Temporal Fluctuations of the Sound Speed Field and How They Affect Acoustic Mode Structures and Coherence PDF Download
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Author: Felipe Lourenco Publisher: ISBN: Category : Languages : en Pages :
Book Description
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.
Author: Felipe Lourenco Publisher: ISBN: Category : Languages : en Pages :
Book Description
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.
Author: Jennifer L Wylie Publisher: ISBN: Category : Languages : en Pages :
Book Description
In an ideal shallow water propagation channel the sound field is accurately described by normal modes and the mode structure is predictable with clean separated modes. However the real ocean environment is rarely ideal, and variations in bottom bathymetry and water column sound speed are usually present. Random fluctuations of the sound speed in time, space, and/or the boundaries can distort modes such that phase coherence is reduced and under some conditions completely lost. The basic research community seeks to understand the effects of internal waves on temporal coherence. Here the study method of choice is to use fixed system experiments that observe both oceanographic and acoustical fluctuations. On the other hand applied Naval research is focused on using mobile platforms to instantaneously measure spatial coherence shipboard, and they have little to no interest in measuring long term coherence. Here we seek to present a unified theory using normal modes. Both spatial and temporal coherence as well as the effects of source motion and Doppler will be addressed. Mode structure can be randomized in two ways: sound speed fluctuations and boundary variations. The research proposed here will emphasize spatial variations of the bottom bathymetry and how they affect mode arrivals. A parabolic equation model is used to predict mode shapes in a range dependent environment and random variations in bottom boundaries will be introduced and distortion in the mode arrival structure will be observed. The mode arrival structures will then be used to estimate temporal and spatial coherence of the mode arrivals and the predictions will be compared to the data from three different shallow water experiments.
Author: Paul C. Etter Publisher: CRC Press ISBN: 1351679724 Category : Technology & Engineering Languages : en Pages : 639
Book Description
This newest edition adds new material to all chapters, especially in mathematical propagation models and special applications and inverse techniques. It has updated environmental-acoustic data in companion tables and core summary tables with the latest underwater acoustic propagation, noise, reverberation, and sonar performance models. Additionally
Author: J. Potter Publisher: Springer Science & Business Media ISBN: 9401133123 Category : Science Languages : en Pages : 599
Book Description
Fifteen years ago NATO organised a conference entitled 'Ocean Acoustic Modelling'. Many of its participants were again present at this variability workshop. One such participant. in concluding his 1975 paper, quoted the following from a 1972 literature survey: ' ... history presents a sad lack of communications between acousticians and oceanographers' Have we done any better in the last 15 years? We believe so, but only moderately. There is still a massive underdeveloped potential for acousticians and oceanographers to make significant progress together. Currently, the two camps talk together insufficiently even to avoid simple misun derstandings. such as those in Table 1. Table 1 Ocsanographic and acoustic jargon (from an idea by Pol/ardi Jargon Oceanographic use Acoustic use dbordB decibar (depth in m) decibel (energy level) PE primitive equations parabolic equations convergence zone converging currents converging rays (downwelling water) (high energy density) front thermohaline front wave, ray or time front speed water current speed sound propagation speed 1 The list goes on.
Author: Denis Makarov Publisher: World Scientific ISBN: 9814273171 Category : Science Languages : en Pages : 412
Book Description
A systematic study of chaotic ray dynamics in underwater acoustic waveguides began in the mid-1990s when it was realized that this factor plays a crucial role in long-range sound propagation in the ocean. The phenomenon of ray chaos and its manifestation at a finite wavelength ? wave chaos ? have been investigated by combining methods from the theory of wave propagation and the theory of dynamical and quantum chaos. This book is the first monograph summarizing results obtained in this field. Emphasis is made on the exploration of ray and modal structures of the wave field in an idealized environmental model with periodic range dependence and in a more realistic model with sound speed fluctuations induced by random internal waves. The book is intended for acousticians investigating the long-range sound transmission through the fluctuating ocean and also for researchers studying waveguide propagation in other media. It will be of major interest to scientists working in the field of dynamical and quantum chaos.
Author: Felipe Lourenco
Author: Felipe Lourenco
Author: Jennifer L Wylie
Author: Acoustical Society of America
Author: Paul C. Etter
Author: Fred Tudor Erskine
Author: 
Author: 
Author: J. Potter
Author: 
Author: Denis Makarov