Using GPR to Find and Mitigate the Risk of UXOs
Finding and mitigating the risks of UXO, IEDs, and other subsurface hazards using GPR – ideally as part of a multi-sensor detection strategy – is essential for restoring safety to post-conflict regions. Although active fighting may have ended, the lethal threat often persists for decades. Today, the global risk from Unexploded Ordnance (UXO), Unexploded Bombs (UXB), and landmines remains critically high, making advanced geophysical methods vital for reclaiming land and restoring safety to these communities.
These Explosive Remnants of War (ERW) represent a systemic threat to human life, infrastructure projects, and the environment. To facilitate safe land development and reconstruction, professional UXO clearance is essential. This multi-stage process involves the detection, mapping, and safe disposal of ordnance ranging from metallic shells to low-metal content plastic mines and this is where Ground Penetrating Radar (GPR) can be a valuable component.
The Multi-Sensor Strategy for Finding UXOs
Due to the vast diversity in target size, material, and burial depth, a single detection method is never sufficient. A robust risk mitigation plan should follow the ALARP (As Low As Reasonably Practicable) principle, utilizing a multi-sensor approach:
- Satellite & Aerial Imagery: For initial site assessment.
- Magnetometer Surveys: Highly effective for ferrous (magnetic) objects.
- EMI (Electromagnetic Induction): Standard for metal detection.
- GPR (Ground Penetrating Radar): Critical for detecting non-metallic (plastic) threats and providing 3D spatial context.
- UWB SAR & LiDAR: For wide-area reconnaissance and surface mapping.
- Note: A mechanical approach can also be applied.
The Role of GPR in UXO Detection
GPR is a premier non-destructive method for subsurface imaging. By transmitting electromagnetic waves and recording reflections, GPR identifies dielectric contrasts between an object and the surrounding soil. A buried UXO typically manifests in the data as a characteristic hyperbola.
Frequency, Resolution, and Depth for finding UXOs with Radar
When selecting a ground penetrating radar system from Guideline Geo, the choice of antenna frequency is paramount. It defines the balance between how deep you can see and how small an object you can resolve:
- Higher Frequencies (up to 2300 MHz): Exceptional resolution for small targets like anti-personnel mines at shallow depths.
- Lower Frequencies (around 450 MHz): Better penetration for larger aerial bombs (UXBs) buried deep in the subsurface.
Critical Limitations for using GPR when searching for UXOs:
- While GPR is a powerful tool, it cannot guarantee 100% detection, and signal interpretation can be complicated by clutter (e.g., stones, roots or other mundane items) that mimic UXO signatures.
- Mapping smaller UXO´s at larger depths also poses a challenge, as the resolution of a GPR decreases with depth.
Advanced GPR Methodologies
2D Versus 3D-Ground Penetrating Radar
While single 2D profiles are useful for quick reconnaissance, modern safety standards often require 3D GPR data volumes. By collecting dense data, we can generate depth slices – horizontal maps of the ground at specific intervals. This allows operators to visualize the shape, orientation, and exact depth of a target, significantly reducing false positives.
Profiles must be spaced closely with a single-channel 2D GPR (e.g., 25 cm spacing for a 50 cm target) to ensure the radar beam crosses the object.
Multi-Channel 3D GPR-systems like the MALÅ MIRA Compact, MALÅ MIRA Flex or MALÅ MIRA HDR offer a fixed 6.5 cm profile spacing. This provides a gapless data web, ensuring even the smallest threats are captured in high resolution.
Drone-Based GPR: Safety vs. Resolution
In “high-threat” areas where ground access is too dangerous, drone-based GPR (such as the MALÅ GeoDrone 600) is an invaluable reconnaissance tool. However, users must account for the air gap (which increases the footprint) between the drone and the ground, which can dissipate signal energy and reduce the ability to detect very small items like landmines. Drone solutions are best suited for larger targets or as a primary tool to identify high-interest zones for further investigation.
Guideline Geo: Industry-Leading Solutions
We provide the full spectrum of GPR technology required for professional UXO risk mitigation:
- MALÅ Ground Explorer & ProEx: Versatile, high-performance GPRs.
- MALÅ GeoDrone 600: Specialized for airborne GPR surveys.
- MALÅ MIRA Series (Compact, HDR, Flex): The gold standard for high-speed, high-resolution 3D GPR-mapping.
- MALÅ Easy Locator Core: Advanced integration for specialized subsurface applications.