Atmospheric Structure of Turbulence

The three primary atmospheric processes that affect optical wave propagation are absorption, scattering, and refractive-index fluctuations. Absorption is a mechanism by which the atmosphere is heated. Scattering occurs in the visible and IR wavelengths when the radiation propagates through certain air molecules and particles. Both absorption and scattering by the constituent gases and particulates of the atmosphere give rise primarily to attenuation of an optical wave. Index-of-refraction fluctuations lead to irradiance fluctuations, beam broadening, angle-of-arrival fluctuations, and loss of spatial coherence of the optical wave. Clearly, these adverse effects have farreaching consequences on astronomical imaging, optical communications, remote sensing, laser radar, and other applications that require the transmission of optical waves through the atmosphere (e.g., see Chapters 11–14 of Ref. 1).