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The ACOS CO_2 retrieval algorithm – Part II: Global X_(CO_2) data characterization

Crisp, D. and Frankenberg, C. and Messerschmidt, J. and Wennberg, P. O. and Wunch, D. and Yung, Y. L. (2012) The ACOS CO_2 retrieval algorithm – Part II: Global X_(CO_2) data characterization. Atmospheric Measurement Techniques, 5 (4). pp. 687-707. ISSN 1867-1381. doi:10.5194/amt-5-687-2012.

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Here, we report preliminary estimates of the column averaged carbon dioxide (CO_2) dry air mole fraction, X_(CO_2), retrieved from spectra recorded over land by the Greenhouse gases Observing Satellite, GOSAT (nicknamed "Ibuki"), using retrieval methods originally developed for the NASA Orbiting Carbon Observatory (OCO) mission. After screening for clouds and other known error sources, these retrievals reproduce much of the expected structure in the global X_(CO_2) field, including its variation with latitude and season. However, low yields of retrieved X_(CO_2) over persistently cloudy areas and ice covered surfaces at high latitudes limit the coverage of some geographic regions, even on seasonal time scales. Comparisons of early GOSAT X_(CO_2) retrievals with X_(CO_2) estimates from the Total Carbon Column Observing Network (TCCON) revealed a global, −2% (7–8 parts per million, ppm, with respect to dry air) X_(CO_2) bias and 2 to 3 times more variance in the GOSAT retrievals. About half of the global X_(CO_2) bias is associated with a systematic, 1% overestimate in the retrieved air mass, first identified as a global +10 hPa bias in the retrieved surface pressure. This error has been attributed to errors in the O_2 A-band absorption cross sections. Much of the remaining bias and spurious variance in the GOSAT X_(CO_2) retrievals has been traced to uncertainties in the instrument's calibration, oversimplified methods for generating O_2 and CO_2 absorption cross sections, and other subtle errors in the implementation of the retrieval algorithm. Many of these deficiencies have been addressed in the most recent version (Build 2.9) of the retrieval algorithm, which produces negligible bias in X_(CO_2) on global scales as well as a ~30% reduction in variance. Comparisons with TCCON measurements indicate that regional scale biases remain, but these could be reduced by applying empirical corrections like those described by Wunch et al. (2011b). We recommend that such corrections be applied before these data are used in source sink inversion studies to minimize spurious fluxes associated with known biases. These and other lessons learned from the analysis of GOSAT data are expected to accelerate the delivery of high quality data products from the Orbiting Carbon Observatory-2 (OCO-2), once that satellite is successfully launched and inserted into orbit.

Item Type:Article
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URLURL TypeDescription
Crisp, D.0000-0002-4573-9998
Frankenberg, C.0000-0002-0546-5857
Wennberg, P. O.0000-0002-6126-3854
Wunch, D.0000-0002-4924-0377
Yung, Y. L.0000-0002-4263-2562
Alternate Title:The ACOS CO2 retrieval algorithm – Part II: Global X(CO2) data characterization
Additional Information:© 2012 Author(s). This work is distributed under the Creative Commons Attribution 3.0 License. Published by Copernicus Publications on behalf of the European Geosciences Union. Received: 24 November 2011; Published in Atmos. Meas. Tech.; Discuss.: 3 January 2012; Revised: 1 March 2012; Accepted: 13 March 2012; Published: 2 April 2012. The GOSAT spectra were provided to the ACOS Team through a GOSAT Research Announcement (RA) agreement between the California Institute of Technology and the three parties, JAXA, NIES and the MOE. The meteorological data used to initialize the retrievals and as a reference for comparison with the surface pressure results were based on data and products of the European Centre for Medium-Range Weather Forecasts (ECMWF). TCCON data were obtained from the TCCON Data Archive, operated by the California Institute of Technology from the website at Part of the research described here was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.
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Issue or Number:4
Record Number:CaltechAUTHORS:20140716-110412369
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Official Citation:Crisp, D., Fisher, B. M., O'Dell, C., Frankenberg, C., Basilio, R., Bösch, H., . . . Yung, Y. L. (2012). The ACOS CO2 retrieval algorithm Part II: Global XCO2 data characterization. Atmos. Meas. Tech., 5(4), 687-707. doi: 10.5194/amt-5-687-2012
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:47265
Deposited By: Joanne McCole
Deposited On:16 Jul 2014 20:02
Last Modified:10 Nov 2021 17:37

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