Research On Stray Light Suppression And Processing Technology Of Space-based Space Target Detection System

With the improvement of space launch capabilities and the increase of various commercial space activities,thousands of space targets,including satellites in orbit and space debris,are in various orbits around the earth.As a result,the space environment has become more and more complex,and it has also posed great challenges to mankind's exploration of space.Therefore,the detection and recognition of space targets has become an important content in current space activities.The space-based space target detection system is not affected by factors such as weather,time,geographic location,etc.,and at the same time,it uses micro-satellites equipped with wide-field optical telescopes to have many advantages such as flexible shooting and strong overall observation capabilities.It has gradually received more and more attention.However,when working in a space environment,the space-based space target detection system is easily disturbed by stray light: on the one hand,stray light limits the space-based space target detection system's ability to detect high-magnitude space targets;On the other hand,stray light causes image degradation,severely reduces the imaging quality of space-based star maps,and greatly increases the difficulty of star map preprocessing.Therefore,this thesis takes the space-based space target detection system as the background.In order to improve the imaging performance of the system,researches on stray light suppression and processing technology are carried out.The main research contents are as follows:Research on optical design and stray light suppression technology of space-based space target detection system.First,according to the requirements of the subject's high resolution and compact optical structure,a wide field of view optical system based on concentric lenses with a field of view of 60°×30°was designed,and its stray light characteristics were analyzed.Afterwards,for the external stray light,a first-level baffle structure was designed under the constraints of the light and small structure of the system.At the same time,a baffle structure with angled vanes was proposed,and a fast optimization model based on the irradiance transmission equation was established.The use of this model can efficiently and accurately complete the optimization design process of the angle of the vanes,and achieve the best stray light suppression performance of the baffle structure in less time.At the same time,the ray tracing results show that without increasing the volume of the baffle,the transmittance of the point source outside the stray light suppression angle of the two fields of view is reduced by an order of magnitude on average.Research on the correction technology of stray light non-uniform background of space-based star map.Firstly,it summarizes and analyzes the existing non-uniform background correction methods and the existing problems in dealing with the stray light non-uniform background of star map.Then,a recursive multi-scale non-uniform background correction algorithm based on gray-scale morphology is proposed.The algorithm does not need any prior information,and can correct the non-uniform background with high precision while preserving the target.Subsequently,on this basis,a more applicable non-uniform background fast correction algorithm is further proposed,which not only greatly reduces the running time required by the algorithm.At the same time,it also compensates for the shortcomings that the recursive multi-scale non-uniform background correction algorithm based on gray-scale morphology will lose the target when the size of different targets changes "discontinuously".The algorithm also does not need any prior information to achieve high-precision correction of various complex non-uniform backgrounds.At the same time,the signal-to-noise ratio of weak and small targets in the star map after correction by the two algorithms is increased by more than 2 times.Research on noise suppression technology of space-based star map.First,combined with the non-uniform background correction technology,the characteristics of residual noise in the star map after the stray light non-uniform background correction is analyzed.Subsequently,in view of the loss of image details caused by traditional median filtering and its improved algorithms,and the difficulty in distinguishing the target from salt-like noise in star maps,an adaptive median filtering algorithm based on neighborhood directional difference was proposed.The algorithm can make use of the similarity between adjacent pixels to perform secondary detection for suspected noise points,and combine the weighted average of noise-free neighborhood points in the adaptive window to recover the noise point.This method not only can effectively remove salt and pepper noise in ordinary images,but also improves the ability to protect image details.At the same time,when dealing with the residual salt-like noise in the star map after the stray light non-uniform background correction,compared with traditional algorithms,it can accurately distinguish and retain target information in the process of eliminating noise,and it has strong robustness in different scenarios.