INVESTIGATION OF NON-STANDARD REFRACTION IN A COASTAL AREA OF NIGERIA USING RADIOSONDE DATA

Abstract

ABSTRACT Radio meteorological data obtained by radiosonde measurements in Lagos (3.350E, 6.060N) were used to calculate the refractivity, N at different altitudes as well as at the ground surface, in order to derive the refractivity gradient. The values were computed to a height of about 12km being the highest level for which complete radiosonde data were available. The refractivity profile were plotted versus altitude for all the data analysed. The observed refractivity distribution is more nearly an exponential function of height than a linear function as assumed by the 4/3 earth atmosphere. It was also observed that the N-values decrease with altitude from the earth surface. Other parameters, such as the k-factor and the values of the gradient exceeded for given percentages of the time were also derived. The analysis of the results have shown that most of the values of the refractivity gradient for this coastal area are larger than the standard (normal) value of -40 N-units/km and therefore the propagation conditions are super-refractive. The shapes of the curves have confirmed the exponential dependence of refractivity on height, irrespective of the season.