OMI total ozone column validation with Aura-AVE CAFS observations

In this paper we present validation results of the total ozone column data products of the Ozone Monitoring Instrument (OMI) by using airborne observations by the CCD Actinic Flux Spectrometer (CAFS) instrument. CAFS was flown during Aura Validation Experiment (AVE) campaigns organized by NASA in support of the validation of EOS-Aura satellite data products. The accuracy of individual CAFS total ozone column estimates of 2.0% on average is sufficient to meet the OMI validation requirements of 3.0%. A climatology was used to estimate the ozone column below the aircraft altitude. AVE validation results show that the OMI-TOMS total ozone column data product is of overall high quality as CAFS and OMI-TOMS agree to within less than 1% with a standard deviation of 8 DU (2–3%) with no significant dependence on total ozone column, latitude, cloud fraction, or solar zenith angle. The primary shortcoming in OMI-DOAS collection 2 total ozone column data is the air mass factor reflected in the dependence on solar zenith angle of the CAFS and OMI-DOAS total ozone column difference. Fortunately, the CAFS aircraft data collected during AVE provided useful insights that could not be obtained in any other way into where OMI satellite data retrieval improvements were needed. For OMI-DOAS collection 3 the air mass factor issue has been solved by calibration optimization and retrieval algorithm improvements, bringing airborne CAFS and OMI-DOAS satellite data to agreement within less than 1.5% with a standard deviation of 9 DU (2–3%), in compliance with the OMI validation requirements.