Abstract: The extinction coefficient of atmospheric aerosol is measured by an instrument in which a single light beam from a graybody source is alternately directed through two similar optical paths to a detector. Each optical path traverses an equal length region of ambient air. Aerosols are filtered from the ambient air region of one optical path .The detector measures the modulation of the incident radiation and its output is a function of the extinction coefficient of the ambient air under test. A second detector is used to monitor the beam power. Processing electronics compute the extinction coefficient of the ambient air under test from the detector outputs. The ambient air regions of the two beam paths are alternately filtered for improved performance.

Abstract: A present weather observing system including a radiation source for providing a beam of radiation in the atmosphere and a detector for detecting scattered radiation from suspended or precipitating particles within a sample volume, the detector having a field of view intersecting the beam to define the sample volume. The invention further includes a device for determining the size and velocity of at least one particle precipitating through the sample volume, and an element responsive to the device for determining size and velocity for identifying the type of precipitation.