Intensity covariance of a point source in a random medium with a Kolmogorov spectrum and an inner scale of turbulence

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Abstract
The intensity covariance of a point source of waves propagating in a random medium is calculated by using the asymptotic theory (strong-scattering regime) and a Kolmogorov refractive-index spectrum with an inner-scale cutoff. The variance and small-scale correlation scale are both larger than predicted for zero inner scale. The behavior of the small-scale structure is dominated by irregularities near the receiver, whereas the behavior of the large-scale structure is dominated by irregularities near the transmitter. The theoretical predictions are compared with experimental results. Higher terms in the asymptotic theory are required for intensity covariance to be predicted adequately. Saturation of intensity fluctuations (variance of unity) is unlikely for laser propagation in typical atmospheric conditions. The calculation of intensity covariance in an extended medium cannot be simplified by substituting an equivalent thin screen in the midpoint of the propagation path.