A modified cardioid model for Processing multiangular radiometric observations

L-band spaceborne microwave radiometers are becoming able to provide estimates of surface soil moisture, on both spatial and temporal scales compatible with applications to meteorology and hydrology. 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 still (e.g., ice-covered or frozen surfaces, barren 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 paper shows that the dielectric constant cannot be fully retrieved from single-frequency multiangular data; it describes, however, a methodology that aims at retrieving in an optimized way the available information.