Seasonality and drought effects of Amazonian forests observed from multi-angle satellite data
Seasonality and drought effects of Amazonian forests observed from multi-angle satellite data
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DOI：
10.1016/j.rse.2015.10.015
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发表时间：
2015-12
影响因子：
13.5
通讯作者：
Y. Moura;T. Hilker;A. Lyapustin;L. Galvão;J. R. Santos;L. Anderson;C. H. R. Sousa;E. Arai
中科院分区：
文献类型：
--
作者：
Y. Moura;T. Hilker;A. Lyapustin;L. Galvão;J. R. Santos;L. Anderson;C. H. R. Sousa;E. Arai
在亚马逊雨林的季节性和干旱一直有争议的文献中讨论，部分原因是目前的遥感技术有限的能力，以检测其对热带植被的影响。我们使用多角度遥感方法来确定植被结构的变化，从不同的方向散射（各向异性）观察到的中分辨率成像光谱仪（MODIS）与数据大气校正的多角度实施大气校正算法（MAIAC）。我们的研究结果表明，即使在密集的冠层（LAI ≤ 7 m2m − 2）中，各向异性与场（r2 = 0.70）和基于激光雷达（r2 = 0.88）的LAI估计之间也存在很强的线性关系。这使我们能够获得改进的估计植被结构的光学遥感。我们使用各向异性分析亚马逊的季节性的基础上，从热带降雨测量使命（TRMM）的旱季的发病和长度的空间明确的估计。在旱季开始时（流域约7%）观察到植被绿化增加，随后在旱季后期（流域约5%）下降（布朗宁）。植被布朗宁的异常在2005年和2010年干旱年份特别强烈（约占流域的10%）。我们发现，季节变化的幅度可以显着影响的区域差异的发病和持续时间的旱季。当假设整个亚马逊流域从6月到9月有一个固定的旱季时，季节性变化就不那么明显了。我们的研究结果与实地观测和模型结果相一致，因为它们为热带植被生长在旱季开始时增加，但在干旱期延长后下降的论点提供了更坚实的基础。这项工作中使用的多角度方法可能有助于量化亚马逊森林的耐旱性和季节性。
Seasonality and drought in Amazon rainforests have been controversially discussed in the literature, partially due to a limited ability of current remote sensing techniques to detect its impacts on tropical vegetation. We use a multi-angle remote sensing approach to determine changes in vegetation structure from differences in directional scattering (anisotropy) observed by the Moderate Resolution Imaging Spectroradiometer (MODIS) with data atmospherically corrected by the Multi-Angle Implementation Atmospheric Correction Algorithm (MAIAC). Our results show a strong linear relationship between anisotropy and field (r2= 0.70) and LiDAR (r2= 0.88) based estimates of LAI even in dense canopies (LAI ≤ 7 m2m− 2). This allowed us to obtain improved estimates of vegetation structure from optical remote sensing. We used anisotropy to analyze Amazon seasonality based on spatially explicit estimates of onset and length of dry season obtained from the Tropical Rainfall Measurement Mission (TRMM). An increase in vegetation greening was observed during the beginning of dry season (across ~ 7% of the basin), which was followed by a decline (browning) later during the dry season (across ~ 5% of the basin). Anomalies in vegetation browning were particularly strong during the 2005 and 2010 drought years (~ 10% of the basin). We show that the magnitude of seasonal changes can be significantly affected by regional differences in onset and duration of the dry season. Seasonal changes were much less pronounced when assuming a fixed dry season from June through September across the Amazon Basin. Our findings reconcile remote sensing studies with field based observations and model results as they provide a sounder basis for the argument that tropical vegetation growth increases during the beginning of the dry season, but declines after extended drought periods. The multi-angle approach used in this work may help quantify drought tolerance and seasonality in the Amazonian forests.