为了模拟玉米冠层内各层叶面积指数（leaf area index, LAI）垂直分布，光合有效辐射（photosynthetically active radiation, PAR）是研究作物群体光合作用和长势的重要特征参数，阐明冠层内PAR的垂直分布规律与冠层结构等参数之间的定量关系，可为遥感定量反演LAI垂直分布提供模型基础。本文基于辐射度模型（RGM），考虑冠层结构如垄宽、垄间距等建立玉米冠层内 不同太阳高度角PAR 垂直分布计算模型，结合指数递减光分布模型，考虑LAI与植被冠层内光分布的关系，运用Campbell椭球分布算法和Bonhomme& Chartier算法两种算法分别计算LAI垂直分布，并就模型的参数如太阳高度角等对 PAR 垂直分布结果的影响进行了分析。结果表明：（1）RGM模型分不同太阳高度角对封垄前的玉米冠层内 PAR 垂直分布的模拟精度较高，60°太阳高度角精度比较高，分别为0.037307和0.064702。（2）两种算法对LAI垂直分布估算能力均较好，不同入射光条件下估算精度不同， Campbell椭球分布算法60°太阳高度角模拟各层LAI垂直分布精度更高。辐射度（RGM）模型可用于玉米冠层内PAR和LAI垂直分布模拟，为模拟垄行结构冠层内LAI垂直分布提供参考。
英文摘要:
Photosynthetically active radiation (PAR) is a crucial parameter in agricultural applications. Some researches show that canopy structure parameters such as leaf area index (LAI) and the heterogeneity of vegetation will affect the vertical distribution of the PAR. Many existing models were constructed to simulate the distribution of PAR such as the canopy structure and sun zenith angle. In this study, the vertical distribution of canopy PAR is simulated based on Radiosity-Graphics Combined(RGM) model and the relationships between PAR and the solar zenith angle, LAI and canopy structure are analyzed, especially for heterogeneous canopies such as crops with wide and narrow ridges. Taking maize as the experimental object, the results indicate that this model can simulate the vertical distribution of canopy PAR transmittance from the tasseling stage to the sealing ridge with a high degree of precision. The results of the modelling are validated using ground measurements made with a SUNSCAN canopy analyzer. The results show that RGM model invert PAR vertical distribution accuracy and 60? solar elevation angle a higher degree of accuracy, with an RMSE of 0.037307 and 0.064702. The LAI is extracted using different algorithms in a model that describes the vertical distribution of PAR transmittance combined with the extinction coefficient and the extracted values are then compared with measured values for layers at different heights. The results show that the Campbell ellipsoid distribution algorithm with 60? solar elevation angle inverts the LAI with a higher degree of accuracy than Bonhomme and Chartier algorithm for different height layers.
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