MICROWAVE DIELECTRIC-PROPERTIES OF A SILT-LOAM AT HIGH-FREQUENCIES

Microwave brightness temperatures at three frequencies (23.8, 36.5, an d 90 GHz) of a carefully smoothed silt-loam were measured over a large range of near-surface soil moisture conditions. The microwave data we re collected simultaneously with ground observations of soil moisture, soil temperature, and bulk density. The atmospheric downwelling radia tion is computed from the French weather forecast model outputs and cl oud coverage surface observations, Assuming that roughness effects are negligible for the studied surface, Fresnel coefficients are used to model soil reflectivities. The relationship between soil moisture and soil reflectivity at high frequencies is then analyzed through existin g semi-empirical models of the soil complex dielectric permittivity.