NASA SNPP Cross Track Infrared Sounder (CrIS) … · (CrIS) Level 1B Delta Algorithm Theoretical Basis Document (ATBD) University of Wisconsin-Madison Space Science and Engineering

NASASNPPCrossTrackInfraredSounder(CrIS)Level1BDeltaAlgorithmTheoreticalBasisDocument(ATBD)UniversityofWisconsin-MadisonSpaceScienceandEngineeringCenter

UniversityofMarylandBaltimoreCountyAtmosphericSpectroscopyLaboratoryVersion1.0 May2017

This research was conducted with funding provided by the National Aeronautics and SpaceAdministration.

NASA SNPP Cross Track Infrared Sounder Level 1B Delta ATBD

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CrISL1BScienceandSoftwareTeam HankRevercomb–PI UW-MadisonLarrabeeStrow–PI UMBCJessicaBraun UW-MadisonRayGarcia UW-MadisonLiamGumley UW-MadisonRobertKnuteson UW-MadisonEliKrenzke UW-MadisonGraemeMartin UW-MadisonHowardMotteler UMBCCodaPhillips UW-MadisonGregQuinn UW-MadisonJoeTaylor UW-MadisonDaveTobin UW-Madison


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Revisions:Draft 24November2015 CreationofinitialdraftdocumentVersion1.0Beta2 05February2016 ReleaseconsistentwithBeta2softwareVersion1.0Beta3 15March2016 ReleaseconsistentwithBeta3softwareVersion1.0 01May2017 Releaseconsistentwith1.0software


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ContactsReadersseekingadditionalinformationaboutthisstudymaycontactthefollowingresearchers:[email protected]


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AbstractThis document describes the theoretical basis of the NASA CrIS Level 1B (L1B) algorithmsoftware and resulting product. Because the theoretical basis is very similar to that of theoperational Joint Polar Satellite System (JPSS) Sensor Data Record (SDR) algorithm, it wasdecidedtoimplementthisdocumentasa"delta"ATBDdescribingthedifferencesbetweenthetwo approaches, rather than implementing a full ATBDwith duplicate information. Thus thisdelta ATBD togetherwith the CrIS SDRATBD form a complete description of the theoreticalbasisoftheNASACrISL1Bsoftware.


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TableofContentsContacts..................................................................................................................................................................................4

Abstract...................................................................................................................................................................................5

ListofFigures....................................................................................................................................................................12

ListofTables.....................................................................................................................................................................13

Introduction.......................................................................................................................................................................14

1.1 PurposeofDocument....................................................................................................................................14

1.2 Scope....................................................................................................................................................................14

1.3 DocumentOverview......................................................................................................................................14

1.4 ReferenceDocuments...................................................................................................................................14

1.5 Acronyms...........................................................................................................................................................15

1.6 NotationsandSymbols.................................................................................................................................16

2 SDRALGORITHMSPRINCIPLES........................................................................................................................17

2.1 ObjectiveoftheSDRAlgorithms..............................................................................................................17

2.2 SpaceSegmentSignalProcessing............................................................................................................17

2.2.1 SpikesDetection/Correction............................................................................................................17

2.2.2 FilteringandDecimation....................................................................................................................17

2.2.3 BitTrimming...........................................................................................................................................20

2.2.4 PacketEncoding.....................................................................................................................................20

2.3 GroundSegmentProcessing......................................................................................................................20

2.4 InterferometerModel...................................................................................................................................20

2.4.1 InstrumentPhase..................................................................................................................................20

2.4.2 OtherSignalContributors..................................................................................................................20

2.4.3 InstrumentLineShape........................................................................................................................20

2.4.4 OtherTypesofErrors..........................................................................................................................20

2.4.5 InterferometerModelingEquations.............................................................................................20

2.5 CrISCharacteristics........................................................................................................................................20

2.5.1 Double-SidedInterferogramMeasurements.............................................................................21


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2.5.2 CrISSpectralBands..............................................................................................................................21

2.5.3 CrISFieldofRegard..............................................................................................................................21

2.5.4 CrISMeasurementSequence............................................................................................................21

2.5.5 CrISSignalProcessing.........................................................................................................................21

2.6 SignalRepresentation...................................................................................................................................21

2.6.1 ArrayDimensions..................................................................................................................................21

2.6.2 DataOrdering..........................................................................................................................................21

3 SPECIALCONSIDERATIONS...............................................................................................................................22

3.1 Non-linearityCorrection.............................................................................................................................22

3.2 ScanMirrorPolarizationCompensation..............................................................................................22

3.3 FringeCountErrorHandling.....................................................................................................................22

3.3.1 PhaseAnalysis........................................................................................................................................22

3.3.2 SpectrumBasedDetectionandCorrection................................................................................22

3.3.3 FCEDetection..........................................................................................................................................22

3.3.4 FCECorrection........................................................................................................................................22

3.4 LunarIntrusionHandling............................................................................................................................22

3.4.1 LunarIntrusionDetection..................................................................................................................23

3.4.2 LunarIntrusionProcessing...............................................................................................................25

3.5 AlignmentofDatatoaCommonSpectralGrid..................................................................................25

3.6 ILSCorrection...................................................................................................................................................26

3.6.1 Introduction.............................................................................................................................................26

3.6.2 CrISOff-AxisSelfApodization..........................................................................................................26

3.6.3 Self-ApodizationRemoval.................................................................................................................26

3.6.4 ResidualTerm.........................................................................................................................................27

3.6.5 GuardBandDamping...........................................................................................................................27

3.6.6 ILSRetrieval.............................................................................................................................................29

3.7 SignalApodization..........................................................................................................................................29

3.7.1 UnapodizedChannelResponseFunction....................................................................................29

3.7.2 Hamming'sFilterFunction................................................................................................................29


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3.7.3 Blackman-Harris’sApodizationFunction...................................................................................30

3.8 CMOUpdates....................................................................................................................................................30

4 SPECTRALCALIBRATION....................................................................................................................................31

4.1 Neon-lampasaSpectralReference........................................................................................................31

4.1.1 WavelengthCalculation......................................................................................................................31

4.1.2 CalculationofLaserMetrologyWavelength..............................................................................31

4.1.3 RejectingBadNeonCountMeasurements(QualityControl).............................................31

4.2 MetrologyWavelengthMonitoring.........................................................................................................31

5 RADIOMETRICCALIBRATION...........................................................................................................................32

5.1 BasicRadiometricRelations......................................................................................................................32

5.2 GeneralCalibrationEquation....................................................................................................................32

5.3 CrISSpecificCalibrationEquation...........................................................................................................32

5.4 ICTRadiometricModel.................................................................................................................................33

5.4.1 RadiometricError.................................................................................................................................34

5.4.2 RadiometricModelFormulation....................................................................................................34

5.5 ICTTemperatureComputation.................................................................................................................34

5.6 SignalCoaddition............................................................................................................................................34

5.6.1 MovingAverage......................................................................................................................................34

5.6.2 ImpactofTemperatureDrift............................................................................................................34

5.6.3 ThroughputDelay.................................................................................................................................34

6 GEOMETRICCALIBRATION................................................................................................................................35

6.1 CoordinateSystems.......................................................................................................................................35

6.1.1 CoordinateSystemDefinition..........................................................................................................35

6.1.2 InterferometerOpticalAxisReference(IOAR).........................................................................35

6.1.3 RotatingMirrorFrame(RMF).........................................................................................................35

6.1.4 SceneSelectionMirrorMountingFeetFrame(SSMF)..........................................................35

6.1.5 SceneSelectionModuleReference(SSMR)................................................................................35

6.1.6 InstrumentAlignmentReference(IAR).......................................................................................35

6.1.7 SpacecraftBodyFrame(SBF)..........................................................................................................36


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6.1.8 OrbitalCoordinateSystem(OCS)...................................................................................................36

6.1.9 EarthCenteredInertial(ECI)...........................................................................................................36

6.1.10 EarthCenteredEarthFixed(ECEF)orEarthCenteredRotating(ECR).....................36

6.1.11 WorldGeodeticSystem1984(WGS84)....................................................................................36

6.1.12 Topocentric-HorizonCoordinateSystem(THCS)................................................................36

6.2 CoordinateSystemTransformations.....................................................................................................36

6.3 AlgorithmPartitioning.................................................................................................................................36

6.4 SensorSpecificAlgorithm...........................................................................................................................36

6.4.1 CrISFOVLOSinSSMFCoordinateSystem.................................................................................36

6.4.2 SSMFtoSBFTransformationOperator.......................................................................................36

6.4.3 CrISFOVLOSinSBFCoordinateSystem.....................................................................................37

6.5 SpacecraftLevelAlgorithm........................................................................................................................37

6.6 TimingConventions.......................................................................................................................................37

7 MODULESDEFINITION.........................................................................................................................................38

7.1 Initialization......................................................................................................................................................41

7.2 InputDataHandling......................................................................................................................................42

7.3 Preprocessing...................................................................................................................................................42

7.3.1 InterferogramtoSpectrumTransformation.............................................................................42

7.3.2 MovingAverageHandling..................................................................................................................43

7.4 SpectralCalibration.......................................................................................................................................43

7.4.1 LaserWavelengthCalibrationfromNeonLampData...........................................................43

7.4.2 LaserWavelengthDriftMonitoring...............................................................................................45

7.4.3 SpectralAxisLabelingandAliasUnfolding................................................................................45

7.5 RadiometricCalibration...............................................................................................................................47

7.5.1 RadiometricComplexCalibration..................................................................................................50

7.5.2 ICTRadianceCalculation...................................................................................................................50

7.5.3 SpectrumCorrection............................................................................................................................50

7.5.4 Non-linearityCorrection....................................................................................................................51

7.6 QualityControl.................................................................................................................................................51


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7.6.1 NEdNEstimation...................................................................................................................................51

7.6.2 FringeCountErrorHandling............................................................................................................53

7.6.3 FringeCountErrorDetection...........................................................................................................53

7.6.4 FringeCountErrorCorrection........................................................................................................53

7.6.5 DataQualityIndicators.......................................................................................................................53

7.7 Post-Processing...............................................................................................................................................53

7.7.1 UserRequiredSpectralBinsSelection.........................................................................................53

7.7.2 SDRDataFormatting...........................................................................................................................53

7.8 OutputDataHandling...................................................................................................................................53

8 CONCLUSION.............................................................................................................................................................54

9 APPENDICES..............................................................................................................................................................55

9.1 FastFourierTransforms..............................................................................................................................55

9.1.1 CommentsonVariousAlgorithms.................................................................................................55

9.1.2 DataTranslationandCentering......................................................................................................55

9.1.3 PrimeFactorAlgorithmFastFourierTransform....................................................................55

9.2 AliasUnfolding.................................................................................................................................................55

9.3 LinearFitting....................................................................................................................................................55

9.3.1 ImplementationoftheLinearInterpolation.............................................................................55

9.4 NumericalIntegration..................................................................................................................................55

9.5 DeterminationoftheGoodnessofFit....................................................................................................55

9.6 Definitions..........................................................................................................................................................56

9.6.1 SensorCalibration.................................................................................................................................56

9.6.2 RawDataRecord(RDR).....................................................................................................................56

9.6.3 SensorDataRecord(SDR).................................................................................................................56

9.6.4 EnvironmentalDataRecord(EDR)................................................................................................56

9.6.5 DataProductLevels..............................................................................................................................56

9.6.6 MeasuredData........................................................................................................................................56

9.6.7 AuxiliaryData..........................................................................................................................................56

9.6.8 AncillaryData..........................................................................................................................................56


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9.6.9 OtherInstrumentSpecificTermsandDefinitions..................................................................56


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ListofFiguresFigure 2.2.2-1 Complex FIR filters used for Suomi NPP CrIS sensor to suppress out of band

signalandnoiseforeachofthelongwave,midwave,andshortwavebands..............................18

Figure2.2.2-2CrISlongwavebandundecimatedsignal(DM)overlaidwithFFTofcorrespondingFIRfilter(FIR).Eachcurveisnormalizedtounity.................................................................................18

Figure2.2.2-3CrISmidwavebandundecimatedsignal(DM)overlaidwithFFTofcorrespondingFIRfilter(FIR).Eachcurveisnormalizedtounity.................................................................................19

Figure 2.2.2-4 CrIS shortwave band undecimated signal (DM) overlaid with FFT ofcorrespondingFIRfilter(FIR).Eachcurveisnormalizedtounity..................................................19

Figure3.6.5-1CalibrationfilterforLWband......................................................................................................28

Figure3.6.5-2CalibrationfilterforMWband....................................................................................................28

Figure3.6.5-3CalibrationfilterforSWband......................................................................................................29

Figure7-1Conventionsusedintheflowchartsincludedinthissection................................................39

Figure7-2:Generalflowdiagramfortheradiometricandspectralcalibration................................40

Figure7.4.1-1Metrologylaserwavelengthcalibrationflowchart(replacesFigure63inCrISSDRATBD).........................................................................................................................................................................44

Figure7.4.3-1SpectralAxisLabelingandAliasUnfoldingFlowchart.....................................................46

Figure7.5-1RadiometricCalibrationFlowchart...............................................................................................48

Figure7.6.1-1NEdNEstimationFlowchart.........................................................................................................51


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ListofTablesTable3.4.1-1Lowerandupperchannellimitsfortheaveragesoverspectralchannelusedinthe

lunarintrusiondetectionalgorithm..............................................................................................................24

Table3.4.1-2Thresholdvaluesusedforlunardetection..............................................................................25

Table3.6.5-1Parametersforthecalibrationfilter. .......................................................................................27

Table7.1-1ParametersdefinedinL1Bprocessingpackage........................................................................41


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Introduction

1.1 PurposeofDocument This document describes the theoretical basis of the NASA CrIS Level 1B (L1B) algorithmsoftwareandresultingproduct.

1.2 Scope Thescopeofthisdocumentis:

• Version1.0RC8oftheNASACrISL1Bsoftware,and• Version1.0oftheNASACrISL1Bproduct

The software was developed by the CrIS L1B Science and Software Team, located at theUniversity ofWisconsin-MadisonSpace Science andEngineeringCenter and theUniversity ofMarylandBaltimoreCountyAtmosphericSpectroscopyLaboratory.The productwas generated by the SNPP Sounder Science Investigator-led Processing System(SIPS), locatedat theNASA JetPropulsionLaboratory (JPL)andGoddardEarthSciencesDataInformationServicesCenter(GESDISC).

1.3 DocumentOverview Because the theoretical basis is very similar to that of the operational Joint Polar SatelliteSystem(JPSS)SensorDataRecord(SDR)algorithm,itwasdecidedtoimplementthisdocumentas a "delta" ATBD describing the differences between the two approaches, rather thanimplementinga fullATBDwithduplicate information.ThusthisdeltaATBDtogetherwiththeCrIS SDR ATBD forms a complete description of the theoretical basis of the NASA CrIS L1Bsoftware.TheCrISSDRATBDthatisacompaniontothisdocumentwasreleasedDecember23,2014bytheJPSSGroundProject,andiscalled“JointPolarSatelliteSystem(JPSS)CrossTrackInfraredSounder(CrIS)SensorDataRecords(SDR)AlgorithmTheoreticalBasisDocument(ATBD),RevC,Code474,474-00032”.The layoutof thisdocumentcorresponds to the layoutof theCrISSDRATBD.Eachsectionofthis document describes the changes relative to the corresponding section in the CrIS SDRATBD,orthewords“Nochange”indicatingtherearenochangestobeapplied.

1.4 ReferenceDocuments ThefollowingreferencesareaddedtothereferencesintheCrISSDRATBD.

1. Joint Polar Satellite System (JPSS) Cross Track Infrared Sounder (CrIS) Sensor DataRecords (SDR) AlgorithmTheoretical Basis Document (ATBD), Rev C, Code 474, 474-00032


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2. Joint Polar Satellite System (JPSS) Visible Infrared Imaging Radiometer Suite (VIIRS)SensorDataRecord(SDR)GeolocationAlgorithmTheoreticalBasisDocument(ATBD),E/RA-00004,Rev.A

3. Interface Control Document between Earth Observing System (EOS) Data and

Operations System (EDOS) and Science Investigator-led Processing Systems for theSuomi National Polar-Orbiting Partnership (SNPP) Science Data Segment (SDS), 423-ICD-010,Original,EarthScienceDataInformationSystems(ESDIS),Code423

4. NASASNPPCrossTrackInfraredSounder(CrIS)Level1BProductUsers’Guide,Version

1.0

5. NASA SNPP Cross Track Infrared Sounder (CrIS) Level 1B Quality Flags DescriptionDocument,Version1.0

6. CrISL1BSoftwareUsers’Guide,Version1.0

1.5 Acronyms In addition to the acronyms defined in the CrIS SDRATBD, the following acronyms are usedthroughoutthisdocument.

EDOS EOSDataandOperationsSystem

EOS EarthObservingSystem

FIFO FirstInFirstOut

FSR FullSpectralResolution

GESDISC GoddardEarthSciencesDataandInformationServicesCenter

JPL JetPropulsionLaboratory

L1A Level1A

L1B Level1B

L2 Level2

LW Long-waveInfrared

MW Mid-waveInfrared

NSR NormalSpectralResolution

SIPS ScienceInvestigator-ledProcessingSystem

SW Short-waveInfrared

XSR ExtendedSpectralResolution


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1.6 NotationsandSymbols Notationalchangeshavebeenmadetomakethisdocumentself-consistent.Themeaningsofthesymbolsaredefinedwheretheyareused.


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2 SDRALGORITHMSPRINCIPLESTheprimaryinputtotheL1BsoftwareisL0data,whichiscomposedofrawCCSDSpacketsasreceived from the spacecraft, together with added metadata. L0 data is produced anddistributedbyEDOS,andisequivalenttoRDRdataintheoperationalJPSSprocessingsystem.The L1B software generates L1A and L1B product files. The L1A product contains unpackedspacecrafttelemetrydatathathasbeengranulatedandgeolocated,aswellasqualityflagsandmetadata. There is no equivalent to the CrIS L1A product in the current operational JPSSprocessing system. The L1B product contains calibrated spectra, together with geolocationinformation,qualityflags,diagnosticinformationandmetadata.L1BisequivalenttoSDRsinthecurrent operational processing system. The L1B product is used as input to L2 processing(equivalenttoEDRsinthecurrentoperationalprocessingsystem).

2.1 ObjectiveoftheSDRAlgorithms Nochange.

2.2 SpaceSegmentSignalProcessing Nochange.

2.2.1 SpikesDetection/Correction Nochange.

2.2.2 FilteringandDecimation TheseadditionalfiguresillustratetheactualFIRfilterusedintheNPPdataprocessingandthespectraltransformofitcomparedtoatypicalunfilteredsignal.


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Figure2.2.2-1ComplexFIRfiltersusedforSuomiNPPCrISsensortosuppressoutofbandsignalandnoiseforeachofthelongwave,midwave,andshortwavebands.

Figure2.2.2-2CrISlongwavebandundecimatedsignal(DM)overlaidwithFFTofcorrespondingFIRfilter(FIR).Eachcurveisnormalizedtounity.

50 100 150 200 250

×104

-1

0

1

Longwave

real partimaginary part

50 100 150 200 250

×104

-2-1012

Midwave


50 100 150 200 250

×104

-1

0

1

Shortwave


0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2#104

0

0.2

0.4

0.6

0.8

1

J1_LW_CO2GasCell sweep 1 Magnitude Spectra

DMFIR

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2#104

10-4

10-2

100DMFIR


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Figure2.2.2-3CrISmidwavebandundecimatedsignal(DM)overlaidwithFFTofcorrespondingFIRfilter(FIR).Eachcurveisnormalizedtounity.

Figure2.2.2-4CrISshortwavebandundecimatedsignal(DM)overlaidwithFFTofcorrespondingFIRfilter(FIR).Eachcurveisnormalizedtounity.

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2×104

0

0.2

0.4

0.6

0.8

1

J1_MW_CO2GasCell sweep 1 Magnitude Spectra

DMFIR

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2×104

10-4

10-2

100DMFIR

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2×104

0

0.2

0.4

0.6

0.8

1

J1_SW_CO2GasCell sweep 1 Magnitude Spectra

DMFIR

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2×104

10-4

10-2

100DMFIR


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2.2.3 BitTrimming Nochange.

2.2.4 PacketEncoding Nochange.

2.3 GroundSegmentProcessing Nochange.

2.4 InterferometerModel Nochange.

2.4.1 InstrumentPhase Nochange.

2.4.2 OtherSignalContributors Nochange.

2.4.3 InstrumentLineShape Nochange.

2.4.4 OtherTypesofErrors Nochange.

2.4.5 InterferometerModelingEquations Nochange.

2.5 CrISCharacteristics Nochange.


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2.5.1 Double-SidedInterferogramMeasurements Nochange.

2.5.2 CrISSpectralBandsTable2andFigure14correctlystatethespectralsamplingusedintheoriginallowresolutioninstrument data collectionmode. The CrIS signal processor on Suomi-NPP was reconfiguredduring themission to collect at full spectral resolution in the MW and SW bands. After thischange the full spectral resolution data can be produced at a uniform spectral resolution of0.625cm-1(0.8cmMOPD)foralldetectorbands(LW,MW,andSW).TheNASAL1Bsoftwarecurrently truncates the full spectral resolution CrIS data to match the original spectralresolutionshowninTable2.

2.5.3 CrISFieldofRegard Nochange.

2.5.4 CrISMeasurementSequenceNochange.

2.5.5 CrISSignalProcessing Nochange.

2.6 SignalRepresentation Nochange.

2.6.1 ArrayDimensions Nochange.

2.6.2 DataOrderingNochange.


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3 SPECIALCONSIDERATIONS

3.1 Non-linearityCorrection Nochange.

3.2 ScanMirrorPolarizationCompensation Nochange.

3.3 FringeCountErrorHandlingNofringecounterrordetectionorcorrectioniscurrentlyincludedintheNASAL1Bprocessing.The correctionalgorithmdescribed in theATBDwasnot included, as it isnotneeded for theSuomi-NPPCrISdataprocessingsincetherearenofringecounterrors.

3.3.1 PhaseAnalysis NotimplementedinV1.0;nofringecounterrorsdetectedforSNPPCrIS.

3.3.2 SpectrumBasedDetectionandCorrection NotimplementedinV1.0;nofringecounterrorsdetectedforSNPPCrIS.

3.3.3 FCEDetection NotimplementedinV1.0;nofringecounterrorsdetectedforSNPPCrIS.

3.3.4 FCECorrection NotimplementedinV1.0;nofringecounterrorsdetectedforSNPPCrIS.

3.4 LunarIntrusionHandlingNochangetolunarintrusionoverview.


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3.4.1 LunarIntrusionDetection “Onrareinstances,thespacelookmeasurementusedtocalibratetheCrISsensorbackgroundmayencounteraviewofthemoon.Typically, thismayonlyoccurononeortwoFOVssimultaneouslyandpossiblyon2to3successivespacelooksasthespacecraftorbitprogressespasttheviewofthemoon. When this happens, then it is necessary to detect this condition and exclude use of thiscontaminatedspacelookdataintheCrIScalibration.”[CrISSDRATBD].

Lunar intrusiondetection is completedby comparing the uncalibrated spectrum for anynewDeep Space scene versus a reference Deep Spacemean that is ideally free of lunar intrusioneffects.Thisiscompletedindependentlyforall27CrISdetectors(9FOVsin3detectorbands)andinterferometersweepdirection.

Thefollowingstepsaretakentodetectalunarintrusion.DeepSpaceandICTspectrafromthecontextgranulesareincludedintheprocesswhencontextgranuleshavebeenprovidedtotheprocessing. The use of context granules is expected to providemore robust lunar intrusiondetection. 1. Iterative detection of Deep Space spectra outliers with respect to the mean Deep Space

spectra.Completethreeiterationsofthefollowingstepsa-f:a. CalculateDeepSpaceuncalibrated(complex)spectralaverage(inband“b”,FOV“p”,

andsweepdirection“d”,averagedoverscan“k”),withoutliersremoved(nooutliersflaggedforfirstiteration),

b. CalculatetheICTuncalibratedspectralaverage(nooutlierdetection), .

c. Subtract the Deep Space uncalibrated (complex) spectral average with outliersremoved(1.a)fromtheindividualDeepSpaceuncalibrated(complex)spectra:

[3.4.1]

d. Subtract the Deep Space uncalibrated (complex) spectral average with outliersremoved(1.a)fromtheICTuncalibratedspectralaverage(1.b):

[3.4.2]

e. Computethemagnitudeofthecomplexratioof[3.4.1]to[3.4.2],averagedoverthespectralchannels limitedby thespectralchannel indicesprovided inTable3.4.1-1( and define thewavenumber bins corresponding to the lower and upperlimitsofthespectralbandaverage,respectively):

Cb,p,d

ds k[ ] =

!Rb,p,dds n,k[ ]!Rb,p,dict n[ ]n=nmin

nmax

∑nmax − nmin

[3.4.3]

f. Compare[3.4.3]toitsmean.Indexvaluesthatexceeda3-σdeviationfromthemean.Deep Space views corresponding to these indices are considered outliers, and areremovedfromsubsequentmeanDeepSpacereferencecalculationswithinthelunardetectionalgorithm.

!Sb,p,dds n,k[ ]

k

!Sb,p,dict n,k[ ]

k

!Rb,p,dds n,k[ ] = !Sb,p,dds n,k[ ]− !Sb,p,dds n,k[ ]

k

!Rb,p,dict n[ ] = !Sb,p,dict n,k[ ]

k− !Sb,p,d

ds n,k[ ]k

nmin nmax


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2. Calculate Deep Space uncalibrated (complex) spectral average (in band “b”, FOV “p”, andsweepdirection“d”),withoutliersidentifiedinStep1removed.

3. CalculatetheICTuncalibratedspectralaverage(nooutlierdetection).4. Subtract the Deep Space uncalibrated (complex) spectral average with outliers removed

fromtheindividualDeepSpaceuncalibrated(complex)spectra(Eq.[3.4.1]).5. Subtract the Deep Space uncalibrated (complex) spectral average with outliers removed

fromtheICTuncalibratedspectralaverage(Eq.[3.4.2]).6. Computethemagnitudeofthecomplexratioof[3.4.1]to[3.4.2],averagedoverthespectral

channelslimitedbythespectralchannelindicesprovidedinTable3.4.1-1(Eq.[3.4.3]).7. Compute Cb,p,d

ds kgood⎡⎣ ⎤⎦ , the mean of Eq. [3.4.3] with scans corresponding to outliers

identifiedinStep1removedfrom :

Cb,p,d

ds kgood⎡⎣ ⎤⎦ =

!Rb,p,dds n,kgood⎡⎣ ⎤⎦!Rb,p,dict n[ ]n=nmin

nmax

∑nmax − nmin

[3.4.4]

8. Compare [3.4.3] to the sum of Cb,p,dds kgood⎡⎣ ⎤⎦ and the band dependent threshold (Table

3.4.1-2). Index values that exceed the sum. Deep Space views corresponding to theseindicesareflaggedpositiveforlunarintrusiondetection.

LIb,p,d k[ ] =0, Cb,p,d

ds ≤ Cb,p,dds kgood⎡⎣ ⎤⎦ + LI lim

100

1, Cb,p,dds > Cb,p,d

ds kgood⎡⎣ ⎤⎦ + LI lim100

⎧

⎨⎪⎪

⎩⎪⎪

[3.4.5]

ThelowerandupperlimitsfortheaveragesoverspectralchannelareprovidedinTable3.4.1-1.ThethresholdvaluesusedforlunardetectionareprovidedinTable3.4.1-2.

Table 3.4.1-1 Lower and upper channel limits for the averages over spectral channel used in the lunarintrusiondetectionalgorithm.

DetectorBand LowerLimit

(channelindex)

LowerLimit

(cm-1)

UpperLimit

(channelindex)

UpperLimit

(cm-1)

LW 201 750 593 950

MW 144 1310 422 1650

SW 64 2255 142 2450

!Rb,p,dds


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Table3.4.1-2Thresholdvaluesusedforlunardetection.

DetectorBand LunarIntrusionThreshold(%)

LW 0.9

MW 1.2

SW 1.8

3.4.2 LunarIntrusionProcessing Ifequation[3.4.5]istrueforanyspecificband,FOV,andsweepdirection,thentheDeepSpacespectrum ismarked as invalid only for that band, FOV, and sweep direction. Any deep spacemeasurements marked invalid from this process are excluded from the Moving Windowaverage and the lunar intrusion flag is also set. Earth scenes calibrated using a Deep SpaceMoving Window average for which Deep Space views have been removed due to a lunarintrusiondetectionarealsomarkedwithalunarintrusionqualityflag.

3.5 AlignmentofDatatoaCommonSpectralGrid

TheprimarychangefortheNASAL1Bprocessing,withrespecttoCrISSDRATBDSection3.5,isthatspectralresamplingisperformedontheundecimatedspectraldomain.

TheF-matrixoperatorisdefinedas:

F[k,k '] = Δσ s

Δσ u

Sin(πσ s,k ' −σ u ,k

Δσ u

)

NO Sin(πσ s,k ' −σ u ,k

NOΔσ u

) [3.5.1]

where,

Δσ s isthesensorspectralgridspacing,

Δσ u istheuserspectralgridspacing,

σ s, ′k isthewavenumberforthebin ′k onthesensorgridσ s ,

σ u ,k isthewavenumberforthebin k ontheuserspectralgridσ u ,and

NO is the undecimated number of interferogram samples truncated to NSR MOPD ( NO =20736fortheLW, NO =10560fortheMW,and NO =5200fortheSW).

ThebanddependenceoftheF-operator,Δσ s ,andΔσ u isnotexplicitlynotedinequation[3.5.1].TheF-matrix operator is computed separately for each granuleusingNeondata contained inthemostcoincidentengineeringpacket.


26

Wavenumbers assigned to each spectral bin prior to resampling are based on the lasermetrologysamplingwavelength(seeSection4.1oftheATBD).Thelaser λL

b valueinband“b”iscomputed by the spectral calibration module and used to recompute the F-matrix operator(basedonthecalibrationneoncount).ThelaserwavelengthisstabilizedontheCrISinstrument( λL

b stabletowithin+/-0.4ppmoveroneorbit).

3.6 ILSCorrection Nochange.

3.6.1 Introduction Nochange.

3.6.2 CrISOff-AxisSelfApodization Nochange.

3.6.3 Self-ApodizationRemoval

Numericalevaluationoftheintegral

Theversion1releaseoftheNASAL1BprocessingsoftwarecalculatestheSelf-Apodization(SA)matrixas:

SA ′k ,k[ ] = d ′σ Psinc σ ′k − ′σΔσ s

,NO⎛⎝⎜

⎞⎠⎟σmin

σmax

∫ ⋅ ILS ′σ ,σ k( ) [3.6.1]

where,

Psinc x, NO( ) = sin π x( )NO sin π x

NO

⎛⎝⎜

⎞⎠⎟

[3.6.2]

Δσ s isthesensorspectralgridspacing

σ k isthewavenumberforthebin k ,

Δσ s isthesensorspectralgridspacing,

NO istheundecimatednumberofinterferogramsamplestruncatedtoNSRMOPD(NO =20736fortheLW, NO =10560fortheMW,and NO =5200fortheSW).

ILS ′σ ,σ k( ) istheselfapodizedinstrumentlineshapedistortionduetooffaxisgeometry.


27

Equation[3.6.1]replacesEquation[41]oftheCrISSDRATBD.

Theinverseselfapodizationmatrixiscalculatedofflineforeachband“b”usinganominallasermetrologysamplingwavelengthvalue, λL ,ISA

b .Thecurrentlasermetrologysamplingwavelengthfor band “b” ( λL

b ) is determined from the spectral calibration module (based on the neoncount). IfλL

b differs from λL ,ISAb bymore thanapre-defined threshold, the ISAdegradedQF is

setto1.

3.6.4 ResidualTerm Theresidualtermisnotcalculated.

3.6.5 GuardBandDamping ThecalibrationfilterformulationisthesameasthatdescribedintheCrISSDRATBDdocument:

fb[k]= 1

ea2 ( k0−a1−k )+1

⎡

⎣⎢⎤

⎦⎥⋅ 1

ea4 ( k−k1−a3 )+1

⎡

⎣⎢⎤

⎦⎥ [3.6.3]

The parameters for the filter have been optimized for use within the NASA L1B complexcalibrationprocedure.TheparametersareprovidedinTable3.6.5-1.

Tobeindependentofwavenumber,equation[3.6.3]isexpressedinbins.Itisimportanttonotethatthebinnumberrangebeginat1,andnotatzero.Incasetherangestartsat0,thethreek'sinTable3.6.5-1needtobereducedby1.

Table3.6.5-1Parametersforthecalibrationfilter. .

LW MW SW

k 1 - 866 1 – 530 1 – 202

k0 37 59 21

k1 757 507 186

a1 18 29 10

a2 1.0 2.0 4.0

a3 54 11 8

a4 1.0 2.0 4.0


28

Figure3.6.5-1CalibrationfilterforLWband.

Figure3.6.5-2CalibrationfilterforMWband.


29

Figure3.6.5-3CalibrationfilterforSWband.

3.6.6 ILSRetrieval

ThespectralcalibrationoftheinstrumentisimpactedbyopticalalignmentsandFOVgeometry(FOVsize,shape,geometryandoff-axisangles).TheILSretrievalprocesshasbeendesignedtoidentifytheFOVdependentparametersrequiredtoconstructinverseselfapodizationmatricesthatprovideoptimalcorrectionoftheself-apodizationofall27detectorchannels.

The process utilizes knowledge of the FOV size, shape, geometry and off-axis angles for eachFOV obtained from instrument design and instrument characterization (conductedTVAC andon-orbit).

3.7 SignalApodization UnapodizedradiancesareoutputforthestandardL1Bproduct.

3.7.1 UnapodizedChannelResponseFunction Nochange.

3.7.2 Hamming'sFilterFunction Thespectraloperators(bandguardfilter,spectralresampling,self-apodizationremoval,andHammingapodizationarenotcombinedintoasingleCMOmatrix.


30

3.7.3 Blackman-Harris’sApodizationFunction Nochange.

3.8 CMOUpdates Thespectraloperators(bandguardfilter,spectralresampling,self-apodizationremoval,andHammingapodizationarenotcombinedintoasingleCMOmatrix.


31

4 SPECTRALCALIBRATION

4.1 Neon-lampasaSpectralReference Nochange.

4.1.1 WavelengthCalculation Nochange.

4.1.2 CalculationofLaserMetrologyWavelength Nochange.

4.1.3 RejectingBadNeonCountMeasurements(QualityControl) Nochange.

4.2 MetrologyWavelengthMonitoring Nochange.


32

5 RADIOMETRICCALIBRATION

5.1 BasicRadiometricRelations Nochange.

5.2 GeneralCalibrationEquation Nochange.

5.3 CrISSpecificCalibrationEquation TheCrISspecificcalibrationequation,asimplementedbytheNASAL1BCrISprocessing,usingnotationconsistentwithSection5.3oftheCrISSDRATBD,iswritten:

Lb,p,d

S = LH ⋅Fb ⋅ fb ⋅SAb,p

−1 ⋅ fb ⋅ΔS1

ΔS2

ΔS2

⎡

⎣⎢

⎤

⎦⎥

Fb ⋅ fb ⋅SAb,p−1 ⋅ fb ⋅ ΔS2

[5.3.1]

ΔS1 = !Sb,p,d

S − !Sb,p,dC( ) [5.3.2]

ΔS2 = !Sb,p,d

H − !Sb,p,dC( ) [5.3.3]

where,

Lb,p,d

S isthecalibratedsceneradiance

!Sb,p,d

S arethecomplexuncalibratedEarthscenespectraasmeasuredbytheinstrument,

!Sb,p,d

C are the complex uncalibrated cold reference (Deep Space) spectra asmeasured by the

instrument(complex),

!Sb,p,d

H arethecomplexuncalibratedhotreference(ICT)spectraasmeasuredbytheinstrument

(complex),

LH isthecalculatedradianceforthehotcalibrationreference(theICT),calculatedontheuser

wavenumberscale


33

Fb isthespectralresamplingmatrixoperator,

fb isthebandcalibrationfiltermatrixoperator,

SAb,p−1 istheSelfApodizationremovalmatrixoperator,

b , p ,and d denoteband,fieldofview,andsweepdirectiondependence,respectively.

Forreference, theCrISspecificcalibrationEq.72presented in theCrISSDRATBDis includedhere:

LS = FINT−1 ⋅

!SS − !SC

!SH − !SC⎡

⎣⎢⎢

⎤

⎦⎥⎥⋅FINT L

H + FINT−1 ⋅

!SH − !SS

!SH − !SC⎡

⎣⎢⎢

⎤

⎦⎥⎥⋅FINT L

C [5.3.4]

Asnoted intheCrISSDRATBD,duringnormalon-orbitoperationthecoldreferenceradianceLC = 0 so that the second term in equation [5.3.4] can be ignored resulting in a furthersimplification:

LS = FINT−1 ⋅

!SS − !SC

!SH − !SC⎡

⎣⎢⎢

⎤

⎦⎥⎥⋅FINT L

H [5.3.5]

In theCrIS SDRATBD implementation, the FINT−1 term in equation [5.3.4] is combined into the

CMO(CorrectionMatrixOperator)matrix.TheCrISSDRATBDasdefinestheCMOmatrix:

CMOb,p = Hb ⋅Rb,p−1 ⋅SAb,p

−1 ⋅Fb ⋅ fb [5.3.6]

where,

Hb istheHammingapodizationmatrixoperator,and

Rb,p−1 residualILSremovalmatrixoperator.

Omitting theHammingapodizationandresidual ILSremoval from[5.3.6], theCrISSDRATBDCrISspecificcalibrationequation(Eq.[5.3.5])canberewritteninaformthatcanbemoreeasilycomparedwiththeNASAL1BCrISCalibrationEquation[5.3.1]:

LS = SAb,p−1 ⋅Fb ⋅ fb ⋅

!SS − !SC

!SH − !SC⎡

⎣⎢⎢

⎤

⎦⎥⎥⋅FINT L

H [5.3.7]

5.4 ICTRadiometricModel Nochange.


34

5.4.1 RadiometricError Nochange.

5.4.2 RadiometricModelFormulation The ICT radiometric model is calculated on the user wavenumber grid. Accordingly, thespectrallyresolvedparametersinTable14areontheuserwavenumbergrid.

5.5 ICTTemperatureComputation Nochange.

5.6 SignalCoaddition Nma=29fortheDSandICTsignalcoaddition.

5.6.1 MovingAverage

TheEarthScene(ES)viewsineachscanlinearecalibratedusingreferenceDeepSpace(DS)andInternal Calibration Target (ICT) views from the current and adjacent scan lines if they areavailable.Intheoptimalsituation,referenceviewsfromthe14precedingscanlinesandthe14followingscanlineswillbeused,inadditiontothereferenceviewsfromthecurrentscanline.However,thecalibrationwillstillbeperformedifasfewasonereferenceviewofeachtypeisavailable.Ifacalibrationisperformedwithfewerthantheoptimalnumberofreferenceviews,for example due to a data drop-out or an instrument change, the noise in the calibrated ESspectrawillbeelevated.Iftherearefewerthan24viewsinthemovingaverage,theradiometriccalibrationqualityflagwillbesettodegraded(value=1).

5.6.2 ImpactofTemperatureDrift Nochange.

5.6.3 ThroughputDelay Nochange.


35

6 GEOMETRICCALIBRATION

The NASA L1B software includes a new geolocation implementation based on the approachoutlined in the CrIS SDR ATBD. Digital elevation model (DEM) based terrain statistics andsurfacelocationcorrectionhavebeenincludedaswell.TheCrISSDRATBDonlydescribesthesensor-dependentportionofthegeolocationalgorithm(line of sight vector calculation from instrument telemetry). The sensor-independent part(earthlocationcomputationfromsensorline-of-sight)isdescribedseparatelyintheJPSSVIIRSSDR Geolocation ATBD. Both the sensor-independent algorithm and the approach to terraincorrectionforVIIRSoutlinedinthatdocumenthavebeenfollowedintheNASAL1Bsoftware.

6.1 CoordinateSystems Nochange.

6.1.1 CoordinateSystemDefinition Nochange.

6.1.2 InterferometerOpticalAxisReference(IOAR) Nochange.

6.1.3 RotatingMirrorFrame(RMF) Nochange.

6.1.4 SceneSelectionMirrorMountingFeetFrame(SSMF)Nochange.

6.1.5 SceneSelectionModuleReference(SSMR) Nochange.

6.1.6 InstrumentAlignmentReference(IAR) Nochange.


36

6.1.7 SpacecraftBodyFrame(SBF) No change.

6.1.8 OrbitalCoordinateSystem(OCS) No change.

6.1.9 EarthCenteredInertial(ECI) No change.

6.1.10 EarthCenteredEarthFixed(ECEF)orEarthCenteredRotating(ECR) No change.

6.1.11 WorldGeodeticSystem1984(WGS84) No change.

6.1.12 Topocentric-HorizonCoordinateSystem(THCS) No change.

6.2 CoordinateSystemTransformations No change.

6.3 AlgorithmPartitioning No change.

6.4 SensorSpecificAlgorithm No change.

6.4.1 CrISFOVLOSinSSMFCoordinateSystem No change.

6.4.2 SSMFtoSBFTransformationOperator No change.


37

6.4.3 CrISFOVLOSinSBFCoordinateSystem No change.

6.5 SpacecraftLevelAlgorithm No change.

6.6 TimingConventions No change.


38

7 MODULESDEFINITIONThis section summarizes the key processing steps necessary to transform L1A into L1B. Theoverallprocessingchaincanbepartitionedintomoduleslistedbelow.

1. Initialization• Softwareinitialization,thealgorithmneedsaone-timeinitialization

2. InputDataHandling• Lowlevelandconfigurationdatahandlingforsoftware• Calibrationandsciencedatahandling

3. Preprocessing• Interferogramtospectrumtransformation• Movingaveragehandling• Non-LinearityCorrection

4. SpectralCalibration• Laserwavelengthcalibrationfromneonlampdata• Laserwavelengthdriftmonitoring• Spectralaxislabelingandaliasunfolding

5. RadiometricCalibration• ICTradiancecalculation• Complexcalibration(removesinstrumentinducedoffsetandphase)• Polarizationcorrection(notincludedinv1.0,willbeincludedinafuturerelease)• Spectrum correction (correct for ILS, calibration filter, and resample to a fixed

wavenumbergrid)6. Geolocation

• FOVLOScalculationrelativetospacecraftbodyframe7. QualityControl

• NEdNestimation• Metrologywavelengthmonitoring• Temperaturesmonitoring• Lunarintrusiondetection• Imaginaryradiancethresholdtests

8. Post-processing• Userrequiredspectralbinsselection• SDRdataformatting

9. OutputDataHandling

TheconventionsusedintheflowchartsshowninthissectionaredescribedinFigure7-1:


39

Figure7-1Conventionsusedintheflowchartsincludedinthissection.

The overall processing chain required to transform raw interferograms into spectrally andradiometricallycalibratedandcorrectedspectraisshowninFigure7-2.ThisreplacesFigure59intheCrISSDRATBD.

Data

Processing Module orOperation

Data Flow


40

Figure7-2:Generalflowdiagramfortheradiometricandspectralcalibration.

DenominatorNumerator

Calibration Filter

Self Apodization Correction

Spectral Resampling

F ⋅ f ⋅SA−1 ⋅ f ⋅ ReΔS1ΔS2

⎛

⎝⎜⎞

⎠⎟ΔS2

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Calibration Filter

Self Apodization Correction

Spectral Resampling

➗

numerator denominator

Multiply byLictRadiometric and

Spectral Calibration

F ⋅ f ⋅SA−1 ⋅ f ⋅ ΔS2

ReΔS1ΔS2

⎧⎨⎩⎪

⎫⎬⎭⎪ΔS2 ΔS2

Truncate Convert to Spectra

ES

DS

ICT

Lunar Intrusion

Moving Average

Moving Average

Nonlinearity Correction



Nma = 29Nma = 29

Mean DS Mean ICT

DS, ICT, ESInterferograms

!I !S

!Sds!Ses !Sict

!Sict!Sds!Ses

NEdNEstimate

std real Lict ⋅!S ict − !S ds

!S ict − !S ds⎛

⎝⎜⎜

⎞

⎠⎟⎟

⎛

⎝⎜⎜

⎞

⎠⎟⎟

Les

Multiply by

Lict

PC filter

Imag Rad EstimateLimages

Trim to user grid plus 2 guard

channels


channels


channels

CrIS Calibration Equation:

ΔS1 = !Ses − !S ds

ΔS2 = !S ict − !S ds

Les = Lict ⋅F ⋅ f ⋅SA−1 ⋅ f ⋅ Re

ΔS1ΔS2

⎛⎝⎜

⎞⎠⎟ΔS2

⎡

⎣⎢⎢

⎤

⎦⎥⎥

F ⋅ f ⋅SA−1 ⋅ f ⋅ ΔS2

ES

ImΔS1ΔS2

⎧⎨⎩⎪

⎫⎬⎭⎪

!Sds!Ses !Sds !Sds!Ses

!Sict !Sds !Sict

!Sict !Sict !Sict


41

7.1 Initialization TheILScurvefitparametersinthereferenceCrISSDRATBD(Table17),whichareintendedforcorrection of modulation efficiency variation with OPD, are not applicable to the NASA L1Bprocessing.

Theconfigurationoptions in theCrISSDRATBD(Table18: TunableParametersProvidedviaConfigurationFiles) thatmodify theprocessingperformedby theCrIS SDRalgorithmarenotapplicabletotheNASAL1Bprocessing.TheinstrumentparametersthatareconfiguredwithintheL1BprocessingarelistedinTable7.1-1.

Table7.1-1ParametersdefinedinL1Bprocessingpackage.

L1bmnemonic Description

sensor.Rf Decimationfactor

sensor.An Aliasnumber

sensor.N Numberofpointsinsensorgridinterferogram

sensor.iflip spectralunfoldingindex

sensor.FOVangle angletocenterofFOV

sensor.FOVradius FOVradius

sensor.startbit FIRaccumulatorstartbit

sensor.ModEff

sensor.Vinst nonlinearitycorrectionVinstvalues

sensor.a2_now nonlinearitycorrectiona2coefficients

user.MOPD MaximumOpticalPathDifference(MOPD)correspondingtooutputresolution

user.output_range spectralrangeforoutputdata

FIRfilter.lw.h.real LWFIRfiltercoefficients(realpart)

FIRfilter.lw.h.imag LWFIRfiltercoefficients(imagpart)

FIRfilter.mw.h.real MWFIRfiltercoefficients(realpart)

FIRfilter.mw.h.imag MWFIRfiltercoefficients(imagpart)

FIRfilter.sw.h.real SWFIRfiltercoefficients(realpart)


42

FIRfilter.sw.h.imag SWFIRfiltercoefficients(imagpart)

invalidNeonCalibrationPercentageThreshold neoncalibrationqualitycontrolparameter

computedWavelengthRejectionThreshold neoncalibrationqualitycontrolparameter

c calibrationfiltercoefficients

fb calibrationfilterfrequencyresponse

h PlanckconstantusedinICTradiancecalculation

k BoltzmannconstantusedinICTradiancecalculation

c speedoflightconstantusedinICTradiancecalculation

orbit_time_vector orbittimescorrespondingtoSSMBaffleOffsetmodelvaluesinengineeringpacket

7.2 InputDataHandling TheimplementationofdatahandlingisconsistentwiththeCrISSDRATBD.Itisnotablethattheconversionof CCSDSpacket data to “raw” interferogramobservations, aswell as science andengineeringcoefficientsandmeasurements,isseparatedintoa“CrISL1A”telemetryconversionstage. That initial processing stage is not responsible for triggering science data processingactivities,i.e.itisasimplifiedmodelfromthe“operational”implementationmodeldescribedintheATBD.L0 telemetryequivalent toRDRs isconverted toL1Agranulesrepresentedas files;groupsofL1Agranule filesare thenused forscienceSDR-equivalentL1Bproductgeneration.GranulationofCrISdataisprincipallydoneintheL1Astageofprocessing.

7.3 PreprocessingTheintroductorysectionistheoreticallyconsistentwiththereferenceCrISSDRATBD.

7.3.1 InterferogramtoSpectrumTransformation Thismodulehandles themovingaverageofcalibration targetmeasurements (DS, ICT).29DSand ICT measurements (14 anterior scans, the current scan, and 14 posterior scans;temperatures and spectra) are averaged per the default setting. The moving average iscalculated for each scan line, and the FIFO method described in the CrIS SDR ATBD is notused. Themovingwindowaverages for theDSand ICTare calculatedusing theuncalibratedspectrapriortonon-linearitycorrection.TheNASACrISL1BprocessingdoesnotcurrentlysupportFCEdetectionandcorrection.


43

AgeneraldescriptionofthemovingwindowaverageprocessisgiveninSection5.6.1.

7.3.2 MovingAverageHandling Thismodulehandles themovingaverageofcalibration targetmeasurements (DS, ICT).29DSand ICT measurements (14 anterior scans, the current scan, and 14 posterior scans;temperatures and spectra) are averaged per the default setting. The moving average iscalculatedforeachscanline,andtheFIFOmethoddescribedinthereferenceATBDisnotused.Themovingwindowaverages for theDSand ICTaremaintainedon theuncalibrated spectrapriortonon-linearitycorrection.

TheNASACrISL1bprocessingdoesnotcurrentlysupportFCEdetectionandcorrection.

AgeneraldescriptionofthemovingwindowaverageprocessisgiveninSection5.6.1. 7.3.2.1 ExceptionHandling If any ICTorDS spectrum isdeclared invalidbyCrIS sensor, lunar intrusion testorotherQCmeasure,thenthecorrespondingmeasurementsareexcludedfromthemovingwindowaverage.

If thenumberofvalidspectra inthemovingwindowdropsbelowathresholdvalue(setsuchthat thenoise increaseduetodecreasedaveragesize in thereferenceviewis less than10%),then the “Degraded Radiometric Calibration” flag is set. If there are no valid spectra in themovingaveragewindow,thenthe“InvalidRadiometricCalibration”flagisset.

Ifsciencetelemetrypacketismissingforagiven8-secondsweep,thenthosetelemetryvaluesshallbeexcludedfromthemovingwindowaverage.

7.4 SpectralCalibration Nochange.

7.4.1 LaserWavelengthCalibrationfromNeonLampData Anupdateofmetrologylaserwavelengthisperformedforeachgranulebasedonthecalibrationneoncount. TheF-matrixresamplingoperator iscomputedseparately foreachgranuleusingNeon data contained in the most coincident engineering packet. The spectral operators(calibrationfilter,spectralresampling,self-apodizationremoval)arenotcombinedintoasingleCMOmatrix.


44

Figure7.4.1-1Metrologylaserwavelengthcalibrationflowchart(replacesFigure63inCrISSDRATBD).

7.4.1.1 DefinitionofVariables

Calibrationdatafromengineeringpacket

NNe i[ ] integerneonfringecountfromithsweep

Tbegin i[ ] integerneonfringecountparameterfromithsweepusedforinterpolation

Tend i[ ] integerneonfringecountparameterfromithsweepusedforinterpolation

ΔTbegin i[ ] integerneonfringecountparameterfromithsweepusedforinterpolation

ΔTend i[ ] integerneonfringecountparameterfromithsweepusedforinterpolation

Nsweep Numberofneoncalibrationsweepscollected&reportedinengineeringpacket

NL number of laser metrology wavelengths used to meter OPD during neoncalibrationsweep(NL=7985always)

Cal.

Laser Diode Wavelength Calibration

Ancil.

λL

Update Spectral Resampling Matrix ‘F’ for all 3 bands

NNe,Int i[ ] = NNe i[ ]+ΔTbegin i[ ]Tbegin i[ ]

−ΔTend i[ ]Tend i[ ]

λL i[ ] = λNe ⋅NNe,Int i[ ]NL

λL = 1Nsweep

λL i[ ]i=0

Nsweep−1

∑



45

Ancillarydatafromengineeringpacket

λNe referenceneonwavelength(703.44835nm)

Localvariables

NNe,Int i[ ] neon wavelengths counted during ith calibration sweep (non integer,interpolated)

Outputvariables

λL Averagemetrologylaserwavelengthcomputedfromcurrentengineeringpacketneoncalibrationdata

7.4.1.2 ExceptionHandlingTheaveragedmetrologylaserwavelengthiscomputedfrommanyneoncalibrationsweeps(30is the default). Outliers are removed before the average is re-computed and reported. Seesection4.1.3ofthisdocumentandthereferenceCrISSDRATBD,andtheNASAL1BQualityFlagDescriptionDocumentformoreinformationonoutlierdefinitionandQFassertion.

7.4.2 LaserWavelengthDriftMonitoring ThissectionisnotapplicabletotheV1.0releaseoftheNASACrISL1Bprocessingsoftware.

7.4.3 SpectralAxisLabelingandAliasUnfoldingThe spectral calibrationmoduledefines theon-axis sensor spectral grid associatedwith eachrawspectrum(banddependent),andtheoutputspectralgrid(banddependent).Basedonthelatestlaserdiodewavelengthestimate,thespectralgridspacingandtheminimumwavenumberof thebandarecomputed.Therawspectrum is thenrotated thedesirednumberofpoints tounfold the spectral alias that was introduced by filtering and decimation on-board the CrISsensor. Spectral foldpointshavebeenderivedforeachband. Thespectralunfoldingyieldsacontinuousspectrumfreeofaliasfoldpointsandwithchannelcentersdefinedbythemetrologysampling interval λs

b ,decimation factorDFb and thenumberofcomplex interferogrampointsprocessed Nb .


46

Figure7.4.3-1SpectralAxisLabelingandAliasUnfoldingFlowchart


Inputvariables

!SbX n[ ] raw complex spectrum for band ‘b’ in [d.u.] prior to spectral unfolding,

corresponding toX=DS, ICT,orES. Thesespectrahavenotyetbeen throughnon-linearitycorrection

CalibrationData

λS metrology sampling interval (cm) ( λs = λL 2 ≈ 775x10−7cm ). The sampling

intervalishalfthelasermetrologywavelength.

AncillaryData

σ 0breq requiredminimumwavenumber channel center of first channel located in the

passbandofband‘b’fortheL1Boutputspectralgrid(cm-1).

(LW=650.000cm-1,MW=1210.000cm-1,SW=2155.000cm-1)

σ 1breq requiredmaximumwavenumber channel center of last channel located in the

passbandofband‘b’fortheL1Boutputspectralgrid(cm-1).

(LW=1095.000cm-1,MW=1750.000cm-1,SW=2550.000cm-1)

Cal.


Ancil.

Spectral Axis Definition

Work

Spectral Axis Labeling and Alias UnfoldingRaw SPC

[d.u.]

Raw SPC[d.u.]

UnfoldingSensor

Grid Params

User Grid Params

!SbX n[ ]

!SbX n[ ]

k1b = AN ⋅N + kb

k2b = k1b + N −1

!SbX n[ ]←Unfold !Sb

X n[ ],kb{ }

Δσ b =1

Nb ⋅λS ⋅DFb

σ b 0[ ] = Δσ b ⋅ k1b


47

DFb decimationfactorforband‘b’

ANb aliasnumberforband‘b’

kb indextowavenumberchanneltobeusedforspectralunfolding

Outputvariables

!SbX n[ ] raw complex spectrum for band ‘b’ in [d.u.] after spectral unfolding,

corresponding toX=DS, ICT,orES. Thesespectrahavenotyetbeen throughnon-linearitycorrection

Sensor grid parameters: including interferogram sampling interval ( Δx ), on-axis spectralsampling interval ( Δσ ), on-axis spectral sampling grid (σ ), and requiredminimum/maximumwavenumberchannelcenteroffirst/lastchannellocatedinthepassbandofband‘b’fortheL1Boutputspectralgrid(σ 0b

req ,σ 1breq )

User grid parameters: including interferogram sampling interval ( Δx ), on-axis spectralsamplinginterval( Δσ ),on-axisspectralsamplinggrid(σ )

Operators

Unfold V n[ ],kb{ } shiftsacomplexnumericalvectorVaccordingtoafoldpoint kb

7.4.3.2 ExceptionHandlingNone.

7.5 RadiometricCalibration TheCrISspecificcalibrationequation,asimplementedbytheNASAL1BCrISprocessing,usingnotationconsistentwithCrISSDRATBD,isprovidedinEquation[7.5.1].

!Lb,p,des n⎡⎣ ⎤⎦ = Lb

ict n⎡⎣ ⎤⎦ ⋅F n, ′n⎡⎣ ⎤⎦ ⋅ fATBD n⎡⎣ ⎤⎦ ⋅SAs

−1 ⋅ fATBD n⎡⎣ ⎤⎦ ⋅ΔS1

ΔS2

ΔS2

⎡

⎣⎢

⎤

⎦⎥

F n, ′n⎡⎣ ⎤⎦ ⋅ fATBD n⎡⎣ ⎤⎦ ⋅SAs−1 ⋅ fATBD n⎡⎣ ⎤⎦ ⋅ ΔS2

[7.5.1]

ΔS1 = !Sb,p,d

es n⎡⎣ ⎤⎦ − !Sb,p,dds n⎡⎣ ⎤⎦( ) [7.5.2]

ΔS2 = !Sb,p,d

it n⎡⎣ ⎤⎦ − !Sb,p,dds n⎡⎣ ⎤⎦( ) [7.5.3]


48

Figure7.5-1RadiometricCalibrationFlowchart

DefinitionofVariables

InputVariables

!Sb,p,d

es n⎡⎣ ⎤⎦ is the complexuncalibratedEarth scene spectra, expressed in [d.u.] at channel

center“n”,andcorrectedfornonlinearity.

!Sb,p,d

ds n⎡⎣ ⎤⎦ isthecomplexuncalibratedcoldreference(DeepSpace)spectraaveragedover

Nma measurements,expressedin[d.u.]atchannelcenter“n”,andcorrectedfornonlinearity;

!Sb,p,d

it n⎡⎣ ⎤⎦ is the complex uncalibrated hot reference (ICT) spectra averaged over Nma

measurements, expressed in [d.u.] at channel center “n”, and corrected fornonlinearity;

λL Averagemetrologylaserwavelengthcomputedfromcurrentengineeringpacketneoncalibrationdata(SeeSection7.4.1)

CalibrationData

SeeparametersinSection7.5.2forICTradiancecalculation

ILSParameters

Cal.


Ancil.Work

Radiometric Calibration (Complex Radiometric Calibration and Spectrum Correction)Raw SPC

[d.u.]

Calibrated complexEarth scene spectrain radiance units on

user wavenumber grid

CrIS Specific Calibration Equation

User Grid Params

!Lb,p,des n⎡⎣ ⎤⎦ = Lb

ict n⎡⎣ ⎤⎦ ⋅F n, ′n⎡⎣ ⎤⎦ ⋅ fATBD n⎡⎣ ⎤⎦ ⋅SAs

−1 ⋅ fATBD n⎡⎣ ⎤⎦ ⋅ΔS1ΔS2

ΔS2⎡

⎣⎢

⎤

⎦⎥

F n, ′n⎡⎣ ⎤⎦ ⋅ fATBD n⎡⎣ ⎤⎦ ⋅SAs−1 ⋅ fATBD n⎡⎣ ⎤⎦ ⋅ ΔS2

ΔS1 = !Sb,p,des n⎡⎣ ⎤⎦ − !Sb,p,d

ds n⎡⎣ ⎤⎦( )ΔS2 = !Sb,p,d

it n⎡⎣ ⎤⎦ − !Sb,p,dds n⎡⎣ ⎤⎦( )

Lbict n[ ]← predictICTrad_L1b σ n[ ],T ,...{ }

σ b n[ ] =σ b 0[ ]+ n ⋅ Δσ b

Averaged calibrationreferences

!Sb,p,des n⎡⎣ ⎤⎦

!Sb,p,dit n⎡⎣ ⎤⎦

!Sb,p,dds n⎡⎣ ⎤⎦

!Lb,p,des ′n⎡⎣ ⎤⎦


49

AncillaryData

Determined from instrument characterization. See description of ICT radianceparametersandcalculationinSection7.5.2.

Nb Numberofoutputspectralbins

WorkData

See Section 7.5.2 formean calculation of ICT telemetry components (SSM baffletemp,ICTPRT1temp,ICTPRT2temp,OMA1temp,OMAtemp).

LocalVariables

σ b 0[ ] wavenumberofchannelhavingn=0[cm-1]

Δσ b channelspacing[cm-1]

σ b n[ ] wavenumberofnthchannelcenter[cm-1](sensorwavenumbergrid)


intervalishalfthelasermetrologywavelength.

Lbict n⎡⎣ ⎤⎦ is thecalculatedradianceforthehotcalibrationreference(theICT),calculated

ontheuserwavenumberscale

Operators

Fb n, ′n⎡⎣ ⎤⎦ isthespectralresamplingmatrixoperator(seesection3.5);

fATBDb

n⎡⎣ ⎤⎦ isthebandguardfilter(seesection3.6.5);

SAs−1 istheself-apodizationremovalmatrixoperator(seesection3.6.2);

p Fieldofview(FOV);

b band

d sweepdirection

predictICTrad_L1b{} is the function that computes the ICT predicted radiance from modelinputs(seeSection5.4and7.5.2formoredetails).

OutputVariables

!Lb,p,d

es ′n⎡⎣ ⎤⎦ isthecalibratedsceneradianceontheuserwavenumberscale;


50

flags QualityflagsasdefinedinNASASNPPCrossTrackInfraredSounder(CrIS)Level1BQualityFlagsDescriptionDocument

7.5.1 RadiometricComplexCalibration Radiometric calibration transforms the digital count signal into radiance units. The complexcalibrationmethod isused for theradiometriccalibrationprocess. Thismethodalsocorrectsfortheinstrumentphase.PolarizationcorrectionisnotincludedintheNASAL1Bprocessingatthistime.RefertoSection7.5forthecompleteCrISspecificcalibrationequation.

7.5.1.1 DefinitionofVariables RefertoSection7.5forthedefinitionofvariables. 7.5.1.2 ExceptionHandlingThe sweep direction “d” of the ICT and DS spectra must be selected to match the sweepdirection“d”oftheEarthscenewhenperformingradiometriccomplexcalibration.

7.5.2 ICTRadianceCalculation Section 7.5.2 is theoretically consistent with the reference CrIS SDR ATBD. However, in theNASAL1Bsoftware,thePlanckradianceiscomputedontheon-axissensorgrid.

7.5.3 SpectrumCorrection Spectrumcorrectionincludesapplicationoftheband-guardfilter,theself-apodizationremovalmatrixoperator,andthespectralresamplingmatrixoperator.Theband-guardfilterisappliedbefore and after the self-apodization removalmatrix operator. All operations are applied toboththenumeratoranddenominatorofthecalibrationequation.

RefertoSection7.5forthecompleteCrISspecificcalibrationequation.7.5.3.1 DefinitionofVariables RefertoSection7.5forthedefinitionofvariables.

7.5.3.2 CMOComputationThe spectral operators (bandguard filter, spectral resampling, self-apodization removal, andHammingapodization)arenotcombinedintoasingleCMOmatrix.Hammingapodizationisnotapplied.

7.5.3.3 ExceptionHandling N/A.


51

7.5.4 Non-linearityCorrection Section7.5.4istheoreticallyconsistentwiththereferenceCrISSDRATBD.

7.6 QualityControl Nochange.

7.6.1 NEdNEstimation TheNEdNestimateisbasedonICTmeasurementsthathavebeencollectedwithinthemovingwindowaveraginginterval.Thedefaultwidthoftheaveragingwindowis29scans( Nma = 29 )whichcorrespondsto14anteriorscans,thecurrentscan,and14posteriorscans.

The calibrated ICTmeasurementsprovideability to calculate anNEdNestimatebasedon thestableICTtargettemperature.PrinciplecomponentfilteringisemployedtospectrallysmooththeNEdNestimate.TheNEdNestimateiscalculatedonthesensorwavenumbergrid,usingonlyradiometric complex calibration (no spectral correction) and then interpolated to the outputSDRwavenumbergrid.

The NEdN calculation uses ICT spectra in place of Earth scene spectra in the radiometriccomplexcalibrationandthespectraarenotcorrectedfornonlinearity.

Figure7.6.1-1NEdNEstimationFlowchart

Cal.


Ancil.Work

NEdN EstimationRaw ICT SPC[d.u.]

Calibrated complexEarth scene spectrain radiance units on

user wavenumber grid

Radiometric Only Calibration Equation

Lbict n[ ]← predictICTrad_L1b σ n[ ],T ,...{ }

σ b n[ ] =σ b 0[ ]+ n ⋅ Δσ b

Averaged calibrationreferences

!Sb,p,dit n⎡⎣ ⎤⎦

!Sb,p,dds n⎡⎣ ⎤⎦

!Lb,p,dict n⎡⎣ ⎤⎦ = Lb

ict n⎡⎣ ⎤⎦ ⋅real!Sb,p,dict n⎡⎣ ⎤⎦ − !Sb,p,d

ds n⎡⎣ ⎤⎦!Sb,p,dit n⎡⎣ ⎤⎦ − !Sb,p,d

ds n⎡⎣ ⎤⎦

⎛

⎝⎜⎜

⎞

⎠⎟⎟

!Sb,p,dict n⎡⎣ ⎤⎦

NEdNb,p,d = Interpolate fPCA stdev real !Lb,p,dict n[ ]{ }{ }{ }{ } NEdNb,p,d


52


InputVariables

!Sb,p,d

ict n⎡⎣ ⎤⎦ complexuncalibratedICTspectra,expressedin[d.u.]atchannelcenter“n”,and

uncorrectedfornonlinearity

!Sb,p,d

ds n⎡⎣ ⎤⎦ isthecomplexuncalibratedcoldreference(DeepSpace)spectraaveragedover

Nma measurements,expressedin[d.u.]atchannelcenter“n”,andcorrectedfornonlinearity;

!Sb,p,d

it n⎡⎣ ⎤⎦ is the complex uncalibrated hot reference (ICT) spectra averaged over Nma

measurements, expressed in [d.u.] at channel center “n”, and corrected fornonlinearity;

Calibrationdatafromengineeringpacket

SeeparametersinSection7.5.2forICTradiancecalculation

Workvariables

See Section 7.5.2 formean calculation of ICT telemetry components (SSM baffletemp,ICTPRT1temp,ICTPRT2temp,OMA1temp,OMAtemp).

Localvariables

σ b 0[ ] wavenumberofchannelhavingn=0[cm-1]’

Δσ b channelspacing[cm-1];

σ b n[ ] wavenumberofnthchannelcenter[cm-1](sensorwavenumbergrid);


intervalishalfthelasermetrologywavelength;

Lbict n⎡⎣ ⎤⎦ is thecalculatedradianceforthehotcalibrationreference(theICT),calculated

ontheuserwavenumberscale;

!Lb,p,d

ict n⎡⎣ ⎤⎦ complexcalibratedICTradiance;

p Fieldofview(FOV);

b band;

d sweepdirection;


53

Outputvariables

NEdNb,p,d NEdNestimatefornthchannelonSDRwavenumberoutputgrid.

7.6.2 FringeCountErrorHandling NotimplementedinVersion1.0.

7.6.3 FringeCountErrorDetection NotimplementedinVersion1.0.

7.6.4 FringeCountErrorCorrectionNotimplementedinVersion1.0.

7.6.5 DataQualityIndicators The NASA L1B software produces Quality Flag (QF) variables describing the quality of theprimary data products. The individual flags in the QF variables are specific to the CrIS L1BalgorithmandthereforearedifferentfromtheflagsintheSDRproduct.ForguidanceonusingQFs,refertothe“NASASNPPCrossTrackInfraredSounder(CrIS)Level1BProductUsers’Guide,Version1.0”.FordetailedinformationregardingthederivationandmeaningoftheindividualflagsthatmakeuptheCrISL1BQFvariable,refertothe“NASASNPPCross-trackInfraredSounder(CrIS)Level1BQualityFlagsDescriptionDocument,Version1.0”.ThisdocumentincludesamappingoftheindividualCrISSDRqualityflagstoCrISL1Bqualityflagswhereapplicable.

7.7 Post-Processing N/A.

7.7.1 UserRequiredSpectralBinsSelection N/A.

7.7.2 SDRDataFormatting N/A.

7.8 OutputDataHandling TheformatoftheCrISL1BproductisdescribedintheNASASNPPCrossTrackInfraredSounder(CrIS)Level1BProductUsers’Guide,Version1.0.


54

8 CONCLUSION TheCrISSDRATBDdefinestheLevel1BalgorithmsneededonthegroundinordertoproducemeaningfuldatameetingalltherequirementsoftheCrISinstrument.ThisdocumentidentifiesonlythechangestotheCrISSDRATBDdocumentnecessarytodescribethealgorithmusedtoproducetheNASASNPPCrISL1BradiancedataproductfortheVersion1.0release.


55

9 APPENDICES

9.1 FastFourierTransforms Nochange.

9.1.1 CommentsonVariousAlgorithms Nochange.

9.1.2 DataTranslationandCentering Nochange.

9.1.3 PrimeFactorAlgorithmFastFourierTransform Nochange.

9.2 AliasUnfolding Nochange.

9.3 LinearFitting Nochange.

9.3.1 ImplementationoftheLinearInterpolation Nochange.

9.4 NumericalIntegration Nochange.

9.5 DeterminationoftheGoodnessofFit Nochange.


56

9.6 Definitions Nochange.

9.6.1 SensorCalibration Nochange.

9.6.2 RawDataRecord(RDR) Nochange.

9.6.3 SensorDataRecord(SDR) Nochange.

9.6.4 EnvironmentalDataRecord(EDR)Nochange.

9.6.5 DataProductLevels Nochange.

9.6.6 MeasuredData Nochange.

9.6.7 AuxiliaryData Nochange.

9.6.8 AncillaryData TheCrISL1BalgorithmrequiresLeapSecondsandUTCPolarWanderfiles.Theserequirementsaredescribedinthe“CrISL1BSoftwareUsers’Guide,Version1.0”.

9.6.9 OtherInstrumentSpecificTermsandDefinitions Nochange.

— End of document —