Our ability to close the Earth's carbon budget and predict feedbacks in a warming climate depends critically on knowing where, when and how carbon dioxide (CO2) is exchanged between the land and atmosphere. A new generation of satellite missions such as GOSAT and OCO-2 aim at retrieving column-averaged mixing ratios of atmospheric CO2 with sufficiently high accuracy and precision to enable inversions of land-atmosphere CO2 fluxes (so called top-down approach), greatly reducing uncertainties in biospheric net fluxes. However, a complementary bottom-up approach is needed to understand how biological processes control this net flux. For example, both the magnitude and its seasonality of photosynthesis (commonly referred to as GPP) are uncertain, and we currently have no direct means of assessing this flux.
The focus of this workshop is on a newly developed capacity to monitor chlorophyll fluorescence from terrestrial vegetation by satellite. This new retrieval promises to provide direct and spatially resolved information on GPP, an ideal bottom-up complement to the atmospheric net CO2 exchange inversions. Sunlight absorbed by chlorophyll in photosynthetic organisms is mostly used to drive photosynthesis, but some can also be dissipated as heat or re-radiated at longer wavelengths (660-800 nm). This re-emitted light is termed solar-induced chlorophyll fluorescence (Fs) and has been found to strongly correlate with GPP.
We will leverage our efforts on previous studies and workshops related to the ESA Earth Explorer FLEX mission concept. These studies, mostly focused on canopy and leaf-level interpretation, will provide the ground-work for our workshop, which will be focused on the global carbon cycle and synergies with atmospheric net flux inversions. Our primary goal is thus to advance our understanding of Fs and its relation to GPP and environmental stress at the planetary scale.