Studies of Super-Refractivity and Ducting of Radiowaves in Nigeria

Abstract

Studies of tropospheric refraction of long and short wavelength radio signals have been carried out in the coastal and savannah areas of Nigeria using meteorological data collected by radiosondes in Lagos (30 45' E, 60 28' N) and Kano (80 30' E, 120 2'N). Daily mean values of the initial refractivity gradients, dN/dh, were computed for the two zones and the results obtained have been used to classify the refractivity profiles as sub-refractive, normal, super-refractive and ducting. The refraction of radiowaves in the lower atmosphere is considered to be normal whenever the refractivity gradient is —40N/km. Between about — 41N/km and —156.9N/km, the atmosphere is super-refractive and when the refractivity gradients become equal to, or more negative than —157N/km ducting occurs. The modified refractive index was also computed for the two zones. A negative gradient of M is a useful indicator as to the occurrence of ducting. The refractivity values obtained show that the propagation conditions are super-refractive at the coastal region, especially during the rainy season. At Oshodi, the surface layer is super-refractive 75% of the time with 38% probability of occurrence of ducting. The surface layer at Kano, on the other hand, is sub-refractive 88% of the time with the probability of occurrence of ducting being only 3.5%.


Nigeria Journal of Pure and Applied Physics VOLUME 1, AUGUST 2000, pp. 5-10