Solar-induced chlorophyll fluorescence (SIF) provides a means to estimate plant photosynthetic activities and to detect early plant stress. The accurate quantification of SIF emitted by various scene components (tree crowns and background) may significantly improve the interpretation of top-of-canopy SIF (SIF_toc) measurements made over heterogeneous canopies. To do so, a three-dimensional (3-D) canopy SIF model (FluorFLiES) was introduced by coupling the excitation-fluorescence matrices (EF-matrices) with a 3-D Monte Carlo canopy radiative transfer model (Forest Light Environmental Simulator, FLiES). A tool was developed to construct forest canopy scene components from LiDAR data and enable their simulated contributions in structurally complex forest scenes. FluorFLiES is able to quantify SIF measurements with good accuracy at both half-hourly (R² = 0.72, RMSE = 0.26 mW m⁻² sr⁻¹ nm⁻¹) and daily (R² = 0.83, RMSE = 0.19 mW m⁻² sr⁻¹ nm⁻¹) scales. This study showed that non-photosynthetic elements in tree crowns, the fractional vegetation cover (FVC), and the background (including understory vegetation and soils) had a strong influence on SIF_toc intensity. Non-photosynthetic woody material suppressed the propagation of photons within crowns, thereby decreasing SIF_toc by around 10%. The canopy background made a significant contribution to SIF_toc in the NIR region by scattering downward SIF photons upward, and the background contribution increased rapidly with decreasing FVC: SIF_toc increased two-fold from 0.15 to 0.3 mW m⁻² sr⁻¹ nm⁻¹ when ground leaf area index increased from 0.5 to 1.5 m²/m². The results showed that the fluorescence escape ratio (f_esc), a key variable relating observed SIF_toc to photosynthesis CO₂ rate, contained a contribution from the background with a magnitude of 42%, even for relatively dense forest canopies. Assuming f_esc simulated by the FluorFLiES model as a reference value, this study demonstrated that the current reflectance-based approach may cause large uncertainties (29%) when understory vegetation and/or FVC changes, largely due to neglecting the contribution of background elements. This study highlights the need to separate scene components and to consider multiple scattering within/among these components in interpreting the SIF_toc signal when working with heterogeneous ecosystems. The source code of FluorFLiES is available for further benchmarking.

太阳诱导的叶绿素荧光 (SIF) 提供了一种估计植物光合活性和检测植物早期胁迫的方法。各种场景成分（树冠和背景）发出的 SIF 的准确量化可以显着改善树冠顶部 SIF (SIF _toc) 在异质檐篷上进行的测量。为此，通过将激发-荧光矩阵（EF-矩阵）与 3-D 蒙特卡罗树冠辐射传递模型（森林光环境模拟器，蝇）。开发了一种工具，用于从 LiDAR 数据构建森林冠层场景组件，并使其能够在结构复杂的森林场景中进行模拟贡献。FluorFLiES 能够在半小时 ( R ²  = 0.72, RMSE = 0.26 mW m ^-2 sr ^-1 nm ^-1 ) 和每天 ( R ²  = 0.83, RMSE = 0.19 mW m ^-2 sr ^-1纳米^-1 ) 尺度。本研究表明，树冠中的非光合元素、植被覆盖率 (FVC) 和背景（包括林下植被和土壤）对 SIF _toc强度有很大影响。非光合木质材料抑制了光子在树冠内的传播，从而将 SIF _toc降低了约 10%。_{树冠背景通过向上散射向下 SIF 光子对 NIR 区域中的 SIF toc}做出了显着贡献，并且背景贡献随着 FVC 的降低而迅速增加：SIF _toc从 0.15 增加到 0.3 mW m ^-2 sr ^-1 nm ^{- 1}当地面叶面积指数从0.5增加到1.5 m ² /m ²时。结果表明，荧光逃逸率 ( f _esc ) 是观察到的 SIF _toc与光合作用 CO ₂速率相关的关键变量，即使对于相对密集的森林冠层，也包含 42% 的背景贡献。假设f _esc以 FluorFLiES 模型作为参考值进行模拟，本研究表明，当前基于反射率的方法在林下植被和/或 FVC 变化时可能会导致较大的不确定性（29%），这主要是由于忽略了背景元素的贡献。这项研究强调了在使用异构生态系统时，在解释 SIF _toc信号时需要分离场景组件并考虑这些组件内部/之间的多重散射。FluorFLiES 的源代码可用于进一步的基准测试。