Applied Underwater Acoustics (eBook)

Leif Bjorno

David Bradley, Thomas Neighbors (Herausgeber)

eBook Download: PDF | EPUB

2017 | 1. Auflage
980 Seiten
Elsevier Science (Verlag)
978-0-12-811247-2 (ISBN)

Applied Underwater Acoustics meets the needs of scientists and engineers working in underwater acoustics and graduate students solving problems in, and preparing theses on, topics in underwater acoustics. The book is structured to provide the basis for rapidly assimilating the essential underwater acoustic knowledge base for practical application to daily research and analysis.

Each chapter of the book is self-supporting and focuses on a single topic and its relation to underwater acoustics. The chapters start with a brief description of the topic's physical background, necessary definitions, and a short description of the applications, along with a roadmap to the chapter. The subtopics covered within individual subchapters include most frequently used equations that describe the topic. Equations are not derived, rather, assumptions behind equations and limitations on the applications of each equation are emphasized. Figures, tables, and illustrations related to the sub-topic are presented in an easy-to-use manner, and examples on the use of the equations, including appropriate figures and tables are also included.

Provides a complete and up-to-date treatment of all major subjects of underwater acoustics
Presents chapters written by recognized experts in their individual field
Covers the fundamental knowledge scientists and engineers need to solve problems in underwater acoustics
Illuminates, in shorter sub-chapters, the modern applications of underwater acoustics that are described in worked examples
Demands no prior knowledge of underwater acoustics, and the physical principles and mathematics are designed to be readily understood by scientists, engineers, and graduate students of underwater acoustics
Includes a comprehensive list of literature references for each chapter

Applied Underwater Acoustics meets the needs of scientists and engineers working in underwater acoustics and graduate students solving problems in, and preparing theses on, topics in underwater acoustics. The book is structured to provide the basis for rapidly assimilating the essential underwater acoustic knowledge base for practical application to daily research and analysis. Each chapter of the book is self-supporting and focuses on a single topic and its relation to underwater acoustics. The chapters start with a brief description of the topic's physical background, necessary definitions, and a short description of the applications, along with a roadmap to the chapter. The subtopics covered within individual subchapters include most frequently used equations that describe the topic. Equations are not derived, rather, assumptions behind equations and limitations on the applications of each equation are emphasized. Figures, tables, and illustrations related to the sub-topic are presented in an easy-to-use manner, and examples on the use of the equations, including appropriate figures and tables are also included. Provides a complete and up-to-date treatment of all major subjects of underwater acoustics Presents chapters written by recognized experts in their individual field Covers the fundamental knowledge scientists and engineers need to solve problems in underwater acoustics Illuminates, in shorter sub-chapters, the modern applications of underwater acoustics that are described in worked examples Demands no prior knowledge of underwater acoustics, and the physical principles and mathematics are designed to be readily understood by scientists, engineers, and graduate students of underwater acoustics Includes a comprehensive list of literature references for each chapter

Applied Underwater Acoustics 2
Applied Underwater Acoustics 4
Copyright 5
Dedication 6
Contents 8
List of Contributors 14
Preface 16
1 - General Characteristics of the Underwater Environment 18
1.1 INTRODUCTION 18
1.2 A BRIEF EXPOSITION OF THE HISTORY OF UNDERWATER ACOUSTICS 22
1.2.1 UNDERWATER ACOUSTICS BEFORE 1912 23
1.2.2 THE YEARS 1912 THROUGH 1918 25
1.2.3 THE YEARS 1919 THROUGH 1939 27
1.2.4 THE YEARS 1940 THROUGH 1946 29
1.2.5 THE YEARS AFTER 1946 29
1.3 INTERNATIONAL STANDARD UNITS 32
1.4 THE DECIBEL SCALES 33
1.5 FEATURES OF OCEANOGRAPHY 35
1.5.1 SOUND SPEED PROFILES 35
1.5.2 THERMOCLINES 39
1.5.3 ARCTIC REGIONS 41
1.5.4 DEEP ISOTHERMAL LAYERS 46
1.5.5 EXPRESSIONS FOR THE SPEED OF SOUND 50
1.5.6 SURFACE WAVES 53
1.5.7 INTERNAL WAVES 60
1.5.8 BUBBLES FROM WAVE BREAKING 63
1.5.9 OCEAN ACIDIFICATION 74
1.5.10 DEEP-OCEAN HYDROTHERMAL FLOWS 77
1.5.11 EDDIES, FRONTS, AND LARGE-SCALE TURBULENCE 80
1.5.12 DIURNAL AND SEASONAL CHANGES 82
1.6 SONAR EQUATIONS 83
1.6.1 DEFINITIONS OF THE SONAR EQUATION TERMS 84
1.6.2 SONAR EQUATIONS 88
1.7 ABBREVIATIONS 92
Acknowledgment 93
REFERENCES 93
2 - Sound Propagation 102
2.1 THE CONCEPT OF WAVES 102
2.1.1 THE WAVE EQUATION FOR AN INVISCID FLUID 103
2.1.2 THE HELMHOLTZ EQUATION 106
2.1.3 HARMONIC WAVES 108
2.1.4 PLANE WAVES 110
2.1.5 CYLINDRICAL WAVES 115
2.1.6 SPHERICAL WAVES 119
2.1.7 PLANE WAVE DECOMPOSITION OF A SPHERICAL WAVE 122
2.2 SOUND PROPAGATION IN A VISCOUS FLUID 124
2.2.1 DISPERSION FORMULAS 125
2.2.2 KRAMERS–KRONIG DISPERSION RELATIONS 127
2.2.3 CAUSALITY AND STOKES' EQUATION 129
2.2.4 PULSE PROPAGATION IN A VISCOUS FLUID 130
2.3 SOUND WAVES AND SHEAR WAVES IN MARINE SEDIMENTS 134
2.3.1 THE BIOT THEORY 135
2.3.2 THE GRAIN-SHEARING THEORY 137
2.4 SOURCE OR RECEIVER IN MOTION 145
2.4.1 DOPPLER FREQUENCY SHIFTS (SOURCE STATIONARY, OBSERVER IN MOTION) 146
2.4.2 DOPPLER FREQUENCY SHIFTS (OBSERVER STATIONARY, SOURCE IN MOTION) 148
2.4.3 ACOUSTIC FIELD FROM A MOVING SOURCE 149
2.5 SOUND REFLECTION AND TRANSMISSION AT A FLUID–FLUID BOUNDARY 153
2.5.1 STRUCTURE OF THE SOLUTION 154
2.5.2 THE STATIONARY PHASE APPROXIMATION 158
2.5.3 PLANE-WAVE REFLECTION 159
2.5.4 WESTON'S EFFECTIVE DEPTH 163
2.5.5 PLANE-WAVE REFRACTION 164
2.5.6 THE LATERAL WAVE 167
2.6 THE “IDEAL” WAVEGUIDE 173
2.6.1 PLANE WAVES AND NORMAL MODES 173
2.6.2 THE ACOUSTIC FIELD IN THE IDEAL WAVEGUIDE 176
2.6.3 INTERMODAL INTERFERENCE 178
2.7 THE PEKERIS CHANNEL 179
2.7.1 THE INTEGRAL-TRANSFORM SOLUTION FOR THE FIELD 180
2.7.2 THE NORMAL MODE SOLUTION 182
2.7.3 THE CHARACTERISTIC EQUATION 184
2.8 THREE-DIMENSIONAL PROPAGATION 187
2.8.1 HORIZONTAL REFRACTION 188
2.8.2 THE “IDEAL” WEDGE 189
2.8.3 THE SHADOW EDGE 192
2.8.4 INTRAMODAL INTERFERENCE 195
2.8.5 THE PENETRABLE WEDGE 196
Acknowledgment 197
REFERENCES 197
3 - Sound Propagation Modeling 202
3.1 RAY MODELS 205
3.1.1 A PARTICULAR TYPE OF ANALYTIC 2-D RAY TRACING 206
3.1.1.1 Kinematic Ray Tracing 207
3.1.1.2 Dynamic Ray Tracing 207
3.1.1.3 Caustics 209
3.1.1.4 Coherent Computation of Propagation Loss and Propagation Time Series 209
3.1.2 EXAMPLE 211
3.2 WAVE NUMBER INTEGRATION OR SPECTRAL METHODS 213
3.2.1 SOLUTION OF THE DEPTH-DEPENDENT ODE SYSTEMS 215
3.2.1.1 Recursive Computation of Reflection-Coefficient Matrices for the Solid Bottom 216
3.2.1.2 Propagator Matrices for the Fluid Region 219
3.2.1.3 Alternative Treatment of the Fluid Region 220
3.2.1.4 Final Remarks 221
3.2.2 ADAPTIVE INTEGRATION 222
3.2.3 EXAMPLE 223
3.3 NORMAL MODE PROPAGATION MODELS 225
3.3.1 MODAL WAVE NUMBERS 226
3.3.2 MODE FUNCTIONS 227
3.3.3 EXCITATION COEFFICIENTS 229
3.3.4 RANGE-DEPENDENT MEDIA 230
3.3.4.1 Equations Relating the Modal Expansion Coefficients 231
3.3.4.2 Solution in Terms of Reflection-Coefficient Matrices 233
3.3.4.3 Final Remarks 234
3.3.5 EXAMPLES 235
3.3.5.1 Range-Invariant Media 235
3.3.5.2 Range-Dependent Media 239
3.4 PARABOLIC EQUATION METHODS 242
3.4.1 INTERFACE CONDITIONS AT THE VERTICAL RANGE-SEGMENT INTERFACES 244
3.4.2 NUMERICAL SOLUTION METHODS 245
3.4.2.1 Start Solution 245
3.4.2.2 Rational-Function Approximations for the Relevant Operators 247
3.4.2.3 Depth Discretization and Range Integration 249
3.4.3 EXTENDED AND ALTERNATIVE PE APPROACHES 250
3.4.3.1 Extension to Media That Vary Regionwise Smoothly With Range and Depth 250
3.4.3.2 Coordinate Transformation Techniques 251
3.4.3.3 Two-Way PE Approaches 252
3.4.3.4 Extension to Fluid-Solid Media 252
3.4.4 EXAMPLES 253
3.5 FINITE-DIFFERENCE AND FINITE-ELEMENT METHODS 256
3.5.1 ONE-DIMENSIONAL FEM AND FDM FOR PARABOLIC AND NORMAL-MODE EQUATIONS 257
3.5.1.1 Application to Normal Modes 258
3.5.2 TWO-DIMENSIONAL FEM AND FDM FOR THE HELMHOLTZ EQUATION 259
3.5.2.1 FEM Discretization 260
3.5.2.2 FDM Discretization 261
3.5.2.3 Methods to Solve the Linear Equation System and Possibilities to Reduce Its Size 262
3.5.3 TIME-DOMAIN MODELING 263
3.5.3.1 FEM Discretization 263
3.5.3.2 FDM Discretization 263
3.5.3.3 Numerical Dispersion, Time Integration, and Stability 264
3.5.3.4 Including Absorption 265
3.5.3.5 Some Recent Developments 265
3.5.4 EXAMPLES 266
3.6 3-D SOUND PROPAGATION MODELS 268
3.6.1 MODELING HORIZONTAL REFRACTION BY A SLOPING BOTTOM OR CHANGING SOUND-SPEED PROFILE 270
3.6.1.1 Fourier Transformation With Respect to the y-Coordinate 271
3.6.1.2 Equations Relating the Modal Expansion Coefficients 272
3.6.1.3 Solution in Terms of Reflection-Coefficient Matrices 273
3.6.1.4 Final Remarks 273
3.6.2 MODELING DIFFRACTION AROUND A CYLINDRICALLY SYMMETRIC ANOMALY 274
3.6.2.1 Fourier Series With Respect to the ? Coordinate 274
3.6.2.2 Equations Relating the Modal Expansion Coefficients 276
3.6.2.3 Solution in Terms of Reflection-Coefficient Matrices 277
3.6.2.4 Final Remarks 278
3.6.3 EXAMPLES 278
LIST OF ABBREVIATIONS AND SYMBOLS 280
Acknowledgments 281
REFERENCES 281
4 - Absorption of Sound in Seawater 290
4.1 PHYSICS AND PHENOMENA 290
4.2 EXPERIMENTAL DATA 292
4.2.1 ABSORPTION PRESSURE DEPENDENCE 295
4.2.2 ABSORPTION TEMPERATURE DEPENDENCE 297
4.2.3 PH DEPENDENCE OF ABSORPTION 299
4.2.4 SALINITY DEPENDENCE 299
4.3 SOUND ABSORPTION MECHANISMS 300
4.3.1 SOUND ABSORPTION IN FRESHWATER 300
4.3.2 MOLECULAR CHEMICAL RELAXATION PROCESSES 301
4.3.2.1 Temperature Dependence 303
4.3.2.2 Pressure Effects 305
4.4 FORMULAS AND EXPRESSIONS 305
4.4.1 FRANCOIS AND GARRISON EQUATION FOR SOUND ABSORPTION IN SEAWATER 305
4.4.1.1 Boric Acid Coefficients 306
4.4.1.2 Magnesium Sulfate Coefficients 307
4.4.1.3 Pure Water Contribution 307
4.4.2 AINSLIE AND MCCOLM SIMPLIFIED EQUATION FOR SOUND ABSORPTION IN SEAWATER 307
4.5 SYMBOLS AND ABBREVIATIONS 308
REFERENCES 309
5 - Scattering of Sound 314
5.1 PHYSICS AND PHENOMENA 314
5.2 SCATTERING FROM POINT-LIKE OBJECTS 320
5.2.1 SINGLE OBJECTS 320
5.2.1.1 Rigid and Elastic Spheres 320
5.2.1.2 Gas Bubbles 322
5.2.1.3 Single Fish 324
5.2.1.4 Canonically Shaped Objects 325
5.2.1.5 Submarines 327
5.2.2 MULTIPLE OBJECTS 330
5.2.2.1 Fish Schools 331
5.2.2.2 Bubble Clouds 331
5.2.2.3 Deep Scattering Layer 334
5.2.2.4 Suspended Sediments 335
5.3 SCATTERING FROM EXTENDED, NEARLY PLANE, ROUGH SURFACES 335
5.3.1 BRAGG SCATTERING 337
5.3.2 REFLECTION FROM FACETS 337
5.3.3 LAMBERT'S LAW 338
5.3.4 SCATTERING FROM THE SEA SURFACE 339
5.3.5 SCATTERING FROM THE SEABED 343
5.4 THEORETICAL BASIS FOR SCATTERING CALCULATIONS 349
5.4.1 THE PERTURBATION APPROXIMATION 349
5.4.2 THE HELMHOLTZ–KIRCHHOFF METHOD 352
5.4.3 SCATTERING FROM SURFACES WITH TWO SCALES OF ROUGHNESS 354
5.5 SCATTERING FROM CURVED, ROUGH SURFACES 357
5.6 REVERBERATION 363
5.7 SYMBOLS AND ABBREVIATIONS 370
REFERENCES 375
6 - Ambient Noise 380
6.1 PHYSICS AND PHENOMENA 380
6.2 SOURCES OF AMBIENT NOISE 381
6.2.1 TIDES AND HYDROSTATIC EFFECTS OF WAVES 381
6.2.2 SEISMIC ACTIVITIES 383
6.2.3 TURBULENCE 384
6.2.4 SURFACE PHENOMENA 384
6.2.4.1 Breaking Waves 385
6.2.4.2 Nonlinear Wave–Wave Interaction 386
6.2.4.3 Bubbles 387
6.2.5 PRECIPITATION 389
6.2.6 BIOLOGICAL ACTIVITY 391
6.2.7 ICE NOISE 392
6.2.8 SHIPPING 392
6.2.9 OTHER MAN-MADE (ANTHROPOGENIC) SOURCES 396
6.2.10 SEDIMENT FLOW–GENERATED NOISE 397
6.2.11 THERMAL NOISE 397
6.3 SPECTRA OF AMBIENT NOISE 398
6.3.1 DEEP-WATER SPECTRA 399
6.3.2 SHALLOW-WATER SPECTRA 400
6.4 DIRECTIVITY OF AMBIENT NOISE 401
6.4.1 NOISE PROPAGATION 401
6.5 COHERENCE OF AMBIENT NOISE 405
6.6 SELF-NOISE 407
6.7 AMPLITUDE DISTRIBUTIONS FOR UNDERWATER NOISE 409
6.8 SYMBOLS AND ABBREVIATIONS 414
REFERENCES 416
7 - Shallow-Water Acoustics 420
7.1 WHAT IS SHALLOW-WATER ACOUSTICS? 420
7.1.1 MILITARY APPLICATIONS 421
7.1.2 DUAL-USE APPLICATIONS 422
7.1.3 OCEAN SCIENCES APPLICATIONS 422
7.1.4 COMMERCIAL APPLICATIONS 423
7.2 PHYSICS AND PHENOMENA 423
7.2.1 SOURCE LEVEL TERM 423
7.2.1.1 Example: Integrating Pseudorandom Noise Sequences and Frequency Modulation Sweeps for Signal Gain 426
7.2.2 ARRAY GAIN TERM 428
7.2.2.1 Examples: Mode Filtration Techniques in Shallow Water 430
7.2.2.1.1 Time Resolution of Modes 430
7.2.2.1.2 Amplitude-Shaded Vertical Array Mode Resolution 430
7.2.2.1.3 Vertical Array Steering 432
7.2.2.1.4 Horizontal Array Steering 432
7.2.2.1.5 Focused Array Mode Filtration 433
7.2.3 TRANSMISSION LOSS TERM 433
7.2.3.1 Simple Geometric Spreading Intensity Arguments 433
7.2.3.2 Popular Propagation Theories and Their Application(s) to Shallow Water 434
7.2.3.2.1 Ray Theory 434
7.2.3.2.2 Normal Modes and Shallow Water 441
7.2.3.2.3 Vertical Modes and Horizontal Rays 448
7.2.3.2.3.1 Example: Ducting Between Nonlinear Internal Waves 449
7.2.3.2.4 Parabolic Equation 451
7.2.3.2.5 Wave Number Integration 453
7.2.4 AMBIENT NOISE TERM 454
7.2.5 REVERBERATION TERM 459
7.2.5.1 The Bottom Boundary Layer 462
7.2.5.2 Water Column Reverberation 463
7.2.5.3 Sea Surface Scattering and Reverberation 463
7.2.5.4 The Sea Surface Plus Bubble Scattering and Reverberation 463
7.3 SOME ADDITIONAL TOPICS OF INTEREST IN SHALLOW-WATER ACOUSTICS 465
7.3.1 ONE- AND TWO-LAYER WATER COLUMN SOUND SPEED PROFILES IN SHALLOW-WATER ACOUSTICS 465
7.3.2 THE OPTIMUM FREQUENCY 466
7.3.3 ARRIVAL STRUCTURES IN SHALLOW-WATER AND RAY/MODE RESOLUTION 467
7.3.4 WAVEGUIDE INVARIANT 468
7.3.5 INTENSITY FLUCTUATION STATISTICS 469
7.4 SOME NEWER TOPICS 472
7.4.1 THE SHELF BREAK, SLOPE, AND CANYON REGIONS AND THE TRANSITION TO DEEP WATER 472
7.4.2 ARCTIC SHALLOW-WATER ACOUSTICS 473
7.4.3 CLIMATE CHANGE AND SHALLOW-WATER ACOUSTICS 474
LIST OF ACRONYMS 475
LIST OF SYMBOLS IN EQUATIONS 476
REFERENCES 477
APPENDIX 7.A1 480
8 - The Seafloor 486
8.1 BACKGROUND AND HISTORY 487
8.2 THE ORIGIN AND NATURE OF SEAFLOOR SEDIMENTS 488
8.3 ACOUSTICS OF SEDIMENTS 488
8.3.1 FLUID MODEL 489
8.3.2 ELASTIC MODEL 491
8.3.3 POROELASTIC MODEL 494
8.4 MODEL FOR SOUND SCATTERING BY THE SEAFLOOR 499
8.4.1 MODEL PARAMETERS 500
8.4.2 SCATTERING BY SEAFLOOR ROUGHNESS 501
8.4.3 SCATTERING BY SEAFLOOR HETEROGENEITY 503
8.4.4 SCATTERING MODEL EXAMPLES 505
8.5 SEDIMENT PHYSICAL PROPERTIES 511
8.5.1 GRAIN SIZE DISTRIBUTION 512
8.5.2 SEDIMENT BULK DENSITY AND POROSITY 516
8.5.3 PORE FLUID AND PORE SPACE PROPERTIES 518
8.5.4 PERMEABILITY 519
8.5.5 GRAIN PROPERTIES 520
8.5.6 SEDIMENT TYPE 520
8.5.7 SUMMARY OF SEDIMENT PROPERTIES 524
8.6 SEDIMENT GEOACOUSTIC PROPERTIES 524
8.6.1 SOUND SPEED AND ATTENUATION 526
8.6.2 SHEAR WAVE MEASUREMENTS 529
8.6.3 INDEX OF IMPEDANCE 532
8.7 SEAFLOOR ROUGHNESS 534
8.7.1 MEASUREMENT OF SEAFLOOR ROUGHNESS 535
8.7.2 STATISTICAL CHARACTERIZATION OF SEAFLOOR ROUGHNESS 537
8.7.3 PREDICTION OF SEAFLOOR ROUGHNESS FROM SEDIMENT PHYSICAL PROPERTIES 537
8.8 SEAFLOOR HETEROGENEITY 539
8.8.1 MEASUREMENTS OF SEDIMENT VOLUME HETEROGENEITY 540
8.8.2 GAS IN SEDIMENTS 541
8.9 SEAFLOOR IDENTIFICATION AND CHARACTERIZATION BY USE OF SONAR 543
8.9.1 FEATURE CLUSTERING 546
8.9.2 IMAGE SEGMENTATION 548
8.9.3 REFLECTION 548
8.9.4 SCATTERING STRENGTH 549
8.9.5 MODEL FITTING TO ECHO TIME SERIES 554
LIST OF SYMBOLS 557
REFERENCES 560
9 - Inverse Methods in Underwater Acoustics 570
9.1 INTRODUCTION 570
9.2 SOME BASIC MATHEMATICAL RELATIONSHIPS 572
9.3 SOURCE LOCALIZATION BY MATCHED FIELD PROCESSING 573
9.4 GEOACOUSTIC INVERSION 576
9.4.1 GEOACOUSTIC MODELS 576
9.4.2 LINEAR INVERSIONS FOR GEOACOUSTIC PROFILES 578
9.4.3 GEOACOUSTIC INVERSION BY BAYESIAN INFERENCE 580
9.4.4 BAYESIAN MATCHED FIELD INVERSION 584
9.4.4.1 Bayesian Matched Field Inversion by Optimization 584
9.4.4.2 Bayesian Matched Field Inversion by Integration of the a Posteriori Probability Density 589
9.5 OCEAN ACOUSTIC TOMOGRAPHY 593
9.5.1 INVERSION OF TRAVEL TIMES 594
9.5.2 ACOUSTIC THERMOMETRY 595
9.5.3 ACOUSTIC TOMOGRAPHY IN SHALLOW WATER 597
REFERENCES 598
10 - Sonar Systems 604
10.1 SONAR SYSTEM APPLICATIONS 605
10.2 SONAR SYSTEM TYPES 608
10.2.1 TRANSDUCER MATERIALS 608
10.2.2 PROJECTORS AND HYDROPHONES 613
10.2.3 PARAMETERS OF PIEZOCERAMICS 618
10.2.4 TRANSDUCER GEOMETRIES 623
10.2.4.1 Plates 624
10.2.4.2 Cylindrical Elements 624
10.2.4.3 Spherical Elements 628
10.2.4.4 Tonpilz Transducers 630
10.2.4.5 Flextensional Transducers 633
10.2.4.6 Flexural Transducers 635
10.2.5 ACOUSTIC FIELD QUALITIES OF TRANSDUCERS 638
10.2.5.1 Single-Element Transducers 639
10.2.5.1.1 The Pole Concept 639
10.2.5.1.2 Piston Sources 643
10.2.5.1.3 Hydrophones 654
10.2.5.2 Arrays 661
10.2.5.2.1 Array Types 662
10.2.5.2.2 Array Qualities 669
10.2.5.2.3 Towed Arrays 677
10.3 SINGLE-BEAM ECHO SOUNDERS 681
10.4 MULTIBEAM ECHO SOUNDERS 689
10.4.1 MULTIBEAM ECHO SOUNDER STRUCTURE 696
10.4.1.1 Projector Unit 697
10.4.1.2 Receiver Unit 698
10.4.1.3 Sonar Processor Unit 699
10.4.1.4 Auxiliary Equipment 701
10.4.2 MULTIBEAM ECHO SOUNDER APPLICATIONS 702
10.4.2.1 Bathymetry 702
10.4.2.2 Snippets 705
10.4.2.3 Side-Scan Data 705
10.4.3 MULTIBEAM ECHO SOUNDER PERFORMANCE LIMITATIONS 705
10.5 SIDE-SCAN SONAR 706
10.5.1 SINGLE-ROW SSS 706
10.5.2 MULTIROW SSS 712
10.6 SYNTHETIC APERTURE SONAR 713
10.7 OTHER SONAR TYPES 718
10.8 TRANSDUCER CALIBRATION 723
10.8.1 DEFINITIONS 723
10.8.2 RECIPROCITY CALIBRATIONS 725
10.8.3 OTHER CALIBRATION METHODS 729
10.9 SONAR SYSTEM EXAMPLE CALCULATIONS 734
10.10 SONAR DESIGN CALCULATIONS 740
10.10.1 TONPILZ TRANSDUCER AND HYDROPHONE CALCULATIONS 741
10.10.2 EQUIVALENT CIRCUITS 745
10.10.3 FINITE-ELEMENT TECHNIQUES 749
10.11 SYMBOLS AND ABBREVIATIONS 753
REFERENCES 755
11 - Signal Processing 760
11.1 BACKGROUND AND DEFINITIONS 760
11.1.1 SIGNALS AND NOISE IN UNDERWATER ACOUSTICS 760
11.1.2 WHAT IS “SIGNAL PROCESSING” AND WHY DO WE DO IT? 761
11.1.3 STRUCTURE OF THIS CHAPTER 763
11.1.4 OTHER RESOURCES 763
11.1.5 MATHEMATICAL NOTATION 764
11.1.6 LIST OF SYMBOLS AND NOTATION 764
11.1.7 LIST OF ABBREVIATIONS 765
11.2 CHARACTERIZING THE SIGNAL AND NOISE 766
11.2.1 SAMPLING AND QUANTIZING ANALOG SIGNALS 766
11.2.2 TIME AND FREQUENCY CHARACTERIZATION 767
11.2.2.1 Signal Consistency: Deterministic and Random Signals 768
11.2.2.2 Temporal Characterization 768
11.2.2.3 Spectral Content: The Fourier Transform and Spectral Density 769
11.2.3 DISCRETE FOURIER TRANSFORM 772
11.2.4 RANDOM PROCESSES: SPECTRA AND CORRELATION FUNCTIONS 773
11.2.5 CROSS-SPECTRA AND COHERENCE 775
11.2.6 CEPSTRUM 775
11.3 FILTERING 776
11.3.1 FILTER TYPES 776
11.3.2 PERFORMANCE METRICS, DESIGN, AND IMPLEMENTATION 777
11.3.2.1 Filtering Performance Metrics 777
11.3.2.2 Digital Filter Design and Implementation 777
11.3.3 BAND-PASS SIGNALS: DIGITAL DOWN-CONVERSION 781
11.3.4 WINDOWING FOR SIDE-LOBE SUPPRESSION 781
11.3.5 DATA-DEPENDENT OR ADAPTIVE FILTERING 784
11.4 DETECTION 784
11.4.1 PERFORMANCE METRICS, DESIGN, IMPLEMENTATION, AND ANALYSIS PROCEDURE 786
11.4.1.1 Detection Performance Metrics 786
11.4.1.2 Required SNR and Detection Threshold 787
11.4.1.3 Detector Design and Implementation 788
11.4.1.4 Analysis of Detection Performance 790
11.4.2 STRUCTURED DESIGN APPROACHES 791
11.4.3 DETECTING SIGNALS OF KNOWN FORM: CORRELATION PROCESSING 794
11.4.3.1 Example: Doppler Filter Bank 794
11.4.3.2 Pulse Compression, Matched Filtering, and the Ambiguity Function 796
11.4.3.3 Example: LFM Pulse Compression 797
11.4.3.4 Other Applications in Underwater Acoustics 798
11.4.4 DETECTING RANDOM OR UNKNOWN SIGNALS: ENERGY DETECTOR 798
11.4.5 DETECTING UNKNOWN SIGNAL ONSET: PAGE'S TEST 799
11.4.6 NORMALIZING FOR CONSTANT FALSE ALARM RATE 801
11.5 ESTIMATION 803
11.5.1 PERFORMANCE METRICS, DESIGN, IMPLEMENTATION, AND ANALYSIS PROCEDURE 804
11.5.1.1 Estimation Performance Metrics 804
11.5.1.2 Estimator Design and Implementation Process 805
11.5.1.3 Estimator Analysis Procedure and the Cramer-Rao Lower Bound 805
11.5.2 STRUCTURED DESIGN APPROACHES 806
11.5.2.1 Maximum Likelihood Estimation 806
11.5.2.2 Method of Moments Estimation 808
11.5.2.3 Other Approaches 809
11.5.3 SPECTROGRAM, PERIODOGRAM, AND POWER SPECTRAL DENSITY ESTIMATION 809
11.5.3.1 Periodogram for Spectral Density Estimation 811
11.5.3.2 Zero-Padding the DFT 814
11.5.4 TIME-DELAY ESTIMATION 815
11.5.5 BEAMFORMING AND ANGLE OF ARRIVAL ESTIMATION 818
REFERENCES 821
12 - Bio- and Fishery Acoustics 826
12.1 INTRODUCTION 826
12.2 MARINE LIFE: FROM WHALES TO PLANKTON 827
12.3 ACOUSTIC SCATTERING BY MARINE LIFE 828
12.3.1 ZOOPLANKTON SCATTERING 830
12.3.2 SWIM BLADDER SCATTERING 832
12.3.3 FISH BODY SCATTERING 834
12.3.4 LARGE-BODY SCATTERING 835
12.3.5 MANY-BODY SCATTERING 838
12.4 ACTIVE IMAGING SYSTEMS 841
12.4.1 SINGLE-BEAM ECHO SOUNDERS 841
12.4.2 SIDE-SCAN SONARS 845
12.4.3 MULTIBEAM ECHO SOUNDERS 846
12.4.4 COMBINING SENSORS 849
12.5 MARINE LIFE AND SOUND 852
12.5.1 GENERAL POINTS 852
12.5.2 MARINE MAMMALS 853
12.5.3 FISH, TURTLES, AND INVERTEBRATES 855
12.6 PASSIVE ACOUSTIC MONITORING 857
12.7 SELECTED PRACTICAL APPLICATIONS 860
12.7.1 ACTIVE ACOUSTICS: FISH SURVEY 860
12.7.2 PASSIVE ACOUSTICS: AMBIENT NOISE MONITORING 861
12.7.3 ACOUSTIC TELEMETRY: FISH BEHAVIOR 863
12.8 CONCLUSIONS: FUTURE DEVELOPMENTS 864
REFERENCES 866
13 - Finite-Amplitude Waves 874
13.1 PHYSICS AND NONLINEAR PHENOMENA 875
13.1.1 HARMONIC DISTORTION 875
13.1.2 FOCUSED SOUND FIELDS 878
13.1.3 CAVITATION 880
13.1.4 ACOUSTIC RADIATION PRESSURE AND ACOUSTIC STREAMING 882
13.2 NONLINEAR UNDERWATER ACOUSTICS 883
13.2.1 PARAMETRIC ACOUSTIC TRANSMITTING ARRAYS 884
13.2.2 PARAMETRIC ACOUSTIC RECEIVING ARRAYS 889
13.2.3 APPLICATIONS OF THE PARAMETRIC ACOUSTIC ARRAY 890
13.3 UNDERWATER EXPLOSIONS 895
13.3.1 THE SHOCK WAVE 895
13.3.2 THE GAS BUBBLE 897
13.3.3 OTHER SOURCES OF HIGH-INTENSITY SOUND 898
13.4 LIST OF SYMBOLS AND ABBREVIATIONS 901
REFERENCES 903
14 - Underwater Acoustic Measurements and Their Applications 906
14.1 INTRODUCTION 906
14.2 ACOUSTICS AND MARINE RENEWABLE ENERGY DEVELOPMENTS 907
14.2.1 NOISE DURING THE CONSTRUCTION PHASE 908
14.2.2 NOISE DURING OPERATION 910
14.3 UNDERWATER ACOUSTICS IN NUCLEAR-TEST-BAN TREATY MONITORING 911
14.3.1 THE HYDROACOUSTIC NETWORK OF THE CTBTO 913
14.3.2 INSTALLATION AND PERFORMANCE OF THE NEWEST IMS HYDROACOUSTIC STATION: HA03, ROBINSON CRUSOE ISLAND, JUAN FERNÁNDEZ ARCHIPEL ... 914
14.4 CHARACTERIZATION OF NOISE FROM SHIPS 916
14.4.1 GENERAL CHARACTERIZATION OF NOISE PRODUCED BY SHIPS 916
14.4.2 NOISE GENERATED BY A PROPULSION SYSTEM 918
14.4.3 NOISE GENERATED BY A PROPELLER 919
14.4.4 IDENTIFICATION OF ACOUSTIC WAVES EMITTED BY A MOVING SHIP 919
14.4.5 SUMMARY 920
14.5 UNDERWATER SOUNDSCAPES 921
14.6 UNDERWATER ACOUSTIC COMMUNICATIONS 925
14.7 UNDERWATER ARCHAEOLOGY 930
14.7.1 THE WORKING CYCLE OF FIELD MARINE ARCHAEOLOGISTS 930
14.7.1.1 Large Area Search 931
14.7.1.2 Local Surveying and Mapping 932
14.7.1.3 Evolving Trends: A Technological Future for the Exploration of Deep Water Archaeological Sites 933
14.8 APPLICATIONS OF UNDERWATER ACOUSTICS IN POLAR ENVIRONMENTS 934
14.8.1 INTRODUCTION 934
14.8.2 ARCTIC 935
14.8.3 ANTARCTIC 938
14.9 TANK EXPERIMENTS 940
14.9.1 INTRODUCTION 940
14.9.2 DESCRIPTION OF DIFFERENT CATEGORIES OF TANKS USED FOR UNDERWATER APPLICATIONS 941
14.9.3 CONCLUSION 944
14.10 ACOUSTIC POSITIONING AT SEA 944
14.10.1 LBL POSITIONING DEVELOPMENT 945
14.10.2 ULTRASHORT BASELINE (USBL) POSITIONING 946
14.10.3 EFFECTS OF NOISE 947
14.10.4 IMPROVED CODING 947
14.10.5 COORDINATION WITH INERTIAL SENSORS 947
14.11 OCEAN OBSERVING SYSTEMS AND OCEAN OBSERVATORIES, OCEANOGRAPHERS, AND ACOUSTICIANS—A PERSONAL PERSPECTIVE 948
14.11.1 INTRODUCTION 948
14.11.2 OCEANOGRAPHERS 949
14.11.3 ACOUSTICIANS 950
14.11.4 FUTURE DIRECTIONS 950
14.12 APPLICATIONS OF UNDERWATER ACOUSTICS TO MILITARY PURPOSES 951
14.12.1 PASSIVE SONAR 952
14.12.2 ACTIVE SONAR 955
REFERENCES 957
Index 966
A 966
B 967
C 968
D 968
E 969
F 969
G 970
H 970
I 970
J 971
K 971
L 971
M 971
N 972
O 972
P 973
Q 974
R 974
S 974
T 979
U 980
V 981
W 981
Y 981
Z 981

Chapter 1

General Characteristics of the Underwater Environment

L. Bjørnø1,†, and M.J. Buckingham2 1UltraTech Holding, Taastrup, Denmark 2Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA, United States

Abstract

This chapter provides a framework and roadmap for the book. It starts with a brief history of underwater acoustics from the time of the Greek philosopher Aristotle (384–322 BC) up to the post–World War II era. This is followed by a discussion of the international system of units used in the book and a discussion on the use of the decibel scale. Next, the chapter deals with the features of oceanography including sound speed profiles, thermoclines, arctic regions, deep isothermal layers, expressions for the speed of sound, surface waves, internal waves, bubbles from wave breaking, ocean acidification, deep-ocean hydrothermal flows, eddies, fronts and large-scale turbulence, and diurnal and seasonal changes. This is followed by a discussion of the sonar equation that is fundamental to underwater acoustics.

Keywords

Arctic regions; Breaking waves; Bubbles; Deep isothermal layers; Deep-ocean hydrothermal flows; Detection probability; Detection threshold; Directivity index; Eddies; False alarm probability; Francois and Garrison equation; Fronts and large-scale turbulence; Internal waves; Noise level; Ocean acidification; Oceanography; Receiver-operating characteristic curves; Reverberation level; Sonar equations; Sound speed profiles; Source level; Speed of sound; Surface waves; Target strength; Thermoclines; Transmission loss; Underwater acoustics history

1.1. Introduction

Over the past about 100 years the exploitation of the seas and their resources has continuously increased. Acoustic waves have turned out to be a very useful tool for detecting resources and objects in the water column and on the seafloor. Other methods have been used with varying degrees of success depending on the objects to be detected or investigated. These methods include magnetics, magnetic anomaly detection, where minor changes in the earth's magnetic field due to presence of an object can be measured; optical methods; electric field changes; hydrodynamics such as pressure changes; thermal methods; and electromagnetic waves. While radar is very useful for detection of objects above water, electromagnetic radar waves are strongly absorbed in seawater. While electromagnetic waves in the visible frequency band from 4 to 8·1014 Hz are much less absorbed, with a minimum absorption coefficient of 3·10−3 cm−1 in the green-blue light near 455 nm wavelength (i.e., 6.59·1014 Hz), electromagnetic wave absorption in the normally used radar bands is several orders of magnitude higher than in the visible band. Seawater salt contains magnesium that makes the water conduct electricity since the 2+ cation constitutes 3.7% of seawater salt. A 1 GHz radar wave in the ultra-high frequency (UHF) band with a 0.3 m wavelength has a 1400 dB/m absorption coefficient while the same wavelength in the 5 kHz sound wave has a 3·10−4 dB/m absorption coefficient. Therefore, radar systems are not useful for detecting objects under water.

Underwater sound is used in many applications, such as hydrography, off-shore activities, dredging, defense and security, marine research, and fishery. Hydrography includes harbor and river surveys, bathymetric surveys, flood damage assessment, engineering inspection, pipeline and cable route surveys, exclusive economic zone (EEZ) mapping, breakwater mapping, and so on. Off-shore activities include pipeline and cable installation and inspection, leakage detection, route and site surveys, subsea structure installation support, renewables, remotely operated vehicle (ROV) intervention guidance, decommissioning, reconnaissance surveys, search and recovery, oil and gas prospecting, and prospecting for minerals and resources on and in the seafloor. Dredging includes sonars used by rock and stone dump vessels, excavator and trailing suction hopper dredgers, cutter suction and bucket dredgers, clamshell grab cranes and underwater plow vessels, and placement support. Defense and security includes mine counter measures, submarine and torpedo detection, obstacle avoidance, search and recovery, underwater communication, vessel and fleet protection, waterside security, diver detection, and so on. Marine research includes environmental monitoring, ambient noise measurements, marine archeology, marine mammal research, and fishery research. Fishery includes fishery operations, fish school detection, catch monitoring and control, trawl position control, phytoplankton and zooplankton investigations, communication between monitoring sensors on fishing gear and the fishing vessel, seabed mapping, bottom discrimination, and so on.

The counterpart to radar above water is sonar under water. SONAR is the acronym for sound navigation and ranging. It was originally used during World War II as an analog to the name “radar” and as a replacement for the name “asdics” for underwater detection systems using sound, which were used by the British Royal Navy during World War I. The two most common sonar types are passive and active. In a passive sonar system, the acoustic signal originates at a target and propagates to a receiver, where the acoustic signal is converted to an electrical signal for processing. In an active sonar system, an electrical signal is converted to an acoustical signal by a transmitter and the sound waves propagate from the transmitter to a target and back to a receiver, where conversion from acoustical to electrical signal takes place followed by electronic signal processing. Signal processing is aimed at enhancing the return signal from the target or reducing the noise in which the return signal may be embedded, as discussed in Chapter 11. The transmitter is normally called the projector and the receiver is called the hydrophone, as discussed in Chapter 10. If the return signal—the echo—from a target is detected, the position and the potential target movement are determined by the time delay of the echo from the target and the direction of the echo, respectively. The speed of a moving target can be estimated from the frequency shift—the Doppler shift—in the echo from the target, as discussed in Chapter 2.

When a sound wave is produced in water it propagates from the site where it is produced. Sound sources can be natural, such as breaking waves, rain falling on the water surface, seismic activities in the seafloor, and so on, or man-made such as sonar signals, underwater explosions, ship noise, and so on, as discussed in Chapter 6. During propagation the sound signal is exposed to a number of processes which may change the sound signal and its propagation, such as sound signal amplitude attenuation due to absorption, divergence, and scattering, as discussed in Chapter 4. Scattering takes place during the sound wave's interaction with the sea surface, seafloor, and inhomogeneities in the water column, as discussed in Chapter 5. These inhomogeneities can be natural, such as plankton, fish and sea mammals, and variations in the sea temperature and salinity. Scattering and reflection of sound signals may cause sound waves to follow different paths, producing multi-path sound propagation, which can make detection of objects in the water column and on the seafloor difficult. The scattering of underwater sound may lead to reverberation which limits detection. Use of advanced signal processing on the transmitted and received signal opens up the possibility to avoid or reduce the degradation of the propagated sound signal, as discussed in Chapter 11. Ambient noise in the sea can also become a limiting factor for signal detection. The sound signal received by a hydrophone carries information about the signal source and what the signal has encountered while propagating from the source to the hydrophone. The signal received by the hydrophone is processed to extract information of value to the user. This complicated “underwater world,” where sound propagation is influenced by many individual sources with effect on the sound signal's amplitude, phase, and spectral composition, is the basis for this book, “Applied Underwater Acoustics.”

Each chapter is introduced with a section giving the necessary definitions and describing the physical background for the subsequent sections of the chapter. The man-made sources of sound from sonar systems of various types are described in Chapter 10. This chapter also describes the different transducer types, their charge forming elements, and their geometries. Chapter 10 illuminates the sonar types available today, characteristic features, as well as their design, calculation, and calibration. Hydrophones, including array types, and their characteristics are also a part of Chapter 10.

The sound wave propagation through the water and the different factors which influence the propagation path are discussed in...

Erscheint lt. Verlag	19.1.2017
Sprache	englisch
Themenwelt	Naturwissenschaften ► Geowissenschaften ► Hydrologie / Ozeanografie
	Naturwissenschaften ► Physik / Astronomie ► Mechanik
	Technik
ISBN-10	0-12-811247-6 / 0128112476
ISBN-13	978-0-12-811247-2 / 9780128112472

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