3.5-cm radar investigation of Mars and Mercury : planetological implications

• Main Author: Butler, Bryan Jay
• Format: Thesis
• Language: English
• Published: 1994
• Subjects: Greenland; Ice cap
• Online Access: https://thesis.library.caltech.edu/7440/; https://thesis.library.caltech.edu/7440/1/Butler_bj_1994.pdf; https://resolver.caltech.edu/CaltechTHESIS:01252013-144953787

Bistatic radar observations have been made using the combined VLA/Goldstone radar instrument at X-Band wavelength (near 8500 MHz). This thesis contains a description of the instrument, observations, data reduction, and implications of some of the measurements. While the instrument has been used to probe many objects, discussion will be restricted to the data sets for Mercury and Mars. This technique has provided the first unambiguous radar cross section maps of both planets, with surface resolutions as good as 150 km for Mercury, and 100 km for Mars. The analysis of the radar cross section maps has provided a rich harvest of new information about the surface and near-surface of both planets. Mars was observed twice during the opposition of 1988, and 3 times during the opposition of 1992/93. During the 1988 observations, the subearth latitude was ∼ -24°, providing a good view into the south polar regions. The Martian season at the time was mid southern summer (L_s ∼ 295°), and thus the seasonal CO_2 ice cap had sublimated away, exposing the residual south polar ice cap (RSPIC). The RSPIC was the area with the highest cross section on the planet in 1988, with a peak normalized cross section of 0.716. This is incredibly high, especially considering that it was at an incidence angle of ∼ 66° at the time. The RSPIC also exhibited the odd characteristic that throughout much of its extent, more echo energy was received in the same sense circular (SS) polarization as that transmitted than in the opposite sense (OS), a so-called polarization inversion. This is a characteristic which has also been observed on the Galilean satellites, and on a portion of Greenland, and may be true for all cold, clear icy regions. This seems to be a result of the radar wave penetrating into a relatively lossless medium containing many volume scatterers. In the case of the RSPIC, the lossless medium is ice, whether CO_2 or H_2O, and the scattering centers are most probably cracks and voids in the ice. Simulations indicate that the radar wave ...