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Acoustic fish models should represent the fish body form. The Atlantic cod were used to model the acoustic scattering function of teleost fish. The model provides a basis for choices of sonar carrier frequencies. Anesthetized live Atlantic cod ranging from 156 to 380 mm (SL) were ‘‘soft’’ x-rayed to image inflated swimbladders and skeletal elements. Maximum body heights and widths were 0.18 and 0.13 of fish lengths. Lengths and diameters of swimbladder were approximately 0.25 and 0.05 of the fish lengths. A series of short-length fluid-filled cylinders were used to represent body flesh. For carrier frequencies above the breathing mode resonance, swimbladders were modeled as a series of short gas-filled volume elements of cylinders. A Kirchhoff-ray approximation was used to compute the high-frequency acoustic scattering. A low mode solution for a gas-filled cylinder was used to compute the low-frequency ‘‘breathing mode resonance.’’ All contributions were added coherently. The scattering lengths ℒ, or target strength=20 log‖ℒ/L0‖ (where L0 is reference length) were sensitive to fish orientation relative to the sonar beam. Theoretical target strengths were compared to the 38-kHz cod data. Agreement was good.

What do shipwrecks, schools of fish, singing whales, and foaming seas have in common? They can all be detected and classified with acoustical methods and they are all described under one cover in this book. The seafloor, objects lying on or buried in the seafloor, suspended sediment, marine organisms of many kinds, eddies and turbulence, bubbles, temperature, salinity, and the sea surface all affect the manner in which sound propagates through the ocean. The purpose of this book is to describe methods that exploit the various effects so that sound can be used as a tool to infer important properties of the corresponding objects or processes in the ocean.Why use sound? Light and other forms of electromagnetic radiation do not travel far in the ocean, giving the ocean a dark and mysterious appearance. As a result, we know, in many respects, more about the surface of the moon than of the interior of the ocean on our very own planet! Sound can travel very large distances in the ocean, especially at lower frequencies.Because of this ability, sound has been widely used as a means to probe the ocean's interior. For example, a patent on use of underwater sound was applied for shortly after the steamship Titanic sank due to its collision with an iceberg in 1912. The patent was for using sound for ''detecting the presence of large objects underwater.'' Since then, the applications using sound as a tool to study the ocean grew in number and diversity. Along with the various applications are a multitude of challenges. Both the applications and their corresponding challenges are addressed formally in this book, with many examples given.Fundamentals of Acoustical Oceanography is written in a style appropriate for a broad audience at many levels. Much of the text is written in a simple tutorial manner so that both nonspecialists and people who are just entering the field can understand it. Furthermore, there is enough detail and references made to the literature so that the specialist can also make use of the material. The book spans areas of marine geology, marine biology, physical oceanography, and marine engineering and would be useful in applications involving ecology, commerce, and the military.This book follows Acoustical Oceanography, published in 1977 by the same authors but with author order reversed. The first book was widely used and cited. It had eleven printings, was translated into Russian, and was cited routinely by scientists in varied disciplines and in many different journals. Since 1977, there have been significant advances in the area of acoustical oceanography. This new book incorporates many of the advances along with a new format. The first work reserved advanced topics for appendices at the end of the book while the present book integrates advanced material along with the rest of the text, but denotes the material as optional to read.Acoustical oceanography, as defined by the authors early in the book, involves the so-called ''inverse problem.'' That is, given solutions to acoustic propagation, inverse me...

By heuristically extending the previously developed ray solution [Stanton et al. J. Acoust. Soc. Am. 94, 3454-3462 (1993)] to predict the scattering by cylinders over all angles of incidence, approximate expressions are derived which describe the echo energy due to sound scattered by finite cylinders averaged over orientation and length. Both straight and bent finite length cylinders of high aspect ratio are considered over the full range of frequencies (Rayleigh through geometric scattering). The results show that for a sufficiently broad range of orientation, the average echo is largely independent of the degree of bend--that is, the results are essentially the same for both the straight and bent cylinders of various radii of curvature (provided the bend is not too great). Also, in the limit of high frequency (i.e., the acoustic wavelength is much smaller than the cross-sectional radius of the object), the averages are independent of frequency.

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