基于Keystone变换的多目标距离走动校正

微弱目标检测中,高速运动目标的跨距离单元走动会影响长时间相参积累的效果,需要预先加以校正。针对以往Keystone变换法在校正走动时,不能同时校正模糊数不同的多目标走动的不足,提出了一种改进的Keystone变换算法,在无模糊的Keystone变换之后,通过单元最大模糊数搜索快速得到多个目标的模糊数,使各目标根据自身运动特性得到校正,从而延长相参积累时间、提高积累增益。仿真结果验证了算法的有效性。     

高速运动目标的越距离走动补偿

对于搜索转跟踪的雷达系统来说,跟踪模式下往往采用较大的带宽,并且如果目标运动速度过快,此时雷达回波会出现距离走动,从而影响到雷达的检测性能。Keystone变换是校正距离走动的常用方法,但须考虑速度模糊的情况。本文在雷达搜索模式下通过多重频法预先得到多普勒模糊度,并对跟踪模式下的回波信号进行处理来校正距离走动。仿真分析和实测数据处理结果表明了实现方法的有效性。     

高速目标距离、多普勒走动及其补偿方法

临近空间飞行器的出现对现役雷达系统提出了严峻挑战,其高超声速特点导致的跨距离单元、跨多普勒单元现象使雷达系统常用的相参积累处理失效,必须通过对目标回波信号进行速度、加速度补偿才能实现有效的积累。本文首先分析了临近空间目标的运动特性,及其导致距离、多普勒走动的原因,然后提出了通过Keystone变换以及加速度补偿处理的方法,并对工程实现中面临的问题进行了分析,最后通过仿真验证了算法的可行性。     

Keystone变换实现方法研究

在传统PD雷达中,当相干积累时间较长或信号带宽很大,目标运动速度很高时,回波会出现越距离单元走动,从而影响雷达探测目标的性能。Keystone变换是校正脉冲回波距离走动的常用方法。在此研究了Keystone变换的3种常用实现方法,通过仿真分析验证了算法的有效性,找出了低复杂度算法,对工程实现具有一定的参考意义。     

基于Keystone变换的多目标ISAR成像算法

提出了一种基于Keystone变换的多目标成像算法。以各目标回波在径向上重叠较小的时刻为基准时间运用Keystone变换，同时校正各目标的线性距离走动，减轻了各目标回波在径向上的重叠，进而在距离-多普勒二维平面上完成各目标回波的分离。对分离出的回波分别进行相关法和PGA法的高次项运动补偿后，可得到各目标的距离-多普勒像。计算机仿真结果证明了该方法的有效性。     

基于二阶Keystone变换的双站前视SAR成像算法

由于回波信号具有剧烈的二维耦合和距离徙动特性,相比传统的单站合成孔径雷达(SAR)而言,双站SAR数据的成像处理更具有挑战性,双站前视SAR则更是如此。由于没有解决距离徙动的空变性和高阶距离-方位耦合,导致目前现存的成像算法效果较差,成像范围也受到较大限制。针对上述问题,文中提出了一种基于二阶Keystone变换(KT)和改进的非线性调频变标(NLCS)方法的成像算法。首先,利用线性距离徙动矫正去除线性距离徙动和多普勒中心频率;然后,采用二阶KT来补偿距离弯曲;最后,采用改进的非线性调频变标方法用于均衡不同点目标方位空变的多普勒调频率。仿真结果证明了该算法的有效性。     

Keystone变换实现方法研究

在传统PD雷达里,当相干积累时间较长或信号带宽很大、目标运动速度很高时,回波会出现越距离单元走动,从而影响雷达探测目标的性能.Keystone变换是校正脉冲回波距离走动的常用方法.本文详细研究了Keystone变换的三种常用实现方法,对它们的运算量作了比较,指出Chirp-Z变换能较好地满足系统实时性的要求.仿真分析和...     

基于距离Keystone变换的改进的多普勒调频率估计方法

多普勒调频率估计是SAR成像处理中的一个重要步骤。针对聚束、滑动聚束SAR采用全孔径算法进行成像时的调频率估计问题,该文提出一种改进的平移相关(SAC)算法。将距离Keystone变换引入到SAC算法中,去除了互相关峰值位置与目标距离间的耦合关系,从而消除了聚焦深度的限制。由于没有时域补零操作,调频率估计过程中将会出现模糊,针对此,给出了一种基于最小熵准则的模糊数估计方法。仿真及实测数据处理结果验证了所提方法的有效性。     

基于最大图像清晰度的泛探雷达目标距离-多普勒走动校正

泛探雷达长时间的相干积累会增加目标二维走动,导致目标在距离多普勒域散焦,回波信噪比降低。有效的目标二维走动校正才能更好地体现泛探雷达的凝视特性,提升雷达目标检测性能。文中利用Keystone变换进行距离维走动校正,并建立多普勒维走动和图像清晰度的数学关系式,基于最大图像清晰度准则进行多普勒维的走动校正。该方法解决了凝视探测下的二维走动,提高目标在多普勒维的高分辨,同时提升了微弱目标检测能力。     

一种毫米波前视合成孔径雷达成像算法

针对传统正侧视和斜视雷达无法对雷达载机前方场景进行成像的缺点,提出了一种基于距离多普勒算法(RDA)的毫米波前视合成孔径雷达(SAR)成像方法。给出了系统的结构模型,分析了系统成像原理。基于空间几何模型和回波信号形式,分析了点目标回波的多普勒历程,给出了方位向多普勒调频率,得到各相位补偿因子和距离徙动校正公式。对成像场景大小和方位向成像分辨率进行了详细分析,采用MATLAB对6个点目标进行了成像仿真,并对仿真结果中点目标峰值中心的64×64点切片和方位向、距离向进行了分析。理论推导和实验仿真表明,基于RDA的前视合成孔径雷达可以对场景中目标有效成像且方位向成像分辨率可达到2 m,该系统可应用与侦查和制导领域。     

Frequency domain volume rendering by the wavelet X-ray transform

We describe a wavelet based X-ray rendering method in the frequency domain with a smaller time complexity than wavelet splatting. Standard Fourier volume rendering is summarized and interpolation and accuracy issues are briefly discussed. We review the implementation of the fast wavelet transform in the frequency domain. The wavelet X-ray transform is derived, and the corresponding Fourier-wavelet volume rendering algorithm (FWVR) is introduced, FWVR uses Haar or B-spline wavelets and linear or cubic spline interpolation. Various combinations are tested and compared with wavelet splatting (WS). We use medical MR and CT scan data, as well as a 3-D analytical phantom to assess the accuracy, time complexity, and memory cost of both FWVR and WS. The differences between both methods are enumerated.     

非扫描激光主动成像的频域特征分析

非扫描激光主动成像过程中的局部频域特征会出现噪声,为了提高非扫描激光主动成像的频域特征质量,提出了非扫描激光主动成像的频域特征分析.基于非扫描激光主动成像原理,引入神经网络—极限学习机,消除非扫描激光主动成像的频域特征样本训练误差,使得神经网络—极限学习机与最小二乘解的问题相同,识别出非扫描激光主动成像的频域特征,通过...     

红外成像制导中前视图的仿真技术研究

红外成像制导技术已发展成为精确制导技术的重要方向之一.但由于成像制导过程中获取的前视图像存在几何失真,它是影响图像匹配性能的一个很重要的因素.分析了前视传感器末制导的工作方式,在此基础上,建立了成像的视场模型.广义坐标系可以把透视变换化为线性变换以便于计算,本文采用广义坐标表示图像的透视变换,推导了从世界坐标系到成像坐标系的变换矩阵,以及变换前后图像问的坐标对应关系.在假定成像平台俯仰角、滚动角参数条件下,应用该算法实现了正摄图对前视红外图像的模拟仿真.     

High range resolution ultrasonographic vascular imaging using frequency domain interferometry with the Capon method

For high range resolution ultrasonographic vascular imaging, we apply frequency domain interferometry with the Capon method to a single frame of in-phase and quadrature (IQ) data acquired using a commercial ultrasonographic device with a 7.5 MHz linear array probe. In order to tailor the adaptive beam forming algorithm for ultrasonography we employ four techniques: frequency averaging, whitening, radio-frequency data oversampling, and the moving average. The proposed method had a range resolution of 0.05 mm in an ideal condition, and experimentally detected the boundary couple 0.17 mm apart, where the boundary couple was indistinguishable from a single boundary utilizing a B-mode image. Further, this algorithm could depict a swine femoral artery with a range beam width of 0.054 mm and an estimation error for the vessel wall thickness of 0.009 mm, whereas using a conventional method the range beam width and estimation error were 0.182 and 0.021 mm, respectively. The proposed method requires 7.7 s on a mobile PC with a single CPU for a 1×3 cm region of interest. These findings indicate the potential of the proposed method for the improvement of range resolution in ultrasonography without deterioration in temporal resolution, resulting in enhanced detection of vessel stenosis.     

PD雷达抗距离-速度同步拖引干扰的频谱识别法

分析了存在距离-速度同步拖引干扰时的信号频谱特征,研究了一种脉冲多普勒(PD)雷达抗距离-速度同步拖引干扰的方法。该方法在高速可编程DSP芯片所构成的距离-速度跟踪系统中,通过对接收机AGC电压和对信号的频谱分析,实现对距离-速度同步欺骗干扰的辨别和对抗。     

Quasi-cyclic dyadic codes in the Walsh-Hadamard transform domain

A code is s-quasi-cyclic (s-QC) if there is an integer s such that cyclic shift of a codeword by s-positions is also a codeword. For s = 1, cyclic codes are obtained. A dyadic code is a code which is closed under all dyadic shifts. An s-QC dyadic (s-QCD) code is one which is both s-QC and dyadic. QCD codes with s = 1 give codes that are cyclic and dyadic (CD). We obtain a simple characterization of all QCD codes (hence of CD codes) over any field of odd characteristic using Walsh-Hadamard transform defined over that finite field. Also, it is shown that dual a code of an s-QCD code is also an s-QCD code and s-QCD codes for a given dimension are enumerated for all possible values of s.     

变换域窄带干扰抑制技术中变换基的选取研究

基于变换域窄带干扰抑制技术的基本思路,研究了几种常用变换基的性质及其对典型窄带干扰形式的识别能力。通过仿真对比了典型窄带干扰在各变换域的谱型,并以CV系数作为标准对各变换基窄带干扰抑制能力进行了比较。仿真结果表明,重叠变换对于单音、窄带等平稳干扰信号的识别能力较优,而对扫频干扰这种非平稳干扰类型,则更适合在分数阶傅里叶变换域进行检测和识别。     

Formulation of the Fourier transform in the spectral domain technique

A way to formulate the transform in spectral domain technique is presented.     

Fast algorithm for FIR filtering in the transform domain

A more efficient algorithm than the overlap-and-add (or overlap-and-save) method is developed for quickly computing the convolution involving very long impulse response. By dividing the input and the impulse response into segments of proper length, the algorithm requires fewer multiplications than the existing methods and therefore reduces the complexity of the filtering process     

Sampling of bandlimited signals in the linear canonical transform domain

The linear canonical transform (LCT) has been shown to be a powerful tool for optics and signal processing. This paper investigates the sampling of bandlimited signals in LCT domain. First, we propose the linear canonical series (LCS) based on the LCT, which is a generalized pattern of Fourier series. Moreover, the LCS inherits all the nice properties from the LCT. Especially, the Parseval’s relation is presented for the LCS, which is used to derive the sampling theorem of LCT. Then, utilizing the generalized form of Parseval’s relation for the complex LCS, we obtain the sampling expansion for bandlimited signals in LCT domain. The advantage of this reconstruction method is that the sampling expansion can be deduced directly not based on the Shannon theorem.