植被聚集度系数的时空变异特征、遥感反演与验证研究

植被冠层的聚集度系数指的是植被叶片在空间上的分布特征（随机、规律或聚集分布等），是反映植被结构特征的一个重要属性。聚集度系数的大小直接影响冠层对光能和降水的截留，以及光在植被冠层内部的分布，进而影响植物的光合作用和植被的蒸散发。虽然目前已有一些研究通过地面实测和遥感反演获取冠层聚集度系数，但对它的时空变化特性目前还还缺乏系统的定量分析，对聚集度系数与冠层光谱各向异性指数之间的关系，目前还没有一个确切的结论。本项目拟选择中国东北三江平原的农田区域，开展植被冠层聚集度系数的理论探讨和遥感反演研究：（1）开展农田聚集度系数的长时间野外观测，探讨农田冠层聚集度的时空变化特征；（2）同步开展地面反射率多角度观测，探索农作物冠层多角度聚集效应与BRDF形态参数之间的关系;（3）系统评价现有MODIS和MISR聚集度产品的不确定性，运用改进的算法生成高质量的聚集度系数产品。

The canopy clumping factor (CF) defines the spatial distribution of foliage elements (leaves, stems, and other organs). It is an important canopy structural parameter that affects the canopy radiative transfer and photosynthetic processes and has been incorporated in several land surface models (LSMs) to characterize the radiation penetration in clumped canopies. Global gross primary production (GPP) and net ecosystem exchange (NEE) will be underestimated when remotely sensed LAI is directly used in land surface models and clumping ignored. Despite the development in some recent years in estimating CF from field measurements and remote sensing methods, there are still some difficulties in the understanding of the spatiotemporal characteristics of CF and its relationship with the canopy anisotropic reflectance features. Problems arise in the intercomparison of the directional CF obtained using different optical instruments. The objective of this proposal is to develop a bidirectional clumping factor (BCF) that synergize the differences in existing CF definitions and can be applied for multiple instruments. Temporal change of the BCF will be analyzed based on seasonal measurements in agricultural fields in the Sanjiang Plain, NE China. Improved CF products will be generated based on an analysis of the relationship between CF and the canopy anisotropic indices.