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Jet Propulsion LaboratoryCalifornia Institute of Technology
1 10th HITRAN Database ConferenceCambridge MA June 22, 2008
Near Infrared CO2 Spectral Database
Charles E. Miller, Linda R. Brown, and Robert A. Toth Jet Propulsion Laboratory, California Institute of Technology,
4800 Oak Grove Dr., Pasadena, California 91109
D. Chris Benner, V. Malathy Devi The College of William and Mary, Box 8795, Williamsburg, Virginia 23187-8795, U.S.A
Acknowledgments
The research at the Jet Propulsion Laboratory (JPL), California Institute of Technology, was performed under contract with National Aeronautics and Space Administration. We thank NASA’s Upper Atmosphere Research Program for support of the McMath-Pierce laboratory facility. CEM thanks NASA’s Tropospheric Chemistry and Atmospheric Composition programs for support. The material presented in this investigation is based upon work supported by the National Science Foundation under Grant No. ATM-0338475 to the College of William and Mary. The authors express sincere appreciation to M. Dulick of NOAO (National Optical Astronomy Observatory) for the assistance in obtaining the data. We also thank Gregory DiComo for assistance in setting up the multispectrum solution.
Jet Propulsion LaboratoryCalifornia Institute of Technology
2 10th HITRAN Database ConferenceCambridge MA June 22, 2008
According to Herzberg…
“The spectrum of carbon dioxide has been studied exhaustively by a large number of investigators.”
The Spectrum of CO2 Below 1.25 J. Opt. Soc. Am. 43, 1037 (1953)
Jet Propulsion LaboratoryCalifornia Institute of Technology
3 10th HITRAN Database ConferenceCambridge MA June 22, 2008
According to Herzberg…
“The spectrum of carbon dioxide has been studied exhaustively by a large number of investigators.”
The Spectrum of CO2 Below 1.25 J. Opt. Soc. Am. 43, 1037 (1953)
Toth et al., JQSRT 109, 906 (2008)Toth et al., J. Mol. Spectrosc. 246, 133 (2007)
Malathy Devi et al., J. Mol. Spectrosc. 245, 52 (2007)Toth et al., J. Mol. Spectrosc. 243, 43 (2007)
Malathy Devi et al., J. Mol. Spectrosc. 242, 90 (2007)Toth et al., J. Mol. Spectrosc. 239, 243 (2006)Toth et al., J. Mol. Spectrosc. 239, 221 (2006)
Miller et al., CR Physique 6, 876 (2005)Miller et al., J. Mol. Spectrosc. 228, 329 (2004)Miller et al., J. Mol. Spectrosc. 228, 355 (2004)
Jet Propulsion LaboratoryCalifornia Institute of Technology
4 10th HITRAN Database ConferenceCambridge MA June 22, 2008
Return global XCO2 data with
0.3% precisionMiller et al., JGR 112, D10314 (2007)
Jet Propulsion LaboratoryCalifornia Institute of Technology
5 10th HITRAN Database ConferenceCambridge MA June 22, 2008
Remote Sensing of GHGs at the Sub-1% Level Challenges Spectroscopic Databases
COCOCO2 OO2
ColumnAbundance
PathDependent
XCO2
Path IndependentMixing Ratio
Measured Spectra
Ratio
Jet Propulsion LaboratoryCalifornia Institute of Technology
6 10th HITRAN Database ConferenceCambridge MA June 22, 2008
How well can we retrieve CO2? - Circa 1990
Wallace & Livingston, J. Geophys. Res. D 95, 9823 (1990)
Wallace and Livingston’s seminal work on CO2 remote sensing [1990] with the Kitt Peak FTS revealed deficiencies in the CO2 spectral database
(HITRAN 1986).
Insufficient NIR Spectroscopic Reference Standard Accuracy
1. Incomplete knowledge of spectrum2. Inadequate position knowledge 3. Intensities known to 5 – 20% unc.4. Unvalidated air-widths5. No pressure shifts
Jet Propulsion LaboratoryCalifornia Institute of Technology
7 10th HITRAN Database ConferenceCambridge MA June 22, 2008
Improved Solar Spectra Retrievals circa 2002
Kitt Peak solar data reanalyzed• Improved retrieval algorithm• Improved HITRAN 2000 database
(HITRAN 1992 + CO2 DND list)
Results• Systematic residuals in spectra• +5.8% bias between observed and
in situ column amounts • 0.5% precision in column CO2
"Remaining errors are dominated by deficiencies in the spectroscopic line lists"
Yang et al., Geophys. Res. Lett. 29(10) GL014537 (2002)
Jet Propulsion LaboratoryCalifornia Institute of Technology
8 10th HITRAN Database ConferenceCambridge MA June 22, 2008
Washenfelder et al. (2006) Park Falls WI The TCCON Prototype
Washenfelder et al., J Geophys. Res. 111 D22305 (2006)
Idea
l 1:1
Lin
e
Uncorrected
New data acquisition hardware and methodology (based around Bruker 125 HR)
Results• 0.1% XCO2 precision• Systematic residuals persist
• +2.12% bias for 30013• +2.40% bias for 30012
“Systematic differences attributed to known
uncertainties in the CO2 line strengths and
pressure broadened widths”
Jet Propulsion LaboratoryCalifornia Institute of Technology
9 10th HITRAN Database ConferenceCambridge MA June 22, 2008
CO2 Nomenclature
Vib. Band Notation follows the HITRAN convention ABCDE where A = No. v1 quanta B = No. v2 quanta C = v2 vib ang mom D = No. v3 quanta E = 1 : normal E 1: Fermi res.
Isotopomer Nomenclature: 16O12C16O 626 16O13C16O 636 16O12C18O 628 16O12C17O 627 16O13C18O 638 16O13C17O 637 18O12C18O 828 18O12C17O 827
Isotopomer
Natural Abundance
626 0.98420 636 0.01106 628 0.0039471 627 0.000734 638 0.00004434 637 0.00000825 828 0.0000039573 827 0.00000147
Jet Propulsion LaboratoryCalifornia Institute of Technology
10 10th HITRAN Database ConferenceCambridge MA June 22, 2008
Kitt Peak FTS used for lab studies
Jet Propulsion LaboratoryCalifornia Institute of Technology
11 10th HITRAN Database ConferenceCambridge MA June 22, 2008
Improving Laboratory Accuracies Requires Precise Knowledge/Control of the Experimental State
• Pristine new cells – no contamination• Temperature monitoring inside the cell• Isotopic enriched samples• Mass spectrometric standard samples• Stable spectrometer performance
Goal for Experimental Uncertainties:Pressure: 0.01 Torr (if P > 10 Torr)Temperature: 0.1 KPath: 2 mm (0.1%)Composition: 0.05%SNR: >1000Resolution: 0.011 cm-1
100% Trans: 0.1% 0% Trans: 0.1%Positions: 0.0001 cm-1
Intensity: 0.1% (Relative)
FourTemp
Probes(PRT)goingInside
theCell
Jet Propulsion LaboratoryCalifornia Institute of Technology
12 10th HITRAN Database ConferenceCambridge MA June 22, 2008
1. Determining the Complete Spectrum
Linear
Log
Accurate CO2 remote sensing to 0.3% requires knowledge of all absorption features that contribute to the CO2 absorption spectrum at the level of approximately 0.1% of Imax
Examination of the known NIR CO2 features on a LOG scale shows that transitions from many weaker bands contribute detectable absorption to the spectrum
Completeness will be a critical requirement for the spectral database
Simulations from HITRAN04
Jet Propulsion LaboratoryCalifornia Institute of Technology
13 10th HITRAN Database ConferenceCambridge MA June 22, 2008
1. Determining the Complete Spectrum
Path = 97 mPres = 2.06 TorrTemp= 294 K
C2H2 in 2nd cell to calibrate line positions
30011
3001230013
30014
Mill
er &
Bro
wn,
J. M
ol. S
pect
rosc
. 228
, 329
(20
04)
16O12C16O = 626
Jet Propulsion LaboratoryCalifornia Institute of Technology
14 10th HITRAN Database ConferenceCambridge MA June 22, 2008
626
626: 15% 16O12C16O628: 48% 16O12C18O828: 33% 18O12C18O
2ν3
1. Determining the Complete Spectrum: Characterize Isotopologue Transitions
In natural CO2
16O12C18O < 0.4 % 18O12C18O < 0.0004 %Note: 628 has 2 x more lines than symmetric isotopologues (626, 828) due to different spin statistical weights.
The 2ν3 band of 628 is allowed, but not for
626, 828.
Note: These 828 bands are not in HITRAN 2004 T
oth
et a
l., J
. Mol
. Spe
ctro
sc. 2
43, 4
3 (2
007)
Jet Propulsion LaboratoryCalifornia Institute of Technology
15 10th HITRAN Database ConferenceCambridge MA June 22, 2008
1. Determining the Complete Spectrum: Characterize Isotopologue Transitions
Tot
h et
al.,
J. M
ol. S
pect
rosc
. 243
, 43
(200
7)
828 628 626
626: 15%628: 48%828: 37%
The region below 6920 cm-1 would be transparent in models neglecting 18O species
Note: These 828 lines are not in HITRAN 2004
Jet Propulsion LaboratoryCalifornia Institute of Technology
16 10th HITRAN Database ConferenceCambridge MA June 22, 2008
2. Improved Line PositionsAbsolute Uncertainties < 0.0001 cm-1
00031
m
-40 -20 0 20 40
E/1
0-4 c
m-1
-10
-5
0
5
10
MB-Vander Auwera
Line position differences of the experimentally measured line positions of Miller & Brown and Vander Auwera et al.
Mill
er &
Bro
wn,
J. M
ol. S
pect
rosc
. 228
, 329
(20
04)
= 5x10-5 cm-1
Jet Propulsion LaboratoryCalifornia Institute of Technology
17 10th HITRAN Database ConferenceCambridge MA June 22, 2008
3. Measured line intensities of 125 Bands
Retrievals: Voigt line shape & line-by-line fitting of individual spectra% Differences between HITRAN 2004 and new band strengths
Toth et al., J. Mol. Spectrosc. 243, 43 (2007)
21 bands of 628 8 bands of 627 25 bands of 828
-10
-5
0
5
% D
iffer
ence
700060005000400030002000
Band Center (cm-1
)
626
628
Toth et al. J. Mol. Spectrosc. 239, 221 (2006)Reported 58 band strengths of 626
Jet Propulsion LaboratoryCalifornia Institute of Technology
18 10th HITRAN Database ConferenceCambridge MA June 22, 2008
3. Measured line intensities of 125 Bands
Tot
h et
al.
J. M
ol. S
pect
rosc
. 239
, 221
(20
06)
626
• Intensities for NIR CO2 bands from multiple laboratories agree at the sub-1% value
• A more accurate intercomparison requires specific line shape specification
– Speed dependence– Line mixing
Jet Propulsion LaboratoryCalifornia Institute of Technology
19 10th HITRAN Database ConferenceCambridge MA June 22, 2008
4. & 5. Self-broadened widths and pressure-shifts 15 bands of 626
0.13
0.12
0.11
0.10
0.09
0.08
0.07
0.06
bo (cm
-1/a
tm)
-80 -60 -40 -20 0 20 40 60 80m
20013-00001 20012-00001 20011-00001 21113-01101 21112-01101 21111-01101 01121-01101
0.13
0.12
0.11
0.10
0.09
0.08
0.07
0.06
bo (cm
-1/a
tm)
-60 -40 -20 0 20 40 60
m
30014-00001 30013-00001 30012-00001 30011-00001 31113-01101 31112-01101 00031-00001 01131-01101
-0.012
-0.010
-0.008
-0.006
-0.004
-0.002
do (cm
-1/a
tm)
-80 -60 -40 -20 0 20 40 60 80m
20013-00001 20012-00001 20011-00001 21113-01101 21112-01101 21111-01101 01121-00001
-0.016
-0.014
-0.012
-0.010
-0.008
-0.006
-0.004
-0.002
0.000
do (cm
-1/a
tm)
-60 -40 -20 0 20 40 60m
30014-00001 30013-00001 30012-00001 30011-00001 31113-01101 31112-01101 00031-00001 01131-01101
Tot
h et
al.,
J. M
ol. S
pect
rosc
. 239
, 243
(20
06)
Self-Widths
Note vibrational dependence
Self-Shifts
Fermi Triad and ν2+2ν3
4700 – 5400 cm-1
Fermi Tetrad and 3ν3 6000 – 7000 cm-1
(in cm-1/atm)
m = J" for P branch, J"+1 for R branch
Jet Propulsion LaboratoryCalifornia Institute of Technology
20 10th HITRAN Database ConferenceCambridge MA June 22, 2008
4. & 5. Air-broadened widths and pressure-shifts 626
Tot
h et
al.,
J. M
ol. S
pect
rosc
. 246
, 133
(20
07)
AirWidths
Note vibrational dependence
Air-Shifts
Fermi Triad and ν2+2ν3
4700 – 5400 cm-1
Fermi Tetrad and 3ν3 6000 – 7000 cm-1
(in cm-1/atm)
m = J" for P branch, J"+1 for R branch
0.100
0.095
0.090
0.085
0.080
0.075
0.070
0.065
0.060
bo (cm
-1/a
tm)
-80 -60 -40 -20 0 20 40 60 80m
20011-00001 20012-00001 20013-00001 21111-01101 21112-01101 21113-01101
0.10
0.09
0.08
0.07
0.06
bo (cm
-1/a
tm)
-60 -40 -20 0 20 40 60m
30011-0000130012-0000130013-0000130014-0000130012-00001-Devi et al.00031-0000130013-00001-Devi et al.
-0.009
-0.008
-0.007
-0.006
-0.005
-0.004
-0.003
-0.002
-0.001
do (cm
-1/a
tm)
-80 -60 -40 -20 0 20 40 60 80m
20011-00001 20012-00001 20013-00001 21111-01101 21112-01101 21113-01101
-0.014
-0.012
-0.010
-0.008
-0.006
-0.004
-0.002
do (cm
-1/a
tm)
-60 -40 -20 0 20 40 60m
30011-00001 30012-00001 30013-00001 30014-00001 00031-00001 30012-00001-Devi et al 30013-00001-Devi et al.
Jet Propulsion LaboratoryCalifornia Institute of Technology
21 10th HITRAN Database ConferenceCambridge MA June 22, 2008
Validate lab results with atmospheric data
Top trace: HITRAN 2004
Right trace:
Current Best line list
JPL MkIV (G. Toon)
29 km Tangent Height
Observed and calculated balloon-based FTS spectra
Jet Propulsion LaboratoryCalifornia Institute of Technology
22 10th HITRAN Database ConferenceCambridge MA June 22, 2008
Small Changes in Widths Affect Retrievals at High Airmass
Test Line List A Test Line List B
Jet Propulsion LaboratoryCalifornia Institute of Technology
23 10th HITRAN Database ConferenceCambridge MA June 22, 2008
Accuracy of ± 0.3% using new Voigt line list
Differences Between In Situ and FTS Column CO2
(Ground- and Balloon-based)
[After Sen et al., 2006 HITRAN Conference]
Bruker 125 HR:Park Falls
Zmin: 0.47 km; SZA: 38.7
MkIV (JPL)
Zmin: 31.65 km; SZA: 91.7
Region
UsedHITRAN
2004JPL
2008HITRAN
2004JPL
2008
2.1 m 9% +0.3% 7% +0.2%
1.6 m 4% -0.1%
1.58 m -1% -0.3%
Precision ~0.1% [Washenfelder et al. 2006]
Jet Propulsion LaboratoryCalifornia Institute of Technology
24 10th HITRAN Database ConferenceCambridge MA June 22, 2008
Active Remote Sensing of CO2 Requires Even Greater Line Shape Accuracy
Candidate transition: R(30) of 20013 00001 @ 2050.967 nm (4875.748 cm-1)
ASCENDSASCOPEGOSAT-II
P = 269.03 TorrL = 0.347 mT = 297.04K.
Jet Propulsion LaboratoryCalifornia Institute of Technology
25 10th HITRAN Database ConferenceCambridge MA June 22, 2008
Improved Multispectrum Fitting[Benner et al., JQSRT 53, 705 (1995)]
• Fit all lines and spectra simultaneously• Use quantum mechanical constraints for positions and
intensities• Increases sensitivity to subtle effects in line shapes• Updated capabilities include non-Voigt line shapes, line
mixing, speed dependence (Benner et al., in preparation)
Line Positions:ni = n0 + B(J(J+1)) + D(J(J+1))2 + H(J(J+1))3 + …ni resonant frequencyn0 band origin B, D, H rotational constantsJ rotational quantum number Line Shape Parameters: i = a1 + a2m + a3m2 +a4m3 + …..
Measured half-width at half-max at each line position
Line Intensities:Si = (i/0)(Sv/Li) exp(-hcEi″/kT)[1-exp(hcvi/kT)].F Si, observed individual line intensity Sv vibrational band intensity,Li Hönl-London factor, where li= (m2l″2)/|m| for CO2
m = J″+1 for the R branch, m = J″ for the P branchJ″ lower-state rotational quantum number. l angular momentum quantum number.Qr lower state rotational partition function at T0=296 KEi″ lower state rotational energy F Herman-Wallis factor = [1+A1m+A2m2+A3m3]
Jet Propulsion LaboratoryCalifornia Institute of Technology
26 10th HITRAN Database ConferenceCambridge MA June 22, 2008
Line Shape Problems!Line Mixing Occurs in CO2 P and R Branches
Mil
ler
et
al.
Co
mp
tes
Ren
du
s P
hys
iqu
e 6
(200
5) 8
76-
887.
Jet Propulsion LaboratoryCalifornia Institute of Technology
27 10th HITRAN Database ConferenceCambridge MA June 22, 2008
Multispectral Fitting of the30012 Spectrum
Mal
ath
y D
evi
et a
l. J
. M
ol.
Sp
ect
rosc
. 24
2, 9
0 (2
007
).
Jet Propulsion LaboratoryCalifornia Institute of Technology
28 10th HITRAN Database ConferenceCambridge MA June 22, 2008
CO2 Line Mixing Coefficients
• Line mixing observed at 6220 cm1 even though this band has no Q-branch, no perturbations and adjacent lines are spaced by ~ 1 cm1
Rosenkranz Off diagonal relaxation matrix
Jet Propulsion LaboratoryCalifornia Institute of Technology
29 10th HITRAN Database ConferenceCambridge MA June 22, 2008
Line Mixing & Speed Dependence Observed for
Self- and Air-broadened Spectra
Jet Propulsion LaboratoryCalifornia Institute of Technology
30 10th HITRAN Database ConferenceCambridge MA June 22, 2008
Conclusions
• Accurate remote sensing of CO2 is critical for climate change science
• CO2 remote sensing poses a significant spectroscopic and algorithm challenge
– This is NOT YET a solved problem
• Consideration of strong 16O12C16O (626) transitions alone is insufficient– Must include hot bands– Must include 16O13C16O (636), 16O12C18O (628), etc
• Line shape choice is crucial to simulate high quality spectra within their experimental uncertainty
– Non-Voigt line shapes improve fits 30% - 50% vs Voigt fits– Line Mixing is needed to remove systematic residuals
Jet Propulsion LaboratoryCalifornia Institute of Technology
31 10th HITRAN Database ConferenceCambridge MA June 22, 2008
Kitt Peak Co-Conspirators
Mike Dulick (KPNO)
$$$ NASA, NSF
Chris Benner (W&M)
Malathy Devi(LaRC)Not shown
Linda BrownBob Toth
(JPL)
Jet Propulsion LaboratoryCalifornia Institute of Technology
32 10th HITRAN Database ConferenceCambridge MA June 22, 2008
Backup
Jet Propulsion LaboratoryCalifornia Institute of Technology
33 10th HITRAN Database ConferenceCambridge MA June 22, 2008
Isotopic Fractionation in Martian CO2
0.2% precision desired
PFS/Mars Express (2004)
Grassi et al., Planet. Space Sci. 53, 1017 (2005)Measured & modeled PFS/Mars spectra
Isotopomer
Natural Abundance
626 0.98420 636 0.01106 628 0.0039471 627 0.000734 638 0.00004434 637 0.00000825 828 0.0000039573 827 0.00000147
****
Jet Propulsion LaboratoryCalifornia Institute of Technology
34 10th HITRAN Database ConferenceCambridge MA June 22, 2008
Unanticipated Behavior for High-J Transitions
High-J transitions may show large (>10-4 cm-1), unexpected deviations from their predicted positions due to
– Poor spectroscopic parameter extrapolations
– Perturbations not observed at low-J
Rare isotopologues and hot bands are especially susceptible to these problems since they are much more difficult to characterize accurately
20012-00001
m
-60 -40 -20 0 20 40 60
Wav
enum
ber/
10-4
cm
-1
-1600
-1400
-1200
-1000
-800
-600
-400
-200
0
200
636
This work – R92
20012- 00001
m
-60 -40 -20 0 20 40 60
Dif
fere
nce/
10-4
cm
-1
-40
-20
0
20
40This work-R92 This work-Ding
638
22211
m
-60 -40 -20 0 20 40 60
E/1
0-4 c
m-1
-500
0
500
1000
1500
2000
2500
3000
MB-R92 (e) MB-R92 (f)
626
Mill
er &
Bro
wn,
J. M
ol. S
pect
rosc
. 228
, 329
(20
04)
Mill
er e
t al.,
J. M
ol. S
pect
rosc
. 228
, 355
(20
04)
Jet Propulsion LaboratoryCalifornia Institute of Technology
35 10th HITRAN Database ConferenceCambridge MA June 22, 2008
Uncharacterized High-J Perturbations May Lead to Gross Retrieval Errors
Short scans of CO2 covering the perturbed R74, R76, R78 and R80 lines in the 20012-00001 band of 626. The calculated positions refer to unperturbed locations calculated from parameters derived from lower J transitions.
Toth et al., J. Mol. Spectrosc. 239, 221 (2006)
Jet Propulsion LaboratoryCalifornia Institute of Technology
36 10th HITRAN Database ConferenceCambridge MA June 22, 2008
Filling the 2 um Atmospheric Window (1/2)
636
626
NEW
CO
C2H2
CO
C2H2
13CO2 constitutes only ~1% of the natural CO2
Isotopic substitution shifts the band centers in the Fermi triad region such that the 13CO2 bands effectively fill the 2 um (5000 cm-1) atmospheric windows
– Significant radiative impact under saturated absorption conditions
The allowed 2v3 band of 638 (NEW) is seen in the 4300 – 4700 cm-1 window