ESTIMATION OF NONSTANDARD PROPAGATION PROBABILITY PARAMETER OVER NIGERIA

Abstract

Nonstandard propagation means the abnormal propagation caused by fluctuation in properties (such as density, refractive index) of the propagation medium due to the variation of atmospheric parameters within the troposphere with altitude. The nonstandard propagation probability parameter, β0, is obtained when the value of vertical refractivity gradient, ΔN, is less than or equal to -100N/km. Eight (8) years (2010-2017) daily satellite data of air temperature and relative humidity at height from the surface (2 m) to 1000hpa (100m) at four synoptic hours of the day were gotten using the grid of 0.750 from the dataset of ERA-Interim at European Centre for Medium-Range Weather Forecasts (ECMWF) over sixteen selected locations across the four climatic regions of Nigeria, and was used to obtain the vertical refractivity gradient, ΔN. The values obtained were used to estimate the nonstandard propagation probability parameter, β0. Variations in β0 and ΔN were observed synoptically, seasonally and yearly. It was be observed that higher values of radio refractivity gradient were recorded during the midnight (00:00 hr. LT) and evening (18:00 hr. LT) period. The cumulative distribution function was done to determine the probability of occurrence of β0. In Abuja (Midland region) for example, the value of ΔN during the evening (18:00 hr. LT) was recorded as 67.28 N-units/km and 23 N-units/km in February and July respectively. This result depicts the occurrence of sub refraction. On a seasonal basis, the probability of occurrence of β0 in July for example across the four climatic regions (Coastal, Guinea savanna, Midland and Sahel) is 0.06, 0.04, 0.07 and 0.2 respectively. On a yearly basis and in Ife (Midland region) for example, β0 occurred in 2010, 2011 and 2013 as -100 N-units/km, -120 N-units/km and -110 N-units/km. The result gotten from the research will assist the radio engineer in their planning and designing of radio circuitry.