三维冠层BRF模型构建与模拟

Construction and simulation of a BRF model for the 3D canopy

三维辐射传输模型能准确刻画异质性植被冠层对太阳辐射的散射,这对利用高空间分辨率光学影像进行植被参数的定量反演具有重要的指导意义。本文基于具有真实植株统计特征的概率株进行三维植被冠层的构建,通过合理设计光能粒子在冠层内的传输过程并结合蒙特卡洛光线追踪技术和冠层孔隙率计算方法,建立了三维冠层辐射传输模型,并利用该模型对不同生长期玉米冠层多角度二向性反射因子BRF (Bidirectional Reflectance Function)进行了模拟。与实测数据的对比结果表明,离散期、垄行期和均一期的玉米冠层BRF模拟结果与实测数据均保持了较好的一致性,红光波段BRF模拟值与实测值的RMSE为0.0085,R2为0.96,近红外波段模拟值与实测值的RMSE为0.013,R2为0.96。水平均一冠层BRF模拟结果与SAIL (Scattering by Arbitrarily Inclined Leaves)模型结果的对比表明,本文模型在光能粒子传输与能量计算方面的是合理准确的。本文发展的概率株三维辐射传输模型为研究异质性冠层BRF提供了一个有效手段,并可为植被生物量以及叶面积指数LAI(Leaf Area Index)等关键冠层参数的定量化反演与验证提供数据支撑。

Vegetation plays an important role in the earth’s ecosystem,and it has always been a focus of quantitative remote sensing research.The spatial heterogeneity of the vegetation canopy results in the complicated Bidirectional Reflectance Factor(BRF)distribution which brings great difficulties to the high-resolution vegetation remote sensing research.The 3D radiation transmission model can accurately describes the interaction between heterogeneous vegetation canopy and solar radiation,which is important for modeling and application of vegetation quantitative remote sensing using high-resolution optical data.In this work,the probabilistic plants with statistical properties similar to actual plants are used to construct a 3D vegetation canopy.Combining Monte Carlo ray tracing technology and canopy porosity calculation,a 3D canopy radiation transmission model is constructed by rationally designing the random transmission process of optical particles in the canopy.Using probabilistic plants to build the canopy not only accurately describes the canopy’s heterogeneity but also takes into account the non-uniform spatial distribution of leaves.The model considers light to be a particle with the dual properties of frequency and energy.The Monte Carlo method is used to simulate the transmission behavior of light particles in the canopy,and the canopy porosity is calculated to improve the model’s calculation stability.Taking the corn canopy with a typical ridge planting structure as an example,the bidirectional reflectance function of the corn canopy in different growth periods is simulated and compared with the multi-angle observation data.The comparison results illustrate that the model has good simulation accuracy for the optical BRF of corn canopy in different growing periods.The RMSE between the model simulation value and the measured value is 0.0085 at the red band,and the R2is 0.96.At the near-infrared band,the RMSE and R2are 0.013 and 0.96,respectively.For the homogeneous canopy,the comparison between the model developed in this work and the SAIL model shows that the model of this paper perfectly describes the transport path and energy transfer of the light particles.The model proposed in this paper can accurately simulate the BRF of the canopy with the centrosymmetric statistical characteristics,and it offers great convenience in constructing inhomogeneous canopy scenes as well as high simulation stability.The model provides an effective simulation tool for studying canopy BRF and supporting verification of key canopy parameters such as vegetation biomass and leaf area index.