CORRELATION OF WATER VAPOUR PRESSURE PROFILE WITH RADIO REFRACTIVITY OVER AKURE, SOUTH-WESTERN, NIGERIA

Abstract

The variability of atmospheric parameters such as temperature, pressure, relative humidity and water vapour pressure as they affect radio wave propagation is very important in the planning and design of microwave communication links. The objectives of this work include: to collect meteorological parameters (Pressure, Temperature and Relative Humidity), to investigate and analyze the diurnal, seasonal and annual variations of radio refractivity and water vapour pressure and to examine the sensitivity of radio refractivity to water vapour pressure over Akure. The measurements of temperature, pressure and relative humidity at the first 200 m height for a period of five years (2007-2011) over Akure (7.15oN, 5.12oE) South-Western Nigeria have been carried out using Davis 6162 Wireless Vantage Pro2 weather station equipped with Integrated Sensor Suite (ISS). The sensors were positioned on the ground surface and at different heights (50 m, 100 m, 150 m and 200 m) on the Nigeria Television Authority NTA mast located at Iju, in Akure North Local Government Area of Ondo State, Nigeria. The measurements were taken round-the-clock from midnight at 30 minutes intervals. From the measured parameters, the diurnal, seasonal and annual variations of water vapour pressure and refractivity were computed and correlated. The results show that the diurnal variation of water vapour pressure has weak linear correlation with refractivity at all altitudes during the wet months of the year. This implies a low degree of sensitivity of radio refractivity to water vapour pressure during the wet seasons. On the contrary, very strong linear correlation of water vapour pressure with radio refractivity was observed at all altitudes during the dry months. This is an indication of radio refractivity being very sensitive to the variability of water vapour pressure during the dry season. The results also show very strong linear correlations of seasonal and annual variation of water vapour pressure with radio refractivity at all altitudes. Hence, radio refractivity can be predicted easily with water vapour pressure.