An automatic system for measuring canopy solar-induced chlorophyll fluorescence in the field for long-term

Abstract. Real-time, long-term and non-destructive measurements of crop photosynthetic functions and environmental factors in field have become a top priority in precision phenotyping. Recently, solar-induced fluorescence (SIF) shows promise for monitoring crop photosynthesis status of global agricultural systems, however, there are some uncertainties like coarser temporal and spatial resolution, and fluctuations of cloud cover that make accurate quantification of SIF and reflectance data more difficult from satellite platforms. In view of above situations, this study developed an automatic FluoSpec 2 system to simultaneously measure time-series canopy SIF, reflectance and meteorological factors in real field, which has high spatial-temporal resolution and allows for continuously unattended observations for months or even years in the proximal sensing. The instrument design, installation, calibration processes and SIF signal extraction methods of this system were detailed in this study. Field experiment was also carried out to evaluate the feasibility of this system in estimating canopy photosynthetic activities of rice. Field trials proved that this system can effectively capture canopy photosynthetic variations of rice during different growth stages. In addition, it also demonstrated that SIF was more sensitive than NDVI in both in diurnal and seasonal dynamics throughout the whole growth stages. Especially in seasonal dynamics, canopy SIF was well consistent with the variation trend of leaf photosynthesis. Thus, reliable canopy photosynthetic activities and growth status were obtained from this automatic FluoSpec 2 system, and provided evidence that this system can be applicable to any farmland ecosystems.