Retrieval of Ozone Profiles Using a Weighted Multiplicative Algebraic Reconstruction Technique from SCIAMACHY Limb Scattering Observations

This study describes the use of the weighted multiplicative algebraic reconstruction technique (WMART) to obtain vertical ozone profiles from limb observations performed by the scanning imaging absorption spectrometer for atmospheric chartography (SCIAMACHY). This technique is based on SaskMART (the combination of the multiplicative algebraic reconstruction technique and SaskTRAN radiative transfer model), which was originally developed for optical spectrometer and infrared imaging system (OSIRIS) data. One of the objectives of this study was to obtain consistent ozone profiles from the two satellites. In this study, the WMART algorithm is combined with a radiative transfer model (SCIATRAN), as well as a set of measurement vectors comprising five Hartley pairing vectors (HPVs) and one Chappuis triplet vector (CTV), to retrieve ozone profiles in the altitude range of 10-69 km. Considering that the weighting factors in WMART have a significant effect on the retrievals, we propose a novel approach to calculate the pair/triplet weighting factors using wavelength weighting functions. The results of the application of the proposed ozone retrieval scheme are compared with the SCIAMACHY v3.5 ozone product by University of Bremen and validated against profiles derived from other passive satellite observations or measured by ozonesondes. Between 18 and 55 km, the retrieved ozone profiles typically agree with data from the SCIAMACHY ozone product within 5% for tropics and middle latitudes, whereas a negative deviation exists between 35 and 50 km for northern high latitudes, with a deviation of less than 10% above 50 km. Comparison of the retrieved profiles with microwave limb sounder (MLS) v5.0 indicates that the difference is within +/- 5% between 18 and 55 km, and an agreement within 10% is achieved in other altitudes for tropics and middle latitudes. Comparison of the retrieved profiles with OSIRIS v7.1 indicates that the average deviation is within +/- 5% between 20 and 59 km, and difference of approximately 10% is achieved below 20 km. Compared with ozonesondes data, a general validity of the retrievals is no more than 5% between 15 and 30 km.