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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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https://doi.org/10.5194/amt-2017-173
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
13 Jun 2017
Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Atmospheric Measurement Techniques (AMT).
Methane profiles from GOSAT thermal infrared spectra
Arno de Lange and Jochen Landgraf SRON Netherlands Institute for Space Research, Utrecht, the Netherlands
Abstract. This paper discusses the retrieval of atmospheric methane profiles from the thermal infrared band of the Japanese Greenhouse Gases Observing Satellite (GOSAT) between 1210 and 1310 cm−1, using the RemoTeC analysis software. Approximately one degree of information on the vertical methane distribution is inferred from the measurements with the main sensitivity at about 9 km altitude but little sensitivity to methane in the lower troposphere. For verification, we compare the GOSAT methane abundance at measurement sites of the Total Carbon Column Observing Network (TCCON) to methane profiles provided by the Monitoring Atmospheric Composition and Climate (MACC) model fields scaled to the total column observations at the sites. Without any radiometric corrections of GOSAT observations, differences between both data sets can be as large as 10 %. To mitigate these differences, we developed a correction scheme using a principal component analysis of spectral fit residuals and airborne observations of methane during the HIAPER Pole-to-Pole Observations (HIPPO) campaign II and III. When the correction scheme is applied, the bias in the methane profile can be reduced to less than 2 % over the whole altitude range with respect to MACC model methane fields. Furthermore, we show that, with this correction, the retrievals result in smooth methane fields over land and ocean crossings and no differences are to be discerned between daytime and nighttime measurements. Finally, a cloud filter is developed for the nighttime and ocean measurements. This filter is rooted in the GOSAT-TIR measurements and is consistent with the cloud filter based on the GOSAT-SWIR measurements, despite the fact that the TIR-filter is less stringent.

Citation: de Lange, A. and Landgraf, J.: Methane profiles from GOSAT thermal infrared spectra, Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2017-173, in review, 2017.
Arno de Lange and Jochen Landgraf
Arno de Lange and Jochen Landgraf
Arno de Lange and Jochen Landgraf

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Short summary
Atmospheric methane abundances as function of altitude derived from the thermal infrared band of the Japanese GOSAT satellite show a systematic bias. It has been shown that simple correction schemes can lead to undesired consequences. The paper discusses a more elaborate approach resulting in methane profiles that fall within 2 % of independent reference measurements and models. This is true for different scenes around the globe and over the full altitude range.
Atmospheric methane abundances as function of altitude derived from the thermal infrared...
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