“Diurnal and Seasonal Variation of Surface Refractivity in Minna and Lapai, North Central Nigeria” (2018) International Journal of Engineering Research and Advanced Technology (ijerat) (E-ISSN 2454-6135) DOI: 10.31695/IJERAT, 4(7), pp. 16–24. doi:10.31695/IJERAT.2018.3283.