Nitrogen dioxide and ozone retrieval from simulated SAGE III transmission measurements

A detailed discussion on the inversion algorithm developed by the Laboratoire d'Optique Atmospherique, University of Lille, France, for the analysis of the Stratospheric Aerosol and Gas Experiment III (SAGE III) solar occultation data is presented. The scope of the paper is limited to nitrogen dioxide, ozone and aerosol retrieval. The forward model algorithm for calculating atmospheric transmittances in the two SAGE III solar channels, at 440 nm and at 600 nm, is presented. Then the inversion algorithm is introduced, accomplished in two sequential steps: the first one is the spatial inversion of the simulated slant optical thickness profile to obtain the extinction coefficient profile and the second is the spectral inversion of the extinction coefficient at each altitude to separate gas and aerosol contributions by using a least squares method over the spectral signatures. Error analysis is also discussed: the results of this analysis indicate regression error of 1% or less in the aerosol retrieval, of 0.1% or less for the ozone retrieval and of about 0.1% for the nitrogen dioxide retrieval. The paper also discuss on the correlation between the relative differences and the relative contribution of the considered constituents in the total extinction coefficient and then can determine the inversion algorithm's performances.