摘要
机载低频超宽带合成孔径雷达(UWB SAR)具有探测隐蔽在叶簇或浅地表覆盖下的目标,对其高分辨成像的能力,军事应用潜力巨大。然而,载机的非理想运动给UWB SAR回波带来了严重的相位误差,直接影响高分辨成像能力,有效的运动补偿技术对高分辨成像至关重要。本论文以装备预研项目为背景,从以下几个方面对机载UWB SAR运动补偿开展了较深入的研究:
首先,研究了在获得了载机运动参数情况下的UWB SAR视线误差补偿方法。论文着重研究了视线误差对UWB SAR成像中的距离迁徙校正影响问题,推导了包含视线误差的点目标二维频谱,并在子孔径视线误差补偿算法的基础上,推导出一种在距离多普勒域、距离迁徙校正前补偿视线误差的新补偿算法,点目标仿真结果验证了该算法在连续大面积实时成像时的优越性。
其次,研究了目前国内机载组合导航系统测量精度不高,不能满足UWB SAR高分辨成像需要时的运动补偿方法。针对UWB SAR特点,论文提出了一种结合全球定位系统(GPS)实时信息和改进MD自聚焦的运动补偿方法,并基于实测数据,提出了几点提高改进MD估计精度的措施。两段实测数据处理的结果验证了所提方法的有效性。论文中还深入分析了该补偿方法中的几个问题,给出了UWB SAR中MD子孔径划分应满足的条件。
然后,深入研究了适合UWB SAR回波特点、以对比度最大为聚焦准则的自聚焦算法。对已广泛应用的对比度最优自聚焦算法进行改进,使其满足实时运动补偿的需要,实际数据处理结果验证了该改进算法的有效性;借鉴频域PACE算法思路,提出一种在时域提取回波中高次多项式相位误差的TD-PACE算法,实际数据处理结果验证了该算法的有效性:针对PACE算法的不足,提出一种减小计算量的IPACE算法,实际数据处理结果表明,IPACE算法执行效率较PACE大幅提高,而聚焦效果相当。论文中还比较了IPACE和PGA聚焦UWB SAR图像的能力,实测数据处理结果表明,IPACE聚焦效果较PGA更好。
最后,结合无人机特点,设计了一种适合无人机UWB SAR高分辨成像要求的低成本运动补偿方案。该方案利用互补滤波器融合GPS接收机输出的速度和单轴加速度计输出的加速度,对UWB SAR回波粗补偿,利用自聚焦进行精补偿。论文中推导了加速度计输出的有用加速度表达式,分析了天线平台稳定精度对加速度计输出的影响,并用仿真数据验证了该补偿方案的有效性。
Airborne ultra-wideband synthetic aperture radar (UWB SAR) working in low frequency band can reconnoitre targets concealed by foliage or earth surface, which is very valuable for military purpose. But trajectory deviation of aircraft will introduce troublesome phase errors into radar echoes, which would influence badly SAR images quality without correction, and effective motion compensation method is crucial to UWB SAR with high resolution. Under the support by some National Defense Research Project, this dissertation researched the motion compensation (MoCo) for UWB SAR from the following subjects:
Firstly, how to compensate the trajectory deviation error in line of sight (LOS) for UWB SAR was discussed in detail with the help of exact motion track. In this dissertation, the influence of error in LOS to range cell migration correction (RCMC) in UWB SAR imaging was analyzed with emphasis, and the spectrum formulation of a point target comprising the LOS error was derived under some approximation. On the basis of sub-aperture compensation method, a new MoCo method with sub-aperture in azimuth direction and sub-swath in range direction was detailedly derived, and computer simulation results validate the new method.
Secondly, how to eliminate effectively errors in UWB SAR echoes was researched when inertial navigation system (INS) on board can not provide exact motion track, which is a universal fact for our country currently. A method combined the real time information from global position system(GPS )receiver with refined map drift(MD) was proposed in the dissertation, and based on the real UWB SAR data, some measurements were added into the refined MD to improve the precision of estimation. The processing results of two data segment validate the proposed method. Some questions in the method were discussed also.
Thirdly, some autofocus algorithms for UWB SAR were deeply investigated, which were on the basis of imaging contrast. On the one hand, the widely used contrast optimization autofocus (COA) was mended to satisfy the demand of the real time MoCo onboard, and the real processing results prove the validation of the mended method. On the other hand, based on phase adjustment by Contrast enhancement(PACE), a new algorithm named as phase adjustment by contrast enhancement in time dimension (TD-PACE) was proposed, which can extract polynomial errors with high order from range compressed echoes, and the real results show that the method can get three order polynomial phase errors. Aimed the disadvantage of PACE algorithm with the huge computation load, an interpolated PACE (IPACE) was advanced also. The processing results of real UWB SAR data prove that the IPACE can greatly accelerate the run time of algorithm with the same quality. Furthermore, the images quality focused by IPACE was better than the images by phase gradient autofocus (PGA), which is considered to be standard nonparametric SAR autofocus algorithm.
Finally, a low cost MoCo scheme for unmanned aerial vehicle (UAV) was designed. A GPS receiver with high sampling and a one-axis accelerometer mounted directly on the SAR antenna phase center (APC) and aligned in LOS were used to measure the motion of UAV in the scheme, and the information from complementary filter (CF), which was used to fuse the speed from GPS and the acceleration from accelerometer, was used to compensate SAR echoes roughly. The useful acceleration expression for accelerometer was derived, and the influence of SAR antenna platform stabilization's precision on the output of accelerometer was discussed also. The computer simulation results justify the scheme.
引文
[1]J.C.Culander,R.N.McDonough.Synthetic aperture radar:System and signal processing.USA,New York:John Wiley & Sons Inc.,1991.
[2]M.Soumekh.Synthetic aperture radar signal processing with MATLAB algorithms.USA,New York:John Wiley & Sons Inc.,1999.
[3]G.Franceschetti,R.Lanari.Synthetic aperture radar processing.USA,Baca Raton:CRC Precss,1999.
[4]I.G.Cumming,F.Wong.Digital processing of synthetic aperture radar data:algorithms and implementation.Boston,MA,USA:Artech House Inc.,2005
[5]J.Sanz,P.Prats,Jordi J.Mallorqui.Platform and mode independent SAR data processor based on the extended chirp scaling algorithm.IEEE Proc.of IGARSS'03,2003:4086-4088.
[6]R.Klemm.10 Years EUSAR-state of the art and trends in SAR.Proc.of 2006CIE international Conf.on radar,ShangHai,China,2006:1-5.
[7]张直中.合成孔径雷达发展概况.2005年中国合成孔径雷达会议论文集,北京电子工业出版社,2006:7-13.
[8]国防科技大学电子工程学院超宽带课题组.叶簇穿透超宽带雷达体制与关键技术研究项目论证报告.技术报告,1996.
[9]梁甸农,周智敏,常文革.叶簇穿透超宽带合成孔径雷达技术发展动态.内部报告,1999年.
[10]L.E.Hoff,L.B.Stotts.ARPA Surveillance Technology for the Detection of Targets Hidden in Foliage.SPIE,Vol.2093,1994:403-426.
[11]Mehrdad Soumekh.Reconnaissance with Ultra wideband UHF synthetic aperture radar.IEEE Signal Processing Magzine.July,1995:21-40.
[12]常文革.UWB SAR系统设计与实现.博士学位论文,长沙:国防科技大学,2001.
[13]刘光平.超宽带合成孔径雷达高效成像算法.博士学位论文,长沙:国防科技大学,2004.
[14]B.Noel.Ultra wideband radar:Processing of the first Los Alamos symposium.USA,Baca Raton:CRC Press,1991.
[15]喻光正.低频超宽带SAR原理何技术问题.电信技术,1999,39(1):53-59.
[16]B.Walker,G.Sander,M.Thompson,etal.A high-resolution,four-band SAR tested with real time image formation.IEEE Proc.of IGARSS'96,Lincoln,Nebraska,May,1996:1881-1885.
[17]D.R.Sheen,T.B.Lewis.The P-3 UWB SAR.SPIE,Vol.2747,1996:20-24.
[18] M.Soumekh,D.A.Nobels,M.C.wicks,etal. Signal processing of wide bandwidth and wide beam width P-3 SAR data. IEEE Trans. On A.E.S., 2001, 37(4):1122-1141.
[19] K.Wheeler,S.Hensley. The GeoSAR airborne mapping system. Proc.of the 2000 international radar Conf.,2000:831-835.
[20] Y.Kim,S.Hensley,L.Veilleux,etal. Design considerations of GeoSAR. SPIE,Vol.2747,2000:61-66.
[21] H.Hellsten, P.O.Frolind, A.Gustavsson, etal. Ultra-wideband VHF SAR-design and measurements . SPIE, Vol.2217,1994:16-25.
[22] H.Hellsten, L.Ulander, A.Gustavsson,etal. Development of VHF CARABASS II SAR. SPIE, Vol.2747,1196:48-60.
[23] Ph.Dreuillet,Ph.Paillou,H.Cantalloube,etal. P-band data collection and investigation utilizing the RAMSES SAR Facility. IEEE proc. of IGARSS'03,2003:4262-4264.
[24] L.Ulander,M.Blorm,B.Flood,etal. The VHF/UHF-band LORA SAR and GMTI system. SPIE,Vol.5095,2003:206-215.
[25] R.Horn.The DLR airborne SAR project E-SAR. IEEE Proc.of IGARSS'96 ,Lincoln,Nebraska,May,1996:1642-1628.
[26] M.Labbate,C.Svara, A.Torre. ARCHEO:A sub-surface imaging SAR. Proc. of EUSAR' 2000,Munich,Germany,2000:165-167.
[27] G.Ossipov,V.Andrianov,A.Lipatov,etal.Double-frequency parametric space-based multipourse SAR of L- and P-wavebands. Proc. of EUSAR'2002 conf.,Cologne, Germeny,Jun.2002:447-449.
[28] W.G.Carrara, R.S.Goodman, R.M.Majewski. Spotlight Synthetic Aperture Radar. Boston:Artech House, 1995.
[29] A.W.Doerry. Autofocus correction of the SAR images exhibiting excessive residual migration. SPIE Vol.5788,2005:34-45.
[30] James L.Frrel. Effect of Navigation Errors in Maneuvering SAR. IEEE Trans.on A.E.S., 1973:758-775.
[31] John C.Kirk. Motion compensation for synthetic aperture radar.IEEE Trans.on A.E.S. Vol.11(3),1975:338-349.
[32] G.E.Haslam. Motion sensing requirement for synthetic aperture radar. Proc.of IEEC&E'83,1983:126-131.
[33] D.Blacknell, A.Freeman,S.Quegan, I.P.Finley. Geometric accuracy in airborne SAR images. IEEE Trans. on A.E.S.,Vol. 25(2) 1989: 241-258.
[34] A.Moreira and Y.H.Huang. Airborne SAR Processing of Highly Squinted Data Using a Chirp Scaling Approach with Integrated Motion Compensation. IEEE Trans .on GRS, Vol. 32(5) ,Sept,1994:1029-1040.
[35] G.Fornaro.Trajectory Deviations in Airborne SAR:Analysis and Compensation. IEEE Trans.on A.E.S.,Vol.35(3),July 1999:997-1009.
[36] S.N.Madsen. Compensating for Motion Errors in UWB SAR Data. NASA TECH BRIEF, NASA's Jet Propulsion Labaoratory,Pasadena,California,2002.
[37] R.Goodman,S.Tummala,W.Carrara. Issues in Ultra-wideband,widebeam SAR Image Formation. Proc.of the 1995 international radar Conf., Alexandria,Virginia,USA, 1995:479-485.
[38] W.Carrara, S.Tummala, R.Goodman. Motion compensation algorithm for wide beam stripmap SAR. SPIE,Vol.2487,1995: 13-23.
[39] S.N.Madsen. Motion compensation for ultra wide band SAR.IEEE Proc. of IGARSS'01,Sydney,Australia,July,2001:1436-1438.
[40] A.Potsis,A.Reigber,J.Mittermayer,A.Moreira and N.Uzunoglou. Sub-aperture algorithm for motion compensation improvement in wide-beam SAR data processing. IEE Electronic Letters, Vol.37(23), 2001:1405-1406.
[41] S.Hensley,E.Chapin,A.Freedman,etal. First P-band results using the GeoSAR mapping system. Proceedings of IGARSS'01, Sydney, Australia, July,2001:126-128.
[42] D.F.Dubberta,A.D.Sweetb,G.R.Sloanc,etal. Results of the sub-thirty-pound,high resolution MiniSAR demonstration. SPIE.Vol.6209:62090Cl-62090Cl 1.
[43] C.E.Mancill,and J.M.Swiger. A Map Drift Autofocus Technique for Correcting Higher Order SAR Phase Error. 27~(th) Annual Tri-Service Radar Symposium Record, Monterey, CA, 1981:391-400.
[44] J. R. Moreira. A New Method Of Aircraft Motion Error Extraction From Radar Raw Data For Real Time Motion Compensation [J], IEEE Trans. on GRS,Vol.28(4), 1990: 620-626.
[45] J.R.Moreira. Estimating the residual error of the reflectivity displacement method for aircraft motion error extraction from SAR raw data. Proc.of IEEE international radar conference, Piscatawy,NJ.,USA,1990: 70-75.
[46] Guo WeiGuang. SAR Motion Compensation Based on Signal Processing Method. Proceedings of RISSP'2003,Changsha,China,May 2003:1240-1244.
[47] F.Berizzi,G.Corsini. Autofocusing of inverse synthetic aperture radar images using contrast optimization. IEEE Trans. on A.E.S., Vol.32(3), 1996:1185-1191.
[48] D.E.Wahl,P.H.Eichel,D.C.Ghiglia,etal. Phase gradient autofocus-a robust tool for high resolution SAR phase correction. IEEE Trans.on A.E.S.,Vol.30(3),1994: 827-834.
[49] J.Kolman. PACE: an autofocus algorithm for SAR. Proc. of the 1999 international radar Conf., Virginia ,USA,2005:310-314.
[50] 徐晓丹,卢凌,何凯.机载SAR运动补偿系统设计与算法研究.武汉理工大
132 学学报,vol.26(6),2002:722-724.
[51]孙永荣,刘建业,陈武.机载SAR运动补偿传感器研究.中国空间科学技术,No.5,2003:28-31.
[52]郭智,丁赤飚,房建成等.一种高分辨率机载SAR的运动补偿方案.电子与信息学报,vol.26(2),2004:174-180.
[53]丁赤飙.基于惯导系统的机载SAR运动补偿精度分析.电子与信息学报,vol.24(1),2004:12-18.
[54]姚萍,陈冰冰,王贞松.采用方位向自适应滤波器提高SAR自聚焦的性能.电子与信息学报,vol.25(8),2003:1066-1072.
[55]高社生,李华星.INS/SAR组合导航定位技术与应用.西安:西北工业大学出版社,2004.
[56]曹福祥,保铮,袁建平,郑谔.用于SAR运动补偿的DGPS/SINS组合系统研究.航空学报,vol.22(2),2001:121-124.
[57]曹福祥.机载合成孔径雷达运动补偿研究.博士学位论文,西安:西北工业大学,1999.
[58]李立伟.高分辨率机载合成孔径雷达中运动补偿问题的研究.博士学位论文,北京:北京航空航天大学,1998.
[59]武昕伟.SAR自聚焦技术及相干斑抑制算法研究.博士学位论文,南京:南京航空航天大学,2002.
[60]钟睿.机载SAR运动补偿的研究.博士学位论文,北京:北京航空航天大学,2004.
[61]邢孟道.基于实测数据的雷达成像方法研究.博士学位论文,西安:西安电子科技大学,2002.
[62]邢孟道,保铮.基于运动参数估计的SAR成像.电子学报,vol.29(12A),2001:1824-1828.
[63]周峰.机载合成孔径雷达基于数据的运动误差分析及补偿.硕士学位论文,西安:西安电子科技大学,2005.
[64]黄源宝,保铮,周峰.一种新的机载条带式SAR沿航向运动补偿方法.电子学报,vol.32(3),2005:459-462.
[65]周峰,邢孟道,保铮.一种无人机机载SAR运动补偿的方法.电子学报,vol.34(6),2006:1002-1007.
[66]保铮,邢孟道,SE彤.雷达成像技术.北京:电子工业出版社,2004.
[67]朱国富.UWB-SAR系统试验与性能评估技术研究.博士学位论文,长沙:国防科技大学,2001.
[68]董臻.UWB.SAR信息处理中的若干问题研究.博士学位论文,长沙:国防科技大学,2001.
[69]郭微光.机载超宽带合成孔径运动补偿技术研究.博士学位论文,长沙:国防科技大学,2003.
[70]赖涛.机载超宽带合成孔径雷达子孔径运动补偿方法研究.硕士学位论文,长沙:国防科技大学,2004.
[71]安道详.基于实测数据的UWB SAR图像自聚焦算法研究.硕士学位论文,长沙:国防科技大学,2006.
[72]王亮.机载超宽带合成孔径雷达实测数据成像处理技术研究.博士学位论文,长沙:国防科技大学,2007年.
[73]张澄波.综合孔径雷达原理、系统分析与应用.北京:科学出版社,1989.
[74]刘永坦.雷达成像技术.哈尔滨:哈尔滨工业大学出版社,1999.
[75]A.Potsis,A.Reigber,J.Mittermayer,etal.Improving the Focusing Properties of SAR Processors for Wide-band and Wide-beam Low Frequency Imaging.IGARSS'01,Sydney,,2001:3047-3049.
[76]A.Reigber,A.Potsis,E.Alivizatos,etal.Wavenumber domain SAR focusing with integrated motion compensation.Proceedings of IGARSS'2003,Joulouse,France,2003:1465-1467.
[77]E.Alivizatos,A.Potsis,A.Moreira,etal.SAR processing with motion compensation using the extended wavenumber algorithm.Proceedings of EUSAR' 2004,Ulm,Germany,May,2004:157-160.
[78]S.N.Madsen,H.A.Zebber,J.Martin.Topographic mapping using radar interferometry:processing and techniques.IEEE Trans.on G.R.S.,Vol.31(1),1993:246-256.
[79]C.Cafforio,C.Prati,F.Rocca.SAR data focusing using seismic migration techniques.IEEE Trans.On G.R.S.,Vol.28(24):627-640.
[80]Richard Bamler.A Comparison of Range-Doppler and Wave-number Domain SAR Focusing Algorithms[J].IEEE Trans.on GRS,Vol.30,July 1992:706-713.
[81]R.K.Raney,H.Runge,R.BAMLE,etal.Precision SAR processing using chirp scaling.IEEE Trans.On G.R.S.,Vol.32(4),1994:786-798.
[82]A.Moreira,J.Mittermayer,R.Scheiber.Extended Chirp Scaling Algorithm for Air- and Spaceborne SAR Data Processing in Stripmap and ScanSAR Imaging Modes.IEEE Trans.On G.R.S,Vol.34(5),1996:1123-1136.
[83]常文革.超宽带合成孔径雷达运动补偿精度分析.电子学报,vol.30(12),2002:1748-1751.
[84]董绪荣,张守信,华仲春.GPS/INS组合导航定位及其应用.长沙:国防科技大 学出版社,1998.
[85]陈哲.捷联惯导系统原理.北京:宇航出版社.1986.
[86]Elliott D.Kalplan著,丘致和,王万义译.GPS原理与应用.北京:电子工业出版社,2001.
[87]叶少华,周荫清.用真实IMU/GPS数据进行机载SAR运动补偿处理.北京航空航天大学学报,vol.31(10),2005:1063-1065.
[88]王雨.机抖激光陀螺捷联惯导系统的初步探索.博士学位论文,长沙:国防科技大学工学,2005.
[89]David R.Kirk,R.Paul Mloney,Mark E.Davis.Impact of platform motion on wide-angle synthetic aperture radar image quality.Proc.of the 1999international radar Conf.,Boston,USA,April,1999:41-46.
[90]B.D.Steinberg.Experimental localized radar cross section of aircraft.Proc.of IEEE,Vol.77(5),1989:663-669.
[91]黄源宝,郑义明.基于多特显点综合的SAR/ISAR自聚焦.西安电子科技大学学报,vol.28(1),2001:105-109.
[92]秦永元,张洪钺,汪叔华.卡尔曼滤波与组合导航原理.西安:西北工业大学出版社,1998.
[931 http://www.unistrong.com
[94]胡小平.自主导航理论与应用.长沙:国防科技大学出版社,2002.
[95]王建,王亮,薛国义等.适合UWB SAR的改进Map Drift自聚焦算法.2005年中国合成孔径雷达会议论文集,北京电子工业出版社,2006:261-265.
[96]吴简彤,王利存等.GPS误差模型参数估计的Hopfield神经网络方法.中国惯性技术学报,vol.6(4),1998:24-27.
[97]Zhangjingwei,Songming.A new method to abstract the noise model in INS-GNS integrated navigation system.Proc.of 2001 CIE international conference on radar,Xi'an,China,2001:1169-1172.
[98]张煜烽.捷联惯导/GPS误差控制技术究.博士学位论文,北京:北京理工大学,2001.
[99]房普堪,陈建文,楼生强.现代数字信号处理.北京:电子工业出版社,2004.
[100]F.Berizzi,G.Corsini,M.Dinani,M.Veltroni.Autofocus of wide azimuth angle SAR images by contrast optimization.IGARSS'96,IEEE Geoscienee and Remote Sensing Symposium,1996:1230-1232.
[10]]刘月花,荆麟角.对比度最优自聚焦算法.电子信息学报,vol.25(1),2003:24-30.
[102]D.F.Shanno,K.H.Phua.Minimization of unconstrained multivariate functions.ACM Trans.On mathematical software,No.6,1980:618-622.
[103]粟塔山,彭维杰,周作益等.最优化计算原理与算法程序设计.长沙:国防科技大学出版社,2001.
[104]雷万明,胡学成.基于回波数据的高分辨率机载SAR运动补偿.电子信息学报,Vol.26(12),2004:1908-1914.
[105]武昕伟,朱兆达.利用对比度最大化实现SAR图像自聚焦.现代雷达,Vol.24(3),2002:20-22.
[106]康雪艳,杨汝良.对比度最优与子孔径相关自聚焦算法的比较.测试技术学报.vol.17(1),2003:19-24.
[107]J.S.Betes.The phase gradient autofocus algorithm with range dependent stripmap SAR.Master's thesis,Brigham Young University,Provo,UT,1998.
[108]Dao.Xang AN,X.T.Huang,L.Wang.Contrast Optimizized PGA algorithm for P-band UWB SAR.Proc.Of 2006 CIE international Conf.on radar,ShangHai,China,2006:171-174.
[109]沈永欢,梁在中,许履瑚等.实用数学手册.北京:科学出版社,1999.
[110]Thomas A.Kennedy.A technique for specifying navigation system performance requirements in SAR motion compensation applications.IEEE PLANS' 90,1990:118-126.
[111]王建.结合MD和特选点的运动补偿.国防科技大学电子工程学院UWB 课题组内部学术交流报告,2006.
[112]龙方,刘湘斌.无人机载合成孔径雷达的发展现状与趋势.电子对抗,No.2,2004:37-40.
[113]J.Meyer-Hillber,C.Neumann.Low-cost one-axis accelerometers in line of sight for Image Focusing in Mini SAR systems.Proceedings of EUSAR'2004,Ulm,Germany,May,2004.
[114]J.F.M.Lorga,W.V.Rossum and E.V.Halsema,etal.The Development of a SAR dedicated navigation system:from scratch to the first test flight.IEEE PLANS'04,2004:249-258.
[115]K.Wheeler,S.Hensley,Yunlin Lou,etal.An L-band SAR for repeat pass deformation measurements on a UAV platform.Proceedings of 2004 IEEE conference,Philadelphia,Pa,USA,2004:317-322.
[116]S.Hensley,Y.L.Lou,P.Rosen,etal.An L-band SAR for repeat pass deformation measurements on a UAV platform.2end AIAA "Unmanned Unlimited"systems,technology,and operations,Sandigo,California,USA,Sep.,2003:1-10.
[117]D.J.DiFilippo,G.E.Haslm,D.William,etal.Evaluation of a Kalman Filter for SAR Motion Compensation.IEEE PLANS'88,1988:259-268.
[118]R.Mahony,T.Hamed,J.M.Pflimlin.Complementary filter design on the special orthogonal group SO(3).Proc.of the 44~(th) IEEE conference on decision and control,Seville,Spain,Dec.,2005:1477-1484.
[119]A.J.Baerveldt,R.Klang.A Low-cost and Low-weight attitude Estimation System for an Autonomous Helicopter.IEEE INES'97,1997:391-395.