Assessment of tropospheric field strength variability and radio horizon distance over the Guinea and coastal climatic zones of Nigeria

Abstract

Proper evaluation of the prevalent refractivity circumstances and the appropriate actions to minimise link degradation and maintain signal integrity at the receiver in such a location may increase the reliability of terrestrial satellite communications in any location. In this study, the measured monthly climatic data of atmospheric pressure, relative humidity and temperature covering a period of forty-two (42) years (from 1981 to 2022) for four (4) different locations situated across two (2) climatic zones in Nigeria were acquired from the National Aeronautics and Space Administration (NASA) to investigate the tropospheric field strength variability (TFSV) and to estimate radio horizon distance (d_RH) for the chosen sites. The study's findings showed that the maximum values of TFSV obtained are 16.2240 dB, 11.7831 dB, 16.7986 dB and 9.4150 dB for Makurdi, Ibadan, Ogoja and Warri respectively. These field strength variability values imply that, for the selected areas, the output of a receiving antenna may vary by not more than 16.2240 dB, 11.7831 dB, 16.7986 dB, and 9.4150 dB, respectively, and by not less than 3.1411 dB, 3.0076 dB, 2.9347 dB, and 2.9089 dB in a year. The average values of TFSV variability obtained are 8.7021 dB, 5.6036 dB, 7.2246 dB and 5.1234 dB for Makurdi, Ibadan, Ogoja and Warri respectively, indicating that Makurdi has the highest average value of TFSV compared to other investigated locations. The Guinea Savannah and Coastal climatic zones of Nigeria typically have higher TFSV values in the dry season when compared to the rainy season. The expressions d_RH = 132.9607√hT, dRH = 132.5453√h_T, d_RH = 132.9456√h_T and d_RH = 133.3587√h_T were established from the calculation of radio horizon distance for Makurdi, Ibadan, Ogoja and Warri respectively if the respective transmitter heights are known.