Application of capacitively‐coupled and DC electrical resistivity imaging for mountain permafrost studies

A capacitively‐coupled resistivity system (OhmMapper) operating in the kilohertz range and a standard galvanically‐coupled multi‐electrode resistivity system (SYSCAL) operating in the direct‐current (DC) limit were compared in terms of permafrost detection. The systems differ mainly in relation to operating frequency and the principle used to ensure sufficient electrical coupling between the sensors and the ground. Both were able to detect isolated permafrost in the Swiss Alps previously found by various geophysical field surveys. However, inter‐year differences between results using the same system were less than differences between the two at the same time and at exactly the same location. There was good agreement between the systems at an unfrozen reference area, whereas at a mountain permafrost site, apparent electrical resistivity values with the capacitively‐coupled system were approximately one quarter of those obtained with the galvanically‐coupled system. As dielectric effects in resistive permafrost terrain become more important at lower frequencies (around 1 kHz) than in comparable but unfrozen environments (around 10 MHz), permafrost resistivity values obtained with the OhmMapper are generally lower than galvanically obtained values near the DC limit. Copyright © 2006 John Wiley & Sons, Ltd.