Reflection of focused Gaussian sound beam at a plane interface of unmoved-moved parts of acoustical medium

The two-dimensional stationary problem of focused Gaussian sound beam reflection on an interface of unmoved-moved liquid half-spaces with the same acoustical properties is considered. It is assumed that the liquid is moved with an subsonic velocity parallel to the boundary surface and the sound beam incidents from an unmoved part of the medium. The problem is solved by use of the exponential Fourier integral transform over a space coordinate. The incident and reflective wave beams are obtained within the limits of the paraxial (parabolic) approximation. It is shown that if the axial ray of a sound beam is incident at a critical angle corresponding to reflection coefficient vanishing, then the Gaussian profile of the reflective beam is destroyed by a characteristic central deep. This sign may be used for identification of flow velocity