Permafrost monitoring by reprocessing and repeating historical geophysical measurements (REP-ERT)

Measurements using electrical resistivity tomography (ERT) make it possible to detect permafrost, i.e. continuously frozen ground, thanks to the very different electrical properties of frozen and unfrozen subsoil. However, for financial and logistical reasons only very few continuous ERT monitoring installations on permafrost exist worldwide. One of the exceptions are six permafrost sites in the Swiss Alps that have been constantly monitored with ERT in the context of the Swiss Permafrost Monitoring Network (PERMOS) since 2005, enabling analysis of the long-term change in the subsurface ice content and associated thawing and freezing processes. In contrast, there are many permafrost sites (estimated at more than 500) where one-off ERT measurements have been performed in the past. The aim of the REP-ERT project is to demonstrate the potential of these datasets for the climatological analysis of permafrost areas and to preserve them for future repeat measurements by incorporating them into a shared database.

 

Research aims:

  1. Initiate and compile a database for historical ERT data on permafrost
  2. Develop and apply suitable QA/QC criteria for data filtering and inversion (Mollaret et al. 2019)
  3. Develop and conduct a protocol for regular repetitions of ERT measurements in a climatic context (repetition rate > 10 years)
  4. Initiate first steps to include electrical resistivities as proxy for ice content changes in the international GTN-P (Global Terrestrial Network - Permafrost) database, where up to now only single-point and sparse borehole temperatures and active layer thicknesses are included.

 

Study area: In a first step the study area is focused on the European Alps, but the project aims to encourage a joint international data base and survey and processing routines for all ERT surveys on permafrost worldwide.

  • Project Overview

    Geophysical methods and especially electrical techniques have been used for permafrost detection and monitoring since more than 50 years. However, only after the development of 2-dimensional tomographic measurement and processing techniques in the late 1990’s, i.e. Electrical Resistivity Tomography (ERT), these methods became generally available and were applied on many mountain permafrost sites in the European Alps. Due to the large contrast in electrical resistivity between unfrozen and frozen material, ERT is well suited to detect, but also to monitor frozen ground, and more specifically the ground ice content (Hauck 2002).

    Within the Swiss permafrost network PERMOS, operational ERT measurements are conducted since 2005 for the monitoring of the changes in subsurface ground ice content at six permafrost stations in the Swiss Alps on a yearly basis (Hilbich et al. 2008, PERMOS 2019). A thorough analysis of this data set has shown its high quality and robustness against potential error sources related with the harsh high mountain field conditions and has indicated common climatic trends at all sites, i.e. a decreasing trend of mean specific resistivity since the first measurements in 1999 (Hauck 2002, Mollaret et al. 2019).

    Because of the comparatively large efforts needed for continuous and long-term ERT monitoring, only a very small number of operational ERT monitoring sites exist worldwide in permafrost terrain. However, a much larger number (estimated to be > 500) of permafrost sites with singular ERT measurements exist, many of them published in the scientific literature (for a review see Hauck 2013). These data sets are neither included in a joint database nor have they been analysed in an integrated way. The GCOS Switzerland funded project REP-ERT addresses this important historical data source. Whereas singular ERT data from different permafrost occurrences are not easily comparable due to the local influence of the geologic material on the obtained electrical resistivities, their use as baseline for repeated measurements and subsequent processing and interpretation in a climatic context is highly promising and could be effectuated with low efforts (e.g. Isaksen et al. 2011). The project plans therefore to establish a database of historical ERT surveys on permafrost, quality criteria, repetition protocols and processing routines in order to be able to interpret repeated ERT surveys in a climatic context.

    Although the proposed project is primarily focused on permafrost occurrences in Switzerland for financial reasons, the approach and processing routines will be developed together with international collaborators with the aim to adopt them in an international context as being currently discussed in international initiatives (Lewkowicz et al. 2017).

     

    1. References

    Hauck, C. (2002): Frozen ground monitoring using DC resistivity tomography. Geophysical Research Letters, 29 (21): 2016, doi: 10.1029/2002GL014995.

     

    Hauck, C. (2013): New concepts in geophysical surveying and data interpretation for permafrost terrain. Permafrost and Periglac. Process. 24, 131–137, doi: 10.1002/ppp.1774.

     

    Hilbich, C., Hauck, C., Delaloye, R. & Hoelzle, M. (2008): A geoelectric monitoring network and resistivity-temperature relationships of different mountain permafrost sites in the Swiss Alps. Proceedings Ninth International Conference on Permafrost, Fairbanks, Vol. 1, Kane D.L. and Hinkel K.M. (eds), Institute of Northern Engineering, University of Alaska Fairbanks, 699-704.

     

    Isaksen, K., Ødegård, R.S., Etzelmüller, B., Hilbich, C., Hauck, C., Farbrot, H., Eiken, T., Hygen H.O., Hipp T. (2011): Degrading Mountain Permafrost in Southern Norway: Spatial and Temporal Variability of Mean Ground Temperatures, 1999–2009, Permafrost and Periglacial Processes 22(4), 361–377.

     

    Lewkowicz, A.G., Douglas, T. and Hauck, C. (2017): Towards a Global Permafrost Electrical Resistivity Survey (GPERS) database. In EGU General Assembly Conference Abstracts (Vol. 19, p. 12241).

     

    Mollaret C, Hilbich C, Pellet C, Flores-Orozco A, Delaloye R, and Hauck C. (2019). Mountain permafrost degradation documented through a network of permanent electrical resistivity tomography sites, The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-272, in review.

     

    PERMOS 2019. Permafrost in Switzerland 2014/2015 to 2017/2018. Noetzli, J., Pellet, C., and Staub, B. (eds.), Glaciological Report (Permafrost) No. 16-19 of the Cryospheric Commission of the Swiss Academy of Sciences, 104 pp, doi:10.13093/permos-rep-2019-16-19. 

Duration :  2019-2021

Funded by : GCOS Switzerland

Collaborators: Prof. Christian Hauck, Dr. Christin Hilbich, Dr. Cécile Pellet, Coline Mollaret

Contact

Prof. Christian Hauck

Geography
Department of Geosciences

University of Fribourg
Chemin du Musée 4

CH–1700 Fribourg

   +41 26 300 90 21

  Email