The Searchlight Beam in the Atmosphere (Prozhektornyi Luch v Atmosfere)
[Technical Report, Book Chapter]
AMERICAN METEOROLOGICAL SOCIETY BOSTON MA
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Air and also the impurities contained in it -- dust, water drops and ice crystals -- posses the ability to scatter and absorb light. Even in clear weather, when the concentration of an aerosol is small, light scattering phenomena do not lose their significance. The brightness and color of the daytime sky convincingly remind us of this. A searchlight beam piercing the atmosphere becomes visible precisely because of the scattering of light by atmospheric air. As a result, the distant object illuminated by the searchlight emerges on a more or less bright background of the searchlight beam itself, which radically changes the conditions of the perceptibility of the object. Furthermore, scattering and also absorption of light by the air leads to an attenuation of the light beams passing through the atmosphere, and in the case of strong turbidity, also to a change in their structure. Therefore the real conditions of the visibility of distant objects illuminated by a searchlight beam depend essentially on the optical condition of the atmosphere. The latter, however, is subject to strong changes depending on the altitude and meteorological conditions influencing the concentration and properties of an atmospheric aerosol.
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