Relative importance of tropospheric and precipitation scatter in interference and co-ordination

An analytical procedure is described which permits comparison of tropospheric forward scatter in clear air and precipitation scatter for the case of great-circle mode of propagation. The basic geometry of the problem concerns the case of cochannel operation of a terrestrial radio-relay link and an earth-space system. Radar data on the scattering from refractive-index variations are used to evaluate the scattering characteristics at oblique incidence for various portions of the common volume in clear air. The data are then compared with results for precipitation scatter for the same locations in the common volume. Results for transmission loss are compared. It is shown that in practice, especially for elevation angles of the earth-station beam of more than about 5 deg, clear-air tropospheric scatter need not be considered for interference and coordination purposes based on criteria for very small time percentages. The coordination area is determined either by superrefraction or by precipitation scatter.