How Drone LiDAR Inspection Enabled Safe Demolition of Nuclear Cooling Towers
Demolishing a nuclear cooling tower is no small feat. The sheer size and age of the structure requires a deeper inspection to assess for erosion, hazardous materials, and structural integrity. This is the challenge that faced the Sopreco team when assessing three towers scheduled for demolition in Metz, France. To ensure the safe, accurate inspection of these cooling giants, they decided to use a LiDAR-equipped drone solution.
Sopreco, a subsidiary of the Eurovia group in France, operates as a prominent referrer for quarry management, inspection, and specialized Geographic Information System Mapping (GIS) solutions. Sopreco also leads the Eurovia drone program for asset inspection, land surveying, LiDAR, and mine detection.
For this four-day project, it was decided that a mixed drone approach using both LiDAR and photogrammetry techniques would suit best under the strict time constraints. In this case, DJI provided Sopreco with a Zenmuse L1 payload for the task.
A tandem approach: Photogrammetry with LiDAR support
The Sopreco team traditionally uses drone photogrammetry for a job of this scope for capturing data to create orthomosaics or 3D models, as do many surveying and mapping professionals.
The affordability and flexibility of photogrammetry to provide detailed maps and models have made this option the most accessible choice for many inspectors of assets or structures such as nuclear towers.
However, there are some minor setbacks to using photogrammetry when surveying. For example, in this project, there were major differences in luminosity on the inside and outside of the cooling towers. Especially on the insides, lighting is much dimmer and it can be difficult to capture high-quality visual data. Additionally, the tight schedule for this project meant that much of the work would need to be completed under low-light conditions, which can result in lower-quality photos, and ultimately a less useful model.
This is where a LiDAR option comes in and fills the gap.
LiDAR (light detection and ranging) works by emitting laser light and measuring the ping time and intensity from the object back to the sensor. It builds topographically accurate terrain models by incorporating the high-accuracy systems of satellite positioning (GNSS data) and an inertial measurement unit (IMU).
A major benefit to LiDAR is that it does not require bright, well-lit conditions, unlike photogrammetry. Moreover, the final data outputs are point-cloud coordinates and are much quicker to process into a workable model with software. In this case, the L1 was a perfect option for Sopreco’s tight schedule and the necessity to work even in the evenings and at dusk.
The result: centimeter-accurate rendered point clouds (3D representation of objects) that are quicker than ground survey or photogrammetry options.