4.2 Discussion
The results show that for soil which has a horizontal expanse over vast areas VH polarization is the obvious choice for modelling, but it gets attenuated when the soil texture is rough and there is sprouting of crop. Hence a combination of both VV and VH backscatter parameters from SAR satellite data were used for modelling. For soil salinity indices development from Sentinel-2 data, Band 3 (Green) and Band 11 (Short Wave InfraRed- SWIR) were used since saline soils reflect more in Green to SWIR Bands. Hence NDSI generated was (refer to Section 3.1) used as another parameter. The other parameters came from field data such as temperature, soil moisture and soil electrical conductivity for surface as well as root zone. Since satellite data is indicative of only surface phenomenon hence a correlation was established between surface parameters from field and root zone parameters. Thereafter, a correlation was established between satellite and root zone parameters collected from field by digging up to 2 ft (0.6 m) depth since crop roots do not extent any further beyond. The Root zone parameters were then used for modelling since all the above-mentioned correlative plots gave an average R2-statistics in correlation above 0.8 (80%). The model gave highly accurate results in the limited resources available with two polarization channels of SAR data and no complex modelling approach and sophisticated chemical lab tests.
The estimated sub-surface soil salinity map in terms of Electrical Conductivity for Rupnagar is shown in Figure 9-