Dissertation
ACOUSTIC SCATTERING BOUNDARY EFFECTS INVESTIGATED USING REVERSIBLE SYNTHETIC APERTURE SONAR FILTERING AND TIME DELAY MODELS
Doctor of Philosophy (PhD), Washington State University
01/2012
Handle:
https://hdl.handle.net/2376/111355
Abstract
ACOUSTIC SCATTERING BOUNDARY EFFECTS INVESTIGATED USING REVERSIBLE SYNTHETIC APERTURE SONAR FILTERING AND TIME DELAY MODELS
Abstract
By Grant Carl Eastland, Ph.D.
Washington State University
August 2012
Chair: Philip L. Marston
In the present investigation, partial exposure was studied by lowering a solid aluminum cylinder through a flat free surface into a tank of water while monitoring the evolution of the scattering as a function of the amount of exposure. Understanding scattering features of cylinders for several different exposures (h/a) is relevant to the scattering by a variety of simple targets. Interactions with the free surface simulate aspects of interactions with flat sediment. Work in both monostatic and bistatic scattering and reversible filtering is used, which is based on a form of synthetic aperture sonar (SAS). The source and receiver grazing angles are held fixed while the amount of exposure of a right circular aluminum cylinder is varied. Short pulses are used to distinguish between different types of scattering contributions. The slope of the feature timing as a function of the target depth h, expressed by the derivative dt/dh where t is the measured time of the feature, depends on the feature type as well as the source and receiver grazing angles. Free surface interactions for features revealed by the slope dt/dh are consistent with feature identification using reversible SAS filtering. The presence of the interface contributes many more paths for scattering to occur, even with the case of broadside illumination considered. Utilizing this information, ray theoretic methods were used to develop absolute time models for the various mechanisms. Three different domains were used in this investigation: target-depth versus time, receiver-depth versus time and SAS image domains.
Reversible SAS filtering of monostatic and bistatic data is used to identify different specular mechanisms involving the target and free surface, in addition to the corresponding elastic responses. Delayed multiple scattering features are also visible involving more than one reflection from the target. During the investigation, additional mechanisms were discovered and studied: Franz wave features, which are from diffracted acoustic surface waves and Rayleigh wave features, which are Surface Elastic Waves.
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Details
- Title
- ACOUSTIC SCATTERING BOUNDARY EFFECTS INVESTIGATED USING REVERSIBLE SYNTHETIC APERTURE SONAR FILTERING AND TIME DELAY MODELS
- Creators
- Grant Carl Eastland
- Contributors
- Philip L. Marston (Advisor)Sukanta Bose (Committee Member)Fred Gittes (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Physics and Astronomy, Department of
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 332
- Identifiers
- 99900581543401842
- Language
- English
- Resource Type
- Dissertation