## Materials and Methods
### Vegetation Indices (VIs)  
Based on the simulated and measured canopy spectral data, a total of 29 VIs constructed using near-infrared and visible bands were selected (Table 3). The selected VIs, including the NDVI, SR and difference vegetation index (DVI), as well as modified indices, were employed to investigate the correlation between the FPAR and VIs. In order to identify the VIs suitable for FPAR estimation using general and specific simulation datasets, the first step was to establish the relationship between the simulated VIs and the FPAR by employing curve-fitting models, such as linear, exponential, power and logarithm models. The second step was to determine the major VIs that exhibited a good correlation with the FPAR using estimated error metrics. Subsequently, the VIs were evaluated by calculating the rank sum and arranging them in ascending order accordingly.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**V Vegetation Index** & **Formulation** & **References** \\ \hline Atmospherically resistant Vegetation index (ARVI) & \(\frac{R_{\rm 840}-(2\times R_{\rm 77}-R_{\rm 85})}{R_{\rm 840}+2\times R_{\rm 77}-R_{ \rm 85})}\) & [41] \\ Chlorophyll index green (CI\({}_{\rm green}\)) & \(\frac{R_{\rm 840}}{R_{\rm 840}}-1\) & [42] \\ Chlorophyll index red-edge & \(\frac{R_{\rm 840}}{R_{\rm 77}}-1\) & [42] \\ (CI\({}_{\rm red-edge}\)) & \(R_{\rm 840}-R_{\rm 664}\) & [43] \\ Difference vegetation index (DVI) & \(2.5\times\frac{R_{\rm 840}-R_{\rm 840}-R_{\rm 840}}{R_{\rm 840}-R_{\rm 840}}\) & [44] \\ Enhanced vegetation index (EVI) & \(2.5\times\frac{1}{1+R_{\rm 840}-2\times R_{\rm 840}}\) & [45] \\ \(\rm Green\ normalized\ difference\) & \(\frac{R_{\rm 840}-R_{\rm 840}}{R_{\rm 840}+R_{\rm 840}}\) & [46] \\ Vegetation index (GNDVI) & \(\frac{R_{\rm 840}}{R_{\rm 840}}\) & [47] \\ Green ratio vegetation index (RVI\({}_{\rm green}\)) & \(\frac{R_{\rm 840}}{R_{\rm 840}}\) & [48] \\ Green-red vegetation index (GRVI) & \(\frac{R_{\rm 840}}{R_{\rm 840}+R_{\rm 840}}\) & [49] \\ Modified chlorophyll absorption ratio vegetation index (MCARVI) & \(\left(\left(R_{\rm 840}\ -\ R_{\rm 717}\right)\ -0.2\times\left(R_{\rm 840}\ -\ R_{\rm 5 60}\right)\right)\ \times\ \left(\frac{R_{\rm 840}}{R_{\rm 717}}\right)\) & [49] \\ Modified normalized difference vegetation index (mNDVI) & \(\frac{R_{\rm 840}-R_{\rm 840}}{R_{\rm 840}+R_{\rm 840}-2\times\left(R_{\rm 8 40}\ -R_{\rm 840}\right)}\) & [50] \\ modified normalized difference vegetation index red-edge & \(\frac{R_{\rm 840}-R_{\rm 840}}{R_{\rm 840}+R_{\rm 840}}\) & [51] \\ (mNDVI\({}_{\rm red-edge}\)) & \(\frac{R_{\rm 840}-1}{\sqrt{\left(\frac{R_{\rm 840}}{R_{\rm 840}}+1\right)}}\) & [52] \\ Modified simple ratio red-edge & \(\frac{R_{\rm 840}-1}{\sqrt{\left(\frac{R_{\rm 840}}{R_{\rm 840}}+1\right)}}\) & [53] \\ Modified simple ratio red-edge & \(\frac{R_{\rm 840}-1}{\sqrt{\left(\frac{R_{\rm 840}}{R_{\rm 840}}+1\right)}}\) & [54] \\ (mSR\({}_{\rm red-edge}\)) & \(0.5\times\left(2\times R_{\rm 840}+1\ -\ (2\times R_{\rm 840}+1)^{2}\ - 8\times\sqrt{R_{\rm 840}\ -R_{\rm 668}}\right)\) & [55] \\ Normalized difference vegetation index red-edge (NDVI\({}_{\rm red-edge}\)) & \(\frac{R_{\rm 840}-R_{\rm 840}}{R_{\rm 840}+R_{\rm 717}}\) & [56] \\ \hline \hline \end{tabular}
\end{table}
Table 3: Multispectral VIs for the FPAR estimation.