Ground Penetrating Radar (GPR)cobalt.cneas.tohoku.ac.jp/users/sato/Ground Penetrating...Ground...

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



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)



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



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( )



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



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


Antenna Design

Vivaldi antenna


Transient Radiation from a Vivaldi antenna (FD-TD)




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)


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


ALIS with Vivaldi antenna GPR Profile A & B -Scan

42



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



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



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



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


2013/4/7GPR

66




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



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:



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



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)



-20 -15 -10 -5 0 5 10 15 20-6

-4

-2

0

2

4x 10-3

Time [ns]

Am

plitu

de




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

]


Rx1Rx2Rx3Rx4Rx5

0 1 2 3 4 5 6-60

-50

-40

-30

-20

-10

0

Frequency [GHz]

Am

plitu

de [d

B]


Rx1Rx2Rx3Rx4Rx5

0 1 2 3 4 5 6-20

-10

0

10

20

30

40

Frequency [GHz]

Am

plitu

de

[dB

]


Rx1Rx2Rx3Rx4Rx5



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]



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



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


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



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



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)



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



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



Nara, Ishibutai

X = 4 m

115

Ishibutai and around

Zuigani-temple, Miyagi

正面入り口



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



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



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



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



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

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