Surface scattering properties at the Opportunity Mars rover's traverse region measured by CRISM

The Opportunity Rover has been exploring Meridiani Planum; concurrently, the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) has been collecting orbital hyperspectral data. Herein, both surface and orbital data are used to characterize surface properties at the Opportunity traverse region around Victoria crater. Results agree with previous studies, which used Opportunity's Panoramic Camera (Pancam) data, and the current study extends estimates of the Hapke single-particle-scattering albedo and asymmetry parameter to a greater spatial and spectral range. Results are useful for determining boundaries between surface units that otherwise look relatively uniform spectrally. This work also provides photometric functions essential for converting spectra to a single viewing geometry to yield more accurate spectral comparisons. Retrieved single-scattering albedos range from 0.42 to 0.57 (0.5663-2.2715 micrometers) and retrieved asymmetry parameters range from -0.27 to -0.17 (moderately backscattering). Surfaces become more backscattering with increasing wavelength above 1 mu m. The majority of Victoria crater's ejecta apron is more backscattering than surrounding regions, indicating a change in physical properties. Images taken when the rover traversed this unit show a cover of basaltic soil with superposed millimeter-scale hematitic spherules. Wind streaks on the apron appear smooth (low backscatter) because basaltic sands have partly buried spherules, lessening millimeter-scale roughness. CRISM-derived scattering parameters also show that bedrock-dominated surfaces are less backscattering than soil-covered surfaces, largely due to lower areal abundance of spherules. The ability to analyze surface unit spherule cover is important because it relates to a wetter period during which spherules formed in Meridiani.