A Normal Mode Theory of an Underwater Acoustic Duct by Means of Green's Function

Abstract

The resolvent Green's function technique is used to find the acoustic field due to a CW point source located in a laminar inhomogeneous medium. Results are in terms of a residue expansion (normal modes) and branch line integrals. This approach is then used to solve the wave equation for an underwater acoustic duct described by an Epstein layer. Only the residue expansion is evaluated. From the residue expansion, propagation loss is found as a function of range. Application to a realistic velocity‐depth profile indicates a pattern of beats resulting from a superposition of the normal modes. A general procedure is next described for obtaining exact solutions of the wave equation for a large variety of velocity‐depth profiles. This procedure may prove useful in developing future normal mode models.