Underwater Acoustics E-Book

Richard P. Hodges

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 402

Veröffentlichungsjahr: 2011

Beschreibung

Offering complete and comprehensive coverage of modern sonar spectrum system analysis, Underwater Acoustics: Analysis, Design and Performance of Sonar provides a state-of-the-art introduction to the subject and has been carefully structured to offer a much-needed update to the classic text by Urick. Expanded to included computational approaches to the topic, this book treads the line between the highly theoretical and mathematical texts and the more populist, non-mathematical books that characterize the existing literature in the field. The author compares and contrasts different techniques for sonar design, analysis and performance prediction and includes key experimental and theoretical results, pointing the reader towards further detail with extensive references. Practitioners in the field of sonar design, analysis and performance prediction as well as graduate students and researchers will appreciate this new reference as an invaluable and timely contribution to the field. Chapters include the sonar equation, radiated, self and ambient noise, active sonar sources, transmission loss, reverberation, transducers, active target strength, statistical detection theory, false alarms, contacts and targets, variability and uncertainty, modelling detections and tactical decision aids, cumulative probability of detection, tracking target motion analysis and localization, and design and evaluation of sonars

Leseprobe

Contents

About the Author

Preface

Acknowledgements

1 Introduction to Sonar

1.1 Acoustic Waves

1.2 Speed of Propagation

1.3 Acoustic Wave Parameters

1.4 Doppler Shift

1.5 Intensity, SPL, and Decibels

1.6 Combining Acoustic Waves

1.7 Comparative Parameter for Sound in Water and Air

2 The Sonar Equations

2.1 Signal-to-Noise Ratio

2.2 Active Sonar Equation

2.3 Signal Excess

2.4 Figure of Merit

3 Transducers, Directionality, and Arrays

3.1 Transducer Response

3.2 Beam Pattern Response

3.3 Linear Arrays

3.4 Rectangular Planar Array

3.5 Amplitude Shading

3.6 Continuous Arrays

3.7 Volumetric Arrays

3.8 Product Theorem

3.9 Broadband Beam Patterns

3.10 Directivity and Array Gain

3.11 Noise Cross-Correlation between Hydrophones

3.12 Directivity of Line Arrays

3.13 Directivity of Area Arrays

3.14 Directivity of Volumetric Arrays

3.15 Difference Arrays

3.16 Multiplicative Arrays

3.17 Sparsely Populated Arrays

3.18 Adaptive Beamforming

4 Active Sonar Sources

4.1 Source Level

4.2 Cavitation

4.3 Near-Field Interactions

4.4 Explosive Sources

4.5 Physics of Shock Waves in Water

4.6 Bubble Pulses

4.7 Pros and Cons of Explosive Charges

4.8 Parametric Acoustic Sources

5 Transmission Loss

5.1 Sound Speed Profile in the Sea

5.2 Snell’s Law and Transmission across an Interface

5.3 Reflection and Transmission Coefficients

5.4 Transmission through a Plate

5.5 Ray Tracing

5.6 Spreading Loss

5.7 Absorption of Sound in the Ocean

6 Transmission Loss: Interaction with Boundaries

6.1 Sea State, Wind Speed, and Wave Height

6.2 Pierson–Moskowitz Model for Fully Developed Seas

6.3 Sea Surface Interaction

6.4 Bottom Loss

6.5 Leakage Out of a Duct, Low-Frequency Cutoff

6.6 Propagation Loss Model Descriptions

7 Ambient Noise

7.1 Ambient Noise Models

7.2 Seismic Noise

7.3 Ocean Turbulence

7.4 Shipping Noise

7.5 Wave Noise

7.6 Thermal Noise

7.7 Rain Noise

7.8 Temporal Variability of Ambient Noise

7.9 Depth Effects on Noise

7.10 Directionality of Noise

7.11 Under Ice Noise

7.12 Spatial Coherence of Ambient Noise

8 Reverberation

8.1 Scattering, Backscattering Strength, and Target Strength

8.2 Reverberation Frequency Spread and Doppler Gain Potential

8.3 Important Observation with Respect to Reverberation

9 Active Target Strength

9.1 Target Strength Definition

9.2 Active Target Strength of a Large Sphere

9.3 Active Target Strength of a Very Small Sphere

9.4 Target Strengths of Simple Geometric Forms

9.5 Target Strength of Submarines

9.6 The TAP Model

9.7 Target Strength of Surface Ships

9.8 Target Strength of Mines and Torpedoes

9.9 Target Strength of Fish

10 Radiated Noise

10.1 General Characteristics of Ship Radiated Noise

10.2 Propeller Radiated Noise

10.3 Machinery Noise

10.4 Resonance Noise

10.5 Hydrodynamic Noise

10.6 Platform Quieting

10.7 Total Radiated Noise

11 Self Noise

11.1 Flow Noise

11.2 Turbulent Noise Coherence

11.3 Strumming Noise

12 Statistical Detection Theory

12.1 Introduction

12.2 Case 1: Signal Is Known Exactly

12.3 Case 2: Signal Is White Gaussian Noise

13 Methodology for Calculation of the Recognition Differential

13.1 Continuous Broadband Signals (PBB)

13.2 Continuous Narrowband Signals (PNB)

13.3 Active Sonar

13.4 Aural Detection

13.5 Display Nomenclature

14 False Alarms, False Contacts, and False Targets

14.1 Sea Story

14.2 Failure to Detect

14.3 Detection Theory

14.4 False Alarm Probability Calculation

14.5 False/Nonthreat Contacts

14.6 False Targets

14.7 Summary and Conclusions

15 Variability and Uncertainty

15.1 Random Variability of a Sonar

15.2 Sources of Variability

16 Modeling Detection and Tactical Decision Aids

16.1 Figure of Merit Range or R50 %

16.2 Tactical Decision Aids

17 Cumulative Probability of Detection

17.1 Why is CPD Important?

17.2 Discrete Glimpse and Continuous Looking

17.3 Lambda–Sigma Jump Model

17.4 Nonjump Processes

17.5 What Are Appropriate Random Parameters?

17.6 Approximation Method for Computation of the Cumulative Probability of Detection (CPD)

18 Tracking, Target Motion Analysis, and Localization

18.1 Bearing Trackers

18.2 General Principle of Tracking and Bearing Measurement

18.3 Other Sources of Bearing Error for Area Arrays

18.4 Additional Sources of Errors for Line Arrays

18.5 Bottom Bounce

18.6 Manual versus Automatic Tracking

18.7 Localization and Target Motion Analysis

18.8 Bearings Only Methodologies

18.9 Four-Bearing TMA

18.10 Ekelund Ranging

18.11 Range and Bearing TMA

18.12 Other Bearings Only TMA Methodologies

18.13 Other TMA and Localization Schemes

19 Design and Evaluation of Sonars

19.1 Choice of Frequency and Size

19.2 Computational Requirements

19.3 Signal Processing after Beamformer

19.4 Active Pulse Choice

19.5 Monostatic, Bistatic, and Multistatic Active Sonars

19.6 Ambiguity Functions

19.7 Mine Hunting and Bottom Survey Sonars

19.8 Echo Sounding and Fishing Sonars

19.9 Navigation

19.10 Vehicle Location and At-Sea Rescue

19.11 Intercept Receivers

19.12 Communications

19.13 Marine Mammals and Active Sonar

A Fourier Transforms

A.1 Definitions

A.2 Parseval’s Theorem and Plancherel’s Theorem

A.3 Properties of Fourier Transforms

A.4 Localization or Uncertainty Property

B Analysis of Errors Associated with a Least Squares Methodology

Index

This edition first published 2010 © 2010

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Library of Congress Cataloging-in-Publication Data

Hodges, Richard P.

Underwater acoustics : analysis, design, and performance of sonar / by Richard P. Hodges.p. cm.

Includes index.

ISBN 978-0-470-68875-5 (cloth)

1. Underwater acoustics. 2. Sonar-Mathematical models. 3. Elastic wave propagation. I. Title. QC242.2.H63 2010621.389’5-dc222010003321

A catalogue record for this book is available from the British Library.

ISBN 978-0-470-68875-5

About the Author

Richard P. Hodges has an SB degree in physics from the Massachusetts Institute of Technology (MIT), three years of graduate studies in physics at Boston University, and forty years’ experience in sonar, operations analysis, modeling, and the simulation of military systems. He is currently working for Sonalysts, Inc. as a principal analyst and is a core member of the Sensor Optimization Working Group (SOWG), which makes recommendations for models to support tactical decision aids for the U.S. Navy. He is a member of the Acoustical Society of America.

He has taught courses at the Naval Undersea Warfare Center (NUWC) and elsewhere in naval analysis of sonar, acoustics, TMA, tactics, weapons, damage and kill mechanisms, C4I, nonacoustic sensors, platform dynamics weapons, tactics, and on the use of NUWC’s SIM II Naval Engagement Simulation. He has been one of SIM II’s principal architects, engineers, analysts, and a user. He was responsible for the development of the expert systems approach to tactics and for the physical algorithmic modeling of sensors, weapons, environments, fire control systems, and platform characteristics. Mr. Hodges has also developed ASW, ASUW, Land Strike, AAW, and Weapon Models, as well as investigations of the tactical employment of existing and proposed sea-based military systems using SIM II.

Preface

I started writing this book in 2004 when I realized that all of the books I used to teach new sonar analysts were out of print since then several have been made available from other publishers.

In writing this book, I have tried to tread the middle ground between theoretical highly mathematical texts and popular nonmathematical texts. I have included not just graphical results but the accompanying equations that can be used in model development. To present what I consider useful and important results, both theoretical and experimental, I have generally left the details to the references. Over the years, I have spent countless hours reading points from historical graphs and developing curve fits in an effort to save others the time.

I primarily view this book as a source for sonar analysts and those interested in naval operations.

Acknowledgements

I would like to express my thanks to all the giants of the field, to my colleagues at Sonalysts, Inc. and the Naval Undersea Warfare Center, from whom I have tried to learn, to Micheley Angelina for her patience and particularly to Stephanie Schuller, without whom this book might have been unreadable.

1

Introduction to Sonar

SONAR (SOund NAvigation and Ranging) systems have many similarities to radar and electro-optical systems. The operation of sonar is based on the propagation of waves between a target and a receiver. The two most common types of sonar systems are passive and active. In a passive sonar system, energy originates at a target and propagates to a receiver, analogous to passive infrared detection. In an active sonar system, waves propagate from a transmitter to a target and back to a receiver, analogous to pulse-echo radar. In addition to these two types, there is also daylight or ambient sonar, where the environment is the source of the sound, which bounces off or is blocked by the target, and the effects of which are observed by the receiver. This latter type of sonar is analogous to human sight.

Sonar differs fundamentally from radar and electro-optical systems because the energy observed by sonar is transferred by mechanical vibrations propagating in water, solids, gases, or plasma, as opposed to electromagnetic waves. Today, sonar refers not only to systems that detect and/or transmit sound, but to the science of sound technology as well.

In military applications, sonar systems are used for detection, classification, localization, and tracking of submarines, mines, or surface contacts, as well as for communication, navigation, and identification of obstructions or hazards (e.g., polar ice). In commercial applications, sonar is used in fish finders, medical imaging, material inspection, and seismic exploration.

Figures 1.1, 1.2, and 1.3 illustrate the basic passive, active, and daylight/ambient sonar systems.

1.1 Acoustic Waves

The term “acoustic” refers to sound waves in any medium. Acoustic waves come in two types: longitudinal or compression and transverse or shear. In fluids, only longitudinal or compression waves are supported because fluids lack shear strength. The easiest way to visualize these two types of waves is to consider a Slinky (see Figure 1.4). If the end or middle portion of a Slinky is moved side to side or up and down, a transverse or shear wave will move along it. This method displaces the material of the Slinky in a direction perpendicular to the direction of travel. As the material is moved off the axis, the spring force exerts a restoring force that pulls it back on axis. If several of the Slinky coils are compressed or stretched, then releasing them will propagate a longitudinal or compression wave along the Slinky. This method displaces the material of the Slinky along the direction of travel. Again, the restoring force will tend to push the material back into place. In this book, we will deal with transverse or shear waves only occasionally, so unless specifically stated, longitudinal or compression waves are assumed.