Presentation on 19th June 2018 by Guido Tronca at GPR 2018 – the 17th International Conference on Ground Penetrating Radar, in Rapperswil, Switzerland. Based on the paper of the same name authored by Guido Tronca, Isaak Tsalicoglou and Samuel Lehner of Proceq SA (Switzerland), together with Gianluca Catanzariti of 3D Geoimaging (Italy). The use of Ground Penetrating Radar (GPR) in structural investigations is based on the detection of features, embedded objects and flaws that cause a reflection of the transmitted electromagnetic wave. Construction types may vary from concrete to masonry and rock and possible targets include metallic reinforcements, ducts, plastic pipes, air voids, as well as the boundaries of the object itself. While a traditional impulse Ground Penetrating Radar (GPR) system uses time-domain measurements of the reflected waves within the investigated objects, a Stepped-Frequency Continuous-Wave (SFCW) system collects data in the frequency domain and converts the data to time-domain data through computer processing. Until recently, the time-consuming calculations associated with the real-time inverse Fourier transforms in SFCW systems limited its application. Thanks to faster processing capabilities available nowadays, this limitation no longer applies to structural GPR. The experimental work on representative concrete and masonry structures presented in this paper shows a systematic comparison of a new SFCW GPR system with traditional impulse radar systems. The results illustrate that SFCW technology combines the highest resolution in the detection of shallow targets, with a very broad detection range, potentially resolving the resolution/penetration trade-off observed in established structural GPR systems.

1. Comparison of pulsed and SFCW GPR systems –
Applications on reinforced concrete and brick/rock
masonries
GPR 2018 - 17th International Conference on Ground Penetrating Radar
Rapperswil, Switzerland, 19th June 2018
G. Tronca, I. Tsalicoglou, S. Lehner,
Proceq SA, Switzerland
© Proceq 2018 1
G. Catanzariti
3D Geoimaging, Italy

2. 1
Overview
Introduction
Comparison testing
Case 1: concrete pillar
Tendon duct analysis
© Proceq 2018 Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 2
2
3
4 Case 2: masonry wall4
Tendon duct analysis4 Conclusion6
Tendon duct analysis4 Case 3: masonry vault5

3. 1
Overview
Introduction
Comparison testing
Case 1: concrete pillar
Tendon duct analysis
© Proceq 2018 Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 3
2
3
4 Case 2: masonry wall4
Tendon duct analysis4 Conclusion6
Tendon duct analysis4 Case 3: masonry vault5

4. Structure type Application
© Proceq 2018 Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 4
Thanks to its flexibility, GPR plays a major role in
Civil Engineering inspections
Reinforced concrete
Brick and rock masonry
Asphalt
Thickness
Steel reinforcement
Embedded objects and voids
Possible targets
As-built verification
Structural assessment
Hit prevention

5. © Proceq 2018 Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 5
Resolution and detection range depend on
antenna frequency
Antenna
frequency
Attenuation
Penetration
depth
Sensitivity to
discontinuities
Resolution

6. © Proceq 2018 Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 6
Traditional concrete scanning solutions require
more than one antenna for different applications
Detectable objectssmall large
Ultra wideband technology
Penetrationdepth
070cm
2.6 GHz 2.0 GHz 1.6 GHz 1.0 GHz
Center frequency

7. t
A
RX
© Proceq 2018 Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 7
Stepped-Frequency Continuous-Wave (SFCW) is
an alternative approach to GPR
Traditional
pulsed GPR
A
tf
A
IFFT
A-scan real-time
calculated, unfiltered
Frequency spectrum
measured (0.9 – 3.5 GHz)
Continuous wave
(0.2 – 4.0 GHz)
A-scan measured,
heavily filtered for display
Single pulse around
single center frequency
Proceq GPR Live
(SFCW)
TX
t
A
RX
RXTX

8. “True ultrawideband” Increased signal-to-noise ratio
© Proceq 2018 Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 8
SFCW is “true ultrawideband”, with a
significantly increased signal-to-noise ratio
• “All frequencies” typically covered by separate
pulsed GPR devices for concrete assessment
• Only a single handheld probe
• Frequency components:
 Higher for shallower objects
 Lower for deeper objects
• More than 30 dB higher dynamic range compared
to pulsed GPR*
• No heavy filtering necessary
 No loss of information
 No artifacts
• Weak reflectors more evident
• Deep targets well distinguished from background
*Reference: “An Ultra High Resolution Stepped Frequency GPR for civil engineering applications”, Filippo Parrini,
Federico Papi* and Massimiliano Pieraccini – 2015 8° International Workshop on Advanced Ground Penetrating Radar,
https://ieeexplore.ieee.org/document/7292624/

9. 1
Overview
Introduction
Comparison testing
Case 1: concrete pillar
Tendon duct analysis
© Proceq 2018 Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 9
2
3
4 Case 2: masonry wall4
Tendon duct analysis4 Conclusion6
Tendon duct analysis4 Case 3: masonry vault5

10. © Proceq 2018 Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 10
Test objects Data acquisition Data processing Evaluation
A practice-driven, systematic approach is more
insightful than comparing specifications
• Detected features
• Resolution
• Investigation depth

11. Part I: B-scan processing Part II: C-scan / volume processing
© Proceq 2018 Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 11
A common post-processing sequence was
applied for all measurements
1. SEG-Y file import in GPR-SLICE
2. Time zero compensation (Npeak response)
3. Linear Gain
4. Bandpass filter 0.2 – 4.0 GHz for removing
wobbles and ripples
 Not needed for Proceq GPR Live
5. Background removal never applied
 Selected exceptions for comparison purposes
1. Migration
2. Hilbert transform
3. Volume math with separate X and Y volume
calculations
4. Depth-slicing

12. © Proceq 2018 Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 12
Three different GPR devices (pulsed and SFCW) were used
in the comparison study
ERA 1.0 GHz
GSSI StructureScan
Mini XT
Proceq GPR Live
GPR technology Pulsed Pulsed SFCW
Nominal frequency 1.0 GHz 2.7 GHz 0.2 … 4.0 GHz
Acquisition time 25 ns 9 ns 20 ns

13. 1
Overview
Introduction
Comparison testing
Case 1: concrete pillar
Tendon duct analysis
© Proceq 2018 Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 13
2
3
4 Case 2: masonry wall4
Tendon duct analysis4 Conclusion6
Tendon duct analysis4 Case 3: masonry vault5

14. © Proceq 2017 14
Case 1
Thin concrete pillar

15. © Proceq 2017 15
Case 1
Challenge: resolving closely-spaced rebar layers

16. © Proceq 2018 Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 16
Case 1
Comparison of selected B-scans
Rebars
Back wall
Rebars
Back wall
Rebars
Back wall

17. Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 17
Case 1
Comparison of time slices
© Proceq 2018
Second mat Back wallFirst mat

18. Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 18
Case 1
Comparison of time slices
© Proceq 2018
Second mat Back wallFirst mat

19. © Proceq 2018 Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 19
Case 1
Comparison of time slices

20. 1
Overview
Introduction
Comparison testing
Case 1: concrete pillar
Tendon duct analysis
© Proceq 2018 Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 20
2
3
4 Case 2: masonry wall4
Tendon duct analysis4 Conclusion6
Tendon duct analysis4 Case 3: masonry vault5

21. © Proceq 2018 Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 21
Case 2
Masonry wall (mixed brick / rock)

22. © Proceq 2017 22
Case 2
Challenge: back wall, cavities , wall texture
Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects

23. © Proceq 2018 Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 23
Case 2
Looking across the full element
Utilities
Back wall
Chimney fumes
Utilities
Back wall
Chimney fumes

24. © Proceq 2018 Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 24
Case 2
Results with high shallow resolution
Utilities
Chimney fumes
Wall texture
(single components)
Utilities
Chimney fumes
Wall texture
(single components)

25. 1
Overview
Introduction
Comparison testing
Case 1: concrete pillar
Tendon duct analysis
© Proceq 2018 Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 25
2
3
4 Case 2: masonry wall4
Tendon duct analysis4 Conclusion6
Tendon duct analysis4 Case 3: masonry vault5

26. © Proceq 2018 Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 26
Case 3
Masonry vault

27. © Proceq 2018 Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 27
Case 3
Challenge: utility network, vault texture and profile

28. © Proceq 2018 Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 28
Case 3
Comparison of selected B-scans
Broad range (full
geometry)
Broad range +
sharp resolution
Sharp resolution
(single brick in the
vault)
Vault
Utilities
Plasterboard ceiling
Vault
Plasterboard ceiling
Vault
Utilities
Plasterboard ceiling
Vault
Plasterboard ceiling
Vault

29. © Proceq 2018 Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 29
Case 3: full insight through Proceq GPR Live time slices
a.
b.
c.
d.

30. 1
Overview
Introduction
Comparison testing
Case 1: concrete pillar
Tendon duct analysis
© Proceq 2018 Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects 30
2
3
4 Case 2: masonry wall4
Tendon duct analysis4 Conclusion6
Tendon duct analysis4 Case 3: masonry vault5

31. Portable pulsed GPR Handheld SFCW GPR
© Proceq 2017 31
Portable SFCW GPR shifts the focus from
on-paper specs to getting the job done
• Multiple devices needed
• Single center frequency
• High resolution OR penetration depth
• Lower max. acquisition time
• In time domain; filtering needed
• One device suffices
• “All frequencies”
• High resolution and penetration depth
• Higher max. acquisition time
• In frequency domain; clean data
The commercial availability of portable SFCW GPR represents a
significant breakthrough in the field of structural investigations
Looking into concrete and masonry structures – usage of multiple frequency radar products to detect structural parameters and defects