The Sonar of Dolphins

287 Pages·1993·16.74 MB·English

by  Whitlow W. L. Au (auth.)

The Sonar of Dolphins
Springer
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Berlin
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Whitlow W.L. Au
The Sonar
of Dolphins
With 237 illustrations
Springer
Hawaii Institute of Marine Biology
University of Hawaii
P.O. Box 1106
Kailua, HI 96734 USA
Library of Congress Cataloging-in-Publication Data
Au, Whitlow, W.L.
The sonar of dolphins I Whitlow W.L. Au.
p. cm.
Includes bibliographical references and index.
ISBN-13:978-1-4612-8745-2
1. Dolphins-Physiology. 2. Sonar. 3. Echolocation-(Physiology)
I. Title.
QL737.C432A92 1993
599.5'3-dc20 92-22696
Printed on acid-free paper.
© 1993 Springer-Verlag New York, Inc.
Softcover reprint of the hardcover 1st edition 1993
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Production managed by Karen Phillips; manufacturing supervised by Vincent Scelta.
Typeset by Asco Trade Typesetting Ltd., Hong Kong.
9 8 7 6 5 4 3
ISBN -13: 978-1-4612-8745-2 e-ISBN -13 :978-1-4612-4356-4
DOl: 10.1007/978-1-4612-4356-4
I dedicate this book to my wife, Dorothy,
and my children: Wagner "Jim," Wailani,
Wesley and Wainani.
And God said, "Let the water teem with
living creatures, and let birds fly above the
earth across the expanse of the sky." So
God created the great creatures of the sea
and every living and moving thing with
which the water teem, according to their
kinds ... And God saw that it was good.
Genesis 1: 20-21
Preface
Over the ages, humans have always been fasci manner and to present a comprehensive and
nated by dolphins. This fascination heightened in organized treatise on the subject. In my opinion,
the 1950s when oceanariums and aquariums such an effort is long overdue, since there is a
began to use dolphins as show performers to paucity of books on this subject. I know of only
demonstrate their prowess and display how one booklet and one book dealing with echoloca
tractable and trainable they were. The televi tion in dolphins. I have attempted to introduce
sion series "Flipper" brought considerable public as many concepts from physics as possible
awareness and, coupled with the growing sophis and also to create mathematical models as an
tication and popularity of dolphin shows, helped aid to the quantification and understanding of
to further heighten public interest in these intri biosonar capabilities. Topics are covered which
guing marine mammals. Soon the alluring but range from auditory pathways and processes, to
unfounded myth began to surface that dolphins anatomy of the dolphin's head, to signal pro
are the smartest of animals, with an intelligence cessing models, to a comparison of the sonar of
approaching and perhaps surpassing that of bats and dolphins.
humans. The popularity of dolphins has grown Research on the sonar of dolphins has always
to the point where many feel that none of these involved scientists of diverse academic back
ever smiling and lovable animals should be kept ground, experience and expertise. I have col
in captivity but that they should all be released laborated with biologists, psychologists, physi
back into the ocean. Such sincere but misplaced ologists, physicists, electrical and mechanical
opinions threaten serious research on these ani engineers, veterinarians and a political scientist
mals. We have much to learn about dolphins in my research. The political scientist was Bill
and small whales, about their physiology, mor Powell, my first division head (later the head of
phology, psychology, and sensory capabilities my department and directorate). The interdisci
including their auditory and sonar capabilities. plinary nature of the field has made my work very
Certain facets of dolphin biology can only be interesting, informative, and enriching, but it did
studied with captive animals, and increased present a unique challenge in writing this book.
knowledge will improve our ability to manage It is my intention to present material that will be
and preserve wild dolphins. useful and informative to anyone interested in
This book is about the sonar of dolphins. My biosonar. This book is the result of many years
goal is to synthesize the many research findings of research on the sonar of dolphins as a civilian
and current pool of knowledge on the auditory scientist at the Naval Command Control and
and sonar capabilities of dolphins in a cohesive Ocean Surveillance Center (NCCOS) [formerly
vii
viii Preface
the Naval Ocean Systems Center] located on assistance of John Tokunaga, an excellent and
Kaneohe Bay, Oahu, Hawaii. Most of the dol dedicated electronics technician. Finally, my var
phin sonar and auditory research in the United ious supervisors through the years, Mr. Richard
States has had some affiliation with the U.s. Soule, Dr. James Fish, Dr. Michael Stallard, and
Navy. An interesting book on the history of the Dr. Paul Nachtigall, have all been extremely
Navy's role in dolphin research was written by supportive and cooperative in allowing me to
Forrest Wood in 1973 under the title Marine pursue various avenues of research I considered
Mammals and Man: The Navy's Porpoises and important. Last but not least, I am very grateful
Sea Lions, published by Robert Luce Inc. to my wife Dorothy who has been extremely
I am indebted to many collaborators who supportive of my career.
have provided valuable assistance in my re I wish to acknowledge Mr. William Friedl, Mr.
search. These include animal behavioral scien Robert Floyd, and Dr. Paul Nachtigall (all of
tists Deborah and Jeffery Pawloski, Patrick NCCOS) who reviewed the original manuscript
Moore, Ralph Penner, and Wayne Turl. Com and provided many helpful suggestions and com
puter systems analyst Perry Keaney provided ments. Special thanks are extended to Dr. Arthur
valuable assistance in configuring the software Popper, Chairman of the Zoology Department,
used for much of my backscatter work. I have University of Maryland, for his helpful sugges
.s pent many hours discussing various aspects of tions and comments and for his role in having
sonar signal processing with Robert Floyd. I .my book published by Springer-Verlag New
have often used Bob as a sounding board, and York.
our many discussions have enhanced and solidi
fied my understanding of the subject. I would Whitlow W.L. Au
have been lost many times without the valuable Kailua, Hawaii, 1992
Contents
Preface vii
Chapter 1 Introduction ................................................... 1
1.1 Historical Perspective ................................................. 1
1.2 Some Underwater Acoustics. . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3 The Time and Frequency Domains ...................................... 11
1.4 Experimental Psychological Methodology ................................ 13
1.5 Signal Detection Theory ............................................... 17
Chapter 2 The Receiving System .......................................... 22
2.1 The Outer Ears ....................................................... 22
2.2 The Middle Ear ...................................................... 26
2.3 The Inner Ear ........................................................ 28
2.4 Summary ............................................................ 30
Chapter 3 Characteristics of the Receiving System for Simple Signals ......... 32
3.1 Hearing Sensitivity .................................................... 32
3.2 Spectral Analysis Sensitivity ............................................ 36
3.3 Directional Hearing ................................................... 41
3.4 Response Bias and Sensitivity in Hearing ................................ 52
3.5 Summary ............................................................ 53
Appendix: Derivation of the Receiving Directivity Index ....................... 54
Chapter 4 Characteristics of the Receiving System for Complex Signals ....... 59
4.1 Perception of Click Signals ............................................. 60
4.2 Perception of Time Separation Pitch .................................... 70
4.3 Summary ............................................................ 74
ix
x Contents
n
Chapter 5 The Sonar Signal Transmission System
5.1 Preliminary Examination of Biosonar Signals ............................. 77
5.2 Sound Production Mechanism. . .. . . . . . . . . .. . . . . . . .... . . .. .. . . .. .. . . .. . . 81
5.3 Acoustic Propagation in the Dolphin's Head ............................. 87
5.4 Summary ............................................................ 94
Chapter 6 Characteristics of the Transmission System ...................... 98
6.1 The Concept of Near and Far Acoustic Fields ............................ 98
6.2 The Dolphin Near- to Far-Field Transition Region ........................ 1oo
6.3 The Acoustic Field on a Dolphin's Head ................................. 101
6.4 Directional Pattern of Biosonar Signals .................................. 104
6.5 Equivalent Planar Circular Aperture .................................... 109
6.6 Summary ............................................................ 113
Chapter 7 Characteristics of Dolphin Sonar Signals ......................... 115
7.1 Click Intervals ........................................................ 115
7.2 Frequency Characteristics .............................................. 118
7.3 Click Source Levels ................................................... 124
7.4 Number of Clicks and Response Latencies ............................... 130
7.5 Signals from Other Species ............................................. 133
7.6 Summary ............................................................ 137
Chapter 8 Target Detection Capability of the Active Sonar System ............ 140
8.1 The Physics of Acoustic Reflection by Targets ............................ 140
8.2 Noise-Limited Form of the Sonar Equation .............................. 143
8.3 Biosonar Detection Capabilities ........................................ 145
8.4 Detection of Complex Echoes .......................................... 157
8.5 Comparison Between a Dolphin and an Ideal Receiver ..................... 162
8.6 Target Detection in Reverberation ...................................... 166
8.7 Summary ............................................................ 174
1n
Chapter 9 Blosonar Discrimination, Recognition, and Classification ...........
9.1 Mathematical Tools for the Analysis of Target Echoes ..................... 178
9.2 Target Size Discrimination ............................................. 179
9.3 Target Structure Discrimination ........................................ 181
9.4 Target Shape Discrimination ........................................... 201
9.5 Delayed Matching to Sample ...... :.................................... 204
9.6 Target Range Difference Discrimination ................................. 205
9.7 Insights from Human Listening Experiments ............................. 208
9.8 Summary ............................................................ 213
Chapter 10 Signal Processing and Signal Processing Models ................ 216
10.1 Analysis of Dolphin Sonar Signals ..................................... 216