Spectrophotometric properties of materials observed by Pancam on the Mars Exploration Rovers: 1. Spirit

Abstract

[1] 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 estimates of local facet orientations in the sky models. Single-term and two-term 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 dust and other coatings, consistent with the results from the Viking Lander and Imager for Mars Pathfinder cameras. Darker ''Gray'' rock surfaces (inferred to be relatively less dust covered) display more narrow, forward scattering behaviors, consistent with particles exhibiting little internal scattering. 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 (q) 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.

Gale crater and impact processes – Curiosity’s first 364 Sols on Mars

“…Interestingly, a recent laboratory study (Souchon et al, 2011) has shown that natural granular surface samples comprising fresh glass or monocrystals in a high proportion are extremely forward-scattering with narrow scattering lobes. A similar photometric behavior has been previously found for a few ''gray rock'' samples using Pancam in situ data (Johnson et al, 2006), as well as for very glassy lunar regolith simulants (Johnson et al, 2008).…”

Derivation of martian surface slope characteristics from directional thermal infrared radiometry

“…A number of studies have investigated the photometric roughness of surfaces within the Viking, Pathfinder, and Mars Exploration Rover landing sites (Arvidson et al, 1989;Guinness et al, 1997;Johnson et al, 1999Johnson et al, , 2006aJohnson et al, , 2006b. These studies have shown the martian soils and dusty surfaces have θ -bar values between 4 • and 27 • .…”

Martian phase function: Modeling the visible to near-infrared surface photometric function using HST-WFPC2 data

“…More recent photometric studies of the surface materials of Mars using telescopic data (e.g., de Vaucouleurs, 1968;O'Leary and Rea, 1968;Binder and Jones, 1972;Thorpe, 1982;de Grenier and Pinet, 1995;Vdovichenko et al, 1997;Bell et al, 1999;Erard, 2000) and spacecraft data (e.g., Guinness, 1981;Arvidson et al, 1989;Johnson et al, 1999Johnson et al, , 2006 have yielded information regarding the photometric properties of the martian surface. For example, O'Leary and Rea (1968) reported a strong opposition surge, which varied inversely with albedo and moderate limb darkening.…”