Analysis of Rain Attenuation over the Geo-climatic Regions of Nigeria Using Attenuation Prediction Models

Abstract

At frequencies above 10GHz, rain drops absorb part of the energy (signal) and part are scattered in different directions, causing unavailability of signals and making the system link unreliable. This study presents analysis of rain-induced attenuation on satellite communications at Ku band and the effects on telecommunications, broadcasting and navigations over the geo-climatic regions in Nigerian. Rainfall parameters were recorded using the ISS automatic weather station, which consists of various weather instruments integrated into one. Rain-induced attenuation data were measured using a satellite beacon setup and the measured values were compared with existing prediction models. Results shows significant attenuation levels ranging from 8.4 to 11.5 dB, demonstrating substantial impact of intense rainfall on radio wave propagation above 10 GHz. The ITU-R model showed mixed performance across locations. Its annual cumulative rain rate at 0.1% (35.6mm/hr.) and 0.01% (95.2mm/hr.) of time exceedance means that satellite link is expected to be available for 99.9% and 99.99% of time with rain attenuation exceeding the threshold of approximately 526min and 52.6min equivalent number of minutes annually. However, in Akure, the ITU-R model underestimated the measured values at 0.1% (38.83mm/hr.) and 0.01% (106.8mm/hr.) respectively with about 11% deviation and it overestimated ENUGU site values within the same range of values. This implies that any rain prediction done with ITU-R values in Akure location, the satellite link availability will experience a down time for more than 526min and 52.6min annually. While the overestimated will experience shorter equivalent number of times like in the case of Enugu within the same range of values. At GUSAU and ABUJA sites, the ITU model consistently overestimated measured rain attenuation. Among the attenuation prediction models, Moupfouma model demonstrated superior accuracy, closely following measured rain attenuation values across all locations.