Path-averaged measurements of rain rate and raindrop size distribution using a fast-response optical sensor.

Abstract

Path-averaged terminal velocity distribution of raindrops is determined from the temporal covariance function of signals from 2 vertically spaced linear optical detectors that respond to raindrop induced amplitude scintillations of a projected laser beam. The known monotonic relationship between drop size and terminal velocity permits the measures velocity distribution to be converted to path-averaged drop-size distribution and, in turn, to rain rate. The large capture area of the measurements over a 200m path allows drop-size distribution to be measured in short time intervals. We present measurements of path-averaged rain rate and raindrop size distribution made at 42s intervals. The terminal velocity distribution during a storm that contained a mixture of rain and hail clearly shows the 2-component nature of the precipitation. -Authors