Design Of Infrared Imaging Optical System For Space-based Space Target Based On Micro Polarization

To ensure the security of space resources in our country,it is necessary to accurately image and identify space-based space targets.Although infrared imaging can solve the problem of target detection under the condition of insufficient illumination by obtaining target radiation information,it is still difficult to distinguish target surface materials and cannot meet the urgent need of accurate identification of key spatial targets.Combining polarization imaging technology and infrared imaging technology,the use of target infrared radiation and reflection polarization information,auxiliary interpretation target information such as material properties,the working condition,the type of load,can provide the decision-making basis for space target management department,has a broad application prospect and important practical significance.In this paper,aiming at the requirements of space-based high-precision detection and identification of on-orbit satellites,a method of infrared polarization imaging of space targets based on micro polarizers is proposed,focusing on the model of target infrared polarization characteristics,the design of infrared polarization optical system and the design of micro polarizers.The specific research contents are as follows:Firstly,the existing polarization model of target infrared radiation does not consider the shadowing effect caused by practical rough surface.In this paper,based on the bidirectional reflection distribution function model of the microelement,a Stokes analytical model of the polarization degree of infrared radiation on rough surface containing the shadowing function is constructed by means of Mueller matrix.This paper studies the methods of time-sharing polarization imaging and real-time polarization imaging,according to the advantages and disadvantages of these two methods and the requirement of real-time of space-based system,the imaging method of micro-polarizer is determined.Then,aiming at the imaging and identification requirements of space-based space objects,a long focal length,large aperture,compact coaxial catadioptric long wave infrared polarization telescope imaging optical system is designed.The system focal length is 600 mm,the field angle is 1.47 °,and the F number is 1.2.The design results show that the optical modulation transfer function(MTF)of the full field of view at the Nyquist frequency 42lp/mm is better than 0.3.In the range of-20??+40?,the imaging quality is close to the diffraction limit.The system adopts an uncooled long-wave infrared detector of 12?m pixel size,which can achieve an imaging resolution of 1m at 50km;This paper also focuses on the design of micro-polarizer array for the adopted infrared detector.By analyzing the influences of grating parameters on the transmittance of transverse magnetic wave(TM wave)and the extinction ratio was analyzed.According to the existing technology level,the long wave infrared micro-polarizer arrays of substrate material zinc selenide,grating material aluminum,period is 1?m,duty cycle is 0.6,aluminum layer depth is 0.5?m and zinc selenide layer depth is 0.4?m,working band 8?12?m were designed.;The instantaneous field of view error of micro polarizer array is analyzed.Bilinear interpolation algorithm,weighted bilinear interpolation algorithm and Newton polynomial interpolation algorithm are used to correct the instantaneous field of view error.The detection accuracy and imaging resolution of infrared micro-polarizer are guaranteed.Finally,the polarization characteristics of two typical spatial target materials with different roughness are simulated and the polarization imaging experiments are carried out.The analysis results show that when the same roughness and same temperature,the polarization degree value of infrared radiation of the metallic is always greater than that of the nonmetal;The polarization degree of infrared radiation increases with the increase of incident angle,and decreases sharply after reaching the peak at specific incident angle.This property is useful to distinguish the metal and nonmetal.In this paper,the long-wave infrared micro-polarization imaging system and the near-infrared polarization imaging system were used to collect polarized images of targets in different real scenes.The experimental results are basically consistent with the theoretical analysis results,which verify the correctness of the theoretical model.It proves that the infrared polarization image can improve the image contrast,highlight the target under certain conditions and distinguish objects with different materials.It can provide a theoretical basis and solution for the subsequent imaging recognition of space objects.