## 3 Results
### Retrievals of SIF from Four Systems  
SIF retrieved from the four systems of hemi-con configuration measuring the plot of _E. aureus_ were compared (Figure 13). Diurnal variations of SIF shown in Figure 13A,C were acquired under slightly cloudy but stable sky conditions and those in Figure 13B,D were acquired under changeable cloudy conditions. All far-red SIF obtained from four systems exhibited minor differences as all sensors have the equivalent FOV and measured the same spot of the canopy with synchronously changed sun-viewer geometry across the day. On May 9 th, red SIF obtained from SIV were a little lower than those from another two systems under slightly cloudy conditions (Figure 13C), probably due to its longer IT (Figure 9) and lower SNR (Figure A4) which affect the detection of red SIF signal, which is much weaker than far-red SIF signal. These results indicate that different constructions and spectrometers used in the four systems have a rare influence on the retrieval of far-red SIF, but may affect retrieval of red SIF if the SNR is not high enough (usually > 1000:1), and a new-built prism system (SII) is effective to acquire a SIF signal. As SIFprism (SII) had proven able to obtain SIF as other systems, we specifically equipped the upwelling sensor with a cosine corrector (CC-3) to measure the hemispherical radiance of the canopy and used the FLoX (SIV) of hemi-con configuration as a reference. Downward sensors of SII of bi-hemi configuration and SIV of hemi-con configuration were set to measure a field of grassland, of which canopy was very homogeneous and large in respect to the FOV of upwelling hemispherical  
Figure 11: Reflectance measured by the four systems (**A**,**B**) of hemi-con and three systems (**C**,**D**) of bi-hemi configurations while the upwelling sensors pointing toward vegetation. (**C**) shows the data that the upwelling sensors of the three systems have almost same field of view as the conical sensor of SIV (different viewer height), while (**D**) shows that those three upwelling sensors were mounted at the same heights as that of SIV (different field of view). fiber. Diurnal variations of retrieved far-red and red SIF from the two systems showed quite similar values and features both at the same (Figure 14A-D) and different heights (Figure 14E-H) under different weather conditions, varying with changes of photosynthetic active radiation (PAR, shaded area) measured by a sunshine sensor BF5 (Delta-T Devices Ltd., Cambridge, UK). Either the upwelling sensors of the two systems set at the same or different heights, the footprints and viewing geometry of hemispherical sensor and conical senor were different, proving that this difference does not affect the variations of SIF signal in the homogenous field. Data shown in this figure were filtered according to the criteria of quality-control presented by [PERSON] et al. (2012), such that there were some small gaps while there were two big gaps in Figure 14A,C due to system failure. On these four days, whether under clear or cloudy conditions, the weather changed very fast, and SII was able to reveal the influence of changeable illumination on SIF observation as it has a shorter IT than that of SIV, and is consequently able to reject poor-quality data. As shown in Figure 11, the reflectance measured by SI, SII, and SIII of hemi-con configuration were different from those of bi-hemi configuration when measuring _E. aureus_ plot, of which canopy was considered as heterogeneous due to background effects. When the SIV of the hemi-con configuration was used as a reference, the values of far-red SIF retrieved from the other three systems were much lower than that from FLox (SIV) on two days under different weather conditions (Figure 15A,B). Meanwhile, diurnal patterns of far-red SIF from SIV were significantly different with that from systems of bi-hemi configuration which did not have clear diurnal patterns.