## 3 Results
### Evaluation of SIF Simulations
#### 3.3.3 Evaluation of SIF Simulations with Variable FQE  
With the above variable FQE as inputs, the systematic deviations in \(\mathrm{SIF_{B}}\), \(\mathrm{SIF_{A}}\), and \(\mathrm{SIF_{A}}\)/\(\mathrm{SIF_{B}}\) simulations can be corrected; meanwhile, the limited range from \(\mathrm{SIF_{A}}\)/\(\mathrm{SIF_{B}}\) simulations can be extended due to the seasonal variations of fqe1/fqe2. Thus, the SCOPE model can provide more accurate SIF simulations related to both the individual bands (\(\mathrm{SIF_{A}}\) and \(\mathrm{SIF_{B}}\)) and the seasonal \(\mathrm{SIF_{A}}\)/\(\mathrm{SIF_{B}}\) values.  
On the one hand, if simulated with variable FQE values, the simulation accuracy of \(\mathrm{SIF_{B}}\) and \(\mathrm{SIF_{A}}\) can be improved greatly. Like the quantitative assessments listed in Table 4, Figure 12 displays the correlation and RRMSE values between the simulated and measured SIF with variable FQE for all 106 spectral measurements (Figure 12a) and the corresponding daily RRMSEs for each single fieldwork day (Figure 12b). As illustrated, both the simulated \(\mathrm{SIF_{B}}\) and \(\mathrm{SIF_{A}}\) were consistent with the measured ones for all 106 spectral measurements: the scatters were located close to the 1:1 line, with the \(R^{2}\) larger than 0.78 and an RRMSE of less than 20%. Additionally, the daily RRMSE values of \(\mathrm{SIF_{B}}\) and \(\mathrm{SIF_{A}}\) were lower than 30% (with a range from 5.97% to 29.80%) and 23% (with a range from 6.99% to 22.55%), respectively, during ten experiments in 2015 and 2016.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & & \multicolumn{4}{c}{**2015**} & \multicolumn{4}{c}{**2016**} \\ \cline{2-11}  & **April 3** & **April 13** & **April 14** & **April 24** & **April 25** & **April 8** & **April 9** & **April 18** & **May 3** & **May 4** \\ \hline fqe2 & 0.013 & 0.011 & 0.01 & 0.008 & 0.009 & 0.012 & 0.011 & 0.009 & 0.007 & 0.008 \\ fqe1/fqe2 & 0.05 & 0.15 & 0.1 & 0.5 & 0.4 & 0.05 & 0.1 & 0.25 & 0.4 & 0.3 \\ \hline \hline \end{tabular}
\end{table}
Table 6: The variable fqe2 and fqe1/fqe2 values on ten fieldwork days in 2015 and 2016.  
Figure 11: The seasonal cycles of fqe2 and fqe1/fqe2 on ten fieldwork days in 2015 and 2016.  
On the other hand, if simulated with variable FQE values, the SCOPE model can credibly reproduce the seasonal \(\text{SIF}_{\text{A}}/\text{SIF}_{\text{B}}\) values. Similar to Figure 12, Figure 13 shows the correlation and RRMSE values between the diurnally simulated and measured \(\text{SIF}_{\text{A}}/\text{SIF}_{\text{B}}\) with variable FQE. Unlike the unsatisfactory results shown in Figure 10, with variable FQE, both the range and values of simulated \(\text{SIF}_{\text{A}}/\text{SIF}_{\text{B}}\) were consistent with the measured ones: for all 106 spectral measurements, most scatters are close to the 1:1 line with an \(R^{2}\) of 0.48 and an RRMSE of only 20.63%, and most daily RRMSE were lower than 20% (with a range from 4.98% to 24.20%) on the ten fieldwork days. All these results indicated that the variable FQE settings were more suitable than the fixed ones for acquiring unbiased SIF simulations.