Sun-sensor geometry effects on vegetation index anomalies in the Amazon rainforest
Sun-sensor geometry effects on vegetation index anomalies in the Amazon rainforest
复制标题
太阳传感器几何形状对亚马逊雨林植被指数异常的影响
DOI：
10.1080/15481603.2015.1038428
复制
发表时间：
2015
影响因子：
6.7
通讯作者：
L. Galvão
中科院分区：
文献类型：
--
作者：
E. Maeda;L. Galvão
近年来，轨道传感器利用植被指数（VI）监测亚马逊雨林植被功能和物候的能力受到了广泛的挑战。特别是，最近的研究表明，与太阳传感器几何形状相关的伪影可能对某些 VI 的可变性产生重大影响。然而，这种影响的大小以及对不同 VI 的影响仍然知之甚少。本研究评估了相位角变化对六个不同 VI 以及用于计算这些指数的各个光谱带的影响的比例和大小。我们的结果表明相位角和 VI 异常之间存在显着且一致的关系。该关系的缩放比例（即 VI 异常随相位角的变化率）根据光谱带和 VI 的不同而变化。各个中分辨率成像光谱仪 (MODIS) 波段的中值异常变化高达 -0.045 度−1，而中位 VI 异常变化达到 -0.047 度−1。所有关系的规模在一年中都是恒定的。亚马逊流域的平均相位角值从 10 月的约 25 度到 6 月的 41 度不等。平均而言，这种变化可能会导致某些 VI 发生高达 0.75 的变化，因此对 VI 与森林物候之间关系的解释产生重大影响。
The capacity of orbital sensors to monitor vegetation functioning and phenology in the Amazon rainforest using vegetation indices (VIs) has been broadly challenged in recent years. In particular, recent studies indicate that artifacts associated with sun-sensor geometry are likely to have major influence on the variability of some VIs. Nevertheless, the magnitude of this influence and the impacts on different VIs are still poorly understood. This study evaluates the scaling and magnitude of the phase angle variation effects on six different VIs, as well as in the individual spectral bands used for computing these indices. Our results show a significant and consistent relationship between phase angle and VI anomalies. The scaling (i.e. the change rate of VI anomaly with phase angle) of this relationship varies according to spectral bands and VIs. Median anomalies in individual Moderate Resolution Imaging Spectroradiometer (MODIS) bands showed a variation of up to −0.045 degree−1, while median VI anomaly variations reached −0.047 degree−1. The scaling of all relationships was shown to be constant throughout the year. Average phase angle values in the Amazon basin ranged from approximately 25 degrees in October to 41 degrees in June. Such variation can, on average, cause changes of up to 0.75 in some VIs, therefore having major impacts on the interpretation of the relationships between VIs and forest phenology.