Monitoring the effect of multiple scattering using Sentinel-1 SAR data: A case study of paddy fields

For the purpose of defining soil moisture in vegetated areas, abstraction from vegetation-soil interactions must be taken into account, and it must be quantified based on multiple scattering effects, due to the various phases of agricultural crop and its effect on vegetation growth due to the wave signal effect. Entropy-alpha cluster-based (entropy and alpha band clusters are obtained by using K-means unsupervised classification) decomposition approach has been utilised using the Sentinel-1 SAR data to determine the principal scattering contributions from the soil and the vegetation in order to take the effects of plant-soil interactions into consideration. The variation of entropy and alpha is plotted in the target decomposition because the first and second eigenvalues of the covariance matrix for dual-pol data, which indicates a controversial second scattering mechanism. However, anisotropy must be taken into consideration in order to account the impact of vegetation-soil multiple scattering interactions.

The entropy, alpha, and anisotropy bands of considered crop pixels were extracted, and examined the correlation of determination (R²) of crop pixels with each band of decomposition. The R² for entropy-alpha was achieved less compared to alpha-anisotropy and entropy-anisotropy bands combination. Even though the R² is high with anisotropy element, anisotropy indicates the presence of a second scattering mechanism and is particularly useful where entropy is high to improve scattering mechanisms. The coefficient of determination between the multiple scattering effects and the backscattering coefficient varies with the crop growth stage. During the initial stages of paddy crop, the R² is very less whereas as the stage of crop changes, the R² showed significant varaition at the late vegetative stage of paddy crop due to the vegetation-soil multiple interactions of wave signal. Hence, from the analysis, it is concluded that, the crops can contribute the multiple-scattering effect irrespective of the dominance of either vegetation or soil contribution, which needs to be properly accounted for retrieving soil moisture.