文献-Evaluating co-relationship between OCO-2 XCO2and in situ CO2measured with portable equipment in Seoul

Spat.Inf.Res.(2016)24:565575DOI10.1007/s41324-016-0053-7Evaluatingco-relationshipbetweenOCO-2XCO2andinsituCO2measuredwithportableequipmentinSeoulYoungSeokHwang1Jung-SupUm2Received:17July2016/Revised:3August2016/Accepted:6September2016/Publishedonline:26September2016KoreanSpatialInformationSociety2016AbstractTheco-relationshipbetweenOCO-2XCO2concentrationandgroundCO2concentrationremainslar-gelyunexplored.ThisraisesquestionsaboutthereliabilityofOCO-2column-averagedCO2concentrations(XCO2)data.Thispaperexaminedtheco-relationshipbetweenOCO-2level2data(29samplepointsacquiredonMarch23,2015)andgroundlevel,ambientcarbondioxide.GroundCO2wassimultaneouslymeasuredusingportableequipment,attheseasonandnearby-locationofthesatellitemeasurements.TheresultrevealsthatOCO-2XCO2datawerecloselyassociatedwithgroundCO2data(R2=0.43).Theoveralluncertaintyforthecarbonmea-surementsrangedfrom398.6to407.9ppmforOCO-2andfrom437.3to503.5ppmforgroundlevel.DatafromtheseexperimentssuggestthattheambientCO2concentrationismuchhigherthantheOCO-2XCO2.InsituCO2levelsdiffersignicantlyfromtheOCO-2XCO2incasethatdominantlandcoverwithinOCO-2columnboundaryisnon-coincidentwiththatofinsitusurveypoint.ItisanticipatedthatthisresearchoutcomecouldbeusedasavaluablereferenceforqualityassuranceofOCO-2datainrelationtoportablecarbonmonitoring.1IntroductionGreenhousegasobservingsatellitessuchasAQUA,ENVISAT,andGOSAThavebeendevelopedtomeasuregreenhousegasintheglobalscale.GOSAThadarelativelyhighresolution(10.5km)incomparisonwithothersatel-lites1.Howeveritwasunabletomeasuregreenhousegasforlocaltargetsuchasspecicdistrictwithinonecountryduetothelimitationofspatialresolution.Toovercomethespatialresolutionproblem,OrbitalCarbonObservatory-2(OCO-2)havingahighspatialresolutionof1.29km92.25kmwaslaunchedonJuly2,20142.ThehighspatialresolutionofOCO-2enablestomonitorgreenhousegasinalocaltargetwithlessthan2kmsize.VericationbetweenthegroundmeasurementandthesatellitedataisnecessarytoputtheOCO-2satellitedataintopractice3.TotalCarbonColumnObservingNetwork(TCCON)1isagroundnetworktoverifysatellitesignalsbythesamemethodusedbygreenhouseobservingsatellites.ItmeasurestotalcolumnatmosphericCO2(itisreferredas1TCCONisafliatedwiththeNetworkfortheDetectionofKeywordsOCO-2XCO2CO2PortableequipmentCo-relationship&Jung-SupUmjsaeomknu.ac.krAtmosphericCompositionChangeInfraredWorkingGroup(NDACC-IRWG)andtheGlobalAtmosphereWatch(GAW)pro-gramme.TheGlobalAtmosphereWatch(GAW)programmeofWMOisapartnershipinvolvingtheMembersofWMO,contributingnetworksandcollaboratingorganizationsandbodieswhichprovidesreliablescienticdataandinformationonthechemicalcompositionoftheatmosphere,itsnaturalandanthropogenicchange,andhelpstoimprovetheunderstandingofinteractionsbetweentheatmosphere,theoceansandthebiosphere.TCCONisanetworkofground-basedFourierTransformSpectrometersrecordingdirectsolarspectrainthe12DepartmentofClimateChange,KyungpookNationalUniversity,Daegu,SouthKoreaDepartmentofGeography,KyungpookNationalUniversity,Daegu,SouthKoreanear-infraredspectralregion.Fromthesespectra,accurateandprecisecolumn-averagedabundanceofCO2,CH4,N2O,HF,CO,H2O,andHDOareretrieved.TCCONprovidesanessentialvalidationresourcefortheOrbitingCarbonObservatory(OCO),Sciamachy,andGOSAT.123566XCO2hereinafter),suchascolumnabundanceinthever-ticaldirectionfromtheground.TheTCCON,havingasensorthesamewiththatofgreenhousegasobservingsatellites(FTS:FourierTransformSpectrometers),mea-suresthecolumnabundanceofgreenhousegasessuchasCO2,CH4,N2O,andCOfromthegroundtotheatmo-sphere4.TheoperationofTCCONhasbeenleadedbyU.S.,Canada,Germany,France,Japan,Australia,NewZealand,andKoreasince2004.Globally,28groundobservatoriesareregisteredtoTCCON,includingtwoTCCONgroundobservatorieslocatedatAnmyeondoIslandinChungcheongnam-doandatGosan,Jeju,SouthKorea.PreviousstudieshavebeenreportedabouttheaccuracyoftheGOSATXCO2dataincomparisonwiththeTCCONdata5,6.Kulawiketal.7comparedtheconsistencyoftheGOSAT,SCIAMACHYXCO2dataincomparisonwiththedatafromvariousTCCONobser-vatories.TheXCO2dataobtainedfromtheOCO-2satellitearecorrectedtohaveahighaccuracyoflessthan1ppmwiththeTCCONdatathroughanalgorithmafterbeingcomparedwiththeTCCONdataoftheregionoverwhichtheOCO-2satellitepasses8.ThereliabilityofOCO-2retrievalalgorithmhasbeenveriedinmanypreviousstudies.Boeschetal.9veriedtheretrievalerrorofOCO-2imagesinanOCOfull-physicsforwardmodelbyusingaformalretrievalerrorcovariancematrix.Thompsonetal.10calculatedtheaccuracyoftheOCO-2imagesbycomparingtheCO2absorptioncoefcientin1.61and2.06lmchannelsfromtheOCO-2simulationXCO2datawiththeGOSAT,TCCON,andFT-IRlabo-ratoryspectra.TheOCO-2XCO2dataareobtainedbycalculatingthecolumnabundanceratiosofdryairandCO2fromthealtitudeofsatellitesensorstothegroundtarget11.TheXCO2valuesaretheratiosconvertedtotheunitofppmbyreectingthealtitude-dependentdensityofCO2anddryair12.Therefore,theXCO2datamaynotreecttheCO2concentrationonthegroundwhereCO2isactuallyemitted.AsanexampleofpreviousstudiesconductedbyusingportableCO2measurementequipment,KimandUm13conductedaninsituinvestigationbyusingModel7535ofTSIandveriedtheCO2concentrationindifferentlandcategories.Meyeretal.14measuredthevariationofCO2concentrationin32typesofsoilbyusingportableequipment.However,thesepreviousstudieswerefocusedontheanalysisoftheCO2concentrationforindividuallandtypesthroughactualmeasurement.WithrespecttoreliabilityvericationoftheOCO-2columndata,previousstudieshavebeenreportedaboutthesimulationdataandtheTCCONdata.HwangandUm15123Y.Hwang,J.-S.UmveriedthecorrelationbetweentheXCO2dataandtheCO2emissionamongindividuallandtypes.However,thecorrelationbetweengroundmeasuredCO2dataandtheXCO2datahasnotbeenveriedbyusingportablecarbonmeasurementequipment.ThepresentstudyisaimedatanalyzingthecorrelationbetweenCO2concentrationmeasuredonthegroundbyusingportableCO2measure-mentequipmentandtheOCO-2XCO2data.TheresultofthepresentstudymaybeusedtoverifytheerrorrangeinapplyingtheOCO-2satellitemeasurementstotheground(ThesatellitedataarereferredasXCO2andtheinsitusurveydataasCO2hereinafter).2Studyarea,materialsandmethodsSeoulcitywasdeterminedasexperimentalstudyareabecausetheOCO-2satelliteightpassesoverthere.ItisaregionadequatetoverifyXCO2signaturesforindi-viduallandtypesbecausevariouslandcategories,includingcentralbusinessareas,residentialareas,parks,andforests,areavailableintheurbanarea.OutoftheentireSeoulregion,districtswhereOCO-2satelliteightpasseswereusedforfurtherempiricalstudysuchasEunpyeong,Seodaemun,Mapo,Yangcheon,Yeongde-ungpo,Dongjak,andGwanakdistrict.TheequipmenttomeasuregroundCO2wasTESTOModel480andIAQprobe(Table1;Fig.1)16.Thisequipmentincludesanon-dispersiveinfrared(NDIR)sensor,whichhasbeenknownasthemostreliablesensorforCO2measurement17.Inmanypreviousstudies,theNDIRsensorandtheTESTOModel480wereemployedtomeasureCO218,19.CatalinaandBanu18reportedthattheCO2datameasuredbyusingtheTESTOModel480guaran-teesthemeasurementreliabilitywithin1%errorrange.TheIAQprobeisanequipmenttodirectlymeasureCO2concentration,andtheModel480analyzesandrecordsthevaluesmeasuredbytheprobe.TheCO2measurementrangeoftheIAQprobeisfrom0to10,000ppminaresolutionof1ppm.Withregardtotheatmosphericmeasurementaccuracy,theerrorrangeis75ppm(within3%ofindicatedvalueranging05000ppm).TheModel480receivingthedatarecordedbytheIAQprobepro-videsreal-timestatisticaldataincludingminimum,maximum,andmeanofthemeasurements.Thewindspeedwasmeasuredbyusinga16-mmvanemeasure-mentprobe.Themeasurementrangeofthe16-mmvanemeasurementprobeis0.650m/s.Theerrorrangewas0.2m/swithin1%ofindicatedvaluesatwindspeedof0.640and0.2m/swithin2%ofindicatedvaluesatwindspeedof40.150m/s16.Evaluatingco-relationshipbetweenOCO-2XCO2andinsituCO2measuredwithportableTable1TechnicalspecicationofTESTOmodel480,IAQprobeandVane16mmprobe16567TESTO480Operatingtemperature0to?40CStoragetemperature-20to?60CProbeconnection29TCTypeK,19differentialpressure,39digitalInterfacesUSBconnection,SDcard,mainsunit,infraredforfastprinterProbetypeVanemeasurementprobe16mmMeasuringrange0.650m/s-10to?70CAccuracy1digit(0.2m/s?1%ofm.v.)(0.6to40m/s)(0.2m/s?2%ofm.v.)Resolution0.1m/s(40.1to50m/s)1.8CIAQprobe0to?50C0to100%RH0to?10,000ppmCO2?700to?1100hPa0.5C(1.8%RH?0.7%ofm.v.)(75ppmCO2?3%ofm.v.)0to?5000ppmCO21ppmCO2(150ppmCO2?5%ofm.v.)5001to?10,000ppmCO23hPaperformedcontinuousmeasurementinanintervalof5minforatotalof25h.PandeyandKim23measuredCO2atevery3stoobtainthemeandatafor304h.Dataobtainedby10sofmeasurementinthisstudywereconvertedtomeanaccumulatedfor30min,tominimizetheobservationerror.TheCO2emissionateachsurveylocationwasmeasuredatalevelof50cmfromtheground24.WindspeedisthevariablethatcouldcausethegreatestdistortiontotherealCO2values25.Therefore,itisnecessarytoverifythevalidityoftheCO2measurementbycomparingthewindspeedmeasuredbyusingportableequipmentwiththosemeasurementvaluesbytheMeteorologicalAdmin-istration.Themeanwindspeedmeasuredat11AutomaticWeatherStations(AWS)2neartoeachCO2measurementlocationwas2.2m/sduringtheinsitusurveyperiod(March30April2,2016)(Table2).ThemeanwindspeedattheactualCO2measurementlocationswas0.54m/swithaminimumof0.06m/sandamaximumof1.89m/s.TheElevenAWSarelocatedinthestudyareaofthepresentstudy,Fig.1ImageofModel480,IAQprobe,16mmVanemeasurementprobeAstandardizedmeasurementmethodforvariousvari-ablessuchastemperatureandwindisrequiredtoobtainreliabledataininsitumeasurementprocess.TheWDCGG20acceptedasinternationalstandardwasusedtoproducedatameasuredinanintervalof30s.AccordingtotheAirMonitoringNetworkInstallation&OperationGuidelinepublishedbytheMinistryofEnvironment,thedataneedtobecollectedasone-hourmeanvalueformeasurementperformedatevery30s21.KimandUm13convertedthedatameasuredfor10stoone-minmeandataandproduced30-minmeanvaluedata.Seongetal.22locationsoftheAWSwerenotexactlythesameastheinsitumeasurementlocations.ThemeanwindspeedmeasuredattheAWSoftheHangangareaandtheMapoarea,installedontheriverside,wasashighas3.9and5m/s,respectively.Inaddition,themeasurementconditionsofthetwotypesofdatawerenotthesamebecausethemeasurementdataofthepresentstudywereobtainedinashortperiodoftimeonlyattheactualCO2surveysites.AccordingtoLeeetal.26,theheightgapbetweenthe2whichareGwanak,Hangang,Seodaemun,Seoul,Mapo,Eunpyeong,Hyeonchungwon,Yongsan,Gangseo,Guro,andYeongdeungpo.http:/www.kma.go.kr/weather/observation/aws_table.jsp#.123568Y.Hwang,J.-S.UmTable2ComparisonbetweeninsituversusAWS(automaticweatherstation)velocity(unitm/s).SourceKoreaMeteorologicalAdministrationIdenticationnumber1234567891011121314Min0.240.060.330.260.26Max0.760.591.321.081.140.740.830.850.890.760.611.340.950.72Mean0.390.190.710.460.670.310.460.520.460.420.380.740.610.36AWS3.9Identicationnumber1617181920212223242526272829Min0.290.240.760.280.470.330.271.070.290.10.25Max1.851.031.890.671.091.511.361.771.130.670.160.710.920.87Mean0.650.630.970.440.740.650.570.740.70.460.550.540.330.47AWS1.153.21.8150.121.070.422.9AWS:mean(2.2),min(0.4),max(5.0)In-situ:mean(0.54),min(0.06),max(1.89)windspeedmeasurementequipmentoftheMeteorologicalAdministrationandtheactualgroundwindspeedmea-surementequipmentis10morlarger,andthusthewindspeeddataoftheMeteorologicalAdministrationmaynotbeconsideredasthegroupwindspeeddata.Kim27reportedthatthewindspeedmeasuredatthegroundlevelwaslowerthanthatoftheMeteorologicalAdministrationby1.4m/s,statingthatthewindspeeddataoftheMete-orologicalAdministrationmaybeusedonlyascompara-tivedataforwindspeedmeasuredatthegroundlevel13,27.ThewindspeedwasmeasuredinthepresentstudybythesamemethodwithKim27.Thegroundwindspeedwasunderestimatedby1.66m/sincomparisonwiththewindspeeddataoftheMeteorologicalAdministration.Thisissimilartotheresultofpreviousstudies,indicatingthattheCO2datafromthepresentstudyareacquiredfromreliableprocedures.TheXCO2measuredonMarch23,2015wereusedinthepresentstudybecausetheatmosphereisrelativelystableinspringincomparisontowinterandsummer28.ThetemporalresolutionofOCO-2is16days,andthesatellitepathismodiedbytherotationoftheearth.TheXCO2dataobtainedfromthesatelliteareupdatedafewmonthslaterthroughoutcorrectionprocessaslevel2data.measurementlocationtoanotherandtoperformmea-surementateachlocation.ThereliabilityofinsitusurveywillbedecreasedifthereisalargetimegapbetweentheOCO-2dataandtheactuallymeasuredCO2data.TheeldsurveyorsmovedfromameasurementlocationtoanotherbycaronthebasisoftheGoogleEarthcoordi-natesduetothelimitedtimeandhumanresourcesfortheresearch(Table3).Theactualmeasurementlocationsthatwerenotaccessiblebycars,suchasforests,areasunderconstruction,andunpavedroads,wereexcludedfromtheeldvisitingsites.Theco-relationshipbetweenXCO2andCO2dataaredependentonlanduseandlandcoveravailablewithinOCO-2columnboundary(1.29km92.25km).Thus,itisnecessarytoinvestigatethelanduseforthesatelliteobservationandtheinsitusurveylocationsinordertointerprettheresults.Thedetailedlandcovermap(1:5000)3producedfromtheaerialortho-photowith0.25mpixelsize(2013)wasusedtoinvestigatethelanduseofthesurveylocations(Fig.2).4ThepredominantlandcoveroftheXCO2dataandtheCO2datawasinvestigatedbyset-tingarectangulardomainof1.29km92.25kmwiththeTherefore,itisimpossibletoperformgroundCO2mea-3ThelandcovermapprovidedbytheMinistryofEnvironmentwasThenumberoflandcoverclassicationfor1:5000was41,whichsurementsimultaneouslywiththesatellitedataacquisi-tion.Thus,theactualmeasurementoftheCO2concentrationwasperformedfor10days(March23April2,2016)atthelocationswheretheOCO-2dataforMarch23,2015areavailable29.Inaninsitusurveyprocess,muchtimeisrequiredtomovefroma123usedbydownloadingthemetadatafromtheEnvironmentalGeographicInformationService(EGIS)athttp:/egis.me.go.kr/ewebgis/webgis.do.4wastoomanytothepointofinterpretatingthesurveyresult.Hence,themiddlescale(1:25,000)landcoverclassicationstandardsincluding22itemswereusedinthepresentstudy.Evaluatingco-relationshipbetweenOCO-2XCO2andinsituCO2measuredwithportable569Table3RMSEbetweenOCO-2versusinsitusurveypoint(UTM)Identicationnumber1(X/Y)2(X/Y)3(X/Y)4(X/Y)5(X/Y)6(X/Y)7(X/Y)8(X/Y)9(X/Y)10(X/Y)11(X/Y)12(X/Y)13(X/Y)14(X/Y)15(X/Y)16(X/Y)17(X/Y)18(X/Y)19(X/Y)20(X/Y)21(X/Y)22(X/Y)23(X/Y)24(X/Y)25(X/Y)26(X/Y)27(X/Y)28(X/Y)29(X/Y)Satelliteobservationpoint314,056.075/4,150,188.712315,197.183/4,149,818.999316,248.641/4,149,430.822317,391.477/4,149,036.871318,445.446/4,148,637.945319,015.411/4,150,467.772317,961.5034,150,878.526316,909.897/4,151,280.512315,769.721/4,151,671.888314,718.026/4,152,052.150314,235.857/4,154,292.772315,288.358/4153902.328316,428.690/4,153,511.957317,481.247/4,153,121.616318,533