Research On Key Technology Of Polarization Extended Range Imaging In Strong Scattering Region In Water

Underwater optical imaging technology has become the mainstream technology in the field of underwater close detection because of its advantages of low cost,high resolution and high speed.It has been widely used in the exploitation and utilization of underwater natural resources and the in-depth protection of ecological environment.However,due to the strong absorption and scattering of light caused by a large number of suspended particles in the natural water body and its interior,the image taken directly has some quality degradation problems such as reduced contrast and resolution and increased noise,which is not conducive to practical application.By using the polarization information of light,the intrinsic properties of the medium can be obtained and interpreted in depth.The underwater polarization imaging technology introduced into the underwater field can realize the sharpness of the underwater image according to the polarization difference between the suspended particles and the target.However,the existing underwater polarization imaging technology is mainly used in the general scattering area where the intensity of the scattered light is much less than the target signal intensity,and the ballistic photons in the strong scattering area are relatively few and the image contrast is further reduced.At this time,the technology is easy to become invalid due to the large increase of imaging noise.In addition,the traditional underwater polarization imaging technology also has some shortcomings,such as poor recovery effect for complex material objects with significant polarization differences,requiring certain prior knowledge,and generally low robustness.Therefore,it is urgent to improve the above defects and improve the image restoration effect and stability of underwater polarization imaging technology,so as to expand the application range of underwater optical imaging technology.Based on the above requirements,this paper starts from the underwater polarization imaging technology based on active illumination,in-depth analysis of the key and difficult problems in the field of underwater strong scattering region extended range imaging,carries out theoretical and experimental research related to polarization imaging,and respectively proposes an underwater polarization extended range imaging technology without prior knowledge and an underwater strong scattering region extended range imaging technology for complex targets.It is a prerequisite to realize polarization scattering imaging to master the polarization characteristics of light reflected by target and scattered by medium.In this paper,the polarization decomposition theory of transmission matrix and Mueller matrix is studied,and the feasibility of using it as the theoretical basis to realize scattering imaging is discussed.Finally,a technique of polarization strong scattering imaging and target recognition based on theory fusion is proposed.Firstly,the technique measures and inversely solves the Mueller matrix image of the target and obtains the parameters corresponding to its polarization properties to achieve a certain effect of image restoration.It is found that the depolarization coefficients of different materials are generally more different,which can be used as the basis to distinguish the target materials.Therefore,the depolarization coefficient image of the target is selected for further enhancement and denoising processing,to achieve more ideal target imaging and recognition effect.In addition,the application range of the proposed technique is discussed according to the law that the image quality evaluation parameters vary with the scattering intensity.This study also lays a foundation for the development of underwater polarization imaging.Aiming at the defect of the traditional underwater polarization imaging technology in the aspect of prior knowledge requirement,the mathematical model of underwater polarization imaging is deeply studied and a new underwater polarization extended range imaging technology without prior knowledge is proposed.Firstly,the technique uses genetic algorithm to scan the polarization degree of both the reflected light and the scattered light of the water body,takes contrast as fitness function and adds the deduced constraint condition to make the calculated imaging results have physical significance,and finally iterates to get the restored image of the target.Then,the stability,robustness and speed of the algorithm are tested to investigate the practical potential of the proposed technique.In addition,the attenuation effect of light with different wavelengths in turbid water was quantitatively measured before the imaging experiment.According to the experimental results,red light with a central wavelength of 620 nm was used as the active illumination source in the underwater polarization imaging experiment.In view of the defect that traditional underwater polarization imaging technology is difficult to achieve ideal restoration effect for complex targets with distinct polarization characteristics,the key problems are analyzed deeply and an extended range imaging technology for complex targets in underwater strong scattering region is proposed.Based on the difference matrix 2-norm and the polarization decomposition of the Mueller matrix,the depolarization vector mutual information algorithm is used to estimate the Mueller matrix of the complex target,and the polarization characteristics of the target with full field of view can be obtained.Then,the polarization state of the incident light which maximizes the polarization difference between the target reflected light and the scattered light of water body is calculated.Finally,the restored image is obtained,and the scattering and noise reduction effect based on the physical model and computational optics is achieved.In addition,the differences of the two estimation algorithms in imaging speed and application range are discussed,and it is concluded that the estimation algorithms should be flexibly selected according to different scenes and needs in practical application.The techniques and algorithms proposed in this paper have been tested by experiments,and the image restoration and related test results have proved the effectiveness,reliability and robustness of the proposed technique.The research content of this paper can solve some important and difficult problems in the field of underwater optical imaging and make it more effectively applied in the field of underwater resource exploration,underwater archaeology and underwater search and rescue,which has important practical value and guiding significance.