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

J Bak,K Chance,J H Kim,X Liu,D P Haffner

doi:10.5194/acp-15-667-2015

Abstract

Abstract. The accuracy of total ozone computed from the Smithsonian Astrophysical Observatory (SAO) optimal estimation (OE) ozone profile algorithm (SOE) applied to the Ozone Monitoring Instrument (OMI) is assessed through comparisons with ground-based Brewer spectrometer measurements from 2005 to 2008. We also compare the three OMI operational ozone products, derived from the NASA Total Ozone Mapping Spectrometer (TOMS) algorithm, the KNMI (Royal Netherlands Meteorological Institute) differential optical absorption spectroscopy (DOAS) algorithm, and KNMI's Optimal Estimation (KOE) algorithm. The best agreement is observed between SAO and Brewer, with a mean difference of within 1% at most individual stations. The KNMI OE algorithm systematically overestimates Brewer total ozone by 2% at low and mid-latitudes and 5% at high latitudes while the TOMS and DOAS algorithms underestimate it by ~1.65% on average. Standard deviations of ~1.8% are calculated for both SOE and TOMS, but DOAS and KOE have higher values of 2.2% and 2.6%, respectively. The stability of the SOE algorithm is found to have insignificant dependence on viewing geometry, cloud parameters, or total ozone column. In comparison, the KOE–Brewer differences are significantly correlated with solar and viewing zenith angles and show significant deviations depending on cloud parameters and total ozone amount. The TOMS algorithm exhibits similar stability to SOE with respect to viewing geometry and total column ozone, but has stronger cloud parameter dependence. The dependence of DOAS on observational geometry and geophysical conditions is marginal compared to KOE, but is distinct compared to the SOE and TOMS algorithms. Comparisons of all four OMI products with Brewer show no apparent long-term drift, but seasonal features are evident, especially for KOE and TOMS. The substantial differences in the KOE vs. SOE algorithm performance 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 factor of 2–3 for KOE.

Highlights

The Dutch–Finnish Ozone Monitoring Instrument (OMI) (Levelt et al, 2006) aboard the NASA Aura satellite was launched on 15 July 2004 to continue the long-term record of satellite total ozone measurements, initiated in 1970 with the launch of the nadir-sounding Backscatter Ultraviolet instrument (BUV) aboard the Nimbus-4 spacecraft, and followed in 1978 with the launch of the Total Ozone Monitoring Spectrometer (TOMS) and Solar Backscatter Ultraviolet (SBUV) instruments aboard Nimbus-7
We have examined how the SOE–Brewer standard deviations change when SOE total ozone is retrieved at locations of TOMS measurements: they are reduced to 1.71 % in the mid-latitudes and 1.78 % in the high latitudes, which is less scatter than TOMS measurements
The OMI total column ozone data processed with SOE and the three OMI operational algorithms (KOE, TOMS, and differential optical absorption spectroscopy (DOAS)) are evaluated using 4 years (2005–2008) of Brewer measurements at 27 stations identified as good references using a selection procedure similar to that of Balis et al (2007)

Summary

Introduction

The Dutch–Finnish Ozone Monitoring Instrument (OMI) (Levelt et al, 2006) aboard the NASA Aura satellite was launched on 15 July 2004 to continue the long-term record of satellite total ozone measurements, initiated in 1970 with the launch of the nadir-sounding Backscatter Ultraviolet instrument (BUV) aboard the Nimbus-4 spacecraft, and followed in 1978 with the launch of the Total Ozone Monitoring Spectrometer (TOMS) and Solar Backscatter Ultraviolet (SBUV) instruments aboard Nimbus-7. There are two independent operational total ozone algorithms applied to OMI measurements to produce the standard OMI total column ozone products. J. Bak et al.: Validation of OMI total ozone retrievals from the SAO ozone profile tage of the spectroscopic capability of the OMI instrument. Bak et al.: Validation of OMI total ozone retrievals from the SAO ozone profile tage of the spectroscopic capability of the OMI instrument These were both developed at the Royal Netherlands Meteorological Institute (KNMI). The variety of OMI operational ozone data products offers a good opportunity to compare the total ozone retrieval performance among the different algorithms and to identify their strengths and shortcomings

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Conclusion