MARTIAN AEROSOLS - NEAR-INFRARED SPECTRAL PROPERTIES AND EFFECTS ON THE OBSERVATION OF THE SURFACE

Imaging spectroscopic measurements of Mars acquired by the ISM instrument on Phobos-2 are used to investigate the NIR spectral properties of aerosols and the effects of atmospheric scattering on inferred mineralogy of the surface. Estimates of aerosols spectra between 0.77 and 2.6 mu m are derived above Tharsis and Ophir Planum. The spectral continua are consistent with the particle size distribution derived using data from the solar occultation experiment on-board the spacecraft (effective radius approximate to 1.2 mu m, with an effective variance approximate to 0.2). The aerosols spectra contain water-ice absorption features and possibly absorptions due to clay and/or sulfates. For these particular observations, aerosol opacity is apparently uncorrelated with surface altimetry, suggesting a spatially uniform column density. The largest effect of the aerosols on surface spectra is in dark regions, where the continuum spectral slope becomes more negative and the 1-mu m absorption due to Fe in pyroxene is shifted toward longer wavelengths. The effects of aerosols on spectra of bright regions are insufficiently large to change mineralogic interpretations based on ISM data, i.e., that bright regions in Tharsis are dominated spectrally by hematite, but that additional ferric minerals are probably present in other areas including Arabia. (C) 1994 Academic Press, Inc.