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.
