Measurement of Radio Refractive Index in the First 100 m Layer Over Minna in North Central Nigeria

Abstract

Tropospheric radio refractivity at surface and 100 m levels is investigated from in-situ measurement of atmospheric pressure, temperature and relative humidity made in Minna (9° 37'' N, 6° 30" E), North Central Nigeria. Daily measurement of the atmospheric variables was made at 30-minute intervals. The instrument used is the Vantage PRO II Automatic Weather Station, and the data used was for a period of 12 months (January to December, 2008). The results obtained show that the values of refractive index at both levels were high in the morning and late evening/night hours, while the values were low during the afternoon hours. Also, statistical analysis of radio refractivity index gradients was carried out, and the cumulative frequency distribution shows that the atmosphere over Minna was sub-refractive for about 50% of the time with positive gradients appearing occasionally, super-refractive for about 40% of the time, while normal refraction occurred for only 10% of the time.