Doctor of Philosophy (PhD)
Physics and Astronomy
Satellite and rover remote sensing of planetary regolith surfaces, in the form of thermal infrared emissivity spectra taken at nadir and off-nadir angles of emergence from the surface, 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 effects that are clearly present in the Mars Global Surveyor Thermal Emission Spectrometer (MGS-TES) and Mars Exploration Rover mini-TES datasets. The research goals of this dissertation directly involve the extraction of information 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. This work shows 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 and also illustrates 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. Also included in the dissertation are detailed 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.
Document Availability at the Time of Submission
Release the entire work immediately for access worldwide.
Pitman, Karly Mariah, "Radiative transfer modeling of thermal infrared emissivity spectra: applications to martian regolith observations" (2005). LSU Doctoral Dissertations. 699.