OCEAN SEISMO-ACOUSTICS Low-Frequency Underwater Acoustics

NATO CONFERENCE SERIES

I Ecology II Systems Science III Human Factors IV Marine Sciences V Air-Sea Interactions VI Materials Science

IV MARINE SCIENCES

Recent volumes in this series

Volume 8 Structure and Development of the Greenland-Scotland Ridge edited by Martin H. P. Batt, Svend Saxov, Manik Talwani, and Jarn Thiede

Volume 9 Trace Metals in Sea Water edited by C. S. Wong, Edward Boyle, Kenneth W. Bruland, J. D. Burton, and Edward D. Goldberg

Volume 10A Coastal Upwelling: Its Sediment Record Responses of the Sedimentary Regime to Present Coastal Upwelling edited by Erwin Suess and Jorn Thiede

Volume 10B Coastal Upwelling: Its Sediment Record Sedimentary Records of Ancient Coastal Upwelling edited by Jarn Thiede and Erwin Suess

Volume 11 Coastal Oceanography edited by Herman G. Gade, Anton Edwards, and Harald Svendsen

Volume 12 Hydrothermal Processes at Seafloor Spreading Centers edited by Peter A. Rona, Kurt Bostrom, Lucien Laubier, and Kenneth L. Smith, Jr. .

Volume 13 Flows of Energy and Materials in Marine Ecosystems: Theory and Practice edited by M. J. R. Fasham

Volume 14 Mechanisms of Migration in Fishes edited by James D. McCleave, Geoffrey P. Arnold, Julian J. Dodson, and William H. Neill

Volume 1 5 Heterotrophic Activity in the Sea edited by John E. Hobbie and Peter J. IeB. Williams

Volume 16 Ocean Seismo-Acoustics: Low-Frequency Underwater Acoustics edited by Tuncay Akal and Jonathan M. Berkson

OCEAN SEISMO-ACOUSTICS Low-Frequency Underwater Acoustics

Edited by

Tuncay Akal and

Jonathan M. Berkson SACLANT ASW Research Center La Spezia, Italy

Published in cooperation with NATO Scientific Affairs Division

PLENUM PRESS· NEW YORK AND LONDON

Library of Congress Cataloging in Publication Data

Ocean seismo-acoustics.

(NATO conference series. IV, Marine sciences; v. 16) Proceedings of the Symposium on Ocean Seismo-Acoustics, organized by

SACLANT ASW Research Centre, held June 10-14, 1985, at La Spezia, Italy. Includes bibliographies and indexes. 1. Underwater acoustics-Congresses. 2. Ocean bottom-Congresses. I. Akal,

Tuncay. II. Berkson, Jonathan M. III. Symposium on Ocean Seismo-Acoustics (1985: La Spezia, Italy) IV. SACLANT ASW Research Center. V. Series. QC242.024 1986 551.46 /01 86-4940 ISBN 978-1-4612-9293-7 ISBN 978-1-4613-2201-6 (eBook) DOl 10.1007/978-1-4613-2201-6

Proceedings of a SACLANT ASW Research Center symposium, held June 10-14, 1985, at San Terenzo di Lerici, La Spezia, Italy

© 1986 Plenum Press, New York Softcover reprint of the hardcover 1st edition 1986

A Division of Plenum Publishing Corporation 233 Spring Street, New York, N.Y. 10013

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

Seafloor investigation has long been a feature of not only seismology but also of acoustics. Indeed it was acoustics that produced depth sounders, giving us the first capability of producing both global and local maps of the seafloor. Subsequently, better instrumentation and techniques led to a clearer, more quantitative picture of the seabed itself, which stimulated new hypotheses such as seafloor spreading through the availability of more reliable data on sediment thickness over ocean basins and other bottom features. Geologists and geophysicists have used both acoustic and seismic methods to study the seabed by considering the propagation of signals arising from both natural seismic events and man-made impulsive sources. Although significant advances have been made in instrumentation, such as long towed geophysical arrays, ai r guns and ocean bot tom seismometers, the pic ture of the seafloor is still far from complete.

Underwater acoustics concerns itself today with the phenomena of propagation and noise at frequencies and ranges that require an understanding of acoustic interaction at both of its boundaries, the sea surface and seafloor, over depths ranging from tens to thousands of meters. Much of the earlier higher frequency (>1 kHz) work included the characterization of the seafloor in regimes of reflection coefficients which were empirically derived from surveys. The results of these studies met with only limited success, confined as they were to those areas where survey data existed and lacking a physical understanding of the processes of reflection and scattering. The development in recent years of systematic methods of measuring the physical and acoustical characteristics of the seabed have led to a much better understanding of propagation. However these techniques are exceedingly slow and expensive and do not fulfill the needs of present day acoustics. The relatively recent recognition of the importance of the role that shear and evanescent waves in the seabed have on water borne sound has been a major factor in the recognition of the need for acousticians and seismologists to exchange and discuss their common goals and developments.

The realization of the benefits that could be achieved from such an exchange led the Centre to organize the Symposium on Ocean Seismo-Acoustics. In their entirety these papers give both the acoustician and the geophysicist a good picture of the other's interests, approaches and techniques. The authors represent a wide span of interests and institutions and, therefore, many different points of view.

v

That the Symposium on Ocean Seismo-Acoustics was organized and hosted by the SACLANT ASW Research Centre is fitting for two reasons. Firstly, one of the Centre's key missions is to promote the exchange of scientific and engineering information for the common benefit and understanding of the nations of the NATO community. Secondly, the Centre, throughout its twenty-six years as a research institution, has actively and significantly contributed to seafloor acoustics.

I have little doubt therefore that this volume will experienced scientists as' well as those who are contemplating research in the difficult environment of the sea.

Ralph R. Goodman Director

serve future

SACLANT ASW Research Centre

vi

PREFACE

Because of the ease with which sound can be transmitted in seawater, acoustic techniques have provided the widest range of tools for accumu­lating knowledge of the environment below the ocean surface. Consequently, the fields of underwater acoustics and marine seismology have both used sound waves for research purposes. Traditionally, the marine seismology communi ty has used earthborne propagation of elastic waves to study the sub-oceanic solid earth; the underwater acoustics community on the other hand has concentrated on studying waterborne, compressional-wave propaga­tion phenomena in oceanic waters and in shallow sub-bottoms.

In recent years, the research interests of these two communities have come closer together; in some areas they have overlapped. Research in underwater acoustics has been extended to the lower part of the frequency spectrum (one to a few hundred hertz), and thus overlaps the spectral domain of the seismologists. Additionally, studies of propagation of earthborne energy into the water column, and of shear-waves, interface waves, and Love waves, have increased. Coincidentally, research in marine seismology has extended to higher frequencies and to the ve10ci ty-depth structure of the uppermost part of the seafloor, overlapping the domain of underwater acousticians. These trends have been driven by the need to understand both water column and sub-bottom phenomena and by advances in technology, particularly the development of ocean bottom seismometers and multi-sensor hydrophone arrays. The overlapping interests have therefore stimulated increased activity that has benefitted both disciplines.

The Symposium on Ocean Seismo-Acoustics, sponsored by SACLANT ASW Research Centre, with partial support from the Office of Naval Research, London, was held at La Spezia, Italy, June 10-14, 1985. Its purpose was to enhance cross-disciplinary dialogue and generate ideas for new research directions. This volume contains papers originating from the Symposium and includes several additional features such as subject and author indexes.

The papers are organized into eight topics:

Propagation: Theoretical Developments Propagation: Modelling and Experiments Propagation: Fluctuations Boundary Scattering Sediments: Seismo-Acoustic Waves and Geoacoustic Characteristics Seismo-Acoustic Waves: Propagation, Attenuation, and Inverse Techniques Seismo-Acoustic Noise Technology and New Approaches in Seismo-Acoustic Measurements

Categorization of papers covering a diversity of topics is at best inexact and ofttimes subjective. Many of -the papers were broad enough in

vii

scope to fit easily into categories other than the one chosen, and in this respect alone the subject and author indexes should prove valuable.

This volume contains 75 research papers and 8 review papers by authors from many nations. The papers cover diverse areas of ocean seismo­acoustics including theory, instrumentation, signal processing, experimen­tal techniques, and experimental results. The number of quoted references is over 1000, an indication of the diversity of topics and a reflection of the fact that the papers might normally be scattered among many acoustical, seismic, geological, and geophysical journals, published . in several languages. Thus, this volume presents the current status of both fields, combining papers that report recent work as well as review papers that pro­vide perspective. As such it consolidates the research activities of these two fields. These characteristics should make this volume not only useful to seismo-acoustic specialists but also to other researchers whose work may be influenced by the interaction of marine seismology and underwater acoustics.

In the preparation of this volume, we received assistance from a large number of individuals at SACLANTCEN; regrettably all of their names cannot be listed. However, we would particularly like to thank O. Toso for secre­tarial assistance and H. Ali for suggesting improvements to several papers. We are especially grateful to R. Nekritz for assistance in preparing the volume, and to Dr. R. Goodman for his guidance and support.

La Spezia, Italy Oc tober, 1985

viii

Tuncay Akal Jonathan M. Berkson

CONTENTS

PROPAGATION: THEORETICAL DEVELOPMENTS

Sound Pulse Propagation in a Weakly Range Dependent Shallow Ocean

E. Topuz and L.B. Felsen

Intrinsic Modes in a Wedge-Shaped Ocean with Stratified Elastic Bottom

I.T. Lu and L.B. Felsen

A Green's Function Method for One-Way Wave Propagation in a Range-Dependent Ocean Environment . . . . . . . . . . . • . .

K.E. Gilbert and R.B. Evans

Factorization and Path Integration of the Helmholtz Equation: Numerical Algorithms

L. Fishman and S.C. Wales

Range Dependent Propagation Codes Based on Wave Field Factorization and Invariant Imbedding ............. .

J.J. McCoy, L. Fishman, and L.N. Frazer

An Acoustic Reflectivity Method for Laterally Varying Layered Media . . . . . .

L.N. Frazer and J.J. McCoy

A Vector Parabolic Equation Model for Elastic Propagation

S.C. Wales

Influence of Bottom Refraction on the Propagation of Underwater Sound

J. Miller, A. Nagl, and H. fiberall

Bottom Interaction Effects on Normal Modes: an Algebraic Approach .

D.H. Wood, M.D. Duston, and G.R. Verma

Gaussian Beams and 3-D Bottom Interacting Acoustic Systems •.........

H:P. Bucker and M.B. Porter

1

11

21

29

39

47

57

67

75

87

ix

Development of a Parabolic Approximation for the Computation of Propagation Loss in a Range-Dependent Environment. . . . . . . . . . . .

B. Grandvuillemin

PROPAGATION: MODELLING AND EXPERIMENTS

*Linear and Nonlinear Ocean Acoustic Propagation Models . . . . .

W.A. Kuperman and B.E. McDonald

Modeling of Pulse Response Functions of Bottom Interacting Sound Using the Parabolic Equation Method ..

F.D. Tappert and L. Nghiem-Phu

A Study of Propagation Loss Dependence on Sediment Layer Thickness using the Fast Field Program . . . . . . . . . . . . .

C.H. Harrison and P.L. Cousins

Shear Wave Effects on Propagation to a Receiver in the Substrate

P.J. Vidmar and R.A. Koch

Description and Some Results of the Operational Propagation Loss Model ALMOST (= Acoustic Loss Model for Qverational ~tudies-and !asks).

P. Schippers

Experimental Confirmation of Horizontal Refraction of Sound Propagation in a Wedge-like Ocean ........ .

R. Doolittle, A. Tolstoy, and M. Buckingham

Acoustic Propagation over Large-Scale Linear Ocean Slopes . . . . . .

D.R. DelBalzo, J.E. Matthews, J.V. Soileau, and C. Feuillade

Predicted Partitioning of VLF Acoustic Energy in a Range-Dependent Environment . . . . . . . .

T.W. Tunnel and G.J. Tango

Experiments on Sound Propagation over Sloped Bottoms ....... .

H. Hobaek, C.T. Tindle, and T.G. Muir

The Effect of Unconsolidated Sediment Rigidity on Low Frequency Acoustic Propagation . . . . . . . . . . . .

J.H. Beebe and C.W. Holland

* Indicates Review Paper

x

103

115

129

139

149

159

169

179

191

199

207

A Propagation Anomaly Observed in the Barents Sea • . • . . . ., .•.......••....• 217

E.H. Hug

Long Range Low Frequency Propagation Measurements in Deep Water Using a Seismic Towed Array . • . . . . . •

A. Plaisant and B. De Raigniac

Some Characteristics of Virtual Modes in Shallow Water with High Speed Bottom ........ .

G.H. Brooke, D.J. Thomson, and . R. F. MacKinnon

The Deduction of Approximate Values of Sediment Depth from Propagation Loss Measurements.

P.H. Lindop

PROPAGATION: FLUCTUATIONS

*Range and Time Dependence of Acoustic Intensity Fluctuations ....••

B.J. Uscinski

Shallow Water Tomography. • ..... H.A. DeFerrari, D.S. Ko, and C.L. Monjo

Medium-Induced Low-Frequency Fluctuations in Acoustic Transmission Loss: Examples from Measurements in Selected Geographical Areas ........ .

H.B. Ali, M.C. Ferla, and S. Fiori

Wave Propagation in Anisotropic Media Using Born Series Through 4th Order .

W.C. Meecham

Coupling of Acoustic Modes in the Ocean, A Comparison of Approximate Solutions .

Y. Desaubies

BOUNDARY SCATTERING

*Long Range, Low frequency Acoustic Backscattering: A Survey.

A.B. Baggeroer and I. Dyer

Directional Measurements of Low-Frequency Acoustic Backscattering from the Seafloor

J.M. Berkson, T. Akal, H.J. Kloosterman, and J.L. Berrou

Seamount Height Estimation from Long-Range, Low Frequency Acoustic Backscatter ....

F.T. Erskine, E.R. Franchi, and B.B. Adams

223

233

243

253

269

281

293

305

313

327

335

xi

An Acoustic Model for Bathymetric Scattering with Low-Frequency Applications • . . .

R.N. Baer, J.S. Perkins, E.B. Wright, and B.B. Adams

Evaluation of Low-Frequency Bottom Backscattering Strength vs Grazing by Means of Multiple Beamforming.

D. Marandino and T.G. Goldsberry

Angle

Near Grazing Propagation over a Low Roughness Hard Ocean Bottom . . • • • • . . . . .

H. Medwin

Estimation of Ice Surface Scattering and Acoustic Attenuation in Arctic Sediments from Long-Range Propagation Data.

G.L. Duckworth and A.B. Baggeroer

345

355

365

373

Low Frequency Attenuation in the Arctic Ocean • . . . • • . • • . .. 387 F.R. DiNapoli and R.H. Mellen

Effect of Sub-Bottom Inhomogenieties on Shallow Water Spatial Coherence

S.T. McDaniel and D.F. McCammon

Mode Coupling from Subbottom Roughness. D.F. McCammon and S.T. McDaniel

SEDIMENTS: SEISMQ-ACOUSTIC WAVES AND GEOACOUSTIC CHARACTERISTICS

397

407

*Acoustic Waves in Marine Sediments . . . . . . . • • • • . • • • .. 417 R.D. Stoll

Pore Shape and the Biot-Stoll Model for Saturated Sediments. . . • . . . . .. . .•.•

K. Attenborough

Low-Frequency Anomalies in the Reflection Behaviour of Marine Sediments . . . . . • . . • • . . .

M. von Haumeder

The Interaction of Low-Frequency Acoustic Waves with a One-Dimensional Random Sediment Model ................. .

I.M. Besieris and W.E. Kohler

Propagator Matrix for Acoustic Wave Propagation through Anisotropic Porous Media .....

T. Yamamoto and M. Badiey

Acoustic-to-Seismic Coupling at Porous Ground Surfaces •..

K. Attenborough

*Geotechnical Characteristics of the Sea Bed Related to Seismo-Acoustics

D. Taylor Smith

435

445

455

463

473

483

Dynamic Properties of Marine Sediments. . . . . . . . • . . . . . .. 501 A.M. Davis and J.D. Benne1l

Relationship between the Acoustical Characteristics of Deep Sea Sediments and their Physical Environment. . . . . . . • . . . . . . .• 511

C.C. Leroy, J.M. Daupleix, and P.J. Longuemard

Low Frequency Measurements of the Acoustic Properties of Marine Sediments . . . . . . . . . • • • . • .. 519

J.I. Dunlop

Spatial Variability of Surficial Shallow Water Sediment Geoacoustic Properties . . . . . . . . . . . . . . .. 527

M.D. Richardson

A Bottom Shear Modulus Profiler: Inverse Analysis of the Field Data on Wave-Induced Bottom Motion

T. Yamamoto and T. Torii

SEISMO-ACOUSTIC WAVES: PROPAGATION, ATTENUATION, AND INVERSE TECHNIQUES

537

Estimation of Subsurface Parameters in Lossy Media. • • • • • • • •• 547 P.M Carrion

Analysis of Ocean-Subbottom Seismograph (OSS) Data J.A. Carter, G.H. Sutton, A. Suteau-Henson,

and F.K. Duennebier

The Relative Amplitudes of Primary and Multiple Signals Refracted in the Ocean Crust. • •

A.B. Baggeroer, G.L. Duckworth, K.J. Ellefsen, and E.K. Scheer

553

565

The Propagation of Pn • • • • • • • • • • • • • • • • • • . •• 579 T. Sereno and J. Orcutt

Effects and Consequences of Transverse Isotropy in the Seafloor • •• ••••••••.

G.J. Fryer and D.J. Miller

Seismic Anisotropy in the Upper Crust at DSDP Site 504B • • • • • • • • •

R.A. Stephen

A Broad-Band Study of Attenuation in Ocean Bottom Sediments •.•••••••••••••.•

J.S. Barker and D.V. Helmberger

*On the Role of Bottom Interface Waves in Ocean Seismo-Acoustics: A Review •••••

D. Rauch

Observations on Interface Waves and Low-Frequency Acoustic Propagation Over a Rough Granite Seabed

P.R. Staal and D.M.F. Chapman

589

599

609

623

M3

A Comparison of Seismic and Hydroacoustic Measurements at Very Low Frequencies in Different Shallow Water Areas . . . . .

B. Schmalfeldt

Interface Wave Studies on the Ligurian Shelf using an OBS Array: Experimental Results and Propagation Models.

M. Snoek, G. Guidi, and E. Michelozzi

A Study of Sea Floor Structure Using Ocean Bottom Shots and Receivers ...

A.W. Sauter, L.M. Dorman, and A.E. Schreiner

Shear Properties of Ocean Sediments Determined from Numerical Modelling of Scholte Wave Data .................. .

F.B. Jensen and H. Schmidt

The Determination of Geoacoustic Models in Shallow Water . . . . . . . .

The

G.V. Frisk, J.F. Lynch, and J.A. Doutt

Estimation of the Density, P-Wave, and S-Wave Speeds of the Top-Most Layer of Sediments, from Water Bottom Reflection Arrivals . . . . .

R. Chapman, S. Levy, J. Cabrera, K. Stinson, and D. Oldenburg

Effects of Upper Crustal Geoacoustic Parameters on Low Frequency Sound.

0.1. Diachok, R.L. Dicus, and S.C. Wales

Evaluation of Experimental Techniques for Determining the Plane Wave Reflection Coefficient at the Sea Floor .....

H. Schmidt and F.B. Jensen

SEISMO-ACOUSTIC NOISE

A Study of Ocean and Seismic Noise at Infrasonic Frequencies . ........... .

A.C. Kibblewhite and K.C. Ewans

Geo-Acoustic Noise Levels in a Deep Ocean Borehole ...

F.K. Duennebier, R.K. Cessaro, and P. Anderson

Low Frequency Noise Fields and Signal Characteristics . . . . . . . .

W.M. Carey, R.A. Wagstaff, B. Brunson, and M. Bradley

Time Dependence of Infrasonic Ambient Seafloor Noise on a Continental Shelf ..

xiv

T. Akal, A. Barbagelata, G. Guidi, and M. Snoek

653

663

673

683

693

703

711

721

731

743

753

767

Infrasonic Attenuation and Ambient Noise. . . . • • • • . • . . . •. 779 R.H. Mellen and D.G. Browning

TECHNOLOGY AND NEW APPROACHES IN SEISMo-ACOUSTIC MEASUREMENTS

*Parametric Sources - Design Considerations in the Generation of Low-Frequency Signals .

H.O. Berktay

The Postcritical Penetration of Low Frequency Parametric Beams through a Water-Sediment Interface ..•..

D.J. Wingham and N.G. Pace

The Use of Low and High Frequency Intensity Fluctuations in Sea-Bed Surface Classification. . . .. . • . . .

M.K. Gurcan. D.J. Creasey. and B.K. Gazey

*Ocean Bottom Seismology: History and Current Status. . . . . . . . . • • . ...

G.H. Sutton

The Use of Love Waves to Determine the Geoacoustic Properties of Marine Sediments T. Aka 1 , H. Schmidt, and P. Curzi

Development of a Deep-Towed Seismic New Capability for Deep-Ocean Measurements ........ .

M.G. Fagot

System A Acoustic

Sea-Floor Seismology : Mobile Ocean Bottom Vertical Seismic Array (OBVSA) for Controlled Source Experiments . • • .

F. Avedik

A 12-Channel Marine Eel for Shallow Refraction Surveying of the Seabottom in Coastal Waters ..•.....•......•

A.G. McKay, J.A. Hunter, R.L. Good, and D.M.F. Chapman

Characterization of Average Geoacoustic Bottom Properties from Expected Propagation Behavior at Very Low Frequencies (VLF) Using a Towed Array Simulation. . • . .

M.F. Werby and G.J. Tango

Contributors ••

Author Index.

Subject Index

785

801

811

821

841

853

863

871

881

891

897

907

xv