A cardioid model for multi-angular radiometric observations

L-band passive microwave remote sensing sensors are able to provide estimates of surface soil moisture, on both spatial and temporal scales compatible with applications in the fields of meteorology and hydrology. A radiometric system using a 2-D interferometric design with multi-angular viewing capabilities will be borne by the Soil Moisture and Ocean Salinity (SMOS) space mission. The basic rationale for retrieving soil moisture from radiometric measurements is the assumption that the surface layer can be modeled as a dielectric medium. Its dielectric constant then depends on several physical parameters, including soil moisture; emissivities for various incidence angles are computed using Fresnel´s formulas. Many controlled field experiments have demonstrated the validity of this approach. Scenes exist however (e.g. ice covered or frozen surfaces, complete desert areas) where surface soil moisture is not a relevant concept. For such scenes, information should however be available on the complex dielectric constant itself. This communication describes a methodology which aims at retrieving in an optimized way the dielectric constant information available from multiangular radiometric data.