Raindrop size distribution and rainfall attenuation modeling in central Africa

Abstract Raindrop sizes were measured in Douala, Cameroon ( 4 o 03'N, 9 o 42'E) using a Parsivel disdrometer. The data obtained are used for the analysis of the drop size distribution (DSD) and specific rain attenuation modeling in the 5-150 GHz frequency range. The Lognormal and gamma distribution models are employed using the method of moments estimation, considering the third, fourth, and sixth-order moments. The parameter fits for the two DSD models proposed here for different values of rain rates are investigated. The specific rainfall attenuation using the Douala DSD models is compared to the ITU-R models in vertical and horizontal polarisation and models for some countries with different climates such as semi-arid, tropical, and subtropical in Africa. The comparison with the ITU-R model shows significant differences occurring at high frequency with both high and low rainfall rates. The comparison with other regions of Africa also shows that Douala is characterized by equatorial climate, and Durban characterized by subtropical climate show similar rainfall attenuation characteristics at operating frequency range 10≤ f ≤150 GHz, especially at a lower rain rate. At a higher rain rate, specific rain attenuation at Douala is always higher than in other African locations. The proposed models are very important for the determination of rainfall attenuation for terrestrial and satellite systems.