Rainfall Attenuation Investigations on the attenuation caused by rain and other hydrometers and their effects on terrestrial communications started as early as in the 1940s. Subsequently, many theoretical and experimental results were obtained and used to predict the effects of interaction between hydrometers and microwave signals. The theories for the prediction of rain attenuation on microwave signals are well established and widely used by many researchers. | Spheroidal Wave Functions in Electromagnetic Theory Le-Wei Li Xiao-Kang Kang Mook-Seng Leong Copyright 2002 John Wiley Sons Inc. ISBNs 0-471-03170-4 Hardback 0-471-22157-0 Electronic Analysis of Rainfall Attenuation Using Oblate Raindrops INTRODUCTION Rainfall Attenuation Investigations on the attenuation caused by rain and other hydrometers and their effects on terrestrial communications started as early as in the 1940s. Subsequently many theoretical and experimental results were obtained and used to predict the effects of interaction between hydrometers and microwave signals. The theories for the prediction of rain attenuation on microwave signals are well established and widely used by many researchers. Conceptually the specific attenuation due to raindrops depends on both the total extinction cross section and the raindrop size distribution. In 1908 Mie 161 formulated and put forth the exact formulation for the calculation of the total cross section TCS of an isotropic homogeneous dielectric sphere of arbitrary size. This is known as Mie theory. Later Stratton 86 expanded the scattered fields into a series of spherical vector wave functions to calculate the TCS from which the attenuation can readily be obtained upon knowing the raindrop size distribution DSD . In the work by Oslen et al. 162 an empirical relationship between the specific attenuation A and a rain rate R was proposed as A aRb where a a f and b b f are frequency-dependent parameters. Based on this formulation a and b can readily be obtained via regression analysis for different frequencies a known drop size distribution and a given atmospheric temperature. The International Radio Consultative Committee CCIR now known as CCITT 163 recommended this relationship based on the Laws 227 228 ANALYSIS OF RAINFALL ATTENUATION USING OBLATE RAINDROPS and Parsons DSD 164 in the frequency range 1 to 1000 GHz. Using interpolation the unknowns a and b can be determined using the formula presented in .
