Publication:
An examination of the ability of ocean obervatory systems to determine merchant ship direction and draft

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Authors
Hunt, Richard S.
Subjects
acoustics
interference
vector sensor
Lloyds mirror
lofargram
Advisors
Kapolka, Daphne
Date of Issue
2013-09
Date
Sep-13
Publisher
Monterey, California: Naval Postgraduate School
Language
Abstract
The objective of this thesis was to analyze data obtained from a network of Ocean Bottom Seismometers to determine if it could be used to provide detailed information regarding merchant vessels such as their direction and draft. The sensors were located in the Strait of Juan de Fuca and collected data from AugustSeptember, 2009. The hydrophone and three orthogonal seismometer channels were beamformed in MATLAB as a vector sensor in an attempt to get bearing data on a passing ship. Frequencies were limited to about 80Hz due to the low sampling frequency. A Lloyds mirror pattern from the ships broadband noise was visible in the lofargrams from all four channels during this transit. The Lloyds mirror pattern was compared qualitatively with theoretical predictions from ray theory as well as with transmission loss predictions from the parabolic equation model run in PC-IMAT. Vector sensor beamforming proved unsuccessful due to the lack of coherence and erratic phase differences among the sensors. This erratic behavior is probably due to multipath effects. Both ray theory and PC-IMAT models show promise for exploiting the Lloyds mirror patterns. The expected interference patterns show a clear dependence on range and draft.
Type
Thesis
Description
Series/Report No
Department
Engineering Acoustics Academic Committee
Other Units
Identifiers
NPS Report Number
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Funder
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Distribution Statement
Approved for public release; distribution is unlimited.
Rights
This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.
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