A method for evaluating bias in global measurements of CO<sub>2</sub> total columns from space
Author:
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.,Wofsy S. C.
Abstract
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.
Publisher
Copernicus GmbH
Reference45 articles.
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