Ocean Acoustics

295 Pages·1979·14.67 MB·English

by  J. A. DeSanto (auth.)

B
Topics in
Current Physics
Topics in Current Physics
Founded by Helmut K. V. Lotsch
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Editor: S. Bashkin
Volume 2 Modern Three-Hadron Physics
Editor: A. W. Thomas
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Editors: S. W. Lovesey and T. Springer
Volume 4 Electron Spectroscopy for Surface Analysis
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Volume 5 Structure and Collisions of Ions and Atoms
Editor: I. A. Sellin
Volume 6 Neutron Diffraction
Editor: H. Dachs
Volume 7 Monte Carlo Methods in Statistical Physics
Editor: K. Binder
Volume 8 Ocean Acoustics
Editor: J. DeSanto
Volume 9 Inverse Source Problems in Optics
Editor: H. P. Baltes
Volume 10 Synchrotron Radiation Techniques and Applications
Editor: C. Kunz
Volume 11 Raman Spectroscopy of Gases and Liquids
Editor: A. Weber
Volume 12 Positrons in Solids
Editor: P. Hautojarvi
Volume 13 Computer Processing of Electron Microscope Images
Editor: P. W. Hawkes
Volume 14 Excitons
Editor: K. Cho
Volume 15 Physics of Superionic Conductors
Editor: M. B. Salamon
Ocean Acoustics
Edited by J. A. DeSanto
With Contributions by
N. Bleistein J. K. Cohen R. L. Deavenport
J. A. DeSanto F. R. DiNapoli J. P. Dugan
R. P. Porter J. G. Zornig
With 109 Figures
Springer-Verlag Berlin Heidelberg New York 1979
Dr. John A. DeSanto
Naval Resarch Laboratory, Washington, DC 20375, USA
ISBN-13:978-3-642-81296-5 e-ISBN-13:978-3-642-81294-1
001: 10.1007/978-3-642-81294-1
Library of Congress Cataloging in Publication Data. Main entry under title: Ocean acoustics. (Topics in
current physics; v. 8), Bibliography: p. Includes index. 1. Underwater acoustics. I. Bleistein, Norman.
II. DeSanto, John A., 1941-. III. Series. QC242.2.023 551.4'601 78-25859
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© by Springer-Verlag Berlin Heidelberg 1979
Softcover reprint of the hardcover 1st edition 1979
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of a specific statement, that such names are exempt from the relevant protective laws and regulations
and therefore free for general use.
2153/3130-543210
Preface
This Topics volume is devoted to a study of sound propagation in the ocean. The
effect of the interior of the ocean on underwater sound is analogous to the effect
of a lens on light. The oceanic lens is related, as in light propagation, to the
index of refraction of the medium. The latter is by the ratio of the sound
giv~n
frequency to the speed of sound in water, typi ca lly about 1500 ms -1. It is the vari
ation of the sound speed due to changing temperature, density, salinity, and pres
sure in the complex ocean environment which creates the lens effect. Many oceanic
processes such as currents, tides, eddies (circulating, translating regions of wa
ter), and internal waves (the wave-like structure of the oceanic density variabil
ity) contri bute in turn to the changes in sound speed'. The net effect of the ocean
lens is to trap and guide sound waves in a channel created by the lens. The trapped
sound can then propagate thousands of miles in this oceanic waveguide.
In addition to the propagation in the interior of the ocean, sound can propagate
into and back out of the ocean bottom as well as scatter from the ocean surface.
Just as the sound produced by a loudspeaker in a room is affected by the walls of
the room, so the ocean boundaries and the material properties below the ocean bottom
are essential ingredients in the problem.
Sever'al techniques are used to study underwater sound propagation. These include
at sea, controlled simulation experiments in a water tank, and modeling
ex~eriments
the phenomenon using mathematical techniques and computer simulation. The experimen
tal methods use a sound source such as an explosive (at sea) or a mechanical device
which radiates sound (like a loudspeaker) and a hydrophone receiver (like a micro
phone). The different paths which the sound waves take result in different modifica
tions of the initial signal. The received signals are recorded and processed using
computers to yield the desired measurement. Mathematical methods model the physical
situation, the resulting equations describing the model are solved using computers,
and the results compared to the experimental data.
All the above methods for the study of underwater sound propagation are discussed
in the articles in this book. They are treated in such a way as to provide a rapid
introduction to the field, as well as a thoroughly referenced review of the state
of-the-art experimental, theoretical, and computational methods in use.
Washington, D.C. JOM A. DeSanto
November 1978
Contents
1. Introduction. By J.A. DeSanto .......................................... ..
1.1 A Brief History ..................................................... 3
1.2 Outl ine of the Book................................................. 4
References ............................................................... 6
2. Theoretical Methods in Ocean Acoustics. By J.A. DeSanto (With 24 Figures) 7
2.1 Conservation Laws. Fluid and Acoustic Equations ...... ..... .......... 9
2.1.1 Conservation Laws and Fluid Equations .... .................... 9
2.1.2 A Parabolic Equation ......................................... 11
2.1.3 Perturbati on Method .......................................... 14
2.1.4 Combined Acoustic-Internal Wave Equations .................... 15
2.1.5 Sound Speed .................................................. 18
2.2 Propagation in Deterministic Media.................................. 19
2.2.1 One-Dimensional Problems ..................................... 19
a) The Pekeri s Wavegu ide ..................................... 20
b) Alternative Representations ...................... '" ...... 26
c) Solvable Profiles......................................... 28
d) Inverse Propaga t i on ....................................... 30
2.2.2 Two-Dimensional Problems..................................... 31
a) Ray-Theory ................................................ 32
b) Corrected Parabolic Approximation ......................... 33
c) Conforma 1 ~~appi ng ......................................... 36
2.2.3 Mu.lti-Dimensional Problems................................... 39
2.3 Wave Propagation in a Random Medium ................................. 40
2.3.1 The Hierarchy Problem........................................ 41
2.3.2 Coherent Waves ............................................... 44
2.3.3 Coherence Function and Related Work .......................... 47
2.3.4 Propagation of the Coherence Function in a Waveguide ......... 50
2.4 Scattering from Rough Surfaces ...................................... 54
2.4.1 The Rayleigh Hypothesis...................................... 55
2.4.2 Peri odi c Surfaces ............................................ 57
a) Rectangular Periodic Surfaces ............................. 57
b) The Sinusoidal Surface .................................... 62
VI II
2.4.3 Arbitrary Deterministic Surfaces ............................. 64
a) Green's Function Formalism ................................ 64
b) Di agrams .................................................. 66
2.4.4 Random Surfaces.............................................. 67
a) Gaussian Surfaces......................................... 67
b) Dyson Equation............................................ 69
c) Coherent Specular Intensity............................... 70
d) Remarks................................................... 73
References 73
3. NumericaZ ModeZs of Underwater Acoustic Propagation
By F.R. DiNapoli and R.L. Deavenport (With 21 Figures) .................. 79
3.1 Range-Independent Models ............................................ 80
3.1.1 Depth-Dependent Green's Function (Impedance Formulation) ..... 82
a) Matrizant Method.......................................... 83
3.1.2 Direct Numerical Integration: Fast Field Program (FFP) ....... 90
3.1. 3 Normal ~1ode (and Branch Line Integral) Models ................ 92
a) Stickler (EJP Cuts). Bartberger (Pekeris Cuts) ............ 92
b) Stickler's Residue Contribution ........................... 95
c) Bartberger's Residue Contribution (Pekeris Cuts) .......... 97
d) Branch Cuts ~nd Branch Cut Integrals ...................... 98
e) Numerical Considerations .................................. 101
3.1.4 Depth Dependent Green's Function (Traveling-Wave Formulation) 103
3.1.5 Multipath Expansion Models ................................ '" 107
3.1.6 Connection Between Modes and Rays ............................. 117
3.1.7 Quantitative Model Assessment ................................ 121
3.1.8 Waveform Prediction Models ................................... 131
3.2 Range-Dependent Model s .............................................. 135
3.2.1 Split Step Algorithm for Parabolic Equation .................. 135
3.2.2 Parabolic Decomposition Method ............................... 137
3.2.3 Finite Differences ........................................... 138
3.2.4 Range-Dependent Normal Mode Theory ........................... 140
3.2.5 Range-Dependent Ray Theory Models ............................ 141
3.2.6 Finite Element ApfJroach ...................................... 142
a) The Finite Element Method ................................. 143
b) Merits/Shortcomings of the FEM ............................ 146
c) Transparent Boundary Simulation Techniques ................ 147
d) Solid Domain Boundaries ................................... 148
e) Fluid Domain Boundaries ................................... 149
f) Combined Solid-Fluid Domain Boundaries .................... 150
g) Fluid Finite Elements ..................................... 153
References 154
IX
4. PhysiaaZ ModeZing of Underwater Aaoustias
By J.G. Zornig (With 17 Figures) ......................................... 159
4.1 Background Information ...........................•.....•....•....... 159
4.1.1 Definition and Purpose ....................................... 159
4.1.2 Relationship to Ocean Experimentation ........................ 160
4.1.3 Historical Overview .......................................... 160
4.2 Water Facilities .................................................... 162
4.2.1 Model Tanks .•...................•..•...•..................... 162
4.2.2 Lakes and Bays ............................................... 163
4.3 Targets .......•......•..•........................................... 164
4.3.1 Wind Driven Surfaces ................. , ....................... 164
4.3.2 Fi xed Surfaces ....................•.......................... 168
4.3.3 Volume Targets ............................................•.. 169
4.4 Instrumentation and Signal Processing ............................... 170
4.4.1 Sources. . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . • . . . • . . . . • . . .. 170
4.4.2 Data Acquisition .............•.........•..................... 173
4.4.3 Signal Processing ............................................ 174
4.5 Results of Physical Model Experimentation .......................•... 176
4.5.1 Scattered Intensity .......................................... 176
4.5.2 Coherence Studies .........................•.................. 178
4.5.3 Second-Order Coherence ....................................... 179
4.5.4 Frequency Spreadi ng .......................................... 181
4.6 Remarks ....••...•..•................................................ 184
References ....................................•.......................... 185
5. Oaeanography in Underwater Aaousties
By J. P. Dugan (With 15 Fi gures) .......................................... 187
5.1 Properties of Seawater .............................................. 187
5.2 Ocean Variability ................................................... 191
5.2.1 Ocean Climatology ............................................ 192
5.2.2 Ocean Weather ................................•............... 196
5.2.3 Internal Waves ............................................... 207
5.2.4 Fi ne Structure ........•............................•......... 214
5.2.5 Near-Surface Structure .................................•..... 216
References 221
6. Inverse Methods for RefZeator Mapping and Sound Speed ProfiZing
By N. Bleistein and J.K. Cohen (With 9 Figures) .•......•................. 225
6.1 The POFFIS Identi ty ......•...•.•••........................•.....•..• 225
6.1.1 Derivation of the POFFIS Identity ...........•.........•...•.• 226
6.1.2 The Limited Aperture Problem for the POFFIS Identity ......... 230
x
6.2 An Inverse Method for Determining Small Inhomogeneities in a Medium. 234
6.2.1 An Integral Equation for Three-Dimensional
Velocity Variation ........................................... 235
6.2.2 Direct Inversion for Backscatter over a Medium
with Two-Dimensional Velocity Variation ...................... 237
6.2.3 Direct Inversion for a Case with Separated
Source and Recei ver .......................................... 240
6.2.4 Direct Inversion for a One-Dimensional Problem ............... 241
6.2.5 Direct Inversion in Free Space ............................... 241
References 242
7. Acoustic Probing of Space-Time Scales in the Ocean
By R.P. Porter (With 23 Figures) ......................................... 243
7.1 Sound Probes of Ocean Currents ...................................... 245
7.1.1 SOFAR Floats for Lagrangian Current Measurements ............. 245
7.1.2 Current Measurements by Reciprocal Transmissions ............. 246
7.2 Acoustic Fluctuations as a Measure of Ocean Dynamics ................ 247
7.2.1 CW Transmissions and Tides ................................... 248
7.2.2 Short Pulse Transmissions Along Single Paths ................. 249
7.2.3 Spatial and Temporal Fluctuations of CW Transmissions ........ 250
7.2.4 Spectra of Phase and Amplitude Fluctuations .................. 252
7.3 Sound Speed Variations and Internal Gravity Waves ................... 260
7.3.1 Internal Gravity Wave Spectra ................................ 261
7.3.2 Fluctuations in the Index of Refraction ...................... 264
7.4 Acoustic Fluctuation Theories and Their Relationship
to Ocean Dynami cs ................................................... 265
7.4.1 Acoustic Fluctuation Theories and Their Relationship
to Ocean Dynami cs ........................................... 266
7.4.2 Effect of Large Scale Flows on Acoustic Amplitude and Phase .. 267
7.4.3 Effect of Internal Waves on Acoustic Amplitudes and Phases ... 269
7.4.4 Multipath Fluctuations for Stable Paths ...................... 272
7.4.5 Stability of Single Paths .................................... 274
7.5 Implications for Ocean Probing ...................................... 276
References 277
Subject Index ................................................................ 279