Research On 3D Information Acquisition Technology Of Underwater Microtopography Based On Line Structured Light

Three-dimensional information of surface micro-topography of underwater objects has broad prospects in underwater engineering applications,such as submarine topography mapping,submarine archaeology and submarine structure measurement.Unknown and complex underwater environment makes underwater manual operation confronted with potentially dangerous factors such as high pressure and oxygen deficiency,which limits underwater manual detection activities.Line structured light underwater vision 3D measurement technology has been widely used in underwater microtopography 3D information acquisition due to its advantages of high precision,non-contact and large scale.During underwater visual measurement,visual equipment is often sealed in transparent glass boxes.Light travels through three stages: air,glass and water.Light refracts as it travels through different media,which makes the linear imaging process non-linear.Traditional linear single-view model is no longer applicable.In view of this problem,this paper proposes a refraction model for underwater visual measurement.At the same time,from the perspective of projection geometry,arguments in vertical refraction when the line structured light projector and projection plane projection light plane through the projection axis light plane in the air and underwater light plane coplanar,can replace the underwater calibration of the land,avoid the difficulty of the underwater calibration,improve the portability of the underwater measurement system.Binary multi-line center rotating structured light is proposed to solve the problems of underwater image degradation and difficult feature extraction caused by sediment turbidity in natural water.This method is suitable for turbid natural water body,at the same time,dense three-dimensional topographic data can be obtained.In this paper,an underwater vision 3D measurement system is built,system parameters are calibrated accordingly,and underwater 3D topography acquisition experiments are carried out.The experimental results show that the underwater vision measurement method proposed in this paper can achieve 3-D measurement accuracy of 0.95 mm at 1300-1600 mm measuring position for regular geometrical objects in clear water environment.The three-dimensional shape information of irregular geometry objects(N,C,W,U character plates)can be reproduced well.In turbid water environment with 30 g,40g,60 g and 90 g sediment,the measurement accuracy of 1.08 mm,1.10 mm,1.58 mm and 2.66 mm can be obtained respectively.The underwater micro-morphology information acquisition method proposed in this paper can meet the accuracy requirements of actual underwater micro-morphology detection,and provide new ideas,new methods,and new starting points for underwater 3D morphology information acquisition research.