## 2 Materials and Methods
### Methodology
\begin{table}
\begin{tabular}{c c c c} \hline
**Index** & **Full Name** & **Formula** & **Reference** \\ \hline
102 & Green normalized difference & \(\mathrm{GNDVI}_{1}=\frac{\mathrm{R_{max}}-\mathrm{R_{500}}}{\mathrm{R_{500}}+ \mathrm{R_{500}}}\) & [8] \\  & vegetation index & \(\mathrm{GNDVI}_{2}=\frac{\mathrm{R_{max}}-\mathrm{R_{500}}}{\mathrm{R_{500}}+ \mathrm{R_{500}}}\) & [8] \\
103 & \(\mathrm{vegetation\ index}\) & \(\mathrm{GNDVI}_{2}=\frac{\mathrm{R_{max}}-\mathrm{R_{500}}}{\mathrm{R_{500}}+ \mathrm{R_{500}}}\) & [8] \\  & \(\mathrm{vegetation\ index}\) & \(\mathrm{RDVI}=\frac{\mathrm{R_{max}}-\mathrm{R_{500}}}{(\mathrm{R_{500}}+ \mathrm{R_{500}})^{3}}\) & [34] \\
105 & Red edge Position Index & \(\mathrm{REP}_{670,700}=700+40\)\(\frac{\frac{\mathrm{R_{max}}+\mathrm{R_{500}}}{\mathrm{R_{500}}-\mathrm{R_{500}}}- \mathrm{R_{500}}}{\mathrm{R_{500}}-\mathrm{R_{500}}}\) & [35] \\
106 & Red edge Position Index & \(\mathrm{REP}_{670,850}=700+45\)\(\frac{\mathrm{R_{max}}-\mathrm{R_{500}}}{\mathrm{R_{500}}-\mathrm{R_{500}}}\) & [36] \\
107 & MERIS terrestrial chlorophyll index & \(\mathrm{MTCI}=\frac{\mathrm{R_{max}}-\mathrm{R_{500}}}{\mathrm{R_{500}}+ \mathrm{R_{500}}}\) & [37] \\
108 & Modified chlorophyll absorption & \(\mathrm{MCARI}_{700,670}=[(\mathrm{R_{700}}-\mathrm{R_{670}})-0.2(\mathrm{R_{ 700}}-\mathrm{R_{500}})]\frac{\mathrm{R_{max}}}{\mathrm{R_{500}}}\) & [38] \\  & ratio index & & \\  & Modified Chlorophyll absorption & \(\mathrm{MCRARI}_{700,670}=\frac{[(\mathrm{R_{700}}-\mathrm{R_{670}})-0.2*( \mathrm{R_{700}}-\mathrm{R_{500}})]\frac{\mathrm{R_{max}}}{\mathrm{R_{500}}}}{ \mathrm{R_{500}}}\) & [33] \\
109 & Reflectance Index/Optimized Soil & \(\mathrm{MSAVI}_{700,670}=\frac{3\left((\mathrm{R_{700}}-\mathrm{R_{500}})-0.2*( \mathrm{R_{700}}-\mathrm{R_{500}})\right)\frac{\mathrm{R_{max}}}{\mathrm{R_{500} }}}{\frac{(1+6\mathrm{R_{max}}-\mathrm{R_{500}})}{\mathrm{R_{500}}+\mathrm{R_ {500}}+\mathrm{R_{500}}}}\) & [33] \\  & \(\mathrm{Adjusted Vegetation\ Index}\) & \(\mathrm{TCARI}_{700,670}=3\Big{(}(\mathrm{R_{700}}-\mathrm{R_{670}})-0.2(\mathrm{ R_{700}}-\mathrm{R_{550}})\frac{\mathrm{R_{max}}}{\mathrm{R_{500}}}\Big{)}\) & [33] \\
111 & \(\mathrm{Transformed\ Chlorophyll}\) & \(\mathrm{MSAVI}_{700,670}=3\Big{(}(\mathrm{R_{700}}-\mathrm{R_{670}})-0.2( \mathrm{R_{700}}-\mathrm{R_{550}})\frac{\mathrm{R_{max}}}{\mathrm{R_{500}}} \Big{)}\) & [38] \\  & Absorption Ratio & \(\mathrm{MCARI}_{750,705}=\Big{(}(\mathrm{R_{750}}-\mathrm{R_{705}})-0.2*( \mathrm{R_{750}}-\mathrm{R_{550}})\Big{)}\frac{\mathrm{R_{max}}}{\mathrm{R_{500} }}\Big{)}\) & [39] \\
112 & Modified Chlorophyll Absorption & \(\mathrm{MCARI}_{750,705}=\Big{(}((\mathrm{R_{750}}-\mathrm{R_{705}})-0.2*( \mathrm{R_{750}}-\mathrm{R_{550}})\Big{)}\frac{\mathrm{R_{max}}}{\mathrm{R_{500} }}\Big{)}\) & [39] \\  & \(\mathrm{Radio\ Index}\) & \(\mathrm{MCARI}_{750,705}=\Big{(}(\mathrm{R_{750}}-\mathrm{R_{705}})-0.2*( \mathrm{R_{750}}-\mathrm{R_{550}})\Big{)}\frac{\mathrm{R_{max}}}{\mathrm{R_{5  
A tentative regression step was run using 10 latent variables (projected components). Its principal objective is to calculate the variable importance in projection (VIP) score. It was defined, for each variable \(j\), as the sum, over latent variables \(f\), of its PLS-weight value \(w_{j}\) weighted by the percentage of explained variance of the specific latent variable \(SSY_{f}\) according to relation [52]  
\[VIP_{j}=\sqrt{\frac{\int\times\left[\sum_{f=1}^{F}w_{fj}^{2}\times SSY_{f} \right]}{\sum_{f=1}^{F}SSY_{f}}}, \tag{2}\]  
where \(F\) is the total number of latent variables and \(J\) the total number of variables (in our case 141). The relation for the calculation of \(SSY_{f}\) is given by [53]  
\[SSY_{f}=b_{f}^{2}t_{f}^{T}t_{f}, \tag{3}\]  
where \(b_{f}\) and \(t_{f}\) are the PLS inner relation coefficients and the score matrix relevant with the \(f\)-th latent variable, respectively. The VIP score varies in a fixed range, being the sum of squared VIP equal to total number of variables.