ALBERT

Description: The European Space Agency's Ozone Climate Change Initiative project [O 3 -CCI] aims at producing and validating a number of high quality ozone data products generated from different satellite sensors. For total ozone, the O 3 -CCI approach consists of minimizing sources of bias and systematic uncertainties by applying a common retrieval algorithm to all level-1 data sets, in order to enhance the consistency between the level-2 data sets from individual sensors. Here we present the evaluation of the total ozone products from the European sensors GOME/ERS-2, SCIAMACHY/Envisat and GOME-2/MetOp-A produced with the GOME-type Direct FITting [GODFIT] algorithm v3. Measurements from the three sensors span more than 16 years, from 1996 to 2012. In this work, we present the latest O 3 -CCI total ozone validation resultsusing as reference ground-based measurements from Brewer and Dobson spectrophotometers archived at the World Ozone and UV Data Centre (WOUDC) of the World Meteorological Organization (WMO) as well as from UV-visible DOAS/SAOZ instruments from the Network for the Detection of Atmospheric Composition Change (NDACC). In particular, we investigate possible dependencies in these new GODFIT_v3 total ozone data sets with respect to latitude, season, solar zenith angle, and different cloud parameters, using the most adequate type of ground-based instrument. We show that these three O 3 -CCI total ozone data products behave very similarly and are less sensitive to instrumental degradation, mainly as a result of the new reflectance soft-calibration scheme. The mean bias to the ground-based observations is found to be within the 1±1% level for all three sensors while the near-zero decadal stability of the total ozone columns provided by the three European instruments falls well within the 1-3% requirement of the European Space Agency's Ozone Climate Change Initiative project.