Strategies for Retrieval of Tropospheric Greenhouse Gases in the Visible and Near Infrared From GOME and SCIAMACHY with a View to Future Missions

The Scanning Imaging Absorption SpectroMeter for Atmospheric CartograpHY (SCIAMACHY) will measure earth-scattered light from the atmosphere in the ultraviolet and visible (channels 1-6) and near infrared (channels 7 and 8). We outline retrieval strategies for the detection of H₂O, N₂O, CO and CH₄ using channel 8 data that are independent of the operational SCIAMACHY data product. In particular, we focus on retrieval method sensitivity and robustness of SCIAMACHY CO/CH₄ data products derived from a combination of the visible and near infrared channels as well as implications for a validation strategy. A complicating factor in the near infrared retrieval is the presence of very strong absorption bands of H₂O. We show how water vapor may be retrieved from visible bands situated in spectral regions which are covered both by GOME (Global Ozone Monitoring Experiment) and SCIAMACHY. These bands have relatively low optical thickness and well-understood scattering and background features. For example, GOME irradiance measurements of the visible water bands may be forward-modelled to high accuracy and thus may be used to facilitate the SCIAMACHY channel 8 retrieval. In addition we review retrieval strategies intended for future missions which are using SCIAMACHY as a benchmark, namely GEOSCIA (Geostationary SCIAMACHY) and ACECHEM (Atmospheric Chemistry Explorer for Chemistry and Climate Interaction).