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...     

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     

Radar Image Processing for Rock-Type Discrimination

Radar images have unique radiometric and geometric characteristics which present unique problems and opportunities for geological application. This paper reviews preprocessing and analytical techniques found useful or promising for applications of radar images to geologic problems such as rock-type discrimination. The use of coherent monochromatic illumination in radar images results in image speckle noise which interferes with characterization of the imaged surface. Median value filtering of the radar images removes speckle with minimal edge effects and resolution degradation. Variations in radar scene illumination due to uncompensated sensor platform motions or antenna pattern effects can be somewhat corrected for by mean and variance equalization in a direction perpendicular to the resulting image gradient. Registration of radar images to a map base and compensation of terrain induced image distortion can be accomplished by registration to digital elevation models and knowledge of imaging geometry. Analysis of SEASAT images with coregistered LANDSAT images indicates that the radar data can make a significant contribution to rock-type discrimination, especially if textural measures are incorporated. The sensitivity of radar backscatter to local slopes makes radar images an excellent medium from which to extract textural measures. Three techniques for extraction of the textural data inherent in the radar images are presented. Computation of image tone variance over various areas can numerically encode image texture. Hue-saturation-intensity split spectrum processing displays low-frequency variations in color while preserving high-frequency detail.     

Terrain influences on SAR backscatter around Mt. Taranaki, NewZealand

An L-band SAR image from the Japanese JERS-1 satellite has been analyzed for the effects of local surface orientation relative to the radar illumination direction. Orthorectification of the SAR imagery and determination of the local surface orientation is achieved with the aid of a high resolution digital terrain model. An improved method of determining scatterer density for a surface in three dimensions is introduced and used to correct radiometrically the image for terrain variation. Residual radiometric effects due to surface orientation are shown to be dependent on the ground cover class. Backscatter from the indigenous forest was more isotropic than that from the farmland. As accurate registration was required for this study, a method for identifying control points in the rectified imagery is described which alleviated the difficulty of identifying them in the raw image     

Evaluation of terrain models for the geocoding and terraincorrection, of synthetic aperture radar (SAR) images

The variability of the resolutions and the presence of artifacts cause inaccurate correction of the terrain-induced geometric distortions in synthetic-aperture radar (SAR) images. To quantify the effects of these inaccuracies on SAR terrain correction, corrections of a Seasat SAR image were performed using a 1° US Geological Survey (USGS) terrain model, a 7.5-min USGS terrain model, and a terrain model derived from stereoimagery acquired from SPOT. Geometric verifications of the corrected imagery showed that the resolution of the 1° terrain model is not adequate to resolve many features in the Seasat image. Geometric verifications of images corrected with the two higher resolution terrain models showed localized errors as large as 52 m for mountain peaks. However, comparison of data corrected with those models shows that both produce results that differ by less than the resolution of either of them. Periodic artifacts observed in the terrain models translated to ground range differences of 18 m, which are well below the resolution of the SAR imagery     

复杂场景微波辐射图像的模拟

模拟生成微波辐射图像是为了用其作地形匹配制导中的基准图。文中分析了光学图像和微波辐射图像之间的几何关系，讨论了光学图像的分割、识别及表面方向获取的方法，论述了地物表面温度、亮度温度、视在温度、天线温度和天空温度之间的关系，并在此基础上提出了一种模拟生成复杂场景微波辐射图像的方法。仿真结果表明，方法完全可行。     

基于级联变换的光学和SAR图像配准算法

针对光学和SAR(Synthetic Aperture Radar)图像配准中存在明显辐射和几何差异的问题,提出了一种基于级联变换的多源遥感图像配准方法.首先,利用灰度变换提取光学和SAR图像间的稳定结构特征,去除辐射差异性;然后,提出一种新的加权对数极坐标变换算法,解决图像间全局几何差异性,保证算法的尺度和旋转不变性,并初步得到整体的平移量;最后,通过局部几何变换,得到一系列的匹配点对,构建薄板样条模型,实现图像的精确配准.实验验证了算法去除辐射差异性和获得全局几何变换参数的能力,与传统的多源图像配准算法相比,基于级联变换的配准算法鲁棒性好,配准精度高.     

基于曲面投影的毫米波InSAR数据成像方法

与其它波段相比,毫米波系统具有体积小、重量轻、分辨率高等优点,成为近几年InSAR技术的研究热点。但因其波长短,毫米波InSAR对平台运动轨迹测量精度要求更高,非理想运动情况下传统成像方法数据处理及干涉相位提取困难,另外传统方法基于平面投影成像,在地形陡变时干涉相位缠绕和目标几何畸变较严重。为了解决传统方法在毫米波InSAR成像的以上不足,该文提出了一种基于曲面投影的毫米波InSAR成像方法,将不同通道回波数据投影到相同地形高程曲面上进行成像及干涉相位提取,并推导了曲面下地形高程与干涉相位的关系。仿真和实测数据结果验证了该文方法的有效性,结果显示该方法在平台非理想运动下较传统算法获得更好的InSAR成像和干涉相位质量,且减小了地形高程起伏引起的几何畸变及干涉相位缠绕,更有利于毫米波InSAR图像地形特征描述及高程提取。      

Improved Spatial Mapping of Rainfall Events with Spaceborne SAR Imagery

The Seasat satellite acquired the first spaceborne synthetic-aperture radar (SAR) images of the earth's surface, in 1978, at a frequency of 1.275 GHz (L-band) in a like-polarization mode at incidence angles of 23 ± 30. Although this may not be the optimum system configuration for radar remote sensing of soil moisture, interpretation of two Seasat images of Iowa demonstrates the sensitivity of microwave backscatter to soil moisture content. In both scenes, increased image brightness, which represents more radar backscatter, can be related to previous rainfall activity in the two areas. Comparison of these images with ground-based rainfall observations illustrates the increased spatial coverage of the rainfall event that can be obtained from the satellite SAR data. These data can then be color-enhanced by a digital computer to produce aesthetically pleasing output products for the user community. When the methodology for extracting accurate information about soil moisture status from radar data is developed, it will prove useful in a wide variety of agronomic and hydrological investigations.     

Sensitivity to soil moisture by active and passive microwavesensors

The backscatter measured by radar and the emission measured by a radiometer are both very sensitive to the moisture content m_υ of bare-soil surfaces. Vegetation cover complicates the scattering and emission processes, and it has been presumed that the addition of vegetation masks the soil surface, thereby reducing the radiometric and radar soil-moisture sensitivities. Even though researchers working in the field of microwave remote sensing of soil moisture are all likely to agree with the preceding two statements, numerous claims and counterclaims have been voiced, primarily at symposia and workshops, espousing the superiority of the radiometric technique over the radar, or vice versa. The discussion is often reduced to disagreements over the answer to the following question “Which of the two sensing techniques is less impacted by vegetation cover?” This paper is an attempt to answer that question. Using realistic radiative-transfer models for the emission and backscatter, calculations were performed for three types of canopies, all at 1.5 GHz. The results lead to two major conclusions. First, the accepted presumption that vegetation cover reduces the soil-moisture sensitivity is not always true. Over certain ranges of the optical depth τ of the vegetation canopy and the roughness of the soil surface, vegetation cover can enhance, not reduce, the radar sensitivity to soil moisture. The second conclusion is that under most vegetation and soil-surface conditions, the radiometric and radar soil-moisture sensitivities decrease with increasing τ, and the rates are approximately the same for both sensors, suggesting that at least as far as vegetation effects are concerned, neither sensor can claim superiority over the other     

Measurement of topography using polarimetric SAR images

A processing technique for polarimetric synthetic aperture radar (SAR) data has been developed which produces profiles of terrain slopes and elevations in the azimuthal (or along-track) direction. This technique estimates the average shift in orientation angle of copolarization backscatter caused by azimuthal tilts of the scattering plane. Using P-band data, tests of this technique have been made for an area in the Black Forest near Villingen/Schwenningen in Baden-Wurttemberg, Germany. The radar measured slope and derived elevation profiles have low rms errors and high correlation values when compared with a stereo-photograph digital-elevation map (DEM) for the area. This algorithm is capable of adaptively making transitions from the forested areas to nearby regions with open-terrain. Subsequent tests of the algorithm have been conducted using polarimetric SAR L-band data for a mountainous, nonforested, region in the Mojave Desert (Ft. Irwin, CA) where an accurate DEM also was available. Complete elevation and slope mapping of the terrain in two dimensions using this technique is possible when azimuthal elevation profiles are produced throughout the range extent of the SAR image     

Design of a monopulse SAR system for the determination of elevationangles

Terrain height variations in mountainous areas cause problems in the radiometric correction of SAR images. The authors propose a novel SAR system which exploits the monopulse principle to determine the elevation angle and thus the height at the different parts of the image. From the ratios of images radiometrically modulated by the difference and sum antenna pattern in cross-track direction, the authors can calculate the appropriate elevation angle at any point in the image. In this paper, they present design considerations for an array antenna for DLR's airborne X-band SAR system and give estimates of the error due to system noise and azimuth ambiguities as well as the expected performance and precision in topographic mapping     

多策略ATLAS数据优选与影像匹配相结合的SAR高程控制点提取

为了精化星载SAR影像几何参数并提高立体定位精度,借鉴星载激光测高数据光学遥感影像高程控制点提取思路,设计了一种多策略高级地形激光测高系统(ATLAS)数据优选与影像匹配相结合的SAR高程控制点提取方法。该方法采用非夜间观测光子滤除、高置信度光子选取、SRTM DEM辅助的粗差剔除、大偏心率椭圆滤波核平坦区域光子筛选等多种策略,从ATLAS数据ATL03级产品中提取高质量、平坦区域的激光高程点,再依据SRTM DEM对斜距SAR影像进行地理编码,按激光高程点的平面坐标选取局部谷歌地球影像作为足印影像,采用秩自相似描述子进行足印影像与SAR地理编码影像的匹配,得到与激光高程点对应的SAR影像像点坐标,从而提取SAR高程控制点。采用中国登封市、日本横须贺市两个区域的ATLAS数据进行了高分三号SAR高程控制点提取实验,利用提取的高程控制点进行SAR影像几何参数精化,大幅提升了立体定位精度,验证了该文高程控制点提取方法的可行性和有效性。      

On the detection of Faraday rotation in linearly polarized L-band SAR backscatter signatures

The potentially measurable effects of Faraday rotation on linearly polarized backscatter measurements from space are addressed. Single-polarized, dual-polarized, and quad-polarized backscatter measurements subject to Faraday rotation are first modeled. Then, the impacts are assessed using L-band polarimetric synthetic aperture radar (SAR) data. Due to Faraday rotation, the received signal will include other polarization characteristics of the surface, which may be detectable under certain conditions. Model results are used to suggest data characteristics that will reveal the presence of Faraday rotation in a given single-polarized, dual-polarized, or quad-polarized L-band SAR dataset, provided the user can identify scatterers within the scene whose general behavior is known or can compare the data to another, similar dataset with zero Faraday rotation. The data characteristics found to be most sensitive to a small amount of Faraday rotation (i.e., a one-way rotation <20/spl deg/) are the cross-pol backscatter [/spl sigma//spl deg/(HV)] and the like-to-cross-pol correlation [e.g., /spl rho/(HHHV/sup */)]. For a diverse, but representative, set of natural terrain, the level of distortion across a range of backscatter measures is shown to be acceptable (i.e., minimal) for one-way Faraday rotations of less than 5/spl deg/, and 3/spl deg/ if the radiometric uncertainty in the HV backscatter is specified to be less than 0.5 dB.     

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     

高分辨率星载SAR单视图像斑点噪声抑制实现方法

本文提出了实现高分辨率星载合成孔径雷达单视图像斑点噪声抑制的TDRGMAP方法.它以最大后验概率滤波器实现斑点平滑,以无偏修正使其适用于单视图像,结合边缘和线条检测,并加以点目标检测及保持,获得高空间分辨率和高辐射分辨率的SAR单视图像.本文详细阐述了TDRGMAP方法的机理和实现,最后利用仿真生成的星载SAR单视图像进行实验,证明了TDRGMAP方法的有效性.     

The generation of SAR layover and shadow maps from digitalelevation models

As almost fully automated techniques as well as expert systems obtain more and more importance in the geocoding of synthetic aperture radar (SAR) images, the solution to the problem of the identification of homologue points between the SAR image and reference system moves into the fields of pattern recognition and feature matching. Shadow regions, which appear as dark regions in the SAR image, are independent from the backscattering of the imaged terrain. Due to the multiplicity of signals, layover regions appear brighter than the surrounding regions. Hence, the phenomena of layover and shadow are stressed in the present paper. The reasons for their occurrence are studied through the digital elevation model representing the Earth's surface. An algorithm to define layover and shadow regions directly in the geometry of the digital elevation model is presented. The results are given in a so-called layover and shadow map     

星载双站SAR地面场景回波仿真

双站SAR回波仿真利用小面单元模型和Kirchhoff双站后向散射模型,给出了地面场景后向散射系数的计算方法;为了保证双站SAR精确的相位信息,在时域中模拟双站SAR回波。根据实际的DEM数据进行了计算机仿真,对仿真数据进行成像和干涉处理,结果表明,该方法能够逼真地模拟地面场景的双站散射特性和相位信息。     

星载SAR原始数据BAQ压缩算法性能评估

对星载合成孔径雷达(SAR)原始数据压缩算法的压缩性能评估是全面了解算法性能、合理选择算法方案的有效手段。该文模拟了以真实SAR图像为背景,引入点目标阵列的SAR回波数据;定义了综合评估指标;对分块自适应量化(BAQ)算法进行了不同分块方案、不同压缩比下的压缩实验;得到了一系列评估指标的计算结果。研究结果表明:BAQ算法对图像域的空间分辨率没有影响;不会引起图像的几何失真;对辐射分辨率影响很小;压缩引起的图像主瓣峰值失真不能够用统一的因子校正。同时该综合评价指标也可以推广到其他压缩算法评估中。     

基于视觉显著性的SAR遥感图像NanoDet舰船检测方法

在合成孔径雷达遥感图像中,舰船由金属材质构成,后向散射强;海面平滑,后向散射弱,因此舰船是海面背景下的视觉显著目标。然而,SAR遥感影像幅宽大、海面背景复杂,且不同舰船目标特征差异大,导致舰船快速准确检测困难。为此,该文提出一种基于视觉显著性的SAR遥感图像NanoDet舰船检测方法。该方法首先通过自动聚类算法划分图像样本为不同场景类别;其次,针对不同场景下的图像进行差异化的显著性检测;最后,使用优化后的轻量化网络模型NanoDet对加入显著性图的训练样本进行特征学习,使系统模型能够实现快速和高精确度的舰船检测效果。该方法对SAR图像应用实时性具有一定的帮助,且其轻量化模型利于未来实现硬件移植。该文利用公开数据集SSDD和AIR-SARship-2.0进行实验验证,体现了该算法的有效性。