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We consider the passage of a beam of light through a layer or a monolayer of a medium consisting of randomly distributed optically rigid scatterers which are large compared to a wavelength. Of the shadow-forming and refracted components of the field scattered from an isolated scatterer, we consider only the former. We obtain as a result a model of a medium consisting of black disks which are oriented with their planes perpendicular to the axis of the light beam. We take all order of mutual correlation between disks into acocunt, without any limitation on their spatial density distribution. With the aid of a parabolic equation, we show that when the disks are 6-correlated in the direction of the light-beam axis, the statistical moments of the wave field can be calculated exactly in two ways: via a Markov random process approximation and via a single-group approximation. We give a graphic geometric/probabilistic interpretation of quantities related to the coefficient of the equation for the statistical moment of the field.

The space-time correlation function of thermal acoustic radiation pressure is measured for a stationary heated source (a narrow plasticine plate). The correlation dependence is obtained by the multiplication of two signals shifted in time with respect to each other and measured by two receivers. The dependence exhibits an oscillating behavior and changes sign when the source is displaced by half the spatial period of the correlation function.