I. Introduction
Synthetic aperture radar (SAR) is a promising option for the temporal monitoring of near-surface soil moisture at a spatial and temporal resolution suitable for hydrological and agricultural applications. The extraction of accurate soil moisture information from SAR data is subject to the accurate modeling of the relative contribution of soil moisture and surface roughness to the power backscattered at the soil surface. Among the numerous surface scattering models reported in the literature, the most widely applied are a physical model, the Integral Equation Model (IEM) developed in [1], and two semiempirical models, the Dubois [2] and the Oh [3] models. Semiempirical models provide relatively simple relationships between surface properties and SAR metrics that reflect to a certain extent the physics of the scattering mechanisms. However, they rely on parameters that are often site specific and therefore valid only for specific soil conditions. Conversely, physical approaches are based on electromagnetic scattering theory and, even though they provide site-independent relationships, are mathematically more complex and involve a heavier computational burden.