DEM from IRS-1C PAN stereo coverages over Himalayan glaciated region - accuracy and its utility

Satellite photogrammetric technique has been used for monitoring of fluctuations of Himalayan glaciers and the resulting changes in the elevations of glacier snouts. Two across-track stereo pairs from the Indian Remote Sensing Satellite (IRS)-1C covering parts of Basapa valley, a high altitude Himalayan glaciated terrain, were processed for generation of digital elevation models (DEM) and orthoimages using a softcopy photogrammetry workstation. Two glacier regions, viz., Janapa Garang and Shaune Garang glacier valley, were taken up for the study. For one glacier region, the stereo pair was generated in a workstation by replacing an image of one pair with an image from the other pair. Interchanging input image and reference image in the new pair has resulted in improvement in image matching. Accuracies related to location ( in terms of latitude and longitude) and elevation of image features in the accumulation zone, ablation zone and nonglaciated regions with respect topographical map were checked. Based on geographical location and elevation of the snout derived from a topographical map of 1962 and the DEM and orthoimage of 1997, the two glaciers have been observed to have a retreat of about 690 m and 925 m, respectively.