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It has recently been shown that the physical properties of a layered ocean floor may in principle be determined from an analysis of the resonances in frequency, or in the angle of incidence, which appear in bottom-reflected acoustic signals. In the present paper we demonstrate how, using sinuosoidal signals of long but finite duration, individual resonances can be selectively excited and analyzed. Multiple-bounce layer resonances interfere destructive with the specular echo, and manifest themselves through a characteristic ringing. (Author).
These 13 papers were part of a May 1989 symposium at the Catholic University of America, Washington, D.C., the home of much of the early theoretical and experimental work in acoustic resonance scattering. Topics include a historical survey of the development of the subject, a description of the MIIR and short- pulse methods, and new developments such as the derivation of exact acoustic background shells, application of the method of moments, and S-matrix product expansions. Annotation copyright by Book News, Inc., Portland, OR
This series of volumes constitutes an outstanding collection of contributions by the most active research workers in the area of acoustics and mechanics. It brings the reader up to date on the status of the various aspects of research in this field. The volumes should preserve their value for a long time, as they represent a monument to the achievements of human research capabilities in the underwater-acoustics aspects of the environment.
The phenomenon of sound transmissions through marine sediments is of extreme interest to both the United States civilian and Navy research communities. Both communities have conducted research within the field of this phenomenon approaching it from different perspectives. The academic research community has approached it as a technique for studying sedimentary and crustal structures of the ocean basins. The Navy research community has approached it as an additional variable in the predictability of sound trans mission through oceanic waters. In order to join these diverse talents, with the principal aim of bringing into sharp focus the state-of-the-science in the problems relating to the behavior of sound in marine sediments, the Office of Naval Research organized and sponsored an invited symposium on this subject. The papers published in this volume are the results of this symposium and mark the frontiers in the state-of-the-art. The symposia series were based on five research areas identified by ONR as being particularly suitable for critical review and for the appraisal of future research trends. These areas include: 1. Physics of Sound in Marine Sediments, 2. Physical and Engineering Properties of Deep-Sea Sediments, 3. The Role of Bottom Currents in Sea Floor Geological Processes, 4. Nephelometry and the Optical Properties of the Ocean I'laters, S. Natural Gases in Marine Sediments and Their Mode of Distribution. These five areas also form some of the research priorities of the ONR program in Marine Geology and Geophysics.
The general objectives of this investigation were to determine and study those characteristics of the sea floor that affect sound propagation and the prediction of sonar performance; to support underwater acoustics' experiments and theory by furnishing information on the mass physical properties of sediments and rocks in the form of geoacoustic models of the sea floor; and to develop models of the sea floor which include gradients of sound velocity and attenuation, density, and elastic properties. Specifically, the minor objectives were to revise and review earlier work on the relations between frequency and attenuation of compressional (sound) waves in marine sediments and on the relations between attenuation and sediment porosity. The major objectives were to determine and predict variations of the attenuation of sound waves with depth in the sea floor.
vi These categories seem to represent the basic breakdown by field of present-day research in this area. Though each paper has been classified into one of these categories (for conference organization purpose), many papers overlapped two or three areas. It is also interesting to note that not only are scientific results being communicated, but the latest techniques and the state-of-the-art tools of the trade (existing and in development) are also being presented. The forty-six papers presented at this conference represent the work of seventy scientists working at universities, government laboratories, and industrial laboratories in seven different countries . We would like to thank the contributors for their efforts and especially for their promptness in providing the editors with their final manuscripts. William A. Kuperman Finn B. Jensen La Spezia, Italy July 1980 CONTENTS GEOACOUSTIC PROPERTIES OF MARINE SEDIMENTS Attenuation of Sound in Marine Sediments . • 1 J. M. Hovem Directivity and Radiation Impedance of a Transducer 15 Embedded in a Lossy Medium . •• •••••• G. H. Ziehm Elastic Properties Related to Depth of Burial, Strontium Content and Age, and Diagenetic Stage in Pelagic Carbonate Sediments . . • • . • • • . 41 M. H. Manghnani, S. O. Schianger, and P. D. Milholland Application of Geophysical Methods 'and Equipment to Explore the Sea Bottom . •• •••. • 53 H. F. Weichart The Acoustic Response of Some Gas-Charged Sediments in the Northern Adriatic Sea • • • • . • • • • 73 A.
We have initiated a program to study the resonances in the acoustic reflection coefficient of a layered ocean bottom, patterned after the resonances of sound reflection from fluid or elastic layers. Computer programs have been written for obtaining the reflection coefficient from multilayered fluid or elastic media, with constant or linearly depth-dependent sound velocities in each layer. Resonances are evident in the reflection coefficient both as functions of frequency and of angle of incidence, and are shown to depend on the properties of the layered ocean bottom. Results will be presented in the form of three-dimensional graphs. (Author).
This book gives an overview ofthe current state of nonlinear wave mechanics with emphasis on strong discontinuities (shock waves) and localized self preserving shapes (solitons) in both elastic and fluid media. The exposition is intentionallyat a detailed mathematical and physical level, our expectation being that the reader will enjoy coming to grips in a concrete manner with advances in this fascinating subject. Historically, modern research in nonlinear wave mechanics began with the famous 1858 piston problem paper of Riemann on shock waves and con tinued into the early part of the last century with the work of Hadamard, Rankine, and Hugoniot. After WWII, research into nonlinear propagation of dispersive waves rapidly accelerated with the advent of computers. Works of particular importance in the immediate post-war years include those of von Neumann, Fermi, and Lax. Later, additional contributions were made by Lighthill, Glimm, Strauss, Wendroff, and Bishop. Dispersion alone leads to shock fronts of the propagating waves. That the nonlinearity can com pensate for the dispersion, leading to propagation with a stable wave having constant velocity and shape (solitons) came as a surprise. A solitary wave was first discussed by J. Scott Russell in 1845 in "Report of British Asso ciations for the Advancement of Science. " He had, while horseback riding, observed a solitary wave travelling along a water channel and followed its unbroken progress for over a mile.