Hyperspectral remote sensing inversion of SPAD values in grape leaves based on fractional differentiation
[Objective]The possibility of inverting chlorophyll content of grape leaves by hyperspectral remote sensing technology was ex-plored,and the inversion models of chlorophyll content of grape leaves were established,which provided the technical references for rapid and non-destructive estimation of the growth potential of grape.[Method]The grape leaves at maturity stage in the southwestern mountainous areas were used as the research objects,and the hyperspectral data and SPAD values of canopy leaves were obtained simultaneously,and then the ability of different fractional differention(0.0-1.4 order,step size 0.2)spectrum inverting SPAD values of grape leaves was stud-ied,and finally the multiple single-factor models based on feature bands and spectral index and multi-factor models based on successive pro-jections algorithm were constructed.[Result]The original spectral curves of grape leaves with different SPAD values were consistent as a whole,and the reflectance of grape leaves was low in the visible light region and high in the near-infrared region.The reflectance of visible light and near-infrared region was inverse proportion and proportion to SPAD value respectively.With the increase of the order,the feature bands moved from near infrared to red edge,the spectral index changed from the combination of near infrared and blue light to the combina-tion of near infrared and green light,and the correlation of the modeling variables of the single-factor models first increased and then de-creased,reaching a peak value at order 0.6.Except for order 0.6 and 0.8,the modeling variables of single-factor models of other fractional differentiation were DSI.The multi-factor models were superior to the single-factor models,and the machine learning algorithm could improve the accuracy of the traditional regression model.Among all the models,the SPA-GA-XGBoost regression model with the best accuracy was the 0.6-order model,whose modeling and verification R2 were 0.79 and 0.75,respectively,and the corresponding nRMSE were 15.54％and 14.45％.[Conclusion]The fractional differentiation transform has great potential in the inversion of SPAD values in grape leaves.Under the specific fractional-order,the spectral index is better than the feature bands,and GA-XGBoost algorithm can get better modeling effect.
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