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.     

A simple and exact solution for the interferometric and stereo SAR geolocation problem

This paper provides a closed-form solution to the geolocation problem arising in the generation of digital elevation models (DEMs) via both stereo and interferometric synthetic aperture radar techniques. The proposed solution is found with no approximations in an arbitrary Cartesian reference system, thus efficiently allowing the generation of DEMs in a chosen cartographic projection. Moreover, it is amenable of an easy and precise sensitivity analysis that exploits the full three-dimensional nature of the problem, thus being particularly useful when high-squinted and/or crossed-track acquisitions are considered.     

A time-domain raw signal Simulator for interferometric SAR

In this paper, we present a time-domain (TD) raw signal simulator for an interferometric synthetic aperture radar (SAR). We consider the case of a spaceborne SAR operating in stripmap, spotlight, and hybrid modes, but the case of an airborne SAR can be considered as well. The spaceborne platform is considered as traveling on its nominal (Keplerian) orbit, and the targets are located on an ellipsoidal earth. We describe an accurate TD simulator, highlighting its usefulness in studying the effects on the SAR impulse response and on images from targets with limited extension due to operational conditions different from the nominal one.     

交轨干涉SAR涌浪干涉相位模型及数值模拟

建立了包含海表面高度和速度聚束的交叉轨迹干涉合成孔径雷达(AcrossTrack Interferometric Synthetic Aperture Radar,XTI-SAR)涌浪干涉相位模型,得到了涌浪成像的解析表达式.进一步研究了XTI-SAR沿方位向传播的涌浪成像机制.定义二次谐波振幅与基波振幅比率来表征成像非线性,通过比较XTI-SAR和沿轨迹干涉合成孔径雷达(Along-Track Interferometric Synthetic Aperture Radar,ATI-SAR)相位的二阶调和分量,分析不同海况和干涉SAR参数情况下的数值模拟,结果表明:当速度聚束弱时,XTI-SAR相位比ATI-SAR相位具有较强的非线性,ATI-SAR比XTI-SAR更适合测量海浪.当速度聚束强时,XTI-SAR相位比ATI-SAR相位具有较弱的非线性,XTI-SAR比ATI-SAR更适合测量海浪.     

基于GPU的SAR方位向信号分解的高效实现方法

提出了一种基于图形处理器(GPU)的SAR方位向信号分解的高效实现方法。SAR方位向信号可以通过四参数Chirplet分解方法来分解。此方法的关键难题是计算量过大,计算量主要由2部分组成:构建Chirp原子库,以及SAR方位向信号在过完备库上分解的计算量。与传统的CPU相比,GPU更加适用于密集型和大量数据并行化的计算。提出将算法的核心部分移植到GPU上进行并行计算,充分挖掘其运算潜能。结果表明:该方法与传统的基于CPU的算法相比有两位数以上的效率提升。     

A Bayesian filtering technique for SAR interferometric phase fields

SAR interferograms are affected by a strong noise component which often prevents correct phase unwrapping and always impairs the phase reconstruction accuracy. To obtain satisfactory performance, most filtering techniques exploit prior information by means of ad hoc, empirical strategies. In this paper, we recast phase filtering as a Bayesian estimation problem in which the image prior is modeled as a suitable Markov random field, and the filtered phase field is the configuration with maximum a posteriori probability. Assuming the image to be residue free and generally smooth, a two-component MRF model is adopted, where the first component penalizes residues, while the second one penalizes discontinuities. Constrained aimulated annealing is then used to find the optimal solution. The experimental analysis shows that, by gradually adjusting the MRF parameters, the algorithm filters out most of the high-frequency noise and, in the limit, eliminates all residues, allowing for a trivial phase unwrapping. Given a limited processing time, the algorithm is still able to eliminate most residues, paving the way for the successful use of any subsequent phase unwrapping technique.     

Using APES for interferometric SAR imaging

We present an adaptive finite impulse response (FIR) filtering approach, which is referred to as the Amplitude and Phase EStimation (APES) algorithm, for interferometric synthetic aperture radar (SAR) imaging. We compare the APES algorithm with other FIR filtering approaches including the Capon and fast Fourier transform (FFT) methods. We show via both numerical and experimental examples that the adaptive FIR filtering approaches such as Capon and APES can yield more accurate spectral estimates with much lower sidelobes and narrower spectral peaks than the FFT method. We show that although the APES algorithm yields somewhat wider spectral peaks than the Capon method, the former gives more accurate overall spectral estimates and SAR images than the latter and the FFT method.     

一种新的SAR图像的相干斑滤波方法

该文分析了合成孔径雷达(SAR)图像中的相干斑(Speckle)的统计特性,基于小波变换(WT),提出了一种新的相干斑滤波方法,该方法将小波变换后的HH分量采用Lee滤波,对HG,GH和GG分量则利用恒虚警技术(CFAR),保留重要的目标和边缘,再将这四个分量进行重构。实验结果表明,该方法具有相当良好的相干斑抑制性能,等效视数得以大幅度提高,并且能很好地保持原图像的边沿特征,其性能明显优于通常采用的Lee算法。     

方位多波束合成孔径雷达压缩感知成像研究

针对高分辨率宽测绘带合成孔径雷达(SAR)成像面临高速采样、大数据量存储等问题,将压缩感知(CS)理论与方位多波束(MAB)技术结合,提出一种基于压缩感知的方位多波束SAR成像方法。该方法对SAR回波信号进行快时间和慢时间维的降采样,然后分别构造距离和方位维的测量矩阵,利用随机滤波CS理论实现对目标的二维稀疏重建。仿真结果表明,该方法不仅能以较少的采样数据解决方位高分辨与宽测绘带之间的矛盾,还能在噪声存在的情况下重建目标的二维图像。     

Options for airborne interferometric SAR motion compensation

Airborne interferometric SAR (InSAR) has the potential to provide topographic data with a precision of the order of one metre. However, to generate data accurate to this level it is essential to measure and compensate for nonlinear motion of the two antennas which constitute the interferometric baseline. Conventional motion compensation techniques are extended to the two-channel imaging scenario of InSAR. Phase compensation of both channels to the same reference track and compensation to two separate tracks are considered and modeled using point target simulation, and real InSAR data. The single track approach allows track segmentation to follow aircraft drifts without causing discontinuities in the differential phase, but is sensitive to range cell migration effects. The dual track approach is not sensitive to these errors but suffers from discontinuous differential phase at segmentation boundaries, which complicates the phase unwrapping process. A new formulation for each approach is presented that compensates for unknown terrain coupled with low frequency aircraft motion. In addition, a new approach that uses the dual track approach initially and then converts to a single reference track after compression is proposed. This realizes the benefits of both approaches with only a small increase in computation     

An algorithm for interferometric SAR data processing

In this paper, an algorithm of generating INSAR unwrapped phase image from SAR single-look complex images is presented. Besides the general processing technique, this article focuses on the methods of flat-earth phase removal, phase noise reduction and phase unwrapping. The availability is tested by the results of processing ERS-1/2 SAR images.     

分布式星载干涉SAR中空间基线的分析和设计

分布式星载干涉SAR可以同时实现三维地形成像、洋流成像和提高空间分辨率等3种SAR于涉成像。其系统基线设计需要同时考虑这3种SAR干涉成像对基线的不同要求,所以比较复杂。该文在给出分布式小卫星被动稳定编队飞行的空间构形和3种SAR干涉成像对系统基线要求的基础上,提出了分布式星载干涉SAR基线设计中存在着3个制约关系;给出了协调这3个制约关系的一种设计准则,并在此准则下对一个L波段的分布式星载干涉SAR进行了系统基线设计。     

干涉合成孔径雷达边缘检测解相位模糊的方法

给出了一种干涉合成孔径雷达相位解模糊方法，该方法利用边缘检测算子确定干涉因子中干涉纹的位置。为了提高干涉纹的检测精度，将纹线检测和纹线跟踪相结合，并采用了中值滤波和相对平均灰度梯度法，该方法具有无积累误差且稳定性好的优点。利用三峡地区的L波段SIR-C并行轨道数据，运用上述方法得到了解模糊的相位图和局部区域的相对地形图，获得了比较满意的结果。     

Tomographic formulation of interferometric SAR for terrainelevation mapping

Topographic mapping with spotlight synthetic aperture radar (SAR) using an interferometric technique is studied. Included is a review of the equations for determination of terrain elevation from the phase difference between a pair of SAR images formed from data collected at two differing imaging geometries. This paper builds upon the systems analysis of Li and Goldstein in which image pair decorrelation as a function of the “baseline” separation between the receiving antennas was first analyzed. In this paper correlation and topographic height error variance models are developed based on a SAR image model derived from a tomographic image formation perspective. The models are general in the sense that they are constructed to analyze the case of single antenna, two-pass interferometry with arbitrary antenna line of sight, and velocity vector directions. Correlation and height error variance sensitivity to SAR system parameters and terrain gradients are studied     

A tethered interferometric synthetic aperture radar (SAR) for atopographic mission

Analyzes a spaceborne interferometric synthetic aperture radar (SAR) for high-resolution, topographic applications. Two physical antennas are vertically spaced and are carried along parallel paths by two different platforms connected by a tether. Tethered space systems have been proposed by several authors for different applications and a joint US-Italian program exists to deploy in 1992 a small satellite (Tethered Satellite System) from a Space Shuttle. A system performance analysis is carried out, considering a theoretical study and a numerical simulation. By evaluating the tethered interferometric SAR impulse response, the height of various point scatterers is computed and an error budget is obtained. Results show that this system is capable of achieving a root-mean-square (RMS) error in height measurement adequate for several applications     

Intensity-driven adaptive-neighborhood technique for polarimetric and interferometric SAR parameters estimation

In this paper, a new method to filter coherency matrices of polarimetric or interferometric data is presented. For each pixel, an adaptive neighborhood (AN) is determined by a region growing technique driven exclusively by the intensity image information. All the available intensity images of the polarimetric and interferometric terms are fused in the region growing process to ensure the validity of the stationarity assumption. Afterward, all the pixels within the obtained AN are used to yield the filtered values of the polarimetric and interferometric coherency matrices, which can be derived either by direct complex multilooking or from the locally linear minimum mean-squared error (LLMMSE) estimator. The entropy/alpha/anisotropy decomposition is then applied to the estimated polarimetric coherency matrices, and coherence optimization is performed on the estimated polarimetric and interferometric coherency matrices. Using this decomposition, unsupervised classification for land applications by an iterative algorithm based on a complex Wishart density function is also applied. The method has been tested on airborne high-resolution polarimetric interferometric synthetic aperture radar (POL-InSAR) images (Oberpfaffenhofen area-German Space Agency). For comparison purposes, the two estimation techniques (complex multilooking and LLMMSE) were tested using three different spatial supports: a fix-sized symmetric neighborhood (boxcar filter), directional nonsymmetric windows, and the proposed AN. Subjective and objective performance analysis, including coherence edge detection, receiver operating characteristics plots, and bias reduction tables, recommends the proposed algorithm as an effective POL-InSAR postprocessing technique.     

Optimal speckle reduction for the product model in multilookpolarimetric SAR imagery and the Wishart distribution

Several optimal techniques exist to reduce speckle effects on polarimetric data, e.g. the Linear Minimum Mean Square Error (LMMSE) vector filter for multilook detected data or optimum summations such as the Polarimetric Whitening Filter (PWF) for one look complex data. Among other drawbacks, these standard methods do not preserve full polarimetric data, or they do not use the a priori texture distribution, or they are restricted to one look data. In the simplified case of data satisfying the so-called “product model”, new optimal techniques are described in this paper that are able to reduce speckle effects on multilook data, while preserving fully polarimetric information and texture variations. This “product model” is valid when the scene texture has a large scale of variation and is polarization independent, for instance in K-distributed clutter. Under this assumption, the measured covariance matrix (multilook data) is the product of a scalar random variable μ (the texture) and the covariance matrix C_zh of an equivalent Gaussian homogeneous surface. C_zh is the mean covariance matrix and contains the polarimetric information. A PWF for multilook complex data (MPWF) is proposed and is shown to be related to optimal statistical estimators of the texture (Maximum Likelihood, Maximum A Posteriori, MMSE…) when the complex Wishart distribution is used. The ML estimation of C _zh for textured areas is given and the adaptive filters based on these new tools are described. The results indicate a large speckle reduction. Moreover, the mean values of polarimetric features such as the magnitude and the phase of the HH-VV complex degree of coherence are preserved     

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.<>     

针对距离向处理的SAR自适应成像算法

在研究传统SAR成像处理过程的基础上,将自聚焦的概念加以拓广,提出了一种自适应成像算法.该算法摒弃了传统自聚焦算法对距离徙动已被完全纠正的假设,将自适应处理的时机前移到距离徙动校正阶段,通过修正若干系统参数使得距离徙动被完美地校正,这些被修正的参数将被应用到后续的处理过程中.该算法具有比传统自聚焦算法更好的成像精度及效果,令输出图像具有更好的相位保持特性.     

基于极化干涉SAR图像的地物监督分类方法

X波段的高分辨率极化干涉合成孔径雷达（synthetic aperture radar,SAR）图像包含较强的斑点噪声,不利于地物分类等应用.针对这一问题,先使用Nonlocal滤波进行预处理,然后提取图像的极化特征和干涉特征,再使用支持向量机（support vector machine,SVM）和AdaBoost分类器对极化和干涉特征矢量进行分类.利用N-SAR系统于渭南市采集的极化干涉SAR数据进行验证,该数据共包含10类地物,并有足够的ground truth用来进行分类器的训练和测试.实验结果表明,AdaBoost分类器能对多类地物取得较好的分类效果,且干涉信息的加入能带来一定改善.