Ground Penetrating Radar (GPR)

Ground Penetrating Radar (GPR) IET-Radar 2013 

Ground Penetrating Radar 

(GPR) /UWB radar 

Fundamentals to applications 

Motoyuki Sato 

Tohoku University, Japan 

sato@cneas.tohoku.ac.jp 

http://magnet.cneas.tohoku.ac.jp/satolab/satolab-j.html 

Contents 

1. 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 

1 

2 

1.Introduction to GPR 

Principle of GPR 

Recorded radar signal 

Antenna Position 

Time 

•Weak reflection from targets 

•Clutter 

•Diffraction 

3 

4 

GPR Profile 

Principle of 

GPR 

5 

6 

Motoyuki Sato (Tohoku University, Japan) 1


出前授業 

1 Introduction 7 1 Introduction 8 

地表レーダ計測 I 

GPR System 

1 Introduction 9 

10 

GPR system 

ALIS 

ALIS: Dual Sensor 

•Metal Detector(MD) 

•Ground Penetrating 

Radar(GPR) 

11 

12 



ALIS in Cambodia 

Mines detected by ALIS 

14 

Deminer’s report 11-32 

MD quality: good 

GPR quality: good 

Object:AP mine 

Deminer’s report 12-33 

MD quality: good 

GPR quality: good 

Object:AP mine 

Real object : PMN @ 10 cm 

Out of test site, VANNA, SOKHA 

Real object : MN79 @ 5 cm 

15 

Out of test site, VANNA, SOKHA 

16 

Application to Geological Survey(Deren Fault, Mongolai) 

Deren Fault 

Trench Observation 

(Gobi, Mongolia) 

:Top soil 

:Weathering rock 

:Basite 

F?Fault 

17 

18 



Pavement Inspection 

Radar Analysis of Asphalt and 

Base Course Thickness 

19 

20 

GPR system 

Application of GPR 

Detection of Buried 

Objects 

•pipe, cable 

•Landmine 

Non Destructive Inspection 

(NDI) 

•Concrete 

•Construction 

•Tunnel 

•Pavement 

Environment 

•Ground water 

•Geology 

Agriculture 

•Irrigation monitoring 

Archaeology 

21 

22 

Feature of GPR 

High speed, High resolution 

–On site subsurface imaging 

Metal +Nonmetal 

–Wide applications 

–High sensitivity to water 

–Detection of water 

2. GPR Principle 

• EM Wave propagation in Soil/Rock 

Wave Velocity 

c 3 

v 10 8 ( m/ s) 

 

r 

Wavelength 

v 

vT ( m) 

f 

r 

23 

24 



Reflection of EM wave 

Travel Time and Depth of 

Target 

v 

d m 

2 ( ) 

Reflectivity of Layer 

Boundary 

 

 

 

 

 

1 2 

1 2 

25 

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 

Electrical 

properties of 

Rock/Soil 

26 

Dielectric Constant of Soil/Rock 

• Water content and Dielectric Constant 

3. GPR System 

• Evaluation of radar System 

Dielectric Constant 

Frequency 

Wavelength 

Attenuation 

Resolution 

Low - High 

Long - Short 

Small - Large 

Low - High 

Water Content 

Penetration depth 

Deep - Shallow 

27 

28 

Penetration 

Depth 

Transmitter 

Direct wave 

Receiver 

Surface reflection 

Target 

Radar 

system 

光 Optical ファイバfiber 

コントロールユニット 

Control Unit 

Transmitter Power 

PF= 

Receiver Noise Level 

送 Transmitter 信アンテナ 

接 Cable 続ケーブル 

29 

受 Receiver 1 信 Introduction アンテナ 

30 

コンピュータ 

PC 



Size of Antenna and its 

operation Frequency 

EM Radiation from a Dipole Antenna 

31 

32 

Transmitted signal 

Antenna for GPR 

1 

30 

Amplitude 

0.8 

0.6 

0.4 

0.2 

0 

-0.2 

-0.4 

-0.6 

-0.8 

-1 

0 50 100 150 200 250 

Time (ns) 

Amplitude (dB(dB) 

p ( ) 

20 

10 

0 

-10 

-20 

-30 

-40 

0 100 200 300 400 500 

Frequency (MHz) 

1.Broadband 

2.Phase characteristics 

3.Polarization 

4.Tx-Rx Isolation 

5.Size 

waveform 

spectrum 

33 

GICHD 21 March 2007 34 

Antenna Design 

Transient Radiation from a 

Vivaldi antenna (FD-TD) 

Vivaldi antenna 





Direct Signal for the Large Antenna 

2 identical large Vivaldi antennas 

Distance 40 cm and 100 cm 

S21 measurement 

Near Field 

4 

Cavity-back Spiral Antenna 

Far field condition 

R>2D 2 / R > 2.38 m 

D=0.189 m 

=0.03 m (f=10 GHz) 



GPR antenna and EMI coil 

Sensor head for Hand-Held 

system: ALIS 

Raw signal 


Reflection from a Metal Plate 


ALIS with Vivaldi antenna 

GPR Profile A & B -Scan 


42 



GPR Profile A & B Scan 

GPR Profile C-Scan & 3D 

A-scope 

B-scope 

C-scope 3-D 

43 

44 

Archaeological Survey by 3D GPR 

(Tohoku University-University of Miami) 

45 

46 

47 48 



4. GPR Signal Processing 

Radar reflection from buried pipes 

49 


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 ) 

After 

Migration 

processing 


profile 

Raw 

signal 

Signal Processing in GPR 

DC removal 

Frequency filtering 

Spatial filtering 

Frequency-Spatial (f-k) filtering 

Deconvolution 

Smoothing 

Average subtraction 

Migration 

Amplitude correction (AGC 、STC) 


52 

図 2 

f-kマイグレーション処理を行った波形 

GPR Profile 

Raw Profile 

What does GPR see? 

Time-shift 

Subtraction of the 

averaged signal 

マイグレーショ 

ン処理 

Image reconstruction 

by Migration 

53 

54 



Forward Modeling 

•Inversion Scheme is not 

always effective 

•Forward Modeling 

Ray Tracing 

Ray Tracing 

FDTD 

55 

56 

GPR profile by Ray Tracing 

GPRMAX 

http://www.gprmax.org 

FDTD 

57 

58 

5. Quantitative Measurements 

Measurement of Electrical 

Properties of Material 

•GPR 

•Laboratory 

•In-Situ 

59 60 



Parallel Plate 

Easy at Low 

Frequency 

(


同軸管法による誘電率測定 

TDR 

Time Domain 

Reflectrometer 

(a) 周波数特性 

(b) 水分率 

•Easy to use 

•Good for In-Situ 

measurement 

•Not applicable to hard 

material 

•Only near surface 

information 

2013/4/7 GPR 67 

2013/4/7 


68 

TDR equipment and a probe 

Dielectric Properties of Water 

Microwave 

Oven 

2.45GHz 

 

S 

 

 

 

' j" 

1 

j 

Debye-Model 

2013/4/7 69 

2013/4/7 70 

Observation of Dynamic Behavior of 

Ground water level by GPR 

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 ) 

71 

72 



GPR A-scope B-scope 

High Water Level 

Low Water Level 

Monitoring of Ground 

Water Migration 

Residual 

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). 

73 

Aスコープ 

Bスコープ 

74 

GPR Survey Techniques 

Wide angle Survey 

Tx Tx Tx Rx Rx Rx 

Ground Surface 

• Common-offset 

Offset Trace Interval 

• Common midpoint 

(CMP) 

CMP 

Groundwater Table 

Tx 

Rx 

Tx 

Rx 

Reflector 

Reflector 

Direct Wave 

Reflection 

75 

76 

Velocity Spectrum 

CMP gathers along survey line N 

Measurement of Material for 

Construction 

Nuclea 

r waste 

35cm 

The low water condition. 

Water Level in the well 

-5.30m(+1.15m offset) 

The high water condition. 

Water Level in the 

well 

-4.65m(+1.15m offset) 

77 

Special material with high 

attenuation to prevent nuclear 

radiation 

Experimental purpose: 

‣ Dielectric constant 

‣ Attenuation 



Electromagnetic wave around a 

Material Specimen 

Air-Coupled Wave 

Air-coupled Wave 

Tx Tx Tx Rx Rx Rx 

Ground Surface 

Lateral Wave 

Time (ns) 

Groundwater Table 

Body Wave 

Offset Distance (m) 

79 

80 

1 Specimen (35cm) 

S11 test of 1 specimen (35cm) 

2 Specimen (70cm) 


4 

35cm (with metal plate) 


35cm (without metal plate) 

2 

2 


Amplitude 

0 

-2 

6 x 10-3 Time [ns] 


Amplitude 

0 

-2 

4 x 10-3 Time [ns] 


6 x 10-3 Time [ns] 

4 x 10-3 Time [ns] 

-4 


4 


35cm 

-6 

-150 -100 

2 

-50 0 50 100 150 

Amplitude 

0 

-2 

-4 

70c 

-4 


2 


m -6 

-150 -100 -50 0 50 100 150 

0 

Amplitude 

-2 

-4 

-6 

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

-6 

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

6.4cm gypsum 

Frequency spectrum 

Vivaldi transmitter Spiral transmitter 

Reflection signals in Frequency Domain Reflection signals in Frequency Domain 

0 

-20 

-10 

-30 

Tx 

6.4cm 

2cm 

Metal plate 

Tx 

Raw data 

Amplitude [dB] 

After 

Deconvolution 


-20 

-30 

Rx1 

-40 

Rx2 

Rx3 

-50 

Rx4 

Rx5 

-60 

0 1 2 3 4 5 6 

Frequency [GHz] 

Reflection signals in Frequency Domain 

40 

Rx1 

30 

Rx2 

Rx3 

20 

Rx4 

Rx5 

10 

0 

-10 

-20 

0 1 2 3 4 5 6 




-40 

-50 

-60 

-70 

-80 

0 1 2 3 4 5 6 


Reflection signals in Frequency Domain 

10 

0 

-10 

-20 

-30 

Rx1 

Rx2 

Rx3 

Rx4 

Rx5 

Rx1 

Rx2 

Rx3 

Rx4 

Rx5 

-40 

0 1 2 3 4 5 6 




Raw data 

Amplitude 

After 

Deconvolution 

Amplitude 

Time domain signal 

Vivaldi transmitter 

Reflection signals 

Rx1 

Rx2 

Rx3 

Rx4 

Rx5 

1.5 x 10-3 1 

0.5 

0 

-0.5 

-1 

-1.5 

-2 

0 1 2 

Time [ns] 

3 4 


0.03 

Rx1 

0.02 

0.01 

0 

-0.01 

-0.02 

c 

Rx2 

Rx3 

Rx4 

Rx5 

-0.03 

0 1 2 3 4 

Time [ns] 

Amplitude 

Amplitude 

Spiral transmitter 


Rx1 

Rx2 

Rx3 

Rx4 

Rx5 

4 x 10-4 2 

0 

-2 

-4 

0 1 2 

Time [ns] 

3 4 


Rx1 

c 

Rx2 

Rx3 

Rx4 

Rx5 

6 x 10-3 4 

2 

0 

-2 

-4 

-6 

0 1 2 

Time [ns] 

3 4 

Velocity and thickness estimate 

Raw data 

(x 2 [m 2 ] 

(x 2 [m 2 ] 

0.02 

0.01 

0.02 

After 0.01 

Deconvolution 

0 

0 

Vivaldi transmitter 

t 2 - x 2 

-0.02 

0 0.2 0.4 0.6 0.8 

t 2 [ns 2 ] 

t 2 - x 2 

-0.02 

0 0.2 0.4 0.6 0.8 

t 2 [ns 2 ] 

(x 2 [m 2 ] 

0.03 

0.02 

0.01 

0 

t 2 - x 2 

-0.03 

0 0.5 1 1.5 

t 2 [ns 2 ] 

-0.01 

-0.01 

Epsilon=2.25, D=6.3cmEpsilon=2.13, -0.02 

D=7.1c 

(x 2 [m 2 ] 

Spiral transmitter 

-0.01 

-0.01 

Epsilon=2.13, D=6.6cm Epsilon=2.0, -0.02 

D=7.5cm 

0.03 

0.02 

0.01 

0 

t 2 - x 2 

-0.03 

0 0.5 1 1.5 

t 2 [ns 2 ] 

Velocity and thickness estimate 

Raw data 

Time (ns) 

Vivaldi transmitter Spiral transmitter 

Velocity spectrum 

0 

0.5 

1 

1.5 

2 

2.5 

2.5 

3 

Epsilon=2.10, 

3 

D=6.7cm3.5 

3.5 

0.1 0.15 0.2 0.25 0.3 

0.1 0.15 0.2 0.25 0.3 

Velocity (m/ns) 


Time (ns) 


0 

0.5 

1 

1.5 

2 

Epsilon=2.12, D=7.6c 

3- Dimensional Subsurface Fracture Estimation 

RX 

After 

Deconvolution 

Time (ns) 


0 

0.5 

1 

1.5 

2 

Time (ns) 


0 

0.5 

1 

1.5 

2 

2.5 

2.5 

3 

3 

Epsilon=2.16, D=6.7cmEpsilon=1.72, D=6.7c 

3.5 

3.5 

TX 

0.1 0.15 0.2 0.25 0.3 


0.1 0.15 0.2 0.25 0.3 


3-D Subsurface 

Fracture 

Orientation 

S E30S E30N 

Survey for Subway 

Construction 

N 

W30N 

W30S 

E30N 

E30S 

S 

N W30N W30S 

W 

N 

S 

E 

90 



Frequency Dependency 

Introduction of GPR Survey 

Time (ns) 

0 

20 

4 

0 

60 

• Selection of Frequency 

• Selection of Survey Lines 

• Accurate Antenna positioning 

• Combination of other methods (c.f. Electrical 

Survey) 

Time (ns) 

0 

20 

4 

0 

60 

Time (ns) 

0 

20 

4 

0 

60 

91 

• Try again 

• Understand the physical limitation 

92 

6. Advanced GPR techniques 

(Practice) 

•Detection of smaller objects 

•Nondestructive Testing 

(Research) 

•Quantitative Evaluation 

•Precise Measurement 

•4D(Time-Lapse) 

•Continuous Monitoring 

Tohoku University 

After 3.11 East Japan Earthquake 

93 

Earthquake and Tsunami 

Grand slide area in Arato-zawa 

North Japan 

• 2006 Banda Ache, Indonesia 

• 2008 Sichuan, China 

• 2008 Iwate-Miyagi, Japan 

• 2011 Christ Church, New Zealand, 

• 2011 East Japan 

• 2012 Bologna, Italy 



GB-SAR system in Aratozawa 

Ground surface deformation 

measured by GB-SAR 

EMI survey for 

buried cars by land 

slide 

Metal Detector Visualization using Differential GPS 

総合評価図 

99 

100 

Pi-SAR2 (NICT, Japan) 



Sendai-Natori 

Pi-SAR2 

(NICT) Mar 

12 th 2011 

HH:R 

HV:G 

VV:B 

Archaeological Survey for 

Moving Houses to higher sites 

Miyako, Iwate 

Iwaki-city, Fukushima, April 2004 

3DGPR imaging 

250MHz Antenna 

Precise Subsurface Structure 

up to 2 ma could be imaged 

100MHz Antenna 

Subsurface 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 

Sakitama Tomb 

112 

111 

GPR survey on the top of a Tomb 

113 

GPR profile 

3D GPR 

High accurate 2D 

GPR acquisition 

and 3D data 

interpretation 

system 



Nara, Ishibutai 

Ishibutai and around 

X = 4 m 

115 

Zuigani-temple, Miyagi 

正面入り口 



Question: 

3D GPR is good for accurate 

imaging 

GPR requires high-density data 

acquisition for better imaging 

Is it true? 

121 

Nyquist criterion 

‣ The Circular Survey Direction 

• Data sampling rate >2B 

• Antenna spacing < /2 

2 Rx ( ' xy , ) 

uxy ( , ) 

dx ( ', t 

) dx' 

v 

‣ The Down-sampling Result 

=10cm 

xy=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-) 

GPR image by 

ALIS 

=5cm xy=2cm 

2 sets of ALIS 

(GPR) have 

detected more 

than 80 land 

mines in 

Cambodia. 

Identification 

rate is more 

than 60% 

Cambodia, July 2009 

Detected target:PMN-2 (USSR) 

127 

128 

Signal Processing for Imaging 

Mine 

Clearance 

October 2010 

After signal processing Raw signal 

March 2010 

129 

Borehole radar for cavity 

detection 

Borehole Radar Profiles 

=50cmx=10cm,y=20m 

Korea, 2000 

B2 

B1 

Tx: 70 m Tx: 75 m Tx: 80 m 

70 m 

19.5 m 

Rx 

Tx 

20 m 

Cavity 

Tx: 85 m 

Tx: 90 m 


このイメージは、現在表示できません。 


Raypaths for an Air-Filled Cavity 

Rx 

x 

z r 

z 

L' 

Inversion Result 

Gradient error scheme 

(Low error = high probability) 

L 2 

Tx 

z t 

L 1 

L 3 

1 2 3 

(z, x) 

(80 m, 4.5 m) 

Cavity 

Simplified refractive model according to Snell’s law 

t (,, z x z , z ) ( L L ) vL c 

cal t r 

Takahashi, Ph.D dissertation 

Results by Other Methods 

Targets (unknowns to be 

determined by GPR)are 

sparse 

B2 

B1 

70 m 

19.5 m 

Rx 

Tx 

Reverse-time migration 

(Zhou and Sato, 2004) 

Travel-time Tomography 

(Zhou and Sato, 2004) 

20 m 

Cavity 

Measured data 

CS (Compact Sensing) 

Randomizing 

Matrix 

Steering Matrix Reflectors 

•Ill-posed Problem M(Measurement)


Problems of CS for GPR 

Application to detection of buried 

Objects by GPR 

1.Sampling Scheme 

2.Strong clutter 

100cm 

100cm 

Metal pipe 2 

Depth=75cm,L=150cm, φ=5cm 

end 

Start 

• 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. 

0 

0.1 

profilemHH 

x 10 -5 

16 

14 

Random Sampling Matrix 

Antenna 

Position 

Metal pipe1 

Depth=20cm,L=120cm, 

φ=2.2cm 

SlantRange [m] 

0.2 

0.3 

0.4 

0.5 

0.6 

12 

10 

8 

6 

4 

2 

Frequency 

0.7 

0 0.5 1 1.5 2 

azimuth[m] 


profilemHH 

x 10 -5 

0 

16 

0.1 

14 

0.2 

12 

0.3 

10 

8 

0.4 

6 

0.5 

4 

0.6 

2 

0.7 

0 0.5 1 1.5 2 

azimuth[m] 

(a) 



outputCsBayesian 

0 

0.1 

0.2 

0.3 

0.4 

0.5 

0.6 

0.7 

0 0.5 1 1.5 2 

azimuth[m] 

outputCsOMP 

0 

0.1 

0.2 

0.3 

0.4 

0.5 

0.6 

0.7 

0 0.5 1 1.5 2 

azimuth[m] 

outputCsCoSaMP 

x 10 -4 

3 

2 

1 

0 

0 

0.1 

0.2 

0.3 

0.4 

0.5 

0.6 

0.7 

0 0.5 1 1.5 2 

azimuth[m] 

(b) 

Fourier Base (a) OMP, t = 100.05s (b) CoSaMP, t = 0.44s 

x 10 -4 

3 

2 

1 

0 

0 

0.1 

0.2 

0.3 

0.4 

0.5 

0.6 

0.7 

0 0.5 

outputCsBayesian 

1 1.5 2 

azimuth[m] 


(c) Bayesian, t = 27.68s (d) Modified Bayesian, t = 0.68s 

Reconstructed Image by CS 


x 10 -4 

3 

2 

1 

0 

x 10 -4 

2.5 

2 

1.5 

1 

0.5 

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 

145

Ground Penetrating Radar (GPR)

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