Underwater 3-D Scanning: Modeling and Fitting of Multilayer Refracted Laser Surface

Laser surface modeling and fitting are essential tasks in underwater 3-D scanning. Traditional methods based on line-plane intersections struggle to achieve high accuracy due to the bending of the laser surface into a complex shape after multilayer refraction. In this article, a ray-based model for multilayer refracted laser surface is established for three typical scenarios: air-water; air-glass-air; and air-glass-water. The corresponding laser surfaces are derived to be quartic, quartic, and 12th-degree surfaces. To fit these surfaces, a general quadric is introduced, with an approximate geometric distance defined for the quadric parameter initialization. The actual geometric distance is formulated as a sixth-degree polynomial and used for the iterative optimization of these parameters. The proposed method enables accurate modeling and fitting of the multilayer refracted laser surfaces. To validate the effectiveness and superiority of the proposed method, simulation and actual experiments are carried out, respectively. The experimental results demonstrate that the proposed method outperforms the previous methods in terms of accuracy and efficiency.