CH 4 retrievals : status of Ulg work HYMN Workshop, Totnes, 22-24 October 2007 Liège team Ph....
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Transcript of CH 4 retrievals : status of Ulg work HYMN Workshop, Totnes, 22-24 October 2007 Liège team Ph....
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 ??