一种超高分辨率机载聚束SAR两维自聚焦算法

受运动参数测量误差和大气扰动等因素影响,合成孔径雷达(SAR)图像通常会发生散焦,利用自聚焦对散焦的SAR图像进行后处理是一种有效的重聚焦手段。传统的自聚焦算法都只是针对方位一维相位误差的估计和补偿。随着成像分辨率的提高,自聚焦时残留距离徙动的校正成为SAR成像面临的一个新挑战。本文推导得到了极坐标格式算法处理后残留距离徙动和方位相位误差的解析表达式,分析了两者之间的内在关系,并利用该关系,提出了一种能够同时进行残留距离徙动和方位相位误差补偿的两维自聚焦算法。实测数据处理结果表明,在残留距离徙动效应不可忽略的条件下,该方法能够极大地改善原有自聚焦算法的聚焦性能。     

机载SAR反投影图像自聚焦处理方法

反投影算法(BPA)是一种经典的时间域合成孔径雷达(SAR)成像处理方法。BPA对回波数据插值累加得到图像,运动误差导致的目标散焦沿不同的倾斜角度存在,无法直接应用现有的自聚焦算法。为此,提出了一种新颖的BPA图像运动补偿方案。基于反投影数据运动相位误差和距离徙动分析,研究了修正投影栅格成像,从而去除重建图像中目标散焦方向的空变特性。在中低分辨率配置下,重建SAR图像能够直接应用相位梯度自聚焦(PGA)等进行运动补偿。点目标仿真实验和实测数据结果验证了该算法的有效性。     

基于时间反转和降阶Keystone的SAR-GMTI快速聚焦方法

对合成孔径雷达（SAR）地面运动目标聚焦技术进行了研究。针对现有运动目标聚焦方法存在的问题,提出了一种基于时间反转和降阶Keystone的SAR地面运动目标检测（SAR-GMTI）快速聚焦方法。首先,根据目标的机动特性建立了3阶距离模型;其次,针对目标多普勒中心模糊引起的多普勒谱分裂现象,结合所提时间反转处理（TRP）和降阶Keystone变换处理估计出运动目标2阶参数。此后,构造2阶相位补偿函数补偿运动目标的2阶距离徙动和多普勒徙动,从而完成运动目标的聚焦。同时,所提方法没有任何参数搜索过程,降低了计算复杂度。最后,仿真实验验证了所提算法的正确性和有效性。     

基于距离子带的机载SAR高精度多级空变运动补偿

运动补偿（MOCO）是机载合成孔径雷达（SAR）获取高质量图像的关键,超高分辨率成像中,如何精确、高效地校正空变运动误差仍是很大的挑战。本文提出了一种改进的多级空变运动补偿方案,兼顾处理的精度和效率。首先,采用一步运动补偿法有效去除运动误差的距离空变分量,避免引起额外的距离徙动校正（RCMC）误差。同时,修正视线方向误差的传统计算方式,保证相位精度的前提下结合距离子带实现无插值的近似距离包络补偿。然后,利用距离子带降低残余方位空变误差的距离空变性和对方位时频关系的影响,显著改善宽波束情况下的聚焦效果,降低孔径依赖补偿算法的运算量。最终分辨率达到0.1 m,具有实际工程应用价值。点目标仿真和实测数据处理验证了所做的研究。     

复杂航迹和起伏地形条件下机载聚束SAR 空变运动补偿

 运动补偿是雷达平台机动飞行条件下合成孔径雷达(SAR)实现精确聚焦成像的前提,而如何精确实现运动误差的空变补偿(误差补偿随目标距离、方位和高度位置的变化而变化)目前还存在很大的挑战。本文提出了一种新的三阶运动补偿方法,能够有效解决复杂雷达航迹和地形起伏条件下运动误差的空变补偿问题。该方法首先以场景中心为参考进行空不变运动补偿,然后以多个子场景中心为参考进行空变运动补偿,最后再利用极坐标格式算法(PFA)统一补偿每个像素的空变误差。仿真数据处理结果验证了本文方法的有效性。     

基于数值计算的机载SAR空变运动补偿算法

针对机载合成孔径雷达(SAR)高分辨率宽测绘带(HRWS)成像问题,在分析结合两步运动误差补偿的距离徙动算法基础上,提出一种基于数值计算的空变运动误差补偿算法。通过对粗聚焦图像进行分块,在子块的两维波数域进行空变运动补偿,补偿的相位包括方位相位误差、距离相位误差以及方位和距离的耦合相位,因此该算法在复杂航迹、高分辨和宽测绘带情况下仍具有较好的鲁棒性。最后对SAR仿真数据和实测数据进行处理,并与结合两步运动误差补偿的距离徙动算法进行比较,处理结果表明该算法能够更好地补偿空变运动误差。     

一种横向机动弹道下SAR成像算法

针对横向机动弹道下SAR成像回波方位向和距离向严重耦合、弹载SAR平台实时性要求高的特点,提出了一种基于频谱分析的扩展SAR成像算法。首先,以初始距离相同的目标作为成像处理对象,建立了横向机动下弹载SAR成像模型,分析了回波相位和瞬时距离的泰勒展开;然后,采用包含水平面速度和偏航加速度参数的相位因子依次进行距离徙动校正、二次相位补偿和多普勒中心频率补偿,实现了SAR图像的精确聚焦。该算法处理流程简单、实时性高,适合横向机动弹道下的中等分辨率的大斜视成像,给出了算法流程,仿真验证了算法有效性。     

大斜视FMCW-SAR波数域成像算法研究

结合FMCW(调频连续波)技术,可有效降低SAR(合成孔径雷达)的质量、成本,同时保证合成孔径雷达成像的二维高分辨率优势。针对大斜视工作模式下的FMCW-SAR成像,推导了FMCW-SAR的信号模型和波数域解析表达,分析了FMCW-SAR信号的多普勒特性,提出一种FMCW-SAR波数域成像算法。算法首先对多普勒偏移相位进行补偿,然后通过插值实现距离徙动的校正,最后进行二维逆傅里叶变换得到高精度成像结果。该方法可以在大斜视条件下获得理想的聚集成像性能,仿真实验对此进行了验证。     

一种孔径和频率二维稀疏的步进频SAR成像方法

 步进频率信号(SFWs)在不增加雷达系统瞬时带宽的情况下能够获得高的距离向分辨率的同时,也存在着抗干扰能力较差及其等效重复频率较低的问题,并且在方位向积累时间内由于雷达载机工作状态的变化,会导致方位向的数据录取不完整。针对上述问题,提出一种孔径和频率二维稀疏的步进频合成孔径雷达(SAR)成像方法。首先,分析了稀疏步进频率信号(SSFWs)的SAR成像模型,然后基于压缩感知理论完成距离向成像处理。其次,针对稀疏孔径的回波数据,通过构造成像算子和压缩感知重建模型的方法实现其距离徙动校正和方位压缩处理,进而获得二维成像结果。相比于传统的步进频率信号SAR成像,利用所提方法能够在少量的频率资源和雷达回波数据情况下实现准确的SAR成像。最后,通过对仿真和实测的步进频率雷达数据进行成像处理,验证了所提方法的有效性和可行性。     

基于CZT的机载并行双站斜视SAR成像算法

建立了机载并行双站斜视合成孔径雷达(SAR)的几何模型,给出了雷达回波的数学表达式,推导了它的二维频谱并对其特点做了分析。在二维频域内,先用聚焦函数对观测场景中心的点目标做精确成像,然后用Chirp-Z变换(CZT)校正中心点两侧目标回波的距离徙动,再通过方位向逆傅里叶变换得到了雷达图像。该算法利用了CZT能够处理非线性调频信号的特点,简化了处理过程,提高了计算效率和成像精度。仿真实验验证了这种基于CZT的新算法在处理并行双站斜视SAR数据时的有效性。     

Taylor expansion of the differential range for monostatic SAR

The polar format algorithm (PFA) for spotlight synthetic aperture radar (SAR) is based on a linear approximation for the differential range to a scatterer. We derive a second-order Taylor series approximation of the differential range. We provide a simple and concise derivation of both the far-field linear approximation of the differential range, which forms the basis of the PFA, and the corresponding approximation limits based on the second-order terms of the approximation.     

SAR imaging of moving targets

A method of forming synthetic aperture radar (SAR) images of moving targets without using any specific knowledge of the target motion is presented. The new method uses a unique processing kernel that involves a one-dimensional interpolation of the deramped phase history which we call keystone formatting. This preprocessing simultaneously eliminates the effects of linear range migration for all moving targets regardless of their unknown velocity. Step two of the moving target imaging technique involves a two-dimensional focusing of the movers to remove residual quadratic range migration errors. The third and last step removes cubic and higher order defocusing terms. This imaging technique is demonstrated using SAR data collected as part of DARPA's Moving Target Exploitation (MTE) program     

Polar format algorithm for bistatic SAR

Matched filtering (MF) of phase history data is a mathematically ideal but computationally expensive approach to bistatic synthetic aperture radar (SAR) image formation. Fast backprojection algorithms (BPAs) for image formation have recently been shown to give improved O(N/sup 2/ log/sub 2/N) performance. An O(N/sup 2/ log/sub 2/N) bistatic polar format algorithm (PFA) based on a bistatic far-field assumption is derived. This algorithm is a generalization of the popular PFA for monostatic SAR image formation and is highly amenable to implementation with existing monostatic image formation processors. Limits on the size of an imaged scene, analogous to those in monostatic systems, are derived for the bistatic PFA.     

基于两维空变滤波的PFA波前弯曲误差补偿

极坐标格式算法(PFA)因受波前弯曲误差的影响,其有效成像场景范围受到一定的限制。采用图像域的空变滤波(SVPF)处理可以有效补偿波前弯曲误差,但为了简化分析,已有SVPF方法在补偿过程中都采取了一定的近似,在对大场景进行高分辨率成像时仍然不能满足聚焦精度要求。对PFA的极坐标格式转换给出了一种新的解析解释,利用该解释推导得到了精确的波前弯曲误差表达式;基于该波前弯曲误差模型,提出了一种基于两维SVPF处理的波前弯曲误差补偿方法。最后通过仿真数据处理验证了该算法的有效性。     

Multiple moving target detection and trajectory estimation using a single SAR sensor

A novel methodology is presented for determining the velocity and location of multiple moving targets using a single strip-map synthetic aperture radar (SAR) sensor. The so-called azimuth position uncertainty problem is therefore solved. The method exploits the structure of the amplitude and phase modulations of the returned echo from a moving target in the Fourier domain. A crucial step in the whole processing scheme is a matched filtering, depending on the moving target parameters, that simultaneously accounts for range migration and compresses two-dimensional signatures into one-dimensional ones without losing moving target information. A generalized likelihood ratio test approach is adopted to detect moving targets and derive their trajectory parameters. The effectiveness of the method is illustrated with synthetic and real data covering a wide range of targets velocities and signal-to-clutter ratios (SCRs). Even in the case of parallel to platform moving target motion, the most unfavorable scenario, the proposed method yields good results for, roughly, SCR > 10 dB.     

Moving target detection via airborne HRR phased array radar

We study moving target detection in the presence of temporally and spatially correlated ground clutter for airborne high range resolution (HRR) phased array radar. We divide the HRR range profiles into large range segments to avoid the range migration problems that occur in the HRR radar data. Since each range segment contains a sequence of HRR range bins, no information is lost due to the division and hence no loss of resolution occurs. We show how to use a vector autoregressive (VAR) filtering technique to suppress the ground clutter. Then a moving target detector based on a generalized likelihood ratio test (GLRT) detection strategy is derived. The detection threshold is determined according to the desired false alarm rate, which is made possible via an asymptotic statistical analysis. After the target Doppler frequency and spatial signature vectors are estimated from the VAR-filtered data as if a target were present, a simple detection variable is computed and compared with the detection threshold to render a decision on the presence of a target. Numerical results are provided to demonstrate the performance of the proposed moving target detection algorithm     

Super resolution feature extraction of moving targets

High range resolution (HRR) moving target indicator (MTI) is becoming increasingly important for many military and civilian applications such as the detection and classification of moving targets in strong clutter background. We consider the problem of extracting the HRR features of moving targets with very closely spaced scatterers in the presence of strong stationary clutter, where the range migration and Doppler frequency are taken into account. A relaxation-based algorithm, which is robust and computationally simple, is proposed to deal with the above problem. Numerical results have shown that the proposed algorithm exhibits super resolution and excellent estimation performance