Automated delineation of debris-covered glaciers based on ASTER data

Large areas of the glacier tongues at Mt. Everest are heavily covered by supraglacial debris. This hampers the automated mapping of the actual ice snout by means of spaceborne imagery due to the similar spectral signal of the surrounding debris. The most significant features which differentiate the glaciers are the typical surface characteristics like a rough surface or “cryokarst” and a number of ablation ponds. At a first glance the outline of these debris-covered glaciers seems to be stable. Looking in detail at these glaciers using multitemporal space imagery it is obvious that recent glacier shrinkage results in an increasing debris coverage and an increasing number and, hence, area of supra-glacial lakes. In addition, the surface, especially at the very distal part of the glacier, looks smoother and shows no significant indications for movement.
Hence, presently ASTER stereo-images represent an ideal tool to develop an automated way of outlining the ice extents of the active and inactive glacier. Combining ASTER’s thermal information with various shape parameters derived from stereo- models, both the actual glacier beds and the marginal moraines could be outlined. Mainly due to the resolution of the ASTER DEM (30 m) this concept is only promising for large glaciers such as the Khumbu Glacier. In future, when high resolution DEMs will be available, the accuracy will be sufficient for a fully automated glacier monitoring, including smaller glaciers.