Estimating leaf chlorophyll content by laser-induced fluorescence technology at different viewing zenith angles

Leaf chlorophyll content (LCC) is a key indicator of a plant's physiological status. Fast and non-destructive monitoring of chlorophyll content in plants through remote sensing is very important for accurate diagnosis and assessment of plant growth. Through the use of laser-induced fluorescence (LIF) technology, this study aims to compare the predictive ability of different single fluorescence characteristic and fluorescence characteristic combinations at various viewing zenith angles (VZAs) combined with multivariate analysis algorithms, such as principal component analysis (PCA) and support vector machine (SVM), for estimating the LCC of plants. The SVM models of LCC estimation were proposed, and fluorescence characteristics-fluorescence peak (FP), fluorescence ratio (FR), PCA, and first-derivative (FD) parameter-and fluorescence characteristic combinations (FP + FR, FP + FD, FR + FD, FP + FR + FD) were used as input variables for the models. Experimental results demonstrated that the effect of single fluorescence characteristics on the predictive performance of SVM models was: FR > FD > FP > PCA. Compared with other models, 0 degrees SVM was the optimal model for estimating LCC by higher R-2. The fluorescence spectra and FD spectra observed at 0 degrees and 30 degrees were superior to those observed at 15 degrees, 45 degrees, and 60 degrees. Thus, appropriate VZA must also be considered, as it can improve the accuracy of LCC monitoring. In addition, compared with single fluorescence characteristic, the FP + FR + FD was the optimal combination of fluorescence characteristics to estimate the LCC for the SVM model by higher R-2, indicating better predictive performance. The experimental results show that the combination of LIF technology and multivariate analysis can be effectively used for LCC monitoring and has broad development prospects. (C) 2020 Optical Society of America