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Estimation of direct, diffuse, and total FPARs from Landsat surface reflectance data and ground-based estimates over six FLUXNET sites

机译：Estimation of direct, diffuse, and total FpaRs from Landsat surface reflectance data and ground-based estimates over six FLUXNET sites

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摘要

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.
机译：绿色元素（FPAR）吸收的光合有效辐射（PAR）的比例是量化冠层吸收PAR（APAR）以及总初级和净初级生产时必不可少的气候变量。当前的卫星FPAR产品通常仅对应于直接照射下的黑色FPAR，但是对于直接和漫射PAR，其辐射传输和植被吸收过程有所不同。为了解决这个问题，本研究开发了一种新方法，可以分别从Landsat表面反射率数据估算直接，漫射和总FPAR。在六个FLUXNET站点上，首先针对农作物，落叶阔叶林和常绿针叶林得出了现场测量的直接和扩散FPAR。然后，使用耦合的土壤-叶-冠层辐射传递模型（SLC）模拟在直接和漫射光照条件下的表面反射率。通过使用查找表方法比较Landsat-5 Thematic Mapper（TM）数据和模拟的表面反射率，可以估算直接，漫射和总FPAR。 Landsat估算的FPAR与现场测量的FPAR之间的差异小于0.05（10％）。漫射FPAR比直接FPAR高出19.38％，而总FPAR比直接FPAR高出高达16.07％。在晴空条件下，直接APAR高于扩散APAR，但平均APAR平均低-277.72 mu mols（-1）m（-2）。可以将此处描述的方法扩展为从其他卫星数据估计直接FPAR，扩散FPAR和总FPAR，并且获得的FPAR变量可能有助于改善植被过程的建模。

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    Li W. J.; Fang, H. L.;

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  • 年度 2015
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  • 正文语种 英语
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