Abstract:
The variation of point refractivity gradient with time of the day as well as seasons of the year
provide information on the occurrence of multipath fading which often cause reduction in signal
strength. For optimum services, it is of much importance to investigate the conditions experienced
along the propagation path of a radiowaves in the troposphere. This study was carried out using
six (6) years (January 2013 – December 2018) reanalysis data of parameters: Temperature,
Pressure and Humidity obtained from the archive of the National European Centre for Medium
Range Weather Forecast (ECMWF) over some locations in the southwestern part of Nigeria
(Osogbo, Lagos, Akure Abeokuta, Ado-Ekiti and Ibadan). The data was employed to estimate the
radio refractivity, point refractivity gradient, geoclimatic factor (K) at different intervals of time
and the percentage of time that a certain fade depth A (dB) is exceeded in the average worst month.
The percentage of time for the fade depth to occur (P w ) was deduced and the results shows that the
diurnal variation of point refractivity gradient have their minimum values at 12 hr local time in all
locations. The seasonal variation of the point refractivity gradient shows that high values of point
refractivity gradient were observed in the dry season, which are well observed at the peak of dry
season (January and December) in the region considered except for Lagos which is observed at
early and late hours (00 hr and 18 hr). The fade probability for the worst month was highest in
Lagos with a value of about 6.5% and the least value was recorded in Ado-Ekiti of about 2.7%.
The values of the Geoclimatic factor K, shows a clear inverse relationship with point refractivity
gradient and it indicated that the geoclimatic factor which represent geographical and climatic
conditions in multipath fading distribution varies with the month, season and year.
