Seasonal Variability of Snow/Ice Facies Using Four Years of RISAT-1 MRS Data Over Glaciers in Himalayan–Karakoram Region

Radar Imaging Satellite-1 (RISAT-1) synthetic aperture radar (SAR), the first indigenous active SAR sensor launched by India, has shown its potential in several natural resource monitoring and disaster related applications. The 2-D signature and linear decision rule classification approach, implemented in in-house developed Microwave Data Analysis Software (MIDAS), was used to process and generate snow/ice facies information using RISAT-1 Medium Resolution ScanSAR (MRS) data over the Himalayan–Karakoram (H-K) region. A criterion of glacier area more than 8 km2 was adopted to minimize topographic effects due to oblique sensor viewing geometry. A total of 1352 RISAT-1 MRS images between 2012 and 2016 were picked up covering almost 1300 glaciers in the H-K region. Sigma-nought (
$\sigma ^{0}$
) images, digital elevation model (DEM), and outline of glaciers were used for generating snow/ice facies products. Processes in the formation of snow and ice facies based on SAR interactions have been discussed during accumulation and ablation months of a year for the respective state of snow/ice. ERA-5 reanalysis temperature data synchronous to SAR-derived facies products have shown a high correlation between the wet snow zone (WSZ) and seasonal frozen percolation zone (SFPZ) with atmospheric temperature at 2 m, respectively, covering glaciers in the H-K region. The detailed analysis was also carried out in view of longitudinal, latitudinal, mean elevation, and mean air temperature, respectively, for individual glacier, showing variation in SFPZ and WSZ class as one move from Western to Central and further in Eastern Himalayas. This work explicates retrieval and analysis of long-term database as a continuing activity for the forthcoming RISAT-1 series and NISAR mission to understand its linkages with the ever changing climate.