Sonar and Underwater Acoustics

Transcription

1 Sonar and Underwater Acoustics Jean-Paul Marage and Yvon Mori m wi L GY

2 Table of Contents Preface ix PART 1. THE MARINE ENVIRONMENT 1 Parí 1. Introduction 3 Chapter 1. Problematics History Underwater acoustics Communications channel Knowledge of the channel Applications Civil applications Militan/ applications Comparison with radar Submarine deteclion and warfare Submarine detection Submarine detection: a veritable challenge Overcoming the effects of the ocean Acousíics Propagation Unknown noise Unknown signal Sonar and nformation processing 16 Chapter 2. Sound Propagation in the Marine Environment General points Characteristics of the marine environment Models used Propagation phenornena Deep water Reflection Coherence and stability of sound channels Application examples Simplified equations, range and opíimum frequency Use of towed sonar Study of transmission problems Vertical telemetry 38 Chapter 3. Noises and Reverberation Classification of ambient noises Analysis of noise sources 45

3 vi Sonar and Underwater Acoustics Hydrodynamic sources Maritime traffic Seismic sources Biológica! sources Additional sources Wenz' model of sea noise Directivity of sea noise Application to antenna production Reverberaron Surface reverberation Volume reverberation Seabed reverberation 62 Chapter 4. Radiatcd and Inherent Moisés Radiated noise Engine noise Propeller noises Hydrodynamic noise Summary ofthe sources ofradiated noise Directivity Level of radiated noise Inherent noise Inherent and radiated noises 78 Chapter 5. Transmission ofthe Acoustic Signal: Sonar Equations Introduction Detection contrast and detection Índex Transmtssion equation Equation of passive sonar Equation of active sonar 89 PART2. ACOUSTIC-ELECTRIClNTERFACE ANTENNA STRUCTURES 93 Part 2. Introduction 95 Chapter 6. Electric-acoustic and Acoustic-electric Transformations Transducers and hydrophones General points Magnetostriction Electrostriction Piezoelectricity Electromagnetism Optics The responses of transducers and hydrophones 106 Chapter 7. Performance and Structures of Acoustic Antennas Antennas and radiation Equations governing propagation Plañe wave solutions Spherical wave solutions Acoustic sources: wave production Directivity and gain of sources and antennas Radiation impedance Structures of sources and antennas Sources and sensors Antenna Structures

4 Tableof Contenta v ChapterS. Electronic Transducer-hydrophone Adaptation Hydrophones Simplified equivalent electric diagram of a hydrophone Association of a hydrophone and an amplifier Noise sources of a hydrophone Noise characterization of a hydrophone-amplifier assembly Hydrophone association Transducers Equivalent diagram of a transducer Input immirtance Transfer function of the transducer Adaption circuit at the emitter 261 Chapter9. Electro-mechano-acoustic Analogies Methods of studying transducers and hydrophones Mechanic-electric equivalence Properties ofthe two equivalences Electric-mechanic refationships Electric-acoustic equivalence Acoustic<=> mechanic connection Acoustic <=> electric matching Equivalent diagram of a piezoelectric ceramic Finite element method (FEM) 320 PART 3. PROCESSING CHAIN OF ACTIVE SONAR 323 Part 3. Introduction 325 Chapter 10. Selection Gritería in Active Processing Selection criteria related to propagation Dipping sonar Towed sonar Selection criteria relative to noise Selection criteria related to reverberaron Selection criteria related to ernission power Selection criíeria related to the antenna Selection criteria forthe operating frequency Selection criteria related to operational considerations Selection criteria related to the nature of targets 337 Chapter 11. Processing Chain in Active Sonar General points Emission The pilot generator Delay control The power amplifier Emission reception switching Recepíion Input conditioning Gain control AGC-TVG Beamforming Adapted processing Information processtng of sonar channels Channel stabilization Audiofrequency channels 449

5 vüi Sonar and Underwater Acoustics Chapter 12. Basic Theoretical Notions in Active Processing The Doppier effect Definition of the Doppier effect Typical cases ofthe Doppier effect The Doppier effect n active sonar conditions Doppier effect on the signal Doppier effecí on reverberaron Reverberaron on a sonar reception channel Treatment of the signal Detection Estirnation Detection performances Choice oían emissíon signal under active sonar conditions The active sonar problem The ambiguity function Ambiguity functions of useful signáis 509 Chapter 13. Measurement in Underwater Acoustics Introduction Background Far-field conditions Wave train method Delermination of measuring parameters Limitations of the wave train method Precauiions before measuring Preparation and set upof transducers within the tank Identification and treatment of disruptive noises Acoustic measurements and calibrations of transducers Measurements ofthe sensitivities ofthe transmitter and receiver Comparison calibration method Reciprocity caübration methods Notion of uncertainíy estimation and of máximum toierated difference Other types of measurements n underwater acoustics Regular/usual measurement types Unusual/specific measurement types Conclusión 554 APRENDICES 555 Appendix 1. Logarithmic Scales 557 Appendix 2. Equation of Sound in Fluids 563 Appendix 3. Piezoelcctricity Fundamentáis 571 Appendix 4. Vector Analysis - Fundamentáis 579 Appendix 5. Reciprocity Theorem 593 Appendix 6. Concrete Example of Uncertainty Estimation Based on the Reciprocity Calibration Method 601 Bibliography 619 Index. 623