SCIAMACHY limb measurements of NO2, BrO and OClO. Retrieval of vertical profiles: Algorithm, first results, sensitivity and comparison studies

The Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) measures scattered sun light also in limb viewing mode (i.e. tangential to Earth's surface and its atmosphere), which allows determining vertical profiles of atmospheric trace gases. First results on the retrieval of NO2, BrO and OClO profiles froth the SCIAMACHY Limb measurements are presented and compared to independent satellite and balloon borne observations. For the profile retrieval we use a two step approach: First, Slant Column Densities (SCDs) of the respective absorber are determined in the UV/VIS spectral range by Differential Optical Absorption Spectroscopy (DOAS). Second, inversion of the retrieved SCDs (as function of tangent height) yields vertical profiles of the trace gas concentration (as function of altitude). For that purpose, we either apply an optimal estimation method (constraining the inversion by a priori information) or invert the measurements by a least squares approach (independently from a priori). For both approaches box air mass factors calculated by the 3D full spherical radiative transfer model TRACY-II are utilized as weighting functions. The agreement of the retrieved profiles with balloon validation measurements as well as with other space borne measurements of stratospheric trace gas profiles (e.g. by SMR on Odin) is investigated. For OClO, case studies on the sensitivity of the retrieved SCDs on fitting parameters (e.g. wavelength range, polarisation correction) and the impact of the a priori on the retrieved profiles are performed. Also, the significance of the obtained dataset of concentration profiles of NO2, BrO and OClO for studies on stratospheric chemistry is discussed. (C) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.