基于树冠层的结构特征,从方向间隙率定义了冠层中不同空间位置对天空散射入照的开放度及其在冠层中的分布,建立了入射辐射在冠层中的衰减与传输模型。应用对冠层结构、总入射辐射、辐射在冠层中衰减等的野外观测数据,对模型进行了验证。模型成功地解释了光在树冠层中辐射传输的变化规律。

In the research of remote sensing mechanism, the Canopy Reflectance (CR) models established the relation between the bidirectional reflectance feature and canopy structure.This makesthe possibility to retrieve the canopystruc ture parameters from multiangular remote sensing data by CRmodel.In our Geometric Optical BRDF modeling study for forestcanopy, we noticethatthereflectancesignature ofsunlitcrownisnotuniform, asub modelfor modeling its feature is needed to evaluatethe contribution ofthis componentto the BRDF of surface. 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.3×3trees wastaken as a sample set.The geometric size and foliage 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 COR quantum 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.