Leaf optical properties with explicit description of its biochemical composition: Direct and inverse problems
Leaf optical properties with explicit description of its biochemical composition: Direct and inverse problems
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DOI：
10.1016/0034-4257(95)00234-0
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发表时间：
1996-05-01
影响因子：
13.5
通讯作者：
Verdebout, J
中科院分区：
文献类型：
--
作者：
Fourty, T;Baret, F;Verdebout, J
这项研究提出了一种估算叶片生化化合物比吸收系数并用它们来预测叶片生化的方法。收集了范围广泛的叶片，包括种类和叶片状态的变化。所有的树叶都干了。生化成分的测定是新兴的经典湿化学技术，以确定木质素、纤维素、半纤维素、淀粉和蛋白质的含量。同时，用高光谱分辨率的分光光度计在800-2500 nm范围内以大约1 nm的光谱分辨率和采样间隔测量叶片的反射率和透射率。此外，还测量了通过堆叠叶片获得的无限反射率。利用叶片反射率、透射率和无限反射率数据，首先在800-2400 nm区域的选定波段上对前景叶片光学特性模型进行反演，以提供对散射特性的估计。然后，使用先前估计的散射特性，在所有波长上再次对该模型进行倒置，以估计全局吸收系数。在减去测量的结构吸水率的贡献后，通过对相应的比吸收系数进行拟合，最终使用测量的生物化学成分来解释总吸收系数。结果表明，所得到的比吸收系数是相当稳健的估计。此外，它们与每种生化化合物的已知吸收特征非常一致。评价了各生化化合物对叶片吸收特性的平均贡献率。糖、纤维素和半纤维素是促进吸收的主要化合物。结果表明，通过对叶片生物化学的明确描述，可以对干燥叶片的光学性质进行建模。在1300-2400 nm光谱域上通过模型反演获得的详细生化组成的估计显示出较差的预测性能。特别是，蛋白质含量的检索非常糟糕。研究了几种生化化合物组合的检索性能。结果表明，单位叶面积干物质总量是唯一可以准确反演的变量。讨论了这些结果可能的改进之处。
This study presents a methodology to estimate the leaf biochemical compounds specific absorption coefficients and to use them to predict leaf biochemistry. A wide range of leaves was collected including variations in species and leaf status. All the leaves were dried out. The biochemical composition was measured rising classical wet chemistry techniques to determine lignin, cellulose, hemicellulose, starch, and protein contents. Concurrently, leaf reflectance and transmittance were measured with a high spectral resolution spectrophotometer in the 800-2500 nm range with approximately 1 nm spectral resolution and sampling interval. In addition, infinite reflectance achieved by stacking leaves was also measured. The PROSPECT leaf optical properties model was first inverted over a selection of wavebands in the 800-2400 nm domain to provide estimates of the scattering characteristics using leaf reflectance, transmittance, and infinite reflectance data. Then, the model was inverted again over all the wavelengths to estimate the global absorption coefficient, using the previously estimated scattering properties. The global absorption coefficient was eventually explained using the measured biochemical composition by fitting the corresponding specific absorption coefficients after substraction of the measured contribution of the residual structural water absorption. Results show that the derived specific absorption coefficients are quite robustly estimated. Further, they are in good agreement with known absorption features of each biochemical compound. The average contribution of each biochemical compound to leaf absorption feature is also evaluated. Sugar, cellulose, and hemicellulose are the main compounds that contribute to absorption. Results demonstrate the possibility of modeling leaf optical properties of dry leaves with explicit description of leaf biochemistry. Estimates of the detailed biochemical composition obtained by model inversion over the 1300-2400 nm spectral domain show poor predictive performances. In particular, the protein content is very poorly retrieved. The retrieval performances of several combinations of the biochemical compounds are investigated. Results show that the total amount of dry matter per unit leaf area is the only variable to be accurately retrieved. Possible improvements of these results are discussed.