Study On Imaging And Positioning Of Missile-borne Monostatic/Bistatic SAR With Curve Tracks

Synthetic Aperture Radar(SAR),as a microwave active imaging system,has the capability of all-weather,all-day,long-distance high-resolution imaging.It has received extensive attention in the field of both military and civil detection.In recent years,with the technology development of radar and propulsion,phased array antennas with fast phase-sweeping and multi-function modes have begun to be transplanted to Missile-Borne SAR(MB-SAR).This can not only strengthen the all-weather detection and combat capabilities of missiles,but also improve the adaptability and autonomy of seekers in complex battlefield environment,which is significant for future military operations.This thesis fully considers the development trend of flexible high maneuverability,single warhead precision guidance,and multi-warhead guidance for future missiles.Combined with the characteristics of curve track and the requirements of detection guidance,key issues in the imaging and positioning of monostatic/bistatic SAR will be discussed.To be specific,the main content of the thesis is organized as follows:Chapter 2: The three-axis velocity and acceleration of missiles not only make traditional linear range models no longer hold,but also requires reconsideration of the "one-step-one-stop" model assumption.For the application requirements of single-warhead guidance and multi-warhead guidance,starting with the range model,the analysis can be divided into two parts,namely the range model of the Missile-Borne Monostatic SAR(MBM-SAR)and the range model of arbitrary configuration of the Missile-Borne Bistatic SAR(MB-BiSAR).Given this analysis,range models for monostatic/bistatic SAR imaging with curve tracks can be further developed step-by-step.First,based on the linear dive configuration of MBM-SAR,a equivalent flat-flying range model is constructed.This enables to analyze the constraints of the "one-step-one-stop" assumption in MBM-SAR imaging.Second,based on the linear dive track,a high-precision equivalent range model is developed for MB-SAR with curved tracks.Considering the requirements of bistatic forward-side-looking and bistatic forward-looking in MB-BiSAR imaging,detailed analysis of the constraint and boundary conditions is provided first for the "one-step-one-stop" assumption based on the bistatic arbitrary configuration with linear track.Third,new equivalent range models are developed further for MB-BiSAR imaging with arbitrary configurations and curve tracks.Results of numerical experiments show that the equivalent range model has the advantages of low complexity and high accuracy,which lays the foundation for the subsequent imaging algorithms.Chapter 3: In view of the high redundancy of traditional time-sequential design methods and the mutual constraints between trajectory and system parameters,research on the working sequence and the trajectory optimization design of MB-SAR is conducted.First,based on the range model in Chapter two,parameters like bandwidth and resolution are analyzed,and a method is proposed for the design of work sequence based on the Method of Traversing Scene Scattering Point(MTSSP).This proposed method can not only effectively solve the problem that the near and the far Doppler points are difficult to be determined due to the inconsistent azimuth and pitch beam width,but also reduce the redundancy of imaging parameters under erroneous trajectory parameters,which improves the real-time imaging capability of the system.Second,given the mutual restriction between trajectory parameters and imaging configuration parameters,an optimization design method is proposed to provide reference criteria for trajectory design.Chapter 4: Given the requirements for single warhead precision guidance,research on integrated fusion algorithm of imaging,space-variant motion error compensation and geometric distortion correction is carried out for MBM-SAR with curve track based on the equivalent range model in Chapter Two.First,the influence of three-axis time-varying acceleration on spectrum is analyzed.For the spectral distortion caused by acceleration,a rough compensation method is proposed to recover the spectrum.Second,given the large resolution span problems in the process of geometric distortion correction caused by large grazing angles and ballistic inclinations,the spectrum is directly projected to the ground plane by using a 2-D spectral interpolation.This can help to solve the problem of image gray-scale distortion.Third,to achieve the final focus of SAR images,a local joint compensation method for space-variant phase errors and image distortions is proposed further based on inverse mapping interpolation.This method can directly obtain the undistorted SAR ground image through pixel-by-pixel inverse mapping and local filter compensation,and pave the way for subsequent image matching,target recognition and positioning.Forth,for the problems of azimuth phase errors caused by inertial parameter errors and mechanical errors,an azimuth autofocus imaging algorithm is constructed which is suitable for high real-time imaging processing of sub-aperture data.The algorithm is based on weighting factors in time-domain and adopts a 2-D sample screening method.The robustness of the algorithm is good,and problems of traditional autofocus imaging algorithms can be solved,such as complex process,low level of adaptive parameters and poor real-time performance.Results of both experiment and measured data verify the effectiveness of the proposed algorithm.Chapter 5: Based on the development trend of future multiple warheads,the design of MB-BiSAR imaging algorithms is further considered given the application requirements of missile-borne bistatic side-looking and bistatic forward-looking.First,the influence of the accelerations on spectrum is analyzed based on the equivalent bistatic range model proposed in Chapter 2.The acceleration Deramp processing is also proposed to restore distorted 2-D spectrum and ensure the follow-up imaging focus.Second,for the problem of focusing plane selection,application requirements of ground image matching are considered for seeker guidance.With the ground plane as the focusing plane,the 2-D spectrum after the azimuth Deramp processing is projected to the ground by using interpolation along the line of sight,which ensures high spectrum utilization.Third,for wavefront bending and residual space-variant motion error,a local joint compensation method of space-variant phase and image distortion is proposed.This method makes the pixel grid in the ground plane inversely mapped back to the coarsely focused complex image.Then sub-image data are intercepted and compensated in the azimuth phase history domain,and the final undistorted SAR ground image is obtained by iterative loop iterations.Chapter 6: Given the results in previous chapters,positioning algorithms for MB-SAR on diving phase are further studied based on the technical framework of imaging,image matching,target recognition,positioning in precision guidance.For the problem of large deviation in position indication of INS during the terminal guidance stage,a positioning algorithm based on the Euler tetrahedral configuration is proposed.The algorithm takes high-precision image ranging information,accurate position of matching point and digital elevation model(DEM)as inputs,and obtains the position between missile and target by solving positioning equations.The positioning method does not require multiple images for data fusion to improve accuracy.On the contrary,a single matching image alone can achieve high-precision positioning.This can avoid the local convergence problem of localization methods based on optimization theories.The proposed positioning method is able to achieve accurate positioning of missiles and targets during the terminal guidance stage,which provides guarantee for accurate guidance.