Time-lapse capacitive resistivity imaging: a new technology concept for the monitoring of permafrost

The British Geological Survey, in partnership with the Universities of Sussex and Bonn, is
investigating and seeking to prove a new technology concept for the non-invasive volumetric
imaging and routine temporal monitoring of the thermal state of permafrost (Figure 1), a key
indicator of global climate change. Capacitive Resistivity Imaging (CRI), a technique based upon a
low-frequency, capacitively-coupled measurement approach (Kuras et al., 2006) is applied in
order to emulate Electrical Resistivity Tomography (ERT) methodology, but without the need for
galvanic contact on frozen soils or rocks. Recent work has shown that temperature-calibrated
ERT using galvanic sensors (Figure 2) is capable of imaging recession and re-advance of rock
permafrost in response to the ambient temperature regime. However, the use of galvanic sensors
can lead to significant practical limitations on field measurements due to high levels of and large
variations in contact resistances between sensors and the host material as it freezes and thaws
Figure 3). The capacitive technology developed here overcomes this problem and provides a more
robust means of making high-quality resistance measurements with permanently installed
sensors over time. Reducing the uncertainty associated with uncontrolled noise from galvanic
sensors increases the value of time-lapse ERT datasets in the context of monitoring permafrost.