Combination of SRTM3 and repeat ASTER data for deriving alpine glacier flow velocities in the Bhutan Himalaya

The present study evaluates the fusion of DEMs from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument and the Shuttle Radar Topography Mission (SRTM). The study area consists of high elevation glaciers draining through the rough topography of the Bhutan Himalayas. It turns out that the ASTER-derived and SRTM3 DEMs have similar accuracy over the study area, but the SRTM3 DEM contains less gross errors. However, for rough topography large sections of the SRTM3 DEM contain no data. We therefore compile a combined SRTM3-ASTER DEM. From this final composite-master DEM, we produce repeat ASTER orthoimages from which we evaluate the DEM quality and derive glacier surface velocities through image matching. The glacier tongues north of the Himalayan main ridge, which enter the Tibet plateau, show maximum surface velocities in the order of 100-200 m year−1. In contrast, the ice within the glacier tongues south of the main ridge flows with a few tens of meters per year. These findings have a number of implications, among others for glacier dynamics, glacier response to climate change, glacier lake development, or glacial erosion. The study indicates that space-based remote sensing can provide new insights into the magnitude of selected surface processes and feedback mechanisms that govern mountain geodynamics.