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UWB SAR遮盖性干扰效果评估及抑制方法研究
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摘要
干扰抑制是超宽带合成孔径雷达(UWB SAR)的关键技术之一。射频干扰(RFI)和噪声干扰是UWB SAR面临的最具代表性的干扰形式,对它们的抑制是UWB SAR干扰抑制的重要内容。本文在理论推导、数据仿真的基础上,分析了原始回波数据在时域、频域和小波变换域的特征以及复图像数据在图像域、图像频域和图像小波变换域的特征,提出了几种行之有效的信号域和图像域抑制方法。
     本文首先建立了回波信号和几种典型噪声干扰的模型,分析了不同功率、带宽和类型的噪声干扰对UWB SAR的干扰效果,为后续工作奠定了良好的基础。并形成了基于复图像的评估方法,即以灰度图、信噪比和相关系数来评估干扰效果及后续干扰方法的优劣。
     对于RFI和窄带噪声干扰,本文研究了频域陷波和谱均衡两种方法,并将之应用到信号域来抑制窄带干扰。分析了小波包变换域上信号与干扰的差异,在信号域上研究了基于小波包变换的窄带干扰抑制方法;考虑到方法的实时性,进而分析了图像小波包变换域上信号与干扰的差异,提出了在图像域上基于小波包变换窄带干扰抑制方法(NJSIDWPT)。通过实验仿真验证了这些方法的有效性,评估参数结果进一步说明了NJSIDWPT在抑制窄带噪声干扰方面远优于其它的方法。
     对于宽带噪声干扰,本文研究了小波包阈值方法,并将之应用到信号域和图像域来抑制宽带噪声干扰。考虑到方法的灵活性,对小波包阈值方法加以改进,提出了基于小波包阈值化和自适应加窗的复图像去噪法(RNCIWPTAW)。经过实验仿真评估,指出了小波包阈值方法在信号域中无效,而RNCIWPTAW有效且性能良好。
Jamming suppression is one of the key techniques of UWB SAR. RFI and noise interferences are the most representative jammings in UWB SAR which receive great considerations in jamming suppression. Based on theoretical deductions and data simulations, this dissertation analyzes properties of echo data in time domain, frequency domain and wavelet packet transform(WPT) domain. We also analysize properties of complex image data in image domain, image frequency domain and image wavelet packet transform domain. Several methods are proposed for jamming suppression in signal domain and image domain respectively.
     At first, we build models of echo signal and several typical noise interferences and then analyze effects on UWB SAR by interferences with different power, bandwidth and type. So a good beginning for later work is made. Evaluation method is formed, in which jamming effects and performances of suppression methods can be evaluated by gray image, SNR and correlation coefficient.
     For RFI and narrowband noise interferences, this dissertation studies notch filter and spectrum equilibrium and uses them to suppress narrow jammings in signal domain. By analysises on difference between signal and jamming in wavelet packet transform domain, we study methods of narrowband jamming suppression in signal domain based on WPT. Considering the real time feature, and by further analysises on difference between signal and jamming in image wavelet packet transform domain, we propose a method of Narrowband Jamming Suppression in Image Domain based on WPT(NJSIDWPT). The efficiencies of all methods mentioned are validated by simulation experiments and the evaluation result shows that performances of NJSIDWPT on narrowband noise interferences suppression outperform other methods greatly.
     For wideband noise interferences, this dissertation studies wavelet packet threshold method and uses it to suppress wideband noise interferences in signal domain and image domain. In order to improve the flexibilities of methods, we propose an approach to Remove Noise from Complex Image based on Wavelet Packet Threholding and Adaptive Windowing(RNCIWPTAW). Evaluating by simulation, we find that wavelet packet theshold method is invalid in signal domain but RNCIWPTAW is valid with fine properties.
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