Properties of dust in the Mars atmosphere: a revised analysis of Phobos/KRFM data

During the 1989 Phobos 2 mission, photometric observations of the equatorial region of Mars were made in eight spectral bands in the range from 315 to 550 nm by the KRFM spectrometer. The first analysis of these data which aimed at extracting the optical properties of the atmospheric dust (Moroz et al., 1993) used an approximate approach for the radiative transfer, underestimating the effect of multiple scattering. The present analysis of the same data corrects for this limitation with the use of a doubling/adding method. The new analysis yields comparable values for the optical depth in the range 0.1–0.15. However, the imaginary part of the refraction index of the atmospheric particles almost doubles: mi = 0.030±0.005 for 315 nm and mi = 0.012±0.003 for 550 nm, compared with 0.015 and 0.005 before, while it continues to decrease as a function of wavelength.