Date of Award

2018

Degree Type

Thesis

Degree Name

Master of Science in Ocean Engineering

Specialization

Acoustics

Department

Ocean Engineering

First Advisor

Gopu R. Potty

Second Advisor

James H. Miller

Abstract

Measurements of underwater acoustic signals were made on a bottom-mounted horizontal line array during the Seabed Characterization Experiment (SBCEX) in the New England Mud Patch south of Martha’s Vineyard in about 70 m of water. The signals were generated by Signals, Underwater Sound (SUS) charges detonated at various locations in the experimental area at a depth of 18 m, during nearly-isovelocity conditions. The broadband signals were analyzed for modal arrival time and amplitude using time-frequency techniques. Ratios of modal amplitudes at the individual hydrophones were used to estimate the modal attenuation coefficients. Hence, these estimates are independent of any uncertainty in the frequency-dependent source level of the SUS charges. These coefficients are directly related to the depth-dependent sediment attenuation profile. Posteriori error analysis provides averages and standard deviations for the estimate of sediment attenuation as function of depth. The frequency bands of interest range from 30 Hz to 120 Hz for modes one through four. We compared our estimates of sediment attenuation with historical measurements. We determined the frequency exponent of mud to be 1.9 with an attenuation coefficient on the order of 10-5 to 10-4 decibels per meter. This work was supported by the Office of Naval Research.

Available for download on Friday, December 11, 2020

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