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Global-Scale Consistency of Spaceborne Vegetation Indices, Chlorophyll Fluorescence, and Photosynthesis
Journal of Geophysical Research: Biogeosciences ( IF 3.7 ) Pub Date : 2021-06-08 , DOI: 10.1029/2020jg006136
Russell Doughty 1, 2 , Xiangming Xiao 1 , Philipp Köhler 2 , Christian Frankenberg 2, 3 , Yuanwei Qin 1 , Xiaocui Wu 1 , Shuang Ma 3 , Berrien Moore 4
Affiliation  

The new TROPOspheric Monitoring Instrument (TROPOMI) solar-induced chlorophyll fluorescence (SIF) data provides new opportunities to corroborate and improve global photosynthesis estimates. Here we report the spatiotemporal consistency between TROPOMI SIF and vegetation indices from the bidirectional reflectance distribution function (BRDF) adjusted (MCD43) and standard MODIS (MOD09) surface reflectance products, estimates of absorbed photosynthetically active radiation by chlorophyll (APARchl) derived from National Centers for Environmental Prediction Reanalysis-2 (NCEP2), MODIS MCD18, and European Reanalysis (ERA5) data, and two GPP products (GPPVPM and GPPMOD17). We find (a) non-adjusted VIs were more highly correlated with SIF at mid and high latitude than BRDF-adjusted VIs, but were less correlated in the tropics, (b) negligible differences in the correlation between SIF and non-adjusted NIRv and EVI, but BRDF-adjusted NIRv had higher correlations with SIF at mid to high latitude than BRDF-adjusted EVI but lower correlations in the tropics, (c) choice of PAR data set likely to cause substantial differences in global and regional GPP estimates and the correlation between modeled GPP and SIF, (d) SIF was more highly correlated with APARchl at high to mid latitude than EVI but more highly correlated with EVI at lower latitudes, and (e) GPPVPM is more highly correlated with SIF than GPPMOD17, except in sub-Sahara Africa. Our results highlight that spaceborne photosynthesis would likely be improved by using a non-linear response to PAR and that the fundamental differences between the vegetation indices and PAR data sets are likely to yield important differences in global and regional estimates of photosynthesis.

中文翻译:

星载植被指数、叶绿素荧光和光合作用的全球尺度一致性

新的对流层监测仪器 (TROPOMI) 太阳诱导叶绿素荧光 (SIF) 数据为证实和改进全球光合作用估计提供了新机会。在这里,我们报告了 TROPOMI SIF 和植被指数之间的时空一致性,这些指数来自双向反射分布函数 (BRDF) 调整 (MCD43) 和标准 MODIS (MOD09) 表面反射产物,叶绿素吸收的光合有效辐射估计值 (APAR chl ) 来自国家环境预测再分析中心-2 (NCEP2)、MODIS MCD18 和欧洲再分析 (ERA5) 数据,以及两个 GPP 产品(GPP VPM和 GPP MOD17))。我们发现 (a) 未调整的 VI 在中高纬度与 SIF 的相关性高于经 BRDF 调整的 VI,但在热带的相关性较低,(b) SIF 与未调整的 NIRv 之间的相关性差异可以忽略不计EVI,但经 BRDF 调整的 NIRv 在中高纬度与 SIF 的相关性高于经 BRDF 调整的 EVI,但在热带地区的相关性较低,(c) PAR 数据集的选择可能导致全球和区域 GPP 估计值和模型化 GPP 和 SIF 之间的相关性,(d) SIF在高至中纬度与 APAR chl 的相关性高于 EVI,但在低纬度与 EVI 的相关性更高,(e) GPP VPM与 SIF 的相关性高于 GPP MOD17,撒哈拉以南非洲除外。我们的结果强调,星载光合作用可能会通过对 PAR 使用非线性响应而得到改善,并且植被指数和 PAR 数据集之间的根本差异可能会导致全球和区域光合作用估计的重要差异。
更新日期:2021-06-28
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