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Klassen, David R., Infrared Imaging Spectroscopy of Martian Volatiles, Ph.D.,
Department of Physics and Astronomy, August 1997.
Infrared spectroscopy has been used since the late 1940's to try to determine the natures of the surface and atmosphere of Mars. Previous technologies have been limited to integrated disk, or single spot spectroscopy which allow only disk averaged properties to be analyzed or large scale spot-to-spot comparisons to be made. Newer, large-format infrared array detectors and circular variable filters allow for more comprehensive spot-to-spot comparisons at moderate spectral resolutions (1-2% in this work).
Presented here are results from infrared imaging spectroscopy using images taken with the NSFCAM at the NASA Infrared Telescope Facility. Using the three techniques of extracted regional spectra, band depth mapping, and principal components analysis/linear mixture modeling (PCA/LMM), polar and atmospheric volatiles are compositionally identified and traced.
Modeling the 3.33µm absorption feature seen in some of the extracted regional
spectra, we calculate that to detect CO2 clouds they would have to have visible optical
depths greater than or equal to 1.0. Band depth mapping techniques of this spectral
region suggest that there are no detectable CO2 clouds. However, band depth maps in this
spectral region are shown to be useful in tracking the seasonal polar cap and band depth
maps at 2.25µm are a good indicator of H2O frosts due to the local maximum of their
spectra. PCA/LMM transforms the image cubes into a space of only two significant
principal components, the first being an albedo unit and the second being an ice/thermal
unit. Using spectral endmembers chosen from those regions with extreme PCA values, the
LMM is used to create fractional abundance maps of a centrally located high albedo
spectral unit, a centrally located low albedo spectral unit and a north polar region/volatile
spectral unit. The north polar region unit has high values along morning and evening
limbs indicating cold and cloudy conditions on Mars.
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