Multiple Disdrometer Observations of Rainfall

Abstract

Raindrop sampling instruments such as disdrometers and optical array probes, have been used by researchers to observe raindrop-size distributions. Estimates of raindrop-size distribution (RSD) can be made from these instruments, which can subsequently be used to study several derived parameters such as liquid-water content, rainfall rate, and radar reflectivity. These instruments have limited sampling volume, which affects the estimates of raindrop-size distribution and the derived integral parameters. Although fluctuations in the derived parameters obtained from the same disdrometer samples are correlated, estimates from independent disdrometers are not. This paper addresses the issues involved in comparing data from disdrometers. Data from four disdrometers sampling the same rain volume are analyzed to study the measurement fluctuations in a single disdrometer with time and between disdrometers at the same time interval. Theoretical analysis and data show that the correlation between deceived parameters of sampled RSD helps in observing the mean feature between the parameters with much less scatter. It is also shown that the scatter between the derived parameters of a single disdrometer, or between different disdrometers, is a function of the correlation between the estimates.