Research On Desensitization And Athermal Technology Of Aerial Catadioptric Optical System Based On The Secondary Mirror Image Motion Compensation

Aerial mapping camera is one of the main optoelectronic devices for obtaining ground image information in the air,and plays an irreplaceable role in many fields,such as environmental protection,ecological resources survey,land and resources management,geological disaster monitoring,climate impact,and so on.During aerial camera imaging,due to vibration,aircraft motion and camera swing,there is relative motion between the subject image and the photosensitive medium when the camera is exposed,resulting in image blur and tail effect,namely image motion.Image motion compensation through moving optical elements can simplify the complexity of aerial mapping camera systems and reduce development costs.However,the movement of optical elements leads to a decline in the imaging quality of the optical system,which poses difficulties and challenges for high-quality imaging of aerial mapping cameras.In this paper,based on the background of the aerial catadioptric optical system based on the secondary mirror image motion compensation,relying on the theoretical knowledge and practical technology in the fields of desensitization design and nodal aberration theory,we explore the optimization method of optical system with high image quality improvement and low sensitivity,aiming at ensuring the imaging quality in the secondary mirror movement.At the same time,according to the environmental conditions of the aerial camera,the athermal design method is explored.The main research contents of this paper can be summarized as follows:Aiming at the problem that the imaging quality of the system changes greatly with the tilt of the secondary mirror,a design scheme for reducing the tilt sensitivity of the secondary mirror is proposed for the catadioptric optical system,and the physical model of the image motion compensation for the tilt of the secondary mirror is established,and the sensitive aberration affecting the imaging quality is determined.The analytical expression of the tilt sensitivity of the secondary mirror in different tilt directions is derived.On this basis,the optimization function and design method for reducing the tilt sensitivity of the secondary mirror based on the nodal aberration theory are established,which can simultaneously improve the image quality of the optical system and reduce the tilt sensitivity of the secondary mirror.A desensitization analysis model based on the relationship between aberration sensitivity and field of view is established.From the analysis results,it can be seen that the reduction of sensitivity mainly depends on the astigmatic coefficient introduced by the first power of element misalignment.The Monte-Carlo analysis results show that the standard deviation of the system after desensitization is 0.020,which is 59% of the system before desensitization.When the transfer function is high,the performance distribution of the optical system is relatively concentrated.Aiming at the problem that the imaging quality of the system changes greatly with the temperature,an athermal design method of catadioptric optical system based on athermal map is proposed.According to the athermal conditions of the catadioptric optical system,that is,to meet the optical power formula,achromatic and thermal aberration formula,the structural grouping method of the catadioptric optical system and the calculation method of the relevant parameters of the equivalent single lens are established,and the graphical conditions of the athermal design of the catadioptric optical system are derived.On this basis,the evaluation method of the combination optimization of the mirror and the housing material based on the comprehensive weight is proposed.This method does not need to simulate the mirror material and the housing material in turn,which improves the efficiency of material optimization.Further,in order to solve the problem of low efficiency of homologous material optimization in the athermal design of optical system,an evaluation method of lens optimization based on the equivalent single lens position in the athermal map is proposed,which avoids the problem of large thermal power change in homologous material optimization,and achieves a better athermal effect through one-time material optimization.The analysis of the thermal defocus and the transfer function of the catadioptric optical system in the temperature range of-40～60℃ show that the thermal defocus in this temperature range is less than 0.004 mm,and within half focal depth,the transfer function of each field of view is close to the diffraction limit and basically remains unchanged,achieving good imaging quality in the wide temperature range of the system.Finally,in order to realize the matching of the mirror material and the housing material between the primary and secondary mirror,an extended athermal glass map suitable for the optimization of the combination of the mirror and housing material between the mirror and the primary and secondary mirror is proposed,and the material selection of the primary and secondary mirrors is microcrystalline,the housing material between the primary and secondary mirror is carbon fiber,and the housing material outside the primary and secondary mirrors is titanium alloy.The temperature adaptation range of the optical system was determined to be 0～30 ℃ through optical,mechanical,and thermal integration analysis.A prototype of the principle is built,and an experimental study on the secondary image motion compensation for the aerial catadioptric optical system is designed.The experimental results of secondary mirror image motion compensation prove that the tilting motion of the secondary mirror can achieve image motion compensation well;The actual temperature adaptation range of the aviation optical system is obtained by testing the discrimination plate image of the system at a temperature range of-10～40 ℃;The actual imaging effect of the aerial optical system is verified by the location imaging results.To sum up,this paper studies the desensitization and athermal techniques of the aerial catadioptric optical system based on the secondary mirror image motion compensation.On the basis of the existing research results,an optimization method for reducing the secondary mirror tilt sensitivity based on the nodal aberration theory is proposed.According to the environmental conditions of the camera,the material optimization method of the catadioptric optical system is designed to effectively ensure the imaging quality of the aerial camera,which is of great significance to the development of the airborne photoelectric measurement field.