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Published May 27, 2012 | Published
Journal Article Open

Methane retrievals from Greenhouse Gases Observing Satellite (GOSAT) shortwave infrared measurements: Performance comparison of proxy and physics retrieval algorithms

Abstract

We compare two conceptually different methods for determining methane column-averaged mixing ratios image from Greenhouse Gases Observing Satellite (GOSAT) shortwave infrared (SWIR) measurements. These methods account differently for light scattering by aerosol and cirrus. The proxy method retrieves a CO_2 column which, in conjunction with prior knowledge on CO_2 acts as a proxy for scattering effects. The physics-based method accounts for scattering by retrieving three effective parameters of a scattering layer. Both retrievals are validated on a 19-month data set using ground-based X_CH_4 at 12 stations of the Total Carbon Column Observing Network (TCCON), showing comparable performance: for the proxy retrieval we find station-dependent retrieval biases from −0.312% to 0.421% of X_CH_4 a standard deviation of 0.22% and a typical precision of 17 ppb. The physics method shows biases between −0.836% and −0.081% with a standard deviation of 0.24% and a precision similar to the proxy method. Complementing this validation we compared both retrievals with simulated methane fields from a global chemistry-transport model. This identified shortcomings of both retrievals causing biases of up to 1ings and provide a satisfying validation of any methane retrieval from space-borne SWIR measurements, in our opinion it is essential to further expand the network of TCCON stations.

Additional Information

© 2012 American Geophysical Union. Received 1 February 2012; revised 12 April 2012; accepted 15 April 2012; published 30 May 2012. A.B. is supported by Deutsche Forschungsgemeinschaft (DFG) through the Emmy-Noether programme, grant BU2599/1–1 (RemoteC). Access to GOSAT data was granted through the 2nd GOSAT research announcement jointly issued by JAXA, NIES, and MOE. TCCON data were obtained from the TCCON Data Archive, operated by the California Institute of Technology from the Web site at http://tccon.ipac.caltech.edu/. GTOPO30 is available from the U.S. Geological Survey through the Earth Resources Observation and Science (EROS) Center (http://eros.usgs.gov/#/Find_Data/Products_and_ Data_Available/GTOPO30_info). MODIS Atmosphere data are distributed through http://ladsweb.nascom.nasa.gov/data/search.html. CarbonTracker results are provided by NOAA-ESRL, Boulder, Colorado, USA through http://www.esrl.noaa.gov/gmd/ccgg/carbontracker/.

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Published - Schepers_et_al-2012-Journal_of_Geophysical_Research_D10307.pdf

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Schepers_et_al-2012-Journal_of_Geophysical_Research_D10307.pdf
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Additional details

Created:
August 22, 2023
Modified:
October 23, 2023