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Hyperspectral Inversion of Phragmites Communis Carbon, Nitrogen, and Phosphorus Stoichiometry Using Three Models

by Lijuan Cui 1,2, Zhiguo Dou 1,2, Zhijun Liu 1,2, Xueyan Zuo 1,2, Yinru Lei 1,2, Jing Li 1,2, Xinsheng Zhao 1,2, Xiajie Zhai 1,2, Xu Pan 1,2 and Wei Li 1,2,*
1
Institute of Wetland Research, Chinese Academy of Forestry, Beijing Key Laboratory of Wetland Services and Restoration, Beijing 100091, China
2
Beijing Hanshiqiao National Wetland Ecosystem Research Station, Beijing 101399, China
*
Author to whom correspondence should be addressed.
Remote Sens. 2020, 12(12), 1998; https://doi.org/10.3390/rs12121998
Received: 25 May 2020 / Revised: 19 June 2020 / Accepted: 21 June 2020 / Published: 22 June 2020
(This article belongs to the Section Remote Sensing in Agriculture and Vegetation)
Studying the stoichiometric characteristics of plant C, N, and P is an effective way of understanding plant survival and adaptation strategies. In this study, 60 fixed plots and 120 random plots were set up in a reed-swamp wetland, and the canopy spectral data were collected in order to analyze the stoichiometric characteristics of C, N, and P across all four seasons. Three machine models (random forest, RF; support vector machine, SVM; and back propagation neural network, BPNN) were used to study the stoichiometric characteristics of these elements via hyperspectral inversion. The results showed significant differences in these characteristics across seasons. The RF model had the highest prediction accuracy concerning the stoichiometric properties of C, N, and P. The R2 of the four-season models was greater than 0.88, 0.95, 0.97, and 0.92, respectively. According to the root mean square error (RMSE) results, the model error of total C (TC) inversion is the smallest, and that of C/N inversion is the largest. The SVM yielded poor predictive results for the stoichiometric properties of C, N, and P. The R2 of the four-season models was greater than 0.82, 0.81, 0.81, and 0.70, respectively. According to RMSE results, the model error of TC inversion is the smallest, and that of C/P inversion is the largest. The BPNN yielded high stoichiometric prediction accuracy. The R2 of the four-season models was greater than 0.87, 0.96, 0.84, and 0.90, respectively. According to RMSE results, the model error of TC inversion is the smallest, and that of C/P inversion is the largest. The accuracy and stability of the results were verified by comprehensive analysis. The RF model showed the greatest prediction stability, followed by the BPNN and then the SVM models. The results indicate that the accuracy and stability of the RF model were the highest. Hyperspectral data can be used to accurately invert the stoichiometric characteristics of C, N, and P in wetland plants. It provides a scientific basis for the long-term dynamic monitoring of plant stoichiometry through hyperspectral data in the future. View Full-Text
Keywords: wetland plant; stoichiometric characteristics; random forest; support vector machine; BP neural network wetland plant; stoichiometric characteristics; random forest; support vector machine; BP neural network
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MDPI and ACS Style

Cui, L.; Dou, Z.; Liu, Z.; Zuo, X.; Lei, Y.; Li, J.; Zhao, X.; Zhai, X.; Pan, X.; Li, W. Hyperspectral Inversion of Phragmites Communis Carbon, Nitrogen, and Phosphorus Stoichiometry Using Three Models. Remote Sens. 2020, 12, 1998.

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