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Comparisons CH 4 SCIAMACHY / GROUND-BASED FTIR

Comparisons CH 4 SCIAMACHY / GROUND-BASED FTIR. B. Dils, BIRA + HYMN partners. Corinne Vigouroux, BIRA, HYMN progress meeting, 7-8 April 2008. The FTIR stations for HYMN. Collocation grid with SCIAMACHY data: Large grid = Lat ± 2.5° Lon ± 10° Small grid = Lat ± 2.5° Lon ± 5°.

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Comparisons CH 4 SCIAMACHY / GROUND-BASED FTIR

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  1. Comparisons CH4SCIAMACHY / GROUND-BASED FTIR B. Dils, BIRA + HYMN partners Corinne Vigouroux, BIRA, HYMN progress meeting, 7-8 April 2008.

  2. The FTIR stations for HYMN • Collocation grid with SCIAMACHY data: Large grid = Lat ± 2.5° Lon ± 10° • Small grid = Lat ± 2.5° Lon ± 5°

  3. Previous work on FTIR / SCIA comparisons • Dils et al., ACP, 6, 1953-1976, 2006 • European stations (as UFTIR, but different retrieval strategies !) + Egbert, Toronto, Wollongong, Lauder and Arrival Heights • 3 Algorithms for SCIA data: 1) IMAP-DOAS (Frankenberg et al.) (only 2003) 2) WFM-DOAS (Buchwitz et al.) 3) IMLM (Gloudemans et al.) • Scarce data in daily coincidence → Compare the SCIA data with a 3rd order polynomial fit through the FTIR data; therefore daily variability cannot be captured. → Large scatters (except IMAP-D: 1.1%, but worst correlation coefficient: 0.7)

  4. Previous work on FTIR / SCIA comparisons • Dils et al., Proceedings of ACVE-3, Dec. 2006. • UFTIR stations only. Homogenize strategy: called this data set “UFTIR data” • WFM-DOAS (improved version) • 2003 + 2004 • Methodology: still polynomial fit (to compare the improvement with respect to previous version WFM-DOAS) → Improvement of the comparisons compared to old data sets WFM-D & UFTIR.

  5. HYMN project • Data sets & methodology • UFTIR stations + Paramaribo and Reunion, using a common strategy ! → UFTIR or improved ? • IMAP-DOAS (new version) • 2004 (+ ???) • Methodology : for the year 2004 & with new IMAP algorithm, more SCIA data are available → polynomial fit through FTIR data or direct comparisons ?

  6. HYMN project • Today, we show : • Comparisons new IMAP-D vs WFM-D used lately in Dils et al., ACVE_3: → same  UFTIR data set & same methodology (polynomial fit) • New IMAP-D, same UFTIR data, but considering direct comparisons of daily mean coincidences • Direct comparisons using new HYMN FTIR data set when available.

  7. IMAP-DOAS & WFM-DOAS vs FTIR polynomial fit (UFTIR data) • Improvement in scatter and correlation coefficient • scat includes natural variability toward polynomial. 0.91 is close to the FTIR scatter = 0.85% (2004)

  8. IMAP-D & WFM-D:bias as a function of latitude IMAP-DOAS bias less pronounced and more homogeneous than for WFM-DOAS

  9. Examples of CH4 monthly time series in 2004

  10. Polynomial fit or direct comparisons ? Both techniques are in agreement: to be done: check in detail if we see daily effects.

  11. HYMN data set → Homogenization problem ?

  12. Conclusions • Today, we show : • Improvement of new IMAP-DOAS data • Methodologies in agreement. Final choice to be decided. • It seems that there is some problems of homogeneity with new HYMN FTIR data set: discussion in progress. • Questions for FTIR (next meeting May): • when should we deliver data for other years than 2004 ? • N2O, CO ? • ECMWF / NCEP ? (at St-Denis: ~ 1% bias on total columns, ~ 0.2% on tropospheric columns)

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