Sound diffraction by an inhomogeneity in an oceanic waveguide

Sound diffraction by a moving inhomogeneity in a shallow sea is considered as applied to a shadow observation system. An expression for the perturbation formed by a group of in-phase excited normal modes is obtained in the WKB approximation. The perturbation characteristics are estimated depending on the shadow contour of the inhomogeneity and the observation conditions. A small-parameter model of diffraction is proposed in the framework of the averaged description of a multimode pattern of the diffraction shading. Conditions for the model applicability are formulated