title: Planetary surface photometry and imaging: progress and perspectives.
abstract: Spacecraft have visited and returned many thousands of images and spectra of all of the planets, many of their moons, several asteroids, and a few comet nuclei during the golden age of planetary exploration. The signal in each pixel of each image or spectral channel is a measurement of the radiance of scattered sunlight into a specific direction. The information on the structure and composition of the surface that is contained in variation of the radiance with scattering geometry and wavelength, including polarization state, has only just begun to be exploited and is the topic of this review. The uppermost surfaces of these bodies are mainly composed of particles that are continuously generated by impacts of micrometeoroids and larger impactors. Models of light scattering by distributions of sizes and irregular shapes of particles and by closely packed particles within a surface are challenging. These are active topics of research where considerable progress has recently been made. We focus on the surfaces of bodies lacking atmospheres.These surfaces are diverse and their morphologies give evidence of their evolution by impacts and resurfacing by a variety of processes including down slope movement and electrostatic transport of particles, gravitational accumulation of debris, volatile outgassing and migration, and magnetospheric interactions. Sampling of scattering geometries and spatial resolution is constrained by spacecraft trajectories. However, the large number of archived images and spectra demand more quantitative interpretation. The scattering geometry dependence of the radiance is underutilized and promises constraints on the compositions and structure of the surface for materials that lack diagnostic wavelength dependence. The general problem is considered in terms of the lunar regolith for which samples have been returned to Earth.
authors.affiliation: Mail Stop 183-401, Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109, USA.
authors.forename: Jay D
authors.initials: JD
authors.lastname: Goguen
mesh_terms: D007090:Image Interpretation, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D016081:Moon; D010781:Photography / Q000295:instrumentation / Q000379:methods* / Q000639:trends*; D010783:Photometry / Q000295:instrumentation / Q000379:methods* / Q000639:trends*; D061351:Telescopes / Q000639:trends*