基于频率变标的调频连续波SAR成像算法

给出了一种改进的频率变标算法,该算法适用于处理距离解线调后的调频连续波SAR数据。对调频连续波SAR回波信号进行了建模,分析了信号的特征,揭示了平台的连续运动在距离向产生了一个多普勒频移的特性,应用频率变标技术,在频域完成补偿。实测数据处理结果表明,该算法能得到较好的成像结果。     

基于条带式SAR与聚束式SAR内在联系的SAR成像研究

针对条带式合成孔径雷达（stripmap sar）与聚束式合成孔径雷达（spotlight sar）的方位向频谱结构,讨论了两种模式SAR之间的区别与联系,利用两者之间的内在联系,提出斜视条件下将条带式SAR数据分块,进行聚束式处理的方法,并对聚束式成像区域大小参数的选择进行了分析.对于相同尺寸的成像区域,对条带式SAR进行聚束式处理可以减小运算量.采用空间频率插值成像算法实现了条带式SAR与聚束式SAR成像算法上的统一,最后应用外场实测数据完成成像,成像结果证实了理论分析的正确性.     

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     

Road detection in spaceborne SAR images using a genetic algorithm

This paper presents a technique for the detection of roads in a spaceborne synthetic aperture radar (SAR) image using a genetic algorithm (GA). Roads in a spaceborne SAR image can be modeled as curvilinear structures that possess width. Curve segments, which represent the candidate positions for roads, are extracted from the image using a curvilinear structure detector, and the roads are accurately detected by grouping those curve segments. For this purpose, the authors designed a grouping method based on a GA, which is a global optimization method. They combined perceptual grouping factors with it and tried to reduce its overall computational cost by introducing a concept of region growing. In this process, a selected initial seed is grown into a finally grouped segment by the iterated GA process, which considers segments only in a search region. To detect roads more accurately, postprocessing, including noisy curve segment removal, is performed after grouping. The authors applied their method to ERS-1 SAR and SIR-C/X-SAR images that have a resolution of about 30 m. The experimental results show that our method can accurately detect road networks as well as single-track roads and is much faster than a globally applied GA approach     

Improved nonlinear frequency scaling algorithm for squint FMCW SAR

An improved nonlinear frequency scaling algorithm is proposed to process squint frequency modulated continuous wave synthetic aperture radar data. The algorithm uses a decimation technique to decrease the bandwidth of the signal introduced by the frequency scaling operation, effectively removing the range frequency aliasing. Simulated results show the validity of the algorithm.     

机载平行等速双基SAR的极坐标格式成像算法

平行等速双基SAR是指收发平台速度大小和方向均相同的双基SAR系统,该构型具有广阔的应用前景。在此将传统适用于单基地SAR成像的极坐标格式算法（PFA）加以改进,使之适用于平行等速双基SAR成像处理。由于收发异置,回波信号在接收平面和发射平面的斜距几何关系比较复杂。为了便于后续的二维插值操作,用一个新的几何模型来描述收发平面上斜距的关系。该算法具有传统PFA算法的操作简单,易于实现的特点。最后通过仿真数据的成像处理对该方法进行了验证。     

Time-varying step-transform algorithm for high squint SAR imaging

High-squint angle synthetic aperture radar (SAR) imaging has applications in specific situations such as providing looking angle-dependent scattering information and revisiting an area of interest. It is very difficult for current SAR-imaging algorithms to be used directly in high-squint configurations. This is due to the large range-cell migration and the nonnegligible cubic-phase term in the signal. In this paper, an improved algorithm called the time-varying step-transform algorithm is proposed. It uses different chirp rates to deramp the signal in different subapertures to alleviate the range-focus problem. The interval between subapertures is also varied according to the deramping chirp rate. The nonnegligible cubic-phase term is included in the focusing procedure. The performance of the proposed algorithm in high-squint-angle mode is excellent. By reducing the subaperture length as the squint angle is increased, the performance of the algorithm is almost independent of squint angle. The proposed algorithm is also flexible for multilook processing and motion-error compensation     

并行机载双站斜视SAR ELBF-CS成像算法

论文建立了并行机载斜视双站SAR的结构模型和信号模型,用收发载机多普勒贡献比为加权系数推导了点目标回波的扩展Loffeld频谱公式(ELBF)。在二维频域内补偿双站扭曲项,然后对剩余相位项做Taylor展开,利用Chirp Scaling(CS)方法,推导了并行机载双站斜视SAR的ELBF-CS成像算法。双站结构参数及双站扭曲项的距离向空变性用回波数据的距离向分块处理,推导了数据分块条件,由此可以实现宽场景成像。算法基于更精确的ELBF,并用CS方法校正点目标距离徙动,处理流程更简单,成像效率更高,仿真验证了本文算法处理并行机载双站斜视SAR数据的有效性。     

机载斜视聚束合成孔径雷达快速成像算法

极坐标格式算法(PFA)是传统聚束SAR的经典成像算法,但用于斜视聚束成像存在二维频域插值计算量巨大、插值精度受插值核函数长度制约以及最终图像旋转带来成像质量下降等问题。针对上述问题,文中提出一种基于尺度变化的快速PFA算法,不仅能避免斜视成像后的图像旋转操作,还具有计算效率高的优势。快速PFA算法只需要FFT和复乘运算即可完成,与直接插值PFA算法相比计算量降低到原来的30%~50%。仿真实验验证了文中方法的有效性。     

适于双站SAR的后向投影高分辨率成像算法

为了研究在双站合成孔径雷达中直达波对成像分辨率的影响,提出基于后向投影的直达波消除高分辨率成像算法。首先,分析直达波的波达时间,获取收发端的距离信息及直达波的空间电磁分布;其次,分析电磁波历经多目标的成像空间后的接收信号(包含目标的反射回波及直达波);最后,分析此时空间的成像谱,并减去先验得到的直达波空间电磁分布,从而提高成像分辨率。研究表明:所提方法,不仅得到目标清晰的像,还适应不同接收器排布的情况,提高双站SAR系统成像分辨率的同时,还增加系统的应用灵活性。并在噪声中表现出良好的分辨率特性。     

地杂波背景下运动点目标的SAR成像算法

以理想面目标回波作为地杂波的近似，对面目标特征、面目标回波信号及其处理进行了分析，给出了以面目标为背景的运动点目标SAR成像算法，通过具体实例模拟仿真出独立运动点目标的SAR成像图和以面目标为背景的运动点目标SAR成像图。     

一种基于chirp信号的空间域鲁棒性水印算法

选取两个chirp信号作为水印信息,嵌入到图像空间域中与该信号有相同数字特征的像素点处,使用两个嵌入位置矩阵作为算法密钥的同时,还根据chirp信号在分数傅立叶变换域呈现冲激的特征来检测水印信号。仿真实验结果表明,该数字水印算法具有良好的不可见性和安全性,算法不仅能抵抗很强的JPEG压缩、加噪、滤波等常用的信号处理操作,对旋转、平移、剪切等几何攻击也有很强的鲁棒性。     

SAR图像上舰船目标检测的一种新算法

提出了一种改进的KSW算法检测SAR图像上的舰船目标.在该算法中,检测门限被选择以最大化背景与目标灰度熵加权和.由于加权系数的引入,该算法能针对SAR图像上舰船目标检测的实际情况,调整背景与目标灰度熵在准则函数中所占比例.当海杂波较弱时,该算法与传统的KSW算法等价.当海杂波较强时,其较传统的KSW算法有更好的表现.     

基于发射信号随机初相结合调频率极性捷变的SAR抗干扰方法

针对合成孔径雷达(SAR)难以抑制场景散射欺骗干扰的问题,提出了将发射信号的随机初相和调频率极性捷变技术相结合的方法,使得干扰信号无法充分获得SAR处理器在距离向和方位向的压缩增益,提高了处理前后的信干比。仿真实验验证了该方法良好的抗干扰性能。     

Complex SAR imagery and speckle filtering for wave imaging

A method is described to predict the wavenumber dependence of the speckle component in spectra of synthetic aperture radar intensity images. Filtering of this component is an important step in recovering waveheight spectra for synthetic-aperture radar (SAR) images of the ocean, and an effective means of doing so is required for the 'wave mode' of the European satellite ERS-1. The method uses the correlation function of the corresponding complex images and has been tested using a variety of airborne and spaceborne imagery obtained over both land and sea. Examples are shown of both successful and unsuccessful applications of the method.<>     

Sparse representation-based algorithm for joint SAR image formation and autofocus

Inaccuracies in the observation model of the synthetic aperture radar (SAR) due to inaccuracies of the velocity and position of the platform or atmospheric turbulence cause degradations in reconstructed images which necessitate the use of autofocus algorithms. In this paper we propose a novel signal processing algorithm for joint SAR image formation and autofocus in a synthesis dictionary based sparse representation framework. Proposed algorithm can be applied broadly to scenes that exhibit sparsity with respect to any dictionary. This is done by extending our previously developed sparse representation-based SAR imaging framework to joint SAR image formation and autofocus. To this end, the phase error vector is separated from the unknown phase of the complex-valued back-scattered field. Phase error vector is estimated using a MAP estimator and compensated through an iterative algorithm to produce focused images. We demonstrate the effectiveness of the proposed approach on synthetic and real imagery.     

A finite mixtures algorithm for finding proportions in SAR images

This correspondence describes an algorithm for estimating the proportions of classes in an SAR image by first assuming that an image consists of a mixture of a known number of different pixel types. A maximum likelihood estimate of the parameters of the resulting mixture distribution is then evaluated using the EM algorithm. An advantage of the finite mixtures approach is that the quantities of interest, the proportions, are directly estimated. The technique is applied to aircraft synthetic aperture radar (SAR) images of sea ice. In addition to finding the proportions of the classes, knowledge of the mixture components allows image displays tailored to a user's requirements.     

Slope-based frame selection and scaling technique for ship ISAR imaging

The authors address the problem of optimum imaging time selection and angular motion estimation for ship ISAR or hybrid SAR/ISAR imaging. The aim is to select proper imaging times and to estimate ship angular motion in order to obtain high-quality top view or side view scaled images of the ship, suitable for processing by classification/identification procedures. For this purpose, a new technique is proposed, able to select the time instants better suited for top or side view image formation and to estimate the rotation motion for image scaling. The technique is based on a novel model of the phase/Doppler frequency of the generic ship scatterer and operates entirely in the range-Doppler image domain (as obtained via Fourier transform) by using the slopes of some extracted linear features, thus without requiring coherent processing. The performance of the complete ISAR technique is analysed in depth; the results of the application of the proposed technique to both simulated and live ISAR data prove the effectiveness of the proposed approach.     

Downward looking sparse linear array 3D SAR imaging algorithm based on back-projection and convex optimization

Downward Looking Sparse Linear Array Three Dimensional SAR （DLSLA 3D SAR） is an important form of 3D SAR imaging,which has a widespread application field.Since its practical equivalent phase centers are usually distributed sparsely and nonuniformly,traditional 3D SAR algorithms suffer from low resolution and high sidelobes in cross-track dimension.To deal with this problem,this paper introduces a method based on back-projection and convex optimization to achieve 3D high accuracy imaging reconstruction.Compared with traditional SAR algorithms,the proposed method sufficiently utilizes the sparsity of the 3D SAR imaging scene and can achieve lower sidelobes and higher resolution in cross-track dimension.In the simulated experiments,the reconstructed results of both simple and complex imaging scene verify that the proposed method outperforms 3D back-projection algorithm and shows satisfying cross-track dimensional resolution and good robustness to noise.     

一种机载SAR成像实时角度补偿方案

为了解决载体的偏航、俯仰和滚转误差难以完全补偿的问题,提出一种利用SINS＋GPS组合导航信息的机载SAR成像实时角度补偿方案。成像处理启动时刻记录载体的姿态信息作为基准,成像过程根据导航信息实时补偿天线指向,计算准确的下视角和斜视角。挂飞实验证明,这种角度补偿方案能够为实时成像提供准确的输入参数,提高成像质量。