Since 2015 Skeye has been commissioned by Tata Steel in the Netherlands to derive volumes using a drone of their stockpiles several times per month. The stockpiles consist of iron ore and coal and are spread out over 20 plus depots.
Skeye is specialised in highly accurate surveys of stockpiles using unmanned aerial helicopters (drones). These helicopters are equipped with a high-resolution digital camera (36 Mp) that has been geometrically calibrated to perform measurements. The measurements are based on the principle of photogrammetry whereby terrain heights are extracted from a series of overlapping images.
This method gives a number of advantages over traditional (land based) survey methods:
- Safe: people are not required to climb on steep and unstable stockpile slopes
- Fast: we can measure up to 100 ha in one day of survey.
- Accurate: typical accuracies of 20 mm are obtained or 0.3% of the volume of a stockpile.
- Complete: the method yields well over 100 measurements per square meter giving a complete image and thus more accurate results.
Prior to the operations Skeye drafted a comprehensive health and safety plan with HSE officials at Tata in order to minimise the risks whilst working with drones on their location. Due to the heavy winds that are frequent at Tata as it located next to the west coast of the Netherlands, Skeye has chosen to fly the AerialTronics Zenith ATX8 in most cases. This drone can carry the Sony A7r 36 MP camera, which is well suited for low light conditions encountered outside the summer months. Using photogrammetry a 3D point cloud is constructed that enable the accurate extraction of heights and the creation of 3D terrain models (DTM), volumes and orthophoto mosaics. The latter are used to accurately define the demarcation between the different stockpiles if these are adjoining.
One of the major challenges in this project for Tata is that the results have to be delivered within 24 hours of data capture. Extra powerful computers were purchased to be able to do the heavy photogrammetric calculations in time. Another challenge is that the terrains on which these stockpiles lie are not flat. In fact many stockpiles are located in throfts and these have to be carefully modelled in 3D in order to derive an accurate volume. Some stockpiles are located in between concrete retaining walls or embankments.