CH 4 retrievals : status of Ulg work HYMN Workshop, Totnes, 22-24 October 2007

1. CH4 retrievals : status of Ulg workHYMN Workshop, Totnes, 22-24 October 2007 Liège team Ph. Demoulin, P. Duchatelet, E. Mahieu, Ch. Servais, S. Trabelsi, R. Zander, G. Roland, J. Bosseloirs, O. Flock, V. Vandeweerdt

2. Content • Part I : CH4 retrievals • tests performed on a « new » µwindow – comparisons with the UFTIR procedure 2. Part II : CH4 isotoplogues (13CH4 and CH3D) • µwindows selection – info content – first results

3. Part I : CH4 retrievals

4. CH4 retrievals : an overview of existing procedures

5. CH4 retrievals : input sources • HITRAN-04 • 41 layers scheme • high (2.85 mK) & low (4.96 mK) resolution FTIR spectra • only FTIR spectra with SZA smaller than 80° • a priori CH4profile from HALOE (~46°N / 1995 annual mean) • a priori CH4 variability from HALOE (diagonal matrix) • SNR value for inversions = 500 Retrieval algorithm : SFIT-2 v.3.91

7. CH4 retrievals : typical info content Simulation performed with a spectrum recorded at ISSJ on 30 March 2003-SZA=51°-4.96mK (*) : DOFS values obtained by Corinne for SZA=51° / SNR=250

8. CH4 retrievals : info content Mean DOFS values averaged over the whole 2003 year (~550 spectra)  The 2 last approaches allow to slightly increase DOFS

9.  No significant advantage to add the 2 UFTIR µwindows to the « new » one (see lower-state energy, DOFS, AvK)

10. CH4 retrievals : daily means for 2003 [(New-UFTIR)/UFTIR]*100 = 0.11±0.44 % [Corinne found a bias of ~3%]

11. CH4 retrievals : mean profiles for 2003  significant differences in the troposphere

12. CH4 retrievals : daily means for 2003 [(New-UFTIR)/UFTIR]*100 = 6.47±2.05 %

13. CH4 retrievals : inter-layer correlation • no ILC parameter has been used here so far • Corinne uses an ILC = 4km for the whole altitude range • M.Schneider et al. (ACP, 2005) adopts an ILC = 2.5km  Do these values look reasonnable ?

14. Tropospheric part • 57 ACE profiles used • ILC ~1.5 km • Stratospheric part • 422 ACE profiles used • ILC between 2 and 4 km CH4 correlation matrices derived from ACE-FTS

15. CH4 retrievals : conclusions • a new µwindow for CH4 retrievals has been tested. This µwindow provides higher info content than the selection of µwindows adopted by the UFTIR community; lines adopted in the new approach are also more consistent in terms of T dependance • for CH4 total columns, the new approach doesn’t introduce any bias relative to the UFTIR approach • a bias is however observed on retrieved VMR profiles as well as on partial columns in the troposphere • oscillations in retrieved CH4 profiles don’t disappear • more investigations needed concerning ILC : which ILC value to adopt ? Which impact on DOFS/ retrievals results ?

16. Part II : CH4 isotoplogues (13CH4 and CH3D)

17. 13CH4 study – a selection of µwindows in the InSb range Inputs & µwindows selection

18. HITRAN-04 and SFIT-2 v3.91 • 4 µ-windows fitted simultaneously • high (2.85 mK) & low (4.96 mK) resolution FTIR spectra • only FTIR spectra with SZA [70-80]° • a priori profile derived from ACE-FTS ([41-51]°N / 2004-2006) • a priori variability derived from ACE-FTS (diagonal matrix)

19. 13CH4 study – a selection of µwindows in the InSb range Interfering species [simulations performed for a SZA = 75°]

21. 13CH4 study – a selection of µwindows in the InSb range Information content

22. Typical values obtained from a spectra recorded @ ISSJ (04/04/2005 - SZA~77°- 4.96 mK)

24. 13CH4 study – a selection of µwindows in the MCT range Inputs & µwindows selection

25. HITRAN-04 and SFIT-2 v3.91 • high (4 mK) & low (6.1 mK) resolution FTIR spectra • only FTIR spectra with SZA [65-80]° • a priori profile derived from ACE-FTS ([41-51]°N / 2004-2006) • a priori variability derived from ACE-FTS (diagonal matrix)

26. 13CH4 study – a selection of µwindows in the MCT range Interfering species [simulations performed for a SZA = 75°]

28. 13CH4 study – a selection of µwindows in the MCT range Information content

30. 13CH4 study – a selection of µwindows First results

33. 13CH4 study – a selection of µwindows Conclusions

34. We have selected two sets (InSb range/MCT range) of µwindows allowing to derive 13CH4 abundances • Each set contains enough sensitivity to retrieve one partial column/VMR profile between 5 and 14 km, with at least 80% of the information coming from the measurement • We have observed a significant bias of ~5% on partial columns/VMR profiles between the InSb and the MCT ranges • However, due to higher information content, wider SZA range for the retrievals ( more data points available) and smaller perturbation by interfering species (e.g. H2O or HDO), we recommend the use of the MCT line for the 13CH4 retrievals

35. CH3D study – a selection of µwindows Inputs & µwindows selection

36. CH3D lines used by ATMOS http://remus.jpl.nasa.gov/atmos/atmosversion3/gaswindows.html#CH3D #1 #2 #3 #4

37. HITRAN-04 and SFIT-2 v3.91 • high (2.85 mK) & low (4 and 4.96 mK) resolution FTIR spectra • only FTIR spectra with SZA [70-80]° • a priori profile derived from ACE-FTS ([41-51]°N / 2004-2006) • a priori variability derived from ACE-FTS (diagonal matrix)

38. Typical values obtained from a spectra recorded @ ISSJ (15/01/2005-SZA~79°- 4.96 mK)  multi µ-windows or single µ-window (#2) strategy ?  single µ-window (#2) and multi spectra strategy ?

39. Complete statistics for year 2005 (373 spectra) 2 8

40. CH3D total columns for year 2005

41. Still difficult to conclude which approach (multi-µwindows or single µwindow with multi-spectra) is the best ! • The consistency between the 2 approaches is good and multi-µwindows provides higher info content but what about water vapor interferences for lower altitude sites ??  To test the multi-µwindows approach on FTIR spectra recorded at low altitude sites could be helpfull