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.