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D. A. Glenar, G. Bjoraker, M. Smith, J. Pearl (NASA GSFC), D. Blaney (JPL), G. Hansen (Univ. of Washington), D. Klassen (Rowan Univ.)
We summarize recent progress derived from the analysis of near infrared long-slit, drift scan spectra of Mars acquired during the 2001 opposition, using the SpeX grating spectrometer at the NASA IRTF. Under stable observing conditions the drift-scan technique produces high spectral resolution, spectral image cubes (x-y-wavelength) with full hemispherical image content. This approach has previously been used in a study of the diurnal properties of aphelion season clouds (Glenar et al., Icarus, v161, 2003).
Temperatures: At SpeX resolving power (R= 1200-1800), the spectral shape of the 2 micron gaseous CO2 absorption band is a sensitive function of temperature. This band thus serves as a low altitude atmospheric thermometer, since the reflectance (R) contribution function dR/dTj (j=layer) within this band mimics the pressure-height profile P(j). Least-squares fits to SpeX measurements using a set of reference opacity spectra allow measurements of temperature versus position in regions of low dust opacity.
Dust Optical Depth: Near-IR dust optical depth can be measured by the extent to which it suppresses the 2 micron CO2 band shape. We have been evolving an IDL-based dust optical depth mapping algorithm which incorporates multi-stream scattering model computations (DISORT), and newly available dust radiative transfer parameters at these wavelengths. However, we presently observe large (20-30 discrepancies between CO2 surface pressures predicted by forcing this model to agree with measurements, and those predicted from Viking lander data with position corrections from the MOLA data set. This latter approach is routinely used as a boundary value for temperature retrievals by the TES team.
CO2 Ice Parameters: Near-IR bidirectional reflectance spectra of the south polar CO2 ice cap has been modeled as a function of grain size and contamination by dust and water ice. These parameters are of direct importance to the cap thermal balance since they affect albedo and emissivity at all wavelengths. We have begun comparing synthetic spectra with the ’01 SpeX measurements in order to constrain these ice parameters, and results show grain size variations on large spatial scales. New data now being acquired during the ’03 Mars opposition will be better suited to this study, due to much improved southern latitude sub-Earth position (~ 20 degrees south).
This work is supported by the NASA Planetary Astronomy Program, under RTOP 693-344-32-52.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.