Determination of Dominant-Scattering Raindrops' Size Using Dual-Polarization Radar Observations

For a flow involved with a number of particles of different sizes, it is difficult to retrieve the flow's characteristic parameters from the particles' Doppler velocity alone because the correspondences between particle sizes and Doppler components are difficult to discriminate. A feasible retrieval approach is to find out the dominant-scattering particles (making the most prominent contribution to the maximum Doppler component) and solve the motion equation of these particles with their Doppler velocity. In this approach, the first key issue is to determine the Dominant-Scattering particles' size. Taking rainfall as the physical medium, this paper proposes the relationships between the Dominant-Scattering raindrops' size $(D_{s})$ and the polarimetric variables (circular depolarization ration $C_{dr}$ or differential reflectivity $Z_{dr}$) through a series of scattering simulations. Results show that $C_{dr}$ is a good polarimetric variable to discriminate the Dominant-Scattering raindrop size, and the relationship $D_{s}-C_{dr}$ for different radar observation angles can be fitted to very simple polynomials.