Climatological Coefficients for Rain Attenuation at Millimeter Wavelengths

Evan J. Dutton; C. E. Lewis; Francis K. Steele

Abstract: It is demonstrated that most of the classical raindrop-size distribution formulations give inconsistent results when used to calculate specific attenuations at millimeter-wave frequencies. For this reason, it was decided it might be desirable to subcategorizes dropsize distributions on the basis of large-scale worldwide climatological zones. This was done in the belief that different distributions will be needed in different environments to produce more accuracy in predicting millimeter-wave rain attenuation for a given location. Raindrop-size data taken over a span of about 40 years in these various climatic zones are discussed briefly in terms of common characteristics. Some empirical methods of drop-size distribution measurements are discussed, and 226 drop-size distributions are grouped broadly into four climatic zones and presented in terms of a well known model drop-size distribution formulation. Using these results, zonal coefficients for the standard specific attenuation-rain rate relationship are obtained by a couple of different least squares-regression procedures. While results are different from previous results, there is no distinct indication that they represent an improvement. A need for further work is then discussed.

Keywords: climate zones; millimeter-wave frequencies; raindrop-size distributions; specific attenuation

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