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T.Z. Martin (Jet Propulsion Laboratory)
The Mars Reconnaissance Orbiter CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) experiment will map Mars in the 0.4-4.0 \mum range, with spatial resolution ~200m for mapping and ~18m for focused study targets. Surface thermal emission beyond 2.5 \mum will be removed to measure water and carbonate absorption bands correctly. That region is dominated by a broad, spatially variable band of bound water, making derivation of temperature from observed spectra difficult. As absorptions may lie in exposed sloping terrain, thermal correction must include slope effects. The CRISM spatial resolution is too fine to use the best MGS MOLA map (1/128\circ, ~460m) for slope information. Photoclinometry is used to estimate slopes in CRISM blue images, where Martian albedo variations are subdued. Inferred slopes are combined with lower resolution MOLA data to obtain slope and azimuth input to a Martian thermal model. The resulting temperature is used to compute Planck radiance for subtraction from the observed spectrum. The algorithm incorporated into mainstream processing of the several terabit CRISM data set must be fast and require no hands-on analysis. The thermal model is a large look-up table indexed by thermal inertia, albedo, dust opacity, latitude, season, and local time. Such a table was used by M. Mellon for TES and THEMIS data processing. For a given CRISM observation season, local time, and latitude are essentially fixed, so the look-up table may be subsetted for speed. To develop and prove the PC system, we use THEMIS blue and IR data, with resolution ~100m. The technique is based on that of Beyer \textit{et al} in assessing MER landing site hazards. The thermal model with slope effects was developed by H. Kieffer for use with TES and THEMIS data.
This research was funded by the Mars Reconnaissance Orbiter project and carried out by the Jet Propulsion Laboratory, California Institute of Technology.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.