Thermal and albedo mapping of Mars during the Viking primary mission

Abstract

Measurements of Martian emission and reflection reveal wide variations of surface properties and indicate the presence of a larger atmospheric contribution to the observed radiances than was anticipated. Temperatures observed during the Viking primary mission range from 130 to 290 K. Surface thermal inertias from 1.6 to 11×10−3 cal cm−2 s−1/2 K−1 are mapped, and they correlate with surficial geologic units. An equatorial map of bolometric albedo generally correlates with prior narrowband observations. These albedos range from 0.09 to 0.43; some regional brightenings are atmospheric in origin. The photometric behavior implies quasi-Lambertian surface reflectance plus a strongly forward-scattering atmosphere. Brightness temperatures at large emission angles are strongly influenced by atmospheric infrared opacity and by the presence of rocks on the surface. The correlation and grouping of albedo and thermal inertia indicate that there are two major components of Martian surface material, with bright regions having a fine particulate covering. Winter polar temperatures show spatial and temporal variations, suggesting variation of atmospheric composition; a strong atmospheric temperature inversion exists above the south polar cap during winter. Surface CO2 condensation may also occur locally near the equator before dawn. Rising temperatures before dawn in a region near Arsia Mons imply the presence of daily local water ice fogs.