CHARACTERIZATION OF GROUND ICE USING COMPLEX RESISTIVITY

Complex resistivity (CR) can provide a synoptic view of the properties of subsurface ice, including distribution, silicate and interfacial-water fractions, concentration of key soluble impurities, and temperature. CR is set up like classical DC resistivity, but records the amplitude and phase of the ground electrical response over a large bandwidth. The diagnostic dielectric relaxation of water ice appears as a decrease in resistivity centered at several kHz. Interfacial water can also be identified where fine-grained silicates exist. Our trial survey of part of the US Army Permafrost Tunnel (Fox, AK) resolved previously identified regions of high and low ice concentration, as well as yielding an average ice fraction in good agreement with the average of analyzed samples. The mapping from electrical properties to ice content depends on the ground temperature, which we determined to be –3±1°C by matching survey results to lab data. This compares well to a median air temperature of –3.3 C. However, broadband CR acquisition is slow: follow-up surveys near Tok, AK, demonstrated that the ice signature can be adequately captured, with greater efficiently (i.e., longer/faster survey lines), using dual surveys with single-frequency systems operating near 1 Hz and 16.5 kHz. Nonetheless, full-spectra data are necessary to resolve the interfacial-water contribution and to assess subsurface temperature. Future terrestrial ground-ice characterization using CR can span controls on the evolution of periglacial landforms, frost-heave risk to infrastructure, and the impact of permafrost melting on the global carbon inventory. Planetary applications include assessment of interfacial-water and cryosuction in forming massive high-latitude ground ice on Mars, searching for preserved, buried ice at low latitude on Mars, determining the ice content in permanently shadowed regions on the Moon and Mercury, and assessing habitability of the shallow subsurface on icy satellites.