Reviews and Syntheses: optical sampling of the flux tower footprint
Reviews and Syntheses: optical sampling of the flux tower footprint
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DOI：
10.5194/bg-12-4509-2015
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发表时间：
2015-01-01
期刊：
影响因子：
4.9
通讯作者：
Gamon, J. A.
中科院分区：
文献类型：
--
作者：
Gamon, J. A.
本综述的目的是讨论在通量塔足迹内进行光学遥感的原因和方法。回顾了近20年来通量塔场近距离遥感的基本原理和结论。这里使用的组织框架是光利用效率(LUE)模型，这既是因为它被广泛使用，也是因为它为将光学遥感与通量测量相结合提供了一个有用的理论构造。近年来出现了从气象测量到遥感等多种推动这一模型的方法，使其成为比较实验研究的便利概念框架。在LUE模型的背景下，讨论了对已建立的光学采样方法的新解释，包括光化学反射指数(PRI)和太阳诱导的叶绿素荧光(SIF)。跨时间和空间轴的多尺度分析是一个中心主题，因为这种尺度可以提供在单个生物体一级可检测到的生态生理机制与在较大尺度上出现的广泛模式之间的联系，从而能够评估紧急特性并推断通量足迹及其以外。对采样尺度的适当分析需要了解采样环境，这对于正确解释光学信号通常是必不可少的。此外，还探讨了光学类型的概念，即在时间和空间上表现出不同光学行为的植被，作为我们理解地面-大气通量控制的一种方式。作为这一假设的一个例子，提供了一个互补的归一化差异植被指数(NDVI)和生态系统间的PRI格局，LUE模型和光响应曲线提供了一个整合的框架。我的结论是，允许在通量塔网络的背景下系统地探索植物光学行为的实验方法提供了一种独特的方式来提高我们对环境约束和生态生理功能的理解。除了加强对生态系统过程的机械理解之外，遥感与通量测量的这种结合还提供了许多丰富的机会，用于扩大规模、卫星验证和告知从评估生态系统健康和生产力到量化生物圈碳封存等实际管理目标。
The purpose of this review is to address the reasons and methods for conducting optical remote sensing within the flux tower footprint. Fundamental principles and conclusions gleaned from over 2 decades of proximal remote sensing at flux tower sites are reviewed. The organizing framework used here is the light-use efficiency (LUE) model, both because it is widely used, and because it provides a useful theoretical construct for integrating optical remote sensing with flux measurements. Multiple ways of driving this model, ranging from meteorological measurements to remote sensing, have emerged in recent years, making it a convenient conceptual framework for comparative experimental studies. New interpretations of established optical sampling methods, including the photochemical reflectance index (PRI) and solar-induced chlorophyll fluorescence (SIF), are discussed within the context of the LUE model. Multiscale analysis across temporal and spatial axes is a central theme because such scaling can provide links between ecophysiological mechanisms detectable at the level of individual organisms and broad patterns emerging at larger scales, enabling evaluation of emergent properties and extrapolation to the flux footprint and beyond. Proper analysis of the sampling scale requires an awareness of sampling context that is often essential to the proper interpretation of optical signals. Additionally, the concept of optical types, vegetation exhibiting contrasting optical behavior in time and space, is explored as a way to frame our understanding of the controls on surface-atmosphere fluxes. Complementary normalized difference vegetation index (NDVI) and PRI patterns across ecosystems are offered as an example of this hypothesis, with the LUE model and light-response curve providing an integrating framework. I conclude that experimental approaches allowing systematic exploration of plant optical behavior in the context of the flux tower network provides a unique way to improve our understanding of environmental constraints and ecophysiological function. In addition to an enhanced mechanistic understanding of ecosystem processes, this integration of remote sensing with flux measurements offers many rich opportunities for upscaling, satellite validation, and informing practical management objectives ranging from assessing ecosystem health and productivity to quantifying biospheric carbon sequestration.