NASASNPPCrossTrackInfraredSounder(CrIS)Level1BDeltaAlgorithmTheoreticalBasisDocument(ATBD)UniversityofWisconsin-MadisonSpaceScienceandEngineeringCenter
UniversityofMarylandBaltimoreCountyAtmosphericSpectroscopyLaboratoryVersion1.0 May2017
This research was conducted with funding provided by the National Aeronautics and SpaceAdministration.
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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
real partimaginary part
50 100 150 200 250
×104
-1
0
1
Shortwave
real partimaginary part
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.
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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.
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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
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Figure3.6.5-1CalibrationfilterforLWband.
Figure3.6.5-2CalibrationfilterforMWband.
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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.
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3.7.3 Blackman-Harris’sApodizationFunction Nochange.
3.8 CMOUpdates Thespectraloperators(bandguardfilter,spectralresampling,self-apodizationremoval,andHammingapodizationarenotcombinedintoasingleCMOmatrix.
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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.
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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
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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.
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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.
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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.
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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.
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6.4.3 CrISFOVLOSinSBFCoordinateSystem No change.
6.5 SpacecraftLevelAlgorithm No change.
6.6 TimingConventions No change.
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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:
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Figure7-1Conventionsusedintheflowchartsincludedinthissection.
The overall processing chain required to transform raw interferograms into spectrally andradiometricallycalibratedandcorrectedspectraisshowninFigure7-2.ThisreplacesFigure59intheCrISSDRATBD.
Data
Processing Module orOperation
Data Flow
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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
Nonlinearity Correction
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
Trim to user grid plus 2 guard
channels
Trim to user grid plus 2 guard
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
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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)
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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.
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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.
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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
∑
Laser Diode Wavelength Calibration
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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 .
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Figure7.4.3-1SpectralAxisLabelingandAliasUnfoldingFlowchart
7.4.3.1 DefinitionofVariables
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.
Laser Diode Wavelength Calibration
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
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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]
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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.
Laser Diode Wavelength Calibration
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⎡⎣ ⎤⎦
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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)
λS metrology sampling interval (cm) ( λs = λL 2 ≈ 775x10−7cm ). The sampling
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;
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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.
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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.
Laser Diode Wavelength Calibration
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
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7.6.1.1 DefinitionofVariables
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);
λS metrology sampling interval (cm) ( λs = λL 2 ≈ 775x10−7cm ). The sampling
intervalishalfthelasermetrologywavelength;
Lbict n⎡⎣ ⎤⎦ is thecalculatedradianceforthehotcalibrationreference(theICT),calculated
ontheuserwavenumberscale;
!Lb,p,d
ict n⎡⎣ ⎤⎦ complexcalibratedICTradiance;
p Fieldofview(FOV);
b band;
d sweepdirection;
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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.
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8 CONCLUSION TheCrISSDRATBDdefinestheLevel1BalgorithmsneededonthegroundinordertoproducemeaningfuldatameetingalltherequirementsoftheCrISinstrument.ThisdocumentidentifiesonlythechangestotheCrISSDRATBDdocumentnecessarytodescribethealgorithmusedtoproducetheNASASNPPCrISL1BradiancedataproductfortheVersion1.0release.
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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.
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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.
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