基于计算机模拟模型的林木冠层太阳短波辐射定量分析方法  

A Quantitative Analysis Method of Solar Shortwave Radiation within Forest Canopy Based on a Computer Simulation Model

作　　者：张宇 张怀清[2] 安锋[3] 蒋玲[1] 云挺[1,4] Zhang Yu;Zhang Huaiqing;An Feng;Jiang Ling;Yun Ting(College of Information Science and Technology,Nanjing Forestry University,Nanjing 210037;Research Institute of Forest Resource Information Techniques,Chinese Academy of Forestry,Beijing 100091;Rubber Research Institute,Chinese Academy of Tropical Agricultural Science Danzhou 571737;College of Forestry,Nanjing Forestry University,Nanjing 210037)

机构地区：[1]南京林业大学信息科学技术学院,南京210037 [2]中国林业科学研究院资源信息研究所,北京100091 [3]中国热带农业科学院橡胶研究所,儋州571737 [4]南京林业大学林学院,南京210037

出　　处：《林业科学》2024年第4期16-30,共15页Scientia Silvae Sinicae

基　　金：国家自然科学基金项目(32371876,32271877);江苏省自然科学基金面上项目(BK20221337);江苏省农业自主创新项目[CX(22)3048]。

摘　　要：【目的】定量模拟和刻画林木冠层太阳短波辐射的分布和截获情况,于时空变换下反演太阳短波辐射在不同林木冠层内的辐射通量变化,为林木培育经营和提质增效提供理论依据。【方法】首先,以公共数据集和真实扫描的校园内林木激光点云数据为例,结合设计的机器视觉算法,对林木激光点云进行枝叶分离和单叶分割,并用合适大小的椭圆形和圆柱体几何单元分别拟合每片叶片和骨架,开展林木真实模型重建;其次,运用计算机图形学方法,结合研究地点的经纬度和时刻,模拟太阳入射光线,并引入物理学的双向反射和透射分布函数及蒙特卡洛光线追踪算法,开展反射和透射光线与冠层内叶片的碰撞模拟;最后,根据仪器测量得到的不同树种叶片平均粗糙度和折射率,结合光线追踪算法,实现林木冠层内短波辐射分布计算和木林冠层光截获效率评估。【结果】利用本研究方法计算时空变换下不同树种(芒果、橡胶、紫薇、樱花)4株树冠及一片香樟树林的直射、反射和透射太阳辐射通量,其中直射辐射通量占比约86%、反射辐射通量占比约5%、透射辐射通量占比约9%。叶面积指数高的树冠会拦截更多直射和透射光线;在太阳高度角较小时刻(上午或下午),斜射的太阳光线反射后易与树冠中其他叶片发生二次求交,产生较多反射辐射通量。同时,由于林木的趋光性,中午树冠光线拦截率高于上午和下午10%左右。比对采用本研究方法计算的树冠辐射通量拦截比值和样地手持光电仪器实测结果,绝对误差小于6%。【结论】在测绘科学、计算机图形学及林学多学科视角融合下,本研究基于激光点云重建树木真实表观形态结构,并将蒙特卡洛光线追踪算法与物理学的双向反射和透射分布函数相融合,真实模拟光线在树冠中的传播过程,可准确获取林木冠层内太阳短波辐射分布与树�【Objective】Tree crown architecture and the leaf optical properties and spatial distribution in the canopy are closely related to the absorption and interception of solar shortwave radiation.It is important to quantitatively simulate and characterize the solar radiation distribution and interception in the forest canopy,and invert the radiation flux changes of solar shortwave radiation in different forest canopy under spatiotemporal transformation,which would provide a theoretical foundation for forest cultivation practices and forest quality enhancement.【Method】Firstly,the public dataset and the terrestrial laser scanned points of trees on campus were used,combined with the designed machine vision algorithm,to separate branches and leaves,and perform individual leaf segmentation from the scanned points.Meanwhile,the elliptical and cylindrical geometric primitives with proper size were employed to approximate the leaves and branches,respectively,and the real model of forest trees was reconstructed.Secondly,the computer graphics methods,combined with the longitude and latitude of the study area and the time of day,were used to simulate the incident solar beams with corresponding solar altitude and azimuth angles.Meanwhile,the bi-directional reflectance and transmittance distribution functions of physics coupled with Monte Carlo ray tracing method were employed to simulate the events of reflected and transmitted solar beams collided with leaf surfaces in the canopy.Finally,based on the average roughness and refractive index of the leaves of different tree species measured by the instrument,combined with ray tracing algorithm,the calculation of the distribution of shortwave radiation within the canopy and the assessment of the canopy light interception efficiency were conducted.【Result】The direct,reflected and transmitted solar radiation fluxes for the four tree crowns of different tree species(mango,rubber,crape myrtle,and cherry)and a camphor forest in both spatial and temporal dimensions were calculate

关 键 词：太阳短波辐射 激光点云 计算机模拟模型 树木三维重建 林木辐射传输 

分 类 号：S758[农业科学—森林经理学]