Study On Key Technology Of Image Motion Compensation Of Agile Satellite Camera

With continuous development of space remote sensing technology, many countries have put forward higher requirements for rapid response capability, earth observation efficiency and imaging scope of satellites besides pursuing high ground resolution. As a new-type earth observing remote sensing satellite, agile satellite has become the development tendency of high-resolution remote sensing satellite because of its rapid, flexible and highly efficient imaging characteristics. During orbit imaging period of space camera, image motion on the focal plane caused by satellite attitude maneuver, orbital motion and earth rotation, etc., is the major reason restricting TDICCD space camera to realize high-quality imaging, and has undesirable influence on agile satellite camera with rapid and flexible maneuvering ability. Hence, establishing image motion velocity field model of agile satellite camera containing attitude maneuver and formulating image motion compensation strategy according to image motion velocity field distribution are problems needing urgent solution.Firstly, the influence of image motion on TDICCD imaging quality was analyzed, and with reference to representative agile satellite, same-orbit multi-target imaging, same-orbit stereo-imaging, same-orbit multi-stripe split joint imaging and dynamic whisk-broom imaging were concluded, and operating principles of each imaging mode were studied. According to difference in earth-pointing directions of satellite attitude during imaging process, these four imaging modes were divided into static imaging mode and dynamic imaging mode. And according to imaging attitudes, static imaging mode was divided into roll imaging, pitch imaging and combination of roll and pitch imaging.Secondly, directing at deficiencies of traditional sub-satellite point image motion velocity model, this paper proposed a modeling method based on rigid body kinematics. Through procedures such as transformation of coordinate system, deduction of vector relation, solution of position vector of target point, solution of model component, etc., it established image motion velocity field model of agile satellite camera containing attitude maneuver. During modeling process, not only the physical truth that the earth was a spheroid but also off-axis angle of off-axis three-mirror anastigmatic(TMA) optical system were taken into consideration, consequently, authenticity and accuracy of the model were improved. Simulation experiment verified that modeling principle of image motion velocity field model proposed in this paper was right and feasible. Simulation results show that calculation results of drift angle and image motion velocity of image motion velocity field were quite close to results of traditional sub-satellite point image motion velocity model, and both drift angle errors and relative errors of image motion velocity were within allowable range.Then, based on image motion velocity field model proposed in this paper and combining actual parameters of one agile satellite and corresponding satellite orbit and attitude parameters, it conducted 3D simulation of distribution rules of image motion velocity and drift angle of focal plane respectively under static imaging mode and dynamic imaging mode, and made a quantitative analysis of difference in image motion velocity and drift angle of positions of different image points on focal plane, and then directing at different imaging modes, analyzed the influence of parameters like off-axis angle, satellite attitude angle, latitude argument and whisk-broom angle velocity on image motion velocity and drift angle on focal plane.Finally, it analyzed errors involved in image motion compensation process and pointed out that relative matching residual error and drift angle residual error of image motion velocity were major factors influencing imaging quality of agile satellite. Moreover, directing at distribution of focal plane MTF and image motion velocity field under different imaging modes of agile satellite, it formulated corresponding compensation strategies. It proposed global optimization and local optimization drift angle matching strategies for combination of roll and pitch imaging mode and then verified feasibility of the two drift angle matching strategies according to simulation of matching effects. Simulation results showed that: global optimization matching strategy could realize full field-of-view distinct imaging and it was applicable to general-investigation imaging task of agile satellite, while local optimization matching strategy could make local imaging quality of camera be significantly improved and it was applicable to detailed-investigation imaging task. For roll imaging, it proposed grouping different-velocity matching strategy of image motion velocity and gave grouping schemes corresponding to different roll angles at 96 integral stages, and simulation results showed that: this strategy could comprehensively improve focal plane MTF without lowering integration stages; for combination of roll and pitch imaging, it proposed image motion velocity matching strategy with combination of integration stages regulation and grouping line frequency regulation, and simulation results showed that this strategy could not only guarantee high integration stages of camera under small attitude angle but also guarantee high MTF under large attitude angle; for dynamic whisk-broom imaging, it pointed out that whisk-broom angle velocity was the main factor influencing line frequency variation of TDICCD and gave upper limit value of whisk-broom angle velocity corresponding to different satellite latitude arguments and whisk-broom angles of 50μs space camera, and simulation results showed that this upper limit value could control line frequency of TDICCD within allowable range while guaranteeing high MTF of focal plane by combining traditional image motion velocity compensation strategy.Image motion velocity field model and image motion compensation strategies proposed in this paper can provide a theoretical basis for image motion compensation of agile satellite camera.