THE EFFECT OF RAIN ON SURFACE RADIO REFRACTIVITY OVER NIGERIA

Abstract

The presence of liquid water in the troposphere not only attenuates radio signal but sometimes cancels out the radio link (fading) and this is too great an impact to be ignored by designers of radio communication systems.Hence; this study investigates the sensitivity of radio refractivity to rainfall. To achieve this, two years (Jan. 2011 - Dec. 2012) meteorological data of air temperature, pressure, relative humidity, rainfall amount for seven locations in Nigeria (Abuja - Lat. 9.080 N, Long. 7.530 E; Akure - 7.250 N, 5.200 E; Lagos - 6.440 N, 3.390 E; Makurdi - 7.190 N, 8.130 E; Nsukka - 6.870 N, 7.830 E; Port-Harcourt - 4.810 N, 7.010 E and Jos - 9.930 N, 8.890 E) was obtained from Tropospheric Data Acquisition Network (TRODAN) of the Centre for Atmospheric Research,a subsidiary of the National Space Research and Development Agency (NASRDA). The Centre is located in the campus of Kogi State University, Anyigba. The collected data; air temperature, pressure and relative humidity was used to compute radio refractivity. The computed data and rainfall amount was then characterized both diurnally and seasonally and the correlation between radio refractivity and rainfall amount was then analyzed. Results showed low level of linearity in the relationship between radio refractivity and rainfall amount across all the locations with correlation coefficient of 0.7116, 0.804, 0.4006, 0.2095, 0.5366, 0.6698, 0.7246 obtained for Abuja, Akure, Lagos, Makurdi, Nsukka, Port-Harcourt and Jos respectively. It was deduced that the variations of refractivity during the rainy periods are mainly due to the variation in the wet terms of refractivity whereas the variation contributed by the dry term of refractivity is mainly due to the temperature. This implies that there is no direct effect of rainfall amount on the surface radio refractivity.