Carbon gas retrievals from SCIAMACHY observations using BIRRA

Abstract

The near infrared (NIR) region of the spectrum contains valuable information about atmospheric greenhouse gases such as CO2, CH4 or H2O. Moreover, down-looking NIR atmospheric spectra are sensitive to variations of molecular concentrations over the whole atmosphere, including the lower layers of troposphere, what makes this spectral region especially suitable for the analysis of emission sources and sinks. SCIAMACHY aboard the ENVISAT satellite is equipped with 3 channels (6, 7, and 8) on the NIR region. Channel 8 (2259--2386 nm) is mainly used for CO retrievals, whereas channel 6 (971--1773 nm) is exploited by most of the existing retrieval algorithms to obtain information on CH4 and CO2. For the processing of SCIAMACHY NIR data, the BIRRA (Beer InfraRed Retrieval Algorithm) has been implemented in the operational processor. In order to estimate the actual atmospheric state, BIRRA performs a separable least squares fit of the measured radiance where the atmospheric parameters are scaled to fit the observed spectra. The current version of the processor includes CO vertical column densities among the official products, whereas a new CH4 column-averaged mixing ratio product is planned for the next release. In this study, we present some representative results of CO and CH4 from SCIAMACHY NIR spectra using BIRRA.