Download - Warn Level, Bias Correction, and Lite File Product …...November 2014 through December 2016 and includes other southern hemisphere TCCON stations (Darwin and Reunion Island) that

OCO-2 XCO2 V8r Lite Products, Warn Levels, and Bias Correction Sept 24, 2017

Orbiting Carbon Observatory–2 (OCO-2)

Warn Level, Bias Correction, and Lite File Product Description

Version 2.0 September 24, 2017 Data Releases 8 and 8r Lite File Version 8r National Aeronautics and Space Administration Jet Propulsion Laboratory California Institute of Technology Pasadena, California TheresearchdescribedinthisdocumentwascarriedoutattheJetPropulsionLaboratory,CaliforniaInstituteofTechnology,underacontractwiththeNationalAeronauticsandSpaceAdministration.Copyright2017CaliforniaInstituteofTechnology.U.S.Governmentsponsorshipacknowledged.


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LiteFiles,BiasCorrection,andWarn

Level

GregoryB.Osterman,AnnmarieEldering,LukasMandrake,ChrisO’Dell,DebraWunch,PaulO.Wennberg,BrendanFisher,YuliyaMarchetti

9-24-2017,PublicDataReleaseForuseonVersion8rdata

OverviewThisdocumentprovidesthedetailsofthecontentoftheV8rreleaseoftheOCO-2Litefiles.Litefilesarecreatedtoprovideareducedfilevolumeaswellasallofthedataforonedayinasinglefile.Thereduceddatavolumecomesfromselectingthelimitednumberofvariablestobeincluded.Inaddition,thefilescontainXCO2_raw,whichcorrespondstothedataintheL2StdandL2Diafiles,aswellasXCO2,whichhashadabiascorrectionappliedtoit.ThefilefollowsthestandardsoftheESAGHGCCIfileformat,andthusXCO2inthesefileshasadifferentmeaningthenintheOCO-2L2StdandL2Diafiles.Datascreeninginformationiscontainedinthequalityflagandthewarnlevels,whicharedescribedinmoredetaillaterinthedocument.Figure1illustratesmapsofmonthlydatathatiscontainedintheLitefiles,afterqualityscreeningisapplied.Themain-levelXCO2datahasalsobeenadjustedusingalinearbiascorrectionscheme,similartotheapproachdescribedinWunchetal.(2011).Similartoderivingqualityflags,weusedifferentXCO2truthproxiestoallowustoidentifyandremoveXCO2biases.Inthisdatarelease,anumberoftruthproxieshavebeenusedtoderiveandvalidatetheXCO2biascorrectionparameters,including

• TheSouthernHemisphereapproximation(seeWunchetal.,2011).• TCCON(asseeninnadir,glintandtargetmodes)• The“SmallAreaAnalysis”,inwhichXCO2isassumedtobeconstantfor

observationstakenoverdistances<~100kmwithinthesameorbit.• Amulti-modelmean,using6modelsthathaveallassimilatedin-situdata,

andonlyusingsoundingsforwhichallthemodelvaluesagreewitheachothertowithinaspecifiedtolerance.


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NotethatthespecificbiascorrectionparametersemployedinthisreleasearegivenintheglobalmetadataofeachLitefile.(Forexample,Bias_Correction_land,withthecorrespondingfootprint-specificcorrectionsgiveninFootprint_bias_land).

QualityFilteringTherearetwomethodsonecanusetoqualityfilterthesoundingscontainedintheLitedatafiles.Thesimplestmethodistousexco2_quality_flag,whichissimplyabytearrayof0sand1s.ThisfilterhasbeenderivedbycomparingretrievedXCO2forasubsetofthedatatovarioustruthproxies,andidentifyingthresholdsfordifferentvariablesthatcorrelatewithpoordataquality.ItappliesanumberofqualityfiltersbasedonretrievedorauxiliaryvariablesthatcorrelatewithexcessiveXCO2scatterorbias.ThealternativemethodforOCO-2andiscalledthe“warnlevel”approach.Thisissimilartotheabovemethodbutisagraduatedmethodthatismorenuancedthanasimple“yes/no”approach.Inthisapproach,eachsoundingisgivenawarn_level,whichmaytakeavaluefrom0-5.0isconsideredthehighestquality,while5isthelowestquality.Ifyouwishtousethisapproachforyourapplication,werecommendyoustudyhowyourresultsdependonthewarnlevelyouusedforqualityfiltering.Formoredetailsonthisapproach,seeMandrakeetal.(2013).

Figure1:MapsofOCO-2XCO2dataafterbiascorrectionfor2015.Eachpanelhasadynamicallyselectedrange,whichspans7.5ppm,centeredonthatmonth’sdistributionofXCO2.

Variable(scaling

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BiasCorrectionThebiascorrection(BC)mapstheoriginalXCO2retrievalsoftheOCO-2L2algorithmtoourbestestimateofXCO2.WeusedV8dataspanningfromNovemberof2014throughMayof2015.TheBCapproachimplementedintheLitefilesusesregionalanalysistoidentify,withintheOCO-2XCO2datarecordsthemselves,whichtermsbestpredictbias(orUnexplainedVariance(%UV))intheretrievals.Ourdefinitionof%UValwaysusesanull-hypothesisdenominatorforeaseofcomparison.Wehaveconstructedseveraltrainingdatasetsforourbiascorrection,suchthatthesetprovidesanapproximationthatpermitsustodefinetheXCO2truthagainstwhichtheretrievalsareevaluatedwhileattemptingtoinsurethatrealXCO2atmosphericgradientsarenotremovedbyintheBC.Weusethesametworegionally-basedtrainingsetsusedtocreatetheWLstosearchforfeaturesthatpredictanomalousvariationsinXCO2.Asareminder,thefirstistheSouthernHemisphereApproximation(SHA),asdescribedinWunchetal.(2011),inwhichweassumequasi-constantXCO2between25°Sand60°Slatitudeduringthetrainingperiod.ThismethodincorporatesheterogeneousenvironmentsacrossthreecontinentsandsurroundingoceanintoasingletrainingsetthatcanbeusedtostudywhatfeaturesoftheretrievalproducevariationinthemeasuredXCO2.WeusedseveralmethodstoevaluatethesensitivityofthebiasevaluationwithrespecttoerrorintheassumptionofinvariantXCO2inthetrainingset.WhiletheSHXCO2datafromTCCONprovidessomeguidance(figure6),severalothermethodswereexploredincludinguseofmodelfields.WefindthatboththebiasfeaturesselectedandthesensitivityofXCO2withrespecttothesefeaturesisrelativelyinsensitivetohowthesmalltemporalandlatitudinalgradientsbetween25°Sand60°Slatitudeareparameterized.

Figure2:TCCONdatainthesouthernhemisphereshowsmalllatitudegradientsandseasonalcyclessouthof25°S.Intheleftpanel,theLauder(45°S)andWollongong


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(34.4°S)TCCONtimeseriesareshownfrom2010tothepresent.Thereisasmall(~1ppmamplitude)seasonalcycle,andanoverallsecularincrease(~2.2ppm/yr).TheWollongongdataarehigherthantheLauderdataby~0.5ppm,leadingtoalatitudinalgradientof~0.05ppm/degree.TherightpanelshowsthedataduringNovember2014throughDecember2016andincludesothersouthernhemisphereTCCONstations(DarwinandReunionIsland)thatarenorthof25°S.WelimittheSHAtosouthof25°S,astheDarwinandReuniondatashowsignificantlymoreseasonalvariations.ThesecondtrainingsetiscreatedusingSmallAreaanalysisinwhichweidentifygroupsofdensesoundings(20-80)obtainedinspatially-smallneighborhoods(<0.9°latitude)obtainedwithinthesameorbit(e.gwithin~30seconds).WeassumethatXCO2isconstantovertheseverysmallareas,andthatanyXCO2variationisanartifactoftheretrieval.WeexpectthatexceptinregionsofintensesourcesorsinksofCO2(e.g.urbanregions)oralongfrontalsystemstruevariationinXCO2ismuchsmallerthanthevarianceproducedbytheL2algorithm.AsshowninFigure3,thesegroupingsaregloballydistributed,samplingawiderheterogeneitythanthesouthernhemisphere.

Figure3–LocationofsmallareasusedinBiasCorrection


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Notethatinthebiascorrection,TCCONdataareusedonlytodefineaglobaloffsetbetweentheOCO-2dataandtheWMOinsituscaleasafinalstep.ThethreestepsofBCdeterminationareasfollows,madeconcretebyhighlightingtermsinthefinalbiascorrectionequation:

𝑿𝑪𝑶𝟐𝑪𝒐𝒓𝒓𝒆𝒄𝒕𝒆𝒅 =𝑿𝑪𝑶𝟐𝑹𝒂𝒘 − 𝑭𝑶𝑶𝑻 𝒇𝒑,𝒎𝒐𝒅𝒆 − 𝑭𝑬𝑨𝑻𝑺[𝒎𝒐𝒅𝒆]

𝑻𝑪𝑪𝑶𝑵_𝑨𝑫𝑱𝑼𝑺𝑻[𝒎𝒐𝒅𝒆]

Step1)RemovingFootprintBias(termFOOT)OCO-2obtains8side-by-side,simultaneous,nearly-collocatedmeasurementscenescalledfootprints.AlthoughtheXCO2retrievalsmadefromthesesoundingsshould,onaverage,beidentical,therearesmallandhighlystatisticallysignificantdifferences.TheseundoubtedlyarisefromimprecisionintheL1calibration.FortheV8dataset,weexaminedhighlyfiltereddatagroupedintosmallareas.Formostmodes,thedatasetcontainedmillionsofsoundings,sotheywerefurtherdownselectedtoonlyincludethebestdata.Datawereselectedfortheanalysiswhenall8footprintsinonesoundingframe(ID)converged.WecomputedthemedianXCO2asthe“groundtruth”value,andsubtractedthisfromtheobservedXCO2tocalculatethedeviationsforeachfootprint.Thereportedvaluesaretheaverageofthedifferencesacrossallsoundingsperfootprint.Thefiltrationresultedinlandselectionsnearbright,clearregionssuchasdeserts.ThefootprintoffsetsarelistedinTable2underthetermFOOTandshowninFigure8.Onceobtained,theymaybesubtractedfromallsoundingXCO2inpreparationforthenextstepsofBC.

Figure4–FootprintBiasvs.Mode


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𝑿𝑪𝑶𝟐𝑪𝒐𝒓𝒓𝒆𝒄𝒕𝒆𝒅 =𝑿𝑪𝑶𝟐𝑹𝒂𝒘 − 𝑭𝑶𝑶𝑻 𝒇𝒑,𝒎𝒐𝒅𝒆 − 𝑭𝑬𝑨𝑻𝑺[𝒎𝒐𝒅𝒆]

𝑻𝑪𝑪𝑶𝑵_𝑨𝑫𝑱𝑼𝑺𝑻[𝒎𝒐𝒅𝒆]

Step2)IdentifyunphysicalXCO2variability(termFEATS)Inthissecondstep,weidentifyvariablesretrievedsimultaneouslywithXCO2thatarecorrelatedwithspuriousXCO2variabilityusingamultivariatelinearregression.ThisistheprocedurefollowedbynearlyallGOSATXCO2biascorrectionstodate(e.g.Wunchetal.2011,Guerletetal.2013).SeveralapproacheswereusedtoexplorethislargespaceoffeaturesintheL2andpreprocessingfields:1)ageneticalgorithmthatpreservespairwiseandhigherrelationshipsbetweenfeaturesvs.allpossiblewarnlevelfiltrationoptions(Mandrakeetal.,2013);2)asimplersearchthatsequentiallyaddsthesinglemost%UV-reducingfeaturefromasmaller,expert-curatedfeatureset;and3)atraditionallinearregressionsensitivityanalysis,againuponasmallerexpert-chosenfeatureset.Usingtheseapproaches,weidentifiedfourvariablesthatappeartodriveapproximatelyhalfofthe%UVinboththeSHAandSAAtrainingsets.Thedifferentanalysisregionsandmodeshaveminordifferencesintheorderoffeatureschosen,buttheoverallfeaturesselectedandtheirslopesareremarkablyconsistent.Table1showsfortheLandNadirsmallareaandSeaGlintsmallareaset,thereductioninunexplainedvariance(UVin%)asfeaturesareaddedtothebiascorrectionfitusingthreedifferentWLfiltrationlevels:Table1:FeaturesusedinbiascorrectionwithreductioninunexplainedvarianceinparenthesesLAND(NADIRANDGLINTMODE)


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OCEANGLINTMODE

Thesetermsarethedifferencesbetweentheretrievedandtheapriorisurfacepressure(dP),theretrievedabundanceofcoarseaerosol(e.g.dust,seasalt,orwaterclouds),and(verylargeandunphysical)variationintheretrievedverticalprofileofCO2(parameterco2_grad_del)fromthatassumedintheprior.Thereisafundamentally-differentbiasbehavioroverlandvs.watersurfacesrequiringseparatebiascorrectionterms.Overland,thereisnosignificantdifferencebetweenthenadir-andglintfeature-dependentbiases.

𝑋𝐶𝑂DEFGGHIJHK =𝑋𝐶𝑂DLMN − 𝐹𝑂𝑂𝑇 𝑓𝑝,𝑚𝑜𝑑𝑒 − 𝐹𝐸𝐴𝑇𝑆[𝑚𝑜𝑑𝑒]

𝑇𝐶𝐶𝑂𝑁_𝐴𝐷𝐽𝑈𝑆𝑇[𝑚𝑜𝑑𝑒]

Step3)DetermineglobaloffsetfromTCCON(termTCCON_ADJUST)TheanalysesdescribedinSteps1&2providenoestimateoftheoverallglobalbiasinXCO2.Todeterminetheoffset,weusedtargetmodeobservationsobtainedovertheTCCONsites.AlinearregressionbetweenTCCONXCO2andthebias-correctedOCO-2targetmodeXCO2wasperformed,withtheinterceptforcedtozero(Figure5).Overall,thisanalysisresultsinthefollowingequationforlandtarget:OCO-2=(0.99581±0.00142)´

Figure5–OCO-2vsTCCONAlignmentPlot


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TCCON.OCO-2retrievalsareconsistentlylowerthanTCCON(about1ppm).ThedatausedtodevelopFigure5hadtheoutlierfiltersappliedasdescribedintheLitefilesection.Inaddition,thesolarzenithangleandretrievalzenithanglesarerestrictedtolessthan40degrees.RegardingTCCONdata,sitesareincludedonlyifthereare5ormoreTCCONretrievalswithinonehouroftheoverpass,ormorethan10TCCONretrievalsavailablewithin2hoursoftheoverpass.TheTCCONadjustmentwasdeterminedrelativetotheOCO-2LandTargetobservations.Weassumethatwiththerestrictedretrievalzenith,thelandTargetandLandGlinthaveidenticalbias.Futureworkwillexaminetheveracityofthisassumptionandexplorealternativemethodsofspreadingthedivisorbetweenmodes.LandNadirandSeaGlintarematchedintimeandspacetoLandGlintinordertopropagatetheTCCONalignmentdivisor.CoastlinemeasurementsareusedtomatchtheLandNadir/SeaGlintdatasets(Figure6).LandNadirandSeaGlintbothproduceddifferentdivisorsbytheequation^_E`abcdefg

KhihjFGg= ^_E`abcdefa

KhihjFGa.ResultscanbefoundinthefinalBias

Correction,Table2.


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Figure6:ScatterplotsofTCCONdatawithnadirandglintmeasurements.

Step4)XCO2QualityFlaggingAfterbiascorrection,additionaloutlierfilteringisdevelopedandapplied.Thexco2_quality_flagissetto“0”forgoodqualitydataandsetto“1”forlowerqualitydata.Notethatthissimplequalityflagisagoodstartingpoint,userscanseethelatersectiononWarnLevelsforamoreadvancedapproachtodataselection.Tables3and4listthedetailsontheparametersthatdefinethedataqualityflag.Figure7illustratestheseparametersasappliedtolanddata.


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Table2BiasCorrectionFormula(foruseonV8.0)

𝑋𝐶𝑂DEFGGHIJHK =𝑋𝐶𝑂DLMN − 𝐹𝑂𝑂𝑇 𝑓𝑝,𝑚𝑜𝑑𝑒 − 𝐹𝐸𝐴𝑇𝑆[𝑚𝑜𝑑𝑒]

𝑇𝐶𝐶𝑂𝑁_𝐴𝐷𝐽𝑈𝑆𝑇[𝑚𝑜𝑑𝑒]

where:

FOOTPRINTBIAS(FOOT)(ppm)

Footprint(fp) 1 2 3 4 5 6 7 8

ALLMODES -0.36 -0.15 -0.16 -0.14 0.02 0.33 0.13 0.34

FEATUREBIAS(FEATS)(ppm)

LAND(ALL) –0.36*(dP)–8.5*(DWS)–0.029*(co2_grad_del–15)

SEAGLINT –0.23*(dP)+0.09*(co2_grad_del+6.0)[secondtermonlyappliedwhenco2_grad_delislessthan-6)

OVERALLDIVISOR(TCCON_ADJUST) Method

LANDGLINTLANDNADIRLANDTARGET

0.9958Targetisassigned

OthermodesderivedfromTCCONpairedND/GLandcomparisontomodels

SEAGLINT 0.9955 ComparisontoTCCON,coastlines,modelbootstrap,andcomparisontomodels

NOTE!ThisconstantisneededfortheL2standardbutnotLiteproducts

Variabledefinitionsusingfull/HDF/pathforL2files

co2_grad_del 1e6*RetrievalResults/co2_vertical_gradient_delta

dP 0.01*(RetrievalResults/surface_pressure_fph–RetrievalResults/surface_pressure_apriori_fph)

DWS sum(dust_aod+water_aod+salt_aod)

dust_aod(1-based) (AerosolResults/aerosol_types_retrieved[1]) ∗ (AerosolResults/aerosol_aod[1,1])

water_aod(1-based) (AerosolResults/aerosol_types_retrieved[7]) ∗ (AerosolResults/aerosol_aod[7,1)

salt_aod(1-based) (AerosolResults/aerosol_types_retrieved[2]) ∗ (AerosolResults/aerosol_aod[2,1)


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Table3:QualityFiltersAppliedtoLandSoundingsAllLandSoundings

Field LowerLimit(>or=)

UpperLimit(<or=)

Preprocessors/co2_ratio 1.00 1.025Preprocessors/h2o_ratio 0.88 1.01Sounding/altitude_stddev 0.0 60.0(20.0)Preprocessors/max_declocking_wco2 0.0 0.75Retrieval/dp -6.0 14.0Preprocessors/dp_abp -10.0 13.0(50.0)Retrieval/co2_grad_del -80.0 100.0Retrieval/albedo_sco2 0.05 0.6Retrieval/rms_rel_wco2 0.0 0.22Retrieval/s31 0.03 0.4Retrieval/albedo_slope_sco2 -0.00018 0.001Retrieval/aod_total 0.0 0.5Retrieval/dws 0.0 0.25Retrieval/aod_water 0.0005 0.1Retrieval/aod_ice 0.00 0.04Retrieval/ice_height -0.5 0.45Retrieval/aod_sulfate+Retrieval/aod_oc

0.0 0.3

Retrieval/aod_strataer 0.0 0.02Retrieval/aod_oc 0.0 0.08Retrieval/aod_seasalt 0.0 0.125

Note:Numbersin(red)areusedfortarget-modesoundings.Table4:QualityFiltersAppliedtoOceanGlintSoundings

OceanGlintSoundingsField LowerLimit

(>or=)UpperLimit(<or=)

Retrieval/eof3_3_rel -0.3 0.25Preprocessors/max_declocking_wco2 0.0 0.2Preprocessors/max_declocking_sco2 0.0 0.3Retrieval/albedo_slope_sco2 5e-6 7e-5Retrieval/rms_rel_wco2 0.0 0.3Preprocessors/h2o_ratio 0.88 1.01Preprocessors/co2_ratio 0.997 1.018Retrieval/dp -4.0 10.0Retrieval/co2_grad_del -20.0 30.0Retrieval/windspeed 1.5 25Preprocessors/dp_abp -50.0 10.0Retrieval/aod_ice 0.0 0.035


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Figure7–Bias&StddevofXCO2errorasafunctionofselectedoutlierfilteringvariablesforlandobservations.Here,theerrorisderivedusingthemodelcomparison.


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HistogramofBiasTermsFigure8showsthehistogramsofbiascontributionsfromStep2aswellastheoverallBiasCorrection.ThebiascorrectiontermforDWS(blue)isalwaysnegativebecauseaerosolopticaldepthmustbepositiveintheretrievalsetup.Avalueof1ppmissubtractedfromtheoverallbiasdeterminationjustasitisforTCCONtomatchtheWorldMeteorologicalOrganization(WMO)insitutracegasmeasurementscales.

Figure8–HistogramofBiasTerms


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GlobalBiasMagnitudeFigures9to11showLandNadir,LandGlint,&SeaGlintregionalbiases(XCO2corrected–XCO2).Whiteindicatesazeromeaneffect,whilegrayregionshavenodata.Extremebiascorrectioneffects(darkred/blue,~3.5ppm)arechieflyobservedinbinswithlowN.

Figure9-LandNadirBiasCorrectionTerms,GeographicDistribution


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Figure10-LandGlintBiasCorrectionTerms,GeographicDistribution


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Figure11-SeaGlintBiasCorrectionTerms,GeographicDistribution

WarnLevelsWarnLevelsrangefrom0(includesthebest50%ofthedata)to5(includingallthedata),andareformulatedusingasetoffiltersthatminimizethemeanmonthlystandarddeviation(MMS)ofXCO2inlocationswheretheatmosphericvariabilityofXCO2issmall.


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Thewarnlevels(0,1,2,3,4,5)correspondto(50%,60%,70%,80%,90%,and100%)ofthedata.Formostsciencedatausers,awarnlevelof0isagoodstartingpoint.Weusetwotestsets:theSouthernHemisphereApproximation(SHA)set(assumesthattheentireregionfrom-25to-60latitudehasminimalvariationinXCO2(Wunchetal.,2011))andtheSmallAreaAnalysis(SAA)set(assumesthatallsoundingswithina0.89degreeslatitudespanandidenticalorbittrackhavethesameXCO2).ThecreationofWLsreliesonahyper-dimensionalfilterandageneticalgorithmthatoptimizesfilterperformanceforevery0.1%incrementofdataaccepted(transparency).Mandrakeetal.(2013)describesthistechniqueindetail.ForOCO-2V8data,theWLsarecalculatedseparatelyforeachmeasurementmode(nadirland,glintland,glintwater,andlandtarget).Landmodesallbehavedthesame,sothereisonlyonesetoflandcriteria.Table5reportsthefeaturesderivedfromtheL2andpreprocessingoutputthatwerecommonlycorrelatedwithXCO2variabilityinthetwotestsets.Manyotherfeaturescouldbeused,butwehaveoptedforthesimplestfilter.ThefieldswiththelabelMandrakeareonesthatwerecalculatedspecificallyforwarnleveldevelopment,andtheyarenotintheL2Stdfiles,buttheyareintheLitefiles.

Table5–FeaturesselectedforWarnLevelDevelopment

Table6showthespecificvaluesthathavebeenusedtodefinetheWLsforV8.TheseWLshavealreadybeencalculatedandinsertedintotheV8Litefiles;usersdonotneedtocalculateWLsdirectlyunlesstheyareusingtheV8L2StdfileswheretheWLvariableisassignedafillvalue.


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HowtoUseWarnLevelsThebasicprocedureforuseofWLsisoutlinedinTable2.Auserfirstdecideshowmuchdatavolumeorregional/globalcoveragetheyrequire.Alternately,shecandecidehowmuchofanerrormetricistolerable(trustedXCO2comparison,regionalXCO2scatter,biasdeviation,extremapopulationpresence,orpresenceofotheranomaloussoundingbehaviors).TheWListhenselectedthatbalancesthetransparencywiththeerrortolerance.Theuserhasthentunedapersonalfilterfortheinvestigationathand.

NotethatWL’sarealmostalwaysusedInclusively(meaningthatusingWL5isdefinedasusingalldataspecifiedbyWL<=5).Thisistheproperusagefordatafiltration.UsingaspecificWLbyitself(dataforwhichWL==2alone)iscalledanExclusiveWLandissometimesusefulforfindingtheWLatwhichcertainconfoundingforcesappear.Byconvention,suchExclusiveWL’sshouldalwaysbeexplicitlynamedtoavoidconfusion.

WLCase1:RegionalStudy

Here,auserinvestigatesadifficultenvironment(e.g.aplumeemittedfromapollutedcity).WewishtoharnesstheWLstoremovethetrulyuselesssoundingsbutstillkeepinterestingyetdifficultsoundings.ThestandardprocedureofTable2isusedintherestrictedregion,watchingcarefullyfortheappearanceoftheplumeandassociatedcitypollution.Oncetheobservationstostudyareclearlypresent,furtherWLsmaybeseentostartincludingcloudsandothernon-plume-likesoundings.TheuserthereforebacksofftheincludedWLsuntilahappymediumbetweenplumeandunwantedcontaminationisreached.Thismethodissimilartotuningthecontrastinanimage,ensuringclearviewingofthedesiredpatternbutnotover-emphasizingnoise.

Case2:UniformGlobalStudyForthisanalysis,auserrequiresuniformglobalcoverageratherthandensecoverageofeasyregions(e.g.deserts)andsparsecoverageofdifficultregions(e.g.tropics).Theuserwoulddefineaglobalgridofbinstofillwiththehighestqualitydatauntileachbinreachesitsdesignateddatavolumegoal.AsinTable2,theco-locateddataaddedtoeachbinisalwaysaddedinorderofWLfromlowesttohighest.Attheendoftheprocess,thesoundingsselectedbythegridrepresentaspatiallyuniformcollectionofthemosttrustedsoundingsperregion.SometroublesomeregionswillthereforeconsistofhigherWL

Table2:BasicProcedureforWarnLevelUsage


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soundingsornoneatallwherenoalternativeswereavailable,whileeasierregionswillonlyselectthemostpristinesoundings.Thisisapowerfulselectionmethodthatallowstheusertodial-intheprecisespatialcoveragedesiredfortheirapplicationwiththeassuranceofusingthebestqualitydataavailable.

CharacterizingWarnLevelBehavior

WarnLevelsandXCO2characteristics

WarnLevelsaredesignedtominimizethevarianceofXCO2inregionsofsmallatmosphericvariability.However,thesignalthatWL’sreduceissoclearlyevidentthateveninlocationswithsignificant,physicalatmosphericvariabilityorentireglobaldatasetsdemonstratethereductionofXCO2variancewithrespecttoWLfiltration.Infigure12,weshowthewarnlevelmetricforV8seaglintandlanddatasetasafunctionofthepercentofdataretained.ThemarkersonthelinescorrespondtotheV8warnlevels,whichweredefinedverydifferentlyinV8comparedtov7.Thefirstwarnlevel(WL0)capturesthebest50%ofthedata,wherethedatacharacteristicsareverysimilar.Aswarnlevelincreases,thestandarddeviationandcomparisonsmetricsworsen.TheyappeartoworsenrathermonotonicallyuptoWL4(whichincludes90%ofthedata).Thelast10%ofdatahasmuchworseperformance.

Figure12:XCO2BiasandScatterasafunctionofWarnLevel


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WarnLevelSpatialCharacteristicsInafutureupdateofthedocumentation,wewillincludemapsthatshowthespatialdatadensityasafunctionofwarnlevels.Thedatasetthatisusedforwarnleveldevelopmentisnotdenseenoughtodothiseffectively,andatthetimeofwriting,wedonothaveglobal,fullmonthwarnlevelsavailable.But,welearnedfromv7thatselectionofdatabywarnlevelimpactsthedatadensity.Typically,withv7,aswarnlevelisdecreasedandoveralldatadensityisdecreased,thelatitudinaldatadensityalsodecreases.WehavenotfullycharacterizedthisforV8,butifyouusethewarnlevelsfordataselection,westronglyencourageyoutoanalyzethespatialcoverage.Table6:ValuesusedforWarnLeveldeterminationMODE WL0 WL1 WL2 WL3 WL4SEA_GL: <L2/RetrievalResults/co2_vertical_gradient_delta -1.18E-05 -1.26E-05 -1.42E-05 -1.60E-05 -1.78E-05>L2/RetrievalResults/co2_vertical_gradient_delta 2.40E-06 5.15E-06 9.63E-06 1.61E-05 2.73E-05>L2/AlbedoResults/albedo_weak_co2_fph 0.04152818 0.04290641 0.04870763 0.05159356 0.183427<L2/AlbedoResults/albedo_slope_strong_co2 9.11E-06 6.77E-06 5.06E-06 8.75E-07 -1.53E-05>Mandrake/abs_minus_1_max_declock_strong_co2 0.00188552 0.002298161 0.002635343 0.00462906 0.009252626

LND_AL: >Mandrake/aerosol_log_dustwatersalt_large_aod -0.8263409 -0.6938695 -0.619922 -0.5784207 -0.05069106<Mandrake/dP_fph -6.404422 -7.054969 -7.561389 -8.995695 -9.690548>L2/RetrievalGeometry/retrieval_surface_roughness 19.90433 29.2552 40.46891 59.79335 97.43734>L2/PreprocessingResults/h2o_ratio_idp 0.9966815 1.005532 1.017087 1.028502 1.046504>L2/SpectralParameters/relative_residual_mean_square_weak_co2 0.002365796 0.002463946 0.002850933 0.003588029 0.00442925


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FormatSpecificationOCO-2B8LiteFiles

OverviewInformationTheOCO-2L2LitefilescontainasubsetoftheinformationinthestandardOCO-2L2product.Theyaremeanttobesignificantlysmallerbutstillcontainallnecessaryinformationfortypicalscienceanalyses.Inaddition,theyhavesomevalueadded:

• OnlycontainL2soundingsthatconverged• Theyincludeanominalrecommendedfilteringflag(xco2_quality_flag)• Theycontainasetof“warnlevels”whichallowstheusertotunethelevelofdata

qualitydesired.• TheyincludetherecommendedbiascorrectionalreadyappliedtoXCO2(theXCO2

withoutbiascorrectionisalsocontainedintheLitefiles)

Thereisonefileperday,foreachdaythathadatleastoneretrievedsounding.TheOCO-2LitefilesareinthenetCDF-4format(http://www.unidata.ucar.edu/software/netcdf/docs/netcdf/NetCDF_002d4-Format.html).BecausenetCDF-4isasubsetofHDF-5,thefilesmaybereadwithbothnetCDFandHDFsoftware.Generallyspeaking,eachfieldinthefileisdescribedintheAttributesofthatfieldwithinthefileitself.Descriptionsforselectedfieldsaregivenbelow,butpleasebesuretoreadtheAttributesofeachusedfieldwithintheactualLitefile.Afterthis,wedescribethefilteringandbiascorrectionapproach.

FileStructure&FieldsTheprimaryvariablesthatmostuserswillneedexistatthemainlevel.Inaddition,therearesomeadditionalvariablesthatcertainusersmightwant,containedinthreegroupswithinthefile:Preprocessors,Retrieval,andSounding.SomeNetCDFreadersmaynotseethesegroups;ifthishappens,pleaseupdateyourNetCDFreaderoruseanHDF-5reader.

1. MainLevelVariables

• latitudeThelatitudeatthecenterofthesoundingfield-of-view.ParentField:L2s/RetrievalGeometry/retrieval_latitude


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• longitudeThelongitudeatthecenterofthesoundingfield-of-view.

ParentField:L2s/RetrievalGeometry/retrieval_longitude

• vertex_latitudeThelatitudeateachofthecornersoftheparallelogramthatdefinesthefield-of-view.ParentField:L2s/RetrievalGeometry/retrieval_vertex_latitude

• vertex_longitudeThelongitudeateachofthecornersoftheparallelogramthatdefinesthefield-of-view.ParentField:L2s/RetrievalGeometry/retrieval_vertex_longitude

• timeThetimeofthesoundinginsecondssince1970-01-0100:00:00UTC.

ParentField:None(computedfromRetrievalHeader/retrieval_time_string)

• dateThefulldateandtimeofthesoundinginUTC,organizedas[year,month,day,hour,minute,second,milliseconds].Thisinformationisredundantwiththatfromthetimevariable.ParentField:None(computedfromRetrievalHeader/retrieval_time_string)

• solar_zenith_angleThesolarzenithangle(indegrees)atthetarget.

ParentField:L2s/RetrievalGeometry/retrieval_solar_zenith

• sensor_zenith_angleThesatellitezenithangle(indegrees)atthetarget.ParentField:L2s/RetrievalGeometry/retrieval_zenith

• xco2Thebias-correctedXCO2(inunitsofppm).Thisshouldbeusedfor

scienceanalysis.Thebiascorrectionformulaearecontainedinthemetadataofthefile.ParentField:None(derivedusingbias-correctionformula)

• xco2_aprioriThepriorXCO2assumedbytheL2retrieval,inppm.ParentField:L2s/RetrievalResults/xco2_apriori*1e6

• xco2_uncertaintyTheposterioruncertaintyinXCO2calculatedbytheL2algorithm,inppm.Thisisgenerally30-50%smallerthanthetrueretrievaluncertainty.ParentField:L2s/RetrievalResults/xco2_uncert*1e6

• xco2_quality_flagAsimplequalityflagdenotingsciencequalitydata.0=higherquality,1=lowerquality.ParentField:None

• warn_levelAgraduatedindicatorofdataquality.0=highestquality;5=lowestquality.


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ParentField:L2s/RetrievalHeader/warn_level

• co2_profile_aprioriThepriorprofileofco2inppm.ParentGroup:L2s/RetrievalResults/co2_profile_apriori*1e6

• xco2_averaging_kernelThenormalizedcolumnavergingkernelforthe

retrievedXCO2(dimensionless).ParentGroup:L2s/RetrievalResults/xco2_avg_kernel

• pressure_levelsTheretrievalpressurelevelgridforeachsoundinginhPa.NotethatissimplyequaltoSigmaBmultipliedbythesurfacepressure.ParentGroup:L2s/RetrievalResults/vector_pressure_levels*0.01

• pressure_weightThepressureweightingfunctiononlevelsusedintheretrieval.Ithasthesamedimensionsasboth“pressurelevels”and“co2_profile_apriori”.ParentGroup:L2s/RetrievalResults/pressure_weighting_function

• sounding_idThesounding_idofthesounding.ForGOSAT,thisisa14-digitnumberdefinedasYYYYMMDDhhmmss.{YYYY=year,MM=month1-12,DD=day1-31,hh=hour0-23,mm=minute0-59,ss=seconds0-59,m=hundredsofmilliseconds0-9,f=footprintnumber1-8}.ForOCO,itisa16-digitnumberdefinedasYYYYMMDDhhmmssmf.{YYYY=year,MM=month1-12,DD=day1-31,hh=hour0-23,mm=minute0-59,ss=seconds0-59,m=hundredsofmilliseconds0-9,f=footprintnumber1-8}.ParentField:L2s/RetrievalHeader/sounding_id

• source_filesTheL2Stdfilesusedtogeneratethisfile.ParentGroup:None

• file_indexThe1-basedindexusedtoidentifywhichsourcefileeachsounding

wasdrawnfrom.Ie,file_index=2foraparticularsoundingmeansthatsoundingwasdrawnfromthe2ndelementofsource_files.ParentGroup:None

Main-LevelDimensionVariables(thesevariablesarepartofthenetcdf-4definitionandwillnotbeneededbymostusers)• bands:ThethreeOCO-2bands.• levels:ThetwentyverticallevelsintheOCO-2level-2full-physicsretrieval.• epoch_dimension:Variableusedfordimensioningthe7-integerdate

variable.• vertices:The4vertexindicesforvertex_latitudeandvertex_longitude.• footprints:The8footprintindicesforfootprint-dimensionedvariablessuch

asPreprocessors/co2_ratio_offset_per_footprint.


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2. PreprocessorsGroup

ThisgroupcontainsinformationforthetwoOCO-2preprocessoralgorithms:TheA-BandPreprocessor(ABP)andtheIMAP-DOASPreporocessor(IDP).

• co2_ratio:ContainstheratiooftheretrievedCO2columnfromtheweakCo2bandrelativetothatfromthestrongCO2band.Thisratioshouldbenearunity.Significantdeparturefromunityiscurrentlyusedasawaytoflagbadsoundings(usuallycloudoraerosol-contaminated).Thisvaluehasalsobeenfootprintcorrectedusingco2_ratio_offset_per_footprint.ParentField:L2s/PreprocessingResults/co2_ratio_idp(andthenfootprint-corrected).

• co2_ratio_offset_per_footprint:Containstheapproximateoffsetinco2_ratiofromthemeanvalueacrossallfootprints,usedintheconstructionofco2_ratio.ParentField:none.

• h2o_ratio:ContainstheratiooftheretrievedH2Ocolumnfromtheweak

CO2bandrelativetothatfromthestrongCO2band.Thisratioshouldbenearunity.Significantdeparturefromunityiscurrentlyusedasawaytoflagbadsoundings(usuallycloudoraerosol-contaminated).Thisvaluehasalsobeenfootprintcorrectedusingh2o_ratio_offset_per_footprint.ParentField:L2s/PreprocessingResults/h2o_ratio_idp(andthenfootprint-corrected).

• h2o_ratio_offset_per_footprint:Containstheapproximateoffsetinh2o_ratiofromthemeanvalueacrossallfootprints,usedintheconstructionofh2o_ratio.ParentField:none.

• dp_abp:Thisistheretrievedsurfacepressureminusthe“best-guess”

surfacepressurefromtheECMWFforecastmodel.Thishasbeenadjustedforaclear-skybiasaswellasthelocalsurfaceelevationoftheobservedfootprint.Avalueofthisgreaterthanabout50hPaabsolutevaluetypicallyindicatescloudoraerosolcontamination.ParentField:L2s/PreprocessingResults/surface_pressure_delta_abp*1e-2

• xco2_strong_idp:EstimateofXCO2usingonlytheIMAP-DOASstrongCO2

bandretrievalat2.06µm.Thedryaircolumnistakenfromtheprior.Itisconstructedastheratiooftheco2columnfromthestrongCO2band,dividedbythedryaircolumn.Unitsareppm.ParentFields:L2s/PreprocessingResults/co2_column_strong_band_idp,L2s/PreprocessingResults/dry_air_column_apriori_idp


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• xco2_weak_idp:EstimateofXCO2usingonlytheIMAP-DOASweakCO2bandretrievalat1.61µm.Thedryaircolumnistakenfromtheprior.Itisconstructedastheratiooftheco2columnfromtheweakCO2band,dividedbythedryaircolumn.Unitsareppm.ParentFields:L2s/PreprocessingResults/co2_column_weak_band_idp,L2s/PreprocessingResults/dry_air_column_apriori_idp

• max_declocking_o2a:Anestimateoftheabsolutevalueoftheclockingerror

intheO2-Aband(usedintheclockingcorrectionalgorithmthatattemptstocorrecttheL1bradiancesforclockingerrors).Expressedinpercent.Typicalvaluesrangefrom0to10%.ParentField:ABS(L2s/L1bSpectralParameters/max_declocking_factor_o2-1)*100

• max_declocking_wco2:Sameasmax_declocking_o2a,butfortheweakco2

band.ParentField:ABS(L2s/L1bSpectralParameters/max_declocking_factor_strong_co2-1)*100

• max_declocking_sco2:Sameasmax_declocking_wco2,butforthestrongco2band.ParentField:L2s/L1bSpectralParameters/max_declocking_factor_strong_co2

3. RetrievalGroup

ThisgroupcontainsinformationfromtheOCO-2level-2retrievalalgorithm.Itcontainsmanyfieldsthatwillonlybrieflybesummarizedhere.Theseareotherfieldsthatmaybeusefultousers.Somewereusedforqualityfiltering,someforbiascorrection,andothersforneither.

• xco2_rawisthe“raw”XCO2retrievedbytheL2codewithoutbiascorrection.Itshouldnotbeusedforscienceanalysis.ParentField:L2s/RetrievalResults/xco2*1e6

• surface_typeSurfacetypeusedintheretrieval:0=oceanandcorrespondstoaCoxmunk+Lambertiansurface;1=landandcorrespondstoanon-LambertiansurfacewithafixedBRDFshape(thisisappliedtolandsurfaces).TheBRDFisdescribedintheL2ATBD.ParentGroup:L2s/RetrievalResults/surface_type(changingCoxmunk,Lambertian->0,Non-Lambertian->1)

• psurfRetrievedsurfacepressure(inhPa)fromtheL2algorithm.Note:thiscanbemultipliedwiththevariableSigmaBtodeterminetheprofileofpressuresforanysounding.ParentGroup:L2s/RetrievalResults/surface_pressure_fph


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• psurf_aprioriApriorisurfacepressure(inhPa)assumedbytheL2algorithm,takenoriginallyfromGEOS5-FP-ITanalysis.Note:thisshouldbeusedinconjunctionwiththevariableSigmaB_Coefficienttodeterminetheaprioriprofileofpressures.ParentGroup:L2s/RetrievalResults/surface_pressure_apriori_fph

• dpThedifferencepsurf–psurf_apriori,inhPa.ThisvariableisusedintheXCO2biascorrectionoverbothlandandwatersurfaces.ParentGroup:None.

• tcwvRetrievedTotalColumnWaterVapor(TWCV)inunitsofkgm-2.

ParentGroup:L2s/RetrievalResults/retrieved_h2o_column*(0.0180153/6.0221415e23).Thelatterisrequiredtoconvertfrommoleculesofh2operm2tokgh2operm2.

• tcwv_aprioriApriorivalueoftheTCWVderivedfromthepriorh2oprofile

inunitsofkgm-2.Obtainedbydividingtheretrievedtcwvbytheretrievedh2o_scalefactor.ParentGroup:RetrievalResults/h2o_scale_factor(alongwithtcwv).

• tcwv_uncertaintyNoise-drivenuncertaintyontheretrievedTWCVinkgm-2.Obtainedfromtheproductoftcwv_aprioritimestheposterioruncertaintyontheh2o_scalefactor.ParentGroup:RetrievalResults/h2o_scale_factor_uncert

• land_brdf_weight_o2aRetrievedamplitudeofthelandBRDFattheband1referencewavelength(0.77µm).ThelandBRDFshapeisfixedforalllandsurfaces,andisdetailedintheL2ATBD.ParentGroup:L2s/BRDFResults/brdf_weight_o2

• land_brdf_weight_wco2RetrievedamplitudeofthelandBRDFattheband2referencewavelength(1.615µm).ThelandBRDFshapeisfixedforalllandsurfaces,andisdetailedintheL2ATBD.ParentGroup:L2s/BRDFResults/brdf_weight_weak_co2

• land_brdf_weight_sco2RetrievedamplitudeofthelandBRDFattheband3referencewavelength(2.06µm).ThelandBRDFshapeisfixedforalllandsurfaces,andisdetailedintheL2ATBD.ParentGroup:L2s/BRDFResults/brdf_weight_strong_co2

• albedo_o2aOver-landretrievals:Surfacereflectanceatareferencewavelengthinband1(0.77µm)intheprimaryscatteringgeometry(sun->ground->sensor)derivedfromtheretrievedBRDF.Over-waterretrievals:RetrievedLambertianalbedoattheband1referencewavelength.


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ParentGroup:L2s/AlbedoResults/albedo_o2_fph(water),L2s/BRDFResults/brdf_reflectance_o2(land).

• albedo_wco2Over-landretrievals:Surfacereflectanceatareferencewavelengthinband2(1.615µm)intheprimaryscatteringgeometry(sun->ground->sensor)derivedfromtheretrievedBRDF.Over-waterretrievals:RetrievedLambertianalbedoattheband2referencewavelength.ParentGroup:L2s/AlbedoResults/albedo_weak_co2_fph(water),L2s/BRDFResults/brdf_reflectance_weak_co2(land).

• albedo_sco2Over-landretrievals:Surfacereflectanceatareference

wavelengthinband3(2.06µm)intheprimaryscatteringgeometry(sun->ground->sensor)derivedfromtheretrievedBRDF.Over-waterretrievals:RetrievedLambertianalbedoattheband3referencewavelength.ParentGroup:L2s/AlbedoResults/albedo_strong_co2_fph(water),L2s/BRDFResults/brdf_reflectance_strong_co2(land).

• albedo_slope_o2aSlopeofthealbedo_o2atermwithrespecttowavenumber.

ParentGroup:L2s/AlbedoResults/albedo_slope_o2_fph(water),L2s/BRDFResults/brdf_reflectance_slope_o2(land).

• albedo_slope_wco2Slopeofthealbedo_wco2termwithrespecttowavenumber.ParentGroup:L2s/AlbedoResults/albedo_slope_weak_co2_fph(water),L2s/BRDFResults/brdf_reflectance_slope_weak_co2(land).

• albedo_slope_sco2Slopeofthealbedo_sco2termwithrespecttowavenumber.ParentGroup:L2s/AlbedoResults/albedo_slope_strong_co2_fph(water),L2s/BRDFResults/brdf_reflectance_slope_strong_co2(land).

• aod_iceRetrievedExtinctionOpticalDepthofcloudiceat0.755μm.

ParentGroup:L2s/AerosolResults/aerosol_aod[*,6,1](1-basedcounting)

• aod_waterRetrievedExtinctionOpticalDepthofcloudwaterat0.755μm.ParentGroup:L2s/AerosolResults/aerosol_aod[*,7,1](1-basedcounting)

• aod_dustRetrievedExtinctionOpticalDepthofdustaerosolat0.755μm.ParentGroup:L2s/AerosolResults/aerosol_aod[*,1,1](1-basedcounting)

• aod_seasaltRetrievedExtinctionOpticalDepthofseasaltaerosolat0.755μm.ParentGroup:L2s/AerosolResults/aerosol_aod[*,2,1](1-basedcounting)

• aod_bcRetrievedExtinctionOpticalDepthofblackcarbonat0.755μm.


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ParentGroup:L2s/AerosolResults/aerosol__aod[*,3,1](1-basedcounting)

• aod_ocRetrievedExtinctionOpticalDepthoforganiccarbonat0.755μm.ParentGroup:L2s/AerosolResults/aerosol_aod[*,4,1](1-basedcounting)

• aod_strataerRetrievedExtinctionOpticalDepthofstratosphericaerosolat0.755μm.ParentGroup:L2s/ AerosolResults/aerosol_aod[*,8,1](1-basedcounting)

• aod_sulfateRetrievedExtinctionOpticalDepthofsulfateaerosolat0.755μm.ParentGroup:L2s/ AerosolResults/aerosol_aod[*,5,1](1-basedcounting)

• aod_totalRetrievedExtinctionOpticalDepthofcloud+aerosolat0.755μm.

ParentGroup:L2s/AerosolResults/aerosol_total_aod

• dwsGivenbyaod_dust+aod_water+aod_seasalt.ThisisusedintheXCO2biascorrectionforsoundingsoverland.

• ice_heightRetrievedcentralpressureoftheicelayer,relativetotheretrievedsurfacepressure.

• deltaTRetrievedoffset(inKelvin)toaprioritemperatureprofile.

ParentGroup:L2s/RetrievalResults/temperature_offset_fph

• h2o_scaleRetrievedwatervaporscalefactor.ParentGroup:L2s/RetrievalResults/h2o_scale_factor

• co2_grad_delChange(betweentheretrievedprofileandthepriorprofile)of

theco2dryairmolefractiondifferencefromthesurfaceminusthatatlevel13,measuredinppm.Level13isatapressureP=0.631579Psurf.ThisvariableisusedintheXCO2biascorrectionoverbothlandandwatersurfaces.DerivedfromL2s/RetrievalResults/co2_profileandco2_profile_apriori.Ifc=co2_profileanda=co2_profile_apriori,thendelta_grad_co2=(c[20]-c[13])*1e6–(a[20]-a[13])*1e6

• fsRetrievedfluorescenceinunitsofWm-2μm-1sr-1at757nm.Derivedfrom:L2s/RetrievalResults/fluorescence_at_reference.

• reduced_chi2_o2aReducedchi-squaredvalueoftheL2fitresidualsforband

1.ParentGroup:L2s/SpectralParameters/reduced_chi_squared_o2_fph


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• reduced_chi2_wco2Reducedchi-squaredvalueoftheL2fitresidualsforband2.ParentGroup:L2s/SpectralParameters/reduced_chi_squared_weak_co2_fph

• reduced_chi2_sco2Reducedchi-squaredvalueoftheL2fitresidualsforband3.ParentGroup:L2s/SpectralParameters/reduced_chi_squared_strong_co2_fph

• rms_rel_wco2RMSoftheL2fitresidualsforband2,relativetothecontinuumsignal,inpercent.ParentGroup:L2s/SpectralParameters/relative_residual_mean_square_weak_co2*100

• windspeedRetrievedsurfacewindspeed(inm/s)fromtheL2algorithm,overwatersurfacesonly.ParentGroup:L2s/RetrievalResults/wind_speed

• windspeed_aprioriPriorsurfacewindspeed(inm/s)usedintheL2algorithm,overwatersurfacesonly.TakenfromtheGEOS5-FP-ITanalysis.ParentGroup:L2s/RetrievalResults/wind_speed_apriori

• windspeed_u_metPriorsurfacewindspeed(inm/s)inthehorizontalU(North-South)direction.PositiveumeanstheN-Swindcomponentisflowingtothenorth(isfromthesouth).TakenfromtheGEOS5-FP-ITanalysis.Canbeusedalongwithwindspeed_v_mettocalculatethepriorwinddirection.ParentGroup:L2s/RetrievalResults/wind_speed_u_met

• windspeed_v_metPriorsurfacewindspeed(inm/s)inthehorizontalV(East-West)direction.PositivevmeanstheE-Wwindcomponentisflowingtotheeast(isfromthewest).TakenfromtheGEOS5-FP-ITanalysis.Canbeusedalongwithwindspeed_u_mettocalculatethepriorwinddirection.ParentGroup:L2s/RetrievalResults/wind_speed_v_met

• t700Theestimatedtemperatureat700hPaforeachsounding,takenfrom

theGEOS5-FP-ITforecastandestimatedusinglinearinterpolation.Invalidforsoundingsinwhichthesurfacepressureislowerthan700hPa.ParentGroup:None.

• s31Ratioofcontinuumsignalinthestrongco2bandtothatoftheo2aband.Derivedfrom:L2s/SpectralParameters/signal_strong_co2_fph

(dividedby)L2s/SpectralParameters/signal_o2_fph


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• s32Ratioofcontinuumsignalinthestrongco2bandtothatoftheweakco2band.Derivedfrom:L2s/SpectralParameters/signal_strong_co2_fph

(dividedby)L2s/SpectralParameters/signal_weak_co2_fph

• iterationsNumberofiterationstakenbytheretrieval.

ParentGroup:L2s/RetrievalResults/iterations

• diverging_stepsNumberofdivergingstepstakenbytheretrieval.ParentGroup:L2s/RetrievalResults/diverging_steps

• eof3_3_relRelativeamplitudeofthe3rdEOFinthestrongCO2band.ParentGroup:(L2s/RetrievalResults/eof_3_scale_strong_co2)/(L2s/SpectralParameters/signal_strong_co2_fph)*1.7e19*100

• SigmaBThecoefficientsbywhichtomultiplypsurftodeterminethepressureateachverticallevelintheprofile.Notethisisasinglelistofnumbers,ratherthanrepeatedforeachsounding(asalltheotherquantitiesare).

4. SoundingGroup

Containsallthegeolocationandtimeinformationforeachsounding.ForGOSAT,thesecontainthecorrectedgeolocationinformation.

• altitudeThemeansurfaceelevationinthetargetfieldofview,inmeters.

ParentField:L2s/RetrievalGeometry/retrieval_altitude

• altitude_stddevThestandarddeviationofthesurfaceelevationinthetargetfieldofview,inmeters.ParentField:L2s/RetrievalGeometry/retrieval_surface_roughness

• orbitistheorbitnumberwithinthecurrentrepeatcycle.

ParentField:L2s/Metadata/StartOrbitNumber

• pathTheWRSpathnumberofthecurrentorbit.1-233.ParentField:L2s/Metadata/StartPathNumber

• footprintThefootprintnumberofeachsounding(1-8).ParentField:L2s/RetrievalHeader/sounding_index

• land_water_indicatordeterminesthelandsurfacepropertiesatthefieldof

view.0:land;1:water;2:inlandwater;3:mixed.ParentField:L2s/RetrievalGeometry/retrieval_land_water_indicator


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• land_fractionThefractionoflandcontainedinthefield-of-viewforeach

sounding.ParentField:L2s/RetrievalGeometry/retrieval_land_fraction.

• l1b_typegivestheversionnumberoftheinputlevel-1Bdata.(e.g.“5000”,

whichmeansB5.0.00)ParentField:Derivedfromparentfilename.

• operation_modeNadir(0),Glint(1),Target(2),orTransition(3).ParentField:DerivedfromMetadata/OperationMode

• solar_azimuth_angleThesolarazimuthangle(indegrees)atthetarget,

measuredeastofnorthfromthepointofviewofanobserveronthegroundatthetarget.ParentField:L2s/RetrievalGeometry/retrieval_solar_azimuth

• sensor_azimuth_angleThesatelliteazimuthangle(indegrees)atthetarget,

measuredeastofnorthfromthepointofviewofanobserveronthegroundatthetarget.ParentField:L2s/RetrievalGeometry/retrieval_sensor_azimuth

• glint_angleTheangle(indegrees)betweenthelocaldirectiontothesensor,andthedirectionforpureglintobservation(i.e.,theoutgoingdirectionfromthesurfaceforspecularlyreflectedsolarrays).

• airmassTherelativeairmassofthesounding,definedas1/cos(solar_zenith_angle)+1/cos(sensor_zenith_angle).

• snr_o2aTheestimatedsignal-to-noiseratiointhecontinuumoftheO2A-

band.ParentField:L2s/L1bScSpectralParameters/snr_o2_l1b

• snr_wco2Theestimatedsignal-to-noiseratiointhecontinuumoftheweak

CO2band.ParentField:L2s/L1bScSpectralParameters/snr_weak_co2_l1b

• snr_sco2Theestimatedsignal-to-noiseratiointhecontinuumofthestrongCO2band.ParentField:L2s/L1bScSpectralParameters/snr_strong_co2_l1b


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FeedbackPleaseprovidefeedbackandcommentstousatoco2_feedback@list.jpl.nasa.gov.Youcanreceiveupdatesandnewsbysubscribingtoourlist.Emailablankmessagetosympa@list.jpl.nasa.govwiththesubject:subscribeoco2_updates.

ReferencesGuerlet,S.,etal:ImpactofaerosolandthincirrusonretrievingandvalidatingXCO2fromGOSATshortwaveinfraredmeasurements,J.Geophys.Res.Atmos.,118,4887–4905,doi:10.1002/jgrd.50332,2013Mandrake,L.,Frankenberg,C.,O'Dell,C.W.,Osterman,G.,Wennberg,P.,andWunch,D.:Semi-autonomoussoundingselectionforOCO-2,Atmos.Meas.Tech.,6,2851-2864,doi:10.5194/amt-6-2851-2013,2013.Wunch,D.,etal:AmethodforevaluatingbiasinglobalmeasurementsofCO2totalcolumnsfromspace,Atmos.Chem.Phys.,11,12317-12337,doi:10.5194/acp-11-12317-2011,2011