Research On Stray Light Characteristics And Correction Of Directional Polarimetric Camera

Stray light is the general term of abnormal transmission light in optical systems,which is mainly caused by the reflection and scattering of optical and mechanical components of the system.The Directional Polarimetric Camera is an ultrawide-angle and frame type imaging polarized sensor with low distortion,which can capture directional imaging information of objects.Stray light can make an influence on the reliability of measured data and thus affect the quantitative inversion of multi-angle polarization information.Therefore,the characteristics and correction of stray light should be studied,which makes significant sense to guarantee the accuracy of instruments and facilitate the quantification capability of atmospheric aerosol observation.Firstly,according to characteristics of the instrument and measurement principle,the behavior of instrumental stray light is emphatically analyzed and components which are likely to arise stray light are searched out by experiment in this paper.Combined with the distribution characteristics of stray light,it is divided into a local one and a global one.By means of software modeling and simulation,the stray light coefficient of the instrument is simulated and analyzed to verify the effectiveness of the suppression.Furtheromore,the main causes of stray light are obtained by simulating the magnitude and distribution characteristics of stray light.Then,stray light coefficient of the instrument is measured based on Black Spot method.The effect of stray light on polarization accuracy is considered so as to establish the analytic model of the influence of stray light.Secondly,the paper carried out the local stray light,global stray light and focus ghost stray light correction study.For local stray light,aimed at the circumstance that the point spread functions are inconsistent at each sub-FOV(Field of View)under the wide field of view,a method of structuring the point spread function of the sub-FOV based on plate model is proposed.Then the point spread function of each sub-FOV is gained by combining mathematical modeling with in situ measurements,and the correction is implemented by least square filtering algorithm.The correction result shows that this model can reduce local stray light to 1/5 of the original.For global stray light,a method of illuminating according to different zones to obtain the distribution matrix of stray light and respective correcting is proposed.In both unsaturated and over-saturated situations,the relationship between radiation in target areas and other stray light in non-target areas is established by the method of two-dimensional rotational scanning imaging to respective rectangular areas and field of views,so that the stray light distribution matrix in 11x11 pixels is obtained finally.The correction result shows that this method exterminates more than 90%of the global effect.Furthermore,the correcting method of ghost artifacts is explored.Considering the relationship between ghost image system distortion and field of view,the position and deformation of ghost are acquired by polynomial fitting.Real images are measured in order to determine the extinction ratio between the original images and ghost images.After that,ghost images correction model in the whole field of view of the instrument is set up.The result manifests that the method can generally wipe out the stray light in the field of view of DPC.Finally,the result of stray light correction and polarization/radiation measurement accuracy of DPC for a native target is verified by comparing polarization/radiation parameters acquired by DPC and CE318 respectively and simultaneously.On-orbit images are corrected and relative correction result for various scenes are obtained.It is concluded that the correction result has a strong relationship with the scene.Furthermore,the influence of stray light on the authenticity of DN value under different bright area conditions is further analyzed,and the linear relationship between the proportion of bright area and the influence of stray light was approximately positive correlation.