CLIMATOLOGICAL STUDIES OF RADAR SIGNAL REFRACTIVITY AT DIFFERENT ALTITUDES OVER NIGERIA

Abstract

The seasonal and diurnal variations of radio refractivity were investigated at different pressure levels for the Coastal, Savannah and Arid regions of Nigeria. The stations studied include Port-Harcourt (5.00°N, 7.50°E), Minna (10.00°N, 5.00°E) and Sokoto (12.50°N, 5.00°E) Two years (Jan. 2010-Dec. 2011) archived data of meteorological parameters (temperature, pressure, and relative humidity) were obtained from the National Centre for Atmospheric Research (NCAR) and National Centre for Environmental Prediction (NCEP). The data were collected at different hours of the day at six pressure levels. The diurnal and seasonal variations as well as vertical and annual profiles of the refractivity were investigated. The results obtained showed that the refractivity values were high in the morning and in the evening hours, while the values were low during the day between 12:00hr and 16:00hr local time, across the regions of Nigeria. Furthermore, the N-values were observed to be higher during wet season months (April –October) than dry season months (November – March). Higher values of refractivity were also recorded at coastal region compared to savannah and Arid regions. The average value of refractivity for Sokoto, Minna and Port-Harcourt were obtained to be 350, 360 and 370 N-units respectively. The overall results of the refractivity variations at 1.5 km height above the ground surface obtained for each region of Nigeria provide useful information for microwave communication systems design for the different regions of the country.