Research On The Design Of Multi-mode Imaging For Agile Satellites

With the development of space remote sensing technology,the satellite is required to have higher time resolution,spatial resolution,imaging efficiency,faster response ability and wider imaging width.With the specialty of fast three-dimensitional mobile ability and high imaging efficiency,agile satellite has become the new trend of high spatial resolution remote sensing satellite,which is widely used in politics,economy,forestry,water conservancy,disaster and many other areas.Especially in the military,agile satellite plays an irreplaceable role.The agile imaging could realize variety of complex imaging modes in coordination with the satellite attitude system which could fit the military and civil requirements.Agile imaging is the inevitable outcome of the development of space remote sensing technology.In recent years,with the increasing demands of satellite imaging ability and imaging mission,the traditional imaging mode could no longer meet the development of satellite.Hence,it is necessary to develop new smart imaging modes according to different imaging demands which is a key technonlogy to improve the efficiency of the satellite.Futhermore,the feasibility and effectiveness of imaging modes are required to be verified and analyzed.The new imaging mode researches were carried out which could solve the problems of the narrow width with large imaging area,narrow field of view for fast moving target and low solar altitude in the night with long time imaging.Firstly,the structure,working principle,and comparison of TDI CCD and CMOS camera were introduced and analyzed.Then the preliminary planning of the observation time window was carried out to get the best observation time.The selection process and clipping algorithm for earth observation time window have been shown.The reference frames were defined according to the requirement of satellite imaging mode.The equations of dynamics and kinematics were given.The generalized image motion compensation model which is suitable for arbitrary imaging mode has been derived,and the specific strategy of the satellite intelligent cooperative control compensation has been presented.Secondly,several imaging modes were designed and improved according to the existing imaging requirements.To overcome the defects of traditional strip mosaic imaging,a classification method basing on certain bands with the overlap rate was proposed,considering the earth is aellipsiod.Then,the staring imaging mode under the low-illuminance condition was designed and an adaptive exposure period algorithm was proposed.The velocity matching exposure imaging relations were set up by establishing the mathematical model of the satellite-ground real-time gaze tracking,and the low-illuminance imaging exposure period of the attitude control accuracy was analyzed.To expand the staring imaging area,a pendulum type searching imaging model was designed with the high resolution CMOS sensor.Based on the division of the long strip layer and the construction of gradual change overlapping rate,the real-time tracking attitude and the imaging parameters of pendulum type imaging mode were calculated.The attitude control precision and the image displacement were analyzed through a multiple small approaching PD controller,and the purpose of staring long strip layer area has been accomplished.Then,the full link mathematical model in Simulink and the STK simulating model were established by combining the orbital dynamics,kinematics,imaging model algorithm and STK real-time display system.The Jilin-1 attitude and orbit parameters were used to realize the engineering applicability of agile imaging mode through the analysis of the characteristic of target,atmospheric turbulence and the optical,mechanical,and electrical mapping relationship of the satellite.The high precision,multi freedom attitude control and real-time accurate imaging of the new multimodal imaging were simulated and analyzed.Finally,the whole physical imaging ground simulation experiment was performed and the on-orbit vertification test was carried out.The satellite imaging principle was introduced,and the necessity of the ground experiment and the geometric zoom system was analyzed.The geometric zoom system was developed,which consists of the cambered LED dynamic target simulation system,three axis air bearing turntable system and high resolution imaging camera system.The simulation experiments have been carried out on the basis of the new three imaging modes,and good imaging results have been obtained.The new developed smart imaging modes for agile satellite and the geometric zoom simulation system platform could be a theoretical basis for improving imaging the imaging efficiency on orbit.