## Materials and Methods
### Experimental Setup  
The experiment was conducted in the Xianlin campus of Nanjing University (32.1147 N, 118.9567 E) of China from May to August 2019. Four observation systems were used to continuously collect spectra of vegetation, soil, and standard reference of grey panel (Labsphere, North Sutton, NH, USA). _Epipremum aureum_ (_E. aureum_, the right in Figure 2) has a small leaf inclination angle which can reduce the influence of canopy structure and was planted in a plastic flowerpot. In total, thirty flowerpots with little difference in terms of growth status were used in this study. In order to reduce the impact of the background, a black cloth was laid beneath all the flowerpots (the left in Figure 2). _E. aureums_ were placed outside for 3 weeks before the experiment to adapt to the high light conditions. In addition, dry soil and grey reference with reflectance around 0.5 were chosen as the observation targets to evaluate the stability of the four systems. In this study, two different installation configurations, i.e., hemi-con (the upper in Figure 1A) and bi-hemi (the lower in Figure 1A) were employed to do four tests (Figure 3) as shown below.  
1 m, respectively. The hemi-con configuration of SIV remained unchanged and treated as a reference for comparison, the measurements of which proved to be reliable. The heights between the upwelling fiber of SIV and _E. aureus_ canopy and soil surface were still 2.6 m and 2.9 m, respectively. The lower heights of SI, SII and SIII were set to restrict the FOV of their upwelling sensors mainly covering the vegetation canopy. The measurement of _E. aureus_ canopy and soil was conducted from 07:00 to 18:00 local time.  
Test 3: Comparison of bi-hemi and hemi-con configurations with same upwelling view heights.  
Test 2 tested the configurations of bi-hemi and hemi-con at different heights. Considering SIF retrieved from sensors at different heights may be affected by different viewing and atmospheric conditions, the only difference in here Test 3 from Test 2 was that the same height between the upwelling fibers of four observation systems and _E. aureus_ canopy were 0.7 m, and the observation target was only _E. aureus_ to directly compare the difference between conical and hemispheric upwelling sensor.  
Test 4: Comparison of bi-hemi and hemi-con configurations over homogeneous canopy.  
Grass canopy is more homogeneous than the _E. aureus_ canopy and is continuous, reducing the effects of canopy heterogeneity and interference from background. Therefore, we designed Test 4 for a comparison of SIF retrieved from bi-hemi and hemi-con configurations between these two different canopies. The direct aim of this test is to find out if the results of bi-hemi and hemi-con configurations could be the same as the results of the two configurations in Tests 2 and 3, which were quite different. The configurations of bi-hemi and hemi-con were only adopted in SII and SIV (Figure 4), respectively. Their upwelling fibers were mounted at the same height (0.5 m) above the canopy of relatively homogeneous grass to measure reflected spectra. Furthermore, the upwelling fiber of SII and the upwelling fiber of SIV were then mounted 0.5 m and 1 m above the canopy to test if different heights of the upwelling sensors affect the results, respectively.  
Finally, we compared the performance of the four observation systems and the two different configurations (hemi-con and bi-hemi) according to integration time (IT), reflectance, and SIF from them, respectively (the orange ellipse in Figure 3).  
Figure 2: Experimental setup (**left**) and the conical footprint (**right**) of the four systems. (A) in the left shows the position of downwelling sensor and (B) shows that of upwelling sensor. The red ring in the right represents the field of view (FOV) of the conical upwelling sensor.