Applicability of the paraboic equation to problems of wave propagation in a turbulent atmosphere. II. Intensity fluctuations
V.A. Banakh, I.V. Zaloznaya, A.V. Falits
V.E. Zuev Institute of Atmospheric Optics of Siberian Branch of the Russian Academy of Science, Tomsk, Russia
Keywords: parabolic equation, wave equation, intensity fluctuations, turbulent atmosphere, path integral
Abstract
An expression for the spatial correlation function of weak intensity fluctuations of a spherical wave propagating in a turbulent atmosphere is derived for the first time based on the stochastic Helmholtz wave equation. Solution of the Helmholtz equation as a path integral is used for that. Using this expression, the spatial correlation function of intensity is calculated for the Kolmogorov turbulence spectrum model for various path-to-wavelength ratios. The comparison with calculations in the parabolic approximation is performed. It is shown that calculations of the intensity correlation function using formulas derived from the wave and parabolic equations yield virtually identical results regardless of the path-length-to-wavelength ratio. This proves the applicability of the parabolic equation for calculating weak intensity fluctuations of a spherical wave with a wavelength significantly longer than optical wavelengths.
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