009 which corresponds to a total volume change of 6.2 km3. This is in a good agreement with simulated average lake level rise of 0.35 m/year obtained from distributed hydrological modelling (Krause et al., 2010). The movements of lakeshore measured on the satellite imagery confirm the trend revealed by the altimetry data and they also indicate the rising trend since 1965. While GFO provides a dense time series of data the more accurate ENVISAT/RA-2 data unfortunately feature large data gaps over Tibet. The measurements from time limited campaigns of ICESat validate the results of radar altimetry and they provide unlike radar altimeters a valid height over lake ice during winter and spring period. The results show that the presented approach is a valuable contribution to understand the impact of changing climate on the hydrology of Tibetan lakes.

  7. Antarctic marine gravity field from high-density satellite altimetry

    NASA Technical Reports Server (NTRS)

    Sandwell, David T.

    1992-01-01

    High-density (about 2-km profile spacing) Geosat/GM altimetry profiles were obtained for Antarctic waters (6-deg S to 72 deg S) and converted to vertical gravity gradient, using Laplace's equation to directly calculate gravity gradient from vertical deflection grids and Fourier analysis to construct gravity anomalies from two vertical deflection grids. The resultant gravity grids have resolution and accuracy comparable to shipboard gravity profiles. The obtained gravity maps display many interesting and previously uncharted features, such as a propagating rift wake and a large 'leaky transform' along the Pacific-Antarctic Rise.

  8. Controls on satellite altimetry over non-ocean surfaces for hydrological purposes

    NASA Astrophysics Data System (ADS)

    Tourian, M. J.; Sneeuw, N.; Bárdossy, A.

    2009-04-01

    Over the past two decades, satellite altimetry has been used to measure non-ocean water level variation for hydrologic studies. Non-ocean surfaces are much rougher than oceans. Moreover, satellite corrections for atmospheric propagation normally include errors in non-ocean surfaces. Hence, due to (1) the effect of topography and heterogeneity of reflecting surface and (2) atmospheric propagation, the expected echo shape for altimeter returns over land differs from that over ocean surfaces. As a result, measurements over non-ocean area include erroneous and missing data. We discuss several methods to retrieving the missing data through retracking. We show water level variations at two test locations: Balaton Lake (Hungary) and Urmia Lake (Iran). Finally we validate the obtained time series from satellite altimetry over mentioned area against in-situ measurements.

  9. Storm surge observed by Chinese HY-2A satellite radar altimetry

    NASA Astrophysics Data System (ADS)

    Yang, J.; Li, X.; Han, G.; Chen, N.; Chen, D.

    2017-02-01

    HY-2A is the first Chinese ocean dynamic environment monitoring satellite, which was launched in August 2011. The satellite repeats its ground track every 14 days. It plays an important role in global monitoring of sea surface winds (especially extreme winds like typhoons and hurricanes), ocean waves, currents, eddies, and extreme events like storm surges by using its four major payloads, i.e. radar altimetry, microwave scatterometer, scanning microwave radiometer and calibration microwave radiometer. The HY-2A data are obtained from China’s National Satellite Ocean Application Service (NSOAS). We use 1 s along-track data with a nominal spatial resolution of about 7 km. For example, a storm surge induced by tropical cyclone Funso in the Southwest Indian Ocean near Mozambique in January 2012 is observed by HY-2A satellite altimetry. The storm surge magnitude is estimated to be 0.49 m and the cross-shelf e-folding decay scale to be 92 km. The present study shows that the HY-2A satellite altimetry is a useful tool for monitoring storm surges and their impacts in the Indian Ocean.

  10. North Atlantic teleconnection patterns signature on sea level from satellite altimetry

    NASA Astrophysics Data System (ADS)

    Iglesias, Isabel; Lázaro, Clara; Joana Fernandes, M.; Bastos, Luísa

    2015-04-01

    Presently, satellite altimetry record is long enough to appropriately study inter-annual signals in sea level anomaly and ocean surface circulation, allowing the association of teleconnection patterns of low-frequency variability with the response of sea level. The variability of the Atlantic Ocean at basin-scale is known to be complex in space and time, with the dominant mode occurring on annual timescales. However, interannual and decadal variability have already been documented in sea surface temperature. Both modes are believed to be linked and are known to influence sea level along coastal regions. The analysis of the sea level multiannual variability is thus essential to understand the present climate and its long-term variability. While in the open-ocean sea level anomaly from satellite altimetry currently possesses centimetre-level accuracy, satellite altimetry measurements become invalid or of lower accuracy along the coast due to the invalidity of the wet tropospheric correction (WTC) derived from on-board microwave radiometers. In order to adequately analyse long-term changes in sea level in the coastal regions, satellite altimetry measurements can be recovered by using an improved WTC computed from recent algorithms that combine wet path delays from all available observations (remote sensing scanning imaging radiometers, GNSS stations, microwave radiometers on-board satellite altimetry missions and numerical weather models). In this study, a 20-year (1993-2013) time series of multi-mission satellite altimetry (TOPEX/Poseidon, Jason-1, OSTM/Jason-2, ERS-1/2, ENVISAT, CryoSat-2 and SARAL), are used to characterize the North Atlantic (NA) long-term variability on sea level at basin-scale and analyse its response to several atmospheric teleconnections known to operate on the NA. The altimetry record was generated using an improved coastal WTC computed from either the GNSS-derived path Delay or the Data Combination methodologies developed by University of

  11. Greenland Ice sheet mass balance from satellite and airborne altimetry

    NASA Astrophysics Data System (ADS)

    Khan, S. A.; Bevis, M. G.; Wahr, J. M.; Wouters, B.; Sasgen, I.; van Dam, T. M.; van den Broeke, M. R.; Hanna, E.; Huybrechts, P.; Kjaer, K.; Korsgaard, N. J.; Bjork, A. A.; Kjeldsen, K. K.

    2013-12-01

    Ice loss from the Greenland Ice Sheet (GrIS) is dominated by loss in the marginal areas. Dynamic induced ice loss and its associated ice surface lowering is often largest close to the glacier calving front and may vary from rates of tens of meters per years to a few meters per year over relatively short distances. Hence, high spatial resolution data are required to accurately estimate volume changes. Here, we estimate ice volume change rate of the Greenland ice sheet using data from Ice, Cloud and land Elevation Satellite (ICESat) laser altimeter during 2003-2009 and CryoSat-2 data during 2010-2012. To improve the volume change estimate we supplement the ICESat and CryoSat data with altimeter surveys from NASA's Airborne Topographic Mapper (ATM) during 2003-2012 and NASA's Land, Vegetation and Ice Sensor (LVIS) during 2007-2012. The Airborne data are mainly concentrated along the ice margin and therefore significantly improve the estimate of the total volume change. Furthermore, we divide the GrIS into six major drainage basins and provide volume loss estimates during 2003-2006, 2006-2009 and 2009-2012 for each basin and separate between melt induced and dynamic ice loss. In order to separate dynamic ice loss from melt processes, we use SMB values from the Regional Atmospheric Climate Model (RACMO2) and SMB values from a positive degree day runoff retention model (Janssens & Huybrechts 2000, Hanna et al. 2011 JGR, updated for this study). Our results show increasing SMB ice loss over the last decade, while dynamic ice loss increased during 2003-2009, but has since been decreasing. Finally, we assess the estimated mass loss using GPS observations from stations located along the edge of the GrIS and measurements from the Gravity Recovery and Climate Experiment (GRACE) satellite gravity mission. Hanna, E., et al. (2011), Greenland Ice Sheet surface mass balance 1870 to 2010 based on Twentieth Century Reanalysis, and links with global climate forcing, J. Geophys. Res

  12. The Geoscience Laser Altimetry/Ranging System (GLARS)

    NASA Technical Reports Server (NTRS)

    Cohen, S. C.; Degnan, J. J.; Bufton, J. L.; Garvin, J. B.; Abshire, J. B.

    1986-01-01

    The Geoscience Laser Altimetry Ranging System (GLARS) is a highly precise distance measurement system to be used for making extremely accurate geodetic observations from a space platform. It combines the attributes of a pointable laser ranging system making observations to cube corner retroreflectors placed on the ground with those of a nadir looking laser altimeter making height observations to ground, ice sheet, and oceanic surfaces. In the ranging mode, centimeter-level precise baseline and station coordinate determinations will be made on grids consisting of 100 to 200 targets separated by distances from a few tens of kilometers to about 1000 km. These measurements will be used for studies of seismic zone crustal deformations and tectonic plate motions. Ranging measurements will also be made to a coarser, but globally distributed array of retroreflectors for both precise geodetic and orbit determination applications. In the altimetric mode, relative height determinations will be obtained with approximately decimeter vertical precision and 70 to 100 meter horizontal resolution. The height data will be used to study surface topography and roughness, ice sheet and lava flow thickness, and ocean dynamics. Waveform digitization will provide a measure of the vertical extent of topography within each footprint. The planned Earth Observing System is an attractive candidate platform for GLARS since the GLAR data can be used both for direct analyses and for highly precise orbit determination needed in the reduction of data from other sensors on the multi-instrument platform. (1064, 532, and 355 nm)Nd:YAG laser meets the performance specifications for the system.

  13. The COASTALT Project: Towards an Operational Use of Satellite Altimetry in the Coastal Zone

    NASA Astrophysics Data System (ADS)

    Vignudelli, S.; Cipollini, P.; Gommenginger, C.; Snaith, H. M.; Coelho, E.; Fernandes, J.; Gomez-Henri, J.; Martin-Puig, C.; Woodworth, P. L.; Dinardo, S.; Benveniste, J. J.

    2009-12-01

    The coastal zone is the unique part of the Earth where land, sea, air and people meet. By its nature it is a complex system where all the processes that influence its functioning, whether physical, biological, chemical, social, climatological or geological, are interconnected. It requires an integrated approach benefiting from a synergy of modeling tools and multiple datasets created from space, air, land and ocean-based earth observing systems. An important property monitored from space using radar altimetry is the sea level, an index of variability of the ocean circulation. Since 1991, satellite altimetry has had exceptional success over the open ocean. However, the processing strategy used in the open ocean has not been of much success in getting sea level in the coastal zone. The advantage of current radar altimetry for coastal studies is that it can fill gaps in the vast areas around tide gauges which are running continu¬ously, but in only a few places. The coastal domain represents a challenging target for processing of satellite data in general; for satellite altimetry, the data retrieval is required to address some problems including: (1) re-tracking (important for the last 10 km next to the coast), (2) a more accurate wet troposphere path delay correction, (3) better modeling of tidal and atmospheric effects. A global record of length 17 years of raw data from a series of altimetry missions is presently available and represents a unique resource for retrospective analysis in the coastal zone. A great impetus has been given to the field by the recent launch of two major projects devoted to the development of coastal altimetry products for specific missions: PISTACH, by CNES focused on Jason-2 and COASTALT, by ESA for Envisat. In parallel, NASA is sustaining coastal altimetry research through specific R&D projects in response to the last OSTST call. This new “coastal altimetry” community, inherently interdisciplinary, has already had two well

  14. Integration of Airborne Laser Scanning Altimetry Data in Alpine Geomorphological and Hazard Studies

    NASA Astrophysics Data System (ADS)

    Seijmonsbergen, A. C.

    2007-12-01

    A digital terrain and surface model derived from an airborne laser scanning (ALS) altimetry dataset was used in the Austrian Alps for the preparation, improvement and the evaluation of a digital geomorphological hazard map. The geomorphology in the study area consists of a wide variety of landforms, which include glacial landforms such as cirques, hanging valleys, and moraine deposits, of pre- and postglacial mass movement landforms and processes, such as deep seated slope failures, rock fall, debris flows and solifluction. The area includes naked and covered gypsum karst, collapse dolines and fluvial landforms and deposits such as river terraces, incisions, alluvial fans and gullies. A detailed symbol based paper geomorphological map served as a basis for the digitalization of basic morphogenetic landform and process units. These units were assigned a `geomorphological unit type`, `hazard type` and `activity` code in the attribute table, according to a morphogenetic classification scheme. Selected zonal statistical attributes - mean height, aspect and slope angle - were calculated in a GIS using the vector based morphogenetic landform and process units and the underlying 1m resolution laser altimetry raster dataset. This statistical information was added to the attribute table of the `geomorphological hazard map`. Interpretation of the zonal statistical information shows that indicative topographic signatures exist for the various geomorphological and hazard units in this region of the Alps. Based on this experience a further step is made towards semi-automated geomorphological hazard classification of segmented laser altimetry data using expert knowledge rules. The first results indicate a classification accuracy of 50-70 percent for most landform associations. Areas affected by slide processes resulted in less accurate classification, probably because of their polygenetic history in this area. It is concluded that the use of lidar data improves visual

  15. Spatiotemporal Interpolation of Elevation Changes Derived from Satellite Altimetry for Jakobshavn Isbrae, Greenland

    NASA Technical Reports Server (NTRS)

    Hurkmans, R.T.W.L.; Bamber, J.L.; Sorensen, L. S.; Joughin, I. R.; Davis, C. H.; Krabill, W. B.

    2012-01-01

    Estimation of ice sheet mass balance from satellite altimetry requires interpolation of point-scale elevation change (dHdt) data over the area of interest. The largest dHdt values occur over narrow, fast-flowing outlet glaciers, where data coverage of current satellite altimetry is poorest. In those areas, straightforward interpolation of data is unlikely to reflect the true patterns of dHdt. Here, four interpolation methods are compared and evaluated over Jakobshavn Isbr, an outlet glacier for which widespread airborne validation data are available from NASAs Airborne Topographic Mapper (ATM). The four methods are ordinary kriging (OK), kriging with external drift (KED), where the spatial pattern of surface velocity is used as a proxy for that of dHdt, and their spatiotemporal equivalents (ST-OK and ST-KED).

  16. Soil Surface Moisture from Cryosat2 and Sentinel-3 Satellite Radar Altimetry

    NASA Astrophysics Data System (ADS)

    Berry, P. A. M.; Balmbra, R.

    2016-08-01

    Measuring soil moisture using remote sensing techniques has been a key application for many years; however, these techniques encounter difficulties in arid and semi-arid terrain. Satellite altimetry presents an attractive option for retrieval of soil surface moisture in these areas [1:2]. Surface soil moisture has now been successfully retrieved from Cryosat2 data as part of the EU LOTUS project; the key to retrieving accurate soil surface moisture estimates is the development of very detailed Dry Earth Models (DREAMS). Soil moisture time series have been derived from Cryosat2 and Jason2 data over the Simpson, Tenere and Kalahari deserts; cross-comparison of the results and validation with independent remote sensed soil moisture data is presented. These results show that the detailed along- track estimates that can be achieved from satellite radar altimetry have a unique contribution to make to soil moisture retrieval in arid and semi-arid terrain.

  17. Determination of Interannual to Decadal Changes in Ice Sheet Mass Balance from Satellite Altimetry

    NASA Technical Reports Server (NTRS)

    Zwally, H. Jay; Busalacchi, Antonioa J. (Technical Monitor)

    2001-01-01

    A major uncertainty in predicting sea level rise is the sensitivity of ice sheet mass balance to climate change, as well as the uncertainty in present mass balance. Since the annual water exchange is about 8 mm of global sea level equivalent, the +/- 25% uncertainty in current mass balance corresponds to +/- 2 mm/yr in sea level change. Furthermore, estimates of the sensitivity of the mass balance to temperature change range from perhaps as much as - 10% to + 10% per K. Although the overall ice mass balance and seasonal and inter-annual variations can be derived from time-series of ice surface elevations from satellite altimetry, satellite radar altimeters have been limited in spatial coverage and elevation accuracy. Nevertheless, new data analysis shows mixed patterns of ice elevation increases and decreases that are significant in terms of regional-scale mass balances. In addition, observed seasonal and interannual variations in elevation demonstrate the potential for relating the variability in mass balance to changes in precipitation, temperature, and melting. From 2001, NASA's ICESat laser altimeter mission will provide significantly better elevation accuracy and spatial coverage to 86 deg latitude and to the margins of the ice sheets. During 3 to 5 years of ICESat-1 operation, an estimate of the overall ice sheet mass balance and sea level contribution will be obtained. The importance of continued ice monitoring after the first ICESat is illustrated by the variability in the area of Greenland surface melt observed over 17-years and its correlation with temperature. In addition, measurement of ice sheet changes, along with measurements of sea level change by a series of ocean altimeters, should enable direct detection of ice level and global sea level correlations.

  18. An inversion method for retrieving soil moisture information from satellite altimetry observations

    NASA Astrophysics Data System (ADS)

    Uebbing, Bernd; Forootan, Ehsan; Kusche, Jürgen; Braakmann-Folgmann, Anne

    2016-04-01

    Soil moisture represents an important component of the terrestrial water cycle that controls., evapotranspiration and vegetation growth. Consequently, knowledge on soil moisture variability is essential to understand the interactions between land and atmosphere. Yet, terrestrial measurements are sparse and their information content is limited due to the large spatial variability of soil moisture. Therefore, over the last two decades, several active and passive radar and satellite missions such as ERS/SCAT, AMSR, SMOS or SMAP have been providing backscatter information that can be used to estimate surface conditions including soil moisture which is proportional to the dielectric constant of the upper (few cm) soil layers . Another source of soil moisture information are satellite radar altimeters, originally designed to measure sea surface height over the oceans. Measurements of Jason-1/2 (Ku- and C-Band) or Envisat (Ku- and S-Band) nadir radar backscatter provide high-resolution along-track information (~ 300m along-track resolution) on backscatter every ~10 days (Jason-1/2) or ~35 days (Envisat). Recent studies found good correlation between backscatter and soil moisture in upper layers, especially in arid and semi-arid regions, indicating the potential of satellite altimetry both to reconstruct and to monitor soil moisture variability. However, measuring soil moisture using altimetry has some drawbacks that include: (1) the noisy behavior of the altimetry-derived backscatter (due to e.g., existence of surface water in the radar foot-print), (2) the strong assumptions for converting altimetry backscatters to the soil moisture storage changes, and (3) the need for interpolating between the tracks. In this study, we suggest a new inversion framework that allows to retrieve soil moisture information from along-track Jason-2 and Envisat satellite altimetry data, and we test this scheme over the Australian arid and semi-arid regions. Our method consists of: (i

  19. Laser altimetry reveals complex pattern of Greenland Ice Sheet dynamics.

    PubMed

    Csatho, Beata M; Schenk, Anton F; van der Veen, Cornelis J; Babonis, Gregory; Duncan, Kyle; Rezvanbehbahani, Soroush; van den Broeke, Michiel R; Simonsen, Sebastian B; Nagarajan, Sudhagar; van Angelen, Jan H

    2014-12-30

    We present a new record of ice thickness change, reconstructed at nearly 100,000 sites on the Greenland Ice Sheet (GrIS) from laser altimetry measurements spanning the period 1993-2012, partitioned into changes due to surface mass balance (SMB) and ice dynamics. We estimate a mean annual GrIS mass loss of 243 ± 18 Gt ⋅ y(-1), equivalent to 0.68 mm ⋅ y(-1) sea level rise (SLR) for 2003-2009. Dynamic thinning contributed 48%, with the largest rates occurring in 2004-2006, followed by a gradual decrease balanced by accelerating SMB loss. The spatial pattern of dynamic mass loss changed over this time as dynamic thinning rapidly decreased in southeast Greenland but slowly increased in the southwest, north, and northeast regions. Most outlet glaciers have been thinning during the last two decades, interrupted by episodes of decreasing thinning or even thickening. Dynamics of the major outlet glaciers dominated the mass loss from larger drainage basins, and simultaneous changes over distances up to 500 km are detected, indicating climate control. However, the intricate spatiotemporal pattern of dynamic thickness change suggests that, regardless of the forcing responsible for initial glacier acceleration and thinning, the response of individual glaciers is modulated by local conditions. Recent projections of dynamic contributions from the entire GrIS to SLR have been based on the extrapolation of four major outlet glaciers. Considering the observed complexity, we question how well these four glaciers represent all of Greenland's outlet glaciers.

  20. Undersea volcano production versus lithospheric strength from satellite altimetry

    NASA Technical Reports Server (NTRS)

    Tapley, B. D.; Sandwell, D. T.

    1986-01-01

    All seamount signatures apparent in the SEASAT altimeter profiles were located and digitized. In addition to locating the seamount signatures, their amplitudes were also estimated. The second phase consisted of determining what basic characteristics of a seamount can be extracted from a single vertical deflection profile. Seven seamounts that had both good bathymetric coverage and good satellite altimeter coverage were used to test a simple flexural model. A method was developed to combine satellite altimeter profiles from several different satellites to construct a detailed and accurate geoid.

  1. Mapping the grounding zone of Ross Ice Shelf using ICESat laser altimetry

    USGS Publications Warehouse

    Brunt, Kelly M.; Fricker, Helen A.; Padman, Laurie; Scambos, Ted A.; O'Neel, Shad

    2010-01-01

    We use laser altimetry from the Ice, Cloud, and land Elevation Satellite (ICESat) to map the grounding zone (GZ) of the Ross Ice Shelf, Antarctica, at 491 locations where ICESat tracks cross the grounding line (GL). Ice flexure in the GZ occurs as the ice shelf responds to short-term sea-level changes due primarily to tides. ICESat repeat-track analysis can be used to detect this region of flexure since each repeated pass is acquired at a different tidal phase; the technique provides estimates for both the landward limit of flexure and the point where the ice becomes hydrostatically balanced. We find that the ICESat-derived landward limits of tidal flexure are, in many places, offset by several km (and up to ∼60 km) from the GL mapped previously using other satellite methods. We discuss the reasons why different mapping methods lead to different GL estimates, including: instrument limitations; variability in the surface topographic structure of the GZ; and the presence of ice plains. We conclude that reliable and accurate mapping of the GL is most likely to be achieved when based on synthesis of several satellite datasets

  2. Refinements in the Combined Adjustment of Satellite Altimetry and Gravity Anomaly Data

    DTIC Science & Technology

    1977-07-12

    of the areas covered by the GEOS-3 satellite when compared with the earlier reported results of the AFGL computer program SARRA ^(Short Arc Reduc...in the partial derivatives may be illustrated as follows. A small set of satellite altimetry data was adjusted by the AFGL program SARRA (Short Arc...1 l+2^(a/rf 2^(C cos mX + S sin mX)P ( sine ) n^2v m=0 nm nm nm i + h u>2r0r 3 co326/(kM) , (4.1) which yields dr (r0/r oo n )^n(a

  3. From Outlet Glacier Changes to Ice Sheet Mass Balance - Evolution of Greenland Ice Sheet from Laser Altimetry Data

    NASA Astrophysics Data System (ADS)

    Csatho, B. M.; Schenk, A.; Nagarajan, S.; Babonis, G. S.

    2010-12-01

    Investigations of ice sheet mass balance and the changing dynamics of outlet glaciers have been hampered by the lack of comprehensive data. In recent years, this situation has been remedied. Satellite laser altimetry data from the Ice Cloud and land Elevation Satellite mission (ICESat), combined with airborne laser altimetry, provide accurate measurements of surface elevation changes, and surface velocities derived from various satellite platforms yield crucial information on changing glacier dynamics. Taken together, a rich and diverse data set is emerging that allows for characterizing the spatial and temporal evolution of ice sheets and outlet glaciers. In particular, it enables quantitative studies of outlet glaciers undergoing rapid and complex changes. Although airborne and laser altimetry have been providing precise measurements of ice sheet topography since the early 1990s, determining detailed and accurate spatial and temporal distribution of surface changes remains a challenging problem. We have developed a new, comprehensive method, called Surface Elevation Reconstruction And Change detection (SERAC), which estimates surface changes by a simultaneous reconstruction of surface topography from fused multisensor data. The mathematical model is based on the assumption that for a small surface area, only the absolute elevation changes over time but not the shape of the surface patch. Therefore, laser points of all time epochs contribute to the shape parameters; points of each time period determine the absolute elevation of the surface patch at that period. This method provides high-resolution surface topography, precise changes and a rigorous error estimate of the quantities. By using SERAC we combined ICESat and ATM laser altimetry data to determine the evolution of surface change rates of the whole Greenland Ice Sheet between 2003 and 2009 on a high-resolution grid. Our reconstruction, consistent with GRACE results, shows ice sheet thinning propagating

  4. Satellite altimetry and hydrologic modeling of poorly-gauged tropical watershed

    NASA Astrophysics Data System (ADS)

    Sulistioadi, Yohanes Budi

    Fresh water resources are critical for daily human consumption. Therefore, a continuous monitoring effort over their quantity and quality is instrumental. One important model for water quantity monitoring is the rainfall-runoff model, which represents the response of a watershed to the variability of precipitation, thus estimating the discharge of a channel (Bedient and Huber, 2002, Beven, 2012). Remote sensing and satellite geodetic observations are capable to provide critical hydrological parameters, which can be used to support hydrologic modeling. For the case of satellite radar altimetry, limited temporal resolutions (e.g., satellite revisit period) prohibit the use of this method for a short (less than weekly) interval monitoring of water level or discharge. On the other hand, the current satellite radar altimeter footprints limit the water level measurement for rivers wider than 1 km (Birkett, 1998, Birkett et al., 2002). Some studies indeed reported successful retrieval of water level for small-size rivers as narrow as 80 m (Kuo and Kao, 2011, Michailovsky et al., 2012); however, the processing of current satellite altimetry signals for small water bodies to retrieve accurate water levels, remains challenging. To address this scientific challenge, this study poses two main objectives: (1) to monitor small (40--200 m width) and medium-sized (200--800 m width) rivers and lakes using satellite altimetry through identification and choice of the over-water radar waveforms corresponding to the appropriately waveform-retracked water level; and (2) to develop a rainfall-runoff hydrological model to represent the response of mesoscale watershed to the variability of precipitation. Both studies address the humid tropics of Southeast Asia, specifically in Indonesia, where similar studies do not yet exist. This study uses the Level 2 radar altimeter measurements generated by European Space Agency's (ESA's) Envisat (Environmental Satellite) mission. The first study

  5. Satellite Altimetry And Radiometry for Inland Hydrology, Coastal Sea-Level And Environmental Studies

    NASA Astrophysics Data System (ADS)

    Tseng, Kuo-Hsin

    In this study, we demonstrate three environmental-related applications employing altimetry and remote sensing satellites, and exemplify the prospective usage underlying the current progressivity in mechanical and data analyzing technologies. Our discussion starts from the improved waveform retracking techniques in need for altimetry measurements over coastal and inland water regions. We developed two novel auxiliary procedures, namely the Subwaveform Filtering (SF) method and the Track Offset Correction (TOC), for waveform retracking algorithms to operationally detect altimetry waveform anomalies and further reduce possible errors in determination of the track offset. After that, we present two demonstrative studies related to the ionospheric and tropospheric compositions, respectively, as their variations are the important error sources for satellite electromagnetic signals. We firstly compare the total electron content (TEC) measured by multiple altimetry and GNSS sensors. We conclude that the ionosphere delay measured by Jason-2 is about 6-10 mm shorter than the GPS models. On the other hand, we use several atmospheric variables to study the climate change over high elevation areas. Five types of satellite data and reanalysis models were used to study climate change indicators. We conclude that the spatial distribution of temperature trend among data products is quite different, which is probably due to the choice of various time spans. Following discussions about the measuring techniques and relative bias between data products, we applied our improved altimetry techniques to three environmental science applications with helps of remote sensing imagery. We first manifest the detectability of hydrological events by satellite altimetry and radiometry. The characterization of one-dimensional (along-track) water boundary using former Backscattering Coefficient (BC) method is assisted by the two-dimensional (horizontal) estimate of water extent using the Moderate

  6. Satellite Altimetry-Based Sea Level at Global and Regional Scales

    NASA Astrophysics Data System (ADS)

    Ablain, M.; Legeais, J. F.; Prandi, P.; Marcos, M.; Fenoglio-Marc, L.; Dieng, H. B.; Benveniste, J.; Cazenave, A.

    2017-01-01

    Since the beginning of the 1990s, sea level is routinely measured using high-precision satellite altimetry. Over the past 25 years, several groups worldwide involved in processing the satellite altimetry data regularly provide updates of sea level time series at global and regional scales. Here we present an ongoing effort supported by the European Space Agency (ESA) Climate Change Initiative Programme for improving the altimetry-based sea level products. Two main objectives characterize this enterprise: (1) to make use of ESA missions (ERS-1 and 2 and Envisat) in addition to the so-called `reference' missions like TOPEX/Poseidon and the Jason series in the computation of the sea level time series, and (2) to improve all processing steps in order to meet the Global Climate Observing System (GCOS) accuracy requirements defined for a set of 50 Essential Climate Variables, sea level being one of them. We show that improved geophysical corrections, dedicated processing algorithms, reduction of instrumental bias and drifts, and careful linkage between missions led to improved sea level products. Regarding the long-term trend, the new global mean sea level record accuracy now approaches the GCOS requirements (of 0.3 mm/year). Regional trend uncertainty has been reduced by a factor of 2, but orbital and wet tropospheric corrections errors still prevent fully reaching the GCOS accuracy requirement. Similarly at the interannual time scale, the global mean sea level still displays 2-4 mm errors that are not yet fully understood. The recent launch of new altimetry missions (Sentinel-3, Jason-3) and the inclusion of data from currently flying missions (e.g., CryoSat, SARAL/AltiKa) may provide further improvements to this important climate record.

  7. Laser altimetry reveals complex pattern of Greenland Ice Sheet dynamics

    PubMed Central

    Csatho, Beata M.; Schenk, Anton F.; van der Veen, Cornelis J.; Babonis, Gregory; Duncan, Kyle; Rezvanbehbahani, Soroush; van den Broeke, Michiel R.; Simonsen, Sebastian B.; Nagarajan, Sudhagar; van Angelen, Jan H.

    2014-01-01

    We present a new record of ice thickness change, reconstructed at nearly 100,000 sites on the Greenland Ice Sheet (GrIS) from laser altimetry measurements spanning the period 1993–2012, partitioned into changes due to surface mass balance (SMB) and ice dynamics. We estimate a mean annual GrIS mass loss of 243 ± 18 Gt⋅y−1, equivalent to 0.68 mm⋅y−1 sea level rise (SLR) for 2003–2009. Dynamic thinning contributed 48%, with the largest rates occurring in 2004–2006, followed by a gradual decrease balanced by accelerating SMB loss. The spatial pattern of dynamic mass loss changed over this time as dynamic thinning rapidly decreased in southeast Greenland but slowly increased in the southwest, north, and northeast regions. Most outlet glaciers have been thinning during the last two decades, interrupted by episodes of decreasing thinning or even thickening. Dynamics of the major outlet glaciers dominated the mass loss from larger drainage basins, and simultaneous changes over distances up to 500 km are detected, indicating climate control. However, the intricate spatiotemporal pattern of dynamic thickness change suggests that, regardless of the forcing responsible for initial glacier acceleration and thinning, the response of individual glaciers is modulated by local conditions. Recent projections of dynamic contributions from the entire GrIS to SLR have been based on the extrapolation of four major outlet glaciers. Considering the observed complexity, we question how well these four glaciers represent all of Greenland’s outlet glaciers. PMID:25512537

  8. The Use of Laser Altimetry in the Orbit and Attitude Determination of Mars Global Surveyor

    NASA Technical Reports Server (NTRS)

    Rowlands, D. D.; Pavlis, D. E.; Lemoine, F. G.; Neumann, G. A.; Luthcke, S. B.

    1999-01-01

    Altimetry from the Mars Observer Laser Altimeter (MOLA) which is carried on board Mars Global Surveyor (MGS) has been analyzed for the period of the MOS mission known as Science Phasing Orbit 1 (SPO-1). We have used these altimeter ranges to improve orbit and attitude knowledge for MGS. This has been accomplished by writing crossover constraint equations that have been derived from short passes of MOLA data. These constraint equations differ from traditional Crossover constraints and exploit the small foot print associated with laser altimetry.

  9. Comments on ocean circulation with regard to satellite altimetry

    NASA Technical Reports Server (NTRS)

    Sturges, W.

    1972-01-01

    Basic features of sea surface topography are reviewed, to show those oceanographic results which may be of value to a geodetic satellite program: (1) the shape and magnitude of the large scale features of the mean sea surface, relative to a level surface; (2) the position and magnitude of the slopes across the western boundary currents, from a variety of data; (3) an estimate of the position of the geoid, tied into the U.S. leveling network; and (4) a documented change of 60 to 70 cm in mean sea level, with respect to the geoid, between the U.S. east and west coasts.

  10. Study of radar pulse compression for high resolution satellite altimetry

    NASA Technical Reports Server (NTRS)

    Dooley, R. P.; Nathanson, F. E.; Brooks, L. W.

    1974-01-01

    Pulse compression techniques are studied which are applicable to a satellite altimeter having a topographic resolution of + 10 cm. A systematic design procedure is used to determine the system parameters. The performance of an optimum, maximum likelihood processor is analysed, which provides the basis for modifying the standard split-gate tracker to achieve improved performance. Bandwidth considerations lead to the recommendation of a full deramp STRETCH pulse compression technique followed by an analog filter bank to separate range returns. The implementation of the recommended technique is examined.

  11. Reconfigurable Computing As an Enabling Technology for Single-Photon-Counting Laser Altimetry

    NASA Technical Reports Server (NTRS)

    Powell, Wesley; Hicks, Edward; Pinchinat, Maxime; Dabney, Philip; McGarry, Jan; Murray, Paul

    2003-01-01

    Single-photon-counting laser altimetry is a new measurement technique offering significant advantages in vertical resolution, reducing instrument size, mass, and power, and reducing laser complexity as compared to analog or threshold detection laser altimetry techniques. However, these improvements come at the cost of a dramatically increased requirement for onboard real-time data processing. Reconfigurable computing has been shown to offer considerable performance advantages in performing this processing. These advantages have been demonstrated on the Multi-KiloHertz Micro-Laser Altimeter (MMLA), an aircraft based single-photon-counting laser altimeter developed by NASA Goddard Space Flight Center with several potential spaceflight applications. This paper describes how reconfigurable computing technology was employed to perform MMLA data processing in real-time under realistic operating constraints, along with the results observed. This paper also expands on these prior results to identify concepts for using reconfigurable computing to enable spaceflight single-photon-counting laser altimeter instruments.

  12. Mass Balance Changes and Ice Dynamics of Greenland and Antarctic Ice Sheets from Laser Altimetry

    NASA Astrophysics Data System (ADS)

    Babonis, G. S.; Csatho, B.; Schenk, T.

    2016-06-01

    During the past few decades the Greenland and Antarctic ice sheets have lost ice at accelerating rates, caused by increasing surface temperature. The melting of the two big ice sheets has a big impact on global sea level rise. If the ice sheets would melt down entirely, the sea level would rise more than 60 m. Even a much smaller rise would cause dramatic damage along coastal regions. In this paper we report about a major upgrade of surface elevation changes derived from laser altimetry data, acquired by NASA's Ice, Cloud and land Elevation Satellite mission (ICESat) and airborne laser campaigns, such as Airborne Topographic Mapper (ATM) and Land, Vegetation and Ice Sensor (LVIS). For detecting changes in ice sheet elevations we have developed the Surface Elevation Reconstruction And Change detection (SERAC) method. It computes elevation changes of small surface patches by keeping the surface shape constant and considering the absolute values as surface elevations. We report about important upgrades of earlier results, for example the inclusion of local ice caps and the temporal extension from 1993 to 2014 for the Greenland Ice Sheet and for a comprehensive reconstruction of ice thickness and mass changes for the Antarctic Ice Sheets.

  13. Measuring Ganymede's Tidal Deformation by Laser Altimetry: A performance Analysis for the GALA Experiment

    NASA Astrophysics Data System (ADS)

    Steinbrügge, G.; Hussmann, H.; Stark, A.; Sohl, F.; Oberst, J.

    2015-12-01

    Since measurements of Ganymede's induced magnetic field suggest a salty water layer underneath the satellite's icy crust [1], we studied the perspectives for the Ganymede Laser Altimeter (GALA) onboard ESA's JUICE mission to infer the ice-I thickness by measuring the dynamic response of Ganymede's ice shell to tidal forces exerted by Jupiter. We found that the uncertainties in the determination of the tidal Lover number h2 is 2% and we will demonstrate that this will constrain the ice-I thickness to ± 20 km. Our model also includes a detailed analysis of the instrument performance taking account of Ganymede's rough small-scale topography. The model is combined with the current mission scenario and spacecraft performance expectation of the JUICE mission giving an estimate for the accuracy of the range measurements in Ganymede orbit. However, the determination of the resulting ice thickness further depends on the tidally effective rheology of the outer ice shell [2]. Laboratory measurements of ice I (e.g. [3]) suggest that the rigidity can be constrained, however, the less well known viscosity can play a major role when inferring the thickness of the outer ice shell. As a consequence we further investigated under which conditions the ice I viscosity could be constrained by measuring the phase-lag of Ganymede's tidal response using laser altimetry. [1] Kivelson et al. 2002. [2] Moore and Schubert, 2003. [3] Sotin et al., 1998

  14. Non-Stationary Internal Tides Observed with Satellite Altimetry

    NASA Technical Reports Server (NTRS)

    Ray, Richard D.; Zaron, E. D.

    2011-01-01

    Temporal variability of the internal tide is inferred from a 17-year combined record of Topex/Poseidon and Jason satellite altimeters. A global sampling of along-track sea-surface height wavenumber spectra finds that non-stationary variance is generally 25% or less of the average variance at wavenumbers characteristic of mode-l tidal internal waves. With some exceptions the non-stationary variance does not exceed 0.25 sq cm. The mode-2 signal, where detectable, contains a larger fraction of non-stationary variance, typically 50% or more. Temporal subsetting of the data reveals interannual variability barely significant compared with tidal estimation error from 3-year records. Comparison of summer vs. winter conditions shows only one region of noteworthy seasonal changes, the northern South China Sea. Implications for the anticipated SWOT altimeter mission are briefly discussed.

  15. Bottom Pressure Tides Along a Line in the Southeast Atlantic Ocean and Comparisons with Satellite Altimetry

    NASA Technical Reports Server (NTRS)

    Ray, Richard D.; Byrne, Deidre A.

    2010-01-01

    Seafloor pressure records, collected at 11 stations aligned along a single ground track of the Topex/Poseidon and Jason satellites, are analyzed for their tidal content. With very low background noise levels and approximately 27 months of high-quality records, tidal constituents can be estimated with unusually high precision. This includes many high-frequency lines up through the seventh-diurnal band. The station deployment provides a unique opportunity to compare with tides estimated from satellite altimetry, point by point along the satellite track, in a region of moderately high mesoscale variability. That variability can significantly corrupt altimeter-based tide estimates, even with 17 years of data. A method to improve the along-track altimeter estimates by correcting the data for nontidal variability is found to yield much better agreement with the bottom-pressure data. The technique should prove useful in certain demanding applications, such as altimetric studies of internal tides.

  16. Contribution of Satellite Altimetry Data in Geological Structure Research in the South China Sea

    NASA Astrophysics Data System (ADS)

    Dung Tran, Tuan; Ho, Thi Huong Mai

    2016-06-01

    The study area is bordered on the East China Sea, the Philippine Sea, and the Australian-Indo plate in the Northeast, in the East and in the South, respectively. It is a large area with the diversely complicated conditions of geological structure. In spite of over the past many years of investigation, marine geological structure in many places have remained poorly understood because of a thick seawater layer as well as of the sensitive conflicts among the countries in the region. In recent years, the satellite altimeter technology allows of enhancement the marine investigation in any area. The ocean surface height is measured by a very accurate radar altimeter mounted on a satellite. Then, that surface can be converted into marine gravity anomaly or bathymetry by using the mathematical model. It is the only way to achieve the data with a uniform resolution in acceptable time and cost. The satellite altimetry data and its variants are essential for understanding marine geological structure. They provide a reliable opportunity to geologists and geophysicists for studying the geological features beneath the ocean floor. Also satellite altimeter data is perfect for planning the more detailed shipboard surveys. Especially, it is more meaningful in the remote or sparsely surveyed regions. In this paper, the authors have effectively used the satellite altimetry and shipboard data in combination. Many geological features, such as seafloor spreading ridges, fault systems, volcanic chains as well as distribution of sedimentary basins are revealed through the 2D, 3D model methods of interpretation of satellite-shipboard-derived data and the others. These results are improved by existing boreholes and seismic data in the study area.

  17. Mapping the nonstationary internal tide with satellite altimetry

    NASA Astrophysics Data System (ADS)

    Zaron, Edward D.

    2017-01-01

    Temporal variability of the internal tide has been inferred from the 23 year long combined records of the TOPEX/Poseidon, Jason-1, and Jason-2 satellite altimeters by combining harmonic analysis with an analysis of along-track wavenumber spectra of sea-surface height (SSH). Conventional harmonic analysis is first applied to estimate and remove the stationary components of the tide at each point along the reference ground tracks. The wavenumber spectrum of the residual SSH is then computed, and the variance in a neighborhood around the wavenumber of the mode-1 baroclinic M2 tide is interpreted as the sum of noise, broadband nontidal processes, and the nonstationary tide. At many sites a bump in the spectrum associated with the internal tide is noted, and an empirical model for the noise and nontidal processes is used to estimate the nonstationary semidiurnal tidal variance. The results indicate a spatially inhomogeneous pattern of tidal variability. Nonstationary tides are larger than stationary tides throughout much of the equatorial Pacific and Indian Oceans.

  18. Satellite Altimetry: A Revolution in Understanding the Wave Climate

    NASA Astrophysics Data System (ADS)

    Challenor, P.; Woolf, D.; Gommenginger, C.; Srokosz, M.; Cotton, D.; Carter, D.; Sykes, N.

    2006-07-01

    Before the advent of radar altimeters our understanding of the world's climate was based on a few instruments moored off the coats of Europe, Japan and North America and visual observations taken from merchant ships. This information was patchy and in many cases of poor quality. It was difficult to relate what was happening at one location with another. The advent of the radar altimeter has changed all that. We had a series of satellite instruments that made consistent measurements of significant wave height across the globe. Initial work concentrated on simply mapping the wave climate and investigating means and seasonal variation. However with longer records came the ability to look at inter-annual variability. It had been known since the late 70's that wave heights measured at a few sites around the North East Atlantic had shown a dramatic increase. It was only the combination of spatial and temporal sampling from the altimeter that allowed us to discover the extent of the changes and how they related to the North Atlantic Oscillation index. Of course it is not only the mean wave conditions that are important, extreme waves are of vital interest to naval architects and the designers of offshore structures. Being able to estimate extreme waves from altimeter data enables us for the first time to establish what extreme conditions might be in any part of the world. At present we do not exploit the spatial nature of the altimeter data in our estimation of the extremes but this is an active research area. Research into further uses of altimeter data for looking at the wave climate continues apace. Algorithms for new parameters such as wave period are being developed. Real time applications are appearing. For such applications space- time sampling is an issue and people are coming up with innovative ideas using constellations of cheap altimeters. In this paper we review the progress made in the study of wave climate using the radar altimeter. In addition we look into

  19. Mapping the Topography of Mercury with MESSENGER Laser Altimetry

    NASA Technical Reports Server (NTRS)

    Sun, Xiaoli; Cavanaugh, John F.; Neumann, Gregory A.; Smith, David E..; Zubor, Maria T.

    2012-01-01

    The Mercury Laser Altimeter onboard MESSENGER involves unique design elements that deal with the challenges of being in orbit around Mercury. The Mercury Laser Altimeter (MLA) is one of seven instruments on NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. MESSENGER was launched on 3 August 2004, and entered into orbit about Mercury on 18 March 2011 after a journey through the inner solar system. This involved six planetary flybys, including three of Mercury. MLA is designed to map the topography and landforms of Mercury's surface. It also measures the planet's forced libration (motion about the spin axis), which helps constrain the state of the core. The first science measurements from orbit taken with MLA were made on 29 March 2011 and continue to date. MLA had accumulated about 8.3 million laser ranging measurements to Mercury's surface, as of 31 July 2012, i.e., over six Mercury years (528 Earth days). Although MLA is the third planetary lidar built at the NASA Goddard Space Flight Center (GSFC), MLA must endure a much harsher thermal environment near Mercury than the previous instruments on Mars and Earth satellites. The design of MLA was derived in part from that of the Mars Orbiter Laser Altimeter on Mars Global Surveyor. However, MLA must range over greater distances and often in off-nadir directions from a highly eccentric orbit. In MLA we use a single-mode diode-pumped Nd:YAG (neodymium-doped yttrium aluminum garnet) laser that is highly collimated to maintain a small footprint on the planet. The receiver has both a narrow field of view and a narrow spectral bandwidth to minimize the amount of background light detected from the sunlit hemisphere of Mercury. We achieve the highest possible receiver sensitivity by employing the minimum receiver detection threshold.

  20. A multi-source satellite data approach for modelling Lake Turkana water level: Calibration and validation using satellite altimetry data

    USGS Publications Warehouse

    Velpuri, N.M.; Senay, G.B.; Asante, K.O.

    2012-01-01

    Lake Turkana is one of the largest desert lakes in the world and is characterized by high degrees of interand intra-annual fluctuations. The hydrology and water balance of this lake have not been well understood due to its remote location and unavailability of reliable ground truth datasets. Managing surface water resources is a great challenge in areas where in-situ data are either limited or unavailable. In this study, multi-source satellite-driven data such as satellite-based rainfall estimates, modelled runoff, evapotranspiration, and a digital elevation dataset were used to model Lake Turkana water levels from 1998 to 2009. Due to the unavailability of reliable lake level data, an approach is presented to calibrate and validate the water balance model of Lake Turkana using a composite lake level product of TOPEX/Poseidon, Jason-1, and ENVISAT satellite altimetry data. Model validation results showed that the satellitedriven water balance model can satisfactorily capture the patterns and seasonal variations of the Lake Turkana water level fluctuations with a Pearson's correlation coefficient of 0.90 and a Nash-Sutcliffe Coefficient of Efficiency (NSCE) of 0.80 during the validation period (2004-2009). Model error estimates were within 10% of the natural variability of the lake. Our analysis indicated that fluctuations in Lake Turkana water levels are mainly driven by lake inflows and over-the-lake evaporation. Over-the-lake rainfall contributes only up to 30% of lake evaporative demand. During the modelling time period, Lake Turkana showed seasonal variations of 1-2m. The lake level fluctuated in the range up to 4m between the years 1998-2009. This study demonstrated the usefulness of satellite altimetry data to calibrate and validate the satellite-driven hydrological model for Lake Turkana without using any in-situ data. Furthermore, for Lake Turkana, we identified and outlined opportunities and challenges of using a calibrated satellite-driven water balance

  1. Assessment of NASA airborne laser altimetry data using ground-based GPS data near Summit Station, Greenland

    NASA Astrophysics Data System (ADS)

    Brunt, Kelly M.; Hawley, Robert L.; Lutz, Eric R.; Studinger, Michael; Sonntag, John G.; Hofton, Michelle A.; Andrews, Lauren C.; Neumann, Thomas A.

    2017-03-01

    A series of NASA airborne lidars have been used in support of satellite laser altimetry missions. These airborne laser altimeters have been deployed for satellite instrument development, for spaceborne data validation, and to bridge the data gap between satellite missions. We used data from ground-based Global Positioning System (GPS) surveys of an 11 km long track near Summit Station, Greenland, to assess the surface-elevation bias and measurement precision of three airborne laser altimeters including the Airborne Topographic Mapper (ATM), the Land, Vegetation, and Ice Sensor (LVIS), and the Multiple Altimeter Beam Experimental Lidar (MABEL). Ground-based GPS data from the monthly ground-based traverses, which commenced in 2006, allowed for the assessment of nine airborne lidar surveys associated with ATM and LVIS between 2007 and 2016. Surface-elevation biases for these altimeters - over the flat, ice-sheet interior - are less than 0.12 m, while assessments of measurement precision are 0.09 m or better. Ground-based GPS positions determined both with and without differential post-processing techniques provided internally consistent solutions. Results from the analyses of ground-based and airborne data provide validation strategy guidance for the Ice, Cloud, and land Elevation Satellite 2 (ICESat-2) elevation and elevation-change data products.

  2. Hurricane Sandy storm surges observed by HY-2A satellite altimetry and tide gauges

    NASA Astrophysics Data System (ADS)

    Chen, Nan; Han, Guoqi; Yang, Jingsong; Chen, Dake

    2014-07-01

    Hurricane Sandy made landfall to the northeast of Atlantic City, New Jersey at 23:30 UTC on 29 October 2012 and caused large storm surges and devastating flooding along the New Jersey and New York coasts. Here we combine sea surface height measurements from the HaiYang-2A (HY-2A) satellite altimeter with coastal tide-gauge data to study the features of the Hurricane Sandy storm surges. The HY-2A altimeter captured the cross-shelf profile of surge at the time of Sandy's peak surge, with a surge magnitude of about 1.83 m at the coast and a cross-shelf decaying scale of 68 km. The altimetric surge magnitude agrees approximately with tide-gauge estimate of 1.73 m at nearby Montauk. Further analysis suggests that continental shelf waves were generated during the passage of Sandy. The continental shelf wave observed by altimetry has a propagating speed of 6.5 m/s. The post landfall free shelf wave at Atlantic City observed by tide gauges has a propagating phase speed of 6.8 m/s and cross-shelf e-folding scale of 75 km. In contrast, the post landfall sea level oscillation at Montauk is not associated with a continental shelf wave. The study indicates that satellite altimetry is capable of observing and useful for understanding features of storm surges, complementing existing coastal tide gauges.

  3. Investigation Seasonal and Interannual Variability of the Caspian Sea Dynamics Based on Satellite Altimetry Data

    NASA Astrophysics Data System (ADS)

    Lebedev, Sergey A.

    2016-08-01

    The investigation is devoted to the study of the variability of the dynamics of the Caspian Sea based on TOPEX/Poseidon and Jason-1/2 satellites altimetry data. The technique of calculating the synoptic dynamic topography (DT) as a superposition of the mean sea climate DT calculated by thermohydrodynamic models and field of sea level anomalies calculated by satellite altimetry data is considered. An analysis of the geostrophic currents vorticity confirmed the predominance of cyclonic circulation in the Northern and Middle Caspian and anticyclonic in the Southern. Analysis of variation of average velocity and vorticity shows that the average velocity is inversely proportional to the vorticity. Since 1993 to 2007. vorticity rose at a rate of -0,17±0,02·10-7 per year, and average velocity has increased at rate of +0,11±0,06 cm/year. After 2008 the situation has changed to the opposite. The vorticity has increased at a rate +0,75±0,12·10-7 per year, average velocity rose at rate of -0,47±0,19 cm/year.

  4. The 26 December 2004 tsunami source estimated from satellite radar altimetry and seismic waves

    NASA Technical Reports Server (NTRS)

    Song, Tony Y.; Ji, Chen; Fu, L. -L.; Zlotnicki, Victor; Shum, C. K.; Yi, Yuchan; Hjorleifsdottir, Vala

    2005-01-01

    The 26 December 2004 Indian Ocean tsunami was the first earthquake tsunami of its magnitude to occur since the advent of both digital seismometry and satellite radar altimetry. Both have independently recorded the event from different physical aspects. The seismic data has then been used to estimate the earthquake fault parameters, and a three-dimensional ocean-general-circulation-model (OGCM) coupled with the fault information has been used to simulate the satellite-observed tsunami waves. Here we show that these two datasets consistently provide the tsunami source using independent methodologies of seismic waveform inversion and ocean modeling. Cross-examining the two independent results confirms that the slip function is the most important condition controlling the tsunami strength, while the geometry and the rupture velocity of the tectonic plane determine the spatial patterns of the tsunami.

  5. Constraints on Energy Dissipation in the Earth's Body Tide From Satellite Tracking and Altimetry

    NASA Technical Reports Server (NTRS)

    Ray, Richard D.; Eanes, Richard J.; Lemoine, Frank G.

    1992-01-01

    The phase lag by which the earth's body tide follows the tidal potential is estimated for the principal lunar semidiurnal tide M(sub 2). The estimate results from combining recent tidal solutions from satellite tracking data and from Topex/Poseidon satellite altimeter data. Each data type is sensitive to the body-tide lag: gravitationally for the tracking data, geometrically for the altimetry. Allowance is made for the lunar atmospheric tide. For the tidal potential Love number kappa(sub 2) we obtain a lag epsilon of 0.20 deg +/- 0.05 deg, implying an effective body-tide Q of 280 and body-tide energy dissipation of 110 +/- 25 gigawatts.

  6. Water volume change in the lower Mekong from satellite altimetry and imagery data

    NASA Astrophysics Data System (ADS)

    Frappart, F.; Minh, K. Do; L'Hermitte, J.; Cazenave, A.; Ramillien, G.; Le Toan, T.; Mognard-Campbell, N.

    2006-11-01

    We have analysed satellite altimetry data from the ERS-2, ENVISAT and Topex/Poseidon satellites to construct water level time-series over a 8 yr period (from 1996 April to 2004 April) over the lower Mekong river basin. The study area includes the Tonle Sap Lake, seasonally inundated areas and several branches of the hydrographic network of the Mekong delta. We found a very strong seasonal signal over the main river north of 13°N, the Tonle Sap Lake and Tonle Sap river, with amplitudes reaching 8-10 m annually. We also found a clear interannual signal in altimetry-derived water level time-series. For example, year 1999 had weak floods (around 6 m amplitude), contrasting with year 2000 during which strong flood was noticed (around 10 m amplitude). Southwards, we also observed large seasonal fluctuations (2-3 m) over inundated floodplains, as identified using satellite imagery data from the SPOT-4 Vegetation instrument. Depending on the location, quite different annual amplitudes were observed, the closer to the Mekong mouth, the smaller the signal (less than 0.5 m seasonal amplitude). Using Normalized Difference Vegetation Index (NDVI) data from the Vegetation instrument, we studied the seasonal extent of flood plains in the delta. Then combining the areal extent of floods with water levels estimated from the ERS-2/ENVISAT data, we computed maps of monthly surface water volume change over six successive years (1998-2003), the period of availability of the NDVI data. Averaged over the lower Mekong basin, this surface water volume change was then compared to the total (i.e. surface plus underground) water volume change inferred from the GRACE satellite. They exhibit in-phase fluctuations.

  7. Using Airborne Laser Altimetry to Detect Topographic Change at Long Valley Caldera California

    NASA Technical Reports Server (NTRS)

    Hofton, M. A.; Minster, J.-B.; Ridgway, J. R.; Williams, N. P.; Blair, J. B.; Rabine, D. L.; Bufton, J. L.

    2000-01-01

    The topography of the Long Valley caldera, California, was sampled using airborne laser altimetry in 1993, 1995, and 1997 to test the feasibility of using airborne laser altimetry for monitoring deformation of volcanic origin. Results show the laser altimeters are able to resolve subtle topographic features such as a gradual slope and to detect small transient changes in lake elevation. Crossover and repeat pass analyses of laser tracks indicate decimeter-level vertical precision is obtained over flat and low-sloped terrain for altimeter systems performing waveform digitization. Comparisons with complementary, ground-based CPS data at a site close to Bishop airport indicate that the laser and GPS-derived elevations agree to within the error inherent in the measurement and that horizontal locations agree to within the radius of the laser footprint. A comparison of the data at two sites, one where no change and the other where the maximum amount of vertical uplift is expected, indicates approximately 10 cm of relative uplift occurred 1993-1997, in line with predictions from continuous CPS measurements in the region. Extensive terrain mapping flights during the 1995 and 1997 missions demonstrate some of the unique abilities of laser altimetry; the straightforward creation of high resolution, high accuracy digital elevation models of overflown terrain, and the ability to determine ground topography in the presence of significant ground cover such as dense tree canopies. These capabilities make laser altimetry an attractive technique for quantifying topographic change of volcanic origin, especially in forested regions of the world where other remote sensing instruments have difficulty detecting the underlying topography.

  8. Digital elevation model of King Edward VII Peninsula, West Antarctica, from SAR interferometry and ICESat laser altimetry

    USGS Publications Warehouse

    Baek, S.; Kwoun, Oh-Ig; Braun, Andreas; Lu, Zhiming; Shum, C.K.

    2005-01-01

    We present a digital elevation model (DEM) of King Edward VII Peninsula, Sulzberger Bay, West Antarctica, developed using 12 European Remote Sensing (ERS) synthetic aperture radar (SAR) scenes and 24 Ice, Cloud, and land Elevation Satellite (ICESat) laser altimetry profiles. We employ differential interferograms from the ERS tandem mission SAR scenes acquired in the austral fall of 1996, and four selected ICESat laser altimetry profiles acquired in the austral fall of 2004, as ground control points (GCPs) to construct an improved geocentric 60-m resolution DEM over the grounded ice region. We then extend the DEM to include two ice shelves using ICESat profiles via Kriging. Twenty additional ICESat profiles acquired in 2003-2004 are used to assess the accuracy of the DEM. After accounting for radar penetration depth and predicted surface changes, including effects due to ice mass balance, solid Earth tides, and glacial isostatic adjustment, in part to account for the eight-year data acquisition discrepancy, the resulting difference between the DEM and ICESat profiles is -0.57 ?? 5.88 m. After removing the discrepancy between the DEM and ICESat profiles for a final combined DEM using a bicubic spline, the overall difference is 0.05 ?? 1.35 m. ?? 2005 IEEE.

  9. Support of the fishery investigations in the southeastern Pacific using satellite radiometry and altimetry data

    NASA Astrophysics Data System (ADS)

    Chernyshkov, P. P.; Sirota, A. M.; Lebedev, S. A.

    2003-04-01

    Because of North Atlantic fish stocks are declined the problem of new fishery region searching or bygone fishery grounds return to come into particular prominence. One of the such region is open part of the southeastern Pacific, which was the traditional fishery ground for horse mackerel fishery in 80-90s. In September 2002 fishery and oceanographic expedition had been sent in the region. The main purposes of the expedition are investigation of biologic state of fish species and oceanographic conditions in the region. These investigations were supported with data of satellite observations. Processing of satellite data and mapping were carried out in the AtlantNIRO. To improve the spatial coverage beyond that available from in situ data from CTD survey, satellite SST and surface dynamic topography data were being prepared and transmitted to the vessel. Data source for SST, derived from AVHRR, was the NOAA Satellite Active Archive. Surface dynamic topography derived from the TOPEX/POSEIDON Quick-Look GDR v.1 data. Preliminary results of analysis of synoptic variability of that region as well as comparison of in situ observation with satellite data are presented. Efficiency of use altimetry products for support of exploratory researches is estimated.

  10. The solar and Southern Oscillation components in the satellite altimetry data

    NASA Astrophysics Data System (ADS)

    Howard, Daniel; Shaviv, Nir J.; Svensmark, Henrik

    2015-05-01

    With satellite altimetry data accumulating over the past two decades, the mean sea level (MSL) can now be measured to unprecedented accuracy. We search for physical processes which can explain the sea level variations and find that at least 70% of the variance in the annually smoothed detrended altimetry data can be explained as the combined effect of both the solar forcing and the El Niño-Southern Oscillation (ENSO). The phase of the solar component can be used to derive the different steric and eustatic contributions. We find that the peak to peak radiative forcing associated with the solar cycle is 1.33 ± 0.34 W/m2, contributing a 4.4 ± 0.8 mm variation. The slow eustatic component (describing, for example, the cryosphere and large bodies of surface water) has a somewhat smaller peak to peak amplitude of 2.4 ± 0.6 mm. Its phase implies that warming the oceans increases the ocean water loss rate. Additional much smaller terms include a steric feedback term and a fast eustatic term. The ENSO contributes a peak to peak variation of 5.5 ± 0.8 mm, predominantly through a direct effect on the MSL and significantly less so indirectly through variations in the radiative forcing.

  11. Sea level variations during rapid changing Arctic Ocean from tide gauge and satellite altimetry

    NASA Astrophysics Data System (ADS)

    Du, Ling; Xu, Daohuan

    2016-04-01

    Sea level variations can introduce the useful information under the circumstance of the rapid changing Arctic. Based on tide gauge records and the satellite altimetry data in the Arctic Ocean, the sea level variations in the 20th century are analyzed with the stochastic dynamic method. The average secular trend of the sea level record is about 1 mm/yr, which is smaller than the global mean cited by the IPCC climate assessment report. The secular trend in the coastal region differs from that in the deep water. After the mid-1970s, a weak acceleration of sea level rise is found along the coasts of the Siberian and Aleutian Islands. Analysis of synchronous TOPEX/Poseidon altimetry data indicates that the amplitude of the seasonal variation is less than that of the inter-annual variation, whose periods vary from 4.7 to 6 years. This relationship is different from that in the mid-latitudes. The climate indices are the pre-cursors of the sea level variations on multi-temporal scales. The model results show that while steric effects contribute significantly to the seasonal variation, the influence of atmospheric wind forcing is an important factor of sea level during ice free region.

  12. Steep Satellite Altimetry Gradients as a Proxy to the Edge of the Continental Crust

    NASA Astrophysics Data System (ADS)

    Lawver, L. A.; Gahagan, L. M.

    2005-05-01

    Tight-fit plate reconstructions are produced using a global database constrained by marine magnetic anomalies tied to a consistent timescale, paleomagnetic poles, seafloor age dates based on drilling results, and fracture zone and transform fault lineations picked from ship-track and satellite altimetry data. Where a prominent steep gradient in the satellite altimetry data is present near the continental-ocean transition, it is used as a proxy to the continental shelf break [CSB]. Continental block outlines are based on digitization of the steep gradient. In some places, notably off Namibia, there is a very close correlation between that gradient and the ocean-continent boundary deduced from seismic refraction and reflection data. In other regions, there may be some stretched continental crust oceanward of the steep gradient but for reconstruction purposes we assume the crust to be predominantly continental landward of the boundary and oceanic, seaward of the line. Good matchs for conjugate CSBs are found in many places world-wide along passive margins and these will be highlighted. Particularly good matches are observed between the cratonic edges of East Antarctica as determined by sub-ice topographic highs seen along the margins of East Antarctica with respect to Madagascar, Sri Lanka, the southern half of the eastern margin of India, and the region of Australia between 124° E and 133° E along the Great Australian Bight (GAB). There are overlaps of the reconstructed conjugate CSBs, with one overlap between India and East Antarctica (70° E to 85° E) and one between East Antarctica and the western section of the GAB (105° E to 120° E). These two overlaps are coincident with the outer margins of the Lambert Graben - Prydz Bay Basin and the Aurora Subglacial Basin, respectively. It is known that there are substantial glacially-derived sediments prograded off the continental margin onto oceanic crust at Prydz Bay where there may be as much as 200 km in width of

  13. Stage-discharge rating curves based on satellite altimetry and modeled discharge in the Amazon basin

    NASA Astrophysics Data System (ADS)

    Paris, Adrien; Dias de Paiva, Rodrigo; Santos da Silva, Joecila; Medeiros Moreira, Daniel; Calmant, Stephane; Garambois, Pierre-André; Collischonn, Walter; Bonnet, Marie-Paule; Seyler, Frederique

    2016-05-01

    In this study, rating curves (RCs) were determined by applying satellite altimetry to a poorly gauged basin. This study demonstrates the synergistic application of remote sensing and watershed modeling to capture the dynamics and quantity of flow in the Amazon River Basin, respectively. Three major advancements for estimating basin-scale patterns in river discharge are described. The first advancement is the preservation of the hydrological meanings of the parameters expressed by Manning's equation to obtain a data set containing the elevations of the river beds throughout the basin. The second advancement is the provision of parameter uncertainties and, therefore, the uncertainties in the rated discharge. The third advancement concerns estimating the discharge while considering backwater effects. We analyzed the Amazon Basin using nearly one thousand series that were obtained from ENVISAT and Jason-2 altimetry for more than 100 tributaries. Discharge values and related uncertainties were obtained from the rain-discharge MGB-IPH model. We used a global optimization algorithm based on the Monte Carlo Markov Chain and Bayesian framework to determine the rating curves. The data were randomly allocated into 80% calibration and 20% validation subsets. A comparison with the validation samples produced a Nash-Sutcliffe efficiency (Ens) of 0.68. When the MGB discharge uncertainties were less than 5%, the Ens value increased to 0.81 (mean). A comparison with the in situ discharge resulted in an Ens value of 0.71 for the validation samples (and 0.77 for calibration). The Ens values at the mouths of the rivers that experienced backwater effects significantly improved when the mean monthly slope was included in the RC. Our RCs were not mission-dependent, and the Ens value was preserved when applying ENVISAT rating curves to Jason-2 altimetry at crossovers. The cease-to-flow parameter of our RCs provided a good proxy for determining river bed elevation. This proxy was validated

  14. New ERP predictions based on (sub-)daily ocean tides from satellite altimetry data

    NASA Astrophysics Data System (ADS)

    Madzak, Matthias; Böhm, Sigrid; Böhm, Johannes; Bosch, Wolfgang; Schuh, Harald

    2013-04-01

    A new model for Earth rotation variations based on ocean tide models is highly desirable in order to close the gap between geophysical Earth rotation models and geodetic observations. We have started a project, SPOT (Short Period Ocean Tidal variations in Earth Rotation), with the goal to develop a new model of short period Earth rotation variations based on one of the best currently available empirical ocean tide models obtained from satellite altimetry. We employ the EOT11a model which is an upgrade of EOT08a, developed at DGFI, Munich. As EOT11a does not provide the tidal current velocities which are fundamental contributors to Earth rotation excitation, the calculation of current velocities from the tidal elevations is one of three main areas of research in project SPOT. The second key aspect is the conversion from ocean tidal angular momentum to the corresponding ERP variations using state-of-the-art transfer functions. A peculiar innovation at this step will be to consider the Earth's response to ocean tidal loading based on a realistic Earth model, including an anelastic mantle. The third part of the project deals with the introduction of the effect of minor tides. Ocean tide models usually only provide major semi-diurnal and diurnal tidal terms and the minor tides have to be inferred through admittance assumptions. Within the proposed project, selected minor tidal terms and the corresponding ERP variations shall be derived directly from satellite altimetry data. We determine ocean tidal angular momentum of four diurnal and five sub-daily tides from EOT11a and apply the angular momentum approach to derive a new model of ocean tidal Earth rotation variations. This poster gives a detailed description of project SPOT as well as the status of work progress. First results are presented as well.

  15. Monitoring changes in the water volume of Hulun Lake by integrating satellite altimetry data and Landsat images between 1992 and 2010

    NASA Astrophysics Data System (ADS)

    Zheng, Jiajia; Ke, Changqing; Shao, Zhude; Li, Fei

    2016-01-01

    Lake level and volume are sensitive to climate change, and their changes can affect the sustainable utilization of regional water resources. Satellite radar/laser altimetry has effectively been used for monitoring water-level changes in recent years. In this study, satellite altimetry data and optical images were used to assess the changes in water level, area, and volume of Hulun Lake in north-eastern China. We derived a time series of lake levels for nearly two decades (1992 to 2010) from the altimetry data of two satellite sensors (Topex/Poseidon and Envisat RA-2); additionally, lake surface extent was extracted from Landsat TM/ETM+ images during the same period. The results indicate that the water level, area, and volume of Hulun Lake decreased over the past two decades. The water level shows a significant decrease (-0.36 m/year) of a total of -5.21 m from 1992 to 2010, specifically including a slight decrease (-0.4 m) during 1992 to 1999 and a sudden drop (-4.81 m) during 2000 to 2010. There has also been a consistent and significant reduction in lake area (-355.35 km2) and volume (-12.92 km3). An integrated examination on changes in temperature, evaporation, precipitation, and runoff during 1992 to 2010 shows that the main changes in the Hulun Lake area are correlated with increasing temperature (0.47°C/year) and evaporation (13.61 mm/year), as well as decreasing precipitation (-6.58 mm/year) and runoff (-1.04×108 m3/year). Thus, we infer that climate warming is likely the main cause of the changes in water level, area, and volume of Hulun Lake. In addition, anthropogenic factors accelerate the degradation of the Hulun Lake wetland to some extent.

  16. A computer code to process and plot laser altimetry data interactively on a microcomputer

    NASA Technical Reports Server (NTRS)

    Safren, H. G.; Bufton, J. L.

    1987-01-01

    A computer program, written in FORTRAN, is described which uses a microcomputer to interactively process and plot laser altimetry data taken with a laser altimeter currently under development at the Goddard Space Flight Center. The program uses a plot routine written for a particular microcomputer, so that the program could only be implemented on a different computer by replacing the plot routine. The altimetry data are taken from an aircraft flying over mountainous terrain. The program unpacks the raw data, processes it into along-track distance and ground height and creates plots of the terrain profile. A zoom capability is provided to expand the plot to show greater detail, along either axis, and provision is made to interactively edit out spurious data points.

  17. Recent volume and mass changes of Penny Ice Cap (Baffin Island, Nunavut) determined from repeat airborne laser altimetry

    NASA Astrophysics Data System (ADS)

    Schaffer, N.; Zdanowicz, C.; Copland, L.; Burgess, D. O.

    2011-12-01

    Recent observations of accelerated glacier wastage in Greenland and Alaska have prompted reassessments of mass balance trends and volume changes on Canadian Arctic glaciers and ice caps. While long surface mass balance measurements are available from ice caps of the Queen Elizabeth Islands (e.g., Axel Heiberg and Devon islands), no such records exist for Baffin Island glaciers. In the absence of such data, air- and space-borne measurements can be used in combination with ice core data and in-situ ground penetrating radar surveys to evaluate historical and recent trends in ice cover changes. Here, we use repeat laser airborne altimetry surveys conducted in 2000 and 2005 to estimate current volume and mass reduction rates of Penny Ice Cap, the southernmost large ice cap on Baffin Island (~66°N). This work builds on previous surveys for the period 1995-2000 [Abdalati et al. (2004) JGR 109: F04007.] Surface elevation changes along altimetry lines are extrapolated to the entire ice cap using a digital elevation model (DEM). Changes in areal extent of the ice cap are constrained using satellite imagery (e.g. Landsat). From these data and using firn density profiles measured in cores, we estimate the total mass wastage of the ice cap and its contribution to sea level rise.

  18. Laser altimetry simulator. Version 3.0: User's guide

    NASA Technical Reports Server (NTRS)

    Abshire, James B.; Mcgarry, Jan F.; Pacini, Linda K.; Blair, J. Bryan; Elman, Gregory C.

    1994-01-01

    A numerical simulator of a pulsed, direct detection laser altimeter has been developed to investigate the performance of space-based laser altimeters operating over surfaces with various height profiles. The simulator calculates the laser's optical intensity waveform as it propagates to and is reflected from the terrain surface and is collected by the receiver telescope. It also calculates the signal and noise waveforms output from the receiver's optical detector and waveform digitizer. Both avalanche photodiode and photomultiplier detectors may be selected. Parameters of the detected signal, including energy, the 50 percent rise-time point, the mean timing point, and the centroid, can be collected into histograms and statistics calculated after a number of laser firings. The laser altimeter can be selected to be fixed over the terrain at any altitude. Alternatively, it can move between laser shots to simulate the terrain profile measured with the laser altimeter.

  19. Integrated Analysis of Interferometric SAR, Satellite Altimetry and Hydraulic Modeling to Quantify Louisiana Wetland Dynamics

    NASA Technical Reports Server (NTRS)

    Lee, Hyongki; Kim, Jin-woo; Lu, Zhong; Jung, Hahn Chul; Shum, C. K.; Alsdorf, Doug

    2012-01-01

    Wetland loss in Louisiana has been accelerating due primarily to anthropogenic and nature processes, and is being advocated as a problem with national importance. Accurate measurement or modeling of wetland-wide water level changes, its varying extent, its storage and discharge changes resulting in part from sediment loads, erosion and subsidence are fundamental to assessment of hurricane-induced flood hazards and wetland ecology. Here, we use innovative method to integrate interferometric SAR (InSAR) and satellite radar altimetry for measuring absolute or geocentric water level changes and applied the methodology to remote areas of swamp forest in coastal Louisiana. Coherence analysis of InSAR pairs suggested that the HH polarization is preferred for this type of observation, and polarimetric analysis can help to identi:fy double-bonnce backscattering areas in the wetland. Envisat radar altimeter-measured 18- Hz (along-track sampling of 417 m) water level data processed with regional stackfile method have been used to provide vertical references for water bodies separated by levees. The high-resolution (approx.40 m) relative water changes measured from ALOS PALSAR L-band and Radarsat-l C-band InSAR are then integrated with Envisat radar altimetry to obtain absolute water level. The resulting water level time series were validated with in situ gauge observations within the swamp forest. Furthermore, we compare our water elevation changes with 2D flood modeling from LISFLOOD hydrodynamic model. Our study demonstrates that this new technique allows retrospective reconstruction and concurrent monitoring of water conditions and flow dynamics in wetlands, especially those lacking gauge networks.

  20. Modeling upper mantle rheology with numerical experiments and mapping marine gravity with satellite altimetry

    NASA Astrophysics Data System (ADS)

    Yale, Mara M.

    This thesis consists of modeling upper mantle rheology with numerical experiments and mapping marine gravity anomalies with satellite altimetry data. Chapter 1 introduces my reasoning for undertaking projects in two distinct fields. Chapters 2 and 3 are numerical modeling projects. Chapters 4 and 5 and the appendix are satellite altimetry projects. Chapter 2 presents numerical modeling experiments of small-scale convection in the asthenosphere beneath California. Using the timing provided by the tectonic history and knowledge of the current thermal state from seismic tomography, our numerical experiments provide upper and lower bounds on the asthenosphere viscosity, and demonstrate the effects of rheologies that depend on temperature, pressure, and strain rate. Chapter 3 presents a numerical model to test the asthenosphere flow paradigm in which hotspots feed the low viscosity asthenosphere, and lithosphere consumes the asthenosphere. The model is applied to two distinct regions--the Iceland hotspot centered on the Mid-Atlantic Ridge, and the Kerguelen hotspot located near the Southeast Indian Ridge. The asthenosphere flow paradigm can explain major features of hotspot-ridge interactions for both on-axis and off-axis hotspots. Chapter 4 presents a resolution analysis of repeat satellite altimeter profiles to compare the along-track resolution capabilities of Geosat, ERS-1 and TOPEX data. On average globally, the along-track resolution (0.5 coherence) of eight-cycle stacks are approximately the same, 28, 29, and 30 km for TOPEX, Geosat, and ERS-1, respectively. TOPEX 31-cycle stacks (22 km) resolve slightly shorter wavelengths than Geosat 31-cycle stacks (24 km). Chapter 5 presents a method to improve global gravity profiles by iterating on the current grid. We use new repeat cycle data to improve stacks (averages) for ERS-1/2 (43 cycles) and Topex (142 cycles), and then implement the method for improving gravity profiles globally. We demonstrate the maximum

  1. Spatiotemporal densification of river water level time series by multimission satellite altimetry

    NASA Astrophysics Data System (ADS)

    Tourian, M. J.; Tarpanelli, A.; Elmi, O.; Qin, T.; Brocca, L.; Moramarco, T.; Sneeuw, N.

    2016-02-01

    Limitations of satellite radar altimetry for operational hydrology include its spatial and temporal sampling as well as measurement problems caused by local topography and heterogeneity of the reflecting surface. In this study, we develop an approach that eliminates most of these limitations to produce an approximately 3 day temporal resolution water level time series from the original typically (sub)monthly data sets for the Po River in detail, and for Congo, Mississippi, and Danube Rivers. We follow a geodetic approach by which, after estimating and removing intersatellite biases, all virtual stations of several satellite altimeters are connected hydraulically and statistically to produce water level time series at any location along the river. We test different data-selection strategies and validate our method against the extensive available in situ data over the Po River, resulting in an average correlation of 0.7, Root-Mean-Square Error of 0.8 m, bias of -0.4 m, and Nash-Sutcliffe Efficiency coefficient of 0.5. We validate the transferability of our method by applying it to the Congo, Mississippi, and Danube Rivers, which have very different geomorphological and climatic conditions. The methodology yields correlations above 0.75 and Nash-Sutcliffe coefficients of 0.84 (Congo), 0.34 (Mississippi), and 0.35 (Danube).

  2. Multiple Scattering of Laser Pulses in Snow Over Ice: Modeling the Potential Bias in ICESat Altimetry

    NASA Technical Reports Server (NTRS)

    Davis, A. B.; Varnai, T.; Marshak, A.

    2010-01-01

    The primary goal of NASA's current ICESat and future ICESat2 missions is to map the altitude of the Earth's land ice with high accuracy using laser altimetry technology, and to measure sea ice freeboard. Ice however is a highly transparent optical medium with variable scattering and absorption properties. Moreover, it is often covered by a layer of snow with varying depth and optical properties largely dependent on its age. We describe a modeling framework for estimating the potential altimetry bias caused by multiple scattering in the layered medium. We use both a Monte Carlo technique and an analytical diffusion model valid for optically thick media. Our preliminary numerical results are consistent with estimates of the multiple scattering delay from laboratory measurements using snow harvested in Greenland, namely, a few cm. Planned refinements of the models are described.

  3. From satellite altimetry to Argo and operational oceanography: three revolutions in oceanography

    NASA Astrophysics Data System (ADS)

    Le Traon, P. Y.

    2013-07-01

    The launch of the US/French mission Topex/Poseidon (T/P) (CNES/NASA) in August 1992 was the start of a revolution in oceanography. For the first time, a very precise altimeter system optimized for large scale sea level and ocean circulation observations was flying. T/P alone could not observe the mesoscale circulation. In the 1990s, the ESA satellites ERS-1/2 were flying simultaneously with T/P. Together with my CLS colleagues, we demonstrated that we could use T/P as a reference mission for ERS-1/2 and bring the ERS-1/2 data to an accuracy level comparable to T/P. Near real time high resolution global sea level anomaly maps were then derived. These maps have been operationally produced as part of the SSALTO/DUACS system for the last 15 yr. They are now widely used by the oceanographic community and have contributed to a much better understanding and recognition of the role and importance of mesoscale dynamics. Altimetry needs to be complemented with global in situ observations. In the end of the 90s, a major international initiative was launched to develop Argo, the global array of profiling floats. This has been an outstanding success. Argo floats now provide the most important in situ observations to monitor and understand the role of the ocean on the earth climate and for operational oceanography. This is a second revolution in oceanography. The unique capability of satellite altimetry to observe the global ocean in near real time at high resolution and the development of Argo were essential to the development of global operational oceanography, the third revolution in oceanography. The Global Ocean Data Assimilation Experiment (GODAE) was instrumental in the development of the required capabilities. This paper provides an historical perspective on the development of these three revolutions in oceanography which are very much interlinked. This is not an exhaustive review and I will mainly focus on the contributions we made together with many colleagues and

  4. From satellite altimetry to Argo and operational oceanography: three revolutions in oceanography

    NASA Astrophysics Data System (ADS)

    Le Traon, P. Y.

    2013-10-01

    The launch of the French/US mission Topex/Poseidon (T/P) (CNES/NASA) in August 1992 was the start of a revolution in oceanography. For the first time, a very precise altimeter system optimized for large-scale sea level and ocean circulation observations was flying. T/P alone could not observe the mesoscale circulation. In the 1990s, the ESA satellites ERS-1/2 were flying simultaneously with T/P. Together with my CLS colleagues, we demonstrated that we could use T/P as a reference mission for ERS-1/2 and bring the ERS-1/2 data to an accuracy level comparable to T/P. Near-real-time high-resolution global sea level anomaly maps were then derived. These maps have been operationally produced as part of the SSALTO/DUACS system for the last 15 yr. They are now widely used by the oceanographic community and have contributed to a much better understanding and recognition of the role and importance of mesoscale dynamics. Altimetry needs to be complemented with global in situ observations. At the end of the 90s, a major international initiative was launched to develop Argo, the global array of profiling floats. This has been an outstanding success. Argo floats now provide the most important in situ observations to monitor and understand the role of the ocean on the earth climate and for operational oceanography. This is a second revolution in oceanography. The unique capability of satellite altimetry to observe the global ocean in near-real-time at high resolution and the development of Argo were essential for the development of global operational oceanography, the third revolution in oceanography. The Global Ocean Data Assimilation Experiment (GODAE) was instrumental in the development of the required capabilities. This paper provides an historical perspective on the development of these three revolutions in oceanography which are very much interlinked. This is not an exhaustive review and I will mainly focus on the contributions we made together with many colleagues and

  5. Coastal sea level changes in Europe from GPS, tide gauge, satellite altimetry and GRACE, 1993-2011

    NASA Astrophysics Data System (ADS)

    Feng, Guiping; Jin, S.; Zhang, T.

    2013-03-01

    Sea level changes are threatening the human living environments, particularly along the European Coasts with highly dense population. In this paper, coastal sea level changes in western and southern Europe are investigated for the period 1993-2011 using Global Positioning System (GPS), Tide Gauge (TG), Satellite Altimetry (SA), Gravity Recovery and Climate Experiment (GRACE) and geophysical models. The mean secular trend is 2.26 ± 0.52 mm/y from satellite altimetry, 2.43 ± 0.61 mm/y from TG+GPS and 1.99 ± 0.67 mm/y from GRACE mass plus steric components, which have a remarkably good agreement. For the seasonal variations, annual amplitudes of satellite altimetry and TG+GPS results are almost similar, while GRACE Mass+Steric results are a little smaller. The annual phases agree remarkably well for three independent techniques. The annual cycle is mainly driven by the steric contributions, while the annual phases of non-steric (mass component) sea level changes are almost a half year later than the steric sea level changes.

  6. Mantle Q at Period 12.4 Hours: New Estimates from Satellite Tracking and Altimetry

    NASA Technical Reports Server (NTRS)

    Ray, Richard D.

    1999-01-01

    The most convincing estimates of mantle Q at periods of many hours have historically come from extrapolating seismic and free-oscillation estimates via some assumed frequency dependence, sometimes contrained by estimates from the Chandler Wobble. At the semidiurnal tidal period, direct estimates of Q have been difficult to obtain because of the dominating signals of the ocean tides, which account for more than 95!k of the tidal energy dissipation. But knowledge of the ocean tides has been rapidly improving, primarily owing to satellite altimetry, and in 1996 we reported (NATURE, 381, 595-7) an estimate of solid-earth tidal energy dissipation and mantle Q based on combining satellite altimeter measurements with tracking observations of tidally induced satellite orbit perturbations. Tidal estimates from both reveal a small systematic difference in the quadrature component of the degree-2, order-2 spherical harmonic coefficients, which we attribute to a small lag in the earth's body tide. The formalism accounts for this lag in both the altimeter and tracking solutions and also accounts for a very small contribution from the lunar atmospheric tide. Since this original report, both altimeter and tracking estimates have improved. Recent solutions for the body-tide lag at the M2 period are 0.20 +/- 0.09 degrees, implying an energy dissipation of 100 +/- 50 gigawatts and a solid-earth Q of 300. Further new solutions will be discussed, as will the prospects for significantly reducing error bars and for obtaining estimates from other tides in the diurnal band.

  7. Improved Estimates of Temporally Coherent Internal Tides and Energy Fluxes from Satellite Altimetry

    NASA Technical Reports Server (NTRS)

    Ray, Richard D.; Chao, Benjamin F. (Technical Monitor)

    2002-01-01

    Satellite altimetry has opened a surprising new avenue to observing internal tides in the open ocean. The tidal surface signatures are very small, a few cm at most, but in many areas they are robust, owing to averaging over many years. By employing a simplified two dimensional wave fitting to the surface elevations in combination with climatological hydrography to define the relation between the surface height and the current and pressure at depth, we may obtain rough estimates of internal tide energy fluxes. Initial results near Hawaii with Topex/Poseidon (T/P) data show good agreement with detailed 3D (three dimensional) numerical models, but the altimeter picture is somewhat blurred owing to the widely spaced T/P tracks. The resolution may be enhanced somewhat by using data from the ERS-1 (ESA (European Space Agency) Remote Sensing) and ERS-2 satellite altimeters. The ERS satellite tracks are much more closely spaced (0.72 deg longitude vs. 2.83 deg for T/P), but the tidal estimates are less accurate than those for T/P. All altimeter estimates are also severely affected by noise in regions of high mesoscale variability, and we have obtained some success in reducing this contamination by employing a prior correction for mesoscale variability based on ten day detailed sea surface height maps developed by Le Traon and colleagues. These improvements allow us to more clearly define the internal tide surface field and the corresponding energy fluxes. Results from throughout the global ocean will be presented.

  8. Improved gravity anomaly fields from retracked multimission satellite radar altimetry observations over the Persian Gulf and the Caspian Sea

    NASA Astrophysics Data System (ADS)

    Khaki, M.; Forootan, E.; Sharifi, M. A.; Awange, J.; Kuhn, M.

    2015-09-01

    Satellite radar altimetry observations are used to derive short wavelength gravity anomaly fields over the Persian Gulf and the Caspian Sea, where in situ and ship-borne gravity measurements have limited spatial coverage. In this study the retracking algorithm `Extrema Retracking' (ExtR) was employed to improve sea surface height (SSH) measurements that are highly biased in the study regions due to land contaminations in the footprints of the satellite altimetry observations. ExtR was applied to the waveforms sampled by the five satellite radar altimetry missions: TOPEX/POSEIDON, JASON-1, JASON-2, GFO and ERS-1. Along-track slopes have been estimated from the improved SSH measurements and used in an iterative process to estimate deflections of the vertical, and subsequently, the desired gravity anomalies. The main steps of the gravity anomaly computations involve estimating improved SSH using the ExtR technique, computing deflections of the vertical from interpolated SSHs on a regular grid using a biharmonic spline interpolation and finally estimating gridded gravity anomalies. A remove-compute-restore algorithm, based on the fast Fourier transform, has been applied to convert deflections of the vertical into gravity anomalies. Finally, spline interpolation has been used to estimate regular gravity anomaly grids over the two study regions. Results were evaluated by comparing the estimated altimetry-derived gravity anomalies (with and without implementing the ExtR algorithm) with ship-borne free air gravity anomaly observations, and free air gravity anomalies from the Earth Gravitational Model 2008 (EGM2008). The comparison indicates a range of 3-5 mGal in the residuals, which were computed by taking the differences between the retracked altimetry-derived gravity anomaly and the ship-borne data. The comparison of retracked data with ship-borne data indicates a range in the root-mean-square-error (RMSE) between approximately 1.8 and 4.4 mGal and a bias between 0

  9. High Resolution Surface Geometry and Albedo by Combining Laser Altimetry and Visible Images

    NASA Technical Reports Server (NTRS)

    Morris, Robin D.; vonToussaint, Udo; Cheeseman, Peter C.; Clancy, Daniel (Technical Monitor)

    2001-01-01

    The need for accurate geometric and radiometric information over large areas has become increasingly important. Laser altimetry is one of the key technologies for obtaining this geometric information. However, there are important application areas where the observing platform has its orbit constrained by the other instruments it is carrying, and so the spatial resolution that can be recorded by the laser altimeter is limited. In this paper we show how information recorded by one of the other instruments commonly carried, a high-resolution imaging camera, can be combined with the laser altimeter measurements to give a high resolution estimate both of the surface geometry and its reflectance properties. This estimate has an accuracy unavailable from other interpolation methods. We present the results from combining synthetic laser altimeter measurements on a coarse grid with images generated from a surface model to re-create the surface model.

  10. Spectral characteristics of Rossby waves in the Northwestern Pacific based on satellite altimetry

    NASA Astrophysics Data System (ADS)

    Belonenko, T. V.; Kubrjakov, A. A.; Stanichny, S. V.

    2016-12-01

    Using satellite altimetry measurement data for 1993-2013, we study the spectral characteristics of Rossby waves in the Northwestern Pacific (25°-50° N, 140°-180° E). For each latitude degree, we draw integral plots of spectral power density calculated with a two-dimensional Fourier transform (2D-FFT). We compare the dispersion equations of Rossby waves calculated from the WKB-approximation and an approximation of a two-layer ocean model with the empirical velocities determined by the slope of isopleths by the Radon method; also, we compare the dispersion equations with the spectral distributions of level variations. It is shown that the main energy of Rossby waves in the Northwestern Pacific corresponds to the first baroclinic mode. At almost all latitudes, there is good agreement between the empirical phase velocities calculated by isopleths by the Radon method and the theoretical values; also, the spectral peaks correspond to graphs of the dispersion equations for the first baroclinic mode Rossby waves, except for the Kuroshio region, where some peaks correspond to the second mode.

  11. Vertical Crustal Motion Derived from Satellite Altimetry and Tide Gauges, and Comparisons with DORIS Measurements

    NASA Technical Reports Server (NTRS)

    Ray, R. D.; Beckley, B. D.; Lemoine, F. G.

    2010-01-01

    A somewhat unorthodox method for determining vertical crustal motion at a tide-gauge location is to difference the sea level time series with an equivalent time series determined from satellite altimetry, To the extent that both instruments measure an identical ocean signal, the difference will be dominated by vertical land motion at the gauge. We revisit this technique by analyzing sea level signals at 28 tide gauges that are colocated with DORIS geodetic stations. Comparisons of altimeter-gauge vertical rates with DORIS rates yield a median difference of 1.8 mm/yr and a weighted root-mean-square difference of2.7 mm/yr. The latter suggests that our uncertainty estimates, which are primarily based on an assumed AR(l) noise process in all time series, underestimates the true errors. Several sources of additional error are discussed, including possible scale errors in the terrestrial reference frame to which altimeter-gauge rates are mostly insensitive, One of our stations, Male, Maldives, which has been the subject of some uninformed arguments about sea-level rise, is found to have almost no vertical motion, and thus is vulnerable to rising sea levels. Published by Elsevier Ltd. on behalf of COSPAR.

  12. Kinematic metrics of the Loop Current in the Gulf of Mexico from satellite altimetry

    NASA Astrophysics Data System (ADS)

    Lugo-Fernández, Alexis; Leben, Robert R.; Hall, Cody A.

    2016-12-01

    We analyzed a 20-year time series (January 1st, 1993 through December 31st, 2012) of Loop Current (LC) surface area derived from satellite altimetry in the eastern Gulf of Mexico to estimate kinematical metrics of this potent flow. On average the LC intrudes to its maximum northward position about 216 ± 126 days after the previous eddy separation; and ∼30 ± 31 days later sheds a large anticyclonic eddy. When the northern extent of the LC intrusion following the previous eddy separation is greater than 27°N, the current retreats very quickly until it sheds another eddy with the entire separation process occurring on the order of 30 days. To first order the change in areal extent of the LC during intrusion into the Gulf occurs at an average rate of 225 km2 day-1, which corresponds to an intrusion velocity of 1.7 cm s-1 of the LC front, and adds Caribbean water to the Gulf at a rate of 2.6 ± 0.7 Sv.

  13. Radial orbit error reduction and sea surface topography determination using satellite altimetry

    NASA Technical Reports Server (NTRS)

    Engelis, Theodossios

    1987-01-01

    A method is presented in satellite altimetry that attempts to simultaneously determine the geoid and sea surface topography with minimum wavelengths of about 500 km and to reduce the radial orbit error caused by geopotential errors. The modeling of the radial orbit error is made using the linearized Lagrangian perturbation theory. Secular and second order effects are also included. After a rather extensive validation of the linearized equations, alternative expressions of the radial orbit error are derived. Numerical estimates for the radial orbit error and geoid undulation error are computed using the differences of two geopotential models as potential coefficient errors, for a SEASAT orbit. To provide statistical estimates of the radial distances and the geoid, a covariance propagation is made based on the full geopotential covariance. Accuracy estimates for the SEASAT orbits are given which agree quite well with already published results. Observation equations are develped using sea surface heights and crossover discrepancies as observables. A minimum variance solution with prior information provides estimates of parameters representing the sea surface topography and corrections to the gravity field that is used for the orbit generation. The simulation results show that the method can be used to effectively reduce the radial orbit error and recover the sea surface topography.

  14. Louisiana/Everglades wetland water level monitoring using satellite radar altimetry

    NASA Astrophysics Data System (ADS)

    Lee, H.; Shum, C.; Lu, Z.; Alsdorf, D.; Ibaraki, M.; Braun, A.; Kuo, C.

    2008-05-01

    Coastal estuaries, which connect coastal ocean, wetlands and coastal land region, play important roles in ecological environments. Wetlands typically occur in low-lying areas on the edges of lakes, and rivers, or in coastal areas protected from waves and are found in a variety of climates on every continent except Antarctica. Wetlands not only provide habitat for thousands of aquatic/terrestrial plant and animal species but also control floods by holding water much like a sponge by absorbing and reducing the velocity of storm-water. Human activities have so many negative impacts on wetlands and they became main contributing factors to the wetlands losses. For example, Louisiana's wetlands have lost more than 100 km2 of its area per year (Walker et al., 1987; Bourne, 2000). The loss of Louisiana wetlands as a result of ecological erosion or geological subsidence potentially have had significant impacts in slowing down storm surge from the devastating Hurricane Katrina. The ability to quantitatively measure accurate wetland water level changes in Louisiana has impacts on ecology and natural hazards mitigation including improved storm surge modeling resulting from hurricanes. Interferometric synthetic aperture radar (InSAR) has been proven to be useful to measure centimeter-scale water level changes over Amazon flood plain and Everglades wetland using L-band SAR imagery. This is based on the fact that flooded forests permit double-bounce returns, which allow InSAR coherence to be maintained. Furthermore, ERS-1/2 C-band InSAR data have been used to demonstrate its feasibility to monitor water level changes over Louisiana wetlands. In addition, satellite radar altimetry has been used to measure inland water level variation over large river basins. In this study, we use the decadal (1992-2002) Topex/Poseidon (T/P) measurements from cycle 9 to 364 to detect water level changes of Louisiana's and Everglades' wetlands, where the water surfaces are calm or vegetated, causing

  15. Mesoscale Eddies, Satellite Altimetry, and New Production in the Sargasso Sea

    NASA Technical Reports Server (NTRS)

    Siegel, David A.; McGillicuddy, Dennis J., Jr.; Fields, Erik A.

    1999-01-01

    Satellite altimetry and hydrographic observations are used to characterize the mesoscale eddy field in the Sargasso Sea near Bermuda and to address the role of physical processes on the supply of new nutrients to the euphotic zone. The observed sea level anomaly (SLA) field is dominated by the occurrence of westward propagating features with SLA signatures as large as 25 cm, Eulerian temporal scales of roughly a month, lifetimes of several months, spatial scales of approximately 200 km, and a propagation of approximately 5 cm/s. Hydrographic estimates of dynamic height anomaly (referenced to 4000 dbar) are well correlated with satellite SLA (r(exp 2) = 0.65), and at least 85% of the observed dynamic height variability is associated with the first baroclinic mode of motion. This allows us to apply the satellite observations to remotely sensed estimate isopycnal displacements and the flux of nutrients into the euphotic zone due to eddy pumping. Eddy pumping is the process by which mesoscale eddies induce isopycnal displacements that lift nutrient-replete waters into the euphotic zone, driving new primary production. A kinematic approach to the estimation of the eddy pumping results in a flux of 0.24 +/- 0.1 mol N/sq m (including a scale estimate for the small contribution due to 18 deg water eddies). This flux is more than an order of magnitude larger than the diapycnal diffusive flux as well as scale estimates for the vertical transport due to isopycnal mixing along sloping isopycnal surfaces. Eddy pumping and wintertime convection are the two dominant mechanisms transporting new nutrients into the euphotic zone, and the sum of all physical new nutrient supply fluxes effectively balances previous geochemical estimates of annual new production for this site. However, if biological transports (e.g., nitrogen fixation, etc.) are significant, the new nitrogen supply budget will be in excess of geochemical new production estimates. This suggests that the various physical

  16. Mesoscale Eddies, Satellite Altimetry, and New Production in the Sargasso Sea

    NASA Technical Reports Server (NTRS)

    Siegel, David A.; McGillicuddy, Dennis J., Jr.; Fields, Erik A.

    1999-01-01

    Satellite altimetry and hydrographic observations are used to characterize the mesoscale eddy field in the Sargasso Sea near Bermuda and to address the role of physical processes on the supply of new nutrients to the euphotic zone. The observed sea level anomaly (SLA) field is dominated by the occurrence of westward propagating features with SLA signatures as large as 25 cm, Eulerian temporal scales of roughly a month, lifetimes of several months, spatial scales of approximately 200 km, and a propagation of approximately 5 cm/s . Hydrographic estimates of dynamic height anomaly (referenced to 4000 dbar) are well correlated with satellite SLA (r(sup 2) = 0.65), and at least 85% of the observed dynamic height variability is associated with the first baroclinic mode of motion. This allows us to apply the satellite observations to remotely estimate isopycnal displacements and the flux of nutrients into the euphotic zone due to eddy pumping. Eddy pumping is the process by which mesoscale eddies induce isopycnal displacements that lift nutrient- replete waters into the euphotic zone, driving new primary production. A kinematic approach to the estimation of the eddy pumping results in a flux of 0.24+/-0.1 mol N/sq m/yr (including a scale estimate for the small contribution due to 18 deg water eddies). This flux is more than an order of magnitude larger than the diapycnal diffusive flux as well as scale estimates for the vertical transport due to isopycnal mixing along sloping isopycnal surfaces. Eddy pumping and wintertime convection are the two dominant mechanisms transporting new nutrients into the euphotic zone, and the sum of all physical new nutrient supply fluxes effectively balances previous geochemical estimates of annual new production for this site. However, if biological transports (e.g., nitrogen fixation, etc.) are significant, the new nitrogen supply budget will be in excess of geochemical new production estimates. This suggests that the various physical and

  17. Lunar topography from Apollo 15 and 16 laser altimetry

    NASA Technical Reports Server (NTRS)

    Kaula, W. M.; Schubert, G.; Lingenfelter, R. E.; Sjogren, W. L.; Wollenhaupt, W. R.

    1973-01-01

    In the orbital plane of Apollo 15 the mean lunar radius is 1737.3 km, the mean altitude of terrae above maria is about 3 km, and the center-of-figure is displaced from the center-of-mass by about 2 km away from longitude 25 E. The Apollo 16 laser altimeter obtained a total of about 7.5 revolutions of partially overlapping data. The principal difference in results from Apollo 16 is the absence of any great far-side basin similar to the 1400-km wide feature found by Apollo 15, 1200 km to the south. This absence of a far-side depression in the Apollo 16 orbital plane largely accounts for a greater mean radius: 1738.1 km; a greater mean altitude of terrae above maria: about 4 km; and a greater offset of centers: about 3 km, also away from 25 E. In the Apollo 16, as well as Apollo 15, data the far-side terrae are much 'rougher' than the near-side terrae. Mare surfaces are generally smooth to within plus or minus 150 m, and have slopes of 1:500 to 1:2000 persisting over distances as great as 500 km.

  18. River discharge estimation at daily resolution from satellite altimetry over an entire river basin

    NASA Astrophysics Data System (ADS)

    Tourian, M. J.; Schwatke, C.; Sneeuw, N.

    2017-03-01

    One of the main challenges of hydrological modeling is the poor spatiotemporal coverage of in situ discharge databases which have steadily been declining over the past few decades. It has been demonstrated that water heights over rivers from satellite altimetry can sensibly be used to deal with the growing lack of in situ discharge data. However, the altimetric discharge is often estimated from a single virtual station suffering from coarse temporal resolution, sometimes with data outages, poor modeling and inconsistent sampling. In this study, we propose a method to estimate daily river discharge using altimetric time series of an entire river basin including its tributaries. Here, we implement a linear dynamic model to (1) provide a scheme for data assimilation of multiple altimetric discharge along a river; (2) estimate daily discharge; (3) deal with data outages, and (4) smooth the estimated discharge. The model consists of a stochastic process model that benefits from the cyclostationary behavior of discharge. Our process model comprises the covariance and cross-covariance information of river discharge at different gauges. Combined with altimetric discharge time series, we solve the linear dynamic system using the Kalman filter and smoother providing unbiased discharge with minimum variance. We evaluate our method over the Niger basin, where we generate altimetric discharge using water level time series derived from missions ENVISAT, SARAL/AltiKa, and Jason-2. Validation against in situ discharge shows that our method provides daily river discharge with an average correlation of 0.95, relative RMS error of 12%, relative bias of 10% and NSE coefficient of 0.7. Using a modified NSE-metric, that assesses the non-cyclostationary behavior, we show that our estimated discharge outperforms available legacy mean daily discharge.

  19. The ICESat-2 Mission: Laser altimetry of ice, clouds and land elevation

    NASA Astrophysics Data System (ADS)

    Neumann, T.; Markus, T.; Abdalati, W.; Zwally, H. J.

    2010-12-01

    Ice sheet and sea level changes have been explicitly identified as a current priority in the President’s Climate Change Science Program, the Arctic Climate Impact Assessment, the 4th Assessment Report of the IPCC and other national and international policy documents. The ICESat mission used a state-of-the-art at the time laser altimetry system to measure changes in the Greenland and Antarctic ice sheets, document changes in sea ice thickness distribution, and has been used to derive important information about the interactions between ice sheets and climate. ICESat stopped collecting data in October 2009, while the IceBridge and CryoSat-2 missions continue these important observations. The well-documented and ongoing dramatic and rapid changes in the Earth’s ice cover have only strengthened the need for sustained observations beyond what CryoSat-2 and IceBridge are expected to provide. Following recommendations from the National Research Council for an ICESat follow-on mission, the ICESat-2 mission is now under development for launch in late 2015. The primary aims of the ICESat-2 mission are to continue measurements of sea-ice thickness change, and ice sheet elevation changes at scales from outlet glaciers to the entire ice sheet. Unlike ICESat, which used a laser operating at 40 Hz and an analog detection system to record reflected laser energy in the infrared as a waveform, ICESat-2 is expected to employ a photon-counting approach. The current concept uses a high repetition rate (>5 kHz) low power laser in conjunction with single-photon sensitive detectors to measure range using ~532nm (green) light. This approach also makes use of multiple beams unlike the single-beam of ICESat, while the higher repetition rate generates dense along track sampling. Combining ICESat-2 data with existing and forthcoming altimetry data will yield a 15+ year record of elevation change. In this presentation, we present the motivation for space-based laser altimetry, the science

  20. Twenty Years of Progress on Global Ocean Tides: The Impact of Satellite Altimetry

    NASA Technical Reports Server (NTRS)

    Egbert, Gary; Ray, Richard

    2012-01-01

    At the dawn of the era of high-precision altimetry, before the launch of TOPEX/Poseidon, ocean tides were properly viewed as a source of noise--tidal variations in ocean height would represent a very substantial fraction of what the altimeter measures, and would have to be accurately predicted and subtracted if altimetry were to achieve its potential for ocean and climate studies. But to the extent that the altimetry could be severely contaminated by tides, it also represented an unprecedented global-scale tidal data set. These new data, together with research stimulated by the need for accurate tidal corrections, led to a renaissance in tidal studies in the oceanographic community. In this paper we review contributions of altimetry to tidal science over the past 20 years, emphasizing recent progress. Mapping of tides has now been extended from the early focus on major constituents in the open ocean to include minor constituents, (e.g., long-period tides; non-linear tides in shelf waters, and in the open ocean), and into shallow and coastal waters. Global and spatially local estimates of tidal energy balance have been refined, and the role of internal tide conversion in dissipating barotropic tidal energy is now well established through modeling, altimetry, and in situ observations. However, energy budgets for internal tides, and the role of tidal dissipation in vertical ocean mixing remain controversial topics. Altimetry may contribute to resolving some of these important questions through improved mapping of low-mode internal tides. This area has advanced significantly in recent years, with several global maps now available, and progress on constraining temporally incoherent components. For the future, new applications of altimetry (e.g., in the coastal ocean, where barotropic tidal models remain inadequate), and new mission concepts (studies of the submesoscale with SWOT, which will require correction for internal tides) may bring us full circle, again pushing

  1. Sea level budget in the Arctic during the satellite altimetry era

    NASA Astrophysics Data System (ADS)

    Carret, Alice; Cazenave, Anny; Meyssignac, Benoît; Prandi, Pierre; Ablain, Michael; Andersen, Ole; Blazquez, Alejandro

    2016-04-01

    Studying sea level variations in the Arctic region is challenging because of data scarcity. Here we present results of the sea level budget in the Arctic (up to 82°N) during the altimetry era. We first investigate closure of the sea level budget since 2002 using altimetry data from Envisat and Cryosat for estimating sea level, temperature and salinity data from the ORAP5 reanalysis and GRACE space gravimetry to estimate the steric and mass components. Two altimetry sea level data sets are considered (from DTU and CLS), based on Envisat waveforms retracking. Regional sea level trends seen in the altimetric map, in particular over the Beaufort Gyre and along the eastern coast of Greenland are of steric origin. However, in terms of regional average, the steric component contributes very little to the observed sea level trend, suggesting a dominant mass contribution in the Arctic region. This is confirmed by GRACE-based ocean mass time series that agree very well with the altimetry-based sea level time series. Direct estimate of the mass component is not possible prior to GRACE. Thus we estimated the mass contribution over the whole altimetry era from the difference between altimetry-based sea level and the ORAP5 steric component. Finally we compared altimetry-based coastal sea level with tide gauge records available along Norwegian, Greenland and Siberian coastlines and investigated whether the Arctic Oscillation that was the main driver of coastal sea level in the Arctic during the past decades still plays a dominant role or if other factors (e.g., of anthropogenic origin) become detectable.

  2. Improving Significant Wave Height detection for Coastal Satellite Altimetry: validation in the German Bight.

    NASA Astrophysics Data System (ADS)

    Passaro, Marcello; Benveniste, Jérôme; Cipollini, Paolo; Fenoglio-Marc, Luciana

    For more than two decades, it has been possible to map the Significant Wave Height (SWH) globally through Satellite Altimetry. SWH estimation is possible because the shape of an altimetric waveform, which usually presents a sharp leading edge and a slowly decaying trailing edge, depends on the sea state: in particular, the higher the sea state, the longer the rising time of the leading edge. The algorithm for SWH also depends on the width of the point target response (PTR) function, which is usually approximated by a constant value that contributes to the rising time. Particularly challenging for SWH detection are coastal data and low sea states. The first are usually flagged as unreliable due to land and calm water interference in the altimeter footprint; the second are characterized by an extremely sharp leading edge that is consequently poorly sampled in the digitalized waveform. ALES, a new algorithm for reprocessing altimetric waveforms, has recently been validated for sea surface height estimation (Passaro et al. 2014). The aim of this work is to check its validity also for SWH estimation in a particularly challenging area. The German Bight region presents both low sea state and coastal issues and is particularly suitable for validation, thanks to the extended network of buoys of the Bundesamt für Seeschifffahrt und Hydrographie (BSH). In-situ data include open sea, off-shore and coastal sea conditions, respectively at the Helgoland, lighthouse Alte Weser and Westerland locations. Reprocessed data from Envisat, Jason-1 and Jason-2 tracks are validated against those three buoys. The in-situ validation is applied both at the nearest point and at points along-track. The skill metrics is based on bias, standard deviation, slope of regression line, scatter index, number of cycles with correlation larger than 90%. The same metrics is applied to the altimeter data obtained by standard processing and the validation results are compared. Data are evaluated at high

  3. A New Glocal Mean Gravity Field Model From The Combination Of Satellite Mission And Altimetry/Gravimetry Surface Gravity Data

    NASA Astrophysics Data System (ADS)

    Rothacher, M.; Reigber, C.; Schmidt, R.; Foerste, C.; Koenig, R.; Flechtner, F.; Meyer, U.; Stubenvoll, R.; Barthelmes, F.; Neumayer, K. H.; Biancale, R.; Bruinsma, S.; Lemoine, J.

    2005-12-01

    High-resolution global mean gravity field models can be derived from the combination of satellite tracking and surface data. With the CHAMP and GRACE satellite missions, a new generation of such global gravity field models became available. Here the latest results of the processing of GRACE, CHAMP and SLR satellite tracking are presented and compared with outcomes of former analyses. The gravity field parameters obtained are the result of a substantial satellite data reprocessing, based on recently improved processing standards and models. On the other hand, surface gravity data derived from altimetry and gravimetry are globally available, providing a higher resolution than pure satellite data but lacking the high precision in the long-wavelength part. In an optimal approach the satellite-based data are combined with latest, partially newly processed surface gravity data sets to derive a global high-resolution gravity field model combining the high precision and homogeneity in the long- to medium-wavelength part from the satellite data with the short-wavelength resolution of the surface data. The obtained Earth gravity field model is an update of former EIGEN models of a resolution corresponding to a wavelength of 100 km and degree/order 360, respectively.

  4. CNES/PISTACH project: an innovative approach to get better measurements over inland water bodies from satellite altimetry. Early results.

    NASA Astrophysics Data System (ADS)

    Mercier, F.; Picot, N.; Thibaut, P.; Cazenave, A.; Seyler, F.; Kosuth, P.; Bronner, E.

    2009-04-01

    Athough initally developped for open ocean purposes, the capabilities of satellite radar altimetry for the monitoring of inland water bodies have been largely demonstrated for many years. However, no specific altimetry products have been developed for continental hydrology. As part of Jason-2 project, CNES is currently funding a dedicated study to improve conventional satellite radar altimetry products over coastal areas and continental waters. The PISTACH (Prototype Innovant de Système de Traitement pour les Applications Côtières et l'Hydrologie) project is organized around 3 phases: Phase 1: user needs and structure of coastal/hydrological products Phase 2: Development of new dedicated algorithms: retracking of the waveforms, wet and dry tropospheric corrections, local models or high resolution global models for topography, geoid, land cover classification, land water mask, data editing Phase 3: prototype implementation, validation and operations during Jason-2 CalVal phases The implementation of the prototype was completed in October 2008 while the exploitation of the prototype is ongoing up to September 2009 at least. The products are freely distributed via FTP since November 2008 (ftp://ftpsedr.cls.fr/pub/oceano/pistach/). The input of the prototype is constituted by Jason-2 Level 2 S-IGDR altimeter products, ECMWF meteo fields, as well as several state of the art static auxiliary datasets. The first version of PISTACH products adopts the same format and structure as Jason-2 standard IGDR to facilitate their appropriation and assessment by expert users. However, more simple and easy to-use products are envisaged for a wider dissemination. The project, the prototype and the products will be presented at the meeting. Early results will be used to illustrate and assess the content of the products over several test areas. The PISTACH products could be used for data assimilation, water resources management, water cycle and climate studies at regional to global

  5. Gravimetric geodesy and sea surface topography studies by means of satellite-to-satellite tracking and satellite altimetry

    NASA Technical Reports Server (NTRS)

    Siry, J. W.

    1972-01-01

    A satellite-to-satellite tracking experiment is planned between ATS-F and GEOS-C with a range accuracy of 2-meters and a range rate accuracy of 0.035 centimeters per second for a 10-second integration time. This experiment is planned for 1974. It is anticipated that it will improve the spatial resolution of the satellite geoid by half an order of magnitude to about 6 degrees. Longer integration times should also permit a modest increase in the acceleration resolution. Satellite altimeter data will also be obtained by means of GEOS-C. An overall accuracy of 5-meters in altitude is the goal. The altimeter, per se, is expected to have an instrumental precision of about 2 meters, and an additional capability to observe with a precision of about 0.2 meters for limited periods.

  6. A New Burst of Seafloor Mapping and Discovery Driven By Advances in Satellite Altimetry

    NASA Astrophysics Data System (ADS)

    Müller, D.; Matthews, K. J.; Sandwell, D. T.

    2014-12-01

    Radar altimetry measurements of the ocean surface topography from two satellites have recently been used to construct a new global marine gravity model that is twice as accurate as previous models. The model reveals previously invisible abyssal hill (AH) fabric in many parts of the ocean basins, placing valuable additional constraints on tectonic events reflected in changes in the orientation of linear AHs, and thus in spreading direction. AH fabric, if dated via marine magnetic anomalies, puts much tighter temporal constraints on changes in seafloor spreading directions than fracture zones, which, depending on their offset, often take many millions of years to adjust to major plate motion events. The new data also reveal previously unmapped microplates in the Pacific and Indian oceans. They preferentially form in spreading corridors where spreading rates were very high, reaching plate tectonic speed limits, or in response to plate reorganization stresses. The mapping of previously unknown or poorly mapped ridge propagation events during the Cretaceous Normal Superchron (CNS), leading to pseudofaults and extinct ridges, is relevant for interpreting marine magnetic anomaly sequences during the CNS in terms of magnetic field variability. The new grid provides breathtakingly detailed views of individual fault structures, previously only mapped via expensive seismic surveys, in the North Falkland Basin. Here narrow vertical gravity gradient highs and lows can be shown to correspond to seismically imaged horsts and grabens bounded by normal faults. The new gravity field allows us to create a detailed regional fault map outside of existing seismic coverage. The fault network that emerges illustrates that this eastern region of the Falkland Plateau is characterised by broadly distributed faulting, reflecting a wide rift that typically occurs in regions of higher than normal heat flow with relatively thick crust, where local crustal buoyancy effects dominate localising

  7. Digital Elevation Models of Greenland based on combined radar and laser altimetry as well as high-resolution stereoscopic imagery

    NASA Astrophysics Data System (ADS)

    Levinsen, J. F.; Smith, B. E.; Sandberg Sorensen, L.; Khvorostovsky, K.; Simonsen, S. B.; Forsberg, R.

    2015-12-01

    A number of Digital Elevation Models (DEMs) of Greenland exist, each of which are applicable for different purposes. This study presents two such DEMs: One developed by merging contemporary radar and laser altimeter data, and one derived from high-resolution stereoscopic imagery. All products are made freely available. The former DEM covers the entire Greenland. It is specific to the year 2010, providing it with an advantage over previous models suffering from either a reduced spatial/ temporal data coverage or errors from surface elevation changes (SEC) occurring during data acquisition. Radar data are acquired with Envisat and CryoSat-2, and laser data with the Ice, Cloud, and land Elevation Satellite, the Land, Vegetation, and Ice Sensor, and the Airborne Topographic Mapper. Correcting radar data for errors from slope effects and surface penetration of the echoes, and merging these with laser data, yields a DEM capable of resolving both surface depressions as well as topographic features at higher altitudes. The spatial resolution is 2 x 2 km, making the DEM ideal for application in surface mass balance studies, SEC detection from radar altimetry, or for correcting such data for slope-induced errors. The other DEM is developed in a pilot study building the expertise to map all ice-free parts of Greenland. The work combines WorldView-2 and -3 as well as GeoEye1 imagery from 2014 and 2015 over the Disko, Narsaq, Tassilaq, and Zackenberg regions. The novelty of the work is the determination of the product specifications after elaborate discussions with interested parties from government institutions, the tourist industry, etc. Thus, a 10 m DEM, 1.5 m orthophotos, and vector maps are produced. This opens to the possibility of using orthophotos with up-to-date contour lines or for deriving updated coastlines to aid, e.g., emergency management. This allows for a product development directly in line with the needs of parties with specific interests in Greenland.

  8. Topography of the Northern Hemisphere of Mercury from MESSENGER Laser Altimetry

    NASA Technical Reports Server (NTRS)

    Zuber,Maria T.; Smith, David E.; Phillips, Roger J.; Solomon, Sean C.; Neumann, Gregory A.; Hauck, Steven A., Jr.; Peale, Stanton J.; Barnouin, Oliver S.; Head, James W.; Johnson, Catherine L.; Lemoine, Frank G.; Mazarico, Erwan; Sun, Xiaoli; Torrence, Mark H.; Freed, Andrew M.; Klimczak, Christian; Margot, Jean-Luc; Oberst, Juergen; Perry, Mark E.; McNutt, Ralph L., Jr.; Balcerski, Jeffrey A.; Michel, Nathalie; Talpe, Matthieu J.; Yang, Di

    2012-01-01

    Laser altimetry by the MESSENGER spacecraft has yielded a topographic model of the northern hemisphere of Mercury. The dynamic range of elevations is considerably smaller than those of Mars or the Moon. The most prominent feature is an extensive lowland at high northern latitudes that hosts the volcanic northern plains. Within this lowland is a broad topographic rise that experienced uplift after plains emplacement. The interior of the 1500-km-diameter Caloris impact basin has been modified so that part of the basin floor now stands higher than the rim. The elevated portion of the floor of Caloris appears to be part of a quasi-linear rise that extends for approximately half the planetary circumference at mid-latitudes. Collectively, these features imply that long-wavelength changes to Mercury s topography occurred after the earliest phases of the planet s geological history.

  9. The use of laser altimetry data in Chang'E-1 precision orbit determination

    NASA Astrophysics Data System (ADS)

    Chang, Sheng-Qi; Huang, Yong; Li, Pei-Jia; Hu, Xiao-Gong; Fan, Min

    2016-09-01

    Accurate altimetric measurement not only can be applied to the calculation of a topography model but also can be used to improve the quality of the orbit reconstruction in the form of crossovers. Altimetry data from the Chang'E-1 (CE-1) laser altimeter are analyzed in this paper. The differences between the crossover constraint equation in the form of height discrepancies and in the form of minimum distances are mainly discussed. The results demonstrate that the crossover constraint equation in the form of minimum distances improves the CE-1 orbit precision. The overlap orbit performance has increased ˜ 30% compared to the orbit using only tracking data. External assessment using the topography model also shows orbit improvement. The results will be helpful for recomputing ephemeris and improving the CE-1 topography model.

  10. Application of Satellite Altimetry to Ocean Circulation Studies: 1987-1994

    NASA Technical Reports Server (NTRS)

    Fu, L. -L.; Cheney, R. E.

    1994-01-01

    Altimetric measurement of the height of the sea surface from space provides global observation of the world's oceans. The last eight years have witnessed a rapid growth in the use of altimetry data from the study of the ocean circulations, thanks to the multiyear data from the Geosat Mission.

  11. Low-frequency variability of the global sea surface height revealed by satellite altimetry

    NASA Technical Reports Server (NTRS)

    Fu, Lee-Lueng

    2004-01-01

    The focus of the paper is the variability of the North Atlantic Ocean. Large-scale low-frequency variability of the North Atlantic has recently been studied based on model simulations, as well as analysis of altimetry data in conjuction with in-situ data. These studies have suggested significant interannual to decadal changes in the North Atlantic in the 1990's.

  12. Investigating Antarctic ice sheet subglacial processes beneath the Whillans Ice Plain, West Antarctica, using satellite altimetry and GPS

    NASA Astrophysics Data System (ADS)

    Siegfried, Matthew Ross

    The Antarctic ice sheet has an extensive basal water system that lubricates the ice-bed interface and enables the fast flow of ice streams and outlet glaciers, which account for a majority of Antarctic ice discharge to the ocean. In the past decade, observational evidence has suggested that the subglacial hydrology of Antarctica can be non-steady, changing on sub-decadal timescales, but the effect of dynamic hydrology on ice flow remains uncertain. The Whillans Ice Plain (WIP), at the confluence of the Whillans and Mercer ice streams, West Antarctica, has been studied for over 50 years and has been identified as a region with extensive active subglacial hydrology. In this dissertation, we develop and implement methods using a combination of ground-based Global Positioning System (GPS) data and satellite-based radar and laser altimetry to observe the surface expression of water movement beneath WIP, quantify the dynamic ice-flow response to an evolving basal water system, and investigate processes driven by the interaction of WIP with ocean tides that may impact subglacial water flow near the grounding line. We find that the coupled subglacial-ice stream system can respond rapidly to basal perturbations on sub-annual timescales and in ways that are not captured by simple models. We demonstrate that the location where subglacial water enters the ocean is a complex interface that requires significant improvement to our measurement precision to better understand important time-varying processes. We also apply our method for observing dynamic ice-surface height changes to the inventory of known subglacial lakes in Antarctica to extend our observational record and assess variability of the subglacial hydrologic system in different physical settings. Through this continent-wide analysis of subglacial lakes, we suggest that our current knowledge of the characteristic spatial and temporal scales of hydrologic variability is still limited by our observational capacity. We

  13. Study of landwater variation over Chao Phraya river basin using GRACE, satellite altimetry and in situ data

    NASA Astrophysics Data System (ADS)

    Yamamoto, K.; Fukuda, Y.; Nakaegawa, T.; Taniguchi, M.

    2009-12-01

    A project to assess the effects of human activities on the subsurface environment in Asian developing cities has been in progress (Research Institute for Humanity and Nature, Japan, 2009). Bangkok, Thailand is one of the study cities in this project. Using GRACE satellite gravity data, we previously recovered landwater mass variation over the Chao Phraya river basin, where Bangkok is located on downstream. However, mainly because of insufficient spatial resolution of the GRACE data then released, it was difficult to distinguish mass variation over the Chao Phraya basin with the ones of the neighboring Mekong, Irrawaddy and Salween river basins. Recently, some new versions of GRACE data sets have been available, and thus we estimated again the mass variations over these basins using version 2 of CNS/GRGS data set. The result shows that mass variations of the each basin could be distinguished due to improvement of the spatial resolution of the data. One of the interesting things is that a negative interannual mass trend is observed only over the Chao Phraya river basin, while the other basins show positive trend values. One of our concerns was which of the landwater components were decreasing. Because GRACE can only detect total terrestrial water storage, we further used satellite altimeter data to separate surface- and groundwater components. EnviSat data were mainly used as satellite altimetry data in this study, because the mission period is overlapping with GRACE mission and the ground track separation is relatively small. River water levels were recovered from satellite altimetry data, and converted to river water storage. Estimated river water storage was subtracted from the GRACE data. Thus, interannual surface- and groundwater trends were discussed separately. Another concern is whether the landwater decrease is caused by meteorological factors or factors of human activities. Thus, we also compared above results with global hydrological simulation model and

  14. From satellite altimetry to operational oceanography and Argo: three revolutions in oceanography (Fridtjof Nansen Medal Lecture)

    NASA Astrophysics Data System (ADS)

    Le Traon, P. Y.

    2012-04-01

    The launch of the US/French mission Topex/Poseidon (T/P) (CNES/NASA) in August 1992 was the start of a revolution in oceanography. For the first time, a very precise altimeter system optimized for large scale sea level and ocean circulation observations was flying. Topex/Poseidon revolutionized our vision and understanding of the ocean. It provided new views of the large scale seasonal and interannual sea level and ocean circulation variations. T/P alone could not observe the mesoscale circulation. In the 1990s, the ESA satellites ERS-1/2 were flying simultaneously with T/P. The ERS-1/2 orbit was well adapted for mesoscale circulation sampling but the orbit determination and altimeter performance were much less precise than for T/P. We demonstrated that we could use T/P as a reference mission for ERS-1/2 and bring the ERS-1/2 data to an accuracy level comparable to T/P. This was an essential first step for the merging of T/P and ERS-1/2. The second step required the development of a global optimal interpolation method. Near real time high resolution global sea level anomaly maps were then derived. These maps have been operationally produced as part of the SSALTO/DUACS system for the last 15 years. They are now widely used by the oceanographic community and have contributed to a much better understanding and recognition of the role and importance of mesoscale dynamics. The unique capability of satellite altimetry to observe the global ocean in near real time at high resolution was essential to the development of global ocean forecasting, a second revolution in oceanography. The Global Ocean Data Assimilation Experiment (GODAE) (1998-2008) was phased with the T/P and ERS-1/2 successors (Jason-1 and ENVISAT) and was instrumental in the development of global operational oceanography capabilities. Europe played a leading role in GODAE. In 1998, the global in-situ observing system was inadequate for the global scope of GODAE. This led to the development of Argo, an

  15. Shuttle Laser Altimeter (SLA): A pathfinder for space-based laser altimetry and lidar

    NASA Technical Reports Server (NTRS)

    Bufton, Jack; Blair, Bryan; Cavanaugh, John; Garvin, James

    1995-01-01

    The Shuttle Laser Altimeter (SLA) is a Hitchhiker experiment now being integrated for first flight on STS-72 in November 1995. Four Shuttle flights of the SLA are planned at a rate of about a flight every 18 months. They are aimed at the transition of the Goddard Space Flight Center airborne laser altimeter and lidar technology to low Earth orbit as a pathfinder for operational space-based laser remote sensing devices. Future alser altimeter sensors such as the Geoscience Laser Altimeter System (GLAS), an Earth Observing System facility instrument, and the Multi-Beam Laser Altimeter (MBLA), the land and vegetation laser altimeter for the NASA TOPSAT (Topography Satellite) Mission, will utilize systems and approaches being tested with SLA. The SLA Instrument measures the distance from the Space Shuttle to the Earth's surface by timing the two-way propagation of short (approximately 10 na noseconds) laser pulses. laser pulses at 1064 nm wavelength are generated in a laser transmitter and are detected by a telescope equipped with a silicon avalanche photodiode detector. The SLA data system makes the pulse time interval measurement to a precision of about 10 nsec and also records the temporal shape of the laser echo from the Earth's surface for interpretation of surface height distribution within the 100 m diam. sensor footprint. For example, tree height can be determined by measuring the characteristic double-pulse signature that results from a separation in time of laser backscatter from tree canopies and the underlying ground. This is accomplished with a pulse waveform digitizer that samples the detector output with an adjustable resolution of 2 nanoseconds or wider intervals in a 100 sample window centered on the return pulse echo. The digitizer makes the SLA into a high resolution surface lidar sensor. It can also be used for cloud and atmospheric aerosol lidar measurements by lengthening the sampling window and degrading the waveform resolution. Detailed test

  16. development of a medium repetition rate (10 Hz - 500 Hz) diode pumped laser transmitter for airborne scanning altimetry

    NASA Technical Reports Server (NTRS)

    Coyle, D. Barry; Lindauer, Steven J., II; Kay, Richard B.

    1998-01-01

    Since the late 1980's, NASA has developed several small, all-solid state lasers of low repetition rates for use as transmitters in prototype LIDAR and raster scanned altimetry retrieval systems. Our early laser transmitters were developed for high resolution airborne altimetry which employed cavity dumping techniques to produce a pulse shape with a 1 ns rise time. The first such laser was the SUMR (Sub-millimeter resolution) transmitter which used a side pumped, D-shaped half-rod of Nd:YAG for the oscillator active media and produced approximately 3 ns pulses of 100 micro-J energy at a 40 Hz repetition rate. (Coyle and Blair, 1993; Coyle et al., 1995) After several upgrades to improve rep rate and pulse energy, the final version produced 1.2 mJ pulses at 120 Hz with a 3.7 ns pulse width. The laser has become known as SPLT (Sharp Pulsed Laser Transmitter), and has flown successfully on a variety of airborne altimetry missions. (Coyle and Blair, 1995; Blair et al., 1994) From building these systems, we have accrued valuable experience in delivering field-deployable lasers and have become aware of the advantages and disadvantages of employing new technologies. For example, even though the laser's main operating environment is in a "cold" aircraft during flight, the laser must still operate in very warm temperatures. This is important if the mission is based in the desert or a tropical climate since ground calibration data from stationary targets must be gathered before and after each data flight. Because conductive cooling is much more convenient than closed loop water flow, achieving the highest possible laser efficiency is becoming a high priority when designing a flight laser. This is especially true for lasers with higher pulse energies and repetition rates which are needed for high altitude scanning altimeters and LIDARs.

  17. Adaptive re-tracking algorithm for retrieval of water level variations and wave heights from satellite altimetry data for middle-sized inland water bodies

    NASA Astrophysics Data System (ADS)

    Troitskaya, Yuliya; Lebedev, Sergey; Soustova, Irina; Rybushkina, Galina; Papko, Vladislav; Baidakov, Georgy; Panyutin, Andrey

    One of the recent applications of satellite altimetry originally designed for measurements of the sea level [1] is associated with remote investigation of the water level of inland waters: lakes, rivers, reservoirs [2-7]. The altimetry data re-tracking algorithms developed for open ocean conditions (e.g. Ocean-1,2) [1] often cannot be used in these cases, since the radar return is significantly contaminated by reflection from the land. The problem of minimization of errors in the water level retrieval for inland waters from altimetry measurements can be resolved by re-tracking satellite altimetry data. Recently, special re-tracking algorithms have been actively developed for re-processing altimetry data in the coastal zone when reflection from land strongly affects echo shapes: threshold re-tracking, The other methods of re-tracking (threshold re-tracking, beta-re-tracking, improved threshold re-tracking) were developed in [9-11]. The latest development in this field is PISTACH product [12], in which retracking bases on the classification of typical forms of telemetric waveforms in the coastal zones and inland water bodies. In this paper a novel method of regional adaptive re-tracking based on constructing a theoretical model describing the formation of telemetric waveforms by reflection from the piecewise constant model surface corresponding to the geography of the region is considered. It was proposed in [13, 14], where the algorithm for assessing water level in inland water bodies and in the coastal zone of the ocean with an error of about 10-15 cm was constructed. The algorithm includes four consecutive steps: - constructing a local piecewise model of a reflecting surface in the neighbourhood of the reservoir; - solving a direct problem by calculating the reflected waveforms within the framework of the model; - imposing restrictions and validity criteria for the algorithm based on waveform modelling; - solving the inverse problem by retrieving a tracking point

  18. DAHITI - an innovative approach for estimating water level time series over inland waters using multi-mission satellite altimetry

    NASA Astrophysics Data System (ADS)

    Schwatke, C.; Dettmering, D.; Bosch, W.; Seitz, F.

    2015-10-01

    Satellite altimetry has been designed for sea level monitoring over open ocean areas. However, for some years, this technology has also been used to retrieve water levels from reservoirs, wetlands and in general any inland water body, although the radar altimetry technique has been especially applied to rivers and lakes. In this paper, a new approach for the estimation of inland water level time series is described. It is used for the computation of time series of rivers and lakes available through the web service "Database for Hydrological Time Series over Inland Waters" (DAHITI). The new method is based on an extended outlier rejection and a Kalman filter approach incorporating cross-calibrated multi-mission altimeter data from Envisat, ERS-2, Jason-1, Jason-2, TOPEX/Poseidon, and SARAL/AltiKa, including their uncertainties. The paper presents water level time series for a variety of lakes and rivers in North and South America featuring different characteristics such as shape, lake extent, river width, and data coverage. A comprehensive validation is performed by comparisons with in situ gauge data and results from external inland altimeter databases. The new approach yields rms differences with respect to in situ data between 4 and 36 cm for lakes and 8 and 114 cm for rivers. For most study cases, more accurate height information than from other available altimeter databases can be achieved.

  19. Advances in Measuring Antarctic Sea-Ice Thickness and Ice-Sheet Elevations with ICESat Laser Altimetry

    NASA Technical Reports Server (NTRS)

    Zwally, H. Jay

    2004-01-01

    NASA's Ice, Cloud and Land Elevation Satellite (ICESat) has been measuring elevations of the Antarctic ice sheet and sea-ice freeboard elevations with unprecedented accuracy. Since February 20,2003, data has been acquired during three periods of laser operation varying from 36 to 54 days, which is less than the continuous operation of 3 to 5 years planned for the mission. The primary purpose of ICESat is to measure time-series of ice-sheet elevation changes for determination of the present-day mass balance of the ice sheets, study of associations between observed ice changes and polar climate, and estimation of the present and future contributions of the ice sheets to global sea level rise. ICESat data will continue to be acquired for approximately 33 days periods at 3 to 6 month intervals with the second of ICESat's three lasers, and eventually with the third laser. The laser footprints are about 70 m on the surface and are spaced at 172 m along-track. The on-board GPS receiver enables radial orbit determinations to an accuracy better than 5 cm. The orbital altitude is around 600 km at an inclination of 94 degrees with a 8-day repeat pattern for the calibration and validation period, followed by a 91 -day repeat period for the rest of the mission. The expected range precision of single footprint measurements was 10 cm, but the actual range precision of the data has been shown to be much better at 2 to 3 cm. The star-tracking attitude-determination system should enable footprints to be located to 6 m horizontally when attitude calibrations are completed. With the present attitude calibration, the elevation accuracy over the ice sheets ranges from about 30 cm over the low-slope areas to about 80 cm over areas with slopes of 1 to 2 degrees, which is much better than radar altimetry. After the first period of data collection, the spacecraft attitude was controlled to point the laser beam to within 50 m of reference surface tracks over the ice sheets. Detection of ice

  20. NASA Satellite Laser Ranging Network

    NASA Technical Reports Server (NTRS)

    Carter, David L.

    2004-01-01

    I will be participating in the International Workshop on Laser Ranging. I will be presenting to the International Laser Ranging Service (ILRS) general body meeting on the recent accomplishments and status of the NASA Satellite Laser Ranging (SLR) Network. The recent accomplishments and NASA's future plans will be outlined and the benefits to the scientific community will be addressed. I am member of the ILRS governing board, the Missions working group, and the Networks & Engineering working group. I am the chairman of the Missions Working and will be hosting a meeting during the week of the workshop. I will also represent the NASA SLR program at the ILRS governing board and other working group meetings.

  1. Arctic sea surface height variability and change from satellite radar altimetry and GRACE, 2003-2014

    NASA Astrophysics Data System (ADS)

    Armitage, Thomas W. K.; Bacon, Sheldon; Ridout, Andy L.; Thomas, Sam F.; Aksenov, Yevgeny; Wingham, Duncan J.

    2016-06-01

    Arctic sea surface height (SSH) is poorly observed by radar altimeters due to the poor coverage of the polar oceans provided by conventional altimeter missions and because large areas are perpetually covered by sea ice, requiring specialized data processing. We utilize SSH estimates from both the ice-covered and ice-free ocean to present monthly estimates of Arctic Dynamic Ocean Topography (DOT) from radar altimetry south of 81.5°N and combine this with GRACE ocean mass to estimate steric height. Our SSH and steric height estimates show good agreement with tide gauge records and geopotential height derived from Ice-Tethered Profilers. The large seasonal cycle of Arctic SSH (amplitude ˜5 cm) is dominated by seasonal steric height variation associated with seasonal freshwater fluxes, and peaks in October-November. Overall, the annual mean steric height increased by 2.2 ± 1.4 cm between 2003 and 2012 before falling to circa 2003 levels between 2012 and 2014 due to large reductions on the Siberian shelf seas. The total secular change in SSH between 2003 and 2014 is then dominated by a 2.1 ± 0.7 cm increase in ocean mass. We estimate that by 2010, the Beaufort Gyre had accumulated 4600 km3 of freshwater relative to the 2003-2006 mean. Doming of Arctic DOT in the Beaufort Sea is revealed by Empirical Orthogonal Function analysis to be concurrent with regional reductions in the Siberian Arctic. We estimate that the Siberian shelf seas lost ˜180 km3 of freshwater between 2003 and 2014, associated with an increase in annual mean salinity of 0.15 psu yr-1. Finally, ocean storage flux estimates from altimetry agree well with high-resolution model results, demonstrating the potential for altimetry to elucidate the Arctic hydrological cycle.

  2. Mass-induced [|#8#|]Sea Level Variations in the Red Sea from Satellite Altimetry and GRACE

    NASA Astrophysics Data System (ADS)

    Feng, W.; Lemoine, J.; Zhong, M.; Hsu, H.

    2011-12-01

    We have analyzed mass-induced sea level variations (SLVs) in the Red Sea from steric-corrected altimetry and GRACE between January 2003 and December 2010. The steric component of SLVs in the Red Sea calculated from climatological temperature and salinity data is relatively small and anti-phase with the mass-induced SLV. The total SLV in the Red Sea is mainly driven by the mass-induced SLV, which increases in winter when the Red Sea gains the water mass from the Gulf of Aden and vice versa in summer. Spatial and temporal patterns of mass-induced SLVs in the Red Sea from steric-corrected altimetry agree very well with GRACE observations. Both of two independent observations show high annual amplitude in the central Red Sea (>20cm). Total mass-induced SLVs in the Red Sea from two independent observations have similar annual amplitude and phase. One main purpose of our work is to see whether GRGS's ten-day GRACE results can observe intra-seasonal mass change in the Red Sea. The wavelet coherence analysis indicates that GRGS's results show the high correlation with the steric-corrected SLVs on intra-seasonal time scale. The agreement is excellent for all the time-span until 1/3 year period and is patchy between 1/3 and 1/16 year period. Furthermore, water flux estimates from current-meter arrays and moorings show mass gain in winter and mass loss in summer, which is also consistent with altimetry and GRACE.

  3. Seasonal fluctuations of surface water levels in the Mekong River basin from satellite altimetry and other remote sensing data

    NASA Astrophysics Data System (ADS)

    Dominh, K.; Letoan, T.; Cazenave, A.; Mognard-Campbell, N.; Lhermitte, J.

    2004-05-01

    Ten years of satellite altimetry data from the Topex/Poseidon satellite have been analysed to construct water level time series and five years of satellite SPOT Vegetation imagery have been used to monitor the flood extent over the Mekong River basin. Areas overflown by T/P include the Tonle Sap Lake, seasonaly inundated areas and several branches of the hydrographic network of the Mekong delta. Very strong seasonal signal is reported over the Tonle Sap, amplitude reaching annually 5-8 meters peak to peak. Clear interannual signal is also visible. For example year 1999 corresponds to weak floods, contrasting with year 2000 during which strong flood is noticed. Southward, we also observe large seasonal fluctuations (2-3 m) over inundated floodplains, as identified using imagery data from the SPOT Vegetation instrument. Several water level time series have also been constructed at intersections of T/P tracks and waterways of the Mekong Delta. Depending on the location, quite different annual amplitudes are observed, the closer to the Mekong mouth, the smaller the signal. We interpret this observation as the effect of dams built over the Delta in the recent years/decades. We also analysed the interannual water level signal together with precipitations over the whole Mekong basin.

  4. Volumetric evolution of Surtsey, Iceland, from topographic maps and scanning airborne laser altimetry

    USGS Publications Warehouse

    Garvin, J.B.; Williams, R.S.; Frawley, J.J.; Krabill, W.B.

    2000-01-01

    The volumetric evolution of Surtsey has been estimated on the basis of digital elevation models derived from NASA scanning airborne laser altimeter surveys (20 July 1998), as well as digitized 1:5,000-scale topographic maps produced by the National Land Survey of Iceland and by Norrman. Subaerial volumes have been computed from co-registered digital elevation models (DEM's) from 6 July 1968, 11 July 1975, 16 July 1993, and 20 July 1998 (scanning airborne laser altimetry), as well as true surface area (above mean sea level). Our analysis suggests that the subaerial volume of Surtsey has been reduced from nearly 0.100 km3 on 6 July 1968 to 0.075 km3 on 20 July 1998. Linear regression analysis of the temporal evolution of Surtsey's subaerial volume indicates that most of its subaerial surface will be at or below mean sea-level by approximately 2100. This assumes a conservative estimate of continuation of the current pace of marine erosion and mass-wasting on the island, including the indurated core of the conduits of the Surtur I and Surtur II eruptive vents. If the conduits are relatively resistant to marine erosion they will become sea stacks after the rest of the island has become a submarine shoal, and some portions of the island could survive for centuries. The 20 July 1998 scanning laser altimeter surveys further indicate rapid enlargement of erosional canyons in the northeastern portion of the partial tephra ring associated with Surtur I. Continued airborne and eventually spaceborne topographic surveys of Surtsey are planned to refine the inter-annual change of its subaerial volume.

  5. Antarctic Peninsula Ice Sheet Mass Balance from Satellite and Airborne Altimetry

    NASA Astrophysics Data System (ADS)

    Briggs, K.; Shepherd, A.; McMillan, M.; Gilbert, L.; Muir, A.; Flament, T.

    2014-12-01

    Substantial environmental changes are occurring over the Antarctic Peninsula (AP), including rapid climate warming, ice shelf collapse, and accelerated glacier thinning and flow. These changes have major implications for the regional ice sheet mass balance and for global sea level rise. Geodetic estimates of the AP Ice Sheet (APIS) mass balance indicate that it lost mass at an average rate of 20 ± 14 Gt/yr over the period 1992-2011 (Shepherd et al., 2012); this equates to approximately 25% of all Antarctic ice sheet mass losses, despite occupying only 4% of the continental area. Past estimates of mass change have either been at a low resolution (gravimetry) or have had sparse spatial sampling (the mass budget method and altimetry). As a consequence, regional patterns of mass change are not well captured which makes understanding the causes difficult. Through the combination of ERS-2, EnviSat, ICESat, ATM and CryoSat-2 altimetry datasets we have succeeded in generating a mass change time series for the APIS with sufficient resolution and spatial sampling to capture regional signals. Here we will present our methods for the optimisation, combination and interpolation of the elevation change measurements, and their conversion to mass change. Furthermore, the observed spatial and temporal trends in APIS mass balance will be examined and the possible causes explored.

  6. Interannual and Annual Variations in the Mediterranean Sea from Satellite Altimetry and Grace Data

    NASA Astrophysics Data System (ADS)

    Garcia, D.; Vigo, I.; Chao, B. F.; Del Río, J.

    2006-07-01

    More than a decade of altimetry data h ave been used to develop thr ee studies in the Med iterranean Sea (and Black sea wh en feasible). Firstly, sea level v ariations (SLV) data from 49 tide g auge ( TG) stations along th e North Med iterranean and Black Sea coast have been compared to close SLV measurements from altimetry. From those compar isons, vertical crustal motions at th e TG sites have b een inf erred. Secondly , in terannual SLV have been explored in the Mediterran ean and Black Sea. A kink of tendency in mid-1999 is observed in sev eral regions of the Med iterranean and in the Black Sea. Thirdly, th e steric and eustatic terms of the annual SLV of the Mediterr anean has been inferred from time- variab le gravity (TVG) data and temperature (T) and salinity (S) profiles. It has been inf erred that the SLV are main ly driven by steric SLV, wh ich are par tially offset by w ater mass changes.

  7. Exploring New Challenges of High-Resolution SWOT Satellite Altimetry with a Regional Model of the Solomon Sea

    NASA Astrophysics Data System (ADS)

    Brasseur, P.; Verron, J. A.; Djath, B.; Duran, M.; Gaultier, L.; Gourdeau, L.; Melet, A.; Molines, J. M.; Ubelmann, C.

    2014-12-01

    The upcoming high-resolution SWOT altimetry satellite will provide an unprecedented description of the ocean dynamic topography for studying sub- and meso-scale processes in the ocean. But there is still much uncertainty on the signal that will be observed. There are many scientific questions that are unresolved about the observability of altimetry at vhigh resolution and on the dynamical role of the ocean meso- and submesoscales. In addition, SWOT data will raise specific problems due to the size of the data flows. These issues will probably impact the data assimilation approaches for future scientific or operational oceanography applications. In this work, we propose to use a high-resolution numerical model of the Western Pacific Solomon Sea as a regional laboratory to explore such observability and dynamical issues, as well as new data assimilation challenges raised by SWOT. The Solomon Sea connects subtropical water masses to the equatorial ones through the low latitude western boundary currents and could potentially modulate the tropical Pacific climate. In the South Western Pacific, the Solomon Sea exhibits very intense eddy kinetic energy levels, while relatively little is known about the mesoscale and submesoscale activities in this region. The complex bathymetry of the region, complicated by the presence of narrow straits and numerous islands, raises specific challenges. So far, a Solomon sea model configuration has been set up at 1/36° resolution. Numerical simulations have been performed to explore the meso- and submesoscales dynamics. The numerical solutions which have been validated against available in situ data, show the development of small scale features, eddies, fronts and filaments. Spectral analysis reveals a behavior that is consistent with the SQG theory. There is a clear evidence of energy cascade from the small scales including the submesoscales, although those submesoscales are only partially resolved by the model. In parallel

  8. Global navigation satellite sounding of the atmosphere and GNSS altimetry : prospects for geosciences

    NASA Technical Reports Server (NTRS)

    Yunck, Tom P.; Hajj, George A.

    2003-01-01

    The vast illuminating power of the Global Positioning System (GPS), which transformed space geodesy in the 199Os, is now serving to probe the earth's fluid envelope in unique ways. Three distinct techniques have emerged: ground-based sensing of the integrated atmospheric moisture; space-based profiling of atmospheric refractivity, pressure, temperature, moisture, and other properties by active limb sounding; and surface (ocean and ice) altimetry and scatterometry with reflected signals detected from space. Ground-based GPS moisture sensing is already in provisional use for numerical weather prediction. Limb sounding, while less mature, offers a bevy of attractions, including high accuracy, stability, and vertical resolution; all-weather operation; and exceptionally low cost. GPS bistatic radar, r 'reflectometry,' is the least advanced but shows promise for a number of niche applications.

  9. An investigation of ensemble-based assimilation of satellite altimetry and tide gauge data in storm surge prediction

    NASA Astrophysics Data System (ADS)

    Etala, Paula; Saraceno, Martín; Echevarría, Pablo

    2015-03-01

    Cyclogenesis and long-fetched winds along the southeastern coast of South America may lead to floods in populated areas, as the Buenos Aires Province, with important economic and social impacts. A numerical model (SMARA) has already been implemented in the region to forecast storm surges. The propagation time of the surge in such extensive and shallow area allows the detection of anomalies based on observations from several hours up to the order of a day prior to the event. Here, we investigate the impact and potential benefit of storm surge level data assimilation into the SMARA model, with the objective of improving the forecast. In the experiments, the surface wind stress from an ensemble prediction system drives a storm surge model ensemble, based on the operational 2-D depth-averaged SMARA model. A 4-D Local Ensemble Transform Kalman Filter (4D-LETKF) initializes the ensemble in a 6-h cycle, assimilating the very few tide gauge observations available along the northern coast and satellite altimeter data. The sparse coverage of the altimeters is a challenge to data assimilation; however, the 4D-LETKF evolving covariance of the ensemble perturbations provides realistic cross-track analysis increments. Improvements on the forecast ensemble mean show the potential of an effective use of the sparse satellite altimeter and tidal gauges observations in the data assimilation prototype. Furthermore, the effects of the localization scale and of the observational errors of coastal altimetry and tidal gauges in the data assimilation approach are assessed.

  10. Satellite-based laser windsounder

    SciTech Connect

    Schultz, J.F.; Czuchlewski, S.J.; Quick, C.R.

    1997-08-01

    This is the final report of a one-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The project`s primary objective is to determine the technical feasibility of using satellite-based laser wind sensing systems for detailed study of winds, aerosols, and particulates around and downstream of suspected proliferation facilities. Extensive interactions with the relevant operational organization resulted in enthusiastic support and useful guidance with respect to measurement requirements and priorities. Four candidate wind sensing techniques were evaluated, and the incoherent Doppler technique was selected. A small satellite concept design study was completed to identify the technical issues inherent in a proof-of-concept small satellite mission. Use of a Mach-Zehnder interferometer instead of a Fabry-Perot would significantly simplify the optical train and could reduce weight, and possibly power, requirements with no loss of performance. A breadboard Mach-Zehnder interferometer-based system has been built to verify these predictions. Detailed plans were made for resolving other issues through construction and testing of a ground-based lidar system in collaboration with the University of Wisconsin, and through numerical lidar wind data assimilation studies.

  11. Reconstruction of the West Spitsbergen Current in 2000-2013 Using In Situ Observations Combined with Satellite Altimetry and Ocean Numerical Model

    NASA Astrophysics Data System (ADS)

    Bulczak, Anna Izabela

    2016-08-01

    The inflow of Atlantic Water (AW) into the Nordic Seas is of fundamental importance for the Arctic, European and global climate. The West Spitsbergen Current (WSC) is a main source of heat for the Arctic, greatly affecting its sea ice conditions and air temperatures. The aim of this study is to analyse the vertical structure of the current and reconstruct it along its path in 2000- 2013 using a synergy of data: i) in situ measurements collected along the WSC by the Institute Oceanology of Polish Academy of Sciences (IOPAS) regularly every July in 2000-2013, ii) satellite altimetry, and iii) an information about the WSC vertical structure simulated in the NEMO (1/12°) numerical model in the same time period. The preliminary results are presented based on the in situ mooring measurements and geostrophic currents calculated using satellite altimetry.

  12. MABEL Photon-Counting Laser Altimetry Data in Alaska for ICESat-2 Simulations and Development

    NASA Technical Reports Server (NTRS)

    Brunt, Kelly; Neumann, T. A.; Amundson, M.; Kavanaugh, J. L.; Moussavi, M. S.; Walsh, K. M.; Cook, W. B.; Markus, T.

    2016-01-01

    Multiple Altimeter Beam Experimental Lidar (MABEL) maps Alaskan crevasses in detail, using 50 of the expected along-track Advanced Topographic Laser Altimeter System (ATLAS) signal-photon densities over summer ice sheets. Ice, Cloud, and Land Elevation Satellite 2 (ICESat-2) along-track data density, and spatial data density due to the multiple-beam strategy, will provide a new dataset to mid-latitude alpine glacier researchers.

  13. Detection and Analysis of Complex Patterns of Ice Dynamics in Antarctica from ICESat Laser Altimetry

    NASA Astrophysics Data System (ADS)

    Babonis, Gregory Scott

    There remains much uncertainty in estimating the amount of Antarctic ice mass change, its dynamic component, and its spatial and temporal patterns. This work remedies the limitations of previous studies by generating the first detailed reconstruction of total and dynamic ice thickness and mass changes across Antarctica, from ICESat satellite altimetry observations in 2003-2009 using the Surface Elevation Reconstruction and Change Detection (SERAC) method. Ice sheet thickness changes are calculated with quantified error estimates for each time when ICESat flew over a ground-track crossover region, at approximately 110,000 locations across the Antarctic Ice Sheet. The time series are partitioned into changes due to surficial processes and ice dynamics. The new results markedly improve the spatial and temporal resolution of surface elevation, volume, and mass change rates for the AIS, and can be sampled at annual temporal resolutions. The results indicate a complex spatiotemporal pattern of dynamic mass loss in Antarctica, especially along individual outlet glaciers, and allow for the quantification of the annual contribution of Antarctic ice loss to sea level rise. Over 5000 individual locations exhibit either strong dynamic ice thickness change patterns, accounting for approximately 500 unique spatial clusters that identify regions likely influenced by subglacial hydrology. The spatial distribution and temporal behavior of these regions reveal the complexity and short-time scale variability in the subglacial hydrological system. From the 500 unique spatial clusters, over 370 represent newly identified, and not previously published, potential subglacial water bodies indicating an active subglacial hydrological system over a much larger region than previously observed. These numerous new observations of dynamic changes provide more than simply a larger set of data. Examination of both regional and local scale dynamic change patterns across Antarctica shows newly

  14. Transport of the Norwegian Atlantic current as determined from satellite altimetry

    NASA Technical Reports Server (NTRS)

    Pistek, Pavel; Johnson, Donald R.

    1992-01-01

    Relatively warm and salty North Atlantic surface waters flow through the Faeroe-Shetland Channel into the higher latitudes of the Nordic Seas, preserving an ice-free winter environment for much of the exterior coast of northern Europe. This flow was monitored along the Norwegian coast using Geosat altimetry on two ascending arcs during the Exact Repeat Mission in 1987-1989. Concurrent undertrack CTD surveys were used to fix a reference surface for the altimeter-derived SSH anomalies, in effect creating time series of alongtrack surface dynamic height topographies. Climatologic CTD casts were then used, with empirical orthogonal function (EOF) analysis, to derive relationships between historical surface dynamic heights and vertical temperature and salinity profiles. Applying these EOF relationships to the altimeter signals, mean transports of volume, heat, and salt were calculated at approximately 2.9 Sverdrups, 8.1 x 10 exp 11 KCal/s and 1.0 x 10 exp 8 Kg/s, respectively. Maximum transports occurred in February/March and minimum in July/August.

  15. Laser beamed power: Satellite demonstration applications

    NASA Technical Reports Server (NTRS)

    Landis, Geoffrey A.; Westerlund, Larry H.

    1992-01-01

    It is possible to use a ground-based laser to beam light to the solar arrays of orbiting satellites, to a level sufficient to provide all or some of the operating power required. Near-term applications of this technology for providing supplemental power to existing satellites are discussed. Two missions with significant commercial pay-off are supplementing solar power for radiation-degraded arrays and providing satellite power during eclipse for satellites with failed batteries.

  16. An Original Processing Method of Satellite Altimetry for Estimating Water Levels and Volume Fluctuations in a Series of Small Lakes of the Pantanal Wetland Complex in Brazil

    NASA Astrophysics Data System (ADS)

    Henrique Costa, Paulo; Oliveira Pereira, Eric; Maillard, Philippe

    2016-06-01

    Satellite altimetry is becoming a major tool for measuring water levels in rivers and lakes offering accuracies compatible with many hydrological applications, especially in uninhabited regions of difficult access. The Pantanal is considered the largest tropical wetland in the world and the sparsity of in situ gauging station make remote methods of water level measurements an attractive alternative. This article describes how satellites altimetry data from Envisat and Saral was used to determine water level in two small lakes in the Pantanal. By combining the water level with the water surface area extracted from satellite imagery, water volume fluctuations were also estimated for a few periods. The available algorithms (retrackers) that compute a range solution from the raw waveforms do not always produce reliable measurements in small lakes. This is because the return signal gets often "contaminated" by the surrounding land. To try to solve this, we created a "lake" retracker that rejects waveforms that cannot be attributed to "calm water" and convert them to altitude. Elevation data are stored in a database along with the water surface area to compute the volume fluctuations. Satellite water level time series were also produced and compared with the only nearby in situ gauging station. Although the "lake" retracker worked well with calm water, the presence of waves and other factors was such that the standard "ice1" retracker performed better on the overall. We estimate our water level accuracy to be around 75 cm. Although the return time of both satellites is only 35 days, the next few years promise to bring new altimetry satellite missions that will significantly increase this frequency.

  17. Satellite radar altimetry water elevations performance over a 200 m wide river: Evaluation over the Garonne River

    NASA Astrophysics Data System (ADS)

    Biancamaria, S.; Frappart, F.; Leleu, A.-S.; Marieu, V.; Blumstein, D.; Desjonquères, Jean-Damien; Boy, F.; Sottolichio, A.; Valle-Levinson, A.

    2017-01-01

    For at least 20 years, nadir altimetry satellite missions have been successfully used to first monitor the surface elevation of oceans and, shortly after, of large rivers and lakes. For the last 5-10 years, few studies have demonstrated the possibility to also observe smaller water bodies than previously thought feasible (river smaller than 500 m wide and lake below 10 km2). The present study aims at quantifying the nadir altimetry performance over a medium river (200 m or lower wide) with a pluvio-nival regime in a temperate climate (the Garonne River, France). Three altimetry missions have been considered: ENVISAT (from 2002 to 2010), Jason-2 (from 2008 to 2014) and SARAL (from 2013 to 2014). Compared to nearby in situ gages, ENVISAT and Jason-2 observations over the lower Garonne River mainstream (110 km upstream of the estuary) have the smallest errors, with water elevation anomalies root mean square errors (RMSE) around 50 cm and 20 cm, respectively. The few ENVISAT upstream measurements have RMSE ranging from 80 cm to 160 cm. Over the estuary, ENVISAT and SARAL water elevation anomalies RMSE are around 30 cm and 10 cm, respectively. The most recent altimetry mission, SARAL, does not provide river elevation measurements for most satellite overflights of the river mainstream. The altimeter remains "locked" on the top of surrounding hilly areas and does not observe the steep-sided river valley, which could be 50-100 m lower. This phenomenon is also observed, for fewer dates, on Jason-2 and ENVISAT measurements. In these cases, the measurement is not "erroneous", it just does not correspond to water elevation of the river that is covered by the satellite. ENVISAT is less prone to get 'locked' on the top of the topography due to some differences in the instrument measurement parameters, trading lower accuracy for more useful measurements. Such problems are specific to continental surfaces (or near the coasts), but are not observed over the open oceans, which are

  18. On estimating the basin-scale ocean circulation from satellite altimetry. Part 1: Straightforward spherical harmonic expansion

    NASA Technical Reports Server (NTRS)

    Tai, Chang-Kou

    1988-01-01

    Direct estimation of the absolute dynamic topography from satellite altimetry has been confined to the largest scales (basically the basin-scale) owing to the fact that the signal-to-noise ratio is more unfavorable everywhere else. But even for the largest scales, the results are contaminated by the orbit error and geoid uncertainties. Recently a more accurate Earth gravity model (GEM-T1) became available, providing the opportunity to examine the whole question of direct estimation under a more critical limelight. It is found that our knowledge of the Earth's gravity field has indeed improved a great deal. However, it is not yet possible to claim definitively that our knowledge of the ocean circulation has improved through direct estimation. Yet, the improvement in the gravity model has come to the point that it is no longer possible to attribute the discrepancy at the basin scales between altimetric and hydrographic results as mostly due to geoid uncertainties. A substantial part of the difference must be due to other factors; i.e., the orbit error, or the uncertainty of the hydrographically derived dynamic topography.

  19. DAHITI - An Innovative Approach for Estimating Water Level Time Series over Inland Water using Multi-Mission Satellite Altimetry

    NASA Astrophysics Data System (ADS)

    Schwatke, Christian; Dettmering, Denise

    2016-04-01

    Satellite altimetry has been designed for sea level monitoring over open ocean areas. However, for some years, this technology has also been used to retrieve water levels from lakes, reservoirs, rivers, wetlands and in general any inland water body. In this contribution, a new approach for the estimation of inland water level time series is presented. The method is the basis for the computation of time series of rivers and lakes available through the web service 'Database for Hydrological Time Series over Inland Water' (DAHITI). It is based on an extended outlier rejection and a Kalman filter approach incorporating cross-calibrated multi-mission altimeter data from Envisat, ERS-2, Jason-1, Jason-2, Topex/Poseidon, and SARAL/AltiKa, including their uncertainties. The new approach yields RMS differences with respect to in situ data between 4 cm and 36 cm for lakes and 8 cm and 114 cm for rivers, respectively. Within this presentation, the new approach will be introduced and examples for water level time series for a variety of lakes and rivers will be shown featuring different characteristics such as shape, lake extent, river width, and data coverage. A comprehensive validation is performed by comparisons with in situ gauge data and results from external inland altimeter databases.

  20. Kalman filter approach for estimating water level time series over inland water using multi-mission satellite altimetry

    NASA Astrophysics Data System (ADS)

    Schwatke, C.; Dettmering, D.; Bosch, W.; Seitz, F.

    2015-05-01

    Satellite altimetry has been designed for sea level monitoring over open ocean areas. However, since some years, this technology is also used for observing inland water levels of lakes and rivers. In this paper, a new approach for the estimation of inland water level time series is described. It is used for the computation of time series available through the web service "Database for Hydrological Time Series over Inland Water" (DAHITI). The method is based on a Kalman filter approach incorporating multi-mission altimeter observations and their uncertainties. As input data, cross-calibrated altimeter data from Envisat, ERS-2, Jason-1, Jason-2, Topex/Poseidon, and SARAL/AltiKa are used. The paper presents water level time series for a variety of lakes and rivers in North and South America featuring different characteristics such as shape, lake extent, river width, and data coverage. A comprehensive validation is performed by comparison with in-situ gauge data and results from external inland altimeter databases. The new approach yields RMS differences with respect to in-situ data between 4 and 38 cm for lakes and 12 and 139 cm for rivers, respectively. For most study cases, more accurate height information than from available other altimeter data bases can be achieved.

  1. MABEL photon-counting laser altimetry data in Alaska for ICESat-2 simulations and development

    NASA Astrophysics Data System (ADS)

    Brunt, Kelly M.; Neumann, Thomas A.; Amundson, Jason M.; Kavanaugh, Jeffrey L.; Moussavi, Mahsa S.; Walsh, Kaitlin M.; Cook, William B.; Markus, Thorsten

    2016-08-01

    Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) is scheduled to launch in late 2017 and will carry the Advanced Topographic Laser Altimeter System (ATLAS), which is a photon-counting laser altimeter and represents a new approach to satellite determination of surface elevation. Given the new technology of ATLAS, an airborne instrument, the Multiple Altimeter Beam Experimental Lidar (MABEL), was developed to provide data needed for satellite-algorithm development and ICESat-2 error analysis. MABEL was deployed out of Fairbanks, Alaska, in July 2014 to provide a test dataset for algorithm development in summer conditions with water-saturated snow and ice surfaces. Here we compare MABEL lidar data to in situ observations in Southeast Alaska to assess instrument performance in summer conditions and in the presence of glacier surface melt ponds and a wet snowpack. Results indicate the following: (1) based on MABEL and in situ data comparisons, the ATLAS 90 m beam-spacing strategy will provide a valid assessment of across-track slope that is consistent with shallow slopes (< 1°) of an ice-sheet interior over 50 to 150 m length scales; (2) the dense along-track sampling strategy of photon counting systems can provide crevasse detail; and (3) MABEL 532 nm wavelength light may sample both the surface and subsurface of shallow (approximately 2 m deep) supraglacial melt ponds. The data associated with crevasses and melt ponds indicate the potential ICESat-2 will have for the study of mountain and other small glaciers.

  2. Measuring Ganymede's tidal deformation by laser altimetry: application to the GALA Experiment

    NASA Astrophysics Data System (ADS)

    Steinbrügge, Gregor; Hussmann, Hauke; Stark, Alexander; Oberst, Jürgen

    2014-05-01

    Measurements of Ganymede's induced magnetic field suggest a salty water layer under the icy crust (Kivelson et al. 2002), in agreement with thermal models based on heat transfer and energy balance equations (e.g., Spohn and Schubert, 2003). Due to the small density contrast between ice-I and liquid water, interior structure models (e.g. Sohl et al. 2003) consistent with Ganymede's moment of inertia and total mass cannot constrain the ice thickness or ocean depth. In order to reduce the ambiguity of the structural models and to constrain the ice thickness, it has been proposed to measure the dynamic response of Ganymede's ice shell to tidal forces exerted by Jupiter characterized by the Love numbers h2 and k2. Similar strategies have been investigated in application to Europa (Wu 2001, Wahr 2006, Hussmann 2011). The body tide Love number h2 depends on the tidal frequency (main tidal cycle is the 7.15 days period of revolution), the internal structure, and the rheology, in particular on the presence of fluid layers, and the thickness and rigidity of an overlaying ice shell. Combined with measurements of the Love number k2, which can be inferred from radio science experiments, and a simultaneous determination of linear combinations of h2 and k2 the obtained data would significantly reduce the ambiguity in structural models (Wahr et al. 2006). A way to determine tidal effects in Ganymede's topography and therefore the h2 value by a spacecraft in orbit is the crossover method: Different orbit tracks will intersect at certain surface locations at different times so that the tidal signal can be extracted from a differential altimetry measurement. The Ganymede Laser Altimeter GALA is one of the instruments selected for the Jupiter Icy Moon Explorer (JUICE). The GALA instrument will perform globally distributed altitude measurements from a low circular orbit. The main challenges for the determination of the tidal amplitude are Ganymede's high surface roughness and low

  3. Retrieval of short scale geophysical signals and improved coastal data from SAR satellite altimetry

    NASA Astrophysics Data System (ADS)

    Fenoglio-Marc, Luciana; Buchhaupt, Christopher; Dinardo, Salvatore; Scharroo, Remko; Benveniste, Jerome; Becker, Matthias

    2016-04-01

    The Delay Doppler/Synthetic Aperture Radar (SAR) altimeter offers a new quality of observational data in comparison to the pulse-limited low resolution mode (LRM) data collected over the past twenty years. Due to the reduced noise in the measurements an improved retrieval of the geophysical signal is expected in SAR. The goal of this study is to characterize these improvements both in open ocean and coastal zone using standard Level 2 and Level 1 data reprocessed with improved algorithms. We have carried out, from CryoSat-2 Level 1a Full Bit Rate (L1a FBR) data, a Delay-Doppler processing and waveform retracking tailored specifically for coastal zone by applying Hamming Window and Zero-Padding, using an extended vertical swath window in order to minimize tracker errors and a dedicated SAMOSA-based coastal retracker (named SAMOSA+). SAMOSA+ accepts mean square slope as free parameter and the epoch's first guess fitting value is decided according to the peak in correlation between 20 consecutive waveforms (in order to mitigate land off-ranging effect). Those products can be extracted from ESA-ESRIN GPOD service (named SARvatore). In order to quantify the improvement with respect to pulse-limited altimetry, we build 20 Hz PLRM (pseudo-LRM) data from CryoSat-1 L1a FBR and retrack them with numerical convolutional Brown-based retracker. Hence, here, PLRM is used as a proxy for real pulse-limited products (LRM), since there is no direct comparison of SAR and LRM possible otherwise. The PLRM data are built and retracked by Technical University of Darmstadt (TUDa). In the open ocean the study consists on the retrieval of short scale geophysical, as the swell signals. The selected areas are the CryoSat-2 Pacific and Atlantic Boxes in which it operated in SAR mode. In the coastal zone of the North Sea the study concentrates on the reduction of land and ships contamination by dedicated procedures including improved retracking. Effects of different options and retracking

  4. Global scale variations in sea surface topography determined from satellite altimetry

    NASA Astrophysics Data System (ADS)

    Koblinsky, C. J.; Nerem, R. S.; Williamson, R. G.; Klosko, S. M.

    Large scale variations in sea surface topography reflect long-term changes in the ocean circulation and air-sea fluxes. The success of the U.S. Navy's Geosat altimeter mission from 1985 to 1989 has provided the first long-term global measurements from space with the apparent accuracy to observe these phenomena. We have used the observations from Geosat to determine the large scale (wavelengths greater than 1000 km) mean and variable sea surface topography of the ocean relative to the geoid. In this paper we will provide a preliminary discussion of these estimates through comparisons with in situ observations and a description of the most robust signals in the altimeter solutions. A two year time series of sea surface topography has been derived for the global ocean between 60° N and 60° S covering 1987 and 1988. Comparisons with monthly averaged tide gauge observations at 42 island sites show a typical difference of 6 cm rms. There is a strong correlation between the altimetry and in situ measurements when the large scale variations in sea level exceed 6 cm rms (altimeter signal-to-noise ratio greater than 1). Such variations include the monsoon-forced semi-annual undulations of the tropical Indian Ocean, the annual expansion and contraction of the upper ocean in the western sides of mid-latitude basins from seasonal heating, and the interannual wind-forced variations in the tropical Pacific. Interannual trends are also found at midlatitudes, which agree with the in situ measurements, and appear to be of basin scale.

  5. Unprecedented Monitoring of the Water Levels in the Ungauged Congo Basin Using Satellite Altimetry.

    NASA Astrophysics Data System (ADS)

    Becker, M.; Calmant, S.; Santos Da Silva, J.; Conchy, T.; Robinet, V.; Seyler, F.; Linguet, L.

    2014-12-01

    Despite the global importance of the Congo Basin, which is the second largest river basin in the world, the limited understanding of its hydro-climatic patterns is in part due to the lack of in-situ monitoring of climate variables there. Climate and hydrological station networks are sparse and poorly maintained; the few networks that were implemented during the colonial period have shrunk considerably. Conversely, the recent improvements in remote sensing technology provide more observations than ever before that can advance hydrological studies, particularly in tropical basins. This work provides the first monitoring of water level at the basin scale for the Congo Basin based on merged data from different altimetry missions: ENVISAT, Jason-2 and SARAL. More than 500 time series of water level are computed for a twenty of contributors, over the period of 2002 to 2010 for 200 ENVISAT series, including using the second orbital period, from 2008 for 75 Jason-2 series and from mid 2013 for 250 SARAL series. The consistency and the quality of this datasets are investigated. First, the ENVISAT and J2 series are compared to in-situ measurements where possible. SARAL is the very first mission collecting water levels over rivers in the Ka band. Therefore, in a second step, we compare the capability of its altimeter AltiKa to that of previous missions working in the Ku band such as ENVISAT and Jason-2 in retrieving water levels over the Congo basin. In the last part of the work, we investigate the river dynamics in the Congo Basin since 2002 until today, using the Multichannel SSA (MSSA) to provide information about the common temporal variability of the dominant variables among the water level datasets.

  6. Study of Sub-basin Scale Groundwater Variations in Asia Using GRACE, Satellite Altimetry and in-situ Data

    NASA Astrophysics Data System (ADS)

    Yamamoto, K.; Fukuda, Y.; Taniguchi, M.

    2008-12-01

    A project to assess the effects of human activities on the subsurface environment in Asian developing cities is now in progress (Research Institute for Humanity and Nature., 2008). In the project, precise in situ gravity and landwater observations combined with GRACE (Gravity Recovery and Climate Experiment) satellite gravity data is proposed to evaluate local groundwater level changes of the developing urban areas in Asia. It is necessary for precise and accurate estimation of the local groundwater variations to separate local groundwater level changes from regional or global scale landwater variations. GRACE data is useful to estimate large scale landwater variations. Using GRACE Level 2 monthly gravity field solutions, we previously recovered landwater mass variation around Bangkok, in Thailand, which is one of the test areas of the project and located on the downstream of Chao Phraya river basin in the Indochina Peninsula. However, it is difficult to distinguish landwater signal of Chao Phraya river basin itself with the neighboring 3 large river basins because of the limitation of the spatial resolution of the GRACE monthly solutions. In this study, we recovered mass variation of Chao Phraya river basin using GRACE"fs along track range rate data instead of the monthly solutions. We used the method developed by Chen et al (2007), which uses GRACE"fs line-of-sight range acceleration measurements. We also tested the recoveries of landwater mass variations in other small scale river basins including Jakarta, Seoul and Taipei, which are also study areas of the project. Using the sub-basin scale landwater mass variation recovered by GRACE, we estimated groundwater level change in the project study areas by combing with in situ landwater and gravity observations. Satellite altimetry data is also used to separate groundwater variation from other landwater components as a constraint of river water storage variations.

  7. Sea-Ice Freeboard Retrieval Using Digital Photon-Counting Laser Altimetry

    NASA Technical Reports Server (NTRS)

    Farrell, Sinead L.; Brunt, Kelly M.; Ruth, Julia M.; Kuhn, John M.; Connor, Laurence N.; Walsh, Kaitlin M.

    2015-01-01

    Airborne and spaceborne altimeters provide measurements of sea-ice elevation, from which sea-ice freeboard and thickness may be derived. Observations of the Arctic ice pack by satellite altimeters indicate a significant decline in ice thickness, and volume, over the last decade. NASA's Ice, Cloud and land Elevation Satellite-2 (ICESat-2) is a next-generation laser altimeter designed to continue key sea-ice observations through the end of this decade. An airborne simulator for ICESat-2, the Multiple Altimeter Beam Experimental Lidar (MABEL), has been deployed to gather pre-launch data for mission development. We present an analysis of MABEL data gathered over sea ice in the Greenland Sea and assess the capabilities of photon-counting techniques for sea-ice freeboard retrieval. We compare freeboard estimates in the marginal ice zone derived from MABEL photon-counting data with coincident data collected by a conventional airborne laser altimeter. We find that freeboard estimates agree to within 0.03m in the areas where sea-ice floes were interspersed with wide leads, and to within 0.07m elsewhere. MABEL data may also be used to infer sea-ice thickness, and when compared with coincident but independent ice thickness estimates, MABEL ice thicknesses agreed to within 0.65m or better.

  8. Surface topography of the Greenland Ice Sheet from satellite radar altimetry

    NASA Technical Reports Server (NTRS)

    Bindschadler, Robert A.; Zwally, H. Jay; Major, Judith A.; Brenner, Anita C.

    1989-01-01

    Surface elevation maps of the southern half of the Greenland subcontinent are produced from radar altimeter data acquired by the Seasat satellite. A summary of the processing procedure and examples of return waveform data are given. The elevation data are used to generate a regular grid which is then computer contoured to provide an elevation contour map. Ancillary maps show the statistical quality of the elevation data and various characteristics of the surface. The elevation map is used to define ice flow directions and delineate the major drainage basins. Regular maps of the Jakobshavns Glacier drainage basin and the ice divide in the vicinity of Crete Station are presented. Altimeter derived elevations are compared with elevations measured both by satellite geoceivers and optical surveying.

  9. Investigation of the seasonal spatial variability of the Caspian Sea level by satellite altimetry.

    NASA Astrophysics Data System (ADS)

    Safarov, Elnur; Mammadov, Ramiz; Cretaux, Jean-Francois; Arsen, Adalbert; Safarov, Said; Amrahov, Elvin

    2016-07-01

    Sea level fluctuations are among the most outstanding and debated issues of the Caspian Sea. Precipitation, underground water and river input are consistent parts of the inflow of the Caspian Sea water balance. The river input is also considered to be the main driver of the seasonal level changes of the Caspian Sea. Sufficiently large amount of this input is provided by the Volga. Although there is a good network of sea level stations covering the coastline of the sea, these facilities are not capable to reflect the sea level variations over the all surface. Meanwhile, the Caspian Sea is well observed by satellites Jason 1, Jason 2 and ENVISAT. Altimetric data taken from these satellites covers the surface of the sea much better than the data from the in-situ network stations. In this paper we investigate the spatial variability of the sea level that could provide more insight into the influence of river input (especially the Volga river), precipitation and other hydro-meteorological parameters on the Caspian Sea level.The altimetric data was averaged per every 10 square kilometers through all the tracks by means of the pre-prepared program made especially for this work. Also new maps of seasonal spatial variability of amplitude and phase of the annual signal of the Caspian Sea level for each investigated satellite were created by employing ARCGIS software. Moreover, these peaks of sea level amplitude and phase of annual signal results were comparatively analyzed with the corresponding river discharge of the Volga.

  10. Hydraulic visibility and effective cross sections based on hydrodynamical modeling of flow lines gained by satellite altimetry

    NASA Astrophysics Data System (ADS)

    Biancamaria, S.; Garambois, P. A.; Calmant, S.; Roux, H.; Paris, A.; Monnier, J.; Santos da Silva, J.

    2015-12-01

    Hydrodynamic laws predict that irregularities in a river bed geometry produce spatial and temporal variations in the water level, hence in its slope. Conversely, observation of these changes is a goal of the SWOT mission with the determination of the discharge as a final objective. In this study, we analyse the relationship between river bed undulations and water surface for an ungauged reach of the Xingu river, a first order tributary of the Amazon river. It is crosscut more than 10 times by a single ENVISAT track over a hundred of km. We have determined time series of water levelsat each of these crossings, called virtual stations (VS), hence slopes of the flow line. Using the discharge series computed by Paiva et al. (2013) between 1998 and 2009, Paris et al. (submitted) determined at each VS a rating curve relating these simulated discharge with the ENVISAT height series. One parameter of these rating curves is the zero-flow depth Z 0 . We show that it is possible to explain the spatial and temporal variations of the water surface slope in terms of hydrodynamical response of the longitudinal changes of the river bed geometry given by the successive values of Z 0 . Our experiment is based on an effective, single thread representation of a braided river, realistic values for the Manning coefficient and river widths picked up on JERS images. This study confirms that simulated flow lines are consistent with water surface elevations (WSE) and slopes gained by satellite altimetry. Hydrodynamical signatures are more visible where the river bed geometry varies significantly, and for reaches with a strong downstream control. Therefore, this study suggests that the longitudinal variations of the slope might be an interesting criteria for the question of river segmentation into elementary reaches for the SWOT mission which will provide continuous measurements of the water surface elevation, the slope and the reach width.

  11. The Surface Water and Ocean Topography Satellite Mission - An Assessment of Swath Altimetry Measurements of River Hydrodynamics

    NASA Technical Reports Server (NTRS)

    Wilson, Matthew D.; Durand, Michael; Alsdorf, Douglas; Chul-Jung, Hahn; Andreadis, Konstantinos M.; Lee, Hyongki

    2012-01-01

    The Surface Water and Ocean Topography (SWOT) satellite mission, scheduled for launch in 2020 with development commencing in 2015, will provide a step-change improvement in the measurement of terrestrial surface water storage and dynamics. In particular, it will provide the first, routine two-dimensional measurements of water surface elevations, which will allow for the estimation of river and floodplain flows via the water surface slope. In this paper, we characterize the measurements which may be obtained from SWOT and illustrate how they may be used to derive estimates of river discharge. In particular, we show (i) the spatia-temporal sampling scheme of SWOT, (ii) the errors which maybe expected in swath altimetry measurements of the terrestrial surface water, and (iii) the impacts such errors may have on estimates of water surface slope and river discharge, We illustrate this through a "virtual mission" study for a approximately 300 km reach of the central Amazon river, using a hydraulic model to provide water surface elevations according to the SWOT spatia-temporal sampling scheme (orbit with 78 degree inclination, 22 day repeat and 140 km swath width) to which errors were added based on a two-dimension height error spectrum derived from the SWOT design requirements. Water surface elevation measurements for the Amazon mainstem as may be observed by SWOT were thereby obtained. Using these measurements, estimates of river slope and discharge were derived and compared to those which may be obtained without error, and those obtained directly from the hydraulic model. It was found that discharge can be reproduced highly accurately from the water height, without knowledge of the detailed channel bathymetry using a modified Manning's equation, if friction, depth, width and slope are known. Increasing reach length was found to be an effective method to reduce systematic height error in SWOT measurements.

  12. Cross-shelf water exchange in the East China Sea as estimated by satellite altimetry and in situ hydrographic measurement

    NASA Astrophysics Data System (ADS)

    Ding, Ruibin; Huang, Daji; Xuan, Jiliang; Mayer, Bernhard; Zhou, Feng; Pohlmann, Thomas

    2016-09-01

    Combining satellite altimetry and in situ hydrographic measurement, we estimated the cross-shelf transport (CST) and its spatial and temporal variations across 200 m isobath in the East China Sea (ECS) from 1993 to 2014. The vertically integrated CST can be dynamically divided into three parts: surface Ekman transport, geostrophic transport, and bottom Ekman transport. The results show that the 22 year-mean, sectionally integrated CST to be 1.7 ± 2.0 Sv (positive in the on-shelf direction), comprised of bottom and surface Ekman transports of 2.7 ± 1.0 Sv and 0.6 ± 0.6 Sv, respectively, that are partially offset by a geostrophic transport of -1.5 ± 1.7 Sv. The sectionally integrated CST shows significantly high power at roughly annual period from 1999 to 2001, with lower power at intra-annual period. The vertically integrated CST to the northeast of Taiwan is the main source of sectionally integrated CST. The vertically integrated CST also shows significant variations in the 6-15 month period band to the northeast of Taiwan as well. The temporal variations of the sectionally integrated and vertically integrated CST are both controlled primarily by geostrophic transport and modulated by bottom Ekman transport. In the upper 50 m, the geostrophic current to the northeast of Taiwan exhibits large mean and significant variability. The empirical orthogonal function analysis of vertical structure of geostrophic current shows two significant modes with strong annual signal. The first mode is associated with the migration of Kuroshio axis near Taiwan, while the second mode is associated with the variation of the meander of the Kuroshio to the northeast of Taiwan.

  13. M2 Internal Tides and Their Observed Wavenumber Spectra from Satellite Altimetry*

    NASA Technical Reports Server (NTRS)

    Ray, R. D.; Zaron, E. D.

    2015-01-01

    A near-global chart of surface elevations associated with the stationary M2 internal tide is empirically constructed from multi-mission satellite altimeter data. An advantage of a strictly empirical mapping approach is that results are independent of assumptions about ocean wave dynamics and, in fact, can be used to test such assumptions. A disadvantage is that present-day altimeter coverage is only marginally adequate to support mapping such short-wavelength features. Moreover, predominantly north-south ground-track orientations and contamination from nontidal oceanographic variability can lead to deficiencies in mapped tides. Independent data from Cryosphere Satellite-2 (CryoSat-2) and other altimeters are used to test the solutions and show positive reduction in variance except in regions of large mesoscale variability. The tidal fields are subjected to two-dimensional wavenumber spectral analysis, which allows for the construction of an empirical map of modal wavelengths. Mode-1 wavelengths show good agreement with theoretical wavelengths calculated from the ocean's mean stratification, with a few localized exceptions (e.g., Tasman Sea). Mode-2 waves are detectable in much of the ocean, with wavelengths in reasonable agreement with theoretical expectations, but their spectral signatures grow too weak to map in some regions.

  14. Altimetry, Orbits and Tides

    NASA Technical Reports Server (NTRS)

    Colombo, O. L.

    1984-01-01

    The nature of the orbit error and its effect on the sea surface heights calculated with satellite altimetry are explained. The elementary concepts of celestial mechanics required to follow a general discussion of the problem are included. Consideration of errors in the orbits of satellites with precisely repeating ground tracks (SEASAT, TOPEX, ERS-1, POSEIDON, amongst past and future altimeter satellites) are detailed. The theoretical conclusions are illustrated with the numerical results of computer simulations. The nature of the errors in this type of orbits is such that this error can be filtered out by using height differences along repeating (overlapping) passes. This makes them particularly valuable for the study and monitoring of changes in the sea surface, such as tides. Elements of tidal theory, showing how these principles can be combined with those pertinent to the orbit error to make direct maps of the tides using altimetry are presented.

  15. Error assessments of widely-used orbit error approximations in satellite altimetry

    NASA Technical Reports Server (NTRS)

    Tai, Chang-Kou

    1988-01-01

    From simulations, the orbit error can be assumed to be a slowly varying sine wave with a predominant wavelength comparable to the Earth's circumference. Thus, one can derive analytically the error committed in representing the orbit error along a segment of the satellite ground track by a bias; by a bias and tilt (linear approximation); or by a bias, tilt, and curvature (quadratic approximation). The result clearly agrees with what is obvious intuitively, i.e., (1) the fit is better with more parameters, and (2) as the length of the segment increases, the approximation gets worse. But more importantly, it provides a quantitative basis to evaluate the accuracy of past results and, in the future, to select the best approximation according to the required precision and the efficiency of various approximations.

  16. On determining the large-scale ocean circulation from satellite altimetry

    NASA Technical Reports Server (NTRS)

    Tai, C.-K.

    1983-01-01

    It is contended that a spherical harmonic expansion of the difference between the altimeter-derived mean sea surface and the geoid estimate should reveal the large-scale circulation of the ocean surface layer when the low-degree terms are examined. Methods based on this principle are proposed and partially demonstrated over the Pacific Ocean with the aid of the mean sea surface derived from the Seasat altimeter and the Goddard Earth Model 9 earth gravity model. The preliminary results reveal a well-defined clockwise gyre in the North Pacific and a much less well defined counterclockwise gyre in the South Pacific. When the dynamic topography thus obtained is compared with Wyrtki's (1975) dynamic topography derived from hydrographic data, the agreement is found to be within the limit of geoid uncertainties and satellite orbital errors.

  17. Ocean eddy structure by satellite radar altimetry required for iceberg towing

    USGS Publications Warehouse

    Campbell, W.J.; Cheney, R.E.; Marsh, J.G.; Mognard, N.M.

    1980-01-01

    Models for the towing of large tabular icebergs give towing speeds of 0.5 knots to 1.0 knots relative to the ambient near surface current. Recent oceanographic research indicates that the world oceans are not principally composed of large steady-state current systems, like the Gulf Stream, but that most of the ocean momentum is probably involved in intense rings, formed by meanders of the large streams, and in mid-ocean eddies. These rings and eddies have typical dimensions on the order of 200 km with dynamic height anomalies across them of tens-of-centimeters to a meter. They migrate at speeds on the order of a few cm/sec. Current velocities as great as 3 knots have been observed in rings, and currents of 1 knot are common. Thus, the successful towing of icebergs is dependent on the ability to locate, measure, and track ocean rings and eddies. To accomplish this systematically on synoptic scales appears to be possible only by using satelliteborne radar altimeters. Ocean current and eddy structures as observed by the radar altimeters on the GEOS-3 and Seasat-1 satellites are presented and compared. Several satellite programs presently being planned call for flying radar altimeters in polar or near-polar orbits in the mid-1980 time frame. Thus, by the time tows of large icebergs will probably be attempted, it is possible synoptic observations of ocean rings and eddies which can be used to ascertain their location, size, intensity, and translation velocity will be a reality. ?? 1980.

  18. Ice Velocity Mapping of Ross Ice Shelf, Antarctica by Matching Surface Undulations Measured by Icesat Laser Altimetry

    NASA Technical Reports Server (NTRS)

    Lee, Choon-Ki; Han, Shin-Chan; Yu, Jaehyung; Scambos, Ted A.; Seo, Ki-Weon

    2012-01-01

    We present a novel method for estimating the surface horizontal velocity on ice shelves using laser altimetrydata from the Ice Cloud and land Elevation Satellite (ICESat; 20032009). The method matches undulations measured at crossover points between successive campaigns.

  19. About uncertainties in sea ice thickness retrieval from satellite radar altimetry: results from the ESA-CCI Sea Ice ECV Project Round Robin Exercise

    NASA Astrophysics Data System (ADS)

    Kern, S.; Khvorostovsky, K.; Skourup, H.; Rinne, E.; Parsakhoo, Z. S.; Djepa, V.; Wadhams, P.; Sandven, S.

    2014-03-01

    One goal of the European Space Agency Climate Change Initiative sea ice Essential Climate Variable project is to provide a quality controlled 20 year long data set of Arctic Ocean winter-time sea ice thickness distribution. An important step to achieve this goal is to assess the accuracy of sea ice thickness retrieval based on satellite radar altimetry. For this purpose a data base is created comprising sea ice freeboard derived from satellite radar altimetry between 1993 and 2012 and collocated observations of snow and sea ice freeboard from Operation Ice Bridge (OIB) and CryoSat Validation Experiment (CryoVEx) air-borne campaigns, of sea ice draft from moored and submarine Upward Looking Sonar (ULS), and of snow depth from OIB campaigns, Advanced Microwave Scanning Radiometer aboard EOS (AMSR-E) and the Warren Climatology (Warren et al., 1999). An inter-comparison of the snow depth data sets stresses the limited usefulness of Warren climatology snow depth for freeboard-to-thickness conversion under current Arctic Ocean conditions reported in other studies. This is confirmed by a comparison of snow freeboard measured during OIB and CryoVEx and snow freeboard computed from radar altimetry. For first-year ice the agreement between OIB and AMSR-E snow depth within 0.02 m suggests AMSR-E snow depth as an appropriate alternative. Different freeboard-to-thickness and freeboard-to-draft conversion approaches are realized. The mean observed ULS sea ice draft agrees with the mean sea ice draft computed from radar altimetry within the uncertainty bounds of the data sets involved. However, none of the realized approaches is able to reproduce the seasonal cycle in sea ice draft observed by moored ULS satisfactorily. A sensitivity analysis of the freeboard-to-thickness conversion suggests: in order to obtain sea ice thickness as accurate as 0.5 m from radar altimetry, besides a freeboard estimate with centimetre accuracy, an ice-type dependent sea ice density is as mandatory

  20. Understanding the Value of Satellite Altimetry for Monitoring Water Level Dynamics of Large Rivers in Bangladesh Delta

    NASA Astrophysics Data System (ADS)

    Hossain, F.; Akbor, S.; Sustainability, Satellites, Water; Environment (Saswe) Research Group

    2010-12-01

    Although transboundary river flow accounts for more than 40% of global surface flow across 145 nations (many of them water-stressed and conflict-prone), most of this flow is difficult to monitor in developing nations at operational timescales. For Bangladesh, this situation is particularly acute because it comprises only 7% of the entire Ganges-Brahmaputra-Meghna basin and is located at the downstream end of the basin. Thus more than 90% of the water is generated in upstream nations and yet this information is hard to obtain in Bangladesh due to lack of transboundary instrumentation or international treaties. This work therefore investigates the value of satellite radar altimetry in detecting the water level changes for large rivers in the Bangladesh Delta. It is founded on the hypothesis that a satellite altimeter can detect water level to the same accuracy for both inside and outside of Bangladesh. First, the river hydraulic model called HEC-RAS (Hydrologic Engineering Center, River Analysis System) is set up and calibrated over Bangladesh using a comprehensive database on in-situ river bathymetry and observed water level records. Next, the calibrated HEC-RAS model is provided boundary flow conditions upstream and downstream of the model domain. At the upstream end where the Ganges, Brahmaputra and Meghan enter Bangladesh, high resolution flow data modeled from a well calibrated hydrologic model called MIKE BASIN is provided as input. The observed tidal flow records of the Meghna estuary near the Bay of Bengal are used as the downstream boundary conditions. HEC-RAS is then used to simulate daily water level data for the period of 2003-2005 for major rivers of Bangladesh. These water level simulations are directly compared with altimeter estimates of water level from the ENVISAT mission. Accuracy of ENVISAT data is characterized as a function of season, flow regime and river type. The important question that this study aims to answer is, “To what extent can

  1. Comparison of marine gravity from shipboard and high-density satellite altimetry along the Mid-Atlantic Ridge, 30.5-35.5 deg S

    NASA Technical Reports Server (NTRS)

    Neumann, Gregory A.; Forsyth, Donald W.; Sandwell, David

    1993-01-01

    We compare new marine gravity fields derived from satellite altimetry with shipboard measurements over a region of more than 120,000 sq km in the central South Atlantic. Newly declassified satellite data were employed to construct free-air anomaly maps on 0.05 degree grids. An extensive gravity and bathymetry data set from four cruises along the Mid-Atlantic Ridge from 30.5-35.5 deg S provides a benchmark for testing the 2D resolution and accuracy of the satellite measurements where their crosstrack spacing is near their widest. The satellite gravity signal is coherent with bathymetry in this region down to wavelengths of 26 km, compared to 12.5 km for shipboard gravity. Residuals between the shipboard and satellite data sets have a roughly normal distribution. The standard deviation of satellite gravity with respect to shipboard measurements is nearly 7 mGal in a region of 140 mGal total variation, whereas the internal standard deviation at crossovers for GPS-navigated shipboard data is 1.8 mGal. The differences between shipboard and satellite data are too large to use satellite gravity to determine crustal thickness variations within a typical ridge segment.

  2. Glacier mass change evaluation in Lambert-Amery Area from 2002 to 2012 using ASTER stereo images and ICESat GLAS laser altimetry

    NASA Astrophysics Data System (ADS)

    Liu, Jun; Tong, Xiaohua; Liu, Shijie; Liu, Shuang; Li, Lingyun; Hong, Zhonghua; Xu, Yusheng

    2014-03-01

    Currently, one of the major issues is to transform different remote sensing observations into a global reference for sustainable global-scale glacier change monitoring. In order to put glacier changes into a broader temporal context, it is desirable to extend the glacier observation time as far back as possible. In this paper, we present a case study of registering ASTER satellite stereo images to ICESat GLAS laser altimetry data, by matching terrain features identified from the ICESat measurements to those corresponding in the ASTER images. Features like ridges and nunatak can be extracted from ICESat data, and these features can also be measured in ASTER stereo images. A rigid body transformation (3 translations, 3 rotations) is applied for an optimal fit of these two sets of feature points. After transforming the ASTER photogrammetry measurements into the ICESat reference frame, we compute elevation change rates at each ICESat point by using a linear interpolation to obtain an estimate of surface elevation from ASTER. The surface firn/ice density model is used in converting the elevation changes to mass changes. Our study indicates that Lambert Glacier is close to being in mass balance between 2002 and 2012.

  3. Sub-basin-scale sea level budgets from satellite altimetry, Argo floats and satellite gravimetry: a case study in the North Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Kleinherenbrink, Marcel; Riva, Riccardo; Sun, Yu

    2016-11-01

    In this study, for the first time, an attempt is made to close the sea level budget on a sub-basin scale in terms of trend and amplitude of the annual cycle. We also compare the residual time series after removing the trend, the semiannual and the annual signals. To obtain errors for altimetry and Argo, full variance-covariance matrices are computed using correlation functions and their errors are fully propagated. For altimetry, we apply a geographically dependent intermission bias [Ablain et al.(2015)], which leads to differences in trends up to 0.8 mm yr-1. Since Argo float measurements are non-homogeneously spaced, steric sea levels are first objectively interpolated onto a grid before averaging. For the Gravity Recovery And Climate Experiment (GRACE), gravity fields full variance-covariance matrices are used to propagate errors and statistically filter the gravity fields. We use four different filtered gravity field solutions and determine which post-processing strategy is best for budget closure. As a reference, the standard 96 degree Dense Decorrelation Kernel-5 (DDK5)-filtered Center for Space Research (CSR) solution is used to compute the mass component (MC). A comparison is made with two anisotropic Wiener-filtered CSR solutions up to degree and order 60 and 96 and a Wiener-filtered 90 degree ITSG solution. Budgets are computed for 10 polygons in the North Atlantic Ocean, defined in a way that the error on the trend of the MC plus steric sea level remains within 1 mm yr-1. Using the anisotropic Wiener filter on CSR gravity fields expanded up to spherical harmonic degree 96, it is possible to close the sea level budget in 9 of 10 sub-basins in terms of trend. Wiener-filtered Institute of Theoretical geodesy and Satellite Geodesy (ITSG) and the standard DDK5-filtered CSR solutions also close the trend budget if a glacial isostatic adjustment (GIA) correction error of 10-20 % is applied; however, the performance of the DDK5-filtered solution strongly depends

  4. Improvement of walking speed prediction by accelerometry and altimetry, validated by satellite positioning.

    PubMed

    Perrin, O; Terrier, P; Ladetto, Q; Merminod, B; Schutz, Y

    2000-03-01

    Activity monitors based on accelerometry are used to predict the speed and energy cost of walking at 0% slope, but not at other inclinations. Parallel measurements of body accelerations and altitude variation were studied to determine whether walking speed prediction could be improved. Fourteen subjects walked twice along a 1.3 km circuit with substantial slope variations (-17% to +17%). The parameters recorded were body acceleration using a uni-axial accelerometer, altitude variation using differential barometry, and walking speed using satellite positioning (DGPS). Linear regressions were calculated between acceleration and walking speed, and between acceleration/altitude and walking speed. These predictive models, calculated using the data from the first circuit run, were used to predict speed during the second circuit. Finally the predicted velocity was compared with the measured one. The result was that acceleration alone failed to predict speed (mean r = 0.4). Adding altitude variation improved the prediction (mean r = 0.7). With regard to the altitude/acceleration-speed relationship, substantial inter-individual variation was found. It is concluded that accelerometry, combined with altitude measurement, can assess position variations of humans provided inter-individual variation is taken into account. It is also confirmed that DGPS can be used for outdoor walking speed measurements, opening up new perspectives in the field of biomechanics.

  5. Characterization of Terrestrial Water Dynamics in the Congo Basin Using GRACE and Satellite Radar Altimetry

    NASA Technical Reports Server (NTRS)

    Lee, Lyongki; Beighley, R. Edward; Alsdorf, Douglas; Jung, Hahn Chul; Shum, C. K.; Duan, Jianbin; Guo, Junyi; Yamazaki, Dai; Andreadis, Konstantinos

    2011-01-01

    The Congo Basin is the world's third largest in size (approximately 3.7 million km^2), and second only to the Amazon River in discharge (approximately 40,200 cms annual average). However, the hydrological dynamics of seasonally flooded wetlands and floodplains remains poorly quantified. Here, we separate the Congo wetland into four 3 degree x 3 degree regions, and use remote sensing measurements (i.e., GRACE, satellite radar altimeter, GPCP, JERS-1, SRTM, and MODIS) to estimate the amounts of water filling and draining from the Congo wetland, and to determine the source of the water. We find that the amount of water annually filling and draining the Congo wetlands is 111 km^3, which is about one-third the size of the water volumes found on the mainstem Amazon floodplain. Based on amplitude comparisons among the water volume changes and timing comparisons among their fluxes, we conclude that the local upland runoff is the main source of the Congo wetland water, not the fluvial process of river-floodplain water exchange as in the Amazon. Our hydraulic analysis using altimeter measurements also supports our conclusion by demonstrating that water surface elevations in the wetlands are consistently higher than the adjacent river water levels. Our research also highlights differences in the hydrology and hydrodynamics between the Congo wetland and the mainstem Amazon floodplain.

  6. Characterization of Terrestrial Water Dynamics in the Congo Basin Using GRACE and Satellite Radar Altimetry

    NASA Technical Reports Server (NTRS)

    Lee, Hyongki; Beighley, R. Edward; Alsdorf, Douglas; Jung, Hahn Chul; Shum, C. K.; Duan, Jianbin; Guo, Junyi; Yamazaki, Dai; Andreadis, Konstantinos

    2011-01-01

    The Congo Basin is the world's third largest in size (approx.3.7 million sq km), and second only to the Amazon River in discharge (approx.40,200 cu m/s annual average). However, the hydrological dynamics of seasonally flooded wetlands and floodplains remains poorly quantified. Here, we separate the Congo wetland into four 3deg 3deg regions, and use remote sensing measurements (i.e., GRACE, satellite radar altimeter, GPCP, JERS-1, SRTM, and MODIS) to estimate the amounts of water filling and draining from the Congo wetland, and to determine the source of the water. We find that the amount of water annually filling and draining the Congo wetlands is 111 cu km, which is about one-third the size of the water volumes found on the mainstem Amazon floodplain. Based on amplitude comparisons among the water volume changes and timing comparisons among their fluxes, we conclude that the local upland runoff is the main source of the Congo wetland water, not the fluvial process of river-floodplain water exchange as in the Amazon. Our hydraulic analysis using altimeter measurements also supports our conclusion by demonstrating that water surface elevations in the wetlands are consistently higher than the adjacent river water levels. Our research highlights differences in the hydrology and hydrodynamics between the Congo wetland and the mainstem Amazon floodplain.

  7. Interannual variability of the lake levels in northwest Russia based on satellite altimetry

    NASA Astrophysics Data System (ADS)

    Lebedev, S. A.; Troitskaya, Y. I.; Rybushkina, G. V.; Dobrovolsky, M. N.

    2015-03-01

    Variability of the largest lakes levels in northwest Russia, a climatic change parameter, is characterized by alternating periods of rise and fall according to altimetric measurements of the TOPEX/Poseidon and Jason-1/2 satellites. Water level was calculated with the use of a regional adaptive retracking algorithm for the lakes Il'men, Ladoga, Onega and Peipus. Applications of this algorithm considerably increase the quantity of actual data records and significantly improve the accuracy of water level evaluation. According to the results, temporal variability of Lake Ilmen, Lake Ladoga and Lake Piepus levels is characterized by a wave with a period of 4-5 years, and that of Lake Onega level is characterized by a wave with a period of 15 years. During the period from 1993 to 2011, lake level rose at a rate of 1.17±0.95 cm/year for Lake Il'men, 0.24 ± 0.10 cm/year for Lake Ladoga, 1.39 ± 0.18 cm/year for Lake Piepus and 0.18 ± 0.09 cm/year for Lake Onega.

  8. Identifying key drivers of sea surface variability from satellite altimetry in the North-East Atlantic

    NASA Astrophysics Data System (ADS)

    Sterlini, Paul; de Vries, Hylke

    2015-04-01

    Sea surface height variability (SSV) operates in varying temporal and spatial scales and acts as a source of noise when trying to perform long term trend analysis on the sea surface height (SSH). SSV can be removed through a simple running average process but this approach takes no account of individual contributors to the SSV. This study seeks to identify (and ultimately remove) the major contributing components of the SSV in the North-East Atlantic to expose the underlying changes in the SSH signal. This allows a trend analysis on the "cleaned" SSH for an accurate determination of sea level rise. Observations of sea level anomalies (SLA) are taken from 21 years of satellite altimeter data and are used to estimate the SSV in the North-East Atlantic. Seasonal signals are removed and monthly means calculated. The SSV is decomposed into global, regional and local components and a simple multiple linear regression model is constructed on the basis of these components to model the explained SSV. Initial results show that a region of high SSV exists off the west coast of Denmark and can be well represented with a regression model which uses local wind and global temperature as primary regressors. The same model does not capture a more diffuse region of high SSV in the Atlantic Ocean which suggests that the SSV is driven by other physical processes and highlights the need for specific spatial analyses when seeking to model SSV. This work will help in understanding regional sea level change over the past 21 years and to provide a foundation for estimates of local sea level change in the near future.

  9. Surface Elevation Changes in West Antarctica from Satellite Altimetry: Mass Balance Implications

    NASA Technical Reports Server (NTRS)

    Zwally, H. Jay; Brenner, Anita C.; Cornejo, Helen; Koblinsky, Chester J. (Technical Monitor)

    2001-01-01

    Time-series of surface elevation change, which are constructed from 7-years (1992-1999) of ERS-1 and 2 satellite radar altimeter data of Antarctica, show significant seasonal, inter-annual, and long-term changes. Elevation time-series are created from altimeter crossovers among 90-day data periods on a 50 km grid to 81.5 degrees S and fit with a multivariate linear/sinusoidal function to give the average rate of elevation change (dH/dt) and account for seasonal changes. On the major Ronne, Filchner, and Ronne ice shelves, the dH/dt are small or near zero. In contrast, the ice shelves of the Antarctic Peninsula and along the West Antarctic coast appear to be thinning significantly, with a 23 +/- 3 cm a(exp -1) surface elevation decrease on the Larsen ice shelf and a 65 +/- 4 cm a(exp -1) decrease on the Dotson ice shelf. Significant elevation decreases are obtained over most of the drainage basins of the Pine Island and Thwaites glaciers. Significant increases are obtained over most of the other grounded ice in Marie Byrd Land, the Antarctic Peninsula, and Coates Land. Over the sector from 85 degrees W to 115 degrees W, which includes the Pine Island and Thwaites basins, the average elevation is significantly decreasing by 8.1 cm a(exp -1). The corresponding ice thickness change is about -11 cm a(exp -1), with a corresponding mass loss of 82 Gt a(exp -1), and a 0.22 mm a(exp -1) contribution to global sea level rise. In terms of elevation change, the decrease in the Pine Island-Thwaites sector is largely balanced by the increase in the Marie Byrd Land, but only balanced by about 1/4 in terms of ice thickness change and contribution to sea level rise. The overall average elevation change for the grounded ice is + 1.2 cm a(exp -1). Using an average bedrock uplift of 2.5 cm a(exp -1), implies an average ice thickness decrease of 1.3 cm a(exp -1), a mass loss of 22 Gt a(exp -1), and a 0.06 mm a(exp -1) contribution to global sea level rise.

  10. Laser data links for communication satellites

    NASA Technical Reports Server (NTRS)

    Ohern, W. L.; Rodenberger, C. A.

    1974-01-01

    Laser data relays potentially offer continuous 1 Gb/sec bandwidths, drastically increasing low-altitude satellite data collection capacity over present store-and-dump techniques. Availability of the laser link as a reliable alternative, operating within conventional low-altitude communication subsystem weight and power allocations, will create customer pressure for adoption. Major communication relay system impacts are discussed including reliability, mechanical design, attitude control, on-board data handling, contamination control, and traffic-net management. Interface parameters which drive the fundamental relay satellite design concepts are discussed, and conditions requiring early quantitative analysis are identified.

  11. Multi-Year Elevation Changes Near the West Margin of the Greenland Ice Sheet from Satellite Radar Altimetry

    NASA Technical Reports Server (NTRS)

    Lingle, Craig S.; Brenner, Anita C.; Zwally, H. Jay; DiMarzio, John P.

    1991-01-01

    Mean changes in the surface elevation near the west margin of the Greenland ice sheet are measured using Seasat altimetry and altimetry from the Geosat Exact Repeat Mission (ERM). The Seasat data extend from early July through early October 1978. The ERM data extend from winter 1986-87 through fall 1988. Both seasonal and multi-year changes are measured using altimetry referenced to GEM T2 orbits. The possible effects of orbit error are minimized by adjusting the orbits into a common ocean surface. Seasonal mean changes in the surface height are recognizable during the Geosat ERM. The multi-year measurements indicate the surface was lower by 0.4 +/- 0.4 m on average in late summer 1987 than in late summer 1978. The surface was lower by 0.2 +/- 0.5 m on average in late summer 1988 than in late summer 1978. As a control case, the computations art also carried out using altimetry referenced to orbits not adjusted into a common ocean surface.

  12. Multi-year elevation changes near the west margin of the Greenland ice sheet from satellite radar altimetry

    SciTech Connect

    Lingle, C.S.; Brenner, A.C.; Zwally, H.J.; DiMarzio, J.P.

    1992-03-01

    Mean changes in the surface elevation near the west margin of the Greenland ice sheet are measured using Seasat altimetry and altimetry from the Geosat Exact Repeat Mission (ERM). The Seasat data extend from early July through early October 1978. The ERM data extend from winter 1986-87 through fall 1988. Both seasonal and multi-year changes are measured using altimetry referenced to GEM T2 orbits. The possible effects of orbit error are minimized by adjusting the orbits into a common ocean surface. Seasonal mean changes in the surface height are recognizable during the Geosat ERM. The multi-year measurements indicate the surface was lower by 0.4 +/- 0.4 m on average in late summer 1987 than in late summer 1978. The surface was lower by 0.2 +/- 0.5 m on average in late summer 1988 than in late summer 1978. As a control case, the computations are also carried out using altimetry referenced to orbits not adjusted into a common ocean surface.

  13. A novel mobile dual-wavelength laser altimetry system for improved site-specific Nitrogen fertilizer applications

    NASA Astrophysics Data System (ADS)

    Eitel, J.; Magney, T. S.; Vierling, L. A.; Brown, T. T.; Huggins, D. R.

    2012-12-01

    Reducing fertilizer inputs while maintaining yield would increase farmer's profits and similarly lessen the adverse environmental effects of production agriculture. The development of technologies that allow precise, site-specific application of Nitrogen (N) fertilizer has thus been an important research goal over the past decades. Remote sensing of foliar crop properties and function with tractor-mountable optical sensors has thought to be useful to optimize N fertilizer applications. However, on-the-go sensing of foliar crop properties and function has proven difficult, particularly during early crop growth stages when fertilizer decisions are often made. This difficulty arises from the fact that the spectral signal measured by on-the-go sensors is dominated by soil reflectance during early crop growth stages. Here, we present the basic principles behind a novel, dual-wavelength, tractor mountable laser altimetry system that measures the laser return intensity of the reflected green and red laser light. The green (532 nm) and the red (660 nm) wavelength combination allows calculation of a modified Photochemical Reflectance Index (mPRI) that have shown to be sensitive to both crop function and foliar chemistry. The small field of view of the laser points (diameter: 4 mm) combined with its high sampling rate (1000 points sec-1) allows vegetation returns to be isolated from ground returns by using simple thresholds. First tests relating foliar N of winter wheat (Triticum aestivum L.) with laser derived mPRI are promising (r2 = 0.72). Further research is needed to test the relationship between laser derived spectral indices and crop function.

  14. Imaging Laser Altimetry in the Amazon: Mapping Large Areas of Topography, Vegetation Height and Structure, and Biomass

    NASA Technical Reports Server (NTRS)

    Blair, J. Bryan; Nelson, B.; dosSantos, J.; Valeriano, D.; Houghton, R.; Hofton, M.; Lutchke, S.; Sun, Q.

    2002-01-01

    A flight mission of NASA GSFC's Laser Vegetation Imaging Sensor (LVIS) is planned for June-August 2003 in the Amazon region of Brazil. The goal of this flight mission is to map the vegetation height and structure and ground topography of a large area of the Amazon. This data will be used to produce maps of true ground topography, vegetation height, and estimated above-ground biomass and for comparison with and potential calibration of Synthetic Aperture Radar (SAR) data. Approximately 15,000 sq. km covering various regions of the Amazon will be mapped. The LVIS sensor has the unique ability to accurately sense the ground topography beneath even the densest of forest canopies. This is achieved by using a high signal-to-noise laser altimeter to detect the very weak reflection from the ground that is available only through small gaps in between leaves and between tree canopies. Often the amount of ground signal is 1% or less of the total returned echo. Once the ground elevation is identified, that is used as the reference surface from which we measure the vertical height and structure of the vegetation. Test data over tropical forests have shown excellent correlation between LVIS measurements and biomass, basal area, stem density, ground topography, and canopy height. Examples of laser altimetry data over forests and the relationships to biophysical parameters will be shown. Also, recent advances in the LVIS instrument will be discussed.

  15. Satellites Would Transmit Power By Laser Beams

    NASA Technical Reports Server (NTRS)

    Williams, M. D.; Walker, Gilbert H.; HUMES D. H.; Kwon, J. H.

    1995-01-01

    Arrays of diode lasers concentrate power into narrow beams. Baseline design of system formulated with regard to two particular missions that differ greatly in power requirements, thus showing scalability and attributes of basic system. Satellite system features large-scale array amplifier of high efficiency, injection-locked amplifiers, coherent combination of beams, and use of advanced lithographic technology to fabricate diode lasers in array. Extremely rapid development of applicable technologies make features realizable within decade.

  16. Laser power beaming for satellite applications

    SciTech Connect

    Friedman, H.W.

    1993-09-22

    A serious consideration of laser power beaming for satellite applications appears to have grown out of a NASA mission analysis for transmitting power to lunar bases during the two week dark period. System analyses showed that laser power beaming to the moon in conjunction with efficient, large area solar cell collection panels, were an attractive alternative to other schemes such as battery storage and nuclear generators, largely because of the high space transportation costs. The primary difficulty with this scheme is the need for very high average power visible lasers. One system study indicated that lasers in excess of 10 MW at a wavelength of approximately 850 nm were required. Although such lasers systems have received much attention for military applications, their realization is still a long term goal.

  17. Ranging performance of satellite laser altimeters

    NASA Technical Reports Server (NTRS)

    Gardner, Chester S.

    1992-01-01

    Topographic mapping of the earth, moon and planets can be accomplished with high resolution and accuracy using satellite laser altimeters. These systems employ nanosecond laser pulses and microradian beam divergences to achieve submeter vertical range resolution from orbital altitudes of several hundred kilometers. Here, we develop detailed expressions for the range and pulse width measurement accuracies and use the results to evaluate the ranging performances of several satellite laser altimeters currently under development by NASA for launch during the next decade. Our analysis includes the effects of the target surface characteristics, spacecraft pointing jitter and waveform digitizer characteristics. The results show that ranging accuracy is critically dependent on the pointing accuracy and stability of the altimeter especially over high relief terrain where surface slopes are large. At typical orbital altitudes of several hundred kilometers, single-shot accuracies of a few centimeters can be achieved only when the pointing jitter is on the order of 10 mu rad or less.

  18. Combining ICESat and Aircraft Laser Altimetry Observations to Examine Recent Changes in Canadian Ice Caps

    NASA Astrophysics Data System (ADS)

    Abdalati, W.; Krabill, W.; Thomas, R.; Golder, J.; Frederick, E.; Manizade, S.; Martin, C.

    2004-12-01

    Precise repeat airborne laser surveys were conducted over the major ice caps in the Canadian Arctic Archipelago during the spring of 1995 and 2000 to measure elevation changes in the region. Our observations reveal thinning at lower elevations (below 1600 m) on most of the ice caps and glaciers, but either very little change or thickening at higher elevations in the ice cap accumulation zones. The behavior of the ice caps in the north on the Queen Elizabeth Islands can be explained by recent temperature and precipitation anomalies, but this is not the case for the more southern ice caps on Baffin Island, which appear to be still shrinking in response to the Little Ice Age. The regional characteristics of elevation change as a function of elevation enables an assessment of the Canadian ice caps' contribution to sea level during the 1995-2000 time period. Our estimates place them among the more significant sources of eustatic sea level rise, though they are not as substantial as Greenland ice sheet, Alaskan glaciers, or the Patagonian ice fields. The spring 2004 campaign of the Ice Cloud and land Elevation Satellite (ICESat) mission provides a means of examining the character of changes since 2000. Comparisons between the ICESat data and the earlier aircraft campaigns where the ICESat ground tracks intersect the aircraft flight lines reveal significant changes in ice cap behavior between the late 1990s and the last four years. The results of these comparisons will be discussed along with the differences in the 1995-2000 and 2000-2004 climate conditions that affect the mass balance and elevation characteristics in those time periods.

  19. Sea level change in the Gulf of Thailand from GPS-corrected tide gauge data and multi-satellite altimetry

    NASA Astrophysics Data System (ADS)

    Trisirisatayawong, Itthi; Naeije, Marc; Simons, Wim; Fenoglio-Marc, Luciana

    2011-04-01

    Investigation of long-term tidal data and short-term altimetry measurements reveals that sea level in the Gulf of Thailand is rising significantly faster than global average rates. Upward land motion detected from repeated precise GPS campaign measurements is used to correct the apparent sea level change from tide gauge, yielding absolute long-term trends as follows: Sattahip (1942-2004) 5.0 ± 1.3 mm/yr, Ko Sichang (1940-1999) 4.5 ± 1.3 mm/yr and Ko Mattaphon (1964-2004) 4.4 ± 1.1 mm/yr. Dual-crossover minimization of multi-mission altimetry data covering the 1993-2009 period reveals the following absolute sea level rates: Sattahip 4.8 ± 0.7 mm/yr, Ko Sichang 5.8 ± 0.8 mm/yr, Ko Lak 3.6 ± 0.7 mm/yr and Ko Mattaphon 3.2 ± 0.7 mm/yr. In other parts of the Gulf, the 1993-2009 rising rates are also in the range of 3 to 5.5 mm/yr. In the entire Gulf we don't find any evidence of sea level falling. At Ko Lak where the collocation of Topex-class altimetry ground track and the tidal station is extremely good, vertical land motion derived from the difference of sea level change rates detected by altimetry and tidal data is used to correct the apparent rate, yielding an absolute long-term (1940-2004) rate of 3.0 ± 1.5 mm/yr. The differences between the altimetry-based rates and the absolute tide gauge sea level trends can be explained by interannual variations like ENSO and decadal variations due to solar activity and lunar nutation. Post-2004 tidal data have been treated separately in our study because reliable values of region-wide vertical co-seismic displacements and post-seismic velocities caused by the 2004 Mw9.2 Sumatra-Andaman earthquake are still not accurately known. Exclusion of these data will not significantly change the determined long-term absolute sea level change rates because of the relatively short time span of post-earthquake sea level data compared to the complete tidal record. The impact of fast rising sea level combined with high rates of post

  20. Two wavelength satellite laser ranging using SPAD

    NASA Technical Reports Server (NTRS)

    Prochazka, Ivan; Hamal, Karel; Jelinkova, Helena; Kirchner, Georg; Koidl, F.

    1993-01-01

    When ranging to satellites with lasers, there are several principal contributions to the error budget: from the laser ranging system on the ground, from the satellite retroarray geometry, and from the atmosphere. Using a single wavelength, we have routinely achieved a ranging precision of 8 millimeters when ranging to the ERS-1 and Starlette satellites. The systematic error of the atmosphere, assuming the existing dispersion models, is expected to be of the order of 1 cm. Multiple wavelengths ranging might contribute to the refinement of the existing models. Taking into account the energy balance, the existing picosecond lasers and the existing receiver and detection technology, several pairs or multiple wavelengths may be considered. To be able to improve the atmospheric models to the subcentimeter accuracy level, the differential time interval (DTI) has to be determined within a few picoseconds depending on the selected wavelength pair. There exist several projects based on picosecond lasers as transmitters and on two types of detection techniques: one is based on photodetectors, like photomultipliers or photodiodes connected to the time interval meters. Another technique is based on the use of a streak camera as an echo signal detector, temporal analyzer, and time interval vernier. The temporal analysis at a single wavelength using the streak camera showed the complexity of the problem.

  1. Current Trends in Satellite Laser Ranging

    NASA Technical Reports Server (NTRS)

    Pearlman, M. R.; Appleby, G. M.; Kirchner, G.; McGarry, J.; Murphy, T.; Noll, C. E.; Pavlis, E. C.; Pierron, F.

    2010-01-01

    Satellite Laser Ranging (SLR) techniques are used to accurately measure the distance from ground stations to retroreflectors on satellites and the moon. SLR is one of the fundamental techniques that define the international Terrestrial Reference Frame (iTRF), which is the basis upon which we measure many aspects of global change over space, time, and evolving technology. It is one of the fundamental techniques that define at a level of precision of a few mm the origin and scale of the ITRF. Laser Ranging provides precision orbit determination and instrument calibration/validation for satellite-borne altimeters for the better understanding of sea level change, ocean dynamics, ice budget, and terrestrial topography. Laser ranging is also a tool to study the dynamics of the Moon and fundamental constants. Many of the GNSS satellites now carry retro-reflectors for improved orbit determination, harmonization of reference frames, and in-orbit co-location and system performance validation. The GNSS Constellations will be the means of making the reference frame available to worldwide users. Data and products from these measurements support key aspects of the GEOSS 10-Year implementation Plan adopted on February 16, 2005, The ITRF has been identified as a key contribution of the JAG to GEOSS and the ILRS makes a major contribution for its development since its foundation. The ILRS delivers weekly additional realizations that are accumulated sequentially to extend the ITRF and the Earth Orientation Parameter (EOP) series with a daily resolution. Additional products are currently under development such as precise orbits of satellites, EOP with daily availability, low-degree gravitational harmonics for studies of Earth dynamics and kinematics, etc. SLR technology continues to evolve toward the next generation laser ranging systems as programmatic requirements become more stringent. Ranging accuracy is improving as higher repetition rate, narrower pulse lasers and faster

  2. Power versus stabilization for laser satellite communication.

    PubMed

    Arnon, S

    1999-05-20

    To establish optical communication between any two satellites, the lines of sight of their optics must be aligned for the duration of the communication. The satellite pointing and tracking systems perform the alignment. The satellite pointing systems vibrate because of tracking noise and mechanical impacts (such as thruster operation, the antenna pointing mechanism, the solar array driver, navigation noise, tracking noise). These vibrations increase the bit error rate (BER) of the communication system. An expression is derived for adaptive transmitter power that compensates for vibration effects in heterodyne laser satellite links. This compensation makes it possible to keep the link BER performance constant for changes in vibration amplitudes. The motivation for constant BER is derived from the requirement for future satellite communication networks with high quality of service. A practical situation of a two-low-Earth-orbit satellite communication link is given. From the results of the example it is seen that the required power for a given BER increases almost exponentially for linear increase in vibration amplitude.

  3. Development of State of the Art Solid State Lasers for Altimetry and other LIDAR Applications

    NASA Technical Reports Server (NTRS)

    Kay, Richard B.

    1997-01-01

    This report describes work performed and research accomplished through the end of 1997. During this time period, we have designed and fabricated two lasers for flight LIDAR applications to medium altitudes (Laser Vegetation Imaging System designs LVIS 1 and LVIS 2), designed one earth orbiting LIDAR transmitter (VCL-Alt), and continued work on a high rep-rate LIDAR laser (Raster Scanned Altimeter, RASCAL). Additionally, a 'White Paper' was prepared which evaluates the current state of the art of Nd:YAG lasers and projects efficiencies to the year 2004. This report is attached as Appendix 1 of this report.

  4. Joint application of the satellite altimetry and radiometry data for the solution of a problem of ecological monitoring of a marine environment

    NASA Astrophysics Data System (ADS)

    Lebedev, S.

    Ecological monitoring of a marine environment of last years has shown, that alongside with processes of a destruction and deposition of pollutants not last role is played by dynamics of a marine surface, as the basic mass transfer. The models, existing on the present time, of calculation of currents usually use oceanographic and meteorological data obtained by the contact measurement methods. The apparent successes in development of ocean remote sensing methods open a path to creation of operating systems of ecological monitoring of a marine environment. The sea surface or dynamic topography calculated by satellite altimetry data, allows to analyze dynamics of the surface currents, which are not having brightly expressed thermal nature, as for instance, strong jet streams. In turn sea surface temperature, obtained by the satellite radiometry data, was used for more precise count of destruction processes of pollutants. Time-space scale of the satellite data from a ocean surface allow actively to use them in different models, that enables with a split-hair accuracy to make the physically reasonable forecast. Surface temperature and dynamic topography data sharing realized in the automated system "Regional Ecological Monitoring of a Marine Environment -- Black Sea", which basis by model of pollutant propagation. The research was undertaken with partial support from the Russian Basic Research Foundation (Project ? 01-07-90106).

  5. Joint Application of The Satellite Altimetry and Radiometry Data For Solution of A Problem of Ecological Monitoring of A Marine Environment

    NASA Astrophysics Data System (ADS)

    Lebedev, S. A.

    Ecological monitoring of a marine environment of last years has shown, that along- side with processes of a destruction and deposition of pollutants not last role is played by dynamics of a marine surface, as the basic mass transfer. The models, existing on the present time, of calculation of currents usually use oceanographic and meteoro- logical data obtained by the contact measurement methods. The apparent successes in development of ocean remote sensing methods open a path to creation of operating systems of ecological monitoring of a marine environment. The sea surface or dy- namic topography calculated by satellite altimetry data, allows to analyze dynamics of the surface currents, which are not having brightly expressed thermal nature, as for instance, strong jet streams. In turn sea surface temperature, obtained by the satellite radiometry data, was used for more precise count of destruction processes of pollu- tants. Time-space scale of the satellite data from a ocean surface allow actively to use them in different models, that enables with a split-hair accuracy to make the physically reasonable forecast. Surface temperature and dynamic topography data sharing real- ized in the automated system SRegional Ecological Monitoring of a Marine Environment U Black SeaT, which basis by model of pollutant propagation. The research was undertaken with partial support from the Russian Basic Research Foundation (Project #01-07-90106).

  6. Radar altimetry systems cost analysis

    NASA Technical Reports Server (NTRS)

    Escoe, D.; Heuring, F. T.; Denman, W. F.

    1976-01-01

    This report discusses the application and cost of two types of altimeter systems (spaceborne (satellite and shuttle) and airborne) to twelve user requirements. The overall design of the systems defined to meet these requirements is predicated on an unconstrained altimetry technology; that is, any level of altimeter or supporting equipment performance is possible.

  7. The impact of snow depth, snow density and ice density on sea ice thickness retrieval from satellite radar altimetry: results from the ESA-CCI Sea Ice ECV Project Round Robin Exercise

    NASA Astrophysics Data System (ADS)

    Kern, S.; Khvorostovsky, K.; Skourup, H.; Rinne, E.; Parsakhoo, Z. S.; Djepa, V.; Wadhams, P.; Sandven, S.

    2015-01-01

    We assess different methods and input parameters, namely snow depth, snow density and ice density, used in freeboard-to-thickness conversion of Arctic sea ice. This conversion is an important part of sea ice thickness retrieval from spaceborne altimetry. A data base is created comprising sea ice freeboard derived from satellite radar altimetry between 1993 and 2012 and co-locate observations of total (sea ice + snow) and sea ice freeboard from the Operation Ice Bridge (OIB) and CryoSat Validation Experiment (CryoVEx) airborne campaigns, of sea ice draft from moored and submarine upward looking sonar (ULS), and of snow depth from OIB campaigns, Advanced Microwave Scanning Radiometer (AMSR-E) and the Warren climatology (Warren et al., 1999). We compare the different data sets in spatiotemporal scales where satellite radar altimetry yields meaningful results. An inter-comparison of the snow depth data sets emphasizes the limited usefulness of Warren climatology snow depth for freeboard-to-thickness conversion under current Arctic Ocean conditions reported in other studies. We test different freeboard-to-thickness and freeboard-to-draft conversion approaches. The mean observed ULS sea ice draft agrees with the mean sea ice draft derived from radar altimetry within the uncertainty bounds of the data sets involved. However, none of the approaches are able to reproduce the seasonal cycle in sea ice draft observed by moored ULS. A sensitivity analysis of the freeboard-to-thickness conversion suggests that sea ice density is as important as snow depth.

  8. Investigation of spatio-temporal water level and mass oscillations by using satellite gravimetry, altimetry and thermal data in Caspian Sea

    NASA Astrophysics Data System (ADS)

    Moradi, A.; de Viron, O.; Metivier, L.

    2012-12-01

    As Caspian Sea does not communicate with the world oceans, its dynamics are very different from the global water. Although -as for the world ocean- its level presents regular annual oscillations, estimations from last century and new more precise measurements shows large interannual fluctuations. Changes in the Caspian Sea water volume are investigated using space altimetry, whereas the GRACE satellite gravimetry mission allows monitoring the change of the surface mass distribution. Under the hypothesis that the change in water mass is the only cause of gravity change, it is possible to convert the mass distribution change into volume change, using a steric equation for the sea water. Combinations of multi-mission gridded altimetry data from AVISO with mono mission time series were used in order to analyze the local fluctuations of the lake, revealing a significant tilt between north and south. Large differences in the surface mass distribution rate of change in the basin and in the lake are evidenced in the GRACE data, as well as small differences in phase, which are due to delayed snow melting. Ignoring the short-term changes in water level due to winds, the main reason to cause periodic spatial water level disuniformity is spatial disuniformity in water density. Steric effect was calculated by interfering 2 factors of temperature and salinity. Steric anomaly maps show that it is able to change water level up to 17 cm. As the northern part of the lake has the least salinity in summers the largest effect would be expected to occur in the northern part, but the opposite is observed, probably due to the fact that this part is the shallowest. For the steric anomaly the lake presents spatially variations of 3 cm in winter but 7 cm in the summers. Generally, the largest steric induced fluctuations are observed in the middle of the lake, mostly in the north and east parts of the lake center. We used altimetry and space gravity data jointly, in order to build an improved

  9. Analysis of laser jamming to satellite-based detector

    NASA Astrophysics Data System (ADS)

    Wang, Si-wen; Guo, Li-hong; Guo, Ru-hai

    2009-07-01

    The reconnaissance satellite, communication satellite and navigation satellite used in the military applications have played more and more important role in the advanced technique wars and already become the significant support and aid system for military actions. With the development of all kinds of satellites, anti-satellite laser weapons emerge as the times require. The experiments and analyses of laser disturbing CCD (charge coupled detector) in near ground have been studied by many research groups, but their results are not suitable to the case that using laser disturbs the satellite-based detector. Because the distance between the satellite-based detector and the ground is very large, it is difficult to damage it directly. However the optical receive system of satellite detector has large optical gain, so laser disturbing satellite detector is possible. In order to determine its feasibility, the theoretical analyses and experimental study are carried out in the paper. Firstly, the influence factors of laser disturbing satellite detector are analyzed in detail, which including laser power density on the surface of the detector after long distance transmission, and laser power density threshold for disturbing etc. These factors are not only induced by the satellite orbit, but dependence on the following parameters: laser average power in the ground, laser beam quality, tracing and aiming precision and atmospheric transmission. A calculation model is developed by considering all factors which then the power density entering into the detector can be calculated. Secondly, the laser disturbing experiment is performed by using LD (laser diode) with the wavelength 808 nm disturbing CCD 5 kilometer away, which the disturbing threshold value is obtained as 3.55×10-4mW/cm2 that coincides with other researcher's results. Finally, using the theoretical model, the energy density of laser on the photosensitive surface of MSTI-3 satellite detector is estimated as about 100m

  10. Ground-based laser radar measurements of satellite vibrations.

    PubMed

    Schultz, K I; Fisher, S

    1992-12-20

    Vibration signatures from the low-power atmospheric compensation (LACE) satellite are obtained by using the MIT Lincoln Laboratory Firepond coherent CO(2) laser radar facility located in Westford, Mass. The LACE satellite is equipped with IR germanium retroreflectors on deployable/retractable booms to enhance ground-based IR laser radar measurements of on-orbit boom vibrations. Analysis of pulsed cw laser radar measurements of the satellite during and subsequent to boom retraction indicates the presence of a complex time-varying model structure. The observed vibration spectra include vibration modes not previously predicted. These data represent the first observations of satellite vibration modes from a ground-based laser radar.

  11. Solar driven lasers for power satellite applications

    NASA Technical Reports Server (NTRS)

    Taussio, R.; Cassady, P.; Klosterman, E.

    1980-01-01

    The technological feasibility of using multimagawatt lasers for space power transmission is discussed. Candidate lasers include electric discharge lasers, direct optically pumped lasers, and free electron lasers.

  12. Ranging performance of satellite laser altimeters

    NASA Technical Reports Server (NTRS)

    Gardner, Chester S.

    1992-01-01

    Detailed expressions for the range and pulse width measurement accuracies are developed and used to evaluate the ranging performances of several satellite laser altimeters currently under development by NASA for launch during the next decade. The analysis includes the effects of the target surface characteristics, spacecraft pointing jitter, and waveform digitizer characteristics. The results show that ranging accuracy is critically dependent on the pointing accuracy and stability of the altimeter especially over high relief terrain where surface slopes are large. At typical orbital altitudes of several hundred kilometers, single-shot accuracies of a few centimeters can be achieved only when the pointing jitter is on the order of 10 microrad or less.

  13. Ocean circulation using altimetry

    NASA Technical Reports Server (NTRS)

    Minster, Jean-Francois; Brossier, C.; Gennero, M. C.; Mazzega, P.; Remy, F.; Letraon, P. Y.; Blanc, F.

    1991-01-01

    Our group has been very actively involved in promoting satellite altimetry as a unique tool for observing ocean circulation and its variability. TOPEX/POSEIDON is particularly interesting as it is optimized for this purpose. It will probably be the first instrument really capable of observing the seasonal and interannual variability of subtropical and polar gyres and the first to eventually document the corresponding variability of their heat flux transport. The studies of these phenomena require data of the best quality, unbiased extraction of the signal, mixing of these satellite data with in situ measurements, and assimilation of the whole set into a dynamic description of ocean circulation. Our group intends to develop responses to all these requirements. We will concentrate mostly on the circulation of the South Atlantic and Indian Oceans: This will be done in close connection with other groups involved in the study of circulation of the tropical Atlantic Ocean, in the altimetry measurements (in particular, those of the tidal issue), and in the techniques of data assimilation in ocean circulation models.

  14. Design and analysis of the satellite laser communications network

    NASA Astrophysics Data System (ADS)

    Ren, Pei-an; Qian, Fengchen; Liu, Qiang; Jin, Linlin

    2015-02-01

    A satellite laser communications network structure with two layers and multiple domains has been proposed, which performance has been simulated by OPENT. To simulation, we design several OPNET models of the network's components based on a satellite constellation with two layers and multiple domains, as network model, node model, MAC layer protocol and optical antenna model. The network model consists of core layer and access layer. The core network consists of four geostationary orbit (GEO) satellites which are uniformly distributed in the geostationary orbit. The access network consists of 6 low Earth orbit (LEO) satellites which is the walker delta (walk-δ) constellation with three orbit planes. In access layer, each plane has two satellites, and the constellation is stably. The satellite constellation presented for space laser network can meet the demand of coverage in the middle and low latitude by a few satellites. Also several terminal device models such as the space laser transmitter, receiver, protocol layer module and optical antenna have been designed according to the inter-satellite links in different orbits t from GEO to LEO or GEO to ground. The influence to network of different transmitting throughput, receiving throughput, network protocol and average time delay are simulated. Simulation results of network coverage, connectivity and traffic load performance in different scenes show that the satellite laser network presented by the paper can be fit for high-speed satellite communications. Such analysis can provide effective reference for the research of satellite laser networking and communication protocol.

  15. On an assessment of surface roughness estimates from lunar laser altimetry pulse-widths for the Moon from LOLA using LROC narrow-angle stereo DTMs.

    NASA Astrophysics Data System (ADS)

    Muller, Jan-Peter; Poole, William

    2013-04-01

    Neumann et al. [1] proposed that laser altimetry pulse-widths could be employed to derive "within-footprint" surface roughness as opposed to surface roughness estimated from between laser altimetry pierce-points such as the example for Mars [2] and more recently from the 4-pointed star-shaped LOLA (Lunar reconnaissance Orbiter Laser Altimeter) onboard the NASA-LRO [3]. Since 2009, the LOLA has been collecting extensive global laser altimetry data with a 5m footprint and ?25m between the 5 points in a star-shape. In order to assess how accurately surface roughness (defined as simple RMS after slope correction) derived from LROC matches with surface roughness derived from LOLA footprints, publicly released LROC-NA (LRO Camera Narrow Angle) 1m Digital Terrain Models (DTMs) were employed to measure the surface roughness directly within each 5m footprint. A set of 20 LROC-NA DTMs were examined. Initially the match-up between the LOLA and LROC-NA orthorectified images (ORIs) is assessed visually to ensure that the co-registration is better than the LOLA footprint resolution. For each LOLA footprint, the pulse-width geolocation is then retrieved and this is used to "cookie-cut" the surface roughness and slopes derived from the LROC-NA DTMs. The investigation which includes data from a variety of different landforms shows little, if any correlation between surface roughness estimated from DTMs with LOLA pulse-widths at sub-footprint scale. In fact there is only any perceptible correlation between LOLA and LROC-DTMs at baselines of 40-60m for surface roughness and 20m for slopes. [1] Neumann et al. Mars Orbiter Laser Altimeter pulse width measurements and footprint-scale roughness. Geophysical Research Letters (2003) vol. 30 (11), paper 1561. DOI: 10.1029/2003GL017048 [2] Kreslavsky and Head. Kilometer-scale roughness of Mars: results from MOLA data analysis. J Geophys Res (2000) vol. 105 (E11) pp. 26695-26711. [3] Rosenburg et al. Global surface slopes and roughness of the

  16. Shape-from-shading using Landsat 8 and airborne laser altimetry over ice sheets: toward new regional DEMs of Greenland and Antarctica

    NASA Astrophysics Data System (ADS)

    Moussavi, M. S.; Scambos, T.; Haran, T. M.; Klinger, M. J.; Abdalati, W.

    2015-12-01

    We investigate the capability of Landsat 8's Operational Land Imager (OLI) instrument to quantify subtle ice sheet topography of Greenland and Antarctica. We use photoclinometry, or 'shape-from-shading', a method of deriving surface topography from local variations in image brightness due to varying surface slope. Photoclinomeetry is applicable over ice sheet areas with highly uniform albedo such as regions covered by recent snowfall. OLI imagery is available from both ascending and descending passes near the summer solstice period for both ice sheets. This provides two views of the surface features from two distinct solar azimuth illumination directions. Airborne laser altimetry data from the Airborne Topographic Mapper (ATM) instrument (flying on the Operation Ice Bridge program) are used to quantitatively convert the image brightness variations of surface undulations to surface slope. To validate the new DEM products, we use additional laser altimetry profiles collected over independent sites from Ice Bridge and ICESat, and high-resolution WorldView-2 DEMs. The photoclinometry-derived DEM products will be useful for studying surface elevation changes, enhancing bedrock elevation maps through inversion of surface topography, and inferring local variations in snow accumulation rates.

  17. Evidence for a slow subsidence of the Tahiti Island from GPS, DORIS, GRACE, and combined satellite altimetry and tide gauge sea level records

    NASA Astrophysics Data System (ADS)

    Fadil, A.; Barriot, J.; Sichoix, L.; Ortega, P.; Willis, P.; Serafini, J.

    2010-12-01

    Monitoring vertical land motion is of crucial interest in observations of long-term sea level change and its reconstruction, but is among of the most, yet highly challenging, tasks of space geodesy. The aim of the paper is to compare the vertical velocity estimates of Tahiti Island obtained from six independent geophysical measurements, namely a decade of GPS, DORIS, and GRACE data, 17 years sea level difference (altimeter minus tide gauge (TG)) time series, ICE-5G (VM2 L90) Post-Glacial Rebound (PGR) model predictions, and coral reef stratigraphy. Except The Glacial Isostatic Adjustment (GIA also known as PGR) model, all the techniques are in a good agreement and reveal a very slow subsidence of the Tahiti Island averaged at -0.3 mm/yr which is barely significant. Neverthless, despite of that vertical motion, Tahiti remains an ideal location for the calibration of satellite altimeter measurements.Estimated vertical crustal motions from GPS, DORIS, GRACE, (altimetry - tide-gauge) sea level records, coral reef stratigraphy, and GIA. GG = GAMIT-GLOBK software packageGOA= GIPSY-OASIS II software package

  18. Quantifying three-dimensional vegetation structure and its responses to disturbances using laser altimetry in the New Jersey Pinelands

    NASA Astrophysics Data System (ADS)

    Skowronski, Nicholas Scott

    2011-12-01

    The use of remotely sensed data to gain insight into large-scale ecological questions has intrigued researchers for decades. Recent technological advances have allowed for new types of data collection that add a third dimension to the realm of remotely sensed data. The work presented in this dissertation is linked by the use of laser altimetry data that allows scaling of field-based estimates of three-dimensional canopy structure to the landscape level. This dissertation strives to determine the repeatability of these measurements, develop robust methodologies for the application of new processing techniques to the data, application of these techniques to carbon accounting through high-resolution biomass mapping, and determine the ecological importance of these through the quantification of successional pathways and disturbance effects on canopy structure. Through examination of spatially-rectified Light Detection and Ranging (LiDAR) datasets, I found that intrinsic differences between LiDAR sensors affect their representation of canopy structure. However, I also found that statistical outputs from these sensors were highly correlated, and thus could be cross-calibrated strongly enough to allow for high resolution change detection of canopy height. Additionally, I calibrated and validated a methodology for processing raw LiDAR data allowing for the generation of high resolution (here 25 m horizontal resolution) maps of canopy height profiles, or canopy shape. I applied these methodologies to a large scale (ca. 1600 km2) scanning LiDAR dataset and developed maps of forest carbon storage and forest canopy shape. Forest carbon analyses illustrated the importance of wetlands systems and the contrasting effects of wildfire and prescribed fire on carbon storage in this system. Analysis of forest canopy shape showed distinct similarities, but also subtle differences, between cover types when compared over a height gradient. My results indicate that canopy shape is

  19. A global water cycle reanalysis (2003-2012) merging satellite gravimetry and altimetry observations with a hydrological multi-model ensemble

    NASA Astrophysics Data System (ADS)

    van Dijk, A. I. J. M.; Renzullo, L. J.; Wada, Y.; Tregoning, P.

    2014-08-01

    We present a global water cycle reanalysis that merges water balance estimates derived from the Gravity Recovery And Climate Experiment (GRACE) satellite mission, satellite water level altimetry and off-line estimates from several hydrological models. Error estimates for the sequential data assimilation scheme were derived from available uncertainty information and the triple collocation technique. Errors in four GRACE storage products were estimated to be 11-12 mm over land areas, while errors in monthly storage changes derived from five global hydrological models were estimated to be 17-28 mm. Prior and posterior water storage estimates were evaluated against independent observations of river water level and discharge, snow water storage and glacier mass loss. Data assimilation improved or maintained agreement overall, although results varied regionally. Uncertainties were greatest in regions where glacier mass loss and subsurface storage decline are both plausible but poorly constrained. We calculated a global water budget for 2003-2012. The main changes were a net loss of polar ice caps (-342 Gt yr-1) and mountain glaciers (-230 Gt yr-1), with an additional decrease in seasonal snowpack (-18 Gt yr-1). Storage increased due to new impoundments (+16 Gt yr-1), but this was compensated by decreases in other surface water bodies (-10 Gt yr-1). If the effect of groundwater depletion (-92 Gt yr-1) is considered separately, subsurface water storage increased by +202 Gt yr-1 due particularly to increased wetness in northern temperate regions and in the seasonally wet tropics of South America and southern Africa. The reanalysis results are publicly available via www.wenfo.org/wald/.

  20. Librations and obliquity of Mercury from the BepiColombo laser altimetry, radio science and camera experiments

    NASA Astrophysics Data System (ADS)

    Pfyffer, G.; van Hoolst, T.; Dehant, V. M.

    2010-12-01

    Through its anomalously high uncompressed density implying a metal fraction of 60% or more by mass, Mercury represents an extreme outcome of planetary formation in the inner solar system. The space missions MESSENGER and BepiColombo are expected to advance largely our knowledge of the structure, formation, and evolution of Mercury. In particular, insight into Mercury's deep interior will be obtained from observations of the obliquity, the 88-day forced libration, the planetary induced librations and the degree-two coefficients of the gravity field of Mercury. We report here on aspects of the observational strategy of ESA’s BepiColombo mission to determine the libration amplitude and obliquity, taking into account the space as well as the ground segment of the experiment. Repeated photographic measurements of selected target positions on the surface of Mercury are central to the strategy to determine the obliquity and libration in the frame of the BepiColombo mission, but a significant constraint is posed by the fact that the planetary surface can only be photographed under very strict illumination conditions. We therefore study the possibility to use the information embedded in the groundtrack crossings (crosstracks) of the BepiColombo laser altimeter (BELA) in addition to the primary photographic data in order to estimate the librations and obliquity of Mercury. An advantage of the laser altimetry data is that it does not depend on the solar incidence angle on the surface nor on the presence of specific surface features as required for the camera data in the camera rotation experiment. Both laser and photographic measurements were simulated in a realistic set-up in order to estimate the accuracy of the reconstruction of the orientation and rotational motion of the planet as a function of the amount of measurements made, the number of different targets and crosstrack points considered and their locations on the surface of the planet. Such an analysis requires the

  1. Laser experiments in light cloudiness with the geostationary satellite ARTEMIS

    NASA Astrophysics Data System (ADS)

    Kuzkov, V.; Kuzkov, S.; Sodnik, Z.

    2016-08-01

    The geostationary satellite ARTEMIS was launched in July 2001. The satellite is equipped with a laser communication terminal, which was used for the world's first inter-satellite laser communication link between ARTEMIS and the low earth orbit satellite SPOT-4. Ground-to-space laser communication experiments were also conducted under various atmospheric conditions involving ESA's optical ground station. With a rapidly increasing volume of information transferred by geostationary satellites, there is a rising demand for high-speed data links between ground stations and satellites. For ground-to-space laser communications there are a number of important design parameters that need to be addressed, among them, the influence of atmospheric turbulence in different atmospheric conditions and link geometries. The Main Astronomical Observatory of NAS of Ukraine developed a precise computer tracking system for its 0.7 m AZT-2 telescope and a compact laser communication package LACES (Laser Atmosphere and Communication experiments with Satellites) for laser communication experiments with geostationary satellites. The specially developed software allows computerized tracking of the satellites using their orbital data. A number of laser experiments between MAO and ARTEMIS were conducted in partial cloudiness with some amount of laser light observed through clouds. Such conditions caused high break-up (splitting) of images from the laser beacon of ARTEMIS. One possible explanation is Raman scattering of photons on molecules of a water vapor in the atmosphere. Raman scattering causes a shift in a wavelength of the photons.In addition, a different value for the refraction index appears in the direction of the meridian for the wavelength-shifted photons. This is similar to the anomalous atmospheric refraction that appears at low angular altitudes above the horizon. We have also estimated the atmospheric attenuation and the influence of atmospheric turbulence on observed results

  2. System requirements for laser power beaming to geosynchronous satellites

    SciTech Connect

    Neal, R.D.; McKechnie, T.S.; Neal, D.R.

    1994-03-01

    Geosynchronous satellites use solar arrays as their primary source of electrical power. During earth eclipse, which occurs 90 times each year, the satellites are powered by batteries, but the heavy charge-discharge cycle decreases their life expectancy. By beaming laser power to satellites during the eclipses, satellite life expectancy can be significantly increased. In this paper, the authors investigate the basic system parameters and trade-offs of using reactor pumped laser technology to beam power from the Nevada Test Site. A first order argument is used to develop a consistent set of requirements for such a system.

  3. Comparison of Surface Elevation Changes of the Greenland and Antarctic Ice Sheets from Radar and Laser Altimetry

    NASA Technical Reports Server (NTRS)

    Zwally, H. Jay; Brenner, Anita C.; Barbieri, Kristine; DiMarzio, John P.; Li, Jun; Robbins, John; Saba, Jack L.; Yi, Donghui

    2012-01-01

    A primary purpose of satellite altimeter measurements is determination of the mass balances of the Greenland and Antarctic ice sheets and changes with time by measurement of changes in the surface elevations. Since the early 1990's, important measurements for this purpose have been made by radar altimeters on ERS-l and 2, Envisat, and CryoSat and a laser altimeter on ICESat. One principal factor limiting direct comparisons between radar and laser measurements is the variable penetration depth of the radar signal and the corresponding location of the effective depth of the radar-measured elevation beneath the surface, in contrast to the laser-measured surface elevation. Although the radar penetration depth varies significantly both spatially and temporally, empirical corrections have been developed to account for this effect. Another limiting factor in direct comparisons is caused by differences in the size of the laser and radar footprints and their respective horizontal locations on the surface. Nevertheless, derived changes in elevation, dHldt, and time-series of elevation, H(t), have been shown to be comparable. For comparisons at different times, corrections for elevation changes caused by variations in the rate offrrn compaction have also been developed. Comparisons between the H(t) and the average dH/dt at some specific locations, such as the Vostok region of East Antarctic, show good agreement among results from ERS-l and 2, Envisat, and ICESat. However, Greenland maps of dHidt from Envisat and ICESat for the same time periods (2003-2008) show some areas of significant differences as well as areas of good agreement. Possible causes of residual differences are investigated and described.

  4. Combining Satellite Altimetry, Tide Gauge Observations and an Oceanographic Model to Derive the Baltic Sea Mean Sea Surface Topography

    NASA Astrophysics Data System (ADS)

    Novotny, K.; Liebsch, G.; Lehmann, A.; Dietrich, R.

    2006-07-01

    Sea-level variability the Baltic Sea is dominated by meteorologically forced fluctuations with large seasonal and interannual variations. In addition to the observations of satellite altimeters, a high-resolution oceanographic model of the Baltic Sea provides sea level heights that largely reflect the high-frequency sea surface variations. This different information can be combined in such a way that the variance of the altimetric sea level heights can be substantially reduced. The resulting reduced altim eter time series form the basis for the estimation of mean sea surface heights. The application of a geoid model yields the mean sea surface topography (MSSTop). A high spatial resolution of the resulting MSSTop is achieved by the combination of different altimetric missions. Observations of ERS-2 and GFO are tied to the observations of TOPEX by minimizing the crossover point differences. This also provides information about the relative biases between the different altimeter missions. The final MSSTop can be estimated with an accuracy of 3 to 5 cm.

  5. Satellite laser ranging work at the Goddard Space Flight Center

    NASA Technical Reports Server (NTRS)

    Mcgunigal, T. E.; Carrion, W. J.; Caudill, L. O.; Grant, C. R.; Johnson, T. S.; Premo, D. A.; Spadin, P. L.; Winston, G. C.

    1975-01-01

    Laser ranging systems, their range and accuracy capabilities, and planned improvements for future systems are discussed, the systems include one fixed and two mobile lasers ranging systems. They have demonstrated better than 10 cm accuracy both on a carefully surveyed ground range and in regular satellite ranging operations. They are capable of ranging to all currently launched retroreflector equipped satellites with the exception of Timation III. A third mobile system is discussed which will be accurate to better than 5 cm and will be capable of ranging to distant satellites such as Timation III and LAGEOS.

  6. Satellite laser ranging work at the Goddard Space Flight Center

    NASA Technical Reports Server (NTRS)

    Mcgunigal, T. E.; Carrion, W. J.; Caudill, L. O.; Grant, C. R.; Johnson, T. S.; Premo, D. A.; Spadin, P. L.; Winston, G. C.

    1975-01-01

    The pulsed-laser satellite ranging systems presently being operated by the Goddard Space Flight Center are described along with their range and accuracy capabilities. The major subsystems are outlined, operation of the fixed system and the two mobile systems is discussed, and the performance of all three systems is evaluated. It is noted that these systems have an accuracy of better than 10 cm on a carefully surveyed range as well as in regular satellite ranging operations and are capable of ranging to all currently launched retroreflector-equipped satellites with the exception of Timation III. Future improvements discussed include a third mobile system which will be able to range distant satellites, such as Timation III, with an accuracy of better than 5 cm and the use of a frequency-doubled Nd:YAG laser in place of the ruby lasers now being employed.

  7. Observing tectonic plate motions and deformations from satellite laser ranging

    NASA Technical Reports Server (NTRS)

    Christodoulidis, D. C.; Smith, D. E.; Kolenkiewicz, R.; Klosko, S. M.; Torrence, M. H.

    1985-01-01

    The scope of geodesy has been greatly affected by the advent of artificial near-earth satellites. The present paper provides a description of the results obtained from the reduction of data collected with the aid of satellite laser ranging. It is pointed out that dynamic reduction of satellite laser ranging (SLR) data provides very precise positions in three dimensions for the laser tracking network. The vertical components of the stations, through the tracking geometry provided by the global network and the accurate knowledge of orbital dynamics, are uniquely related to the center of mass of the earth. Attention is given to the observations, the methodologies for reducing satellite observations to estimate station positions, Lageos-observed tectonic plate motions, an improved temporal resolution of SLR plate motions, and the SLR vertical datum.

  8. Satellite laser ranging work at the Goddard Space Flight Center

    NASA Technical Reports Server (NTRS)

    Mcgunigal, T. E.; Carrion, W. J.; Caudill, L. O.; Grant, C. R.; Johnson, T. S.; Premo, D. A.; Spadin, P. L.; Winston, G. C.

    1975-01-01

    The paper describes the satellite laser ranging system at the Goddard Space Flight Center, its range and accuracy capabilities, and planned improvements for future systems. Major subsystems are described, including the laser, optical/mechanical, receiver, computer/software, timing, and laser data preprocessing subsystems. Operational considerations are examined, with attention given the mobile station layout, manpower requirements, and transportability. System performance is considered, with emphasis on system accuracy (calibration, stability, clock synchronization, atmospheric propagation correction) and range capability.

  9. Laser Guidestar Satellite for Ground-based Adaptive Optics Imaging of Geosynchronous Satellites

    NASA Astrophysics Data System (ADS)

    Marlow, W.; Carlton, A.; Yoon, H.; Clark, J.; Haughwout, C.; Cahoy, K.; Males, J.; Close, L.; Morzinski, K.

    2016-09-01

    In this study, we assess the utility of using a maneuverable nanosatellite laser guidestar from a geostationary equatorial orbit to enable ground-based, adaptive optics imaging of geosynchronous satellites with next-generation extremely large telescopes. The concept for a satellite guide star was rst discussed in the literature by Greenaway in the early 1990s, and expanded upon by Albert in 2012. With a satellite-based laser as an adaptive optics guidestar, the source laser does not need to scatter, and is well above atmospheric turbulence. When viewed from the ground through a turbulent atmosphere, the angular size of the satellite guidestar is much smaller than a back-scattered source. Advances in small satellite technology and capability allow us to revisit the concept on a 6U CubeSat, measuring 10 cm by 20 cm by 30 cm. We show that a system that uses a satellite-based laser transmitter can be relatively low power (1 W transmit power), operated intermittently, and requires little propellant to relocate within the geosynchronous belt. We present results of a design study on the feasibility of a small satellite guidestar and highlight the potential benets to the space situational awareness community.

  10. Estimation of the vertical distribution of tree biomass using last significant return laser altimetry returns from Eucalypt trees in New South Wales, Australia

    NASA Astrophysics Data System (ADS)

    Davenport, I. J.; Walker, J.; Gurney, R. J.

    2010-12-01

    Snow mass and soil moisture are important features of the environment governing the availability of drinking and irrigation water, food and hydro-power. They are estimated globally by measuring the microwave emission of the Earth’s surface. Soil’s microwave emissivity is strongly affected by its liquid moisture content, and the attenuation of soil-emitted radiation by snow is a function of the snow mass. The high water content of vegetation affects these results through attenuation, scattering and emission, so improving knowledge of vegetation mass and distribution will enable more accurate global characterisation of snow and soil moisture. Airborne laser altimetry systems acquire information about the environment by pulsing laser light at the ground, and interpreting the returning light curve using onboard differential GPS and inertial navigation systems. Such systems are primarily used to acquire topography by assuming that the last light returning to the sensor has been returned from the ground. By continuously recording the intensity of the light returned before the ground return, information about the vegetation between the aircraft and the ground can be derived. Recording the full intensity curves consumes a large volume of recording space, however, and is a relatively new instrument innovation, having in the past usually been combined with a reduced pulse rate to conserve storage. Deriving some information from systems which only record the last light returned would be of use in characterising large areas without using complete light curve return recording systems, allowing greater spatial cover and resolution with the same instrument and resources. Our previous work has characterised the error budget of single-return laser altimetry systems, and used this to distinguish different soil roughness at the centimetric scale, and show vegetation density variations within crops around 2m high. This work shows the vertical information on vegetation density that

  11. Velocity aberration and atmospheric refraction in satellite laser communication experiments.

    PubMed

    Nugent, L J; Condon, R J

    1966-11-01

    The effects of satellite velocity aberration and atmospheric refraction on the direction of propagation of lagser radiation reflected from a satellite back to an observer on the earth are examined. A velocity aberration analysis for the two-dimensional case where the satellite passes directly overhead at velocity v is presented to first order in v/c in order to illustrate the method. The equations for the more general threedimensional case are then given to first order in v/c, and it is indicated that higher order treatments are normally unnecessary in typical experimental considerations. Following this, a simple approximate equation giving the atmospheric refraction to an accuracy of a few microradians is developed; it is indicated that greater accuracy is not important because of laser pointing limitations imposed by atmospheric scattering and turbulence. The atmospheric refraction equation depends only on the apparent zenith angle of the satellite reflector relative to the earth-based laser, on the satelli-te altitude, and on the index of refraction of the laser radiation in the atmosphere at the earth's surface. Both of these developments should be useful in the design and interpretation of satellite laser-communication experiments.

  12. Tracking strategies for laser ranging to multiple satellite targets

    NASA Technical Reports Server (NTRS)

    Robbins, J. W.; Smith, D. E.; Kolenkiewicz, R.

    1994-01-01

    By the middle of the decade, several new Laser Geodynamic Satellites will be launched to join the current constellation comprised of the laser geodynamic satellite (LAGEOS) (US), Starlette (France), Ajisai (Japan), and Etalon I and II (USSR). The satellites to be launched, LAGEOS II and III (US & Italy), and Stella (France), will be injected into orbits that differ from the existing constellation so that geodetic and gravimetric quantities are sampled to enhance their resolution and accuracy. An examination of various possible tracking strategies adopted by the network of laser tracking stations has revealed that the recovery of precise geodetic parameters can be obtained over shorter intervals than is currently obtainable with the present constellation of satellites. This is particularly important in the planning of mobile laser tracking operations, given a network of permanently operating tracking sites. Through simulations, it is shown that laser tracking of certain satellite passes, pre-selected to provide optimal sky-coverage, provides the means to acquire a sufficient amount of data to allow the recovery of 1 cm station positions.

  13. Integrated laser/radar satellite ranging and tracking system

    NASA Technical Reports Server (NTRS)

    Hoge, F. E.

    1974-01-01

    A laser satellite ranging system that is mounted upon and integrated with a microwave tracking radar is reported. The 1-pulse/sec ruby laser transmitter is attached directly to the radar's elevation axis and radiates through a new opening in the radar's parabolic dish. The laser photomultiplier tube receiver utilizes the radar's existing 20-cm diam f/11 boresight telescope and observes through a similar symmetrically located opening in the dish. The laser system possesses separate ranging system electronics but shares the radar's timing, computer, and data handling/recording systems. The basic concept of the laser/radar is outlined together with a listing of the numerous advantages over present singular laser range-finding systems. The developmental laser hardware is described along with preliminary range-finding results and expectations.

  14. Laser ranging error budget for the TOPEX/POSEIDON satellite.

    PubMed

    Schwartz, J A

    1990-09-01

    A laser ranging error budget is detailed, and a specific error budget is derived for the TOPEX/POSEIDON satellite. A ranging uncertainty of 0.76 cm is predicted for TOPEX/POSEIDON at 20 degrees elevation using the presently designed laser retroreflector array and only modest improvements in present system operations. Atmospheric refraction and satellite attitude effects cause the predicted range error to vary with satellite elevation angle from 0.71 cm at zenith to 0.76 cm at 20 degrees elevation. This a priori error budget compares well with the ~1.2-cm rms a posteriori polynomial orbital fit using existing data taken for an extant satellite of similar size and orbit.

  15. Diode laser satellite systems for beamed power transmission

    NASA Technical Reports Server (NTRS)

    Williams, M. D.; Kwon, J. H.; Walker, G. H.; Humes, D. H.

    1990-01-01

    A power system composed of an orbiting laser satellite and a surface-based receiver/converter is described. Power is transmitted from the satellite to the receiver/converter by laser beam. The satellite components are: (1) solar collector; (2) blackbody; (3) photovoltaic cells; (4) heat radiators; (5) laser system; and (6) transmission optics. The receiver/converter components are: receiver dish; lenticular lens; photocells; and heat radiator. Although the system can be adapted to missions at many locations in the solar system, only two are examined here: powering a lunar habitat; and powering a lunar rover. Power system components are described and their masses, dimensions, operating powers, and temperatures, are estimated using known or feasible component capabilities. The critical technologies involved are discussed and other potential missions are mentioned.

  16. Scaling of solid state lasers for satellite power beaming applications

    SciTech Connect

    Friedman, H.W.; Albrecht, G.F.; Beach, R.J.

    1994-01-01

    The power requirements for a satellite power beaming laser system depend upon the diameter of the beam director, the performance of the adaptive optics system, and the mission requirements. For an 8 meter beam director and overall Strehl ratio of 50%, a 30 kW laser at 850 nm can deliver an equivalent solar flux to a satellite at geostationary orbit. Advances in Diode Pumped Solid State Lasers (DPSSL) have brought these small, efficient and reliable devices to high average power and they should be considered for satellite power beaming applications. Two solid state systems are described: a diode pumped Alexandrite and diode pumped Thulium doped YAG. Both can deliver high average power at 850 nm in a single aperture.

  17. Scaling of solid state lasers for satellite power beaming applications

    SciTech Connect

    Friedman, H.; Albrecht, G.; Beach, R.

    1994-12-31

    The power requirements for a satellite power beaming laser system depend upon the diameter of the beam director, the performance of the adaptive optics system, and the mission requirements. For an 8 meter beam director and overall Strehl ratio of 50%, a 30 kW laser at 850 nm can deliver an equivalent solar flux to a satellite at geostationary orbit. Advances in Diode Pumped Solid State Lasers (DPSSL) have brought these small, efficient and reliable devices to high average power and they should be considered for satellite power beaming applications. Two solid state systems are described: a diode pumped Alexandrite and diode pumped Thulium doped YAG. Both can deliver high average power at 850 nm in a single aperture.

  18. Satellite Altimetry for Naval Oceanography

    DTIC Science & Technology

    1990-11-01

    mesoscale map. H. Beresford and E. McNutt assisted with analses of An added capability of the SSH residual is the ability herod ad.uttaSs alyesofd to...wave energy. It should be gnd) Gulf of Mexico vmidoon. tal Da, 1536. ihi Day 0󈧴. lei Da. noted that a more sophisticated technioue for determiring...the 1560. (d) Day 1572. lei Day 1602 For contour interval. ee Figure A KINDLF SAMPLING STRArEGiIUS AND Mot As iSMitt IioN of A L risit IRI( D.I A _ (a

  19. Demonstration of centimeter-level precision, swath mapping, full-waveform laser altimetry from high altitude on the Global Hawk UAV for future application to cryospheric remote sensing

    NASA Astrophysics Data System (ADS)

    Blair, J. B.; Wake, S.; Rabine, D.; Hofton, M. A.; Mitchell, S.

    2013-12-01

    The Land Vegetation and Ice Sensor (LVIS) is a high-altitude, wide-swath laser altimeter that has, for over 15 years, demonstrated state-of-the-art performance in surface altimetry, including many aspects of remote sensing of the cryosphere such as precise topography of ice sheets and sea ice. NASA Goddard, in cooperation with NASA's Earth Science Technology Office (ESTO), has developed a new, more capable sensor that can operate autonomously from a high-altitude UAV aircraft to further enhance the LVIS capability and extend its reach and coverage. In June 2012, this latest sensor, known as LVIS-GH, was integrated onto NASA's Global Hawk aircraft and completed a successful high-altitude demonstration flight over Death Valley, Owens Valley, and the Sierra Nevada region of California. Data were collected over a wide variety of terrain types from 58,000' (> 17 km) altitude during the 6 hour long test flight. The full-waveform laser altimetry technique employed by LVIS and LVIS-GH provides precise surface topography measurements for solid earth and cryospheric applications and captures the vertical structure of forests in support of territorial ecology studies. LVIS-GH fully illuminates and maps a 4 km swath and provides cm-level range precision, as demonstrated in laboratory and horizontal range testing, as well as during this test flight. The cm range precision is notable as it applies to accurate measurements of sea ice freeboard and change detection of subtle surface deformation such as heaving in permafrost areas. In recent years, LVIS has primarily supported Operation IceBridge activities, including deployments to the Arctic and Antarctic on manned aircraft such as the NASA DC-8 and P-3. The LVIS-GH sensor provides an major upgrade of coverage capability and remote access; LVIS-GH operating on the long-duration Global Hawk aircraft can map up to 50,000 km^2 in a single flight and can provide access to remote regions such as the entirety of Antarctica. Future

  20. Prospects of the ICESat-2 laser altimetry mission for savanna ecosystem structural studies based on airborne simulation data

    NASA Astrophysics Data System (ADS)

    Gwenzi, David; Lefsky, Michael A.; Suchdeo, Vijay P.; Harding, David J.

    2016-08-01

    The next planned spaceborne lidar mission is the Ice, Cloud and land Elevation Satellite 2 (ICESat-2), which will use the Advanced Topographic Laser Altimeter System (ATLAS) sensor, a photon counting technique. To pre-validate the capability of this mission for studying three dimensional vegetation structure in savannas, we assessed the potential of the measurement approach to estimate canopy height in an oak savanna landscape. We used data from the Multiple Altimeter Beam Experimental Lidar (MABEL), an airborne photon counting lidar sensor developed by NASA's Goddard Space Flight Center. ATLAS-like data was generated using the MATLAS simulator, which adjusts MABEL data's detected number of signal and noise photons to that expected from the ATLAS instrument. Transects flown over the Tejon ranch conservancy in Kern County, California, USA were used for this work. For each transect we chose to use data from the near infrared channel that had the highest number of photons. We segmented each transect into 50 m, 25 m and 14 m long blocks and aggregated the photons in each block into a histogram based on their elevation values. We then used an automated algorithm to identify cut off points where the cumulative density of photons from the highest elevation indicates the presence of the canopy top and likewise where such cumulative density from the lowest elevation indicates the mean terrain elevation. MABEL derived height metrics were moderately correlated to discrete return lidar (DRL) derived height metrics (r2 and RMSE values ranging from 0.60 to 0.73 and 2.9 m to 4.4 m respectively) but MATLAS simulation resulted in more modest correlations with DRL indices (r2 ranging from 0.5 to 0.64 and RMSE from 3.6 m to 4.6 m). Simulations also indicated that the expected number of signal photons from ATLAS will be substantially lower, a situation that reduces canopy height estimation precision especially in areas of low density vegetation cover. On the basis of the simulated

  1. Development of Shanghai satellite laser ranging station

    NASA Technical Reports Server (NTRS)

    Yang, Fu-Min; Tan, De-Tong; Xiao, Chi-Kun; Chen, Wan-Zhen; Zhang, J.-H.; Zhang, Z.-P.; Lu, Wen-Hu; Hu, Z.-Q.; Tang, W.-F.; Chen, J.-P.

    1993-01-01

    The topics covered include the following: improvement of the system hardware; upgrading of the software; the observation status; preliminary daylight tracking capability; testing the new type of laser; and future plans.

  2. A comparison and evaluation between ICESat/GLAS altimetry and mean sea level in Thailand

    NASA Astrophysics Data System (ADS)

    Naksen, Didsaphan; Yang, Dong Kai

    2015-10-01

    Surface elevation is one of the importance information for GIS. Usually surface elevation can acquired from many sources such as satellite imageries, aerial photograph, SAR data or LiDAR by photogrammetry, remote sensing methodology. However the most trust information describe the actual surface elevation is Leveling from terrestrial survey. Leveling is giving the highest accuracy but in the other hand is also long period process spending a lot of budget and resources, moreover the LiDAR technology is new era to measure surface elevation. ICESat/GLAS is spaceborne LiDAR platform, a scientific satellite lunched by NASA in 2003. The study area was located at the middle part of Thailand between 12. ° - 14° North and 98° -100° East Latitude and Longitude. The main idea is to compare and evaluate about elevation between ICESat/GLAS Altimetry and mean sea level of Thailand. Data are collected from various sources, including the ICESat/GLAS altimetry data product from NASA, mean sea level from Royal Thai Survey Department (RTSD). For methodology, is to transform ICESat GLA14 from TOPX/Poseidon-Jason ellipsoid to WGS84 ellipsoid. In addition, ICESat/GLAS altimetry that extracted form centroid of laser footprint and mean sea level were compared and evaluated by 1st Layer National Vertical Reference Network. The result is shown that generally the range of elevation between ICESat/GLAS and mean sea level is wildly from 0. 8 to 25 meters in study area.

  3. Laser Communication Demonstration System (LSCS) and Future Mobile Satellite Services

    NASA Technical Reports Server (NTRS)

    Chen, C. -C.; Lesh, J. R.

    1995-01-01

    The Laser Communications Demonstration System (LCDS) is a proposed in-orbit demonstration of high data rate laser communications technology conceived jointly by NASA and U.S. industry. The program objectives are to stimulate industry development and to demonstrate the readiness of high data rate optical communications in Earth Orbit. For future global satellite communication systems using intersatellite links (ISLs), laser communications technology can offer reduced mass , reduced power requirements, and increased channel bandwidths without regulatory restraint. This paper provides comparisons with radio systems and status of the program.

  4. Power transmission by laser beam from lunar-synchronous satellite

    NASA Technical Reports Server (NTRS)

    Williams, M. D.; Deyoung, R. J.; Schuster, G. L.; Choi, S. H.; Dagle, J. E.; Coomes, E. P.; Antoniak, Z. I.; Bamberger, J. A.; Bates, J. M.; Chiu, M. A.

    1993-01-01

    The possibility of beaming power from synchronous lunar orbits (the L1 and L2 Lagrange points) to a manned long-range lunar rover is addressed. The rover and two versions of a satellite system (one powered by a nuclear reactor, the other by photovoltaics) are described in terms of their masses, geometries, power needs, missions, and technological capabilities. Laser beam power is generated by a laser diode array in the satellite and converted to 30 kW of electrical power at the rover. Present technological capabilities, with some extrapolation to near future capabilities, are used in the descriptions. The advantages of the two satellite/rover systems over other such systems and over rovers with onboard power are discussed along with the possibility of enabling other missions.

  5. Satellite laser ranging and gravity field modeling accuracy

    NASA Technical Reports Server (NTRS)

    Rosborough, George W.

    1990-01-01

    Gravitational field mismodeling procedures errors in the estimated orbital motion of near Earth satellites. This effect is studied using a linear perturbation approach following the analysis of Kaula. The perturbations in the orbital position as defined by either orbital elements or Cartesian components are determined. From these perturbations it is possible to ascertain the expected signal due to gravitational mismodeling that would be present in station-to-satellite laser ranging measurements. This expected signal has been estimated for the case of the Lageos satellite and using the predicted uncertainties of the GEM-T1 and GEM-T2 gravity field models. The results indicate that observable signal still exists in the laser range residuals given the current accuracy of the range measurements and the accuracy of the gravity field models.

  6. Power transmission by laser beam from lunar-synchronous satellite

    NASA Astrophysics Data System (ADS)

    Williams, M. D.; De Young, R. J.; Schuster, G. L.; Choi, S. H.; Dagle, J. E.; Coomes, E. P.; Antoniak, Z. I.; Bamberger, J. A.; Bates, J. M.; Chiu, M. A.

    1993-11-01

    The possibility of beaming power from synchronous lunar orbits (the L1 and L2 Lagrange points) to a manned long-range lunar rover is addressed. The rover and two versions of a satellite system (one powered by a nuclear reactor, the other by photovoltaics) are described in terms of their masses, geometries, power needs, missions, and technological capabilities. Laser beam power is generated by a laser diode array in the satellite and converted to 30 kW of electrical power at the rover. Present technological capabilities, with some extrapolation to near future capabilities, are used in the descriptions. The advantages of the two satellite/rover systems over other such systems and over rovers with onboard power are discussed along with the possibility of enabling other missions.

  7. Evaluation of a satellite laser ranging technique using pseudonoise code modulated laser diodes

    NASA Technical Reports Server (NTRS)

    Ball, Carolyn Kay

    1987-01-01

    Several types of Satellite Laser Ranging systems exist, operating with pulsed, high-energy lasers. The distance between a ground point and an orbiting satellite can be determined to within a few centimeters. A new technique substitutes pseudonoise code modulated laser diodes, which are much more compact, reliable and less costly, for the lasers now used. Since laser diode technology is only now achieving sufficiently powerful lasers, the capabilities of the new technique are investigated. Also examined are the effects of using an avalanche photodiode detector instead of a photomultiplier tube. The influence of noise terms (including background radiation, detector dark and thermal noise and speckle) that limit the system range and performance is evaluated.

  8. Geodetic Imaging Lidar: Applications for high-accuracy, large area mapping with NASA's upcoming high-altitude waveform-based airborne laser altimetry Facility

    NASA Astrophysics Data System (ADS)

    Blair, J. B.; Rabine, D.; Hofton, M. A.; Citrin, E.; Luthcke, S. B.; Misakonis, A.; Wake, S.

    2015-12-01

    Full waveform laser altimetry has demonstrated its ability to capture highly-accurate surface topography and vertical structure (e.g. vegetation height and structure) even in the most challenging conditions. NASA's high-altitude airborne laser altimeter, LVIS (the Land Vegetation, and Ice Sensor) has produced high-accuracy surface maps over a wide variety of science targets for the last 2 decades. Recently NASA has funded the transition of LVIS into a full-time NASA airborne Facility instrument to increase the amount and quality of the data and to decrease the end-user costs, to expand the utilization and application of this unique sensor capability. Based heavily on the existing LVIS sensor design, the Facility LVIS instrument includes numerous improvements for reliability, resolution, real-time performance monitoring and science products, decreased operational costs, and improved data turnaround time and consistency. The development of this Facility instrument is proceeding well and it is scheduled to begin operations testing in mid-2016. A comprehensive description of the LVIS Facility capability will be presented along with several mission scenarios and science applications examples. The sensor improvements included increased spatial resolution (footprints as small as 5 m), increased range precision (sub-cm single shot range precision), expanded dynamic range, improved detector sensitivity, operational autonomy, real-time flight line tracking, and overall increased reliability and sensor calibration stability. The science customer mission planning and data product interface will be discussed. Science applications of the LVIS Facility include: cryosphere, territorial ecology carbon cycle, hydrology, solid earth and natural hazards, and biodiversity.

  9. Broadview Radar Altimetry Toolbox

    NASA Astrophysics Data System (ADS)

    Mondéjar, Albert; Benveniste, Jérôme; Naeije, Marc; Escolà, Roger; Moyano, Gorka; Roca, Mònica; Terra-Homem, Miguel; Friaças, Ana; Martinho, Fernando; Schrama, Ernst; Ambrózio, Américo; Restano, Marco

    2016-07-01

    The universal altimetry toolbox, BRAT (Broadview Radar Altimetry Toolbox) which can read all previous and current altimetry missions' data, incorporates now the capability to read the upcoming Sentinel-3 L1 and L2 products. ESA endeavoured to develop and supply this capability to support the users of the future Sentinel-3 SAR Altimetry Mission. BRAT is a collection of tools and tutorial documents designed to facilitate the processing of radar altimetry data. This project started in 2005 from the joint efforts of ESA (European Space Agency) and CNES (Centre National d'Études Spatiales), and it is freely available at http://earth.esa.int/brat. The tools enable users to interact with the most common altimetry data formats. The BratGUI is the front-end for the powerful command line tools that are part of the BRAT suite. BRAT can also be used in conjunction with MATLAB/IDL (via reading routines) or in C/C++/Fortran via a programming API, allowing the user to obtain desired data, bypassing the data-formatting hassle. BRAT can be used simply to visualise data quickly, or to translate the data into other formats such as NetCDF, ASCII text files, KML (Google Earth) and raster images (JPEG, PNG, etc.). Several kinds of computations can be done within BRAT involving combinations of data fields that the user can save for posterior reuse or using the already embedded formulas that include the standard oceanographic altimetry formulas. The Radar Altimeter Tutorial, that contains a strong introduction to altimetry, shows its applications in different fields such as Oceanography, Cryosphere, Geodesy, Hydrology among others. Included are also "use cases", with step-by-step examples, on how to use the toolbox in the different contexts. The Sentinel-3 SAR Altimetry Toolbox shall benefit from the current BRAT version. While developing the toolbox we will revamp of the Graphical User Interface and provide, among other enhancements, support for reading the upcoming S3 datasets and

  10. Broadview Radar Altimetry Toolbox

    NASA Astrophysics Data System (ADS)

    Escolà, Roger; Garcia-Mondejar, Albert; Moyano, Gorka; Roca, Mònica; Terra-Homem, Miguel; Friaças, Ana; Martinho, Fernando; Schrama, Ernst; Naeije, Marc; Ambrozio, Americo; Restano, Marco; Benveniste, Jérôme

    2016-04-01

    The universal altimetry toolbox, BRAT (Broadview Radar Altimetry Toolbox) which can read all previous and current altimetry missions' data, incorporates now the capability to read the upcoming Sentinel-3 L1 and L2 products. ESA endeavoured to develop and supply this capability to support the users of the future Sentinel-3 SAR Altimetry Mission. BRAT is a collection of tools and tutorial documents designed to facilitate the processing of radar altimetry data. This project started in 2005 from the joint efforts of ESA (European Space Agency) and CNES (Centre National d'Etudes Spatiales), and it is freely available at http://earth.esa.int/brat. The tools enable users to interact with the most common altimetry data formats. The BratGUI is the front-end for the powerful command line tools that are part of the BRAT suite. BRAT can also be used in conjunction with MATLAB/IDL (via reading routines) or in C/C++/Fortran via a programming API, allowing the user to obtain desired data, bypassing the data-formatting hassle. BRAT can be used simply to visualise data quickly, or to translate the data into other formats such as NetCDF, ASCII text files, KML (Google Earth) and raster images (JPEG, PNG, etc.). Several kinds of computations can be done within BRAT involving combinations of data fields that the user can save for posterior reuse or using the already embedded formulas that include the standard oceanographic altimetry formulas. The Radar Altimeter Tutorial, that contains a strong introduction to altimetry, shows its applications in different fields such as Oceanography, Cryosphere, Geodesy, Hydrology among others. Included are also "use cases", with step-by-step examples, on how to use the toolbox in the different contexts. The Sentinel-3 SAR Altimetry Toolbox shall benefit from the current BRAT version. While developing the toolbox we will revamp of the Graphical User Interface and provide, among other enhancements, support for reading the upcoming S3 datasets and

  11. Solar power satellite system definition study. Volume 3: Laser SPS analysis, phase 3

    NASA Technical Reports Server (NTRS)

    1980-01-01

    The potential use of lasers for transmitting power to Earth from Solar Power Satellites was examined. Free electron lasers appear most promising and would have some benefits over microwave power transmission. Further research in laser technology is needed.

  12. Baseline estimation from simultaneous satellite laser tracking

    NASA Technical Reports Server (NTRS)

    Dedes, George C.

    1987-01-01

    Simultaneous Range Differences (SRDs) to Lageos are obtained by dividing the observing stations into pairs with quasi-simultaneous observations. For each of those pairs the station with the least number of observations is identified, and at its observing epochs interpolated ranges for the alternate station are generated. The SRD observables are obtained by subtracting the actually observed laser range of the station having the least number of observations from the interpolated ranges of the alternate station. On the basis of these observables semidynamic single baseline solutions were performed. The aim of these solutions is to further develop and implement the SRD method in the real data environment, to assess its accuracy, its advantages and disadvantages as related to the range dynamic mode methods, when the baselines are the only parameters of interest. Baselines, using simultaneous laser range observations to Lageos, were also estimated through the purely geometric method. These baselines formed the standards the standards of comparison in the accuracy assessment of the SRD method when compared to that of the range dynamic mode methods. On the basis of this comparison it was concluded that for baselines of regional extent the SRD method is very effective, efficient, and at least as accurate as the range dynamic mode methods, and that on the basis of a simple orbital modeling and a limited orbit adjustment. The SRD method is insensitive to the inconsistencies affecting the terrestrial reference frame and simultaneous adjustment of the Earth Rotation Parameters (ERPs) is not necessary.

  13. Site evaluation for laser satellite-tracking stations

    NASA Technical Reports Server (NTRS)

    Mao, N. H.; Mohr, P. A.

    1976-01-01

    Twenty-six locations for potential laser satellite-tracking stations, four of them actually already occupied in this role, are reviewed in terms of their known local and regional geology and geophysics. The sites are also considered briefly in terms of weather and operational factors. Fifteen of the sites qualify as suitable for a stable station whose motions are likely to reflect only gross plate motion. The others, including two of the present laser station sites (Arequipa and Athens), fail to qualify unless extra monitoring schemes can be included, such as precise geodetic surveying of ground deformation.

  14. Stability of laser-propelled wafer satellites

    NASA Astrophysics Data System (ADS)

    Srinivasan, Prashant; Hughes, Gary B.; Lubin, Philip; Zhang, Qicheng; Madajian, Jonathan; Brashears, Travis; Kulkarni, Neeraj; Cohen, Alexander; Griswold, Janelle

    2016-09-01

    For interstellar missions, directed energy is envisioned to drive wafer-scale spacecraft to relativistic speeds. Spacecraft propulsion is provided by a large array of phase-locked lasers, either in Earth orbit or stationed on the ground. The directed-energy beam is focused on the spacecraft, which includes a reflective sail that propels the craft by reflecting the beam. Fluctuations and asymmetry in the beam will create rotational forces on the sail, so the sail geometry must possess an inherent, passive stabilizing effect. A hyperboloid shape is proposed, since changes in the incident beam angle due to yaw will passively counteract rotational forces. This paper explores passive stability properties of a hyperboloid reflector being bombarded by directed-energy beam. A 2D cross-section is analyzed for stability under simulated asymmetric loads. Passive stabilization is confirmed over a range of asymmetries. Realistic values of radiation pressure magnitude are drawn from the physics of light-mirror interaction. Estimates of beam asymmetry are drawn from optical modeling of a laser array far-field intensity using fixed and stochastic phase perturbations. A 3D multi-physics model is presented, using boundary conditions and forcing terms derived from beam simulations and lightmirror interaction models. The question of optimal sail geometry can be pursued, using concepts developed for the baseline hyperboloid. For example, higher curvature of the hyperboloid increases stability, but reduces effective thrust. A hyperboloid sail could be optimized by seeking the minimum curvature that is stable over the expected range of beam asymmetries.

  15. Lasers for coherent optical satellite links with large dynamics.

    PubMed

    Chiodo, Nicola; Djerroud, Khelifa; Acef, Ouali; Clairon, André; Wolf, Peter

    2013-10-20

    We present the experimental realization of a laser system for ground-to-satellite optical Doppler ranging at the atmospheric turbulence limit. Such a system needs to display good frequency stability (a few parts in 10-14) while allowing large and well-controlled frequency sweeps of ±12  GHz at rates exceeding 100  MHz/s. Furthermore it needs to be sufficiently compact and robust for transportation to different astronomical observation sites, where it is to be interfaced with satellite ranging telescopes. We demonstrate that our system fulfills those requirements and should therefore allow operation of ground to low Earth orbit satellite coherent optical links limited only by atmospheric turbulence.

  16. Integrated laser/radar satellite ranging and tracking system.

    PubMed

    Hoge, F E

    1974-10-01

    A laser satellite ranging system that is mounted upon and integrated with a microwave tracking radar is reported. The 1-pulse sec/ruby laser transmitter is attached directly to the radar's elevation axis and radiates through a new opening in the radar's parabolic dish. The laser photomultiplier tube receiver utilizes the radar's existing 20-cm diam f11 boresight telescope and observes through a similar symmetrically located opening in the dish. The laser system possesses separate ranging system electronics but shares the radar's timing, computer, and data handling[equation]recording systems. The basic concept of the laser[equation]radar is outlined together with a listing of the numerous advantages over present singular laser rangefinding systems. The developmental laser hardware is described along with preliminary rangefinding results and expectations. The prototype system was assembled to investigate the feasibility of such systems and aid in the development of detailed specifications for an operational system. Both the feasibility and desirability of such systems integrations have been adequately demonstrated.

  17. Stratified object-based image analysis of high-res laser altimetry data for semi-automatic geomorphological mapping in an alpine area

    NASA Astrophysics Data System (ADS)

    Anders, Niels S.; Seijmonsbergen, Arie C.; Bouten, Willem

    2010-05-01

    Classic geomorphological mapping is gradually replaced by (semi) automated techniques to rapidly obtain geomorphological information in remote, steep and/or forested areas. To ensure a high accuracy of these semi-automated maps, there is a need to optimize automated mapping procedures. Within this context, we present a novel approach to semi-automatically map alpine geomorphology using a stratified object-based image analysis approach, in contrast to traditional object-based image analysis. We used a 1 m ‘Light Detection And Ranging' (LiDAR) Digital Terrain Model (DTM) from a mountainous area in Vorarlberg (western Austria). From the DTM, we calculated various terrain derivatives which served as input for segmentation of the DTM and object-based classification. We assessed the segmentation results by comparing the generated image objects with a reference dataset. In this way, we optimized image segmentation parameters which were used for classifying karst, glacial, fluvial and denudational landforms. To evaluate our approach, the classification results were compared with results from traditional object-based image analysis. Our results show that landform-specific segmentation parameters are needed to extract and classify alpine landforms in a step-wise manner, producing a geomorphological map with higher accuracy than maps resulting from traditional object-based image analysis. We conclude that the stratified object-based image analysis of high-resolution laser altimetry data substantially improves classification results in the study area. Using this approach, geomorphological maps can be produced more accurately and efficiently than before in difficult-to-access alpine areas. A further step may be the development of specific landform segmentation/classification signatures which can be transferred and applied in other mountain regions.

  18. Note: Digital laser frequency auto-locking for inter-satellite laser ranging.

    PubMed

    Luo, Yingxin; Li, Hongyin; Yeh, Hsien-Chi

    2016-05-01

    We present a prototype of a laser frequency auto-locking and re-locking control system designed for laser frequency stabilization in inter-satellite laser ranging system. The controller has been implemented on field programmable gate arrays and programmed with LabVIEW software. The controller allows initial frequency calibrating and lock-in of a free-running laser to a Fabry-Pérot cavity. Since it allows automatic recovery from unlocked conditions, benefit derives to automated in-orbit operations. Program design and experimental results are demonstrated.

  19. Using TOPEX Satellite El Niño Altimetry Data to Introduce Thermal Expansion and Heat Capacity Concepts in Chemistry Courses

    NASA Astrophysics Data System (ADS)

    Blanck, Harvey F.

    1999-12-01

    draw and is a reasonable visual representation of the way in which the thermocline is depressed by warm water along a warm-water ridge. Discussion Various factors must be taken into account to modify the raw TOPEX radar altimeter data to obtain meaningful information. For example, as mentioned at JPL's TOPEX Web site, radar propagation speed is altered slightly by variations in water vapor in the atmosphere, and therefore atmospheric water vapor content must be determined by the satellite to correct the radar altimeter data. Studies of heat storage using direct temperature measurements have been conducted (5), and comparison of TOPEX altimetry data with actual temperature measurements shows them to be in reasonably good agreement (6). Low-profile hills and valleys on the ocean are generated or influenced by a variety of factors other than thermal energy. Ocean dynamics are complex indeed. Comparisons of thermal energy (steric effect) and wind-induced surface changes have been examined in relation to TOPEX data (7). The calculations of thermal energy excess in warm-water ocean bumps from radar altimetry data alone, while not unreasonable, must be understood to be a simplification for an extremely complex system. The Gaussian model proposed for the cross section of a warm-water ridge requires more study, but it is a useful visual model of the warm-water bump above the normal surface and its subsurface warm-water wedge. I believe students will enjoy these relevant calculations and learn a bit about density, thermal expansion, and heat capacity in the process. I have tried to present sufficient data and detail to allow teachers to pick and choose calculations appropriate to the level of their students. It is evident that dimensional analysis is a distinct advantage in using these equations. I have also tried to include enough descriptive detail of the TOPEX data and El Niño to answer many of the questions students may ask. The Web sites mentioned are very informative with

  20. Laser beaming demonstrations to high-orbit satellites

    SciTech Connect

    Lipinski, R.J.; Meister, D.C.; Tucker, S.

    1994-12-31

    Laser power beaming to satellites and orbital transfer vehicles requires the accurate pointing of a low-divergence laser beam to its target, whether the target is in the sunlight or the earth`s shadow. The Air Force Phillips Laboratory (AFPL) has demonstrated reduction in the image size of stars by a factor of 10 or more by using laser beacons and adaptive optics for atmospheric compensation. This same technology is applicable to reducing the divergence of laser beams propagated from earth to space. A team of Phillips Laboratory, COMSAT Laboratories, and Sandia National Laboratories plans to demonstrate the state of the art in this area with laser-beaming demonstrations to high-orbit satellites. The demonstrations will utilize the 1.5-m diameter telescope with adaptive optics at the AFPL Starfire Optical Range (SOR) and a ruby laser provided by the Air Force and Sandia (1--50 kW and 6 ms at 694.3 nm). The first targets will be corner-cube retro-reflectors left on the moon by the Apollo 11, 14, and 15 landings. The authors will attempt to use adaptive optics for atmospheric compensation to demonstrate accurate and reliable beam projection with a series of shots over a span of time and shot angle. The authors will utilize the return signal from the retro-reflectors to help determine the beam diameter on the moon and the variations in pointing accuracy caused by atmospheric tilt. This will be especially challenging because the retro-reflectors will need to be in the lunar shadow to allow detection over background light. If the results from this experiment are encouraging, the authors will at a later date direct the beam at a COMSAT satellite in geosynchronous orbit as it goes into the shadow of the earth. The authors will utilize an onboard monitor to measure the current generated in the solar panels on the satellite while the beam is present. A threshold irradiance of about 4 W/m{sup 2} on orbit is needed for this demonstration.

  1. Laser beaming demonstrations to high-orbit satellites

    SciTech Connect

    Lipinski, R.J.; Meister, D.C.; Tucker, S.

    1993-12-31

    Laser power beaming to satellites and orbital transfer vehicles requires the accurate pointing of a low-divergence laser beam to its target, whether the target is in the sunlight or the earth`s shadow. The Air Force Phillips Laboratory (AFPL) has demonstrated reduction in the image size of stars by a factor of 10 or more by using laser beacons and adaptive optics for atmospheric compensation. This same technology is applicable to reducing the divergence of laser beams propagated from earth to space. A team of Phillips Laboratory, COMSAT Laboratories, and Sandia National Laboratories plans to demonstrate the state of the art in this area with laser-beaming demonstrations to high-orbit satellites. The demonstrations will utilize the 1.5-m diameter telescope with adaptive optics at the AFPL Starfire Optical Range (SOR) and a ruby laser provided by the Air Force and Sandia (1--50 kill and 6 ms at 694.3 nm). The first targets will be corner-cube retro-reflectors left on the moon by the Apollo 11, 14, and 15 landings. We will attempt to use adaptive optics for atmospheric compensation to demonstrate accurate and reliable beam projection with a series of shots over a span of time and shot angle. We will utilize the return signal from the retro-reflectors to help determine the beam diameter on the moon and the variations in pointing accuracy caused by atmospheric tilt. This will be especially challenging because the retro-reflectors will need to be in the lunar shadow to allow detection over background light. If the results from this experiment are encouraging, we will at a later date direct the beam at a COMSAT satellite in geosynchronous orbit as it goes into the shadow of the earth. We will utilize an onboard monitor to measure the current generated in the solar panels on the satellite while the beam is present. A threshold irradiance of about 4 W/m{sup 2} on orbit is needed for this demonstration.

  2. A laser communication experiment utilizing the ACT satellite and an airborne laser transceiver

    NASA Technical Reports Server (NTRS)

    Provencher, Charles E., Jr.; Spence, Rodney L.

    1988-01-01

    The launch of a laser communication transmitter package into geosynchronous Earth orbit onboard the Advanced Communications Technology Satellite (ACTS) will present an excellent opportunity for the experimental reception of laser communication signals transmitted from a space orbit. The ACTS laser package includes both a heterodyne transmitter (Lincoln Labs design) and a direct detection transmitter (Goddard Space Flight Center design) with both sharing some common optical components. NASA Lewis Research Center's Space Electronics Division is planning to perform a space communication experiment utilizing the GSFC direct detection laser transceiver. The laser receiver will be installed within an aircraft provided with a glass port for the reception of the signal. This paper describes the experiment and the approach to performing such an experiment. Described are the constraints placed on the NASA Lewis experiment by the performance parameters of the laser transmitter and by the ACTS spacecraft operations. The conceptual design of the receiving terminal is given; also included is the anticipated capability of the detector.

  3. Transmission media appropriate laser-microwave solar power satellite system

    NASA Astrophysics Data System (ADS)

    Schäfer, C. A.; Gray, D.

    2012-10-01

    As a solution to the most critical problems with Solar power Satellite (SPS) development, a system is proposed which uses laser power transmission in space to a receiver high in the atmosphere that relays the power to Earth by either cable or microwave power transmission. It has been shown in the past that such hybrid systems have the advantages of a reduction in the mass of equipment required in geostationary orbit and avoidance of radio frequency interference with other satellites and terrestrial communications systems. The advantage over a purely laser power beam SPS is that atmospheric absorption is avoided and outages due to clouds and precipitation will not occur, allowing for deployment in the equatorial zone and guaranteeing year round operation. This proposal is supported by brief literature surveys and theoretical calculations to estimate crucial parameters in this paper. In relation to this concept, we build on a recently proposed method to collect solar energy by a tethered balloon at high altitude because it enables a low-cost start for bringing the first Watt of power to Earth giving some quick return on investment, which is desperately missing in the traditional SPS concept. To tackle the significant problem of GW-class SPSs of high launch cost per kg mass brought to space, this paper introduces a concept which aims to achieve a superior power over mass ratio compared to traditional satellite designs by the use of thin-film solar cells combined with optical fibres for power delivery. To minimise the aperture sizes and cost of the transmitting and receiving components of the satellite and high altitude receiver, closed-loop laser beam pointing and target tracking is crucial for pointing a laser beam onto a target area that is of similar size to the beam's diameter. A recently developed technique based on optical phase conjugation is introduced and its applicability for maintaining power transmission between the satellite and high altitude receiver is

  4. Laser Communication Demonstration System (LCDS) and future mobile satellite services

    NASA Technical Reports Server (NTRS)

    Chen, Chien-Chung; Wilhelm, Michael D.; Lesh, James R.

    1995-01-01

    The Laser Communications Demonstration System (LCDS) is a proposed in-orbit demonstration of high data rate laser communications technology conceived jointly by NASA and U.S. industry. The program objectives are to stimulate industry development and to demonstrate the readiness of high data rate optical communications in Earth orbit. For future global satellite communication systems using intersatellite links, laser communications technology can offer reduced mass and power requirements and higher channel bandwidths without regulatory constraints. As currently envisioned, LCDS will consist of one or two orbiting laser communications terminals capable of demonstrating high data rate (greater than 750Mbps) transmission in a dynamic space environment. Two study teams led by Motorola and Ball Aerospace are currently in the process of conducting a Phase A/B mission definition study of LCDS under contracts with JPL/NASA. The studies consist of future application survey, concept and requirements definition, and a point design of the laser communications flight demonstration. It is planned that a single demonstration system will be developed based on the study results. The Phase A/B study is expected to be completed by the coming June, and the current results of the study are presented in this paper.

  5. Assessment Study of Small Space Debris Removal by Laser Satellites

    NASA Technical Reports Server (NTRS)

    Choi, Sang H.; Papa, Richard S.

    2011-01-01

    Space debris in Earth orbit poses significant danger to satellites, humans in space, and future space exploration activities. In particular, the increasing number of unidentifiable objects, smaller than 10 cm, presents a serious hazard. Numerous technologies have been studied for removing unwanted objects in space. Our approach uses a short wavelength laser stationed in orbit to vaporize these small objects. This paper discusses the power requirements for space debris removal using lasers. A short wavelength laser pumped directly or indirectly by solar energy can scan, identify, position, and illuminate the target, which will then be vaporized or slow down the orbital speed of debris by laser detonation until it re-enters the atmosphere. The laser-induced plasma plume has a dispersive motion of approximately 105 m/sec with a Lambertian profile in the direction of the incoming beam [1-2]. The resulting fast ejecting jet plume of vaporized material should prevent matter recombination and condensation. If it allows any condensation of vaporized material, the size of condensed material will be no more than a nanoscale level [3]. Lasers for this purpose can be indirectly pumped by power from an array of solar cells or directly pumped by the solar spectrum [4]. The energy required for vaporization and ionization of a 10 cm cube ( 2700 gm) of aluminum is 87,160 kJ. To remove this amount of aluminum in 3 minutes requires a continuous laser beam power of at least 5.38 MW under the consideration of 9% laser absorption by aluminum [5] and 5% laser pumping efficiency. The power needed for pumping 5.38 MW laser is approximately 108 MW, which can be obtained from a large solar array with 40% efficiency solar cells and a minimal area of 450 meters by 450 meters. This solar array would collect approximately 108 MW. The power required for system operation and maneuvering can be obtained by increasing solar panel size. This feasibility assessment covers roughly the power requirement

  6. Precise attitude determination of defunct satellite laser ranging tragets

    NASA Astrophysics Data System (ADS)

    Pittet, Jean-Noel; Schildknecht, Thomas; Silha, Jiri

    2016-07-01

    The Satellite Laser Ranging (SLR) technology is used to determine the dynamics of objects equipped with so-called retro-reflectors or retro-reflector arrays (RRA). This type of measurement allows to range to the spacecraft with very high precision, which leads to determination of very accurate orbits. Non-active spacecraft, which are not any more attitude controlled, tend to start to spin or tumble under influence of the external and internal torques. Such a spinning can be around one constant axis of rotation or it can be more complex, when also precession and nutation motions are present. The rotation of the RRA around the spacecraft's centre of mass can create both a oscillation pattern of laser range signal and a periodic signal interruption when the RRA is hidden behind the satellite. In our work we will demonstrate how the SLR ranging technique to cooperative targets can be used to determine precisely their attitude state. The processing of the obtained data will be discussed, as well as the attitude determination based on parameters estimation. Continuous SLR measurements to one target can allow to accurately monitor attitude change over time which can be further used for the future attitude modelling. We will show our solutions of the attitude states determined for the non-active ESA satellite ENVISAT based on measurements acquired during year 2013-2015 by Zimmerwald SLR station, Switzerland. The angular momentum shows a stable behaviour with respect to the orbital plane but is not aligned with orbital momentum. The determination of the inertial rotation over time, shows it evolving between 130 to 190 seconds within two year. Parameter estimation also bring a strong indication of a retrograde rotation. Results on other former satellites in low and medium Earth orbit such as TOPEX/Poseidon or GLONASS type will be also presented.

  7. Prelaunch optical characterization of the Laser Geodynamic Satellite (LAGEOS 2)

    NASA Technical Reports Server (NTRS)

    Minott, Peter O.; Zagwodzki, Thomas W.; Varghese, Thomas; Seldon, Michael

    1993-01-01

    The optical range correction (the distance between the apparent retroreflective skin of the satellite and the center of mass) of the LAGEOS 2 was determined using computer analysis of theoretical and experimentally measured far field diffraction patterns, and with short pulse lasers using both streak camera-based range receivers and more conventional PMT-based range receivers. The three measurement techniques yielded range correction values from 248 to 253 millimeters dependent on laser wavelength, pulsewidth, and polarization, location of the receiver in the far field diffraction pattern and detection technique (peak, half maximum, centroid, or constant fraction). The Lidar cross section of LAGEOS 2 was measured at 4 to 10 million square meters, comparable to the LAGEOS 1.

  8. Satellite Laser Ranging Photon-Budget Calculations for a Single Satellite Cornercube Retroreflector: Attitude Control Tolerance

    DTIC Science & Technology

    2015-11-01

    were omitted from the earlier work. The first is the shift in reflected beam angle due to the satellite speed ; an effect known as the velocity...rotate the reflected distribution of light due to the satellite’s high speed . These two effects are considered in some detail in the present work. It is...photos emitted during a pulse of the laser source of energy Et and wavelength λ, with h the Plank constant and c the speed of light in a vacuum. The

  9. Prelaunch testing of the laser geodynamic satellite (LAGEOS)

    NASA Technical Reports Server (NTRS)

    Fitzmaurice, M. W.; Minott, P. O.; Abshire, J. B.; Rowe, H. E.

    1977-01-01

    The LAGEOS was extensively tested optically prior to launch. The measurement techniques used are described and resulting data is presented. Principal emphasis was placed on pulse spreading characteristics, range correction for center of mass tracking, and pulse distortion due to coherent effects. A mode-locked freqeuncy doubled Nd:YAG laser with a pulse width of about 60 ps was used as the ranging transmitter and a crossfield photo-multiplier was used in the receiver. High speed sampling electronics were employed to increase receiver bandwidth. LAGEOS reflected pulses typically had a width of 250 ps with a variability in the range correction of less than 2 mm rms. Pulse distortion due to coherent effects was inferred from average waveforms and appears to introduce less than + or - 50 ps jitter in the location of the pulse peak. Analytic results on this effect based on computer simulations are also presented. Theoretical and experimental data on the lidar cross section were developed in order to predict the strength of lidar echoes from the satellite. Cross section was measured using a large aperture laser collimating system to illuminate the LAGEOS. Reflected radiation far-field patterns were measured using the collimator in an autocollimating mode. Data were collected with an optical data digitzer and displayed as a three-dimensional plot of intensity versus the two far-field coordinates. Measurements were made at several wavelengths, for several types of polarizations, and as a function of satellite orientation.

  10. Potential utility of three-dimensional temperature and salinity fields estimated from satellite altimetry and Argo data for improving mesoscale reproducibility in regional ocean modeling

    NASA Astrophysics Data System (ADS)

    Kanki, R.; Uchiyama, Y.; Miyazaki, D.; Takano, A.; Miyazawa, Y.; Yamazaki, H.

    2014-12-01

    Mesoscale oceanic structure and variability are required to be reproduced as accurately as possible in realistic regional ocean modeling. Uchiyama et al. (2012) demonstrated with a submesoscale eddy-resolving JCOPE2-ROMS downscaling oceanic modeling system that the mesoscale reproducibility of the Kuroshio meandering along Japan is significantly improved by introducing a simple restoration to data which we call "TS nudging" (a.k.a. robust diagnosis) where the prognostic temperature and salinity fields are weakly nudged four-dimensionally towards the assimilative JCOPE2 reanalysis (Miyazawa et al., 2009). However, there is not always a reliable reanalysis for oceanic downscaling in an arbitrary region and at an arbitrary time, and therefore alternative dataset should be prepared. Takano et al. (2009) proposed an empirical method to estimate mesoscale 3-D thermal structure from the near real-time AVISO altimetry data along with the ARGO float data based on the two-layer model of Goni et al. (1996). In the present study, we consider the TS data derived from this method as a candidate. We thus conduct a synoptic forward modeling of the Kuroshio using the JCOPE2-ROMS downscaling system to explore potential utility of this empirical TS dataset (hereinafter TUM-TS) by carrying out two runs with the T-S nudging towards 1) the JCOPE2-TS and 2) TUM-TS fields. An example of the comparison between the two ROMS test runs is shown in the attached figure showing the annually averaged surface EKE. Both of TUM-TS and JCOPE2-TS are found to help reproducing the mesoscale variance of the Koroshio and its extension as well as its mean paths, surface KE and EKE reasonably well. Therefore, the AVISO-ARGO derived empirical 3-D TS estimation is potentially exploitable for the dataset to conduct the T-S nudging to reproduce mesoscale oceanic structure.

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

    NASA Technical Reports Server (NTRS)

    Welch, Bryan W.

    2007-01-01

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

  12. Study on feasibility of laser reflective tomography with satellite-accompany

    NASA Astrophysics Data System (ADS)

    Gu, Yu; Hu, Yi-hua; Hao, Shi-qi; Gu, You-lin; Zhao, Nan-xiang; Wang, Yang-yang

    2015-10-01

    Laser reflective tomography is a long-range, high-resolution active detection technology, whose advantage is that the spatial resolution is unrelated with the imaging distance. Accompany satellite is a specific satellite around the target spacecraft with encircling movement. When using the accompany satellite to detect the target aircraft, multi-angle echo data can be obtained with the application of reflective tomography imaging. The feasibility of such detection working mode was studied in this article. Accompany orbit model was established with horizontal circular fleet and the parameters of accompany flight was defined. The simulation of satellite-to-satellite reflective tomography imaging with satellite-accompany was carried out. The operating mode of reflective tomographic data acquisition from monostatic laser radar was discussed and designed. The flight period, which equals to the all direction received data consuming time, is one of the important accompany flight parameters. The azimuth angle determines the plane of image formation while the elevation angle determines the projection direction. Both of the azimuth and elevation angles guide the satellite attitude stability controller in order to point the laser radar spot on the target. The influences of distance between accompany satellite and target satellite on tomographic imaging consuming time was analyzed. The influences of flight period, azimuth angle and elevation angle on tomographic imaging were analyzed as well. Simulation results showed that the satellite-accompany laser reflective tomography is a feasible and effective method to the satellite-to-satellite detection.

  13. Basic Radar Altimetry Toolbox: tools to teach altimetry for ocean

    NASA Astrophysics Data System (ADS)

    Rosmorduc, Vinca; Benveniste, Jerome; Bronner, Emilie; Niemeijer, Sander; Lucas, Bruno Manuel; Dinardo, Salvatore

    2013-04-01

    The Basic Radar Altimetry Toolbox is an "all-altimeter" collection of tools, tutorials and documents designed to facilitate the use of radar altimetry data, including the next mission to be launched, CryoSat. It has been available from April 2007, and had been demonstrated during training courses and scientific meetings. More than 2000 people downloaded it (January 2013), with many "newcomers" to altimetry among them. Users' feedbacks, developments in altimetry, and practice, showed that new interesting features could be added. Some have been added and/or improved in version 2 and 3. Others are in discussion for the future, including addition of the future Sentinel-3. The Basic Radar Altimetry Toolbox is able: - to read most distributed radar altimetry data, including the one from future missions like Saral, - to perform some processing, data editing and statistic, - and to visualize the results. It can be used at several levels/several ways, including as an educational tool, with the graphical user interface As part of the Toolbox, a Radar Altimetry Tutorial gives general information about altimetry, the technique involved and its applications, as well as an overview of past, present and future missions, including information on how to access data and additional software and documentation. It also presents a series of data use cases, covering all uses of altimetry over ocean, cryosphere and land, showing the basic methods for some of the most frequent manners of using altimetry data. Example from education uses will be presented, and feedback from those who used it as such will be most welcome. BRAT is developed under contract with ESA and CNES. It is available at http://www.altimetry.info and http://earth.esa.int/brat/

  14. Synchronous Tests of Laser Active ARTEMIS Satellite at Different Ground Stations

    NASA Astrophysics Data System (ADS)

    Kozyryev, Yevgen; Sybiryakova, Yevgeniya; Shulga, Alexander; Kuzkov, Volodymyr; Kuzkov, Sergii; Lopachenko, Vladimir; Kozhukhov, Alexander; Rikhal'sky, Vladimir; Caramia, Vincenzo

    2014-05-01

    In July 2001, the geostationary satellite ARTEMIS with laser communication terminal OPALE on board was launched. Successful laser communication sessions were performed between ARTEMIS and low Earth orbiting (LEO) satellite SPOT-4. Regular laser communication experiments between the Optical Ground Station (OGS) of ESA and ARTEMIS were also performed. The laser communication sessions were successfully established between LEO satellite KIRARI and ARTEMIS. A laser communication link between LEO satellites with the data rate of 5.625 Gbps (5100 km distance) was established by the TESAT Spacecom in 2008. First laser communication experiments between the LADEE spacecraft at the lunar orbit and Earth OGS with a rate of 622 Mbps were realized in October 2013. The amount of information sent from telecommunication satellites located at the geostationary orbit is constantly increasing. There is a certain demand in high speed laser link data transmission between ground stations and satellites. For some LEO satellites, the direct transmission of information to a ground station is required. To reduce the influence of atmosphere, some of ground stations located in different climatic regions are needed. The Main Astronomical Observatory of Ukraine (MAO) have developed a compact laser communication system named LACES (Laser Atmospheric and Communicational Experiments with Satellites) using the Cassegrain focus of its 0.7 m telescope. The laser link between the LACES terminal of MAO and the OPALE terminal of ARTEMIS was established. During the pointing, OPALE terminal performs the beacon laser scanning of the territory where a MAO ground station is located. Several experimental observations of OPALE beacon laser scanning by ground stations located in different regions of Ukraine took place in 2012-2013 years. During the sessions, laser beacon peaks from OPALE were detected by the stations in Kyiv, Mykolaiv (500 km from Kyiv), Yevpatoriya (800 km from Kyiv), Odesa, and other stations

  15. Satellite Geodesy—Foundations, Methods, and Applications

    NASA Astrophysics Data System (ADS)

    Fell, Patrick

    This text is an updated English translation of Satellitengeodasie, a book that was published in German in 1989. The text is the first in many years that attempts to cover the broad spectrum of methods, applications, and systems, both classical and current, that have developed in the field of satellite geodesy.The material is presented in a structure that follows the major observational methods used in satellite geodesy: classical techniques, Doppler, GPS, laser, altimetry, and special methods including satellite-to-satellite tracking, satellite radiometry, and VLBI. Before introducing these observational techniques in detail, the author provides the fundamentals on reference frames, time signal propagation, orbital mechanics and basic applications of satellite geodesy in positioning, gravity field modeling, navigation, marine geodesy, kinematics, and geodynamics. An excellent reference list completes the text.

  16. Direct Measurements of Laser Communication Point-Ahead Angles from the ARTEMIS Geostationary Satellite Through Clouds

    NASA Astrophysics Data System (ADS)

    Kuzkov, V.; Sodnik, Z.; Kuzkov, S.

    2017-01-01

    Laser experiments with ARTEMIS geostationary satellite have been performed in partly cloudy weather using the developed system for the telescope. It has been found that the part of the laser beam is observed simultaneously at the points in direction of the velocity vector where the satellite would arrive at when the laser light reaches the telescope. These results agree with the theory of relativity for light aberration in transition from fixed to moving coordinate system.Observation results open the way for research and development of systems to compensate atmospheric turbulence in laser communications between ground stations and satellites through the atmosphere.

  17. Theoretical Investigation of Laser-Radiation Effects on Satellite Solar Cells

    NASA Astrophysics Data System (ADS)

    Abdel-Hadi, Yasser; El-Hameed, Afaf; Hamdy, Ola

    This research concerns with the studying of laser-powered solar panels for space applications. A model describing the laser effects on satellite solar cell has been developed. These effects are studied theoretically in order to determine the performance limits of the solar cells when they are powered by laser radiation during the satellite eclipse. A comparison between some different common types of the solar cells used for these purpose is considered in this study. The obtained results are reported to optimize the use of laser-powered satellites.

  18. Basic Radar Altimetry Toolbox & Tutorial

    NASA Astrophysics Data System (ADS)

    Rosmorduc, Vinca; Benveniste, Jerome; Breebaart, Leo; Bronner, Emilie; Dinardo, Salvatore; Earith, Didier; Lucas, Bruno Manuel; Niejmeier, Sander; Picot, Nicolas

    2010-12-01

    The Basic Radar Altimetry Toolbox is an "all-altimeter" collection of tools, tutorials and documents designed to facilitate the use of radar altimetry data, including the last mission launched, CryoSat. It has been available from April 2007, and had been demonstrated during training courses and scientific meetings. Nearly 1200 people downloaded it (as of end of June 2010), with many "newcomers" to altimetry among them. Users' feedbacks, developments in altimetry, and practice, showed that new interesting features could be added. Some have been added and/or improved in version 2. Others are ongoing, some are in discussion. The Basic Radar Altimetry Toolbox is able: - to read most distributed radar altimetry data, from ERS-1 & 2, Topex/Poseidon, Geosat Follow-on, Jason- 1, Envisat, Jason- 2, CryoSat and also the future Saral and Sentinel 3 missions, - to perform some processing, data editing and statistic, - and to visualize the results. It can be used at several levels/several ways: - as a data reading tool, with APIs for C, Fortran, Matlab and IDL - as processing/extraction routines, through the on-line command mode - as an educational and a quick-look tool both, with the graphical user interface As part of the Toolbox, a Radar Altimetry Tutorial gives general information about altimetry, the technique involved and its applications, as well as an overview of past, present and future missions, including information on how to access data, additional software and documentation. It also presents a series of data use cases, covering all uses of altimetry over ocean, cryosphere and land, showing the basic methods for some of the most frequent manners of using altimetry data. BRAT is developed under contract with ESA and CNES. It is available at http://www.altimetry.info and http://earth.esa.int/brat/

  19. The role of satellite laser ranging through the 1990's

    NASA Technical Reports Server (NTRS)

    Christodoulidis, D. C.; Smith, D. E.

    1983-01-01

    Contributions of Satellite Laser Ranging (SLR) in the fields of geodesy, oceanography, geodynamics, and geopotential are reviewed. With the best current systems SLR has successfully defined an absolute vertical datum to 3 cm and a relative horizontal datum with comparable accuracy. In the areas of Earth and space physics SLR has demonstrated its ability to provide information regarding the vertical and horizontal movements of the lithosphere, the rheology of the Earth, improved understanding of the evolution of the Earth-Moon system, the Earth's albedo and upper atmosphere, the polar wander, the frequency structure of the polar motion and in the definition of fundamental constants. Future options are discussed. It is indicated that SLR will continue to provide a unique and powerful tool for the study of space and geosciences.

  20. Envisat Radar Altimetry Products For Cryospheric Studies

    NASA Astrophysics Data System (ADS)

    Benveniste, J.; Roca, M.; Baker, S.; Wingham, D.; Laxon, S.; Zanife, O.-Z.; Legresy, B.; Remy, F.

    Ice sheets and sea ice play a key role in the global climate system due to their albedo and as a huge store of freshwater. Sea-ice is also a barrier between the ocean and the atmosphere and drives the thermohaline circulation of the oceans. These critical components of the climate system are not well modelled but are clearly important if accurate predictions of the consequences of global warming are to be made. The vast, remote and inhospitable polar regions experience frequent cloud cover and long periods of darkness. They are best observed by satellite-borne active radars. The Altimetry mission on-board ENVISAT, ESA's largest environmental remote sens- ing satellite to be launched on 1st March 2002, is designed to guarantee the continu- ity of observations started by ERS-1 and ERS-2. It includes an advanced dual fre- quency new generation Radar Altimeter (RA-2), the Microwave Radiometer (MWR), the positioning instrument DORIS and the laser retro reflector (LRR). RA-2 has a new tracker philosophy: robust collection of accurately quantified radar echo data, particularly robust at handling non-ocean like echoes and conversion to meaningful geophysical quantities (re-tracking) done solely on ground. Moreover, RA-2 switches autonomously between 3 different range window width to adapt to different surfaces and avoid losing track. RA-2 has also the new capability of providing limited bursts of individual, i.e. un-averaged, Ku-band echoes at 1800 Hz, for theoretical research on backscattering and precise monitoring of bright targets. The data products are greatly improved. All data -over all surfaces- are processed si- multaneously by 4 different retrackers (Ocean, Ice1, Ice2 and Sea-Ice) to let the users choose the most suitable for their particular application. The Ice1 retracking is the range estimation technique for ice-sheet echoes used on ERS data. Ice 2 retracking is aimed at ocean-like echoes returned from ice-sheets. The Sea-Ice retracking is for specular echoes

  1. Determination of crustal motions using satellite laser ranging

    NASA Technical Reports Server (NTRS)

    1991-01-01

    Satellite laser ranging has matured over the last decade into one of the essential space geodesy techniques. It has demonstrated centimeter site positioning and millimeter per year velocity determinations in a frame tied dynamically to the mass center of the solid Earth hydrosphere atmosphere system. Such a coordinate system is a requirement for studying long term eustatic sea level rise and other global change phenomena. Earth orientation parameters determined with the coordinate system have been produced in near real time operationally since 1983, at a relatively modest cost. The SLR ranging to Lageos has also provided a rich spectrum of results based upon the analysis of Lageos orbital dynamics. These include significant improvements in the knowledge of the mean and variable components of the Earth's gravity field and the Earth's gravitational parameter. The ability to measure the time variations of the Earth's gravity field has opened as exciting area of study in relating global processes, including meteorologically derived mass transport through changes in the satellite dynamics. New confirmation of general relativity was obtained using the Lageos SLR data.

  2. Altimetry Using GPS-Reflection/Occultation Interferometry

    NASA Technical Reports Server (NTRS)

    Cardellach, Estel; DeLaTorre, Manuel; Hajj, George A.; Ao, Chi

    2008-01-01

    A Global Positioning System (GPS)- reflection/occultation interferometry was examined as a means of altimetry of water and ice surfaces in polar regions. In GPS-reflection/occultation interferometry, a GPS receiver aboard a satellite in a low orbit around the Earth is used to determine the temporally varying carrier- phase delay between (1) one component of a signal from a GPS transmitter propagating directly through the atmosphere just as the GPS transmitter falls below the horizon and (2) another component of the same signal, propagating along a slightly different path, reflected at glancing incidence upon the water or ice surface.

  3. Photon counting altimetry for Operation Ice Bridge over East Antarctica: Comparison of ICECAP's ALAMO dataset to GLAS altimetry

    NASA Astrophysics Data System (ADS)

    Young, D. A.; Lindzey, L. E.; Blankenship, D. D.; Greenbaum, J. S.; Kempf, S. D.; Fisher, J. R.

    2013-12-01

    The ICECAP portion of NASA's Operation Ice Bridge collected over 200,000 line kilometers of low elevation swath photon counting lidar data over both East Antarctic and Greenland between 2010 and 2012, as part of a comprehensive multi-instrumented campaign of aerogeophysical mapping. A primary goal of this project was to refly GLAS satellite altimetry tracks collected between 2003 and 2009, to reduce the cross track uncertainty inherent in the GLAS dataset and obtain a longer time series of ice sheet change. We combined data from our well understood nadir pointing laser altimeter and a subset version of the photon counting lidar to obtain the hybrid Airborne Laser Altimeter with Mapping Optics (ALAMO) product, which provides accurate cross track slope information. We compare this with the GLAH12 Release 33 product with the new gaussian-centroid correction applied. Over the Wilkes land margin, we find this comparison yields more stable dhdt results for the 2003-2009 record than GLAS alone approaches, and continue the time series for an additional three years in places.

  4. The contribution of local gravimetric geoid models to the calibration of satellite altimetry data and an outlook of the latest GOCE GGM performance in Gavdos

    NASA Astrophysics Data System (ADS)

    Tziavos, I. N.; Vergos, G. S.; Mertikas, S. P.; Daskalakis, A.; Grigoriadis, V. N.; Tripolitsiotis, A.

    2013-04-01

    The use of geoid heights has been one of the available methodologies utilized for the independent calibration/validation of altimeters on-board satellites. This methodology has been employed for long in the Gavdos dedicated cal/val facility (Crete, Greece), where calibration results for the Jason satellites have been estimated, both for ascending and descending passes. The present work gives a detailed overview of the methodology followed in order to estimate a high-resolution and accuracy gravimetric geoid model for the wider Gavdos area, in support of the on-going calibration work. To estimate the geoid model, the well-known remove-compute-restore method is used while residual geoid heights are estimated through least-squares collocation so that associated errors are determined as well. It is found that the estimated formal geoid errors from LSC along passes 018 and 109 of Jason satellites, used for the bias estimation, range between ±0.8-1.6 cm. The so-derived geoid heights are employed in the determination of the Jason-2 altimeter bias for all available cycles (cycles 1-114, spanning the period from July 2008 to August 2011) together with the RioMed DOT model. From the results acquired the Jason-2 bias has been estimated to be +196.1 ± 3.2 mm for pass 109 and +161.9 ± 5.1 mm for pass 018. Within the same frame, the GOCE/GRACE-based geopotential model GOCO02s has been used to estimate the mean dynamic ocean topography and the steady-state circulation in the area around Gavdos. The so-derived DOT model was used to estimate the Jason-2 bias in an effort to evaluate the performance of satellite-only geoid models and investigate whether their spatial resolution and accuracy provides some improvement w.r.t. traditional local gravimetric geoids. From the results acquired with geoid heights from GOCO02s, the estimated Jason-2 bias deviates significantly from that of the local gravimetric model, which can be attributed to a possible mean offset and the low resolution

  5. Experimental verification of fiber-coupling efficiency for satellite-to-ground atmospheric laser downlinks.

    PubMed

    Takenaka, Hideki; Toyoshima, Morio; Takayama, Yoshihisa

    2012-07-02

    Optical communication is a high-capacity method that can handle considerable satellite data. When common-fiber optical devices such as optical fiber amplifiers based on single mode fibers are used in free-space laser communication systems, the laser beam has to be coupled to a single-mode fiber. Under atmospheric turbulence it would be difficult to make the required fiber coupling efficiency in satellite-to-ground laser propagation paths. A fast-steering mirror that can operate at high frequencies under atmospheric turbulence is fabricated, and its tracking performance is verified in real satellite-to-ground laser communication experiments. The measured fiber coupling loss of 10-19 dB in satellite-to-ground laser communication links under atmospheric turbulence shows good agreement with the predicted fiber coupling efficiency of 17 dB.

  6. Testing the gravitational interaction in the field of the Earth via satellite laser ranging and the Laser Ranged Satellites Experiment (LARASE)

    NASA Astrophysics Data System (ADS)

    Lucchesi, D. M.; Anselmo, L.; Bassan, M.; Pardini, C.; Peron, R.; Pucacco, G.; Visco, M.

    2015-08-01

    In this work, the Laser Ranged Satellites Experiment (LARASE) is presented. This is a research program that aims to perform new refined tests and measurements of gravitation in the field of the Earth in the weak field and slow motion (WFSM) limit of general relativity (GR). For this objective we use the free available data relative to geodetic passive satellite lasers tracked from a network of ground stations by means of the satellite laser ranging (SLR) technique. After a brief introduction to GR and its WFSM limit, which aims to contextualize the physical background of the tests and measurements that LARASE will carry out, we focus on the current limits of validation of GR and on current constraints on the alternative theories of gravity that have been obtained with the precise SLR measurements of the two LAGEOS satellites performed so far. Afterward, we present the scientific goals of LARASE in terms of upcoming measurements and tests of relativistic physics. Finally, we introduce our activities and we give a number of new results regarding the improvements to the modelling of both gravitational and non-gravitational perturbations to the orbit of the satellites. These activities are a needed prerequisite to improve the forthcoming new measurements of gravitation. An innovation with respect to the past is the specialization of the models to the LARES satellite, especially for what concerns the modelling of its spin evolution, the neutral drag perturbation and the impact of Earth's solid tides on the satellite orbit.

  7. Aviso: altimetry products & services in 2013

    NASA Astrophysics Data System (ADS)

    Mertz, F.; Bronner, E.; Rosmorduc, V.; Maheu, C.

    2013-12-01

    Since the launch of Topex/Poseidon, more than 20 years ago, satellite altimetry has evolved in parallel with the user community and oceanography. As a result of this evolution, we now have: - a wide range of products, more and more easy-to-use, spanning complete GDRs to pre-computed sea level anomalies, gridded datasets and indicators such as MSL index or ENSO index. - a wide range of applications in the oceanographic community: ocean observation, biology, climate, ... - a mature approach, combining altimetric data from various satellites and merging data acquired using different observation techniques, including altimetry, to give us a global view of the ocean; - data available in real or near-real time for operational use. Different services are available either to choose between the various datasets, or to download, extract or even visualize the data. An Ipad-Iphone application, AvisOcean has also been opened in September 2012, for information about the data and their updates. 2013 has seen major changes in Aviso data distribution, both in data products themselves and in their distribution, including an online extraction tool in preparation (Online Data Extraction Service). An overview of available products & services, how to access them today, will be presented.

  8. Aviso: altimetry products and services in 2013

    NASA Astrophysics Data System (ADS)

    Rosmorduc, Vinca; Bronner, Emilie; Maheu, Caroline; Mertz, Françoise

    2013-04-01

    Since the launch of Topex/Poseidon, more than 20 years ago, satellite altimetry has evolved in parallel with the user community and oceanography. As a result of this evolution, we now have: - A bigger choice of products, more and more easy-to-use, spanning complete GDRs to pre-computed sea level anomalies and gridded datasets and indicators such as MSL index or ENSO index. - a mature approach, combining altimetric data from various satellites and merging data acquired using different observation techniques, including altimetry, to give us a global view of the ocean; - data available in real or near-real time for operational use. Different services are available either to choose between the various datasets, or to download, extract or even visualize the data. An Ipad-Iphone application, AvisOcean has also been opened in September 2012, for information about the data and their updates. 2013 will see major changes in Aviso data distribution, both in data products themselves and in their distribution, including an online extraction tool in preparation (Online Data Extraction Service). An overview of available products & services, how to access them today, will be presented.

  9. Limitations to testing the equivalence principle with satellite laser ranging

    NASA Astrophysics Data System (ADS)

    Nobili, A. M.; Comandi, G. L.; Bramanti, D.; Doravari, Suresh; Lucchesi, D. M.; Maccarrone, F.

    2008-07-01

    We consider the possibility of testing the equivalence principle (EP) in the gravitational field of the Earth from the orbits of LAGEOS and LAGEOS II satellites, which are very accurately tracked from ground by laser ranging. The orbital elements that are affected by an EP violation and can be used to measure the corresponding dimensionless parameter η are semimajor axis and argument of pericenter. We show that the best result is obtained from the semimajor axis, and it is limited—with all available ranging data to LAGEOS and LAGEOS II—to η ≃ 2 × 10-9, more than 3 orders of magnitude worse than experimental results provided by torsion balances. The experiment is limited because of the non uniformity of the gravitational field of the Earth and the error in the measurement of semimajor axis, precisely in the same way as they limit the measurement of the product GM of the Earth. A better use of the pericenter of LAGEOS II can be made if the data are analyzed searching for a new Yukawa-like interaction with a distance scale of one Earth radius. It is found that the pericenter of LAGEOS II is 3 orders of magnitude more sensitive to a composition dependent new interaction with this particular scale than it is to a composition dependent effect expressed by the η parameter only. Nevertheless, the result is still a factor 500 worse than EP tests with torsion balances in the gravitational field of the Earth (i.e. at comparable distance), though a detailed data analysis has yet to be performed. While EP tests with satellite laser ranging are not competitive, laser ranging to the Moon has been able to provide a test of the EP almost 1 order of magnitude better than torsion balances. We show that this is due to the much greater distance of the test masses (the Earth and the Moon) from the primary body (the Sun) and the correspondingly smaller gradients of its gravity field. We therefore consider a similar new experiment involving the orbit of LAGEOS: testing LAGEOS

  10. Controlling laser beam irradiation area using an optical duplicate system to improve satellite-ground laser communications

    NASA Astrophysics Data System (ADS)

    Nakayama, Tomoko; Takayama, Yoshihisa; Fujikawa, Chiemi; Kodate, Kashiko

    2016-08-01

    To improve the quality of ground to satellite laser communications, we propose an optical duplicate system of the optical ground station. Our proposed approach can be used to control the beam irradiation area for a satellite position without changing the total power of the output beam and the mechanical drive unit; this is performed by controlling the input pattern of a liquid crystal filter inserted in the input plane of the optical duplicate system. Most of the power of the diffracted laser beam emitted from the ground is focused on the optical axis. By distributing the power to side lobes, it is possible to extend the coverage area for a satellite position. This system allows the laser beam irradiation area to be controlled by a sufficient degree by adjusting the threshold of the satellite reception level. We verify the efficacy of the system using wave optics numerical calculations.

  11. Satellite laser ranging and geological constraints on plate motion

    NASA Astrophysics Data System (ADS)

    Harrison, C. G. A.; Douglas, Nancy B.

    1990-10-01

    Satellite laser ranging (SLR) observed baseline rates of change were measured and compared with rates determined from sea floor spreading rates and directions, and earth-quake solutions. With the number of years of observation now over six for many of the baselines, the inaccuracy of determining baseline rates of change has diminished so that in some cases it is less than a few mm per year. Thus, a direct comparison between baseline rates of change and rates of change established using geophysical information (called geological rates) is now feasible. In most cases, there is good agreement between the rates determined from SLR and geological rates, but in some cases there appear to be discrepancies. These discrepancies involve many of the data for which one end of the baseline is either Quincy (California), Huahine (French Polynesia), or Simosato (Japan). A method for looking at the discrepancies for these SLR observatories has been devised which makes it possible to calculate the motion not modeled by the geologic information.

  12. Satellite laser ranging and geological constraints on plate motion

    NASA Technical Reports Server (NTRS)

    Harrison, C. G. A.; Douglas, Nancy B.

    1990-01-01

    Satellite laser ranging (SLR) observed baseline rates of change were measured and compared with rates determined from sea floor spreading rates and directions, and earth-quake solutions. With the number of years of observation now over six for many of the baselines, the inaccuracy of determining baseline rates of change has diminished so that in some cases it is less than a few mm per year. Thus, a direct comparison between baseline rates of change and rates of change established using geophysical information (called geological rates) is now feasible. In most cases, there is good agreement between the rates determined from SLR and geological rates, but in some cases there appear to be discrepancies. These discrepancies involve many of the data for which one end of the baseline is either Quincy (California), Huahine (French Polynesia), or Simosato (Japan). A method for looking at the discrepancies for these SLR observatories has been devised which makes it possible to calculate the motion not modeled by the geologic information.

  13. Temporal variations of the segmentation of slow to intermediate spreading mid-ocean ridges 1. Synoptic observations based on satellite altimetry data

    NASA Astrophysics Data System (ADS)

    Briais, Anne; Rabinowicz, Michel

    2002-05-01

    The high-resolution geoid and gravity maps derived from ERS-1 and Geosat satellite geodetic missions reveal a set of small-scale lineations on the flanks of slow to intermediate spreading mid-ocean ridges. Assuming that these lineations reflect the variations in crustal structure induced by mid-ocean ridge axial discontinuities, we use them to investigate how the discontinuities, and the segments they bound, appear, migrate, and disappear. We provide a synoptic description of the main characteristics of the crustal structure variations, as well as their evolution in time, over the flanks of the Mid-Atlantic, Indian, and Pacific-Antarctic Ridges. The second-order segment length does not appear to vary with the spreading rate for the slow to intermediate spreading ridges investigated here. The amplitude of the gravity signal associated with off-axis discontinuity traces increases with the obliquity of the ridge to spreading and decreases with spreading rate and with the proximity of a ridge section to a hot spot. The patterns of the gravity lineations appear to be very homogeneous over 500- to 1000-km-large corridors bounded by large fracture zones. Far from hot spots, corridors are characterized either by segments bounded by discontinuities migrating back and forth along the axis, implying a lifetime of 10-30 Myr for the segments, or by segments and discontinuities very stable in space and time, surviving for 40-50 Myr. Closer to hot spots, the segmentation is affected in two ways. First, segments tend to migrate along axis away from hot spots, or toward cold spots. Second, asymmetric spreading tends to keep sections of ridges closer to hot spots than normal spreading would. These observations support the hypothesis that ridge segmentation and its evolution are controlled by mantle dynamics. Our analysis provides observational constraints for further models of crustal production along ridges, which are presented in the companion paper by Rabinowicz and Briais [2002].

  14. The statistics of laser returns from cube-corner arrays on satellite

    NASA Technical Reports Server (NTRS)

    Lehr, C. G.

    1973-01-01

    A method first presented by Goodman is used to derive an equation for the statistical effects associated with laser returns from satellites having retroreflecting arrays of cube corners. The effect of the distribution on the returns of a satellite-tracking system is illustrated by a computation based on randomly generated numbers.

  15. Altimetry, ship gravimetry, and the general circulation of the North Atlantic

    NASA Technical Reports Server (NTRS)

    Zlotnicki, Victor; Marsh, James G.

    1989-01-01

    Gravity accelerations estimated from satellite altimetric mean sea surfaces (Seasat and Geos-3) are compared to ship gravity measurements. Ship gravity are closer to an estimate based on least squares collocation, orbit perturbations, altimetry and terrestrial gravity than to an estimate based on Fourier transforms, orbit perturbations and altimetry only. Both altimetric estimates yield a smoothed picture of the geostrophic component of sea surface currents in the North Atlantic when gravity acceleration data from only nine cruises are subtracted from the altimetric gravity.

  16. Altimetry, ship gravimetry, and the general circulation of the North Atlantic

    SciTech Connect

    Zlotnicki, V. ); Marsh, J.G. )

    1989-09-01

    Gravity accelerations estimated from satellite altimetric mean sea surfaces (Seasat and Geos-3) are compared to ship gravity measurements. Ship gravityare closer to an estimate based on least squares collocation, orbit perturbations, altimetry and terrestrial gravity than to an estimate based on Fourier transforms, orbit perturbations and altimetry only. Both altimetric estimates yield a smoothed picture of the geostrophic component of sea surface currents in the North Atlantic when gravity acceleration data from only nine cruises are subtracted from the altimetric gravity.

  17. An Ocean Science Revolution: 23 Years of Precision Altimetry

    NASA Astrophysics Data System (ADS)

    Willis, J. K.

    2015-12-01

    The world's Oceans cover more than two-thirds of the Earth's surface, so measurements of their shape and height play a key role in the advancement of geodesy. In 1992 NASA and CNES launched TOPEX/Poseidon to measure the global oceans on a 10-day repeat with an accuracy of just a few centimeters. Referred to as the most successful oceanographic experiment of all time, TOPEX and its successors Jason-1 and Jason-2 revolutionized the field of oceanography. Satellite altimeters are now used routinely to chart and predict ocean currents, track global and regional climate phenomena such as El Nino, predict hurricane intensity and even to estimate the shape and depth of the sea floor. But one of the greatest accomplishments of satellite altimetry is the unbroken, 23-year record of global and regional sea level change. No other climate record provides a more direct and far reaching measure of Earth's changing climate. As satellite altimetry evolves, it will continue to provide key information about the oceans and climate, but it will also provide information on increasingly smaller scales. This paper will cover these and other major advances and discoveries made possible by satellite altimetry, and discuss the roadmap for the future.

  18. Laser ranging application to time transfer using geodetic satellite and to other Japanese space programs

    NASA Technical Reports Server (NTRS)

    Kunimori, Hiroo; Takahashi, Fujinobu; Itabe, Toshikazu; Yamamoto, Atsushi

    1993-01-01

    Communications Research Laboratory (CRL) has been developing a laser time transfer system using a satellite laser ranging (SLR) system. We propose Japanese geodetic satellite 'AJISAI', launched in 1986 as a target satellite. The surface is covered not only with corner cube reflectors but also with mirrors. The mirrors are originally designed for observation of flushing solar light reflected by the separate mirrors while the satellite is spinning. In the experiment, synchronized laser pulses are transferred via specified mirror from one station to another while the satellite is up on the horizon to both stations. The system is based on the epoch timing ranging system with 40 ps ranging precision, connected together with UTC(CRL). Simulation study indicates that two stations at thousands of km distance from each other can be linked with signal strength of more than 10 photons and the distributed images of laser beam from AJISAI mirrors give many chances for two stations to link each other during a single AJISAI pass. Retro-reflector In Space for Advanced Earth Observation Satellite (ADEOS) and RendDezVous docking mission of Experimental Technology Satellite-7 (ETS-7) are briefly presented.

  19. MLRS - A lunar/artificial satellite laser ranging facility at the McDonald Observatory

    NASA Technical Reports Server (NTRS)

    Shelus, P. J.

    1985-01-01

    Experience from lunar and satellite laser ranging experiments carried out at McDonald Observatory has been used to design the McDonald Laser Ranging Station (MLRS). The MLRS is a dual-purpose installation designed to obtain observations from the LAGEOS satellite and lunar targets. The instruments used at the station include a telescope assembly 0.76 meters in diameter; a Q-switched doubled neodymium YAG laser with a pulse rate of three nanoseconds; and a GaAs photodetector with Fabry-Perot interferometric filter. A functional diagram of the system is provided. The operating parameters of the instruments are summarized in a table.

  20. Laser tracking test under satellite microvibrational disturbances by OICETS ATP system

    NASA Astrophysics Data System (ADS)

    Jono, Takashi; Toyoshima, Morio; Takahashi, Nobuhiro; Yamawaki, Toshihiko; Nakagawa, Keizo; Yamamoto, Akio

    2002-07-01

    Free-space laser communication systems offer many advantages such as high data rate, small sized equipment, low consumption electric power and others. There are, however, many development factors to construct a realistic laser communication system in space. Precise Acquisition, Tracking, and Pointing (ATP) functions are key issue to establish the laser communication system in space. OICETS (Optical Inter-orbit Communications Engineering Test Satellite) has been developed by National Space Development Agency of Japan (NASDA) to verify an optical data link technology in space. ATP functions of the OICETS satellite for a laser inter-orbit link system must be controlled with an angular accuracy better than a few micro radian under vibrational disturbances of the host satellite. The microvibrational disturbances continually come from the satellite subsystem operations such as reaction wheels, solar paddle motors, scan sensors and so on. NASDA performed an on-ground microvibration test to evaluate vibration characteristics of the OICETS satellite and to verify laser tracking performances of the ATP system. The test was carried out by using a simulated OICETS satellite that consists of a mechanical structure model and an engineering model of the laser communication terminal. The mechanical structure model is equipped with some flight components and mass dummy components. The satellite is suspended from a lifting tackle by four straps and the free-free configuration was simulated using a suspension device. As a result, the incremental residual tracking error of 0.19 micro radians was measured due to the microvibration of the disturbing sources from the satellite platform.

  1. Miniaturization and Evaluation of Laser Communication System for Satellite by 2-Axis Steering Mirror Mechanism

    NASA Astrophysics Data System (ADS)

    Aoyanagi, Yoshihide; Kato, Toshiki; Yasunaka, Toshihiko; Uematsu, Tsutomu; Satori, Shin

    A laser communication system has an advantage of realizing the high speed transmission under the conditions of small size and low electrical power. The laser communication system requires a high accuracy of pointing control because of the directional characteristics of laser beam. Due to the attitude control accuracy of micro-satellites, the pointing device carried in micro-satellite is required to have mitigated pointing accuracy, wide range pointing, small size, mass and low electrical power. We have developed a new pointing device characterized by two-axis pointing control mechanism. Breadboard model of pointing control mechanism consists of steering mirror, angular sensor and electrical unit. The steering mirror mechanism is accomplished using rod-end-bearings. The pointing accuracy and the performance of tracking system of the laser communication device were evaluated in simulator of between satellite and ground station. This paper describes development of the breadboard model of pointing control mechanism and the performance evaluation.

  2. The link availability analysis of GEO satellite-to-ground laser communication

    NASA Astrophysics Data System (ADS)

    Chen, Erhu; Mei, Haiping; Zhang, Changquan; Chang, Chengwu

    2015-08-01

    The performance of satellite-to-ground laser communication is affected by the atmospheric environment seriously, so it is a key issue for system design and operation to analyze the link availability quantitatively according to the channel characteristics. Firstly, the basic concept of laser communication link availability is put forward. Secondly, the preliminary theory model and calculation method of geostationary satellite-to-ground laser communication link availability are established by analyzing influencing factors. Lastly, the link availability of 77°E GEO satellite-to-ground laser communication is analyzed, combining with the atmospheric statistics data of typical optical ground stations in China. The results show that, it is feasible to achieve more than 90% joint link availability by implementing two stations, or to achieve more than 95% joint link availability by implementing three stations.

  3. Application of Satellite Laser Ranging Techniques for Space Situational Awareness Efforts

    NASA Astrophysics Data System (ADS)

    Shappirio, M.; McGarry, J. F.; Bufton, J.; Cheek, J. W.; Coyle, D. B.; Hull, S. M.; Stysley, P. R.; Sun, X.; Young, R. P.; Zagwodzki, T.

    2016-09-01

    With the numbers of conjunction avoidance maneuvers for the International Space Station and other Low Earth Orbit satellites rising and likely to continue to increase, the need to develop methods to produce accurate 72+ hour orbital predictions is becoming critical. One emerging solution is to utilize satellite laser ranging techniques to range to debris and refine the initial positions to improve the orbital predictions for objects predicted to experience a close approach. Some stations in Europe have already demonstrated that this technique is possible, but it has not been employed to refine the likelihood of collision. We will present a notional architecture for laser ranging to debris utilizing existing satellite laser ranging or visual tracking facilities. We will also discuss the capabilities of laser ranging for Space Situational Awareness and provide a direct comparison to current visual and radar tracking methods.

  4. CO2 laser as a possible candidate for optical transmitter in free-space satellite-ground-satellite laser communication: a case study

    NASA Astrophysics Data System (ADS)

    Kumar, M. A.; Naik, Govind; Shenoy, N. V.; Rao, Mandavilli M.

    1999-04-01

    Terrestrial fiber optic communication systems handle most of the inter-continental communication systems today. However recent studies indicate that these links, in spite of their huge bandwidth will be saturated in the near future. Hence attempts are being made is augment and may be even replace these by inter satellite links (ISLs). Though high power laser diodes have been found to be suitable for ISLs, they are unfortunately inadequate for satellite-ground links (SGL and GSL) as they are not powerful enough. So we have to look for more powerful lasers for SGLs & GSLs. One possible candidate is the CO2 laser. It is a gas laser. It provides a number of advantages over other sources. They include high life time, high efficiency and stability. Besides it can generate a high power continuous wave and requires only radiative cooling. CO2 can provide a high bit rate and long range transmission with low bit error rate. Also CO2 laser is in near infra-red and hence the turbulence effects due to clouds is minimum. All these make CO2 laser a very economical choice. The use of optical communication in GSLs provides many advantages over radio links. Laser being a high energy source provides the advantage of greater bandwidth, smaller beam divergence angles, smaller antennae, greater security and a new spectrum. Lesser power consumption and smaller size make it more suitable for use in a satellite. The present paper deals with a case study of a CO2 laser based free space optical communication link by making the link budget analysis.

  5. CBSIT 2009: Airborne Validation of Envisat Radar Altimetry and In Situ Ice Camp Measurements Over Arctic Sea Ice

    NASA Technical Reports Server (NTRS)

    Connor, Laurence; Farrell, Sinead; McAdoo, David; Krabill, William; Laxon, Seymour; Richter-Menge, Jacqueline; Markus, Thorsten

    2010-01-01

    The past few years have seen the emergence of satellite altimetry as valuable tool for taking quantitative sea ice monitoring beyond the traditional surface extent measurements and into estimates of sea ice thickness and volume, parameters that arc fundamental to improved understanding of polar dynamics and climate modeling. Several studies have now demonstrated the use of both microwave (ERS, Envisat/RA-2) and laser (ICESat/GLAS) satellite altimeters for determining sea ice thickness. The complexity of polar environments, however, continues to make sea ice thickness determination a complicated remote sensing task and validation studies remain essential for successful monitoring of sea ice hy satellites. One such validation effort, the Arctic Aircraft Altimeter (AAA) campaign of2006. included underflights of Envisat and ICESat north of the Canadian Archipelago using NASA's P-3 aircraft. This campaign compared Envisat and ICESat sea ice elevation measurements with high-resolution airborne elevation measurements, revealing the impact of refrozen leads on radar altimetry and ice drift on laser altimetry. Continuing this research and validation effort, the Canada Basin Sea Ice Thickness (CBSIT) experiment was completed in April 2009. CBSIT was conducted by NOAA. and NASA as part of NASA's Operation Ice Bridge, a gap-filling mission intended to supplement sea and land ice monitoring until the launch of NASA's ICESat-2 mission. CBIST was flown on the NASA P-3, which was equipped with a scanning laser altimeter, a Ku-band snow radar, and un updated nadir looking photo-imaging system. The CB5IT campaign consisted of two flights: an under flight of Envisat along a 1000 km track similar to that flown in 2006, and a flight through the Nares Strait up to the Lincoln Sea that included an overflight of the Danish GreenArc Ice Camp off the coast of northern Greenland. We present an examination of data collected during this campaign, comparing airborne laser altimeter measurements

  6. Somali current studied from SEASAT altimetry

    NASA Technical Reports Server (NTRS)

    Perigaud, C.; Minster, J. F.; Zlotnicki, V.; Balmino, G.

    1984-01-01

    Mesoscale variability has been obtained for the world ocean from satellite altimetry by using the repetitive tracks data of SEASAT. No significant results were obtained for the Somali current area for two main reasons: the repetitive tracks are too sparse to cover the expected eddy pattern and these data were obtained in late September and early October when the current is strongly decaying. The non-repetitive period of SEASAT offers the possibility to study a dozen of tracks parallel to the eddy axis or crossing it. These are used here to deduce the dynamic topography of the Somali current. Data error reduction and tide and orbit corrections are addressed. A local geoid was built using a collocation inverse method to combine surface gravity data and altimetry: the repetitive tracks show no variability (which confirms that the current is quasi-inexistent at that time) and can be used as data for the local geoid. This should provide a measure of the absolute dynamic topography of the Somali current.

  7. Proposal of Liquid Cannon Target Driven by Fiber Laser for Micro-Thruster in Satellite

    SciTech Connect

    Yabe, Takashi; Ohzono, Hirokazu; Ohkubo, Tomomasa; Baasandash, Choijil; Yamaguchi, Masashi; Oku, Takehiro; Taniguchi, Kazumoto; Miyazaki, Sho; Akoh, Ryosuke; Ogata, Yoichi; Rosenberg, Benjamin; Yoshida, Minoru

    2004-03-30

    We propose a new concept controlling a satellite by a fiber laser loaded in it and demonstrated the acceleration of pendulum with 7kW/2n and 2kHz fiber laser, and measured the Cm of 16Ns/MJ corresponding to the scaling of YAG laser. This laser can be easily bundled to generate much larger power. For more efficient acceleration, we propose 'metal-free water cannon target', the new concept of propulsion using only water. The momentum coupling coefficient of 2500[Ns/MJ] was achieved with vacuum pump oil instead of water, and we succeeded in controlling the driving direction by the system based on the new concept. This can be used for thrusting a satellite and controlling its posture in combination with fiber lasers.

  8. Technology assessment of high pulse energy CO(2) lasers for remote sensing from satellites

    NASA Technical Reports Server (NTRS)

    Hess, R. V.; Brockman, P.; Schryer, D. R.; Miller, I. M.; Bair, C. H.; Sidney, B. D.; Wood, G. M.; Upchurch, B. T.; Brown, K. G.

    1985-01-01

    Developments and needs for research to extend the lifetime and optimize the configuration of CO2 laser systems for satellite based on remote sensing of atmospheric wind velocities and trace gases are reviewed. The CO2 laser systems for operational satellite application will require lifetimes which exceed 1 year. Progress in the development of efficient low temperature catalysts and gas mixture modifications for extending the lifetime of high pulse energy closed cycle common and rare isotope CO2 lasers and of sealed CW CO2 lasers is reviewed. Several CO2 laser configurations are under development to meet the requirements including: unstable resonators, master oscillator power amplifiers and telescopic stable resonators, using UV or E-beam preionization. Progress in the systems is reviewed and tradeoffs in the system parameters are discussed.

  9. Gulf of Mexico satellite radar altimetry

    NASA Technical Reports Server (NTRS)

    Parra, C. G.; Forsythe, R. G.; Parsons, C. L.

    1981-01-01

    The dynamic topography of the sea surface was measured. The radar altimeter measurements yield average ocean topographic data which are mapped. Seasonal deviations from a 3 year mean topography are presented. The altimeters are also instrumented with sample and hold gates which provide information about the shape and amplitude of the return waveform. Parameters including ocean surface wind speed and the significant wave height are determined. One hundred eighty six wind speed and significant wave height histograms are presented.

  10. Satellite altimetry reveals seafloor tectonic fabric

    SciTech Connect

    Mcadoo, D.C.; Marks, K.M. )

    1992-01-01

    Seasat altimeter observations of sea-surface topography have revealed much that was unsuspected about the marine gravity field and seafloor topography, which in conjunction with crustal/upper-mantle density variations generates short wavelength (less than 200-km) marine gravity field fluctuations. Such high-resolution altimeter data is currently available, however, only for 6 percent of the world's ocean surface area; future efforts with Geosat Geodetic Mission and ERS-1 data will expand coverage to the entire world ocean. 4 refs.

  11. Satellites

    SciTech Connect

    Burns, J.A.; Matthews, M.S.

    1986-01-01

    The present work is based on a conference: Natural Satellites, Colloquium 77 of the IAU, held at Cornell University from July 5 to 9, 1983. Attention is given to the background and origins of satellites, protosatellite swarms, the tectonics of icy satellites, the physical characteristics of satellite surfaces, and the interactions of planetary magnetospheres with icy satellite surfaces. Other topics include the surface composition of natural satellites, the cratering of planetary satellites, the moon, Io, and Europa. Consideration is also given to Ganymede and Callisto, the satellites of Saturn, small satellites, satellites of Uranus and Neptune, and the Pluto-Charon system.

  12. Sentinel-3 SAR Altimetry Toolbox

    NASA Astrophysics Data System (ADS)

    Benveniste, Jerome; Lucas, Bruno; DInardo, Salvatore

    2015-04-01

    The prime objective of the SEOM (Scientific Exploitation of Operational Missions) element is to federate, support and expand the large international research community that the ERS, ENVISAT and the Envelope programmes have build up over the last 20 years for the future European operational Earth Observation missions, the Sentinels. Sentinel-3 builds directly on a proven heritage of ERS-2 and Envisat, and CryoSat-2, with a dual-frequency (Ku and C band) advanced Synthetic Aperture Radar Altimeter (SRAL) that provides measurements at a resolution of ~300m in SAR mode along track. Sentinel-3 will provide exact measurements of sea-surface height along with accurate topography measurements over sea ice, ice sheets, rivers and lakes. The first of the two Sentinels is expected to be launched in early 2015. The current universal altimetry toolbox is BRAT (Basic Radar Altimetry Toolbox) which can read all previous and current altimetry mission's data, but it does not have the capabilities to read the upcoming Sentinel-3 L1 and L2 products. ESA will endeavour to develop and supply this capability to support the users of the future Sentinel-3 SAR Altimetry Mission. BRAT is a collection of tools and tutorial documents designed to facilitate the processing of radar altimetry data. This project started in 2005 from the joint efforts of ESA (European Space Agency) and CNES (Centre National d'Etudes Spatiales), and it is freely available at http://earth.esa.int/brat. The tools enable users to interact with the most common altimetry data formats, the BratGUI is the front-end for the powerful command line tools that are part of the BRAT suite. BRAT can also be used in conjunction with Matlab/IDL (via reading routines) or in C/C++/Fortran via a programming API, allowing the user to obtain desired data, bypassing the data-formatting hassle. BRAT can be used simply to visualise data quickly, or to translate the data into other formats such as netCDF, ASCII text files, KML (Google Earth

  13. Study, optimization, and design of a laser heat engine. [for satellite applications

    NASA Technical Reports Server (NTRS)

    Taussig, R. T.; Cassady, P. E.; Zumdieck, J. F.

    1978-01-01

    Laser heat engine concepts, proposed for satellite applications, are analyzed to determine which engine concept best meets the requirements of high efficiency (50 percent or better), continuous operation in space using near-term technology. The analysis of laser heat engines includes the thermodynamic cycles, engine design, laser power sources, collector/concentrator optics, receiving windows, absorbers, working fluids, electricity generation, and heat rejection. Specific engine concepts, optimized according to thermal efficiency, are rated by their technological availability and scaling to higher powers. A near-term experimental demonstration of the laser heat engine concept appears feasible utilizing an Otto cycle powered by CO2 laser radiation coupled into the engine through a diamond window. Higher cycle temperatures, higher efficiencies, and scalability to larger sizes appear to be achievable from a laser heat engine design based on the Brayton cycle and powered by a CO laser.

  14. Radar Altimetry Backscattering Signatures at Ka, Ku, C and S Bands over Land

    NASA Astrophysics Data System (ADS)

    Blarel, F.; Frappart, F.; Legresy, B.; Blumstein, D.; Fatras, C.; Mougin, E.; Papa, F.; Prigent, C.; Remy, F.; Nino, F.; Borderies, P.; Biancamaria, S.; Calmant, S.

    2016-08-01

    Satellite radar altimetry, initially designed for studying ocean surface topography, demonstrated a strong potential for the continuous monitoring of ice sheets and land surfaces over the last 25 years. If radar altimetry is mostly used for its capacity to determine surface height, the backscattering coefficients provide information on the surface properties.Spatio-temporal variations of radar altimetry backscattering over land were related to the nature of the surface and its changes against time. This study presents the results of an along-track analysis of radar altimetry echoes over land at S, C, Ku and Ka bands using data from Jason-2, ERS-2, ENVISAT and SARAL on their nominal orbit. Temporal average and deviations are presented at global scale.

  15. Power transmission by laser beam from lunar-synchronous satellites to a lunar rover

    NASA Technical Reports Server (NTRS)

    Williams, M. D.; Deyoung, R. J.; Schuster, G. L.; Choi, S. H.; Dagle, J. E.; Coomes, E. P.; Antoniak, Z. I.; Bamberger, J. A.; Bates, J. M.; Chiu, M. A.

    1992-01-01

    This study addresses the possibility of beaming laser power from synchronous lunar orbits (L1 and L2 LaGrange points) to a manned long-range lunar rover. The rover and two versions of a satellite system (one powered by a nuclear reactor; the other by photovoltaics) are described in terms of their masses, geometry, power needs, mission and technological capabilities. Laser beam power is generated by a laser diode array in the satellite and converted to 30 kW of electrical power at the rover. Present technological capabilities, with some extrapolation to near future capabilities, are used in the descriptions. The advantages of the two satellite/rover systems over other such systems and over rovers with on-board power are discussed along with the possibility of enabling other missions.

  16. Power transmission by laser beam from lunar-synchronous satellites to a lunar rover

    NASA Astrophysics Data System (ADS)

    Williams, M. D.; De Young, R. J.; Schuster, G. L.; Choi, S. H.; Dagle, J. E.; Coomes, E. P.; Antoniak, Z. I.; Bamberger, J. A.; Bates, J. M.; Chiu, M. A.

    This study addresses the possibility of beaming laser power from synchronous lunar orbits (L1 and L2 LaGrange points) to a manned long-range lunar rover. The rover and two versions of a satellite system (one powered by a nuclear reactor; the other by photovoltaics) are described in terms of their masses, geometry, power needs, mission and technological capabilities. Laser beam power is generated by a laser diode array in the satellite and converted to 30 kW of electrical power at the rover. Present technological capabilities, with some extrapolation to near future capabilities, are used in the descriptions. The advantages of the two satellite/rover systems over other such systems and over rovers with on-board power are discussed along with the possibility of enabling other missions.

  17. Thermal rocketing and the Laser Geodynamic Satellite (LAGEOS-1)

    SciTech Connect

    Miller, W.A.

    1997-08-01

    This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory. LAGEOS is the most accurately tracked satellite in orbit. It is a totally passive, dense spherical satellite covered with 426 cube corner reflectors. Besides its great utility in measuring the Earth`s length of day and polar wobble, this satellite can be used to measure, for the first time, the general relativistic frame-dragging effect. Of the five dominant error sources in such an experiment, the largest one involves surface interaction of thermal forces (thermal rocketing) and its influence on the orbital nodal precession. The project objective was to enhance an already available theoretical model (computer code) developed at Los Alamos based on new optical-spin data obtained at the University of Maryland. The project objective was met and the enhanced code will serve as the new spin-dynamics model for future LAGEOS satellite missions.

  18. Method for Ground-to-Satellite Laser Calibration System

    NASA Technical Reports Server (NTRS)

    Lukashin, Constantine (Inventor); Wielicki, Bruce A. (Inventor)

    2015-01-01

    The present invention comprises an approach for calibrating the sensitivity to polarization, optics degradation, spectral and stray light response functions of instruments on orbit. The concept is based on using an accurate ground-based laser system, Ground-to-Space Laser Calibration (GSLC), transmitting laser light to instrument on orbit during nighttime substantially clear-sky conditions. To minimize atmospheric contribution to the calibration uncertainty the calibration cycles should be performed in short time intervals, and all required measurements are designed to be relative. The calibration cycles involve ground operations with laser beam polarization and wavelength changes.

  19. Harnessing Light: Laser/Satellite Relay Mirror Systems and Deterrence in 2035

    DTIC Science & Technology

    2010-02-16

    satellites. 49 Shutter Controls – Shutter controls on a satellite would enable the electronics and optical sensors to be protected, either as a...from a high-energy laser beam, but it would be a prudent precaution, especially if the shutters were constructed out of one of the advanced materials...October 2009). Fusion Energy Foundation. Beam Defense: An Alternative to Nuclear Destruction. Fallbrook, CA: Aero Publishers, Inc., 1983

  20. Preliminary results from the portable standard satellite laser ranging intercomparison with MOBLAS-7

    NASA Technical Reports Server (NTRS)

    Selden, Michael; Varghese, Thomas K.; Heinick, Michael; Oldham, Thomas

    1993-01-01

    Conventional Satellite Laser Ranging (SLR) instrumentation has been configured and successfully used to provide high-accuracy laboratory measurements on the LAGEOS-2 and TOPEX cube-corner arrays. The instrumentation, referred to as the Portable Standard, has also been used for field measurements of satellite ranges in tandem with MOBLAS-7. Preliminary results of the SLR measurements suggest that improved range accuracy can be achieved using this system. Results are discussed.

  1. Prototype Test Results for the Single Photon Detection SLR2000 Satellite Laser Ranging System

    NASA Technical Reports Server (NTRS)

    Zagwodzki, Thomas W.; McGarry, Jan F.; Degnan, John J.; Cheek, Jack W.; Dunn, Peter J.; Patterson, Don; Donovan, Howard

    2004-01-01

    NASA's aging Satellite Laser Ranging (SLR) network is scheduled to be replaced over the next few years with a fully automated single photon detection system. A prototype of this new system, called SLR2000, is currently undergoing field trials at the Goddard Space Flight Center in Greenbelt, Maryland to evaluate photon counting techniques and determine system hardware, software, and control algorithm performance levels and limitations. Newly developed diode pumped microchip lasers and quadrant microchannel plate-based photomultiplier tubes have enabled the development of this high repetition rate single photon detection SLR system. The SLR2000 receiver threshold is set at the single photoelectron (pe) level but tracks satellites with an average signal level typically much less than 1 pe. The 2 kHz laser fire rate aids in satellite acquisition and tracking and will enable closed loop tracking by accumulating single photon count statistics in a quadrant detector and using this information to correct for pointing errors. Laser transmitter beamwidths of 10 arcseconds (FWHM) or less are currently being used to maintain an adequate signal level for tracking while the receiver field of view (FOV) has been opened to 40 arcseconds to accommodate point ahead/look behind angular offsets. In the near future, the laser transmitter point ahead will be controlled by a pair of Risley prisms. This will allow the telescope to point behind and enable closure of the receiver FOV to roughly match the transmitter beam divergence. Bandpass filters (BPF) are removed for night tracking operations while 0.2 nm or 1 nm filters are used during daylight operation. Both day and night laser tracking of Low Earth Orbit (LEO) satellites has been achieved with a laser transmitter energy of only 65 microjoules per pulse. Satellite tracking is presently limited to LEO satellites until the brassboard laser transmitter can be upgraded or replaced. Simultaneous tracks have also been observed with NASA s

  2. Normalized GNSS interference pattern technique for altimetry.

    PubMed

    Ribot, Miguel Angel; Kucwaj, Jean-Christophe; Botteron, Cyril; Reboul, Serge; Stienne, Georges; Leclère, Jérôme; Choquel, Jean-Bernard; Farine, Pierre-André; Benjelloun, Mohammed

    2014-06-11

    It is well known that reflected signals from Global Navigation Satellite Systems (GNSS) can be used for altimetry applications, such as monitoring of water levels and determining snow height. Due to the interference of these reflected signals and the motion of satellites in space, the signal-to-noise ratio (SNR) measured at the receiver slowly oscillates. The oscillation rate is proportional to the change in the propagation path difference between the direct and reflected signals, which depends on the satellite elevation angle. Assuming a known receiver position, it is possible to compute the distance between the antenna and the surface of reflection from the measured oscillation rate. This technique is usually known as the interference pattern technique (IPT). In this paper, we propose to normalize the measurements in order to derive an alternative model of the SNR variations. From this model, we define a maximum likelihood estimate of the antenna height that reduces the estimation time to a fraction of one period of the SNR variation. We also derive the Cramér-Rao lower bound for the IPT and use it to assess the sensitivity of different parameters to the estimation of the antenna height. Finally, we propose an experimental framework, and we use it to assess our approach with real GPS L1 C/A signals.

  3. Normalized GNSS Interference Pattern Technique for Altimetry

    PubMed Central

    Ribot, Miguel Angel; Kucwaj, Jean-Christophe; Botteron, Cyril; Reboul, Serge; Stienne, Georges; Leclère, Jérôme; Choquel, Jean-Bernard; Farine, Pierre-André; Benjelloun, Mohammed

    2014-01-01

    It is well known that reflected signals from Global Navigation Satellite Systems (GNSS) can be used for altimetry applications, such as monitoring of water levels and determining snow height. Due to the interference of these reflected signals and the motion of satellites in space, the signal-to-noise ratio (SNR) measured at the receiver slowly oscillates. The oscillation rate is proportional to the change in the propagation path difference between the direct and reflected signals, which depends on the satellite elevation angle. Assuming a known receiver position, it is possible to compute the distance between the antenna and the surface of reflection from the measured oscillation rate. This technique is usually known as the interference pattern technique (IPT). In this paper, we propose to normalize the measurements in order to derive an alternative model of the SNR variations. From this model, we define a maximum likelihood estimate of the antenna height that reduces the estimation time to a fraction of one period of the SNR variation. We also derive the Cramér–Rao lower bound for the IPT and use it to assess the sensitivity of different parameters to the estimation of the antenna height. Finally, we propose an experimental framework, and we use it to assess our approach with real GPS L1 C/A signals. PMID:24922453

  4. Scintillation characterization of multiple transmitters for ground-to-satellite laser communication

    NASA Astrophysics Data System (ADS)

    Pan, Feng; Ma, Jing; Tan, Liying; Yu, SiYuan; Gao, Chong

    2005-01-01

    Using high data optical transmitters for satellite communication channels has generated an interest in laser communication systems ground-to-satellite data links. The atmospheric turbulence causes laser intensity fluctuations that can seriously degrade the reliability and performance of such laser communication links. In the ground-to-satellite link, the atmospheric turbulent's thickness is much less than the path length. Taking into account the large size of the beam at a satellite in orbit, the spatial coherence radius at the satellite is many times larger than the probable receiving aperture of the satellite's optical antenna. Thus the aperture behave of uplink essentially like a point detector without aperture averaging. An analysis of multiple beams compensation for atmospheric turbulence induced scintillation is carried out in this paper. Using multiple incoherent beams transmit synchronically optical signal from dividable apertures, separated by a distance larger than the atmospheric coherence diameter. The convolution integration to determine what happens for two independent random variable, we generalized this method to multiple independent random variables. According to probability theorem, the multiple beams distribution of the irradiance is given with different scintillation index. For this analysis we assume that the single-beam probability distribution function model of the irradiance is the gamma-gamma distribution. In our analysis of this simulation model, it shows that the adverse effect of scintillation on the communication lasers can be minimized with multiple transmitters under weak, moderate, and strong turbulence conditions. The scintillation index was reduced as the number of laser transmitters was increased. So, fluctuation on the uplink/downlink communication beams can effective reduced by multiple transmitters.

  5. Testing fundamental physics with laser ranged satellites: perspectives and goals of the LARASE experiment

    NASA Astrophysics Data System (ADS)

    Lucchesi, David; Anselmo, Luciano; Pardini, Carmen; Peron, Roberto; Pucacco, Giuseppe; Visco, Massimo

    Passive laser-ranged satellites, launched for geodynamics and geophysics purposes, not only have contributed to significant measurements in space geodesy that enabled, among several aspects, a deeper knowledge of the Earth's geopotential (both in its static and dynamic behavior), as well as of the geocenter motion and GM value up to the definition of the terrestrial reference frame, but they also provided an outstanding test bench to fundamental physics, as in the case of the first measurement of the Lense-Thirring precession on the combined nodes of the two LAGEOS satellites, or in the case of the total relativistic precession of the argument of pericenter of LAGEOS II. Indeed, the physical characteristics of such satellites -- such as their low area-to-mass ratio -- as well as those of their orbits, and the availability of high-quality tracking data provided by the International Laser Ranging Service (ILRS), allow for precise tests of gravitational theories. The aim of LARASE (LAser RAnged Satellites Experiment) is to go a step further in the tests of the gravitational interaction in the field of Earth, i.e. in the weak-field and-slow motion limit of general relativity, by the joint analysis of the orbits of the two LAGEOS satellites and that of the most recent LARES satellite. One of the key ingredients to reach such a goal is to provide high-quality updated models for the perturbing non-gravitational forces acting on the surface of such satellites. A large amount of Satellite Laser Ranging (SLR) data of LAGEOS and LAGEOS II has been analyzed using a set of dedicated models for satellite dynamics, and the related post-fit residuals have been analyzed. A parallel work is on-going in the case of LARES that, due to its much lower altitude, is subject to larger gravitational and non-gravitational effects; the latter are mitigated in part by its much lower area-to-mass ratio. Recent work on the data analysis of the orbit of such satellites will be presented together

  6. Compact, Passively Q-Switched Nd:YAG Laser for the MESSENGER Mission to the Planet Mercury

    NASA Technical Reports Server (NTRS)

    Krebs, Danny J.; Novo-Gradac, Anne-Marie; Li, Steven X.; Lindauer, Steven J.; Afzal, Robert S.; Yu, Antony

    2004-01-01

    A compact, passively Q-switched Nd:YAG laser has been developed for the Mercury Laser Altimeter (MLA) instrument which is an instrument on the MESSENGER mission to the planet Mercury. The laser achieves 5.4 percent efficiency with a near diffraction limited beam. It has passed all space flight environmental tests at system, instrument, and satellite integration. The laser design draws on a heritage of previous laser altimetry missions, specifically ISESAT and Mars Global Surveyor; but incorporates thermal management features unique to the requirements of an orbit of the planet Mercury.

  7. Laser power beaming to extend lives of GSO NiCd satellites

    SciTech Connect

    Monroe, D.K.

    1993-12-31

    It is proposed that a ground-based laser can beam power to commercial communication satellites in geosynchronous orbit and reduce battery depth-of-discharge during eclipses. Two laser system designs are presented which have the capability of reducing battery discharge by 100%. Both utilize a steerable beam director, with a mirror diameter of 4 meters in one case and 8 meters in the other. Both also use an adaptive optics unit within the beam train to provide real-time corrections for wavefront distortions caused by atmospheric turbulence. The required system power output is in the range of 100 to 200 kW for a transmitted wavelength just under 900 nm. Laser power beaming can nearly double the remaining lifetime of a satellite that uses NiCd batteries. However, by the time such lasers become available, nearly all NiCd satellites will be replaced by NiH{sub 2} satellites, which stand to benefit much less from power beaming.

  8. Compensation for the distortion in satellite laser range predictions due to varying pulse travel times

    NASA Technical Reports Server (NTRS)

    Paunonen, Matti

    1993-01-01

    A method for compensating for the effect of the varying travel time of a transmitted laser pulse to a satellite is described. The 'observed minus predicted' range differences then appear to be linear, which makes data screening or use in range gating more effective.

  9. Investigation of a new method for determination of atmospheric refractivity corrections in satellite laser ranging.

    NASA Astrophysics Data System (ADS)

    Mironov, N. T.; Prokopov, A. V.; Remaev, E. V.

    1997-08-01

    A new algorithm is investigated for calculating atmospheric refractivity corrections in satellite laser ranging in the Earth's spherically stratified atmosphere based on results of measuring meteorological parameters on the Earth's surface. A numerical experiment with 125 meteorological sounding profiles shows that the new method allows to determine atmospheric refractivity corrections with the accuracy better than the Marini-Murray method does.

  10. Satellite Laser Ranging in the 1990s: Report of the 1994 Belmont Workshop

    NASA Technical Reports Server (NTRS)

    Degnan, John J. (Editor)

    1994-01-01

    An international network of 43 stations in 30 countries routinely collects satellite ranging data which is used to study the solid Earth and its interactions with the oceans, atmosphere, and Moon. Data products include centimeter accuracy site positions on a global scale, tectonic plate motions, regional crustal deformation, long wavelength gravity field and geoid, polar motion, and variations in the Earth's spin rate. By calibrating and providing precise orbits for spaceborne microwave altimeters, satellite laser ranging also enables global measurement of sea and ice surface topography, mean sea level, global ocean circulation, and short wavelength gravity fields and marine geoids. It provides tests of general relativity and a means or subnanosecond time transfer. This workshop was convened to define future roles and directions in satellite laser ranging.

  11. Low-energy laser irradiation affects satellite cell proliferation and differentiation in vitro.

    PubMed

    Ben-Dov, N; Shefer, G; Irintchev, A; Wernig, A; Oron, U; Halevy, O; Irinitchev, A

    1999-01-11

    Low-energy laser (He-Ne) irradiation was found to promote skeletal muscle regeneration in vivo. In this study, its effect on the proliferation and differentiation of satellite cells in vitro was evaluated. Primary rat satellite cells were irradiated for various time periods immediately after preparation, and thymidine incorporation was determined after 2 days in culture. Laser irradiation affected thymidine incorporation in a bell-shaped manner, with a peak at 3 s of irradiation. Three seconds of irradiation caused an induction of cell-cycle regulatory proteins: cyclin D1, cyclin E and cyclin A in an established line of mouse satellite cells, pmi28, and proliferating cell nuclear antigen (PCNA) in primary rat satellite cells. The induction of cyclins by laser irradiation was compatible with their induction by serum refeeding of the cells. Laser irradiation effect on cell proliferation was dependent on the rat's age. At 3 weeks of age, thymidine incorporation in the irradiated cells was more than twofold higher than that in the controls, while at 6 weeks of age this difference had almost disappeared. Myosin heavy chain (MHC) protein levels were twofold lower in the irradiated than in the control cells, whereas the proliferation of the irradiated cells was twofold higher. Fusion percentage was lower in the irradiated compared to non-irradiated cells. In light of these data, the promoting effect of laser irradiation on skeletal muscle regeneration in vivo may be due to its effect on the activation of early cell-cycle regulatory genes in satellite cells, leading to increased proliferation and to a delay in cell differentiation.

  12. Satellite Power Systems (SPS) laser studies. Volume 1: Laser environmental impact study

    NASA Technical Reports Server (NTRS)

    Beverly, R. E., III

    1980-01-01

    The environmental impact of space to Earth power transmission using space borne laser subsystems is emphasized. A laser system is defined, estimates of relevant efficiencies for laser power generation and atmospheric transmission are developed, and a comparison is made to a microwave system. Ancillary issues, such as laser beam spreading, safety and security, mass and volume estimates and technology growth are considered.

  13. The design and fabrication of the satellite relative-movement trajectory simulator for inter-satellite laser communications

    NASA Astrophysics Data System (ADS)

    Sun, Jianfeng; Liu, Liren; Yun, Maojin; Zhang, Dejiang; Xu, Nan

    2005-08-01

    The characteristics of the terminals for the inter-satellite laser communication must be tested and verified on ground before flight test. Satellite relative-movement trajectory optical simulator is one of the most important devices of the ground test and verification system. It is used for simulation of the relative-movement between arbitrary satellites. Cooperating with the standard satellite laser communication terminal, the dynamical performance such as acquisition time and probability, pointing accuracy and tracking accuracy etc, of the terminal to be tested can be obtained. To keep the base of the terminal to be tested fixed, the clear aperture must be relatively large compare to the terminal's effect aperture. And for the practical application as well as in considering the size of optical glass commercially available, the optical aperture of the scanner was determined as φ420mm, the random accuracy for the simulation is 50-200μrad, Scanning angular coverage: azimuth +/-180°, elevation +/-15°. So the satellite relative-movement trajectory simulator belongs to the large-scale high-precision opto-mechanic and electrical equipment. In this paper, the design and fabrication of the simulator are introduced in detail. The simulator has the features as compact in construction, high accuracy in measurement, simple realization of the far-field condition in the near-field use, and direct simulation of 2D trajectory and consists of eight main elements: two wedge prisms, two pairs of worm and gear, damping gears, two actuating motors, two damping motors, rotating optical encoders, control computer and relevant electronics and mechanisms. The motivation of the design is to improve the accuracy as high as possible. The fabrication of the element of the simulator is stringent because of large-scale and high accuracy. For example, to solve the gap problem of the transmission mechanics, the damping method is introduced to the system. During the progress of the design and

  14. Pearson type VII distribution of errors of laser satellite observations.

    NASA Astrophysics Data System (ADS)

    Dzhun', I. V.

    The distribution of the difference O-C between observed and calculated satellite distances obtained on execution of the short MERIT program is studied. It is shown that the distribution of these differences is described better by the curve of a Pearson type VII distribution than by the normal law. This can be explained by fluctuations in the accuracy of the observations due to instability of the metrological situation. It is shown that the parameter m of the Pearson distribution varies from 2.7 to ∞ (normal law).

  15. Laser satellite constellations for strategic defense - an analytic model

    SciTech Connect

    Parmentola, J.A.; Milton, A.F.

    1987-10-01

    Using mainly geometric reasoning, an analytic model is constructed that predicts the required characteristics of an orbiting constellation of laser battle stations, each of which is designed to destroy ballistic missiles during their boost phase. The geometry of the constellation configuration and some general aspects of the coverage problem are discussed. The determination of the absentee ratio falls into two main categories that depend upon whether the Soviet ICBM threat is concentrated at a single location or whether it is distributed as it is now. A point-threat model and a distributive threat model are considered, the determination of the respective kill rates for these models is discussed, and the scaling properties of the laser constellation with respect to a change in the quantitative nature of the two types of ICBM threats are considered.

  16. A Global Ocean Tide Model From TOPEX/POSEIDON Altimetry: GOT99.2

    NASA Technical Reports Server (NTRS)

    Ray, Richard D.

    1999-01-01

    Goddard Ocean Tide model GOT99.2 is a new solution for the amplitudes and phases of the global oceanic tides, based on over six years of sea-surface height measurements by the TOPEX/POSEIDON satellite altimeter. Comparison with deep-ocean tide-gauge measurements show that this new tidal solution is an improvement over previous global models, with accuracies for the main semidiurnal lunar constituent M2 now below 1.5 cm (deep water only). The new solution benefits from use of prior hydrodynamic models, several in shallow and inland seas as well as the global finite-element model FES94.1. This report describes some of the data processing details involved in handling the altimetry, and it provides a comprehensive set of global cotidal charts of the resulting solutions. Various derived tidal charts are also provided, including tidal loading deformation charts, tidal gravimetric charts, and tidal current velocity (or transport) charts. Finally, low-degree spherical harmonic coefficients are computed by numerical quadrature and are tabulated for the major short-period tides; these are useful for a variety of geodetic and geophysical purposes, especially in combination with similar estimates from satellite laser ranging.

  17. The Benefit of Multi-Mission Altimetry Series for the Calibration of Hydraulic Models

    NASA Astrophysics Data System (ADS)

    Domeneghetti, Alessio; Tarpanelli, Angelica; Tourian, Mohammad J.; Brocca, Luca; Moramarco, Tommaso; Castellarin, Attilio; Sneeuw, Nico

    2016-04-01

    The growing availability of satellite altimetric time series during last decades has fostered their use in many hydrological and hydraulic applications. However, the use of remotely sensed water level series still remains hampered by the limited temporal resolution that characterizes each sensor (i.e. revisit time varying from 10 to 35 days), as well as by the accuracy of different instrumentation adopted for monitoring inland water. As a consequence, each sensor is characterized by distinctive potentials and limitations that constrain its use for hydrological applications. In this study we refer to a stretch of about 140 km of the Po River (the longest Italian river) in order to investigate the performance of different altimetry series for the calibration of a quasi-2d model built with detailed topographic information. The usefulness of remotely sensed water surface elevation is tested using data collected by different altimetry missions (i.e., ERS-2, ENVISAT, TOPEX/Poseidon, JASON-2 and SARAL/Altika) by investigating the effect of (i) record length (i.e. number of satellite measurements provided by a given sensor at a specific satellite track) and (ii) data uncertainty (i.e. altimetry measurements errors). Since the relatively poor time resolution of satellites constrains the operational use of altimetric time series, in this study we also investigate the use of multi-mission altimetry series obtained by merging datasets sensed by different sensors over the study area. Benefits of the highest temporal frequency of multi-mission series are tested by calibrating the quasi-2d model referring in turn to original satellite series and multi-mission datasets. Jason-2 and ENVISAT outperform other sensors, ensuring the reliability on the calibration process for shorter time series. The multi-mission dataset appears particularly reliable and suitable for the calibration of hydraulic model. If short time periods are considered, the performance of the multi-mission dataset

  18. Optical design of satellite laser communication integrative transceiver

    NASA Astrophysics Data System (ADS)

    Cheng, Yanyan; Fan, Xuewu; Zou, Gangyi; Yan, Peipei; Liu, Kai

    According to technical requirements of satellite optical communication, a set of optical system of transmitter and receiver with a common optical antenna is designed at 850nm. We select a Cassegrain-type afocal off-axis system as the optical antenna structure. The entrance pupil diameter is 150 mm. The field of view of transmitter and receiver is +/-100μrad and +/-5mrad, respectively. This optical system has a simple and feasible configuration. The design results show that system performances are acceptable. The MTF is close to the diffraction limit. The energy concentration ratios are more than 90% at 30μm of diameter of circle. The RMS of wave front aberration is less than λ/20.

  19. Massive information sharing among global data centers based on satellite laser communication

    NASA Astrophysics Data System (ADS)

    Yi, Longteng; Li, Cong; Liu, Naijin

    2015-10-01

    With the development of big data and information globalization, the requirements of massive information transmitting and sharing among data centers are expanding, especially among those data centers which are extremely far away from each other. In the above field, conventional optical fiber transmission faces many problems such as complex networking, poor security, long node switching delay, high lease and maintain cost and low migration flexibility. Besides, in the near future, data centers may tend to be built in the remote Polar Regions or on the sea for natural cooling. For the above situation, sharing the massive information among global data centers based on satellite laser communication is proposed in this paper. This proposal includes advantage analysis, research of restraining atmosphere interference, etc. At last, by comparison with conventional technology, the research result shows that massive information transmitting and sharing among global data centers based on satellite laser communication has far reaching application potential.

  20. Performance of laser inter-satellite links with dynamic beam waist adjustment.

    PubMed

    Song, Tianyu; Wang, Qian; Wu, Ming-Wei; Kam, Pooi-Yuen

    2016-05-30

    In this paper, we propose the idea of dynamic beam waist adjustment for laser inter-satellite communications, and study the performance of this dynamic-beam scheme. The beam waist adjustment is based on continuous detection of the instantaneous pointing error angle, which is performed at the transmitter side. Using a square to approximate the circular detector region, we obtain a closed-form expression for calculating the proportion of power that can be collected by the receiver aperture, and derive a simple algebraic solution for the optimum dynamic beam waist. Due to its simple form, the dynamic beam waist value can be computed in real time at the transmitter, and therefore, the adjustment is practically implementable. It is shown that the performance of laser inter-satellite links with dynamic beam waist is better than that with fixed beam waist.

  1. Remote sensing of atmospheric pressure and sea state from satellites using short-pulse multicolor laser altimeters

    NASA Technical Reports Server (NTRS)

    Gardner, C. S.; Tsai, B. M.; Abshire, J. B.

    1983-01-01

    Short pulse multicolor laser ranging systems are currently being developed for satellite ranging applications. These systems use Q-switched pulsed lasers and streak tube cameras to provide timing accuracies approaching a few picoseconds. Satellite laser ranging systems was used to evaluate many important geophysical phenomena such as fault motion, polar motion and solid earth tides, by measuring the orbital perturbations of retroreflector equipped satellites. Some existing operational systems provide range resolution approaching a few millimeters. There is currently considerable interest in adapting these highly accurate systems for use as airborne and satellite based altimeters. Potential applications include the measurement of sea state, ground topography and atmospheric pressure. This paper reviews recent progress in the development of multicolor laser altimeters for use in monitoring sea state and atmospheric pressure.

  2. SAR Satellite Images and Terrestrial Laser Scanning in Forest Damages Mapping in Finland

    NASA Astrophysics Data System (ADS)

    Karjalainen, Mika; Kaasalainen, Sanna; Hyyppa, Juha; Holopainen, Markus; Lyytikainen-Saarenmaa, Paivi; Krooks, Anssi; Jaakkola, Anttoni

    2010-12-01

    Forests are of high importance for the Finnish economy and environment. Forests inventories should not only provide information about the volume of growing stock, but also about the health status of forests, which is an indicator of the annual growth of forests and Carbon balance. One of the forest damage types is defoliation, which causes forest growth reduction and consequently potentially economical losses to the forest owners, but can be seen as an environmental indicator also. For example, in the past ten years, extensive and persistent needle defoliation caused by insects has been observed in the areas of Palokangas and Outokumpu in Eastern Finland. It is expected that the insect outbreaks are becoming more common and new species of insects may be spreading out in Finland due to the climate warming. Traditionally the intensity of needle defoliation has been estimated using visual observations, which are prone to errors and their areal extent is limited. Therefore, remote sensing can be seen as a potential tool for mapping defoliation. In this study, both Terrestrial Laser Scanning data and SAR satellite images have been exploited. On the one hand, Terrestrial Laser Scanning provides means to rapidly and objectively measure critical forest related information. On the other hand, SAR satellite images enable wide-area mapping and constant monitoring, which would be impossible in Finland using optical satellite images due to the cloudiness. The fusion of Laser scanning and SAR information could make a difference in forest health mapping. In this paper, preliminary results of the estimation of the needle defoliation intensity based on Terrestrial Laser Scanning and ERS and Envisat SAR (non-interferometric) satellite data are presented.

  3. Scintillation statistics caused by atmospheric turbulence and speckle in satellite laser ranging

    NASA Technical Reports Server (NTRS)

    Bufton, J. L.; Iyer, R. S.; Taylor, L. S.

    1977-01-01

    We study the statistics of scintillation at the ground-based receiver for the earth-space-earth retroreflector configuration of satellite laser ranging. These statistics are governed by the joint effects of atmospheric turbulence and speckle produced by the retroreflector array. An expression for the probability density function of scintillation is obtained and evaluated numerically. Comparison of the normalized variance of scintillation calculated by using this function shows good agreement with results obtained by other methods.

  4. Investigation of a new method for the determination of atmospheric correction in satellite laser ranging.

    NASA Astrophysics Data System (ADS)

    Mironov, N. T.; Prokopov, A. V.; Remaev, E. V.

    The authors investigate a new algorithm for calculating atmospheric correction in satellite laser ranging in the spherically stratified terrestrial atmosphere. The algorithm is based on results of measuring meteorological parameters on the Earth's surface. A numerical experiment with 125 meteorological sounding profiles shows that the new method allows the atmospheric corrections to be determined in the range of zenith angles from 0° to 80° more accurately than with the Marini-Murray method.

  5. Proposed satellite laser ranging and very long baseline interferometry sites for crustal dynamics investigations

    NASA Technical Reports Server (NTRS)

    Lowman, P. D.; Allenby, R. J.; Frey, H. V.

    1979-01-01

    Recommendations are presented for a global network of 125 sites for geodetic measurements by satellite laser ranging and very long baseline interferometry. The sites were proposed on the basis of existing facilities and scientific value for investigation of crustal dynamics as related to earthquake hazards. Tectonic problems are discussed for North America peripheral regions and for the world. The sites are presented in tables and maps, with bibliographic references.

  6. Satellite Laser Ranging and the Modelling of Non-gravitational Perturbations: the LARASE experiment

    NASA Astrophysics Data System (ADS)

    Lucchesi, David; Anselmo, Luciano; Pardini, Carmen; Peron, Roberto; Pucacco, Giuseppe; Visco, Massimo

    Laser ranging to passive (cannonball) satellites like the two LAGEOS still represents a way to extract relevant information on Earth’s internal structure, its surface and the way it interacts with the surrounding medium, the atmosphere. The related precise orbit determination (POD) represents the first issue to be fulfilled, to be followed by a solve for the unknown global parameters. The POD requires two main features: i) high-quality observations and ii) high-quality dynamical models. The first item, i.e., the availability of high-quality tracking data, is provided by the International Laser Ranging Service (ILRS) by means of the very precise Satellite Laser Ranging (SLR) technique. With regard to the second point, a big effort has been done to develop models for the non-gravitational forces (i.e., non-conservative forces) on passive satellites, especially for the two LAGEOS, since early ’80s, with significant results in the literature. However, some of the models built were valid only under particular approximations or simplifications, as for the spin model and the thermal thrust forces, and have not been generalized or tested under different conditions. Other aspects, such as the asymmetric reflectivity of the two LAGEOS satellites, are not fully understood. For instance, one of the main parameters that enters in these models is the spin rate of the satellite and its slowing down due to the coupling of the induced magnetic moment produced by eddy currents with the external geomagnetic field. Once the value of the spin period is close to other characteristics time scales, as the thermal inertia of the cube corner retroreflectors or the orbital period of the satellite, resonances are present and more complicated (non-averaged) equations have to be considered for a reliable model of the spin evolution. In order to account for such effects and also to extend/apply (correctly) the models to the new LARES satellite, new efforts are needed in the field of the non

  7. State-of-the-art satellite laser range modeling for geodetic and oceanographic applications

    NASA Technical Reports Server (NTRS)

    Klosko, Steve M.; Smith, David E.

    1993-01-01

    Significant improvements have been made in the modeling and accuracy of Satellite Laser Range (SLR) data since the launch of LAGEOS in 1976. Some of these include: improved models of the static geopotential, solid-Earth and ocean tides, more advanced atmospheric drag models, and the adoption of the J2000 reference system with improved nutation and precession. Site positioning using SLR systems currently yield approximately 2 cm static and 5 mm/y kinematic descriptions of the geocentric location of these sites. Incorporation of a large set of observations from advanced Satellite Laser Ranging (SLR) tracking systems have directly made major contributions to the gravitational fields and in advancing the state-of-the-art in precision orbit determination. SLR is the baseline tracking system for the altimeter bearing TOPEX/Poseidon and ERS-1 satellites and thus, will play an important role in providing the Conventional Terrestrial Reference Frame for instantaneously locating the geocentric position of the ocean surface over time, in providing an unchanging range standard for altimeter range calibration, and for improving the geoid models to separate gravitational from ocean circulation signals seen in the sea surface. Nevertheless, despite the unprecedented improvements in the accuracy of the models used to support orbit reduction of laser observations, there still remain systematic unmodeled effects which limit the full exploitation of modern SLR data.

  8. Scintillation model of laser beam propagation in satellite-to-ground bidirectional atmospheric channels

    NASA Astrophysics Data System (ADS)

    Toyoshima, Morio; Sasaki, Takashi; Takenaka, Hideki; Takayama, Yoshihisa

    2012-11-01

    This paper discusses a scintillation model of laser beam propagation in satellite-to-ground bidirectional atmospheric channels. The frequency characteristics of the downlink were theoretically derived on the basis of measurements in low Earth orbit satellite-to-ground laser communication experiments. The speckle patterns were averaged and the frequency response of the received optical signal was filtered by a telescope aperture. The model parameters were obtained by fitting the results to the model. This paper introduces scaling factors for the uplink and extends the theory for the downlink to that for the uplink. The proposed model can generate time-varying optical signals based on the von Kármán spectrum for space-to-ground laser links. The scintillation index was estimated using the modified Hufnagel-Valley model, which was obtained from real measurements. The probability density function was fitted by the estimated scintillation index and compared to the gamma-gamma distribution under strong turbulence conditions. The scaling factor for the root mean square wind speed was newly introduced to fit the frequency spectra for the uplink. The simulation results are presented in this paper. The proposed scintillation model can contribute to improving the fading simulation of satellite-to-ground communication links as well as add to the future discussion of standards, like those proposed by the Consultative Committee for Space Data Systems.

  9. New progress of ranging technology at Wuhan Satellite Laser Ranging Station

    NASA Technical Reports Server (NTRS)

    Xia, Zhiz-Hong; Ye, Wen-Wei; Cai, Qing-Fu

    1993-01-01

    A satellite laser ranging system with an accuracy of the level of centimeter has been successfully developed at the Institute of Seismology, State Seismological Bureau with the cooperation of the Institute of Geodesy and Geophysics, Chinese Academy of Science. With significant improvements on the base of the second generation SLR system developed in 1985, ranging accuracy of the new system has been upgraded from 15 cm to 3-4 cm. Measuring range has also been expanded, so that the ETALON satellite with an orbit height of 20,000 km launched by the former U.S.S.R. can now be tracked. Compared with the 2nd generation SLR system, the newly developed system has the following improvements. A Q modulated laser is replaced by a mode-locked YAG laser. The new device has a pulse width of 150 ps and a repetition rate of 1-4 pps. A quick response photomultiplier has been adopted as the receiver for echo; for example, the adoption of the MCP tube has obviously reduced the jitter error of the transit time and has improved the ranging accuracy. The whole system is controlled by an IBM PC/XT Computer to guide automatic tracking and measurement. It can carry out these functions for satellite orbit calculation, real-time tracking and adjusting, data acquisition and the preprocessed of observing data, etc. The automatization level and reliability of the observation have obviously improved.

  10. Global ocean circulation by altimetry

    NASA Technical Reports Server (NTRS)

    Wunsch, Carl; Haidvogel, D.

    1991-01-01

    The overall objectives of this project are to determine the general circulation of the oceans and many of its climate and biochemical consequences through the optimum use of altimetry data from TOPEX/POSEIDON and related missions. Emphasis is on the global-scale circulation, as opposed to the regional scale, but some more local studies will be carried out. Because of funding limitations, the primary initial focus will be on the time-dependent global-scale circulation rather than the mean; eventually, the mean circulation must be dealt with as well.

  11. Simulation Studies of Satellite Laser CO2 Mission Concepts

    NASA Technical Reports Server (NTRS)

    Kawa, Stephan Randy; Mao, J.; Abshire, J. B.; Collatz, G. J.; Sun X.; Weaver, C. J.

    2011-01-01

    Results of mission simulation studies are presented for a laser-based atmospheric CO2 sounder. The simulations are based on real-time carbon cycle process modeling and data analysis. The mission concept corresponds to ASCENDS as recommended by the US National Academy of Sciences Decadal Survey. Compared to passive sensors, active (lidar) sensing of CO2 from space has several potentially significant advantages that hold promise to advance CO2 measurement capability in the next decade. Although the precision and accuracy requirements remain at unprecedented levels of stringency, analysis of possible instrument technology indicates that such sensors are more than feasible. Radiative transfer model calculations, an instrument model with representative errors, and a simple retrieval approach complete the cycle from "nature" run to "pseudodata" CO2. Several mission and instrument configuration options are examined, and the sensitivity to key design variables is shown. Examples are also shown of how the resulting pseudo-measurements might be used to address key carbon cycle science questions.

  12. Precise relative location estimation from satellite laser observations. [Geos 3 satellite

    NASA Technical Reports Server (NTRS)

    Dunn, P. J.

    1979-01-01

    Laser data from the Greenbelt, Bermuda, and Grand Turk Island tec tracking stations, and from observation at Patrick Air Force Base were used in an experiment to determine precise inter-station baselines and relative heights in short orbital arcs of no more than 12 minutes duration. The relative locations obtained are sensitive to reasonable variations in the gravity field to less than 15 cm in inter-station baseline and less than 35 cm in relative height. The formal standard deviations for range measurements at the observed 7 cm noise level are less than 10 cm for either baseline or relative height determinations from the twenty-arc combination solution. The method of data analysis is described, the baseline and relative height results are presented, and gravity model dependence is considered.

  13. Technique Errors and Limiting Factors in Laser Ranging to Geodetic Satellites

    NASA Astrophysics Data System (ADS)

    Appleby, G. M.; Luceri, V.; Mueller, H.; Noll, C. E.; Otsubo, T.; Wilkinson, M.

    2012-12-01

    The tracking stations of the International Laser Ranging Service (ILRS) global network provide to the Data Centres a steady stream of very precise laser range normal points to the primary geodetic spherical satellites LAGEOS (-1 and -2) and Etalon (-1 and -2). Analysis of these observations to determine instantaneous site coordinates and Earth orientation parameters provides a major contribution to ongoing international efforts to define a precise terrestrial reference frame, which itself supports research into geophysical processes at the few mm level of precision. For example, the latest realization of the reference frame, ITRF2008, used weekly laser range solutions from 1983 to 2009, the origin of the Frame being determined solely by the SLR technique. However, in the ITRF2008 publication, Altamimi et al (2011, Journal of Geodesy) point out that further improvement in the ITRF is partly dependent upon improving an understanding of sources of technique error. In this study we look at SLR station hardware configuration that has been subject to major improvements over the last four decades, at models that strive to provide accurate translations of the laser range observations to the centres of mass of the small geodetic satellites and at the considerable body of work that has been carried out via orbital analyses to determine range corrections for some of the tracking stations. Through this study, with specific examples, we start to put together an inventory of system-dependent technique errors that will be important information for SLR re-analysis towards the next realization of the ITRF.

  14. Analytical study of pulsed laser irradiation on some materials used for photovoltaic cells on satellites

    NASA Astrophysics Data System (ADS)

    Abd El-Hameed, Afaf M.

    2015-12-01

    The present research concerns on the study of laser-powered solar panels used for space applications. A mathematical model representing the laser effects on semiconductors has been developed. The temperature behavior and heat flow on the surface and through a slab has been studied after exposed to nano-second pulsed laser. The model is applied on two different types of common active semiconductor materials that used for photovoltaic cells fabrication as silicon (Si), and gallium arsenide (GaAs). These materials are used for receivers' manufacture for laser beamed power in space. Various values of time are estimated to clarify the heat flow through the material sample and generated under the effects of pulsed laser irradiation. These effects are theoretically studied in order to determine the performance limits of the solar cells when they are powered by laser radiation during the satellite eclipse. Moreover, the obtained results are carried out to optimize conversion efficiency of photovoltaic cells and may be helpful to give more explanation for layout of the light-electricity space systems.

  15. Shuttle Laser Altimeter

    NASA Technical Reports Server (NTRS)

    Bufton, Jack L.; Harding, David J.; Garvin, James B.

    1999-01-01

    The Shuttle Laser Altimeter (SLA) is a Hitchhiker experiment that has flown twice; first on STS-72 in January 1996 and then on STS-85 in August 1997. Both missions produced successful laser altimetry and surface lidar data products from approximately 80 hours per mission of SLA data operations. A total of four Shuttle missions are planned for the SLA series. This paper documents SLA mission results and explains SLA pathfinder accomplishments at the mid-point in this series of Hitchhiker missions. The overall objective of the SLA mission series is the transition of the Goddard Space Flight Center airborne laser altimeter and lidar technology to low Earth orbit as a pathfinder for NASA operational space-based laser remote sensing devices. Future laser altimeter sensors will utilize systems and approaches being tested with SLA, including the Multi-Beam Laser Altimeter (MBLA) and the Geoscience Laser Altimeter System (GLAS). MBLA is the land and vegetation laser sensor for the NASA Earth System Sciences Pathfinder Vegetation Canopy Lidar (VCL) Mission, and GLAS is the Earth Observing System facility instrument on the Ice, Cloud, and Land Elevation Satellite (ICESat). The Mars Orbiting Laser Altimeter, now well into a multi-year mapping mission at the red planet, is also directly benefiting from SLA data analysis methods, just as SLA benefited from MOLA spare parts and instrument technology experience [5] during SLA construction in the early 1990s.

  16. Laser Materials and Laser Spectroscopy - A Satellite Meeting of IQEC '88

    NASA Astrophysics Data System (ADS)

    Wang, Zhijiang; Zhang, Zhiming

    1989-03-01

    The Table of Contents for the book is as follows: * Laser Materials * Laser Site Spectroscopy of Transition Metal Ions in Glass * Spectroscopy of Chromium Doped Tunable Laser Materials * Spectroscopic Properties of Nd3+ Ions in LaMgAl11O19 Crystal * Spectral Study and 2.938 μm Laser Emission of Er3+ in the Y3Al5O12 Crystal * Raman-infrared Spectra and Radiationless Relaxation of Laser Crystal NdAl3(BO3)4 * A Study on HB and FLN in BaFCl0.5Br0.5:Sm2+ at 77K * Pair-pumped Upconversion Solid State Lasers * CW Upconversion Laser Action in Neodymium and Erbium doped Solids * Ultra-high Sensitive Upconversion Fluorescence of YbF3 Doped with Trace Tm3+ and Er3+ * The Growth and Properties of NYAB and EYAB Multifunctional Crystal * Study on Fluorescence and Laser Light of Er3+ in Glass * Growth and Properties of Single Crystal Fibers for Laser Materials * A Study on the Quality of Sapphire, Ruby and Ti3+ Doped Sapphire Grown by Temperature Gradient Technique (TGT) and Czochralski Technique (CZ) * The Measurement of Output Property of Ti3+ Al2O3 Laser Crystal * An Xα Study of the Laser Crystal MgF2 : V2+ * Q-switched NAB Laser * Miniature YAG Lasers * Study of High Efficiency {LiF}:{F}^-_2 Color Center Crystals * Study on the Formation Conditions and Optical Properties of (F2+)H Color Center in NaCl:OH- Crystals * Novel Spectroscopic Properties of {LiF}:{F}^+_3 - {F}_2 Mixed Color Centers Laser Crystals * Terraced Substrate Visible GaAlAs Semiconductor Lasers with a Large Optical Cavity * The Temperature Dependence of Gain Spectra, Threshold Current and Auger Recombination in InGaAsP-InP Double Heterojunction Laser diode * Time-resolved Photoluminescence and Energy Transfer of Bound Excitons in GaP:N Crystals * Optical Limiting with Semiconductors * A Critical Review of High-efficiency Crystals for Tunable Lasers * Parametric Scattering in β - BaB2O4 Crystal Induced by Picosecond Pulses * Generation of Picosecond Pulses at 193 nm by Frequency Mixing in β - BaB2O4

  17. Packet error rate analysis of OOK, DPIM, and PPM modulation schemes for ground-to-satellite laser uplink communications.

    PubMed

    Jiang, Yijun; Tao, Kunyu; Song, Yiwei; Fu, Sen

    2014-03-01

    Performance of on-off keying (OOK), digital pulse interval modulation (DPIM), and pulse position modulation (PPM) schemes are researched for ground-to-satellite laser uplink communications. Packet error rates of these modulation systems are compared, with consideration of the combined effect of intensity fluctuation and beam wander. Based on the numerical results, performances of different modulation systems are discussed. Optimum divergence angle and transmitted beam radius of different modulation systems are indicated and the relations of the transmitted laser power to them are analyzed. This work can be helpful for modulation scheme selection and system design in ground-to-satellite laser uplink communications.

  18. Satellite laser ranging using superconducting nanowire single-photon detectors at 1064  nm wavelength.

    PubMed

    Xue, Li; Li, Zhulian; Zhang, Labao; Zhai, Dongsheng; Li, Yuqiang; Zhang, Sen; Li, Ming; Kang, Lin; Chen, Jian; Wu, Peiheng; Xiong, Yaoheng

    2016-08-15

    Satellite laser ranging operating at 1064 nm wavelength using superconducting nanowire single-photon detectors (SNSPDs) is successfully demonstrated. A SNSPD with an intrinsic quantum efficiency of 80% and a dark count rate of 100 cps at 1064 nm wavelength is developed and introduced to Yunnan Observatory in China. With improved closed-loop telescope systems (field of view of about 26''), satellites including Cryosat, Ajisai, and Glonass with ranges of 1600 km, 3100 km, and 19,500 km, respectively, are experimentally ranged with mean echo rates of 1200/min, 4200/min, and 320/min, respectively. To the best of our knowledge, this is the first demonstration of laser ranging for satellites using SNSPDs at 1064 nm wavelength. Theoretical analysis of the detection efficiency and the mean echo rate for typical satellites indicate that it is possible for a SNSPD to range satellites from low Earth orbit to geostationary Earth orbit.

  19. Superconducting nanowire single photon detector at 532 nm and demonstration in satellite laser ranging.

    PubMed

    Li, Hao; Chen, Sijing; You, Lixing; Meng, Wengdong; Wu, Zhibo; Zhang, Zhongping; Tang, Kai; Zhang, Lu; Zhang, Weijun; Yang, Xiaoyan; Liu, Xiaoyu; Wang, Zhen; Xie, Xiaoming

    2016-02-22

    Superconducting nanowire single-photon detectors (SNSPDs) at a wavelength of 532 nm were designed and fabricated aiming to satellite laser ranging (SLR) applications. The NbN SNSPDs were fabricated on one-dimensional photonic crystals with a sensitive-area diameter of 42 μm. The devices were coupled with multimode fiber (ϕ = 50 μm) and exhibited a maximum system detection efficiency of 75% at an extremely low dark count rate of <0.1 Hz. An SLR experiment using an SNSPD at a wavelength of 532 nm was successfully demonstrated. The results showed a depth ranging with a precision of ~8.0 mm for the target satellite LARES, which is ~3,000 km away from the ground ranging station at the Sheshan Observatory.

  20. Oceanic tides from Geosat altimetry

    NASA Technical Reports Server (NTRS)

    Cartwright, D. E.; Ray, R. D.

    1990-01-01

    Direct tidal analysis of the altimetry from the Geosat Exact Repeat Mission's first year is used to derive estimates of the diurnal and semidiurnal oceanic tides. The geoid is removed by collinear differences at 34.1-day separation, and the orbit error is reduced by subtracting a slowly modulated 1-cycle/revolution term. A sequence of independent analyses at grid areas of 1 deg latitude x 1.5 deg longitude using 'orthotide' functions ensures complete definition of the diurnal and semidiurnal species. Global admittance maps for M2 and S2 within the latitudes 58 deg N and 59 deg S compare well with ground truth at 66 open-ocean sites. Maps of differences between Geosat and the Naval Surface Weapons Center model show important areas of the order of 10-15 cm.

  1. Antarctic ice shelf thickness from CryoSat-2 radar altimetry

    NASA Astrophysics Data System (ADS)

    Chuter, Stephen; Bamber, Jonathan

    2016-04-01

    The Antarctic ice shelves provide buttressing to the inland grounded ice sheet, and therefore play a controlling role in regulating ice dynamics and mass imbalance. Accurate knowledge of ice shelf thickness is essential for input-output method mass balance calculations, sub-ice shelf ocean models and buttressing parameterisations in ice sheet models. Ice shelf thickness has previously been inferred from satellite altimetry elevation measurements using the assumption of hydrostatic equilibrium, as direct measurements of ice thickness do not provide the spatial coverage necessary for these applications. The sensor limitations of previous radar altimeters have led to poor data coverage and a lack of accuracy, particularly the grounding zone where a break in slope exists. We present a new ice shelf thickness dataset using four years (2011-2014) of CryoSat-2 elevation measurements, with its SARIn dual antennae mode of operation alleviating the issues affecting previous sensors. These improvements and the dense across track spacing of the satellite has resulted in ˜92% coverage of the ice shelves, with substantial improvements, for example, of over 50% across the Venable and Totten Ice Shelves in comparison to the previous dataset. Significant improvements in coverage and accuracy are also seen south of 81.5° for the Ross and Filchner-Ronne Ice Shelves. Validation of the surface elevation measurements, used to derive ice thickness, against NASA ICESat laser altimetry data shows a mean bias of less than 1 m (equivalent to less than 9 m in ice thickness) and a fourfold decrease in standard deviation in comparison to the previous continental dataset. Importantly, the most substantial improvements are found in the grounding zone. Validation of the derived thickness data has been carried out using multiple Radio Echo Sounding (RES) campaigns across the continent. Over the Amery ice shelf, where extensive RES measurements exist, the mean difference between the datasets is 3

  2. Laser-based satellite communication systems stabilized by non-mechanical electro-optic scanners

    NASA Astrophysics Data System (ADS)

    Ziemkiewicz, Michael; Davis, Scott R.; Rommel, Scott D.; Gann, Derek; Luey, Benjamin; Gamble, Joseph D.; Anderson, Mike

    2016-05-01

    Laser communications systems provide numerous advantages for establishing satellite-to-ground data links. As a carrier for information, lasers are characterized by high bandwidth and directionality, allowing for fast and secure transfer of data. These systems are also highly resistant to RF influences since they operate in the infrared portion of the electromagnetic spectrum, far from radio bands. In this paper we will discuss an entirely non-mechanical electro-optic (EO) laser beam steering technology, with no moving parts, which we have used to form robust 400 Mbps optical data connections through air. This technology will enable low cost, compact, and rugged free space optical (FSO) communication modules for small satellite applications. The EO beam-steerer at the heart of this system is used to maintain beam pointing as the satellite orbits. It is characterized by extremely low values for size, weight and power consumption (SWaP) - approximately 300 cm3, 300 g, and 5 W respectively, which represents a marked improvement compared to heavy, and power-consuming gimbal mechanisms. It is capable of steering a 500 mW, 1 mm short wave infrared (SWIR) beam over a field of view (FOV) of up to 50° x 15°, a range which can be increased by adding polarization gratings, which provide a coarse adjust stage at the EO beam scanner output. We have integrated this device into a communication system and demonstrated the capability to lock on and transmit a high quality data stream by modulation of SWIR power.

  3. Quick topological method for acquiring the beacon in inter-satellite laser communications.

    PubMed

    Wang, Qiang; Ma, Jing; Tan, Liying; Yu, Siyuan

    2014-11-20

    Background starlight can lead to some spot noise in the image collected by a CCD, disturbing the beacon acquisition in inter-satellite laser communications. Removing the spot noise takes much time by using the existing method that is based on the reference star calendar table. We present a novel method to reduce the processing time in this paper. The key point is to use the topological characteristic of the spot noise in the graph that is obtained through threshold segmentation to the image on the CCD. The method helps to improve the acquisition probability and to save valuable onboard computing resources.

  4. Effects of horizontal refractivity gradients on the accuracy of laser ranging to satellites

    NASA Technical Reports Server (NTRS)

    Gardner, C. S.

    1976-01-01

    Numerous formulas have been developed to partially correct laser ranging data for the effects of atmospheric refraction. All the formulas assume the atmospheric refractivity profile is spherically symmetric. The effects of horizontal refractivity gradients are investigated by ray tracing through spherically symmetric and three-dimensional refractivity profiles. The profiles are constructed from radiosonde data. The results indicate that the horizontal gradients introduce an rms error of approximately 3 cm when the satellite is near 10 deg elevation. The error decreases to a few millimeters near zenith.

  5. Two color satellite laser ranging upgrades at Goddard's 1.2m telescope facility

    NASA Technical Reports Server (NTRS)

    Zagwodzki, Thomas W.; Mcgarry, Jan F.; Degnan, John J.; Varghese, Thomas K.

    1993-01-01

    The ranging laboratory at Goddard's 1.2 m telescope tracking facility has recently been upgraded to include a single photoelectron sensitive Hamamatsu streak camera-based range receiver which uses doubled and tripled Nd:YAG frequencies for satellite laser ranging. Other ranging system upgrades include a new continuum laser, which will deliver up to 30 millijoules (mJ) at both 532 and 355 nm at a pulsewidth of 30 picoseconds (FWHM), and replacement of both ranging and tracking computers with COMPAQ 386 based systems. Preliminary results using a photomultiplier-tube based receiver and waveform digitizer indicate agreement within the accuracy of the measurement with the theoretical Marini and Murray model for atmospheric refraction. Two color streak camera measurements are used to further analyze the accuracy of these and other atmospheric refraction models.

  6. Compact, passively Q-switched Nd:YAG laser for the MESSENGER mission to Mercury.

    PubMed

    Krebs, Danny J; Novo-Gradac, Anne-Marie; Li, Steven X; Lindauer, Steven J; Afzal, Robert S; Yu, Anthony W

    2005-03-20

    A compact, passively Q-switched Nd:YAG laser has been developed for the Mercury Laser Altimeter, an instrument on the Mercury Surface, Space Environment, Geochemistry, and Ranging mission to the planet Mercury. The laser achieves 5.4% efficiency with a near-diffraction-limited beam. It passed all space-flight environmental tests at subsystem, instrument, and satellite integration testing and successfully completes a postlaunch aliveness check en route to Mercury. The laser design draws on a heritage of previous laser altimetry missions, specifically the Ice Cloud and Elevation Satellite and the Mars Global Surveyor, but incorporates thermal management features unique to the requirements of an orbit of the planet Mercury.

  7. Societal Benefits of Ocean Altimetry Data

    NASA Technical Reports Server (NTRS)

    Srinivasen, Margaret; Leben, Robert

    2004-01-01

    The NASA/CNES Jason satellite, follow-on to the highly successful TOPEX/Poseidon mission, continues to provide oceanographers and marine operators across the globe with a continuous twelve-year, high quality stream of sea surface height data. The mission is expected to extend through 2007, when the NASA/NOAA/CNES follow-on mission, OSTM, will be launched with the wide-swath ocean altimeter on board. This unprecedented resource of valuable ocean data is being used to map sea surface height, geostrophic velocity, significant wave height, and wind speed over the global oceans. Altimeter data products are currently used by hundreds of researchers and operational users to monitor ocean circulation and improve our understanding of the role of the oceans in climate and weather. Ocean altimeter data has many societal benefits and has proven invaluable in many practical applications including; a) Ocean forecasting systems; b) Climate research and forecasting; c) Ship routing; d) Fisheries management; e) Marine mammal habitat monitoring; f) Hurricane forecasting and tracking; g) Debris tracking; and h) Precision marine operations such as cable-laying and oil production. The data has been cited in nearly 2,000 research and popular articles since the launch of TOPEX/Poseidon in 1992, and almost 200 scientific users receive the global coverage altimeter data on a monthly basis. In addition to the scientific and operational uses of the data, the educational community has seized the unique concepts highlighted by these altimeter missions as a resource for teaching ocean science to students from grade school through college. This presentation will highlight societal benefits of ocean altimetry data in the areas of climate studies, marine operations, marine research, and non-ocean investigations.

  8. Precision orbit determination of altimetric satellites

    NASA Technical Reports Server (NTRS)

    Shum, C. K.; Ries, John C.; Tapley, Byron D.

    1994-01-01

    The ability to determine accurate global sea level variations is important to both detection and understanding of changes in climate patterns. Sea level variability occurs over a wide spectrum of temporal and spatial scales, and precise global measurements are only recently possible with the advent of spaceborne satellite radar altimetry missions. One of the inherent requirements for accurate determination of absolute sea surface topography is that the altimetric satellite orbits be computed with sub-decimeter accuracy within a well defined terrestrial reference frame. SLR tracking in support of precision orbit determination of altimetric satellites is significant. Recent examples are the use of SLR as the primary tracking systems for TOPEX/Poseidon and for ERS-1 precision orbit determination. The current radial orbit accuracy for TOPEX/Poseidon is estimated to be around 3-4 cm, with geographically correlated orbit errors around 2 cm. The significance of the SLR tracking system is its ability to allow altimetric satellites to obtain absolute sea level measurements and thereby provide a link to other altimetry measurement systems for long-term sea level studies. SLR tracking allows the production of precise orbits which are well centered in an accurate terrestrial reference frame. With proper calibration of the radar altimeter, these precise orbits, along with the altimeter measurements, provide long term absolute sea level measurements. The U.S. Navy's Geosat mission is equipped with only Doppler beacons and lacks laser retroreflectors. However, its orbits, and even the Geosat orbits computed using the available full 40-station Tranet tracking network, yield orbits with significant north-south shifts with respect to the IERS terrestrial reference frame. The resulting Geosat sea surface topography will be tilted accordingly, making interpretation of long-term sea level variability studies difficult.

  9. Basic Radar Altimetry Toolbox: Tools and Tutorial To Use Radar Altimetry For Cryosphere

    NASA Astrophysics Data System (ADS)

    Benveniste, J. J.; Bronner, E.; Dinardo, S.; Lucas, B. M.; Rosmorduc, V.; Earith, D.

    2010-12-01

    Radar altimetry is very much a technique expanding its applications. If quite a lot of efforts have been made for oceanography users (including easy-to-use data), the use of those data for cryosphere application, especially with the new ESA CryoSat-2 mission data is still somehow tedious, especially for new Altimetry data products users. ESA and CNES thus had the Basic Radar Altimetry Toolbox developed a few years ago, and are improving and upgrading it to fit new missions and the growing number of altimetry uses. The Basic Radar Altimetry Toolbox is an "all-altimeter" collection of tools, tutorials and documents designed to facilitate the use of radar altimetry data. The software is able: - to read most distributed radar altimetry data, from ERS-1 & 2, Topex/Poseidon, Geosat Follow-on, Jason-1, Envisat, Jason- 2, CryoSat and the future Saral missions, - to perform some processing, data editing and statistic, - and to visualize the results. It can be used at several levels/several ways: - as a data reading tool, with APIs for C, Fortran, Matlab and IDL - as processing/extraction routines, through the on-line command mode - as an educational and a quick-look tool, with the graphical user interface As part of the Toolbox, a Radar Altimetry Tutorial gives general information about altimetry, the technique involved and its applications, as well as an overview of past, present and future missions, including information on how to access data and additional software and documentation. It also presents a series of data use cases, covering all uses of altimetry over ocean, cryosphere and land, showing the basic methods for some of the most frequent manners of using altimetry data. It is an opportunity to teach remote sensing with practical training. It has been available from April 2007, and had been demonstrated during training courses and scientific meetings. About 1200 people downloaded it (Summer 2010), with many "newcomers" to altimetry among them, including teachers

  10. Horizontal crustal motion in the central and eastern Mediterranean inferred from Satellite Laser Ranging measurements

    NASA Technical Reports Server (NTRS)

    Smith, David E.; Kolenkiewicz, Ron; Robbins, John W.; Dunn, Peter J.; Torrence, Mark H.

    1994-01-01

    Four campaigns to acquire Satellite Laser Ranging (SLR) measurements at sites in the Mediterranean region have been completed. These measurements to the LAGEOS satellite, made largely by mobile systems, cover a time span beginning in November 1985 and ending in June 1993. The range data from 18 sites in the central and eastern Mediterranean have been simultaneously analyzed with data acquired by the remainder of the global laser tracking network. Estimates of horizontal motion were placed into a regional, northern Europe-fixed, kinematic reference frame. Uncertainties are on the order of 5 mm/yr for sites having at least four occupations by mobile systems and approach 1 mm/yr for permanently located sites with long histories of tracking. The resulting relative motion between sites in the Aegean exhibit characteristics of broadly distributed pattern of radial extension, but at rates that are about 50% larger than those implied from studies of seismic strain rates based on seismicity of magnitude 6 or greater or across the region. The motion estimated for sites in Turkey exhibit velocity components associated with the westward motion of the Anatolian Block relative to Eurasia. These results provide a present-day 'snapshot' of ongoing deformational processes as experienced by the locations occupied by SLR systems.

  11. Aerosol Impacts on Cirrus Clouds and High-Power Laser Transmission: A Combined Satellite Observation and Modeling Approach

    DTIC Science & Technology

    2010-02-28

    Subject: Final Report for AFOSR Grant FA9550-09-1-0386, “Aerosol Impacts on Cirrus Clouds and High-Power Laser Transmission: A Combined Satellite...of the Weather Research Forecast (WRF) model for cirrus cloud simulation and prediction in conjunction with satellite observations to support the...features, the Fu-Liou-Gu scheme is now an ideal tool for the simulation of radiative transfer associated with cirrus clouds in weather and climate

  12. Geophysical interpretation of satellite laser ranging measurements of crustal movement in California

    NASA Technical Reports Server (NTRS)

    Cohen, S. C.

    1984-01-01

    As determined by satellite laser ranging the rate of contraction of a 900 kilometer baseline between sites located near Quincy in northern California and San Diego in southern California is about 61 to 65 mm/yr with a formal uncertainty of about 10 mm/yr. The measured changes in baseline length are a manifestation of the relative motion between the North America and Pacific tectonic plates. This long baseline result is compared to measurements made by more conventional means on shorter baselines. Additional information based on seismicity, geology, and theoretical modelling is also analyzed. Deformation lying within a few tens of kilometers about the major faults in southern California accounts for most, but not all of the observed motion. Further motion is attributable to a broader scale deformation in southern California. Data suggesting crustal movements north of the Garlock fault, in and near the southern Sierra Nevada and local motion at an observatory are also critically reviewed. The best estimates of overall motion indicated by ground observations lie between 40 and 60 mm/yr. This lies within one or two standard deviations of that deduced by satellite ranging but the possibility of some unresolved deficit cannot be dismissed. The long time scale RM2 plate tectonic model of Minster and Jordan predicts a contraction between 47 and 53 mm/yr depending on the extension rate of the Basin and Range. Thus the ground based observations, satellite laser ranging (SLR) results, and RM2 rates differ at about the 10 mm/yr level and are consistent with one another within the data and model uncertainties.

  13. Geophysical interpretation of satellite laser ranging measurements of crustal movement in California

    NASA Astrophysics Data System (ADS)

    Cohen, S. C.

    1984-08-01

    As determined by satellite laser ranging the rate of contraction of a 900 kilometer baseline between sites located near Quincy in northern California and San Diego in southern California is about 61 to 65 mm/yr with a formal uncertainty of about 10 mm/yr. The measured changes in baseline length are a manifestation of the relative motion between the North America and Pacific tectonic plates. This long baseline result is compared to measurements made by more conventional means on shorter baselines. Additional information based on seismicity, geology, and theoretical modelling is also analyzed. Deformation lying within a few tens of kilometers about the major faults in southern California accounts for most, but not all of the observed motion. Further motion is attributable to a broader scale deformation in southern California. Data suggesting crustal movements north of the Garlock fault, in and near the southern Sierra Nevada and local motion at an observatory are also critically reviewed. The best estimates of overall motion indicated by ground observations lie between 40 and 60 mm/yr. This lies within one or two standard deviations of that deduced by satellite ranging but the possibility of some unresolved deficit cannot be dismissed. The long time scale RM2 plate tectonic model of Minster and Jordan predicts a contraction between 47 and 53 mm/yr depending on the extension rate of the Basin and Range. Thus the ground based observations, satellite laser ranging (SLR) results, and RM2 rates differ at about the 10 mm/yr level and are consistent with one another within the data and model uncertainties.

  14. SLR2000: a microlaser-based single photoelectron satellite laser ranging system

    NASA Technical Reports Server (NTRS)

    Degnan, John J.; McGarry, Jan F.

    1998-01-01

    SLR2000 is an autonomous and eyesafe satellite laser ranging (SLR) station with an expected single shot range precision of about one centimeter and a normal point (time-averaged) precision better than 3 mm. The system wil provide continuous 24 hour tracking coverage for a constellation of over twenty artificial satellites. Replication costs are expected to be roughly an order of magnitude less than current operational systems, and the system will be about 75% less expensive to operate and maintain relative to manned systems. Computer simulations have predicted a daylight tracking capability to GPS and lower satellites with telescope apertures of 40 cm and have demonstrated the ability of our current autotracking algorithm to extract mean signal strengths below .001 photoelectrons per pulse from daytime background noise. The dominant cost driver in present SLR systems is the onsite and central infrastructure manpower required to operate the system, to service and maintain the complex subsystems, and to ensure that the transmitted laser beam is not a hazard to onsite personnel or to overflying aircraft. To keep development, fabrication, and maintenance costs at a minimum, we adopted the following design philosophies: (1) use off the shelf commercial components wherever possible; this allows rapid component replacement and "outsourcing" of engineering support; (2) use smaller telescopes (less than 50 cm) since this constrains the cost, size, and weight of the telescope and tracking mount; and (3) for low maintenance and failsafe reliability, choose simple versus complex technical approaches and, where possible, use passive techniques and components rather than active ones. Adherence to these philosophies has led to the SLR2000 design described here.

  15. Comparison of Arabian plate motion using satellite laser ranging and GPS observations

    NASA Astrophysics Data System (ADS)

    Alothman, A. O.; Fernandes, R. M.; Schillak, S. R.

    2013-12-01

    Two different space based observations have been used to estimate the velocity of the Arabian plate motion. The first set of observations is using the Saudi Arabia Laser Ranging Observatory (SALRO - 7832), which is situated in the middle of Arabian tectonic plate. Satellite Laser Ranging (SLR) observations of about 20 global SLR stations to LAGEOS-1 and LAGEOS-2 satellites collected for 14 years (1996-2009) have been used to determine Riyadh SLR station positions. The NASA Godard's GEODYN-II orbital software has been used to perform orbit determination of these two satellites. The velocities of SALRO were computed in reference to the ITRF2008 terrestrial reference frame. The second set of observations consists of Global Positioning System (GPS) observations of 15 GPS stations acquired in campaign and continuous mode for the period 2003 to 2009 (having at least 3 years' data span). Multi-year processing of stations having at least 3 years' time span and excluding stations within the deformation zone of Red Sea Ridge, such that they are distributed evenly within the rigid (interior) part of the Arabian plate. The Bernese 5.0/ADNEQ2 and GIPSY/OASIS 6.1 software packages were used to compute the daily solutions of coordinate time series applying the Precise Point Positioning (PPP) strategy. The velocities were estimated with respect to ITRF2008 and four estimates of the angular velocities for the Arabian plate have been computed using different datasets: independent Bernese and GIPSY solutions, combination of the GPS solutions only, and including the SLR solution. We present direct comparison between all different solutions showing that the Arabian tectonic plate motion determined from Riyadh SLR data and GPS data are in a good agreement with recent estimates, in particular with the global geodetic model GEODVEL and the geophysical MORVEL model.

  16. Influence of beam wander on uplink of ground-to-satellite laser communication and optimization for transmitter beam radius.

    PubMed

    Guo, Hong; Luo, Bin; Ren, Yongxiong; Zhao, Sinan; Dang, Anhong

    2010-06-15

    We restudy the influence of beam wander on the uplink of ground-to-satellite laser communication, using the effective pointing error method, for a collimated untracked Gaussian beam under a weak atmospheric turbulence condition. It shows that the beam wander may cause significant increase in bit error rate (BER), and there exists an optimal transmitter radius for minimizing the value of BER. Further studies manifest that this optimal radius only changes with the laser wavelength and zenith angle, while independent on the satellite altitude and the fade threshold at the receiver. These results can be used in system design and optimization for the transmitter.

  17. Influence of beam wander on bit-error rate in a ground-to-satellite laser uplink communication system.

    PubMed

    Ma, Jing; Jiang, Yijun; Tan, Liying; Yu, Siyuan; Du, Wenhe

    2008-11-15

    Based on weak fluctuation theory and the beam-wander model, the bit-error rate of a ground-to-satellite laser uplink communication system is analyzed, in comparison with the condition in which beam wander is not taken into account. Considering the combined effect of scintillation and beam wander, optimum divergence angle and transmitter beam radius for a communication system are researched. Numerical results show that both of them increase with the increment of total link margin and transmitted wavelength. This work can benefit the ground-to-satellite laser uplink communication system design.

  18. Outreaching a space technique through its climate applications: altimetry and COP21 meeting example

    NASA Astrophysics Data System (ADS)

    Rosmorduc, Vinca; Bronner, Emilie; De Staerke, Danielle

    2015-04-01

    Climate, and Climate change, are among the main general public interests. Altimetry is one of the most important tools for monitoring ocean dynamics, and as such is a source of vital data for including in forecasting models of ocean-atmosphere coupled events such as El Niño, monsoons, the North Atlantic Oscillation or decadal oscillations. Seasonal climate forecasting is also showing interesting results. The oceans are in turn affected by climate variations, as the sea level rises and falls in response to their fluctuations. Two radar altimetry satellites will be launched in 2015, with a strong French contribution (Jason-3 is a CNES/EUMETSAT/NASA/NOAA mission, Sentinel-3 is an ESA mission, with support from French expertise for the altimeter and altimetry processing). On another plan, the United Nations Climate Change Conference 21st yearly session of the Conference of the Parties (COP 21) meeting will take place in Paris end of 2015 (30 November to 11 December 2015). Outreaching radar altimetry through its climate-related applications using both the conference and the launches is thus an evidence. However, how, what and when? We will detail the points we consider as focus for this outreach (e.g. sea level rise measurement, but also El Niño, monsoons, etc.), how to broach them in order to reach the general public interest, via web, journalists, teachers etc. In particular, the Argonautica educational project (http://www.cnes.fr/web/CNES-fr/7161-argonautica.php) will focus in 2015 on climate issue, in relation also with formal school curricula, other satellite data and animal tracking. Past experience will be detailed, from the Aviso altimetry data distribution center, but also from partners, and future plans.

  19. Assessment of the accuracy of global geodetic satellite laser ranging observations 1993-2013

    NASA Astrophysics Data System (ADS)

    Appleby, Graham; Rodriguez, Jose

    2014-05-01

    We continue efforts to estimate the intrinsic accuracy of range measurements made by the major satellite laser ranging stations of the ILRS Network using normal point observations of the primary geodetic satellites LAGEOS and LAGEOS-II. In a novel, but risky, approach we carry out weekly, loosely constrained, reference frame solutions for satellite initial state vectors, station coordinates and daily EOPs (X-pole, Y-pole and LoD), as well as estimating range bias for all the stations. We apply known range errors a-priori from the table developed and maintained through the efforts of the ILRS Analysis Working Group and apply station- and time-specific satellite centre of mass corrections (Appleby and Otsubo, 2014), both corrections that are currently implemented in the standard ILRS reference frame products. Our approach, to solve simultaneously for station coordinates and possible range bias for all the stations, has the strength that any bias results are independent of the coordinates taken for example from ITRF2008; thus the approach has the potential to discover bias that may have become absorbed primarily in station height had the coordinates been determined on the assumption of zero bias. A serious complication of the approach is that correlations will inevitably exist between station height and range bias. However, for the major stations of the Network, and using LAGEOS and LAGEOS-II observations simultaneously in our weekly solutions, we are developing techniques and testing their sensitivity in performing a partial separation between these parameters at the expense of an increase in the variance of the stations' height time series. In this paper we discuss the results in terms of potential impact on coordinate solutions, including the reference frame scale, and in the context of preparations for ITRF2013.

  20. Earth-satellite-Earth laser long-path absorption experiment using the Retroreflector in Space (RIS) on the Advanced Earth Observing Satellite (ADEOS)

    NASA Astrophysics Data System (ADS)

    Sugimoto, Nobuo; Koga, Nobuhiko; Matsui, Ichiro; Sasano, Yasuhiro; Minato, Atsushi; Ozawa, Kenichi; Saito, Yasunori; Nomura, Akio; Aoki, Tetsuo; Itabe, Toshikazu; Kunimori, Hiroo; Murata, Isao; Fukunishi, Hiroshi

    1999-03-01

    This paper reports the results of the laser long-path absorption experiments carried out with the Retroreflector in Space (RIS) on the Advanced Earth Observing Satellite (ADEOS). The RIS is a 0.5 m diameter single-element hollow retroreflector with a unique optical design which uses a curved mirror surface to correct velocity aberrations caused by the satellite movement. In the RIS experiments a laser beam was transmitted from a ground station, reflected by the RIS, and received back at the ground station. The absorption of the intervening atmosphere was measured in the round-trip optical path. After the launch of the ADEOS in August 1996, the optical characteristics of the RIS were tested, and it was confirmed that the RIS worked well in orbit. The spectroscopic measurement was carried out with the single-longitudinal-mode TEA 1464-4258/1/2/015/img12 lasers by means of the method utilizing the Doppler shift of the reflected beam caused by the movement of the satellite. The spectrum of ozone was successfully measured in the 1464-4258/1/2/015/img13 region, and the measurement of the column contents of ozone was validated with the simultaneous heterodyne spectrometer measurement. In June 1997, however, the experiment with the RIS was discontinued due to the malfunction of the ADEOS solar paddle.

  1. Reduction of Influences of the Earth's Surface Fluid Loads on GPS Site Coordinate Time Series and Global Satellite Laser Ranging Analysis

    NASA Astrophysics Data System (ADS)

    Takiguchi, H.; Otsubo, T.; Fukuda, Y.

    2006-12-01

    Temporal change of surface loadings due to the mass redistribution of the fluid envelope of the Earth, deform the Earth and cause the coordinate changes of the observation sites. We estimated the crustal displacements due to the atmospheric load (AL), the non-tidal ocean load (NTOL), the continental water load (CWL) and the snow load (SL) influences using the several meteorological data and model. And then, we tried to eliminate the load influences from the GPS site coordinate time series and global Satellite Laser Ranging (SLR) analysis. As the time series of GPS site coordinates, we employed a solution of IGS which was calculated by using GIPSY-OASIS II (Heflin et al., 2002) by the Jet Propulsion Laboratory (JPL) and the routine solution of GEONET called F2 solution which was calculated by Bernese version 4.2 software (Hatanaka et al., 2003) by the Geographical Survey Institute. To eliminate periodic signals of the loading effects, we calculated Corrected GPS = GPS - (Load1 + Load2 + . . . . . + Loadn). The results show that a combination of atmospheric, non-tidal ocean, continental water, and snow loads can eliminate about 20% of the annual signal in the coordinate time series for vertical components. We applied the loading correction to the data of the 1997 Bungo channel slow slip event and showed that the correction can benefit the analysis of such a non-periodic event. Next, we applied the time series of NTOL and CWL to precise SLR analysis that used the "concerto" program version 4 developed by the National Institute of Information and Communications Technology (NICT). The LAGEOS orbit analysis reveals that the Estimating the Circulation and Climate of the Ocean (ECCO) model makes the root mean square (RMS) of the range residual 0.2% smaller, and that the CWL makes it 0.8% smaller, compared with the case where loading displacement is neglected. On the other hand, with the NTOL derived from Topex/Poseidon altimetry data, the SLR orbit fit is not improved.

  2. Time-varying land subsidence detected by radar altimetry: California, Taiwan and north China

    PubMed Central

    Hwang, Cheinway; Yang, Yuande; Kao, Ricky; Han, Jiancheng; Shum, C. K.; Galloway, Devin L.; Sneed, Michelle; Hung, Wei-Chia; Cheng, Yung-Sheng; Li, Fei

    2016-01-01

    Contemporary applications of radar altimetry include sea-level rise, ocean circulation, marine gravity, and icesheet elevation change. Unlike InSAR and GNSS, which are widely used to map surface deformation, altimetry is neither reliant on highly temporally-correlated ground features nor as limited by the available spatial coverage, and can provide long-term temporal subsidence monitoring capability. Here we use multi-mission radar altimetry with an approximately 23 year data-span to quantify land subsidence in cropland areas. Subsidence rates from TOPEX/POSEIDON, JASON-1, ENVISAT, and JASON-2 during 1992–2015 show time-varying trends with respect to displacement over time in California’s San Joaquin Valley and central Taiwan, possibly related to changes in land use, climatic conditions (drought) and regulatory measures affecting groundwater use. Near Hanford, California, subsidence rates reach 18 cm yr−1 with a cumulative subsidence of 206 cm, which potentially could adversely affect operations of the planned California High-Speed Rail. The maximum subsidence rate in central Taiwan is 8 cm yr−1. Radar altimetry also reveals time-varying subsidence in the North China Plain consistent with the declines of groundwater storage and existing water infrastructure detected by the Gravity Recovery And Climate Experiment (GRACE) satellites, with rates reaching 20 cm yr−1 and cumulative subsidence as much as 155 cm. PMID:27324935

  3. Time-varying land subsidence detected by radar altimetry: California, Taiwan and north China

    USGS Publications Warehouse

    Hwang, Cheinway; Yang, Yuande; Kao, Ricky; Han, Jiancheng; Shum, C.K.; Galloway, Devin L.; Sneed, Michelle; Hung, Wei-Chia; Cheng, Yung-Sheng; Li, Fei

    2016-01-01

    Contemporary applications of radar altimetry include sea-level rise, ocean circulation, marine gravity, and ice sheet elevation change. Unlike InSAR and GNSS, which are widely used to map surface deformation, altimetry is neither reliant on highly temporally-correlated ground features nor as limited by the available spatial coverage, and can provide long-term temporal subsidence monitoring capability. Here we use multi-mission radar altimetry with an approximately 23 year data-span to quantify land subsidence in cropland areas. Subsidence rates from TOPEX/POSEIDON, JASON-1, ENVISAT, and JASON-2 during 1992–2015 show time-varying trends with respect to displacement over time in California’s San Joaquin Valley and central Taiwan, possibly related to changes in land use, climatic conditions (drought) and regulatory measures affecting groundwater use. Near Hanford, California, subsidence rates reach 18 cm/yr with a cumulative subsidence of 206 cm, which potentially could adversely affect operations of the planned California High-Speed Rail. The maximum subsidence rate in central Taiwan is 8 cm/yr. Radar altimetry also reveals time-varying subsidence in the North China Plain consistent with the declines of groundwater storage and existing water infrastructure detected by the Gravity Recovery And Climate Experiment (GRACE) satellites, with rates reaching 20 cm/yr and cumulative subsidence as much as 155 cm.

  4. Time-varying land subsidence detected by radar altimetry: California, Taiwan and north China.

    PubMed

    Hwang, Cheinway; Yang, Yuande; Kao, Ricky; Han, Jiancheng; Shum, C K; Galloway, Devin L; Sneed, Michelle; Hung, Wei-Chia; Cheng, Yung-Sheng; Li, Fei

    2016-06-21

    Contemporary applications of radar altimetry include sea-level rise, ocean circulation, marine gravity, and icesheet elevation change. Unlike InSAR and GNSS, which are widely used to map surface deformation, altimetry is neither reliant on highly temporally-correlated ground features nor as limited by the available spatial coverage, and can provide long-term temporal subsidence monitoring capability. Here we use multi-mission radar altimetry with an approximately 23 year data-span to quantify land subsidence in cropland areas. Subsidence rates from TOPEX/POSEIDON, JASON-1, ENVISAT, and JASON-2 during 1992-2015 show time-varying trends with respect to displacement over time in California's San Joaquin Valley and central Taiwan, possibly related to changes in land use, climatic conditions (drought) and regulatory measures affecting groundwater use. Near Hanford, California, subsidence rates reach 18 cm yr(-1) with a cumulative subsidence of 206 cm, which potentially could adversely affect operations of the planned California High-Speed Rail. The maximum subsidence rate in central Taiwan is 8 cm yr(-1). Radar altimetry also reveals time-varying subsidence in the North China Plain consistent with the declines of groundwater storage and existing water infrastructure detected by the Gravity Recovery And Climate Experiment (GRACE) satellites, with rates reaching 20 cm yr(-1) and cumulative subsidence as much as 155 cm.

  5. Time-varying land subsidence detected by radar altimetry: California, Taiwan and north China

    NASA Astrophysics Data System (ADS)

    Hwang, Cheinway; Yang, Yuande; Kao, Ricky; Han, Jiancheng; Shum, C. K.; Galloway, Devin L.; Sneed, Michelle; Hung, Wei-Chia; Cheng, Yung-Sheng; Li, Fei

    2016-06-01

    Contemporary applications of radar altimetry include sea-level rise, ocean circulation, marine gravity, and icesheet elevation change. Unlike InSAR and GNSS, which are widely used to map surface deformation, altimetry is neither reliant on highly temporally-correlated ground features nor as limited by the available spatial coverage, and can provide long-term temporal subsidence monitoring capability. Here we use multi-mission radar altimetry with an approximately 23 year data-span to quantify land subsidence in cropland areas. Subsidence rates from TOPEX/POSEIDON, JASON-1, ENVISAT, and JASON-2 during 1992–2015 show time-varying trends with respect to displacement over time in California’s San Joaquin Valley and central Taiwan, possibly related to changes in land use, climatic conditions (drought) and regulatory measures affecting groundwater use. Near Hanford, California, subsidence rates reach 18 cm yr‑1 with a cumulative subsidence of 206 cm, which potentially could adversely affect operations of the planned California High-Speed Rail. The maximum subsidence rate in central Taiwan is 8 cm yr‑1. Radar altimetry also reveals time-varying subsidence in the North China Plain consistent with the declines of groundwater storage and existing water infrastructure detected by the Gravity Recovery And Climate Experiment (GRACE) satellites, with rates reaching 20 cm yr‑1 and cumulative subsidence as much as 155 cm.

  6. Simultaneous Laser Ranging and Communication from an Earth-Based Satellite Laser Ranging Station to the Lunar Reconnaissance Orbiter in Lunar Orbit

    NASA Technical Reports Server (NTRS)

    Sun, Xiaoli; Skillman, David R.; Hoffman, Evan D.; Mao, Dandan; McGarry, Jan F.; Neumann, Gregory A.; McIntire, Leva; Zellar, Ronald S.; Davidson, Frederic M.; Fong, Wai H.; Krainak, Michael A.; Zuber, Maria T.; Smith, David E.

    2013-01-01

    We report a free space laser communication experiment from the satellite laser ranging (SLR) station at NASA Goddard Space Flight Center (GSFC) to the Lunar Reconnaissance Orbiter (LRO) in lunar orbit through the on board one-way Laser Ranging (LR) receiver. Pseudo random data and sample image files were transmitted to LRO using a 4096-ary pulse position modulation (PPM) signal format. Reed-Solomon forward error correction codes were used to achieve error free data transmission at a moderate coding overhead rate. The signal fading due to the atmosphere effect was measured and the coding gain could be estimated.

  7. Mass Evolution of Mediterranean, Black, Red, and Caspian Seas from GRACE and Altimetry: Accuracy Assessment and Solution Calibration

    NASA Technical Reports Server (NTRS)

    Loomis, B. D.; Luthcke, S. B.

    2016-01-01

    We present new measurements of mass evolution for the Mediterranean, Black, Red, and Caspian Seas as determined by the NASA Goddard Space Flight Center (GSFC) GRACE time-variable global gravity mascon solutions. These new solutions are compared to sea surface altimetry measurements of sea level anomalies with steric corrections applied. To assess their accuracy, the GRACE and altimetry-derived solutions are applied to the set of forward models used by GSFC for processing the GRACE Level-1B datasets, with the resulting inter-satellite range acceleration residuals providing a useful metric for analyzing solution quality.

  8. A Hybrid Fiber/Solid-State Regenerative Amplifier with Tunable Pulse Widths for Satellite Laser Ranging

    NASA Technical Reports Server (NTRS)

    Coyle, Barry; Poulios, Demetrios

    2013-01-01

    A fiber/solid-state hybrid seeded regenerative amplifier, capable of achieving high output energy with tunable pulse widths, has been developed for satellite laser ranging applications. The regenerative amplifier cavity uses a pair of Nd:YAG zigzag slabs oriented orthogonally to one another in order to make thermal lensing effects symmetrical and simplify optical correction schemes. The seed laser used is a fiber-coupled 1,064-nm narrowband (<0.02 nm) diode laser that is discretely driven in a new short-pulsed mode, enabling continuously tunable seed pulse widths in the 0.2-to-0.4-ns range. The amplifier gain unit consists of a pair of Brewster-cut 6-bounce zigzag Nd:YAG laser slabs, oriented 90deg relative to each other in the amplifier head. This arrangement creates a net-symmetrical thermal lens effect (an opposing singleaxis effect in each slab), and makes thermo-optical corrections simple by optimizing the curvature of the nearest cavity mirror. Each slab is pumped by a single 120-W, pulsed 808-nm laser diode array. In this configuration, the average pump beam distribution in the slabs had a 1-D Gaussian shape, which matches the estimated cavity mode size. A half-wave plate between the slabs reduces losses from Fresnel reflections due to the orthogonal slabs Brewster-cut end faces. Successful "temporal" seeding of the regenerative amplifier cavity results in a cavity Q-switch pulse envelope segmenting into shorter pulses, each having the width of the input seed, and having a uniform temporal separation corresponding to the cavity round-trip time of approx. =10 ns. The pulse energy is allowed to build on successive passes in the regenerative amplifier cavity until a maximum is reached, (when cavity gains and losses are equal), after which the pulse is electro- optically switched out on the next round trip The overall gain of the amplifier is approx. =82 dB (or a factor of 1.26 million). After directing the amplified output through a LBO frequency doubling

  9. Satellite and Opacity Effects on Resonance Line Shapes Produced from Short-Pulse Laser Heated Foils

    SciTech Connect

    Shepherd, R; Audebert, P; Chen, H-K; Fournier, K B; Peyreusse, O; Moon, S; Lee, R W; Price, D; Klein, L; Gauthier, J C; Springer, P

    2002-12-03

    We measure the He-like, time-resolved emission from thin foils consisting of 250 {angstrom} of carbon-250 {angstrom} of aluminum and 500 {angstrom} aluminum illuminated with a 150 fs laser pulse at an intensity of 1 x 10{sup 19} W/cm{sup 2}. Dielectronic satellite contributions to the 1s{sup 2}-1s2p({sup 1}P), 1s{sup 2}-1s3p({sup 1}P), and 1s{sup 2}1s4p({sup 1}P) line intensities are modeled using the configuration averaged code AVERROES and is found to be significant for all three resonance lines. The contribution of opacity broadening is inferred from the data and found to be significant only in the 1s{sup 2}-1s2p({sup 1}P).

  10. In-orbit verification of small optical transponder (SOTA): evaluation of satellite-to-ground laser communication links

    NASA Astrophysics Data System (ADS)

    Takenaka, Hideki; Koyama, Yoshisada; Akioka, Maki; Kolev, Dimitar; Iwakiri, Naohiko; Kunimori, Hiroo; Carrasco-Casado, Alberto; Munemasa, Yasushi; Okamoto, Eiji; Toyoshima, Morio

    2016-03-01

    Research and development of space optical communications is conducted in the National Institute of Information and Communications Technology (NICT). The NICT developed the Small Optical TrAnsponder (SOTA), which was embarked on a 50kg-class satellite and launched into a low earth orbit (LEO). The space-to-ground laser communication experiments have been conducted with the SOTA. Atmospheric turbulence causes signal fadings and becomes an issue to be solved in satellite-to-ground laser communication links. Therefore, as error-correcting functions, a Reed-Solomon (RS) code and a Low-Density Generator Matrix (LDGM) code are implemented in the communication system onboard the SOTA. In this paper, we present the in-orbit verification results of SOTA including the characteristic of the functions, the communication performance with the LDGM code via satellite-to-ground atmospheric paths, and the link budget analysis and the comparison between theoretical and experimental results.

  11. SAR Altimetry in Coastal Zone: Performances, Limits, Perspectives

    NASA Astrophysics Data System (ADS)

    Dinardo, S.; Benveniste, J.

    2011-12-01

    Up to now, any effort to retrieve the coastal zone phenomena from the space has been hindered by the intrinsic incapacity of conventional radar altimeters to sample all but largest scales involved in the coastal processes due to its insufficient along- track resolution. However, nowadays, a new technology in Space-borne Altimetry has become reality: the Synthetic Aperture Radar (SAR) Altimeter. The acquisition of altimetric data in SAR mode ensures a higher resolving measurement power that shall enable scientists for the first time to aspire to measure even short-scale weak coastal phenomena, thanks to the 20- fold smaller along track radar resolution and 10 dB higher Signal to Noise ratio. The secondary, but significant in coastal zone, effect of the radar footprint shrinking is the expected reduced impact of land contamination on the radar waveforms in the proximity of the shore. As a consequence of this effect, the advent of SAR focusing promises to bring the satellite altimetry remote sensing closer to the shore up to around 500 meters. Anyway, this lower bound of 500 meter on coastal proximity is not always reachable, as the footprint shrinking occurs only in along track direction while the across track resolution shall remain basically unaltered. Hence, the orientation of the satellite ground-track with respect the coastline plays a role crucial for an effective filtering out of the off-nadir land-originated signals. In the present work, utilizing the current CryoSat-2 Altimeter Dataset (SAR L1b) acquired over coastal sea water, and by retracking the SAR L1b waveforms, a performances study of SAR altimetry in coastal zone will be addressed and the benefits and limits of this new technology highlighted. As particular study area, the Tyrrhenian Sea has been selected: statistics and metrics for sea surface height and significant wave height, as calculated from a cycle of passes, will be assessed, shown and interpreted. Finally, employing the Cryo

  12. Pointing and tracking errors due to localized deformation in inter-satellite laser communication links.

    PubMed

    Tan, Liying; Yang, Yuqiang; Ma, Jing; Yu, Jianjie

    2008-08-18

    Instead of Zernike polynomials, ellipse Gaussian model is proposed to represent localized wave-front deformation in researching pointing and tracking errors in inter-satellite laser communication links, which can simplify the calculation. It is shown that both pointing and tracking errors depend on the center deepness h, the radiuses a and b, and the distance d of the Gaussian distortion and change regularly as they increase. The maximum peak values of pointing and tracking errors always appear around h=0.2lambda. The influence of localized deformation is up to 0.7microrad for pointing error, and 0.5microrad for tracking error. To reduce the impact of localized deformation on pointing and tracking errors, the machining precision of optical devices, which should be more greater than 0.2?, is proposed. The principle of choosing the optical devices with localized deformation is presented, and the method that adjusts the pointing direction to compensate pointing and tracking errors is given. We hope the results can be used in the design of inter-satellite lasercom systems.

  13. Monitoring of coastal areas using radar altimetry data: examples along the southwest of the Bay of Biscay coastline

    NASA Astrophysics Data System (ADS)

    Frappart, Frédéric; Marieu, Vincent; Spodar, Alexandra; Parisot, Jean-Paul; Valle-Levinson, Arnoldo; Sottolichio, Aldo

    2015-04-01

    Satellite radar altimetry was developed to accurately measure ocean surface topography. Important effort in the development of new applications of altimetry is oriented towards extending the capabilities of current and future altimeters as close as possible to the coast. We present two examples located along the southwest French Atlantic coast: i) the determination of the shapes of river cross sections and changes in slope related to tide intensity in the Gironde Estuary, ii) the potential of radar altimetry for the monitoring of sea level and along-track topography at low-tide in the Arcachon Bay. In both cases, the results obtained using ENVISAT (2002-2012) and SARAL (since February 2013) are validated against ancillary data (i.e., tide gauges records, LIDAR topography) and show the evolution of the performances from Ku to Ka-bands.

  14. Dynamic techniques for studies of secular variations in position from ranging to satellites. [using laser range measurements

    NASA Technical Reports Server (NTRS)

    Smith, D. E.; Kolenkiewicz, R.; Agreen, R. W.; Dunn, P. J.

    1974-01-01

    Satellite laser range measurements were applied to the study of latitude variation arising from polar motion, and the solid-earth and ocean tidal distortion of the earth's gravity field. Experiments involving two laser tracking stations were conducted. The relative location of one station with respect to the other was determined by performing simultaneous range measurements to a satellite from two stations several hundred kilometers apart. The application of this technique to the San Andreas Fault Experiment in California is discussed. Future capabilities of spacecraft equipped with laser retroreflectors include: (1) determination of the product of the earth's mass and gravitational constant; (2) measurement of crustal and tectonic motions; (3) determination of the elastic response of the solid-earth tidal forces; (4) measurement of the amplitudes and phase of certain components of the ocean tides; and (5) self-monitoring of the latitude and height variations of the tracking station.

  15. First successful satellite laser ranging with a fibre-based transmitter

    NASA Astrophysics Data System (ADS)

    Hampf, D.; Sproll, F.; Wagner, P.; Humbert, L.; Hasenohr, T.; Riede, W.

    2016-08-01

    Satellite laser ranging (SLR) is an established technology used for geodesy, fundamental science and precise orbit determination. This paper reports on the first successful SLR measurement from the German Aerospace Center research observatory in Stuttgart. While many SLR stations are in operation, the experiment described here is unique in several ways: The modular system has been assembled completely from commercial off-the-shelf components, which increases flexibility and significantly reduces hardware costs. To our knowledge it has been the first time that an SLR measurement has been conducted using an optical fibre rather than a coudé path to direct the light from the laser source onto the telescope. The transmitter operates at an output power of about 75 mW and a repetition rate of 3 kHz, and at a wavelength of 1064 nm. Due to its rather small diameter of only 80 μm, the receiver detector features a low noise rate of less than 2 kHz and can be operated without gating in many cases. With this set-up, clear return signals have been received from several orbital objects equipped with retroreflectors. In its current configuration, the system does not yet achieve the same performance as other SLR systems in terms of precision, maximum distance and the capability of daylight ranging; however, plans to overcome these limitations are outlined.

  16. Basic Radar Altimetry Toolbox: Tools to Use Radar Altimetry for Geodesy

    NASA Astrophysics Data System (ADS)

    Rosmorduc, V.; Benveniste, J. J.; Bronner, E.; Niejmeier, S.

    2010-12-01

    Radar altimetry is very much a technique expanding its applications and uses. If quite a lot of efforts have been made for oceanography users (including easy-to-use data), the use of those data for geodesy, especially combined witht ESA GOCE mission data is still somehow hard. ESA and CNES thus had the Basic Radar Altimetry Toolbox developed (as well as, on ESA side, the GOCE User Toolbox, both being linked). The Basic Radar Altimetry Toolbox is an "all-altimeter" collection of tools, tutorials and documents designed to facilitate the use of radar altimetry data. The software is able: - to read most distributed radar altimetry data, from ERS-1 & 2, Topex/Poseidon, Geosat Follow-on, Jason-1, Envisat, Jason- 2, CryoSat and the future Saral missions, - to perform some processing, data editing and statistic, - and to visualize the results. It can be used at several levels/several ways: - as a data reading tool, with APIs for C, Fortran, Matlab and IDL - as processing/extraction routines, through the on-line command mode - as an educational and a quick-look tool, with the graphical user interface As part of the Toolbox, a Radar Altimetry Tutorial gives general information about altimetry, the technique involved and its applications, as well as an overview of past, present and future missions, including information on how to access data and additional software and documentation. It also presents a series of data use cases, covering all uses of altimetry over ocean, cryosphere and land, showing the basic methods for some of the most frequent manners of using altimetry data. It is an opportunity to teach remote sensing with practical training. It has been available from April 2007, and had been demonstrated during training courses and scientific meetings. About 1200 people downloaded it (Summer 2010), with many "newcomers" to altimetry among them. Users' feedbacks, developments in altimetry, and practice, showed that new interesting features could be added. Some have been

  17. Remote sensing of three-dimensional cirrus clouds from satellites: application to continuous-wave laser atmospheric transmission and backscattering.

    PubMed

    Liou, K N; Ou, Szu-Cheng; Takano, Yoshihide; Cetola, Jeffrey

    2006-09-10

    A satellite remote sensing methodology has been developed to retrieve 3D ice water content (IWC) and mean effective ice crystal size of cirrus clouds from satellite data on the basis of a combination of the conventional retrieval of cloud optical depth and particle size in a horizontal plane and a parameterization of the vertical cloud profile involving temperature from sounding and/or analysis. The inferred 3D cloud fields of IWC and mean effective ice crystal size associated with two impressive cirrus clouds that occurred in the vicinity of northern Oklahoma on 18 April 1997 and 9 March 2000, obtained from the Department of Energy's Atmospheric Radiation Measurement Program, have been validated against the ice crystal size distributions that were collected independently from collocated and coincident aircraft optical probe measurements. The 3D cloud results determined from satellite data have been applied to the simulation of cw laser energy propagation, and we show the significance of 3D cloud geometry and inhomogeneity and spherical atmosphere on the transmitted and backscattered laser powers. Finally, we demonstrate that the 3D cloud fields derived from satellite remote sensing can be used for the 3D laser transmission and backscattering model for tactical application.

  18. Mass balance of Icelandic ice caps from CryoSat swath mode altimetry

    NASA Astrophysics Data System (ADS)

    Foresta, L.; Gourmelen, N.; Pálsson, F.; Willis, I. C.; Nienow, P. W.; Shepherd, A.

    2015-12-01

    Satellite altimetry has been traditionally used in the past to infer elevation of land ice, quantify changes in ice topography and infer mass balance over large and remote areas such as the Greenland and Antarctic ice sheets. Radar Altimetry (RA) is particularly well suited to this task due to its all-weather year-round capability for observing the ice surface. However, monitoring of ice caps has proven more challenging. The large footprint of a conventional radar altimeter and relatively coarse ground track coverage are less suited to monitoring comparatively small regions with complex topography, so that mass balance estimates from RA rely on extrapolation methods to regionalize elevation change.Since 2010, the Synthetic Interferometric Radar Altimeter (SIRAL) on board the ESA radar altimetry CryoSat mission has collected ice elevation measurements over ice caps. Ground track interspacing (~4km at 60°) is one order of magnitude smaller than ERS/ENVISAT missions and half of ICESAT's, providing dense spatial coverage. Additionally the Synthetic Aperture Radar Interferometric (SARIn) mode of CryoSat provides a reduced footprint and the ability to locate accurately the position of the surface reflection. Conventional altimetry provides the elevation of the Point Of Closest Approach (POCA) within each waveform, every 250 m along the flight path. Time evolution of POCA elevation is then used to investigate ice elevation change.Here, we present an assessment of the geodetic mass balance of Icelandic ice caps using a novel processing approach, swath altimetry, applied to CryoSat SARIn mode data. In swath mode altimetry, elevation beyond the POCA is extracted from the waveform when coherent echoes are present providing between one and two orders of magnitude more elevations when compared to POCA. We generate maps of ice elevation change that are then used to compute geodetic mass balance for the period 2010 to 2015. We compare our results to estimates generated using

  19. Sea-surface altimetry airborne observations using synoptic GNSS reflectometry at the Baltic Sea

    NASA Astrophysics Data System (ADS)

    Ribó, Serni; Fabra, Fran; Cardellach, Estel; Li, Weiqiang; Rius, Antonio; Praks, Jaan; Rouhe, Erkka; Seppänen, Jaakko; Martín-Neira, Manuel

    2016-04-01

    Recent GNSS-R (Global Navigation Satellite System-Reflections) observations over the Baltic Sea have been taken using the SPIR (Software PARIS Interferometric Receiver) from an airborne platform at 3 km altitude. This newly developed instrument is capable of acquiring GNSS signals transmitted by multiple satellites simultaneously that have been reflected of the sea-surface. Reflections are usually gathered in off-nadir configuration using the instrument's beam-forming capabilities, which results in an increase of the instrument's swath. In this way, this technique opens the door to densify in space and time sea-altimetry observations to enhance future mesoscale and sub-mesoscale ocean altimetry. The altimetric observations collected during the Baltic Sea campaign have been analysed in terms of their power spectral densities. We consider the sequence of observations as an ergodic process that has contributions from the actual true altimetry as well as the observation noise. In this way it is possible to relate the expected ground resolution of the observations with the obtainable altimetric uncertainty. Results will be presented.

  20. Lively data: discover, browse and access ocean altimetry data on internet

    NASA Astrophysics Data System (ADS)

    Rosmorduc, V.; Jolibois, T.; Lauret, O.

    2006-06-01

    The Products and Services (P&S) department in the Space Oceanography Division at CLS (Collecte, Localisation, Satellites) is in charge of distributing and promoting altimetry and operational oceanography data. The department is thus involved in the Aviso satellite altimetry project (the French service which distributes altimetry products since 1992), in the Mercator ocean operational forecasting system, and in the European Godae/Mersea ocean portal. Aiming to a standardisation and a common vision and management of all these ocean data, all these projects, led to the implementation of several Opendap/LAS Internet servers (Baudel et al., 2004). Some of the possibilities of the tools, as well as how-to information will be highlighted, as they are in the "Lively data'' section of Aviso website (see http://www.aviso.oceanobs.com/html/donnees/las/). Moreover, with a two-year experience we now have some feedback and analysis of how people - users, would-be users and students alike - are using this tool, some ideas for possible enhancements, etc.

  1. Assimilation of CryoSat-2 altimetry to a hydrodynamic model of the Brahmaputra river

    NASA Astrophysics Data System (ADS)

    Schneider, Raphael; Nygaard Godiksen, Peter; Ridler, Marc-Etienne; Madsen, Henrik; Bauer-Gottwein, Peter

    2016-04-01

    Remote sensing provides valuable data for parameterization and updating of hydrological models, for example water level measurements of inland water bodies from satellite radar altimeters. Satellite altimetry data from repeat-orbit missions such as Envisat, ERS or Jason has been used in many studies, also synthetic wide-swath altimetry data as expected from the SWOT mission. This study is one of the first hydrologic applications of altimetry data from a drifting orbit satellite mission, namely CryoSat-2. CryoSat-2 is equipped with the SIRAL instrument, a new type of radar altimeter similar to SRAL on Sentinel-3. CryoSat-2 SARIn level 2 data is used to improve a 1D hydrodynamic model of the Brahmaputra river basin in South Asia set up in the DHI MIKE 11 software. CryoSat-2 water levels were extracted over river masks derived from Landsat imagery. After discharge calibration, simulated water levels were fitted to the CryoSat-2 data along the Assam valley by adapting cross section shapes and datums. The resulting hydrodynamic model shows accurate spatio-temporal representation of water levels, which is a prerequisite for real-time model updating by assimilation of CryoSat-2 altimetry or multi-mission data in general. For this task, a data assimilation framework has been developed and linked with the MIKE 11 model. It is a flexible framework that can assimilate water level data which are arbitrarily distributed in time and space. Different types of error models, data assimilation methods, etc. can easily be used and tested. Furthermore, it is not only possible to update the water level of the hydrodynamic model, but also the states of the rainfall-runoff models providing the forcing of the hydrodynamic model. The setup has been used to assimilate CryoSat-2 observations over the Assam valley for the years 2010 to 2013. Different data assimilation methods and localizations were tested, together with different model error representations. Furthermore, the impact of

  2. Why commercial broadband satellites absolutely must have laser intersatellite links (ISLs) and how the free-space laser communications community could let them down

    NASA Astrophysics Data System (ADS)

    Freidell, James E.

    1998-05-01

    Large commercial satellite programs needing high bandwidth inter-satellite links (ISLs) are growing rapidly in number. Precious few are visibly maturing. These commercial needs present greater customer diversity and opportunity for free- space laser communications application than the current plans of all the world's governments combined, multiplied manyfold. However, commercial customers generally do not have access to the independent, knowledgeable, but often heterogeneous laser communications expertise upon which government programs have historically relied. Moreover, commercial needs differ substantially from those of governments, particularly in the areas of price sensitivity and assured delivery on schedule and meeting all requirements. And the number of would-be laser ISL terminal suppliers also grows despite little verifiable expertise in actually delivering complete, working space-based laser ISL terminals, regardless of price or performance. Consequently, the opportunity for mistakes, disappointments, and outright failure is intensified. More 'red meatballs' are unfortunately on the horizon and neither customers nor suppliers recognize the warning signs. Is ignorance bliss? Virtually the entire space communications community appears oblivious to emerging terrestrial broadband communications projects which appear better backed with superior management far more attentive to time-to-market and other schedule and business considerations than any space venture. Space systems offer advantages through realizing global network operations not possible terrestrially, yet few promoters recogni the potential. Might these be omens worth capitalizing upon, or perhaps from which escape may be warranted? This paper provides a commercial market status update to that presented in preceding years' papers. Laser ISL applications are reviewed which enable commercial broadband satellite customer opportunities not yet recognized among most in the customer community, despite

  3. Tracking mesoscale ocean features in the Caribbean Sea using Geosat Altimetry

    SciTech Connect

    Nystuen, J.A.; Andrade, C.A. )

    1993-05-15

    The authors use Geosat Exact Repeat Mission altimetry data to track mesoscale ocean features in the Caribbean Sea. Because of the topography of the basin extensive mesoscale features exist, and have been studied and modeled. Models indicate the presence of eddy flow patterns in parts of the basin. The meteorology of the region is dominated by the Intertropical Convergence Zone, which shifts with the seasons. It has been shown that the seasonal wind stress curl positively correlates with total volume transport through the Caribbean Sea. Satellite altimetry provides an accepted means of studying mesoscale features of ocean dynamics which vary with time. The data reveals the appearance of two anticyclonic features, one each year, which appear and drift westward at speed considerably less that surface flow speeds. It also indicates the presence of a cyclonic feature in the southwest corner of the Columbian basin which varies with time. Marine geoid corrections unfortunately remove any features which are not time dependent from the data.

  4. Geophysical interpretation of satellite laser ranging measurements of crustal movement in California

    NASA Astrophysics Data System (ADS)

    Cohen, Steven C.

    1985-12-01

    As determined by satellite laser ranging the rate of contraction of a 900 km baseline between sites located near Quincy in northern California and San Diego in southern California is about 61-65 mm/yr with a formal uncertainty of about 10 mm/yr (Christodoulidis et al., 1985). The measured changes in baseline length are a manifestation of the relative motion between the North America and Pacific tectonic plates. This long baseline result is compared to measurements made by more conventional means on shorter baselines. Additional information based on seismiscity, geology, and theoretical modelling is also analyzed. Deformation lying within a few tens of kilometers about the major faults in southern California accounts for most, but not all, of the observed motion. Further motion is attributable to a broader-scale deformation in southern California. Data suggesting crustal movements north of the Garlock fault, in and near the southern Sierra Nevada and local motion at an observatory are also critically reviewed. The best estimates of overall motion indicated by ground observations lie between 40 and 60 mm/yr. This lies within one or two standard deviations of that deduced from satellite ranging but the possibility of some unresolved deficit cannot be entirely dismissed. The long time scale RM2 plate tectonic model of Minster and Jordan (1978) predicts a contraction between 47 and 53 mm/yr depending on the extension rate of the Basin and Range. Thus the ground based observations, SLR results, and RM2 rates differ at about the 10 mm/yr level but are not inconsistent with one another within the data and model uncertainties.

  5. (Nearly) Fifteen Years of Altimetry Outreach at CNES and NASA/JPL

    NASA Astrophysics Data System (ADS)

    Rosmorduc, V.; Richardson, A.; Srinivasan, M.

    2006-07-01

    Since the 1992 launch of Topex/Poseidon, CNES and NASA/JPL have been involved in providing information about satellite altimetry techniques, applications, and ocean science to the world. From the beginning, the TOPEX/Poseidon and Jason-1 Outreach Team has focused on reaching out to a wide range of people: from educators, students and the general public, to scientists and professionals who use the data. Our objective is to provide information and support appropriate to each audience. We have developed an extensive series of products on many relevant topics related to ocean science and altimetry, with levels ranging from easy-to-read to the expert point of view. Through presentation of mission first results, the focus in the early years was on data quality and the varied data applications. Since 1997, El Niño forecasting was of major interest to the public, whereas the oceanographic community sought contributions to true operational oceanography. With the launch of Jason-1, the focus is now on the need for a long-term data series and continuity in the missions. Educational activities related to ocean altimetry are continuing and expanding. Our aim in this realm is to help teachers and students across the world appreciate the ocean environment and the role satellites play in increasing our understanding of this crucial resource. The evolution in our outreach activities is mirrored in the printed material distributed as hardcopy, and significantly in the regular updates to the web sites. As we approach nearly 15 years of continuous altimetry outreach our efforts are directed toward supporting the move toward operational oceanography (with GODAE and Jason-2/OSTM) and converging upon an integrated, multi-institutional outreach program.

  6. ESA activities on satellite laser ranging to non-cooperative objects

    NASA Astrophysics Data System (ADS)

    Flohrer, Tim; Krag, Holger; Funke, Quirin; Jilete, Beatriz; Mancas, Alexandru

    2016-07-01

    Satellite laser ranging (SLR) to non-cooperative objects is an emerging technology that can contribute significantly to operational, modelling and mitigation needs set by the space debris population. ESA is conducting various research and development activities in SLR to non-cooperative objects. ESA's Space Situational Awareness (SSA) program supports specific activities in the Space Surveillance and Tracking (SST) segment. Research and development activities with operational aspects are run by ESA's Space Debris Office. At ESA SSA/SST comprises detecting, cataloguing and predicting the objects orbiting the Earth, and the derived applications. SST aims at facilitating research and development of sensor and data processing technologies and of related common components while staying complementary with, and in support of, national and multi-national European initiatives. SST promotes standardisation and interoperability of the technology developments. For SLR these goals are implemented through researching, developing, and deploying an expert centre. This centre shall coordinate the contribution of system-external loosely connected SLR sensors, and shall provide back calibration and expert evaluation support to the sensors. The Space Debris Office at ESA is responsible for all aspects related to space debris in the Agency. It is in charge of providing operational support to ESA and third party missions. Currently, the office studies the potential benefits of laser ranging to space debris objects to resolve close approaches to active satellites, to improve re-entry predictions of time and locations, and the more general SLR support during contingency situations. The office studies the determination of attitude and attitude motion of uncooperative objects with special focus on the combination of SLR, light-curve, and radar imaging data. Generating sufficiently precise information to allow for the acquisition of debris objects by a SLR sensor in a stare

  7. The use of coastal altimetry to support storm surge studies in project eSurge

    NASA Astrophysics Data System (ADS)

    Cipollini, P.; Harwood, P.; Snaith, H.; Vignudelli, S.; West, L.; Zecchetto, S.; Donlon, C.

    2012-04-01

    One of the most promising applications of the new field of coastal altimetry, i.e. the discipline aiming to recover meaningful estimates of geophysical parameters (sea level, significant wave height and wind speed) from satellite altimeter data in the coastal zone, is the study of storm surges. The understanding and realistic modelling of surges supports both preparation and mitigation activities and should eventually bring enormous societal benefits, especially to some of the world's poorest countries (like Bangladesh). Earth Observation data have an important role to play in storm surge monitoring and forecasting, but the full uptake of these data by users (such as environmental agencies and tidal prediction centres) must first be encouraged by showcasing their usefulness, and then supported by providing easy access. Having recognized the above needs, The European Space Agency has recently launched a Data User Element (DUE) project called eSurge. The main purposes of eSurge are a) to contribute to an integrated approach to storm surge, wave, sea-level and flood forecasting through Earth Observation, as part of a wider optimal strategy for building an improved forecast and early warning capability for coastal inundation; and b) to increase the use of the advanced capabilities of ESA and other satellite data for storm surge applications. The project is led by Logica UK, with NOC (UK), DMI (Denmark), CMRC (Ireland) and KNMI (Netherlands) as scientific partners. A very important component of eSurge is the development, validation and provision of dedicated coastal altimetry products, which is the focus of the present contribution. Coastal altimetry has a prominent role to play as it measures the total water level envelope directly, and this is one of the key quantities required by storm surge applications and services. But it can also provide important information on the wave field in the coastal strip, which helps the development of more realistic wave models that in

  8. A Unified Global Reference Frame of Vertical Crustal Movements by Satellite Laser Ranging

    PubMed Central

    Zhu, Xinhui; Wang, Ren; Sun, Fuping; Wang, Jinling

    2016-01-01

    Crustal movement is one of the main factors influencing the change of the Earth system, especially in its vertical direction, which affects people’s daily life through the frequent occurrence of earthquakes, geological disasters, and so on. In order to get a better study and application of the vertical crustal movement, as well as its changes, the foundation and prerequisite areto devise and establish its reference frame; especially, a unified global reference frame is required. Since SLR (satellite laser ranging) is one of the most accurate space techniques for monitoring geocentric motion and can directly measure the ground station’s geocentric coordinates and velocities relative to the centre of the Earth’s mass, we proposed to take the vertical velocity of the SLR technique in the ITRF2008 framework as the reference frame of vertical crustal motion, which we defined as the SLR vertical reference frame (SVRF). The systematic bias between other velocity fields and the SVRF was resolved by using the GPS (Global Positioning System) and VLBI (very long baseline interferometry) velocity observations, and the unity of other velocity fields and SVRF was realized, as well. The results show that it is feasible and suitable to take the SVRF as a reference frame, which has both geophysical meanings and geodetic observations, so we recommend taking the SLR vertical velocity under ITRF2008 as the global reference frame of vertical crustal movement. PMID:26867197

  9. A Unified Global Reference Frame of Vertical Crustal Movements by Satellite Laser Ranging.

    PubMed

    Zhu, Xinhui; Wang, Ren; Sun, Fuping; Wang, Jinling

    2016-02-08

    Crustal movement is one of the main factors influencing the change of the Earth system, especially in its vertical direction, which affects people's daily life through the frequent occurrence of earthquakes, geological disasters, and so on. In order to get a better study and application of the vertical crustal movement,as well as its changes, the foundation and prerequisite areto devise and establish its reference frame; especially, a unified global reference frame is required. Since SLR (satellite laser ranging) is one of the most accurate space techniques for monitoring geocentric motion and can directly measure the ground station's geocentric coordinates and velocities relative to the centre of the Earth's mass, we proposed to take the vertical velocity of the SLR technique in the ITRF2008 framework as the reference frame of vertical crustal motion, which we defined as the SLR vertical reference frame (SVRF). The systematic bias between other velocity fields and the SVRF was resolved by using the GPS (Global Positioning System) and VLBI (very long baseline interferometry) velocity observations, and the unity of other velocity fields and SVRF was realized,as well. The results show that it is feasible and suitable to take the SVRF as a reference frame, which has both geophysical meanings and geodetic observations, so we recommend taking the SLR vertical velocity under ITRF2008 as the global reference frame of vertical crustal movement.

  10. Optimization of a laser satellite communication system with an optical preamplifier.

    PubMed

    Polishuk, Anna; Arnon, Shlomi

    2004-07-01

    We derive a model that optimizes the performance of a laser satellite communication link with an optical preamplifier in the presence of random jitter in the transmitter-receiver line of sight. The system utilizes a transceiver containing a single telescope with a circulator. The telescope is used for both transmitting and receiving and thus reduces communication terminal dimensions and weight. The optimization model was derived under the assumption that the dominant noise source was amplifier spontaneous-emission noise. It is shown that, given the required bit-error rate (BER) and the rms random pointing jitter, an optimal transceiver gain exists that minimizes transmitted power. We investigate the effect of the amplifier spontaneous-emission noise on the optimal transmitted power and gain by performing an optimization procedure for various combinations of amplifier gain and noise figure. We demonstrate that the amplifier noise figure determines the optimal transmitted power needed to achieve the desired BER but does not affect the optimal transceiver telescope gain. Our numerical example shows that for a BER of 10(-9), doubling the amplifier noise figure results in an 80% increase in minimal transmitted power for a rms pointing jitter of 0.44 microrad.

  11. Integrating optical satellite data and airborne laser scanning in habitat classification for wildlife management

    NASA Astrophysics Data System (ADS)

    Nijland, W.; Coops, N. C.; Nielsen, S. E.; Stenhouse, G.

    2015-06-01

    Wildlife habitat selection is determined by a wide range of factors including food availability, shelter, security and landscape heterogeneity all of which are closely related to the more readily mapped landcover types and disturbance regimes. Regional wildlife habitat studies often used moderate resolution multispectral satellite imagery for wall to wall mapping, because it offers a favourable mix of availability, cost and resolution. However, certain habitat characteristics such as canopy structure and topographic factors are not well discriminated with these passive, optical datasets. Airborne laser scanning (ALS) provides highly accurate three dimensional data on canopy structure and the underlying terrain, thereby offers significant enhancements to wildlife habitat mapping. In this paper, we introduce an approach to integrate ALS data and multispectral images to develop a new heuristic wildlife habitat classifier for western Alberta. Our method combines ALS direct measures of canopy height, and cover with optical estimates of species (conifer vs. deciduous) composition into a decision tree classifier for habitat - or landcover types. We believe this new approach is highly versatile and transferable, because class rules can be easily adapted for other species or functional groups. We discuss the implications of increased ALS availability for habitat mapping and wildlife management and provide recommendations for integrating multispectral and ALS data into wildlife management.

  12. Polar motion and length of day determination from satellite laser ranging

    NASA Technical Reports Server (NTRS)

    Smith, David E.; Christodoulidis, Demosthenes C.; Torrence, Mark H.; Klosko, Steven M.; Dunn, Peter J.

    1986-01-01

    The kinematic and dynamic models used in obtaining the GSFC MERIT solution (using data from satellite laser ranging) for the x and y coordinates of the earth's rotation pole and the excess length-of-day (LOD) are discussed together with the analysis technique. Comparisons of the GSFC polar motion time series with the time series from the Bureau International de l'Heure shows small but consistent systematic differences (4.6 milliarcsec rms about a mean offset of 1 milliarcsec in the x component, and 2.9 milliarcsec rms about a 21 milliarcsec offset in the y component). A comparison with the data of the National Geodetic Survey's IRIS network shows departures of 2.5 milliarcsec rms about the mean for the x component and 2.0 milliarcsec rms for the y component. The precision of the GSFC earth orientation is estimated to be better than 1 milliarcsec for polar motion and 0.1 msec for excess LOD.

  13. Precise Orbit Determination for GEOSAT Follow-On Using Satellite Laser Ranging Data and Intermission Altimeter Crossovers

    NASA Technical Reports Server (NTRS)

    Lemoine, Frank G.; Rowlands, David D.; Luthcke, Scott B.; Zelensky, Nikita P.; Chinn, Douglas S.; Pavlis, Despina E.; Marr, Gregory

    2001-01-01

    The US Navy's GEOSAT Follow-On Spacecraft was launched on February 10, 1998 with the primary objective of the mission to map the oceans using a radar altimeter. Following an extensive set of calibration campaigns in 1999 and 2000, the US Navy formally accepted delivery of the satellite on November 29, 2000. Satellite laser ranging (SLR) and Doppler (Tranet-style) beacons track the spacecraft. Although limited amounts of GPS data were obtained, the primary mode of tracking remains satellite laser ranging. The GFO altimeter measurements are highly precise, with orbit error the largest component in the error budget. We have tuned the non-conservative force model for GFO and the gravity model using SLR, Doppler and altimeter crossover data sampled over one year. Gravity covariance projections to 70x70 show the radial orbit error on GEOSAT was reduced from 2.6 cm in EGM96 to 1.3 cm with the addition of SLR, GFO/GFO and TOPEX/GFO crossover data. Evaluation of the gravity fields using SLR and crossover data support the covariance projections and also show a dramatic reduction in geographically-correlated error for the tuned fields. In this paper, we report on progress in orbit determination for GFO using GFO/GFO and TOPEX/GFO altimeter crossovers. We will discuss improvements in satellite force modeling and orbit determination strategy, which allows reduction in GFO radial orbit error from 10-15 cm to better than 5 cm.

  14. Seasat orbit refinement for altimetry application

    NASA Astrophysics Data System (ADS)

    Mohan, S. N.; Hamata, N. E.; Stavert, R. L.; Bierman, G. J.

    1980-12-01

    This paper describes the use of stochastic differential correction models in refining the Seasat orbit based on post-flight analysis of tracking data. The objective is to obtain orbital-height precision that is commensurate with the inherent Seasat altimetry data precision level of 10 cms. Local corrections to a mean ballistic arc, perturbed principally by atmospheric drag variations and local gravitational anomalies, are obtained by the introduction of stochastic dynamical models in conjunction with optimal estimation/smoothing techniques. Assessment of the resulting orbit with 'ground truth' provided by Seasat altimetry data shows that the orbital height precision is improved by 32% when compared to a conventional least-squares solution using the same data set. The orbital height precision realized by employing stochastic differential correction models is in the range of 73 cms to 208 cms rms.

  15. Satellite remote sensing over ice

    NASA Technical Reports Server (NTRS)

    Thomas, R. H.

    1984-01-01

    Satellite remote sensing provides unique opportunities for observing ice-covered terrain. Passive-microwave data give information on snow extent on land, sea-ice extent and type, and zones of summer melting on the polar ice sheets, with the potential for estimating snow-accumulation rates on these ice sheets. All weather, high-resolution imagery of sea ice is obtained using synthetic aperture radars, and ice-movement vectors can be deduced by comparing sequential images of the same region. Radar-altimetry data provide highly detailed information on ice-sheet topography, with the potential for deducing thickening/thinning rates from repeat surveys. The coastline of Antarctica can be mapped accurately using altimetry data, and the size and spatial distribution of icebergs can be monitored. Altimetry data also distinguish open ocean from pack ice and they give an indication of sea-ice characteristics.

  16. Evolution of Altimetry Calibration and Future Challenges

    NASA Technical Reports Server (NTRS)

    Fu, Lee-Lueng; Haines, Bruce J.

    2012-01-01

    Over the past 20 years, altimetry calibration has evolved from an engineering-oriented exercise to a multidisciplinary endeavor driving the state of the art. This evolution has been spurred by the developing promise of altimetry to capture the large-scale, but small-amplitude, changes of the ocean surface containing the expression of climate change. The scope of altimeter calibration/validation programs has expanded commensurately. Early efforts focused on determining a constant range bias and verifying basic compliance of the data products with mission requirements. Contemporary investigations capture, with increasing accuracies, the spatial and temporal characteristics of errors in all elements of the measurement system. Dedicated calibration sites still provide the fundamental service of estimating absolute bias, but also enable long-term monitoring of the sea-surface height and constituent measurements. The use of a network of island and coastal tide gauges has provided the best perspective on the measurement stability, and revealed temporal variations of altimeter measurement system drift. The cross-calibration between successive missions provided fundamentally new information on the performance of altimetry systems. Spatially and temporally correlated errors pose challenges for future missions, underscoring the importance of cross-calibration of new measurements against the established record.

  17. Terrain profiling from Seasat altimetry

    NASA Technical Reports Server (NTRS)

    Brooks, R. L.

    1981-01-01

    To determine their applicability for terrain profiling, Seasat altimeter measurements were analyzed for the following geographic areas: (1) Andean salars of southern Bolivia; (2) Alaska; (3) south-central Arizona; (4) imperial Valley of California; (5) Yuma Valley of Arizona; and (6) Great Salt Lake Desert. Analysis of the data over all of these geographic areas shows that the satellite altimeter servo did not respond quickly enough to changing terrain features. However, it is demonstrated that retracking of the archived surface return waveforms yields surface elevations over smooth terrain accurate to + or - 1 m when correlated with large scale maps. The retracking algorithm used and its verification over the salars of southern Bolivia are described. Results are presented for each of the six geographic areas.

  18. Design of smart composite platforms for adaptive trust vector control and adaptive laser telescope for satellite applications

    NASA Astrophysics Data System (ADS)

    Ghasemi-Nejhad, Mehrdad N.

    2013-04-01

    This paper presents design of smart composite platforms for adaptive trust vector control (TVC) and adaptive laser telescope for satellite applications. To eliminate disturbances, the proposed adaptive TVC and telescope systems will be mounted on two analogous smart composite platform with simultaneous precision positioning (pointing) and vibration suppression (stabilizing), SPPVS, with micro-radian pointing resolution, and then mounted on a satellite in two different locations. The adaptive TVC system provides SPPVS with large tip-tilt to potentially eliminate the gimbals systems. The smart composite telescope will be mounted on a smart composite platform with SPPVS and then mounted on a satellite. The laser communication is intended for the Geosynchronous orbit. The high degree of directionality increases the security of the laser communication signal (as opposed to a diffused RF signal), but also requires sophisticated subsystems for transmission and acquisition. The shorter wavelength of the optical spectrum increases the data transmission rates, but laser systems require large amounts of power, which increases the mass and complexity of the supporting systems. In addition, the laser communication on the Geosynchronous orbit requires an accurate platform with SPPVS capabilities. Therefore, this work also addresses the design of an active composite platform to be used to simultaneously point and stabilize an intersatellite laser communication telescope with micro-radian pointing resolution. The telescope is a Cassegrain receiver that employs two mirrors, one convex (primary) and the other concave (secondary). The distance, as well as the horizontal and axial alignment of the mirrors, must be precisely maintained or else the optical properties of the system will be severely degraded. The alignment will also have to be maintained during thruster firings, which will require vibration suppression capabilities of the system as well. The innovative platform has been

  19. Calibration and evaluation of Skylab altimetry for geodetic determination of the geoid

    NASA Technical Reports Server (NTRS)

    Mourad, A. G. (Principal Investigator); Gopalapillai, S.; Kuhner, M.; Fubara, D. M.

    1975-01-01

    The author has identified the following significant results. The Skylab altimeter experiment has proven the capability of the altimeter for measurement of sea surface topography. The geometric determination of the geoid/mean sea level from satellite altimetry is a new approach having significant applications in many disciplines including geodesy and oceanography. A generalized least squares collocation technique was developed for determination of the geoid from altimetry data. The technique solves for the altimetry geoid and determines one bias term for the combined effect of sea state, orbit, tides, geoid, and instrument error using sparse ground truth data. The influence of errors in orbit and a priori geoid values are discussed. Although the Skylab altimeter instrument accuracy is about plus or minus 1m, significant results were obtained in identification of large geoidal features such as over the Puerto Rico trench. Comparison of the results of several passes shows that good agreement exists between the general slopes of the altimeter geoid and the ground truth, and that the altimeter appears to be capable of providing more details than are now available with best known geoids.

  20. Numerical Analysis of the Sea State Bias for Satellite Altimetry

    NASA Technical Reports Server (NTRS)

    Glazman, R. E.; Fabrikant, A.; Srokosz, M. A.

    1996-01-01

    Theoretical understanding of the dependence of sea state bias (SSB) on wind wave conditions has been achieved only for the case of a unidirectional wind-driven sea. Recent analysis of Geosat and TOPEX altimeter data showed that additional factors, such as swell, ocean currents, and complex directional properties of realistic wave fields, may influence SSB behavior. Here we investigate effects of two-dimensional multimodal wave spectra using a numerical model of radar reflection from a random, non-Gaussian surface. A recently proposed ocean wave spectrum is employed to describe sea surface statistics. The following findings appear to be of particular interest: (1) Sea swell has an appreciable effect in reducing the SSB coefficient compared with the pure wind sea case but has less effect on the actual SSB owing to the corresponding increase in significant wave height. (2) Hidden multimodal structure (the two-dimensional wavenumber spectrum contains separate peaks, for swell and wind seas, while the frequency spectrum looks unimodal) results in an appreciable change of SSB. (3) For unimodal, purely wind-driven seas, the influence of the angular spectral width is relatively unimportant; that is, a unidirectional sea provides a good qualitative model for SSB if the swell is absent. (4) The pseudo wave age is generally much better fo parametrization the SSB coefficient than the actual wave age (which is ill-defined for a multimodal sea) or wind speed. (5) SSB can be as high as 5% of the significant wave height, which is significantly greater than predicted by present empirical model functions tuned on global data sets. (6) Parameterization of SSB in terms of wind speed is likely to lead to errors due to the dependence on the (in practice, unknown) fetch.

  1. Numerical analysis of the sea state bias for satellite altimetry

    NASA Astrophysics Data System (ADS)

    Glazman, R. E.; Fabrikant, A.; Srokosz, M. A.

    1996-02-01

    Theoretical understanding of the dependence of sea state bias (SSB) on wind wave conditions has been achieved only for the case of a unidirectional wind-driven sea [Jackson, 1979; Rodriguez et al., 1992; Glazman and Srokosz, 1991]. Recent analysis of Geosat and TOPEX altimeter data showed that additional factors, such as swell, ocean currents, and complex directional properties of realistic wave fields, may influence SSB behavior. Here we investigate effects of two-dimensional multimodal wave spectra using a numerical model of radar reflection from a random, non-Gaussian surface. A recently proposed ocean wave spectrum is employed to describe sea surface statistics. The following findings appear to be of particular interest: (1) Sea swell has an appreciable effect in reducing the SSB coefficient compared with the pure wind sea case but has less effect on the actual SSB, owing to the corresponding increase in significant wave height. (2) Hidden multimodal structure (the two-dimensional wavenumber spectrum contains separate peaks, for swell and wind seas, while the frequency spectrum looks unimodal) results in an appreciable change of SSB. (3) For unimodal, purely wind-driven seas, the influence of the angular spectral width is relatively unimportant; that is, a unidirectional sea provides a good qualitative model for SSB if the swell is absent. (4) The pseudo wave age is generally much better for parametrizing the SSB coefficient than the actual wave age (which is ill-defined for a multimodal sea) or wind speed. (5) SSB can be as high as 5% of the significant wave height, which is significantly greater than predicted by present empirical model functions tuned on global data sets. (6) Parameterization of SSB in terms of wind speed is likely to lead to errors due to the dependence on the (in practice, unknown) fetch.

  2. A daily global mesoscale ocean eddy dataset from satellite altimetry

    PubMed Central

    Faghmous, James H.; Frenger, Ivy; Yao, Yuanshun; Warmka, Robert; Lindell, Aron; Kumar, Vipin

    2015-01-01

    Mesoscale ocean eddies are ubiquitous coherent rotating structures of water with radial scales on the order of 100 kilometers. Eddies play a key role in the transport and mixing of momentum and tracers across the World Ocean. We present a global daily mesoscale ocean eddy dataset that contains ~45 million mesoscale features and 3.3 million eddy trajectories that persist at least two days as identified in the AVISO dataset over a period of 1993–2014. This dataset, along with the open-source eddy identification software, extract eddies with any parameters (minimum size, lifetime, etc.), to study global eddy properties and dynamics, and to empirically estimate the impact eddies have on mass or heat transport. Furthermore, our open-source software may be used to identify mesoscale features in model simulations and compare them to observed features. Finally, this dataset can be used to study the interaction between mesoscale ocean eddies and other components of the Earth System. PMID:26097744

  3. A daily global mesoscale ocean eddy dataset from satellite altimetry.

    PubMed

    Faghmous, James H; Frenger, Ivy; Yao, Yuanshun; Warmka, Robert; Lindell, Aron; Kumar, Vipin

    2015-01-01

    Mesoscale ocean eddies are ubiquitous coherent rotating structures of water with radial scales on the order of 100 kilometers. Eddies play a key role in the transport and mixing of momentum and tracers across the World Ocean. We present a global daily mesoscale ocean eddy dataset that contains ~45 million mesoscale features and 3.3 million eddy trajectories that persist at least two days as identified in the AVISO dataset over a period of 1993-2014. This dataset, along with the open-source eddy identification software, extract eddies with any parameters (minimum size, lifetime, etc.), to study global eddy properties and dynamics, and to empirically estimate the impact eddies have on mass or heat transport. Furthermore, our open-source software may be used to identify mesoscale features in model simulations and compare them to observed features. Finally, this dataset can be used to study the interaction between mesoscale ocean eddies and other components of the Earth System.

  4. Variations of the Earth's figure axis from satellite laser ranging and GRACE

    NASA Astrophysics Data System (ADS)

    Cheng, Minkang; Ries, John C.; Tapley, Byron D.

    2011-01-01

    Satellite laser ranging (SLR) data were used to determine the variations in the Earth's principal figure axis represented by the degree 2 and order 1 geopotential coefficients: C21 and S21. Significant variations at the annual and Chandler wobble frequencies appear in the SLR time series when the rotational deformation or "pole tides" (i.e., the solid Earth and ocean pole tides) were not modeled. The contribution of the ocean pole tide is estimated to be only ˜8% of the total annual variations in the normalized coefficients: ?/? based on the analysis of SLR data. The amplitude of the nontidal annual variation of ? is only ˜ 30% of ? from the SLR time series. The estimates of the annual variation in ? from SLR, the Gravity Recovery and Climate Experiment (GRACE) and polar motion excitation function, are in a good agreement. The nature of the linear trend for the Earth's figure axis determined by these techniques during the last several years is in general agreement but does not agree as well with results predicted from current glacial isostatic adjustment (GIA) models. The "fluid Love number" for the Earth is estimated to be ˜0.9 based on the position of the mean figure axis from the GRACE gravity model GGM03S and the mean pole defined by the IERS 2003 conventions. The estimate of ?/? from GRACE and SLR provides an improved constraint on the relative rotation of the core. The results presented here indicate a possible tilt of the inner core figure axis of ˜2° and ˜3 arc sec displacement for the figure axis of the entire core.

  5. Technique-Dependent Errors in the Satellite Laser Ranging Contributions to the ITRF

    NASA Astrophysics Data System (ADS)

    Pavlis, Erricos C.; Kuzmicz-Cieslak, Magdalena; König, Daniel

    2013-04-01

    Over the past decade Satellite Laser Ranging (SLR) has focused on its unique strength of providing accurate observations of the origin and scale of the International Terrestrial Reference Frame (ITRF). The origin of the ITRF is defined to coincide with the center of mass of the Earth system (geocenter). SLR realizes this origin as the focal point of the tracked satellite orbits, and being the only (nominally) unbiased ranging technique, it provides the best realization for it. The goal of GGOS is to provide an ITRF with accuracy at epoch of 1 mm or better and a stability of 0.1 mm/y. In order to meet this stringent goal, Space Geodesy is taking a two-pronged approach: modernizing the engineering components (ground and space segments), and revising the modeling standards to take advantage of recent improvements in many areas of geophysical modeling for system Earth components. As we gain improved understanding of the Earth system components, space geodesy adjusts its underlying modeling of the system to better and more completely describe it. Similarly, from the engineering side we examine the observational process for improvement of the calibration and reduction procedures that will enhance the accuracy of the individual observations thence the final SLR products. Two areas that are currently under scrutiny are (a) the station-dependent and tracking-mode-dependent correction of the observations for the "center-of-mass-offset" of each satellite target, and (b) the station- and pass-dependent correction for the calibrated delay that refers each measurement to the nominal "zero" of the instrument. The former affects primarily the accuracy of the scale definition, while the latter affects both, the scale and the origin. However, because of the non-uniform data volume and non-symmetric geographic locations of the SLR stations, the major impact of the latter is on the definition of the origin. The ILRS is currently investigating the quality of models available for the

  6. Coastal Sea Level From CRYOSAT-2 SAR and SAR-In Altimetry

    NASA Astrophysics Data System (ADS)

    Andersen, O. B.; Abulaitijiang, A.; Knudsen, P.; Stenseng, L.

    2014-12-01

    Cryosat-2 offers the first ever possibility to perform coastal altimetric studies using bor SAR-altimetry and SAR-In altimetry. With this technological leap forward Cryosat-2 is now able to observe sea level in very small water bodies and also to provide coastal sea level very close to the shore. We perform an investigation into the retrieval of sea surface height around Denmark and Greenland. These regions have been chosen as the coastal regions around Denmark falls within the SAR mask and the coastal regions of Greenland falls in under the SAR-in mask employed on Cryosat-2. SAR-in was mainly used in coastal regions of Greenland because of its huge topographic changes as Cryosat-2 is designed to map the margins of the ice-sheet. The coastal region around Denmark is a test region of the EU FP7 sponsored project LOTUS esablishing SAR altimetry product in preparation for Sentinel-3. With the increased spatial resolution of Cryosat-2 SAR we provide valuable sea level observations within the Straits around Denmark which are crucial to constrain the waterflow in and out of the Baltic Sea. The investigation of SAR-in data in Greenland adds an entire new dimension to coastal altimetry. An amazing result of the investigation is the ability of Cryosat-2 to detect and recover sea level even though the coast (sealevel) is up to 15 km away from the nadir location of the satellite. This ability of capture and use returns from outside the main (-3Db) loop in theory enables Cryosat-2 SAR-in to map sea level height of fjords more frequently than the 369 days repeat.

  7. Impacts of reprocessed altimetry on the surface circulation and variability of the Western Alboran Gyre

    NASA Astrophysics Data System (ADS)

    Juza, Mélanie; Escudier, Romain; Pascual, Ananda; Pujol, Marie-Isabelle; Taburet, Guillaume; Troupin, Charles; Mourre, Baptiste; Tintoré, Joaquín

    2016-08-01

    New altimetry products in semi-enclosed seas are of major interest given the importance of the coastal-open ocean interactions. This study shows how reprocessed altimetry products in the Mediterranean Sea from Archiving, Validation and Interpolation of Satellite Oceanographic data (AVISO) have improved the representation of the surface circulation over the 1993-2012 period. We focus on the Alboran Sea, which is the highest mesoscale activity area of the western Mediterranean. The respective impacts of the new mean dynamic topography (MDT) and mapped sea level anomaly (MSLA) on the description of the Western Alboran Gyre (WAG) are quantitatively evaluated. The temporal mean and variability of the total kinetic energy have been significantly increased in the WAG considering both the new MDT and MSLA (by more than 50%). The new MDT has added 39% to the mean kinetic energy, while the new MSLA has increased the eddy kinetic energy mean (standard deviation) by 53% (30%). The new MSLA has yielded higher variability of total (eddy) kinetic energy, especially in the annual frequency band by a factor of 2 (3). The MDT reprocessing has particularly increased the low-frequency variability of the total kinetic energy by a factor of 2. Geostrophic velocities derived from the altimetry products have also been compared with drifter data. Both reprocessed MDT and MSLA products intensify the velocities of the WAG making them closer to the in situ estimations, reducing the root mean square differences and increasing the correlation for the zonal and meridional components. The results obtained using refined coastal processing of altimetry products and new observational data are very encouraging to better understand the ocean circulation variability and coastal-open ocean interactions, and for potential improvements in other sub-basins, marginal seas and coastal global ocean.

  8. Noise Assessment and Error Analysis of GNSS Reflectometry Data for Water Surface Altimetry

    NASA Astrophysics Data System (ADS)

    Mendes, Tiago; Castro, Rita; Peres, Tiago; Carola, Jorge; Bandeiras, Jorge; Catarino, Nuno; Antunes, Carlos; Freire da Silva, Pedro

    2015-04-01

    The field of GNSS reflectometry has been gaining a lot of popularity in recent years, mostly because of its potential to generate multiple types of measurements on a global scale with a high repeatability rate. However, the challenge is to operationalize a GNSS reflectometry system with accuracy compatible with other technologies, such as satellite altimetry. Deimos Engenharia is currently leading the FP7 E-GEM project, which aims to evolve the current status of GNSS reflectometry in order to allow the implementation of operational applications (mainly in the domains of ocean altimetry and scatterometry). Within E-GEM Deimos is developing a ground instrument to collect reflectometry observables - namely, direct and reflected waveforms or autocorrelation functions that will be used to derive sea surface altimetry through the delay differences method. This paper presents the work that has been done in order to assess the expected noise for the Galileo E1 signal for the direct and reflected waveforms, as well as their delay differences that are used to obtain the final altimetric result. Several methods were used to estimate the noise, including tracking methods, fits and maxima determination, and the comparison with Gaussian noise expectations is performed. The results obtained using different methods will be presented. The Water Surface Altimetry is also derived, based on the delay differences and satellite elevation, and compared with concurrent tide gauge data. It can be concluded that without integration the noise level is of the order of 8 m, in good agreement with the expected values, taken into account that no filtering is applied. Moreover, some effects were detected and were not eliminated with delay differences, indicating that other error sources may be contributing to the noise (such as unwanted multipath). When the integration is performed the noise level is of the order of 50 cm, and for the delay differences the noise seems to approach a Gaussian

  9. Estimability and simple dynamical analyses of range (range-rate range-difference) observations to artificial satellites. [laser range observations to LAGEOS using non-Bayesian statistics

    NASA Technical Reports Server (NTRS)

    Vangelder, B. H. W.

    1978-01-01

    Non-Bayesian statistics were used in simulation studies centered around laser range observations to LAGEOS. The capabilities of satellite laser ranging especially in connection with relative station positioning are evaluated. The satellite measurement system under investigation may fall short in precise determinations of the earth's orientation (precession and nutation) and earth's rotation as opposed to systems as very long baseline interferometry (VLBI) and lunar laser ranging (LLR). Relative station positioning, determination of (differential) polar motion, positioning of stations with respect to the earth's center of mass and determination of the earth's gravity field should be easily realized by satellite laser ranging (SLR). The last two features should be considered as best (or solely) determinable by SLR in contrast to VLBI and LLR.

  10. Sea surface retracking and classification of CryoSat-2 altimetry observations in the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Stenseng, L.; Piccioni, G.; Andersen, O. B.; Knudsen, P.

    2015-12-01

    In this study we present the retracking and classification methods for CryoSat-2 SAR waveforms, developed for the determination of sea surface heights in the Arctic Ocean. The obtained sea surface heights (SSH) are used to decrease the gap in satellite observations from 82 degrees North to 88 degrees North in the DTU15 mean sea surface (MSS) and mean dynamic topography (MDT).Radar altimetry satellites has observed the sea surface for more than 25 years and thereby obtain data to determine accurate MSSs and estimate sea level trends related to climate changes. In combination with the improvements of global geoids it has furthermore provided an opportunity to improve the MDT related to ocean currents.After the launch of CryoSat-2 in 2010 the coverage was increased dramatically while the introduction of the synthetic aperture radar (SAR) and SAR interferometry (SARin) mode increased the amount of useful echoes in the Arctic Ocean. The new types of radar observation modes have been investigated and methods to retrack and classify the waveforms have been implemented in LARS the advanced retracking system (LARS). Finally the SSH observations obtained from CryoSat-2 with LARS is merged with previous satellite radar altimetry data to derive the DTU15 MSS.

  11. Ice sheet elevation change in West Antarctica from CryoSat interferometric altimetry

    NASA Astrophysics Data System (ADS)

    McMillan, M.; Shepherd, A.; Ridout, A.; Sundal, A.

    2013-12-01

    Two decades of radar altimetry have shown accelerating mass losses from the Amundsen Sea Sector of West Antarctica. The mass imbalance of this region, which dominates that of all Antarctica, manifests as sustained ice thinning focussed upon fast-flowing ice streams and their tributaries. Ongoing observations are required to determine whether rates of mass loss continue to increase and, more widely, to monitor the stability of this sector of the ice sheet. With the retirement of the ERS-2 satellite in 2011 and the loss of Envisat in 2012, CryoSat-2 offers the unique potential to extend the current altimetry record. In coastal regions of Antarctica the satellite operates in a novel Synthetic Aperture Radar interferometric (SARin) mode, which enables improved resolution and echo location. Here, we apply a repeat track algorithm to SARin mode data to derive ice sheet elevation, volume and mass changes during the period 2010-2013, focussing upon the Amundsen Sea Sector of West Antarctica. Binning elevation change measurements at 5 km resolution gives on average 40 observations per grid cell, illustrating the high sampling density offered by CryoSat-2. We find that, since the cessation of ERS and Envisat measurements, thinning continues to be most pronounced along the fast-flowing ice streams and tributaries, with rates of 4-8 m/yr near the grounding lines of the Pine Island, Thwaites and Smith Glaciers. We compare these new observations to previous measurements made by the ERS and Envisat satellites.

  12. Coastal Sea-Level in Norway from Cryosat-2 Interferometric SAR Altimetry

    NASA Astrophysics Data System (ADS)

    Idzanovic, Martina; Ophaug, Vegard; Andersen, Ole B.

    2016-08-01

    Conventional altimeters determine the sea surface height with an accuracy of a few centimeters over the open ocean. Although satellite altimetry is a mature discipline, altimeter observations collected over coastal regions suffer from numerous effects which degrade their quality. The Norwegian coast adds further complications, due to many islands, mountains, and deep, narrow fjords. The European Space Agency (ESA) CryoSat-2 satellite carries a Synthetic aperture Interferometric Radar ALtimeter (SIRAL). Due to the SIRAL instrument, CryoSat-2 is able to observe closer to the coast than conventional altimeters. This motivates the current paper, in which we investigate the potential of CryoSat-2 data to provide improved observations in the Norwegian coastal zone. We make use of CryoSat-2 SARIn mode observations and determine sea surface heights at 23 tide gauges along the coast, and compare these with independent sea-level observations. Using standard CryoSat-2 geophysical (tide + IB) corrections gives a standard deviation of differences of ˜15 cm with respect to tide-gauge observations. Replacing standard corrections with refined corrections using tide-gauge information suggests an improvement of ˜5 cm. A special case study at the Stavanger tide-gauge shows an improvement of ˜3 cm comparing CryoSat-2 sites and conventional altimeter sites with respect to the tide-gauge. These results highlight a great development of satellite altimetry in coastal zones and raises expectations for future missions such as Sentinel-3.

  13. Verification of Geosat altimetry for operational use in the Gulf of Mexico

    SciTech Connect

    Forristall, G.Z. ); Schaudt, K.J. ); Calman, J. )

    1990-03-15

    Geosat altimetry is well suited for locating large eddies shed by the Loop Current in the Gulf of Mexico. The authors have compared the altimeter data with in situ data obtained during a survey of Eddy Murphy in June 1988. Since there is no significant mean circulation in the central gulf, they used the mean sea surface from the first year of altimeter data as a geoid estimate. The dynamic height change due to the eddy closely matched the altimeter data, although the eddy moved about one third of a degree between the survey and the satellite pass. The motion of the eddy was confirmed by the track of an Argos buoy.

  14. Estimates of Internal Tide Energy Fluxes from Topex/Poseidon Altimetry: Central North Pacific

    NASA Technical Reports Server (NTRS)

    Ray, Richard D.; Cartwright, David E.; Smith, David E. (Technical Monitor)

    2000-01-01

    Energy fluxes for first-mode M(sub 2) internal tides are deduced throughout the central North Pacific Ocean from Topex/Poseidon satellite altimeter data. Temporally coherent internal tide signals in the altimetry, combined with climatological hydrographic data, determine the tidal displacements, pressures, and currents at depth, which yield power transmission rates. For a variety of reasons the deduced rates should be considered lower bounds. Internal tides were found to emanate from several large bathymetric structures, especially the Hawaiian Ridge, where the integrated flux amounts to about six gigawatts. Internal tides are generated at the Aleutian Trench near 172 deg west and propagate southwards nearly 2000 km.

  15. Evaluation of altimetry-derived surface current products using Lagrangian drifter trajectories in the eastern Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Liu, Yonggang; Weisberg, Robert H.; Vignudelli, Stefano; Mitchum, Gary T.

    2014-05-01

    Lagrangian particle trajectory models based on several altimetry-derived surface current products are used to hindcast the drifter trajectories observed in the eastern Gulf of Mexico during May to August 2010 (the Deepwater Horizon oil spill incident). The performances of the trajectory models are gauged in terms of Lagrangian separation distances (d) and a nondimensional skill score (s), respectively. A series of numerical experiments show that these altimetry-based trajectory models have about the same performance, with a certain improvement by adding surface wind Ekman components, especially over the shelf region. However, their hindcast skills are slightly better than those of the data assimilative numerical model output. After 3 days' simulation the altimetry-based trajectory models have mean d values of 75-83 and 34-42 km (s values of 0.49-0.51 and 0.35-0.43) in the Gulf of Mexico deep water area and on the West Florida Continental Shelf, respectively. These satellite altimetry data products are useful for providing essential information on ocean surface currents of use in water property transports, offshore oil and gas operations, hazardous spill mitigation, search and rescue, etc.

  16. Determination of positions and velocity of Riyadh SLR station using satellite laser ranging observations to Lageos1 and Lageos2 satellites

    NASA Astrophysics Data System (ADS)

    Alothman, A.; Schillak, S.

    2012-04-01

    Riyadh Satellite Laser Ranging (SLR) station (7832) has been established since 1995 and situated in the Arabian plate which is countering a north east motion. Laser ranging observations of about 20 global SLR stations to the LAGEOS-1/LAGEOS-2 for 13-year (1996-2010) have been used to determine station positions and velocity of Riyadh SLR station. The NASA Godard's GEODYN-II orbital software has been used to perform orbit determination of these two satellites. The computations were performed based on 114 monthly arcs of observations with total number of normal points of 33708 and 40168 for LAGEOS-1 and LAGEOS-2 respectively. The geocentric coordinates were computed and then transformed to the topocentric North-South, East-West, and Vertical components in the ITRF2008 reference frame. Effects of normal points for each arc and the empirical acceleration coefficients on estimated station coordinates have been investigated. In order to achieve a lower standard deviation (less than 1 cm) of estimated coordinates, the number of the normal points per SLR station had to be greater than 50. The range biases were 7.5mm and 7.2 mm with long term biases stability 2.5 mm and 2.0 mm for LAGEOS-1 and LAGEOS-2 satellites, respectively. RMS of fit was calculated for all stations and found to be 17.2 mm for the whole period. Time series of positions and velocities have been computed for Riyadh SLR station with stability of ±10.1 mm, ±9.3 mm, and ±9.0 mm for X, Y, and Z coordinates, respectively. The estimated velocity is 29.1 mm/year, 31.6 mm/year, and 1.9 mm/year in North-South, East-West and vertical directions, respectively, with a 3D velocity 42.9 mm/year. 3D deviation from the ITRF2008 was equal 4.5 mm. To recover tectonic motion affecting the station, further analysis of velocity estimates has shown general agreement of Riyadh SLR station in comparison with recent GPS estimates for the Arabian plate motion.

  17. Variability in the Gulf of Alaska from Geosat altimetry data

    NASA Technical Reports Server (NTRS)

    Bhaskaran, Shyam; Lagerloef, Gary S. E.; Born, George H.; Emery, W. J.; Leben, Robert R.

    1993-01-01

    Satellite altimetry was used to examine annual and interannual variability in the Gulf of Alaska region. Crossover data from the Geosat Geodetic Mission (GM) and collinear data from the Exact Repeat Mission (ERM) were processed separately to form sea surface height anomalies at grid points. The time series from the GM and ERM were then combined to produce a 3.75-year data set. The time series from the ERM data set agreed fairly well with hydrographic dynamic heights at several locations, with an average correlation of 0.70 between the two data sets. The combined and ERM altimetric data sets were analyzed using empirical orthogonal functions (EOFs). These revealed variability that occurs primarily on annual and interannual time scales. A comparison with EOF analysis of the atmospheric pressure field during the same time periods showed that the annual variation in pressure seemed to be reflected in both the combined and ERM altimetric data sets. The amplitude time series of the first mode in the combined data set was very similar to the North Pacific pressure index during the 1985-1989 time frame. The maximum correlation was at a lag of 250 days. Finally, an interannual mode was present in all three data sets which was closely linked to the baroclinic variations measured by the hydrographic data.

  18. Seasonal variability in global sea level observed with Geosat altimetry

    NASA Technical Reports Server (NTRS)

    Zlotnicki, V.; Fu, L.-L.; Patzert, W.

    1989-01-01

    Time changes in global mesoscale sea level variances were observed with satellite altimetry between November 1986 and March 1988, showing significant, geographically coherent seasonal patterns. The NE Pacific and NE Atlantic variances show the most reliable patterns, higher than their yearly averages in both the fall and winter. The response to wind forcing appears as the major contributor to the NE Pacific and Atlantic signals; errors in the estimated inverse barometer response due to errors in atmospheric pressure, residual orbit errors, and errors in sea state bias are evaluated and found to be negligible contributors to this particular signal. The equatorial regions also show significant seasonal patterns, but the uncertainties in the wet tropospheric correction prevent definitive conclusions. The western boundary current changes are very large but not statistically significant. Estimates of the regression coefficient between sea level and significant wave height, an estimate of the sea state bias correction, range between 2.3 and 2.9 percent and vary with the type of orbit correction applied.

  19. Global ocean tide mapping using TOPEX/Poseidon altimetry

    NASA Technical Reports Server (NTRS)

    Sanchez, Braulio V.; Cartwright, D. E.; Estes, R. H.; Williamson, R. G.; Colombo, O. L.

    1991-01-01

    The investigation's main goals are to produce accurate tidal maps of the main diurnal, semidiurnal, and long-period tidal components in the world's deep oceans. This will be done by the application of statistical estimation techniques to long time series of altimeter data provided by the TOPEX/POSEIDON mission, with additional information provided by satellite tracking data. In the prelaunch phase, we will use in our simulations and preliminary work data supplied by previous oceanographic missions, such as Seasat and Geosat. These results will be of scientific interest in themselves. The investigation will also be concerned with the estimation of new values, and their uncertainties, for tidal currents and for the physical parameters appearing in the Laplace tidal equations, such as bottom friction coefficients and eddy viscosity coefficients. This will be done by incorporating the altimetry-derived charts of vertical tides as boundary conditions in the integration of those equations. The methodology of the tidal representation will include the use of appropriate series expansions such as ocean-basin normal modes and spherical harmonics. The results of the investigation will be space-determined tidal models of coverage and accuracy superior to that of the present numerical models of the ocean tides, with the concomitant benefits to oceanography and associated disciplinary fields.

  20. Mass-induced sea level variations in the Red Sea from GRACE, steric-corrected altimetry, in situ bottom pressure records, and hydrographic observations

    NASA Astrophysics Data System (ADS)

    Feng, W.; Lemoine, J.-M.; Zhong, M.; Hsu, H. T.

    2014-08-01

    An annual amplitude of ∼18 cm mass-induced sea level variations (SLV) in the Red Sea is detected from the Gravity Recovery and Climate Experiment (GRACE) satellites and steric-corrected altimetry from 2003 to 2011. The annual mass variations in the region dominate the mean SLV, and generally reach maximum in late January/early February. The annual steric component of the mean SLV is relatively small (<3 cm) and out of phase of the mass-induced SLV. In situ bottom pressure records at the eastern coast of the Red Sea validate the high mass variability observed by steric-corrected altimetry and GRACE. In addition, the horizontal water mass flux of the Red Sea estimated from GRACE and steric-corrected altimetry is validated by hydrographic observations.

  1. Verification for robustness to laser-induced damage for the Aladin instrument on the ADM-Aeolus satellite

    NASA Astrophysics Data System (ADS)

    Wernham, Denny; Ciapponi, Alessandra; Riede, Wolfgang; Allenspacher, Paul; Era, Fabio; D'Ottavi, Alessandro; Thibault, Dominique

    2016-12-01

    The Aladin instrument will fly on the European Space Agency's ADM Aeolus satellite. The instrument is a Doppler wind LIDAR, primarily designed to measure global wind profiles to improve the accuracy of numerical weather prediction models. At the heart of the instrument is a frequency stabilized 355nm laser which will emit approximately 100mJ of energy in the form of 20ns pulses with a fluence around 1Jcm-2. The pulse repetition frequency is 50Hz meaning that Aladin will eventually have to accumulate 5Gshots over its 3 years planned lifetime in orbit. Due to anomalies that have occurred on previous spaceborne lasers, as well as a number of failures that we have observed in previous tests, an extensive development and verification campaign was undertaken in order to ensure that the Aladin instrument is robust enough to survive the mission. In this paper, we shall report the logic and the results of this verification campaign.

  2. Effect of non-Kolmogorov turbulence on BER performance in uplink ground-to-satellite laser communication

    NASA Astrophysics Data System (ADS)

    Wang, Yi; Zhang, Ao; Ma, Jing; Guo, Qiang

    2016-12-01

    Based on the non-Kolmogorov turbulence model of the stratosphere, a theoretical model for the influence of the angle of arrival (AOA) fluctuations on the performance of the bit error rate (BER) is established. A closed form expression of BER is then derived based on this model. Then, considering the combined effect of scintillation, beam wander and AOA fluctuations, the probability density function of the received intensity and the closed form expressions of BER for uplink are derived. Coherent detection of Circle Polarization Shift Keying modulation which is suitable for ground-to-satellite laser communication is employed. For an uplink, the BER performance is emulation analyzed and compared to the