Evaluation of Small-Scale Dual-Polarimetric Measurements of Iowa XPOL Radars During the IFloodS Campaign (Invited)

The University of Iowa X-band polarimetric (XPOL) radar system consists of four scanning, mobile, dual-polarimetric, Doppler weather radars. These units are equipped with several engineering and operational features particularly suited for studying hydrological processes at smaller scales. During Apr-Jun 2013, Iowa XPOLs participated in their first field campaign - Iowa Flood Studies (IFloodS) - organized in central and north-eastern Iowa in the Midwestern United States by NASA in collaboration with The University of Iowa. As an important component of the Ground Validation (GV) program of the NASA Global Precipitation Measurement (GPM) satellite mission, IFloodS was one of the first field campaigns dedicated to hydrological studies. The XPOL-2 and XPOL-4 units were deployed with overlapping coverage over the Turkey River watershed. XPOL-3 and XPOL-5 were similarly deployed over the Clear Creek watershed. During IFloodS, XPOL-2 and XPOL-4 units collected data for diverse meteorological events (light rain to severe mesoscale storms) with nearly uninterrupted operation for 45 days of the campaign at different spatio-temporal scales. The radars made polarimetric observations at multiple range resolutions (75 m and 30 m) with oversampled range spacings of 75 m, 30 m, 15 m and 7.5 m. This data was collected at the azimuthal sampling of a degree in both PPI and RHI scans. Early analyses of the stand-alone observations by a specific XPOL unit suggest that research-quality data were obtained at smaller scales during IFloodS campaign. The drop in signal quality across different sampling regimes was insignificant. The radars were able to detect maximum unambiguous Doppler velocity up to 18 m/s in dual pulse-pair transmission mode. In this study, we further evaluate the performance of the XPOLs by comparing their multiple-scale observations with the calibrated S-band radars (such as NPOL and WSR-88D) in the mutually overlapping coverage regions. This numerical comparison provides anchor points to validate XPOL observations. An inter-XPOL comparison of the overlapping PPI and RHI data is also carried out to evaluate the consistency of observations across different XPOL units.