基于RADARSAT-2数据的SAR图像双视向几何校正方法研究

针对山区高分辨率雷达卫星Radarsat-2图像的严重几何变形,提出了一种新的双视向雷达图像几何校正方法.实验证明该方法可以有效祛除地形引起的各种几何变形,防止地形引起的后向散射系数的失真,特别是能够有效祛除叠掩和阴影的影响,而这个问题是基于单幅雷达图像的传统几何校正方法无法解决的.为合成孔径雷达(SAR)图像在山区的...     

一种InSAR建筑物图像仿真及高程反演方法

城市建筑区域叠掩、阴影严重,图像理解困难且干涉相位变化复杂紊乱,一直是InSAR处理的困难区域。SAR图像仿真能为图像理解和处理方法研究提供数据支撑,然而现有建筑区域SAR图像仿真方法大多无法获得具有相干性的干涉SAR图像对。该文提出了一种面向建筑区域的干涉SAR复图像对仿真方法,能够获得建筑的复数图像对、干涉相位图以及叠掩成分数目等信息,为城区干涉SAR处理及信息提取研究提供仿真数据支撑。同时,基于仿真中对相位变化规律的分析,提出叠掩区相位解缠时的基准确定方法,解决传统解缠方法面临的叠掩区域干涉相位不连续问题,进而反演建筑高程信息。最后,通过建模仿真结果与实际SAR图像和干涉相位的对比,验证了仿真方法的正确性,并对仿真及实际干涉相位进行解缠和高程反演处理,验证了该文高程反演方法的有效性。      

Accurate and efficient determination of the shoreline in ERS-1 SARimages

Extraction of the shoreline in SAR images is a difficult task to perform using simple image processing operations such as grey-value thresholding, due to the presence of speckle and because the signal returned from the sea surface may be similar to that from the land. A semiautomatic method for detecting the shoreline accurately and efficiently in ERS-1 SAR images is presented. This is aimed primarily at a particular application, namely the construction of a digital elevation model of an intertidal zone using SAR images and hydrodynamic model output, but could be carried over to other applications. A coarse-fine resolution processing approach is employed, in which sea regions are first detected as regions of low edge density in a low resolution image, then image areas near the shoreline are subjected to more elaborate processing at high resolution using an active contour model. Over 90% of the shoreline detected by the automatic delineation process appear visually correct     

Spotlight mode SAR stereo technique for height computation

This paper examines the feasibility of extracting three-dimensional (3-D) or topographic information in spotlight mode stereo synthetic aperture radar (SAR). A display of a SAR (intensity) image has two axes: range and cross-range. Elevated scatterers appear closer in range; this phenomenon is called radar image layover. How the height of each scatterer can be computed from the difference in its layover between two images is investigated. This is analogous to computing height from disparity distance (triangulation) in optical stereo. The same procedure can be applied on pixel by pixel basis for terrain elevation mapping. A general expression is derived for the accuracy of the height estimate as a function of the range resolution and the angular difference between the image planes. Accuracy increases as the angle between the image planes increases, but the bright scatterers in one image tend to fade in the other image. This limited angular persistence of radar scatterers is also discussed. Trajectories for data collection are examined that provide near-optimal height estimates while eliminating the scatterer persistency problem.     

几何模型约束的SAR图像建筑物提取

利用高分辨率SAR图像进行建筑物提取的常规方法是首先利用二次散射特征线确定建筑物边界, 然后利用叠掩、阴影等散射特征来提取建筑物高度.当建筑物目标走向与星载SAR方位向夹角较大时, 其二次散射特征不明显, 常规重建方法不能取得理想结果.针对这类建筑物目标, 在分析SAR图像上的散射特征为平行四边形条带的基础上, 提出一种基于几何模型约束的建筑物自动提取与三维重建方法.将该方法应用于TerraSAR-X聚束模式图像, 并对提取结果进行了分析和评价, 表明该方法能够有效提取建筑物目标及其三维信息.     

The Recognition of Extended Targets: SAR Images for Level And Hilly Terrain

An experiment was performed using radar image simulation techniques to determine what a SAR image would look like for a collection of area extensive targets, first with flat underlying terrain and second, in the presence of moderate relief. Although compression, layover, and shadow are well known from the one-dimensional geometry analyses, it has not been previously demonstrated in a pictorial fashion what happens to the appearance of the same controlled reflectivity pattern, for level and hilly ground. It is not surprising to radargrammetrists that even modest elevation changes seriously affect the detection and recognition of boundaries and shapes. The image results clearly demonstrate these effects, and are valuable for many researchers who have previously used, or are just beginning to apply SAR imagery to crops and soils, minerals, and water resources assessment, etc. This research was performed during the course of an investigation to establish the performance of the Seasat-A SAR, in terms of user-oriented features, thus the radar system model and geometry are pertinent to that sensor, although the results can be applied to radar imaging in general. A review of range perspective imaging is included, since information extraction from radar imagery necessitates the knowledge of geometry/propagation effects.     

无先验模型复杂结构设施SAR全方位三维成像方法研究

复杂结构设施的SAR三维成像是SAR成像领域的热点和难点问题。现有SAR三维成像依赖于高程方向的多通道或多次飞行,对雷达系统或数据获取的要求较高。该文提出无先验模型复杂结构设施三维成像方法,仅需一次飞行即可获得先验信息未知区域全场景全方位三维图像。该方法充分利用圆迹SAR的全方位观测、解叠掩和解高程模糊优势,无需目标预先建模和三维成像网格构建,适用于大面积区域复杂结构设施的精细三维成像,在雷达三维成像实用化技术方面取得了重要进展。通过该方法首次获得FAST射电望远镜的雷达全方位三维图像,验证了理论与方法的正确性与有效性。      

Removal of terrain effects from SAR satellite imagery of Arctictundra

Synthetic aperture radar (SAR) images of the Earth's terrestrial surface contain geometric and radiometric image effects which are caused by varying terrain elevation and slope. The radiometric effects tend to mask signal variations caused by other physical variables such as soil moisture and surface vegetation type, which are known to influence SAR backscatter signals. As a result, raw SAR images are of limited use in classifying surface vegetation type or quantifying the spatial distribution of soil moisture in regions of terrain relief, The authors present a technique for removing radiometric terrain effects from SAR images. Image correction was carried out in two steps. First, an existing modeling package was used in combination with digital elevation data in order to map the raw image pixels onto a geodetic coordinate system, thereby removing the geometric portion of the image distortion. Radiometric effects were then removed with the aid of a backscatter model which treats the reflected radiation as a combination of diffuse-Lambertian and specular components. Parameters in the backscatter model were determined by comparing two C-band SAR images of a test area in a region of Arctic tundra which were taken from ascending and descending orbit tracks of the ERS-1 satellite. The ascending and descending images displayed reductions in pixel value variance of 30% and 13%, respectively, after processing. Direct comparison of the two test area images reveals a dramatic improvement in image similarity after processing     

Special Phenomena of the Shadow Region in the High Resolution Synthetic Aperture Radar Image due to Synthetic Aperture

With the development of several High Resolution (HR) Synthetic Aperture Radar (SAR) systems, many special phenomena appear in the SAR image, especially for the SAR image with millimeter wave. We firmly believed that every detail in the SAR image should have its own special mechanisms and these details may provide some key clues for us to build up the frame work on understanding the SAR image. The synthetic aperture is one of the important particularities about SAR, and the radar is moving during the data is collected, which leads many special phenomena in the SAR image; one of these is the shadow with blurred boundary. In this work, the effect on the shadow region in the SAR image by synthetic aperture is expanded on. The blurred boundary of the shadow is analyzed using imaging formation theory, and the Quadratic Phase Errors (QPE) brought by the synthetic aperture progress is deduced for the first time, which builds up the relationship between the parameters of the shadow caster and the behavior of the shadow in the SAR image. It is found that the QPE is approximately a linear function of the height of the shadow caster. Furthermore, an approach for shadow enhancement based on height variant phase compensation is proposed and it could provide a better effect on shadow enhancement than the traditional technique called Fixed Focus Shadow Enhancement (FFSE), which is proved by theoretical analysis and experiments. Based on the analysis, some typical application of the shadow in SAR image is designed and some mini-SAR image with Ku-band is analyzed about the shadow region. It is expected that the work in this paper could be some helpful for the SAR image understanding and the microwave imaging with high resolution.     

机载双天线InSAR对飞数据处理与分析

干涉合成孔径雷达(InSAR)技术具有高精度的地形测绘能力。然而在山区地形条件下,受SAR侧视成像的影响,存在较多的几何畸变区域,干涉相位表现为不连续或者缺少有效信息的情况,对单一的干涉图像对处理难以得到精确的数字高程模型(DEM)。融合两个或多角度的干涉数据可以用于解决这一问题。该文根据这一思路利用机载双天线InSAR对飞数据进行实验,针对山区地形条件下参考高程近似影响运动补偿精度的问题提出了基于高程迭代的运动补偿方法,对于阴影、叠掩区域容易导致相位解缠误差的问题提出基于地形特征的相位解缠方法,从而尽可能降低单一角度数据的DEM误差,以达到消除对飞数据重叠区域3维定位不一致的目的,拼接实验结果验证了处理方法的有效性。      

新体制SAR三维成像技术研究进展

常规SAR成像,平台沿直线飞行,形成直线型合成孔径,仅能获取2维图像,即3维空间中的观测场景在斜距-方位平面的2维投影,图像具有叠掩、透视缩短、阴影等畸变现象。SAR 3维成像突破了斜距-方位2维频率信息获取,能够获取第3维频率信息,实现3维分辨,可获得观测场景的散射中心在3维空间中的分布,从而解决叠掩问题,消除透视缩短、顶底倒置等几何形变现象,更直观地描述客观场景,已成为国际研究热点。该文介绍SAR 3维成像的概念和主要观测模式,分析该领域国内外研究现状和进展,重点阐述作者所在研究团队的SAR 3维成像研究进展,最后对SAR 3维成像技术进行总结和展望。      

Opposite side ERS-1 SAR stereo mapping over rolling topography

Opposite-side radar stereo images have been considered unsuitable for stereo viewing due to illumination differences which limit the ability to identify the same features in the image pair. In some contexts, like a rolling topography (slope less than 10°), the shadow, layover, and foreshortening effects, specific to radar images, will not be overwhelming with an opposite-side stereo pair. This paper reports on some issues of stereo viewing and plotting, as well as on quantitative results of mapping and features extraction from ascending and descending orbit ERS-1 SAR stereo images. Planimetric accuracy of 17 m and altimetric accuracy of 23.9 m have been achieved for lake shorelines and DEM extractions, respectively. Impacts of different parameters on the accuracy are also evaluated     

一种联合阴影和目标区域图像的SAR目标识别方法

地面目标的SAR图像中除了包含目标散射回波形成的区域,还包括由目标遮挡地面形成的阴影区域。但是由于这两种区域中的图像特性不相同,所以传统的SAR图像自动目标识别主要利用目标区域信息进行目标识别,或者单独使用阴影区域进行识别。该文提出一种阴影区域与目标区域图像联合的稀疏表示模型。通过使用1\2范数最小化方法求解该模型得到联合的稀疏表示,然后根据联合重构误差最小准则进行SAR图像目标识别。在运动和静止目标获取与识别(MSTAR)数据集上的识别实验结果表明,通过联合稀疏表示模型可以有效地将目标区域与阴影区域信息进行融合,相对于采用单独区域图像的稀疏表示识别方法性能更好。     

基于分层多区域CV模型的SAR图像分割

在SAR图像分割中,尤其是车辆目标的SAR图像分割中,一般需要得到目标和阴影两个区域的分割结果。文中为了解决车辆目标的SAR图像多区域分割,提出了一种分层多区域CV模型,该模型结合了一种新的惩罚项,并且同时使用水平集函数的阶跃初始化,使模型具有了良好的水平集演化的属性。同时,模型对噪声的敏感性下降,使模型适用于未预处理的SAR图像。最后,对比Chan-Vese多区域分割模型,将分层多区域CV模型应用于未预处理的SAR图像,实验结果验证了模型的有效性。     

多方位角多基线星载SAR三维成像方法研究

传统星载合成孔径雷达(Sythetic Aperture Radar, SAR)采用多基线的方式可获取目标区域的3维图像,解决了SAR 2维图像中的叠掩问题,但仍存在因遮挡导致的信息获取不足的问题。为此,该文首次提出了多方位角多基线星载SAR 3维成像方法,其不仅解决了叠掩问题,还通过融合不同方位角下获取的3维点云减少了遮挡区域,提升了星载SAR信息获取能力。文中首先建立多方位角多基线星载SAR空间观测模型,并通过推导论证斜视多基线观测和正侧视多基线观测具有相同的数学信号模型,为直接将正侧视时的3维成像方法应用于斜视时的3维处理提供理论支撑;在此基础上,给出多方位角多基线星载SAR 3维成像方法及处理流程,其包括SAR斜视3维处理和多方位角3维点云融合两个步骤;最后,通过方位角45°下的点阵目标实验验证SAR斜视3维处理方法的有效性,并利用方位角45°和–45°下的直升机目标仿真验证多方位角3维点云融合方法的有效性。      

基于空间聚类种子生长算法的阵列干涉SAR点云滤波

阵列干涉合成孔径雷达(Synthetic Aperture Radar, SAR)通过在交轨向布置多个天线,结合方位向的合成孔径和斜距向的大带宽信号,具备了3维分辨能力,且多个阵元保证了其在高程向的空间采样,能够解决干涉SAR(Interferometric SAR, InSAR)测绘中的叠掩问题,实现观测场景的3维成像。但是获得场景区域的3维点云分布中存在较多杂点,高程向误差较大,所以传统的激光雷达(Light Detection And Ranging, LiDAR)点云滤波方法不适用于阵列干涉SAR点云的滤波处理。针对该问题,该文提出基于空间聚类种子生长算法的阵列干涉SAR点云滤波算法,应用密度和高程双重阈值生成密度-高程图像,通过图像处理手段去除小型杂点,利用空间聚类种子生长算法将植被等从点云数据中去除,完成点云滤波处理。利用国内首次机载阵列干涉SAR实验数据,通过与传统LiDAR滤波方法进行比较,验证了该文算法的有效性,为后续建筑物提取和精细化处理提供保障。      

Exact closed-form geolocation for SAR interferometry

Exact closed-form algorithms for InSAR-derived digital elevation model (DEM) geolocation are described. They are based on the knowledge of orbit parameters and time/Doppler frequency coordinates of each SAR image, as well as of their interferometric phase. The proposed scheme gives a simple framework for deriving the geolocation accuracy     

Terrain influences in SAR backscatter and attempts to theircorrection

Synthetic aperture radar (SAR) images reveal radiometric image distortions that are caused by terrain undulations. The authors present the results of a study extracting and investigating the various components of these terrain influences. An imaging model, is set up for the geometric rectification of the SAR image and for a reconstruction of the imaging geometry. A prerequisite for the setup of this model is the use of a digital elevation model. Eight different geometric parameters are derived and investigated for their influence on grey-value variations in the geocoded SAR image. Image grey-value variations of three major land-use classes-forest, agricultural land, and urban/suburban areas-are examined. Empirical models of the SAR-backscatter variations are used to describe the relations between image grey values and various geometric parameters     

基于SAR影像模拟几何校正算法参数误差影响分析

基于SAR影像模拟的几何校正算法以其不需要提供地面控制点、精确的成像参数以及所有操作可自动完成等优点,在SAR图像几何校正中受到了广泛的关注和应用。然而测量设备误差的存在,使得算法输入参数（航向角、飞行高度、近端斜距、DEM高程）存在误差,这会引起SAR模拟图像特征发生变化,严重时还会引起图像匹配参数（控制点）误差,降低几何校正精度。论文分析了算法输入参数和控制点对SAR影像模拟和图像匹配的影响,在此基础上完成了关于参数误差影响的较完整的分析,导出了一套相应的计算公式,弥补了现有文献中的一些空缺。      

Advantages of multiscale product filters for dynamic range compression in images

A multiscale product filter (MSPF) structure is proposed for use in digital image enhancement. The objective for this type of image processing is to mitigate the effect of uneven illumination on perceived image quality, a process known as dynamic range compression (DRC). The properties of the MSPF for DRC are investigated, a theoretical model is presented, and this model is used to predict the performance of the filter under step changes in illumination such as those caused by shadows. The advantage of the MSPF is that it provides a relatively rapid response for transitions from shadow regions to well-lit regions. This property is verified using random Mondrian textures with simulated illumination changes. The estimated illumination profile is compared with that used to generate the synthetic image using the Pearson's correlation coefficient. The improved performance of the MSPF is also confirmed by the mitigation of shadow artefacts in real images