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Spectroscopy for the Atmospheric Chemistry Experiment (ACE)

Spectroscopy for the Atmospheric Chemistry Experiment (ACE). Chris Boone, Kaley Walker, and Peter Bernath HITRAN Meeting June, 2010. Atmospheric Chemistry Experiment. Satellite mission for remote sensing of the Earth’s atmosphere, with a primary focus on Arctic ozone

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Spectroscopy for the Atmospheric Chemistry Experiment (ACE)

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  1. Spectroscopy for the Atmospheric Chemistry Experiment (ACE) Chris Boone, Kaley Walker, and Peter Bernath HITRAN Meeting June, 2010

  2. Atmospheric Chemistry Experiment • Satellite mission for remote sensing of the Earth’s atmosphere, with a primary focus on Arctic ozone • Developed by the Canadian Space Agency • Launched August 2003, science operations began February 2004 • Operating well, no major problems yet. • Primary instrument ACE-FTS: 0.02 cm-1 resolution, 750-4400 cm-1, ~300:1 SNR.

  3. Line mixing (Voigt) • Rosenkranz first order line mixing (Voigt) • gV,LM is the Voigt function with line mixing, W(z) is the complex probability function, and Y is the line mixing parameter. In the absence of line mixing (Y = 0), only the K(x,y) term contributes to the line shape.

  4. Analytical expressions derived for L(x,y) using the Humlicek algorithm. A paper describing these expressions is about to be submitted to JQSRT.

  5. Line mixing (speed-dependent) • Some methane lines feature both line mixing and speed dependence. • Simple empirical extension of the first order Rosenkranz approximation for line mixing • Assume coupling coefficient Y has no speed dependence

  6. Line mixing plus speed-dependence (continued)

  7. For these lines, speed-dependence appears to be a stronger effect than line mixing. It is the opposite for other CH4 lines in the vicinity.

  8. With CH4 line mixing and speed-dependent Voigt parameters in place (derived from ACE-FTS spectra), we can now retrieve acetone from the ACE-FTS.

  9. Line shape benefits • Analytical, simple, and efficient. The most complicated is line mixing + SDV: requires real parts + imaginary parts of 2 Voigt-type functions. • Well-suited to line-by-line calculations. One extra parameter per line for speed-dependence (2) and one extra parameter per line for line mixing (Y). Extra parameters for temperature dependences? • Not aiming for the truest physical model or the most accurate calculation approach. Aiming for “accurate enough:” a significant improvement over the Voigt function, improved fitting residuals, improved VMRs • Geared toward atmospheric VMR retrievals.

  10. H2O • Obtained a set of 27 lab spectra from Manfred Birk at DLR (23 air-broadening), covering the range 1250-1750 cm-1. • Currently exclude 4 with poorer SNR but will include them in final analysis. • Awaiting a few higher-P measurements. • Analyzing spectra with a speed-dependent Voigt line shape, generating spectroscopic parameters.

  11. Self-broadened spectra

  12. Temperature-dependent Pressure-shift

  13. Difficult Doublets • Pairs of closely spaced H2O lines (same isotopologue, nearly the same E’’, etc.) can often be difficult to fit • Something else going on. Including line mixing improves results, but far from perfect.

  14. H2O in ACE-FTS • Speed-dependent Voigt parameters derived from gas cell measurements improve fitting residuals in ACE-FTS, but problems remain. • Deficiencies in the forward model for H2O in the troposphere. • Forward model employs a 1-km altitude grid. H2O VMR can double over the span of 1 km in the troposphere. • Changing the forward model.

  15. Missing HNO3 H15NO3 HNO3 HNO3 HNO3 Residual spectra full of missing HNO3. O2 continuum N2 continuum

  16. CHF3 • Fluorine budget in the stratosphere is an important measure of anthropogenic activity (unlike Chlorine, few natural sources). • No spectroscopic data available for the molecule. Found a set of lab measurements with various problems. • Used low-resolution measurements from PNNL for absolute calibration, and then Geoff Toon generated a set of pseudo-lines for the molecule.

  17. No CH3OH in this region in HITRAN ACE-FTS window for CH3OH retrievals

  18. Missing CH3Cl Red curve = CH3Cl calculated with HITRAN 2008 CH3Cl excluded from calculation Missing a lot of CH3Cl lines in HITRAN 2008. Looking at the program for this meeting, is this now fixed?

  19. Wish list: CH3OOH K.H. Becker et al, “Tunable diode laser measurements of CH3OOH cross-sections near 1320 cm-1”, Geophys Res Lett, 16, 1367-1370 (1989).

  20. 17O12C16O Is the isotopic differentiation really this large, or are there problems with the intensities of the isotopologue 4 lines?

  21. 18O13C16O

  22. Conclusions • Refining ACE-FTS line shape calculations to improve residuals (and thereby retrievals). • Continuing to search for weak absorbers. • Would especially like spectroscopy for the 3-micron region. • Generating spectroscopic parameters for H2O and CH4 from lab spectra.

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