The intensity and spectral properties of solar-induced chlorophyll fluorescence (SIF) carry valuable information on plant photosynthesis and productivity, but are also influenced by leaf and canopy structure. Physically based models provide a quantitative means to investigate how SIF intensity and spectra propagate and scale from the photosystem to the leaf and to the canopy levels. However, the validation of canopy SIF models is limited by the lack of methods that combine direct, independent, and complementary measurements of the full fluorescence spectrum at the leaf and canopy levels. Here, we propose a novel validation approach that combines in situ measurements of leaf and canopy fluorescence spectra. The approach is demonstrated with measurements in a rice crop at two contrasting stages of canopy development. We measured leaf reflectance, transmittance, and fluorescence spectra in situ, and subsequently inverted leaf structural and biochemical parameters and determined the leaf fluorescence quantum efficiency (FQE) using the Fluspect-Cx model. Two FQE inversion methods (Inversion-IIA and Inversion-IIB) were tested for the forward simulation of leaf fluorescence spectra. Leaf fluorescence spectra were then scaled up to the canopy level using 1D, 2D, and 3D radiative transfer schemes (SCOPE, mSCOPE, and DART), and compared with the direct canopy fluorescence spectral observations measured under red, green, blue, and white illumination. The validation results demonstrate that accounting for 3D canopy structure, as in the DART model, is critical to successfully scale the fluorescence spectrum from the leaf to the canopy level, whereas 1D SCOPE or even 2D mSCOPE were unable to fully reproduce the canopy fluorescence spectra. The results also demonstrate that the Inversion-IIB method matches relatively well the measurements with mean relative absolute errors (MRAE) of 20 %, 37 %, and 43 % versus Inversion-IIA with mean relative absolute errors (MRAE) of 62 %, 100 %, and 108 % for DART, mSCOPE, and SCOPE, respectively. We suggest that our validation approach is transferable to other plant species and canopy geometries, providing a means to standardize and evaluate the performance of canopy SIF models and improve our understanding of canopy SIF observations.

中文翻译：

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一种使用全发射光谱验证冠层叶绿素荧光辐射转移模型的原位方法


太阳诱导叶绿素荧光 （SIF） 的强度和光谱特性为植物光合作用和生产力提供了有价值的信息，但也受到叶片和树冠结构的影响。基于物理的模型提供了一种定量方法来研究 SIF 强度和光谱如何从光系统传播和缩放到叶子和树冠水平。然而，冠层 SIF 模型的验证受到缺乏在叶片和冠层水平上结合直接、独立和互补测量全荧光光谱的方法的限制。在这里，我们提出了一种新的验证方法，该方法结合了叶片和冠层荧光光谱的原位测量。该方法通过在树冠发育的两个相反阶段对水稻作物的测量来证明。我们原位测量了叶片反射率、透射率和荧光光谱，随后倒置了叶片结构和生化参数，并使用 Fluspect-Cx 模型测定了叶片荧光量子效率 （FQE）。测试了两种 FQE 反演方法 （Inversion-IIA 和 Inversion-IIB） 用于叶片荧光光谱的正向模拟。然后使用 1D、2D 和 3D 辐射传输方案（SCOPE、mSCOPE 和 DART）将叶荧光光谱放大到冠层水平，并与在红色、绿色、蓝色和白色照明下测量的直接冠层荧光光谱观测进行比较。验证结果表明，考虑 3D 冠层结构（如 DART 模型）对于成功将荧光光谱从叶片扩展到冠层水平至关重要，而 1D SCOPE 甚至 2D mSCOPE 无法完全再现冠层荧光光谱。 结果还表明，反演 IIB 方法与测量值匹配相对较好，平均相对绝对误差 （MRAE） 为 20 %、37 % 和 43 %，而反演 IIA 的平均相对绝对误差 （MRAE） 分别为 62 %、100 % 和 108 %，DART、mSCOPE 和 SCOPE 分别为 108 %。我们建议我们的验证方法可以转移到其他植物物种和树冠几何形状，提供了一种标准化和评估树冠 SIF 模型性能的方法，并提高了我们对树冠 SIF 观测的理解。