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Satellite Chartography of Atmospheric Methane and carbon monoxide from SCIAMACHY onboard ENVISAT

Christian Frankenberg(1), Thomas Wagner(1), Ulrich Platt(1), Peter Bergamaschi(2) and Jan Fokke Meirink(3)

(1) IUP Heidelberg, INF 229, 69120 Heidelberg, Germany
(2) Joint Research Centre IES, TP 263, 21020 Ispra, Italy
(3) IMAU, Princetonplein 5, 3584 Utrecht, Netherlands


The UV/Vis/near infrared spectrometer SCIAMACHY onboard the European ENVISAT satellite enables total column retrieval of atmospheric methane with high sensitivity to the lower troposphere. We apply an Iterative Maximum A Posteriori DOAS approach to derive vertical column densities of methane and carbon dioxide. Due to the low variability of CO2, its total column retrievals are used as proxy for the probed atmospheric column and thereby allow us to convert methane column densities to column averaged mixing ratios. In addition, CO2 abundances are modeled to account for possibly large seasonal variations in its total column. We discuss the retrieval algorithm and quantify possible impact factors on precision and accuracy (such as clouds and aerosols). The retrievals have been compared with methane abundances derived from the atmospheric transport models TM4 and TM5. High correlations between observed and simulated global CH4 column averaged mixing ratios are calculated for the entire 2-year period from 2003 through 2004. The theoretical retrieval precision of about 1.8% corresponds well with the observed average standard deviation between observations and simulations, which is on the order of 30 ppb. On the global scale, the most pronounced CH4 signal arises from source regions over India and South East Asia, broadly consistent with model simulations. SCIAMACHY retrievals, however, indicate higher CH4 abundances over tropical Africa and tropical America, pointing to hitherto underestimated CH4 emissions from tropical landmasses. First inverse modeling results using the methane retrievals will be shown to underline the enormous potential of SCIAMACHY with respect to global methane source inversions. Further, latest results of carbon monoxide retrievals revealing strongly enhanced abundances over the industrial regions in China and the seasonal patterns in biomass burning regions are shown.


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Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry