SASKMART is the program we use at the Odin-OSIRIS processing centre in Saskatoon to retrieve profiles of ozone (O3) and aerosols from the line of sight radiances measured by the OSIRIS spectrograph. The program was first deployed in October 2009 and has been used since that time to produce version 5.0.xx Level 2 products. The program uses the Sasktran V2 radiative transfer model as a forward model and a Multiplicative Algebraic Reconstruction Technique (MART) as the inversion scheme. Later versions of the code, 5.0.7 onwards, employ an error analysis scheme similar to those found in Optimal Estimation techniques. The algorithm does not require a-priori information in the weighted statistical sense used by optimal estimation techniques but does need initial guesses which we take from existing climatologies for NO2, aerosols and O3 and ECWMF for atmopsheric density and temperature. In our experience the final solution is insensitive to the initial guess.
The ozone data product has had considerbale validation work and is in excellent agreement with other instrumentation over the entire stratosphere. Greater variability occurs in the upper troposphere, part of which can be explained by natural variability. The aerosol product has had less validation but is still an excellent product. The aerosol product currently fits the radiances with an assumed aerosol particle size distribution which undoubtedly results in systematic errors associated with the incorrect choice of phase matrix. None-the-less we are confident the aerosol product does reflect true variations of radiance in the atmosphere due to the prescence of aerosols in the atmosphere. We are working on new algorithms to improve the data products but we truly believe the Saskmart version 5.0.xx family will continue to be a high quality product for years to come.