Nature and distribution of surficial deposits in Chryse Planitia and vicinity, Mars.

Color images of bright red dust deposits at the Mutch Memorial Station were acquired at variable incidence angles during sol 611 (subsolar longitude ≡70°, northern spring season). After removing effects due to atmospheric scattering and absorption, the data were used to estimate the independent variables in the Hapke (1986) photometric function. In blue, green, and red coordinates the vector representing the space radiance factor of the landing site extracted from Viking orbiter images acquired on sol 609 is separated by a Euclidean distance of only 0.022 units and an angle of only 1.5° from the vector estimated from the station data for the orbiter lighting and viewing geometries. This result implies that light reflected from dust exposures dominates the orbiter signal; multiplicative and additive atmospheric terms cancel one another and surface roughness is a second-order effect in the orbiter data.