Ship Hull Inspection Using Autonomous an Underwater Vehicle with a Stereo Camera

Abstract

Regular visual inspection of the underwater surface of the ship’s hull to check its integrity and the degree of biofouling is necessary to ensure the safety and efficient operation of the ship. The article proposes a method for the automated solution of this problem using an autonomous uninhabited underwater vehicle (AUV) equipped with a stereo camera controlled by a tilt actuator. The movement of the AUV is carried out along equidistant lines along the ship’s hull with simultaneous video filming of the hull surface. The AUV trajectory is calculated using the visual navigation method (visual odometry). Estimated data on the localization of the AUV relative to the ship’s hull are used in the method of controlling the movement of the vehicle to ensure the stable movement of the vehicle at a given distance from the inspected surface. Direct calculation of AUV localization data is done using the proposed original algorithm, which is implemented in the form of a software tool "stereo rangefinder". The operation of the "stereo rangefinder" is based on the matching of features in images using the SURF detector, followed by the construction of a 3D point cloud. The technique for performing automatic inspection of the ship as a whole is described. Fixed stereo images are also used to build a 3D model of the surface being examined. The applied method of constructing a global spatial model of the surface is based on the union of 3D point clouds obtained for local views. The construction of a 3D point cloud for a particular view is based on a matching of 2D point features on images of a stereo pair (SURF detector / correlation calculation), followed by the use of the ray triangulation method to obtain the spatial coordinates of the points. The presence of a 3D model makes it possible to conduct a detailed visual analysis of the state of the ship’s hull. Simulation modeling of the functioning of the developed tools on virtual scenes was carried out. Quantitative and qualitative performance evaluations obtained as a result of testing showed the acceptability of the proposed method for automatic inspection of the underwater part of the ship’s hull.