Estimation and comparison of the derived Dmass and Nw parameters between NASA's S-band Polarimetric Radar (NPOL) and disdrometers.

The NASA's S-band polarimetric radar (NPOL) has recently participated to four Global Precipitation Measurement (GPM ) mission Ground Validation (GV) field campaigns: Midlatitude Continental Convective Clouds Experiment (MC3E) between April-June 2011, Iowa Flooding Studies (IFloods) between April-June 2013, Integrated Precipitation Hydrology Experiment (IPHEx) between May-June 2014, and Olympic Mountain Experiment (OLYMPEx) between November 2015-January 2016. These field campaigns represent diverse climate regimes over flat and orographically complex terrain. The measurement fields present also different characteristics in terms of instruments arrangement and area covered. The ground based observations in these field campaigns also included a number of two-dimensional video disdrometers (2DVD) and PARticle Size VELocity (PARSIVEL2) disdrometers, tipping bucket and weighing bucket gauges. The NPOL and ground instruments were also operated at Wallops Island, Virginia between the field campaigns. Level 1 requirements of the NASA's Global Precipitation Measurement (GPM) mission considers the ground based radar based derived parameters as a reference. The objective of this study is to investigate the level of agreement between mass weighted drop diameter (Dmass), expressed as a function of Zdr, and the normalized intercept Nw, expressed as function of both Zh and Dmass, through the simultaneous measurements of NASA's S-band dual-polarization radar (NPOL) and disdrometers underneath. The analysis has been carried out through different statistical indicators as Person correlation coefficient, bias and absolute bias. Different relationships have been tested to analyze the sensitivity of the parameters estimation. The reliability of the relationships is investigated comparing the parameters estimated and measured by disdrometers, while the areal-point comparison is obtained comparing the NPOL and disdrometers. The comparison between DPR and NPOL highlights the relationships efficiency for airborne and ground-based radar.