Precipitation onset detection with a rain sensor of improved sensitivity

A classical rain sensor was modified to meet the demand to detect all the precipitation of the minimum intensity of R=0.1 mm h−1, in a time interval of not longer than 30 s. The calculation of the response time of the sensor is based on the raindrop size distribution for drizzle type of rain. Theoretical solution of the response time, for any type of raindrop size distribution and any intensity of rainfall, is presented. The response time was measured in an experiment in situ, and the results of measurement for various intensities of rainfall (0.02–1.44 mm h−1), and snowfall (0.0012–1 mm h−1) are presented. The experimental response times for rainfall are somewhat shorter than predicted by theory. In addition, it was shown that the sensor was sensitive even to the snowfall of 0.0012 mm h−1 intensity.