Impact of Refractivity Gradient and Effective Earth’s Radius Factor on Radio Signal Propagation at 100 m under Clear Air in Ibadan, South Western, Nigeria

Abstract

Radio refractivity gradient and effective earth’s radius factor are very significant parameters in planning radio communication links. The refractivity gradient statistics for the lowest 100 m in the troposphere are used to determine the probability of occurrence of anomalous propagation condition known as ducting. In this work, twelve months data of primary radio climatic parameters were obtained using high resolution radiosonde data. A radiosonde is an airborne weather station equipped with a radio transmitter. This transmitter measures meteorological parameters with a given frequency rate at various heights. International telecommunication union (ITU) recommendation models were used in obtaining refractivity gradient, G and effective earth radius factor over Ibadan, Nigeria. The results obtained show that the average radio refractivity, N, was higher during the rainy season (382.7 N-unit) due to the rise in the atmospheric moisture content in the region, it was lower during the dry season (365.8 N-unit) and the value of N also decreases with height. At 100 m, the mean radio refractivity gradient and the average effective earth’s radius obtained were -41.9167 Nunit/km and 1.43 respectively. Since the value of effective earth’s factor obtained is greater than the global standard value (1.333), the implications of the result are that propagation in this geographic region is mostly super-refractive. It is suggested that the mean refractivity gradient should be used to plan wireless links on short time basis while the average effective earth’s radius factor 1.43 should be used to plan long-time wireless communication in this understudy environment.      Key words: Effective earth’s radius, Radio signal, Refractivity gradient, Super-refractivity, Troposphere