CHARACTERIZATION AND EFFECTS OF RADAR-MEASURED RAINFALL PARAMETERS ON MILLIMETRE RADIOWAVE PROPAGATION IN AKURE, SOUTHWESTERN NIGERIA

Abstract

Measurements of rainfall parameters such as the liquid water content (M), radar reflectivity factor (Z), rain rates (R) and the falling velocities (w) were carried out in this study using a vertically looking Micro Rain Radar (MRR) located at the Department of Physics of The Federal University of Technology Akure (7o15΄N, 5o15΄E). The parameters were measured from the ground level to a height of 4.8 km above sea level with a vertical resolution of 0.16 km and over a total of 30 range gates with 1-minute integration time. The measurements covered a period of four years (2008, 2009, 2010 and 2014). The study established relationships between all the parameters measured and in particular between radar reflectivity (Z) and rain rates (R) and liquid water conductivity (M) and rain rates (R). The results show that the values of the correlation coefficients obtained for the relationships were more than 0.64 showing good Z-R and M- R relationships and the values of coefficients, a and exponents, b are in good agreement with what was obtained in other locations around the world. The results of rain attenuation computed show a consistent increase in the specific attenuation from drizzle rain type to thunderstorm rain type until the values reach a critical stage at frequencies ranging from 31-100 GHz. Specific attenuation as much as 80 dB/km for thunderstorm rain type was observed and the higher attenuation may result in total signal outage if not properly compensated for in the systems design. It was also observed that at 0.01% of time, the measured rain rate was underestimated by 35% when compared with the ITU-R recommendation for this region.