Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 5 3 2005 10.5194/acpd-5-3701-2005 http://www.atmos-chem-phys-discuss.net/5/3701/2005/ http://www.atmos-chem-phys-discuss.net/5/3701/2005/acpd-5-3701-2005.html http://www.atmos-chem-phys-discuss.net/5/3701/2005/acpd-5-3701-2005.pdf 3701 3722 2005-06-07 Spatial and temporal characterization of SCIAMACHY limb pointing errors during the first three years of the mission C. von Savigny J. W. Kaiser H. Bovensmann J. P. Burrows I. S. McDermid T. Leblanc Institute of Environmental Physics (IUP/IFE), University of Bremen, Otto-Hahn-Allee 1, 28334 Bremen, Germany Remote Sensing Laboratories, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland Jet Propulsion Laboratory, California Institute of Technology, Table Mountain Facility, Wrightwood, CA 92397-0367, USA Limb scattering retrievals of atmospheric minor constituent profiles require highly accurate knowledge of the tangent heights during the measurements. The limb scattering measurements of the Scanning Imaging Absorption spectrometer for Atmospheric CartograpHY (SCIAMACHY) on Envisat are affected by tangent height errors of up to 2 km. This contribution provides a summary of the temporal and spatial variation of the SCIAMACHY limb pointing errors during the first three years of the SCIAMACHY mission. The tangent height errors are retrieved from the limb measurements in the UV-B spectral range. A seasonal modulation of the monthly mean tangent height offsets is identified with amplitudes of 800 m (220 m) before (after) the improvement of the Envisat orbit propagator model in December 2003. Even after the December 2003 orbit model improvement a constant offset component of about 1 km is present. Furthermore, pointing discontinuities are identified that coincide with the daily updates of the on-board orbit propagator model. In order to reduce the errors in ozone profile retrievals caused by pointing errors to less than 5%, the tangent heights have to be known to within 250 m.