Drop-Size Distribution Retrieval With Dual-Frequency Dual-Polarization Radars

A new drop size distribution (DSD) retrieval algorithm using dual frequencies dual-polarization radars is proposed in this work. Given the same DSD and drop size shape relation, the reflectivity (Z), specific attenuation and specific differential phase (K_DP) for S- and C-band radars are different, which provides the opportunity to retrieve the DSD using dual frequencies observations. This algorithm utilizes radar variables of Z and K_DP from S- and C-band polarimetric radars as the inputs. Reflectivity fields from both frequencies are without any attenuation correction. A three-parameter Gamma DSD is assumed in the current work. Specifically, radar data is first processed with a physics based quality control approach to remove those non-precipitations contaminated radar echoes. The forward and backward scattering amplitudes from horizontal and vertical polarizations at S- and C-band wavelengths are then calculated using a T-matrix method. For a given initial DSD assumption, the attenuated Z and K_DP from each radar gate are then calculated with the obtained forward and backward scattering amplitudes. Through adjusting the coefficients in the Gamma distribution using a Gauss-Newton method, the DSD from each radar gate can be estimated when the calculated and measured Z and K_DP match to each other. The proposed algorithm is validated on two co-located S- and C-band polarimetric radars on Taiwan with three 24-hours stratiform and convective precipitation events. The retrieval results are further validated with Parsivel disdrometers observations.