Abstract
Tropospheric radio wave signals experience loss due to multipath effect, scattering and other forms of attenuation through the atmospheric medium, primarily due to variations in weather conditions with time. The knowledge of surface refractivity profile is important for optimal planning of Very High Frequency/Ultra High Frequency (VHF/UHF) terrestrial radio links in a region. The study of surface refractivity (Ns) over the North-Central Nigeria was carried out using meteorological data from seven locations in North-Central zone of Nigeria. The seasonal variations of Ns were also derived using the monthly summaries of surface data obtained from Nigerian Meteorological Agency (NIMET) over seven stations of Abuja, Lafia, Lokoja, Makurdi, Jos, Minna and Ilorin between 2005 and 2010.The results indicated that the monthly averages of radio refractivity during the rainy season months (April to October) are greater than the Ns values during the dry season months (November to March) for all the locations throughout the years of the study. The computed of mean monthly Ns over all the seven stations in the first 1 km above the ground level is 348 N-units, which gives mean refractivity gradient (dN/dh) of -49 N/k, these shows that the region is characterised by low scale super-refraction. The mean k-factor over the entire region in the first 1 km above the ground level is 1.4; the mean Field Strength Variability (FSV) in first 1 km of height in the region was calculated to be 14 dB. The mean Radio Horizon distance within 1 km height for a transmitter height of 100 m over the stations is 42 km. The results provide useful information needed by radio engineers to set up new terrestrial radio propagation links or to improve on the existing ones especially at VHF, UHF in the North-Central region of Nigeria, as recommended by International Telecommunication Union Recommendations (ITU-R P.453, 2013), which observed the need for local reference data on refractivity and refractivity gradients all over the world.
Highlights
Radio communications use electromagnetic waves propagation through the earth’s atmosphere to send information over long distances without the use of wires [1]
The effect of meteorological variables of pressure, temperature and relative humidity on radio wave propagation at UHF and microwave frequencies has been analysed from the study of radio refractive index derived from these three parameters [5]
The manner in which the refractive index changes with height has much consequence for radio wave propagation at frequencies greater than 30 MHz, these effects become significant at frequencies greater than about 100 MHz in the lower atmosphere [9]
Summary
Radio communications use electromagnetic waves propagation through the earth’s atmosphere to send information over long distances without the use of wires [1]. The effect of meteorological variables of pressure, temperature and relative humidity on radio wave propagation at UHF and microwave frequencies has been analysed from the study of radio refractive index derived from these three parameters [5]. An important derivative of the refractive index used in studying the effects of the troposphere on radio propagation is vertical refractivity gradient [7]. The variations in the vertical profile of the refractive index and its gradients are responsible for the change in the trajectory of radio rays in the troposphere [8]. The manner in which the refractive index changes with height has much consequence for radio wave propagation at frequencies greater than 30 MHz, these effects become significant at frequencies greater than about 100 MHz in the lower atmosphere [9].
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