Fig. 2. Number of articles involving use of multivariate calibration technique in each EO domain (PLSR stands for Partial Least Squares Regression, SMLR stands for Stepwise Multiple Linear Regression, SVM stands for Support Vector Machines, SLR stands for Simple Linear Regression, ANN stands for Artificial Neural Networks, PSR stands for Penalized-spline Signal Regression and MLR stands for Multiple Linear Regression). Reproduced with permission from (Angelopoulou, Tziolas et al. 2019)