## 3 Results
### The Relationship between \(SIF_{canopy}\) and \(APAR_{chl}\) Based on the Experimental Data  
3.1 The Diurnal Cycle of Incoming PAR and SIF Signal for \(\mathrm{XTS}_{\mathrm{Apr}}\) and Sanya Station  
Figure 9 illustrates the diurnal observations of incoming PAR and SIF at O\({}_{2}\)-A and O\({}_{2}\)-B bands of the diurnal experiments at XTS Farm in April and Sanya Station. As shown in Figure 9, the diurnal variation in the SIF signal at O\({}_{2}\)-A and O\({}_{2}\)-B bands are similar to that for the incoming PAR, and the emitted SIF is synchronously responded to the incoming PAR. 3.2 The Influence of Different Fertilization Treatments and Varieties on the Relationship between \(\mathrm{SIF}_{canopy}\) and \(\mathrm{APAR}_{chl}\)  
The effect of different fertilization treatments and varieties on the relationship between \(\mathrm{APAR}_{chl}\) and \(\mathrm{SIF}_{canopy}\) was shown in Figure 10. There was no obvious effect of fertilization treatment on the slope of the relationship so the fertilization treatment only influenced the growth status, which only showed a higher \(\mathrm{SIF}_{canopy}\) and \(\mathrm{APAR}_{chl}\) with the most appropriate fertilization treatment (N2). We can also conclude that the discrepancy of this relationship between different varieties was negligible. Figure 8: The relationship between \(\mathrm{SIF}_{canopy}\) and \(\mathrm{APAR}_{chl}\) at the O\({}_{2}\)-A (a) and O\({}_{2}\)-B (b) bands for different plant types, as obtained using the simulated dataset (LAI = 3 m\({}^{2}\) m\({}^{-2}\), Cab = 40 \(\mu\)g cm\({}^{-2}\)). Figure 9: The diurnal cycle of incoming PAR (**a**) and SIF (**b**,**c**) at O\({}_{2}\)-A and O\({}_{2}\)-B bands for \(\mathrm{XTS}_{\mathrm{Apr}}\) and Sanya Station measurements. 3.3 Effect of Cab and \(f_{c}\) on the Relationship between \(\mathrm{SIF}_{canopy}\) and \(\mathrm{APAR}_{chl}\)  
As illustrated in Figure 11, the relationship between \(\mathrm{SIF}_{canopy}\) at O\({}_{2}\)-A band and \(\mathrm{APAR}_{chl}\) is not significantly affected by Cab content based on the experimental measurements conducted on Nanbin and XTS Farm. However, for the O\({}_{2}\)-B band, the plots are more diverse if Cab varies greatly as shown in Figure 11a,b for observations at Nanbin Farm. The diurnal experiments were conducted during two periods in April 2016 at XTS Farm, and the Cab content of the wheat leaves at each period varied little during the period of the experiments, with a Cab value of 55.29 and 53.62 \(\mathrm{\SIUnitSymbolMicro g}\)/\(\mathrm{cm}^{2}\). So, the relationship was linear at the O\({}_{2}\)-B band. The effect of \(f_{c}\) on the relationship between \(\mathrm{SIF}_{canopy}\) at both bands and \(\mathrm{APAR}_{chl}\) was also analyzed using the experimental measurements (see Figure 12). Similar to the effect of the Cab content, the response of \(\mathrm{SIF}_{canopy}\) at the O\({}_{2}\)-A band to \(\mathrm{APAR}_{chl}\) was linear under different \(f_{c}\) conditions. But at the O\({}_{2}\)-B band, the relationship varies as the \(f_{c}\) changes for Nanbin Farm. 3.4 Effect of Plant Structure Type on the Relationship between \(\mathrm{SIF}_{canopy}\) and \(\mathrm{APAR}_{chl}\)  
Figure 13 shows scatter plots of \(\mathrm{SIF}_{canopy}\) against \(\mathrm{APAR}_{chl}\) at the O\({}_{2}\)-A and O\({}_{2}\)-B bands based on all the experimental data. Compared to the simulated data, the measured \(\mathrm{SIF}_{canopy}\mathrm{APAR}_{chl}\) patterns show a more diverse distribution while also presenting approximate linear relationships for experiments at different sites. It clearly shows that the slope of \(\mathrm{SIF}_{canopy}\) to \(\mathrm{APAR}_{chl}\) is higher for experimental observations with planophile canopy structure at Nanbin Farm and Sanya Station than that for winter wheat with spherical canopy structure at XTS Farm.