1. Ground Penetrating Radar
MANSOOR-UL-HASSAN SIDDIQUE
Telecommunication
PAF-Karachi Institute of Economics and Technology
R-48A Hina Homes Block 21 F.B.Area Karachi
PAKISTAN
digitronics@fsmail.net, Mansoor_habibian@yahoo.com
Abstract: - Geophysical methods can be very useful in exploring for oil, minerals, or for locating buried objects. Most
methods in use today were developed five or six decades ago and have not been improved upon greatly since their
inception. Each method has its strengths---and often severe limitations that are imposed by nature. The advantage of
geophysical survey techniques is that they do not disturb the site, can usually be performed quickly, and they are very
cost effective compared to excavation costs. When they can be used these methods can be very helpful in evaluating
the site geologically and for delineating areas of interest and eliminating barren ground. Among the more recent tools
developed for probing beneath the surface of the earth is ground-penetrating radar [1], [2]
.
Key-Words: - Ground penetrating radar, dielectric permittivity, medium,
1 Introduction
Ground penetrating radar is a nondestructive
geophysical method that produces a continuous cross-
sectional profile or record of subsurface features,
without drilling, probing, or digging. Ground penetrating
radar (GPR) profiles are used for evaluating the location
and depth of buried objects and to investigate the
presence and continuity of natural subsurface conditions
and features [3], [4]
.
Ground penetrating radar operates by transmitting pulses
of ultra high frequency radio waves (microwave
electromagnetic energy) down into the ground through a
transducer (also called an antenna). The transmitted
energy is reflected from various buried objects or
distinct contacts between different earth materials. The
antenna then receives the reflected waves and stores
them in the digital control unit [5]
.
2 Problem Formulation
GPR works by sending a tiny pulse of energy into a
material and recording the strength and the time required
for the return of any reflected signal. A series of pulses
over a single area make up what is called a scan.
Reflections are produced whenever the energy pulse
enters into a material with different electrical conduction
properties (dielectric permittivity) from the material it
left. The strength, or amplitude, of the reflection is
determined by the contrast in the dielectric constants of
the two materials. This means that a pulse which moves
from dry sand (diel of 5) to wet sand (diel of 30) will
produce a very strong, brilliantly visible reflection,
while one moving from dry sand (5) to limestone (7)
will produce a very weak reflections. Materials with a
high dielectric are very conductive [6]
.
Figure 1: GPR Emits a Pulse of Energy
While some of the GPR energy pulse is reflected back to
the antenna, energy also keeps traveling through the
material until it either dissipates (attenuates) or the GPR
control unit has closed its time window (Figure 1). The
rate of signal attenuation varies widely and is dependant
on the dielectric properties of the material through which
the pulse is passing [6]
.
Materials with a high dielectric are very conductive and
thus attenuate the signal rapidly. Water saturation
dramatically raises the dielectric of a material, so a
survey area should be carefully inspected for signs of
water penetration. Radar surveys should never be
conducted through standing water, no matter how
Proceedings of the 5th WSEAS International Conference on MATHEMATICAL BIOLOGY and ECOLOGY (MABE'09)
ISSN: 1790-5125 51 ISBN: 978-960-474-038-3

2. shallow. Depth penetration through a material with a
high dielectric will not be very good [7]
.
Figure 2: Radar Energy is emitted in a Cone Shape
Metals are considered to be a complete reflector and do
not allow any amount of signal to pass through.
Materials beneath a metal sheet, fine metal mesh, or pan
decking will not be visible.
Radar energy is not emitted from the antenna in a
straight line. It is emitted in a cone shape (Figure 2). The
two-way travel time for energy at the leading edge of the
cone is longer than for energy directly beneath the
antenna. This is because that leading edge of the cone
represents the hypotenuse of a right triangle.
Because it takes longer for that energy to be received, it
is recorded farther down in the profile. As the antenna is
moved over a target, the distance between them
decreases until the antenna is over the target and
increases as the antenna is moved away. It is for this
reason that a single target will appear in a data as a
hyperbola, or inverted “U.” The target is actually at the
peak amplitude of the positive wavelet (Figure 2) [8]
.
Data are collected in parallel transects and then placed
together in their appropriate locations for computer
processing in a specialized software program such as
GSSI’s RADAN. The computer then produces a
horizontal surface at a particular depth in the record.
This is referred to as a depth slice, which allows
operators to interpret a plan view of the survey area.
2.1 GPR Equipment
A GPR system is made up of three main components:
1) Control unit, 2) Antenna and 3) Power supply as
seen in Figure 1.
GPR equipment can be run with a variety of power
supplies ranging from small rechargeable batteries to
vehicle batteries and normal 110-volt current.
Connectors and adapters are available for each power
source type. The unit in the photo above can run from a
small internal rechargeable battery or external power.
The control unit contains the electronics that produce
and regulate the pulse of radar energy that the antenna
sends into the ground. It also has a built in computer and
hard disk to record and store data for examination after
fieldwork. Some systems, such as the SIR-20, are
controlled by an attached Windows laptop computer with
pre-loaded control software. This system allows data
processing and interpretation without having to
download radar files into another computer.
The antenna receives the electrical pulse produced by the
control unit, amplifies it and transmits it into the ground
or other medium at a particular frequency. Antenna
frequency is a major factor in depth penetration. The
higher the frequency of the antenna, the shallower into
the ground it will penetrate. A higher frequency antenna
will also ‘see’ smaller targets. Antenna choice is one of
the most important factors in survey design. The
following table shows antenna frequency, approximate
depth penetration and appropriate application [9]
.
Depth
Range
(approximate)
Primary
Antenna
Choice
Secondary
Antenna
Choice
Appropriate
Application
0-1.5 ft
0-0.5 m
1600 MHz 900 MHz Structural
Concrete,
Roadways,
Bridge Decks,
0-3 ft
0-1 m
900 MHz 400 MHz Concrete,
Shallow Soils,
Archaeology
0-12 ft
0-9 M
400 MHz 200 MHz Shallow
Geology,
Utilities, UST's,
Archaeology
0-25 ft
0-9 m
200 MHz 100 MHz Geology,
Environmental,
Utility,
Archaeology
0-90 ft
0-30 m
100 MHz Sub-Echo 40 Geologic
Profiling
Greater than
90 ft or 30 m
MLF
(80, 40, 32,
20, 16 MHz)
20 m Geologic
Profiling
Table 1: Brief table for choosing appropriate GPR
3 Problem Solution
When the transmitted signal enters the ground, it
contacts objects or subsurface strata with different
electrical conductivities and dielectric constants. Part of
the ground penetrating radar waves reflect off of the
Proceedings of the 5th WSEAS International Conference on MATHEMATICAL BIOLOGY and ECOLOGY (MABE'09)
ISSN: 1790-5125 52 ISBN: 978-960-474-038-3

3. object or interface; while the rest of the waves pass
through to the next interface [6]
.
Figure 3: Three Buried Tanks and Irregular Bedrock
Topography
The reflected signals return to the antenna, pass through
the antenna, and are received by the digital control unit.
The control unit registers the reflections against two-
way travel time in nanoseconds and then amplifies the
signals. The output signal voltage peaks are plotted on
the ground penetrating radar profile as different color
bands by the digital control unit.
Ground penetrating radar waves can reach depths up to
100 feet (30 meters) in low conductivity materials such
as dry sand or granite. Moist clays, shale, and other
high conductivity materials, may attenuate or absorb
GPR signals, greatly decreasing the depth of
penetration to 3 feet (1 meter) or less.
The depth of penetration is also determined by the GPR
antenna used. Antennas with low frequencies of from
25 to 200 MHz obtain subsurface reflections from
deeper depths (about 30 to 100 feet or more), but have
low resolution. These low frequency antennas are used
for investigating the geology of a site, such as for
locating sinkholes or fractures, and to locate large, deep
buried objects.
Antennas with higher frequencies of from 300 to 1,500
MHz obtain reflections from shallow depths (0 to about
30 feet), and have high resolution. These high
frequency antennas are used to investigate surface soils
and to locate small or large, shallow, buried objects,
such as utilities, and also rebar in concrete [4].
Figure 4: PR Profile of an area of Bridgehampton and Enfield
Soils. The GPR profile (right) shows the eolian/outwash
interface and stratification in the outwash deposits. Photo
(left) is a profile of and Enfield soil series, the eolian/outwash
contact is at 50 to 55 cm.
For each reflected wave, the radar signal changes
polarity twice. These polarity changes produce three
bands on the radar profile for each interface contacted
by the radar wave [6]
.
4 Conclusion
The radar transmits high frequency, short duration
pulses of energy into the ground from a coupled
antenna. Transient electromagnetic waves are reflected,
refracted, and diffracted in the subsurface by changes in
electrical conductivity and dielectric properties. Travel
times of reflected, refracted and diffracted waves are
analyzed to give depths, geometry and material type
information. The energy returning to the antenna is
processed within the control unit and displayed on
graphic paper.
GPR Advantages GPR Limitations
Hi resolution,
vertically and
laterally.
Site specific
applications.
Rapid.
Generally, shallow
depth of observation
(1)
Cost effective.
Generally, near real
time interpretation.
Numerous areas of
application.
Non destructive.
Table 2: GPR Advantages and Limitations
Radar depth of observation; decreases as frequency
(antenna) increases, decreases as water content
increases, decreases as clay/salt content increases,
decreases as scattering increases, increases as
transmitter power increases [3]
.
Uses of GPR
Investigating the
variability of
soil properties.
Mapping peat thickness
and volume.
Mapping
geologic
deposits.
Sedimentation surveys.
Locating buried Engineering application.
Proceedings of the 5th WSEAS International Conference on MATHEMATICAL BIOLOGY and ECOLOGY (MABE'09)
ISSN: 1790-5125 53 ISBN: 978-960-474-038-3

4. objects.
Hydrologic
Investigations.
Soil survey
investigations.
Locating
contamination
plumes.
Cultural
resources/Archeological
investigations.
Table 3: Uses of GPR
References:
[1] Penguin Dictionary of Civil Engineering p347
(Radar)
[2] EUROGPR - The European GPR regulatory body
http://www.wseas.org/conferences/2008/bucharest/d
ncoco/deadlines.htm
[3] GprMax - GPR numerical simulator based on the
FDTD method http://www.gprmax.org/
[4] GPRSim.net - GPR ray trace simulator with GPR
tutorial
[5] Work Smart http://www.worksmartinc.net/sample-
ground-penetrating-radar-data.php
[6] GEO MODEL
http://www.geomodel.com/gprtext.htm
[8] Ground Penetrating Radar for Archeologist by
Lawrence B. Conyers
[9] Ground Penetrating Radar: Un'introduzione per gli
archeology ISBN 978-88-548-0951-2
Proceedings of the 5th WSEAS International Conference on MATHEMATICAL BIOLOGY and ECOLOGY (MABE'09)
ISSN: 1790-5125 54 ISBN: 978-960-474-038-3