Measurements of CO2 concentrations over half a century have revealed that the terrestrial biosphere has accumulated carbon for decades at about a quarter of the rate of fossil fuel emissions. The…

This federal contract award, identified as 80NSSC18K1312, was granted to Colorado State University (CSU) by the National Aeronautics and Space Administration (NASA) for research related to measurements of atmospheric carbon dioxide (CO2) concentrations. The contract aims to develop an inverse modeling system using data from the Orbiting Carbon Observatory-2 (OCO-2) satellite to better understand regional carbon flux processes. Key objectives include incorporating eddy covariance flux data to constrain regional gross primary production (GPP) and respiration, estimating a leaf-to-canopy scaling factor for fluorescence, and improving the radiation code in the SiB4 biosphere model. The $431,823.16 grant also supports continued atmospheric inversions of OCO-2 data and participation in related research activities. This contract does not have a set-aside designation.

Measurements of CO2 concentrations over half a century have revealed that the terrestrial biosphere has accumulated carbon for decades at about a quarter of the rate of fossil fuel emissions. The terrestrial carbon sink may or may not be close to saturating [canadell ET AL., 2007; lequere ET AL., 2009; hayes ET AL., 2011; pan ET AL., 2011; ballantyne ET AL., 2012], with potentially dire consequences for amplification of future climate change [COX ET AL., 2000; fung ET AL., 2005; friedlingstein ET AL., 2006; LUO, 2007; reay ET AL., 2007; huntingford ET AL., 2008; gregory ET AL., 2009]. Atmospheric CO2 data clearly contains information that can be used to better understand sources and sinks of carbon. However, concentration data contain a mix of signals from a variety of upwind sources and sinks which forces one to employ atmospheric flux inversion techniques, a blend of atmospheric transport modeling and statistical modeling, to detangle the convolution of surface CO2 fluxes and atmospheric transport and allow insight into regional carbon flux processes. In the last OCO-2 science team call we were selected (#NNX15AG93G) to develop a pulse-based inversion system where CO2 flux corrections took the form of low order seasonal harmonics of CO2 flux, partitioned spatially and by plant functional type, from the SIB4 biosphere model. We also proposed to incorporate OCO-2 solar induced fluorescence (SIF) measurements into the inversion scheme as a constraint to GPP. We'RE in our third year of the proposal and have built the inversion system and used IT in several capacities (section 2). We are using our last year of the proposal to focus on incorporating SIF but have noticed several deficiencies with its use as a direct constraint on GPP in the inversion. We therefore are proposing an effort to continue performing inverse modeling of OCO-2 data (and OCO-3 when available) where we will focus on four items. First, we will incorporate the use of GPP flux data from eddy covariance towers into the inversion framework to overcome an obstacle in the use of OCO-2 SIF to constrain regional GPP and respiration. Second, as somewhat of a bonus, this additional eddy flux constraint will allow the constraining of a leaf-to-canopy scaling factor specific to fluorescence to be estimated, empirically, as part of the inversion framework. Third, we will investigate the modifications of radiation code in SIB4 to better model SIF from first principles, allowing bottom-up top-down comparisons of a leaf-to-canopy PFT specific scaling factor. Finally, we will continue to perform atmospheric inversions of emerging OCO-2 XCO2 data sets, as we have for two years, and assist in both intercomparison exercises (MIP), transport error -- carbon flux relationships (jointly with act-a campaign) and XCO2 L2 bias evaluation exercises.