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The accuracy of total ozone computed from the Smithsonian AstrophysicalObservatory (SAO) optimal estimation (OE) ozone profile algorithm (SOE)applied to the Ozone Monitoring Instrument (OMI) is assessed throughcomparisons with ground-based Brewer spectrometer measurements from 2005 to2008. We also compare the three OMI operational ozone products, derived fromthe NASA Total Ozone Mapping Spectrometer (TOMS) algorithm, the KNMI (Royal Netherlands MeteorologicalInstitute)differential optical absorption spectroscopy (DOAS) algorithm, and KNMI'sOptimal Estimation (KOE) algorithm. The best agreement is observed betweenSAO and Brewer, with a mean difference of within 1% at most individualstations. The KNMI OE algorithm systematically overestimates Brewer totalozone by 2% at low and mid-latitudes and 5% at high latitudes while theTOMS and DOAS algorithms underestimate it by ~1.65% onaverage. Standard deviations of ~1.8% are calculated forboth SOE and TOMS, but DOAS and KOE have higher values of 2.2% and2.6%, respectively. The stability of the SOE algorithm is found to haveinsignificant dependence on viewing geometry, cloud parameters, or totalozone column. In comparison, the KOE–Brewer differences are significantlycorrelated with solar and viewing zenith angles and show significantdeviations depending on cloud parameters and total ozone amount. The TOMSalgorithm exhibits similar stability to SOE with respect to viewing geometryand total column ozone, but has stronger cloud parameter dependence. Thedependence of DOAS on observational geometry and geophysical conditions ismarginal compared to KOE, but is distinct compared to the SOE and TOMSalgorithms. Comparisons of all four OMI products with Brewer show noapparent long-term drift, but seasonal features are evident, especially forKOE and TOMS. The substantial differences in the KOE vs. SOE algorithmperformance cannot be sufficiently explained by the use of soft calibration(in SOE) and the use of different a priori error covariance matrices;however, other algorithm details cause fitting residuals larger by a factorof 2–3 for KOE

Validation of OMI total ozone retrievals from the SAO ozone profile algorithm and three operational algorithms with Brewer measurements