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K.J. Snook, J.L. Bandfield (NASA Ames Research Center), F. Forget (Lab. de Meteorologie Dynamique, CNRS, Paris), C.P. McKay (NASA Ames Research Center)
Infrared optical constants of dust suspended in the Martian atmosphere are derived from MGS Thermal Emission Spectrometer (TES) data. In this research, theoretical infrared emission spectra of the emergent intensity from the Martian dust clouds were generated using a 2-stream source-function radiative transfer code. The code computed the radiation field in a plane parallel, vertically homogeneous, multiple scattering atmosphere. The calculated intensity spectra were compared with the TES spectra and refined in an iterative fashion to retrieve optical properties and opacity of the dust, surface temperatures, and particle size distributions. The dust particles are assumed to be spherical and the atmospheric temperature profile was obtained from the 15 micron CO2 fundamental [1]. Optical constants have been derived previously using Mariner 9 IRIS data [2] however, the measurements were not sufficient to constrain particle size distributions. The TES data provide multiple emission angle measurements of the same location on the surface obtained within a time span of several minutes. These measurements, obtained from as many as 49 separate emission angles, provide a much more robust dataset with the ability of constraining additional variables, including particle size distributions and surface emissivity. Initial results from targeted TES measurements will be presented and compared with the results of [1] and previous atmospheric dust studies [e.g. 3-5]. The derived optical constants provide an improvement in the accuracy of one-dimensional heating flux applications, verification of existing opacity and surface temperature determination algorithms, and an improved ability to determine the composition of the atmospheric dust. 1) Conrath, B.J. et al., J. Geophys. Res., 105, 2000. 2) Snook, K. J., Ph.D. thesis, 1999. 3) Pollack, J. et al., J Geophys. Res., 84, 1979. 4) Clancy, R. et al., J. Geophys. Res., 100, 1995. 5) Forget, F., Geophys. Res. Lett., 1997.