HR: 0800h
AN: C11A-0081    [Abstracts]
TI: The rate of ice sheet mass-loss from southeast Greenland from combined GLAS and ASTER observations
AU: * Howat, I M
EM: ihowat@apl.washington.edu
AF: Applied Physics Lab, University of Washington 1013 NE 40th Street, Seattle, 98105,
AU: * Howat, I M
EM: ihowat@apl.washington.edu
AF: National Snow and Ice Data Center, University of Colorado 1540 30th St., Boulder, 80309,
AU: Smith, B
EM: smithcommaben@gmail.com
AF: Applied Physics Lab, University of Washington 1013 NE 40th Street, Seattle, 98105,
AU: Joughin, I
EM: ian@apl.washington.edu
AF: Applied Physics Lab, University of Washington 1013 NE 40th Street, Seattle, 98105,
AU: Scambos, T
EM: teds@kryos.colorado.edu
AF: National Snow and Ice Data Center, University of Colorado 1540 30th St., Boulder, 80309,
AB: Repeat laser altimetry from the Geoscience Laser Altimeter System (GLAS) aboard the Ice, Cloud and Elevation Satellite (ICESat) provides direct measurements of changes in ice sheet volume at unprecedented temporal and spatial scale. However, recent observations show that the rate of loss from many of Greenland's large outlet glaciers has substantially increased over the past several years and there is concern that GLAS may not capture this contribution to mass-loss due to the spacing of altimeter tracks. Furthermore, GLAS measurements are much poorer at lower elevations where the ice slopes are high and the track-offset errors are larger. To test the importance of these sources of uncertainty in GLAS estimates of Greenland mass-loss, we combine these measurements with concurrent elevation changes obtained from repeat digital elevation models (DEMs) from the Advanced Spaceborne Thermal Emissivity and Radiation Radiometer (ASTER). In complement to GLAS, ASTER DEMs provide complete spatial coverage at high resolution over limited areas and work best below the equilibrium line because the parallax image generation relies on correlation of surface features. We constructed repeat DEM's for the outlet glaciers of the southeast Greenland coast between 2002 and 2005, with some imagery from 2001 and 2006, and combined them with higher-elevation GLAS point measurements using a simple linear interpolation to produce a map of elevation change rate from the coast to the divide. Our estimates for total mass-loss agree closely with other regional estimates from the same time period, but emphasize the importance of the period of observation for these rapidly changing glaciers. We also find that the added constraint provided by ASTER DEM's do not substantially impact the estimates for total mass-loss provided by GLAS alone. While the outlet glaciers are thinning at rates of 10's of m/yr, the area of this thinning (100's of sq. km) is small compared to the 1000's of sq. km of thinning at 1-10 m/yr captured by GLAS. This suggests that GLAS repeat altimetry is an effective tool for measuring Greenland mass-loss, even during times of rapid outlet glacier change. However, the high spatial resolution of the combined GLAS-ASTER maps provide detailed information into the distribution of mass-loss and will aid process-oriented studies of ice sheet change.
DE: 0720 Glaciers
DE: 0726 Ice sheets
DE: 0758 Remote sensing
DE: 0762 Mass balance (1218, 1223)
DE: 0794 Instruments and techniques
SC: Cryosphere [C]
MN: 2007 Fall Meeting