The presentation reviews SCIAMACHY calibration and presents the lessons to be learned for future/current instrument

Lichtenberg, Günter

Slijkhuis, Sander

Institute of Transport Research:Publications

Intro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesSCIAMACHY Calibration Lessons LearnedG. Lichtenberg, S. Slijkhuis and many moreNovember 6, 2019SCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesOutline1 Intro2 Calibration Team3 The Instrument4 Calibration Concept5 What?6 Summary7 Additional SlidesSCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesIntroductionThis is not a blame game: there were always reasons for thedecisions madeHindsight is easy: some things were just unknownNo great revelations: most things here are no-brainers (or soyou would think)In the following we present generic, high level lessons that canbe applied to any spectrometerSCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesCalibration TeamIn no particular order!Institutions: SRON, TPD/TNO, DLR-IMF, IUP Bremen, ESA,KNMIPeople (I could remember): R. Snel, J.M. Krijger, R. Hoogeveen,Q. Kleipool B. Ahlers, G. Otter, H. Visser, C. Schrijvers, M.Dobber, R. Soffer, M. te Plate S. Noel, K. Bramstedt, P. Liebing,R. de Beek, M. Wuttke, J. Skupin, H. Bovensmann, J. Burrows J.Frerick. P. Lützow-Wentzky, R. Mager S. Slijkhuis, G. Lichtenberg,M.Gottwald, E. Krieg P. Stammes, G. Tilstra, . . .SCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesReminder: The InstrumentMeasurement Principle: 2 scanning mirrors & 1-dimphotodiode arrays, Polarisation with broadband PMDsObservation Modes:: Nadir, Limb, OccultationTargets: Earth, Sun, Moon (& Venus)Spectral Range: 213 - 1773 nm, 1934 - 2044* nm, 2259 -2386 nm in 8 channelsSpectral Resolution: 0.22 - 0.56 nm, 1.48 nm (ch. 6)Detectors Passively cooled RETICON (UV/VIS) and EPITAXXInGaAs (SWIR)Calibration: WLS, SLS, backside of scanner modules withdiffusersSCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesModesSCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesCalibration Concept - on-groundSpecial SCIA needs:(a range of) scan angles had to be measuredno polarisation scrambler or fixing of observed polarisationThere was no T/V tank available to measure all needed anglesin vacuum ⇒ combined ambient & T/V calibrationAmbient measurement on the scanner (combination) with anumber of incidence angles and wavelengthsAssume this covers the geometric dependencies of the wholeinstrumentMeasure a reference incidence angle in T/V and ambientget the angle dependency from ambient measurements and theabsolute values from T/VMeasure polarisation sensitivity for s/p and -45/45Mathematically the Mueller Matrix formalism was usedSCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesCalibration Concept - in-flightDark: 5 measurements into deep space (250km TH) to derivedarks for all ITsSpectral: Sun and SLS measurementsDegradation:Use Sun over mirror and WLS in different light pathsSun was observed in Limb mode (Nadir & Limb mirror andExtra mirror), subsolar (Nadir mirror)Observe MoonThe combination of all measurements allowed to characterisethe individual light path degradationSCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesSource: SRONSCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesNot enough photonsSource: IUP BremenENVISAT carbon fibre frameoutgassed waterVenting was (partially)blocked (MLI ENVISAT +MLI SCIA)Detectors cool down to 140 -200 K⇒ IceLesson: Detector should notbe the coldest surfaceRecovery: DecontaminationschemeSCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesNot enough photonsSource: IUP BremenENVISAT carbon fibre frameoutgassed waterVenting was (partially)blocked (MLI ENVISAT +MLI SCIA)Detectors cool down to 140 -200 K⇒ IceLesson: Detector should notbe the coldest surfaceRecovery: DecontaminationschemeSCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesToo many photonsSource: DLR-IMF/SRONThe housing of channel 7 is not light tightLight from an unknown place falls on thedetectorTests for light tightness were done butonly in ambientSWIR detector noise under ambientconditions was too high to discover theleak (if it was there and did not happenduring launch)Position of light leak could not beidentified with certaintyLesson: no shortcutsThis is the one case which we did notrecover from (yet)SCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesToo many photonsSource: DLR-IMF/SRONThe housing of channel 7 is not light tightLight from an unknown place falls on thedetectorTests for light tightness were done butonly in ambientSWIR detector noise under ambientconditions was too high to discover theleak (if it was there and did not happenduring launch)Position of light leak could not beidentified with certaintyLesson: no shortcutsThis is the one case which we did notrecover from (yet)SCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesPixels go bad/die/resurrectSWIR Detectors are EPITAXXdetectors with a light detectingInGaAs layer on top of a InPsubstrateThe doting of the InGaAs layerwas changed to get sensitivity atlonger wavelengths⇒ Lattice mismatch betweenInGaAs and substrate⇒ Sensitivity to proton impactdamaging pixelsSolution: Monitor all pixels withvarious measurementsLesson: Monitoring concept,Calibration goes onSCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesPixels go bad/die/resurrectSWIR Detectors are EPITAXXdetectors with a light detectingInGaAs layer on top of a InPsubstrateThe doting of the InGaAs layerwas changed to get sensitivity atlonger wavelengths⇒ Lattice mismatch betweenInGaAs and substrate⇒ Sensitivity to proton impactdamaging pixelsSolution: Monitor all pixels withvarious measurementsLesson: Monitoring concept,Calibration goes onSCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesUnexpected Detector Behaviour (I)Source: SRONOn-ground measurements of theNL were done but hampered byan instable light sourceOnly one average per multiplexerNL was derived, butcommissioning phasemeasurements showed that this isnot sufficientIncorporation of more on-groundmeasurements and a re-analysisled 14 new curvesNL correction was checked withon-ground dataLesson: redundant measurements,availability of on-ground data isneededSCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesUnexpected Detector Behaviour (I)Source: SRONOn-ground measurements of theNL were done but hampered byan instable light sourceOnly one average per multiplexerNL was derived, butcommissioning phasemeasurements showed that this isnot sufficientIncorporation of more on-groundmeasurements and a re-analysisled 14 new curvesNL correction was checked withon-ground dataLesson: redundant measurements,availability of on-ground data isneededSCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesUnexpected Detector Behaviour (II)Source: SRONThe memory effect correction wasmeasured on-groundMeasurements for one channel weretaken (scaled for ch. 1) for allchannels, reason not entirely clearfrom documentationKey data derivation was notdescribed in detailIn-flight measurements could bedefined to measure the MECAnalyses resulted in dedicated curvesfor each channel and the discovery ofa saturation effect (which was seenbut not investigated before)Lesson: Document everything, noshort cuts, keep the instrumentflexibleSCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesUnexpected Detector Behaviour (II)Source: SRONThe memory effect correction wasmeasured on-groundMeasurements for one channel weretaken (scaled for ch. 1) for allchannels, reason not entirely clearfrom documentationKey data derivation was notdescribed in detailIn-flight measurements could bedefined to measure the MECAnalyses resulted in dedicated curvesfor each channel and the discovery ofa saturation effect (which was seenbut not investigated before)Lesson: Document everything, noshort cuts, keep the instrumentflexibleSCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesRadiance & Polarization (I)Radiometricfirst comparisons showed a significant difference betweenexpected and measured (ir)radiancesthis required a major re-analysis and led to the re-calculationof key datathe exact set-up of measurements could not always recoveredin order to recover, all redundant measurements were needed(FEL lamp with different geometries, sphere measurements)SCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesRadiance & Polarisation (II)Source: IUP BremenThe polarisation correction is acombination of on-groundcalibration, in-flight PMDmeasurements and theoreticalassumptionsThe instrument showed anunexpected polarisation phase shiftThe initially used polarisation keydata were not consistent with eachotherThe reference frame for thepolarisation data had to be newlyderived, because from themeasurement logs it was not clearLeft: L01 V8 and V9 polarisationcalculation (V9 used completelyrevised correction)SCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesRadiance & Polarisation (III) - LessonsRedundant measurementsRadiometric: different distances in a given config and differentset-ups (e.g. FEL & Sphere)Documentation!Quick looks and pre-analysisUse L01 processor already in on-ground calibration (Formats,Algorithms)Polarisation: Eithermeasure polarisation on same spectral resolution as sciencechannelsscramble itor fix itSCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesOn-ground → In-flightSource: IUP BremenThere will be always a difference between the on-ground calibration and the firstin-flight measurementsThe longer the storage the more likely are larger changesIn SCIA the internal WLS was used to correct the effectFor the correction we also had to take into account a 97K higher lamptemperature (micro-gravity effect)Lessons:Incorporate on-ground → in-flight in calibration scheme (using internallight sources)Do this measurement as early as possible to have a properreference point and avoid ageing effects of the light sourceSCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesOn-ground → In-flightSource: IUP BremenThere will be always a difference between the on-ground calibration and the firstin-flight measurementsThe longer the storage the more likely are larger changesIn SCIA the internal WLS was used to correct the effectFor the correction we also had to take into account a 97K higher lamptemperature (micro-gravity effect)Lessons:Incorporate on-ground → in-flight in calibration scheme (using internallight sources)Do this measurement as early as possible to have a properreference point and avoid ageing effects of the light sourceSCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesSummary1 Document. Each. And. Every. Step.2 Redundant measurements are mandatory (and not "nice tohave")3 There are no short cuts4 Quick looks + first analysis on-site are essential5 Calibration goes on (and on) ⇒ access to on-groundcalibration data6 Do not neglect the technical stuff (data formats, analysis S/W)7 Develop an integrated calibration concept for on-ground,in-flight and monitoring8 Have a flexible instrument operation concept (even if notneeded during nominal operation)9 Fight for your calibration timeSCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesChannels & PMDsChannel Range/Resolution PMD Range1 214 - 334/0.24 nm2 300 - 412/0.26 nm A 310 - 365 nm3 383 - 628/0.44 nm B 455 - 415 nm4 595 - 812/0.48 nm C 610 - 690 nm5 773 - 1063/0.54 nm D,45 800 - 900 nm6 971 - 1773/1.48 nm E 1500 - 1635 nm7 1934 - 2044/0.22 nm8 2259 - 2386/0.26 nm F 2280 - 2400 nmSCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesMueller MatrixMueller MatrixSQUVdet=MII MIQ MIU MIVMQI MQQ MQU MQVMUI MUQ MUU MUVMVI MVQ MVU MVV ·IQUV0(I ,Q,U,V ): Stokes VectorSCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesSCIAMACHY Calibration Lessons LearnedIntro Calibration Team The Instrument Calibration Concept What? Summary Additional SlidesCalibration Concept - in-flightSource: DLR-IMF/SRONSCIAMACHY Calibration Lessons Learned

SCIAMACHY Calibration Lessons Learned

https://elib.dlr.de/135543/1/witso_sciaLessLearned.pdf

SCIAMACHY Calibration Lessons Learned

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Institute of Transport Research:Publications