Ray-based description of mode coupling by sound speed fluctuations in the ocean

TL;DR

This paper introduces an analytical high-frequency approach to analyze mode coupling in fluctuating underwater waveguides, offering a simpler alternative to traditional statistical methods and validated through numerical simulations.

Contribution

It presents a novel analytical solution for mode coupling in ocean acoustics based on geometrical rays, simplifying statistical analysis compared to existing methods.

Findings

Analytical expressions for statistical moments of mode amplitudes derived.

Good agreement with full wave numerical simulations demonstrated.

Abstract

A traditional approach to the analysis of mode coupling in a fluctuating underwater waveguide is based on solving the system of coupled equations for the second statistical moments of mode amplitudes derived in the Markov approximation [D.B. Creamer, J.Acoust. Soc. Am. 99, 2825--2838 (1996)]. In the present work an alternative approach is considered. It is based on an analytic solution of the mode coupling equation derived in the high frequency approximation [A.L. Virovlyanskii and A.G. Kosterin, Sov. Phys. Acoust. 35, 138-142 (1987)]. This solution representing the mode amplitude as a sum of contributions from two geometrical rays is convenient for statistical averaging. It allows one to easily derive analytical expressions for any statistical moments of mode amplitudes. The applicability of this approach is demonstrated by comparing its predictions for a deep water acoustic waveguide with results of full wave numerical simulation carried out using the method of wide angle parabolic equation.