A Variational Approach for Retrieving Raindrop Size Distribution from Polarimetric Radar Measurements in the Presence of Attenuation

This study presents a two-dimensional variational approach to retrieving raindrop size distributions (DSDs) from polarimetric radar data in the presence of attenuation. A two-parameter DSD model, the constrained-gamma model, is used to represent rain DSDs. Three polarimetric radar measurements, reflectivity (ZH), differential reflectivity (ZDR) and specific differential phase (KDP), are optimally used to correct for the attenuation and retrieve DSDs by taking into account measurement error effects. Retrieval results with simulated data demonstrate that the proposed algorithm performs well. Applications to real data collected by the X-band CASA (Center for Collaborative Adaptive Sensing of the Atmosphere) radars and the C-band OU-PRIME (University of Oklahoma – Polarimetric Radar for Innovations in Meteorology and Engineering) radar also demonstrate the efficacy of this approach.