Evaluation of the New Version of the Laser-Optical Disdrometer, OTT Parsivel2

Abstract

A comparative study of raindrop size distribution measurements has been conducted at NASA’s Goddard Space Flight Center where the focus was to evaluate the performance of the upgraded laser-optical OTT Particle Size Velocity (Parsivel2; P2) disdrometer. The experimental setup included a collocated pair of tipping-bucket rain gauges, OTT Parsivel (P1) and P2 disdrometers, and Joss–Waldvogel (JW) disdrometers. Excellent agreement between the two collocated rain gauges enabled their use as a relative reference for event rain totals. A comparison of event total showed that the P2 had a 6% absolute bias with respect to the reference gauges, considerably lower than the P1 and JW disdrometers. Good agreement was also evident between the JW and P2 in hourly raindrop spectra for drop diameters between 0.5 and 4 mm. The P2 drop concentrations mostly increased toward small sizes, and the peak concentrations were mostly observed in the first three measurable size bins. The P1, on the other hand, underestimated small drops and overestimated the large drops, particularly in heavy rain rates. From the analysis performed, it appears that the P2 is an improvement over the P1 model for both drop size and rainfall measurements. P2 mean fall velocities follow accepted terminal fall speed relationships at drop sizes less than 1 mm. As a caveat, the P2 had approximately 1 m s−1 slower mean fall speed with respect to the terminal fall speed near 1 mm, and the difference between the mean measured and terminal fall speeds reduced with increasing drop size. This caveat was recognized as a software bug by the manufacturer and is currently being investigated.

Retrieval of the raindrop size distribution from polarimetric radar data using double-moment normalisation

“…IFloodS Xband radar data is publicly available in Krajewski et al (2016). IFloods Parsivel data is publicly available in Petersen et al (2014). Table A3.…”

“…The scans covered the region over three of the disdrometers. The third data set was from a network of 14 Parsivel 2 disdrometers (Petersen et al, 2014) deployed in Iowa, US, during the National Aeronautics and Space Administration Iowa Flood Studies (IFloodS) Global Precipitation Measurement ground validation campaign. Overlooking this network was the University of Iowa's X-band radar XPOL5 .…”

“…Parsivel data are subject to uncertainty due to differences across individual instruments and instrument generations (e.g. Jaffrain and Berne, 2011;Tokay et al, 2014;Thurai et al, 2011, Raupach andBerne, 2015a), and their limited sampling area introduces a bias, as reported by Tapiador et al (2017). The Iowa data were provided in diameter class definitions that differed from those of the instrument manufacturer (Petersen et al, 2014).…”

“…Jaffrain and Berne, 2011;Tokay et al, 2014;Thurai et al, 2011, Raupach andBerne, 2015a), and their limited sampling area introduces a bias, as reported by Tapiador et al (2017). The Iowa data were provided in diameter class definitions that differed from those of the instrument manufacturer (Petersen et al, 2014). The HyMeX and Payerne data sets used the manufacturer's diameter class definitions, which implies the assumption of a raindrop axis ratio to equivolume diameter relationship (Battaglia et al, 2010).…”

Drop Size Distribution Climatology in Cévennes-Vivarais Region, France

“…However, two generations of this model have been installed over time; the oldest station is of the first generation (marked in italics on the map. It was shown that the second generation was an improvement over the first generation for both drop size and rainfall measurements [35]. This network was initiated in 2004 (Alès station, [30]) and was densified during the HyMeX project, whose special observation period (SOP) took place in 2012 [33].…”