WorldWideScience

Sample records for satellite altimetry based

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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.

  5. Observing storm surges from satellite altimetry

    Science.gov (United States)

    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.

  6. Arctic Sea Level During the Satellite Altimetry Era

    Science.gov (United States)

    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.

  7. Arctic Sea Level During the Satellite Altimetry Era

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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. Arctic sea-level reconstruction analysis using recent satellite altimetry

    DEFF Research Database (Denmark)

    Svendsen, Peter Limkilde; Andersen, Ole Baltazar; Nielsen, Allan Aasbjerg

    2014-01-01

    We present a sea-level reconstruction for the Arctic Ocean using recent satellite altimetry data. The model, forced by historical tide gauge data, is based on empirical orthogonal functions (EOFs) from a calibration period; for this purpose, newly retracked satellite altimetry from ERS-1 and -2...... and Envisat has been used. Despite the limited coverage of these datasets, we have made a reconstruction up to 82 degrees north for the period 1950–2010. We place particular emphasis on determining appropriate preprocessing for the tide gauge data, and on validation of the model, including the ability...... to reconstruct known data. The relationship between the reconstruction and climatic variables, such as atmospheric pressure, and climate oscillations, including the Arctic Oscillation (AO), is examined....

  10. Satellite Altimetry for Rivers : Review and Perspectives

    Science.gov (United States)

    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

  11. River monitoring from satellite radar altimetry in the Zambezi River basin

    DEFF Research Database (Denmark)

    Michailovsky, Claire Irene B.; McEnnis, S.; Berry, P. A. M.;

    2012-01-01

    Satellite radar altimetry can be used to monitor surface water levels from space. While current and past altimetry missions were designed to study oceans, retracking the waveforms returned over land allows data to be retrieved for smaller water bodies or narrow rivers. The objective of this study...... is the assessment of the potential for river monitoring from radar altimetry in terms of water level and discharge in the Zambezi River basin. Retracked Envisat altimetry data were extracted over the Zambezi River basin using a detailed river mask based on Landsat imagery. This allowed for stage measurements...

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

    DEFF Research Database (Denmark)

    Korsgaard, Niels Jákup; Kjær, Kurt H.; Nuth, Christopher

    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...

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

    Science.gov (United States)

    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.

  14. A Fiducial Reference Stie for Satellite Altimetry in Crete, Greece

    Science.gov (United States)

    Mertikas, Stelios; Donlon, Craig; Mavrocordatos, Constantin; Bojkov, Bojan; Femenias, Pierre; Parrinello, Tommaso; Picot, Nicolas; Desjonqueres, Jean-Damien; Andersen, Ole Baltazar

    2016-08-01

    With the advent of diverse satellite altimeters and variant measuring techniques, it has become mature in the scientific community, that an absolute reference Cal/Val site is regularly maintained to define, monitor, control the responses of any altimetric system.This work sets the ground for the establishment of a Fiducial Reference Site for ESA satellite altimetry in Gavdos and West Crete, Greece. It will consistently and reliably determine (a) absolute altimeter biases and their drifts; (b) relative bias among diverse missions; but also (c) continuously and independently connect different missions, on a common and reliable reference and also to SI-traceable measurements. Results from this fiducial reference site will be based on historic Cal/Val site measurement records, and will be the yardstick for building up capacity for monitoring climate change. This will be achieved by defining and assessing any satellite altimeter measurements to known, controlled and absolute reference signals with different techniques, processes and instrumentation.

  15. Satellite Altimetry, Ocean Circulation, and Data Assimilation

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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.

  17. Observing and Modelling the HighWater Level from Satellite Radar Altimetry During Tropical Cyclones

    DEFF Research Database (Denmark)

    Deng, Xiaoli; Gharineiat, Zahra; Andersen, Ole Baltazar

    2016-01-01

    This paper investigates the capability of observing tropical cyclones using satellite radar altimetry. Two representative cyclones Yasi (February 2011) and Larry (March 2006) in the northeast Australian coastal area are selected based also on available tide gauge sea level measurements. It is shown...... levels predicted by the model taken into account of both altimetry and tide-gauge data agree well with those observed at Townsville during cyclone Larry....

  18. Interdisciplinary Earth Science Applications Using Satellite Radar Altimetry

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  20. Time-evolving mass loss of the Greenland ice sheet from satellite altimetry

    Directory of Open Access Journals (Sweden)

    R. T. W. L. Hurkmans

    2014-02-01

    Full Text Available Mass changes of the Greenland ice sheet may be estimated by the Input Output Method (IOM, satellite gravimetry, or via surface elevation change rates (dH / dt. Whereas the first two have been shown to agree well in reconstructing mass changes over the last decade, there are few decadal estimates from satellite altimetry and none that provide a time evolving trend that can be readily compared with the other methods. Here, we interpolate radar and laser altimetry data between 1995 and 2009 in both space and time to reconstruct the evolving volume changes. A firn densification model forced by the output of a regional climate model is used to convert volume to mass. We consider and investigate the potential sources of error in our reconstruction of mass trends, including geophysical biases in the altimetry, and the resulting mass change rates are compared to other published estimates. We find that mass changes are dominated by SMB until about 2001, when mass loss rapidly accelerates. The onset of this acceleration is somewhat later, and less gradual, compared to the IOM. Our time averaged mass changes agree well with recently published estimates based on gravimetry, IOM, laser altimetry, and with radar altimetry when merged with airborne data over outlet glaciers. We demonstrate, that with appropriate treatment, satellite radar altimetry can provide reliable estimates of mass trends for the Greenland ice sheet. With the inclusion of data from CryoSat II, this provides the possibility of producing a continuous time series of regional mass trends from 1992 onward.

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

    Science.gov (United States)

    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.

  2. Flood Monitoring and Hydrologic Studies Using Retracked Satellite Radar Altimetry

    Science.gov (United States)

    Zhang, M.; Shum, C.; Lee, H.; Alsdorf, D.; Schwartz, F.

    2008-12-01

    Nadir, pulse-limited radar altimetry measurements have been used to monitor large surface-water bodies. In spite of progress, there is a need for a robust and automated procedure, which allows classification and stage measurements in small water bodies, which lying along the orbital path, using multiple radar altimeter measurements. Here we used an algorithm, which is mainly based on radar scatter waveform response and statistical analysis of mean and standard deviation of the resulting water level change to classify surface- waters from other land covers. We tested the algorithm using 10-Hz retracked radar altimetry measurements from TOPEX over regions including the Amazon River basin, the Prairie Pothole Region in North America, and south-western Taiwan. The estimated water-level stages are compared with data from available stage measurements, and altimetry data available from public data centers. We also applied the algorithm to study the 1997 hundred-year Red River flood, and the June 2008 fifty-year flood in the Upper Midwest of the United States. For the1997 flood, it is found that the flooded regions detected by altimetry include the Red River Basin in North Dakota and Minnesota, the Missouri River Basin in North Dakota and South Dakota, the Minnesota River Basin and the Mississippi River Basin in Minnesota and Iowa. The extent of the flood agrees with the USGS record. The observed water height in Grand Forks reaches 6 meters above the normal. The ENVISAT altimetry is shown to be able to track the ebb and recede of the 2008 Iowa City flood. The results of this study could be applied to provide improved accuracy and potentially automated classification of nadir radar altimetry observed small inland water body measurements for hydrologic studies and for flood monitoring.

  3. SEA SURFACE ALTIMETRY BASED ON AIRBORNE GNSS SIGNAL MEASUREMENTS

    Directory of Open Access Journals (Sweden)

    K. Yu

    2012-07-01

    Full Text Available In this study the focus is on ocean surface altimetry using the signals transmitted from GNSS (Global Navigation Satellite System satellites. A low-altitude airborne experiment was recently conducted off the coast of Sydney. Both a LiDAR experiment and a GNSS reflectometry (GNSS-R experiment were carried out in the same aircraft, at the same time, in the presence of strong wind and rather high wave height. The sea surface characteristics, including the surface height, were derived from processing the LiDAR data. A two-loop iterative method is proposed to calculate sea surface height using the relative delay between the direct and the reflected GNSS signals. The preliminary results indicate that the results obtained from the GNSS-based surface altimetry deviate from the LiDAR-based results significantly. Identification of the error sources and mitigation of the errors are needed to achieve better surface height estimation performance using GNSS signals.

  4. Mesoscale eddies in the northeastern Pacific tropical-subtropical transition zone : statistical characterization from satellite altimetry

    OpenAIRE

    Kurczyn, J. A.; Beier, Emilio; Lavín, Miguel,; Chaigneau, Alexis

    2012-01-01

    Mesoscale eddies in the northeastern Pacific tropical-subtropical transition zone (16 degrees N-30 degrees N; 130 degrees W-102 degrees W) are analyzed using nearly 18 years of satellite altimetry and an automated eddy-identification algorithm. Eddies that lasted more than 10 weeks are described based on the analysis of 465 anticyclonic and 529 cyclonic eddy trajectories. We found three near-coastal eddy-prolific areas: (1) Punta Eugenia, (2) Cabo San Lucas, and (3) Cabo Corrientes. These thr...

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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

  7. The DNSC08GRA global marine gravity field from double retracked satellite altimetry

    DEFF Research Database (Denmark)

    Andersen, Ole Baltazar; Knudsen, Per; Berry, P.A.M.

    2010-01-01

    Satellite radar altimetry has been monitoring the earth's oceans from space for several decades. However, only the GEOSAT and ERS-1 geodetic mission data recorded more than a decade ago provide altimetry with adequate spatial coverage to derive a high-resolution marine gravity field. The original...

  8. Sea level reconstruction from satellite altimetry and tide gauge data

    DEFF Research Database (Denmark)

    Svendsen, Peter Limkilde; Andersen, Ole Baltazar; Nielsen, Allan Aasbjerg

    2012-01-01

    transformations such as maximum autocorrelation factors (MAF), which better take into account the spatio-temporal structure of the variation. Rather than trying to maximize the amount of variance explained, the MAF transform considers noise to be uncorrelated with a spatially or temporally shifted version...... of itself, whereas the desired signal will exhibit autocorrelation. This will be applied to a global dataset, necessitating wrap-around consideration of spatial shifts. Our focus is a timescale going back approximately 50 years, allowing reasonable global availability of tide gauge data. This allows......Ocean satellite altimetry has provided global sets of sea level data for the last two decades, allowing determination of spatial patterns in global sea level. For reconstructions going back further than this period, tide gauge data can be used as a proxy. We examine different methods of combining...

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

    Science.gov (United States)

    Sulistioadi, Yohanes Budi

    closer to the true water level anomaly than the water level anomaly converted from HEC-HMS simulated discharge. Some critical recommendations for future studies include the use of waveform shape selection procedure in the satellite altimetry based water level measurement of small and medium-sized rivers and small lakes, as well as the exploration to implement data assimilation between satellite altimetry and the hydrologic model for better discharge and water level estimations.

  10. Time evolving mass loss of the Greenland ice sheet from satellite altimetry

    Science.gov (United States)

    Hurkmans, Ruud; Bamber, Jonathan; Davis, Curt

    2013-04-01

    Mass changes of the Greenland ice sheet (GrIS) may be estimated by the mass budget method (MBM), satellite gravimetry, or via surface elevation changes (dH/dt). Whereas the first two have been shown to agree well in reconstructing mass changes over the last decade, there are few decadal estimates from satellite altimetry and none that provide a time evolving trend that can be readily compared with the other methods. Here, we interpolate radar and laser altimetry data between 1995 and 2009 in both space and time to reconstruct the evolving volume changes. The interpolation algorithm uses ice velocity to constrain the interpolated dH/dt in sparsely sampled areas, in particular narrow, rapidly changing outlet glaciers. The underlying assumption that the spatial patterns of surface velocity and dH/dt are linearly related, which was previously demonstrated for Jakobshavn Isbrae, is here validated for other major outlet glaciers and extended to the entire GrIS. A firn densification model forced by the output of a regional climate model is used to convert volume to mass. We consider and investigate the potential sources of error in our reconstruction of mass trends, and the resulting mass changes are compared to other published estimates. We find that mass changes are dominated by SMB until about 2001, when mass loss rapidly accelerates. The onset of this acceleration is somewhat later, and less gradual, compared to MBM. Our time averaged mass changes agree with published estimates based on gravimetry, MBM, laser altimetry, and with radar altimetry when this is merged with airborne data over outlet glaciers.

  11. Ice Surface Elevation Changes in East Antarctica from Satellite Altimetry

    Science.gov (United States)

    Zwally, H. Jay; Brenner, Anita C.; DiMarzio, John

    1998-01-01

    Estimates of the overall mass balance and seasonal and inter-annual variations in the surface mass balance are obtainable from time-series of ice surface elevations measured by satellite altimetry. Beginning in 2001, NASA's ICESat laser altimeter and lidar mission will significantly improve the range accuracy, the orbit accuracy, and the spatial coverage for measurement of ice sheet elevations (to 86 S) , as compared to previous radar altimeters designed for ocean measurements The radar altimeters on Seasat and Geosat provided ice sheet measurements to 72 S, and on ERS-1 and ERS-2 to 81 S. Although radar altimetry has significant limitations in coverage (due to loss of tracking) and accuracy over sloping surfaces, information on ice-sheet surface-elevation changes has been derived for parts of Antarctica. Recently, the accuracy of the ice measurements by Seasat (3 months of 1978) and Geosat (1985 to 1989) have been improved by new calculations of the satellite orbit heights and other altimeter corrections. Residual orbit errors and inter-satellite biases are evaluated by crossover analysis and by global adjustments to an ocean surface derived from altimeter data. The standard deviation of the orbit error is less than 9 cm, and the long-term trend in the error appears to be less than 1 cm/yr. Orbit errors can be further reduced by adjustment to the ocean surface, but false signals of several cm/yr may be also introduced by the adjustments. These false signals are caused mainly by residual errors in the altimeter corrections over the ocean, and secondary by real changes in the ocean surface elevation. Maps of ice sheet elevation changes north of 72 S are derived from Seasat-Geosat crossovers and from 4.5 years of Geosat crossovers. A notable ice thinning rate of about 50 cm/yr is found at elevations below 2200 meters between 70 and 72 S to the East of the Amery ice shelf, in both the Seasat-Geosat and Geosat-Geosat time intervals Above 2200 meters, to the ridge

  12. River monitoring from satellite radar altimetry in the Zambezi River Basin

    Directory of Open Access Journals (Sweden)

    C. I. Michailovsky

    2012-03-01

    Full Text Available Satellite radar altimetry can be used to monitor surface water levels from space. While current and past altimetry missions were designed to study oceans, retracking the waveforms returned over land allows data to be retrieved for smaller water bodies or narrow rivers. In this study, retracked Envisat altimetry data was extracted over the Zambezi River Basin using a detailed river mask based on Landsat imagery. This allowed for stage measurements to be obtained for rivers down to 80 m wide with an RMSE relative to in situ levels of 0.32 to 0.72 m at different locations. The altimetric levels were then converted to discharge using three different methods adapted to different data-availability scenarios: first with an in situ rating curve available, secondly with one simultaneous field measurement of cross-section and discharge, and finally with only historical discharge data available. For the two locations at which all three methods could be applied the accuracies of the different methods were found to be comparable, with RMSE values ranging from 5.5 to 7.4 % terms of high flow estimation relative to in situ gauge measurements. The precision obtained with the different methods was analyzed by running Monte Carlo simulations and also showed comparable values for the three approaches with standard deviations found between 8.2 and 25.8 % of the high flow estimates.

  13. River monitoring from satellite radar altimetry in the Zambezi River basin

    Directory of Open Access Journals (Sweden)

    C. I. Michailovsky

    2012-07-01

    Full Text Available Satellite radar altimetry can be used to monitor surface water levels from space. While current and past altimetry missions were designed to study oceans, retracking the waveforms returned over land allows data to be retrieved for smaller water bodies or narrow rivers. The objective of this study is the assessment of the potential for river monitoring from radar altimetry in terms of water level and discharge in the Zambezi River basin. Retracked Envisat altimetry data were extracted over the Zambezi River basin using a detailed river mask based on Landsat imagery. This allowed for stage measurements to be obtained for rivers down to 80 m wide with an RMSE relative to in situ levels of 0.32 to 0.72 m at different locations. The altimetric levels were then converted to discharge using three different methods adapted to different data-availability scenarios: first with an in situ rating curve available, secondly with one simultaneous field measurement of cross-section and discharge, and finally with only historical discharge data available. For the two locations at which all three methods could be applied, the accuracies of the different methods were found to be comparable, with RMSE values ranging from 4.1 to 6.5% of the mean annual in situ gauged amplitude for the first method and from 6.9 to 13.8% for the second and third methods. The precision obtained with the different methods was analyzed by running Monte Carlo simulations and also showed comparable values for the three approaches with standard deviations found between 5.7 and 7.2% of the mean annual in situ gauged amplitude for the first method and from 8.7 to 13.0% for the second and third methods.

  14. Tests of daily time variable Earth gravity field solutions for precise orbit determination of altimetry satellites

    Science.gov (United States)

    Rudenko, Sergei; Gruber, Christian

    2016-04-01

    This study makes use of current GFZ monthly and daily gravity field products from 2002 to 2014 based on radial basis functions (RBF) instead of time variable gravity field modeling for precise orbit determination of altimetry satellites. Since some monthly solutions are missing in the GFZ GRACE RL05a solution and in order to reach a better quality for the precise orbit determination, daily generated RBF solutions obtained from Kalman filtered GRACE data processing and interpolated in case of gaps have been used. Moreover, since the geopotential coefficients of low degrees are better determined using SLR observations to geodetic satellites like Lageos, Stella, Starlette and Ajisai than from GRACE observations, these terms are co-estimated in the RBF solutions by using apriori SLR-derived values up to degree and order 4. Precise orbits for altimetry satellites Envisat (2002-2012), Jason-1 (2002-2013) and Jason-2 (2008-2014) are then computed over the given time intervals using this approach and compared with the orbits obtained when using other models such as EIGEN-6S4. An analysis of the root-mean-square values of the observation fits of SLR and DORIS observations and the orbit arcs overlaps will allow us to draw a conclusion on the quality of the RBF solution and to use these new trajectories for sea level trend estimates and geophysical application.

  15. Assimilation of satellite altimetry data in hydrological models for improved inland surface water information: Case studies from the "Sentinel-3 Hydrologic Altimetry Processor prototypE" project (SHAPE)

    Science.gov (United States)

    Gustafsson, David; Pimentel, Rafael; Fabry, Pierre; Bercher, Nicolas; Roca, Mónica; Garcia-Mondejar, Albert; Fernandes, Joana; Lázaro, Clara; Ambrózio, Américo; Restano, Marco; Benveniste, Jérôme

    2017-04-01

    This communication is about the Sentinel-3 Hydrologic Altimetry Processor prototypE (SHAPE) project, with a focus on the components dealing with assimilation of satellite altimetry data into hydrological models. The SHAPE research and development project started in September 2015, within the Scientific Exploitation of Operational Missions (SEOM) programme of the European Space Agency. The objectives of the project are to further develop and assess recent improvement in altimetry data, processing algorithms and methods for assimilation in hydrological models, with the overarching goal to support improved scientific use of altimetry data and improved inland water information. The objective is also to take scientific steps towards a future Inland Water dedicated processor on the Sentinel-3 ground segment. The study focuses on three main variables of interest in hydrology: river stage, river discharge and lake level. The improved altimetry data from the project is used to estimate river stage, river discharge and lake level information in a data assimilation framework using the hydrological dynamic and semi-distributed model HYPE (Hydrological Predictions for the Environment). This model has been developed by SMHI and includes data assimilation module based on the Ensemble Kalman filter method. The method will be developed and assessed for a number of case studies with available in situ reference data and satellite altimetry data based on mainly the CryoSat-2 mission on which the new processor will be run; Results will be presented from case studies on the Amazon and Danube rivers and Lake Vänern (Sweden). The production of alti-hydro products (water level time series) are improved thanks to the use of water masks. This eases the geo-selection of the CryoSat-2 altimetric measurements since there are acquired from a geodetic orbit and are thus spread along the river course in space and and time. The specific processing of data from this geodetic orbit space

  16. Satellite radar altimetry for monitoring small river and lakes in Indonesia

    Directory of Open Access Journals (Sweden)

    Y. B. Sulistioadi

    2014-03-01

    Full Text Available Remote sensing and satellite geodetic observations are capable for hydrologic monitoring of freshwater resources. For the case of satellite radar altimetry, limited temporal resolutions (e.g., satellite revisit period prohibit the use of this method for a short ( To address this scientific challenge, this study tries 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. This study addresses the humid tropics of Southeast Asia, specifically in Indonesia, where similar studies do not yet exist and makes use Level 2 radar altimeter measurements generated by European Space Agency's (ESA's Envisat (Environmental Satellite mission. This experiment proves that satellite altimetry provides a good alternative, or the only means in some regions, to measure the water level of medium-sized river (200–800 m width and small lake (extent 2 in Southeast Asia humid tropic with reasonable accuracy. In addition, the procedure to choose retracked Envisat altimetry water level heights via identification or selection of standard waveform shapes for inland water is recommended and should be a standard measure especially over small rivers and lakes. This study also found that Ice-1 is not necessarily the best retracker as reported by previous studies, among the four standard waveform retracking algorithms for Envisat radar altimetry observing inland water bodies.

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

    Science.gov (United States)

    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

  18. Satellite radar altimetry for monitoring small rivers and lakes in Indonesia

    NARCIS (Netherlands)

    Sulistioadi, Y.B.; Tseng, K.H.; Shum, C.K.; Hidayat, Hidayat; Sumaryono, M.; Suhardiman, A.; Setiawan, F.; Sunarso, S.

    2015-01-01

    Remote sensing and satellite geodetic observations are capable of hydrologic monitoring of freshwater resources. Although satellite radar altimetry has been used in monitoring water level or discharge, its use is often limited to monitoring large rivers (>1 km) with longer interval periods (&g

  19. Sea level variability in the Arctic Ocean observed by satellite altimetry

    Directory of Open Access Journals (Sweden)

    P. Prandi

    2012-07-01

    Full Text Available We investigate sea level variability in the Arctic Ocean from observations. Variability estimates are derived both at the basin scale and on smaller local spatial scales. The periods of the signals studied vary from high frequency (intra-annual to long term trends. We also investigate the mechanisms responsible for the observed variability. Different data types are used, the main one being a recent reprocessing of satellite altimetry data in the Arctic Ocean.

    Satellite altimetry data is compared to tide gauges measurements, steric sea level derived from temperature and salinity fields and GRACE ocean mass estimates. We establish a consistent regional sea level budget over the GRACE availability era (2003–2009 showing that the sea level drop observed by altimetry over this period is driven by ocean mass loss rather than steric effects. The comparison of altimetry and tide gauges time series show that the two techniques are in good agreement regarding sea level trends. Coastal areas of high variability in the altimetry record are also consistent with tide gauges records. An EOF analysis of September mean altimetry fields allows identifying two regions of wind driven variability in the Arctic Ocean: the Beaufort Gyre region and the coastal European and Russian Arctic. Such patterns are related to atmospheric regimes through the Arctic Oscillation and Dipole Anomaly.

  20. Improved sea level record over the satellite altimetry era (1993-2010) from the Climate Change Initiative project

    DEFF Research Database (Denmark)

    Ablain, M.; Cazenave, A.; Larnicol, G.

    2015-01-01

    Sea level is one of the 50 Essential Climate Variables (ECVs) listed by the Global Climate Observing System (GCOS) in climate change monitoring. In the past two decades, sea level has been routinely measured from space using satellite altimetry techniques. In order to address a number of importan...... present preliminary independent validations of the SL_cci products, based on tide gauges comparison and a sea level budget closure approach, as well as comparisons with ocean reanalyses and climate model outputs....

  1. Vertical Motion Determined Using Satellite Altimetry and Tide Gauges

    Directory of Open Access Journals (Sweden)

    Chung-Yen Kuo

    2008-01-01

    Full Text Available A robust method to estimate vertical crustal motions by combining geocentric sea level measurements from decadal (1992 - 2003 TOPEX/POSEIDON satellite altimetry and long-term (> 40 years relative sea level records from tide gauges using a novel Gauss-Markov stochastic adjustment model is presented. These results represent an improvement over a prior study (Kuo et al. 2004 in Fennoscandia, where the observed vertical motions are primarily attributed to the incomplete Glacial Isostatic Adjustment (GIA in the region since the Last Glacial Maximum (LGM. The stochastic adjustment algorithm and results include a fully-populated a priori covariance matrix. The algorithm was extended to estimate vertical motion at tide gauge locations near open seas and around semi-enclosed seas and lakes. Estimation of nonlinear vertical motions, which could result from co- and postseismic deformations, has also been incorporated. The estimated uncertainties for the vertical motion solutions in coastal regions of the Baltic Sea and around the Great Lakes are in general < 0.5 mm yr-1, which is a significant improvement over existing studies. In the Baltic Sea, the comparisons of the vertical motion solution with 10 collocated GPS radial rates and with the BIFROST GIA model show differences of 0.2 ¡_ 0.9 and 1.6 ¡_ 1.8 mm yr-1, respectively. For the Great Lakes region, the comparisons with the ICE-3G model and with the relative vertical motion estimated using tide gauges only (Mainville and Craymer 2005 show differences of -0.2 ¡_ 0.6 and -0.1 ¡_ 0.5 mm yr-1, respectively. The Alaskan vertical motion solutions (linear and nonlinear models have an estimated uncertainty of ~1.2 - 1.6 mm yr-1, which agree qualitatively with GPS velocity and tide gauge-only solutions (Larsen et al. 2003. This innovative technique could potentially provide improved estimates of the vertical motion globally where long-term tide gauge records exist.

  2. Arctic Sea Level During the Satellite Altimetry Era

    DEFF Research Database (Denmark)

    Carret, A.; Johannessen, J. A.; Andersen, Ole Baltazar

    2017-01-01

    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...

  3. Long-term vertical land motion from double-differenced tide gauge and satellite altimetry data

    Science.gov (United States)

    Santamaría-Gómez, Alvaro; Gravelle, Médéric; Wöppelmann, Guy

    2014-03-01

    We present a new approach to estimate precise long-term vertical land motion (VLM) based on double-differences of long tide gauge (TG) and short altimetry data. We identify and difference rates of pairs of highly correlated sea level records providing relative VLM estimates that are less dependent on record length and benefit from reduced uncertainty and mitigated biases (e.g. altimeter drift). This approach also overcomes the key limitation of previous techniques in that it is not geographically limited to semi-enclosed seas and can thus be applied to estimate VLM at TGs along any coast, provided data of sufficient quality are available. Using this approach, we have estimated VLM at a global set of 86 TGs with a median precision of 0.7 mm/year in a conventional reference frame. These estimates were compared to previous VLM estimates at TGs in the Baltic Sea and to estimates from co-located Global Positioning System (GPS) stations and Glacial Isostatic Adjustment (GIA) predictions. Differences with respect to the GPS and VLM estimates from previous studies resulted in a scatter of around 0.6 mm/year. Differences with respect to GIA predictions had a larger scatter in excess of 1 mm/year. Until satellite altimetry records reach enough length to estimate precise VLM at each TG, this new approach constitutes a substantial advance in the geodetic monitoring of TGs with major applications in long-term sea level change and climate change studies.

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

    Science.gov (United States)

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

    2016-11-01

    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.

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

    Science.gov (United States)

    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.

  6. Combining satellite altimetry and gravimetry data to improve Antarctic mass balance and gia estimates

    NARCIS (Netherlands)

    Gunter, B.C.; Didova, O.; Riva, R.E.M.; van den Broeke, M.R.; Ligtenberg, S.R.M.; Lenaerts, J.T.M.; King, M.; Urban, T.

    2012-01-01

    This study explores an approach that simultaneously estimates Antarctic mass balance and glacial isostatic adjustment (GIA) through the combination of satellite gravity and altimetry data sets. The results improve upon previous efforts by incorporating reprocessed data sets over a longer period of t

  7. Combining satellite altimetry and gravimetry data to improve Antarctic mass balance and gia estimates

    NARCIS (Netherlands)

    Gunter, B.C.; Didova, O.; Riva, R.E.M.; van den Broeke, M.R.; Ligtenberg, S.R.M.; Lenaerts, J.T.M.; King, M.; Urban, T.

    2012-01-01

    This study explores an approach that simultaneously estimates Antarctic mass balance and glacial isostatic adjustment (GIA) through the combination of satellite gravity and altimetry data sets. The results improve upon previous efforts by incorporating reprocessed data sets over a longer period of

  8. Merging of airborne gravity and gravity derived from satellite altimetry: Test cases along the coast of greenland

    DEFF Research Database (Denmark)

    Olesen, Arne Vestergaard; Andersen, Ole Baltazar; Tscherning, C.C.

    2002-01-01

    for the use of gravity data especially, when computing geoid models in coastal regions. The presence of reliable marine gravity data for independent control offers an opportunity to study procedures for the merging of airborne and satellite data around Greenland. Two different merging techniques, both based...... on collocation, are investigated in this paper. Collocation offers a way of combining the individual airborne gravity observation with either the residual geoid observations derived from satellite altimetry or with gravity derived from these data using the inverse Stokes method implemented by Fast Fourier...

  9. A review of satellite radar altimetry applied to coastal ocean studies

    Science.gov (United States)

    Vignudelli, Stefano

    2016-07-01

    Satellite radar altimetry is today considered a mature technique in open ocean. The data stream from the various satellite missions are routinely used for a number of applications. In the last decade, significant research has been carried out into overcoming the problems to extend the capabilities of radar altimeters to the coastal zone, with the aim to integrate the altimeter-derived measurements of sea level, wind speed and significant wave height into coastal ocean observing systems. More/better (and new) datasets are being produced. Moreover, the advent of new satellite missions, both nadir-viewing (e.g., Sentinel-3) and wide-swath (e.g. SWOT), should globally improve both quantity and quality of coastal altimetry data. In this talk, after a brief review of the challenges in coastal altimetry and description of the new products, we showcase some application examples how the new products can be exploited, and we discuss directions for a global coastal altimetry dataset as an asset for long term monitoring of sea level and sea state in the coastal ocean.

  10. The role of satellite altimetry in gravity field modelling in coastal areas

    DEFF Research Database (Denmark)

    Andersen, Ole Baltazar; Knudsen, Per

    2000-01-01

    During recent years altimetry from the two geodetic missions of GEOSAT and ERS-1 has enabled the derivation of high resolution near global gravity field from altimetry [Andersen and Knudsen, 1995, 1996; Sandwell and Smith, 1997]. Altimetric gravity fields are unique in the sense that they provide...... global uniform gravity information with very high resolution, and these global marine gravity fields are registered on a two by two minute grid corresponding to 4 by 4 kilometres at the equator. In this presentation several coastal complications in deriving the marine gravity field from satellite...... altimetry will be investigated using the KMS98 gravity field. Comparison with other sources of gravity field information like airborne and marine gravity observations will be carried out and two fundamentally different test areas (Azores and Skagerak) will be studied to investigated the different role...

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

    Science.gov (United States)

    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.

  12. The use of airborne laser data to calibrate satellite radar altimetry data over ice sheets

    DEFF Research Database (Denmark)

    Ekholm, Simon; Bamber, J.L.; Krabill, W.B.

    2002-01-01

    -correlated noise can be effectively removed by the so-called relocation error correction method. The adjustment, however, produces a different spatial sampling of the data, which introduces a non-negligible slope related bias to the computation of digital elevation models. In this paper we incorporate high......Satellite radar altimetry is the most important data source for ice sheet elevation modeling but it is well established that the accuracy of such data from satellite borne radar altimeters degrade seriously with increasing surface slope and level of roughness. A significant fraction of the slope...... as a linear function of surface slope. This linear correspondence is in turn tested as a model for adjusting the satellite altimetry data for the observed slope correlated bias. The adjustment is shown to have a significant effect in terms of reducing the bias, thus improving the modeling accuracy of the data....

  13. A fiducial reference site for satellite altimetry in Crete, Greece

    DEFF Research Database (Denmark)

    Mertikas, Stelios; Donlon, Craig; Mavrokordatos, Constantin;

    With the advent of diverse satellite altimeters and variant measuring techniques, it has become mature in the scientific community, that an absolute reference Cal/Val site is regularly maintained to define, monitor, control the responses of any altimetric system. This work sets the ground......, on a common and reliable reference and also to SI-traceable measurements. Results from this fiducial reference site will be based on historic Cal/Val site measurement records, and will be the yardstick for building up capacity for monitoring climate change. This will be achieved by defining and assessing any...

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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.

  16. Water storage variations in the Poyang Lake Basin estimated from GRACE and satellite altimetry

    Institute of Scientific and Technical Information of China (English)

    Yang Zhou; Shuanggen Jin; Robert Tenzer; Jialiang Feng

    2016-01-01

    The Gravity Recovery and Climate Experiment (GRACE) satellite mission provides a unique opportunity to quantitatively study terrestrial water storage (TWS) variations. In this paper, the terrestrial water storage variations in the Poyang Lake Basin are recovered from the GRACE gravity data from January 2003 to March 2014 and compared with the Global Land Data Assimilation System (GLDAS) hydrological models and satellite altimetry. Further-more, the impact of soil moisture content from GLDAS and rainfall from the Tropical Rainfall Measuring Mission (TRMM) on TWS variations are investigated. Our results indi-cate that the TWS variations from GRACE, GLDAS and satellite altimetry have a general consistency. The TWS trends in the Poyang Lake Basin determined from GRACE, GLDAS and satellite altimetry are increasing at 0.0141 km3/a, 0.0328 km3/a and 0.0238 km3/a, respectively during the investigated time period. The TWS is governed mainly by the soil moisture content and dominated primarily by the precipitation but also modulated by the flood season of the Yangtze River as well as the lake and river exchange water.

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

    Science.gov (United States)

    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. A decade of ERS satellite orbits and altimetry

    NARCIS (Netherlands)

    Scharroo, R.

    2002-01-01

    The First European Remote Sensing Satellite, ERS-1, was launched in July 1991, fol- lowed by ERS-2 in April 1995. Both satellites carry a radar altimeter to serve oper- ational applications and scientific research in the fields of geodesy, oceanography, glaciology and meteorology. Together, the sate

  19. Validation of satellite altimetry by kinematic GNSS in central East Antarctica

    Science.gov (United States)

    Schröder, Ludwig; Richter, Andreas; Fedorov, Denis V.; Eberlein, Lutz; Brovkov, Evgeny V.; Popov, Sergey V.; Knöfel, Christoph; Horwath, Martin; Dietrich, Reinhard; Matveev, Alexey Y.; Scheinert, Mirko; Lukin, Valery V.

    2017-05-01

    Ice-surface elevation profiles of more than 30 000 km in total length are derived from kinematic GNSS (GPS and the Russian GLONASS) observations on sledge convoy vehicles along traverses between Vostok Station and the East Antarctic coast. These profiles have accuracies between 4 and 9 cm. They are used to validate elevation data sets from both radar and laser satellite altimetry as well as four digital elevation models. A crossover analysis with three different processing versions of Envisat radar altimetry elevation profiles yields a clear preference for the relocation method over the direct method of slope correction and for threshold retrackers over functional fit algorithms. The validation of CryoSat-2 low-resolution mode and SARIn mode data sets documents the progress made from baseline B to C elevation products. ICESat laser altimetry data are demonstrated to be accurate to a few decimetres over a wide range of surface slopes. A crossover adjustment in the region of subglacial Lake Vostok combining ICESat elevation data with our GNSS profiles yields a new set of ICESat laser campaign biases and provides new, independent evidence for the stability of the ice-surface elevation above the lake. The evaluation of the digital elevation models reveals the benefits of combining laser and radar altimetry.

  20. Satellite altimetry and GOCE contribution to the pre-definition of the Kingdom of Saudi Arabia (KSA) Vertical Network

    Science.gov (United States)

    Vergos, Georgios S.; Grebenitcharsky, Rossen S.; Natsiopoulos, Dimitrios A.; Al-Kherayef, Othman; Al-Muslmani, Bandar

    2017-04-01

    The availability of a unified and well-established national vertical system and frame is of outmost importance in support of everyday geodetic, surveying and engineering applications. Vertical reference system (VRS) modernization and unification has gained increased importance especially during the last years due to the advent of gravity-field dedicated missions and GOCE in particular, since it is the first time that an unprecedented in accuracy dataset of gravity field functionals has become available at a global scale. The Kingdom of Saudi Arabia VRS is outdated and exhibits significant tilts and biases, so that during the last couple of years an extensive effort has been put forth in order to: re-measure by traditional levelling the entire network, establish new benchmarks (BMs), perform high-quality absolute and relative gravity observations and construct new tide-gauge (TG) stations in both the Arab and Red Seas. The Current work focuses on the combined analysis of the existing, recently collected, terrestrial observations with satellite altimetry data and the latest GOCE-based Earth Geopotential Models (EGMs) in order to provide a pre-definition of the KSA VRS. To that respect, a 30-year satellite altimetry time-series is constructed for each TG station in order to derive both the Mean Sea Level (MSL) as well as the sea level trends. This information is analyzed, through Wavelet (WL) Multi-resolution Analysis (MRA), with the TG sea level records in order to determine annual, semi-annual and secular trends of the Red and Arab Sea variations. Finally, the so-derived trends and MSL are combined with local gravity observations at the TG BMs, levelling offsets between the TGs and the network BMs, levelling observations between the network BMs themselves and GOCE-based EGM-derived geoid heights and potential values. The validation of GOCE contribution and of the satellite altimetry derived MSL and trends is based on a simultaneous adjustment of the entire KSA

  1. Gravity Anomalies and Estimated Topography Derived from Satellite Altimetry

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — In many areas of the global ocean, the depth of the seafloor is not well known because survey lines by ships are hundreds of kilometers apart. Satellites carrying...

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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

  4. Establishment of mean sea surface height model for Zhejiang coastal areas based on satellite altimetry technique%基于卫星测高技术的浙江近海平均海面高模型建立

    Institute of Scientific and Technical Information of China (English)

    李静; 吉渊明; 岳建平; 彭刚跃; 宋亚宏

    2015-01-01

    Based on the Waveform data from Jason⁃2 and SARAL/AltiKa satellites, a new method of eliminating the gross error of altimetry data was developed. By eliminating the sea surface height that was not in the predetermined trajectory , the gross error in each segment of altimetry data was eliminated according to the sea surface height in each cycle of each Pass file, in order to improve the usability of satellite data in coastal areas. Through crossover adjustment, the time⁃varying signals for the radial orbit error and sea level were further weakened. The discrete sea surface height with high accuracy, which was obtained with the remove⁃restore technique, was gridded using the radial basis function method. A mean sea surface height model with grid resolutions of 2. 5′×2. 5′was established. The root mean square error between the sea surface height data from the established model and the data from tidal stations is ±0. 017 m, and the standard deviation between the established model and MSS⁃CNES⁃CLS11 was ±0. 070 m. The results show that the established mean sea surface height model for Zhejiang coastal areas is reliable.%利用Jason⁃2卫星与SARAL/AltiKa卫星的Waveform数据,研究一种新的测高数据粗差剔除方法,即剔除不在预定轨迹的海面高后,参考拟合各Pass每个Cycle的海面高值,对测高数据分段剔除粗差,以提高近海卫星数据的可用性;经过交叉点平差,进一步削弱径向轨道误差和海平面时变信号;采用“移去⁃恢复”法得到较高精度的离散海面高;采用径向基函数法格网化离散海面高,建立2.5′×2.5′格网分辨率的平均海面高模型;将所得模型与验潮站提供的海面高比较,均方根为±0.017 m,与MSS⁃CNES⁃CLS11比较,标准差为±0.070 m。研究结果表明,采用本文方法建立的浙江近海平均海面高模型精度可靠。

  5. Long-term monitoring of ocean deep convection using multisensors altimetry and ocean color satellite data

    Science.gov (United States)

    Herrmann, Marine; Auger, Pierre-Amael; Ulses, Caroline; Estournel, Claude

    2017-02-01

    Deep convection occurs in oceanic regions submitted to strong atmospheric buoyancy losses and results in the formation of deep water masses (DWF) of the ocean circulation. It shows a strong interannual variability, and could drastically weaken under the influence of climate change. In this study, a method is proposed to monitor quantitatively deep convection using multisensors altimetry and ocean color satellite data. It is applied and evaluated for the well-observed Northwestern Mediterranean Sea (NWMS) case study. For that, a coupled hydrodynamical-biogeochemical numerical simulation is used to examine the signature of DWF on sea level anomaly (SLA) and surface chlorophyll concentration. Statistically significant correlations between DWF annual indicators and the areas of low surface chlorophyll concentration and low SLA in winter are obtained, and linear relationships between those indicators and areas are established. These relationships are applied to areas of low SLA and low chlorophyll concentration computed, respectively, from a 27 year altimetry data set and a 19 year ocean color data set. The first long time series (covering the last 2 decades) of DWF indicators obtained for the NWMS from satellite observations are produced. Model biases and smoothing effect induced by the low resolution of gridded altimetry data are partly taken into account by using corrective methods. Comparison with winter atmospheric heat flux and previous modeled and observed estimates of DWF indicators suggests that those DWF indicators time series capture realistically DWF interannual variability in the NWMS. The advantages as well as the weaknesses and uncertainties of the method are finally discussed.

  6. Bathymetric Inversion of South China Sea from Satellite Altimetry Data

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    This paper focuses on the study of ocean bathymetric inversion from satellite altimeter data by using FFT technique.In this study,the free-air gravity anomalies over the South China Sea are determined by the satellite altimeter data of GEOSAT,ERS-1,ERS-2 and T/P.And the 2.5′×2.5′ bathymetry model in South China Sea is calculated from the gravity anomalies with the inversion model given.After the analysis of the inversion and the comparison between the results,some conclusions can be drawn.

  7. Vertical crustal motion determined by satellite altimetry and tide gauge data in Fennoscandia

    Science.gov (United States)

    Kuo, C. Y.; Shum, C. K.; Braun, A.; Mitrovica, J. X.

    2004-01-01

    We present a new method of combining satellite altimetry and tide gauge data to obtain improved estimates of absolute (or geocentric) vertical crustal motion at tide gauges within a semi-enclosed sea. As an illustration, we combine TOPEX/POSEIDON altimetry data (1992-2001) and 25 long-term (>40 years) tide gauge records around the Baltic Sea region of Fennoscandia, an area where crustal deformation is dominated by glacial isostatic adjustment (GIA). A comparison of the estimated vertical motion, at 1-11 mm/yr, with independent solutions from 10 collocated BIFROST GPS sites, shows a difference of 0.2 +/- 0.9 mm/yr, thus verifying the accuracy and robustness of the procedure. The solution uncertainty is estimated at 0.4 mm/yr, which is significantly lower than previous analyses of this type. We conclude that our technique can potentially provide accurate vertical motion observations globally where long-term tide gauge records exist.

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

    Science.gov (United States)

    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

  9. Measurements of sea ice by satellite and airborne altimetry

    DEFF Research Database (Denmark)

    Kildegaard Rose, Stine

    A changing sea ice cover in the Arctic Ocean is an early indicator of a climate in transition, the sea ice has in addition a large impact on the climate. The annual and interannual variations of the sea ice cover have been observed by satellites since the start of the satellite era in 1979......, and it has been in retreat every since. The mass balance of the sea ice is an important input to climate models, where the ice thickness is the most uncertain parameter. In this study, data from the CryoSat-2 radar altimeter satellite are used. CryoSat-2 has been measuring the sea ice in the Arctic Ocean...... freeboard is found to be 35 cm for both the airborne and satellite data implying, that the radar signal is here reflected from the snow surface, probably due to weather conditions. CryoSat-2 is very sensitive to returns from specular surfaces, even if they appear o_-nadir. This contaminates the “true...

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

    DEFF Research Database (Denmark)

    Andersen, O. B.; Cheng, Yongcun; Deng, X.

    2014-01-01

    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...

  11. A fiducial reference site for satellite altimetry in Crete, Greece

    DEFF Research Database (Denmark)

    Mertikas, Stelios; Donlon, Craig; Mavrokordatos, Constantin

    With the advent of diverse satellite altimeters and variant measuring techniques, it has become mature in the scientific community, that an absolute reference Cal/Val site is regularly maintained to define, monitor, control the responses of any altimetric system. This work sets the ground...

  12. Satellite altimetry in sea ice regions - detecting open water for estimating sea surface heights

    Science.gov (United States)

    Müller, Felix L.; Dettmering, Denise; Bosch, Wolfgang

    2017-04-01

    The Greenland Sea and the Farm Strait are transporting sea ice from the central Arctic ocean southwards. They are covered by a dynamic changing sea ice layer with significant influences on the Earth climate system. Between the sea ice there exist various sized open water areas known as leads, straight lined open water areas, and polynyas exhibiting a circular shape. Identifying these leads by satellite altimetry enables the extraction of sea surface height information. Analyzing the radar echoes, also called waveforms, provides information on the surface backscatter characteristics. For example waveforms reflected by calm water have a very narrow and single-peaked shape. Waveforms reflected by sea ice show more variability due to diffuse scattering. Here we analyze altimeter waveforms from different conventional pulse-limited satellite altimeters to separate open water and sea ice waveforms. An unsupervised classification approach employing partitional clustering algorithms such as K-medoids and memory-based classification methods such as K-nearest neighbor is used. The classification is based on six parameters derived from the waveform's shape, for example the maximum power or the peak's width. The open-water detection is quantitatively compared to SAR images processed while accounting for sea ice motion. The classification results are used to derive information about the temporal evolution of sea ice extent and sea surface heights. They allow to provide evidence on climate change relevant influences as for example Arctic sea level rise due to enhanced melting rates of Greenland's glaciers and an increasing fresh water influx into the Arctic ocean. Additionally, the sea ice cover extent analyzed over a long-time period provides an important indicator for a globally changing climate system.

  13. Comments on ocean circulation with regard to satellite altimetry

    Science.gov (United States)

    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.

  14. Accurate Linking of Lake Erie Water Level with Shoreline Datum Using GPS Buoy and Satellite Altimetry

    Directory of Open Access Journals (Sweden)

    Kai-Chien Cheng

    2008-01-01

    Full Text Available There is a need to accurately link the water level to the shoreline vertical datum for various applications including coastal management, lake/river/estuary/wetland hydrological or storm surge modeling/forecasting. Coastal topography is historically surveyed and referenced to the predetermined vertical datum in terms of orthometric heights, or the heights above the geoid, which is poorly known in terms of accuracy and lack of adequate spatial resolution for coastal applications such as estuary or storm surge modeling. We demonstrate an accurate linking of the lake surface to a shoreline datum using satellite techniques, including GPS buoy and satellite altimetry, water level gauges, and local geoid and lake circulation models. The possible error sources are analyzed and an error budget is reported in this study. An innovated method to estimate geoid height near the water level gauge using a GPS buoy is proposed. It is found that at a 95% confidence interval, the method is consistent with the National Geodetic Survey GEOID03 geoid model. The lake surface represented using a lake circulation model provided by the Great Lakes Forecasting Systems is also verified with kriging based on the data (1999 - 2001 from the water level gauge, and TOPEX/POSEIDON altimeter. Mean discrepancies of 2.7 and 7.2 cm are found with the data from the gauges around Lake Erie, and from the combination of the gauges and the altimeter, respectively. It reveals that the current dominant limitation of more accurate linking of water surface to shoreline is the insufficient knowledge of geoid in the current models. Further improvement is feasible through more accurate and higher resolution modeling of the lake geoid.

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

    Science.gov (United States)

    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].

  16. Mapping the nonstationary internal tide with satellite altimetry

    Science.gov (United States)

    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.

  17. CONTRIBUTION OF SATELLITE ALTIMETRY DATA IN GEOLOGICAL STRUCTURE RESEARCH IN THE SOUTH CHINA SEA

    Directory of Open Access Journals (Sweden)

    T. D. Tran

    2016-06-01

    Full Text Available 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.

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

    Science.gov (United States)

    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.

  19. HYDROGRAV - Hydrological model calibration and terrestrial water storage monitoring from GRACE gravimetry and satellite altimetry, First results

    DEFF Research Database (Denmark)

    Andersen, O.B.; Krogh, P.E.; Michailovsky, C.

    2008-01-01

    Space-borne and ground-based time-lapse gravity observations provide new data for water balance monitoring and hydrological model calibration in the future. The HYDROGRAV project (www.hydrograv.dk) will explore the utility of time-lapse gravity surveys for hydrological model calibration and terre......Space-borne and ground-based time-lapse gravity observations provide new data for water balance monitoring and hydrological model calibration in the future. The HYDROGRAV project (www.hydrograv.dk) will explore the utility of time-lapse gravity surveys for hydrological model calibration...... and terrestrial water storage monitoring. Merging remote sensing data from GRACE with other remote sensing data like satellite altimetry and also ground based observations are important to hydrological model calibration and water balance monitoring of large regions and can serve as either supplement or as vital...... change from 2002 to 2008 along with in-situ gravity time-lapse observations and radar altimetry monitoring of surface water for the southern Africa river basins will be presented....

  20. Semi-automatic determination of the Azores Current axis using satellite altimetry: Application to the study of the current variability during 1995-2006

    Science.gov (United States)

    Lázaro, C.; Juliano, M. F.; Fernandes, M. J.

    2013-06-01

    Satellite altimetry has been widely used to study the variability of the ocean currents such as the Azores Current (AzC) in the North Atlantic. Most analyses are performed over the region that encloses the current, thus being somehow affected by other oceanographic signals, e.g., eddies. In this study, a new approach for extracting the axis of a zonal current solely based on satellite altimetry is presented. This is a semi-automatic procedure that searches for the maximum values of the gradient of absolute dynamic topography (ADT), using the geostrophic velocity as auxiliary information. The advantage of this approach is to allow the analyses to be performed over a buffer centered on the current axis instead of using a wider region. It is here applied to the AzC for the period June 1995-October 2006.

  1. Thirty years of elevation change on Antarctic Peninsula ice shelves from multimission satellite radar altimetry

    Science.gov (United States)

    Fricker, Helen Amanda; Padman, Laurie

    2012-02-01

    We use data acquired between 1978 and 2008 by four satellite radar altimeter missions (Seasat, ERS-1, ERS-2 and Envisat) to determine multidecadal elevation change rates (dhi/dt) for six major Antarctic Peninsula (AP) ice shelves. In areas covered by the Seasat orbit (to 72.16°S), regional-averaged 30-year trends were negative (surface lowering), with rates between -0.03 and -0.16 m a-1. Surface lowering preceded the start of near-continuous radar altimeter operations that began with ERS-1 in 1992. The average rate of lowering for the first 14 years of the period was typically smaller than the 30-year average; the exception was the southern Wilkins Ice Shelf, which experienced negligible lowering between 2000 and 2008, when a series of large calving events began. Analyses of the continuous ERS/Envisat time series (to 81.5°) for 1992-2008 reveal a period of strong negative dhi/dt on most ice shelves between 1992 and 1995. Based on prior studies of regional atmospheric and oceanic conditions, we hypothesize that the observed elevation changes on Larsen C Ice Shelf are driven primarily by firn compaction while the western AP ice shelves are responding to changes in both surface mass balance and basal melt rates. Our time series also show that large changes in dhi/dt can occur on interannual time scales, reinforcing the importance of long time series altimetry to separate long-term trends associated with climate change from interannual to interdecadal natural variability.

  2. Satellite altimetry reveals spatial patterns of variations in the Baltic Sea wave climate

    Science.gov (United States)

    Kudryavtseva, Nadezhda; Soomere, Tarmo

    2017-08-01

    The main properties of the climate of waves in the seasonally ice-covered Baltic Sea and its decadal changes since 1990 are estimated from satellite altimetry data. The data set of significant wave heights (SWHs) from all existing nine satellites, cleaned and cross-validated against in situ measurements, shows overall a very consistent picture. A comparison with visual observations shows a good correspondence with correlation coefficients of 0.6-0.8. The annual mean SWH reveals a tentative increase of 0.005 m yr-1, but higher quantiles behave in a cyclic manner with a timescale of 10-15 years. Changes in the basin-wide average SWH have a strong meridional pattern: an increase in the central and western parts of the sea and a decrease in the east. This pattern is likely caused by a rotation of wind directions rather than by an increase in the wind speed.

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

    DEFF Research Database (Denmark)

    Zhang, X.H.; Forsberg, René

    2007-01-01

    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 c...

  4. Improved sea level record over the satellite altimetry era (1993-2010) from the Climate Change Initiative project

    DEFF Research Database (Denmark)

    Ablain, M.; Cazenave, A.; Larnicol, G.;

    2015-01-01

    Sea level is one of the 50 Essential Climate Variables (ECVs) listed by the Global Climate Observing System (GCOS) in climate change monitoring. In the past two decades, sea level has been routinely measured from space using satellite altimetry techniques. In order to address a number of importan...

  5. Errors of Mean Dynamic Topography and Geostrophic Current Estimates in China's Marginal Seas from GOCE and Satellite Altimetry

    DEFF Research Database (Denmark)

    Jin, Shuanggen; Feng, Guiping; Andersen, Ole Baltazar

    2014-01-01

    and geostrophic current estimates from satellite gravimetry and altimetry are investigated and evaluated in China's marginal seas. The cumulative error in MDT from GOCE is reduced from 22.75 to 9.89 cm when compared to the Gravity Recovery and Climate Experiment (GRACE) gravity field model ITG-Grace2010 results...

  6. Merging of airborne gravity and gravity derived from satellite altimetry: Test cases along the coast of greenland

    DEFF Research Database (Denmark)

    Olesen, Arne Vestergaard; Andersen, Ole Baltazar; Tscherning, C.C.

    2002-01-01

    The National Survey and Cadastre - Denmark (KMS) has for several years produced gravity anomaly maps over the oceans derived from satellite altimetry. During the last four years, KMS has also conducted airborne gravity surveys along the coast of Greenland dedicated to complement the existing onsh...

  7. Estimation of Reservoir Discharges from Lake Nasser and Roseires Reservoir in the Nile Basin Using Satellite Altimetry and Imagery Data

    NARCIS (Netherlands)

    Muala, E.; Mohamed, Y.A.; Duan, Z.; Van der Zaag, P.

    2014-01-01

    This paper presents the feasibility of estimating discharges from Roseires Reservoir (Sudan) for the period from 2002 to 2010 and Aswan High Dam/Lake Nasser (Egypt) for the periods 1999–2002 and 2005–2009 using satellite altimetry and imagery with limited in situ data. Discharges were computed using

  8. Observing the oceanic mesoscale processes with satellite altimetry: the state of the art and outlook

    Science.gov (United States)

    Fu, L.-L.

    2012-04-01

    Satellite altimetry has enabled the study of global oceanic mesoscale variability with increasing accuracy and resolution for the past three decades. The combination of the series of precision missions beginning with TOPEX/Poseidon and the series of missions beginning with ERS-1 has created a data record of sea surface height measurement from at least two simultaneously operating altimeters. This 19-year record has fundamentally expanded our knowledge about the dynamics of ocean circulation, in particular at the mesoscale. The progress made to date from the data record will be briefly reviewed, with emphasis on the remaining open questions. Spectral analysis of the existing altimeter data suggests that the spatial resolution is about 150 km in wavelength in space-time gridded data, and about 70-100 km in along-track data. The unresolved short scales, however, have important roles in the energy balance of ocean dynamics as well as the transport and dissipation of many properties of the ocean such as heat and dissolved chemicals. The prospect of the technique of radar interferometry for making high-resolution wide-swath measurement of sea surface height will be discussed with an update on the development of the SWOT (Surface Water and Ocean Topography) Mission, which is being jointly developed by NASA and CNES with contributions from the Canadian Space Agency. SWOT is being designed for applications in both oceanography and land surface hydrology and setting a standard for the next-generation altimetry missions.

  9. Improved sea level record over the satellite altimetry era (1993–2010 from the Climate Change Initiative Project

    Directory of Open Access Journals (Sweden)

    M. Ablain

    2014-08-01

    Full Text Available Sea level is one of the 50 Essential Climate Variables (ECVs listed by the Global Climate Observing System (GCOS in climate change monitoring. In the last two decades, sea level has been routinely measured from space using satellite altimetry techniques. In order to address a number of important scientific questions such as: "Is sea level rise accelerating?", "Can we close the sea level budget?", "What are the causes of the regional and interannual variability?", "Can we already detect the anthropogenic forcing signature and separate it from the internal/natural climate variability?", and "What are the coastal impacts of sea level rise?", the accuracy of altimetry-based sea level records at global and regional scales needs to be significantly improved. For example, the global mean and regional sea level trend uncertainty should become better than 0.3 and 0.5 mm year−1, respectively (currently of 0.6 and 1–2 mm year−1. Similarly, interannual global mean sea level variations (currently uncertain to 2–3 mm need to be monitored with better accuracy. In this paper, we present various respective data improvements achieved within the European Space Agency (ESA Climate Change Initiative (ESA CCI project on "Sea Level" during its first phase (2010–2013, using multi-mission satellite altimetry data over the 1993–2010 time span. In a first step, using a new processing system with dedicated algorithms and adapted data processing strategies, an improved set of sea level products has been produced. The main improvements include: reduction of orbit errors and wet/dry atmospheric correction errors, reduction of instrumental drifts and bias, inter-calibration biases, intercalibration between missions and combination of the different sea level data sets, and an improvement of the reference mean sea surface. We also present preliminary independent validations of the SL_cci products, based on tide gauges comparison and sea level budget closure approach

  10. Bathymetry Prediction in Shallow Water by the Satellite Altimetry-Derived Gravity Anomalies

    Science.gov (United States)

    Kim, Kwang Bae; Yun, Hong Sik

    2017-04-01

    The satellite altimetry-derived free-air gravity anomalies (SAFAGAs) are correlated with undulations of crustal density variations under the seafloor. In this study, shipborne bathymetry from the Korea Rural Community Corporation (KRC) and the SAFAGAs from Scripps Institution of Oceanography were combined to predict bathymetry in shallow water. Density contrast of 5.0 g/cm3 estimated by the check points method of the gravity-geologic method (GGM) between seawater and the seafloor topographic mass was applied to predict bathymetry in shallow water areas outside of the Saemangeum Seawall located on the southwest coast of the Korean peninsula. Bathymetry predicted by the GGM was compared with depth measurements on the shipborne locations to analyze the bathymetry accuracy. The root mean square error (RMSE) of the differences of bathymetry between GGM and KRC on the KRC shipborne tracks in shallow water around the Saemangeum Seawall is 0.55 m. The topographic effects in off-tracks extracted from SAFAGAs in the GGM can be effectively utilized to predict bathymetry by combining with shipborne depth data in shallow water where shipborne depth data are limited. In addition, bathymetry and the SAFAGAs have a linear correlation in the 20 160 km wavelength. The coherency analysis was performed by computing the cross-spectral coherence between satellite altimetry derived bathymetry and the SAFAGAs. Acknowledgement This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2016R1A6A3A11931032).

  11. Novel Algorithms for Retrieval of Hydrology and Ice Regimes of Middle-sized Inland Water Bodies from Satellite Altimetry

    Science.gov (United States)

    Troitskaya, Y. I.; Rybushkina, G. V.; Kuznetsova, A. M.; Baidakov, G. A.; Soustova, I.

    2014-12-01

    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. The algorithm includes four consecutive steps: a) constructing a local piecewise model of a reflecting surface in the neighbourhood of the reservoir; b) solving a direct problem by calculating the reflected waveforms within the framework of the model; c) imposing restrictions and validity criteria for the algorithm based on waveform modelling; d) solving the inverse problem by retrieving a tracking point by the improved threshold algorithm. The results obtained on the basis of standard algorithm and method for adaptive re-tracking at Rybinsk , Gorky, Kuibyshev, Saratov and Volgograd reservoirs and middle-sized lakes of Russia: Chany, Segozero, Hanko, Onego, Beloye are compared to each other and to the field data of hydrological stations in reservoirs and lakes. The possibility of determination of significant wave height (SWH) in the lakes through a two-step adaptive retracking is investigated. Comparing results of retracting of SGDR data and ground measurements shows, that retrieving wave parameters in medium sized water bodies still meets difficulties. The direction of improvement of the existing algorithm is associated with comprehensive use of altimetry data, field studies and numerical modeling of high resolution. A simple method for timing of water freezing and ice break-up in lakes based on analysis of along-track dependencies of brightness temperatures at 18.7 and 34 GHz registered by microwave radiometer of altimetry satellite Jason-2. Comparison with in situ data of Russian Register of hydraulic structures on the example of reservoirs of the Volga River and the Don River confirms ability of the proposed method to determine quantitatively the freezing and break-up times for middle-sized inland water bodies.

  12. Recent improvements in mesoscale characterization of the western Mediterranean Sea: synergy between satellite altimetry and other observational approaches

    Directory of Open Access Journals (Sweden)

    Ananda Pascual

    2013-03-01

    Full Text Available Satellite altimetry is a key component of the global observing system and plays a major role in the study of the mesoscale processes that drive most of the ocean circulation variability at middle and high latitudes. However, satellite altimetry alone provides only surface information at a limited spatio-temporal resolution. To address these limitations and to better describe the mesoscale three-dimensional variability, it is necessary to complement altimetry data with additional remote and in situ measurements. This study provides an update of the recent advances in the study of the mesoscale variability using a combination of altimetry and other independent observations, with an emphasis on the results obtained for the western Mediterranean Sea. The circulation in this area is complex because of the presence of multiple interacting scales, including basin-scale, sub-basin–scale and mesoscale structures. Thus, characterizing these processes requires high-resolution observations and multi-sensor approaches. Accordingly, multi-platform experiments and analyses have been designed and undertaken in the different sub-basins of the western Mediterranean Sea. These studies have demonstrated the advantages of synergetic approaches that use a combination of observation techniques and are able to resolve different spatio-temporal scales with the aim of better understanding mesoscale dynamics.

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

    Science.gov (United States)

    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.

  14. Using ocean satellites altimetry to observe geoid change caused by large earthquakes

    Science.gov (United States)

    Lun Chiang, Hui; Fong Chao, Benjamin

    2017-04-01

    The geoid is the gravitational equipotential surface that is closest to the shape of the real earth. Sea water, being fluid, flows to a lowest gravitational state such that the mean sea surface conforms to the geoid, while the dynamic height departure between them are caused by tides, winds, ocean currents, and other dynamic or even anthropogenic effects. Here we use the sea surface height data, from altimetry satellites of Topex/Poseidon, Jason-1 and Jason-2 to detect possible geoid changes due to three recent large earthquakes, namely the Sumatra-Andaman event of December 26 in 2004, Chile event of February 27 in 2010 and the Tohoku-Oki event of March 11 in 2011. Instead of applying directly the gridded sea surface height data processed by AVISO, we download the "along-track" altimetric data in the respective regions to take advantage of their detailed information content and higher resolutions. With the data, we constructed for 1-year each the pre- and post-seismic sea surface height maps in order to detect the coseismic geoid changes, and analyzing longer time series for postseismic phenomena. We found moderate geoid change signals that are above the noise level. We compared them with the observed geoid change from the GRACE satellite data and with those calculated by elastic dislocation theory given seismic rupture models. The comparison is encouraging and promises further studies.

  15. A topographic parameter inversion method based on laser altimetry

    Institute of Scientific and Technical Information of China (English)

    HUANG ChunMing; ZHANG ShaoDong; CHEN Xi

    2012-01-01

    A topographic parameter inversion method based on laser altimetry is developed in this paper,which can be used to deduce the surface vertical profile and retrieve the topographic parameters within the laser footprints by analyzing and simulating return waveforms.This method comprises three steps.The first step is to build the numerical models for the whole measuring procedure of laser altimetry,construct digital elevation models for surfaces with different topographic parameters,and calculate return waveforms.The second step is to analyze the simulated return waveforms to obtain their characteristics parameters,summarize the effects of the topographic parameter variations on the characteristic parameters of simulated return waveforms,and analyze the observed return waveforms of laser altimeters to acquire their characteristic parameters at the same time.The last step is to match the characteristic parameters of the simulated and observed return waveforms,and deduce the topographic parameters within the laser footprint.This method can be used to retrieve the topographic parameters within the laser footprint from the observed return waveforms of spaceborne laser altimeters and to get knowledge about the surface altitude distribution within the laser footprint other than only getting the height of the surface encountered firstly by the laser beam,which extends laser altimeters' function and makes them more like radars.

  16. Identifiability of altimetry-based rating curve parameters in function of river morphological parameters

    Science.gov (United States)

    Paris, Adrien; André Garambois, Pierre; Calmant, Stéphane; Paiva, Rodrigo; Walter, Collischonn; Santos da Silva, Joecila; Medeiros Moreira, Daniel; Bonnet, Marie-Paule; Seyler, Frédérique; Monnier, Jérôme

    2016-04-01

    Estimating river discharge for ungauged river reaches from satellite measurements is not straightforward given the nonlinearity of flow behavior with respect to measurable and non measurable hydraulic parameters. As a matter of facts, current satellite datasets do not give access to key parameters such as river bed topography and roughness. A unique set of almost one thousand altimetry-based rating curves was built by fit of ENVISAT and Jason-2 water stages with discharges obtained from the MGB-IPH rainfall-runoff model in the Amazon basin. These rated discharges were successfully validated towards simulated discharges (Ens = 0.70) and in-situ discharges (Ens = 0.71) and are not mission-dependent. The rating curve writes Q = a(Z-Z0)b*sqrt(S), with Z the water surface elevation and S its slope gained from satellite altimetry, a and b power law coefficient and exponent and Z0 the river bed elevation such as Q(Z0) = 0. For several river reaches in the Amazon basin where ADCP measurements are available, the Z0 values are fairly well validated with a relative error lower than 10%. The present contribution aims at relating the identifiability and the physical meaning of a, b and Z0given various hydraulic and geomorphologic conditions. Synthetic river bathymetries sampling a wide range of rivers and inflow discharges are used to perform twin experiments. A shallow water model is run for generating synthetic satellite observations, and then rating curve parameters are determined for each river section thanks to a MCMC algorithm. Thanks to twin experiments, it is shown that rating curve formulation with water surface slope, i.e. closer from Manning equation form, improves parameter identifiability. The compensation between parameters is limited, especially for reaches with little water surface variability. Rating curve parameters are analyzed for riffle and pools for small to large rivers, different river slopes and cross section shapes. It is shown that the river bed

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

    Science.gov (United States)

    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

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

    Directory of Open Access Journals (Sweden)

    P. Y. Le Traon

    2013-10-01

    Full Text Available 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

  19. Improvement of global and regional mean sea level derived from satellite altimetry multi missions

    Science.gov (United States)

    Ablain, M.; Faugere, Y.; Larnicol, G.; Picot, N.; Cazenave, A.; Benveniste, J.

    2012-04-01

    With the satellite altimetry missions, the global mean sea level (GMSL) has been calculated on a continual basis since January 1993. 'Verification' phases, during which the satellites follow each other in close succession (Topex/Poseidon--Jason-1, then Jason-1--Jason-2), help to link up these different missions by precisely determining any bias between them. Envisat, ERS-1 and ERS-2 are also used, after being adjusted on these reference missions, in order to compute Mean Sea Level at high latitudes (higher than 66°N and S), and also to improve spatial resolution by combining all these missions together. The global mean sea level (MSL) deduced from TOPEX/Poseidon, Jason-1 and Jason-2 provide a global rate of 3.2 mm from 1993 to 2010 applying the post glacial rebound (MSL aviso website http://www.jason.oceanobs.com/msl). Besides, the regional sea level trends bring out an inhomogeneous repartition of the ocean elevation with local MSL slopes ranging from + 8 mm/yr to - 8 mm/year. A study published in 2009 [Ablain et al., 2009] has shown that the global MSL trend unceratainty was estimated at +/-0.6 mm/year with a confidence interval of 90%. The main sources of errors at global and regional scales are due to the orbit calculation and the wet troposphere correction. But others sea-level components have also a significant impact on the long-term stability of MSL as for instance the stability of instrumental parameters and the atmospheric corrections. Thanks to recent studies performed in the frame of the SALP project (supported by CNES) and Sea-level Climate Change Initiative project (supported by ESA), strong improvements have been provided for the estimation of the global and regional MSL trends. In this paper, we propose to describe them; they concern the orbit calculation thanks to new gravity fields, the atmospheric corrections thanks to ERA-interim reanalyses, the wet troposphere corrections thanks to the stability improvement, and also empirical corrections

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

    Science.gov (United States)

    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

  1. Mass loss of the Greenland peripheral glaciers and ice caps from satellite altimetry

    Science.gov (United States)

    Wouters, Bert; Noël, Brice; Moholdt, Geir; Ligtenberg, Stefan; van den Broeke, Michiel

    2017-04-01

    At its rapidly warming margins, the Greenland Ice Sheet is surrounded by (semi-)detached glaciers and ice caps (GIC). Although they cover only roughly 5% of the total glaciated area in the region, they are estimated to account for 15-20% of the total sea level rise contribution of Greenland. The spatial and temporal evolution of the mass changes of the peripheral GICs, however, remains poorly constrained. In this presentation, we use satellite altimetry from ICESat and Cryosat-2 combined with a high-resolution regional climate model to derive a 14 year time series (2003-2016) of regional elevation and mass changes. The total mass loss has been relatively constant during this period, but regionally, the GICs show marked temporal variations. Whereas thinning was concentrated along the eastern margin during 2003-2009, western GICs became the prime sea level rise contributors in recent years. Mass loss in the northern region has been steadily increasing throughout the record, due to a strong atmospheric warning and a deterioration of the capacity of the firn layer to buffer the resulting melt water.

  2. Statistical Characteristics of Mesoscale Eddies in the North Pacific Derived from Satellite Altimetry

    Directory of Open Access Journals (Sweden)

    Yu-Hsin Cheng

    2014-06-01

    Full Text Available The sea level anomaly data derived from satellite altimetry are analyzed to investigate statistical characteristics of mesoscale eddies in the North Pacific. Eddies are detected by a free-threshold eddy identification algorithm. The results show that the distributions of size, amplitude, propagation speed, and eddy kinetic energy of eddy follow the Rayleigh distribution. The most active regions of eddies are the Kuroshio Extension region, the Subtropical Counter Current zone, and the Northeastern Tropical Pacific region. By contrast, eddies are seldom observed around the center of the eastern part of the North Pacific Subarctic Gyre. The propagation speed and kinetic energy of cyclonic and anticyclonic eddies are almost the same, but anticyclonic eddies possess greater lifespans, sizes, and amplitudes than those of cyclonic eddies. Most eddies in the North Pacific propagate westward except in the Oyashio region. Around the northeastern tropical Pacific and the California currents, cyclonic and anticyclonic eddies propagate westward with slightly equatorward (197° average azimuth relative to east and poleward (165° deflection, respectively. This implies that the background current may play an important role in formation of the eddy pathway patterns.

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

    Science.gov (United States)

    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.

  4. CAWRES: A Waveform Retracking Fuzzy Expert System for Optimizing Coastal Sea Levels from Jason-1 and Jason-2 Satellite Altimetry Data

    Directory of Open Access Journals (Sweden)

    Nurul Hazrina Idris

    2017-06-01

    Full Text Available This paper presents the Coastal Altimetry Waveform Retracking Expert System (CAWRES, a novel method to optimise the Jason satellite altimetric sea levels from multiple retracking solutions. CAWRES’ aim is to achieve the highest possible accuracy of coastal sea levels, thus bringing measurement of radar altimetry data closer to the coast. The principles of CAWRES are twofold. The first is to reprocess altimeter waveforms using the optimal retracker, which is sought based on the analysis from a fuzzy expert system. The second is to minimise the relative offset in the retrieved sea levels caused by switching from one retracker to another using a neural network. The innovative system is validated against geoid height and tide gauges in the Great Barrier Reef, Australia for Jason-1 and Jason-2 satellite missions. The regional investigations have demonstrated that the CAWRES can effectively enhance the quality of 20 Hz sea level data and recover up to 16% more data than the standard MLE4 retracker over the tested region. Comparison against tide gauge indicates that the CAWRES sea levels are more reliable than those of Sensor Geophysical Data Records (SGDR products, because the former has a higher (≥0.77 temporal correlation and smaller (≤19 cm root mean square errors. The results demonstrate that the CAWRES can be applied to coastal regions elsewhere as well as other satellite altimeter missions.

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

    Directory of Open Access Journals (Sweden)

    Shijie Liu

    2016-11-01

    Full Text Available 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.

  6. Determination of the Earth gravity Field Parameters in Persian Gulf and Oman Sea with the Satellite Altimetry Data

    Science.gov (United States)

    Emadi, S. R.; Najafi-Alamardi, M.; Toosi, K. N.; Sedighi, M.; Nankali, H. R.

    2006-07-01

    Satellite altimetry provides continuous, accur ate, and homogenous data ser ies in marine areas .Th e Sea Surf ace Heigh ts (SSH) ex tracted from altimetry data w as used in a method sear ching for the least squares of the sea surface topography to simultaneously d etermine the geoidal height and the sea surface topography as well in the Persian Gulf and the Oman sea. This is contrary to th e methods wh ich r equire the knowledge of one parameter to estimate the other. The North and East componen ts of the deflections of vertical w ere also estimated by differentiating the der ived geoid al heights in the corresponding directions, and finally the free- air grav ity anomalies w ere computed utilizing the inverse V ening- Meinesz integral.

  7. Assimilation of radar altimetry to a routing model of the Brahmaputra River

    DEFF Research Database (Denmark)

    Michailovsky, Claire Irene B.; Milzow, Christian; Bauer-Gottwein, Peter

    2013-01-01

    predictions at daily or even subdaily temporal resolutions. One way to exploit satellite radar altimetry is therefore to combine the data with hydrological models in a data assimilation framework. In this study, radar altimetry data from six ENVISAT virtual stations were assimilated to a routing model...... quantities of interest. This is the case for satellite-based radar altimetry. River-level variations can be tracked using radar altimetry at a temporal resolution between 10 and 35 days, depending on the satellite, but hydrologists are typically interested in river flows rather than levels and require...

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

    NARCIS (Netherlands)

    van Dijk, A. I. J. M.; Renzullo, L. J.; Wada, Y.|info:eu-repo/dai/nl/341387819; Tregoning, P.

    2014-01-01

    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

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

    NARCIS (Netherlands)

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

    2014-01-01

    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 assimila

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

    Science.gov (United States)

    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.

  11. 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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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.

  15. Quantifying Freshwater Mass Balance in the Central Tibetan Plateau by Integrating Satellite Remote Sensing, Altimetry, and Gravimetry

    Directory of Open Access Journals (Sweden)

    Kuo-Hsin Tseng

    2016-05-01

    Full Text Available The Tibetan Plateau (TP has been observed by satellite optical remote sensing, altimetry, and gravimetry for a variety of geophysical parameters, including water storage change. However, each of these sensors has its respective limitation in the parameters observed, accuracy and spatial-temporal resolution. Here, we utilized an integrated approach to combine remote sensing imagery, digital elevation model, and satellite radar and laser altimetry data, to quantify freshwater storage change in a twin lake system named Chibuzhang Co and Dorsoidong Co in the central TP, and compared that with independent observations including mass changes from the Gravity Recovery and Climate Experiment (GRACE data. Our results show that this twin lake, located within the Tanggula glacier system, remained almost steady during 1973–2000. However, Dorsoidong Co has experienced a significant lake level rise since 2000, especially during 2000–2005, that resulted in the plausible connection between the two lakes. The contemporary increasing lake level signal at a rate of 0.89 ± 0.05 cm·yr−1, in a 2° by 2° grid equivalent water height since 2002, is higher than the GRACE observed trend at 0.41 ± 0.17 cm·yr−1 during the same time span. Finally, a down-turning trend or inter-annual variability shown in the GRACE signal is observed after 2012, while the lake level is still rising at a consistent rate.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  18. Northern South China Sea Surface Circulation and its Variability Derived by Combining Satellite Altimetry and Surface Drifter Data

    Directory of Open Access Journals (Sweden)

    N. Peter Benny

    2015-01-01

    Full Text Available The present study analyses the mean and seasonal mesoscale surface circulation of the Northern South China Sea (NSCS and determines the influence of El Niño/SouthernNiño/Southern Oscillation (ENSO. High resolution Eulerian velocity field is derived by combining the available satellite tracked surface drifter data with satellite altimetry during 1993 - 2012. The wind driven current is computed employing the weekly ocean surface mean wind fields derived from the scatterometers on board ERS 1/2, QuikSCAT and ASCAT. The derived mean velocity field exhibits strong boundary currents and broad zonal flow across NSCS. The anomalous field is quite strong in the southern part and the Seasonal circulation clearly depicts the monsoonal forcing. Eddy Kinetic Energy (EKE distribution and its spatial and temporal structures are determined employing Empirical Orthogonal Function (EOF analysis. The ENSO influence on NSCS surface circulation has been analyzed using monthly absolute geostrophic velocity fields during 1996 - 1999.

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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

  2. PRETTY: Grazing altimetry measurements based on the interferometric method

    DEFF Research Database (Denmark)

    Fragner, Heinrich; Dielacher, Andreas; Zangerl, Franz

    2017-01-01

    The exploitation of signals stemming from global navigation systems for passive bistatic radar applications has beenproposed and implemented within numerous studies. The fact that such missions do not rely on high power amplifiersand that the need of high gain antennas with large geometrical...... dimensions can be avoided, makes them suitable forsmall satellite missions. Applications where a continuous high coverage is needed, as for example disaster warning,have the demand for a large number of satellites in orbit, which in turn requires small and relatively low cost satellites.The proposed PRETTY...... (Passive Reflectometry and Dosimetry) mission includes a demonstrator payload for passivereflectometry and scatterometry focusing on very low incidence angles whereby the direct and reflected signal will bereceived via the same antenna. The correlation of both signals will be done by a specific FPGA based...

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

    Science.gov (United States)

    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. Estimation of Reservoir Discharges from Lake Nasser and Roseires Reservoir in the Nile Basin Using Satellite Altimetry and Imagery Data

    Directory of Open Access Journals (Sweden)

    Eric Muala

    2014-08-01

    Full Text Available This paper presents the feasibility of estimating discharges from Roseires Reservoir (Sudan for the period from 2002 to 2010 and Aswan High Dam/Lake Nasser (Egypt for the periods 1999–2002 and 2005–2009 using satellite altimetry and imagery with limited in situ data. Discharges were computed using the water balance of the reservoirs. Rainfall and evaporation data were obtained from public domain data sources. In situ measurements of inflow and outflow (for validation were obtained, as well. The other water balance components, such as the water level and surface area, for derivation of the change of storage volume were derived from satellite measurements. Water levels were obtained from Hydroweb for Roseires Reservoir and Hydroweb and Global Reservoir and Lake Monitor (GRLM for Lake Nasser. Water surface areas were derived from Landsat TM/ETM+ images using the Normalized Difference Water Index (NDWI. The water volume variations were estimated by integrating the area-level relationship of each reservoir. For Roseires Reservoir, the water levels from Hydroweb agreed well with in situ water levels (RMSE = 0.92 m; R2 = 0.96. Good agreement with in situ measurements were also obtained for estimated water volume (RMSE = 23%; R2 = 0.94 and computed discharge (RMSE = 18%; R2 = 0.98. The accuracy of the computed discharge was considered acceptable for typical reservoir operation applications. For Lake Nasser, the altimetry water levels also agreed well with in situ levels, both for Hydroweb (RMSE = 0.72 m; R2 = 0.81 and GRLM (RMSE = 0.62 m; R2 = 0.96 data. Similar agreements were also observed for the estimated water volumes (RMSE = 10%–15%. However, the estimated discharge from satellite data agreed poorly with observed discharge, Hydroweb (RMSE = 70%; R2 = 0.09 and GRLM (RMSE = 139%; R2 = 0.36. The error could be attributed to the high sensitivity of discharge to errors in storage volume because of the immense reservoir compared to inflow

  5. Assessment of SRTM Precision for River Slope and Cross Section by Comparison with Satellite Altimetry

    Science.gov (United States)

    Calmant, S.; Seyler, F.; Bonnet, M.; Santos da Silva, J.; Leon, J. G.; Medeiros, D. M.; Roux, E.

    2008-12-01

    Slope of the river is a widely used parameter for discharge estimation. In poorly monitored basins, SRTM have been used to determine river slope (Le Favour et Alsdorf, 2005). Also, SRTM is expected to constrain long wavelength slope in future altimetry mission, such as SWOT. It is then important to assess the quality of SRTM data over river surface, floodplains and wetlands, in particular in case of dense vegetated cover of the river banks, in order to evaluate if such data can reach modeling requirements. We present two types of analysis : river longitudinal profiles and river cross sections extracted from SRTM compared with altitudes computed from altimetry data (ENVISAT, T/P, ICESAT, GPS surveys).

  6. Use of surface drifters to increase resolution and accuracy of oceanic geostrophic circulation mapped from satellite only (altimetry and gravimetry)

    Science.gov (United States)

    Mulet, Sandrine; Rio, Marie-Hélène; Etienne, Hélène

    2017-04-01

    Strong improvements have been made in our knowledge of the surface ocean geostrophic circulation thanks to satellite observations. For instance, the use of the latest GOCE (Gravity field and steady-state Ocean Circulation Explorer) geoid model with altimetry data gives good estimate of the mean oceanic circulation at spatial scales down to 125 km. However, surface drifters are essential to resolve smaller scales, it is thus mandatory to carefully process drifter data and then to combine these different data sources. In this framework, the global 1/4° CNES-CLS13 Mean Dynamic Topography (MDT) and associated mean geostrophic currents have been computed (Rio et al, 2014). First a satellite only MDT was computed from altimetric and gravimetric data. Then, an important work was to pre-process drifter data to extract only the geostrophic component in order to be consistent with physical content of satellite only MDT. This step include estimate and remove of Ekman current and wind slippage. Finally drifters and satellite only MDT were combined. Similar approaches are used regionally to go further toward higher resolution, for instance in the Agulhas current or along the Brazilian coast. Also, a case study in the Gulf of Mexico intends to use drifters in the same way to improve weekly geostrophic current estimate.

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

    Science.gov (United States)

    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.

  8. Observing storm surges in the Bay of Bengal from satellite altimetry

    Digital Repository Service at National Institute of Oceanography (India)

    Antony, C.; Testut, L.; Unnikrishnan, A.S.

    usage of altimetry data in the coastal regions. In addition to X-TRACK processed data, PISTACH (Prototype Innovant de Système de Traitement pour l’Altimétrie Côtière et l’Hydrologie; Mercier et al., 2010) and COASTALT (Gomez-Enri et al., 2008) projects... Igor off Newfoundland. Scientific Reports 2 1010, doi:10.1038/srep01010. Harwood, P., Cipollini, P., Snaith, H., HØyer, J., Dwyer, N., Dunne, D., Stoffelen, A., Donlon, C., 2013. Earth observation in aid of surge monitoring and forecasting: ESA’s e...

  9. The Solar and Southern Oscillation Components in the Satellite Altimetry Data

    DEFF Research Database (Denmark)

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

    2015-01-01

    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...... 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....

  10. Assessment of NASA Airborne Laser Altimetry Data Using Ground-Based GPS Data near Summit Station, Greenland

    Science.gov (United States)

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

    2017-01-01

    A series of NASA airborne lidars have been used in support of satellite laser altimetry missions. These airbornelaser 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.

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

    Science.gov (United States)

    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

  12. A Preliminary Analysis of Lake Level and Water Storage Changes over Lakes Baikal and Balkhash from Satellite Altimetry and Gravimetry

    Directory of Open Access Journals (Sweden)

    Cheinway Hwang

    2011-01-01

    Full Text Available Lakes Baikal and Balkhash are two of the world¡¦s major lakes affecting fresh water supplies in their catchments. Measurements from satellite altimetry (TOPEX/Poseidon, Jason-1 and -2, satellite gravimetry (GRACE and a hydrological model (LDAS are used to see the relationship between lake level change (LLC and water storage change in these two lakes. At Lake Baikal, the average rate of LLC is negative for 1992 - 1998 and positive for 1998 - 2007, and the reversal of the LLC trend concurs with that of the temperature trend during the 1997 - 1998 El Nino. The rate of gravity change ranges from -0.5 to 0.5 ugal yr-1 with a low over the Tian Shan and a high over western Lake Baikal. Due to the climates over the two lakes, the phases of the annual gravity changes differ by up to 100 days. Using the rates of LLC and gravity changes, the ratios between the mass changes of the lake and its catchment over Lakes Baikal and Balkhash are estimated to 0.6 and 0.3, respectively. The result may help to establish water balance models over these two lakes.

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

    Science.gov (United States)

    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.

  14. Assessment of the Impact of Reservoirs in the Upper Mekong River Using Satellite Radar Altimetry and Remote Sensing Imageries

    Directory of Open Access Journals (Sweden)

    Kuan-Ting Liu

    2016-04-01

    Full Text Available Water level (WL and water volume (WV of surface-water bodies are among the most crucial variables used in water-resources assessment and management. They fluctuate as a result of climatic forcing, and they are considered as indicators of climatic impacts on water resources. Quantifying riverine WL and WV, however, usually requires the availability of timely and continuous in situ data, which could be a challenge for rivers in remote regions, including the Mekong River basin. As one of the most developed rivers in the world, with more than 20 dams built or under construction, Mekong River is in need of a monitoring system that could facilitate basin-scale management of water resources facing future climate change. This study used spaceborne sensors to investigate two dams in the upper Mekong River, Xiaowan and Jinghong Dams within China, to examine river flow dynamics after these dams became operational. We integrated multi-mission satellite radar altimetry (RA, Envisat and Jason-2 and Landsat-5/-7/-8 Thematic Mapper (TM/Enhanced Thematic Mapper plus (ETM+/Operational  Land Imager (OLI optical remote sensing (RS imageries to construct composite WL time series with enhanced spatial resolutions and substantially extended WL data records. An empirical relationship between WL variation and water extent was first established for each dam, and then the combined long-term WL time series from Landsat images are reconstructed for the dams. The R2 between altimetry WL and Landsat water area measurements is >0.95. Next, the Tropical Rainfall Measuring Mission (TRMM data were used to diagnose and determine water variation caused by the precipitation anomaly within the basin. Finally, the impact of hydrologic dynamics caused by the impoundment of the dams is assessed. The discrepancy between satellite-derived WL and available in situ gauge data, in term of root-mean-square error (RMSE is at 2–5 m level. The estimated WV variations derived from combined RA

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

    Science.gov (United States)

    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.

  16. Sea surface height variability in the North East Atlantic from satellite altimetry

    Science.gov (United States)

    Sterlini, Paul; de Vries, Hylke; Katsman, Caroline

    2016-08-01

    Data from 21 years of satellite altimeter measurements are used to identify and understand the major contributing components of sea surface height variability (SSV) on monthly time-scales in the North East Atlantic. A number of SSV drivers is considered, which are categorised into two groups; local (wind and sea surface temperature) and remote (sea level pressure and the North Atlantic oscillation index). A multiple linear regression model is constructed to model the SSV for a specific target area in the North Sea basin. Cross-correlations between candidate regressors potentially lead to ambiguity in the interpretation of the results. We therefore use an objective hierarchical selection method based on variance inflation factors to select the optimal number of regressors for the target area and accept these into the regression model if they can be associated to SSV through a direct underlying physical forcing mechanism. Results show that a region of high SSV exists off the west coast of Denmark and that it can be represented well with a regression model that uses local wind, sea surface temperature and sea level pressure as primary regressors. The regression model developed here helps to understand sea level change in the North East Atlantic. The methodology is generalised and easily applied to other regions.

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

    Science.gov (United States)

    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.

  18. 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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  20. Patterns of upper layer circulation variability in the South China Sea from satellite altimetry using the self-organizing map

    Institute of Scientific and Technical Information of China (English)

    LIU Yonggang; WEISBERG Robert H; YUAN Yaochu

    2008-01-01

    Patterns of the South China Sea (SCS) circulation variability are extracted from merged satellite altimetry data from October 1992 through August 2004 by using the self-organizing map (SOM). The annual cycle, seasonal and inter-annual variations of the SCS surface circulation are identified through the evolution of the characteristic circulation patterns. The annual cycle of the SCS gener- al circulation patterns is described as a change between two opposite basin-scale SW-NE oriented gyres embedded with eddies: low sea surface height anomaly (SSHA) (cyclonic) in winter and high SSHA (anticyclonic) in summer half year. The transition starts from July--August (January--February) with a high (low) SSHA tongue east of Vietnam around 12°~14° N, which de- velopa into a big anticyclonic (cyclonic) gyre while moving eastward to the deep basin. During the transitions, a dipole structure, cyclonic (anticyclonic) in the north and anticyclonic (cyclonic) in the south, may be formed southeast off Vietnam with a strong zonal jet around 10°~12° N. The seasonal variation is modulated by the interannual variations. Besides the strong 1997/1998 e- vent in response to the peak Pacific El Nino in 1997, the overall SCS sea level is found to have a significant rise during 1999~ 2001, however, in summer 2004 the overall SCS sea level is lower and the basin-wide anticyclonic gyre becomes weaker than the other years.

  1. Treating the Hooking Effect in Satellite Altimetry Data: A Case Study along the Mekong River and Its Tributaries

    Directory of Open Access Journals (Sweden)

    Eva Boergens

    2016-01-01

    Full Text Available This study investigates the potential of satellite altimetry for water level time series estimation of smaller inland waters where only very few measurements above the water surface are available. A new method was developed using off-nadir measurements to estimate the parabola generated by the hooking effect. For this purpose, a new waveform retracker was used as well as an adopted version of the RANdom SAmple Consensus (RANSAC algorithm. The method is applied to compute time series of the water levels height of the Mekong River and some of its tributaries from Envisat high-frequency data. Reliable time series can be obtained from river crossings with widths of less than 500 m and without direct nadir measurements over the water. The expected annual variations are clearly depicted and the time series well agree with available in situ gauging data. The mean RMS value is 1.22 m between the resulting time series and in situ data, the best result is 0.34 m, the worst 2.26 m, and 80% of the time series have an RMS below 1.5 m.

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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.

  4. Satellite Altimetry and GRACE Gravimetry for Studies of Annual Water Storage Variations in Bangladesh

    Directory of Open Access Journals (Sweden)

    Ole Andersen

    2008-01-01

    Full Text Available Four different data sources have been compared with respect to observations of the annual water storage variations in the region of Bangladesh. Data from satellite altimeters and river gauges estimates the variation in surface water storage in the major rivers of Bangladesh.

  5. Satellite Altimetry and GRACE Gravimetry for Studies of Annual Water Storage Variations in Bangladesh

    Directory of Open Access Journals (Sweden)

    Ole Andersen

    2008-01-01

    Full Text Available Four different data sources have been compared with respect to observations of the annual water storage variations in the region of Bangladesh. Data from satellite altimeters and river gauges estimates the variation in surface water storage in the major rivers of Bangladesh. The GRACE satellites measure the integrated mass change and hence the terrestrial soil moisture variations, which can also be estimated by a hydrological model (GLDAS. These types of observations enable the derivation of the integrated water storage in the entire region of Bangladesh. For all data types, the annual signal has been estimated from a common dataset spanning the period 2003 and 2004. All four different data observe that water storage in Bangladesh is largely dominated by an annual signal with a phase peaking in early September. The annual variations in river level peaks roughly two weeks earlier than terrestrial soil moisture observations by GRACE observations and GLDAS model output.

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

    Science.gov (United States)

    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.

  7. Satellite altimetry and GRACE gravimetry for studies of annual water storage variations in Bangladesh

    DEFF Research Database (Denmark)

    Andersen, Ole Baltazar; Berry, P.; Freeman, J.;

    2008-01-01

    Four different data sources have been compared with respect to observations of the annual water storage variations in the region of Bangladesh. Data from satellite altimeters and river gauges estimates the variation in surface water storage in the major rivers of Bangladesh. The GRACE satellites...... measure the integrated mass change and hence the terrestrial soil moisture variations, which can also be estimated by a hydrological model (GLDAS). These types of observations enable the derivation of the integrated water storage in the entire region of Bangladesh. For all data types, the annual signal...... has been estimated from a common dataset spanning the period 2003 and 2004. All four different data observe that water storage in Bangladesh is largely dominated by an annual signal with a phase peaking in early September. The annual variations in river level peaks roughly two weeks earlier than...

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

    Science.gov (United States)

    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.

  9. Estimating boundary currents from satellite altimetry: A case study for the east coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Durand, F.; Shankar, D.; Birol, F.; Shenoi, S.S.C.

    in our area (Chelton et al., 1998). We can see that the other dynamical effects not accounted for by the linear theory tend to spread the coastal trapping of the energy in the offshore direction. About 200 km off the coast, the power of the annual... by means of a 3.notdef.g0002 filter, where .notdef.g0002 is the standard deviation of the original along track record. One value of .notdef.g0002 is computed per satellite cycle and per corrective parameter, so as to account for the natural temporal...

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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.

  12. Mean dynamic topography over Peninsular Malaysian seas using multimission satellite altimetry

    Science.gov (United States)

    Abazu, Isaac Chidi; Din, Ami Hassan Md; Omar, Kamaludin Mohd

    2017-04-01

    The development of satellite altimeters (SALTs) has brought huge benefits, among which is the ability to more adequately sense ocean-surface topography. The radar altimeter database system was used to capture and process ENVISAT, CRYOSAT-2, SARAL, JASON-1, and JASON-2 SALT data of 5 years between 2011 and 2015. The time series of monthly multimission SALT data showed an estimated sea level trend of 1.0, 2.4, 2.4, 3.6, and 12.0 mm/year at Gelang, Port Kelang, Kukup, Cendering, and Keling. The correlation analysis for the selected tide gauge stations produced satisfying results of R-squared with 0.86, 0.89, 0.91, and 0.97 for Cendering, Sedili, Gelang, and Geting, respectively. The ITG-Grace2010s geoid model was used to compute the mean dynamic topography (MDT) and plot to a grid of 0.25 deg for the Malacca Strait and South China Sea of Peninsular Malaysia, with Keling, Port Kelang, Geting, Sedili, and Johor Bahru tide gauge stations having values determined by interpolation to be 1.14, 1.19, 1.26, 1.88, and 2.91 m, respectively. MDT is computed from the SALT with respect to Port Kelang, the north-south sea slope ranges between -0.64 and 0.29 m/50 km and -0.01 and 0.52 m/50 km along the east and west coasts of Peninsular Malaysia, respectively.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  15. Satellite radar altimetry over ice. Volume 4: Users' guide for Antarctica elevation data from Seasat

    Science.gov (United States)

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

    1990-01-01

    A gridded surface-elevation data set and a geo-referenced data base for the Seasat radar altimeter data over Greenland are described. This is a user guide to accompany the data provided to data centers and other users. The grid points are on a polar stereographic projection with a nominal spacing of 20 km. The gridded elevations are derived from the elevation data in the geo-referenced data base by a weighted fitting of a surface in the neighborhood of each grid point. The gridded elevations are useful for the creating of large-scale contour maps, and the geo-referenced data base is useful for regridding, creating smaller-scale contour maps, and examinating individual elevation measurements in specific geographic areas. Tape formats are described, and a FORTRAN program for reading the data tape is listed and provided on the tape.

  16. Terrestrial Water Storage from GRACE and Satellite Altimetry in the Okavango Delta (Botswana)

    DEFF Research Database (Denmark)

    Andersen, Ole Baltazar; Krogh, Pernille Engelbredt; Bauer-Gottwein, Peter;

    2010-01-01

    New technology can for the first time enable the accurate retrieval of the global and regional water budgets from space-borne and ground-based gravity surveys. Water is mankind’s most critical natural resource, but it is being heavily used throughout the globe. The aim of this paper is to outline...

  17. Satellite radar altimetry over ice. Volume 2: Users' guide for Greenland elevation data from Seasat

    Science.gov (United States)

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

    1990-01-01

    A gridded surface-elevation data set and a geo-referenced data base for the Seasat radar altimeter data over Antarctica are described. It is intended to be a user's guide to accompany the data provided to data centers and other users. The grid points are on a polar stereographic projection with a nominal spacing of 20 km. The gridded elevations are derived from the elevation data in the geo-referenced data base by a weighted fitting of a surface in the neighborhood of each grid point. The gridded elevations are useful for the creating smaller-scale contour maps, and examining individual elevation measurements in specific geographic areas. Tape formats are described, and a FORTRAN program for reading the data tape is listed and provided on the tape.

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

    Science.gov (United States)

    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.

  19. Topography over South America from ERS altimetry

    Science.gov (United States)

    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. CryoSat-2 satellite radar altimetry for river analysis and modelling

    DEFF Research Database (Denmark)

    Schneider, Raphael

    households, restaurants and commercial and industrial sources by 2020 in Denmark and throughout the European Union. In Denmark, conventionally organic household waste has been incinerated, so the biological treatment of organic household waste is very limited. Current policies promote moving away from......) Developing a near-infrared reflectance spectroscopy (NIRS)-based computational model for predicting the methane potential of urban organic waste, (ii) Performance of co-digestion of urban organic waste with mixed sludge from wastewater treatment plants in a continuous reactor operation, (iii) Analysis....... The main objective of this PhD study was systematic quantification of biogas production and biochemical transformation of urban organic waste comprising organic household waste, garden waste and industrial organic waste. The overall objective of this PhD research has been carried out in four phases: (i...

  1. Mapping error in Southern Ocean transport computed from satellite altimetry and argo

    Science.gov (United States)

    Kosempa, Michael; Chambers, Don P.

    2016-11-01

    In an effort to better estimate transport dynamics in response to wind forcing (primarily the Southern Annual Mode), this study quantifies the uncertainty in mapping zonal geostrophic transport of the Antarctic Circumpolar Current from sparse temperature, salinity and sea surface height observations. To do this, we sampled an ocean state estimate at the locations of both Argo floats and the Jason-1 altimeter groundtrack. These sampled values were then optimally interpolated to create SSH and temperature/salinity grids with 1° resolution. The temperature, salinity and SSH grids were then combined to compute the zonal geostrophic transport and compared to that estimated from the full state estimate. There are significant correlations between the baroclinic and barotropic error contributions to the total transport error. The increase in Argo floats in the Southern Ocean is effective in reducing mapping error. However, that error improvement is not uniform. By analyzing systematic errors in transport time series, we find the transects that are most appropriate for analyzing the dynamics of ACC transport using Argo and altimetric gridded fields. Based on our analysis, we conclude region south of Tasmania is most appropriate, with lowest uncertainty. Using real-world data, we calculated zonal transport variability at a transect south of Tasmania. There is an insignificant trend (0.3 ± 0.4 Sv yr-1, 90% confidence) but significant low-frequency variability correlated with the Southern Annular Mode (0.53, p < 0.05). The barotropic component is most responsible for the low-frequency variability, and this would be unobservable from ship casts without velocity measurements at depth.

  2. 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

    DEFF Research Database (Denmark)

    Kern, S.; Khvorostovsky, K.; Skourup, H.

    2015-01-01

    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...

  3. Arctic sea level change over the past 2 decades from GRACE gradiometry and multi-mission satellite altimetry

    DEFF Research Database (Denmark)

    Andersen, O. B.; Stenseng, L.; Sørensen, C. S.

    2014-01-01

    gradiometer observations from the ESA GOCE mission, we are now able to derive a mean dynamic topography of the Arctic Ocean with unprecedented accuracy to constrain the Arctic Ocean circulation controlling sea level variations in the Arctic. We present both a new estimation of the mean ocean circulation......The Arctic is still an extremely challenging region for theuse of remote sensing for sea level studies. Despite the availability of 20 years of altimetry, only very limited sea level observations exist in the interior of the Arctic Ocean. However, with Cryosat-2 SAR altimetry the situation...... is changing and through development of tailored retrackers dealing with presence of sea ice within the radar footprint, we can now develop sea surface height and its variation in most of the Arctic Ocean. We have processed 3 years of Cryosat-2 data quantified as either Lead or Ocean data within the Cryosat-2...

  4. Ocean circulation using altimetry

    Science.gov (United States)

    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.

  5. Challenges for Greenland-wide mass balance from Cryosat-2 radar-altimetry

    DEFF Research Database (Denmark)

    Simonsen, Sebastian Bjerregaard; Forsberg, René; Sørensen, Louise Sandberg

    be interpreted as actual surface elevation changes seen from the satellite radar altimetry (Nilsson et al., 2015).Here, we investigate how to correct the elevation change observed from the ESA Cryosat-2 radar altimetry mission to derive elevation change of the air/snow interface of the Greenland ice sheet......As the Greenland ice sheet warms, a change in the structure of the upper snow/firn occurs. This change further induces changes in the reflective properties of the firn seen from satellite radar altimetry. If not identified as changes in the reflective properties of the firn, these may....... The elevation change of this “real” physical surface is crucial, if the goal is to derive Greenland mass balance as done for LiDAR missions.The investigations look into waveform parameters to correct for the observed bias between Radar and LiDAR observations when using Croysat-2 level-2 data. Based...

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

    Science.gov (United States)

    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

  7. High-frequency Earth rotation variations deduced from altimetry-based ocean tides

    Science.gov (United States)

    Madzak, Matthias; Schindelegger, Michael; Böhm, Johannes; Bosch, Wolfgang; Hagedoorn, Jan

    2016-06-01

    A model of diurnal and semi-diurnal variations in Earth rotation parameters (ERP) is constructed based on altimetry-measured tidal heights from a multi-mission empirical ocean tide solution. Barotropic currents contributing to relative angular momentum changes are estimated for nine major tides in a global inversion algorithm that solves the two-dimensional momentum equations on a regular 0.5° grid with a heavily weighted continuity constraint. The influence of 19 minor tides is accounted for by linear admittance interpolation of ocean tidal angular momentum, although the assumption of smooth admittance variations with frequency appears to be a doubtful concept for semi-diurnal mass terms in particular. A validation of the newly derived model based on post-fit corrections to polar motion and universal time (Δ UT1) from the analysis of Very Long Baseline Interferometry (VLBI) observations shows a variance reduction for semi-diurnal Δ UT1 residuals that is significant at the 0.05 level with respect to the conventional ERP model. Improvements are also evident for the explicitly modeled K_1 , Q_1 , and K_2 tides in individual ERP components, but large residuals of more than 15 μ as remain at the principal lunar frequencies of O_1 and M_2 . We attribute these shortcomings to uncertainties in the inverted relative angular momentum changes and, to a minor extent, to violation of mass conservation in the empirical ocean tide solution. Further dedicated hydrodynamic modeling efforts of these anomalous constituents are required to meet the accuracy standards of modern space geodesy.

  8. High-frequency Earth rotation variations deduced from altimetry-based ocean tides

    Science.gov (United States)

    Madzak, Matthias; Schindelegger, Michael; Böhm, Johannes; Bosch, Wolfgang; Hagedoorn, Jan

    2016-11-01

    A model of diurnal and semi-diurnal variations in Earth rotation parameters (ERP) is constructed based on altimetry-measured tidal heights from a multi-mission empirical ocean tide solution. Barotropic currents contributing to relative angular momentum changes are estimated for nine major tides in a global inversion algorithm that solves the two-dimensional momentum equations on a regular 0.5° grid with a heavily weighted continuity constraint. The influence of 19 minor tides is accounted for by linear admittance interpolation of ocean tidal angular momentum, although the assumption of smooth admittance variations with frequency appears to be a doubtful concept for semi-diurnal mass terms in particular. A validation of the newly derived model based on post-fit corrections to polar motion and universal time (Δ UT1) from the analysis of Very Long Baseline Interferometry (VLBI) observations shows a variance reduction for semi-diurnal Δ UT1 residuals that is significant at the 0.05 level with respect to the conventional ERP model. Improvements are also evident for the explicitly modeled K_1, Q_1, and K_2 tides in individual ERP components, but large residuals of more than 15 μ as remain at the principal lunar frequencies of O_1 and M_2. We attribute these shortcomings to uncertainties in the inverted relative angular momentum changes and, to a minor extent, to violation of mass conservation in the empirical ocean tide solution. Further dedicated hydrodynamic modeling efforts of these anomalous constituents are required to meet the accuracy standards of modern space geodesy.

  9. The DTU13 MSS (Mean Sea Surface) and MDT (Mean Dynamic Topography) from 20 Years of Satellite Altimetry

    DEFF Research Database (Denmark)

    Andersen, Ole Baltazar; Knudsen, Per; Stenseng, Lars

    2015-01-01

    enables the determination of sea level in leads in the ice, which has enabled us to derive an accurate MSS all the way to 88°N.With the availability to determine the geoid with higher accuracy than ever before due to the launch of the GRACE and GOCE satellites, is hence become possible to derive...... a satellite only mean dynamic topography (MDT) from the difference between the MSS and the geoid. Here the DTU13MSS and DTU13MDT are presented and we demonstrate how these can be used to derive realistic geostrophic currents in the world’s ocean comparable to oceanographic derived MDT....

  10. Updating river basin models with radar altimetry

    DEFF Research Database (Denmark)

    Michailovsky, Claire Irene B.

    response of a catchment to meteorological forcing. While river discharge cannot be directly measured from space, radar altimetry (RA) can measure water level variations in rivers at the locations where the satellite ground track and river network intersect called virtual stations or VS. In this PhD study...... been between 10 and 35 days for altimetry missions until now. The location of the VS is also not necessarily the point at which measurements are needed. On the other hand, one of the main strengths of the dataset is its availability in near-real time. These characteristics make radar altimetry ideally...... suited for use in data assimilation frameworks which combine the information content from models and current observations to produce improved forecasts and reduce prediction uncertainty. The focus of the second and third papers of this thesis was therefore the use of radar altimetry as update data...

  11. A Super-Resolution Laser Altimetry Concept

    Science.gov (United States)

    Lu, Xiaomei; Hu, Yongxiang; Trepte, Charles; Liu, Zhaoyan

    2014-01-01

    A super-resolution laser altimetry technique has been proposed to provide improved lidar altimetry from Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) lidar data, and it is applicable to other similar atmospheric profiling lidar with low-pass filters. To achieve high altimetry resolution, the new technique relies on an empirical relationship between the peak signal ratio and the distance between land surface and the peak signal range bin center, which is directly derived from the CALIPSO lidar measurements and does not require the CALIPSO's transient response. The CALIPSO surface elevation results in Northern America retrieved by the new technique agree with the National Elevation Database high resolution elevation maps, and the comparisons suggest that the precision of the technique is much better than 1.4 m. The preliminary data product of land surface elevation retrieved by the new technique from CALIPSO lidar measurements is available to the altimetry community for evaluation.

  12. Biogeography based Satellite Image Classification

    CERN Document Server

    Panchal, V K; Kaur, Navdeep; Kundra, Harish

    2009-01-01

    Biogeography is the study of the geographical distribution of biological organisms. The mindset of the engineer is that we can learn from nature. Biogeography Based Optimization is a burgeoning nature inspired technique to find the optimal solution of the problem. Satellite image classification is an important task because it is the only way we can know about the land cover map of inaccessible areas. Though satellite images have been classified in past by using various techniques, the researchers are always finding alternative strategies for satellite image classification so that they may be prepared to select the most appropriate technique for the feature extraction task in hand. This paper is focused on classification of the satellite image of a particular land cover using the theory of Biogeography based Optimization. The original BBO algorithm does not have the inbuilt property of clustering which is required during image classification. Hence modifications have been proposed to the original algorithm and...

  13. On the surface circulation of the Levantine sub-basin derived from Lagrangian drifters and satellite altimetry data

    Science.gov (United States)

    Menna, Milena; Poulain, Pierre-Marie; Zodiatis, George; Gertman, Isaac

    The surface currents of the Levantine sub-basin (Mediterranean Sea) are described using 18 years (1992-2010) of drifter data and satellite-derived sea level anomalies. The combination of drifter and satellite data allowed to estimate maps of surface geostrophic circulation and to obtain more accurate pseudo-Eulerian velocity statistics for different time periods. Seasonal and interannual variability of surface currents are investigated with particular focus on the main sub-basin eddies of the eastern Levantine. The mean velocity field depicts the typical patterns of the along-slope and offshore currents and outlines the sub-regions where eddies are generated recurrently (west Egyptian coast, Ierapetra, Mersa-Matruh, south-west of Cyprus, Israel-Lebanon coast, Latakia) or persist steadily (Rhodes Gyre). Highly variable and energetic currents are observed between the Ierapetra and Mersa-Matruh regions, as the result of the interaction of the Mid-Mediterranean Jet meandering in between, and interacting with, the eddies generated by the instability of the coastal current. Seasonal pseudo-Eulerian maps show the current field stronger in summer and weaker in winter, mainly in the western Levantine and in the Cyprus-Syria Passage. The Shikmona Eddy displays a periodic nature with higher intensities during the cold months and an enhanced activity in the period 1998-2005. The Cyprus Eddy has a less periodic nature, characterised by events of high activity and periods in which it dominates as a single enlarged eddy in the southeast Levantine, eventually including the Shikmona Eddy. The Latakia Eddy is mainly cyclonic with higher intensities in summer and fall; occasional weekly or monthly inversions of circulation from cyclonic to anticyclonic are triggered by the interaction between the MMJ and the northward coastal meandering current.

  14. HYDROGRAV - Hydrological model calibration and terrestrial water storage monitoring from GRACE gravimetry and satellite altimetry, First results

    DEFF Research Database (Denmark)

    Andersen, O.B.; Krogh, P.E.; Michailovsky, C.

    2008-01-01

    Space-borne and ground-based time-lapse gravity observations provide new data for water balance monitoring and hydrological model calibration in the future. The HYDROGRAV project (www.hydrograv.dk) will explore the utility of time-lapse gravity surveys for hydrological model calibration and terre...

  15. Assessment of altimetry data in Amazonian forest based in INSAR, LIDAR; and GPS technologies.

    Directory of Open Access Journals (Sweden)

    Corina da Costa Freitas

    2006-12-01

    Full Text Available There is a great amount of altimetry data collected by several experiments taken in the Tapajós National Forest located in the Brazilian Amazon State of Pará. Some of these data were produced by current state of the art technology whose effectiveness is still being proven by scientific investigations. In 1999 LIDAR profiles associated to videography data were taken in the region. In 2000 it was collected P and X band interferometric multifrequency data over areas of different vegetation types. The backscatter response collected by P band radar antenna potentially produces a real digital terrain model (DTM due to its penetration capability across forest canopy toward the soil. When collected in X band radiation is reflected in the top forest canopy which produces a digital surface model (DSM. The availability of digital terrain model and digital surface model covering the same forested area is of great interest for many purposes, especially cartographic applications and carbon stock estimation. Also in 2000, the SRTM mission provided global interferometric cover in C and X bands that permitted the use of these data in the present work. In 2001, 2002, 2003 e 2005 several field control positions were surveyed using GPS dual frequency receivers and by topography surveying methods using total stations. The purpose of this work is to make an evaluation of the errors affecting the original multiple sensor data collected in the study area and apply an effective correction in order to eliminate those errors to permit using the models in other applications. An effective correction type was developed that reduced the original errors. The correction methodology consisted in altimetry offset determination and its application to the original data. Evaluations confirmed that the correction methodology produced good results and the corrected models presented global and local errors lesser than those in the original models.

  16. Computer based satellite design

    Science.gov (United States)

    Lashbrook, David D.

    1992-06-01

    A computer program to design geosynchronous spacecraft has been developed. The program consists of four separate but interrelated executable computer programs. The programs are compiled to run on a DOS based personnel computer. The source code is written in DoD mandated Ada programming language. The thesis presents the design technique and design equations used in the program. Detailed analysis is performed in the following areas for both dual spin and three axis stabilized spacecraft configurations: (1) Mass Propellent Budget and Mass Summary; (2) Battery Cell and Solar Cell Requirements for a Payload Power Requirement; and (3) Passive Thermal Control Requirements. A user's manual is included as Appendix A, and the source code for the computer programs as Appendix B.

  17. Satellite-Based Quantum Communications

    Energy Technology Data Exchange (ETDEWEB)

    Hughes, Richard J [Los Alamos National Laboratory; Nordholt, Jane E [Los Alamos National Laboratory; McCabe, Kevin P [Los Alamos National Laboratory; Newell, Raymond T [Los Alamos National Laboratory; Peterson, Charles G [Los Alamos National Laboratory

    2010-09-20

    Single-photon quantum communications (QC) offers the attractive feature of 'future proof', forward security rooted in the laws of quantum physics. Ground based quantum key distribution (QKD) experiments in optical fiber have attained transmission ranges in excess of 200km, but for larger distances we proposed a methodology for satellite-based QC. Over the past decade we have devised solutions to the technical challenges to satellite-to-ground QC, and we now have a clear concept for how space-based QC could be performed and potentially utilized within a trusted QKD network architecture. Functioning as a trusted QKD node, a QC satellite ('QC-sat') could deliver secret keys to the key stores of ground-based trusted QKD network nodes, to each of which multiple users are connected by optical fiber or free-space QC. A QC-sat could thereby extend quantum-secured connectivity to geographically disjoint domains, separated by continental or inter-continental distances. In this paper we describe our system concept that makes QC feasible with low-earth orbit (LEO) QC-sats (200-km-2,000-km altitude orbits), and the results of link modeling of expected performance. Using the architecture that we have developed, LEO satellite-to-ground QKD will be feasible with secret bit yields of several hundred 256-bit AES keys per contact. With multiple ground sites separated by {approx} 100km, mitigation of cloudiness over any single ground site would be possible, potentially allowing multiple contact opportunities each day. The essential next step is an experimental QC-sat. A number of LEO-platforms would be suitable, ranging from a dedicated, three-axis stabilized small satellite, to a secondary experiment on an imaging satellite. to the ISS. With one or more QC-sats, low-latency quantum-secured communications could then be provided to ground-based users on a global scale. Air-to-ground QC would also be possible.

  18. 14 CFR 141.91 - Satellite bases.

    Science.gov (United States)

    2010-01-01

    ... 14 Aeronautics and Space 3 2010-01-01 2010-01-01 false Satellite bases. 141.91 Section 141.91... OTHER CERTIFICATED AGENCIES PILOT SCHOOLS Operating Rules § 141.91 Satellite bases. The holder of a... assistant chief instructor is designated for each satellite base, and that assistant chief instructor...

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

    Science.gov (United States)

    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.

  20. Water discharge estimates from large radar altimetry datasets in the Amazon basin

    Directory of Open Access Journals (Sweden)

    A. C. V. Getirana

    2012-06-01

    Full Text Available In this study, we evaluate the use of a large radar altimetry dataset as a complementary gauging network capable of providing water discharge in ungauged regions within the Amazon basin. A rating-curve-based methodology is adopted to derive water discharge from altimetric data provided by Envisat at 444 virtual stations (VS. The stage-discharge relations at VS are built based on radar altimetry and outputs from a global flow routing scheme. In order to quantify the impact of modeling uncertainties on rating-curve based discharges, another experiment is performed using simulated discharges derived from a simplified data assimilation procedure. Discharge estimates at 90 VS are evaluated against observations during the curve fitting calibration (2002–2005 and evaluation (2006–2008 periods, resulting in mean relative RMS errors as high as 52% and 12% for experiments without and with assimilation, respectively. Without data assimilation, uncertainty of discharge estimates can be mostly attributed to forcing errors at smaller scales, generating a positive correlation between performance and drainage area. Mean relative errors (RE of altimetry-based discharges varied from 15% to 92% for large and small drainage areas, respectively. Rating curves produced a mean RE of 54% versus 68% from model outputs. Assimilating discharge data decreases the mean RE from 68% to 12%. These results demonstrate the feasibility of applying the proposed methodology to the regional or global scales. Also, it is shown the potential of satellite altimetry for predicting water discharge in poorly-gauged and ungauged river basins.

  1. Icesat full waveform altimetry compared to airborne laser altimetry over the Netherlands

    NARCIS (Netherlands)

    Duong, H.; Lindenbergh, R.; Pfeifer, N.; Vosselman, G.

    2007-01-01

    Since 2003 the spaceborne laser altimetry system on board of NASA’s Ice, Cloud and land Elevation Satellite (ICESat) has acquired a large world-wide database of full waveform data organized in 15 products. In this research three products are evaluated over The Netherlands. For this purpose the raw f

  2. ICESat Full-Waveform Altimetry Compared to Airborne Laser Scanning Altimetry Over The Netherlands

    NARCIS (Netherlands)

    Duong, H.; Lindenbergh, R.; Pfeifer, N.; Vosselman, G.

    2009-01-01

    Since 2003, the full-waveform laser altimetry system onboard NASA's Ice, Cloud and land Elevation Satellite (ICESat) has acquired a worldwide elevation database. ICESat data are widely applied for change detection of ice sheet mass balance, forest structure estimation, and digital terrain model gene

  3. Icesat full waveform altimetry compared to airborne laser altimetry over the Netherlands

    NARCIS (Netherlands)

    Duong, H.; Lindenbergh, R.; Pfeifer, N.; Vosselman, G.

    2007-01-01

    Since 2003 the spaceborne laser altimetry system on board of NASA’s Ice, Cloud and land Elevation Satellite (ICESat) has acquired a large world-wide database of full waveform data organized in 15 products. In this research three products are evaluated over The Netherlands. For this purpose the raw f

  4. Broadview Radar Altimetry Toolbox

    Science.gov (United States)

    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

  5. The principle of the positioning system based on communication satellites

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    It is a long dream to realize the communication and navigation functionality in a satellite system in the world. This paper introduces how to establish the system, a positioning system based on communication satellites called Chinese Area Positioning System (CAPS). Instead of the typical navigation satellites, the communication satellites are configured firstly to transfer navigation signals from ground stations, and can be used to obtain service of the positioning, velocity and time, and to achieve the function of navigation and positioning. Some key technique issues should be first solved; they include the accuracy position determination and orbit prediction of the communication satellites, the measur- ing and calculation of transfer time of the signals, the carrier frequency drift in communication satellite signal transfer, how to improve the geometrical configuration of the constellation in the system, and the integration of navigation & communication. Several innovative methods are developed to make the new system have full functions of navigation and communication. Based on the development of crucial techniques and methods, the CAPS demonstration system has been designed and developed. Four communication satellites in the geosynchronous orbit (GEO) located at 87.5°E, 110.5°E, 134°E, 142°E and barometric altimetry are used in the CAPS system. The GEO satellites located at 134°E and 142°E are decommissioned GEO (DGEO) satellites. C-band is used as the navigation band. Dual frequency at C1=4143.15 MHz and C2=3826.02 MHz as well as dual codes with standard code (CA code and precision code (P code)) are adopted. The ground segment consists of five ground stations; the master station is in Lintong, Xi’an. The ground stations take a lot of responsibilities, including monitor and management of the operation of all system components, determination of the satellite position and prediction of the satellite orbit, accomplishment of the virtual atomic clock

  6. Major improvement of altimetry sea level estimations using pressure-derived corrections based on ERA-Interim atmospheric reanalysis

    Science.gov (United States)

    Carrere, Loren; Faugère, Yannice; Ablain, Michaël

    2016-06-01

    The new dynamic atmospheric correction (DAC) and dry tropospheric (DT) correction derived from the ERA-Interim meteorological reanalysis have been computed for the 1992-2013 altimeter period. Using these new corrections significantly improves sea level estimations for short temporal signals (SSH) error by more than 3 cm in the Southern Ocean and in some shallow water regions. The impact of DT_ERA (DT derived from ERA-Interim meteorological reanalysis) is also significant in the southern high latitudes for these missions. Concerning more recent missions (Jason-1, Jason-2, and Envisat), results are very similar between ERA-Interim and ECMWF-based corrections: on average for the global ocean, the operational DAC becomes slightly better than DAC_ERA only from the year 2006, likely due to the switch of the operational forcing to a higher spatial resolution. At regional scale, both DACs are similar in the deep ocean but DAC_ERA raises the residual crossovers' variance in some shallow water regions, indicating a slight degradation in the most recent years of the study. In the second decade of altimetry, unexpectedly DT_ERA still gives better results compared to the operational DT. Concerning climate signals, both DAC_ERA and DT_ERA have a low impact on global mean sea level rise (MSL) trends, but they can have a strong impact on long-term regional trends' estimation, up to several millimeters per year locally.

  7. The principle of the positioning system based on communication satellites

    Institute of Scientific and Technical Information of China (English)

    AI GuoXiang; SHI HuLi; WU HaiTao; LI ZhiGang; GUO Ji

    2009-01-01

    It is a long dream to realize the communication and navigation functionality in a satellite system in the world.This paper introduces how to establish the system,a positioning system based on communication satellites called Chinese Area Positioning System (CAPS).Instead of the typical navigation satelIites,the communication satellites are configured firstly to transfer navigation signals from ground stations,and can be used to obtain service of the positioning,velocity and time,and to achieve the function of navigation and positioning.Some key technique issues should be first solved; they include the accuracy position determination and orbit prediction of the communication satellites,the measuring and calculation of transfer time of the signals,the carrier frequency drift in communication satellite ignal transfer,how to improve the geometrical configuration of the constellation in the system,and the integration of navigation & communication.Several innovative methods are developed to make the new system have full functions of navigation and communication.Based on the development of crucial techniques and methods,the CAPS demonstration system has been designed and developed.Four communication satellites in the geosynchronous orbit (GEO) located at 87.5°E,110.5°E,134°E,142°E and barometric altimetry are used in the CAPS system.The GEO satellites located at 134°E and 142°E re decommissioned GEO (DGEO) satellites.C-band is used as the navigation band.Dual frequency at C1=4143.15 MHz and C2=3826.02 MHz as well as dual codes with standard code (CA code and precision code (P code)) are adopted.The ground segment consists of five ground stations; the master station is in Lintong,Xi'an.The ground stations take a lot of responsibilities,including monitor and management of the operation of all system components,determination of the satellite position and prediction of the satellite orbit,accomplishment of the virtual atomic clock measurement,transmission and receiving

  8. Satellite-Based Sunshine Duration for Europe

    Directory of Open Access Journals (Sweden)

    Bodo Ahrens

    2013-06-01

    Full Text Available In this study, two different methods were applied to derive daily and monthly sunshine duration based on high-resolution satellite products provided by the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT Satellite Application Facility on Climate Monitoring using data from Meteosat Second Generation (MSG SEVIRI (Spinning Enhanced Visible and Infrared Imager. The satellite products were either hourly cloud type or hourly surface incoming direct radiation. The satellite sunshine duration estimates were not found to be significantly different using the native 15-minute temporal resolution of SEVIRI. The satellite-based sunshine duration products give additional spatial information over the European continent compared with equivalent in situ-based products. An evaluation of the satellite sunshine duration by product intercomparison and against station measurements was carried out to determine their accuracy. The satellite data were found to be within ±1 h/day compared to high-quality Baseline Surface Radiation Network or surface synoptic observations (SYNOP station measurements. The satellite-based products differ more over the oceans than over land, mainly because of the treatment of fractional clouds in the cloud type-based sunshine duration product. This paper presents the methods used to derive the satellite sunshine duration products and the performance of the different retrievals. The main benefits and disadvantages compared to station-based products are also discussed.

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

    Science.gov (United States)

    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

  10. CryoSat-2 radar altimetry for monitoring freshwater resources of China

    DEFF Research Database (Denmark)

    Jiang, Liguang; Nielsen, Karina; Andersen, Ole Baltazar

    2017-01-01

    -scale monitoring dataset of surface water bodies in China is not available. Over the last two decades, satellite altimetry has been used successfully for inland water monitoring. Here, we use CryoSat-2 radar altimetry to monitor water level variations of large lakes, reservoirs and rivers across China...

  11. Triaxial ellipsoid models of the Moon based on the laser altimetry data of Chang’E-1

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Lunar geodetic parameters, which play an important role in lunar exploration, can be calculated from the gravity and topography data. With the CE-1 altimetry data and LP gravity model, we calculate such geodetic parameters as the principle moment of inertia, the principle inertia axes, equatorial radius, polar radius, mean radius, flattening and offset between center of mass and center of figure (DCOM-COF). According to the CE-1 altimetry data and the above geodetic parameters, a tri-axial ellipsoid (CE-1-LAM-GEO) and a tri-axial level ellipsoid (CE-1-LAM-LEVEL) are calculated individually, providing mass center and figure center offset (DCOM-COF) and parameters more reliable in direction and magnitude.

  12. Assimilation of CryoSat-2 altimetry to a hydrodynamic model of the Brahmaputra river

    Science.gov (United States)

    Schneider, Raphael; Nygaard Godiksen, Peter; Ridler, Marc-Etienne; Madsen, Henrik; Bauer-Gottwein, Peter

    2016-04-01

    different filtering and clustering methods and error descriptions of the CryoSat-2 observations was evaluated. Performance improvement in terms of discharge and water level forecast due to the assimilation of satellite altimetry data was then evaluated. The model forecasts were also compared to climatology and persistence forecasts. Using ensemble based filters, the evaluation was done not only based on performance criteria for the central forecast such as root-mean-square error (RMSE) and Nash-Sutcliffe model efficiency (NSE), but also based on sharpness, reliability and continuous ranked probability score (CRPS) of the ensemble of probabilistic forecasts.

  13. Challenges for Greenland-wide mass balance from Cryosat-2 radar-altimetry

    DEFF Research Database (Denmark)

    Simonsen, Sebastian Bjerregaard; Forsberg, René; Sørensen, Louise Sandberg

    be interpreted as actual surface elevation changes seen from the satellite radar altimetry (Nilsson et al., 2015).Here, we investigate how to correct the elevation change observed from the ESA Cryosat-2 radar altimetry mission to derive elevation change of the air/snow interface of the Greenland ice sheet....... The elevation change of this “real” physical surface is crucial, if the goal is to derive Greenland mass balance as done for LiDAR missions.The investigations look into waveform parameters to correct for the observed bias between Radar and LiDAR observations when using Croysat-2 level-2 data. Based...... on the knowledge gained by analyzing the elevation change derived from the inclusion of various waveform parameters, we pinpoint the challenges associated with the using Croysat-2 observation in mass balance studies. As for mass balance studies utilizing LiDAR observation (ICESat), a strong firn-modeling component...

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

    Science.gov (United States)

    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/

  15. The use of coastal altimetry to support storm surge studies in project eSurge

    Science.gov (United States)

    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

  16. Operational reservoir inflow forecasting with radar altimetry: The Zambezi case study

    DEFF Research Database (Denmark)

    Michailovsky, Claire Irene B.; Bauer-Gottwein, Peter

    2014-01-01

    cannot be measured from space, radar altimetry can track surface water level variations at crossing locations between the satellite ground track and the river system called virtual stations (VS). Use of radar altimetry versus traditional monitoring in operational settings is complicated by the low...... temporal resolution of the data (between 10 and 35 days revisit time at a VS depending on the satellite) as well as the fact that the location of the measurements is not necessarily at the point of interest. However, combining radar altimetry from multiple VS with hydrological models can help overcome...

  17. River Discharge Estimation by Using Altimetry Data and Simplified Flood Routing Modeling

    Directory of Open Access Journals (Sweden)

    Tommaso Moramarco

    2013-08-01

    Full Text Available A methodology to estimate the discharge along rivers, even poorly gauged ones, taking advantage of water level measurements derived from satellite altimetry is proposed. The procedure is based on the application of the Rating Curve Model (RCM, a simple method allowing for the estimation of the flow conditions in a river section using only water levels recorded at that site and the discharges observed at another upstream section. The European Remote-Sensing Satellite 2, ERS-2, and the Environmental Satellite, ENVISAT, altimetry data are used to provide time series of water levels needed for the application of RCM. In order to evaluate the usefulness of the approach, the results are compared with the ones obtained by applying an empirical formula that allows discharge estimation from remotely sensed hydraulic information. To test the proposed procedure, the 236 km-reach of the Po River is investigated, for which five in situ stations and four satellite tracks are available. Results show that RCM is able to appropriately represent the discharge, and its performance is better than the empirical formula, although this latter does not require upstream hydrometric data. Given its simple formal structure, the proposed approach can be conveniently utilized in ungauged sites where only the survey of the cross-section is needed.

  18. Basic Radar Altimetry Toolbox & Tutorial

    Science.gov (United States)

    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. Comparison of space borne radar altimetry and airborne laser altimetry over sea ice in the Fram Strait

    DEFF Research Database (Denmark)

    Giles, K.A.; Hvidegaard, Sine Munk

    2006-01-01

    This paper describes the first comparison of satellite radar and airborne laser altimetry over sea ice. In order to investigate the differences between measurements from the two different instruments we explore the statistical properties of the data and determine reasonable scales in space and ti...

  20. An SDR based AIS receiver for satellites

    DEFF Research Database (Denmark)

    Larsen, Jesper Abildgaard; Mortensen, Hans Peter; Nielsen, Jens Frederik Dalsgaard

    2011-01-01

    For a few years now, there has been a high interest in monitoring the global ship traffic from space. A few satellite, capable of listening for ship borne AIS transponders have already been launched, and soon the AAUSAT3, carrying two different types of AIS receivers will also be launched. One...... of the AIS receivers onboard AAUSAT3 is an SDR based AIS receiver. This paper serves to describe the background of the AIS system, and how the SDR based receiver has been integrated into the AAUSAT3 satellite. Amongst some of the benefits of using an SDR based receiver is, that due to its versatility, new...

  1. A Space Based Solar Power Satellite System

    Science.gov (United States)

    Engel, J. M.; Polling, D.; Ustamujic, F.; Yaldiz, R.; et al.

    2002-01-01

    (SPoTS) supplying other satellites with energy. SPoTS is due to be commercially viable and operative in 2020. of Technology designed the SPoTS during a full-time design period of six weeks as a third year final project. The team, organized according to the principles of systems engineering, first conducted a literature study on space wireless energy transfer to select the most suitable candidates for use on the SPoTS. After that, several different system concepts have been generated and evaluated, the most promising concept being worked out in greater detail. km altitude. Each SPoTS satellite has a 50m diameter inflatable solar collector that focuses all received sunlight. Then, the received sunlight is further redirected by means of four pointing mirrors toward four individual customer satellites. A market-analysis study showed, that providing power to geo-stationary communication satellites during their eclipse would be most beneficial. At arrival at geo-stationary orbit, the focused beam has expended to such an extent that its density equals one solar flux. This means that customer satellites can continue to use their regular solar arrays during their eclipse for power generation, resulting in a satellite battery mass reduction. the customer satellites in geo-stationary orbit, the transmitted energy beams needs to be pointed with very high accuracy. Computations showed that for this degree of accuracy, sensors are needed, which are not mainstream nowadays. Therefore further research must be conducted in this area in order to make these high-accuracy-pointing systems commercially attractive for use on the SPoTS satellites around 2020. Total 20-year system lifetime cost for 18 SPoT satellites are estimated at approximately USD 6 billion [FY2001]. In order to compete with traditional battery-based satellite power systems or possible ground based wireless power transfer systems the price per kWh for the customer must be significantly lower than the present one

  2. Lorentz Force Based Satellite Attitude Control

    Science.gov (United States)

    Giri, Dipak Kumar; Sinha, Manoranjan

    2016-07-01

    Since the inception of attitude control of a satellite, various active and passive control strategies have been developed. These include using thrusters, momentum wheels, control moment gyros and magnetic torquers. In this present work, a new technique named Lorentz force based Coulombic actuators for the active control is proposed. This method uses electrostatic charged shells, which interact with the time varying earth's magnetic field to establish a full three axes control of the satellite. It is shown that the proposed actuation mechanism is similar to a satellite actuated by magnetic coils except that the resultant magnetic moment vanishes under two different conditions. The equation for the required charges on the the Coulomb shells attached to the satellite body axes is derived, which is in turn used to find the available control torque for actuating the satellite along the orbit. Stability of the proposed system for very high initial angular velocity and exponential stability about the origin are proved for a proportional-differential control input. Simulations are carried out to show the efficacy of the proposed system for the attitude control of the earth-pointing satellite.

  3. Wind Statistics Offshore based on Satellite Images

    DEFF Research Database (Denmark)

    Hasager, Charlotte Bay; Mouche, Alexis; Badger, Merete

    2009-01-01

    Ocean wind maps from satellites are routinely processed both at Risø DTU and CLS based on the European Space Agency Envisat ASAR data. At Risø the a priori wind direction is taken from the atmospheric model NOGAPS (Navel Operational Global Atmospheric Prediction System) provided by the U.S. Navy......’s Master Environmental Library. At CLS the a priori wind direction is taken from the ECMWF (European Centre of Medium-range Weather Forecasting). It is also possible to use other sources of wind direction e.g. the satellite-based ASCAT wind directions as demonstrated by CLS. The wind direction has to known...

  4. CryoSat-2 Altimetry Applications over Rivers and Lakes

    Directory of Open Access Journals (Sweden)

    Liguang Jiang

    2017-03-01

    Full Text Available Monitoring the variation of rivers and lakes is of great importance. Satellite radar altimetry is a promising technology to do this on a regional to global scale. Satellite radar altimetry data has been used successfully to observe water levels in lakes and (large rivers, and has also been combined with hydrologic/hydrodynamic models. Except CryoSat-2, all radar altimetry missions have been operated in conventional low resolution mode with a short repeat orbit (35 days or less. CryoSat-2, carrying a Synthetic Aperture Radar (SAR altimeter, has a 369-day repeat and a drifting ground track pattern and provides new opportunities for hydrologic research. The narrow inter-track distance (7.5 km at the equator makes it possible to monitor many lakes and rivers and SAR mode provides a finer along-track resolution, higher return power and speckle reduction through multi-looks. However, CryoSat-2 challenges conventional ways of dealing with satellite inland water altimetry data because virtual station time series cannot be directly derived for rivers. We review the CryoSat-2 mission characteristics, data products, and its use and perspectives for inland water applications. We discuss all the important steps in the workflow for hydrologic analysis with CryoSat-2, and conclude with a discussion of promising future research directions.

  5. Satellite Formation based on SDDF Method

    Directory of Open Access Journals (Sweden)

    Yu Wang

    2014-04-01

    Full Text Available The technology of satellite formation flying has being a research focus in flight application. The relative position and velocity between satellites are basic parameters to achieve the control of formation flight during the satellite formation flying mission. In order to improve the navigation accuracy, a new filter different from Extended Kalman Filter (EKF should be adopted to estimate the errors of relative position and velocity, which is based on the nonlinearity of the kinetic model for the satellite formation flying. A nonlinear Divided Difference Filter (DDF based on Stirling interpolation formula was proposed in this paper. According to the linearity of the measurement equation for the filter, a simplified differential filter was designed by means of expanding the polynomial of the nonlinear system equation and linear approximating of the finite differential interpolation. Digital simulation experiment for the relative positioning of satellite formation flying was carried out. The result demonstrates that the filter proposed in this paper has a higher filtering accuracy, faster convergence speed and better stability. Compared with the EKF, the estimation accuracy of the relative position and velocity has improved by 77.1%and 47% respectively in the method of simplified DDF, which indicates the significance for practical applications. 

  6. A Positioning System based on Communication Satellites and the Chinese Area Positioning System (CAPS)

    Science.gov (United States)

    Ai, Guo-Xiang; Shi, Hu-Li; Wu, Hai-Tao; Yan, Yi-Hua; Bian, Yu-Jing; Hu, Yong-Hui; Li, Zhi-Gang; Guo, Ji; Xian-DeCai

    2008-12-01

    The Chinese Area Positioning System (CAPS) is a positioning system based on satellite communication that is fundamentally different from the 3``G'' (GPS, GLONASS and GALILEO) systems. The latter use special-purpose navigation satellites to broadcast navigation information generated on-board to users, while the CAPS transfers ground-generated navigation information to users via the communication satellite. In order to achieve accurate Positioning, Velocity and Time (PVT), the CAPS employs the following strategies to overcome the three main obstacles caused by using the communication satellite: (a) by real-time following-up frequency stabilization to achieve stable frequency; (b) by using a single carrier in the transponder with 36 MHz band-width to gain sufficient power; (c) by incorporating Decommissioned Geostationary Orbit communication satellite (DGEO), barometric pressure and Inclined Geostationary Orbit communication satellite (IGSO) to achieve the 3-D positioning. Furthermore, the abundant transponders available on DGEO can be used to realize the large capacity of communication as well as the integrated navigation and communication. With the communication functions incorporated, five new functions appear in the CAPS: (1) combination of navigation and communication; (2) combination of navigation and high accuracy orbit measurement; (3) combination of navigation message and wide/local area differential processing; (4) combination of the switching of satellites, frequencies and codes; and (5) combination of the navigation message and the barometric altimetry. The CAPS is thereby labelled a PVT5C system of high accuracy. In order to validate the working principle and the performance of the CAPS, a trial system was established in the course of two years at a cost of about 20 million dollars. The trial constellation consists of two GEO satellites located at E87.5° and E110.5°, two DGEOs located at E130° and E142°, as well as barometric altimetry as a virtual

  7. A Positioning System based on Communication Satellites and the Chinese Area Positioning System (CAPS)

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The Chinese Area Positioning System (CAPS) is a positioning system based on satellite communication that is fundamentally different from the 3"G" (GPS, GLONASS and GALILEO) systems. The latter use special-purpose navigation satellites to broadcast navi-gation information generated on-board to users, while the CAPS transfers ground-generated navigation information to users via the communication satellite. In order to achieve accurate Positioning, Velocity and Time (PVT), the CAPS employs the following strategies to over-come the three main obstacles caused by using the communication satellite: (a) by real-time following-up frequency stabilization to achieve stable frequency; (b) by using a single carrier in the transponder with 36 MHz band-width to gain sufficient power; (c) by incorporating Decommissioned Geostationary Orbit communication satellite (DGEO), barometric pressure and Inclined Geostationary Orbit communication satellite (IGSO) to achieve the 3-D posi-tioning. Furthermore, the abundant transponders available on DGEO can be used to realize the large capacity of communication as well as the integrated navigation and communication. With the communication functions incorporated, five new functions appear in the CAPS: (1) combination of navigation and communication; (2) combination of navigation and high accu-racy orbit measurement; (3) combination of navigation message and wide/local area differen-tial processing; (4) combination of the switching of satellites, frequencies and codes; and (5) combination of the navigation message and the barometric altimetry. The CAPS is thereby labelled a PVT5C system of high accuracy. In order to validate the working principle and the performance of the CAPS, a trial system was established in the course of two years at a cost of about 20 million dollars. The trial constellation consists of two GEO satellites located at E87.5°and E110.5°, two DGEOs located at E130° and E142°, as well as barometric altimetry as a virtual

  8. Using radar altimetry to update a routing model of the Zambezi River Basin

    DEFF Research Database (Denmark)

    Michailovsky, Claire Irene B.; Bauer-Gottwein, Peter

    2012-01-01

    Satellite radar altimetry allows for the global monitoring of lakes and river levels. However, the widespread use of altimetry for hydrological studies is limited by the coarse temporal and spatial resolution provided by current altimetric missions and the fact that discharge rather than level...... is needed for hydrological applications. To overcome these limitations, altimetry river levels can be combined with hydrological modeling in a dataassimilation framework. This study focuses on the updating of a river routing model of the Zambezi using river levels from radar altimetry. A hydrological model...... of the basin was built to simulate the land phase of the water cycle and produce inflows to a Muskingum routing model. River altimetry from the ENVISAT mission was then used to update the storages in the reaches of the Muskingum model using the Extended Kalman Filter. The method showed improvements in modeled...

  9. Satellite-based terrestrial production efficiency modeling

    Directory of Open Access Journals (Sweden)

    Obersteiner Michael

    2009-09-01

    Full Text Available Abstract Production efficiency models (PEMs are based on the theory of light use efficiency (LUE which states that a relatively constant relationship exists between photosynthetic carbon uptake and radiation receipt at the canopy level. Challenges remain however in the application of the PEM methodology to global net primary productivity (NPP monitoring. The objectives of this review are as follows: 1 to describe the general functioning of six PEMs (CASA; GLO-PEM; TURC; C-Fix; MOD17; and BEAMS identified in the literature; 2 to review each model to determine potential improvements to the general PEM methodology; 3 to review the related literature on satellite-based gross primary productivity (GPP and NPP modeling for additional possibilities for improvement; and 4 based on this review, propose items for coordinated research. This review noted a number of possibilities for improvement to the general PEM architecture - ranging from LUE to meteorological and satellite-based inputs. Current PEMs tend to treat the globe similarly in terms of physiological and meteorological factors, often ignoring unique regional aspects. Each of the existing PEMs has developed unique methods to estimate NPP and the combination of the most successful of these could lead to improvements. It may be beneficial to develop regional PEMs that can be combined under a global framework. The results of this review suggest the creation of a hybrid PEM could bring about a significant enhancement to the PEM methodology and thus terrestrial carbon flux modeling. Key items topping the PEM research agenda identified in this review include the following: LUE should not be assumed constant, but should vary by plant functional type (PFT or photosynthetic pathway; evidence is mounting that PEMs should consider incorporating diffuse radiation; continue to pursue relationships between satellite-derived variables and LUE, GPP and autotrophic respiration (Ra; there is an urgent need for

  10. Intercomparison of numerical simulations, satellite altimetry and glider observations in the Algerian Basin during fall 2014 and 2015: focus on a SARAL/AltiKa track

    Science.gov (United States)

    Aulicino, Giuseppe; Cotroneo, Yuri; Ruiz, Simon; Sanchez Roman, Antonio; Pascual, Ananda; Fusco, Giannetta; Tintoré, Joaquin; Budillon, Giorgio

    2017-04-01

    The Algerian Basin is a key-place for the study of the general circulation of the Western Mediterranean Sea and its role in reaction to climate change. The presence of both fresh Atlantic waters and more saline resident Mediterranean ones characterizes the basin with an intense inflow/outflow regime and complex circulation patterns. Very energetic mesoscale structures, that evolve from meander of the Algerian Current to isolated cyclonic and anti-cyclonic eddies, dominate the area with marked repercussions on the biological activity. Despite their remarkable importance, this region and its variability are still poorly known and basin-wide high resolution knowledge of its mesoscale and sub-mesoscale features is still incomplete. The monitoring of such complex processes requires a synergic approach that involves integrated observing systems. In recent years, several studies proved the advantages of the combined use of autonomous underwater vehicles, such as gliders, with a new generation of satellite altimeters. In this context, we present the first results of a new integrated oceanographic observing system built up in the Algerian Basin during fall 2014 and 2015, aiming at advancing our knowledge on its main features. The study was realized through the analysis of glider high resolutions three-dimensional observations, collected along the Algerian BAsin Circulation Unmanned Survey (ABACUS) monitoring line, in synergy with co-located SARAL/AltiKa altimetric products and CMEMS numerical simulations. The achieved results confirm that glider derived dynamic height and SARAL/AltiKa absolute dynamic topography present similar patterns, with RMS of the differences ranging between 1.11 and 2.90 cm. Generally, the maximum discrepancies are located nearby the Balearic Islands and the Algerian Coast, but it is important to remark that the correlation coefficients seem to mostly depend on the synopticity between in situ and satellite measurements. Still, this study confirm that

  11. Using radar altimetry to update a large-scale hydrological model of the Brahmaputra river basin

    DEFF Research Database (Denmark)

    Finsen, F.; Milzow, Christian; Smith, R.

    2014-01-01

    Measurements of river and lake water levels from space-borne radar altimeters (past missions include ERS, Envisat, Jason, Topex) are useful for calibration and validation of large-scale hydrological models in poorly gauged river basins. Altimetry data availability over the downstream reaches...... of the Brahmaputra is excellent (17 high-quality virtual stations from ERS-2, 6 from Topex and 10 from Envisat are available for the Brahmaputra). In this study, altimetry data are used to update a large-scale Budyko-type hydrological model of the Brahmaputra river basin in real time. Altimetry measurements...... are converted to discharge using rating curves of simulated discharge versus observed altimetry. This approach makes it possible to use altimetry data from river cross sections where both in-situ rating curves and accurate river cross section geometry are not available. Model updating based on radar altimetry...

  12. An SDR based AIS receiver for satellites

    DEFF Research Database (Denmark)

    Larsen, Jesper Abildgaard; Mortensen, Hans Peter; Nielsen, Jens Frederik Dalsgaard

    2011-01-01

    For a few years now, there has been a high interest in monitoring the global ship traffic from space. A few satellite, capable of listening for ship borne AIS transponders have already been launched, and soon the AAUSAT3, carrying two different types of AIS receivers will also be launched. One...... of the AIS receivers onboard AAUSAT3 is an SDR based AIS receiver. This paper serves to describe the background of the AIS system, and how the SDR based receiver has been integrated into the AAUSAT3 satellite. Amongst some of the benefits of using an SDR based receiver is, that due to its versatility, new...... detection algorithms are easily deployed, and it is easily adapted the new proposed AIS transmission channels....

  13. Coastal GPS Altimetry for Eddy Monitoring

    Science.gov (United States)

    Cardellach, E.; Treuhaft, R. N.; Chao, Y.; Lowe, S. T.; Young, L. E.; Zuffada, C.

    2003-04-01

    Coastal zones (within approximately 20-30 km of the coast) are dominated by fast-changing (on the order of days) and small-scale (on the order of km or less) processes. The dynamics and thermodynamics associated with these coastal processes influence the physics, biogeochemistry and the associated carbon cycling in the coastal zones. To monitor these important processes at the highest possible resolution (both spatial and temporal) is therefore an integrated component of the Earth's observing system. Coastal processes are currently not adequately monitored from existing spaceborne observations. The infrared instruments can measure the sea surface temperature in coastal zones with a resolution of approximately 1km daily, but are heavily contaminated by clouds usually found in the land-sea boundaries. The conventional radar altimetry, even with the wide-swath (e.g., OSTM) configuration, can only provide measurements every 10 days, too long to resolve the fast-changing coastal processes, not mentioning the land contamination within the first few footprints (on the order of 20 km) away from the coast. Coastal GPS altimetry from cliffs or structures near the coastline provides a complementary way to measure these coastal processes. The precision of such ground-based grazing angle GPS measurements has been proven to be 2-cm over the smooth surface at Crater Lake [Treuhaft et al., 2001]. Nevertheless, the accuracy of the GPS altimetry over the open sea, significantly affected by roughness, has yet to be assessed. This poster aims to present a set of experiments and analyses to prove the coastal GPS altimetry concept with a few-cm accuracy goal. It includes the analysis of data gathered over the ocean from an oil platform, Platform Harvest, as well as simulations of the GPS reflected signal to identify and correct the effects of the sea roughness. The results of this research are planned to feed the design, execution and processing of an eddy monitoring experiment. It will

  14. SAR Altimetry Applications over Water

    CERN Document Server

    Martin-Puig, C; Ruffini, G; Raney, R K; Benveniste, J

    2008-01-01

    The application of Synthetic Aperture Radar (SAR) techniques to classical radar altimetry offers the potential for greatly improved Earth surface mapping. This paper provides an overview of the progress of SAMOSA, Development of SAR Altimetry Studies and Applications over Ocean, Coastal zones and Inland waters, an on-going ESA-funded project. The main objective of SAMOSA is to better quantify the improvement of SAR altimetry over conventional altimetry on water surfaces. More specifically, one of the tasks focuses on the reduction of SAR mode data to pulse-limited altimeter data, and a theoretical modelling to characterize the expected gain between high Pulse Repetition Frequency (PRF) reduced SAR mode data and low PRF classical Low-Resolution Mode (LRM) data. To this end, theoretical modelling using the Cramer-Rao bound (CRB) will be used and the results will be compared to previous theoretical estimates [7], using an analysis akin to that in [8].

  15. Satellite Contamination and Materials Outgassing Knowledge base

    Science.gov (United States)

    Minor, Jody L.; Kauffman, William J. (Technical Monitor)

    2001-01-01

    Satellite contamination continues to be a design problem that engineers must take into account when developing new satellites. To help with this issue, NASA's Space Environments and Effects (SEE) Program funded the development of the Satellite Contamination and Materials Outgassing Knowledge base. This engineering tool brings together in one location information about the outgassing properties of aerospace materials based upon ground-testing data, the effects of outgassing that has been observed during flight and measurements of the contamination environment by on-orbit instruments. The knowledge base contains information using the ASTM Standard E- 1559 and also consolidates data from missions using quartz-crystal microbalances (QCM's). The data contained in the knowledge base was shared with NASA by government agencies and industry in the US and international space agencies as well. The term 'knowledgebase' was used because so much information and capability was brought together in one comprehensive engineering design tool. It is the SEE Program's intent to continually add additional material contamination data as it becomes available - creating a dynamic tool whose value to the user is ever increasing. The SEE Program firmly believes that NASA, and ultimately the entire contamination user community, will greatly benefit from this new engineering tool and highly encourages the community to not only use the tool but add data to it as well.

  16. Satellite-based Tropical Cyclone Monitoring Capabilities

    Science.gov (United States)

    Hawkins, J.; Richardson, K.; Surratt, M.; Yang, S.; Lee, T. F.; Sampson, C. R.; Solbrig, J.; Kuciauskas, A. P.; Miller, S. D.; Kent, J.

    2012-12-01

    Satellite remote sensing capabilities to monitor tropical cyclone (TC) location, structure, and intensity have evolved by utilizing a combination of operational and research and development (R&D) sensors. The microwave imagers from the operational Defense Meteorological Satellite Program [Special Sensor Microwave/Imager (SSM/I) and the Special Sensor Microwave Imager Sounder (SSMIS)] form the "base" for structure observations due to their ability to view through upper-level clouds, modest size swaths and ability to capture most storm structure features. The NASA TRMM microwave imager and precipitation radar continue their 15+ yearlong missions in serving the TC warning and research communities. The cessation of NASA's QuikSCAT satellite after more than a decade of service is sorely missed, but India's OceanSat-2 scatterometer is now providing crucial ocean surface wind vectors in addition to the Navy's WindSat ocean surface wind vector retrievals. Another Advanced Scatterometer (ASCAT) onboard EUMETSAT's MetOp-2 satellite is slated for launch soon. Passive microwave imagery has received a much needed boost with the launch of the French/Indian Megha Tropiques imager in September 2011, basically greatly supplementing the very successful NASA TRMM pathfinder with a larger swath and more frequent temporal sampling. While initial data issues have delayed data utilization, current news indicates this data will be available in 2013. Future NASA Global Precipitation Mission (GPM) sensors starting in 2014 will provide enhanced capabilities. Also, the inclusion of the new microwave sounder data from the NPP ATMS (Oct 2011) will assist in mapping TC convective structures. The National Polar orbiting Partnership (NPP) program's VIIRS sensor includes a day night band (DNB) with the capability to view TC cloud structure at night when sufficient lunar illumination exits. Examples highlighting this new capability will be discussed in concert with additional data fusion efforts.

  17. Operational evapotranspiration based on Earth observation satellites

    Science.gov (United States)

    Gellens-Meulenberghs, Françoise; Ghilain, Nicolas; Arboleda, Alirio; Barrios, Jose-Miguel

    2016-04-01

    Geostationary satellites have the potential to follow fast evolving atmospheric and Earth surface phenomena such those related to cloud cover evolution and diurnal cycle. Since about 15 years, EUMETSAT has set up a network named 'Satellite Application Facility' (SAF, http://www.eumetsat.int/website/home/Satellites/GroundSegment/Safs/index.html) to complement its ground segment. The Land Surface Analysis (LSA) SAF (http://landsaf.meteo.pt/) is devoted to the development of operational products derived from the European meteorological satellites. In particular, an evapotranspiration (ET) product has been developed by the Royal Meteorological Institute of Belgium. Instantaneous and daily integrated results are produced in near real time and are freely available respectively since the end of 2009 and 2010. The products cover Europe, Africa and the Eastern part of South America with the spatial resolution of the SEVIRI sensor on-board Meteosat Second Generation (MSG) satellites. The ET product algorithm (Ghilain et al., 2011) is based on a simplified Soil-Vegetation-Atmosphere transfer (SVAT) scheme, forced with MSG derived radiative products (LSA SAF short and longwave surface fluxes, albedo). It has been extensively validated against in-situ validation data, mainly FLUXNET observations, demonstrating its good performances except in some arid or semi-arid areas. Research has then been pursued to develop an improved version for those areas. Solutions have been found in reviewing some of the model parameterizations and in assimilating additional satellite products (mainly vegetation indices and land surface temperature) into the model. The ET products will be complemented with related latent and sensible heat fluxes, to allow the monitoring of land surface energy partitioning. The new algorithm version should be tested in the LSA-SAF operational computer system in 2016 and results should become accessible to beta-users/regular users by the end of 2016/early 2017. In

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

    Science.gov (United States)

    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

  19. Airborne laser altimetry in the Ionian Sea, Greece

    Science.gov (United States)

    Cocard, M.; Geiger, A.; Kahle, H.-G.; Veis, G.

    2002-09-01

    Airborne laser techniques have evolved during the last years and have been tested in several pilot projects which cover a wide range of geodetic applications. In this project, airborne laser altimetry was used to determine the sea level in coastal areas of Greece, and to connect satellite radar altimetry results over the deep sea with tide gauge stations at the coast. Because airborne laser altimetry is capable to provide sea surface heights at the decimeter to centimeter level, it allows for an independent validation of spaceborne radar altimetry results. Airborne laser data acquired along densely spaced tracks of a total of 30-h flight time were used to determine instantaneous sea surface heights of the Ionian Sea, Greece. Differential GPS and inertial platform data were utilized as ancillary information for the purpose of ensuring a precise trajectography of the aircraft. Emphasis was put on the assessment of errors and the reduction of the raw data to mean sea level by crossover analysis and the incorporation of tidal predictions. The airborne laser data yield a high-resolution sea surface over the coastal areas of the Ionian Sea. The most prominent feature is a steep gradient of the sea surface amounting to 15 m over a distance of 150 km. This slope can be followed all along the bathymetric relief between the Hellenic Arc and Hellenic Trench.

  20. Combined ICESat and CryoSat-2 Altimetry for Accessing Water Level Dynamics of Tibetan Lakes over 2003–2014

    Directory of Open Access Journals (Sweden)

    Chunqiao Song

    2015-08-01

    Full Text Available Long-term observations of lake water level are essential to our understanding of the evolution of Tibetan lake system. CryoSat-2 radar altimetry data over the Tibetan Plateau (2010–2014, P2 is used to extend lake level measurements from ICESat laser altimetry (2003–2009, P1. This study evaluates the performance of CryoSat-2 data by comparing with gauge-based water levels that are calibrated by ICESat-observed water level time series, and quantifies the uncertainty of water-level change rate estimates from satellite altimetry measurements. We completely investigate the 131 lakes that were observed by both ICESat and CryoSat-2. The mean change rate of water level for all of examined lakes in P2 (0.19 ± 0.03 m·year–1 is slightly lower than that (0.21 ± 0.02 m·year–1 observed in P1. The extended lake level time series also indicates that, in the past few years, lakes in the Northern Changtang (especially in Hol Xil showed accelerated growth; and that the extensive lake level rises north to the Gangdise Mountains, during 2003–2009, were found dampened during the CryoSat-2 observation period. The spatio-temporal heterogeneity of precipitation observed from weather stations can be used to partly explain the observed temporal pattern of lake level changes over different sub-zones of the plateau.

  1. Combining Envisat and CryoSat-2 altimetry to inform hydrodynamic models

    DEFF Research Database (Denmark)

    Schneider, Raphael; Nygaard Godiksen, Peter; Ridler, Marc-Etienne

    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. Many studies have used satellite altimetry data from repeat-orbit missions such as Envisat, ERS or Jason......, or 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...... fitted to the CryoSat-2 data: In a first step, the average simulated water levels along the river were calibrated to the CryoSat-2 data by adapting the hydrodynamic cross section datums. Subsequently the simulated water level amplitudes were fitted to those obtained from Envisat virtual station time...

  2. Monitoring objects orbiting earth using satellite-based telescopes

    Energy Technology Data Exchange (ETDEWEB)

    Olivier, Scot S.; Pertica, Alexander J.; Riot, Vincent J.; De Vries, Willem H.; Bauman, Brian J.; Nikolaev, Sergei; Henderson, John R.; Phillion, Donald W.

    2015-06-30

    An ephemeris refinement system includes satellites with imaging devices in earth orbit to make observations of space-based objects ("target objects") and a ground-based controller that controls the scheduling of the satellites to make the observations of the target objects and refines orbital models of the target objects. The ground-based controller determines when the target objects of interest will be near enough to a satellite for that satellite to collect an image of the target object based on an initial orbital model for the target objects. The ground-based controller directs the schedules to be uploaded to the satellites, and the satellites make observations as scheduled and download the observations to the ground-based controller. The ground-based controller then refines the initial orbital models of the target objects based on the locations of the target objects that are derived from the observations.

  3. Earth Observation Satellites Scheduling Based on Decomposition Optimization Algorithm

    Directory of Open Access Journals (Sweden)

    Feng Yao

    2010-11-01

    Full Text Available A decomposition-based optimization algorithm was proposed for solving Earth Observation Satellites scheduling problem. The problem was decomposed into task assignment main problem and single satellite scheduling sub-problem. In task assignment phase, the tasks were allocated to the satellites, and each satellite would schedule the task respectively in single satellite scheduling phase. We adopted an adaptive ant colony optimization algorithm to search the optimal task assignment scheme. Adaptive parameter adjusting strategy and pheromone trail smoothing strategy were introduced to balance the exploration and the exploitation of search process. A heuristic algorithm and a very fast simulated annealing algorithm were proposed to solve the single satellite scheduling problem. The task assignment scheme was valued by integrating the observation scheduling result of multiple satellites. The result was responded to the ant colony optimization algorithm, which can guide the search process of ant colony optimization. Computation results showed that the approach was effective to the satellites observation scheduling problem.

  4. Normalized GNSS interference pattern technique for altimetry.

    Science.gov (United States)

    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.

  5. Normalized GNSS Interference Pattern Technique for Altimetry

    Directory of Open Access Journals (Sweden)

    Miguel Angel Ribot

    2014-06-01

    Full Text Available 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.

  6. SAW based systems for mobile communications satellites

    Science.gov (United States)

    Peach, R. C.; Miller, N.; Lee, M.

    1993-01-01

    Modern mobile communications satellites, such as INMARSAT 3, EMS, and ARTEMIS, use advanced onboard processing to make efficient use of the available L-band spectrum. In all of these cases, high performance surface acoustic wave (SAW) devices are used. SAW filters can provide high selectivity (100-200 kHz transition widths), combined with flat amplitude and linear phase characteristics; their simple construction and radiation hardness also makes them especially suitable for space applications. An overview of the architectures used in the above systems, describing the technologies employed, and the use of bandwidth switchable SAW filtering (BSSF) is given. The tradeoffs to be considered when specifying a SAW based system are analyzed, using both theoretical and experimental data. Empirical rules for estimating SAW filter performance are given. Achievable performance is illustrated using data from the INMARSAT 3 engineering model (EM) processors.

  7. Global Ocean Surveillance With Electronic Intelligence Based Satellite System

    Science.gov (United States)

    Venkatramanan, Haritha

    2016-07-01

    The objective of this proposal is to design our own ELINT based satellite system to detect and locate the target by using satellite Trilateration Principle. The target position can be found by measuring the radio signals arrived at three satellites using Time Difference of Arrival(TDOA) technique. To locate a target it is necessary to determine the satellite position. The satellite motion and its position is obtained by using Simplified General Perturbation Model(SGP4) in MATLAB. This SGP4 accepts satellite Two Line Element(TLE) data and returns the position in the form of state vectors. These state vectors are then converted into observable parameters and then propagated in space. This calculations can be done for satellite constellation and non - visibility periods can be calculated. Satellite Trilateration consists of three satellites flying in formation with each other. The satellite constellation design consists of three satellites with an inclination of 61.3° maintained at equal distances between each other. The design is performed using MATLAB and simulated to obtain the necessary results. The target's position can be obtained using the three satellites ECEF Coordinate system and its position and velocity can be calculated in terms of Latitude and Longitude. The target's motion is simulated to obtain the Speed and Direction of Travel.

  8. Improved inland water levels from SAR altimetry using novel empirical and physical retrackers

    Science.gov (United States)

    Villadsen, Heidi; Deng, Xiaoli; Andersen, Ole B.; Stenseng, Lars; Nielsen, Karina; Knudsen, Per

    2016-06-01

    Satellite altimetry has proven a valuable resource of information on river and lake levels where in situ data are sparse or non-existent. In this study several new methods for obtaining stable inland water levels from CryoSat-2 Synthetic Aperture Radar (SAR) altimetry are presented and evaluated. In addition, the possible benefits from combining physical and empirical retrackers are investigated. The retracking methods evaluated in this paper include the physical SAR Altimetry MOde Studies and Applications (SAMOSA3) model, a traditional subwaveform threshold retracker, the proposed Multiple Waveform Persistent Peak (MWaPP) retracker, and a method combining the physical and empirical retrackers. Using a physical SAR waveform retracker over inland water has not been attempted before but shows great promise in this study. The evaluation is performed for two medium-sized lakes (Lake Vänern in Sweden and Lake Okeechobee in Florida), and in the Amazon River in Brazil. Comparing with in situ data shows that using the SAMOSA3 retracker generally provides the lowest root-mean-squared-errors (RMSE), closely followed by the MWaPP retracker. For the empirical retrackers, the RMSE values obtained when comparing with in situ data in Lake Vänern and Lake Okeechobee are in the order of 2-5 cm for well-behaved waveforms. Combining the physical and empirical retrackers did not offer significantly improved mean track standard deviations or RMSEs. Based on these studies, it is suggested that future SAR derived water levels are obtained using the SAMOSA3 retracker whenever information about other physical properties apart from range is desired. Otherwise we suggest using the empirical MWaPP retracker described in this paper, which is both easy to implement, computationally efficient, and gives a height estimate for even the most contaminated waveforms.

  9. COASTALT Project's contribution to the development and dissemination of coastal altimetry

    Science.gov (United States)

    Cipollini, P.; Benveniste, J.

    2012-04-01

    Satellite altimeters have been monitoring the global ocean for 20 years, with an excellent degree of accuracy; but in the coastal strip data are normally flagged as bad because of a number of technical problems, and therefore rejected. However this situation is rapidly changing: prompted by the tantalizing prospect of recovering 20 years of data over the coastal ocean, and encouraged by the improved suitability for coastal applications of new and future altimeters (like those on Cryosat-2, AltiKa and Sentinel-3), a lively community of researchers in coastal altimetry has coalesced in the last few years, and is developing techniques to recover useful measurements of sea level and significant wave height in the coastal strip, as well as implementing and promoting new applications. The major space agencies are strongly supporting R&D in this new field with initiatives like ESA's COASTALT (for Envisat) and CNES' PISTACH (for Jason-2). The coastal altimetry community holds regular workshops (see http://www.coastalt.eu/community) where the science and techniques of coastal altimetry are reviewed and various applications are showcased and discussed. The present contribution revisits briefly the many recent technical improvements that are contributing to the steady progress of this new field and in particular focuses on the results of the COASTALT project, which has recently concluded. COASTALT has been an excellent incubator of ideas and new techniques for the improvement of coastal altimetry: first of all it has contributed to establish user requirements for this new field, and it has defined detailed product specifications for the new coastal altimetry products and produced the relevant documentation. At the same time COASTALT has tackled the two main areas of improvement for coastal altimetry. These are: 1) retracking, i.e. fitting a waveform model to the waveforms to obtain an estimate of the geophysical parameters: and 2) designing and validating improved coastal

  10. Mesoscale Ocean Altimetry Requirements and Impact of GPS-R measurements for Ocean Mesoscale Circulation Mapping

    CERN Document Server

    Le Traon, P Y; Ruffini, G; Cardellach, E

    2002-01-01

    In the framework of the PARIS Beta project, fundamental milestones have been reached for the definition of future GNSS-R (Global Navigation Satellite System signal Reflections) altimetry missions (the PARIS concept). The most important one is the confirmation of the significant impact that GNSS-R data can have on mesoscale oceanography, as we discuss here. In this report, we first briefly review the contribution of satellite altimetry to mesoscale oceanography. We then summarise recent results obtained on the mapping capabilities of existing and future altimeter missions. From these analyses, refined requirements for mesoscale ocean altimetry (in terms of space/time sampling and accuracy) are derived. A review of on-going and planned altimetric missions is then performed and we analyse how these configurations match the user requirements. Then we will describe the simulation approach and impact analysis of GPS-R data.

  11. Satellite-Based EMI Detection, Identification, and Mitigation

    Science.gov (United States)

    Stottler, R.; Bowman, C.

    2016-09-01

    Commanding, controlling, and maintaining the health of satellites requires a clear operating spectrum for communications. Electro Magnetic Interference (EMI) from other satellites can interfere with these communications. Determining which satellite is at fault improves space situational awareness and can be used to avoid the problem in the future. The Rfi detection And Prediction Tool, Optimizing Resources (RAPTOR) monitors the satellite communication antenna signals to detect EMI (also called RFI for Radio Frequency Interference) using a neural network trained on past cases of both normal communications and EMI events. RAPTOR maintains a database of satellites that have violated the reserved spectrum in the past. When satellite-based EMI is detected, RAPTOR first checks this list to determine if any are angularly close to the satellite being communicated with. Additionally, RAPTOR checks the Space Catalog to see if any of its active satellites are angularly close. RAPTOR also consults on-line databases to determine if the described operating frequencies of the satellites match the detected EMI and recommends candidates to be added to the known offenders database, accordingly. Based on detected EMI and predicted orbits and frequencies, RAPTOR automatically reschedules satellite communications to avoid current and future satellite-based EMI. It also includes an intuitive display for a global network of satellite communications antennas and their statuses including the status of their EM spectrum. RAPTOR has been prototyped and tested with real data (amplitudes versus frequency over time) for both satellite communication signals and is currently undergoing full-scale development. This paper describes the RAPTOR technologies and results of testing.

  12. Sensitivity of a Floodplain Hydrodynamic Model to Satellite-Based DEM Scale and Accuracy: Case Study—The Atchafalaya Basin

    Directory of Open Access Journals (Sweden)

    Hahn Chul Jung

    2015-06-01

    Full Text Available The hydrodynamics of low-lying riverine floodplains and wetlands play a critical role in hydrology and ecosystem processes. Because small topographic features affect floodplain storage and flow velocity, a hydrodynamic model setup of these regions imposes more stringent requirements on the input Digital Elevation Model (DEM compared to upland regions with comparatively high slopes. This current study provides a systematic approach to evaluate the required relative vertical accuracy and spatial resolution of current and future satellite-based altimeters within the context of DEM requirements for 2-D floodplain hydrodynamic models. A case study is presented for the Atchafalaya Basin with a model domain of 1190 km2. The approach analyzes the sensitivity of modeled floodplain water elevation and velocity to typical satellite-based DEM grid-box scale and vertical error, using a previously calibrated version of the physically-based flood inundation model (LISFLOOD-ACC. Results indicate a trade-off relationship between DEM relative vertical error and grid-box size. Higher resolution models are the most sensitive to vertical accuracy, but the impact diminishes at coarser resolutions because of spatial averaging. The results provide guidance to engineers and scientists when defining the observation scales of future altimetry missions such as the   Surface Water and Ocean Topography (SWOT mission from the perspective of numerical modeling requirements for large floodplains of O[103] km2 and greater.

  13. Observer-based Satellite Attitude Control and Simulation Researches

    Institute of Scientific and Technical Information of China (English)

    王子才; 马克茂

    2002-01-01

    Observer design method is applied to the realization of satellite attitude control law baaed on simplified control model. Exact mathematical model of the satellite attitude control system is also constructed, together with the observer-based control law, to conduct simulation research. The simulation results justify the effectiveness andfeasibility of the observer-based control method.

  14. Barometric altimetry system as virtual constellation applied in CAPS

    Institute of Scientific and Technical Information of China (English)

    AI GuoXiang; SHENG PeiXuan; DU JinLin; ZHENG YongGuang; CAI XianDe; WU HaiTao; HU YongHui; HUA Yu; LI XiaoHui

    2009-01-01

    This work describes the barometric altimetry as virtual constellation applied to the Chinese Area Positioning System (CAPS),which uses the transponders of communication satellites to transfer navigation messages to users.Barometric altimetry depends on the relationship of air pressure varying with altitude in the Earth's atmosphere.Once the air pressure at a location is measured the site altitude can be found.This method is able to enhance and improve the availability of three-dimensional positioning.The difficulty is that the relation between barometric pressure and altitude is variable in different areas and under various weather conditions.Hence,in order to obtain higher accuracy,we need to acquire the real-time air pressure corresponding to an altimetric region's reference height.On the other hand,the altimetry method will be applied to satellite navigation system,but the greatest difficulty lies in how to get the real-time air pressure value at the reference height in the broad areas overlaid by satellite navigation.We propose an innovational method to solve this problem.It is to collect the real-time air pressures and temperatures of the 1860 known-altitude weather observatories over China and around via satellite communication and to carry out time extrapolation forecast uniformly.To reduce data quantity,we first partition the data and encode them and then broadcast these information via navigation message to CAPS users' receivers.Upon the interpolations being done in receivers,the reference air pressure and temperature at the receiver's nearby place is derived.Lastly,combing with the receiver-observed real air pressure and temperature,the site's altitude can be determined.The work is presented in the following aspects:the calculation principle,formulae,data collection,encoding,prediction,interpolation method,navigation message transmission together with errors causes and analyses.The advantages and shortcomings of the technique are discussed at the end.

  15. Barometric altimetry system as virtual constellation applied in CAPS

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    This work describes the barometric altimetry as virtual constellation applied to the Chinese Area Positioning System (CAPS), which uses the transponders of communication satellites to transfer navigation messages to users. Barometric altimetry depends on the relationship of air pressure varying with altitude in the Earth’s atmosphere. Once the air pressure at a location is measured the site altitude can be found. This method is able to enhance and improve the availability of three-dimensional positioning. The difficulty is that the relation between barometric pressure and altitude is variable in different areas and under various weather conditions. Hence, in order to obtain higher accuracy, we need to acquire the real-time air pressure corresponding to an altimetric region’s reference height. On the other hand, the altimetry method will be applied to satellite navigation system, but the greatest difficulty lies in how to get the real-time air pressure value at the reference height in the broad areas overlaid by satellite navigation. We propose an innovational method to solve this problem. It is to collect the real-time air pressures and temperatures of the 1860 known-altitude weather observatories over China and around via satellite communication and to carry out time extrapolation forecast uniformly. To reduce data quantity, we first partition the data and encode them and then broadcast these information via navigation message to CAPS users’ receivers. Upon the interpolations being done in receivers, the reference air pressure and temperature at the receiver’s nearby place is derived. Lastly, combing with the receiver-observed real air pressure and temperature, the site’s altitude can be determined. The work is presented in the following aspects: the calculation principle, formulae, data collection, encoding, prediction, interpolation method, navigation message transmission together with errors causes and analyses. The advantages and shortcomings of the

  16. Crisis in geosciences in epoch of altimetry measurments and ways of its overcoming

    Science.gov (United States)

    Barkin, Yu. V.

    2009-04-01

    Scientific results by determination of increase of a global sea level, basing on altimetry measurements, are erroneous. Unfortunately, modern researches of global behavior of ocean in present period have resulted in a lot of paradoxes, to the inexplicable phenomena for today and to contradictions with the classical data of ground (coastal) observations. The basic contradiction consists that values of rate of increase of mean sea level, obtained with the help of satellite methods - methods of altimetry, in 2 - 3 times and more surpass classical determinations of this velocity by coastal methods with the help of measurements at tidal stations. Some authors actually resort to a juggling of the facts in the attempts to explain the found out contradictions (for example, with the help of selection of stations and regions of ocean with the increased values of rates). Thus rather big series of works has lost the scientific importance. The purpose of the report - to show, that conclusions about global increase of a level of the ocean, obtained with application of a method of satellite altimetry are rough - erroneous. "The global sea level rise estimate in the 20th century has been reported at 1.8 mm/yr [Church et al., 2004; Douglas, 2001], which is consistent with the IPCC TAR estimate of 1.5+/-0.5 mm/yr for the 20th Century [Church et al., 2001]. In contrast to the 1.8 mm/yr sea level rise estimate derived from tide gauges, sea level trend estimate from satellite altimetry since 1993 has increased to 3.1+/-0.4 mm/yr [Cazenave and Nerem, 2004]. Although the sea level rise during the TOPEX/POSEIDON period or the last decade is observed to rise almost 50% faster than the average rate over the last Century, visual inspection and fitting a quadratic to the time series confirms there is no significant increase in the rate [Church et al., 2004]." [2], p.7. The statement is rather eloquent. We shall notice only, that the marked difference in rates of MSLR not 50 %, and 100 % and

  17. System refinement for content based satellite image retrieval

    Directory of Open Access Journals (Sweden)

    NourElDin Laban

    2012-06-01

    Full Text Available We are witnessing a large increase in satellite generated data especially in the form of images. Hence intelligent processing of the huge amount of data received by dozens of earth observing satellites, with specific satellite image oriented approaches, presents itself as a pressing need. Content based satellite image retrieval (CBSIR approaches have mainly been driven so far by approaches dealing with traditional images. In this paper we introduce a novel approach that refines image retrieval process using the unique properties to satellite images. Our approach uses a Query by polygon (QBP paradigm for the content of interest instead of using the more conventional rectangular query by image approach. First, we extract features from the satellite images using multiple tiling sizes. Accordingly the system uses these multilevel features within a multilevel retrieval system that refines the retrieval process. Our multilevel refinement approach has been experimentally validated against the conventional one yielding enhanced precision and recall rates.

  18. Radio occultation based on BeiDou satellite navigation

    Science.gov (United States)

    Jiang, Hu; Hu, Haiying; Shen, Xue-min; Gong, Wenbin; Zhang, Yonghe

    2014-11-01

    With the development of GNSS systems, it has become a tendency that radio occultation is used to sense the Earth's atmosphere. By this means, the moisture, temperature, pressure, and total electron content can be derived. Based on the sensing results, more complicated models for atmosphere might come into being. Meteorology well benefits from this technology. As scheduled, the BD satellite navigation system will have a worldwide coverage by the end of 2020. Radio occultation studies in China have been highlighted in the recent decade. More and more feasibilities reports have been published in either domestic or international journals. Herein, some scenarios are proposed to assess the coverage of radio occultation based on two different phases of BD satellite navigation system. Phase one for BD is composed of GEO,IGSO and several MEO satellites. Phase two for BD consists mostly of 24 MEO satellites, some GEO and IGSO satellites. The characteristics of radio occultation based on these two phases are presented respectively.

  19. Coastal sea-level in Norway from CryoSat-2 SAR altimetry

    DEFF Research Database (Denmark)

    Idžanović, Martina; Ophaug, Vegard; Andersen, Ole Baltazar

    Conventional spaceborne altimeters determine the sea surface height with an accuracy of a few centimeters. Although satellite altimetry may be regarded as a mature technology, altimeter observations collected over coastal regions suffer from numerous effects which degrade their quality. For examp...

  20. Long-term sea level change in the Malaysian seas from multi-mission altimetry data

    NARCIS (Netherlands)

    Din, A.H.; Omar, K.M.; Naeije, M.C.; Ses, S.

    2012-01-01

    The long-term sea level change during 1993 to 2008 was investigated in the Malaysian seas from satellite altimetry data of the TOPEX, JASON-1, ERS-1, ERS-2 and ENVISAT missions. Sea level data retrieval and reduction were carried out using the radar altimeter database system (RADS). In RADS data pro

  1. Satellite based wind resource assessment over the South China Sea

    DEFF Research Database (Denmark)

    Badger, Merete; Astrup, Poul; Hasager, Charlotte Bay

    2014-01-01

    modeling to develop procedures and best practices for satellite based wind resource assessment offshore. All existing satellite images from the Envisat Advanced SAR sensor by the European Space Agency (2002-12) have been collected over a domain in the South China Sea. Wind speed is first retrieved from...

  2. Statistical analysis of Lagrangian transport of subtropical waters in the Japan Sea based on AVISO altimetry data

    Science.gov (United States)

    Prants, Sergey V.; Budyansky, Maxim V.; Uleysky, Michael Yu.

    2017-02-01

    Northward near-surface Lagrangian transport of subtropical waters in the Japan Sea frontal zone is simulated and analysed based on altimeter data for the period from 2 January 1993 to 15 June 2015. Computing different Lagrangian indicators for a large number of synthetic tracers launched weekly for 21 years in the southern part of the Sea, we find preferred transport pathways across the Subpolar Front. This cross-frontal transport is statistically shown to be meridionally inhomogeneous with gates and barriers whose locations are determined by the local advection velocity field. The gates open due to suitable dispositions of mesoscale eddies facilitating propagation of subtropical waters to the north. It is documented for the western, central and eastern gates with the help of different kinds of Lagrangian maps and verified by some tracks of available drifters. The transport through the gates occurs by a portion-like manner, i.e. subtropical tracers pass the gates in specific places and during specific time intervals. There are some forbidden zones in the frontal area where the northward transport has not been observed during all the observation period. They exist due to long-term peculiarities of the advection velocity field.

  3. The Kriging Method for Combining Multi-Mission Altimetry over the Mekong River

    Science.gov (United States)

    Boergens, Eva; Buhl, Sven; Dettmering, Denise; Schwatke, Christian; Seitz, Florian

    2016-08-01

    In recent years, water level variations of inland water bodies such as lakes, reservoirs, and rivers measured by satellite altimetry got well established. Most inland water level time series are only assembled from measurements of one pass of one single satellite mission. Only a few multi-mission approaches combine different missions and passes over lakes and reservoirs in order to increase the accuracy and temporal resolution of the time series. This is possible because the lake surface can be considered to be constant everywhere at a given time. However, it is not possible so far to combine different altimeter missions and passes over rivers.We developed a new methodology to combine altimetry data from different missions in a statistical robust way along the river. The methodology is based on kriging which is an interpolation method originating from geostatistics. We expanded the concept to spatio-temporal kriging along the river. The interpolation is a weighted average of available measurements based on empirical correlations not only in the spatial domain but in the temporal domain as well. The higher the correlation, the more weight a measurement obtains in the average. With this approach we are able to combine data not only along the river at a given time or a given location but also data at another location at another time. We developed a statistical model to describe the dependencies between different measurement locations; a prerequisite for the kriging algorithm.We employed the kriging method on altimeter measurements of the Mekong River in South-east Asia. Data of the Envisat, Envisat EM, Jason-2, and SARAL/AltiKa mission were incorperated. With this we are able to achieve a higher temporal resolution time series at any given location. The resulting estimated time series are compared to in-situ data from gauging stations along the river and show a high agreement with these.

  4. Global trends in satellite-based emergency mapping.

    Science.gov (United States)

    Voigt, Stefan; Giulio-Tonolo, Fabio; Lyons, Josh; Kučera, Jan; Jones, Brenda; Schneiderhan, Tobias; Platzeck, Gabriel; Kaku, Kazuya; Hazarika, Manzul Kumar; Czaran, Lorant; Li, Suju; Pedersen, Wendi; James, Godstime Kadiri; Proy, Catherine; Muthike, Denis Macharia; Bequignon, Jerome; Guha-Sapir, Debarati

    2016-07-15

    Over the past 15 years, scientists and disaster responders have increasingly used satellite-based Earth observations for global rapid assessment of disaster situations. We review global trends in satellite rapid response and emergency mapping from 2000 to 2014, analyzing more than 1000 incidents in which satellite monitoring was used for assessing major disaster situations. We provide a synthesis of spatial patterns and temporal trends in global satellite emergency mapping efforts and show that satellite-based emergency mapping is most intensively deployed in Asia and Europe and follows well the geographic, physical, and temporal distributions of global natural disasters. We present an outlook on the future use of Earth observation technology for disaster response and mitigation by putting past and current developments into context and perspective.

  5. Global trends in satellite-based emergency mapping

    Science.gov (United States)

    Voigt, Stefan; Giulio-Tonolo, Fabio; Lyons, Josh; Kučera, Jan; Jones, Brenda; Schneiderhan, Tobias; Platzeck, Gabriel; Kaku, Kazuya; Hazarika, Manzul Kumar; Czaran, Lorant; Li, Suju; Pedersen, Wendi; James, Godstime Kadiri; Proy, Catherine; Muthike, Denis Macharia; Bequignon, Jerome; Guha-Sapir, Debarati

    2016-01-01

    Over the past 15 years, scientists and disaster responders have increasingly used satellite-based Earth observations for global rapid assessment of disaster situations. We review global trends in satellite rapid response and emergency mapping from 2000 to 2014, analyzing more than 1000 incidents in which satellite monitoring was used for assessing major disaster situations. We provide a synthesis of spatial patterns and temporal trends in global satellite emergency mapping efforts and show that satellite-based emergency mapping is most intensively deployed in Asia and Europe and follows well the geographic, physical, and temporal distributions of global natural disasters. We present an outlook on the future use of Earth observation technology for disaster response and mitigation by putting past and current developments into context and perspective.

  6. Global trends in satellite-based emergency mapping

    Science.gov (United States)

    Voigt, Stefan; Giulio-Tonolo, Fabio; Lyons, Josh; Kučera, Jan; Jones, Brenda; Schneiderhan, Tobias; Platzeck, Gabriel; Kaku, Kazuya; Hazarika, Manzul Kumar; Czaran, Lorant; Li, Suju; Pedersen, Wendi; James, Godstime Kadiri; Proy, Catherine; Muthike, Denis Macharia; Bequignon, Jerome; Guha-Sapir, Debarati

    2016-07-01

    Over the past 15 years, scientists and disaster responders have increasingly used satellite-based Earth observations for global rapid assessment of disaster situations. We review global trends in satellite rapid response and emergency mapping from 2000 to 2014, analyzing more than 1000 incidents in which satellite monitoring was used for assessing major disaster situations. We provide a synthesis of spatial patterns and temporal trends in global satellite emergency mapping efforts and show that satellite-based emergency mapping is most intensively deployed in Asia and Europe and follows well the geographic, physical, and temporal distributions of global natural disasters. We present an outlook on the future use of Earth observation technology for disaster response and mitigation by putting past and current developments into context and perspective.

  7. Digital, Satellite-Based Aeronautical Communication

    Science.gov (United States)

    Davarian, F.

    1989-01-01

    Satellite system relays communication between aircraft and stations on ground. System offers better coverage with direct communication between air and ground, costs less and makes possible new communication services. Carries both voice and data. Because many data exchanged between aircraft and ground contain safety-related information, probability of bit errors essential.

  8. Model-based satellite image fusion

    DEFF Research Database (Denmark)

    Aanæs, Henrik; Sveinsson, J. R.; Nielsen, Allan Aasbjerg

    2008-01-01

    A method is proposed for pixel-level satellite image fusion derived directly from a model of the imaging sensor. By design, the proposed method is spectrally consistent. It is argued that the proposed method needs regularization, as is the case for any method for this problem. A framework for pixel...

  9. Delivery of satellite based broadband services

    Science.gov (United States)

    Chandrasekhar, M. G.; Venugopal, D.

    2007-06-01

    Availability of speedy communication links to individuals and organizations is essential to keep pace with the business and social requirements of this modern age. While the PCs have been continuously growing in processing speed and memory capabilities, the availability of broadband communication links still has not been satisfactory in many parts of the world. Recognizing the need to give fillip to the growth of broadband services and improve the broadband penetration, the telecom policies of different counties have placed special emphasis on the same. While emphasis is on the use of fiber optic and copper in local loop, satellite communications systems will play an important role in quickly establishing these services in areas where fiber and other communication systems are not available and are not likely to be available for a long time to come. To make satellite communication systems attractive for the wide spread of these services in a cost effective way special emphasis has to be given on factors affecting the cost of the bandwidth and the equipment. As broadband services are bandwidth demanding, use of bandwidth efficient modulation technique and suitable system architecture are some of the important aspects that need to be examined. Further there is a need to re-look on how information services are provided keeping in view the user requirements and broadcast capability of satellite systems over wide areas. This paper addresses some of the aspects of delivering broadband services via satellite taking Indian requirement as an example.

  10. Co-Channel Interference Mitigation Using Satellite Based Receivers

    Science.gov (United States)

    2014-12-01

    While there is some phase noise present in the continuous time-shifted signal, it is important to recognize that this signal is plotted over the [−π...NAVAL POSTGRADUATE SCHOOL MONTEREY, CALIFORNIA THESIS CO-CHANNEL INTERFERENCE MITIGATION USING SATELLITE BASED RECEIVERS by John E. Patterson...07-02-2012 to 12-19-2014 4. TITLE AND SUBTITLE CO-CHANNEL INTERFERENCE MITIGATION USING SATELLITE BASED RE- CEIVERS 5. FUNDING NUMBERS 6. AUTHOR(S

  11. Global ocean circulation by altimetry

    Science.gov (United States)

    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.

  12. Efficient chaotic based satellite power supply subsystem

    Energy Technology Data Exchange (ETDEWEB)

    Ramos Turci, Luiz Felipe [Technological Institute of Aeronautics (ITA), Sao Jose dos Campos, SP (Brazil)], E-mail: felipeturci@yahoo.com.br; Macau, Elbert E.N. [National Institute of Space Research (Inpe), Sao Jose dos Campos, SP (Brazil)], E-mail: elbert@lac.inpe.br; Yoneyama, Takashi [Technological Institute of Aeronautics (ITA), Sao Jose dos Campos, SP (Brazil)], E-mail: takashi@ita.br

    2009-10-15

    In this work, we investigate the use of the Dynamical System Theory to increase the efficiency of the satellite power supply subsystems. The core of a satellite power subsystem relies on its DC/DC converter. This is a very nonlinear system that presents a multitude of phenomena ranging from bifurcations, quasi-periodicity, chaos, coexistence of attractors, among others. The traditional power subsystem design techniques try to avoid these nonlinear phenomena so that it is possible to use linear system theory in small regions about the equilibrium points. Here, we show that more efficiency can be drawn from a power supply subsystem if the DC/DC converter operates in regions of high nonlinearity. In special, if it operates in a chaotic regime, is has an intrinsic sensitivity that can be exploited to efficiently drive the power subsystem over high ranges of power requests by using control of chaos techniques.

  13. Improving the assessment of ICESat water altimetry accuracy accounting for autocorrelation

    Science.gov (United States)

    Abdallah, Hani; Bailly, Jean-Stéphane; Baghdadi, Nicolas; Lemarquand, Nicolas

    2011-11-01

    Given that water resources are scarce and are strained by competing demands, it has become crucial to develop and improve techniques to observe the temporal and spatial variations in the inland water volume. Due to the lack of data and the heterogeneity of water level stations, remote sensing, and especially altimetry from space, appear as complementary techniques for water level monitoring. In addition to spatial resolution and sampling rates in space or time, one of the most relevant criteria for satellite altimetry on inland water is the accuracy of the elevation data. Here, the accuracy of ICESat LIDAR altimetry product is assessed over the Great Lakes in North America. The accuracy assessment method used in this paper emphasizes on autocorrelation in high temporal frequency ICESat measurements. It also considers uncertainties resulting from both in situ lake level reference data. A probabilistic upscaling process was developed. This process is based on several successive ICESat shots averaged in a spatial transect accounting for autocorrelation between successive shots. The method also applies pre-processing of the ICESat data with saturation correction of ICESat waveforms, spatial filtering to avoid measurement disturbance from the land-water transition effects on waveform saturation and data selection to avoid trends in water elevations across space. Initially this paper analyzes 237 collected ICESat transects, consistent with the available hydrometric ground stations for four of the Great Lakes. By adapting a geostatistical framework, a high frequency autocorrelation between successive shot elevation values was observed and then modeled for 45% of the 237 transects. The modeled autocorrelation was therefore used to estimate water elevations at the transect scale and the resulting uncertainty for the 117 transects without trend. This uncertainty was 8 times greater than the usual computed uncertainty, when no temporal correlation is taken into account. This

  14. Evaluation of Ocean Tide Models Used for Jason-2 Altimetry Corrections

    DEFF Research Database (Denmark)

    Fok, H.S.; Baki Iz, H.; Shum, C. K.

    2010-01-01

    –3 cm RMS (root-mean-square) level. The Gulf of Mexico and Northwest Atlantic regions present the least reduction of altimetry sea surface height variability after ocean tides are removed, primarily because of large oceanic variability associated with loop currents in the Gulf of Mexico and the Gulf......It has been more than a decade since the last comprehensive accuracy assessment of global ocean tide models. Here, we conduct an evaluation of the barotropic ocean tide corrections, which were computed using FES2004 and GOT00.2, and other models on the Jason-2 altimetry Geophysical Data Record (GDR......), with a focus on selected coastal regions with energetic ocean dynamics. We compared nine historical and contemporary ocean tide models with pelagic tidal constants and with multiple satellite altimetry mission (T/P, ERS-1/-2, Envisat, GFO, Jason-1/-2) sea level anomalies using variance reduction studies...

  15. 日本海西南海域现场观测和卫星高度计获取的海面高度距平的比较研究%Comparison of sea surface height anomalies derived by pres-sure-sensor-equipped inverted echo sounders and satellite al-timetry in the Southwest Japan/East Sea

    Institute of Scientific and Technical Information of China (English)

    葛磊; 徐永生; 尹宝树

    2016-01-01

    Pressure-sensor-equipped inverted echo sounders (PIES) can be used to measure sea bottom pressure and the acoustic-wave propagation time from the seabed to the surface. Bottom pressure and the acoustic propagation time are used to estimate the contribution of the sea surface height anomaly (SLA) to water quality changes (positive pressure) and hema-tocrit changes (baroclinic), respectively. In this paper, we compare SLAs derived by PIES with SLAs derived from satellite altimetry data in the Southwest Japan/East Sea. Using correlation analysis, we compared the PIES SLAs with SLAs meas-ured by the along-track T/P satellite (TP SLA) and the ERS-2 satellite (ERS-2 SLA). We then compared the PIES SLA and AVISO gridded SLAs to estimate possible sources of error. We also analyzed the contributions of the PIES SLA positive pressure and baroclinic aspects of the SLA. The comparison results show that the correlation coefficient of the PIES SLA and Sat SLA is relatively high, and the root mean square error is relatively small. Further, we studied data from specific re-gions to identify possible causes of site-specific errors. Based on our results, we draw the following conclusions: (1) with respect to the Gulf Stream and the Kuroshio region, the contribution of positive sea surface height is relatively large; (2) if we consider the contribution of baroclinic changes in sea surface height, the PIES SLA and Sat SLA correlation coefficient will improve; (3) in the high-energy zone, the PIES SLA and Sat SLA correlation coefficient is relatively high and relatively better. Overall, in the Japan/East Sea, the PIES SLA and satellite altimeter SLA correlation coefficient is relatively high with a high level of consistency, providing a reliable way for checking the operation of Ocean II satellite (HY-2) altimeters. The research results have significance for the development and design of PIES, and for the selection of the placement of PIES.%压力传

  16. Autonomous sensor-based dual-arm satellite grappling

    Science.gov (United States)

    Wilcox, Brian; Tso, Kam; Litwin, Todd; Hayati, Samad; Bon, Bruce

    1989-01-01

    Dual-arm satellite grappling involves the integration of technologies developed in the Sensing and Perception (S&P) Subsystem for object acquisition and tracking, and the Manipulator Control and Mechanization (MCM) Subsystem for dual-arm control. S&P acquires and tracks the position, orientation, velocity, and angular velocity of a slowly spinning satellite, and sends tracking data to the MCM subsystem. MCM grapples the satellite and brings it to rest, controlling the arms so that no excessive forces or torques are exerted on the satellite or arms. A 350-pound satellite mockup which can spin freely on a gimbal for several minutes, closely simulating the dynamics of a real satellite is demonstrated. The satellite mockup is fitted with a panel under which may be mounted various elements such as line replacement modules and electrical connectors that will be used to demonstrate servicing tasks once the satellite is docked. The subsystems are housed in three MicroVAX II microcomputers. The hardware of the S&P Subsystem includes CCD cameras, video digitizers, frame buffers, IMFEX (a custom pipelined video processor), a time-code generator with millisecond precision, and a MicroVAX II computer. Its software is written in Pascal and is based on a locally written vision software library. The hardware of the MCM Subsystem includes PUMA 560 robot arms, Lord force/torque sensors, two MicroVAX II computers, and unimation pneumatic parallel grippers. Its software is written in C, and is based on a robot language called RCCL. The two subsystems are described and test results on the grappling of the satellite mockup with rotational rates of up to 2 rpm are provided.

  17. Moving Target Information Extraction Based on Single Satellite Image

    Directory of Open Access Journals (Sweden)

    ZHAO Shihu

    2015-03-01

    Full Text Available The spatial and time variant effects in high resolution satellite push broom imaging are analyzed. A spatial and time variant imaging model is established. A moving target information extraction method is proposed based on a single satellite remote sensing image. The experiment computes two airplanes' flying speed using ZY-3 multispectral image and proves the validity of spatial and time variant model and moving information extracting method.

  18. A comparative study of satellite and ground-based phenology.

    Science.gov (United States)

    Studer, S; Stöckli, R; Appenzeller, C; Vidale, P L

    2007-05-01

    Long time series of ground-based plant phenology, as well as more than two decades of satellite-derived phenological metrics, are currently available to assess the impacts of climate variability and trends on terrestrial vegetation. Traditional plant phenology provides very accurate information on individual plant species, but with limited spatial coverage. Satellite phenology allows monitoring of terrestrial vegetation on a global scale and provides an integrative view at the landscape level. Linking the strengths of both methodologies has high potential value for climate impact studies. We compared a multispecies index from ground-observed spring phases with two types (maximum slope and threshold approach) of satellite-derived start-of-season (SOS) metrics. We focus on Switzerland from 1982 to 2001 and show that temporal and spatial variability of the multispecies index correspond well with the satellite-derived metrics. All phenological metrics correlate with temperature anomalies as expected. The slope approach proved to deviate strongly from the temporal development of the ground observations as well as from the threshold-defined SOS satellite measure. The slope spring indicator is considered to indicate a different stage in vegetation development and is therefore less suited as a SOS parameter for comparative studies in relation to ground-observed phenology. Satellite-derived metrics are, however, very susceptible to snow cover, and it is suggested that this snow cover should be better accounted for by the use of newer satellite sensors.

  19. DIGITAL VIDEO BROADCAST RETURN CHANNEL VIA SATELLITE (DVB-RCS HUB FOR SATELLITE BASED E-LEARNING

    Directory of Open Access Journals (Sweden)

    N.G.Vasantha Kumar

    2011-02-01

    Full Text Available This paper discusses in-house designed and developed scale-down DVB-RCS hub along with the performance of the realized hub. This development is intended to support the Satellite Based e-Learning initiative in India. The scale-down DVB-RCS HUB is implemented around a single PC with other subsystems making it very cost effective and unique of its kind. This realization will drastically reduce the total cost of Satellite based Education Networks as very low cost commercially available Satellite Interactive Terminals (SITs complying to open standard could be used at remote locations. The system is successfully tested to work with a commercial SIT using a GEO satellite EDUSAT which is especially dedicated for satellite based e-Learning. The internal detail of the DVB-RCS Forward and Return Link Organization and how it manages the Satellite Interactive Terminals access to the satellite channel using MF-TDMA approach has been described.

  20. Technology status of HNF-based monopropellants for satellite propulsion

    NARCIS (Netherlands)

    Marée, A.G.M.; Moerel, J.L.P.A.; Weiland-Veltmans, W.H.M.; Wierkx, F.J.M.; Zevenbergen, J.

    2004-01-01

    This paper reports on significant technological progress made over the last few years in determining the feasibility of HNF-based monopropellants. An HNF-based monopropellant is an interesting alternative for hydrazine as monopropellant for satellite propulsion. New non-toxic monopropellants based o

  1. Technology status of HNF-based monopropellants for satellite propulsion

    NARCIS (Netherlands)

    Marée, A.G.M.; Moerel, J.L.P.A.; Weiland-Veltmans, W.H.M.; Wierkx, F.J.M.; Zevenbergen, J.

    2004-01-01

    This paper reports on significant technological progress made over the last few years in determining the feasibility of HNF-based monopropellants. An HNF-based monopropellant is an interesting alternative for hydrazine as monopropellant for satellite propulsion. New non-toxic monopropellants based o

  2. Advances in satellite oceanography

    Science.gov (United States)

    Brown, O. B.; Cheney, R. E.

    1983-01-01

    Technical advances and recent applications of active and passive satellite remote sensing techniques to the study of oceanic processes are summarized. The general themes include infrared and visible radiometry, active and passive microwave sensors, and buoy location systems. The surface parameters of sea surface temperature, windstream, sea state, altimetry, color, and ice are treated as applicable under each of the general methods.

  3. Defining a Sea Ice Flag for Envisat Altimetry Mission

    OpenAIRE

    Tran, N; Ardhuin, Fanny; Ezraty, Robert; Feng, H.; Femenias, P

    2009-01-01

    This letter presents the development of a sea ice flag algorithm for the Envisat altimetry mission to detect sea ice corrupted sea surface height data within quality control processing. The algorithm takes advantage of having both passive and active microwave sensors on the same platform with coregistered measurements. Its performances have been evaluated based on collocations between the along-track Envisat data with reference maps built from combination of daily grids of sea ice concentrati...

  4. A satellite based telemetry link for a UAV application

    Science.gov (United States)

    Bloise, Anthony

    1995-01-01

    The requirements for a satellite based communication facility to service the needs of the Geographical Information System (GIS) data collection community are addressed in this paper. GIS data is supplied in the form of video imagery at sub-television rates in one or more spectral bands / polarizations laced with a position correlated data stream. The limitations and vicissitudes of using a terrestrial based telecommunications link to collect GIS data are illustrated from actual mission scenarios. The expectations from a satellite based communications link by the geophysical data collection community concerning satellite architecture, operating bands, bandwidth, footprint agility, up link and down link hardware configurations on the UAV, the Mobile Control Vehicle and at the Central Command and Data Collection Facility comprise the principle issues discussed in the first section of this paper. The final section of the paper discusses satellite based communication links would have an increased volume and scope of services the GIS data collection community could make available to the GIS user community, and the price the data collection community could afford to pay for access to the communication satellite described in the paper.

  5. Application of CryoSat-2 altimetry data for river analysis and modelling

    Science.gov (United States)

    Schneider, Raphael; Nygaard Godiksen, Peter; Villadsen, Heidi; Madsen, Henrik; Bauer-Gottwein, Peter

    2017-02-01

    Availability of in situ river monitoring data, especially of data shared across boundaries, is decreasing, despite growing challenges for water resource management across the entire globe. This is especially valid for the case study of this work, the Brahmaputra Basin in South Asia. Commonly, satellite altimeters are used in various ways to provide information about such river basins. Most missions provide virtual station time series of water levels at locations where their repeat orbits cross rivers. CryoSat-2 is equipped with a new type of altimeter, providing estimates of the actual ground location seen in the reflected signal. It also uses a drifting orbit, challenging conventional ways of processing altimetry data to river water levels and their incorporation in hydrologic-hydrodynamic models. However, CryoSat-2 altimetry data provides an unprecedentedly high spatial resolution. This paper suggests a procedure to (i) filter CryoSat-2 observations over rivers to extract water-level profiles along the river, and (ii) use this information in combination with a hydrologic-hydrodynamic model to fit the simulated water levels with an accuracy that cannot be reached using information from globally available digital elevation models (DEMs) such as from the Shuttle Radar Topography Mission (SRTM) only. The filtering was done based on dynamic river masks extracted from Landsat imagery, providing spatial and temporal resolutions high enough to map the braided river channels and their dynamic morphology. This allowed extraction of river water levels over previously unmonitored narrow stretches of the river. In the Assam Valley section of the Brahmaputra River, CryoSat-2 data and Envisat virtual station data were combined to calibrate cross sections in a 1-D hydrodynamic model of the river. The hydrologic-hydrodynamic model setup and calibration are almost exclusively based on openly available remote sensing data and other global data sources, ensuring transferability of

  6. ALTWAVE: Toolbox for use of satellite L2P altimeter data for wave model validation

    Science.gov (United States)

    Appendini, Christian M.; Camacho-Magaña, Víctor; Breña-Naranjo, José Agustín

    2016-03-01

    To characterize some of the world's ocean physical processes such as its wave height, wind speed and sea surface elevation is a major need for coastal and marine infrastructure planning and design, tourism activities, wave power and storm surge risk assessment, among others. Over the last decades, satellite remote sensing tools have provided quasi-global measurements of ocean altimetry by merging data from different satellite missions. While there is a widely use of altimeter data for model validation, practical tools for model validation remain scarce. Our purpose is to fill this gap by introducing ALTWAVE, a MATLAB user-oriented toolbox for oceanographers and coastal engineers developed to validate wave model results based on visual features and statistical estimates against satellite derived altimetry. Our toolbox uses altimetry information from the GlobWave initiative, and provides a sample application to validate a one year wave hindcast for the Gulf of Mexico. ALTWAVE also offers an effective toolbox to validate wave model results using altimeter data, as well as a guidance for non-experienced satellite data users. This article is intended for wave modelers with no experience using altimeter data to validate their results.

  7. Multi-spectral band selection for satellite-based systems

    Energy Technology Data Exchange (ETDEWEB)

    Clodius, W.B.; Weber, P.G.; Borel, C.C.; Smith, B.W.

    1998-09-01

    The design of satellite based multispectral imaging systems requires the consideration of a number of tradeoffs between cost and performance. The authors have recently been involved in the design and evaluation of a satellite based multispectral sensor operating from the visible through the long wavelength IR. The criteria that led to some of the proposed designs and the modeling used to evaluate and fine tune the designs will both be discussed. These criteria emphasized the use of bands for surface temperature retrieval and the correction of atmospheric effects. The impact of cost estimate changes on the final design will also be discussed.

  8. Tracking target objects orbiting earth using satellite-based telescopes

    Energy Technology Data Exchange (ETDEWEB)

    De Vries, Willem H; Olivier, Scot S; Pertica, Alexander J

    2014-10-14

    A system for tracking objects that are in earth orbit via a constellation or network of satellites having imaging devices is provided. An object tracking system includes a ground controller and, for each satellite in the constellation, an onboard controller. The ground controller receives ephemeris information for a target object and directs that ephemeris information be transmitted to the satellites. Each onboard controller receives ephemeris information for a target object, collects images of the target object based on the expected location of the target object at an expected time, identifies actual locations of the target object from the collected images, and identifies a next expected location at a next expected time based on the identified actual locations of the target object. The onboard controller processes the collected image to identify the actual location of the target object and transmits the actual location information to the ground controller.

  9. SOFT project: a new forecasting system based on satellite data

    Science.gov (United States)

    Pascual, Ananda; Orfila, A.; Alvarez, Alberto; Hernandez, E.; Gomis, D.; Barth, Alexander; Tintore, Joaquim

    2002-01-01

    The aim of the SOFT project is to develop a new ocean forecasting system by using a combination of satellite dat, evolutionary programming and numerical ocean models. To achieve this objective two steps are proved: (1) to obtain an accurate ocean forecasting system using genetic algorithms based on satellite data; and (2) to integrate the above new system into existing deterministic numerical models. Evolutionary programming will be employed to build 'intelligent' systems that, learning form the past ocean variability and considering the present ocean state, will be able to infer near future ocean conditions. Validation of the forecast skill will be carried out by comparing the forecasts fields with satellite and in situ observations. Validation with satellite observations will provide the expected errors in the forecasting system. Validation with in situ data will indicate the capabilities of the satellite based forecast information to improve the performance of the numerical ocean models. This later validation will be accomplished considering in situ measurements in a specific oceanographic area at two different periods of time. The first set of observations will be employed to feed the hybrid systems while the second set will be used to validate the hybrid and traditional numerical model results.

  10. GRRATS: A New Approach to Inland Altimetry Processing for Major World Rivers

    Science.gov (United States)

    Coss, S. P.

    2016-12-01

    Here we present work-in-progress results aimed at generating a new radar altimetry dataset GRRATS (Global River Radar Altimetry Time Series) extracted over global ocean-draining rivers wider than 900 m. GRATTS was developed as a component of the NASA MEaSUREs project (PI: Dennis Lettenmaier, UCLA) to generate pre-SWOT data products for decadal or longer global river elevation changes from multi-mission satellite radar altimetry data. The dataset at present includes 909 time series from 39 rivers. A new method of filtering VS (virtual station) height time series is presented where, DEM based heights were used to establish limits for the ice1 retracked Jason2 and Envisat heights at present. While GRRATS is following in the footsteps of several predecessors, it contributes to one of the critical climate data records in generating a validated and comprehensive hydrologic observations in river height. The current data product includes VSs in north and south Americas, Africa and Eurasia, with the most comprehensive set of Jason-2 and Envisat RA time series available for North America and Eurasia. We present a semi-automated procedure to process returns from river locations, identified with Landsat images and updated water mask extent. Consistent methodologies for flagging ice cover are presented. DEM heights used in height filtering were retained and can be used as river height profiles. All non-validated VS have been assigned a letter grade A-D to aid end users in selection of data. Validated VS are accompanied with a suite of fit statistics. Due to the inclusiveness of the dataset, not all VS were able to undergo validation (415 of 909), but those that were demonstrate that confidence in the data product is warranted. Validation was accomplished using records from 45 in situ gauges from 12 rivers. Meta-analysis was performed to compare each gauge with each VS by relative height. Preliminary validation results are as follows. 89.3% of the data have positive Nash

  11. Validation of an Innovative Satellite-Based UV Dosimeter

    Science.gov (United States)

    Morelli, Marco; Masini, Andrea; Simeone, Emilio; Khazova, Marina

    2016-08-01

    We present an innovative satellite-based UV (ultraviolet) radiation dosimeter with a mobile app interface that has been validated by exploiting both ground-based measurements and an in-vivo assessment of the erythemal effects on some volunteers having a controlled exposure to solar radiation.Both validations showed that the satellite-based UV dosimeter has a good accuracy and reliability needed for health-related applications.The app with this satellite-based UV dosimeter also includes other related functionalities such as the provision of safe sun exposure time updated in real-time and end exposure visual/sound alert. This app will be launched on the global market by siHealth Ltd in May 2016 under the name of "HappySun" and available both for Android and for iOS devices (more info on http://www.happysun.co.uk).Extensive R&D activities are on-going for further improvement of the satellite-based UV dosimeter's accuracy.

  12. Characterization of SAR Mode Altimetry over Inland Water

    Science.gov (United States)

    Fabry, Pierre; Bercher, Nicolas

    2015-12-01

    Radar altimetry over the inland water domain is a difficult topic that still requires a lot of human expertise as well as manual editing and verifications. This is mainly due to the fact that inland water scenes are highly variable, both in space and time, which leads to a much broader range of radar signatures than in oceanography. The remark is particularly true for LRM altimetry and remains valid in many cases in SAR mode (SARM). In preparation for the operational Sentinel-3 mission and to better benefit from the improved SARM along-track resolution it is required to: 1. better characterize the SARM Individual Echoes, Multi-Look Stacks, 20Hz waveforms as well as the Range Integrated Power (RIP) over the inland water domain, 2. step toward processing schemes that account for the actual content of the illuminated scene. In this work, we introduce an automated technique to assess the water fraction within the Beam-limited Doppler footprint through its intersection area of with a water mask. This framework opens up new ways toward the automated characterization and processing of altimetry data based on regularly updated water masks.

  13. Basic Radar Altimetry Toolbox: Tools and Tutorial To Use Radar Altimetry For Cryosphere

    Science.gov (United States)

    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

  14. Engineering satellite-based navigation and timing global navigation satellite systems, signals, and receivers

    CERN Document Server

    Betz, J

    2016-01-01

    This book describes the design and performance analysis of satnav systems, signals, and receivers. It also provides succinct descriptions and comparisons of all the world’s satnav systems. Its comprehensive and logical structure addresses all satnav signals and systems in operation and being developed. Engineering Satellite-Based Navigation and Timing: Global Navigation Satellite Systems, Signals, and Receivers provides the technical foundation for designing and analyzing satnav signals, systems, and receivers. Its contents and structure address all satnav systems and signals: legacy, modernized, and new. It combines qualitative information with detailed techniques and analyses, providing a comprehensive set of insights and engineering tools for this complex multidisciplinary field. Part I describes system and signal engineering including orbital mechanics and constellation design, signal design principles and underlying considerations, link budgets, qua tifying receiver performance in interference, and e...

  15. Atmospheric Corrections for Altimetry Studies over Inland Water

    Directory of Open Access Journals (Sweden)

    M. Joana Fernandes

    2014-05-01

    Full Text Available Originally designed for applications over the ocean, satellite altimetry has been proven to be a useful tool for hydrologic studies. Altimeter products, mainly conceived for oceanographic studies, often fail to provide atmospheric corrections suitable for inland water studies. The focus of this paper is the analysis of the main issues related with the atmospheric corrections that need to be applied to the altimeter range to get precise water level heights. Using the corrections provided on the Radar Altimeter Database System, the main errors present in the dry and wet tropospheric corrections and in the ionospheric correction of the various satellites are reported. It has been shown that the model-based tropospheric corrections are not modeled properly and in a consistent way in the various altimetric products. While over the ocean, the dry tropospheric correction (DTC is one of the most precise range corrections, in some of the present altimeter products, it is the correction with the largest errors over continental water regions, causing large biases of several decimeters, and along-track interpolation errors up to several centimeters, both with small temporal variations. The wet tropospheric correction (WTC from the on-board microwave radiometers is hampered by the contamination on the radiometer measurements of the surrounding lands, making it usable only in the central parts of large lakes. In addition, the WTC from atmospheric models may also have large errors when it is provided at sea level instead of surface height. These errors cannot be corrected by the user, since no accurate expression exists for the height variation of the WTC. Alternative and accurate corrections can be computed from in situ data, e.g., DTC from surface pressure at barometric stations and WTC from Global Navigation Satellite System permanent stations. The latter approach is particularly favorable for small lakes and reservoirs, where GNSS-derived WTC at a single

  16. Methods of satellite oceanography

    Science.gov (United States)

    Stewart, R. H.

    1985-01-01

    The theoretical basis for remote sensing measurements of climate and ocean dynamics is examined. Consideration is given to: the absorption of electromagnetic radiation in the atmosphere; scattering in the atmosphere; and satellite observations using visible light. Consideration is also given to: the theory of radio scatter from the sea; scatter of centimeter waves from the sea; and the theory of operation of synthetic aperture radars. Additional topics include: the coordinate systems of satellite orbits for oceanographic remote sensing applications; the operating features of the major U.S. satellite systems for viewing the ocean; and satellite altimetry.

  17. A Satellite Based Fog Study of the Korean Peninsula

    Science.gov (United States)

    2007-06-01

    total number of fog and fog likely days detected from the two MODIS satellites, Aqua and Tera , respectively. Results from all nine areas of...trends in fog detection based on the satellite differences. 46 0 20 40 60 80 100 120 N um be r o f D ay s 1 2 3 4 5 6 7 8 9 Areas Four Month Tera vs...Aqua Fog Totals Tera Fog Tera Fog Likely Aqua Fog Aqua Fog Likely Figure 29. Comparisons of the four month total number of fog and fog likely days

  18. Satellite Type Estination from Ground-based Photometric Observation

    Science.gov (United States)

    Endo, T.; Ono, H.; Suzuki, J.; Ando, T.; Takanezawa, T.

    2016-09-01

    The optical photometric observation is potentially a powerful tool for understanding of the Geostationary Earth Orbit (GEO) objects. At first, we measured in laboratory the surface reflectance of common satellite materials, for example, Multi-layer Insulation (MLI), mono-crystalline silicon cells, and Carbon Fiber Reinforced Plastic (CFRP). Next, we calculated visual magnitude of a satellite by simplified shape and albedo. In this calculation model, solar panels have dimensions of 2 by 8 meters, and the bus area is 2 meters squared with measured optical properties described above. Under these conditions, it clarified the brightness can change the range between 3 and 4 magnitudes in one night, but color index changes only from 1 to 2 magnitudes. Finally, we observed the color photometric data of several GEO satellites visible from Japan multiple times in August and September 2014. We obtained that light curves of GEO satellites recorded in the B and V bands (using Johnson filters) by a ground-base optical telescope. As a result, color index changed approximately from 0.5 to 1 magnitude in one night, and the order of magnitude was not changed in all cases. In this paper, we briefly discuss about satellite type estimation using the relation between brightness and color index obtained from the photometric observation.

  19. Trellis-coded CPM for satellite-based mobile communications

    Science.gov (United States)

    Abrishamkar, Farrokh; Biglieri, Ezio

    1988-01-01

    Digital transmission for satellite-based land mobile communications is discussed. To satisfy the power and bandwidth limitations imposed on such systems, a combination of trellis coding and continuous-phase modulated signals are considered. Some schemes based on this idea are presented, and their performance is analyzed by computer simulation. The results obtained show that a scheme based on directional detection and Viterbi decoding appears promising for practical applications.

  20. Possible satellite-based observations of the 1997 Leonid meteoroids

    Energy Technology Data Exchange (ETDEWEB)

    Pongratz, M.B.; Carlos, R.C.; Cayton, T.

    1998-12-01

    The Block IIA GPS satellites are equipped with a sensor designed to detect electromagnetic transients. Several phenomena will produce triggers in this sensor. They include earth-based electromagnetic transients such as lightning and two space-based phenomena--deep dielectric discharge and meteoroid or hyper-velocity micro-gram particle impact (HMPI). Energetic electrons in the GPS environment cause the deep dielectric charging. HMPIs cause triggers through the transient electric fields generated by the ejecta plasma. During the 1997 Leonid passage the energetic particle fluxes were very low. In the presence of such low fluxes the typical median trigger rate is 20 per minute with a standard deviation of about 20 per minute. Between 0800 UT and 1200 UT on November 17, 1997, the sensor on a specially configured satellite observed trigger rates more than 10 sigma above the nominal median rate. Sensors on other Block IIA GPS satellites also observed excess triggers during November. Detection is enhanced when the sensor antenna is oriented into the Leonid radiant. While many questions persist the authors feel that it is likely that the excess events during the November interval were caused by the close approach of the satellites to the Leonid meteoroid path.

  1. An Ontology Based Methodology for Satellite Data Semantic Interoperability

    Directory of Open Access Journals (Sweden)

    ABBURU, S.

    2015-08-01

    Full Text Available Satellites and ocean based observing system consists of various sensors and configurations. These observing systems transmit data in heterogeneous file formats and heterogeneous vocabulary from various data centers. These data centers maintain a centralized data management system that disseminates the observations to various research communities. Currently, different data naming conventions are being used by existing observing systems, thus leading to semantic heterogeneity. In this work, sensor data interoperability and semantics of the data are being addressed through ontologies. The present work provides an effective technical solution to address semantic heterogeneity through semantic technologies. These technologies provide interoperability, capability to build knowledge base, and framework for semantic information retrieval by developing an effective concept vocabulary through domain ontologies. The paper aims at a new methodology to interlink the multidisciplinary and heterogeneous sensor data products. A four phase methodology has been implemented to address satellite data semantic interoperability. The paper concludes with the evaluation of the methodology by linking and interfacing multiple ontologies to arrive at ontology vocabulary for sensor observations. Data from Indian Meteorological satellite INSAT-3D satellite have been used as a typical example to illustrate the concepts. This work on similar lines can also be extended to other sensor observations.

  2. Time-varying land subsidence detected by radar altimetry: California, Taiwan and north China.

    Science.gov (United States)

    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.

  3. Time-varying land subsidence detected by radar altimetry: California, Taiwan and north China

    Science.gov (United States)

    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

    Science.gov (United States)

    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.

  5. Satellite Based Extrusion Rates for the 2006 Augustine Eruption

    Science.gov (United States)

    Dehn, J.; Bailey, J. E.; Dean, K. G.; Skoog, R.; Valcic, L.

    2006-12-01

    Extrusion rates were calculated from polar orbiting infrared satellite data for the 2006 eruption of Augustine Volcano, Alaska. The pixel integrated brightness temperatures from the satellite data were converted to estimates of ground temperature by making assumptions and using first hand observations about the geometry of the hot area (lava dome, flows and pyroclastic flow deposits) relative to the cold area in the kilometer scale pixels. Extrusion rate is calculated by assuming that at a given temperature, a lava emits an amount of radiation proportional to its volume. On ten occasions during the activity, helicopter based infrared imagers were used to validate the satellite observations. The pre-January 11 thermal activity was not significantly above background in satellite data. The first strong thermal anomalies were recorded during the first explosive phase on January 11. During successive explosive phases in January, bright thermal signals were observed, often saturating the sensors. Large areas (many km2) were observed to be warm in the satellite data, indicative of pyroclastic flows. Sometime during or after January 29, during a phase of sustained ash emission, the thermal signal became persistent, suggesting the beginning of lava effusion. The extrusion rates derived from satellite data varied from 0 to nearly 7 m3/s, giving an eruption rate of 2.7 m3/s. The extrusion event produced two blocky lava flows which moved down the north flank of the volcano. Extrusion occurred through at least March 15 (day 76) when a sharp drop in extrusion rate and thermal signal is observed. Based on the derived extrusion rates, it is estimated that 18 million m3 of lava was extruded during the course of the eruption. This value agreed well with photogrammetric measurements, but does not agree with volumes derived through subtraction of digital elevation models post- and pre- eruption. It should be noted that the thermal approach only works for hot lavas, and does not

  6. Evaluating the hydrological consistency of satellite based water cycle components

    KAUST Repository

    Lopez Valencia, Oliver M.

    2016-06-15

    Advances in multi-satellite based observations of the earth system have provided the capacity to retrieve information across a wide-range of land surface hydrological components and provided an opportunity to characterize terrestrial processes from a completely new perspective. Given the spatial advantage that space-based observations offer, several regional-to-global scale products have been developed, offering insights into the multi-scale behaviour and variability of hydrological states and fluxes. However, one of the key challenges in the use of satellite-based products is characterizing the degree to which they provide realistic and representative estimates of the underlying retrieval: that is, how accurate are the hydrological components derived from satellite observations? The challenge is intrinsically linked to issues of scale, since the availability of high-quality in-situ data is limited, and even where it does exist, is generally not commensurate to the resolution of the satellite observation. Basin-scale studies have shown considerable variability in achieving water budget closure with any degree of accuracy using satellite estimates of the water cycle. In order to assess the suitability of this type of approach for evaluating hydrological observations, it makes sense to first test it over environments with restricted hydrological inputs, before applying it to more hydrological complex basins. Here we explore the concept of hydrological consistency, i.e. the physical considerations that the water budget impose on the hydrologic fluxes and states to be temporally and spatially linked, to evaluate the reproduction of a set of large-scale evaporation (E) products by using a combination of satellite rainfall (P) and Gravity Recovery and Climate Experiment (GRACE) observations of storage change, focusing on arid and semi-arid environments, where the hydrological flows can be more realistically described. Our results indicate no persistent hydrological

  7. Periodic material-based vibration isolation for satellites

    Directory of Open Access Journals (Sweden)

    Xinnan Liu

    2016-01-01

    Full Text Available The vibration environment of a satellite is very severe during launch. Isolating the satellitevibrations during launch will significantly enhance reliability and lifespan, and reduce the weight of satellite structure and manufacturing cost. Guided by the recent advances in solid-state physics research, a new type of satellite vibration isolator is proposed by usingperiodic material that is hence called periodic isolator. The periodic isolator possesses a unique dynamic property, i.e., frequency band gaps. External vibrations with frequencies falling in the frequency band gaps of the periodic isolator are to be isolated. Using the elastodynamics and the Bloch-Floquet theorem, the frequency band gaps of periodic isolators are determined. A parametric study is conducted to provide guidelines for the design of periodic isolators. Based on these analytical results, a finite element model of a micro-satellite with a set of designed periodic isolators is built to show the feasibility of vibration isolation. The periodic isolator is found to be a multi-directional isolator that provides vibration isolation in the three directions.

  8. The satellite based augmentation system – EGNOS for non-precision approach global navigation satellite system

    Directory of Open Access Journals (Sweden)

    Andrzej FELLNER

    2012-01-01

    Full Text Available First in the Poland tests of the EGNOS SIS (Signal in Space were conducted on 5th October 2007 on the flight inspection with SPAN (The Synchronized Position Attitude Navigation technology at the Mielec airfield. This was an introduction to a test campaign of the EGNOS-based satellite navigation system for air traffic. The advanced studies will be performed within the framework of the EGNOS-APV project in 2011. The implementation of the EGNOS system to APV-I precision approach operations, is conducted according to ICAO requirements in Annex 10. Definition of usefulness and certification of EGNOS as SBAS (Satellite Based Augmentation System in aviation requires thorough analyses of accuracy, integrity, continuity and availability of SIS. Also, the project will try to exploit the excellent accuracy performance of EGNOS to analyze the implementation of GLS (GNSS Landing System approaches (Cat I-like approached using SBAS, with a decision height of 200 ft. Location of the EGNOS monitoring station Rzeszów, located near Polish-Ukrainian border, being also at the east border of planned EGNOS coverage for ECAC states is very useful for SIS tests in this area. According to current EGNOS programmed schedule, the project activities will be carried out with EGNOS system v2.2, which is the version released for civil aviation certification. Therefore, the project will allow demonstrating the feasibility of the EGNOS certifiable version for civil applications.

  9. A Consistent Radar Altimetry Dataset for Major World Rivers: Extraction Methods and Preliminary Data Products

    Science.gov (United States)

    Coss, S. P.; Durand, M. T.; Tuozzolo, S.; Yi, Y.; Jia, Y.; Guo, Q.; Shum, C. K.

    2015-12-01

    Our group has made several efforts to develop the systematics for processing multiple satellite mission inland altimetry data with the purpose of creating a pre-SWOT climate data record of world's rivers greater than 900m in width. The project is a component of a NASA MEaSUREs (Making Earth System Data Records for Use in Research Environments) project undertaken by UCLA, Princeton U., NASA/GSFC and Ohio State Univ. The first method developed allows for the identification of measurements that represent the target river through height filtering and is based on USGS flow data from 105 gauges on rivers with watersheds over 20,000 km2. Proximal topographic variations led to some contamination of the radar returns. We were able to identify them using the previously mentioned height filter, and correlated their frequency with near-river topographic indices. Significant efforts have also been made to detect river ice using only radar backscatter. Over 631 Landsat images were processed and given an ice cover designation then compared with measured backscatter profiles; demonstrating that isolating a one- to-one relationship between ice and backscatter will be challenging. An additional focus of the group has been automation of detecting altimeter/river intersections as well as the creation of "virtual stations" or masks for data extraction at those locations. Using RivWidth parameters to generate polygons and a raster proximity based intersection detection methods have both shown promising results for automation of this process. This project will soon be producing validated climate data records in the form of geocentric river height changes, both in terms of scale of the study area and access to previously unmonitored regions. Once established, these methods will also be applicable to the study of future satellite cycles. Preliminary river height change data products have been produced for the Mississippi, St Lawrence, Yukon, Mackenzie, and part of the Ganges

  10. GPS SATELLITE SIMULATOR SIGNAL ESTIMATION BASED ON ANN

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    Multi-channel Global Positioning System (GPS) satellite signal simulator is used to provide realistic test signals for GPS receivers and navigation systems. In this paper, signals arriving the antenna of GPS receiver are analyzed from the viewpoint of simulator design. The estimation methods are focused of which several signal parameters are difficult to determine directly according to existing experiential models due to various error factors. Based on the theory of Artificial Neural Network (ANN), an approach is proposed to simulate signal propagation delay,carrier phase, power, and other parameters using ANN. The architecture of the hardware-in-the-loop test system is given. The ANN training and validation process is described. Experimental results demonstrate that the ANN designed can statistically simulate sample data in high fidelity.Therefore the computation of signal state based on this ANN can meet the design requirement,and can be directly applied to the development of multi-channel GPS satellite signal simulator.

  11. Ice measurements by Geosat radar altimetry

    Science.gov (United States)

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

    1987-01-01

    Radar altimetry for ice-covered ocean and land is more complex and variable than open ocean radar altimetry; attention is presently given to Geosat ice-sheet topography for the Greenland and Antarctic ice sheets between 72 deg N and 72 deg S which owes its excellent accuracy to the well separated spacing of the orbital tracks and an 18-month geodetic mission duration. A surface elevation map of southern Greenland, produced from 110 days of retracked Geosat data, is presented in color-coded three-dimensional perspective. Comparisons are made between Seasat and Geosat data for ice mass elevations in Greenland.

  12. Satellite Formation Design for Space Based Radar Applications

    Science.gov (United States)

    2007-07-30

    Practical Guidance Methodology for Relative Motion of LEO Spacecraft Based on the Clohessy-Wiltshire Equations,” AAS Paper 04-252, AAS/AIAA Space...Non- Circular Reference Orbit," AAS Paper 01-222, AAS/AIAA Space Flight Mechanics Meeting, Santa Barbara, CA, Feb 11-16, 2001. 11. D. Brouwer ...Small Eccentricities or Inclinations in the Brouwer Theory of the Artificial Satellite,” The Astronomical Journal, Vol. 68, October 1963, pp. 555

  13. Detecting surface geostrophic currents using wavelet filter from satellite geodesy

    Institute of Scientific and Technical Information of China (English)

    HSU; HouTse

    2007-01-01

    According to the features of spatial spectrum of the dynamic ocean topography (DOT),wavelet filter is proposed to reduce short-wavelength and noise signals in DOT. The surface geostrophic currents calculated from the DOT models filtered by wavelet filter in global and Kuroshio regions show more detailed information than those from the DOT models filtered by Gaussian filter. Based on a satellite gravity field model (CG01C) and a gravity field model (EGM96),combining an altimetry-derived mean sea surface height model (KMSS04),two mean DOT models are estimated. The short-wavelength and noise signals of these two DOT models are removed by using wavelet filter,and the DOT models asso-ciated global mean surface geostrophic current fields are calculated separately. Comparison of the surface geostrophic currents from CG01C and EGM96 model in global,Kuroshio and equatorial Pacific regions with that from oceanography,and comparison of influences of the two gravity models errors on the precision of the surface geostrophic currents velocity show that the accuracy of CG01C model has been greatly improved over pre-existing models at long wavelengths. At large and middle scale,the surface geostrophic current from satellite gravity and satellite altimetry agrees well with that from oceanography,which indicates that ocean currents detected by satellite measurement have reached relatively high precision.

  14. Detecting surface geostrophic currents using wavelet filter from satellite geodesy

    Institute of Scientific and Technical Information of China (English)

    ZHANG ZiZhan; LU Yang; HSU HouTse

    2007-01-01

    According to the features of spatial spectrum of the dynamic ocean topography (DOT), wavelet filter is proposed to reduce short-wavelength and noise signals in DOT. The surface geostrophic currents calculated from the DOT models filtered by wavelet filter in global and Kuroshio regions show more detailed information than those from the DOT models filtered by Gaussian filter. Based on a satellite gravity field model (CG01C) and a gravity field model (EGM96), combining an altimetry-derived mean sea surface height model (KMSS04), two mean DOT models are estimated. The short-wavelength and noise signals of these two DOT models are removed by using wavelet filter, and the DOT models associated global mean surface geostrophic current fields are calculated separately. Comparison of the surface geostrophic currents from CG01C and EGM96 model in global, Kuroshio and equatorial Pacific regions with that from oceanography, and comparison of influences of the two gravity models errors on the precision of the surface geostrophic currents velocity show that the accuracy of CG01C model has been greatly improved over pre-existing models at long wavelengths. At large and middle scale, the surface geostrophic current from satellite gravity and satellite altimetry agrees well with that from oceanography, which indicates that ocean currents detected by satellite measurement have reached relatively high precision.

  15. Efficient enhancing scheme for TCP performance over satellite-based internet

    Institute of Scientific and Technical Information of China (English)

    Wang Lina; Gu Xuemai

    2007-01-01

    Satellite link characteristics drastically degrade transport control protocol (TCP) performance. An efficient performance enhancing scheme is proposed. The improvement of TCP performance over satellite-based Intemet is accomplished by protocol transition gateways at each end ora satellite link. The protocol which runs over a satellite link executes the receiver-driven flow control and acknowledgements- and timeouts-based error control strategies. The validity of this TCP performance enhancing scheme is verified by a series of simulation experiments. Results show that the proposed scheme can efficiently enhance the TCP performance over satellite-based Intemet and ensure that the available bandwidth resources of the satellite link are fully utilized.

  16. Biomass prediction model in maize based on satellite images

    Science.gov (United States)

    Mihai, Herbei; Florin, Sala

    2016-06-01

    Monitoring of crops by satellite techniques is very useful in the context of precision agriculture, regarding crops management and agricultural production. The present study has evaluated the interrelationship between maize biomass production and satellite indices (NDVI and NDBR) during five development stages (BBCH code), highlighting different levels of correlation. Biomass production recorded was between 2.39±0.005 t ha-1 (12-13 BBCH code) and 51.92±0.028 t ha-1 (83-85 BBCH code), in relation to vegetation stages studied. Values of chlorophyll content ranged from 24.1±0.25 SPAD unit (12-13 BBCH code) to 58.63±0.47 SPAD unit (71-73 BBCH code), and the obtained satellite indices ranged from 0.035641±0.002 and 0.320839±0.002 for NDVI indices respectively 0.035095±0.034 and 0.491038±0.018 in the case of NDBR indices. By regression analysis it was possible to obtain predictive models of biomass in maize based on the satellite indices, in statistical accurate conditions. The most accurate prediction was possible based on NDBR index (R2 = 0.986, F = 144.23, p<0.001, RMSE = 1.446), then based on chlorophyll content (R2 = 0.834, F = 16.14, p = 0.012, RMSE = 6.927) and NDVI index (R2 = 0.682, F = 3.869, p = 0.116, RMSE = 12.178).

  17. Evaluation of SAMOSA3 adapted retracker using Cryosat-2 SAR altimetry data over the Arctic ocean

    DEFF Research Database (Denmark)

    Jain, Maulik; Martin-Puig, Cristina; Andersen, Ole Baltazar

    2014-01-01

    European Space Agency's Cryosat-2 comes with the first ever SAR (Synthetic Aperture Radar) altimeter onboard a satellite. In this work precise sea surface heights and gravity fields are determined using Cryosat-2 SAR data. These determinations through satellite altimetry are difficult in the Arctic...... for the Arctic. Through this research it has been demonstrated that the SAMOSA3 retracker has a better performance as compared to other SAR retrackers when sea surface height and gravity field determination needs to be done. The performance evaluation of the SAMOSA3 retracker as compared to other retrackers has...

  18. Basic Radar Altimetry Toolbox: Tools to Use Radar Altimetry for Geodesy

    Science.gov (United States)

    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

  19. SAMIRA - SAtellite based Monitoring Initiative for Regional Air quality

    Science.gov (United States)

    Schneider, Philipp; Stebel, Kerstin; Ajtai, Nicolae; Diamandi, Andrei; Horalek, Jan; Nicolae, Doina; Stachlewska, Iwona; Zehner, Claus

    2016-04-01

    Here, we present a new ESA-funded project entitled Satellite based Monitoring Initiative for Regional Air quality (SAMIRA), which aims at improving regional and local air quality monitoring through synergetic use of data from present and upcoming satellites, traditionally used in situ air quality monitoring networks and output from chemical transport models. Through collaborative efforts in four countries, namely Romania, Poland, the Czech Republic and Norway, all with existing air quality problems, SAMIRA intends to support the involved institutions and associated users in their national monitoring and reporting mandates as well as to generate novel research in this area. Despite considerable improvements in the past decades, Europe is still far from achieving levels of air quality that do not pose unacceptable hazards to humans and the environment. Main concerns in Europe are exceedances of particulate matter (PM), ground-level ozone, benzo(a)pyrene (BaP) and nitrogen dioxide (NO2). While overall sulfur dioxide (SO2) emissions have decreased in recent years, regional concentrations can still be high in some areas. The objectives of SAMIRA are to improve algorithms for the retrieval of hourly aerosol optical depth (AOD) maps from SEVIRI, and to develop robust methods for deriving column- and near-surface PM maps for the study area by combining satellite AOD with information from regional models. The benefit to existing monitoring networks (in situ, models, satellite) by combining these datasets using data fusion methods will be tested for satellite-based NO2, SO2, and PM/AOD. Furthermore, SAMIRA will test and apply techniques for downscaling air quality-related EO products to a spatial resolution that is more in line with what is generally required for studying urban and regional scale air quality. This will be demonstrated for a set of study sites that include the capitals of the four countries and the highly polluted areas along the border of Poland and the

  20. Efficient Satellite Scheduling Based on Improved Vector Evaluated Genetic Algorithm

    Directory of Open Access Journals (Sweden)

    Tengyue Mao

    2012-03-01

    Full Text Available Satellite scheduling is a typical multi-peak, many-valley, nonlinear multi-objective optimization problem. How to effectively implement the satellite scheduling is a crucial research in space areas.This paper mainly discusses the performance of VEGA (Vector Evaluated Genetic Algorithm based on the study of basic principles of VEGA algorithm, algorithm realization and test function, and then improves VEGA algorithm through introducing vector coding, new crossover and mutation operators, new methods to assign fitness and hold good individuals. As a result, the diversity and convergence of improved VEGA algorithm of improved VEGA algorithm have been significantly enhanced and will be applied to Earth-Mars orbit optimization. At the same time, this paper analyzes the results of the improved VEGA, whose results of performance analysis and evaluation show that although VEGA has a profound impact upon multi-objective evolutionary research,  multi-objective evolutionary algorithm on the basis of Pareto seems to be a more effective method to get the non-dominated solutions from the perspective of diversity and convergence of experimental result. Finally, based on Visual C + + integrated development environment, we have implemented improved vector evaluation algorithm in the satellite scheduling.

  1. Covariance analysis of differential drag-based satellite cluster flight

    Science.gov (United States)

    Ben-Yaacov, Ohad; Ivantsov, Anatoly; Gurfil, Pini

    2016-06-01

    One possibility for satellite cluster flight is to control relative distances using differential drag. The idea is to increase or decrease the drag acceleration on each satellite by changing its attitude, and use the resulting small differential acceleration as a controller. The most significant advantage of the differential drag concept is that it enables cluster flight without consuming fuel. However, any drag-based control algorithm must cope with significant aerodynamical and mechanical uncertainties. The goal of the current paper is to develop a method for examination of the differential drag-based cluster flight performance in the presence of noise and uncertainties. In particular, the differential drag control law is examined under measurement noise, drag uncertainties, and initial condition-related uncertainties. The method used for uncertainty quantification is the Linear Covariance Analysis, which enables us to propagate the augmented state and filter covariance without propagating the state itself. Validation using a Monte-Carlo simulation is provided. The results show that all uncertainties have relatively small effect on the inter-satellite distance, even in the long term, which validates the robustness of the used differential drag controller.

  2. Satellite Imagery Assisted Road-Based Visual Navigation System

    Science.gov (United States)

    Volkova, A.; Gibbens, P. W.

    2016-06-01

    There is a growing demand for unmanned aerial systems as autonomous surveillance, exploration and remote sensing solutions. Among the key concerns for robust operation of these systems is the need to reliably navigate the environment without reliance on global navigation satellite system (GNSS). This is of particular concern in Defence circles, but is also a major safety issue for commercial operations. In these circumstances, the aircraft needs to navigate relying only on information from on-board passive sensors such as digital cameras. An autonomous feature-based visual system presented in this work offers a novel integral approach to the modelling and registration of visual features that responds to the specific needs of the navigation system. It detects visual features from Google Earth* build a feature database. The same algorithm then detects features in an on-board cameras video stream. On one level this serves to localise the vehicle relative to the environment using Simultaneous Localisation and Mapping (SLAM). On a second level it correlates them with the database to localise the vehicle with respect to the inertial frame. The performance of the presented visual navigation system was compared using the satellite imagery from different years. Based on comparison results, an analysis of the effects of seasonal, structural and qualitative changes of the imagery source on the performance of the navigation algorithm is presented. * The algorithm is independent of the source of satellite imagery and another provider can be used

  3. Entropy-Based Block Processing for Satellite Image Registration

    Directory of Open Access Journals (Sweden)

    Ikhyun Lee

    2012-11-01

    Full Text Available Image registration is an important task in many computer vision applications such as fusion systems, 3D shape recovery and earth observation. Particularly, registering satellite images is challenging and time-consuming due to limited resources and large image size. In such scenario, state-of-the-art image registration methods such as scale-invariant feature transform (SIFT may not be suitable due to high processing time. In this paper, we propose an algorithm based on block processing via entropy to register satellite images. The performance of the proposed method is evaluated using different real images. The comparative analysis shows that it not only reduces the processing time but also enhances the accuracy.

  4. Chaos Based Secure IP Communications over Satellite DVB

    Science.gov (United States)

    Caragata, Daniel; El Assad, Safwan; Tutanescu, Ion; Sofron, Emil

    2010-06-01

    The Digital Video Broadcasting—Satellite (DVB-S) standard was originally conceived for TV and radio broadcasting. Later, it became possible to send IP packets using encapsulation methods such as Multi Protocol Encapsulation, MPE, or Unidirectional Lightweight Encapsulation, ULE. This paper proposes a chaos based security system for IP communications over DVB-S with ULE encapsulation. The proposed security system satisfies all the security requirements while respecting the characteristics of satellite links, such as the importance of efficient bandwidth utilization and high latency time. It uses chaotic functions to generate the keys and to encrypt the data. The key management is realized using a multi-layer architecture. A theoretical analysis of the system and a simulation of FTP and HTTP traffic are presented and discussed to show the cost of the security enhancement and to provide the necessary tools for security parameters setup.

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

    Science.gov (United States)

    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.

  6. Lively data: discover, browse and access ocean altimetry data on internet

    Directory of Open Access Journals (Sweden)

    V. Rosmorduc

    2006-01-01

    Full Text Available 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.

  7. Interoperability of satellite-based augmentation systems for aircraft navigation

    Science.gov (United States)

    Dai, Donghai

    The Federal Aviation Administration (FAA) is pioneering a transformation of the national airspace system from its present ground based navigation and landing systems to a satellite based system using the Global Positioning System (GPS). To meet the critical safety-of-life aviation positioning requirements, a Satellite-Based Augmentation System (SBAS), the Wide Area Augmentation System (WAAS), is being implemented to support navigation for all phases of flight, including Category I precision approach. The system is designed to be used as a primary means of navigation, capable of meeting the Required Navigation Performance (RNP), and therefore must satisfy the accuracy, integrity, continuity and availability requirements. In recent years there has been international acceptance of Global Navigation Satellite Systems (GNSS), spurring widespread growth in the independent development of SBASs. Besides the FAA's WAAS, the European Geostationary Navigation Overlay Service System (EGNOS) and the Japan Civil Aviation Bureau's MTSAT-Satellite Augmentation System (MSAS) are also being actively developed. Although all of these SBASs can operate as stand-alone, regional systems, there is increasing interest in linking these SBASs together to reduce costs while improving service coverage. This research investigated the coverage and availability improvements due to cooperative efforts among regional SBAS networks. The primary goal was to identify the optimal interoperation strategies in terms of performance, complexity and practicality. The core algorithms associated with the most promising concepts were developed and demonstrated. Experimental verification of the most promising concepts was conducted using data collected from a joint international test between the National Satellite Test Bed (NSTB) and the EGNOS System Test Bed (ESTB). This research clearly shows that a simple switch between SBASs made by the airborne equipment is the most effective choice for achieving the

  8. Development and validation of satellite based estimates of surface visibility

    Science.gov (United States)

    Brunner, J.; Pierce, R. B.; Lenzen, A.

    2015-10-01

    A satellite based surface visibility retrieval has been developed using Moderate Resolution Imaging Spectroradiometer (MODIS) measurements as a proxy for Advanced Baseline Imager (ABI) data from the next generation of Geostationary Operational Environmental Satellites (GOES-R). The retrieval uses a multiple linear regression approach to relate satellite aerosol optical depth, fog/low cloud probability and thickness retrievals, and meteorological variables from numerical weather prediction forecasts to National Weather Service Automated Surface Observing System (ASOS) surface visibility measurements. Validation using independent ASOS measurements shows that the GOES-R ABI surface visibility retrieval (V) has an overall success rate of 64.5% for classifying Clear (V ≥ 30 km), Moderate (10 km ≤ V skill during June through September, when Heidke skill scores are between 0.2 and 0.4. We demonstrate that the aerosol (clear sky) component of the GOES-R ABI visibility retrieval can be used to augment measurements from the United States Environmental Protection Agency (EPA) and National Park Service (NPS) Interagency Monitoring of Protected Visual Environments (IMPROVE) network, and provide useful information to the regional planning offices responsible for developing mitigation strategies required under the EPA's Regional Haze Rule, particularly during regional haze events associated with smoke from wildfires.

  9. Convolutional neural network features based change detection in satellite images

    Science.gov (United States)

    Mohammed El Amin, Arabi; Liu, Qingjie; Wang, Yunhong

    2016-07-01

    With the popular use of high resolution remote sensing (HRRS) satellite images, a huge research efforts have been placed on change detection (CD) problem. An effective feature selection method can significantly boost the final result. While hand-designed features have proven difficulties to design features that effectively capture high and mid-level representations, the recent developments in machine learning (Deep Learning) omit this problem by learning hierarchical representation in an unsupervised manner directly from data without human intervention. In this letter, we propose approaching the change detection problem from a feature learning perspective. A novel deep Convolutional Neural Networks (CNN) features based HR satellite images change detection method is proposed. The main guideline is to produce a change detection map directly from two images using a pretrained CNN. This method can omit the limited performance of hand-crafted features. Firstly, CNN features are extracted through different convolutional layers. Then, a concatenation step is evaluated after an normalization step, resulting in a unique higher dimensional feature map. Finally, a change map was computed using pixel-wise Euclidean distance. Our method has been validated on real bitemporal HRRS satellite images according to qualitative and quantitative analyses. The results obtained confirm the interest of the proposed method.

  10. Annual cycle in lakes and rivers from CryoSat-2 altimetry — The Brahmaputra river

    DEFF Research Database (Denmark)

    Villadsen, Heidi; Andersen, Ole Baltazar; Stenseng, Lars

    2014-01-01

    A key concern of the CryoSat-2 orbit has been its long repeat period of 369 days, which is usually undesirable for river and lake monitoring. However, the results of this study show that CryoSat-2 data can indeed be used for such monitoring by utilizing the high spatial coverage and the sub......-cycle period of 30 days. The performance of CryoSat-2/SIRAL altimetry for river level monitoring is investigated by studying river levels retrieved from Ganges and Brahmaputra. An evaluation of CryoSat-2 river levels from LRM, SAR and SARIn data is performed by comparing with Envisat data from the period...... data to continue river level archives from satellite radar altimetry....

  11. (Nearly) Fifteen Years of Altimetry Outreach at CNES and NASA/JPL

    Science.gov (United States)

    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.

  12. Application of TOPEX Altimetry for Solid Earth Deformation Studies

    Directory of Open Access Journals (Sweden)

    Hyongki Lee

    2008-01-01

    Full Text Available This study demonstrates the use of satellite radar altimetry to detect solid Earth deformation signals such as Glacial Isostatic Adjustment (GIA. Our study region covers moderately flat land surfaces seasonally covered by snow/ice/vegetation. The maximum solid Earth uplift of ~10 mm yr-1 is primarily due to the incomplete glacial isostatic rebound that occurs around Hudson Bay, North America. We use decadal (1992 - 2002 surface height measurements from TOPEX/POSEIDON radar altimetry to generate height changes time series for 12 selected locations in the study region. Due to the seasonally varying surface characteristics, we first perform radar waveform shape classification and have found that most of the waveforms are quasi-diffuse during winter/spring and specular during summer/fall. As a result, we used the NASA £]-retracker for the quasi-diffuse waveforms and the Offset Center of Gravity or the threshold retracker for the specular waveforms, to generate the surface height time series. The TOPEX height change time series exhibit coherent seasonal signals (higher amplitude during the winter and lower amplitude during the summer, and the estimated deformation rates agree qualitatively well with GPS vertical velocities, and with altimeter/tide gauge combined vertical velocities around the Great Lakes. The TOPEX observations also agree well with various GIA model predictions, especially with the ICE-5G (VM2 model with differences at 0.2 ¡_ 1.4 mm yr-1, indicating that TOPEX has indeed observed solid Earth deformation signals manifested as crustal uplift over the former Laurentide Ice Sheet region.

  13. Sea Ice Leads and Polynya Detection Using Multi-Mission Altimetry in the Greenland Sea

    Science.gov (United States)

    Muller, Felix L.; Passaro, Marcello; Dettmering, Denise; Bosch, Wolfgang

    2016-08-01

    In this study, we present two methods to detect open water areas in the Greenland Sea based on altimetry measurements. For this purpose, high-frequency data from ENVISAT (pulse-limited altimeter) and Delay-Doppler data from CryoSat-2 are used. The radar echoes of both missions contain information about the reflectance of the overflown surface area. For ENVISAT, we use an unsupervised classification approach to distinguish between water and ice returns. The waveforms are the main input for the classification process. Training data from known surfaces are not necessary for our method. For CryoSat- 2 SAR mode, an advanced approach is used in order to exploit the multi-look processing of the same resolution cell from different look angles. We analyse the Range Integrated Power, a side product providing additional information about the backscatter properties. All classification results are compared with pictures of imaging SAR satellite missions (ALOS and Sentinel-1A). In order to take the time lag between the two observation sets into account, a mean ice-motion is applied to the images. This ensures realistic comparison results. The classification approach allows for an identification of open water (leads and polynyas) in sea-ice regions and will help to improve sea level estimation in these regions.

  14. A Time and Space-based Dynamic IP Routing in Broadband Satellite Networks

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    The topology architecture, characteristics and routing technologies of broadband satellite networks are studied in this paper. The authors propose the routing scheme of satellite networks and design a time and space-based distributed routing algorithm whose complexity is O(1). Simulation results aiming at satellite mobility show that the new algorithm can determine the minimum propagation delay paths effectively.

  15. Comparison of Ocean Dynamics with a Regional Circulation Model and Improved Altimetry in the North-Western Mediterranean

    Directory of Open Access Journals (Sweden)

    Jérôme Bouffard

    2008-01-01

    Full Text Available The spatial and temporal resolution of satellite altimetry is usually sufficient for monitoring the changes of sea surface topography in the open ocean. However, coastal ocean dynamics are much more complex, being characterized by smaller spatial and temporal scales of variability. The quality and availability of satellite-derived products along the coasts have to be improved, with a strategy optimized for coastal targets. Therefore a coastal multi-satellite altimetry dataset (TOPEX/Poseidon, Jason-1; Envisat; GFO at a 10 - 20 Hz sampling rate has been derived from routine geophysical data products using a new processing software dedicated to coastal zone applications. Improved along-track sea level variations with fine space scales are available in the North-western Mediterranean Sea from 2001 to 2003, and are compared with high-resolution numerical model elevations from the eddy-resolving model SYMPHONIE. This preparatory work emphasizes the potential of improved multi-satellite altimetry for validating coastal hydro-dynamical models and could contribute in the future to a better tuning of the boundary conditions of the simulations.

  16. A new DEM of the Austfonna ice cap by combining differential SAR interferometry with ICESat laser altimetry

    Directory of Open Access Journals (Sweden)

    Geir Moholdt

    2012-05-01

    Full Text Available We present a new digital elevation model (DEM of the Austfonna ice cap in the Svalbard Archipelago, Norwegian Arctic. Previous DEMs derived from synthetic aperture radar (SAR and optical shape-from-shading have been tied to airborne radio echo-sounding surface profiles from 1983 which contain an elevation-dependent bias of up to several tens of metres compared with recent elevation data. The new and freely available DEM is constructed purely from spaceborne remote sensing data using differential SAR interferometry (DInSAR in combination with ICESat laser altimetry. Interferograms were generated from pairs of SAR scenes from the one-day repeat tandem phase of the European Remote Sensing Satellites 1/2 (ERS-1/2 in 1996. ICESat elevations from winter 2006–08 were used as ground control points to refine the interferometric baseline. The resulting DEM is validated against the same ground control points and independent surface elevation profiles from Global Navigation Satellite Systems (GNSS and airborne laser altimetry, yielding root mean square (RMS errors of about 10 m in all cases. This quality is sufficient for most glaciological applications, and the new DEM will be a baseline data set for ongoing and future research at Austfonna. The technique of combining satellite DInSAR with high-resolution satellite altimetry for DEM generation might also be a good solution in other glacier regions with similar characteristics, especially when data from TanDEM-X and CryoSat-2 become available.

  17. Scheduler for monitoring objects orbiting earth using satellite-based telescopes

    Energy Technology Data Exchange (ETDEWEB)

    Olivier, Scot S; Pertica, Alexander J; Riot, Vincent J; De Vries, Willem H; Bauman, Brian J; Nikolaev, Sergei; Henderson, John R; Phillion, Donald W

    2015-04-28

    An ephemeris refinement system includes satellites with imaging devices in earth orbit to make observations of space-based objects ("target objects") and a ground-based controller that controls the scheduling of the satellites to make the observations of the target objects and refines orbital models of the target objects. The ground-based controller determines when the target objects of interest will be near enough to a satellite for that satellite to collect an image of the target object based on an initial orbital model for the target objects. The ground-based controller directs the schedules to be uploaded to the satellites, and the satellites make observations as scheduled and download the observations to the ground-based controller. The ground-based controller then refines the initial orbital models of the target objects based on the locations of the target objects that are derived from the observations.

  18. A new 25 years Arctic Sea level record from ESA satellites

    DEFF Research Database (Denmark)

    Andersen, Ole Baltazar; Cheng, Yongcun; Knudsen, Per

    the ESA GOCE mission we are now able to derive a mean dynamic topography of the Arctic Ocean with unprecedented accuracy to constrain the ocean circulation. We present both a new estimation of the mean ocean circulation and new estimates of large scale sea level changes based on satellite data and perform......The Arctic is an extremely challenging region for the use of remote sensing for ocean studies. One is the fact that despite 25 years of altimetry only very limited sea level observations exists in the interior of the Arctic Ocean. However, with Cryosat-2 SAR altimetry the situation is changing...... and through development of tailored retrackers dealing with presence of sea ice within the radar footprint, we can now develop sea surface height and its variation in most of the Arctic Ocean. We have processed 5 years of Cryosat-2 data quantified as either Lead or Ocean data within the Cryosat-2 SAR mask...

  19. A new 25 years Arctic Sea level record from ESA satellites

    DEFF Research Database (Denmark)

    Andersen, Ole Baltazar; Cheng, Yongcun; Knudsen, Per

    the ESA GOCE mission we are now able to derive a mean dynamic topography of the Arctic Ocean with unprecedented accuracy to constrain the ocean circulation. We present both a new estimation of the mean ocean circulation and new estimates of large scale sea level changes based on satellite data and perform......The Arctic is an extremely challenging region for the use of remote sensing for ocean studies. One is the fact that despite 25 years of altimetry only very limited sea level observations exists in the interior of the Arctic Ocean. However, with Cryosat-2 SAR altimetry the situation is changing...... and through development of tailored retrackers dealing with presence of sea ice within the radar footprint, we can now develop sea surface height and its variation in most of the Arctic Ocean. We have processed 5 years of Cryosat-2 data quantified as either Lead or Ocean data within the Cryosat-2 SAR mask...

  20. Decadal Variation in Surface Characteristics over Xinjiang, Western China, from T/P Altimetry Backscatter Coefficients: Evidence of Climate Change

    Directory of Open Access Journals (Sweden)

    Jinyun Guo

    2013-01-01

    Full Text Available The backscatter coefficient, known as sigma0, is an important measurement of satellite radar altimetry and a key parameter for land altimetry because of its close relationship with the physical properties and geometric features of land coverage under global/regional climate change effects. Using the TOPEX/Poseidon GDR-M dataset from January 1993 to December 2004, we study the spatial and temporal distribution of sigma0 at bands Ku and C over Xinjiang, western China. The results show that the sigma0 is influenced by the water distribution over land and the time evolution of sigma0 has clear seasonal changes. River basins or deserts are classified over the spatial distribution based on different sigma0 values. For example, high sigma0 values are found in the Tarim River Basin and low values are found in the Taklimakan Desert. The periodic components of sigma0 time series are determined using the fast Fourier transformation method. The annual variation is the dominating cycle and the semi-annual variation is the secondary signal. The amplitudes of sigma0 time series at bands Ku and C are also given and most areas have quite low amplitudes except for the Tarim River Basin. Several areas including the Tarim River Basin, Tianshan Mountain and Taklimakan Desert are selected for sigma0 time series spacial analysis to discuss the reasons for variations in sigma0. The main factors are precipitation and vegetation growth, which are affected by the global/regional climate change. The correlation between the brightness temperature, which is related to the water-vapor content in the atmosphere measured by TMR at the 21 GHz channel and sigma0 at two bands, is analyzed.

  1. Planning for a data base system to support satellite conceptual design

    Science.gov (United States)

    Claydon, C. R.

    1976-01-01

    The conceptual design of an automated satellite design data base system is presented. The satellite catalog in the system includes data for all earth orbital satellites funded to the hardware stage for launch between 1970 and 1980, and provides a concise compilation of satellite capabilities and design parameters. The cost of satellite subsystems and components will be added to the base. Data elements are listed and discussed. Sensor and science and applications opportunities catalogs will be included in the data system. Capabilities of the BASIS storage, retrieval, and analysis system are used in the system design.

  2. Zenith Pass Problem of Inter-satellite Linkage Antenna Based on Program Guidance Method

    Institute of Scientific and Technical Information of China (English)

    Zhai Kun; Yang Di

    2008-01-01

    While adopting an elevation-over-azimuth architecture by an inter-satellite linkage antenna of a user satellite, a zenith pass problem always occurs when the antenna is tracing the tracking and data relay satellite (TDRS). This paper deals with this problem by way of,firstly, introducing movement laws of the inter-satellite linkage to predict the movement of the user satellite antenna followed by analyzing the potential pass moment and the actual one of the zenith pass in detail. A number of specific orbit altitudes for the user satellite that can remove the blindness zone are obtained. Finally, on the base of the predicted results from the movement laws of the inter-satellite linkage, the zenith pass tracing strategies for the user satellite antenna are designed under the program guidance using a trajectory preprocessor. Simulations have confirmed the reasonability and feasibility of the strategies in dealing with the zenith pass problem.

  3. GPD+ Wet Tropospheric Corrections for CryoSat-2 and GFO Altimetry Missions

    Directory of Open Access Journals (Sweden)

    M. Joana Fernandes

    2016-10-01

    Full Text Available Due to its large space-time variability, the wet tropospheric correction (WTC is still considered a significant error source in satellite altimetry. This paper presents the GNSS (Global Navigation Satellite Systems derived Path Delay Plus (GPD+, the most recent algorithm developed at the University of Porto to retrieve improved WTC for radar altimeter missions. The GPD+ are WTC estimated by space-time objective analysis, by combining all available observations in the vicinity of the point: valid measurements from the on-board microwave radiometer (MWR, from GNSS coastal and island stations and from scanning imaging MWR on board various remote sensing missions. The GPD+ corrections are available both for missions which do not possess an on-board microwave radiometer such as CryoSat-2 (CS-2 and for all missions which carry this sensor, by addressing the various error sources inherent to the MWR-derived WTC. To ensure long-term stability of the corrections, the large set of radiometers used in this study have been calibrated with respect to the Special Sensor Microwave Imager (SSM/I and the SSM/I Sounder (SSM/IS. The application of the algorithm to CS-2 and Geosat Follow-on (GFO, as representative altimetric missions without and with a MWR aboard the respective spacecraft, is described. Results show that, for both missions, the new WTC significantly reduces the sea level anomaly (SLA variance with respect to the model-based corrections. For GFO, the new WTC also leads to a large reduction in SLA variance with respect to the MWR-derived WTC, recovering a large number of observations in the coastal and polar regions and full sets of tracks and several cycles when MWR measurements are missing or invalid. Overall, the algorithm allows the recovery of a significant number of measurements, ensuring the continuity and consistency of the correction in the open-ocean/coastal transition zone and at high latitudes.

  4. Improving the Accuracy of Coastal Sea Surface Heights by Retracking Decontaminated Radar Altimetry Waveforms

    Science.gov (United States)

    Huang, Zhengkai; Wang, Haihong; Luo, Zhicai

    2017-04-01

    Due to the complex coastal topography and energetic ocean dynamics effect, the return echoes are contaminated while the satellite footprint approaches or leaves the coastline. Specular peaks are often induced in the trailing edges of contaminated waveforms, thus leading the error in the determination of the leading edge and associated track offset in the waveform retracking process. We propose an improved algorithm base on Tseng's modification method to decontaminated coastal (0-7 km from coastline) waveforms, thus improving both the utilization and precision of coastal sea surface height (SSH). Using the Envisat/Jason-2 SGDR data, the shortcoming of Tseng's method is pointed out and the novel algorithm is proposed by revising the strategy of selecting reference waveform and determining weight for removing outlier. The reference waveform of the decontaminated technology is closer to the real waveform of the offshore area, which avoids the over-modification problem of Tseng method. The sea-level measurements from tide gauge station and geoid height from EGM2008 model were used to validate the retracking strategy. Experimental results show that decontaminated waveform was more suitable than original and Tseng modified waveform and has uniform performance in both compare to the tide gauge and geoid. The retrieved altimetry data in the 0-1km and 1-7km coastal zone indicate that threshold retracker with decontaminated waveform have STD of 73.8cm and 33cm as compared with in situ gauge data,which correspond to 62.1% and 58% in precession compared to the unretracked altimetry measurements. The retracked SSHs are better in two coastal (0-1 km and 1-7km) zones, which have STD of 11.9cm and 22.7cm as compared with geoid height. Furthermore, the comparisons shows that the precision of decontaminated technology improve 0.3cm and 3.3cm than the best result of PISTACH product in coastal sea. This work is supported by the National Natural Science Foundation of China (Grant Nos

  5. Tide Gauge and Satellite Altimetry Integration for Storm Surge Prediction

    DEFF Research Database (Denmark)

    Andersen, Ole Baltazar; Cheng, Yongcun; Deng, X.

    2013-01-01

    of the Northeast Australia, we have investigated several large cyclones causing much destruction when they hit the coast. One of these being the Cyclone Larry, which hit the Queensland coast in March 2006 and caused both losses of lives as well as huge devastation. Here we demonstrate the importance of integrating...

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

    DEFF Research Database (Denmark)

    Khan, Shfaqat Abbas; Bevis, M. G.; Wahr, J. M.

    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......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...

  7. Tide Gauge and Satellite Altimetry Integration for Storm Surge Prediction

    DEFF Research Database (Denmark)

    Andersen, Ole Baltazar; Cheng, Yongcun; Deng, X.;

    2013-01-01

    of the Northeast Australia, we have investigated several large cyclones causing much destruction when they hit the coast. One of these being the Cyclone Larry, which hit the Queensland coast in March 2006 and caused both losses of lives as well as huge devastation. Here we demonstrate the importance of integrating...

  8. Advanced Multipath Mitigation Techniques for Satellite-Based Positioning Applications

    Directory of Open Access Journals (Sweden)

    Mohammad Zahidul H. Bhuiyan

    2010-01-01

    Full Text Available Multipath remains a dominant source of ranging errors in Global Navigation Satellite Systems (GNSS, such as the Global Positioning System (GPS or the future European satellite navigation system Galileo. Multipath is generally considered undesirable in the context of GNSS, since the reception of multipath can make significant distortion to the shape of the correlation function used for time delay estimation. However, some wireless communications techniques exploit multipath in order to provide signal diversity though in GNSS, the major challenge is to effectively mitigate the multipath, since we are interested only in the satellite-receiver transit time offset of the Line-Of-Sight (LOS signal for the receiver's position estimate. Therefore, the multipath problem has been approached from several directions in order to mitigate the impact of multipath on navigation receivers, including the development of novel signal processing techniques. In this paper, we propose a maximum likelihood-based technique, namely, the Reduced Search Space Maximum Likelihood (RSSML delay estimator, which is capable of mitigating the multipath effects reasonably well at the expense of increased complexity. The proposed RSSML attempts to compensate the multipath error contribution by performing a nonlinear curve fit on the input correlation function, which finds a perfect match from a set of ideal reference correlation functions with certain amplitude(s, phase(s, and delay(s of the multipath signal. It also incorporates a threshold-based peak detection method, which eventually reduces the code-delay search space significantly. However, the downfall of RSSML is the memory requirement which it uses to store the reference correlation functions. The multipath performance of other delay-tracking methods previously studied for Binary Phase Shift Keying-(BPSK- and Sine Binary Offset Carrier- (SinBOC- modulated signals is also analyzed in closed loop model with the new Composite

  9. Parameterization of oceanic whitecap fraction based on satellite observations

    Directory of Open Access Journals (Sweden)

    M. F. M. A. Albert

    2015-08-01

    Full Text Available In this study the utility of satellite-based whitecap fraction (W values for the prediction of sea spray aerosol (SSA emission rates is explored. More specifically, the study is aimed at improving the accuracy of the sea spray source function (SSSF derived by using the whitecap method through the reduction of the uncertainties in the parameterization of W by better accounting for its natural variability. The starting point is a dataset containing W data, together with matching environmental and statistical data, for 2006. Whitecap fraction W was estimated from observations of the ocean surface brightness temperature TB by satellite-borne radiometers at two frequencies (10 and 37 GHz. A global scale assessment of the data set to evaluate the wind speed dependence of W revealed a quadratic correlation between W and U10, as well as a relatively larger spread in the 37 GHz data set. The latter could be attributed to secondary factors affecting W in addition to U10. To better visualize these secondary factors, a regional scale assessment over different seasons was performed. This assessment indicates that the influence of secondary factors on W is for the largest part imbedded in the exponent of the wind speed dependence. Hence no further improvement can be expected by looking at effects of other factors on the variation in W explicitly. From the regional analysis, a new globally applicable quadratic W(U10 parameterization was derived. An intrinsic correlation between W and U10 that could have been introduced while estimating W from TB was determined, evaluated and presumed to lie within the error margins of the newly derived W(U10 parameterization. The satellite-based parameterization was compared to parameterizations from other studies and was applied in a SSSF to estimate the global SSA emission rate. The thus obtained SSA production for 2006 of 4.1 × 1012 kg is within previously reported estimates. While recent studies that account for

  10. Integrating Non-Tidal Sea Level data from altimetry and tide gauges for coastal sea level prediction

    DEFF Research Database (Denmark)

    Cheng, Yongcun; Andersen, Ole Baltazar; Knudsen, Per

    2012-01-01

    The main objective of this paper is to integrate Non-Tidal Sea Level (NSL) from the joint TOPEX, Jason-1 and Jason-2 satellite altimetry with tide gauge data at the west and north coast of the United Kingdom for coastal sea level prediction. The temporal correlation coefficient between altimetric...... frequency NSL variation (i.e., every 15min) during a storm surge event at an independent tide gauge station at the Northeast of the UK (Aberdeen)....

  11. Combining Envisat type and CryoSat-2 altimetry to inform hydrodynamic models

    Science.gov (United States)

    Schneider, Raphael; Nygaard Godiksen, Peter; Villadsen, Heidi; Madsen, Henrik; Bauer-Gottwein, Peter

    2015-04-01

    Hydrological models are developed and used for flood forecasting and water resources management. Such models rely on a variety of input and calibration data. In general, and especially in data scarce areas, remote sensing provides valuable data for the parameterization and updating of such models. Satellite radar altimeters provide water level measurements of inland water bodies. So far, many studies making use of satellite altimeters have been based on data from repeat-orbit missions such as Envisat, ERS or Jason or on synthetic wide-swath altimetry data as expected from the SWOT mission. This work represents one of the first hydrologic applications of altimetry data from a drifting orbit satellite mission, using data from CryoSat-2. We present an application where CryoSat-2 data is used to improve a hydrodynamic model of the Ganges and Brahmaputra river basins in South Asia set up in the DHI MIKE 11 software. The model's parameterization and forcing is mainly based on remote sensing data, for example the TRMM 3B42 precipitation product and the SRTM DEM for river and subcatchment delineation. CryoSat-2 water levels were extracted over a river mask derived from Landsat 7 and 8 imagery. After calibrating the hydrological-hydrodynamic model against observed discharge, simulated water levels were fitted to the CryoSat-2 data, with a focus on the Brahmaputra river in the Assam valley: The average simulated water level in the hydrodynamic model was fitted to the average water level along the river's course as observed by CryoSat-2 over the years 2011-2013 by adjusting the river bed elevation. In a second step, the cross section shapes were adjusted so that the simulated water level dynamics matched those obtained from Envisat virtual station time series. The discharge calibration resulted in Nash-Sutcliffe coefficients of 0.86 and 0.94 for the Ganges and Brahmaputra. Using the Landsat river mask, the CryoSat-2 water levels show consistency along the river and are in

  12. Internet-Protocol-Based Satellite Bus Architecture Designed

    Science.gov (United States)

    Slywczak, Richard A.

    2004-01-01

    NASA is designing future complex satellite missions ranging from single satellites and constellations to space networks and sensor webs. These missions require more interoperability, autonomy, and coordination than previous missions; in addition, a desire exists to have scientists retrieve data directly from the satellite rather than a central distribution source. To meet these goals, NASA has been studying the possibility of extending the Transmission Control Protocol/Internet Protocol (TCP/IP) suite for spacebased applications.

  13. Satellite-based Flood Modeling Using TRMM-based Rainfall Products

    Directory of Open Access Journals (Sweden)

    Greg Easson

    2007-12-01

    Full Text Available Increasingly available and a virtually uninterrupted supply of satellite-estimatedrainfall data is gradually becoming a cost-effective source of input for flood predictionunder a variety of circumstances. However, most real-time and quasi-global satelliterainfall products are currently available at spatial scales ranging from 0.25o to 0.50o andhence, are considered somewhat coarse for dynamic hydrologic modeling of basin-scaleflood events. This study assesses the question: what are the hydrologic implications ofuncertainty of satellite rainfall data at the coarse scale? We investigated this question onthe 970 km2 Upper Cumberland river basin of Kentucky. The satellite rainfall productassessed was NASA’s Tropical Rainfall Measuring Mission (TRMM Multi-satellitePrecipitation Analysis (TMPA product called 3B41RT that is available in pseudo real timewith a latency of 6-10 hours. We observed that bias adjustment of satellite rainfall data canimprove application in flood prediction to some extent with the trade-off of more falsealarms in peak flow. However, a more rational and regime-based adjustment procedureneeds to be identified before the use of satellite data can be institutionalized among floodmodelers.

  14. Coastal Sea-Level in Norway from Cryosat-2 Interferometric SAR Altimetry

    Science.gov (United States)

    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.

  15. Dsm Based Orientation of Large Stereo Satellite Image Blocks

    Science.gov (United States)

    d'Angelo, P.; Reinartz, P.

    2012-07-01

    High resolution stereo satellite imagery is well suited for the creation of digital surface models (DSM). A system for highly automated and operational DSM and orthoimage generation based on CARTOSAT-1 imagery is presented, with emphasis on fully automated georeferencing. The proposed system processes level-1 stereo scenes using the rational polynomial coefficients (RPC) universal sensor model. The RPC are derived from orbit and attitude information and have a much lower accuracy than the ground resolution of approximately 2.5 m. In order to use the images for orthorectification or DSM generation, an affine RPC correction is required. In this paper, GCP are automatically derived from lower resolution reference datasets (Landsat ETM+ Geocover and SRTM DSM). The traditional method of collecting the lateral position from a reference image and interpolating the corresponding height from the DEM ignores the higher lateral accuracy of the SRTM dataset. Our method avoids this drawback by using a RPC correction based on DSM alignment, resulting in improved geolocation of both DSM and ortho images. Scene based method and a bundle block adjustment based correction are developed and evaluated for a test site covering the nothern part of Italy, for which 405 Cartosat-1 Stereopairs are available. Both methods are tested against independent ground truth. Checks against this ground truth indicate a lateral error of 10 meters.

  16. On the exploitation of optical and thermal band for river discharge estimation: synergy with radar altimetry

    Science.gov (United States)

    Tarpanelli, Angelica; Filippucci, Paolo; Brocca, Luca

    2017-04-01

    River discharge is recognized as a fundamental physical variable and it is included among the Essential Climate Variables by GCOS (Global Climate Observing System). Notwithstanding river discharge is one of the most measured components of the hydrological cycle, its monitoring is still an open issue. Collection, archiving and distribution of river discharge data globally is limited, and the currently operating network is inadequate in many parts of the Earth and is still declining. Remote sensing, especially satellite sensors, have great potential in offering new ways to monitor river discharge. Remote sensing guarantees regular, uniform and global measurements for long period thanks to the large number of satellites launched during the last twenty years. Because of its nature, river discharge cannot be measured directly and both satellite and traditional monitoring are referred to measurements of other hydraulic variables, e.g. water level, flow velocity, water extent and slope. In this study, we illustrate the potential of different satellite sensors for river discharge estimation. The recent advances in radar altimetry technology offered important information for water levels monitoring of rivers even if the spatio-temporal sampling is still a limitation. The multi-mission approach, i.e. interpolating different altimetry tracks, has potential to cope with the spatial and temporal resolution, but so far few studies were dedicated to deal with this issue. Alternatively, optical sensors, thanks to their frequent revisit time and large spatial coverage, could give a better support for the evaluation of river discharge variations. In this study, we focus on the optical (Near InfraRed) and thermal bands of different satellite sensors (MODIS, MERIS, AATSR, Landsat, Sentinel-2) and particularly, on the derived products such as reflectance, emissivity and land surface temperature. The performances are compared with respect to the well-known altimetry (Envisat/Ra-2, Jason

  17. Three-Axis Satellite Attitude Control Based on Magnetic Torquing

    DEFF Research Database (Denmark)

    Wisniewski, Rafal

    1995-01-01

    Recently small satellite missions have gained considerable interest due to low-cost launch opportunities and technilogical improvement of micro-electronics.......Recently small satellite missions have gained considerable interest due to low-cost launch opportunities and technilogical improvement of micro-electronics....

  18. Three-Axis Satellite Attitude Control Based on Magnetic Torquing

    DEFF Research Database (Denmark)

    Wisniewski, Rafal

    1995-01-01

    Recently small satellite missions have gained considerable interest due to low-cost launch opportunities and technilogical improvement of micro-electronics.......Recently small satellite missions have gained considerable interest due to low-cost launch opportunities and technilogical improvement of micro-electronics....

  19. Fuel type characterization based on coarse resolution MODIS satellite data

    Directory of Open Access Journals (Sweden)

    Lanorte A

    2007-01-01

    Full Text Available Fuel types is one of the most important factors that should be taken into consideration for computing spatial fire hazard and risk and simulating fire growth and intensity across a landscape. In the present study, forest fuel mapping is considered from a remote sensing perspective. The purpose is to delineate forest types by exploring the use of coarse resolution satellite remote sensing MODIS imagery. In order to ascertain how well MODIS data can provide an exhaustive classification of fuel properties a sample area characterized by mixed vegetation covers and complex topography was analysed. The study area is located in the South of Italy. Fieldwork fuel type recognitions, performed before, after and during the acquisition of remote sensing MODIS data, were used as ground-truth dataset to assess the obtained results. The method comprised the following three steps: (I adaptation of Prometheus fuel types for obtaining a standardization system useful for remotely sensed classification of fuel types and properties in the considered Mediterranean ecosystems; (II model construction for the spectral characterization and mapping of fuel types based on two different approach, maximum likelihood (ML classification algorithm and spectral Mixture Analysis (MTMF; (III accuracy assessment for the performance evaluation based on the comparison of MODIS-based results with ground-truth. Results from our analyses showed that the use of remotely sensed MODIS data provided a valuable characterization and mapping of fuel types being that the achieved classification accuracy was higher than 73% for ML classifier and higher than 83% for MTMF.

  20. Combination of multi-mission altimetry data along the Mekong River with spatio-temporal kriging

    Science.gov (United States)

    Boergens, Eva; Buhl, Sven; Dettmering, Denise; Klüppelberg, Claudia; Seitz, Florian

    2016-12-01

    River water-level time series at fixed geographical locations, so-called virtual stations, have been computed from single altimeter crossings for many years. Their temporal resolution is limited by the repeat cycle of the individual altimetry missions. The combination of all altimetry measurements along a river enables computing a water-level time series with improved temporal and spatial resolutions. This study uses the geostatistical method of spatio-temporal ordinary kriging to link multi-mission altimetry data along the Mekong River. The required covariance models reflecting the water flow are estimated based on empirical covariance values between altimetry observations at various locations. In this study, two covariance models are developed and tested in the case of the Mekong River: a stationary and a non-stationary covariance model. The proposed approach predicts water-level time series at different locations along the Mekong River with a temporal resolution of 5 days. Validation is performed against in situ data from four gauging stations, yielding RMS differences between 0.82 and 1.29 m and squared correlation coefficients between 0.89 and 0.94. Both models produce comparable results when used for combining data from Envisat, Jason-1, and SARAL for the time period between 2002 and 2015. The quality of the predicted time series turns out to be robust against a possibly decreasing availability of altimetry mission data. This demonstrates that our method is able to close the data gap between the end of the Envisat and the launch of the SARAL mission with interpolated time series.

  1. Combination of multi-mission altimetry data along the Mekong River with spatio-temporal kriging

    Science.gov (United States)

    Boergens, Eva; Buhl, Sven; Dettmering, Denise; Klüppelberg, Claudia; Seitz, Florian

    2017-05-01

    River water-level time series at fixed geographical locations, so-called virtual stations, have been computed from single altimeter crossings for many years. Their temporal resolution is limited by the repeat cycle of the individual altimetry missions. The combination of all altimetry measurements along a river enables computing a water-level time series with improved temporal and spatial resolutions. This study uses the geostatistical method of spatio-temporal ordinary kriging to link multi-mission altimetry data along the Mekong River. The required covariance models reflecting the water flow are estimated based on empirical covariance values between altimetry observations at various locations. In this study, two covariance models are developed and tested in the case of the Mekong River: a stationary and a non-stationary covariance model. The proposed approach predicts water-level time series at different locations along the Mekong River with a temporal resolution of 5 days. Validation is performed against in situ data from four gauging stations, yielding RMS differences between 0.82 and 1.29 m and squared correlation coefficients between 0.89 and 0.94. Both models produce comparable results when used for combining data from Envisat, Jason-1, and SARAL for the time period between 2002 and 2015. The quality of the predicted time series turns out to be robust against a possibly decreasing availability of altimetry mission data. This demonstrates that our method is able to close the data gap between the end of the Envisat and the launch of the SARAL mission with interpolated time series.

  2. PARFAIT: GNSS-R coastal altimetry

    CERN Document Server

    Caparrini, M; Ruffini, G

    2003-01-01

    GNSS-R signals contain a coherent and an incoherent component. A new algorithm for coherent phase altimetry over rough ocean surfaces, called PARFAIT, has been developed and implemented in Starlab's STARLIGHT GNSS-R software package. In this paper we report our extraction and analysis of the coherent component of L1 GPS-R signals collected during the ESTEC Bridge 2 experimental campaign using this technique. The altimetric results have been compared with a GPS-buoy calibrated tide model with a resulting precision of the order 1 cm.

  3. A Hybrid Algorithm for Satellite Data Transmission Schedule Based on Genetic Algorithm

    Institute of Scientific and Technical Information of China (English)

    LI Yun-feng; WU Xiao-yue

    2008-01-01

    A hybrid scheduling algorithm based on genetic algorithm is proposed in this paper for reconnaissance satellite data transmission. At first, based on description of satellite data transmission request, satellite data transmission task modal and satellite data transmission scheduling problem model are established. Secondly, the conflicts in scheduling are discussed. According to the meaning of possible conflict, the method to divide possible conflict task set is given. Thirdly, a hybrid algorithm which consists of genetic algorithm and heuristic information is presented. The heuristic information comes from two concepts, conflict degree and conflict number. Finally, an example shows the algorithm's feasibility and performance better than other traditional algorithms.

  4. ICESat-2: Next-Generation Laser Altimetry from Space

    Science.gov (United States)

    Webb, C. E.; Neumann, T.; Markus, T.

    2014-12-01

    Despite technical challenges encountered after its launch in 2003, NASA's original Ice, Cloud and land Elevation Satellite (ICESat) produced a rich topographic record, and provided our first large-scale assessments of elevation change and mass balance of the polar ice sheets. The lessons learned from this mission, combined with the availability of new technologies, have guided the design and development of the follow-on ICESat-2 mission and its Advanced Topographic Laser Altimeter System (ATLAS). Scheduled for launch in 2017, ICESat-2 will operate year-round, at a lower orbit inclination, extending coverage to +/- 88 degrees latitude, and at a lower altitude, yielding 1,387 revolutions in a 91-day repeat ground track. The ATLAS instrument uses photon-counting detectors to record surface returns from six laser beams, grouped into three pairs, yielding denser spatial coverage and enabling direct measurements of local slopes. As a result, ICESat-2 will provide a more detailed view of the Earth's surface. Here, we discuss the mission design and concepts of operations. We focus primarily on the strategies being developed for collecting altimetry data over different surfaces, including the ice sheets, sea ice, oceans, vegetation and other scientific targets of opportunity.

  5. Application of altimetry data assimilation on mesoscale eddies simulation

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Mesoscale eddy plays an important role in the ocean circulation. In order to improve the simulation accuracy of the mesoscale eddies, a three-dimensional variation (3DVAR) data assimilation system called Ocean Variational Analysis System (OVALS) is coupled with a POM model to simulate the mesoscale eddies in the Northwest Pacific Ocean. In this system, the sea surface height anomaly (SSHA) data by satellite altimeters are assimilated and translated into pseudo temperature and salinity (T-S) profile data. Then, these profile data are taken as observation data to be assimilated again and produce the three-dimensional analysis T-S field. According to the characteristics of mesoscale eddy, the most appropriate assimilation parameters are set up and testified in this system. A ten years mesoscale eddies simulation and comparison experiment is made, which includes two schemes: assimilation and non-assimilation. The results of comparison between two schemes and the observation show that the simulation accuracy of the assimilation scheme is much better than that of non-assimilation, which verified that the altimetry data assimilation method can improve the simulation accuracy of the mesoscale dramatically and indicates that it is possible to use this system on the forecast of mesoscale eddies in the future.

  6. New dynamic routing algorithm based on MANET in LEO/MEO satellite network

    Institute of Scientific and Technical Information of China (English)

    LI Zhe; LI Dong-ni; WANG Guang-xing

    2006-01-01

    The features of low earth orbit/medium earth orbit (LEO/MEO) satellite networks routing algorithm based on inter-satellite link are analyzed and the similarities between satellite networks and mobile Ad Hoc network (MANET) are pointed out.The similar parts in MANET routing protocol are used in the satellite network for reference.A new dynamic routing algorithm based on MANET in LEO/MEO satellite networks,which fits for the LEO/MEO satellite communication system,is proposed.At the same time,the model of the algorithm is simulated and features are analyzed.It is shown that the algorithm has strong adaptability.It can give the network high autonomy,perfect function,low system overhead and great compatibility.

  7. A virtual maintenance-based approach for satellite assembling and troubleshooting assessment

    Science.gov (United States)

    Geng, Jie; Li, Ying; Wang, Ranran; Wang, Zili; Lv, Chuan; Zhou, Dong

    2017-09-01

    In this study, a Virtual Maintenance (VM)-based approach for satellite troubleshooting assessment is proposed. By focusing on various elements in satellite assemble troubleshooting, such as accessibility, ergonomics, wiring, and extent of damage, a systematic, quantitative, and objective assessment model is established to decrease subjectivity in satellite assembling and troubleshooting assessment. Afterwards, based on the established assessment model and satellite virtual prototype, an application process of this model suitable for a virtual environment is presented. Finally, according to the application process, all the elements in satellite troubleshooting are analyzed and assessed. The corresponding improvements, which realize the transformation from a conventional way to a virtual simulation and assessment, are suggested, and the flaws in assembling and troubleshooting are revealed. Assembling or troubleshooting schemes can be improved in the early stage of satellite design with the help of a virtual prototype. Repetition in the practical operation is beneficial to companies as risk and cost are effectively reduced.

  8. GNSS-derived Path Delay Plus (GPD+): a methodology for the computation of improved wet tropospheric corrections for coastal altimetry

    Science.gov (United States)

    Fernandes, Joana; Lázaro, Clara; Ambrózio, Américo; Restano, Marco; Benveniste, Jérôme

    2017-04-01

    Satellite altimetry missions provide the sea surface height above a reference ellipsoid with centimetric accuracy as long as all terms involved in the altimeter measurement system (satellite orbit, altimeter range between the satellite and the sea surface, and instrumental, range and geophysical corrections) are known with the same accuracy. The wet tropospheric correction (WTC), the range correction that accounts for the delay induced by the presence of water vapour and liquid water in the troposphere, has an absolute value less than 50 cm but large space-time variability, being therefore difficult to model. Despite the progress observed in WTC modelling from numerical weather models (NWM), the accuracy of present NWM-derived WTC is still deficient for most altimetry applications such as e.g. sea level variation. Actually, accurate WTC at time and location of the altimetric measurements can only be achieved through observations of the atmospheric water vapour content, acquired by on-board microwave radiometers (MWR). In open ocean, MWR-derived WTC are centimeter-level accurate; in coastal regions, WTC degrades due to several reasons, among which is the contamination, from the surrounding land surfaces, of the signal measured by the MWR. Also the presence of ice and rain contaminates the MWR observations. Therefore, MWR-derived WTC are generally incorrect or invalid in coastal, rainy and high-latitude regions, and altimeter measurements cannot benefit from MWR corrections. The GNSS-derived Path Delay (GPD) algorithm was developed by the University of Porto (UPorto) aiming at computing the WTC for coastal regions where MWR observations are invalid, envisaging the recovery of the altimeter data in these regions. The GPD-derived WTC is based on a space-time optimal interpolation that combines path delays measured by MWR and computed at more than 800 coastal/island GNSS stations. Its most recent version, the GPD Plus (GPD+) estimates the WTC globally relying also on

  9. Object Based and Pixel Based Classification Using Rapideye Satellite Imager of ETI-OSA, Lagos, Nigeria

    OpenAIRE

    Esther Oluwafunmilayo Makinde; Ayobami Taofeek Salami; James Bolarinwa Olaleye; Oluwapelumi Comfort Okewusi

    2016-01-01

    Several studies have been carried out to find an appropriate method to classify the remote sensing data. Traditional classification approaches are all pixel-based, and do not utilize the spatial information within an object which is an important source of information to image classification. Thus, this study compared the pixel based and object based classification algorithms using RapidEye satellite image of Eti-Osa LGA, Lagos. In the object-oriented approach, the image was segmented to homog...

  10. Coastal applications from nadir altimetry: Example of the X-TRACK regional products

    Science.gov (United States)

    Birol, F.; Fuller, N.; Lyard, F.; Cancet, M.; Niño, F.; Delebecque, C.; Fleury, S.; Toublanc, F.; Melet, A.; Saraceno, M.; Léger, F.

    2017-02-01

    In the coastal ocean zones, satellite altimetry data processing and interpretation poses specific difficulties, due to the interaction of the radar signal with land topography, inaccuracies in some of the geophysical corrections and to the fast changes in the sea level. In order to optimize the completeness and the accuracy of the sea surface height information derived from satellite altimetry in coastal ocean areas, a dedicated post-processing software, called X-TRACK, has been developed by the Center of Topography of the Ocean and Hydrosphere in Toulouse. It is tailored for extending the use of altimetry data to coastal ocean applications and provides freely available along-track Sea Level Anomaly time series that cover today all the coastal oceans. Here, we present the improvements made in version 2016 of X-TRACK and show the gain in near-coastal data accuracy using in situ tide gauge observations. The correlations between altimeter and tide gauge sea level anomalies are higher (by 15% in average) compared with the previous version of X-TRACK. Three examples of applications are shown. The recent evolutions done in the X-TRACK processing result in an improved observation of the seasonal variations of the boundary circulation in the Bay of Biscay. Along Western Africa, sea-level variations derived from X-TRACK data are observed closer to land (5 km) compared to AVISO (10 km), and the sea-level statistics are more robust due to the larger and more stable data availability. Along-track empirical tidal constants derived from X-TRACK Sea Level Anomaly time series are also used to validate tidal models. By improving the altimetric data accuracy in coastal areas, we extend the field of marine applications.

  11. A Collective Detection Based GPS Receiver for Small Satellites Project

    Data.gov (United States)

    National Aeronautics and Space Administration — To solve the problem of autonomous navigation on small satellite platforms less than 20 kg, we propose to develop an onboard orbit determination receiver for small...

  12. Satellite Image Time Series Decomposition Based on EEMD

    Directory of Open Access Journals (Sweden)

    Yun-long Kong

    2015-11-01

    Full Text Available Satellite Image Time Series (SITS have recently been of great interest due to the emerging remote sensing capabilities for Earth observation. Trend and seasonal components are two crucial elements of SITS. In this paper, a novel framework of SITS decomposition based on Ensemble Empirical Mode Decomposition (EEMD is proposed. EEMD is achieved by sifting an ensemble of adaptive orthogonal components called Intrinsic Mode Functions (IMFs. EEMD is noise-assisted and overcomes the drawback of mode mixing in conventional Empirical Mode Decomposition (EMD. Inspired by these advantages, the aim of this work is to employ EEMD to decompose SITS into IMFs and to choose relevant IMFs for the separation of seasonal and trend components. In a series of simulations, IMFs extracted by EEMD achieved a clear representation with physical meaning. The experimental results of 16-day compositions of Moderate Resolution Imaging Spectroradiometer (MODIS, Normalized Difference Vegetation Index (NDVI, and Global Environment Monitoring Index (GEMI time series with disturbance illustrated the effectiveness and stability of the proposed approach to monitoring tasks, such as applications for the detection of abrupt changes.

  13. Satellite-Based Study of Glaciers Retreat in Northern Pakistan

    Science.gov (United States)

    Munir, Siraj

    Glaciers serve as a natural regulator of regional water supplies. About 16933 Km 2 area of glaciers is covered by Pakistan. These glaciers are enormous reservoirs of fresh water and their meltwater is an important resource which feed rivers in Pakistan. Glacier depletion, especially recent melting can affect agriculture, drinking water supplies, hydro-electric power, and ecological habitats. This can also have a more immediate impact on Pakistan's economy that depends mainly on water from glacier melt. Melting of seasonal snowfall and permanent glaciers has resulted not only in reduction of water resources but also caused flash floods in many areas of Pakistan. With the advent of satellite technology, using optical and SAR data the study of glaciers, has become possible. Using temporal data, based on calculation of snow index, band ratios and texture reflectance it has been revealed that the rate of glacier melting has increased as a consequent of global warming. Comparison of Landsat images of Batura glacier for October 1992 and October 2000 has revealed that there is a decrease of about 17 sq km in Batura glaciers. Although accurate changes in glacier extent cannot be assessed without baseline information, these efforts have been made to analyze future changes in glaciated area.

  14. Population-based geographic access to parent and satellite National Cancer Institute Cancer Center Facilities.

    Science.gov (United States)

    Onega, Tracy; Alford-Teaster, Jennifer; Wang, Fahui

    2017-09-01

    Satellite facilities of National Cancer Institute (NCI) cancer centers have expanded their regional footprints. This study characterized geographic access to parent and satellite NCI cancer center facilities nationally overall and by sociodemographics. Parent and satellite NCI cancer center facilities, which were geocoded in ArcGIS, were ascertained. Travel times from every census tract in the continental United States and Hawaii to the nearest parent and satellite facilities were calculated. Census-based population attributes were used to characterize measures of geographic access for sociodemographic groups. From the 62 NCI cancer centers providing clinical care in 2014, 76 unique parent locations and 211 satellite locations were mapped. The overall proportion of the population within 60 minutes of a facility was 22% for parent facilities and 32.7% for satellite facilities. When satellites were included for potential access, the proportion of some racial groups for which a satellite was the closest NCI cancer center facility increased notably (Native Americans, 22.6% with parent facilities and 39.7% with satellite facilities; whites, 34.8% with parent facilities and 50.3% with satellite facilities; and Asians, 40.0% with parent facilities and 54.0% with satellite facilities), with less marked increases for Hispanic and black populations. Rural populations of all categories had dramatically low proportions living within 60 minutes of an NCI cancer center facility of any type (1.0%-6.6%). Approximately 14% of the population (n = 43,033,310) lived more than 180 minutes from a parent or satellite facility, and most of these individuals were Native Americans and/or rural residents (37% of Native Americans and 41.7% of isolated rural residents). Racial/ethnic and rural populations showed markedly improved geographic access to NCI cancer center care when satellite facilities were included. Cancer 2017;123:3305-11. © 2017 American Cancer Society. © 2017 American

  15. Preliminary Analysis of a Novel SAR Based Emergency System for Earth Orbit Satellites using Galileo

    NARCIS (Netherlands)

    Gill, E.K.A.; Helderweirt, A.

    2010-01-01

    This paper presents a preliminary analysis of a novel Search and Rescue (SAR) based emergency system for Low Earth Orbit (LEO) satellites using the Galileo Global Navigation Satellite System (GNSS). It starts with a description of the space user SAR system including a concept description, mission ar

  16. Operational Testing of Satellite based Hydrological Model (SHM)

    Science.gov (United States)

    Gaur, Srishti; Paul, Pranesh Kumar; Singh, Rajendra; Mishra, Ashok; Gupta, Praveen Kumar; Singh, Raghavendra P.

    2017-04-01

    Incorporation of the concept of transposability in model testing is one of the prominent ways to check the credibility of a hydrological model. Successful testing ensures ability of hydrological models to deal with changing conditions, along with its extrapolation capacity. For a newly developed model, a number of contradictions arises regarding its applicability, therefore testing of credibility of model is essential to proficiently assess its strength and limitations. This concept emphasizes to perform 'Hierarchical Operational Testing' of Satellite based Hydrological Model (SHM), a newly developed surface water-groundwater coupled model, under PRACRITI-2 program initiated by Space Application Centre (SAC), Ahmedabad. SHM aims at sustainable water resources management using remote sensing data from Indian satellites. It consists of grid cells of 5km x 5km resolution and comprises of five modules namely: Surface Water (SW), Forest (F), Snow (S), Groundwater (GW) and Routing (ROU). SW module (functions in the grid cells with land cover other than forest and snow) deals with estimation of surface runoff, soil moisture and evapotranspiration by using NRCS-CN method, water balance and Hragreaves method, respectively. The hydrology of F module is dependent entirely on sub-surface processes and water balance is calculated based on it. GW module generates baseflow (depending on water table variation with the level of water in streams) using Boussinesq equation. ROU module is grounded on a cell-to-cell routing technique based on the principle of Time Variant Spatially Distributed Direct Runoff Hydrograph (SDDH) to route the generated runoff and baseflow by different modules up to the outlet. For this study Subarnarekha river basin, flood prone zone of eastern India, has been chosen for hierarchical operational testing scheme which includes tests under stationary as well as transitory conditions. For this the basin has been divided into three sub-basins using three flow

  17. Improved threshold retracker for satellite altimeter waveform retracking over coastal sea

    Institute of Scientific and Technical Information of China (English)

    GUO Jinyun; HWANG Cheiway; CHANG Xiaotao; LIU Yuting

    2006-01-01

    Data quality is a key factor for the application of satellite altimetry to geodesy and oceanography. Accuracy of altimetry is limited in the coastal area because the altimeter waveforms are seriously contaminated by topography and environmental pollution. So waveform retracking is needed to compute the range correction of geophysical data records (GDRs) for better accuracy. In this paper, a new waveform retracker named the improved threshold retracker (ITR) is put forward. The retracker first builds sub-waveforms based on leading edges detected in a waveform, then determines the middle point of each leading edge to compute the retracking range correction,finally calculates the referenced sea surface heights according to the geoid undulation from a local geopotential model and tide heights from an ocean tide model, and compares it with all retracking ranges to determine the best one. As a test, altimeter waveforms of Geosat/GM are retracked around the Taiwan coastal area. The result shows that accuracy of ITR method is two times better than that of theβ-5-parameter function-fitting method and threshold method, and three times better than that of GDRs. ITR can efficiently improve the altimetry accuracy of the coastal sea area.

  18. Groundwater Modelling For Recharge Estimation Using Satellite Based Evapotranspiration

    Science.gov (United States)

    Soheili, Mahmoud; (Tom) Rientjes, T. H. M.; (Christiaan) van der Tol, C.

    2017-04-01

    Groundwater movement is influenced by several factors and processes in the hydrological cycle, from which, recharge is of high relevance. Since the amount of aquifer extractable water directly relates to the recharge amount, estimation of recharge is a perquisite of groundwater resources management. Recharge is highly affected by water loss mechanisms the major of which is actual evapotranspiration (ETa). It is, therefore, essential to have detailed assessment of ETa impact on groundwater recharge. The objective of this study was to evaluate how recharge was affected when satellite-based evapotranspiration was used instead of in-situ based ETa in the Salland area, the Netherlands. The Methodology for Interactive Planning for Water Management (MIPWA) model setup which includes a groundwater model for the northern part of the Netherlands was used for recharge estimation. The Surface Energy Balance Algorithm for Land (SEBAL) based actual evapotranspiration maps from Waterschap Groot Salland were also used. Comparison of SEBAL based ETa estimates with in-situ abased estimates in the Netherlands showed that these SEBAL estimates were not reliable. As such results could not serve for calibrating root zone parameters in the CAPSIM model. The annual cumulative ETa map produced by the model showed that the maximum amount of evapotranspiration occurs in mixed forest areas in the northeast and a portion of central parts. Estimates ranged from 579 mm to a minimum of 0 mm in the highest elevated areas with woody vegetation in the southeast of the region. Variations in mean seasonal hydraulic head and groundwater level for each layer showed that the hydraulic gradient follows elevation in the Salland area from southeast (maximum) to northwest (minimum) of the region which depicts the groundwater flow direction. The mean seasonal water balance in CAPSIM part was evaluated to represent recharge estimation in the first layer. The highest recharge estimated flux was for autumn

  19. Global Crop Monitoring: A Satellite-Based Hierarchical Approach

    Directory of Open Access Journals (Sweden)

    Bingfang Wu

    2015-04-01

    Full Text Available Taking advantage of multiple new remote sensing data sources, especially from Chinese satellites, the CropWatch system has expanded the scope of its international analyses through the development of new indicators and an upgraded operational methodology. The approach adopts a hierarchical system covering four spatial levels of detail: global, regional, national (thirty-one key countries including China and “sub-countries” (for the nine largest countries. The thirty-one countries encompass more that 80% of both production and exports of maize, rice, soybean and wheat. The methodology resorts to climatic and remote sensing indicators at different scales. The global patterns of crop environmental growing conditions are first analyzed with indicators for rainfall, temperature, photosynthetically active radiation (PAR as well as potential biomass. At the regional scale, the indicators pay more attention to crops and include Vegetation Health Index (VHI, Vegetation Condition Index (VCI, Cropped Arable Land Fraction (CALF as well as Cropping Intensity (CI. Together, they characterize crop situation, farming intensity and stress. CropWatch carries out detailed crop condition analyses at the national scale with a comprehensive array of variables and indicators. The Normalized Difference Vegetation Index (NDVI, cropped areas and crop conditions are integrated to derive food production estimates. For the nine largest countries, CropWatch zooms into the sub-national units to acquire detailed information on crop condition and production by including new indicators (e.g., Crop type proportion. Based on trend analysis, CropWatch also issues crop production supply outlooks, covering both long-term variations and short-term dynamic changes in key food exporters and importers. The hierarchical approach adopted by CropWatch is the basis of the analyses of climatic and crop conditions assessments published in the quarterly “CropWatch bulletin” which

  20. Introducing multisensor satellite radiance-based evaluation for regional Earth System modeling

    Science.gov (United States)

    Matsui, T.; Santanello, J.; Shi, J. J.; Tao, W.-K.; Wu, D.; Peters-Lidard, C.; Kemp, E.; Chin, M.; Starr, D.; Sekiguchi, M.; Aires, F.

    2014-07-01

    Earth System modeling has become more complex, and its evaluation using satellite data has also become more difficult due to model and data diversity. Therefore, the fundamental methodology of using satellite direct measurements with instrumental simulators should be addressed especially for modeling community members lacking a solid background of radiative transfer and scattering theory. This manuscript introduces principles of multisatellite, multisensor radiance-based evaluation methods for a fully coupled regional Earth System model: NASA-Unified Weather Research and Forecasting (NU-WRF) model. We use a NU-WRF case study simulation over West Africa as an example of evaluating aerosol-cloud-precipitation-land processes with various satellite observations. NU-WRF-simulated geophysical parameters are converted to the satellite-observable raw radiance and backscatter under nearly consistent physics assumptions via the multisensor satellite simulator, the Goddard Satellite Data Simulator Unit. We present varied examples of simple yet robust methods that characterize forecast errors and model physics biases through the spatial and statistical interpretation of various satellite raw signals: infrared brightness temperature (Tb) for surface skin temperature and cloud top temperature, microwave Tb for precipitation ice and surface flooding, and radar and lidar backscatter for aerosol-cloud profiling simultaneously. Because raw satellite signals integrate many sources of geophysical information, we demonstrate user-defined thresholds and a simple statistical process to facilitate evaluations, including the infrared-microwave-based cloud types and lidar/radar-based profile classifications.

  1. Introducing Multisensor Satellite Radiance-Based Evaluation for Regional Earth System Modeling

    Science.gov (United States)

    Matsui, T.; Santanello, J.; Shi, J. J.; Tao, W.-K.; Wu, D.; Peters-Lidard, C.; Kemp, E.; Chin, M.; Starr, D.; Sekiguchi, M.; hide

    2014-01-01

    Earth System modeling has become more complex, and its evaluation using satellite data has also become more difficult due to model and data diversity. Therefore, the fundamental methodology of using satellite direct measurements with instrumental simulators should be addressed especially for modeling community members lacking a solid background of radiative transfer and scattering theory. This manuscript introduces principles of multisatellite, multisensor radiance-based evaluation methods for a fully coupled regional Earth System model: NASA-Unified Weather Research and Forecasting (NU-WRF) model. We use a NU-WRF case study simulation over West Africa as an example of evaluating aerosol-cloud-precipitation-land processes with various satellite observations. NU-WRF-simulated geophysical parameters are converted to the satellite-observable raw radiance and backscatter under nearly consistent physics assumptions via the multisensor satellite simulator, the Goddard Satellite Data Simulator Unit. We present varied examples of simple yet robust methods that characterize forecast errors and model physics biases through the spatial and statistical interpretation of various satellite raw signals: infrared brightness temperature (Tb) for surface skin temperature and cloud top temperature, microwave Tb for precipitation ice and surface flooding, and radar and lidar backscatter for aerosol-cloud profiling simultaneously. Because raw satellite signals integrate many sources of geophysical information, we demonstrate user-defined thresholds and a simple statistical process to facilitate evaluations, including the infrared-microwave-based cloud types and lidar/radar-based profile classifications.

  2. Helmand river hydrologic studies using ALOS PALSAR InSAR and ENVISAT altimetry

    Science.gov (United States)

    Lu, Zhiming; Kim, J.-W.; Lee, H.; Shum, C.K.; Duan, J.; Ibaraki, M.; Akyilmaz, O.; Read, C.-H.

    2009-01-01

    The Helmand River wetland represents the only fresh-water resource in southern Afghanistan and one of the least mapped water basins in the world. The relatively narrow wetland consists of mostly marshes surrounded by dry lands. In this study, we demonstrate the use of the Advanced Land Observing Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR) Interferometric SAR (InSAR) to detect the changes of the Helmand River wetland water level. InSAR images are combined with the geocentric water level measurements from the retracked high-rate (18-Hz) Environmental Satellite (Envisat) radar altimetry to construct absolute water level changes over the marshes. It is demonstrated that the integration of the altimeter and InSAR can provide spatio-temporal measurements of water level variation over the Helmand River marshes where in situ measurements are absent. ?? Taylor & Francis Group, LLC.

  3. Satellite link augmentation of ground based packet switched data networks

    Science.gov (United States)

    Farrell, J. B.; McLane, P. J.; Campbell, L. L.

    Use of satellite link augmentation to improve the performance of a packet switched data network is considered. Particular attention is paid to the analysis of two queues in series from the standpoint of time delay. A finite state machine model is used to aid the analysis. The results from the analysis are then used in a flow deviation routing algorithm. This algorithm is applied to study the performance improvement when satellite links are used to augment the Canadian DATAPAC network. The results are backed up by extensive simulations on a digital computer.

  4. Real-time remote sensing driven river basin modeling using radar altimetry

    Directory of Open Access Journals (Sweden)

    S. J. Pereira-Cardenal

    2011-01-01

    Full Text Available Many river basins have a weak in-situ hydrometeorological monitoring infrastructure. However, water resources practitioners depend on reliable hydrological models for management purposes. Remote sensing (RS data have been recognized as an alternative to in-situ hydrometeorological data in remote and poorly monitored areas and are increasingly used to force, calibrate, and update hydrological models.

    In this study, we evaluate the potential of informing a river basin model with real-time radar altimetry measurements over reservoirs. We present a lumped, conceptual, river basin water balance modeling approach based entirely on RS and reanalysis data: precipitation was obtained from the Tropical Rainfall Measuring Mission (TRMM Multisatellite Precipitation Analysis (TMPA, temperature from the European Centre for Medium-Range Weather Forecast's (ECMWF Operational Surface Analysis dataset and reference evapotranspiration was derived from temperature data. The Ensemble Kalman Filter was used to assimilate radar altimetry (ERS2 and Envisat measurements of reservoir water levels. The modeling approach was applied to the Syr Darya River Basin, a snowmelt-dominated basin with large topographical variability, several large reservoirs and scarce hydrometeorological data that is located in Central Asia and shared between 4 countries with conflicting water management interests.

    The modeling approach was tested over a historical period for which in-situ reservoir water levels were available. Assimilation of radar altimetry data significantly improved the performance of the hydrological model. Without assimilation of radar altimetry data, model performance was limited, probably because of the size and complexity of the model domain, simplifications inherent in model design, and the uncertainty of RS and reanalysis data. Altimetry data assimilation reduced the mean absolute error of the simulated reservoir water levels from 4.7 to 1.9 m, and

  5. Real-time remote sensing driven river basin modelling using radar altimetry

    Directory of Open Access Journals (Sweden)

    S. J. Pereira-Cardenal

    2010-10-01

    Full Text Available Many river basins have a weak in-situ hydrometeorological monitoring infrastructure. However, water resources practitioners depend on reliable hydrological models for management purposes. Remote sensing (RS data have been recognized as an alternative to in-situ hydrometeorological data in remote and poorly monitored areas and are increasingly used to force, calibrate, and update hydrological models.

    In this study, we evaluate the potential of informing a river basin model with real-time radar altimetry measurements over reservoirs. We present a lumped, conceptual, river basin water balance modelling approach based entirely on RS and reanalysis data: precipitation was obtained from the Tropical Rainfall Measuring Mission (TRMM Multisatellite Precipitation Analysis (TMPA, temperature from the European Centre for Medium-Range Weather Forecast's (ECMWF Operational Surface Analysis dataset and reference evapotranspiration was derived from temperature data. The Ensemble Kalman Filter was used to assimilate radar altimetry (ERS2 and Envisat measurements of reservoir water levels. The modelling approach was applied to the Syr Darya River Basin, a snowmelt-dominated basin with large topographical variability, several large reservoirs and scarce hydrometeorological data that is shared between 4 countries with conflicting water management interests.

    The modelling approach was tested over a historical period for which in-situ reservoir water levels were available. Assimilation of radar altimetry data significantly improved the performance of the hydrological model. Without assimilation of radar altimetry data, model performance was limited, probably because of the size and complexity of the model domain, simplifications inherent in model design, and the uncertainty of RS and reanalysis data. Altimetry data assimilation reduced the mean error of the simulated reservoir water levels from 4.7 to 1.9 m, and overall model RMSE from 10.3 m to 6

  6. Evaluation of satellite-based precipitation estimates in winter season using an object-based approach

    Science.gov (United States)

    Li, J.; Hsu, K.; AghaKouchak, A.; Sorooshian, S.

    2012-12-01

    Verification has become an integral component of satellite precipitation algorithms and products. A number of object-based verification methods have been proposed to provide diagnostic information regarding the precipitation products' ability to capture the spatial pattern, intensity, and placement of precipitation. However, most object-based methods are not capable of investigating precipitation objects at the storm-scale. In this study, an image processing approach known as watershed segmentation was adopted to detect the storm-scale rainfall objects. Then, a fuzzy logic-based technique was utilized to diagnose and analyze storm-scale object attributes, including centroid distance, area ratio, intersection area ratio and orientation angle difference. Three verification metrics (i.e., false alarm ratio, missing ratio and overall membership score) were generated for validation and verification. Three satellite-based precipitation products, including PERSIANN, CMORPH, 3B42RT, were evaluated against NOAA stage IV MPE multi-sensor composite rain analysis at 0.25° by 0.25° on a daily scale in the winter season of 2010 over the contiguous United States. Winter season is dominated by frontal systems which usually have larger area coverage. All three products and the stage IV observation tend to find large size storm objects. With respect to the evaluation attributes, PERSIANN tends to obtain larger area ratio and consequently has larger centroid distance to the stage IV observations, while 3B42RT are found to be closer to the stage IV for the object size. All evaluation products give small orientation angle differences but vary significantly for the missing ratio and false alarm ratio. This implies that satellite estimates can fail to detect storms in winter. The overall membership scores are close for all three different products which indicate that all three satellite-based precipitation products perform well for capturing the spatial and geometric characteristics of

  7. Airborne gravimetry, altimetry, and GPS navigation errors

    Science.gov (United States)

    Colombo, Oscar L.

    1992-01-01

    Proper interpretation of airborne gravimetry and altimetry requires good knowledge of aircraft trajectory. Recent advances in precise navigation with differential GPS have made it possible to measure gravity from the air with accuracies of a few milligals, and to obtain altimeter profiles of terrain or sea surface correct to one decimeter. These developments are opening otherwise inaccessible regions to detailed geophysical mapping. Navigation with GPS presents some problems that grow worse with increasing distance from a fixed receiver: the effect of errors in tropospheric refraction correction, GPS ephemerides, and the coordinates of the fixed receivers. Ionospheric refraction and orbit error complicate ambiguity resolution. Optimal navigation should treat all error sources as unknowns, together with the instantaneous vehicle position. To do so, fast and reliable numerical techniques are needed: efficient and stable Kalman filter-smoother algorithms, together with data compression and, sometimes, the use of simplified dynamics.

  8. Performance tests of a satellite-based asymmetric communication network for the 'hyper hospital'.

    Science.gov (United States)

    Yamaguchi, T

    1997-01-01

    The Hyper Hospital is a prototype networked telemedicine system which uses virtual reality. We measured the performance of a novel multimedia network based on satellite communications. The network was a hybrid system consisting of a satellite channel in one direction and a terrestrial channel in the other. Each user was equipped with a standard satellite communication receiver and a telephone connection. Requests from the users were sent by modern and telephone line and responses were received by satellite. The user requests were initiated by clicking buttons on a World Wide Web browser screen. The transmission rates of satellite and normal telephone-line communications were compared for standardized text data. Satellite communication was three to five times faster. The transmission rate was also measured for standardized graphical data (GIF format). With a file size of about 400 kByte, satellite-mediated communication was 10 times faster than telephone lines. The effect of simultaneous access on performance was also explored. For simultaneous access of nine users to a single graphics file, 78% of the transmission speed was obtained in comparison with that of a single user. The satellite-based system showed excellent high-speed communication performance, particularly for multimedia data.

  9. Recent Developments for Satellite-Based Fire Monitoring in Canada

    Science.gov (United States)

    Abuelgasim, A.; Fraser, R.

    2002-05-01

    Wildfires in Canadian forests are a major source of natural disturbance. These fires have a tremendous impact on the local environment, humans and wildlife, ecosystem function, weather, and climate. Approximately 9000 fires burn 3 million hectares per year in Canada (based on a 10-year average). While only 2 to 3 percent of these wildfires grow larger than 200 hectares in size, they account for almost 97 percent of the annual area burned. This provides an excellent opportunity to monitor active fires using a combination of low and high resolution sensors for the purpose of determining fire location and burned areas. Given the size of Canada, the use of remote sensing data is a cost-effective way to achieve a synoptic overview of large forest fire activity in near-real time. In 1998 the Canada Centre for Remote Sensing (CCRS) and the Canadian Forest Service (CFS) developed a system for Fire Monitoring, Mapping and Modelling (Fire M3;http://fms.nofc.cfs.nrcan.gc.ca/FireM3/). Fire M3 automatically identifies, monitors, and maps large forest fires on a daily basis using NOAA AVHRR data. These data are processed daily using the GEOCOMP-N satellite image processing system. This presentation will describe recent developments to Fire M3, included the addition of a set of algorithms tailored for NOAA-16 (N-16) data. The two fire detection algorithms are developed for N-16 day and night-time daily data collection. The algorithms exploit both the multi-spectral and thermal information from the AVHRR daily images. The set of N-16 day and night algorithms was used to generate daily active fire maps across North America for the 2001 fire season. Such a combined approach for fire detection leads to an improved detection rate, although day-time detection based on the new 1.6 um channel was much less effective (note - given the low detection rate with day time imagery, I don't think we can make the statement about capturing the diurnal cycle). Selected validation sites in western

  10. GPS/Magnetometer Based Satellite Navigation and Attitude Determination

    Science.gov (United States)

    Deutschmann, Julie; Bar-Itzhack, Itzhack; Harman, Rick; Bauer, Frank H. (Technical Monitor)

    2001-01-01

    In recent years algorithms were developed for orbit, attitude and angular-rate determination of Low Earth Orbiting (LEO) satellites. Those algorithms rely on measurements of magnetometers, which are standard, relatively inexpensive, sensors that are normally installed on every LEO satellite. Although magnetometers alone are sufficient for obtaining the desired information, the convergence of the algorithms to the correct values of the satellite orbital parameters, position, attitude and angular velocity is very slow. The addition of sun sensors reduces the convergence time considerably. However, for many LEO satellites the sun data is not available during portions of the orbit when the spacecraft (SC) is in the earth shadow. It is here where the GPS space vehicles (SV) can provide valuable support. This is clearly demonstrated in the present paper. Although GPS measurements alone can be used to obtain SC position, velocity, attitude and angular-rate, the use of magnetometers improve the results due to the synergistic effect of sensor fusion. Moreover, it is possible to obtain these results with less than three SVs. In this paper we introduce an estimation algorithm, which is a combination of an Extended Kalman Filter (EKF) and a Pseudo Linear Kalman Filter (PSELIKA).

  11. A Constraint Based Approach for Building Operationally Responsive Satellites

    Science.gov (United States)

    2008-09-01

    discipline specific software codes into a common environment. LLB team also uses MATLAB R© to integrate CAD tools such as Catia , Pro/Engineer with FE...satellite configuration through a Catia CAD tool. The LLB approach is similar to the approach discussed in this research because it provides a method

  12. The ESRC: A Web-based Environmental Satellite Resource Center

    Science.gov (United States)

    Abshire, W. E.; Guarente, B.; Dills, P. N.

    2009-12-01

    The COMET® Program has developed an Environmental Satellite Resource Center (known as the ESRC), a searchable, database-driven Website that provides easy access to a wide range of useful information training materials on polar-orbiting and geostationary satellites. Primarily sponsored by the NPOESS Program and NOAA, the ESRC is a tool for users seeking reliable sources of satellite information, training, and data. First published in September 2008, and upgraded in April 2009, the site is freely available at: http://www.meted.ucar.edu/esrc. Additional contributions to the ESRC are sought and made on an ongoing basis. The ESRC was created in response to a broad community request first made in May 2006. The COMET Program was asked to develop the site to consolidate and simplify access to reliable, current, and diverse information, training materials, and data associated with environmental satellites. The ESRC currently includes over 400 significant resources from NRL, CIMSS, CIRA, NASA, VISIT, NESDIS, and EUMETSAT, and improves access to the numerous satellite resources available from COMET’s MetEd Website. The ESRC is designed as a community site where organizations and individuals around the globe can easily submit their resources via online forms by providing a small set of metadata. The ESRC supports languages other than English and multi-lingual character sets have been tested. COMET’s role is threefold: 1) maintain the site, 2) populate it with our own materials, including smaller, focused learning objects derived from our larger training modules, and 3) provide the necessary quality assurance and monitoring to ensure that all resources are appropriate and well described before being made available. Our presentation will demonstrate many of the features and functionality of searching for resources using the ESRC, and will outline the steps for users to make their own submissions. For the site to reach its full potential, submissions representing diverse

  13. Satellite Remote Sensing of Snow Depth on Antarctic Sea Ice: An Inter-Comparison of Two Empirical Approaches

    OpenAIRE

    Stefan Kern; Burcu Ozsoy-Çiçek

    2016-01-01

    Snow on Antarctic sea ice plays a key role for sea ice physical processes and complicates retrieval of sea ice thickness using altimetry. Current methods of snow depth retrieval are based on satellite microwave radiometry, which perform best for dry, homogeneous snow packs on level sea ice. We introduce an alternative approach based on in-situ measurements of total (sea ice plus snow) freeboard and snow depth, which we use to compute snow depth on sea ice from Ice, Cloud, and land Elevation S...

  14. Mass loss of Greenland's glaciers and ice caps 2003-2008 revealed from ICES at laser altimetry data

    DEFF Research Database (Denmark)

    Bolch, T.; Sørensen, Louise Sandberg; Simonsen, Sebastian Bjerregaard;

    2013-01-01

    The recently finalized inventory of Greenland's glaciers and ice caps (GIC) allows for the first time to determine the mass changes of the GIC separately from the ice sheet using space-borne laser altimetry data. Corrections for firn compaction and density that are based on climatic conditions...

  15. Spline model of the high latitude scintillation based on in situ satellite data

    Science.gov (United States)

    Priyadarshi, S.; Wernik, A. W.

    2013-12-01

    We present a spline model for the high latitude ionospheric scintillation using satellite in situ measurements made by the Dynamic Explorer 2 (DE 2) satellite. DE 2 satellite measurements give observations only along satellite orbit but our interpolation model fills the gaps between the satellite orbits. This analytical model is based on products of cubic B-splines and coefficients determined by least squares fit to the binned data and constrained to make the fit periodic in 24 hours of geomagnetic local time, periodic in 360 degrees of invariant longitude, in geomagnetic indices and solar radio flux. Discussion of our results clearly shows the seasonal and diurnal behavior of ionospheric parameters important in scintillation modeling for different geophysical and solar activity conditions. We also show that results obtained from our analytical model match observations obtained from in situ measurements. Shishir Priyadarshi Space Research Centre, Poland

  16. An Image-Based Sensor System for Autonomous Rendez-Vous with Uncooperative Satellites

    CERN Document Server

    Miravet, Carlos; Krouch, Eloise; del Cura, Juan Manuel

    2008-01-01

    In this paper are described the image processing algorithms developed by SENER, Ingenieria y Sistemas to cope with the problem of image-based, autonomous rendez-vous (RV) with an orbiting satellite. The methods developed have a direct application in the OLEV (Orbital Life Extension Extension Vehicle) mission. OLEV is a commercial mission under development by a consortium formed by Swedish Space Corporation, Kayser-Threde and SENER, aimed to extend the operational life of geostationary telecommunication satellites by supplying them control, navigation and guidance services. OLEV is planned to use a set of cameras to determine the angular position and distance to the client satellite during the complete phases of rendez-vous and docking, thus enabling the operation with satellites not equipped with any specific navigational aid to provide support during the approach. The ability to operate with un-equipped client satellites significantly expands the range of applicability of the system under development, compar...

  17. A Satellite Based Method for Wetland Inundation Mapping

    Science.gov (United States)

    Di Vittorio, C.; Georgakakos, A. P.

    2016-12-01

    Hydrologic models of wetlands enable hydrologists and water resources managers to appreciate the environmental and societal roles of wetlands and manage them in ways that preserve their integrity and sustain their valuable services. However, wetland model reliability and accuracy are often unsatisfactory due to the complexity of the underlying processes and the lack of adequate in-situ data. In this research, we demonstrate how MODIS satellite imagery can be used to characterize wetland flooding over time and to support the development of more reliable wetland models. We apply this method to the Sudd, a seasonal wetland in South Sudan that is part of the Nile River Basin. The database consists of 16 years of 8-day composite ground surface reflectance data with a 500 m spatial resolution downloaded from Earth Explorer. After masking poor quality pixels, monthly mean NDWI and NDVI values were extracted. Based on literature and personal accounts describing the Sudd as well as Google Earth imagery, a set of ground truth locations were identified for each land class and monthly distributions of the indices were derived. The indices were then combined in a unique way and statistics of the new distributions were used to classify land types present in the full area of interest. Subsequently, annual statistics were derived from the same indices and used to identify pixels that undergo flooding as well as the timing and duration of flooding for each year (2000-2015). An independent set of ground truth locations were selected for method validation. The combined indices demonstrate high land classification accuracy and outperform the individual indices as well as other existing land classification algorithms. The derived monthly inundation series agrees well with literature and anecdotal observations. This information is currently being used to develop wetland models as part of a comprehensive modeling system for the Nile River Basin. The new method is general and can be used

  18. Cost Analysis of Algorithm Based Billboard Manger Based Handover Method in LEO satellite Networks

    Directory of Open Access Journals (Sweden)

    Suman Kumar Sikdar

    2012-12-01

    Full Text Available Now-a-days LEO satellites have an important role in global communication system. They have some advantages like low power requirement and low end-to-end delay, more efficient frequency spectrum utilization between satellites and spot beams over GEO and MEO. So in future they can be used as a replacement of modern terrestrial wireless networks. But the handover occurrence is more due to the speed of the LEOs. Different protocol has been proposed for a successful handover among which BMBHO is more efficient. But it had a problem during the selection of the mobile node during handover. In our previous work we have proposed an algorithm so that the connection can be established easily with the appropriate satellite. In this paper we will evaluate the mobility management cost of Algorithm based Billboard Manager Based Handover method (BMBHO. A simulation result shows that the cost is lower than the cost of Mobile IP of SeaHO-LEO and PatHOLEO

  19. Simultaneous ground- and satellite-based observation of MF/HF auroral radio emissions

    Science.gov (United States)

    Sato, Yuka; Kumamoto, Atsushi; Katoh, Yuto; Shinbori, Atsuki; Kadokura, Akira; Ogawa, Yasunobu

    2016-05-01

    We report on the first simultaneous measurements of medium-high frequency (MF/HF) auroral radio emissions (above 1 MHz) by ground- and satellite-based instruments. Observational data were obtained by the ground-based passive receivers in Iceland and Svalbard, and by the Plasma Waves and Sounder experiment (PWS) mounted on the Akebono satellite. We observed two simultaneous appearance events, during which the frequencies of the auroral roar and MF bursts detected at ground level were different from those of the terrestrial hectometric radiation (THR) observed by the Akebono satellite passing over the ground-based stations. This frequency difference confirms that auroral roar and THR are generated at different altitudes across the F peak. We did not observe any simultaneous observations that indicated an identical generation region of auroral roar and THR. In most cases, MF/HF auroral radio emissions were observed only by the ground-based detector, or by the satellite-based detector, even when the satellite was passing directly over the ground-based stations. A higher detection rate was observed from space than from ground level. This can primarily be explained in terms of the idea that the Akebono satellite can detect THR emissions coming from a wider region, and because a considerable portion of auroral radio emissions generated in the bottomside F region are masked by ionospheric absorption and screening in the D/E regions associated with ionization which results from auroral electrons and solar UV radiation.

  20. Research on Coal Exploration Technology Based on Satellite Remote Sensing

    Directory of Open Access Journals (Sweden)

    Dong Xiao

    2016-01-01

    Full Text Available Coal is the main source of energy. In China and Vietnam, coal resources are very rich, but the exploration level is relatively low. This is mainly caused by the complicated geological structure, the low efficiency, the related damage, and other bad situations. To this end, we need to make use of some advanced technologies to guarantee the resource exploration is implemented smoothly and orderly. Numerous studies show that remote sensing technology is an effective way in coal exploration and measurement. In this paper, we try to measure the distribution and reserves of open-air coal area through satellite imagery. The satellite picture of open-air coal mining region in Quang Ninh Province of Vietnam was collected as the experimental data. Firstly, the ENVI software is used to eliminate satellite imagery spectral interference. Then, the image classification model is established by the improved ELM algorithm. Finally, the effectiveness of the improved ELM algorithm is verified by using MATLAB simulations. The results show that the accuracies of the testing set reach 96.5%. And it reaches 83% of the image discernment precision compared with the same image from Google.

  1. A Novel Method for Optimum Global Positioning System Satellite Selection Based on a Modified Genetic Algorithm.

    Science.gov (United States)

    Song, Jiancai; Xue, Guixiang; Kang, Yanan

    2016-01-01

    In this paper, a novel method for selecting a navigation satellite subset for a global positioning system (GPS) based on a genetic algorithm is presented. This approach is based on minimizing the factors in the geometric dilution of precision (GDOP) using a modified genetic algorithm (MGA) with an elite conservation strategy, adaptive selection, adaptive mutation, and a hybrid genetic algorithm that can select a subset of the satellites represented by specific numbers in the interval (4 ∼ n) while maintaining position accuracy. A comprehensive simulation demonstrates that the MGA-based satellite selection method effectively selects the correct number of optimal satellite subsets using receiver autonomous integrity monitoring (RAIM) or fault detection and exclusion (FDE). This method is more adaptable and flexible for GPS receivers, particularly for those used in handset equipment and mobile phones.

  2. A Novel Onboard-gateway-based Mechanism to Improve TCP Performance in Aeronautical Satellite Networks

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The IP-based networks on aircraft serve to support Internet services via satellites. However, in aeronautical satellite hybrid networks, the TCP protocol performance often deteriorates due to improper decreases and slow recovery of the congestion window. This paper proposes a window size determination and notification mechanism, onboard-gateway-based mechanism (OGBM), which is based on the onboard gateway in the networks on aircraft. A cross-layer approach is adopted by the onboard gateway to obtain the satellite link bandwidth information. And then, by the gateway, through changing the receiver's advertised window field in ACK packets, TCP sources are notified of the window size of each TCP source calculated on the ground of bandwidth delay product and flow numbers. The mechanism is able to avoid improper changes of TCP window and serve multiple users. Simulation results show that the mechanism with the fairness index close to 1 improves TCP performance in aeronautical satellite networks.

  3. A comparing design of satellite attitude control system based on reaction wheel

    Institute of Scientific and Technical Information of China (English)

    CHENG Hao; GE Sheng-min; SHEN Yi

    2008-01-01

    The disturbance caused by the reaction wheel with a current controller greatly influences the accuracy and stability of the satellite attitude control system.To solve this problem,the idea of speed feedback compensation control reaction wheel is put forward.This paper introduces the comparison on design and performance of two satellite attitude control systems,which are separately based on the current control reaction wheel and the speed feedback compensation control reaction wheel.Analysis shows that the speed feedback compensation control flywheel system may effectively suppress the torque fluctuation.Simulation results indicate that the satellite attitude control system with the speed feedback compensation control flywheel has improved performance.

  4. A DISTRIBUTED QOS ROUTING BASED ON ANT ALGORITHM FOR LEO SATELLITE NETWORK

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Low Earth Orbit (LEO) satellites provide short round-trip delays and are becoming increasingly important. One of the challenges in LEO satellite networks is the development of specialized and efficient routing algorithms. To satisfy the QoS requirements of multimedia applications, satellite routing protocols should consider handovers and minimize their effect on the active connections. A distributed QoS routing scheme based on heuristic ant algorithm is proposed for satisfying delay bound and avoiding link congestion. Simulation results show that the call blocking probabilities of this algorithm are less than that of Shortest Path First (SPF) with different delay bound.

  5. Smoothing of Fused Spectral Consistent Satellite Images with TV-based Edge Detection

    DEFF Research Database (Denmark)

    Sveinsson, Johannes; Aanæs, Henrik; Benediktsson, Jon Atli

    2007-01-01

    Several widely used methods have been proposed for fusing high resolution panchromatic data and lower resolution multi-channel data. However, many of these methods fail to maintain the spectral consistency of the fused high resolution image, which is of high importance to many of the applications...... based on satellite data. Additionally, most conventional methods are loosely connected to the image forming physics of the satellite image, giving these methods an ad hoc feel. Vesteinsson et al. [1] proposed a method of fusion of satellite images that is based on the properties of imaging physics...... in a statistically meaningful way and was called spectral consistent panshapening (SCP). In this paper we improve this framework for satellite image fusion by introducing a better image prior, via data-dependent image smoothing. The dependency is obtained via total variation edge detection method....

  6. A Novel Sampling Method for Satellite-Based Offshore Wind Resource Estimation

    DEFF Research Database (Denmark)

    Badger, Merete; Badger, Jake; Hasager, Charlotte Bay

    Synthetic aperture radar (SAR) measurements from satellites can be used to estimate the spatial wind speed variation offshore in great detail. The radar senses cm-scale roughness at the sea surface which can be translated to wind speed at the height 10 m using an empirical geophysical model......-based wind climatology have improved gradually as more data were collected. The satellite scenes have been treated as random samples and weighted equally in our previous analyses. Here we introduce a novel sampling strategy based on the wind class methodology that is normally applied in numerical modeling...... climatologically representative large-scale meteorological conditions for the region of interest. The wind classes are used to make the most representative selection of satellite images from the ENVISAT image catalogue. A minimum of one satellite image is chosen per wind class. The frequency of occurrence of each...

  7. Design and simulation of satellite attitude control system based on Simulink and VR

    Science.gov (United States)

    Zhang, Yang; Gan, Qingbo; Kang, Jingshu

    2016-01-01

    In order to research satellite attitude control system design and visual simulation, the simulation framework of satellite dynamics and attitude control using Simulink were established. The design of satellite earth-oriented control system based on quaternion feedback was completed. The 3D scene based on VR was created and models in the scene were driven by simulation data of Simulink. By coordinate transformation. successful observing the scene in inertial coordinate system, orbit coordinate system and body coordinate system. The result shows that application of simulation method of Simulink combined with VR in the design of satellite attitude control system field, has the advantages of high confidence level, hard real-time property, multi-perspective and multi-coordinate system observing the scene, and improves the comprehensibility and accuracy of the design.

  8. UKF-based attitude determination method for gyroless satellite

    Institute of Scientific and Technical Information of China (English)

    张红梅; 邓正隆

    2004-01-01

    UKF (unscented Kalman filtering) is a new filtering method suitable to nonlinear systems. The method need not linearize nonlinear systems at the prediction stage of filtering, which is indispensable in EKF (extended Kalman filtering). As a result, the linearization error is avoided, and the filtering accuracy is greatly improved. UKF is applied to the attitude determination for gyroless satellite. Simulations are made to compare the new filter with the traditional EKF.The results indicate that under same conditions, compared with EKF, UKF has faster convergence speed, higher filtering accuracy and more stable estimation performance.

  9. Satellite -Based Networks for U-Health & U-Learning

    Science.gov (United States)

    Graschew, G.; Roelofs, T. A.; Rakowsky, S.; Schlag, P. M.

    2008-08-01

    The use of modern Information and Communication Technologies (ICT) as enabling tools for healthcare services (eHealth) introduces new ways of creating ubiquitous access to high-level medical care for all, anytime and anywhere (uHealth). Satellite communication constitutes one of the most flexible methods of broadband communication offering high reliability and cost-effectiveness of connections meeting telemedicine communication requirements. Global networks and the use of computers for educational purposes stimulate and support the development of virtual universities for e-learning. Especially real-time interactive applications can play an important role in tailored and personalised services.

  10. Space-Based Observations of Satellites From the MOST Microsatellite

    Science.gov (United States)

    2006-11-01

    observations spatiales canadiennes d’un objet en orbite terrestre . Deux satellites de géolocalisation GPS ont été suivis à l’aide du télescope optique monté...the derived orbital metric data with high precision ephemerides yielded root mean square errors of 13 arcseconds. The errors are shown to result...space surveillance from an orbiting platform. Résumé Le 12 octobre 2005, le microsatellite MOST du Canada a acquis les premières images

  11. Exploiting coastal altimetry to improve the surface circulation scheme over the central Mediterranean Sea

    Science.gov (United States)

    Jebri, Fatma; Birol, Florence; Zakardjian, Bruno; Bouffard, Jérome; Sammari, Cherif

    2016-07-01

    This work is the first study exploiting along track altimetry data to observe and monitor coastal ocean features over the transition area between the western and eastern Mediterranean Basins. The relative performances of both the AVISO and the X-TRACK research regional altimetric data sets are compared using in situ observations. Both products are cross validated with tide gauge records. The altimeter-derived geostrophic velocities are also compared with observations from a moored Acoustic Doppler Current Profiler. Results indicate the good potential of satellite altimetry to retrieve dynamic features over the area. However, X-TRACK shows a more homogenous data coverage than AVISO, with longer time series in the 50 km coastal band. The seasonal evolution of the surface circulation is therefore analyzed by conjointly using X-TRACK data and remotely sensed sea surface temperature observations. This combined data set clearly depicts different current regimes and bifurcations, which allows us to propose a new seasonal circulation scheme for the central Mediterranean. The analysis shows variations of the path and temporal behavior of the main circulation features: the Atlantic Tunisian Current, the Atlantic Ionian Stream, the Atlantic Libyan Current, and the Sidra Gyre. The resulting bifurcating veins of these currents are also discussed, and a new current branch is observed for the first time.

  12. A Survey of ICESat Coastal Altimetry Applications: Continental Coast, Open Ocean Island, and Inland River

    Directory of Open Access Journals (Sweden)

    Timothy J. Urban

    2008-01-01

    Full Text Available ICESat satellite laser altimetry provides an unprecedented set of global elevation measurements of the Earth, yielding great detail over ice, land and ocean surfaces. Coastal regions in particular, including seamless land-water transitions, benefit from the small footprint (50 to 90 m, high resolution (40 Hz, ~170 m along-track, and high precision (2 to 3 cm of ICESat. We discuss the performance and character of ICESat data in three example coastal scenarios: continental coast (Louisiana-Mississippi Gulf Coast, USA, including Lake Pontchartrain, open ocean island (Funafuti, Tuvalu, and an inland river (confluence of Tapajos and Amazon rivers, Brazil. Water elevations are compared to tide gauge heights and to TOPEX and Jason-1 radar altimetry. In demonstrating the utilization of ICESat, we also present examples of: laser waveform shapes over a variety of surface types (water, land, and vegetation; vegetation canopy heights (detecting large-scale destruction from Hurricane Katrina comparing data before and after; sub-canopy surface water; measurements of waves; and examination of along-stream river slope and comparisons of river stage to hydrologically-driven GRACE geoid change.

  13. A Step Towards the Characterization of SAR Mode Altimetry to Inform Hydrodynamic Models

    Science.gov (United States)

    Fabry, Pierre; Bercher, Nicolas; Ambrozio, Americo; Restano, Marco; Benveniste, Jerome

    2016-08-01

    Inland water scenes are highly variable, both in space and time, which leads to a much broader range of radar signatures than ocean surfaces. This applies to both LRM and "SAR" mode (SARM) altimetry. Nevertheless the enhanced along-track resolution of SARM altimeters should help improve the accuracy and precision of inland water height measurements from satellite. The SHAPE project - Sentinel-3 Hydrologic Altimetry Processor prototypE - which is funded by ESA through the Scientific Exploitation of Operational Missions Programme Element (contract number 4000115205/15/I-BG) aims at preparing for the exploitation of Sentinel-3 data over the inland water domain. In order to define refine the L1B processor and the retrackers for alti-hydrology applications, we need to characterise the SARM Individual Echoes, Multi- Look Stacks as well as 20Hz waveforms over the inland water domain.This paper deals with the continuation of works presented in 2015 [Fabry et Bercher, Venice 2015b] [Fabry et Bercher, Frascati 2015a/c] where we introduced an automated technique to assess the water fraction within the Beam-Doppler limited footprint through its intersection area with a water mask. We hereby refine the utilisation of these water classes and run the classification on a wider dataset so as to improve the readout of the Range Integrated Power1 (RIP) parameters and the waveforms versus the Water Fraction.

  14. Developing a Near-Continuous Estimation of Volumetric Fluctuations in Tropical Lakes and Reservoirs Using Satellite Remote Sensing

    Science.gov (United States)

    Keys, T.; Scott, D.

    2015-12-01

    Lakes and reservoirs play an integral role in water resources management by storing large quantities of water commonly used for irrigation, hydroelectric power, water supply, and flood mitigation. Knowing the exact quantity of stored water and necessary water for each of these usages is a critical component of sustainable water resources management. However, limited amounts of hydrologic data in developing nations, most of which are located in the tropics, hinders the accurate monitoring of water storage and allocation. Recent improvements in remote sensing have greatly enhanced the ability to calculate volumetric fluctuations of lakes and reservoirs at given points through time but are limited by temporal resolution as well as the computational time required for image processing. This study utilizes the newly developed MODISTools package for the programming language R in conjunction with satellite altimetry from three different altimetry databases to estimate lake and reservoir volumes at eight day intervals over a 15 year period. The study specifically examines three large lakes and reservoirs: Balbina Reservoir in the Amazon River Basin, Lake Tana in the Nile River Basin, and Tonle Sap Lake in the Mekong River Basin. Altimetry-based water level estimations are validated by in situ water level data from monitoring stations while surface area estimations are validated by Sound Navigation and Ranging (SONAR) generated bathymetric maps with corresponding stage-area relationships. Preliminary results indicate that both remotely sensed water levels and surface areas agree well with in situ measurements, supporting the appropriateness of this methodology.

  15. Satellite image based methods for fuels maps updating

    Science.gov (United States)

    Alonso-Benito, Alfonso; Hernandez-Leal, Pedro A.; Arbelo, Manuel; Gonzalez-Calvo, Alejandro; Moreno-Ruiz, Jose A.; Garcia-Lazaro, Jose R.

    2016-10-01

    Regular updating of fuels maps is important for forest fire management. Nevertheless complex and time consuming field work is usually necessary for this purpose, which prevents a more frequent update. That is why the assessment of the usefulness of satellite data and the development of remote sensing techniques that enable the automatic updating of these maps, is of vital interest. In this work, we have tested the use of the spectral bands of OLI (Operational Land Imager) sensor on board Landsat 8 satellite, for updating the fuels map of El Hierro Island (Spain). From previously digitized map, a set of 200 reference plots for different fuel types was created. A 50% of the plots were randomly used as a training set and the rest were considered for validation. Six supervised and 2 unsupervised classification methods were applied, considering two levels of detail. A first level with only 5 classes (Meadow, Brushwood, Undergrowth canopy cover >50%, Undergrowth canopy cover <15%, and Xeric formations), and the second one containing 19 fuel types. The level 1 classification methods yielded an overall accuracy ranging from 44% for Parellelepided to an 84% for Maximun Likelihood. Meanwhile, level 2 results showed at best, an unacceptable overall accuracy of 34%, which prevents the use of this data for such a detailed characterization. Anyway it has been demonstrated that in some conditions, images of medium spatial resolution, like Landsat 8-OLI, could be a valid tool for an automatic upgrade of fuels maps, minimizing costs and complementing traditional methodologies.

  16. Authentication Scheme Based on Principal Component Analysis for Satellite Images

    Directory of Open Access Journals (Sweden)

    Ashraf. K. Helmy

    2009-09-01

    Full Text Available This paper presents a multi-band wavelet image content authentication scheme for satellite images by incorporating the principal component analysis (PCA. The proposed schemeachieves higher perceptual transparency and stronger robustness. Specifically, the developed watermarking scheme can successfully resist common signal processing such as JPEG compression and geometric distortions such as cropping. In addition, the proposed scheme can be parameterized, thus resulting in more security. That is, an attacker may not be able to extract the embedded watermark if the attacker does not know the parameter.In an order to meet these requirements, the host image is transformed to YIQ to decrease the correlation between different bands, Then Multi-band Wavelet transform (M-WT is applied to each channel separately obtaining one approximate sub band and fifteen detail sub bands. PCA is then applied to the coefficients corresponding to the same spatial location in all detail sub bands. The last principle component band represents an excellent domain forinserting the water mark since it represents lowest correlated features in high frequency area of host image.One of the most important aspects of satellite images is spectral signature, the behavior of different features in different spectral bands, the results of proposed algorithm shows that the spectral stamp for different features doesn't tainted after inserting the watermark.

  17. A scalable satellite-based crop yield mapper: Integrating satellites and crop models for field-scale estimation in India

    Science.gov (United States)

    Jain, M.; Singh, B.; Srivastava, A.; Lobell, D. B.

    2015-12-01

    Food security will be challenged over the upcoming decades due to increased food demand, natural resource degradation, and climate change. In order to identify potential solutions to increase food security in the face of these changes, tools that can rapidly and accurately assess farm productivity are needed. With this aim, we have developed generalizable methods to map crop yields at the field scale using a combination of satellite imagery and crop models, and implement this approach within Google Earth Engine. We use these methods to examine wheat yield trends in Northern India, which provides over 15% of the global wheat supply and where over 80% of farmers rely on wheat as a staple food source. In addition, we identify the extent to which farmers are shifting sow date in response to heat stress, and how well shifting sow date reduces the negative impacts of heat stress on yield. To identify local-level decision-making, we map wheat sow date and yield at a high spatial resolution (30 m) using Landsat satellite imagery from 1980 to the present. This unique dataset allows us to examine sow date decisions at the field scale over 30 years, and by relating these decisions to weather experienced over the same time period, we can identify how farmers learn and adapt cropping decisions based on weather through time.

  18. Validation of PV performance models using satellite-based irradiance measurements : a case study.

    Energy Technology Data Exchange (ETDEWEB)

    Stein, Joshua S.; Parkins, Andrew (Clean Power Research); Perez, Richard (University at Albany)

    2010-05-01

    Photovoltaic (PV) system performance models are relied upon to provide accurate predictions of energy production for proposed and existing PV systems under a wide variety of environmental conditions. Ground based meteorological measurements are only available from a relatively small number of locations. In contrast, satellite-based radiation and weather data (e.g., SUNY database) are becoming increasingly available for most locations in North America, Europe, and Asia on a 10 x 10 km grid or better. This paper presents a study of how PV performance model results are affected when satellite-based weather data is used in place of ground-based measurements.

  19. Discharge forecasting using MODIS and radar altimetry: potential application for transboundary flood risk management in Niger-Benue River basin

    Science.gov (United States)

    Tarpanelli, Angelica; Amarnath, Giriraj; Brocca, Luca; Moramarco, Tommaso

    2016-04-01

    Flooding is one of most widespread natural disasters in the world. Its impact is particularly severe and destructive in Asia and Africa, because the living conditions of some settlements are inadequate to cope with this type of natural hazard. In this context, the estimation of discharge is extremely important to address water management and flood risk assessment. However, the inadequate monitoring network hampers any control and prediction activity that could improve these disastrous situations. In the last few years, remote sensing sensors have demonstrated their effectiveness in retrieving river discharge, especially in supporting discharge nowcasting and forecasting activities. Recently, the potential of radar altimetry was apparent when used for estimating water levels in an ungauged river site with good accuracy. It has also become a very useful tool for estimation and prediction of river discharge. However, the low temporal resolution of radar altimeter observations (10 or 35 days, depending on the satellite mission) may be not suitable for day-by-day hydrological forecasting. Differently, MODerate resolution Imaging Spectroradiometer (MODIS), considering its proven potential for quantifying the variations in discharge of the rivers at daily time resolution may be more suited to this end. For these reasons, MODIS and radar altimetry data were used in this study to predicting and forecasting the river discharge along the Niger-Benue River, where severe flooding with extensive damage to property and loss of lives occurred. Therefore, an effective method to forecast flooding can support efforts towards creating an early warning system. In order to estimate river discharge, four MODIS products (daily, 8-day, and from AQUA and TERRA satellites) connected at three sites (two gauged and one ungauged) were used. The capability of remote sensing sensors to forecast discharge a few days in advance at a downstream section using MODIS and ENVISAT radar altimetry data

  20. Towards a satellite-based sea ice climate data record

    Science.gov (United States)

    Meier, W. N.; Fetterer, F.; Stroeve, J.; Cavalieri, D.; Parkinson, C.; Comiso, J.; Weaver, R.

    2005-12-01

    Sea ice plays an important role in the Earth's climate through its influence on the surface albedo, heat and moisture transfer between the ocean and the atmosphere, and the thermohaline circulation. Satellite data reveal that since 1979, summer Arctic sea ice has, overall, been declining at a rate of almost 8%/decade, with recent summers (beginning in 2002) being particularly low. The receding sea ice is having an effect on wildlife and indigenous peoples in the Arctic, and concern exists that these effects may become increasingly severe. Thus, a long-term, ongoing climate data record of sea ice is crucial for tracking the changes in sea ice and for assessing the significance of long-term trends. Since the advent of passive microwave satellite instruments in the early 1970s, sea ice has been one of the most consistently monitored climate parameters. There is now a 27+ year record of sea ice extent and concentration from multi-channel passive microwave radiometers that has undergone inter-sensor calibration and other quality controls to ensure consistency throughout the record. Several algorithms have been developed over the years to retrieve sea ice extent and concentration and two of the most commonly used algorithms, the NASA Team and Bootstrap, have been applied to the entire SMMR-SSM/I record to obtain a consistent time series. These algorithms were developed at NASA Goddard Space Flight Center and are archived at the National Snow and Ice Data Center. However, the complex surface properties of sea ice affect the microwave signature, and algorithms can yield ambiguous results; no single algorithm has been found to work uniformly well under all sea ice conditions. Thus there are ongoing efforts to further refine the algorithms and the time series. One approach is to develop data fusion methods to optimally combine sea ice fields from two or more algorithms. Another approach is to take advantage of the improved capabilities of JAXA's AMSR-E sensor on NASA's Aqua

  1. Energy-Efficient Network Transmission between Satellite Swarms and Earth Stations Based on Lyapunov Optimization Techniques

    Directory of Open Access Journals (Sweden)

    Weiwei Fang

    2014-01-01

    Full Text Available The recent advent of satellite swarm technologies has enabled space exploration with a massive number of picoclass, low-power, and low-weight spacecraft. However, developing swarm-based satellite systems, from conceptualization to validation, is a complex multidisciplinary activity. One of the primary challenges is how to achieve energy-efficient data transmission between the satellite swarm and terrestrial terminal stations. Employing Lyapunov optimization techniques, we present an online control algorithm to optimally dispatch traffic load among different satellite-ground links for minimizing overall energy consumption over time. Our algorithm is able to independently and simultaneously make control decisions on traffic dispatching over intersatellite-links and up-down-links so as to offer provable energy and delay guarantees, without requiring any statistical information of traffic arrivals and link condition. Rigorous analysis and extensive simulations have demonstrated the performance and robustness of the proposed new algorithm.

  2. Satellite Fault Diagnosis Using Support Vector Machines Based on a Hybrid Voting Mechanism

    Directory of Open Access Journals (Sweden)

    Hong Yin

    2014-01-01

    Full Text Available The satellite fault diagnosis has an important role in enhancing the safety, reliability, and availability of the satellite system. However, the problem of enormous parameters and multiple faults makes a challenge to the satellite fault diagnosis. The interactions between parameters and misclassifications from multiple faults will increase the false alarm rate and the false negative rate. On the other hand, for each satellite fault, there is not enough fault data for training. To most of the classification algorithms, it will degrade the performance of model. In this paper, we proposed an improving SVM based on a hybrid voting mechanism (HVM-SVM to deal with the problem of enormous parameters, multiple faults, and small samples. Many experimental results show that the accuracy of fault diagnosis using HVM-SVM is improved.

  3. Validation of satellite-based noontime UVI with NDACC ground-based instruments: influence of topography, environment and satellite overpass time

    Science.gov (United States)

    Brogniez, Colette; Auriol, Frédérique; Deroo, Christine; Arola, Antti; Kujanpää, Jukka; Sauvage, Béatrice; Kalakoski, Niilo; Riku Aleksi Pitkänen, Mikko; Catalfamo, Maxime; Metzger, Jean-Marc; Tournois, Guy; Da Conceicao, Pierre

    2016-12-01

    Spectral solar UV radiation measurements are performed in France using three spectroradiometers located at very different sites. One is installed in Villeneuve d'Ascq, in the north of France (VDA). It is an urban site in a topographically flat region. Another instrument is installed in Observatoire de Haute-Provence, located in the southern French Alps (OHP). It is a rural mountainous site. The third instrument is installed in Saint-Denis, Réunion Island (SDR). It is a coastal urban site on a small mountainous island in the southern tropics. The three instruments are affiliated with the Network for the Detection of Atmospheric Composition Change (NDACC) and carry out routine measurements to monitor the spectral solar UV radiation and enable derivation of UV index (UVI). The ground-based UVI values observed at solar noon are compared to similar quantities derived from the Ozone Monitoring Instrument (OMI, onboard the Aura satellite) and the second Global Ozone Monitoring Experiment (GOME-2, onboard the Metop-A satellite) measurements for validation of these satellite-based products. The present study concerns the period 2009-September 2012, date of the implementation of a new OMI processing tool. The new version (v1.3) introduces a correction for absorbing aerosols that were not considered in the old version (v1.2). Both versions of the OMI UVI products were available before September 2012 and are used to assess the improvement of the new processing tool. On average, estimates from satellite instruments always overestimate surface UVI at solar noon. Under cloudless conditions, the satellite-derived estimates of UVI compare satisfactorily with ground-based data: the median relative bias is less than 8 % at VDA and 4 % at SDR for both OMI v1.3 and GOME-2, and about 6 % for OMI v1.3 and 2 % for GOME-2 at OHP. The correlation between satellite-based and ground-based data is better at VDA and OHP (about 0.99) than at SDR (0.96) for both space-borne instruments. For all

  4. Fairness based channel borrowing strategy in multimedia LEO satellite communications

    Institute of Scientific and Technical Information of China (English)

    HUANG Fei; XU Hui; WU Shiqi

    2007-01-01

    A novel bandwidth allocation strategy along with a connection admission control technique was proposed to improve the utilization of network resources.It provides the network with better quality-of-service (QoS) guarantees,such as new call blocking probability (CBP) and handoff call dropping probability (CDP) in multimedia low earth orbit (LEO) satellite networks.Simulation results show that,compared with other bandwidth allocation schemes,the proposed scheme offers very low call dropping probability for real-time connections while,at the same time,keeping resource utilization high.Finally we discussed the fairness for the borrowed nonreal-time connections under three different channel borrowing methods.

  5. A new algorithm for agile satellite-based acquisition operations

    Science.gov (United States)

    Bunkheila, Federico; Ortore, Emiliano; Circi, Christian

    2016-06-01

    Taking advantage of the high manoeuvrability and the accurate pointing of the so-called agile satellites, an algorithm which allows efficient management of the operations concerning optical acquisitions is described. Fundamentally, this algorithm can be subdivided into two parts: in the first one the algorithm operates a geometric classification of the areas of interest and a partitioning of these areas into stripes which develop along the optimal scan directions; in the second one it computes the succession of the time windows in which the acquisition operations of the areas of interest are feasible, taking into consideration the potential restrictions associated with these operations and with the geometric and stereoscopic constraints. The results and the performances of the proposed algorithm have been determined and discussed considering the case of the Periodic Sun-Synchronous Orbits.

  6. Characterization of satellite based proxies for estimating nucleation mode particles over South Africa

    Directory of Open Access Journals (Sweden)

    A.-M. Sundström

    2014-10-01

    Full Text Available In this work satellite observations from the NASA's A-Train constellation were used to derive the values of primary emission and regional nucleation proxies over South Africa to estimate the potential for new particle formation. As derived in Kulmala et al. (2011, the satellite based proxies consist of source terms (NO2, SO2 and UV-B radiation, and a sink term describing the pre-existing aerosols. The first goal of this work was to study in detail the use of satellite aerosol optical depth (AOD as a substitute to the in situ based condensation sink (CS. One of the major factors affecting the agreement of CS and AOD was the elevated aerosol layers that increased the value of column integrated AOD but not affected the in situ CS. However, when the AOD in the proxy sink was replaced by an estimate from linear bivariate fit between AOD and CS, the agreement with the actual nucleation mode number concentration improved somewhat. The second goal of the work was to estimate how well the satellite based proxies can predict the potential for new particle formation. For each proxy the highest potential for new particle formation were observed over the Highveld industrial area, where the emissions were high but the sink due to pre-existing aerosols was relatively low. Best agreement between the satellite and in situ based proxies were obtained for NO2/AOD and UV-B/AOD2, whereas proxies including SO2 in the source term had lower correlation. Even though the OMI SO2 boundary layer product showed reasonable spatial pattern and detected the major sources over the study area, some of the known minor point sources were not detected. When defining the satellite proxies only for days when new particle formation event was observed, it was seen that for all the satellite based proxies the event day medians were higher than the entire measurement period median.

  7. Wave energy resource assessment based on satellite observations around Indonesia

    Science.gov (United States)

    Ribal, Agustinus; Zieger, Stefan

    2016-06-01

    A preliminary assessment of wave energy resource around Indonesian's ocean has been carried out by means of analyzing satellite observations. The wave energy flux or wave power can be approximated using parameterized sea states. Wave power scales with significant wave height, characteristic wave period and water depth. In this approach, the significant wave heights were obtained from ENVISAT (Environmental Satellite) data which have been calibrated. However, as the characteristic wave period is rarely specified and therefore must be estimated from other variables when information about the wave spectra is unknown. Here, the characteristic wave period was calculated with an empirical model that utilizes altimeter estimates of wave height and backscatter coefficient originally proposed. For the Indonesian region, wave power energy is calculated over two periods of one year each and was compared with the results from global hindcast carried out with a recent release of wave model WAVEWATCH III. We found that, the most promising wave power energy regions around the Indonesian archipelago are located in the south of Java island and the south west of Sumatera island. In these locations, about 20 - 30 kW/m (90th percentile: 30-50 kW/m, 99th percentile: 40-60 kW/m) wave power energy on average has been found around south of Java island during 2010. Similar results have been found during 2011 at the same locations. Some small areas which are located around north of Irian Jaya (West Papua) are also very promising and need further investigation to determine its capacity as a wave energy resource.

  8. Simulation and Analysis of Autonomous Time Synchronization Based on Asynchronism Two-way Inter-satellite Link

    Science.gov (United States)

    Fang, L.; Yang, X. H.; Sun, B. Q.; Qin, W. J.; Kong, Y.

    2013-09-01

    The measurement of the inter-satellite link is one of the key techniques in the autonomous operation of satellite navigation system. Based on the asynchronism inter-satellite two-way measurement mode in GPS constellation, the reduction formula of the inter-satellite time synchronization is built in this paper. Moreover, the corrective method of main systematic errors is proposed. Inter-satellite two-way time synchronization is simulated on the basis of IGS (International GNSS Service) precise ephemeris. The impacts of the epoch domestication of asynchronism inter-satellite link pseudo-range, the initial orbit, and the main systematic errors on satellite time synchronization are analyzed. Furthermore, the broadcast clock error of each satellite is calculated by the ``centralized'' inter-satellite autonomous time synchronization. Simulation results show that the epoch domestication of asynchronism inter-satellite link pseudo-range and the initial orbit have little impact on the satellite clock errors, and thus they needn't be taken into account. The errors caused by the relativistic effect and the asymmetry of path travel have large impact on the satellite clock errors. These should be corrected with theoretical formula. Compared with the IGS precise clock error, the root mean square of the broadcast clock error of each satellite is about 0.4 ns.

  9. Object Based and Pixel Based Classification Using Rapideye Satellite Imager of ETI-OSA, Lagos, Nigeria

    Directory of Open Access Journals (Sweden)

    Esther Oluwafunmilayo Makinde

    2016-12-01

    Full Text Available Several studies have been carried out to find an appropriate method to classify the remote sensing data. Traditional classification approaches are all pixel-based, and do not utilize the spatial information within an object which is an important source of information to image classification. Thus, this study compared the pixel based and object based classification algorithms using RapidEye satellite image of Eti-Osa LGA, Lagos. In the object-oriented approach, the image was segmented to homogenous area by suitable parameters such as scale parameter, compactness, shape etc. Classification based on segments was done by a nearest neighbour classifier. In the pixel-based classification, the spectral angle mapper was used to classify the images. The user accuracy for each class using object based classification were 98.31% for waterbody, 92.31% for vegetation, 86.67% for bare soil and 90.57% for Built up while the user accuracy for the pixel based classification were 98.28% for waterbody, 84.06% for Vegetation 86.36% and 79.41% for Built up. These classification techniques were subjected to accuracy assessment and the overall accuracy of the Object based classification was 94.47%, while that of Pixel based classification yielded 86.64%. The result of classification and accuracy assessment show that the object-based approach gave more accurate and satisfying results

  10. Roughness of the marine geoid from Seasat altimetry

    Science.gov (United States)

    Brown, R. D.; Himwich, W. E.; Kahn, W. D.; Mcadoo, D. C.

    1983-01-01

    The geographical variability of short wavelength geoid power spectra (geoid roughness) has been mapped for the world's oceans between latitudes 72 deg N and 72 deg S. A spectral analysis of Seasat altimeter data, reduced to sea surface heights, has been performed at 2-min intervals for 15 consecutive days of the 3-day repeat orbit. The geoid roughness represented by these spectra for wavelengths shorter than about 220 km is separated from the total sea height variance and is displayed in the form of a global contour map. The global average geoid roughness is 32 cm RMS, varying from a high in excess of 2 m RMS near deep ocean trenches to a low of 2 cm RMS in the southeast Pacific near the east Pacific rise. This average value agrees well with previous estimates based on gravimetry and GEOS 3 altimetry. In general, the smoothest areas in the marine geoid overlie relatively young sea floor adjacent mid-ocean spreading centers, where even short wavelength topographic variations tend to be isostatically compensated.

  11. Coastal SAR and PLRM Altimetry in German Bight and West Baltic Sea

    Science.gov (United States)

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

    2016-08-01

    The CryoSat-2 altimeter (SIRAL) features a novel Synthetic Aperture Radar (SAR) mode that allows higher resolution and more accurate altimeter-derived parameters in the coastal zone, thanks to the reduced along-track footprint.This study is a regional analysis and validation of CryoSat-2 SAR altimeter products along the German coasts at distance to shore smaller than 10 km. The validation in performed against regional models and an in-situ network of tide gauges and Global Navigation Satellite Systems (GNSS) stations. The goal is an assessment of the geophysical altimeter parameters sea surface height above the ellipsoid (SSH), significant sea wave height (SWH) and wind speed (U10), all estimated at 20 Hz over the time interval from October 2010 to July 2015.We have carried out from FBR (L1a) data a Delay- Doppler processing and waveform retracking tailored to coastal zone by a dedicated SAMOSA-based coastal retracker (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 to reduce land off-ranging effects.Since the remaining uncertainty in the altimeter products for coastal shallow waters arises mainly from residual errors in the applied corrections, we use the regional model TPXO8 for tides, EGM 2008 for geoid and DTU13 for mean sea surface and the regionally improved wet tropospheric correction GNSS-based Path Delay Plus (GPD+) computed at University of Porto.To quantify the improvement with respect to pulse- limited altimetry, we build 20 Hz PLRM (pseudo-LRM) data from FBR as a proxy for real pulse-limited products (LRM). They are retracked with a numerical Brown-based retracker. The L2 SAR ocean data products are generated and extracted from ESA-ESRIN GPOD service (named SARvatore) while the PLRM data are built and retracked by Technical University of Darmstadt (TUDa).The validation shows that the accuracy of sea level in coastal

  12. Calculating the Marine Gravity Anomaly of the South China Sea based on the Inverse Stokes Formula

    Science.gov (United States)

    Liu, Liang; Jiang, Xiaoguang; Liu, Shanwei; Zheng, Lei; Zang, Jinxia; Zhang, Xuehua; Liu, Longfei

    2016-11-01

    Marine gravity field information has a great significance for the resource, environment and military affairs. As a new way to get marine gravity data, the satellite altimetry technique makes up for what ship measuring means lack. The paper carries out the researches on how altimeter data applied for calculating marine gravity anomaly based on inverse Stokes formula. In the article, the editing of 14-track Jason-1 data over South China Sea for 7 years is for collinear processing and cross-point adjustment. The inverse Stokes formula and fast Flourier transform technique are applied to calculate marine gravity anomaly of the region (0°∼23°N, 103°∼120°E), and to draw gravity anomaly map. Compared with the gravity anomaly by ship observation, RMS is 12.6mGal, and single altimetry satellite has a good precision.

  13. Adjusting thresholds of satellite-based convective initiation interest fields based on the cloud environment

    Science.gov (United States)

    Jewett, Christopher P.; Mecikalski, John R.

    2013-11-01

    The Time-Space Exchangeability (TSE) concept states that similar characteristics of a given property are closely related statistically for objects or features within close proximity. In this exercise, the objects considered are growing cumulus clouds, and the data sets to be considered in a statistical sense are geostationary satellite infrared (IR) fields that help describe cloud growth rates, cloud top heights, and whether cloud tops contain significant amounts of frozen hydrometeors. In this exercise, the TSE concept is applied to alter otherwise static thresholds of IR fields of interest used within a satellite-based convective initiation (CI) nowcasting algorithm. The convective environment in which the clouds develop dictate growth rate and precipitation processes, and cumuli growing within similar mesoscale environments should have similar growth characteristics. Using environmental information provided by regional statistics of the interest fields, the thresholds are examined for adjustment toward improving the accuracy of 0-1 h CI nowcasts. Growing cumulus clouds are observed within a CI algorithm through IR fields for many 1000 s of cumulus cloud objects, from which statistics are generated on mesoscales. Initial results show a reduction in the number of false alarms of ~50%, yet at the cost of eliminating approximately ~20% of the correct CI forecasts. For comparison, static thresholds (i.e., with the same threshold values applied across the entire satellite domain) within the CI algorithm often produce a relatively high probability of detection, with false alarms being a significant problem. In addition to increased algorithm performance, a benefit of using a method like TSE is that a variety of unknown variables that influence cumulus cloud growth can be accounted for without need for explicit near-cloud observations that can be difficult to obtain.

  14. Detecting Anomaly Regions in Satellite Image Time Series Based on Sesaonal Autocorrelation Analysis

    Science.gov (United States)

    Zhou, Z.-G.; Tang, P.; Zhou, M.

    2016-06-01

    Anomaly regions in satellite images can reflect unexpected changes of land cover caused by flood, fire, landslide, etc. Detecting anomaly regions in satellite image time series is important for studying the dynamic processes of land cover changes as well as for disaster monitoring. Although several methods have been developed to detect land cover changes using satellite image time series, they are generally designed for detecting inter-annual or abrupt land cover changes, but are not focusing on detecting spatial-temporal changes in continuous images. In order to identify spatial-temporal dynamic processes of unexpected changes of land cover, this study proposes a method for detecting anomaly regions in each image of satellite image time series based on seasonal autocorrelation analysis. The method was validated with a case study to detect spatial-temporal processes of a severe flooding using Terra/MODIS image time series. Experiments demonstrated the advantages of the method that (1) it can effectively detect anomaly regions in each of satellite image time series, showing spatial-temporal varying process of anomaly regions, (2) it is flexible to meet some requirement (e.g., z-value or significance level) of detection accuracies with overall accuracy being up to 89% and precision above than 90%, and (3) it does not need time series smoothing and can detect anomaly regions in noisy satellite images with a high reliability.

  15. DETECTING ANOMALY REGIONS IN SATELLITE IMAGE TIME SERIES BASED ON SESAONAL AUTOCORRELATION ANALYSIS

    Directory of Open Access Journals (Sweden)

    Z.-G. Zhou

    2016-06-01

    Full Text Available Anomaly regions in satellite images can reflect unexpected changes of land cover caused by flood, fire, landslide, etc. Detecting anomaly regions in satellite image time series is important for studying the dynamic processes of land cover changes as well as for disaster monitoring. Although several methods have been developed to detect land cover changes using satellite image time series, they are generally designed for detecting inter-annual or abrupt land cover changes, but are not focusing on detecting spatial-temporal changes in continuous images. In order to identify spatial-temporal dynamic processes of unexpected changes of land cover, this study proposes a method for detecting anomaly regions in each image of satellite image time series based on seasonal autocorrelation analysis. The method was validated with a case study to detect spatial-temporal processes of a severe flooding using Terra/MODIS image time series. Experiments demonstrated the advantages of the method that (1 it can effectively detect anomaly regions in each of satellite image time series, showing spatial-temporal varying process of anomaly regions, (2 it is flexible to meet some requirement (e.g., z-value or significance level of detection accuracies with overall accuracy being up to 89% and precision above than 90%, and (3 it does not need time series smoothing and can detect anomaly regions in noisy satellite images with a high reliability.

  16. Object-based illumination normalization for multi-temporal satellite images in urban area

    Science.gov (United States)

    Su, Nan; Zhang, Ye; Tian, Shu; Yan, Yiming

    2016-09-01

    Multi-temporal satellite images acquisition with different illumination conditions cause radiometric difference to have a huge effect on image quality during remote sensing image processing. In particular, image matching of satellite stereo images with great difference between acquisition dates is very difficult for the high-precision DSM generation in the field of satellite photogrammetry. Therefore, illumination normalization is one of the greatest application technology to eliminate radiometric difference for image matching and other image applications. In this paper, we proposed a novel method of object-based illumination normalization to improve image matching of different temporal satellite stereo images in urban area. Our proposed method include two main steps: 1) the object extraction 2) multi-level illumination normalization. Firstly, we proposed a object extraction method for the same objects extraction among the multi-temporal satellite images, which can keep the object structural attribute. Moreover, the multi-level illumination normalization is proposed by combining gradient domain method and singular value decomposition (SVD) according to characteristic information of relevant objects. Our proposed method has great improvement for the illumination of object area to be benefit for image matching in urban area with multiple objects. And the histogram similarity parameter and matching rate are used for illumination consistency quantitative evaluation. The experiments have been conducted on different satellite images with different acquisition dates in the same urban area to verify the effectiveness of our proposed method. The experimental results demonstrate a good performance by comparing other methods.

  17. Assessing Satellite-Based Fire Data for use in the National Emissions Inventory

    Science.gov (United States)

    Soja, Amber J.; Al-Saadi, Jassim; Giglio, Louis; Randall, Dave; Kittaka, Chieko; Pouliot, George; Kordzi, Joseph J.; Raffuse, Sean; Pace, Thompson G.; Pierce, Thomas E.; Moore, Tom; Biswadev, Roy; Pierce, R. Bradley; Szykman, James J.

    2009-01-01

    Biomass burning is significant to emission estimates because: (1) it can be a major contributor of particulate matter and other pollutants; (2) it is one of the most poorly documented of all sources; (3) it can adversely affect human health; and (4) it has been identified as a significant contributor to climate change through feedbacks with the radiation budget. Additionally, biomass burning can be a significant contributor to a regions inability to achieve the National Ambient Air Quality Standards for PM 2.5 and ozone, particularly on the top 20% worst air quality days. The United States does not have a standard methodology to track fire occurrence or area burned, which are essential components to estimating fire emissions. Satellite imagery is available almost instantaneously and has great potential to enhance emission estimates and their timeliness. This investigation compares satellite-derived fire data to ground-based data to assign statistical error and helps provide confidence in these data. The largest fires are identified by all satellites and their spatial domain is accurately sensed. MODIS provides enhanced spatial and temporal information, and GOES ABBA data are able to capture more small agricultural fires. A methodology is presented that combines these satellite data in Near-Real-Time to produce a product that captures 81 to 92% of the total area burned by wildfire, prescribed, agricultural and rangeland burning. Each satellite possesses distinct temporal and spatial capabilities that permit the detection of unique fires that could be omitted if using data from only one satellite.

  18. ICESat laser altimetry over small mountain glaciers

    Science.gov (United States)

    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

  19. Satellite-Based actual evapotranspiration over drying semiarid terrain in West-Africa

    NARCIS (Netherlands)

    Schuttemeyer, D.; Schillings, Ch.; Moene, A.F.; Bruin, de H.A.R.

    2007-01-01

    A simple satellite-based algorithm for estimating actual evaporation based on Makkink¿s equation is applied to a seasonal cycle in 2002 at three test sites in Ghana, West Africa: at a location in the humid tropical southern region and two in the drier northern region. The required input for the algo

  20. Assessment of GPS Reflectometry from TechDemoSat-1 for Scatterometry and Altimetry Applications

    Science.gov (United States)

    Shah, R.; Hajj, G. A.

    2015-12-01

    The value of GPS reflectometry for scatterometry and altimetry applications has been a topic of investigation for the past two decades. TechDemoSat-1 (TDS-1), a technology demonstration satellite launched in July of 2014, with an instrument to collect GPS reflections from 4 GPS satellites simultaneously, provide the first extensive data that allows for validation and evaluation of GPS reflectometry from space against more established techniques. TDS-1 uses a high gain (~13 dBi) L1 antenna pointing 6 degrees off nadir with a 60ohalf-beam width. Reflected GPS L1 signals are processed into Delay Doppler Maps (DDMs) inside the receiver and made available (through Level-1b) along with metadata describing the bistatic geometry, antenna gain, etc., on a second-by-second basis for each of the 4 GPS tracks recorded at any given time. In this paper we examine level-1b data from TDS-1 for thousands of tracks collected over the span of Jan.-Feb., 2015. This data corresponds to reflections from various types of surfaces throughout the globe including ice, deserts, forests, oceans, lakes, wetlands, etc. Our analysis will consider how the surface type manifests itself in the DDMs (e.g., coherence vs. non-coherence reflection) and derivable physical quantities. We will consider questions regarding footprint resolution, waveform rise time and corresponding bistatic range accuracy, and level of precision for altimetry (sea surface height) and scatterometry (significant wave height and sea surface wind). Tracks from TDS-1 that coincide with Jason-1 or 2 tracks will be analyzed, where the latter can be used as truth for comparison and validation. Where coincidences are found, vertical delay introduced by the media as measured by Jason will be mapped to bistatic propagation path to correct for neutral atmospheric and ionospheric delays.

  1. Operational reservoir inflow forecasting with radar altimetry: the Zambezi case study

    Science.gov (United States)

    Michailovsky, C. I.; Bauer-Gottwein, P.

    2014-03-01

    River basin management can greatly benefit from short-term river discharge predictions. In order to improve model produced discharge forecasts, data assimilation allows for the integration of current observations of the hydrological system to produce improved forecasts and reduce prediction uncertainty. Data assimilation is widely used in operational applications to update hydrological models with in situ discharge or level measurements. In areas where timely access to in situ data is not possible, remote sensing data products can be used in assimilation schemes. While river discharge itself cannot be measured from space, radar altimetry can track surface water level variations at crossing locations between the satellite ground track and the river system called virtual stations (VS). Use of radar altimetry versus traditional monitoring in operational settings is complicated by the low temporal resolution of the data (between 10 and 35 days revisit time at a VS depending on the satellite) as well as the fact that the location of the measurements is not necessarily at the point of interest. However, combining radar altimetry from multiple VS with hydrological models can help overcome these limitations. In this study, a rainfall runoff model of the Zambezi River basin is built using remote sensing data sets and used to drive a routing scheme coupled to a simple floodplain model. The extended Kalman filter is used to update the states in the routing model with data from 9 Envisat VS. Model fit was improved through assimilation with the Nash-Sutcliffe model efficiencies increasing from 0.19 to 0.62 and from 0.82 to 0.88 at the outlets of two distinct watersheds, the initial NSE (Nash-Sutcliffe efficiency) being low at one outlet due to large errors in the precipitation data set. However, model reliability was poor in one watershed with only 58 and 44% of observations falling in the 90% confidence bounds, for the open loop and assimilation runs respectively, pointing to

  2. Neural Network Based Lna Design for Mobile Satellite Receiver

    Directory of Open Access Journals (Sweden)

    Abhijeet Upadhya

    2014-08-01

    Full Text Available Paper presents a Neural Network Modelling approach to microwave LNA design. To acknowledge the specifications of the amplifier, Mobile Satellite Systems are analyzed. Scattering parameters of the LNA in the frequency range 0.5 to 18 GHz are calculated using a Multilayer Perceptron Artificial Neural Network model and corresponding smith charts and polar charts are plotted as output to the model. From these plots, the microwave scattering parameter description of the LNA are obtained. Model is efficiently trained using Agilent ATF 331M4 InGaAs/InP Low Noise pHEMT amplifier datasheet and the neural model’s output seem to follow the various device characteristic curves with high regression. Next, Maximum Allowable Gain and Noise figure of the device are modelled and plotted for the same frequency range. Finally, the optimized model is utilized as an interpolator and the resolution of the amplifying capability with noise characteristics are obtained for the L Band of MSS operation.

  3. Region of Interest Detection Based on Histogram Segmentation for Satellite Image

    Science.gov (United States)

    Kiadtikornthaweeyot, Warinthorn; Tatnall, Adrian R. L.

    2016-06-01

    High resolution satellite imaging is considered as the outstanding applicant to extract the Earth's surface information. Extraction of a feature of an image is very difficult due to having to find the appropriate image segmentation techniques and combine different methods to detect the Region of Interest (ROI) most effectively. This paper proposes techniques to classify objects in the satellite image by using image processing methods on high-resolution satellite images. The systems to identify the ROI focus on forests, urban and agriculture areas. The proposed system is based on histograms of the image to classify objects using thresholding. The thresholding is performed by considering the behaviour of the histogram mapping to a particular region in the satellite image. The proposed model is based on histogram segmentation and morphology techniques. There are five main steps supporting each other; Histogram classification, Histogram segmentation, Morphological dilation, Morphological fill image area and holes and ROI management. The methods to detect the ROI of the satellite images based on histogram classification have been studied, implemented and tested. The algorithm is be able to detect the area of forests, urban and agriculture separately. The image segmentation methods can detect the ROI and reduce the size of the original image by discarding the unnecessary parts.

  4. Japanese Global Precipitation Measurement (GPM) mission status and application of satellite-based global rainfall map

    Science.gov (United States)

    Kachi, Misako; Shimizu, Shuji; Kubota, Takuji; Yoshida, Naofumi; Oki, Riko; Kojima, Masahiro; Iguchi, Toshio; Nakamura, Kenji

    2010-05-01

    As accuracy of satellite precipitation estimates improves and observation frequency increases, application of those data to societal benefit areas, such as weather forecasts and flood predictions, is expected, in addition to research of precipitation climatology to analyze precipitation systems. There is, however, limitation on single satellite observation in coverage and frequency. Currently, the Global Precipitation Measurement (GPM) mission is scheduled under international collaboration to fulfill various user requirements that cannot be achieved by the single satellite, like the Tropical Rainfall Measurement Mission (TRMM). The GPM mission is an international mission to achieve high-accurate and high-frequent rainfall observation over a global area. GPM is composed of a TRMM-like non-sun-synchronous orbit satellite (GPM core satellite) and constellation of satellites carrying microwave radiometer instruments. The GPM core satellite carries the Dual-frequency Precipitation Radar (DPR), which is being developed by the Japan Aerospace Exploration Agency (JAXA) and the National Institute of Information and Communications Technology (NICT), and microwave radiometer provided by the National Aeronautics and Space Administration (NASA). Development of DPR instrument is in good progress for scheduled launch in 2013, and DPR Critical Design Review has completed in July - September 2009. Constellation satellites, which carry a microwave imager and/or sounder, are planned to be launched around 2013 by each partner agency for its own purpose, and will contribute to extending coverage and increasing frequency. JAXA's future mission, the Global Change Observation Mission (GCOM) - Water (GCOM-W) satellite will be one of constellation satellites. The first generation of GCOM-W satellite is scheduled to be launched in 2011, and it carries the Advanced Microwave Scanning Radiometer 2 (AMSR2), which is being developed based on the experience of the AMSR-E on EOS Aqua satellite

  5. Satellite-based assessment of yield variation and its determinants in smallholder African systems

    Science.gov (United States)

    Lobell, David B.

    2017-01-01

    The emergence of satellite sensors that can routinely observe millions of individual smallholder farms raises possibilities for monitoring and understanding agricultural productivity in many regions of the world. Here we demonstrate the potential to track smallholder maize yield variation in western Kenya, using a combination of 1-m Terra Bella imagery and intensive field sampling on thousands of fields over 2 y. We find that agreement between satellite-based and traditional field survey-based yield estimates depends significantly on the quality of the field-based measures, with agreement highest (R2 up to 0.4) when using precise field measures of plot area and when using larger fields for which rounding errors are smaller. We further show that satellite-based measures are able to detect positive yield responses to fertilizer and hybrid seed inputs and that the inferred responses are statistically indistinguishable from estimates based on survey-based yields. These results suggest that high-resolution satellite imagery can be used to make predictions of smallholder agricultural productivity that are roughly as accurate as the survey-based measures traditionally used in research and policy applications, and they indicate a substantial near-term potential to quickly generate useful datasets on productivity in smallholder systems, even with minimal or no field training data. Such datasets could rapidly accelerate learning about which interventions in smallholder systems have the most positive impact, thus enabling more rapid transformation of rural livelihoods. PMID:28202728

  6. PARTICLE SWARM OPTIMIZATION BASED ON PYRAMID MODEL FOR SATELLITE MODULE LAYOUT

    Institute of Scientific and Technical Information of China (English)

    Zhang Bao; Teng Hongfei

    2005-01-01

    To improve the global search ability of particle swarm optimization (PSO), a multi-population PSO based on pyramid model (PPSO) is presented. Then, it is applied to solve the layout optimization problems against the background of an international commercial communication satellite (INTELSAT-Ⅲ) module. Three improvements are developed, including multi-population search based on pyramid model, adaptive collision avoidance among particles, and mutation of degraded particles. In the numerical examples of the layout design of this simplified satellite module, the performance of PPSO is compared to global version PSO and local version PSO (ring and Neumann PSO). The results show that PPSO has higher computational accuracy, efficiency and success ratio.

  7. A MEMS-based Adaptive AHRS for Marine Satellite Tracking Antenna

    DEFF Research Database (Denmark)

    Wang, Yunlong; Hussain, Dil Muhammed Akbar; Soltani, Mohsen

    2015-01-01

    Satellite tracking is a challenging task for marine applications. An attitude determination system should estimate the wave disturbances on the ship body accurately. To achieve this, an Attitude Heading Reference System (AHRS) based on Micro-Electro-Mechanical Systems (MEMS) sensors, composed...... of three-axis gyroscope, accelerometer and magnetometer, is developed for Marine Satellite Tracking Antenna (MSTA). In this paper, the attitude determination algorithm is improved using an adaptive mechanism that tunes the attitude estimator parameters based on an estimation of ship motion frequency...

  8. Evaluation of satellite soil moisture products over Norway using ground-based observations

    Science.gov (United States)

    Griesfeller, A.; Lahoz, W. A.; Jeu, R. A. M. de; Dorigo, W.; Haugen, L. E.; Svendby, T. M.; Wagner, W.

    2016-03-01

    In this study we evaluate satellite soil moisture products from the advanced SCATterometer (ASCAT) and the Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E) over Norway using ground-based observations from the Norwegian water resources and energy directorate. The ASCAT data are produced using the change detection approach of Wagner et al. (1999), and the AMSR-E data are produced using the VUA-NASA algorithm (Owe et al., 2001, 2008). Although satellite and ground-based soil moisture data for Norway have been available for several years, hitherto, such an evaluation has not been performed. This is partly because satellite measurements of soil moisture over Norway are complicated owing to the presence of snow, ice, water bodies, orography, rocks, and a very high coastline-to-area ratio. This work extends the European areas over which satellite soil moisture is validated to the Nordic regions. Owing to the challenging conditions for soil moisture measurements over Norway, the work described in this paper provides a stringent test of the capabilities of satellite sensors to measure soil moisture remotely. We show that the satellite and in situ data agree well, with averaged correlation (R) values of 0.72 and 0.68 for ASCAT descending and ascending data vs in situ data, and 0.64 and 0.52 for AMSR-E descending and ascending data vs in situ data for the summer/autumn season (1 June-15 October), over a period of 3 years (2009-2011). This level of agreement indicates that, generally, the ASCAT and AMSR-E soil moisture products over Norway have high quality, and would be useful for various applications, including land surface monitoring, weather forecasting, hydrological modelling, and climate studies. The increasing emphasis on coupled approaches to study the earth system, including the interactions between the land surface and the atmosphere, will benefit from the availability of validated and improved soil moisture satellite datasets, including those

  9. An ASIFT-Based Local Registration Method for Satellite Imagery

    Directory of Open Access Journals (Sweden)

    Xiangjun Wang

    2015-05-01

    Full Text Available Imagery registration is a fundamental step, which greatly affects later processes in image mosaic, multi-spectral image fusion, digital surface modelling, etc., where the final solution needs blending of pixel information from more than one images. It is highly desired to find a way to identify registration regions among input stereo image pairs with high accuracy, particularly in remote sensing applications in which ground control points (GCPs are not always available, such as in selecting a landing zone on an outer space planet. In this paper, a framework for localization in image registration is developed. It strengthened the local registration accuracy from two aspects: less reprojection error and better feature point distribution. Affine scale-invariant feature transform (ASIFT was used for acquiring feature points and correspondences on the input images. Then, a homography matrix was estimated as the transformation model by an improved random sample consensus (IM-RANSAC algorithm. In order to identify a registration region with a better spatial distribution of feature points, the Euclidean distance between the feature points is applied (named the S criterion. Finally, the parameters of the homography matrix were optimized by the Levenberg–Marquardt (LM algorithm with selective feature points from the chosen registration region. In the experiment section, the Chang’E-2 satellite remote sensing imagery was used for evaluating the performance of the proposed method. The experiment result demonstrates that the proposed method can automatically locate a specific region with high registration accuracy between input images by achieving lower root mean square error (RMSE and better distribution of feature points.

  10. Unmodelled magnetic contributions in satellite-based models

    Science.gov (United States)

    Tozzi, Roberta; Mandea, Mioara; De Michelis, Paola

    2016-06-01

    A complex system of electric currents flowing in the ionosphere and magnetosphere originates from the interaction of the solar wind and the Interplanetary Magnetic Field (IMF) with the Earth's magnetic field. These electric currents generate magnetic fields contributing themselves to those measured by both ground observatories and satellites. Here, low-resolution (1 Hz) magnetic vector data recorded between 1 March 2014 and 31 May 2015 by the recently launched Swarm constellation are considered. The core and crustal magnetic fields and part of that originating in the magnetosphere are removed from Swarm measurements using CHAOS-5 model. Low- and mid-latitude residuals of the geomagnetic field representing the ionospheric and the unmodelled magnetospheric contributions are investigated, in the Solar Magnetic frame, according to the polarity of IMF B y (azimuthal) and B z (north-south) components and to different geomagnetic activity levels. The proposed approach makes it possible to investigate the features of unmodelled contributions due to the external sources of the geomagnetic field. Results show, on one side, the existence of a relation between the analysed residuals and IMF components B y and B z , possibly due to the long distance effect of high-latitude field-aligned currents. On the other side, they suggest the presence of a contribution due to the partial ring current that is activated during the main phase of geomagnetic storms. The perturbation observed on residuals is also compatible with the effect of the net field-aligned currents. Moreover, we have quantitatively estimated the effect of these current systems on computed residuals.

  11. Variability and trends of surface solar radiation in Europe based on CM SAF satellite data records

    Science.gov (United States)

    Trentmann, Jörg; Pfeifroth, Uwe; Sanchez-Lorenzo, Arturo; Urbain, Manon; Clerbaux, Nicolas

    2017-04-01

    The EUMETSAT Satellite Application Facility on Climate Monitoring (CM SAF) generates satellite-based high-quality climate data records, with a focus on the global energy and water cycle. Here, the latest releases of the CM SAF's data records of surface solar radiation, Surface Solar Radiation Data Set - Heliosat (SARAH), and CM SAF cLouds, Albedo and Radiation dataset from AVHRR data (CLARA), are analyzed and validated with reference to ground-based measurements, e.g., provided by the Baseline Surface Radiation Network (BSRN), the World Radiation Data Center (WRDC) and the Global Energy Balance Archive (GEBA). Focus is given to the trends and the variability of the surface irradiance in Europe as derived from the surface and the satellite-based data records. Both data sources show an overall increase (i.e., brightening) after the 1980s, and indicate substantial decadal variability with periods of reduced increase (or even a decrease) and periods with a comparable high increase. Also the increase shows a pronounced spatial pattern, which is also found to be consistent between the two data sources. The good correspondence between the satellite-based data records and the surface measurements highlight the potential of the satellite data to represent the variability and changes in the surface irradiance and document the dominant role of clouds over aerosol to explain its variations. Reasons for remaining differences between the satellite- and the surface-based data records (e.g., in Southern Europe) will be discussed. To test the consistency of the CM SAF solar radiation data records we also assess the decadal variability of the solar reflected radiation at the top-of-the atmosphere (TOA) from the CM SAF climate data record based on the MVIRI / SEVIRI measurements from 1983 to 2015. This data record complements the SARAH data record in its temporal and spatial coverage; fewer and different assumptions are used in the retrieval to generate the TOA reflected solar

  12. Developing an improved soil moisture dataset by blending passive and active microwave satellite-based retrievals

    Directory of Open Access Journals (Sweden)

    Y. Y. Liu

    2010-09-01

    Full Text Available Combining information derived from satellite-based passive and active microwave sensors has the potential to offer improved retrievals of surface soil moisture variations at global scales. Here we propose a technique to take advantage of retrieval characteristics of passive (AMSR-E and active (ASCAT microwave satellite estimates over sparse-to-moderately vegetated areas to obtain an improved soil moisture product. To do this, absolute soil moisture values from AMSR-E and relative soil moisture derived from ASCAT are rescaled against a reference land surface model date set using a cumulative distribution function (CDF matching approach. While this technique imposes the bias of the reference to the rescaled satellite products, it adjusts both satellite products to the same range and almost preserves the correlation between satellite products and in situ measurements. Comparisons with in situ data demonstrated that over the regions where the correlation coefficient between rescaled AMSR-E and ASCAT is above 0.65 (hereafter referred to as transitional regions, merging the different satellite products together increases the number of observations while minimally changing the accuracy of soil moisture retrievals. These transitional regions also delineate the boundary between sparsely and moderately vegetated regions where rescaled AMSR-E and ASCAT are respectively used in the merged product. Thus the merged product carries the advantages of better spatial coverage overall and increased number of observations particularly for the transitional regions. The combination approach developed in this study has the potential to be applied to existing microwave satellites as well as to new microwave missions. Accordingly, a long-term global soil moisture dataset can be developed and extended, enhancing basic understanding of the role of soil moisture in the water, energy and carbon cycles.

  13. Contribution de l'altimetrie satellitaire a l'etude de la variabilite du niveau d'eau du Delta interieur du fleuve Niger

    Science.gov (United States)

    Telly Diepkile, Adama

    Title: Contribution of satellite altimetry to the study of the spatial and temporal variability of water level in the Inner Delta of Niger River Content: The radar altimeter was originally developed to contribute to the study of ocean waters dynamics. The large size of oceans and their relative homogeneity favor the use of satellite altimetry. The success on the oceans led many researchers to investigate the use of satellite altimetry for the characterization of inland waters and land surfaces. Encouraging results have been reported by some studies on the hydrology of inland seas, lakes and rivers and floodplains. In this thesis, we evaluate the contribution of satellite altimetry in the analysis of changes in water level in the Inner Delta of Niger River in Mali, in West Africa. Classified among the sites of the Ramsar Convention on Wetlands, the Inner Delta plays a leading role for Mali and the whole sub-region, both on the socio-economic and environmental scales. The Delta is characterized by a flooding period, during which an area of over 20,000 km2 of land is flooded. The water withdraws completely during the recession. These dynamic flooding-recession conditions practically control all the human activities in the region and significantly influence the ecological processes. On the other hand, the Delta is becoming more and more fragile due to desertification, climate change and agricultural activities. A better characterization of water level variations and understanding the hydrological regime are of critical importance in the Delta. Satellite altimetry data considered in the study come from Topex/Poseidon (1992-2005) and Envisat (2002-2009). The data were corrected for environmental effects. In order to develop time series including data from both satellites, we analyzed their overlapping period (2002-2005). This analysis revealed a good correlation between the two sets of measurements (R2 = 0,76), and a systematic bias of about 89 cm. The Envisat

  14. Understanding satellite-based monthly-to-seasonal reservoir outflow estimation as a function of hydrologic controls

    Science.gov (United States)

    Bonnema, Matthew; Sikder, Safat; Miao, Yabin; Chen, Xiaodong; Hossain, Faisal; Ara Pervin, Ismat; Mahbubur Rahman, S. M.; Lee, Hyongki

    2016-05-01

    Growing population and increased demand for water is causing an increase in dam and reservoir construction in developing nations. When rivers cross international boundaries, the downstream stakeholders often have little knowledge of upstream reservoir operation practices. Satellite remote sensing in the form of radar altimetry and multisensor precipitation products can be used as a practical way to provide downstream stakeholders with the fundamentally elusive upstream information on reservoir outflow needed to make important and proactive water management decisions. This study uses a mass balance approach of three hydrologic controls to estimate reservoir outflow from satellite data at monthly and annual time scales: precipitation-induced inflow, evaporation, and reservoir storage change. Furthermore, this study explores the importance of each of these hydrologic controls to the accuracy of outflow estimation. The hydrologic controls found to be unimportant could potentially be neglected from similar future studies. Two reservoirs were examined in contrasting regions of the world, the Hungry Horse Reservoir in a mountainous region in northwest U.S. and the Kaptai Reservoir in a low-lying, forested region of Bangladesh. It was found that this mass balance method estimated the annual outflow of both reservoirs with reasonable skill. The estimation of monthly outflow from both reservoirs was however less accurate. The Kaptai basin exhibited a shift in basin behavior resulting in variable accuracy across the 9 year study period. Monthly outflow estimation from Hungry Horse Reservoir was compounded by snow accumulation and melt processes, reflected by relatively low accuracy in summer and fall, when snow processes control runoff. Furthermore, it was found that the important hydrologic controls for reservoir outflow estimation at the monthly time scale differs between the two reservoirs, with precipitation-induced inflow being the most important control for the Kaptai

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

    NARCIS (Netherlands)

    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 l

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

    DEFF Research Database (Denmark)

    Csatho, Beata M.; Schenk, Anton F.; van der Veen, Cornelis J.

    2014-01-01

    Significance We present the first detailed reconstruction of surface elevation changes of the Greenland Ice Sheet from NASA’s laser altimetry data. Time series at nearly 100,000 locations allow the characterization of ice sheet changes at scales ranging from individual outlet glaciers to larger d...

  17. Airborne laser altimetry survey of Glaciar Tyndall, Patagonia

    DEFF Research Database (Denmark)

    Keller, K.; Casassa, G.; Rivera, A.

    2007-01-01

    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 pol...

  18. Motivating Students to Develop Satellites in a Problem and Project-Based Learning Environment

    DEFF Research Database (Denmark)

    Larsen, Jesper Abildgaard; Nielsen, Jens Frederik Dalsgaard; Zhou, Chunfang

    2013-01-01

    During the last decade, a total of three student satellites have been developed by engineering students in a Problem and Project-Based Learning (PBL) environment at Aalborg University (AAU), Denmark. As solving such a complex project, we emphasize that a high level of motivation is needed...... satellite projects in a PBL environment. Empirically, a total of 12 student participants were interviewed. The results show that students’ motivation is highly stimulated by the project management with a series of factors, such as the task characteristics, support of peers, help of supervisors, and openness...

  19. Research of Multi-Agent System based satellite fault diagnosis technology

    Institute of Scientific and Technical Information of China (English)

    范显峰; 姜兴渭; 黄文虎; 谷吉海

    2002-01-01

    Following the theory of Multi-Agent System (MAS) and using series-wound structure and shunt-wound structure of Agents, the performance of Agent was improved to satisfy the need of satellite fault diagno-sis, and a tridimensional MAS model of satellite fault diagnosis was thus established for the MAS based planardiagnosis system, which decentralizes the whole diagnosing task into subtasks to be performed by different func-tional Agents to make the complicated fault diagnosis very simple and the diagnosis system more intelligent.This method improved the reliability and accuracy of diagnosis and made the maintenance and upgrading of thesatellite fault diagnosis system very easy as well.

  20. Evaluation of Clear Sky Models for Satellite-Based Irradiance Estimates

    Energy Technology Data Exchange (ETDEWEB)

    Sengupta, M.; Gotseff, P.

    2013-12-01

    This report describes an intercomparison of three popular broadband clear sky solar irradiance model results with measured data, as well as satellite-based model clear sky results compared to measured clear sky data. The authors conclude that one of the popular clear sky models (the Bird clear sky model developed by Richard Bird and Roland Hulstrom) could serve as a more accurate replacement for current satellite-model clear sky estimations. Additionally, the analysis of the model results with respect to model input parameters indicates that rather than climatological, annual, or monthly mean input data, higher-time-resolution input parameters improve the general clear sky model performance.

  1. Satellite-based empirical models linking river plume dynamics with hypoxic area andvolume

    Science.gov (United States)

    Satellite-based empirical models explaining hypoxic area and volume variation were developed for the seasonally hypoxic (O2 < 2 mg L−1) northern Gulf of Mexico adjacent to the Mississippi River. Annual variations in midsummer hypoxic area and ...

  2. Efficient GOCE satellite gravity field recovery based on least-squares using QR decomposition

    NARCIS (Netherlands)

    Baur, O.; Austen, G.; Kusche, J.

    2007-01-01

    We develop and apply an efficient strategy for Earth gravity field recovery from satellite gravity gradiometry data. Our approach is based upon the Paige-Saunders iterative least-squares method using QR decomposition (LSQR). We modify the original algorithm for space-geodetic applications: firstly,

  3. MISAT : Designing a Series of Powerful Small Satellites Based upon Micro Systems Technology

    NARCIS (Netherlands)

    Gill, E.; Monna, G.L.E.; Scherpen, J.M.A.; Verhoeven, C.J.M.

    2007-01-01

    MISAT is a research and development cluster which will create a small satellite platform based on Micro Systems Technology (MST) aiming at innovative space as well as terrestrial applications. MISAT is part of the Dutch MicroNed program which has established a microsystems infrastructure to fully

  4. MISAT : Designing a Series of Powerful Small Satellites Based upon Micro Systems Technology

    NARCIS (Netherlands)

    Gill, E.; Monna, G.L.E.; Scherpen, J.M.A.; Verhoeven, C.J.M.

    2007-01-01

    MISAT is a research and development cluster which will create a small satellite platform based on Micro Systems Technology (MST) aiming at innovative space as well as terrestrial applications. MISAT is part of the Dutch MicroNed program which has established a microsystems infrastructure to fully ex

  5. Autonomous Sub-Pixel Satellite Track Endpoint Determination for Space Based Images

    Energy Technology Data Exchange (ETDEWEB)

    Simms, L M

    2011-03-07

    An algorithm for determining satellite track endpoints with sub-pixel resolution in spaced-based images is presented. The algorithm allows for significant curvature in the imaged track due to rotation of the spacecraft capturing the image. The motivation behind the subpixel endpoint determination is first presented, followed by a description of the methodology used. Results from running the algorithm on real ground-based and simulated spaced-based images are shown to highlight its effectiveness.

  6. THE SATELLITE STRUCTURE TOPOLOGY OPTIMIZATION BASED ON HOMOGENIZATION METHOD AND ITS SIZE SENSITIVITY ANALYSIS

    Institute of Scientific and Technical Information of China (English)

    ChenChangya; PanJin; WangDeyu

    2005-01-01

    With the development of satellite structure technology, more and more design parameters will affect its structural performance. It is desirable to obtain an optimal structure design with a minimum weight, including optimal configuration and sizes. The present paper aims to describe an optimization analysis for a satellite structure, including topology optimization and size optimization. Based on the homogenization method, the topology optimization is carried out for the main supporting frame of service module under given constraints and load conditions, and then the sensitivity analysis is made of 15 structural size parameters of the whole satellite and the optimal sizes are obtained. The numerical result shows that the present optimization design method is very effective.

  7. Protocol Support for a New Satellite-Based Airspace Communication Network

    Science.gov (United States)

    Shang, Yadong; Hadjitheodosiou, Michael; Baras, John

    2004-01-01

    We recommend suitable transport protocols for an aeronautical network supporting Internet and data services via satellite. We study the characteristics of an aeronautical satellite hybrid network and focus on the problems that cause dramatically degraded performance of the Transport Protocol. We discuss various extensions to standard TCP that alleviate some of these performance problems. Through simulation, we identify those TCP implementations that can be expected to perform well. Based on the observation that it is difficult for an end-to-end solution to solve these problems effectively, we propose a new TCP-splitting protocol, termed Aeronautical Transport Control Protocol (AeroTCP). The main idea of this protocol is to use a fixed window for flow control and one duplicated acknowledgement (ACK) for fast recovery. Our simulation results show that AeroTCP can maintain higher utilization for the satellite link than end-to-end TCP, especially in high BER environment.

  8. Satellites vs. fiber optics based networks and services - Road map to strategic planning

    Science.gov (United States)

    Marandi, James H. R.

    An overview of a generic telecommunications network and its components is presented, and the current developments in satellite and fiber optics technologies are discussed with an eye on the trends in industry. A baseline model is proposed, and a cost comparison of fiber- vs satellite-based networks is made. A step-by-step 'road map' to the successful strategic planning of telecommunications services and facilities is presented. This road map provides for optimization of the current and future networks and services through effective utilization of both satellites and fiber optics. The road map is then applied to different segments of the telecommunications industry and market place, to show its effectiveness for the strategic planning of executives of three types: (1) those heading telecommunications manufacturing concerns, (2) those leading communication service companies, and (3) managers of telecommunication/MIS departments of major corporations. Future networking issues, such as developments in integrated-services digital network standards and technologies, are addressed.

  9. Deep Learning-Based Large-Scale Automatic Satellite Crosswalk Classification

    Science.gov (United States)

    Berriel, Rodrigo F.; Lopes, Andre Teixeira; de Souza, Alberto F.; Oliveira-Santos, Thiago

    2017-09-01

    High-resolution satellite imagery have been increasingly used on remote sensing classification problems. One of the main factors is the availability of this kind of data. Even though, very little effort has been placed on the zebra crossing classification problem. In this letter, crowdsourcing systems are exploited in order to enable the automatic acquisition and annotation of a large-scale satellite imagery database for crosswalks related tasks. Then, this dataset is used to train deep-learning-based models in order to accurately classify satellite images that contains or not zebra crossings. A novel dataset with more than 240,000 images from 3 continents, 9 countries and more than 20 cities was used in the experiments. Experimental results showed that freely available crowdsourcing data can be used to accurately (97.11%) train robust models to perform crosswalk classification on a global scale.

  10. Multi-Objective Reinforcement Learning for Cognitive Radio-Based Satellite Communications

    Science.gov (United States)

    Ferreira, Paulo Victor R.; Paffenroth, Randy; Wyglinski, Alexander M.; Hackett, Timothy M.; Bilen, Sven G.; Reinhart, Richard C.; Mortensen, Dale J.

    2016-01-01

    Previous research on cognitive radios has addressed the performance of various machine-learning and optimization techniques for decision making of terrestrial link properties. In this paper, we present our recent investigations with respect to reinforcement learning that potentially can be employed by future cognitive radios installed onboard satellite communications systems specifically tasked with radio resource management. This work analyzes the performance of learning, reasoning, and decision making while considering multiple objectives for time-varying communications channels, as well as different cross-layer requirements. Based on the urgent demand for increased bandwidth, which is being addressed by the next generation of high-throughput satellites, the performance of cognitive radio is assessed considering links between a geostationary satellite and a fixed ground station operating at Ka-band (26 GHz). Simulation results show multiple objective performance improvements of more than 3.5 times for clear sky conditions and 6.8 times for rain conditions.

  11. A Handover Strategy in the LEO Satellite-Based Constellation Networks with ISLs

    Institute of Scientific and Technical Information of China (English)

    LIU Gang; GOU Dingyong; WU Shiqi

    2003-01-01

    A new handover strategy named minimal-hops handover(MHH) strategy for the low earth orbit(LEO) satellite constellations networks equipped with inter-satellite links(ISLs) is proposed.MHH strategy, which is based on the hops of the end-to-end connection paths and makes good use of the regularity of the constellation network topology, can appropriately combine the handover procedure with routing and efficiently solve the inter-satellite handover issue. Moreover, MHH strategy can provide quality of services( QoS) guarantees to some extent. The system performances of the MHH strategy, such as time propagation delay and handover frequency, are evaluated and compared with that of other previous strategies. The simulation results show that MHH strategy performs better than other previous handover strategies.

  12. Satellite-based annual evaporation estimates of invasive alien plant ...

    African Journals Online (AJOL)

    2013-12-17

    Dec 17, 2013 ... Water (WFW) programme, have on total evaporation (ET) and the availability of water resources in two highly-invaded ... on water resources were based on the results from the paired catchment ...... Tourism, Pretoria. 85 pp.

  13. Developing an improved soil moisture dataset by blending passive and active microwave satellite-based retrievals

    Directory of Open Access Journals (Sweden)

    Y. Y. Liu

    2011-02-01

    Full Text Available Combining information derived from satellite-based passive and active microwave sensors has the potential to offer improved estimates of surface soil moisture at global scale. We develop and evaluate a methodology that takes advantage of the retrieval characteristics of passive (AMSR-E and active (ASCAT microwave satellite estimates to produce an improved soil moisture product. First, volumetric soil water content (m3 m−3 from AMSR-E and degree of saturation (% from ASCAT are rescaled against a reference land surface model data set using a cumulative distribution function matching approach. While this imposes any bias of the reference on the rescaled satellite products, it adjusts them to the same range and preserves the dynamics of original satellite-based products. Comparison with in situ measurements demonstrates that where the correlation coefficient between rescaled AMSR-E and ASCAT is greater than 0.65 ("transitional regions", merging the different satellite products increases the number of observations while minimally changing the accuracy of soil moisture retrievals. These transitional regions also delineate the boundary between sparsely and moderately vegetated regions where rescaled AMSR-E and ASCAT, respectively, are used for the merged product. Therefore the merged product carries the advantages of better spatial coverage overall and increased number of observations, particularly for the transitional regions. The combination method developed has the potential to be applied to existing microwave satellites as well as to new missions. Accordingly, a long-term global soil moisture dataset can be developed and extended, enhancing basic understanding of the role of soil moisture in the water, energy and carbon cycles.

  14. Validation of Sentinel-3A altimetry data by using in-situ multi-platform observations near Mallorca Island (western Mediterranean)

    Science.gov (United States)

    Sánchez-Román, Antonio; Heslop, Emma; Reeve, Krissy; Rodriguez, Daniel; Pujol, Isabelle; Faugère, Yannice; Torner, Marc; Tintoré, Joaquín; Pascual, Ananda

    2017-04-01

    In the frame of the Copernicus Marine Environment Monitoring Service (CMEMS) Sea Level Thematic Assembly Center (SL-TAC), a glider mission was undertaken between May and June 2016 along the same track as the overpass of the Sentinel 3A satellite in the Southern Mallorca region. Moreover, a one-day ship mission on May 30, synchronous with the overpass of the satellite, captured two transects of moving vessel ADCP close to the coastal area. The aim was to compare the along track altimeter products and multi-platform in-situ observations in the southern coastal zone of the Mallorca Island and the Algerian Basin. In addition, we explored the potential of the Synthetic Aperture Radar Mode (SARM) instrumentation of Sentinel-3 mission, which enables the satellite to measure nearest the coasts with both higher spatial resolution and higher precision than previous missions. With the ultimate goal of contributing to a more complete understanding of both ocean and coastal physical processes and the biogeochemical impacts. The analyses presented here are conducted through the comparison of Absolute Dynamic Topography (ADT) obtained from the Sentinel-3A altimetry measurements along ground-track #713 and Dynamic Height (DH) derived from temperature and salinity profiles measured by the glider along the trajectory followed by the satellite. Moreover, currents derived from altimetry and in-situ glider data along the track followed by the satellite; and from ADCP data collected in the coastal region are analysed. Results show a good agreement between ADT from altimetry and DH from glider data with maximum differences of around 2 cm that promote a root mean square error (RMSE) of 1 cm, the correlation coefficient between both datasets is 0.89. The satellite data closely resemble the geostrophic velocity pattern observed by the glider measurements along the Algerian Current, and also the ADCP data in the coastal zone, exhibiting a RMSE lower than 10 cm/s and a correlation coefficient

  15. Bias adjustment of satellite-based precipitation estimation using gauge observations: A case study in Chile

    Science.gov (United States)

    Yang, Zhongwen; Hsu, Kuolin; Sorooshian, Soroosh; Xu, Xinyi; Braithwaite, Dan; Verbist, Koen M. J.

    2016-04-01

    Satellite-based precipitation estimates (SPEs) are promising alternative precipitation data for climatic and hydrological applications, especially for regions where ground-based observations are limited. However, existing satellite-based rainfall estimations are subject to systematic biases. This study aims to adjust the biases in the Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Cloud Classification System (PERSIANN-CCS) rainfall data over Chile, using gauge observations as reference. A novel bias adjustment framework, termed QM-GW, is proposed based on the nonparametric quantile mapping approach and a Gaussian weighting interpolation scheme. The PERSIANN-CCS precipitation estimates (daily, 0.04°×0.04°) over Chile are adjusted for the period of 2009-2014. The historical data (satellite and gauge) for 2009-2013 are used to calibrate the methodology; nonparametric cumulative distribution functions of satellite and gauge observations are estimated at every 1°×1° box region. One year (2014) of gauge data was used for validation. The results show that the biases of the PERSIANN-CCS precipitation data are effectively reduced. The spatial patterns of adjusted satellite rainfall show high consistency to the gauge observations, with reduced root-mean-square errors and mean biases. The systematic biases of the PERSIANN-CCS precipitation time series, at both monthly and daily scales, are removed. The extended validation also verifies that the proposed approach can be applied to adjust SPEs into the future, without further need for ground-based measurements. This study serves as a valuable reference for the bias adjustment of existing SPEs using gauge observations worldwide.

  16. Evaluation of Satellite and Ground Based Precipitation Products for Flood Forecasting

    Science.gov (United States)

    Chintalapudi, S.; Sharif, H.; Yeggina, S.

    2012-04-01

    The development in satellite-derived rainfall estimates encouraged the hydrological modeling in sparse gauged basins or ungauged basins. Especially, physically-based distributed hydrological models can benefit from the good spatial and temporal coverage of satellite precipitation products. In this study, three satellite derived precipitation datasets (TRMM, CMORPH, and PERSIANN), NEXRAD, and rain gauge precipitation datasets were used to drive the hydrological model. The physically-based, distributed hydrological model Gridded Surface Subsurface Hydrological Analysis (GSSHA) was used in this study. Focus will be on the results from the Guadalupe River Basin above Canyon Lake and below Comfort, Texas. The Guadalupe River Basin above Canyon Lake and below Comfort Texas drains an area of 1232 km2. Different storm events will be used in these simulations. August 2007 event was used as calibration and June 2007 event was used as validation. Results are discussed interms of accuracy of satellite precipitation estimates with the ground based precipitation estimates, predicting peak discharges, runoff volumes, time lag, and spatial distribution. The initial results showed that, model was able to predict the peak discharges and runoff volumes when using NEXRAD MPE data, and TRMM 3B42 precipitation product. The results also showed that there was time lag in hydrographs driven by both PERSIANN and CMORPH data sets.

  17. Satellite-based estimation of rainfall erosivity for Africa

    NARCIS (Netherlands)

    Vrieling, A.; Sterk, G.; Jong, S.M. de

    2010-01-01

    Rainfall erosivity is a measure for the erosive force of rainfall. Rainfall kinetic energy determines the erosivity and is in turn greatly dependent on rainfall intensity. Attempts for its large-scale mapping are rare. Most are based on interpolation of erosivity values derived from rain gauge data.

  18. Linear and Nonlinear Relative Navigation Strategies for Small Satellite Formation Flying Based on Relative Position Measurement

    Science.gov (United States)

    Zhang, Xiaomin; Zheng, You

    Based on linear and nonlinear mathematical model of spacecraft formation flying and technology of relative position measurement of small satellites, the linear and nonlinear relative navigation strategies are developed in this paper. The dynamical characteristics of multi spacecraft formation flying have been researched in many references, including the authors' several International Astronautical Congress papers with numbers of IAF-98-A.2.06, IAA-99-IAA.11.1.09, IAA-01-IAA.11.4.08. Under conditions of short distance and short time, the linear model can describe relative orbit motion; otherwise, nonlinear model must be adopted. Furthermore the means of measurement and their error will influence relative navigation. Thus three kinds of relative navigation strategy are progressed. With consideration of difficulty in relative velocity measurement of small satellites, the three relative navigation strategies are proposed and only depend on sequential data of relative position through measuring the relative distance and relative orientation. The first kind of relative navigation strategy is based on linear model. The second relative navigation strategy is based on nonlinear model, with inclusion of the second order item. In fact the measurement error can not be avoided especially for small satellites, it is mainly considered in the third relative navigation strategy. This research is theoretical yet and a series of formulas of relative navigation are presented in this paper. Also the authors analyzed the three strategies qualitatively and quantitatively. According to results of simulation, the ranges of application are indicated and suggested in allusion to the three strategies of relative navigation. On the view of authors, the relative navigation strategies for small satellite formation flying based on relative position measurement are significant for engineering of small satellite formation flying.

  19. Detecting weather radar clutter using satellite-based nowcasting products

    DEFF Research Database (Denmark)

    Jensen, Thomas B.S.; Gill, Rashpal S.; Overgaard, Søren

    2006-01-01

    for the detecting and removal of clutter. Naturally, the improved spatio-temporal resolution of the Meteosat Second Generation sensors, coupled with its increased number of spectral bands, is expected to yield even better detection accuracies. Weather radar data from three C-band Doppler weather radars...... Application Facility' of EUMETSAT and is based on multispectral images from the SEVIRI sensor of the Meteosat-8 platform. Of special interest is the 'Precipitating Clouds' product, which uses the spectral information coupled with surface temperatures from Numerical Weather Predictions to assign probabilities...... by the resolution of the radar data. Subsequently, a supervised classifier was developed based on training data selected by a weather radar expert. Results of classification of data from several different meteorological events are shown. Cases of widespread sea clutter caused by anomalous propagation are especially...

  20. Spacetime effects on satellite-based quantum communications

    Science.gov (United States)

    Bruschi, David Edward; Ralph, Timothy C.; Fuentes, Ivette; Jennewein, Thomas; Razavi, Mohsen

    2014-08-01

    We investigate the consequences of space-time being curved on space-based quantum communication protocols. We analyze tasks that require either the exchange of single photons in a certain entanglement distribution protocol or beams of light in a continuous-variable quantum key distribution scheme. We find that gravity affects the propagation of photons, therefore adding additional noise to the channel for the transmission of information. The effects could be measured with current technology.

  1. Spacetime effects on satellite-based quantum communications

    CERN Document Server

    Bruschi, David Edward; Fuentes, Ivette; Jennewein, Thomas; Razavi, Mohsen

    2013-01-01

    We investigate the effects of space-time curvature on space-based quantum communication protocols. We analyze tasks that require either the exchange of single photons in a certain entanglement distribution protocol or beams of light in a continuous-variable quantum key distribution scheme. We find that gravity affects the propagation of photons, therefore acting as a noisy channel for the transmission of information. The effects can be measured with current technology.

  2. Implementing earth observation and advanced satellite based atmospheric sounders for water resource and climate modelling

    DEFF Research Database (Denmark)

    Boegh, E.; Dellwik, Ebba; Hahmann, Andrea N.;

    This paper discusses preliminary remote sensing (MODIS) based hydrological modelling results for the Danish island Sjælland (7330 km2) in relation to project objectives and methodologies of a new research project “Implementing Earth observation and advanced satellite based atmospheric sounders...... for effective land surface representation in water resource modeling” (2009- 2012). The purpose of the new research project is to develop remote sensing based model tools capable of quantifying the relative effects of site-specific land use change and climate variability at different spatial scales....... For this purpose, a) internal catchment processes will be studied using a Distributed Temperature Sensing (DTS) system, b) Earth observations will be used to upscale from field to regional scales, and c) at the largest scale, satellite based atmospheric sounders and meso-scale climate modelling will be used...

  3. Neural network-based recognition of whistlers on spectrograms detected by satellite

    Science.gov (United States)

    Conti, Livio

    2016-04-01

    We present a system to automatically recognize and classify the occurrence of whistler waves on spectrograms of electric field measurements performed by satellite. Whistlers - VLF waves generated by lightning, with a specific spectral dispersion relation - can induce precipitation of trapped Van Allen particles and have a role in the chemistry of some atmospheric components (mainly NOx). Moreover, it has also been suggested that the increase of the number of anomalous whistlers (i.e. whistlers with high value of dispersion constant) could be induced by disturbances in the Earth-ionosphere wave-guide, generated by seismo-electromagnetic emissions. On satellite, the recognition of whistlers asks for analyzing high-resolution spectrograms that cannot be downloaded to Earth, due to the limits of data transmission. For this reason, a real time identification and classification must be performed on satellite, by avoiding downloading all the unprocessed data. The procedure that we have developed is based on a Time Delay Neural Network (TDNN). The TDNN, proposed some years ago for speech recognition, can be fruitfully also applied in real-time analysis of electromagnetic spectrograms in order to detect phenomena characterized by a specific shape/signature such as those of the whistler waves. Some studies have been performed by the RNF experiment on board of the DEMETER satellite and our algorithm could be adopted on board of the satellite CSES (China Seismo-Electromagnetic Satellite), launch scheduled by the end of 2016. Moreover, the procedure can be also adopted to automatic analysis of whistlers detected on ground.

  4. Comparison of NO2 vertical profiles from satellite and ground based measurements over Antarctica

    OpenAIRE

    Kulkarni, Pavan; Bortoli, Daniele; Costa, Maria João; Silva, Ana Maria; Ravegnani, Fabrizio; Giovanelli, Giorgio

    2011-01-01

    The Intercomparison of nitrogen dioxide (NO2) vertical profiles, derived from the satellite based HALogen Occultation Experiment (HALOE) measurements and from the ground based UV-VIS spectrometer GASCOD (Gas Analyzer Spectrometer Correlating Optical Differences) observations at the Mario Zucchelli Station (MZS), in Antarctica, are done for the first time. It is shown here that both datasets are in good agreement showing the same features in terms of magnitude, profile structure, a...

  5. A Satellite-Based Multi-Pollutant Index of Global Air Quality

    Science.gov (United States)

    Cooper, Mathew J.; Martin, Randall V.; vanDonkelaar, Aaron; Lamsal, Lok; Brauer, Michael; Brook, Jeffrey R.

    2012-01-01

    Air pollution is a major health hazard that is responsible formillions of annual excess deaths worldwide. Simpleindicators are useful for comparative studies and to asses strends over time. The development of global indicators hasbeen impeded by the lack of ground-based observations in vast regions of the world. Recognition is growing of the need for amultipollutant approach to air quality to better represent human exposure. Here we introduce the prospect of amultipollutant air quality indicator based on observations from satellite remote sensing.

  6. Heavy precipitation retrieval from combined satellite observations and ground-based lightning measurements

    Science.gov (United States)

    Mugnai, A.; Dietrich, S.; Casella, D.; di Paola, F.; Formenton, M.; Sanò, P.

    2010-09-01

    We have developed a series of algorithms for the retrieval of precipitation (especially, heavy precipitation) over the Mediterranean area using satellite observations from the available microwave (MW) radiometers onboard low Earth orbit (LEO) satellites and from the visible-infrared (VIS-IR) SEVIRI radiometer onboard the European geosynchronous (GEO) satellite Meteosat Second Generation (MSG), in conjunction with lightning data from ground-based networks - such as ZEUS and LINET. These are: • A new approach for precipitation retrieval from space (which we call the Cloud Dynamics and Radiation Database approach, CDRD) that incorporates lightning and environmental/dynamical information in addition to the upwelling microwave brightness temperatures (TB’s) so as to reduce the retrieval uncertainty and improve the retrieval performance; • A new combined MW-IR technique for producing frequent precipitation retrievals from space (which we call PM-GCD technique), that uses passive-microwave (PM) retrievals in conjunction with lightning information and the Global Convection Detection (GCD) technique to discriminate deep convective clouds within the GEO observations; • A new morphing approach (which we call the Lightning-based Precipitation Evolving Technique, L-PET) that uses the available lightning measurements for propagating the rainfall estimates from satellite-borne MW radiometers to a much higher time resolution than the MW observations. We will present and discuss our combined MW/IR/lightning precipitation algorithms and analyses with special reference to some case studies over the western Mediterranean.

  7. Planetary gearbox condition monitoring of ship-based satellite communication antennas using ensemble multiwavelet analysis method

    Science.gov (United States)

    Chen, Jinglong; Zhang, Chunlin; Zhang, Xiaoyan; Zi, Yanyang; He, Shuilong; Yang, Zhe

    2015-03-01

    Satellite communication antennas are key devices of a measurement ship to support voice, data, fax and video integration services. Condition monitoring of mechanical equipment from the vibration measurement data is significant for guaranteeing safe operation and avoiding the unscheduled breakdown. So, condition monitoring system for ship-based satellite communication antennas is designed and developed. Planetary gearboxes play an important role in the transmission train of satellite communication antenna. However, condition monitoring of planetary gearbox still faces challenges due to complexity and weak condition feature. This paper provides a possibility for planetary gearbox condition monitoring by proposing ensemble a multiwavelet analysis method. Benefit from the property on multi-resolution analysis and the multiple wavelet basis functions, multiwavelet has the advantage over characterizing the non-stationary signal. In order to realize the accurate detection of the condition feature and multi-resolution analysis in the whole frequency band, adaptive multiwavelet basis function is constructed via increasing multiplicity and then vibration signal is processed by the ensemble multiwavelet transform. Finally, normalized ensemble multiwavelet transform information entropy is computed to describe the condition of planetary gearbox. The effectiveness of proposed method is first validated through condition monitoring of experimental planetary gearbox. Then this method is used for planetary gearbox condition monitoring of ship-based satellite communication antennas and the results support its feasibility.

  8. Satellite image blind restoration based on surface fitting and multivariate model

    Institute of Scientific and Technical Information of China (English)

    CHEN Xin-bing; YANG Shi-zhi; WANG Xian-hua; QIAO Yan-li

    2009-01-01

    Owing to the blurring effect from atmosphere and camera system in the satellite imaging a blind image restoration algo-rithm is proposed which includes the modulation transfer function (MTF) estimation and the image restoration. In the MTF estimation stage, based on every degradation process of satellite imaging-chain, a combined parametric model of MTF is given and used to fit the surface of normalized logarithmic amplitude spectrum of degraded image. In the image restoration stage, a maximum a posteriori (MAP) based edge-preserving image restoration method is presented which introduces multivariate Laplacian model to characterize the prior distribution of wavelet coefficients of original image. During the image restoration, in order to avoid solving high nonlinear equations, optimization transfer algorithm is adopted to decom-pose the image restoration procedure into two simple steps: Landweber iteration and wavelet thresholding denoising. In the numerical experiment, the satellite image restoration results from SPOT-5 and high resolution camera (HR) of China & Brazil earth resource satellite (CBERS-02B) ane compared, and the proposed algorithm is superior in the image edge preservation and noise inhibition.

  9. A MODIS-Based Robust Satellite Technique (RST for Timely Detection of Oil Spilled Areas

    Directory of Open Access Journals (Sweden)

    Teodosio Lacava

    2017-02-01

    Full Text Available Natural crude-oil seepages, together with the oil released into seawater as a consequence of oil exploration/production/transportation activities, and operational discharges from tankers (i.e., oil dumped during cleaning actions represent the main sources of sea oil pollution. Satellite remote sensing can be a useful tool for the management of such types of marine hazards, namely oil spills, mainly owing to the synoptic view and the good trade-off between spatial and temporal resolution, depending on the specific platform/sensor system used. In this paper, an innovative satellite-based technique for oil spill detection, based on the general robust satellite technique (RST approach, is presented. It exploits the multi-temporal analysis of data acquired in the visible channels of the Moderate Resolution Imaging Spectroradiometer (MODIS on board the Aqua satellite in order to automatically and quickly detect the presence of oil spills on the sea surface, with an attempt to minimize “false detections” caused by spurious effects associated with, for instance, cloud edges, sun/satellite geometries, sea currents, etc. The oil spill event that occurred in June 2007 off the south coast of Cyprus in the Mediterranean Sea has been considered as a test case. The resulting data, the reliability of which has been evaluated by both carrying out a confutation analysis and comparing them with those provided by the application of another independent MODIS-based method, showcase the potential of RST in identifying the presence of oil with a high level of accuracy.

  10. Improvement of Global and Regional Mean Sea Level Trends Derived from all Altimetry Missions.

    Science.gov (United States)

    Ablain, Michael; Benveniste, Jérôme; Faugere, Yannice; Larnicol, Gilles; Cazenave, Anny; Johannessen, Johnny A.; Stammer, Detlef; Timms, Gary

    2012-07-01

    The global mean sea level (GMSL) has been calculated on a continual basis since January 1993 using data from satellite altimetry missions. The global mean sea level (MSL) deduced from TOPEX/Poseidon, Jason-1 and Jason-2 is increasing with a global trend of 3.2 mm from 1993 to 2010 applying the post glacial rebound (MSL Aviso website http://www.jason.oceanobs.com/msl). Besides, the regional sea level trends bring out an inhomogeneous repartition of the ocean elevation with local MSL slopes ranging from +/- 8 mm/year. A study published in 2009 [Ablain et al., 2009] has shown that the global MSL trend uncertainty was estimated at +/-0.6 mm/year with a confidence interval of 90%. The main sources of errors at global and regional scales are due to the orbit calculation and the wet troposphere correction. But others sea-level components have also a significant impact on the long-term stability of MSL as for instance the stability of instrumental parameters and the atmospheric corrections. Thanks to recent studies performed in Sea Level Essential Climate Variable Project in the frame of the Climate Change Initiative, an ESA Programme, in addition to activities performed within the SALP/CNES, strong improvements have been provided for the estimation of the global and regional MSL trends. In this paper, we propose to describe them; they concern the orbit calculation thanks to new gravity fields, the atmospheric corrections thanks to ERA-interim reanalyses, the wet troposphere corrections thanks to the stability improvement, and also empirical corrections allowing us to link regional time series together better. These improvements are described at global and regional scale for all the altimetry missions.

  11. Validation of Sea levels from coastal altimetry waveform retracking expert system: a case study around the Prince William Sound in Alaska

    Science.gov (United States)

    Idris, N. H.; Deng, X.; Idris, N. H.

    2017-05-01

    This paper presents the validation of Coastal Altimetry Waveform Retracking Expert System (CAWRES), a novel method to optimize the Jason satellite altimetric sea levels from multiple retracking solutions. The validation is conducted over the region of Prince William Sound in Alaska, USA, where altimetric waveforms are perturbed by emerged land and sea states. Validation is performed in twofold. First, comparison with existing retrackers (i.e. MLE4 and Ice) from the Sensor Geophysical Data Records (SGDR), and second, comparison with in-situ tide gauge data. From the first validation assessment, in general, CAWRES outperforms the MLE4 and Ice retrackers. In 4 out of 6 cases, the value of improvement percentage (standard deviation of difference) is higher (lower) than those of the SGDR retrackers. CAWRES also presents the best performance in producing valid observations, and has the lowest noise when compared to the SGDR retrackers. From the second assessment with tide gauge, CAWRES retracked sea level anomalies (SLAs) are consistent with those of the tide gauge. The accuracy of CAWRES retracked SLAs is slightly better than those of the MLE4. However, the performance of Ice retracker is better than those of CAWRES and MLE4, suggesting the empirical-based retracker is more effective. The results demonstrate that the CAWRES would have potential to be applied to coastal regions elsewhere.

  12. Volcview: A Web-Based Platform for Satellite Monitoring of Volcanic Activity and Eruption Response

    Science.gov (United States)

    Schneider, D. J.; Randall, M.; Parker, T.

    2014-12-01

    The U.S. Geological Survey (USGS), in cooperation with University and State partners, operates five volcano observatories that employ specialized software packages and computer systems to process and display real-time data coming from in-situ geophysical sensors and from near-real-time satellite sources. However, access to these systems both inside and from outside the observatory offices are limited in some cases by factors such as software cost, network security, and bandwidth. Thus, a variety of Internet-based tools have been developed by the USGS Volcano Science Center to: 1) Improve accessibility to data sources for staff scientists across volcano monitoring disciplines; 2) Allow access for observatory partners and for after-hours, on-call duty scientists; 3) Provide situational awareness for emergency managers and the general public. Herein we describe VolcView (volcview.wr.usgs.gov), a freely available, web-based platform for display and analysis of near-real-time satellite data. Initial geographic coverage is of the volcanoes in Alaska, the Russian Far East, and the Commonwealth of the Northern Mariana Islands. Coverage of other volcanoes in the United States will be added in the future. Near-real-time satellite data from NOAA, NASA and JMA satellite systems are processed to create image products for detection of elevated surface temperatures and volcanic ash and SO2 clouds. VolcView uses HTML5 and the canvas element to provide image overlays (volcano location and alert status, annotation, and location information) and image products that can be queried to provide data values, location and measurement capabilities. Use over the past year during the eruptions of Pavlof, Veniaminof, and Cleveland volcanoes in Alaska by the Alaska Volcano Observatory, the National Weather Service, and the U.S. Air Force has reinforced the utility of shared situational awareness and has guided further development. These include overlay of volcanic cloud trajectory and

  13. Satellite-based RAR performance simulation for measuring directional ocean wave spectrum based on SAR inversion spectrum

    Institute of Scientific and Technical Information of China (English)

    REN Lin; MAO Zhihua; HUANG Haiqing; GONG Fang

    2010-01-01

    Some missions have been carried out to measure wave directional spectrum by synthetic aperture radar (SAR) and airborne real aperture radar (RAR) at a low incidence. Both them have their own advantages and limitations. Scientists hope that SAR and satellite-based RAR can complement each other for the research on wave properties in the future. For this study, the authors aim to simulate the satellite-based RAR system to validate performance for measuring the directional wave spectrum. The principal measurements are introduced and the simulation methods based on the one developed by Hauser are adopted and slightly modified. To enhance the authenticity of input spectrum and the wave spectrum measuring consistency for SAR and satellite-based RAR, the wave height spectrum inversed from Envisat ASAR data by cross spectrum technology is used as the input spectrum of the simulation system. In the process of simulation, the sea surface, backscattering signal, modulation spectrum and the estimated wave height spectrum are simulated in each look direction. Directional wave spectrum are measured based on the simulated observations from 0° to 360~. From the estimated wave spectrum, it has an 180° ambiguity like SAR, but it has no special high wave number cut off in all the direction. Finally, the estimated spectrum is compared with the input one in terms of the dominant wave wavelength, direction and SWH and the results are promising. The simulation shows that satellite-based RAR should be capable of measuring the directional wave properties. Moreover, it indicates satellite-based RAR basically can measure waves that SAR can measure.

  14. Multiangle Bistatic SAR Imaging and Fusion Based on BeiDou-2 Navigation Satellite System

    Directory of Open Access Journals (Sweden)

    Zeng Tao

    2015-01-01

    Full Text Available Bistatic Synthetic Aperture Radar (BSAR based on the Global Navigation Service System (GNSSBSAR uses navigation satellites as radar transmitters, which are low in cost. However, GNSS-BSAR images have poor resolution and low Signal-to-Noise Ratios (SNR. In this paper, a multiangle observation and data processing strategy are presented based on BeiDou-2 navigation satellite imagery, from which twenty-six BSAR images in different configurations are obtained. A region-based fusion algorithm using region of interest segmentation is proposed, and a high-quality fusion image is obtained. The results reveal that the multiangle imaging method can extend the applications of GNSS-BSAR.

  15. BeiDou satellite's differential code biases estimation based on uncombined precise point positioning with triple-frequency observable

    Science.gov (United States)

    Fan, Lei; Li, Min; Wang, Cheng; Shi, Chuang

    2017-02-01

    The differential code bias (DCB) of BeiDou satellite is an important topic to make better use of BeiDou system (BDS) for many practical applications. This paper proposes a new method to estimate the BDS satellite DCBs based on triple-frequency uncombined precise point positioning (UPPP). A general model of both triple-frequency UPPP and Geometry-Free linear combination of Phase-Smoothed Range (GFPSR) is presented, in which, the ionospheric observable and the combination of triple-frequency satellite and receiver DCBs (TF-SRDCBs) are derived. Then the satellite and receiver DCBs (SRDCBs) are estimated together with the ionospheric delay that is modeled at each individual station in a weighted least-squares estimator, and the satellite DCBs are determined by introducing the zero-mean condition of all available BDS satellites. To validate the new method, 90 day's real tracking GNSS data (from January to March in 2014) collected from 9 Multi-GNSS Experiment (MGEX) stations (equipped with Trimble NETR9 receiver) is used, and the BDS satellite DCB products from German Aerospace Center (DLR) are taken as reference values for comparison. Results show that the proposed method is able to precisely estimate BDS satellite DCBs: (1) the mean value of the day-to-day scattering for all available BDS satellites is about 0.24 ns, which is reduced in average by 23% when compared with the results derived by only GFPSR. Moreover, the mean value of the day-to-day scattering of IGSO satellites is lower than that of GEO and MEO satellites; (2) the mean value of RMS of the difference with respect to DLR DCB products is about 0.39 ns, which is improved by an average of 11% when compared with the results derived by only GFPSR. Besides, the RMS of IGSO and MEO satellites is at the same level which is better than that of GEO satellites.

  16. Formulation of geopotential difference determination using optical-atomic clocks onboard satellites and on ground based on Doppler cancellation system

    Science.gov (United States)

    Shen, Ziyu; Shen, Wen-Bin; Zhang, Shuangxi

    2016-08-01

    In this study, we propose an approach for determining the geopotential difference using high-frequency-stability microwave links between satellite and ground station based on Doppler cancellation system. Suppose a satellite and a ground station are equipped with precise optical-atomic clocks (OACs) and oscillators. The ground oscillator emits a signal with frequency fa towards the satellite and the satellite receiver (connected with the satellite oscillator) receives this signal with frequency fb which contains the gravitational frequency shift effect and other signals and noises. After receiving this signal, the satellite oscillator transmits and emits, respectively, two signals with frequencies fb and fc towards the ground station. Via Doppler cancellation technique, the geopotential difference between the satellite and the ground station can be determined based on gravitational frequency shift equation by a combination of these three frequencies. For arbitrary two stations on ground, based on similar procedures as described above, we may determine the geopotential difference between these two stations via a satellite. Our analysis shows that the accuracy can reach 1 m2 s- 2 based on the clocks' inaccuracy of about 10-17 (s s-1) level. Since OACs with instability around 10-18 in several hours and inaccuracy around 10-18 level have been generated in laboratory, the proposed approach may have prospective applications in geoscience, and especially, based on this approach a unified world height system could be realized with one-centimetre level accuracy in the near future.

  17. Integration between terrestrial-based and satellite-based land mobile communications systems

    Science.gov (United States)

    Arcidiancono, Antonio

    A survey is given of several approaches to improving the performance and marketability of mobile satellite systems (MSS). The provision of voice/data services in the future regional European Land Mobile Satellite System (LMSS), network integration between the Digital Cellular Mobile System (GSM) and LMSS, the identification of critical areas for the implementation of integrated GSM/LMSS areas, space segment scenarios, LMSS for digital trunked private mobile radio (PMR) services, and code division multiple access (CDMA) techniques for a terrestrial/satellite system are covered.

  18. Integration between terrestrial-based and satellite-based land mobile communications systems

    Science.gov (United States)

    Arcidiancono, Antonio

    1990-01-01

    A survey is given of several approaches to improving the performance and marketability of mobile satellite systems (MSS). The provision of voice/data services in the future regional European Land Mobile Satellite System (LMSS), network integration between the Digital Cellular Mobile System (GSM) and LMSS, the identification of critical areas for the implementation of integrated GSM/LMSS areas, space segment scenarios, LMSS for digital trunked private mobile radio (PMR) services, and code division multiple access (CDMA) techniques for a terrestrial/satellite system are covered.

  19. Multivariate Regression Approach To Integrate Multiple Satellite And Tide Gauge Data For Real Time Sea Level Prediction

    DEFF Research Database (Denmark)

    Cheng, Yongcun; Andersen, Ole Baltazar; Knudsen, Per

    2010-01-01

    The Sea Level Thematic Assembly Center in the EUFP7 MyOcean project aims at build a sea level service for multiple satellite sea level observations at a European level for GMES marine applications. It aims to improve the sea level related products to guarantee the sustainability and the quality o...... stations with satellite altimetry....

  20. Satellite-based phenology detection in broadleaf forests in South-Western Germany

    Science.gov (United States)

    Misra, Gourav; Buras, Allan; Menzel, Annette

    2016-04-01

    Many techniques exist for extracting phenological information from time series of satellite data. However, there have been only a few successful attempts to temporarily match satellite-derived observations with ground based phenological observations (Fisher et al., 2006; Hamunyela et al., 2013; Galiano et al., 2015). Such studies are primarily plagued with problems relating to shorter time series of satellite data including spatial and temporal resolution issues. A great challenge is to correlate spatially continuous and pixel-based satellite information with spatially discontinuous and point-based, mostly species-specific, ground observations of phenology. Moreover, the minute differences in phenology observed by ground volunteers might not be sufficient to produce changes in satellite-measured reflectance of vegetation, which also exposes the difference in the definitions of phenology (Badeck et al., 2004; White et al., 2014). In this study Start of Season (SOS) was determined for broadleaf forests at a site in south-western Germany using MODIS-sensor time series of Normalised Difference Vegetation Index (NDVI) data for the years covering 2001 to 2013. The NDVI time series raster data was masked for broadleaf forests using Corine Land Cover dataset, filtered and corrected for snow and cloud contaminations, smoothed with a Gaussian filter and interpolated to daily values. Several SOS techniques cited in literature, namely thresholds of amplitudes (20%, 50%, 60% and 75%), rates of change (1st, 2nd and 3rd derivative) and delayed moving average (DMA) were tested for determination of satellite SOS. The different satellite SOS were then compared with a species-rich ground based phenology information (e.g. understory leaf unfolding, broad leaf unfolding and greening of evergreen tree species). Working with all the pixels at a finer resolution, it is seen that the temporal trends in understory and broad leaf species are well captured. Initial analyses show promising

  1. Developing a sustainable satellite-based environmental monitoring system In Nigeria

    Science.gov (United States)

    Akinyede, J. O.; Adepoju, K. A.; Akinluyi, F. O.; Anifowose, A. Y. B.

    2015-10-01

    Increased anthropogenic activities over the year have remained a major factor of the Earth changing environment. This phenomenon has given rise to a number of environmental degraded sites that characterize the Nigeria's landscape. The human-induced elements include gully erosion, mangrove ecosystems degradation, desertification and deforestation, particularly in the south east, Niger Delta, north east and south west of Nigeria respectively, as well as river flooding/flood plain inundation and land degradation around Kainji lake area. Because of little or no effective management measures, the attendant environmental hazards have been extremely damaging to the infrastructures and socio-economic development of the affected area. Hence, a concerted effort, through integrated and space-based research, is being intensified to manage and monitor the environment in order to restore the stability, goods and services of the environment. This has justified Nigeria's investment in its space programme, especially the launch of NigeriaSat-1, an Earth observation micro-satellite in constellation with five (5) other similar satellites, Alsat-1, China DMC, Bilsat-1, DEMOS and UK DMC belonging to Algeria, China, Turkey, Spain and United Kingdom respectively. The use of data from these satellites, particularly NigeriaSat-1, in conjunction with associated technologies has proved to be very useful in understanding the influence of both natural and human activities on the Nigeria's ecosystems and environment. The results of some researches on specific applications of Nigerian satellites are presented in this paper. Appropriate sustainable land and water resources management in the affected areas, based on Nigeria's satellite data capture and integration, are also discussed.

  2. DroughtView: Satellite Based Drought Monitoring and Assessment

    Science.gov (United States)

    Hartfield, K. A.; Van Leeuwen, W. J. D.; Crimmins, M.; Marsh, S. E.; Torrey, Y.; Rahr, M.; Orr, B. J.

    2014-12-01

    Drought is an ever growing concern within the United States and Mexico. Extended periods of below-average precipitation can adversely affect agricultural production and ecosystems, impact local water resources and create conditions prime for wildfire. DroughtView (www.droughtview.arizona.edu) is a new on-line resource for scientists, natural resource managers, and the public that brings a new perspective to remote-sensing based drought impact assessment that is not currently available. DroughtView allows users to monitor the impact of drought on vegetation cover for the entire continental United States and the northern regions of Mexico. As a spatially and temporally dynamic geospatial decision support tool, DroughtView is an excellent educational introduction to the relationship between remotely sensed vegetation condition and drought. The system serves up Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI) data generated from 250 meter 16-day composite Moderate-resolution Imaging Spectroradiometer (MODIS) imagery from 2000 to the present. Calculation of difference from average, previous period and previous year greenness products provide the user with a proxy for drought conditions and insight on the secondary impacts of drought, such as wildfire. The various image products and overlays are served up via the ArcGIS Server platform. DroughtView serves as a useful tool to introduce and teach vegetation time series analysis to those unfamiliar with the science. High spatial resolution imagery is available as a reference layer to locate points of interest, zoom in and export images for implementation in reports and presentations. Animation of vegetation time series allows users to examine ecosystem disturbances and climate data is also available to examine the relationship between precipitation, temperature and vegetation. The tool is mobile friendly allowing users to access the system while in the field. The systems capabilities and

  3. A space weather forecasting system with multiple satellites based on a self-recognizing network.

    Science.gov (United States)

    Tokumitsu, Masahiro; Ishida, Yoshiteru

    2014-05-05

    This paper proposes a space weather forecasting system at geostationary orbit for high-energy electron flux (>2 MeV). The forecasting model involves multiple sensors on multiple satellites. The sensors interconnect and evaluate each other to predict future conditions at geostationary orbit. The proposed forecasting model is constructed using a dynamic relational network for sensor diagnosis and event monitoring. The sensors of the proposed model are located at different positions in space. The satellites for solar monitoring equip with monitoring devices for the interplanetary magnetic field and solar wind speed. The satellites orbit near the Earth monitoring high-energy electron flux. We investigate forecasting for typical two examples by comparing the performance of two models with different numbers of sensors. We demonstrate the prediction by the proposed model against coronal mass ejections and a coronal hole. This paper aims to investigate a possibility of space weather forecasting based on the satellite network with in-situ sensing.

  4. An Attitude Modelling Method Based on the Inherent Frequency of a Satellite Platform

    Science.gov (United States)

    Mo, F.; Tang, X.; Xie, J.; Yan, C.

    2017-05-01

    The accuracy of attitude determination plays a key role in the improvement of surveying and mapping accuracy for high-resolution remote-sensing satellites, and it is a bottleneck in large-scale satellite topographical mapping. As the on-board energy is constrained and the performance of an attitude-measurement device is limited, the attitude acquired is discretely sampled with a settled time interval. The larger the interval, the easier the data transmission, and the more deviation the attitude data will have. Meanwhile, several kinds of jitter frequencies have been detected in satellite platforms. This paper presents a novel attitude modelling (AttModel) method that sufficiently considers the discrete and periodic characteristics, and the attitude model built is continuous and consists of several inherent waves of different frequencies. The process of modelling includes two steps: (a) frequency detection, which uses raw gyroscope data within a period of time to detect the attitude frequencies (as the gyroscope data can actually reflect continuous, very small changes of the satellite platform), and (b) attitude modelling , which processes the attitude data that was filtered by extended Kalman filtering based on general polynomial and trigonometric polynomials, and these trigonometric polynomials are rebuilt by those frequencies detected in the first part of the modelling process. Finally, one experiment designed for verifying the effectiveness of the presented method shows that the AttModel method can reach a slightly better pointing accuracy without ground-control points than traditional attitude-interpolation methods.

  5. Evaluation of satellite based indices for primary production estimates in a sparse savanna in the Sudan

    Directory of Open Access Journals (Sweden)

    M. Sjöström

    2008-07-01

    Full Text Available One of the more frequently applied methods for integrating controls on primary production through satellite data is the Light Use Efficiency (LUE approach. Satellite indices such as the Enhanced Vegetation Index (EVI and the Shortwave Infrared Water Stress Index (SIWSI have previously shown promise as predictors of primary production in several different environments. In this study, we evaluate EVI and SIWSI derived from the Moderate Resolution Imaging Spectroradiometer (MODIS satellite sensor against in-situ measurements from central Sudan in order to asses their applicability in LUE-based primary production modelling within a water limited environment. Results show a strong correlation between EVI against gross primary production (GPP, demonstrating the significance of EVI for deriving information on primary production with relatively high accuracy at similar areas. Evaluation of SIWSI however, reveal that the fraction of vegetation apparently is to low for the index to provide accurate information on canopy water content, indicating that the use of SIWSI as a predictor of water stress in satellite data-driven primary production modelling in similar semi-arid ecosystems is limited.

  6. Constellation design for earth observation based on the characteristics of the satellite ground track

    Science.gov (United States)

    Luo, Xin; Wang, Maocai; Dai, Guangming; Song, Zhiming

    2017-04-01

    This paper responds to the increasing need for Earth observation missions and deals with the design of Repeating Sun-Synchronous Constellations (RSSCs) which takes into consideration of constellations composed of one or more orbital planes. Based on the mature design approach of Repeating Sun-synchronous orbits, a novel technique to design RSSCs is presented, which takes the second gravitational zonal harmonic into consideration. In order to obtain regular cycles of observation of the Earth by a single satellite, the orbital relationships have to be satisfied firstly are illustrated. Then, by making full analyses of the characteristics of the satellite ground track, orbital parameters are properly calculated to make other satellites pass on the same or different ground track of the single satellite. Last, single-plane or multi-plane constellations are used to improve the repetitions of the observation and the ground resolution. RSSCs allow observing the same region once at the same local time in a solar day and several times at the different local time in a solar day. Therefore, this kind of constellations meets all requirements for the remote sensing applications, which need to observe the same region under the same or different visible conditions. Through various case studies, the calculation technique is successfully demonstrated.

  7. Sensitivity of Distributed Hydrologic Simulations to Ground and Satellite Based Rainfall Products

    Directory of Open Access Journals (Sweden)

    Singaiah Chintalapudi

    2014-05-01

    Full Text Available In this study, seven precipitation products (rain gauges, NEXRAD MPE, PERSIANN 0.25 degree, PERSIANN CCS-3hr, PERSIANN CCS-1hr, TRMM 3B42V7, and CMORPH were used to force a physically-based distributed hydrologic model. The model was driven by these products to simulate the hydrologic response of a 1232 km2 watershed in the Guadalupe River basin, Texas. Storm events in 2007 were used to analyze the precipitation products. Comparison with rain gauge observations reveals that there were significant biases in the satellite rainfall products and large variations in the estimated amounts. The radar basin average precipitation compared very well with the rain gauge product while the gauge-adjusted TRMM 3B42V7 precipitation compared best with observed rainfall among all satellite precipitation products. The NEXRAD MPE simulated streamflows matched the observed ones the best yielding the highest Nash-Sutcliffe Efficiency correlation coefficient values for both the July and August 2007 events. Simulations driven by TRMM 3B42V7 matched the observed streamflow better than other satellite products for both events. The PERSIANN coarse resolution product yielded better runoff results than the higher resolution product. The study reveals that satellite rainfall products are viable alternatives when rain gauge or ground radar observations are sparse or non-existent.

  8. Assessment of the quality of OSIRIS mesospheric temperatures using satellite and ground-based measurements

    Directory of Open Access Journals (Sweden)

    P. E. Sheese

    2012-12-01

    Full Text Available The Optical Spectrograph and InfraRed Imaging System (OSIRIS on the Odin satellite is currently in its 12th year of observing the Earth's limb. For the first time, continuous temperature profiles extending from the stratopause to the upper mesosphere have been derived fr