elf/vlf phased array generation via frequency-matched steering of a

228 Pages·2009·6.92 MB·English

ELF/VLF PHASED ARRAY GENERATION VIA
FREQUENCY-MATCHED STEERING OF A CONTINUOUS HF
IONOSPHERIC HEATING BEAM
A DISSERTATION
SUBMITTED TO THE DEPARTMENT OF
ELECTRICAL ENGINEERING
AND THE COMMITTEE ON GRADUATE STUDIES
OF STANFORD UNIVERSITY
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
Morris Bernard Cohen
October 2009
(cid:13)c Copyright by Morris Bernard Cohen 2010
All Rights Reserved
ii
I certify that I have read this dissertation and that, in my opinion, it
is fully adequate in scope and quality as a dissertation for the degree
of Doctor of Philosophy.
(Umran S. Inan) Principal Adviser
I certify that I have read this dissertation and that, in my opinion, it
is fully adequate in scope and quality as a dissertation for the degree
of Doctor of Philosophy.
(Timothy F. Bell)
I certify that I have read this dissertation and that, in my opinion, it
is fully adequate in scope and quality as a dissertation for the degree
of Doctor of Philosophy.
(Butrus T. Khuri-Yakub)
Approved for the University Committee on Graduate Studies.
iii
.
To life, to life, l’chaim!
L’chaim, l’chaim, to life!
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Abstract
The radio spectrum between 300 Hz and 10 kHz (ELF/VLF) has broad applications
to global communication, remote sensing of the ionosphere and magnetosphere, and
subterranean prospecting. While lightning is a dominant source of these radio waves,
artificial generation of these waves has posed an enduring challenge to scientists and
engineers, due to the extremely long wavelengths (30-1000 km) and the lossiness of
the Earth’s surface at these frequencies.
Recently, ELF/VLF waves have been successfully generated by high frequency
(HF, 3-10 MHz) heating of the lower ionosphere (60-100 km altitude), which changes
the atmospheric plasma conductivity. In the presence of natural currents such as the
auroral electrojet, ON-OFF modulation of this HF energy can impose an ELF/VLF
alternating current onto those natural currents. This technique turns the lower
atmosphere into a large antenna, which radiates energy downward into the Earth-
ionosphere waveguide and upward into the magnetosphere.
While this technique remains one of the few means of reliable ELF/VLF wave
generation, HFtoELF/VLFconversionefficienciesremainquitelow. Utilizingthe3.6
MW HAARP HF heating facility in Alaska, we show that proper utilization of motion
oftheHFbeamcanboostthegeneratedELF/VLFwavepowerbyasmuchastenfold.
Furthermore, as a result of having effectively created the world’s first controllable
large-element ELF/VLF phased array, directional launching of this energy becomes
possible. We utilize theoretical models of the HF heating and cooling process, and of
ELF/VLF wave propagation, to illuminate the observations and identify the physical
mechanisms underlying the wave generation, particularly as it relates to motion of
the HF beam.
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Acknowledgements
I begin with a slightly paraphrased quote from the ancient Jewish law book Talmud,
Pirkei Avot, Chapter 3, attributed to Rabbi Yochanan Ben Zakai.
If you have learned much (scholarly wisdom), do not take credit for your-
self; it is for this reason that you have been formed.
Indeed, it may be my name printed on the front of this thesis, but really none of
it would have happened without the support of a lot of other people.
First and foremost, I’ve been blessed with a fantastic family. My parents have
truly been role models to me for my entire life. I say with no qualification that I have
the best parents I possibly could have. My brothers, Sam and Dave, have always
been terrific and very supportive, and I’m delighted that both of them have grown
the family, with my sisters-in-law Fern and Audria, and their children Josh, Ian,
Rachel, and Ethan.
I thank my teachers and friends from Beth Tfiloh School in Pikesville, Maryland,
where a great general education was complemented with a firm grounding in Jew-
ish teachings that I still proudly carry. I thank all my friends from my Stanford
undergraduate years, who made my early years on ‘The Farm’ a great experience.
I owe another thanks to all the VLF group members with whom I’ve interacted.
Marek Go(cid:32)lkowski has been a very able collaborator in planning so many HAARP
experiments (and absurd arctic adventures), and a reliable scientific counsel. Denys
Piddyachiy and George Jin were extensive contributors to the late night chat room
watches during campaigns. Robb Moore, Joe Payne, and Nikolai Lehtinen paved
the way for this thesis with excellent earlier work. Tim Bell provided some valuable
counsel with this dissertation.
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Justin Tan and Eddie Kim were critical in developing the ‘AWESOME’ receiver
with me, which has by now gotten so much use worldwide, and serves as the primary
source of data for this thesis. Ev Paschal, with his decades of experience in hardware
design, was a treasure trove of information on VLF receivers and field installation.
Although not part of this dissertation effort, for the exciting ‘AWESOME’ Inter-
national Heliophycial Year (IHY) global distribution program, I worked extensively
with Sheila Bijoor, Ben Cotts, and Naoshin Haque. Debbie and Phil Scherrer were
instrumental in the program’s development. I thank all our AWESOME collaborators
and site hosts around the world for their friendship.
Many other VLF members have been colleagues and friends. I’ve learned a lot
from Ryan Said, Prajwal Kulkarni, Jeff Chang, Charles Wang, Mark Daniel, Brant
Carlson, Bob Marshall, Dan Golden, Nader Moussa, Kevin Graf, Robert Newsome,
Max Klein, and others.
I thank Shaolan Min and Helen Niu for keeping so much important VLF group
business running smoothly, and Dan Musetescu for managing so much data and keep-
ing it all organized.
The operation of the HAARP facility has been possible thanks in part to the hard
work of Mike McCarrick, Helio Zwi, and David Seafolk-Kopp. I would like to thank
DoyleandNormaTraw, ofChistochinaBedandBreakfast, inAlaska, forhelpingwith
receiver maintenance and always being great hosts during my various trips there.
The experience working with my advisor, Umran Inan, has been terrific, as from
it I have learned so much. The journey has been long since I took on my first
VLF project (rather unrelated to this thesis) as a college junior, but through several
differentwidelydisparateprojectsIwasnevershortofopportunitiestogrow, develop,
and pursue new ideas. For that reason my time in this research group has never felt
static at all. Thanks for giving me the chance.
This work has been supported by the Defense Advanced Research Projects Agency
and the Air Force Research Laboratory under Office of Naval Research (ONR) grants
N00014-09-1 and N00014-06-1-1036 to Stanford University.
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Contents
Abstract v
Acknowledgements vi
1 Introduction 1
1.1 The ionosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Magnetosphere-ionosphere coupling . . . . . . . . . . . . . . . . . . . 4
1.3 ELF and VLF waves . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.4 ELF/VLF wave generation . . . . . . . . . . . . . . . . . . . . . . . . 9
1.5 Some history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.6 Review of past work . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
1.6.1 Local geomagnetic conditions . . . . . . . . . . . . . . . . . . 19
1.6.2 Earth-ionosphere waveguide injection . . . . . . . . . . . . . . 20
1.6.3 Harmonic radiation and saturation . . . . . . . . . . . . . . . 21
1.6.4 Magnetospheric injection . . . . . . . . . . . . . . . . . . . . . 22
1.6.5 Mobile heated region . . . . . . . . . . . . . . . . . . . . . . . 23
1.6.6 Beam painting . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
1.6.7 Alternative methods . . . . . . . . . . . . . . . . . . . . . . . 24
1.6.8 Ionospheric array . . . . . . . . . . . . . . . . . . . . . . . . . 25
1.7 Scientific contributions . . . . . . . . . . . . . . . . . . . . . . . . . . 26
1.8 Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2 ELF/VLF Generation and Propagation Physics 28
2.1 Waves in plasmas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
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2.1.1 Plasma properties . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.1.2 Magnetic field and the whistler wave . . . . . . . . . . . . . . 30
2.1.3 Anisotropy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
2.1.4 Collisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
2.1.5 The D-region . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2.2 HF heating theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
2.2.1 Electron temperature . . . . . . . . . . . . . . . . . . . . . . . 39
2.2.2 Modified ionosphere . . . . . . . . . . . . . . . . . . . . . . . 41
2.2.3 HF wave propagation . . . . . . . . . . . . . . . . . . . . . . . 44
2.3 Model construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
2.3.1 Energy balance at one altitude . . . . . . . . . . . . . . . . . . 45
2.3.2 Vertical structure . . . . . . . . . . . . . . . . . . . . . . . . . 50
2.3.3 Extension to 3D . . . . . . . . . . . . . . . . . . . . . . . . . . 57
2.4 The Earth-ionosphere waveguide . . . . . . . . . . . . . . . . . . . . . 65
2.4.1 Reflection coefficients . . . . . . . . . . . . . . . . . . . . . . . 68
2.4.2 Modal solutions . . . . . . . . . . . . . . . . . . . . . . . . . . 70
2.4.3 Propagation model . . . . . . . . . . . . . . . . . . . . . . . . 70
2.5 Model results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
3 HF Beam Motion: Experiments 79
3.1 ELF/VLF generation and beam motion . . . . . . . . . . . . . . . . . 80
3.2 Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
3.3 Experimental setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
3.4 Comparative frequency response . . . . . . . . . . . . . . . . . . . . . 90
3.4.1 Generated amplitudes from beam painting . . . . . . . . . . . 91
3.4.2 Directionality from beam painting . . . . . . . . . . . . . . . . 93
3.4.3 Generated amplitudes from geometric modulation . . . . . . . 94
3.4.4 Directionality from geometric modulation . . . . . . . . . . . . 95
3.4.5 Geometric modulation compared to oblique-AM . . . . . . . . 95
3.4.6 Summary of ground-based observations . . . . . . . . . . . . . 97
3.4.7 Magnetospheric injection . . . . . . . . . . . . . . . . . . . . . 99
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4 HF Beam Motion: Modeling 100
4.1 Modulated currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
4.2 Fields on the ground . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
4.3 Magnetospheric injection . . . . . . . . . . . . . . . . . . . . . . . . . 112
4.4 Directional pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
5 Physical Mechanisms 120
5.1 Heat-cool duty cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
5.2 Phasing from oblique heating . . . . . . . . . . . . . . . . . . . . . . 127
5.3 HF pulsing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
5.4 ELF/VLF phased array control . . . . . . . . . . . . . . . . . . . . . 136
5.5 Phased array parameters . . . . . . . . . . . . . . . . . . . . . . . . . 140
5.6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
6 Summary and Suggestions for Future Work 144
6.1 Future work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
6.1.1 Equatorial electrojet . . . . . . . . . . . . . . . . . . . . . . . 146
6.1.2 Intersweep delay times . . . . . . . . . . . . . . . . . . . . . . 146
6.1.3 HF heating model with lookup table . . . . . . . . . . . . . . 146
6.1.4 Parallel conductivity changes . . . . . . . . . . . . . . . . . . 147
6.1.5 Directional pattern . . . . . . . . . . . . . . . . . . . . . . . . 147
6.1.6 Beam painting diurnal variations . . . . . . . . . . . . . . . . 148
6.1.7 Variation with HF frequency . . . . . . . . . . . . . . . . . . . 148
6.2 Concluding remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
A Long Distance Reception 149
B HAARP HF Radiation Pattern 152
C ELF/VLF Reception and Detection 155
C.1 Antenna characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . 156
C.2 System design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
C.3 Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
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