Mass Balance of the Himalayan Glaciers and Their Regional Variations

Aim: Popular methods of glacial mass balance studies are time consuming, laborious and therefore, not repetitive at yearly manner. A compact, user-friendly classification algorithm has been applied to estimate Equilibrium Line Altitude (ELA) and mass balance of mountain or valley glaciers at yearly basis using Synthetic Aperture Radar (SAR) data for a period of 2012 to 2015. Cloud cover over the glacier catchment areas was studied to identify major seasons of precipitation over the study areas. The results were also compared to study the regional characteristics of the glaciers.

Study Area: The proposed module was used to analyze data over three Himalayan glaciers, namely, Durung Drung, Gangorti and Zemu. Chhota Shigri glacier was also studied with these three glaciers to understand the regional variations of the Himalayan glaciers.

Methodology: The classification algorithm was fixed for all glaciers and also independent from season, therefore, required least user intervention. The conditional loop based logics, consist of linear equations, classified glaciated region in different physical zones. Purely backscatter based classification result produced error by mixing zones due to overlapped signatures. Altitude thresholds of accumulation zones were employed to segregate the mixing in next level. The method required calibrated ortho-rectified sigma naught dual-pol SAR imagery as primary input. The glaciated area should be provided as Area of Interest (AOI). A Digital Elevation Model (DEM) file is required for altitude threshold. The output classes are saved in separate files with Boolean values. Optical data were used to estimate cloud coverage over the catchments of the glaciers.

Results: Average mass balance of the selected glaciers is estimated as - 0.44 m w.e.a-1 during the study period. The mass balance of the glaciers are comparatively studied with variation in melting seasons, duration of melting periods, on set and cease of melting for each glacier to understand the regional pattern of mass loss.

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 result derived from the developed method is ± 50 mm. Collection of field data on the surface topography is difficult for Mountain glaciers, especially over Himalaya. Use of satellite data can generate detailed information of glacier surface which will be further help to understand role of debris in glacier mass balance.