Globalmonitoringofwetlands

GlobalmonitoringofwetlandsethevalueofENVISATASARGlobalmodeA.Bartscha,*,W.Wagnera,K.Scipala,b,C.Pathea,D.Sabela,P.WolskicaInstituteofPhotogrammetryandRemoteSensing,ViennaUniversityofTechnology,Gusshausstraße27-29,1040Vienna,AustriabEuropeanCentreforMediumRangeWeatherForecast,ShinfieldPark,Reading,RG29AX,UKcHarryOppenheimerOkavangoResearchCentre,PrivateBag285,Maun,BotswanaReceived20October2006;receivedinrevisedform28February2007;accepted26June2007Availableonline17March2008AbstractThispaperelaboratesonrecentadvancesintheuseofScanSARtechnologiesforwetland-relatedresearch.Applicationsofactivesatelliteradarsystemsincludethemonitoringofinundationdynamicsaswellastimeseriesanalysesofsurfacesoilwetness.Formanagementpurposesmanywetlands,especiallythoseindryregions,needtobemonitoredforshortandlong-termchanges.Anotherapplicationofthesetechnologiesismonitoringtheimpactofclimatechangeinpermafrosttransitionzoneswherepeatlandsformoneofthemajorlandcovertypes.Therefore,examplesfromborealandsubtropicalenvironmentsarepresentedusingtheanalysedENVISATASARGlobalmode(GM,1kmresolution)dataacquiredin2005and2006.InthecaseoftheENVISATASARinstrument,dataavailabilityoftherathercoarseGlobalModedependsonrequestprioritiesofothercompetingmodes,butacquisitionfrequencymaystillbeonaveragefortnightlytomonthlydependingonlatitude.PeatlandtypescoveringvaryingpermafrostregimesoftheWestSiberianLowlandscanbedistinguishedfromeachotherandotherlandcoverbymulti-temporalanalyses.Upto75%ofoligotrophicbogscanbeidentifiedintheseasonalpermafrostzoneinbothyears.Thehighseasonalandinter-annualdynamicsofthesubtropicOkavangoDeltacanalsobecapturedbyGMtimeseries.Responsetoincreasedprecipitationin2006differsfromfloodpropagationpatterns.Inaddition,relativesoilmoisturemapsmayprovideavaluabledatasourceinordertoaccountforexternalhydrologicalfactorsofsuchcomplexwetlandecosystems.2008ElsevierLtd.Allrightsreserved.Keywords:Wetland;Peatland;Satelliteradar;Timeseries;Inundation;Soilmoisture1.IntroductionSpecificmechanismsofwatersupplyandstorageareessen-tialformaintainingtheparticularcharacterofawetland.Anychange,directlyby,e.g.waterabstractionorindirectlythroughclimatevariation,canhaveaconsiderableimpactonawetlandecosystem.Disturbancecanimpedetheirroleasnaturalhabi-tats,culturallandscapesandaltergreenhousegascycling(Mitraetal.,2005).Inaddition,shallowlakesandstreamsthatundergoseasonalandlongtermdrying(e.g.StulinaandSektimenko,2004)aremajorsourcesofatmosphericmineraldust.Theextentandbiophysicalpropertiesofwetlandsarevariableinspaceandtime.Informationontheextentofwet-landareasdinparticularthetemporaldynamicsdislackingataglobalscale(Finlaysonetal.,1999).Inrecentyears,activeradar(microwave)remotesensinghasbeenprovenausefultechniqueformonitoringcomponentsofthehydrosphereandhasahighapplicationpotentialforwetlands(e.g.Oldaketal.,2002;Alvarez-Mozosetal.,2005;Frappartetal.,2005;Wagneretal.,2007a).ActiveradarsensorscanbegroupedintoSAR,ScanSARandscatterometersystems.SARshavegoodspatialsamplingcharacteristics(e.g.Euro-peanremotesensingsatellites(ERS)with25m)butthelowesttemporalsampling(approx.monthly)andhavemainlybeenusedforinundationmapping.Scatterometerontheotherhandcanprovideseveralmeasurementsperdaydependingonlatitude.Thefootprint,however,isintherangeofseveral*Correspondingauthor.Tel.:þ4315880112221;fax:þ4315880112299.E-mailaddress:[e-mail](A.Bartsch).0301-4797/$-seefrontmatter2008ElsevierLtd.Allrightsreserved.doi:10.1016/j.jenvman.2007.06.023JournalofEnvironmentalManagement90(2009)2226e2233(Wagneretal.,2003).ScanSARsystemsarecharacterizedbysamplinginbetweenSARsandscatter-ometers.Itisproposedthattheyaresuitableforbothinunda-tionandsoilmoisturemapping.TheENVISATASARisaScanSARsystemandwhenoperatinginGlobalmode(GM)severalimagesperweekcanbeacquiredwithvaryingincidenceanglesand1kmresolution(500mpixelspacing).Radarsignalsarestronglydependentonhydrologicalcon-ditionsinadditiontosurfaceroughnessandvegetationstruc-ture.Thus,multi-temporalapproachesallowthedetectionofenvironmentalprocessesthatareimportantforthefunctioningofterrestrialbiota,inparticularinundationdynamics,soilmoisture(Wagneretal.,2007b)andfreezeethawchanges(Bartschetal.,2007).Theobjectiveofthispaperistodiscussthecapabilitiesofmediumresolutionsatellitemicrowavedataforglobalmoni-toringofwetlands.Themajoradvantageofthesedataisthecomparablyshortrevisitintervals.Theglobalavailabilityandusefulnessofsuchdataisanalysedfromtheviewpointofprovidinginformationonwetlandtypesandtheirdistribu-tion.Theparameterswhichcanbederivedareinundationex-tentanddurationandpotentiallyalsorelativesoilmoisture.Thisstudyconcentratesonthefirsttwoparameters.Twoex-amplesareshownwhichrepresentdifferentwetlandtypesandenvironments.Bothsubtropicandsubarcticregionsareenvironmentswhicharehighlysensitivetoclimatechange.ThesubtropicalOkavangoDeltaisawetlandwithpronouncedseasonaldynamics.TheborealpeatlandsoftheWestSiberianLowlandsarecharacterizedbypermafrostfea