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1、IEEETRANSACTIONSONGEOSCIENCEANDREMOTESENSING,VOL.34,NO.5,SEPTEMBER19961115RadiometricSlopeCorrectionofSynthetic-ApertureRadarImagesLarsM.H.Ulander,Member,ZEEEAbstract-ThebrightnessinaSARimageisaffectedbytopo-methodisthenusedtodeterminetheradiometriccalibrationgraphicheight
2、variationsdueto1)theprojectionbetweengroundconstantKaccordingto[SI-[lo]andimagecoordinates,and2)variationsinbackscatteringcoef-ficientwiththelocalscatteringgeometry.Thispaperderivesanewequationforl),Le.,theradiometricslopecorrection,basedonacalibrationequationwhichisinvari
3、antunderacoordi-natetransformation.AnalgorithmisdescribedtoobtainthewhereEisthepointtargetenergy,i.e.,thearea-integralofslopecorrectionfromaSARinterferogram,whichalsoenablestheimagepowerresponseofthepointtargetwithaverageretrievalofthefullscatteringgeometry.SincetheSARimag
4、ebackgroundclutterandnoisepowersubtracted,andPistheandinterferogramarederivedfromthesamedataset,thereisdistributedtargetpower,i.e.,theaverageimagepowerofthenoneedtomatchtheimagewiththecalibrationdata.Thereisalsononeedforphaseunwrappingsincethealgorithmonlyusesdistributedta
5、rgetwithaveragenoisepowersubtracted.Thethefringefrequencies.Amaximum-likelihoodestimatorforthebackscatteringcoefficientnomaynowbedeterminedfromfringefrequencyisanalyzedandthealgorithmisillustratedbyPobyageometricalprojectionfactorwhichrelatesaunitprocessingERS-1SARdata.The
6、exampledemonstratesthattheimagetogroundarea.Notethatthecalibrationconstantisspatialresolutionandcalibrationerrorareadequateformostnotatrueconstantovertheimageandvariesduetovariousapplications.uncompensatedradiometricvariations,e.g.,duetoantennagain,rangespreadingloss,propa
7、gationloss,andprocessorI.INTRODUCTIONloss,whichmustbecompensatedforseparately.ADIOMETRICcalibrationofsyntheticapertureradarEquation(1)isindependentofthechoiceofimagegeometryR(swsystemshasshownsignificantprogressduringthe(coordinatesystem).WhentheSARimagehasbeentrans-lastde
8、cade[11-[5].Theradiometricprecisionisnowroutinelyformedtotruegroundcoordinates,itfollowst
