Reduced-to-sea-level value of microwave radio refractivity over three stations in Nigeria

Abstract

Adequate knowledge of the temporal and spatial variations of surface refractivity, Ns is required for planning of broadcasting services including terrestrial radio links over a region. The reduced–to–sea–level refractivity, N0 values removes the elevation–dependence of surface refractivity in a bit to enhance comparison and contouring of values for different meteorological stations. In this study, in–situ measurement of atmospheric pressure, temperature and relative humidity using Wireless Weather Stations (Integrated Sensor Suit, ISS) was carried out over three different meteorological stations in Nigeria, namely: Akure (7.15⁰N, 5.12⁰E) South – Western Nigeria, Minna (9.61⁰N, 6.55⁰E) North – Central Nigeria and Nsukka (6.85⁰N, 7.39⁰E) South – Eastern Nigeria. Two years of measurement (January, 2008 to December, 2009) were used to compute the surface radio refractivity and its reduced – to – sea – level value. The results show that surface refractivity has seasonal tendency and is highest in the wet season and low in the dry season months. The surface refractivity values and the climatic tendency for reduced–to–sea–level refractivity were highest in Nsukka compared to the other two stations (Akure and Minna). The implication of the results is that the correlation of VHF/UHF field strengths with diurnal and seasonal variations of Ns partly explains the low signal reception in some locations especially from long distance transmitting stations when Ns is minimum. It further shows that the worst case propagation parameters are used for design purposes.

Keywords: microwave, surface refractivity, reduced-to-sea-level, troposphere, scale height