【作者】 李廷军；

【导师】 周正欧；

【作者基本信息】 电子科技大学 ， 信号与信息处理， 2009， 博士

【摘要】 探地雷达(Ground Penetrating Radar，GPR)是一种探测隐蔽目标的有效手段，在国内外已经得到非常广泛的应用。探地雷达也一直是国际学术的研究热点之一，并且已成为遥感技术的重要分支。探地雷达具有探测速度快、探测过程连续、分辨率高、操作方便灵活等优越性，在国防、反恐、城市建设、公路、铁路、桥梁、隧道、矿山、地质、考古等许多领域都表现出强劲的生命力和广阔的应用前景。探地雷达是一个非常复杂的系统，其研究远不及探空雷达的研究成熟。特别是浅地层探地雷达，采用了超宽带技术以满足分辨率的高要求，对探地雷达系统的天线、信号源、数据采集和信号处理都有了新的更高要求。同时随着探地雷达应用的深入发展，探地雷达的应用环境越来越复杂和恶劣。如在城市中越来越多的射频干扰、越来越复杂的杂波信号，探地雷达天线离地较远时必须考虑的空气-土壤双层介质等，这些情况对探地雷达的信号处理和系统优化都提出了更高的要求。此时的信号处理技术已不只是探地雷达数据采集后的处理，而应从系统角度对探地雷达系统结构提出改进，使探地雷达整体性能达到最优。本论文的主要工作及创新点如下：1．针对冲激脉冲探地雷达提出随机等效采样抑制射频干扰的方法。对三种信息数据采集方式(实时采样、周期等效采样和随机等效采样)下，射频干扰经均值滤波后的特征进行了分析。分析指出采用随机等效采样，在无失真地获取目标回波的情况下，能将射频干扰变为零均值随机信号，进而用经典的均值滤波方法进行干扰抑制。仿真和实验结果验证了分析的正确性和本方法抑制射频干扰的有效性。2．针对步进频率探地雷达提出随机相位编码抑制射频干扰的方法。使用随机相位编码技术在不影响目标回波的情况下，可将步进频率探地雷达中的射频干扰变为零均值随机信号进行抑制。分析表明使用随机相位编码技术使步进频率探地雷达具有噪声雷达的射频干扰抑制能力，同时保留了步进频率良好的主旁瓣比性能和利用FFT进行快速信号处理的优点。蒙特卡洛仿真结果验证了本文分析的正确性和本方法抑制射频干扰的有效性。3．根据探地雷达数据记录B-scan中目标回波与杂波的频谱特性和对称特性差异，分别提出二维频域带通滤波和对称滤波抑制探地雷达杂波的方法。二维频域带通滤波能有效抑制天线直耦杂波、地面杂波及雷达设备抖动引入的噪声成分。对称滤波能有效抑制传统方法较难抑制的起伏地面杂波、地下介质杂波和无关目标回波。实测数据处理结果显示所提方法具有优良性能。4．提出一种快速有效的波速估计方法。本文根据B-scan中点目标形成双曲线的机理，利用双曲线的对称特性及目标回波主峰跟踪法等，提取双曲线及顶点。分析了双曲线顶点区域对波速估计的误差影响，提出加权估计波速的方法，并给出相应的估计方差。实测数据处理结果显示本方法具有良好效果。5．提出一种横向等效变波速合成孔径成像方法。在复杂的探地雷达应用环境中，目标回波信号常常偏离标准双曲线关系式，使用传统的恒定波速成像效果难以达到最优。本文利用目标回波在B-scan中形成的曲线信号，快速估计横向等效波速以修正目标回波延时的波动，采用变波速频率-波数域(F-K)偏移算法进行精确成像。实测数据处理结果显示本方法性能优于恒定波速成像。更多还原

【Abstract】 Ground Penetrating Radar (GPR) is an effective tool to detect the buried targets, and it’s application is worldwide in many areas. The study of the GPR is one of the international researching hotspots and has become an important branch of the remote sensing technology. Because the GPR can detect the target rapidly, continuously and conveniently with high resolution, it has a broad prospect of application in many areas, such as national defense, anti-terrorism, civil engineering, construction of highway, railway, bridge, tunnel, prospecting, geologic studies, and archaeological studies.GPR is a very complex system, and its study is far from maturity as compared to that of traditional radar. Especially when GPR is used to detect the shallow buried target with high resolution, it must adopt the ultra wideband (UWB) technology and faces a series of new challenges to antenna design, signal modulation, signal sampling and processing. As the application of GPR goes wider and deeper, its working environment becomes worse and more complex, such as the increased radio frequency interference in the city, the more complex clutter and the influence of the half-space between the air and soil. All these require more consideration on both signal processing and system design. In order to optimize the whole performance of GPR, the signal processing is no longer a simple processing of the echo data of radar signal, it also requires the improvement of the radar system structure.The contents and innovations of this dissertation are as follows:1. A method of radio frequency interference (RFI) suppressing is proposed by using random equivalent time sampling in the impulse GPR. The property of the RFI after average filter is compared among real time sampling mode, periodic equivalent time sampling mode and random equivalent time sampling mode. The analysis indicates that the RFI can be transformed into zero-mean random signal by random equivalent time sampling without effect on the object’s information and it can be suppressed easily by a classical average filter. Experimental results conform to the theoretic analysis and indicate the proposed method is effective.2. A RFI suppression method is proposed by using random phase codes in the stepped-frequency GPR. The random phase-coded method transforms the RFI into zero-mean random signal without effect on the object’s information and makes the RFI be suppressed easily. It makes the stepped-frequency radar have the same Anti-RFI performance as that of the noise radar and reserve the low sidelobe performance. Monte Carlo simulations conform to the theoretic analysis and indicate the proposed method is effective.3. A novel clutter reduction method is proposed by using two-dimensional band-pass filter in frequency domain and symmetry filter based on the symmetry difference between the target reflection and the clutter in B-scan. The two-dimensional band-pass filter can effectively reduce the antenna coupling clutter, the ground clutter and the radar vibration noise. The symmetry filter can reduce the undulated ground clutter, soil roughness reflection and reflection signals from external anomalies. Experimental results confirm the effectiveness of the method.4. A fast method of propagation velocity estimation is proposed. The hyperbolic signatures and the apex in B-scan are extracted based on peak tracing and the symmetry of hyperbola. Moreover, according to the effect to velocity estimation in the apex section of the hyperbola, a weighted method of velocity estimation is proposed. The method is evaluated to be effective by using experimental results.5. A method of equivalent lateral velocity synthetic aperture imaging (SAI) is proposed. The object signal often is departure from the standard hyperbola in practice. The traditional algorithm using constant velocity can hardly amend the different. The proposed method amends it by using the equivalent lateral velocity which can be estimated quickly by using the hyperbolic signatures of echo in B-scan. The precise SAR imaging can be achieved by lateral variable velocity F-K migration. The experimental results demonstrate that the proposed method is more effective than constant velocity migration.更多还原