1. Full-waveform Airborne and Spaceborne Laser Altimetry for Mapping and Sampling the Earth's Forests, Cryosphere, and Land surfaces
    Blair, J. B. and Dubayah, R. and Hofton, M. A. and Luthcke, S. B. and Rabine, D. and Wake, S. and Coyle, B. and Stysley, P. and Salerno, C.    December 2014

    Laser altimetry is an established technique for providing precise and accurate measurements of topography, vegetation, ice sheets, glaciers and sea ice. The Land, Vegetation, and Ice Sensor (LVIS) is a wide swath, full-waveform laser altimeter that has been operational since the late 1990's and has mapped 100,000's of square kilometers around the globe. NASA is developing a Facility version of the LVIS sensor to make it more cost-effective and more easily available to the broader science community. Based heavily on the existing LVIS sensor, the Facility LVIS instrument includes numerous improvements for reliability, resolution, real-time performance monitoring, lower cost for integration and ops, and data consistency. Building upon the foundation provided by LVIS, the Global Ecosystem Dynamics Investigation (GEDI) Lidar was recently selected for funding as a part of NASA's Earth Venture Program and will use multiple laser beams to measure high-resolution forest structure and surface topography from the International Space Station (ISS). Dependent on the funding profile and availability of launch options to ISS, GEDI could launch as early as 2018. Within a single year of operations GEDI will provide billions of vegetation height and structure measurements for the precise estimation of biomass within the orbital coverage provided by ISS (+/- 51.6 degrees latitude). GEDI uses the same high-SNR waveform measurement technique as the airborne LVIS sensor. LVIS will provide calibration and validation of GEDI's on-orbit performance.



  2. Surface Elevation Measurements of Greenland and Antarctica Using NASA's Land, Vegetation and Ice Sensor (LVIS)
    Hofton, M. A. and Blair, J. B. and Rabine, D. and Beckley, M. and Brooks, C. and Cornejo, H. and Wake, S.    December 2014

    Since 2007, NASA's Land Vegetation and Ice Sensor (LVIS) has been used to collect wide-swath, waveform-based laser altimetry (lidar) measurements of large areas of Greenland and Antarctica from medium-high altitude airborne platforms. To date, ~350,000 km2 of data have been collected, processed and released via NSIDC under the auspices of NASA's Operation Icebridge. In November 2013, the LVIS was paired with the LVIS-GH sensor (an updated version of the instrument developed for high-altitude operations in the Global Hawk UAV) and used to overfly Spring 2013 Icebridge or Cryosat-2 tracks in Greenland and the Arctic, providing data for seasonal change assessments and validation of Cryosat-2. The precise and accurate, large-area coverage capabilities provided by the LVIS systems are important to supporting and enhancing future space-based lidar missions such as ICESat-2 and GEDI. To maximize such support as well as provide targeted data sets for end users in the cryosphere and other communities, the LVIS Facility capability is currently under development with goals of providing up to 5 times more data than present with 2 month turnaround at much reduced cost to the end user. A summary of the Facility as well as airborne LVIS data collected to date and comparisons utilizing data will be presented.



  3. Modelled and observed present-day state of the Jakobshavn Isbræ, west Greenland
    Khan, S. A. and Muresan, I. S. and Aschwanden, A. and Khroulev, C.    December 2014

    Jakobshavn Isbræ located in west Greenland drains approximately 7.5 \% of the area of the Greenland ice sheet (GrIS). Understanding its sensitivity to climatic forcing is critical for assessing mass balance of the GrIS. Here we use a high-resolution, three dimensional and time-dependent regional outlet glacier model developed as part of the Parallel Ice Sheet Model (PISM) forced by climatology datasets from RACMO2 to model present-day state of Jakobshavn Isbræ. Our choice of modelling consists of a forward integration in time (hindcasting) for 1990-2012 with monthly climatic forcing. To assess the modeled mass change, we use observed ice volume change from airborne and satellite laser altimetry from ATM, ICESat, and LVIS during 1997-2013 and convert to mass change. However, the airborne and satellite measurements are conducted few times per year, and may provide yearly mass loss rates only. To assess weekly to monthly scale mass variability, we use measurements of bedrock displacement from permanent GPS sites during 2005-2013. The GPS data provide daily to monthly scale estimates of bedrock displacements caused by the earth's elastic response to ice mass change from Jakobshavn Isbræ. Additionally, we assess modeled ice velocities (and velocity changes) with observed velocities obtained from measurements of ice motion by satellite interferometric synthetic-aperture radar (InSAR) data from the RADARSAT-1 satellite.Our results show good agreement between modeled and observed mass change and velocity change from weekly to long-term timespan. Both model and observations show huge mass loss anomalies in 2010 and 2012 caused by enhanced melting during summer months.



  4. Beyond Radar Backscatter: Estimating Forest Structure and Biomass with Radar Interferometry and Lidar Remote Sensing
    Lavalle, M. and Ahmed, R.    December 2014

    Mapping forest structure and aboveground biomass globally is a major challenge that the remote sensing community has been facing for decades. Radar backscatter is sensitive to biomass only up to a certain amount (about 150 tons/ha at L-band and 300 tons/ha at P-band), whereas lidar remote sensing is strongly limited by poor spatial coverage. In recent years radar interferometry, including its extension to polarimetric radar interferometry (PolInSAR), has emerged as a new technique to overcome the limitations of radar backscatter. The idea of PolInSAR is to use jointly interferometric and polarimetric radar techniques to separate different scattering mechanisms and retrieve the vertical structure of forests. The advantage is to map ecosystem structure continuously over large areas and independently of cloud coverage. Experiments have shown that forest height - an important proxy for biomass - can be estimated using PolInSAR with accuracy between 15\% and 20\% at plot level. At AGU we will review the state-of-art of repeat-pass PolInSAR for biomass mapping, including its potential and limitations, and discuss how merging lidar data with PolInSAR data can be beneficial not only for product cross-validation but also for achieving better estimation of ecosystem properties over large areas. In particular, lidar data are expected to aid the inversion of PolInSAR models by providing (1) better identification of ground under the canopy, (2) approximate information of canopy structure in limited areas, and (3) maximum tree height useful for mapping PolInSAR temporal decorrelation. We will show our tree height and biomass maps using PolInSAR L-band JPL/UAVSAR data collected in tropical and temperate forests, and P-band ONERA/TROPISAR data acquired in French Guiana. LVIS lidar data will be used, as well as SRTM data, field measurements and inventory data to support our study. The use of two different radar frequencies and repeat-pass JPL UAVSAR data will offer also the opportunity to compare our results with the new airborne P-band ECOSAR and L-band DBSAR instruments developed at the NASA Goddard Space Flight Center.



  5. A Digital Elevation Model of the Greenland Ice Sheet based on Envisat and CryoSat-2 Radar Altimetry
    Levinsen, J. F. and Smith, B. E. and Sandberg Sørensen, L. and Khvorostovsky, K. and Forsberg, R.    December 2014

    With the launch of the first radar altimeter by ESA in 1992, more than two decades of radar altimetry data are now available. Therefore, one goal of ESA's Ice Sheet Climate Change Initiative is the estimation of surface elevation changes of the Greenland Ice Sheet (GrIS) based on ERS-1, -2, Envisat, CryoSat-2, and, in the longer term, Sentinel-3 data. This will create a data record from 1992 until present date. In addition to elevation-change records, such data can be processed to produce digital elevation models, or DEMs, of the ice sheets. The DEMs can be used to correct radar altimetry data for slope-induced errors resulting from the large footprint (e.g. 2-10 km for Envisat vs. 60 m for ICESat laser altimetry) or to correct for the underlying surface topography when applying the repeat-track method. DEMs also provide key information in e.g. SAR remote sensing of ice velocities to remove the interferograms' topographic signal or in regional climate modeling. This work focuses on the development of a GrIS DEM from Envisat and CryoSat-2 altimetry, corrected with temporally and spatially coincident NASA ICESat, ATM, and LVIS laser data. The spatial resolution is 2 x 2 km and the reference year 2010. It is based on 2009 and 2010 data, the 2009 data adjusted to 2010 by accounting for the intermediate elevation changes. This increases the spatial data coverage and reduces data errors. The GIMP DEM has been corrected for negative elevations and errors in the north, and used to constrain the final DEM. The recently acquired observations and increased data coverage give a strong advantage to this DEM relative to previous models, based on lower-resolution, more temporally scattered data (e.g. a decade of observations or only ICESat data, limited to three annual 35-day acquisition periods). Furthermore, as surface changes occur continuously, an up-to-date DEM is necessary to correctly constrain the observations, thereby ensuring an accurate change detection or modeling process.



  6. Impact of External Forcing on Glacier Dynamics at Jakobshavn Isbræ during 1840-2012
    Muresan, I. S. and Khan, S. A. and Aschwanden, A. and Khroulev, C. and Bjork, A. A. and Box, J. E.    December 2014

    Greenland's main outlet glaciers have more than doubled their contribution to global sea-level rise over the past decade through acceleration of ice discharge. One of the triggering mechanisms is a reduction in resistance (buttressing) at the marine based glacier front (i.e. through reduced thickness or retreat of the floating tongue of a glacier) caused by enhanced calving or a longer-term thinning due to a mass deficit of the ice sheet. Recent findings indicate the reduced buttressing at the marine terminus is responsible for the recent dynamic changes observed in Greenland, but the controlling processes and triggering mechanisms are still unclear. Furthermore, our current understanding is almost entirely based on observations from a short-term record spanning only from a year to a decade, and is characterized by short-term fluctuations and therefore not representative for longer-term trends of several decade time scales. Here, we study the mechanisms controlling dynamic changes at the terminus of Jakobshavn Isbræ over a period of 172 years. The recent glacier acceleration began in late 1990s but there is evidence for glacier retreat of comparable magnitude in 1930s, when a similarly warm period occurred. To control the acceleration and retreat based on observed front positions during 1840-2012, we use an ocean model modifier that implements forcing at the ocean boundary using melange back pressure offsets. The mean temperature anomaly in west Greenland, the North Atlantic oscillation (NAO) winter index and the Atlantic multidecadal oscillation (AMO) index anomalies for the period 1900-2012 sustain our modelling results. The modelled surface elevation changes near the front are considered and compared with observed surface elevation changes for the period 1880-2012. Furthermore, the modelled mass loss signal between 1997-2012 is validated based on ice mass change observations which we estimate using altimeter surveys from NASA's ATM flights during 1997-2012 supplemented with high-resolution Ice, Cloud and land Elevation Satellite (ICESat) data during 2003-2009 and Land, Vegetation and Ice Sensor (LVIS) data during 2007-2012. Our choice of ice sheet model comprises the Parallel Ice Sheet Model (PISM) and a continuous 172 years reconstruction of surface mass balance and its sub-components (Box, 2013).



  7. Estimating Canopy Height of a Temperate Forest from TanDEM-X and LVIS Data
    Qi, W. and Dubayah, R. and Kugler, F.    December 2014

    The recently launched TanDEM-X mission is the first single-pass polarimetric interferometer in space allowing global estimation of forest parameters without any temporal decorrelation. This study investigates the potential of single-polarized TanDEM-X data for forest height inversion and structure characterization. For this purpose, a temperate forest - Hubbard Brook Experimental Forest (HBEF) in New Hampshire is chosen for experiment. Stripmap-mode HH-polarized TanDEM-X bistatic data (with resolution at 3 m) acquired at different baselines was used. LVIS data was applied to remove the ground phase component of the TanDEM-X interferogram and to validate the derived results. Forest parameters, e.g. canopy height and extinction coefficient were estimated based on Random Volume over Ground (RVoG) model. Scattering phase height (SPH) was also calculated and validated against LVIS rh100. A clear correlation was observed between TanDEM-X SPH and the reference height with an r2 of around 0.6 at 150m resolution. The inverted tree height had an RMSE of less than 3.4 m and an r2 of around 0.7 at the same resolution. It is shown that TanDEM-X data has great potential for improving the understanding and quantification of global forest canopy height and structure.



  8. Forest Biomass Mapping from Prism Triplet, Palsar and Landsat Data
    Ranson, J. and Sun, G. and Ni, W.  AGU  December 2014

    The loss of sensitivity at higher biomass levels is a common problem in biomass mapping using optical multi-spectral data or radar backscattering data due to the lack of information on canopy vertical structure. Studies have shown that adding implicit information of forest vertical structure improves the performance of forest biomass mapping from optical reflectance and radar backscattering data. LiDAR, InSAR and stereo imager are the data sources for obtaining forest structural information. The potential of providing information on forest vertical structure by stereoscopic imagery data has drawn attention recently due to the availability of high-resolution digital stereo imaging from space and the advances of digital stereo image processing software. The Panchromatic Remote-sensing Instrument for Stereo Mapping (PRISM) onboard the Advanced Land Observation Satellite (ALOS) has acquired multiple global coverage from June 2006 to April 2011 providing a good data source for regional/global forest studies. In this study, five PRISM triplets acquired on June 14, 2008, August 19 and September 5, 2009; PALSAR dual-pol images acquired on July 12, 2008 and August 30, 2009; and LANDSAT 5 TM images acquired on September 5, 2009 and the field plot data collected in 2009 and 2010 were used to map forest biomass at 50m pixel in an area of about 4000 km2in Maine, USA ( 45.2 deg N 68.6 deg W). PRISM triplets were used to generate point cloud data at 2m pixel first and then the average height of points above NED (National Elevation Dataset) within a 50m by 50m pixel was calculated. Five images were mosaicked and used as canopy height information in the biomass estimation along with the PALSAR HH, HV radar backscattering and optical reflectance vegetation indices from L-5 TM data. A small portion of this region was covered by the Land Vegetation and Ice Sensor (LVIS) in 2009. The biomass maps from the LVIS data was used to evaluate the results from combined use of PRISM, PALSAR and LANDSAT data. The results show that the canopy height index from PRISM stereo images significantly improves the biomass mapping accuracy and extends the saturation level of biomass, and results in a biomass map comparable with those generated from LVIS data.



  9. Landscape and forest structural controls on wood density and aboveground biomass along a tropical elevation gradient in Costa Rica
    Robinson, C. M. and Saatchi, S. S. and Clark, D. B. and Gillespie, T. W. and Andelman, S.    December 2014

    This research seeks to understand how tree wood density and taxonomic diversity relate to topography and three-dimensional vegetation structure in the tropical montane forest of Braulio Carrillo National Park in Costa Rica. The study utilized forest inventory and botanical data from twenty 1-ha plots ranging from 55 m to 2800 m above sea level and remote sensing data from an airborne lidar sensor (NASA's Land, Vegetation, and Ice Sensor [LVIS]) to quantify variations in forest structure. There is growing evidence that ecosystem structure plays an important role in defining patterns of species diversity and help to control the phenotypic and functional variations across landscapes. Elevation gradients along mountains provide landscape-size scales through which variations in topography, climate, and edaphic conditions as drivers of biodiversity can be tested. In this study we report on the effectiveness of relating patterns of tree wood density and alpha diversity to three-dimensional structure of a tropical montane forest using remote sensing observations of forest structure. Wood density is an important parameter for aboveground biomass and carbon estimations. Tree cores were analyzed for wood density and compared to existing database values for the same species. In this manner we were able to test the effect of the gradient on wood density and on the subsequent aboveground biomass estimations. Understanding these patterns has implications for conservation of both ecosystem services and biodiversity. Our results indicate that there is a strong relationship between LVIS-derived forest 3D-structure and alpha diversity, likely controlled controlled by variations in abiotic factors and topography along the elevation. Using spatial analysis with the aid of remote sensing data, we found distinct patterns along the environmental gradients defining species composition and forest structure. Wood density values were found to vary significantly from database values for the same species. This variation in tree growth has repercussions on overall forest structure, and subsequent carbon estimates extrapolated from field measurements. Because these wood density values are directly tied to biomass estimates, it is possible that carbon storage has been overestimated along this gradient using prior methods.



  10. Amundsen Sea sector ice shelf thickness, melt rates, and inland response from annual high-resolution DEM mosaics
    Shean, D. E. and Joughin, I. R. and Smith, B. E. and Alexandrov, O. and Moratto, Z. and Porter, C. C. and Morin, P. J.    December 2014

    Significant grounding line retreat, acceleration, and thinning have occurred along the Amundsen Sea sector of West Antarctica in recent decades. These changes are driven primarily by ice-ocean interaction beneath ice shelves, but existing observations of the spatial distribution, timing, and magnitude of ice shelf melt are limited. Using the NASA Ames Stereo Pipeline, we generated digital elevation models (DEMs) with ~2 m posting from all ~450 available WorldView-1/2 along-track stereopairs for the Amundsen Sea sector. A novel iterative closest point algorithm was used to coregister DEMs to filtered Operation IceBridge ATM/LVIS data and ICESat-1 GLAS data, offering optimal sub-meter horizontal/vertical accuracy. The corrected DEMs were used to produce annual mosaics for the entire ~500x700 km region with focused, sub-annual products for ice shelves and grounding zones. These mosaics provide spatially-continuous measurements of ice shelf topography with unprecedented detail. Using these data, we derive estimates of ice shelf thickness for regions in hydrostatic equilibrium and map networks of sub-shelf melt channels for the Pine Island (PIG), Thwaites, Crosson, and Dotson ice shelves. We also document the break-up of the Thwaites ice shelf and PIG rift evolution leading up to the 2013 calving event. Eulerian difference maps document 2010-2014 thinning over fast-flowing ice streams and adjacent grounded ice. These data reveal the greatest thinning rates over the Smith Glacier ice plain and slopes beyond the margins of the fast-flowing PIG trunk. Difference maps also highlight the filling of at least two subglacial lakes ~30 km upstream of the PIG grounding line in 2011. Lagrangian difference maps reveal the spatial distribution of ice shelf thinning, which can primarily be attributed to basal melt. Preliminary results show focused ice shelf thinning within troughs and large basal channels, especially along the western margin of the Dotson ice shelf. These new data provide critical observations that will improve our understanding ice-ocean interaction and mass loss for the Amundsen Sea sector on local and regional scales.



  11. Estimation of canopy height using lidar and radar interferometry: an assessment of combination methods and sensitivity to instrument, terrain and canopy height profile
    Simard, M. and Neumann, M. and Pinto, N. and Brolly, M. and Brigot, G.    December 2014

    The combined use of Lidar and radar interferometry to estimate canopy height can be classified into 3 categories: cross-validation, simple combination and fusion methods. In this presentation, we investigate the potential of each category for local and regional scale applications, and assess their sensitivity to instrument configuration, terrain topography and variations in the vertical forest canopy profiles. In addition to field data, we use data from TanDEM-X, UAVSAR (Uninhabited Aerial Vehicle Synthetic Aperture Radar), LVIS (Laser Vegetation Imaging Sensor) and a commercial discrete lidar. TanDEM-X is a pair of X-band spaceborne radars flying in formation to provide a global digital surface model and can also be used to perform polarimetric synthetic aperture radar (polinSAR) inversion of canopy height. The UAVSAR is an airborne fully polarimetric radar enabling repeat-pass interferometry and has been used for polinsar. While LVIS records the full waveform within a 20m footprint, the discrete lidar collects a cloud of points. The lidar data can be used to validate the polinSAR results (validation), to obtain ground elevation (simple combination with radar surface models) or within the polinSAR inversion model through a common model framework. The data was collected over the Laurentides Wildlife Reserve, a managed territory covering 7861km2 which is located between Québec city and Saguenay. The variety of management practices offers the possibility for long term and comparative studies of natural forest dynamics as well as the impact of human, fires and insect disturbances. The large elevational gradient of the region (~1000m) allows study of variations in structure and type of forests. Depending on the method used, several factors may degrade the accuracy of canopy height estimates from the combined use of lidar and radar interferometry. Here we will consider misregistration of datasets, differences in spatial resolution and viewing geometry, geometric decorrelation and the vertical wavenumber. Finally we investigate the sensitivity of estimate to forest vertical profile and terrain topography.



  12. Repeat-pass InSAR processing for Vegetation Height Calculation: Theory and a validated example
    Siqueira, P. and Lei, Y.    December 2014

    Knowledge of the vegetation height for a forested region is often used as a proxy for stem volume, biomass, and for characterizing habitats of a variety of plant and animal species. For this reason, remote sensing measures available from stereography, lidar, and InSAR have been important tools for airborne and spaceborne platforms. Among these and other candidates for measuring vegetation heights, InSAR has the advantage of achieving wide coverage areas (on the order of 100 km in cross-track swath) over short time periods, thus making it practical for large-scale assessments of the global environment. The determination of forest stand height (FSH), which is an assessment made on the order of one to ten hectares of resolution, InSAR can provide measures that are proportional to FSH. These are: 1.) interferometric phase compared to a known DEM, preferably of the bald earth, 2.) interferometric correlation (polarimetric or otherwise), which is related to the volume scattering nature of the target, and 3.) interferometric correlation which is related to the temporal decorrelation of the target. Of these, while the volumetric aspect of interferometric correlation is of keen interest, because of the dominant error source of temporal decorrelation, it comes at the cost of the need to perform single-pass interferometry. While such satellite systems do exist (notably the TanDEM-X mission), for vegetation applications, lower frequency systems such as ALOS-1 and -2, and the future NASA radar mission at L-band, provides better signal returns from throughout the vegetation canopy. Hence, rather than relying on volumetric correlation to provide the desired FSH signature, repeat-pass observations of temporal decorrelation are coupled with a vegetation model for this decorrelation to determine the vegetation height. In order to demonstrate this technique, the University of Massachusetts has used 46-day repeat-pass ALOS data to estimate FSH over the US State of Maine, nearly a 10 million hectare region. The results have been validated using the LVIS lidar system and a map of vegetation height provided by Woods Hole Research Center. This talk will describe the process that was used for creating this map, and how the data processing was automated to account for differences in temporal decorrelation over this large study area.



  13. Twelve years of Amundsen and Bellingshausen Coast Thinning Observed with Altimetry and Photogrammetry.
    Smith, B. E. and Shean, D. E. and Huth, A. and Morin, P. J. and Joughin, I. R.    December 2014

    From the start of the airborne laser surveys in late 2002 until the present, the elevation record for the Amundsen Coast of Antarctica from small-footprint elevation measurements now spans more than a dozen years: Laser-altimetry measurements on tracks spaced tens of km apart are available from ATM, LVIS, and ICESat; Worldview stereophotogrammetry (SP) gives high-resolution snapshots of surface topography for selected parts of the coast, and CRYOSAT gives high-temporal-resolution, spatially dense radar measurements, at modestly lower precision than the other sensors. We present synoptic estimates of elevation change based on judicious combinations of these data. Two sets of techniques yield complementary results: Combining laser-derived elevations with SP DEMs gives an elevation-change map covering most outlets with near-annual resolution between 2003 and the present, while combining Cryosat data with SP DEMs gives a database of radar elevations with improved ambiguity resolution that we process to estimate surface elevation changes between mid 2010 and the present. Firn and accumulation models help reduce the effects of accumulation variability on the derived elevation rates, allowing estimates of steady-atmosphere (''dynamic'') mass-change rates. These data reveal variable but increasing mass loss from Thwaites and Haynes glaciers, continuing mass loss from the glaciers draining into the Dotson and Crosson ice shelves, and significant losses on Alison ice stream and Ferrigno glacier on the Bellingshausen coast. There is also evidence for a recent hiatus in strong elevation change in parts of the grounding zone of Pine Island glacier, after nearly a decade of accelerating losses there. We discuss these findings in the context of measured surface speed changes and model estimates of ocean temperature variations.



  14. NASA's Operation Icebridge: Using Instrumented Aircraft to Bridge the Observational Gap Between Icesat and Icesat-2 Laser Altimeter Measurements
    Studinger, M.    December 2014

    NASA's Operation IceBridge images Earth's polar ice in unprecedented detail to better understand processes that connect the polar regions with the global climate system. Operation IceBridge utilizes a highly specialized fleet of research aircraft and the most sophisticated suite of innovative science instruments ever assembled to characterize annual changes in thickness of sea ice, glaciers, and ice sheets. In addition, Operation IceBridge collects critical data used to predict the response of Earth's polar ice to climate change and resulting sea-level rise. IceBridge also helps bridge the gap in polar observations between NASA's ICESat satellite missions. Combined with previous aircraft observations, as well as ICESat, CryoSat-2 and the forthcoming ICESat-2 observations, Operation IceBridge will produce a cross-calibrated 17-year time series of ice sheet and sea-ice elevation data over Antarctica, as well as a 27-year time series over Greenland. These time series will be a critical resource for predictive models of sea ice and ice sheet behavior. In addition to laser altimetry, Operation IceBridge is using a comprehensive suite of instruments to produce a three-dimensional view of the Arctic and Antarctic ice sheets, ice shelves and the sea ice. The suite includes two NASA laser altimeters, the Airborne Topographic Mapper (ATM) and the Land, Vegetation and Ice Sensor (LVIS); four radar systems from the University of Kansas' Center for Remote Sensing of Ice Sheets (CReSIS), a Ku-band radar altimeter, accumulation radar, snow radar and the Multichannel Coherent Radar Depth Sounder (MCoRDS); a Sander Geophysics airborne gravimeter (AIRGrav), a magnetometer and a high-resolution stereographic camera (DMS). Since its start in 2009, Operation IceBridge has deployed 8 geophysical survey aircraft and 19 science instruments. All IceBridge data is freely available from NSIDC (http://nsidc.org/data/icebridge) 6 months after completion of a campaign.



  15. Derive Icebridge Sea-Ice Freeboard and Thickness Data through Full Waveform Analysis
    Yi, D. and Harbeck, J. P. and Manizade, S. and Hofton, M. A. and Kurtz, N. T. and Studinger, M.    December 2014

    The current Operation IceBridge Airborne Topographic Mapper (ATM) sea-ice freeboard and thickness data product at the National Snow and Ice Data Center (NSIDC) requires coincident Digital Mapping System (DMS) imagery or Continuous Airborne Mapping By Optical Translator (CAMBOT) imagery to produce. However, some of the IceBridge ATM and Land, Vegetation, and Ice Sensor (LVIS) sea-ice flights have no coincident imagery data. In particular, the IceBridge ''South Basin Transect'' flights just north of the Canadian Archipelago have historically been flown under darkness (nighttime) and coincident imagery data are not available. Here we apply an algorithm using ATM waveform parameters to identify leads to derive sea-ice freeboard. ATM waveforms were fitted with Gaussian curves to calculate pulse width, peak location, pulse amplitude, and signal baseline. For each waveform, centroid, skewness, kurtosis, and pulse area were also calculated. Received waveform parameters, such as pulse width, pulse amplitude, pulse area, skewness, kurtosis, and transmitted/received pulse area ratio show a coherent response to variations of geophysical features along an ATM profile. These parameters, combined with elevation, were used to identify leads to enable sea-ice freeboard calculation. A similar algorithm is applied to the LVIS data to calculate sea-ice freeboard. Arctic sea-ice freeboards for ATM and LVIS data with no coincident visual imagery are derived in this study, extending the IceBridge sea-ice record over a large portion of thick multi-year sea ice. The results are evaluated/validated by using ATM data with coincident DMS imagery and near coincident ATM and LVIS data comparison.



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