Wave chaos in underwater acoustics

The problem of long-range sound propagation in an oceanic waveguide is considered. Even a weak range-dependent sound-speed perturbation is sufficient to cause chaotic dynamics in the ray limit. In the real ocean, an important role in the ray instability is played by small-scale depth oscillations of the sound-speed perturbation. Those small-scale oscillations should violate ray-wave correspondence. We carry out a comparative analysis of ray- and wave-based patterns in phase space and track how their discrepancies grow with decreasing the depth scale of a sound-speed perturbation. It is shown that the semiclassical theory can reproduce qualitative peculiarities of wave behavior even with small perturbation's scales. A strong conflict occurs only with very low acoustic frequencies.