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Introduction to Acoustics

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4.8.3 Typical Speed of Sound Profiles .............................. 135<br />

4.8.4 Atmospheric Turbulence Effects .............................. 138<br />

4.9 Concluding Remarks ...................................................... 142<br />

4.9.1 Modeling Meteorological and Topographical Effects ........ 142<br />

4.9.2 Effects of Trees and Tall Vegetation .......................... 142<br />

4.9.3 Low-Frequency Interactionwith the Ground ................ 143<br />

4.9.4 Rough-Sea Effects ............................................. 143<br />

4.9.5 Predicting Outdoor Noise ..................................... 143<br />

References ........................................................................ 143<br />

5 Underwater <strong>Acoustics</strong><br />

William A. Kuperman, Philippe Roux ........................................... 149<br />

5.1 Ocean Acoustic Environment ............................................ 151<br />

5.1.1 Ocean Environment ........................................... 151<br />

5.1.2 Basic Acoustic Propagation Paths ............................ 152<br />

5.1.3 Geometric Spreading Loss ..................................... 154<br />

5.2 Physical Mechanisms ..................................................... 155<br />

5.2.1 Transducers .................................................... 155<br />

5.2.2 Volume Attenuation ........................................... 157<br />

5.2.3 Bot<strong>to</strong>m Loss .................................................... 158<br />

5.2.4 Scattering and Reverberation ................................ 159<br />

5.2.5 Ambient Noise ................................................. 160<br />

5.2.6 Bubbles and Bubbly Media ................................... 162<br />

5.3 SONAR and the SONAR Equation ......................................... 165<br />

5.3.1 Detection Threshold and Receiver Operating<br />

Characteristics Curves .......................................... 165<br />

5.3.2 Passive SONAR Equation ....................................... 166<br />

5.3.3 Active SONAR Equation ........................................ 167<br />

5.4 Sound Propagation Models .............................................. 167<br />

5.4.1 The Wave Equation and Boundary Conditions .............. 168<br />

5.4.2 Ray Theory ...................................................... 168<br />

5.4.3 Wavenumber Representation or Spectral Solution .......... 169<br />

5.4.4 Normal-Mode Model .......................................... 169<br />

5.4.5 Parabolic Equation (PE) Model ................................ 172<br />

5.4.6 Propagation and Transmission Loss .......................... 174<br />

5.4.7 Fourier Synthesis of Frequency-Domain Solutions ......... 175<br />

5.5 Quantitative Description of Propagation ............................... 177<br />

5.6 SONAR Array Processing .................................................. 179<br />

5.6.1 Linear Plane-Wave Beam-Forming<br />

and Spatio-Temporal Sampling .............................. 179<br />

5.6.2 Some Beam-Former Properties ............................... 181<br />

5.6.3 Adaptive Processing ........................................... 182<br />

5.6.4 Matched Field Processing, Phase Conjugation and Time<br />

Reversal ........................................................ 182<br />

5.7 Active SONAR Processing ................................................. 185<br />

5.7.1 Active SONAR Signal Processing ............................... 185<br />

5.7.2 Underwater Acoustic Imaging ................................ 187<br />

Detailed Contents 1151<br />

Detailed Cont.

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