Abstract Many plant species have distinct optical properties between upper and lower leaf faces. These differences between faces are mainly attributed to the non-homogeneous distribution of absorbing and scattering materials within the leaf depth as well as particular surface features of both epidermises. We proposed the FASPECT model which is an evolution of the PROSPECT model to describe the differences in reflectance and transmittance between leaf faces. The upper and lower epidermis layers are characterized by distinct wavelength-independent reflectivities. Leaf mesophyll is made of a palisade and a spongy parenchyma layers using two parameters that describe the distribution of pigments and leaf structure between these two layers. As compared to the original PROSPECT model that treats the two leaf faces symmetrically, six additional parameters are required to describe the differences in leaf optical properties between the two faces. The specific absorption coefficients of chlorophyll and carotenoids have been recalibrated for the FASPECT model over a dedicated dataset. FASPECT was validated over eight datasets and compared with PROSPECT-5 and PROSPECT-D as well as with the DLM model that also accounts for the differences between the two faces. Results show that the FASPECT model simulates accurately the reflectance and transmittance of the two faces for species presenting distinct reflectance and transmittance properties between the faces. FASPECT outperforms PROSPECT-5 and PROSPECT-D, while providing generally more realistic simulations as compared to DLM. The capacity of the FASPECT model to retrieve leaf biochemical composition from reflectance and transmittance measurements was also evaluated. Marginal improvement is observed for the estimation of chlorophyll, carotenoids, and water content. Conversely, significant improvement is observed for dry matter content estimation. Conclusions are finally drawn on the interest and limits of the FASPECT model.

中文翻译：

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FASPECT：考虑上下表面差异的叶片光学特性模型

摘要 许多植物物种在上下叶面之间具有明显的光学特性。面之间的这些差异主要归因于吸收和散射材料在叶片深度内的非均匀分布以及两个表皮的特定表面特征。我们提出了 FASPECT 模型，它是 PROSPECT 模型的演变，用于描述叶面之间反射率和透射率的差异。上表皮层和下表皮层的特征在于与波长无关的不同反射率。叶肉由栅栏和海绵薄壁组织层组成，使用两个参数来描述这两层之间的色素分布和叶结构。与对称处理两个叶面的原始PROSPECT模型相比，需要六个附加参数来描述两个面之间叶片光学特性的差异。叶绿素和类胡萝卜素的特定吸收系数已在专用数据集上针对 FASPECT 模型重新校准。FASPECT 在八个数据集上进行了验证，并与 PROSPECT-5 和 PROSPECT-D 以及 DLM 模型进行了比较，该模型也解释了两个人脸之间的差异。结果表明，FASPECT 模型准确地模拟了两个面的反射率和透射率，用于在面之间呈现不同反射率和透射率特性的物种。FASPECT 的性能优于 PROSPECT-5 和 PROSPECT-D，同时与 DLM 相比，它通常提供更逼真的模拟。还评估了 FASPECT 模型从反射率和透射率测量中检索叶片生化成分的能力。观察到叶绿素、类胡萝卜素和水含量的估计有边际改善。相反，观察到干物质含量估计的显着改进。最后得出关于 FASPECT 模型的兴趣和局限性的结论。