MILLILITRE RADIOWAVE SCATTERING BY TROPICAL RAIN TYPES

Abstract

This study presents the results of calculations of propagation impairments to millimetre wave signals by spherical raindrops in different types of tropical rainfall. The Mie scattering theory, for spherical raindrops, has been adopted in this study to calculate scattering parameters such as forward scattering amplitude, backscattering amplitudes scattering cross section, total cross section and scattering albedo, Typical results of the propagation parameters calculated are presented for the frequency range of 1400 GHz. Thirteen raindrop sizes of radius ranging from 0.25mm to 3.25mm with 0.25mm interval are assumed. The lognormal drop size distribution model in four rain types; drizzle, widespread, shower and thunderstorm in Nigeria, has been employed. The results of the computed scattering parameters Obtained in this study are in good agreement with similar ones for spherical raindrops. These parameters have been used to calculate the specific attenuation and phase shift and the results are presented for the various types of precipitation found in Nigeria. The results are also Compared With some existing tropical and temperate results. Good agreements were obtained between the specific attenuation and specific phase shift of the present study and similar ones utilizing oblate spheroidal raindrop shape in tropical rainfall, Results are also presented for parameters of the power law relationship between attenuation, phase shift and rain rate The results of specific attenuation and specific phase shift obtained using the Mie theory compares well with similar ones obtained utilizing power law,