The Detection of Supra-Glacial Debris Size over the Himalayan Glaciers Using Synthetic Aperture Radar and In-situ Data

Aim: Estimation of the glacial debris size from the Synthetic Aperture Radar (SAR) data is the primary objective of the study. The debris cover is of interest to glaciologists due to its influence on the glacier melt processes. Previous studies show a negative correlation between thicknesses of supra-glacial debris melting of glacial mass.

Study Area: This study involves collection of debris size information from the Chhota Shigri glacier of Himachal Pradesh during the year 2014. The developed model is tested to detect supra-glacial debris size over the Gangotri and Zemu glaciers.

Methodology: Backscattering signals of the SAR data from the ground truth sites are correlated with debris size. A linear regression was identified and used to detect the distribution of debris size from SAR backscattering. Satellite data of RISAT-1 Medium Resolution SAR mode is the primary input. A Surface profiler is used to collect the in-situ data of debris. Predicted debris size has been cross-check by measured debris size from high resolution optical data.

Results: From the model derived outputs, the average debris size of the Gangotri glacier is around 100 – 200 mm and that of the Zemu glacier is around 300 – 400 mm.

Conclusion: Co and cross polarized SAR data are employed to derived debris size; however, cross polarized SAR backscattering has better correlation with debris size. The accuracy of the results derived from the developed method is ± 50 mm. The rugged terrain of the mountain glaciers limits collection of in-situ data. Use of satellite data can overcome this limitation to some extent and help to understand the role of debris in glacier mass balance.