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*
*
*
U IN
*
TESTING
THE
PROGRAM
*
*
THE
BEST WAY
TO TEST
THE
PROGRAM
IS TO GENERATE A SYNTHETIC
INPUT ARRAY
OF
OATA POINTS CONTAINING
SIGNALS AT KNOWN
FREQUENCIES,
AND
PROCESS THEM
AND CHECK THAT THE
RESULTING
SPECTRUM
IS CORRECT.
TO GENERATE A
SIGNAL
ARRAY WHICH CONTAINS A
SIGNAL AT A FREQUENCY Q*DF
USE
THE
FOLLOWING CODE
BEFORE
THE
BIT-REVERSAL
ROUTINE:
2000
Q
-
...
2010
DP
-
P I 2*Q/NX
2020
FOR
I
- 0 TO
NXM1
2030
X<
I
>
S I N ( DP* I
>
2040
NEXT
I
'FREQUENCY
IN
UNITS OF
DF
PHASE
INCREMENT PER
SAMPLE
'DATA GENERATION
LOOP
•CALCULATE A DATA POINT
’END
OF
LOOP
jQ
IS A REAL
NUMBER,
AND
SHOULD
BE CHOSEN
SO THAT 0
<-
Q O
NX/2.
NOTE
( THAT THE ARRAY
X WILL CONTAIN
Q CYCLES
OF
A SINEWAVE
SIGNAL.
; AFTER PROCESSING,
THE
SPECTRUM SHOULD CONTAIN ONLY COMPONENTS
NEAR
THE
: FREQUENCY Q*DF
.
THAT
IS,
SPECTRAL
LINES
X(j)
SHOULD
BE
SMALL
EXCEPT FOR
( J
NEAR
Q.
IF
Q
IS AN
INTEGER,
THE
SPECTRAL
LINE
X(Q)
SHOULD
BE
1 AND
: ALL
THE OTHERS
SHOULD
BE 0
(OR
OF
ORDER
IE-6,
DEPENDING
ON
THE
ROUND-OFF
? ERRORS
IN THE
PROCESSING).
USING
NON-INTEGER VALUES
OF
Q WILL
RESULT
IN
lA SPECTRUM WITH A CLUSTER
OF
RESPONSES
NEAR
X<INT<Q>>
BUT LINES
FAR AWAY
l FROM
Q SHOULD
BE
SMALL.
THE
FALLOFF
IN
RESPONSE
IN
THE
SPECTRUM AS
ONE
(MOVES AWAY
FROM THE
LINE
X(INT(Q>)
DEPENDS
ON
THE
EFFECTIVENESS
OF
THE
(WINDOW FUNCTION, AND
THE
SHAPE
OF
THE
SYNTHESIZED
FILTER RESPONSE
CAN
BE
(PLOTTED
BY USING VARIOUS VALUES
OF
Q.
(NOTE
THAT
IF
NMAX
<
Q <
NX/2,
THE
SIGNAL GENERATED
LIES
IN
THE
UPPER
(PART OF
THE
SPECTRUM,
WHICH
IS THROWN AWAY
(DON’T EXAMINE
SPECTRAL
LINES
(X(j) WHERE
j
>
NMAX,
AS THEY HAVEN'T
BEEN CALCULATED).
ALSO,
IF
( NX/2
<
Q
<
NX,
THE
SIGNAL WILL
BE ALIASED
IN
THE
SPECTRUM,
APPEARING AT
(A FREQUENCY
OF
NX/2-Q.
t
j ************************************************************************
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UNCLASSIFIED
Appendix
B
ULF TREE POTENTIALS AND GEOMAGNETIC PULSATIONS
(U)
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Appendix
B
CPYRGHT
ULF TREE POTENTIALS AND GEOMAGNETIC PULSATIONS
High-sensitivity
measurements
of
ultra-low-frequency
(ULF;
frequencies
less than
5 Hz) geomagnetic pulsations
usually
require
elaborate
receiving
antennas ranging from
large air-cored
coils
2 through multi-turn
steel, or mumetal-
cored solenoids*"* to small superconducting loops immersed
in liquid helium*.
Pairs of electrodes inserted in the ground
have
also
been
used
as antennas
7,1
. The
need
for
a
large
spacing between
the
electrodes (varying from hundreds
to
thousands
of
metres) and
the
difficulty
of
calibrating
the
measurements absolutely have resulted in the almost univer-
sal
use
of the more compact and
easily calibrated
coil-type
antennas
in recent years.
I
describe here
a new method for
measuring ULF
geomagnetic
pulsations,
which
requires
a
minimum of elaborate equipment. The method
is based on
the use of trees, or, more specifically, on the use of pairs of
electrodes inserted into trees, as ULF receiving antennas.
There
are
several
reasons
that
this
new
method
of
measurement may
be of
interest. The equipment
is simple
and thus the method could lead to more widespread observa-
tions
of
ULF
geomagnetic
pulsation
phenomena.
The
method
of
measurement
also
provides
new
information
about
tree
potentials,
that
is,
it
shows
that
some,
and
perhaps
all, of the ULF components of these .potentials are
induced
by ULF geomagnetic
field fluctuations and do not
originate
in
the
trees themselves.
Finally, although
it
is not
clear at present what effect induced ULF electric fields may
have on the growth and other
vital processes
in a
tree, the
link
between
these ULF
electric
fields
and
geomagnetic
field
fluctuations
suggests
that
some
environment-related
changes
in
trees
could
also
be
influenced
by
changes
in
geomagnetic
activity.
These
changes may
have
a
natural
origin
(for example,
the changes
that occur during
a
solar
cycle") or they may be caused by a variety of human
activi-
ties
(by modern
d.c.-powered
mass
transit
systems,
which
can produce
large amplitude ULF electromagnetic
fields
).
The ULF measurements
reported
here
were
stimulated
by
the work
of Burr on
relatively
steady-state
tree
poten-
tials'
.
Burr
recorded
these
potentials
for
more
than
a
decade
using
a
pair
of
specially-designed
non-polarisable
electrodes
inserted
in
the cambium
of an
unspecified
tree
(which was probably a maple). The electrodes were about
a
metre
apart
along
the
long
axis
of
the
tree
and
Burr
observed diurnal,
27-d, and seasonal variations, as well as a
suggestion
of
a
correlation
with
sunspot
activity,
in
their
potential difference.
Most
of
Burr's
observations
were
at
frequencies
far
below the frequency range for ULF geomagnetic pulsations.
One
series of measurement
obtained,
however,
during an
electrical
storm
suggested
that
ULF
variations
of
tree
potentials
might
occur
on
occasion.
I
therefore
began
a
search
for variations with frequencies predominantly
in the
Pc
geomagnetic
pulsation
range
(0.2-5 Hz).
These
frequencies correspond
approximately
to
the
delta regime
for human brain waves.
The measurements were made
using
a
large
native oak,
Quercus
lobata,
that was
located
near
conventional ULF
recording equipment
at
a
site on
the Stanford
University
campus. This
latter equipment uses 20,000 turn
steel-cored
solenoids
as ULF
antennas and
it
operated
continuously
throughout the interval during which the tree measurements
were made. Thus, simultaneous measurements of ULF geo-
magnetic pulsations using both conventional loop antennas
and a tree ‘antenna’ were obtained at the one location.
Two steel nails were used as electrodes. Following Burr’s
configuration, they were inserted about 0.05 m into the tree
along
the
long
axis,
with
a spacing of 0.76 m. The lower
electrode was approximately
1 m above the ground, and the
two electrodes faced toward the geomagnetic west. Because
the tree was not completely vertical, a
line joining the two
electrodes
would
have
been
inclined
approximately
20°
toward the geomagnetic east. The diameter of the tree mid-
way between the two electrodes was 0.65 m.
A resistance of about 5 k£l was typically observed between
the electrodes, increasing to about 10k$2
if polarisation was
allowed
to
occur. A
d.c.
potential
difference
was
also
observed
that
varied from day
to day
but whose
absolute
value was usually in the range 10 to 100 mV, with the upper
electrode
positive. The electrodes were connected to a low-
frequency
high-gain
amplifier
through
an RC
filter (R=
22 Mfl, C=50/xF). The amplifier was usually
set
for 50 db
gain, and
its output was
filtered
(0.02-7 Hz)
before
being
recorded,
generally
without
additional
amplification,
on
a
chart
record and on analog magnetic
tape.
The
ULF
signals
measured
by
this
system
were
undoubtedly induced
in
the
tree
‘antenna’ and not
in
the
shielded
cabling between
the
electrodes and
the
recording
system:
when
the
electrodes
were
disconnected
from
the
tree and connected
to an equivalent
5 k£1
resistor, without
any
other
change
in
the
wiring
or
configuration
of
the
system, only a steady low level of white noise (typical resistor
thermal noise) was observed.
Similarities between
the ULF
signals
recorded
conven-
tionally
and
with
the
tree
‘antenna’
were
immediately
apparent on
the chart
records. More detailed
analysis con-
firmed
that
Pc
pulsation
events
recorded
by
the
two
systems
were
very
nearly
identical
in
all
their
important
Reprintedfrom Nature, Vol 271 , No, 5646, pp. 641-642, February 16, 1978
)
C Macmillan Joumats Ltd„ 1978
Approved For Release UN/Q(A:Se&I1rI&&-00788R001 8001 60001 -6
Approved For Release 202 PNBOR ACGS4 FP F4-90788R001800160001-6 CPYRGHT characteristics. Figure 1, for example, shows spectrograms of a sequence of four Pc! pulsation events that occurred during the interval 1200 to 1500 ur on 17 January 1976, and which were received by the tree ‘antenna’ (a) and the conventional north-south solenoid antenna (b). With the exception of a lower signal-to-noise ratio for the tree measurements, the two Pc! pulsation records are closely alike. It will also be noticed that the lower frequency Pc 2/ Pc 3 geomagnetic activity (frequencies in the range 0.02 to 0.2 Hz) is recorded similarly by both systems. The amplitude of the ULF pulsations in the tree potentials is very small. For the Pc! pulsations shown in Fig. 1, the maximum amplitude of the potential fluctuations was about 0.1 mV. The nearly identical occurrence and spectral character- istics of ULF events measured by the tree electrodes and by the conventional ULF equipment indicated that the tree potentials were largely induced by ULF time variations of the geomagnetic field. To investigate this possibility, a portable planar search: coil powered by a 1!Hz signal generator was moved around the tree near the electrodes. It was found that a 1 Hz oscillation of the potential dif- ference between the tree electrodes was produced only when the search coil was orientated with its moment vector in the north-south direction. When the two electrodes were moved to the north face of the tree, a response from the electrodes could be obtained only when the search coil moment vector was orientated in the east-west direction. These results, and the observations of natural Pc 1 pulsa- tions, can possibly be best understood by considering the tree/electrode pair combination to form a collection of conducting loop antennas in which e.m.fs may be induced by magnetic field fluctuations in the appropriate direction. The conducting paths are provided by the conducting material of the tree (and the cambium in particular'’), and, for field fluctuations in a particular direction, the area of Frequency (Hz) the relevant loop antenna is defined by the intersection of the tree with a vertical plane perpendicular to the particular field direction and passing through the two electrodes. Thus, in the measurements reported here, the Pc | pulsation events observed in the tree potentials were produced by Pc } pulsa- tions of the north-south component of the geomagnetic field. Further tests showed that the tree potentials could only be detected in a living tree. Thus, when a tree dies, the potentials gradually disappear as the wood dries and loses its conductivity. In conclusion, measurements with tree electrodes show that trees may be used as ‘antennas’ to detect ULF geo- magnetic pulsations. The measurements also show that ULF tree potentials are largely produced by ULF fluctuations of the geomagnetic field (the remaining component of the potentials is probably thermal noise). Presman’ noted that electromagnetic fields usually have an adverse effect on living processes. If the ULF geomagnetic pulsations have any adverse effect on; the growth of trees (and, as we have seen, they must induce electric currents in the living material) these effects could possibly be observed in tree ring data. Pcl geomagnetic pulsation occurrences vary markedly over a solar cycle’ and thus, if these particular pulsations effect tree growth, a solar cycle in tree ring data could occur. LaMarche and Fritts” searched unsuccessfully for a relation between tree ring data and sunspot numbers. The phase of the Pc f pulsation solar cycle, however, differs by several years from the sunspot cycle and, assuming the two cycles affect tree ring data, they may tend to obscure each other’s effects. Furthermore, other geomagnetic pulsa- tions and higher-frequency electromagnetic signals have their own cycles of occurrence, and their effects on tree ring formation, if any, could add further to the complexity of the tree ring data} Studies of these possible effects are Fig. 1 Spectrograms of a series of Pc 1 geomagnetic pulsation events recorded at Stanford, Cali- fornia, using tree potentials (a) and a conventional solenoid an- tenna (5). Short intervals of a 1 Hz calibration signal appear at the start of each hour. The vertical lines in the upper spectro- gram are caused either by local electromagnetic transients or by natural sferics; similar lines occur in the lower spectrogram, but they are not as obvious because the background noise is com- paratively suppressed. 34 Approved For Release NG AS 2 HER 00788R001800160001-6
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CPYRGHT
desirable, because the tree ring data could provide a unique
record
of
past
ULF
and
higher-frequency
geomagnetic
activity.
I thank D.
B. Coates for technical
assistance. This work
was supported
in
part by
the Advanced
Research
Projects
Agency of the US Department of Defence and
in
part by
the US Office of Naval Research.
A. C. Fraser-Smith
Radioscience Laboratory ,
Stanford Electronics Laboratories ,
Stanford University ,
Stanford , California 94305
Received
16 August: accepted
15 December 1977.
1. Jacobs, J. A. Geomagnetic Microputsations 15 (Springer, New York, 1970).
2. Campbell. W. H. Proc. IEEE SI, 1337-1342 (1963).
3.
Tepley, L. R. J. geophys. Res. 66, 1651-1658 (1961).
4. Lokken, J. E.. Shand. j. A. & Wright, C. S. J. geophys.
Res. 68, 789
794 (1963).
5.
Lokken,
J.
E. in Sutural Electromagnetic Phenomena Below 30 Kefs (ed.
Bleil
D.
F.) 373-428 (Plenum, New York
1964).
6.
Buxton,
J. L. & Fraser-Smith. A. C. IEEE Trans. Ceosci. Elec. GE-12 109-11
(1974).
7. Troitskaya. V. A. J , geophys. Res. 66, 5-18 (1961).
8.
Heacock. R, R, & Hessler, V.
P. J. geophys. Res
67, 3985-3995
( 1962).
9.
Fraser-Smith. A. C. J. geophys. Res. 75, 4735-4745 (1970); J : geophys. Res. 77
4209-4220
(1972).
10.
Fraser-Smith. A. C. & Coates. D.
B.
Radio
Sei. (submitted).
11.
Burr, H. S.
Yale J. Biol. Med.
17, 727-734
( 1945);
Yale J.
Biol. Med. 19, 311-31
(1947); Science
124,
1204-1205
(1956).
12. Presman, A.
S.
Electromagnetic
Fields and
Life
(transl.
Sinclair,
F.
L..
ed
Brown.
F. A. Jr) 155 (Plenum. New York.
1970).
13. LaMarchc, Jr, V. C. & Fritts, H. C. Tree-Ring Bull. 32, 19-33 (1972).
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