Performance of ASTER and SRTM DEMs, and their potential for assessing glacial lakes in the Lunana region, Bhutan Himalaya

To assess the potential volume of a glacial lake outburst flood (GLOF) more precisely than in previous studies, we analyze ground survey data and remote-sensing digital elevation models (DEMs) around glacial lakes in the Lunana region, Bhutan. Based on a DEM generated from differential GPS ground surveys, we first evaluate the relative accuracies of DEMs produced by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and the Shuttle Radar Topography Mission (SRTM). Root-mean-square errors of the altitudinal difference between these DEMs and ground survey data were 11.0m for ASTER and 11.3m for SRTM. These errors are similar to those of previous studies. We show that a topographical classification allows a better estimate of elevation on lakes/ ponds, riverbeds and glaciers due to their flat surfaces, while the relative accuracy is worse over moraines and hill slopes due to their narrow ridges and steep slopes. Using the optical satellite images and the ground survey data, we re-evaluate the GLOF volume in 1994 as (17.2 5.3) 10m. We show GLOF-related information such as distance, altitudinal difference and gradient at possible outburst points where the lake level is higher than the neighboring riverbed and/or glacial lake.