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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).
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.
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.
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).
This monograph is devoted to the systematic presentation of the theory of sound wave propagation in layered structures. These structures can be man-made, such as ultrasonic filters, lenses, surface-wave delay lines, or natural media, such as the ocean and the atmosphere, with their marked horizontal stratification. A related problem is the propagation of elastic (seismic) waves in the earth's crust These topics have been treated rather completely in the book by L. M. Brek hovskikh, Waves in Layered Media, the English version of the second edition of which was published by Academic Press in 1980. Due to progress in experimental and computer technology it has become possible to analyze the influence of factors such as medium motion and density stratification upon the propagation of sound waves. Much attention has been paid to propagation theory in near-stratified media, Le. , media with small deviations from strict stratification. Interesting results have also been obtained in the fields of acoustics which had been previously considered to be "completely" developed. For these reasons, and also because of the inflow of researchers from the related fields of physics and mathematics, the circle of persons and research groups engaged in the study of sound propagation has rather expanded. Therefore, the appearance of a new summary review of the field of acoustics of layered media has become highly desirable. Since Waves in Layered Media became quite popular, we have tried to retain its positive features and general structure.
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.
Underwater acoustics is important in all underwater sonar systems for object detection, classification, surveillance and for communications links for military and civilian purposes. Sound is also a major tool for studying the ocean environment and the interaction of sound and marine life in general. Understanding Ocean Acoustics emphasises such applications and issues relevant to studies of the ocean environment and aquatic life. Its focus is therefore environmental research and development using low frequencies relevant to fish and sea mammals. For such frequencies, the geoacoustic properties of the bottom cannot be ignored, which requires knowledge about waves in solids, which is missing in most books on underwater acoustics.