Investigating the Wavelength Dependence of the Single-Scattering Albedo of Martian Dust Aerosols with CRISM and MARCI Observations of the Very Dusty Atmosphere in 2007

Details Investigating the Wavelength Dependence of the Single-Scattering Albedo of Martian Dust Aerosols with CRISM and MARCI Observations of the Very Dusty Atmosphere in 2007 Investigating the Wavelength Dependence of the Single-Scattering Albedo of Martian Dust Aerosols with CRISM and MARCI Observations of the Very Dusty Atmosphere in 2007

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p31d..03w&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #P31D-03

Mathematics

Logic

0305 Aerosols And Particles (0345, 4801, 4906), 5405 Atmospheres (0343, 1060), 5464 Remote Sensing, 6225 Mars

Scientific paper

The very dusty Martian atmosphere during the 2007 perihelion season offers an excellent opportunity to revisit the microphysical nature of dust aerosols. Through the use of MARCI wide-angle images and CRISM "emission phase function" sequences, one can robustly derive the mean single scattering albedo from the ultraviolet through the near-infrared (~4 micrometers). The detailed behavior of this particular dust property over the relatively wide wavelength coverage afforded by MRO has application to the detailed energy balance of the Martian atmosphere (i.e., solar energy input), as well as to the composition of the dust itself (e.g., iron oxidation state) and subsequent geological implications. Our general analysis approach combines CRISM and MARCI observations during the decay phase of the dust activity (to attempt to minimize column variability) with a DISORT-based radiative transfer retrieval scheme (Wolff et al., 2006; Wolff et al., 2007). We derive the optical depth and the single scattering albedo while fixing the other key parameters in the following ways: 1) The surface properties are specified using a generic "Hapke function" approach that includes the roughness parameter, thetabar. Constraints on the individual "Hapke" parameters are taken from both "ground-truth" analyses of MER observations (Seelos, 2005; Johnson et al., 2006a,b) and analyses of pre-perihelion observations of the same or similar regions. 2) The dust single scattering phase functions is computed using the Tomasko et al. (1999) phase function at 965 nm and scaling it to the desired wavelength using a ratio of non-spherical particle phase functions (e.g., oblate disks) calcuated with the T-Matrix method (Mishchenko and collaborators, http://www.giss.nasa.gov/~crmim/). Our methodology is iterative in the sense that once we derive a single scattering albedo spectrum, we adjust the refractive indices to reproduce the albedo values and then recompute the T-matrix phase functions. In our presentation, we will provide the details of the derived mean single scattering albedo and the associated estimates of precision and accuracy. We will also discuss some potential implications for dust composition and atmospheric energy balance.

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