Atmos. Chem. Phys. Discuss., 11, 20899-20946, 2011
www.atmos-chem-phys-discuss.net/11/20899/2011/
doi:10.5194/acpd-11-20899-2011
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
A method for evaluating bias in global measurements of CO2 total columns from space
D. Wunch1, P. O. Wennberg1, G. C. Toon1,2, B. J. Connor3, B. Fisher2, G. B. Osterman2, C. Frankenberg2, L. Mandrake2, C. O'Dell4, P. Ahonen5, S. C. Biraud14, R. Castano2, N. Cressie6, D. Crisp2, N. M. Deutscher7,8, A. Eldering2, M. L. Fisher14, D. W. T. Griffith8, M. Gunson2, P. Heikkinen5, G. Keppel-Aleks1, E. Kyrö5, R. Lindenmaier15, R. Macatangay8, J. Mendonca15, J. Messerschmidt7, C. E. Miller2, I. Morino9, J. Notholt7, F. A. Oyafuso2, M. Rettinger10, J. Robinson12, C. M. Roehl1, R. J. Salawitch11, V. Sherlock12, K. Strong15, R. Sussmann10, T. Tanaka9,*, D. R. Thompson2, O. Uchino9, T. Warneke7, and S. C. Wofsy13
1California Institute of Technology, Pasadena, CA, USA
2Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
3BC Consulting, Ltd., Alexandra, New Zealand
4Colorado State University, Fort Collins, CO, USA
5Arctic Research Centre of the Finnish Meteorological Institute, Helsinki, Finland
6Department of Statistics, The Ohio State University, Columbus, OH, USA
7University of Bremen, Bremen, Germany
8University of Wollongong, Wollongong, NSW, Australia
9National Institute for Environmental Studies, Tsukuba, Japan
10IMK-IFU, Garmisch-Partenkirchen, Germany
11Atmospheric & Oceanic Science, University of Maryland, College Park, MD, USA
12National Institute of Water & Atmospheric Research, Wellington, New Zealand
13Harvard University, Cambridge, MA, USA
14Lawrence Berkeley National Laboratories, Berkeley, CA, USA
15Department of Physics, University of Toronto, Toronto, ON, Canada
*now at: Japan Aerospace Exploration Agency, Tsukuba, Japan

Abstract. We describe a method of evaluating systematic errors in measurements of total column dry-air mole fractions of CO2 (XCO2) from space, and we illustrate the method by applying the method to the Atmospheric CO2 Observations from Space retrievals of the Greenhouse Gases Observing Satellite (ACOS-GOSAT) v2.8 data. The approach exploits the lack of large gradients in XCO2 south of 25° S to identify large-scale offsets and other biases in the ACOS-GOSAT data with several retrieval parameters and errors in instrument calibration. We demonstrate the effectiveness of the method by comparing the ACOS-GOSAT data in the Northern Hemisphere with ground truth provided by the Total Carbon Column Observing Network (TCCON). We use the correlation between free-tropospheric temperature and XCO2 in the Northern Hemisphere to define a dynamically informed coincidence criterion between the ground-based TCCON measurements and the ACOS-GOSAT measurements. We illustrate that this approach provides larger sample sizes, hence giving a more robust comparison than one that simply uses time, latitude and longitude criteria. Our results show that the agreement with the TCCON data improves after accounting for the systematic errors.

Citation: Wunch, D., Wennberg, P. O., Toon, G. C., Connor, B. J., Fisher, B., Osterman, G. B., Frankenberg, C., Mandrake, L., O'Dell, C., Ahonen, P., Biraud, S. C., Castano, R., Cressie, N., Crisp, D., Deutscher, N. M., Eldering, A., Fisher, M. L., Griffith, D. W. T., Gunson, M., Heikkinen, P., Keppel-Aleks, G., Kyrö, E., Lindenmaier, R., Macatangay, R., Mendonca, J., Messerschmidt, J., Miller, C. E., Morino, I., Notholt, J., Oyafuso, F. A., Rettinger, M., Robinson, J., Roehl, C. M., Salawitch, R. J., Sherlock, V., Strong, K., Sussmann, R., Tanaka, T., Thompson, D. R., Uchino, O., Warneke, T., and Wofsy, S. C.: A method for evaluating bias in global measurements of CO2 total columns from space, Atmos. Chem. Phys. Discuss., 11, 20899-20946, doi:10.5194/acpd-11-20899-2011, 2011.
 
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