Research On Stray Radiation Suppression Of Dual Band Integrative Optical System Used To Low-orbit Spaceborne Earth Observation

Compared to earth observation visible optical payload on low-orbit,visible and MWIR dual-band optical payloads can obtain more information and have wider applications.Visible and MWIR dual-band optical system can not only obtain high resolution visible image and infrared image at the same time,but also achieve observation on day and night.So it can realize full-time observation.Besides,the MWIR system can identify military camouflage and detect the wake of the suspicious ship,so it is more advantageous in the field of military application.In addition,MWIR band can also obtain the earth background data for different seasons.It has important application value in the field of environmental monitoring.Moreover,multi spectral system integrative design becomes the trend of space payload miniaturization.Therefore,developing earth observation visible and MWIR dual-band integrated optical system on low-orbit can bring great military and economic benefits to our country.It has strong practical significances.To the earth observation imaging system,it has higher requirement to stray radiation suppression to adapt complex working conditions.If stray radiation is not suppressed successfully,the image quality and target resolution would degrade dramatically.To the dual-band integrated optical system on the low-orbit satellite platform,the reflection of earth and the infrared radiation of the earth cannot be neglected.The stray light environments are more complicated.So the Stray radiation suppression for this system is more difficult than the system on high-orbit.At the same time,it has great differences between visible system and MWIR system in stray radiation suppression,even in some cases there are contradictions and mutual constraints.Therefore,it has great significance and great application value to research the stray radiation suppression of earth observation dual-band integrated optical system on low-orbit.In this paper,we focused on the research of stray radiation suppression about earth observation dual-band integrated optical system on low-orbit,aming at mathematical modeling of external stray light and internal radiation,analysis of stray radiation environmental characteristics about 500 km orbit,optimal design,imaging quality evaluation,stray radiation suppression of dual-band integrated optical system and so on.The main research results and innovation points of this paper were as follows:First,on the basis of the mathematical model of the BSDF,the mathematical models of the internal and external stray radiation analysis of optical system were established,and the differences between the diffuse reflection model,the Aeroglaze Z-306 scattering model and the ABg model which was obtained by the measured BSDF parameter fitting in the external stray light suppression simulation were analyzed.Second,the grid division method was proposed and the uniform sampling was used in every small area to analyze the earth's stray radiation,and the position of a surface cell was transformed from the sphere reference frame into the J2000.0 inertial frame.By means of numerical integration,the earth's reflective radiation could be calculated.PST as the evaluation index of stray radiation suppression was calculated.Third,in the optimization design of MWIR optical system,the design method which was combined aberration correction with lens radiation suppression was proposed,and the design results under the combination of different lens materials were given.By comparing MTF and total radiation of optical elements,the radiation of the optical elements was greatly reduced under the premise of ensuring the image quality.Fourth,in order to achieve the F number matching between the optical system and the cooled infrared detector,a method which used a warm shield to change the F number of the cooled infrared detector was presented.And the models of ordinary planar warm shield and new spherical reflecting warm shield were developed in Tracepro simulation software to simulate and analyze the self-radiation.The simulation results showed that radiation of spherical reflecting warm shield was significantly less than planar warm shield.The method provided theoretical analysis and simulation verification reference for the optimization design of this kind of system.Fifth,in Tracepro software,the stray radiation analysis model of dual-band integrated optical system was established.Moreover,the suppression methods of external stray light and internal self-radiation were given,and the method of comprehensive evaluation of internal and external stray radiation suppression results by using the parameter of equivalent black body temperature was put forward.