Doppler Distrometer For The Measurement Of Hydrometer Size Distribution

Abstract

An apparatus and method are disclosed which employ the Doppler principle to measure the terminal velocity and, hence, the size distribution of hydrometeors such as raindrops and hailstones. The apparatus of the present invention employs a ground-based, upwardly directed, low power, 10.525 GHz homodyne continuous wave radar module to transmit microwave signals to falling hydrometeors within the size range of 0.5 mm through 4.0 cm, to record the frequency distribution and power spectrum of the reflected signals, and to process these data with "terminal velocity"-to-"hydrometeor diameter" calibration data to generate information on the hydrometeor size distribution in the precipitation under observation. The disclosed method permits a user of the apparatus to select the Doppler velocity threshold above which data are recorded for processing with a Fast Fourier Transform technique to determine hydrometer velocity values.