Research On Payload Parameter Design And Non-ideal Factor Effect Analysis For Geosynchronous SAR

Geosynchronous synthetic aperture radar(GEO SAR)is the spaceborne SAR running in the inclined geosynchronous orbit with an orbital altitude of 36000 km and an orbital period of one day.Compared with the conventional low-earth orbit(LEO)SAR,GEO SAR has the advantages of wide coverage,short revisit time and excellent continuous observation capability,and can satisfy the requirements of the disaster monitoring,emergency response,military application and so on.However,the system characteristics and the non-ideal factor effects in GEO SAR are different from those in LEO SAR.The local circular track model(LCTM)in LEO SAR cannot describe the curved satellite track and the complex Doppler feature of GEO SAR.The conventional methods of Doppler feature analysis and work mode design based on LCTM are invalid in GEO SAR.The conventional range-azimuth resolutions cannot precisely describe the non-uniform distribution of the ground resolution on the condtions of the squint observation in GEO SAR,and the ground resolution design method based on the range-azimuth resolutions is invalid.The conventional analysis methods of the antenna vibration,the height error and the geo-location error is based on the assumption of the straight track and the boresight observation,and they are invalid on the conditions of the curved satellite track and squint observation.This thesis investigates on the key techniques of the system characteristics analysis,the payload parameter design,and the non-ideal factor effect analysis in GEO SAR.The main research work and innovations can be summarized as follows:(1)A system characteristic analysis and work mode design method based on the curvature motion model(CMM)is proposed for GEO SAR.Firstly,a curvature motion model is established to describe the curved satellite track of GEO SAR.Based on the CMM,the Doppler parameters are expressed with the model parameters,and the time-frequency features are analyzed.After that,the key parameters of the beam scan mode are presented,and a beam scan mode design method base on the CMM is proposed.The related researches are helpful to deeply understand the complex motion feature and Doppler feature of GEO SAR,and provide effective tools for the work mode design.(2)Based on the optimal uniformity criterion,a ground resolution design method is proposed for GEO SAR.Firstly,the projection relationship from the slant range plane to the ground plane is established by using the geometry of GEO SAR.The two-dimensional ground general ambiguity function is obtained,and the resolution area is found to be an ellipse approximately.Then,the ratio of the short axis and long axis of the resolution ellipse is used to present the degree of non-uniform distribution,and the condition for the most uniform distribution is obtained.Finally,a ground resolution design method based on the optimal uniformity criterion is proposed,and provides an effective tool for the resolution parameter design of GEO SAR.(3)An analysis method of the non-ideal factor effects is proposed for GEO SAR,and the non-ideal factors include the antenna vibration,the height error and the geo-location error.For the problem of antenna vibration effects,an antenna vibration model is firstly established for GEO SAR.The antenna vibration is divided into the antenna translation vibration(ATV)and the antenna rotation vibration(ARV),which affect the phase and the amplitude of the echo,respectively.Then,the point spread function(PSF)affected by the APV is derived based on the high-order spectrum and curved satellite track of GEO SAR,and the frequency range required to be suppressed are analyzed.After that,a time-varying antenna gain model is established considering the curved satellite track and squint observation,the PSF affected by the ARV are derived,and the quantitative relationship between the vibration amplitude and the paired-echo amplitude is presented.For the problem of height error effects,the Doppler phase error caused by the height error is derived considering the curved satellite track and squint observation.The defocusing and the two-dimensional displacements of the image are analyzed,and the constraint of the image quality on the height accuracy is presented.For the problem of geo-location error analysis,the expression of the geo-location error,which is effective for the zero Doppler rate and the squint observation,is derived based on the range-Doppler location principle.The non-ideal factors effects analysis method is verified by computer simulation,and can provide supports for the system accuracy analysis of GEO SAR.