# FluoC Spec 2--An Automated Field Spectroscopy System to Monitor Canopy Solar-Induced Fluorescence
## 4 Discussion  
Continuous and long-term observations of ecosystem functioning can provide important insights into ecosystem responses to environmental drivers and constraints to ecosystem models. Photosynthesis is one of the key ecosystem processes and its variations over space and time provide valuable information on the carbon, water, and nutrient cycles [50]. Automating measurements like SIF and canopy reflectance can also allow a shift in the focus on measurements which are equally important but difficult to measure automatically [51]. A network of these sensors is a tool to allow the understanding of inter-ecosystem differences in plant functioning, responses to environmental stresses, and up-scaling to regional and global scales. We showed that, with careful design, continuous observations of SIF could be achieved in various types of ecosystems. The following are key issues to address when designing the system: (1) the use of a spectrometer with a high signal-to-noise ratio (SNR, \(\sim\)1000:1 @755 nm). It should be noted that the SNR during actual measurements varies from wavelength to wavelength and is also related to the changes in the signal, i.e., solar radiation. It also needs a well-documented nonlinear, spectral resolution, fine enough to resolve Fraunhofer lines. QEpro represents a significant advancement compared with other OceanOptics spectrometers, including HR2000+. (2) stable temperature control is required. We showed that with the temperature control, background noise drops dramatically (Figure 4C). Considering that the SIF at 760 nm is only 1\(\sim\)5% of the incoming radiation at 760 nm, a small improvement in noise reduction can be significant for SIF retrieval. (3) Humidity control is required. Under high humidity (relative humidity >80%), we found that there were significant changes in the spectra, shown as wiggles randomly appearing along the spectra as a result of water condensation on the detector (data not shown). The spectrometer needs to be better protected from humidity than many other field instruments (e.g., dataloggers) as it is not designed for outdoor use. This automated system has been evolving and improving since its first measurement in 2012 at Harvard Forest [2]. Steps have been taken to make the system more reliable in complicated environments. Additional changes will be made in the near future. For example, a multi-angle system would allow observations of more individuals and an estimation of the angular effect of SIF. As a remote sensing measurement, it is subjected to sun-sensor-object geometry [52]. Measurements are subjected to both leaf physiological controls [53; 54] and structural effects [55; 56]. It is important to disentangle these two effects on the temporal variations of SIF to answer the question whether whether the changes are a result of changes in the fraction of sunlit and shaded leaves, or leaf-level physiology, such as varying non-photochemical quenching [12; 54]. Measurements of multi-angle SIF and canopy reflectance may allow us to solve this issue using existing radiative transfer theories [52; 55; 57]. Several important research questions can potentially be addressed with FluoNet: (1) the diurnal variations of SIF, photosynthesis, and non-photochemical quenching (NPQ). As the three main pathways for absorbed photosynthetically active radiation, the variation in SIF, photosynthesis,