Springer Theses Recognizing Outstanding Ph.D. Research Jian Yang Study on Ground Moving Target Indication and Imaging Technique of Airborne SAR Springer Theses Recognizing Outstanding Ph.D. Research Aims and Scope The series “Springer Theses” brings together a selection of the very best Ph.D. theses from around the world and across the physical sciences. Nominated and endorsed by two recognized specialists, each published volume has been selected foritsscientificexcellenceandthehighimpactofitscontentsforthepertinentfield of research. For greater accessibility to non-specialists, the published versions includeanextendedintroduction,aswellasaforewordbythestudent’ssupervisor explainingthespecialrelevanceoftheworkforthefield.Asawhole,theserieswill provide a valuable resource both for newcomers to the research fields described, and for other scientists seeking detailed background information on special questions. 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More information about this series at http://www.springer.com/series/8790 Jian Yang Study on Ground Moving Target Indication and Imaging Technique of Airborne SAR Doctoral Thesis accepted by Chinese Academy of Sciences, Beijing, China 123 Author Supervisor Dr. Jian Yang Prof. YanfeiWang ChinaAcademy of Launch Vehicle Institute of Electronics Technology ChineseAcademy of Sciences Beijing Beijing China China ISSN 2190-5053 ISSN 2190-5061 (electronic) SpringerTheses ISBN978-981-10-3074-1 ISBN978-981-10-3075-8 (eBook) DOI 10.1007/978-981-10-3075-8 LibraryofCongressControlNumber:2016961666 ©SpringerNatureSingaporePteLtd.2017 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpart of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission orinformationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar methodologynowknownorhereafterdeveloped. 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Theregisteredcompanyaddressis:152BeachRoad,#22-06/08GatewayEast,Singapore189721,Singapore ’ Supervisor s Foreword GMTIandGMTImareimportantfunctionsofairborneSARsystems,whichendow the SAR system with the abilities of indication, parameter estimation, relocation and focusing of moving targets, as well as high-resolution imaging of stationary scenes. With these advantages, the moving target processing functions of SAR systems are widely used in both military and civilian applications, and are becoming hot research issues recent years. With the development of signal processing theory and electronic technique, the airborne SAR system has also exploitedseveral new operatingmodes. Besides the classical stripmap SAR/GMTI mode, the WAS-GMTI mode and FMCW SAR system are two representative new operating modes, which are drawing more attention of researchers. Based on the deep analysis of the signal model of the moving target, Dr. Yang focuses on the theories and applications of GMTI and GMTIm algorithms in SAR/GMTI mode, WAS-GMTI mode and FMCW SAR system,andalsostudiesthecorrespondingkeytechniquesoftheseoperatingmodes in this thesis. In addition, the non-ideal errors that deteriorate the performance of GMTImalgorithminrealSARdataprocessingarediscussed,andthecompensation methods are provided. This thesis is highly original and its results not only significantly deepen the theoryofmovingtargetprocessingtechniquebutalsohavegreatpracticalvaluesin real SAR data processing. I feel very lucky to have Yang as one of my Ph. D. students because he is a talented and diligent student. His work during the Ph. D. study promoted the moving target processing performance of the airborne SAR systemsinourlab,andwonhimthePresident’sSpecialAwardofChineseAcademy ofSciences.ThisthesisimprovestheGMTIandGMTImtheoriesofairborneSAR, and paved away for furtherdevelopment of real data moving targetprocessing. September 2016 Prof. Yanfei Wang v Preface GMTIandGMTImareimportantfunctions,whichendowtheSARsystemwiththe abilitiesoftheindication,parameterestimation,relocation,andfocusingofmoving targets, as well as high-resolution imaging of stationary scenes. With these advantages, the moving target processing functions of SAR systems are widely usedinbothmilitaryandcivilianapplications,andarebecominghotresearchissues in recent years. With the development of signal processing theory and electronic technique, the airborne SAR system has also exploitedseveral new operatingmodes. Besides the classical stripmap SAR/GMTI mode, the WAS-GMTI mode and FMCW SAR system are two representative new operating modes, which are drawing increas- inglymoreattentionofresearchers.Basedonthedeepanalysisofthesignalmodel of the moving target, this book focuses on the theories and applications of GMTI andGMTImalgorithmsinSAR/GMTImode,WAS-GMTImode,andFMCWSAR system, and also studies the corresponding key techniques of these operating modes.Inaddition,thenonidealerrorsthatdeterioratetheperformanceofGMTIm algorithm in real SAR data processing are discussed, and the compensation methodsareprovided.Themainworkandinnovationsofthisbookareasfollows: (a) The echo signal model of the ground moving target in stripmap SAR/GMTI modeisestablished.Bydeeplyanalyzingtherelationshipbetweenthemotions and Doppler phases of the targets with fast radial velocities, the effects of Dopplerambiguityandthird-orderphaseerrorarestudied,andanewclassify scheme of the moving targets is presented by concerning the Doppler ambi- guity. Through the Doppler centroid estimation algorithm based on curve fitting,theDopplercentroiderrorofthecluttercanbeestimatedandcorrected, which is the foundation of the following processing steps. With the two-step GMTI algorithm, fast-moving targets that submerged by the clutter can be indicated and extracted. Using the GMTIm algorithm based on Hough transform and third-order PFT, the Doppler ambiguity of the moving target vii viii Preface can be accurately estimated, and the moving target can be correctly focused and relocated. Besides the advantages of indicating and imaging fast-moving targets, the proposed algorithms are also effective in slow-moving target processing, which makes them highly suitable for real SAR data processing. (b) TheprinciplesoftheWAS-GMTImodeandtheDBSalgorithmareresearched and introduced, and a new system design scheme is presented by combining the mechanic scanning mode and the airborne SAR system, which keeps the sharpening ratio constant without increasing the complexity of either the system or the processing. To find a balance between the resolution of DBS imagingandprocessingefficiency,areal-timeDBSalgorithmbasedonCZTis proposed, which is able to correct the RCM and meanwhile circumvents the Doppler centroid estimation. And then, a moving target indication and parameter relocation method in mechanic scanning mode is proposed. This method indicates the targets in each DBS image, and uses the radial move- ments of the moving targets between the DBS images of different scans to estimate the motion parameter. The effectiveness of the proposed method is confirmed by real WAS-SAR data processing results. (c) Thenonlinearitycorrection andGMTIofFMCWSARsystemareresearched and analyzed. The principle of FMCW SAR is first introduced, and the echo model differences between the FMCW SAR and pulse SAR systems are del- icately analyzed. The nonlinearity of transmitted signal in FMCW SAR is an importantissuesinceitaffectsboththestationaryFMCWSARimagingquality and the moving target processing performance. The shortcoming of the clas- sicalderivativealgorithmisanalyzed,andthenanovelnonlinearitycorrection algorithm based on homomorphic deconvolution isproposed, which provides accuratecorrectionswithouttherestrainsofthelengthofthecontrollabledelay line. Based on the modeling of the moving target in FMCW SAR, a new azimuth moving target indication algorithm is proposed using the additional RWM induced by FMCW SAR system. This algorithm makes use of the additional phase, which is viewed as phase error in traditional GMTI algo- rithms, andtherefore broadensthe GMTI ability ofFMCWSAR systems. (d) Currently, the performances of most GMTIm algorithms that are effective in simulations are not satisfying in real SAR data processing. The effects of nonideal errors during the real data acquisition are analyzed, and the estima- tion and compensation method is provided. First of all, the motion errors of high-resolution SAR imaging are introduced, and the PGA technique is induced to correct the high-order phase error caused by these motion errors. Then,byestablishingamorecommonmovingtargetsignalmodelconcerning theeffectofnonideal errors, theconclusionthatthealong-trackvelocityerror of the aircraft and the radial velocity error can make the Doppler centroid of the moving target disperse, and deteriorate the imaging resolution. The effects of these two nonideal errors are confirmed by mathematical analysis and simulation, and a nonideal error estimation and compensation method is Preface ix proposed. Together with the proposed GMTI and GMTIm algorithms in this book, a whole moving target processing scheme is presented, which is very robust and highly suitable for real SAR data processing. Beijing, China Jian Yang Parts of this thesis have been published in the following journal articles: [1] Jian Yang, Chang Liu, and Yanfei Wang. Detection and imaging of ground moving targets with real SAR data. IEEE Transactions on Geoscience and Remote Sensing, vol. 53, no. 2, Feb. 2015. [2] JianYang,ChangLiu,andYanfeiWang.Imagingandparameterestimationof fast moving targets with single-antenna SAR. IEEE Geoscience and Remote Sensing Letters, vol.11, no. 2, Feb. 2014. [3] Jian Yang, Chang Liu, and Yanfei Wang. Nonlinearity correction of FMCW SAR based on homomorphic deconvolution. IEEE Geoscience and Remote Sensing Letters, vol. 10, no. 5, Sept. 2013. [4] Jian Yang, Chang Liu, and Yanfei Wang. Indication and imaging of along-track moving target in frequency modulated continuous wave synthetic aperture radar systems. Remote Sensing Letters, vol. 4, no. 9, pp. 891–899, Jun. 2013. [5] Jian Yang, Chang Liu, and Yanfei Wang. Real-time DBS imaging algorithm based on chirp z-transform. IEICE Electronics Express, vol. 9, no. 21, pp. 1660–1665, Nov. 2012. [6] Jian Yang, Chang Liu, and Yanfei Wang. Adaptive Doppler centroid esti- mationalgorithmofairborneSAR.IEICEElectronicsExpress,vol.9,no.13, pp. 1135–1140, Jul. 2012. [7] JianYang,ChangLiu,andYanfeiWang.Groundmovingtargetindicationin single-antennaairborneSAR.ThefifthYouthAcademicForumofInstituteof Electronics, Chinese Acadmey of Sciences, 2013. 9.23–24. [8] Leye Wang, Jian Yang, and Xianghui Xu. Fast moving target indication and imaging in FMCW SAR. Science technique and Engineering. 2013, vol. 13, no. 16, pp. 4534–4540. xi