Spectra of intensity fluctuations of scattered radiation of a focused laser beam in rain, drizzle, fog, and haze
R.Sh. Tsvyk, N.A. Vostretsov
V.E. Zuev Institute of Atmospheric Optics of Siberian Branch of the Russian Academy of Science, Tomsk, Russia
Keywords: fluctuation, scattered radiation, focused beam, spectrum, rain, drizzle, fog, haze, turbulence
Abstract
The results of experimental studies of the spectra of fluctuations of the scattered radiation intensity of a laser beam propagating through the surface atmosphere in rains, drizzle, haze, and fog are presented. The laser beam radiation was focused at the end of a 130 m path. The intensity fluctuations were measured at a distance of 10 mm from the focal spot, in the region of radiation scattered on the particles in the atmosphere. The spectrum of scattered radiation fluctuations U ( ƒ ) = ƒW ( ƒ )/∫ W ( ƒ ) dƒ in rain, drizzle, and haze is characterized by four parameters: the maximum frequency ƒ max, the inclination of the low-frequency part of the spectrum 1 > γv > 0 at ƒ < ƒ max and two inclinations of the high-frequency region γv = -2.5…-5/3 and γv1 = -3…-5 at ƒ > ƒ max; and in a weak fog, mainly by two negative inclinations γv = -0.5 and γv1 = -4…5. The frequency of the scattered field spectrum maximum is determined by the interaction of the vortex field of wind speed fluctuations, the field of particle size and mass distributions, and the drag coefficient.
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