Solar Occultation Measurements with SCIAMACHY in the UV-visible-IR Wavelength Region

Abstract

The focus of this thesis is the evaluation of the first solar occultation measurements performed by SCIAMACHY onboard ENVISAT in the UV-vis-NIR wavelength range. Vertical trace gas concentration profiles have been retrieved from atmospheric measurement spectra, fitting the differential structures of extinction signals. An introduction is given about the foundations of the occultation geometry. The underlying studies are separated into theoretical investigations about the sensitivity of the instrument with respect to atmospheric constituents and trace gas retrievals from the first real measurement data. It is shown that the spectrometer works as expected in occultation geometry. Spectral data have a high signal-to-noise ratio except for the UV wavelength range at low altitudes. First standard data products of ozone and nitrogen dioxide vertical profiles in the stratosphere and upper troposphere have been produced with errors in the order of 10 and 15 %, respectively. The inversion algorithm is based on the optimal estimation method or, alternatively, on the eigenvector decomposition method. Correction algorithms have been implemented concerning the tangent height of the line of sight and the pointing on the solar disk. The radiative transfer model is based on the Lambert-Beer law of extinction. The retrieval algorithm assumes the measured spectra to consist only of transmitted light rather than scattered light. Theoretical studies have been performed to demonstrate that this assumption is true. An estimation of different error sources is discussed as well.