RYTOV APPROXIMATION OF THE IRRADIANCE COVARIANCE AND VARIANCE OF A RETROREFLECTED OPTICAL BEAM IN ATMOSPHERIC-TURBULENCE

The irradiance (intensity) covariance and variance functions associate d with a reflected Gaussian-beam wave from a glint target (retroreflec tor) are calculated and compared with similar results based on a specu lar target (smooth finite mirror). Detailed results are presented for the normalized irradiance variance, or scintillation index, of the ref lected wave for both types of reflector in an improved model of atmosp heric turbulence that incorporates a high-wave-number rise just before the dissipation range in addition to inner-outer-scale parameters. Nu merical comparisons show that values of the normalized irradiance vari ance based on the improved model of refractive-index fluctuations (hen ceforth called the modified spectrum) can be up to 32% greater than th ose predicted by the Kolmogorov power-law spectrum when the inner scal e is comparable in size with the first Fresnel zone. All analytic expr essions derived here are based on weak-fluctuation theory using genera lized spectral representations of the complex phase perturbations. (C) 1997 Optical Society of America.