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

NASA Technical Reports Server (NTRS)

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

2012-01-01

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

The Beauty and Complexity of the Brunt Ice Shelf from MOA and ICESat

NASA Technical Reports Server (NTRS)

Humbert, Angelika; Shuman, Christopher A.

2005-01-01

Beginning in February 2003, NASA's Ice, Cloud, and land Elevation Satellite (ICESat) has determined surface elevations from approx. 86degN to 86degS latitude. To date, altimetry data have been acquired in a series of observation periods in repeated track patterns using all three Geoscience Laser Altimeter System (GLAS) lasers. This paper will focus on ice shelf elevation data that were obtained in 2003 across the Brunt Ice Shelf and the Stancomb-Wills Ice Tongue. Integrating the altimetry with the recently available MODIS Mosaic of Antarctica (MOA), quantifies the relative accuracy and precision of the resulting ice shelf elevations. Furthermore, the elevation data was processed onto an elevation grid, by regional interpolation across the area s complex glacial features only. Ice thickness estimation from the altimetry of the floating ice is discussed. ICESat operates at 40Hz and its elevation data is obtained every 172m along track. These elevations have a relative accuracy of about 14cm based on the standard deviation of low-slope crossover differences and a precision of close to 2cm for the Laser 2a, Release 21, GLA12 data used here.

The Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2): Science Requirements, Concept, and Implementation

NASA Technical Reports Server (NTRS)

Markus, Thorsten; Neumann, Tom; Martino, Anthony; Abdalati, Waleed; Brunt, Kelly; Csatho, Beata; Farrell, Sinead; Fricker, Helen; Gardner, Alex; Harding, David;

ICESat and ICESat-2: Preparing to assess decadal-scale elevation change over the ice sheets

NASA Astrophysics Data System (ADS)

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

2016-12-01

One of the first, and most dramatic, assessments of elevation change to occur after the Ice, Cloud and land Elevation Satellite-2 (ICESat-2) enters its science orbit in early 2018 will be to compare the altimetry data being collected to the baseline established by the original ICESat mission between 2003 and 2009. Both missions use altimeters that send laser pulses from the satellite to the Earth. By measuring the travel time, the range to the surface can be inferred, and then combined with the position of the satellite and the pointing direction of the laser to determine where the pulse landed on the surface and its height there. The first ICESat mission employed a single-beam, full-waveform altimeter with a near-infrared (1064-nm wavelength) laser pulsed at 40 Hz. This produced surface heights at 170-meter intervals along reference tracks that extended to +/- 86 degrees latitude. ICESat-2 will carry an altimeter that sends a green (532-nm wavelength) laser through a diffractive optical element to be split into six beams, and pulsed at 10kHz. This will yield overlapping footprints every 70 cm along each beam track, extending to +/-88 degrees latitude. Rather than capturing the full returned waveform, however, the altimeter will use photon-counting detectors to measure the travel times of individual photons. Once on the ground, these data will be used in the science data processing system to produce a latitude, longitude and ellipsoidal height, marking the location from which each photon returned from the surface. Higher-level data products will characterize the surface more precisely by aggregating photons to reduce noise along each of the six beam tracks. Here, we describe the ICESat and ICESat-2 measurements and ice sheet data products, and discuss possible methods for comparing them to assess elevation change over the Greenland and Antarctic ice sheets in the nine years between the two missions.

ICESat Contributions to Understanding Coastal Processes

NASA Astrophysics Data System (ADS)

Urban, T. J.; Schutz, B. E.; Neuenschwander, A. L.

2006-12-01

ICESat (Ice, Cloud, and land Elevation Satellite) has been obtaining global elevation measurements of the Earth since 2003. These data have shed new light in unprecedented detail over ice, land and ocean surfaces. In particular, coastal altimetry including transitions from land to water and back benefit from ICESat's small footprint (~70 m diameter), high resolution (40 Hz and 170 m spot separation), and high precision (3 cm over non-vegetated surfaces). ICESat data support a wide variety of interdisciplinary investigations incorporating other data such as GRACE, GPS, SRTM, InSAR, Landsat, radar altimetry (TOPEX/Jason/Envisat), airborne LIDAR, and tide gauges. This paper provides an introduction to the potential capabilities of using ICESat coastal data in cooperative efforts. Several examples of coastal topography and change detection are shown, including the Texas-Louisiana Gulf Coast and the Mississippi Delta.

ICESAT GLAS Altimetry Measurements: Received Signal Dynamic Range and Saturation Correction

NASA Technical Reports Server (NTRS)

Sun, Xiaoli; Abshire, James B.; Borsa, Adrian A.; Fricker, Helen Amanda; Yi, Donghui; Dimarzio, John P.; Paolo, Fernando S.; Brunt, Kelly M.; Harding, David J.; Neumann, Gregory A.

2017-01-01

NASAs Ice, Cloud, and land Elevation Satellite (ICESat), which operated between 2003 and 2009, made the first satellite-based global lidar measurement of earths ice sheet elevations, sea-ice thickness, and vegetation canopy structure. The primary instrument on ICESat was the Geoscience Laser Altimeter System (GLAS), which measured the distance from the spacecraft to the earth's surface via the roundtrip travel time of individual laser pulses. GLAS utilized pulsed lasers and a direct detection receiver consisting of a silicon avalanche photodiode and a waveform digitizer. Early in the mission, the peak power of the received signal from snow and ice surfaces was found to span a wider dynamic range than anticipated, often exceeding the linear dynamic range of the GLAS 1064-nm detector assembly. The resulting saturation of the receiver distorted the recorded signal and resulted in range biases as large as approximately 50 cm for ice- and snow-covered surfaces. We developed a correction for this saturation range bias based on laboratory tests using a spare flight detector, and refined the correction by comparing GLAS elevation estimates with those derived from Global Positioning System surveys over the calibration site at the salar de Uyuni, Bolivia. Applying the saturation correction largely eliminated the range bias due to receiver saturation for affected ICESat measurements over Uyuni and significantly reduced the discrepancies at orbit crossovers located on flat regions of the Antarctic ice sheet.

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

NASA Astrophysics Data System (ADS)

Babonis, Gregory Scott

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

ICESat-2 simulated data from airborne altimetery

NASA Astrophysics Data System (ADS)

Brunt, K. M.; Neumann, T.; Markus, T.; Brenner, A. C.; Barbieri, K.; Field, C.; Sirota, M.

2010-12-01

Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) is scheduled to launch in 2015 and will carry onboard the Advanced Topographic Laser Altimeter System (ATLAS), which represents a new approach to spaceborne determination of surface elevations. Specifically, the current ATLAS design is for a micropulse, multibeam, photon-counting laser altimeter with lower energy, a shorter pulse width, and a higher repetition rate relative to the Geoscience Laser Altimeter (GLAS), the instrument that was onboard ICESat. Given the new and untested technology associated with ATLAS, airborne altimetry data is necessary (1) to test the proposed ATLAS instrument geometry, (2) to validate instrument models, and (3) to assess the atmospheric effects on multibeam altimeters. We present an overview of the airborne instruments and datasets intended to address the ATLAS instrument concept, including data collected over Greenland (July 2009) using an airborne SBIR prototype 100 channel, photon-counting, terrain mapping altimeter, which addresses the first of these 3 scientific concerns. Additionally, we present the plan for further simulator data collection over vegetated and ice covered regions using Multiple Altimeter Beam Experimental Lidar (MABEL), intended to address the latter two scientific concerns. As the ICESAT-2 project is in the design phase, the particular configuration of the ATLAS instrument may change. However, we expect this work to be relevant as long as ATLAS pursues a photon-counting approach.

Overview of the ICESat Mission and Results

NASA Astrophysics Data System (ADS)

Zwally, H.

2004-12-01

NASA's Ice, Cloud, and Land Elevation Satellite (ICESat), launched in January, 2003, has been measuring surface elevations of ice and land, vertical distributions of clouds and aerosols, vegetation-canopy heights, and other features with unprecedented accuracy and sensitivity. The ICESat mission, which was designed to operate continuously for 3 to 5 years, has so far acquired science data during five periods of laser operation ranging from 33 to 54 days each. The primary purpose of ICESat has been to acquire time-series of ice-sheet elevation changes for determination of the present-day mass balance of the ice sheets, study of associations between observed ice changes and polar climate, and improve estimates of the present and future contributions to global sea level rise. ICEsat's atmospheric measurements are providing fundamentally new information on the precise vertical structure of clouds and aerosols. In particular, cloud heights are important for understanding radiation balance and their effects on climate change. Other applications include mapping of polar sea-ice freeboard and thickness, high-resolution mapping of ocean eddies, glacier topography, and lake and river levels. ICESat has a 1064 nm laser channel for near-surface altimetry with a designed range precision of 10 cm that is actually 2 cm on-orbit. Vertical distributions of clouds and aerosols are obtained with 75 m resolution from both the 1064 nm channel and the more sensitive 532 nm channel. The laser footprints are about 70 m spaced at 170 m along-track. The accuracy of the satellite-orbital heights is about 3 cm. The star-tracking attitude-determination system should enable footprints to be located to 6 m horizontally when attitude calibration is completed. The spacecraft attitude is controlled to point the laser beam to within 100 m (35 m goal) of reference surface tracks at high latitudes and to point off-nadir up to 5 degrees to targets of interest. The remaining laser lifetime will be used

A Decade of Arctic Sea Ice Thickness Change from Airborne and Satellite Altimetry (Invited)

NASA Astrophysics Data System (ADS)

Farrell, S. L.; Richter-Menge, J.; Kurtz, N. T.; McAdoo, D. C.; Newman, T.; Zwally, H.; Ruth, J.

2013-12-01

Altimeters on both airborne and satellite platforms provide direct measurements of sea ice freeboard from which sea ice thickness may be calculated. Satellite altimetry observations of Arctic sea ice from ICESat and CryoSat-2 indicate a significant decline in ice thickness, and volume, over the last decade. During this time the ice pack has experienced a rapid change in its composition, transitioning from predominantly thick, multi-year ice to thinner, increasingly seasonal ice. We will discuss the regional trends in ice thickness derived from ICESat and IceBridge altimetry between 2003 and 2013, contrasting observations of the multi-year ice pack with seasonal ice zones. ICESat ceased operation in 2009, and the final, reprocessed data set became available recently. We extend our analysis to April 2013 using data from the IceBridge airborne mission, which commenced operations in 2009. We describe our current efforts to more accurately convert from freeboard to ice thickness, with a modified methodology that corrects for range errors, instrument biases, and includes an enhanced treatment of snow depth, with respect to ice type. With the planned launch by NASA of ICESat-2 in 2016 we can expect continuity of the sea ice thickness time series through the end of this decade. Data from the ICESat-2 mission, together with ongoing observations from CryoSat-2, will allow us to understand both the decadal trends and inter-annual variability in the Arctic sea ice thickness record. We briefly present the status of planned ICESat-2 sea ice data products, and demonstrate the utility of micro-pulse, photon-counting laser altimetry over sea ice.

The Multiple Altimeter Beam Experimental Lidar (MABEL), an Airborne Simulator for the ICESat-2 Mission

NASA Technical Reports Server (NTRS)

McGill, Matthew; Markus, Thorsten; Scott, V. Stanley; Neumann, Thomas

2012-01-01

The Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) mission is currently under development by NASA. The primary mission of ICESat-2 will be to measure elevation changes of the Greenland and Antarctic ice sheets, document changes in sea ice thickness distribution, and derive important information about the current state of the global ice coverage. To make this important measurement, NASA is implementing a new type of satellite-based surface altimetry based on sensing of laser pulses transmitted to, and reflected from, the surface. Because the ICESat-2 measurement approach is different from that used for previous altimeter missions, a high-fidelity aircraft instrument, the Multiple Altimeter Beam Experimental Lidar (MABEL), was developed to demonstrate the measurement concept and provide verification of the ICESat-2 methodology. The MABEL instrument will serve as a prototype for the ICESat-2 mission and also provides a science tool for studies of land surface topography. This paper outlines the science objectives for the ICESat-2 mission, the current measurement concept for ICESat-2, and the instrument concept and preliminary data from MABEL.

Vertical Accuracy Assessment of ZY-3 Digital Surface Model Using Icesat/glas Laser Altimeter Data

NASA Astrophysics Data System (ADS)

Li, G.; Tang, X.; Yuan, X.; Zhou, P.; Hu, F.

2017-05-01

The Ziyuan-3 (ZY-3) satellite, as the first civilian high resolution surveying and mapping satellite in China, has a very important role in national 1 : 50,000 stereo mapping project. High accuracy digital surface Model (DSMs) can be generated from the three line-array images of ZY-3, and ZY-3 DSMs of China can be produced without using any ground control points (GCPs) by selecting SRTM (Shuttle Radar Topography Mission) and ICESat/GLAS (Ice, Cloud, and land Elevation Satellite, Geo-science Laser Altimeter System) as the datum reference in the Satellite Surveying and Mapping Application Center, which is the key institute that manages and distributes ZY-3 products. To conduct the vertical accuracy evaluation of ZY-3 DSMs of China, three representative regions were chosen and the results were compared to ICESat/GLAS data. The experimental results demonstrated that the root mean square error (RMSE) elevation accuracy of the ZY-3 DSMs was better than 5.0 m, and it even reached to less than 2.5 m in the second region of eastern China. While this work presents preliminary results, it is an important reference for expanding the application of ZY-3 satellite imagery to widespread regions. And the satellite laser altimetry data can be used as referenced data for wide-area DSM evaluation.

Variability in Annual and Average Mass Changes in Antarctica from 2004 to 2009 using Satellite Laser Altimetry

NASA Astrophysics Data System (ADS)

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

2016-12-01

We present a new record of Antarctic ice thickness changes, reconstructed from ICESat laser altimetry observations, from 2004-2009, at over 100,000 locations across the Antarctic Ice Sheet (AIS). This work generates elevation time series at ICESat groundtrack crossover regions on an observation-by-observation basis, with rigorous, quantified, error estimates using the SERAC approach (Schenk and Csatho, 2012). The results include average and annual elevation, volume and mass changes in Antarctica, fully corrected for glacial isostatic adjustment (GIA) and known intercampaign biases; and partitioned into contributions from surficial processes (e.g. firn densification) and ice dynamics. The modular flexibility of the SERAC framework allows for the assimilation of multiple ancillary datasets (e.g. GIA models, Intercampaign Bias Corrections, IBC), in a common framework, to calculate mass changes for several different combinations of GIA models and IBCs and to arrive at a measure of variability from these results. We are able to determine the effect these corrections have on annual and average volume and mass change calculations in Antarctica, and to explore how these differences vary between drainage basins and with elevation. As such, this contribution presents a method that compliments, and is consistent with, the 2012 Ice sheet Mass Balance Inter-comparison Exercise (IMBIE) results (Shepherd 2012). Additionally, this work will contribute to the 2016 IMBIE, which seeks to reconcile ice sheet mass changes from different observations,, including laser altimetry, using a different methodologies and ancillary datasets including GIA models, Firn Densification Models, and Intercampaign Bias Corrections.

Evaluation of the Global Multi-Resolution Terrain Elevation Data 2010 (GMTED2010) using ICESat geodetic control

USGS Publications Warehouse

Carabajal, C.C.; Harding, D.J.; Boy, J.-P.; Danielson, Jeffrey J.; Gesch, D.B.; Suchdeo, V.P.

2011-01-01

Supported by NASA's Earth Surface and Interior (ESI) Program, we are producing a global set of Ground Control Points (GCPs) derived from the Ice, Cloud and land Elevation Satellite (ICESat) altimetry data. From February of 2003, to October of 2009, ICESat obtained nearly global measurements of land topography (?? 86?? latitudes) with unprecedented accuracy, sampling the Earth's surface at discrete ???50 m diameter laser footprints spaced 170 m along the altimetry profiles. We apply stringent editing to select the highest quality elevations, and use these GCPs to characterize and quantify spatially varying elevation biases in Digital Elevation Models (DEMs). In this paper, we present an evaluation of the soon to be released Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010). Elevation biases and error statistics have been analyzed as a function of land cover and relief. The GMTED2010 products are a large improvement over previous sources of elevation data at comparable resolutions. RMSEs for all products and terrain conditions are below 7 m and typically are about 4 m. The GMTED2010 products are biased upward with respect to the ICESat GCPs on average by approximately 3 m. ?? 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

Evaluation of the Global Multi-Resolution Terrain Elevation Data 2010 (GMTED2010) Using ICESat Geodetic Control

NASA Technical Reports Server (NTRS)

Carabajal, Claudia C.; Harding, David J.; Boy, Jean-Paul; Danielson, Jeffrey J.; Gesch, Dean B.; Suchdeo, Vijay P.

2011-01-01

Supported by NASA's Earth Surface and Interior (ESI) Program, we are producing a global set of Ground Control Points (GCPs) derived from the Ice, Cloud and land Elevation Satellite (ICESat) altimetry data. From February of 2003, to October of 2009, ICESat obtained nearly global measurements of land topography (+/- 86deg latitudes) with unprecedented accuracy, sampling the Earth's surface at discrete approx.50 m diameter laser footprints spaced 170 m along the altimetry profiles. We apply stringent editing to select the highest quality elevations, and use these GCPs to characterize and quantify spatially varying elevation biases in Digital Elevation Models (DEMs). In this paper, we present an evaluation of the soon to be released Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010). Elevation biases and error statistics have been analyzed as a function of land cover and relief. The GMTED2010 products are a large improvement over previous sources of elevation data at comparable resolutions. RMSEs for all products and terrain conditions are below 7 m and typically are about 4 m. The GMTED2010 products are biased upward with respect to the ICESat GCPs on average by approximately 3 m.

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

NASA Astrophysics Data System (ADS)

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

2010-12-01

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

Estimation of Greenland's Ice Sheet Mass Balance Using ICESat and GRACE Data

NASA Astrophysics Data System (ADS)

Slobbe, D.; Ditmar, P.; Lindenbergh, R.

2007-12-01

Data of the GRACE gravity mission and the ICESat laser altimetry mission are used to create two independent estimates of Greenland's ice sheet mass balance over the full measurement period. For ICESat data, a processing strategy is developed using the elevation differences of geometrically overlapping footprints of both crossing and repeated tracks. The dataset is cleaned using quality flags defined by the GLAS science team. The cleaned dataset reveals some strong, spatially correlated signals that are shown to be related to physical phenomena. Different processing strategies are used to convert the observed temporal height differences to mass changes for 6 different drainage systems, further divided into a region above and below 2000 meter elevation. The results are compared with other altimetry based mass balance estimates. In general, the obtained results confirm trends discovered by others, but we also show that the choice of processing strategy strongly influences our results, especially for the areas below 2000 meter. Furthermore, GRACE based monthly variations of the Earth's gravity field as processed by CNES, CSR, GFZ and DEOS are used to estimate the mass balance change for North and South Greenland. It is shown that our results are comparable with recently published GRACE estimates (mascon solutions). On the other hand, the estimates based on GRACE data are only partly confirmed by the ICESat estimates. Possible explanations for the obvious differences will be discussed.

GPS-Based Precision Orbit Determination for a New Era of Altimeter Satellites: Jason-1 and ICESat

NASA Technical Reports Server (NTRS)

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

2003-01-01

Accurate positioning of the satellite center of mass is necessary in meeting an altimeter mission's science goals. The fundamental science observation is an altimetric derived topographic height. Errors in positioning the satellite's center of mass directly impact this fundamental observation. Therefore, orbit error is a critical Component in the error budget of altimeter satellites. With the launch of the Jason-1 radar altimeter (Dec. 2001) and the ICESat laser altimeter (Jan. 2003) a new era of satellite altimetry has begun. Both missions pose several challenges for precision orbit determination (POD). The Jason-1 radial orbit accuracy goal is 1 cm, while ICESat (600 km) at a much lower altitude than Jason-1 (1300 km), has a radial orbit accuracy requirement of less than 5 cm. Fortunately, Jason-1 and ICESat POD can rely on near continuous tracking data from the dual frequency codeless BlackJack GPS receiver and Satellite Laser Ranging. Analysis of current GPS-based solution performance indicates the l-cm radial orbit accuracy goal is being met for Jason-1, while radial orbit accuracy for ICESat is well below the 54x1 mission requirement. A brief overview of the GPS precision orbit determination methodology and results for both Jason-1 and ICESat are presented.

ICESat-2 laser technology development

NASA Astrophysics Data System (ADS)

Edwards, Ryan; Sawruk, Nick W.; Hovis, Floyd E.; Burns, Patrick; Wysocki, Theodore; Rudd, Joe; Walters, Brooke; Fakhoury, Elias; Prisciandaro, Vincent

2013-09-01

A number of ICESat-2 system requirements drove the technology evolution and the system architecture for the laser transmitter Fibertek has developed for the mission.. These requirements include the laser wall plug efficiency, laser reliability, high PRF (10kHz), short-pulse (<1.5ns), relatively narrow spectral line-width, and wave length tunability. In response to these requirements Fibertek developed a frequency-doubled, master oscillator/power amplifier (MOPA) laser that incorporates direct pumped diode pumped Nd:YVO4 as the gain media, Another guiding force in the system design has been extensive hardware life testing that Fibertek has completed. This ongoing hardware testing and development evolved the system from the original baseline brass board design to the more robust flight laser system. The final design meets or exceeds all NASA requirements and is scalable to support future mission requirements.

ICESat-2 laser Nd:YVO4 amplifier

NASA Astrophysics Data System (ADS)

Sawruk, Nicholas W.; Burns, Patrick M.; Edwards, Ryan E.; Litvinovitch, Viatcheslav; Martin, Nigel; Witt, Greg; Fakhoury, Elias; Iskander, John; Pronko, Mark S.; Troupaki, Elisavet; Bay, Michael M.; He, Charles C.; Wang, Liqin L.; Cavanaugh, John F.; Farrokh, Babak; Salem, Jonathan A.; Baker, Eric

2018-02-01

We report on the cause and corrective actions of three amplifier crystal fractures in the space-qualified laser systems used in NASA Goddard Space Flight Center's (GSFC) Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2). The ICESat-2 lasers each contain three end-pumped Nd:YVOO4 amplifier stages. The crystals are clamped between two gold plated copper heat spreaders with an indium foil thermal interface material, and the crystal fractures occurred after multiple years of storage and over a year of operational run-time. The primary contributors are high compressive loading of the NdYVO4 crystals at the beginning of life, a time dependent crystal stress caused by an intermetallic reaction of the gold plating and indium, and slow crack growth resulting in a reduction in crystal strength over time. An updated crystal mounting scheme was designed, analyzed, fabricated and tested. Thee fracture slab failure analysis, finite-element modeling and corrective actions are presented.

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

NASA Technical Reports Server (NTRS)

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

2009-01-01

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

Development Considerations for the ICESat-2 ATL18 Terrain and Canopy Global Gridded Product

NASA Astrophysics Data System (ADS)

Pitts, K. L.; Neuenschwander, A. L.

2016-12-01

The ICESat-2 mission, expected to launch in late 2017 or early 2018, will provide estimates of terrain and canopy heights along the satellite ground track which will provide a significant benefit to society through a variety of applications ranging from improved global digital terrain models to mapping the distribution of above ground vegetation structure. Shortly after launch of ICESat-2, the Global Ecosystem Dynamics Investigation (GEDI) mission will be placed on the International Space Station (ISS) and will also derive terrain and canopy heights using laser altimetry for latitudes covered by the ISS. NASA's GEDI mission is designed to capture forest structure in densely covered regions over a period of 12-18 months. This study will present the factors required to produce a global gridded product that fuses information from both ICESat-2 and GEDI. The gridded values from ICESat-2 will be calculated from the along-track geodetic measurements of the terrain and relative canopy heights (ATL08), but considerations must be made on how best to combine ICESat-2 terrain and canopy height estimates with GEDI terrain and canopy height estimates. In particular, factors such as phenology, spatial and temporal resolution, surface interpolation methods, and error propagation are presented.

Inferring unknow boundary conditions of the Greenland Ice Sheet by assimilating ICESat-1 and IceBridge altimetry intothe Ice Sheet System Model.

NASA Astrophysics Data System (ADS)

Larour, E. Y.; Khazendar, A.; Seroussi, H. L.; Schlegel, N.; Csatho, B. M.; Schenk, A. F.; Rignot, E. J.; Morlighem, M.

2014-12-01

Altimetry signals from missions such as ICESat-1, CryoSat, EnviSat, as well as altimeters onboard Operation IceBridge provide vital insights into processes such as surface mass balance, mass transport and ice-flow dynamics. Historically however, ice-flow models have been focused on assimilating surface velocities from satellite-based radar observations, to infer properties such as basal friction or the position of the bedrock. Here, we leverage a new methodology based on automatic differentation of the Ice Sheet System Model to assimilate surface altimetry data into a reconstruction of the past decade of ice flow on the North Greenland area. We infer corrections to boundary conditions such as basal friction and surface mass balance, as well as corrections to the ice hardness, to best-match the observed altimetry record. We compare these corrections between glaciers such as Petermann Glacier, 79 North and Zacchariae Isstrom. The altimetry signals exhibit very different patterns between East and West, which translate into very different signatures for the inverted boundary conditions. This study gives us greater insights into what differentiates different basins, both in terms of mass transport and ice-flow dynamics, and what could bethe controlling mechanisms behind the very different evolutions of these basins.

Verification of ICESat-2/ATLAS Science Receiver Algorithm Onboard Databases

NASA Astrophysics Data System (ADS)

Carabajal, C. C.; Saba, J. L.; Leigh, H. W.; Magruder, L. A.; Urban, T. J.; Mcgarry, J.; Schutz, B. E.

2013-12-01

NASA's ICESat-2 mission will fly the Advanced Topographic Laser Altimetry System (ATLAS) instrument on a 3-year mission scheduled to launch in 2016. ATLAS is a single-photon detection system transmitting at 532nm with a laser repetition rate of 10 kHz, and a 6 spot pattern on the Earth's surface. A set of onboard Receiver Algorithms will perform signal processing to reduce the data rate and data volume to acceptable levels. These Algorithms distinguish surface echoes from the background noise, limit the daily data volume, and allow the instrument to telemeter only a small vertical region about the signal. For this purpose, three onboard databases are used: a Surface Reference Map (SRM), a Digital Elevation Model (DEM), and a Digital Relief Maps (DRMs). The DEM provides minimum and maximum heights that limit the signal search region of the onboard algorithms, including a margin for errors in the source databases, and onboard geolocation. Since the surface echoes will be correlated while noise will be randomly distributed, the signal location is found by histogramming the received event times and identifying the histogram bins with statistically significant counts. Once the signal location has been established, the onboard Digital Relief Maps (DRMs) will be used to determine the vertical width of the telemetry band about the signal. University of Texas-Center for Space Research (UT-CSR) is developing the ICESat-2 onboard databases, which are currently being tested using preliminary versions and equivalent representations of elevation ranges and relief more recently developed at Goddard Space Flight Center (GSFC). Global and regional elevation models have been assessed in terms of their accuracy using ICESat geodetic control, and have been used to develop equivalent representations of the onboard databases for testing against the UT-CSR databases, with special emphasis on the ice sheet regions. A series of verification checks have been implemented, including

Antarctic Megadunes - Assessment of Topographic Form and Windward Progradation from ICESat Altimetry, 2003-2009

NASA Astrophysics Data System (ADS)

Shuman, C. A.; Scambos, T. A.; Fahnestock, M. A.; Suchdeo, V. P.

2011-12-01

More than 900,000 square kilometers of East Antarctica are covered by distinctive megadune features (Fahnestock et al., 2000, Courville et al., 2007) as first defined by Swithinbank (1988). These long, undulating, sinuous dunes are due to persistent gravity-driven katabatic winds and spatially variable accumulation. In the field, they have a distinctive morphology, but characterization of the evolution of these active landscape features requires detailed elevation data as well as radar backscatter and grain size information. In this study, we utilize NASA's ICESat laser altimetry data during 2003-2009 (corrected for intercampaign biases) in the vicinity of an NSF-OPP funded research site near 80.78°S, 124.5°E, occupied and instrumented during the 2002-2003 and 2003-2004 summer seasons with additional limited field observations from January 2011. Using remote sensing data sets and field observations, we can characterize these features including their extent, variability, and elevation change with time. Field measurements from ground penetrating radar, automatic weather stations, surface photos, snowpits, and shallow cores provide in situ and subsurface information on local dune structure. Based on these data, Antarctic megadunes can be characterized as linear strips of higher accumulation (~30 to 80 kg m-2 a-1 maximum, typically toward the lower part of the range) consisting of fine-grained, wind-packed snow, generally forming 2-8 meter high, 1-2 km wide ridges up to 100 km long and separated by 2-6 km of near-zero-accumulation wind glaze regions. Glaze surfaces overlie extremely metamorphosed firn composed of very coarse recrystallized grains with poorly expressed layering. Our study extends site-specific results summarized in Courville et al. (2007) across the megadune study area with co-located MODIS-based Mosaic of Antarctica (MOA) images and surface optical grain size (e.g. Scambos et al., 2007), calibrated SAR backscatter data from the Radarsat Antarctic

On the retrieval of sea ice thickness and snow depth using concurrent laser altimetry and L-band remote sensing data

NASA Astrophysics Data System (ADS)

Zhou, Lu; Xu, Shiming; Liu, Jiping; Wang, Bin

2018-03-01

detailed analysis, we show that the error of the retrieval mainly arises from the difference between the modeled and the observed (SMOS) L-band brightness temperature (TB). The narrow swath and the limited coverage of the sea ice cover by altimetry is the potential source of error associated with the modeling of L-band TB and retrieval. The proposed retrieval methodology can be applied to the basin-scale retrieval of sea ice thickness and snow depth, using concurrent passive remote sensing and active laser altimetry based on satellites such as ICESat-2 and WCOM.

Efficient Swath Mapping Laser Altimetry Demonstration Instrument Incubator Program

NASA Technical Reports Server (NTRS)

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

2010-01-01

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

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

NASA Astrophysics Data System (ADS)

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

2015-12-01

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

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

NASA Technical Reports Server (NTRS)

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

2010-01-01

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

Ranging error analysis of single photon satellite laser altimetry under different terrain conditions

NASA Astrophysics Data System (ADS)

Huang, Jiapeng; Li, Guoyuan; Gao, Xiaoming; Wang, Jianmin; Fan, Wenfeng; Zhou, Shihong

2018-02-01

Single photon satellite laser altimeter is based on Geiger model, which has the characteristics of small spot, high repetition rate etc. In this paper, for the slope terrain, the distance of error's formula and numerical calculation are carried out. Monte Carlo method is used to simulate the experiment of different terrain measurements. The experimental results show that ranging accuracy is not affected by the spot size under the condition of the flat terrain, But the inclined terrain can influence the ranging error dramatically, when the satellite pointing angle is 0.001° and the terrain slope is about 12°, the ranging error can reach to 0.5m. While the accuracy can't meet the requirement when the slope is more than 70°. Monte Carlo simulation results show that single photon laser altimeter satellite with high repetition rate can improve the ranging accuracy under the condition of complex terrain. In order to ensure repeated observation of the same point for 25 times, according to the parameters of ICESat-2, we deduce the quantitative relation between the footprint size, footprint, and the frequency repetition. The related conclusions can provide reference for the design and demonstration of the domestic single photon laser altimetry satellite.

Prospects of the ICESat-2 Laser Altimetry Mission for Savanna Ecosystem Structural Studies Based on Airborne Simulation Data

NASA Technical Reports Server (NTRS)

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

2016-01-01

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 r(sub 2) 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 r(sub 2) 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

ICESat Lidar and Global Digital Elevation Models: Application to DESDynI

NASA Technical Reports Server (NTRS)

Carabajal, Claudia C.; Harding, David J.; Suchdeo, Vijay P.

2010-01-01

Geodetic control is extremely important in the production and quality control of topographic data sets, enabling elevation results to be referenced to an absolute vertical datum. Global topographic data with improved geodetic accuracy achieved using global Ground Control Point (GCP) databases enable more accurate characterization of land topography and its change related to solid Earth processes, natural hazards and climate change. The multiple-beam lidar instrument that will be part of the NASA Deformation, Ecosystem Structure and Dynamics of Ice (DESDynI) mission will provide a comprehensive, global data set that can be used for geodetic control purposes. Here we illustrate that potential using data acquired by NASA's Ice, Cloud and land Elevation Satellite (ICEsat) that has acquired single-beam, globally distributed laser altimeter profiles (+/-86deg) since February of 2003 [1, 2]. The profiles provide a consistently referenced elevation data set with unprecedented accuracy and quantified measurement errors that can be used to generate GCPs with sub-decimeter vertical accuracy and better than 10 m horizontal accuracy. Like the planned capability for DESDynI, ICESat records a waveform that is the elevation distribution of energy reflected within the laser footprint from vegetation, where present, and the ground where illuminated through gaps in any vegetation cover [3]. The waveform enables assessment of Digital Elevation Models (DEMs) with respect to the highest, centroid, and lowest elevations observed by ICESat and in some cases with respect to the ground identified beneath vegetation cover. Using the ICESat altimetry data we are developing a comprehensive database of consistent, global, geodetic ground control that will enhance the quality of a variety of regional to global DEMs. Here we illustrate the accuracy assessment of the Shuttle Radar Topography Mission (SRTM) DEM produced for Australia, documenting spatially varying elevation biases of several meters

Geoscience Laser Altimetry System (GLAS) Loop Heat Pipe Anomaly and On Orbit Testing

NASA Technical Reports Server (NTRS)

Baker, Charles; Butler, Dan; Grob, Eric; Jester, Peggy

2011-01-01

The Geoscience Laser Altimetry System (GLAS) is the sole instrument on the ICESat Satellite. On day 230 of 2003, the GLAS Component Loop Heat Pipe (CLHP) entered a slow circulation mode that resulted in the main electronics box reaching its hot safing temperature, after which the entire instrument was turned off. The CLHP had a propylene working fluid and was actively temperature controlled via a heater on the compensation chamber. The slow circulation mode happened right after a planned propulsive yaw maneuver with the spacecraft. It took several days to recover the CLHP and ensure that it was still operational. The recovery occurred after the entire instrument was cooled to survival temperatures and the CLHP compensation chamber cycled on a survival heater. There are several theories as to why this slow circulation mode exhibited itself, including: accumulation of Non-Condensible Gas (NCG), the secondary wick being under designed or improperly implemented, or an expanded (post-launch) leak across the primary wick. Each of these is discussed in turn, and the secondary wick performance is identified as the most likely source of the anomalous behavior. After the anomaly, the CLHP was controlled to colder temperatures to improve its performance (as the surface tension increases with lower temperature, as does the volume of liquid in the compensation chamber) and only precursor pulses occurred later in the mission. After GLAS s last laser failed, in late 2009, a decision was made to conduct engineering tests of both LHPs to try and duplicate this flight anomaly. The engineering tests consisted of control setpoint changes, sink changes, and one similar propulsive Yaw maneuver. The only test that showed any similar anomaly precursors on the CLHP was the propulsive maneuver followed by a setpoint increase. The ICESat Satellite was placed in a decaying orbit and ended its mission on August 30, 2010 in Barents Sea.

Mission design concepts for repeat groundtrack orbits and application to the ICESat mission

NASA Astrophysics Data System (ADS)

Pie, Nadege

The primary objective of the NASA sponsored ICESat mission is to study the short and long term changes in the ice mass in the Greenland and Antarctica regions. The satellite was therefore placed into a frozen near-polar near-circular repeat groundtrack to ensure an adequate coverage of the polar regions while keeping the groundtrack periodic and reducing the variations in the orbital elements, and more specifically the semi-major axis of the ICESat orbit. After launch, a contingency plan had to be devised to compensate for a laser that dangerously compromised the lifetime of the ICESat mission. This new plan makes an intensive use of the ICESat subcycles, a characteristic of the repeat groundtrack orbits often over-looked. The subcycle of a repeat groundtrack orbit provide global coverage within a time shorter than the groundtrack repetition period. For a satellite with an off-nadir pointing capacity, the subcycles provide near-repeat tracks which represents added opportunity for altimetry measurement over a specific track. The ICESat subcycles were also used in a very innovative fashion to reposition the satellite within its repeat cycle via orbital maneuvers called phasing maneuver. The necessary theoretical framework is provided for the subcycle analysis and the implementation of phasing maneuvers for any future repeat orbit mission. In the perspective of performing cross-validation of missions like CryoSat using the ICESat off-nadir capacity, a study was conducted to determine the geolocations of crossovers between two different repeat groundtrack Keplerian orbits. The general analytical solution was applied to ICESat vs. several other repeat groundtrack orbit mission, including the future ICESat-II mission. ICESat's repeat groundtrack orbit was designed using a disturbing force model that includes only the Earth geopotential. Though the third body effect from the Sun and the Moon was neglected in the orbit design, it does in fact disrupt the repeatability

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

NASA Astrophysics Data System (ADS)

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

2017-03-01

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

Sand dune tracking from satellite laser altimetry

NASA Astrophysics Data System (ADS)

Dabboor, Mohammed

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

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

NASA Astrophysics Data System (ADS)

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

2016-06-01

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

Water Level Monitoring on Tibetan Lakes Based on Icesat and Envisat Data Series

NASA Astrophysics Data System (ADS)

Li, H. W.; Qiao, G.; Wu, Y. J.; Cao, Y. J.; Mi, H.

2017-09-01

Satellite altimetry technique is an effective method to monitor the water level of lakes in a wide range, especially in sparsely populated areas, such as the Tibet Plateau (TP). To provide high quality data for time-series change detection of lake water level, an automatic and efficient algorithm for lake water footprint (LWF) detection in a wide range is used. Based on ICESat GLA14 Release634 data and ENVISat GDR 1Hz data, water level of 167 lakes were obtained from ICESat data series, and water level of 120 lakes were obtained from ENVISat data series. Among them, 67 lakes contained two data series. Mean standard deviation of all lakes is 0.088 meters (ICESat), 0.339 meters (ENVISat). Combination of multi-source altimetry data is helpful for us to get longer and more dense periods cover water level, study the lake level changes, manage water resources and understand the impacts of climate change better. In addition, the standard deviation of LWF elevation used to calculate the water level were analyzed by month. Based on lake data set for the TP from the 1960s, 2005, and 2014 in Scientific Data, it is found that the water level changes in the TP have a strong spatial correlation with the area changes.

Delta II ICESat-2 Booster Transport

NASA Image and Video Library

2018-04-17

At Vandenberg Air Force Base in California, on Tuesday, April 17, 2018, a United Launch Alliance (ULA) Delta II booster is transported to Space Launch Complex-2 where it will launch NASA's Ice, Cloud and land Elevation Satellite-2, or ICESat-2, satellite. This will be the last flight for the venerable Delta II rocket. ICESat-2, which is being built and tested by Orbital ATK in Gilbert, Arizona, will carry a single instrument called the Advanced Topographic Laser Altimeter System, or ATLAS. The ATLAS instrument is being built and tested at NASA’s Goddard Space Flight Center in Greenbelt Maryland. Once in orbit, the satellite is designed to measure the height of a changing Earth, one laser pulse at a time, 10,000 laser pulses a second. ICESat-2 will help scientists investigate why, and how much, Earth’s frozen and icy areas, called the cryosphere, are changing.

Delta II ICESat-2 Booster Transport

NASA Image and Video Library

2018-04-17

At Vandenberg Air Force Base in California, on Tuesday, April 17, 2018, a United Launch Alliance (ULA) Delta II booster arrives at Space Launch Complex-2 where it will launch NASA's Ice, Cloud and land Elevation Satellite-2, or ICESat-2, satellite. This will be the last flight for the venerable Delta II rocket. ICESat-2, which is being built and tested by Orbital ATK in Gilbert, Arizona, will carry a single instrument called the Advanced Topographic Laser Altimeter System, or ATLAS. The ATLAS instrument is being built and tested at NASA’s Goddard Space Flight Center in Greenbelt Maryland. Once in orbit, the satellite is designed to measure the height of a changing Earth, one laser pulse at a time, 10,000 laser pulses a second. ICESat-2 will help scientists investigate why, and how much, Earth’s frozen and icy areas, called the cryosphere, are changing.

Development of a multi-sensor elevation time series pole-ward of 86°S in support of altimetry validation and ice sheet mass balance studies

NASA Astrophysics Data System (ADS)

Studinger, M.; Brunt, K. M.; Casey, K.; Medley, B.; Neumann, T.; Manizade, S.; Linkswiler, M. A.

2015-12-01

In order to produce a cross-calibrated long-term record of ice-surface elevation change for input into ice sheet models and mass balance studies it is necessary to "link the measurements made by airborne laser altimeters, satellite measurements of ICESat, ICESat-2, and CryoSat-2" [IceBridge Level 1 Science Requirements, 2012] and determine the biases and the spatial variations between radar altimeters and laser altimeters using different wavelengths. The convergence zones of all ICESat tracks (86°S) and all ICESat-2 and CryoSat-2 tracks (88°S) are in regions of relatively low accumulation, making them ideal for satellite altimetry calibration. In preparation for ICESat-2 validation, the IceBridge and ICESat-2 science teams have designed IceBridge data acquisitions around 86°S and 88°S. Several aspects need to be considered when comparing and combining elevation measurements from different radar and laser altimeters, including: a) foot print size and spatial sampling pattern; b) accuracy and precision of each data sets; c) varying signal penetration into the snow; and d) changes in geodetic reference frames over time, such as the International Terrestrial Reference Frame (ITRF). The presentation will focus on the analysis of several IceBridge flights around 86 and 88°S with the LVIS and ATM airborne laser altimeters and will evaluate the accuracy and precision of these data sets. To properly interpret the observed elevation change (dh/dt) as mass change, however, the various processes that control surface elevation fluctuations must be quantified and therefore future work will quantify the spatial variability in snow accumulation rates pole-ward of 86°S and in particular around 88°S. Our goal is to develop a cross-validated multi-sensor time series of surface elevation change pole-ward of 86°S that, in combination with measured accumulation rates, will support ICESat-2 calibration and validation and ice sheet mass balance studies.

Delta II ICESat-2 Booster Transport

NASA Image and Video Library

2018-04-17

At NASA's Building 836, the Spacecraft Labs Telemetry Station at Vandenberg Air Force Base in California, on Tuesday, April 17, 2018, a United Launch Alliance (ULA) Delta II booster is transported to Space Launch Complex-2 where it will launch NASA's Ice, Cloud and land Elevation Satellite-2, or ICESat-2, satellite. This will be the last flight for the venerable Delta II rocket. ICESat-2, which is being built and tested by Orbital ATK in Gilbert, Arizona, will carry a single instrument called the Advanced Topographic Laser Altimeter System, or ATLAS. The ATLAS instrument is being built and tested at NASA’s Goddard Space Flight Center in Greenbelt Maryland. Once in orbit, the satellite is designed to measure the height of a changing Earth, one laser pulse at a time, 10,000 laser pulses a second. ICESat-2 will help scientists investigate why, and how much, Earth’s frozen and icy areas, called the cryosphere, are changing.

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

NASA Technical Reports Server (NTRS)

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.

Geoscience Laser Altimetry System (GLAS) On-Orbit Flight Report on the Propylene Loop Heat Pipes (LHPs)

NASA Technical Reports Server (NTRS)

Baker, Charles L.; Grob, Eric W.; McCarthy, Thomas V.; Nikitkin, Michael N.; Ancarrow, Walter C.

2003-01-01

The Geoscience Laser Altimetry System (GLAS) instrument which is the sole instrument on ICESat was launched on January 12, 2003. GLAS utilizes two actively controlled propylene Loop Heat Pipes (LHPs) as the core of its thermal system. The LHPs started quickly when the Dale Ohm starter heaters were powered and have as designed. The low control heater power and on-orbit tight temperature control appear independent of gravity effects when comparing ground testing to flight data. The use of coupling blocks was also unique to these LHPs. Their application reduced control heater power by reducing the subcooling from the radiator. The effectiveness in reducing subcooling of the coupler blocks decreased during flight from ground testing, but internal thermal isolation in the compensation chamber between the subcooled returning liquid increased in flight resulting in no net increase in control heater power versus ground measurements. Overall the application of LHPs in the thermal system for GLAS met instrument requirements and provided flexibility for the overall system as last minute requirements became known.

Geoscience Laser Altimeter System (GLAS) for the ICESat Mission

NASA Technical Reports Server (NTRS)

Abshire, James B.; Sun, Xiaoli; Ketchum, Eleanor A.; Millar, Pamela S.; Riris, Haris

2002-01-01

The Geoscience Laser Altimeter System (GLAS) is a new generation lidar and is the primary science payload for NASA's ICESat Mission. The GLAS design combines a 10 cm precision surface lidar with a sensitive dual wavelength cloud and aerosol lidar. GLAS will precisely measure the heights of the Earth's polar ice sheets, establish a grid of accurate height profiles of the Earth's land topography, and profile the vertical distribution of clouds and aerosols on a global scale. GLAS will be integrated onto a small spacecraft built by Ball Aerospace, and will be launched into a polar orbit with a 590-630 km altitude at an inclination of 94 degrees. ICESat is is currently planned to launch in winter 2002/03 and GLAS is designed to operate continuously in space for a minimum of 3 years. GLAS will measure the vertical distance from orbit to the Earth's surface with pulses from a ND:YAG laser at a 40 Hz rate. Each 6 nsec wide 1064 nm laser pulse is used to produce a single range measurement. On the surface, the laser footprints have 66 m diameter and approx. 170 m center-center spacings. The GLAS receiver uses a I m diameter telescope to detect laser backscatter and a Si APD to detect the 1064 nm signals. The detector's output is sampled by a digital ranging receiver, which records each transmitted pulse and surface echo waveform with 1 nsec (15 cm) resolution. Each echo pulse is digitized and is reported to ground with a record length of from 200 to 544 samples, depending on the spacecraft's location . The GLAS location and epoch times are measured by a precision GPS receiver carried on the ICESat spacecraft. Initial processing of the echo waveforms within GLAS permits discrimination between cloud and surface echoes for selecting appropriate waveform samples. This selection is guided by an on-board DEM which is used to set the boundaries for the echo pulse search algorithm. Subsequent ground-based echo pulse analysis, along with GPS-based clock frequency estimates, permit

The ICESat/GLAS Instrument Operations Report. Volume 4

NASA Technical Reports Server (NTRS)

Jester, Peggy L.

2012-01-01

The Geoscience Laser Altimeter System (GLAS) was the primary instrument aboard the first ICESat spacecraft. ICESat's primary objectives are to determine the mass balance of the polar ice sheets and their contributions to global sea level change, and to obtain essential data for prediction of future changes in ice volume and sea-level. ICESat launched successfully from Vandenberg Air Force Base on January 12, 2003 23:45 UT. The ICESat science mission began in February 2003 and ended on October 11, 2009. De-orbit of the spacecraft occurred on August 30, 2010. This document focusses on the GLAS instrument operations during the ICESat mission. This document will not discuss science results.

SAR Altimetry for Mean Sea Surface Determination in the Arctic DTU15MSS

NASA Astrophysics Data System (ADS)

Piccioni, G.; Andersen, O. B.; Stenseng, L.

2015-12-01

A reliable MSS that includes high-latitude regions within the 82 degree parallel is required for the Sentinel-3 data processing. In this paper we present the new DTU15MSS which is an update of the DTU13MSS with more years of CryoSat-2. CryoSat-2 offers a unique dataset in the Arctic Ocean for testing SAR altimetry with nearly five years of high-resolution SAR altimetry. In the Arctic Ocean older conventional altimetry satellites (ERS-1/ERS-2/Envisat) have only been able to provide sparse data for the past 20 years. Here we present the development of the DTU13MSS in the Arctic being the latest release of the global high resolution mean sea surface from DTU Space based on 4 years/repeat of Cryostat-2. The analysis shows that Laser Altimetry from the ICESat satellite being the basis of DTU10 and DTU13MSS between 82 and 86N is now obsolete for mean sea surface determination. The study also highlight the problems of integrating altimetry from various modes (LRM, SAR and SAR-in) as well as the problems relating to the fact that the averaging period of CryoSat-2 is adjacent to the 20 years (1993-2012) period used to develop DTU13MSS. Evaluation of the new MSS is performed and comparison with existing MSS models is performed to evaluate the impact of these updates into MSS computation.

Assimilation of river altimetry data for effective bed elevation and roughness coefficient

NASA Astrophysics Data System (ADS)

Brêda, João Paulo L. F.; Paiva, Rodrigo C. D.; Bravo, Juan Martin; Passaia, Otávio

2017-04-01

Hydrodynamic models of large rivers are important prediction tools of river discharge, height and floods. However, these techniques still carry considerable errors; part of them related to parameters uncertainties related to river bathymetry and roughness coefficient. Data from recent spatial altimetry missions offers an opportunity to reduce parameters uncertainty through inverse methods. This study aims to develop and access different methods of altimetry data assimilation to improve river bottom levels and Manning roughness estimations in a 1-D hydrodynamic model. The case study was a 1,100 km reach of the Madeira River, a tributary of the Amazon. The tested assimilation methods are direct insertion, linear interpolation, SCE-UA global optimization algorithm and a Kalman Filter adaptation. The Kalman Filter method is composed by new physically based covariance functions developed from steady-flow and backwater equations. It is accessed the benefits of altimetry missions with different spatio-temporal resolutions, such as ICESAT-1, Envisat and Jason 2. Level time series of 5 gauging stations and 5 GPS river height profiles are used to assess and validate the assimilation methods. Finally, the potential of future missions are discussed, such as ICESAT-2 and SWOT satellites.

Temporal changes in surface roughness around 88°S from repeat high-resolution Airborne Topographic Mapper laser altimetry

NASA Astrophysics Data System (ADS)

Studinger, M.; Brunt, K. M.; Medley, B.; Casey, K.; Neumann, T.

2017-12-01

The southern convergence of all ICESat-2 and CryoSat-2 tracks at 88°S is in a region of relatively low accumulation and surface slope making it ideal for satellite altimetry calibration and validation. In order to evaluate the stability and surface characteristics of the area we have analyzed repeat airborne laser altimetry measurements acquired around 88°S during 2014 and 2016 by NASA's Airborne Topographic Mapper (ATM) as part of Operation IceBridge. ATM is a conical scanner that operates at a wavelength of 532 nm, with a footprint of 1 meter and a 250-m-wide swath on the ground. The ATM Level 2 ICESSN data product includes slope and roughness estimates in 80 m × 80 m platelets across the swath. The mean surface roughness around 88°S for the 2014 data is 9.4 ± 2.0 cm, with the repeat flights in 2016 showing 8.6 ± 2.8 cm. The 2014 data reveals several areas where surface roughness doubles over very short spatial scales of only a few hundred meters. These features are several tens of km wide and appear to be oriented parallel to the main sastrugi direction visible in ATM spot elevation data and Digital Mapping System (DMS) visual imagery collected simultaneously. The rougher surface features are also present in the CReSIS snow radar data collected at the same time. These areas of increased surface roughness disappear in 2016 or seem to be significantly reduced in amplitude with the sharpness of the edges significantly reduced. The combination of simultaneous altimetry, snow radar and visual imagery on a regional scale provides a unique data set to study small scale deposition and erosional processes and their temporal variability. Our long-term goal is to quantify the spatial variability in snow accumulation rates south of 86°S in support of past, current and future altimetry measurements and surface mass balance model evaluation.

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

NASA Technical Reports Server (NTRS)

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

1999-01-01

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

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

NASA Technical Reports Server (NTRS)

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

2000-01-01

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

Space Qualification of the Optical Filter Assemblies for the ICESat-2/ATLAS Instrument

NASA Technical Reports Server (NTRS)

Troupaki, Elisavet; Denny, Zachary; Wu, Stewart; Bradshaw, Heather; Smith, Kevin; Hults, Judy; Ramos-Izquierdo, Luis; Cook, William

2015-01-01

The Advanced Topographic Laser Altimeter System (ATLAS) will be the only instrument on the Ice, Cloud, and Land Elevation Satellite -2 (ICESat-2). ICESat-2 is the 2nd-generation of the orbiting laser altimeter ICESat, which will continue polar ice topography measurements with improved precision laser-ranging techniques. In contrast to the original ICESat design, ICESat-2 will use a micro-pulse, multi-beam approach that provides dense cross-track sampling to help scientists determine a surface's slope with each pass of the satellite. The ATLAS laser will emit visible, green laser pulses at a wavelength of 532 nm and a rate of 10 kHz and will be split into 6 beams. A set of six identical, thermally-tuned etalon filter assemblies will be used to remove background solar radiation from the collected signal while transmitting the laser light to the detectors. A seventh etalon assembly will be used to monitor the laser center wavelength during the mission. In this paper, we present the design and optical performance measurements of the ATLAS optical filter assemblies (OFA) in air and in vacuum before integration on the ATLAS instrument.

Space Qualification of the Optical Filter Assemblies for the ICESat-2/ATLAS Instrument

NASA Technical Reports Server (NTRS)

Troupaki, E.; Denny, Z. H.; Wu, S.; Bradshaw, H. N.; Smith, K. A.; Hults, J. A.; Ramos-Izquierdo, L. A.; Cook, W. B.

2015-01-01

The Advanced Topographic Laser Altimeter System (ATLAS) will be the only instrument on the Ice, Cloud, and Land Elevation Satellite -2 (ICESat-2). ICESat-2 is the 2nd-generation of the orbiting laser altimeter ICESat, which will continue polar ice topography measurements with improved precision laser-ranging techniques. In contrast to the original ICESat design, ICESat-2 will use a micro-pulse, multi-beam approach that provides dense cross-track sampling to help scientists determine a surface's slope with each pass of the satellite. The ATLAS laser will emit visible, green laser pulses at a wavelength of 532 nm and a rate of 10 kHz and will be split into 6 beams. A set of six identical, thermally tuned optical filter assemblies (OFA) will be used to remove background solar radiation from the collected signal while transmitting the laser light to the detectors. A seventh assembly will be used to monitor the laser center wavelength during the mission. In this paper, we present the design and optical performance measurements of the ATLAS OFA in air and in vacuum prior to their integration on the ATLAS instrument.

Space-Borne Laser Altimeter Geolocation Error Analysis

NASA Astrophysics Data System (ADS)

Wang, Y.; Fang, J.; Ai, Y.

2018-05-01

This paper reviews the development of space-borne laser altimetry technology over the past 40 years. Taking the ICESAT satellite as an example, a rigorous space-borne laser altimeter geolocation model is studied, and an error propagation equation is derived. The influence of the main error sources, such as the platform positioning error, attitude measurement error, pointing angle measurement error and range measurement error, on the geolocation accuracy of the laser spot are analysed by simulated experiments. The reasons for the different influences on geolocation accuracy in different directions are discussed, and to satisfy the accuracy of the laser control point, a design index for each error source is put forward.

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

NASA Technical Reports Server (NTRS)

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

2003-01-01

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

Delta II ICESat-2 Booster Arrival

NASA Image and Video Library

2018-03-09

A United Launch Alliance Delta II booster arrives at NASA's Building 836, the Spacecraft Labs Telemetry Station at Vandenberg Air Force Base in California. It will be offloaded and begin preliminary checkouts and preflight processing for launch of the agency's Ice, Cloud and land Elevation Satellite-2, or ICESat-2. Liftoff from Space Launch Complex-2 at Vandenberg is scheduled for Sept. 12, 2018, and will be the last for the venerable Delta II rocket. Once in orbit, the satellite is designed to measure the height of a changing Earth, one laser pulse at a time, 10,000 laser pulses a second. The satellite will carry a single instrument, the Advanced Topographic Laser Altimeter System. ICESat-2 will help scientists investigate why, and how much, Earth's frozen and icy areas are changing. These area make up Earth's the cryosphere.

Delta II ICESat-2 Fairing Cleaning and Sampling

NASA Image and Video Library

2018-04-06

On Friday, April 6, 2018, in NASA’s Building 8337 at Vandenberg Air Force Base in California, a technician cleans and takes samples from the payload fairing the will protect NASA's Ice, Cloud and land Elevation Satellite-2, or ICESat-2, satellite during launch. Liftoff atop a United Launch Alliance Delta II rocket is scheduled for Sept. 12, 2018, from Space Launch Complex-2 at Vandenberg. It will be the last for the venerable Delta II rocket. ICESat-2, which is being built and tested by Orbital ATK in Gilbert, Arizona, will carry a single instrument called the Advanced Topographic Laser Altimeter System, or ATLAS. The ATLAS instrument is being built and tested at NASA’s Goddard Space Flight Center in Greenbelt Maryland. Once in orbit, the satellite is designed to measure the height of a changing Earth, one laser pulse at a time, 10,000 laser pulses a second. ICESat-2 will help scientists investigate why, and how much, Earth’s frozen and icy areas, called the cryosphere, are changing.

Delta II ICESat-2 Fairing Cleaning and Sampling

NASA Image and Video Library

2018-04-06

On Friday, April 6, 2018, in NASA’s Building 8337 at Vandenberg Air Force Base in California, technicians and engineers clean and take samples from the payload fairing the will protect NASA's Ice, Cloud and land Elevation Satellite-2, or ICESat-2, satellite during launch. Liftoff atop a United Launch Alliance Delta II rocket is scheduled for Sept. 12, 2018, from Space Launch Complex-2 at Vandenberg. It will be the last for the venerable Delta II rocket. ICESat-2, which is being built and tested by Orbital ATK in Gilbert, Arizona, will carry a single instrument called the Advanced Topographic Laser Altimeter System, or ATLAS. The ATLAS instrument is being built and tested at NASA’s Goddard Space Flight Center in Greenbelt Maryland. Once in orbit, the satellite is designed to measure the height of a changing Earth, one laser pulse at a time, 10,000 laser pulses a second. ICESat-2 will help scientists investigate why, and how much, Earth’s frozen and icy areas, called the cryosphere, are changing.

Delta II ICESat-2 Fairing Cleaning and Sampling

NASA Image and Video Library

2018-04-06

On Friday, April 6, 2018, in NASA’s Building 8337 at Vandenberg Air Force Base in California, technicians and engineers check samples during cleaning of the payload fairing that will protect NASA's Ice, Cloud and land Elevation Satellite-2, or ICESat-2, satellite during launch. Liftoff atop a United Launch Alliance Delta II rocket is scheduled for Sept. 12, 2018, from Space Launch Complex-2 at Vandenberg. It will be the last for the venerable Delta II rocket. ICESat-2, which is being built and tested by Orbital ATK in Gilbert, Arizona, will carry a single instrument called the Advanced Topographic Laser Altimeter System, or ATLAS. The ATLAS instrument is being built and tested at NASA’s Goddard Space Flight Center in Greenbelt Maryland. Once in orbit, the satellite is designed to measure the height of a changing Earth, one laser pulse at a time, 10,000 laser pulses a second. ICESat-2 will help scientists investigate why, and how much, Earth’s frozen and icy areas, called the cryosphere, are changing.

High-quality seamless DEM generation blending SRTM-1, ASTER GDEM v2 and ICESat/GLAS observations

NASA Astrophysics Data System (ADS)

Yue, Linwei; Shen, Huanfeng; Zhang, Liangpei; Zheng, Xianwei; Zhang, Fan; Yuan, Qiangqiang

2017-01-01

The absence of a high-quality seamless global digital elevation model (DEM) dataset has been a challenge for the Earth-related research fields. Recently, the 1-arc-second Shuttle Radar Topography Mission (SRTM-1) data have been released globally, covering over 80% of the Earth's land surface (60°N-56°S). However, voids and anomalies still exist in some tiles, which has prevented the SRTM-1 dataset from being directly used without further processing. In this paper, we propose a method to generate a seamless DEM dataset blending SRTM-1, ASTER GDEM v2, and ICESat laser altimetry data. The ASTER GDEM v2 data are used as the elevation source for the SRTM void filling. To get a reliable filling source, ICESat GLAS points are incorporated to enhance the accuracy of the ASTER data within the void regions, using an artificial neural network (ANN) model. After correction, the voids in the SRTM-1 data are filled with the corrected ASTER GDEM values. The triangular irregular network based delta surface fill (DSF) method is then employed to eliminate the vertical bias between them. Finally, an adaptive outlier filter is applied to all the data tiles. The final result is a seamless global DEM dataset. ICESat points collected from 2003 to 2009 were used to validate the effectiveness of the proposed method, and to assess the vertical accuracy of the global DEM products in China. Furthermore, channel networks in the Yangtze River Basin were also extracted for the data assessment.

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

NASA Technical Reports Server (NTRS)

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

2015-01-01

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

ICESat Observations of Southern Alaska Glaciers

NASA Technical Reports Server (NTRS)

Sauber, Jeanne; Molnia, Bruce F.; Mitchell, Darius

2003-01-01

In late February and March, 2003, the Ice, Cloud, and land Elevation Satellite (ICESat) measured ice and land elevations along profiles across southern Alaska. During this initial data acquisition stage ICESat observations were made on 8-day repeat tracks to enable calibration and validation of the ICESat data products. Each profile consists of a series of single point values derived from centroid elevations of an $\\approx$70 m diameter laser footprint. The points are s4pakated by $\\approx$172 m along track. Data siets of 8-day observations (an ascending and descending ground track) crossed the Bering and Malaspina Glacier. Following its 1993--1995 surge; the Bering Glacier has undergone major terminus retreat as well as ike thinning in the abtation zone. During the later part of the 20th century, parts of the Malaspina thinned by about 1 m/yr. The multiple observation profiles across the Bering and Malaspina piedmont lobes obtained in February/March are being geolocated on Landsat images and the elevation profiles will be used for a number o scientific objectives. Based on our simulations of ICESat performance over the varied ice surface of the Jakobshavn Glacier of GReenland, 2003, we expect to measure annual, and possibly seasonal, ice elevation changes on the large Alaskan glaciers. Using elevation data obtained from a second laser, we plan to estimate ice elevation changes on the Bering Glacier between March and October 2003.

The ICESat-2 mission: design, status, applications and pre-launch performance assessments for monitoring cryopsheric changes

NASA Astrophysics Data System (ADS)

Neumann, T.; Markus, T.; Csatho, B. M.; Martino, A. J.

2013-12-01

NASA's Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) is the next-generation orbiting laser altimeter, following the ICESat mission, which operated between 2003 and 2009. Its primary aim is to monitor sea-ice thickness and ice sheet elevation change at scales from outlet glaciers to the entire ice sheet, and enable global assessment of vegetation canopy height as established by ICESat. ICESat-2 is now in Phase C (Design and Development). It is scheduled to launch in 2016 on a Delta II rocket from Vandenberg Air Force Base in California. ICESat-2 will carry the Advanced Topographic Laser Altimeter System (ATLAS) and collect data to a latitudinal limit of 88 degrees. In contrast to Geoscience Laser Altimeter System (GLAS) on ICESat, ATLAS employs a 6-beam micro-pulse laser photon-counting approach. It uses a high repetition rate (10 kHz; resulting in 70 cm footprint spacing on the ground along the direction of travel) low-power laser in conjunction with single-photon sensitive detectors to measure ranges using 532 nm (green) laser light. In the polar regions, the 91-day repeat orbit pattern with a roughly monthly sub-cycle is designed to monitor seasonal and interannual variations of Greenland and Antarctic ice sheet elevations and monthly sea ice thickness changes. Dense ground-tracks over the rest of the globe achieved through a systematic sequence of off-nadir pointing (resulting in < 2 km ground-track spacing at the equator after two years) will enable measurements of land topography and vegetation canopy heights, allowing estimates of biomass and carbon in above-ground vegetation. While the ICESat-2 mission was optimized for cryospheric science, elevation measurements will be collected over land and oceans as well as histograms of backscatter from the atmosphere. These observations will provide a wealth of opportunities in addition to the primary science objectives, ranging from the retrieval of cloud properties, to river stages, to snow cover, to land

Simulation of ICESat-2 canopy height retrievals for different ecosystems

NASA Astrophysics Data System (ADS)

Neuenschwander, A. L.

2016-12-01

Slated for launch in late 2017 (or early 2018), the ICESat-2 satellite will provide a global distribution of geodetic measurements from a space-based laser altimeter of both the terrain surface and relative canopy heights which will provide a significant benefit to society through a variety of applications ranging from improved global digital terrain models to producing distribution of above ground vegetation structure. The ATLAS instrument designed for ICESat-2, will utilize a different technology than what is found on most laser mapping systems. The photon counting technology of the ATLAS instrument onboard ICESat-2 will record the arrival time associated with a single photon detection. That detection can occur anywhere within the vertical distribution of the reflected signal, that is, anywhere within the vertical distribution of the canopy. This uncertainty of where the photon will be returned from within the vegetation layer is referred to as the vertical sampling error. Preliminary simulation studies to estimate vertical sampling error have been conducted for several ecosystems including woodland savanna, montane conifers, temperate hardwoods, tropical forest, and boreal forest. The results from these simulations indicate that the canopy heights reported on the ATL08 data product will underestimate the top canopy height in the range of 1 - 4 m. Although simulation results indicate the ICESat-2 will underestimate top canopy height, there is, however, a strong correlation between ICESat-2 heights and relative canopy height metrics (e.g. RH75, RH90). In tropical forest, simulation results indicate the ICESat-2 height correlates strongly with RH90. Similarly, in temperate broadleaf forest, the simulated ICESat-2 heights were also strongly correlated with RH90. In boreal forest, the simulated ICESat-2 heights are strongly correlated with RH75 heights. It is hypothesized that the correlations between simulated ICESat-2 heights and canopy height metrics are a

The ICESat-2 Mission: Concept, pre-launch activities, and opportunities

NASA Astrophysics Data System (ADS)

Markus, T.; Neumann, T.; Csatho, B. M.

2011-12-01

Ice sheet and sea level changes have been explicitly identified as a priority in the President's Climate Change Science Program, the Arctic Climate Impact Assessment, the 4th Assessment Report of the IPCC and other national and international policy documents. Following recommendations from the National Research Council for an ICESat follow-on mission, the ICESat-2 mission is now under development for launch in early 2016. The primary aims of the ICESat-2 mission are to continue measurements of sea-ice thickness change, and ice sheet elevation changes at scales from outlet glaciers to the entire ice sheet as established by ICESat. In contrast to ICESat, ICESat-2 will employ a 6-beam micro-pulse laser photon-counting approach. The current concept uses a high repetition rate (10 kHz; equivalent to 70 cm on the ground) low-power laser in conjunction with single-photon sensitive detectors to measure range using ~532nm (green) light. The concept will enable the generation of seasonal maps of ice sheet elevation of Greenland and Antarctica, monthly maps of sea ice thickness of the polar ocean, a dense map of land elevation (2 km track spacing at the equator after two years) enabling the determination of canopy height, as well as ocean heights. While the mission has been optimized for cryospheric science and vast amount of high precision elevation measurements taken over land and over the ocean as well as of the atmosphere will provide scientists with a wealth of opportunities to explore the utility of ICESat-2. Those will range from the retrieval of cloud properties, to river stages, to snow cover, to land use changes and more. The presentation will review the measurement concept and physical principles of ICESat-2, current and planned activities to assess instrument performance and develop geophysical algorithms, as well as potential opportunities outside the main objectives of ICESat-2.

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

NASA Technical Reports Server (NTRS)

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

1999-01-01

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

Using Laser Altimetry to Detect Topographic Change at Long Valley Caldera, California

NASA Technical Reports Server (NTRS)

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

1997-01-01

Long Valley caldera, California, is a site of extensive volcanism, persistent seismicity, and uplift of a resurgent dome, currently at a rate of approximately 3 cm/year. Airborne laser altimetry was used to determine the surface topography of the region in 1993. A repeat mission occurred in 1995. Three different laser altimeters were flown, dubbed ATLAS, SLICER and RASCAL. Data processing consists of the combination of the aircraft trajectory and attitude data with the laser range, the determination of an atmospheric delay, laser pulse timing errors, laser system biases, and data geolocation to obtain the position of the laser spot on the ground. Results showed that using the ATLAS and SLICER instruments, the elevation of an overflown lake is determined to precisions of 3.3 cm and 2.9 cm from altitudes of 500 m and 3 km above the ground, and approximately 10 cm using the RASCAL instrument from 500 m above ground. Comparison with tide gauge data showed the laser measurements are able to resolve centimeter-level changes in the lake elevation over time. Repeat pass analysis of tracks over flat surfaces indicate no systematic biases affect the measurement procedure of the ATLAS and SLICER instruments. Comparison of GPS and laser-derived elevations of easily-identifiable features in the caldera confirm the horizontal accuracy of the measurement is within the diameter of the laser footprint, and vertical accuracy is within the error inherent in the measurement. Crossover analysis shows that the standard error of the means at track intersection points within the caldera and dome (i.e., where zero and close to the maximum amount of uplift is expected) are about 1 cm, indicating elevation change at the 3 cm/year level should be detectable. We demonstrate one of the powerful advantages of scanning laser altimetry over other remote sensing techniques; the straightforward creation of precise digital elevation maps of overflown terrain. Initial comparison of the 1993-1995 data

Using Laser Altimetry to Detect Topographic Change in Long Valley Caldera, California

NASA Technical Reports Server (NTRS)

Hofton, M. A.; Minster, J.-B.; Ridgway, J. R.; Blair, J. B.

1997-01-01

Long Valley caldera California, is a site of extensive volcanism, persistent seismicity, and uplift of a resurgent dome, currently at a rate of about 3 cm/year. Airborne laser altimetry was used to determine the surface topography of the region in 1993. A repeat mission occurred in 1995. Three different laser altimeters were flown, dubbed ATLAS, SLICER and RASCAL. Data processing consists of the combination of the aircraft trajectory and attitude data with the laser range, the determination of an atmospheric delay, laser pulse timing errors, laser system biases, and data geolocation to obtain the position of the laser spot on the ground. Results showed that using the ATLAS and SLICER instruments, the elevation of an overflown lake is determined to precisions of 3.3 cm and 2.9 cm from altitudes of 500 m and 3 km above the ground, and about 10 cm using the RASCAL instrument from 500 m above ground. Comparison with tide gauge data showed the laser measurements are able to resolve centimeter-level changes in the lake elevation over time. Repeat pass analysis of tracks over flat surfaces indicate no systematic biases affect the measurement procedure of the ATLAS and SLICER instruments. Comparison of GPS and laser-derived elevations of easily-identifiable features in the caldera confirm the horizontal accuracy of the measurement is within the diameter of the laser footprint, and vertical accuracy is within the error inherent in the measurement. Crossover analysis shows that the standard error of the means at track intersection points within the caldera, and dome (i.e., where zero and close to the maximum amount of uplift is expected) are about I cm, indicating elevation change at the 3 cm/year level should be detectable. We demonstrate one of the powerful advantages of scanning laser altimetry over other remote sensing techniques; the straightforward creation of precise digital elevation maps of overflown terrain. Initial comparison of the 1993-1995 data indicates uplift

ICESat's First Year of Measurements Over the Polar Ice Sheets

NASA Astrophysics Data System (ADS)

Shuman, C. A.

2004-05-01

NASA's Ice, Cloud and Land Elevation Satellite (ICESat) mission was developed to measure changes in elevation of the Greenland and Antarctic ice sheets. Its primary mission goal is to significantly refine estimates of polar ice sheet mass balance. Obtaining precise, spatially dense, ice sheet elevations through time is the first step towards this goal. ICESat data will then enable study of associations between observed ice changes and dynamic or climatic forcing factors, and thus enable improved estimation of the present and future contributions of the ice sheets to global sea level rise. ICESat was launched on January 12, 2003 and acquired science data from February 20th to March 29th with the first of the three lasers of the Geoscience Laser Altimeter System (GLAS). Data acquisition with the second laser began on September 25th and continued until November 18th, 2003. For one-year change detection, the second laser is scheduled for operation from approximately February 17th to March 20th, 2004. Additional operational periods will be selected to 1) enable periodic measurements through the year, and 2) to support of other NASA Earth Science Enterprise missions and activities. To obtain these precise ice sheet elevations, GLAS has a 1064 nm wavelength laser operating at 40 Hz with a designed range precision of about 10 cm. The laser footprints are about 70 m in diameter on the Earth's surface and are spaced every 172 m along-track. The on-board GPS receiver enables radial orbit determinations to an accuracy better than 5 cm. The star-tracking attitude-determination system will enable laser footprints to be located to 6 m horizontally when attitude calibration is completed. The orbital altitude averages 600 km at an inclination of 94 degrees with coverage extending from 86 degrees N and S latitude. The spacecraft attitude can be controlled to point the laser beam to within 50 m of surface reference tracks over the ice sheets and to point off-nadir up to 5 degrees to

Delta II ICESat-2 Booster Offload onto Transporter

NASA Image and Video Library

2018-04-16

At NASA's Building 836, the Spacecraft Labs Telemetry Station at Vandenberg Air Force Base in California, a United Launch Alliance Delta II booster has been removed from its shipping container. Preliminary checkouts and preflight processing will begin leading to launch of the agency's Ice, Cloud and land Elevation Satellite-2, or ICESat-2. Liftoff from Space Launch Complex-2 at Vandenberg is scheduled for Sept. 12, 2018, and will be the last for the venerable Delta II rocket. Once in orbit, the satellite is designed to measure the height of a changing Earth, one laser pulse at a time, 10,000 laser pulses a second. The satellite will carry a single instrument, the Advanced Topographic Laser Altimeter System. ICESat-2 will help scientists investigate why, and how much, Earth's frozen and icy areas are changing. These area make up Earth's the cryosphere.

Delta II ICESat-2 Booster Offload onto Transporter

NASA Image and Video Library

2018-04-16

A United Launch Alliance Delta II booster arrives at NASA's Building 836, the Spacecraft Labs Telemetry Station at Vandenberg Air Force Base in California. It will be offloaded and begin preliminary checkouts and preflight processing for launch of the agency's Ice, Cloud and land Elevation Satellite-2, or ICESat-2. Liftoff from Space Launch Complex-2 at Vandenberg is scheduled for Sept. 12, 2018, and will be the last for the venerable Delta II rocket. Once in orbit, the satellite is designed to measure the height of a changing Earth, one laser pulse at a time, 10,000 laser pulses a second. The satellite will carry a single instrument, the Advanced Topographic Laser Altimeter System. ICESat-2 will help scientists investigate why, and how much, Earth's frozen and icy areas are changing. These area make up Earth's the cryosphere.

On Orbit Receiver Performance Assessment of the Geoscience Laser Altimeter System (GLAS) on ICESAT

NASA Technical Reports Server (NTRS)

Sun, Xiaoli; Abshire, James B.; Spinhirne, James D.; McGarry, Jan; Jester, Peggy L.; Yi, Donghui; Palm, Stephen P.; Lancaster, Redgie S.

2006-01-01

The GLAS instrument on the NASA's ICESat mission has provided over a billion measurements of the Earth surface elevation and atmosphere backscattering at both 532 and 1064-nm wavelengths. The receiver performance has stayed nearly unchanged since ICESat launch in January 2003. The altimeter receiver has achieved a less than 3-cm ranging accuracy when excluding the effects of the laser beam pointing angle determination uncertainties. The receiver can also detect surface echoes through clouds of one-way transmission as low as 5%. The 532-nm atmosphere backscattering receiver can measure aerosol and clouds with cross section as low as 1e-7/m.sr with a 1 second integration time and molecular backscattering from upper atmosphere with a 60 second integration time. The 1064-nm atmosphere backscattering receiver can measure aerosol and clouds with a cross section as low as 4e-6/m.sr. This paper gives a detailed assessment of the GLAS receiver performance based on the in-orbit calibration tests.

Sea Ice Mass Reconciliation Exercise (SIMRE) for altimetry derived sea ice thickness data sets

NASA Astrophysics Data System (ADS)

Hendricks, S.; Haas, C.; Tsamados, M.; Kwok, R.; Kurtz, N. T.; Rinne, E. J.; Uotila, P.; Stroeve, J.

2017-12-01

Satellite altimetry is the primary remote sensing data source for retrieval of Arctic sea-ice thickness. Observational data sets are available from current and previous missions, namely ESA's Envisat and CryoSat as well as NASA ICESat. In addition, freeboard results have been published from the earlier ESA ERS missions and candidates for new data products are the Sentinel-3 constellation, the CNES AltiKa mission and NASA laser altimeter successor ICESat-2. With all the different aspects of sensor type and orbit configuration, all missions have unique properties. In addition, thickness retrieval algorithms have evolved over time and data centers have developed different strategies. These strategies may vary in choice of auxiliary data sets, algorithm parts and product resolution and masking. The Sea Ice Mass Reconciliation Exercise (SIMRE) is a project by the sea-ice radar altimetry community to bridge the challenges of comparing data sets across missions and algorithms. The ESA Arctic+ research program facilitates this project with the objective to collect existing data sets and to derive a reconciled estimate of Arctic sea ice mass balance. Starting with CryoSat-2 products, we compare results from different data centers (UCL, AWI, NASA JPL & NASA GSFC) at full resolution along selected orbits with independent ice thickness estimates. Three regions representative of first-year ice, multiyear ice and mixed ice conditions are used to compare the difference in thickness and thickness change between products over the seasonal cycle. We present first results and provide an outline for the further development of SIMRE activities. The methodology for comparing data sets is designed to be extendible and the project is open to contributions by interested groups. Model results of sea ice thickness will be added in a later phase of the project to extend the scope of SIMRE beyond EO products.

Analysis of water level variation of lakes and reservoirs in Xinjiang, China using ICESat laser altimetry data (2003–2009)

PubMed Central

Liu, Hongxing; Chen, Yaning; Shu, Song; Wu, Qiusheng; Wang, Shujie

2017-01-01

This study utilizes ICESat Release 33 GLA14 data to analyse water level variation of Xinjiang’s lakes and reservoirs from 2003 to 2009. By using Landsat images, lakes and reservoirs with area larger than 1 km2 are numerically delineated with a software tool. Based on ICESat observations, we analyse the characteristics of water level variation in different geographic environments, as well as investigate the reasons for the variation. Results indicate that climatic warming contributes to rising water levels in lakes in mountainous areas, especially for lakes that are recharged by snow and glacial melting. For lakes in oases, the water levels are affected jointly by human activity and climate change, while the water levels of reservoirs are mainly affected by human activity. Comparing the annual average rates of water levels, those of lakes are higher than those of reservoirs in oasis areas. The main reasons for the decreasing water levels in desert regions are the reduction of recharged runoff and high evaporation. By analysing the variation of water levels and water volume in different geologic environments, it is found that water level and volume increased in mountainous regions, and decreased in oasis regions and desert regions. Finding also demonstrate that decreasing volume is greater than increasing volume, which results in decreasing total volume of Xinjiang lakes and reservoirs. PMID:28873094

Improving Altimetry Height-change Retrieval on the Fringes of the Antarctic Ice Sheet

NASA Astrophysics Data System (ADS)

Paolo, F. S.; Nilsson, J.; Gardner, A. S.

2017-12-01

Projections of sea-level change over the next century are highly uncertain, in part, due to insufficient understanding of ice-sheet sensitivity to changes in oceanic and atmospheric circulation. This limitation is, to a large degree, related to the lack of long and continuous observational records covering critical regions along the ice-sheet margins where the ice interacts with the ocean. Of particular importance are accurate records of changes in ice thickness that provide information on how mass fluctuates on the floating extensions of ice streams and glaciers through which the ice-sheet drains. These changes can modify the stability of the grounded ice sheet through changing back-stress, for example, through loss of ice-shelf buttressing. Here, we synthetize 25+ years of satellite altimetry observations to extend the time span and improve the resolution and accuracy of the existing record of Antarctic floating ice thickness. We incorporate data from ESA's ERS-1, ERS-2, Envisat and Cryosat-2 radar altimeters (1992-present) and NASA's ICESat laser altimeter (2003-2009) and Operation IceBridge surveys (2009-present); with plans to include ICESat-2 data soon after its launch in September 2018. Towards this effort, we revisit some of the main corrections applied to altimeter data, such as minimization of the difference between measurements from radar and laser systems; and we improve the approach for the synthesis of heterogeneous measurements of ice-surface topography and uncertainty estimation. We report on our progress in constructing this long-term and homogeneous record, with a particular focus on the floating ice shelves.

Estimating the rates of mass change, ice volume change and snow volume change in Greenland from ICESat and GRACE data

NASA Astrophysics Data System (ADS)

Slobbe, D. C.; Ditmar, P.; Lindenbergh, R. C.

2009-01-01

The focus of this paper is on the quantification of ongoing mass and volume changes over the Greenland ice sheet. For that purpose, we used elevation changes derived from the Ice, Cloud, and land Elevation Satellite (ICESat) laser altimetry mission and monthly variations of the Earth's gravity field as observed by the Gravity Recovery and Climate Experiment (GRACE) mission. Based on a stand alone processing scheme of ICESat data, the most probable estimate of the mass change rate from 2003 February to 2007 April equals -139 +/- 68 Gtonyr-1. Here, we used a density of 600+/-300 kgm-3 to convert the estimated elevation change rate in the region above 2000m into a mass change rate. For the region below 2000m, we used a density of 900+/-300 kgm-3. Based on GRACE gravity models from half 2002 to half 2007 as processed by CNES, CSR, DEOS and GFZ, the estimated mass change rate for the whole of Greenland ranges between -128 and -218Gtonyr-1. Most GRACE solutions show much stronger mass losses as obtained with ICESat, which might be related to a local undersampling of the mass loss by ICESat and uncertainties in the used snow/ice densities. To solve the problem of uncertainties in the snow and ice densities, two independent joint inversion concepts are proposed to profit from both GRACE and ICESat observations simultaneously. The first concept, developed to reduce the uncertainty of the mass change rate, estimates this rate in combination with an effective snow/ice density. However, it turns out that the uncertainties are not reduced, which is probably caused by the unrealistic assumption that the effective density is constant in space and time. The second concept is designed to convert GRACE and ICESat data into two totally new products: variations of ice volume and variations of snow volume separately. Such an approach is expected to lead to new insights in ongoing mass change processes over the Greenland ice sheet. Our results show for different GRACE solutions a snow

Mass Balance of the West Antarctic Ice-Sheet from ICESat Measurements

NASA Technical Reports Server (NTRS)

Zwally, H. Jay; Li, Jun; Robins, John; Saba, Jack L.; Yi, Donghui

2011-01-01

Mass balance estimates for 2003-2008 are derived from ICESat laser altimetry and compared with estimates for 1992-2002 derived from ERS radar altimetry. The net mass balance of 3 drainage systems (Pine Island, Thwaites/Smith, and the coast of Marie Bryd) for 2003-2008 is a loss of 100 Gt/yr, which increased from a loss of 70 Gt/yr for the earlier period. The DS including the Bindschadler and MacAyeal ice streams draining into the Ross Ice Shelf has a mass gain of 11 Gt/yr for 2003-2008, compared to an earlier loss of 70 Gt/yr. The DS including the Whillans and Kamb ice streams has a mass gain of 12 Gt/yr, including a significant thickening on the upper part of the Kamb DS, compared to a earlier gain of 6 Gt/yr (includes interpolation for a large portion of the DS). The other two DS discharging into the Ronne Ice Shelf and the northern Ellsworth Coast have a mass gain of 39 Gt/yr, compared to a gain of 4 Gt/yr for the earlier period. Overall, the increased losses of 30 Gt/yr in the Pine Island, Thwaites/Smith, and the coast of Marie Bryd DSs are exceeded by increased gains of 59 Gt/yr in the other 4 DS. Overall, the mass loss from the West Antarctic ice sheet has decreased to 38 Gt/yr from the earlier loss of 67 Gt/yr, reducing the contribution to sea level rise to 0.11 mm/yr from 0.19 mm/yr

In Orbit Performance of Si Avalanche Photodiode Single Photon Counting Modules in the Geoscience Laser Altimeter System on ICESat

NASA Technical Reports Server (NTRS)

Sun, X.; Jester, P. L.; Palm, S. P.; Abshire, J. B.; Spinhime, J. D.; Krainak, M. A.

2006-01-01

Si avalanche photodiode (APD) single photon counting modules (SPCMs) are used in the Geoscience Laser Altimeter System (GLAS) on Ice, Cloud, anti land Elevation Satellite (ICESat), currently in orbit measuring Earth surface elevation and atmosphere backscattering. These SPCMs are used to measure cloud and aerosol backscatterings to the GLAS laser light at 532-nm wavelength with 60-70% quantum efficiencies and up to 15 millions/s maximum count rates. The performance of the SPCMs has been closely monitored since ICESat launch on January 12, 2003. There has been no measurable change in the quantum efficiency, as indicated by the average photon count rates in response to the background light from the sunlit earth. The linearity and the afterpulsing seen from the cloud and surface backscatterings profiles have been the same as those during ground testing. The detector dark count rates monitored while the spacecraft was in the dark side of the globe have increased almost linearly at about 60 counts/s per day due to space radiation damage. The radiation damage appeared to be independent of the device temperature and power states. There was also an abrupt increase in radiation damage during the solar storm in 28-30 October 2003. The observed radiation damage is a factor of two to three lower than the expected and sufficiently low to provide useful atmosphere backscattering measurements through the end of the ICESat mission. To date, these SPCMs have been in orbit for more than three years. The accumulated operating time to date has reached 290 days (7000 hours). These SPCMs have provided unprecedented receiver sensitivity and dynamic range in ICESat atmosphere backscattering measurements.

Delta II ICESat-2 Booster Offload onto Transporter

NASA Image and Video Library

2018-04-16

At NASA's Building 836, the Spacecraft Labs Telemetry Station at Vandenberg Air Force Base in California, a United Launch Alliance Delta II booster is removed from its shipping container. After it is offloaded, preliminary checkouts and preflight processing will begin leading to launch of the agency's Ice, Cloud and land Elevation Satellite-2, or ICESat-2. Liftoff from Space Launch Complex-2 at Vandenberg is scheduled for Sept. 12, 2018, and will be the last for the venerable Delta II rocket. Once in orbit, the satellite is designed to measure the height of a changing Earth, one laser pulse at a time, 10,000 laser pulses a second. The satellite will carry a single instrument, the Advanced Topographic Laser Altimeter System. ICESat-2 will help scientists investigate why, and how much, Earth's frozen and icy areas are changing. These area make up Earth's the cryosphere.

ICESat-2: An overview of science objectives, status, data products and expected performance

NASA Astrophysics Data System (ADS)

Neumann, T.; Markus, T.; Anthony, M.

2016-12-01

NASA's Ice, Cloud, and land Elevation Satellite-2's (ICESat-2) mission objectives are to quantify polar ice sheet contributions to sea level change, quantify regional signatures of ice sheet changes to assess driving mechanisms, estimate sea ice thickness, and to enable measurements of canopy height as a basis for estimating large-scale biomass. With a scheduled launch date in late 2017 most of the flight hardware has been assembled, integrated and tested and algorithm implementation for its standard geophysical products is well underway. The spacecraft, built by Orbital ATK, is completed and is undergoing testing. ICESat-2's single instrument, the Advanced Topographic Laser Altimeter System (ATLAS), is built by NASA Goddard Space Flight Center and by the time of the Fall Meeting will be undergoing integration and testing with the spacecraft, becoming the ICESat-2 observatory. In parallel, high level geophysical data products and associated algorithms are in development using airborne laser altimeter data. This presentation will give an overview of the design of ICESat-2, of its hardware and software status, as well as examples of ICESat-2's coverage and what the data will look like.

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

NASA Technical Reports Server (NTRS)

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

2012-01-01

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

The ICESat-2 Mission: Concept, Pre-Launch Activities, and Opportunities

NASA Technical Reports Server (NTRS)

Markus, Thorsten; Neumann, Tom; Csatho, Beata M.

2011-01-01

Ice sheet and sea level changes have been explicitly identified as a priority in the President's Climate Change Science Program, the Arctic Climate Impact Assessment, the 4th Assessment Report of the IPee and other national and international policy documents. Following recommendations from the National Research Council for an ICESat follow-on mission, the ICESat-2 mission is now under development for launch in early 2016. The primary aims of the ICESat-2 mission are to continue measurements of sea-ice thickness change, and ice sheet elevation changes at scales from outlet glaciers to the entire ice sheet as established by ICES at. In contrast to ICES at, ICESat-2 will employ a 6-beam micro-pulse laser photon-counting approach. The current concept uses a high repetition rate (10 kHz; equivalent to 70 cm on the ground) low-power laser in conjunction with single-photon sensitive detectors to measure range using approximately 532nm (green) light. The concept will enable the generation of seasonal maps of ice sheet elevation of Greenland and Antarctica, monthly maps of sea ice thickness of the polar ocean, a dense map of land elevation (2 km track spacing at the equator after two years) enabling the determination of canopy height, as well as ocean heights. While the mission has been optimized for cryospheric science and vast amount of high precision elevation measurements taken over land and over the ocean as well as of the atmosphere will provide scientists with a wealth of opportunities to explore the utility of ICESat-2. Those will range from the retrieval of cloud properties, to river stages, to snow cover, to land use changes and more. The presentation will review the measurement concept and physical principles of ICESat-2, current and planned activities to assess instrument performance and develop geophysical algorithms, as well as potential opportunities outside the main objectives of ICESat-2.

The GLAS Algorithm Theoretical Basis Document for Precision Attitude Determination (PAD)

NASA Technical Reports Server (NTRS)

Bae, Sungkoo; Smith, Noah; Schutz, Bob E.

2013-01-01

The Geoscience Laser Altimeter System (GLAS) was the sole instrument for NASAs Ice, Cloud and land Elevation Satellite (ICESat) laser altimetry mission. The primary purpose of the ICESat mission was to make ice sheet elevation measurements of the polar regions. Additional goals were to measure the global distribution of clouds and aerosols and to map sea ice, land topography and vegetation. ICESat was the benchmark Earth Observing System (EOS) mission to be used to determine the mass balance of the ice sheets, as well as for providing cloud property information, especially for stratospheric clouds common over polar areas.

Lasers, penguins, and polar bears: Novel outreach and education approaches for NASA's ICESat-2 mission

NASA Astrophysics Data System (ADS)

Casasanto, Valerie A.; Campbell, Brian; Manrique, Adriana; Ramsayer, Kate; Markus, Thorsten; Neumann, Thomas

2018-07-01

NASA's Ice, Cloud, and land Elevation Satellite (ICESat-2), to be launched in 2018, will measure the height of Earth from space using lasers, collecting the most precise and detailed account yet of our planet's elevation. The mission will allow scientists to investigate how global warming is changing the planet's icy polar regions and to take stock of Earth's vegetation. ICESat-2's emphasis on polar ice, as well as its unique measurement approach, will provide an intriguing and accessible focus for the mission's education and outreach programs. Sea ice and land ice are areas that have experienced significant change in recent years. It is key to communicate why we are measuring these areas and their importance. ICESat-2 science data will provide much-needed answers to climate change questions such as, "Is the ice really melting in the polar regions?" and "What does studying Earth's frozen regions tell us about our changing climate?" In this paper, lessons-learned and novel techniques for engaging and educating all audiences in the mission will be discussed, such as including results of a unique collaboration with art design school the Savannah College of Art Design (SCAD) to create fun and exciting products such as animated characters and interactive stories. Future collaborations with wildlife researchers, a new citizen science program in collaboration with GLOBE, and evidence from other STEAM (Science, Technology, Engineering, Arts, Math) education approaches will also be detailed in this paper.

Elevation Change of Drangajokull, Iceland, from Cloud-Cleared ICESat Repeat Profiles and GPS Ground-Survey Data

NASA Technical Reports Server (NTRS)

Shuman, Christopher A.; Sigurdsson, Oddur; Williams, Richard, Jr.; Hall, Dorothy K.

2009-01-01

Located on the Vestfirdir Northwest Fjords), DrangaJokull is the northernmost ice map in Iceland. Currently, the ice cap exceeds 900 m in elevation and covered an area of approx.l46 sq km in August 2004. It was about 204 sq km in area during 1913-1914 and so has lost mass during the 20th century. Drangajokull's size and accessibility for GPS surveys as well as the availability of repeat satellite altimetry profiles since late 2003 make it a good subject for change-detection analysis. The ice cap was surveyed by four GPS-equipped snowmobiles on 19-20 April 2005 and has been profiled in two places by Ice, Cloud. and land Elevation Satellite (ICESat) 'repeat tracks,' fifteen times from late to early 2009. In addition, traditional mass-balance measurements have been taken seasonally at a number of locations across the ice cap and they show positive net mass balances in 2004/2005 through 2006/2007. Mean elevation differences between the temporally-closest ICESat profiles and the GPS-derived digital-elevation model (DEM)(ICESat - DEM) are about 1.1 m but have standard deviations of 3 to 4 m. Differencing all ICESat repeats from the DEM shows that the overall elevation difference trend since 2003 is negative with losses of as much as 1.5 m/a from same season to same season (and similar elevation) data subsets. However, the mass balance assessments by traditional stake re-measurement methods suggest that the elevation changes where ICESat tracks 0046 and 0307 cross Drangajokull are not representative of the whole ice cap. Specifically, the area has experienced positive mass balance years during the time frame when ICESat data indicates substantial losses. This analysis suggests that ICESat-derived elevations may be used for multi-year change detection relative to other data but suggests that large uncertainties remain. These uncertainties may be due to geolocation uncertainty on steep slopes and continuing cloud cover that limits temporal and spatial coverage across the

First Assessments of Predicted ICESat-2 Performance Using Aircraft Data

NASA Technical Reports Server (NTRS)

Neumann, Thomas; Markus, Thorsten; Cook, William; Hancock, David; Brenner, Anita; Kelly, Brunt; DeMarco, Eugenia; Reed, Daniel; Walsh, Kaitlin

2012-01-01

The Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) is a next-generation laser altimeter designed to continue key observations of ice sheet elevation change, sea ice freeboard, vegetation canopy height, earth surface elevation, and sea surface height. Scheduled for launch in mid-2016, ICESat-2 will use a high repetition rate (10 kHz), small footprint (10 m nominal ground diameter) laser, and a single-photon-sensitive detection strategy (photon counting) to measure precise range to the earth's surface. Using green light (532 nm), the six beams of ICESat-2 will provide improved spatial coverage compared with the single beam of ICESat, while the differences in transmit energy among the beams provide a large dynamic range. The six beams are arranged into three pairs of beams which allow slopes to measured on an orbit-by-orbit basis. In order to evaluate models of predicted ICESat-2 performance and provide ICESat-2-like data for algorithm development, an airborne ICESat-2 simulator was developed and first flown in 2010. This simulator, the Multiple Altimeter Beam Experimental Lidar (MABEL) was most recently deployed to Iceland in April 2012 and collected approx 85 hours of science data over land ice, sea ice, and calibration targets. MABEL uses a similar photon-counting measurement strategy to what will be used on ICESat-2. MABEL collects data in 16 green channels and an additional 8 channels in the infrared aligned across the direction of flight. By using NASA's ER-2 aircraft flying at 20km altitude, MABEL flies as close to space as is practical, and collects data through approx 95% of the atmosphere. We present background on the MABEL instrument, and data from the April 2012 deployment to Iceland. Among the 13 MABEL flights, we collected data over the Greenland ice sheet interior and outlet glaciers in the southwest and western Greenland, sea ice data over the Nares Strait and Greenland Sea, and a number of small glaciers and ice caps in Iceland and Svalbard

A Range Correction for Icesat and Its Potential Impact on Ice-sheet Mass Balance Studies

NASA Technical Reports Server (NTRS)

Borsa, A. A.; Moholdt, G.; Fricker, H. A.; Brunt, Kelly M.

2014-01-01

We report on a previously undocumented range error in NASA's Ice, Cloud and land Elevation Satellite (ICESat) that degrades elevation precision and introduces a small but significant elevation trend over the ICESat mission period. This range error (the Gaussian-Centroid or 'G-C'offset) varies on a shot-to-shot basis and exhibits increasing scatter when laser transmit energies fall below 20 mJ. Although the G-C offset is uncorrelated over periods less than1 day, it evolves over the life of each of ICESat's three lasers in a series of ramps and jumps that give rise to spurious elevation trends of -0.92 to -1.90 cm yr(exp -1), depending on the time period considered. Using ICESat data over the Ross and Filchner-Ronne ice shelves we show that (1) the G-C offset introduces significant biases in ice-shelf mass balance estimates, and (2) the mass balance bias can vary between regions because of different temporal samplings of ICESat.We can reproduce the effect of the G-C offset over these two ice shelves by fitting trends to sample-weighted mean G-C offsets for each campaign, suggesting that it may not be necessary to fully repeat earlier ICESat studies to determine the impact of the G-C offset on ice-sheet mass balance estimates.

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

NASA Technical Reports Server (NTRS)

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

2001-01-01

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

Airborne Polarimetric, Two-Color Laser Altimeter Measurements of Lake Ice Cover: A Pathfinder for NASA's ICESat-2 Spaceflight Mission

NASA Technical Reports Server (NTRS)

Harding, David; Dabney, Philip; Valett, Susan; Yu, Anthony; Vasilyev, Aleksey; Kelly, April

2011-01-01

The ICESat-2 mission will continue NASA's spaceflight laser altimeter measurements of ice sheets, sea ice and vegetation using a new measurement approach: micropulse, single photon ranging at 532 nm. Differential penetration of green laser energy into snow, ice and water could introduce errors in sea ice freeboard determination used for estimation of ice thickness. Laser pulse scattering from these surface types, and resulting range biasing due to pulse broadening, is assessed using SIMPL airborne data acquired over icecovered Lake Erie. SIMPL acquires polarimetric lidar measurements at 1064 and 532 nm using the micropulse, single photon ranging measurement approach.

Using airborne laser altimetry to determine fuel models for estimating fire behavior

Treesearch

Carl A. Seielstad; Lloyd P. Queen

2003-01-01

Airborne laser altimetry provides an unprecedented view of the forest floor in timber fuel types and is a promising new tool for fuels assessments. It can be used to resolve two fuel models under closed canopies and may be effective for estimating coarse woody debris loads. A simple metric - obstacle density - provides the necessary quantification of fuel bed roughness...

Surface-Height Determination of Crevassed Glaciers-Mathematical Principles of an Autoadaptive Density-Dimension Algorithm and Validation Using ICESat-2 Simulator (SIMPL) Data

NASA Technical Reports Server (NTRS)

Herzfeld, Ute C.; Trantow, Thomas M.; Harding, David; Dabney, Philip W.

2017-01-01

Glacial acceleration is a main source of uncertainty in sea-level-change assessment. Measurement of ice-surface heights with a spatial and temporal resolution that not only allows elevation-change calculation, but also captures ice-surface morphology and its changes is required to aid in investigations of the geophysical processes associated with glacial acceleration.The Advanced Topographic Laser Altimeter System aboard NASAs future ICESat-2 Mission (launch 2017) will implement multibeam micropulse photon-counting lidar altimetry aimed at measuring ice-surface heights at 0.7-m along-track spacing. The instrument is designed to resolve spatial and temporal variability of rapidly changing glaciers and ice sheets and the Arctic sea ice. The new technology requires the development of a new mathematical algorithm for the retrieval of height information.We introduce the density-dimension algorithm (DDA) that utilizes the radial basis function to calculate a weighted density as a form of data aggregation in the photon cloud and considers density an additional dimension as an aid in auto-adaptive threshold determination. The auto-adaptive capability of the algorithm is necessary to separate returns from noise and signal photons under changing environmental conditions. The algorithm is evaluated using data collected with an ICESat-2 simulator instrument, the Slope Imaging Multi-polarization Photon-counting Lidar, over the heavily crevassed Giesecke Braer in Northwestern Greenland in summer 2015. Results demonstrate that ICESat-2 may be expected to provide ice-surface height measurements over crevassed glaciers and other complex ice surfaces. The DDA is generally applicable for the analysis of airborne and spaceborne micropulse photon-counting lidar data over complex and simple surfaces.

Airborne laser altimetry and multispectral imagery for modeling Golden-cheeked Warbler (Setophaga chrysoparia) density

Treesearch

Steven E. Sesnie; James M. Mueller; Sarah E. Lehnen; Scott M. Rowin; Jennifer L. Reidy; Frank R. Thompson

2016-01-01

Robust models of wildlife population size, spatial distribution, and habitat relationships are needed to more effectively monitor endangered species and prioritize habitat conservation efforts. Remotely sensed data such as airborne laser altimetry (LiDAR) and digital color infrared (CIR) aerial photography combined with well-designed field studies can help fill these...

Cascading water underneath Wilkes Land, East Antarctic ice sheet, observed using altimetry and digital elevation models

NASA Astrophysics Data System (ADS)

Flament, T.; Berthier, E.; Rémy, F.

2014-04-01

We describe a major subglacial lake drainage close to the ice divide in Wilkes Land, East Antarctica, and the subsequent cascading of water underneath the ice sheet toward the coast. To analyse the event, we combined altimetry data from several sources and subglacial topography. We estimated the total volume of water that drained from Lake CookE2 by differencing digital elevation models (DEM) derived from ASTER and SPOT5 stereo imagery acquired in January 2006 and February 2012. At 5.2 ± 1.5 km3, this is the largest single subglacial drainage event reported so far in Antarctica. Elevation differences between ICESat laser altimetry spanning 2003-2009 and the SPOT5 DEM indicate that the discharge started in November 2006 and lasted approximately 2 years. A 13 m uplift of the surface, corresponding to a refilling of about 0.6 ± 0.3 km3, was observed between the end of the discharge in October 2008 and February 2012. Using the 35-day temporal resolution of Envisat radar altimetry, we monitored the subsequent filling and drainage of connected subglacial lakes located downstream of CookE2. The total volume of water traveling within the theoretical 500-km-long flow paths computed with the BEDMAP2 data set is similar to the volume that drained from Lake CookE2, and our observations suggest that most of the water released from Lake CookE2 did not reach the coast but remained trapped underneath the ice sheet. Our study illustrates how combining multiple remote sensing techniques allows monitoring of the timing and magnitude of subglacial water flow beneath the East Antarctic ice sheet.

The Geoscience Laser Altimetry/Ranging System (GLARS)

NASA Technical Reports Server (NTRS)

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

1986-01-01

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

Recent Elevation Changes on Bagley Ice Valley, Guyot and Yahtse Glaciers, Alaska, from ICESat Altimetry, Star-3i Airborne, and SRTM Spaceborne DEMs

NASA Astrophysics Data System (ADS)

Muskett, R. R.; Sauber, J. M.; Lingle, C. S.; Rabus, B. T.; Tangborn, W. V.; Echelmeyer, K. A.

2005-12-01

.5 m at 1562 m altitude, -2.6 ± 2.8 m at 1378 m altitude, 6.1 ± 3.5 m at 1142 m altitude, 1.4 ± 12.1 m at 1232 m altitude, -4.0 ± 4.2 m at 250 m to 1217 m altitude, -1.8 ± 3.3 m at 1200 m altitude, and 8.0 ± 6.4 m at 940 m altitude. One ICESat-derived track-to-DEM comparison on Guyot Glacier indicates a preliminary mean elevation change in the 478 m to 1150 m altitude range of -2.8 ± 14.1 m. Results, including additional comparisons to small-aircraft laser altimeter data, with more fully-corrected for estimated snow and ice accumulation / ablation between acquisitions times, will be presented. [Muskett, R.R., C.S. Lingle, W.V. Tangborn, and B.T. Rabus, Multi-decadal elevation changes on Bagley Ice Valley and Malaspina Glacier, Alaska, GRL, 30 (16), 1857, doi:10.1029/2003GL017707, 2003.

Estimating Forest Canopy Heights and Aboveground Biomass with Simulated ICESat-2 Data

NASA Astrophysics Data System (ADS)

Malambo, L.; Narine, L.; Popescu, S. C.; Neuenschwander, A. L.; Sheridan, R.

2016-12-01

The Ice, Cloud and Land Elevation Satellite (ICESat) 2 is scheduled for launch in 2017 and one of its overall science objectives will be to measure vegetation heights, which can be used to estimate and monitor aboveground biomass (AGB) over large spatial scales. This study serves to develop a methodology for utilizing vegetation data collected by ICESat-2 that will be on a five-year mission from 2017, for mapping forest canopy heights and estimating aboveground forest biomass (AGB). The specific objectives are to, (1) simulate ICESat-2 photon-counting lidar (PCL) data, (2) utilize simulated PCL data to estimate forest canopy heights and propose a methodology for upscaling PCL height measurements to obtain spatially contiguous coverage and, (3) estimate and map AGB using simulated PCL data. The laser pulse from ICESat-2 will be divided into three pairs of beams spaced approximately 3 km apart, with footprints measuring approximately 14 m in diameter and with 70 cm along-track intervals. Using existing airborne lidar data (ALS) for Sam Houston National Forest (SHNF) and known ICESat-2 beam locations, footprints are generated along beam locations and PCL data are then simulated from discrete return lidar points within each footprint. By applying data processing algorithms, photons are classified into top of canopy points and ground surface elevation points to yield tree canopy height values within each ICESat-2 footprint. AGB is then estimated using simple linear regression that utilizes AGB from a biomass map generated with ALS data for SHNF and simulated PCL height metrics for 100 m segments along ICESat-2 tracks. Two approaches also investigated for upscaling AGB estimates to provide wall-to-wall coverage of AGB are (1) co-kriging and (2) Random Forest. Height and AGB maps, which are the outcomes of this study, will demonstrate how data acquired by ICESat-2 can be used to measure forest parameters and in extension, estimate forest carbon for climate change

Application of glas laser altimetry to detect elevation changes in East Antarctica

NASA Astrophysics Data System (ADS)

Scaioni, M.; Tong, X.; Li, R.

2013-10-01

In this paper the use of ICESat/GLAS laser altimeter for estimating multi-temporal elevation changes on polar ice sheets is afforded. Due to non-overlapping laser spots during repeat passes, interpolation methods are required to make comparisons. After reviewing the main methods described in the literature (crossover point analysis, cross-track DEM projection, space-temporal regressions), the last one has been chosen for its capability of providing more elevation change rate measurements. The standard implementation of the space-temporal linear regression technique has been revisited and improved to better cope with outliers and to check the estimability of model's parameters. GLAS data over the PANDA route in East Antarctica have been used for testing. Obtained results have been quite meaningful from a physical point of view, confirming the trend reported by the literature of a constant snow accumulation in the area during the two past decades, unlike the most part of the continent that has been losing mass.

Synthesis of a quarter-century of satellite and airborne altimetry records to resolve long-term ice sheet elevation change

NASA Astrophysics Data System (ADS)

Nilsson, J.; Paolo, F. S.; Simonsen, S.; Gardner, A. S.

2017-12-01

Satellite and airborne altimetry provide the longest continuous record from which the mass balance of the Antarctic ice sheet can be derived, starting with the launch of ERS-1 in 1992. Accurate knowledge of the long-term mass balance is vital for understanding the geophysical processes governing the ice sheet contribution to present day sea-level rise. However, this record is comprised of several different measurement systems, with different accuracies and varying resolution. This poses a major challenge on the interpretation and reconstruction of consistent elevation-change time series for determining long-term ice sheet trends and variability. Previous studies using data from multiple satellite altimetry missions have relied on a cross-calibration technique based on crossover bias analysis to merge records from different sensors. This methodology, though accurate, limits the spatial coverage to typical resolutions of 10-50 km, restricting the approach to regional or continental-wide studies. In this study, we present a novel framework for seamless integration of heterogeneous altimetry records, using an adaptive least-squares minimization technique. The procedure allows reconstructing time series at fine spatial (<5 km) and temporal (monthly) scales, while accounting for sensor-dependent biases and heterogeneous data quality. We synthesize altimetry records spanning the time period 1992-2016 to derive long-term time series of elevation change for the Antarctica ice sheet, including both data from the European Space Agency (ERS-1, ERS-2, Envisat and CryoSat-2) and NASA (ICESat and Operation IceBridge), with future inclusion of data from NASA's ICESat-2. Mission specific errors, estimated from independent airborne measurements and crossover analysis, are propagated to derive uncertainty bounds for each individual time series. We also perform an extensive analysis of the major corrections applied to raw satellite altimetry data to assess their overall effect on the

Mapping Ross Ice Shelf with ROSETTA-Ice airborne laser altimetry

NASA Astrophysics Data System (ADS)

Becker, M. K.; Fricker, H. A.; Padman, L.; Bell, R. E.; Siegfried, M. R.; Dieck, C. C. M.

2017-12-01

The Ross Ocean and ice Shelf Environment and Tectonic setting Through Aerogeophysical surveys and modeling (ROSETTA-Ice) project combines airborne glaciological, geological, and oceanographic observations to enhance our understanding of the history and dynamics of the large ( 500,000 square km) Ross Ice Shelf (RIS). Here, we focus on the Light Detection And Ranging (LiDAR) data collected in 2015 and 2016. This data set represents a significant advance in resolution: Whereas the last attempt to systematically map RIS (the surface-based RIGGS program in the 1970s) was at 55 km grid spacing, the ROSETTA-Ice grid has 10-20 km line spacing and much higher along-track resolution. We discuss two different strategies for processing the raw LiDAR data: one that requires proprietary software (Riegl's RiPROCESS package), and one that employs open-source programs and libraries. With the processed elevation data, we are able to resolve fine-scale ice-shelf features such as the "rampart-moat" ice-front morphology, which has previously been observed on and modeled for icebergs. This feature is also visible in the ROSETTA-Ice shallow-ice radar data; comparing the laser data with radargrams provides insight into the processes leading to their formation. Near-surface firn state and total firn air content can also be investigated through combined analysis of laser altimetry and radar data. By performing similar analyses with data from the radar altimeter aboard CryoSat-2, we demonstrate the utility of the ROSETTA-Ice LiDAR data set in satellite validation efforts. The incorporation of the LiDAR data from the third and final field season (December 2017) will allow us to construct a DEM and an ice thickness map of RIS for the austral summers of 2015-2017. These products will be used to validate and extend observations of height changes from satellite radar and laser altimetry, as well as to update regional models of ocean circulation and ice dynamics.

Precision and Deviation Comparison Between Icesat and Envisat in Typical Ice Gaining and Losing Regions of Antarctica

NASA Astrophysics Data System (ADS)

Du, W.; Chen, L.; Xie, H.; Hai, G.; Zhang, S.; Tong, X.

2017-09-01

This paper analyzes the precision and deviation of elevations acquired from Envisat and The Ice, Cloud and Land Elevation Satellite (ICESat) over typical ice gaining and losing regions, i.e. Lambert-Amery System (LAS) in east Antarctica, and Amundsen Sea Sector (ASS) in west Antarctica, during the same period from 2003 to 2008. We used GLA12 dataset of ICESat and Level 2 data of Envisat. Data preprocessing includes data filtering, projection transformation and track classification. Meanwhile, the slope correction is applied to Envisat data and saturation correction for ICESat data. Then the crossover analysis was used to obtain the crossing points of the ICESat tracks, Envisat tracks and ICESat-Envisat tracks separately. The two tracks we chose for cross-over analysis should be in the same campaign for ICESat (within 33 days) or the same cycle for Envisat (within 35 days).The standard deviation of a set of elevation residuals at time-coincident crossovers is calculated as the precision of each satellite while the mean value is calculated as the deviation of ICESat-Envisat. Generally, the ICESat laser altimeter gets a better precision than the Envisat radar altimeter. For Amundsen Sea Sector, the ICESat precision is found to vary from 8.9 cm to 17 cm and the Envisat precision varies from 0.81 m to 1.57 m. For LAS area, the ICESat precision is found to vary from 6.7 cm to 14.3 cm and the Envisat precision varies from 0.46 m to 0.81 m. Comparison result between Envisat and ICESat elevations shows a mean difference of 0.43 ±7.14 m for Amundsen Sea Sector and 0.53 ± 1.23 m over LAS.

Determination of Local Slope on the Greenland Ice Sheet Using a Multibeam Photon-Counting Lidar in Preparation for the ICESat-2 Mission

NASA Technical Reports Server (NTRS)

Brunt, Kelly M.; Neumann, Thomas Allen; Walsh, Kaitlin M.; Markus, Thorsten

2013-01-01

The greatest changes in elevation in Greenland and Antarctica are happening along the margins of the ice sheets where the surface frequently has significant slopes. For this reason, the upcoming Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) mission utilizes pairs of laser altimeter beams that are perpendicular to the flight direction in order to extract slope information in addition to elevation. The Multiple Altimeter Beam Experimental Lidar (MABEL) is a high-altitude airborne laser altimeter designed as a simulator for ICESat-2. The MABEL design uses multiple beams at fixed angles and allows for local slope determination. Here, we present local slopes as determined by MABEL and compare them to those determined by the Airborne Topographic Mapper (ATM) over the same flight lines in Greenland. We make these comparisons with consideration for the planned ICESat-2 beam geometry. Results indicate that the mean slope residuals between MABEL and ATM remain small (< 0.05 degrees) through a wide range of localized slopes using ICESat-2 beam geometry. Furthermore, when MABEL data are subsampled by a factor of 4 to mimic the planned ICESat-2 transmit-energy configuration, the results are indistinguishable from the full-data-rate analysis. Results from MABEL suggest that ICESat-2 beam geometry and transmit-energy configuration are appropriate for the determination of slope on approx. 90-m spatial scales, a measurement that will be fundamental to deconvolving the effects of surface slope from the ice-sheet surface change derived from ICESat-2.

Determination of Local Slope on the Greenland Ice Sheet Using a Multibeam Photon-Counting Lidar in Preparation for the ICESat-2 Mission

NASA Technical Reports Server (NTRS)

Brunt, Kelly M.; Neumann, Thomas A.; Walsh, Kaitlin M.; Markus, Thorsten

2014-01-01

The greatest changes in elevation in Greenland and Antarctica are happening along the margins of the ice sheets where the surface frequently has significant slopes. For this reason, the upcoming Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) mission utilizes pairs of laser altimeter beams that are perpendicular to the flight direction in order to extract slope information in addition to elevation. The Multiple Altimeter Beam Experimental Lidar (MABEL) is a high-altitude airborne laser altimeter designed as a simulator for ICESat-2. The MABEL design uses multiple beams at fixed angles and allows for local slope determination. Here, we present local slopes as determined by MABEL and compare them to those determined by the Airborne Topographic Mapper (ATM) over the same flight lines in Greenland. We make these comparisons with consideration for the planned ICESat-2 beam geometry. Results indicate that the mean slope residuals between MABEL and ATM remain small (< 0.05?) through a wide range of localized slopes using ICESat-2 beam geometry. Furthermore, when MABEL data are subsampled by a factor of 4 to mimic the planned ICESat-2 transmit-energy configuration, the results are indistinguishable from the full-data-rate analysis. Results from MABEL suggest that ICESat-2 beam geometry and transmit-energy configuration are appropriate for the determination of slope on 90-m spatial scales, a measurement that will be fundamental to deconvolving the effects of surface slope from the ice-sheet surface change derived from ICESat-2.

Improved estimate of accelerated Antarctica ice mass loses from GRACE, Altimetry and surface mass balance from regional climate model output

NASA Astrophysics Data System (ADS)

Velicogna, I.; Sutterley, T. C.; A, G.; van den Broeke, M. R.; Ivins, E. R.

2016-12-01

We use Gravity Recovery and Climate Experiment (GRACE) monthly gravity fields to determine the regional acceleration in ice mass loss in Antarctica for 2002-2016. We find that the total mass loss is controlled by only a few regions. In Antarctica, the Amundsen Sea (AS) sector and the Antarctic Peninsula account for 65% and 18%, respectively, of the total loss (186 ± 10 Gt/yr) mainly from ice dynamics. The AS sector contributes most of the acceleration in loss (9 ± 1 Gt/yr2 ), and Queen Maud Land, East Antarctica, is the only sector with a significant mass gain due to a local increase in SMB (57 ± 5 Gt/yr). We compare GRACE regional mass balance estimates with independent estimates from ICESat-1 and Operation IceBridge laser altimetry, CryoSat-2 radar altimetry, and surface mass balance outputs from RACMO2.3. In the Amundsen Sea Embayment of West Antarctica, an area experiencing rapid retreat and mass loss to the sea, we find good agreement between GRACE and altimetry estimates. Comparison of GRACE with these independent techniques in East Antarctic shows that GIA estimates from the new regional ice deglaciation models underestimate the GIA correction in the EAIS interior, which implies larger losses of the Antarctica ice sheet by about 70 Gt/yr. Sectors where we are observing the largest losses are closest to warm circumpolar water, and with polar constriction of the westerlies enhanced by climate warming, we expect these sectors to contribute more and more to sea level as the ice shelves that protect these glaciers will melt faster in contact with more heat from the surrounding oc

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

NASA Technical Reports Server (NTRS)

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

2001-01-01

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

Shuttle Laser Altimeter

NASA Technical Reports Server (NTRS)

Bufton, Jack L.; Harding, David J.; Garvin, James B.

1999-01-01

The Shuttle Laser Altimeter (SLA) is a Hitchhiker experiment that has flown twice; first on STS-72 in January 1996 and then on STS-85 in August 1997. Both missions produced successful laser altimetry and surface lidar data products from approximately 80 hours per mission of SLA data operations. A total of four Shuttle missions are planned for the SLA series. This paper documents SLA mission results and explains SLA pathfinder accomplishments at the mid-point in this series of Hitchhiker missions. The overall objective of the SLA mission series is the transition of the Goddard Space Flight Center airborne laser altimeter and lidar technology to low Earth orbit as a pathfinder for NASA operational space-based laser remote sensing devices. Future laser altimeter sensors will utilize systems and approaches being tested with SLA, including the Multi-Beam Laser Altimeter (MBLA) and the Geoscience Laser Altimeter System (GLAS). MBLA is the land and vegetation laser sensor for the NASA Earth System Sciences Pathfinder Vegetation Canopy Lidar (VCL) Mission, and GLAS is the Earth Observing System facility instrument on the Ice, Cloud, and Land Elevation Satellite (ICESat). The Mars Orbiting Laser Altimeter, now well into a multi-year mapping mission at the red planet, is also directly benefiting from SLA data analysis methods, just as SLA benefited from MOLA spare parts and instrument technology experience [5] during SLA construction in the early 1990s.

Data assimilation of surface altimetry on the North-Easter Ice Stream using the Ice Sheet System Model (ISSM)

NASA Astrophysics Data System (ADS)

Larour, Eric; Utke, Jean; Morlighem, Mathieu; Seroussi, Helene; Csatho, Beata; Schenk, Anton; Rignot, Eric; Khazendar, Ala

2014-05-01

Extensive surface altimetry data has been collected on polar ice sheets over the past decades, following missions such as Envisat and IceSat. This data record will further increase in size with the new CryoSat mission, the ongoing Operation IceBridge Mission and the soon to launch IceSat-2 mission. In order to make the best use of these dataset, ice flow models need to improve on the way they ingest surface altimetry to infer: 1) parameterizations of poorly known physical processes such as basal friction; 2) boundary conditions such as Surface Mass Balance (SMB). Ad-hoc sensitivity studies and adjoint-based inversions have so far been the way ice sheet models have attempted to resolve the impact of 1) on their results. As for boundary conditions or the lack thereof, most studies assume that they are a fixed quantity, which, though prone to large errors from the measurement itself, is not varied according to the simulated results. Here, we propose a method based on automatic differentiation to improve boundary conditions at the base and surface of the ice sheet during a short-term transient run for which surface altimetry observations are available. The method relies on minimizing a cost-function, the best fit between modeled surface evolution and surface altimetry observations, using gradients that are computed for each time step from automatic differentiation of the ISSM (Ice Sheet System Model) code. The approach relies on overloaded operators using the ADOLC (Automatic Differentiation by OverLoading in C++) package. It is applied to the 79 North Glacier, Greenland, for a short term transient spanning a couple of decades before the start of the retreat of the Zachariae Isstrom outlet glacier. Our results show adjustments required on the basal friction and the SMB of the whole basin to best fit surface altimetry observations, along with sensitivities each one of these parameters has on the overall cost function. Our approach presents a pathway towards assimilating

ICESat Calibration and Validation Experiments at White Sands, New Mexico, 2003-2010

NASA Astrophysics Data System (ADS)

Schutz, B. E.; Urban, T. J.

2010-12-01

The Center for Space Research (CSR) at the University of Texas at Austin has operated a primary site for ICESat cal/val activities near the White Sands Space Harbor (WSSH) area of the White Sands Missile Range, NM. This site was chosen for both geophysical (flat, reflective) and logistical (domestic, secure site) reasons. Before launch in 2003, a several-hundred-meter-scale grid comprised of hundreds of numbered PVC base-plates was installed at the chosen site to permanently mark the locations of various pieces of experiment hardware. In summary, CSR has supported four primary types of experiments at the cal/val site: (1) a permanent grid of laser retro-reflectors (corner cube reflectors) placed on top of poles of various known heights and collocated with 25 of the base plates, in use for the duration of the mission, (2) a set of computer-monitored position and timing detectors utilized for cal/val during the first three years of the project, (3) several camera-equipped aircraft flyovers of the area designed to capture images of the green and infrared footprints on the surface at the precise time of ICESat overflights, (4) elevation comparisons between the ICESat data and a high-resolution (1 m) DEM derived via small-footprint airborne lidar collections in 2003 and 2007. The experiments at WSSH were targeted by the ICESat spacecraft approximately four times per campaign, making this cal/val site one of the most sampled locations in the world. This presentation will chronicle the extensive collection of ICESat and experimental data collected at WSSH from 2003 to 2010.

Basic Radar Altimetry Toolbox and Radar Altimetry Tutorial: Tools for all Altimetry Users

NASA Astrophysics Data System (ADS)

Rosmorduc, Vinca; Benveniste, J.; Breebaart, L.; Bronner, E.; Dinardo, S.; Earith, D.; Lucas, B. M.; Maheu, C.; Niejmeier, S.; Picot, N.

2013-09-01

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, Saral.It has been available from April 2007, and had been demonstrated during training courses and scientific meetings. Nearly 2000 people downloaded it (January 2012), 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 to 4. Others are under development, some are in discussion for the future.The Basic Radar Altimetry Toolbox is able:- to read most distributed radar altimetry data, including the one from future missions like Saral, Jason-3- 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.BRAT is developed under contract with ESA and CNES. It is available at http://www.altimetry.info and http://earth.esa.int/brat/It has been available from April 2007, and had been demonstrated during training courses and scientific meetings. More than 2000 people downloaded it (as of end of September 2012), with many "newcomers" to altimetry among them, and teachers/students. Users' feedbacks, developments in altimetry, and practice, showed that new interesting features could be added. Some have been

Crevasse Migration in Southern Greenland as inferred from ICESat-1 Altimetry

NASA Astrophysics Data System (ADS)

Grigsby, S.; Abdalati, W.; Colgan, W. T.

2017-12-01

In an increasingly warm world, more and more of the Greenland ice sheet is susceptible to melt during the summer, raising the possibility of greater contributions to sea level rise from ice melt. However, meltwater deep within the interior of the ice sheet must still find a way to the ocean, otherwise it will simply refreeze within the firn or on top of the ice without impacting sea level rise. One way that water can make it off the ice sheet and into the ocean is via crevasses that allow water to access the bed beneath the ice sheet, where the water will float the ice above it and eventually drain to the coast. It is therefore essential to understand how the Greenland crevasse system is evolving in time, both for understanding meltwater inputs to the englacial hydrological system, and to understand how these inputs are impacting glacial stability. We utilize three years (2004—2006) of ICESat-1 waveform data processed by machine learning to establish a 100m resolution baseline grid of crevassed probability over the ice sheet, then compare against present day crevasses mapped from optical imagery at sites in Southwest and Southeast Greenland. Inland migration of crevasses strongly suggests that increasing meltwater inputs provide positive reinforcement to additional upslope crevassing and access to progressively greater drainage catchments.

Estimates of forest canopy height and aboveground biomass using ICESat.

Treesearch

Michael A. Lefsky; David J. Harding; Michael Keller; Warren B. Cohen; Claudia C. Carabajal; Fernando Del Bom Espirito-Santo; Maria O. Hunter; Raimundo de Oliveira Jr.

2005-01-01

Exchange of carbon between forests and the atmosphere is a vital component of the global carbon cycle. Satellite laser altimetry has a unique capability for estimating forest canopy height, which has a direct and increasingly well understood relationship to aboveground carbon storage. While the Geoscience Laser Altimeter System (GLAS) onboard the Ice, Cloud and land...

ICESat/GLAS-derived changes in the water level of Hulun Lake, Inner Mongolia, from 2003 to 2009

NASA Astrophysics Data System (ADS)

Li, Chunlan; Wang, Jun; Hu, Richa; Yin, Shan; Bao, Yuhai; Li, Yuwei

2017-07-01

Hulun Lake is the largest freshwater lake in northern Inner Mongolia and even minor changes in its level may have major effects on the ecology of the lake and the surrounding area. In this study, we used high-precision elevation data for the interval from 2003-2009 measured by the Geoscience Laser Altimetry System (GLAS) on board the Ice, Cloud, and land Elevation Satellite (ICESat) to assess annual and seasonal water level variations of Hulun Lake. The altimetry data of 32 satellite tracks were processed using the RANdom SAmple Consensus algorithm (RANSAC) to eliminate elevation outliers, and subsequently the Normalized Difference Water Index (NDWI) was used to delineate the area of the lake. From 2003-2009, the shoreline of Hulun Lake retreated westwards, which was especially notable in the southern part of the lake. There was only a small decrease in water level, from 530.72 m to 529.22 m during 2003-2009, an average rate of 0.08 m/yr. The area of the lake decreased at a rate of 49.52 km2/yr, which was mainly the result of the shallow bathymetry in the southern part of the basin. The decrease in area was initially rapid, then much slower, and finally rapid again. Generally, the lake extent and water level decreased due to higher temperatures, intense evaporation, low precipitation, and decreasing runoff. And their fluctuations were caused by a decrease in intraannual temperature, evaporation, and a slight increase in precipitation. Overall, a combination of factors related to climate change were responsible for the variations of the water level of Hulun Lake during the study interval. The results improve our understanding of the impact of climate change on Hulun Lake and may facilitate the formulation of response strategies.

ICESat/GLAS-derived changes in the water level of Hulun Lake, Inner Mongolia, from 2003 to 2009

NASA Astrophysics Data System (ADS)

Li, Chunlan; Wang, Jun; Hu, Richa; Yin, Shan; Bao, Yuhai; Li, Yuwei

2018-06-01

Hulun Lake is the largest freshwater lake in northern Inner Mongolia and even minor changes in its level may have major effects on the ecology of the lake and the surrounding area. In this study, we used high-precision elevation data for the interval from 2003-2009 measured by the Geoscience Laser Altimetry System (GLAS) on board the Ice, Cloud, and land Elevation Satellite (ICESat) to assess annual and seasonal water level variations of Hulun Lake. The altimetry data of 32 satellite tracks were processed using the RANdom SAmple Consensus algorithm (RANSAC) to eliminate elevation outliers, and subsequently the Normalized Difference Water Index (NDWI) was used to delineate the area of the lake. From 2003-2009, the shoreline of Hulun Lake retreated westwards, which was especially notable in the southern part of the lake. There was only a small decrease in water level, from 530.72 m to 529.22 m during 2003-2009, an average rate of 0.08 m/yr. The area of the lake decreased at a rate of 49.52 km2/yr, which was mainly the result of the shallow bathymetry in the southern part of the basin. The decrease in area was initially rapid, then much slower, and finally rapid again. Generally, the lake extent and water level decreased due to higher temperatures, intense evaporation, low precipitation, and decreasing runoff. And their fluctuations were caused by a decrease in intraannual temperature, evaporation, and a slight increase in precipitation. Overall, a combination of factors related to climate change were responsible for the variations of the water level of Hulun Lake during the study interval. The results improve our understanding of the impact of climate change on Hulun Lake and may facilitate the formulation of response strategies.

The Geoscience Laser Altimeter System (GLAS) for the ICESAT Mission

NASA Technical Reports Server (NTRS)

Abshire, James B.; Sun, Xia-Li; Ketchum, Eleanor A.; Afzal, Robert S.; Millar, Pamela S.; Smith, David E. (Technical Monitor)

2000-01-01

The Laser In space Technology Experiment, Shuttle Laser Altimeter and the Mars Observer Laser Altimeter have demonstrated accurate measurements of atmospheric backscatter and Surface heights from space. The recent MOLA measurements of the Mars surface have 40 cm vertical resolution and have reduced the global uncertainty in Mars topography from a few km to about 5 m. The Geoscience Laser Altimeter System (GLAS) is a next generation lidar for Earth orbit being developed as part of NASA's Icesat Mission. The GLAS design combines a 10 cm precision surface lidar with a sensitive dual wavelength cloud and aerosol lidar. GLAS will precisely measure the heights of the Earth's polar ice sheets, establish a grid of accurate height profiles of the Earth's land topography, and profile the vertical backscatter of clouds and aerosols on a global scale. GLAS is being developed to fly on a small dedicated spacecraft in a polar orbit with a 590 630 km altitude at inclination of 94 degrees. GLAS is scheduled to launch in the summer 2001 and to operate continuously for a minimum of 3 years with a goal of 5 years. The primary mission for GLAS is to measure the seasonal and annual changes in the heights of the Greenland and Antarctic ice sheets. GLAS will continuously measure the vertical distance from orbit to the Earth's surface with 1064 nm pulses from a ND:YAG laser at a 40 Hz rate. Each 5 nsec wide laser pulse is used to produce a single range measurement, and the laser spots have 66 m diameter and about 170 m center-center spacings. When over land GLAS will profile the heights of the topography and vegetation. The GLAS receiver uses a 1 m diameter telescope and a Si APD detector. The detector signal is sampled by an all digital receiver which records each surface echo waveform with I nsec resolution and a stored echo record lengths of either 200, 400, or 600 samples. Analysis of the echo waveforms within the instrument permits discrimination between cloud and surface echoes

Sumatra-Andaman Megathrust Earthquake Slip: Insights From Mechanical Modeling of ICESat Surface Deformation Measurements

NASA Astrophysics Data System (ADS)

Harding, D. J.; Miuller, J. R.

2005-12-01

Modeling the kinematics of the 2004 Great Sumatra-Andaman earthquake is limited in the northern two-thirds of the rupture zone by a scarcity of near-rupture geodetic deformation measurements. Precisely repeated Ice, Cloud, and Land Elevation Satellite (ICESat) profiles across the Andaman and Nicobar Islands provide a means to more fully document the spatial pattern of surface vertical displacements and thus better constrain geomechanical modeling of the slip distribution. ICESat profiles that total ~45 km in length cross Car Nicobar, Kamorta, and Katchall in the Nicobar chain. Within the Andamans, the coverage includes ~350 km on North, Central, and South Andaman Islands along two NNE and NNW-trending profiles that provide elevations on both the east and west coasts of the island chain. Two profiles totaling ~80 km in length cross South Sentinel Island, and one profile ~10 km long crosses North Sentinel Island. With an average laser footprint spacing of 175 m, the total coverage provides over 2700 georeferenced surface elevations measurements for each operations period. Laser backscatter waveforms recorded for each footprint enable detection of forest canopy top and underlying ground elevations with decimeter vertical precision. Surface elevation change is determined from elevation profiles, acquired before and after the earthquake, that are repeated with a cross-track separation of less than 100 m by precision pointing of the ICESat spacecraft. Apparent elevation changes associated with cross-track offsets are corrected according to local slopes calculated from multiple post-earthquake repeated profiles. The surface deformation measurements recorded by ICESat are generally consistent with the spatial distribution of uplift predicted by a preliminary slip distribution model. To predict co-seismic surface deformation, we apply a slip distribution, derived from the released energy distribution computed by Ishii et al. (2005), as the displacement discontinuity

ICESat Observations of Arctic Sea Ice: A First Look

NASA Technical Reports Server (NTRS)

Kwok, Ron; Zwally, H. Jay; Yi, Dong-Hui

2004-01-01

Analysis of near-coincident ICESat and RADARSAT imagery shows that the retrieved elevations from the laser altimeter are sensitive to new openings (containing thin ice or open water) in the sea ice cover as well as to surface relief of old and first-year ice. The precision of the elevation estimates, measured over relatively flat sea ice, is approx. 2 cm Using the thickness of thin-ice in recent openings to estimate sea level references, we obtain the sea-ice free-board along the altimeter tracks. This step is necessitated by the large uncertainties in the time-varying sea surface topography compared to that required for accurate determination of free-board. Unknown snow depth introduces the largest uncertainty in the conversion of free-board to ice thickness. Surface roughness is also derived, for the first time, from the variability of successive elevation estimates along the altimeter track Overall, these ICESat measurements provide an unprecedented view of the Arctic Ocean ice cover at length scales at and above the spatial dimension of the altimeter footprint.

The Geoscience Laser Altimeter System (GLAS) for the ICESAT Mission

NASA Technical Reports Server (NTRS)

Abshire, James B.; Sun, Xiao-Li; Ketchum, Eleanor A.; Afzal, Robert S.; Millar, Pamela S.

1999-01-01

Accurate measurements of surface heights and atmospheric backscatter have been demonstrated with the SLA, MOLA and LITE space lidar. Recent MOLA measurements of the Mars surface have 40 cm resolution and have reduced the global uncertainty in Mars topography from a few km to approx. 10 m. GLAS is a next generation lidar being developed as part of NASA's Icesat Mission for Earth orbit . The GLAS design combines a 10 cm precision surface lidar with a sensitive dual wavelength cloud and aerosol lidar. GLAS will precisely measure the heights of the Earth's polar ice sheets, determine the height profiles of the Earth's land topography, and profile the vertical backscatter of clouds and aerosols on a global scale. GLAS will fly on a small dedicated spacecraft in a polar orbit at 598 km altitude with an inclination of 94 degrees. GLAS is scheduled to launch in summer 2001 and to operate continuously for a minimum of 3 years with a goal of 5 years. The primary mission for GLAS is to measure the seasonal and annual changes in the heights of the Greenland and Antarctic ice sheets. GLAS will measure the vertical distance to the ice sheet from orbit with 1064 nm pulses from a Nd:Yag laser at 40 Hz. Each 5 nsec wide laser pulse is used for a single range measurement. When over land GLAS will profile the heights of the topography and vegetation. The GLAS receiver uses a I m diameter telescope and a Si APD detector. The detector signal is sampled by an all digital receiver which records each surface echo waveform with I nsec resolution and a stored echo record lengths of either 200, 400, or 600 samples. Analysis of the echo waveforms within the instrument permits discrimination between cloud and surface echoes. Ground based echo analysis permits precise ranging, determining the roughness or slopes of the surface as well as the vertical distributions of vegetation illuminated by the laser, Errors in knowledge of the laser beam pointing angle can bias height measurements of sloped

Testing Land-Vegetation retrieval algorithms for the ICESat-2 mission

NASA Astrophysics Data System (ADS)

Zhou, T.; Popescu, S. C.

2017-12-01

The upcoming spaceborne satellite, the Ice, Cloud and land Elevation Satellite 2 (ICESat-2), will provide topography and canopy profiles at the global scale using photon counting LiDAR. To prepare for the mission launch, the aim of this research is to develop a framework for retrieving ground and canopy height in different forest types and noise levels using two ICESat-2 testbed sensor data: MABEL (Multiple Altimeter Beam Experimental Lidar) data and simulated ICESat-2 data. The first step of the framework is to reduce as many noise photons as possible through grid statistical methods and cluster analysis. Subsequently, we employed the overlapping moving windows and estimated quantile heights in each window to characterize the possible ground and canopy top using the filtered photons. Both MABEL and simulated ICESat-2 data generated satisfactory results with reasonable accuracy, while the results of simulated ICESat-2 data were better than that of MABEL data with smaller root mean square errors (RMSEs). For example, the RMSEs of canopy top identification in various vegetation using simulated ICESat-2 data were less than 3.78 m comparing to 6.48 m for the MABE data. It is anticipated that the methodology will advance data processing of the ICESat-2 mission and expand potential applications of ICESat-2 data once available such as mapping vegetation canopy heights.

The GLAS Science Algorithm Software (GSAS) Detailed Design Document Version 6. Volume 16

NASA Technical Reports Server (NTRS)

Lee, Jeffrey E.

2013-01-01

The Geoscience Laser Altimeter System (GLAS) is the primary instrument for the ICESat (Ice, Cloud and Land Elevation Satellite) laser altimetry mission. ICESat was the benchmark Earth Observing System (EOS) mission for measuring ice sheet mass balance, cloud and aerosol heights, as well as land topography and vegetation characteristics. From 2003 to 2009, the ICESat mission provided multi-year elevation data needed to determine ice sheet mass balance as well as cloud property information, especially for stratospheric clouds common over polar areas. It also provided topography and vegetation data around the globe, in addition to the polar-specific coverage over the Greenland and Antarctic ice sheets.This document describes the detailed design of GLAS Science Algorithm Software (GSAS). The GSAS is used to create the ICESat GLAS standard data products. The National Snow and Ice Data Center (NSDIC) distribute these products. The document contains descriptions, flow charts, data flow diagrams, and structure charts for each major component of the GSAS. The purpose of this document is to present the detailed design of the GSAS. It is intended as a reference source to assist the maintenance programmer in making changes that fix or enhance the documented software.

Preparing for ICESat-2: Simulated Geolocated Photon Data for Cryospheric Data Products

NASA Astrophysics Data System (ADS)

Harbeck, K.; Neumann, T.; Lee, J.; Hancock, D.; Brenner, A. C.; Markus, T.

2017-12-01

ICESat-2 will carry NASA's next-generation laser altimeter, ATLAS (Advanced Topographic Laser Altimeter System), which is designed to measure changes in ice sheet height, sea ice freeboard, and vegetation canopy height. There is a critical need for data that simulate what certain ICESat-2 science data products will "look like" post-launch in order to aid the data product development process. There are several sources for simulated photon-counting lidar data, including data from NASA's MABEL (Multiple Altimeter Beam Experimental Lidar) instrument, and M-ATLAS (MABEL data that has been scaled geometrically and radiometrically to be more similar to that expected from ATLAS). From these sources, we are able to develop simulated granules of the geolocated photon cloud product; also referred to as ATL03. These simulated ATL03 granules can be further processed into the upper-level data products that report ice sheet height, sea ice freeboard, and vegetation canopy height. For ice sheet height (ATL06) and sea ice height (ATL07) simulations, both MABEL and M-ATLAS data products are used. M-ATLAS data use ATLAS engineering design cases for signal and background noise rates over certain surface types, and also provides large vertical windows of data for more accurate calculations of atmospheric background rates. MABEL data give a more accurate representation of background noise rates over areas of water (i.e., melt ponds, crevasses or sea ice leads) versus land or solid ice. Through a variety of data manipulation procedures, we provide a product that mimics the appearance and parameter characterization of ATL03 data granules. There are three primary goals for generating this simulated ATL03 dataset: (1) allowing end users to become familiar with using the large photon cloud datasets that will be the primary science data product from ICESat-2, (2) the process ensures that ATL03 data can flow seamlessly through upper-level science data product algorithms, and (3) the process

The Geoscience Laser Altimeter System Laser Transmitter

NASA Technical Reports Server (NTRS)

Afzal, R. S.; Dallas, J. L.; Yu, A. W.; Mamakos, W. A.; Lukemire, A.; Schroeder, B.; Malak, A.

2000-01-01

The Geoscience Laser Altimeter System (GLAS), scheduled to launch in 2001, is a laser altimeter and lidar for tile Earth Observing System's (EOS) ICESat mission. The laser transmitter requirements, design and qualification test results for this space- based remote sensing instrument are presented.

Basic Radar Altimetry Toolbox: tools to teach altimetry for ocean

NASA Astrophysics Data System (ADS)

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

2013-04-01

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

Antarctic Sea-Ice Freeboard and Estimated Thickness from NASA's ICESat and IceBridge Observations

NASA Technical Reports Server (NTRS)

Yi, Donghui; Kurtz, Nathan; Harbeck, Jeremy; Manizade, Serdar; Hofton, Michelle; Cornejo, Helen G.; Zwally, H. Jay; Robbins, John

2016-01-01

ICESat completed 18 observational campaigns during its lifetime from 2003 to 2009. Data from all of the 18 campaign periods are used in this study. Most of the operational periods were between 34 and 38 days long. Because of laser failure and orbit transition from 8-day to 91-day orbit, there were four periods lasting 57, 16, 23, and 12 days. IceBridge data from 2009, 2010, and 2011 are used in this study. Since 2009, there are 19 Airborne Topographic Mapper (ATM) campaigns, and eight Land, Vegetation, and Ice Sensor (LVIS) campaigns over the Antarctic sea ice. Freeboard heights are derived from ICESat, ATM and LVIS elevation and waveform data. With nominal densities of snow, water, and sea ice, combined with snow depth data from AMSR-E/AMSR2 passive microwave observation over the southern ocean, sea-ice thickness is derived from the freeboard. Combined with AMSR-E/AMSR2 ice concentration, sea-ice area and volume are also calculated. During the 2003-2009 period, sea-ice freeboard and thickness distributions show clear seasonal variations that reflect the yearly cycle of the growth and decay of the Antarctic pack ice. We found no significant trend of thickness or area for the Antarctic sea ice during the ICESat period. IceBridge sea ice freeboard and thickness data from 2009 to 2011 over the Weddell Sea and Amundsen and Bellingshausen Seas are compared with the ICESat results.

Mapping vegetation heights in China using slope correction ICESat data, SRTM, MODIS-derived and climate data

NASA Astrophysics Data System (ADS)

Huang, Huabing; Liu, Caixia; Wang, Xiaoyi; Biging, Gregory S.; Chen, Yanlei; Yang, Jun; Gong, Peng

2017-07-01

Vegetation height is an important parameter for biomass assessment and vegetation classification. However, vegetation height data over large areas are difficult to obtain. The existing vegetation height data derived from the Ice, Cloud and land Elevation Satellite (ICESat) data only include laser footprints in relatively flat forest regions (<5°). Thus, a large portion of ICESat data over sloping areas has not been used. In this study, we used a new slope correction method to improve the accuracy of estimates of vegetation heights for regions where slopes fall between 5° and 15°. The new method enabled us to use more than 20% additional laser data compared with the existing vegetation height data which only uses ICESat data in relatively flat areas (slope < 5°) in China. With the vegetation height data extracted from ICESat footprints and ancillary data including Moderate Resolution Imaging Spectroradiometer (MODIS) derived data (canopy cover, reflectances and leaf area index), climate data, and topographic data, we developed a wall to wall vegetation height map of China using the Random Forest algorithm. We used the data from 416 field measurements to validate the new vegetation height product. The coefficient of determination (R2) and RMSE of the new vegetation height product were 0.89 and 4.73 m respectively. The accuracy of the product is significantly better than that of the two existing global forest height products produced by Lefsky (2010) and Simard et al. (2011), when compared with the data from 227 field measurements in our study area. The new vegetation height data demonstrated clear distinctions among forest, shrub and grassland, which is promising for improving the classification of vegetation and above-ground forest biomass assessment in China.

Topography of the Northern Hemisphere of Mercury from MESSENGER Laser Altimetry

NASA Technical Reports Server (NTRS)

Zuber,Maria T.; Smith, David E.; Phillips, Roger J.; Solomon, Sean C.; Neumann, Gregory A.; Hauck, Steven A., Jr.; Peale, Stanton J.; Barnouin, Oliver S.; Head, James W.; Johnson, Catherine L.;

The GLAS Algorithm Theoretical Basis Document for Precision Orbit Determination (POD)

NASA Technical Reports Server (NTRS)

Rim, Hyung Jin; Yoon, S. P.; Schultz, Bob E.

2013-01-01

The Geoscience Laser Altimeter System (GLAS) was the sole instrument for NASA's Ice, Cloud and land Elevation Satellite (ICESat) laser altimetry mission. The primary purpose of the ICESat mission was to make ice sheet elevation measurements of the polar regions. Additional goals were to measure the global distribution of clouds and aerosols and to map sea ice, land topography and vegetation. ICESat was the benchmark Earth Observing System (EOS) mission to be used to determine the mass balance of the ice sheets, as well as for providing cloud property information, especially for stratospheric clouds common over polar areas. The GLAS instrument operated from 2003 to 2009 and provided multi-year elevation data needed to determine changes in sea ice freeboard, land topography and vegetation around the globe, in addition to elevation changes of the Greenland and Antarctic ice sheets. This document describes the Precision Orbit Determination (POD) algorithm for the ICESat mission. The problem of determining an accurate ephemeris for an orbiting satellite involves estimating the position and velocity of the satellite from a sequence of observations. The ICESatGLAS elevation measurements must be very accurately geolocated, combining precise orbit information with precision pointing information. The ICESat mission POD requirement states that the position of the instrument should be determined with an accuracy of 5 and 20 cm (1-s) in radial and horizontal components, respectively, to meet the science requirements for determining elevation change.

Art as a key tool for engaging the public with the ICESat-2 mission

NASA Astrophysics Data System (ADS)

Casasanto, V.; Markus, T.

2017-12-01

NASA's Ice, Cloud, and land Elevation Satellite (ICESat-2), to be launched in the Fall of 2018, will measure the height of Earth from space using lasers, collecting the most precise and detailed account yet of our planet's elevation. The mission will allow scientists to investigate how global warming is changing the planet's icy polar regions and to take stock of Earth's vegetation. ICESat-2's emphasis on polar ice, as well as its unique measurement approach, has provided an intriguing and accessible focus for the mission's education and outreach programs. Sea ice and land ice are areas have experienced significant change in recent years. It is key to communicate what is happening, why we are measuring these areas and their importance to our global climate. Art is a powerful tool to inspire, engage, and provide an emotional connection to these remote areas. This paper will detail ICESat-2's art/science collaborations, including results from a unique collaboration with art and design school the Savannah College of Art Design (SCAD). Additional programs will be discussed including a multimedia live music program to engage on an emotional level, to communicate the importance of the polar regions to our global climate, and to inspire to take action.

The Algorithm Theoretical Basis Document for the Atmospheric Delay Correction to GLAS Laser Altimeter Ranges. Volume 8

NASA Technical Reports Server (NTRS)

Herring, Thomas A.; Quinn, Katherine J.

2012-01-01

NASA s Ice, Cloud, and Land Elevation Satellite (ICESat) mission will be launched late 2001. It s primary instrument is the Geoscience Laser Altimeter System (GLAS) instrument. The main purpose of this instrument is to measure elevation changes of the Greenland and Antarctic icesheets. To accurately measure the ranges it is necessary to correct for the atmospheric delay of the laser pulses. The atmospheric delay depends on the integral of the refractive index along the path that the laser pulse travels through the atmosphere. The refractive index of air at optical wavelengths is a function of density and molecular composition. For ray paths near zenith and closed form equations for the refractivity, the atmospheric delay can be shown to be directly related to surface pressure and total column precipitable water vapor. For ray paths off zenith a mapping function relates the delay to the zenith delay. The closed form equations for refractivity recommended by the International Union of Geodesy and Geophysics (IUGG) are optimized for ground based geodesy techniques and in the next section we will consider whether these equations are suitable for satellite laser altimetry.

The Geoscience Laser Altimeter System (GLAS) Laser Transmitter

NASA Technical Reports Server (NTRS)

Afzal, Robert S.; Yu, Anthony W.; Dallas, Joseph L.; Melak, Anthony; Lukemir, Alan; Ramos-Izqueirdo, L.; Mamakos, William

2007-01-01

The Geoscience Laser Altimeter System (GLAS), launched in January 2003, is a laser altimeter and lidar for the Earth Observing System's (EOS) ICESat mission. GLAS accommodates three, sequentially operated, diode-pumped, solid-state, Nd:YAG laser transmitters. The laser transmitter requirements, design and qualification test results for this space-based remote sensing instrument is summarized and presented

Optical development system lab alignment solutions for the ICESat-2 ATLAS instrument

NASA Astrophysics Data System (ADS)

Evans, T.

The ATLAS Instrument for the ICESat-2 mission at NASA's Goddard Space Flight Center requires an alignment test-bed to prove out new concepts. The Optical Development System (ODS) lab was created to test prototype models of individual instrument components to simulate how they will act as a system. The main ICESat-2 instrument is the Advanced Topographic Laser Altimeter System (ATLAS). It measures ice elevation by transmitting laser pulses, and collecting the reflection in a telescope. Because the round trip time is used to calculate distance, alignment between the outgoing transmitter beam and the incoming receiver beams are critical. An automated closed loop monitoring control system is currently being tested at the prototype level to prove out implementation for the final spacecraft. To achieve an error of less than 2 micro-radians, an active deformable mirror was used to correct the lab wave front from the collimated “ ground reflection” beam. The lab includes a focal plane assembly set up, a one meter diameter collimator optic, and a 0.8 meter flight spare telescope for alignment. ATLAS prototypes and engineering models of transmitter and receiver optics and sub-systems are brought in to develop and integrate systems as well as write procedures to be used in integration and testing. By having a fully integrated system with prototypes and engineering units, lessons can be learned before flight designs are finalized.

Ancient Multiring Basins on the Moon Revealed by Clementine Laser Altimetry

NASA Astrophysics Data System (ADS)

Spudis, Paul D.; Reisse, Robert A.; Gillis, Jeffrey J.

1994-12-01

Analysis of laser altimetry data from Clementine has confirmed and extended our knowledge of nearly obliterated multiring basins on the moon. These basins were formed during the early bombardment phase of lunar history, have been filled to varying degrees by mare lavas and regional ejecta blankets, and have been degraded by the superposition of large impact craters. The Mendel-Rydberg Basin, a degraded three-ring feature over 600 kilometers in diameter on the lunar western limb, is about 6 kilometers deep from rim to floor, only slightly less deep than the nearby younger and much better preserved Orientale Basin (8 kilometers deep). The South Pole-Aitken Basin, the oldest discernible impact feature on the moon, is revealed as a basin 2500 kilometers in diameter with an average depth of more than 13 kilometers, rim crest to floor. This feature is the largest, deepest impact crater yet discovered in the solar system. Several additional depressions seen in the data may represent previously unmapped ancient impact basins.

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

NASA Astrophysics Data System (ADS)

Rosmorduc, V.; Benveniste, J. J.; Bronner, E.; Niejmeier, S.

2010-12-01

Radar altimetry is very much a technique expanding its applications and uses. If quite a lot of efforts have been made for oceanography users (including easy-to-use data), the use of those data for geodesy, especially combined witht ESA GOCE mission data is still somehow hard. ESA and CNES thus had the Basic Radar Altimetry Toolbox developed (as well as, on ESA side, the GOCE User Toolbox, both being linked). The Basic Radar Altimetry Toolbox is an "all-altimeter" collection of tools, tutorials and documents designed to facilitate the use of radar altimetry data. The software is able: - to read most distributed radar altimetry data, from ERS-1 & 2, Topex/Poseidon, Geosat Follow-on, Jason-1, Envisat, Jason- 2, CryoSat and the future Saral missions, - to perform some processing, data editing and statistic, - and to visualize the results. It can be used at several levels/several ways: - as a data reading tool, with APIs for C, Fortran, Matlab and IDL - as processing/extraction routines, through the on-line command mode - as an educational and a quick-look tool, with the graphical user interface As part of the Toolbox, a Radar Altimetry Tutorial gives general information about altimetry, the technique involved and its applications, as well as an overview of past, present and future missions, including information on how to access data and additional software and documentation. It also presents a series of data use cases, covering all uses of altimetry over ocean, cryosphere and land, showing the basic methods for some of the most frequent manners of using altimetry data. It is an opportunity to teach remote sensing with practical training. It has been available from April 2007, and had been demonstrated during training courses and scientific meetings. About 1200 people downloaded it (Summer 2010), with many "newcomers" to altimetry among them. Users' feedbacks, developments in altimetry, and practice, showed that new interesting features could be added. Some have been

ICESat Observations of Topographic Change in the Northern Segment of the 2004 Sumatra-Andaman Islands Earthquake Rupture Zone

NASA Technical Reports Server (NTRS)

Harding, David; Sauber, J.; Luthcke, S.; Carabajal, C.; Muller, J

2005-01-01

The Andaman Islands are located 120 km east of the Sunda trench in the northern quarter of the 1300 km long rupture zone of the 2004 Sumatra-Andaman Islands earthquake inferred from the distribution of aftershocks. Initial field reports indicate that several meters of uplift and up to a meter of submergence occurred on the western and eastern shorelines of the Andaman Islands, respectively, associated with the earthquake (Bilham, 2005). Satellite images also document uplift of western shoreline coral reef platforms above sea level. Body-wave (Ji, 2005; Yamamaka, 2005) and tide-gauge (Ortiz, 2005) slip inversions only resolve coseismic slip in the southern one-third to one-half of the rupture zone. The amount of coseismic slip in the Andaman Islands region is poorly constrained by these inversions. The Ice, Cloud, and land Elevation Satellite (ICESat), a part of the NASA Earth Observing System, is being used to document the spatial pattern of Andaman Islands vertical displacements in order to constrain models of slip distribution in the northern part of the rupture zone. ICESat carries the Geoscience Laser Altimeter System (GLAS) that obtains elevation measurements from 80 m diameter footprints spaced 175 m apart along profiles. For surfaces of low slope, single-footprint absolute elevation and horizontal accuracies of 10 cm and 6 m (1 sigma), respectively, referenced to the ITRF 2002 TOPEX/Poseidon ellipsoid are being obtained. Laser pulse backscatter waveforms enable separation of ground topography and overlying vegetation cover. During each 33-day observing period ICESat acquires three profiles crossing the Andaman Islands. A NNE-SSW oriented track consists of 1600 laser footprints along the western side of North, Middle, and South Andaman Islands and 240 laser footprints across the center of Great Andaman Island. Two NNW-SSE tracks consist of 440 footprints across Middle Andaman Island and 25 footprints across the west side of Sentinel Island. Cloud

Estimates of Ice Sheet Mass Balance from Satellite Altimetry: Past and Future

NASA Technical Reports Server (NTRS)

Zwally, H. Jay; Zukor, Dorothy J. (Technical Monitor)

2001-01-01

observations also demonstrate the potential for relating the variability in mass balance to changes in precipitation, temperature, and melting. Beginning in January 2002, NASA's ICESat laser altimeter mission will provide significantly better elevation accuracy and spatial coverage to 86E latitude and to the margins of the ice sheets.

A Decade of High-Resolution Arctic Sea Ice Measurements from Airborne Altimetry

NASA Astrophysics Data System (ADS)

Duncan, K.; Farrell, S. L.; Connor, L. N.; Jackson, C.; Richter-Menge, J.

2017-12-01

Satellite altimeters carried on board ERS-1,-2, EnviSat, ICESat, CryoSat-2, AltiKa and Sentinel-3 have transformed our ability to map the thickness and volume of the polar sea ice cover, on seasonal and decadal time-scales. The era of polar satellite altimetry has coincided with a rapid decline of the Arctic ice cover, which has thinned, and transitioned from a predominantly multi-year to first-year ice cover. In conjunction with basin-scale satellite altimeter observations, airborne surveys of the Arctic Ocean at the end of winter are now routine. These surveys have been targeted to monitor regions of rapid change, and are designed to obtain the full snow and ice thickness distribution, across a range of ice types. Sensors routinely deployed as part of NASA's Operation IceBridge (OIB) campaigns include the Airborne Topographic Mapper (ATM) laser altimeter, the frequency-modulated continuous-wave snow radar, and the Digital Mapping System (DMS). Airborne measurements yield high-resolution data products and thus present a unique opportunity to assess the quality and characteristics of the satellite observations. We present a suite of sea ice data products that describe the snow depth and thickness of the Arctic ice cover during the last decade. Fields were derived from OIB measurements collected between 2009-2017, and from reprocessed data collected during ad-hoc sea ice campaigns prior to OIB. Our bespoke algorithms are designed to accommodate the heterogeneous sea ice surface topography, that varies at short spatial scales. We assess regional and inter-annual variability in the sea ice thickness distribution. Results are compared to satellite-derived ice thickness fields to highlight the sensitivities of satellite footprints to the tails of the thickness distribution. We also show changes in the dynamic forcing shaping the ice pack over the last eight years through an analysis of pressure-ridge sail-height distributions and surface roughness conditions

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

NASA Astrophysics Data System (ADS)

Benveniste, J. J.; Bronner, E.; Dinardo, S.; Lucas, B. M.; Rosmorduc, V.; Earith, D.

2010-12-01

Radar altimetry is very much a technique expanding its applications. If quite a lot of efforts have been made for oceanography users (including easy-to-use data), the use of those data for cryosphere application, especially with the new ESA CryoSat-2 mission data is still somehow tedious, especially for new Altimetry data products users. ESA and CNES thus had the Basic Radar Altimetry Toolbox developed a few years ago, and are improving and upgrading it to fit new missions and the growing number of altimetry uses. The Basic Radar Altimetry Toolbox is an "all-altimeter" collection of tools, tutorials and documents designed to facilitate the use of radar altimetry data. The software is able: - to read most distributed radar altimetry data, from ERS-1 & 2, Topex/Poseidon, Geosat Follow-on, Jason-1, Envisat, Jason- 2, CryoSat and the future Saral missions, - to perform some processing, data editing and statistic, - and to visualize the results. It can be used at several levels/several ways: - as a data reading tool, with APIs for C, Fortran, Matlab and IDL - as processing/extraction routines, through the on-line command mode - as an educational and a quick-look tool, with the graphical user interface As part of the Toolbox, a Radar Altimetry Tutorial gives general information about altimetry, the technique involved and its applications, as well as an overview of past, present and future missions, including information on how to access data and additional software and documentation. It also presents a series of data use cases, covering all uses of altimetry over ocean, cryosphere and land, showing the basic methods for some of the most frequent manners of using altimetry data. It is an opportunity to teach remote sensing with practical training. It has been available from April 2007, and had been demonstrated during training courses and scientific meetings. About 1200 people downloaded it (Summer 2010), with many "newcomers" to altimetry among them, including teachers

Overview of Ice-Sheet Mass Balance and Dynamics from ICESat Measurements

NASA Technical Reports Server (NTRS)

Zwally, H. Jay

2010-01-01

The primary purpose of the ICESat mission was to determine the present-day mass balance of the Greenland and Antarctic ice sheets, identify changes that may be occurring in the surface-mass flux and ice dynamics, and estimate their contributions to global sea-level rise. Although ICESat's three lasers were planned to make continuous measurements for 3 to 5 years, the mission was re-planned to operate in 33-day campaigns 2 to 3 times each year following failure of the first laser after 36 days. Seventeen campaigns were conducted with the last one in the Fall of 2009. Mass balance maps derived from measured ice-sheet elevation changes show that the mass loss from Greenland has increased significantly to about 170 Gt/yr for 2003 to 2007 from a state of near balance in the 1990's. Increased losses (189 Gt/yr) from melting and dynamic thinning are over seven times larger'than increased gains (25 gt/yr) from precipitation. Parts of the West Antarctic ice sheet and the Antarctic Peninsula are losing mass at an increasing rate, but other parts of West Antarctica and the East Antarctic ice sheet are gaining mass at an increasing rate. Increased losses of 35 Gt/yr in Pine Island, Thwaites-Smith, and Marie-Bryd.Coast are more than balanced by gains in base of Peninsula and ice stream C, D, & E systems. From the 1992-2002 to 2003-2007 period, the overall mass balance for Antarctica changed from a loss of about 60 Gt/yr to near balance or slightly positive.

Broadview Radar Altimetry Toolbox

NASA Astrophysics Data System (ADS)

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

2017-04-01

The universal altimetry toolbox, BRAT (Broadview Radar Altimetry Toolbox) which can read all previous and current altimetry missions' data, incorporates now the capability to read the upcoming Sentinel3 L1 and L2 products. ESA endeavoured to develop and supply this capability to support the users of the future Sentinel3 SAR Altimetry Mission. BRAT is a collection of tools and tutorial documents designed to facilitate the processing of radar altimetry data. This project started in 2005 from the joint efforts of ESA (European Space Agency) and CNES (Centre National d'Etudes Spatiales), and it is freely available at http://earth.esa.int/brat. The tools enable users to interact with the most common altimetry data formats. The BratGUI is the frontend 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 dataformatting 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 Sentinel3 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 specific

The GLAS Standard Data Products Specification-Data Dictionary, Version 1.0. Volume 15

NASA Technical Reports Server (NTRS)

Lee, Jeffrey E.

2013-01-01

The Geoscience Laser Altimeter System (GLAS) is the primary instrument for the ICESat (Ice, Cloud and Land Elevation Satellite) laser altimetry mission. ICESat was the benchmark Earth Observing System (EOS) mission for measuring ice sheet mass balance, cloud and aerosol heights, as well as land topography and vegetation characteristics. From 2003 to 2009, the ICESat mission provided multi-year elevation data needed to determine ice sheet mass balance as well as cloud property information, especially for stratospheric clouds common over polar areas. It also provided topography and vegetation data around the globe, in addition to the polar-specific coverage over the Greenland and Antarctic ice sheets.This document contains the data dictionary for the GLAS standard data products. It details the parameters present on GLAS standard data products. Each parameter is defined with a short name, a long name, units on product, type of variable, a long description and products that contain it. The term standard data products refers to those EOS instrument data that are routinely generated for public distribution. These products are distributed by the National Snow and Ice Data Center (NSDIC).

Broadview Radar Altimetry Toolbox

NASA Astrophysics Data System (ADS)

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

2016-04-01

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

Broadview Radar Altimetry Toolbox

NASA Astrophysics Data System (ADS)

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

2016-07-01

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

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

NASA Astrophysics Data System (ADS)

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

2012-12-01

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

ICESat-2 / ATLAS Flight Science Receiver Algorithms

NASA Astrophysics Data System (ADS)

Mcgarry, J.; Carabajal, C. C.; Degnan, J. J.; Mallama, A.; Palm, S. P.; Ricklefs, R.; Saba, J. L.

2013-12-01

NASA's Advanced Topographic Laser Altimeter System (ATLAS) will be the single instrument on the ICESat-2 spacecraft which is expected to launch in 2016 with a 3 year mission lifetime. The ICESat-2 orbital altitude will be 500 km with a 92 degree inclination and 91-day repeat tracks. ATLAS is a single photon detection system transmitting at 532nm with a laser repetition rate of 10 kHz and a 6 spot pattern on the Earth's surface. Without some method of eliminating solar background noise in near real-time, the volume of ATLAS telemetry would far exceed the normal X-band downlink capability. To reduce the data volume to an acceptable level a set of onboard Receiver Algorithms has been developed. These Algorithms limit the daily data volume by distinguishing surface echoes from the background noise and allow the instrument to telemeter only a small vertical region about the signal. This is accomplished through the use of an onboard Digital Elevation Model (DEM), signal processing techniques, and an onboard relief map. Similar to what was flown on the ATLAS predecessor GLAS (Geoscience Laser Altimeter System) the DEM provides minimum and maximum heights for each 1 degree x 1 degree tile on the Earth. This information allows the onboard algorithm to limit its signal search to the region between minimum and maximum heights (plus some margin for errors). The understanding that the surface echoes will tend to clump while noise will be randomly distributed led us to histogram the received event times. The selection of the signal locations is based on those histogram bins with statistically significant counts. Once the signal location has been established the onboard Digital Relief Map (DRM) is used to determine the vertical width of the telemetry band about the signal. The ATLAS Receiver Algorithms are nearing completion of the development phase and are currently being tested using a Monte Carlo Software Simulator that models the instrument, the orbit and the environment

Antarctic ice shelf thickness from CryoSat-2 radar altimetry

NASA Astrophysics Data System (ADS)

Chuter, Stephen; Bamber, Jonathan

2016-04-01

The Antarctic ice shelves provide buttressing to the inland grounded ice sheet, and therefore play a controlling role in regulating ice dynamics and mass imbalance. Accurate knowledge of ice shelf thickness is essential for input-output method mass balance calculations, sub-ice shelf ocean models and buttressing parameterisations in ice sheet models. Ice shelf thickness has previously been inferred from satellite altimetry elevation measurements using the assumption of hydrostatic equilibrium, as direct measurements of ice thickness do not provide the spatial coverage necessary for these applications. The sensor limitations of previous radar altimeters have led to poor data coverage and a lack of accuracy, particularly the grounding zone where a break in slope exists. We present a new ice shelf thickness dataset using four years (2011-2014) of CryoSat-2 elevation measurements, with its SARIn dual antennae mode of operation alleviating the issues affecting previous sensors. These improvements and the dense across track spacing of the satellite has resulted in ˜92% coverage of the ice shelves, with substantial improvements, for example, of over 50% across the Venable and Totten Ice Shelves in comparison to the previous dataset. Significant improvements in coverage and accuracy are also seen south of 81.5° for the Ross and Filchner-Ronne Ice Shelves. Validation of the surface elevation measurements, used to derive ice thickness, against NASA ICESat laser altimetry data shows a mean bias of less than 1 m (equivalent to less than 9 m in ice thickness) and a fourfold decrease in standard deviation in comparison to the previous continental dataset. Importantly, the most substantial improvements are found in the grounding zone. Validation of the derived thickness data has been carried out using multiple Radio Echo Sounding (RES) campaigns across the continent. Over the Amery ice shelf, where extensive RES measurements exist, the mean difference between the datasets is 3

ICESat-2, its retrievals of ice sheet elevation change and sea ice freeboard, and potential synergies with CryoSat-2

NASA Astrophysics Data System (ADS)

Neumann, Thomas; Markus, Thorsten; Smith, Benjamin; Kwok, Ron

2017-04-01

Understanding the causes and magnitudes of changes in the cryosphere remains a priority for Earth science research. Over the past decade, NASA's and ESA's Earth-observing satellites have documented a decrease in both the areal extent and thickness of Arctic sea ice, and an ongoing loss of grounded ice from the Greenland and Antarctic ice sheets. Understanding the pace and mechanisms of these changes requires long-term observations of ice-sheet mass, sea-ice thickness, and sea-ice extent. NASA's ICESat-2 mission is the next-generation space-borne laser altimeter mission and will use three pairs of beams, each pair separated by about 3 km across-track with a pair spacing of 90 m. The spot size is 17 m with an along-track sampling interval of 0.7 m. This measurement concept is a result of the lessons learned from the original ICESat mission. The multi-beam approach is critical for removing the effects of ice sheet surface slope from the elevation change measurements of most interest. For sea ice, the dense spatial sampling (eliminating along-track gaps) and the small footprint size are especially useful for sea surface height measurements in the, often narrow, leads needed for sea ice freeboard and ice thickness retrievals. Currently, algorithms are being developed to calculate ice sheet elevation change and sea ice freeboard from ICESat-2 data. The orbits of ICESat-2 and Cryosat-2 both converge at 88 degrees of latitude, though the orbit altitude differences result in different ground track patterns between the two missions. This presentation will present an overview of algorithm approaches and how ICESat-2 and Cryosat-2 data may augment each other.

ICESat Science Investigator led Processing System (I-SIPS)

NASA Astrophysics Data System (ADS)

Bhardwaj, S.; Bay, J.; Brenner, A.; Dimarzio, J.; Hancock, D.; Sherman, M.

2003-12-01

The ICESat Science Investigator-led Processing System (I-SIPS) generates the GLAS standard data products. It consists of two main parts the Scheduling and Data Management System (SDMS) and the Geoscience Laser Altimeter System (GLAS) Science Algorithm Software. The system has been operational since the successful launch of ICESat. It ingests data from the GLAS instrument, generates GLAS data products, and distributes them to the GLAS Science Computing Facility (SCF), the Instrument Support Facility (ISF) and the National Snow and Ice Data Center (NSIDC) ECS DAAC. The SDMS is the Planning, Scheduling and Data Management System that runs the GLAS Science Algorithm Software (GSAS). GSAS is based on the Algorithm Theoretical Basis Documents provided by the Science Team and is developed independently of SDMS. The SDMS provides the processing environment to plan jobs based on existing data, control job flow, data distribution, and archiving. The SDMS design is based on a mission-independent architecture that imposes few constraints on the science code thereby facilitating I-SIPS integration. I-SIPS currently works in an autonomous manner to ingest GLAS instrument data, distribute this data to the ISF, run the science processing algorithms to produce the GLAS standard products, reprocess data when new versions of science algorithms are released, and distributes the products to the SCF, ISF, and NSIDC. I-SIPS has a proven performance record, delivering the data to the SCF within hours after the initial instrument activation. The I-SIPS design philosophy gives this system a high potential for reuse in other science missions.

Interpretation of ICESat-Derived Elevation Change on the Malaspina-Seward Glacier

NASA Astrophysics Data System (ADS)

Sauber, J.; Ramage, J.; Kopczynski, S.; Muskett, R.

2005-12-01

In this study, we report and interpret ICESat-derived short-term variability in surface elevation in the snow accumulation region of the Seward-Malaspina Glacier, one of the largest glacier systems in southern Alaska. The Seward-Malaspina complex consists of an extensive icefield, the upper Seward Glacier, and a narrower lower outlet glacier (lower Seward) through which ice drains to the enormous piedmont of the Malaspina Glacier. Although the upper Seward is just 80 km north of the Gulf of Alaska it has an environment more continental than maritime because of shielding afforded by high mountains to the south [Sharp, 1951]. The Malaspina Glacier by contrast lies completely within the moist maritime environment of the southern Alaska coast. In an earlier study of the Malaspina Glacier, we reported elevation differences between ICESat Laser 1-3 observations (February 2003 - November 2004) and a Shuttle Radar Topography Mission (SRTM)-derived DEM from February 2000 [Sauber et al., 2005]. Elevation decreases of up to 20-25 m over a 3-4 year time period were observed across the folded loop moraine on the southern portion of the piedmont lobe of the Malaspina Glacier. For the western portion of the Upper Seward we will estimate elevation change over a comparable time period by using an X-band InSAR-derived DEM from Intermap Tech. (Sept. 2000) and ICESat-derived elevations. Early field measurements (1945-1949) from the Upper Seward Glacier indicated an average annual net surplus of 75 cm water equivalent in the Upper Seward basin [Sharp, 1951]. However, even over this short time period, Sharp [1951] found large interannual variability in net accumulation of 41-168 cm. To further constrain and understand surface changes, we examined ICESat-derived elevations from a variable set of repeated ICESat upper Seward profiles made between Feb. 2003 and May 2005. Additionally we compared the elevation change profiles to snowmelt timing and ablation season length derived from the

Global Lidar Measurements of Clouds and Aerosols from Space Using the Geoscience Laser Altimeter System (GLAS)

NASA Technical Reports Server (NTRS)

Hlavka, Dennis L.; Palm, S. P.; Welton, E. J.; Hart, W. D.; Spinhirne, J. D.; McGill, M.; Mahesh, A.; Starr, David OC. (Technical Monitor)

2001-01-01

The Geoscience Laser Altimeter System (GLAS) is scheduled for launch on the ICESat satellite as part of the NASA EOS mission in 2002. GLAS will be used to perform high resolution surface altimetry and will also provide a continuously operating atmospheric lidar to profile clouds, aerosols, and the planetary boundary layer with horizontal and vertical resolution of 175 and 76.8 m, respectively. GLAS is the first active satellite atmospheric profiler to provide global coverage. Data products include direct measurements of the heights of aerosol and cloud layers, and the optical depth of transmissive layers. In this poster we provide an overview of the GLAS atmospheric data products, present a simulated GLAS data set, and show results from the simulated data set using the GLAS data processing algorithm. Optical results from the ER-2 Cloud Physics Lidar (CPL), which uses many of the same processing algorithms as GLAS, show algorithm performance with real atmospheric conditions during the Southern African Regional Science Initiative (SAFARI 2000).

NASA'S Earth Science Enterprise Embraces Active Laser Remote Sensing from Space

NASA Technical Reports Server (NTRS)

Luther, Michael R.; Paules, Granville E., III

1999-01-01

Several objectives of NASA's Earth Science Enterprise are accomplished, and in some cases, uniquely enabled by the advantages of earth-orbiting active lidar (laser radar) sensors. With lidar, the photons that provide the excitation illumination for the desired measurement are both controlled and well known. The controlled characteristics include when and where the illumination occurs, the wavelength, bandwidth, pulse length, and polarization. These advantages translate into high signal levels, excellent spatial resolution, and independence from time of day and the sun's position. As the lidar technology has rapidly matured, ESE scientific endeavors have begun to use lidar sensors over the last 10 years. Several more lidar sensors are approved for future flight. The applications include both altimetry (rangefinding) and profiling. Hybrid missions, such as the approved Geoscience Laser Altimeter System (GLAS) sensor to fly on the ICESat mission, will do both at the same time. Profiling applications encompass aerosol, cloud, wind, and molecular concentration measurements. Recent selection of the PICASSO Earth System Science Pathfinder mission and the complementary CLOUDSAT radar-based mission, both flying in formation with the EOS PM mission, will fully exploit the capabilities of multiple sensor systems to accomplish critical science needs requiring such profiling. To round out the briefing a review of past and planned ESE missions will be presented.

A Newly Updated Database of Elevation-changes of the Greenand Ice Sheet to Study Surface Processes and Ice Dynamics

NASA Astrophysics Data System (ADS)

Schenk, A. F.; Csatho, B. M.; van den Broeke, M.; Kuipers Munneke, P.

2015-12-01

This paper reports about important upgrades of the Greenland Ice Sheet (GrIS) surface elevation and elevation-change database obtained with our Surface Elevation And Change detection (SERAC) software suite. We have developed SERAC to derive information from laser altimetry data, particularly time series of elevation changes and their partitioning into changes caused by ice dynamics. This allows direct investigation of ice dynamic processes that is much needed for improving the predictive power of ice sheet models. SERAC is different from most other change detection methods. It is based on detecting changes of surface patches, about 1 km by 1 km in size, rather than deriving elevation changes from individual laser points. The current database consists of ~100,000 time series with satellite laser altimetry data from ICESat, airborne laser observations obtained by NASA's Airborne Topographic Mapper (ATM) and the Land, Vegetation and Ice Sensor (LVIS). The upgrade is significant, because not only new observations from 2013 and 2014 have been added but also a number of improvements lead to a more comprehensive and consistent record of elevation-changes. First, we used the model that gives in addition to ice sheet also information about ice caps and glaciers (Rastner et al., 2012) for deciding if a laser point is on the ice sheet or ice cap. Then we added small gaps that exist in the ICESat GLA12 data set because the ice sheet mask is not wide enough. The new database is now more complete and will facilitate more accurate comparisons of mass balance studies obtained from the Gravity Recovery and Climate Experiment system (GRACE). For determining the part of a time series caused by ice dynamics we used the new firn compaction model and Surface Mass Balance (SMB) estimates from RACMO2.3. The new database spans the time period from 1993 to 2014. Adding new observations amounts to a spatial densification of the old record and at the same time extends the time domain by two

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

NASA Astrophysics Data System (ADS)

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.

Decomposition Techniques for Icesat/glas Full-Waveform Data

NASA Astrophysics Data System (ADS)

Liu, Z.; Gao, X.; Li, G.; Chen, J.

2018-04-01

The geoscience laser altimeter system (GLAS) on the board Ice, Cloud, and land Elevation Satellite (ICESat), is the first long-duration space borne full-waveform LiDAR for measuring the topography of the ice shelf and temporal variation, cloud and atmospheric characteristics. In order to extract the characteristic parameters of the waveform, the key step is to process the full waveform data. In this paper, the modified waveform decomposition method is proposed to extract the echo components from full-waveform. First, the initial parameter estimation is implemented through data preprocessing and waveform detection. Next, the waveform fitting is demonstrated using the Levenberg-Marquard (LM) optimization method. The results show that the modified waveform decomposition method can effectively extract the overlapped echo components and missing echo components compared with the results from GLA14 product. The echo components can also be extracted from the complex waveforms.

Changes in the Earth's largest surge glacier system from satellite and airborne altimetry and imagery

NASA Astrophysics Data System (ADS)

Trantow, T.; Herzfeld, U. C.

2015-12-01

The Bering-Bagley Glacier System (BBGS), Alaska, one of the largest ice systems outside of Greenland and Antarctica, has recently surged (2011-2013), providing a rare opportunity to study the surge phenomenon in a large and complex system. Understanding fast-flowing glaciers and accelerations in ice flow, of which surging is one type, is critical to understanding changes in the cryosphere and ultimately changes in sea level. It is important to distinguish between types of accelerations and their consequences, especially between reversible or quasi-cyclic and irreversible forms of glacial acceleration, but current icesheet models treat all accelerating ice identically. Additionally, the surge provides an exceptional opportunity to study the influence of surface roughness and water content on return signals of altimeter systems. In this presentation, we analyze radar and laser altimeter data from CryoSat-2, NASA's Operation IceBridge (OIB), the ICESat Geoscience Laser Altimeter System (GLAS), ICESat-2's predecessor the Multiple Altimeter Beam Experimental Lidar (MABEL), and airborne laser altimeter and imagery campaigns by our research group. These measurements are used to study elevation, elevation change and crevassing throughout the glacier system. Analysis of the imagery from our airborne campaigns provides comprehensive characterizations of the BBGS surface over the course of the surge. Results from the data analysis are compared to numerical modeling experiments.

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

USGS Publications Warehouse

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

2000-01-01

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

ICESat (GLAS) Science Processing Software Document Series. Volume 3; GLAS Science Software Requirements Document; Ver 2.1

NASA Technical Reports Server (NTRS)

Jester, Peggy L.; Lee, Jeffrey; Zukor, Dorothy J. (Technical Monitor)

2001-01-01

This document addresses the software requirements of the Geoscience Laser Altimeter System (GLAS) Standard Data Software (SDS) supporting the GLAS instrument on the EOS ICESat Spacecraft. This Software Requirements Document represents the initial collection of the technical engineering information for the GLAS SDS. This information is detailed within the second of four main volumes of the Standard documentation, the Product Specification volume. This document is a "roll-out" from the governing volume outline containing the Concept and Requirements sections.

Forest Aboveground Biomass Mapping and Canopy Cover Estimation from Simulated ICESat-2 Data

NASA Astrophysics Data System (ADS)

Narine, L.; Popescu, S. C.; Neuenschwander, A. L.

2017-12-01

The assessment of forest aboveground biomass (AGB) can contribute to reducing uncertainties associated with the amount and distribution of terrestrial carbon. With a planned launch date of July 2018, the Ice, Cloud and Land Elevation Satellite-2 (ICESat-2) will provide data which will offer the possibility of mapping AGB at global scales. In this study, we develop approaches for utilizing vegetation data that will be delivered in ICESat-2's land-vegetation along track product (ATL08). The specific objectives are to: (1) simulate ICESat-2 photon-counting lidar (PCL) data using airborne lidar data, (2) utilize simulated PCL data to estimate forest canopy cover and AGB and, (3) upscale AGB predictions to create a wall-to-wall AGB map at 30-m spatial resolution. Using existing airborne lidar data for Sam Houston National Forest (SHNF) located in southeastern Texas and known ICESat-2 beam locations, PCL data are simulated from discrete return lidar points. We use multiple linear regression models to relate simulated PCL metrics for 100 m segments along the ICESat-2 ground tracks to AGB from a biomass map developed using airborne lidar data and canopy cover calculated from the same. Random Forest is then used to create an AGB map from predicted estimates and explanatory data consisting of spectral metrics derived from Landsat TM imagery and land cover data from the National Land Cover Database (NLCD). Findings from this study will demonstrate how data that will be acquired by ICESat-2 can be used to estimate forest structure and characterize the spatial distribution of AGB.

Performance of the GLAS Laser Transmitter in Space

NASA Technical Reports Server (NTRS)

Yu, Anthony W.; Afzal, Robert S.; Dallas, Joseph L.; Melak, Anthony; Mamakos, William

2006-01-01

The Geoscience Laser Altimeter System (GLAS), launched in January 2003, is a laser altimeter and lidar for the Earth Observing System's (EOS) ICESat mission. The laser transmitter requirements, design and qualification test results and in-flight performance for this space-based remote sensing instrument is summarized and presented.

The Ice, Cloud, and land Elevation Satellite (ICESat) Summary Mission Timeline and Performance Relative to Pre-Launch Mission Success Criteria

NASA Technical Reports Server (NTRS)

Webb, Charles E.; Zwally H. Jay; Abdalati, Waleed

2012-01-01

The Ice, Cloud and land Elevation Satellite (ICESat) mission was conceived, primarily, to quantify the spatial and temporal variations in the topography of the Greenland and Antarctic ice sheets. It carried on board the Geoscience Laser Altimeter System (GLAS), which measured the round-trip travel time of a laser pulse emitted from the satellite to the surface of the Earth and back. Each range derived from these measurements was combined with precise, concurrent orbit and pointing information to determine the location of the laser spot centroid on the Earth. By developing a time series of precise topographic maps for each ice sheet, changes in their surface elevations can be used to infer their mass balances.

Laser altimetry reveals complex pattern of Greenland Ice Sheet dynamics.

PubMed

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

2014-12-30

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

Mapping the Antarctic grounding line with CryoSat-2 radar altimetry

NASA Astrophysics Data System (ADS)

Bamber, J. L.; Dawson, G. J.

2017-12-01

The grounding line, where grounded ice begins to float, is the boundary at which the ocean has the greatest influence on the ice-sheet. Its position and dynamics are critical in assessing the stability of the ice-sheet, for mass budget calculations and as an input into numerical models. The most reliable approaches to map the grounding line remotely are to measure the limit of tidal flexure of the ice shelf using differential synthetic aperture radar interferometry (DInSAR) or ICESat repeat-track measurements. However, these methods are yet to provide satisfactory spatial and temporal coverage of the whole of the Antarctic grounding zone. It has not been possible to use conventional radar altimetry to map the limit of tidal flexure of the ice shelf because it performs poorly near breaks in slope, commonly associated with the grounding zone. The synthetic aperture radar interferometric (SARin) mode of CryoSat-2, performs better over steeper margins of the ice sheet and allows us to achieve this. The SARin mode combines "delay Doppler" processing with a cross-track interferometer, and enables us to use elevations based on the first return (point of closest approach or POCA) and "swath processed" elevations derived from the time-delayed waveform beyond the first return, to significantly improve coverage. Here, we present a new method to map the limit of tidal motion from a combination of POCA and swath data. We test this new method on the Siple Coast region of the Ross Ice Shelf, and the mapped grounding line is in good agreement with previous observations from DinSAR and ICESat measurements. There is, however, an approximately constant seaward offset between these methods and ours, which we believe is due to the poorer precision of CryoSat-2. This new method has improved the coverage of the grounding zone across the Siple Coast, and can be applied to the rest of Antarctica.

Sentinel-3 SAR Altimetry Toolbox

NASA Astrophysics Data System (ADS)

Benveniste, Jerome; Lucas, Bruno; DInardo, Salvatore

2015-04-01

The prime objective of the SEOM (Scientific Exploitation of Operational Missions) element is to federate, support and expand the large international research community that the ERS, ENVISAT and the Envelope programmes have build up over the last 20 years for the future European operational Earth Observation missions, the Sentinels. Sentinel-3 builds directly on a proven heritage of ERS-2 and Envisat, and CryoSat-2, with a dual-frequency (Ku and C band) advanced Synthetic Aperture Radar Altimeter (SRAL) that provides measurements at a resolution of ~300m in SAR mode along track. Sentinel-3 will provide exact measurements of sea-surface height along with accurate topography measurements over sea ice, ice sheets, rivers and lakes. The first of the two Sentinels is expected to be launched in early 2015. The current universal altimetry toolbox is BRAT (Basic Radar Altimetry Toolbox) which can read all previous and current altimetry mission's data, but it does not have the capabilities to read the upcoming Sentinel-3 L1 and L2 products. ESA will endeavour to develop and supply this capability to support the users of the future Sentinel-3 SAR Altimetry Mission. BRAT is a collection of tools and tutorial documents designed to facilitate the processing of radar altimetry data. This project started in 2005 from the joint efforts of ESA (European Space Agency) and CNES (Centre National d'Etudes Spatiales), and it is freely available at http://earth.esa.int/brat. The tools enable users to interact with the most common altimetry data formats, the BratGUI is the front-end for the powerful command line tools that are part of the BRAT suite. BRAT can also be used in conjunction with Matlab/IDL (via reading routines) or in C/C++/Fortran via a programming API, allowing the user to obtain desired data, bypassing the data-formatting hassle. BRAT can be used simply to visualise data quickly, or to translate the data into other formats such as netCDF, ASCII text files, KML (Google Earth

Three Year Aging of Prototype Flight Laser at 10 Khz and 1 Ns Pulses with External Frequency Doubler for the Icesat-2 Mission

NASA Technical Reports Server (NTRS)

Konoplev, Oleg A.; Chiragh, Furqan L.; Vasilyev, Aleksey A.; Edwards, Ryan; Stephen, Mark A.; Troupaki, Elisavet; Yu, Anthony W.; Krainak, Michael A.; Sawruk, Nick; Hovis, Floyd;

Three-year aging of prototype flight laser at 10 kHz and 1 ns pulses with external frequency doubler for ICESat-2 mission

NASA Astrophysics Data System (ADS)

Konoplev, Oleg A.; Chiragh, Furqan L.; Vasilyev, Aleksey A.; Edwards, Ryan; Stephen, Mark A.; Troupaki, Elisavet; Yu, Anthony W.; Krainak, Michael A.; Sawruk, Nick; Hovis, Floyd; Culpepper, Charles F.; Strickler, Kathy

2016-05-01

We present the results of a three-year operational-aging test of a specially designed prototype flight laser operating at 1064 nm, 10 kHz, 1ns, 15W average power and externally frequency-doubled. Fibertek designed and built the q-switched, 1064nm laser and this laser was in a sealed container of dry air pressurized to 1.3 atm. The external frequency doubler was in a clean room at a normal air pressure. The goal of the experiment was to measure degradation modes at 1064 and 532 nm separately. The external frequency doubler consisted of a Lithium triborate, LiB3O5, non-critically phase-matched crystal. After some 1064 nm light was diverted for diagnostics, 13.7W of fundamental power was available to pump the doubling crystal. Between 8.5W and 10W of 532nm power was generated, depending on the level of stress and degradation. The test consisted of two stages, the first at 0.3 J/cm2 for almost 1 year, corresponding to expected operational conditions, and the second at 0.93 J/cm2 for the remainder of the experiment, corresponding to accelerated optical stress testing. We observed no degradation at the first stress-level and linear degradation at the second stress-level. The linear degradation was linked to doubler crystal output surface changes from laser-assisted contamination. We estimate the expected lifetime for the flight laser at 532 nm using fluence as the stress parameter. This work was done for NASA's Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) LIDAR at Goddard Space Flight Center in Greenbelt, MD with the goal of 1 trillion shots lifetime.

ICESat-2 bathymetry: an empirical feasibility assessment using MABEL

NASA Astrophysics Data System (ADS)

Forfinski, Nick; Parrish, Christopher

2016-10-01

The feasibility of deriving bathymetry from data acquired with ATLAS, the photon-counting lidar on NASA's upcoming ICESat-2 satellite, is assessed empirically by examining data from NASA's airborne ICESat-2 simulator, MABEL. The primary objectives of ICESat-2 will be to measure ice-sheet elevations, sea-ice thickness, and global biomass. However, the 6-beam, green-wavelength photon-counting lidar, combined with the 91-day repeat period and near-polar orbit, may provide unique opportunities to measure coastal bathymetry in remote, poorly-mapped areas of the globe. The study focuses on high-probability bottom returns in Keweenaw Bay, Lake Superior, acquired during the "Transit to KPMD" MABEL mission in August, 2012 at an AGL altitude of 20,000 m. Water-surface and bottom returns were identified and manually classified using MABEL Viewer, an in-house prototype data-explorer web application. Water-surface returns were observed in 12 green channels, and bottom returns were observed in 10 channels. Comparing each channel's mean water-surface elevation to a regional NOAA Nowcast water-level estimate revealed channel-specific elevation biases that were corrected for in our bathymetry estimation procedure. Additionally, a first-order refraction correction was applied to each bottom return. Agreement between the refraction-corrected depth profile and NOAA data acquired two years earlier by Fugro LADS with the LADS Mk II airborne system indicates that MABEL reliably detected bathymetry in depths up to 8 m, with an RMS difference of 0.7 m. In addition to feeding coastal bathymetry models, MABEL (and potentially ICESat-2 ATLAS) has the potential to seed algorithms for bathymetry retrieval from passive, multispectral satellite imagery by providing reference depths.

The GLAS Science Algorithm Software (GSAS) User's Guide Version 7

NASA Technical Reports Server (NTRS)

Lee, Jeffrey E.

2013-01-01

The Geoscience Laser Altimeter System (GLAS) is the primary instrument for the ICESat (Ice, Cloud and Land Elevation Satellite) laser altimetry mission. ICESat was the benchmark Earth Observing System (EOS) mission for measuring ice sheet mass balance, cloud and aerosol heights, as well as land topography and vegetation characteristics. From 2003 to 2009, the ICESat mission provided multi-year elevation data needed to determine ice sheet mass balance as well as cloud property information, especially for stratospheric clouds common over polar areas. It also provided topography and vegetation data around the globe, in addition to the polar-specific coverage over the Greenland and Antarctic ice sheets.This document is the final version of the GLAS Science Algorithm Software Users Guide document. It contains the instructions to install the GLAS Science Algorithm Software (GSAS) in the production environment that was used to create the standard data products. It also describes the usage of each GSAS program in that environment with their required inputs and outputs. Included are a number of utility programs that are used to create ancillary data files that are used in the processing but generally are not distributed to the public as data products. Of importance is the values for the large number of constants used in the GSAS algorithm during processing are provided in an appendix.

AVISO+, the new reference web portal for altimetry

NASA Astrophysics Data System (ADS)

Rosmorduc, Vinca; Bronner, Emilie; Guinle, Thierry; Maheu, Caroline; Morrow, Rosemary; Nino, Fernando; Birol, Florence

2014-05-01

AVISO is the showcase of CNES activities in altimetry. Indeed, the altimetric products processed by the SALP service from CNES (Service d'Altimetrie et de Localisation Precise) are disseminated via AVISO portal since 1995. In recent years, AVISO became a reference in the international oceanographic and altimetry communities, with more than 5,000 registered users in 2013. In 2014 AVISO is enlarging its applications outside the purely ocean-oriented ones, thus becoming AVISO + (www.aviso.altimetry.fr). The portal opens to new applications such as hydrology / coastal / ice. Moreover, it merges with the CTOH (French Observation Service dedicated to satellite altimetry studies) website to provide users with operational as well as demonstration products and expertise in a unique website. We present here all the novelties - new look, new functionnalities, new products, new data access service… hoping to see you soon on our brand-new altimetry portal, www.aviso.altimetry.fr!

Local processes and regional patterns - Interpreting a multi-decadal altimetry record of Greenland Ice Sheet changes

NASA Astrophysics Data System (ADS)

Csatho, B. M.; Schenk, A. F.; Babonis, G. S.; van den Broeke, M. R.; Kuipers Munneke, P.; van der Veen, C. J.; Khan, S. A.; Porter, D. F.

2016-12-01

This study presents a new, comprehensive reconstruction of Greenland Ice Sheet elevation changes, generated using the Surface Elevation And Change detection (SERAC) approach. 35-year long elevation-change time series (1980-2015) were obtained at more than 150,000 locations from observations acquired by NASA's airborne and spaceborne laser altimeters (ATM, LVIS, ICESat), PROMICE laser altimetry data (2007-2011) and a DEM covering the ice sheet margin derived from stereo aerial photographs (1970s-80s). After removing the effect of Glacial Isostatic Adjustment (GIA) and the elastic crustal response to changes in ice loading, the time series were partitioned into changes due to surface processes and ice dynamics and then converted into mass change histories. Using gridded products, we examined ice sheet elevation, and mass change patterns, and compared them with other estimates at different scales from individual outlet glaciers through large drainage basins, on to the entire ice sheet. Both the SERAC time series and the grids derived from these time series revealed significant spatial and temporal variations of dynamic mass loss and widespread intermittent thinning, indicating the complexity of ice sheet response to climate forcing. To investigate the regional and local controls of ice dynamics, we examined thickness change time series near outlet glacier grounding lines. Changes on most outlet glaciers were consistent with one or more episodes of dynamic thinning that propagates upstream from the glacier terminus. The spatial pattern of the onset, duration, and termination of these dynamic thinning events suggest a regional control, such as warming ocean and air temperatures. However, the intricate spatiotemporal pattern of dynamic thickness change suggests that, regardless of the forcing responsible for initial glacier acceleration and thinning, the response of individual glaciers is modulated by local conditions. We use statistical methods, such as principal

Current state of art of satellite altimetry

NASA Astrophysics Data System (ADS)

Łyszkowicz, Adam Bolesław; Bernatowicz, Anna

2017-12-01

One of the fundamental problems of modern geodesy is precise defi nition of the gravitational fi eld and its changes in time. This is essential in positioning and navigation, geophysics, geodynamics, oceanography and other sciences related to the climate and Earth's environment. One of the major sources of gravity data is satellite altimetry that provides gravity data with almost 75% surface of the Earth. Satellite altimetry also provides data to study local, regional and global geophysical processes, the geoid model in the areas of oceans and seas. This technique can be successfully used to study the ocean mean dynamic topography. The results of the investigations and possible products of altimetry will provide a good material for the GGOS (Global Geodetic Observing System) and institutions of IAS (International Altimetry Service). This paper presents the achievements in satellite altimetry in all the above disciplines obtained in the last years. First very shorly basic concept of satellite altimetry is given. In order to obtain the highest accuracy on range measurements over the ocean improved of altimetry waveforms performed on the ground is described. Next, signifi cant improvements of sea and ocean gravity anomalies models developed presently is shown. Study of sea level and its extremes examined, around European and Australian coasts using tide gauges data and satellite altimetry measurements were described. Then investigations of the phenomenon of the ocean tides, calibration of altimeters, studies of rivers and ice-sheets in the last years are given.

Detecting elevation changes over mountain glaciers in Tibet and the Himalayas by TOPEX/Poseidon and Jason-2 radar altimeters: comparison with ICESat results

NASA Astrophysics Data System (ADS)

Hwang, C.; Cheng, Y. S.

2015-12-01

In most cases, mountain glaciers are narrow and situated over steep slopes. A laser-based altimeter such as ICESat has a small illuminated footprint at about 70 m, thus allowing to measure precise elevations over narrow mountain glaciers. However, unlike a typical radar altimeter mission, ICESat does not have repeat ground tracks (except in its early phase) to measure heights of a specific point at different times. Within a time span, usually a reference digital elevation model is used to compute height anomalies at ICESat's measurement sites over a designated area, which are then averaged to produce a representative height change (anomaly) in this area. In contrast, a radar altimeter such as TOPEX/Poseidon (TP; its follow-on missions are Jason-1 and -2), repeats its ground tracks at an even time interval (10 days for TP), but has a larger illuminated footprint than ICESat's (about 1 km or larger), making it difficult to measure precise elevations over narrow mountain glaciers. Here we demonstrate the potential of TP and Jason-2 radar altimeters in detecting elevation changes over mountain glaciers that are sufficiently wide and smooth. We select several glacier-covered sites in Mt. Tanggula (Tibet) and the Himalayas to experiment with methods that can generate precise height measurements from the two altimeters. Over the same spot, ranging errors due to slope, volume scattering and radar penetration can be common between repeat cycles, and may be reduced by differencing successive heights. We retracked radar waveforms and classify the surfaces using the SRTM-derived elevations. The effects of terrain and slope are reduced by fitting a surface to the height measurements from repeat cycles. We remove outlier heights and apply a smoothing filter to form final time series of glacier elevation change at the selected sites, which are compared with the results from ICESat (note the different mission times). Because TP and Jason-2 measure height changes every 10 days

Topography of the Flattest Surface on Earth: using ICESAT, GPS, and MISR to Measure Salt Surface Topography on Salar de Uyuni, Bolivia

NASA Technical Reports Server (NTRS)

Comstock, Robert L.; Bills, Bruce G.

2004-01-01

Salt flats are aptly named: they are composed largely of salt, and are maintained as nearly equipotential surfaces via frequent flooding. The salar de Uyuni, on the Altiplano in southwestern Bolivia, is the largest salt flat on Earth, with an area of 9,800 sq km. Except for a few bedrock islands, it has less than 40 cm of relief. The upper-most salt unit averages 5 m thick and contains 50 cu km of nearly pure halite. It includes most of the salt that was in solution in paleolake Minchin, which attained a maximum area of 60,000 sq km and a maximum depth of 150 m, roughly 15 kyr ago. Despite approx. 10 m of differential isostatic rebound since deposition, the salar surface has been actively maintained as an extraordinarily flat and smooth surface by annual flooding during the rainy season. We have used the strong optical absorption properties of water in the visible band to map spatial variations in water depth during a time when the salar was flooded. As water depth increases, the initially pure white surface appears both darker and bluer. We utilized MISR images taken during the interval from April to November 2001. The red and infra-red bands (672 and 867 nm wavelength) were most useful since the water depth is small and the absorption at those wavelengths is quite strong. Nadir pointed MISR images have 275 m spatial resolution. To aid in our evaluation of water depth variations over the saiar surface, we utilized two sources of direct topographic measurements: several ICESAT altimetry tracks cross the area, and a 40x50 km GPS grid was surveyed to calibrate ICESAT. A difficulty in using these data types is that both give salt surface elevations relative to the ellipsoid, whereas the water surface will, in the absence of wind or tidal disturbances, follow an equipotential surface. Geoid height is not known to the required accuracy of a few cm in the central Andes. As a result, before comparing optical absorption from MISR to salt surface topography from GPS or

Three Three-Year Aging of Prototype Flight Laser at 10 kHz and 1 ns Pulses With External Frequency Doubler for ICESat-2 Mission

NASA Technical Reports Server (NTRS)

Konoplev, Oleg A.; Chiragh, Furqan L.; Vasilyev, Aleksey A.; Edwards, Ryan; Stephen, Mark A.; Troupaki, Elisavet; Yu, Anthony W.; Krainak, Michael A.; Sawruk, Nick; Hovis, Floyd;

Landsat 8 and ICESat-2: Performance and potential synergies for quantifying dryland ecosystem vegetation cover and biomass

USGS Publications Warehouse

Glenn, Nancy F.; Neuenschwander, Amy; Vierling, Lee A.; Spaete, Lucas; Li, Aihua; Shinneman, Douglas; Pilliod, David S.; Arkle, Robert; McIlroy, Susan

2016-01-01

To estimate the potential synergies of OLI and ICESat-2 we used simulated ICESat-2 photon data to predict vegetation structure. In a shrubland environment with a vegetation mean height of 1 m and mean vegetation cover of 33%, vegetation photons are able to explain nearly 50% of the variance in vegetation height. These results, and those from a comparison site, suggest that a lower detection threshold of ICESat-2 may be in the range of 30% canopy cover and roughly 1 m height in comparable dryland environments and these detection thresholds could be used to combine future ICESat-2 photon data with OLI spectral data for improved vegetation structure. Overall, the synergistic use of Landsat 8 and ICESat-2 may improve estimates of above-ground biomass and carbon storage in drylands that meet these minimum thresholds, increasing our ability to monitor drylands for fuel loading and the potential to sequester carbon.

Laser altimetry reveals complex pattern of Greenland Ice Sheet dynamics

PubMed Central

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

2014-01-01

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

Simultaneous retrieval of sea ice thickness and snow depth using concurrent active altimetry and passive L-band remote sensing data

NASA Astrophysics Data System (ADS)

Zhou, L.; Xu, S.; Liu, J.

2017-12-01

The retrieval of sea ice thickness mainly relies on satellite altimetry, and the freeboard measurements are converted to sea ice thickness (hi) under certain assumptions over snow loading. The uncertain in snow depth (hs) is a major source of uncertainty in the retrieved sea ice thickness and total volume for both radar and laser altimetry. In this study, novel algorithms for the simultaneous retrieval of hi and hs are proposed for the data synergy of L-band (1.4 GHz) passive remote sensing and both types of active altimetry: (1) L-band (1.4GHz) brightness temperature (TB) from Soil Moisture Ocean Salinity (SMOS) satellite and sea ice freeboard (FBice) from radar altimetry, (2) L-band TB data and snow freeboard (FBsnow) from laser altimetry. Two physical models serve as the forward models for the retrieval: L-band radiation model, and the hydrostatic equilibrium model. Verification with SMOS and Operational IceBridge (OIB) data is carried out, showing overall good retrieval accuracy for both sea ice parameters. Specifically, we show that the covariability between hs and FBsnow is crucial for the synergy between TB and FBsnow. Comparison with existing algorithms shows lower uncertainty in both sea ice parameters, and that the uncertainty in the retrieved sea ice thickness as caused by that of snow depth is spatially uncorrelated, with the potential reduction of the volume uncertainty through spatial sampling. The proposed algorithms can be applied to the retrieval of sea ice parameters at basin-scale, using concurrent active and passive remote sensing data based on satellites.

Assessment of Cloud Screening with Apparent Surface Reflectance in Support of the ICESat-2 Mission

NASA Technical Reports Server (NTRS)

Yang, Yuekui; Marshak, Alexander; Palm, Stephen P.; Wang, Zhuosen; Schaaf, Crystal

2011-01-01

The separation of cloud and clear scenes is usually one of the first steps in satellite data analysis. Before deriving a geophysical product, almost every satellite mission requires a cloud mask to label a scene as either clear or cloudy through a cloud detection procedure. For clear scenes, products such as surface properties may be retrieved; for cloudy scenes, scientist can focus on studying the cloud properties. Hence the quality of cloud detection directly affects the quality of most satellite operational and research products. This is certainly true for the Ice, Cloud, and land Elevation Satellite-2 (lCESat-2), which is the successor to the ICESat-l. As a top priority mission, ICESat-2 will continue to provide measurements of ice sheets and sea ice elevation on a global scale. Studies have shown that clouds can significantly affect the accuracy of the retrieved results. For example, some of the photons (a photon is a basic unit of light) in the laser beam will be scattered by cloud particles on its way. So instead of traveling in a straight line, these photons are scattered sideways and have traveled a longer path. This will result in biases in ice sheet elevation measurements. Hence cloud screening must be done and be done accurately before the retrievals.

Atmospheric Multiple Scattering Effects on GLAS Altimetry. Part 2; Analysis of Expected Errors in Antarctic Altitude Measurements

NASA Technical Reports Server (NTRS)

Mahesh, Ashwin; Spinhirne, James D.; Duda, David P.; Eloranta, Edwin W.; Starr, David O'C (Technical Monitor)

2001-01-01

The altimetry bias in GLAS (Geoscience Laser Altimeter System) or other laser altimeters resulting from atmospheric multiple scattering is studied in relationship to current knowledge of cloud properties over the Antarctic Plateau. Estimates of seasonal and interannual changes in the bias are presented. Results show the bias in altitude from multiple scattering in clouds would be a significant error source without correction. The selective use of low optical depth clouds or cloudfree observations, as well as improved analysis of the return pulse such as by the Gaussian method used here, are necessary to minimize the surface altitude errors. The magnitude of the bias is affected by variations in cloud height, cloud effective particle size and optical depth. Interannual variations in these properties as well as in cloud cover fraction could lead to significant year-to-year variations in the altitude bias. Although cloud-free observations reduce biases in surface elevation measurements from space, over Antarctica these may often include near-surface blowing snow, also a source of scattering-induced delay. With careful selection and analysis of data, laser altimetry specifications can be met.

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

NASA Technical Reports Server (NTRS)

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

2002-01-01

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

Improved algorithms for the retrieval of the h2 Love number of Mercury from laser altimetry data

NASA Astrophysics Data System (ADS)

Thor, Robin; Kallenbach, Reinald; Christensen, Ulrich; Oberst, Jürgen; Stark, Alexander; Steinbrügge, Gregor

2017-04-01

We simulate measurements to be performed by the BepiColombo laser altimeter (BELA) aboard the Mercury Planetary Orbiter (MPO) of the BepiColombo mission and investigate whether coverage and accuracy will be sufficient to retrieve the h2 Love number of Mercury. The h2 Love number describes the tidal response of Mercury's surface and is a function of the materials in its interior and their properties and distribution. Therefore, it can serve as an important constraint for models of the internal structure. The tide-generating potential from the Sun causes periodic radial displacements of up to ˜2 m on Mercury which can be detected by laser altimetry. In this study, we simultaneously extract the static global shape, parametrized by local basis functions, and its variability in time. The usage of cubic splines as local basis functions in both longitudinal and latitudinal direction provides an improvement over the methodology of Koch et al. (2010, Planetary and Space Science, 58(14), 2022-2030) who used cubic splines in longitudinal direction, but only step functions in latitudinal direction. We achieve a relative 1σ accuracy of the h2 Love number of 1.7% assuming nominal data acquisition for BELA during a one-year mission, but considering only stochastic noise.

The GLAS Standard Data Products Specification--Level 2, Version 9. Volume 14

NASA Technical Reports Server (NTRS)

Lee, Jeffrey E.

2013-01-01

The Geoscience Laser Altimeter System (GLAS) is the primary instrument for the ICESat (Ice, Cloud and Land Elevation Satellite) laser altimetry mission. ICESat was the benchmark Earth Observing System (EOS) mission for measuring ice sheet mass balance, cloud and aerosol heights, as well as land topography and vegetation characteristics. From 2003 to 2009, the ICESat mission provided multi-year elevation data needed to determine ice sheet mass balance as well as cloud property information, especially for stratospheric clouds common over polar areas. It also provided topography and vegetation data around the globe, in addition to the polar-specific coverage over the Greenland and Antarctic ice sheets.This document defines the Level-2 GLAS standard data products. This document addresses the data flow, interfaces, record and data formats associated with the GLAS Level 2 standard data products. The term standard data products refers to those EOS instrument data that are routinely generated for public distribution. The National Snow and Ice Data Center (NSDIC) distribute these products. Each data product has a unique Product Identification code assigned by the Senior Project Scientist. The Level 2 Standard Data Products specifically include those derived geophysical data values (i.e., ice sheet elevation, cloud height, vegetation height, etc.). Additionally, the appropriate correction elements used to transform the Level 1A and Level 1B Data Products into Level 2 Data Products are included. The data are packaged with time tags, precision orbit location coordinates, and data quality and usage flags.

The GLAS Standard Data Products Specification-Level 1, Version 9

NASA Technical Reports Server (NTRS)

Lee, Jeffrey E.

2013-01-01

The Geoscience Laser Altimeter System (GLAS) is the primary instrument for the ICESat (Ice, Cloud and Land Elevation Satellite) laser altimetry mission. ICESat was the benchmark Earth Observing System (EOS) mission for measuring ice sheet mass balance, cloud and aerosol heights, as well as land topography and vegetation characteristics. From 2003 to 2009, the ICESat mission provided multi-year elevation data needed to determine ice sheet mass balance as well as cloud property information, especially for stratospheric clouds common over polar areas. It also provided topography and vegetation data around the globe, in addition to the polar-specific coverage over the Greenland and Antarctic ice sheets.This document defines the Level-1 GLAS standard data products. This document addresses the data flow, interfaces, record and data formats associated with the GLAS Level 1 standard data products. GLAS Level 1 standard data products are composed of Level 1A and Level 1B data products. The term standard data products refers to those EOS instrument data that are routinely generated for public distribution. The National Snow and Ice Data Center (NSDIC) distribute these products. Each data product has a unique Product Identification code assigned by the Senior Project Scientist. GLAS Level 1A and Level 1B Data Products are composed from those Level 0 data that have been reformatted or transformed to corrected and calibrated data in physical units at the full instrument rate and resolution.

Multi-beam laser altimeter

NASA Technical Reports Server (NTRS)

Bufton, Jack L.; Harding, David J.; Ramos-Izquierdo, Luis

1993-01-01

Laser altimetry provides a high-resolution, high-accuracy method for measurement of the elevation and horizontal variability of Earth-surface topography. The basis of the measurement is the timing of the round-trip propagation of short-duration pulses of laser radiation between a spacecraft and the Earth's surface. Vertical resolution of the altimetry measurement is determined primarily by laser pulsewidth, surface-induced spreading in time of the reflected pulse, and the timing precision of the altimeter electronics. With conventional gain-switched pulses from solid-state lasers and sub-nsec resolution electronics, sub-meter vertical range resolution is possible from orbital attitudes of several hundred kilometers. Horizontal resolution is a function of laser beam footprint size at the surface and the spacing between successive laser pulses. Laser divergence angle and altimeter platform height above the surface determine the laser footprint size at the surface, while laser pulse repetition-rate, laser transmitter beam configuration, and altimeter platform velocity determine the space between successive laser pulses. Multiple laser transitters in a singlaltimeter instrument provide across-track and along-track coverage that can be used to construct a range image of the Earth's surface. Other aspects of the multi-beam laser altimeter are discussed.

ICESat (GLAS) Science Processing Software Document Series. Volume 2; Science Data Management Plan; 4.0

NASA Technical Reports Server (NTRS)

Jester, Peggy L.; Hancock, David W., III

1999-01-01

This document provides the Data Management Plan for the GLAS Standard Data Software (SDS) supporting the GLAS instrument of the EOS ICESat Spacecraft. The SDS encompasses the ICESat Science Investigator-led Processing System (I-SIPS) Software and the Instrument Support Facility (ISF) Software. This Plan addresses the identification, authority, and description of the interface nodes associated with the GLAS Standard Data Products and the GLAS Ancillary Data.

Implementation of Altimetry Data in the GIPSY POD Software Package

NASA Technical Reports Server (NTRS)

Stauch, Jason R.; Gold, Kenn; Born, George H.

2001-01-01

Altimetry data has been used extensively to acquire data about characteristics of the Earth, the Moon, and Mars. More recently, the idea of using altimetry for orbit determination has also been explored. This report discusses modifications to JPL's GIPSY/OASIS II software to include altimetry data as an observation type for precise orbit determination. The mathematical foundation of using altimetry for the purpose of orbit determination is presented, along with results.

Report from the School of Experience: Lessons-Learned on NASA's EOS/ICESat Mission

NASA Technical Reports Server (NTRS)

Anselm, William

2003-01-01

Abstract-NASA s Earth Observing System EOS) Ice, Cloud, and Land Elevation Satellite (ICESat) mission was one of the first missions under Goddard Space Flight Center s (then-) new Rapid Spacecraft Development Office. This paper explores the lessons-learned under the ICESat successful implementation and launch, focusing on four areas: Procurement., Management, Technical, and Launch and Early Operations. Each of these areas is explored in a practical perspective of communication, the viewpoint of the players, and the interactions among the organizations. Conclusions and lessons-learned are summarized in the final section.

ICESat GLAS Elevation Changes and ALOS PALSAR InSAR Line-Of-Sight Changes on the Continuous Permafrost Zone of the North Slope, Alaska

NASA Astrophysics Data System (ADS)

Muskett, Reginald

2016-04-01

Measuring centimeter-scale and smaller surface changes by satellite-based systems on the periglacial terrains and permafrost zones of the northern hemisphere is an ongoing challenge. We are investigating this challenge by using data from the NASA Ice, Cloud, and land Elevation Satellite Geoscience Laser Altimeter System (ICESat GLAS) and the JAXA Advanced Land Observing Satellite Phased Array type L-band Synthetic Aperture Radar (ALOS PALSAR) on the continuous permafrost zone of the North Slope, Alaska. Using the ICESat GLAS exact-repeat profiles in the analysis of ALOS PALSAR InSAR Line-Of-Sight (LOS) changes we find evidence of volume scattering over much of the tundra vegetation covered active-layer and surface scattering from river channel/banks (deposition and erosion), from rock outcropping bluffs and ridges. Pingos, ice-cored mounds common to permafrost terrains can be used as benchmarks for assessment of LOS changes. For successful InSAR processing, topographic and tropospheric phase cannot be assumed negligible and must be removed. The presence of significant troposphere phase in short-period repeat interferograms renders stacking ill suited for the task of deriving verifiable centimeter-scale surface deformation phase and reliable LOS changes. Ref.: Muskett, R.R. (2015), ICESat GLAS Elevation Changes and ALOS PALSAR InSAR Line-Of-Sight Changes on the Continuous Permafrost Zone of the North Slope, Alaska. International Journal of Geosciences, 6 (10), 1101-1115. doi:10.4236/ijg.2015.610086 http://www.scirp.org/Journal/PaperDownload.aspx?paperID=60406

Yb:YAG Lasers for Space Based Remote Sensing

NASA Technical Reports Server (NTRS)

Ewing, J.J.; Fan, T. Y.

1998-01-01

Diode pumped solid state lasers will play a prominent role in future remote sensing missions because of their intrinsic high efficiency and low mass. Applications including altimetry, cloud and aerosol measurement, wind velocity measurement by both coherent and incoherent methods, and species measurements, with appropriate frequency converters, all will benefit from a diode pumped primary laser. To date the "gold standard" diode pumped Nd laser has been the laser of choice for most of these concepts. This paper discusses an alternate 1 micron laser, the YB:YAG laser, and its potential relevance for lidar applications. Conceptual design analysis and, to the extent possible at the time of the conference, preliminary experimental data on the performance of a bread board YB:YAG oscillator will be presented. The paper centers on application of YB:YAG for altimetry, but extension to other applications will be discussed.

Basic Radar Altimetry Toolbox: Tools and Tutorial to Use Cryosat Data

NASA Astrophysics Data System (ADS)

Benveniste, J.; Bronner, E.; Dinardo, S.; Lucas, B. M.; Rosmorduc, V.; Earith, D.; Niemeijer, S.

2011-12-01

Radar altimetry is very much a technique expanding its applications. Even If quite a lot of effort has been invested for oceanography users, the use of Altimetry data for cryosphere application, especially with the new ESA CryoSat-2 mission data is still somehow tedious for new Altimetry data products users. ESA and CNES therfore developed the Basic Radar Altimetry Toolbox 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, the future Saral missions and is ready for adaptation to Sentinel-3 products - 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 since April 2007, and had been demonstrated during training courses and scientific meetings. About 2000 people downloaded it (Summer 2011), with many "newcomers" to altimetry among them

Using ATM laser altimetry to constrain surface mass balance estimates and supraglacial hydrology of the Greenland Ice Sheet

NASA Astrophysics Data System (ADS)

Studinger, M.; Medley, B.; Manizade, S.; Linkswiler, M. A.

2016-12-01

Repeat airborne laser altimetry measurements can provide large-scale field observations to better quantify spatial and temporal variability of surface processes contributing to seasonal elevation change and therefore surface mass balance. As part of NASA's Operation IceBridge the Airborne Topographic Mapper (ATM) laser altimeter measured the surface elevation of the Greenland Ice Sheet during spring (March - May) and fall (September - October) of 2015. Comparison of the two surveys reveals a general trend of thinning for outlet glaciers and for the ice sheet in a manner related to elevation and latitude. In contrast, some thickening is observed on the west (but not on the east) side of the ice divide above 2200 m elevation in the southern half, below latitude 69°N.The observed magnitude and spatial patterns of the summer melt signal can be utilized as input into ice sheet models and for validating reanalysis of regional climate models such as RACMO and MAR. We use seasonal anomalies in MERRA-2 climate fields (temperature, precipitation) to understand the observed spatial signal in seasonal change. Aside from surface elevation change, runoff from meltwater pooling in supraglacial lakes and meltwater channels accounts for at least half of the total mass loss. The ability of the ATM laser altimeters to image glacial hydrological features in 3-D and determine the depth of supraglacial lakes could be used for process studies and for quantifying melt processes over large scales. The 1-meter footprint diameter of ATM laser on the surface, together with a high shot density, allows for the production of large-scale, high-resolution, geodetic quality DEMs (50 x 50 cm) suitable for fine-scale glacial hydrology research and as input to hydrological models quantifying runoff.

Analysis of Airborne Radar Altimetry Measurements of the Greenland Ice Sheet

NASA Technical Reports Server (NTRS)

Ferraro, Ellen J.

1994-01-01

This dissertation presents an analysis of airborne altimetry measurements taken over the Greenland ice sheet with the 13.9 GHz Advanced Application Flight Experiment (AAFE) pulse compression radar altimeter. This Ku-band instrument was refurbished in 1990 by the Microwave Remote Sensing Laboratory at the University of Massachusetts to obtain high-resolution altitude measurements and to improve the tracking, speed, storage and display capabilities of the radar. In 1991 and 1993, the AAFE altimeter took part in the NASA Multisensor Airborne Altimetry Experiments over Greenland, along with two NASA laser altimeters. Altitude results from both experiments are presented along with comparisons to the laser altimeter and calibration passes over the Sondrestroem runway in Greenland. Although it is too early to make a conclusion about the growth or decay of the ice sheet, these results show that the instrument is capable of measuring small-scale surface changes to within 14 centimeters. In addition, results from these experiments reveal that the radar is sensitive to the different diagenetic regions of the ice sheet. Return waveforms from the wet- snow, percolation and dry-snow zones show varying effects of both surface scattering and sub-surface or volume scattering. Models of each of the diagenetic regions of Greenland are presented along with parameters such as rms surface roughness, rms surface slope and attenuation coefficient of the snow pack obtained by fitting the models to actual return waveforms.

Fusion of GEDI, ICESAT2 & NISAR data for above ground biomass mapping in Sonoma County, California

NASA Astrophysics Data System (ADS)

Duncanson, L.; Simard, M.; Thomas, N. M.; Neuenschwander, A. L.; Hancock, S.; Armston, J.; Dubayah, R.; Hofton, M. A.; Huang, W.; Tang, H.; Marselis, S.; Fatoyinbo, T.

2017-12-01

Several upcoming NASA missions will collect data sensitive to forest structure (GEDI, ICESAT-2 & NISAR). The LiDAR and SAR data collected by these missions will be used in coming years to map forest aboveground biomass at various resolutions. This research focuses on developing and testing multi-sensor data fusion approaches in advance of these missions. Here, we present the first case study of a CMS-16 grant with results from Sonoma County, California. We simulate lidar and SAR datasets from GEDI, ICESAT-2 and NISAR using airborne discrete return lidar and UAVSAR data, respectively. GEDI and ICESAT-2 signals are simulated from high point density discrete return lidar that was acquired over the entire county in 2014 through a previous CMS project (Dubayah & Hurtt, CMS-13). NISAR is simulated from L-band UAVSAR data collected in 2014. These simulations are empirically related to 300 field plots of aboveground biomass as well as a 30m biomass map produced from the 2014 airborne lidar data. We model biomass independently for each simulated mission dataset and then test two fusion methods for County-wide mapping 1) a pixel based approach and 2) an object oriented approach. In the pixel-based approach, GEDI and ICESAT-2 biomass models are calibrated over field plots and applied in orbital simulations for a 2-year period of the GEDI and ICESAT-2 missions. These simulated samples are then used to calibrate UAVSAR data to produce a 0.25 ha map. In the object oriented approach, the GEDI and ICESAT-2 data are identical to the pixel-based approach, but calibrate image objects of similar L-band backscatter rather than uniform pixels. The results of this research demonstrate the estimated ability for each of these three missions to independently map biomass in a temperate, high biomass system, as well as the potential improvement expected through combining mission datasets.

Pre-Launch Performance Testing of the ICESat-2/ATLAS Flight Science Receiver Algorithms

NASA Astrophysics Data System (ADS)

Mcgarry, J.; Carabajal, C. C.; Saba, J. L.; Rackley, A.; Holland, S.

2016-12-01

NASA's Advanced Topographic Laser Altimeter System (ATLAS) will be the single instrument on the ICESat-2 spacecraft which is expected to launch in late 2017 with a 3 year mission lifetime. The ICESat-2 planned orbital altitude is 500 km with a 92 degree inclination and 91-day repeat tracks. ATLAS is a single-photon detection system transmitting at 532nm with a laser repetition rate of 10 kHz and a 6 spot pattern on the Earth's surface. Without some method of reducing the received data, the volume of ATLAS telemetry would far exceed the normal X-band downlink capability. To reduce the data volume to an acceptable level a set of onboard Receiver Algorithms has been developed. These Algorithms limit the daily data volume by distinguishing surface echoes from the background noise and allowing the instrument to telemeter data from only a small vertical region about the signal. This is accomplished through the use of an onboard Digital Elevation Model (DEM), signal processing techniques, and onboard relief and surface reference maps. The ATLAS Receiver Algorithms have been completed and have been verified during Instrument testing in the spacecraft assembly area at the Goddard Space Flight Center in late 2015 and early 2016. Testing has been performed at ambient temperature with a pressure of one atmosphere as well as at the expected hot and cold temperatures in a vacuum. Results from testing to date show the Receiver Algorithms have the ability to handle a wide range of signal and noise levels with a very good sensitivity at relatively low signal to noise ratios. Testing with the ATLAS instrument and flight software shows very good agreement with previous Simulator testing and all of the requirements for ATLAS Receiver Algorithms were successfully verified during Run for the Record Testing in December 2015. This poster will describe the performance of the ATLAS Flight Science Receiver Algorithms during the Run for Record and Comprehensive Performance Testing performed

Uncertainties in Ice-Sheet Altimetry from a Spaceborne 1064-nm Single-Channel Lidar Due to Undetected Thin Clouds

NASA Technical Reports Server (NTRS)

Yang, Yuekui; Marshak, Alexander; Varnai, Tamas; Wiscombe, Warren; Yang, Ping

2010-01-01

In support of the Ice, Cloud, and land Elevation Satellite (ICESat)-II mission, this paper studies the bias in surface-elevation measurements caused by undetected thin clouds. The ICESat-II satellite may only have a 1064-nm single-channel lidar onboard. Less sensitive to clouds than the 532-nm channel, the 1064-nm channel tends to miss thin clouds. Previous studies have demonstrated that scattering by cloud particles increases the photon-path length, thus resulting in biases in ice-sheet-elevation measurements from spaceborne lidars. This effect is referred to as atmospheric path delay. This paper complements previous studies in the following ways: First, atmospheric path delay is estimated over the ice sheets based on cloud statistics from the Geoscience Laser Altimeter System onboard ICESat and the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Terra and Aqua. Second, the effect of cloud particle size and shape is studied with the state-of-the-art phase functions developed for MODIS cirrus- cloud microphysical model. Third, the contribution of various orders of scattering events to the path delay is studied, and an analytical model of the first-order scattering contribution is developed. This paper focuses on the path delay as a function of telescope field of view (FOV). The results show that reducing telescope FOV can significantly reduce the expected path delay. As an example, the average path delays for FOV = 167 microrad (a 100-m-diameter circle on the surface) caused by thin undetected clouds by the 1064-nm channel over Greenland and East Antarctica are illustrated.

Detailed gravity anomalies from GEOS-3 satellite altimetry data

NASA Technical Reports Server (NTRS)

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

1978-01-01

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

Conquering the Coastal Zone: A New Frontier for Satellite Altimetry

NASA Astrophysics Data System (ADS)

Cipollini, Paolo; Benveniste, Jerome; Miller, Laury; Picot, Nicolas; Scharroo, Remko; Strub, Ted; Vandemark, Doug; Vignudelli, Stefano; Zoffoli, Simona; Andersen, Ole; Bao, Lifeng; Birol, Florence; Coelho, Emanuel; Deng, Xiaoli; Emery, William; Fenoglio, Luciana; Fernandes, Joana; Gomez-Enri, Jesus; Griffin, David; Han, Guoqi; Hausman, Jessica; Ichikawa, Kaoru; Kostianoy, Andrey; Kourafalou, Villy; Labroue, Sylvie; Ray, Richard; Saraceno, Martin; Smith, Walter; Thibault, Pierre; Wilkin, John; Yenamandra, Somayajulu

2013-09-01

Coastal altimetry, that is the effort to recover meaningful measurements of sea level and significant wave height in the coastal strip from satellite-borne radar instruments, is successfully extending altimetry to a previously uncharted domain. This success is apparent at the annual Coastal Altimetry Workshops, whose 6th edition (Riva del Garda 20-21 September, 2012) was held just before the "20 Year of Progress in Radar Altimetry" Symposium.The efforts of such a vibrant international community are bringing coastal altimetry to maturity, as a science topic of great relevance to monitor the coastal environment and assess the impact of global change on the coasts. Datasets are being produced, results are coming out and being disseminated, applications are pioneered. The Springer book Coastal Altimetry, published in 2011, is a good account of such efforts. The cross-fertilization of ideas with OSTST (of which the coastal altimetry community constitutes a special splinter) brings significant mutual benefits, both in terms of technical insight and in terms of synergy of open-ocean and coastal applications.The present contribution is meant as a 'community white paper' and aims at giving an account of the development and accomplishments of the new field. We summarize the main technical achievements and the many diverse applications of the new discipline, as well as the recommendations that stemmed from recent discussion. While coastal altimetry techniques are recovering extremely valuable information from the 20+ years of data already in the archives, even more exciting prospects are ahead of us with the processing of higher resolution altimetric missions (CryoSat, Sentinel-3, Jason-CS, SWOT).

ICESat (GLAS) Science Processing Software Document Series. Volume 1; Science Software Management Plan; 3.0

NASA Technical Reports Server (NTRS)

Hancock, David W., III

1999-01-01

This document provides the Software Management Plan for the GLAS Standard Data Software (SDS) supporting the GLAS instrument of the EOS ICESat Spacecraft. The SDS encompasses the ICESat Science Investigator-led Processing System (I-SIPS) Software and the Instrument Support Terminal (IST) Software. For the I-SIPS Software, the SDS will produce Level 0, Level 1, and Level 2 data products as well as the associated product quality assessments and descriptive information. For the IST Software, the SDS will accommodate the GLAS instrument support areas of engineering status, command, performance assessment, and instrument health status.

Louisiana Wetland Monitoring Using TOPEX/POSEIDON Altimetry

NASA Astrophysics Data System (ADS)

Yi, Y.; Lee, H.; Ibaraki, M.; Shum, C.

2006-12-01

Conventional satellite radar altimetry is designed to observe ocean topography and significant technological advance has enabled our capability to measure sea level change, ice sheet elevation and sea ice freeboard height changes, hydrologic changes for large inland lake and rivers, and potentially land deformation. Wide- swath altimetry or interferometric altimetry onboard proposed and planned platforms are anticipated to significantly improve the spatial resolution of observations over ocean, land water, and ice surfaces. Coastal estuaries and wetlands play important roles in ecological environments. They not only provide habitat for thousands of aquatic/terrestrial plant and animal species but also control floods and storm surges by absorbing and reducing the velocity of storm water. Regional measurement of wetland water level changes from space is essential for hydrological studies. To our knowledge, there have been no reported successful attempts to use Ku-band altimetry for this purpose, especially over wetlands with seasonally varying vegetations. Here we demonstrate the use of the pulsed-limited radar altimeter (TOPEX), for the potential monitoring of wetland water level changes. The specific study regions are over the vegetated wetland in Louisiana. In addition to the retracking of Ku-band radar waveforms and generate a water level change time series over Louisiana wetland, we study the effect of media corrections, including the ionosphere and wet troposphere delays which are largely not applied for inland hydrological studies using altimetry. We find that most of the TOPEX waveform responses over the study region are specular or narrow-peaked, and we have tested various retrackers including the conventional OCOG, threshold, and the modified threshold algorithms which result in a decadal (1992-2002) height time series over several specific regions of the Louisiana wetland. It is found that the use of various corrections including wet troposphere delays

Land, Ocean and Ice sheet surface elevation retrieval from CALIPSO lidar measurements

NASA Astrophysics Data System (ADS)

Lu, X.; Hu, Y.

2013-12-01

Since launching in April 2006 the main objective of the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission has been studying the climate impact of clouds and aerosols in the atmosphere. However, CALIPSO also collects information about other components of the Earth's ecosystem, such as lands, oceans and polar ice sheets. The objective of this study is to propose a Super-Resolution Altimetry (SRA) technique to provide high resolution of land, ocean and polar ice sheet surface elevation from CALIPSO single shot lidar measurements (70 m spot size). The land surface results by the new technique agree with the United States Geological Survey (USGS) National Elevation Database (NED) high-resolution elevation maps, and the ice sheet surface results in the region of Greenland and Antarctic compare very well with the Ice, Cloud and land Elevation Satellite (ICESat) laser altimetry measurements. The comparisons suggest that the obtained CALIPSO surface elevation information by the new technique is accurate to within 1 m. The effects of error sources on the retrieved surface elevation are discussed. Based on the new technique, the preliminary data products of along-track topography retrieved from the CALIPSO lidar measurements is available to the altimetry community for evaluation.

Laser altimetry simulator. Version 3.0: User's guide

NASA Technical Reports Server (NTRS)

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

1994-01-01

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

SPCOLA: Combining laser altimetry and stereophotoclinometery to obtain topography for Bennu

NASA Astrophysics Data System (ADS)

Roberts, J. H.; Barnouin, O. S.; Palmer, E. E.; Gaskell, R. W.; Weirich, J. R.; Daly, M. G.; Seabrook, J.; Nair, H.; Espiritu, R. C.; Lauretta, D. S.; Perry, M. E.

2017-12-01

The Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission will return pristine samples of carbonaceous material from the surface of asteroid (101955) Bennu. Two instruments on OSIRIS-REx enable independent determination of topography: the OSIRIS-REx Laser Altimeter (OLA) and the OSIRIS-REx Camera Suite (OCAMS). OLA is a scanning lidar that ranges to the surface, returning altimetry information. OCAMS returns imaging data that are used to perform stereophotoclinometery (SPC) on these images to construct slope and albedo "maplets", small patches of the surface with central control points. Here we present a technique to combine topographic maplets generated using SPC with a compatible set of "mapolas" generated from OLA data. This "SPCOLA" process leverages the strengths of both while mitigating their respective weaknesses. A key advantage of SPC is that it allows a solution of the topography at accuracies similar to those of the best images used. SPC can make use of images at a wide range of viewing geometries and resolutions to simultaneously solve for slope and albedo. SPC also provides precise control point location from large stereo separation over multiple trajectories and can fill in gaps where point-based lidar data may not exist. Key strengths of lidar ranging include the ability to operate under any illumination conditions (including in the dark), insensitivity to albedo variations, robustness over large changes in slope, and provision of an absolute measurement of the range constraint to the surface. This range can be used to derive a control network for SPC, to improve the knowledge of the spacecraft position, to provide an independent scale for imagery and spectral data, and to provide constraints for any gravity solution obtained with radio science. Our goal in combining OLA data sets with image-based data is to generate Digital Elevation Models (DEMs) with higher accuracy than those using either

Height and Biomass of Mangroves in Africa from ICEsat/GLAS and SRTM

NASA Technical Reports Server (NTRS)

Fatoyinbo, Temilola E.; Simard, Marc

2012-01-01

The accurate quantification of forest 3-D structure is of great importance for studies of the global carbon cycle and biodiversity. These studies are especially relevant in Africa, where deforestation rates are high and the lack of background data is great. Mangrove forests are ecologically significant and it is important to measure mangrove canopy heights and biomass. The objectives of this study are to estimate: 1. The total area, 2. Canopy height distributions and 3. Aboveground biomass of mangrove forests in Africa. To derive mangrove 3-D structure and biomass maps, we used a combination of mangrove maps derived from Landsat ETM+, LiDAR canopy height estimates from ICEsat/GLAS (Ice, Cloud, and land Elevation Satellite/Geoscience Laser Altimeter System) and elevation data from SRTM (Shuttle Radar Topography Mission) for the African continent. More specifically, we extracted mangrove forest areas on the SRTM DEM using Landsat based landcover maps. The LiDAR (Light Detection and Ranging) measurements from the large footprint GLAS sensor were used to derive local estimates of canopy height and calibrate the Interferometric Synthetic Aperture Radar (InSAR) data from SRTM. We then applied allometric equations relating canopy height to biomass in order to estimate above ground biomass (AGB) from the canopy height product. The total mangrove area of Africa was estimated to be 25 960 square kilometers with 83% accuracy. The largest mangrove areas and greatest total biomass was 29 found in Nigeria covering 8 573 km2 with 132 x10(exp 6) Mg AGB. Canopy height across Africa was estimated with an overall root mean square error of 3.55 m. This error also includes the impact of using sensors with different resolutions and geolocation error which make comparison between measurements sensitive to canopy heterogeneities. This study provides the first systematic estimates of mangrove area, height and biomass in Africa. Our results showed that the combination of ICEsat/GLAS and

Revised method for forest canopy height estimation from Geoscience Laser Altimeter System waveforms.

Treesearch

Michael A. Lefskya; Michael Keller; Yong Panga; Plinio B. de Camargod; Maria O. Hunter

2007-01-01

The vertical extent of waveforms collected by the Geoscience Laser Altimeter System (onboard ICESat - the Ice, Cloud, and land Elevation Satellite) increases as a function of terrain slope and footprint size (the area on the ground that is illuminated by the laser). Over sloped terrain, returns from both canopy and ground surfaces can occur at the same elevation. As a...

Observing storm surges from satellite altimetry

NASA Astrophysics Data System (ADS)

Han, Guoqi

2016-07-01

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

Altimetry, Orbits and Tides

NASA Technical Reports Server (NTRS)

Colombo, O. L.

1984-01-01

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

Sea level budget in the Arctic during the satellite altimetry era

NASA Astrophysics Data System (ADS)

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

2016-04-01

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

The fiber optic system for the advanced topographic laser altimeter system instrument (ATLAS)

NASA Astrophysics Data System (ADS)

Ott, Melanie N.; Thomes, W. Joe; Onuma, Eleanya; Switzer, Robert; Chuska, Richard; Blair, Diana; Frese, Erich; Matyseck, Marc

2016-09-01

The Advanced Topographic Laser Altimeter System (ATLAS) Instrument has been in integration and testing over the past 18 months in preparation for the Ice, Cloud and Land Elevation Satellite - 2 (ICESat-2) Mission, scheduled to launch in 2017. ICESat-2 is the follow on to ICESat which launched in 2003 and operated until 2009. ATLAS will measure the elevation of ice sheets, glaciers and sea ice or the "cryosphere" (as well as terrain) to provide data for assessing the earth's global climate changes. Where ICESat's instrument, the Geo-Science Laser Altimeter (GLAS) used a single beam measured with a 70 m spot on the ground and a distance between spots of 170 m, ATLAS will measure a spot size of 10 m with a spacing of 70 cm using six beams to measure terrain height changes as small as 4 mm.[1] The ATLAS pulsed transmission system consists of two lasers operating at 532 nm with transmitter optics for beam steering, a diffractive optical element that splits the signal into 6 separate beams, receivers for start pulse detection and a wavelength tracking system. The optical receiver telescope system consists of optics that focus all six beams into optical fibers that feed a filter system that transmits the signal via fiber assemblies to the detectors. Also included on the instrument is a system that calibrates the alignment of the transmitted pulses to the receiver optics for precise signal capture. The larger electro optical subsystems for transmission, calibration, and signal receive, stay aligned and transmitting sufficiently due to the optical fiber system that links them together. The robust design of the fiber optic system, consisting of a variety of multi fiber arrays and simplex assemblies with multiple fiber core sizes and types, will enable the system to maintain consistent critical alignments for the entire life of the mission. Some of the development approaches used to meet the challenging optical system requirements for ATLAS are discussed here.

The fiber optic system for the Advanced Topographic Laser Altimeter System (ATLAS) instrument.

PubMed

Ott, Melanie N; Thomes, Joe; Onuma, Eleanya; Switzer, Robert; Chuska, Richard; Blair, Diana; Frese, Erich; Matyseck, Marc

2016-08-28

The Advanced Topographic Laser Altimeter System (ATLAS) Instrument has been in integration and testing over the past 18 months in preparation for the Ice, Cloud and Land Elevation Satellite - 2 (ICESat-2) Mission, scheduled to launch in 2017. ICESat-2 is the follow on to ICESat which launched in 2003 and operated until 2009. ATLAS will measure the elevation of ice sheets, glaciers and sea ice or the "cryosphere" (as well as terrain) to provide data for assessing the earth's global climate changes. Where ICESat's instrument, the Geo-Science Laser Altimeter (GLAS) used a single beam measured with a 70 m spot on the ground and a distance between spots of 170 m, ATLAS will measure a spot size of 10 m with a spacing of 70 cm using six beams to measure terrain height changes as small as 4 mm.[1] The ATLAS pulsed transmission system consists of two lasers operating at 532 nm with transmitter optics for beam steering, a diffractive optical element that splits the signal into 6 separate beams, receivers for start pulse detection and a wavelength tracking system. The optical receiver telescope system consists of optics that focus all six beams into optical fibers that feed a filter system that transmits the signal via fiber assemblies to the detectors. Also included on the instrument is a system that calibrates the alignment of the transmitted pulses to the receiver optics for precise signal capture. The larger electro optical subsystems for transmission, calibration, and signal receive, stay aligned and transmitting sufficiently due to the optical fiber system that links them together. The robust design of the fiber optic system, consisting of a variety of multi fiber arrays and simplex assemblies with multiple fiber core sizes and types, will enable the system to maintain consistent critical alignments for the entire life of the mission. Some of the development approaches used to meet the challenging optical system requirements for ATLAS are discussed here.

The Fiber Optic System for the Advanced Topographic Laser Altimeter System (ATLAS) Instrument

NASA Technical Reports Server (NTRS)

Ott, Melanie N.; Thomes, Joe; Onuma, Eleanya; Switzer, Robert; Chuska, Richard; Blair, Diana; Frese, Erich; Matyseck, Marc

2016-01-01

The Advanced Topographic Laser Altimeter System (ATLAS) Instrument has been in integration and testing over the past 18 months in preparation for the Ice, Cloud and Land Elevation Satellite - 2 (ICESat-2) Mission, scheduled to launch in 2017. ICESat-2 is the follow on to ICESat which launched in 2003 and operated until 2009. ATLAS will measure the elevation of ice sheets, glaciers and sea ice or the "cryosphere" (as well as terrain) to provide data for assessing the earth's global climate changes. Where ICESat's instrument, the Geo-Science Laser Altimeter (GLAS) used a single beam measured with a 70 m spot on the ground and a distance between spots of 170 m, ATLAS will measure a spot size of 10 m with a spacing of 70 cm using six beams to measure terrain height changes as small as 4 mm. The ATLAS pulsed transmission system consists of two lasers operating at 532 nm with transmitter optics for beam steering, a diffractive optical element that splits the signal into 6 separate beams, receivers for start pulse detection and a wavelength tracking system. The optical receiver telescope system consists of optics that focus all six beams into optical fibers that feed a filter system that transmits the signal via fiber assemblies to the detectors. Also included on the instrument is a system that calibrates the alignment of the transmitted pulses to the receiver optics for precise signal capture. The larger electro optical subsystems for transmission, calibration, and signal receive, stay aligned and transmitting sufficiently due to the optical fiber system that links them together. The robust design of the fiber optic system, consisting of a variety of multi fiber arrays and simplex assemblies with multiple fiber core sizes and types, will enable the system to maintain consistent critical alignments for the entire life of the mission. Some of the development approaches used to meet the challenging optical system requirements for ATLAS are discussed here.

Analysis of ICESat Data Using Kalman Filter and Kriging to Study Height Changes in East Antarctica

NASA Technical Reports Server (NTRS)

Herring, Thomas A.

2005-01-01

We analyze ICESat derived heights collected between Feb. 03-Nov. 04 using a kriging/Kalman filtering approach to investigate height changes in East Antarctica. The model's parameters are height change to an a priori static digital height model, seasonal signal expressed as an amplitude Beta and phase Theta, and height-change rate dh/dt for each (100 km)(exp 2) block. From the Kalman filter results, dh/dt has a mean of -0.06 m/yr in the flat interior of East Antarctica. Spatially correlated pointing errors in the current data releases give uncertainties in the range 0.06 m/yr, making height change detection unreliable at this time. Our test shows that when using all available data with pointing knowledge equivalent to that of Laser 2a, height change detection with an accuracy level 0.02 m/yr can be achieved over flat terrains in East Antarctica.

Airborne Laser Altimetry Measurements of Glacier Wastage in Alaska and NW Canada

NASA Astrophysics Data System (ADS)

Larsen, C. F.; Hock, R. M.; Arendt, A. A.; Zirnheld, S. L.

2009-12-01

Laser altimetry elevation profiles of glaciers in NW North America (Alaska, Yukon, and NW British Columbia) have been collected by the University of Alaska Geophysical Institute (UAF-GI) beginning in 1993. Since then, more than 200 glaciers throughout NW North America have been measured, many of them multiple times with typical repeat intervals of 3 to 5 years. All of the largest glaciers here have been profiled, including at least some representative glaciers from every major icefield in NW North America. Over 40 glaciers were surveyed again in the summer of 2009, a significant and unusually large annual addition to our database of surface elevation changes. Beginning in August 2009 we flew the surveys using the new UAF-GI swath mapping LiDAR system which records a 0.5 km wide 3-d map of survey points on an approximately 1 m x 1 m grid along the glacier centerlines. Over 40 glaciers and icefields have now been surveyed 3 or more times over the past 15 years, and these regions have been analyzed for changes in their rates of wastage. These regions include the Stikine Icefield of southeast Alaska, the Columbia Glacier, the Bering-Bagley and Seward-Malaspina systems, the Yakutat Icefield, Glacier Bay, the Harding Icefield, and the Alaska Range. Increased melt rates are generally observed over the most recent 3 to 5 year interval when compared to the previous 5 to 10 years, with many glaciers experiencing a factor of two or greater in their recent area-averaged thinning rates. Hypsometry appears to be a significant factor, with those areas that have relatively low average elevation and low accumulation areas showing stronger effects of the accelerated thinning. In particular, those icefields near the Gulf of Alaska coast, such as the Yakutat, Harding and Brady Icefields, are now rapidly wasting. A few areas that have relatively high elevation accumulation areas appear to have steady rates of thinning, such as within the St. Elias Mountains.

Validation of multi-mission satellite altimetry for the Baltic Sea region

NASA Astrophysics Data System (ADS)

Kudryavtseva, Nadia; Soomere, Tarmo; Giudici, Andrea

2016-04-01

Currently, three sources of wave data are available for the research community, namely, buoys, modelling, and satellite altimetry. The buoy measurements provide high-quality time series of wave properties but they are deployed only in a few locations. Wave modelling covers large domains and provides good results for the open sea conditions. However, the limitation of modelling is that the results are dependent on wind quality and assumptions put into the model. Satellite altimetry in many occasions provides homogeneous data over large sea areas with an appreciable spatial and temporal resolution. The use of satellite altimetry is problematic in coastal areas and partially ice-covered water bodies. These limitations can be circumvented by careful analysis of the geometry of the basin, ice conditions and spatial coverage of each altimetry snapshot. In this poster, for the first time, we discuss a validation of 30 years of multi-mission altimetry covering the whole Baltic Sea. We analysed data from RADS database (Scharroo et al. 2013) which span from 1985 to 2015. To assess the limitations of the satellite altimeter data quality, the data were cross-matched with available wave measurements from buoys of the Swedish Meteorological and Hydrological Institute and Finnish Meteorological Institute. The altimeter-measured significant wave heights showed a very good correspondence with the wave buoys. We show that the data with backscatter coefficients more than 13.5 and high errors in significant wave heights and range should be excluded. We also examined the effect of ice cover and distance from the land on satellite altimetry measurements. The analysis of cross-matches between the satellite altimetry data and buoys' measurements shows that the data are only corrupted in the nearshore domain within 0.2 degrees from the coast. The statistical analysis showed a significant decrease in wave heights for sea areas with ice concentration more than 30 percent. We also checked and

DEM generation and tidal deformation detection for sulzberger ice shelf, West Antarctica using SAR interferometry

USGS Publications Warehouse

Baek, S.; Kwoun, Oh-Ig; Bassler, M.; Lu, Z.; Shum, C.K.; Dietrich, R.

2004-01-01

In this study we generated a relative Digital Elevation Model (DEM) over the Sulzberger Ice Shelf, West Antarctica using ERS1/2 synthetic aperture radar (SAR) interferometry data. Four repeat pass differential interferograms are used to find the grounding zone and to classify the study area. An interferometrically derived DEM is compared with laser altimetry profile from ICESat. Standard deviation of the relative height difference is 5.12 m and 1.34 m in total length of the profile and at the center of the profile respectively. The magnitude and the direction of tidal changes estimated from interferogram are compared with those predicted tidal differences from four ocean tide models. Tidal deformation measured in InSAR is -16.7 cm and it agrees well within 3 cm with predicted ones from tide models.

Generating High-Resolution Lake Bathymetry over Lake Mead using the ICESat-2 Airborne Simulator

NASA Astrophysics Data System (ADS)

Li, Y.; Gao, H.; Jasinski, M. F.; Zhang, S.; Stoll, J.

2017-12-01

Precise lake bathymetry (i.e., elevation/contour) mapping is essential for optimal decision making in water resources management. Although the advancement of remote sensing has made it possible to monitor global reservoirs from space, most of the existing studies focus on estimating the elevation, area, and storage of reservoirs—and not on estimating the bathymetry. This limitation is attributed to the low spatial resolution of satellite altimeters. With the significant enhancement of ICESat-2—the Ice, Cloud & Land Elevation Satellite #2, which is scheduled to launch in 2018—producing satellite-based bathymetry becomes feasible. Here we present a pilot study for deriving the bathymetry of Lake Mead by combining Landsat area estimations with airborne elevation data using the prototype of ICESat-2—the Multiple Altimeter Beam Experimental Lidar (MABEL). First, an ISODATA classifier was adopted to extract the lake area from Landsat images during the period from 1982 to 2017. Then the lake area classifications were paired with MABEL elevations to establish an Area-Elevation (AE) relationship, which in turn was applied to the classification contour map to obtain the bathymetry. Finally, the Lake Mead bathymetry image was embedded onto the Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM), to replace the existing constant values. Validation against sediment survey data indicates that the bathymetry derived from this study is reliable. This algorithm has the potential for generating global lake bathymetry when ICESat-2 data become available after next year's launch.

Changes in the Mass Balance of the Greenland Ice Sheet in a Warming Climate During 2003-2009

NASA Technical Reports Server (NTRS)

Zwally, H. Jay; Luthcke, Scott

2010-01-01

Mass changes of the Greenland ice sheet (GIS) derived from ICESat and GRACE data both show that the net mass loss from GIS during 2003-2009 is about 175 Gt/year, which contributes 0.5mm/yr global sea-level rise. The rate of mass loss has increased significantly since the 1990's when the GIS was close to mass balance. Even though the GIS was close to mass balance during the 1990's, it was already showing characteristics of responding to8 warmer climate, specifically thinning at the margins and thickening inland at higher elevations. During 2003-2009, increased ice thinning due to increases in melting and acceleration of outlet glaciers began to strongly exceed the inland thickening from increases in accumulation. Over the entire GIS, the mass loss between the two periods, from increased melting and ice dynamics, increased by about 190 Gt/year while the mass gain, from increased precipitation and accumulation, increased by only about 15Gt/year. These ice changes occurred during a time when the temperature on GIS changed at rate of about 2K/decade. The distribution of elevation and mass changes derived from ICESat have high spatial resolution showing details over outlet glaciers, by drainage systems, and by elevation. However, information on the seasonal cycle of changes from ICESat data is limited, because the ICESat lasers were only operated during two to three campaigns per year of about 35 days duration each. In contrast, the temporal resolution of GRACE data, provided by the continuous data collection, is much better showing details of the seasonal cycle and the inter-annual variability. The differing sensitivity of the ICESat altimetry and the GRACE gravity methods to motion of the underlying bedrock from glacial isostatic adjustment (GIA) is used to evaluate the GIA corrections provided by models. The two data types are also combined to make estimates of the partitioning of the mass gains and losses among accumulation, melting, and ice discharge from outlet

COASTALT Project's Contribution to the Development and Dissemination of Coastal Altimetry

NASA Astrophysics Data System (ADS)

Cipollini, Paolo; Barbosa, Susana; Benveniste, Jérôme; Bos, Machiel; Caparrini, Marco; Challenor, Peter; Coelho, Henrique; Dinardo, Salvatore; Fernandes, Joana; Gleason, Scott; Gómez-Enri, Jesus; Gommenginger, Christine; Lázaro, Clara; Lucas, Bruno M.; Martin-Puig, Cristina; Moreno, Laura; Nunes, Alexandra; Pires, Nelson; Quartly, Graham; Scozzari, Andrea; Snaith, Helen; Tsimplis, Mikis; Vignudelli, Stefano; West, Luke; Wolf, Judith; Woodworth, Phil

2013-09-01

The present contribution revisits briefly the many recent technical improvements that are contributing to the steady progress of the new field of Coastal Altimetry, and in particular focuses on the results of the ESA-funded COASTALT project (2008- 2011), 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, i.e. 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 corrections for the effects of the atmosphere and/or other geophysical phenomena, like tides.The main results of COASTALT, as far as retracking is concerned, are the innovative techniques to deal with the waveforms in proximity of the coast, where there are often quasi-specular returns due to stretches of calm water which prevent a successful use of the standard (open-ocean) Brown-model retracker. This issue has been investigated in a number of cases around islands, and we present a hyperbolic pre-tracker that has been suggested as a way to precondition the waveform stack prior to conventional retracking. In terms of coastal-specific corrections, the main contribution by COASTALT has been the implementation of an innovative scheme for the Wet Tropospheric Correction (i.e. the path delay due to water vapour in the troposphere) based on GPSobservations and following pioneering research by the University of Porto.An important part of the COASTALT mission has been to facilitate the coming together of the international coastal altimetry community of researchers. This has been achieved via the moderation of the

Evolution of Altimetry Calibration and Future Challenges

NASA Technical Reports Server (NTRS)

Fu, Lee-Lueng; Haines, Bruce J.

2012-01-01

Over the past 20 years, altimetry calibration has evolved from an engineering-oriented exercise to a multidisciplinary endeavor driving the state of the art. This evolution has been spurred by the developing promise of altimetry to capture the large-scale, but small-amplitude, changes of the ocean surface containing the expression of climate change. The scope of altimeter calibration/validation programs has expanded commensurately. Early efforts focused on determining a constant range bias and verifying basic compliance of the data products with mission requirements. Contemporary investigations capture, with increasing accuracies, the spatial and temporal characteristics of errors in all elements of the measurement system. Dedicated calibration sites still provide the fundamental service of estimating absolute bias, but also enable long-term monitoring of the sea-surface height and constituent measurements. The use of a network of island and coastal tide gauges has provided the best perspective on the measurement stability, and revealed temporal variations of altimeter measurement system drift. The cross-calibration between successive missions provided fundamentally new information on the performance of altimetry systems. Spatially and temporally correlated errors pose challenges for future missions, underscoring the importance of cross-calibration of new measurements against the established record.

ICESat GLAS Elevation Changes and ALOS PALSAR InSAR Line-Of-Sight Changes on the Continuous Permafrost Zone of the North Slope, Alaska

NASA Astrophysics Data System (ADS)

Muskett, R. R.

2016-12-01

Measuring centimeter-scale and smaller surface changes by satellite-based systems on the periglacial terrains and permafrost zones of the northern hemisphere is an ongoing challenge. We are investigating this challenge by using data from the NASA Ice, Cloud, and land Elevation Satellite Geoscience Laser Altimeter System (ICESat GLAS) and the JAXA Advanced Land Observing Satellite Phased Array type L-band Synthetic Aperture Radar (ALOS PALSAR) on the continuous permafrost zone of the North Slope, Alaska. Using the ICESat GLAS exact-repeat profiles in the analysis of ALOS PALSAR InSAR Line-Of-Sight (LOS) changes we find evidence of volume scattering over much of the tundra vegetation covered active-layer and surface scattering from river channel/banks (deposition and erosion), from rock outcropping bluffs and ridges. Pingos, ice-cored mounds common to permafrost terrains can be used as benchmarks for assessment of LOS changes. For successful InSAR processing, topographic and tropospheric phase cannot be assumed negligible and must be removed. The presence of significant troposphere phase in short-period repeat interferograms renders stacking ill suited for the task of deriving verifiable centimeter-scale surface deformation phase and reliable LOS changes. Ref.: Muskett, R.R. (2015), Int. Journal of Geosciences, 6 (10), 1101-1115. doi:10.4236/ijg.2015.610086 http://www.scirp.org/Journal/PaperDownload.aspx?paperID=60406

The Ebb and Flow of Tidal Science, and the Impact of Satellite Altimetry

NASA Technical Reports Server (NTRS)

Ray, Richard; Egbert, Gary

2006-01-01

In the years immediately preceding the launches of Geosat and Topex/Poseidon, tidal science had lapsed into a period of uncertainty and discouragement, brought about by the failure of once-exciting new ideas that eventually proved overly optimistic. A long list of outstanding problems presented themselves, but progress had reached a "low water mark". What was lacking was a high-quality global dataset of tidal measurements, which satellite altimetry -- and especially Topex/Poseidon -- provided. With these data in hand, a "flood tide" of marked progress resulted. In this paper we review some of that progress. An important area of progress, with potentially important implications for other areas of physical oceanography, falls under the topic of "energy dissipation." With precise global constraints provided by altimetry -- combined with precise laser tracking of the altimeter, other geodetic satellites like Lageos, as well as the moon -- the planetary energy budgets of both Earth and ocean tides are now well determined. Moreover, the local energy balances, and thus local estimates of tidal dissipation, have now been mapped, although somewhat coarsely, throughout the ocean. This work has pointed to internal-tide generation in the deep ocean as the once missing sink of tidal energy, and has led to a plethora of new observational and theoretical studies of internal tides, and their role in vertical mixing of the deep ocean. The discovery that internal tides, or some part of them, can be directly mapped with an altimeter opens new lines of research on this topic. Low-mode internal tides have been found, at least in some regions, to propagate several thousand kilometers across open ocean. The study of such waves with altimetry gives us a global view heretofore unattainable, allowing strong observational constraints to be placed on possible ocean mixing processes, such as subharmonic instabilities.

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

NASA Astrophysics Data System (ADS)

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

2015-12-01

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

Preliminary Global Topographic Model of Mars Based on MOLA Altimetry, Earth-Based Radar, and Viking, Mariner and MGS Occultations

NASA Technical Reports Server (NTRS)

Smith, David E.; Zuber, Maria T.; Neumann, Gregory A.

1999-01-01

The recent altimetry data acquired by MOLA over the northern hemisphere of Mars have been combined with the Earth-based radar data obtained between 1971 and 1982, and occultation measurements of the Viking 1 and 2 Orbiters, Mariner 9, and MGS to derive a global model of the shape and topography of Mars. This preliminary model has a horizontal resolution of about 300 km. Vertical accuracy is on average a few hundred meters in the region of the data. Datasets: The altimetry and radar datasets were individually binned in 1.25 degree grids and merged with the occultation data. The Viking and Mariner occultation data in the northern hemisphere were excluded from the combined dataset where MOLA altimetry were available. The laser altimetry provided extensive and almost complete coverage of the northern hemisphere north of latitude 30 while the radar provided longitudinal coverage at several latitude bands between 23N and 23S. South of this region the only data were occultations. The majority of the occultations were obtained from Mariner 9, and the rest from Viking 1 & 2, and MGS. Earlier studies had shown that the Viking and Mariner occultations were on average only accurate to 500 meters. The recent MGS occultations are accurate to a few tens of meters. However, the highest southern latitude reached by the MGS occultations is only about 64S and data near the target region for the Mars 98 lander is limited to a few Viking and Mariner observations of relatively poor quality. In addition to the above datasets the locations of the Viking 1, Viking 2, and Pathfinder landers, obtained from the radio tracking of their signals, were included.

High Artic Glaciers and Ice Caps Ice Mass Change from GRACE, Regional Climate Model Output and Altimetry.

NASA Astrophysics Data System (ADS)

Ciraci, E.; Velicogna, I.; Fettweis, X.; van den Broeke, M. R.

2016-12-01

The Arctic hosts more than the 75% of the ice covered regions outside from Greenland and Antarctica. Available observations show that increased atmospheric temperatures during the last century have contributed to a substantial glaciers retreat in all these regions. We use satellite gravimetry by the NASA's Gravity Recovery and Climate Experiment (GRACE), and apply a least square fit mascon approach to calculate time series of ice mass change for the period 2002-2016. Our estimates show that arctic glaciers have constantly contributed to the sea level rise during the entire observation period with a mass change of -170+/-20 Gt/yr equivalent to the 80% of the total ice mass change from the world Glacier and Ice Caps (GIC) excluding the Ice sheet peripheral GIC, which we calculated to be -215+/-32 GT/yr, with an acceleration of 9+/-4 Gt/yr2. The Canadian Archipelago is the main contributor to the total mass depletion with an ice mass trend of -73+/-9 Gt/yr and a significant acceleration of -7+/-3 Gt/yr2. The increasing mass loss is mainly determined by melting glaciers located in the northern part of the archipelago.In order to investigate the physical processes driving the observed ice mass loss we employ satellite altimetry and surface mass balance (SMB) estimates from Regional climate model outputs available for the same time period covered by the gravimetry data. We use elevation data from the NASA ICESat (2003-2009) and ESA CryoSat-2 (2010-2016) missions to estimate ice elevation changes. We compare GRACE ice mass estimates with time series of surface mass balance from the Regional Climate Model (RACMO-2) and the Modèle Atmosphérique Régional (MAR) and determine the portion of the total mass change explained by the SMB signal. We find that in Iceland and in the and the Canadian Archipelago the SMB signal explains most of the observed mass changes, suggesting that ice discharge may play a secondary role here. In other region, e.g. in Svalbar, the SMB signal

Multibeam Laser Altimeter for Planetary Topographic Mapping

NASA Technical Reports Server (NTRS)

Garvin, J. B.; Bufton, J. L.; Harding, D. J.

1993-01-01

Laser altimetry provides an active, high-resolution, high-accuracy method for measurement of planetary and asteroid surface topography. The basis of the measurement is the timing of the roundtrip propagation of short-duration pulses of laser radiation between a spacecraft and the surface. Vertical, or elevation, resolution of the altimetry measurement is determined primarily by laser pulse width, surface-induced spreading in time of the reflected pulse, and the timing precision of the altimeter electronics. With conventional gain-switched pulses from solid-state lasers and nanosecond resolution timing electronics, submeter vertical range resolution is possible anywhere from orbital altitudes of approximately 1 km to altitudes of several hundred kilometers. Horizontal resolution is a function of laser beam footprint size at the surface and the spacing between successive laser pulses. Laser divergence angle and altimeter platform height above the surface determine the laser footprint size at the surface, while laser pulse repetition rate, laser transmitter beam configuration, and altimeter platform velocity determine the spacing between successive laser pulses. Multiple laser transmitters in a single laser altimeter instrument that is orbiting above a planetary or asteroid surface could provide across-track as well as along-track coverage that can be used to construct a range image (i.e., topographic map) of the surface. We are developing a pushbroom laser altimeter instrument concept that utilizes a linear array of laser transmitters to provide contiguous across-track and along-track data. The laser technology is based on the emerging monolithic combination of individual, 1-sq cm diode-pumped Nd:YAG laser pulse emitters. Details of the multi-emitter laser transmitter technology, the instrument configuration, and performance calculations for a realistic Discovery-class mission will be presented.

Altimetry, gravimetry, GPS and viscoelastic modeling data for the joint inversion for glacial isostatic adjustment in Antarctica (ESA STSE Project REGINA)

NASA Astrophysics Data System (ADS)

Sasgen, Ingo; Martín-Español, Alba; Horvath, Alexander; Klemann, Volker; Petrie, Elizabeth J.; Wouters, Bert; Horwath, Martin; Pail, Roland; Bamber, Jonathan L.; Clarke, Peter J.; Konrad, Hannes; Wilson, Terry; Drinkwater, Mark R.

2018-03-01

The poorly known correction for the ongoing deformation of the solid Earth caused by glacial isostatic adjustment (GIA) is a major uncertainty in determining the mass balance of the Antarctic ice sheet from measurements of satellite gravimetry and to a lesser extent satellite altimetry. In the past decade, much progress has been made in consistently modeling ice sheet and solid Earth interactions; however, forward-modeling solutions of GIA in Antarctica remain uncertain due to the sparsity of constraints on the ice sheet evolution, as well as the Earth's rheological properties. An alternative approach towards estimating GIA is the joint inversion of multiple satellite data - namely, satellite gravimetry, satellite altimetry and GPS, which reflect, with different sensitivities, trends in recent glacial changes and GIA. Crucial to the success of this approach is the accuracy of the space-geodetic data sets. Here, we present reprocessed rates of surface-ice elevation change (Envisat/Ice, Cloud,and land Elevation Satellite, ICESat; 2003-2009), gravity field change (Gravity Recovery and Climate Experiment, GRACE; 2003-2009) and bedrock uplift (GPS; 1995-2013). The data analysis is complemented by the forward modeling of viscoelastic response functions to disc load forcing, allowing us to relate GIA-induced surface displacements with gravity changes for different rheological parameters of the solid Earth. The data and modeling results presented here are available in the PANGAEA database (https://doi.org/10.1594/PANGAEA.875745). The data sets are the input streams for the joint inversion estimate of present-day ice-mass change and GIA, focusing on Antarctica. However, the methods, code and data provided in this paper can be used to solve other problems, such as volume balances of the Antarctic ice sheet, or can be applied to other geographical regions in the case of the viscoelastic response functions

Studies of oceanic tectonics based on GEOS-3 satellite altimetry

NASA Technical Reports Server (NTRS)

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

1979-01-01

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

Investigation Hydrometeorological Regime of the White Sea Based on Satellite Altimetry Data

NASA Astrophysics Data System (ADS)

Lebedev, Sergey A.

2016-08-01

The White Sea are the seas of the Arctic Ocean. Today complicated hydrodynamic, tidal, ice, and meteorological regimes of these seas may be investigated on the basis of remote sensing data, specifically of satellite altimetry data. Results of calibration and validation of satellite altimetry measurements (sea surface height and sea surface wind speed) and comparison with regional tidal model show that this type of data may be successfully used in scientific research and in monitoring of the environment. Complex analysis of the tidal regime of the White Sea and comparison between global and regional tidal models show advantages of regional tidal model for use in tidal correction of satellite altimetry data. Examples of using the sea level data in studying long-term variability of the Barents and White Seas are presented. Interannual variability of sea ice edge position is estimated on the basis of altimetry data.

A review of satellite radar altimetry applied to coastal ocean studies

NASA Astrophysics Data System (ADS)

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.

Thermal Design, Tvac Testing, and Lessons Learned for Critical GSE of ATLAS and the ICESat-2 Mission

NASA Technical Reports Server (NTRS)

Bradshaw, Heather

2016-01-01

This presentation describes the thermal design of the three main of optical components which comprise the Bench Checkout Equipment (BCE) for the Advanced Topographic Laser Altimeter System (ATLAS) instrument, which is flying on the ICESat-2 mission. Thermal vacuum testing of these components is also described in this presentation, as well as a few lessons learned. These BCE components serve as critical GSE for the mission; their purpose is to verify ATLAS is performing well. It has been said that, in one light, the BCE is the most important part of ATLAS, since, without it, ATLAS cannot be aligned properly or its performance verified before flight. Therefore, careful attention was paid to the BCEs thermal design, development, and component-level Tvac testing prior to its use in instrument-level and spacecraft-level Tvac tests with ATLAS. This presentation describes that thermal design, development, and testing, as well as a few lessons learned.

Radar altimetry systems cost analysis

NASA Technical Reports Server (NTRS)

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

1976-01-01

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

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

NASA Astrophysics Data System (ADS)

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

2015-12-01

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

Ice sheet radar altimetry

NASA Technical Reports Server (NTRS)

Zwally, J.

1988-01-01

The surface topography of the Greenland and Antarctic ice sheets between 72 degrees north and south was mapped using radar altimetry data from the U.S. Navy GEOSAT. The glaciological objectives of this activity were to study the dynamics of the ice flow, changes in the position of floating ice-shelf fronts, and ultimately to measure temporal changes in ice surface elevation indicative of ice sheet mass balance.

Glacier Acceleration and Thinning after Ice Shelf Collapse in the Larsen B Embayment, Antarctica

NASA Technical Reports Server (NTRS)

Scambos, T. A.; Bohlander, J. A.; Shuman, C. A.; Skvarca, P.

2004-01-01

Ice velocities derived from five Landsat 7 images acquired between January 2000 and February 2003 show a two- to six-fold increase in centerline speed of four glaciers flowing into the now-collapsed section of the Larsen B Ice Shelf. Satellite laser altimetry from ICEsat indicates the surface of Hektoria Glacier lowered by up to 38 +/- 6 m a six-month period beginning one year after the break-up in March 2002. Smaller elevation losses are observed for Crane and Jorum glaciers over a later 5-month period. Two glaciers south of the collapse area, Flask and Leppard, show little change in speed or elevation. Seasonal variations in speed preceding the large post-collapse velocity increases suggest that both summer melt percolation and changes in the stress field due to shelf removal play a major role in glacier dynamics.

Satellite altimetry and hydrologic modeling of poorly-gauged tropical watershed

NASA Astrophysics Data System (ADS)

Sulistioadi, Yohanes Budi

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

CryoSat-2 altimetry derived Arctic bathymetry map: first results and validation

NASA Astrophysics Data System (ADS)

Andersen, O. B.; Abulaitijiang, A.; Cancet, M.; Knudsen, P.

2017-12-01

The Technical University of Denmark (DTU), DTU Space has been developing high quality high resolution gravity fields including the new highly accurate CryoSat-2 radar altimetry satellite data which extends the global coverage of altimetry data up to latitude 88°. With its exceptional Synthetic Aperture Radar (SAR) mode being operating throughout the Arctic Ocean, leads, i.e., the ocean surface heights, is used to retrieve the sea surface height with centimeter-level range precision. Combined with the long repeat cycle ( 369 days), i.e., dense cross-track coverage, the high-resolution Arctic marine gravity can be modelled using the CryoSat-2 altimetry. Further, the polar gap can be filled by the available ArcGP product, thus yielding the complete map of the Arctic bathymetry map. In this presentation, we will make use of the most recent DTU17 marine gravity, to derive the arctic bathymetry map using inversion based on best available hydrographic maps. Through the support of ESA a recent evaluation of existing hydrographic models of the Arctic Ocean Bathymetry models (RTOPO, GEBCO, IBCAO etc) and various inconsistencies have been identified and means to rectify these inconsistencies have been taken prior to perform the inversion using altimetry. Simultaneously DTU Space has been placing great effort on the Arctic data screening, filtering, and de-noising using various altimetry retracking solutions and classifications. All the pre-processing contributed to the fine modelling of Actic gravity map. Thereafter, the arctic marine gravity grids will eventually be translated (downward continuation operation) to a new altimetry enhanced Arctic bathymetry map using appropriate band-pass filtering.

Arctic Sea Ice Freeboard from Icebridge Acquisitions in 2009: Estimates and Comparisons with ICEsat

NASA Technical Reports Server (NTRS)

Kwok, R.; Cunningham, Glenn F.; Manizade, S. S.; Krabill, W. B.

2012-01-01

During the spring of 2009, the Airborne Topographic Mapper (ATM) system on the IceBridge mission acquired cross-basin surveys of surface elevations of Arctic sea ice. In this paper, the total freeboard derived from four 2000 km transects are examined and compared with those from the 2009 ICESat campaign. Total freeboard, the sum of the snow and ice freeboards, is the elevation of the air-snow interface above the local sea surface. Prior to freeboard retrieval, signal dependent range biases are corrected. With data from a near co-incident outbound and return track on 21 April, we show that our estimates of the freeboard are repeatable to within 4 cm but dependent locally on the density and quality of sea surface references. Overall difference between the ATM and ICESat freeboards for the four transects is 0.7 (8.5) cm (quantity in bracket is standard deviation), with a correlation of 0.78 between the data sets of one hundred seventy-eight 50 km averages. This establishes a level of confidence in the use of ATM freeboards to provide regional samplings that are consistent with ICESat. In early April, mean freeboards are 41 cm and 55 cm over first year and multiyear sea ice (MYI), respectively. Regionally, the lowest mean ice freeboard (28 cm) is seen on 5 April where the flight track sampled the large expanse of seasonal ice in the western Arctic. The highest mean freeboard (71 cm) is seen in the multiyear ice just west of Ellesmere Island from 21 April. The relatively large unmodeled variability of the residual sea surface resolved by ATM elevations is discussed.

Lessons Learned from the Advanced Topographic Laser Altimeter System

NASA Technical Reports Server (NTRS)

Garrison, Matt; Patel, Deepak; Bradshaw, Heather; Robinson, Frank; Neuberger, Dave

2016-01-01

The ICESat-2 Advanced Topographic Laser Altimeter System (ATLAS) instrument is an upcoming Earth Science mission focusing on the effects of climate change. The flight instrument passed all environmental testing at GSFC (Goddard Space Flight Center) and is now ready to be shipped to the spacecraft vendor for integration and testing. This presentation walks through the lessons learned from design, hardware, analysis and testing perspective. ATLAS lessons learned include general thermal design, analysis, hardware, and testing issues as well as lessons specific to laser systems, two-phase thermal control, and optical assemblies with precision alignment requirements.

Sentinel-3 SAR Altimetry Toolbox - Scientific Exploitation of Operational Missions (SEOM) Program Element

NASA Astrophysics Data System (ADS)

Benveniste, Jérôme; Lucas, Bruno; Dinardo, Salvatore

2014-05-01

The prime objective of the SEOM (Scientific Exploitation of Operational Missions) element is to federate, support and expand the large international research community that the ERS, ENVISAT and the Envelope programmes have build up over the last 20 years for the future European operational Earth Observation missions, the Sentinels. Sentinel-3 builds directly on a proven heritage pioneered by ERS-1, ERS-2, Envisat and CryoSat-2, with a dual-frequency (Ku and C band) advanced Synthetic Aperture Radar Altimeter (SRAL) that provides measurements at a resolution of ~300m in SAR mode along track. Sentinel-3 will provide exact measurements of sea-surface height along with accurate topography measurements over sea ice, ice sheets, rivers and lakes. The first of the Sentinel-3 series is planned for launch in early 2015. The current universal altimetry toolbox is BRAT (Basic Radar Altimetry Toolbox) which can read all previous and current altimetry mission's data, but it does not have the capabilities to read the upcoming Sentinel-3 L1 and L2 products. ESA will endeavour to develop and supply this capability to support the users of the future Sentinel-3 SAR Altimetry Mission. BRAT is a collection of tools and tutorial documents designed to facilitate the processing of radar altimetry data. This project started in 2005 from the joint efforts of ESA (European Space Agency) and CNES (Centre National d'Etudes Spatiales, the French Space Agency), 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 net

Sentinel-3 SAR Altimetry Toolbox - Scientific Exploitation of Operational Missions (SEOM) Program Element

NASA Astrophysics Data System (ADS)

Benveniste, Jérôme; Dinardo, Salvatore; Lucas, Bruno Manuel

The prime objective of the SEOM (Scientific Exploitation of Operational Missions) element is to federate, support and expand the large international research community that the ERS, ENVISAT and the Envelope programmes have build up over the last 20 years for the future European operational Earth Observation missions, the Sentinels. Sentinel-3 builds directly on a proven heritage pioneered by ERS-1, ERS-2, Envisat and CryoSat-2, with a dual-frequency (Ku and C band) advanced Synthetic Aperture Radar Altimeter (SRAL) that provides measurements at a resolution of ~300m in SAR mode along track. Sentinel-3 will provide exact measurements of sea-surface height along with accurate topography measurements over sea ice, ice sheets, rivers and lakes. The first of the Sentinel-3 series is planned for launch in early 2015. The current universal altimetry toolbox is BRAT (Basic Radar Altimetry Toolbox) which can read all previous and current altimetry mission’s data, but it does not have the capabilities to read the upcoming Sentinel-3 L1 and L2 products. ESA will endeavour to develop and supply this capability to support the users of the future Sentinel-3 SAR Altimetry Mission. BRAT is a collection of tools and tutorial documents designed to facilitate the processing of radar altimetry data. This project started in 2005 from the joint efforts of ESA (European Space Agency) and CNES (Centre National d’Etudes Spatiales, the French Space Agency), 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

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

NASA Technical Reports Server (NTRS)

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

1995-01-01

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

Somali current studied from SEASAT altimetry

NASA Technical Reports Server (NTRS)

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

1984-01-01

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

Malvinas Current variability from Argo floats and satellite altimetry

NASA Astrophysics Data System (ADS)

Artana, Camila; Ferrari, Ramiro; Koenig, Zoé; Saraceno, Martin; Piola, Alberto R.; Provost, Christine

2016-07-01

The Malvinas Current (MC) is an offshoot of the Antarctic Circumpolar Current (ACC). Downstream of Drake Passage, the northern fronts of the ACC veer northward, cross over the North Scotia Ridge (NSR) and the Malvinas Plateau, and enter the Argentine Basin. We investigate the variations of the MC circulation between the NSR and 41°S and their possible relations with the ACC circulation using data from Argo floats and satellite altimetry. The data depict meandering and eddy shedding of the northern ACC jets as they cross the NSR. The altimetry fields show that these eddies are trapped, break down, and dissipate over the Malvinas Plateau, suggesting that this region is a hot spot for dissipation of mesoscale variability. Variations of sea level anomalies (SLA) across the NSR do not impact the MC further north, except for intra-seasonal variability associated with coastal trapped waves. Altimetry and float trajectories show events during which a large fraction of the MC is cut off from the ACC. Blocking events at around 48.5°S are a recurrent feature of the MC circulation. Over the 23 year altimetry record, we detected 26 events during which the MC surface transport at 48.5°S was reduced to less than half its long-term mean. Blocking events last from 10 to 35 days and do not present any significant trend. These events were tracked back to positive SLA that built up over the Argentine Abyssal Plain. Future work is needed to understand the processes responsible for these blocking events.

In-Flight Thermal Performance of the Geoscience Laser Altimeter System (GLAS) Instrument

NASA Technical Reports Server (NTRS)

Grob, Eric; Baker, Charles; McCarthy, Tom

2003-01-01

The Geoscience Laser Altimeter System (GLAS) instrument is NASA Goddard Space Flight Center's first application of Loop Heat Pipe technology that provides selectable/stable temperature levels for the lasers and other electronics over a widely varying mission environment. GLAS was successfully launched as the sole science instrument aboard the Ice, Clouds, and Land Elevation Satellite (ICESat) from Vandenberg AFB at 4:45pm PST on January 12, 2003. After SC commissioning, the LHPs started easily and have provided selectable and stable temperatures for the lasers and other electronics. This paper discusses the thermal development background and testing, along with details of early flight thermal performance data.

Toward Automated Generation of Reservoir Water Elevation Changes From Satellite Radar Altimetry.

NASA Astrophysics Data System (ADS)

Okeowo, M. A.; Lee, H.; Hossain, F.

2015-12-01

Until now, processing satellite radar altimetry data over inland water bodies on a large scale has been a cumbersome task primarily due to contaminated measurements from their surrounding topography. It becomes more challenging if the size of the water body is small and thus the number of available high-rate measurements from the water surface is limited. A manual removal of outliers is time consuming which limits a global generation of reservoir elevation profiles. This has limited a global study of lakes and reservoir elevation profiles for monitoring storage changes and hydrologic modeling. We have proposed a new method to automatically generate a time-series information from raw satellite radar altimetry without user intervention. With this method, scientist with little knowledge of altimetry can now independently process radar altimetry for diverse purposes. The method is based on K-means clustering, backscatter coefficient and statistical analysis of the dataset for outlier detection. The result of this method will be validated using in-situ gauges from US, Indus and Bangladesh reservoirs. In addition, a sensitivity analysis will be done to ascertain the limitations of this algorithm based on the surrounding topography, and the length of altimetry track overlap with the lake/reservoir. ­­ Finally, a reservoir storage change will be estimated on the study sites using MODIS and Landsat water classification for estimating the area of reservoir and the height will be estimated using Jason-2 and SARAL/Altika satellites.

Twenty Years of Progress on Global Ocean Tide: The Impact of Satellite Altimetry

NASA Astrophysics Data System (ADS)

Egbert, Gary D.; Ray, Richard D.

2013-09-01

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

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

NASA Technical Reports Server (NTRS)

Egbert, Gary; Ray, Richard

2012-01-01

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

The Slope Imaging Multi-Polarization Photon-Counting Lidar: Development and Performance Results

NASA Technical Reports Server (NTRS)

Dabney, Phillip

2010-01-01

The Slope Imaging Multi-polarization Photon-counting Lidar is an airborne instrument developed to demonstrate laser altimetry measurement methods that will enable more efficient observations of topography and surface properties from space. The instrument was developed through the NASA Earth Science Technology Office Instrument Incubator Program with a focus on cryosphere remote sensing. The SIMPL transmitter is an 11 KHz, 1064 nm, plane-polarized micropulse laser transmitter that is frequency doubled to 532 nm and split into four push-broom beams. The receiver employs single-photon, polarimetric ranging at 532 and 1064 nm using Single Photon Counting Modules in order to achieve simultaneous sampling of surface elevation, slope, roughness and depolarizing scattering properties, the latter used to differentiate surface types. Data acquired over ice-covered Lake Erie in February, 2009 are documenting SIMPL s measurement performance and capabilities, demonstrating differentiation of open water and several ice cover types. ICESat-2 will employ several of the technologies advanced by SIMPL, including micropulse, single photon ranging in a multi-beam, push-broom configuration operating at 532 nm.

Geoscience Laser Ranging System design and performance predictions

NASA Technical Reports Server (NTRS)

Anderson, Kent L.

1991-01-01

The Geoscience Laser System (GLRS) will be a high-precision distance-measuring instrument planned for deployment on the EOS-B platform. Its primary objectives are to perform ranging measurements to ground targets to monitor crustal deformation and tectonic plate motions, and nadir-looking altimetry to determine ice sheet thicknesses, surface topography, and vertical profiles of clouds and aerosols. The system uses a mode-locked, 3-color Nd:YAG laser source, a Microchannel Plate-PMT for absolute time-of-flight (TOF) measurement (at 532 nm), a streak camera for TOF 2-color dispersion measurement (532 nm and 355 nm), and a Si avalanche photodiode for altimeter waveform detection (1064 nm). The performance goals are to make ranging measurements to ground targets with about 1 cm accuracy, and altimetry height measurements over ice with 10 cm accuracy. This paper presents an overview of the design concept developed during a phase B study. System engineering issues and trade studies are discussed, with particular attention to error budgets and performance predictions.

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

NASA Astrophysics Data System (ADS)

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

Using ICESat/GLAS Data Produced in a Self-Describing Format

NASA Astrophysics Data System (ADS)

Fowler, D. K.; Webster, D.; Fowler, C.; McAllister, M.; Haran, T. M.

2015-12-01

For the life of the ICESat mission and beyond, GLAS data have been distributed in binary format by NASA's National Snow and Ice Data Center Distributed Active Archive Center (NSIDC DAAC) at the University of Colorado in Boulder. These data have been extremely useful but, depending on the users, not always the easiest to use. Recently, with release 33 and 34, GLAS data have been produced in an HDF5 format. The NSIDC User Services Office has found that most users find this HDF5 format to be more user friendly than the original binary format. Some of the advantages include being able to view the actual data using HDFView or any of a number of open source tools freely available for users to view and work with the data. Also with this format NSIDC DAAC has been able to provide more selective and specific services which include spatial subsetting, file stitching, and the much sought after parameter subsetting through the use of Reverb, the next generation Earth science discovery tool. The final release of GLAS data in 2014 and the ongoing user questions not just about the data, but about the mission, satellite platform, and instrument have also spurred NSIDC DAAC efforts to make all of the mission documents and information available to the public in one location. Thus was born the ICESat/GLAS Long Term Archive now available online. The data and specifics from this mission are archived and made available to the public at NASA's NSIDC DAAC.

Photogrammetry and altimetry. Part A: Apollo 16 laser altimeter

NASA Technical Reports Server (NTRS)

Wollenhaupt, W. R.; Sjogren, W. L.

1972-01-01

The laser altimeter measures precise altitudes of the command and service module above the lunar surface and can function either with the metric (mapping) camera or independently. In the camera mode, the laser altimeter ranges at each exposure time, which varies between 20 and 28 sec (i.e., 30 to 43 km on the lunar surface). In the independent mode, the laser altimeter ranges every 20 sec. These altitude data and the spacecraft attitudes that are derived from simultaneous stellar photography are used to constrain the photogrammetric reduction of the lunar surface photographs when cartographic products are generated. In addition, the altimeter measurements alone provide broad-scale topographic relief around the entire circumference of the moon. These data are useful in investigating the selenodetic figure of the moon and may provide information regarding gravitational anomalies on the lunar far side.

An observational philosophy for GEOS-C satellite altimetry

NASA Technical Reports Server (NTRS)

Weiffenbach, G. C.

1972-01-01

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

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

NASA Astrophysics Data System (ADS)

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

2010-12-01

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

Mapping the Topography of Mercury with MESSENGER Laser Altimetry

NASA Technical Reports Server (NTRS)

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

2012-01-01

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

Seafloor Tectonic Fabric from Satellite Altimetry

NASA Astrophysics Data System (ADS)

Smith, Walter H. F.

Ocean floor structures with horizontal scales of 10 to a few hundred kilometers and vertical scales of 100 m or more generate sea surface gravity anomalies observable with satellite altimetry. Prior to 1990, altimeter data resolved only tectonic lineaments, some seamounts, and some aspects of mid-ocean ridge structure. New altimeter data available since mid-1995 resolve 10-km--scale structures over nearly all the world's oceans. These data are the basis of new global bathymetric maps and have been interpreted as exhibiting complexities in the sea floor spreading process including ridge jumps, propagating rifts, and variations in magma supply. This chapter reviews the satellite altimetry technique and its resolution of tectonic structures, gives examples of intriguing tectonic phenomena, and shows that structures as small as abyssal hills are partially resolved. A new result obtained here is that the amplitude of the fine-scale (10--80 km) roughness of old ocean floor is spreading-rate dependent in the same that it is at mid-ocean ridges, suggesting that fine-scale tectonic fabric is generated nearly exclusively by ridge-axis processes.

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

NASA Astrophysics Data System (ADS)

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

2013-12-01

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

The fiber optic system for the Advanced Topographic Laser Altimeter System (ATLAS) instrument

PubMed Central

Ott, Melanie N.; Thomes, Joe; Onuma, Eleanya; Switzer, Robert; Chuska, Richard; Blair, Diana; Frese, Erich; Matyseck, Marc

2017-01-01

The Advanced Topographic Laser Altimeter System (ATLAS) Instrument has been in integration and testing over the past 18 months in preparation for the Ice, Cloud and Land Elevation Satellite – 2 (ICESat-2) Mission, scheduled to launch in 2017. ICESat-2 is the follow on to ICESat which launched in 2003 and operated until 2009. ATLAS will measure the elevation of ice sheets, glaciers and sea ice or the “cryosphere” (as well as terrain) to provide data for assessing the earth’s global climate changes. Where ICESat’s instrument, the Geo-Science Laser Altimeter (GLAS) used a single beam measured with a 70 m spot on the ground and a distance between spots of 170 m, ATLAS will measure a spot size of 10 m with a spacing of 70 cm using six beams to measure terrain height changes as small as 4 mm.[1] The ATLAS pulsed transmission system consists of two lasers operating at 532 nm with transmitter optics for beam steering, a diffractive optical element that splits the signal into 6 separate beams, receivers for start pulse detection and a wavelength tracking system. The optical receiver telescope system consists of optics that focus all six beams into optical fibers that feed a filter system that transmits the signal via fiber assemblies to the detectors. Also included on the instrument is a system that calibrates the alignment of the transmitted pulses to the receiver optics for precise signal capture. The larger electro optical subsystems for transmission, calibration, and signal receive, stay aligned and transmitting sufficiently due to the optical fiber system that links them together. The robust design of the fiber optic system, consisting of a variety of multi fiber arrays and simplex assemblies with multiple fiber core sizes and types, will enable the system to maintain consistent critical alignments for the entire life of the mission. Some of the development approaches used to meet the challenging optical system requirements for ATLAS are discussed here. PMID

Greenland GPS network: Measurements and Models of 3D Elastic deformation

NASA Astrophysics Data System (ADS)

Khan, S. A.; van Dam, T. M.; Bevis, M. G.; Sasgen, I.; Bamber, J. L.; Helm, V.; Bjork, A. A.; Liu, L.; Kjaer, K. H.; Knudsen, P.; Kjeldsen, K. K.

2017-12-01

The Greenland GPS Network (GNET) uses the Global Positioning System (GPS) to measure the displacement of bedrock exposed near the margins of the Greenland ice sheet. The entire network is uplifting in response to past and present-day changes in ice mass. Here, we focus on present-day changes and compare measurements with models. To retrieve 3D elastic displacements from GPS time series, we correct our observations for glacial-isostatic adjustment and tectonic plate motion, and study the effect of the underlying mantle viscosity, ice load history and Euler parameters. To model 3D elastic displacements, we first estimate mass loss using 1995-2014 NASA's Airborne Topographic Mapper (ATM) flights derived altimetry, supplemented with laser altimetry observations from the Ice, Cloud, and Land Elevation Satellite (ICESat) during 2003-2009; the airborne Land, Vegetation, and Ice Sensor (LVIS) instrument during 2007-2013; radar altimetry from the CryoSat-2 satellite during 2010-2017; and European Remote-Sensing Satellite-1 (ERS-1) and ERS-2 data during 1995-2003. We converted the volume loss rate into a mass loss rate accounting for firn compaction as described by Kuipers Munneke et al. (2015). We predict the elastic displacements by convolving mass loss estimates with Green's functions for vertical and horizontal displacements. We use a variety of elastic Green's functions and mass change grid resolutions, respectively, to study the sensitivity of 3D elastic deformation on Earth model parameters different from the Preliminary Reference Earth Reference Model (PREM; Dziewonski & Anderson 1981) and the forcing ice load.

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

NASA Astrophysics Data System (ADS)

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

2017-01-01

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

The Basic Radar Altimetry Toolbox for Sentinel 3 Users

NASA Astrophysics Data System (ADS)

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

2013-04-01

The Basic Radar Altimetry Toolbox (BRAT) is a collection of tools and tutorial documents designed to facilitate the processing of radar altimetry data. This project started in 2006 from the joint efforts of ESA (European Space Agency) and CNES (Centre National d'Etudes Spatiales). The latest version of the software, 3.1, was released on March 2012. The tools enable users to interact with the most common altimetry data formats, being the most used way, the Graphical User Interface (BratGui). This GUI is a 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. The BratDisplay (graphic visualizer) can be launched from BratGui, or used as a stand-alone tool to visualize netCDF files - it is distributed with another ESA toolbox (GUT) as the visualizer. The most frequent uses of BRAT are teaching remote sensing, altimetry data reading (all missions from ERS-1 to Saral and soon Sentinel-3), quick data visualization/export and simple computation on the data fields. BRAT can be used for importing data and having a quick look at his contents, with several different types of plotting available. One can also use it 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 BratGui 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 (MSS, -SSH, MSLA, editing of spurious data, etc.). The documentation collection includes the standard user manual explaining all the ways to interact with the set of software tools but the most important item is the Radar Altimeter Tutorial, that contains a strong introduction to

Laser Transmitter Design and Performance for the Slope Imaging Multi-Polarization Photon-Counting Lidar (SIMPL) Instrument

NASA Technical Reports Server (NTRS)

Yu, Anthony W.; Harding, David J.; Dabney, Philip W.

2016-01-01

The Slope Imaging Multi-polarization Photon-counting Lidar (SIMPL) instrument is a polarimetric, two-color, multibeam push broom laser altimeter developed through the NASA Earth Science Technology Office Instrument Incubator Program and has been flown successfully on multiple airborne platforms since 2008. In this talk we will discuss the laser transmitter performance and present recent science data collected over the Greenland ice sheet and sea ice in support of the NASA Ice Cloud and land Elevation Satellite 2 (ICESat-2) mission to be launched in 2017.

Energy scaling of passively Q-switched lasers In the Mj-range

NASA Astrophysics Data System (ADS)

Neumann, J.; Huss, R.; Kolleck, C.; Kracht, Dietmar

2017-11-01

Q-switched lasers systems with ns pulse duration and energies ranging from 1 to more than 100mJ are utilized for many spaceborne applications such as altimetry of planets and moons. Furthermore, Q-switched lasers can be used for distance measurements during docking and landing manoeuvres. To keep the diameter of the beam small over a large distance and to consequently achieve a good lateral resolution, a good beam propagation factor M² is required. Moreover, Q-switched lasers can be used directly on the planetary surface for exploration by laser-induced breakdown spectroscopy or laser desorption mass spectrometry.

North Atlantic teleconnection patterns signature on sea level from satellite altimetry

NASA Astrophysics Data System (ADS)

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

2015-04-01

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

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)

NASA Astrophysics Data System (ADS)

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

Algorithm for Detection of Ground and Canopy Cover in Micropulse Photon-Counting Lidar Altimeter Data in Preparation for the ICESat-2 Mission

NASA Technical Reports Server (NTRS)

Herzfeld, Ute Christina; McDonald, Brian W.; Neumann, Thomas Allen; Wallin, Bruce F.; Neumann, Thomas A.; Markus, Thorsten; Brenner, Anita; Field, Christopher

2014-01-01

NASA's Ice, Cloud and Land Elevation Satellite-II (ICESat-2) mission is a decadal survey mission (2016 launch). The mission objectives are to measure land ice elevation, sea ice freeboard, and changes in these variables, as well as to collect measurements over vegetation to facilitate canopy height determination. Two innovative components will characterize the ICESat-2 lidar: 1) collection of elevation data by a multibeam system and 2) application of micropulse lidar (photon-counting) technology. A photon-counting altimeter yields clouds of discrete points, resulting from returns of individual photons, and hence new data analysis techniques are required for elevation determination and association of the returned points to reflectors of interest. The objective of this paper is to derive an algorithm that allows detection of ground under dense canopy and identification of ground and canopy levels in simulated ICESat-2 data, based on airborne observations with a Sigma Space micropulse lidar. The mathematical algorithm uses spatial statistical and discrete mathematical concepts, including radial basis functions, density measures, geometrical anisotropy, eigenvectors, and geostatistical classification parameters and hyperparameters. Validation shows that ground and canopy elevation, and hence canopy height, can be expected to be observable with high accuracy by ICESat-2 for all expected beam energies considered for instrument design (93.01%-99.57% correctly selected points for a beam with expected return of 0.93 mean signals per shot (msp), and 72.85%-98.68% for 0.48 msp). The algorithm derived here is generally applicable for elevation determination from photoncounting lidar altimeter data collected over forested areas, land ice, sea ice, and land surfaces, as well as for cloud detection.

Application of precise altimetry to the study of precise leveling of the sea surface, the Earth's gravity field, and the rotation of the Earth

NASA Technical Reports Server (NTRS)

Segawa, J.; Ganeko, Y.; Sasaki, M.; Mori, T.; Ooe, M.; Nakagawa, I.; Ishii, H.; Hagiwara, Y.

1991-01-01

Our program includes five research items: (1) determination of a precision geoid and gravity anomaly field; (2) precise leveling and detection of tidal changes of the sea surface and study of the role of the tide in the global energy exchange; (3) oceanic effect on the Earth's rotation and polar motion; (4) geological and geophysical interpretation of the altimetry gravity field; and (5) evaluation of the effectiveness of local tracking of TOPEX/POSEIDON by use of a laser tracker.

A new digital elevation model of Antarctica derived from CryoSat-2 altimetry

NASA Astrophysics Data System (ADS)

Slater, Thomas; Shepherd, Andrew; McMillan, Malcolm; Muir, Alan; Gilbert, Lin; Hogg, Anna E.; Konrad, Hannes; Parrinello, Tommaso

2018-05-01

We present a new digital elevation model (DEM) of the Antarctic ice sheet and ice shelves based on 2.5 × 108 observations recorded by the CryoSat-2 satellite radar altimeter between July 2010 and July 2016. The DEM is formed from spatio-temporal fits to elevation measurements accumulated within 1, 2, and 5 km grid cells, and is posted at the modal resolution of 1 km. Altogether, 94 % of the grounded ice sheet and 98 % of the floating ice shelves are observed, and the remaining grid cells north of 88° S are interpolated using ordinary kriging. The median and root mean square difference between the DEM and 2.3 × 107 airborne laser altimeter measurements acquired during NASA Operation IceBridge campaigns are -0.30 and 13.50 m, respectively. The DEM uncertainty rises in regions of high slope, especially where elevation measurements were acquired in low-resolution mode; taking this into account, we estimate the average accuracy to be 9.5 m - a value that is comparable to or better than that of other models derived from satellite radar and laser altimetry.

Advances in using satellite altimetry to observe storm surge

NASA Astrophysics Data System (ADS)

Han, Guoqi

2017-04-01

Storm surges are the major cause for coastal flooding, resulting in catastrophic damage to properties and loss of life in coastal communities. Thus it is important to utilize new technology to enhance our capabilities of observing storm surges and ultimately to improve our capacity for forecasting storm surges and mitigating damage and loss. In this talk we first review traditional methods of monitoring storm surges. We then provide examples of storm surges observed by nadir satellite altimetry, during Hurricane Sandy and Igor, as well as typhoon and cyclone events. We further evaluate satellite results against tide-gauge data and explain storm surge features. Finally, we discuss the potential of a wide-swath altimetry mission, the Surface Water and Ocean Topography (SWOT), for observing storm surges.

Aviso: altimetry products & services in 2013

NASA Astrophysics Data System (ADS)

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

2013-12-01

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

New Techniques for Radar Altimetry of Sea Ice and the Polar Oceans

NASA Astrophysics Data System (ADS)

Armitage, T. W. K.; Kwok, R.; Egido, A.; Smith, W. H. F.; Cullen, R.

2017-12-01

Satellite radar altimetry has proven to be a valuable tool for remote sensing of the polar oceans, with techniques for estimating sea ice thickness and sea surface height in the ice-covered ocean advancing to the point of becoming routine, if not operational, products. Here, we explore new techniques in radar altimetry of the polar oceans and the sea ice cover. First, we present results from fully-focused SAR (FFSAR) altimetry; by accounting for the phase evolution of scatterers in the scene, the FFSAR technique applies an inter-burst coherent integration, potentially over the entire duration that a scatterer remains in the altimeter footprint, which can narrow the effective along track resolution to just 0.5m. We discuss the improvement of using interleaved operation over burst-more operation for applying FFSAR processing to data acquired by future missions, such as a potential CryoSat follow-on. Second, we present simulated sea ice retrievals from the Ka-band Radar Interferometer (KaRIn), the instrument that will be launched on the Surface Water and Ocean Topography (SWOT) mission in 2021, that is capable of producing swath images of surface elevation. These techniques offer the opportunity to advance our understanding of the physics of the ice-covered oceans, plus new insight into how we interpret more conventional radar altimetry data in these regions.

Quantifying Seasonal Skill in Coupled Sea Ice Models using Freeboard Measurements from Spaceborne Laser Altimeters

NASA Astrophysics Data System (ADS)

Roberts, A.; Bench, K.; Maslowski, W.; Farrell, S. L.; Richter-Menge, J.

2016-12-01

We have developed a method to quantitatively assess the skill of predictive sea ice models using freeboard measurements from spaceborne laser altimeters. The method evaluates freeboard from the Regional Arctic System Model (RASM) against those derived from NASA ICESat and Operation IceBridge (OIB) missions along individual ground tracks, and assesses the variance- and correlation-weighted model skill. This allows quantifying the accuracy of sea ice volume simulations and taking measurement error into account. As part of this work, we inter-compare simulations with two different sea ice rheologies: one using Elastic-Viscous-Plastic (EVP), and the other using Elastic-Anisotropic-Plastic (EAP) ice mechanics. Both are simulated for 2004 and 2007, during which ICESat was in operation. RASM variance skill scores ranged from 0.712 to 0.824 and correlation skill scores were between 0.319 and 0.511, with EAP providing a better estimate of spatial ice volume variance, but with a larger bias in the central Arctic relative to EVP. The skill scores were calculated for monthly periods and require little adaption to rate short-term operational forecasts of the Arctic. This work will help quantify model limitations and facilitate optimal use of ICESat-2 freeboard measurements after that satellite is launched next year.

Compact, Passively Q-Switched Nd:YAG Laser for the MESSENGER Mission to the Planet Mercury

NASA Technical Reports Server (NTRS)

Krebs, Danny J.; Novo-Gradac, Anne-Marie; Li, Steven X.; Lindauer, Steven J.; Afzal, Robert S.; Yu, Antony

2004-01-01

A compact, passively Q-switched Nd:YAG laser has been developed for the Mercury Laser Altimeter (MLA) instrument which is an instrument on the MESSENGER mission to the planet Mercury. The laser achieves 5.4 percent efficiency with a near diffraction limited beam. It has passed all space flight environmental tests at system, instrument, and satellite integration. The laser design draws on a heritage of previous laser altimetry missions, specifically ISESAT and Mars Global Surveyor; but incorporates thermal management features unique to the requirements of an orbit of the planet Mercury.

Recent Ice Loss from the Fleming and Other Glaciers, Wordie Bay, West Antarctic Peninsula

NASA Technical Reports Server (NTRS)

Rignot, E.; Casassa, G.; Gogineni, S.; Kanagaratnam, P.; Krabill, W.; Pritchard, H.; Rivera, A.; Thomas, R.; Turner, J.; Vaughan, D.

2005-01-01

Satellite radar interferometry data from 1995 to 2004, and airborne ice thickness data from 2002, reveal that the glaciers flowing into former Wordie Ice Shelf, West Antarctic Peninsula, discharge 6.8 +/- 0.3 km(exp 3)/yr of ice, which is 84 +/- 30 percent larger than a snow accumulation of 3.7 +/- 0.8 km(exp 3)/yr over a 6,300 km(exp 2) drainage basin. Airborne and ICESat laser altimetry elevation data reveal glacier thinning at rates up to 2 m/yr. Fifty km from its ice front, Fleming Glacier flows 50 percent faster than it did in 1974 prior to the main collapse of Wordie Ice Shelf. We conclude that the glaciers accelerated following ice shelf removal, and have been thinning and losing mass to the ocean over the last decade. This and other observations suggest that the mass loss from the northern part of the Peninsula is not negligible at present.

Satellite Observations of Antarctic Sea Ice Thickness and Volume

NASA Technical Reports Server (NTRS)

Kurtz, Nathan; Markus, Thorsten

2012-01-01

We utilize satellite laser altimetry data from ICESat combined with passive microwave measurements to analyze basin-wide changes in Antarctic sea ice thickness and volume over a 5 year period from 2003-2008. Sea ice thickness exhibits a small negative trend while area increases in the summer and fall balanced losses in thickness leading to small overall volume changes. Using a five year time-series, we show that only small ice thickness changes of less than -0.03 m/yr and volume changes of -266 cu km/yr and 160 cu km/yr occurred for the spring and summer periods, respectively. The calculated thickness and volume trends are small compared to the observational time period and interannual variability which masks the determination of long-term trend or cyclical variability in the sea ice cover. These results are in stark contrast to the much greater observed losses in Arctic sea ice volume and illustrate the different hemispheric changes of the polar sea ice covers in recent years.

Refined Simulation of Satellite Laser Altimeter Full Echo Waveform

NASA Astrophysics Data System (ADS)

Men, H.; Xing, Y.; Li, G.; Gao, X.; Zhao, Y.; Gao, X.

2018-04-01

The return waveform of satellite laser altimeter plays vital role in the satellite parameters designation, data processing and application. In this paper, a method of refined full waveform simulation is proposed based on the reflectivity of the ground target, the true emission waveform and the Laser Profile Array (LPA). The ICESat/GLAS data is used as the validation data. Finally, we evaluated the simulation accuracy with the correlation coefficient. It was found that the accuracy of echo simulation could be significantly improved by considering the reflectivity of the ground target and the emission waveform. However, the laser intensity distribution recorded by the LPA has little effect on the echo simulation accuracy when compared with the distribution of the simulated laser energy. At last, we proposed a refinement idea by analyzing the experimental results, in the hope of providing references for the waveform data simulation and processing of GF-7 satellite in the future.

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

NASA Astrophysics Data System (ADS)

Tseng, Kuo-Hsin

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

Radar Altimetry for Hydrological Modeling and Monitoring in the Zambezi River Basin

NASA Astrophysics Data System (ADS)

Michailovsky, C. I.; Berry, P. A.; Smith, R. G.; Bauer-Gottwein, P.

2011-12-01

Hydrological model forecasts are subject to large uncertainties stemming from uncertain input data, model structure, parameterization and lack of sufficient calibration/validation data. For real-time or near-real-time applications data assimilation techniques such as the Ensemble Kalman Filter (EnKF) can be used to reduce forecast uncertainty by updating model states as new data becomes available. The use of remote sensing data is attractive for such applications as it provides wide geographical coverage and continuous time-series without the typically long delays that exist in obtaining in-situ data. River discharge is one of the main hydrological variables of interest, and while it cannot currently be directly measured remotely, water levels in rivers can be obtained from satellite based radar altimetry and converted to discharge through rating curves. This study aims to give a realistic assessment of the improvements that can be derived from the use of satellite radar altimetry measurements from the Envisat mission for discharge monitoring and modeling on the basin scale for the Zambezi River. The altimetry data used is the Radar AlTimetry (RAT) product developed at the Earth and Planetary Remote Sensing Laboratory at the De Montfort University. The first step in analyzing the data is the determination of potential altimetry targets which are the locations at which the Envisat orbit and the river network cross in order to select data points corresponding to surface water. The quality of the water level time-series is then analyzed for all targets and the exploitable targets identified. Rating curves are derived from in-situ or remotely-sensed data depending on data-availability at the various locations and discharge time-series are established. A Monte Carlo analysis is carried out to assess the uncertainties on the computed discharge. It was found that having a single cross-section and associated discharge measurement at one point in time significantly reduces

Considerations in the Design of Future Planetary Laser Altimeters

NASA Astrophysics Data System (ADS)

Smith, D. E.; Neumann, G. A.; Mazarico, E.; Zuber, M. T.; Sun, X.

2017-12-01

Planetary laser altimeters have generally been designed to provide high accuracy measurements of the nadir range to an uncooperative surface for deriving the shape of the target body, and sometimes specifically for identifying and characterizing potential landing sites. However, experience has shown that in addition to the range measurement, other valuable observations can be acquired, including surface reflectance and surface roughness, despite not being given high priority in the original altimeter design or even anticipated. After nearly 2 decades of planetary laser altimeter design, the requirements are evolving and additional capabilities are becoming equally important. The target bodies, once the terrestrial planets, are now equally asteroids and moons that in many cases do not permit simple orbital operations due to their small mass, radiation issues, or spacecraft fuel limitations. In addition, for a number of reasons, it has become necessary to perform shape determination from a much greater range, even thousands of kilometers, and thus ranging is becoming as important as nadir altimetry. Reflectance measurements have also proved important for assessing the presence of ice, water or CO2, and laser pulse spreading informed knowledge of surface roughness; all indicating a need for improved instrument capability. Recently, the need to obtain accurate range measurement to laser reflectors on landers or on a planetary surface is presenting new science opportunities but for which current designs are far from optimal. These changes to classic laser altimetry have consequences for many instrument functions and capabilities, including beam divergence, laser power, number of beams and detectors, pixelation, energy measurements, pointing stability, polarization, laser wavelengths, and laser pulse rate dependent range. We will discuss how a new consideration of these trades will help make lidars key instruments to execute innovative science in future planetary

Characteristics of ocean-reflected short radar pulses with application to altimetry and surface roughness determination

NASA Technical Reports Server (NTRS)

Miller, L. S.; Hayne, G. S.

1972-01-01

Current work related to geodetic altimetry is summarized. Special emphasis is placed on the effects of pulse length on both altimetry and sea-state estimation. Some discussion is also given of system tradeoff parameters and sea truth requirements to support scattering studies. The problem of analyzing signal characteristics and altimeter waveforms arising from rough surface backscattering is also considered.

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

NASA Astrophysics Data System (ADS)

Cipollini, P.; Harwood, P.; Snaith, H.; Vignudelli, S.; West, L.; Zecchetto, S.; Donlon, C.

2012-04-01

One of the most promising applications of the new field of coastal altimetry, i.e. the discipline aiming to recover meaningful estimates of geophysical parameters (sea level, significant wave height and wind speed) from satellite altimeter data in the coastal zone, is the study of storm surges. The understanding and realistic modelling of surges supports both preparation and mitigation activities and should eventually bring enormous societal benefits, especially to some of the world's poorest countries (like Bangladesh). Earth Observation data have an important role to play in storm surge monitoring and forecasting, but the full uptake of these data by users (such as environmental agencies and tidal prediction centres) must first be encouraged by showcasing their usefulness, and then supported by providing easy access. Having recognized the above needs, The European Space Agency has recently launched a Data User Element (DUE) project called eSurge. The main purposes of eSurge are a) to contribute to an integrated approach to storm surge, wave, sea-level and flood forecasting through Earth Observation, as part of a wider optimal strategy for building an improved forecast and early warning capability for coastal inundation; and b) to increase the use of the advanced capabilities of ESA and other satellite data for storm surge applications. The project is led by Logica UK, with NOC (UK), DMI (Denmark), CMRC (Ireland) and KNMI (Netherlands) as scientific partners. A very important component of eSurge is the development, validation and provision of dedicated coastal altimetry products, which is the focus of the present contribution. Coastal altimetry has a prominent role to play as it measures the total water level envelope directly, and this is one of the key quantities required by storm surge applications and services. But it can also provide important information on the wave field in the coastal strip, which helps the development of more realistic wave models that in

Study of elevation changes along a profile crossing the Greenland Ice Sheet

NASA Astrophysics Data System (ADS)

Hvidegaard, S. M.; Sandberg, L.

2009-04-01

In recent years much research has focused on determining how the Greenland Ice Sheet is responding to the observed climate changes. There is wide agreement on the fact that the Ice Sheet is currently loosing mass, and studies have shown that the mass loss is found near the ice edge and that no significant changes are found in the central part of the Ice Sheet. As a part of European Space Agency's CryoSat Validation Experiment (CryoVEx) running from 2004 to 2008, the National Space Institute (DTU Space) measured the elevations along a profile crossing the Greenland Ice Sheet. The elevation observations were carried out in 2004, 2006 and 2008 using airborne laser altimetry from a Twin Otter aircraft. The observed profile follows the old EGIG line (Expédition Glaciologique au Groenland, measured in the 1950's) situated between 69-71N, heading nearly east-west. This unique dataset gives the opportunity to study elevation changes along the profile crossing the ice sheet. With this work, we outline the observed elevation changes from the different zones of the ice sheet. We furthermore compare elevation changes based on coincident ICESat and airborne laser altimeter data.

USA Science and Engineering Festival 2014

NASA Image and Video Library

2014-04-25

An attendee of the USA Science and Engineering Festival is measured by a laser at the NASA Stage. A NASA Staff member describes the Ice, Cloud, and land Elevation Satellite (ICESat) mission, which operated from 2003-2009, and pioneered the use of laser altimeters in space to study the elevation of the Earth's surface and its changes. ICESat-2 is a follow-on mission to continue the ICESat observations and is scheduled to launch in 2017. The USA Science and Engineering Festival took place at the Washington Convention Center in Washington, DC on April 26 and 27, 2014. Photo Credit: (NASA/Aubrey Gemignani)

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

NASA Astrophysics Data System (ADS)

Hwang, Cheinway; Yang, Yuande; Kao, Ricky; Han, Jiancheng; Shum, C. K.; Galloway, Devin L.; Sneed, Michelle; Hung, Wei-Chia; Cheng, Yung-Sheng; Li, Fei

2016-06-01

Contemporary applications of radar altimetry include sea-level rise, ocean circulation, marine gravity, and icesheet elevation change. Unlike InSAR and GNSS, which are widely used to map surface deformation, altimetry is neither reliant on highly temporally-correlated ground features nor as limited by the available spatial coverage, and can provide long-term temporal subsidence monitoring capability. Here we use multi-mission radar altimetry with an approximately 23 year data-span to quantify land subsidence in cropland areas. Subsidence rates from TOPEX/POSEIDON, JASON-1, ENVISAT, and JASON-2 during 1992-2015 show time-varying trends with respect to displacement over time in California’s San Joaquin Valley and central Taiwan, possibly related to changes in land use, climatic conditions (drought) and regulatory measures affecting groundwater use. Near Hanford, California, subsidence rates reach 18 cm yr-1 with a cumulative subsidence of 206 cm, which potentially could adversely affect operations of the planned California High-Speed Rail. The maximum subsidence rate in central Taiwan is 8 cm yr-1. Radar altimetry also reveals time-varying subsidence in the North China Plain consistent with the declines of groundwater storage and existing water infrastructure detected by the Gravity Recovery And Climate Experiment (GRACE) satellites, with rates reaching 20 cm yr-1 and cumulative subsidence as much as 155 cm.

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

PubMed Central

Hwang, Cheinway; Yang, Yuande; Kao, Ricky; Han, Jiancheng; Shum, C. K.; Galloway, Devin L.; Sneed, Michelle; Hung, Wei-Chia; Cheng, Yung-Sheng; Li, Fei

2016-01-01

Contemporary applications of radar altimetry include sea-level rise, ocean circulation, marine gravity, and icesheet elevation change. Unlike InSAR and GNSS, which are widely used to map surface deformation, altimetry is neither reliant on highly temporally-correlated ground features nor as limited by the available spatial coverage, and can provide long-term temporal subsidence monitoring capability. Here we use multi-mission radar altimetry with an approximately 23 year data-span to quantify land subsidence in cropland areas. Subsidence rates from TOPEX/POSEIDON, JASON-1, ENVISAT, and JASON-2 during 1992–2015 show time-varying trends with respect to displacement over time in California’s San Joaquin Valley and central Taiwan, possibly related to changes in land use, climatic conditions (drought) and regulatory measures affecting groundwater use. Near Hanford, California, subsidence rates reach 18 cm yr−1 with a cumulative subsidence of 206 cm, which potentially could adversely affect operations of the planned California High-Speed Rail. The maximum subsidence rate in central Taiwan is 8 cm yr−1. Radar altimetry also reveals time-varying subsidence in the North China Plain consistent with the declines of groundwater storage and existing water infrastructure detected by the Gravity Recovery And Climate Experiment (GRACE) satellites, with rates reaching 20 cm yr−1 and cumulative subsidence as much as 155 cm. PMID:27324935

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

PubMed

Hwang, Cheinway; Yang, Yuande; Kao, Ricky; Han, Jiancheng; Shum, C K; Galloway, Devin L; Sneed, Michelle; Hung, Wei-Chia; Cheng, Yung-Sheng; Li, Fei

2016-06-21

Contemporary applications of radar altimetry include sea-level rise, ocean circulation, marine gravity, and icesheet elevation change. Unlike InSAR and GNSS, which are widely used to map surface deformation, altimetry is neither reliant on highly temporally-correlated ground features nor as limited by the available spatial coverage, and can provide long-term temporal subsidence monitoring capability. Here we use multi-mission radar altimetry with an approximately 23 year data-span to quantify land subsidence in cropland areas. Subsidence rates from TOPEX/POSEIDON, JASON-1, ENVISAT, and JASON-2 during 1992-2015 show time-varying trends with respect to displacement over time in California's San Joaquin Valley and central Taiwan, possibly related to changes in land use, climatic conditions (drought) and regulatory measures affecting groundwater use. Near Hanford, California, subsidence rates reach 18 cm yr(-1) with a cumulative subsidence of 206 cm, which potentially could adversely affect operations of the planned California High-Speed Rail. The maximum subsidence rate in central Taiwan is 8 cm yr(-1). Radar altimetry also reveals time-varying subsidence in the North China Plain consistent with the declines of groundwater storage and existing water infrastructure detected by the Gravity Recovery And Climate Experiment (GRACE) satellites, with rates reaching 20 cm yr(-1) and cumulative subsidence as much as 155 cm.

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

USGS Publications Warehouse

Hwang, Cheinway; Yang, Yuande; Kao, Ricky; Han, Jiancheng; Shum, C.K.; Galloway, Devin L.; Sneed, Michelle; Hung, Wei-Chia; Cheng, Yung-Sheng; Li, Fei

2016-01-01

Contemporary applications of radar altimetry include sea-level rise, ocean circulation, marine gravity, and ice sheet elevation change. Unlike InSAR and GNSS, which are widely used to map surface deformation, altimetry is neither reliant on highly temporally-correlated ground features nor as limited by the available spatial coverage, and can provide long-term temporal subsidence monitoring capability. Here we use multi-mission radar altimetry with an approximately 23 year data-span to quantify land subsidence in cropland areas. Subsidence rates from TOPEX/POSEIDON, JASON-1, ENVISAT, and JASON-2 during 1992–2015 show time-varying trends with respect to displacement over time in California’s San Joaquin Valley and central Taiwan, possibly related to changes in land use, climatic conditions (drought) and regulatory measures affecting groundwater use. Near Hanford, California, subsidence rates reach 18 cm/yr with a cumulative subsidence of 206 cm, which potentially could adversely affect operations of the planned California High-Speed Rail. The maximum subsidence rate in central Taiwan is 8 cm/yr. Radar altimetry also reveals time-varying subsidence in the North China Plain consistent with the declines of groundwater storage and existing water infrastructure detected by the Gravity Recovery And Climate Experiment (GRACE) satellites, with rates reaching 20 cm/yr and cumulative subsidence as much as 155 cm.

Surface mass balance model evaluation from satellite and airborne lidar mapping

NASA Astrophysics Data System (ADS)

Sutterley, T. C.; Velicogna, I.; Fettweis, X.; van den Broeke, M. R.

2016-12-01

We present estimates of Greenland Ice Sheet (GrIS) surface elevation change from a novel combination of satellite and airborne laser altimetry measurements. Our method combines measurements from the Airborne Topographic Mapper (ATM), the Land, Vegetation and Ice Sensor (LVIS) and ICESat-1 to generate elevation change rates at high spatial resolution. This method allows to extend the records of each instrument, increases the overall spatial coverage compared to a single instrument, and produces high-quality, coherent maps of surface elevation change. In addition by combining the lidar datasets, we are able to investigate seasonal and interannual surface elevation change for years where Spring and Fall Operation IceBridge campaigns are available. We validate our method by comparing with the standard NSIDC elevation change product calculated using overlapping Level-1B ATM data. We use the altimetry-derived mass changes to evaluate the uncertainty in surface mass balance, particularly in the runoff component, from two Regional Climate Models (RCM's), the Regional Atmospheric Climate Model (RACMO) and the Modéle Atmosphérique Régional (MAR), and one Global Climate Model (GCM), MERRA2/GEOS-5. We investigate locations with low ice sheet surface velocities that are within the estimated ablation zones of each regional climate model. We find that the surface mass balance outputs from RACMO and MAR show good correspondence with mass changes derived from surface elevation changes over long periods. At two sites in Northeast Greenland (NEGIS), the MAR model has better correspondence with the altimetry estimate. We find that the differences at these locations are primarily due to the characterization of meltwater refreeze within the ice sheet.

Airborne laser scanning for high-resolution mapping of Antarctica

NASA Astrophysics Data System (ADS)

Csatho, Bea; Schenk, Toni; Krabill, William; Wilson, Terry; Lyons, William; McKenzie, Garry; Hallam, Cheryl; Manizade, Serdar; Paulsen, Timothy

In order to evaluate the potential of airborne laser scanning for topographic mapping in Antarctica and to establish calibration/validation sites for NASA's Ice, Cloud and land Elevation Satellite (ICESat) altimeter mission, NASA, the U.S. National Science Foundation (NSF), and the U.S. Geological Survey (USGS) joined forces to collect high-resolution airborne laser scanning data.In a two-week campaign during the 2001-2002 austral summer, NASA's Airborne Topographic Mapper (ATM) system was used to collect data over several sites in the McMurdo Sound area of Antarctica (Figure 1a). From the recorded signals, NASA computed laser points and The Ohio State University (OSU) completed the elaborate computation/verification of high-resolution Digital Elevation Models (DEMs) in 2003. This article reports about the DEM generation and some exemplary results from scientists using the geomorphologic information from the DEMs during the 2003-2004 field season.

Aviso: altimetry products and services in 2013

NASA Astrophysics Data System (ADS)

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

2013-04-01

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

Compact, passively Q-switched Nd:YAG laser for the MESSENGER mission to Mercury.

PubMed

Krebs, Danny J; Novo-Gradac, Anne-Marie; Li, Steven X; Lindauer, Steven J; Afzal, Robert S; Yu, Anthony W

2005-03-20

A compact, passively Q-switched Nd:YAG laser has been developed for the Mercury Laser Altimeter, an instrument on the Mercury Surface, Space Environment, Geochemistry, and Ranging mission to the planet Mercury. The laser achieves 5.4% efficiency with a near-diffraction-limited beam. It passed all space-flight environmental tests at subsystem, instrument, and satellite integration testing and successfully completes a postlaunch aliveness check en route to Mercury. The laser design draws on a heritage of previous laser altimetry missions, specifically the Ice Cloud and Elevation Satellite and the Mars Global Surveyor, but incorporates thermal management features unique to the requirements of an orbit of the planet Mercury.

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

NASA Astrophysics Data System (ADS)

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

2016-04-01

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

An Algorithm for Detection of Ground and Canopy Cover in Micropulse Photon-Counting Lidar Altimeter Data in Preparation of the ICESat-2 Mission

NASA Technical Reports Server (NTRS)

Herzfeld, Ute C.; McDonald, Brian W.; Wallins, Bruce F.; Markus, Thorsten; Neumann, Thomas A.; Brenner, Anita

2012-01-01

The Ice, Cloud and Land Elevation Satellite-II (ICESat-2) mission has been selected by NASA as a Decadal Survey mission, to be launched in 2016. Mission objectives are to measure land ice elevation, sea ice freeboard/ thickness and changes in these variables and to collect measurements over vegetation that will facilitate determination of canopy height, with an accuracy that will allow prediction of future environmental changes and estimation of sea-level rise. The importance of the ICESat-2 project in estimation of biomass and carbon levels has increased substantially, following the recent cancellation of all other planned NASA missions with vegetation-surveying lidars. Two innovative components will characterize the ICESat-2 lidar: (1) Collection of elevation data by a multi-beam system and (2) application of micropulse lidar (photon counting) technology. A micropulse photon-counting altimeter yields clouds of discrete points, which result from returns of individual photons, and hence new data analysis techniques are required for elevation determination and association of returned points to reflectors of interest including canopy and ground in forested areas. The objective of this paper is to derive and validate an algorithm that allows detection of ground under dense canopy and identification of ground and canopy levels in simulated ICESat-2-type data. Data are based on airborne observations with a Sigma Space micropulse lidar and vary with respect to signal strength, noise levels, photon sampling options and other properties. A mathematical algorithm is developed, using spatial statistical and discrete mathematical concepts, including radial basis functions, density measures, geometrical anisotropy, eigenvectors and geostatistical classification parameters and hyperparameters. Validation shows that the algorithm works very well and that ground and canopy elevation, and hence canopy height, can be expected to be observable with a high accuracy during the ICESat

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

NASA Technical Reports Server (NTRS)

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

1991-01-01

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

On the unification of geodetic leveling datums using satellite altimetry

NASA Technical Reports Server (NTRS)

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

1978-01-01

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

Satellite Laser Ranging operations

NASA Technical Reports Server (NTRS)

Pearlman, Michael R.

1994-01-01

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

Impact of the Combination of GNSS and Altimetry Data on the Derived Global Ionosphere Maps

NASA Astrophysics Data System (ADS)

Todorova, S.; Schuh, H.; Hobiger, T.; Hernandez-Pajares, M.

2007-05-01

The classical input data for development of Global Ionosphere Maps (GIM) of the Total Electron Content (TEC) is the so called "geometry free linear combination", obtained from the dual-frequency Global Navigation Satellite System (GNSS) observations. Such maps in general achieve good quality of the ionosphere representation. However, the GNSS stations are inhomogeneously distributed, with large gaps particularly over the sea surface, which lowers the precision of the GIM over these areas. On the other hand, the dual-frequency satellite altimetry missions such as Jason-1 and TOPEX/Poseidon provide information about the parameter of the ionosphere precisely above the sea surface, where the altimetry observations are preformed. Due to the limited spread of the measurements and some open issues related to systematic errors, the ionospheric data from satellite altimetry is used only for cross-validation of the GNSS GIM. It can be anticipated however, that some specifics of the ionosphere parameter derived by satellite altimetry will partly balance the inhomogeneity of the GNSS data. Such important features are complementing in the global resolution, different biasing and the absence of additional mapping, as it is the case in GNSS. In this study we create two-hourly GIM from GNSS data and additionally introduce satellite altimetry observations, which help to compensate the insufficient GNSS coverage of the oceans. The combination of the data from around 180 GNSS stations and the satellite altimetry mission Jason-1 is performed on the normal equation level. The comparison between the integrated ionosphere models and the GNSS-only maps shows a higher accuracy of the combined GIM over the seas. A further effect of the combination is that the method allows the independent estimation of daily values of the Differential Code Biases (DCB) for all GNSS satellites and receivers, and of the systematic errors affecting the altimetry measurements. Such errors should include a

ERS-ENVISAT radar altimetry over the Amazon basin

NASA Astrophysics Data System (ADS)

Santos da Silva, J.; Calmant, S.; Rotunno Filho, O. C.; Seyler, F.; Mansur, W. J.; Cochonneau, G.

2009-12-01

Since the launch of satellite embarking radar altimeters in the late 80’s, scientists have investigated the feasibility of using these ocean-dedicated data over the continental waters. In fact, satellite radar altimetry is being recognized as a powerful tool to obtain time series of water stage consistent to those obtained by conventional in situ gauge stations. In addition, this technology has been proved to provide reliable information about the dynamics of large water bodies such as lakes and inner seas. However, the results should be deeply examined as we shift the analysis to water levels acquired during satellite crosses over rivers. Yet, hydrologists are still reluctant in using these data, as neither the neces¬sary time sampling nor accuracy is achieved, leading to endless debates in specialized workshops. Noteworthy to highlight, few published studies are dedicated to an in depth assessment of the radar altimetry over rivers, in¬cluding comparisons with water levels at fluviometric gauges. In this work, we present an extensive analysis of the quality of times series of river stages that we have constructed in the Amazon basin for a variety of water bodies such as large rivers, narrow stems, lakes and flooded areas using radar altimeters embarked on¬board ERS-2 and ENVISAT. The approach includes the sensitivity to the raw data processing methodology such as the tracking algorithm, the data selection at the crossings between satellite track and river bed (so-called virtual stations) and correction for off-nadir effects. The VALS toolbox was developed to process altimetry data at virtual stations under the framework of this study. Results of internal validation at cross-overs and external validation by comparison with in situ gauges are presented.

CryoSat swath altimetry to measure ice cap and glacier surface elevation change

NASA Astrophysics Data System (ADS)

Tepes, P.; Gourmelen, N.; Escorihuela, M. J.; Wuite, J.; Nagler, T.; Foresta, L.; Brockley, D.; Baker, S.; Roca, M.; Shepherd, A.; Plummer, S.

2016-12-01

Satellite altimetry has been used extensively in the past few decades to observe changes affecting large and remote regions covered by land ice such as the Greenland and Antarctic ice sheets. Glaciers and ice caps have been studied less extensively due to limitation of altimetry over complex topography. However their role in current sea-level budgets is significant and is expected to continue over the next century and beyond (Gardner et al., 2011), particularly in the Arctic where mean annual surface temperatures have recently been increasing twice as fast as the global average (Screen and Simmonds, 2010). Radar altimetry is well suited to monitor elevation changes over land ice due to its all-weather year-round capability of observing ice surfaces. Since 2010, the Synthetic Interferometric Radar Altimeter (SIRAL) on board the European Space Agency (ESA) radar altimetry CryoSat (CS) mission has been collecting ice elevation measurements over glaciers and ice caps. Its Synthetic Aperture Radar Interferometric (SARIn) processing feature reduces the size of the footprint along-track and locates the across-track origin of a surface reflector in the presence of a slope. This offers new perspectives for the measurement of regions marked by complex topography. More recently, data from the CS-SARIn mode have been used to infer elevation beyond the point of closest approach (POCA) with a novel approach known as "swath processing" (Hawley et al., 2009; Gray et al., 2013; Christie et al., 2016; Smith et al., 2016). Together with a denser ground track interspacing of the CS mission, the swath processing technique provides unprecedented spatial coverage and resolution for space borne altimetry, enabling the study of key processes that underlie current changes of ice caps and glaciers. In this study, we use CS swath observations to generate maps of ice elevation change for selected ice caps and glaciers. We present a validation exercise and discuss the benefit of swath

Nineteenth International Laser Radar Conference. Part 2

NASA Technical Reports Server (NTRS)

Singh, Upendra N. (Editor); Ismail, Syed (Editor); Schwemmer, Geary K. (Editor)

1998-01-01

This publication contains extended abstracts of papers presented at the Nineteenth International Laser Radar Conference, held at Annapolis, Maryland, July 6-10, 1998; 260 papers were presented in both oral and poster sessions. The topics of the conference sessions were Aerosol Clouds, Multiple Scattering; Tropospheric Profiling, Stratospheric/Mesospheric Profiling; Wind Profiling; New Lidar Technology and Techniques; Lidar Applications, Including Altimetry and Marine; Space and Future Lidar; and Lidar Commercialization/Eye Safety. This conference reflects the breadth of research activities being conducted in the lidar field. These abstracts address subjects from lidar-based atmospheric investigations, development of new lasers and lidar system technology, and current and future space-based lidar systems.

Nineteenth International Laser Radar Conference. Part 1

NASA Technical Reports Server (NTRS)

Singh, Upendra N. (Editor); Ismail, Syed (Editor); Schwemmer, Geary K. (Editor)

1998-01-01

This publication contains extended abstracts of papers presented at the Nineteenth International Laser Radar Conference, held at Annapolis, Maryland, July 6-10, 1998; 260 papers were presented in both oral and poster sessions. The topics of the conference sessions were Aerosol Clouds, Multiple Scattering; Tropospheric Profiling; Stratospheric/Mesospheric Profiling; Wind Profiling; New Lidar Technology and Techniques; Lidar Applications, including Altimetry and Marine; Space and Future Lidar; and Lidar Commercialization/Eye Safety. This conference reflects the breadth of research activities being conducted in the lidar field. These abstracts address subjects from lidar-based atmospheric investigations, development of new lasers and lidar system technology, and current and future space-based lidar systems.

Dynamic sea surface topography from GEOS-3 altimetry - Determination of some dominant parameters

NASA Technical Reports Server (NTRS)

Mather, R. S.; Lerch, F. J.; Rizos, C.; Masters, E. G.; Hirsch, B.

1979-01-01

The second, third and fourth degree zonal harmonics of the quasi-stationary dynamic sea surface topography can be recovered from the GEOS-3 altimetry despite the adverse levels of noise indicated by the crossover discrepancies generated from the best orbits available at the end of 1977 and the GEOS-3 altimetry. Techniques for modelling the global sea surface topography are discussed along with methods for signal recovery in the presence of significant levels of noise. The analysis also provides a means of defining the geocentricity of the system of reference used in preparing the GEOS-3 ephemeris.

Merging IceSAT GLAS and Terra MODIS Data in Order to Derive Forest Type Specific Tree Heights in the Central Siberian Boreal Forest

NASA Technical Reports Server (NTRS)

Ranson, K. Jon; Sun, Guoqing; Kimes, Daniel; Kovacs, Katalin; Kharuk, Viatscheslav

2006-01-01

Mapping of boreal forest's type, biomass, and other structural parameters are critical for understanding of the boreal forest's significance in the carbon cycle, its response to and impact on global climate change. We believe the nature of the forest structure information available from MISR and GLAS can be used to help identify forest type, age class, and estimate above ground biomass levels beyond that now possible with MODIS alone. The ground measurements will be used to develop relationships between remote sensing observables and forest characteristics and provide new information for understanding forest changes with respect to environmental change. Lidar is a laser altimeter that determines the distance from the instrument to the physical surface by measuring the time elapsed between the pulse emission and the reflected return. Other studies have shown that the returned signal may identify multiple returns originating from trees, building and other objects and permits the calculation of their height. Studies using field data have shown that lidar data can provide estimates of structural parameters such as biomass, stand volume and leaf area index and allows remarkable differentiation between primary and secondary forest. NASA's IceSAT Geoscience Laser Altimeter System (GLAS) was launched in January 2003 and collected data during February and September of that year. This study used data acquired over our study sites in central Siberia to examine the GLAS signal as a source of forest height and other structural characteristics. The purpose of our Siberia project is to improve forest cover maps and produce above-ground biomass maps of the boreal forest in Northern Eurasia from MODIS by incorporating structural information inherent in the Terra MISR and ICESAT Geoscience Laser Altimeter System (GLAS) instruments. A number of forest cover classifications exist for the boreal forest. We believe the limiting factor in these products is the lack of structural

What We Do Not Yet Know About Global Ocean Depths, and How Satellite Altimetry Can Help

NASA Astrophysics Data System (ADS)

Smith, W. H. F.; Sandwell, D. T.; Marks, K. M.

2017-12-01

Half Earth's ocean floor area lies several km or more away from the nearest depth measurement. Areas more than 50 km from any sounding sum to a total area larger than the entire United States land area; areas more than 100 km from any sounding comprise a total area larger than Alaska. In remote basins the majority of available data were collected before the mid-1960s, and so often are mis-located by many km, as well as mis-digitized. Satellite altimetry has mapped the marine gravity field with better than 10 km horizontal resolution, revealing nearly all seamounts taller than 2 km; new data can detect some seamounts less than 1 km tall. Seafloor topography can be estimated from satellite altimetry if sediment is thin and relief is due to seafloor spreading and mid-plate volcanism. The accuracy of the estimate depends on the geological nature of the relief and on the accuracy of the soundings available to calibrate the estimation. At best, the estimate is a band-pass-filtered version of the true depth variations, but does not resolve the small-scale seafloor roughness needed to model mixing and dissipation in the ocean. In areas of thick or variable sediment cover there can be little correlation between depth and altimetry. Yet altimeter-estimated depth is the best guess available in most of the ocean. The MH370 search area provides an illustration. Prior to the search it was very sparsely (1% to 5%) covered by soundings, many of these were old, low-tech data, and plateaus with thick sediments complicate the estimation of depth from altimetry. Even so, the estimate was generally correct about the tectonic nature of the terrain and the extent of depth variations to be expected. If ships will fill gaps strategically, visiting areas where altimetry shows that interesting features will be found, and passing near the centroids of the larger gaps, the data will be exciting in their own right and will also improve future altimetry estimates.

Next-generation laser retroreflectors for GNSS, solar system exploration, geodesy, gravitational physics and earth observation

NASA Astrophysics Data System (ADS)

Dell'Agnello, S.; Boni, A.; Cantone, C.; Ciocci, E.; Martini, M.; Patrizi, G.; Tibuzzi, M.; Delle Monache, G.; Vittori, R.; Bianco, G.; Currie, D.; Intaglietta, N.; Salvatori, L.; Lops, C.; Contessa, S.; Porcelli, L.; Mondaini, C.; Tuscano, P.; Maiello, M.

2017-11-01

The SCF_Lab (Satellite/lunar/gnss laser ranging and altimetry Characterization Facility Laboratory) of INFNLNF is designed to cover virtually LRAs (Laser Retroreflector Arrays) of CCRs (Cube Corner Retroreflectors) for missions in the whole solar system, with a modular organization of its instrumentation, two redundant SCF (SCF_Lab Characterization Facilities), and an evolutionary measurement approach, including customization and potentially upgrade on-demand. See http://www.lnf.infn.it/esperimenti/etrusco/ for a general description.

Evaluation of Coastal Sea Level from Jason-2 Altimetry Offshore Hong Kong

NASA Astrophysics Data System (ADS)

Birol, F.; Xu, X. Y., , Dr; Cazenave, A. A.

2017-12-01

In the recent years, several coastal altimetry products of Jason-2 mission have been distributed by different agencies, the most advance ones of which are XTRACK, PISTACH and ALES. Each product represents extraordinary endeavors on some aspects of retracking or advanced geophysical corrections, and each has its advantage. The motivation of this presentation is to evaluate these products in order to refine the sea level measurements at the coast. Three retrackers: MLE4, MLE3 and ALES are focused on. Within 20km coastward, neither GDR nor ALES readily provides sea level anomaly (SLA) measurements, so we recomputed the 20Hz GDR and ALES SLA from the raw data, adopting auxiliary information (such as waveform classification and wet tropospheric delay) from PISTACH. The region of interest is track #153 of the Jason-2 satellite (offshore Hong Kong, China), and the altimetry products are processed over seven years (2008-2015, cycles 1-252). The coastline offshore Hong Kong is rather complicated and we feel that it can be a good indicator of the performance of coastal altimetry under undesirable coast conditions. We computed the bias and noise level of ALES, MLE3 and MLE4 SLA over open ocean and in the coastal zone (within 10km or 5km coast-ward). The results showed that, after outlier-editing, ALES performs better than MLE4 and MLE3 both in terms of noise level and uncertainty in sea level trend estimation. We validated the coastal altimetry-based SLA by comparing with data from the Hong Kong tide gauge (located 10km across-track). An interesting , but still preliminary, result is that the computed sea level trend within 5 km from the coast is significantly larger than the trend estimated at larger distances from the coast. Keywords: Jason-2, Hong Kong coast, ALES, MLE3, MLE4

NASA's Long-Term Archive (LTA) of ICESat Data at the National Snow and Ice Data Center (NSIDC)

NASA Astrophysics Data System (ADS)

Fowler, D. K.; Moses, J. F.; Dimarzio, J. P.; Webster, D.

2011-12-01

Data Stewardship, preservation, and reproducibility are becoming principal parts of a data manager's work. In an era of distributed data and information systems, where the host location ought to be transparent to the internet user, it is of vital importance that organizations make a commitment to both current and long-term goals of data management and the preservation of scientific data. NASA's EOS Data and Information System (EOSDIS) is a distributed system of discipline-specific archives and mission-specific science data processing facilities. Satellite missions and instruments go through a lifecycle that involves pre-launch calibration, on-orbit data acquisition and product generation, and final reprocessing. Data products and descriptions flow to the archives for distribution on a regular basis during the active part of the mission. However there is additional information from the product generation and science teams needed to ensure the observations will be useful for long term climate studies. Examples include ancillary input datasets, product generation software, and production history as developed by the team during the course of product generation. These data and information will need to be archived after product data processing is completed. Using inputs from the USGCRP Workshop on Long Term Archive Requirements (1998), discussions with EOS instrument teams, and input from the 2011 ESIPS Federation meeting, NASA is developing a set of Earth science data and information content requirements for long term preservation that will ultimately be used for all the EOS missions as they come to completion. Since the ICESat/GLAS mission is one of the first to come to an end, NASA and NSIDC are preparing for long-term support of the ICESat mission data now. For a long-term archive, it is imperative that there is sufficient information about how products were prepared in order to convince future researchers that the scientific results are accurate, understandable

Evaluation of the Sentinel-3 Hydrologic Altimetry Processor prototypE (SHAPE) methods.

NASA Astrophysics Data System (ADS)

Benveniste, J.; Garcia-Mondéjar, A.; Bercher, N.; Fabry, P. L.; Roca, M.; Varona, E.; Fernandes, J.; Lazaro, C.; Vieira, T.; David, G.; Restano, M.; Ambrózio, A.

2017-12-01

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. The SHAPE Processor implements all of the steps necessary to derive rivers and lakes water levels and discharge from Delay-Doppler Altimetry and perform their validation against in situ data. The processor uses FBR CryoSat-2 and L1A Sentinel-3A data as input and also various ancillary data (proc. param., water masks, L2 corrections, etc.), to produce surface water levels. At a later stage, water level data are assimilated into hydrological models to derive river discharge. This poster presents the improvements obtained with the new methods and algorithms over the regions of interest (Amazon and Danube rivers, Vanern and Titicaca lakes).

GNSS, Satellite Altimetry and Formosat-3/COSMIC for Determination of Ionosphere Parameters

NASA Astrophysics Data System (ADS)

Mahdi Alizadeh Elizei, M.; Schuh, Harald; Schmidt, Michael; Todorova, Sonya

The dispersion of ionosphere with respect to the microwave signals allows gaining information about the parameters of this medium in terms of the electron density (Ne), or the Total Elec-tron Content (TEC). In the last decade space geodetic techniques, such as Global Navigation Satellite System (GNSS), satellite altimetry missions, and Low Earth Orbiting (LEO) satel-lites have turned into a promising tool for remote sensing the ionosphere. The dual-frequency GNSS observations provide the main input data for development of Global Ionosphere Maps (GIM). However, the GNSS stations are heterogeneously distributed, with large gaps particu-larly over the sea surface, which lowers the precision of the GIM over these areas. Conversely, dual-frequency satellite altimetry missions provide information about the ionosphere precisely above the sea surface. In addition, LEO satellites such as Formosat-3/COSMIC (F-3/C) pro-vide well-distributed information of ionosphere around the world. In this study we developed GIMs of VTEC from combination of GNSS, satellite altimetry and F-3/C data with temporal resolution of 2 hours and spatial resolution of 5 degree in longitude and 2.5 degree in latitude. The combined GIMs provide a more homogeneous global coverage and higher precision and reliability than results of each individual technique.

Mapping Error in Southern Ocean Transport Computed from Satellite Altimetry and Argo

NASA Astrophysics Data System (ADS)

Kosempa, M.; Chambers, D. P.

2016-02-01

Argo profiling floats afford basin-scale coverage of the Southern Ocean since 2005. When density estimates from Argo are combined with surface geostrophic currents derived from satellite altimetry, one can estimate integrated geostrophic transport above 2000 dbar [e.g., Kosempa and Chambers, JGR, 2014]. However, the interpolation techniques relied upon to generate mapped data from Argo and altimetry will impart a mapping error. We quantify this mapping error by sampling the high-resolution Southern Ocean State Estimate (SOSE) at the locations of Argo floats and Jason-1, and -2 altimeter ground tracks, then create gridded products using the same optimal interpolation algorithms used for the Argo/altimetry gridded products. We combine these surface and subsurface grids to compare the sampled-then-interpolated transport grids to those from the original SOSE data in an effort to quantify the uncertainty in volume transport integrated across the Antarctic Circumpolar Current (ACC). This uncertainty is then used to answer two fundamental questions: 1) What is the minimum linear trend that can be observed in ACC transport given the present length of the instrument record? 2) How long must the instrument record be to observe a trend with an accuracy of 0.1 Sv/year?

Recent Changes in Ices Mass Balance of the Amundsen Sea Sector

NASA Astrophysics Data System (ADS)

Sutterley, T. C.; Velicogna, I.; Rignot, E. J.; Mouginot, J.; Flament, T.; van den Broeke, M. R.; van Wessem, M.; Reijmer, C.

2014-12-01

The glaciers flowing into the Amundsen Sea Embayment (ASE) sector of West Antarctica were confirmed in the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) to be the dominant contributors to the current Antarctic ice mass loss, and recently recognized to be undergoing marine ice sheet instability. Here, we investigate their regional ice mass balance using a time series of satellite and airborne data combined with model output products from the Regional Atmospheric and Climate Model (RACMO). Our dataset includes laser altimetry from NASA's ICESat-1 satellite mission and from Operation IceBridge (OIB) airborne surveys, satellite radar altimetry data from ESA's Envisat mission, time-variable gravity data from NASA/DLR's GRACE mission, surface mass balance products from RACMO, ice velocity from a combination of international synthetic aperture radar satellites and ice thickness data from OIB. We find a record of ice mass balance for the ASE where all the analyzed techniques agree remarkably in magnitude and temporal variability. The mass loss of the region has been increasing continuously since 1992, with no indication of a slow down. The mass loss during the common period averaged 91 Gt/yr and accelerated 20 Gt/yr2. In 1992-2013, the ASE contributed 4.5 mm global sea level rise. Overall, our results demonstrate the synergy of multiple analysis techniques for examining Antarctic Ice Sheet mass balance at the regional scale. This work was performed at UCI and JPL under a contract with NASA.

Combining GRACE and Altimetry to solve for present day mass changes and GIA

NASA Astrophysics Data System (ADS)

Rietbroek, R.; Lück, C.; Uebbing, B.; Kusche, J.; King, M. A.

2017-12-01

Past and present day sea level rise is closely linked to geoid and surface deformation changes from the ongoing glacial isostatic adjustment (GIA). Sea level, as detected by radar altimetry, senses the radial deformation of the ocean floor as mantle material slowly flows back to the locations of the former glacial domes. This manifests itself as a net subsidence when averaged over the entire ocean, but can regionally be seen as an uplift for locations close to the former ice sheets. Furthermore, mass driven sea level as derived from GRACE, is even more sensitive to GIA induced mass redistribution in the solid Earth. Consequently, errors in GIA corrections, most notably errors in mantle viscosity and ice histories, have a different leverage on regional sea level estimates from GRACE and altimetry. In this study, we discuss the abilities of a GRACE-altimetry combination to co-estimate GIA corrections together with present day contributors to sea level, rather than simply prescribing a GIA correction from a model. The data is combined in a joint inversion scheme which makes use of spatial patterns to parameterize present day loading effects and GIA. We show that the GRACE-altimetry combination requires constraints, but generally steers the Antarctic GIA signal towards a weaker present day signal in Antarctica compared to a ICE5-G(VM2) derived model. Furthermore, in light of the aging GRACE mission, we show sensitivity studies of how well one could estimate GIA corrections when using other low earth orbiters such as SWARM or CHAMP. Finally, we show whether the Antarctic GNSS station network may be useful in separating GIA from present day mass signals in this type of inversion schemes.

Evaluation of altimetry-derived surface current products using Lagrangian drifter trajectories in the eastern Gulf of Mexico

NASA Astrophysics Data System (ADS)

Liu, Yonggang; Weisberg, Robert H.; Vignudelli, Stefano; Mitchum, Gary T.

2014-05-01

Lagrangian particle trajectory models based on several altimetry-derived surface current products are used to hindcast the drifter trajectories observed in the eastern Gulf of Mexico during May to August 2010 (the Deepwater Horizon oil spill incident). The performances of the trajectory models are gauged in terms of Lagrangian separation distances (d) and a nondimensional skill score (s), respectively. A series of numerical experiments show that these altimetry-based trajectory models have about the same performance, with a certain improvement by adding surface wind Ekman components, especially over the shelf region. However, their hindcast skills are slightly better than those of the data assimilative numerical model output. After 3 days' simulation the altimetry-based trajectory models have mean d values of 75-83 and 34-42 km (s values of 0.49-0.51 and 0.35-0.43) in the Gulf of Mexico deep water area and on the West Florida Continental Shelf, respectively. These satellite altimetry data products are useful for providing essential information on ocean surface currents of use in water property transports, offshore oil and gas operations, hazardous spill mitigation, search and rescue, etc.

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

NASA Technical Reports Server (NTRS)

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

1993-01-01

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

Radarclinometry: Bootstrapping the radar reflectance function from the image pixel-signal frequency distribution and an altimetry profile

USGS Publications Warehouse

Wildey, R.L.

1988-01-01

A method is derived for determining the dependence of radar backscatter on incidence angle that is applicable to the region corresponding to a particular radar image. The method is based on enforcing mathematical consistency between the frequency distribution of the image's pixel signals (histogram of DN values with suitable normalizations) and a one-dimensional frequency distribution of slope component, as might be obtained from a radar or laser altimetry profile in or near the area imaged. In order to achieve a unique solution, the auxiliary assumption is made that the two-dimensional frequency distribution of slope is isotropic. The backscatter is not derived in absolute units. The method is developed in such a way as to separate the reflectance function from the pixel-signal transfer characteristic. However, these two sources of variation are distinguishable only on the basis of a weak dependence on the azimuthal component of slope; therefore such an approach can be expected to be ill-conditioned unless the revision of the transfer characteristic is limited to the determination of an additive instrumental background level. The altimetry profile does not have to be registered in the image, and the statistical nature of the approach minimizes pixel noise effects and the effects of a disparity between the resolutions of the image and the altimetry profile, except in the wings of the distribution where low-number statistics preclude accuracy anyway. The problem of dealing with unknown slope components perpendicular to the profiling traverse, which besets the one-to-one comparison between individual slope components and pixel-signal values, disappears in the present approach. In order to test the resulting algorithm, an artificial radar image was generated from the digitized topographic map of the Lake Champlain West quadrangle in the Adirondack Mountains, U.S.A., using an arbitrarily selected reflectance function. From the same map, a one-dimensional frequency

Using altimetry and seafloor pressure data to estimate vertical deformation offshore: Vanuatu case study

NASA Astrophysics Data System (ADS)

Ballu, V.; Bonnefond, P.; Calmant, S.; Bouin, M.-N.; Pelletier, B.; Laurain, O.; Crawford, W. C.; Baillard, C.; de Viron, O.

2013-04-01

Measuring ground deformation underwater is essential for understanding Earth processes at many scales. One important example is subduction zones, which can generate devastating earthquakes and tsunamis, and where the most important deformation signal related to plate locking is usually offshore. We present an improved method for making offshore vertical deformation measurements, that involve combining tide gauge and altimetry data. We present data from two offshore sites located on either side of the plate interface at the New Hebrides subduction zone, where the Australian plate subducts beneath the North Fiji basin. These two sites have been equipped with pressure gauges since 1999, to extend an on-land GPS network across the plate interface. The pressure series measured at both sites show that Wusi Bank, located on the over-riding plate, subsides by 11 ± 4 mm/yr with respect to Sabine Bank, which is located on the down-going plate. By combining water depths derived from the on-bottom pressure data with sea surface heights derived from altimetry data, we determine variations of seafloor heights in a global reference frame. Using altimetry data from TOPEX/Poseidon, Jason-1, Jason-2 and Envisat missions, we find that the vertical motion at Sabine Bank is close to zero and that Wusi Bank subsides by at least 3 mm/yr and probably at most 11 mm/yr.This paper represents the first combination of altimetry and pressure data to derive absolute vertical motions offshore. The deformation results are obtained in a global reference frame, allowing them to be integrated with on-land GNSS data.

Enhancing the Arctic Mean Sea Surface and Mean Dynamic Topography with CryoSat-2 Data

NASA Astrophysics Data System (ADS)

Stenseng, Lars; Andersen, Ole B.; Knudsen, Per

2014-05-01

A reliable mean sea surface (MSS) is essential to derive a good mean dynamic topography (MDT) and for the estimation of short and long-term changes in the sea surface. The lack of satellite radar altimetry observations above 82 degrees latitude means that existing mean sea surface models have been unreliable in the Arctic Ocean. We here present the latest DTU mean sea surface and mean dynamic topography models that includes CryoSat-2 data to improve the reliability in the Arctic Ocean. In an attempt to extrapolate across the gap above 82 degrees latitude the previously models included ICESat data, gravimetrical geoids, ocean circulation models and various combinations hereof. Unfortunately cloud cover and the short periods of operation has a negative effect on the number of ICESat sea surface observations. DTU13MSS and DTU13MDT are the new generation of state of the art global high-resolution models that includes CryoSat-2 data to extend the satellite radar altimetry coverage up to 88 degrees latitude. Furthermore the SAR and SARin capability of CryoSat-2 dramatically increases the amount of useable sea surface returns in sea-ice covered areas compared to conventional radar altimeters like ENVISAT and ERS-1/2. With the inclusion of CryoSat-2 data the new mean sea surface is improved by more than 20 cm above 82 degrees latitude compared with the previous generation of mean sea surfaces.

The Uncertainty of Biomass Estimates from Modeled ICESat-2 Returns Across a Boreal Forest Gradient

NASA Technical Reports Server (NTRS)

Montesano, P. M.; Rosette, J.; Sun, G.; North, P.; Nelson, R. F.; Dubayah, R. O.; Ranson, K. J.; Kharuk, V.

2014-01-01

The Forest Light (FLIGHT) radiative transfer model was used to examine the uncertainty of vegetation structure measurements from NASA's planned ICESat-2 photon counting light detection and ranging (LiDAR) instrument across a synthetic Larix forest gradient in the taiga-tundra ecotone. The simulations demonstrate how measurements from the planned spaceborne mission, which differ from those of previous LiDAR systems, may perform across a boreal forest to non-forest structure gradient in globally important ecological region of northern Siberia. We used a modified version of FLIGHT to simulate the acquisition parameters of ICESat-2. Modeled returns were analyzed from collections of sequential footprints along LiDAR tracks (link-scales) of lengths ranging from 20 m-90 m. These link-scales traversed synthetic forest stands that were initialized with parameters drawn from field surveys in Siberian Larix forests. LiDAR returns from vegetation were compiled for 100 simulated LiDAR collections for each 10 Mg · ha(exp -1) interval in the 0-100 Mg · ha(exp -1) above-ground biomass density (AGB) forest gradient. Canopy height metrics were computed and AGB was inferred from empirical models. The root mean square error (RMSE) and RMSE uncertainty associated with the distribution of inferred AGB within each AGB interval across the gradient was examined. Simulation results of the bright daylight and low vegetation reflectivity conditions for collecting photon counting LiDAR with no topographic relief show that 1-2 photons are returned for 79%-88% of LiDAR shots. Signal photons account for approximately 67% of all LiDAR returns, while approximately 50% of shots result in 1 signal photon returned. The proportion of these signal photon returns do not differ significantly (p greater than 0.05) for AGB intervals greater than 20 Mg · ha(exp -1). The 50m link-scale approximates the finest horizontal resolution (length) at which photon counting LiDAR collection provides strong model

The role of satellite altimetry in climate studies

NASA Technical Reports Server (NTRS)

Parsons, C. L.

1980-01-01

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

Altimetry Using GPS-Reflection/Occultation Interferometry

NASA Technical Reports Server (NTRS)

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

2008-01-01

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

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

NASA Technical Reports Server (NTRS)

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

1994-01-01

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

Interannual Variations of Surface Currents and Transports in the Sicily Channel Derived From Coastal Altimetry

NASA Astrophysics Data System (ADS)

Jebri, Fatma; Zakardjian, Bruno; Birol, Florence; Bouffard, Jérôme; Jullion, Loïc.; Sammari, Cherif

2017-11-01

A 20 year coastal altimetry data set (X-TRACK) is used, for the first time, to gain insight into the long-term interannual variations of the surface circulation in the Sicily Channel. First, a spectral along with a time/space diagram analysis are applied to the monthly means. They reveal a regionally coherent current patterns from track to track with a marked interannual variability that is unequally shared between the Atlantic Tunisian Current and Atlantic Ionian Stream inflows in the Sicily Channel and the Bifurcation Tyrrhenian Current outflow northeast of Sicily. Second, an empirical altimetry-based transport-like technique is proposed to quantify volume budgets inside the closed boxes formed by the crossing of the altimetry tracks and coastlines over the study area. A set of hydrographic measurements is used to validate the method. The inferred altimetry transports give a well-balanced mean eastward Atlantic Waters baroclinic flow of 0.4 Sv and standard deviations of 0.2 Sv on a yearly basis throughout the Sicily Channel and toward the Ionian Sea, which is fairly coherent with those found in the literature. Furthermore, the analysis allows to quantify the intrusions of Atlantic Waters over the Tunisian Shelf (0.12 ± 0.1 Sv) and highlights two main modes of variability of the main surface waters path over the Sicily Channel through the Bifurcation Atlantic Tunisian Current and Atlantic Ionian Stream systems. Some physical mechanisms are finally discussed with regards to changes in the observed currents and transports.

Airborne and spaceborne DEM- and laser altimetry-derived surface elevation and volume changes of the Bering Glacier system, Alaska, USA, and Yukon, Canada, 1972-2006

NASA Astrophysics Data System (ADS)

Muskett, Reginald R.; Lingle, Craig S.; Sauber, Jeanne M.; Post, Austin S.; Tangborn, Wendell V.; Rabus, Bernhard T.; Echelmeyer, Keith A.

Using airborne and spaceborne high-resolution digital elevation models and laser altimetry, we present estimates of interannual and multi-decadal surface elevation changes on the Bering Glacier system, Alaska, USA, and Yukon, Canada, from 1972 to 2006. We find: (1) the rate of lowering during 1972-95 was 0.9±0.1 m a-1; (2) this rate accelerated to 3.0±0.7 m a-1 during 1995-2000; and (3) during 2000-03 the lowering rate was 1.5±0.4 m a-1. From 1972 to 2003, 70% of the area of the system experienced a volume loss of 191±17 km3, which was an area-average surface elevation lowering of 1.7±0.2 m a-1. From November 2004 to November 2006, surface elevations across Bering Glacier, from McIntosh Peak on the south to Waxell Ridge on the north, rose as much as 53 m. Up-glacier on Bagley Ice Valley about 10 km east of Juniper Island nunatak, surface elevations lowered as much as 28 m from October 2003 to October 2006. NASA Terra/MODIS observations from May to September 2006 indicated muddy outburst floods from the Bering terminus into Vitus Lake. This suggests basal-englacial hydrologic storage changes were a contributing factor in the surface elevation changes in the fall of 2006.

Greenland Ice Sheet Mass Balance: Distribution of Increased Mass Loss with Climate Warming; 2003-07 Versus 1992-2002

NASA Technical Reports Server (NTRS)

Zwally, H. Jay; Li, Jun; Benner, Anita C.; Beckley, Matthew; Cornejo, Helen G.; DiMarzio, John; Giovinetto, Mario B.; Neumann, Thomas A.; Robbins, John; Saba, Jack L.;

Mean Dynamic Topography of the Arctic Ocean

NASA Technical Reports Server (NTRS)

Farrell, Sinead Louise; Mcadoo, David C.; Laxon, Seymour W.; Zwally, H. Jay; Yi, Donghui; Ridout, Andy; Giles, Katherine

2012-01-01

ICESat and Envisat altimetry data provide measurements of the instantaneous sea surface height (SSH) across the Arctic Ocean, using lead and open water elevation within the sea ice pack. First, these data were used to derive two independent mean sea surface (MSS) models by stacking and averaging along-track SSH profiles gathered between 2003 and 2009. The ICESat and Envisat MSS data were combined to construct the high-resolution ICEn MSS. Second, we estimate the 5.5-year mean dynamic topography (MDT) of the Arctic Ocean by differencing the ICEn MSS with the new GOCO02S geoid model, derived from GRACE and GOCE gravity. Using these satellite-only data we map the major features of Arctic Ocean dynamical height that are consistent with in situ observations, including the topographical highs and lows of the Beaufort and Greenland Gyres, respectively. Smaller-scale MDT structures remain largely unresolved due to uncertainties in the geoid at short wavelengths.

Snow Grain Size Retrieval over the Polar Ice Sheets with the Ice, Cloud, and land Elevation Satellite (ICESat) Observations

PubMed Central

Yang, Yuekui; Marshak, Alexander; Han, Mei; Palm, Stephen P.; Harding, David J.

2018-01-01

Snow grain size is an important parameter for cryosphere studies. As a proof of concept, this paper presents an approach to retrieve this parameter over Greenland, East and West Antarctica ice sheets from surface reflectances observed with the Geoscience Laser Altimeter System (GLAS) onboard the Ice, Cloud, and land Elevation Satellite (ICESat) at 1064 nm. Spaceborne lidar observations overcome many of the disadvantages in passive remote sensing, including difficulties in cloud screening and low sun angle limitations; hence tend to provide more accurate and stable retrievals. Results from the GLAS L2A campaign, which began on 25 September and lasted until 19 November, 2003, show that the mode of the grain size distribution over Greenland is the largest (~300 μm) among the three, West Antarctica is the second (~220 μm) and East Antarctica is the smallest (~190 μm). Snow grain sizes are larger over the coastal regions compared to inland the ice sheets. These results are consistent with previous studies. Applying the broadband snow surface albedo parameterization scheme developed by Garder and Sharp (2010) to the retrieved snow grain size, ice sheet surface albedo is also derived. In the future, more accurate retrievals can be achieved with multiple wavelengths lidar observations. PMID:29636591

Snow Grain Size Retrieval over the Polar Ice Sheets with the Ice, Cloud and Land Elevation Satellite (ICESat) Observations

NASA Technical Reports Server (NTRS)

Yang, Yuekui; Marshak, Alexander; Han, Mei; Palm, Stephen P.; Harding, David J.

2016-01-01

Snow grain size is an important parameter for cryosphere studies. As a proof of concept, this paper presents an approach to retrieve this parameter over Greenland, East and West Antarctica ice sheets from surface reflectances observed with the Geoscience Laser Altimeter System (GLAS) onboard the Ice, Cloud, and land Elevation Satellite (ICESat) at 1064 nanometers. Spaceborne lidar observations overcome many of the disadvantages in passive remote sensing, including difficulties in cloud screening and low sun angle limitations; hence tend to provide more accurate and stable retrievals. Results from the GLAS L2A campaign, which began on 25 September and lasted until 19 November, 2003, show that the mode of the grain size distribution over Greenland is the largest (approximately 300 microns) among the three, West Antarctica is the second (220 microns) and East Antarctica is the smallest (190 microns). Snow grain sizes are larger over the coastal regions compared to inland the ice sheets. These results are consistent with previous studies. Applying the broadband snow surface albedo parameterization scheme developed by Garder and Sharp (2010) to the retrieved snow grain size, ice sheet surface albedo is also derived. In the future, more accurate retrievals can be achieved with multiple wavelengths lidar observations.

The BRAT and GUT Couple: Broadview Radar Altimetry and GOCE User Toolboxes

NASA Astrophysics Data System (ADS)

Benveniste, J.; Restano, M.; Ambrózio, A.

2017-12-01

The Broadview Radar Altimetry Toolbox (BRAT) is a collection of tools designed to facilitate the processing of radar altimetry data from previous and current altimetry missions, including Sentinel-3A L1 and L2 products. A tutorial is included providing plenty of use cases. BRAT's next release (4.2.0) is planned for October 2017. Based on the community feedback, the front-end has been further improved and simplified whereas the capability to use BRAT in conjunction with MATLAB/IDL or C/C++/Python/Fortran, allowing users to obtain desired data bypassing the data-formatting hassle, remains unchanged. Several kinds of computations can be done within BRAT involving the combination of data fields, that can be saved for future uses, either by using embedded formulas including those from oceanographic altimetry, or by implementing ad-hoc Python modules created by users to meet their needs. BRAT can also be used to quickly visualise data, or to translate data into other formats, e.g. from NetCDF to raster images. The GOCE User Toolbox (GUT) is a compilation of tools for the use and the analysis of GOCE gravity field models. It facilitates using, viewing and post-processing GOCE L2 data and allows gravity field data, in conjunction and consistently with any other auxiliary data set, to be pre-processed by beginners in gravity field processing, for oceanographic and hydrologic as well as for solid earth applications at both regional and global scales. Hence, GUT facilitates the extensive use of data acquired during GRACE and GOCE missions. In the current 3.1 version, GUT has been outfitted with a graphical user interface allowing users to visually program data processing workflows. Further enhancements aiming at facilitating the use of gradients, the anisotropic diffusive filtering, and the computation of Bouguer and isostatic gravity anomalies have been introduced. Packaged with GUT is also GUT's Variance-Covariance Matrix tool (VCM). BRAT and GUT toolboxes can be freely

Lasers in space

NASA Astrophysics Data System (ADS)

Michaelis, M. M.; Forbes, A.; Bingham, R.; Kellett, B. J.; Mathye, A.

2008-05-01

A variety of laser applications in space, past, present, future and far future are reviewed together with the contributions of some of the scientists and engineers involved, especially those that happen to have South African connections. Historically, two of the earliest laser applications in space, were atmospheric LIDAR and lunar ranging. These applications involved atmospheric physicists, several astronauts and many of the staff recruited into the Soviet and North American lunar exploration programmes. There is a strong interest in South Africa in both LIDAR and lunar ranging. Shortly after the birth of the laser (and even just prior) theoretical work on photonic propulsion and space propulsion by laser ablation was initiated by Georgii Marx, Arthur Kantrowitz and Eugen Saenger. Present or near future experimental programs are developing in the following fields: laser ablation propulsion, possibly coupled with rail gun or gas gun propulsion; interplanetary laser transmission; laser altimetry; gravity wave detection by space based Michelson interferometry; the de-orbiting of space debris by high power lasers; atom laser interferometry in space. Far future applications of laser-photonic space-propulsion were also pioneered by Carl Sagan and Robert Forward. They envisaged means of putting Saenger's ideas into practice. Forward also invented a laser based method for manufacturing solid antimatter or SANTIM, well before the ongoing experiments at CERN with anti-hydrogen production and laser-trapping. SANTIM would be an ideal propellant for interstellar missions if it could be manufactured in sufficient quantities. It would be equally useful as a power source for the transmission of information over light year distances. We briefly mention military lasers. Last but not least, we address naturally occurring lasers in space and pose the question: "did the Big Bang lase?"

Greenland uplift and regional sea level changes from ICESat observations and GIA modelling

NASA Astrophysics Data System (ADS)

Spada, G.; Ruggieri, G.; Sørensen, L. S.; Nielsen, K.; Melini, D.; Colleoni, F.

2012-06-01

We study the implications of a recently published mass balance of the Greenland ice sheet (GrIS), derived from repeated surface elevation measurements from NASA's ice cloud and land elevation satellite (ICESat) for the time period between 2003 and 2008. To characterize the effects of this new, high-resolution GrIS mass balance, we study the time-variations of various geophysical quantities in response to the current mass loss. They include vertical uplift and subsidence, geoid height variations, global patterns of sea level change (or fingerprints), and regional sea level variations along the coasts of Greenland. Long-wavelength uplifts and gravity variations in response to current or past ice thickness variations are obtained solving the sea level equation, which accounts for both the elastic and the viscoelastic components of deformation. To capture the short-wavelength components of vertical uplift in response to current ice mass loss, which is not resolved by satellite gravity observations, we have specifically developed a high-resolution regional elastic rebound (ER) model. The elastic component of vertical uplift is combined with estimates of the viscoelastic displacement fields associated with the process of glacial-isostatic adjustment (GIA), according to a set of published ice chronologies and associated mantle rheological profiles. We compare the sensitivity of global positioning system (GPS) observations along the coasts of Greenland to the ongoing ER and GIA. In notable contrast with past reports, we show that vertical velocities obtained by GPS data from five stations with sufficiently long records and from one tide gauge at the GrIS margins can be reconciled with model predictions based on the ICE-5G deglaciation model and the ER associated with the new ICESat-derived mass balance.

A Global Ocean Tide Model From TOPEX/POSEIDON Altimetry: GOT99.2

NASA Technical Reports Server (NTRS)

Ray, Richard D.

1999-01-01

Goddard Ocean Tide model GOT99.2 is a new solution for the amplitudes and phases of the global oceanic tides, based on over six years of sea-surface height measurements by the TOPEX/POSEIDON satellite altimeter. Comparison with deep-ocean tide-gauge measurements show that this new tidal solution is an improvement over previous global models, with accuracies for the main semidiurnal lunar constituent M2 now below 1.5 cm (deep water only). The new solution benefits from use of prior hydrodynamic models, several in shallow and inland seas as well as the global finite-element model FES94.1. This report describes some of the data processing details involved in handling the altimetry, and it provides a comprehensive set of global cotidal charts of the resulting solutions. Various derived tidal charts are also provided, including tidal loading deformation charts, tidal gravimetric charts, and tidal current velocity (or transport) charts. Finally, low-degree spherical harmonic coefficients are computed by numerical quadrature and are tabulated for the major short-period tides; these are useful for a variety of geodetic and geophysical purposes, especially in combination with similar estimates from satellite laser ranging.

Re-assessment of the mass balance of the Abbot and Getz sectors of West Antarctica

NASA Astrophysics Data System (ADS)

Chuter, S.; Bamber, J. L.

2016-12-01

Large discrepancies exist in mass balance estimates for the Getz and Abbot drainage basins, primarily due to previous poor knowledge of ice thickness at the grounding line, poor coverage by previous altimetry missions and signal leakage issues for GRACE. Large errors arise when using ice thickness measurements derived from ERS-1 and/or ICESat altimetry data due to poor track spacing, `loss of lock' issues near the grounding line and the complex morphology of these shelves, requiring fine resolution to derive robust and accurate elevations close to the grounding line. However, the advent of CryoSat-2 with its unique orbit and SARIn mode of operation has overcome these issues and enabled the determination of ice shelf thickness at a much higher accuracy than possible from previous satellites, particularly within the grounding zone. Here we present a contemporary estimate of ice sheet mass balance for the both the Getz and Abbot drainage basins. This is achieved through the use of contemporary velocity data derived from Landsat feature tracking and the use of CryoSat-2 derived ice thickness measurements. Additionally, we use this new ice thickness dataset to reassess mass balance estimates from 2008/2009, where there were large disparities between results from radar altimetry and Input-Output methodologies over the Abbot region in particular. These contemporary results are compared with other present day estimates from gravimetry and altimetry elevation changes.

INRRI-EDM/2016: the first laser retroreflector on the surface of Mars

NASA Astrophysics Data System (ADS)

Dell'Agnello, S.; Delle Monache, G.; Porcelli, L.; Boni, A.; Contessa, S.; Ciocci, E.; Martini, M.; Tibuzzi, M.; Intaglietta, N.; Salvatori, L.; Tuscano, P.; Patrizi, G.; Mondaini, C.; Lops, C.; Vittori, R.; Maiello, M.; Flamini, E.; Marchetti, E.; Bianco, G.; Mugnuolo, R.; Cantone, C.

2017-01-01

During Summer 2015 the SCF_Lab (Satellite/lunar/GNSS laser ranging/altimetry and cube/microsat Characterization Facilities Laboratory, http://www.lnf.infn.it/esperimenti/etrusco, Team of INFN-LNF, with support by ASI, carried out an intense activity of final design, manufacturing and testing in order to construct, space qualify and finally integrate INRRI-EDM/2016 on ESA's ExoMars EDM spacecraft (also dubbed "Schiaparelli"), which was successfully launched on March 14, 2016. INRRI (INstrument for landing-Roving laser Retroreflector Investigation) for the EDM (Entry descent and landing Demonstration Module) 2016 mission is a compact, lightweight, passive, maintenance-free array of eight cube corner laser retroreflectors fixed to an aluminum alloy frame through the use of silicon rubber suitable for space applications. INRRI was installed on the top panel of the EDM Central Bay on October 14, 2015. It will enable the EDM to be laser-located from Mars orbiters, through laser ranging and altimetry, lidar atmospheric observations from orbit, laser flashes emitted by orbiters, and lasercom. One or all of the above means of observation can be supported by INRRI when there is an active, laser-equipped orbiter, especially after EDM end-of-life and for a long time. INRRI goals will cover science (Mars geodesy/geophysics, future Mars test of General Relativity, GR), technology and exploration. Concerning the latter two, INRRI will support mars-georeferencing of the EDM landing site, support potential precision lidar-based landing next to the EDM, support test & diagnostics of lasercom for data exchange among Mars orbit, Mars surface and Earth, and it will be a precursor for additional Mars surface retroreflectors, for example on exploration rovers. This paper describes in detail our innovative payload, hopefully the very first to be deployed safely with the lander Schiaparelli on the Mars surface, and its space qualification for the ExoMars EDM 2016 mission. Despite the fate

Gravity model improvement using GEOS 3 /GEM 9 and 10/. [and Seasat altimetry data

NASA Technical Reports Server (NTRS)

Lerch, F. J.; Wagner, C. A.; Klosko, S. M.; Laubscher, R. E.

1979-01-01

Although errors in previous gravity models have produced large uncertainties in the orbital position of GEOS 3, significant improvement has been obtained with new geopotential solutions, Goddard Earth Model (GEM) 9 and 10. The GEM 9 and 10 solutions for the potential coefficients and station coordinates are presented along with a discussion of the new techniques employed. Also presented and discussed are solutions for three fundamental geodetic reference parameters, viz. the mean radius of the earth, the gravitational constant, and mean equatorial gravity. Evaluation of the gravity field is examined together with evaluation of GEM 9 and 10 for orbit determination accuracy. The major objectives of GEM 9 and 10 are achieved. GEOS 3 orbital accuracies from these models are about 1 m in their radial components for 5-day arc lengths. Both models yield significantly improved results over GEM solutions when compared to surface gravimetry, Skylab and GEOS 3 altimetry, and highly accurate BE-C (Beacon Explorer-C) laser ranges. The new values of the parameters discussed are given.

Coastal and mesoscale dynamics characterization combining glider and altimetry: case study over the Western Mediterranean Sea

NASA Astrophysics Data System (ADS)

Jerome, Bouffard; Pascual, Ananda; Ruiz, Simon; Isabelle Pujol, Marie; Faugere, Yannice; Larnicol, Gilles; Tintore, Joaquin

Satellite altimetry allows a direct computation of geostrophic velocity anomalies. However, conventional altimetry measurements remain largely spurious in coastal zone, due to several factors such as inaccurate geophysical corrections (e.g. atmospheric and tidal signals) as well as environmental issues (land contamination in the altimetric and radiometric footprints). At the present time and in the attempt of future relevant technologies (cf. SWOT satellite), experimen-tal coastal altimeter products are under development (XTRACK, PISTACH, COASTALT. . . ). The main efforts consist in the application of coastal-oriented corrections and the review of the data recovery strategies near the coast. The new coastal altimetric products need to be assessed with independent data before to be used in synergy with other measurements and fully exploited for scientific applications. This is the frame of this study as part of an intensive observational program conducted in the Western Mediterranean Sea. We present here the main outcomes resulting from the combination of coastal altimetry and gliders. Gliders -autonomous underwater vehicles -allow to provide precise and high resolution data complementary to altimetry (temperature, salinity, pressure, velocity. . . ) both at surface and over the whole water column. Since July 2007, several glider missions have been performed along Jason-1, Jason-2 and ENVISAT altimeters. The altimetric sea level anomalies have been processed from both standard and coastal-oriented strategies. Furthermore, new methodologies have also been developed in order to combine surface glider geostrophic velocities (derived from CTD measurements) with integrated currents estimated by the glider (derived from GPS locations every 6 hours). These approaches prove to be very efficient to improve the budget errors and homogenize the physical contents of altimetry and glider data. Further, the combined analysis of the two datasets provides interesting insights of

Theoretical and experimental analysis of laser altimeters for barometric measurements over the ocean

NASA Technical Reports Server (NTRS)

Tsai, B. M.; Gardner, C. S.

1984-01-01

The statistical characteristics and the waveforms of ocean-reflected laser pulses are studied. The received signal is found to be corrupted by shot noise and time-resolved speckle. The statistics of time-resolved speckle and its effects on the timing accuracy of the receiver are studied in the general context of laser altimetry. For estimating the differential propagation time, various receiver timing algorithms are proposed and their performances evaluated. The results indicate that, with the parameters of a realistic altimeter, a pressure measurement accuracy of a few millibars is feasible. The data obtained from the first airborne two-color laser altimeter experiment are processed and analyzed. The results are used to verify the pressure measurement concept.

Coastal Sea Level along the North Eastern Atlantic Shelf from Delay Doppler Altimetry

NASA Astrophysics Data System (ADS)

Fenoglio-Marc, L.; Benveniste, J.; Andersen, O. B.; Gravelle, M.; Dinardo, S.; Uebbing, B.; Scharroo, R.; Kusche, J.; Kern, M.; Buchhaupt, C.

2017-12-01

Satellite altimetry data of the CryoSat-2 and Sentinel-3 missions processed with Delay Doppler methodology (DDA) provide improved coastal sea level measurements up to 2-4 km from coast, thanks to an along-track resolution of about 300m and a higher signal to noise ratio. We investigate the 10 Kilometre stripe along the North-Eastern Atlantic shelf from Lisbon to Bergen to detect the possible impacts in sea level change studies of this enhanced dataset. We consider SAR CryoSat-2 and Sentinel-3 altimetry products from the ESA GPOD processor and in-house reduced SAR altimetry (RDSAR) products. Improved processing includes in RDSAR the application of enhanced retrackers for the RDSAR waveform. Improved processing in SAR includes modification both in the generation of SAR waveforms, (as Hamming weighting window on the burst data prior to the azimuth FFT, zero-padding prior to the range FFT, doubling of the extension for the radar range swath) and in the SAMOSA2 retracker. Data cover the full lifetime of CryoSat-2 (6 years) and Sentinel-3 (1 year). Conventional altimetry are from the sea level CCI database. First we analyse the impact of these SAR altimeter data on the sea level trend and on the estimation of vertical motion from the altimeter minus tide gauge differences. VLM along the North-Eastern Atlantic shelf is generally small compared to the North-Western Atlantic Coast VLM, with a smaller signal to noise ratio. Second we investigate impact on the coastal mean sea level surface and the mean dynamic topography. We evaluate a mean surface from the new altimeter data to be combined to state of the art geoid models to derive the mean dynamic topography. We compare the results to existing oceanographic and geodetic mean dynamic topography solutions, both on grid and pointwise at the tide gauge stations. This study is supported by ESA through the Sea Level CCI and the GOCE++DYCOT projects

GNSS-R Altimetry Performance Analysis for the GEROS Experiment on Board the International Space Station.

PubMed

Camps, Adriano; Park, Hyuk; Sekulic, Ivan; Rius, Juan Manuel

2017-07-06

The GEROS-ISS (GNSS rEflectometry, Radio Occultation and Scatterometry onboard International Space Station) is an innovative experiment for climate research, proposed in 2011 within a call of the European Space Agency (ESA). This proposal was the only one selected for further studies by ESA out of ~25 ones that were submitted. In this work, the instrument performance for the near-nadir altimetry (GNSS-R) mode is assessed, including the effects of multi-path in the ISS structure, the electromagnetic-bias, and the orbital height decay. In the absence of ionospheric scintillations, the altimetry rms error is <50 cm for a swath <~250 km and for U 10 <10 m/s. If the transmitted power is 3 dB higher (likely to happen at beginning of life of the GNSS spacecrafts), mission requirements (rms error is <50 cm) are met for all ISS heights and for U 10 up to 15 m/s. However, around 1.5 GHz, the ionosphere can induce significant fading, from 2 to >20 dB at equatorial regions, mainly after sunset, which will seriously degrade the altimetry and the scatterometry performances of the instrument.

GNSS-R Altimetry Performance Analysis for the GEROS Experiment on Board the International Space Station

PubMed Central

Sekulic, Ivan

2017-01-01

The GEROS-ISS (GNSS rEflectometry, Radio Occultation and Scatterometry onboard International Space Station) is an innovative experiment for climate research, proposed in 2011 within a call of the European Space Agency (ESA). This proposal was the only one selected for further studies by ESA out of ~25 ones that were submitted. In this work, the instrument performance for the near-nadir altimetry (GNSS-R) mode is assessed, including the effects of multi-path in the ISS structure, the electromagnetic-bias, and the orbital height decay. In the absence of ionospheric scintillations, the altimetry rms error is <50 cm for a swath <~250 km and for U10 <10 m/s. If the transmitted power is 3 dB higher (likely to happen at beginning of life of the GNSS spacecrafts), mission requirements (rms error is <50 cm) are met for all ISS heights and for U10 up to 15 m/s. However, around 1.5 GHz, the ionosphere can induce significant fading, from 2 to >20 dB at equatorial regions, mainly after sunset, which will seriously degrade the altimetry and the scatterometry performances of the instrument. PMID:28684724

ESA BRAT (Broadview Radar Altimetry Toolbox) and GUT (GOCE User Toolbox) toolboxes

NASA Astrophysics Data System (ADS)

Benveniste, J.; Ambrozio, A.; Restano, M.

2016-12-01

The Broadview Radar Altimetry Toolbox (BRAT) is a collection of tools designed to facilitate the processing of radar altimetry data from previous and current altimetry missions, including the upcoming Sentinel-3A L1 and L2 products. A tutorial is included providing plenty of use cases. BRAT's future release (4.0.0) is planned for September 2016. Based on the community feedback, the frontend has been further improved and simplified whereas the capability to use BRAT in conjunction with MATLAB/IDL or C/C++/Python/Fortran, allowing users to obtain desired data bypassing the data-formatting hassle, remains unchanged. Several kinds of computations can be done within BRAT involving the combination of data fields, that can be saved for future uses, either by using embedded formulas including those from oceanographic altimetry, or by implementing ad-hoc Python modules created by users to meet their needs. BRAT can also be used to quickly visualise data, or to translate data into other formats, e.g. from NetCDF to raster images. The GOCE User Toolbox (GUT) is a compilation of tools for the use and the analysis of GOCE gravity field models. It facilitates using, viewing and post-processing GOCE L2 data and allows gravity field data, in conjunction and consistently with any other auxiliary data set, to be pre-processed by beginners in gravity field processing, for oceanographic and hydrologic as well as for solid earth applications at both regional and global scales. Hence, GUT facilitates the extensive use of data acquired during GRACE and GOCE missions. In the current 3.0 version, GUT has been outfitted with a graphical user interface allowing users to visually program data processing workflows. Further enhancements aiming at facilitating the use of gradients, the anisotropic diffusive filtering, and the computation of Bouguer and isostatic gravity anomalies have been introduced. Packaged with GUT is also GUT's VCM (Variance-Covariance Matrix) tool for analysing GOCE

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

NASA Technical Reports Server (NTRS)

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

2012-01-01

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

Moving toward a Biomass Map of Boreal Eurasia based on ICESat GLAS, ASTER GDEM, and field measurements: Amount, Spatial distribution, and Statistical Uncertainties

NASA Astrophysics Data System (ADS)

Neigh, C. S.; Nelson, R. F.; Sun, G.; Ranson, J.; Montesano, P. M.; Margolis, H. A.

2011-12-01

The Eurasian boreal forest is the largest continuous forest in the world and contains a vast quantity of carbon stock that is currently vulnerable to loss from climate change. We develop and present an approach to map the spatial distribution of above ground biomass throughout this region. Our method combines satellite measurements from the Geoscience Laser Altimeter System (GLAS) that is carried on the Ice, Cloud and land Elevation Satellite ( ICESat), with the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global Digital Elevation Model (GDEM), and biomass field measurements collected from surveys from a number of different biomes throughout Boreal Eurasia. A slope model derived from the GDEM with quality control flags, and Moderate-resolution Imaging Spectroradiometer (MODIS) water mask was implemented to exclude poor quality GLAS shots and stratify measurements by MODIS International Geosphere Biosphere (IGBP) and World Wildlife Fund (WWF) ecozones. We derive equations from regional field measurements to estimate the spatial distribution of above ground biomass by land cover type within biome and present a map with uncertainties and limitations of this approach which can be used as a baseline for future studies.

Continental Scale Vegetation Structure Mapping Using Field Calibrated Landsat, ALOS Palsar And GLAS ICESat

NASA Astrophysics Data System (ADS)

Scarth, P.; Phinn, S. R.; Armston, J.; Lucas, R.

2015-12-01

Vertical plant profiles are important descriptors of canopy structure and are used to inform models of biomass, biodiversity and fire risk. In Australia, an approach has been developed to produce large area maps of vertical plant profiles by extrapolating waveform lidar estimates of vertical plant profiles from ICESat/GLAS using large area segmentation of ALOS PALSAR and Landsat satellite image products. The main assumption of this approach is that the vegetation height profiles are consistent across the segments defined from ALOS PALSAR and Landsat image products. More than 1500 field sites were used to develop an index of fractional cover using Landsat data. A time series of the green fraction was used to calculate the persistent green fraction continuously across the landscape. This was fused with ALOS PALSAR L-band Fine Beam Dual polarisation 25m data and used to segment the Australian landscapes. K-means clustering then grouped the segments with similar cover and backscatter into approximately 1000 clusters. Where GLAS-ICESat footprints intersected these clusters, canopy profiles were extracted and aggregated to produce a mean vertical vegetation profile for each cluster that was used to derive mean canopy and understorey height, depth and density. Due to the large number of returns, these retrievals are near continuous across the landscape, enabling them to be used for inventory and modelling applications. To validate this product, a radiative transfer model was adapted to map directional gap probability from airborne waveform lidar datasets to retrieve vertical plant profiles Comparison over several test sites show excellent agreement and work is underway to extend the analysis to improve national biomass mapping. The integration of the three datasets provide options for future operational monitoring of structure and AGB across large areas for quantifying carbon dynamics, structural change and biodiversity.

Geoscience Laser Altimeter System (GLAS) Loop Heat Pipes: An Eventual First Year On-Orbit

NASA Technical Reports Server (NTRS)

Grob, E.; Baker, C.; McCarthy, T.

2004-01-01

Goddard Space Flight Center's Geoscience Laser Altimeter System (GLAS) is the sole scientific instrument on the Ice, Cloud and land Elevation Satellite (ICESat) that was launched on January 12, 2003 from Vandenberg AFB. A thermal control architecture based on propylene Loop Heat Pipe technology was developed to provide selectable/stable temperature control for the lasers and other electronics over the widely varying mission environment. Following a nominal LHP and instrument start-up, the mission was interrupted with the failure of the first laser after only 36 days of operation. During the 5-month failure investigation, the two GLAS LHPs and the electronics operated nominally, using heaters as a substitute for the laser heat load. Just prior to resuming the mission, following a seasonal spacecraft yaw maneuver, one of the LHPs deprimed and created a thermal runaway condition that resulted in an emergency shutdown of the GLAS instrument. This paper presents details of the LHP anomaly, the resulting investigation and recovery, along with on-orbit flight data during these critical events.

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

NASA Astrophysics Data System (ADS)

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

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

Mesoscale resolution capability of altimetry: Present and future

NASA Astrophysics Data System (ADS)

Dufau, Claire; Orsztynowicz, Marion; Dibarboure, Gérald; Morrow, Rosemary; Le Traon, Pierre-Yves

2016-07-01

Wavenumber spectra of along-track Sea Surface Height from the most recent satellite radar altimetry missions [Jason-2, Cryosat-2, and SARAL/Altika) are used to determine the size of ocean dynamical features observable with the present altimetry constellation. A global analysis of the along-track 1-D mesoscale resolution capability of the present-day altimeter missions is proposed, based on a joint analysis of the spectral slopes in the mesoscale band and the error levels observed for horizontal wavelengths lower than 20km. The global sea level spectral slope distribution provided by Xu and Fu with Jason-1 data is revisited with more recent altimeter missions, and maps of altimeter error levels are provided and discussed for each mission. Seasonal variations of both spectral slopes and altimeter error levels are also analyzed for Jason-2. SARAL/Altika, with its lower error levels, is shown to detect smaller structures everywhere. All missions show substantial geographical and temporal variations in their mesoscale resolution capabilities, with variations depending mostly on the error level change but also on slight regional changes in the spectral slopes. In western boundary currents where the signal to noise ratio is favorable, the along-track mesoscale resolution is approximately 40 km for SARAL/AltiKa, 45 km for Cryosat-2, and 50 km for Jason-2. Finally, a prediction of the future 2-D mesoscale sea level resolution capability of the Surface Water and Ocean Topography (SWOT) mission is given using a simulated error level.

Experimental and theoretical determination of sea-state bias in radar altimetry

NASA Technical Reports Server (NTRS)

Stewart, Robert H.

1991-01-01

The major unknown error in radar altimetry is due to waves on the sea surface which cause the mean radar-reflecting surface to be displaced from mean sea level. This is the electromagnetic bias. The primary motivation for the project was to understand the causes of the bias so that the error it produces in radar altimetry could be calculated and removed from altimeter measurements made from space by the Topex/Poseidon altimetric satellite. The goals of the project were: (1) observe radar scatter at vertical incidence using a simple radar on a platform for a wide variety of environmental conditions at the same time wind and wave conditions were measured; (2) calculate electromagnetic bias from the radar observations; (3) investigate the limitations of the present theory describing radar scatter at vertical incidence; (4) compare measured electromagnetic bias with bias calculated from theory using measurements of wind and waves made at the time of the radar measurements; and (5) if possible, extend the theory so bias can be calculated for a wider range of environmental conditions.

A new Ellipsoidal Gravimetric-Satellite Altimetry Boundary Value Problem; Case study: High Resolution Geoid of Iran

NASA Astrophysics Data System (ADS)

Ardalan, A.; Safari, A.; Grafarend, E.

2003-04-01

A new ellipsoidal gravimetric-satellite altimetry boundary value problem has been developed and successfully tested. This boundary value problem has been constructed for gravity observables of the type (i) gravity potential (ii) gravity intensity (iii) deflection of vertical and (iv) satellite altimetry data. The developed boundary value problem is enjoying the ellipsoidal nature and as such can take advantage of high precision GPS observations in the set-up of the problem. The highlights of the solution are as follows: begin{itemize} Application of ellipsoidal harmonic expansion up to degree/order and ellipsoidal centrifugal field for the reduction of global gravity and isostasy effects from the gravity observable at the surface of the Earth. Application of ellipsoidal Newton integral on the equal area map projection surface for the reduction of residual mass effects within a radius of 55 km around the computational point. Ellipsoidal harmonic downward continuation of the residual observables from the surface of the earth down to the surface of reference ellipsoid using the ellipsoidal height of the observation points derived from GPS. Restore of the removed effects at the application points on the surface of reference ellipsoid. Conversion of the satellite altimetry derived heights of the water bodies into potential. Combination of the downward continued gravity information with the potential equivalent of the satellite altimetry derived heights of the water bodies. Application of ellipsoidal Bruns formula for converting the potential values on the surface of the reference ellipsoid into the geoidal heights (i.e. ellipsoidal heights of the geoid) with respect to the reference ellipsoid. Computation of the high-resolution geoid of Iran has successfully tested this new methodology!

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

NASA Technical Reports Server (NTRS)

Kay, Richard B.

1997-01-01

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

Satellite altimetry based rating curves throughout the entire Amazon basin

NASA Astrophysics Data System (ADS)

Paris, A.; Calmant, S.; Paiva, R. C.; Collischonn, W.; Silva, J. S.; Bonnet, M.; Seyler, F.

2013-05-01

The Amazonian basin is the largest hydrological basin all over the world. In the recent past years, the basin has experienced an unusual succession of extreme draughts and floods, which origin is still a matter of debate. Yet, the amount of data available is poor, both over time and space scales, due to factor like basin's size, access difficulty and so on. One of the major locks is to get discharge series distributed over the entire basin. Satellite altimetry can be used to improve our knowledge of the hydrological stream flow conditions in the basin, through rating curves. Rating curves are mathematical relationships between stage and discharge at a given place. The common way to determine the parameters of the relationship is to compute the non-linear regression between the discharge and stage series. In this study, the discharge data was obtained by simulation through the entire basin using the MGB-IPH model with TRMM Merge input rainfall data and assimilation of gage data, run from 1998 to 2010. The stage dataset is made of ~800 altimetry series at ENVISAT and JASON-2 virtual stations. Altimetry series span between 2002 and 2010. In the present work we present the benefits of using stochastic methods instead of probabilistic ones to determine a dataset of rating curve parameters which are consistent throughout the entire Amazon basin. The rating curve parameters have been computed using a parameter optimization technique based on Markov Chain Monte Carlo sampler and Bayesian inference scheme. This technique provides an estimate of the best parameters for the rating curve, but also their posterior probability distribution, allowing the determination of a credibility interval for the rating curve. Also is included in the rating curve determination the error over discharges estimates from the MGB-IPH model. These MGB-IPH errors come from either errors in the discharge derived from the gage readings or errors in the satellite rainfall estimates. The present

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

NASA Astrophysics Data System (ADS)

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

2015-09-01

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

Analysis of short pulse laser altimetry data obtained over horizontal path

NASA Technical Reports Server (NTRS)

Im, K. E.; Tsai, B. M.; Gardner, C. S.

1983-01-01

Recent pulsed measurements of atmospheric delay obtained by ranging to the more realistic targets including a simulated ocean target and an extended plate target are discussed. These measurements are used to estimate the expected timing accuracy of a correlation receiver system. The experimental work was conducted using a pulsed two color laser altimeter.

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

NASA Astrophysics Data System (ADS)

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

2016-04-01

Remote sensing provides valuable data for parameterization and updating of hydrological models, for example water level measurements of inland water bodies from satellite radar altimeters. Satellite altimetry data from repeat-orbit missions such as Envisat, ERS or Jason has been used in many studies, also synthetic wide-swath altimetry data as expected from the SWOT mission. This study is one of the first hydrologic applications of altimetry data from a drifting orbit satellite mission, namely CryoSat-2. CryoSat-2 is equipped with the SIRAL instrument, a new type of radar altimeter similar to SRAL on Sentinel-3. CryoSat-2 SARIn level 2 data is used to improve a 1D hydrodynamic model of the Brahmaputra river basin in South Asia set up in the DHI MIKE 11 software. CryoSat-2 water levels were extracted over river masks derived from Landsat imagery. After discharge calibration, simulated water levels were fitted to the CryoSat-2 data along the Assam valley by adapting cross section shapes and datums. The resulting hydrodynamic model shows accurate spatio-temporal representation of water levels, which is a prerequisite for real-time model updating by assimilation of CryoSat-2 altimetry or multi-mission data in general. For this task, a data assimilation framework has been developed and linked with the MIKE 11 model. It is a flexible framework that can assimilate water level data which are arbitrarily distributed in time and space. Different types of error models, data assimilation methods, etc. can easily be used and tested. Furthermore, it is not only possible to update the water level of the hydrodynamic model, but also the states of the rainfall-runoff models providing the forcing of the hydrodynamic model. The setup has been used to assimilate CryoSat-2 observations over the Assam valley for the years 2010 to 2013. Different data assimilation methods and localizations were tested, together with different model error representations. Furthermore, the impact of

Progress in diode-pumped alexandrite lasers as a new resource for future space lidar missions

NASA Astrophysics Data System (ADS)

Damzen, M. J.; Thomas, G. M.; Teppitaksak, A.; Minassian, A.

2017-11-01

Satellite-based remote sensing using laser-based lidar techniques provides a powerful tool for global 3-D mapping of atmospheric species (e.g. CO2, ozone, clouds, aerosols), physical attributes of the atmosphere (e.g. temperature, wind speed), and spectral indicators of Earth features (e.g. vegetation, water). Such information provides a valuable source for weather prediction, understanding of climate change, atmospheric science and health of the Earth eco-system. Similarly, laser-based altimetry can provide high precision ground topography mapping and more complex 3-D mapping (e.g. canopy height profiling). The lidar technique requires use of cutting-edge laser technologies and engineered designs that are capable of enduring the space environment over the mission lifetime. The laser must operate with suitably high electrical-to-optical efficiency and risk reduction strategy adopted to mitigate against laser failure or excessive operational degradation of laser performance.

Mass Evolution of Mediterranean, Black, Red, and Caspian Seas from GRACE and Altimetry: Accuracy Assessment and Solution Calibration

NASA Technical Reports Server (NTRS)

Loomis, B. D.; Luthcke, S. B.

2016-01-01

We present new measurements of mass evolution for the Mediterranean, Black, Red, and Caspian Seas as determined by the NASA Goddard Space Flight Center (GSFC) GRACE time-variable global gravity mascon solutions. These new solutions are compared to sea surface altimetry measurements of sea level anomalies with steric corrections applied. To assess their accuracy, the GRACE and altimetry-derived solutions are applied to the set of forward models used by GSFC for processing the GRACE Level-1B datasets, with the resulting inter-satellite range acceleration residuals providing a useful metric for analyzing solution quality.

Tunable solid-state laser technology for applications to scientific and technological experiments from space

NASA Technical Reports Server (NTRS)

Allario, F.; Taylor, L. V.

1986-01-01

Current plans for the Earth Observing System (EOS) include development of a lidar facility to conduct scientific experiments from a polar orbiting platforms. A recommended set of experiments were scoped, which includes techniques of atmospheric backscatter (Lidar), Differential Absorption Lidar (DIAL), altimetry, and retroranging. Preliminary assessments of the resources (power, weight, volume) required by the Eos Lidar Facility were conducted. A research program in tunable solid state laser technology was developed, which includes laser materials development, modeling and experiments on the physics of solid state laser materials, and development of solid state laser transmitters with a strong focus on Eos scientific investigations. Some of the system studies that were conducted which highlight the payoff of solid state laser technology for the Eos scientific investigations will be discussed. Additionally, a summary of some promising research results which have recently emerged from the research program will be presented.

Assessing altimetry close to the coast

NASA Astrophysics Data System (ADS)

Quartly, G. D.; Nencioli, F.; Conley, D.; Abdalla, S.

2017-10-01

Radar altimetry provides measurements of sea surface elevation, wind speed and wave height, which are used operationally by many agencies and businesses, as well as for scientific research to understand the changes in the oceanatmosphere interface. For the data to be trustworthy they need to be assessed for consistency, and for bias relative to various validation datasets. Sentinel-3A, launched in Feb. 2016, promises, through new technology, to be better able to retrieve useful measurements in the coastal zone; the purpose of this paper is develop ideas on how the performance of this instrument can be assessed in that specific environment. We investigate the magnitude of short-term variability in wave height and range, and explain how two validation facilities in the southwest UK may be used.

Mass-induced sea level variations in the Red Sea from GRACE, steric-corrected altimetry, in situ bottom pressure records, and hydrographic observations

NASA Astrophysics Data System (ADS)

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

2014-08-01

An annual amplitude of ∼18 cm mass-induced sea level variations (SLV) in the Red Sea is detected from the Gravity Recovery and Climate Experiment (GRACE) satellites and steric-corrected altimetry from 2003 to 2011. The annual mass variations in the region dominate the mean SLV, and generally reach maximum in late January/early February. The annual steric component of the mean SLV is relatively small (<3 cm) and out of phase of the mass-induced SLV. In situ bottom pressure records at the eastern coast of the Red Sea validate the high mass variability observed by steric-corrected altimetry and GRACE. In addition, the horizontal water mass flux of the Red Sea estimated from GRACE and steric-corrected altimetry is validated by hydrographic observations.

Vertical land motion along the coast of Louisiana: Integrating satellite altimetry, tide gauge and GPS

NASA Astrophysics Data System (ADS)

Dixon, T. H.; A Karegar, M.; Uebbing, B.; Kusche, J.; Fenoglio-Marc, L.

2017-12-01

Coastal Louisiana is experiencing the highest rate of relative sea-level rise in North America due to the combination of sea-level rise and subsidence of the deltaic plain. The land subsidence in this region is studied using various techniques, with continuous GPS site providing high temporal resolution. Here, we use high resolution tide-gauge data and advanced processing of satellite altimetry to derive vertical displacements time series at NOAA tide-gauge stations along the coast (Figure 1). We apply state-of-the-art retracking techniques to process raw altimetry data, allowing high accuracy on range measurements close to the coast. Data from Jason-1, -2 and -3, Envisat, Saral and Cryosat-2 are used, corrected for solid Earth tide, pole tide and tidal ocean loading, using background models consistent with the GPS processing technique. We reprocess the available GPS data using precise point positioning and estimate the rate uncertainty accounting for correlated noise. The displacement time series are derived by directly subtracting tide-gauge data from the altimetry sea-level anomaly data. The quality of the derived displacement rates is evaluated in Grand Isle, Amerada Pass and Shell Beach where GPS data are available adjacent to the tide gauges. We use this technique to infer vertical displacement at tide gauges in New Orleans (New Canal Station) and Port Fourchon and Southwest Pass along the coastline.

Imaging Small-scale Seafloor and Sub-seafloor Tectonic Fabric Using Satellite Altimetry

NASA Astrophysics Data System (ADS)

Sandwell, D. T.; Müller, D.; Matthews, K. J.; Smith, W. H. F.

2017-12-01

Marine gravity anomalies derived from satellite radar altimetry now provide an unprecedented resolution of about 7 km for mapping small-scale seafloor and sub-seafloor tectonic fabric. These gravity maps are improving rapidly because three satellite altimeters are currently collecting data with dense track coverage: (1) CryoSat-2 has routinely collected altimetry data over ice, land, and ocean since July 2010. The satellite has a long 369-day repeat cycle resulting in an average ground track spacing of 3.5 km at the equator. To date it has completed more than 7 geodetic mappings of the ocean surface. (2) The SARAL AltiKa altimeter began a non-repeat orbit phase in July 2016. AltiKa has a new Ka-band instrument with a factor of 2 better range precision than all previous altimeters. (3) Jason-2 was placed in a geodetic orbit starting July 2017. It has lower inclination coverage to provide improved gravity recovery for N-S trending anomalies. These data combined with sparse soundings will provide a dramatic improvement in predicted bathymetry and thus help guide future deep ocean surveys. The most recent global marine gravity anomaly map based on these geodetic mission data with 2-pass retracking for optimal range precision has an accuracy that is 2-4 times better than the maps derived from Geosat and ERS-1. The new data reveal the detailed fabric of fracture zones, previously unmapped, now extinct oceanic microplates in the central Pacific, and fault networks buried beneath thick sediments along continental margins. By combining satellite altimetry with marine magnetic anomalies and seafloor age dates from rock samples we are able to pinpoint the geometry and age of major plate reorganizations, particularly the enigmatic 100 Ma event, which occurred during the Cretaceous Magnetic Superchron.

An empirical determination of the effects of sea state bias on Seasat altimetry

NASA Technical Reports Server (NTRS)

Born, G. H.; Richards, M. A.; Rosborough, G. W.

1982-01-01

A linear empirical model has been developed for the correction of sea state bias effects, in Seasat altimetry data altitude measurements, that are due to (1) electromagnetic bias caused by the fact that ocean wave troughs reflect the altimeter signal more strongly than the crests, shifting the apparent mean sea level toward the wave troughs, and (2) an independent instrument-related bias resulting from the inability of height corrections applied in the ground processor to compensate for simplifying assumptions made for the processor aboard Seasat. After applying appropriate corrections to the altimetry data, an empirical model for the sea state bias is obtained by differencing significant wave height and height measurements from coincident ground tracks. Height differences are minimized by solving for the coefficient of a linear relationship between height differences and wave height differences that minimize the height differences. In more than 50% of the 36 cases examined, 7% of the value of significant wave height should be subtracted for sea state bias correction.

Guiding Biogeochemical Campaigns with High Resolution Altimetry: Waiting for the SWOT Mission

NASA Astrophysics Data System (ADS)

d'Ovidio, Francesco; Zhou, Meng; Park, Young Hyang; Nencioli, Francesco; Resplandy, Laure; Doglioli, Andrea; Petrenko, Anne; Blain, Stephane; Queguiner, Bernard

2013-09-01

Biogeochemical processes in the ocean are strongly affected by the horizontal mesoscale ( 10-100 km) and submesoscale (1-10 km) circulation. Eddies and filaments can create strong dishomogeneity, either amplifying small-scale diffusion processes (mixing) or creating tracer reservoirs. This variability has a direct effect on the biogeochemical budgets - controlling for instances tracer fluxes across climatological fronts, or part of the vertical exchanges. This variability also provides a challenge to in situ studies, because sites few tens of kms or few weeks apart may be representative of very different situations. Here we discuss how altimetry observation can be exploited in order to track in near- real-time transport barriers and mixing regions and guide a biogeochemical adaptative sampling strategy. As a case study, we focus on the recent KEOPS2 campaign (Kerguelen region, October-November 2012) which employed Lagrangian diagnostics of a specifically designed high resolution, regional altimetric product produced by CLS (with support from CNES) analyzed with several Lagrangian diagnostics. Such approach anticipates possible uses of incoming high resolution altimetry data for biogeochemical studies.

Potential Elevation Biases for Laser Altimeters from Subsurface Scattered Photons: Laboratory and Model Exploration of Green Light Scattering in Snow

NASA Astrophysics Data System (ADS)

Greeley, A.; Neumann, T.; Markus, T.; Kurtz, N. T.; Cook, W. B.

2015-12-01

Existing visible light laser altimeters such as MABEL (Multiple Altimeter Beam Experimental Lidar) - a single photon counting simulator for ATLAS (Advanced Topographic Laser Altimeter System) on NASA's upcoming ICESat-2 mission - and ATM (Airborne Topographic Mapper) on NASA's Operation IceBridge mission provide scientists a view of Earth's ice sheets, glaciers, and sea ice with unprecedented detail. Precise calibration of these instruments is needed to understand rapidly changing parameters like sea ice freeboard and to measure optical properties of surfaces like snow covered ice sheets using subsurface scattered photons. Photons travelling into snow, ice, or water before scattering back to the altimeter receiving system (subsurface photons) travel farther and longer than photons scattering off the surface only, causing a bias in the measured elevation. We seek to identify subsurface photons in a laboratory setting using a flight-tested laser altimeter (MABEL) and to quantify their effect on surface elevation estimates for laser altimeter systems. We also compare these estimates with previous laboratory measurements of green laser light transmission through snow, as well as Monte Carlo simulations of backscattered photons from snow.

Development of Elevation and Relief Databases for ICESat-2/ATLAS Receiver Algorithms

NASA Astrophysics Data System (ADS)

Leigh, H. W.; Magruder, L. A.; Carabajal, C. C.; Saba, J. L.; Urban, T. J.; Mcgarry, J.; Schutz, B. E.

2013-12-01

The Advanced Topographic Laser Altimeter System (ATLAS) is planned to launch onboard NASA's ICESat-2 spacecraft in 2016. ATLAS operates at a wavelength of 532 nm with a laser repeat rate of 10 kHz and 6 individual laser footprints. The satellite will be in a 500 km, 91-day repeat ground track orbit at an inclination of 92°. A set of onboard Receiver Algorithms has been developed to reduce the data volume and data rate to acceptable levels while still transmitting the relevant ranging data. The onboard algorithms limit the data volume by distinguishing between surface returns and background noise and selecting a small vertical region around the surface return to be included in telemetry. The algorithms make use of signal processing techniques, along with three databases, the Digital Elevation Model (DEM), the Digital Relief Map (DRM), and the Surface Reference Mask (SRM), to find the signal and determine the appropriate dynamic range of vertical data surrounding the surface for downlink. The DEM provides software-based range gating for ATLAS. This approach allows the algorithm to limit the surface signal search to the vertical region between minimum and maximum elevations provided by the DEM (plus some margin to account for uncertainties). The DEM is constructed in a nested, three-tiered grid to account for a hardware constraint limiting the maximum vertical range to 6 km. The DRM is used to select the vertical width of the telemetry band around the surface return. The DRM contains global values of relief calculated along 140 m and 700 m ground track segments consistent with a 92° orbit. The DRM must contain the maximum value of relief seen in any given area, but must be as close to truth as possible as the DRM directly affects data volume. The SRM, which has been developed independently from the DEM and DRM, is used to set parameters within the algorithm and select telemetry bands for downlink. Both the DEM and DRM are constructed from publicly available digital

Improved satellite observations in coastal areas from altimetry and SAR

NASA Astrophysics Data System (ADS)

Cipollini, Paolo; Martin, Adrien; Gommenginger, Christine; Calafat, Francisco

2017-04-01

The coastal environment is under constant pressure by natural forces and anthropogenic activities and is very sensitive to climate change. Observations of many physical and biological parameters are critical for its monitoring and management. Satellite observations constitute an efficient way to observe the global coastal environment, but ocean satellite observations have often been designed and optimised for the open ocean: algorithms and processing techniques need to be revisited and adapted for application in the coastal zone. A case in point is that of satellite altimetry, which over the oceans is regarded as one of the most successful remote sensing techniques, as it has allowed an unprecedented mapping of the ocean surface dynamics at the large- and meso-scale. With the improvements in orbit models, radar processing, atmospheric and geophysical effect corrections that have emerged over the years, altimetry gives today also a very accurate estimation of the rate of sea level rise and its geographical variability. However, altimetric data in the near-land strip (0 to 50 km from the coastline) are often flagged as bad and left unused, essentially owing to 1) difficulties with the corrections; and/or 2) the modification of the radar returns due to the presence of land in the footprint, which makes the fitting of the altimetric echoes with a waveform model (the so-called "retracking") problematic. Techniques to recover meaningful estimates of the altimeter-derived parameters (height, significant wave height and wind) in the coastal zone have been developed and lead to a number of new applications, which will be presented here. The new observation from coastal altimetry are highly synergistic with Synthetic Aperture Radar (SAR). SAR imagers measure the backscattered signal from the ocean surface at spatial resolution better than 100m. This backscattered signal gives knowledge on the sea surface roughness, which is related to wind and waves. The very high resolution

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

NASA Astrophysics Data System (ADS)

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

GNSS VTEC calibration using satellite altimetry and LEO data

NASA Astrophysics Data System (ADS)

Alizadeh, M. Mahdi; Schuh, Harald

2015-04-01

Among different systems remote sensing the ionosphere, space geodetic techniques have turned into a promising tool for monitoring and modeling the ionospheric parameters. Due to the fact that ionosphere is a dispersive medium, the signals travelling through this medium provide information about the parameters of the ionosphere in terms of Total Electron Content (TEC) or electron density along the ray path. The classical input data for development of Global Ionosphere Maps (GIM) of the Vertical Total Electron Content (VTEC) is obtained from the dual-frequency Global Navigation Satellite Systems (GNSS) ground-based observations. Nevertheless due to the fact that GNSS ground stations are in-homogeneously distributed with poor coverage over the oceans (namely southern Pacific and southern Atlantic) and also parts of Africa, the precision of VTEC maps are rather low in these areas. From long term analyses it is believed that the International GNSS Service (IGS) VTEC maps have an accuracy of 1-2 TECU in areas well covered with GNSS receivers; conversely, in areas with poor coverage the accuracy can be degraded by a factor of up to five. On the other hand dual-frequency satellite altimetry missions (such as Jason-1&2) provide direct VTEC values exactly over the oceans, and furthermore the Low Earth Orbiting (LEO) satellites such as the Formosat-3/COSMIC (F/C) provide about a great number of globally distributed occultation measurements per day, which can be used to obtain VTEC values. Combining these data with the ground-based data improves the accuracy and reliability of the VTEC maps by closing of observation gaps that arise when using ground-based data only. In this approach an essential step is the evaluation and calibration of the different data sources used for the combination procedure. This study investigates the compatibility of calibrated TEC observables derived from GNSS dual-frequency data, recorded at global ground-based station networks, with space-based TEC

Lidar Technology at the Goddard Laser and Electro-Optics Branch

NASA Technical Reports Server (NTRS)

Heaps, William S.; Obenschain, Arthur F. (Technical Monitor)

2000-01-01

The Laser and Electro-Optics Branch at Goddard Space flight Center was established about three years ago to provide a focused center of engineering support and technology development in these disciplines with an emphasis on spaced based instruments for Earth and Space Science. The Branch has approximately 15 engineers and technicians with backgrounds in physics, optics, and electrical engineering. Members of the Branch are currently supporting a number of space based lidar efforts as well as several technology efforts aimed at enabling future missions. The largest effort within the Branch is support of the Ice, Cloud, and land Elevation Satellite (ICESAT) carrying the Geoscience Laser Altimeter System (GLAS) instrument. The ICESAT/GLAS primary science objectives are: 1) To determine the mass balance of the polar ice sheets and their contributions to global sea level change; and 2) To obtain essential data for prediction of future changes in ice volume and sea-level. The secondary science objectives are: 1) To measure cloud heights and the vertical structure of clouds and aerosols in the atmosphere; 2) To map the topography of land surfaces; and 3) To measure roughness, reflectivity, vegetation heights, snow-cover, and sea-ice surface characteristics. Our efforts have concentrated on the GLAS receiver component development, the Laser Reference Sensor for the Stellar Reference System, the GLAS fiber optics subsystems, and the prelaunch calibration facilities. We will report on our efforts in the development of the space qualified interference filter [Allan], etalon filter, photon counting detectors, etalor/laser tracking system, and instrument fiber optics, as well as specification and selection of the star tracker and development of the calibration test bed. We are also engaged in development work on lidar sounders for chemical species. We are developing new lidar technology to enable a new class of miniature lidar instruments that are compatible with small

25 years of elevation changes of the Greenland Ice Sheet from ERS, Envisat, and CryoSat-2 radar altimetry

NASA Astrophysics Data System (ADS)

Sandberg Sørensen, Louise; Simonsen, Sebastian B.; Forsberg, René; Khvorostovsky, Kirill; Meister, Rakia; Engdahl, Marcus E.

2018-08-01

The shape of the large ice sheets responds rapidly to climate change, making the elevation changes of these ice-covered regions an essential climate variable. Consistent, long time series of these elevation changes are of great scientific value. Here, we present a newly-developed data product of 25 years of elevation changes of the Greenland Ice Sheet, derived from satellite radar altimetry. The data product is made publicly available within the Greenland Ice Sheets project as part of the ESA Climate Change Initiative programme. Analyzing repeated elevation measurements from radar altimetry is widely used for monitoring changes of ice-covered regions. The Greenland Ice Sheet has been mapped by conventional radar altimetry since the launch of ERS-1 in 1991, which was followed by ERS-2, Envisat and currently CryoSat-2. The recently launched Sentinel-3A will provide a continuation of the radar altimetry time series. Since 2010, CryoSat-2 has for the first time measured the changes in the coastal regions of the ice sheet with radar altimetry, with its novel SAR Interferometric (SARIn) mode, which provides improved measurement over regions with steep slopes. Here, we apply a mission-specific combination of cross-over, along-track and plane-fit elevation change algorithms to radar data from the ERS-1, ERS-2, Envisat and CryoSat-2 radar missions, resulting in 25 years of nearly continuous elevation change estimates (1992-2016) of the Greenland Ice Sheet. This analysis has been made possible through the recent reprocessing in the REAPER project, of data from the ERS-1 and ERS-2 radar missions, making them consistent with Envisat data. The 25 years of elevation changes are evaluated as 5-year running means, shifted almost continuously by one year. A clear acceleration in thinning is evident in the 5-year maps of elevation following 2003, while only small elevation changes observed in the maps from the 1990s.

Self-Raman Nd:YVO4 laser and electro-optic technology for space-based sodium lidar instrument

NASA Astrophysics Data System (ADS)

Krainak, Michael A.; Yu, Anthony W.; Janches, Diego; Jones, Sarah L.; Blagojevic, Branimir; Chen, Jeffrey

2014-02-01

We are developing a laser and electro-optic technology to remotely measure Sodium (Na) by adapting existing lidar technology with space flight heritage. The developed instrumentation will serve as the core for the planning of an Heliophysics mission targeted to study the composition and dynamics of Earth's mesosphere based on a spaceborne lidar that will measure the mesospheric Na layer. We present performance results from our diode-pumped tunable Q-switched self-Raman c-cut Nd:YVO4 laser with intra-cavity frequency doubling that produces multi-watt 589 nm wavelength output. The c-cut Nd:YVO4 laser has a fundamental wavelength that is tunable from 1063-1067 nm. A CW External Cavity diode laser is used as a injection seeder to provide single-frequency grating tunable output around 1066 nm. The injection-seeded self-Raman shifted Nd:VO4 laser is tuned across the sodium vapor D2 line at 589 nm. We will review technologies that provide strong leverage for the sodium lidar laser system with strong heritage from the Ice Cloud and Land Elevation Satellite-2 (ICESat-2) Advanced Topographic Laser Altimeter System (ATLAS). These include a space-qualified frequency-doubled 9W @ 532 nm wavelength Nd:YVO4 laser, a tandem interference filter temperature-stabilized fused-silica-etalon receiver and high-bandwidth photon-counting detectors.

Self-Raman Nd:YVO4 Laser and Electro-Optic Technology for Space-Based Sodium Lidar Instrument

NASA Technical Reports Server (NTRS)

Krainak, Michael A.; Yu, Anthony W.; Janches, Diego; Jones, Sarah L.; Blagojevic, Branimir; Chen, Jeffrey

2014-01-01

We are developing a laser and electro-optic technology to remotely measure Sodium (Na) by adapting existing lidar technology with space flight heritage. The developed instrumentation will serve as the core for the planning of an Heliophysics mission targeted to study the composition and dynamics of Earth's mesosphere based on a spaceborne lidar that will measure the mesospheric Na layer. We present performance results from our diode-pumped tunable Q-switched self-Raman c-cut Nd:YVO4 laser with intra-cavity frequency doubling that produces multi-watt 589 nm wavelength output. The c-cut Nd:YVO4 laser has a fundamental wavelength that is tunable from 1063-1067 nanometers. A CW (Continuous Wave) External Cavity diode laser is used as a injection seeder to provide single-frequency grating tunable output around 1066 nanometers. The injection-seeded self-Raman shifted Nd:VO4 laser is tuned across the sodium vapor D2 line at 589 nanometers. We will review technologies that provide strong leverage for the sodium lidar laser system with strong heritage from the Ice Cloud and Land Elevation Satellite-2 (ICESat-2) Advanced Topographic Laser Altimeter System (ATLAS). These include a space-qualified frequency-doubled 9 watts-at-532-nanometer wavelength Nd:YVO4 laser, a tandem interference filter temperature-stabilized fused-silica-etalon receiver and high-bandwidth photon-counting detectors.

High-resolution measurements of surface topography with airborne laser altimetry and the global positioning system

NASA Technical Reports Server (NTRS)

Garvin, James B.; Bufton, Jack L.; Cavanaugh, John F.; Krabill, William B.; Clem, Thomas D.; Frederick, Earl B.; Ward, John L.

1991-01-01

Recently, an airborne lidar system that measures laser pulse time-of-flight and the distortion of the pulse waveform upon reflection from earth surface terrain features was developed and is now operational. This instrument is combined with Global Positioning System (GPS) receivers and a two-axis gyroscope for accurate recovery of aircraft position and pointing attitude. The laser altimeter system is mounted on a high-altitude aircraft platform and operated in a repetitively-pulsed mode for measurements of surface elevation profiles at nadir. The laser transmitter makes use of recently developed short-pulse diode-pumped solid-state laser technology in Q-switched Nd:YAG operating at its fundamental wavelength of 1064 nm. A reflector telescope and silicon avalanche photodiode are the basis of the optical receiver. A high-speed time-interval unit and a separate high-bandwidth waveform digitizer under microcomputer control are used to process the backscattered pulses for measurements of terrain. Other aspects of the lidar system are briefly discussed.

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

NASA Astrophysics Data System (ADS)

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

2011-12-01

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

Increasing Wastage of the Bering and Malaspina Glacier Systems, Alaska-Yukon, 1972 to 2006

NASA Astrophysics Data System (ADS)

Muskett, R. R.; Lingle, C. S.; Sauber, J. M.; Tangborn, W. V.; Rabus, B. T.; Echelmeyer, K. A.

2007-12-01

Ice dynamics are integral to the net mass balances of the huge Bagley-Bering and Seward-Malaspina Glacier systems of south-central Alaska. Quasi-periodic surging of the main trunks and some large tributaries of these exceptionally active glacier systems are important contributors to their increasing volume losses in the present rapidly-warming climate, because surges rapidly transport ice from higher elevations, where it is "safe," to lower elevations where it subject to increased ablation. New estimates of mass losses from the Bering and Malaspina Glacier systems during 1972-2006 were derived from analysis of (i) digital elevation models (DEMs) synthesized from airborne and spaceborne interferometric synthetic aperture radar (InSAR); (ii) small-aircraft laser altimetry; and (iii) spaceborne laser altimetry acquired by ICESat. Adjustments for estimated seasonal snow accumulation were applied to datasets acquired at times subsequent to late summer. Adjustments for systematic DEM biases were also applied. The area-average lowering rate on the main-trunk of the Bering Glacier system from 1972 to 1995 was 0.9 ± 0.1 m/yr. The major 1993 to '95 surge moved ice rapidly from the surge reservoir into the piedmont lobe where rapid surface melting was facilitated by the heavily crevassed surface. The lowering rate accelerated to 3.0 ± 0.1 m/yr during 1995 to 2000, then moderated to 1.4 ± 0.1 m/yr during 2000 to 2003. On the Malaspina Glacier system, the area-average rate of surface lowering was 1.4 ± 0.1 m/yr during 1972 to 1999. It then increased by 30% to 1.8 ± 0.1 m/yr during 1999 to 2002. Near-concurrent surges of Agassiz Glacier (a west piedmont lobe tributary), lower Seward Glacier (main source for the central Seward lobe), and Marvine Glacier (a detached former tributary of the eastern piedmont lobe) were observed during this 3-year time span of increased surface lowering. Recent ICESat-derived elevation changes from 2003 to 2006 indicate increasing wastage on the

National-scale aboveground biomass geostatistical mapping with FIA inventory and GLAS data: Preparation for sparsely sampled lidar assisted forest inventory

NASA Astrophysics Data System (ADS)

Babcock, C. R.; Finley, A. O.; Andersen, H. E.; Moskal, L. M.; Morton, D. C.; Cook, B.; Nelson, R.

2017-12-01

Upcoming satellite lidar missions, such as GEDI and IceSat-2, are designed to collect laser altimetry data from space for narrow bands along orbital tracts. As a result lidar metric sets derived from these sources will not be of complete spatial coverage. This lack of complete coverage, or sparsity, means traditional regression approaches that consider lidar metrics as explanatory variables (without error) cannot be used to generate wall-to-wall maps of forest inventory variables. We implement a coregionalization framework to jointly model sparsely sampled lidar information and point-referenced forest variable measurements to create wall-to-wall maps with full probabilistic uncertainty quantification of all inputs. We inform the model with USFS Forest Inventory and Analysis (FIA) in-situ forest measurements and GLAS lidar data to spatially predict aboveground forest biomass (AGB) across the contiguous US. We cast our model within a Bayesian hierarchical framework to better model complex space-varying correlation structures among the lidar metrics and FIA data, which yields improved prediction and uncertainty assessment. To circumvent computational difficulties that arise when fitting complex geostatistical models to massive datasets, we use a Nearest Neighbor Gaussian process (NNGP) prior. Results indicate that a coregionalization modeling approach to leveraging sampled lidar data to improve AGB estimation is effective. Further, fitting the coregionalization model within a Bayesian mode of inference allows for AGB quantification across scales ranging from individual pixel estimates of AGB density to total AGB for the continental US with uncertainty. The coregionalization framework examined here is directly applicable to future spaceborne lidar acquisitions from GEDI and IceSat-2. Pairing these lidar sources with the extensive FIA forest monitoring plot network using a joint prediction framework, such as the coregionalization model explored here, offers the

Polarimetric, Two-Color, Photon-Counting Laser Altimeter Measurements of Forest Canopy Structure

NASA Technical Reports Server (NTRS)

Harding, David J.; Dabney, Philip W.; Valett, Susan

2011-01-01

Laser altimeter measurements of forest stands with distinct structures and compositions have been acquired at 532 nm (green) and 1064 nm (near-infrared) wavelengths and parallel and perpendicular polarization states using the Slope Imaging Multi-polarization Photon Counting Lidar (SIMPL). The micropulse, single photon ranging measurement approach employed by SIMPL provides canopy structure measurements with high vertical and spatial resolution. Using a height distribution analysis method adapted from conventional, 1064 nm, full-waveform lidar remote sensing, the sensitivity of two parameters commonly used for above-ground biomass estimation are compared as a function of wavelength. The results for the height of median energy (HOME) and canopy cover are for the most part very similar, indicating biomass estimations using lidars operating at green and near-infrared wavelengths will yield comparable estimates. The expected detection of increasing depolarization with depth into the canopies due to volume multiple-scattering was not observed, possibly due to the small laser footprint and the small detector field of view used in the SIMPL instrument. The results of this work provide pathfinder information for NASA's ICESat-2 mission that will employ a 532 nm, micropulse, photon counting laser altimeter.

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

NASA Astrophysics Data System (ADS)

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.

ICESat Observations of Seasonal and Interannual Variations of Sea-Ice Freeboard and Estimated Thickness in the Weddell Sea, Antarctica (2003-2009)

NASA Technical Reports Server (NTRS)

Yi, Donghui; Robbins, John W.

2010-01-01

Sea-ice freeboard heights for 17 ICESat campaign periods from 2003 to 2009 are derived from ICESat data. Freeboard is combined with snow depth from Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) data and nominal densities of snow, water and sea ice, to estimate sea-ice thickness. Sea-ice freeboard and thickness distributions show clear seasonal variations that reflect the yearly cycle of growth and decay of the Weddell Sea (Antarctica) pack ice. During October-November, sea ice grows to its seasonal maximum both in area and thickness; the mean freeboards are 0.33-0.41 m and the mean thicknesses are 2.10-2.59 m. During February-March, thinner sea ice melts away and the sea-ice pack is mainly distributed in the west Weddell Sea; the mean freeboards are 0.35-0.46 m and the mean thicknesses are 1.48-1.94 m. During May-June, the mean freeboards and thicknesses are 0.26-0.29 m and 1.32-1.37 m, respectively. The 6 year trends in sea-ice extent and volume are (0.023+/-0.051) x 10(exp 6)sq km/a (0.45%/a) and (0.007+/-1.0.092) x 10(exp 3)cu km/a (0.08%/a); however, the large standard deviations indicate that these positive trends are not statistically significant.

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

NASA Astrophysics Data System (ADS)

Montenbruck, Oliver; Hackel, Stefan; Jäggi, Adrian

2017-11-01

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

Observations of the Mf ocean tide from Geosat altimetry

NASA Technical Reports Server (NTRS)

Cartwright, David E.; Ray, Richard D.

1990-01-01

Zonal averages of the 13.66-day Mf tide are derived from one year of Geosat altimetry records. The orbit errors are reduced by 1/revolution corrections taken over long (several day) arcs. The short-period tides are removed using a model previously derived from the same data. The Mf zonal averages indicate definite nonequilibrium character at nearly all latitudes. The imaginary admittances indicate a Q of at least 8; such a value is consistent with a simplified theory of coupled gravitational and vorticity modes and suggests a value for Proudman's 'friction period' about 123 days.

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

NASA Astrophysics Data System (ADS)

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

2016-05-01

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

Sea ice thickness derived from radar altimetry: achievements and future plans

NASA Astrophysics Data System (ADS)

Ricker, R.; Hendricks, S.; Paul, S.; Kaleschke, L.; Tian-Kunze, X.

2017-12-01

The retrieval of Arctic sea ice thickness is one of the major objectives of the European CryoSat-2 radar altimeter mission and the 7-year long period of operation has produced an unprecedented record of monthly sea ice thickness information. We present CryoSat-2 results that show changes and variability of Arctic sea ice from the winter season 2010/2011 until fall 2017. CryoSat-2, however, was designed to observe thick perennial sea ice, while an accurate retrieval of thin seasonal sea ice is more challenging. We have therefore developed a method of completing and improving Arctic sea ice thickness information within the ESA SMOS+ Sea Ice project by merging CryoSat-2 and SMOS sea ice thickness retrievals. Using these satellite missions together overcomes several issues of single-mission retrievals and provides a more accurate and comprehensive view on the state of Arctic sea-ice thickness at higher temporal resolution. However, stand-alone CryoSat-2 observations can be used as reference data for the exploitation of older pulse-limited radar altimetry data sets over sea ice. In order to observe trends in sea ice thickness, it is required to minimize inter-mission biases between subsequent satellite missions. Within the ESA Climate Change Initiative (CCI) on Sea Ice, a climate data record of sea ice thickness derived from satellite radar altimetry has been developed for both hemispheres, based on the 15-year (2002-2017) monthly retrievals from Envisat and CryoSat-2 and calibrated in the 2010-2012 overlap period. The next step in promoting the utilization of sea ice thickness information from radar altimetry is to provide products by a service that meets the requirements for climate applications and operational systems. This task will be pursued within a Copernicus Climate Change Service project (C3S). This framework also aims to include additional sensors such as onboard Sentinel-3 and we will show first results of Sentinel-3 Arctic sea-ice thickness. These

Data Stewardship and Long-Term Archive of ICESat Data at the National Snow and Ice Data Center (NSIDC)

NASA Astrophysics Data System (ADS)

Fowler, D. K.; Moses, J. F.; Duerr, R. E.; Webster, D.; Korn, D.

2010-12-01

Data Stewardship is becoming a principal part of a data manager’s work at NSIDC. It is vitally important that our organization makes a commitment to both current and long-term goals of data management and the preservation of our scientific data. Data must be available to researchers not only during active missions, but long after missions end. This includes maintaining accurate documentation, data tools, and a knowledgeable user support staff. NSIDC is preparing for long-term support of the ICESat mission data. Though ICESat has seen its last operational day, the data is still being improved and NSIDC is scheduled to archive the final release, Release 33, starting late in 2010. This release will include the final adjustments to the processing algorithms and will produce the best possible products to date. Along with the higher-level data sets, all supporting documentation will be archived at NSIDC. For the long-term archive, it is imperative that there is sufficient information about how products were prepared in order to convince future researchers that the scientific results are reproducible. The processing algorithms along with the Level 0 and ancillary products used to create the higher-level products will be archived and made available to users. This can enable users to examine production history, to derive revised products and to create their own products. Also contained in the long-term archive will be pre-launch, calibration/validation, and test data. These data are an important part of the provenance which must be preserved. For longevity, we’ll need to archive the data and documentation in formats that will be supported in the years to come.

Evaluation of multi-mode CryoSat-2 altimetry data over the Po River against in situ data and a hydrodynamic model

NASA Astrophysics Data System (ADS)

Schneider, Raphael; Tarpanelli, Angelica; Nielsen, Karina; Madsen, Henrik; Bauer-Gottwein, Peter

2018-02-01

Coverage of in situ observations to monitor surface waters is insufficient on the global scale, and decreasing across the globe. Satellite altimetry has become an increasingly important monitoring technology for continental surface waters. The ESA CryoSat-2 altimetry mission, launched in 2010, has two novel features. (i) The radar altimeter instrument on board of CryoSat-2 is operated in three modes; two of them reduce the altimeter footprint by using Delay-Doppler processing. (ii) CryoSat-2 is placed on a distinct orbit with a repeat cycle of 369 days, leading to a drifting ground track pattern. The drifting ground track pattern challenges many common methods of processing satellite altimetry data over rivers. This study evaluates the observation error of CryoSat-2 water level observations over the Po River, Italy, against in situ observations. The average RMSE between CryoSat-2 and in situ observations was found to be 0.38 meters. CryoSat-2 was also shown to be useful for channel roughness calibration in a hydrodynamic model of the Po River. The small across-track distance of CryoSat-2 means that observations are distributed almost continuously along the river. This allowed resolving channel roughness with higher spatial resolution than possible with in situ or virtual station altimetry data. Despite the Po River being extensively monitored, CryoSat-2 still provides added value thanks to its unique spatio-temporal sampling pattern.

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

NASA Astrophysics Data System (ADS)

Andersen, O. B.; Krogh, P. E.; Michailovsky, C.; Bauer-Gottwein, P.; Christiansen, L.; Berry, P.; Garlick, J.

2008-12-01

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 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 information in un-gauged regions. A system of GRACE custom designed Mass Concentration blocks (Mascons) have been designed to model time-variable gravity changes for the largest basins in Southern Africa (Zambezi, Okavango, Limpopo and Orange) covering an area of 9 mill km2 with a resolution of 1 by 1.25 degree. Satellite altimetry have been used to derive high resolution point-wise river height in some of the un-gauged rivers in the region by using dedicated retracking to recovers nearly un-interrupted time series over these rivers. First result from the HYDROGRAV project analyzing GRACE derived mass 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.

Mass-induced sea level variations in the Red Sea from steric-corrected altimetry, GRACE, in-situ bottom pressure records, and hydrographic observations

NASA Astrophysics Data System (ADS)

Feng, Wei; Lemoine, Jean-Michel; Zhong, Min; Xu, Houze

2014-05-01

An annual amplitude of ~18 cm mass-induced sea level variations (SLV) in the Red Sea is detected from steric-corrected altimetry and the Gravity Recovery and Climate Experiment (GRACE) satellites from 2003 to 2011, which dominates the mean sea level in the region. Seawater mass variations here generally reach maximum in late January/early February. The steric component of SLV calculated from oceanographic temperature and salinity data is relatively small and peaks about seven months later than mass variations. The phase difference between the steric SLV and the mass-induced SLV indicates that when the Red Sea gains the mass from inflow water in winter, the steric SLV fall, and vice versa in summer. In-situ bottom pressure records in the eastern coast of the Red Sea validate the high mass variability observed by steric-corrected altimetry and GRACE. Furthermore, we compare the horizontal water mass flux in the Red Sea from steric-corrected altimetry and GRACE with that estimated from hydrographic observations.

Comparison of retracked coastal altimetry sea levels against high frequency radar on the continental shelf of the Great Barrier Reef, Australia

NASA Astrophysics Data System (ADS)

Idris, Nurul Hazrina; Deng, Xiaoli; Idris, Nurul Hawani

2017-07-01

Comparison of Jason-1 altimetry retracked sea levels and high frequency (HF) radar velocity is examined within the region of the Great Barrier Reef, Australia. The comparison between both datasets is not direct because the altimetry derives only the geostrophic component, while the HF radar velocity includes information on both geostrophic and ageostrophic components, such as tides and winds. The comparison of altimetry and HF radar data is performed based on the parameter of surface velocity inferred from both datasets. The results show that 48% (10 out of 21 cases) of data have high (≥0.5) spatial correlation. The mean of spatial correlation for all 21 cases is 0.43. This value is within the range (0.42 to 0.5) observed by other studies. Low correlation is observed due to disagreement in the trend of velocity signals in which sometimes they have contradictions in the signal direction and the position of the peak is shifted. In terms of standard deviation of difference and root mean square error, both datasets show reasonable agreement with ≤2.5 cm s-1.

Poleward currents from coastal altimetry: The west coast of Southern Baja California, Mexico

NASA Astrophysics Data System (ADS)

Valle-Rodríguez, J.; Trasviña-Castro, A.

2017-05-01

The west coast of Southern Baja California is subject to intense seasonal variability, presenting lowest temperatures from February to April partly due to the upwelling season but also to cold water advection associated to the California Current. The summer advance of a poleward current is responsible for the coastal temperature maxima. In this work we use a time series of currents from a moored Acoustic Doppler Profiler (ADP) to validate coastal altimetry data, in order to study seasonal and interannual coastal current variability. Almost eleven years of coastal altimetry data (2002-2012) from X-TRACK, 20-40 km from the coast, reveal a persistent seasonal poleward flow from July to October and equatorward flow, modulated by mesoscale processes the rest of the year. Near the coast of the peninsula sea level raises towards the coast while the poleward current carries a warm water mass against the climatological wind. It is present from July to October in a coastal band 100 km wide from the surface to 80 m depth with speeds 0.2-0.3 m s-1. The interannual variability observed in this period is unusually weak, compared to the previous decade.

Ice elevations and surface change on the Malaspina Glacier, Alaska

USGS Publications Warehouse

Sauber, J.; Molnia, B.; Carabajal, C.; Luthcke, S.; Muskett, R.

2005-01-01

Here we use Ice, Cloud and land Elevation Satellite (ICESat)-derived elevations and surface characteristics to investigate the Malaspina Glacier of southern Alaska. Although there is significant elevation variability between ICESat tracks on this glacier, we were able to discern general patterns in surface elevation change by using a regional digital elevation model (DEM) as a reference surface. Specifically, we report elevation differences between ICESat Laser 1-3 observations (February 2003 - November 2004) and a Shuttle Radar Topography Mission (SRTM)-derived DEM from February 2000. Elevation decreases of up to 20-25 m over a 3-4 year time period were observed across the folded loop moraine on the southern portion of the Malaspina Glacier. Copyright 2005 by the American Geophysical Union.

Assessing backscatter change due to backscatter gradient over the Greenland ice sheet using Envisat and SARAL altimetry

NASA Astrophysics Data System (ADS)

Su, Xiaoli; Luo, Zhicai; Zhou, Zebing

2018-06-01

Knowledge of backscatter change is important to accurately retrieve elevation change time series from satellite radar altimetry over continental ice sheets. Previously, backscatter coefficients generated in two cases, namely with and without accounting for backscatter gradient (BG), are used. However, the difference between backscatter time series obtained separately in these two cases and its impact on retrieving elevation change are not well known. Here we first compare the mean profiles of the Ku and Ka band backscatter over the Greenland ice sheet (GrIS), with results illustrating that the Ku-band backscatter is 3 ∼ 5 dB larger than that of the Ka band. We then conduct statistic analysis about time series of backscatter formed separately in the above two cases for both Ku and Ka bands over two regions in the GrIS. It is found that the standard deviation of backscatter time series becomes slightly smaller after removing the BG effect, which suggests that the method for the BG correction is effective. Furthermore, the impact on elevation change from backscatter change due to the BG effect is separately assessed for both Ku and Ka bands over the GrIS. We conclude that Ka band altimetry would benefit from a BG induced backscatter analysis (∼10% over region 2). This study may provide a reference to form backscatter time series towards refining elevation change time series from satellite radar altimetry over ice sheets using repeat-track analysis.

Extensive dynamic thinning on the margins of the Greenland and Antarctic ice sheets.

PubMed

Pritchard, Hamish D; Arthern, Robert J; Vaughan, David G; Edwards, Laura A

2009-10-15

Many glaciers along the margins of the Greenland and Antarctic ice sheets are accelerating and, for this reason, contribute increasingly to global sea-level rise. Globally, ice losses contribute approximately 1.8 mm yr(-1) (ref. 8), but this could increase if the retreat of ice shelves and tidewater glaciers further enhances the loss of grounded ice or initiates the large-scale collapse of vulnerable parts of the ice sheets. Ice loss as a result of accelerated flow, known as dynamic thinning, is so poorly understood that its potential contribution to sea level over the twenty-first century remains unpredictable. Thinning on the ice-sheet scale has been monitored by using repeat satellite altimetry observations to track small changes in surface elevation, but previous sensors could not resolve most fast-flowing coastal glaciers. Here we report the use of high-resolution ICESat (Ice, Cloud and land Elevation Satellite) laser altimetry to map change along the entire grounded margins of the Greenland and Antarctic ice sheets. To isolate the dynamic signal, we compare rates of elevation change from both fast-flowing and slow-flowing ice with those expected from surface mass-balance fluctuations. We find that dynamic thinning of glaciers now reaches all latitudes in Greenland, has intensified on key Antarctic grounding lines, has endured for decades after ice-shelf collapse, penetrates far into the interior of each ice sheet and is spreading as ice shelves thin by ocean-driven melt. In Greenland, glaciers flowing faster than 100 m yr(-1) thinned at an average rate of 0.84 m yr(-1), and in the Amundsen Sea embayment of Antarctica, thinning exceeded 9.0 m yr(-1) for some glaciers. Our results show that the most profound changes in the ice sheets currently result from glacier dynamics at ocean margins.

Oceanic tide maps and spherical harmonic coefficients from Geosat altimetry

NASA Technical Reports Server (NTRS)

Cartwright, D. E.; Ray, R. D.; Sanchez, B. V.

1991-01-01

Maps and tables for the global ocean tides, 69 degree N to 68 degree S, derived from two years of Geosat altimetry are presented. Global maps of local and Greenwich admittance of the (altimetric) ocean tide, and maps of amplitude and Greenwich phase lag of the ocean tide are shown for M(sub 2), S(sub 2), N(sub 2), O(sub 1), and K(sub 1). Larger scale maps of amplitude and phases are also shown for regional areas of special interest. Spherical harmonic coefficients of the ocean tide through degree and order 8 are tabulated for the six major constituents.

Assessment of ocean models in Mediterranean Sea against altimetry and gravimetry measurements

NASA Astrophysics Data System (ADS)

Fenoglio-Marc, Luciana; Uebbing, Bernd; Kusche, Jürgen

2017-04-01

This work aims at assessing in a regional study in the Mediterranean Sea the agreement between ocean model outputs and satellite altimetry and satellite gravity observations. Satellite sea level change are from altimeter data made available by the Sea Level Climate Change Initiative (SLCCI) and from satellite gravity data made available by GRACE. We consider two ocean simulations not assimilating satellite altimeter data and one ocean model reanalysis assimilating satellite altimetry. Ocean model simulations can provide some insight on the ocean variability, but they are affected by biases due to errors in model formulation, specification of initial states and forcing, and are not directly constrained by observations. Their trend can be quite different from the altimetric observations due to surface radiation biases, however they are physically consistent. Ocean reanalyses are the combination of ocean models, atmospheric forcing fluxes and ocean observations via data assimilation methods and have the potential to provide more accurate information than observation-only or model-only based ocean estimations. They will be closer to altimetry at long and short timescales, but assimilation may destroy mass consistency. We use two ocean simulations which are part of the Med-CORDEX initiative (https://www.medcordex.eu). The first is the CNRM-RCM4 fully-coupled Regional Climate System Model (RCMS) simulation developed at METEOFRANCE for 1980-2012. The second is the PROTHEUS standalone hindcast simulation developed at ENEA and covers the interval 1960-2012. The third model is the regional model MEDSEA_REANALYSIS_PHIS_006_004 assimilating satellite altimeter data (http://marine.copernicus.eu/) and available over 1987-2014. Comparison at basin and regional scale are made. First the steric, thermo-steric, halosteric and dynamic components output of the models are compared. Then the total sea level given by the models is compared to the altimeter observations. Finally the mass

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

NASA Astrophysics Data System (ADS)

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

Estimating the arrival times of photon-limited laser pulses in the presence of shot and speckle noise

NASA Technical Reports Server (NTRS)

Abshire, James B.; Mcgarry, Jan F.

1987-01-01

Maximum-likelihood (ML) receivers are frequently used to optimize the timing performance of laser-ranging and laser-altimetry systems in the presence of shot and speckle noise. Monte Carlo method was used to examine ML-receiver performance with return signals in the 10-5000-photoelectron (pe) range. The simulations were performed for shot noise only and for shot and speckle noise. The results agree with previous theory for signal strengths greater than about 100 pe's but show that the theory can significantly underestimate timing errors for weaker received signals. Sharp high-bandwidth features in the detected signals are shown to improve timing performance only if their signal levels are greater than 4-5 pe's.

Airborne gravimetry, altimetry, and GPS navigation errors

NASA Technical Reports Server (NTRS)

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.

Satellite altimetry and the intensification of Hurricane Katrina

NASA Astrophysics Data System (ADS)

Scharroo, Remko; Smith, Walter H. F.; Lillibridge, John L.

Remotely sensed infrared images of Hurricane Katrina taken on 26, 27, and 28 August 2005 (Figure 1, left panels) show the aerial extent of the cloud cover and the central “eye” increasing as the storm that swamped areas of the U.S. Gulf Coast intensified. Computer animations of such image sequences show forecasters the tracks of storms and are a familiar staple of weather news. Less well known is the role that satellite altimetry plays both in forecasting conditions that can intensify a tropical storm and in observing the storm conditions at the sea surface.Satellite altimeter data indicate that Katrina intensified over areas of anomalously high dynamic topography rather than areas of unusually warm surface waters. Altimeter data from Katrina also for the first time observed the building of a storm surge.

Correcting the hooking effect in satellite altimetry data for time series estimation over smaller rivers

NASA Astrophysics Data System (ADS)

Boergens, Eva; Dettmering, Denise; Schwatke, Christian

2015-04-01

Since many years the numbers of in-situ gauging stations are declining. Satellite altimetry can be used as a gap-filler even over smaller inland waters like rivers. However, since altimetry measurements are not designed for inland water bodies a special data handling is necessary in order to estimate reliable water level heights over inland waters. We developed a new routine for estimating water level heights over smaller inland waters with satellite altimetry by correcting the hooking effect. The hooking effect occurs when the altimeter is not measuring in nadir before and after passing a water body due to the stronger reflectance of the water than the surrounding land surface. These off-nadir measurements, together with the motion of the satellite, lead to overlong ranges and heights declining in a parabolic shape. The vertex of this parabola is on the water surface. Therefore, by estimating the parabola we are able to determine the water level height without the need of any point over the water body itself. For estimating the parabola we only use selected measurements which are effected by the hooking effect. The applied search approach is based on the RANSAC algorithm (random sample consensus) which is a non-deterministic algorithm especially designed for finding geometric entities in point clouds with many outliers. With the hooking effect correction we are able to retrieve water level height time series from the Mekong River from Envisat and Saral/Altika high frequency data. It is possible to determine reliable time series even if the river has only a width of 500m or less. The expected annual variations are clearly depicted and the comparison of the time series with available in-situ gauging data shows a very good agreement.

Investigation of Controls on Ice Dynamics in Northeast Greenland from Ice-Thickness Change Record Using Ice Sheet System Model (ISSM)

NASA Astrophysics Data System (ADS)

Csatho, B. M.; Larour, E. Y.; Schenk, A. F.; Schlegel, N.; Duncan, K.

2015-12-01

We present a new, complete ice thickness change reconstruction of the NE sector of the Greenland Ice Sheet for 1978-2014, partitioned into changes due to surface processes and ice dynamics. Elevation changes are computed from all available stereoscopic DEMs, and laser altimetry data (ICESat, ATM, LVIS). Surface Mass Balance and firn-compaction estimates are from RACMO2.3. Originating nearly at the divide of the Greenland Ice Sheet (GrIS), the dynamically active North East Ice Stream (NEGIS) is capable of rapidly transmitting ice-marginal forcing far inland. Thus, NEGIS provides a possible mechanism for a rapid drawdown of ice from the ice sheet interior as marginal warming, thinning and retreat continues. Our altimetry record shows accelerating dynamic thinning of Zachariæ Isstrom, initially limited to the deepest part of the fjord near the calving front (1978-2000) and then extending at least 75 km inland. At the same time, changes over the Nioghalvfjerdsfjorden (N79) Glacier are negligible. We also detect localized large dynamic changes at higher elevations on the ice sheet. These thickness changes, often occurring at the onset of fast flow, could indicate rapid variations of basal lubrication due to rerouting of subglacial drainage. We investigate the possible causes of the observed spatiotemporal pattern of ice sheet elevation changes using the Ice Sheet System Model (ISSM). This work build on our previous studies examining the sensitivity of ice flow within the Northeast Greenland Ice Stream (NEGIS) to key fields, including ice viscosity, basal drag. We assimilate the new altimetry record into ISSM to improve the reconstruction of basal friction and ice viscosity. Finally, airborne geophysical (gravity, magnetic) and ice-penetrating radar data is examined to identify the potential geologic controls on the ice thickness change pattern. Our study provides the first comprehensive reconstruction of ice thickness changes for the entire NEGIS drainage basin during

Status of the Ganymede Laser Altimeter (GALA) for ESA's Jupiter Icy Moons Explorer (JUICE)

NASA Astrophysics Data System (ADS)

Hussmann, Hauke; Luedicke, Fabian

2017-04-01

The Ganymede Laser Altimeter (GALA) is one of the instruments selected for ESA's Jupiter Icy Moons Explorer (JUICE). A fundamental goal of any exploratory space mission is to characterize and measure the shape, topography, and rotation of the target bodies. A state of the art tool for this task is laser altimetry because it can provide absolute topographic height and position with respect to a body centered reference system. With respect to Ganymede, the GALA instrument aims at mapping of global, regional and local topography; confirming the global subsurface ocean and further characterization of the water-ice/liquid shell by monitoring the dynamic response of the ice shell to tidal forces; providing constraints on the forced physical librations and spin-axis obliquity; determining Ganymede's shape; obtaining detailed topographic profiles across the linear features of grooved terrain, impact structures, possible cryo-volcanic features and other different surface units; providing information about slope, roughness and albedo (at 1064nm) of Ganymede's surface. After several flyby's (Ganymede, Europa, Callisto) it is scheduled that the JUICE orbiter will enter first into an elliptical orbit (200 km x 10.000 km) for around 150 days and then into a circular orbit (500 km) around Ganymede for 130 days. Accordingly to the different orbits and trajectories, distances to the moons respectively, the spot size of the GALA laser varies between 21 m and 140 m. GALA uses the direct-detection (classical) approach of laser altimetry. Laser pulses are emitted at a wavelength of 1064 nm by using an actively Q-switched Nd:Yag laser. The pulse energy and pulse repetition frequency are 17 mJ at 30 Hz (nominal), respectively. For targeted observations and flybys the frequency can be switched to 50 Hz. The emission time of each pulse is measured by the detector. The beam is reflected from the surface and received at a 25 cm diameter telescope. The returning laser pulse is refocused onto

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

NASA Astrophysics Data System (ADS)

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

2014-03-01

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

Continuous measurements of surface mass balance, firn compaction, and meltwater retention in Greenland for altimetry validation.

NASA Astrophysics Data System (ADS)

de la Peña, S.; Howat, I.; Behar, A.; Price, S. F.; Thanga, J.; Crowell, J. M.; Huseas, S.; Tedesco, M.

2016-12-01

Observations made in recent years by repeated altimetry from CryoSat-2 and NASA's Operation IceBridge reveal large fluctuations in the firn volume of the Greenland Ice Sheet. Although an order of magnitude smaller than ice thinning rates observed in some areas at the margins of the ice sheet, short-term departures in surface elevation trends occur over most of the accumulation zone of Greenland. Changes in the thickness of the firn column are influenced by variability in surface mass balance, firn compaction, and abrupt seasonal densification near the surface caused by refreezing at depth of variable amounts of surface meltwater in the summer. These processes and dynamic thinning cannot be differentiated from each other by altimetry alone. Until recently, nearly all information on density and surface mass balance changes over the firn layer came from ice core and snow pit stratigraphy that provided annual rates with relatively large uncertainties. Here we present direct, continuous measurements of firn density and surface mass balance along with annual estimates of firn ice content used to assess observed elevation change in the percolation zone of western Greenland in relation to firn processes. Since 2012, autonomous in-situ firn compaction sensors have monitored several sites in the catchment area of Jakobshavn Isbrae, and since 2015 surface mass balance and surface displacement has been measured continuously using a combination of sensors. In addition to identify the different components in the altimetry signal, The temporal resolution of the data acquired provide a means to monitor short-term changes in the near-surface firn, and identifying individual events causing surface elevation displacement.

Modes of Arctic Ocean Change from GRACE, ICESat and the PIOMAS and ECCO2 Models of the Arctic Ocean

NASA Astrophysics Data System (ADS)

Peralta Ferriz, C.; Morison, J. H.; Bonin, J. A.; Chambers, D. P.; Kwok, R.; Zhang, J.

2012-12-01

EOF analysis of month-to-month variations in GRACE derived Arctic Ocean bottom pressure (OBP) with trend and seasonal variation removed yield three dominant modes. The first mode is a basin wide variation in mass associated with high atmospheric pressure (SLP) over Scandinavia mainly in winter. The second mode is a shift of mass from the central Arctic Ocean to the Siberian shelves due to low pressure over the basins, associated with the Arctic Oscillation. The third mode is a shift in mass between the Eastern and Western Siberian shelves, related to strength of the Beaufort High mainly in summer, and to eastward alongshore winds on the Barents Sea in winter. The PIOMAS and ECCO2 modeled OBP show fair agreement with the form of these modes and provide context in terms of variations in sea surface height SSH. Comparing GRACE OBP from 2007 to 2011 with GRACE OBP from 2002 to 2006 reveals a rising trend over most of the Arctic Ocean but declines in the Kara Sea region and summer East Siberian Sea. ECCO2 bears a faint resemblance to the observed OBP change but appears to be biased negatively. In contrast, PIOMAS SSH and ECCO2 especially, show changes between the two periods that are muted but similar to ICESat dynamic ocean topography and GRACE-ICESat freshwater trends from 2005 through 2008 [Morison et al., 2012] with a rising DOT and freshening in the Beaufort Sea and a trough with decreased freshwater on the Russian side of the Arctic Ocean. Morison, J., R. Kwok, C. Peralta-Ferriz, M. Alkire, I. Rigor, R. Andersen, and M. Steele (2012), Changing Arctic Ocean freshwater pathways, Nature, 481(7379), 66-70.

On the nature of the Madagascar dipoles: An analysis from Argo profiling floats and altimetry measurements

NASA Astrophysics Data System (ADS)

Aguiar-González, Borja; Ponsoni, Leandro; Ridderinkhof, Herman; de Ruijter, Will P. M.; Maas, Leo R. M.

2016-04-01

The South East Madagascar Current (SEMC) flows poleward along the eastern coast of Madagascar as a western boundary current which further south provides some of the source waters of the Agulhas Current, either directly or in the form of eddies. We investigate the region of dipole formation south of Madagascar combining vertical T/S profiles from Argo floats, altimetry measurements and an existing eddy detection algorithm. Results from our analysis show that the dipole consists of an anticyclonic intrathermocline eddy (ITE) formed on its southern flank and a cyclonic ITE formed on its northern flank. Both lobes of the dipole exhibit similar T/S properties throughout the water column, although vertically shifted within the thermocline depending on its nature: upward in a cyclonic ITE and downward in an anticyclonic ITE. A subsurface salinity maximum of about 35.5 psu characterizes the upper layers with Subtropical Surface Water (STSW). At intermediate levels, a well defined path of South Indian Central Water (SICW) extends throughout the water column up to reach a minimum in salinity of 34.5 psu, corresponding to Antarctic Intermediate Water (AAIW). Below, at deep layers, the North Atlantic Deep Water (NADW) is found. The intrathermocline nature of the Madagascar dipoles has not been previously reported and represents an important feature to be considered when assessing the heat and salt fluxes driven by eddy movement and contributing to the Agulhas Current. Unlike surface eddies, intrathermocline eddies strongly influence the intermediate/deeper layers in the oceans and, hence, may have a larger contribution in the spreading rates and pathways of water masses. Because the intrathermocline nature of eddies is invisible to altimetry measurements, these results stress the importance of combining altimetry with historical records of Argo profiles which uncover eddy dynamics below the sea surface. Lastly, we further investigate from altimetry the area of dipole formation

The Reference Elevation Model of Antarctica (REMA): A High Resolution, Time-Stamped Digital Elevation Model for the Antarctic Ice Sheet

NASA Astrophysics Data System (ADS)

Howat, I.; Noh, M. J.; Porter, C. C.; Smith, B. E.; Morin, P. J.

2017-12-01

We are creating the Reference Elevation Model of Antarctica (REMA), a continuous, high resolution (2-8 m), high precision (accuracy better than 1 m) reference surface for a wide range of glaciological and geodetic applications. REMA will be constructed from stereo-photogrammetric Digital Surface Models (DSM) extracted from pairs of submeter resolution DigitalGlobe satellite imagery and vertically registred to precise elevations from near-coincident airborne LiDAR, ground-based GPS surveys and Cryosat-2 radar altimetry. Both a seamless mosaic and individual, time-stamped DSM strips, collected primarily between 2012 and 2016, will be distributed to enable change measurement. These data will be used for mapping bed topography from ice thickness, measuring ice thickness changes, constraining ice flow and geodynamic models, mapping glacial geomorphology, terrain corrections and filtering of remote sensing observations, and many other science tasks. Is will also be critical for mapping ice traverse routes, landing sites and other field logistics planning. REMA will also provide a critical elevation benchmark for future satellite altimetry missions including ICESat-2. Here we report on REMA production progress, initial accuracy assessment and data availability.

Satellite Altimetry Outreach During Hurricane Rita: Lessons Learned

NASA Astrophysics Data System (ADS)

Leben, R.; Born, G. H.; Srinivasan, M.

2006-07-01

The 2005 hurricane season was th e most costly on record with estimated d amages in th e U.S. of over 100 billion. What may hav e been lost in the signif icant after math of these storms is the pr imary role th at Gulf of Mexico oceanography played in this very active hurricane season. The four most destructive storms - Dennis (1.84 B), Katrin a (80B), Rita (9.4B) , and Wilma ($14.4 B) - all interacted w ith deep warm ocean currents in th e Gulf contributing to the intensity of these storms and their destructive po ten tial. In the aftermath of Hurrican e K atr ina and during Hurricane Rita we made a concer ted effort to tell this story through satellite altimetry ou treach activ ities at the Un iversity of Colorado, Boulder .

Tidal Energy Available for Deep Ocean Mixing: Bounds from Altimetry Data

NASA Technical Reports Server (NTRS)

Egbert, Gary D.; Ray, Richard D.

1999-01-01

Maintenance of the large-scale thermohaline circulation has long presented a problem to oceanographers. Observed mixing rates in the pelagic ocean are an order of magnitude too small to balance the rate at which dense bottom water is created at high latitudes. Recent observational and theoretical work suggests that much of this mixing may occur in hot spots near areas of rough topography (e.g., mid-ocean ridges and island arcs). Barotropic tidal currents provide a very plausible source of energy to maintain these mixing processes. Topex/Poseidon (T/P) satellite altimetry data have made precise mapping of open ocean tidal elevations possible for the first time. We can thus obtain empirical, spatially localized, estimates of barotropic tidal dissipation. These provide an upper bound on the amount of tidal energy that is dissipated in the deep ocean, and hence is available for deep mixing. We will present and compare maps of open ocean tidal energy flux divergence, and estimates of tidal energy flux into shallow seas, derived from T/P altimetry data using both formal data assimilation methods and empirical approaches. With the data assimilation methods we can place formal error bars on the fluxes. Our results show that 20-25% of tidal energy dissipation occurs outside of the shallow seas, the traditional sink for tidal energy. This suggests that up to 1 TW of energy may be available from the tides (lunar and solar) for mixing the deep ocean. The dissipation indeed appears to be concentrated over areas of rough topography.

Tidal Energy Available for Deep Ocean Mixing: Bounds From Altimetry Data

NASA Technical Reports Server (NTRS)

Egbert, Gary D.; Ray, Richard D.

1999-01-01

Maintenance of the large-scale thermohaline circulation has long presented a problem to oceanographers. Observed mixing rates in the pelagic ocean are an order of magnitude too small to balance the rate at which dense bottom water is created at high latitudes. Recent observational and theoretical work suggests that much of this mixing may occur in hot spots near areas of rough topography (e.g., mid-ocean ridges and island arcs). Barotropic tidal currents provide a very plausible source of energy to maintain these mixing processes. Topex/Poseidon satellite altimetry data have made precise mapping of open ocean tidal elevations possible for the first time. We can thus obtain empirical, spatially localized, estimates of barotropic tidal dissipation. These provide an upper bound on the amount of tidal energy that is dissipated in the deep ocean, and hence is available for deep mixing. We will present and compare maps of open ocean tidal energy flux divergence, and estimates of tidal energy flux into shallow seas, derived from T/P altimetry data using both formal data assimilation methods and empirical approaches. With the data assimilation methods we can place formal error bars on the fluxes. Our results show that 20-25% of tidal energy dissipation occurs outside of the shallow seas, the traditional sink for tidal energy. This suggests that up to 1 TW of energy may be available from the tides (lunar and solar) for mixing the deep ocean. The dissipation indeed appears to be concentrated over areas of rough topography.

Tidal Energy Available for Deep Ocean Mixing: Bounds from Altimetry Data

NASA Technical Reports Server (NTRS)

Ray, Richard D.; Egbert, Gary D.

1999-01-01

Maintenance of the large-scale thermohaline circulation has long presented an interesting problem. Observed mixing rates in the pelagic ocean are an order of magnitude too small to balance the rate at which dense bottom water is created at high latitudes. Recent observational and theoretical work suggests that much of this mixing may occur in hot spots near areas of rough topography (e.g., mid-ocean ridges and island arcs). Barotropic tidal currents provide a very plausible source of energy to maintain these mixing processes. Topex/Poseidon satellite altimetry data have made precise mapping of open ocean tidal elevations possible for the first time. We can thus obtain empirical, spatially localized, estimates of barotropic tidal dissipation. These provide an upper bound on the amount of tidal energy that is dissipated in the deep ocean, and hence is available for deep mixing. We will present and compare maps of open ocean tidal energy flux divergence, and estimates of tidal energy flux into shallow seas, derived from T/P altimetry data using both formal data assimilation methods and empirical approaches. With the data assimilation methods we can place formal error bars on the fluxes. Our results show that 20-25% of tidal energy dissipation occurs outside of the shallow seas, the traditional sink for tidal energy. This suggests that up to 1 TW of energy may be available from the tides (lunar and solar) for mixing the deep ocean. The dissipation indeed appears to be concentrated over areas of rough topography.

Use of altimetry data in a sampling-function approach to the geoid

NASA Technical Reports Server (NTRS)

Lundquist, C. A.; Giacaglia, G. E. O.

1972-01-01

Problems associated with using an altimetry sampling function approach to the geoid are examined. They include: (1) conventent mathematical representation of short-wavelength (eventually approximately 1 deg) features of the geoid or geopotential, (2) utilization of detailed data from only part of the globe (i.e., the oceans) (3) application of appropriate formalism to relate the sea-level equipotential below the atmospheric mass to the external potential above the atmosphere, (4) mathematical applicability of an adopted geopotential representation on the surface of the physical geoid.

Altimetry data over trenches and island-arcs and convection in the mantle

NASA Technical Reports Server (NTRS)

1980-01-01

Transfer function techniques were developed to calculate the isostatic component of the geoid signal over trench/island arc/back arc systems. Removal of this isostatic component from geoid profiles determined by GEOS 3 radar altimetry leaves a residual geoid that can be attributed to the effect of mass inhomogeneities below the depth of compensation. Efforts are underway to extend the analysis to all the major trench/island arc systems of the world in order to provide more detailed understanding of the dynamic processes occurring beneath island arcs.

Thermal Testing and Model Correlation for Advanced Topographic Laser Altimeter Instrument (ATLAS)

NASA Technical Reports Server (NTRS)

Patel, Deepak

2016-01-01

The Advanced Topographic Laser Altimeter System (ATLAS) part of the Ice Cloud and Land Elevation Satellite 2 (ICESat-2) is an upcoming Earth Science mission focusing on the effects of climate change. The flight instrument passed all environmental testing at GSFC (Goddard Space Flight Center) and is now ready to be shipped to the spacecraft vendor for integration and testing. This topic covers the analysis leading up to the test setup for ATLAS thermal testing as well as model correlation to flight predictions. Test setup analysis section will include areas where ATLAS could not meet flight like conditions and what were the limitations. Model correlation section will walk through changes that had to be made to the thermal model in order to match test results. The correlated model will then be integrated with spacecraft model for on-orbit predictions.

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

NASA Astrophysics Data System (ADS)

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

Southern Alaska Glaciers: Spatial and Temporal Variations in Ice Volume

NASA Technical Reports Server (NTRS)

Sauber, J.; Molnia, B. F.; Lutchke, S.; Rowlands, D.; Harding, D.; Carabajal, C.; Hurtado, J. M.; Spade, G.

2004-01-01

Although temperate mountain glaciers comprise less than 1% of the glacier-covered area on Earth, they are important because they appear to be melting rapidly under present climatic conditions and, therefore, make significant contributions to rising sea level. In this study, we use ICESat observations made in the last 1.5 years of southern Alaska glaciers to estimate ice elevation profiles, ice surface slopes and roughness, and bi-annual and/or annual ice elevation changes. We report initial results from the near coastal region between Yakutat Bay and Cape Suckling that includes the Malaspina and Bering Glaciers. We show and interpret ice elevations changes across the lower reaches of the Bagley Ice Valley for the period between October 2003 and May 2004. In addition, we use off-nadir pointing observations to reference tracks over the Bering and Malaspina Glaciers in order to estimate annual ice elevation change. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Shuttle Radar Topography Mission (SRTM) derived DEMs are used to estimate across track regional slopes between ICESat data acquisitions. Although the distribution and quantity of ICESat elevation profiles with multiple, exact repeat data is currently limited in Alaska, individual ICESat data tracks, provide an accurate reference surface for comparison to other elevation data (e.g. ASTER and SRTM X- and C-band derived DEMs). Specifically we report the elevation change over the Malaspina Glacier's piedmont lobe between a DEM derived from SRTM C-band data acquired in Feb. 2000 and ICESat Laser #2b data from Feb.-March 2004. We also report use of ICESat elevation data to enhance ASTER derived absolute DEMs. Mountain glaciers generally have rougher surfaces and steeper regional slopes than the ice sheets for which the ICESat design was optimized. Therefore, rather than averaging ICESat observations over large regions or relying on crossovers, we are working with well-located ICESat

SWOT: A high-resolution wide-swath altimetry mission for oceanography and hydrology

NASA Astrophysics Data System (ADS)

Morrow, Rosemary; Fu, Lee-Lueng; Rodriguez, Ernesto

2013-04-01

A new satellite mission called Surface Water and Ocean Topography (SWOT) has been developed jointly by the U.S. National Aeronautics and Space Administration and France's Centre National d'Etudes Spatiales. Based on the success of nadir-looking altimetry missions in the past, SWOT will use the technique of radar interferometry to make wide-swath altimetric measurements of the elevation of surface water on land and the ocean's surface topography. The new measurements will provide information on the changing ocean currents that are key to the prediction of climate change, as well as the shifting fresh water resources resulting from climate change. Conventional satellite altimetry has revolutionized oceanography by providing nearly two decades' worth of global measurements of ocean surface topography. However, the noise level of radar altimeters limits the along-track spatial resolution to 50-100 km over the oceans. The large spacing between the satellite ground tracks limits the resolution of 2D gridded data to 200 km. Yet most of the kinetic energy of ocean circulation takes place at the scales unresolved by conventional altimetry. About 50% of the vertical transfer of heat and chemical properties of the ocean (e.g., dissolved CO2 and nutrients) is also accomplished by processes at these scales. SWOT observations will provide the critical new information at these scales for developing and testing ocean models that are designed for predicting future climate change. SWOT measurements will be in Ka band (~35 GHZ), chosen for the radar to achieve high precision with a much shorter inteferometry baseline of 10 m. Small look angles (~ 4 degrees) are required to minimize elevation errors, which limits the swath width to 120 km. An orbit with inclination of 78 degrees and 22 day repeat period was chosen for gapless coverage and good tidal aliasing properties. With this configuration, SWOT is expected to achieve 1 cm precision at 1 km x 1 km pixels over the ocean and 10 cm

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

NASA Astrophysics Data System (ADS)

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

Monitoring of Water-Level Fluctuation of Lake Nasser Using Altimetry Satellite Data

NASA Astrophysics Data System (ADS)

El-Shirbeny, Mohammed A.; Abutaleb, Khaled A.

2018-05-01

Apart from the Renaissance Dam and other constructed dams on the River Nile tributaries, Egypt is classified globally as a state of scarce water. Egypt's water resources are very limited and do not contribute a significant amount to its water share except the River Nile (55.5 billion m3/year). While the number of population increases every year, putting more stress on these limited resources. This study aims to use remote-sensing data to assess the change in surface area and water-level variation in Lake Nasser using remote-sensing data from Landsat-8 and altimetry data. In addition, it investigates the use of thermal data from Landsat-8 to calculate water loss based on evaporation from Lake Nasser. The eight Landsat-8 satellite images were used to study the change in surface area of Lake Nasser representing winter (January) and summer (June/July) seasons in two consecutive years (2015 and 2016). Time series analyses for 10-day temporal resolution water-level data from Jason-2/OSTM and Jason-3 altimetry was carried out to investigate water-level trends over the long term (1993 and 2016) and short term (2015-2016) in correspondence with the change of the surface area. Results indicated a shrink in the lake surface area in 2016 of approximately 14% compared to the 2015 area. In addition, the evaporation rate in the lake is very high causing a loss of approximately 20% of the total water share from the river Nile.

Sea level reconstructions from altimetry and tide gauges using independent component analysis

NASA Astrophysics Data System (ADS)

Brunnabend, Sandra-Esther; Kusche, Jürgen; Forootan, Ehsan

2017-04-01

Many reconstructions of global and regional sea level rise derived from tide gauges and satellite altimetry used the method of empirical orthogonal functions (EOF) to reduce noise, improving the spatial resolution of the reconstructed outputs and investigate the different signals in climate time series. However, the second order EOF method has some limitations, e.g. in the separation of individual physical signals into different modes of sea level variations and in the capability to physically interpret the different modes as they are assumed to be orthogonal. Therefore, we investigate the use of the more advanced statistical signal decomposition technique called independent component analysis (ICA) to reconstruct global and regional sea level change from satellite altimetry and tide gauge records. Our results indicate that the used method has almost no influence on the reconstruction of global mean sea level change (1.6 mm/yr from 1960-2010 and 2.9 mm/yr from 1993-2013). Only different numbers of modes are needed for the reconstruction. Using the ICA method is advantageous for separating independent climate variability signals from regional sea level variations as the mixing problem of the EOF method is strongly reduced. As an example, the modes most dominated by the El Niño-Southern Oscillation (ENSO) signal are compared. Regional sea level changes near Tianjin, China, Los Angeles, USA, and Majuro, Marshall Islands are reconstructed and the contributions from ENSO are identified.

Merging Satellite Optical Sensors and Radar Altimetry for Daily River Discharge Estimation

NASA Astrophysics Data System (ADS)

Tarpanelli, A.; Santi, E. S.; Tourian, M. J.; Filippucci, P.; Amarnath, G.; Brocca, L.; Benveniste, J.

2017-12-01

River discharge is a fundamental physical variable of the hydrological cycle and notwithstanding its importance the monitoring of the flow in many parts of the Earth is still an open issue. Satellite sensors have great potential in offering new ways to monitor river discharge, because they guarantees regular, uniform and global measurements for long period thanks to the large number of satellites launched during the last twenty-five years. The multi-mission approach has been becoming a useful tool to integrate measurements and intensify the number of samples in space and time. In this study, we investigated the possibility to merge data from optical, i.e. Near InfraRed bands (from MODIS, MERIS, Landsat, and OLCI) and altimetry data (from Topex-Poseidon, Envisat/RA-2, Jason-2, SARAL/AltiKa and CryoSat-2) for estimating daily river discharge in Nigeria and Italy. The merging procedure is carried out by using artificial neural networks. Regarding the optical sensors, results are more affected by the temporal resolution than the spatial resolution. Landsat fails in the estimation of extreme events missing most of the peak values because of the long revisit time (14-16 days). Better performances are obtained with the Near InfraRed bands from MODIS and MERIS that give similar results in river discharge estimation. Finally, the multi-mission approach involving also radar altimetry data is found to be the most reliable tool to estimate river discharge in medium to large rivers.

Southern Alaska Glaciers: Spatial and Temporal Variations in Ice Volume

NASA Astrophysics Data System (ADS)

Sauber, J.; Molnia, B. F.; Luthcke, S.; Rowlands, D.; Harding, D.; Carabajal, C.; Hurtado, J. M.; Spada, G.

2004-12-01

Although temperate mountain glaciers comprise less than 1% of the glacier-covered area on Earth, they are important because they appear to be melting rapidly under present climatic conditions and, therefore, make significant contributions to rising sea level. In this study, we use ICESat observations made in the last 1.5 years of southern Alaska glaciers to estimate ice elevation profiles, ice surface slopes and roughness, and bi-annual and/or annual ice elevation changes. We report initial results from the near coastal region between Yakutat Bay and Cape Suckling that includes the Malaspina and Bering Glaciers. We show and interpret ice elevations changes across the lower reaches of the Bagley Ice Valley for the period between October 2003 and May 2004. In addition, we use off-nadir pointing observations to reference tracks over the Bering and Malaspina Glaciers in order to estimate annual ice elevation change. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Shuttle Radar Topography Mission (SRTM) derived DEMs are used to estimate across track regional slopes between ICESat data acquisitions. Although the distribution and quantity of ICESat elevation profiles with multiple, exact repeat data is currently limited in Alaska, individual ICESat data tracks, provide an accurate reference surface for comparison to other elevation data (e.g. ASTER and SRTM X- and C-band derived DEMs). Specifically we report the elevation change over the Malaspina Glacier's piedmont lobe between a DEM derived from SRTM C-band data acquired in Feb. 2000 and ICESat Laser #2b data from Feb.-March 2004. We also report use of ICESat elevation data to enhance ASTER derived absolute DEMs. Mountain glaciers generally have rougher surfaces and steeper regional slopes than the ice sheets for which the ICESat design was optimized. Therefore, rather than averaging ICESat observations over large regions or relying on crossovers, we are working with well-located ICESat

Representativeness of regional and global mass-balance measurement networks (Invited)

NASA Astrophysics Data System (ADS)

Cogley, J. G.; Moholdt, G.; Gardner, A. S.

2013-12-01

We showed in a recent publication that regional estimates of glacier mass budgets, obtained by interpolation from in-situ measurements, were markedly more negative than corresponding estimates by satellite gravimetry (GRACE) and satellite altimetry (ICESat) during 2003-2009. Examining the ICESat data in more detail, we found that in-situ records tend to be located in areas where glaciers are thinning more rapidly than as observed in their regional surroundings. Because neither GRACE nor ICESat can provide information for times before 2002-2003, and may not operate without interruption in the future, we explore possible explanations of and remedies for the identified bias in the in-situ network. Sparse spatial sampling, coupled with previously undetected spatial variability of mass balance at scales between the 10-km in-situ scale and the 350-km gravimetric scale, appears to be the leading explanation. Satisfactory remedies are not obvious. Selecting glaciers for in-situ measurement that are more representative will yield only incremental improvements. There appears to be no alternative to mass-balance modelling as a versatile tool for estimation of regional mass balance. However the meteorological data for forcing the surface components of glacier models have coarser resolution than is desirable and are themselves uncertain, especially in the remote regions where much of the glacier ice is found. Measurements of frontal (dynamic) mass changes are still difficult, and modelling of these changes remains underdeveloped in spite of recent advances. Thus research on a broad scale is called for in order to meet the challenge of producing more accurate hindcasts and projections of glacier mass budgets with fine spatial and temporal resolution.

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

NASA Astrophysics Data System (ADS)

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.

Cross-calibrating ALES Envisat and CryoSat-2 Delay-Doppler: A coastal altimetry study in the Indonesian Seas

NASA Astrophysics Data System (ADS)

Passaro, Marcello; Dinardo, Salvatore; Quartly, Graham D.; Snaith, Helen M.; Benveniste, Jérôme; Cipollini, Paolo; Lucas, Bruno

2016-08-01

A regional cross-calibration between the first Delay-Doppler altimetry dataset from CryoSat-2 and a retracked Envisat dataset is here presented, in order to test the benefits of the Delay-Doppler processing and to expand the Envisat time series in the coastal ocean. The Indonesian Seas are chosen for the calibration, since the availability of altimetry data in this region is particularly beneficial due to the lack of in situ measurements and its importance for global ocean circulation. The Envisat data in the region are retracked with the Adaptive Leading Edge Subwaveform (ALES) retracker, which has been previously validated and applied successfully to coastal sea level research. The study demonstrates that CryoSat-2 is able to decrease the 1-Hz noise of sea level estimations by 0.3 cm within 50 km of the coast, when compared to the ALES-reprocessed Envisat dataset. It also shows that Envisat can be confidently used for detailed oceanographic research after the orbit change of October 2010. Cross-calibration at the crossover points indicates that in the region of study a sea state bias correction equal to 5% of the significant wave height is an acceptable approximation for Delay-Doppler altimetry. The analysis of the joint sea level time series reveals the geographic extent of the semiannual signal caused by Kelvin waves during the monsoon transitions, the larger amplitudes of the annual signal due to the Java Coastal Current and the impact of the strong La Niña event of 2010 on rising sea level trends.

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

NASA Astrophysics Data System (ADS)

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.

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

NASA Astrophysics Data System (ADS)

Du, Ling; Xu, Daohuan

2016-04-01

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

An Assessment of IPCC 20th Century Climate Simulations Using the 15-year Sea Level Record from Altimetry

NASA Astrophysics Data System (ADS)

Leuliette, E.; Nerem, S.; Jakub, T.

2006-07-01

Recen tly, multiple ensemble climate simulations h ave been produced for th e forthco ming Fourth A ssessment Report of the Intergovernmental Panel on Climate Change (IPCC). N early two dozen coupled ocean- atmo sphere models have contr ibuted output for a variety of climate scen arios. One scenar io, the climate of the 20th century exper imen t (20C3 M), produces model output that can be comp ared to th e long record of sea level provided by altimetry . Generally , the output from the 20C3M runs is used to initialize simulations of future climate scenar ios. Hence, v alidation of the 20 C3 M experiment resu lts is crucial to the goals of th e IPCC. We present compar isons of global mean sea level (G MSL) , global mean steric sea level change, and regional patterns of sea lev el chang e from these models to r esults from altimetry, tide gauge measurements, and reconstructions.

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

NASA Astrophysics Data System (ADS)

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

2008-12-01

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

Towards the inversion of GRACE gravity fields for present-day ice-mass changes and glacial-isostatic adjustment in North America and Greenland

NASA Astrophysics Data System (ADS)

Sasgen, Ingo; Klemann, Volker; Martinec, Zdeněk

2012-09-01

We perform an inversion of gravity fields from the Gravity Recovery and Climate Experiment (GRACE) (August 2002 to August 2009) of four processing centres for glacial-isostatic adjustment (GIA) over North America and present-day ice-mass change in Alaska and Greenland. We apply a statistical filtering approach to reduce noise in the GRACE data by confining our investigations to GRACE coefficients containing a statistically significant linear trend. Selecting the subset of reliable coefficients in all GRACE time series (GFZ RL04, ITG 2010, JPL RL04 and CSR RL04) results in a non-isotropic smoothing of the GRACE gravity fields, which is effective in reducing the north-south oriented striping associated with correlated errors in GRACE coefficients. In a next step, forward models of GIA induced by the glacial history NAWI (Zweck and Huybrechts, 2005), as well as present-day ice mass changes in Greenland from ICESat (Sørensen et al., 2011) and Alaska from airborne laser altimetry (Arendt et al., 2002) are simultaneously adjusted in scale to minimize the misfit to the filtered GRACE trends. From the adjusted models, we derive the recent sea-level contributions for Greenland and Alaska (August 2002 to August 2009), and, interpret the residual misfit over the GIA-dominated region around the Hudson Bay, Canada, in terms of mantle viscosities beneath North America.

Generation of a high-accuracy regional DEM based on ALOS/PRISM imagery of East Antarctica

NASA Astrophysics Data System (ADS)

Shiramizu, Kaoru; Doi, Koichiro; Aoyama, Yuichi

2017-12-01

A digital elevation model (DEM) is used to estimate ice-flow velocities for an ice sheet and glaciers via Differential Interferometric Synthetic Aperture Radar (DInSAR) processing. The accuracy of DInSAR-derived displacement estimates depends upon the accuracy of the DEM. Therefore, we used stereo optical images, obtained with a panchromatic remote-sensing instrument for stereo mapping (PRISM) sensor mounted onboard the Advanced Land Observing Satellite (ALOS), to produce a new DEM ("PRISM-DEM") of part of the coastal region of Lützow-Holm Bay in Dronning Maud Land, East Antarctica. We verified the accuracy of the PRISM-DEM by comparing ellipsoidal heights with those of existing DEMs and values obtained by satellite laser altimetry (ICESat/GLAS) and Global Navigation Satellite System surveying. The accuracy of the PRISM-DEM is estimated to be 2.80 m over ice sheet, 4.86 m over individual glaciers, and 6.63 m over rock outcrops. By comparison, the estimated accuracy of the ASTER-GDEM, widely used in polar regions, is 33.45 m over ice sheet, 14.61 m over glaciers, and 19.95 m over rock outcrops. For displacement measurements made along the radar line-of-sight by DInSAR, in conjunction with ALOS/PALSAR data, the accuracy of the PRISM-DEM and ASTER-GDEM correspond to estimation errors of <6.3 mm and <31.8 mm, respectively.

The application of Skylab altimetry to marine geoid determination

NASA Technical Reports Server (NTRS)

Mourad, A. G.; Gopalapillai, S.; Kuhner, M.; Fubara, D. M. (Principal Investigator)

1975-01-01

The author had identified the following significant results. The major results can be divided broadly into two groups. One group is concerned with the effects of errors inherent in the various input data, such as the orbit emphemeris, a priori geoid etc. The other consists of the results of the actual analysis of the data from the Skylab EREP passes 4, 6, 7, and 9. Results from the first group were obtained from the analysis of some preliminary data from EREP pass 9 mode 5. The second group of results consists of a set of recovered bias terms for each of the submodes of observations and a set of nine altimetry geoid profiles corresponding to the various passes and modes. Along with each of these profiles, the a priori geoid, gravity anomaly, and the bathymetric data profiles are also presented for easy comparison.

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

NASA Astrophysics Data System (ADS)

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

ICESat-derived lithospheric flexure as caused by an endorheic lake's expansion on the Tibetan Plateau and the comparison to modeled flexural responses

NASA Astrophysics Data System (ADS)

Madson, Austin; Sheng, Yongwei; Song, Chunqiao

2017-10-01

A substantial and rapid expansion beginning in the late 1990s of Siling Co, the largest endorheic lake on the central Tibetan Plateau (TP), has caused a measurable lithospheric deflection in the region adjacent to the lake. Current broad-scale measuring of this flexural response is mainly derived from InSAR processing techniques or time-consuming field campaigns. The rheological constraints of the lithosphere from the underlying lithospheric response to large lake loads in this region are not well understood. This paper highlights a more efficient spaceborne LiDAR remote sensing technique to measure the deflection in the vicinity of Siling Co and to investigate the mechanisms of the observed lithospheric response in order to garner a better understanding of the local rheology. A lake-adjacent deflection rate and Siling Co water load variations are calculated utilizing the Geoscience Laser Altimeter System (GLAS) onboard NASA's Ice, Cloud and land Elevation Satellite (ICESat) and the joint NASA/USGS Landsat series of Earth observing satellites. A downward deflection rate of ∼5.6 mm/yr for the first 4 km of lake-adjacent land is calculated from the GLAS instrument, and this response is compared to the flexural outputs from a spherically symmetric, non-rotating, elastic, and isotropic (SNREI) Earth model in order to better understand the underlying mechanisms of the lithospheric response to the rapid increase of Siling Co loads. The modeled elastic response is ∼6.9 times lower than the GLAS derived flexure, thereby providing further evidence that a purely elastic lithospheric response cannot explain the deflection in this region. The relationship between the modeled elastic response and the GLAS derived flexure is applied to a long-term lake load change dataset to create the longest-running flexural response curve as caused by the last ∼40 years of Siling Co load variations, and these results show an accumulated lake-adjacent flexure of ∼12.6 cm from an

Towards decadal time series of Arctic and Antarctic sea ice thickness from radar altimetry

NASA Astrophysics Data System (ADS)

Hendricks, S.; Rinne, E. J.; Paul, S.; Ricker, R.; Skourup, H.; Kern, S.; Sandven, S.

2016-12-01

The CryoSat-2 mission has demonstrated the value of radar altimetry to assess the interannual variability and short-term trends of Arctic sea ice over the existing observational record of 6 winter seasons. CryoSat-2 is a particular successful mission for sea ice mass balance assessment due to its novel radar altimeter concept and orbit configuration, but radar altimetry data is available since 1993 from the ERS-1/2 and Envisat missions. Combining these datasets promises a decadal climate data record of sea ice thickness, but inter-mission biases must be taken into account due to the evolution of radar altimeters and the impact of changing sea ice conditions on retrieval algorithm parametrizations. The ESA Climate Change Initiative on Sea Ice aims to extent the list of data records for Essential Climate Variables (ECV's) with a consistent time series of sea ice thickness from available radar altimeter data. We report on the progress of the algorithm development and choices for auxiliary data sets for sea ice thickness retrieval in the Arctic and Antarctic Oceans. Particular challenges are the classification of surface types and freeboard retrieval based on radar waveforms with significantly varying footprint sizes. In addition, auxiliary data sets, e.g. for snow depth, are far less developed in the Antarctic and we will discuss the expected skill of the sea ice thickness ECV's in both hemispheres.

Subsurface Scattered Photons: Friend or Foe? Improving visible light laser altimeter elevation estimates, and measuring surface properties using subsurface scattered photons

NASA Astrophysics Data System (ADS)

Greeley, A.; Kurtz, N. T.; Neumann, T.; Cook, W. B.; Markus, T.

2016-12-01

Photon counting laser altimeters such as MABEL (Multiple Altimeter Beam Experimental Lidar) - a single photon counting simulator for ATLAS (Advanced Topographical Laser Altimeter System) - use individual photons with visible wavelengths to measure their range to target surfaces. ATLAS, the sole instrument on NASA's upcoming ICESat-2 mission, will provide scientists a view of Earth's ice sheets, glaciers, and sea ice with unprecedented detail. Precise calibration of these instruments is needed to understand rapidly changing parameters such as sea ice freeboard, and to measure optical properties of surfaces like snow covered ice sheets using subsurface scattered photons. Photons that travel through snow, ice, or water before scattering back to an altimeter receiving system travel farther than photons taking the shortest path between the observatory and the target of interest. These delayed photons produce a negative elevation bias relative to photons scattered directly off these surfaces. We use laboratory measurements of snow surfaces using a flight-tested laser altimeter (MABEL), and Monte Carlo simulations of backscattered photons from snow to estimate elevation biases from subsurface scattered photons. We also use these techniques to demonstrate the ability to retrieve snow surface properties like snow grain size.

The Caspian Sea water dynamics based on satellite imagery and altimetry

NASA Astrophysics Data System (ADS)

Kostianoy, Andrey G.; Lebedev, Sergey

The Caspian Sea water dynamics is poorly known due to a lack of special hydrographic measurements. The known schemes of general circulation of the sea proposed by N.M. Knipovich in 1914-1915 and 1921, A.I. Mikhalevskiy (1931), G.N. Zaitsev (1935) and V.N. Zenin (1942) represent the basin-scale cyclonic gyres in the Middle and Southern Caspian, and no clear scheme for the shallow Northern Caspian. Later numerical models could move forward from these simple schemes of circulation to the more detailed seasonal or climatic schemes of currents, but different approaches and models give different results which significantly differ from each other (Trukhchev et al., 1995; Ibrayev et al., 2003, 2010; Popov, 2004, 2009; Knysh et al., 2008). Satellite monitoring of the Caspian Sea, we perform since 2000, is a useful tool for investigation of water dynamics in the Caspian Sea. To determine mesoscale water structure and dynamics, we used different kind of physical (SST and ice), chemical (suspended matter and water turbidity) and biological (chlorophyll concentration and algal bloom) tracers on satellite imagery. Satellite altimetry (sea level anomalies in combination with the mean dynamic level derived from numerical modeling) provides fields of currents in the whole Caspian Sea on a regular basis (every 10 days). Seasonal fields of currents derived from satellite altimetry also differ from those obtained in numerical models. Finally, we show the results of the first drifter experiment performed in the Caspian Sea in 2006-2008 in the framework of the MACE Project. Special attention is paid to the seasonal upwelling along the eastern coast of the sea, coastal currents, and a giant intrusion of warm water from the Southern to the Middle Caspian Sea.

Investigating ice shelf mass loss processes from continuous satellite altimetry

NASA Astrophysics Data System (ADS)

Fricker, H. A.

2017-12-01

The Antarctic Ice Sheet continually gains mass through snowfall over its large area and, to remain approximately in equilibrium, it sheds most of this excess mass through two processes, basal melting and iceberg calving, that both occur in the floating ice shelves surrounding the continent. Small amounts of mass are also lost by surface melting, which occurs on many ice shelves every summer to varying degrees, and has been linked to ice-shelf collapse via hydrofracture on ice shelves that have been pre-weakened. Ice shelves provide mechanical support to `buttress' seaward flow of grounded ice, so that ice-shelf thinning and retreat result in enhanced ice discharge to the ocean. Ice shelves are susceptible to changes in forcing from both the atmosphere and the ocean, which both change on a broad range of timescales to modify mass gains and losses at the surface and base, and from internal instabilities of the ice sheet itself. Mass loss from iceberg calving is episodic, with typical intervals between calving events on the order of decades. Since ice shelves are so vast, the only viable way to monitor them is with satellites. Here, we discuss results from satellite radar and laser altimeter data from one NASA satellite (ICESat), and four ESA satellites (ERS-1, ERS-2, Envisat, CryoSat-2) to obtain estimates of ice-shelf surface height since the early 1990s. The continuous time series show accelerated losses in total Antarctic ice-shelf volume from 1994 to 2017, and allow us to investigate the processes causing ice-shelf mass change. For Larsen C, much of the variability comes from changing atmospheric conditions affecting firn state. In the Amundsen Sea, the rapid thinning is a combination of accelerated ocean-driven thinning and ice dynamics. This long-term thinning signal is, however, is strongly modulated by ENSO-driven interannual variability. However, observations of ocean variability around Antarctica are sparse, since these regions are often covered in sea ice

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

NASA Astrophysics Data System (ADS)

Khaki, Mehdi; Sneeuw, Nico

2015-04-01

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

Mapping sub-surface geostrophic currents from altimetry and a fleet of gliders

NASA Astrophysics Data System (ADS)

Alvarez, A.; Chiggiato, J.; Schroeder, K.

2013-04-01

Integrating the observations gathered by different platforms into a unique physical picture of the environment is a fundamental aspect of networked ocean observing systems. These are constituted by a spatially distributed set of sensors and platforms that simultaneously monitor a given ocean region. Remote sensing from satellites is an integral part of present ocean observing systems. Due to their autonomy, mobility and controllability, underwater gliders are envisioned to play a significant role in the development of networked ocean observatories. Exploiting synergism between remote sensing and underwater gliders is expected to result on a better characterization of the marine environment than using these observational sources individually. This study investigates a methodology to estimate the three dimensional distribution of geostrophic currents resulting from merging satellite altimetry and in situ samples gathered by a fleet of Slocum gliders. Specifically, the approach computes the volumetric or three dimensional distribution of absolute dynamic height (ADH) that minimizes the total energy of the system while being close to in situ observations and matching the absolute dynamic topography (ADT) observed from satellite at the sea surface. A three dimensional finite element technique is employed to solve the minimization problem. The methodology is validated making use of the dataset collected during the field experiment called Rapid Environmental Picture-2010 (REP-10) carried out by the NATO Undersea Research Center-NURC during August 2010. A marine region off-shore La Spezia (northwest coast of Italy) was sampled by a fleet of three coastal Slocum gliders. Results indicate that the geostrophic current field estimated from gliders and altimetry significantly improves the estimates obtained using only the data gathered by the glider fleet.

Polar Dunes Resolved by the Mars Orbiter Laser Altimeter Gridded Topography and Pulse Widths

NASA Technical Reports Server (NTRS)

Neumann, Gregory A.

2003-01-01

The Mars Orbiter Laser Altimeter (MOLA) polar data have been refined to the extent that many features poorly imaged by Viking Orbiters are now resolved in densely gridded altimetry. Individual linear polar dunes with spacings of 0.5 km or more can be seen as well as sparsely distributed and partially mantled dunes. The refined altimetry will enable measurements of the extent and possibly volume of the north polar ergs. MOLA pulse widths have been recalibrated using inflight data, and a robust algorithm applied to solve for the surface optical impulse response. It shows the surface root-mean-square (RMS) roughness at the 75-m-diameter MOLA footprint scale, together with a geological map. While the roughness is of vital interest for landing site safety studies, a variety of geomorphological studies may also be performed. Pulse widths corrected for regional slope clearly delineate the extent of the polar dunes. The MOLA PEDR profile data have now been re-released in their entirety (Version L). The final Mission Experiment Gridded Data Records (MEGDR's) are now provided at up to 128 pixels per degree globally. Densities as high as 512 pixels per degree are available in a polar stereographic projection. A large computational effort has been expended in improving the accuracy of the MOLA altimetry themselves, both in improved orbital modeling and in after-the-fact adjustment of tracks to improve their registration at crossovers. The current release adopts the IAU2000 rotation model and cartographic frame recommended by the Mars Cartography Working Group. Adoption of the current standard will allow registration of images and profiles globally with an uncertainty of less than 100 m. The MOLA detector is still operational and is currently collecting radiometric data at 1064 nm. Seasonal images of the reflectivity of the polar caps can be generated with a resolution of about 300 m per pixel.

Recent Ice Sheet and Glacier Elevation Changes in Greenland from Aircraft Laser Altimetry

NASA Technical Reports Server (NTRS)

Krabill, William B.; Thomas, R.; Sonntag, J.; Manizade, S.; Yungel, J.

2008-01-01

The Arctic Ice Mapping group (Project AIM) at the NASA Goddard Space Flight Center Wallops Flight Facility has been conducting systematic topographic surveys of the Greenland Ice Sheet (GIS) since 1993, using scanning airborne laser altimeters combined with Global Positioning System (UPS) technology. Earlier surveys showed the ice sheet above 2000-rn elevation to be in balance, but with localized regions of thickening or thinning. Thinning predominates at lower elevations and thinning rates have recently increased, resulting in a negative mass balance for the entire ice sheet. Recently, critical segments of near-coastal flight lines in Greenland were resurveyed. Results from the new data will be presented.

Sulzberger Ice Shelf Tidal Signal Reconstruction Using InSAR

NASA Astrophysics Data System (ADS)

Baek, S.; Shum, C.; Yi, Y.; Kwoun, O.; Lu, Z.; Braun, A.

2005-12-01

Synthetic Aperture Radar Interferometry (InSAR) and Differential InSAR (DInSAR) have been demonstrated as useful techniques to detect surface deformation over ice sheet and ice shelves over Antarctica. In this study, we use multiple-pass InSAR from the ERS-1 and ERS-2 data to detect ocean tidal deformation with an attempt towards modeling of tides underneath an ice shelf. High resolution Digital Elevation Model (DEM) from repeat-pass interferometry and ICESat profiles as ground control points is used for topographic correction over the study region in Sulzberger Ice Shelf, West Antarctica. Tidal differences measured by InSAR are obtained by the phase difference between a point on the grounded ice and a point on ice shelf. Comparison with global or regional tide models (including NAO, TPXO, GOT, and CATS) of a selected point shows that the tidal amplitude is consistent with the values predicted from tide models to within 4 cm RMS. Even though the lack of data hinders the effort to readily develop a tide model using longer term data (time series span over years), we suggest a method to reconstruction selected tidal constituents using both vertical deformation from InSAR and the knowledge on aliased tidal frequencies from ERS satellites. Finally, we report the comparison results of tidal deformation observed by InSAR and ICESat altimetry.

ATLAS Beam Steering Mechanism (BSM) Lessons Learned

NASA Technical Reports Server (NTRS)

Blumenstock, Kenneth A.; Cramer, Alexander K.; Gosten, Alan B.; Hakun, Claef F.; Haney, Paul G.; Hinkle, Matthew R.; Lee, Kenneth Y.; Lugo, Carlos F.; Matuszeski, Adam J.; Morell, Armando;

ATLAS Beam Steering Mechanism Lessons Learned

NASA Technical Reports Server (NTRS)

Blumenstock, Kenneth A.; Cramer, Alexander K.; Gostin, Alan B.; Hakun, Claef F.; Haney, Paul G.; Hinkle, Matthew R.; Lee, Kenneth Y.; Lugo, Carlos F.; Matuszeski, Adam J.; Morrell, Armando;

Large-scale Estimates of Leaf Area Index from Active Remote Sensing Laser Altimetry

NASA Astrophysics Data System (ADS)

Hopkinson, C.; Mahoney, C.

2016-12-01

Leaf area index (LAI) is a key parameter that describes the spatial distribution of foliage within forest canopies which in turn control numerous relationships between the ground, canopy, and atmosphere. The retrieval of LAI has demonstrated success by in-situ (digital) hemispherical photography (DHP) and airborne laser scanning (ALS) data; however, field and ALS acquisitions are often spatially limited (100's km2) and costly. Large-scale (>1000's km2) retrievals have been demonstrated by optical sensors, however, accuracies remain uncertain due to the sensor's inability to penetrate the canopy. The spaceborne Geoscience Laser Altimeter System (GLAS) provides a possible solution in retrieving large-scale derivations whilst simultaneously penetrating the canopy. LAI retrieved by multiple DHP from 6 Australian sites, representing a cross-section of Australian ecosystems, were employed to model ALS LAI, which in turn were used to infer LAI from GLAS data at 5 other sites. An optimally filtered GLAS dataset was then employed in conjunction with a host of supplementary data to build a Random Forest (RF) model to infer predictions (and uncertainties) of LAI at a 250 m resolution across the forested regions of Australia. Predictions were validated against ALS-based LAI from 20 sites (R2=0.64, RMSE=1.1 m2m-2); MODIS-based LAI were also assessed against these sites (R2=0.30, RMSE=1.78 m2m-2) to demonstrate the strength of GLAS-based predictions. The large-scale nature of current predictions was also leveraged to demonstrate large-scale relationships of LAI with other environmental characteristics, such as: canopy height, elevation, and slope. The need for such wide-scale quantification of LAI is key in the assessment and modification of forest management strategies across Australia. Such work also assists Australia's Terrestrial Ecosystem Research Network, in fulfilling their government issued mandates.

KSC-02pd2052

NASA Image and Video Library

2002-10-25

KENNEDY SPACE CENTER, FLA. - The Ice, Cloud, and Land Elevation Satellite, or ICESat, undergoes final processing before launch. ICESat is a 661-pound satellite known as Geoscience Laser Altimeter System (GLAS) that will revolutionize our understanding of ice and its role in global climate change and how we protect and understand our home planet. It will help scientists determine if the global sea level is rising or falling. It will look at the ice sheets that blanket the Earth's poles to see if they are growing or shrinking. It will assist in developing an understanding of how changes in the Earth's atmosphere and climate effect polar ice masses and global sea level. ICESat is scheduled for launch, with the Cosmic Hot Interstellar Plasma Spectrometer or CHIPSat, on a Delta II expendable launch vehicle from Vandenberg Air Force Base, Calif., on Jan. 11, 2003, between 4:45 p.m. - 5:30 p.m. PST.

KSC-02pd2050

NASA Image and Video Library

2002-10-24

KENNEDY SPACE CENTER, FLA. - The Ice, Cloud, and Land Elevation Satellite, or ICESat, logo features an artist's rendition of the satellite orbiting the Earth. ICESat is a 661-pound satellite known as Geoscience Laser Altimeter System (GLAS) that will revolutionize our understanding of ice and its role in global climate change and how we protect and understand our home planet. It will help scientists determine if the global sea level is rising or falling. It will look at the ice sheets that blanket the Earth's poles to see if they are growing or shrinking. It will assist in developing an understanding of how changes in the Earth's atmosphere and climate effect polar ice masses and global sea level. ICESat is scheduled for launch, with the Cosmic Hot Interstellar Plasma Spectrometer or CHIPSat, on a Delta II expendable launch vehicle from Vandenberg Air Force Base, Calif., on Jan. 11, 2003, between 4:45 p.m. - 5:30 p.m. PST.

KSC-02pd2051

NASA Image and Video Library

2002-10-25

KENNEDY SPACE CENTER, FLA. - The Ice, Cloud, and Land Elevation Satellite, or ICESat, undergoes final processing before launch. ICESat is a 661-pound satellite known as Geoscience Laser Altimeter System (GLAS) that will revolutionize our understanding of ice and its role in global climate change and how we protect and understand our home planet. It will help scientists determine if the global sea level is rising or falling. It will look at the ice sheets that blanket the Earth's poles to see if they are growing or shrinking. It will assist in developing an understanding of how changes in the Earth's atmosphere and climate effect polar ice masses and global sea level. ICESat is scheduled for launch, with the Cosmic Hot Interstellar Plasma Spectrometer or CHIPSat, on a Delta II expendable launch vehicle from Vandenberg Air Force Base, Calif., on Jan. 11, 2003, between 4:45 p.m. - 5:30 p.m. PST.

Energetics of global ocean tides from Geosat altimetry

NASA Technical Reports Server (NTRS)

Cartwright, David E.; Ray, Richard D.

1991-01-01

The present paper focuses on resonance and energetics of the daily tides, especially in the southern ocean, the distribution of gravitational power input of daily and half-daily tides, and comparison with other estimates of global dissipation rates. The present global tidal maps, derived from Geosat altimetry, compare favorably with ground truth data at about the same rms level as the models of Schwiderski (1983), and are slightly better in lunar than in solar tides. Diurnal admittances clearly show Kelvin wave structure in the southern ocean and confirm the resonant mode of Platzman (1984) at 28.5 + or - 0.1 hr with an apparent Q of about 4. Driving energy is found to enter dominantly in the North Pacific for the daily tides and is strongly peaked in the tropical oceans for the half-daily tides. Global rates of working on all major tide constituents except S2 agree well with independent results from analyses of gravity through satellite tracking. Comparison at S2 is improved by allowing for the air tide in gravitational results but suggests deficiencies in all solar tide models.

ICESat-2 ATLAS Beam Steering Mechanism (BSM)

NASA Technical Reports Server (NTRS)

Hinkle, Matthew

2015-01-01

This work covers the design and test of a beam steering mechanism (BSM) used to accurately guide a laser on the Advanced Topographic Laser Altimeter System (ATLAS) down to Earth in order to measure elevation. It describes the main components in the BSM that allows it to perform and meet stringent requirements. Requirements of the BSM include two-axis steering of the transmitted laser beam, +-5000 uRad mechanical motion in each axis, and 1.5 uRad RMS pointing stability among many other requirements. The BSM uses four voice coil actuators in order to locate the mirror at the angle we need. There are four Differential Position Sensors that determine the position and angle of the mirror at all times. These sensors were verified through optical testing in both ambient and thermal conditions. Testing and extensive analyses were performed on the two-axis flexure throughout the program to check flexure thickness, positive margins, and infinite life. The mirror mount design has been modified to eliminate radial preload, while incorporating a titanium wave spring to provide an axial preload of 10.8N. The BSM underwent multiple tests in order to verify all components work as required under various conditions.

Water Storage Changes using Floodplain Bathymetry from InSAR and satellite altimetry in the Congo River Basin

NASA Astrophysics Data System (ADS)

Yuan, T.; Lee, H.; Jung, H. C.; Beighley, E.; Alsdorf, D. E.

2016-12-01

Extensive wetlands and swamps expand along the Congo River and its tributaries. These wetlands store water and attenuate flood wave during high water season. Substantial dissolved and solid substances are also transported with the water flux, influencing geochemical environment and biogeochemistry processes both in the wetlands and the river. To understand the role of the wetlands in partitioning the surface water and the accompanied material movement, water storage change is one of the most fundamental observations. The water flow through the wetlands is complex, affected by topography, vegetation resistance, and hydraulic variations. Interferometric Synthetic Aperture Radar (InSAR) has been successfully used to map relative water level changes in the vegetated wetlands with high spatial resolution. By examining interferograms generated from ALOS PALSAR along the middle reach of the Congo River floodplain, we found greater water level changes near the Congo mainstem. Integrated analysis of InSAR and Envisat altimetry data has shown that proximal floodplain with higher water level change has lower elevation during dry season. This indicates that the spatial variation of water level change in the Congo floodplain is mostly controlled by floodplain bathymetry. A method based on water level and bathymetry model is proposed to estimate water storage change. The bathymetry model is composed of (1) elevation at the intersection of the floodplain and the river and (2) floodplain bathymetry slope. We first constructed the floodplain bathymetry by selecting an Envisat altimetry profile during low water season to estimate elevation at the intersection of the floodplain and the river. Floodplain bathymetry slope was estimated using InSAR measurements. It is expected that our new method can estimate water storage change with higher temporal resolution corresponding to altimeter's repeat cycle. In addition, given the multi-decadal archive of satellite altimetry measurements

Space-based Swath Imaging Laser Altimeter for Cryospheric Topographic and Surface Property Mapping

NASA Technical Reports Server (NTRS)

Abshire, James; Harding, David; Shuman, Chris; Sun, Xiaoli; Dabney, Phil; Krainak, Michael; Scambos, Ted

2005-01-01

Uncertainties in the response of the Greenland and Antarctic polar ice sheets to global climatic change inspired the development of ICESat/GLAS as part of NASA's Earth Observing System. ICESat's primary purpose is the measurement of ice sheet surface elevation profiles with sufficient accuracy, spatial density, and temporal coverage so that elevation changes can be derived with an accuracy of <1.5 cm/year for averages of measurements over the ice sheets with areas of 100 x 100 km. The primary means to achieve this elevation change detection is spatial averaging of elevation differences at cross-overs between ascending and descending profiles in areas of low ice surface slope. Additional information is included in the original extended abstract.

The Cryosphere Model Comparison Tool (CmCt): Ice Sheet Model Validation and Comparison Tool for Greenland and Antarctica

NASA Astrophysics Data System (ADS)

Simon, E.; Nowicki, S.; Neumann, T.; Tyahla, L.; Saba, J. L.; Guerber, J. R.; Bonin, J. A.; DiMarzio, J. P.

2017-12-01

The Cryosphere model Comparison tool (CmCt) is a web based ice sheet model validation tool that is being developed by NASA to facilitate direct comparison between observational data and various ice sheet models. The CmCt allows the user to take advantage of several decades worth of observations from Greenland and Antarctica. Currently, the CmCt can be used to compare ice sheet models provided by the user with remotely sensed satellite data from ICESat (Ice, Cloud, and land Elevation Satellite) laser altimetry, GRACE (Gravity Recovery and Climate Experiment) satellite, and radar altimetry (ERS-1, ERS-2, and Envisat). One or more models can be uploaded through the CmCt website and compared with observational data, or compared to each other or other models. The CmCt calculates statistics on the differences between the model and observations, and other quantitative and qualitative metrics, which can be used to evaluate the different model simulations against the observations. The qualitative metrics consist of a range of visual outputs and the quantitative metrics consist of several whole-ice-sheet scalar values that can be used to assign an overall score to a particular simulation. The comparison results from CmCt are useful in quantifying improvements within a specific model (or within a class of models) as a result of differences in model dynamics (e.g., shallow vs. higher-order dynamics approximations), model physics (e.g., representations of ice sheet rheological or basal processes), or model resolution (mesh resolution and/or changes in the spatial resolution of input datasets). The framework and metrics could also be used for use as a model-to-model intercomparison tool, simply by swapping outputs from another model as the observational datasets. Future versions of the tool will include comparisons with other datasets that are of interest to the modeling community, such as ice velocity, ice thickness, and surface mass balance.

Detailed gravity anomalies from Geos 3 satellite altimetry data

NASA Technical Reports Server (NTRS)