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Research:
Theoretical
line shape calculations to determine the half-width and line shift for methane
transitions in the Earth's atmosphere in support of measurement campaigns on
NASA's Earth Observing System (EOS) satellites Aqua and Aura. The measurement platforms of these satellites contain the Atmospheric Infrared Sounder (AIRS) on Aqua,
and the Tropospheric Emission Spectrometer (TES) and the High Resolution
Dynamics Limb Sounder (HIRDLS) on AURA. Both instruments will measure both H2O
and CH4. CAitie's work was for the systems CH4-N2
and CH4-O2 in order to determine air-broadening and
shifting of methane.
The spectral region
covered by the instruments is 3.2 to 17.76 µm
(AIRS, TES, HIRDLS), here the focus was on the range 1000 to 3200 cm-1
for methane which contains 23 951 transitions. For methane the dominant bands are the 00011001 < 00000000 (10-17), 00000111 < 00000000 (10-18), 01100001 < 00000000 (10-19), and 01100112 < 00000000 (10-19) bands, where
the intensity units in parenthesis are in HITRAN units. Calculations were made for all strong and intermediate intensity transitions. Initial calculations to adjust the intermolecular potential (atom-atom contribution) were done after which production runs were made to generate a database of half-widths and line shifts for v3 band of methane with air as the bath gas. These data were provided to the Jet Propulsion Laboratory for use in retrievals from the instruments on AQUA and AURA.
Caitlin has also made CRB calculations for CO2-broadening of water vapor
in both the rotational and v2 fundamental regions. Such pressure
broadening coefficients are needed throughout the infrared for remote sensing of Mars
and Venus. In both these planets, the most abundant species is carbon dioxide, but
the two atmospheres are at very different pressures and temperatures. For Mars, the
temperatures range from 150 to 300 K, and the pressures is only 10 mbars. For Venus,
temperatures range from 200 to 750 K, but the pressure is very high (up to 90 bar at the
surface). The present study, in collaboration with Dr. Linda Brown of the Jet Propulsion
Laboratory in Pasedena, CA, provides the first comprehensive step towards satisfying
these needs; presently there are numerous observations from ground-based and orbiting
observatories (such as Venus Express with the Venus IR Thermal Imaging Spectrometer
and the Mars Reconnaissance Orbiter Mission with the Mars Climate Sounder) being
interpreted to understand the effects of water vapor on both of these planetary atmospheres.
The vibrational dependences of the broadening coefficients, which must be understood
because the various instruments utilize water transitions at microwave, infrared and visible
wavelengths, was also considered in this study. Caitlin's work has provided a database of half-widths,
line shifts, and the temperature dependence of the line shift for ~1000 rotation band and ~300 v2
band transitions of water vapor. These data have been given to scientists at JPL and the European
Space Agency (ESA) who are working on profile retrievals on Mars and Venus.
For a short description of the CRB formalism click here
Robert R. Gamache, Bobby Antony, Danielle L. Niles, Sarah B. Wroblewski, Caitlin M. Humphrey, Tony Gabard , "Half-widths and Line Shifts for Transitions in the v3 Band of Methane in the 2726-3200 cm-1 Spectral Region for Atmospheric Applications," the 10th Biennial HITRAN Database Conference, Harvard-Smithsonian Center for Astrophysics, June 22-24, 2008
Robert R. Gamache, Bobby Antony, Danielle L. Niles, Sarah B. Wroblewski, Caitlin M. Humphrey, Tony Gabard, "Line Shape Parameters for v3 Transitions of 12CH4," the 19th International Conference on Spectral Line Shapes, Valladolid, Spain, June 15-20, 2008
Caitlin M. Humphrey, Robert R. Gamache, Bobby Antony, Danielle L. Niles, Sarah B. Wroblewski, Tony Gabard , "N2-, O2- and Air-broadened Half-widths and Line Shifts for Transitions in the v3 Band of Methane in the 2726-3200 cm-1 Spectral Region," the 11th Annual Student Research Symposium, The University of Massachusetts Lowell, April 29, 2008
Robert R. Gamache, Linda R. Brown, Caittlin M. Humphrey, "Line shape of H2O in CO2-rich atmospheres for remote sensing of Mars and Venus", UML Research: Creating the Future of the Commonwealth, Inauguration of Martin T. Meehan, April 2, 2008
L. Brown, B. Drouin, C. Miller, J. Pearson, G. Orton, R. Toth, C. Benner, M. Devi, T. Blake, T. Masiello, R. Sams, R. Butler, J. Champion, P. Chelin, A. Dehayem, I. Kleiner, J.Orphal, L. Sagui, R. Gamache, C. Humphrey, W. Liu, A. Predoi-Cross, A. Unnikrishnan, H. Muller, A. Nikitin, C. Rinsland, M. Smith, "Laboratory Spectroscopy of Planetary Molecules," Workshop on Planetary Atmospheres, Greenbelt, MD, Nov. 6-7, 2007
C. M. Humphrey, R. R. Gamache, L. R. Brown, "Line Shape of H2O Broadened by CO2 for Applications to the Atmospheres of Mars and Venus," The Twentieth Colloquium on High-Resolution Molecular Spectroscopy, Dijon, France, September 3-7, 2007
L. Brown, B. Drouin, C. Miller, J. Pearson, G. Orton, R. Toth, C. Benner, M. Devi, T. Blake, T. Masiello, R. Sams, R. Butler, J. Champion, P. Chelin, A. Dehayem, I. Kleiner, J.Orphal, L. Sagui, R. Gamache, C. Humphrey, W. Liu, A. Predoi-Cross, A. Unnikrishnan, H. Muller, A. Nikitin, C. Rinsland, M. Smith, "Laboratory Spectroscopy of Planetary Molecules," European Planetary Science Congress 2007, Potsdam, Germany, 20 - 24 August 2007
Linda R. Brown, Caitlin M. Humphrey, Robert R. Gamache, "CO2-Broadened H2O in the Pure Rotation and v2 Fundamental Regions," paper RD01, 62nd International Symposium on Molecular Spectroscopy, June 18-22, 2007, The Ohio State University, Columbus, OH
Publications
Bobby K. Antony, Danielle L. Niles, Sarah B. Wroblewski, Caitlin M. Humphrey, Tony Gabard and Robert R. Gamache , "N2-, O2- and air-broadened half-widths and line shifts for transitions in the v3 band of methane in the 2726-3200 cm-1 spectral region," J. Mol. Spectrosc., 251, 268-281, 2008. PDF of article or JMS archive
L. R. Brown, C. M. Humphrey and R. R. Gamache, "CO2-broadened water in the pure rotation and v2 fundamental regions," J. Mol. Spectrosc. 246, 1-21, 2007. PDF of article or JMS archive