New global observations of the terrestrial carbon cycle from GOSAT: Patterns of vegetation fluorescence with gross primary productivity

Christian Frankenberg, Jet Propulsion Laboratory / Caltech, christian.frankenberg@jpl.nasa.gov (Presenter)
Joshua B. Fisher, JPL, jbfisher@jpl.nasa.gov
Jung-Eun Lee, JPL, jung-eun.lee@jpl.nasa.gov
Luis Guanter, Atmospheric, Oceanic and Planetary Physics, University of Oxford, UK., guanter@atm.ox.ac.uk
Christiaan Van der Tol, ITC International Institute for Geo-Information Science and Earth Observation, Enschede, The Netherlands., tol@itc.nl
Sassan Saatchi, CALTECH/JPL, sassan.saatchi@jpl.nasa.gov

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 is exchanged between the land and atmosphere. Terrestrial gross primary production (GPP) constitutes the largest flux component in the global carbon budget, however significant uncertainties remain in GPP estimates and its seasonality. Solar-induced chlorophyll fluorescence is a powerful proxy for assessing biomass photosynthetic activity since photosynthesis and fluorescence are directly coupled processes. This gives rise to re-emission of light

between approximately 670 and 780 nm. Passive methods to quantify the fluorescence signal are mainly based on the filling-in of highly saturated O2 absorption structures. This method, however, was mostly applied in field-based measurements and is not directly applicable to space-borne retrievals. We show that variability of aerosols

in the atmosphere load and surface pressure cannot be unequivocally disentangled from fluorescence since all these factor impact the absorption depths of O2 lines. This gives rise to biases in the retrieved scattering properties in typical multi-spectral XCO2 retrievals when using the O2 A band but not when focussing solely of solar Fraunhofer lines.

We will a) present our retrieval method based on an iterative, non-linear least-squares fitting of Fraunhofer lines, b) discuss the potential impact on XCO2 retrievals and c) show recent fluorescence results from more than one year of GOSAT data.

Empirically, we show that global spaceborne observations of solar induced chlorophyll fluorescence exhibit a strong linear correlation with GPP. We found that the fluorescence emission even without any additional meteorological, vegetation type or model information has the same or better predictive skill in estimating GPP as those derived from traditional remotely-sensed vegetation indices using ancillary data and model assumptions. Our results demonstrate that retrievals of chlorophyll fluorescence provide direct global observational constraints for GPP and open an entirely new viewpoint on the global carbon cycle. We anticipate that global fluorescence data in combination with consolidated plant physiological fluorescence models will be a step-change in carbon cycle research and enable an unprecedented robustness in the understanding of the current and future carbon cycle.

Presentation Type:  Poster

Session:  Coupled Processes at Land-Atmosphere-Ocean Interfaces   (Mon 4:00 PM)

Associated Project(s): 

• Related Activity

Poster Location ID: 25