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Theory and Application of Scattering from an Object in an Ocean Waveguide
NAVAL OCEANOGRAPHIC AND ATMOSPHERIC RESEARCH LAB STENNIS SPACE CENTER MS
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A method was developed to describe acoustical scattering from an object in a waveguide by using normal mode theory to describe the incident field. Each mode is decomposed at the object into a pair of upgoing and downgoing plane waves. A transition matrix was used developed via the extended boundary condition method of Waterman to determine the resulting near-field scattered field. The far-field scattered field was determined by invoking Huygens principle. This far-field solution satisfies all boundary conditions and preserves continuity of the solution throughout all space. The examples show that the object is correctly coupled to the waveguide. This was done by showing that the objects scattered field acts as a secondary source and that this scattered field obeyed the same boundary conditions as the point source field. This method of determining the scattered field from a three-dimensional object allows one to determine not only the correct target strength intensity, but also to properly determine the phase. In addition this method allows the investigation of the interaction between the incident field and the waveguide, the incident field with the object, and the objects scattered field with the waveguide. In this manner a better understanding of the ongoing physical processes can be obtained. Acoustic scattering, Shallow water, Waveguide propagation.
APPROVED FOR PUBLIC RELEASE