Parameterization of vegetation and soil parameters of the modified water cloud model (MWCM) for hybrid-polarized SAR data over wheat dominating area

Abstract

Using hybrid-polarized SAR observations of RISAT-1 (Fine Resolution Stripmap, FRS-1), the parameters of soil and vegetation (S & V) for the modified water cloud model (MWCM) at a regional scale are calculated for further application in the soil moisture (SM) retrieval algorithm. Vegetation and soil backscattering is derived with the help of MWCM because of the incorporation of vegetation canopy effect. The parameters of soil and vegetation are calculated by the idea of minimum differences between the hybrid-polarized (RH and RV backscattering coefficient (σ°) retrieved from RISAT-1) and synthetic aperture radar (SAR) observations of RISAT-1 and σ° simulated by the MWCM. In original WCM, V1 and V2 are two vegetation and canopy discrepter which are replaced by possible combination of NDVI and LAI (NDVI-NDVI, LAI-LAI, NDVI-LAI, LAI-NDVI) in MWCM.The RMSE is 0.35 dB for LAI-LAI (V1-V2) combination for RH polarization and the correlation is also strong (R2 = 0.91) while the estimated Vegetation (a = 0.652 with SE of 0.386 and b = 0.129 with SE of 0.170) and soil (c = 5.756 with SE of 4.238 and d = -3.097 with SE of 1.809) parameters were in proper range for study area. The S & V parameters were used to retrieve RH polarized backscatte of FRS-1 data from RISAT-1 Indian satellite. The statistical tests also applied to the observed and derived or simulated RH polarized backscatte using these parameters (a, b, c, and d) show low RMSE with better correlation among other possible combinations (NDVI-NDVI, LAI-NDVI, NDVI-LAI) of NDVI and LAI. Levenberg-Marquardt simulation in SPSS is used for the estimation of S & V parameters to analyse the effect of errors in the input parameters of the MWCM. If sheed data is error-free, Levenberg-Marquardt provide real values of the S & V parameters. This study demonstrates that the RH polarized FRS-1 data could be applied to parametrization of MWCM.