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

D. Schepers, S. Guerlet, A. Butz, J. Landgraf, C. Frankenberg, O. Hasekamp, J.-F. Blavier, N.M. Deutscher, D.W.T. Griffith, F. Hase, E. Kyro, I. Morino, V. Scherlock, R. Sussmann, E.A.A. Aben

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Abstract

We compare two conceptually different methods for determining methane column-averaged mixing ratios (X<inf>CH4</inf>) 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<inf>2</inf> column which, in conjunction with prior knowledge on CO<inf>2</inf> 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<inf>CH4</inf> measurements 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<inf>CH4</inf> with 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. © Copyright 2012 by the American Geophysical Union.
Original languageEnglish
Article numberD10307
JournalJournal of Geophysical Research. Atmospheres
Volume117
DOIs
Publication statusPublished - 2012

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