机载正侧视合成孔径雷达地面运动目标参数估计方法

 针对距离向速度估计中存在的模糊问题,提出一种利用目标距离包络的走动轨迹,通过Radon变换技术来无模糊地估计距离向速度的方法.针对距离向加速度影响方位向速度估计问题,提出了利用目标多普勒参数来估计运动目标真实合成孔径时间,通过真实合成孔径时间与方位向速度的关系来确定目标方位向速度.该方法能很好估计方位向速度而不受距离加速度的影响.所提方法适合于单/多通道系统.仿真和实测数据验证了方法的有效性.     

机载双频曲线SAR系统与试验

曲线合成孔径雷达(SAR)是一种孔径流形特殊的成像雷达,其所搭载平台通过作曲线运动,能观测到目标更多的方位散射信息、获取更高的空间分辨率,同时还具备一定的三维成像能力.随着成像技术的不断发展,机载曲线SAR在重点区域侦测相关任务中呈现广阔的应用前景.本文主要介绍了研究团队近年研制的机载双频曲线SAR系统,以及于2020...     

分布式小卫星合成孔径雷达三维地形成像的最优垂直轨迹基线

分布式小卫星合成孔径雷达 (DSS-SAR)中垂直轨迹基线和沿轨迹基线同时存在、相互耦合,且具备多个基线,因此与单星SAR干涉相比,DSS-SAR三维地形成像最优垂直轨迹基线的确定更为复杂。该文提出了一种确定DSS-SAR三维地形成像最优垂直轨迹基线的新方法。该方法根据DSS-SAR干涉复图像对的相位差的统计特性,推导了DSS-SAR多基线干涉的干涉相位的克拉美-罗界,并由此求得测高误差与垂直轨迹基线之间的关系式,令测高误差对垂直轨迹基线的导数为零,得出DSS-SAR三维地形成像的最优垂直轨迹基线。最后根据最优垂直轨迹基线的计算式,详细分析并推导了由3颗小卫星构成的不同空间编队构形DSS-SAR的最优垂直轨迹基线,结果表明,当基线数为1时,论文推导的DSS-SAR多基线干涉最优垂直轨迹基线与已有单星SAR干涉最优基线设计结果一致。此分析结果验证了论文方法的正确性。     

SAR辐射定标的融合算法研究

针对机载SAR辐射定标外场试验可重复性较差的问题,提出了一种结合内场仿真信息进行辐射定标的参数估计新算法:首先建立机载SAR定标成像模型,在进行模型有效性检验之后,利用定标成像模型得到SAR线性动态范围内定标体RCS的渐进经验分布,然后结合定标试验实测数据进行辐射定标参数的融合估计。仿真表明该算法可以减小估计结果的误差方差,提高定标精度。     

一种新的机载宽波束SAR前向运动补偿算法

工作于低频段的机载宽波束SAR为了获取高分辨图像,对前向运动误差补偿精度的要求很高。前向运动补偿通常采用方位向重采样或实时PRF调整,前者的计算量较大,而后者又需要额外的硬件设备。文中提出一种新的适用于机载宽波束SAR的前向运动补偿算法,利用信号的时频对应关系,在子孔径距离多普勒域中构造相位补偿因子以消除前向运动误差的影响。算法计算量较小,适合于机载宽波束SAR实时处理。仿真和实测数据处理结果验证了算法的有效性。     

Ocean wave imaging using an airborne single pass across-trackinterferometric SAR

An airborne single pass across-track interferometric synthetic aperture radar (InSAR) is used to image ocean waves. A theoretical model explaining the imaging mechanisms is developed, and simulations of the interferogram as well as the conventional SAR intensity image are presented for given ocean wave spectra. Distortions of digital elevation models (DEM) derived from InSAR data are explained by the motion of the sea surface. A Monte Carlo method based on forward simulations is used to estimate variance spectra of the distorted elevation models. It is shown that a straightforward estimation of wave height using the distorted InSAR elevation model is in good agreement with true wave height for low amplitude swell with about 10% error depending on propagation direction and coherence time. However, severe underestimation of wave height is found for wind seas propagating in flight direction. Forward simulations show that the distorted InSAR DEM is less dependent an the model chosen for the real aperture radar mechanism than conventional SAR images. Data acquired during an experiment over the North Sea by a high precision InSAR system are compared with simulations     

Estimation of the Surface Velocity Field of the Aletsch Glacier Using Multibaseline Airborne SAR Interferometry

This paper presents a methodology to process airborne interferometric synthetic aperture radar (SAR) data to measure surface velocity fields (SVFs) of temperate glaciers, and applies it to data acquired over the Aletsch glacier. The first part of this paper deals with the main limitation in airborne interferometric SAR to retrieve reliable interferometric products, namely, the existence of the so-called residual motion errors—inaccuracies on the order of a few centimeters in the navigation system. An extended multisquint approach is proposed for their estimation in the case of nonstationary scenes. The second part of this paper expounds an efficient methodology to derive SVFs with airborne systems, where the line-of-sight displacement is estimated using differential interferometry and the along-track component by estimating the azimuth coregistration offsets. The necessary steps to finally obtain the 3-D SVF are also presented, as well as the possibility of combining different acquisition geometries. Airborne interferometric SAR data acquired by the Experimental SAR system of the German Aerospace Center over the Aletsch glacier, located in the Swiss Alps, are used to evaluate the performance of the proposed approach. The motion of the corner reflectors deployed in the scene is retrieved with an accuracy between 1 and 5 cm/day using L-band data.      

SAR-GMTI构型下分布式小卫星误差估计方法

 针对合成孔径雷达(SAR)成像、地面动目标检测(GMTI)功能的实现,分布式小卫星的最佳构型为沿航向分布,但误差的存在会使性能下降.提出了一种基于距离脉压后时间－方位多普勒域回波数据的分布式小卫星误差估计方法.通过距离向脉压,提高了信噪比,采用预先估计并补偿幅度误差的方法,克服了幅度误差与沿航向位置误差的相互影响.仿真结果表明,与传统方法相比,本文方法收敛速度加快,估计精度得到提高.     

Blind-velocity SAR/ISAR imaging of a moving target in a stationarybackground

A synthetic aperture radio/inverse synthetic aperture radar (SAR/ISAR) coherent system model and inversion to image a target moving with an unknown constant velocity in a stationary background are presented. The approach is based on a recently developed system modelling and inversion principle for SAR/ISAR imaging that utilizes the spatial Fourier decomposition of SAR data in the synthetic aperture domain to convert the SAR system model's nonlinear phase functions into linear phase functions suitable for a computationally manageable inversion. It is shown that SAR/ISAR imaging of a moving target can be converted into imaging the target in a stationary squint-mode SAR problem where the parameters of the squint-mode geometry depend on the target's velocity. A method for estimating the moving target's velocity that utilizes a spatial Doppler analysis of the SAR data within overlapping subapertures is presented. The spatial Doppler technique does not require the radar signal to be narrowband, so the reconstructed image's resolution is not sacrificed to improve the target's velocity estimator.     

机载雷达技术的发展现状及趋势

经历了长期的发展,机载雷达技术面临着隐身目标、非均匀杂波、复杂电磁环境、多种作战任务的严峻挑战。文中针对这些挑战分析了几种技术的发展趋势,主要介绍了机载预警雷达技术、机载SAR技术、机载雷达组网探测技术以及隐身雷达技术的发展现状,为下一代机载雷达的研制提供参考。     

基于后验数据辅助的雷达系统补偿方法

在警戒、精密跟踪雷达与逆合成孔径成像雷达中,准确地估计目标距离、速度和角度对目标捕获与跟踪至关重要。在实际的雷达系统中,由于实现电路的非理想性,生成的信号往往难以精确符合理论设计,导致目标距离、速度估计结果与理论真值存在不同程度的偏差;同时,雷达接收通道不可避免地存在由系统各部分相互耦合产生的幅相不一致性,对目标角度估计带来潜在影响,且常规补偿过程复杂,往往难以获得一套最优的补偿系数。本文结合某实际雷达系统,建立了典型目标参数估计方法的数学模型,理论分析了影响雷达目标参数估计结果的各类因素,提出了一种基于后验数据辅助的系统补偿方案,并通过实测数据与外场试验验证了方法的有效性。     

Statistical analysis of multilook SAR interferograms for CFAR detection of ground moving targets

This paper examines the statistics of the phase and magnitude of multilook synthetic aperture radar (SAR) interferograms toward deployment of along-track interferometry (ATI) for slow ground moving-target indication (GMTI). While the known probability density function (pdf) of the interferogram's phase (derived under the assumption of Gaussian backscatter) is shown to agree almost perfectly for a wide variety of backscatter conditions, the corresponding magnitude's pdf tends to deviate strongly in most cases. Motivated by this discrepancy, a novel distribution is derived for the interferogram's magnitude. This pdf, called the polynomial or p-distribution, matches the real data much more accurately, particularly for heterogeneous composite terrain. For extremely heterogeneous terrain, such as urban areas, both pdfs for interferometric phase and magnitude fail and are extended. Based on these statistics, a completely automatic detection scheme with constant false-alarm rates (CFARs) for slow moving targets is proposed. All involved parameters required to determine the detection thresholds are estimated from the sample data. It is demonstrated, on the basis of experimental airborne SAR data, that this detector is capable of detecting slow moving vehicles within severe ground clutter.     

基于最小熵DCFT的双基地SAR多普勒参数估计

多普勒参数估计是SAR成像技术研究中的一项关键技术,多普勒参数估计精度将直接影响机载双基地SAR系统成像质量,为了实现对感兴趣目标区域有效地成像,需要对回波信号的参数进行准确估计。本文提出基于最小熵的离散调频傅里叶法(DCFT),该方法基于线性调频信号,可同时估计多普勒质心和多普勒斜率,并用RD算法对双基地SAR仿真数据成像,通过仿真验证了该方法的性能。     

机载视频合成孔径雷达成像技术研究

机载视频合成孔径雷达(ViSAR)工作在太赫兹波段,具有5 Hz以上的无孔径交叠成像帧率。其采用一发四收系统架构,具备合成孔径雷达(SAR)成像、地面动目标检测(GMTI)和干涉合成孔径雷达(InSAR)测高等功能,兼具光学传感器成像速度快以及微波雷达环境与气候适应性好等优势。论文介绍了机载视频合成孔径雷达研究进展,实验表明,其成像分辨率优于0.2 m,合成孔径时间可缩短至0.2 s。利用阴影信息可以对运动目标(如卡车等)进行检测,结合传统的GMTI与InSAR技术,实现对复杂运动目标的成像、跟踪和定位。     

Dual-beam interferometry for ocean surface current vector mapping

The recent use of along-track interferometry (ATI) in synthetic aperture radar (SAR) has shown promise for synoptic measurement of ocean surface currents. ATI-SARs have been used to estimate wave fields, currents, and current features. This paper describes and analyzes a dual-beam along-track interferometer to provide spatially resolved vector surface velocity estimates with a single pass of an aircraft. The design employs a pair of interferometer beams, one squinted forward and one squinted aft. Each interferometric phase is sensitive to the component of surface Doppler velocity in the direction of the beam. Therefore, a proper combination of these measurements provides a vector surface velocity estimate in one pass of the aircraft. The authors find that precise measurements dictate widely spaced beams and that the spatial resolution for the squinted SAR is essentially identical to the sidelooking case. Practical instrument design issues are discussed, and an airborne system currently in development is described. Through computer simulation, they observe the azimuthal displacement of interferometric phases by moving surfaces identical to those of conventional SAR and find that such displacement can bias the estimated surface velocity     

一种结合运动补偿的RD成像算法研究

合成孔径雷达是一种重要的遥感手段。对于高分辨率机载合成孔径雷达成像来说，由于载机不可能完全理想地沿着直线进行匀速运动，高精度的运动补偿是至关重要的。载机的平台运动误差通常可以由运动传感器得到，分为地速误差和视线方向误差。文中对存在运动误差情况下的合成孔径雷达回波数据进行了分析，结合RD算法提出一种对运动误差进行有效补偿的方案。并通过仿真，验证了该方案的有效性和可行性。     

抑制SAR图像中静止杂波背景检测慢速动目标

动目标的二次相位误差是方位向速度和距离向加速度作用的结果,导致信号的调频率改变.本文提出了一种抑制SAR图像中静止杂波背景检测慢速动目标的方法,它搜索动目标二次相位误差,汇聚动目标能量,同时利用包含正负对称二次相位误差的静止背景复图像模处处相等的规律,对消静止杂波背景,从而提高了检测动目标的性能.实测数据表明本算法有效.     

Focused synthetic aperture radar processing of ice-sounder datacollected over the Greenland ice sheet

The authors developed a synthetic aperture radar (SAR) processing algorithm for airborne/spaceborne ice-sounding radar systems and applied it to data collected in Greenland. By using focused SAR (phase-corrected coherent averaging), they improved along-track resolution by a factor of four and provided a 6-dB processing gain over unfocused SAR (coherent averaging without phase correction) based on a point-target analysis for a Greenland ice-sounding data set. Also, They demonstrated that the focused-SAR processing reduced clutter and enabled them to identify bedrock-interface returns buried in clutter. Using focused-SAR technique, they processed data collected over a key 360-km-long portion of the 2000-m contour line of southwest Greenland. To the best of their knowledge, these are the first high-quality radar ice thickness measurements over this key location. Moreover, these ice-thickness measurements have been used for improving mass-balance estimates of the Greenland ice sheet     

基于联合特征空间投影的SAR图像域杂波抑制

杂波抑制是实现地面慢速目标检测(GMTI,Ground Moving Target Indication)的前提条件.本文研究基于高分辨合成孔径雷达(SAR,Synthetic Aperture Radar)图像在杂波起伏时地面动目标检测问题.利用沿航迹(along-track)多幅SAR图像的相关性,提出一种基于广义特征分解的联合噪声子空间投影杂波相消算法.理论分析和仿真结果表明该算法在一定程度上能够有效抑制杂波内部起伏,并且对SAR图像配准误差具有稳健性.     

浅地层探地雷达波速估计和成像方法的研究

在分析探地雷达图像特点的基础上,将图像处理方法应用于雷达波速估计和合成孔径成像,提出了基于模板匹配的浅地层探地雷达波速估计方法和基于图像分割的快速合成孔径成像方法;实测数据的处理结果验证了该方法的可行性和有效性。