Stray Light Analysis And Suppression Of Multi-spectral Cameras In Phenology Network

In recent years,with the change of climate,people pay more and more attention to phenological observation.Developed countries such as the United States,Japan and other developed countries have already set up complete phenological observation networks.Although China also has its own phenological observation network,compared with developed countries,the equipment is relatively backward,spending a lot of manpower,material and financial resources,and the results are not accurate as developed countries.In this paper,based on the optical system of phenological network multispectral camera,the main sources of stray light in the optical system are analyzed,and the stray light of the optical system is suppressed.In this paper,the necessity of the design of multi-spectral camera for phenological network in China is illustrated by the construction of phenological observation network at home and abroad and the gap between the construction of phenological network in China and that in developed countries.Then,based on the relationship between phenological network and multi-spectral camera,the phenological network multi-spectral camera is introduced,and the necessity of stray light analysis of phenological network multi-spectral camera is further explained.Then the basic knowledge of stray light is introduced,including the evaluation of stray light,the classification of stray light and the mechanism of stray light generation.The main sources of stray light of the multi-spectral camera are analyzed according to the theory and the characteristics of the structure of the phenological network multi-spectral camera.According to the analysis results of stray light sources of phenological network multispectral camera and the common methods of stray light suppression,four kinds of stray light suppression measures are proposed for this phenological network multispectral camera,including surface blackening,coating and shading.For the first two measures,this paper proposes processing requirements after a large number of investigations.Subsequently,the design of the shield for the phenological multi-spectral camera is mainly carried out,including the determination of the shape of the shield,the calculation of the length of the shield,the determination of the position and height of the shielding,and the determination of the shape of the shielding ring.According to the actual situation,two kinds of shielding are designed.In order to verify the theoretical analysis of stray light path and the performance of the designed shielding,In the following,the phenomenological network multi-spectral camera is physically modeled and imported into TrancePro to define the properties of each object,set the threshold of ray tracing,set the light source,etc.Then light tracing is performed.The original optical system and the optical system with two different shades are tracked at different off-axis angles.The tracing results were also analyzed,At the same time,the data obtained from tracing are processed with MATLAB,and the PST(point source transmittance)curves under different conditions are compared.Finally,a better shielding is selected.In the next part,two main experimental methods of stray light are introduced,including surface source method and point source method,and the two experimental methods are compared.Based on the point source method,a simple experimental method-outdoor direct measurement method is used to measure the point source transmittance of optical system.In this experiment,the azimuth and altitude angles of the sun at different times are calculated.Then,the sun is used as stray light source,and the angle between the sun's rays and the optical axis is set to collect data.In this experiment,blinds were used to filter background radiation such as clouds.Then,in order to reduce the data error,the data are normalized and the PST curves of different channels are obtained in MATLAB.Finally,the experiment is analyzed and the results of experiment and simulation are compared.The software simulation results are obviously smaller than the experimental results,and we have analyzed the results to find the reason for the difference.