Estimation of direct, diffuse, and total FPARs from Landsat surface reflectance data and ground-based estimates over six FLUXNET sites
Estimation of direct, diffuse, and total FPARs from Landsat surface reflectance data and ground-based estimates over six FLUXNET sites
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根据 Landsat 表面反射率数据和六个 FLUXNET 站点的地面估计来估计直接、漫射和总 FPAR
DOI：
10.1002/2014jg002754
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发表时间：
2015-01-01
影响因子：
3.7
通讯作者：
Fang, Hongliang
中科院分区：
文献类型：
--
作者：
Li, Wenjuan;Fang, Hongliang
绿色元素吸收的光合有效辐射（PAR）是定量测定冠层吸收PAR（APAR）、总初级生产力和净初级生产力的重要气候变量。目前的卫星FPAR产品通常对应于直接照明下的黑色天空FPAR，但直接和漫射PAR的辐射传输和植被吸收过程不同。为了解决这个问题，本研究开发了一种新的方法来估计直接，漫射和总FPAR，分别从陆地卫星表面反射率数据。实地测量的直接和扩散FPAR首先来自农作物，落叶阔叶林，万年青针叶林在六个FLUXNET网站。在此基础上，利用土壤-叶片-冠层耦合辐射传输模型（SLC）模拟了直射光和漫射光条件下的地表反射率。直接，扩散，和总FPAR估计比较Landsat-5专题制图仪（TM）数据和模拟的表面反射率使用查找表的方法。Landsat估算的FPAR与实地测量的FPAR之间的差异小于0.05（10%）。弥散FPAR比直接FPAR高19.38%，而总FPAR比直接FPAR高16.07%。在晴天条件下，直接APAR比散射APAR高，但平均低估总APAR-277.72 μ mol（-1）m（-2）。这里描述的方法可以扩展到估计直接，扩散，和总FPAR从其他卫星数据和获得的FPAR变量可能有助于改善植被过程的建模。
The fraction of photosynthetically active radiation (PAR) absorbed by green elements (FPAR) is an essential climate variable in quantifying canopy absorbed PAR (APAR) and gross and net primary production. Current satellite FPAR products typically correspond to black-sky FPAR under direct illumination only, but the radiation transfer and vegetation absorption processes differ for direct and diffuse PARs. To address this, the present study developed a new approach to estimate direct, diffuse, and total FPARs, separately, from Landsat surface reflectance data. Field-measured direct and diffuse FPARs were first derived for crops, deciduous broadleaf forests, and evergreen needleleaf forests at six FLUXNET sites. Then, a coupled soil-leaf-canopy radiative transfer model (SLC) was used to simulate surface reflectance under direct and diffuse illumination conditions. Direct, diffuse, and total FPARs were estimated by comparing Landsat-5 Thematic Mapper (TM) data and simulated surface reflectances using a lookup table approach. The differences between the Landsat-estimated and the field-measured FPARs are less than 0.05 (10%). The diffuse FPAR is higher than the direct FPAR by up to 19.38%, whereas the total FPAR is larger than the direct FPAR by up to 16.07%. The direct APAR is higher than the diffuse APAR under clear-sky conditions, but underestimates the total APAR by -277.72 mu mols(-1)m(-2) on average. The approach described here can be extended to estimate direct, diffuse, and total FPARs from other satellite data and the obtained FPAR variables could be helpful to improve modeling of vegetation processes.