Research On Chaotic Lidar Underwater Target Detection Technology

Underwater target detection technology plays a very important role in different application scenarios such as underwater obstacle location search.Compared with sonar detection,lidar has the advantages of large detection area,high detection accuracy and high collimation,so it has become an effective underwater detection technology.Due to the peculiarity of the composition of seawater,suspended particles and dissolved substances exist irregularly in seawater,so light is absorbed and scattered by seawater during the transmission of seawater,causing attenuation of light energy.Among them,the backscattering noise restricts the detection effect of the lidar system.Therefore,the method of suppressing the backscattering noise is a necessary aspect of the research on the underwater detection technology of lidar.By analyzing the frequency energy distribution of the backscatter and target reflection channel,it can be known that the backscatter signal exhibits lowfrequency characteristics,and the frequency characteristics of the target reflection signal and the detection signal remain consistent.Therefore,the frequency domain filtering method can be used to suppress the backscatter noise,and the wide frequency characteristics of the chaotic signal make it have the potential to suppress the backscatter.In this thesis,the research of underwater target detection technology by chaotic lidar is studied.First,through simulation analysis,it is confirmed that the chaotic laser detection signal combined with the frequency domain filtering method can effectively suppress the seawater backscatter and improve the target contrast.Secondly,a chaotic lidar system was built in a laboratory environment to realize the distance measurement and 3D imaging of underwater targets.The simulation and experimental research process is as follows:(1)Simulation analysis of chaotic lidar underwater target detectionBy simulation,the optical feedback chaotic laser signal was generated as the lidar detection signal.Based on MATLAB software,the signal was used to perform underwater detection simulation with frequency domain filtering method.The effects of attenuation coefficient,noise,and target depth on the detection results are analyzed.The results verify that the chaotic signal has suppression on backscatter when used in underwater detection,and achieves a distance resolution of 2cm.(2)Experimental research on chaotic lidar underwater target detectionAn experimental system for underwater detection of chaotic lidar was built.The effects of driving current,feedback cavity length,feedback intensity and temperature on the signal characteristics of optical feedback chaotic laser source are studied,and the parameters of chaotic light source suitable for underwater detection of lidar are selected.The characteristics of the chaotic source set according to the parameters are: output power 18 m W,1.2GHz chaotic signal spectrum bandwidth,autocorrelation function approximate to pushpin,and its full width at half maximum is 0.3ns.The 3D imaging MATLAB data processing program was compiled to achieve the purpose of imaging by drawing the depth information matrix of the imaging target after the scan.After completing the ranging experiment,the system's ranging resolution is about 3.4cm in the range of 40-140 cm,and the mean absolute error of ranging is 1.2cm.Finally,the imaging experiment of the cooperative target at 84 cm was completed by adjusting the two-axis scanning mirror.