RADAR REFLECTIVITY OVER A TROPICAL LOCATION (AKURE), FOR SATELLITE LINK APPLICATION

Abstract

Hydrometeors, especially rain attenuate transmitted and received signals at higher frequencies thereby having effect on the Quality of Signal (QoS). Hence, the need to assess the behavior and implications of some of the rainfall parameters on signal interference at microwave frequencies especially at tropical locations like Akure, Nigeria. This study utilizes three years (2013-2015) data of rainfall parameters such as radar reflectivity (Z) and rain rate (R) obtained from the 24.1 GHz vertically-pointing micro rain radar installed at the Department of Physics, The Federal University of Technology Akure, Nigeria. The rainfall events were categorized based on rain intensity namely: thunderstorm (> 40 mm/hr.), shower (10 – 40 mm/hr.), widespread (5 – 10 mm/hr.) and drizzle (0.1 – 5 mm/hr.). The characterization of rain rate and radar reflectivity were carried out diurnally, seasonally and annually at different heights ranging from 160 to 4800 m. The parameters ‘a’ and ‘b’ associated with Z-R relation of the power law relation Z = aRb was deduced alongside the characterization at each of the heights. The result shows that the Z-R relationship varies for different rainfall rates at different heights. Also, it can be seen from the result that linear Z-R relationship fit the data well with an average coefficient of determination R2 value ranging from 0.5-0.6 across the specified heights while power law fit well with coefficient of determination R2 values of 0.7 - 0.9 range especially at heights 160 - 960 m. The result of the distribution shows that normal distribution presented the best statistical goodness of fit for drizzle rain type, lognormal for widespread and shower rain types while gamma distribution predicted well for thunderstorm rain type. The overall results are quite important especially in the design of improvement techniques for microwave and millimeter wave satellite signals.