Using Simulated OCO Measurements for Assessing Terrestrial Carbon Pools in the Southern United States

PI: Nicolas H. Younan

Roger L. King, Surya S. Durbha, Fengxiang Han,Zhiling Long, Jian Chen

Project Goal

This projectis focused on the assessment of terrestrial carbon pools in the south east and south central United States. In particular, this investigation intends to:

  • Leverage multiple NASA sensors, the terrestrial ecosystem model (CASA), and a transport model (GISSGCM Model E).
  • Undertake a Rapid Prototyping (RPC) experiment to address the need to quantify the carbon exchange over different ecosystems.
  • Test how well data from Orbiting Carbon Observatory (OCO) observations and CO2 measurement networks, models constrain CO2 fluxes at model-grid resolution.

Societal Impact

Carbon dioxide (CO2) is a greenhouse gas, whose atmospheric concentration has increased from 280 to 370 parts per million since the beginning of the industrial age (Figure 1). These rapid increases have heightenedconcerns about CO2’s role in global climate change. The analyses of regional carbon sources and sinks are essential to assess the economic feasibility of various carbon sequestration technologies for mitigating atmospheric CO2 accumulation and for mitigating impacts of global warming. Such an inventory is a prerequisite for regional trading of CO2 emissions.Results from the team’sDOE funded work has indicated that the annual terrestrial carbon sequestration in south east and south central United States (soil, forest, crop, pasture and house/furniture) can offset 40% of the total annual greenhouse gas emission in this region (Figure 2). Through proper policies and best management, about 10.1% of the total greenhouse gas in the region can be further offset by terrestrial sequestration.

This RPC experiment is aligned with the NASA Earth-Sun System Applied Sciences Program’s Carbon Management Program Element (FY 2006) plan that focuses on evaluation of OCO products through simulations of observations and baseline impact of OCO observations on existing decision support tools for carbon sequestration and emissions.

Methodology

The Orbiting Carbon Observatory (OCO) [ mission will make the first global, space-based measurements of atmospheric carbon dioxide (CO2) with the precision, resolution, and coverage needed to characterize CO2 sources and sinks on regional scales. This RPC experiment is focused towards the evaluation of CO2 column measurements from simulated OCO data and relating these datasets to terrestrial biospheric exchange of carbon from terrestrial surfaces (Figure 3).

Sensitivity analysis of how much Net Primary Production (NPP) increase is required to sustain the regional terrestrial carbon sink of the study area. Net Ecosystem Productivity (NEP) defined as Net Primary Production (NPP) minus the heterotrophic soil respiration predictions would be used to infer variability in regional scale carbon fluxes and to better understand patterns over terrestrial carbon sinks. The CASA model estimates of carbon products would be calibrated with field-based measurements of crop production, forest ecosystem fluxes, and inventory estimates of carbon pool sizes at multiple locations in the southeastern and south central United States. Comparative predictions from an atmospheric transport model (e.g. GISS Model E) and measurements of atmospheric carbon abundances from OCO and at observation sites distributed over the regions of interest will also be conducted. The spatial pattern of the observed and predicted differences can be used to infer the spatial distribution of sources and sinks of carbon dioxide by seeking a distribution of fluxes that, in a least squares sense, minimizes the difference between the model predictions and observation, as well as any prior information used to constrain the problem.

Science Questions

This RPC experiment seeks to address the following questions:

  • What information about carbon exchange can be obtained from OCO high-precision column measurements of CO2?
  • How can we integrate top-down OCO measurements with ground based measurements, atmospheric and terrestrial ecosystem models to quantify carbon exchange over different ecosystems?
  • What are the current annual rates of terrestrial carbon sequestration in each state of the South-east and South-central U.S.?