Theory Of Optical Scintillation: Gaussian-Beam Wave Model


Irradiance Probability Density Function; Moderate and strong turbulence; Optical Scintillation


Under the assumption that small-scale irradiance fluctuations are modulated by large-scale irradiance fluctuations, we develope a heuristic model of irradiance fluctuations for a propagating optical wave in a weakly inhomogeneous medium. This model takes into account the loss of spatial coherence as the optical wave propagates through atmospheric turbulence by eliminating effects of certain turbulent scale sizes that exist between two scale size, hereafter called the upper bound and the lower bound. These mid-range scale size effects are eliminated through the formal introduction of spatial frequency filters that continually adjust spatial cutoff frequencies as the optical wave propagates. By applying a modification of the Rytov method that incorporates an amplitude spatial frequency filter function under strong fluctuation conditions, tractable expressions are developed for the scintillation index of a Gaussian beam wave that are valid under moderate-to-strong irradiance fluctuations. Inner scale effects are taken into account by use of a modified atmospheric spectrum that exhibits a "bump" at large spatial frequencies. We also include the effect of a finite outer scale in addition to inner scale. With a finite outer scale, the scintillation index can be substantially lower in strong turbulence than that predicted by a model with an infinite outer scale. Based on this doubly stochastic theory of scintillation we also develop a probability density function (PDF) for the irradiance fluctuation of and optical wave propagation through a turbulent medium. The resulting il-radiance PDF takes the form of a generalized K distribution which we call the gamma-gamma distribution. The two parameters of this PDF are determined from the large-scale and small-scale scintillation terms above. We make a number of comparisons of the gamma-gamma PDF with published plane wave and spherical wave simulation data. © 2002 SPIE · 0277-786X/02/$15.00.

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Proceedings of SPIE - The International Society for Optical Engineering



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0036029776 (Scopus)

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