Electronic system can rapidly determine location of lightning strikes occurring within 30 km range. Longer distances are also determined, but with reduced accuracy. Studies have shown that lightning bolt emits electromagnetic wavefront; distance to lightning is determined from ratio of magnetic to electric field

Ruhnke, L. H.

English

NASA Technical Reports Server

June 1973	 B73-10178 
NASA TECH BRIEF 
John F Kennedy Space Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code Kr, Washington, D.C. 20546. 
Determining Distance to Lightning Strokes 
from a Single Station 
[I
The problem: 
Lightning, a well known threat to buildings and man, 
also causes extensive forest fires as well as breakdown 
in electronic equipment. The methods for rapid de-
tection of the distance to a lightning strike, however, 
have been less than adequate. Under the present 
circumstances, one approach requires two observers at 
separate fixed locations. Each observer has to spot the 
same strike; then both have to communicate with each 
other to determine the exact spot by triangulation. 
Clearly this method is subject to a large human error. In 
another approach, two automatic cameras at two loca-
tions photograph each lightning strike. The distance is 
determined later by triangulation. This method is slow 
and useful only for a future study. 
The solution: 
An electronic system was developed which can 
rapidly determine the location of lightning strikes 
occurring within a 3- to 30-km range. Longer distances 
are also determined, but with a reduced accuracy.
How it's done: 
The distance to lightning is determined from the 
ratio of the magnetic to electric field. Studies have 
shown that a lightning bolt emits an electromagnetic 
wavefront whose magnetic field decreases with the 
square of the distance, while the electric field decreases 
with the cube of the distance. Both the magnetic and 
electric fields received at 1 kHz can be processed to form 
distinct ratios over the range of 3 to 30 km. It is from 
this ratio that the system determines the distance to the 
lightning strike. 
The block diagram of the system is shown in the 
illustration. In this configuration, the electric field is 
sensed by a horizontal wire antenna, approximately 
10 m long and 2 m above ground. The antenna is 
connected to ground through a 10-kiohm resistor in 
order to be properly matched to a passive filter. The 
filter has a center frequency of 1 kHz, attenuation which 
drops 2 dB at ± 3 percent off the center frequency, and 
slopes of 40 dB/octave on both sides of the center 
frequency. 
Filter 
qj^a.sfo,nnje,—jjkHJ—
Square agnetic Field 
T7,1
Loop Antenna Rooter omponent Output 
Filter	
p 
Transformer	
1 kHz	
Operational 
Amplifier
Ratio 
Output Wire
AAmplifier
 
Antenna Multi- 
I	 LT 
vibrator 
Onehot	
Electric Field 
 Absolute ______ Peak Hold  ____  Value Component Output 
(continued overleaf) 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights.
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The output of the 1-kHz filter produces peak 
amplitudes of 1 volt for a very close lightning strike and 
10 uV for a strike about 160 km (100 miles) away. Peak 
voltage detectors as well as strip chart recorders do not 
usually handle such a large range accurately enough. The 
signal, therefore, is amplified before the peak voltage 
detector using an operational amplifier with a three-
position control to vary the gain, by orders of 10, from 
10 to 1000. 
After amplification, the signal is fed into an absolute-
value circuit. The information on strike polarity, which 
is lost by this procedure, is already obscured by the 
sharp filter and is not needed in this method of de-
termining distance to the strike. 
The output of the absolute-value circuit is fed to a 
peak-hold module. The output of this module is a 
positive pulse one second long whose amplitude is 
proportional to the magnitude of the electric field at 
1 kHz. This output voltage appears at an output 
terminal on the front of an electric-field processing 
instrument and can be fed to a strip chart recorder. 
The magnetic field, on the other hand, is sensed by 
two loop antennas. Each loop produces a voltage 
Urn, which depends on the angle 0 of the loop planes 
to the signal source, the frequency of observation 
co, the loop area F and the number of turns n 
Um = /.1•H	 n cos0 
This voltage usually appears as a very low impedance 
source because of technical difficulties in constructing 
high loop inductances. The source inductance L (henry) 
is approximately given by 
L = 2.6 10-6 n 
For the prototype model, each loop antenna consists 
of 50 turns and a loop area of 4 m 2 . The measured 
inductance is 12.4 mH. Both loop antennas are followed 
by identical transformers with a turn ratio of 1:18. 
These transformers match the loop impedance to the 
1-kHz filter. The loop antenna produces a voltage
equivalent to an electrical antenna of an effective height 
of 4 mm. This makes it necessary to eliminate electro-
static pickup, which otherwise will interfere with the 
magnetic pickup. Therefore, the center tap of the 
primary winding of the transformer is grounded, and the 
two-conductor cables and the loop antennas are shielded. 
The filters, amplifiers, and peak voltage detector are 
identical to the electric-field branch. A rectifier module 
is used as a "square-rooter" to add the signals from both 
loop antennas such that the directional characteristic 
of the loop antennas is eliminated. 
The trigger signal for the peak detector is produced 
by a conventional one-shot multivibrator using an 
operational amplifier with an R-C network to produce 
10-V, one-second pulses. This multivibrator is fed by 
pulses from the output of the "square-rooter" after a 
100-fold amplification. 
Note: 
Requests for further information may be directed to: 
Technology Utilization Office 
Kennedy Space Center 
Code AD-PAT 
Kennedy Space Center, Florida 32899 
Reference: TSP73-10178 
Patent status: 
This invention is owned by NASA, and a patent 
application has been filed. Inquiries concerning non-
exclusive or exclusive license for its commercial de-
velopment should be addressed to: 
Patent Counsel 
Kennedy Space Center 
Code AD-PAT 
Kennedy Space Center, Florida 32899 
Source: Lothar H. Ruhnke of 
National Oceanic and
Atmospheric Administration 
under contract to
Kennedy Space Center
(KSC- 10698)
. 
B73-10178	 Category 02,03


Determining distance to lightning strokes from a single station

Apparatus is described for determining the distance to lightning strokes from a single station. The apparatus includes a first loop antenna system for sensing the magnetic field produced by the lightning which is filtered, square rooted, and fed into a peak voltage holding circuit. A second antenna is provided for sensing the electric field produced by the lightning which is fed into a filter, an absolute value meter, and to a peak voltage holding circuit. A multivibrator gates the magnetic and electric signals through the peak holding circuits to a ratio meter which produces a signal corresponding to the ratio between the magnetic component and the electric component. The amplitude of this signal is proportional to the distance from the apparatus to the lightning stroke

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
D.C. 20546
N73-20T75
TOi KSI/Scientific & Technical Information Division
Attentions Miss Winnie M. Morgan
FROMs GP/Office of Assistant General Counsel for
Patent Matters
SUBJECTs Announcement of NASA-Owned U.S. Patents in STAR
In accordance with the procedures agreed upon by Code GP
and Code KSI, the attached NASA-owned U.S. Patent is being
forwarded for abstracting and announcement in NASA STAR.
The following information is provided;
U.S. patent No. ; 3,
Government or
Corporate Employee
Supplementary Corporate
Source (if applicable)
NASA patent Case No.
NOTE -• If this patent covers an invention made by a corporate
employee of a NASA Contractor, the following is applicable:
Yes /^ (/ No / J
Pursuant to Section 305(a) of the National Aeronautics and
Space Act, the name of the Administrator of NASA appears on
the first page of the patent; however, the name of the actual
inventor (author) appear^ at the heading of column No. 1 of
the Specification, following the words "... with respect to
an invention of .
Elizabeth A. Carter
Enclosure
Copy of Patent cited above
NASA-HQ
https://ntrs.nasa.gov/search.jsp?R=19730011448 2020-03-17T08:17:03+00:00Z
United States Patent
Ruhnke
Hi j 3,715,660
[45] Feb. 6,1973
I
[ 54 ]
[75]
[73]
[22]
[21]
DETERMINING DISTANCE TO
LIGHTNING STROKES FROM A
SINGLE STATION
Inventor: Lothar H. Ruhnke, Boulder, Colo.
Assignee: The United States of America as
represented by the Administrator of
the National Aeronautics and Space
Administration
Filed: Dec. 30, 1971
Appl. No.: 213,949
[52] U.S. Cl ................................... .324/72, 73/170 R
[51] Int. Cl .............................................. GOlr 31/02
[58] Field of Search ........ 324/72; 73/170 R; 340/227,
340/420,421
[56] References Cited
UNITED STATES PATENTS
3,611,365 10/1971
3,465,245 9/1969
Lundquist 73/170 R
Fischer 324/72
2,953,020 9/1960 Hunt 324/72
Primary Examiner— Michael J. Lynch
Attorney—James O. Harrell et al.
[57] ABSTRACT
Apparatus for determining the distance to lightning
strokes from a single station. The apparatus includes a
first loop antenna system for sensing the magnetic
field produced by the lightning which signal is filtered,
square rooted, and fed into a peak voltage holding cir-
cuit. A second antenna is provided for sensing the
electric field produced by the lightning which is fed
into a filter, an absolute value meter, and to a peak
voltage holding circuit. A multivibrator gates the mag-
netic and electric signals through the peak holding cir-
cuits to a ratio meter which produces a signal cor-
responding to the ratio between the magnetic com-
ponent and the electric component. The amplitude of
this signal is proportional to the distance from the ap-
paratus to the lightning stroke.
4 Claims, 1 Drawing Figure
,16
PATENTED FEB 61973 !, 715.660
oO
O
/NVENTOR.
LOTHAR H. RUHNKE
BY
ATTORNEY
3,715,660
1 2
DETERMIMNG DISTANCE TO LIGHTNING the electric signal received by the second antenna, (7)
STROKES FROM A SINGLE STATION an absolute value instrument coupled to the output of
The invention described herein was made in per- the filter for producing an electric signal free of polari-
formance of work under a NASA contract and is sub- ty, (8) a second peak voltage circuit coupled to the out-
ject to the provisions of Section 305 of the National 5 put of the absolute value instrument for generating a
Aeronautics and Space Act of 1968, Public Law signal having an amplitude proportional to the mag-
85-568 (72 Stat. 435, 402 U.S.C.P. 2457).
 nitude of the electric field generated by the lightning
The invention relates to an apparatus for determin- stroke, (9) a one-shot multivibrator for gating the
ing the distance to lightning strokes from a single sta- signals received by the first and second peak voltage
tion, and more particularly to an apparatus which com- '0
 circuits to an.ow the signal representing the magnetic
pares the electric and magnetic fields generated by the component and the signal representing the electrical
lightning for producing a signal having an amplitude component to be fed through the respective peak volt-
corresponding to the distance from the apparatus to the
 age circuits, and (10) a ratio meter coupled to the out-
hghtnmg stroke.
 puts of the first and second peak voltage circuits for
It has become increasingly important, especially in » generating a signal having an amplitude proportional to
launching missiles and the like to know if lightning
 the distance between the apparatus and the lightning
storms are in the launch vicinity so as to avoid the pos- strokes
sibility of lightning striking space vehicles during Accordingly, it is an important object of the present
launch. The space industry has become particularly
 invention to provide an apparatus for producing a
aware of thunder storms since one of the recently
 si , indicative of the distance between a lightning
launched Saturn vehicles was hit by lightning during
 stroke and the apparatus
launch. As a result, extreme precaution has been taken
 Another important object of the present invention is
to locate all lightning storms within the general vicinity
 to jde an a ratus for determining the distance to
prior to launch. Heretofore, one method of determin-
 25 iightning strokes from a single station,
ing the distance to lightning was by measuring the
 Qther objects and advantages wil, become more ap.
period of time between visually observing a lightning
 t from a reading of the followin detailed descri
stroke and hearing the thunder produced thereby.
 don and ded claims taken in conjunction with the
However, locating lightning strokes is usually done
 accomPanying drawing wherein:
from two stations with direction finders that sense the
 30 Jhe FIGURE is a schernatic diagram showing the ap-
electromagnetic field produced by the lightning. For a
 ug constructed in accordance with the present in-
rapid readout of information such an installation, needs vention
a data transmission link between the two observation Referring in more detail to the drawing, a schematic
sites and a computational device to calculate the posi-
 di of the atus for detennining the distance
tion of the lightning stroke from the location of the ob- 35
 tQ H htni strokes from a si ,e station is illustrated.
servation sites and the direction of the lightning. One
 Jhe m tic fieW duced b the lightening stroke is
problem with such devices ,s the requirement that the
 sensed fe a ., Qf, antennas lfl and u tive,
directional finder must be located at different s,tes_
 TWQ ^ ^ ^^ ^ nece to
 F
roduce
The apparatus constructed in accordance with the J . . . . . . , . . . . < . L
... . ui f j . • • L.' a~ signal that is independent of the azimuth of thepresent invention is capable of determining the 40 TUI . • m j«i j rj. !• u. • . i * • i . »• c source. The loop antennas 10 and 12 are constructed ofdistance to lightning strokes from a single station. From • • . - j. j . <• • ..
tests and calculations it has been determined that the a c°'' havl"8 a predetermined number .of windings,
distance to a lightning stroke within approximately 30 l"ch as in one Partlc"lar dfev'f m the ran«e of,5 to I0'
miles is directly proportional to the ratio of the mag- ^"1 may vary according to the particular application.
netic field to the electrical field generated by the lightn- 45 EachJ°oP a"tenna.I0 and \2 Pr°d"ces a ™ltaSe Y-
ing stroke. The subject apparatus is capable of measur- wh*cht depends on the angle tf of the loops plane to the
ing both the electric and magnetic field to generate a signal source the frequency of observation «, the loop
signal corresponding to such ratio. area F- and t!Je number of turns " a«ordmg to the fol-
In accordance with the present invention, it has been lowing formula:
found that'difficulties encountered with determining 50 . y =a-H • a t - F - n - c o s 6 •
the distance to lightning strokes may be overcome by -
providing a novel apparatus. This apparatus when used This voltage Vra appears usually as a very.low im-
for determining the distance to the lightning strokes in- pedance source having a very small value. A wire an-
cludes the following basic parts: (1) An antenna system tenna 14 is utilized to sense the electric field produced
for sensing the magnetic field generated by a lightning 5S by the lightning stroke and is a high impedance device
stroke, (2) a filter for isolating a predetermined which produces a higher voltage than that produced by
-frequency of the signal generated by the magnetic field the loop antennas 10 and 12. Therefore, it is essential
out of the magnetic signal, (3) a square rooter for tak- in order to accurately compare the voltages produced
ing the square root.of the signals produced by the an- by the magnetic and electrical fields that the antenna
tenna system so as to generate a magnetic signal free of 60 systems produce signals that are comparable. The volt-
polarity and direction, (4) a peak voltage hold circuit age Mm produced by the loop antennas 10 and 12 ap-
coupled to the output of the square rooter for general- pears usually as a very low impedance source because
ing a signal having an amplitude corresponding to the of technical difficulties to construct high loop in-
amplitude of the magnetic signal produced by the ,, ductances. A transformer 16 can be used to match this
lightning, (5) a second antenna provided for sensing inductance to a following filter 18 for bringing the volt-
the electric field generated by the lightning stroke, (6) age Vm to a magnitude comparable with the voltage
a filter for isolating a predetermined frequency out of received by the electrical antenna 14. Since there is a
3,715,660
3 4
difference in the internal impedance of the loop anten- 28 produces a pulse of one second duration so as to
nas 10 and 12 and the wire antenna 14, it is necessary hold the output signals from the peak voltage holding
to utilize the transformers 16 having an impedance, circuit 24 at the maximum voltage produced by the
which in combination with the low impedance of the square rooter 22.
loop antenna is equal to the high impedance of the loop 5 Referring now to the circuit which includes the wire
antenna is equal to the high impedance of the wire an- antenna 14 for measuring the electrical field produced
tenna 14. Therefore, the loop antenna plus the trans- by the lightning stroke such includes identical corn-
former 16 have the same impedance as the wire anten- ponents such as the filter 18, the amplifier 20 and the
na 14. The output of the transformer 16 is coupled to 1 peak voltage holding circuit 24 as the circuits provided
kHz filter 18, which filters out a predetermined I0 with the loop antennas. The absolute value instrument
frequency, which in the particular embodiment illus- 26 is the same as the square rooter 24 with a single
trated, is 1 kHz. The internal impedance of the filter 18 input since there in only one signal being fed thereto. It
should be matched with the following amplifier 20 is important that all of the components in the electric
which is utilized to amplify the magnetic signal ,
 5 circuit modify the signal received from the wire anten-
received by the loop antenna 10. A similar filter 18 and na the same degree as the same components in the
amplifier 20 are utilized with the loop antenna 12. Of magnetic circuit. In one particular embodiment in
course, it is to be understood that instead of using a order to make the wire antenna compatible with the
transformer in combination with the loop antenna 10 to fllter 18 a 10 kilohom resistor is connected between the
match the impedance of the wire antenna 14 a loop an-
 20 wire antenna 14 and ground- As previously mentioned,
tenna having many windings and the same impedance the '™Pedance of the 10 kilohom resistor and the wire
as the wire antenna could be utilized. However, such is antenna e1uals the impedance of a loop antenna 12 and
not practical due to the large number of windings a transformer 16. The output of the wire antenna 14 is
required ^ed 'nto a one fci'°hertz filter 18, amplified by amplifier
The filter 18 is a narrow band filter which averages 25 20 and fed to an absolute value instrument 26. A peak
the signal being received over a short period of time holdinS circuit 24 is provided for producing a voltage
and in one particular embodiment is approximately havln8 an amplitude corresponding to the maximum
one-half a second value of the signal produced by the absolute value in-
The reason that a pair of loop antennas are utilized is stniment a"d holding that signal as long as a pulse from
to produce a resultant signal which is independent of 30 the one-shot multivibrator 28 is present. The magnetic
the direction that the loop antennas receive the mag- and el«trical components from the peak holding volt-
netic signal. Since the magnetic field has a direction age circuits 24 are fed into a ratio meter which
and the loop antennas 10 and 12 are directionally sensi- generates a signal on its output having an amplitude
tive, if one of the loop antennas were placed in a North- corresponding to H/E. The ratio meter 30 is a conven-
South direction and the other antenna were placed in 35 tlonal analo*ue de;"ce which dlvldes the eleuctnca!
an East-West direction the resultant signal produced by component '"to the magnetic component H and
both of the antennas 10 and 12 would compensate for Produces an output voltage wh.ch .sproport.onal to the
variations in direction. The electric antenna 14 does ""'o of the magnetic component of the lightning wave
. ... ,. . ... . . received over the electrical component of the lightning
not encounter this problem since it does not have any
 An . , _,. . T ,. .
. . . . . . . • .
 40
 wave received. This ratio vanes according to thedirectional characteristics. ... , . ,. . . . , e
—.
 f ... . . , i-r tn • c distance from the lightning stroke to the apparatus,Therefore the outputs of amplifier 20 coming from . . . . 6 5 .. vv
... . «/» j ••» .-i ii since the electric and magnetic components varythe: loop antennas 10 and 12, respectively, are normally
 dj wjth ^ djstance tQ ^  P
different and are fed into a conventional square rooter
 whjfe a rred embodimen* of th* jnvention has
22 for adding the voltage together to produce a voltage
 45 been described usj jfk such descri tion is
on the output of the square rooter which is mdependent
 for i|lustrative Bses onl and it is to be und^ntood
of direction and polarity The output of the square
 that ch anrf variations be made wjthout de.
rooter is, in turn, fed to a peak voltage holding circuit
 tj from the ifit Qr of the followin claims.
24, as well as to an amplifier 26 coupled to the input of What is claimed is-
a one-shot multivibrator 28. The output of the one-shot 50
 l An apparatus for determining the distance to
multivibrator 28 is, in turn, coupled to a gating input of lightning strokes comprising:
the peak voltage holding circuit 24. The output voltage
 A a first antenna system for sensing the magnetic
from the square rooter 22 takes the form of a positive
 fleld generated by the lightning stroke and
pulse which rises according to the distance to the generating a magnetic signal responsive thereto,
lightening stroke and magnitude of the lightning. Since 55
 B f,|ter means coupied to said first antenna system
the maximum amplitude of the pulse coming out of the
 for isolating a predetermined frequency from said
square rooter is proportional to the distance from the magnetic signal,
apparatus to the lightning stroke, it is desired to C. a square rooter coupled to the output of said first
generate the magnetic signal having an amplitude over filter means for producing a non-polarity magnetic
a predetermined duration equal to the maximum am- "u signal,
plitude of the output voltage from the square rooter. D. a first peak voltage meter coupied to said square
The peak voltage holding circuit stays at a peak voltage rooter for generating a signal having an amplitude
as long as a pulse is present from the one-shot mul- proportional to the magnitude of the magnetic
tivibrator 28. The output of the peak voltage holding ,. field generated by said lightning stroke,
circuit is a pulse having an amplitude corresponding to E. a second antenna system for sensing the electric
the magnetic field produced by the lightning stroke. In field generated by said lightning stroke and
one particular embodiment the one-shot multivibrator generating an electric signal responsive thereto.
3,715,660
F. a filter coupled to said second antenna system for
isolating a predetermined signal from said electric
signal,
G. an absolute value instrument coupled to said filter
for producing a non-polarity electric signal,
H. a second peak voltage meter coupled to said ab-
solute value instrument for generating a signal hav-
ing an amplitude proportional to the magnitude of
the electric field generated by said lightning
stroke, and
1. means for comparing said signal having an am-
plitude proportional to the magnitude of the mag-
netic field with said signal having an amplitude
proportional to the magnitude of said electric field
for generating a signal having an amplitude pro-
portional to the distance between said apparatus
and said lightning stroke.
2. The apparatus as set forth in claim 1 wherein said
first antenna system includes:
10
15
A. a pair of directional loop antennas, and
B. said directional antennas being positioned perpen-
dicular to each other.
3. The apparatus as set forth in claim 1 further com-
prising:
A. a pulse generating source, and
B. means for coupling said pulse generating source to
said first and second peak voltage meters for ac-
tivating said peak voltage meters.
4. The apparatus as set forth in claim 3 wherein:
A. said pulse generating source is a one shot mul-
tivibrator, and
B. means for coupling said one shot multivibrator to
the output of said square rooter for generating a
pulse of a predetermined duration responsive to
said square rooter producing said non-polarity
magnetic signal.
20
25
30
35
40
45
50
55
60
65
-A.


Determining distance to lightning strokes from a single station

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