Numerical simulation of propagation through atmospheric turbulence of an initially spherical wave is used to calculate irradiance variance , variance of log irradiance , and mean of log irradiance 〈ln I〉 for 13 values of l 0/RF (i.e., of turbulence inner scale l 0 normalized by Fresnel scale RF) and 10 values of Rytov variance , which is the irradiance variance, including the inner-scale effect, predicted by perturbation methods; l 0/RF was varied from 0 to 2.5 and from 0.06 to 5.0. The irradiance probability distribution function (PDF) and, hence, , , and 〈ln I〉 are shown to depend on only two dimensionless parameters, such as l 0/RF and . Thus the effects of the onset of strong scintillation on the three statistics are characterized completely. Excellent agreement is obtained with previous simulations that calculated . We find that , , and 〈ln I〉 are larger than their weak-scintillation asymptotes (namely, , and , respectively) for the onset of strong scintillation for all l 0/RF. An exception is that for the largest l 0/RF, the onset of strong scintillation causes to decrease relative to its weak-scintillation limit, . We determine the efficacy of each of the three statistics for measurement of l 0, taking into account the relative difficulties of measuring each statistic. We find that measuring is most advantageous, although it is not the most sensitive to l 0 of the three statistics. All three statistics and, hence, the PDF become insensitive to l 0 for roughly (where is for l 0 = 0); this is a condition for which retrieval of l 0 is problematic.
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