The droplet spectrometer - A measuring concept for detailed precipitation characterization

Abstract

The climate change issue increasingly attracts the interest of the media and the public. In southern Europe, for example, devastating forest fires are noted more often after long dry periods; also reports for intense storms and damaging floods are more frequent. The winter in Germany in 20062007 recorded about two degrees warmer mean temperatures than for the average winter and in some regions the deviation was even higher. The climate change is endorsed by several International bodies. Hence, it becomes more and more important to be able to observe and analyze in detail the changing climate and weather with suitable measuring instruments. Focusing on the observation of precipitation and its effects, a simple information like 10 mm of precipitation were recorded in two hours is already much imprecise. In order to be able to carry out a detailed precipitation analysis, size and speed is of special interest; even more the momentum of the hydrometeors is. To measure these parameters some concepts have already been available for some time. Optical and mechanical measuring instruments exist which are used for the local determination of precipitation intensity or the drop size distribution. Some rain detectors are able to calculate these parameters, like laser disdrometers (e.g., OTTs Parsivel) or the Joss-Waldvogel Disdrometer (by Distromet LTD), by measuring the size of single raindrops (see also Tokay et al. 2005). However, there is no compact measuring instrument in the market which records information about detection time, size and momentum of every single drop directly without carrying out a projection on more inexact parameters (e.g., intensity or whole amount of precipitation). Hence, the authors saw the need to develop a measuring instrument which stores the raw data and allows a very detailed characterization of precipitation. The early development process begun in 2005 and the first prototypes are already in use. The so-called Droplet Spectrometer is a three-part measuring system basically consisting of a droplet sensor, a measuring amplifier and a computer with the software Rainalyser for analysis and calculation of the momentum of the individual drops and for displaying the results (see Fig. 1).