# FluoC Spec 2--An Automated Field Spectroscopy System to Monitor Canopy Solar-Induced Fluorescence
## 3 Results
This result implies that there is no need for routine dark measurements when the spectrometer is kept at a stable temperature (e.g., -10 \({}^{\circ}\)C). A look-up-table (LUT) that stores the dark current under various temperatures and integration times could be created before the field installation and used in the post-processing. We used the Kautsky effect as a test of the sensitivity of FluoSpec2 ([PERSON], 1931). A blue LED light was used as an excitation light source to induce fluorescence. A clear fluorescence peak and a gradual relaxation of fluorescence were detected by FluoSpec 2 in the lab (Figure 5). Examples of field irradiance, radiance, and reflectance data collected within ten minutes are shown in Figure 6.  
A network of FluoSpec 2, FluoNet, has been established in various types of terrestrial ecosystems in the past a few years, including grassland, forests, and agricultural fields (Table 1 and Figure 7). Figure 8 shows SIF data collected at four representative ecosystems during a growing season. SIF data have a clear diurnal pattern, and also a day-to-day variation as a result of changes in incoming radiation (cloudiness). During the summer at the Alaska tundra site, we observed a low (-0.05 mw/m\({}^{2}\)/nm/sr) but non-zero fluorescence from 10p-5a as a result of the midnight sun. In Howland, Maine, a higher sampling rate (every minute) results in a denser time-series. Across the biomes, SIF is highest in crop and lowest in tundra (which has 24 h\({}^{\prime}\) sunlight during the measurement period); temperate mixed forests and evergreen forests have similar magnitudes of SIF. The magnitudes of SIF values observed by FluoSpec 2 at various ecosystems were consistent with satellite-based retrievals [8; 9; 47]. This international ground remote sensing network is an important data sources for ecosystem research, combined with some regional in situ spectral networks under development, including EuroSpec [48] and ChinaSpec [49], and a few individual sites where SIF observations are being made or planned. Figure 4: **(A)** Dark current under various integration times (100 ms, 400 ms, 700 ms, 1000 ms, and 2500 ms). **(B)** The relationship between integration time and the dark current. **(C)** Dark current collected at different TEC temperatures. **(D)** Non-linear relationship between temperature and dark current, indicating the importance of keeping a stable detector temperature. Figure 5: Kautsky Effect detected by FluoSpec 2 in the lab using a blue light-emitting diode (LED) light. Figure 6: An example of data collected by FluoSpec 2 at noon. (**A**) Irradiance collected by the upward-looking cosine corrector and radiance collected by fiber optics pointing to the tree canopy. (**B**) Five consecutive reflectance spectra collected in ten minutes, calculated as radiance/irradiance. Figure 8: Examples of SIF collected during the growing season at four representative ecosystems. Figure 7: FluoNet. A network of sensors that measure SIF. The authors are also aware of installations conducted by other researchers in various types of ecosystems. Like FLUXNET, a global network of SIF measurements will benefit the scientific community.