Measurement of simulated drop size distribution with an optical spectro pluviometer: Sample size considerations

Knowledge of drop size distributions is important for deriving various rain erosivity parameters. This study investigates the potential of an optical spectro pluviometer (OSP) to measure drop size distributions. Particular at tention is paid to the impact of drop sample size and derived erosivity par ameters. An experimental set-up using a rainfall simulator and an OSP is de scribed. The OSP allows a continuous real-time sampling of the drops. Resul ts on drop size distributions and sampling effects are discussed. A simulat ion aimed at reproducing the sampling made with the widely used flour-pelle t or filter-paper method is described. From this simulation, recommendation s on the sample size of the collected drops needed for an accurate determin ation of median drop size and kinetic energy are given. Past studies report ing drop size characteristics have often used too small a sample for an ade quate description of rain erosivity. Copyright (C) 1999 John Wiley & Sons, Ltd.