InSAR课件-b

3.CharacteristicsofSARImagesSAR图像的特点：几何特点辐射特点（物理）SARImaging-SlantRangeProjection（斜距投影）AntennaAcrosstrackEFNadirefImageplaneRYHGgThelocationofpixelsintheimageplaneisdependentontheslantrangesbetweentheantennaandthegroundobjects（像元的位置决定于天线至目标点的距离）投影与测距（光学与雷达成像区别）--正射投影与距离投影ReliefdisplacementsoccurinoppositedirectionsforopticalandSARsensors(Copyright,CCRS)（地貌变形）IncidentAngle（入射角）•(Nominal)Incidentangle（名义上的，定义的）--anglebetweentheradarilluminationandthenormaltothegroundsurface.--theincidentangleincreasesfromthenearrangetothefarrange•Localincidentangle（局部的）--anglebetweentheradarLOSandthelinenormaltothelocalslope.雷达影像的三类几何变形RADARReliefDisplacement,ImageForeshortening,andShadowingGeometricdistortionsexistinalmostallradarimagery,including:•foreshortening（透视缩短）,•layover（顶底倒置）,and•shadowing（阴影）.？Forshortening,Layover,andShadow区别：下视角入射角局部入射角ilociIncidentangleLocalincidentangleRADARReliefDisplacement:ForeshorteningandLayoverWhentheterrainisflat,itisaeasytousetheappropriateequationtoconvertaslant-rangeradarimageintoaground-rangeradarimagethatisplanimetrically（平面的）correctinx,y.However,whentrees,tallbuildings,ormountainsarepresentinthescene,radarreliefdisplacementoccurs.•Inradarreliefdisplacement,thehorizontaldisplacementofanobjectintheimagecausedbytheobject’selevationisinadirectiontowardtheradarantenna（高度使物体指向天线）.Becausetheradarimageisformedintherange(cross-track)direction,thehighertheobject,thecloseritistotheradarantenna,andthereforethesooner(intime)itisdetectedontheradarimage.Thiscontrastssharplywithreliefdisplacementinopticalaerialphotographywherethereliefdisplacementisradiallyoutwardfromtheprincipalpoint(center)ofaphotograph.Theelevation-induceddistortions（高度引起的变形）inradarimageryarereferredtoasforeshorteningandlayover.RADARReliefDisplacement:ForeshorteningAllterrainthathasaslopeinclinedtowardtheradarwillappearcompressedorforeshortenedrelativetoslopesinclinedawayfromtheradar.Theforeshorteningfactor（透视缩短比例）,Ff,isapproximately:Ff=sin(-)wheretheincidentangleistheanglebetweentheverticalplaneatnadirandalinethatlinkstheimagingradarantennatoafeatureontheground,andistheslopeangle（地表倾角，坡度角）ofthesurface.Alphaispositive(+)wheretheslopeisinclinedtowardtheradar(foreslope),andnegative(-)wheretheslopeisinclinedawayfromit(backslope).（正角，负角的定义：指向雷达或背向雷达）Foreshortening•Compression（压缩）oftopographicfeaturesinthescenes.•Foreshorteningisatmaximumwhensteepslopeisorthogonaltotheradarbeam,i.e.,whenthelocalincidentangleiszero.•Foreshorteningeffectsarereducedwithincreasinglocalincidentangle.Whenlocalincidentangleapproach900,foreshorteningeffectsareeliminated,butsevereshadowingmayoccur.DiagramofForeshorteningidisplacementforeshorteningForeshorteninga.b.C-bandERS-1depressionangle=67?lookangle=23?L-bandJERS-1depressionangle=54?lookangle=36?lookdirectionc.d.X-bandAerialPhotographlookdirectionN引起的因素：RADARForeshorteningisInfluencedby:•objectheight（高程）:Thegreatertheheightoftheobjectabovelocaldatum,thegreatertheforeshortening.•depressionangle(orincidentangle)（角度）:Thegreaterthedepressionangle(g)orsmallertheincidentangle(),thegreatertheforeshortening.•locationofobjectsintheacross-trackrange（距离卫星下试点的距离）:Featuresinthenear-rangeportionoftheswatharegenerallyforeshortenedmorethanidenticalfeaturesinthefar-range.Foreshorteningcausesfeaturestoappeartohavesteeperslopesthantheyactuallyhaveinthenear-rangeoftheradarimageandtohaveshallowerslopesthantheyactuallyhaveintheimagefar-range.更陡了Layover•Occurswhenechowavefromtheupperportionofafeatureisreceivedbeforethatofthelowerportionofthefeature.•Thetopofthefeaturewillbedisplaced,or“laidover”relativetoitsbaseimage.•Layoverisanextremecaseofforeshortening•Ingeneral,layoverismoreprevalentforviewinggeometrieswithsmallincidentanglesRADARReliefDisplacement:ImageLayoverImagelayoverisanextremecaseofimageforeshortening.Itoccurswhentheincidentangle()issmallerthantheforeslope(+)i.e.,+.入射角小于地面坡度倾角•Thisdistortioncannotbecorrectedevenwhenthesurfacetopographyisknown.（无法改正，需特别小心）Greatcaremustbeexercisedwheninterpretingradarimagesofmountainousareaswherethethresholdsforimagelayoverexist.（特别在SLC、以及SLC与DEM配准检视时！）DiagramofLayoverilayoverLayoverL-bandSIR-C(HH)July20,1995lookdirectionNPasadenaRADARShadowsShadowsinradarimagescanenhancethegeomorphologyandtextureoftheterrain（可以突出地形以及纹理）.Shadowscanalsoobscurethemostimportantfeatures（使重要特征模糊）inaradarimage,suchastheinformationbehindtallbuildingsorlanduseindeepvalleys.Ifcertainconditionsaremet,anyfeatureprotruding（突出）abovethelocaldatumcancausetheincidentpulseofmicrowaveenergytoreflectallofitsenergyontheforeslopeoftheobjectandproduceablackshadowforthebackslope.迎坡亮，背坡暗RADARShadows：三种情况•Abackslope（背坡）isinradarshadowwhenitsangle-issteeperthanthedepressionangle(g),i.e.,-g.•Ifthebackslopeequalsthedepressionangle,-=g,thenthebackslopeisjustbarelyilluminatedbytheincidentenergy.Thisiscalledgrazing（切线，掠射）illuminationbecausetheradarpulsejustgrazesthebackslope.•Thebackslopeisfullyilluminatedwhenitislessthanthedepressionangle(-g.)RADARShadowCharacteristics•Unlikeairphotos,wherelightmaybescatter