A new normal mode program SWAMP as a tool for modeling scattering effects in oceanic waveguides

摘要

A recently developed normal mode numerical technique implemented in the computer program "SWAMP" (Shallow Water Acoustic Modal Propagation: on a web at http://www.ucs.louisiana.edu/ ~nxs7560), which offers a unique opportunity to couple propagation and scattering phenomena in oceanic waveguides with complicated multi-layered bottom structure and variable sound speed profile in the water column, is discussed. The SWAMP algorithm for obtaining the modal solution for an arbitrary waveguide is based on a warping matrix transformation of the solution of an isovelocity (reference) waveguide to one of an arbitrary sound speed profile. It is shown that the resulting modal functions for an azimuthally symmetrical cylindrical variable-sound-speed waveguide can be transformed into the superposition of spherical harmonics suitable for mapping incident field onto the scattered one through a Transition Matrix (T-matrix). The important fact is that the T-matrix is a third rank tensor in a spherical representation, so any incident field must be expressed in the same representation in order to map it onto the scattered field. The closed analytical form of the modal functions in SWAMP's algorithm provides an unique opportunity to incorporate SWAMP with the T-matrix model to solve one of the most complicated problems in a waveguide, namely the scattering of guided waves by an object embedded in the waveguide. [This work was partially supported by ONR and Louisiana Board of Regents through the Board of Regents Support Fund (Contract No. LEQSF(2001-04)-RD-A-38).]