## 3 Results  
### Correlation Between ChlF Parameters and FOD Spectra  
To analyze the relationship between ChlF parameters and FOD spectra, correlation coefficients were calculated to assess the association between ChlF parameters and various FOD spectra (Figures 2 and 3). For PSIImax, it was observed that the number of wavelengths with significant correlation gradually decreased with an increasing FOD order (Figure 4). Across all FOD spectra datasets, the higher correlation coefficients (top 20) of wavelengths with PSIImax were primarily located in the VIS and red-edge regions. The wavelength exhibiting the strongest correlation was identified as 697 nm in the 1.5-order FOD spectra (Figure 2p). This wavelength demonstrated the highest sensitivity to changes in PSIImax, exhibiting a correlation coefficient of -0.56. For NPQ, it was found that as the FOD order increased, the number of wavelengths with significant correlations first showed a gradual increase, peaking at the 0.9-order FOD spectra, and then gradually decreased (Figure 4). The wavelengths that exhibited higher correlation coefficients with NPQ were predominantly located within the VIS and red-edge regions, with a smaller proportion detected in the SWIR region. At the 1.0-order FOD spectra, the wavelength 1675 nm exhibited the strongest association with NPQ, yielding a correlation coefficient of 0.55 (Figure 2k). As with NPQ, the number of wavelengths that exhibited a significant correlation with qL increased initially and then decreased as the FOD spectra progressed from the 0.8 to the 2.0 order. The 0.8-order FOD spectra exhibited the highest number of significant wavelengths (Figure 4). In the lower-order FOD spectra (0-0.6), wavelengths exhibiting stronger correlations with qL were predominantly found in the VIS region. In the 0.7- to 1.1-order FOD spectra, these wavelengths were primarily distributed in the VIS and NIR regions. At higher-order FOD spectra (>1.1), the wavelengths with stronger correlations shifted to the red-edge region. The wavelength exhibiting the strongest correlation with qL was identified as 1071 nm in the 0.9-order FOD spectra, with a correlation coefficient of 0.38 (Figure 2j). The maximum number of wavelengths that exhibited a significant correlation with \(\Phi\)P was observed in the 0.6-order FOD spectra, while the minimum number was noted in the 2.0-order FOD spectra (Figure 4). The wavelengths exhibiting high correlation coefficients for \(\Phi\)P were predominantly distributed in the VIS and red-edge regions. As the FOD order increased, wavelengths in the red-edge region became increasingly dominant. The strongest correlation with \(\Phi\)P was identified at 577 nm in the 1.0-order FOD spectra, with a correlation coefficient of 0.51 (Figure 2k). For \(\Phi\)N, the maximum number of significantly correlated wavelengths was observed in the 0.7-order FOD spectra, while the minimum number occurred in the 0.1-order spectra (Figure 4). Wavelengths with strong correlations with \(\Phi\)N were primarily distributed in the VIS and red-edge regions. The highest correlation with \(\Phi\)N was found at 533 nm in the 0.9-order FOD spectra, with a correlation coefficient of 0.57 (Figure 2j). From 0- to 2.0-order FOD spectra, the number of wavelengths that exhibited a significant correlation with \(\Phi\)F initially increased, reaching a peak at the 0.7-order spectra, and then decreased (Figure 4). In FOD spectra up to the 1.6 order, wavelengths with higher correlation coefficients for \(\Phi\)F were primarily located in the NIR and SWIR regions. Beyond the 1.6-order spectra, wavelengths with higher correlation coefficients were observed in the VIS and red-edge regions, in addition to the NIR and SWIR regions. The strongest correlation with \(\Phi\)F was identified at 1667 nm in the 0.9-order FOD spectra (Figure 2j, r = -0.44). Figure 2: Correlation coefficient (r) between wavelength and ChIF parameters across different FOD spectra (**a**–**u**). Different ChIF parameters are represented by distinct colors.