A new comprehensive lightning instrumentation system has been designed for Launch Complex 39B (LC39B) at the Kennedy Space Center, Florida. This new instrumentation system includes six synchronized high-speed video cameras, current sensors installed on the nine downcouductors of the new lightning protection system (LPS) for LC39B; four dH/dt, 3-axis measurement stations; and five dE/dt stations composed of two antennas each. The LPS received 8 direct lightning strikes (a total of 19 strokes) from March 31 through December 31, 2011. The measured peak currents and locations are compared to those reported by the CGLSS 11 and the NLDN. Results of comparison are presented and analyzed in this paper

Mata, Angel G.

Mata, Carlos T.

Nag, A.

Rakov, V. A.

Saul, Jon

NASA Technical Reports Server

31'1 International Conference on
lightning Protection
2nd - 7lh September 2012 - Vienna, Austria
ICLP 2012
EVALUATION OF THE PERFORMANCE CHARACTERISTICS OF CGLSS II
AND U.S. NLDN USING GROUND-TRUTH DATA FROM LAUNCH COMPLEX
39B, KENNEDY SPACE CENTER, FLORIDA
11k 2 3 S )4C.T. Mata , A.G. Mata , V.A. Ra OV ,A. Nag, J. au
1. ESC, Kennedy Space Center, Florida, USA.
2. Department of Electrical and Computer Engineering, University of Florida, Gainesville, Florida, USA.
3. Vaisala Inc, Tucson Arizona, USA.
4. 4S th Weather Squadron, Patrick AFB, Florida, USA.
~,-,-"",,,-,,-,,-,-,,-,~a,"-,n,,,,,as,,,,a,,,,.g,,,,o,-,-v, angel.g.mata@nasa.gov, rakov<Ulece.utl.edu, amitabh.nagl vaisala.com ,
jon.saul<Ulpatrick.af.mil )
ABSTRACT
A new comprehensive lightning instrumentation system has
been designed for Launch Complex 398 (LC398) at the
Kennedy Space Center, Florida. This new instrumentation
system includes six synchronized high-speed video cameras,
current sensors installed on the nine downcouductors of the
new lightning protection system (LPS) for LC398; four dO/dt,
3-axis measurement stations; and five dE/dt stations composed
of two antennas each. The LPS received 8 direct lightning
strikes (a total of 19 strokes) from March 31 through
December 31201 t. The measured peak currents and locations
are compared to those reported by the CGLSS 11 and the
LD . Results of comparison are presented and analyzed in
this paper.
The most recent comparison between CGLSS and NLD
was performed using historical data from 200S and 2006
(Ward et aI., 2008).
The WX LPS provides precise location and total
detection of only a relatively small location at KSC (LC39B
and its vicinities) but there is a possibility of implementing
this system in multiple launch pads (like LC39A and
CCAFS) which could all be interconnected and would
provide 100% detection efficiency for all the launch pads
within KSC and CCAFS.
2 KSC LIGHT 1 G LOCATIO SYSTEMS
DESCRlPTION
INTRODUCTION 2.1 LC39B LPS, KSC
After over 40 years of deploying and using Lightning
Instrumentation (Lightning Detection and Location
Systems) at or around the vicinities of the Kennedy Space
Center (KSC) much has been improved and gained; from
monitoring the electric field during the Apollo days (mid-
late 1960's) to the precise location of a lightning strike near
and within LC39B with the deployment of the WX LPS
lightning instrumentation (2011).
Both CGLSS and NLDN have been providing lightning
detection and location data for the KSC with an expected
margin of error (both detection and location) since these
systems monitor big areas. Even though the margin of error
has improved over the years, it is not possible for these
systems to offer error free results.
The most recent NLDN performance characteristics has
been evaluated using rocket triggered lightning data
corresponding to 2004 through 2009 (Nag et aI., 20 II)
where the resulting flash and stroke detection efficiencies
were 92% and 76%, respectively; The median absolute
location error was 308 m, and the largest error was 4.2 km.
The LC39B LPS and its lightning instrumentation are
described in detail in [I] and [2], respectively. This
lightning instrumentation can be seen as an event-driven
fast (up to IOOMS/s) sampling DAQ system running 24/7
with sub-microsecond time accuracy which trigger signal
comes from any of the thirty one (31) ground level sensors
(9 downconductor currents, 12 dB/dt, 10 dE/dt),
additionally a TTL signal from the LC39A lightning
instrumentation system has been provided (mainly due to
the use of LC39A for the Space Shuttle launches). After a
qualified trigger is received, the signal of all the ground
level sensors is recorded on a 30ms time window with SO%
pre-trigger sampling at 100MS/s, additionally seven I high
speed video cameras record up to 4SS frames with 312.Sus
lOne additional high-speed video camera was temporarily
instaUed (June 20 II) about five kilometers southwest of LC39B.
This camera is located in the firing room I of the Launch Control
Center (LCC) and is currently pending final installation atop the
Vehicle Assembly Building (YAH).
https://ntrs.nasa.gov/search.jsp?R=20120004043 2019-08-30T19:47:35+00:00Z
200 4CO
......
w-------+---~+_____:pr--+_+_---ll2S.
Figure 3. Map showing the locations of 15 U.S. National
Lightning Detection Network (NLDN) sensors in aaround the
Florida region (pending updated version)
it.O 110.9 eo. i 80.7 8fl,8 QO.6 &0.4. ill.3 BO.l
Figure 2. Map showing the location of6 CGLSS 11 sensors
(pending updated version)
As of the last reported nationwide hardware update, the
NLDN currently has 114 IMPACT-Enhanced Sensitivity
and Performance (IMPACT-ESP) sensors and based on the
last published performance characteristic evaluation results
The U.S. National Lightning Detection Network (NLDN)
has been providing real-time, continental-scale lightning
information since 1989 and it has undergone several
improvements and updates. It consists of a nationwide
network of "Improved Accuracy from Combined
Technology" (IMPACT) sensors which basically use a
combination of the Magnetic Direction Finder and Time of
Arrival techniques [6] and is capable of producing the
following estimated parameters: latitude, longitude,
microsecond time, peak current, polarity, CloudiCloud-to-
Ground indication and multiplicity for lightning strikes.
"1995-1998, the system was converted to a 6-station, short-
baseline network of medium-gain IMPACT (IMproved
Accuracy from Combined Technology) sensors (Cummins
et aI., 1998)."
2.3 U.S. NLDN
are known and roughly constant, the CGLSS can also
provide an estimate of the peak current in the stroke and its
polarity." [5].
According to a time-domain antenna theory developed by
M. A. Uman and his collaborators shortly after the Apollo
12 incident (see for example Uman et aI., 1975), the initial
peak of the electromagnetic pulse that is radiated by a
return stroke is proportional the peak current in the stroke,
multiplied by the speed of the stroke up the leader channel,
and divided by the distance to the stroke. [Note: this theory
is sometimes called the simple 'Transmission-Line Model'
or TLM because it assumes the current pulse propagates up
a straight channel, without distortion, and at a constant
speed.] Since the CGLSS measures the peak field and can
compute the stroke location, and since the stroke velocities
2.2 CGLSS II, 45th Weather Squadron
"KSC has made major contributions to the development
of two complementary systems for detecting and locating
lightning, the Cloud-to-Ground Lightning Surveillance
System (or CGLSS) and the Lightning Detection and
Ranging (or LDAR) system. The CGLSS utilizes a network
of gated, broadband electric and magnetic field sensors
(Krider and Noggle, 1975) to detect the waveform
signatures that are characteristic of return strokes, the high-
current components of CG flashes (Krider et ai, 1976;
Herrman et aI., 1976). When a proper signature is detected
(in the time-domain) at two or more known locations (the
antenna sites), the coincident times-of-arrival and magnetic
directions can be used to compute the points where return
strokes strike the ground (Krider et aI., 1980; Cummins et
aI., 1998; 2006).
The LC398 LPS acquired data offers the capability of
locating lightning strikes by means of:
• Time of Arrival (using dE/dt waveforms)
• Magnetic Direction Finder (using dH/dt
waveforms)
• Visual inspection (using video camera records)
Additionally, downconductor waveforms offer a mean to
corroborate between a direct and nearby lightning strike by
its characteristic behavior.
Figure I. Lightning protection system of LC39B, Kennedy Space
Center, Florida. Seen at the launch pad is the standby rescue
Shuttle during the Hubble repair mission in 2009.
intervals (up to 142.1 ms of video at 3,200fps) with a
resolution of I280x800, also with 50% pre-trigger.
###-2
[7] it has a flash and stroke detection efficiencies of 92%
and 76%, respectively, with a median absolute location
error of 308m (the largest error of 4.2km) and the peak
current estimation errors never exceeded 129%. It is worth
noting the validation test referenced was done at the
International Center for Lightning Research and Testing
(ICLRT), at Camp Blanding, Florida, using rocket-triggered
lightning techniques where intentionally the strike location
is know but the acquired return strokes are only
representative of regular subsequent strokes in natural
lightning, consequently, the given performance
characteristics a) are representative of the portion of the
NLDN covering the Florida region (whose performance
characteristics are not expected to be superior to those of
the other parts of the network) and b) the flash detection
efficiency is expected to be an underestimate of the true
value for natural negative lightning flashes (since first
strokes typically have larger peak currents than subsequent
ones).
3 DATA
During the year 20 II, from late March until December,
the LPS was subject to a total of 48 lightning flashes (8
direct and 40 nearby) with a total of 89 return strokes (19
direct and 70 nearby) recorded on 16 different days.
This work will use only direct strikes to the LC39B LPS,
all of which were negative flashes.
CGLSS II and NLDN data was provided for each day the
LC39B LPS was directly stroke by lightning. Data consists
of a text file providing: date, time stamp (UTC) with
millisecond accuracy, decimal coordinates (latitude and
longitude) with six significant figures, peak current
(positive or negative) number of sensors, cloud or ground
discharge (only for NLDN) and ellipse parameters.
The following CGLSS II and NLDN performance
characteristics were determined: I) stroke detection
efficiency, 2) location errors, and 3) differences in peak
currents estimates. Both systems, CGLSS n and NLDN,
were compared against LC39B LPS data.
Each direct return stroke was correlated using GPS
(Global Positioning System) time stamps to determine
stroke detection efficiencies.
Geographical coordinates were used to calculate location
errors. Only 4 strokes did not attach to the towers' air strike
terminal, so downconductor current waveforms and video
records were used to estimate their strike location. LC39B
LPS towers' coordinates correspond to the center of each
tower.
LC39B LPS peak current values are calculated from the
algebraic sum of all (9) downconductors. From acquired
data it is seen that the faster the return stroke is then more
oscillations will be present in this algebraic sum due to the
length of the downleads of the downconductors which are
about 250 meters each.
Out of 5 multi-stroke direct flashes, ranging from a
minimum of 2 and a maximum of 8 return strokes, only one
flash had all return strokes (3) attaching to the same
termination point with both, CGLSS II and NLDN,
detecting 2 return strokes (the first and the third). It is
believed the second return stroke was not detected due to
the threshold of these systems. For the remaining 4 multi-
stroke direct flashes the subsequent return strokes did not
attach to the same strike location of the first return stroke.
There were two strokes attaching at two different
locations simultaneously, both these strokes were reported
by NLDN (one as cloud and one as ground discharge) but
CGLSS II failed to report both of them. In both cases the
attachment points were: I) the air strike terminal atop the
insulator of Tower 2 (about 181 meter height above ground
level) and 2) ground level east and outside the LC39B
perimeter about 550m and 620m (east and south-east,
respectively) from Tower 2. Tower 2 is the east-most tower
of the LC39B LPS and its closest distance to the coast line
is about 650m (north-east direction). For the extent of this
work, location calculations of these return strokes were
made using the direct strike location to the LPS.
There was one 2-return stroke flash where the first RS
stroke the LPS and the second RS was a nearby strike, both
CGLSS II and NLDN detected both strokes but only the
first RS is included in this work, additionally there was one
3-return stroke flash where the first RS stroke the LPS
(tower 3), the second RS had two simultaneous attachment
points (tower 2 and nearby, south-east of LC39B) and the
third RS was a nearby strike (striking the same nearby
location as the second RS). CGLSS II reported only the first
RS and NLDN reported all three RS, the third RS of this
flash is not included in this work.
4 RESULTS
4.1 Stroke Detection Efficiencies
Table I shows the CGLSS II and NLDN stroke detection
efficiencies for 20 II were 19 return strokes attached
directly to the LC39B LPS. For NLDN, the total stroke
detection efficiency is 84% (16 of 19) which is better than
the 76% reported by Nag et aI., 2011, taken as an
underestimate since rocket triggered lightning data (for
2004-2009) was used. The stroke detection efficiency for
return strokes identified as impacting ground is 74% (14 of
19) which is about the same as the underestimate gi ven by
Nag et aI., 2011. NLDN additionally exceeds at detecting
all the first return strokes if these are not categorized as
ground or cloud discharges, if so then the first return stroke
detection efficiency is 75% (6 of 8). For CGLSS 11 the
detection efficiency is 63% (12 of 19), maintaining this
number for the detection efficiency of first return strokes
and improving to 64% (7 of II) for subsequent return
strokes.
For more specific cases NLDN outperformed CGLSS II
significantly with 100% (3 of 3) detection efficiency for
single-stroke flashes compared to 33% (I of 3) and again
100% (2 of 2) detection efficiency for strokes with multiple
simultaneous attachment points (direct and nearby) but only
50% (I of 2) once ground/cloud categories were taken into
account compared to 0% (0 of 3) for CGLSS II.
Figure 4.1.1 shows the distribution of the detected strokes
(CGLSS II, NLDN and LC39B LPS) by the LC39B LPS
###-3
current rise time. Rise times were between 1 and 7
microseconds.
Table I. Summary of LC39B LPS Direct Strikes (March-
December, 2011) with CGLSSII and NLDN Detection
Efficiencies (DE),
Direct CIl WJ CIl ..... CIl (l.)CIl zJ;l 0 "'0 ..... (l.) ~(l.) z (l.) §WJ VJ"><: ~Return ~ o 0 (l.) O~ VJ 00 ~~ ~ ,....lb 00 ,....lbStrokes b 0 o (l.) oVJVJ ... ZVJ ..... WJ....
(March- <+-< <+-<"'0 VJ <+-< "'0 ~ u"O ;;;00 o E o I':: Z 0 t....,.2
December, .0 Z • ::l Ob o 0 VJci o (l.) 0 o 0 ,....lVJ (l.) ,....l
2011) Z Zd$ ,....l Zo Z ci t> 00 Z ZO u
Total 19 16 84% 14 74% 12 63%
First 8 8 100% 6 75% 5 63%
Subsequent II 8 73% 8 73% 7 64%
Single- 3 3 100% I 33% I 33%Stroke Flash
Multiple
simultaneous 2 2 100% I 50% 0 0%
attachment
points
4.2 Location Accuracy
Figure 4.2.1 shows a spatial distribution of locations for
all the direct strokes detected by CGLSS (12) and NLDN
(16). The origin (marked X at the center of Figure 4.2.1)
correspond to the center of each tower of the LC398 LPS
since each tower was directly stroke by lightning at least
once during 2011. These locations are known from site
surveys, additionally for 1 case (CGLSS 11) and 3 cases
(NLDN) the attachment point was along the downleads of
the downconductors. For the purpose of this work,
geographical coordinates of these locations were obtained
after reviewing the downconductors current waveforms,
and half the distance from the tower to the downcondutor
grounding point was selected as the attachment point.
Figure 4.2.2 shows the histogram ofNLDN and GCLSS
II absolute stroke location errors for the 16 and 12 strokes
shown in Figure 4.2.1. CGLSS outperforms NLDN
regarding location errors with minimum, median and
maximum location errors of 51, 155 and 467 m (for CGLSS
II) compared to 133,555 and 1,714 m (for NLDN) which in
turn can be compared to 23, 308 and 4,239 given by Nag et
al., 2011.
Figure 4.2.3 shows the absolute location error with
respect to the number of reporting sensors. The range of
reporting sensors was 2-5 for CGLSS 11 and 2 - 15 for
NLDN with the largest absolute location error given when
15 sensors where used as part of the solution for the NLDN.
It is not obvious that the location error tends to decrease as
the number of reporting sensors increases, for both CGLSS
11 andNLDN.
4.3 Peak Current Estimates
Figure 4.3.1 shows the perceptual peak current difference
between both systems, CGLSS 11 and NLDN, and the
LC398 LPS, both systems underestimate the peak current
between 20-40% even though it is important to point out
that the LC398 LPS measured peak current is the
combination of multiple (9) currents. There are two events
where NLDN measured more current that the LC398 LPS
and these correspond to 2 return strokes with multiple
simultaneous attachment points (CGLSS did not detect any
of these strokes).
Figure 4.3.2 shows a histogram with all the LC398 LPS
peak currents and identify the range of peak currents for
which CGLSS and NLDN detected strokes. The largest
recorded current saturated the LC39B LPS at 174.3 leA and,
excluding this event, the average LC398 LPS peak current
was about 30 leA.
Figure 4.3.3 shows a relation between LC398 LPS and
the number of reporting sensors for each system, CGLSS
andNLDN.
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[I] C.T. Mata, VA Rakov, "Evaluation oflightning incidence to
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2008.
[2] C.T. Mata, V.A Rakov, T. Bonilla, A.G. Mata, E. Navedo,
G.P. Snyder, "A new comprehensive lightning
instrumentation system for PAD 39B at the Kennedy Space
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[3]
[4] VA Rakov and M.A Uman, Lightning Physics and Effects.
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###-4


Evaluation of the Performance Characteristics of CGLSS II and U.S. NLDN Using Ground-Truth Data from Launch Complex 398, Kennedy Space Center, Florida

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