Description

Shallow water acoustics (SWA), the study of how low and medium frequency sound propagates and scatters on the continental shelves of the worlds oceans, has both technical interest and a large number of practical applications. Technically, shallow water poses an interesting medium for the study of acoustic scattering, inverse theory, and propagation physics in a complicated oceanic waveguide. Practically, shallow water acoustics has interest for geophysical exploration, marine mammal studies, and naval applications. Additionally, one notes the very interdisciplinary nature of shallow water acoustics, including acoustical physics, physical oceanography, marine geology, and marine biology. In this specialized volume the authors, all of whom have extensive at-sea experience in US and Russian research efforts, have tried to summarize the main experimental, theoretical, and computational results in shallow water acoustics, with an emphasis on providing physical insight into the topics presented. Dr. James F. Lynch was born in Jersey City, New Jersey on June 3, 1950. He obtained his B.S. in Physics from Stevens Institute of Technology in 1972 and his Ph.D. in Physics from the University of Texas at Austin in 1978. He then worked for three years at the Applied Research Laboratories of the University of Texas at Austin (ARL/UT) from 1978 to 1981, after which he joined the scientific staff at the Woods Hole Oceanographic Institution (WHOI). He has worked at WHOI since then, and currently holds the position of Senior Scientist in the Applied Ocean Physics and Engineering Department. His research specialty areas are ocean acoustics and acoustical oceanography. He also greatly enjoys occasional forays into physical oceanography, marine geology, and marine biology. Dr. Lynch is a Fellow of the Acoustical Society of America, a Fellow of IEEE, the former Editor-in-Chief of the IEEE Journal of Oceanic Engineering, and present Editor of JASA-EL. He recently received the 2009 Walter Munk Award in Oceanography from the Oceanography Society and the Secretary of the Navy. His hobbies include kempo karate and amateur astronomy and meteorology. B.Katsnelson was born in Kursk, Russia on April 2, 1950. He obtained his B.S. in Physics from Voronezh State University in 1972 and his Ph.D. in Theoretical Physics from Voronezh University in 1976. He then worked in the Physics Dept of Voronezh University as a Senior Scientist and then as Professor up to now. His research areas at different times were the theory of the interaction of laser fields with atoms and molecules, the propagation of electromagnetic waves in plasma and currently sound propagation in the ocean. He is a Fellow of the Acoustical Society of America and member of the Russian Acoustical Society. His hobbies are tennis and classical music. Prof. Valery G. Petnikov was born in Moscow, Russia on December 20, 1947. He obtained his B.S. /M.S. in Physics and his Ph.D in Physics and Mathematics from M.V. Lomonosov Moscow State University, faculty of Physics in 1972 and in 1977 correspondingly. He obtained his Doctor of Sciences in Physics and Mathematics from the General Physics Institute, Russian Academy of Sciences in 2000. After the Post-Graduate Course at the M.V. Lomonosov Moscow State University, faculty of Physics he worked at O.Yu. Shmidt Institute of Physics of Earth, Academy of Sciences of the USSR (Moscow) from 1975 to 1979. He then worked at the Hydrophysics Laboratory in the P.N. Lebedev Physics Institute, Academy of Sciences of the USSR (Moscow) from1979 to 1982 and at the Laboratory of Acoustic Sensing of the Ocean in the General Physics Institute, Academy of Sciences of the USSR (Moscow) from1982 to 1998. He has been Head of the Laboratory from 1986-1998. In 1998, he joined Wave Research Center of General Physics Institute, Russian Academy of Sciences (Moscow) as Head of the same Laboratory, Leading Research Associate. His scientific interests are underwater acoustics, specifically: shallow water acoustics, arctic acoustics, acoustic tomography and acoustics signal processing. He has more than 80 publications in peer-reviewed journals. Prof. Petnikov is a Fellow of the Russian Acoustical Society. He is also a Real member of the editorial board of the Acoustical Physics journal. Table of Contents.- Preface.- 1. What is shallow water acoustics?.- 1.1. Deep versus shallow.- 1.2 Past and Present of shallow water acoustics.- 1.3 The future of shallow water acoustics.- 1.4 Some “old favorite” research areas revisited and updated.- 2. Coastal Oceanography, Geology, and Biology.- 2.1. The coast as acoustic waveguide.- 2.2. Properties of sea water: Vertical stratification and its seasonal variability.- 2.3. Horizontal stratification and its variability: Fronts and eddies, surface ducts and storm surges.- 2.4 Dynamics of the ocean surface: Surface waves.- 2.5. Dynamical processes inside the ocean: Tides and internal waves.- 2.6. Experimental studies of coastal internal waves.- 2.7. Coastal Geology and Geophysics.- 2.8. Acoustics of sediments.- 2.9. Bottom roughness.- 2.10 Solid and multi-component layered bottom models.- 2.11. Acoustics of biological objects in a coastal area.- 3. Foundations of the theory of the propagation of sound.- 3.1. Field of a point source in a layered waveguide with absorbing boundaries.- 3.2. The Pekeris Model.- 3.3 Perturbation theory and WKB methods.- 3.4. Ray description of the sound field and ray-mode connections.- 3.4.1 Ray theory.- 3.4.2 Rays as interfering modes.- 3.4.3 Modes as interfering rays.- 3.4.4 Distinguishing between ray and mode arrivals.- 3.5. Mode coupling in a shallow water waveguide with small inhomogeneities.- 3.6. Mode coupling in shallow water with smooth inhomogeneities.- 3.7. Horizontal refraction in shallow water (the 3D problem).- 3.8 Parabolic equation (PE).- 4. Examples Illustrating the Characteristics of Waveguide Propagation.- 4.1. A General Transmission Loss Example, including a simplified theory of shallow water attenuation.- 4.2. Simplified description of solid, multi-component, poro-elastic and layered bottom models.- 4.3. Optimum frequency.- 4.4. Interference structure and interference invariant of the sound field.- 4.5 Waveguide dispersion of sound signals in shallow water.- 4.6. Averaged description of the sound field in a waveguide.- 5. Sound field in shallow water with random inhomogeneities.- 5.1. Structure and models of different kinds of random inhomogeneities.- 5.2. Description of a random sound field by coherent and incoherent parts.- 5.3 Equations for mode interactions.- 5.4 Equations for intensity.- 5.5. The Diffusion equation and averaged decay laws.- 5.6. Some examples.- 5.6.1 Waveguide of constant depth.- 5.6.2 Irregular waveguide.- 5.6.3 Dependence of the intensity on depth.- 5.7. Sound field fluctuations in the presence of background internal waves.- 5.8 Models and statistics of intensity fluctuations.- 6. Low frequency bottom reverberation in shallow water.- 6.1 Introduction – Sound scattering by the sea bottom.- 6.2 Mode theory of bottom reverberation in a regular waveguide.- 6.3 Numerical simulation of low frequency bottom reverberation.- 6.4 Long range reverberation studies using extended arrays.- 6.5 Long range reverberation in a randomly inhomogeneous waveguide.- 7. The inverse problem.- 7.1 General considerations. The linear inverse problem.- 7.2 Bottom versus water column influences on the dq_l and inverse.- 7.3 The generalized inverse, its error, and an example from the Corpus Christi GEMINI experiment.- 7.4 Examples of nonlinear bottom property inversion using various data types.- 7.5 Broadband experiments and the frequency dependence of the bottom parameters.- 7.6 Bottom geoacoustic inversions using ambient noise sources.- 8. Signal processing.- 8.1 Fundamentals of data processing techniques.- 8.2 Matched field processing in shallow water.- 8.2.1 Conventional MFP, Bartlett Processor.- 8.2.2 Two (analytic) examples of the parameter ambiguity function.- 8.2.3 Maximum likelihood beamformer.- 8.2.4 Variable coefficient likelihood beamformer.- 8.3 Spatial coherence of the sound field in shallow water and array signal gain.- 8.4 Mode filtration.- 8.5 Time reversal mirror of the sound field in shallow water.- 8.6 Acoustic uncertainty.- 9. Noise field in shallow water.- 9.1 Introduction. Model of a noise source. General equations.- 9.2 Relationship between the continuous and the discrete components of the field of surface noise sources in a waveguide.- 9.3 Effect of the frequency dependence of the bottom absorption coefficient on the noise spectrum.- 9.4 Vertical directivity of the sound field and the effect of random inhomogeneities.- 9.5 Effect of the sound speed profile on the vertical distribution of the noise field intensity.- 10. Equipment for shallow water acoustics and experimental considerations.- 10.1 The frequency band used for large scale acoustic monitoring.- 10.2 Low frequency sources of sound.- 10.3 Receiving acoustic arrays and the design of large scale acoustic monitoring experiments on the shelf.- 11. The future.- 11.1 Introduction.- 11.2 Physical oceanography.- 11.3 Bottom acoustic properties.- 11.4 New directions in the theory and modeling of sound propagation.- 11.4.1. 3-D problems.- 11.4.2 Interference invariant.- 11.43 Dislocations of the wave field.- 11.5 Physical phenomena concerned with stochastic effects.- 11.6 Inverse problems.- 11.6.1 Water layer.- 11.6.2 Bottom layer.- 11.7 Signal processing.- 11.8 New and prospective developments in oceanographic and acoustical equipment and survey methods.- 11.8.1 AUV’s, gliders, and the construction of detailed oceanographic models.- Appendix A. Waves and signals.- A.1. Analytic signals and waves.- A.2 Surface waves.- A.3. Internal waves.- Appendix B. Modal decomposition of the sound field from the point source Green function.- Appendix C. Mode coupling equations.- Appendix D. Empirical orthogonal functions.- Appendix E. Scattering at localized inhomogeneities in the waveguide-approximate description.- Appendix F. Reflection of a plane wave from a half space.- Main Provisional Notation.- Bibliography and References.- List of Acronyms.- Index.