Hogging and Sagging Deformation Measurement of Ships Using an Oblique CCD Moiré Super-Resolution Method

Hogging and sagging deformations are fundamental indicators of the longitudinal structural integrity and navigational safety of ships. While camera-based measurement systems offer advantages such as non-contact operation, large measurement range, and rapid deployment, their adoption in ship structural monitoring has been constrained by the shipboard environment, which renders conventional orthogonal front-view layouts infeasible. This paper proposes an oblique CCD moiré super-resolution method for measuring hogging and sagging deformation on operational ships. In this approach, the camera is mounted on elevated superstructures (e.g., the island superstructure), with the deformation carrier plane positioned on the deck surface, forming an oblique optical axis that avoids interference with routine deck operations. A rigorous geometric model is developed to characterize the mapping between vertical deck deformation and image-plane displacement under oblique imaging conditions. To overcome the inherent reduction in displacement sensitivity caused by the oblique configuration—the core technical challenge of this work—a novel CCD moiré super-resolution strategy employing a non-uniform grating carrier is introduced, substantially enhancing measurement sensitivity. Validation experiments demonstrate that the proposed method achieves a measurement resolution on the order of 10⁻⁵ of the observation field of view, markedly surpassing corner detection, digital image correlation (DIC), and conventional fringe analysis methods. Scaled ship model tests confirm a maximum measurement error of 0.022 mm within a 1 mm deformation range, validating the method's high-precision performance and engineering readiness. The proposed approach provides a practical solution for structural deformation monitoring of ships and advances the engineering deployment of ship structural health monitoring technology.