Satellite Measurements of Solar-Induced Fluorescence Help to Constrain CO2 Fluxes in Atmospheric Inversions

Abstract:

We examine the ability of satellite-based measurements of solar-induced fluorescence (SIF) from GOME-2 to help explain the variability in atmospheric CO₂ observations over North America. This work presents the first application where remotely sensed SIF measurements have been incorporated into a CO₂ flux inversion. We utilize a geostatistical inverse modelling (GIM) framework to examine if SIF provides additional information over traditional vegetation indices in explaining the spatiotemporal patterns of CO₂ flux, and if so, what is the influence of SIF on the resulting flux estimates. Results show that at the 16 day scale, SIF offers substantial information, beyond that of Leaf Area Index (LAI), fraction of photosynthetically active radiation (fPAR), normalized difference vegetation index (NDVI), and enhanced vegetation index (EVI), for constraining inverse-modeling estimates of CO₂ flux. Inverse-modeling estimates of CO­₂ flux that incorporate SIF show an increase in CO₂ uptake in the midwest US (temperate savanna, grasslands, and cropland) and a reduction in uptake in Canada (boreal forests) and the pacific northwest US (temperate coniferous forests) with differences occurring primarily during the peak of the growing season. These results confirm previous results from site-level studies showing an apparent increase in estimated GPP over U.S. cropland regions when using SIF to inform estimates. Additionally, this work highlights the utility of combining satellite measurements of SIF with atmospheric CO₂ observations to improve our understanding of the terrestrial carbon cycle.