Rain rate and rain drop size distribution models for line-of-sight millimetric systems in South Africa.

Abstract

Radio frequencies at millimeter wavelengths suffer greatly from rain attenuation. It is therefore essential to study rainfall characteristics for efficient and reliable design of radio networks at frequencies above 10GHz. These characteristics of rain are geographically based, which need to be studied for estimation of rain induced attenuation. The ITU-R, through recommendations P.837 and P.838, have presented global approaches to rain-rate variation and rain-induced attenuation in line-of-sight radio links. Therefore, in this dissertation characteristics of rainfall rate and its applications for South Africa are evaluated. The cumulative distributions of rain intensity for 12 locations in seven regions in South Africa are presented in this dissertation based on five-year rainfall data. The rain rate with an integration time of 60 minutes is converted into an integration time of 1 minute in accordance with ITU-R recommendations. The resulting cumulative rain intensities and relations between them are compared with the global figures presented in ITU-R Recommendation P.837, as well as with the work in other African countries, notably by Moupfuma and Martin. Based on this work, additional rain-climatic zones are proposed alongside the five identified by ITU-R for South Africa. Finally, the study compares the semi-empirical raindrop-size distribution models such as Laws and Parsons, Marshall and Palmer, Joss, Thams and Waldvogel, and Gamma distribution with the estimated South Africa models.