The color of Mars: Spectrophotometric measurements at the Pathfinder landing site

We calculate the color of the Martian sky and surface directly using the ab solute calibration of the Mars Pathfinder (MPF) lander camera, which was ob served to be stable during the mission. The measured colors of the Martian sky and surface at the Pathfinder site are identical to the Viking sites, i .e., a predominantly yellowish brown color with only subtle variations. The se colors are distributed continuously and fall into five overlapping group s with distinct average colors and unique spatial characteristics: shadowed soil, soil, soil/rock mixtures, rock, and sky. We report that the primary difference between the sky color and the color of the rocks is due to a dif ference in brightness. Measurements of the sky color show that the sky redd ens away from the Sun and toward the horizon and that the sky color varies with time of day and is reddest at local noon. We present a true color pict ure of the Martian surface and color enhancement techniques that increase i mage saturation, maximize color discriminability while preserving hue, and eliminate brightness variations while preserving the chromaticity of the sc ene. Although Mars has long been called the "red" planet, quantitative meas urements of the surface color from telescopic and surface observations indi cate a light to moderate yellowish brown color. The Pathfinder camera measu rements presented here support the claim that the red planet is not red but indeed yellowish brown.