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GlobCoverlandcoveroverSouthAmerica

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Olivier Arino DirectorateofEarthObservation,ESRIN,Frascati,Italy

Patrice BicheronMEDIASFrance,Toulouse,France

Frederic Achard JRC,Ispra,Italy

John Latham FAO,Roma,Italy

Ron Witt UNEP,Chatelaine,Switzerland

Jean-Louis WeberEEA,Copenhagen,Denmark

Thenewglobalportraitisbasedon40terabytesofimagery–equivalenttothecontentof40millionbooks–acquiredbyEnvisat’sMediumResolutionImagingSpectrometer(MERIS)

The most detailed portrait of Earth

instrument.ESAmadeacontinuousefforttoensuretheacquisitionsandtheproductionoftheMERIS300mFullResolutionFullSwath(FRS)productsfortheperiodfrom1December2004to30June2006.

InadditiontobeingmadefullyavailabletothepublicuponitscompletioninSeptemberthisyear,scientistswillusethedatatoplotworldwideland-covertrends,studynaturalandmanagedecosystemsandtomodelclimatechangeextentandimpacts.Theyarehailingtheproduct–generatedundertheESA-initiatedGlobCoverproject–asa‘milestone’.

The most detailed maps ever of Earth’s land surface have been created with the help of ESA’s Envisat environmental satellite. Land cover has been charted from space before, but this global map has a resolution 10 times sharper than any of its predecessors.

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theregionalandglobalmodellingthatisvitalforclimateimpactandsustainabilityresearch.

The land cover productTheGlobCoverlandcoverproductisthefirstfreelyavailableproductat300mresolutionandisthereforeamilestoneproductthatwillbefundamentaltoabroad-levelstakeholdercommunity.Thereare22differentlandcovertypesshowninthemap,includingcroplands,wetlands,forests,artificialsurfaces,waterbodiesandpermanentsnowandice.Formaximumuserbenefit,themap’sthematiclegendiscompatiblewiththeUNLandCoverClassificationSystem(LCCS).

Inordertodeliverthefulldataset,theMERIS(FRS)acquisitioncapacitieshadtobedramaticallyincreased.ThiswasachievedthroughabetterstrategyofacquisitionbetweenASARandMERISinstrumentsoutsidetheviewoftheArtemisDataRelaySatellite.Neverthelesssomepartsoftheworld(eastoftheAmazonianbasin,CentralAmerica,thePhilippines,north-eastQuebecandLabrador,theKorean

More than a mapBi-monthlyproductsfromJanuary2005toJune2006areavailableonline.TheycanbeaccessedthroughanewlydevelopedmapservertoolonESA’sGlobCoverwebsite.InJune2007,additionalbimonthlyglobalcompositesweremadeavailableaswellasthefirstpartofagloballandcovermapoverEurasia.

HowevertheGlobCoverproductismuchmorethanamap.Itisascientificandtechnicaldemonstrationofthefirstautomatedmappingoflandcoveronaglobalscale,andprovidesabasisforthedetaileddescriptionofthelandsurfacestatesneededforregionalclimatemodelling.

Informationonlandcoverisanessentialrequirementofthesustainablemanagementofnaturalresources,environmentalprotection,foodsecurity,climatechangeandhumanitarianprogrammes.Itformsabasisforongoingstudiesofland-coverandland-usedynamicsparticularlytoimproveourunderstandingofthevariationofthenature-societydynamicsoflandmanagement,therebyfacilitating

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TheGlobCoverlandcoverproduct

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peninsula)arestillsparselycovered.AnewmethodologycombiningMERISFRandMERISRRisunderinvestigationtocovertheseproblematicareas.

Inordertobeabletousethetimeseriesofmeasurementsproperly,ESAalsomadeaconsiderableefforttoimproveMERISdatageo-locationaccuracy.Aresolutionof150mwasrequestedbytheusercommunityand,asaconsequence,GlobCovercanuseMERISonlyifsuchrequirementissatisfied.Forthispurpose,ESAcommissionedACRItodeveloptheAMORGOSsoftwarethattakesasinputtheLevel1BMERISFR,therestitutedattitudefileandoperationalorpreciseorbitfile.AMORGOSwasintegratedintheGlobCoverprocessingchainbyMEDIAS,completewithaprojectiontoolbox.

Thequalityofthegeolocationaccuracywasassessedusing146pairsofMERISproductsfortheco-registrationestimation.Theabsolutegeolocationoftheortho-rectifiedMERISFRSproductwasverifiedusing10scenesfromLandsatETM+(30mspatialresolution)overatestareainSpainandMorocco.TheresultofthisexercisewasthatthetotalRMSerrorassociatedwithgeolocationofMERISFRSdatawas77.1mandthustheaccuracyrequirementsetfortheprojectwasachieved,withonlyisolatedimagesexceeding150mresolution.

The GlobCover systemTheGlobCoversystemconsistsofthreecomponents:(1)theGlobCoversoftware,(2)theexecutionenvironmentand(3)thehardware.ThesystemhastobecapabletoingestallLevel1BMERISFRSdataacquiredoverafullyearplusintermediateandfinalproductsofthepre-processingandclassificationchain.Intotalthisamountstoadataloadof46TB.

Thepre-processingchainstartswiththegeometriccorrectionoftheMERISLevel1Bdata.Afterthegeometriccorrection,thedatarunthroughseveralprocessingstepstocalculatesurfacedirectionalreflectance(SDR).Algorithmshavebeenimplementedtoadjustimagesforatmosphericinfluences(i.e.gaseousabsorption,Rayleighscattering,aerosoleffects),todetectandflagclouds,snowareasandland/waterbodies,andtocorrecttheimagesforthesmileeffectinherentinMERISdata.BeforearchivingtheresultingMERISFRLevel2data,theimagesareprojectedandresampledintotheplate-carréeprojection.Thepreviousfullswathimagesarealsosubsetinto5°x5°tiles,whichrepresentsthestandardsizeforaGlobCoverproduct(HDFformat).

Level3processingcomputesbi-monthly,seasonalandannualmosaics.AcompositingtechniqueusingtheBidirectionalReflectionDistributionFunctiontocorrectthereflectancefordifferentilluminationandviewinggeometriesisappliedforthebi-monthlymosaics.Temporalcompositingisthenusedtogenerateseasonalandannualmosaicsbyaveragingmonthlymosaicsovertheselectedperiod.

Theclassificationsubsystemgeneratesagloballandcovermapoutofthesecloud-freemosaics.Theclassificationrunsseparatelyfor22equal-reasoningareasandisorganisedintofivesteps.Thefirstprocessclassifiestheselectedmosaicsspectrallyinalargenumberofclasses.Theseclassesarethentemporallycharacterisedbythecomputationofphenologicalparameters(start,endanddurationofthevegetationperiod),usingthetimeseriesofMERISmosaics.Thesubsequentclusteringalgorithmusesthepreviousspectralandtemporalinformationtogroupclasseswithsimilarcharacteristicsinamanageablenumberofspectro-temporalclasses.Thefourthprocessor,thereferenced-basedlabellingfunction,transformsthesespectro-temporalclassesintopreviouslydefinedLCCSlandcoverclasses.Thefinalprocedureistheexpert-basedlabelling.Thisappliesanupgradedsetoflabellingrulestoimprovethereferenced-basedlabellingandtoproducethefinallandcovermap.

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GeolocationaccuracyoftheMERISproductsafterAMORGOSprocessing.UpperplotshowstherelativeaccuracybetweenMERIS-MERIScouples.PlotonthebottomshowstheabsoluteaccuracybetweenMERIS-Landsatcouples.SemicirclesrepresenttheminimumaccuracyrequestedbytheGlobCoverproject

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(Basedonarandomsamplingof2186cases,theexpertsachievedthefollowingresultsforhomogeneouslandcover.Fortheprincipalclasses,theusers’accuraciesareasfollows:82.7%forcultivatedandmanagedterrestrialland,69.5%fornaturalandseminaturalterrestrialvegetation,19%fornaturalandsemi-naturalaquaticvegetation,63.6%forartificialsurfaces,88.1forbareareas,74.1%forwatersnowandice,whilethatforproducersaccuraciesare69.6,87.8,19.0,43.8,77.1and82.2%,leadingtoanoverallaccuracyof77.9%.Thisvalueisprincipallyduetothedifficultyinmappingaquaticvegetationandartificialsurfaces,whichisbeingaddressedinversion2.)

Interfacing with expert communitiesAninternationalnetworkofpartnersisworkingwithESAontheGlobCoverproject,includingtheUNEnvironmentProgramme(UNEP),theUNFoodandAgricultureOrganization(FAO),theEuropeanCommission’sJointResearchCentre(JRC),theEuropeanEnvironmentalAgency(EEA),theInternationalGeosphereBiosphereProgramme(IGBP)andtheGlobalObservationsofForestCoverandGlobalObservationsofLandDynamics(GOFC-GOLD)ImplementationTeamProjectOffice.

BuildingonthesuccessoftheGLC-2000project(GlobalLandCovermapfortheyear2000)coordinatedbytheJRC,ESA

decidedtolaunchtheGlobCoverinitiativeintheframeworkofitsDataUserElement(DUE).TheGlobCoversystem,developedandoperatedbyMedias-France,togetherwithBrockmannConsult,theUniversitéCatholiquedeLouvainandpartners,isagreatstepforwardinourcapacitytoautomaticallyproducenewgloballandcoverproductswithafinerresolutionandamoredetailedthematiccontentthaneverachievedinthepast.

Auniqueandfundamentalcomponentoftheprojectwasthecontinuousinterfacewiththiscommunityofeventualusersandthelandcoverexpertcommunity,tomakesurethattheresultingproductswere‘fitforpurpose’andthattheusercommunitywasreadytoexploittheproductsoncetheybecameavailable.

TheusercommunityisrepresentedintheprojectbykeyindividualsfromUNEP,FAO,JRC,EEA,IGBPandGOFC-GOLD.TheirinvolvementwasmanagedthroughfouruserconsultationsheldatESRIN,JRCandFAOwhereallelementsoftheprojectwerediscussedandreviewed.Theautomaticrulesweretunedaccordingtofeedbackfromtheusercommunityreceivedatthesemeetings.Inaddition,ateamofregionallandcoverexpertswasengagedtoadviseontheinterpretationofthespectral-temporalclassesandthusimprovetheautomaticlabellingprocedure.

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Online distributionThe‘online’distributionofgigabytesofdatawasalsoakeyissuethatESAhadtoface.ThesolutionwasprovidedbythedevelopmentoftheIONIAGlobCoverAccessTool(GCAT)thatprovideseasyandfastinternetaccesstotheGlobCoverdataproducts.Itisaccessibletoany‘authorisedwebuser’throughasimplepassword-protectedregistrationscheme.Onceauthorised,userscanselectanysubsetoftheGlobCoverdataproductthroughaGraphicUserInterfacefromwherethetypeofproduct(bi-monthly,seasonal,annual),geographicalareaandtimeperiodcanbeset.

DatadistributionusestheBitTorrentprotocol(P2P)tocapitaliseonthenumberofsimultaneoususersandreducetheoverallstressontheserverduringpeakuseraccess.Forthisreason,theGlobCoverteam(ESAandpartners)participatinginthedistributionoperateas‘seeders’,inbittorrentterminology.Inotherwords,theyshareserverswhereGlobCoverproductsarestored.Tooptimisedistributionperformance,eachGlobCovercompositeissub-dividedinMacroTiles(4x4GlobCoverTiles).UserscanselectwhichtypeofGCATproducttheywishtodownload

(GlobCovertile,Macrotile,continentalorworldcoverage).Moreinformationanddataaccesscanbefoundat:www.esa.int/due/ionia/globcover

Thefollowingpeoplealsocontributedtothisproject:

FranckRanera,NigelHoughton,PhilippeGoryl,HenriLaur&StephenBriggs

ESADirectorateofEarthObservation,ESRIN,Frascati,Italy.

MarcLeroyMEDIASFrance,Toulouse,France.

CarstenBrockmanBrockmannConsult,Geesthacht,Germany.

SophieBontemps,PierreDefournyandChristelleVancutsem

UniversitéCatholiquedeLouvain,Louvain-La-Neuve,Belgium.

HughEva,HansJürgenStiebigandPhilippeMayauxJRC,Ispra,Italy.

AntonioDiGregorioFAO,Roma,Italy.

JaapVanVoerdenUNEP,Chatelaine,Switzerland.

AndrusMeinerEEA,Copenhagen,Denmark.

CristianaSchumulliusMartinHerold,GOFC-GOLD,Jena,Germany.

StephenPlummer,TobiasLangankeIGBP,Stockholm,Sweden.

LeonShoutenInfram,TheNetherlands.

LudovicBourgACRI-ST,Sophia-Antipolis,France.

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Thefollowingpeoplealsocontributedtothisproject:

FranckRanera,NigelHoughton,PhilippeGoryl,HenriLaur&StephenBriggs

ESADirectorateofEarthObservation,ESRIN,Frascati,Italy.

MarcLeroyMEDIASFrance,Toulouse,France.

CarstenBrockmanBrockmannConsult,Geesthacht,Germany.

SophieBontemps,PierreDefournyandChristelleVancutsem

UniversitéCatholiquedeLouvain,Louvain-La-Neuve,Belgium.

HughEva,HansJürgenStiebigandPhilippeMayauxJRC,Ispra,Italy.

AntonioDiGregorioFAO,Roma,Italy.

JaapVanVoerdenUNEP,Chatelaine,Switzerland.

AndrusMeinerEEA,Copenhagen,Denmark.

CristianaSchumulliusMartinHerold,GOFC-GOLD,Jena,Germany.

StephenPlummer,TobiasLangankeIGBP,Stockholm,Sweden.

LeonShoutenInfram,TheNetherlands.

LudovicBourgACRI-ST,Sophia-Antipolis,France.

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GlobCoverlandcoveroverSouthEastAsia