Sonar and Underwater Acoustics

Preface ix

PART 1. THE MARINE ENVIRONMENT 1

Part 1. Introduction 3

Chapter 1. Problematics 5

1.1. History 5

1.2. Underwater acoustics 7

1.3. Applications 9

1.4. Comparison with radar 10

1.5. Submarine detection and warfare 11

1.6. Submarine detection 11

1.7. Submarine detection: a veritable challenge 12

1.8. Overcoming the effects of the ocean 13

1.9. Sonar and information processing 16

Chapter 2. Sound Propagation in the Marine Environment 19

2.1. General points 19

2.2. Characteristics of the marine environment 19

2.3. Models used 22

2.4. Propagation phenomena 28

2.5. Application examples 33

Chapter 3. Noises and Reverberation 41

3.1. Classification of ambient noises 41

3.2. Analysis of noise sources 45

3.3. Wenz’ model of sea noise 51

3.4. Directivity of sea noise 52

3.5. Reverberation 55

Chapter 4. Radiated and Inherent Noises 65

4.1. Radiated noise 65

Chapter 5. Transmission of the Acoustic Signal: Sonar Equations 79

5.1. Introduction 79

5.2. Detection contrast and detection index 80

5.3. Transmission equation 81

5.4. Equation of passive sonar 88

5.5. Equation of active sonar 89

PART 2. ACOUSTIC-ELECTRIC INTERFACE ANTENNA STRUCTURES 93

Part 2. Introduction 95

Chapter 6. Electric-acoustic and Acoustic-electric Transformations 97

6.1. Transducers and hydrophones 97

Chapter 7. Performance and Structures of Acoustic Antennas 113

7.1. Antennas and radiation 113

7.2. Structures of sources and antennas 189

Chapter 8. Electronic Transducer-hydrophone Adaptation 211

8.1. Hydrophones 211

8.2. Transducers 243

Chapter 9. Electro-mechano-acoustic Analogies 269

9.1. Methods of studying transducers and hydrophones 269

9.2. Mechanic-electric equivalence 270

9.3. Electric-acoustic equivalence 275

9.4. Finite element method (FEM) 320

PART 3. PROCESSING CHAIN OF ACTIVE SONAR 323

Part 3. Introduction 325

Chapter 10. Selection Criteria in Active Processing 327

10.1. Selection criteria related to propagation 327

10.2. Selection criteria relative to noise 331

10.3. Selection criteria related to reverberation 332

10.4. Selection criteria related to emission power 333

10.5. Selection criteria related to the antenna 335

10.6. Selection criteria for the operating frequency 336

10.7. Selection criteria related to operational considerations 337

10.8. Selection criteria related to the nature of targets 337

Chapter 11. Processing Chain in Active Sonar 341

11.1. General points 341

11.2. Emission 341

11.3. Reception 345

Chapter 12. Basic Theoretical Notions in Active Processing 459

12.1. The Doppler effect 459

12.2. The Doppler effect in active sonar conditions 464

12.3. Treatment of the signal 485

12.4. Choice of an emission signal under active sonar conditions 503

Chapter 13. Measurement in Underwater Acoustics 525

13.1. Introduction 525

13.2. Wave train method 531

13.3. Precautions before measuring 539

13.4. Acoustic measurements and calibrations of transducers 542

13.5. Notion of uncertainty estimation and of maximum tolerated difference 551

13.6. Other types of measurements in underwater acoustics 553

APPENDICES 555

Appendix 1. Logarithmic Scales 557

Appendix 2. Equation of Sound in Fluids 563

Appendix 3. Piezoelectricity Fundamentals 571

Appendix 4. Vector Analysis ?Ï?nFundamentals 579

Appendix 5. Reciprocity Theorem 593

Appendix 6. Concrete Example of Uncertainty Estimation Based on the Reciprocity Calibration Method 601

Bibliography 619

Index 623