VERTICAL DISTRIBUTION OF RADIO REFRACTIVE INDEX GRADIENT OVER AKURE, NIGERIA

Abstract

To achieve good design of line-of-sight (LOS) at the VHF/UHF band/communication networks, knowledge of the radio refractive index of the atmosphere is required. The measurements of meteorological parameters of atmospheric pressure, temperature and relative humidity at the first 200 m altitude have been taken over five years in Akure. The annual, seasonal and diurnal variation of radio refractivity and its gradient have been computed using these five year data - spanning from January 2007 to December 2011 over Akure (7.150N, 5.120E), Southwestern Nigeria. The data utilized are those obtained from a Wireless weather station installed on the 220 m Nigeria Television Authority (NTA) TV tower/mast at Iju in Akure North Local Government area of Ondo State. The weather stations were positioned at five different height levels beginning from the ground surface, and at intervals of 50 m from the ground to a height of 200 m (0, 50, 100, 150 and 200 m) on the tower, and are calibrated to log in data every day at an interval of 30 minutes. The result shows that radio refractivity gradient varies with the time of the day as well as the seasons of the year and was also observed to have greater variability in the dry season months of November to March but lower in the wet season months from May to September. The results also show that at antenna heights of 100 m and 200 m in Akure, there is a prevalence of super-refractive conditions but at lower antenna heights and during the dry season months sub refractive conditions are observed in all the years considered for this study