Ikumi NAKAJIMA

Study on Estimation of Precipitation Amount with the Optical Disdrometer

Toshiro KUMAKURA

Accurate measurement of precipitation amount is necessary for snow disaster count measures, weather forecasting and snow water supply. However, solid precipitation amount such as snow and hail is difficult to accurately measure due to greatly different shapes and densities by precipitation type. Currently, a method of using the optical disdrometer is used to measure the solid precipitation. However, its accuracy is not good enough. Furthermore the measuring instrument do not disclose the internal processing procedure and the output is the only result available. Therefore, it is not possible to analyze the particles one by one.
This study uses Snow Particle Counter (SPC) as an optical disdrometer, attempt to estimate the precipitation from its output. This SPC can directly resolve single particle, especially small particles. The reduction of light power caused by passage of snow particles is output as voltage in SPC. Therefore I tried to calculate precipitation amount from this voltage. The area formed by the waveform and duration of the voltage is used to represent precipitation amount. The result is Pre = 9.80S^(3/2) where Pre is precipitation amount and S is the area of the voltage and the duration. The RMSE is 0.41 mm/h. Although not very accurate, it shows the possibility to determine the approximate value. However, as precipitation intensity increases, S becomes smaller. The possible reasons, 1) shape of the particle is not sphere; 2) the particles pass the edge of the light sheet, will be considered in future works.


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