【作者】 张伟；

【导师】 刘文波；

【作者基本信息】 南京航空航天大学 ， 测试计量技术及仪器， 2008， 硕士

【摘要】 合成孔径雷达(Synthetic Aperture Radar, SAR)凭其独特的优势在军事侦察和民用方面得到了广泛的应用,开展SAR图像的目标检测工作具有实际意义和应用前景。本文基于方向滤波技术、非抽样Contourlet变换(Nonsubsampled Contourlet Transform, NSCT)和扩展分形技术研究了SAR图像特定目标检测技术,并通过实验加以验证。提出一种基于NSCT域自适应收缩的SAR图像相干斑抑制算法,算法借助NSCT所具有的平移不变性、多方向性和多分辨性,同时结合Pizurica自适应收缩对系数的空间方向相关性及局部噪声进行度量并修正各高频子带系数。结果表明,该算法在有效滤波的同时能清晰地保持边缘等细节特征。提出一种基于方向滤波器的SAR图像直线目标检测算法,利用方向滤波器良好的方向选择性将直线目标分解到对应的方向子带中,在各方向子带中通过对直线平行边缘对的检测实现直线目标的检测。用实测SAR图像进行实验,获得了较好的检测效果。根据NSCT域目标点和背景点能量特征的不同分布,提出了一种基于NSCT域能量特征的SAR图像目标检测及目标方位角估计算法。利用目标点与背景点能量跨尺度传递的不同特性及其分布的方向特性,在原SAR图像的能量特征图和方向特征图中实现目标检测和目标方位角估计。实验证明,该算法在有效检测目标的同时能准确估计出目标的方位角范围。分析了扩展分形目标检测算法产生虚警的主要原因,利用目标区域像素点灰度一致性及与背景灰度差异性对原有算法进行改进,实验结果表明,改进的算法在特定尺寸目标检测的虚警数和品质因数性能指标上较原算法均有所改善。更多还原

【Abstract】 Synthetic Aperture Radar (SAR) has been widely used in both military reconnaissance and civil activity based on its unique advantages, so it’s meaningful and has application prospect to study target detection method of SAR images. In this dissertation, we detailedly analyze the special targets detection methods of SAR images based on directional filter, Nonsubsampled Contourlet Transform (NSCT) and extended fractal feature, and validate them by experiments.A new algorithm for SAR images speckle reduction is proposed based on adaptive shrinkage in NSCT Domain. The Nonsubsampled Contourlet coefficients of SAR images at high frequency subband are modified by the corresponding Pizurica adaptive shrinkage factors. The shrinkage factor takes into account not only the local noise measure, but also prior directional spatial consistency, and combines the shift-invariance, direction selectivity and multiresolution of the Nonsubsampled Contourlet transform. Experiments show that the filter algorithm can reduce speckle noise more effectively while preserving the edges of the SAR images.Based on directional selectivity of directional filter bank, an algorithm for straight line targets detection in SAR images is put forward. The straight line target can be detected by searching two parallel straight lines along its edges. Many real SAR images are used to illustrate our method, and the performance is satisfactory.A new method of detecting target and estimating target azimuth in SAR images is proposed based on NSCT energy feature. The technique mainly focuses on the different NSCT energy distribution feature of the background and the targets. Considering the cross-scale distribution character and manifest directional character of target pixels, we can detect targets and estimate their azimuth in energy feature image and directional feature image. The results of experiments prove that this method has good performance on target detection and meanwhile can get accurate targets azimuth range.The false alarm causation of the algorithm for target-sized objects detection in SAR images based on extended fractal feature is analyzed. The original algorithm is improved by combining consistency of target pixels gray and contrast of targets and background. Experiments show that this improved algorithm provides a lower false alarm rate and higher figures of merit than the original one.更多还原