| Bistatic/Multistatic Synthetic Aperture Radar Imaging refers to the configuration of the radar,which has two or more moving platforms,and the coherent accumulation of radar signals using multi-platform data links to share information.Then,the imaging system produces a SAR image in the detection area.Bistatic/multistatic SAR imaging not only has the advantages of traditional SAR imaging such as all-sky,all-weather,long-range action and mask penetration,but also has the characteristics of flexible platform,multi-angle observation and passive receiver reception silence due to its transceiver separation system.It can be flexibly adapted to mission requirements to acquire target characteristics in different directions and enhance radar reconnaissance capability.Increasing the difficulty of noncooperative target interference provides a unique advantage in the subsequent target refinement identification and sorting process.Therefore,Therefore,the multi-platform cooperation of bistatic/multistatic SAR can flexibly complete the observation task.The multi-angle observation mode enriches the electromagnetic scattering characteristics of ground objects,greatly increases the difficulty of non-cooperative interference,effectively reduces the cost and increases the concealability of the receiver,which has wide application prospects in both civil and military fields.However,bistatic/multistatic SAR imaging of complex moving platforms has many problems that need to be solved.For example,accurate and unified signal model with complex moving truck,serious two-dimensional space-variant signal parameters,accurate target location without reference points,space-variant range cell migration and twodimensional space-variant Doppler parameters.As a result,the image is defocused and the target cannot be effectively detected.At the same time,the location relationship between the two platforms and the target is coupled in the range Doppler information of the target due to the separation of transceiver and receiver,which increases the difficulty of accurate target positioning.Therefore,this paper carries out research on dual-multi-base high-resolution imaging and positioning methods of complex moving platforms,which mainly includes the following four parts:1.To address the problem that bistatic/multistatic SAR signal models are difficult to establish accurately and consistently,the mathematical forms,advantages and disadvantages of existing SAR signal models are reviewed in detail.First,imaging systems are classified by platform type.On this basis,the concepts of homotypic platform shift invariance and azimuthal translation invariance are introduced,and the reasons for the loss of azimuthal translation invariance of bistatic/multistatic systems are explained.Next,the LBF model and its extended form are introduced,and the derivation idea and physical meaning of the model are explained.Then,the fixed and shift-varying system of bistatic/multistatic SAR is introduced,and the high-precision signal spectrum is obtained by the method of series inversion and Taylor expansion.Finally,the accuracy and imaging results of various signal models are simulated and the applicability of the signal models is confirmed,which provides a theoretical basis for the subsequent algorithm design.2.In order to solve the problem that the acceleration of high maneuverability bistatic forward looking SAR(HMBF-SAR)imaging,which leads to the increase of the spatial variant residual range curvature and the deepening of the two-dimensional space variant Doppler parameters,the azimuth extension NCS imaging algorithm of Bistatic/Multistatic SAR is studied,which lays a technical foundation for the efficient acquisition of HMBF-SAR images.First,the range slant model with acceleration is proposed and an improved accurate signal model is derived.Next,we clarify the range and azimuth direction in the signal processing of HMBF-SAR.Then,a fast reference point selection method(i.e.,azimuth and range reference points)is proposed to analyze the two-dimensional spatial variant characteristics of the signal frequency spectrum,and a high-order spatial variant model of the residual range migration and Doppler parameters is proposed.Based on the model,an imaging algorithm combining second-order keystone and extended azimuth nonlinear chirp scaling(EANCS)is proposed.This is used to compensate for the phase errors caused by severe residual range migration and Doppler parameter variability.Finally,the imaging is compared between the algorithms using the digital simulation data and the measured original data,and the effectiveness of the algorithm is verified.3.In order to solve the problems of frequency spectrum overlap,severe two-dimensional coupling space variation of range and azimuth parameters,and severe geometric deformation of the image caused by the acceleration of bistatic SAR with curve track,a frequency back projection imaging algorithm of bistatic SAR is introduced.First,a local Cartesian coordinate system is constructed to analyze the problem of severe two-dimensional spatial variant range migration.The keystone transform is used to compensate for the spatially variant linear range cell migration to reduce the two-dimensional coupling of the parameters and to reduce the number of range sub-regions.Then,the sub-regional criterion is introduced and the effects of zero-variable parameters on the echo spectrum are analyzed in detail.Subsequently,the sub-regional uniform residual range cell migration correction(RCMC)and range compression(RC)processing are proposed.Finally,the frequency domain coherent integration is used to directly obtain the bistatic SAR ground radar image of the sub-regions.The results of the simulation and raw data show that the performance of the proposed algorithm is superior to other methods,the image does not require geometric correction,and both image quality and imaging efficiency are considered.4.To the application of bistatic/multistatic SAR in precision guidance,a target location method based on multistatic and continuous SAR images is proposed.First,a positioning geometric model was constructed with the subsatellite point of the transmitter as the origin,and the Range-Doppler model of bistatic/multistatic SAR is established.From the inertial derivative data and the SAR image,the initial position of the target can be calculated.Then,the equation set is established by the RD model and the radar track.The position of transmitter and target can be estimated jointly by the Jacobina matrix with the RD position of targets in continuous SAR images.Finally,the target Doppler position changes in multiple transceiver systems are converted into multi-base data Doppler joint equations,which can be used to estimated the accurate target position.The simulation results verify that the proposed method has great accuracy when the inertial navigation position deviation and velocity measurement deviation are existed. |
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