Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 5 2 2005 10.5194/acpd-5-1733-2005 http://www.atmos-chem-phys-discuss.net/5/1733/2005/ http://www.atmos-chem-phys-discuss.net/5/1733/2005/acpd-5-1733-2005.html http://www.atmos-chem-phys-discuss.net/5/1733/2005/acpd-5-1733-2005.pdf 1733 1770 2005-03-18 The impact of SCIAMACHY near-infrared instrument calibration on CH₄ and CO total columns A. M. S. Gloudemans H. Schrijver Q. Kleipool M. M. P. van den Broek A. G. Straume G. Lichtenberg R. M. van Hees I. Aben J. F. Meirink SRON National Institute for Space Research, Utrecht, The Netherlands Royal Netherlands Meteorological Institute (KNMI), De Bilt, The Netherlands now at: Royal Netherlands Meteorological Institute (KNMI), De Bilt, The Netherlands now at: the European Space Agency, European Space Research & Technology Centre (ESA-ESTEC), Noordwijk, The Netherlands The effects of three important SCIAMACHY near-infrared instrument calibration issues on the retrieved methane (CH₄) and carbon monoxide (CO) total columns have been investigated: the effects of the growing ice layer on the near-infrared detectors, the effects of the orbital variation of the instrument dark signal, and the effects of the dead/bad detector pixels. Corrections for each of these instrument calibration issues have been defined. The retrieved CH₄ and CO total columns including these corrections show good agreement with CO measurements from the MOPITT satellite instrument and with CH₄ model calculations by the chemistry transport model TM3. Using a systematic approach, it is shown that all three instrument calibration issues have a significant effect on the retrieved CH₄ and CO total columns, although the impact on the CH₄ total columns is more pronounced than for CO. Results for three different wavelength ranges are compared and show good agreement. The growing ice layer and the orbital variation of the dark signal show a systematic, but time-dependent effect on the retrieved CH₄ and CO total columns, whereas the dead/bad pixels show a more random effect. The importance of accurate corrections for each of these instrument calibration issues is illustrated using examples where inaccurate corrections lead to a wrong interpretation of the results.