The escape probability of Solar-induced chlorophyll fluorescence (SIF) can be remotely estimated using reflectance measurements based on spectral invariants theory. This can then be used to correct the effects of canopy structure on canopy-leaving SIF. However, the feasibility of these estimation methods is untested in heterogeneous vegetation such as the discontinuous forest canopy layer under evaluation here. In this study, the Discrete Anisotropic Radiative Transfer (DART) model is used to simulate canopy-leaving SIF, canopy total emitted SIF, canopy interceptance, and the fraction of absorbed photosynthetically active radiation (fAPAR) in order to evaluate the estimation methods of SIF escape probability in discontinuous forest canopies. Our simulation results show that the normalized difference vegetation index (NDVI) can be used to partly eliminate the effects of background reflectance on the estimation of SIF escape probability in most cases, but fails to produce accurate estimations if the background is partly or totally covered by vegetation. We also found that SIF escape probabilities estimated at a high solar zenith angle have better estimation accuracy than those estimated at a lower solar zenith angle. Our results show that additional errors will be introduced to the estimation of SIF escape probability with the use of satellite products, especially when the product of leaf area index (LAI) and clumping index (CI) was underestimated. In other results, fAPAR has comparable estimation accuracy of SIF escape probability when compared to canopy interceptance. Additionally, fAPAR for the entire canopy has better estimation accuracy of SIF escape probability than fPAR for leaf only in sparse forest canopies. These results help us to better understand the current estimation results of SIF escape probability based on spectral invariants theory, and to improve its estimation accuracy in discontinuous forest canopies.

中文翻译：

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不连续林冠层中远红太阳诱导的叶绿素荧光逃逸概率估计方法的基于仿真的评估

可以使用基于光谱不变性理论的反射率测量值来远程估算太阳诱发的叶绿素荧光（SIF）的逸出概率。然后可以将其用于纠正冠层结构对离开冠层的SIF的影响。但是，这些评估方法的可行性尚未在非均质植被（例如，正在评估的不连续森林冠层）中进行测试。在这项研究中，离散各向异性辐射转移（DART）模型用于模拟离开树冠的SIF，冠层总发射SIF，冠层截距和吸收的光合有效辐射的比例（fAPAR），以评估SIF的估算方法不连续林冠层的逃逸概率。我们的仿真结果表明，在大多数情况下，归一化植被指数（NDVI）可用于部分消除背景反射率对SIF逃逸概率估计的影响，但如果背景被部分或全部覆盖，则无法产生准确的估计植被。我们还发现，以较高的太阳天顶角估算的SIF逃逸概率比以较低的太阳天顶角估算的SIF逃逸概率更好。我们的结果表明，使用卫星产品时，SIF逃逸概率的估计将引入其他误差，尤其是当叶面积指数（LAI）和聚集指数（CI）的乘积被低估时。在其他结果中，与树冠拦截相比，fAPAR具有相当的SIF逃逸概率估计准确性。另外，相对于仅在稀疏森林冠层的叶子的fPAR而言，整个冠层的fAPAR的SIF逃逸概率估计精度更高。这些结果有助于我们更好地了解基于谱不变性理论的SIF逃逸概率的当前估计结果，并提高其在不连续森林冠层中的估计准确性。