Digital terrain modelling using Corona and ALOS PRISM data to investigate the distal part of Imja Glacier, Khumbu Himal, Nepal

This study used Corona KH-4A and Advanced Land Observing Satellite (ALOS) PRISM images to generate digital terrain models (DTMs) of the distal part of Imja Glacier, where a few supraglacial ponds (～0.07 km²) expanded into the large Imja Glacier Lake (Imja Tsho, ～0.91 km²) between 1964 and 2006. DTMs and subsequently derived topographical maps with contour intervals of 1 m were created from the high-resolution images (Corona in 1964 and ALOS in 2006) in the Leica Photogrammetric Suite (LPS) platform. The DTMs and topographic maps provided excellent representation of the elevation and micro-topography of the glacier surface, such as its supra-glacial ponds/lake, surface depressions, and moraine ridges, with an error of about +/? 4 m (maximum). The DTMs produced from the Corona and ALOS PRISM images are suitable for use in studies of the surface change of glaciers. The topographical maps produced from the Corona data (1964) showed that part of the dead ice in the down-glacier area was even higher than the top of the lateral moraine ridges, while the glacier surface in the up-glacier area was noticeably lower than the moraine crests. This suggests more extensive melting of glacier ice in the up-glacier area before 1964. The average lowering of the glacier surface from 1964 to 2006 was 16.9 m for the dead-ice area west of the lake and 47.4 m for the glacier surface east of the lake; between 1964 and 2002, the lake surface lowered by 82.3 m. These figures represent average lowering rates of 0.4, 1.1, and 2.2 m/year for the respective areas.