摘要
线性调频连续波（Linear Frequency Modulated Continuous Wave, LFMCW）雷达具有距离分辨率高、发射功率低、接收灵敏度高、结构简单以及盲区距离极小的优点，因此，基于线性调频连续波的探地雷达是目前研究的热点之一。线性调频连续波探空雷达的理论相对成熟，在军事上也有较广泛的应用，但地层介质与空气介质有着较大差异，其层状介质和孤立介质形态各异，导电性能也不相同，即使是同一介质的电性分布也不均匀，造成电磁波在地下介质中的传播要复杂得多，因而在研制调频连续波的探地雷达时，不能完全照搬调频连续波探空雷达的理论。因此，本文首先从线性调频连续波在地层介质中的传播特性出发，对调频连续波探地雷达的发射功率、探测能力和探测精度间的关系进行了仿真研究；其次从硬件实现的角度，对调频连续波探地雷达的发射波形、回波信号进行了研究，给出了调频连续波探地雷达的系统框图，并用硬件加以实现，研制出了样机；最后对调频连续波探地雷达的高分辨率处理方法和成像技术进行了研究；并通过试验测试证明调频连续波探地雷达的优点和本文所提出的处理方法和成像技术的有效性。论文取得的主要成果及创新点有：
1.从分层波阻抗与反射系数关系式出发，推导了不同介电常数与电磁谐波相位吸收和幅度吸收的关系式和特定吸收条件下传播系数的表达式，计算了浅地表探测典型地质体的电磁波传播参数；
2.从探地雷达信号传递函数推导出步进频率增量与最大不模糊距离的关系式；以三角波的线性调频形式为例，讨论了差拍信号的表达式，与距离信息提取的处理方法组合，形成了线性调频连续波探地雷达信号处理体系。
3.从步进调频连续波的信号传递过程出发，推导了宽频带合成的时域算法、频域算法和合成距离包络三种算法公式，并用三层模型和五层模型进行了验证和对比，得出：从合成的效果上看，合成距离包络法信息损失较大，对弱信号识别效果最差，时域合成和频域合成的效果相对较好；从波速的影响方面来说，这三种方法对速度都很敏感，合成距离包络法尤其严重，对波速需要进行较精确的估计；从计算量方面看，合成距离包络法计算量最少，时域算法计算量最大。另外，选取不同的介电常数用三层模型研究了介电常数和分辨能力间的关系。
4.从波速宽度、近景场、远边缘、与测线垂直距离等因素出发，研究了距离徒动和距离徒动差与距离分辨率和横向分辨率间的关系，提出了正侧视距离徒动校正算法、斜侧视距离徒动校正方法，并根据综合分辨率要求，分四种情况对距离徒动对包络时延的影响进行了校正讨论；结合合成孔径成像理论提出了基于Stolt迁移的探地雷达合成孔径成像改进方法。
5.采用DDS器件，设计了发射信号产生电路，根据成像算法，分析了系统信号处理的运算量，提出了基于高性能FPGA技术和DSP技术的实时信号处理技术，设计了信号处理硬件实施框图和信号处理板卡，研制了一套原理样机，并进行了现场试验。
Linear Frequency Modulated Continuous Wave（LFMCW） Ground Penetrating Radarhas advantages of high range resolution, low transmit power, high receiver sensitivity, simplestructure and minimal blind spot distance. So, LFMCW ground penetrating radar has becomea research hotspot. The theory of linear frequency modulated continuous wave air radar isvrelatively mature, and some air radars based on LFMCW have been used to detect militarytargets. Because of big difference between stratum media and air media, varies shapes and thedifferent electrical conductivity of layered medium and isolated medium, the theory ofelectromagnetic wave propagation in the air is more complicate than that in the stratum media.Therefore, in the development of a LFMCW ground penetrating radar, the theory of LFMCWair radar can't be copied. This paper began with the propagation characteristics of linearfrequency modulation continuous wave in the stratum medium. Firstly, the relations amongthe transmiting power, the detecting distance and the detecting accuracy were studied.Secondly, the principle prototype of LFMCW ground penetrating radar was designed afteranalyzing the transmitted waveform and the echo signal. Thirdly, the high resolution processmethod and imaging technology of LFMCW ground penetrating radar were launched adetailed studied. Finally, the test proved that LFMCW ground penetrating radar has thoseadvantageous and the method and the technology are effective. The innovative achievementsare follows:
1. In according to the formulation of stratified impedance and reflecting coefficient,introduces the formula among different dielectric constant, electromagnetic harmonic phaseabsorption and magnitude absorption derivate. Electromagnetic wave propagation parametersof the typical geological bodies under shallow surface were calculated.
2. Beginning with the transfer equation of ground-penetrating radar signal this paperdeducted the relationship formulation between stepping frequency increment and themaximum unambiguous range. Taking the triangular wave form of linear frequencymodulation as the transmission wave, this paper formulated the expression of the beat signal.This formulation and the distance information formed a signal processing system of LFMWground penetrating radar.
3. Broadband synthetic time-domain algorithm, frequency domain algorithms, syntheticdistance algorithms were derived from the signal transfer process of the stepping frequencymodulated continuous wave. These algorithms are verified and compared in the three-layermodel and the five-layer model. The following conclusions can be made: As far as syntheticeffect is concerned, the synthetic distance envelope algorithm is worst because of energyleakage. But time-domain synthesis and frequency-domain synthesis is relatively good. As faras the effect of wave velocity is concerned, the three algorithms are all sensitive to velocity.the synthetic distance envelope algorithm is particularly serious, and it needs extracalculations. As far as amount of computation is concerned, the time-domain algorithms needlargest amount of the computation. Furthermore, the relationship between the dielectricconstant and the ability to distinguish were studied by changing dielectric constant ofthree-layer model.
4. Taking the width, the close-range field and the far edge, the vertical distance of thesurvey line of wave velocity into account, the relationship between the range migration, thedistance migration and distance resolution and lateral resolution were studied. Side lookingrange migration correction algorithm and oblique lateral view distance dynamic correctionmethod were put forward. Then in according to requirements of total resolution, the delaytime of the synthetic distance envelope algorithm were discussed in four cases. Finally, asynthetic imaging algorithm based on stolt migration was put forward.
5. A DDS device was employed to produce transmission waveform, and the amount ofcomputation was analyzed according to imaging algorithms. Then the sign processing systemwas designed by employing FPGA and DSP technology. Finally, a developed principleprototype was used to test.
引文
[1]陈义群,肖柏勋.论探地雷达现状与发展[J].工程地球物理学报.2005(2):149-155.
[2]肖志俊.多小波变换对探地雷达信号的去噪处理及工程应用研究[D].重庆大学,2006.
[3]左峥嵘.国外探地雷达技术新进展[J].地球科学,1993(03):69-76+122.
[4]白冰,周健.探地雷达测试技术发展概况及其应用现状[J].岩石力学与工程学报,2001(04):527-531.
[5]史凌峰.探地雷达检测中的关键技术研究[D].西安电子科技大学,2008.
[6]张安学,蒋延生,汪文秉.探地雷达频率波数域速度估计和成像方法的实验研究[J].电子学报,2001(03):315-317.
[7]游日,董茂干.探地雷达的发展与应用[J].筑路机械与施工机械化,2010(05):20-24.
[8]纪丽静,施养杭.探地雷达在工程检测中的应用与发展[J].无损检测,2010(03):201-217.
[9]董茂干,陆俊.探地雷达的工作原理及其在公路检测中的应用[J].筑路机械与施工机械化,2010(05):28-32.
[10]蔡毅.探地雷达检测的原理方法及在水利工程中的应用[J].河南水利与南水北调,2010,(08):72-73.
[11]谢昭晖,李金铭.我国探地雷达的应用现状及展望[J].工程勘察,2007,(11):71-75.
[12]李海华.探地雷达体制综述[J].测试技术学报,2003,17(01):25-28.
[13]赵燕峰,娄海.道路探地雷达在高速公路检测技术中的应用[J].河南师范大学学报,2004,32(2):98-100.
[14]李金铭,罗延钟.电法勘探新进展[M].北京:石油工业出版社,1996.119-130.
[15]牛一雄,苑守成,武建章.地质雷达在公路建设中的应用[J].物探与化探,1996,20(2):116-123.
[16]沈飚,石庆华,孙忠良.道路铺砌层中探地雷达波传播的正演模拟及应用[J].石油地球物理勘探,1997,(1):135-140.
[17]李成香,强建科,王建军.地质雷达在公路裂缝检测中的应用[J].工程地球物理学报,2004,(6):282-286.
[18]韦宏鹄,高文,吕继东.地质雷达技术在软地基及复合地基检测中的应用.中国地质学会工程地质专业委员会.第五届全国工程地质大会文集.北京:地震出版社,1996.597-600.
[19]隋景峰.隧道衬砌质量检测新技术[J].工程勘察,1998,(2):65-67.
[20]刘敦文,黄仁东.应用探地雷达技术检测衬砌质量[J].物探与化探,2001,25(6):469-473.
[21]何继善,柳建新.隧道超前探测方法技术与应用研究[J].工程地球物理学报,2004(8):293-298.
[22]师丽萍.探地雷达技术应用综述[J].国土资源情报，2007(5):50-52.
[23]李大心.探地雷达方法与应用[M].北京：地质出版社，1994.
[24]杨顺安,韦宏鹄,刘国伟.探地雷达在岩土工程中的应用[J].地质科技情报,1998,17(3):95-100.
[25]葛双成,江影,颜学军.综合物探技术在堤坝隐患探测中的应用[J].地球物理学进展,2006,21(1):263-272.
[26]刘传孝,杨永杰,蒋金泉.探地雷达技术在采矿工程中的应用[J].岩土工程学报,1998,20(6):99-101.
[27]刘传孝,杨永杰,蒋金泉.煤矿井下巷道围岩松动圈的雷达探测研究[J].山东矿业学院学报,1997,16(专辑):48-50.
[28]刘传孝,杨永杰,蒋金泉.探地雷达探测煤厚的应用[J].阜新矿业学院学报,1997,16(增):261-262.
[29]杨永杰,刘传孝,蒋金泉等.地质雷达及其在煤矿中的应用[J].中国煤炭,1996,(5):33-36.
[30]李建斌,陈自力,江涛.频率步进探地雷达的SAR成像处理方法[J].火控雷达技术.2009,38(4):28-33.
[31]宋雷,黄家会.钻孔地质雷达工作原理及应用[J].物探与化探,1999,24(6):454-458.
[32]曹忠权,谢平,金花.星载合成孔径雷达遥感技术的地学应用[J].地球物理学进展,2004,19(2):291-295.
[33]刘四新,曾昭发,徐波.利用钻孔雷达探测地下含水裂缝[J].地球物理学进展,2006,21(2):620-624.
[34]李嘉,郭成超,王复明等.探地雷达应用概述[J].地球物理学进展，2007,22(2):629-637.
[35]王小龙. LFMCW随钻雷达信号模拟分析[J].煤田地质与勘探.2012,(40):85-87.
[36]刘喆,杨建宇. LFMCW雷达运动目标高精度检测方法[J].电子信息对抗技术,2007,(01):33-40.
[37]方广有,佐藤源之.频率步进探地雷达及其在地雷探测中的应用[J].电子学报,2005,(03):436-439.
[38]张军,毛二可.线性调频连续波SAR成像处理研究[J].现代雷达,2005,(04):42-45.
[39]江志红,赵懿,皇甫堪,万建伟,程翥.调频连续波SAR的研究进展[J].现代雷达,2008,(02):20-24.
[40]王平.基于距离—多普勒算法的调频连续波SAR成像研究[D].南京理工大学,2008.
[41]肖汉. LFMCW雷达信号处理算法研究与实现[D].电子科技大学,2005.
[42]宋景唯.线性度对线性调频雷达距离分辨力的影响[J].电子科技大学学报,1992,(02):121-126.
[43]张永强. LFMCW高线性度信号源技术研究[D].电子科技大学,2001.
[44]杨建宇. LFMCW雷达信号模糊函数分析[J].信号处理,2002,18(1):39-42.
[45]包敏.线性调频连续波雷达信号处理技术研究与硬件实现[D].西安电子科技大学,2009.
[46]刘国岁,孙光明,顾红等.连续波雷达及其信号处理技术[J].现代雷达,1995,(6):20-36.
[47]沈新江,李世翔.连续波雷达中频对消技术研究[J].上海航天，1998,(02):37-40.
[48]陈淞.线性调频雷达信号特征提取方法研究[D].哈尔滨工业大学,2011.
[49]张涛,马长征,张群,张守宏.基于线性调频步进信号的ISAR成像技术研究[J].电子与信息学报,2001,(03):268-274.
[50]刘欢.频率步进雷达信号处理与系统仿真实现[D].国防科学技术大学,2008.
[51]彭岁阳,张军,沈振康.随机频率步进雷达成像分析[J].国防科技大学学报,2011,(01)：59-64.
[52]李磊,任丽香,毛二可,何佩琨,赵保军.频率步进信号宽带模糊函数及其应用[J].北京理工大学学报,2011,(07):844-848.
[53]朱永锋.频率步进雷达运动目标成像的理论与方法研究[D].国防科学技术大学,2009.
[54]龙腾,李眈,吴琼之.频率步进雷达参数设计与目标抽取算法[J].系统工程与电子技术,2001,23(6):26-31.
[55] Skolnik M I. Introduction to Radar Systems(2ed). McGraw-Hil l,1980.
[56] Wehner D R. High Resolution Radar(2ed). Art ech House,1995.
[57]徐晋.频率步进技术研究及其在战术雷达中的应用分析[D].电子科技大学,2007.
[58]王绍江.频率步进雷达导引头信号处理系统研究[D].南京理工大学,2007.
[59]刘峥,刘宏伟,张守宏.步进频率信号分析[J].西安电子科技大学学报,1999,(01)：71-74.
[60]李眈,龙腾.步进频率雷达目标去冗余算法[J].电子学报,2000,(06):60-67.
[61]张焕颖,张守宏,李强.调频步进雷达目标抽取算法及系统参数设计[J].电子学报,2007,(06):1153-1158.
[62]毛二可,龙腾,韩月秋.频率步进雷达数字信号处理[J].航空学报,2001,(S1):16-25.
[63]李星爽,何佩琨.频率步进雷达中波形分析法精确测距的研究[J].现代雷达,2005,(08):7-13.
[64]朱永锋,左衍琴,付强.频率步进雷达高速机动目标运动补偿新方法[A].第十四届全国信号处理学术年会(CCSP-2009)论文集[C],2009.
[65]张学磊,肖健华.步进频率的实现及其在SAR中的应用[A].中国电子学会第十五届信息论学术年会暨第一届全国网络编码学术年会论文集（上册）[C],2008.
[66]郭俊芳.调频步进雷达信号理论与应用研究[D].南京理工大学,2009.
[67]龙腾,毛二可，何佩琨.调频步进雷达信号分析与处理[J].电子学报,1998,(12):84-88.
[68]蒋楠稚,王毛路,李少洪,毛士艺.频率步进脉冲距离高分辨一维成像速度补偿分析[J].电子科学学刊,1999,(05):665-670.
[69]陈行勇,魏玺章,黎湘等.调频步进雷达扩展目标高分辨距离像分析[J].电子学报,2005,(9):1599-1602.
[70]雷文,龙腾,韩月秋.调频步进雷达运动目标信号处理的新方法[J].电子学报,2000,(12):34-37.
[71]孔祥春.探地雷达的基本理论[A].地质雷达技术及其在工程检测中的应用学术研讨会[C],2005.
[72]苗书立. LFMCW雷达信号处理方法及实现研究[D].电子科技大学,2004.
[73]黄伟.步进频率连续波探地雷达耦合抑制技术研究[D].国防科学技术大学,2010.
[74]张广军,陆珉,黄春琳.基于高性能DDS芯片AD9959的超宽带步进频率探地雷达设计[J].电子工程师,2008,34(4):10-12.
[75]邓怀东.探地雷达信号处理机的设计与实现[D].西安电子科技大学,2004.
[76]李明.雷达目标识别技术研究进展及发展趋势分析[J].现代雷达,2010,32(10):1-8.
[77]王菁.光学区雷达目标散射中心提取及其应用研究[D].南京航空航天大学,2010.
[78]王晓丹,王积勤.雷达目标识别技术综述[J].现代雷达,2003,25(5):22-26.
[79] Ratches J A. Aided and automatic target recognition based upon sensory inputs fromimage forming systems, IEEE Trans. PAMI,1997,119(9):1004-1009.
[80]岳素林.基于高分辨距离像的雷达目标识别方法研究[D].西安电子科技大学,2005.
[81]李盾,肖顺平,王雪松.基于回波趋向伪本征极化特性的目标识别研究[J].电子学报,1999,27(9):1-4.
[82]黄培康.雷达目标特征信号[M].北京:北京宇航出版社,1993.
[83]田海南,贾维敏,杨慧杰.天线罩去极化效应及其补偿[J].通信技术,2011,44(3):18-20.
[84]杜玩文.空中雷达目标识别技术研究[D].南京理工大学,2009.
[85]肖顺平,王雪松,郭桂荣.基于极化域能量谱的飞机目标识别[J].1998,19(3):24-28.
[86]文树梁.基于双距离像的雷达目标识别技术[J].现代雷达,1996,18(1):15-21.
[87]裴炳南.高分辨率雷达自动目标识别方法研究[D].西安电子科技大学,2002.
[88] Chamberlain N F, Walton E K, Garber F D. Radar Target Identification of Aircraft UsingPolarization-Diverse Features. IEEE Trans. on AES,1991,27(1):58-67.
[89] M. Jankiraman. Design of Multi-Frequency CW Radars [M]. U.S.A: SciTech PublishingInc,2007.
[90] Pace, P. E. Detecting and Classifying Low Probability of Intercept Radar [M], ArtechHouse, Norwood, MA,2004.
[91] Skolnik, M. I. Introduction to Radar Systems [M],3rd EDN., McGraw-Hill, Boston, MA,2001.
[92]刘喆,杨建宇. LFMCW雷达运动目标高精度检测方法[J].电子信息对抗技术,2007,22（1）:33-35.
[93]保铮,邢孟道等.雷达成像技术[M].电子工业出版社,2005.
[94]高昭昭.高分辨ISAR成像新技术研究[D].西安电子科技大学,2009.
[95]刘晓宏.高距离分辨成像雷达的信号分析与处理[D].西安电子科技大学,2006.
[96]熊君君,王贞松,姚建平.星载SAR实时成像处理器的FPGA实现[J].电子学报,2005,33（6）:1070-1072.
[97]吴井红.远程战场侦察雷达SAR实时信号处理机研制[D].电子科技大学,1995.
[98] Altera Corporation. Stratix III Device Handbook, Volume1. November2006.
[99] Altera Corporation. Stratix II Device Handbook, Volume1. November2006.
[100] Altera Corporation. Stratix II Device Handbook, Volume2. November2006.
[101] Altera Corporation. FFT MegaCore Function User Guide, Version7.1. May2007.
[102] Altera Corporation. FFT MegaCore Function Release Note, Version7.1. May2007.
[103] Synplicity, Inc. Synplicity FPGA Synthesis User Guide, Version8.6.2. December2005.
[104] Synplicity, Inc. Synplicity FPGA Synthesis Reference Manual, Version8.6.2. December2005.
[105] Synplicity, Inc. Release Note for Synplicity FPGA Products: Synplify, Synplify pro, andSynplify Premier. Version8.6.2, December2005.
[106] Wai Chi Fang, Le C. Taft S. On-board fault-tolerant SAR processor for space borneimaging radar systems. IEEE International Symposium on Circuits and Systems (ISCAS)(IEEE Cat. No.05CH37618),2005, pt1,420-3Vol.1.
[107]吴秉横,纪奕才,方广有.一种新型探地雷达天线的设计分析[J].电子与信息学报,2009,31(6):1487-1489.
[108] Olhoeft G R, Capron D E; Buried Object Detection with Ground Penetrating Radar,Proc. of5th Internet of Unexploded Ordnance Detection and Range Remediation. Conf,1994:207-233.