Spaceborne Multi-azimuth Observation SAR 3D Information Extraction Technology

With the rapid development of high resolution spaceborne synthetic aperture radar(SAR)technology,a novel operation mode called multiple azimuth observation(MAO)is proposed in recent years.MAO is a type of stereo observation mode,which gain access to a hot area or scene from various azimuth aspect.For spaceborne SAR,it can be achieved by radar beam steering,multiple passes or satellite constellation.MAO can obtain the geometrical and scattering characateristics of ground features from multiple views,which makes up the loss of information of conventional narrow angle SAR.The products of MAO-SAR is more interpretable and contains richer traits of objects.What's more,the cuvature of satellite orbits and different view angle bring three dimensional(3D)reconstruction potentiality to MAO,greatly improving its remote sensing and detecting performance.However,due to the large orbit cuvatrue,variation of radar beam pointing,and drastic change of ground scattering fetures,there exist some challenges in spaceborne MAO-SAR system parameter design and signal process.This dissertion endevor to investigate problems in spaceborne MAO-SAR system design and 3D reconstruction,whose main contribution and innovation are summarized as follows:(1)Spaceborne MAO-SAR system parameter and constellation configuration designAccording to the difference of data taking geometry,spaceboren SAR MAO is divided into single pass MAO(SP-MAO)and multiple pass MAO(MP-MAO).SP-MAO is achieved by radar beam steering in one pass,and MP-MAO is implemented by multiple pass of one satellite or the forming a satellite constellation.In Chapter 3,the design of both SP-MAO and MP-MAO are researched:Restricted by satellite orbit,radar beam steering has to be utilized to increase the SP-MAO,which is similar to spotlight mode with large rotation angle.According to the geometry,the connection between the radar beam state and satellite postions and scene center is established.In radar beam control,the expansion of Doppler bandwith is considered so that a satellite attitude parameter design method based on minimization of instantanous Doppler bandwith is proposed.This method approximates Doppler plane surface to a plane and controls its normal vector to minimize the instantanous Doppler bandwith.Simulation experiments with Satellite Tool Kit(STK)prove the effectiveness of the method.MP-MAO can expand observation angle span by either adding number of passes or satellites.In special cases,the observation azimuth angle can be increased to 360,or achieving all azimuth observation(AAO).For single satellite,Chapter 3 rasied a orbit desgin method to accomplish MP-MAO with multiple passes.It uses the intersection points of satellite ground track to construct all azimuth observation window(AAOW).By matching the ceters of AAOW and the illuminated scene,the orbit Kepler elements can be deducted.Due to the high frequence access characateristic of the areas near the intersection points,the designed orbits can not only achieve AAO to a targeted area in short time(within 10 hours),but also possess the ability of daily AAO revisit.The advantages of the design method are both reducing the scene change with single AAO and keeping long time supervision of the same area.After that,based on the MP-MAO orbit desgin method,a consetallation configuration design method is proposed to further increase the efficiency of MAO.The constellation design method makes the all satellites nadir point tracks overlap,and consquently lead to the superposition of the AAOWs of all satellites.Then,combined with the time difference of the satellites passing through the arcs of the AAOW,the orbits' elements of all satellites are obtained.Simulation experiments with STK validate the effectiveness of the proposed spaceborne SAR MP-MAO orbit design and constellation design method.Design cases show that a four satellite MP-MAO constellation can reduce the AAO time into several minites.(2)Spaceborne SP-MAO SAR 3D reconstuction technologyChapter 4 invetigates the 3D reconstruction technology with spaceborne SP-MAO SAR.In the beginning,three dimensional resolution of spaceborne SP-MAO SAR is anlyzed,followed with the deduction of the expression of multiple aspect SAR locating equations.Theoretical and simulation results shows that both digital beam forming or multiple aspect SAR locating cannot obtain 3D results with high accuracy.To overcome this limitation,a 3-D imaging method based on joint multiple azimuth angle Doppler frequency rate estimation is raised.First,a relationship is proposed between the height error and Doppler frequency rate at different azimuth angle.Then,the Doppler frequency modulation rate error is estimated by map drift(MD)technique.Next,the height estimation results of different azimuth angle are combined to improve the estimation accuracy.From the estimated height and the target location in the SAR images,3-D geometric information is retrieved and 3-D imaging is achieved.Simulation experiments validate that the height estimation can achieve an accuracy of few meters with the proposed method.(3)Spaceborne MP-MAO SAR 3D reconstuction technologyChapter 5 studies the 3D reconstuction technology with MP-MAO geometry.Since the corelation between the datas with large observation angle gap,the corelating based image coregistration methods are not longer suitable in MP-MAO geometry.To solve the problem,we proposed a voxel area sculpturing based 3D scene reconstruction method.Firstly,the connection between an object and its projections in multi-aspect SAR images is established with no auxiliary model.Based on the connection,voxels are classified into inner voxels(voxels beneath the target profile)and outside voxels(voxels outside of the target profile).Discarding all outside voxels,the remained inner voxels are combined to form the 3D point cloud of the target.It is similar to the sculpturing process from a raw material to a piece of craft.The advatage of this method is avoding the procedure of image coregistration,which is still effective without any auxiliary information of the target.Simulation and real data experiments indicate that the correctness,robustness and generality of proposed 3D reconstruction method,which is suitable for various types of targets,including complex shaped case tractor.