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高分辨率SAR图像散射中心特征提取 总被引:6,自引:0,他引:6
合成孔径雷达(SAR)目标检测和识别是SAR实用化的瓶颈技术之一,提取有效的目标特征是SAR目标检测与识别的关键环节。高分辨率SAR图像中,目标属性散射中心特征反映了目标散射中心的位置、类型等信息,精确获取目标散射中心属性特征能够提高对目标的检测识别性能。针对SAR目标属性散射中心特征的提取,该文提出了一种基于改进的空间-波数分布(ISWD)的特征提取方法,该方法首先利用ISWD估计散射中心关于频率与方位角的函数,然后利用该函数来获得目标属性散射中心模型参数。最后利用仿真实验验证了方法的有效性。 相似文献
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本文提出一种新的频率步进超宽带高分辨雷达信号检测方案,即先从目标距离像中提取强散射中心,再进行广义似然比检测。进而研究了从目标的一维距离像中提取强散射中心算法,分析了检测器结构和性能。 相似文献
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从高分辨一维距离像(high range resolution profile,HRRP)出发,针对HRRP姿态敏感以及锥体目标识别中姿态获取困难的问题,推导分析了散射中心极化比与锥体目标姿态的关联关系,提出了基于散射中心极化比姿态反演的方法:利用散射中心参数估计模型对锥体目标不同极化下的宽带数据进行分析,分别提取其散射中心参数,同时计算散射中心参数的极化比,并与理论的极化比曲线进行匹配,最终获取目标的姿态角.基于球头锥的数值计算与极化特征提取结果验证了方法的有效性.利用此方法能够做到对目标姿态的快速反演,为进一步的目标识别提供支撑. 相似文献
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为快速获取超宽带电磁脉冲激励下雷达目标在时域上的电磁响应,提出一种基于属性散射中心正向建模的方法用于目标时域回波仿真.从目标几何模型出发,利用射线追踪、分集技术对空间中所有射线进行标记与归类,分离并定量表征目标的强散射源.基于属性散射中心模型,正向确定模型参数,构建出目标属性散射中心模型,在选定的辐射源激励下进行仿真计... 相似文献
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Energy dependence of nonstationary scatter subtraction--restoration in high resolution PET 总被引:1,自引:0,他引:1
In previous works, the determination of object and detector scatter kernels from line source measurements was described and their application in scatter correction was investigated. It was also shown that low energy data contains a large fraction of useful events (true and detector scatter events). In the present work, data acquired in multispectral mode was summed in single broad energy windows of lower energy thresholds varying from 129 to 516 keV in steps of 43 keV and a constant upper energy threshold of 645 keV. Line-source projections were fitted by extracting the object and detector scatter kernels as a function of energy threshold. These kernels were then used to process scatter by the nonstationary convolution subtraction-restoration method in phantom images. After scatter correction, the sensitivity is found to increase by up to 64% at the lower threshold of 129 keV, relative to the conventional photopeak energy window (344-645 keV). Whereas contrast and spatial resolution are degraded as the energy discriminator is lowered, such degradation is fully recovered by the scatter correction. As a result of scatter correction, the noise increases insignificantly in hot regions but substantially in cold regions, in proportion of the amount of scatter. 相似文献
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对噪声背景中插值FFT方法估计正弦信号频率的精度进行了研究,导出了不加窗和加Hanning窗时频率估计均方根误差与信噪比及FFT长度的关系式;分析了不加窗情况下当信号频率接近FFT频率分辨率Δf的整数倍时,由于插值的方向错误对频率估计精度的影响;指出了不加窗时该方法在噪声背景中的频率估计误差远远大于文[2]中用一个特定的纯测试信号得到的结果;讨论了加窗对频率估计误差的影响.最后给出了Monte Carlo模拟实验与理论分析的对比结果. 相似文献
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Mazoyer B Trebossen R Deutch R Casey M Blohm K 《IEEE transactions on medical imaging》1991,10(4):499-504
A high spatial resolution brain positron tomograph, the ECAT 953B/31, is presented. The machine consists of two 76.5 cm diameter rings (patient port diameter: 36 cm) made of 24 8x8 BGO detector blocks each, each block being coupled to four 1 in(2) Hammamatsu phototubes. The machine has 15 9 cmx1 mm motorized removable septa, which allows reconstruction of 31 slices 3.375 mm apart. The transaxial resolution (FWHM) in the reconstructed image (with wobbling) is 4.5 mm at center, 5.2 mm (tangential) and 5.6 mm at 10 cm from center. With septa out of the field of view (FOV), the axial resolution degrades to 5.5 mm a center and 6.3 mm at 10 cm from center. At 1 muCi/cc with a 250 keV threshold and a 12 ns coincidence window, the sensitivity is 146100 true events, the ratio of randoms to trues is 0.10, the scatter fraction is 17% and the dead-time losses are 30%. With septa out of the FOV, the sensitivity is increased by a factor 3.6, while the scatter fraction reaches 0.9. Images obtained with (18 )F-DG and H(2)(15)O in human brains and (18 )F-DOPA in a baboon brain demonstrate that the ECAT 953B/31 will be suitable for high resolution and for low count rate brain studies. 相似文献
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High resolution images in PET based on small individual detectors are obtained at the cost of low sensitivity and increased detector scatter. These limitations can be partially overcome by enlarging discrimination windows to include more low-energy events and by developing more efficient energy-dependent methods to correct for scatter radiation from all sources. The feasibility of multispectral scatter correction was assessed by decomposing response functions acquired in multiple energy windows into four basic components: object, collimator and detector scatter, and trues. The shape and intensity of these components are different and energy-dependent. They are shown to contribute to image formation in three ways: useful (true), potentially useful (detector scatter), and undesirable (object and collimator scatter) information to the image over the entire energy range. With the Sherbrooke animal PET system, restoration of detector scatter in every energy window would allow nearly 90% of all detected events to participate in image formation. These observations suggest that multispectral acquisition is a promising solution for increasing sensitivity in high resolution PET. This can be achieved without loss of image quality if energy-dependent methods are made available to preserve useful events as potentially useful events are restored and undesirable events removed. 相似文献
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距离扩展目标的双门限恒虚警检测器及性能分析 总被引:2,自引:0,他引:2
针对普通积累检测器检测稀疏散射点目标存在坍塌损失以及依赖于散射点密度的二元积累(SDD-BI)检测器检测密集散射点目标存在信杂比损失的问题,该文充分利用目标的散射点密度及幅度信息,提出了一种距离扩展目标的双门限恒虚警检测器(DT-CFAR),在高斯杂波背景下推导了DT-CFAR虚警概率和检测概率与检测门限关系的解析表达式,并给出了最优第1门限的确定方法。仿真结果表明,DT-CFAR对不同散射点密度目标都具有较优的检测性能,并且对散射点密度估计失配具有鲁棒性。 相似文献
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改进的SAR图像双参数CFAR舰船检测算法 总被引:3,自引:0,他引:3
双参数CFAR检测中设置了目标窗口、保护窗口和背景窗口3个窗口,并且窗口的大小,滑动步长都要进行经验训练得到,效率低,对距离很近的舰船SAR图像会产生漏检。针对这些不足, 该文提出了一种改进的双参数CFAR检测算法,该算法只取目标窗口和背景窗口,通过把泄露到背景窗口中的舰船部分去除并对背景窗口中的剩余部分进行均值和方差估计来检测舰船,并且将窗口滑动步长取为目标窗口尺寸。相对双参数CFAR算法,结构得到了简化,检测结果的虚警率减小, 对距离很近的舰船不会产生漏检, 计算效率得到了改善。仿真结果表明了方法的有效性。 相似文献
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基于多目标跟踪的空间锥体目标微多普勒频率提取方法 总被引:4,自引:0,他引:4
该文在等效散射中心模型下,分析了光滑空间锥体目标进动和章动时回波的微多普勒频率与运动参数的关系。针对目标微多普勒频率的复杂形式,该文提出一种在时频分布(TFD)的基础上,利用多目标跟踪(MTT)技术分离空间锥体目标各等效散射中心微多普勒频率变化曲线的方法。该方法首先应用经典的短时傅里叶变换得到回波的TFD,然后将目标在TFD上的时频曲线看作机动目标的航迹,利用MTT技术跟踪TFD上的时频曲线,从而达到提取目标各等效散射中心微多普勒频率的目的。实验中利用电磁仿真数据验证了提出算法的有效性。 相似文献