Physical properties of the Martian surface from spectrophotometric observations

Abstract

ABSTRACT The reflection of visible and near-infrared light from Mars can vary significantly depending on the directional scattering characteristics of surface materials. Observations acquired under a range of illumination and viewing angles can be input to radiative transfer models to constrain the albedo, surface roughness, grain size, and/or porosity of these materials. This chapter reviews multiangular measurements of Mars obtained by Earth-based telescopes (including the Hubble Space Telescope), orbiters (Mariner, Viking, Mars Express), landers (Viking, Mars Pathfinder), and rovers (Mars Exploration Rovers), and how the photometric analyses of these datasets have been used to understand the surface properties of local and regional geologic units and terrain types. Although acquisition of data covering sufficient incidence, emission, or phase angles to fully constrain all parameters within photometric models is challenging, a common theme among these studies is the dominantly backscattering nature of the Martian surface, the magnitude of which is often related to the presence of high-albedo aeolian dust. The local and regional photometric variability observed in these data encourages further refinement of radiative transfer methods and atmospheric correction algorithms to provide additional tools with which to categorize and map distinct photometric units on Mars, particularly to provide support for ongoing and upcoming orbital and landed missions.