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J. Moersch (NASA Ames / NRC), K. Horton, P. Lucey (Univ. Hawaii), T. Roush (NASA Ames), S. Ruff (Ariz. St. Univ.), M. Smith (NASA GSFC)
Current plans for future Mars missions include small lander- and rover-borne thermal infrared spectrometers for use in exploring the surface. While the utility of infrared spectrometers in determining the composition of geologic surfaces from airborne and spaceborne platforms has been amply demonstrated, little experience exists in using functionally similar instruments on the ground in the context of planetary science. What work has been done on this problem has mostly utilized field spectrometers that look down on geologic surfaces, not horizontally, as the spectrometers on the Mars Surveyor '01 lander and '03 and '05 rovers often will.
There are important differences between downward-looking and horizontal-looking thermal emission spectra related to the very different radiative environment seen by targets with non-horizontal orientations. These effects include: the reflection of upward-welling radiance from the ground as a function of the orientation of target rock surfaces; spectral effects of temperature differences between high thermal inertia rocks and low themal inertia fines in the soil; spectral effects of emission and reflection between nearby rocks on the surface. When individual spectra of adjacent locations are combined to produce hyperspectral image cubes (one of the intended modes of operation for the planned Mars instruments), additional peculiarities associated with large depths of field in the scene (compared to down-viewing data acquired from orbiters or aircraft) must be taken into account during analysis.
Using a combination of controlled experiments in the lab, field spectroscopy in natural geologic settings, and analysis tools created or modified for this project, we are currently characterizing and quantifying each of these effects. The experience and understanding we hope to gain will allow us to develop observational strategies for use in the Mars experiments that will return the true emissivity spectra of targets and extract the most useful information from hyperspectral cubes.
The author(s) of this abstract have provided an email address for comments about the abstract: jmoersch@mail.arc.nasa.gov