Synergy between polarimetric radar and radiometer ADMIRARI for estimation of precipitating parameters. Overview from selected GPM/GV field experiments

C- and X-band polarimetric radars have been an important component among a large set of in-situ ground-based instrumental suite during the past GPM/GV field experiments. Polarization diversity radars have the potential to discriminate hydrometeor types as well as estimate rain rates in a large spatial domain. However rain rate estimation from radar observations might be prone to uncertainties due to unknowns like DSD , attenuation and radar calibration. Although X-band (3 cm) polarimetric radars suffer more from attenuation compared to C or S- band radars, they offer finer spatial resolution, reduced ground clutter problems, and increased sensitivity for weaker targets due to the much larger specific differential phase shift KDP and due to the larger dynamic range in differential reflectivity (ZDR ). Thus they are ideal tools to monitor rain fields in short to medium distances from the radar site, as intended in the present study.

Furthermore, during most of the GPM/GV field campaigns the microwave radiometer ADMIRARI has been taking measurements along specific RHI scans at different radar frequency bands, e.g. X-band at CHUVA, C-band at LPVEx, MC3E and GCPEx. A dual-wavelength approach has also been pursued in cases like GCPEx and at the CHILL radar facility (CHILL and D3R radars) and recently at Jülich research center in Germany (X- and Ka-band radars). These observations allow to reconstruct a set of radar polarimetric variables along the ADMIRARI line of sight, and built-up a multi-sensor multi-frequency database. The reconstruction of the rain field within the ADMIRARI beam will leave the cloud liquid water field as a last unknown. Most of the cloud liquid content is located above the cloud base, which can be detected by either a ceilometer or be retrieved independently by the radiometer, leading to a further reduction of the degree of freedom of the problem. By means of 3D polarimetric radiative transfer simulations a set of synthetic observations will be produced to be used as a first guess in the frame of a optimal estimation theory (OST) retrieval approach.

The feasibility to built the OST capable to reconstruct precipitating parameter will be presented. The retrieval will use data from the polarimetric C/X-band radars, and will produce estimations for DSD and rain water content including error assessments. Such a closure study is a direct counterpart of the attempt of coherently integrating active and passive microwave instruments as a support study for developing multi-sensor algorithms for ground validation.