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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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Atmos. Meas. Tech., 9, 4327-4353, 2016
http://www.atmos-meas-tech.net/9/4327/2016/
doi:10.5194/amt-9-4327-2016
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
06 Sep 2016
Seven years of IASI ozone retrievals from FORLI: validation with independent total column and vertical profile measurements
Anne Boynard1, Daniel Hurtmans2, Mariliza E. Koukouli3, Florence Goutail1, Jérôme Bureau1, Sarah Safieddine4, Christophe Lerot5, Juliette Hadji-Lazaro1, Catherine Wespes2, Jean-Pierre Pommereau1, Andrea Pazmino1, Irene Zyrichidou3, Dimitris Balis3, Alain Barbe6, Semen N. Mikhailenko7,8, Diego Loyola9, Pieter Valks9, Michel Van Roozendael5, Pierre-François Coheur2, and Cathy Clerbaux1,2 1LATMOS/IPSL, UPMC Sorbonne Universités, UVSQ, CNRS, Paris, France
2Spectroscopie de l'Atmosphère, Chimie Quantique et Photophysique, Université libre de Bruxelles, Brussels, Belgium
3Laboratory of Atmospheric Physics, Aristotle University of Thessaloniki, Thessaloniki, Greece
4Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
5Belgian Institute for Space Aeronomy, Brussels, Belgium
6Université de Reims-Champagne-Ardenne, Groupe de Spectrométrie Moléculaire et Atmosphérique, 51062 Reims, France
7V.E. Zuev Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences, Academician Zuev Square 1, 634021 Tomsk, Russia
8Climate and Environmental Physics Laboratory, Ural Federal University, 19, Mira Avenue, 620002 Yekaterinburg, Russia
9Institut für Methodik der Fernerkundung (IMF), Deutsches Zentrum für Luft- und Raumfahrt (DLR), Oberpfaffenhofen, Germany
Abstract. This paper presents an extensive intercomparison and validation for the ozone (O3) product measured by the two Infrared Atmospheric Sounding Interferometers (IASIs) launched on board the MetOp-A and MetOp-B satellites in 2006 and in 2012 respectively. IASI O3 total columns and vertical profiles obtained from Fast Optimal Retrievals on Layers for IASI (FORLI) v20140922 software (running up until recently) are validated against independent observations during the period 2008–2014 on a global scale. On average for the period 2013–2014, IASI-A and IASI-B total ozone columns (TOCs) retrieved using FORLI are consistent, with IASI-B providing slightly lower values with a global difference of only 0.2 ± 0.8 %. The comparison between IASI-A and IASI-B O3 vertical profiles shows differences within ± 2 % over the entire altitude range. Global validation results for 7 years of IASI TOCs from FORLI against the Global Ozone Monitoring Experiment-2 (GOME-2) launched on board MetOp-A and Brewer–Dobson data show that, on average, IASI overestimates the ultraviolet (UV) data by 5–6 % with the largest differences found in the southern high latitudes. The comparison with UV–visible SAOZ (Système d'Analyse par Observation Zénithale) measurements shows a mean bias between IASI and SAOZ TOCs of 2–4 % in the midlatitudes and tropics and 7 % at the polar circle. Part of the discrepancies found at high latitudes can be attributed to the limited information content in the observations due to low brightness temperatures. The comparison with ozonesonde vertical profiles (limited to 30 km) shows that on average IASI with FORLI processing underestimates O3 by  ∼  5–15 % in the troposphere while it overestimates O3 by ∼  10–40 % in the stratosphere, depending on the latitude. The largest relative differences are found in the tropical tropopause region; this can be explained by the low O3 amounts leading to large relative errors. In this study, we also evaluate an updated version of FORLI-O3 retrieval software (v20151001), using look-up tables recalculated to cover a larger spectral range using the latest HITRAN spectroscopic database (HITRAN 2012) and implementing numerical corrections. The assessment of the new O3 product with the same set of observations as that used for the validation exercise shows a correction of ∼  4 % for the TOC positive bias when compared to the UV ground-based and satellite observations, bringing the overall global comparison to ∼  1–2 % on average. This improvement is mainly associated with a decrease in the retrieved O3 concentration in the middle stratosphere (above 30 hPa/25 km) as shown by the comparison with ozonesonde data.

Citation: Boynard, A., Hurtmans, D., Koukouli, M. E., Goutail, F., Bureau, J., Safieddine, S., Lerot, C., Hadji-Lazaro, J., Wespes, C., Pommereau, J.-P., Pazmino, A., Zyrichidou, I., Balis, D., Barbe, A., Mikhailenko, S. N., Loyola, D., Valks, P., Van Roozendael, M., Coheur, P.-F., and Clerbaux, C.: Seven years of IASI ozone retrievals from FORLI: validation with independent total column and vertical profile measurements, Atmos. Meas. Tech., 9, 4327-4353, doi:10.5194/amt-9-4327-2016, 2016.
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Short summary
Seven years of O3 observations retrieved from IASI/MetOp satellite instruments are validated with independent data (UV satellite and ground-based data along with ozonesonde profiles). Overall IASI overestimates the total ozone columns (TOC) by 2–7 % depending on the latitude. The assessment of an updated version of the IASI O3 retrieval sofware shows a correction of ~ 4 % in the IASI TOC product, bringing the overall global bias with UV ground-based and satellite data to ~ 1–2 % on average.
Seven years of O3 observations retrieved from IASI/MetOp satellite instruments are validated...
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