New opportunities and challenges in surveying underground cavities using photogrammetric methods

The exploitation of the underground is currently undergoing a major transformation process. Besides mining, alternative ways of utilization are playing an increasingly important role. These alternative utilizations include the storage of gases, the disposal of radioactive wastes, and the implementation of geothermal storage facilities. In addition, more and more mining operations are being shut down, like the German hard coal mining industry in 2018. But the integrity of closed mines must be ensured in the post-mining phase. In order to capture such large and complex structures efficiently and reliably, new surveying techniques are required. A promising approach is the use of photogrammetric methods to generate three-dimensional models of the cavity. Photogrammetry is currently known mainly from aerial photography. It is conceivable to use such methods for underground applications. In recent years, significant progress has been made in the algorithm-based orientation of unstructured image sets. More powerful computer systems and the growing range of unmanned aerial vehicles could enable partially automated capture. However, a number of problems have to be solved for underground imaging techniques. Unfavorable exposure conditions complicate image alignment. Furthermore, the models must be integrated into existing surveying systems with a sufficiently high degree of accuracy. In order to consider the numerous technical aspects, the development of an integrated capture and evaluation approach is necessary. This could make an important contribution to the monitoring of critical cavities of different commodities. Such an approach would also fit into the current digitization trend in the mining industry and provide new opportunities for ground control in particular.