PERFORMANCE ANALYSIS OF VHF INTERFEROMETER
BETWEEN ORIGINAL AND FILTERED SIGNALS BASED ON
SIGNAL PROCESSING METHOD
NUR AMIRAH ILYANA BINTI AZMI
PERFORMANCE ANALYSIS OF VHF INTERFEROMETER
BETWEEN ORIGINAL AND FILTERED SIGNALS BASED ON
SIGNAL PROCESSING METHOD
NUR AMIRAH ILYANA BINTI AZMI
This report is submitted in partial fulfilment of the requirements
for the degree of Bachelor of Electronic Engineering with Honours
Faculty of Electronic and Computer Engineering
Universiti Teknikal Malaysia Melaka
Tajuk Projek : Performance analysis of VHF Interferometer between original and filtered signals based on signal processing method.
Sesi Pengajian : 2017/2018
Saya NUR AMIRAH ILYANA BINTI AZMI mengaku membenarkan laporan Projek Sarjana Muda ini disimpan di Perpustakaan dengan syarat-syarat kegunaan seperti berikut:
1. Laporan adalah hakmilik Universiti Teknikal Malaysia Melaka.
2. Perpustakaan dibenarkan membuat salinan untuk tujuan pengajian sahaja. 3. Perpustakaan dibenarkan membuat salinan laporan ini sebagai bahan
pertukaran antara institusi pengajian tinggi. 4. Sila tandakan ():
SULIT*
(Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysia seperti yang termaktub di dalam AKTA RAHSIA RASMI 1972)
TERHAD* (Mengandungi maklumat terhad yang telah ditentukan oleh organisasi/badan di
mana penyelidikan dijalankan.
TIDAK TERHAD
Disahkan oleh:
(TANDATANGAN PENULIS) (COP DAN TANDATANGAN PENYELIA)
Alamat Tetap: No 42, Kampung Tok Oh, 16200 Tumpat, Kelantan
Tarikh : 27 May 2018 Tarikh : 27 May 2018
*CATATAN: Jika laporan ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/organisasi berkenaan dengan menyatakan sekali tempoh laporan ini perlu dikelaskan sebagai SULIT atau TERHAD.
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
FAKULTI KEJUTERAAN ELEKTRONIK DAN KEJURUTERAAN KOMPUTER BORANG PENGESAHAN STATUS LAPORAN
DECLARATION
I declare that this report entitled “Performance analysis of VHF Interferometer
between original and filtered signals based on signal processing method” is the result
of my own work except for quotes as cited in the references.
Signature : ………
Author : ………
APPROVAL
I hereby declare that I have read this thesis and in my opinion this thesis is sufficient
in terms of scope and quality for the award of Bachelor of Electronic Engineering with
Honours.
Signature : ………
Supervisor Name : ………
DEDICATION
Thank you to all family members, my supervisor and friends for supporting me and
i
ABSTRACT
A lightning interferometer is a system that can determine the location of Very High
Frequency (VHF) radiation of lightning. Such system has been studied and used for
several decades ago. In this project, VHF Interferometer is used to determine the
location of VHF radiations emitted by Narrow Bipolar Event (NBE) lightning flash
by correlating the signals that received at three antennas. In order to get the better
result, cross-correlation algorithm technique is employed to process the signals. This
algorithm can determine the time delay between the antennas baselines and then
determine the azimuth and elevation angles which are used to locate the location of
the NBE flash. This interferometer system also can act as an earlier warning system
as it detects the first cloud flash and a forecast can be made before cloud-to-ground
flashes occur. Therefore, this interferometer system is very useful for the public
ii
ABSTRAK
Interferometer kilat ialah satu sistem dimana ianya boleh menentukan lokasi
radiasi VHF hasil daripada kilat yang telah berlaku. Sistem sebegini telah dikaji oleh
ahli saintifik dan telah digunakan pada beberapa dekad yang lalu. Oleh kerana radiasi
kilat senang dikenal pasti dengan data yang boleh diukur, justeru ketiadaan data
sedemikian akan menghalang kemajuan dalam sebuah penyelidikan. Untuk projek ini,
Frekuensi Amat Tinggi (VHF) Interferometer adalah salah satu kaedah untuk
menentukan lokasi radiasi kilat dengan menghubungkaitkan isyarat yang diterima
pada dua atau lebih antena. Untuk mendapatkan hasil yang lebih baik, teknik algoritma
korelasi silang digunakan untuk memproses isyarat. Algoritma ini dapat mengesan
tempoh kedatangan radiasi pada antenna kemudian sudut bacaan bagi azimuth dan
sudut ketinggian untuk menentukan arah kilat yang berlaku. Sistem interferometer ini
juga boleh bertindak sebagai sistem amaran awal kerana ia mengesan kilat awan
pertama dan ramalan boleh dibuat sebelum kilat dari awan ke tanah berlaku. Oleh itu,
sistem interferometer ini sangat berguna untuk rakyat awam dalam melindungi diri
iii
ACKNOWLEDGEMENTS
The work presented in this report could not have been completed without the help
of the others people. First and foremost, I would like to convey my gratefulness to my
final year project supervisor, Dr. Mohd Riduan bin Ahmad for giving me his guidance,
motivation and invaluable discussion throughout the project. Despite he is being
extraordinarily busy with his jobs and duties, he is still managed to guide me along
and keep me on track to complete this project.
Furthermore, I would also have to appreciate the guidance given by panels who
share their expertise and recommendation during the project presentation and give me
a right direction toward completion of my project.
Besides, I wish to dedicate my deepest thanks and appreciation to all my family
members, friends and course-mates for their cooperation, encouragement, constructive
suggestion and full of support not only for the report completion but also for my entire
study in Universiti Teknikal Malaysia Melaka.
Finally, my sense of gratitude express to Universiti Teknikal Malaysia Melaka and
also my academic advisor (PA) Dr Norhashimah bt Mohd Saad, for great commitment
iv
TABLE OF CONTENTS
Declaration i
Approval i
Dedication i
Abstract i
Abstrak ii
Acknowledgements iii
Table of Contents iv
List of Figures vii
List of Tables x
List of Symbols and Abbreviations xi
List of Appendices xii
INTRODUCTION 1
1.1 Project Background 1
1.2 Problem Statements 2
1.3 Objectives 3
v
1.5 Thesis Structure 4
CHAPTER 2 LITERATURE REVIEW 5
2.1 Lightning Locating System 5
2.2 History of Lightning Interferometry 15
2.3 Terminology and Definitions 19
2.3.1 Tri-Polar Charge Structure 19
2.3.2 Streamers and Leaders 20
2.3.3 Intracloud, Cloud-to-Ground, and Bolt from the Blue Flashes 20
2.3.4 Azimuth, Elevation, and Altitude 21
2.3.5 Phase Fitting and Cross Correlation 22
2.4 Cross Correlation Technique 22
2.4.1 Basic Algorithm 22
2.5 Summary 25
METHODOLOGY 26
3.1 Overview of the system 26
3.2 Description of the Project Implementation 29
3.3 Signal Processing in MATLAB 29
3.3.1 Implementation of MATLAB Code into Signal Processing 32
3.4 Summary 41
vi
4.1 Lightning Signal in Picoscope Application 42
4.2 Signal Processing in MATLAB Application 44
4.3 Final Result of Lightning Mapping 52
4.4 Summary 57
CONCLUSION AND FUTURE WORKS 58
5.1 Conclusion 58
5.2 Future Works 59
REFERENCES 60
APPENDIX A 64
APPENDIX B 67
APPENDIX C 70
vii
LIST OF FIGURES
Figure 2.1 First published interferometric observation of lightning[6] 15
Figure 2.2 First published 2-D interferometric map of lightning [19] 16
Figure 2.3 Interferometer configuration for each year of deployment [1] 18
Figure 2.4 Tri-polar charge of the cloud structure [20] 20
Figure 2.5 Three general types of lightning flashes [25] 21
Figure 2.6 Basic geometry of interferometer measurements [9] 23
Figure 2.7 Two baselines interferometer [9] 23
Figure 2.8 The cosine projection [9] 24
Figure 3.1 Block diagram of the system 27
Figure 3.2 Flowchart for the whole project 28
Figure 3.3 VHF Interferometer System 28
Figure 3.4 Gantt chart 29
Figure 3.5 Flowchart for Signal Processing Part 33
Figure 3.6 Filter designer in MATLAB 34
Figure 4.1 Captured Signal in PicoScope 43
Figure 4.2 The signals were combined 43
Figure 4.3 Zoomed in the lightning signal 44
viii
Figure 4.5 VHF Radiation Sources in MATLAB Application 45
Figure 4.6 Filtered Signal for Channel B 45
Figure 4.7 Filtered Signal for Channel C 46
Figure 4.8 Filtered Signal for Channel D 46
Figure 4.9 Normalization for Original Signal of B 47
Figure 4.10 Normalization for Original Signal of C 47
Figure 4.11 Normalization for Original Signal of D 47
Figure 4.12 Normalization for Filtered Signal of B 48
Figure 4.13 Normalization for Filtered Signal of C 48
Figure 4.14 Normalization for Filtered Signal of D 48
Figure 4.15 Lightning Signal 49
Figure 4.16 256 samples for single window 50
Figure 4.17 Cross Correlation for Channel B and C 50
Figure 4.18 Cross Correlation of Channel B and D 51
Figure 4.19 Single point of a Single Window 52
Figure 4.20 Visualization for Overlapped windows 53
Figure 4.21 The time difference of ‘tauBC’ for original signal 54
Figure 4.22 The time difference of ‘tauBD’ for original signal 54
Figure 4.23 The time difference of ‘tauBC’ for filtered signal 54
Figure 4.24 The time difference of ‘tauBD’ for filtered signal 55
Figure 4.25 Lightning mapping for filtered signal 55
Figure 4.26 Lightning mapping for original signal 56
ix
x
LIST OF TABLES
Table 5.1 Time difference for each window for Filtered Signal 64
Table 5.2 Time difference for each window for Original Signal 67
Table 5.3 Difference angle between original and filtered signal for azimuth 70
xi
LIST OF SYMBOLS AND ABBREVIATIONS
VHF : Very High Frequency
ELF : Extremely Low Frequency
VLF : Very Low Frequency
UHF : Ultra High Frequency
SHF : Super High Frequency
NBE : Narrow Bipolar Event
CC : Clod-to-Cloud
IC : Intra-Cloud
BFB : Bolts from the Blue
TOA : Time of Arrival
MDF : Magnetic Direction Finding
2-D : Two Dimensional
3-D : Three Dimensional
DC : Direct Current
SCOT : Smoothed Coherence Window
xii
LIST OF APPENDICES
Appendix A: Time difference for Filtered Signal
………... 76
Appendix B: Time difference for Original Signal
………..
Appendix C: Angle difference for Azimuth Angle
………..
Appendix D: Angle difference for Elevation Angle
……….. 79
82
1
INTRODUCTION
This chapter explains the introduction of the project for background, problem
statements and objectives of this project. In addition, the scope of work and structure
of thesis are also included in this section.
1.1 Project Background
In nature, there are so many physical processes in cloud and ground flashes that
emit electric and magnetic fields. Lightning produces electromagnetic emission over
broad frequency spectrum. The lightning can occur between cloud to ground and some
are happen in cloud that continue for one or two seconds. The lightning strikes give a
big impact to human and animal safety, interruption on the transmission line and the
electrical equipment failure to function. This problem can be partially solved by
2
detect the locations of the lightning strikes. There are three popular methods to locate
the lightning namely magnetic direction finder (MDF), time of arrival (TOA) and
direction of arrival (DOA) or also known as interferometer which is the focus of this
thesis. A VHF broadband interferometer is a system to locate sources of VHF based
on the digital interferometric technique. It can be done by obtaining the phase
differences at various frequency components of Fourier spectra between a pair of
antennas.
VHF lightning mapping has been done in two ways. The first one is by using
interferometric technique to determine the direction of arrival of the radiation. For
another one is using TOA technique to map the lightning in 3-dimensions. The
differences are the use of coherence during processing the signal. The interferometer
system has a wide detection frequency range and takes no account of a carrier
frequency. It observes the electric field change due to a lightning discharge in the
ultra-wide VHF band. Fast Fourier Transform (FFT) is then applied to calculate various
components of the received Electromagnetic (EM) pulses. Computed phase difference
for each Fourier component between two antennas is a function of the incident angle
of the EM pulse against the baseline. A couple of antenna as a two-element array of a
broadband interferometer is able to estimate the incident angle. Two pairs of antennas
and independent two baselines enable two-dimensional (2D) mapping of sources in
azimuth and elevation format.
1.2 Problem Statements
Nowadays, there’s a lot of interest in lightning-related research. In particular,
studies have been done to understand better about lightning phenomenon including
3
the Blue (BLB). The locating system is very useful because it can detect and warn an
incoming lightning strike anytime. It gives a lot of benefit to public citizens because
they will receive the warning message at the very earliest time when lightning strikes
are approaching. It may expose the people near the lightning strike location to danger
when they are doing the outdoor activities. A lightning detector was created which is
able to detect the lightning strike distance will be useful for the public citizens in
protecting themselves from lightning strikes. In the end of the project, I need to
analyze the differences between original and filtered signal based on signal processing
method.
1.3 Objectives
I. To design and develop the VHF interferometer with two baselines.
II. To process the analog signal of VHF radiation by using MATLAB
application.
III. To produce VHF lightning mapping by using interferometer techniques to
determine the direction of arrival of the radiation.
IV. To analyze the differences between original and filtered signal based on
signal processing method.
1.4 Scope of Work
Several scopes are listed to ensure the research is conducted within its intended
boundary. In this project, it has two parts; first is experimental work. For the
experimental part, the measurement was conducted in wide area such as at Pantai
Klebang or in open field in UTeM. The second part is software which is signal
processing plays the main role in order to locate the lightning location by using cross
4
1.5 Thesis Structure
The thesis is organized and separated into five major chapters. In chapter 1, the
overview of VHF interferometer is discussed in project background. In addition, the
problem statement, objective and scope of the project are outlined clearly in this
section. In chapter 2, the past studies related to VHF interferometer are included in
this chapter. In chapter 3, all relevant experiments and techniques used in the project
are discussed in detail. In chapter 4, the results of the project are presented and
interpreted in this section. The obtained and collected data are analyzed carefully to
verify whether the objectives have been achieved or not. In the final chapter, a
conclusion is drawn from the project. Besides, the recommendation for the future plan
5
CHAPTER 2
LITERATURE REVIEW
This chapter discusses the literature review and background studies on topics which
are related. The discussions in this chapter are supported by the knowledge that refers
to the books, journals, articles, and papers.
2.1 Lightning Locating System
The geolocation of lightning discharges, or specific physical procedures within
discharges, is vital in a wide variety of applications. These incorporate lightning
cautioning and security applications, thunderstorm nowcasting and forecasting,
locating lightning-caused harm assets and infrastructure, risk assessment, geophysical
research, insurance, and an assortment of other continuous and forensic applications.
Typical users of lightning data incorporate national and provincial meteorological
6
management entities, forest services, electric power transmission and distribution
operators, wind farm operators, and other open utilities.
Lightning locating system involves with the detection process of the electric and
magnetic fields. There are three popular methods to locate the lightning namely
magnetic direction finder (MDF), time of arrival (TOA) and direction of arrival
(DOA) or also known as interferometer which is the focus of this thesis. All of these
techniques depend on the frequency or equivalent to the wavelength, λ. There has a
various frequency spectrum that involving with LLS which is VHF that has very short
wavelength so that the frequency is from 30 MHz to 300 MHz and the λ is between 10
and 1 m. For the Very Low Frequency (VLF), it has frequency range from 3 to 30 kHz
and the λ is between 10 and 1km. Meanwhile the Low Frequency (LF) has frequency
range from 30 kHz to 300 kHz and the λ is between 1km to 100km. The best
electromagnetic channel imaging method is VHF while for the best
ground-strike-point locating techniques is VLF and LF. The bandwidth measurement is important to
have a measurement system that can reproduce the field changes of the process. So
that the multiple sensors is needed to get an accurate LLS systems whether an image
of the whole lightning or locating only the ground strike points. However, single
station ground-based sensor cannot be used to locate an individual flash basis but can
detect the occurrence of lightning.
We have known that MDF is the most common technique to locate CG flashes. The
MDF is constructed by using two orthogonal loops with planes oriented through
North-South (NS) and East-West (EW). So that the direction to the source can be
obtained because the output voltage of a given loop, by Faraday’s Law, is proportional