Transcript RB09 Gorshelev Victor

IMPROVED LINE PARAMETERS FOR CH 4
AROUND 1.6 MICRONS
Victor Gorshelev, A. Serdyuchenko, M. Buchwitz, J. Burrows,
University of Bremen, Germany;
N. Humpage, J. Remedios, University of Leicester, UK
OUTLINE
• Motivation and background
• HITRAN database
• Experimental setup
• Matlab model for quick quality control
• Preliminary results
• Conclusion and outlook
IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS
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MOTIVATION AND BACKGROUND
Goals
•
Perform laboratory measurements and corresponding data analysis in order
to improve spectroscopic line parameters for CH 4 in the spectral regions
used by SCIAMACHY and GOSAT methane retrieval (~1625 – 1685 nm)
•
Compare the resulting broadening coefficients with ones from HITRAN and
perform error budget analysis
IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS
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HITRAN DATABASE
Pressure broadened line halfwidth according to HITRAN:
gp(p,T)=[ gair(pref , Tref)  (p - pself)+gself(pref,Tref)pself ]  [ Tref / T ] n
 gair and gself - the air-broadened and the self-broadened
HWHM [cm-1/atm] at Tref = 296 K , pref= 1 atm.
 gair=0.79 gN2 + 0.21 gO2
- n – coefficient of temperature dependence of the airbroadened half-width (transition dependent).
d - air-broadened pressure shift [cm-1/atm] at Tref=296 K,
pref=1 atm, of the line transition frequency nhh:
nhh*=nhh+ d(pref)p
(transition dependent).
IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS
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HITRAN DATABASE
Fundamental line parameters for each spectral line
Parameter
Meaning
Comments or units
M
Molecule number
HITRAN chronological assignment
Ia
Isotopologue number
n
Vacuum wavenumber
Ordering within a molecule by
terrestrial abundance
cm-1
S
Intensity
cm-1/(molecule cm-2) at standard 296K
R
A
Weighted square of the transition moment Debye2 (for an electric dipole transition)
E’’
Einstein A-coefficient
Air-broadened half-width
Self-broadened half-width
Lower-state energy
s-1
HWHM @ 296K (in cm-1atm-1)
HWHM @ 296K (in cm-1atm-1)
cm-1
nair
Temperature dependence exponent for gair
Unitless
gair
gself
IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS
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HITRAN DATABASE
Fundamental line parameters for each spectral line
Parameter
Meaning
Comments or units
dair
Air pressure-induced line shift
cm-1 atm-1 at 296K
v’
v’’
q’
q’’
Upper-state “global” quanta
Lower-state “global” quanta
Upper-state “local” quanta
Lower-state “local” quanta
Ierr
Uncertainty indices
Accuracy for 3/6 critical parameters
Iref
Reference indices
References for 3/6 critical parameters
*
Flag
Availability of program and data for the
case of line mixing
g’
g’’
Statistical weight of upper state
Statistical weight of lower state
IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS
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HITRAN DATABASE
Error codes for intensity, half-width (air-, and self-), and temperature dependence
Intensity, half-width (air-, and self-)
and temperature dependence
Code
Uncertainty range
0
Unreported or unavailable
1
Default or constant
2
Average or estimate
3
≥ 20%
4
≥ 10% and <20%
5
≥ 5% and <10%
6
≥ 2% and <5%
7
≥ 1% and <2%
8
< 1%
IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS
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HITRAN UNCERTAINTIES FOR METHANE
Upper panel – spectral
windows of SCIAMACHY,
OCO and GOSAT and line
intensities of CH4 taken
from the HITRAN 2008.
Lower panels- HITRAN
2008 uncertainty codes for
broadening coefficients:
self- and air-broadening,
Temperature dependence
and pressure shift for CH 4
IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS
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PREVIOUS STUDIES ON LINE PARAMETERS
•
There are 2 key publications relevant for this research:
- /Frankenberg et al., 2008c/
- /Lyulin et al., 2009/.
Key parameters of the experimental set up and mixtures
Frankenberg (2008)
Lyulin (2009)
Instrument
Bruker FTS 120 HR, 25 scans
Bruker IFS 125 HR
Absorption path
2×140 cm
20×100 cm
Resolution
0.011/0.1 cm-1
spectra/background
0.005 cm-1
IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS
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PREVIOUS STUDIES ON LINE PARAMETERS
Experimental conditions
Lyulin (2009)
T, K
296
267
240
CH4,
mbar
2.5, 5, 10
5
5
10
5
5
10
2.5, 5, 10
5
5
10
5
5
10
2.5, 5, 10
5
5
10
5
5
10
Frankenberg (2008)
N2,
mbar
500
1000
500
500
1000
500
500
760
500
-
O 2,
mbar
500
1000
500
500
1000
500
500
1000
500
IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS
T, K
295.65
295.65
296,15
297.15
CH4,
mbar (%)
10 (1%)
10 (2%)
5 (2%)
2.5 (2%)
N2,
mbar
890
490
235
123
Total,
mbar
900
500
240
126
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CURRENT RESEARCH ON LINE PARAMETERS
•
New experimental conditions
Low pressure
High pressure
T, K
CH4, mbar
T, K
296
5
296
263
243
223
195
5
2
5
2
5
2
2
263
243
223
195
CH4, mbar
O2, mbar
N2, mbar
Ptotal,
mbar
10
490, 990
490, 990
500, 1000
5
495
495
500
10
490, 990
490, 990
500, 1000
5
495
495
500
10
490, 990
490, 990
500, 1000
5
495
495
500
10
490, 990
490, 990
500, 1000
5
495
495
500
10
490, 990
490, 990
500, 1000
5
495
495
500
IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS
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EXPERIMENTAL SETUP
Main parameters of the set-up:
• Bruker HR 120 Fourier Transform
spectrometer (FTS).
• Light source: tungsten lamp (OSRAM);
• Detector: InGaAs photodiode;
• Cell: Double jacket quartz cell, cryogenic
cooling, single (130 cm) or double path
(260 cm).
• Resolution 0.01 cm-1
IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS
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MATLAB EVALUATION MODEL ALGORITHM
The principle scheme of computation uses a small home-made Matlab routine
Experimental CH4 spectra
and conditions : Texp, Pexp, l
Line parameters:
Vi, Si, gs, gA, , n
(HITRAN);
Matlab
Line profile function:
Gaussian, Lorentzian
Calculated profile,
difference between
experimental and
modeled profiles
IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS
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RESULTS: LOW PRESSURE
Transmittance, a.u.
Experimental IUP data:
2 mbar CH4, T = 293 K
Homemade model:
Relative difference to model, %
Wavenumber, cm-1
Assuming HITRAN
parameters and Doppler line
profile for region 5997-6007
cm-1.
The difference (%) between
experimental and model
spectra.
Wavenumber, cm-1
IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS
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RESULTS: LOW PRESSURE
Transmittance, a.u.
Zoom on the region
around 6003 cm-1.
Relative difference to model, %
Wavenumber, cm-1
Wavenumber, cm-1
IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS
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RESULTS: HIGH PRESSURE
Transmittance, a.u.
Experimental IUP data:
10 mbar CH4 + 990 mbar N2
T= 293 K
Home-made Model:
Relative difference to model, %
Wavenumber, cm-1
Assuming HITRAN parameters
and Lorentz line profile for
region 5997-6007 cm-1.
The difference (%) between
experimental and model
spectra.
Wavenumber, cm-1
IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS
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RESULTS: HIGH PRESSURE
Transmittance, a.u.
Zoom on the region
around 6003 cm-1.
Relative difference to model, %
Wavenumber, cm-1
Wavenumber, cm-1
IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS
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UNIVERSITY OF LEICESTER LPC ALGORITHM
Line Parameter Calculation
software uses a LevenbergMarquardt optimal
estimation method
(Rodgers, 2000) to
calculate line parameters
from laboratory spectra
IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS
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LPC: RETRIEVED PARAMETERS
Parameter
Case 1 a priori
Case 1 retrieved
Case 2 a priori
Case 2 retrieved
Transition
wavenumber
(cm-1)
6015.6643
6015.6643
6026.2274
6026.2273
Line intensity
5.809E-22
5.762E-22
(-0.047E-22, 0.8%)
5.721E-22
5.654E-22
(-0.067E-22, 1.1%)
Air-broadened width
0.0583
0.0555
(-0.0028, 4.8%)
0.0634
0.0598
(-0.0036, 5.7%)
Self-broadened width
0.079
0.0787
(-0.003, 3,8%)
0.079
0.0787
(-0.003, 3,8%)
Temperature
dependence of air
broadening
0.850
0.850
0.850
0.850
Pressure shift (cm-1)
-0.0126
-0.0126
-0.0111
-0.0111
IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS
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CONCLUSIONS AND OUTLOOK
•
When University of Leicester software is available, use it to derive line parameters from
our experimental data
•
Communicate with GOSAT team on the issue of impact of line parameters precision on
the retrieval result
IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS
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