Co workers at BIRA-IASB

1. Contribution to the validation of SCIAMACHY scientific data products for CO, CH4, CO2 and N2O total column amounts using ground-based FTIR network data.M. De Mazière, B. Dils, M. Buchwitz, R. De Beek, C. Frankenberg, A. Gloudemans, H. Schrijver, M. van den Broek et al.Belgian Institute for Space Aeronomy, Ringlaan 3, B-1180 Brussels, Belgium, martine@oma.be, bartd@oma.be

2. Coworkers at BIRA-IASB Contributing PI’s J. Notholt, T. Warneke Institute of Environmental Physics, University of Bremen, Germany T. Blumenstock, S. Mikuteit Forschungszentrum Karlsruhe, IMK, Germany E. Mahieu, P. Demoulin, P. Duchatelet Institut d'Astrophysique et de Géophysique, University of Liège, Belgium J. Mellqvist, A. Strandberg Chalmers University of Technology, Sweden R. Sussmann, W. Stremme Forschungszentrum Karlsruhe, IFU, Germany H. Fast, R. L. Mittermeier Meteorological Service of Canada (MSC) T. Kerzenmacher, K. Strong, J.Taylor, A.Wiacek University of Toronto, Canada S. Wood,D. Smale National Institute for Water and Air Research (NIWA), New-Zealand D. Griffith, N. Jones University of Wollongong, Australia C. Rinsland NASA Langley Research Center, USA J. Granville P. Gérard T. Jacobs J.C. Lambert C. Vigouroux

3. Correlative dataset

4. SCIAMACHY retrieval methods WFM-DOAS: Weighting Function Modified DOAS Channel 8 Two windows: CH4 + N2O → 2265.0 – 2280.0 nm CO → 2359.0 – 2370.0 nm CO2 → 1558.0 – 1594.0 nm (channel 6) IMLM : Iterative Maximum likelihood Method Channel 8: 2354.00 – 2370.45 nm CH4 and CO from the same window IMAP : Interactive Maximum A Posteriori-DOAS CH4 from channel 6 CO from channel 8: 2324.2 – 2334.9 nm

5. Comparison remarks (FT)IR is the only GB technique to provide correlative total column data – but number of GB measurements is limited - cf. need clear sky Comparisons between total column data at high altitude stations;  adopted approach:  to use altitude-normalised data which is a better compromise for CH4 and N2O than for CO * still in mountainous regions, pixels do not represent uniform elevation Comparisons at stations situated near the coast (e.g. Wollongong)  - cf colocated pixels may be over sea  Verify whether SCIA data are over land

6. Maximizing Data overlap Maximizing data overlap: → polynomial fit through GB data But no extrapolation! *Good representation of seasonal variability (average std= 1-2%, except CO, 10%) *Loss of information on certain possible short term events

7. Selection criteria Data processed for two grids around the GB stations: Large grid = Lat ± 2.5° Lon ± 10° Small grid = Lat ± 2.5° Lon ± 5° Sciamachy data cover the jan → okt/nov time period Except CH4-IMAP: aug-nov

8. Data overlap Large data loss when restricted to point-to-point comparison Global time series for WFMDOAS and GB CO and CH4 (no additional filtering, fixed offset/station, + = GB data)

9. Additional Selection criteria WFM-DOAS: Cloud-free, Over land (altitude > 0), Solar Zenith Angle < 85 deg, Error (fitting) <10% for CH4 and CO2 , < 60% for CO and N2O IMLM-SRON: Cloud-free, Albedo >=0.01, Error (instrumental) < 2E18 for CH4 (~7%) and <1.5E18 for CO (~70%) IMAP: No further selection needed for CH4, variance of the fit residual (without weighting) < 0.017, with weighting between 10 and 0.1, error < 7E17 and 30% for CO Note: Several selection criteria have already been applied to the starting dataset

10. Timeseries plots IMLM-SRON

11. Timeseries plots WFM-DOAS

12. Timeseries plots WFM-DOAS

13. Timeseries plots IMAP

14. CO Bias = mean (SCIA-polyfitFTIR)/polyfitFTIR *IMLM-SRON data is preliminary dataset! → further improvement of std likely

15. CH4 *IMLM-SRON data is preliminary dataset! → further improvement of std likely

16. Latitude dependence?

17. CO2 + N2O

18. Remarks • No information on the time dependence of the bias! • Of major importance in determining the accuracy of the retrieval model, is assessing whether or not the SCIA data ‘follows’ the GB data over time. • No data averaging was performed • Outliner detection and removal (criteria?) • All algorithms, IMLM (correction for dark current over orbits) and IMAP (implementation of the cloud retrieval utility for CO), undergo continuous improvements.

19. Future work • In depth analysis of the time/lat dependence of the bias • Comparing daily/ weekly/ monthly averages of SCIA and FTIR data • Further investigation of various selection criteria • Comparisons between Ground Based data and Theoretical Models