Analysis of tropospheric radio refractivity over Julius Nyerere International Airport, Dar es Salaam

Abstract

meteorological parameters-is of fundamental importance in planning and advancing the understanding of radio wave propagation and wireless communication systems within the troposphere. The vertical profiles of radio refractivity gradient (G) within 1km above the earth’s surface are important for the estimation of anomalous propagation (AP) of microwave radiation. Furthermore the effect of AP in weather radar measurements may be important as spurious echoes from distant ground targets may appear as precipitation leading to incorrect rainfall estimations. AP may also affect dramatically the quality of clear air radar observations. In this paper,we present the vertical and temporal variations of refractive index represented by refractivity (N-units) and refractivity gradient (G) (N-units km-1) in the troposphere to evaluate the occurrence of AP over Julius Nyerere International Airport (JNIA), Dar es Salaam, Tanzania. Meteorological data of air temperature, relative humidity, and atmospheric pressure collected from radiosonde station at JNIA during January, February, August, 2012 and September, October, and November, 2013, were used to compute refractivity, refractive index and refractivity gradient. The percentage of occurrences of super-refraction, sub-refraction, normal-refraction and ducting conditions are presented. Results reveal that, the tropospheric radio wave propagation conditions over JNIA have varying degree of occurrence with normalrefraction conditions prevalent at all the levels except in February, 2012. During this month, super-refraction and normal-refraction conditions have prevailed at the altitude of 1km. The presented results in this paper indicate how the variation in meteorological parameters such as humidity and temperature in the lower troposphere can cause AP. These results can be used by air traffic controllers at: Tanzania Civil Aviation Authority (TCAA) surveillance radar, which is located at JNIA and TMA weather radar, which is located 10km from JNIA, to improve performance of their radars to detect and eliminate false echoes from AP of the radar beam.