ACCURACY OF SATELLITE ALTIMETER ELEVATIONS OVER THE GREENLAND ICE-SHEET

The accuracy of Geosat satellite altimetry over the Greenland ice shee t is evaluated by comparing the measured heights to radar elevations f rom the airborne Greenland Aerogeophysics Project. At the center of th e ice sheet where the ice surface is nearly level, surface comparisons show a fit at the 1 to 3 m level as expected, but even at moderately sloping ice regions (0.3 degrees - 0.6 degrees), satellite altimetry m ean errors in the range of 10 to 35 m are observed. These errors are f ound for slope-corrected and waveform-retracked data, so most previous accuracy estimates of current satellite altimetry ice sheet elevation s in regions of sloping or undulating ice appear to be too optimistic.