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 project is 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 (GISS GCM 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
heightened concerns 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
Figure 1: Variation of CO2 concentrations over 5
decades
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’s DOE 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.
Forestland
29.4 Tg C/yr
54.6%
Cropland
15.1 Tg C/yr
28%
Grassland
9.4Tg C/yr
17.5%
Potential Annual C Sink: 53.9 Tg C/yr
Figure 2: Current Annual Carbon sequestration in
south east and south central U.S
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)
[http://oco.jpl.nasa.gov/] mission will make the
first global, space-based measurements of
Figure 3: RPC experiment to assess terrestrial carbon pools in Southern United States
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 Southeast
and
South-central
U.S.?