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E. Keim (The Aerospace Corporation), L. Kirkland (Lunar and Planetary Insitute), K. Herr, P. Adams, J. Hackwell (The Aerospace Corporation)
Hyperspectral data recorded of indurated, weathered carbonates by the airborne imaging spectrometer SEBASS show that some massive carbonates exhibit dramatically reduced spectral contrast for the strong carbonate bands at 6.5 and 11.25 microns. If massive carbonates are present on Mars, this type of reduced spectral contrast could explain why they have not been detected using thermal infrared data sets, including the Global Surveyor Thermal Emission Spectrometer (TES). It could also cause similarly rough carbonates to be missed by the planned 2001 nine-band radiometer THEMIS, and could affect measurements by a landed spectrometer. On the other hand, SEBASS data demonstrate that these deposits can be detected by spectra recorded with sufficient signal-to-noise ratio (SNR).
The observed reduction in band contrast is significant, and we conclude it is cause by surface roughness effects . The nature of carbonate and other formations on Mars is uncertain, but a rough surface is certainly a possibility that must be taken into account. These results should be considered in planning for future instruments and when utilizing current data sets to set detection limits.
Most spectral studies to determine detection limits rely predominantly on laboratory measurements of well-crystalline, pure end-members, with desirable instrument parameters and detection limits based on those results. However, our results show the importance of extending thermal infrared spectral studies to the field, and the relevance to spectral studies of Mars.
This effect was found by drawing on expertise and unique technology most commonly used for the Department of Defense (DoD). The significance of the lessons learned illustrate the importance both of extending spectral studies to the field, and of drawing on non-traditional groups in order to best define what is needed to detect and identify interesting materials on Mars using infrared spectroscopy.
 Kirkland L. et al. (2000) LPSC abs.1876 and LPSC abs.1915.
This study was funded by The Aerospace Corporation and the Lunar and Planetary Institute.
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