The observed variability in the drop size distribution (DSD) or its integrated parameters is attributable to two main sources: instrumental effects and natural (spatial or temporal) variability. It is therefore important to compare different kinds of instruments in order to understand whether the DSD variability is due to nature or to differences among the instruments. The object of this work is to compare the performances of different disdrometers, which measure the DSD using different principles. In particular, it aims to test a recent device, called the Pludix. All the instruments analysed here are collocated: although in the past numerous DSD studies have used various types of disdrometers, only a few have compared the simultaneous DSD measurements by collocated disdrometers. The X-band rain-gauge disdrometer Pludix was employed over three months, from May 13 to August 13, 2003 in the BBC-2 (Baltex Bridge Cloud Campaign 2) at CESAR (Cabauw Experimental Site for Atmospheric Research) in The Netherlands, near Utrecht. The campaign was a large cloud measurement campaign, organized by the Royal Netherlands Meteorological Institute (KNMI), involving different kinds of instruments. One of the aims of the ground precipitation analysis was to compare different kinds of disdrometers in order to measure and parameterise the rainfall microstructure. Also used in the experiment were a two-dimensional video disdrometer (2DVD), two optical (infrared) disdrometers and different tipping-bucket rain-gauges (TB-RG). For the first time, Pludix was used alongside optical disdrometers. The aim of the present study is to compare the performances of these instruments, based on different measuring principles in the rainfall-rate (R) and DSD estimates. Moreover, several events are analysed at the Ferrara (Italy) site (Dept. of Physics-University of Ferrara), where the Pludix has been collocated since November 2001 alongside a Joss-Waldvogel impact disdrometer. Many more samples of simultaneous Pludix and JW measurements than in previous studies were collected, in order to provide a more robust DSD parameterization and to study the instrument dependency on the relationships between R integral parameters and precipitation types for different R regimes.
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