Reconstruction of Lightning Channel Based on Acoustic ...International Journal on Electrical...

International Journal on Electrical Engineering and Informatics - Volume 11, Number 2, June 2019

Reconstruction of Lightning Channel Based on Acoustic Radiation

Ariadi Hazmi1, Primas Emeraldi1, Muhammad Imran Hamid1, Suci Melati1, and Nobuyuki Takagi2

1Andalas University, Department of Electrical Engineering, Padang, Indonesia

2Gifu University, Department of Electrical, Electronic and Computer Engineering, Gifu, Japan

[email protected]

Abstract: The acoustic radiation of lightning was used to get information on the lightning

channel, such as images and locations. A single station of short baseline lightning location was

installed to record the acoustic signals of lightning using a microphone array observation system

(MAOS). In this study, the differential time of arrival (DTOA) method was used to examine the

time variation in the acoustic signals of lightning and to reconstruct the 3D lightning channel

imaging. The results showed that there was good agreement between images recorded by

cameras and MAOS. The height of negative charge center in thundercloud is at 4.37-4.83 km.

The azimuth and elevation angles of the acoustic radiation source at higher latitude inside a

thundercloud of two recorded natural lightning discharges were 70.67o, 90o and 67.83o, 73.82o,

respectively. The acoustic signal of thunder lasted about 15.15-16.038 s. The system was able to

reconstruct the 3D lightning channel imaging.

Keywords: Lightning; cloud to ground; image; mapping; acoustic radiation.

1. Introduction

The stepped leader and attachment process prior to return strokes are closely related to

thundercloud to produce the electric field. The height of the bottom of the thundercloud to the

ground plays a significant role in increasing the leader step length occurring in virgin air [1]. It

is generally believed that the lightning stroke distance has been determined by the height of the

bottom of the thundercloud to ground. The leader propagation of natural lightning also plays an

important role in the lightning protection designs of tall objects on the ground has become a

concern of many researchers [2-5].

When the stepped leader approaches the ground (downward leader), its negative charge

attracts concentrated positive charge on the ground (upward leader) [6-9]. Furthermore, one of

these upward leaders will attach with a branch of the downward leader, causing a return stroke.

The return stroke impulsively heats the current-carrying air which then generates thunder and

radiates acoustic signals. The largest amplitudes of the acoustic signal are usually associated

with the return stroke of the lightning discharge. The acoustic signal can provide information on

the image of the lightning channel. The frequency range of acoustic emissions from lightning is

20-20,000 Hz [10-17]. Because the acoustic radiations from lightning include low frequencies,

a short baseline lightning location can be applied to reconstruct the lightning channel imaging

using a microphone array observation system (MAOS) with a single station. The method used

in finding the height of thundercloud and lightning location are the differential time of arrival

(DTOA). In addition, the acoustic radiation of lightning can be captured in a 360° perspective

and flashes hidden in clouds can be observed, which could increase the probability of capturing

lightning flashes compared with using the cameras [18-21].

The purpose of this study is to determine the height of thundercloud to ground and reconstruct

the lightning channel based on the acoustic radiation sources. As far we know, this is the first

time to measure the height of negative charge center in thundercloud in Padang, Indonesia. Our

observation results are compared with a few of previous studies in other regions.

2. Method

In this study, to analyze the acoustic signals of a lightning discharge and to reconstruct the

Received: April 12nd, 2019. Accepted: June 30th, 2019

DOI: 10.15676/ijeei.2019.11.2.8

341

3D imaging of the lightning channel, differential time of arrival (DTOA) was used as described

in the following section.

Differential time of arrival

The acoustic radiation of lightning discharges was recorded simultaneously by four different

microphones (for convenience ‘mic’ refers to microphone). Next, to obtain the DTOA at the

different microphones, all acoustic signals were examined by cross correlation. The equations of

DTOA used in this study are similar with used by Zhang et al. [18]. The time difference between

signal 2 (S2) and signal 3 (S3) is ∆𝑡 = 𝑡2 − 𝑡3 as shown in Figure 1.

|𝐷𝐻| = 𝑣 ∙ ∆𝑡 (1)

𝑣 = 322 + 0.6 𝑇 (2)

𝑣 = 353 𝑚/𝑠

Where v and T are the speed of thunder sound propagation and temperature, respectively.

cos(∠ 𝑂𝐷𝐻) =|𝐷𝐻|

|𝑂𝐷|=

𝑣×Δ𝑡

𝐿2 (3)

cos(∠ 𝐸𝐷𝐻) =|𝐷𝐸|

|𝐷𝐻|=

𝑣×Δ𝑡

𝐿2 (4)

|𝐷𝐸| = |𝐷𝐹| × cos(∠𝐺𝑂𝐹) (5)

|𝐷𝐸| = |𝐷𝐻| × cos(∠𝐻𝐷𝐹) cos(∠𝐺𝐷𝐹)

𝑣 × ∆𝑡

𝐿2

=|𝐷𝐻| × cos(∠𝐻𝐷𝐹) cos(∠𝐺𝐷𝐹)

|𝐷𝐻|= cos 𝛼 sin 𝛽

𝐿2 × cos 𝛼 cos 𝛽 = 𝑣 × ∆𝑡 = 𝑣 × |𝑡2 − 𝑡3| (7)

Figure 1. Schematic diagram of differential time of arrival of acoustic signals [18].

The azimuth (β) and elevation (α) in Figure 1 can be resolved by least square method for

nonlinear equations 8-10 as follows:

𝐿1 × 𝑠𝑖𝑛 𝛼 = 𝑣 × |𝑡2 − 𝑡1| = 𝑣 × ∆𝑡1 (8)

𝐿2 × 𝑐𝑜𝑠 𝛼 𝑐𝑜𝑠 𝛽 = 𝑣 × |𝑡2 − 𝑡3| = 𝑣 × ∆𝑡2 (9)

𝐿3 × 𝑐𝑜𝑠 𝛼 𝑠𝑖𝑛 𝛽 = 𝑣 × |𝑡2 − 𝑡4| = 𝑣 × ∆𝑡3 (10)

Where L is distance between the microphones.

Ariadi Hazmi, et al.

342

3. Observation and Data

Acoustic radiation of lightning was recorded using a single station of MAOS located in

Padang, Indonesia (-0.912° N, 100.418° E). The system consisted of one slow, one fast and one

loop antenna, two surveillance video cameras, four condenser microphones with a frequency

range of 20-20,000 Hz, and two digitizers. All the equipment was controlled by a computer that

was used to capture the electromagnetic, optic and acoustic signals of lightning. The slow

antenna was used as an external trigger to simultaneously trigger the acoustic signals of the

lightning discharge by the four microphones. The four acoustic signals were amplified by an

audiophile vacuum tube preamplifier with gain at 26-60 dB and maximum output at 10 dB. The

record length was set to 20 s with a pre-trigger of 10% of the record length and a sampling rate

of 100 kS/s. A schematic of the MAOS is shown in Figure 2, with the distance between the

microphones at 2 m.

Figure 2. Schematic of the MAOS.

4. Result and Discussions

In this study, two negative cloud to ground (-CG) lightning discharges were examined to

evaluate the MAOS and the algorithm of the DTOA lightning mapping system based on acoustic

radiation. Due to limited data, in this study only two acoustic signals of natural lightning were

analyzed, which were recorded at 16:49:28 PM and 19:02:33 PM on 8 September 2018 and 9

December 2018, respectively. The following section analyzes in detail the two -CG lightning

discharges, which will be referred to as -CG A and -CG B, respectively.

Detailed description of -CG A

The -CG A lightning discharge was recorded at 16:49:28 PM (local time). One of the video

camera frames that captured the lightning is shown in Figure 3. The electric field and magnetic

field changes recorded by the fast antenna and the loop antenna respectively are presented in

Figure 4a. Figure 4a indicates that 6 return strokes (RS) occurred in the lightning event. At the

same time, the associated acoustic signal of the lightning discharge was recorded by four

microphones, namely mic 1, mic 2, mic 3, and mic 4, respectively, as shown in Figure 4b.

According to the time difference between the optic and the first acoustic data records, the

lightning discharge occurred around 1 km from the observation site. Furthermore, using the

DTOA method, the azimuth-elevation angles and time of the acoustic signals were obtained by

calculating the different times of arrival for each microphone using the least square method and

cross correlation to find the peak values of the four microphone signals (see appendix A). The

3D lightning channel mapping can be reconstructed from the acoustic signal, the height of

Mic

rophones

Video Camera

Slow antenna

Fast antenna

Loop antenna

Dig

itiz

er 1

Dig

itiz

er 2

PCP

rea

mp

lifie

r

Amplifier

Amplifier

Amplifier

Ground

Thundercloud

Downward

leader

Upward

leader

Height

-

-

-

-

+

+

+


343

negative charges of thundercloud was 4.83 km as shown in Figure 5. The x, y, z directions and

time order origin from the azimuth and elevation angles and the acoustic signal of the lightning

channel, respectively, are displayed in Table 1.

Detailed description of -CG B

The -CG B lightning discharge was recorded at 16:49:28 PM (local time). One of the video

camera frames associated with the lightning discharge is displayed in Figure 3. In addition, the

electric field and magnetic field changes recorded by the fast antenna and the loop antenna,

respectively, are shown in Figure 6a. The recorded acoustic signals of the lightning discharge by

the four microphones, namely mic 1, mic 2, mic 3, and mic 4, respectively, are shown in Figure

4b. Based on the time difference between the optic and the first acoustic data records, the

lightning discharge occurred around 0.2 km from the observation site. The location of -CG B

was closer than that of -CG A, as can be seen in Figures 6 and 7b. The amplitude of the acoustic

signal of -CG B was higher than that of -CG A. Moreover, in the same way (see appendix A),

the azimuth-elevation angles and time for the acoustic signal were obtained by using the DTOA

method. A projection of the 3D lightning mapping results can be seen in Figure 5. The height of

negative charges of thundercloud was 4.37 km. The Cartesian coordinates (x, y, z) of the

radiation source and time order origin from the azimuth and elevation angles and acoustic signal

of the lightning channel, respectively, are presented in Table 2.

Figure 3. –CG A lightning flash image. (a) One of video camera frames, (b) The expanded

lightning channel image.

Table 1 and 2 tell us that the azimuth and elevation angles of the radiation sources at higher

latitude inside the thundercloud of both lightning were at 70.67°, 90° and 67.83°, 73.82°,

respectively. The minimum values of the azimuth and elevation angles were 56.16°, 2.38° and

1.28°, 0.56°, respectively. In the previous study, in China [18] using a rocket triggered lightning

and Sri Lanka [19] with natural lightning reported that they found the height of negative charges

of thundercloud were 0.74 km and 4.56 km, respectively. Compared with the value revealed in

China, the height of thundercloud in Indonesia and Sri Lanka were higher. The differences may

be due to different thundersorm types between the two regions. The propagation path of the

acoustic radiation sources was initiated from the ground to the cloud can be seen from the 3D

lightning mapping in Figures 5 and 8. Because the video camera speed was 30 fps, the cameras

were not able to record the branches of the lightning channels so that there are slight differences

between the lightning images recorded by the camera and the lightning images detected by the

MAOS. This may also be caused by errors in calculating the time difference measurements

because of background noise. The accuracy of the DTOA also depends on the time difference

measurement between the microphones. Furthermore, the acoustic signal of thunder lasted about

15.15-16.038 s as can be seen in Table 1 and 2.

(a) (b)


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Figure 4. The measured lightning discharge of –CG A. (a) Electric field and magnetic field

changes, (b) Acoustic radiation.

Figure 5. 3D lightning channel mapping of –CG A.

Figure 6. –CG B lightning flash image. (a) One of video camera frames, (b) The expanded

lightning channel image.

RS1 RS2RS3 RS4

RS5 RS6

(a) (b)

(a) (b)


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Figure 7. The measured lightning discharge of –CG B. (a) Electric field and magnetic field

changes, (b) Acoustic radiation.

Table 1. 2D location of –CG A. Table 2. 2D location of –CG B.

Azimuth

(o)

Elevation

(o) Time (s) Azimuth (o)

Elevation

(o) Time (s)

68.78 7.39 0.077 67.00 4.82 0.507

70.15 2.65 0.095 43.67 12.08 1.510

69.85 9.28 0.136 17.69 55.06 2.149

74.76 7.09 0.199 7.80 23.66 4.032

69.31 11.17 0.227 10.58 17.16 4.066

66.87 31.65 0.812 34.81 0.59 4.109

78.11 11.58 1.739 6.62 63.10 4.334

73.59 11.17 1.985 2.38 59.04 4.380

74.96 16.54 2.147 13.24 66.32 5.586

72.46 47.81 3.252 40.21 66.32 5.647

75.99 30.39 3.273 52.66 67.83 6.030

77.93 39.51 4.710 85.46 66.32 7.987

75.96 48.54 4.957 80.74 66.08 8.752

73.98 48.69 5.876 85.34 65.84 8.938

76.09 50.51 5.911 86.82 65.13 9.276

80.21 48.25 6.376 78.27 59.23 10.232

89.19 56.64 7.677 85.68 57.54 10.411

70.87 60.60 8.233 81.78 65.84 11.506

56.16 11.47 8.495 87.03 63.32 12.077

67.38 1.28 9.698 82.43 59.61 12.909

84.31 52.89 10.796 87.03 61.41 13.148

80.05 57.18 10.919 88.81 63.10 13.699

62.76 62.46 10.987 87.14 62.88 14.111

70.67 67.83 11.053 89.71 60.60 14.231

85.87 57.73 14.152 87.71 60.01 14.535

83.07 61.41 15.014 85.43 33.52 14.627

82.61 45.66 15.333 90.00 73.82 14.912

90.00 61.41 16.038 90.00 55.06 15.150

(a) (b)


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Figure 8. 3D lightning channel mapping of –CG B.

5. Conclusion

A microphone array observation system (MAOS) with a short baseline lightning mapping

system was used to record and analyze the acoustic radiation from natural lightning. The system

utilized the TDOA method and a number of signal processing tools, such as cross correlation

method to calculate the time delay and the least square method to estimate the azimuth and

elevation angles. The system was able to determine the height of thundercloud and reconstruct

the 3D imaging of the lightning channel. More data are needed to perfect and complement the

understanding of the acoustic radiation of the lightning channel.

6. Acknowledgment

This work is supported by Universitas Andalas of KRP2GB-PDU scheme, with grant no.

046/UN.16.17/PP.MGB/LPPM/2018.

Appendix A

Here t1, t2, t3 and t4 are the time values at correlated peaks of the same phase of the four signals

cross correlated the time values. t0 is the time difference between the light and the sound signal

of the lightning and t21, t31 and t41 are time differences between relevant microphone pairs.

Table 3. Time differences of –CG A

Time values of each considered signals (s) Time differences (s)

t1(sig1) t2(sig2) t3(sig3) t4(sig4) t21 t31 t41 t0

0.077 0.079 0.072 0.076 0.002 -0.005 -0.001 3.000

0.095 0.097 0.090 0.095 0.002 -0.005 0.000 3.018

0.136 0.138 0.131 0.135 0.002 -0.005 -0.001 3.059

0.199 0.200 0.194 0.198 0.001 -0.005 -0.001 3.122

0.227 0.229 0.222 0.226 0.002 -0.005 -0.001 3.150

0.812 0.814 0.808 0.809 0.002 -0.004 -0.003 3.735

1.739 1.740 1.734 1.738 0.001 -0.005 -0.001 4.662

1.985 1.987 1.980 1.984 0.001 -0.005 -0.001 4.908

2.147 2.148 2.142 2.145 0.001 -0.005 -0.002 5.070

3.252 3.253 3.249 3.247 0.001 -0.003 -0.004 6.175

3.273 3.274 3.269 3.270 0.001 -0.004 -0.003 6.196


347



4.710 4.710 4.706 4.706 0.001 -0.004 -0.004 7.633

4.957 4.958 4.954 4.953 0.001 -0.003 -0.004 7.880

5.876 5.877 5.873 5.871 0.001 -0.003 -0.004 8.799

5.911 5.912 5.908 5.907 0.001 -0.003 -0.004 8.834

6.376 6.376 6.373 6.372 0.001 -0.003 -0.004 9.299

7.677 7.677 7.675 7.673 0.000 -0.003 -0.005 10.601

8.233 8.233 8.232 8.228 -0.001 -0.002 -0.005 11.156

8.495 8.497 8.497 8.494 0.001 0.002 -0.001 11.418

9.698 9.698 9.699 9.697 0.001 0.002 0.000 12.621

10.796 10.796 10.794 10.792 0.000 -0.002 -0.005 13.719

10.919 10.919 10.916 10.914 0.000 -0.002 -0.005 13.842

10.987 10.988 10.985 10.982 0.001 -0.002 -0.005 13.910

11.053 11.054 11.051 11.047 0.001 -0.002 -0.005 13.976

14.152 14.153 14.151 14.147 0.000 -0.002 -0.005 17.075

15.014 15.014 15.013 15.009 0.000 -0.001 -0.005 17.938

15.333 15.334 15.332 15.329 0.000 -0.002 -0.004 18.256

16.038 16.038 16.037 16.033 0.000 -0.002 -0.005 18.961

Table 4. Time differences of –CG B



0.507 0.506 0.505 0.506 -0.001 -0.001 0.000 0.500

1.510 1.513 1.507 1.511 0.003 -0.003 0.001 1.503

2.149 2.151 2.148 2.144 0.003 -0.001 -0.005 2.142

4.032 4.034 4.031 4.029 0.002 0.000 -0.002 4.025

4.066 4.068 4.065 4.064 0.003 0.000 -0.002 4.059

4.109 4.106 4.111 4.109 -0.003 0.002 0.000 4.102

4.334 4.336 4.333 4.328 0.002 0.000 -0.005 4.327

4.380 4.382 4.380 4.375 0.002 0.000 -0.005 4.373

5.586 5.587 5.586 5.580 0.002 0.000 -0.005 5.579

5.647 5.648 5.648 5.641 0.001 0.001 -0.005 5.640

6.030 6.031 6.031 6.025 0.001 0.001 -0.005 6.024

7.987 7.987 7.988 7.981 0.000 0.001 -0.005 7.980

8.752 8.752 8.753 8.747 0.000 0.001 -0.005 8.745

8.938 8.938 8.939 8.932 0.000 0.001 -0.005 8.931

9.276 9.276 9.278 9.271 0.000 0.001 -0.005 9.270

10.232 10.233 10.234 10.227 0.000 0.002 -0.005 10.226

10.411 10.411 10.412 10.406 0.000 0.002 -0.005 10.404

11.506 11.507 11.508 11.501 0.000 0.002 -0.005 11.500


348



12.909 12.909 12.911 12.904 0.000 0.002 -0.005 12.902

13.148 13.148 13.149 13.143 0.000 0.002 -0.005 13.141

13.699 13.699 13.701 13.694 0.000 0.002 -0.005 13.692

14.111 14.111 14.113 14.106 0.000 0.002 -0.005 14.104

14.231 14.231 14.233 14.226 0.000 0.002 -0.005 14.224

14.535 14.535 14.537 14.530 0.000 0.002 -0.005 14.528

14.627 14.627 14.629 14.630 0.000 0.002 0.003 14.620

14.912 14.912 14.914 14.906 0.000 0.002 -0.006 14.905

15.150 15.150 15.152 15.145 0.000 0.002 -0.005 15.143

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Ariadi Hazmi was born in Lahat, South Sumatra, Indonesia in 1975. He

received B. Eng., M. Eng., and Dr. Eng. degrees in Electrical Engineering

from Universitas Sriwijaya, Institut Teknologi Bandung, Indonesia, and Gifu

University of Japan in 1998, 2002, 2008, respectively. Since 1999, He is

lecturer at Universitas Andalas of Indonesia and now serves as a Professor.

His research interest is lightning and plasma physics and lightning protection.

He is a member of the Society of Atmospheric Electricity of Japan and IEEE.

Primas Emeraldi was born in Pariaman, West Sumatera, Indonesia in 1986.

He received B. Eng., M. Eng. degrees in Electrical Engineering from

Universitas Andalas and Institut Teknologi Bandung, Indonesia, in 2009,

2013, respectively. Since 2015, He is a lecturer at Universitas Andalas,

Indonesia. His research interest is plasma physics and lightning protection.


350

Muhammad Imran Hamid was born in Bulukumba, South Sulawesi,

Indonesia in 1971. He received B. Eng., M. Eng., and Ph.D. in Electrical

Engineering from Universitas Hasanuddin, Institut Teknologi Bandung,

Indonesia, and University Technology Malaysia in 1996, 2001, 2014,

respectively. Since 1999, He is a lecturer at Universitas Andalas, Indonesia.

His research interest is power electronics for electrical energy conversion and

high voltage application.

Suci Melati was born in Padang, West Sumatra, Indonesia in 1993. She

received B. Eng. in Electrical Engineering from Universitas Andalas,

Indonesia in 2015. Now, she is a master student in Electrical Engineering of

Universitas Andalas.

Nobuyuki Takagi was born in 1957. He received MS and Ph.D from Nagoya

University of Japan. He joined Gifu University from 1985 and presently serves

as a professor. His research interests are atmospheric electricity, lightning

physics and lightning protection. He is a member of the Society of

Atmospheric Electricity of Japan and AGU.


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Reconstruction of Lightning Channel Based on Acoustic ...International Journal on Electrical...

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Transcript of Reconstruction of Lightning Channel Based on Acoustic ...International Journal on Electrical...