Research On Ocean Target Imaging Lidar System Based On Line Scan

Ocean target is a general term for objects detected in the marine environment,which can be divided into two categories: surface target and underwater target.With the great progress in global ocean development in recent years,ocean target detection technology develops rapidly.Lidar has the characteristics of high range resolution and strong target recognition ability,and can detect surface targets and underwater targets at the same time.Therefore,it has become a very attractive ocean target detection method.At present,many different imaging systems such as spot-scanning,non-scanning and line scan method have been developed.With the advantages of simple structure,high imaging efficiency and relatively concentrated energy,line scan lidar has become one of the most widely used imaging methods of ocean objects.But the marine environment is complex and changeable,and the sea breeze,wave,current and other factors lead to many challenges such as high noise intensity and rapid environmental change in the process of ocean target detection.Based on the development status of line scan imaging lidar and the characteristics of ocean targets,the ocean target imaging lidar based on triangulation method and streak tube method is deeply researched in this paper.The former is suitable for high-precision imaging of close range targets,which has the advantages of simple structure,low cost and high precision.The latter is suitable for long-range targets with strong detection ability and high resolution.In experimental study,a real-time color 3D imaging of the target is carried out by using the developed line scan lidar,and the imaging research of the coastal target is carried out by using the UAV.In addition,the streak tube imaging lidar is used to detect the island,ship and underwater targets.The main content of this paper is as follows:(1)The domestic and foreign technical progress of spot-scanning,non-scanning imaging and line scan imaging lidar was investigated,and the advantages and disadvantages of each imaging method were analyzed.The triangulation method and the streak tube imaging method were respectively investigated.Based on the research results of domestic and foreign scholars in recent years,the methods to further improve the performance of the imaging system are analyzed.(2)The transmission characteristics of laser in the atmosphere and sea water were studied theoretically.According to Mie scattering theory,the scattering characteristics of laser in marine atmosphere and underwater were analyzed.Based on the software platform of Light Tools,the transmission characteristics of 532 nm line laser beam in both atmospheric and underwater environment were simulated and the optical properties of laser transmission were studied.(3)The imaging principle of triangular imaging was introduced.The effects of different structures and installation errors on the imaging results were calculated,and the relationship between imaging distance and resolution was analyzed.In addition,the imaging principle of STIL is introduced.The influence of each subsystem parameter on the imaging accuracy of lidar is calculated,which provides theoretical guidance for the overall development of STIL and device selection.A cathode gate method is proposed to improve the SNR of the raw image.(4)A real-time color 3D laser line scan imaging system was designed and manufactured,including the timing control,scanning system and image processing system.Based on the theoretical basis,the laser,CCD camera,stepping table and other key devices were selected.Real-time color 3D imaging experiment was carried out by the developed system,and the color 3D image with high resolution was displayed in real-time.A laser line scan system for UAV was designed and manufactured,including UAV system,airborne image acquisition and processing system and ground monitoring system.By using the developed system,the imaging experiments are carried out on the coastal target and the target at a certain depth underwater.It realizes the high speed acquisition and real time reconstruction of the 3D information of the target,and provides a new solution for the la rge-scale rapid imaging of the ocean target.(5)A streak tube imaging system with large field of view,high frame frequency and high resolution was designed and developed.The parameter calculation and type selection of several key devices such as receiving lens,intensifier and light cone were completed.What's more,3D image real-time reconstruction system based on Lab VIEW software was also developed.A new imaging method based on cathode gating is proposed,which can effectively improve the SNR of the raw image and provide a guarantee for the marine application of the lidar system.Using the developed STIL system,the experiments of targets above and below the sea surface were carried out respectively.Experimental results show that,the STIL system based on cathode gating method has a good imaging ability to the ocean target,and the 3D image of the target can be obtained in real time during scanning,which has a broad application prospect in the fields of ocean monitoring,tracking and rescue.