ESTIMATION OF FREEZING-HEIGHT DISTRIBUTION OVER SOME SELECTED LOCATIONS IN NIGERIA USING TRMM-PRECIPITATION DATA FOR RADIO COMMUNICATION STUDIES

Abstract

To make an appropriate estimation of the fade margins required to meet user-specified availability criteria, a number of meteorological factors specific to the earth-station location like the annual average of the freezing level height (FLH) and bright band height (BBH) need to be considered. This research investigates the average values of these meteorological factors as specific to some selected locations in Nigeria. In the study, we used two years data from the precipitation radar (PR) onboard the Tropical Rain measuring Mission (TRMM) Satellite over six locations from the climatic regions to obtain the 0°C Isotherm height (ZDI) and the bright-band height associated with the stratiform type of rain. The result shows a good seasonal dependence and a slight year-to-year variability of both the freezing level and bright-band heights. The bright band height is higher in the wet months than the dry months. We estimated the rain height, hr, from the ZDI height measured and this was used to calculate the attenuation due to rain at different elevation angles of 23°, 42.5°, and 55° using the model in the International Telecommunication Union Recommendation ITU-R P.618-10. The result showed that the value of rain height quoted in the Recommendation ITU-R P.839 overestimates rain attenuation over Nigeria at frequencies of 10 GHz and above. Between 0.1% and 0.001% probability levels needed for the design of low margin ka-band communication systems and multimedia applications, rain attenuation becomes more pronounced at frequencies above 10 GHz. The result showed that Port Harcourt with higher value of point rainfall rate recorded the highest values of rain attenuation as compared to the least values recorded by Bauchi with the least point rainfall rate among all the locations considered. It could be observed that a direct proportionality exists between rain rate and rain attenuation and an indirect proportionality between elevation angle and rain attenuation. The information established will be a good tool for the system designer of earth-space communication links operating at 10 GHz and above for proper link design and improved quality of services (QoS) in this part of the world.