Publication Date

2012-12-11

Availability

Open access

Embargo Period

2012-12-11

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Applied Marine Physics (Marine)

Date of Defense

2012-10-17

First Committee Member

Harry A. DeFerrari

Second Committee Member

Jorge F. Willemsen

Third Committee Member

Arthur J. Mariano

Fourth Committee Member

Kevin B. Smith

Abstract

In an idealized shallow water propagation channel with smooth boundaries and range independent sound speed profiles, normal modes can accurately describe the entire sound field which can be predicted using normal mode models. We also know that fluctuations in the sound field can be caused by fluctuations in the sound speed profile or by source/receiver motion. These phenomena are deterministic and can be simulated by changes in the mode shape or by a combination of the motion of modes past the receiver. If the fluctuations are small then small changes will occur in mode shape or in the mode positions, hence the phase response will be approximately linear and our propagation is “phase coherent” relative to the background noise. Furthermore, spatial and temporal averaging is possible, which enhances the signal-to-noise ratio (SNR). But random fluctuations of the sound speed caused by multipath interactions with the boundaries can totally distort the acoustic modes reducing and sometimes annihilating phase coherence. In this work we seek to understand coherence in terms of the normal acoustic mode structure. This structure can be randomized by fluctuations of the sound field and fluctuations of the boundaries. The research proposed here emphasizes the temporal fluctuations of the sound speed profile and how they affect acoustic mode structures and coherence. To achieve that, the Monterey-Miami Parabolic Equation model will be used to predict the mode shapes in a range dependent channel and random fluctuations will be introduced to observe how the modes are distorted in space and time.

Keywords

Acoustic Mode Structures; Coherence of Acoustic Mode Structures; MMPE Model and Coherence of Acoustic Modes; Temporal Fluctuations of the Sound Speed Field; SW06 Experiment and Acoustic Modes

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