Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 5 2 2005 10.5194/acpd-5-1469-2005 http://www.atmos-chem-phys-discuss.net/5/1469/2005/ http://www.atmos-chem-phys-discuss.net/5/1469/2005/acpd-5-1469-2005.html http://www.atmos-chem-phys-discuss.net/5/1469/2005/acpd-5-1469-2005.pdf 1469 1499 2005-03-14 Surface pressure retrieval from SCIAMACHY measurements in the O₂A Band: validation of the measurements and sensitivity on aerosols B. van Diedenhoven O. P. Hasekamp I. Aben SRON National Institute for Space Research, The Netherlands We perform surface pressure retrievals from cloud-free Oxygen A band measurements of SCIAMACHY. These retrievals can be well validated because surface pressure is a quantity that is, in general, accurately known from meteorological models. Therefore, surface 5 pressure retrievals and their validation provide important insight into the quality of the instrument calibration. Furthermore, they can provide insight into retrievals which are affected by similar radiation transport processes, for example the retrieval of total columns of H₂O, CO, CO₂ and CH₄. In our retrieval aerosols are neglected. Using synthetic measurements, we show that for low to moderate or high surface albedos this 10 leads to an under- or overestimation of the retrieved surface pressures, respectively. The surface pressures retrieved from the SCIAMACHY measurements indeed show this dependence on surface albedo, when compared to the corresponding pressures from a meteorological database. However, an offset of about 30 hPa was found, which can not be caused by neglecting aerosols in the retrieval. The same offset was found 15 when comparing the retrieved surface pressures to those retrieved from co-located GOME Oxygen A band measurements. This implies a calibration error in the SCIAMACHY measurements. By adding an offset of 1% of the continuum reflectance at 756nm to the SCIAMACHY reflectance measurements, this systematic bias vanishes.