Retreat of glaciers is an important phenomenon to be monitored as they have a direct bearing on flow of water in rivers and rise of water level in sea. Use of Synthetic Aperture Radar (SAR) images in glacier dynamics studies has been gaining interest in the recent years. The present study discusses the use of SAR coherence images for demarking the snout position on a glacier and thus measure the retreat. Being sensitive for even the slightest changes over the terrain, SAR coherence images seems to be very useful in glacier retreat measurement.
Gangotri is one of the major Himalayan glaciers which has been subjected to dominant retreat since 1850 AD.16 The retreat of Gangotri glacier has a huge impact on the flow of Ganges, the largest perennial river in India. Coherence images were generated over Gangotri glacier from SAR images with different repeat periods from 1996 (ERS-1 & 2), 2004 (Envisat) & 2012 (TerraSAR-X) and are resampled to 50x50 m grid using SRTM DEM. Profiles near the snout position were precisely marked in a GIS environment and the distance between the profiles (1996, 2004, 2012) is reported as retreat. It has been observed that the Gangotri glacier has been retreating at the rate of 24+/- 1 m per year which is in good agreement with several other studies.