INVESTIGATION OF RADIOWAVE PROPAGATION IMPAIRMENTS AT SUPER HIGH FREQUENCY DUE TO RAIN IN AKURE

Abstract

The measurement of the vertical profiles of rainfall parameters such as drop size distribution, rain rate, liquid water content, fall velocity and radar reflectivity were carried out by using Micro Rain Radar in 2006 and 2008 at Akure (Lat 5° 150E, long 70 15'N) in South- Western Nigeria. The vertical distributions of these parameters with heights are presented for 0 - 4800 m. The range gates for the measurement are 30 with a height step of 160 m. The variation of the drop size distribution, rain rate and liquid water content with height were evaluated. The highest rain rate and liquid water content were observed within -the height range 0-160 m. For the all cases considered, the largest concentration of drop size with a diameter of 0.246 mm occurred in the height range 0-160 m. Empirical relations in the form Y= aRh have been obtained for the rainfall rate, the radar reflectivity factor Z. and liquid water content using the least square power law' regression. The results show that the relationship obtained for height range 0-160 m for the two years were in good agreement with the values available in the literatures. For all cases considered, there is a good correlation between the parameters. The measured rainfall rates were divided into classes using the same criteria as described in Joss et at (1968) for stratiform rain type, rain rate R < 50mm/h and convective rain type, rain rate R > 50 mm/h. These empirical relations were compared with results obtained at other locations. Though there is a good agreement between the relationships Z-R in stratiform rain type with those in the literatures, however, there is a slight difference with that of convective rain type. These parameters are then used to calculate specific attenuation due to rain at different rain types and rain rates. The specific attenuation was then evaluated for frequencies from 1 - 100 GHz. Results obtained show that specific attenuation increases with increasing frequency for both rain types; at a critical frequency (around 31 GHz), the increasing specific attenuation starts to decrease.

2.2.3 Radar Constant. 9 2.2.4 Radar Resolution