OMPSNadirMapperLevel2Description

1.PurposeandScope

ThepurposeofthisdocumentistoprovideanoverviewoftheOMPS-NPPNadirMapperLevel2dataproductformatforitsusers.TheNMTO3-L2APPretrievestotalcolumnozonefrommeasurednormalizedradiancescontainedwiththeL1Bfile.

2.NadirMapper

TheOMPSnadirinstrumentiscomposedoftwospectrometersthatsharethesametelescope.AdichroicfilterdownstreamofthetelescoperedirectsphotonsintoeithertheNMortheNadirProfiler(NP)spectrometer.Thetelescopeitselfhasa110°totalacross-trackfieldofview(FOV),resultingin2800kminstantaneouscoverageattheEarth’ssurface;thisissufficienttoprovidedailyfullglobalcoverageattheequatorfortheNMsensor.Thetelescopeincludesapseudodepolarizer[McClainetal.,1992]designedtominimizethesystem’ssensitivitytoincomingpolarization.Thedichroicfilterisoptimizedtoreflectmostofthe250–310nmlighttotheNPspectrometerandtransmitmostofthe300–380nmlighttotheNMspectrometer.Oncesplit,thelightfromtheNMspectrometerisdispersedviaadiffractiongratingontoonedimensionofatwodimensionalcharge-coupleddevice(CCD)locatedatthespectrometer’sfocalplane.Theseconddimensionreflectsthecross-trackspatialcoverageprovidedbytheslitapertureandoptics.TheCCDconsistsof340pixelsalongthespectraldimensionand740pixelsintheacross-trackspatialdimension.Measurementsmeetingthe300–380nmwavelengthrangespecificationrequiredbytheNMsensorareobtainedbyilluminating196ofthe340pixelsinthespectraldimension.Intheacross-trackdimension,708pixelsareilluminated.Fornominaloperations,thepixelsignalsaresummedinto35separate“macropixel”FOVs;allbutthetwoouterFOVscontain20pixelspermacropixel;theleftoutermostmacropixelcontains26pixels,whiletherightoutermostcontains22.SincethereadoutoftheCCDissplitinthecenter,measurementscomprisingthecentralFOVareactuallysplit(althoughnotsymmetrically).Ratherthanrebinningthesemeasurementsingroundprocessing,theyremainsplit,resultingin36cross-trackFOVs.Inthiscase,thecentraltwoFOVscomprise12pixels(30×50km)and8pixels(20×50km),respectively.Becausemacropixelsareconstructedinprogrammableflightelectronics,theOMPSnadirtemporal(along-track)andspatial(across-track)resolutionsarehighlyconfigurable.High-resolutionmeasurements,approximately10km×10kmatnadir,havebeenroutinelycollected

1dayperweekforthefirst2yearsofthemission.Toremainwithinthetelemetrybandwidthconstraints,asetofonly59wavelengthswasselected;thisselectionstillallowsretrievalsoftotalcolumnozoneandotherquantities(suchasSO2).3.0AlgorithmBackground

ThebasicalgorithmusedfortheV2.1datasetisNASA’sV8.5totalcolumnretrievalalgorithm,whichuses2wavelengths(317.5and331.2nmundermostconditions,and331.2and360nmforhighozoneandhighsolarzenithangleconditions).Thelongerofthetwowavelengthsisusedtoderiveeffectivecloudfraction(fc)basedontheMixedLambertEquivalentReflectivity(MLER)model[Ahmadetal.2004]thatwasdevelopedtomodeltheeffectofcloudsonRayleighscattering.Whenfcbecomeslessthanzeroorwhenthereissnow/ice,weassumethatnocloudispresentandusetheLambertEquivalentReflectivity(LER)modeldescribedbyAhmadetal.[2004]toderivetheclearscenereflectivityR.Whenfcexceeds1,weassume100percentcloudcoverandderivedcloudreflectivityusingtheLERmodel.Giventhefc/R,theshorter(strongerozone-absorbing)wavelengthisusedtoderivetotalozone.

AnimportantdifferencebetweentheV8.5algorithmandpreviousversions,aswellwiththearchivedTOMSdataset,istheassignmentofeffectivecloudheight.Ithasbeenassumedinthepreviousalgorithmsthattheabsorptionofbackscatteredsolarradiationessentiallystopsatthecloud-toplevelwhenthecloudsareopticallythick.Toestimatethetotalcolumnamount,the“un-measured”columnbelowthecloud-top(computedusingclimatology)isaddedtothemeasuredcolumn.RecentanalysisoftheOMIdatainconjunctionwithCloudSatradardata[Vasilkovetal.2008]indicatesthatthisassumptionisinvalid.MiescatteringcalculationsusingCloudSatdataindicatethatinallcloudyscenes,includingdeepconvectiveclouds,theUVradiationreceivedatthesatelliteissensitivetotheozonecolumnbelowthenominalcloud-toppressurereportedbythermalinfraredsensorssuchasMODIS.Analysisshowsthatphotonsactuallypenetratesomedistanceintoacloud.InV8.5,weuseaclimatologyoftheOpticalCentroidCloudPressure(OCCP)inferredfromRotational-RamanScattering(OMCLDRR)toderivethetotalozonecolumn.TheclimatologywasdevelopedusingOCCPretrievalsfromtheOzoneMonitoringInstrument(OMI)onboardtheAurasatellite.SincethepressurecorrespondingtoOCCPisusuallysignificantlybelowthecloud-toppressureclimatologyassumedintheV8algorithm,theV8.5derivedcolumnamountshavedecreasedoverclouds.Themagnitudeofthedecreasedependsoncloudfraction,location,andsolarzenithangle.

Theeffectivecloudfraction(fc)derivedfromtheMLERmodelisusedtoestimatetheCloudRadianceFraction(CRF).CRFcharacterizesthefractionofmeasuredradiationthatisscatteredbyclouds.MiescatteringcalculationsindicatethattheclearandcloudyozonecolumnsweightedbyCRFprovidesavalueveryclosetowhatonewouldfromtheplaneparallelMie

cloudmodelwiththeindependentpixelapproximationtoaccountformixedscenes.TheadvantageoftheMLERmodelisthatonedoesn’tneedindependentknowledgeofgeometricalcloudfractiontocalculatetheozonecolumnaccuratelyincloudyscenes.

ThealgorithmalsocalculatestheabsorbingAerosolIndex(AI)fromtheradianceresidualsat360nm.TheAIisusefulfortrackingglobaltransportofsmokeanddust,foritcantracktheseaerosolsaboveandthroughclouds,aswellasoversnow/icecoveredsurfaces.VariousstudieshaveindicatedthatAIisverynearlyproportionaltotheaerosolabsorptionopticaldepthat360nm.However,theproportionalityconstantvarieswiththealtitude(ofthecenterofmass)oftheaerosollayer-thelowerthealtitudethesmallertheconstant.MostaerosolshavestrongerabsorptionintheUVthaninthevisible,includingmineraldustfromdesertsandcarbonaceousaerosolscontainingorganicandblackcarbon.SincetheAIisalsoaffectedbythespectraldependenceofsurfacealbedocausedbysea-glintandwater–leavingradiance,andsincethereareresidualerrorsintheMLERmodelinestimatingRayleighscatteringinpresenceofclouds,werecommendthatonlytheAIvalueslargerthan+1shouldbeusedforaerosolstudiesandareascontaminatedbysea-glintshouldbeavoidedcompletely.Sinceabsorbingaerosolscausetheozonederivedfromthebasicozoneretrievalalgorithmtobeoverestimated,aparametricrelationshipbasedonAIisusedtocorrecttheinitialretrievedozonecolumn.Thisrelationshipalsoappearstoremovealargeportionoferrorscausedbysea-glint.

Otherthanthethreeprimarywavelengthsmentionedabove,theOMTO3algorithmusesadditionalwavelengthsforqualitycontrolanderrorcorrectioninmorerestrictedgeophysicalsituations.Theseincludecorrectionforozoneprofileshapeerrorsatlargesolarzenithanglesusing312.6nmmeasurements,andthedetectionofstrongsulfur-dioxidecontaminationusingmultiplewavelengthpairs.ForamoredetaileddescriptionofthealgorithmpleaserefertotheAlgorithmTheoreticalBasisDocument(ATBD)on

http://eospso.gsfc.nasa.gov/eos_homepage/for_scientists/atbd/viewInstrument.php?instrument=13.

NotethatV2.1willbethelastversiontousethisalgorithm;thenextreleaseofNMTO3-L2willutilizeanew,improvedretrievalalgorithmbasedontheRogersOptimalEstimationmethod.ThenewalgorithmwasrecentlyusedtoreprocesstheOMIdatasetaswellasdatasetsfromtheNimbus-7TotalOzoneMappingSpectrometer(TOMS)andtheEarth-ProbeTOMSinstruments.

4.What’sNew?

V2.0isthefirstversionofthedatasetreleasedthroughtheGESDISC.ThepreviousV1.0datasetwasavailablethroughNASA’sOMPSscienceteam’swebsite:

https://ozoneaq.gsfc.nasa.gov/omps

ChangesfromV1.0toV2.0include:

Nonsciencerelatedchanges

NomenclatureandNamingConvention

1) ThenamingconventionfortheL1BdatasethasbeenchangedfromTC_SDR_EV_NASAtoNMEV-L1B:

a. TC(TotalColumn)hasbeenreplacedbyNM(NadirMapper).b. NOAAnomenclature(SDR)hasbeenreplacedbyNASAnomenclature(L1B).

2) Allcapitalizationofnameswithinthefilehasbeenreplacedbycamelcasing.3) Underlinesinallnameshavebeeneliminated.

Sciencerelatedchanges

1) TheV2.1datasetusesV2.0ofNMEV-L1Basinput.TheV2.0L1Bprovidesimprovedradiancecalibration.

2) SurfaceCategoryhasbeenaddedtotheAncillaryDatagroup.ItisbasedontheInternationalGeosphere–BiosphereProgramme(IGBP)surfaceclassification.

3) GroundPixelQualityFlagsandInstrumentQualityFlagshavebeenaddedtotheGeolocationGroup

4) ATrendingDatagrouphasbeenaddeda) QualityFlagsFrequencyprovidesthepercentfrequencyofoccurrenceforeachofthe

definedAlgorithmQualityFlags

TheV2.0filecontainsswath-basedradiancedataforthedaylitpartofoneorbit.Therearetypically36cross-trackmeasurementsperswathand400swatchbasedobservationsperorbit.

5.FileNamingConvention

TheOMPSNadirMapperdataproductsusethefollowingfilenameconvention:OMPS-satellite_sensorproduct-Llevel_vm.n_observationDate_productionTime.h5

Where:

• satellite=NPP• sensorproduct=NMTO3• level=2• m.n=algorithmversionidentifier(m=major,n=minor)• observationDate=startdateofmeasurementsinyyyymmddformat

o yyyy=4-digityearnumber[2012-current]o mm=2-digitmonthnumber[01-12]o dd=2-digitdaynumber[01-31]

• productionTime=filecreationstampinyyyymmmddthhmmssformat

o hhmmss=productiontime[localtime]

Filenameexample:

OMPS-NPP_NMTO3-L2_v2.1_2012m0403t103340_o02243_2017m0223t154258.h56.FileFormatandStructure

NMTO3-L2datafilesareprovidedintheHDF5format(HierarchicalDataFormatVersion5),developedattheNationalCenterforSupercomputingApplicationshttps://www.hdfgroup.org/.ThesefilesusetheSwathdatastructureformat.Thetop-mostlevelintheHDF5hierarchyofNMTO3-L2filescontainsthreedifferentdirectories,oneforeachtypeofpixel-dependentdata:CalibrationData(containingdatausedtocreatecalibratedradiances),GeolocationData(containingdatatogeolocateeachpixel,aswellasspacecraftlocationandpointinginformation),andScienceData(containingthecalibratedradiances,qualityflags,anderrorterms).Thesethreegroupsaredescribedinmoredetailinthenextsection.7.DataContents

The data fields most likely to be used by typical users of the NMEV-L1B product are listedbelow.

Parameter Group Date GeolocationFieldsLatitude GeolocationFieldsLongitude GeolocationFieldsBandCenterWavelengths CalibrationDataSolarFlux CalibrationDataSolarFluxWavelengths CalibrationDataColumnAmountO3 ScienceDataUVAerosolIndex ScienceDataReflectivity331 ScienceData

The first OMPS NMEVmeasurements used to create the NMEV-L1B product were taken onJanuary 28, 2012. Data for February-March 2012 have numerous gaps due to variations ininstrument. Regular operationsbeganonApril 2, 2012. Note that theOMPSNadirMapperconductedhigh-resolutionmeasurementsapproximatelyonedayperweekfromApril2012toJune2016.

NMTO3-L2includesthefollowingdimensionterms:Name long_name Value

DimAlongTrack Along-trackdimension 400DimCrossTrack Across-trackdimension 36DimWavelength 12DimCorners 4DimPressureLevel 11 Metadata inNMEV-L1Bdata files includesattributeswhosevalue is constant forall filesandattributeswhosevalue isunique toeach individual file. Table3.2.1summarizes theseglobalattributes.

GlobalAttribute Type DescriptionAPPName String SoftwarenameAPPVersion String SoftwareversionArchiveSetName String ArchivesetnameforprocessingArchiveSetNumber Integer*8 ArchivesetnumberforprocessingConventions String Nameofconvention(s)formetadataDATA_QUALITY Integer QualityofthedataDOI String DOIvalueDayNightFlag String IdentifydayornightmeasurementsEquatorCrossingDate String DateofequatorcrossingEquatorCrossingLongitude Real*4 LongitudeofequatorcrossingEquatorCorssingTime String TimeofequatorcrossingFormat String DatafileformatLocalGranuleID String FilenameLongName String FullproductnameOrbitNumber Integer*8 FirstorbitnumberofdayPGEVersion String Softwareversion(sameasAPPVersion)ProductDateTime String TimeoffilecreationRangeBeginningDateTime String StartingdateandtimeofdataRangeEndingDateTime String EndingdateandtimeofdataSAMP_TBL Integer NumberofsampletableusedtotakedataSAMP_TBL_VER Integer VersionofthesampletableusedtotakedataShortName String ShortproductnameVersionID Integer*4 VersionIDforthisproductVersionNumber String Versionnumberforthisproductacknowledgement String Acknowledgementofdataproducercomment String Anyadditionalcommentscontributor_name String Nameofdatacreatorcontributor_role String Roleofdatacreatorcreator_email String e-mailaddressofdatacreatorcreator_institution String Organizationofdatacreatorcreator_name String Nameofdatacreatorcreator_type String Typeofdatacreator(e.g.person,organization)date_created String Dateoffilecreationhistory String Historyoffile

id String Shortproductnameinstitution String Producerofdatainstrument String Instrumentmakingmeasurementsinstrument_vocabulary String Sourceofinstrumenttermskeywords String Identifyingkeywordskeywords_vocabulary String Sourceofkeywordsusedinmetadatalicense String Sourceofdatainformationregulationsmetadatalink String WebaddressformetadataDOInaming_authority String Organizationprovidingnaminginformationplatform String Platformformeasuringinstrumentprocessing_level String Levelofdataproduct(e.g.L1B,L2)program String Typeofmeasurementprogramproject String Nameofprojectpublisher_email String e-mailaddressofdatapublisherpublisher_institution String Organizationofdatapublisherpublisher_name String Nameofdatapublisherpublisher_type String Organizationtypeofdatapublisherpublisher_url String URLofdatapublisherreferences String Referencematerialfordataproductsource String Sourceofmeasurementdatasummary String Anyadditionalsummarytime_coverage_end String Endingdataandtimeofdatatime_coverage_start String Startingdateandtimeofdatatitle String Titleofdataproduct8.Products/Parameters

CalibrationDataGroupDatasetName Description Dimensions Units

APrioriLayerO3 Aprioriozoneprofile DimAlongTrackDimCrossTrack

DobsonUnits

CloudPressure Opticalcentroidpressure DimAlongTrackDimCrossTrack

SurfaceCategory Surfacecategory DimAlongTrackDimCrossTrack

TerrainPressure Terrainpressure DimAlongTrackDimCrossTrack

Atmospheres

CalibrationDataGroupDatasetName Description Dimensions Units

Wavelength WavelengthsinputfromL1B(note:L1Bwavelengthsinterpolatedtomatchthesevalues)

DimWavelengths nm

GeolocationDataGroupDatasetName Description Dimensions Units

GroundPixelQualityFlags Ground pixel quality flag (bit packed) DimAlongTrackDimCrossTrack Nounits

InstrumentQualityFlags Bit-packederrorflagsforeachpixelDimAlongTrackDimCrossTrack Nounits

Latitude Groundpixellatitude DimAlongTrack,DimCrossTrack

Degrees

LatitudeCorner GroundpixellatitudecornersDimAlongTrack,DimCrossTrack4

Degrees

Longitude Groundpixellongitude DimAlongTrack,DimCrossTrack

Degrees

LongitudeCorner GroundpixellongitudecornersDimAlongTrack,DimCrossTrack4

Degrees

RelativeAzimuthAngle DifferencebetweenviewingandsolarazimuthanglesDimAlongTrack,DimCrossTrack Degrees

SecondsinDayTimewhenswathmeasurementwastaken(innumberofsecondssincebeggingoftheday) DimAlongTrack, Seconds

ViewingAzimuthAngle SatelliteazimuthofeachpixelDimAlongTrack,DimCrossTrack Degrees

ViewingZenithAngle Satellitezenithangleofeachpixel DimAlongTrack,DimCrossTrack

Degrees

SolarAzimuthAngle Solarazimuthofeachpixel DimAlongTrack,DimCrossTrack

Degrees

SolarBetaAngle AnglesbetweenageocentricSunvectoranditsprojectionontheNPPorbitalplane

DimAlongTrack NoUnits

SolarZenithAngle Solarzenithangleofeachpixel DimAlongTrack,DimCrossTrack

Degrees

SpacecraftAltitude Spacecraftaltitude DimAlongTrack MetersSpacecraftLatitude SpacecraftLatitude DimAlongTrack DegreesSpacecraftLongitude SpacecraftLongitude DimAlongTrack DegreesSubSatelliteSolarZenithAngle Solarzenithangleatsubsatellitepoint DimAlongTrack Degrees

Time TAI93timeofmeasurement(numberofsecondssince1January1993)

DimAlongTrack Seconds

UTC_CCDSDS_A Twenty-sevencharacterUTCdate-and-timestring DimAlongTrack NoUnits

GroundPixelQualityFlags SAA,eclipse,Sunglint,terraintypeflags DimAlongTrack,DimCrossTrack NoUnits

Definitionofbit-packedGroundPixelQualityFlags0-3 Unused 4-5 SAAFlag WARNING Indicateslocationofspacecraftw.r.t.SAA

0=outsideSAAboundaries1=<5%ofnominalmaximumSAAeffect2=between5%and40%ofnominalmaximumSAAeffect3=>40%ofnominalmaximumSAAeffect

6-19 Unused 20 ManeuverFlag WARNING Indicatesaspacecraftattitudemaneuverwasinprogressduringthe

measurement21 AttitudeThresholdFlag WARNING Indicatesanyofthe3geodeticspacecraftattitudeEulerangles

exceedsadefinedthreshold22-31 Unused

DefinitionofInstrumentQualityFlags0-7 Unused 8 EclipseFlag WARNING Indicatesgroundpixeliswithinumbraorpenumbraofthemoon9-15 Unused

ScienceDataGroupDatasetName Description Dimensions Units

AlgorithmFlags DimAlongTrack,DimCrossTrack Nounits

ColumnAmountO3 FinalTotalcolumnozoneamountsDimAlongTrack,DimCrossTrack DobsonUnits

Layerefficiency DimAlongTrack,DimCrossTrack Nounits

MeasurementQualityFlags DimAlongTrack,DimCrossTrack

Nounits

NValue Nvalue[-100*log10(normalizedradiance)] DimAlongTrack,DimCrossTrack

Nounits

NValueAdjustment SoftcalibrationappliedtoNvalues DimAlongTrack,DimCrossTrack

Nounits

O3BelowCLoud Estimateofozoneamountbelowcloud DimAlongTrack,DimCrossTrack

DobsonUnits

QualityFlags DimAlongTrack,DimCrossTrack NoUnits

RadiativeCloudFraction DimAlongTrack, DimCrossTrack

Fractionbetween0and1

Reflectivity331 331nmreflectivity DimAlongTrack, DimCrossTrack Fraction

Reflectivity360 360nmreflectivity DimAlongTrack, DimCrossTrack Fraction

SO2index EstimateofSO2contamination DimAlongTrack, DimCrossTrack DobsonUnits

Sensitivity SensitivityofNvaluetochangeinozone DimAlongTrack, DimCrossTrack

1/DobsonUnits

StepOneO3 Estimateoftotalozonefromstep1ofalgorithm

DimAlongTrack, DimCrossTrack DobsonUnits

StepTwoO3 Estimateoftotalooznefromstep2ofalgorithm

DimAlongTrack, DimCrossTrack DobsonUnits

UVAerosolIndex AerosolIndex DimAlongTrack, DimCrossTrack Nounits

dN_dR SensitivityofNvaluetochangeinreflectivity DimAlongTrack, DimCrossTrack

dN_dT SensitivityofNvaluetochangeintemperature

DimAlongTrack, DimCrossTrack 1/Degrees

Fc Radcl radgr 9.References

PawanK.BhartiaandCharlesW.Wellemeyer,OMIAlgorithmTheoreticalBasisDocument,VolumeII,Chapter2,https://eospso.nasa.gov/atbd-category/49.

Kramarova,N.,E.Nash,P.Newman,P.K.Bhartia,R.McPeters,D.Rault,C.Seftor,P.Q.Xu,andG.Labow(2013),MeasuringtheAntarcticozoneholewiththenewOzoneMappingandProfilerSuite(OMPS),Atmos.Chem.Phys.,14,2353-2361,doi:10.5194/acp-14-2353-2014,2014.