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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  08 May 2020

08 May 2020

Review status
This preprint is currently under review for the journal AMT.

Evaluation of single-footprint AIRS CH4 Profile Retrieval Uncertainties Using Aircraft Profile Measurements

Susan S. Kulawik1, John R. Worden2, Vivienne H. Payne2, Dejian Fu2, Steve C. Wofsy3, Kathryn McKain4,5, Colm Sweeney4, Bruce C. Daube Jr.6, Alan Lipton7, Igor Polonsky7, Yuguang He7, Karen E. Cady-Pereira7, Edward J. Dlugokencky8, Daniel J. Jacob6, and Yi Yin9 Susan S. Kulawik et al.
  • 1BAER Institute, 625 2nd Street, Suite 209, Petaluma, CA, USA
  • 2Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA,USA
  • 3School of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA
  • 4National Oceanic and Atmospheric Administration, Earth System Research Laboratory, Boulder, CO, USA
  • 5University of Colorado, Cooperative Institute for Research in Environmental Sciences, Boulder, CO, USA
  • 6Harvard University, Cambridge, MA 02138, USA
  • 7Atmospheric and Environmental Research, Inc., Lexington, Massachusetts, USA
  • 8NOAA ESRL Global Monitoring Division, Boulder, Colorado, USA
  • 9California Institute of Technology, USA

Abstract. We evaluate the uncertainties of methane optimal estimation retrievals from single footprint thermal infrared observations from the Atmospheric Infrared Sounder (AIRS). These retrievals are primarily sensitive to atmospheric methane in the mid-troposphere through the lower stratosphere (~2 to ~17 km). We compare to in situ observations made from aircraft during the Hiaper Pole to Pole Observations (HIPPO), the NASA Atmospheric Tomography Mission (ATom) campaigns, and from the NOAA ESRL aircraft network, between the surface and 5–13 km, across a range of years, latitudes between 60 S to 80 N, and over land and ocean. After a global, pressure dependent bias correction, we find that the land and ocean have similar biases and that the reported observation error (combined measurement and interference errors) of ~27  ppb is consistent with the standard deviation between aircraft and individual AIRS observations. A single measurement has measurement (noise related) uncertainty of ~17 ppb, a ~20 ppb uncertainty from radiative interferences (e.g. from water, temperature, etc.), and ~ 30 ppb due to smoothing error, which is partially removed when making comparisons to in situ measurements or models in a way that account for this regularization. We estimate a 16 ppb validation error because the aircraft typically did not measure methane at altitudes where the AIRS measurements have some sensitivity, e.g. the stratosphere. Daily averaged AIRS measurements of at least 9 observations over spatio-temporal domains of < 1 degree and 1 hour have a standard deviation of ~17 ppb versus aircraft, likely because the observation errors from temperature and water vapor (for example) are only partly reduced through averaging. Seasonal averages can reduce this ~17 ppb uncertainty further to ~10 ppb, as determined through comparison with NOAA aircraft, likely because uncertainties related to radiative effects of temperature and water vapor can be reduced when averaged over a season.

Susan S. Kulawik et al.

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Status: final response (author comments only)
Status: final response (author comments only)
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Susan S. Kulawik et al.

Susan S. Kulawik et al.


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Latest update: 20 Sep 2020
Publications Copernicus
Short summary
This paper shows comparisons of a new methane product from the AIRS satellite to aircraft-based observations. We show that this AIRS methane product provides useful information to study seasonal and global methane trends of this important greenhouse gas.
This paper shows comparisons of a new methane product from the AIRS satellite to aircraft-based...