中文摘要：

基于通量塔常规辐射测量的宽带植被指数（BVI）具有高时间分辨率的优点,有利于获得更详细的森林冠层叶面积指数（LAI）动态信息.本文以帽儿山通量观测站的温带落叶阔叶林为例,研究宽带归一化差值植被指数（NDVI_B）、宽带增强型植被指数（EVIB）、近红外反射率与光合有效辐射反射率比值（SR_（NP））和太阳辐射反射率与光合有效辐射反射率比值（SR_（SP））4种BVI时间序列的控制因子及其滤波方法,并以凋落物收集法为参考,评估采用BVI估测冠层LAI的可行性.结果表明：Huemmrich、Wilson和Jenkins 3种方法计算的同一BVI值略有不同,但其季节变化趋势高度一致.BVI主要受太阳高度角和太阳高度角与坡度夹角的影响而呈现明显的日变化,太阳高度角与坡度夹角最大时刻（12：30）前后的BVI相对稳定.晴空指数可以作为BVI日值滤波的有效参数,不同时刻数据构成的日BVI时间序列的晴空指数阈值以及滤波后的有效数据率存在差异,应综合考虑平滑效果和有效数据率选择合适的时间点代表BVI日值.NDVI_B与凋落物收集法测定的LAI呈显著的线性关系,而EVIB、SR_（NP）和SRSP与LAI均呈显著的对数关系.因此,NDVI_B在表征冠层LAI季节动态和LAI外推中更为精确、方便.鉴于大部分森林碳水通量观测塔配备能量平衡观测系统,如果同时测定光合有效辐射反射率,即可实现冠层LAI长期连续联网监测.

英文摘要：

Broadband vegetation indices（ BVIs） derived from routine radiation measurements on eddy flux towers have the advantage of high temporal resolutions,and thus have the potential to obtain detailed information of dynamics in canopy leaf area index（ LAI）. Taking the temperate broadleaved deciduous forest around the Maoershan flux tower in Northeast China as a case,we investigated the controlling factors and smoothing method of four BVI time-series,i. e.,broadband normalized difference vegetation index（ NDVI_B）,broadband enhanced vegetation index（ EVIB）,the ratio of the near-infrared radiation reflectance to photosynthetically active radiation reflectance（ SR_（NP））,and the ratio of the shortwave radiation reflectance to photosynthetically active radiation reflectance（ SR_（SP））. We compared the seasonal courses of the BVIs with the LAI based on litterfall collection method. The values for each BVI were slightly different among the three calculation methods by Huemmrich,Wilson,and Jenkins,but showed similar seasonal patterns. The diurnal variations in BVIs were mainly influenced by the solar elevation and the angle between the solar elevation and slope,but the BVIs were relatively stable around 12： 30. The noise of daily BVI time- series could be effectively smoothed by a threshold of clearness index（ K）. The seasonal courses of BVIs for each time of day around the noon had similar patterns,but their thresholds of K and the percentages of remaining data were different. Therefore,the daily values of BVIs might be optimized based on the smoothing and the proportion of remaining data. The NDVI_Bwas closely correlated linearly with the LAI derived from the litterfall collection method,while the EVIB,SR_（NP）,and SRSPhad a logarithmic relationship with the LAI. The NDVI_Bhad the advantage in tracking the seasonal dynamics in LAI and extrapolating LAI to a broader scale. Given that most eddy flux towers had equipped with energy balance measurements,a network of monitoring canopy LAI co