Validation and comparison of SRTM and ASTER/GDEM in the Tibetan Plateau using ICESat/GLAS data

Both the Shuttle Radar Topographic Mission (STRM) topography and the Advanced Space borne Thermal Emission and Reflection Radiometer (ASTER) Global Digital Elevation Model (GDEM) have been widely used in hydrology, climatology, glaciology, and others since they were made access to the public. Their vertical accuracies are concerns to users in applications. The Ice, Cloud and land Elevation Satellite (ICESat) Geosciecne Laser Altimetry system (GLAS) global land altimetry data were used to validate the accuracy of DEMs worldwide. In this study we selected a square area (Lat. 27-37°N and Lon. 85-95°E) in the Tibetan Plateau for the validation of both SRTM and ASTER/GDEM using ICESat/GLAS data because a variety of landforms could be tested including different range of altitude, land covers, and slope and roughness. The areas covered with glaciers were excluded by erasing the glacier distributions based on the Global Land Ice Measuremnets from Space (GLIMS) data. All data of ICESat/GLAS, SRTM, ASTER/GDEM and GLIMS data downloaded were assigned with the same geographic coordination, WGS84 datum and EGM96 geoid system. For quality assurance the saturation parameter of ICESat was used to exclude those saturated ICESat data thus pairs of ICESat and ATRM/ASTER data, in addition, pairs were removed for comparison if the difference of elevation between ICESat and SRTM (or ASTER/GDEM) is less than -100 m or greater than 100 m, assuming that these data are affected by clouds. We found: 1) both SRTM and ASTER/GDEM are highly correlated with ICESat data (99.99%); 2) SRTM/DEM data are greater than ICESat measurements (-2.72 ± 12.04 m), but ASTER/GDEM data are less than ICESat measurements (1.60 ± 17.68 m); 3) SRTM and ASTER/GDEM have consistent accuracy of elevations for all ICESat tracks tested; 4) the average elevation of ASTER/GDEM is closer to the ICESat measurements but with a wider variation comparing to SRTM/DEM; 5) no impact of the altitude on the accuracy of SRTM and ASTER/GDEM is seen in the study area; and 6) the surface slope and roughness have apparent impacts on the accuracy of ASTER/GDEM.