B) Interpretation and exploitation of global fluorescence data: GFZ

B) Interpretation and exploitation of global fluorescence data

Gross primary production (GPP) from Martin Jung’s data-driven model and space-based sun-induced fluorescence (SIF) data from GOME-2 for the northern hemisphere in July 2010. The spatial differences reflect different land cover types and imply that different environmental and plant structure parameters must be considered for the global scaling of SIF to GPP (figure by Max Voigt).

Spatial patterns of maximum monthly gross primary production (GPP) per 0.5° grid box for 2009 from data-driven (A) and process-based (B) models together with maximum monthly SIF at 740 nm (C). The fraction of C4 crop area (mostly corn in this region) depicts the approximate area of the US Corn Belt (D) (figure from Guanter et al., 2014).

We evaluate the potential of the derived global fluorescence data sets as a proxy for vegetation photosynthesis and gross primary production (GPP, output from photosynthesis). Because of the coarse spatial resolution of the global data sets currently available, we mostly rely on a data-driven approach, in which we compare fluorescence with other relevant data sets, such as space-based vegetation indices and geophysical parameters derived from spectral reflectance measurements, GPP estimates from carbon models and a range of meteorological parameters expected to drive vegetation photosynthesis at the synoptic scale.

Two main questions to be answered by this research are: (i) how can we link our space-based top-of-canopy fluorescence measurements to GPP on a global scale, and (ii) where and under which conditions the fluorescence observations can provide a better handle for vegetation functioning than other existing data sets like vegetation indices. We performe specific studies on those areas where we identify that fluorescence data can be particularly useful, such as large cropland areas and boreal forests, in order to gain a better understanding of the terrestrial carbon cycle through fluorescence data.