Abstract:
Characterization of rainfall structure and attenuation are among the steps to be considered when analyzing microwave propagation. Signal degradation due to rain for terrestrial and Earth-space propagation satellite paths were characterized in this research, by measuring rainfall rate; determine the monthly, seasonal and annual rainfall distributions. 2-year (2010 – 2012) rainfall data of 5-minute integration time were obtained from the Nigerian Environmental Climatic Observatory Program (NECOP) pro-weather station in two tropical stations, Akure and Lagos, in the Southwestern Nigeria. The data were converted to one-minute equivalent rainfall data using an improved version of ‘Lavergnant and Gole’ model. The results were compared with conventional models such as the ITU-R model, Kitami, Rice-Holmberg, and Moupfouma models to characterize the rainfall structure. Rainfall attenuation over terrestrial paths in the two locations for frequencies of 12, 20, 30 and 40 GHz and time percentages of 0.001%, 0.01% and 0.1% of time were also studied for path-lengths not exceeding 20 km using three different models: the ITU-R, Moupfouma and Crane Global model. It was observed from the results that the 5-minute rainfall data does not present a true representation of the rain-induced attenuation. The average monthly rainfall accumulation during the period observed reveals that rain continues to fall even in the dry season in the rainforest and coastal regions which is due to the effects of movement of the Intertropical Convergence Zone (ITCZ). The measured data compared with the other predefined models show that Moupfouma model gives better prediction in the two stations (Akure and Lagos). A worst month over the years reveals the effect of convective type of rainfall experienced over both stations. Evolution of rainfall rate indicated the outages over the stations which revealed that the outages occurred during the time that communication services are needed most. The rainfall-induced attenuation predictions obtained from the three models of Moupfouma, ITU-R and Crane Global model at frequencies 12, 20, 30 and 40 GHz for 0.1%, 0.01% and 0.001% of time gives
variation in attenuation and increased as the transmission path increases. The overall result will provide an enabling platform for system designers to achieve improved quality of service for terrestrial and Earth-space communication systems in the region
