TEMPORAL VARIABILITY OF THE VERTICAL PROFILE OF RAIN DROP SIZE DISTRIBUTION IN A TROPICAL LOCATION.

Abstract

The presence of hydrometeors on Earth-space communication links has long been identified as one of the natural factors that affect the reliability and performance of an Earth-space communication system. At frequencies above 10 GHz, variation in the sizes of rain drops present along the communication path can cause severe signal outages which may affect the reliability of a communication link. Hence, the knowledge of the variation of raindrop sizes and amount of precipitation on an Earth-space communication link are crucial to the design of reliable communication system along a slant communication path. This study presents the temporal variation of the vertical profile of rain Drops Size Distribution (DSD) in a tropical location, Akure, Nigeria. The analysis was based on 20 months’(Nov. 2013 - July. 2015) rainfall data measured using a vertically pointing Micro Rain radar (MRR) installed at the Communication Research Laboratory of the Department of Physics, the Federal University of Technology Akure, Nigeria. The data collected was characterized into different rain types and modelled using the method of moments for different probability distributions. The probability distributions considered are Exponential, Gamma and Lognormal distributions. The Micro Rain radar has the capability of profiling the measured data form the ground level to a height of 4800 m. However, in this study, the data at the height of 160 m from the ground was chosen due to the preponderance of a large number of raindrops at this height compared to the other heights. The study revealed that among the probability distributions considered, the exponential distribution agreed best with the observed DSD spectra. However, at high rain rates > 10 mm/hr. Furthermore, the results obtained in this study are also presented as contour plots and they revealed the following: the concentration of number of rain drops was found to increase as the rain rate increases; and the possibility of coalescence and break up of rain drops during collision of drop sizes was also evident. The results obtained in this study would be very useful for design and budget link mitigation analysis for Earth-space communication systems in this tropical location as well as for interpreting weather radar observations.