Modeling of a tropical raindrop size distribution for microwave and millimeter wave applications

The paper describes the modeling of the average raindrop size distribution measured at Ile-Ife, a tropical station in South Western Nigeria. The new “method of moment regression” employed is a systematic one that has allowed a single lognormal function to be accurately fitted over the entire range of rain rates measured, a convenient result for rain attenuation and scattering applications. The Marshall and Palmer law, frequently used for such calculations, has been shown to be inadequate as a model for this tropical station, especially at the high rain rates important for communications systems design. This result suggests that the similar Laws and Parsons dropsize distribution currently adopted by the International Radio Consultative Committee for estimating rain attenuation from 1 to 1000 GHz may not be adequate over such a large frequency range in such tropical locations. Some comparisons are also made with the lognormal models and modeling approaches of other workers. The results confirm the utility of the ram rate parameterization used in the model for Ile-Ife, while giving further support to the accuracy of the lognormal distribution.