The physical model of strong optical scintillation of plane waves is extended to the case of spherical-wave propagation. The spherical-wave amplitude filter function is derived and compared to the corresponding plane-wave result. Specifically, we calculate the spherical- to plane-wave log-amplitude-variance ratio. For weak fluctuations, our results are identical to the results of perturbation theory, with which the spherical-wave log-amplitude variance is less than the corresponding plane-wave result. On the other hand, for’-strong fluctuations (i.e., in the saturation regime), the plane- and spherical-wave log-amplitude variances saturate to the same constant value. Expressions are presented, in the saturation regime, for the plane- and spherical-wave log-amplitude covariance function and compared with the corresponding results in the regime of weak fluctuations.
H. T. Yura, "Irradiance fluctuations of a spherical wave propagating under saturation conditions," J. Opt. Soc. Am. 64, 1526-1530 (1974)