The use of Sentinel 2 data for mapping European landscapes ... · Sentinel 2 imagery can result in...
Transcript of The use of Sentinel 2 data for mapping European landscapes ... · Sentinel 2 imagery can result in...
The use of Sentinel 2 data for mapping European landscapes: the case of Denmark
HenningStenHansen,VladRosca,MarkTakacs,CasperTrock,Algirdas Vepstas,JamalJokarArsanjani
Geoinformatics researchgroup,AalborgUniversityCopenhagen
AalborgUniversityCopenhagen
Background&Introduction
§ Lackofglobalandregionalfinescalelandcoverproducts§ Sentinel2-Aand2-Brecentlylaunched§ Potentialforup-to-date,finescalelanduse/landcoverproducts§ EarlystageofexploringthepotentialofSentinelfordevelopingdiverseapplications
§ FutureEuropeanlandcoverinformationshouldbeimprovedintermsofspatialandtemporalresolution
§ CanSentinelplayabigroleinthefuturegenerationoflandcovermaps
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Objectives
Themainobjectivesofthisstudyare:§ toexplorethepotentialofusingSentineldataforlandcover/usemappingparticularlyinEurope,
§ toprovideacomparisonofseveralpixel-basedimageandmachinelearningalgorithmsfortheclassificationofdiscretelanduseclassesusingremotesensingsatelliteimagery.
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ImageSelection
§ Sentinel2imagery10x10mresolution§ FreeandeasytodownloadattheESAwebsite§ Cloudfree§ NorthernDenmark§ Area12,000km2including120millionpixels§ 9Bands
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LandCoverClassificationNomenclature
§ BasedonIPCC(IntergovernmentalPanelonClimateChange)§ SevenClasses
§ Settlement§ Forest§ Cropland§ Grassland§ Wetland§ OtherLand§ Water(user-defined)
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AlgorithmSelection
§ Supportvectormachines(SVM)§ Randomforests(RF) § MaximumLikelihood(ML)
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Groundtruthdata
§ AnintegrationofdataSources:§ Kort10§ DanishAgrifish Agency§ DanishNaturalEnvironmentPortal
§ Reliable,accurate,andtimelydata
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SelectionofSamplePoints
§ Equalizedstratifiedsampling
§ Equalnumberofrandom,spatiallydistributedpointsselectedfromeachclass
§ Selectedcellsthenvisuallyverifiedusing12.5cmhighresolutionaerialphotos
§ Cellspreparedforinputastrainingandtestingpixels
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SelectionofSamplePoints
§ Goal:Twosetsoftrainingandtestingpixels,splitwitha75%-25%ratio§ 1)225trainingpixels,75testingpixelsforeachclass§ 2)750trainingpixels,250testingpixelsforeachclass
§ Filteringtoremovedatawherethereisoverlayoruncertaintyaboutwhichclassapixelbelongsto
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AlgorithmImplementation
§ UsingPython(Scikit Learn)allowedustoimplementrandomforestsandSVMandML.
§ Easytoimplement,user-friendly,nolicensingcost
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Results
TheresultsfromtheMLclassifier,onthe9bandimagewith225trainingpixelswasselectedasabaseline,becauseMLwasconsideredasthemostpopularclassifierinremotesensing.
MLprovedtoshowthelowestaccuracyresultswhencomparedtorandomforestsandsupportvectormachines.
Thebestaccuracywasachievedinfavorofthemostnumberofbands(9),trainingsites(750)andSVMalgorithm.
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Results– Baseline
§ MaximumLikelihood:9bands– 225trainingpixels
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Results:Bestclassifier
§ SupportVectorMachines:§ 9bands– 750trainingpixels
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Results:Weakclassifier
§ MaximumLikelihood:§ 4bands– 225trainingpixels
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Sentinel:opportunitiesandchallenges
§ Theimprovedspatial,spectral,radiometricandtemporalcoverageandalong-termoperationalcommitmentfromESAprovidesuswithanenormouscapacityforearthobservation.
§ Continuityofobservationisbecomingextreme.
§ CrosssensordatafusionwithinSentinelcanboostthequalityandtemporalityofourobservations.
§ AglobalperspectiveinearthobservationshouldbetakenintoaccountasmassiveareasinAfrica,middleeast,andAsiaarethreatenedduetoclimatechange.Asaresult,theentireglobeisatriskofoverexploitationofresources.
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Sentinel:opportunitiesandchallenges
§ CrossplatformapproachesforintegratingSentinelwithpre-Sentinelremotesensingdatae.g.,Landsatshouldbedevelopedinordertoachievelong-termobservations.
§ ToolsforSentineldata-to-productconversionforawidespectrumofusersshouldbedevelopedinordertominimizedataprocessingtime.
§ Now,wearelivinginrichfreedataeraalongwithsmartercitizensandubiquitousmobileapps,therefore,realtimeearthobservationcancometrue.
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Conclusions
§ ThestudyshowedthattheuseofmachinelearningalgorithmsonnewlyacquiredSentinel2imagerycanresultinrelativelyaccuratelandcover/landuseproducts.
§ Improvingtheaccuracyofthealgorithmsshouldbeafirstpriority.Thiscanbedonebyfurthertuningofthetrainingandtestingpixels,byfurthertuningofalgorithmparameters(e.g.moretreesinrandomforests),orbytheadditionofancillarydata(e.g. DEMs)
§ Oncegreateraccuracyisachieved,applyingthebestperformingalgorithmstoalargerareawithamorevariedgeographyforfurthertestingcanbebeneficial.
§ TheuseofSentinel2imageryhasthepotentialtoresultinbetterresolution,andpossiblymoreaccuratelandcover/landuseproducts.ForexampleincreasingtheresolutionofCORINEto10maswellasincludingmoretimestamps.
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FutureDirections
§ Improvementofaccuracyresultsthroughinclusionofimageindicesandancillarydata
§ Considerationofotheralgorithmse.g.deeplearning
§ ApplicationoftheapproachtolargerareaswithinEU
§ PotentialforimprovingCORINEandUrbanAtlasdataintermsofspatialresolution,temporalresolutionandmorerecentdatasets.
§ Lookingforwardtoseeingthefirstgloballandcoverproductat10m