ABSORPTION AND SCATTERING PROPERTIES OF THE MARTIAN DUST IN THE SOLARWAVELENGTHS

A new wavelength-dependent model of the single-scattering properties o f the Martian dust is presented. The model encompasses the solar wavel engths (0.3 to 4.3 mu m at 0.02 mu m resolution) and does not assume a particular mineralogical composition of the particles. We use the par ticle size distribution, shape, and single-scattering properties at Vi king Lander wavelengths presented by Pollack et al. [1995]. We expand the wavelength range of the aerosol model by assuming that the atmosph eric dust complex index of refraction is the same as that of dust part icles in the bright surface geologic units. The new wavelength-depende nt model is compared to observations taken by the Viking Orbiter infra red Thermal Mapper solar channel instrument during two dust storms. Th e model accurately matches afternoon observations and some morning obs ervations, Some of the early morning observations are much brighter th an the model results. The increased reflectance can be ascribed to the formation of a water ice shell around the dust particles, thus creati ng the water ice clouds which Colburn et;al. [1989], among others, hav e predicted.