# Monitoring Rainfed Alfafa Growth in Semiarid Agrosystems Using Sentinel-2 Imagery
## 2 Material and Methods
### Data Analysis  
The FVC values at the pixel or parcel level were calculated as described in Section 2.2. The VI values at the pixel or parcel level were calculated from Sentinel-2 images as described in Section 2.3. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Vegetation Index** & **Equation** & **Reference** \\ \hline Normalized difference VI & \(NDVI=\frac{\rho_{0}-\rho_{4}}{\rho_{5}+\rho_{6}}\) & [PERSON] et al. (1974) \\ Soil adjusted VI & \(SAVI=\frac{(\rho_{0},\rho_{4})}{\rho_{5}+\rho_{6}}*(1+l)\) & [PERSON] (1988) \\ Ratio VI & \(RVI=\frac{\rho_{0}}{\rho_{4}}\) [PERSON] (1968) \\ Perpendicular VI & \(PVI=\sin a*\rho_{8}-\cos a*\rho_{4}\) & [PERSON] (1977) \\ Green normalized difference VI & \(GNDVI=\frac{\rho_{0}-\rho_{2}}{\rho_{5}+\rho_{7}}\) & [PERSON] et al. (1996) \\ Kernel-based NDVI & \(kNDVI=tanh(INDVI)\) & [PERSON] et al. (2021) \\ Normalized difference water index & \(NDVI=\frac{\rho_{0}-\rho_{1}}{\rho_{5}+\rho_{1}}\) & [PERSON] et al. (1992) \\ Specific leaf area vegetation index & \(SAVI=\frac{\rho_{0}}{\rho_{2}+\rho_{1}}\) & [PERSON] et al. (2000) \\ Modified chlorophyll absorption in ratio index & \(MCARI=[(\rho_{5}-\rho_{4})-\frac{\rho_{0}}{\rho_{5}-\rho_{3}})(\rho_{5}-\rho_{4})\) & [PERSON] et al. (2000) \\ MERIS terrestrial chlorophyll Index & \(MTCI=\frac{\rho_{0}-\rho_{1}}{\rho_{5}-\rho_{4}}\) & [PERSON] et al. (2010) \\ NDVI\({}_{705}=\frac{\rho_{0}-\rho_{5}}{\rho_{5}+\rho_{7}}\) & [PERSON] (2002) \\ Sentinel-2 LAI index & \(SeLI=\frac{\rho_{0}-\rho_{5}}{\rho_{5}+\rho_{7}}\) & [PERSON] et al. (2019) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Equations described for the different vegetation indices evaluated in the present study. \(\rho\) represents reflectance values; 1 represents the leaf area index defined as 0.5; a represents the angle between the soil line and the NIR axis in degrees and is established in 49\({}^{\circ}\). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Band Number** & **Function** & **Central Wavelength (nm)** & **Spatial Resolution (m)** \\ \hline
1 & Coastal aerosol & 443 & 60 \\
2 & Blue & 490 & 10 \\
3 & Green & 560 & 10 \\
4 & Red & 665 & 10 \\
5 & Red edge & 705 & 20 \\
6 & Red edge & 740 & 20 \\
7 & Red edge & 783 & 20 \\
8 & NIR & 842 & 10 \\
8a & Red edge & 865 & 20 \\
9 & Water vapor & 945 & 60 \\
10 & SWIR & 1380 & 60 \\
11 & SWIR & 1610 & 20 \\
12 & SWIR & 2190 & 20 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Sentinel-2 bands’ setting. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Date** & **E1** & **E2** & **Date** & **E1** & **E2** & **Date** & **E1** & **E2** & **Date** & **E1** & **E2** \\ \hline
14/05/2019 & & X & 03/07/2018 & & X & 26/10/2017 & & X \\
29/04/2019 & & X & 28/06/2018 & & X & 16/10/2017 & & X \\
30/03/2019 & & X & **23/06/2018** & **X** & **X** & 06/10/2017 & & X \\
05/03/2019 & & X & **19/05/2018** & **X** & **X** & 21/08/2017 & X & 21/10/2016 & & X \\
13/02/2019 & & X & 04/05/2018 & & X & **28/07/2017** & **X** & 01/10/2016 & & X \\
30/11/2018 & & X & 24/04/2018 & & X & **18/07/2017** & **X** & **X** & 11/09/2016 & & X \\
16/10/2018 & & X & 19/04/2018 & & X & **18/06/2017** & **X** & **X** & 22/08/2016 & & X \\
01/09/2018 & & X & 29/01/2018 & & X & 19/04/2017 & & X & 12/08/2016 & & X \\
02/08/2018 & & X & 04/01/2018 & & X & 09/04/2017 & & X & 02/08/2016 & & X \\
**28/07/2018** & **X** & **X** & 30/12/2017 & & X & 30/03/2017 & & X & 03/07/2016 & & X \\
23/07/2018 & & X & 05/12/2017 & & X & 20/03/2017 & & X & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Overview of the Sentinel-2 images available for the study site during the 2016–2019 seasons: Experiment 1 (E1; marked in black) analyzed the images corresponding to 3–4 days in the spring of 2018 and 2017, respectively. Experiment 2 (E2) analyzed the images for all of the dates from July 2016 to May 2019. In the first experiment (E1), FVC values from the 1 m\({}^{2}\) sampling points were compared with the VI values derived from Sentinel-2 images at the parcel level.