Research on Inteferometric Inverse Synthetic Aperture Radar Three-dimensional Imaging
|School||National University of Defense Science and Technology|
|Course||Information and Communication Engineering|
|Keywords||Interferometric Inverse Synthetic Aperture Radar (InISAR) Three-dimensional Imaging Image Registration Squint One Antenna ShipImaging Optimum Time Selection Glint Coherent Compensation AntennaArray|
Interferometric inverse synthetic aperture radar (InISAR) is able to carry outthree-dimensional (3-D) image of far-field moving targets. Compared with traditionalISAR imaging, InISAR reflects3-D construction of the target which is not sensitive totarget orientation, and is capable of providing a more reliable description of targetfeatures, resulting in great advantage to target identification. Therefore, InISAR3-Dimaging has become a promising technique in the radar signal processing community.This dissertation investigates problems such as theory model, system characteristics andimaging methods, which can be applied to practical system design and configuration.Chapter1illustrates the background and significance of this research, and reviewsthe development of InISAR imaging system. Then the current signal processingtechniques in InISAR imaging are summarized, and the development trend of InISARimaging is analyzed, followed with the introduction of main content in this dissertation.Chapter2investigates the InISAR3-D imaging model and image registrationmethod. We develop an L-shape three-antenna InISAR imaging model and detail theimaging principles. With regard to the image mismatching problem in InISAR system, aquantitative analysis of the offset and its influence on the following interferometricprocessing was studied. From the view of reference range selection, a novel imageregistration method based on phase correction is proposed to solve the mismatchingproblem in InISAR imaging. The proposed method is suitable for both three-antennaand multi-antenna configuration. We introduce “respective focusing (RF)” and “uniformfocusing (UF)” for reference range selection process of InISAR. An InISAR referencerange error model is built and a comparison of interferometric imaging capability forboth reference range selection methods is performed. It is concluded that RF is a betterchoice in conquering problems such as image mismatching and phase ambiguity, whichcan be seen as a theoretical reference for practical reference range selection.Chapter3focuses on the squint-mode InISAR3-D imaging algorithm. Theinfluence of squint on InISAR imaging is theoretically investigated. First, coupling ofthe squint additive phase and the target azimuth/altitude coordinates to be solved maymake the solution more difficult. Second, the squint angle may lead to estimation errorof the vertical coordinates and distortion of the ultimate image. Aiming at the above twoproblems, we propose a new method combining nonlinear least square (NLS) andcoordinates transform (CT) to estimate the target coordinates, which overcomesdeficiencies of traditional methods, and effectively solves the squint-mode InISAR3-Dimaging problem. We also suggest a “peak detection” method for ISAR pretreatment,which eliminates the illusive scatterers and restrains the scatterer clusters problem,resulting in improvement of the3-D image quality. Chapter4studies the one-antenna InISAR3-D imaging method. We propose theassumption of InISAR imaging with only one antenna: to acquire the equivalentaperture and baseline based on the equivalent relationship between the time and thespace. Aiming at the difficulty of measuring equivalent baseline for one-antennaInISAR system, we propose a one-antenna InISAR3-D imaging method based oncoordinate transform and equation union, where the target scatterer position informationis estimated from the interferometric phases between ISAR images obtained fromdifferent measurement intervals. The applicability and performance of the proposedone-antenna InISAR imaging method is analyzed. At last, the practical difficulties of theproposed method are pointed out and can be seen as the direction of further study.Chapter5discusses the ship InISAR3-D imaging problem. For the sake of solvingthe3-D imaging problem of ship target in heavy sea-state, we establish a practicalairborne observation model using three antennas for ship targets, and propose a novelship InISAR3-D imaging method based on the model. Three-antenna configuration ismore suitable to the interferometric imaging of non-cooperative moving target and canavoid the cross-range scaling problem. Moreover, the prior knowledge of ship positionis not necessary in the proposed method. A multi-strategy-fusion based optimum timeselection algorithm for ship InISAR imaging is given. The proposed scheme estimatesthe initial time window from the radar system parameters, and then utilizes themeasurements of ISAR image focus, such as the image contrast, the image entropy, thescatterer number and the Doppler spread, to finish the InISAR imaging optimum timeselection. The proposed method avoids the deficiency of single measure, and improvesthe quality of InISAR3-D image.Chapter6concentrates on the glint restraint problem of InISAR imaging. We studythe mechanism of glint in virtue of vector addition, and show the location of synthesisscatterer relative to the multiple true scatterers, which provides a theoretical referencefor detecting and restraining the glint phenomenon. To increase the resolution, wepropose a new data-based coherent compensation method of multiband radar signalfusion imaging, compensating for lack of mutual coherence among different radars.Compared with the existing model-based coherent compensation method, the proposedmethod is simpler and the precision of phase parameters estimation is higher becausethe modeling error is eliminated. Moreover, it has better anti-noise capability. In orderto exploit the space separation capability of antenna array, we present anAMOD-PD-ERVP based L-shape antenna array3-D imaging method in the presence ofsquint. The proposed method overcomes the glint problem, and a3-D resolution isindeed realized.Chapter7summarizes this dissertation and discusses the future work.The research results achieved in this paper enrich the high-resolution radar3-Dimaging techniques of non-cooperative targets, and will be valuable for development of InISAR3-D imaging both in theory and in practice.