PALSAR_Radiometric_and_Geometric_Calibration

IEEETRANSACTIONSONGEOSCIENCEANDREMOTESENSING,VOL.47,NO.12,DECEMBER20093915PALSARRadiometricandGeometricCalibrationMasanobuShimada,SeniorMember,IEEE,OsamuIsoguchi,TakeoTadono,Member,IEEE,andKazuoIsonoAbstract—ThispapersummarizestheresultsobtainedfromgeometricandradiometriccalibrationsofthePhased-ArrayL-BandSyntheticApertureRadar(PALSAR)ontheAdvancedLandObservingSatellite,whichhasbeeninspaceforthreeyears.AlloftheimagingmodesofthePALSAR,i.e.,single,dual,andfullpolarimetricstripmodesandscanningsyntheticapertureradar(SCANSAR),werecalibratedandvalidatedusingatotalof572calibrationpointscollectedworldwideanddistributedtargetsselectedprimarilyfromtheAmazonforest.Throughraw-datacharacterization,antenna-patternestimationusingthedistrib-utedtargetdata,andpolarimetriccalibrationusingtheFaradayrotation-freeareaintheAmazon,weperformedthePALSARradiometricandgeometriccalibrationsandconfirmedthatthegeometricaccuracyofthestripmodeis9.7-mrootmeansquare(rms),thegeometricaccuracyofSCANSARis70m,andtheradiometricaccuracyis0.76dBfromacorner-reflectoranalysisand0.22dBfromtheAmazondataanalysis(standarddeviation).Polarimetriccalibrationwassuccessful,resultinginaVV/HHamplitudebalanceof1.013(0.0561dB)withastandarddeviationof0.062andaphasebalanceof0.612◦withastandarddeviationof2.66◦.IndexTerms—AdvancedLandObservingSatellite(ALOS),calibrationandvalidation(CALVAL),Phased-ArrayL-BandSyntheticApertureRadar(PALSAR),POLarimetricCALibra-tion(POLCAL),syntheticapertureradar(SAR).NOMENCLATUREAAAzimuthambiguity.AAPAzimuthantennapattern.AGCAutomaticgaincontrol.ALOSAdvancedLandObservingSatellite.ASFAlaskaSatelliteFacility.BOSBasicobservationscenario.CALVALCalibrationandvalidation.CFCalibrationfactor.CRCornerreflector.DEMDigitalelevationmodel.DSNDownlinkSiNglemode.FBDFine-beamdual.FBSFine-beamsingle.IBGEInstitutoBrasileirodeGeografiaeEstatistica.IRFImpulse-responsefunction.ISLRIntegratedside-loberatio.JAXAJapanAerospaceExplorationAgency.ManuscriptreceivedDecember7,2008;revisedMarch30,2009.FirstpublishedAugust7,2009;currentversionpublishedNovember25,2009.M.Shimada,O.Isoguchi,andT.TadonoarewiththeEarthObservationRe-searchCenter,JapanAerospaceExplorationAgency,Tsukuba305-8505,Japan(e-mail:[e-mail];[e-mail];[e-mail]).K.IsonoiswiththeRemoteSensingTechnologyCenterofJapan,Minato-ku,Tokyo106-0032,Japan(e-mail:[e-mail]).Colorversionsofoneormoreofthefiguresinthispaperareavailableonlineat–receivemodule.I.INTRODUCTIONJAXA’Sflagshipsatellite,ALOS(nicknamedDaichi),waslaunchedintoapolarorbitof691.25-kmheightfromtheTanegashimaSpaceCenteronJanuary24,2006,car-ryingthreehigh-resolutionsensors.Oneofthesensors,anL-bandSAR(PALSAR),wasexpectedtocontributetodefor-estationmonitoring,biomassestimation,anddeformationmea-surementsusinginterferometryandamplitudedifferentiation,owingtothehighersignalpenetrationthroughvegetationcoveroftheSARascomparedwithC-andX-bandSARs.Onemonthafterlaunch,thefirstimagewasacquiredfromtheascendingpathoverKyushuIslandinthePALSARhigh-resolutionmodeatanoff-nadirangleof41.5◦overalengthof1000kmalongthetrackandover70kmofimageswathcoveringtheIzuPeninsula,Mt.Fuji,andSadoIsland.ThisimagesufferedfromAAandRAandsaturation.AsastartingpointforPALSARCALVAL,theinitialimageprovidedimpor-tantinformationonhowtoidentifytheproblem.GroundtestsanddataanalysessolvedtheproblemsintheAAP,andnewradarparametersuploadedinmid-March2006eliminatedthisproblem[1],[2].PALSARwassubsequentlyactivatedtomonitorthefunc-tionalityofmostofitsvariousmodesovertwomonths.CRsandactiveradarcalibratorsweredeployedbothinJapanandoverseasandwerefullyutilizedtoevaluatethePALSARperfor-manceandtoconductgeometricandradiometriccalibrationsofPALSAR.TheresultsconfirmedthatthePALSARstandardproductsretainedhighradiometricandgeometricaccuracyandthatthesensoritselfwashighlystable.0196-2892/$26.00©2009IEEE3916IEEETRANSACTIONSONGEOSCIENCEANDREMOTESENSING,VOL.47,NO.12,DECEMBER2009TABLEIPALSARCHARACTERISTICSThispaperdescribesthePALSARcalibration.SectionIIpresentsageneraldescriptionofPALSAR.SectionIIIdescribesthetheoreticalapproachofthePALSARcalibration.SectionIVreviewstheCALVAL.SectionVdiscussestheimagequality.SectionVIpresentsthediscussionsandconclusions,andtheAppendixprovidestheraw-datacharacteristics.II.PALSARSYSTEMDESCRIPTIONPALSARwasdevelopedasanadvancedL-bandSARwithsuperiorfunctionalityandhighperformancetosucceedJERS-1SAR.SinceitisanL-bandSAR,PALSARcanmonitorforestsandcrustaldeform