Although remote sensing (RS) of solar-induced chlorophyll fluorescence (SIF) is increasingly used as a valuable source of information about vegetation photosynthetic activity, the RS SIF observations are significantly influenced by canopy-specific structural features (i.e., canopy architecture including leaf area index and presence of woody components), atmospheric conditions during their acquisition (e.g., proportion of direct and diffuse irradiance) and observational geometric configurations (e.g., sun and viewing directions). Radiative transfer (RT) models have the potential to provide a better understanding of the canopy structural effects on the SIF emission and RS signals. Here, we used the DART model to assess the daily influence, from morning to evening, of forest 3D architecture on SIF nadir radiance, emission, escape factor and nadir yield of eight 100 m × 100 m forest study plots established in a temperate deciduous forest of the Smithsonian Environmental Research Center (Edgewater, MD, USA). The 3D architecture of each plot was derived from airborne LiDAR. DART simulations of these 3D forest plots and their 1D (i.e., vertical profile of sun-adapted and shade-adapted leaves) and 0D (i.e., homogeneous layer of sun-adapted leaves above an homogeneous layer of shade-adapted leaves) abstractions were compared to assess the relative errors (ε_1D−3D and ε_0D−3D) associated with horizontal and vertical structural heterogeneity, respectively. Forest 3D structure, especially horizontal heterogeneity, had a great influence on forest nadir SIF radiance, resulting in ε_1D−3D up to 55% at 8:00 and 18:00 (i.e., for oblique sun directions). The key indicators of this impact, in the descending order of importance, were the SIF escape factor (ε_1D−3D up to 40%), the attenuation of incident photosynthetically active radiation (ε_1D−3D less than 5%), and the SIF emission yield (ε_1D−3D less than 2%). The influence of forest architecture on the nadir SIF escape factor and SIF yield (ε_1D−3D up to 40%) varied over time, with differences in forest stand structure, and per spectral domain, being always larger between 640 and 700 nm than between 700 and 850 nm. In addition, woody elements demonstrated a large influence on forest SIF radiance due to their “shading” effect (ε up to 17%) and their “blocking” effect (ε ≈ 10%), both of them higher for far-red than for red SIF. These results underline the importance of 3D forest canopy architecture, especially 2D heterogeneity, and inclusion of woody elements in RT modeling used for interpretation of the RS SIF signal, and subsequently for the estimation of gross primary production and detection of vegetation stress.

尽管太阳诱导叶绿素荧光 (SIF) 的遥感 (RS) 越来越多地用作有关植被光合活动的宝贵信息来源，但 RS SIF 观测受到冠层特定结构特征（即，包括叶面积在内的冠层结构）的显着影响。指数和木质成分的存在），获取期间的大气条件（例如，直接和漫射辐照度的比例）和观测几何配置（例如、太阳和观看方向）。辐射传输 (RT) 模型有可能更好地了解冠层结构对 SIF 发射和 RS 信号的影响。在这里，我们使用 DART 模型来评估森林 3D 建筑从早到晚对温带落叶林中建立的八个 100 m × 100 m 森林研究地块的 SIF 最低点辐射、发射、逃逸因子和最低点产量的影响史密森尼环境研究中心 (Edgewater, MD, USA)。每个地块的 3D 架构都来自机载 LiDAR。这些 3D 森林图及其 1D（即适应阳光和适应阴凉的叶子的垂直剖面）和 0D（即，均质适应日光叶片层之上的均质适应遮荫叶片层）抽象被比较以评估分别与水平和垂直结构异质性相关的相对误差（ε _1D-3D和ε _0D-3D）。森林 3D 结构，尤其是水平异质性，对森林天底 SIF 辐射有很大影响，导致8:00 和 18:00（即斜太阳方向）的ε _1D−3D高达 55% 。这种影响的关键指标，按重要性降序排列，是 SIF 逃逸因子（ε _1D−3D高达 40%）、入射光合有效辐射的衰减（ε _1D−3D小于 5%）和 SIF 发射率（ε _1D−3D小于 2%）。森林结构对最低点 SIF 逃逸因子和 SIF 产量的影响 ( ε _1D−3D高达 40%）随时间变化，林分结构和每个光谱域的差异在 640 和 700 纳米之间总是大于 700 和 850 纳米之间。此外，木质元素由于其“遮蔽”效应（ε 高达 17%）和它们的“阻挡”效应（ε ≈ 10%）对森林 SIF 辐射有很大影响，两者对远红光的影响都高于对远红光的影响。红色 SIF。这些结果强调了 3D 森林冠层结构的重要性，尤其是 2D 异质性，并在 RT 建模中包含木质元素，用于解释 RS SIF 信号，随后用于估计总初级生产和检测植被压力。