Inversion of Chlorophyll Content and SPAD Value of Vegetable Leaves Based on PROSPECT Model
LEI Xiang-xiang1, ZHAO Jing1, LIU Hou-cheng2, ZHANG Ji-ye2, LIANG Wen-yue1, TIAN Jia-ling2, LONG Yong-bing1*
1. School of Electronic Engineering, South China Agricultural University, Guangzhou 510642, China
2. School of Horticulture, South China Agricultural University, Guangzhou 510642, China
Abstract：Chlorophyll content is an important indicator for evaluation of plant nutrition and the occurrence of the pests. The traditional spectrophotometry causes damage to plant leaves and can not be used to obtain the chlorophyll content in a real time, fast and non-destructive way. The chlorophyll meter is recently developed to measure the relative content of chlorophyll (referred to as SPAD value). But this method cannot be used to quantitatively obtain the actual content. The optical radiation transmission model PROSPECT can quantitatively describe the effects of leaf pigment, moisture and structural parameters on the reflection spectrum of the leaves with careful consideration of the biophysics, chemistry and the process of energy transfer in the leaves. In the paper, therefore, this model is used to simultaneously inverse the chlorophyll content and SPAD value of vegetable leaves, and obtain the chlorophyll content of plant leaves real-timely, quickly, non-destructively and quantitatively. First, the reflection spectra of the leaves for three vegetables were measured several times, and the SPAD values of these leaves were measured with a chlorophyll meter. Then, the spectral data were preprocessed to obtain the average reflectance spectrum. Second, the averaged reflectance spectra were fitted by the PROSPECT model with the Euclidean distance as the evaluation function. The maximum distance of the three vegetables in the fitting process was 0.008 9, the minimum was 0.006 4, and the average was 0.007 5. Such a low Euclidean distance indicated that the model could well fit the reflectance spectrum of vegetable leaves. Thirdly, according to the fitting results, the chlorophyll content and the transmittance spectrum were inversed, and the inversed SPAD value of the leaves was calculated with the light transmittance of the leaves at 940 and 650 nm as input parameters. Fourth, this paper established a relationship model between the inversed chlorophyll content, the inversed SPAD value and the measured SPAD value. Two main results were obtained: (1) the chlorophyll content obtained by the model has a good linear relationship with the measured SPAD value and the relationship model is y=1.463 3x+16.374 3. The correlation coefficient between them is 0.927 1. The coefficient of determination of the model is 0.862 and the root mean square error is 2.11. (2) A good linear relationship of y=0.986 9x-0.668 3 is obtained for the inversed SPAD value and the measured SPAD value. The correlation coefficient between them is 0.845 1.The coefficient of determination of the model is 0.714 3 and the root mean square error is 3.380 2. The research shows that the PROSPECT model can be used to obtain the chlorophyll content and SPAD value of vegetable leaves nondestructively and quantitatively with the measured reflectance spectrum of plant leaves as input parameters. This method can be extended to other plants for chlorophyll measurement and real-time monitoring and can provide reliable data support for variable rate fertilization and precision planting. The results presented in this paper can be applied to monitor the growth of the vegetables nondestructively.
雷祥祥，赵 静，刘厚诚，张继业，梁文跃，田佳灵，龙拥兵. 基于PROSPECT模型的蔬菜叶片叶绿素含量和SPAD值反演[J]. 光谱学与光谱分析, 2019, 39(10): 3256-3260.
LEI Xiang-xiang, ZHAO Jing, LIU Hou-cheng, ZHANG Ji-ye, LIANG Wen-yue, TIAN Jia-ling, LONG Yong-bing. Inversion of Chlorophyll Content and SPAD Value of Vegetable Leaves Based on PROSPECT Model. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2019, 39(10): 3256-3260.
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