Jet Propulsion Laboratory California Institute of Technology 1 10 th HITRAN Database Conference...

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.



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)



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)



Return global XCO2 data with

0.3% precisionMiller et al., JGR 112, D10314 (2007)



Remote Sensing of GHGs at the Sub-1% Level Challenges Spectroscopic Databases

COCOCO2 OO2

ColumnAbundance

PathDependent

XCO2

Path IndependentMixing Ratio

Measured Spectra

Ratio



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



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)



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”



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



Kitt Peak FTS used for lab studies



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



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



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



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)



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



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



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



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



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



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.



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



Small Changes in Widths Affect Retrievals at High Airmass

Test Line List A Test Line List B



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]



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.



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]



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.



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

).



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



Line Mixing & Speed Dependence Observed for

Self- and Air-broadened Spectra



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



Kitt Peak Co-Conspirators

Mike Dulick (KPNO)

$$$ NASA, NSF

Chris Benner (W&M)

Malathy Devi(LaRC)Not shown

Linda BrownBob Toth

(JPL)



Backup



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

****



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)



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)



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

Jet Propulsion Laboratory California Institute of Technology 1 10 th HITRAN Database Conference...

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