温度反演经典文章(7)

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Z.-L.Lietal./RemoteSensingofEnvironment131(2013)14–37

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fortemperatureand10%forwatervapor(Maetal.,1999),andtheyaremostlyassociatedtotwotypesofuncertainties:1)theactualsoundinglocationandplacewheretheballoonissetfreemaybeseveralkilome-tersapart(upto60km);2)theatmosphericstatuswillchangewhentheballoonriseswhichmeanstheatmosphericpro lesatdifferentheightsaremeasuredatdifferenttimes.ThoseuncertaintiesabouttheatmospherewillfurtherpropagateintotheretrievedLST.Finally,asradiosoundingsarenotcurrentlyavailablewithsuf cientspatialdensi-tyorincoincidencewiththetimeofthesatelliteoverpass,theycanbeonlyusedoccasionallyforvalidationpurposesatsomespecialsites(Colletal.,2005).Incontrast,atmosphericpro lesderivedfromsatellitever-ticalsounderscan,intheory,beusedtoretrievetheLSTfromconcur-rentTIRdataintheatmosphericwindowusingthesingle-channelmethod.Unfortunately,theaccuracyoftheretrievedatmosphericpro- lesnearthesurfaceisinsuf cientforthesingle-channelmethod(Chédinetal.,1985;Ottlé&Stoll,1993;Susskindetal.,1984),andlargeerrorsintheLSTretrievalcanresult.Today,thepro lesprovidedasforecasts,analysisorreanalysisbynumericalweatherpredictioncen-ters,suchastheNationalCentersforEnvironmentalPrediction(NCEP)andtheEuropeanCentreforMedium-RangeWeatherForecasts(ECMWF),constituteapracticalalternativetotheuseofradiosoundings.Colletal.(2012a)andJiménez-Muñozetal.(2010)reportedeitherat-mosphericpro leproductsorreanalysismayyieldreasonableresultstomeettherequiredaccuracyformanycases.Furthermore,Freitasetal.(2010)quanti edtheimpactofECMWFforecasterrorsofatmospher-ichumidityonLSTretrievals,showingthatitisgenerallylessthan0.5K.Nevertheless,theatmosphericpro lesareoftenprovidedatspatialcoarserthanthatofthesatelliteanditisthereforenecessarytointerpo-latetheatmosphericquantitiesintermsoftheviewingzenithangle,theterrainaltitude,spaceandtime(Jiangetal.,2006;Schroedteretal.,2003;Tang&Li,2008).

Toreducethedependenceonradiosoundingdata,severalsingle-channelalgorithmshavebeenproposedwithinthepastdecadetoesti-matetheLSTfromsatellitedataassumingthattheLSEisknown.Qinetal.(2001)proposedamethodtoestimatetheLSTspeci callyfromLandsat-5(ThematicMapperchannel6,TM6)datausingonlythenear-surfaceairtemperatureandwatervaporcontentinsteadofatmo-sphericpro lesusingempiricallinearrelationshipsbetweentheatmo-spherictransmittanceandthewatervaporcontentandbetweenthemeanatmospherictemperatureandthenear-surfaceairtemperature.Jiménez-MuñozandSobrino(2003)andJiménez-Muñozetal.(2009)developedageneralizedsingle-channelalgorithmforretrievingtheLSTfromanyTIRchannelwithaFWHM(fullwidthathalfmaximum)of~1μm,providedthattheLSEandthetotalatmosphericwatervaporcon-tentareknown.Thisgeneralizedsingle-channelalgorithmrequirestheminimuminputdataandcanbeappliedtodifferentthermalsensorsusingthesameequationandcoef cient.Cristóbaletal.(2009)foundthattheinclusionofnear-surfaceairtemperaturetogetherwithwatervaporcontentinthesingle-channelmethodimprovesLSTretrievalespe-ciallyunderintermediateandhighatmosphericwatervaporcontentconditions.Sobrinoetal.(2004b),SobrinoandJiménez-Muñoz(2005)andJiménez-MuñozandSobrino(2010)analyzedandcomparedtheaforementionedalgorithmsandpointedoutthatallofthesingle-channelalgorithmsthatuseempiricalrelationshipsprovidepoorresultsathighatmosphericwatervaporcontentsbecausetherelation-shipsincludedinthealgorithmsbecomeunstableathighwatervaporconcentrations.

Itshouldbekeptinmindthatthesingle-channelmethodsinvolveasimpleinversionoftheRTE,providedthattheLSEandtheatmo-sphericpro lesareknowninadvance.ThesemethodscanprovidetheoreticallyaccurateLSTretrieval,butLSEisrarelyknownwiththenecessaryaccuracy.

3.1.2.Multi-channelmethod

AshighlightedinSection3.1.1,theuseofthesingle-channelmethodrequiresthatLSEisknowna-prioriforeachpixelaswellas

anaccurateRTMandaccurateknowledgeoftheatmosphericpro lesoverthestudyareaatthesatelliteoverpass.Theserequirementsaredif cultorevenimpossibletosatisfyinmostpracticalsituations.ToobtaintheLSTfromsatelliteTIRdatawithsuf cientaccuracyonaglobalorregionalscale,othermethodsmustbedeveloped.Analter-nateapproachusedovertheoceansutilizesthedifferentialatmo-sphericabsorptioninthetwoadjacentchannelscenteredat11and12μmintheso-calledsplit-windowalgorithm(SW) rstproposedbyMcMillin(1975)whichdoesnotrequireanyinformationabouttheatmosphericpro lesatthetimeoftheacquisition.Sincethen,avarietyofSWtechniqueshavebeendevelopedandmodi edtosuc-cessfullyretrievetheseasurfacetemperature(SST)(Bartonetal.,1989;Deschamps&Phulpin,1980;França&Carvalho,2004;Llewellyn-Jonesetal.,1984;McClainetal.,1985;Niclòsetal.,2007;Sobrinoetal.,1993).

EncouragedbythesuccessoftheSWmethodforestimatingtheSSTfromspacemeasurements,manyeffortshavebeenmadesincethelate1980stoextendtheSWmethodtoretrievetheLST.Withmodi cationstotreatthespatio-temporalandspectralvariationsoftheLSE,thelargedifferencebetweentheLSTandtheairtemperature,thetotalcolumnwatervapor(WV)intheatmosphere,andtheviewingzenithangle(VZA),avarietyofSWalgorithmsforLSTretrievalhavebeenproposed.ThesealgorithmsassumethattheLSEsinbothSWchannelsareknownapriori(Atitar&Sobrino,2009;Becker,1987;Becker&Li,1990b;Colletal.,1994;Prata,1994a,b;Price,1984;Sobrinoetal.,1991,1994,1996;Tangetal.,2008;Ulivierietal.,1994;Wan&Dozier,1996).BelowisabroadoverviewofthedifferentSWalgorithmsfoundintheliterature.3.1.2.1.Linearsplit-windowalgorithm.AlinearSWalgorithmcanbedevelopedutilizingthedifferentialabsorptionintwoadjacentTIRchannelsi,jinthe10–12.5μmlinearizingtheRTEwithrespecttothetemperatureorwavelength.ThisalgorithmexpressestheLSTasasimplelinearcombinationofthetwobrightnesstemperaturesTiandTjmeasuredinthetwoTIRchannels(McMillin,1975).Atypicallinearsplit-windowalgorithmcanbewrittenasLST¼aT

0þa1iþa2Ti Tj;

ð7Þ

whereak(k=0,1,and2)arecoef cientsthatdependprimarilyonthespectralresponsefunctionofthetwochannelsgi(λ)andgj(λ), …… 此处隐藏：5016字，全部文档内容请下载后查看。喜欢就下载吧 ……