Study of wave chaos in a randomly-inhomogeneous oceanic acoustic waveguide: spectral analysis of the finite-range evolution operator

TL;DR

This paper investigates wave chaos in a randomly-inhomogeneous oceanic waveguide by analyzing spectral properties of the finite-range evolution operator, revealing how chaos develops with propagation distance and its implications for underwater acoustics.

Contribution

It introduces a spectral analysis framework for the finite-range evolution operator in oceanic waveguides, linking wave chaos to classical phase space structures and classical Poincaré map analysis.

Findings

Near-axial sound propagation remains stable over hundreds of kilometers.

Increasing wavelength reduces scattering and enhances localization.

Eigenfunction analysis provides more insight than eigenvalue statistics.

Abstract

The proplem of sound propagation in an oceanic waveguide is considered. Scattering on random inhomogeneity of the waveguide leads to wave chaos. Chaos reveals itself in spectral properties of the finite-range evolution operator (FREO). FREO describes transformation of a wavefield in course of propagation along a finite segment of a waveguide. We study transition to chaos by tracking variations in spectral statistics with increasing length of the segment. Analysis of the FREO is accompanied with ray calculations using the one-step Poincar\'e map which is the classical counterpart of the FREO. Underwater sound channel in the Sea of Japan is taken for an example. Several methods of spectral analysis are utilized. In particular, we approximate level spacing statistics by means of the Berry-Robnik and Brody distributions, explore the spectrum using the procedure elaborated by A. Relano with coworkers (Relano et al, Phys. Rev. Lett., 2002; Relano, Phys. Rev. Lett., 2008), and analyze modal expansions of the eigenfunctions. We show that the analysis of FREO eigenfunctions is more informative than the analysis of eigenvalue statistics. It is found that near-axial sound propagation in the Sea of Japan preserves stability even over distances of hundreds kilometers. This phenomenon is associated with the presence of a shearless torus in the classical phase space. Increasing of acoustic wavelength degrades scattering, resulting in recovery of localization near periodic orbits of the one-step Poincar\'e map. Relying upon the formal analogy between wave and quantum chaos, we suggest that the concept of FREO, supported by classical calculations via the one-step Poincar\'e map, can be efficiently applied for studying chaos-induced decoherence in quantum systems.