2013 International Symposium on Lightning Protection (XII SIPDA), Belo Horizonte, Brazil, October 7-11, 2013.
Validation of Detection of Positive Flashes by the
Austrian Lightning Location System ALDIS
W. Schulz, H. Pichler, G. Diendorfer
C. Vergeiner, S. Pack
OVE-ALDIS
Vienna, Austria
Institute of High Voltage Engineering and System
Management, Graz University of Technology
Graz Austria
flashes and especially for two positive flashes with subsequent
strokes following the same channel as the first stroke.
Abstract — In this paper we present a detailed evaluation of the
performance of the Austrian Lightning location system (LLS)
ALDIS regarding detection of positive flashes. Additional to the
performance of the LLS some parameters of positive flashes are
determined. We also present detailed information about two
positive flashes with a subsequent stroke following the same
channel to ground as the first stroke.
II.
A. Lightning location system
The Austrian lightning location system ALDIS was used to
determine the distance from the recording location to the
stroke, the polarity and the peak current of the stroke. The
Austrian LLS is an eight sensor LLS (type LS7000)
manufactured by Vaisala Inc. This eight sensor network is
incorporated in the European LLS called EUCLID (see Fig. 1).
Therefore the performance determined for the ALDIS network
is basically identical with the performance of the EUCLID
network in the region of Austria. More details about the
ALDIS network and about the EUCLID network can be found
in [12] and in [9], [13], respectively.
Keywords-component; Lightning location systems; positive
lightning; performance evaluation; E-Field measurements, video
recording,
I.
INTRODUCTION
Naturally occurring positive flashes are not as frequent as
negative flashes [1] and therefore available information about
the parameters of positive flashes are not as complete as for
negative flashes. Recently Saba et al. [2] published the most
comprehensive review about those parameters based on highspeed video observations, lightning location data and E-field
measurement data. In their dataset they included and examined
also nine positive flashes from measurements in Austria which
are also part of the dataset used for the study presented in this
paper.
B. Video and Field Recording System (VFRS)
The electric field recording system consisted of a flat plate
antenna, an integrator/amplifier, a fiber optic link, a GPS
receiver, a PC with two PCI cards (a Meinberg GPS card and a
National Instruments data acquisition card NI PCI-6111) and a
data acquisition box from National Instruments. It is important
to note that for all measurements a fiber optic link was used to
connect the integrator with the data acquisition box in order to
avoid any erroneously induced voltages due to the
electromagnetic lightning fields.
Performance evaluation for lightning location systems
(LLS) are currently performed all over the world with ground
truth data typically from



INSTRUMENTATION
triggered lightning [3], [4]
tower lightning [5], [6] or
video and field measurement data [7], [8], [9].
As video camera a Basler Pilot piA640–210gm camera was
used. This monochrome camera (8 bit per pixel) produces, at a
maximum frame rate of 200 frames per second (fps), data of
about 60 Mbytes per second. The camera is time synchronized
to the field recording system and therefore also the camera data
are GPS synchronized. A red filter type 29 (dark red) was used
in front of the camera lens in order to get better image contrast
during daytime recordings. We have set the camera to record
with 200 fps for all recordings except five flashes of the data
collected in 2008 were recorded with 100 fps.
To our best knowledge, for triggered and tower lightning no
performance evaluation of LLS regarding positive lightning
exists today. Only very limited performance analysis based on
video and field measurements are available for positive flashes.
In [8] the characteristics of cloud to ground lightning in the
great plains were analyzed and a detection efficiency (DE) of
the NLDN of 89%/88% for positive flashes/strokes is reported.
Ballarotti and coworkers included positive flashes in their
general DE statistics and found flash DE of 68% [10] for all
flashes independent of their polarity for the Brazilian LLS
RINDAT.
The VFRS is described in more detail in [11], [14].
In this paper we are presenting an extended version of the
initial analyses presented in [11] with more data. In addition
some detailed information is given about parameters of positive
75
2013 International Symposium on Lightning Protection (XII SIPDA), Belo Horizonte, Brazil, October 7-11, 2013.
two flashes a subsequent stroke followed the channel of the
preceding stoke clearly visible on the video records. All the
other observed subsequent strokes created a new channel to
ground.
For the majority of the following analyses we used data
from all the 109 flashes but in some cases we could use only a
subset of the data, e.g. when observation conditions (poor
visibility) did not allow determination of the continuing current
(CC) duration with sufficient accuracy.
Figure 1: EUCLID network – state of sensor locations March 2013
III.
Figure 2: Locations of temporary operation of the VFRS in Austria
from 2008 to 2012 where positive flashes where recorded
DATA AND METHODOLOGY
Contrary to negative flashes it is not possible to estimate
the location accuracy of the LLS with E-field and video data as
done in [15] because positive flashes with subsequent strokes
in the same channel are much too rare.
During 15 storms in summer periods from 2008 to 2012 we
have recorded a total of 109 positive flashes (see Table I).
TABLE I: Number of recorded positive flashes recorded with the
VFRS
Year
2008
2009
2010
2012
Total
# storms
1
1
6
7
15
IV.
# flashes
9
1
72
27
109
RESULTS
For all the 109 positive flashes in our data set we
determined a mean multiplicity of 1.1 and a percentage of
single stroke flashes of 91%.
The peak current for the recorded strokes was provided by
the Austrian lightning location system. The median peak
current of all the positive cloud-to-ground strokes was 34 kA,
the smallest peak current was 7 kA and the largest was 208 kA.
The median peak current of 34 kA is somewhat lower than
reported in [2] for similar observations in the U.S. where a
median peak current of 39.4 kA was determined for 116
positive strokes. We have to note that there exists no peak
current calibration of the lightning location data for positive
strokes [5] and therefore the values given above are rough
estimates, nevertheless the same field to peak current
conversion used by the LLS was used in [2] and in this study.
Fig. 3 shows the histogram of the peak currents separated in
first and subsequent strokes.
The E-field and video records were collected at different
locations in the east and south of Austria (see Fig. 2). Flashes
are considered as positive if all strokes are of positive polarity.
Information about stroke location, peak current and polarity of
each stroke was obtained from the LLS data. The polarity of
the LLS data was also compared to the polarity provided by the
VFRS. No discrepancy was found for all the flashes. The mean
distance of all strokes to the recording locations was 22 km
(ranging from a minimum distance of 3 km to a maximum
distance of 39 km). The grouping of strokes to flashes was
basically done applying the same criteria as normally used by
LLS with a maximum distance between the stroke locations of
10 km and a maximum flash duration of 1s. No maximum
interstroke interval criterion was applied. Positive lightning is
typically a single stroke flash and only 10 of the 109 (9 %)
positive flashes had a multiplicity of greater than one. Only in
76
2013 International Symposium on Lightning Protection (XII SIPDA), Belo Horizonte, Brazil, October 7-11, 2013.
the recording site (verified as IC with the E-field and video
data). 65% (133/205) of those IC discharges were actually
misclassified as CG strokes. 69% (92/133) of the misclassified
events were of negative and 31% (41/133) of positive polarity.
A reason that the network misclassified more negative than
positive events is that the LLS is configured to classify positive
events with peak current less than 5 kA as IC discharges. It is
interesting to note that only 11% (15/133) had amplitudes |Ip| >
10kA. Having in mind that only 5 +CG strokes out of 119 (4%)
were misclassified as IC (+CG → +IC misclassification) this
means that the network misclassifies mainly in the direction
+IC → +CG.
Subsequent strokes in positive lightning flashes are really
rare events. Even less frequent are positive subsequent strokes
which follow the same channel to ground as the previous
stroke. Therefore in the following section we describe in more
detail the only two positive flashes we have recorded up to now
with a subsequent stroke in the same channel as the first stroke.
Figure 3: Histogram of the estimated peak currents for positive
strokes
With the video data it is also possible to determine the
duration of the CC. For a total of 78 strokes a CC was clearly
visible. Because of the 5 ms time resolution of the video
images we analyzed only CC with a duration longer than 40 ms
(long CC according to [16], [17]). Out of the 78 strokes 49
(63%) exhibited a CC with a duration exceeding 40 ms. The
mean duration of all long CC was 144 ms. A histogram of all
long CC durations is given in Fig. 4.
Both flashes were recorded on the same day (15.7.2010) in
the same thunderstorm. During this particular thunderstorm the
majority of recorded flashes (34 out of 44 or 77%) exhibited
positive polarity, indicating that this thunderstorm was an
unusual type of storm. We categorized them as flashes with
subsequent stroke in the same channel because on the video
frames visible geometric features of the stroke channel between
1st and subsequent stroke are identical. Of course we are
limited in our analysis by the field of view.
The distance between the LLS provided locations for the
two strokes in the same channel of flash #158 (see Fig. 5) is
about 500 m and therefore within the range of location
uncertainty of the LLS. The interstroke interval between these
two strokes was about 19 ms.
Figure 4: Histogram of the long CC durations
90 ms
70 ms
Out of the 109 positive flashes captured by our VFRS, the
LLS located and correctly classified 106 flashes (flash
detection efficiency 97%), and out of the 119 strokes the
system located and correctly classified 110 (stroke detection
efficiency 92%). The criteria to determine the DEs are quite
strict because not only the location of the stroke has to be
provided with certain quality criteria (chisqu < 10 and semi
major axis of the error ellipse smaller than 7.5 km), but also the
CG/IC categorization by the LLS has to be correct.
A)
B)
Figure 5: Flash #158, striking point ~25 km from the recording site.
A) first stroke, B) subsequent stroke following the same channel
Out of the 9 “missed” strokes 5 were still detected but
misclassified as intracloud (IC) discharges. This means that
basically only 4 (3%) strokes were not detected by the LLS. It
is interesting to note that all these four strokes exhibited a long
CC. On the other hand the LLS misclassifies also ICs as CGs.
For each flash the VFRS records a total of 6 seconds of E-field
and video data, 2 seconds before and 3 seconds after the trigger
and the second where the trigger occurred. Within these 6
seconds of all recorded flashes the LLS located 205 IC
discharges (112 negative and 93 positive ICs) within 30km of
77
2013 International Symposium on Lightning Protection (XII SIPDA), Belo Horizonte, Brazil, October 7-11, 2013.
For the second positive flash (#164 – see Fig. 6) with a
subsequent stroke in the same channel we estimated an
interstroke interval of about 90 ms (determined from the Efield data).
875 ms
flashes of 91%. The median peak current of all the positive
cloud-to-ground strokes was 34 kA (based on LLS data), the
smallest peak current was 7 kA and the largest was 208 kA. 49
(63%) out of the 78 strokes exhibited a CC with a duration
exceeding 40 ms and the mean duration of all long CC was
144 ms.
Because positive flashes with subsequent strokes in the
same channel are really rare we documented two cases of them.
The categorization of flashes with strokes in the same channel
was done based on identical geometric features visible on the
video frames showing the different strokes. The interstroke
intervals of both flashes (19 ms for flash #158 and 90 ms for
flash #164) are smaller compared to the mean interstroke
interval of positive flashes with subsequent strokes creating a
new channel (202 ms based on 7 flashes).
970 ms
A)
B)
Figure 6: Flash #164, striking point ~27 km from the recording site.
A) first stroke, B) subsequent stroke following the same channel
REFERENCES
The positive flashes with subsequent strokes creating a new
channel to ground exhibit a mean interstroke interval of 202 ms
(only 7 flashes are included because for one flash only light
appears on the video image).
V.
[1]
[2]
SUMMARY AND DISCUSSION
With data from the VFRS the performance of the Austrian
LLS ALDIS regarding positive flashes was analyzed. As a
result a flash/stroke DE of 97%/92% was determined. The
stroke DE of 92% is significantly higher than the 83% stroke
DE for negative strokes [18] because the average peak current
for positive strokes is greater than for negative strokes. Flash
and stroke DE for positive lightning are somewhat higher in
Austria compared to the corresponding values for the NLDN
(89%/88% [7]) because the mean sensor baseline (average
distance between neighboring sensor locations) in Austria is
smaller than in the NLDN. We could further show that the LLS
mainly misclassifies in the direction of +IC being erroneously
classified as +CG (20%). A comparison of the results from this
paper to results from the NLDN for positive flashes [8] is
shown in Table II.
[3]
[4]
[5]
TABLE II: Number of detected and independently validated positive
CG events
ALDIS
NLDN [8]
detected
+CGs
151
195
validated
+CGs
110
82
[6]
validated
+ICs
41
113
[7]
Table 2 shows that the NLDN misclassified 58% (113/195)
and ALDIS misclassified 27% (41/151) of the detected +CGs.
The percentage of misclassified NLDN +CGs is higher because
[8]

In the NLDN data duplicated events are included
[9]

ALDIS classifies positive events with peak current less
than 5 kA as ICs
[10]
Nevertheless the current result means that positive CG
lightning data is significantly contaminated with IC data.
[11]
The data recorded with the VFRS are also useful to
determine some specific lightning parameters in Austria. For
all the 109 positive flashes in our data set we determined a
mean multiplicity of 1.1 and a percentage of single stroke
[12]
78
V. A. Rakov and M. A. Uman, Lightning - Physics and Effects.
Cambridge University Press, 2003.
M. M. F. Saba, W. Schulz, T. A. Warner, L. Z. S. Campos, C.
Schumann, E. P. Krider, K. L. Cummins, and R. E. Orville, “Highspeed video observations of positive lightning flashes to ground,”
Journal of Geophysical Research: Atmospheres, vol. 115, no. D24,
pp. 1–4, Dec. 2010.
J. Jerauld, V. A. Rakov, M. A. Uman, K. J. Rambo, D. M. Jordan,
K. L. Cummins, and J. A. Cramer, “An evaluation of the
performance characteristics of the U.S. National Lightning
Detection Network in Florida using rocket-triggered lightning,”
Journal of Geophysical Research: Atmospheres, vol. 110, no. D19,
p. D19106, Oct. 2005.
A. Nag, S. Mallick, V. A. Rakov, J. S. Howard, C. J. Biagi, J. D.
Hill, M. A. Uman, D. M. Jordan, K. J. Rambo, J. E. Jerauld, B. A.
DeCarlo, K. L. Cummins, and J. A. Cramer, “Evaluation of U.S.
National Lightning Detection Network performance characteristics
using rocket-triggered lightning data acquired in 2004–2009,”
Journal of Geophysical Research: Atmospheres, vol. 116, no. D2, p.
D02123, Jan. 2011.
G. Diendorfer, W. Schulz, C. Cummins, V. A. Rakov, M. Bernardi,
F. De la Rosa, B. Hermoso, A. M. Hussein, T. Kawamura, F.
Rachidi, and H. Torres, “Review of CIGRE Report ‘Cloud-toGround Lightning Parameters Derived from Lightning Location
Systems – The Effects of System Performance’,” in CIGRE, 2009,
no. 376.
G. Diendorfer, “LLS Performance Validation using Lightning to
Towers,” in International Lightning Detection Conference (ILDC),
2010, vol. 230, no. 1, pp. 1–15.
C. J. Biagi, K. L. Cummins, K. E. Kehoe, and E. P. Krider,
“National Lightning Detection Network (NLDN) performance in
southern Arizona, Texas, and Oklahoma in 2003–2004,” Journal of
Geophysical Research: Atmospheres, vol. 112, no. D5, p. D05208,
Mar. 2007.
S. A. Fleenor, C. J. Biagi, K. L. Cummins, E. P. Krider, and X.-M.
Shao, “Characteristics of cloud-to-ground lightning in warm-season
thunderstorms in the Central Great Plains,” Atmospheric Research,
vol. 91, no. 2–4, pp. 333–352, Feb. 2009.
W. Schulz, “Performance Evaluations of the European Lightning
Location System EUCLID,” ECSS, 2011.
M. M. F. Saba, O. Pinto, M. G. Ballarotti, K. P. Naccarato, and G.
F. Cabral, “Monitoring the Performance of the Lightning Detection
Network by means of a High-Speed Camera,” in International
Lightning Detection Conference (ILDC), 2004.
W. Schulz and M. M. F. Saba, “First Results of Correlated
Lightning Video Images and Electric Field Measurements in
Austria,” in Lightning Protection (X SIPDA), 2009 International
Symposium on, 2009, pp. 2005–2007.
W. Schulz, K. Cummins, G. Diendorfer, and M. Dorninger, “Cloudto-ground lightning in Austria: A 10-year study using data from a
2013 International Symposium on Lightning Protection (XII SIPDA), Belo Horizonte, Brazil, October 7-11, 2013.
[13]
[14]
[15]
[16]
lightning location system,” Journal of Geophysical Research:
Atmospheres, vol. 110, no. D9, p. D09101, May 2005.
G. Diendorfer, K. L. Cummins, and W. Schulz, “EUCLID – State of
the Art Lightning Detection,” EUMETNET Lightning Taks Force.
pp. 1–21, 2010.
W. Schulz, B. Lackenbauer, H. Pichler, and G. Diendorfer, “LLS
data and correlated continous E-Field measurements,” in Lightning
Protection (VIII SIPDA), 2005 International Symposium on, 2005.
W. Schulz, C. Vergeiner, H. Pichler, G. Diendorfer, and K.
Cummins, “Location Accuracy Evalution of the Austrian Lightning
Location Systems ALDIS,” in International Lightning Detection
Conference (ILDC), 2012, no. 1.
[17]
[18]
79
M. Brook, N. Kitagawa, and E. J. Workman, “Quantitative study of
strokes and continuing currents in lightning discharges to ground,”
Journal of Geophysical Research, vol. 67, no. 2, pp. 649–659, Jan.
1962.
N. Kitagawa, M. Brook, and E. J. Workman, “Continuing currents
in cloud-to-ground lightning discharges,” Journal of Geophysical
Research, vol. 67, no. 2, pp. 637–647, Jan. 1962.
W. Schulz, C. Vergeiner, H. Pichler, G. Diendorfer, and S. Pack,
“Validation of the Austrian Lightning Location System ALDIS for
negative Flashes,” in CIGRE C4 Colloquium on Power Quality and
Lightning, 2012, pp. 13–16.