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.
