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D. A. Glenar, W. C. Maguire, G. Bjoraker, M. Smith (NASA GSFC), D. Blaney (JPL)
The spectral shape of the strong 12C16O2, 2nu1+nu3 Fermi triad near 2 microns is sensitive to both atmospheric temperature and pressure. The former is due to the temperature dependence of rotational line intensities and the latter arises from the pressure dependence of the CO2-CO2 self broadening parameter. These properties make the CO2 band-shape a diagnostic of the low-atmosphere temperature-pressure relation. We have modeled line-by-line intensities in this band as a function of temperature and pressure using the HITRAN 2004 spectral data-base, and we present an algorithm whereby CRISM-resolution spectra can be used to retrieve the lower atmosphere (below ~25 km) temperature and lapse rate by fitting to reflectance models, with dust scattering taken into account.
This retrieval method was tested by comparing IRTF SpeX observations of the Mars' two micron CO2 band shape acquired on July 29 and Sept 20, 2003, with simultaneous TES daytime atmospheric temperature measurements (OCKS 21302 and 21947). Within the uncertainties, SpeX temperature retrievals merge with the low-altitude portion of the TES-derived, vertical temperature profiles. Likewise, surface pressures retrieved from the algorithm agree with values derived from MOLA topography and seasonal pressure corrections (Tillman et al., JGR, 1993), after allowing for the low spatial resolution of the ground-based measurements.
This work is being supported by the NASA Planetary Astronomy Program.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.