Influence of the canopy BRDF characteristics and illumination conditions on the retrieval of solar-induced chlorophyll fluorescence
Influence of the canopy BRDF characteristics and illumination conditions on the retrieval of solar-induced chlorophyll fluorescence
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冠层BRDF特性和光照条件对日光诱导叶绿素荧光反演的影响
DOI：
10.1080/01431161.2017.1404165
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发表时间：
2018-01-01
影响因子：
3.4
通讯作者：
Liu, Liangyun
中科院分区：
文献类型：
--
作者：
Liu, Xinjie;Liu, Liangyun
摘要夫琅和费线分辨(FLD)原理是反演太阳诱导的叶绿素荧光(SIF)的主要方法。FLD原理的基本假设是，没有填充SIF的表观反射光谱在吸收带区域是平滑的。但实际上，这种假设是不成立的，因为在地面SIF反演中，直接辐射和漫射辐射对氧吸收带的非线性贡献导致了所谓的“直接辐射填充”效应。在这项研究中，我们首先分析了直接辐射填充效应对氧吸收带的物理机制，根据模拟数据集，发现氧-A(O2-A)带的直接辐射填充效应在SIF反演中的偏差小于20%。其次，我们建立了一个简单的直接辐射填充效应修正模型。我们发现O2-A波段的直接辐射填充效应与直接辐射和漫射辐射的反射率之差成正比，比例系数与漫射比呈二次函数关系，决定系数(R2)为0.97。最后，利用模拟数据集和现场数据集对模型进行了验证。验证结果表明，利用本文提出的模型可以有效地校正直接辐射填充效应在SIF反演中产生的偏差。因此，这项研究提供了一种可能的方法，利用对特定目标的直接和漫射辐射的双向反射分布函数特征的先验知识来估计和校正直接辐射填充效应。
ABSTRACT The Fraunhofer line discrimination (FLD) principle is the main approach used for the retrieval of solar-induced chlorophyll fluorescence (SIF). The basic assumption of the FLD principle is that the apparent reflectance spectra without SIF in-filling are smooth in the region of the absorption bands. However, in fact, this assumption is not valid due to the so-called ‘direct radiation in-filling’ effect caused by the nonlinear contribution of direct and diffuse radiation at the oxygen absorption bands, which are widely used for ground-based SIF retrieval. In this study, we first analysed the physical mechanism of the direct radiation in-filling effect on the oxygen absorption bands and found that the bias in the SIF retrieval caused by the direct radiation in-filling effect at the oxygen-A (O2-A) band was less than 20% based on the use of a simulated data set. Second, we established a simple correction model of the direct radiation in-filling effect. We found that the direct radiation in-filling effect at the O2-A band was directly proportional to the difference between the reflectance of the direct and diffuse radiation, and that the coefficient of proportionality was well correlated with the diffuse-to-global radiation ratio in the form of a quadratic function, with a coefficient of determination (R2) of 0.97. Finally, the model was validated using both simulated and field data sets. The validation results show that the bias in the SIF retrieval caused by the direct radiation in-filling effect can be efficiently corrected using the model proposed in this article. This study thus provides a possible approach to estimating and correcting for the direct radiation-infilling effect using prior knowledge of the bidirectional reflectance distribution function characteristics of direct and diffuse radiation for specific targets.