PhD project title: Coupled thermo-geophysical inversion for permafrost monitoring.
Traditional methods of assessing permafrost thermal state are based on ground
temperature measurements in boreholes. However in particular geological settings (fine-grained sediments, sediments with residual salinity in pore water), ground temperature observations may fail to document anomalies such as lowered freezing point.
In ice-rich and ice-bonded permafrost, changing thermal state of the ground is
reflected in changing ground ice content. Due to the contrasting physical properties of ice and water, a geophysical methods called electrical resistivity tomography has been increasingly used to delineate frozen ground and areas of high ground-ice content and to map changes in ground ice content. When operated in monitoring mode, and with acquisition of sufficiently long and complete timeseries, the geophysical data provide insight into the in-situ processes rather than discrete (in time and space) ground properties. Demonstrated quantitative link between electrical and thermal properties of geological materials allows for quantitative temperature-geophysical interpretations.
In this work we designed and evaluated a coupled modeling framework for calibrating ground thermal model with time lapse geoelectrical measurements. The method allows for gaining inside into ground thermal regime while reducing the need for invasive, costly and logistically demanding drilling investigations.
The main contributions of this PhD thesis work were the following:
1) Reporting the longest timeseries of time lapse electrical resistivity
from high-latitude permafrost;
2) Design, setup and successful operation of an automated ground resistivity
3) The focus-one protocol: description of a measurement protocol for estimating
electrode grounding resistances of multi-electrode arrays used for ERT
4) Electrode design optimization for monitoring applications;
5) Timeseries of field-measured grounding resistances;
6) Freeze-thaw hysteresis of unfrozen water content;
7) Freeze-thaw hysteresis of ground electrical resistivity;
8) Simple heat transport model for active layer and permafrost;
9) Automated iterative parameter optimization;
10) Validation of resistivity mixing relationship for the effective resistivity
of a multi-phase soil;
11) Validation of a fully coupled inversion scheme using geoelectrical data for heat model calibration;
|Effective start/end date||01/01/2012 → 07/12/2017|
In 2015, UN member states agreed to 17 global Sustainable Development Goals (SDGs) to end poverty, protect the planet and ensure prosperity for all. This project contributes towards the following SDG(s):