ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-5-2593-2005 Spatial and temporal characterization of SCIAMACHY limb pointing errors during the first three years of the mission von Savigny C. 1 Kaiser J. W. 2 Bovensmann H. 1 Burrows J. P. 1 McDermid I. S. 3 Leblanc T. 3 Institute of Environmental Physics (IUP/IFE), University of Bremen, Otto-Hahn-Allee 1, 28334 Bremen, Germany Remote Sensing Laboratories, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland Jet Propulsion Laboratory, California Institute of Technology, Table Mountain Facility, Wrightwood, CA 92397–0367, USA 29 09 2005 5 10 2593 2602 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/5/2593/2005/acp-5-2593-2005.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/5/2593/2005/acp-5-2593-2005.pdf

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 800m (220m) 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 1km 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 250m.