3.1 Band Rationing for NDSI
From the clipped image of Rupnagar, the salinity sensitive bands were used for generation of NDSI. The NDSI values range from -1 to1 with 1 representing high salinity values in soil(Konukcu et al., 2006). Studies reveal that the Red and NIR bands are the most sensitive to the soil ions causing salinity(Rengasamy et al., 2003). The following formula was used for the purpose-
NDSI=\(\frac{(Green-SWIR)}{(Green+SWIR)}\) (1)
Since the bands 3 (GREEN) and Band 11 (Short Wave InfraRed-SWIR) have spatial resolutions of 10 m and 20 m respectively, the optical image bands were resampled at 14 m spatial resolution (same as that of multilooked Sentinel-1 SAR image). Based on this, surface Salinity maps for entire Rupnagar district were generated for the study dates of 4th December and 27th December 2019 and 20th January 2020. The application of fertilizers mainly DDT (Dichlorodiphenyltrichloroethane) affected the salinity levels, declining between the first two dates of early stage of wheat crop growth to slightly rising in January. The details are shown in the maps in Figure 3-