Patent ID: 6914674

Claim:
In a weather identification system having a light beam source that transmits a partially coherent beam of light along a prescribed path, a first receiver positioned directly in said light beam path to produce signals in response to scintillations occurring in said beam of light, a second receiver obliquely positioned relative to said prescribed path to produce output signals responsive to forward scattering of light from scintillations occurring in said beam of light and a signal processing means, wherein said signal processing means has means for detecting a signal indicative of intensity of light received from said light beam by said first detector, means for detecting a signal indicative of light intensity of said forward scattering of light from said second receiver, and means for synchronizing said signal indicative of light intensity of said forward scattering of light and said signal indicative of intensity of light from said light beam to produce said signal characteristic of drizzle, said signal processing means being responsive to output signals from both said first and said second receivers to produce a signal from said first receiver characteristic of rain and another signal from said first receiver characteristic of snow that is independent of intensity of said light source, the improvement wherein said signal processing means also measures the fluctuation of said signal indicative of forward scattering of light from said second receiver so that said signal characteristic of rain is characteristic of rain that includes drizzle and excludes fog.