Research On The Effect Of Oceanic Turbulence On Imaging Quality Of Optical System

Underwater optical imaging technology is the key means of ocean exploration,and the study of underwater optical system imaging has far-reaching significance for marine resource exploration,marine environment monitoring and submarine archaeological discovery.The imaging quality of underwater optical system is affected by many factors at the same time,among which ocean turbulence is one of the important factors restricting the imaging quality of the system.At present,the research on the imaging quality of optical system in turbulent ocean environment focuses on simulation,and there is no study on the influence of average temperature and average salinity on the imaging quality of optical system.In this paper,an underwater optical imaging model is improved based on the Power spectrum of Yao refractive index fluctuation,and the effects of average temperature and average salinity on the optical imaging quality of the system under turbulent ocean environment are studied,and the accuracy of the model is verified by experiments.The main content of the article is as follows:(1)Based on the refractive index fluctuation power spectral density function of the turbulence statistical model,the analytical expressions of wave structure function and phase structure function of two wave types,plane wave and spherical wave,are derived to improve the underwater optical imaging model.According to underwater optical imaging model,the simulation analysis of the long and short exposure in both cases the average temperature of the water body and average salinity effect on the modulation transfer function of optical imaging system,the simulation results show that with the increase of average temperature and the average salinity,modulation transfer function curve of the optical imaging system can present downward trend,optical system imaging quality.The Greenwood time constant,a parameter representing turbulent time period,was solved and used as the standard to define long exposure and short exposure,and the influence of average temperature and average salinity on turbulent time period was analyzed.(2)On the basis of the wave structure function,the parametric coherence length,which represents the coherence of the beam,is solved,and the influence of average temperature and average salinity on the coherence length is analyzed.The conclusion is that the correlation length and average salinity show a linear negative correlation.The Strehl ratio is obtained by modulation transfer function and analyzed.It is found that the Sterhl ratio reaches its peak value when the entry pupil diameter of the underwater optical imaging system is 2.1 times the coherence length.(3)An underwater optical imaging experiment platform with a length of three meters is built,which can control water temperature and salinity,generate turbulence,and record the imaging results of the resolution plate through the underwater turbulence using CCD.The modulation transfer function of the optical system under different temperature and salinity conditions is obtained through experiments.The experimental results show that,under the condition of short exposure optical system imaging quality is superior,by comparing the different temperature and salinity conditions changes in spatial frequency contrast,found that the average temperature fluctuations compared to the average salinity fluctuation on the modulation transfer function is more significant,the influence of the experimental conclusion proves that the accuracy of the model of underwater optical imaging.