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DETERMINE AND ANALYZE THE MAGNETIC FIELD MAGNITUDE OVER
THE UNIVERSITI TUN HUSSEIN ONN AREA USING MAGNETOMETER
NOOR SYAZANA BINTI ARSHAD
A project report submitted in partial
fulfillment of the requirement for the award of the
Master of Electrical Engineering
Faculty of Electrical and Electronic Engineering
Universiti Tun Hussein Onn Malaysia
JANUARY 2012
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ABSTRACT
In this project, the magnitude of the magnetic field were observed and analyzed
around Universiti Tun Hussein Onn (UTHM) using Magnetometer. The
measurement of magnetic field magnitude was obtained from Overhauser
Magnetometer reading. The magnetic field data was analyzed using Surfer 10
software. Initially, the Overhauser Magnetometer was assembled and the magnetic
survey was conducted in walking mode. The magnetic field survey locations are
Wireless and Radio Science Center (WARAS), Open Field, UTHM Library and Tun
Fatimah College. The survey was conducted on 1st, 17th and 30th November 2011 also
on 9th and 12th December 2011, on three periods on each survey day, which are
morning, noon and evening. Consecutively, the results were given in the form of
contour map of magnetic field on each survey location which was later compared
with the International Geomagnetic Reference Field (IGRF-11). IGRF-11 is a
standard mathematical description of the Earth's main magnetic field. The contour
map reveals that the Earths magnetic field fluctuates unpredictably during
geomagnetic storm occasion and yet fluctuates considerably during quiet
geomagnetic days. The magnetic field survey data shows that the Earths magnetic
field varies throughout the day thus proved that IGRF-11 geomagnetic model cannot
be used to predict exact value of Earths magnetic field magnitude. It can be
concluded that the space weather disturbance greatly affect the Earths magnetic field
in equatorial region.
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ABSTRAK
Projek ini merujuk kepada kajian dan analisis magnitud medan magnet bumi di
sekitar kawasan Universiti Tun Hussein Onn (UTHM) menggunakan Magnetometer.
Nilai pengukuran medan magnet merujuk kepada bacaan Overhouser Magnetometer.
Data medan magnet di analisis menggunakan perisian Surfer 10. Pada peringkat
permulaan, Overhouser Magnetometer di pasang dan kajian medan magnet di
jalankan menggunakan mod berjalan. Lokasi-lokasi kajian medan magnet bertempat
di Wireless and Radio Science Center (WARAS), padang terbuka, perpustakaan
UTHM dan Kolej Tun Fatimah. Kajian ini telah dijalankan pada 1, 17 dan 30
November 2011 juga pada 9 dan 12 Disember 2011. Data medan magnet telah di
ambil pada tiga waktu berbeza iaitu waktu pagi, waktu tengahari dan waktu petang.
Berikutnya, hasil kajian di dalam bentuk peta kontur pada setiap lokasi kajian telah
dibandingkan dengan International Geomagnetic Reference Field (IGRF-11). IGRF-
11 ialah model piawaian matematik merujuk kepada medan magnet bumi. Peta
kontur menunjukkan medan magnet bumi berubah dengan tidak terjangka semasa
berlakunya kejadian ribut medan magnet tetapi kembali stabil sewaktu ketiadaan
kejadian ribut medan magnet. Data medan magnet yang diukur menunjukkan medan
magnet bumi berubah sepanjang hari sekaligus membuktikan bahawa IGRF-11
model tidak boleh digunakan untuk meramal nilai magnitud medan magnet bumi.
Kesimpulannya, gangguan kepada keadaan cuaca di angkasa lepas kuat
mempengaruhi medan magnet bumi di kawasan Khalutistiwa.
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TABLE OF CONTENTS
TITLE i
DECLARATION ii
DEDICATION iii
ACKNOWLEDGEMENT iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENTS vii
LIST OF FIGURES xii
LIST OF TABLES xvii
LIST OF SYMBOL AND ABBREVIATION xviii
LIST OF APPENDICES xx
CHAPTER 1 INTRODUCTION 1
1.1 Background 1
1.2 Problem Statement 3
1.3 Objectives 4
1.4 Scope 4
1.5 Expected Result 5
1.6 Thesis Organization 6
CHAPTER 2 LITERATURE REVIEW 7
2.1 Introduction 7
2.2 Earths Magnetic Field 8
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2.2.1 Static Anomalies 9
2.2.2 Dynamic Anomalies 11
2.2.2.1 Solar Cycle 11
2.2.2.2 Solar Wind 14
2.2.2.3 Geomagnetic Storm 16
2.3 Effects of Earths Magnetic Field to Our Lives 17
2.3.1 Effects on Satellite Operation 18
2.3.2 Effects on Communication and Navigation System 18
2.3.3 Effects on Power System and Pipelines 18
2.3.4 Effects on Magnetic Surveys 19
2.4 Overhouser Magnetometer (GSM-19GW) 19
2.4.1 Overview 19
2.4.2 Standard Magnetometer Components 20
2.5 Global Positioning System (GPS) 23
2.5.1 GPS Overview 23
2.5.2 GPS Operation 23
2.5.3 GPS Signal 25
2.5.4 Sources of GPS signal errors 26
2.6 Universal Transverse Mercator (UTM) 27
2.6.1 Benefit of using UTM coordinate system 27
2.6.2 UTM Coordinate Reading 28
2.6.3 UTM Coordinate System in GPS 29
2.7 International Geomagnetic Reference Field (IGRF) 30
2.7.1 Overview 30
2.7.2 IGRF-11 Online Calculator 33
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CHAPTER 3 METHODOLOGY 35
3.1 Introduction 35
3.2 Equipment Assembly 38
3.2.1 The GSM-19GW Magnetometer Assembly 38
3.2.2 The GSM-19GW Magnetometer Setting 39
3.2.2.1 Setting the Positioning System 39
3.2.2.2 Setting the Time 41
3.2.3 Garmin GPS Navigator 42
3.3 Data Collection 43
3.3.1 Selecting Magnetic Survey Site 43
3.3.2 Data Acquisition by Magnetometer 45
3.3.3 Precaution to Conduct Magnetic Survey 46
3.4 Contour Map Design 47
3.4.1 Surfer 10 Software Overview 47
3.4.2 Contour Map 48
3.4.3 3D Surface Map 49
3.4.4 Contour Map Design Procedure 50
3.5 Contour Map Visualization 52
3.5.1 Google Earth 6 Overview 52
3.5.2 Contour Map Visualization Procedure 54
CHAPTER 4 RESULT AND ANALYSIS 55
4.1 Introduction 55
4.2 Space Weather Report 56
4.3 IGRF-11 Geomagnetic Model 61
4.4 Data Analysis 62
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4.4.1 WARAS Area 63
4.4.2 Open Field Area 65
4.4.3 Tun Fatimah College Area 67
4.4.4 UTHM Library Area 69
4.4.5 Earths Magnetic Field Variation at Different
Places in UTHM 72
4.4.6 Comparison of Actual Data and IGRF-11
Data at Different Places in UTHM 74
4.4.7 Analysis Discussion 76
4.4.8 Analysis Summary 79
4.5 Contour Map Design 82
4.5.1 The Earths magnetic field fluctuations are
unpredictable during geomagnetic storm occasion 82
4.5.2 The Earths magnetic field fluctuations are stable
during quiet geomagnetic days 86
4.5.3 The daily Earths magnetic field variation during
quiet geomagnetic days begin with lowest value
at morning and slowly increases until reach its
peak at local noon and gradually reduces at evening 90
4.5.4 Earths magnetic field magnitude higher at high
interference area than low interference area 94
4.5.5 Wi-Fi hotspot areas are exposed wireless
communication disturbance due to Type II Radio
Emission which occurs due to solar burst 100
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4.6 Contour Map Visualization 102
4.6.1 Earths magnetic field magnitude higher at high
interference area than low interference area 102
4.6.2 Wi-Fi hotspot areas are exposed wireless
communication disturbance due to Type II Radio
Emission which occurs due to solar burst 103
CHAPTER 5: CONCLUSION AND RECOMMENDATION 104
5.1 Conclusion 104
5.2 Recommendation 106
REFERENCES 107
APPENDICES 111
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LIST OF FIGURES
2.1 The total intensity of the earths magnetic field 9
2.2 Vertical distribution of the total field lines of flux 10
2.3 The magnetic susceptibility of Earth mineral 10
2.4 Sunspot polarity 12
2.5 Sunspot during solar maximum 12
2.6 Sunspot during solar minimum 13
2.7 Solar flares 13
2.8 Distortion of magnetosphere by solar wind 14
2.9 Van Allen Radiation Belt 15
2.10 Charged particles ejected from the Sun distort
Earth's magnetic field 16
2.11 Space weather effects on technology 17
2.12 Standard magnetometer components 20
2.13 Magnetometer sensor 21
2.14 Magnetometer console 21
2.15 Sectional staff rods 22
2.16 Magnetometer backpack 22
2.17 GPS Satellite 24
2.18 24 satellite constellation orientation 24
2.19 UTM grid zones of the world 29
http://astronomy.swin.edu.au/cosmos/S/Sun
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2.20 Components of Earths geomagnetic field 32
2.21 Geomagnetic model of IGRF-11 in UTM coordinates 34
3.1 Methodology flow chart 37
3.2 Magnetometer and backpack assembly 38
3.3 A magnetometer console screen with highlighted
position option 39
3.4 X/Y Positioning system menu 40
3.5 A magnetometer console screen with highlighted time
option 41
3.6 A magnetometer console screen with highlighted time
inserting option 41
3.7 Garmin GPS Navigator attached to the GSM-19GW
Console 42
3.8 WARAS survey area 43
3.9 Tun Fatimah College Survey Area 44
3.10 Open Field Survey Area 44
3.11 UTHM Library Survey Area 44
3.12 a) Data acquisition method 45
b) Magnetic field survey grid 45
3.13 X/Y Positioning system menu with waypoint 1 coordinate 46
3.14 A contour map with color scale bar 48
3.15 A 3D surface map 49
3.16 Contour map in Surfer 10 in UTM coordinates 51
3.17 Google Earth virtual globe 52
3.18 KLCC Petronas Twin Tower viewed in Google Earth
with 3D buildings layer 53
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3.19 Mount Everest viewed in Google Earth with 3D terrain layer 53
3.10 The contour map in correct location on Google Earth 54
4.1 Space Weather Alerts and Warnings Timeline from
1st November 2011 until 15th November 2011 57
4.2 Space Weather Alerts and Warnings Timeline from
16th November 2011 until 30th November 2011 57
4.3 Space Weather Alerts and Warnings Timeline from
1st December 2011 until 15th December 2011 58
4.4 Comparison between Actual Magnetic Field Data and
IGRF 11 Magnetic Field Data at WARAS 63
4.5 Comparison between Actual Magnetic Field Data and
IGRF 11 Magnetic Field Data at Open Field 65
4.6 Comparison between Actual Magnetic Field Data and
IGRF 11 Magnetic Field Data at Tun Fatimah College 67
4.7 Comparison between Actual Magnetic Field Data and
IGRF 11 Magnetic Field Data at UTHM Library 69
4.8 Earths Magnetic Field Variation at different places in UTHM 72
4.9 Comparison of Actual Magnetic Field Data and IGRF 11
Magnetic Field Data at different places in UTHM 74
4.10 Effect of solar Ultra-Violet and X-Ray radiation on ionospheric
conductivity throughout the day 76
4.11 Solar wind and the Earth's magnetosphere 77
4.12 Solar flare eruption 78
4.13 Contour map at Open Field during morning (top left),
noon (top right) and evening (below) on 1st November 2011 82
4.14 3D Surface map at Open Field during morning (top left),
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noon (top right) and evening (below) on 1st November 2011 83
4.15 Contour map at WARAS during morning (top left),
noon (top right) and evening (below) on 1st November 2011 84
4.16 3D Surface map at WARAS during morning (top left),
noon (top right) and evening (below) on 1st November 2011 85
4.17 Contour map at Open Field during morning (top left),
noon (top right) and evening (below) on 12th December 2011 86
4.18 3D Surface map at Open Field during morning (top left),
noon (top right) and evening (below) on 12th December 2011 87
4.19 Contour map at WARAS during morning (top left),
noon (top right) and evening (below) on 12th December 2011 88
4.20 3D Surface map at WARAS during morning (top left),
noon (top right) and evening (below) on 12th December 2011 89
4.21 Contour map at WARAS during morning (top left),
noon (top right) and evening (below) on 9th December 2011 90
4.22 3D Surface map at WARAS during morning (top left),
noon (top right) and evening (below) on 9th December 2011 91
4.23 Contour map at UTHM Library during morning (top left),
noon (top right) and evening (below) on 9th December 2011 92
4.24 3D Surface map at UTHM Library during morning (top left),
noon (top right) and evening (below) on 9th December 2011 93
4.25 Contour map and 3D surface map at UTHM Library(left) and
Open Field (right) during morning on 30th November 2011 94
4.26 Contour map and 3D surface map at UTHM Library (left) and
Open Field (right) during noon on 30th November 2011 95
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4.27 Contour map and 3D surface map at UTHM Library(left) and
Open Field (right) during evening on 30th November 2011 96
4.28 Contour map and 3D surface map at UTHM Library (left) and
Open Field (right) during morning on 9th December 2011 97
4.29 Contour map and 3D Surface map at UTHM library (left) and
Open Field (right) during noon on 9th December 2011 98
4.30 Contour map and 3D surface map at UTHM Library (left) and
Open Field (right) during evening on 9th December 2011 99
4.31 Contour map and 3D surface map at UTHM Library during
noon (left) and evening (right) on 17th November 2011 100
4.32 Contour map and 3D surface map at Tun Fatimah College
during morning (left) and noon (right) on 17th November 2011 101
4.33 Contour map at UTHM during morning on 30th November 2011 102
4.34 Contour map at UTHM during noon on 9th December 2011 102
4.35 Contour map at UTHM during morning on 17th November 2011 103
4.36 Contour map at UTHM during noon on 17th November 2011 103
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LIST OF TABLES
2.1 The abbreviated format for the UTM coordinates 28
2.2 Definitive and International Geomagnetic Reference
Field Values 31
2.3 Characteristics of magnetic field in Parit Raja
based on IGRF-11 33
4.1 Space Weather Alert Description 59
4.2 IGRF-11 magnetic field value at different places in
UTHM 60
4.3 Comparison between Actual Magnetic Field Data and
IGRF 11 Magnetic Field Data at WARAS 61
4.4 Comparison between Actual Magnetic Field Data and
IGRF 11 Magnetic Field Data at Open Field 66
4.5 Comparison between Actual Magnetic Field Data and
IGRF 11 Magnetic Field Data at Tun Fatimah College 68
4.6 Comparison between Actual Magnetic Field Data and
IGRF 11 Magnetic Field Data at UTHM Library 70
4.7 Earth Magnetic Field Variation at different places in UTHM 73
4.8 Comparison value of Actual Magnetic Field Data and
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IGRF 11 Magnetic Field Data at different places in UTHM 75
LIST OF SYMBOLS AND ABBREVIATIONS
B Magnetic Flux Density
F Total Magnetic Field Magnitude
mng the expansions Gauss coefficients at time t
mnh the expansions Gauss coefficients at time t
H Magnetic Field Strength
nT nano Tesla
mnP the Schmidt semi-normalized associated Legendre function of
degree n and order m
R Earth reference radius
r distance from the center of the Earth
sv secular variation
colatitudes from the center of the Earth
longitude from the center of the Earth
AC Alternating Current
DC Direct Current
GPS Global Positioning System
HF High Frequency
IAGA International Association of Geomagnetism and Aeronomy
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IGRF International Geomagnetic Reference Field
KML Keyhole Markup Language
NOAA National Oceanic and Atmospheric Administration
UHF Ultra High Frequency
UTHM Universiti Tun Hessein Onn Malaysia
UTM Universal Transverse Mercator
WARAS Wireless and Radio Science Centre
WGS 84 World Geodetic System 1984
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LIST OF APPENDICES
APPENDIX TITLE PAGE
A GANTT Chart 111
B Data Statistics for WARAS area 114
C Data Statistic for Open Field area 116
D Data Statistic for Tun Fatimah College area 118
E Data Statistic for UTHM Library area 120
F NOAA Space Weather Scale 122
G GSM-19GW Overhouser Magnetometer
Technical Paper 123
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CHAPTER 1
INTRODUCTION
1.1 Background
According to Wallace (2003), Earths magnetic field or geomagnetic field is
approximately a magnetic dipole. It consists of N pole which is located near Earths
geographic South Pole and S pole which is located near Earths geographic North Pole.
A magnetic field strength weakens if it is far from its source. The strongest magnetic
field located at the poles, and the weakest field located near the equatorial region. The
Earth's magnetic field is measure in "nano Tesla" (nT). On the Earth's surface, the
magnitude of magnetic field varies from about 30 000 nT near the equator to about 60
000 nT near the poles (Lowes.F.J, 2010).
The magnitude of magnetic field varies on different values daily. A study by
Hrvoic & Hollyer (2007) shows that the Earths magnetic field varies due to either
dynamic or static effects. Dynamic anomalies are related to solar activity and storms
from outer space. Static anomalies are related to different materials present in the Earth's
crust.
Magnetic field plays a very important part in our lives. It protects the Earth from
radiation penetration of solar wind. Extreme geomagnetic field would cause significant
damage to transformers and generators, disconnections of electric stations, power grid
blackouts, explosions on oil and gas pipelines, failures in work of computers and board
system and degradation of satellite navigation (Thompson,2007).
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Magnetic field variations can be measured by a magnetometer. Magnetometer is
an electronic device that can measure the properties of the magnetic field near the
surface. As referred to GEM System (2008), an Overhouser Magnetometer (GSM-19) is
a superior magnetic measuring device with high sensitivity, high cycling speed, low
noise, and very low power consumption over a wide temperature range. In addition, it
can be easily configured for high sensitivity readings in low magnetic fields (for
equatorial survey) which are suitable for magnetic survey conducted in University Tun
Hussein Onn, Parit Raja, Johor.
In this project, the main aim is to observe Earths magnetic field magnitude
variation on different day, time and location. Thus, the magnetic field survey has been
conducted at four different locations in University Tun Hussein Onn Malaysia (UTHM)
namely, Wireless and Radio Science Centre (WARAS), Open Field, UTHM Library and
Tun Fatimah College. The magnetic field data has been taken on 1st, 17th and 30th
November 2011 also on 9th and 12th December 2011. For each survey day, there are
three magnetic field survey periods which are morning, noon and evening.
The magnetic survey was conducted as an attempt to provide a general overview
of Earths magnetic field magnitude anomalies during morning, noon and evening.
These magnetic field anomalies pattern can be illustrated in a contour map as well as
surface map using Surfer 10 software.
On the other hand, the International Geomagnetic Reference Field (IGRF-11)
geomagnetic model was used to provide initial approximation of Earths magnetic field
magnitude at the survey area. The primary analysis involved on comparison of actual
magnetic field magnitude and IGRF-11 magnetic field magnitude at four locations in
UTHM.
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1.2 Problem Statement
Nowadays, people are totally relying on technological systems to do daily routine. These
systems improve the quality of our lives and make our lives easier. However, these
facilities can be affected by magnetic field variation and are used in various areas mainly
in power grid supply, fuel supply, computer operation, communication and navigation.
According to Space Weather Canada (2009), extreme variations of geomagnetic
field can be caused by extreme magnetic storm that can affect power systems, spacecraft
operations and other systems. For example, surge currents are induced in power lines
that could lead to the failure of power grids. In addition, currents in long pipelines can
cause increase corrosion. Furthermore, HF radio propagation may be impossible in many
areas for one to two days and satellite navigation may be degraded for days.
Moreover, power system experience widespread voltage control problems,
damaging transformers, and could lead to worst situation where some grid systems may
experience complete collapse or blackouts. Additionally, spacecraft operation may
experience extensive surface charging, problems with orientation, uplink/downlink and
tracking satellites.
This research is significant as it provides a fundamental information and
overview of magnetic field variation in equatorial region specifically in UTHM area. It
is essential to investigate the magnetic field as its variation can affect our daily lives
routine. A significant changes of magnetic field in a specific area can be detected and
observed by identifying and comparing with the local magnetic field variation pattern
during quiet geomagnetic day and geomagnetic storm. The variation pattern can be
observed in a contour map of Earth magnetic field.
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1.3 Objectives
The objectives of this project are:
1. To acquire and observe the magnetic field magnitude variations using magnetometer
in UTHM area.
2. To produce a contour map of Earth magnetic field magnitude specifically in UTHM
area.
3. To compare the contour map of magnetic field magnitude in UTHM area with IGRF-
11 magnetic model.
1.4 Scope
This project is focused on certain aspects which are:
i. The magnetic field magnitude variation will be determined in UTHM area only.
ii. The magnetic field survey will be conducted by Overhouser Magnetometer
(GSM-19GW) in walking mode.
iii. A magnetic field contour map will be designed in Surfer 10 software.
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1.5 Expected Result
The magnetic field of Earths surface varies from about 40,000 nT near the equator and
about 60,000 nT near the poles. The Universal Transverse Mercator (UTM) coordinates
for Parit Raja is 290496E 206438N. The latitude and longitude of Parit Raja is 1.867
and 103.117 which are in equatorial area. Therefore, it is expected that the total field is
approximately above 40,000 nT at the magnetic field survey area in UTHM.
For comparison, the magnetic model of IGRF-11 shows that the total field is
42,026.9 nT at Parit Raja location. However, the value is not accurate due to the
contribution of various interferences such as fixed interference, man-made interference
and natural interference(Lowes,2010).
Lowes(2010) states that fixed interference such buildings and parked cars are
typically contribute of magnitude 200 nT. There are also a large variety of time-varying
fields, both man-made (traffic) and natural (from electric currents in the ionosphere and
magnetosphere). The ionosphere and magnetosphere minimum contribution is about 20
nT but can be increased significantly up to 1000 nT and more during a geomagnetic
storm.
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1.6 Report Organization
There are five chapters in this report.
Chapter 1 :
First chapter introduces the project report. Project background such as objectives and the
project scope was clearly explained in this chapter.
Chapter 2 :
The second chapter covers literature reviews regarding to this project. This chapter
provides reader key information on Earths magnetic field variation as well as the
interaction between Sun and Earth.
Chapter 3 :
Chapter three provide reader the methodology to complete this report. It also focuses on
explanations concerning method of conducting magnetic field survey. The procedure to
design contour map are also displayed in this chapter.
Chapter 4 :
Chapter four consists of analysis data in term of several aspects such as location, time
and weather condition. The results of each survey were discussed and analyzed in detail
in this chapter.
Chapter 5 :
Chapter five concludes the overall project works and provides some suggestions for
further study and improvement.
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CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
This chapter is a crucial part of this thesis. A literature review is a body of text that aims
to review the critical points of current knowledge on a research topic. Its ultimate goal is
to keep the reader update with current literature on a topic that could be useful for future
research.
This part consists of general knowledge of all section in this thesis such as
Earths magnetic field, the effect of Earths magnetic field to our lives, Magnetometer,
Global Positioning System (GPS), Universal Transverse Mercator (UTM) and
International Geomagnetic Reference Field (IGRF).
In first section, the explanations on Earths magnetic field intensity are stated.
The factors that contribute to Earths magnetic field intensity are Static Anomalies and
Dynamic Anomalies. It is important to identify the relationship between solar cycle,
solar wind and geomagnetic storm which contributes to Dynamic Anomalies.
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In next section, the Earths magnetic field major roles to our lives are
enlightened. It is vital to clarify the effects of Earths magnetic field disturbance to our
technology such as satellite, power system and pipeline, communication and navigation,
and magnetic survey.
On the other hand, the overview of magnetometer has been described. This section
provides the description on magnetometer benefits and application. It is essential to
identify the magnetometer components and how to assemble it.
Besides that, a section has been allocated to provide the overview of GPS. A
brief explanations regarding GPS operation, GPS signal and sources of GPS signal errors
are provided. Moreover, the benefits of using UTM coordinates system in magnetic
survey are clarified. It is essential to know how to apply UTM coordinates in GPS in
order to conduct magnetic survey.
Lastly, brief explanations on theory of constructing IGRF geomagnetic model
have been depicted. The IGRF 11 model provides the magnetic field characteristics of
Parit Raja.
2.2 Earths Magnetic Field
According to Wallace (2003), the magnetic field is produced by a single dipole. It
consists of N pole which is located near Earths geographic South Pole and S pole which
is located near Earths geographic North Pole. The magnetic field has no distinct
boundary. It simply decreases in intensity until it is no longer detectable. The Earths
magnetic field varies from about 30 000 nT near the equator region to about 60 000 nT
near the polar region (Lowes, 2010).
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Figure 2.1: The total intensity of the Earths magnetic field (Smekalova,Voss & Smekalov,2008)
The magnitude of magnetic field varies on different values daily. Hrvoic &
Hollyer (2007) states that the magnetic field variation pattern can be due to either
dynamic or static effects. Static anomalies are related to different materials present in the
Earth's crust. Dynamic anomalies are related to solar activity and storms from outer
space.
2.2.1 Static Anomalies
As well cited by Smekalova,Voss & Smekalov (2008), iron constitutes about 6% of the
Earths crust. Most of it is dispersed through soils, clays and rocks as chemical
compounds which are magnetically very weak. Mans activities in the past (especially
the use of fire for heating, cooking, production and industry) have changed these
compounds into more magnetic forms, creating special patterns of anomalies in the
Earths magnetic field. These anomalies are detectable with sensitive instrument, which
is magnetometer.
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If the Earth were composed of uniform material, the magnetic lines of force would be
evenly distributed between the poles. The magnetic lines in a small area would be
parallel. However, since various materials have different magnetic susceptibilities due to
their composition, the Earths magnetic lines of force are distorted. The local
disturbances of the global magnetic field are called magnetic anomalies.
Figure 2.2: Vertical distribution of the total field lines of flux (Smekalova,Voss &
Smekalov,2008)
The anomalies from natural rocks and minerals are due chiefly to the presence of
the most common magnetic mineral, magnetite, FeOFe2O3, or its related minerals. All
rocks contain some magnetite, ranging from very small fractions of a percent to several
percent.
Figure 2.3: The magnetic susceptibility of Earth mineral (Smekalova,Voss &
Smekalov,2008)
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Magnetic susceptibility is the ease with which a substance is magnetized by the Earths
magnetic field. The variations in magnetic susceptibility between different kinds of
mineral affect the Earths field locally.
2.2.2 Dynamic Anomalies
Hrvoic & Hollyer (2007) briefly describe that the dynamic anomalies are related to solar
wind and geomagnetic storms from outer space. These phenomena occur due to solar
cycle.
2.2.2.1 Solar cycle
The solar cycle is manifest in many properties of the Sun but is most evident in the
appearance of sunspots on the solar disk. Sunspots are regions of stronger magnetic field
which appear darker than the surrounding surface. At certain times, sunspots are rare and
the Sun appears almost without blemish. This is known as solar minimum. Later,
sunspots become more common and it is normal for many groups of spots to be visible.
The peak of common sunspots called solar maximum as well cited by Thompson (2007).
A Suns image (magnetogram) can be taken by an instrument which can detect
the strength and location of the magnetic fields on the Sun. In a magnetogram, grey areas
indicate that there is no magnetic field, while black and white areas indicate regions
where there is a strong magnetic field.
Magnetograms can show the directions of magnetic fields travel towards Earth.
The darkest areas are regions of "south" magnetic polarity (inward directed or moving
toward the center of the Sun) and the whiter regions "north" (outward directed or moving
toward Earth) polarity.
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Figure 2.4: Sunspot polarity (Scherrer,2008)
Figure 2.5: Sunspot during solar maximum (Scherrer,2008)
The above figure shows the surface distribution and polarity of the Sun's
magnetic fields and sunspots at a very active time during its sunspot cycle. When the
Sun is very active, the number of sunspots is at a maximum, and solar magnetism is
dominated by large bipolar sunspots within two parallel bands oriented in the east-west
direction.
As a comparison, Figure 2.6 shows some sunspot during a solar minimum or low
magnetic activity period. At times of solar minimum, there are very few large sunspots,
and only tiny magnetic fields can be seen.
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Figure 2.6: Sunspot during solar minimum (Scherrer,2008)
According to Scherrer (2008), when the magnetic fields of sunspots become
twisted and distorted due to the differential rotation of the sun, stored energy is released.
Thus, solar flares which are huge outbursts of energy are created.
Figure 2.7: Solar flares (The Watchers, 2011)
Further discussed by Thompson (2007), along with the production of
electromagnetic radiation, the flare can be associated with the ejection of clouds of
charged particles into the solar wind. This process is called a Coronal Mass Ejection
(CME) and may occur with flares. The result of the charged particles reaching the Earth
is a geomagnetic storm.
http://thetruthbehindthescenes.files.wordpress.com/2010/09/mega-storm.jpg
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2.2.2.2 Solar Wind
Referred to Marine Magnetics Corp (2007), the Earths magnetic field is within the
influence of the Suns which is comparatively gigantic magnetic field. The Suns larger
field interacts with the Earths, giving it a distinct boundary which can be extends up to
several tens of thousands of kilometers into space. The space within that boundary is
known as the magnetosphere.
Earths magnetosphere dominates the surface magnetic field at large distances
from the planet. The magnitude of magnetic field varies daily. These phenomena occur
due to constant stream of free ions and electrons that flows from the Sun which is called
the solar wind. The Earths magnetic field interacts with the Suns magnetic field. The
Earths magnetic field is distorted by the solar wind.
The solar wind is a stream of ionized gases that blows outward from the Sun at
about 400 km/second and that varies in intensity with the amount of sunspots on the Sun.
The Earth's magnetic field shields the ionized gases of the solar wind. When the solar
wind encounters Earth's magnetic field it is deflected like water around the bow of a
ship, as illustrated in Figure 2.8.
javascript:locscrollmenu('http://www
spof.gsfc.nasa.gov/Education/Figures/stsys.gif','magnetic',755,335)
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Figure 2.8 : Distortion of magnetosphere by solar wind (Steigerwald,2008)
As shown in Figure 2.8, the Earths magnetic field acts as a shield against the
bombardment of particles continuously streaming from the Sun (Steigerwald,2008). The
solar particles (ions and electrons) are electrically charged and most of them are
deflected by our planet's magnetic field.
The imaginary surface at which the solar wind is first deflected is called the bow
shock. The corresponding region of space sitting behind the bow shock and surrounding
the Earth is magnetosphere. However, some high energy charged particles from the solar
wind leak into the magnetosphere. The charged particles are then trapped in the Van
Allen Radiation Belt (Stern,2001).
Figure 2.9: Van Allen Radiation Belt (Stern,2001)
As illustrated in Figure 2.9, Van Allen Radiation Belt has a magnetic field that
can trap charged particles such as electrons and protons and forced them to execute a
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spiraling motion back and forth along the field lines. The charged particles are reflected
at "mirror points" where the field lines come close together and the spirals tighten.
The solar wind changes in the speed or density distorts the Earth's magnetic field,
compressing it in the direction of the Sun and stretching it out in the anti-Sun direction.
Fluctuations in the flow of solar wind cause variations in the strength and direction of
the magnetic field measured near the surface of the Earth. Abrupt changes in solar wind
speed or density are called geomagnetic storm (Thompson,2007).
2.2.2.3 Geomagnetic Storm
As referred to Swinburne Astronomy Online (2009), geomagnetic storms are a solar-
induced electromagnetic phenomenon which occurs both in atmosphere and across the
Earth's surface. The variation flow of charged particles from solar flares through the
Earth's atmosphere is causing a fluctuating magnetic field. These fluctuating magnetic
fields will induce electrical currents across Earth surface.
Figure 2.10 : Charged particles ejected from the Sun distort Earth's magnetic field
(Swinburne Astronomy Online,2009)
http://astronomy.swin.edu.au/cosmos/S/Sun
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A geomagnetic storm could cause the Earth's ionosphere (the electrified layers of
the upper atmosphere) severely disturbed by flows of charged particles. This is important
because the ionosphere acts as a "mirror" that reflect the High Frequency (HF) signals
(Thompson, 2007).
2.3 Effects of Earths Magnetic Field to Our Lives
The Earth's magnetic field is an ever-changing phenomenon that influences human
activity and the natural world in a countless of ways. The geomagnetic field changes
from place to place and from time to time. The changes are caused by geomagnetic
storm that originates from sunspot. Sunspot activity produce solar flares that leads to
solar wind and geomagnetic storm. These space weathers can greatly affect our modern
way of life and technology.
Figure 2.11: Space weather effects on technology (Space Weather Canada,2009)
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Space weather phenomena have a variety of effects on technology. Energetic
particles thrown out from the Sun interact with the Earth's magnetic field producing
magnetic disturbances and increased ionization in the ionosphere. These space
phenomena occur at 100 to 1000 km above the Earth (Space Weather Canada,2009).
The space weather phenomena can degrade navigation and surveying techniques.
In addition, it can impede geophysical exploration, disrupt electric power utilities and
pipeline operations. Moreover, it can disturb modern communications system and
satellite operation.
2.3.1 Effects on Satellite Operation
The high energy particles affect satellites causing disoperation or equipment damage that
can put the satellite out of operation. When a satellite passed through a cloud of high-
velocity electrons, an electrostatic discharge occur that actually fired the satellites rocket
thrusters, resulting in a loss of control from ground tracking stations (Space Weather
Canada,2009).
2.3.2 Effects on Modern Communication and Navigation System
Thompson (2007), state that radio waves used for satellite communications or GPS
navigation are affected by the increased ionization with disruption of the communication
or navigation systems. Geomagnetic storm corresponds with a disturbed ionosphere
causing difficult HF communications. HF is significant in various areas including
defense, emergency services, broadcasters, and marine and aviation operators.
2.3.3 Effects on Power System and Pipelines
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According to Swinburne Astronomy Online (2009), magnetic disturbances also induce
electric currents in long conductors such as power lines and pipelines causing power
system outages or pipeline corrosion. The ground induced currents tend to flow through
power lines or man-made pipeline networks because the electricity encounters less
resistance when it flows through metal, compared to rock or water. The ground induced
currents are direct currents. In contrast, the power-grid transformer operates in
alternating current. Therefore, the combination of the Direct Currents (DC) and
Alternating Currents (AC) causing the transformers to catch on fire and breakdown.
2.3.4 Effects on Magnetic Surveys
The geomagnetic storm directly affects operations that use the magnetic field, such as
magnetic surveys. Magnetic storms cause considerable disruption to magnetic field due
to the unpredictable and irregular nature of the geomagnetic field fluctuations. As a
result, the temporal variations of the Earth's magnetic field causing difficulty to interpret
magnetic survey data (Marshall,2007).
2.4 Overhouser Magnetometer (GSM-19GW)
2.4.1 Overview
Overhauser magnetometers were introduced by GEM Systems, Inc. following R&D in
the 80s and 90s. It is the standard equipment for archeology activities, magnetic
observatory measurement and long term magnetic field monitoring in volcanologist and
earthquake prediction (Hrvoic, Wilson & Lopez, 2009).
A magnetometer is an instrument with a single sensor that measures magnetic
flux density B (inTesla). The Earth generates a weak magnetic field that produces flux
densities (in air) of about 30 microTesla in some parts of South America to a high of
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over 60 microTesla in the Arctic Circle and Antarctica. Since magnetic flux density in
air is directly proportional to magnetic field strength H [A/m], a magnetometer is
capable of detecting fluctuations in the Earth's magnetic field (Hrvoic & Hollyer ,2007).
Overhauser magnetometer offers several benefits that can facilitate in conducting
magnetic field survey. The benefits are:
High resolution exploration mapping
Ground portable magnetic surveying for environmental and engineering
applications
The innovative "Walking" option that enables the acquisition of nearly
continuous data on survey lines.
The system records data at discrete time intervals (up to 5 readings per second)
as the instrument is carried along the line.
It also increases survey efficiency because the operator can record data almost
continuously.
It has a built-in GPS which offers many advantages such as minimizing weight.
2.4.2 Standard Magnetometer Components
An Overhouser Magnetometer (GSM-19GW) consists of standard magnetometer
components, sectional staff rods and a backpack. Figure 2.12 displays the standard
magnetometer components.
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Figure 2.12: Standard magnetometer components
The following list is a standard parts of a GSM-19GW magnetometer:
Two sensors for gradiometer application and one sensor for magnetometer
application. Sensors are dual-coils designed to reduce noise and improve gradient
tolerance.
Figure 2.13: Magnetometer sensor
One coaxial sensor cable per channel, typically RG-58/U and 206 cm long.
Console with 16 keys keyboard, graphic display (64 x 240 pixel), sensor and
power / input / output connectors. The keyboard also serves as an ON-OFF
switch.
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Figure 2.14: Magnetometer console
6-pin console connector for RS-232, external power, battery charging or external
trigger.
Sealed connectors (i.e. keyboard and front panel mounting screws are sealed so that
the instrument can operate under rainy conditions).
Charger with 2 levels of charging (full and trickle) that switch automatically from
one to another. The power supply input is 110 250V, 50 / 60 Hz.
Aluminum staffs with 4 strong tubing sections as refer to Figure 2.15. This
construction allows for a selection of sensor elevations above ground during surveys.
Figure 2.15: Sectional staff rods
A backpack is provided for walking mode magnetometer as shown in Figure
2.16.
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Figure 2.16 : Magnetometer backpack
2.5 Global Positioning System (GPS)
2.5.1. GPS Overview
Global Positioning System (GPS) is a Satellite Navigation System which is developed
by the U.S Department of Defense. It can be accessed by users on the land, sea or in the
air. However, it is not available in underwater or underground such as in a mine (UK
Telematics Online,2009).
GPS is the best navigation system available at the present time. It can provide
immediate information regarding position on the earths surface, altitude, speed,
direction of travel and time. GPS is a revolutionary system of navigation because it
works anywhere in the world, in any weather condition, 24 hours a day and has no cost
to the user (UK Telematics Online,2009).
Nowadays, the application of GPS technology is widening in magnetic survey.
GPS have the ability to make better decisions in locating and following up on anomalies.
Thus, GPS features can improve the survey cost effectiveness and time management
(UK Telematics Online,2009).
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2.5.2 GPS Operation
GPS satellites are powered by solar energy. They have backup batteries onboard to keep
them running in the event of a solar eclipse, when there's no solar power. Small rocket
boosters on each satellite keep them flying in the correct path (Garmin,1996).
Figure 2.17 : GPS satellite (Garmin,1996)
The GPS system relies on 24 satellites orbiting the Earth about 12,000 miles
above Earth surface. They are constantly moving, making two complete orbits in less
than 24 hours. These satellites are travelling at speeds of roughly 7,000 miles an hour
(Garmin,1996).
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Figure 2.9: Van Allen Radiation Belt (Stern,2001)
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