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The remote sensing of the atmospheric greenhouse gases methane (CH4) andcarbon dioxide (CO2) in the troposphere from instrumentation aboardsatellites is a new area of research.In this manuscript, results obtained fromobservations of the up-welling radiation in the near-infrared by SCIAMACHYon board ENVISATare presented.Vertical columns of CH4, CO2 andoxygen (O2) have been retrieved and the (air or) O2-normalised CH4 andCO2 column amounts, the dry air columnaveraged mixing ratios XCH4 and XCO2derived.In this manuscript the first results, obtained by using the version 0.4 of theWeighting Function Modified (WFM) DOAS retrieval algorithm applied to SCIAMACHYdata, are described and compared with global models.For the set of individual cloud free measurements over landthe standard deviation of thedifference with respect to the models is in the range ~100–200 ppbv(5–10%) for XCH4 and ~14–32 ppmv(4–9%) for XCO2.The inter-hemispheric difference of the methane mixing ratio,as determined from single day data,is in the range30–110 ppbv and in reasonable agreement with the corresponding model data (48–71 ppbv).The weak inter-hemispheric difference of the CO2 mixing ratio can also be detectedwith single day data.The spatiotemporal pattern of the measured and the modelled XCO2are in reasonable agreement. However,the amplitude of the difference between the maximum and theminimum for SCIAMACHY XCO2 is about ±20 ppmv which is about a factor of four larger thanthe variability of the model data which is about ±5 ppmv.More studies are needed to explain the observed differences.The XCO2 model field shows low CO2 concentrations beginning of January 2003 over aspatially extended CO2 sink region located in southern tropical/sub-tropicalAfrica. The SCIAMACHY data also show low CO2 mixing ratiosover this area.According to the model the sink region becomes a source regionabout six monthslater and exhibits higher mixing ratios. The SCIAMACHY and the model dataover this region show asimilar time dependence over the period from Januaryto October 2003.These results indicate that for the first time a regionalCO2 surface source/sink region has been detected by measurements from space.The interpretation of the SCIAMACHY CO2 and CH4 measurements isdifficult, e.g., because the error analysis of the currently implemented retrievalalgorithm indicates that the retrieval errors are on the same order as the smallgreenhouse gas mixing ratio changes that are to be detected

Atmospheric methane and carbon dioxide from SCIAMACHY satellite data: initial comparison with chemistry and transport models