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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/amt-2018-353
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2018-353
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 19 Nov 2018

Research article | 19 Nov 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).

How bias correction goes wrong: Measurement of XCO2 affected by erroneous surface pressure estimates

Matthäus Kiel1, Christopher W. O'Dell4, Brendan Fisher3, Annmarie Eldering3, Ray Nassar5, Cameron G. MacDonald6, and Paul O. Wennberg1,2 Matthäus Kiel et al.
  • 1Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
  • 2Division of Engineering and Applied Sciences, California Institute of Technology, Pasadena, CA, USA
  • 3Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
  • 4Colorado State University, Fort Collins, CO, USA
  • 5Climate Research Division, Environment and Climate Change Canada, Toronto, ON, Canada
  • 6Department of Physics and Astronomy, University of Waterloo, Waterloo, ON, Canada

Abstract. Currently all measurements of XCO2 from space have systematic errors. To reduce a large fraction of these errors, a bias correction is applied to XCO2 retrieved from GOSAT and OCO-2 spectra using the ACOS retrieval algorithm. The bias correction uses, among other parameters, the surface pressure difference between the retrieval and the meteorological reanalysis. Erroneous surface pressure estimates, however, propagate nearly 1:1 into bias-corrected XCO2. For OCO-2, small errors in the knowledge of the pointing of the observatory (up to ∼130arcsec) introduce a bias in XCO2 in regions with rough topography. Erroneous surface pressure estimates are also caused by a bug in ACOS version 8, sampling meteorological analyses at wrong times (up to three hours after the overpass time). Here, we derive new geolocations for OCO-2's eight footprints and show how using improved knowledge of surface pressure estimates in the bias correction reduces errors in OCO-2's v9 XCO2 data.

Matthäus Kiel et al.
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Matthäus Kiel et al.
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