Key Technical Research Of An Underwater3D Structured Light System

Key technical research of an underwater3D structured light system is carried onin this paper to satisfy the requirements in the fields of ocean resources development,marine scientific research, underwater engineering. An underwater3D structured lightsystem is designed，and based on which the mathematical measurement model wasbuilt. The system is calibrated with a method that separates the camera parametersfrom the system parameters. A refraction correction method is proposed which makesthe underwater measurement after land calibration of the system realized. The effectof water opacity is analysed, for which the solution is proposed briefly.The underwater mathematical measurement model built on the structured lightsystem describes the geometrical relationship among the camera, the laser plane andthe target. The effect of the laser refraction is shown by the optical path in the model.The camera parameters separated from the system are calibrated based on theradial alignment constraint in non-coplanar condition, with the virtual3D target whichis created by a three coordinate measuring machine. The rotation and translationvector are calibrated with the help of a matrix planar grid target.A new refraction correction method is proposed to reduce the effect to theaccuracy. The laser plane and the pixel coordinates of the optical image points arecorrected when the light was refracted. The data after correction could be used tosolve the coordinates of target in coordinate system.The view of the structured light system is provided and the difference ofmeasurement field between land and underwater measurement is analysed. Solutionsare proposed to reduce the effect of the water opacity. The power of laser could beraised to increase the measurement distance, and the progressive image processingmethod could be used to improve accuracy.A series of experiments are conducted to test and verify this system. Thecalibration experiments of structured light system shows that the calibration method iseasy to be realized and has high accuracy. The land3D measurement experimentsshows the rationality of the mathematical model. The effectiveness of the refractioncorrection method is proved by the underwater3D measurements. The results ofunderwater experiments in different distance and different water opacity shows highaccuracy, wide measurement fields and good robustness.