HR: 0800h
AN: C51B-0386    [Abstracts]
TI: Enhancing a RADARSAT/ICESat Digital Elevation Model of West Antarctica Using MODIS Imagery
AU: * Haran, T M
EM: tharan@nsidc.org
AF: National Snow and Ice Data Center, Cooperative Institute for Research in Environmental Sciences, 449 UCB University of Colorado at Bouler, Boulder, CO 80309-0449, United States
AU: Scambos, T A
EM: teds@icehouse.colorado.edu
AF: National Snow and Ice Data Center, Cooperative Institute for Research in Environmental Sciences, 449 UCB University of Colorado at Bouler, Boulder, CO 80309-0449, United States
AB: An image enhancement approach is used to develop a new digital elevation map of West Antarctica, combining multiple MODIS images and both radar altimetry and ICESat laser altimetry Digital Elevation Model (DEM) data. The method combines the wide image coverage of MODIS, and its high radiometric sensitivity (which equates to high sunward slope sensitivity), with the high precision and accuracy of ICESat and combined ICESat and radar altimetry DEMs. We calibrate brightness-to-slope relationships for several MODIS images of the central West Antarctic using smoothed DEMs derived from both sources. Using the calibrations, we then created, first, a slope map of the ice sheet surface from the image data (regressing slope information from many images), and then integrated this absolute slope map to yield complete DEMs for the region. ICESat (as of September 2007) has acquired a series of eleven near-repeat tracks over the Antarctic during the period September 2003 to April 2007, covering the continent to 86 deg S. ICESat data are acquired as a series of spot elevations, averaging a ~60m diameter surface region every ~172m. However, ICESat track paths have spacings wide enough (2 km at 85 deg; 20 - 50 km at 75 deg) that some surface ice dynamical features (e.g. flowlines, undulations, ice rises) are missed by the track data used to construct the ICESat DEM. Radar altimetry can provide some of the missing data north of 81.5 deg, but only to a maximum resolution of about 5 km. A set of cloud-cleared MODIS band 1 data from both the Aqua and Terra platforms acquired during the 2003-2004 austral summer, used in generating the Mosaic of Antarctica, MOA, surface morphology image map, were used for the image enhancement. Past analyses of the slope-brightness relationship for MODIS have shown ice surface slope precisions of +/- 0.00015. ICESat spot elevations have nominal precisions of ~5 cm under ideal conditions, although thin-cloud effects and mislocation errors can magnify these. Only cloud-free areas of MODIS scenes that also meet specific slope, grain-size, solar zenith, brightness, latitude, and elevation criteria are used for image enhancement. A suite of applications for an enhanced DEM are identified and explored. A full representation of the WAIS undulation field permits a better investigation of the relationship between accumulation and topography, and surface temperature and topography. Further, addressing the shape modifications introduced by the variations in accumulation across undulations is a necessary prerequisite before inverting surface topography for bed elevation. Lastly, surface topography and detailed bed topography are both required for inferring sub-ice-sheet hydrostatic pressure. We will discuss these potential applications.
DE: 0726 Ice sheets
DE: 0758 Remote sensing
DE: 0776 Glaciology (1621, 1827, 1863)
DE: 0794 Instruments and techniques
DE: 0798 Modeling
SC: Cryosphere [C]
MN: 2007 Fall Meeting