What is Ground Penetrating Radar (GPR)?
Ground Penetrating Radar (GPR), also known as georadar, is a non-destructive testing (NDT) method that uses radio-frequency electromagnetic waves to investigate the subsurface and the interior of structures without excavation or drilling. Developed since the 1970s, GPR has become an indispensable tool for civil engineers, geologists, archaeologists, and infrastructure inspection technicians.
The technology is based on emitting pulses of electromagnetic energy — typically between 50 MHz and 2600 MHz — and receiving echoes reflected at interfaces between materials with different dielectric properties. The two-way travel time (TWT) of the signal is converted into depth using the propagation velocity of waves in the medium, which depends on the dielectric permittivity of the material.
How GPR Works: Electromagnetic Principles
A GPR system consists of a transmitting antenna, a receiving antenna (often integrated in a single unit), and a control and recording unit. The operating cycle is as follows:
- Transmission: The antenna emits a short-duration electromagnetic pulse (nanoseconds) directed at the ground or structure.
- Propagation: The signal propagates through the medium at a velocity proportional to the relative dielectric constant (εr). In dry concrete, εr ≈ 6–9; in moist clay soil, εr can reach 30.
- Reflection: When the signal encounters an interface between two materials with different εr (e.g., concrete and steel rebar; soil and PVC pipe), part of the energy is reflected back to the surface.
- Reception and Recording: The receiving antenna captures reflected signals. Amplitude and arrival time are recorded, generating a trace (A-scan). Continuous scanning produces a 2D section (B-scan) or a 3D volume (C-scan).
Resolution and penetration depth are inversely proportional: high-frequency antennas (>1000 MHz) provide greater resolution but less penetration; low-frequency antennas (<500 MHz) penetrate deeper but with less detail.
GPR Applications
1. Underground Utility Detection
One of the most critical GPR applications is locating underground utilities before excavation works. Water, gas, and sewer pipes; electrical and telecommunications cables; fibre optic conduits; and buried chambers can all be detected without service interruption or exploratory excavation.
The GSSI UtilityScan with a 300 MHz or 400 MHz antenna is the reference solution for utility surveys, reaching depths of 6 to 9 metres in favourable soils. For sites with complex infrastructure, the UtilityScan DF combines GPR with electromagnetic (EM) field technology, enhancing detection of energised cables and metallic conductors.
2. Concrete Structure Inspection
In concrete inspection, GPR locates steel rebar, post-tensioning tendons, prestressing ducts, voids, delamination zones, moisture, and chloride contamination — without any damage to the structure.
The GSSI StructureScan Mini XT is the most advanced system for field concrete inspection. Equipped with integrated 1600 MHz and 2300 MHz antennas, it provides penetration depth up to 76 cm in concrete with millimetre-level resolution. RADAN 7 software automatically processes data and generates real-time 3D reports.
For larger area surveys with additional depth, the StructureScan Pro offers a robust platform ideal for bridge, tunnel, and industrial building inspection.
3. Road Pavement Evaluation
GPR is widely used by road management authorities to assess pavement condition without traffic disruption. It measures bituminous layer thickness, detects voids and sub-base deformation, identifies water infiltration, and predicts rehabilitation needs.
Standard ASTM D4748 defines the procedure for determining bound pavement layer thickness by GPR. The GSSI SIR 30 system, with multi-channel antenna capability, is the professional reference platform for high-speed road surveys.
4. Bridge and Deck Inspection
Reinforced concrete bridges are subject to rebar corrosion, cover concrete delamination, and chloride degradation. GPR enables systematic structural condition mapping of bridge decks, identifying critical zones requiring priority intervention, without closing the road to traffic.
5. Archaeology and Heritage Investigation
In archaeology, GPR enables non-invasive prospection of historical sites, detecting buried foundations, walls, graves, chambers, and artefacts without any excavation. This approach is particularly valuable in contexts where excavation would cause irreversible heritage damage.
6. Geology and Geotechnics
In geological and geotechnical applications, GPR is used for soil/rock interface mapping, karst cavity detection, soil stratigraphy studies, permafrost monitoring, and shallow aquifer mapping. With low-frequency antennas (50–200 MHz), penetration can exceed 15 metres in dry or frozen soils.
GSSI Equipment — Official Interphysix Distributor
GSSI (Geophysical Survey Systems, Inc.), founded in 1969, is the world’s leading manufacturer of GPR systems. Interphysix is the official GSSI distributor in Portugal, providing the full equipment range with local technical support, training, and after-sales service.
| Equipment | Antenna Frequency | Max. Depth | Main Application |
|---|---|---|---|
| StructureScan Mini XT | 1600 MHz + 2300 MHz | 76 cm (concrete) | Concrete inspection, rebar, slabs |
| StructureScan Mini LXT | 1600 MHz | 60 cm (concrete) | Concrete inspection, compact |
| StructureScan Pro | 900 MHz / 1600 MHz | 100 cm (concrete) | Bridges, decks, large structures |
| UtilityScan | 300 MHz or 400 MHz | 6–9 m (soil) | Underground utility detection |
| UtilityScan DF | 300 MHz GPR + EM | 6–9 m (soil) | Utilities + energised cables (dual freq.) |
| UtilityScan Pro | 200–600 MHz | up to 15 m | Deep surveys, geology |
| SIR 30 | Multi-channel (external antennas) | Variable | Road pavements, advanced surveys |
GPR Advantages Over Other Methods
- Non-destructive: No excavation, drilling, or structural cutting required.
- Real-time: Results visualised instantly in the field, enabling immediate decisions.
- Portability: Compact equipment like the StructureScan Mini XT weighs under 3 kg, operable by a single technician.
- Versatility: Works in concrete, soil, asphalt, ice, timber, and masonry.
- Safety: No ionising radiation — can be operated in inhabited areas and around people.
- Depth range: From millimetres (high-resolution concrete) to tens of metres (geology).
- Speed: Large area surveys in a fraction of the time of destructive methods.
Standards and Regulations
- ASTM D4748 — Standard Test Method for Determining the Thickness of Bound Pavement Layers Using Short-Pulse Radar
- ASTM D6432 — Standard Guide for Using the Surface Ground Penetrating Radar Method for Subsurface Investigation
- ASTM D6760 — Standard Test Method for Integrity Testing of Concrete Deep Foundations by Ultrasonic Crosshole Testing
- EN 1997 (Eurocode 7) — Geotechnical Design
- BS 5930 — Code of Practice for Ground Investigations
Frequently Asked Questions about GPR
What is GPR ground penetrating radar?
GPR is a non-destructive testing method that uses electromagnetic waves to detect buried or embedded structures and materials without excavation.
What is the maximum depth?
The UtilityScan (300–400 MHz) reaches 6–9 m in soils. The StructureScan Mini XT penetrates to 76 cm in concrete. With low-frequency antennas, geological surveys exceed 15 m.
Is GPR safe to use?
Yes. GPR uses non-ionising electromagnetic radiation, similar to Wi-Fi signals, with very low power levels. It is completely safe to operate near people and in sensitive areas.
To explore the full range of GPR equipment available, visit our Georadar category or contact us for a demonstration.
Última actualização: 21/03/2026