A Discussion on the Applicable Condition of Rayleigh Scattering

Abstract

Based on the mechanism of particle scattering, rain detection radars are able to receive the backscattering and thus can detect the precipitation particles. For radars with different wavelength, scattering from precipitation particles may be approximated with different kinds of scattering theory, i.e. Mie scattering and Rayleigh scattering. When Mie scattering is used, the computation of the physical quantity that characterizes backscattering of the particle is completed, and the computation is much simpler when Rayleigh scattering is used. In traditional methods, a fixed threshold of the particle scale parameter is used as the criterion to discriminate Rayleigh scattering, that is, the particle size should be smaller than the wavelength of electromagnetic wave. In this work, the analysis on raindrop scattering against radars with different wavelength are discussed. It is concluded that the backscattering cross-section ratio of Mie scattering to Rayleigh scattering is more reasonable than the particle scale parameter for the measure of the criterion to discriminate Rayleigh scattering. Moreover, a small particle compared with the wavelength is a sufficient but not necessary condition for Rayleigh scattering.