Mariner 9 ultraviolet spectrometer experiment: Photometry and topography of Mars

Abstract

Reflectance properties of Mars are measures in a 100-Å band centered at 3050 Å by the ultraviolet spectrometer. The instrument has an angular resolution which is equivalent to an area of 10 × 30 km on the surface of Mars. The transition from dusty conditions, which prevailed at the time of arrival of Mariner 9 on 14 November 1971, began on 1 January 1972, and relatively clear conditions existed after 23 January 1972. As the atmosphere became clearer, the scattering properties began to show a morning enhancement in both terminator and illuminated disk reflectance. A topographic map of Mars based on the scattering of ultraviolet light from the Mars atmosphere is shown. This map is based upon 3050-Å data obtained after the Mars atmosphere had cleared in the ultraviolet. Ultraviolet light which is Rayleigh-scattered by the Mars molecular atmosphere, with allowance for uniform turbidity, is proportional to surface pressure independent of atmospheric temperature structure. Comparison with Mariner 9 radio occultation measurements determines the fraction of total reflectance that is due to atmospheric scattering.