Research On Three-dimensional Detection Of Underwater Targets Based On Line Laser

Under the influence of many factors,such as water erosion,floating collision and chemical corrosion,corrosion and cracks will occur on the surface of pipelines and Bridges in underwater environment,affecting the safety and stability of objects.Therefore,it is very necessary to carry out regular detection of underwater targets.In recent years,non-contact underwater detection has been used more and more widely.Three-dimensional detection technology based on line laser presents a high resolution underwater three-dimensional target surface and can obtain detailed three-dimensional information of the target surface.Therefore,based on the line laser detection system,this dissertation studies the key technologies of underwater detection system.The main contents are as follows:Design and calibration of system device.Firstly,various methods of 3D reconstruction detection are introduced.Line laser scanning is selected as the basis of underwater 3D detection.According to the principle,the optical path of the system is designed,and the hardware required by the system is selected.This system can be used for underwater image acquisition with little impact.Secondly,the imaging model of the camera is studied,and the equivalent refraction model is studied for the refraction effect in the underwater environment,so as to reduce the effect of refraction.The equivalent model can be used to realize the underwater image acquisition calibration on the water,and the camera and laser plane calibration in the air is carried out based on this equivalent model.Optimization of underwater laser fringe extraction algorithm.In view of the image quality problems existing in the acquisition of images in the complex underwater environment,the image after bilateral filtering is preprocessed by using gamma transform to enhance the contrast between laser and background.After this processing,the image details can be preserved as far as possible and the image quality can be improved.The image is segmsegmed by using the Otsu method,which successfully distinguishes the fringe from the background.It lays a good foundation for the subsequent center extraction.At the same time,in order to improve the accuracy of laser fringe center extraction,the Steger method is improved to obtain the laser fringe center quickly and accurately,and generate a better three-dimensional target model.Scan test verification.The designed system structure is built,and the target surface detection experiment is carried out in the pool.After the underwater image obtained by the device scanning is processed by the model algorithm,a high-precision three-dimensional point cloud model of the outer surface of the measured target is obtained,which fully proves that the system,model and algorithm built can realize the rapid and high-precision detection of the underwater target surface.