Assessing the impact of polarization on soil moisture retrieval using C-band SAR data across diverse crop structures

SAR operating at shorter wavelengths, exhibits shallower penetration depth and interacts primarily with the upper canopy layer. Consequently, its scattering mechanisms differ from those observed at longer wavelengths. Using this as a basis, this study presents a comprehensive evaluation of Soil Moisture retrieval using C-band data from two satellites missions, EOS-04 and Sentinel-1A through the application of Water Cloud Model. The in-situ datasets were acquired over southern India between June 2022 and January 2024. A total of 43 Sentinel-1A and 32 EOS-04 images were analysed alongside in situ measurements of SM and LAI collected over four crops, as well as bare soil. The novelty of this work lies in the comparative assessment of polarization configurations operating at the shorter wavelength, providing new insights into their relative sensitivity, retrieval performance and development of scattering mechanism across diverse canopy structures. The WCM was calibrated using LAI as the vegetation descriptor, the resulting SM estimates achieved RMSE ranging from 6.28% to 10.15%. HH polarization exhibited greater sensitivity under dense canopies, such as turmeric, whereas VV yielded slightly higher overall retrieval accuracy for most crop structures. Analysis of the scattering behaviour revealed that vegetation influence becomes dominant in VV at relatively lower biomass at this wavelength. Results also indicated that at higher SM levels, sensitivity and retrieval accuracy decline due to saturation effects. Overall, this study provides insights into polarization-dependent scattering mechanism in shorter wavelength and highlighting the importance of accounting for crop structure for SM retrieval. • Analysis performed with WCM in short wavelength using different polarizations • VV gave best SM retrieval; HH accuracy dropped under tall, dense vegetation • VV shows higher SM sensitivity in bare soil; HH stronger under low dense vegetation • Sensitivity drops with higher SM; VV performs best under dry, low-dielectric soils • Vegetation scattering later in sparse crops, earlier in maize; VV sensitive to angle