Abstract

Vertically constrained COVertically constrained CO22 retrievals from TCCON Measurements retrievals from TCCON Measurements Le Kuai1, Brain Connor2, Debra Wunch1, Run-Lie Shia1, Charles E Miller3, Geoffrey C Toon3, Paul O Wennberg1 and Yuk Yung1

1. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, United States.2. BC Consulting Ltd., 6 Fairway Dr, Alexandra 9320, New Zealand.

3. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States.

AbstractMapping the sources and sinks of carbon flux is one of the principle challenges in

the current study of carbon cycle. Both the ground measurements and spacecraft observations improve our understanding of the spatial and temporal distributions of the carbon dioxide (CO2) in the atmosphere. Although the sources and sinks of CO2 are mostly located near surface, its transport in the atmosphere connects the sources and sinks. Therefore, vertical profile of CO2 is also important.

Total Carbon Column Observing Network (TCCON) is a network of ground-based Fourier Transform Spectrometers recording direct sunlight in the near-infrared spectral region. Its CO2 product provides an essential validation resource for the Orbiting Carbon Observatory-2 (OCO-2), Sciamachy, and GOSAT. The information analysis shows that there is 2.6 degrees of freedom of the CO2 retrievals from TCCON measurements. Thus, the profile retrieval could estimate 3 state vectors in vertical levels. The synthetic work shows successful results. The error in XCO2 is less than 0.5 ppm. In the real measurement retrievals, the aircraft observations of the CO2 profile is treated as a true CO2 profile. The spectra within +/- 1 hour window are considered as simultaneous measurements with aircraft data. The error in XCO2 from real measurement retrieval is less than 0.8 ppm. The improvement of real measurement retrieval is expected by using updated voigt profiles in the forward model. The success of the vertical profile retrieval contributes to the progress of carbon problem.

Definition of information content (H) and degree of freedom (ds)

Future work • Channel selection using information analysis (Kuai et al., 2010)• Update spectroscopic parameters and line shape function in forward model• Study the seasonal cycle and interannual variability in lower, middle and upper troposphere.• Compare with AIRS measurements• Compare with the simultaneous retrievals of CO2 profile (AIRS/TES + GOSAT/OCO-2)

The purpose for the vertically constrained CO2 retrievals• Estimate the sources and sinks near surface• Understand the dynamics in the vertical transport

• Study the seasonal and interannual variability of CO2 in different levels of the

atmosphere.

A51C-0121

€

In − A = (KT Sξ−1K + Sa

−1)Sa−1 = ˆ S Sa

−1

H =1

2ln(1+ λ i

2) = −1

2ln In − A

i∑

ds = λ i2 /(1+ λ i

2) = tr(A)i

∑

˜ K = Sξ

1

2KSa

1

2

Sa: the a priori covariance matrix;

Sξ: the measurement error covariance matrix;

K: the Jacobian; A: the averaging Kernel;

λi: the eigenvalues of

€

˜ K

Realistic retrievals from TCCON

•Flight measurement of CO2 profile• Time: 16:30 on July 12, 2004

•CO2 retrieval from TCCON measurements• 1.6 micron band (resolution:0.02/cm)• Within ± 1 hour: 15:30~17:30• 32 spectra

•Sa: 1% CO2 variation

•Levels in box: 0~3 km, 3~5 km,5~70 km

Conclusions1) It is possible to retrieve the vertical information of CO2 from TCCON measurement.2) The quality of the profile retrieval depends on the shape of a priori.3) Using model or constant CO2 profile as a priori, the retrieval error in partial XCO2 in each box is less than 1 ppm and in total XCO2 is less than 0.8 ppm.

The Total Carbon Column Observing Network (TCCON) is a network of ground-based Fourier Transform Spectrometers recording direct solar spectra in the near-infrared spectral region. Accurate and precise column-averaged abundance of CO2 are retrieved. It provides an essential validation resource for the Orbiting Carbon Observatory (OCO), Sciamach, and GOSAT.

1)

2)

snr H DOF

885 14.2 4.2

200 6.9 2.6

Sa(i, i) = (3%)2

Noise=max(Tr)/snr

Synthetic Retrievals• Measured spectrum is GFIT calculation using flight measured CO2 profile on Jul. 12, 2004.

• The scaling factors of a priori profiles to flight profile are 0.99 and1.01.

• Retrieve 3 scaling factors for the CO2- (0~5 km) (6 ~10 km) (11 ~ 70 km)

XCO2_flt=374.24 ppm XCO2_ret=374.29 ppm XCO2_ret=374.20 ppm

XCO2_flt 374.2 ppm Error (ppm)

XCO2_prf 373.9 ppm -0.3

XCO2_scl 373.2 ppm -1

Total Column averaged CO2

Partial Column averaged CO2

A prior = flight * 1.01The vertically constrained retrieval has a better agreement with aircraft CO2 profile than the

scaling retrieval. The robust analysis shows that the error in total XCO2 is no more than 0.6 ppm.

3)XCO2_flt 374.2 ppm Error

(ppm)

XCO2_prf 373.7 ppm -0.5

XCO2_scl 373.1 ppm -0.9

Total column averaged CO2

Partial column averaged CO2

A priori = modeled CO2

The retrieval with a priori profile from model that fits the GLOBALVIEW values has a good agreement with aircraft CO2 profile.

The increase of error is due to the mismatch of the profile shape. The error is total XCO2 is less than 0.8 ppm which is still smaller than that for scaling retrieval.

A priori = constant profile

With the constant profile as a priori, the error in partial column averaged CO2 is less

than 1 ppm. It is less than 0.7 for error in total column averaged CO2. Relaxing the

CO2 constrain at lower troposphere results in a better agreement in partial column

averaged CO2.

4)

The CO2 profile

from synthetic retrievals are less than 0.2 ppm away from the true profile. The error in total XCO2 is less than 0.05 ppm.

Diag(Sa)=[1%,1%,1%]2 Diag(Sa)=[2%,1%,1%]2

a) b) a) b)

XCO2_flt 374.2 ppm Error (ppm)

XCO2_prf_a 373.8 ppm -0.4

XCO2_prf_b 373.5 ppm -0.7

XCO2_scl 373.6 ppm -0.6

Total Column averaged CO2