基于干涉图幅度和相位联合的慢动目标CFAR检测方法

 提出了一种新的基于干涉图幅度和相位联合的慢动目标CFAR检测方法.在理论层面上,基于复Wishart分布,推导出了均匀区域、不均匀区域和极度不均匀区域等不同环境下IMP检测量的统计分布族,并根据Mellin变换导出了各分布模型的参数估计器.在算法层面上,通过结合邻域平均这种等效的多视处理方式获得IMP检测量图像后,根据推导出的IMP检测量各分布模型对应的CFAR阈值求解方式,利用滑动窗口的形式实现慢动目标的自动检测.对双通道SAR实测数据进行实验,采用KL度量、MSE度量和K-S检验作为定量评估准则,结果证明了IMP检测量分布模型族及对应参数估计器的有效性以及基于IMP检测量实现慢动目标CFAR检测的更优性能.     

利用样本协方差矩阵特征值分解实现双通道SAR动目标检测

该文针对机载双通道SAR-GMTI系统及实测数据,提出一种新的地面慢动目标检测方法。该方法基于双通道样本协方差矩阵特征值分解,将杂波第2特征值和干涉相位联合统计特性的研究结果用于慢动目标检测,即根据给定的恒虚警概率确定一条联合分布的第2特征值干涉相位等高线作为门限检测曲线,同时结合第2特征值、干涉相位门限预处理,实现地面慢动目标的精确检测。实测数据实验结果表明:该方法不但扩大了慢动目标的可检测速度范围,同时还降低了系统的虚警概率。     

Dictionary-based stochastic expectation-maximization for SAR amplitude probability density function estimation

In remotely sensed data analysis, a crucial problem is represented by the need to develop accurate models for the statistics of the pixel intensities. This paper deals with the problem of probability density function (pdf) estimation in the context of synthetic aperture radar (SAR) amplitude data analysis. Several theoretical and heuristic models for the pdfs of SAR data have been proposed in the literature, which have been proved to be effective for different land-cover typologies, thus making the choice of a single optimal parametric pdf a hard task, especially when dealing with heterogeneous SAR data. In this paper, an innovative estimation algorithm is described, which faces such a problem by adopting a finite mixture model for the amplitude pdf, with mixture components belonging to a given dictionary of SAR-specific pdfs. The proposed method automatically integrates the procedures of selection of the optimal model for each component, of parameter estimation, and of optimization of the number of components by combining the stochastic expectation-maximization iterative methodology with the recently developed "method-of-log-cumulants" for parametric pdf estimation in the case of nonnegative random variables. Experimental results on several real SAR images are reported, showing that the proposed method accurately models the statistics of SAR amplitude data.     

SAR Slow Moving Target Imaging Based on Over-Sampling Smooth Algorithm

A novel Synthetic aperture radar (SAR) signal processing technique has been proposed which re-focused slow moving targets based on phase retrieval al-gorithm. After theoretical derivation, we can get that the raw data Fourier magnitude of slow moving targets is ap-proximate to the stationary ones in the SAR system. By applying the Fourier magnitude of received data to phase retrieval algorithms, the blur and defocusing eff ect caused by the moving of the targets can be eliminated. The sim-ulated results demonstrate the validity of this algorithm.     

An improved SAR-GMTI method based on eigen-decomposition of the sample covariance matrix

An improved two-channel Synthetic Aperture Radar Ground Moving Target Indication (SAR-GMTI) method based on eigen-decomposition of the covariance matrix is investigated. Based on the joint Probability Density Function (PDF) of the Along-Track Interferometric (ATI) phase and the similarity between the two SAR complex images, a novel ellipse detector is presented and is applied to the indication of ground moving targets. We derive its statistics and analyze the performance of detection process in detail. Compared with the approach using the ATI phase, the ellipse detector has a better performance of detection in homogenous clutter. Numerical experiments on simulated data are presented to validate the improved performance of the ellipse detector with respect to the ATI phase approach. Finally, the detection capability of the proposed method is demonstrated by measured SAR data.     

相似度动目标检测量的修正与第二特征值 检测量的有效性证明

SAR地面慢动目标检测是利用SAR实现空间对地观测应用的一个主要方面,具有重要的理论意义和迫切的实际需求.目前,通过对协方差矩阵进行特征值分解得到三个检测量(第二特征值、干涉相位和相似度),为慢动目标检测的实现开辟了一条新途径.本文针对相似度和第二特征值检测量存在的理论缺陷,首先,根据对角化矩阵与Pauli自旋矩阵构成的单位上半球面点具有一一对应的特点,从理论上修正了相似度检测量表达式.进而,首次提出并证明了"对协方差矩阵进行邻域平均预处理是第二特征值作为有效动目标检测量的前提条件"这一命题,有力地补充和完善了特征值分解检测量的理论体系.仿真实验结果也证明了理论推导的正确性.     

分布式小卫星SAR顺轨基线解耦合分析

地面动目标检测是分布式小卫星SAR研究的热点之一,但是分布式小卫星的空间构形导致混合基线的存在,使得地形变化和地面目标运动引起的相位难以区分以致从地面杂波中发现动目标非常困难。该文利用矢量法分析了基线耦合产生的原因,研究了一种能够实现顺轨基线解耦合的轨道构形,计算和仿真表明该文的方法能够有效地把影响动目标检测的垂直航迹基线引起的相位去除。     

星载双站SAR地面场景回波仿真

双站SAR回波仿真利用小面单元模型和Kirchhoff双站后向散射模型,给出了地面场景后向散射系数的计算方法;为了保证双站SAR精确的相位信息,在时域中模拟双站SAR回波。根据实际的DEM数据进行了计算机仿真,对仿真数据进行成像和干涉处理,结果表明,该方法能够逼真地模拟地面场景的双站散射特性和相位信息。     

三孔径天线DPCA实现星载SAR动目标检测的方法

地杂波抑制是实现星栽合成孔径雷达地面运动目标检测的一个关键问题。本文给出了对DPCA条件下的三孔径天线回波数据，利用类似动目标显示(MTI)雷达中三脉冲对消滤波器的原理来抑制地杂波，从而实现星栽合成孔径雷达(SAR)动目标检测的方法。首先介绍了三脉冲对消器的原理及其频率响应特性，然后在建立星载SAR沿航迹向三孔径天线空间几何模型和机理分析的基础上，推导了对三孔径天线回波用三脉冲对消实现被地面背景杂波淹没的运动目标的检测方法。最后，用计算机仿真结果验证了其有效性。     

Extraction of power line maps from millimeter-wave polarimetric SARimages

Radar backscatter of power lines has lower values than those of the surrounding ground clutter when the power line is oriented at an off-normal direction with respect to the radar line of sight. For power lines, the traditional detection algorithms that are commonly based on the statistics of the backscatter power of the clutter and target result in excessive false-alarm rates due to very low signal-to-clutter ratio. The application of a statistical polarimetric detection algorithm that significantly improves the signal-to-clutter ratio is demonstrated. The coherence between the co- and cross-polarized backscatter components is used as the detection parameter. This statistical detection parameter can be applied to any extended targets such as a suspended cable in clutter background. Detection criteria based on clutter backscattering coefficients, power line size, and aspect angle, as well as the number of independent samples are obtained. The performance of the algorithm for mapping power lines in SAR images is demonstrated using a number of low-grazing incidence polarimetric SAR images at 35 GHz     

Detecting scene changes using synthetic aperture Radar interferometry

In repeat-pass interferometric synthetic aperture radar (SAR), man-made scene disturbances are commonly detected by identifying changes in the mean backscatter power of the scene or by identifying regions of low coherence. Change statistics such as the sample mean backscatter-power ratio and the sample coherence, however, are susceptible to high false-alarm rates unless the change in the mean backscatter power is large or there is sufficient contrast in scene coherence between the changed and unchanged regions of the image pair. Furthermore, as the sample mean backscatter-power ratio and sample coherence measure different properties of a SAR image pair, both change statistics need to be considered to properly characterize scene changes. In this paper, models describing the changed and unchanged regions of a scene are postulated, and the detection problem is expressed in a Bayesian hypothesis-testing framework. Forming the log-likelihood ratio gives a single sufficient statistic, encoding changes in both the coherence and the mean backscatter power, for discriminating between the unchanged- and changed-scene models. The theoretical detection performance of the change statistic is derived and shows a significant improvement over both the sample mean backscatter-power ratio and sample coherence change statistics. Finally, the superior detection performance of the log-likelihood change statistic is demonstrated using experimental data collected using the Defence Science and Technology Organisation's Ingara X-band airborne SAR.     

机载SAR 对地面慢速运动目标的DPCA-CFAR 联合检测方法

在机载合成孔径雷达(SAR)动目标检测中,由于地面慢速运动目标速度较小,因此很容易被地面强主瓣杂波淹没而检测不到。文中针对地面慢速运动目标的运动特点,提出基于分数阶傅里叶变换(Frft)的DPCA鄄CFAR 联合检测的方法,在采用天线相位中心偏置(DPCA)技术进行杂波抑制的基础上进行恒虚警(CFAR)处理,从而检测到运动目标,并且根据DPCA 对消后的信号幅度和CFAR 检测门限推导了最小可检测速度,说明了提出的算法对慢速运动目标的检测性能,并进一步采用Frft 方法估计出目标速度,最后通过仿真对算法的有效性进行了验证。     

Measurement of topography using polarimetric SAR images

A processing technique for polarimetric synthetic aperture radar (SAR) data has been developed which produces profiles of terrain slopes and elevations in the azimuthal (or along-track) direction. This technique estimates the average shift in orientation angle of copolarization backscatter caused by azimuthal tilts of the scattering plane. Using P-band data, tests of this technique have been made for an area in the Black Forest near Villingen/Schwenningen in Baden-Wurttemberg, Germany. The radar measured slope and derived elevation profiles have low rms errors and high correlation values when compared with a stereo-photograph digital-elevation map (DEM) for the area. This algorithm is capable of adaptively making transitions from the forested areas to nearby regions with open-terrain. Subsequent tests of the algorithm have been conducted using polarimetric SAR L-band data for a mountainous, nonforested, region in the Mojave Desert (Ft. Irwin, CA) where an accurate DEM also was available. Complete elevation and slope mapping of the terrain in two dimensions using this technique is possible when azimuthal elevation profiles are produced throughout the range extent of the SAR image     

Theory of synthetic aperture radar imaging of a moving target

Two novel image processing techniques have been developed to refocus a moving target image from its smeared response in the synthetic aperture radar (SAR) image which is focused on the stationary ground. Both approaches may be implemented with efficient fast Fourier transform (FFT) routines to process the Fourier spatial spectrum of the image data. The first approach utilizes a matched target filter that is derived from the signal history along the range-Doppler migration path mapped onto the SAR image from the moving target trajectory in real space. The coherent spatial filter is specified by the apparent target range in the image and the magnitude of the relative target-to-radar velocity. The second approach eliminates the range-dependence by reconstructing the moving target image from a spectral function that is obtained from the SAR image data spectrum via a spatial frequency coordinate transformation     

Automatic Extraction of Traffic Flows Using TerraSAR-X Along-Track Interferometry

Spaceborne synthetic aperture radar (SAR) offers great potential for the measurement of ground traffic flows. A SAR with multiple receiving apertures aligned in flight direction repeatedly images the same ground area with a short time lag. This allows for an effective detection of moving ground objects, whose range variation translates into an interferometric phase signal between the receiving channels. The high-resolution German SAR satellite TerraSAR-X offers several ways to create multiple along-track apertures. We exploit this to demonstrate satellite-based traffic-flow measurements using along-track interferometry (ATI) and Displaced Phase Center Array techniques. In this paper, we address the usage of different TerraSAR-X ATI modes for data acquisition and describe an automatic near-real-time processing chain for the extraction of traffic information. The performance of this TerraSAR-X traffic processor is significantly driven by incorporating a priori knowledge of road networks. We present examples of automatic traffic detection as well as empirical evaluations thereof using different kind of reference data.      

Estimating the effective number of looks in interferometric SAR data

The probability density function (pdf) of the multi-look interferometric phase between two complex synthetic aperture radar (SAR) images is parameterized by the number of looks and the complex correlation coefficient. In practice, adjacent pixels in a real SAR interferogram, are statistically dependent due to filtering, and hence, the number of looks is usually smaller than the number of samples averaged. It has been shown that compensation with an effective number of looks, rather than an intractable rederivation of the pdf, can account for the statistical dependence. This paper addresses the challenge of how to determine a suitable value for the effective number of looks. It is shown that an optimum value can be found via a maximum-likelihood estimator (MLE) based on the interferometric phase pdf. However, since such an MLE is computationally intensive and numerically unstable, an estimator based on the method of moments (MoM) possessing similar fidelity is proposed. MoM is fast and robust and can be used in operational applications, such as determining constant false alarm rate (CFAR) detection thresholds for moving-target detection in SAR along-track interferometry.     

基于MIMO-SAR体制的空频域自适应动目标检测技术研究

多发多收星载SAR使用多天线从不同的相位中心发射正交编码信号,多个接收相位中心接收回波后形成多通道信号,显著增大了空间自由度,有利于地面动目标检测.该文研究了多发多收星载SAR空时自适应信号处理进行地面动目标检测的技术,针对星载SAR回波信号的特点,在研究空频自适应处理算法的基础上,使用基于特征值分解的空频自适应处理算法对多发多收星载SAR的杂波进行抑制,最后完成对动目标的检测.仿真数据处理结果验证了该文方法的有效性.     

Evaluation of terrain models for the geocoding and terraincorrection, of synthetic aperture radar (SAR) images

The variability of the resolutions and the presence of artifacts cause inaccurate correction of the terrain-induced geometric distortions in synthetic-aperture radar (SAR) images. To quantify the effects of these inaccuracies on SAR terrain correction, corrections of a Seasat SAR image were performed using a 1° US Geological Survey (USGS) terrain model, a 7.5-min USGS terrain model, and a terrain model derived from stereoimagery acquired from SPOT. Geometric verifications of the corrected imagery showed that the resolution of the 1° terrain model is not adequate to resolve many features in the Seasat image. Geometric verifications of images corrected with the two higher resolution terrain models showed localized errors as large as 52 m for mountain peaks. However, comparison of data corrected with those models shows that both produce results that differ by less than the resolution of either of them. Periodic artifacts observed in the terrain models translated to ground range differences of 18 m, which are well below the resolution of the SAR imagery     

Statistics of the Stokes parameters and of the complex coherenceparameters in one-look and multilook speckle fields

Barakat [1987] derived the Stokes parameter statistics, applicable to one-look synthetic aperture radar (SAR) images, of a partially polarized wave backscattered from a Gaussian area. In this paper, the statistics of the Stokes parameters and of the phase difference are derived as a function of the mean effective phase difference and the degree of coherence for one-look and multilook SAR data. The statistics of the degree of coherence are also derived for multilook SAR data. It is shown that the estimator currently used for calculation of the degree of coherence is biased under low coherence conditions     

基于联合像素特征对消动目标检测方法

提出了基于三通道联合像素的最小功率特征对消的方法来检测SAR图像中的地面运动目标。文中的方法不要求多天线间距、载机速度、脉冲重复频率满足特定的条件,它通过构造三通道联合像素矢量来产生协方差矩阵,然后对协方差矩阵进行特征分解,选取噪声的特征向量来构成噪声子空间,最后利用噪声子空间来抑制地面杂波,从而检测出地面慢速运动目标;同时还分析了针对实测数据中存在系统误差的情况下选取不同的特征向量分别构成的噪声子空间对于该方法的运动目标检测性能的影响。实测数据处理结果验证了该方法的有效性。