Physics of Sound in Marine Sediments

567 Pages·1974·12.541 MB·English

by  Avtar S. Ahuja (auth.), Loyd Hampton (eds.)

PHYSICS OF SOUND
IN
MARINE SEDIMENTS
MARINE SCIENCE
Coordinating Editor: Ronald]. Gibbs, Northwestern University
Volume 1-Physics of Sound in Marine Sediments
Edited by Loyd Hampton, 1974
An Office of Naval Research symposium
Consulting Editors: Alexander Malahoff and Donald Heinrichs
Department of the Navy
Volume 2 -Deep-Sea Sediments: Physical and Mechanical Properties
Edited by Anton L. Inderbitzen, 1974
An Office of Naval Research symposium
Consulting Editors: Alexander Malahoff and Donald Heinrichs
Department of the Navy
In Preparation:
Natural Gases in Marine Spdiments
Edited by Isaac R. Kaplan
An Office of Naval Research symposium
Consulting Editors: Alexander Malahoff and Donald Heinrichs
Department of the Navy
Suspended Solids in Watel'
Edited by Ronald J. Gibbs
An Office of Naval Research symposium
Consulting Editors: Alexander Malahoff and Donald Heinrichs
Department of the Navy
A Continuation Order Plan is available for this series. A continuation order will bring
delivery of each new volume immediately upon publication. Volumes are billed only upon
actual shipment. For further information please contact the publisher.
PHYSICS OF SOUND
IN
MARINE SEDIMENTS
Edited by
Loyd Hampton
Applied Research Laboratories
The University of Texas at Austin
Austin, Texas
PLENUM PRESS • NEW YORK AND LONDON
Library of Congress Cataloging in Publication Data
Symposium on Physics of Sound in Marine Sediments, Austin, Tex., 1973.
Physics of sound in marine sediments.
(Marine science, v. 1)
Conducted by the Ocean Science and Technology Division of the Office of Naval
Research.
Includes bibliographies.
1. Marine sediments-Acoustic properties-Congresses. I. Hampton, Loyd,
1930- ed. II. United States. Office of Naval Research. Ocean Science and
Technology Division. III. Title.
GC380.2.A25S95 1973 551.4'6083 74-8022
ISBN-13: 978-1-4684-0840-9 e-ISBN-13: 978-1-4684-0838-6
DOl: 10.1007/978-1-4684-0838-6
Proceedings of a symposium conducted by the Ocean Science and Technology
Division of the Office of Naval Research on Physics of Sound in Marine Sedi
ments held in Austin, Texas, May 8-10, 1973
© 1974 Plenum Press, New York
Softcover reprint of the hardcover 1st edition 1974
A Division of Plenum Publishing Corporation
227 West 17th Street, New York, N.Y. 10011
United Kingdom edition published by Plenum Press, London
A Division of Plenum Publishing Company, Ltd.
4a Lower John Street, London, W1R 3PD, England
All rights reserved
No part of this book may be reproduced, stored in a retrieval system, or transmitted,
in any form or by any means, electronic, mechanical, photocopying, microfilming,
recording, or otherwise, without written permission from the Publisher
FOREWORD
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 Marine Geology and Geophysics Program is the section of
the Navy Ocean Science Program that provides research into the
ocean floor phenomena of interest to naval systems. The basic
research objective of the program is to determine the acoustical,
physical, chemical, and geological properties of the ocean floor.
To accomplish this objective, research studies are directed toward
understanding the deep ocean processes that generate oceanic sedi
ments and crustal layers. These processes directly affect the
physical and acoustic properties of the sea floor and are the
origin of bathymetric, gravity, and magnetic variations in the
ocean basins. Acoustic and nonacoustic submarine and antisubmarine
v
vi FOREWORD
operations; surveillance system design and construction; inertial
navigation, guidance, and trajectory calculations; search, rescue,
and recovery operations; and a variety of other Navy operations are
directly influenced by the ocean floor.
The Marine Geology and Geophysics Program is divided into
five areas, which are summarized here and detailed in the following
sections.
Particular emphasis is directed toward studies of ocean floor
acoustical processes, namely the physics of high frequency reflec
tivity of the ocean floor; the physics of low frequency acoustical
propagations through the sea floor; the formation of ocean floor
acoustic reflectors; and the areal variations in these acoustic
phenomena.
Another part of the program is directed toward studies of the
source and location of the major bathymetric, gravity, and magnetic
variables, together with the application of the knowledge gained
to the prediction of trends and amplitudes of these anomalies to
unsurveyed areas.
Additional studies are carried out in the dynamics of
sediment transport, including the effect of bottom currents on
microtopography and rates of sediment deposition and erosion; the
effects of sediment composition, chemical changes, and ocean floor
properties on ocean floor stability; and, the relationships of
sediment parameters to acoustic parameters.
The variations in acoustical and physical properties of marine
sediments, the morphology of the sea floor, magnetic anomaly trends,
and changes in the wavelength of marine gravity anomalies are not
random phenomena, but result from discrete physical processes.
Although the individual research tasks of the program are described
in terms of specific program objectives, data and concepts from
other classes of studies are often required for solutions of the
problem. For example, ocean floor acoustic studies directed toward
determining the continuity and source of prominent low frequency
refracting layers of the ocean floor utilize sediment properties
obtained from sediment dynamic studies and information on major
structural discontinuities from physiographic and magnetic field
studies. Results from the acoustic studies, in turn, provide
significant constraints on gravity field models. Thus research
cruises tend to be devoted to integrated marine geological and
geophysical investigations and take place in geographic areas that
are an integral part of the entire program. A typical cruise would
involve the use of seismic reflection and refraction, precision
echo sounding, gravity and magnetic sensors, sea floor coring,
dredging, and bottom photographic instrumentation. These ocean-
FOREWORD vii
going research programs are backed by theoretical, laboratory, and
specialized offshore investigations of limited duration. Require
ments for specialized, expensive equipment, including a sizeable
research vessel, and multidisciplinary inputs lead to a concentra
tion of research tasks at the major oceanographic institutions.
The symposium on the physics of sound in marine sediments was
formulated to enhance the scientific viability of the program in
ocean floor acoustics. This field is directed towards the under
standing of the physics of sound propagation through the sea floor.
The prime frequencies of interest to the ONR sponsored program are
200 hertz and below (long range surveillance), 100 to 1000 hertz
(short range passive surveillance and tactical sonar), and 1000 to
5000 hertz (tactical bottom bounce sonar). The specific objectives
are attacked through the following outstanding scientific questions:
(1) What is the distribution of energy in long range
ENERGY water and bottom paths? How can the bottom
paths be exploited?
(2) What is the continuity and source of the promi
nent refracting layers of the ocean floor
important in the propagation frequency range
REFRACTION
below 100 hertz? Can these refracted paths be
exploited at very low, infrasonic frequencies
below 10 hertz?
(3) What are the variations in reflectivity of
sediments, both in the vertical sense and in
horizontal continuity? In the sea floor these
REFLECTION
are important in the range below 4000 hertz.
Which sediments or basement layers give rise to
the prominent reflectors?
(4) How is coherence and attenuation of reflected
and refracted acoustic waves affected by the
topography of the ocean floor surface, by the
COHERENCE
passage of the signal through the ocean floor,
and by changes in the physical properties of the
sedimentary and crustal layers?
Solutions to the above problems are being pursued through three
major classes of studies:
(1) Underwa investigations. These studies use
3.5 kilohertz echo sounders, sparker arrays 100-500 hertz),
and airguns (20-200 hertz) as continuous underway pulsed sound
sources giving an acoustic source energy in the range from
3.5 kilohertz to 20 hertz. The detectors used are multisensor
towed arrays for vertical incidence reflections off the sea floor
and sonobuoys for wide-angle reflections and for refraction path
studies.
viii FOREWORD
(2) Ocean floor instrumentation. These are used for the
measurement of shallow sedimentary layers of the ocean floor, and
for crustal propagation paths. Three component seismometers are
used for the study of refracted P, S, and Stoneley Wave propagation
in the frequency range of 1 hertz to 100 hertz through the ocean
floor. The instruments are usually deployed on the sea floor for
periods ranging from days to months.
(3) Physical properties of sediments. A direct relationship
between the physical properties of marine sediments and their
velocity gradients, acoustic reflectivities, and attenuations is
known to exist. It is not known which of the physical properties
or mineralogical properties are the most influential upon sound
transmission through the sea floor. In-situ sound velocity
measurements are carried out simultaneously with ocean coring
procedures in order to relate acoustic boundaries in the sediments
to mineralogical or physical boundaries. Laboratory examination
of the samples is undertaken to determine their physical, mechanical,
and mineralogical properties, which are compared with the in-situ
measurements and to acoustic reflection and refraction horizons
in the sediments as measured from the ocean surface.
The ONR objectives for this symposium were fully realized,
as is shown by the content of the book. The excellent mix of both
civilian and Navy laboratory authors indicates the diverse talent
that was focused upon the general problem of sound propagation
through the marine sediments. All aspects of the ONR program in
sea floor acoustics were covered by the symposium, bringing focus
upon the new research frontiers within this particular discipline.
Alexander Malahoff
PREFACE
The fact that approximately 500 references are used by the
authors of the articles in this collection illustrates the
problems addressed by this book. The topic of Physics of Sound in
Marine Sediments is a very complex one; it is a field in which
rapid changes are occurring and one which crosses many scientific
disciplines. For these reasons comprehensive reporting is
difficult and is very seldom timely. A need for a useful assess
ment of our knowledge in this area (and several others) was
recognized by the Ocean Science and Technology Division of the
Office of Naval Research and a series of Symposia were convened
during the winter and spring of 1972-73. One of the goals of the
Symposia was to obtain a useful and timely summary of our state of
knowledge, and that is the purpose of this book.
The Symposium on Physics of Sound in Marine Sediments was
held at Lakeway Inn near Austin, Texas, on 8, 9, and 10 May 1973.
Those attending (see accompanying photograph and list) were
selected to represent as many scientific interests as appropriate
and, also, to represent the "user" of the information as well.
Selection was also based on contributions to the field and, of
those 500 references mentioned previously, approximately one fourth
are citing works published by those attending the Symposium.
The papers presented here are the versions submitted by the
participants after the Symposium. In many cases there were
revisions to reflect the interaction and discussions which occurred
at the Symposium. In general the emphasis of the papers is
summary and interpretation, and thus the papers are structured
differently from most journal papers. The collection of papers
should therefore be useful not only to those working in this area
but especially to those who have less familiarity and who desire a
status report on such a diverse topic.
Special recognition must go to N. A. Ostenso and A. Malahoff
of the Office of Naval Research for making this Symposium possible.
One of the responsibilities of the editor was to prepare submitted
papers for this volume. If there are mistakes from this process,
they are the responsibility of the editor and should in no way
reflect on the authors.
Loyd Hampton
Austin, Texas
February 1974
ix
CONTENTS
I. Theory
A. Derivation
A Review of the Derivations of the Formulas for the 1
Acoustical Properties of Liquid-Solid Mixtures
Avtar S. Ahuja
Acoustic Waves in Saturated Sediments 19
Robert D. Stoll
B. Interpretation
Acoustic and Mechanical Loading of Marine Sediments 41
Denzil Taylor Smith
Influence of Anisotropy and Soil Structure 63
on Elastic Properties of Sediments
V. A. Nacci, M. C. Wang, J. Gallagher
The Seismic Wide Angle Reflection Method in the 89
Study of Ocean Sediment Velocity Structure
G. L. Maynard, G. H. Sutton, D. M. Hussong,
L. W. Kroenke
Sonobuoy Measurements in Thin Layers 119
George M. Bryan
II. Applications
The Interaction of Underwater Acoustics 131
and Marine Geophysics
A. C. Kibblewhite
Underwater Sound Transmission Through the Ocean Floor 161
R. J. Urick
Geoacoustic Models of the Sea Floor 181
Edwin L. Hamilton
Sound Propagation Calculations Using 223
Bottom Reflection Functions
H. P. Bucker
xi