Publication Date:
2015-02-18
Description:
Low-frequency (LF, 〈〈1 kHz) electrical resistivity is useful in discriminating frozen from unfrozen ground in periglacial environments, but it cannot distinguish whether frozen materials are dry or ice-rich, nor can it provide reliable estimates of ice content. However, polarisabilities due to unfrozen, interfacial water and protonic defects in ice both have strong dielectric relaxations (frequency dependence), resulting in a large decrease in resistivity at high frequencies (HF, 〉 〉 1 kHz). From laboratory measurements of samples collected at the US Army Permafrost Tunnel (Fox, Alaska), we find temperature-dependent relationships between ice volume fraction and the resistivity frequency effect (RFE, defined as the LF-normalised difference in LF and HF resistivities). We report the first field detection of H 2 O polarisability in permafrost, using a broadband spectral-induced polarisation system at the permafrost tunnel. By comparing laboratory and field spectra, we found a best-fitting ice temperature of -3 ± 0.5 °C. Laboratory RFE at the selected temperature was then used to map the RFE in the tunnel wall to 45 − 95 per cent ice by volume. Both of these results agreed quantitatively with the bulk properties of the tunnel, and the ice content image correlated qualitatively with major permafrost features. The RFE approach may be expedient using simpler instrumentation, but the close agreement of laboratory and field spectra indicates that the ice and interfacial water signatures can be individually quantified by broadband fitting of both amplitude and phase. This will provide more accurate constitutive relations, but more importantly will yield better remote temperature measurement of the subsurface using known dependencies of the dielectric relaxation frequencies. Copyright © 2015 John Wiley & Sons, Ltd.
Print ISSN:
1045-6740
Electronic ISSN:
1099-1530
Topics:
Geography
,
Geosciences
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