离散植被组分几何结构和光学特性对遥感反射分布的影响

A model for molding the openness distribution and radiative transmission within tree crown canopy is set up. It is constructed by combining the path-scattering model for homogenous layers (Li Xiaowen and Ni Wenge et ai,1996, Science in China (Series E)) and an approach to calculate.the openness distribution within tree crown, based on the directional gap probability model (LiXiaowen and Wang Jindi et al, 1995, Science in China (Series B)). It is a simplified model.compared with the radiative transfer models in tree stands usually used in the micrometeorological study. The simplified model is hopeful to support the inversion study of the canopy reflectance model. Based on digital imaging and the reverent measured data of plant canopy geometry in the field, a digital imaging approach is established to evaluate leaf area index (LAI) and leaf inclination distribution (LAD). Then with an OpenGL approach a visual research on the canopy of summer.maize is carried out by application of the canopy structure parameters attained. In the early growing period of winter wheat and summer maize the plant canopy is an inhomogeneous pronouncedly, especially for the maize canopy. Based on the data of several.varieties of the two crops acquired at Beijing, Yucheng and Luancheng experimental stations, CAS,.the change of parameters of geometry and optics of foliage components and the optics of soil background in the main growing period are presented. It is a set of representative results in the region covering the above three stations. Based on the above provided parameters the change of BRDF of winter wheat canopy as the growing stages effected by these parameters is simulated. The values of input parameters are changing dynamicly as the growing progress of the crop. Therefore, the simulated results can.reflect the change of the natural canopy BRDF during the growing period in the above concerned region. The simulated results are helpful to understand the effect of geometry and optics of vegetation foliage on the reflectance distribution of tree canopy.The result of the last two paragraphs can be used as a priori knowledge in BRDF inversion and the.quantitative interpretation of remote sensing images from space-born and air-born, and to provide.the parameters for crop growth simulation in the concerned region.

对稀疏林地的遥感反射研究中，尚没有既能仔细考虑太阳辐射在树冠和林地内的传输过程、又能适用于遥感反演的辐射传输模型，鉴于此， 我们建立的“考虑开放度的树冠辐射传输模型”， 仔细考虑了太阳辐射在树冠和林地内的传输过程，但比用于小气候研究中的类似模型的计算要简便，可望用于遥感反射模型反演。是一项创新成果。将几何图形法、参数法和直接测量法相结合，建立了用数字图象法对作物结构参数叶面积指数和叶角分布（LAI、LAD）的定量计算方法。进而用获得的结构参数，采用OpenGL 方法重建了大田玉米三维特征和行播结构随生长进程变化的数字图像。这是定量遥感中模拟植物群体反射分布中的一项基础工作。本工作.与其它同类工作相比的特点是，提出了一套系统而行之有效的用数字图象法对作物结构参数定量计算的方法，该方法具有代表性和普遍应用意义.在冬小麦、夏玉米的生长早期，尤其是夏玉米是典型的离散植被。我们根据多年积累的实测数据，对影响作物群体二向反射的主要影响因子：植被组分的几何结构、光学特性和群体土壤背景光学特性进行系统研究，得到了具有区域代表性的季相变化结果。是一项创新成果。进而，根据以上获得的群体参数，用多组分植被的二向反射模型，模拟计算了这些参数对冬小麦群体二向反射影响的季相变化，输入参数中涵盖了平均值和可能出现的高值和低值，以及它们随生长进程的动态变化。首次给出了最贴近实际作物生长动态的模拟计算结果。模拟计算结果与本项目的主题“离散植被组分几何结构和光学特性对遥感反射分布的影响”密切有关，有重要借鉴意义。这些结果可以作为先验知识，广泛应用于遥感模型的检验、反演和航天遥感数据的定量解译，亦可为区域作物生长模拟提供基础数据。