第三章 合成空间雷达图像特征VIP免费

第三章CharacteristicsofSARImages（合成孔径雷达图像特征）SARImaging-SlantRangeProjection（斜距投影）AntennaAcrosstrackEFNadiref像平面RYSlantrangeHGgThelocationofpixelsintheimageplaneisdependentontheslantrangesbetweentheantennaandthegroundobjects地物目标在像平面上的位置取决于目标与雷达天线之间的距离光学与SAR成像差异，地形起伏引起的位移方向相反(Copyright,CCRS)IncidentAngle（入射角）(Nominal)Incidentangle(名义入射角)--anglebetweentheradarilluminationandthenormaltothegroundsurface.（雷达入射方向和地面法线的夹角）--theincidentangleincreasesfromthenearrangetothefarrange（雷达图像的近距到远距，入射角增大）Localincidentangle（局部入射角）--anglebetweentheradarLOSandthelinenormaltothelocalslope.（雷达入射方向与局部坡度法线的夹角）ilociIncidentangle（入射角）Localincidentangle（局部入射角）GeometricCharacteristicsofSARImaging（几何特征）Foreshortening（透视收缩）Radarshadow（雷达阴影）Layover（叠影）DiagramofForeshortening（透视收缩）RadarBeamWavefrontidisplacementforeshortening地形特征压缩.斜坡面与雷达入射方向正交（局部入射角为0）时，透视收缩最严重局部入射角增大时，透视收缩减弱；当到90度时，透视收缩消失，但阴影出现DiagramofShadow（阴影）WavefrontiShadowingRadarbeam雷达波没有照射到的地方没有回波，暗色调高目标的背面容易出现阴影局部入射角增大时，阴影变严重Exampleofradarshadoweffectsunderlargeincidenceangle(>45°)illumination.(Copyright,CCRS)DiagramofLayover（叠影）RadarbeamWavefrontilayover目标顶部的回波比底部的回波先到达接收天线目标的顶部发生位移，相对与底部倒置叠影是透视收缩的极端情况名义入射角小时，叠影更显著Exercise:区分几何形变?123Understandinggeometricdistortionsfromlocalincidentangle理解几何形变90000叠影透视收缩阴影局部入射角(Courtesy:CCRS)强弱强弱弱强ERS-2image,incidenceanglesbetween24°to26°RADARSATimage,incidenceanglebetween41°and44°(Acknowledgement:H.Rott,UniversityofInnsbruck.)RadiometricCharacteristicsofSARImage（辐射特征）Fading（衰退）Speckle（斑点）Fadingandspeckle（衰退和斑点）Fadingandspecklearetheinherent“noise-like”processesinacoherentimagingsystem（衰退和斑点是相干成像系统固有的噪声过程）Radartotalechowaveinaresolutioncellisthejointcontributionofechowavefromdifferentsmallscatterswithintheresolutioncell.（分辨单元的雷达回波是分辨单元内小散射体回波的综合贡献）Sketchmapofjointcontribution（综合贡献示意图）Fadingandspeckle（衰退和斑点）Fadingisthevariationofamplitudeoftotalradarechowave（衰退是总雷达回波幅度的变化）Specklereferstheconstructive(相长)anddestructive(相消)interferenceofradarechowaves,appearingintheimageasbrightordark（斑点指雷达回波的相长或相消叠加，在影像上表现为明或暗）CourtesyofCCRSCourtesyofCCRS为什么要削弱斑点噪声ThepresenceofspecklenoisemustbeconsideredbeforefurtheranalysisReductionofspecklenoiseallow:Betterdiscriminationofscenetargets目标识别Easier(automatic)imageregistration影像匹配Easier(automatic)imagesegmentation图像分割…Specklesuppression（斑点抑制）Averagemultipleamplitudeimage（多图平均）DegradetemporalresolutionSeparatethemaximumsyntheticapertureintosmallersub-apertures,generateindependentlooks(withreducedresolution)attargetareas,registerandaddthelooks（子孔径叠加）DegradespatialresolutionAveragingadjacentpixels（相邻像素平均）DegradespatialresolutionSpecklefiltering（斑点滤波）Notsacrificingtheresolution（不牺牲空间分辨率）Theadoptionofclassicalen...