Using Simulated OCO Measurements for Assessing Terrestrial Carbon

Pools in the Southern United StatesPI: Nick Younan

Roger King, Surya Durbha, Fengxiang HanZhiling Long, Narendra Rongali, Haiqing Zhu

Orbiting Carbon Observatory (OCO)

Estimated global total net flux of carbon from changes in land use increased from 503 Tg C (1012 g) in 1850 to 2376 Tg C in 1991 and then declined to 2081 Tg C in 2000.

The global net flux during the period 1850-2000 was 156 Pg C (1015 g), about 63% of which was from the tropics.

The US estimated flux is a net source to the atmosphere of 7 Pg C for the period 1850-2000, but a net sink of 1.2 Pg C for the 1980s and 1.1 Pg C for the 1990s.

Hence, better estimates at regional level are required to understand and reduce the uncertainties in the sink/source estimations

Introduction

Data Source: Houghton, R.A, 1999. The annual net flux of carbon to the atmosphere from the changes in land use 1850-1990. Tellus 51B:298-313

Source:http://www.netl.doe.gov/technologies/carbon_seq/overview/images/carbon-flux-diagram.gif

What are the current annual rates of terrestrial carbon sequestration in each state of the region?

What's the overall contribution of terrestrial carbon sequestration in each state of the region to mitigating its total greenhouse gas emission?

What's the current baseline for possible carbon trading in the region?

What's the potential of further enhancing terrestrial carbon sequestration in the region?

What are the overall economic impacts of current and potential terrestrial carbon sequestration on the region?

Currently funded DOE project for leverage

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

State SW SE Central Delta North

C De

nsity

, kg

C/m

2

County-level Surface Soil organic C Density (0-30 cm, kg C/m2)

Total Soil Organic C Density (kg C/m2)

State SW SE Central Delta North0

5

10

15

20

25

C De

nsity

, kg

C/m

2

County-level MS Forest C density (kg C/m2)

0

3

5

8

10

State SW SE Central Delta North

C De

nsity

, kg

C/m

2

Total Soil C: 809 Tg C

SWSECen-tralDeltaNorth

Comparison of Soil C and Forest C Storage in regions of MS

Total Forest C: 392 Tg C

Soil Organic C:

16535 Tg C, 76%

Forest C:

4454 Tg C, 20.5%

Housing/Furniture C: 661 Tg C, 3.0%

Crop C: 85 Tg C, 0.4%

Pasture C: 27.8 Tg C,

0.13%

Total Terrestrial C Storage: 21762 Tg C

Total terrestrial carbon storage and pools in the Study Area

Focus Areas of the Project (Plan B) The 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.?

What is the current baseline in the region for possible carbon trading?

What is the potential for enhancing terrestrial carbon sequestration?

NASA-CASA (Carnegie Ames Stanford Approach) model is designed to estimate monthly patterns in carbon fixation, plant biomass, nutrient allocation, litter fall, soil nutrient mineralization, and CO2 exchange, including carbon emissions from soils world-wide.

Assimilates satellite NDVI data from the MODIS sensor into the NASA-CASA model to estimate

Spatial variability in monthly net primary production (NPP), biomass accumulation, and litter fall inputs to soil carbon pools

NASA-CASA Model

Data Inputs:

NDVI ( MODIS) , Soil (SSURGO), Precipitation (PRISM), Air Temperature (PRISM), Land Mask, Solar Radiation (NARR), Vegetation type.

Outputs: Carbon pools, LAI, NPP, NEP, AET,APAR , FAPR, LEAFFR, NBP, NPP

moist, NPP temp, PET, resp, rootfr, soilc, stemfr. Other:

Soil, Land cover, Parameters.

CASA Model-Inputs/Outputs

Soil Types (SSURGO) Precipitation (PRISM)

CASA output fits/reflects well with the combination of Soil C and forest C in county-level of MS

Soil Microbial Respiration source of Carbon

Total Soil Carbon

Leaf Area Index (LAI)-2002

May

Jun July

Net Primary Productivity (NPP)-2002

May

Jun July

Monthly NPP was estimated in CASA as :NPP=f(NDVI)x PAR x LUE x g(T) x h(W)

Net Ecosystem Productivity (NEP)-2002

May

Jun July

RPC Experimental Design (Modified)

• Assimilation of aircraft measurements, satellite data (precipitable water, surface winds)

• Vegetation Indices• Biome type• Soil properties• Weather Reanalysis

Meteorology(e.g. GOES

data analysis)

• 1 year spinup• Monthly

• Terrestrial CO2 surface flux

• Winds, cloud mass fluxes, model Parameters

• Forward Transport Model

• Fossil Fuels

1 year spinup (2002)Land

Surface Model (CASA)

Transport Model [CO2] OBS

• OCO, Networks

Inversion

Design of Simulation Experiments

Simulated OCO data not available from NASA yet. Currently use data generated on our own.

Evaluation

TransportModel

EnsembleBased

Inversion

CASAModel

PerturbationWith Errors

Simulated OCO Observations

Surface Fluxes

Simulated PriorsPerturbationWith Errors

Estimated Fluxes

Kalman Filter

Bayesian data assimilation is conceptually simple but computationally prohibitive for application on large problems.

Kalman filter is a simplified approximation to the Bayesian estimation, which assumes: Normality of error statistics,

and Linearity of error growth.

Two main approaches can be followed to handle observations (Mathieu et al, 2008):1.A Filter, whereby the

analysis is only influenced by observations made in the past, which is the case for real-time applications and forecasting.

2. A smoother, where the analysis is influenced by all observation available over a given period “T” ( assimilation window)

Ensemble Based Assimilation

Ensemble based approaches combine the Kalman filter concept with Monte-Carlo techniques.

More accurate than the Kalman filter because there are no assumptions about the normality and linearity of errors.

Investigated two methods for the update process: deterministic (EnSRF) and stochastic (EnKF).

ModelErrors

AdditionForecast

Ensemble-based Update

Update

Initial Ensemble

Background Ensemble

StatisticalAnalysis

ObservationsMeanError Covariance

Kalman GainReduced Kalman Gain

Updated Ensemble

Example Assimilation Results (I)

The synthetic ground truth fluxes simulate one source area and one sink area.

The ensemble based technique was able to assimilate the observations to generate flux estimates with small errors.

Observations

Assimilation Results Assimilation Errors

Ground Truth Fluxes

100

75

50

25

0

-25

-50

source

sink

Example Assimilation Results (II)

Errors are consistent throughout all time steps. Results are similar in this case for both the deterministic (EnSRF) and the

stochastic (EnKF) methods. Working on Implementing the covariance localization technique for the

update process. Estimates for background error covariance may be inaccurate when

small ensembles are utilized. This technique helps to improve the accuracy for such estimation based on small ensembles.

Time Steps

Error Statistics Obtained from a 10-Step Assimilation Experiment

Time Steps

Mean Standard Deviation

Input data sets for the CASA model conditioned ( written several scripts, ArcMap models) for the southern United States

CASA model simulations for the entire Southern United states in progress.

Sensitivity studies of CASA model outputs with NASA-CQUEST is being performed.

In situ soil carbon studies completed for Southern United States Explored several transport models for suitability for carbon fluxes

transport. Currently working on WRF-CHEM for this purpose. Assimilation Code-based on Ensemble Kalman filter(both stochastic

and deterministic update methods) developed in Matlab. Participated in 2008 Carbon Cycle and Ecosystems Joint Science

Workshop to be held April 28 - May 2, 2008

Tasks Completed/Ongoing

Publications Younan, N. H. , Durbha, S. S., King, R. L., Han, F. X, Long, Z., Rongali, N.,

Zhu, H., (2009) . "Data Assimilation for Assessing Terrestrial Carbon Pools in the Southern United States”. 33rd International Symposium on Remote Sensing of Environment (ISRSE), Italy.

Younan, N. H., King, R. L., Durbha, S. S., Han, F. X, Long,  Z., Chen, J. (2007). “Using Simulated OCO Measurements for Assessing Terrestrial Carbon Pools in the Southern United States”. American Geophysical Union ( AGU) , Fall Meeting .

Durbha, S. S., Younan, N., King, R., Han, F. X., Long, Z. (2008). A Rapid Prototyping Capability Experiment to Assess Terrestrial Carbon Pools in Southern United States. 2008 NASA Carbon Cycle and Ecosystems Joint Science Workshop, Maryland, USA.

Nutrient fertilizer requirements for sustainable biomass supply to meet U.S. bioenergy goal (In revision).

County-level distribution of soil and forest carbon storage in Mississippi ( under preparation)

Validation of NASA-CASA model for terrestrial carbon pools in Mississippi. ( under preparation)

Questions?

Source :http://earthobservatory.nasa.gov/Features/CarbonCycle/Images/carbon_cycle_diagram.jpg