ENVISAT-ASAR Data Analysis for Snow Cover Mapping over Gangotri Region

摘要

Snow cover area (SCA) mapping is very important parameter for snowmelt runoff modeling and forecasting. Snow cover information is also useful for managing transportation and avalanche forecasting. For SCA mapping, we selected Gangotri area and ENVISAT ASAR swath-2 data sets acquired during 2003-2004. The ASAR SLC data are converted into backscattering coefficient. The backscattering coefficient images are co-registered, multi-looked and geocoded using freely available DORIS InSAR software package. Out of available images during 2 years, Nov. 2003 image was taken as a reference image to form a ratio image with respect to others. Snow covered and non-snow areas are classified using threshold value (less than -3 dB is considered as snow) based on change detection method as given by Nagler and Rott. This value is shifted to -2dB to match with the classified snow cover area from optical data of IRS-ID. With five pairs of ratio images we could observe seasonal change of snow. The problem with the technique is that it can not be used with different ASAR mode data. The threshold value also depends on the location of the area.