Developments and Applications of Modern Airborne Electromagnetic Surveys US Geological ...

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Developments and Applications of
Modern Airborne Electromagnetic Surveys
U.S. Geological Survey Bulletin 1925
Front Cover: Past and present U.S. Geological Survey aircraft
used for geophysical surveys are depicted flying over terrain
typical of the foothills west of Denver, Colorado. The aircraft,
in order of age (from left to right), are Beech Model 17,
Staggerwing; Douglas DC-3; Convair CV-240; and Fairchild
Porter PC 6/C-H2.
Cover design by Art Isom, U.S. Geological Survey.
Developments and Applications of
Modern Airborne Electromagnetic Surveys
Edited by DAVID V. FITIERMAN
Proceedings of the U.S. Geological Survey Workshop on
Developments and Applications of Modern Airborne
Electromagnetic Surveys, October 7-9, 1987
U.S. GEOLOGICAL SURVEY BULLETIN 1925

DEDICATION
Frank C. Frischknecht, a geophysicist with the U.S. used for geologic mapping. He oversaw initial develop
Geological Survey and a pioneer in the field of airborne ment and construction of the first airborne power-line
geophysics, was killed August 12, 1987, in a helicopter receiver, which has since been successfully used to pro
plane collision near Ketchikan, Alaska. duce resi.stivity maps with greater depth of exploration
Frank was born in Bicknell, Utah. He received a that is possible with VLF systems. At the time of his
Bachelor of Science degree in Electrical Engineering death, Frank had completed and was working on
(1950) and a Master of Science degree in Geophysics chapters on electromagnetic scale modeling, profiling
(1953) from the University of Utah. He continued his techniques, VLF, and electromagnetic sounding for the
education at the University of Colorado, earning a Society of Exploration Geophysicists two-volume series
second Master of Science degree in Geophysical Mathe "Electromagnetic Methods in Applied Geophysics."
matics (1967) and a Doctor of Philosophy (1973) in Frank served as the Chief of the Branch of
Electrical Engineering Physics. Electromagnetism and Geomagnetism (1976-1980) and
Frank's professional career with the U.S. Geologi the Branch of Geophysics (1984-1986), during which
cal Survey spanned more than 35 years, beginning in time he directed expansion of the electromagnetics
1952 with work on airborne geophysical instrumentation, program and oversaw the modernization of the geomag
data compilation, and interpretation problems. From netic observatories. Between his tours as Branch Chief he
1955 to 1962, he developed a variety of controlled- and pioneered in the application of traditional geophysical
natural-source electromagnetic techniques that were techniques to the many environmental problems asso
applied to numerous geological problems. In 1962, the ciated with locating contamination from land fills and
U.S. Geological Survey acquired a Convair 240 aircraft injection wells and mapping abandoned wells. With the
and Frank became involved in developing, acquiring, and Survey's increased involvement in environmental prob
testing geophysical instrumentation for airborne surveys. lems, he realized the need for and potential scientific
Of particular interest to him were a new INPUT crippling power of quality assurance programs. He
electromagnetic system and an automated magnetome played a key role in developing an approach to quality
ter system. assurance for the Survey that would be scientifically
His accumulated experience resulted in the now acceptable while meeting regulatory requirements.
classic textbook "Electrical Methods in Geophysical Recognized internationally as an authority in geo
Prospecting," published in 1966 in collaboration with physics, Frank lectured and conducted field studies in
George V. Keller. In 1967, Frank published the first many countries. He was active in the Society of Explora
computer-generated, layered-earth theoretical electro tion Geophysicists, serving on several committees and
magnetic sounding curves that became the basis for most as an Associate Editor of Geophysics. In recognition of
early airborne electromagnetic interpretational methods. Frank's scientific achievements he served on the Geo
During this same period, Frank also developed a scale logic Division Scientific Advisory Committee and
model electromagnetic test facility that provided data received both the Department of the Interior's Meritor
crucial to understanding field observations and testing ious Service and Distinguished Service Awards.
interpretational methods. His model results are inter For all of his professional accomplishments, Frank
nationally recognized as standards against which numer was a very unassuming person who derived great plea
ical results are checked. He developed an airborne very sure from music, ballet, art, hiking, and photography.
low frequency (VLF) receiver incorporating an electric With a great sense of loss and admiration, this volume is
field reference that enabled it to produce resistivity maps dedicated to him.
DEPARTMENT OF THE INTERIOR
MANUEL LUJAN, JR., Secretary
U.S. GEOLOGICAL SURVEY
Dallas L. Peck, Director
Any use of trade, product, or firm names in this publication is for descriptive
purposes only and does not imply endorsement by the U.S. Government.
UNITED STATES GOVERNMENT PRINTING OFFICE: 1990
For sale by the
Books and Open-File Reports Section
U.S. Geological Survey
Federal Center
Box 25425
Denver, CO 80225
Library of Congress Cataloging-in-Publication Data
U.S. Geological Survey Workshop on Developments and Applications of
Modern Airborne Electromagnetic Surveys (1987: Golden, Colo.)
Developments and applications of modern airborne electromagnetic
surveys : proceedings of the U.S. Geological Survey Workshop on
Developments and Applications of Modern Airborne Electromagnetic
Surveys, October 7-9, 1987 I edited by David V. Fitterman.
p. cm.-(U.S. Geological Survey bulletin ; 1925)
Includes bibliographical references.
Supt. of Docs. no.: I 19.3:1925
1. Geomagnetism-Congresses. I. Fitterman, David V. II. Title.
Ill. Title: Airborne electromagnetic surveys. IV. Series.
QE75.B9 no. 1925
[OC811]
557.3 s-dc20 90-3332
[538' .7] CIP
CONTENTS
Introduction, by David V. Fitterman 1
SECTION 1: BACKGROUND AND HISTORY
National airborne geophysics program, by Thomas G. Hildenbrand,
Gary L. Raines, and David V. Fitterman 3
Historical aspects of airborne electromagnetic development,
by Anthony R. Barringer 7
Airborne electromagnetics 1978-1988, by A. Becker, A.R. Barringer, and
A.P. Annan 9
SECTION 2: INTERPRETATION AND MODELING
Synthetic modeling and airborne electromagnetic interpretation,
by Melvyn E. Best 21
Layered-earth resistivity mapping, by Douglas C. Fraser 33
Applications of a new three-dimensional modeling program to airborne
electromagnetic exploration, by Gerald W. Hohmann 43
Electromagnetic anomaly recognition within geological and cultural noise,
by Douglas C. Fraser 53
Theory of the modified image method for airborne electromagnetic data,
by Clyde J. Bergeron, Jr., Juliette W. Ioup, and Gus A. Michel, II 65
Interpretation of airborne electromagnetic data using the modified image
method, by Juliette W. Ioup, Clyde J. Bergeron, Jr., and
Gus A. Michel, II 75
A novel approach to airborne electromagnetic data compilation,
by C. Vaughan 81
SECTION 3: RESOURCE AND GEOLOGICAL APPLICATIONS
Airborne electromagnetics, geological mapping, and prospecting for
nontraditional targets, by G.J. Palacky 89
Estimation of overburden thickness using helicopter electromagnetic data,
by R.L.S. Hogg and G .A. Boustead 103
Application of airborne very low frequency electromagnetic surveys in
geophysical exploration, by Ajit K. Sinha 117
Development of airborne very low frequency electromagnetic techniques at
the Geological Survey of Finland, by Ari Poikonen 133
SECTION 4: ENVIRONMENTAL AND RELATED APPLICATIONS
Rapid reconnaissance mapping of freshwater lenses on small oceanic islands,
by Mark Stewart 139
Theoretical and practical aspects of ground-water exploration using airborne
electromagnetic techniques, by Klaus-Peter Sengpiel 149
Airborne electromagnetic bathymetry, by I.J. Won and K. Smits 155
Airborne electromagnetic measurement of sea ice thickness and sub-ice
bathymetry, by Austin Kovacs and Nicholas C. Valleau 165
Airborne radar sounding in temperate and polar ice, by David L. Wright,
Steven M. Hodge, and Raymond D. Watts 171
Contents V
SECTION 5: RECENT HARDWARE DEVELOPMENTS
Examples of two modern, integrated airborne geophysical systems,
by T. R. Bodger 181
Airborne electromagnetic mapping using powerline fields,
by Victor F. Labson 189
Mini remotely piloted vehicle systems in mineral exploration, earth sciences,
and environmental studies, by H. Zafrir, G. Steinitz, and M. Granot 193
APPENDIX-WORKING GROUP REPORTS, PANEL DISCUSSION, AND
NAMES AND ADDRESSES OF PARTICIPANTS 197
VI Contents
Introduction
By David V. Fitterman1
This publication serves as a written record of the applications, and the section on environmental and re
U.S. Geological Survey-sponsored workshop on Devel lated applications documents some of the more recent
opments and Applications of Modern Airborne Elec uses of AEM methods for ground -water exploration,
tromagnetic Surveys held October 7-9, 1987, in bathymetry, and ice-thickness determination.
Golden, Colorado. The workshop was one of a series The section on recent hardware developments
sponsored by the U.S. Geological Survey to foster in contains papers describing commercially available air
terest in a national airborne geophysical program. At borne geophysical systems, a powerline-energized map
tendees were invited from domestic and foreign gov ping system being developed by the U.S. Geological
ernment organizations, industry, and academia; more Survey, and a remotely piloted aircraft capable of being
than 60 scientists from 7 countries participated. The used as a geophysical platform.
meeting consisted of technical presentations detailing The appendix contains written reports of the five
the history and state of the art of airborne electromag working groups. The working groups were made up of
netics (AEM), working group discussions on various workshop participants who discussed assigned topics in
aspects of data collection, interpretation, and applica an attempt to reach a consensus on the state of current
tions, and a panel discussion to summarize the conclu technology, suggest areas for further research and new
sions drawn from the meeting. applications, and propose recommendations for a na
In this bulletin are papers from the technical pre tional airborne geophysical program. An edited tran
sentations, written summaries of the working group script of the panel discussion, the purpose of which was
recommendations, and a transcript of the panel discus to assess the conclusions of the working groups, is also
sion. The papers are grouped in five sections. The first included.
section, background and history, describes the involve The workshop was very successful in achieving its
ment of the U.S. Geological Survey in airborne geo goal of bringing together active researchers in the area
physical methods in the past and our plans for the fu of airborne electromagnetics to assess the status of
ture. Also included are two papers describing the his modern AEM technology and propose areas for future
tory of early AEM developments and advances during research. The key next step of acting on these recom
the past decade. These papers set the stage for reports mendations to produce and utilize AEM systems that
about current technology. The section on interpretation are able to answer the many geological, resource,
and modeling contains papers on theoretical and real ground-water, and environmental problems we face to
world studies that show the types of interpretational day rests with the U.S. Geological Survey, its foreign
products being developed today, and consider the geo counterparts, industry, and academia. With hard work,
logic models that play havoc with layered-earth inter perseverance, and funding, we will achieve this goal.
pretations. As computational methods are being devel Acknowledgments.-Until the time of his death,
oped to handle complicated geometries, further work the workshop organizing committee was headed by
and advances in computer technology are needed be Frank Frischknecht; his efforts in formulating and or
fore these models can be used on a routine basis. ganizing the workshop contributed to its success. Don
The next two sections report on the application Hoover, Bruce Smith, Dal Stanley, and I served on the
of several AEM methods to a diverse spectrum of committee, saw that the workshop ran smoothly, and
problems. The section on resource and geological ap helped review the workshop articles. Special thanks go
plications contains papers on geological and exploration to the authors whose articles and working group re
ports are contained in this volume. The work of Mary
Ignelzi, Pamela Ketterer, and Leona Treloar with work
Manuscript approved for publication, February 19, 1990. shop registration, working group report typing, and
lU .S. Geological Survey, Box 25046, MS964, Denver, Colorado
preparation of the manuscripts is greatly appreciated.
80225.
Introduction