Intraseasonal dynamics and directional dependencies in novel tower-based SIF observations over a temperate deciduous forest

Solar-Induced chlorophyll Fluorescence (SIF) is increasingly being used as a proxy for photosynthetic activity and gross primary productivity (GPP). However, the SIF signal exhibits a dynamic diurnal cycle and is sensitive to small-scale variation of vegetation type and canopy structure. Satellite-based remote sensing of SIF is limited in spatial and temporal resolution and may be sensitive to these small-scale effects. We present analysis of tower-based observations of SIF using a PhotoSpec system deployed to the AmeriFlux site (US-UMB) at the University of Michigan Biological Station in the northern lower peninsula of Michigan. The PhotoSpec system comprises three spectrometers (red, far-red, and broadband) and a 2D scanning telescope. These observations, the first of their kind at a temperate deciduous forest, are made at smaller spatial scales and higher temporal resolution than satellite observations, which allows us to assess how canopy structure and diurnal variations of photosynthesis and its drivers affect the SIF signal.

We compare intraseasonal dynamics and diurnal patterns of the SIF signal with eddy covariance derived GPP. We further analyze the relationships between SIF and temperature and precipitation variability. Preliminary analysis suggests that summer SIF/productivity increases in response to precipitation, but decreases in response to above-average temperatures. Our observations also allow for the investigation of directional dependencies and influences on the red:far-red SIF ratio, as well as other vegetation parameters such as NDVI and PRI. This analysis provides insight into the interpretation of SIF observations over temperate deciduous forest and will improve our ability to effectively use the recent proliferation of available satellite observations.