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Harvard Forest Research Project 2023

  • Title: A tower-based monitoring system to complement mutli-angular solar-induced fluorescence measurements from low Earth orbit.
  • Principal investigator: Lucy Hutyra (lrhutyra@bu.edu)
  • Institution: Boston University
  • Primary contact: Lucy Hutyra (lrhutyra@bu.edu)
  • Team members: Taylor Jones
  • Abstract:

    The terrestrial biosphere is a crucial sink for anthropogenic emissions of carbon to the atmosphere. However, it is also the source of the largest uncertainties in estimated global carbon budgets, due to insufficient on-the-ground data to fully constrain fluxes and feedbacks in modeled global gross primary productivity (GPP). In response to this challenge, there has been increasing interest in measuring solar-induced fluorescence (SIF), a faint chlorophyll fluorescence signal emitted by vegetation in a process related to photosynthesis. Several satellite platforms currently measure SIF from space, in an effort to remotely monitor vegetation productivity at large scales. Satellite SIF retrievals show a direct, linear relationship with GPP model outputs and flux tower estimates across biomes. However, the link between SIF and leaf or whole-plant physiology on the ground and on shorter time scales remains a crucial area of study. The Orbiting Carbon Observatory 3 (OCO-3) is a SIF-monitoring instrument currently on board the International Space Station, whose low Earth orbit will provide a crucial opportunity to obtain SIF measurements made at a fine scale at differing times of day, and from multiple viewing angles. OCO-3 allows for targeted monitoring of areas of interest, including the Harvard Forest. These data will likely offer key insights into the effects of the diurnal cycle in photosynthetic activity on the remotely measured SIF signal. In order to complement and contextualize these satellite observations, we installed a SIF-measuring spectrometer system on the walk-up tower at the Harvard Forest in July 2020. The field of view of this system is pointed into the fetch of the eddy-covariance flux tower in order to relate SIF measurements made from a proximal vantage point to estimates of primary productivity. In addition, individual trees or branches closer to the walk-up tower can be targeted in order to examine the effects of sun angle, shading, and environmental drivers of variability in the retrieved SIF signal. The subsequent scaling of insights gained from this instrument deployment will allow for better-constrained relationships between SIF and its environmental controls for use by the broader modeling and remote sensing community, which can inform the next generation of remote sensing-driven productivity models.