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A first-order accuracy assessment of GLAS elevation data near Summit, Greenland


The Geoscience Laser Altimeter System (GLAS) onboard the Ice, Cloud, and land Elevation Satellite (ICESat) has been collecting surface elevation data over continental ice sheets since early 2003. GLAS was designed with the explicit purpose of measuring ice sheet topography for the purpose of calculating a more accurate ice sheet mass balance. Therefore it is essential to assess both the accuracy and precision of the instrument over its intended target: continental ice sheets. While the precision of the GLAS instrumentation has been extensively studied, its accuracy has only been estimated using independent (non-laser) methods over desert salt flats. Here, we performed monthly 8 kilometer differential GPS transects under track 412 of ICESat in order to directly compare GLAS surface elevation data to a GPS groundtruth. We kinetmatically processed the GPS data using the Track module of the GAMIT/GLOBK suite and used consecutive transects on the same day to calculate a GPS precision of .035 m. All of the GPS points within each 70m GLAS footprint, ranging from 12 to 22 individual GPS measurements, were averaged to determine the true elevation. Preliminary results from campaign L3i indicate that GLAS overestimates the true elevation by 0.973±0.062m (mean±SD, n=6). Results from other campaigns will illuminate whether this accuracy bias is constant or variable based on instrument or environmental parameters through time.