Extending the Capability of the Complex Effective Depth Approximation

The Pekeris waveguide, comprising a homogeneous water layer of sound speed c sub(w) and density rho sub(w) above a homogeneous fluid half-space (usually of greater sound speed and density), provides a canonical configuration for studying low-frequency sound propagation in shallow water. Numerical results for the pressure in the upper layer due to a water-borne harmonic point source are readily obtained using an acoustic propagation code derived from one of the standard representations for the field, e.g., wavenumber integration, normal mode, multipath expansion, or parabolic equation [1]. Although the Pekeris waveguide represents an idealized description of a shallow water environment, it is important conceptually as it exhibits several features that are characteristic of normal mode propagation. Even for this simple configuration, however, the normal mode wave-numbers satisfy a complicated dispersion relation. As a result, they must be determined numerically using root-finding procedures. A detailed numerical analysis of a modal solution to the Pekeris waveguide for the case of a lossy fluid bottom was recently presented by Buckingham and Giddens [2].