## 3 Materials and Methods
### Methodology
#### 3.3.2 Principal Component Analysis  
Principal component analysis (PCA) is one of the most popular multivariate statistical methods used in various fields of science; it allows to reduce the number of variables, while \begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Spectral Index** & **Full Name** & **General Equation** & **Index Description** & **Reference** \\ \hline \multirow{2}{*}{GNDVI} & Green Normalized & \multirow{2}{*}{(NIR \(-\) G)/(NIR + G)} & Sensitive to chlorophyll & \multirow{2}{*}{[30]} \\  & Vegetation Index & & concentration in a wide range of & \\  & & & chlorophyll changes. & \\ \hline \multirow{2}{*}{IRECI} & Inverted Red-Edge & \multirow{2}{*}{(NIR \(-\) R)/(RE1 / RE2)} & The reflectance in four S-2 bands is & \multirow{2}{*}{[31]} \\  & Chlorophyll Index & & incorporated to estimate the & \\  & & chlorophyll content of the canopy. & & \\ \hline \multirow{2}{*}{MCARI} & Modified Chlorophyll & \multirow{2}{*}{[\((\)RE \(-\) R\()\) - 0.2(RE \(-\) G\()\)] +} & Sensitive to the effects of & \multirow{2}{*}{[32]} \\  & Absorption in & (RE \(-\) R) & non-photosynthetic elements; & \\  & Reflectance Index & & measures the depth of & \\  & & chlorophyll absorption. & & \\ \hline \multirow{2}{*}{MSAVI} & Modified Soil-Adjusted & \multirow{2}{*}{(NIR \(-\) R)/(NIR + R + L) \(\times\)} & A modified version of the SAVI, which & \multirow{2}{*}{[33]} \\  & Vegetation Index & (1 + L) & replaces the constant soil adjustment factor L with a & \\  & & self-adjusting L. & & \\ \hline \multirow{2}{*}{MTCI} & MERIS Terrestrial & \multirow{2}{*}{(NIR \(-\) RE)/(RE \(-\) R)} & Characterized by sensitivity to high & \multirow{2}{*}{[34]} \\  & Chlorophyll Index & & chlorophyll content and limited & \\  & Chlorophyll Index & & sensitivity to atmospheric effects or & \\  & & & spatial resolution. & \\ \hline \multirow{2}{*}{NDI45} & Normalized Difference & \multirow{2}{*}{(NIR \(-\) R)/(NIR + R)} & It has a good correlation with the & \multirow{2}{*}{[35]} \\  & Index 45 & & green LAI because of the red-edge & \\  & & band usage. & & \\ \hline \multirow{2}{*}{NDVI} & Normalized Difference & \multirow{2}{*}{(NIR \(-\) R)/(NIR + R)} & Sensitive to the presence of & \multirow{2}{*}{[36]} \\  & Vegetation Index & & chlorophyll, making it possible to & \\  & Vegetation Index & & measure the plant health status; & \\  & & & saturated to flourishing vegetation. & \\ \hline \multirow{2}{*}{PSSRa} & Pigment Specific & \multirow{2}{*}{NIR/R} & Sensitive for high concentrations of & \multirow{2}{*}{[37]} \\  & Simple Ratio & & chlorophyll a. & \\ \hline \multirow{2}{*}{REIP} & \multirow{2}{*}{Red Edge Inflation Point} & \multirow{2}{*}{\(700+40\times\) ((R + NIR)/2 \(-\) RE1)/(RE2 \(-\) RE1)} & Depends on the amount of & \multirow{2}{*}{[38]} \\  & & & chlorophyll seen by the sensor and & \\  & & RE1)/(RE2 \(-\) RE1) & is strongly correlated & \\  & & with foliar chlorophyll content; & \\  & & sensitive indicator of vegetation stress. & \\ \hline \multirow{2}{*}{S2 REP} & Sentinel-2 Red-Edge & \multirow{2}{*}{\(705+35\times\) ((((NIR + R)/2)\)} & A version of REP estimation for S-2 & \multirow{2}{*}{[31]} \\  & Position index & \(-\) RE1)/(RE2 \(-\) RE1) & using linear interpolation. & \\ \hline \multirow{2}{*}{SAVI} & Soil-Adjusted & \multirow{2}{*}{(NIR \(-\) R)/(NIR + R + L) \(\times\)} & Minimizes the influence of & \multirow{2}{*}{[39]} \\  & Vegetation Index & (1 + L) & soil brightness. & \\ \hline \multirow{2}{*}{WDVI} & Weighted Difference & \multirow{2}{*}{(NIR \(-\) 0.5 \(\times\) R)} & Corrects near-infrared reflectance for & \multirow{2}{*}{[40]} \\  & Vegetation Index & & the soil background. & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Spectral indices applied in the study. NIR—Near Infrared, R—Red band, G—Green bands and RE—Red Edge. retaining the most important information from a dataset [41]. This method is based on finding linear combinations along which there is a maximum variability in the data, called principal components [42].