Retrieval of tropospheric carbon monoxide profiles from high-resolution interferometer observations: A new digital gas correlation (DGC) method and applications

Global tropospheric carbon monoxide (CO) distributions can be retrieved fro m observations by spaceborne gas correlation radiometers and high-resolutio n interferometers. The Measurement of Pollution in the Troposphere (MOPITT) is a gas correlation radiometer designed for tropospheric CO and CH4 remot e sensing. It is being developed at the University of Toronto and the Natio nal Center for Atmospheric Research for launch on the EOS/AM-1 platform in 1999. Spaceborne high-resolution interferometers with troposphere CO remote sensing capability include the Interferometric Monitor for Greenhouse gase s (IMG) instrument and the Troposphere Emission Spectrometer (TES). IMG was developed by the Ministry of International Trade and Industry (MITI) of Ja pan. It was on the ADEOS-1 spacecraft launched in October 1996. TES is bein g developed by the Jet Propulsion Laboratory for launch on the EOS/CHEM-1 p latform in 2002. For the purpose of testing the MOPITT data processing algorithms before lau nch, a new digital gas correlation (DGC) method was developed. This method makes it possible to use existing IMG observations to validate the MOPITT r etrieval algorithms. The DGC method also allows the retrieval of global tro posphere CO from MOPITT, IMG, and TES observations with a consistent algori thm. The retrieved CO profiles can be intercompared, and a consistent long time series of tropospheric CO measurements can be created. In this paper, the DGC method is described. The procedures for using the DGC method to ret rieve atmospheric trace species profiles are discussed. As an example, CO p rofiles from IMG observations have been retrieved with the DGC method as a demonstration of its feasibility and application in MOPITT retrieval algori thm validation.