1. Page 1 Sciamachy Validation Workshop – Bremen - 6-8 December 2004 Contribution to the validation of SCIAMACHY scientific data products for CO, CH 4, CO 2 and N 2 O 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 martine@oma.bebartd@oma.be

2. Page 2 Sciamachy Validation Workshop – Bremen - 6-8 December 2004 Coworkers at BIRA-IASB J. Granville P. Gérard T. Jacobs J.C. Lambert C. Vigouroux 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 Contributing PI’s

3. Page 3 Sciamachy Validation Workshop – Bremen - 6-8 December 2004 Correlative dataset StationLat NLon EAlt(m) NY.ALESUND78,9111,8820 KIRUNA67,820,4419 HARESTUA60,2210,75580 ZUGSPITZE47,411,12964 JUNGFRAUJOCH46,557,983580 EGBERT44,23-79,78251 TORONTO43,7-79,4174 IZANA28-162367 WOLLONGONG-34,45150,8830 LAUDER-45,05169,68370 ARRIVAL.HEIGHTS-77,85166,78190

4. Page 4 Sciamachy Validation Workshop – Bremen - 6-8 December 2004 SCIAMACHY retrieval methods WFM-DOAS: Weighting Function Modified DOAS Channel 8 Two windows: CH 4 + N 2 O → 2265.0 – 2280.0 nm CO → 2359.0 – 2370.0 nm CO 2 → 1558.0 – 1594.0 nm (channel 6) IMLM : Iterative Maximum likelihood Method Channel 8: 2354.00 – 2370.45 nm CH 4 and CO from the same window IMAP : Interactive Maximum A Posteriori-DOAS CH 4 from channel 6 CO from channel 8: 2324.2 – 2334.9 nm

5. Page 5 Sciamachy Validation Workshop – Bremen - 6-8 December 2004 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 CH 4 and N 2 O 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. Page 6 Sciamachy Validation Workshop – Bremen - 6-8 December 2004 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. Page 7 Sciamachy Validation Workshop – Bremen - 6-8 December 2004 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 CH 4 -IMAP: aug-nov

8. Page 8 Sciamachy Validation Workshop – Bremen - 6-8 December 2004 Data overlap Global time series for WFMDOAS and GB CO and CH 4 (no additional filtering, fixed offset/station, + = GB data) Large data loss when restricted to point-to-point comparison

9. Page 9 Sciamachy Validation Workshop – Bremen - 6-8 December 2004 Additional Selection criteria WFM-DOAS: Cloud-free, Over land (altitude > 0), Solar Zenith Angle < 85 deg, Error (fitting) <10% for CH 4 and CO 2, < 60% for CO and N 2 O IMLM-SRON: Cloud-free, Albedo >=0.01, Error (instrumental) < 2E18 for CH 4 (~7%) and <1.5E18 for CO (~70%) IMAP: No further selection needed for CH 4, 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. Page 10 Sciamachy Validation Workshop – Bremen - 6-8 December 2004 Timeseries plots IMLM-SRON

11. Page 11 Sciamachy Validation Workshop – Bremen - 6-8 December 2004 Timeseries plots WFM-DOAS

12. Page 12 Sciamachy Validation Workshop – Bremen - 6-8 December 2004 Timeseries plots WFM-DOAS

13. Page 13 Sciamachy Validation Workshop – Bremen - 6-8 December 2004 Timeseries plots IMAP

14. Page 14 Sciamachy Validation Workshop – Bremen - 6-8 December 2004 CO Retrieval algorithm Average Bias over all stations and time (small grid) Average Bias over all stations and time (large grid) WFM-DOAS(24.56 ± 33.22)%(21.76 ± 30.05)% IMLM-SRON*(-3.51 ± 82.51)%(-1.56 ± 83.60)% IMAP(-21.86 ± 27.58)%(-19.14 ± 26.36)% Std GB-FTIR10.56% *IMLM-SRON data is preliminary dataset! → further improvement of std likely Bias = mean (SCIA-polyfitFTIR)/polyfitFTIR

15. Page 15 Sciamachy Validation Workshop – Bremen - 6-8 December 2004 CH 4 Retrieval algorithm Average Bias over all stations and time (small grid) Average Bias over all stations and time (large grid) WFM-DOAS v4.1(-1.70 ± 7.93)%(-1.75 ± 7.34)% IMLM-SRON*(-2.59 ± 15.83)%(-3.68 ± 18.39)% IMAP(-4.23 ± 3.54)%(-5.22 ± 4.04)% Std GB-FTIR2.09% *IMLM-SRON data is preliminary dataset! → further improvement of std likely

16. Page 16 Sciamachy Validation Workshop – Bremen - 6-8 December 2004 Latitude dependence?

17. Page 17 Sciamachy Validation Workshop – Bremen - 6-8 December 2004 CO 2 + N 2 O Retrieval algorithm Average Bias over all stations and time (small grid) Average Bias over all stations and time (large grid) WFM-DOAS CO 2 (-11.06 ± 7.42)%(-11.39 ± 6.64)% Std GB-FTIR CO 2 1.06% WFM-DOAS N 2 O(-1.10 ± 26.83)%(-0.34 ± 26.60)% Std GB-FTIR N 2 O1.75%

18. Page 18 Sciamachy Validation Workshop – Bremen - 6-8 December 2004 Remarks F No information on the time dependence of the bias! o 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. F No data averaging was performed F Outliner detection and removal (criteria?) F All algorithms, IMLM (correction for dark current over orbits) and IMAP (implementation of the cloud retrieval utility for CO), undergo continuous improvements.

19. Page 19 Sciamachy Validation Workshop – Bremen - 6-8 December 2004 Future work F In depth analysis of the time/lat dependence of the bias  Comparing daily/ weekly/ monthly averages of SCIA and FTIR data F Further investigation of various selection criteria F Comparisons between Ground Based data and Theoretical Models