Inthe research ofremote sensing mechanism

the Canopy Reflectance （CR） models established the relation between the bidirectionalreflectancefeature and canopystructure.This makesthe possibilitytoretrievethe canopystruc ture parametersfrom multiangularremote sensing data by CRmodel.In our Geometric Optical BRDFmodeling study for forestcanopy

we noticethatthereflectancesignature ofsunlitcrownisnotuniform

asub modelfor modelingitsfeature is needed to evaluatethe contribution ofthis componentto the BRDFofsurface . In this approach

to model the effect of canopy structure on the radiation transmittance and reflectance within canopy

Li’s path scattering modelfor homogeneouslayersis developed to calculate thetransmittancein differentlayers within crown .In the positions wherethefoliage volume density arelower

such as nearthe surface ofcrown

the contri bution ofincidentradiationis modeled bythe openness distribution withintree crown

based on our directionalgap proba bility model. Field measurements were madein the apple orchard

North of Beijing .3 ×3 trees wastaken as a sample set.The geometric size andfoliage area volume density（FAVD） distribution oftree crowns were measured using our Tree Comput ed Tomography indirect measuring System （TCTS） .The solarradiation

diffused skylight

hemisphericalradiation atthe given test points within and below the crowns were measured by LI CORquantum sensor （LI 190SA

400 —700 nm） . The measured incidentradiation wastaken asinput ofthe modelto calculate the radiative transmission within and below crowns

the canopy architecture was described by FAVDdistribution and LAD.The measured radiation at points was used to validate the calculated one .The model

measurements and validation results are presented in this paper

which show thatthe modeledradiativetransmissionfitthe measurementdatavery well.The simplified modelis hopefulto supportthe CRmodelinversion study .