Radar range dependent validation of spaceborne cloud profiling radar precipitation detection: lessons from CloudSat and the Canadian C band network for the EarthCARE era

Abstract. Ground based validation of spaceborne precipitation detection algorithms depends critically on the quality of the reference radar observations, which degrades in a range dependent fashion due to ground clutter contamination and beam geometry effects. This study quantifies that dependence using five years (2006–2010) of coincident CloudSat Cloud Profiling Radar (CPR) overpasses and observations from the King City C band dual polarisation radar in southern Ontario, Canada, supplemented by automated and human METAR observations from twelve Environment and Climate Change Canada (ECCC) weather stations. Across 75,239 matched profiles, the CloudSat precipitation occurrence product achieves a probability of detection (POD) of 54.6 %, a critical success index (CSI) of 48.9 %, and a false alarm ratio (FAR) of 17.7 %. A systematic range bin decomposition reveals anomalously elevated Network Radar Precipitation (NRP) algorithm detection frequencies within 70 km of the King City radar, attributable to ground clutter passing the NRP 480 m vertical extent filter before Doppler discrimination becomes reliable. Excluding profiles within this range raises the POD to 66.8 % and the CSI to 56.3 %. Combining this range filter with the Z_CPR > -10 dBZ threshold recommended for the Great Lakes winter precipitation regime further reduces the FAR to 13.8 % (CSI = 58.7 %). The 519 independent METAR comparisons yield a POD of 55.8 % and a low FAR of 9.2 %, confirming the radar based findings through a fully instrument independent pathway and demonstrating that the dominant CloudSat error mode is precipitation detection failure rather than false alarming. The performance degradation relative to the winter only benchmark of Hudak et al. (2008) is shown to arise primarily from near range clutter contamination and year round sampling rather than from algorithmic limitations. Critically, the 70 km threshold is governed by antenna beam geometry rather than radar wavelength and is therefore transferable to validation frameworks employing the new Canadian S band dual polarisation network. Implications for the design of ground validation campaigns for the recently launched EarthCARE Cloud Profiling Radar are discussed.