Investigation of Tropospheric Radio Refractivity and other Relevant Parameters across Some Selected Locations in the Sahelian Region of Nigeria

The troposphere's internal processes are complex and exhibit nonlinear trends, which have a significant impact on the transmission and reception of high-quality signals worldwide. This study used measured monthly climatic data of temperature, relative humidity, and atmospheric pressure for Maiduguri and Sokoto from the National Aeronautic and Space Administration (NASA) over a forty-two-years period (1981 to 2022) to estimate the seasonal tropospheric radio refractivity and examine its variations with other meteorological parameters and refractive index. The refractivity gradiant, effective earth radius, and percentage contribution of the dry and wet term radio refractivity were also examined. According to the results, radio refractivity was found to be highest at the two locations during the rainy season and lowest during the dry season. In Maiduguri, during the rainy season and dry seasons are 361.4837 N-units in August, 272.4506 N-units in March while for Sokoto are 366.7093 N-units in August, 277.1162 N-units in February. For Maiduguri and Sokoto, the wet term (Nwet) contributes to the significant variation with 19.9753 % and 21.1831%, respectively, while the dry term (Ndry) contributes 80.0247 % and 78.8169 % to the total value of radio refractivity. The average refractivity gradients in the studied locations were found to be -42.3746 and -42.3928 N-units/km. Furthermore, it was discovered that Maiduguri and Sokoto had average effective earth radiuses (k-factors) of 1.3697 and 1.3698, respectively. These values implied super refraction propagation condition.