A Method for Calculating Rain Attenuation Distributions on Microwave Paths

An important problem in designing radio relay systems at frequencies above 10 GHz is the radio outage caused by rain attenuation. Determination of the appropriate radio repeater spacings for economic and reliable operation requires a knowledge of the probability distribution of rain attenuation as a function of repeater spacing at various geographic locations. Most available data on rain rate statistics are measured by a single rain gauge at a given geographic location. A procedure for calculating a rain attenuation distribution from a point rain rate distribution is, therefore, needed. The results of rain gauge network measurements 1-5 indicate, however, that the measured short-term distributions of point rain rate vary significantly from gauge to gauge. For example, at Holmdel, New Jersey, there was considerable variation 1 among the measured point rain rate distributions obtained from 96 rain gauges located in a grid with 1.3-km spacing over a 6-month period. Among these 96 distributions, the incidence of 100-mm/h rains is higher by a factor of 1051