WF-DOAS Algorithm Theoretical Basis Document

A novel total ozone retrieval algorithm that we call weighting function DOAS has been successfully implemented as an alternative approach to the standard DOAS differential optical absorption spectroscopy) that is currently operational in the GOME retrieval Gome Data Processor Version 3.0). The weighting function DOAS method, abbreviated WF-DOAS, attempts to fit the vertical column density directly from the differential optical depth spectra and it can be applied to strong and weak absorption. This method has been demonstrated to be applicable to near-infrared trace gas column retrieval with CIAMACHY and it has been adapted for total ozone retrieval in the near UV region. The processing of the GOME data is done in a non-linear least squares fitting using look-up-tables of reference intensities, weighting functions, and Ring spectra derived from the multiple scattering radiative transfer model SCIATRAN/CDI. Particular attention has been placed on proper modeling of the Ring effect that show significant dependence on the ozone profile shape due to molecular (ozone) filling-in. Other geophysical parameters such as effective albedo, cloud-top-height, cloud fraction, and effective height that are retrieved from GOME spectral information are used for the first time in combination to improve the ozone retrieval.