Abstract
The aim of this study was to determine the effect of radioclimatic variables on radio signal propagation at Sokoto, Nigeria. The statistical analysis for the 5 years (2006 – 2010) data has been carried out and the result has shown how these meteorological parameters vary within the study period in Sokoto. The effects of radioclimatic variables on signal propagation in Sokoto, Nigeria has been investigated. The results show that there is an increase in the values of the effective earth radius (k-factor) and radio refractive index (n) in the region. It was also observed that there was a significant increase in the atmospheric temperature during the dry season and as well an increase in the months of the rainy season due to the rise in the atmospheric moisture content in the region. All these variations affects the microwave propagation in the area, especially the rise in the values of k-factor above the global standard value of 1.333. The result of the k-factor (Table 4.8) show a monthly variation from 1.370 - 1.695, indicating that signal distortion is possible in the study area since the k-factor value is > 1.333. The effect of this result (large k-factor value) is that it will lead to major propagation condition known as super- refraction which mostly affects radio waves and then lead to signal interference over Sokoto area.
1.0 INTRODUCTION
1.1 Background of Study
Since the late 1950’s, Microwave Radio Frequencies have become the dominant form of communication for TV’s, Cell Phones, Weather Stations, and a host of others uses. Each of these companies having millions of subscribers! Satellite transmitters and Earth antennas transmit UHF and higher microwave frequencies all over the planet (Global Microwave, 2007). Just like a Vacuum tube in old electronic technology, radio climates are insulated by the vacuum of space. Because the vacuum of space acts as an insulator, radio frequencies are scattered through our atmosphere at an accelerated rate. The Earth is a rotating electromagnetic field containing a dielectric material called water. Sending oscillating radio frequencies through an electromagnetic field into a dielectric material, such as water, creates radio frequency heating (also called RF heating) at the molecular level of water (Global Microwave, 2007).
Because Earth’s electromagnetic field points directly towards the North Pole and the Earth’s atmosphere is circulating through ordinary convection towards the North pole, the RF and Microwave transmissions are guided directly towards the Polar Ice Caps. This is causing erratic weather pattern effecting the Polar Ice caps (Global Microwave, 2007). Since our atmosphere is made of water and the Earth is covered with water and ice, radio frequencies pass through our atmosphere, oceans, and ice caps. Because the wattage levels are minimal, warming is caused by a constant flow of waves that are never turned off. It is similar to cooking food in the microwave oven at a lower wattage setting. It takes longer, but still achieves it’s goal. Global Warming or Climate Change is exacerbated since the mass use of artificial satellites and the use of radio frequencies. The industrial Revolution happened at the beginning of the 1800’s. Yet, in the late 1950’s is when Global Warming or Climate Change became an issue. The timeline of Global Warming or Climate Change does not coincide with the Industrial Revolution or Automobiles at all (Global Microwave, 2007).
Tropospheric surface refractivity poses a major setback to the phenomenon of communication globally. Research done by Oyedun (2007), indicate that the interaction between some tropospheric factors and radio frequencies > 30 Mhz, exposes the signals to important propagation characteristics which often degrades communication links especially at higher frequencies. Korak (2003) opined that the propagation of electromagnetic waves in the atmosphere (especially the troposphere) is greatly influenced by the composition of the atmosphere, and attributed it to the fluctuations of atmospheric parameters such as; temperature, pressure and relative humidity. Other important variable, “the tropospheric refractive index” is also a function of pressure, temperature and humidity and this implies that fluctuations of these atmospheric parameters (pressure, temperature and humidity) do cause significant variation in the refractive index of the air in the troposphere (Okpani et al., 2015).
An appropriate procedure is required for proper planning of terrestrial and earth-space radio links, this is important for assessing the refractivity effects on signals (Afullo and Odedina, 2004). The propagation of electromagnetic waves around the earth is influenced by the properties of the earth and the atmosphere (International Telecommunication Union (ITU), 2003). The earth is an inhomogeneous body whose electromagnetic properties vary considerably as we go from one point to another.
Sea water has high conductivity whereas desert sands are dielectric, having virtually zero conductivity but dissipating energy by virtue of polarization (Afullo and Odedina, 2006). The atmosphere over the earth is a dynamic medium, its properties varying with temperature, pressure and humidity.
According to ITU-R Recommendation P.530 (ITU, 2003), the propagation loss on a terrestrial line-of-sight path relative to free space loss is the sum of different contributions, including the following: attenuation due to atmospheric gases; diffraction fading due to obstruction or partial obstruction of the path; fading due to multipath; and attenuation due to precipitation.
Each of these contributions has its own characteristic as a function of frequency, path length and geographical location (Afullo and Odedina, 2006). Most current predictions of tropospheric propagation effects are made either for the average worst month or the year. However, the radio-climatological frameworks for such predictions are more than thirty years old for clear-air effects and more than twenty years old for precipitation effects.
Moreover, radioclimatological data required to improve on the existing frameworks have been sparse for some regions of the world, including Africa. Radio propagation data for testing prediction techniques based on radioclimatological models have been even scantier.
1.2 Statement of the Problem
A recent effort by the international community to update the radioclimatological data base for tropospheric propagation predictions has led to an increase in the number of meteorological stations included in the analysis, the introduction of new potential prediction variables, and improved mapping and other presentation procedures (Olsen and Terje, 1999). The consequences of this scenario lies in the fact that the signal propagating through the troposphere does not arrive at its destination with the same amount of energy with which it was propagated from the source. This paper therefore focuses on the effect of radioclimatic variables on radio signal propagation at Sokoto metropolis.
1.3 Aims and Objectives
The aim of this research work is to determine the radioclimatic variables on radio signal propagation of Sokoto, Sokoto State over the period of five years (2006-2010).
The specific objectives are;
i. To determine the effect of temperature on radio signal propagation in Sokoto metropolis
ii. To determine the effect of relative humidity on radio signal propagation in Sokoto metropolis
iii. To determine the effect of atmospheric pressure on radio signal propagation in Sokoto metropolis
1.4 Significant of the Study
This research work will provide adequate information about radioclimatic variables (temperature, relative humidity and atmospheric pressure) and knowledge of the radio signal propagation of Sokoto, hence providing vital information for planning on health, urban development, tourism and migration, among other matters in Sokoto metropolis.
1.5 Scope and Limitation of the Study
This research work is limited to the monthly mean maximum temperature, relative humidity and atmospheric pressure data over Sokoto metropolis sourced from the Institute of Tropical Agriculture, Ibadan for the period of five years (2006-2010).
1.6 Definition of Terms
Temperature: the degree of heat as an inherent quality of objects expressed as hotness or coldness relative to something else.
Relative humidity: the amount of water vapour present in air expressed as a percentage of the amount needed for saturation at the same temperature.
Atmospheric pressure: the pressure exerted by the weight of the atmosphere, which at sea level has a mean value of 101,325 pascals (roughly 14.6959 pounds per square inch).
Refractive index: the ratio of the velocity of light in a vacuum to its velocity in a specified medium.
Refractivity: is a measure of the total polarizability of a mole of a substance and is dependent on the temperature, the index of refraction, and the pressure.
Weather: the short term state of the atmosphere at a specific time and place, including temperature humidity cloud cover wind etc.
Climate: is the long term pattern of weather on a particular area; it is the average weather over a long time period, usually 30 years
