Retrieval of microphysical properties for the mixture of rain and hail using Doppler spectral analysis and genetic algorithm

The mixed-phase precipitation comprising rain and melting hailstones is commonly observed within a region close to the bright band. The melting ratio, defined as the ratio of water mass over the total mass of melting hailstone, is usually used to characterize the melting status of a hailstone. In this work, a novel approach is developed based on spectral polarimetry to retrieve the microphysical properties of the mixture of rain and hail. Spectral polarimetry capitalizes on both Doppler and polarimetric measurements to reveal the polarimetric variables as a function of radial velocity within the radar resolution volume. Specifically, Doppler spectra from H channel and spectral differential reflectivity, observed from high elevation angle, were proposed to retrieve the drop size distribution (DSD) of both raindrops and hailstones, melting ratio, and environment parameters of mean wind and turbulence broadening. First of all, the forward model Doppler spectra and spectral differential reflectivity was developed from the input microphysical parameters. The retrieval is postulated as a minimization of mean square errors between the observed and model spectra. In this work, the genetic algorithm (GA) was proposed for the retrieval process. The GA has been used to solve multi-variables and non-standard optimization problems. In the presentation, the performance of the proposed approach will be demonstrated through numerical simulation based on a C-band dual-polarization radar. Our preliminary statistical analysis shows that various melting ratio for the mixture of raindrops and hailstones can be retrieved with small normalized errors.