victor gorshelev, a. serdyuchenko, m. buchwitz, j. burrows, university of bremen, germany; n....

Victor Gorshelev, A. Serdyuchenko, M. Buchwitz, J. Burrows, University of Bremen, Germany;

N. Humpage, J. Remedios, University of Leicester, UK

IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS

2

OUTLINE

• Motivation and background

• HITRAN database

• Experimental setup

• Matlab model for quick quality control

• Preliminary results

• Conclusion and outlook


3

MOTIVATION AND BACKGROUND

Goals

• Perform laboratory measurements and corresponding data analysis in order to improve spectroscopic line parameters for CH4 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


4

gp(p,T)=[ gair(pref , Tref) (p - pself)+gself(pref,Tref)pself ] [ Tref / T ] n


HITRAN DATABASE

- 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 air-broadened 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).

Pressure broadened line halfwidth according to HITRAN:

HITRAN DATABASE

Parameter Meaning Comments or units

M Molecule number HITRAN chronological assignment

Ia Isotopologue number Ordering within a molecule by terrestrial abundance

n Vacuum wavenumber cm-1

S Intensity cm-1/(molecule cm-2) at standard 296K

R Weighted square of the transition moment Debye2 (for an electric dipole transition)

A Einstein A-coefficient s-1

gair Air-broadened half-width HWHM @ 296K (in cm-1atm-1)gself Self-broadened half-width HWHM @ 296K (in cm-1atm-1)E’’ Lower-state energy cm-1

nair Temperature dependence exponent for gair Unitless

5

Fundamental line parameters for each spectral line


6

HITRAN DATABASE

Parameter Meaning Comments or units

dair Air pressure-induced line shift cm-1 atm-1 at 296K

v’ Upper-state “global” quanta v’’ Lower-state “global” quanta q’ Upper-state “local” quanta q’’ 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’ Statistical weight of upper state g’’ Statistical weight of lower state

Fundamental line parameters for each spectral line

s


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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 range0 Unreported or unavailable1 Default or constant2 Average or estimate3 ≥ 20%4 ≥ 10% and <20%5 ≥ 5% and <10%6 ≥ 2% and <5%7 ≥ 1% and <2%8 < 1%


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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 CH4

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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


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PREVIOUS STUDIES ON LINE PARAMETERSExperimental conditions


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CURRENT RESEARCH ON LINE PARAMETERS

• New experimental conditions

Low pressure High pressure

T, K CH4, mbar T, K CH4, mbar O2, mbar N2, mbar Ptotal, mbar

296 5 29610 490, 990 490, 990 500, 1000

5 495 495 500

2635

26310 490, 990 490, 990 500, 1000

2 5 495 495 500

2435

24310 490, 990 490, 990 500, 1000

2 5 495 495 500

2235

22310 490, 990 490, 990 500, 1000

2 5 495 495 500

195 2 19510 490, 990 490, 990 500, 1000

5 495 495 500


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

12IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS

13

MATLAB EVALUATION MODEL ALGORITHM

Experimental CH4 spectra and conditions : Texp, Pexp, l

Line parameters: Vi, Si, gs, gA, , n (HITRAN);

Matlab

Calculated profile, difference between experimental and modeled profiles

The principle scheme of computation uses a small home-made Matlab routine

Line profile function: Gaussian, Lorentzian


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RESULTS: LOW PRESSURE

Wavenumber, cm-1

Wavenumber, cm-1

Tran

smitt

ance

, a.u

. Re

lativ

e di

ffere

nce

to m

odel

, %

Experimental IUP data: 2 mbar CH4, T = 293 K

Homemade model:Assuming HITRAN parameters and Doppler line profile for region 5997-6007 cm-1.

The difference (%) between experimental and model spectra.


15

RESULTS: LOW PRESSURETr

ansm

ittan

ce, a

.u.

Wavenumber, cm-1

Wavenumber, cm-1

Rela

tive

diffe

renc

e to

mod

el, %

Zoom on the region around 6003 cm-1.


16

RESULTS: HIGH PRESSURE

Wavenumber, cm-1

Wavenumber, cm-1

Tran

smitt

ance

, a.u

. Re

lativ

e di

ffere

nce

to m

odel

, %

Experimental IUP data: 10 mbar CH4 + 990 mbar N2

T= 293 K

Home-made Model:Assuming HITRAN parameters and Lorentz line profile for region 5997-6007 cm-1.

The difference (%) between experimental and model spectra.


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RESULTS: HIGH PRESSURE

Wavenumber, cm-1

Wavenumber, cm-1

Tran

smitt

ance

, a.u

. Re

lativ

e di

ffere

nce

to m

odel

, %

Zoom on the region around 6003 cm-1.


18IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS

UNIVERSITY OF LEICESTER LPC ALGORITHM

Line Parameter Calculation software uses a Levenberg-Marquardt optimal estimation method (Rodgers, 2000) to calculate line parameters from laboratory spectra

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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


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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


Thank you for your attention.

victor gorshelev, a. serdyuchenko, m. buchwitz, j. burrows, university of bremen, germany; n....

Documents

air p ref

fundamental line parameters

spectroscopic line parameters

t ref p p self self

uk improved line parameters

line halfwidth

microns hitran database

p ref p transition dependent