Jet Propulsion LaboratoryCalifornia Institute of Technology 1 V-1 11th HITRAN Conference, Cambridge, MA, June 16-18, 2010

The importance of being earnest about line shapes!!

Charles E. Miller and Linda R. Brown

Jet Propulsion Laboratory, California Institute of Technology

4800 Oak Grove Dr., Pasadena, California 91109

Acknowledgments

The research at the Jet Propulsion Laboratory (JPL), California Institute of Technology, was performed under contract with National Aeronautics and Space Administration.

Jet Propulsion LaboratoryCalifornia Institute of Technology 2 V-1 11th HITRAN Conference, Cambridge, MA, June 16-18, 2010

Return global XCO2 data with

0.3% precision

Our Research Goal: Improve CO2 and O2 line

parameters

Jet Propulsion LaboratoryCalifornia Institute of Technology 3 V-1 11th HITRAN Conference, Cambridge, MA, June 16-18, 2010

Better Accuracies Require Precise Knowledge/Control of the Experimental State

• Pristine cells – no contamination• Temperature monitoring inside the cell• Isotopic enriched samples• Mass spectrometric standard samples• Stable spectrometer performance

Goal for Experimental Uncertainties:Abundances: 0.05% (purity, Isotope)Pressure: 0.01 Torr (if P > 10 Torr)Temperature: 0.1 K Path: 2 mm (0.1%) Signal/noise: 2000:1 Resolution: nearly Doppler-limited100% Trans: 0.1% 0% Trans: 0.1%Instrumental line shape

FourTemp

Probes(PRT)goingInside

theCell

Jet Propulsion LaboratoryCalifornia Institute of Technology 4 V-1 11th HITRAN Conference, Cambridge, MA, June 16-18, 2010

Molecular Line Shape Problem!

Miller et al. Comptes Rendus Physique 6 (2005).

Voigt onlyStrange residuals Strange residuals (!)

Multispectrum retrievals one solution for all lines

fitting all spectra simultaneously

[modified from Benner et al. JQSRT 53, 705 (1995)]

NEW CO2 Lab parameters could not be used in (Voigt only) atmospheric retrievals.

non-Voigt line shapes (line mixing + speed

dependence + narrowing)

Jet Propulsion LaboratoryCalifornia Institute of Technology 5 V-1 11th HITRAN Conference, Cambridge, MA, June 16-18, 2010

Too many line shape choices!

Lisak et al. 2010 O2 B-band

Jet Propulsion LaboratoryCalifornia Institute of Technology 6 V-1 11th HITRAN Conference, Cambridge, MA, June 16-18, 2010

What we have to do now!

• Learn what combination of line shapes can produce the best atmospheric retrievals.

• Create and Validate universal software using the required molecular shapes to compute synthetic spectra (radiances etc….).

• Give standardized software to both atmospheric and lab spectroscopists:

So that new lab parameters will be consistent

with atmospheric calculations.

Jet Propulsion LaboratoryCalifornia Institute of Technology 7 V-1 11th HITRAN Conference, Cambridge, MA, June 16-18, 2010

Need to do better lab studies

• Use community-validated multi-spectrum retrieval codes that permit us to obtain consistent values of line shape parameters.

(do intercomparisons)• Use gas pressure that can

reveal all activated line shapes (Voigt, speed dependence, line mixing, narrowing …..).

• Excellent instrumental performance (usual stuff).

Conventional Strategy: Sequential L-B-L analyses

Quantum modeling Pres. (atm) 1st Positions: < 0.001 2nd Intensities: < ~ 0.010 To Create good database for broadening retrievals

3rd Shapes:Lorentz: 0.10 – 1. Narrowing & 0.03 – 0.1 Speed Dependence (Lorentz=Doppler)Line mixing: 0.5 – 10 Collision Induced Abs: 1 – 20 ?

Jet Propulsion LaboratoryCalifornia Institute of Technology 8 V-1 11th HITRAN Conference, Cambridge, MA, June 16-18, 2010

Constraining multispectrum fits!

• STRATEGY: Fit all lines and spectra simultaneously BUT• Constrain positions and intensities and adjust constants in the

quantum mechanical equations (instead of fitting line-by-line)• Pressure broadening parameters still fitted line-by-line

Line Positions:νi = ν0 + B(J(J+1)) - D(J(J+1))2 + H(J(J+1))3 – E" ν i Resonant frequency ν 0 Band origin J Rotational quantum number E" Lower state rotational energy

(fixed)

ν0, B, D, H, upper state constants of each band in the region, are the

adjusted instead of individual positions.

Line Intensities:Si = (i/0)(Sv/Li) exp(-hcEi″/kT)[1-exp(hcvi/kT)]F

Si, observed individual line intensity Sv vibrational band intensity,F Herman-Wallis factor = [1+A1m+A2m2+A3m3]2

Li Hönl-London factor, where li= (m2l″2)/|m| for CO2

m = J″+1 R branch, m = J″ for the P branchJ″, l lower-state rotational & angular momentum quanta Qr lower state rotational partition function at T0=296 KEi″ lower state rotational energy

Sv, A1, A2 are the adjusted parametersCan we do this for asymmetric tops? symmetric tops?

Jet Propulsion LaboratoryCalifornia Institute of Technology 9 V-1 11th HITRAN Conference, Cambridge, MA, June 16-18, 2010

CALL TO ACTION!

Fits to laboratory and atmospheric spectra must use the same line shape formulations

• Create new universal line shape (LS) software• Validate LS formulations• Expand databases to include all necessary LS parameters• Convince sponsors to fund it!

Coming goal: 0.1% accuracy for strongest bands