Computer Science – Sound
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p11d..03p&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P11D-03
Computer Science
Sound
[5416] Planetary Sciences: Solid Surface Planets / Glaciation, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [6225] Planetary Sciences: Solar System Objects / Mars, [6297] Planetary Sciences: Solar System Objects / Instruments And Techniques
Scientific paper
SHARAD (SHAllow RADar) is a sounding radar provided by the Italian Space Agency for the Mars Reconnaissance Orbiter mission. Its 20-MHz center frequency and 10-MHz bandwidth complement the lower frequency and narrower bandwidth of the MARSIS sounding radar. SHARAD is particularly useful for mapping the internal, fine-scale layering of the deposits in the polar regions of Mars. In the north, SHARAD paints a three-dimensional picture of the stratigraphy, previously mapped from visible images only in canyon exposures on the periphery of the cap. Regional differences in elevation across the cap are caused by a coarsely layered, variable thickness Basal Unit partially underlying a relatively constant thickness (~2-km) ice-rich layered unit. Of particular interest are the subsurface patterns of ice and dust layers, which are likely tied to the martian climate history over the last several million years and thus to time variations in the planet’s orbit and in its spin-axis obliquity and precession. In the layered deposits at both poles SHARAD has mapped angular unconformities, and at the northern cap SHARAD has unraveled the stratigraphic records of trough migration. The subsurface structures of the ice-rich layered deposits are on the whole different between the two poles, and this may reflect their age difference. The radars have also mapped subsurface reflections in other areas of Mars, including many locales in the northern lowlands. In southern Elysium Planitia, some have interpreted the geomorphology seen in imagery in terms of a frozen sea, but SHARAD shows that the electrical properties of the shallow subsurface material in this region are inconsistent with ice. Elsewhere, geological evidence points to the possibility of ice-rich deposits (such as lobate debris aprons) at mid-latitudes, relics of past glaciations driven by high obliquities. Here, SHARAD confirms the ice hypothesis based on the dielectric behavior of the subsurface material. A subsurface reflector at a depth of ~30-40 m is seen pervasively at the high northern latitudes that include the Phoenix landing site, and it may indicate a shallow ice boundary. SHARAD has mapped non-ice reflectors at other locales, such as Amazonis Planitia, Arcadia Planitia, the Medusae Fossae Formation, and the lava flows west of Ascraeus Mons. In the last case, the electrical properties of the shallow interior are consistent with those of terrestrial and lunar basalts. A next-generation SHARAD would benefit from a higher signal-to-noise ratio design and from a larger bandwidth, although arguably the next radar flown to Mars should focus on imaging of features buried by up to 5-8 m of dust and on characterization of physical properties for deeper mantling or ice deposits.
Campbell Bruce A.
Carter Lynn Marie
Holt Jeremy William
Nunes Daniel C.
Orosei Roberto
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