HR: 0800h
AN: P21A-0128    [Abstracts]
TI: Spectrophotometric Modeling of Geologic Materials at Gusev Crater, Mars
AU: * Johnson, J R
EM: jrjohnson@usgs.gov
AF: USGS, 2255 N Gemini Dr, Flagstaff, AZ 86001 United States
AB: Multispectral observations of rocks and soils were acquired under varying illumination and viewing geometries in visible/near-infrared wavelengths by the Panoramic Camera (Pancam) on the Spirit Mars Exploration Rover to provide constraints on the physical and mineralogical nature of geologic materials in Gusev Crater. Data sets were acquired at six sites located near the landing site, in the surrounding plains, and in the West Spur and Husband Hill regions of the Columbia Hills. From these ~600 images over 10,000 regions of interest were selected of rocks and soils over a wide range of phase angles (0-130°). Corrections for diffuse skylight incorporated sky models based on observations of atmospheric opacity throughout the mission. Disparity maps created from Pancam stereo images allowed inclusion of local facet orientation estimates in the sky models. Henyey-Greenstein phase functions derived from Hapke scattering models exhibit a dominantly broad backscattering trend for soils and "Red" rocks inferred to be covered with variable amounts of dusty coatings, consistent with the results from the Viking and Mars Pathfinder data. Darker "Gray" rock surfaces (inferred to be less dusty) display more narrow, forward scattering behaviors, consistent with particles exhibiting little internal scattering. Gray rocks usually exhibit the highest single scattering albedos at 430 nm and 600 nm (consistent with their less dusty nature). Gray and Red rocks are macroscopically rougher than most soil units, although a "dust-cleaning" event observed near the Paso Robles site caused an increase in soil surface roughness in addition to a substantial decrease in surface single scattering albedo. Gray rocks near the rim of Bonneville Crater exhibit the largest macroscopic roughness among all units, as well as the greatest backscattering among Gray rocks. Photometric properties of coated Red rocks vary in the West Spur region, possibly as a result of weathering differences related to elevation-dependent aeolian regimes. Future photometric imaging sequences will be acquired on the southern flank of the Husband Hill. These data will be analyzed for comparison to previous Pancam observations as well as data acquired in Gusev by orbiting cameras such as the Mars Express HRSC.
DE: 5410 Composition (1060, 3672)
DE: 5460 Physical properties of materials
DE: 5464 Remote sensing
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: Fall Meeting 2005