The DC resistivity method is a common tool in periglacial research because it can delineate zones of large resistivities, which are often associated with frozen water. The interpretation can be ambiguous, however, because large resistivities may also have other causes, like solid dry rock. One possibility to reduce the ambiguity is to measure the frequency-dependent resistivity. At low frequencies (< 100 Hz) the corresponding method is called induced polarization, which has also been used in periglacial environments. For the detection and possibly quantification of water ice, a higher frequency range, between 100 Hz and 100 kHz, may be particularly interesting because in that range, the electrical properties of water ice exhibit a characteristic behaviour. In addition, the large frequencies allow a capacitive coupling of the electrodes, which may have logistical advantages. The capacitively coupled resistivity (CCR) method tries to combine these logistical advantages with the potential scientific benefit of reduced ambiguity.
In this paper, we discuss CCR data obtained at two field
sites with cryospheric influence: the Schilthorn massif in the Swiss
Alps and the frozen Lake Prestvannet in the northern part of Norway. One
objective is to add examples to the literature where the method is
assessed in different conditions. Our results agree reasonably well with
known subsurface structure: at the Prestvannet site, the transition
from a frozen lake to the land is clearly visible in the inversion
results, whereas at the Schilthorn site, the boundary between a snow
cover and the bedrock below can be nicely delineated. In both cases, the
electrical parameters are consistent with those expected from
literature.
The second objective is to discuss useful methodological
advancements: first, we investigate the effect of capacitive sensor
height above the surface and corroborate the assumption that it is
negligible for highly resistive conditions. For the inversion of the
data, we modified an existing 2-D inversion code originally developed
for low-frequency induced polarization data by including a
parametrization of electrical permittivity. The new inversion code
allows the extraction of electrical parameters that may be directly
compared with literature values, which was previously not possible.
