Comparison of three types of laser optical disdrometers under natural rainfall conditions

Lisbeth Lolk Johannsen,Nives Zambon,Peter Strauss,Tomas Dostal,Martin Neumann,David Zumr,Thomas A Cochrane,Günter Blöschl,Andreas Klik

doi:10.1080/02626667.2019.1709641

Abstract

ABSTRACTOptical disdrometers can be used to estimate rainfall erosivity; however, the relative accuracy of different disdrometers is unclear. This study compared three types of optical laser-based disdrometers to quantify differences in measured rainfall characteristics and to develop correction factors for kinetic energy (KE). Two identical PWS100 (Campbell Scientific), one Laser Precipitation Monitor (Thies Clima) and a first-generation Parsivel (OTT) were collocated with a weighing rain gauge (OTT Pluvio2) at a site in Austria. All disdrometers underestimated total rainfall compared to the rain gauge with relative biases from 2% to 29%. Differences in drop size distribution and velocity resulted in different KE estimates. By applying a linear regression to the KE–intensity relationship of each disdrometer, a correction factor for KE between the disdrometers was developed. This factor ranged from 1.15 to 1.36 and allowed comparison of KE between different disdrometer types despite differences in measured drop size and velocity.

Highlights

Accurate and comparable rainfall measurements are important in many fields of hydrological research in order to ensure detailed knowledge of rainfall characteristics
The total rainfall measured by the disdrometers was smaller than that with a percentage error of −3% for PWS100 by Campbell Scientific (PWS) 1, –14% for PWS 2, – 20% for Thies and –30% for Parsivel
All three parameters show the smallest deviation to the rain gauge (RG) for PWS 1, followed by PWS 2, Thies and Parsivel having the largest deviation

Summary

Introduction

Accurate and comparable rainfall measurements are important in many fields of hydrological research in order to ensure detailed knowledge of rainfall characteristics. Automated methods were developed such as impact disdrometers (Joss and Waldvogel 1967) and optical disdrometers (Hauser et al 1984, Löffler-Mang and Joss 2000, Kruger and Krajewski 2002, Ellis et al 2006), which are capable of continuous measurements. Optical laser-based disdrometers use laser beams to measure the number, size and velocity of raindrops. The measurement of the drop size distribution (DSD) and velocity enables the estimation of rainfall characteristics such as the accumulated rainfall amount (R), intensity (I) and kinetic energy (KE). The initial detachment of soil particles through splash erosion is dependent on the KE of the raindrops. The ability of the disdrometers to measure the number, size and velocity of the falling drops accurately is essential in soil erosion studies

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