## 3 Results  
Parameter Sensitivity Analysis of the Soil Canopy Observation, Photochemistry and Energy Fluxes (SCOPE) Model  
We performed a sensitivity analysis of all parameters related to photosynthesis and SIF simulations. The first sensitivity index (SI 1 st) and the total sensitivity index (SI total) of model parameters for SCOPE-simulated SIF (in OCO-2 SIF wavelengths of 757 nm and 771 nm) and GPP are illustrated in Figure 3. The results of the sensitivity analysis showed that for the SIF estimation, fqe was the most sensitive parameter, while V\({}_{\text{Cmax}}\) was one of the least sensitive parameters (Figure 3a). The simulated SIF was sensitive to fqe, Cab, and LAI with the total-order impact ratio of 48.0%, 18.1%, and 16.7%, respectively. The other parameters had relatively low impact ratios (less than 5%). However, for the GPP simulation, the most sensitive parameters were V\({}_{\text{Cmax}}\), LAI, Rd, and Cab with the total-order impact ratio of 41.7%, 31.4%, 16.1%, and 5.4%, respectively, and other parameters had relatively low impact ratio (Figure 3b). For the objective function of both SIF and GPP, both fqe and V\({}_{\text{Cmax}}\) were the most sensitive parameters (Figure 3c); both GPP and SIF were sensitive to V\({}_{\text{Cmax}}\), Cab, Rd, fqe, and LAI with the total-order impact ratio of 21.9%, 21.2%, 17.7%, 15.3%, and 13.2%, respectively, while other parameters had relatively low impact ratio. Both LAI and Cab were used as input variables for the simulation of GPP and SIF and were therefore not optimized in this study.  
To determine the feasibility and sensitivity of satellite measured SIF derived from different sensors (i.e., GOME-2 and OCO-2) to V\({}_{\text{Cmax}}\), we conducted a sensitivity analysis with different V\({}_{\text{Cmax}}\) values ranging from 10 to 200 \(\upmu\)mol m\({}^{-2}\) s\({}^{-1}\) (Figure 4). The SIF spectrum ranged from 640 to 850 nm with two peaks centered at 685 nm and 740 nm. The sensitivity of SIF to V\({}_{\text{Cmax}}\) was higher at 757 nm than at 771 nm. The GOME-2 wavelength (740 nm) is right at one of the SIF emission peaks, which is also the V\({}_{\text{Cmax}}\) sensitivity band for SIF prediction. The sensitivity of SIF to V\({}_{\text{Cmax}}\) at the GOME-2 wavelength (740 nm) was higher than that of the OCO-2 wavelengths (757 nm and 771 nm).  
To investigate how both GPP and SIF responded to V\({}_{\text{cmax}}\) and light conditions, we further performed a sensitivity analysis with varying V\({}_{\text{cmax}}\) values and light conditions (Figure 5). With varying V\({}_{\text{cmax}}\) at the constant irradiance, SIF did not significantly increase with increasing V\({}_{\text{cmax}}\); for a given V\({}_{\text{cmax}}\) value, SIF increased with increasing solar irradiance (Figure 5a). In contrast, GPP increased with increasing V\({}_{\text{cmax}}\), particularly at higher light conditions, and light saturation of GPP occurred under lower light conditions with lower V\({}_{\text{cmax}}\) values (Figure 5b).  
Figure 4: The sensitivity of simulated SIF to V\({}_{\text{cmax}}\) values in the SCOPE model. We used 20 different V\({}_{\text{cmax}}\) values ranging from 10 to 200 \(\upmu\)mol m\({}^{-2}\) s\({}^{-1}\).  
Figure 3: Global sensitivity analysis (GSA) total sensitivity index for SCOPE-simulated SIF Orbiting Carbon Observatory-2 solar-induced chlorophyll fluorescence (OCO-2 SIF) and gross primary production (GPP). Three different objective functions were used: (**a**) SIF, (**b**) GPP, and (**c**) SIF and GPP together.