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1、REMOTESENSINGOFENVIRONMENT21:143-183(1987)143CanopyReflectance,Photosynthesis,andTranspiration.II.TheRoleofBiophysicsintheLinearityofTheirInterdependenceP.J.SELLERSCOLAI,DepartmentofMeteorology,UniversityofMaryland,CollegePark,Maryland20742Atwo-streamapproximationmodelof
2、radiativetransferisusedtocalculatevaluesofhemisphericcanopyreflectanceinthevisibleandnear-infraredwavelengthintervals.Simpleleafmodelsofphotosynthesisandstomatalresistanceareintegratedoverleatorientationandcanopydepthtoobtainestimatesofcanopyphotosynthesisandbulkstomatal
3、orcanopyresistance.Thesimpleratio(SR)ofthenear-infraredandvisiblecanopyreflectanceshasbeenfoundtobeanear-linearindicatorofthephotosyntheticallyactiveradiationabsorbedbythecanopy,APAR,minimumcanopyresistance,1/rc,andphotosyntheticcapacityPc,butahighlynonlinearandtherefore
4、lessreliablepredictorofleafareaindexorbiomass(Sellers,1985).Thispaperextendspreviousworkandinvestigatesthebiophysicalprocessesgivingrisetothenear-lineardependenceofAPAR,Pcandl/r,,onSR.Itisdemonstratedthatundernormalfieldconditions,i.e.,darksoft,thenear-infraredreflectanc
5、etermcontrolsthevariationofSRwithleafareaindex.Asaresultofthis,near-linearitybetweenSRandAPAR,Pcor1/r~willoccurifthelea[scatteringcoefficientinthenear-infraredregion,toN,satisfiesthefollowingequality:ton=1-[G(~)/2/t]2(1-to,,),whereto,,istheleaf'seffectivescatteringcoeffi
6、cientforPAR,G(/~)istheaveragelea[projectioninthedirection/x,and/xisthecosineofthezenithangleoftheincomingflux.Thisconditionisapproximatelymetinnature.ItisshownthatavarietyofsatellitesensorcombinationsarewellconfiguredfortheestimationofAPAR,Pcand1/rCbyrespondingtoleafscat
7、teringcoefficientsinbandsthatconformtotheaboveexpression.TherelationshipsbetweenSRandAPAR,PcorI/r,.becomesincreasinglynonlinearasthesoilreflectivityincreases.IntroductionND-RNRN+-RvRv'(lb)Thepastfewyearshaveseenaconsid-erableriseininterestintherelationshipwherebetweenthe
8、spectralreflectanceofthevegetatedlandsurfaceandbiometricorbiophysicalquantitiesassociatedwithSR=simpler
