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Ground-Penetrating Radar Investigations of Terrestrial Analogs to the
Martian Crust, 20-9458

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Principal Investigator
Cynthia Dinwiddie

Inclusive Dates:  01/13/04 - 05/13/04

Background - The Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) aboard the European Space Agency's Mars Express spacecraft will acquire the first global data set of Martian subsurface radar properties, including, perhaps, inferred depth to water. Because only limited ground-penetrating radar investigations of the Earth have been made within the low-frequency range of MARSIS, an accurate interpretation of its forthcoming data is uncertain. Terrestrial analogs to Mars provide the opportunity to collect low-frequency radar data from well-known, well-characterized sites so that uncertainties may be minimized when interpreting Mars radar data.

Approach - A team of geoscientists and geophysicists from SwRI and the Lunar and Planetary Institute in Houston conducted transient electromagnetic and ground-penetrating radar investigations of three well-characterized terrestrial analog sites in the U.S. southwest at frequencies similar to those proposed for Mars studies: (1) sand dunes overlying alluvium, (2) an alluvium-basalt-alluvium sequence, and (3) alluvium with a shallow water table. Transient electromagnetic soundings were performed to measure ground conductivity and estimate absorptive losses. Prior to field work, the principal geologic units were studied in the laboratory to determine their frequency-specific electromagnetic properties.

Accomplishments - Radar identified the geologic contact between sand dune and alluvium. Elevated electrical conductivity of the ground at the alluvium-basalt-alluvium site precluded identification of the geologic contacts; however, transient electromagnetics indicate the shallow water table site may be a good target for future radar investigations. This project provided SwRI with crucial proof-of-concept field data, laying the necessary foundation for development of two Mars Fundamental Research Program proposals. Results from this project also will support the submission of future proposals to secure funding for MARSIS data analysis and development of next-generation planetary geophysical instruments.

Ground-penetrating radar unit and 100-MHz bistatic antenna at the base of a sounding transect, Big Dune, Nevada Two-dimensional radar profile of the sand dune and alluvium contact (red line) generated with soundings obtained using the 100-MHz bistatic antenna

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