Ray and wave chaos in problems of sound propagation in the ocean

In the 1990s, a new area of research appeared in underwater acoustics: the investigation of the chaotic behavior of ray trajectories in inhomogeneous waveguides. It was found that, at distances on the order of 1000 km, the ray chaos already is fully developed, and this phenomenon should be taken into account in describing long-range sound propagation in the ocean. The present review, using specific examples, describes the methods of theoretical studies of both the ray chaos and its manifestations at a finite wavelength, as well as the results obtained in this area of research.