Date of Award

Summer 8-2014

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

Committee Chair

Michael Vera

Committee Chair Department

Physics and Astronomy

Committee Member 2

Khin Maung

Committee Member 2 Department

Physics and Astronomy

Committee Member 3

Ras Pandey

Committee Member 3 Department

Physics and Astronomy

Committee Member 4

Partha Biswas

Committee Member 4 Department

Physics and Astronomy

Committee Member 5

Sungwook Lee

Committee Member 5 Department

Mathematics

Abstract

Ocean acoustics is the study of sound in the oceans. Electromagnetic waves attenuate rapidly in the water medium. Sound is the best means to transmit information underwater. Computational numerical simulations play an important role in ocean acoustics. Simulations of acoustic propagation in the oceans are challenging due to the complexities involved in the ocean environment. Different methods have been developed to simulate underwater sound propagation. The Parabolic-Equation (PE) method is the best choice in several ocean acoustic problems. In shallow water acoustic experiments, sound loses some of its energy when it interacts with the bottom. An equivalent fluid technique was developed by Zhang and Tindle (ZT) to model sound propagation which is affected by shear in the sea bottom. The reflection coefficient of a soft solid seabed with a low shear speed can be well approximated by replacing the seafloor with a Complex-Density (CD) equivalent fluid of suitably chosen parameters. This is called an equivalent fluid approximation. The ZT method works well in cases where low grazing angles are relevant. This technique was expanded to also perform well in cases where higher grazing angle intervals are relevant. This method is called the Expanded Equivalent Fluid (EEF) method. The EEF method gives an effective CD, r0 = r0r +ir0 i , and an effective sound speed in the bottom, c0 p, when a set of bottom parameters (density r, sound speed in the bottom cp, and shear speed cs) are given as input. The performance of the EEF method has been investigated in several different ocean acoustic environments. Far-field simulations for an array of airgun sources were performed using the CD equivalent fluid parameters. Another application of the EEF method in the geoacoustic inversion process to find an estimate of the elastic bottom parameters of the seafloor was explored. PE broadband simulations were performed to model shear-affected, bottom-interacting sound.

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