Assessing the potential of sun-induced fluorescence and the canopy scattering coefficient to track large-scale vegetation dynamics in Amazon forests
Assessing the potential of sun-induced fluorescence and the canopy scattering coefficient to track large-scale vegetation dynamics in Amazon forests
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DOI：
10.1016/j.rse.2017.09.025
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发表时间：
2018-01-01
影响因子：
13.5
通讯作者：
Yang, Wei
中科院分区：
文献类型：
--
作者：
Koehler, Philipp;Guanter, Luis;Yang, Wei
评价了两种新的遥感植被参数：(I)太阳诱导的叶绿素荧光(SIF)，这是一种由光合作用活跃的植被发出的独特信号；(Ii)冠层散射系数(CSC)，这是一个与定向面积散射因子(DASF)一起得出的植被参数，预计将对叶片的光学性质特别敏感。在这里，我们介绍了DASF/CSC的第一个全球数据集，并研究了CSC和SIF在提供关于亚马逊森林植被季节性的有争议的补充信息方面的潜力。全球臭氧监测实验-2(GOME-2)仪器和轨道碳观测站-2(000-2)(分别在上午和中午的飞越时间)的近红外SIF的比较揭示了SIF对瞬时光合作用有效辐射(PAR)的响应。国美-2SIF的大范围季节波动高达21%(关于年最大值)，并在10月份和2月左右达到峰值，而000-2SIF的峰值在2月份。然而，如果将SIF按天桥时间和波长进行归一化，则两个时间序列的一致性很好。我们进一步研究了各向异性反射特性，发现热点效应对观测到的GOME-2 SIF值有显著影响。相反，我们的灵敏度分析表明，CSC与太阳敏感器的几何形状以及大气效应高度无关。CSC的微小年变率(3%)没有显示出明显的季节循环，而相对较高的空间标准差表明，我们研究的区域在亚马逊盆地中部具有高度的空间异质性。
Two new remote sensing vegetation parameters derived from spaceborne spectrometers and simulated with a three dimensional radiative transfer model have been evaluated in terms of their prospects and drawbacks for the monitoring of dense vegetation canopies: (i) sun-induced chlorophyll fluorescence (SIF), a unique signal emitted by photosynthetically active vegetation and (ii) the canopy scattering coefficient (CSC), a vegetation parameter derived along with the directional area scattering factor (DASF) and expected to be particularly sensitive to leaf optical properties. Here, we present the first global data set of DASF/CSC and examine the potential of CSC and SIF for providing complementary information on the controversially discussed vegetation seasonality in Amazon forests. A comparison between near-infrared SIF derived from the Global Ozone Monitoring Experiment-2 (GOME-2) instrument and the Orbiting Carbon Observatory-2 (000-2) (overpass time in the morning and noon, respectively) reveals the response of SIF to instantaneous photosynthetically active radiation (PAR). Large-scale seasonal swings of GOME-2 SIF amount up to 21% (regarding the annual maximum) and peak in October and around February, while 000-2 SIF peaks in February. However, both time series agree very well if SIF is normalized by overpass time and wavelength. We further examine anistropic reflectance characteristics with the finding that the hot spot effect significantly impacts observed GOME-2 SIF values. On the contrary, our sensitivity analysis suggests that CSC is highly independent of sun-sensor geometry as well as atmospheric effects. The slight annual variability of CSC (3%) shows no clear seasonal cycle, while a relatively high spatial standard deviation points to a high degree of spatial heterogeneity in our study domain within the central Amazon Basin.