Underwater laser scanning: Evaluating the performance of ULi in laboratory and real-world environments to determine the achievable level-of-detail

With the global expansion of underwater infrastructure elements, which all require regular inspection, maintenance and repair operations, precise and high-resolution monitoring solutions become crucial. Subsequently, technologies which are able to detect deformations in the range of millimetres, indicating damage at an early stage, are required. Since underwater laser scanning systems are supposed to achieve a much higher accuracy and measurement speed than acoustic techniques, they deliver an enormous potential. However, since water presents physical difficulties to optical systems in terms of turbidity and reachable distance, up to date, only sparse information regarding the performance of an underwater laser scanner and only view estimates about to the actual usability of such a system for corresponding monitoring purposes, are available. For that purpose, the underwater lidar system ULi was tested in two laboratory and one real-world environment. It can be concluded, that (1) manmade and organic structures down to a size of 2.36 mm can be detected at a close-range of ≤ 0.56 m in static laboratory environments, (2) a Böhler star with an arc length of 2.95 mm can be fully resolved at a mid-range of ≤ 8.03 m in static laboratory environments and that (3) the operation of ULi is not suitable for water bodies with a turbidity level of ≥ 6 NTU or a Secchi depth of ≤ 1.10 m.