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Collisional effects on spectral shapes and remote sensing

Collisional effects on spectral shapes and remote sensing. H. Tran LISA, CNRS UMR 7583, Université Paris-Est Créteil and Université Paris Diderot. 1. HiResMIR@CAES-Frejus-2013. Outline. Introduction: Atmospheric observation and spectral shape Isolated line :

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Collisional effects on spectral shapes and remote sensing

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  1. Collisional effects on spectral shapes and remote sensing H. Tran LISA, CNRS UMR 7583, Université Paris-Est Créteil and Université Paris Diderot 1 HiResMIR@CAES-Frejus-2013

  2. Outline • Introduction: Atmospheric observation and spectral shape • Isolated line : • - The Doppler, Lorentzian and Voigt profiles • - Limits of the Voigt profile • - Laboratory studies • - Influence on atmospheric retrieval • Line-mixing for closely spaced lines • - Line-mixing effects • - Laboratory studies • - Influence on spectroscopic data extraction • - Influence on atmospheric retrieval • Conclusions 2 HiResMIR@CAES-Frejus-2013

  3. Input spectroscopic data (Position, Intensity, spectral shape,…) Radiative transfer Forward model • P, T profiles • Molecule mole fraction profiles • Cloud altitude, aerosol • etc. … Introduction: Atmospheric retrievals Measured spectra (satellite, balloon, ground,…) Spectral shapes  Collisional (pressure) effects on the spectral shape 3 HiResMIR@CAES-Frejus-2013

  4. Comparaison between the Gaussian, the Lorentz and the Voigt profiles. Introduction: The Voigt profile Gaussien Voigt Lorentzian Doppler Doppler+Collision Collisions Pressure 4 HiResMIR@CAES-Frejus-2013

  5. Introduction: isolated lines and closely spaced lines ACE spectra at different tangent altitudes (1-0) R(0) n3 R(9) Bernath et al., GRL, 32, L15S01 (2005) 5 HiResMIR@CAES-Frejus-2013

  6. Isolated lines 6 HiResMIR@CAES-Frejus-2013

  7. H2O/N2, n3 band, 111,11101,10 110,11 100,10 Limits of the Voigt profile Measured and adjusted spectra using the Voigt profile. 7 HiResMIR@CAES-Frejus-2013

  8. Limits of the Voigt profile It neglects: • The velocity changes induced by collisions. • The detailed balance: •  change from v to v’ < v is more probable than that from v to v’ > v. •  reduction of the Doppler broadening  Dicke narrowing effect • The speed-dependences of the collisional width G(v) and shift D(v) of the line. • This also (in general) leads to a narrowed line 8 HiResMIR@CAES-Frejus-2013

  9. Simple and widely used non-Voigt approaches • For the velocity changes effect: The Galatry (soft collisions) and Rautian (hard collisions) line-shapes. Introducing a parameter nVC • (or b) - the velocity changing collisions frequency. • For the speed dependences of the line-width and shift: The speed-dependent Voigt profile, assuming a simple quadratic dependence on the absolute speed or polynomial dependence on the relative speed 9 HiResMIR@CAES-Frejus-2013

  10. Influence of non-Voigt effects on atmospheric retrievals In situ absorption spectrum of tropospheric H2O recorded by balloonborne diode laser and its fits using the Voit profile and the Hard Collision profile Durry et al, JQSRT 94, 387,2005 10 HiResMIR@CAES-Frejus-2013

  11. Influence of non-Voigt effects on atmospheric retrievals HF profile retrieved from ground-based absorption FTIR measurements (Jungfraujoch station) in the (1-0) R(1) micro-window by using the Voigt profile and the Soft Collision model, compared with the HALOE profiles smoothed. 11 Barret et al, JQSRT 95, 499, 2005 HiResMIR@CAES-Frejus-2013

  12. HC HC Influence of non-Voigt effects on line parameters determination (Diode laser) Measured absorption of pure H2O (left) and H2O in air (right) and their differences with those adjusted using the VP, HC, and SDVP 12 HiResMIR@CAES-Frejus-2013

  13. Influence of non-Voigt effect on line parameters Ratios of the self-broadening coefficients and intensity obtained by the HC (o) and SDVP () to those obtained by the VP, for 13 H2O lines in the near-infrared. 13 HiResMIR@CAES-Frejus-2013

  14. nVC rate in red (SC) Remaining problems with these non-Voigt approaches Dependence of nVC on pressure Relaxation of the 317.2 GHz line of O3 in collision with O2 at 240 K. Rohart et al, J Mol Spectrosc 251, 282, 2008  Need to take into account both Dicke and speed dependence effects 14 HiResMIR@CAES-Frejus-2013

  15. Velocity changing by the Keilson and Storer model : memory parameter 2 limits Hard collision model Soft collision model  KS more realistic than these two extreme cases and more suitable for intermediate cases 15 HiResMIR@CAES-Frejus-2013

  16. Pure H2O, 296K, 2n1+n2+n3 band:  measured,  calculated Model-experiment comparison : pure H2O With the model we compute the line shape. Then we fit the calculated spectra (as the measured ones) by Voigt profiles and look at the residuals. 606707 515414 16 HiResMIR@CAES-Frejus-2013

  17. Model-experiment comparison: H2O/air H2O/N2, 296K, n3, 1111110110 , 1101110010 doublet H2O/air, 296K, 2n1+n2+n3, 515414 line  measured,  calculated 17 HiResMIR@CAES-Frejus-2013

  18. 296 K, Q(1) m= 0.92, 0= 0.41 995 K, Q(1) m= 0.95, 0= 0.50 Model-experiment comparison: H2/N2 Collisional width Bonamy et al., Eur. Phys. J. D, 2004 18 HiResMIR@CAES-Frejus-2013

  19. Non-isolated transitions: Line-mixing effects 19 HiResMIR@CAES-Frejus-2013

  20. Line-mixing effects In some cases, for closely spaced lines, the Voigt profile fails when P increases. It predicts shapes that are too broad. Collisions induce transfers of populations between the levels of the two lines that lead to transfers of intensity between the lines. 20 HiResMIR@CAES-Frejus-2013

  21. Line-mixing effects: Absorption coefficient rk populations dk matrix element of radiation-matter coupling tensor , L0 matrix of positions W relaxation operator. All effects of collisions. Independent of s within the impact approximation (not too far in the wings) Wlk0  Line coupling between |k> and |l> Wlk=0  No line coupling (Lorentz) 21 HiResMIR@CAES-Frejus-2013

  22. Line-mixing effects: Relaxation matrix Relations for W For moderate line overlapping, a first order perturbation approach is possible. Then we only need to know one coupling parameter (Y, related to the W matrix elements) per line 22 HiResMIR@CAES-Frejus-2013

  23. Line-mixing and remote sensing: Monitoring GreenHouse Gases from space Nadir looking instruments onboard satellites Greenhouse gases Observation SATellite (GOSAT, JAXA-NIES, in orbit) Orbiting Carbon Observatory (OCO 2, NASA) MicroCarb (CNES, under study), CarbonSat (ESA, under study) • Spectral regions and aims • CO2 from 1.6 mm (weak) and 2.1 mm (strong) bands • Air mass from O2 A band (0.76 mm) • CH4 from 2n3 band (near 1.7 mm) • aerosols from CO2 and O2 bands Detection/quantifying sinks and sources (1 ppm for xCO2, 0.3 %) → Extreme accuracy of spectra modelling. Huge constraints on the spectroscopic data and the prediction of pressure effects (collisions and spectral-shape) 23 HiResMIR@CAES-Frejus-2013

  24. Sza 79.9°, Park Falls, region 1.6 mm CO2 retrieved Sza 79.9°, Park Falls, region 2.1 mm Wrong air-mass (and time) dependences CO2: ground-based measurements HiResMIR@CAES-Frejus-2013

  25. O2: Ground-based measurements Sza 79.9°, Park Falls, A band Wrong time (and air-mass) dependences Sza 79.9°, Park Falls, 1.27 mm band HiResMIR@CAES-Frejus-2013

  26. CH4: Ground-based atmospheric solar absorption Spectra: air mass 5.7, Park Falls Wrong time and airmass dependences → Largely erroneous conclusions on sinks and sources HiResMIR@CAES-Frejus-2013

  27. Modeling of line-mixing effect CO2 bands: Scaling model, self consistent model for all bands. Adjustment of model in 720 cm-1 Q branch. No use of present NIR bands CH4: Semi-classical model. Self consistent model for n3, n4 and 2n3 bands. Adjustment of model in n3 band at high pressure. No use of present 2n3 band O2 A-band: Scaling model. Model developed from O2 A band at elevated pressure. No use of low pressure spectra Collision induced absorption: From analysis of O2 A band at elevated pressures HiResMIR@CAES-Frejus-2013

  28. O2/N2 A band CO2/N2 Line-mixing effects: Laboratory studies ___ measurement, ___ Line-mixing ___ Lorentz 76.0 atm 47.6 atm 28.1 atm 28 HiResMIR@CAES-Frejus-2013

  29. Line-mixing effects: Influence on spectroscopic parameters retrieval CH4/N2, 2n3, R(6), 296 K 29 HiResMIR@CAES-Frejus-2013

  30. 1.0 0.8 0.6 Transmission 0.4 0.2 0.0 0.15 observed-Voigt 0.10 0.05 0.00 -0.05 Residual 0.15 observed-(LM+CIA) 0.10 0.05 0.00 -0.05 12990 13020 13050 13080 13110 13140 13170 -1 wavenumber (cm ) Influence on retrievals: O2 ground-based measurements Spectra: Sza 79.9°, Park Falls O2 A band region O2 A band: Relative errors on surface pressures retrieved from atmospheric spectra 30 HiResMIR@CAES-Frejus-2013

  31. Influence on retrievals: CO2 ground-based measurements  Fits of a ground based transmission spectra in the region of the 2 n1+ n3 band of CO2 Significant errors (10%) on the CO2 atmospheric amount. Sinks and sources !!!  31 HiResMIR@CAES-Frejus-2013

  32. Influence on retrievals: CH4 ground-based measurements Methane amounts retrieved from atmospheric spectra 32 HiResMIR@CAES-Frejus-2013

  33. Influence on planetary spectra Jupiter ISO/SWS spectrum in the n4 band region of CH4 33 HiResMIR@CAES-Frejus-2013

  34. Summary • Spectral shape has become a key issue for high precision soundings (OCO, ACE, …) • When line is isolated: • - The Voigt profile fails to model isolated line-shape -> need to take into account Dicke narrowing and speed dependence effects (velocity effects) • - Influence of velocity effects on atmospheric retrieval is quite small (but few studies available) • When lines are closely spaced (especially at high pressure): • - line-mixing can be observed • - Increasing evidences of influence of line-mixing for remote sensing • - Need to take into account both line-mixing and velocity effects 34 HiResMIR@CAES-Frejus-2013

  35. -General Equations -Isolated Lines -Line-mixing -Far wings -Collision Induced processes -Consequences for applications -Remaining problems HiResMIR@CAES-Frejus-2013

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