Inferring glacier mass balance from Sentinel-1 derived ice thickness changes using geoinformatics: A case study of Gangotri glacier, Uttarakhand, India

All glaciers respond to climatic changes by fluctuating their mass. Investigations of glacier dynamics are necessary for glacier monitoring. Himalayan glaciers make ongoing glacier observations challenging due to their location in a severe topographic environment and inhospitable terrain. Glacier area contraction or extension, together with a corresponding snout shift, can be linked to oscillations in glacier mass. Sentinel-1 dual-polarized datasets were used in this investigation to retrieve glacier surface velocity. Estimates of ice thickness were enhanced by segmenting the glacier into 100-m height intervals. Also, ice thickness variations between 2017 and 2022 have been used to compute glacier mass balance, and the results for several glacier zones have been briefly analyzed. The study revealed that the maximum surface velocity above Gangotri Glacier was approximately 0.33 m/day, with an estimated average of 0.09 m/day. Surface velocities of the central trunk have been seen to range from 0.12 m/day to 0.23 m/day. Additionally, between 2017 and 2022, the surface velocity was spotted between 0.19 m/day to 0.35 m/day. For the glacier, an average ice thickness of 189 ± 17.01 m was calculated. In the central parts, where the drag was least noticeable, thicknesses up to 587 ± 52.83 m were estimated. In the lower accumulation zone and middle reaches, the thickness was found to be decreasing between 2017 and 2022, which can be attributed to increased melting and glacier slowdown. Due to the increased glacier movement throughout time, the lower accumulation reaches over the main glacier body, and its tributaries have experienced mass balancing rates ranging from −1.3 m.w.e./year to −0.5 m.w.e./year (thickness change between −3 m/year and −0.6 m/year). With the help of previous research and existing data, the results were compared and validated. The suggested algorithm and findings can serve as inputs for satellite-based ice thickness measurements and as fundamental research for the forthcoming NISAR mission (expected by mid-2024) which will carry L- and S-band antennas.