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Published November 2012 | Published
Journal Article Open

Atmospheric validation of high accuracy CO_2 absorption coefficients for the OCO-2 mission


We describe atmospheric validation of View the MathML source and View the MathML source CO_2 absorption coefficient databases for use by the Orbiting Carbon Observatory (OCO-2). The OCO-2 mission will collect the measurements needed to estimate column-averaged CO_2 dry air mole fraction within 1 ppm accuracy without the region- or airmass-dependent biases that would significantly degrade efforts to understand carbon sources and sinks on a global scale. To accomplish this, the forward radiative transfer model used to generate synthetic atmospheric spectra for retrievals must achieve unprecedented spectroscopic fidelity within the short wave infrared CO_2 bands sampled by the sensors. The failure of Voigt line shapes and conventional line mixing formulations for such objectives has motivated significant revisions to line shape models used to generate the gas absorption cross sections for the OCO-2 forward model. In this paper, we test line mixing and speed dependent line shapes combined with improved experimental line parameters. We evaluate pre-computed absorption coefficients in the two spectral regions of CO_2 absorbtion using high resolution FT-IR laboratory spectra, atmospheric spectra from the Total Carbon Column Observing Network (TCCON), and medium resolution soundings from the space-based Greenhouse Gases Observing Satellite (GOSAT).

Additional Information

© 2012, California Institute of Technology. . Received 13 March 2012; Received in revised form; 25 May 2012; Accepted 29 May 2012; Available online 12 June 2012. We thank the OCO-2 ACOS Level 2 algorithm team including Annmarie Eldering, Vivienne Payne and Michael Gunson. We thank the members of the OCO-2 science team including Eli Mlawer and Iouli Gordon. We have also benefited from the counsel of Mitchio Okumura, Joseph Hodges, and David Long. GOSAT TANSO-FTS 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 MOE. The European Centre for Medium-Range Weather Forecasts (ECMWF) provided meteorological data for initializing the retrievals. The Total Carbon Column Observing Network (TCCON) Archive, operated by he California Institute of Technology, supplied upward-looking measurement. U. S. funding for the Park Falls TCCON station comes from NASA's Terrestrial Ecology Program, grant number NNX11AG01G. A portion of the research described was carried out at the Jet Propulsion Laboratory, California Institute of Technology and The College of William and Mary under contracts with the National Aeronautics and Space Administration. US Government support acknowledged.

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