植被光合有效辐射吸收分量及最大光能利用率算法的改进

植被冠层对入射光有效辐射的吸收系数 (FPAR) 和最大光能利用率是NPP模拟的重要参数。利用光量子仪实测了典型草原植被类型关键生育期光合有效辐射值,根据NDVI与FPAR之间的良好相关性,建立了2个FAPR估算模型。结果表明,实测的FPAR值与模型估算的FPAR之间的相关性均达到极显著水平,2个模型的估测值之间没有显著性差异。因此,本研究中采取求均值后计算了我国草原的FPAR,并与NASA-FPAR产品进行了嵌套和互补,形成全国完整的草原FPAR空间分布图。同时,基于归一化植被指数和叶面积指数,以中国草原18大类分类结果为基础单元,对中国草原18大类的最大光能利用率进行调整,调整后的最大光能利用率输入NPP模型后,改善了NPP估算精度,在大类尺度上,总体预测精度为85.71%。

Algorithm improvements for two important parameters of FPAR and maximum solar energy utilization efficiency

Photosynthetically active radiation and solar energy utilization efficiency are two of the most important parameters in NPP (net primary productivity) simulation. The solar effective radiation value of key phenological phases for typical steppe was tested using the light quantum instrument, and two models for FPAR (fraction of photosynthetically active radiation) estimation according to correlation between NDVI (normalized difference vegetation index) and FPAR were established. The correlations between measured and estimated FPAR values were significant, and there was no significant difference between the two groups value of model estimation. Therefore, mean values of estimated FPAR were calculated, and nested with NASA (national aeronautics and space administration)-FPAR products, to form a complete FPAR spatial distribution map of grassland in China. In addition, the study also adjusted maximum solar energy utilization efficiency of 18 categories of grassland in China based on normalized difference vegetation index (NDVI) and leaf area index (LAI). The result also showed that adjustment of maximum solar energy utilization efficiency could improve accuracy (85.71% at larger scale) of NPP estimation after inputting the NPP model.