叶面积指数是地学相关研究领域重要参数，其测定精度直接决定着碳循环模型从单位叶片推算到冠层尺度的净初级生产力的模拟精度。光学仪器法测定叶面积指数的基础是贝尔定律，然而贝尔定律的连续植被水平均一垂直分层的假定以及贝尔定律与几何光学模型的不协调使得贝尔定律测定叶面积指数存在局限性。针对该问题本研究采用理论推导与实验数据验证相结合的方法重点研究森林植被叶面积指数测定的改进方法，从单棵树、样地尺度（或像元尺度）及区域尺度（从数学角度可认为像元无限大尺度）三种尺度研究贝尔定律与几何光学模型背景可视概率数学公式的一致性，分析贝尔定律的适用条件，从而找到贝尔定律失效的像元空间尺度。在贝尔定律失效的像元空间尺度下以聚集度指数为突破点，研究树冠空间分布与树冠内叶子聚集分布的定量关系，进而确定像元尺度内总冠层聚集度指数，提出叶面积指数测定的改进方法，提高真实叶面积指数的测定精度。

Leaf area index is an important parameter to related studies on geosciences, its measurement accuracy directly determines the simulation precision of net primary productivity from leaf level to the canopy scale by using carbon cycle model. Optical instruments were developed to measure leaf area index based on the theory of Bell-Lambert’s law. However, Bell-Lambert’s law with the assumption of continuous vegetation of uniform vertical stratification, and the mismatch between Bell-Lambert’s law and geometrical optics model make some limitations of leaf area index measurement based on Bell-Lambert’s law. In view of this problem, this study focuses on the method improvement of leaf area index measurement combining the theoretical derivation with experimental data validation. From three scales, including a single tree scale, sample area scale (or pixel scale), and regional scale (it can be thought as infinite dimension from the mathematics), the consistency of mathematical formula for the background visual probability calculation from Bell-Lambert’s law and geometrical optics model was studied, and the application condition of Bell-Lambert’s law is analyzed, to find the spatial scale at which Bell-Lambert’s law is ineffective and impracticable. When Bell-Lambert’s law is ineffective and impracticable, taking clumping index as the breakthrough point, the quantitative relationship between canopy clumping index and leaf clumping index in the canopy is developed to determine the final total clumping index of the pixel, put forward the improvement method for the true leaf area index measurement, and improve its measurement accuracy.