Carbon Monoxide Total Column Retrievals from Sentinel-5P Short-Wave Infrared Nadir Measurements

Kurzfassung

We present our first results in the Level1-2 processing of carbon monoxide (CO) total columns from Sentinel-5P (S5P) Short-Wave Infrared (SWIR) observations. The retrievals will be performed using the Beer Infrared Retrieval (BIRRA). BIRRA performs a least squares fit of Earth#s radiance (essentially transmission) to retrieve the molecular column densities (essentially density scaling factors) along with some auxiliary parameters (reflectivity etc.) [Gimeno Garcia et al., AMT 2011]. It has been developed at DLR since about 2005 and its computational core modules have been integrated in the operational SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Chartography) L1b-2 processor to retrieve CO from channel 8 (2.3 microns) and methane from channel 6 (1.6 microns) nadir observations. In the framework of DLR's SCIAMACHY activities BIRRA CO columns have been thoroughly examined in several intercomparisons [e.g. Hochstaffl et al., Remote Sens. 2018]. The forward model of BIRRA is essentially based on the GARLIC (Generic Atmospheric Radiation Line-by-line Infrared Code, Schreier et al. 2014) which has also been thoroughly verified and validated in numerous studies [Schreier et al., JQSRT 2018; Schreier et al., Molec. Astrophysics 2018]. In this study we will use the latest version of the BIRRA prototype featuring new enhancements such as advanced line shapes accounting for line mixing and speed dependence. An updated framework is providing appropriate auxiliary information (e.g. latest molecular spectroscopy data, a priori atmospheric profiles of pressure, temperature, and concentrations of interfering species, topography, ...). Finally, for diagnostic analysis we will consider the residual norms, residual spectra, the distribution of errors of the state vector elements, and comparisons with other data products. More specifically, we intend to estimate the quality of the product in view of the accuracy requirements defined in the mission preparation phase (i.e. 15% for CO) using NDACC (Network for the Detection of Atmospheric Composition Change) or TCCON (Total Carbon Column Observing Network) ground-based observations.