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Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 1
1
Ground Penetrating Radar (GPR) /UWB radar
Fundamentals to applications
Motoyuki SatoTohoku University, [email protected]
http://magnet.cneas.tohoku.ac.jp/satolab/satolab-j.html
2
Contents1. Introduction to GPR How it looks How it works Applications
2. GPR Principle EM wave in material EM properties of Rock and
Soil Frequency
3. GPR System Antennas for GPR Display of GPR Profile
4. GPR Signal Processing SAR processing- Migration Simulation – Ray Tracing,
FDTD GPR signal processing
software
5. Quantitative Measurements Material Evaluation 3D survey
6. Advanced GPR Imaging Effective Sampling Compressive Sensing Inverse Problem
3
1.Introduction to GPR
4
Principle of GPRRecorded radar signal
Antenna Position
Tim
e
Weak reflection from targets
Clutter
Diffraction
5
GPR Profile
6
Principle of GPR
Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 2
1 Introduction 7 1 Introduction 8
出前授業
1 Introduction 9
地表レーダ計測 I
10
GPR System
11
GPR system ALIS
12
ALIS: Dual Sensor•Metal Detector(MD)•Ground Penetrating Radar(GPR)
Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 3
ALIS in Cambodia
14
Mines detected by ALIS
15
Deminer’s report 11-32MD quality: goodGPR quality: goodObject:AP mine
Out of test site, VANNA, SOKHA
Real object : PMN @ 10 cm
16
Deminer’s report 12-33MD quality: goodGPR quality: goodObject:AP mine
Out of test site, VANNA, SOKHA
Real object : MN79 @ 5 cm
17
Deren FaultTrench Observation
(Gobi, Mongolia)18
Application to Geological Survey(Deren Fault, Mongolai)
F?Fault
:Top soil:Weathering rock
:Basite
Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 4
19
Pavement Inspection
20
Radar Analysis of Asphalt and Base Course Thickness
21
GPR system
22
Application of GPRDetection of Buried Objects •pipe, cable•Landmine
Non Destructive Inspection (NDI)•Concrete•Construction•Tunnel•Pavement
Environment•Ground water•Geology
Agriculture•Irrigation monitoring
Archaeology
23
Feature of GPR
High speed, High resolution–On site subsurface imaging
Metal +Nonmetal–Wide applications
–High sensitivity to water
–Detection of water
24
2. GPR Principle
• EM Wave propagation in Soil/Rock
vc
m sr r
3 108
( / )
Wave Velocity
Wavelength
vTv
fm( )
Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 5
25
Reflection of EM wave
dv
m2
( )
1 2
1 2
Travel Time and Depth of Target
Reflectivity of Layer Boundary
26
Electrical properties of
Rock/Soil
Material Attenuation (dB/m) Relative
permittivity
Air 0 1
Clay 10-100 2-40
Coal: dry 1-10 3.5-9
Coal: wet 2-20 8-25
Concrete: dry 2-12 4-10
Concrete: wet 10-25 10-20
Fresh water 0.1 80
Fresh water ice 0.1-2 4
Granite: dry 0.5-3 5
Granite: wet 2-5 7
Lime stone: dry 0.5-10 7
Lime stone: wet 10-25 8
Permafrost 0.1-5 4-8
Sand: dry 0.01-1 4-6
Sand: saturated 0.03-0.3 10-30
Sandstone: dry 2-10 2-3
Sandstone: wet 10-20 5-10
Shale: saturated 10-100 6-9
Soil: firm 0.1-2 8-12
Soil: sandy dry 0.1-2 4-6
Soil: sandy wet 1-5 15-30
27
Dielectric Constant of Soil/Rock
• Water content and Dielectric Constant
Water ContentD
ielectric Constant
28
3. GPR System• Evaluation of radar System
Frequency
Wavelength
Attenuation
Resolution
Penetration depth
Low - High
Long - Short
Small - Large
Low - High
Deep - Shallow
29
Penetration Depth
Transmitter Power
Receiver Noise LevelPF=
1 Introduction 30コンピュータ
光ファイバ
送信アンテナ
受信アンテナ
接続ケーブル
コントロールユニット
PC
Optical fiber
Transmitter
Receiver
Cable
Control Unit
Radar system
TransmitterReceiver
Direct wave
Surface reflection
Target
Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 6
31
Size of Antenna and its operation Frequency
EM Radiation from a Dipole Antenna
32
33
Transmitted signal
0 50 100 150 200 250-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
Am
plit
ude
Time (ns)0 100 200 300 400 500
-40
-30
-20
-10
0
10
20
30
p(
)A
mpl
itude
(dB
(dB
)
Frequency (MHz)
waveform spectrum
GICHD 21 March 2007 34
Antenna for GPR
1.Broadband2.Phase characteristics3.Polarization4.Tx-Rx Isolation5.Size
GICHD 21 March 2007 35
Antenna Design
Vivaldi antenna
GICHD 21 March 2007 36
Transient Radiation from a Vivaldi antenna (FD-TD)
Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 7
GICHD 21 March 2007 37
4Direct Signal for the Large Antenna
2 identical large Vivaldi antennas
Distance 40 cm and 100 cm
S21 measurement
Near Field
Far field condition
R > 2D2/ R > 2.38 m
D=0.189 m
=0.03 m (f=10 GHz)
GICHD 21 March 2007 38
Cavity-back Spiral Antenna
GICHD 21 March 2007 39Raw signal
Reflection from a Metal PlateGICHD 21 March 2007 40
GPR antenna and EMI coilSensor head for Hand-Held
system: ALIS
GICHD 21 March 2007 41
ALIS with Vivaldi antenna GPR Profile A & B -Scan
42
Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 8
43
GPR Profile A & B Scan
A-scope B-scope
44
GPR Profile C-Scan & 3D
C-scope 3-D
Archaeological Survey by 3D GPR (Tohoku University-University of Miami)
4546
47 48
Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 9
49
4. GPR Signal Processing
1 Introduction 50
Radar reflection from buried pipes
1 Introduction 51
図1地中レーダによる埋設管検知例(大阪ガス早川秀樹氏提供)
図2 f-kマイグレーション処理を行った波形
GPR profile
After Migration processing
Raw signal
52
Signal Processing in GPRDC removalFrequency filteringSpatial filteringFrequency-Spatial (f-k) filteringDeconvolutionSmoothingAverage subtractionMigrationAmplitude correction (AGC 、STC)
53
GPR Profile
マイグレーション処理
Raw Profile
Time-shift
Subtraction of the averaged signal
Image reconstruction by Migration
What does GPR see?
54
Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 10
Forward Modeling
55
Ray Tracing
FDTD
•Inversion Scheme is not always effective•Forward Modeling
Ray Tracing
56
GPR profile by Ray Tracing
57
FDTD
58
GPRMAXhttp://www.gprmax.org
5. Quantitative Measurements
59 60
Measurement of Electrical Properties of Material
•GPR•Laboratory•In-Situ
Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 11
2013/4/7GPR
61
Parallel Plate
Easy at Low Frequency (<1MHz)
2013/4/7GPR
62
Coaxial Probe
Good for Powder, Liquid, Flat surface
2013/4/7GPR
63
Vector Network Analyzer
2013/4/7GPR
64
Coaxial Sample Holder
•At any Frequency
•Difficult to prepare sample
2013/4/7 GPR 65
Coaxial Sample Holder
2013/4/7GPR
66
Coaxial Sample Holder
Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 12
2013/4/7 GPR 67
同軸管法による誘電率測定
(a)周波数特性 (b)水分率
2013/4/7GPR
68
TDRTime Domain
Reflectrometer
•Easy to use
•Good for In-Situ measurement
•Not applicable to hard material
•Only near surface information
2013/4/7 69
TDR equipment and a probe
2013/4/7 70
Dielectric Properties of Water
' "1
S jj
Debye-Model
Microwave Oven2.45GHz
Observation of Dynamic Behavior of Ground water level by GPR
71
Static State Production State
ポンプ小屋の前での地中レーダ計測(モンゴル・ウランバートル市)
72
Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 13
Monitoring of Ground Water Migration
73
Residual
High Water Level Low Water Level
GPR profile along the survey line N.(a)Profile1,water level is 5.30m(+1.15m).(b)Profile12,water level is 4.65m(+1.15m offset).(c)Residual profile of (a) and (b).
GPR A-scope B-scope
74
Aスコープ Bスコープ
GPR Survey Techniques
• Common-offset • Common midpoint (CMP)
75
Reflector
Offset Trace Interval
Tx Rx
Reflector
Tx Rx
CMP
Direct Wave
Reflection
Wide angle Survey Tx Tx Tx Rx Rx Rx
Groundwater Table
Ground Surface
Tx Tx Tx Rx Rx Rx
Groundwater Table
Ground Surface
76
Velocity Spectrum
77
CMP gathers along survey line N
The low water condition. The high water condition.
Water Level in the well-5.30m(+1.15m offset)
Water Level in the well-4.65m(+1.15m offset)
Measurement of Material for Construction
35cm
Nuclear waste
radiation
Special material with high attenuation to prevent nuclear radiation
Dielectric constant Attenuation
Experimental purpose:
Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 14
Electromagnetic wave around a Material Specimen
79
Body Wave
Lateral Wave
Air-coupled Wave
Air-Coupled Wave
80
Offset Distance (m)
Tim
e(n
s)
Tx Tx Tx Rx Rx Rx
Groundwater Table
Ground Surface
Tx Tx Tx Rx Rx Rx
Groundwater Table
Ground Surface
1 Specimen (35cm)
35cm -150 -100 -50 0 50 100 150-6
-4
-2
0
2
4
6x 10-3
Time [ns]
Am
plitu
de
S11 test of 1 specimen (35cm)
35cm (with metal plate)
35cm (without metal plate)
-20 -15 -10 -5 0 5 10 15 20-6
-4
-2
0
2
4
6x 10-3
Time [ns]
Am
plitu
de
S11 test of 1 specimen (35cm)
35cm (with metal plate)
35cm (without metal plate) 70cm -150 -100 -50 0 50 100 150
-6
-4
-2
0
2
4x 10-3
Time [ns]
Am
plitu
deS11 test of 2 specimen (70cm)
70cm (with metal plate)
70cm (without metal plate)
-20 -15 -10 -5 0 5 10 15 20-6
-4
-2
0
2
4x 10-3
Time [ns]
Am
plitu
de
S11 test of 2 specimen (70cm)
70cm (with metal plate)
70cm (without metal plate)
2 Specimen (70cm)
6.4cm gypsum
Tx Tx
Metal plate
2cm
6.4cm
Frequency spectrumVivaldi transmitter Spiral transmitter
Raw data
AfterDeconvolution
0 1 2 3 4 5 6-40
-30
-20
-10
0
10
Frequency [GHz]
Am
plitu
de [
dB]
Reflection signals in Frequency Domain
Rx1Rx2Rx3Rx4Rx5
0 1 2 3 4 5 6-80
-70
-60
-50
-40
-30
-20
Frequency [GHz]
Am
plitu
de
[dB
]
Reflection signals in Frequency Domain
Rx1Rx2Rx3Rx4Rx5
0 1 2 3 4 5 6-60
-50
-40
-30
-20
-10
0
Frequency [GHz]
Am
plitu
de [d
B]
Reflection signals in Frequency Domain
Rx1Rx2Rx3Rx4Rx5
0 1 2 3 4 5 6-20
-10
0
10
20
30
40
Frequency [GHz]
Am
plitu
de
[dB
]
Reflection signals in Frequency Domain
Rx1Rx2Rx3Rx4Rx5
Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 15
0 1 2 3 4-4
-2
0
2
4x 10
-4
Time [ns]A
mpl
itud
e
Reflection signals
Rx1Rx2Rx3Rx4Rx5
0 1 2 3 4-6
-4
-2
0
2
4
6x 10
-3
Time [ns]
Am
plitu
de
Reflection signals
Rx1Rx2Rx3Rx4Rx5
Time domain signalVivaldi transmitter Spiral transmitter
Raw data
AfterDeconvolution
c
0 1 2 3 4-2
-1.5
-1
-0.5
0
0.5
1
1.5x 10
-3
Time [ns]
Am
plitu
de
Reflection signals
Rx1Rx2Rx3Rx4Rx5
0 1 2 3 4-0.03
-0.02
-0.01
0
0.01
0.02
0.03
Time [ns]
Am
plitu
de
Reflection signals
Rx1Rx2Rx3Rx4Rx5
c
0 0.2 0.4 0.6 0.8-0.02
-0.01
0
0.01
0.02t2 - x2
t2 [ns2]
(x2
[m2]
0 0.5 1 1.5-0.03
-0.02
-0.01
0
0.01
0.02
0.03t2 - x2
t2 [ns2]
(x2
[m2]
0 0.5 1 1.5-0.03
-0.02
-0.01
0
0.01
0.02
0.03t2 - x2
t2 [ns2]
(x2
[m2]
Velocity and thickness estimateVivaldi transmitter Spiral transmitter
Raw data
AfterDeconvolution
Epsilon=2.13, D=7.1c
Epsilon=2.0, D=7.5cm
0 0.2 0.4 0.6 0.8-0.02
-0.01
0
0.01
0.02t2 - x2
t2 [ns2]
(x2
[m2]
Epsilon=2.13, D=6.6cm
Epsilon=2.25, D=6.3cm
Velocity (m/ns)
Tim
e (
ns)
Velocity spectrum
0.1 0.15 0.2 0.25 0.3
0
0.5
1
1.5
2
2.5
3
3.5
Velocity (m/ns)
Tim
e (
ns)
Velocity spectrum
0.1 0.15 0.2 0.25 0.3
0
0.5
1
1.5
2
2.5
3
3.5
Velocity (m/ns)
Tim
e (
ns)
Velocity spectrum
0.1 0.15 0.2 0.25 0.3
0
0.5
1
1.5
2
2.5
3
3.5
Velocity and thickness estimateVivaldi transmitter Spiral transmitter
Raw data
AfterDeconvolution
Epsilon=1.72, D=6.7c
Epsilon=2.12, D=7.6c
Velocity (m/ns)
Tim
e (
ns)
Velocity spectrum
0.1 0.15 0.2 0.25 0.3
0
0.5
1
1.5
2
2.5
3
3.5Epsilon=2.16, D=6.7cm
Epsilon=2.10, D=6.7cm
3- Dimensional Subsurface Fracture Estimation
TX
RX
3-D Subsurface Fracture
Orientation
S E30S E30N
N
S
E
W
N
S
E30N
E30S
W30S
W30N
N W30N W30S
Survey for Subway Construction
90
Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 16
Frequency Dependency
91
20
40
60
Tim
e(n
s)
0
20
40
60
Tim
e(n
s)
0
20
40
60
Tim
e(n
s)
0
Introduction of GPR Survey
• Selection of Frequency
• Selection of Survey Lines
• Accurate Antenna positioning
• Combination of other methods (c.f. Electrical Survey)
• Try again
• Understand the physical limitation
92
6. Advanced GPR techniques(Practice)
Detection of smaller objects
Nondestructive Testing
93
(Research)Quantitative EvaluationPrecise Measurement4D(Time-Lapse)Continuous Monitoring
Tohoku University After 3.11 East Japan Earthquake
Earthquake and Tsunami
• 2006 Banda Ache, Indonesia• 2008 Sichuan, China• 2008 Iwate-Miyagi, Japan• 2011 Christ Church, New Zealand,• 2011 East Japan• 2012 Bologna, Italy
Grand slide area in Arato-zawaNorth Japan
Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 17
GB-SAR system in Arato-zawa
Ground surface deformation measured by GB-SAR
99
EMI survey for buried cars by land slide
総合評価図
100
Metal Detector Visualization using Differential GPS
Pi-SAR2 (NICT, Japan)
Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 18
Pi-SAR2 (NICT) Mar 12th 2011HH:R HV:GVV:B
Sendai-Natori
Archaeological Survey for Moving Houses to higher sites
Miyako, Iwate
Iwaki-city, Fukushima, April 2004 3DGPR imaging
250MHz AntennaPrecise Subsurface Structure up to 2 ma could be imaged
100MHz AntennaSubsurface Structure up to 10m could be visualized
Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 19
3DGPR
• The system was originally developed by Mark Grasumeck
• High Density Data Acquisition
• Accurate image
Subsurface Grave(Saoito-baru, Miyazaki)
• 3DGPR-horizontal slice
111
112Sakitama Tomb
GPR survey on the top of a Tomb113
3D GPR
High accurate 2D GPR acquisition and 3D data interpretation system
GPR profile
Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 20
Nara, Ishibutai
X = 4 m
115
Ishibutai and around
Zuigani-temple, Miyagi
正面入り口
Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 21
121
Question:3D GPR is good for accurate
imaging
GPR requires high-density data acquisition for better imaging
Is it true?
Nyquist criterion
• Data sampling rate >2B
• Antenna spacing < / 2
2 ( ' , )( , ) ( ', ) '
R x x yu x y d x t dx
v
The Circular Survey Direction
The Down-sampling Result =10cmxy=2cm xy=3cm xy=6cm
The Down-sampling Result xy=8cm xy=10cm xy=15cm
=10cm
Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 22
Operation of ALIS (GPR) in real mine fields in Cambodia (July 2009-)
127
2 sets of ALIS (GPR) have detected more than 80 land mines in Cambodia.
Identification rate is more than 60%
128
GPR image by ALIS
Cambodia, July 2009Detected target:PMN-2 (USSR)
=5cm xy=2cm
129
Signal Processing for Imaging
After signal processing Raw signal
Mine Clearance
March 2010
October 2010
Borehole radar for cavity detection
Rx
Cavity
19.5 m70 m
20 m
B1
B2
Tx
Korea, 2000
Borehole Radar Profiles
Tx: 70 m Tx: 75 m Tx: 80 m
Tx: 90 mTx: 85 m
=50cmx=10cm,y=20m
Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 23
Raypaths for an Air-Filled Cavity
Tx
Rxx
z
zt
zr
Cavity
(z, x)
L1
L'
L2
L3
1 2 3( , , , ) ( )cal t rt z x z z L L v L c Simplified refractive model according to Snell’s law
Inversion Result
(80 m, 4.5 m)
Gradient error scheme(Low error = high probability)
Takahashi, Ph.D dissertation
Results by Other Methods
Reverse-time migration(Zhou and Sato, 2004)
Travel-time Tomography(Zhou and Sato, 2004)
Rx
Cavity
19.5 m70 m
20 m
B1
B2
Tx
Targets (unknowns to be determined by GPR)are
sparse
CS (Compact Sensing)
Measured data
ReflectorsSteering Matrix
RandomizingMatrix
•Ill-posed Problem M(Measurement)<N(Unknowns)•If we know the location of non-zero coefficient?
K<<N -- M>K
Compact Sensing (CS)• CS Solution can be derived by solving
L1 minimization problem:
α ψ φy
このイメージは、現在表示できません。
21
1
.. min
.. min
φψαyα
φψαyα
ts
ts
Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 24
Problems of CS for GPR
1.Sampling Scheme2.Strong clutter
Application to detection of buried Objects by GPR
100cm
100cm
• Frequency span: 50MHz-1500MHz
• Number of point: 137 • Sampling point along spatial
direction : 201• Start Position = 0m• Stop Position = 2.06m• Antenna Separation = 0.3 m.
Start
end
Metal pipe1Depth=20cm,L=120cm,
φ=2.2cm
Metal pipe 2Depth=75cm,L=150cm, φ=5cm
0 0.5 1 1.5 2
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
profilemHH
azimuth[m]
Sla
ntR
ange
[m
]
2
4
6
8
10
12
14
16
x 10-5
Random Sampling Matrix
Frequency
Antenna Position
0 0.5 1 1.5 2
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
outputCsOMP
azimuth[m]
Sla
ntR
an
ge
[m]
0
1
2
3
x 10-4
0 0.5 1 1.5 2
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
outputCsCoSaMP
azimuth[m]
Sla
ntR
an
ge
[m]
0.5
1
1.5
2
2.5x 10
-4
0 0.5 1 1.5 2
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
outputCsBayesian
azimuth[m]
Sla
ntR
an
ge
[m]
0
1
2
3
x 10-4
0 0.5 1 1.5 2
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
outputCsBayesian
azimuth[m]
Sla
ntR
an
ge
[m]
0
1
2
3
x 10-4
(a) (b)
Reconstructed Image by CS
Fourier Base (a) OMP, t = 100.05s (b) CoSaMP, t = 0.44s
(c) Bayesian, t = 27.68s (d) Modified Bayesian, t = 0.68s
0 0.5 1 1.5 2
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
profilemHH
azimuth[m]
Sla
ntR
ange
[m
]
2
4
6
8
10
12
14
16
x 10-5
Summary- For better Imaging
• GPR and GB-SAR technologies for Humanitarian activities and Disaster mitigation
• Effective data acquisition with signal processing will improve the GPR image quality
Ground Penetrating Radar (GPR) IET-Radar 2013
Motoyuki Sato (Tohoku University, Japan) 25
Information on GPR
• http://cobalt.cneas.tohoku.ac.jp/users/sato/newpage9.htm• (Motoyuki Sato HP: Lectures on GPR)
• http://magnet.cneas.tohoku.ac.jp• Sato Lab, Tohoku University• http://www.earth.tohoku.ac.jp/gpr96.html• International Conference on GPR • www.ibam.cnr.it/gpr2010
145