Electrical Conductivity of the Bishop Tuff, Bishop, CA: Implications for Ground-Penetrating Radar Performance | INSTITUT DE PHYSIQUE DU GLOBE DE PARIS

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  Electrical Conductivity of the Bishop Tuff, Bishop, CA: Implications for Ground-Penetrating Radar Performance

Type de publication:

Journal Article

Source:

AGU Fall Meeting Abstracts, Volume 11, p.0826 (2004)

URL:

http://adsabs.harvard.edu/abs/2004AGUFMGP11A0826G

Mots-clés:

Etudes spatiales et planétologie ; 8404 Ash deposits; 5109 Magnetic and electrical properties; 6969 Remote sensing; 0609 Antennas; 0684 Transient and time domain, UMR 7154

Résumé:

Ideal terrestrial analogues to Mars combine known features such as an arid environment, cold climate, deep water table, saline pore waters, and bedrock dominated by igneous or clastic sedimentary units. Terrestrial analogues best suited for calibrating a suite of planetary geophysical instruments, especially radar sounders, need to be sufficiently characterized to provide an accurate understanding of the local geologic context. The Bishop Tuff, Bishop, California is one of a number of recommended Mars analogue sites (National Research Council Decadal Study report on Terrestrial Analogues to Mars, 2001). While not cold, the Volcanic Tableland is situated in an arid environment, and is underlain by a relatively deep water table (100 to 180 m). These factors, combined with availability of detailed characterization data, made this a potentially appealing location in east-central California for testing the performance of existing and planned radar sounders for future Mars exploration. To take advantage of potential synergies that support improved subsurface resolution when applying multiple geophysical techniques, we developed a collaboration to mutually benefit from coordination of field and laboratory activities. Transient electromagnetic (TEM) soundings at several locations on the Volcanic Tableland were performed in preparation for potential ground-penetrating radar (GPR) investigations, and are documented in this paper. Laboratory data from Bishop Tuff samples, determined using capacitive cells in the frequency range of 1 to 1000 MHz, are also presented to assess the dielectric behavior of the local geologic units. Interpretation of geophysical data resulting from this field study is aided significantly by the wide range of geological, structural, and hydrogeological data collected by our team over the last 8 years. Knowledge about the subsurface electrical conductivity structure, determined through application of TEM, is used to quantify the expected magnitude of GPR signal loss due to absorption. One-dimensional TEM inversions suggest a relatively resistive (approximately 1000 to 5000 ohm-m) near-surface, overlying a conductive (approximately 15 to 40 ohm-m) region at depths ranging from approximately 100 to 180 m, depending on sounding location. This conductive region is preliminarily interpreted to be the saturated zone because its depth correlates with measured average local surface water elevations. Low to mid-frequency ground-penetrating radar soundings should be able to image the water table below the Volcanic Tableland because of the relatively resistive nature of the subsurface. We discuss implications of these results on radar performance in similar Martian environments.