Detecting ground ice in warm permafrost with the dielectric relaxation time from SIP observations

Abstract. The melting of ground ice poses significant hazards in permafrost regions, making effective detection methods essential. Conventional geophysical techniques like electrical resistivity, seismic surveys, or ground-penetrating radar alone often produce ambiguous results due to the overlap of material characteristics between frozen and unfrozen ground. This study addresses these limitations by using the dielectric relaxation time of ice as a unique indicator of ground ice. We developed a method to quantify relaxation time from Spectral Induced Polarization (SIP) data measured by the FUCHS III device. The method's effectiveness was demonstrated through synthetic data and two field surveys. SIP field measurements, ranging from 1.46 Hz to 40 kHz, were conducted on a retrogressive thaw slump and a pingo in Yukon, Canada. The extracted relaxation times were mapped to pseudo-depths obtained from single-frequency inversion. This study proposes a relaxation time range from 10 to 400 µs for ground ice, and the results demonstrate that this range can detect ground ice spectra in field studies. Comparison with observations in a borehole and an exposure of permafrost indicate that relaxation time is less ambiguous in detecting ground ice in warm permafrost than conventional methods such as electrical resistivity tomography.