Debris-covered glaciers make up about 80% of the glacierized area in the Khumbu Himal region of the Nepalese Himalaya, and, in the absence of in situ measurements, remotely sensed geodetic mass balances based on digital surface model (DSM) differencing offers the best means of measuring current change in these glaciers.
The role of different processes contributing to the mass change of debris-covered Himalayan glaciers is currently poorly understood. In particular, avalanched snow is known to contribute significantly to accumulation, and rapid melting at exposed ice faces within the debris covered zone are thought to significantly influence the total glacier ablation, but both of these processes remain unquantified at the glacier scale.
In the proposed project GlHima-Sat, we aim at exploring the utility of very high resolution tri-stereo Pléiades imagery in quantifying these processes and determining their contribution to annual glacier mass balance. DSMs of the highest possible accuracy and precision will be produced for the study area, which encompasses 780km² of the main Himalayan divide and 5 southward flowing glaciers of varying size and complexity.
Three sets of Pléiades tri-stereo data will be acquired for the study area, to enable analyses based on differencing DSMs over both the monsoon and non-monsoon seasons. Pixel and object based surface classification will be used to assist with the interpretation of the data.
- estimate the volume of snow in the avalanche cones within the regions, and relate these volumes to topographic properties,
- compute the volume change over avalanche cones and at exposed ice faces within the debris cover on the five study glaciers and
- compute the geodetic annual mass balance for these five glaciers. These analyses will test the capabilities of the Pléiades data for studying high resolution glaciological processes, while the volume estimation of avalanche cones, supplemented by analysis of avalanche frequency from freely available satellite data over the last decade will provide the first estimates of the regional pattern of avalanche accumulation.
The analysis of mass balance and glaciological processes will allow to assess the imporctance of both avalanche accumulation and ice face ablation to total glacier mass balance, and by comparing across 5 different glaciers, how the role of these processes may vary depending on the glacier size and accumulation characteristics.
Completion of this work will not only test the limits of the glaciological applications of the high quality Pléiades data, but will address important open questions that are currently presenting obstacles to our complete understanding of Himalayan glaciers and how they will change in the coming years.