摘要
在文献［１］中作者建立了计算多组分植被方向反射系数（ＢＲＦ）的综合解析模型。本文采用该模型研究植被空间结构对常用的归一化植被指数（ＮＤＶＩ）的影响，文中讨论了ＮＤＶＩ与叶（或植被其它组分）角分布（ＬＡＤ）、植被组分（如叶片）的特征尺度和它们在空间的散布方式，以及非叶器官面积在总面积中所占比例间的依赖关系，同时给出了ＮＤＶＩ随太阳／观测角度的变化情况。结果表明即使在叶面积指数（ＬＡＩ）固定不变时，冠层结构及植被组分光学性质的空间非均匀性对ＮＤＶＩ的大小及角分布也有十分显著的影响。通常ＮＤＷ随角度的变化是很大的，如果植被不同组分的光学性质差异很大，且事先不知道它们的空间散布方式时，那么利用ＤＮＶＩ就无法准确地估算出ＬＡＩ。但是对于组分随机分布的植被，利用远离“热点”区域的光谱资料可以使冠层其它结构参数的影响减至最小。
A comprehensive, analytical model for calculating bidirectional reflchnce factor(BRF) of multicomponent vegetation canopies [1] is employed to study the influence of canopy spatial stricture on the commonly used normaled difference vegetation index(NDVI). The dependencies of NDVI on leaf (or other forliage elements) angle distribution(LAD), dimension of foliage elements(e.g., leaf), foliage dispersion mode and the areal feac tion of non-leaf organs are discussed, and the variation of NDVI with solar /viewing zenith is examined. The result shows that the spatial inhomogeneity of canopy architecture and the optical properties of foliage elements siedficanhy affect the magnitude and angular distribution of NDVI for canopies even with a fixed leaf area index (LAI) Usually, the angular variation of NDVI is pronounced. And it is unlikely to correctly estimate LAI through NDVI without a prior knowledge of the spatial dispersion mode of foliage elements or if the optical properties of different foliage elements much differ. But for a canopy consisting of randomly dispersed foliage elements, effects of other architectural parameters of canopy on LAI estimation can be minimized by using spectral data far away from the hotspot direction.
出处
《环境遥感》
CSCD
1996年第4期285-290,共6页
基金
国家自然科学基金
中国科学院院长基金
