滑动聚束模式SAR影像干涉处理方法

合成孔径雷达聚焦成像时,因地球旋转和传感器姿态控制误差而产生的非零多普勒中心在聚焦影像方位线中引入了线性相位,因此在干涉处理时方位线不能作为基带信号进行重采样。为了确保相位信息在重采样过程中不出现损失,一般采用内插核调制的方法完成方位线重采样。滑动聚束模式影像因成像的特殊性,聚焦影像的多普勒中心分布更加复杂,其方位线为时变信号。分析了滑动聚束模式影像点目标的多普勒历程,多普勒中心在方位线的变化规律,时变信号的内插方法,并通过模拟实验验证非零多普勒中心对内插精度的影响,最后对DORIS软件重采样环节进行改进,即采用新的多普勒中心表达式对内插核进行调制完成影像重采样,实现TerraSAR-X卫星滑动聚束模式影像的干涉处理。     

A Chirp Transform Algorithm for Processing Squint Mode FMCW SAR Data

Frequency-modulated continuous-wave (FMCW) synthetic aperture radar (SAR) is a lightweight cost-effective high-resolution airborne imaging radar. In squint case, the frequency scaling algorithm, which is suitable for processing nonchirped raw data, cannot be used directly in FMCW SAR data processing because of low system sampling frequency. On the other hand, the continuous antenna motion of FMCW SAR can cause serious distortions in the reconstructed images. In this letter, an improved algorithm called the chirp transform algorithm is proposed. When the effects of the residual video phase are negligible, the algorithm uses a chirp transform to perform the time scaling operation to alleviate the sampling frequency problem. It requires only fast Fourier transforms and multiplications. The range cell migration introduced by the continuous motion is also compensated completely in range-Doppler domain. The algorithm performances are analyzed and are supported by point target simulation experiments.     

基线抖动对干涉SAR 相位的影响

提出并分析了基线抖动造成的干涉SAR 相位误差模型。基于干涉SAR 基线抖动模型, 分为水平抖动和 垂直抖动, 推导了存在基线抖动情况下辅天线复图像信号模型及基线抖动带来的干涉相位误差公式, 分析了基线 抖动对成像质量和干涉相位的影响, 针对SRTM 系统进行了计算机仿真。通过基于基线抖动的干涉SAR 原始回波 数据计算, 仿真了点目标和面目标场景的回波信号, 并进行成像得到了复图像和干涉条纹, 仿真结果验证了理论分 析的正确性。     

非理想航迹城市建筑群MIMO下视阵列SAR三维仿真

在缺少真实下视阵列合成孔径雷达（synthetic aperture radar,SAR）系统而带来数据获取和成像算法研究等困难的当下,下视阵列SAR三维仿真的研究具有重要意义。为了还原载机平台真实的飞行航迹,验证阵列SAR技术在高层建筑物密集城区的地形测绘能力,摒弃传统仿真研究基于匀速直线运动的假设,以高度骤变的城市建筑物为对象,分析构建了多输入多输出（multiple input multiple output,MIMO）下视阵列SAR非理想航迹运动误差模型,提出了非理想航迹城市建筑群MIMO下视阵列SAR三维距离多谱勒成像算法。利用航空平台的航迹与姿态建模仿真技术,以及快速高效的回波仿真技术对成像算法进行了仿真实验,验证了方法的正确性和有效性。     

典型地形SAR回波模拟与SAR图像仿真

SAR成像算法的验证需要相应的回波数据, 同时SAR图像目标识别算法的检验需要大量的SAR图像, 针对这一要求, 提出了一种典型地形SAR回波模拟与图像仿真的方法。首先分析了分形布朗曲面及其水平集的特征。在此基础上, 运用中点位移法生成了描述山脉地形的数字高程数据, 提出了生成海岸地形(“归零法”)及河流沟壑地形(“归零取反法”)的新方法。引入电磁散射模型, 计算了每个分辨单元的后向散射系数。给出了基于二维快速傅立叶变换的SAR回波模拟算法的推导过程及相应的仿真结果, 并对结果进行了分析和讨论, 证明了该方法的正确性。     

基于RPC的TerraSAR-X影像立体定向平差模型

针对新型高分辨率雷达卫星TerraSAR-X立体像对,本文提出采用基于RPC的平差模型,通过少量的地面控制点来拟合因传感器不稳定、平台星历数据不精确及测距误差引起的影像几何畸变,从而达到精确定向目的.为验证RPC平差模型的适用性,通过在立体成像区域均匀市设人工角反射器点的方法验证其模型精度,并评估了其三维定向平差后的精...     

基于距离模型的波数域算法

合成孔径雷达(SAR)存在四种距离模型,本文利用这四种模型推导出四种波数域算法,给出了四种算法详细的推导过程,并得到了四种算法和四种模型之间的一一对应关系。文章提出了单色等效斜视波数域算法,该算法不需要插值,因而提高了计算效率,适合于小斜视角且测绘带宽度不大的情况下的快速成像。最后利用该算法对星载SAR的实际数据进行成像,结果表明在成像精度牺牲不大的情况下可以大大提高成像速度。     

基于影像模拟的SAR几何校正准自动方法

合成孔径雷达影像的几何校正是许多微波遥感应用中必须解决的问题，当无法获得准确的轨道数据时，这个问题变得非常困难。本文提出了利用合成孔径雷达模拟影像进行准确的几何校正的原理及方法，并以RADARSAT SAR影像进行了实验。该方法利用不准确的轨道数据及数字高程模型生成模拟的SAR影像，用影像匹配的方法自动获取模拟影像与真实影像之间同名点的坐标差值，而这个差值信息正好提供了对不准确轨道数据的控制。本方法无须地面控制点，并基本上可以自动进行，是解决目前SAR几何校正问题的有效方法。     

SAR残余相位误差对森林高度反演影响的全链路模拟与分析

利用合成孔径雷达(SAR)遥感数据可以有效地估测平均树高、生物量、蓄积量等森林生物学参数。但是遥感数据精度易受SAR系统不确定性因素的影响,造成森林参数反演精度降低甚至异常。遥感系统的全链路模拟可以将遥感过程的各类影响因素解耦,获取大量具有指定参数特征的遥感数据,有利于对不确定性因素单独或联合分析。建立了SAR三维森林场景全链路模拟模型,基于E-SAR样地参数及数据验证了模型的有效性,并以森林高度反演这一典型的林业应用为对象,定量分析了运动补偿残余相位误差这一典型的SAR系统不确定性因素对反演精度的影响程度,得到了残余相位误差与高度反演RMSE测量结果之间的关系曲线。     

Mitigation of atmospheric perturbations and solid Earth movements in a TerraSAR-X time-series

The TerraSAR-X (TSX) synthetic aperture radar (SAR) marks the recent emergence of a new generation of spaceborne radar sensors that can for the first time lay claim to localization accuracies in the sub-meter range. The TSX platform’s extremely high orbital stability and the sensor’s hardware timing accuracy combine to enable direct measurements of atmospheric refraction and solid Earth movements. By modeling these effects for individual TSX acquisitions, absolute pixel geolocation accuracy on the order of several centimeters can be achieved without need for even a single tiepoint. A 16-month time series of images was obtained over a fixed test site, making it possible to validate both an atmospheric refraction and a solid Earth tide model, while at the same time establishing the instrument’s long-term stability. These related goals were achieved by placing trihedral corner reflectors (CRs) at the test site and estimating their phase centers with centimeter-level accuracy using differential GPS (DGPS). Oriented in pairs toward a given satellite track, the CRs could be seen as bright “points” in the images, providing a geometric reference set. SAR images from the high-resolution spotlight (HS) mode were obtained in alternating ascending and descending orbit configurations. The highest-resolution products were selected for their small sample dimensions, as positions can be more precisely determined. Based on the delivered product annotations, the CR image positions were predicted, and these predictions were compared with their measured image positions both before and after compensation for atmospheric refraction and systematic solid Earth deviations. It was possible to show that when the atmospheric distortion and Earth tides are taken into account, the TSX HS products have geolocation accuracies far exceeding the specified requirements. Furthermore, this accuracy was maintained for the duration of the 16-month test period. It could be demonstrated that with a correctly calibrated sensor, and after accounting for atmospheric and tidal effects, tiepoint-free geolocation is possible with TSX with an absolute product accuracy of about 5 cm.     

小波变换块自适应量化算法压缩SAR原始数据

本文研究了如何使用基于小波变换的块自适应量化（WT-BAQ）算法压缩合成孔径雷达原始数据。结合一组实测SAR原始数据,进行了压缩和解压缩,并计算了数据域及图像域评价参数,给出了压缩算法最终所成的图像。并与块自适应量化（BAQ）、块自适应矢量量化（BAVQ）以及小波包变换块自适应量化（WPT-BAQ）方法进行了性能比较。实验表明,在相同比特率条件下,本文算法得到的数据域信噪比和图像域信噪比均比另外三种算法高。本文算法具有一定实用价值。最后文章给出了结论和将来进一步的工作。     

Unambiguous Reconstruction and High-Resolution Imaging for Multiple-Channel SAR and Airborne Experiment Results

Azimuth ambiguity occurs in synthetic aperture radar (SAR) systems due to the well-known constraint of minimum antenna area, particularly at high resolutions and wide swaths. A space time domain method can be utilized to remove this ambiguity if the multiple-channel data are available. In this letter, a modified approach is presented to determine the filter weight vectors. This approach was successfully applied to the real data, which were collected by an experimental airborne multiple-channel SAR system. The channel imbalance and the error in antenna phase center position are analyzed in detail.     

基于静态模型的多视角SAR图像目标识别方法

传统的多视角SAR图像集合对于目标姿态角具有高度敏感性,因此在用于目标识别时存在一些不足之处。针对该问题提出一种多视角SAR图像的静态建模方法,它将来自一个目标多个视角下的图像信息集成到一个综合的数据结构中,并且该数据结构与目标散射中心有关而与角度无关。然后利用静态模型对不完全姿态角的目标数据进行静态建模,利用模板匹配法对输入多视角图像进行目标识别。理论分析和仿真结果表明,本方法在每个目标只有少量姿态角模板数据可用的情形下比传统模型具有优势。     

利用经验模态分解方法抑制SAR斑点噪声

提出了一种利用经验模态分解（EMD）方法抑制SAR斑点噪声的方法。利用经验模态分解方法，可以将SAR图像分解为一系列的以空间周期尺度不同为特征的模态，定义空间特征尺度不大于4的为噪声。通过从图像中减掉噪声成分使SAR斑点噪声得以抑制。用这种方法处理SAR图像在斑点抑制和纹理信息保护两方面取得令人满意的结果。     

Narrow-Band Interference Suppression for SAR Based on Complex Empirical Mode Decomposition

Narrow-band interference (NBI) is a common interference source in synthetic aperture radar (SAR) imaging. Its existence will degrade the imaging quality greatly. Based on detailed analysis on the characteristics of NBI, this letter proposes a new NBI suppression algorithm using the complex empirical mode decomposition (CEMD) method. In this algorithm, echoes that include NBI are recognized in the time domain first. Then, these echoes are decomposed into a number of intrinsic mode functions (IMFs) via the CEMD. After that, IMFs that correspond to NBI are subtracted from the echoes by thresholding. Finally, well-focused SAR imagery can be obtained from the separated target echoes using traditional SAR imaging algorithms. The effective data loss in this algorithm is smaller than other NBI suppression approaches. In addition, this algorithm is robust to time-varying NBI. Imaging results of measured data have proved the validity of this algorithm.      

基于FFT的快速SAR分布目标回波模拟算法

大面积分布目标的合成孔径雷达 (SAR)回波模拟需要大量的运算 ,文中提出了一种合成孔径雷达回波模拟的快速算法 ,算法利用时域插值和FFT来缩减运算量 ,对于大面积目标回波模拟时 ,该算法有很高的效率。文中详细分析sinc函数插值所带来的误差以及补偿方法 ,并在次基础上提出了一种利用增采样插值方法 ,该方法以增加少量运算为代价 ,使得模拟精度的大幅度提高。文中比较了传统方法和基于FFT的快速SAR分布目标回波模拟算法的模拟结果 ,证明了这种快速算法确实行之有效     

Urban DEM generation,analysis and enhancements using TanDEM-X

This paper analyzes the potential of the TanDEM-X mission for the generation of urban Digital Elevation Models (DEMs). The high resolution of the sensors and the absence of temporal decorrelation are exploited. The interferometric chain and the problems encountered for correct mapping of urban areas are analyzed first. The operational Integrated TanDEM-X Processor (ITP) algorithms are taken as reference. The ITP main product is called the raw DEM. Whereas the ITP coregistration stage is demonstrated to be robust enough, large improvements in the raw DEM such as fewer percentages of phase unwrapping errors, can be obtained by using adaptive fringe filters instead of the conventional ones in the interferogram generation stage. The shape of the raw DEM in the layover area is also shown and determined to be regular for buildings with vertical walls. Generally, in the presence of layover, the raw DEM exhibits a height ramp, resulting in a height underestimation for the affected structure. Examples provided confirm the theoretical background. The focus is centered on high resolution DEMs produced using spotlight acquisitions. In particular, a raw DEM over Berlin (Germany) with a 2.5 m raster is generated and validated. For this purpose, ITP is modified in its interferogram generation stage by adopting the Intensity Driven Adaptive Neighbourhood (IDAN) algorithm. The height Root Mean Square Error (RMSE) between the raw DEM and a reference is about 8 m for the two classes defining the urban DEM: structures and non-structures. The result can be further improved for the structure class using a DEM generated with Persistent Scatterer Interferometry. A DEM fusion is thus proposed and a drop of about 20% in the RMSE is reported.     

后向投影算法的地理坐标系下的合成孔径雷达成像

传统的机载合成孔径雷达(SAR)一般依赖于GPS/INS组合系统补偿平台的运动误差,并获得高分辨率的图像。GPS获取的地理坐标(即经度,纬度和高度)需要转换为本地的直角坐标,原始雷达数据在这个直角坐标系下才能引入成像及运动补偿算法进行处理,并获得本地直角坐标系下的图像。这种图像是通过局部坐标描述的,对于其他部门是不通用的,因为其他部门需要的是经过全球地理坐标标绘的图像。本文提出了一种由后向投影算法BP(Back Projection)引出的新的SAR成像算法,它直接在地理坐标下处理,可避免坐标转换的过程。而且生成德图像像素均和地理坐标一一对应,能够很方便地被情报或其他部门使用。而且在仿真试验以及外场试验中,证明了本文算法和常规BP算法成像效果是相当的。     

A Keystone Transform Without Interpolation for SAR Ground Moving-Target Imaging

Synthetic aperture radar (SAR) image formation for a ground moving target necessitates the compensation of the unknown target trajectory. The keystone transform has been employed to remove the linear component of the range migration for the moving target, where interpolation is required. In this letter, a realization of the keystone transform avoiding interpolation is presented. The kernel of this transform, i.e., the range-frequency-dependent azimuth time rescaling, is implemented using only complex multiplications and fast Fourier transforms based on the scaling principle, which has been successfully applied in the equalization of the space-variant range cell migration in SAR processing. In addition, the moving target is coarsely focused according to the SAR geometry and the platform velocity while exploiting the scaling principle. This preliminary focusing is helpful in the isolation of the moving target from ground clutter, so as to facilitate a more refined processing with respect to each mover. SAR raw data combined with simulated echoes of moving targets are utilized to validate the presented approach     

SIMO-MIMO模式城市建筑群下视阵列SAR三维仿真

真实下视阵列SAR系统的缺失,给该技术数据获取及进一步技术研究带来了困难,下视阵列SAR三维仿真的研究具有重要意义。为了有效反映下视阵列SAR技术在建筑物耸立的城市区域的三维成像优势,本文采用单输入多输出（SIMO）和多输入多输出（MIMO）两种模式仿真了城市建筑群下视阵列SAR回波数据,并对两种模式的回波数据进行了三维距离多普勒成像处理,通过SIMO模式成像结果、MIMO模式成像结果分别与原始地形的差分对比,验证了本文方法的有效性及两种模式的优劣性。