Wet Reflectors in Millimeter-Wave Radiometry-Expenrment and Theory

Microwave radiometers are often required to operate under all weather conditions, including those under which an exposed surface of the antenna system becomes wetted by rain. Here we discuss the special case of a wetted flat reflector, with energy at 20.60 and 31.65 GHz linearly and orthogonally polarized at an incidence angle of 45°. The brightness temperatures produced by the wet reflector are computed from conventional theory, and are measured for various thicknesses of water layer. Both theory and experiment show that the brightness temperatures produced by the wet reflector have the same behavior throughout a range of water-layer thicknesses. The impact of these results on design of radiometers for research and operational application is discussed.