Conventional microwave radar is used extensively by meteorologists in locating and tracking percipitating storms, and to some extent, by cloud physicists in determining physical characteristics of dense cloud. The more recent availability of highly collimated, nearly monochromatic, short-pulse light beau s from laser sources makes it possible to use the radar technique for remote detection and easurement of minute concentrations of very small particles, down to those having dimensions on the order of the wavelength of light.
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