## 5 Conclusions  
In this study, we evaluated the performance of SIF obtained by OCO-2 and GOME-2 in the estimation of GPP for maize and alpine meadow areas at the Daman and A'rou sites. The main conclusions of this study are as follows. The results showed that daily SIF\({}_{757}\) had stronger correlations with daily tower GPP than daily SIF\({}_{771}\), and the correlation between daily SIF\({}_{757\text{ and }}\)daily tower GPP was stronger than the correlation between 16-d averaged SIF\({}_{740}\) and 16-d averaged tower GPP. The 16-d averaged APAR and RSIF had the strongest linear correlations with 16-d averaged tower GPP. GPP\({}_{\text{-}}\)VPM and GPP\({}_{\text{-}}\)RSIF exhibited the best performance in GPP estimation, closely followed by GPP\({}_{\text{-}}\)SIF\({}_{757}\), then GPP\({}_{\text{-}}\)SIF\({}_{771}\) and GPP\({}_{\text{-}}\)SIF\({}_{740}\). The robustness of the correlation coefficients of GOME-2 SIF with OCO-2 SIF was highly dependent on the size of the spatial footprint overlaps, indicating that the spatial differences between the GOME-2 and OCO-2 footprints and flux tower footprints played a role in explaining the differences in GPP estimates from towers and satellites. The scale effect of GOME-2 SIF was weaker than that of OCO-2 SIF on the SIF values and GPP-SIF relationships. Moreover, the VZA had a significant effect on the SIF values and the GPP-SIF relationships because directional effects on SIF added variations to the OCO-2 SIF observations. Our results showed that SIF was significantly correlated with APAR as well as environmental scalars (T\({}_{\text{scalar}}\)\(\times\) W\({}_{\text{scalar}}\)). **Supplementary Materials:** The following are available online at [[http://www.mdpi.com/2072-4292/10/12/2039/s1](http://www.mdpi.com/2072-4292/10/12/2039/s1)]([http://www.mdpi.com/2072-4292/10/12/2039/s1](http://www.mdpi.com/2072-4292/10/12/2039/s1)), Figure S1: Effect of OCO-2 pixel extraction on the GPP-SIF relationship: (a) 0.2\({}^{\circ}\); (b) 0.3\({}^{\circ}\); (c) 0.4\({}^{\circ}\); and (d) 0.5\({}^{\circ}\). The relationships shown above are for 757 nm and 771 nm at instantaneous timescales, Figure S2: Effect of GOME-2 pixel extraction on the GPP-SIF relationship: (a) 0.2\({}^{\circ}\); (b) 0.3\({}^{\circ}\); (c) 0.4\({}^{\circ}\); and (d) 0.5\({}^{\circ}\). The relationships shown above are for 740 nm at the instantaneous timescale, Figure S3: Effects of clouds on the relationships between GOME-2 SIF\({}_{740}\) and tower GPP at instantaneous timescales, Figure S4: Spatial overlap of OCO-2 overpasses and the nearest GOME-2 SIF pixels within the 0.5\({}^{\circ}\) grid cell at the Daman and A'rou sites, Figure S5: Number of soundings of OCO-2 overpasses within the overlaps of OCO-2 and GOME-2 SIF for the 0.5\({}^{\circ}\) grid cell on the corresponding date at the Daman and A'rou sites, Table S1: Number of OCO-2 and GOME-2 retrievals for each bin. **Author Contributions:** [PERSON]. ([PERSON]) and [PERSON] ([PERSON]) designed research; [PERSON]. ([PERSON]) and [PERSON] ([PERSON]) performed research; [PERSON]([PERSON]) and [PERSON]([PERSON]) analyzed data; [PERSON]. ([PERSON]) and [PERSON] ([PERSON]) wrote the paper; [PERSON]. ([PERSON]) and [PERSON] ([PERSON]) provided comments and suggestions on the manuscript. **Funding:** This research was funded by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA19040504), the National Natural Science Foundation of China (Grant No. 41771466, 41730752 and 41861040), the National Key Research and Development Program of China (Grant No. 2016 YFC0500201) and the Special Fund for Key Program of Science and Technology of Qinghai Province (Grant No. 2017-SF-A6). **Acknowledgments:** The authors would like to thank all anonymous reviewers and editors for their constructive comments on this paper.