Computer Science – Sound
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p14b..02p&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #P14B-02
Computer Science
Sound
5494 Instruments And Techniques, 6225 Mars, 6964 Radio Wave Propagation
Scientific paper
The SHARAD radar on the Mars Reconnaissance Orbiter has carried out successful subsurface soundings in a number of locales since operations began in late 2006. NORTH POLAR LAYERED DEPOSITS (NPLD): These consist of a thick (up to 2 km+), layered ice-rich unit (Apl) overlying a basal unit (BU), which differs from APl, principally in its lower albedo but additionally because it is platy and irregular compared to Apl. The circumpolar erg, most prevalent at Olympia Undae, is likely material shed from the BU. SHARAD shows that Apl is divided into a finely-layered upper facies of variable thickness, containing dozens of apparent reflectors that likely under-resolve a more finely layered ice-dust sequence, and a lower facies, typically a kilometer or more thick, which contains a limited number of distinct reflectors. SHARAD shows that BU is up to approximately a kilometer thick under the main lobe of the NPLD and is largely absent beneath the minor lobe (centered on the prime meridian), as was suggested earlier by mapping exposures in chasmata on the periphery of the NPLD. SHARAD does not see a sharp reflector at the base of the BU, likely due to volume scattering within the BU, but its sister radar MARSIS, operating at lower frequencies, does see such an interface and its extension beneath Olympia Undae. SOUTH POLAR LAYERED DEPOSITS (SPLD): SHARAD typically does not penetrate to the base of the SPLD, but maps fine-scale layering within this unit. Dipping layers are truncated at the surface and at depth there is good evidence for angular unconformities in the layers, which are likely tied to surface erosion followed by new episodes of ice and dust deposition. AMAZONIS PLANITIA: This roughly circular lowland north of the hemispheric dichotomy boundary is one of the flattest places on Mars, with a smooth cover of sediment. Younger flow-like features with ridged and platy surface structures occur in southwestern Amazonis. These flows are widely held to be volcanic, but some workers suggest that they are instead related to past and/or present ground ice. SHARAD shows clear evidence in places for a subsurface reflector at ~40-90 m depth that is well correlated with areas of high Earth-based radar backscatter at 12.6-cm wavelength, likely indicative of lava flows. Loss tangent estimates are in the range of lunar basalts and seem to preclude a major component of ice. ELYSIUM PLANITA: SHARAD has detected a subsurface reflector as deep as 200 m over a ~500,000 km2 area. The evidence from SHARAD is consistent with volcanic material, not ice-rich material, for the intervening layer.
Biccari Daniela
Campbell Bruce A.
Carter Lynn Marie
Egan Anthony F.
Holt Jeremy William
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