Ground penetrating radar uses electromagnetic pulses to detect objects and interfaces between materials underground. It works by sending a pulse into the ground and measuring the reflected signals, which contain information about subsurface layers and objects. GPR systems include antennas, a control unit, and display for data collection and analysis. Data analysis involves calibrating the system and determining dielectric constants to interpret reflection signals and identify subsurface features like pipes, tanks, rebar, and voids. GPR offers fast, nondestructive scanning but performance depends on material properties and density of targets. Common manufacturers provide handheld to vehicular GPR systems ranging in price from $6,500 to $48,000.

1. Ground Penetrating Radar
Gonzalo Gallo
CEE 498KM

2. Outline
• Introduction
• Principle
• Instrumentation
• Data Analysis
• Advantages and Limitations
• Manufacturers and costs

3. Introduction
• RADAR → Radio Detection and Ranging
– Detect target in free space
– Determine the range
• Civil engineering applications
– Probing into soil to detect pipelines and tanks
– Cavities
– Thickness determination
– Locating reinforcement
– Identifying deterioration

4. 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 constants is
encountered
http://www.cait.rutgers.edu/finalreports/GPR-RU4474.pdf

5. Principle
• The reflected signal has • The thickness of a layer
information on: is given by:
– how quickly the signal
traveled Ct i
di =
– how much was attenuated 2 ε r ,i
• These quantities depend
on spatial configuration where di is the thickness
and materials of layer i, ti the total
travel time through that
layer, C is the speed of
light and εr,i the dielectric
constant of the layer

6. Principle
• The amount of Typical Dielectric Constants
reflected energy at an Material Dielectric
interface is governed Constant
by:
ε r1 − ε r 2 Air 1
ρ1, 2 =
ε r1 + ε r 2 Water 81
where ρ1,2 is the Concrete 6-12
reflection coefficient HMA 4-7
and εr1 and εr2 are the Ice 1.5
dielectric constants
Metals ∞

7. Instrumentation
• The typical instrumentation for GPR
includes the following:
– Antenna
• Air-couple
• Ground-coupled
– Control Unit
– Display device
– Storage device

8. Instrumentation
http://www.cait.rutgers.edu/finalreports/GPR-RU4474.pdf http://georadar.ids-spa.it/images/new/gpr_products/antennas.gif

9. Instrumentation
• Another configuration
is a portable
arrangement
– Small, hand-held
dipole antenna
• Used for locating
rebar, embedments,
voids, and other
abnormalities
http://www.ndtjames.com/catalog/rebarLocators/datascanMKII.html
• 2.4lbs – 10”
penetration

10. Data Analysis
• Before using calibrate
– Copper plate → Complete reflection
– Air → Complete transmission
• Establish dielectric constant of test surface
with reflected energy equation

11. Data Analysis
• Techniques for
analysis
– Cluster
analysis
– Topographic
plotting
– Quantitative
peak tracking
– Peak plotting
http://www.cait.rutgers.edu/finalreports/GPR-RU4474.pdf

12. Advantages and Limitations
• Advantages • Limitations
– Fast speed scanning with – Rebar reflects as arch
non-contact antennas patterns – if dense,
– Very sensitive to presence individual bars are no
of embedded metal objects longer discerned
– Sensitive to the presence – Limitations if dielectric
of moisture properties are similar
– Dielectric properties
unknown
– Material “loss”
– Difficult in thin layers
In general, fast scanning
and saves money – Extensive data
– Operator dependant

13. Manufacturers and costs
• Hand-held
– Datascan MKII
• James Instruments ND
• $12.000
– IRIS systems
• Penetradar
– GSSI handy-scan
• $6.500 b&w
• $10.000 color
http://ndtdirect.com/shop/products.asp?viewall=1&stritem=CN-JA-RB1,CN-JA-RB2,CN-JA-RB3&keyword=Concrete&id1=44&id2=136
http://www.penetradar.com/GPR_Vehicles.htm

14. Manufacturers and costs
• Antennas
– Air-coupled
– Ground-coupled
Penetradar Corporation
http://www.penetradar.com/GPR_Vehicles.htm

15. Manufacturers and costs
• Vehicular GPR’s
– Single antenna
– Multiple antennas
– Custom configurations
Penetradar Corporation
GSSI
(GeographicalSurvey
Systems, Inc.)
$48.000 (includes
vehicle, antenna,
software and training)
http://www.penetradar.com/GPR_Vehicles.htm

16. Links and References
• http://www.geophysical.com/
• http://www.penetradar.com/
• http://ndtdirect.com/
• http://www.ndtjames.com/
• http://www.cait.rutgers.edu/finalreports/GPR-RU4474.pdf
• Al-Qadi, I.L. and Lahouar (2005). “Measuring layer
thickness with GPR –Theory to practice”. Construction
and Building Materials, 19, 763-772
• ACI Committee 228, (2003). “In-place methods to
estimate concrete strength (ACI 228.1R-03).”
Farmington Hills: American Concrete Institute.