Physics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p23c1276t&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P23C-1276
Physics
[5464] Planetary Sciences: Solid Surface Planets / Remote Sensing
Scientific paper
The Apollo 15, 16, and 17 core tubes show that the uppermost few meters of the lunar regolith are interlaced layers of a fine grained powders and blocky crater ejecta. The layers of crater ejecta have dielectric constants in the range of 7-9 while the fine-grained powders has dielectric constant on the order of 2.7. These differences in dielectric constant, in turn, create radar reflections that are both refracted and reflected back through the space-regolith interface. Note that for a dielectric constant of 2.7 for the lunar regolith, radio waves incident on the lunar surface at the angle of 30-degrees from the normal will propagate in the regolith at an angle of 18-degrees. At the limb, radio waves incident on the lunar surface at an angle near 90-degrees from the normal will propagate in the regolith at an angle of about 37-degrees. These angles are within the range where radar backscatter is in the quasi-specular regime. When these buried crater ejecta layers are modeled using Hagfors’ formulation (Hagfors, 1963), echo powers match the behavior observed for average lunar backscatter at centimeter wavelengths for higher (30° to 90°) angles of incidence. In addition, Hagfors et al. (1965) conducted an experiment where the Moon was illuminated at 23-cm wavelength with circular polarization and the differences were observed in orthogonal linear polarizations. Modeling of these observations and assuming again that the buried crater ejecta scatter in a quasi-specular manner, echo differences in horizontal and vertical linear polarizations are in relatively good agreement with the observations. The data from Chandrayaan Mini-RF radar, which operated at S-Band (13cm) wavelength, and the Lunar Reconnaissance Orbiter (LRO) Mini-RF radar, which is operating at S-Band and X-Band (4-cm) wavelengths, provide an opportunity for a new examination of whether radar backscatter from buried crater ejecta behaves like a quasi-specular scatter. These radars reproduce the geometry of the Hagfors et al. (1965) observations as they transmit circular polarization and record echoes in horizontal and vertical linear polarizations. References Hagfors, T. (1964), Backscattering from an undulating surface with application to radar returns from the Moon, J. Geophys. Res., 97, 13,319-13,346. Hagfors, T., R. A. Brockelman, H. H. Danforth, I. Hanson, and G. M. Hyde (1965), Tenuous surface layer on the Moon: Evidence derived from radar observations, Science, 150, 1153-1156.
Heggy Essam
Thompson William T.
Ustinov Eugene A.
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