Ground Penetrating Radar Theory": Syahrul Fithry Senin, Uitm Penang

GROUND PENETRATING RADAR
THEORY
Syahrul Fithry Senin, UiTM Penang
Contents:
1. Introduction
2. Components of GPR
3. GPR working principle
4. Reflected signal
5. GPR depth determination
6. How deep can GPR go into ground?
7. GPR data acquisition
8. Available GPR technology
9. GPR received signal and graphics display
10.Principles of GPR
11.Conclusions
Introduction
GPR has gained its popularity worldwide for embedded
object detection (shallow and deep range)

Uses radar pulses to image the subsurface.
Finding and detecting buried object.
Is a short range pulse system for remote sensing
applications.
The understanding of GPR components and
electromagnetic wave propagation principles is very

essential
Components of GPR:
1. Transmitting
and receiving
unit
2. Control unit
3. Display unit
4. Power
supplies
GPR Working Principle:

An EM pulse is sent
through an antenna,
penetrating into the
surveyed material.
A portion of the energy
is reflected back to the
antenna when an
interface between
materials of dissimilar
dielectric constant is
encountered.
Reflected Signal:
The amount of
reflected energy at an
interface is governed
by:
r1 r 2
1, 2
r1 r 2
where 1,2 is the

reflection coefficient
and r1 and r2 are the
dielectric constants.
Typical Dielectric Constants:

Material
Relative
permittivity
Air
Asphalt: dry
2-4
Clay
2-40
Dry sand
3-5
Concrete: dry
4-10
Fresh water
80
Metals
GPR Depth Determination:

The reflected signal The depth of a layer is given by:
has information on:

how quickly
the signal traveled

how much was
attenuated
These quantities
depend on spatial
configuration and
materials.
D = (5.9t)/sqrt. of(Er)
D = depth of target (inch.)
t = wave travel time (nanosecond)
5.9 = a constant incorporating speed of
light and unit conversions
Er = dielectric constant of subsurface
material
Maximum
How deep can GPR
go into
ground?:
Antenna
Appropriate
Penetration
It depend upon two condition: Frequency

The type of soil or rock in
1500 MHz
the GPR survey area.
The frequency of the
900 MHz
antenna used.
Depth
0.5 m
1m
Low frequency systems are
more penetrating but data

resolution is lower.
400 MHz
High frequency systems have
limited penetration but offer
a much higher resolution.
270 MHz
Application
Rebar mapping
and concrete
evaluation.
Pipe and void
detection or
assessing concrete
thickness.
4m
Utility surveys,
pavement
evaluation, storage
tank detection and
assessing
structural integrity
6m
Utility surveys,
geology and
archaeology
GPR Data Acquisition

GPR uses high frequency radio waves and transmits into the
ground.
When the waves hits the buried object or a boundary with
different dielectric constants, the receiving antenna records
variations in the reflected return signal.
The depth range of GPR is limited by electrical conductivity of
the ground ,the transmitted frequency and the radiated power.
As conductivity increases the penetration depth decreases.
Schematic diagram of a GPR

MULTI TARGET DETECTION USING
4-Mar-16 RADAR
Available GPR Technology
Fig no.:-04 ,GPR technology [4]
GPR Technology(cont.)
Air coupled antenna.
Ground coupled antenna.
Fig no.:-05,Air coupled antenna
Fig no.:-06,Ground
coupled antenna
GPR Received signal and graphic

profile display:
PRINCIPLES OF GPR
Electromagnetic waves have both electric and
magnetic components.
The propagation of EM waves through a material depends
on both electrical and magnetic properties of the

material:
Magnetic permeability ()
Electrical permeability ()
Electrical conductivity ()
However, for most civil engineering materials,
is more important than
The velocity of EM radiation will greatly
affected by the electrical and magnetic

properties of the passing medium.
What happens when an EM wave meets

medium?
Medium
property
Good conductor
Good insulator
Behavior of EM
wave
REFLECT
TRANSMIT
Object size almost

same as EM
wavelength
SCATTERED
Scattered object in
medium
ABSORPTION
How GPR can see the objects?

GPR can be used in two basic ways:
Looking at the transmitted signal between separate

transmitter and receiver antennae
How GPR can see the objects?
Looking at the reflected signal from transmitter

back to the integrated receiver antennae
Transmitted mode
In this mode, only object with HIGH
absorbance (relative the surrounding medium)

can be seen or detected
The power of received signal, Pr, varies as
the inverse square of the distance from the

transmitter
Reflected mode
The depth of the object depends on
ABSORBENCE of the object

Object with HIGH reflectance (relative the
surrounding medium) can be seen or

detected by GPR
The power of returned signal, Pr , varies
inversely as the fourth power of the distance

to the reflector
Object absorption determine

depth
Absorption depends on GPR

frequency, f
Data resolution depends on GPR

frequency
Resolution of GPR data is inversely
proportionate with GPR frequency

Low frequency (MHz); good depth of
penetration, low resolution

High frequency (GHz); can resolved cm-sized
object, but penetrate only a meter or less
Reflection
A contrast in electrical properties between
two materials will reflect as least some of the

radiation from the interface
The strength of reflection depends on the
properties of the two materials and the
geometry of the interface
High conductivity will give high reflectivity
Surface roughness will diffuse reflection
How does GPR see the subsurface

object?
The
transmitter sends out

very short pulses (in
nanoseconds) with frequency
of about 50 percent of
nominal frequency of just a
few cycles
i.e. For 1 GHz nominal

frequency, the short pulses
will have frequency of 0.5 to
1.5 GHz
How does GPR see the subsurface

object?
As the pulses enter the
subsurface, their
wavelength is shortened in
proportion to the
decreased in velocity
VIDEO
The data give the time travel of pulses from
the transmitter to the receiver

In order to know the depth of reflecting
object, the velocity in the subsurface must be

known/assumed
Conclusion:
GPR has been developed into a
sophisticated technique that can provide
detailed images of the near surface. As opposed
to other locating techniques that are capable of detecting
only metallic or conductive utilities and underground
targets, GPR can locate and characterize both metallic and
non-metallic subsurface features. It is completely nonintrusive, non-destructive and safe.
References :
vashov, S. I.; Razevig, V. V.; Vasiliev, I. A.; Zhuravlev, A. V.; Bechtel, T. D.;
Capineri, L. (2011). "Holographic Subsurface Radar of RASCAN Type:

Development and Application". IEEE Journal of Selected Topics in Applied Earth
Observation and Remote Sensing 4 (4): 763778.
doi:10.1109/JSTARS.2011.2161755. Retrieved 26 September 2013.
ETSI EG 202 730 V1.1.1 (200909), "Electromagnetic compatibility and Radio
spectrum Matters (ERM); Code of Practice in respect of the control, use and
application of Ground Probing Radar (GPR) and Wall Probing Radar (WPR)
systems and equipment
Wilson, M. G. C.; Henry, G.; Marshall, T. R. (2006). "A review of the alluvial
diamond industry and the gravels of the North West Province, South Africa". South
African Journal of Geology (Geological Society of South Africa) 109 (3): 301314
Daniels DJ (ed.) (2004). Ground Penetrating Radar (2nd ed.). Knoval (Institution of
Engineering and Technology). pp. 14. ISBN 978-0-86341-360-5
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GROUND PENETRATING RADAR

object detection (shallow and deep range)

electromagnetic wave propagation principles is very

GPR Working Principle:

where 1,2 is the

Typical Dielectric Constants:

GPR Depth Determination:

has information on:

the signal traveled

It depend upon two condition: Frequency

Low frequency systems are

more penetrating but data

GPR Data Acquisition

Schematic diagram of a GPR

Available GPR Technology

Fig no.:-04 ,GPR technology [4]

Fig no.:-05,Air coupled antenna

GPR Received signal and graphic

The propagation of EM waves through a material depends

on both electrical and magnetic properties of the

However, for most civil engineering materials,

is more important than

The velocity of EM radiation will greatly

affected by the electrical and magnetic

What happens when an EM wave meets

Object size almost

How GPR can see the objects?

Looking at the transmitted signal between separate

How GPR can see the objects?

Looking at the reflected signal from transmitter

absorbance (relative the surrounding medium)

the inverse square of the distance from the

ABSORBENCE of the object

surrounding medium) can be seen or

inversely as the fourth power of the distance

Object absorption determine

Absorption depends on GPR

Data resolution depends on GPR

proportionate with GPR frequency

penetration, low resolution

object, but penetrate only a meter or less

two materials will reflect as least some of the

How does GPR see the subsurface

transmitter sends out

i.e. For 1 GHz nominal

How does GPR see the subsurface

As the pulses enter the

The data give the time travel of pulses from

the transmitter to the receiver

object, the velocity in the subsurface must be

Capineri, L. (2011). "Holographic Subsurface Radar of RASCAN Type:

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