Performance Analysis of Tropospheric Radio Refractivity on Radio Field Strength and Radio Horizon Distance and Its Variation with Meteorological Parameters over Osogbo, Nigeria
Keywords:Radio refractivity, field strength variability (FSV), radio horizon distance, refractivity gradient, effective earth radius, descriptive statistics.
Radio refractivity estimation is paramount in the planning and design of radio link/systems for the purpose of achieving optimal performances. In this study, the monthly average daily atmospheric pressure, relative humidity and temperature data obtained from the National Aeronautics and Space Administration (NASA) during the period of twenty two years (July 1983 – June 2005) for Osogbo (Latitude 7.47 0N, Longitude 4.29 0E, and 302.0 m above sea level) were used to estimate the monthly tropospheric radio refractivity and to investigate its variation with other meteorological parameters of monthly average daily atmospheric pressure, relative humidity, absolute temperature, saturation vapour pressure and radio refractive index. The field strength variability (FSV) and the radio horizon distance were also computed. The monthly variation of FSV using two years of data (2003 – 2004) was also investigated. The results of this study revealed that the values of radio refractivity are more during the rainy season than in the dry season. It was found that the maximum average value of tropospheric radio refractivity of 370.98 N-units and the minimum average value of 332.36 N-units occurred in the months of May and January during the rainy and dry seasons respectively. 71.45 % of the total value of the radio refractivity was contributed by the dry term while the major variation is by the wet term radio refractivity. The average refractivity gradient computed for the study area under investigation was −42.69 N-units/km and the average effective earth radius (k – factor) was 1.37 which corresponds to the conditions of super refraction. The annual maximum mean value of FSV is 7.72 dB and the minimum monthly mean value of 0.07 dB was obtained for the study area. The implication of this FSV values is that the output of a receiving antenna in Osogbo may generally be subjected to changes not less than 0.07 dB in a year and not greater than 7.72 dB. The descriptive statistical analysis shows that the radio refractivity, relative humidity, absolute temperature and radio refractive index data spread out more to the left of their mean value (negatively skewed), while the atmospheric pressure data spread out more to the right of their mean value (positively skewed). The radio refractivity, relative humidity and radio refractive index data have positive kurtosis which indicates a relatively peaked distribution and the possibility of a leptokurtic distribution. The atmospheric pressure and absolute temperature data have negative kurtosis which indicates a relatively flat distribution and possibility of platykurtic distribution.
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