Underwater acoustic modeling: principles, techniques and applications

303 Pages·1995·9.18 MB·English

by  P.C. Etter

Underwater Acoustic Modeling
Underwater Acoustic Modeling
Principles, techniques and applications
Second edition
Paul C.Etter
E & FN SPON
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First edition 1991
This edition published in the Taylor & Francis e-Library, 2005.
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© Elsevier Science Publishers Ltd.
Second edition 1996
© 1996 Paul C.Etter
ISBN 0-203-47565-8 Master e-book ISBN
ISBN 0-203-78389-1 (Adobe eReader Format)
ISBN 0 419 20190 4 (Print Edition)
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To my wife Alice and my sons Gregory and Andrew
Contents
Preface ix
Preface to the first edition xi
Acknowledgments xiii
1 Introduction 1
1.1 Background 1
1.2 Measurements and prediction 2
1.3 Developments in modeling 4
1.4 Inverse acoustic sensing of the oceans 5
2 Acoustical oceanography 8
2.1 Background 8
2.2 Physical and chemical properties 8
2.3 Sound speed 11
2.4 Boundaries 16
2.5 Dynamic features 27
2.6 Biologics 39
3 Propagation I. Observations and physical models 41
3.1 Background 41
3.2 Nature of measurements 42
3.3 Basic concepts 43
3.4 Sea-surface boundary 47
3.5 Sea-floor boundary 52
3.6 Attenuation and absorption 58
3.7 Surface ducts 58
3.8 Deep sound channel 64
vi
3.9 Convergence zones 65
3.10 Reliable acoustic path 67
3.11 Shallow-water ducts 69
3.12 Arctic half-channel 70
3.13 Coherence 72
4 Propagation II. Mathematical models (Part One) 74
4.1 Background 74
4.2 Theoretical basis for propagation modeling 75
4.3 Ray theory models 77
4.4 Normal mode models 86
4.5 Multipath expansion models 91
4.6 Fast-field models 92
4.7 Parabolic equation models 93
4.8 The RAYMODE model—a specific example 98
4.9 Numerical model summaries 102
5 Propagation II. Mathematical models (Part Two) 109
5.1 Background 109
5.2 Surface duct models 109
5.3 Shallow-water duct models 114
5.4 Arctic models 124
5.5 Data support requirements 126
5.6 Special applications 131
6 Noise I. Observations and physical models 143
6.1 Background 143
6.2 Noise sources and spectra 143
6.3 Depth dependence 149
6.4 Directionality 150
6.5 Arctic ambient noise 151
6.6 Acoustic daylight 152
7 Noise II. Mathematical models 154
vii
7.1 Background 154
7.2 Theoretical basis for noise modeling 154
7.3 Ambient noise models 155
7.4 The RANDI model—a specific example 157
7.5 The noise notch 159
7.6 Beam noise statistics models 163
7.7 Data support requirements 164
7.8 Numerical model summaries 164
8 Reverberation I. Observations and physical models 168
8.1 Background 168
8.2 Volume reverberation 169
8.3 Boundary reverberation 171
9 Reverberation II. Mathematical models 178
9.1 Background 178
9.2 Theoretical basis for reverberation modeling 178
9.3 Cell-scattering models 181
9.4 The REVMOD model—a specific example 183
9.5 Bistatic reverberation 187
9.6 Point-scattering models 190
9.7 Numerical model summaries 193
10 Sonar performance models 194
10.1 Background 194
10.2 Sonar equations 195
10.3 The NISSM model—a specific example 197
10.4 Model-operating systems 205
10.5 Data sources and availability 212
10.6 Numerical model summaries 217
11 Model evaluation 218
11.1 Background 218
11.2 Past evaluation efforts 219
viii
11.3 Analytical benchmark solutions 220
11.4 Quantitative accuracy assessments 222
11.5 The POSSM experience—a specific example 223
11.6 Evaluation guidelines 226
11.7 Documentation standards 229
Appen Abbreviations and acronyms 232
dix A:
Appen Glossary of terms 241
dix B:
References 247
Author index 274
Subject index 282
Preface
The subject of underwater acoustic modeling deals with the translation of our physical understanding of
sound in the sea into mathematical formulas solvable by computers. This book divides the subject of
underwater acoustic modeling into three fundamental aspects: the physical principles used to formulate
underwater acoustic models; the mathematical techniques used to translate these principles into computer
models; and modeling applications in sonar technology and oceanographic research.
The material presented here emphasizes aspects of the ocean as an acoustic medium. It shows
mathematicians and physical scientists how to use this information to model the behavior of sound in a
spatially complex and temporally variable ocean. This approach diminishes the need for discussions of
engineering issues such as transducers, arrays and targets. Aspects of hardware design and modeling in
underwater acoustics are discussed in other excellent texts.
Recent developments in underwater acoustic modeling have been influenced by changes in global
geopolitics. These changes are evidenced by strategic shifts in military priorities as well as by efforts to transfer
defense technologies to non-defense applications.
The strategic shift in emphasis from deep-water to shallow-water naval operations has focused attention
on improving sonar performance in coastal regions. These near-shore regions, which are sometimes referred
to as the littoral zone, are characterized by complicated and highly variable acoustic environments. Such
difficult environments challenge the abilities of those sonar models intended for use in deep-water scenarios.
This situation has prompted further development of underwater acoustic models suitable for forecasting and
analyzing sonar performance in shallow-water areas.
The policy of defense conversion has encouraged the transfer of sonar modeling technology to non-
defense applications. Much of this transfer has benefited the growing field of environmental acoustics,
which seeks to expand exploration of the oceans through acoustic sensing. Such technology conversion is
exemplified by the utilization of naval underwater acousic models as both prognostic and diagnostic tools in
sophisticated experiments employing inverse acoustic sensing of the oceans.
These rapid developments in modeling have created a need for a second edition. The intent is to update
recent advances in underwater acoustic modeling and to emphasize new applications in oceanographic
research. This edition also reflects a broader international interest in the development and application of
underwater acoustic models. The coming years promise to be challenging in terms of defining research
directions, whether for defense or industry, and this edition should provide technology planners with a
useful baseline.
The original organization of material into eleven chapters has served well and therefore remains
unchanged. When required, new material has been arranged into additional subsections.
Comments from users of the first edition have evidenced appeal from acousticians, as well as
oceanographers, who have enthusiastically endorsed this book as both a practical tool and an instructional