Using the ray method, an investigation has been carried out on the structure of caustics in the wa- veguide assuming the canonical distribution of the sound velocity with depth. Monochromatic point source of sound was on the axis of the waveguide. There is considered water rays only. It is shown that the spatial part of the phase of a running sound wave does not contain the wave propagation direction and is always a positive quantity. When the trajectories are calculated, it is assumed that inversion of rays occurs at an angle of total internal reflection where the reflection coefficient is equal to unity. This eliminates the horizontal part of the trajectories. At other points, the reflection coefficient is assumed to be zero, and the passing coefficient is equal to unity. With this change in the calculation of ray’s trajectories, the basic structure of the caustics remained the same. It is shown that the boundary line of the caustic is a number of foci in which rays intersect with similar angles out of the source and have neighbour times of propagation. Structure of the sound field along the boundary line of the caustic is periodic. Its period coincides with the wavelength of the field radiated by the source.
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