Microwave depolarization of an earth-space path

The nonspherical shapes of both rain and ice particles contribute to microwave depolarization on an earth-space path. A two-tier Gaussian model for rain, which assumes Gaussian distributions both for instantaneous canting angle and time-varying mean canting angle, together with gross features of ice particles, provides a theoretical framework to organize the experimental data and to yield functional dependence of cross polarization on freqency, polarization, and elevation angle. In spite of the lack of physical data on ice clouds, we have obtained agreement between measured depolarization data and theoretical results that are essentially independent of details of ice clouds. In particular, we have found a linear relation between cross-polarization amplitude and frequency throughout the centimeter wavelengths for a given earth-space path. The dependence of depolarization on orientation of an arbitrary linear polarization can be described by a simple, nearly sinusoidal expression that is relatively insensitive to the mean canting angle except within about ten degrees of the local “vertical” or horizonta1l direction. We show measured depolarization data for paths of various elevation angles to be consistent with each other using an empirical effective path length and the approximate cos2 θel factor for the differential attenuation and differential phase shift. Procedures of estimating cross polarizations for satellite communication systems and typical numerical results are summarized.