合成孔径雷达图像特征

第三章CharacteristicsofSARImages（合成孔径雷达图像特征）,SARImaging-SlantRangeProjection（斜距投影）,Thelocationofpixelsintheimageplaneisdependentontheslantrangesbetweentheantennaandthegroundobjects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）,GeometricCharacteristicsofSARImaging（几何特征）,Foreshortening（透视收缩）Radarshadow（雷达阴影）Layover（叠影）,DiagramofForeshortening（透视收缩）,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）,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）,目标上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?,123,Understandinggeometricdistortionsfromlocalincidentangle理解几何形变,(Courtesy:CCRS),ERS-2image,incidenceanglesbetween24to26,RADARSATimage,incidenceanglebetween41and44,(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（衰退之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）,CourtesyofCCRS,CourtesyofCCRS,为什么要削弱斑点噪声,ThepresenceofspecklenoisemustbeconsideredbeforefurtheranalysisReductionofspecklenoiseallow: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）DegradetemporalresolutionSeparatethemaximumsyntheticapertureintosmallersub-apertures,generateindependentlooks(withreducedresolution)attargetareas,registerandaddthelooks（子孔径叠加）DegradespatialresolutionAveragingadjacentpixels（相邻像素平均）Degradespatialresolution,Specklefiltering（斑点滤波）,Notsacrificingtheresolution（不牺牲空间分辨率）Theadoptionofclassicalenhancementtoolsdevelopedforimageryfromopticalsensors（可以借鉴经典的方法）,(afterESA),SARImageExpression（SAR图像表达）,Eachpixelisrepresentedbyacomplexvalue,i.e.,Amplitude（灰度）:reflectivity(intensity)oftheimagedpatchPhase（相位）:proportionaltosensor-to-targetrange,Example:SARImage（SAR图像）,StatisticalModelofSARData（SAR数据统计模型）,Realpart（实部）Imaginarypart（虚部）Amplitudecomponents（灰度）RayleighdistributionPhasecomponents（相位）uniformdistribution,(Franceschetti&Lanari,1999),Example:HistogramofSARData（直方图）,FromtestdatasetoverYuanLong,HongKong,Example:HistogramofSARData（直方图）,Keyparameters:(example)Sceneidentification:ORBIT18795,DATE24-NOV-1998,2:54:44Scenelocation:FRAME3159,LAT22.24,LON114.34Pulse_repetition_frequency(actual,Hz):1679.9020000Total_azimuth_band_width(Hz):1378.0000000Weighting_azimuth:HAMMINGXtrack_f_DC_constant(Hz,earlyedge):-117.6290000Xtrack_f_DC_linear(Hz/s,earlyedge):444430.0000000Xtrack_f_DC_quadratic(Hz/s/s,earlyedge):-2016000000.0000Range_time_to_first_pixel(2way)(ms):5.5272710Range_sampling_rate(leaderfile,MHz):18.9624680Total_range_band_width(MHz):15.5500000Weighting_range:HAMMINGRadar_wavelength(m):0.0566660First_pixel_azimuth_time(UTC):24-NOV-199802:54:44.888First_pixel_slant_range(m):828424Pixe