Research On Underwater Long-distance Ghost Imaging Technology

Seawater is rich in many kinds of solute,and the complexity of seawater channel is far more than that of atmospheric channel.The propagation of light in seawater is affected by many factors,which is divided into absorption and scattering.Although blue-green laser in seawater has "window" characteristics,its propagation effect is still not ideal.Traditional underwater imaging technology cannot meet the long-distance and highquality requirements for underwater imaging.Because of its advantages of pseudothermal light easy-to-obtain,non-local imaging,wide wave range of applycation,high imaging resolution and strong anti-noise performance,the ghost imaging technology has been widely used in atmospheric remote sensing and laser radar.Therefore,the main content of the thesis is to research the ghost imaging technology in underwater imaging environment,and the purpose is to improve the distance and quality of underwater imaging.The main work is as follows:1 Analysis of the overall architecture of the underwater ghost imaging system.The connections and differences between thermal light and pseudo-thermal light are studied and the actual production process of the thermal light source is analyzed.The diffraction model of light in the underwater environment is established by combining the attenuation characteristics of light in seawater.Then the characteristics of the detectors in the receiver module are analyzed.Finally,the traditional ghost imaging algorithm is studied and the factors that affect the ghost imaging are simulated and analyzed.2 Establish a simulation platform of underwater ghost imaging systems.The underwater second-order and third-order ghost imaging systems are designed,then the properties of the pseudo-thermal light are analyzed,and the underwater diffraction process of light is simulated,in the end the underwater second-and third-order ghost imaging systems were simulated and analyzed.The simulation results show that the maximum imaging distance of the system in the Jerlov II seawater reaches 5.4 attenuation length,and the underwater third-order ghost imaging system has a little advantage than the second order one.3 A scheme of applying the photon counting technique to underwater second-order reflective ghost imaging is designed.In order to improve the system imaging distance,the single photon detector is introduced and the photon counting imaging is implemented.An underwater photon counting ghost imaging system based on differential ghost imaging algorithm and correspondence ghost imaging algorithm are designed.Through simulation experiments,the advantages of the two systems in imaging distance and imaging quality are analyzed.Simulation results show that the maximum imaging distance of the underwater photon counting ghost imaging system in Jerlov II seawater is about 13.5 attenuation length.4 A system improvement scheme based on compressive sensing technology is designed.The reason for the slow speed of the underwater ghost imaging system is the excessive number of samples,although correspondence ghost imaging algorithm can reduce samples to be processed,but do not reduce the total samples,so the imaging speed of correspondence ghost imaging system is still not ideal.Compressive sensing technology is introduced to deal with this problem,the compressive sensing ghost imaging systems respectively based on bi-objective function iterative algorithm combined with image denoising algorithm and TV optimization algorithm are designed,which reduce sampling times and improve imaging quality,the simulation analyzes the improvement of system performance using these algorithms.