Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1999. / Includes bibliographical references (p. 335-338). / The diffusive nature of shallow water environment limits the fidelity of high performance target sonar systems. The multi-layered ocean waveguide increases the reverberation and the stochastic nature of interface inhomogeneities distorts the target signal. In order to improve the performance in such an environment, an accurate description and a better understanding of background reverberant field are essential. As a theoretical approach, two numerical models have been developed in a consistent framework to simulate multi-static scattered fields produced by rough interfaces and targets in ocean waveguides. The first model describes a scattered field generated by interface roughness in a multi-layered medium. The strong interaction between seismo-acoustic waves and rough interfaces causes a significant amount of surface reverberation. A perturbational approach has been developed for the rough interface scattering. It was combined with 3-D OASES - a seismo-acoustic wave propagation model for a horizontally stratified medium, in order to express multi-layered media efficiently. The model is capable of producing random realizations and spatial statistics of scattered fields in a 3-D space with arbitrary horizontal stratification. Its deterministic scattering formulation for random roughness enables the use of a wide range of roughness types as well as experimental roughness data directly. The second model describes deterministic target scattering. It is based on the plane wave scattering functions of various targets in a free space and the single scattering approximation. As the target models, a rigid sphere, a pressure-release sphere, and a finite cylindrical elastic shell have been used. A scattering theory of finite cylindrical elastic shells has been chosen to investigate the 3-D effects caused by an aspect-dependent object. The plane wave scattering functions are incorporated with 3-D OASES to produce a unified target scattering model within multi-layered media. Compared to the discretization models using full wave theories, the target scattering model developed in this thesis provides a fast way to understand the physics of target scattering in multilayered media without the heavy computational burden of the discretization models. Finally, the rough interface and target scattering models are combined to build a numerical simulator. The numerical simulator is capable of simulating multi-static scattered fields produced by a target in a reverberant background. In order to investigate the feasibility of using a multi-static system, a numerical experiment is performed by using the numerical simulator and the scenario of the GOATS '98 experiment. The numerical simulator provides a realistic forward modeling to aid in understanding the physics of seismo-acoustic scattering in multi-layered media. / by Jaiyong Lee. / Ph.D.
| Identifer | oai:union.ndltd.org:MIT/oai:dspace.mit.edu:1721.1/61837 |
| Date | January 1999 |
| Creators | Lee, Jaiyong, 1970- |
| Contributors | Henrik Schnidt., Massachusetts Institute of Technology. Dept. of Ocean Engineering |
| Publisher | Massachusetts Institute of Technology |
| Source Sets | M.I.T. Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 338 p., application/pdf |
| Rights | M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission., http://dspace.mit.edu/handle/1721.1/7582 |
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