CH4 retrievals : status of Ulg work

HYMN 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

Content

1. 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

Part I : CH4 retrievals

µwindows[cm-1]

Interf. species

CH4 line

#

E’’ Remarks

2613.70-2615.402650.60-2651.302835.50-2835.802903.60-2904.032921.00-2921.60

CO2,HDO,sun

CO2,HDO

none

NO2

H2O,HDO, NO2,sun

22111

10/31105/31

63220293

UFTIR µwindows

2741.80-2743.10 CO2,HDO,O3,sun 4 220

« New » µwindow suggested by

Corinne Vigouroux in Ténérife

(May 2007)

2741.80-2743.102835.50-2835.802903.60-2904.03

CO2,HDO,O3,sun

noneNO2

411

22063

220

« New » µwindow + 2 UFTIR µwindows

CH4 retrievals : an overview of existing procedures

CH4 retrievals : input sources

HITRAN-04

a priori CH4 profile from HALOE (~46°N / 1995 annual

mean) a priori CH4 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 = 500

41 layers scheme

Retrieval algorithm : SFIT-2 v.3.91

CH4 retrievals : typical info content

Approach DOFS

λ1 to λ4 Total error on

columns (%)

5 UFTIR 2.622.4*

0.990.920.580.10

2.07 for [3.58-7] km1.36 for [7-17 ] km

1.96 for [17-27] km 0.28 for [3.58-100] km

«New» 3.133.0*

1.000.970.820.31

1.55 for [3.58-7] km1.14 for [7-17 ] km

1.88 for [17-27] km 0.13 for [3.58-100] km

«New» + 2 UFTIR 3.183.1*

1.000.970.840.33

1.54 for [3.58-7] km1.13 for [7-17 ] km

1.86 for [17-27] km 0.13 for [3.58-100] 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

CH4 retrievals : info content

Approach DOFS

5 UFTIR 2.97 ± 0.24

«New» 3.31 ± 0.14

«New» + 2 UFTIR 3.40 ± 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)

CH4 retrievals : daily means for 2003

[(New-UFTIR)/UFTIR]*100 = 0.11±0.44 % [Corinne found a bias of ~3%]

CH4 retrievals : mean profiles for 2003

significant differences in the troposphere

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

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 ?

CH4 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

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 ?

Part II : CH4 isotoplogues (13CH4 and CH3D)

13CH4 study – a selection of µwindows in the InSb range

Inputs & µwindows selection

Target

species

µ-windows

[cm-1]

Interf. species

13CH4

line #Lower state

E’’

[cm-1]

13CH4

2817.38-2817.522846.15-2846.712892.45-2892.752924.15-2925.10

noneCH4,HDO,H2O,sun

CH4,HDO,H2O,NO2

CH4,HDO,H2O,NO2, OCS,O3,sun

1222

15763/6363/63

157/157

4 µ-windows fitted simultaneously

a priori profile derived from ACE-FTS ([41-51]°N / 2004-2006) 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

13CH4 study – a selection of µwindows in the InSb range

Interfering species[simulations performed for a SZA = 75°]

13CH4 study – a selection of µwindows in the InSb range

Information content

# µwindows[cm-1]

DOFS λ1

1 2817.38-2817.52 0.21 0.20

2 2846.15-2846.71 0.47 0.41

3 2892.45-2892.75 0.58 0.48

4 2924.15-2925.10 0.48 0.41

All 1.05 0.77

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

13CH4 study – a selection of µwindows in the MCT range

Inputs & µwindows selection

Target

species

µ-windows

[cm-1]

Interf. species

13CH4

line #Lower state

E’’

[cm-1]

13CH41234.04-1234.44 CH4,CO18O,COF2 1 575

a priori profile derived from ACE-FTS ([41-51]°N / 2004-2006)

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

13CH4 study – a selection of µwindows in the MCT range

Interfering species[simulations performed for a SZA = 75°]

13CH4 study – a selection of µwindows in the MCT range

Information content

13CH4 study – a selection of µwindows

First results

13CH4 study – a selection of µwindows

Conclusions

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

CH3D study – a selection of µwindows

Inputs & µwindows selection

CH3D

Center (cm-1) Interfering species

2951.00 H2O O3 CH4

2960.43 H2O O3 CH4

3061.46 H2O O3 CH4

3065.06 H2O O3 CH4

3070.80 H2O O3 CH4

3072.65 O3 CH4

3078.40 H2O O3 CH4

3089.53 O3 CH4

3091.30 H2O O3 CH4

3100.30 H2O O3 CH4

3106.41 H2O O3 CH4

CH3D lines used by ATMOShttp://remus.jpl.nasa.gov/atmos/atmosversion3/gaswindows.html#CH3D

#1

#2

#3

#4

Target

species

µ-windows

[cm-1]

Interf. species

CH3D line #

Lower state E’’

[cm-1]

CH3D

2950.77-2951.003070.71-3071.003072.70-3073.153089.15-3089.70

HDO,H2O,O3

CH4,O3

CH4,H2O,O3,sun

CH4,H2O,O3

1212

266163/138

151285/266

a priori profile derived from ACE-FTS ([41-51]°N / 2004-2006)

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 λ1

1 2950.77-2951.25 0.32 0.28

2 3070.71-3071.00 0.51 0.43

3 3072.70-3073.15 0.51 0.44

4 3089.15-3089.70 0.50 0.43

All 1.00 0.76

single µ-window (#2) and multi spectra strategy ?

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 ?

Approach DOFS λ1 RMS of µw #2

#2 0.4 ± 0.1 [0.19 – 0.60] 0.18 ± 0.04

#2 with multispectra

0.8 ± 0.2 [0.35 – 0.80] 0.18 ± 0.04

4 µw 0.9 ± 0.1 [0.49 – 0.87] 0.20 ± 0.04

Complete statistics for year 2005 (373 spectra)

2 8

CH3D 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 ??