Comparison of pulsed and SFCW GPR systems – Applications on reinforced concrete and brick/rock masonries
•
4 likes•1,108 views
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.
Comparison of pulsed and SFCW GPR systems – Applications on reinforced concrete and brick/rock masonries
- 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