## 5 Conclusions  
In this study, we conducted a field experiment for SIF measurements from four different observation systems (SI and SIII built from existing construction, SII newly built and SIV bought as a commercial product) together to find out whether SIF from different systems are comparable. We also investigated the impacts of different FOV on the SIF observations. IT, reflectance, and SIF retrieved from different systems with hemi-con and bi-hemi configurations were compared. Generally, the IT of spectrometer with large spectral range or a large slit is much shorter than the opposite one. We have demonstrated that the newly built prism system (SIFprism, SII) has the shortest IT and highest SNR giving credits to less light loss than splitter fiber and higher efficiency nearly two times of the construction using TTL and splitter fiber (SI). This advantage is also helpful to improve the data quality for SIF retrieval, especially where the weather is changeable. Reflectance collected from different systems showed small difference when measuring different targets, and correspondingly, diurnal courses of SIF (either red or far-red SIF) retrieved from different systems displayed marginal difference, either with hemi-con or bi-hemi configuration when (only) measuring homogeneous (continuous) vegetation canopy (grassland), demonstrating the consistency of different systems for spectra and SIF observations. We found that, however, when the target is heterogeneous (discontinuous) as in the _E. aureus_ plot, the values and diurnal pattern of far-red SIF derived from systems (SI, SII and SIII) with a bi-hemi configuration were obviously distinct from those derived from the system (SIV) with a hemi-con configuration.  
This is probably due to the different footprint sizes and viewing geometries between hemispherical and conical upwelling sensor attributed by multiple scattering at the far-red region. A larger FOV of the hemispherical sensor than conical sensor is suitable for the observation of a heterogeneous canopy and better matches the footprint of EC measurements, but was restricted for observation of a discontinuous canopy (such as small plots of control experiment). Our results highlight the importance of conducting the bi-hemi measurements for SIF retrievals to integrate with EC flux measurements which have a larger footprint. This study is of more technical than scientific importance, but it may nevertheless serve further studies on the comparison of SIF acquired from various sites with different observation systems.  
All of the authors conceived of, designed and performed the laboratory and field experiments.; Writing--Review & Editing, Q.Z., X.Z. and Y.Z.; Funding Acquisition, Q.Z. and Y.Z.  
This research was funded by National Natural Science Foundation of China, grant number: (41701393 and 41671421); by International Cooperation and Exchange Programs between NSFC and DFG grant number: (41761134082), by Natural Science Foundation of Jiangsu Province for Youth grant number: (BK20170641); and by China Postdoctoral Science Foundation, grant number: (2018T110477).  
We gratefully acknowledge the support from [PERSON] and [PERSON] (Department of Global Ecology, Carnegie Institution for Science) for helping us to build the prism system. We further acknowledge our group members for their help in the field work.  
The authors declare no conflict of interest.