CHARACTERIZATION OF ANOMALOUS RADIO PROPAGATION CONDITIONS OVER WEST AFRICAN ATLANTIC OCEAN

Abstract

Radiowave signals from transmitters are collected by receivers after propagating between their antennas, Radio signals are affected by several phenomena during propagation. Meteorological parameters like temperature and humidity influence radio signal propagation which leads to abnormal propagation conditions such as ducting, sub refraction and super refraction. It becomes pertinent to study the influence of these anomalous conditions over West Africa coastal regions, Island and West Africa Atlantic Ocean. In this thesis, five years of surface and profile data (atmospheric temperature, dew temperature, sea surface temperature and relative humidity) for twenty locations across the Atlantic Ocean and coastal regions of West Africa were obtained from the archive of the European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-Interim). Using the derived data, the refractivity gradient, G needed to characterize anomalous radio propagation were calculated. The values of G varies from -513 N-units/km to -0.76 Nunits/ km over the study area. It was observed that the seasonal variation of refractivity gradient over the study area have a similar trend, with high values of G in the rainy season (April – October) and lower during the dry seasons (November- March). Nouakchott, however underwent an unusual trend, with the highest values of G (-170 N-units/km) observed during the dry season at 12:00UTC, and lowest value (-480 N-units/km) during the wet season at 18:00UTC. This is because this region is characterized with prolonged dry season due to its proximity to the Western Sahara. The percentage occurrence of anomalous conditions over the study region was examined, super refraction and ducting are the prevalent occurrence with variations from 25% - 100% and 45% - 95% respectively.