Metrological evaluation of vessel-based mobile lidar for survey of coastal structures

Abstract

Surveying of coastal structures is necessary to ensure that the structures are in good operating condition. Mobile lidar systems could be installed on vessels to monitor the coastal structures, even if there is no previous metrological information about their reliability. The aim of this work is to perform the metrological verification of the mentioned survey instruments. The verification methodology is based on the comparison of mobile lidar data from a breakwater with ground truth data provided by a Riegl LMS Z390i terrestrial lidar. Mobile lidar data are obtained from an Optech Lynx system installed on a vessel. The results show errors lower than 0.09 m based on distance measurements. Universal Transverse Mercator (UTM) coordinates show absolute errors lower than 0.12 m in the horizontal plane and 0.18 m in height. Precision analysis from the mobile lidar shows error values up to 0.055 m, while the terrestrial lidar gives 0.018 m for the same region of interest. The spatial resolution from the mobile lidar gives values of 321 points m‒2, in comparison with the 22,013 points m‒2 from the terrestrial lidar. Two point clouds from the same region of the breakwaters, obtained using the mobile and the terrestrial lidar, were triangulated and rasterized. The standard deviation of the vertical distances between the nodes of the raster data shows a value of 0.064 m. The results obtained show the potential of mobile lidar systems in combination with vessels for the monitoring of certain coastal structures, such as breakwaters, sea walls, bridges, wharves, and jetties.