Radiative transfer modeling of thermal infrared emissivity spectra: Applications to Martian regolith observations

Details Radiative transfer modeling of thermal infrared emissivity spectra: Applications to Martian regolith observations Radiative transfer modeling of thermal infrared emissivity spectra: Applications to Martian regolith observations

Nov 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005phdt.........6p&link_type=abstract

Ph.D dissertation, 2005. Section 0107, Part 0606 131 pages; United States -- Louisiana: Louisiana State University and Agricult

Physics

Radiative Transfer, Thermal Infrared Emissivity Spectra, Martian, Regolith, Emissivity

Scientific paper

Proper analysis of satellite and rover thermal infrared emissivity spectra taken at nadir and off-nadir angles of emergence from planetary regolith surfaces requires use of theoretical models for interpretation of constituent grain physical properties. However, such models have remained in stasis in recent years, with nearly a ten-year gap in significant advances. To date, no radiative transfer model (semiempirical, exact, or hybrid solution) has been able to adequately predict the nadir emissivity behavior of simple mineral assemblages. Few measurements have been attempted in the laboratory or field regarding directional emissivity effects of planetary regoliths; such measurements are necessary for modeling and interpreting directional emissivity offsets that are clearly present in the Mars Global Surveyor Thermal Emission Spectrometer (MGS-TES) dataset. This investigation focuses on two major dust microphysical properties: particle size and packing fraction. Results of a theoretical model are compared to laboratory-measured thermal infrared (wavenumber = 2000-200 cm -1 ) emissivities for micron-sized quartz particles. I show that Mie theory, a widely used but poor approximation to irregular grain shape, fails to produce the single scattering properties needed to arrive at the desired laboratory emissivity values; I also illustrate shortcomings of popular dense packing correction methods. Through numerical experiments, I provide evidence that, assuming RT methods work given sufficiently well quantified inputs, assumptions about the scatterer itself constitute the most crucial aspect of modeling nadir emissivity values. I present laboratory investigations used to obtain realistic and quantifiable input parameters to the theoretical model, i.e., particle size distribution and particle shape. Nadir and directional emissivity comparison datasets obtained in the laboratory and in the field at Mars terrestrial analog sites are presented to set the stage for modeling directional emissivity. Future directions (e.g., how to incorporate nonspherical particle shapes into the model) are briefly discussed.

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