The global distribution of leaf chlorophyll content
The global distribution of leaf chlorophyll content
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DOI：
10.1016/j.rse.2019.111479
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发表时间：
2020-01-01
影响因子：
13.5
通讯作者：
Bonal, D.
中科院分区：
文献类型：
--
作者：
Croft, H.;Chen, J. M.;Bonal, D.
叶子叶绿素对于生物圈和大气之间的碳、水和能量交换以及陆地生态系统的运作至关重要。本文提出了全球范围内陆地叶子叶绿素含量 (Chl(Leaf)) 的第一个空间连续视图。 Chl(Leaf) 的每周地图是使用两阶段基于物理的辐射传输建模方法根据 ENVISAT MERIS 全分辨率 (300 m) 卫星数据生成的。首先，叶级反射率是分别使用木本和非木本植被的 4 尺度和 SAIL 冠层辐射传输模型从冠层顶部卫星反射率观测得出的。其次，将建模的叶级反射率输入到 PROSPECT 叶级辐射传输模型中以导出 Chl(Leaf)。 Chl(Leaf) 检索算法使用来自 28 个田间地点的 248 个样本测量的 Chi(Leaf) 数据进行了验证，涵盖六种植物功能类型 (PFT)。模拟结果显示与实地测量有很强的相关性，特别是对于落叶阔叶林（R-2 = 0.67；RMSE = 9.25 mu g cm(-2)；p < 0.001）、农田（R-2 = 0.41；RMSE = 13.18 mu g cm(-2)；p < 0.001）和常绿针叶林（R-2 = 0.47；p < 0.001）。 RMSE = 10.63 μg cm(-2)；p < 0.001)。当所有 PFT 的建模结果一起考虑时，与测量的 Chl(Leaf ) 的总体关系仍然良好 (R-2 = 0.47，RMSE = 10.79 mu g cm(-2)；p < 0.001）。这一结果改进了测量的 Chl(Leaf) 与常用的叶绿素敏感光谱植被指数之间的关系； MERIS 陆地叶绿素指数 (MTCI；R-2 = 0.27，p < 0.001)。全球地图显示叶绿素存在较大的时空变化，其中常绿阔叶林的叶片叶绿素值最高，全球年中值为54.4 mu g cm(-2)。独特的季节性叶绿素物候也是可见的，特别是在落叶植物中，与发芽和作物生长以及叶子衰老有关。预计这一全球 Chl(Leaf) 产品将朝着在陆地水、能源和碳循环建模中明确考虑叶级生物化学迈出重要一步。
Leaf chlorophyll is central to the exchange of carbon, water and energy between the biosphere and the atmosphere, and to the functioning of terrestrial ecosystems. This paper presents the first spatially-continuous view of terrestrial leaf chlorophyll content (Chl(Leaf)) at the global scale. Weekly maps of Chl(Leaf) were produced from ENVISAT MERIS full resolution (300 m) satellite data using a two-stage physically-based radiative transfer modelling approach. Firstly, leaf-level reflectance was derived from top-of-canopy satellite reflectance observations using 4-Scale and SAIL canopy radiative transfer models for woody and non-woody vegetation, respectively. Secondly, the modelled leaf-level reflectance was input into the PROSPECT leaf-level radiative transfer model to derive Chl(Leaf). The Chl(Leaf) retrieval algorithm was validated using measured Chi(Leaf) data from 248 sample measurements at 28 field locations, and covering six plant functional types (PFTs). Modelled results show strong relationships with field measurements, particularly for deciduous broadleaf forests (R-2 = 0.67; RMSE = 9.25 mu g cm(-2); p < 0.001), croplands (R-2 = 0.41; RMSE = 13.18 mu g cm(-2); p < 0.001) and evergreen needleleaf forests (R-2 = 0.47; RMSE = 10.63 mu g cm(-2); p < 0.001). When the modelled results from all PFTs were considered together, the overall relationship with measured Chl(Leaf )remained good (R-2 = 0.47, RMSE = 10.79 mu g cm(-2); p < 0.001). This result is an improvement on the relationship between measured Chl(Leaf) and a commonly used chlorophyll-sensitive spectral vegetation index; the MERIS Terrestrial Chlorophyll Index (MTCI; R-2 = 0.27, p < 0.001). The global maps show large temporal and spatial variability in Chl(Leaf), with evergreen broadleaf forests presenting the highest leaf chlorophyll values, with global annual median values of 54.4 mu g cm(-2). Distinct seasonal Chl(Leaf) phenologies are also visible, particularly in deciduous plant forms, associated with budburst and crop growth, and leaf senescence. It is anticipated that this global Chl(Leaf) product will make an important step towards the explicit consideration of leaf-level biochemistry in terrestrial water, energy and carbon cycle modelling.