Performance Analysis of Tropospheric Radio Refractivity on Radio Field Strength and Radio Horizon Distance and Its Variation with Meteorological Parameters over Osogbo, Nigeria

Abstract

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 0 N, Longitude 4.29 0 E, 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 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 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 Nunits/km and the average effective earth radius (kfactor) was 1.37 which corresponds to the conditions of super refraction. The annual maximum mean value of FSV is 7.72 dB and 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 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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“…The result from the analysis showed that the dry term radio refractivity contributes more to the total value of the radio refractivity for Accra. The pattern of variation of the wet term radio refractivity is similar to that of the radio refractivity while the dry term radio refractivity exhibit similar variation with the atmospheric pressure except that the minimum values of dry term radio refractivity and atmospheric pressure were found in the months and March and February respectively and this is similar to the study carried out by Akpootu et al [25], the pattern of variation indicates that the dry term radio refractivity is proportional to the atmospheric pressure and is related to air density.…”

“…The value of radio refractivity dropped from April to August exhibiting a trough; this may be attributed to August break when there could be a short period of dryness. Similar observations were found in the study investigated by Akpootu and Iliyasu [17]; Emmanuel et al [20] and Akpootu et al [25]. Figure 4 shows the yearly variation of radio refractivity with radio refractive index for Accra.…”

“…The atmospheric pressure decrease from January to its minimum value of 1010.3000 hPa in February and then decrease steadily from February to its maximum value of 1014.0700 hPa in August; and then decreases to December. The figure from the analysis showed that as the maximum value with a dip upward was found for the atmospheric pressure a dip downward was also noticed for the radio refractivity in August indicating that during August break Accra experiences the highest value of atmospheric pressure; this observation is in line with those carried out by Akpootu and Iliyasu [17] for Ikeja, Nigeria and Akpootu et al [25] for Osogbo, Nigeria. Figure 11 shows the monthly variation of radio refractivity with relative humidity for Accra.…”

“…The atmospheric pressure, temperature and humidity (water vapour content) are basically the three factors upon which the refractive index, of the atmosphere depends on [25]. The values of the refractive index, , varies between 1.000250 and 1.000400 indicating that it is very close to unity at or near the earth's surface and variation in this value is very small in time and in space.…”

“…The results of their study showed that the local climate has a substantial influence on the radio refractivity and consequently on the transmitted radio signals. Similarly, researchers like Adediji et al [16]; Ajewole et al [23]; Adediji et al [24] and Akpootu et al [25] have studied electromagnetic wave (EMW) medium interaction processes and the propagation implications over Nigeria, especially the study of variation of radio field strength and radio horizon distance over few stations in Nigeria. As a result of the variation of meteorological parameters in each geographical location; it is inadequate to generalize the variation of radio field strength and radio horizon distance over Nigeria.…”