一种改进的星载聚束SAR子孔径ECS算法

在分析原有ECS算法的基础上,提出了一种适合于星栽聚束SAR成像的子孔径ECS算法。该算法对数据进行子孔径划分,可降低系统对PRF及运算存储量的要求。距离压缩采用斜视等效距离模型,实现精确的距离徙动校正。方位压缩采用方位scaling和频谱分析来实现,并分析推导了合理的方位scaling因子取值。最后,通过仿真验证了算法的有效性。     

Airborne SAR processing of highly squinted data using a chirpscaling approach with integrated motion compensation

Proposes a new approach for high-resolution airborne SAR data processing, which uses a modified chirp scaling algorithm to accommodate the correction of motion errors, as well as the variations of the Doppler centroid in range and azimuth. By introducing a cubic phase term in the chirp scaling phase, data acquired with a squint angle up to 30° can be processed with no degradation of the impulse response function. The proposed approach is computationally very efficient, since it accommodates the variations of Doppler centroid without using block processing. Furthermore, a motion error extraction algorithm can be incorporated into the proposed approach by means of subaperture processing in azimuth. The new approach, denoted as extended chirp scaling, is considered to be a generalized algorithm suitable for the high-resolution processing of most airborne SAR systems     

星载聚束式SAR改进的Frequency Scaling成像算法

本文提出一种适用于星载聚束式合成孔径雷达(SAR)的改进Frequency Scaling算法.基于斜视距离等效模型,推导出改进的FS算法,给出改进的FS因子和相关因子以及算法的实现步骤.在斜视情况下改进的FS因子可避免距离向频谱混迭,并可进行更精确的二次距离压缩,改进的方位因子可以减小算法所需要的方位时间展宽,提高方位处理效率.为解决高分辨率星载聚束式 SAR脉冲重复频率(PRF)过高等问题,在算法中结合了子孔径处理,并分析了采用子孔径处理的必要性及其实现方法.最后,通过计算机仿真,验证了算法的有效性.     

高分辨星载SAR改进ChirpScaling成像算法

本文提出了一种用于星载合成孔径雷达(SAR)的改进Chirp Scaling成像处理算法.本文分析了三种星载SAR距离模型,根据误差最小的斜视等效距离模型,推导了改进Chirp Scaling算法,给出了实现步骤.该算法适用于大距离徙动高分辨率星载SAR精确成像.并且基于改进的Chirp Scaling算法,分析了多普勒参数误差对成像质量的影响.最后通过计算机仿真,验证了算法的有效性.     

Spotlight SAR data focusing based on a two-step processing approach

The authors present a new spotlight SAR data-focusing algorithm based on a two-step processing strategy that combines the advantages of two commonly adopted processing approaches: the efficiency of SPECAN algorithms and the precision of stripmap focusing techniques. The first step of the proposed algorithm implements a linear and space-invariant azimuth filtering that is carried out via a deramping-based technique representing a simplified version of the SPECAN approach. This operation allows the authors to perform a bulk azimuth raw data compression and to achieve a pixel spacing smaller than (or equal to) the expected azimuth resolution of the fully focused image. Thus, the azimuth spectral folding phenomenon, typically affecting the spotlight data, is overcome, and the space-variant characteristics of the stripmap system transfer function are preserved. Accordingly, the residual and precise focusing of the SAR data is achieved by applying a conventional stripmap processing procedure requiring a minor modification and implemented in the frequency domain. The extension of the proposed technique to the case of high bandwidth transmitted chirp signals is also discussed. Experiments carried out on real and simulated data confirm the validity of the presented approach, which is mainly focused on spaceborne systems     

利用粗DEM信息的分布式卫星InSAR图像精配准算法

针对分布式卫星干涉合成孔径雷达图像配准中最大相干相关法在实际应用中缺乏理想相位估计值问题,提出利用粗数字高程模型反演干涉相位图作为理想相位估计值的处理方法。该方法通过在图像粗配准后利用主辅SAR图像的轨道信息、粗DEM以及主图像雷达成像几何反演出干涉条纹图,并将其作为理想干涉条纹估计值应用在最大相干相关法求取精配准偏移量中。此外,本文根据多基星载SAR雷达成像几何给出了利用粗DEM对SAR图像各像素对应目标点通用的空间定位方法及其干涉相位反演方法。ERS-1/2数据实验结果验证了本文方法的有效性。      

基于ChirpScaling算法的星载SAR成像处理实现方法

本文提出一种基于ＣｈｉｒｐＳｃａｌｉｎｇ（ＣＳ）算法的星载合成孔径雷达成像处理实现方法，该算法与目前国际上通用的距离－多普勒算法相比，由于避免了插值运算，且能够精确地进行距离徒动校正，使得成像质量优于精的ＲＤ算法。     

机载前视合成孔径雷达Chirp Scaling成像算法研究

针对目前机载侧视合成孔径雷达(SAR)无法对飞行路线正前方进行高分辨率成像的问题,该文研究了一种新型机载前视SAR,分析了前视SAR的工作原理和方位分辨率提高的可行性。基于空间几何模型和回波信号形式,推导并给出了适用于机载前视SAR成像的chirp scaling算法,给出了各相位补偿因子表达式及算法实现步骤。模拟了前视SAR点目标回波数据,并利用该方法对分布于场景中心及边缘的点目标阵进行了成像仿真,分析了成像效果,成像质量指标与理论值基本吻合,证实了算法的有效性。     

CNES general-purpose SAR correlator

CNES has designed a new SAR correlator to process both airborne and spaceborne data. This correlator allows data presumming prior to their radar processing. The migration compensation is performed in the range frequency/azimuth frequency domain and a constant phase reference is kept for further interferometric applications. The correlator offers great flexibility for the output geometry and formats: standard single-look complex product, any kind of multilooking, and a quick-look. Some image quality functions are included: raw data correction through look-up tables, a contrast seeker, and a radiometric equalization map. The architecture of the correlator is based on only two computer intensive functions: the fast-Fourier transform and a polynomial law generator. As a result, the software has good portability and good efficiency. Proved performances concerning various spaceborne or airborne sensors are given     

基于干涉图的星载MIMO-SAR动目标检测

受动目标径向速度影响,星载多输入多输出合成孔径雷达(MIMO SAR)等效通道回波模型中将引入周期误差信号的调制,进而导致动目标方位像存在“假峰”效应,其会增加动目标检测的虚警。基于ATI(along track interferometry)干涉图,提出一种星载MIMO SAR动目标检测方法。可在不补偿误差信号的前提下,先通过调节系统参数降低动目标“假峰”幅值,进而经干涉处理用杂波去弱化“假峰”干涉相位,最后利用ATI干涉图幅度和相位的联合处理实现动目标检测。数值试验验证了方法的有效性。      

非线性CS算法的前斜视SAR成像

针对SAR的前途斜视工作模式,该文建立了雷达信号的回波模型,详细分析了回波信号的瞬时方位频率和瞬时多普勒频率及距离Chirp斜率对方位频率的影响。然后结合经典的CS算法,提出了一种基于前斜视的改进CS算法,并利用该方法进行了仿真试验。理论分析和仿真结果表明,该方法更符合斜视SAR的几何关系,能有效地进行距离压缩、距离徒动校正和方位聚焦,改善了成像质量。     

星载斜视滑动聚束SAR子孔径成像处理算法研究

斜视滑动聚束大幅提升了星载SAR单航过多角度观测能力和观测灵活性,但随着斜视角和扫描角度增加,斜视附加带宽和非线性变化的瞬时多普勒中心给多普勒解混叠带来困难。针对上述问题,本文提出了一种基于子孔径处理的星载斜视滑动聚束成像算法。该算法首先改进了传统子孔径划分方法,通过两维频谱拼接和多普勒滤波,解决了子孔径数据仍存在的多普勒混叠,然后利用基于四阶斜距模型的CS算法完成聚焦成像。最后,通过计算机仿真验证了方法的有效性。      

四阶模型方位NCS高分辨SAR成像

针对长积累时间SAR回波耦合性强,聚焦困难的问题,从提高成像模型近似精度和距离徙动校正精度两方面开展了SAR成像研究,推导了一种考虑方位非线性调频变标(NCS)的四阶近似成像模型。首先,为了提高模型近似度,将斜距展开到四次项;然后,为了将距离向和方位向进行初步解耦,在时域进行走动补偿,但是带来了聚焦深度问题,高分辨成像时,这种现象更明显;为此,二维频域解耦后又在方位向采用二阶非线性变标方法解决这一问题。仿真结果表明,从主观分析和量化指标两方面来讲,该算法优于传统的高分辨斜视SAR成像算法。     

An effective focusing approach for azimuth invariant bistatic SAR processing

This paper proposes a processing method to extend monostatic imaging algorithms for the azimuth invariant bistatic SAR (BISAR) data where the transmitter and the receiver move on parallel tracks with equal velocities. The bistatic range history is approached by a polynomial of the azimuth time. Based on this model, an analytic 2-D signal spectrum derived by the method of series reversion is utilized and a simple one-to-one mapping between the transmitter and the receiver closest ranges is established. In this way, efficient monostatic imaging algorithms which operate in the 2-D frequency domain or the range-Doppler domain are easily modified to handle the BISAR data. In this paper, a chirp scaling algorithm for the BISAR is developed as an application of the new method. By implementing two key operations, range cell migration correction by a chirp scaling, and azimuth compression by a curve fitting technique, this algorithm is able to process the azimuth invariant BISAR data. Simulation results are presented to demonstrate the validity and the efficiency of the proposed algorithm.     

星载干涉SAR中的基线问题

基线在星载干涉SAR的系统设计和数据处理中起着非常重要的作用.本文比较全面地阐述了空间基线在星载干涉SAR中的作用.特别分析了星载干涉SAR中空间基线对SAR图像相关性、地距分辨率以及干涉SAR数据处理中的距离向平地效应和多视平均处理的影响.讨论了星载干涉SAR空间基线的设计问题,推导了空间最优基线的确定公式.最后进行了计算机仿真,仿真结果表明分析正确.     

一种面向无参考点的顺轨干涉SAR海面复图像配准方法

顺轨干涉SAR海面复图像通常利用静止陆地参考点进行配准,获得精确有效的海洋流场干涉相位信息。复图像中无参考点时,仅能依据海浪纹理进行配准,受海面随机运动以及低信噪比的影响,配准像素偏移往往会出现像素级误差,并导致干涉相位图质量严重下降。根据大尺度海浪变化周期较长,在干涉成像间隔内可视作静止这一特征,该文提出保留大尺度海浪对应的方位谱分量以提高数据信噪比和相关性,进而提高配准精度的方法,并选用海面实际方位分辨率作为大尺度海浪方位谱选取范围的约束条件。通过机载顺轨干涉SAR实验数据证明,所提方法可有效提高无参考点海面复图像的配准精度。     

提高双通道低频SAR干涉图性能的方法

沿航向干涉法是一种检测运动目标简单易行的有效方法。在低频双通道SAR系统中,为了保证干涉性能,不仅要考虑降低图像相干性的各类误差,还要考虑实时成像过程中残留的RFI对通道图像的影响。本文首先与高频系统中的误差进行比较,分析了影响低频双通道SAR系统的主要误差及其特点;其次分析了RFI对干涉图干扰的基本原理与特征,进而提出了一种提高双通道低频SAR干涉图性能的误差校正方法。该方法充分考虑了低频SAR系统的接收机频率特性误差、天线方向图误差、干涉相位误差及图像配准误差,利用基于方位时域距离频域干涉图的中值滤波器能够有效抑制具有窄带特性、时变性和空变性的RFI信号。国内首批机载双通道低频SAR实测数据验证了该方法的有效性与可靠性。该算法运算简单,效率高,适合对沿航向干涉法的实时处理。     

一种适于机载前斜视SAR成象处理的Chirp Scaling算法

Ｃｈｉｒｐ Ｓｃａｌｉｎｇ算法是一种高效、高精度的ＳＡＲ成象处理算法，算法解决了在宽天线波束或者天线高斜视角情况下获得高分辨力图象的问题。本文在Ｃｈｉｒｐ Ｓｃａｌｉｎｇ算法的基础上，提出采用新的结构和新的相位函数来接纳机载ＳＡＲ成象处理所需的运动补偿相位，使得Ｃｈｉｒｐ Ｓｃａｌｉｎｇ算法成为机载前斜视ＳＡＲ的一种实用的、高效算法。本文给出了一幅采用该算法处理的德国宇航院（ＤＬＲ）的Ｅ－ＳＡＲ图     

New applications of nonlinear chirp scaling in SAR data processing

New applications of nonlinear chirp scaling (NLCS) have been found in processing monostatic and bistatic SAR data acquired in the strip-map mode. When the effects in impulse response broadenings due to quadratic range migration are negligible for short radar wavelengths, a time domain range cell migration correction (RCMC) can be applied. After the correction, the FM rates of targets confined in a range gate will differ from each other. A nonlinear chirp perturbation function can be applied to each range gate to equalize the targets' FM rates before azimuth compression. This algorithm is analyzed in the paper and is supported by point target simulation experiments     

星载TOPSAR方位变标成像算法

Burst工作模式和方位波束主动扫描使得TOPSAR回波信号同时存在多普勒频率混叠和方位输出时间混叠的问题.时域和频域同时升采样操作的"全孔径"方法虽然能够解决混叠问题,但同时带来成像运算量和内存消耗显著增加.根据星载TOPSAR回波特殊的方位时频关系,提出了一种结合方位变标操作的CS成像算法.方位变标操作可以避免"子...