Surface Roughness and Infrared Emission from the Lunar Surface.
Abstract
In order to understand thermal infrared spectra of the Moon and solid-surfaced planetary bodies in terms of surface roughness and composition, a two-part project involving thermophysical computer models and infrared photometry has been pursued. The computer models calculate the infrared radiation emitted by an atmosphereless body with a macroscopically rough surface using radiative heat transfer methods. Multiple scattering of incident solar radiation, and multiple scattering and remission of thermal infrared radiation onto surrounding surface elements are included in the model. Surface roughness is modeled as paraboloidal holes characterized by a fractional coverage of a spherical object and a single depth-to-diameter ratio. Thermal emission from the rough surface is anisotropic and deviates from a gray body emission assumed by standard thermal models. The model explains to first-order published, mid infrared, measurements of the Moon and Galilean Satellites. Surface composition is included by using results from Hapke (1981, 1984, 1990) for reflectance and emittance properties of a particulate surface. It is concluded that negative surface relief is required to explain the continuum behavior of the lunar thermal spectrum. An infrared photometer was constructed from an existing design and was configured in order to perform whole disk photometry of the Moon at various phase angles. Measurements at 5.03, 8.4 and 11.5 μm were made at seven phase angles, ranging from -151 ^circ55^' to 53^circ27 ^'. The thermophysical computer models were modified so that disk-integrated emission as a function of phase angle could be calculated. Effects due to thermal inertia of the surface are not included in this simplified version of the model. The Model calculations compare favorably with measurements of the Moon made by the author, Sarri and Shorthill (1965) and Murdock (1972). It is concluded that surface roughness necessary in explaining the shape of the lunar thermal emission with phase angle.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- January 1994
- Bibcode:
- 1994PhDT.........9V
- Keywords:
-
- Physics: Astronomy and Astrophysics, Geophysics;
- Surface Roughness;
- Infrared Spectra;
- Lunar Surface;
- Thermal Emission;
- Computerized Simulation;
- Radiative Heat Transfer;
- Moon;
- Galilean Satellites;
- Solar Radiation;
- Incident Radiation;
- Anisotropy;
- Reflectance;
- Emittance;
- Infrared Photometry;
- Surface Properties;
- Phase Shift;
- Thermophysical Properties;
- Lunar and Planetary Exploration