Anisotropic Scattering Due to Rain at Radio-Relay Frequencies

Recently L. T. Gusler and D. C. Hogg 1 calculated the degree of coupling between satellite-communications and terrestrial radio-relay systems due to scattering by rain at frequencies of 4, 6, 11, 18.5 and 30 GHz. In their work they took the scattering by raindrops to be isotropic and to be based on the Laws and Parsons drop-size distribution. 2 They have pointed out correctly that it is known that raindrops do not scatter isotropically. Since the isotropic assumption is incorrect, it is of interest to examine the magnitude of the resulting error. Also, for the purposes of documentation, we present the scattering patterns at selected frequencies in the range 1.4 to 300 GHz at rain rates in the range 1 to 150 mm/hr. It has been shown that the Mie solution to the problem of scattering from a single sphere can be used to generate the Stokes scattering matrix for atmospheric type aerosols, such as rain, and in particular for Laws and Parsons type rains. 3,4 One of the elements of this matirx is the angular scattering function [Piid) + P>{8)], sometimes referred to as the normalized Mie intensity function. Here, 9 is the scattering 861