Determination of rain anisotropy and effective spreading of the orientation of ellipsoidal raindrops during intense rainfall

Depolarization measurements performed in circular polarization at centimeter wavelength have frequently shown depolarization values lower than those theoretically expected by application of the Oguchi theory, which assumes equioriented ellipsoidal raindrops. This discrepancy can be explained by considering that in reality the drop-axes are oriented at a given instant according to a certain statistical distribution the spreading of which causes a decrease in the anisotropy (differential propagation constants along the principal planes), which is the prime source of rain depolarization (both in circular and in linear polarization). The reduction of anisotropy with respect to the equioriented drops model is experimentally assessed and the spreading necessary in a particular model distribution for the same reduction is determined in this communication. The study is based upon simultaneous measurements of attenuation and depolarization in circular polarization gathered in 1974-1975 during the Magnola experiment (Italy) on a low-elevation terrestrial path ( ) at 11.6 GHz. The results confirmed that the equiorientation of raindrops is too severe an assumption, being the true anisotropy 20-30 percent (on average) less than the expected value in case of equiorientation. This figure corresponds to an average spreading of about which is in agreement with the results given by other authors.