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Spectral Modeling and Remote Sensing of Greenhouse Gases

This article explores the use of spectral shapes and modeling techniques for remote sensing of greenhouse gases, focusing on the OCO and GOSAT experiments and future issues with the HITRAN database.

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Spectral Modeling and Remote Sensing of Greenhouse Gases

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  1. Spectral shapes modeling and remote sensing of greenhouse gases. Toward the OCO and GOSAT experiments and future HITRAN issues Jean-Michel HARTMANN L.I.S.A. (CNRS and Université Paris VII and Paris XII) Créteil, FRANCE and Geoffrey TOON (JPL), Ha TRAN (LISA) but also Christian BOULET, Linda BROWN, André BUTZ, Christian FRANKENBERG, Robert GAMACHE, Frank HASE, J. LAMOUROUX, Ann LARIA,, … hartmann@lisa.univ-paris12.fr

  2. Monitoring GreenHouse Gases from space Nadir looking instruments onbord sattelites Orbiting Carbon Observatory (OCO, NASA, launch failed but OCO2 coming) Greenhouse gases Observation SATellite (GOSAT, JAXA-NIES, in orbit) MiniCarb (CNES, under study) • Spectral regions and aims. • CO2 from 1.6 mm (weak) and 2.1 mm (strong) bands • Air mass from O2 A band (near 762 nm • CH4 from 2n3 band (near 1.7 mm) • aerosols from CO2 and O2 bands Detection/quantifying sinks and source → Extreme accuracy of spectra modelings (0.3 %). Huge constraints on the spectroscopic data and the prediction of pressure effects (collisions and spectral-shape → New issues for HITRAN database

  3. Spectral shapes and HITRAN Basic Isolated line shape: Voigt Convolution of Lorentz (collisions) and Gaussian (Doppler). HITRAN provides almost all needed data (except T dep of shift and self broad, broadening by H2O) Refined Isolated line shape: speed dependence and Dicke narrowing Effects of the speed dependences of collisional width and shift and of velocity changes. HITRAN does not provide any data. _______________________________________________________________ Collisionally coupled Lines: Line-mixing, no SD nor Dicke Modeled through the “relaxation matrix” W whose size is NCxNC where NC is the number of coupled lines (block diagonal with respect to bands) HITRAN does not provide any data. Speed dependent Dicke narrowed Line-mixing profiles: Very complex problem, still to be studied in laboratories _______________________________________________________________ Collision Induced Absorption (CIA) Electric dipole moment induced during collisions. Weak and broad absorption features. HITRAN does not provide any data

  4. CO2: Ground-based atmospheric solar absorption 2.1 mm band Spectra: Sza 79.9°, Park Falls Wrong time and air-mass dependences → Largely erroneous conclusions on sinks and sources (huge source at poles, huge sink at mid-latitudes

  5. CO2 1.6 micron band

  6. O2: Ground-based atmospheric solar absorption A-band Spectra: Sza 79.9°, Park Falls Wrong time and airmass dependences → Large errors on air masses or pressure vertical profiles for high North and South latitudes

  7. O2 1.27 micron band

  8. CH4: Ground-based atmospheric solar absorption 2n3 band Spectra: air mass 5.7, Park Falls Wrong time and airmass dependences → Largely erroneous conclusions on sinks and sources

  9. What we have used (state of the art ?) Spectroscopic data: isolated lines Voigt profiles (no SD, no Dicke) CO2 bands: Toth essentially identical to HITRAN2008 except for widths O2 A-band: HITRAN2008 (Brown, Robichaud, others) CH4 2n3: a mixture of Frankenberg, Nikitin and Pine Line mixing data: off-diagonal W matrix elements CO2 bands: Niro et al (2005). Self consistent model for all bands NB: Adjustment of model in 720 cm-1 Q branch. No use of present NIR bands O2 A-band: Tran et al (2008). Model developed from O2 A band at elevated pressure. NB: No use of low pressure spectra CH4: Tran et al (2006). Self consistent model for n3, n4 and 2n3 bands) NB: Adjustment of model in n3 band at high pressure. No use of present NIR band Collision Induced Absorption O2 A-band: Tran et al (2008). From analysis of O2 A band at elevated pressure. NB: No use of low pressure spectra

  10. Validation of LM model using laboratory spectra: O2 and CO2 ___ measurement, ___ LM ___ Lorentz O2 A band CO2 band 76.0 atm 47.6 atm 28.1 atm

  11. Validation of LM model using laboratory spectra: CH4 2n3 band With “effective” line-broadening and –shifting and with Voigt profiles: Frankenberg et al., ACP, 2008 (and HITRAN 2008) With “true” line-broadening and –shifting coeffs. and with LM (black), Voigt (red)

  12. Consequences for atmospheric spectra: O2 A band case Spectra: Sza 79.9°, Park Falls Significantly reduced residuals but some structures remain

  13. O2 A band: Relative errors on surface pressures retrieved from atmospheric spectra

  14. Consequences for atmospheric spectra: CO2 2.1 mm region Spectra: Sza 79.9°, Park Falls Significantly reduced residuals but some structures remain

  15. Scaling factor, applied to the a priori CO2 vmr profile, retrieved from fits Inclusion of LM reduces air mass dependence and inconsistency between Results from weak and strong CO2 band. But still slight air mass dependence for large air masses

  16. Consequences for atmospheric spectra: The CH4 2n3 case

  17. Methane amounts (ratio of the total CH4 column to the total air column) retrieved from atmospheric spectra

  18. Getting closer to OCO/GOSAT needed accuracy Accounting for LM in CH4 (2n3), CO2 (2.1 mm) and O2 (A-band) and for CIA in O2necessary. When done, transmission fits residuals between -0.01 and +0.01. Small but still above noise level and showing systematic and structured features. Still insufficient → HITRAN 2008 may not be the best → Need for a very careful and critical inter-comparison of available isolated line data CO2: Toth et al, Predoi-Cross et al, Benner et al, …. O2: Brown et al, Predoi-Cross et al, Robichaud et al, Hodges et al, …. CH4: Frankenberg et al, Nikitin et al, Lyulin et al, Wang et al, … Analysis of CH4 lab measurements by including LM to be done Lab recordings of 2 mm CO2 band and analysis with LM needed → Need for a very careful and critical intercomparison of Line-Mixing CO2: Tran et al, Predoi-Cross et al, Benner et al O2: Tran et al, Filippov et al → Need for a very careful and critical intercomparison of CIA O2: Tran et al, van der Zande et al → Need to study SD and Dicke effects:Theoretical work need, influence on atmospheric transmissions to be done

  19. Future HITRAN issues • Updates Include results of intercomparison and new measurements for isolated line parameters. • New features: • Include line shift T dependence (some results available) • Include self broadening T dependence for O2 (some results available) • - Include broadening by H2O and T dep (some results available for CO2 lines, no negligible effect in remote sensing) • - Include LM: must be done “on the side” since different structure. Store relaxation files and related spectroscopic data. Eventually provide software (eg: Lamouroux et al, Tran et al) • NB: needs to kind of standardization • -Speed dependence and Dicke effects: What is to be stored ? Not obvious, thinking necessary. Theoretical work starting at LISA

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