IEC 62858:2015

IEC 62858 ®
Edition 1.0 2015-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Lightning density based on lightning location systems (LLS) – General
principles
Densité de foudroiement basée sur des systèmes de localisation de la foudre
(LLS) – Principes généraux
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IEC 62858 ®
Edition 1.0 2015-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Lightning density based on lightning location systems (LLS) – General

principles
Densité de foudroiement basée sur des systèmes de localisation de la foudre

(LLS) – Principes généraux
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS : 29.020, 91.120.40 ISBN 978-2-8322-2820-3

– 2 – IEC 62858:2015 © IEC 2015

CONTENTS
FOREWORD . 3

INTRODUCTION . 5

1 Scope . 6

2 Normative references . 6

3 Terms, definitions and abbreviations . 6

3.1 Terms and definitions . 6

3.2 Abbreviations . 7
4 General requirements . 8
4.1 General . 8
4.2 Stroke-to-flash grouping . 9
4.3 Minimum observation periods . 9
4.4 Observation area . 9
4.5 Grid cell size . 9
4.6 Edge effect correction . 10
5 Validation of lightning location system performance characteristics . 10
Bibliography . 12

INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
LIGHTNING DENSITY BASED ON LIGHTNING LOCATION SYSTEMS (LLS) –

GENERAL PRINCIPLES
FOREWORD
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International Standard IEC 62858 has been prepared by IEC technical committee 81:

Lightning protection.
The text of this standard is based on the following documents:
FDIS Report on voting
81/470/FDIS 81/494/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

– 4 – IEC 62858:2015 © IEC 2015

The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC website under "http://webstore.iec.ch" in the data

related to the specific publication. At this date, the publication will be

• reconfirmed,
• withdrawn,
• replaced by a revised edition, or

• amended.
INTRODUCTION
International standards for lightning protection (e.g. IEC 62305-2) provide methods for the

evaluation of the lightning risk on buildings and structures.

The lightning ground flash density N , defined as the mean number of lightning flashes to

G
ground per square kilometer per year is the primary input parameter to perform such an

evaluation.
In many areas of the world N is derived from data provided by lightning location systems
G
(LLS), but no common rule exists defining requirements either for their performance or for the

elaboration of the measured data.

– 6 – IEC 62858:2015 © IEC 2015

LIGHTNING DENSITY BASED ON LIGHTNING LOCATION SYSTEMS (LLS) –

GENERAL PRINCIPLES
1 Scope
This International Standard introduces and discusses all necessary measures to make
reliable and homogeneous the values of N obtained from LLS in various countries. Only

G
parameters that are relevant to risk assessment are considered.

2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 62305-1, Protection against lightning – Part 1: General principles
IEC 62305-2, Protection against lightning – Part 2: Risk management
3 Terms, definitions and abbreviations
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 62305-1 and
IEC 62305-2, as well as the following, apply.
3.1.1
cloud-to-ground lightning
CG
discharge that is comprised of one or more cloud-to-ground lightning strokes that propagate
from cloud to ground or vice versa and lead to a net transfer of charge between cloud and
ground
Note 1 to entry: This note applies to the French language only.
3.1.2
cloud lightning
IC
discharge occurring within or among thunderclouds (intracloud), or between thunderclouds
(intercloud), or between cloud and air, without a ground termination
Note 1 to entry: This note applies to the French language only.
3.1.3
first return stroke
first stroke to ground of a cloud-to-ground lightning discharge
Note 1 to entry: The stepped leader and attachment process precede the first return stroke.
3.1.4
subsequent stroke
subsequent stroke to ground that follows a previous (return) stroke in the same flash

Note 1 to entry: A subsequent stroke is preceded by a dart leader and may or may not have the same ground

strike-point as any previous (return) stroke in the same flash.

3.1.5
multiplicity
number of first and subsequent strokes in a cloud-to-ground lightning flash

3.1.6
ground flash density
N
G
–2 –1
mean number of cloud-to-ground flashes per unit area per unit time (flashes × km × year )

3.1.7
ground strike-point density
N
SG
mean number of strike-points to ground or to ground based objects per unit area per unit time
–2 –1
(strike-points × km × year )
3.1.8
lightning sensor
device that measures electromagnetic signals produced by lightning discharges
3.1.9
lightning location system
LLS
network of lightning sensors that work together to detect and geolocate lightning events within
the area of the system’s coverage
Note 1 to entry: This note applies to the French language only.
3.1.10
confidence ellipse
ellipse centred on the estimated ground strike-point, describing the degree of confidence of
the location estimation (e.g. 50 %, 90 %, 99 %) based on sensor measurement errors
Note 1 to entry: The confidence ellipse is described in terms of the lengths of the semi-major and semi-minor
axes as well as the bearing of the semi-major axis.
3.1.11
uptime
duration of fully functional operation of a lightning location system sensor, expressed as a
percentage of the total observation time

3.1.12
stroke detection efficiency
flash detection efficiency
percentage of strokes or flashes detected as a percentage of the total number of strokes or
flashes occurring in reality
3.1.13
median location accuracy
median value of the distances between real stroke locations and the stroke locations given by
the lightning location system
3.2 Abbreviations
CG cloud-to-ground lightning
DE flash detection efficiency
– 8 – IEC 62858:2015 © IEC 2015

IC cloud lightning
LA location accuracy
LLS lightning location system
N ground flash density
G
N ground strike-point density
SG
4 General requirements
4.1 General
The performance characteristics of a lightning location system (LLS) [3, 15] determine the
quality of the lightning data available for calculating N . A value of N with an error of ± 20 %
G G
or less is deemed to be acceptable for lightning risk assessment. Data from any LLS that is
able to detect CG lightning and accurately determine the point of strike of CG strokes can be
used for the purpose of N computation. The following LLS performance characteristics are
G
required for computation of N with adequate accuracy.
G
• Flash detection efficiency (DE): the value of the annual average flash detection
efficiency of an LLS for CG lightning shall be at least 80 % in the region over which N
G
has to be computed. This DE is usually obtained within the interior of the network. The
interior of the network is defined as the region within the boundary defined by the
outermost adjacent sensors of the network.
• Location accuracy (LA): the value of the median location accuracy of an LLS for CG
strokes shall be better than 500 m in all regions in the region over which N has to be
G
computed. This LA is usually obtained within the interior of the network.
• Classification accuracy: in a network with a flash DE that meets the criteria set for N
G
calculation, if too many CG strokes are misclassified as cloud pulses, or vice versa, this
may lead to erroneously low or high values of N This is especially true for single-stroke
G.
CG flashes. A classification accuracy (CG flashes not misclassified as IC) of at least 85 %
is required.
It is not recommended to use N values having more than 2 decimals.
G
These performance characteristics of LLS can be determined using a variety of methods
including network self-referencing (using statistical analysis of parameters such as standard
deviation of sensor timing error, semi-major axis length of the 50 % confidence ellipse, and
the number of reporting sensors, which may be known from the LLS manufacturer or available
from the LLS data) and comparison against ground-truth lightning data obtained using various

techniques. These methods are discussed in Clause 5.
The flash DE, LA, and classification accuracy of LLS depend on a few fundamental
characteristics of the network. LLS owners, operators, and data-providers should consider the
following factors while designing and maintaining their networks to ensure that the lightning
data are of adequate quality for N computation.
G
• Sensor baseline distance: the distance between adjacent sensors in an LLS or sensor
baseline distance is influenced by the area of desired coverage and the sensitivity of
individual sensors. Sensor baseline distance is one of the factors that determine the DE
and LA of an LLS. The maximum sensor baseline distance of an LLS shall be such that
the DE and LA of the network meet the criteria for N calculation described above.
G
_______________
Numbers in square brackets refer to the Bibliography

• Sensor sensitivity: the sensitivity of sensors in an LLS primarily determines the ability of

the network to detect lightning events of different peak currents. The sensitivity of sensors

in an LLS shall be such that lightning events with peak currents in the range of 5 kA to

300 kA are detected and reported by the LLS. Sensor sensitivity is determined by various

factors such as trigger threshold, electronic gain, sensor bandwidth and background

electromagnetic noise.
• Sensor uptime: the uptime of different sensors in a network determines the DE and LA of

the network. The spatial and temporal variations of DE and LA are determined by the

location of sensors that are up and contributing to the network. Hence it is important to

guarantee that LLS sensors are up and running with no interruption.

4.2 Stroke-to-flash grouping
Return strokes detected by lightning location systems shall be grouped into flashes for N
G
calculation. This grouping is done based on a spatio-temporal window.
A subsequent stroke is grouped with the first return stroke to form a flash if the following
criteria are met:
a) the stroke occurs less than or equal to 1 s after the first return stroke;
b) the location of the stroke is less than or equal to 10 km from the first return stroke;
c) the time interval for successive strokes is less than or equal to 500 ms.
The flash position is assumed to be the location of the first stroke.
Multiple ground strike-points shall be included in the same flash using the above criteria.
Currently a multiplication factor of 2, relating N to N shall be used [2].
G SG
4.3 Minimum observation periods
A sufficiently long sampling period is required to ensure that short time scale variations in
lightning parameters due to a variety of meteorological oscillations are accounted for.
Additionally, large scale climatological variations limit the validity of historic data. Some
lightning detection networks have been recording lightning data for several decades and
during this time there have been measurable changes to the global meteorology.
Lightning data for at least ten years is required, with the newest data used not being older
than five years.
4.4 Observation area
The observation area is an area over which lightning data of quality as described above are
available.
Different networks and sensor technologies will have different sensitivities with which they
detect lightning. Network coverage falls off outside the boundaries of a network. In general,
lightning data within half the average sensor baseline distance (distance between adjacent
sensors in the network) from the boundary of the network should be of sufficient quality for N
G
calculation [11].
4.5 Grid cell size
Ground flash density (N ) values vary annually and regionally. Lightning data have to be
G
evaluated as a raster map, i.e. a gridded array of cells constrained by a geographic boundary:
the area of interest is divided into a regular grid (tessellation of the geographic area) and the
N calculation function is applied to all the flashes occurring within the grid. The resulting
G
value is then assumed to be the meaningful value within that area.

– 10 – IEC 62858:2015 © IEC 2015

The grid size shall be chosen in such a way that the dimensions of each cell and the number

of years considered both comply with the minimum requirements obtained from Formula (1),

following Poisson distribution and the law of rare events, thus obtaining an uncertainty of less

than 20% at 90% confidence level [8].

× T × A ≥ 80 (1)
N
G obs cell
where
–2 –1
N is the ground flash density, in km × year ;

G
T is the observation period, in years;
obs
A is the area of each single cell, in km .
cell
The data used in this analysis shall conform to both the requirements of 4.2 and 4.3. The
minimum permissible cell dimension, irrespective of ground flash density and observation
period, shall not be less than double the median location accuracy.
4.6 Edge effect correction
As defined in 4.5 the size of the smallest cell that can be considered should be such that it
contains at least 80 flashes. In order to avoid edge effects for this cell, the N value shall be
G
obtained by integrating over a finer sub-grid of 1 km × 1 km resolution.
5 Validation of lightning location system performance characteristics
The performance characteristics of an LLS determine the quality of the lightning data
available. These performance characteristics include:
– detection efficiency for IC and CG flashes and CG strokes;
– location accuracy;
– peak current estimation accuracy; and
– lightning classification accuracy.
As stated in Clause 4, for N and N determination of CG flash DE, LA, and lightning,
G SG
classification accuracy is of primary importance. These performance characteristics can be
evaluated using a variety of techniques which are summarized below.
a) Network self-reference: In this technique, statistical analysis of parameters (e.g. [11])
such as standard deviation of sensor timing error, semi-major axis length of the 50 %
confidence ellipse, and the number of reporting sensors, is used to infer the LA and DE of
an LLS. Examples of such studies are found in [4] and [7]. This method requires data

collected by the network after it has been properly calibrated. It can provide a good
estimate of the network’s performance in a cost-effective, practical manner.
b) Rocket-triggered lightning and tall object studies: This method uses data from rocket-
triggered lightning experiments or lightning strikes to tall objects (e.g., instrumented
towers) as ground-truth to evaluate the performance characteristics of an LLS within
whose coverage area the triggered lightning facility or the tall object is located. The LA,
DE, peak current estimation accuracy, and lightning classification accuracy of an LLS can
be measured using this method. Examples of studies using rocket-triggered lightning for
LLS performance evaluation include [6], [8], and [12], [13]. While these methods provide
the best ground-truth data for performance characteristics validation for CG lightning (and
are the only ways to directly validate peak current estimation accuracy of an LLS), they
may be very expensive, may not be practical for all regions (as there are only a few
triggered lightning facilities and instrumented towers across the world), and are a valid
indicator of LLS performance only for the region where the rocket-triggered lightning
facility or tall object is located (especially in cases where the performance of the LLS is
expected to vary significantly from region to region). Additionally, rocket-triggered
lightning provides data for return strokes similar to only subsequent strokes in natural

lightning. No data for first strokes in natural lightning can be obtained using this

technique. This is also often the case for lightning strikes to tall objects depending upon

the height of the object, local terrain, storm type, and other factors. Since first strokes in

natural lightning are expected to have, on average, peak fields and currents that are a

factor of two larger than those for subsequent strokes (e.g. [9]), CG flash and stroke DE

estimated for an LLS using these methods may be somewhat of an underestimate.

c) Video camera studies: Lightning data obtained using video cameras can be used as

ground-truth to evaluate the performance characteristics of an LLS within whose coverage

area the lightning discharges occur. The LA, DE and lightning classification accuracy of an

LLS can generally be estimated using this method. Examples of studies using video

camera for LLS performance evaluation include [1] and [14]. In this method, data
collection can be time-consuming and challenging because the exact locations of lightning
discharges to be captured on video cannot be predicted. Additional instrumentation such
as antennas measuring electric field from lightning discharges is often required for this
technique.
d) Inter-comparison among networks: The performance of one LLS that is being tested
can be compared against another LLS that may be used as reference, as long as the
reference LLS is extremely well calibrated and its performance has been characterized
independently. This method allows inferences to be made about the detection efficiency
and location accuracy of the test LLS relative to the reference LLS. If the reference
network provides VHF lightning mapping, inference about the test network’s IC detection
efficiency can be made. Examples of such studies include [10]. One limitation of this
technique is that the test and reference networks have to overlap substantially. Further, if
the performance of the reference network is unknown or if the reference network is not
well calibrated, any inferences about the test network’s performance are invalid.
While one or a combination of the above techniques can be used to evaluate the performance
characteristics of an LLS, it is important to understand the strengths and weaknesses of the
methods used in order to obtain reliable estimates of LLS performance characteristics.

– 12 – IEC 62858:2015 © IEC 2015

Bibliography
[1] BIAGI, C.J., CUMMINS, K.L., KEHOE, K.E. and KRIDER, E:P. (2007), National

Lightning Detection Network (NLDN) Performance in Southern Arizona, Texas, and

Oklahoma in 2003–2004, J. Geophys. Res., 112, D05208, doi:10.1029/2006JD007341.

[2] BOUQUEGNEAU, C., KERN, A. and ROUSSEAU, A. (2012), Flash Density applied to

th
Lightning Protection Standards, Ground’2012 & 5 LPE, Bonito, Brazil, 26-30

November.
[3] CIGRE Report 376, April 2009, Working Group C4.404: Cloud-to-ground Lightning

Parameters derived from Lightning Location Systems – The Effects of System
Performance
[4] CUMMINS, K.L., MURPHY, M.J., CRAMER, J.A., SCHEFTIC, W., DEMETRIADES, N.
and NAG, A. (2010), Location accuracy improvements using propagation corrections: a
st
case study of the U.S. National Lightning Detection Network, 21 Intl. Lightning
Detection Conf., Orlando, FL, U.S., 19-20 April.
[5] DIENDORFER, G. (2008): Some Comments on the Achievable Accuracy of Local
Ground Flash Density Values, International Conference on Lightning Protection (ICLP).
[6] JERAULD, J., RAKOV, V.A., UMAN, M.A., RAMBO, K.J., JORDAN, D.M., CUMMINS,
K.L. and CRAMER, J.A. (2005), An Evaluation of the Performance Characteristics of
the U.S. National Lightning Detection Network in Florida using Rocket-triggered
lightning, J. Geophys. Res., 110, D19106, doi:10.1029/2005JD005924.
[7] NACCARATO, K.P., PINTO Jr., O. and MURPHY, M.J. (2008), Performance Analysis
rd
Intl. Conf.
of the BrasilDAT network, 2008 Intl. Conf. on Grounding and Earthing / 3
on Lightning Physics and Effects, Florianopolis, Brazil, 16-20 November, pp. 329-338.
[8] NAG, A., MALLICK, S., RAKOV, V.A., HOWARD, J.S., BIAGI, C.J., HILL, J.D., UMAN,
M.A., JORDAN, D.M., RAMBO, K.J., JERAULD, J.E., DeCARLO, B.A., CUMMINS, K.L.
and CRAMER, J.A. (2011): Evaluation of U.S. National Lightning Detection Network
Performance Characteristics using Rocket-triggered Lightning Data acquired in 2004-
2009, J. Geophys. Res., vol. 116, D02123, doi:10.1029/2010JD014929.
[9] NAG, A., RAKOV, V.A., SCHULZ, W., SABA, M.M.F., THOTTAPPILLIL, R., BIAGI,
C.J., OLIVEIRA FILHO, A., KAFRI, A., THEETHAYI, N. and GOTSCHL, T. (2008), First
versus Subsequent Return-stroke Current and Field Peaks in Negative Cloud-to-
ground Lightning Discharges, J. Geophys. Res., 113, D19112,

doi:10.1029/2007JD009729.
[10] POELMAN, D.R., SCHULZ, W. and VERGEINER, C. (2013): Performance
Characteristics of Distinct Lightning Detection Networks covering Belgium, J. Atmos.
Ocean. Tech., vol. 30, pp. 942-951.
[11] SCHULZ, W. (1997), Performance Evaluation of Lightning Location Systems. Ph.D.
Thesis, Technical University of Vienna.
[12] SCHULZ, W., VERGEINER, C., PICHLER, H., DIENDORFER, G., PACKET, S. et al.
(2012), Validation of the Austrian Lightning Location System ALDIS for Negative
Flashes. CIGRE Symposium.
[13] SCHULZ, W., PICHLER, H., DIENDORFER, G., VERGEINER, C., PACK, S. (2013):
Validation of Detection of Positive Flashes by the Austrian Lightning Location System

th
(ALDIS), 12 Intl. Symposium on Lightning Protection (XII SIPDA), Belo Horizonte,

Brazil, 7-11 October, paper 2.2.

[14] SCHULZ, W., PEDEBOY, S., VERGEINER, C., DEFER, E. and RISON, W. (2014):

Validation of the EUCLID LLS during HyMeX SOP1, International Lightning Detection

Conference, Tucson.
[15] SCHULZ, W., PEDEBOY, S., SCHULZ, W. (2014): Validation of the ground strike-point

identification algorithm based on ground truth data, International Lightning Detection

Conference, Tucson.
_____________
– 14 – IEC 62858:2015 © IEC 2015

SOMMAIRE
AVANT-PROPOS . 15

INTRODUCTION . 17

1 Domaine d'application . 18

2 Références normatives . 18

3 Termes, définitions et abréviations . 18

3.1 Termes et définitions . 18

3.2 Abréviations . 20
4 Exigences générales . 20
4.1 Généralités . 20
4.2 Regroupement de décharges en éclairs . 21
4.3 Périodes d'observation minimales . 21
4.4 Zone d'observation . 22
4.5 Taille de cellule de grille . 22
4.6 Correction de l'effet de bord . 22
5 Validation des caractéristiques de performance d'un système de localisation de la
foudre . 22
Bibliographie . 25

COMMISSION ÉLECTROTECHNIQUE INTERNATIONALE

____________
DENSITÉ DE FOUDROIEMENT BASÉE SUR DES SYSTÈMES

DE LOCALISATION DE LA FOUDRE (LLS) –

PRINCIPES GÉNÉRAUX
AVANT-PROPOS
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de brevets et de ne pas avoir signalé leur existence.
La Norme internationale IEC 62858 a été établie par le comité d'études 81 de l'IEC:
Protection contre la foudre.
Le texte de cette norme est issu des documents suivants:
FDIS Rapport de vote
81/470/FDIS 81/494/RVD
Le rapport de vote indiqué dans le tableau ci-dessus donne toute information sur le vote ayant
abouti à l'approbation de cette norme.
Cette publication a été rédigée selon les Directives ISO/IEC, Partie 2.

– 16 – IEC 62858:2015 © IEC 2015

Le comité a décidé que le contenu de cette publication ne sera pas modifié avant la date de

stabilité indiquée sur le site web de l'IEC sous "http://webstore.iec.ch" dans les données

relatives à la publication recherchée. A cette date, la publication sera

• reconduite,
• supprimée,
• remplacée par une édition révisée, ou

• amendée.
INTRODUCTION
Les normes internationales pour la protection contre la foudre (p. ex.: IEC 62305-2)

fournissent des méthodes pour l'évaluation des risques de foudre sur les immeubles et autres

structures.
La densité de foudroiement N , définie comme le nombre moyen de coups de foudre au sol
G
par kilomètre carré et par an, est le paramètre d'entrée principal pour effectuer de telles

évaluations.
Dans de nombreuses régions du monde, N est dérivée de données fournies par des
G
systèmes de localisation de la foudre (LLS), mais il n'existe aucune règle commune
définissant les exigences en termes de performances ou d'élaboration de données de
mesure.
– 18 – IEC 62858:2015 © IEC 2015

DENSITÉ DE FOUDROIEMENT BASÉE SUR DES SYSTÈMES

DE LOCALISATION DE LA FOUDRE (LLS) –

PRINCIPES GÉNÉRAUX
1 Domaine d'application
La présente Norme internationale présente et évoque toutes les mesures nécessaires qui

visent à rendre fiables et homogènes les valeurs de N obtenues par les LLS dans différents
G
pays. Seuls les paramètres essentiels à l'analyse du risque sont pris en compte.
2 Références normatives
Les documents suivants sont cités en référence de manière normative, en intégralité ou en
partie, dans le présent document et sont indispensables pour son application. Pour les
références datées, seule l’édition citée s’applique. Pour les références non datées, la
dernière édition du document de référence s’applique (y compris les éventuels
amendements).
IEC 62305-1, Protection contre la foudre – Partie 1: Principes généraux
IEC 62305-2, Protection contre la foudre – Partie 2: Evaluation des risques
3 Termes, définitions et abréviations
3.1 Termes et définitions
Pour les besoins du présent document, les termes et définitions donnés dans l'IEC 62305-1 et
dans l'IEC 62305-2 ainsi que les suivants s'appliquent.
3.1.1
éclair nuage-sol
CG
décharge constituée d'un ou de plusieurs coups de foudre nuage-sol qui se propagent du
nuage vers le sol ou inversement et qui entraînent un transfert de charge entre le nuage et le
sol
Note 1 à l'article: L'abréviation "CG" est dérivée du terme anglais "cloud-to-ground lightning".
3.1.2
éclair nuage-nuage
IC
décharge à l'intérieur d'un nuage d'orage (intranuage), entre plusieurs nuages d'orage
(internuages) ou entre un nuage et l'air, qui ne touche pas le sol
Note 1 à l'article: L'abréviation "IC" est dérivée du terme anglais "intracloud – cloud lightning".
3.1.3
première décharge en retour
première décharge au sol d'une décharge orageuse nuage-sol
Note 1 à l'article: Le traceur par bonds et le processus de jointure précèdent la première décharge en retour.

3.1.4
décharge consécutive
décharge au sol consécutive qui suit une précédente décharge (en retour) au cours d'un

même éclair
Note 1 à l'article: Une décharge consécutive est précédée par un traceur en dard et peut avoir ou peut ne pas
avoir le même point d'impact au sol que toute décharge (en ret
...