1. Victor Gorshelev, A. Serdyuchenko, M. Buchwitz, J. Burrows, University of Bremen, Germany; N. Humpage, J. Remedios, University of Leicester, UK IMPROVED LINE PARAMETERS FOR CH 4 AROUND 1.6 MICRONS

2. 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 2

3. 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 3 IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS

4. 4  p (p,T)= [  air (p ref, T ref )  (p - p self )+  self (p ref,T ref )  p self ]  [ T ref / T ] n IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS HITRAN DATABASE  air and  self - the air-broadened and the self-broadened HWHM [cm -1 /atm] at T ref = 296 K, p ref = 1 atm.  air =0.79  N2 + 0.21  O2 - n – coefficient of temperature dependence of the air- broadened half-width (transition dependent).  - air-broadened pressure shift [cm -1 /atm] at T ref =296 K, p ref =1 atm, of the line transition frequency  :   *=  +  (p ref )p (transition dependent). Pressure broadened line halfwidth according to HITRAN:

5. HITRAN DATABASE ParameterMeaningComments or units M Molecule numberHITRAN chronological assignment IaIa Isotopologue number Ordering within a molecule by terrestrial abundance Vacuum wavenumbercm -1 S Intensitycm -1 /(molecule cm -2 ) at standard 296K R Weighted square of the transition momentDebye 2 (for an electric dipole transition) A Einstein A-coefficients -1  air Air-broadened half-widthHWHM @ 296K (in cm -1 atm -1 )  self Self-broadened half-widthHWHM @ 296K (in cm -1 atm -1 ) E’’ Lower-state energycm -1 n air Temperature dependence exponent for  air Unitless 5 Fundamental line parameters for each spectral line IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS

6. HITRAN DATABASE ParameterMeaningComments or units  air Air pressure-induced line shiftcm -1 atm -1 at 296K v’v’ Upper-state “global” quanta v ’’ Lower-state “global” quanta q’q’ Upper-state “local” quanta q ’’ Lower-state “local” quanta I err Uncertainty indicesAccuracy for 3/6 critical parameters I ref Reference indicesReferences 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 6 Fundamental line parameters for each spectral line s IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS

7. HITRAN DATABASE 7 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

8. HITRAN UNCERTAINTIES FOR METHANE 8 IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS Upper panel – spectral windows of SCIAMACHY, OCO and GOSAT and line intensities of CH 4 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

9. PREVIOUS STUDIES ON LINE PARAMETERS 9 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 scansBruker IFS 125 HR Absorption path 2×140 cm20×100 cm Resolution 0.011/0.1 cm -1 spectra/background 0.005 cm -1 IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS

10. PREVIOUS STUDIES ON LINE PARAMETERS 10 Experimental conditions IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS

11. CURRENT RESEARCH ON LINE PARAMETERS 11 New experimental conditions Low pressureHigh pressure T, KCH 4, mbarT, KCH 4, mbarO 2, mbarN 2, mbar P total, mbar 2965 10490, 990 500, 1000 5495 500 263 5 10490, 990 500, 1000 25495 500 243 5 10490, 990 500, 1000 25495 500 223 5 10490, 990 500, 1000 25495 500 1952 10490, 990 500, 1000 5495 500 IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS

12. 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 12 IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS

13. MATLAB EVALUATION MODEL ALGORITHM 13 Experimental CH 4 spectra and conditions : T exp, P exp, l Line parameters: V i, S i, g s, g A,, 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 IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS

14. RESULTS: LOW PRESSURE 14 Wavenumber, cm -1 Transmittance, a.u. Relative difference to model, % Experimental IUP data: 2 mbar CH 4, 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. IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS

15. RESULTS: LOW PRESSURE 15 Transmittance, a.u. Wavenumber, cm -1 Relative difference to model, % Zoom on the region around 6003 cm -1. IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS

16. RESULTS: HIGH PRESSURE 16 Wavenumber, cm -1 Transmittance, a.u. Relative difference to model, % Experimental IUP data: 10 mbar CH 4 + 990 mbar N 2 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. IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS

17. RESULTS: HIGH PRESSURE 17 Wavenumber, cm -1 Transmittance, a.u. Relative difference to model, % Zoom on the region around 6003 cm -1. IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS

18. 18 IMPROVED 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

19. 19 LPC: RETRIEVED PARAMETERS Parameter Case 1 a priori Case 1 retrieved Case 2 a priori Case 2 retrieved Transition wavenumber (cm -1 ) 6015.6643 6026.22746026.2273 Line intensity5.809E-225.762E-22 (-0.047E-22, 0.8%) 5.721E-225.654E-22 (-0.067E-22, 1.1%) Air-broadened width0.05830.0555 (-0.0028, 4.8%) 0.06340.0598 (-0.0036, 5.7%) Self-broadened width0.0790.0787 (-0.003, 3,8%) 0.0790.0787 (-0.003, 3,8%) Temperature dependence of air broadening 0.850 Pressure shift (cm -1 )-0.0126 -0.0111 IMPROVED LINE PARAMETERS FOR CH4 AROUND 1.6 MICRONS

20. CONCLUSIONS AND OUTLOOK 20 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