## 3 Results
### Impact of Illumination and Background on Individual Tree fAPAR/fIPAR  
Both fIPAR and fAPAR are affected by illumination conditions and sunlit/shaded leaves distributions, as shown in Figure 4. Sunlit leaves show higher levels of fAPAR and fIPAR than shaded leaves. Both fAPAR and fIPAR are more dispersed at lower SKYL, likely due to radiance heterogeneity at direct illumination. Conversely, they are less dispersed at higher SKYL, as PAR tends to be more homogenous with the increase of SKYL (as shown in Figure 4b,d). Similar results were observed for the concrete background (not shown here for the sake of brevity).  
Table 2 summarizes the effects of illumination and background conditions on tree-wise average fractions of absorbed and intercepted PAR for sunlit and shaded leaf partitions. The values of fAPAR and fIPAR for sunlit leaves decreased with the level of diffuse illumination (SKYL) for both grass and concrete backgrounds but remain relatively stable for shaded leaves for all illumination conditions. The degree to which the sunlit/shaded leaves distribution affected both fAPAR and fIPAR was influenced by both SZA and SKYL.  
Figure 3: Examples of discrepancies between manual and automatic classification results: nadir HSI (R, G, B channels assigned to 605 nm, 850 nm, and 860 nm, respectively, for visual classification) and the corresponding manual and ANN classifications, together with normalized confusion matrices. The tick labels in the confusion matrices correspond to the categories and the numbers within fields indicate the ratio of manually classified pixels to model outputs within each category for the particular scene containing discrepancies.  
Figure 5a,b compare the impacts of the background (concrete vs. grass) on estimations of fAPAR and fIPAR for sunlit leaves, respectively. Higher values of both parameters for the concrete background were probably due to the stronger multiple scattering compared to the other models.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Grass**} & \multicolumn{4}{c}{**Concrete**} \\
**SKYL** & \multicolumn{2}{c}{**fAPAR**} & \multicolumn{2}{c}{**fIPAR**} & \multicolumn{2}{c}{**fAPAR**} & \multicolumn{2}{c}{**fIPAR**} \\  & **sunlit** & **shaded** & **sunlit** & **shaded** & **sunlit** & **shaded** & **sunlit** & **shaded** \\ \hline
0\% & 0.672 & 0.434 & 0.777 & 0.502 & 0.682 & 0.448 & 0.789 & 0.518 \\
20\% & 0.608 & 0.404 & 0.700 & 0.466 & 0.626 & 0.424 & 0.722 & 0.488 \\
40\% & 0.575 & 0.398 & 0.664 & 0.459 & 0.595 & 0.418 & 0.687 & 0.483 \\
60\% & 0.558 & 0.397 & 0.644 & 0.459 & 0.576 & 0.416 & 0.666 & 0.480 \\
80\% & 0.542 & 0.402 & 0.627 & 0.464 & 0.561 & 0.420 & 0.649 & 0.486 \\
100\% & 0.516 & 0.396 & 0.596 & 0.458 & 0.534 & 0.413 & 0.615 & 0.477 \\
**SZA** & **sunlit** & **shaded** & **sunlit** & **shaded** & **sunlit** & **shaded** & **sunlit** & **shaded** \\
0\({}^{\circ}\) & 0.620 & 0.437 & 0.717 & 0.505 & 0.636 & 0.450 & 0.735 & 0.520 \\
45\({}^{\circ}\) & 0.537 & 0.374 & 0.620 & 0.432 & 0.556 & 0.397 & 0.641 & 0.458 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Averages of fAPAR and fIPAR depending on the background and illumination conditions.  
Figure 4: Fraction of absorbed photosynthetically active radiation (fAPAR) and fraction of intercepted photosynthetically active radiation (fIPAR) density distribution based on illumination conditions: sunlit/shaded leaves (subfigures **a** and **c**), and diffuse ratio (subfigures **b** and **d**).  
to grass (Figure 5). The background had a larger impact on fIPAR, with an overall relative difference between the grass and concrete background of approximately 2%. The effect of background on fAPAR/fIPAR increased with the increase of SKYL (Table 2).