Using ROVs for Tilt Angle Measurement of Pier Foundation Piles at Pier-Type Docks

Regular inspection of pier foundation piles is essential for ensuring the structural integrity and operational safety of pier-type docks. Traditional approaches rely on divers to manually measure pile tilt angles using inclinometers, but these methods pose significant safety risks and are increasingly constrained by the dwindling availability of skilled divers. This study investigates the use of remotely operated vehicles (ROVs) equipped with advanced sonar technology as a safer, more efficient alternative for underwater pile inspections. A mini-ROV outfitted with dual-frequency forward-looking sonar (FLS) and supplementary sensors was employed, with the sonar system mounted vertically to facilitate tilt angle measurements through edge detection of sonar images. To enhance the robustness of data processing under complex underwater environments, algorithmic improvements in noise suppression and edge detection were implemented. Field experiments conducted at Xingda Harbor in Taiwan involved inspecting 65 pier foundation piles. The ROV's sonar-based measurements were compared to diver-acquired tilt angles, which served as the ground truth. Results revealed that the ROV method achieved an average error of −1.37 degrees, with final error rates remaining within 4% after compensating for ROV attitude changes. These findings confirm that the ROV-based approach delivers accuracy comparable to traditional diver methods while significantly reducing operational risks and reliance on human divers. This study underscores the potential of ROVs to revolutionize underwater inspections, offering a safe and efficient solution for real-world applications.