【作者】 周峰；

【导师】 保铮；

【作者基本信息】 西安电子科技大学 ， 信号与信息处理， 2007， 博士

【摘要】 经过五十多年的发展,合成孔径雷达(SAR)成像的理论和基本算法已经逐渐完善。但是随着合成孔径雷达在军事和民用方面日益广泛地应用,SAR成像将面临许多新的问题和挑战。雷达平台的运动误差将造成SAR成像的困难,并导致SAR图像散焦,特别在机载SAR惯导有限的情况下,研究基于回波数据的运动补偿对国内的机载SAR成像有着重要的意义。同时,由于窄带干扰的存在会明显地降低SAR图像的信干比,研究有效的窄带干扰检测与抑制算法可以显著地提高SAR图像的质量。此外,场景中的运动目标会在SAR图像中散焦或移位,如何对地面运动目标进行检测和精确成像是SAR领域的研究热点。本文以提高SAR图像质量为宗旨,紧密结合工程应用,利用概念分析、理论推导和数据验证等手段对机载SAR运动补偿、窄带干扰抑制和SAR地面运动目标成像三个方面进行深入地研究。现将本文的主要工作概括如下:1、详细地阐述了距离-多普勒(R-D)和线频变标(CS)两种有效的成像算法。该R-D算法为时域距离走动校正频域弯曲校正的R-D算法,它不仅适应于正侧视SAR成像,而且适应于大斜视SAR成像。而CS算法则可应用于高分辨率正侧视或小斜视SAR成像。2、系统地研究了机载SAR的运动补偿。从SAR成像几何模型和经验公式出发,分析了机载SAR系统对运动误差的控制要求。在SAR系统运动误差分析的基础上提出了一种有效的机载SAR运动补偿方案,即利用两维天线伺服系统来补偿载机的转动误差,从回波数据的瞬时多普勒调频率中估计得到平动误差,并且利用其对数据包络和相位的校正来实现平动误差补偿。3、提出一种适用于大斜视SAR的运动补偿方法。该方法从大斜视SAR成像的几何模型出发,分析并推导了大斜视SAR的运动误差与多普勒参数的关系。同时,利用瞬时多普勒调频率和部分载机惯导参数通过伪逆求解估计出运动误差的空间分量,然后根据所得到的运动误差对数据进行有效的运动补偿。4、系统地研究了SAR窄带干扰特性,提出基于特征子空间滤波的窄带干扰抑制方法。该方法属于非参数化方法,它在频域对窄带干扰进行简单的定性识别,在时域通过特征子空间分析把干扰数据和有用数据投影到不同子空间,并通过特征子空间滤波有效地抑制窄带干扰。5、提出基于改进的最小均方(ILMS)算法的参数化窄带干扰抑制方法。该方法通过Pisarenko谐波分析较精确地确定窄带干扰的频率,并利用分段LMS和插值处理估计出时变窄带干扰的复包络,然后通过干扰数据的时域相消和信号增益恢复完成对窄带干扰的抑制。6、系统地研究了单通道地面运动目标检测和成像。提出一种基于两视处理的单通道SAR运动目标检测和定位方法。该方法适用于低信杂比下具有径向速度的运动目标检测,根据地面运动目标相对于静止场景的多普勒谱偏移,把回波的多普勒谱分成对称两段分别成像,通过将两子视图像进行配准和非相干相消来抑制地杂波,提高对运动目标的检测能力。另外,在SAR图像中加窗取出运动目标的复信号并计算其多普勒谱相对于静止目标的平移量,通过该平移量可以实现对地面运动目标较准确的定位,并可进一步地降低虚警概率。7、提出一种适合高信杂比条件的地面运动目标参数估计和精确成像方法。此方法根据运动目标的回波包络和多普勒频谱的特性,利用广义Keystone变换校正回波数据的距离弯曲,然后估计回波包络的斜率并进行走动校正,再对运动目标的多普勒频谱进行分析得到运动目标的多普勒参数,进而对运动目标进行成像。同时,该方法利用地面运动目标的多普勒参数与运动参数的关系不仅可以估计出运动目标的速度分量,而且还能够估计运动目标的径向加速度。更多还原

【Abstract】 After fifty years’ development, the fundamentals and the key algorithms of synthetic aperture radar (SAR) imaging have been improved greatly. However, as SAR has been applied to military and civil fields extensively, this technique will face many new problems and challenges. For example, the motion error of Radar platform may add difficulty to SAR imaging and thus causes image defocusing, especially when the inertia navigation system (INS) of airborne SAR is limited. Therefore, the research on raw data based motion compensation is of great significance in domestic SAR imaging. On the other hand, the existence of narrow band interference (NBI) will decrease the signal-interference ratio dramatically, so research on the algorithm of estimating and prohibiting narrow band interference can increase SAR imaging quality effectively. In addition, the moving target in the scene may exhibit defocusing or shifting, so how to locate and image them accurately has become a hotspot in SAR research field. This dissertation represents detailed research on airborne SAR motion compensation, suppression of NBI and SAR ground moving target detection, based on conceptual analysis, theory derivation and data validation. The main contents are summarized as follows:1. Two valid algorithm, Range-Doppler (R-D) and chirp scaling (CS) algorithm are discussed in detail. The R-D algorithm compensates for the range curvature in Doppler domain while adjusts range walk in slow time domain. It can be applied not only to broadside SAR imaging, but also to high squint SAR imaging. The CS algorithm can be applied to broadside SAR and low squint SAR imaging with high resolution.2. The motion compensation of airborne SAR is researched systematically. Based on the geometric model and empirical formulas, this paper analyses the control requirements of SAR system on motion error and introduces a motion compensation method based on the measuring system. Then an effective airborne SAR motion compensation program is proposed according to the analysis of SAR system’s motion error. In this approach, the attitude errors are compensated through the two- dimensional antenna servo system and translational errors are estimated by the instantaneous Doppler chirp rate in the echo data. Then, the translational errors are compensated through envelope correction and phase correction.3. A motion compensation method applied to high squint SAR is proposed. Based on the established imaging geometry of high squint SAR, the relationship between motion compensation and Doppler parameters has been analyzed and deduced. Meanwhile, the components of motion errors are estimated with pseudo-inverse technique in virtue of instantaneous Doppler chirp rate and partial airborne INS parameters. Then effective motion compensation is implemented to raw data according to the acquired motion errors.4. Single channel ground moving target detection and imaging is investigated systematically. A new approach to ground moving target detection, based on two-look processing, is proposed for single channel SAR system. This approach can be applied to the detection of moving target with radial velocity under low signal-to-clutter ratio (SCR). In this approach, the Doppler spectra of echoes are separated into two parts and are focused separately to obtain two sub-images. Then by matching the two sub-images and implementing non-coherent cancellation, the ground clutters are suppressed and hence the moving target detection ability is increased, according to the Doppler spectra shifts of moving targets relative to that of a stationary scene. In addition, windows are added to SAR images to get complex signals of the moving target and to calculate the translational shifts of the Doppler spectra relative to that of the stationary scene. In this way, the ground moving target can be located precisely and the false warning probability can be decreased greatly.5. A method on ground moving target parameter estimation and precise imaging is proposed, which can be applied to high signal-to-clutter ratio. Based on the characteristics of envelopes and the Doppler frequency spectrum of the echoes, a new method is proposed. Firstly, a second-order generalized keystone formatting algorithm is used to compensate for the range curvature. Secondly, the estimated slope of the target echo’s envelope is used for range walk compensation. Thirdly, Doppler parameters of moving targets obtained via spectral analysis are used for the imaging and positioning of ground moving targets. Finally, motion parameters of moving targets can be estimated based on the relationship between Doppler and motion parameters.6. Analyzes the characteristics of the common Narrow Band Interference (NBI) systematically. A method which uses eigen-subspace based filtering on the echo data is proposed. It determines the nature of NBI in the frequency domain and implements adaptive NBI suppression in the temporal domain, which constructs interference subspace from the raw data and then subtracts the projected components of the original data onto the interference subspace. It is a nonparametric approach and is more robust than the conventional modeling based approaches. 7. A parameterized NBI Suppression method based on improved LMS algorithm is proposed. Firstly, the frequencies of NBI are obtained by Pisarenko harmonic analysis. Secondly, the complex envelopes of NBI are estimated by implementing the LMS algorithm segmentally and by applying data interpolation. Finally, the suppression of NBI is accomplished by time domain cancellation and signal gain recovery of the data.更多还原