Study on underwater dual-laser structured-light system for ROV guiding

Remotely Operated underwater Vehicles (ROVs) equipped with manipulators have increasingly been used for underwater operation. An ROV is usually operated manually with the aid of an underwater camera for approaching and grasping a target using its manipulator. Owing to the low quality of underwater imaging, it is quite difficult for the human operator to determine accurate distances and orientations between the ROV and the target of interest. This paper presents a proposal for developing an automatic three-dimensional measurement and guidance system for ROVs in an effort to facilitate this process. Based on optical triangulation principles, dual laser lines and a camera are utilized to calculate the position and orientation of a cylindrical target. A measurement model considering refraction compensation and a joint system calibration method are proposed. The experimental study shows that the proposed system is feasible for automatically determining the position and orientation of a cylindrical target in an accurate and efficient manner. The accuracy of the measurement system is verified in air and underwater, respectively, by a prototype system.