Computer Science – Sound
Scientific paper
Mar 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995jgr...100.5525c&link_type=abstract
Journal of Geophysical Research (ISSN 0148-0227), Vol. 100, no. E3, p. 5525-5539
Computer Science
Sound
43
Altitude, Atmospheric Models, Dust, Mars Atmosphere, Particle Density (Concentration), Particle Size Distribution, Data Reduction, Infrared Spectroscopy, Opacity, Phobos, Spatial Distribution
Scientific paper
Four experiments flown on board Phobus 2 provided information on the characteristics of the dust particles suspended in the Martian atmosphere: Auguste (Uv-visible-IR spectrometer working in solar occultation geometry), ISM (IR spectrometer measuring the light of the Sun reflected by the planet), Termoskan (scanning radiometer mapping the planetary thermal radiation), KRFM (UV-visible multiphotometer providing limb-to-limb profiles). These experiments, which sounded equatorial regions (20 deg S-20 deg N) near the northern spring equinox LS = 0-20 deg), are shown to yield a reasonably consistent picture of the dust distribution over the whole altitude range from the ground level, or just above, outside the boundary layer, up to approximately equals 25 km. The vertical profiles of particle volume mixing ratio and effective (projected area-weighted) radius deduced from Auguste measurements, performed in the 15-25 km altitude range, are extrapolated down to the ground by using a simple, physical parameterization of the altitude dependence of dust mixing ratio and radius. The vertically averaged effective radius and optical depth of dust particles, as well as vertical profiles of related quantities, are obtained. Optical depth at 1.9-micrometers wavelength is found to be 0.2 on average, with a typical variation of +/- 0.1 with time and space. The particle number density near the surface, as derived from extrapolation of solar occulation profiles, is in the range 1-3/cu cm, in good agreement with Termoskan results (1-2/cu cm). The scale height of the dust volume mixing ratio just above the surface is approximately equals 8-9 km on average, that is, of the same order as the background atmospheric scale height. The vertically averaged effective radius of dust particles is found to lie in the range 1.7 +/- 0.2 micrometers, possibly approximately equals 2 micrometers in the case of a large effective variance of 0.4. The most likely ISM value is 1.2 micrometers with a rather large uncertainty of +/- 0.4 micrometers, mainly due to the fact that the spectral dependence of the Minnaert coefficient is not very well known. Because ISM data used in the present work were obtained on the Tharsis plateau, at a mean altitude of approximately equals 7 km, the ISM radius must be compared to the Auguste vertically averaged radius for z greater than 7 km, that is, approximately equals 1.5 +/- 0.2 micrometers. Auguste and ISM radii are therefore consistent at the 1-sigma level. Three typical vertical profiles of the dust particle radius and number density, obtained by averaging all solar occulation profiles, including their extrapolated parts below approximately equals 15 km, are proposed as reference models, for three selected values of the effective variance of the particle size distribution (0.10, 0.25, and 0.40).
Chassefiere Eric
Drossart Pierre
Korablev Oleg
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