CH 4 retrievals : status of Ulg work HYMN Workshop, Totnes, October 2007 Liège team Ph. Demoulin, P. Duchatelet, E. Mahieu, Ch. Servais, S. Trabelsi, R. Zander, G. Roland, J. Bosseloirs, O. Flock, V. Vandeweerdt

Content 1. Part I : CH 4 retrievals tests performed on a « new » µwindow – comparisons with the UFTIR procedure 2. Part II : CH 4 isotoplogues ( 13 CH 4 and CH 3 D) µwindows selection – info content – first results

Part I : CH 4 retrievals

µwindows [cm -1 ] Interf. species CH 4 line # E’’Remarks CO 2,HDO,sun CO 2,HDO none NO 2 H 2 O,HDO, NO 2, sun /31 105/ UFTIR µwindows CO 2,HDO,O 3,sun4220 « New » µwindow suggested by Corinne Vigouroux in Ténérife (May 2007) CO 2,HDO,O 3,sun none NO « New » µwindow + 2 UFTIR µwindows CH 4 retrievals : an overview of existing procedures

CH 4 retrievals : input sources HITRAN-04 a priori CH 4 profile from HALOE (~46°N / 1995 annual mean) a priori CH 4 variability from HALOE (diagonal matrix) high (2.85 mK) & low (4.96 mK) resolution FTIR spectra only FTIR spectra with SZA smaller than 80° SNR value for inversions = layers scheme Retrieval algorithm : SFIT-2 v.3.91

CH 4 retrievals : typical info content ApproachDOFS λ 1 to λ 4 Total error on columns (%) 5 UFTIR * for [3.58-7] km 1.36 for [7-17 ] km 1.96 for [17-27] km 0.28 for [ ] km «New» * for [3.58-7] km 1.14 for [7-17 ] km 1.88 for [17-27] km 0.13 for [ ] km «New» + 2 UFTIR * for [3.58-7] km 1.13 for [7-17 ] km 1.86 for [17-27] km 0.13 for [ ] km 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

CH 4 retrievals : info content ApproachDOFS 5 UFTIR2.97 ± 0.24 «New»3.31 ± 0.14 «New» + 2 UFTIR3.40 ± 0.15 Mean DOFS values averaged over the whole 2003 year (~550 spectra)  The 2 last approaches allow to slightly increase DOFS

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

CH 4 retrievals : daily means for 2003 [(New-UFTIR)/UFTIR]*100 = 0.11±0.44 % [Corinne found a bias of ~3%]

CH 4 retrievals : mean profiles for 2003  significant differences in the troposphere

CH 4 retrievals : daily means for 2003 [(New-UFTIR)/UFTIR]*100 = 6.47±2.05 %

CH 4 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 ?

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

CH 4 retrievals : conclusions a new µwindow for CH 4 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 CH 4 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 CH 4 profiles don’t disappear more investigations needed concerning ILC : which ILC value to adopt ? Which impact on DOFS/ retrievals results ?

Part II : CH 4 isotoplogues ( 13 CH 4 and CH 3 D)

13 CH 4 study – a selection of µwindows in the InSb range Inputs & µwindows selection

Target species µ-windows [cm -1 ] Interf. species 13 CH 4 line # Lower state E ’’ [cm -1 ] 13 CH none CH 4,HDO,H 2 O,sun CH 4,HDO,H 2 O,NO 2 CH 4,HDO,H 2 O,NO 2, OCS,O 3,sun /63 157/157 4 µ-windows fitted simultaneously a priori profile derived from ACE-FTS ([41-51]°N / ) a priori variability derived from ACE-FTS (diagonal matrix) high (2.85 mK) & low (4.96 mK) resolution FTIR spectra only FTIR spectra with SZA [70-80]° HITRAN-04 and SFIT-2 v3.91

13 CH 4 study – a selection of µwindows in the InSb range Interfering species [simulations performed for a SZA = 75°]

13 CH 4 study – a selection of µwindows in the InSb range Information content

#µwindows [cm -1 ] DOFS λ1λ All Typical values obtained from a spectra ISSJ (04/04/ SZA~77° mK)

13 CH 4 study – a selection of µwindows in the MCT range Inputs & µwindows selection

Target species µ-windows [cm -1 ] Interf. species 13 CH 4 line # Lower state E ’’ [cm -1 ] 13 CH CH 4,CO 18 O,COF a priori profile derived from ACE-FTS ([41-51]°N / ) a priori variability derived from ACE-FTS (diagonal matrix) high (4 mK) & low (6.1 mK) resolution FTIR spectra only FTIR spectra with SZA [65-80]° HITRAN-04 and SFIT-2 v3.91

13 CH 4 study – a selection of µwindows in the MCT range Interfering species [simulations performed for a SZA = 75°]

13 CH 4 study – a selection of µwindows in the MCT range Information content

13 CH 4 study – a selection of µwindows First results

13 CH 4 study – a selection of µwindows Conclusions

We have selected two sets (InSb range/MCT range) of µwindows allowing to derive 13 CH 4 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. H 2 O or HDO), we recommend the use of the MCT line for the 13 CH 4 retrievals

CH 3 D study – a selection of µwindows Inputs & µwindows selection

CH 3 D Center (cm -1 )Interfering species H 2 O O 3 CH H 2 O O 3 CH H 2 O O 3 CH H 2 O O 3 CH H 2 O O 3 CH O 3 CH H 2 O O 3 CH O 3 CH H 2 O O 3 CH H 2 O O 3 CH H 2 O O 3 CH 4 CH 3 D lines used by ATMOS #1 #2 #3 #4

Target species µ-windows [cm -1 ] Interf. species CH 3 D line # Lower state E ’’ [cm -1 ] CH 3 D HDO,H 2 O,O 3 CH 4,O 3 CH 4,H 2 O,O 3,sun CH 4,H 2 O,O / /266 a priori profile derived from ACE-FTS ([41-51]°N / ) a priori variability derived from ACE-FTS (diagonal matrix) high (2.85 mK) & low (4 and 4.96 mK) resolution FTIR spectra only FTIR spectra with SZA [70-80]° HITRAN-04 and SFIT-2 v3.91

#µ-windows [cm -1 ]DOFS λ1λ All  single µ-window (#2) and multi spectra strategy ? Typical values obtained from a spectra ISSJ (15/01/2005-SZA~79° mK)  multi µ-windows or single µ-window (#2) strategy ?

ApproachDOFS λ1λ1 RMS of µw #2 #20.4 ± 0.1[0.19 – 0.60]0.18 ± 0.04 #2 with multispectra 0.8 ± 0.2[0.35 – 0.80]0.18 ± µw0.9 ± 0.1[0.49 – 0.87]0.20 ± 0.04 Complete statistics for year 2005 (373 spectra) 28

CH 3 D total columns for year 2005

Still difficult to conclude which approach (multi- µwindows or single µwindow with multi-spectra) is the best !  To test the multi-µwindows approach on FTIR spectra recorded at low altitude sites could be helpfull 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 ??