## 3 Results
### Linear Correlations Among the Yield, All Bands, and VIs in the Three Main Growth Stages
#### 3.2.2 Linear Correlations Between Yield and VIs  
The study of linear correlation at MT between the yield and VIs is shown in Table 8 with the mean \(R\) for all locations and years. The correlation coefficients in the yield were similar to the maximum values obtained with the spectral bands (0.48), except for LSWI, which was lower. Most indices showed a high \(R\) in their correlations, except for the LSWI. The differences between years and locations were identical to the results of the spectral bands, in the analysis of yield variability and collinearity (Table  
At PI, the results are shown in Table 9. In this case, correlations with the yield were lower and very similar in all indices (0.33-0.37). Compared with previous results in the spectral bands, \(R\) values were lower than B07, B08, and B8A but higher than B02, B03, B04, and B05. Thus, the VI performance for the yield estimation differed from the surface reflectance, mainly for visible bands. Furthermore, the decrease in the correlation experimented in the VIs at PI was inconsistent with the increase in B07, B08, and B8A. Regarding temporal variability, there were differences between years with a similar pattern to the spectral bands results. Considering collinearity, all VIs were correlated with each other, and this result was consistent between locations and years.  
Finally, Table 10 shows the results at GF. The correlations with yield followed a similar pattern to the previous stage, with correlations decreasing to a maximum value of 0.27 in LSWI. VIs did not improve spectral band results; the correlations were lower than those of NIR region bands, showing more similarities to those of the visible region bands. Again, differences between years were notable and similar to spectral bands in the correlation with yields, showing non-uniform behavior with a similar pattern in both locations. Collinearity between indices was high (0.86-0.97) and significant in NDVI, GNDVI, NDRE1, and NDRE2, but between LSWI and the rest, it was lower (0.68-0.75).  
\begin{table}
\begin{tabular}{c c c c c c c} \hline  & **NDVI** & **LSWI** & **GNDVI** & **NDRE1** & **NDRE2** & **NCMI** \\ \hline Yield & 0.13 & 0.27 & 0.12 & 0.10 & 0.12 & 0.13 \\ NDVI & & 0.75 & 0.87 & 0.88 & 0.88 & 0.96 \\ LSWI & & & 0.68 & 0.70 & 0.71 & 0.75 \\ GNDVI & & & & 0.86 & 0.89 & 0.97 \\ NDRE1 & & & & & 0.98 & 0.90 \\ NDRE2 & & & & & & 0.92 \\ \hline \end{tabular}
\end{table}
Table 10: Mean values of correlation coefficients between the yield and VIs for years and locations at GF. Individual results per location and year are shown in Supplementary Materials Table S6.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline  & **NDVI** & **LSWI** & **GNDVI** & **NDRE1** & **NDRE2** & **NCMI** \\ \hline Yield & 0.42 & 0.19 & 0.47 & 0.47 & 0.48 & 0.46 \\ NDVI & & 0.11 & 0.98 & 0.97 & 0.96 & 0.99 \\ LSWI & & & 0.19 & 0.12 & 0.14 & 0.17 \\ GNDVI & & & & 0.97 & 0.97 & 1.00 \\ NDRE1 & & & & & 1.00 & 0.98 \\ NDRE2 & & & & & & 0.98 \\ \hline \end{tabular}
\end{table}
Table 8: Mean values of correlation coefficients between the yield and VIs for years and locations at MT. Individual results per location and year are shown in Supplementary Materials Table S4.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline  & **NDVI** & **LSWI** & **GNDVI** & **NDRE1** & **NDRE2** & **NCMI** \\ \hline Yield & 0.33 & 0.35 & 0.34 & 0.35 & 0.37 & 0.35 \\ NDVI & & 0.77 & 0.91 & 0.86 & 0.85 & 0.97 \\ LSWI & & & 0.81 & 0.75 & 0.80 & 0.82 \\ GNDVI & & & & 0.86 & 0.89 & 0.98 \\ NDRE1 & & & & & 0.98 & 0.88 \\ NDRE2 & & & & & & 0.90 \\ \hline \end{tabular}
\end{table}
Table 9: Mean values of correlation coefficients between the yield and VIs for years and locations at PI. Individual results per location and year are shown in Supplementary Materials Table S5.