Evaluating the Transferability of a Bistatic Radiative Transfer Model to Monostatic Scattering for Wheat Crop with Sentinel-1 SAR Dual Polarimetric Data

The study presents a first-order Radiative Transfer model for monostatic scattering by integrating a modified Oh model for soil surface scattering and radiative transfer model with higher order interaction terms for volumetric scattering. The approach aims to improve crop signature analysis for monitoring and retrieval purposes of biophysical parameters, particularly soil moisture (SM) and leaf area index (LAI) in our case, with the use of Sentinel-1 satellite dual-polarized SAR data. The SAR data (GRD and SLC), along with the in situ LAI and SM data from February to April 2024, has been used for training and testing purposes of the model. The Oh model shows the surface scattering part, and it has been modified by the incorporation of attenuation factor and one soil-scaling factor fsoil. Similarly, the volumetric scattering part has been described for the vegetation components, along with the 1st order interaction terms from the soil-veg, veg-soil double bounce scattering has been used in this model. Least-square optimization technique has been used to calibrate the scattering albedo and the loss factor present in the attenuation term. Finally, the inversion algorithm to retrieve the soil moisture data, has been done again with the Look-up Table (LUT) approach and the least square technique again for the sake of simplicity. The backscattering coefficient retrieval performance metric for VV polarization ($\mathrm{R}=0.8922$; $\mathrm{RMSE}=$ 0.6126) shows a better correlation with RMSE slightly higher when compared with VH polarization ($\mathrm{R}=0.8745$; RMSE = 0.4150). However, for soil moisture, the VH ($\mathrm{R}=\mathbf{0. 6 0 7 4}$; RMSE =0.1065) polarization shows better results than $\mathrm{VV}(\mathrm{R}=0.4169$; RMSE = 0.1576).