Hyperspectral Analysis and Regression Modeling of SPAD Measurements in Leaves of Three Mangrove Species

Mangroves have important roles in regulating climate change, and in reducing the impact of wind and waves. Analysis of the chlorophyll content of mangroves is important for monitoring their health, and their conservation and management. Thus, this study aimed to apply four regression models, eXtreme Gradient Boosting (XGBoost), Random Forest (RF), Partial Least Squares (PLS) and Adaptive Boosting (AdaBoost), to study the inversion of Soil Plant Analysis Development (SPAD) values obtained from near-ground hyperspectral data of three dominant species, Bruguiera sexangula (Lour.) Poir. (B. sexangula), Ceriops tagal (Perr.) C. B. Rob. (C. tagal) and Rhizophora apiculata Blume (R. apiculata) in Qinglan Port Mangrove Nature Reserve. The accuracy of the model was evaluated using R-2, RMSE, and MAE. The mean SPAD values of R. apiculata (SPAD(avg) = 66.57), with a smaller dispersion (coefficient of variation of 6.59%), were higher than those of C. tagal (SPAD(avg) = 61.56) and B. sexangula (SPAD(avg) = 58.60). The first-order differential transformation of the spectral data improved the accuracy of the prediction model; R-2 was mostly distributed in the interval of 0.4 to 0.8. The accuracy of the XGBoost model was less affected by species differences with the best stability, with RMSE at approximately 3.5 and MAE at approximately 2.85. This study provides a technical reference for large-scale detection and management of mangroves.