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
