High‐frequency acoustic propagation in a range‐dependent guiding‐to‐antiguiding ocean channel transition

Abstract

Variations in the ambient physical parameters in the ocean may be such as to change a depth‐dependent profile with weak range dependence from guiding to antiguiding. This paper examines conversion of an initially well‐guided high‐frequency adiabatic mode into a nonguided sound field after passing through the transitional profile region. A theory is developed which smoothly patches a parabolic equation for the transitional domain onto trapped adiabatic mode fields on the guiding side and onto leaky modes on the nonguiding side. The parabolic equation is implemented numerically where it cannot be reduced to the simpler asymptotic forms. Numerical results for the dominant mode in a model profile confirm the analytical features of the theory, and reveal clearly the phenomenology of initial confinement in a surface duct, with subsequent detachment and “beaming” into deep water after passing through the transition to the antiguiding environment. [Work supported by ONR.]