Ring effect: Impact of rotational Raman scattering on radiative transfer in earth's atmosphere

One significant limitation to the accuracy of the remote sensing of trace gas constituents in the atmosphere, using UV-visible spectroscopy and scattered sunlight, has often been a reliable knowledge of the so-called Ring effect. In this study it is demonstrated that the filling-in of Fraunhofer and gas absorption features, resulting from Rotational Raman scattering (RRS), explains to high accuracy the Ring effect. A radiative transfer model has been adapted to include RRS and carefully validated by comparison with Ring effect data by other models and from ground-based and satellite data. The analysis of the principle components of the simulated Ring spectra enabled the Fraunhofer and gas absorption filling-in to be separated. This yields a simple, and therefore computational fast, parameterization of the Ring effect suitable for trace gas retrievals.,This approach was tested for the retrieval of NO2 which is considered to be a worst case with respect to absorption feature filling-in for a trace gas retrieved from scattered light. Analysis of the errors in the vertical column of NO2 derived using differential optical absorption spectroscopy (DOAS) technique indicate that they are;dependent on the amount of NO2 present in the atmosphere when regarding the experimental Ring spectra. This implies that calculated Ring spectra may be superior for DOAS retrievals, compared to the experimentally determined Ring spectra. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.