ESA Tuesday, 18 October 2016 Slide 2

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2 Validating the NRT Total Ozone Retrieval Algorithm for TROPOMI/S5P based on GOME- 2/Metop-A observations M. E. Koukouli 1, D. S. Balis 1, N. Hao 2, S. Gimeno Garcia 2, D. G. Loyola 2, W. Zimmer 2, C. Lerot 3 and M. Van Roozendael 3 (1)Laboratory of Atmospheric Physics, Aristotle University of Thessaloniki, Thessaloniki, Greece. (2)Institut für Methodik der Fernerkundung (IMF), Deutsches Zentrum für Luft- und Raumfahrt (DLR), Oberpfaffenhofen, Germany. (3) Belgian Institute for Space Aeronomy, Brussels, Belgium. ESA Tuesday, 18 October 2016 Slide 2

3 Historical perspective If I have seen further it is by standing on the shoulders of giants. - Isaac Newton, Letter to Robert Hooke, English Scientist, February 5 th, 1676 Cambridge University Library ESA Tuesday, 18 October 2016 Slide 3

4 Historical perspective McPeters, R. D., and G. J. Labow, An assessment of the accuracy of 14.5 years of Nimbus 7 TOMS version 7 ozone data by comparison with the Dobson network, Geophys. Res. Lett., Bramstedt, K., Gleason, J., Loyola, D., et al., Comparison of total ozone from the satellite instruments GOME and TOMS with measurements from the Dobson network , Atmos. Chem. Phys., ESA Tuesday, 18 October 2016 Slide 4

5 Historical perspective Latitude OMITOMS-DOBSON in % Latitude OMITOMS-BREWER in % Month Month Balis, D., M. Kroon, M. E. Koukouli, et al., Validation of Ozone Monitoring Instrument total ozone column measurements using Brewer and Dobson spectrophotometer ground-based observations, J. Geophys. Res., Balis D., J-C. Lambert, M.Van Roozendael, et al., Reprocessing the 10-year GOME/ERS-2 total ozone record for trend analysis: the new GOME Data Processor Version 4.0, Validation, J. Geophys. Res., ESA Tuesday, 18 October 2016 Slide 5

6 Historical perspective Antón, M., M. E. Koukouli, M. Kroon, et al., Global validation of empirically corrected EP-Total Ozone Mapping Spectrometer (TOMS) total ozone columns using Brewer and Dobson ground-based measurements, J. Geophys. Res., Labow, G. J., R. D. McPeters, P. K. Bhartia, and N. Kramarova, A comparison of 40 years of SBUV measurements of column ozone with data from the Dobson/Brewer network, J. Geophys. Res. Atmos., ESA Tuesday, 18 October 2016 Slide 6

7 Historical perspective Fioletov, V. E., Labow, G., Evans, R., et al., Performance of the groundbased total ozone network assessed using satellite data, J. G. R., Redondas, A., Evans, R., Stuebi, R., et al., Evaluation of the use of five laboratorydetermined ozone absorption cross sections in Brewer and Dobson retrieval algorithms, Atmos. Chem. Phys.,2014. ESA Tuesday, 18 October 2016 Slide 7

8 OR ELSE, GOING FROM THE GOME2 ALGORITHM VERSION GDP4.7 TO GDP4.8 TO UPAS2-CAL ESA Tuesday, 18 October 2016 Slide 8

9 The current status of the GDP4.7 algorithm Hao, N., Koukouli, M. E., Inness, A., et al., GOME-2 total ozone columns from MetOp-A/MetOp-B and assimilation in the MACC system, Atmos. Meas. Tech., ESA Tuesday, 18 October 2016 Slide 9

10 From GDP4.7 to GDP4.8 - I DOAS algorithms Improved Kurucz Solar reference spectrum (SAO2010) for wavelength calibration. Improved Ozone (I0 effect) and Ring Cross sections (using new high resolution solar spectra, SAO2010) Iterative AMF/VCD Updated scan angle correction. In GDP4.8, the correction factors were calculated using 7 years GOME-2A data for GOME-2A and 2 years GOME-2B data for GOME-2B respectively. Valks et al., Algorithm Theoretical Basis Document for GOME-2 Total Column Products of Ozone, NO 2, BrO, SO 2, H 2 O, HCHO and Cloud Properties (GDP 4.8 for O3M-SAF OTO and NTO), DLR/GOME-2/ATBD/01, Rev. 3/A, March ESA Tuesday, 18 October 2016 Slide 10

11 From GDP4.7 to GDP4.8 - II Cloud treatment: Using new cloud (version 3.0) algorithms: OCRA: PMD degradation correction + new cloud-free map based on GOME-2A data ROCINN: New Tikhonov inversion + updated RTM (spectroscopy, a-priori surface albedo, etc) Lutz, R., Loyola, D., Gimeno García, S., and Romahn, F.: OCRA radiometric cloud fractions for GOME-2 on MetOp-A/B, Atmos. Meas. Tech., ESA Tuesday, 18 October 2016 Slide 11

12 The current status of the GDP4.8 algorithm Koukouli, M. E., Zyrichidou, I., Balis, D., et al., O3M-SAF Total Ozone Column Validation Report, SAF/O3M/AUTH/VRR/O3, December 2015, ESA Tuesday, 18 October 2016 Slide 12

13 From GDP4.8 to UPAS2-CAL Optimal wavelength for AMF From nm to nm The typical GDP4.x errors increasing as function of SZA should be reduced significantly Polarization correction for AMF instead of normalizing O 3 This correction should improve the viewing angle dependency (removed in GDP 4.x by normalizing the O 3 ). TOMS V8 + OMI/MLS a priori That is the same combined climatology as the one used in ESA O 3 -CCI GODFIT algorithm and therefore we expect the same kind of improvements in Tropical Regions. ESA Tuesday, 18 October 2016 Slide 13

14 From GDP4.8 to UPAS2-CAL Cloud treatment: CAL instead of CRB CRB (cloud as reflecting boundary or MLER) is the old cloud model used in previous missions. Requires ad-hoc semi-empirical corrections for ghost column (G) and intra-cloud (v) effects with two calls to RTM v CRB CLOUD CAL G The smaller pixel size of the atmospheric missions Sentinel-5P/4/5 requires a more precise treatment of clouds: CAL (clouds as layers) No corrections needed, one single call to RTM ESA Tuesday, 18 October 2016 Slide 14

15 VALIDATING THE UPAS2-CAL ALGORITHM GOME2A TOCS USING BREWER & DOBSON SPECTROPHOTOMETERS ESA Tuesday, 18 October 2016 Slide 15

16 BREWER & DOBSON STATIONS ESA Tuesday, 18 October 2016 Slide 16

17 Global validation on the Dobson network ESA Tuesday, 18 October 2016 Slide 17

18 Monthly mean time series - the Dobson network ESA Tuesday, 18 October 2016 Slide 18

19 Monthly mean time series - the Brewer network ESA Tuesday, 18 October 2016 Slide 19

20 SZA dependency Optimal wavelength for AMF ESA Tuesday, 18 October 2016 Slide 20

21 Scan angle dependency Polarization correction for AMF instead of normalizing O 3 ESA Tuesday, 18 October 2016 Slide 21

22 Using new cloud (version 3.0) algorithms: Cloud parameters depedency ESA Tuesday, 18 October 2016 Slide 22

23 Concluding The aim of this work was to ascertain that the new UPAS2-CAL algorithm performs to high standards and is equally stable as the current operational UPAS1-GDP4.8 algorithm. The comparisons with the Dobson and Brewer spectrophotometer TOCs for the two years of GOME2/MetopA TOCs provided showed that: In the NH, the comparisons with the Dobsons provide a mean difference of 1.23±1.40% to UPAS1-GDP4.8 and 1.50±0.97% to UPAS2-CAL. In the SH, the comparisons with the Dobsons provide a mean difference of 1.82±1.12% to UPAS1-GDP4.8 and 2.640±1.27% to UPAS2-CAL. Between 60 S and 60 N, UPAS2-CAL introduces an extra 0.5 to 1% overestimation to the ground compared to UPAS1-GDP4.8. In the Poles, however, UPAS2-CAL appears to reduce the current overestimations, from 1.25% to 0.57%. The comparisons to the Brewer NH network are stable at +2% up to 75 in SZA, whereas the GDP4.8 comparisons show a dependency from 40 onwards. ESA Tuesday, 18 October 2016 Slide 23

24 Well, I must endure the presence of a few caterpillars if I wish to become acquainted with the butterflies. Antoine de Saint-Exupéry, The Little Prince ESA Tuesday, 18 October 2016 Slide 24

25 S5P Total Ozone Heritage NRT: DOAS DOAS fit for ozone slant column and effective temperature Iterative AMF/VCD computation using a single wavelength Molecular Ring correction (Van Roozendael et al., JGR 2006) On-the-fly RTM simulations LIDORT v3.x (Spurr, 2003) Cloud using OCRA&ROCINN v3.0 (Loyola et al., TGRS 2007) Adaption to SCIAMACHY (Lerot et al., AMT 2009) Intra-cloud, sun-glint and scan angle (Loyola et al., JGR 2011) Adaptation to GOME-2 (Hao et al., 2014) OFL: GODFIT Direct-Fitting algorithm retrieval total ozone, effective temperature, effective albedo, and Ring Baseline Algorithm for generating the CCI total O3 data sets Successfully applied to GOME, SCIAMACHY, GOME-2A/B and OMI (Lerot et al., JGR, 2014, Koukouli et al., JGR, 2015) ESA Tuesday, 18 October 2016 Slide 25 Chart 25