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

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22 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 HiResMIR@CAES-Frejus-2013

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

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44 Pressure DopplerDoppler+CollisionCollisions GaussienVoigtLorentzian Comparaison between the Gaussian, the Lorentz and the Voigt profiles. Introduction: The Voigt profile HiResMIR@CAES-Frejus-2013

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55 Bernath et al., GRL, 32, L15S01 (2005) ACE spectra at different tangent altitudes (1-0) R(0) 3 R(9) Introduction: isolated lines and closely spaced lines HiResMIR@CAES-Frejus-2013

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66 Isolated lines HiResMIR@CAES-Frejus-2013

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77 Measured and adjusted spectra using the Voigt profile. H 2 O/N 2, 3 band, 11 1,11 10 1,10 11 0,11 10 0,10 Limits of the Voigt profile HiResMIR@CAES-Frejus-2013

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88 Limits of the Voigt profile HiResMIR@CAES-Frejus-2013 It neglects: 1.The velocity changes induced by collisions. The detailed balance: change from v to v v. reduction of the Doppler broadening Dicke narrowing effect 2.The speed-dependences of the collisional width (v) and shift (v) of the line. This also (in general) leads to a narrowed line

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99 - For the velocity changes effect: The Galatry (soft collisions) and Rautian (hard collisions) line-shapes. Introducing a parameter VC (or ) - 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 Simple and widely used non-Voigt approaches HiResMIR@CAES-Frejus-2013

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10 In situ absorption spectrum of tropospheric H 2 O recorded by balloonborne diode laser and its fits using the Voit profile and the Hard Collision profile Durry et al, JQSRT 94, 387,2005 Influence of non-Voigt effects on atmospheric retrievals HiResMIR@CAES-Frejus-2013

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11 Barret et al, JQSRT 95, 499, 2005 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. Influence of non-Voigt effects on atmospheric retrievals HiResMIR@CAES-Frejus-2013

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12 (Diode laser) Measured absorption of pure H 2 O (left) and H 2 O in air (right) and their differences with those adjusted using the VP, HC, and SDVP HC Influence of non-Voigt effects on line parameters determination HiResMIR@CAES-Frejus-2013

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13 Ratios of the self-broadening coefficients and intensity obtained by the HC (o) and SDVP ( ) to those obtained by the VP, for 13 H 2 O lines in the near-infrared. Influence of non-Voigt effect on line parameters HiResMIR@CAES-Frejus-2013

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14 VC rate in red (SC) Rohart et al, J Mol Spectrosc 251, 282, 2008 Dependence of VC on pressure Relaxation of the 317.2 GHz line of O 3 in collision with O 2 at 240 K. Remaining problems with these non-Voigt approaches HiResMIR@CAES-Frejus-2013 Need to take into account both Dicke and speed dependence effects

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

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16 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. Pure H 2 O, 296K, 2 1 + 2 + 3 band: measured, calculated 6 06 7 07 5 15 4 14 Model-experiment comparison : pure H 2 O HiResMIR@CAES-Frejus-2013

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17 H 2 O/N 2, 296K, 3, 11 111 10 110, 11 011 10 010 doublet H 2 O/air, 296K, 2 1 + 2 + 3, 5 15 4 14 line measured, calculated Model-experiment comparison: H 2 O/air HiResMIR@CAES-Frejus-2013

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18 Model-experiment comparison: H 2 /N 2 Collisional width 296 K, Q(1) m = 0.92, 0 = 0.41 Bonamy et al., Eur. Phys. J. D, 2004 995 K, Q(1) m = 0.95, 0 = 0.50 HiResMIR@CAES-Frejus-2013

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

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20 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. Line-mixing effects HiResMIR@CAES-Frejus-2013

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

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22 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 Line-mixing effects: Relaxation matrix HiResMIR@CAES-Frejus-2013 Relations for W

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23 HiResMIR@CAES-Frejus-2013 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 - CO 2 from 1.6 m (weak) and 2.1 m (strong) bands - Air mass from O 2 A band (0.76 m) - CH 4 from 2 3 band (near 1.7 m) - aerosols from CO 2 and O 2 bands Detection/quantifying sinks and sources (1 ppm for x CO2, 0.3 %) Extreme accuracy of spectra modelling. Huge constraints on the spectroscopic data and the prediction of pressure effects (collisions and spectral-shape) Line-mixing and remote sensing: Monitoring GreenHouse Gases from space

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24 Sza 79.9, Park Falls, region 2.1 m Wrong air-mass (and time) dependences CO 2 retrieved Sza 79.9, Park Falls, region 1.6 m CO 2 : ground-based measurements HiResMIR@CAES-Frejus-2013

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25 Sza 79.9, Park Falls, 1.27 m band Sza 79.9, Park Falls, A band Wrong time (and air-mass) dependences O 2 : Ground-based measurements HiResMIR@CAES-Frejus-2013

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26 Spectra: air mass 5.7, Park Falls Wrong time and airmass dependences Largely erroneous conclusions on sinks and sources CH 4 : Ground-based atmospheric solar absorption HiResMIR@CAES-Frejus-2013

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27 No use CO 2 bands: Scaling model, self consistent model for all bands. Adjustment of model in 720 cm -1 Q branch. No use of present NIR bands CH 4 : Semi-classical model. Self consistent model for 3, 4 and 2 3 bands. Adjustment of model in 3 band at high pressure. No use of present 2 3 band No use O 2 A-band: Scaling model. Model developed from O 2 A band at elevated pressure. No use of low pressure spectra Collision induced absorption: From analysis of O 2 A band at elevated pressures Modeling of line-mixing effect HiResMIR@CAES-Frejus-2013

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28 O 2 /N 2 A band 76.0 atm 47.6 atm 28.1 atm ___ measurement, ___ Line-mixing ___ Lorentz CO 2 /N 2 Line-mixing effects: Laboratory studies HiResMIR@CAES-Frejus-2013

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29 Line-mixing effects: Influence on spectroscopic parameters retrieval CH 4 /N 2, 2 3, R(6), 296 K HiResMIR@CAES-Frejus-2013

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30 12990130201305013080131101314013170 -0.05 0.00 0.05 0.10 0.15 observed-(LM+CIA) Residual wavenumber (cm ) -0.05 0.00 0.05 0.10 0.15 observed-Voigt 0.0 0.2 0.4 0.6 0.8 1.0 Transmission Influence on retrievals: O 2 ground-based measurements HiResMIR@CAES-Frejus-2013 Spectra: Sza 79.9, Park Falls O 2 A band region O 2 A band: Relative errors on surface pressures retrieved from atmospheric spectra

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31 Fits of a ground based transmission spectra in the region of the 2 1 + 3 band of CO 2 Significant errors (10%) on the CO 2 atmospheric amount. Sinks and sources !!! Influence on retrievals: CO 2 ground-based measurements HiResMIR@CAES-Frejus-2013

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32 Influence on retrievals: CH 4 ground-based measurements Methane amounts retrieved from atmospheric spectra HiResMIR@CAES-Frejus-2013

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33 Jupiter ISO/SWS spectrum in the 4 band region of CH 4 Influence on planetary spectra HiResMIR@CAES-Frejus-2013

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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 HiResMIR@CAES-Frejus-2013

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