Updates and Verification of the SAO ozone profile algorithm for the long-term OMI Ozone Profile (PROFOZ) product

The Smithsonian Astrophysical Observatory (SAO) O₃ retrieval algorithm has been implemented to produce the long-term Ozone Monitoring Instrument (OMI) O₃ profile (PROFOZ) data from October 2004 to present. Since the first data release, the efforts to improve the retrieval accuracy and long-term consistency of this product have continued. In this study, we will introduce updates to our algorithm and verify improvements of O₃ profile retrievals against long-term ozonesonde data. We improve a priori O₃ information using a tropopause-based O₃ profile climatology, which better constrains the O₃ retrievals in the upper troposphere and lower stratosphere. OMI slit functions are parameterized with a Super Gaussian, calibrated through cross-correlation between OMI irradiances and a high-resolution solar spectrum, instead of a Gaussian. Moreover, in order to account for slit function differences between radiance and irradiance, the spectral fit response to changes in the slit parameters is linearized and then included as a pseudo absorber in the fit process. The OMI irradiance spectrum is tabled as a 31 day-moving average instead of a climatological mean for 4 years to cancel out degradation offset between radiances and irradiances; 4 % degradation at 320 nm is observed in irradiances. The empirical soft calibration is re-derived to be consistent with updated implementation using average percent differences between measured and simulated radiance derived from one week of the MLS data in the tropics. MLS profiles are merged with climatological profiles below 215 hPa and then normalized with OMI-TOMS total O₃ to account for the spatial O₃ variability. These soft spectra are tabled in every year as a function of cross-track positions at UV1 spatial resolution in 270-365 nm, which also reveals linear degradations of radiances ( 1% @ 320 nm for 10 years). Use of time-dependent empirical soft spectra and irradiance spectra helps to improve the long-term consistency of O₃ retrievals. A final set "common mode" spectra are computed from remaining fitting residual spectra after soft calibration as a function of solar zenith angle in every month for 2006. The common mode is included as a pseudo absorber during fitting, which significantly reduces the discrepancy of O₃ retrieval accuracy between lower and higher solar zenith angles.