Raindrop size distribution and rainfall attenuation modeling in equatorial and subtropical Africa: the critical diameters

Abstract

Raindrop sizes were obtained from Butare, Rwanda (2.6°S, 29.74°E) and Durban, South Africa (29°52′S, 30°58′E) using the Joss–Waldvogel RD-80 disdrometer. The obtained data is used for the analysis of the drop size distribution (DSD) and specific rainfall attenuation modeling in these African countries identified as equatorial (Butare) and subtropical (Durban) regions. The influence of the raindrop diameters that are critical to the DSD and specific rain attenuation at operating frequencies of 10–150 GHz is investigated using the estimated R0.01 values for Butare and Durban. Parameter fittings for the proposed DSD models at these locations for different rain rate values are investigated. The proposed drop size distribution models are also compared with those of other countries. At operating frequency range 10 ≤ f ≤ 40 GHz, the specific attenuation in Rwanda tends to be higher when compared to Durban. However, at frequency above 40 GHz, Durban shows a higher specific attenuation than Rwanda. The largest contributions to the overall specific rain attenuation are formed by drop diameters in the range 1.5 ≤ D ≤ 3.5 and 1.0 ≤ D ≤ 3.0 mm for Rwanda and South Africa, respectively, especially at higher frequencies. A minimal contribution is observed at the larger diameters. The influence of the disdrometer bins on the attenuation due to rain is also analyzed for these locations. The estimation will be useful to properly design adequate fade margin levels and for the purpose of link budget design by service providers and system engineers in the regions.