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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

Spectroscopy for the Atmospheric Chemistry Experiment (ACE)

Chris Boone, Kaley Walker, and Peter Bernath

HITRAN Meeting

June, 2010

atmospheric chemistry experiment
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.
line mixing voigt
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.
Analytical expressions derived for L(x,y) using the Humlicek algorithm. A paper describing these expressions is about to be submitted to JQSRT.
line mixing speed dependent
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
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.
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.
line shape benefits
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.
h 2 o
  • 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.
difficult doublets
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.
h 2 o 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.
missing hno 3
Missing HNO3





Residual spectra

full of missing


O2 continuum

N2 continuum

chf 3
  • 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.
No CH3OH in this region in HITRAN

ACE-FTS window for CH3OH retrievals

missing ch 3 cl
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?

wish list ch 3 ooh
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).

17 o 12 c 16 o

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

  • 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.