Research on canopy water content of different forest stands based on hyperspectral analysis

ZHANG Shuifeng, ZHANG Jinchi, ZHANG Yang, ZHENG Huaibing, GU Zheyan, LIU Xin

Journal of Nanjing Forestry University (Natural Sciences Edition) ›› 2025, Vol. 49 ›› Issue (6) : 238-246.

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Journal of Nanjing Forestry University (Natural Sciences Edition) ›› 2025, Vol. 49 ›› Issue (6) : 238-246. DOI: 10.12302/j.issn.1000-2006.202411004

Research on canopy water content of different forest stands based on hyperspectral analysis

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Abstract

【Objective】Canopy fuel moisture parameters play a crucial role in assessing the physiological status of forest plants and fire risk. This study primarily explores methods for estimating vegetation canopy fuel moisture characteristic parameters using field hyperspectral data, providing a new approach for rapidly and non-destructively acquiring vegetation canopy moisture characteristic information to assess forest fuel fire risk.【Method】For canopy samples from four forest types, including Pinus massoniana, P. taeda, Camphora officinarum and Photinia serratifolia, spectral reflectance data, leaf area, fresh weight, dry weight, and leaf area index (LAI) were obtained through field sampling and laboratory experiments. Correlations between LAI and moisture characteristic variables (FMC, EWT, FMCC and EWTC) were analyzed. Partial least squares regression (PLSR) and artificial neural networks (ANN) were used to predict and estimate the moisture characteristic parameters FMCC and EWTC.【Result】The correlation between LAI and FMCC (R2=0.86) was significantly higher than that between LAI and EWTC(R2=0.04), while the correlation between LAI and EWT (R2=0.52) was slightly higher than that between LAI and FMC (R2=0.50). The estimation and validation processes for the aggregated samples of FMCC and EWTC across the four forest stand types showed that the coefficient of determination for the PLSR method was higher than that for the ANN, while the root mean square error was lower. In the estimation of EWTC and FMCC values for canopy fuel moisture characteristic variables in the four different forest types, the mean R2 value was 0.73 and the mean RMSEcv was 0.22 when using the PLSR method. P. massoniana showed the best performance (FMCC: R2=0.80, RMSECV=0.02; EWTC: R2=0.74, RMSECV=0.19). When using the ANN method, the mean R2 value was 0.76 and the mean RMSEcv was 0.20. The best performance was observed for the estimation of FMCC in P. massoniana ( R C V 2=0.91, RMSECV=0.12) and EWTC in P. taeda ( R C V 2=0.90, RMSECV=0.01) using ANN-2 as input.【Conclusion】Both EWTC and FMCC can be accurately predicted from reflectance spectra. As a mass-based variable, FMCC can achieve higher estimation accuracy than the area-based variable EWTC through both PLSR and ANN methods. Plant mass may play a more significant role than plant area in determining spectral emissivity, indicating that fuel mass factors have a greater impact on the inversion of spectral reflectance moisture characteristics, while leaf area has a relatively smaller influence. Overall, the hyperspectral data of forest stand canopy obtained through field measurements are effective in estimating fuel moisture characteristic parameters, and can provide valuable support for forest fuel fire risk prediction, forecasting, and level assessment.

Key words

canopy / hyperspectral / fuel moisture content / equivalent water thickness / north subtropical zone

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ZHANG Shuifeng , ZHANG Jinchi , ZHANG Yang , et al . Research on canopy water content of different forest stands based on hyperspectral analysis[J]. Journal of Nanjing Forestry University (Natural Sciences Edition). 2025, 49(6): 238-246 https://doi.org/10.12302/j.issn.1000-2006.202411004

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