RAIN ATTENUATION CHARACTERISTICS FOR SATELLITE LINKS IN PARTS OF NORTH-EAST AND SOUTH-WEST NIGERIA

Abstract

ABSTRACT Characteristics of rain attenuation for Satellite links in three Northeast States (Adamawa, Gombe and Taraba) and three Southwest States (Lagos, Oyo and Ogun) of Nigeria is presented in this work. 33 years (1985 -2017) rainfall data obtainedfrom the Nigerian Meteorological Agency (NIMET) was used.Chebil rain rate model was used to compute the point rainfall rate, while the ITU-R P.618-9 model was used to compute the rain attenuation for the six locations. Point rainfall rate of 90.34 mm/h was obtained at Yola while 94.4 mm/h was obtained at Gombe and 96.2 mm/h was obtained at Jalingo. Higher rainfall rates of 108.2 mm/h, 104.8 mm/h and 99.7 mm/h were recorded at Ikeja, Ibadan and Abeokuta respectively. An elevation angles 23°, 42.5° and 55° were considered. Rain attenuation for the Northeastern States ranged between 10.22 dB and 20.24 dB at 55° elevation angle, 11.89 dB to 24.01 dB at 42.5° elevation angle and 19.83 dB to 37.14 dB at 23° elevation angle while the rain attenuation computed for the Southwestern states ranged between 10.60 dB to 22.34 dB at 55° elevation angle, 12.85 dB to 26.44 dB at 42.5° elevation angle and 20.56 dB to 40.99 dB at 23° for exceedance time percentage of 0.01% at Ku-band. For the Ka-band, attenuation varied for the Northeastern States ranged between 33.79 dB and 110.10 dB at 55°elevation angle, 37.88 dB and 121.03 dB at 42.5° elevation angle and between 57.51 dB and 167.19 dB at 23° elevation angle while the rain attenuation computed for the Southwestern states ranged between 44.63 dB and 122.11 dB at 55°elevation angle, 40.39 dB and 133.48 dB at 42.5° elevation angle and between59.71 dB and 183.75 dB at 23° elevation angle for same 0.01% exceedance time percentage in all the stations. From the values of rain attenuation predicted for 0.01% time exceedance, availability of signal is possible at 42.5° and 55° elevation angles but impossible at 23° elevation angle at Ku-band. At Ka-band, the predicted rain attenuation values for 0.01% time exceedance have shown that availability of signal is impossible at all three elevation angles, which implies total signal fade out during such rain fall events in the region.