ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-6-127-2006 Overview of SCIAMACHY validation: 2002–2004 Piters A. J. M. 1 Bramstedt K. 2 Lambert J.-C. 3 Kirchhoff B. 4 5 Royal Netherlands Meteorological Institute, Department of Climate Research and Seismology, De Bilt, The Netherlands Institute for Environmental Physics, University of Bremen, Germany Belgian Institute for Space Aeronomy, Brussels, Belgium Institute for Environmental Physics, University of Heidelberg, Germany Max Planck Institute for Chemistry, Department for Atmospheric Chemistry, Mainz, Germany 25 01 2006 6 1 127 148 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/6/127/2006/acp-6-127-2006.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/6/127/2006/acp-6-127-2006.pdf

SCIAMACHY, on board Envisat, has been in operation now for almost three years. This UV/visible/NIR spectrometer measures the solar irradiance, the earthshine radiance scattered at nadir and from the limb, and the attenuation of solar radiation by the atmosphere during sunrise and sunset, from 240&nbsp;to 2380 nm and at moderate spectral resolution. Vertical columns and profiles of a variety of atmospheric constituents are inferred from the SCIAMACHY radiometric measurements by dedicated retrieval algorithms. With the support of ESA and several international partners, a methodical SCIAMACHY validation programme has been developed jointly by Germany, the Netherlands and Belgium (the three instrument providing countries) to face complex requirements in terms of measured species, altitude range, spatial and temporal scales, geophysical states and intended scientific applications. This summary paper describes the approach adopted to address those requirements. <P style="line-height: 20px;"> Since provisional releases of limited data sets in summer 2002, operational SCIAMACHY processors established at DLR on behalf of ESA were upgraded regularly and some data products &ndash; level-1b spectra, level-2 O<sub>3</sub>, NO<sub>2</sub>, BrO and clouds data &ndash; have improved significantly. Validation results summarised in this paper and also reported in this special issue conclude that for limited periods and geographical domains they can already be used for atmospheric research. Nevertheless, current processor versions still experience known limitations that hamper scientific usability in other periods and domains. Free from the constraints of operational processing, seven scientific institutes (BIRA-IASB, IFE/IUP-Bremen, IUP-Heidelberg, KNMI, MPI, SAO and SRON) have developed their own retrieval algorithms and generated SCIAMACHY data products, together addressing nearly all targeted constituents. Most of the UV-visible data products &ndash; O<sub>3</sub>, NO<sub>2</sub>, SO<sub>2</sub>, H<sub>2</sub>O total columns; BrO, OClO slant columns; O<sub>3</sub>, NO<sub>2</sub>, BrO profiles &ndash; already have acceptable, if not excellent, quality. Provisional near-infrared column products &ndash; CO, CH<sub>4</sub>, N<sub>2</sub>O and CO<sub>2</sub> &ndash; have already demonstrated their potential for a variety of applications. Cloud and aerosol parameters are retrieved, suffering from calibration with the exception of cloud cover. In any case, scientific users are advised to read carefully validation reports before using the data. It is required and anticipated that SCIAMACHY validation will continue throughout instrument lifetime and beyond and will accompany regular processor upgrades.