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TheContribu-onsofSatelliteLaserRangingtoSatelliteAl-metry

FrankG.LemoineNASAGoddardSpaceFlightCenter

October12,2016

20thInterna+onalWorkshoponLaserRangingPotsdam,Germany

WithcontribuBonsfromN.Zelensky(SGT@NASAGSFC),A.Couhert(CNES,Toulouse)

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•Introduc+on•ThescienceofSatelliteAl+metry.•Role&Contribu+onofSLR.(1)POD.(2)ITRF.(3)Geocenter.(4)Time-VariableGravity.(5)OrbitValida+on..•Somecurrentchallenges.

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POD-Schema-c

Inordertodeterminetheheightoftheseasurface,wemustknowthesatelliteposi-on(meaningitsorbitalephemerides)toaprecisioncommensuratetoorbeFerthantheaccuracyoftheal-meter

ThisexampleisforTOPEX,butthesameprincipleappliesforallal-metersatellites.

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Example Ground Track Coverage for TOPEX (& Jason-1, Jason-2, Jason-3)

ImagefromAVISO(Toulouse,France) Al-tude1336km.Inclin.=66.039°;Groundtrackrepeat:9.9156days.Cross-tracksepara-on(equator):315km

TOPEX/Poseidon 1992-2006

Jason-3 2016 –

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Example: Ground Track Coverage for TOPEX vs. ERS/Envisat

Al-tude~785km.Inclin.98.543°;(sun-synchronous)Groundtrackrepeat:35days.Cross-tracksepara-on(equator):80km

TOPEX/Jason-1,2,3 ERS&Envisat&SARAL

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•Introduc+on•ThescienceofSatelliteAl+metry.•Role&Contribu+onofSLR.(1)POD.(2)ITRF.(3)Geocenter.(4)Time-VariableGravity.(5)OrbitValida+on.•Somecurrentchallenges.

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ScienceofAl-metry-IMeanSeaSurface

Meandisplacementoftheseasurfacefromareferenceellipsoid;FollowsthegeoidoftheEarthandincludesthedynamicoceantopography.MSSareconstructedfrommanyyearsofsatelliteal-metryanddatafromdifferentsatellites:E.g.TOPEX/Poseidon,Jason,ERS-2,ENVISAT

DNSC08MSS&DTU10(DTUSpace)(Andersen&Knudsen,JGR,2009,doi:10.1029/2008JC005179)

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ScienceofAl-metry-IIDynamicOceanTopography

Withindependentinforma-ononthegravityfieldoftheEarth(e.g.GOCE)itispossibletoseparateouttheDOTcontribu-ontoaMeanSeaSurfaceandimagethemeanshapeoftheoceanscausedbytheoceancurrents...andalsocomputethemeangeostropicveloci-es.(a)  GOCEDOTfilteredwitha140kmGaussianfilter(b)  SurfacegeostrophiccurrentspeedscomputedfromthefilteredGOCEDOT.(Knudsen,P.,etal.,“Aglobalmeandynamictopographyandoceancircula-ones-ma-onusingapreliminaryGOCEgravitymodel”,J.Geodesy,2011)

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(GeodynamicsandEarthOceanSatellite:GEOS-3)Launched:Apr.9,1975OperatedthroughJuly1979.

B.Douglasetal.,JGR,1983,hFp://dx.doi.org/10.1029/JC088iC14p09595

ScienceofAl-metry-IIIGulfStreamMeanVeloci+es:Al+metry+gravityfromGOCE

Sanchez-Reales,etal.,2012,MarineGeodesy.

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ThepreciseorbitsforTOPEX/Poseidon,Jason-1,Jason-2,allcomputedinaconsistentreferenceframe(ITRF2008,andinfutureITRF2014)areusedtocomputetheglobalchangeinmeansealevelfromsatelliteoceanradaral-meterdata.

hcp://podaac.jpl.nasa.gov/Integrated_Mul+-Mission_Ocean_Al+meterData

ScienceofAl-metry-IV

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ScienceofAl-metry-V

Regionalmeansealevelvaria+onsfromTOPEX,Jason-1,andJason-2withrespectto1993-2002mean;hcp://podaac.jpl.nasa.gov/Integrated_Mul+-Mission_Ocean_Al+meterData

MeasurementofRegionalandGlobalMeanSeaLevelChange

TOPEX/Poseidon 1992-2002 (-2006)

Jason-1, 2001-2009 (-2013) Jason-2, 2008- Jason-3, 2016-

1993-2016

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ScienceofAl-metry-VIElNino:1997(TOPEX/Poseidon)vs.2015(Jason-2)

Seeupdatesevery~10daysathcp://sealevel.jpl.nasa.gov/science/elninopdo/latestdata/archive/

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ScienceofAl-metry-VIIHurricaneIntensifica+onfromPassageoverWarmCoreEddies

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CU CCAR Sea Surface Height (cm) 08/27Max winds in miles/hr

hFp://oceanmo-on.org/html/impact/natural-hazards.htmhFp://www.nasa.gov/centers/jpl/news/ostm-20080701.html

MappingofGulfofMexicoSeaSurfaceHeightVaria-onsbyDr.RobertR.Leben,UniversityofColorado,Boulder.

SeaSurfaceHeightvaria-onsshowtheloca-onofwarmwatereddies–whichappearhigherinabsoluteheight.Theirlatentheightcancontributetohurricaneintensifica-on.

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Oceanographic&GeophysicalSignalSummary

Phenomenon Amplitude

MeanSeaSurface ±~100m Geoid+D.O.T.

GlobalDynamicOceanTopography

±~1.5m Onlyresolvablewithindependentsatellitegravityinforma-on

SeaLevelChange ~3mm/yr(globalaverage)

Regionalvaria-ons

WarmCoreEddies ~50cm e.g.HurricaneKatrina

ElNino ±~30cm

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Oceanographic&GeophysicalSignalSummary

Phenomenon Amplitude

MeanSeaSurface ±~100m Geoid+D.O.T.

GlobalDynamicOceanTopography

±~1.5m Onlyresolvablewithindependentsatellitegravityinforma-on

SeaLevelChange ~3mm/yr(globalaverage)

Regionalvaria-ons

WarmCoreEddies ~50cm e.g.HurricaneKatrina

ElNino/LaNina ±~30cm aperiodic(inter-annual)phenomenon.

Requirementsfororbitaccuracy:TOPEX/Poseidon•ini-alorbiterrorbudget:~13cm(Tapleyetal.,1994,JGR-Oceans).•Achieved2.5cmby1994(tunedgravitymodel,JGM-2,JGM-3)•PostprocessingITRF2005&ITRF2008;GRACEgravitymodels):1.5-2.0cmorbits.Jason-1->Jason-3•Goalis1cmradialorbiterroraccuracy!!***REQUIRESVERIFICATION****•Wemustalsohaveanorbitthatisstableenoughtoaccuratelymeasureglobalandregionalchangesinmeansealevel

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OrbitStabilityrequirement(global&regionalmeansealevel)

AblainM.etal.,“Improvedsealevelrecordoverthesatelliteal-metryera(1993–2010)fromtheClimateChangeIni-a-veproject”OceanSci.,11,67–82,2015

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•Introduc+on•ThescienceofSatelliteAl+metry.•Role&Contribu+onofSLR.(1)POD.(2)ITRF.(3)Geocenter.(4)Time-VariableGravity.(5)OrbitValida+on.(6)(ModelValida+on).•Somecurrentchallenges.

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FirstLaserRanging,Oct.31,1964,NASAGSFC

GEOS-3

SEASAT, 1978

ERS-1 ERS-2

Envisat

TOPEX,Jason1,2,3

Representa+veSLRprecisionvs.+me

AdaptedfromJ.Degnan.“ImpactofSLRTechnologyInnova-onsonModernScience”,18thILRSWorkshop,Fujiyoshida,Japan,Nov.11,2013.hFp://cddis.gsfc.nasa.gov/lw18/docs/presenta-ons/Session0/13-0001-Degnan_2.pdf

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Onaverageweobtain20-30passes/dayfromthedifferentsta-onsoftheglobalILRSnetwork.

Onaverage20-30sta-onshavetrackedTP,J1,J2&J3perday

SLR–TP,J1,J2,J3trackingsummary

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TrackingDataforAl-meterPOD

SLR

DORIS

TOPEX,Jason-1,Jason-2,Jason-3(en-re-mespan:1993-2016)

TOPEX,Jason-1,Jason-2,Jason-3(NoDORISonTOPEX:2004-2006)

GPS TOPEX(1993-1994only.Demo.)Jason-1(2001-2006)Jason-2,(July2008-present)Jason-3:(Jan.2016-present)

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SLR–TP,J1,J2RMSResiduals

TOPEXLRA.(Schwartz,AppliedOp-cs,1990)

LRAforJason-1,Jason-2,Jason-3(courtesyoftheILRS)

SLRRMSResidualstoNASAGSFCstd1504orbitsforTOPEX/Poseidon,Jason-1,Jason-2.

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SLR–J2&J3RMSResiduals

LRAforJason-1,Jason-2,Jason-3(courtesyoftheILRS)

SLRRMSResidualstoNASAGSFCstd1504orbitsforJason-2andJason-3duringtandemcalibra+onperiod(February–September2016)(fromN.Zelensky,SGT@NASAGSFC)

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SLR–J1&J2OrbitAccuracyAchievedJason-1andJason-2RadialRMSOrbitDifferencesby10-daycycle(2002-2014)

(DifferencesbyOrbitTypeandbyAnalysisCenters)

Couhert,A.,etal.,“Towardsthe1mm/ystabilityoftheradialorbiterroratregionalscales”,Adv.SpaceRes.,2015,doi:10.1016/j.asr.2014.06.041.

NASAGSFCvs.JPLvs.CNESvs.ESOCSLR/DORIS(NASAGSFC)vsGPS-only(JPL)vs.GPS+DORIS+SLR(ESOC)vs.GPS+DORIS+SLR(CNES-GDR-D)

JASON-1

JASON-2

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SLR–Valida-onofJason-2GPS&DORISorbits

Thefactthattheseorbitsfromdifferenttrackingsystemsagreeat~1cmradialRMS,isareasonwhywecanhavesuchhighconfidenceinthedetermina+onofMeanSeaLevelchangefromsatelliteal+metry.

InthesetestswithDORIS&GPSdata,SatelliteLaserRangingMeasurementsofJason-2areindependentanddirectlymeasureorbitaccuracy.

SLRRMSoffit(Coresta+ons,Alleleva+ons)forCNESGDR-Eorbits(basedonDORIS+GNSS,reduced-dynamicorbits)(fromAlexandreCouhert,CNES)

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SLR–Evalua-onofDORIS-onlyorbits(Saral)

(Zelenskyetal.,2016,“Towardsthe1-cmSARALorbit”,Adv.SpaceRes,doi:10.1016/j.asr.2015.12.011)

Athigheleva-onsSLRmeasuresdirectlytheradialorbiterror;Sointhisexample,wecansaytheDORIS-onlyorbitsonSARALhaveanorbitalaccuracyof10-15mm.

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SLR–Contribu-ontoITRF

FiguresfromZuheirAltamimi,IGN/France

Areferenceframerealiza-onconsistsofposi+onsandveloci+esofthereferencepoints.ForITRF2014,post-seismicrelaxa-onisalsomodeledforthefirst-me.

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SLR–Contribu-ontoITRF

FiguresfromZuheirAltamimi,IGN/FranceSeealsoAltamimietal.(2016)

SLRcontributestotheoriginandscaleoftheterrestrialreferenceframeaswellasposi-on/velocityofkeyreferencepoints(coreSLRsta-ons).

ILRS/SLRorigincomponentswrt.ITRF2014

VLBISLR

SLR/VLBIscaleswrt.ITRF2014

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TP,J1,J2,J3.PrimedataforMeasureofchangeinglobalMeanSeaLevel.(Keyclimateindicator).•Mustbedeterminedinastable&consistentreferenceframe•ITRF2008atpresent.(ITRF2014resultsbyOSTSTInLaRochelleNov.2016)•OnlySLR&DORISspanen+re+meseries!!(GPSonTOPEX:1993-1994only;GPSonJason-1:2001-2006;GPSonJason-2:2008-present).

ITRF&MeanSeaLevel

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Regional TOPEX (1993-2002) Sea Surface Height Trend differences from direct impact of the ITRF2005 (GGM02C) minus CSR95 (JGM3) orbit differences. (from Beckley et al., Geophys. Res. Lett., 2007). Errors in the Z component of the TRF can produce large regional errors in MSL rate determination.

MeanSeaLevel:ImpactofTRFerror

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SLR–Geocenter&Al-metryPOD(I)

InthesolidEarthcenterofmassframe,geocentermo-onoftheTotalEarth’smassreferencedtoCF:

rc(t) = rcm(t)–rcf(t)

rcm(t): displacementofthecenterofmass(CM)largelyduetoredistribu+onofcon+nentalwater,atmosphericandoceanicmassattheEarth’ssurface.

rcf(t): displacementofthecenteroffigure(CF)dueinlargeparttoelas+cdeforma+onoftheEarth’ssurfacecausedbyloading. Note.TheSLRcenterofnetwork(CN)becomesthe

centeroffigure(CF)originintheSLRgeocenteres+mate.

L1/L2GeocenterSolu+onfromRies(2013)

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SLR–Geocenter&Al-metryPOD(II)

CSRCMmodellargelyremovesannualZdifferencesignaturebetweenSLR/DORIS&JPL13a/GPSReduced-dynamicorbits

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SLR–Time-VariableGravity(1)

•SLRcontributestodetermina-onofthe-me-variablegravityvaria-onsoftheEarth.•Pre-GRACE–itistheprimarysourceofinforma-onforlowdegreeterms.•IneraofGRACE---determina-onofzonalterms(C20,C40)–towhichGRACEdataarerela-velyinsensi-veorstronglyaliasedwithS2-likesignal.

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SLR–Time-VariableGravity(1)

1990 1995 2000 2005 2010 2015−2

−1

0

1

2 x 10−10 c22

9c5CSR SLR

NASAGSFCSLR+DORIS-derivedTVG+meseriesvs.CSR/SLR/RL05series.

C22

4x4&5x5-meseriesdeveloped@NASAGSFCforal-metrysatellitePOD,andforDORISreprocessingassociatedwithITRF2014.

IMPROVEMENTSEENBYSLR(TP,J1,J2)

(Lemoineetal.,2014,OSTST)

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SARAL, 2013-

CRYOSAT-2, 2010- Jason-2, 2008- Jason-3, 2016-

ISRO (India)

Haiyang (HY)-2A, 2011

(CNSA) Sentinel-3A

2016

CurrentOcean-radarmappingal+metersatellites(Oct.2016)

SLR+DORIS+GNSSSLR+DORIS

SLR+DORIS

(SLR)+DORIS+GNSS

SLR+DORIS+...(GNSS*)

Thesesatellitesforma“virtual”constella+onthatmonitorstheoceansurfacetopography.GoldenAgeofSatelliteAl+metry!!

35Space Geodesy Applications, June 7, 2012

Summary:Whydoweneedmul+pletrackingsystems?

15Space Geodesy Applications, June 7, 2012

Whydoweneedmul-pletrackingsystems?

We need multiple tracking systems (a) to ensure and establish orbit accuracy; This is especially important for the demanding application of measurement of the change in global mean sea level & to demonstrate orbit accuracy. (b) to ensure redundancy; in the event one tracking system has “problems”, or even fails. (I) GFO. Failure of GPS. SLR + altimeter crossovers only reliable tracking system. (II) Jason-1. DORIS Oscillator not hardened before launch – perturbed by passage through S. Atlantic anomaly, Apply a “correction” model.

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SLR–ModelImprovement&Valida-onforAl-meterSatellites(Examples)

1.  ImprovementsinTime-variablegravitymodeling,andintheITRF.

CouhertAetal.(2015)“Towardsthe1mm/ystabilityoftheradialorbiterroratregionalscales”,Adv.SpaceRes.,doi:10.1016/j.asr.2014.06.041.2.ImprovementinNon-conserva+veforcemodelling.Zelenskyetal.,(2010).“DORIS/SLRPODmodelingimprovementsforJason-1andJason-2”,Adv.SpaceRes.,doi:10.1016/j.asr.2010.05.0083. TuningofphasemapsforGPS-satellitereceivers:LuthckeS.etal.(2003),MarineGeodesy,“The1-cmOrbit:...”HainesBr.etal.(2004),MarineGeodesy,“OnecmPODforJason-1...”MercierFl.etal.(2009),OSTSTmee+ng,SeaFleWashingtonJune2009.4. MonitoringPerformanceofDORIS/USOonJason-2

usingT2L2instrument.BelliA.etal.,inpress(2016).“Temperature,radia+onandaginganalysisoftheDORISUltraStableOscillatorbymeansoftheTimeTransferbyLaserLinkexperimentonJason-2”,Adv.SpaceRes.,doi:10.1016/j.asr.2015.11.025.

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•Introduc+on•ThescienceofSatelliteAl+metry.•Role&Contribu+onofSLR.(1)POD.(2)ITRF.(3)Geocenter.(4)Time-VariableGravity.(5)OrbitValida+on.(6)ModelValida+on.•Somecurrentchallenges.

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SLR–CurrentChallenges:SLRbiases

Challenge:WeuseSLRdatatovalidatetheperformanceofDORIS-onlyandGPS-onlyorGPS+DORISorbits(e.g.CNESGDR-E).WealsowishtousetheSLRdatatomonitorlong-termdrixsintheorbits.SLRbiasesinterferewithandcomplicatethisdirectorbitaccuracyvalida-on.Thisisconfoundedby(possible)referenceframeissues(GPSvs.SLR)andpossiblevelocityerrorsofsta-ons.

Couhert,A.,etal.,“Towardsthe1mm/ystabilityoftheradialorbiterroratregionalscales”,Adv.SpaceRes.,2015,doi:10.1016/j.asr.2014.06.041.

Graz

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SLR–CurrentChallenges:TargetSignature

Jason-1:SLRResidualstoGPSorbitvs.boresightangle

Cerrietal.,2010,MarineGeodesy(Figure5)

Zelenskyetal.,2016,Adv.SpaceRes.(Figure3.2)

SARAL:ArnoldLRAmodelvs.meancorrec-on&datadistribu-onvs

eleva-on

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Summary•TOPEX,Jason-1,Jason-2,Jason-3formaseriesofsatellitesthatprovideessen-alkey“climatedatarecords”tomeasureglobal&regionalsealevelchange.•Thesesatellitesarepartofavirtualconstella-onofal-metersatellitestomonitortheglobaloceantopography.•Alltheal-metersatellitesuseSLRdirectlyforPOD,indirectlyforvalida-on,ortoestablishimprovementinunderlyingmodels.•Challenges:(1) MaintainingstabilityandaccuracyofSLRdata–aswellasminimizingbiases–

orbitRMSradialaccuracygoalis1cmradialRMS.(2) Targetsignaturesonal+metersatellites.(3) Con+nuingtoImprovingmodelsforGeocenter,Non-conserva+veforce

modellingandcoherencebetweenthedifferenttechniquesasmanifestedintheorbitscomputedwiththedifferentgeode+cdatatypesforanygivenal+metersatellite.