Optical precipitation detection and identification system using

Abstract

A weather identification system is provided for remotely detecting precipitation and for determining the nature of precipitation in an open environment, as at an aircraft landing field. The system employs an optical transmitter and receiver, wherein particles of precipitation passing through a light beam from the transmitter cause scintillations which are detected at the receiver. A drastic reduction in spatial separation between the light transmitter and receiver makes possible the use of a partially coherent light beam in place of a conventional laser beam. The transmitter and receiver are spaced apart a distance of approximately one meter, and the product of one half of the angle of incoherency multiplied by the spatial separation between the transmitter and receiver is no greater than about 2.5 millimeters. Rain passing through the light beam produces scintillations with substantial frequency components above one kilohertz. Snow induced frequencies are primarily below a few hundred hertz. The receiver is coupled to an automatic gain control means and a signal processor. By measuring the spectrum energy in various frequency bands, and by comparing the ratios of the measurements, the existence of precipitation may be ascertained and the type of precipitation can be identified remotely.