Abstract:
The meteorological effects on radio wave signals propagating through the troposphere are of great concerns in the design and performance of radio communication systems. These effects which lead to anomalous propagation conditions such as ducting, super refraction and sub refraction are time and location dependent. This research work investigated the spatial-temporal distribution of modified refractivity gradient and the effects on radio waves propagating at 875 hPa and 700 hPa pressure levels over sixteen selected locations across the four climatic regions of Nigeria. Five years (2013-2017) meteorological parameters comprising air temperature, relative humidity and atmospheric pressure at ground level and 1 km above ground level were obtained from the European Center for Medium-Range Weather Forecast (ECMWF) at four synopses hours of the day at a grid of 0.75°. Modified radio refractivity and its gradient at these pressure levels were computed using ITU-R, P.453-13 model. Results on a daily and seasonal basis shows similar trends at both 875 hPa and 700 hPa pressure levels, with higher values of modified refractivity recorded at 700 hPa pressure level and also at the morning and night hours of the day. Results on seasonal basis show that during the rainy season, modified radio refractivity gradients were high. On location basis, Port Harcourt (coastal region) recorded the highest value of modified refractivity gradient of about 115.5 M-units/km in the night time (00:00 hr. LT). The value depicts the occurrence of normal refraction in this location. Lowest values of modified refractivity gradient of about 22, 25 and 40 M-units/km were recorded in Abuja, Bida and Akure respectively at 12:00 hr. LT in the dry season months. These values depict the occurrence of super refraction in these locations. Spatial maps showed the distribution of modified radio refractivity gradient across all the selected locations in this study. The highest values were recorded in the coastal region (115.5 M-units/km) and least values in the midland (22 M-units/km) and guinea savannah (40 M-units/km) regions. The overall results will be useful for microwave links budgeting and design in Nigeria.
