Electrical Resistivity Tomography (ERT) datasets from the Otemma glacier forefield and outwash plain

Electrical Resistivity Tomography (ERT) datasets collected in the Otemma forefield (Switzerland) from 2019 to 2021.
Data were collected by the research teams of Bettina Schaefli1,2, Stuart N. Lane1 and James Irving3.

1 Institute of Earth Surface Dynamics (IDYST), University of Lausanne, 1015 Lausanne, Switzerland

2 Institute of Geography (GIUB), University of Bern, 3012 Bern, Switzerland

3 Institute of Earth Sciences (ISTE), University of Lausanne, 1015 Lausanne, Switzerland

For further information, please contact:

[e-mail]

This dataset is first referenced and discussed in the research paper by Müller et al., 2022.

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Data Description

Electrical Resistivity Tomography (ERT) profiles were collected around the outwash plain of the Otemma glacier forefield (WGS84 : 45.93434 / 7.41209). All data were collected with a Syscal Pro Switch 48 from Iris Instruments, using an array of maximum 48 electrodes with a spacing between 1 and 10 meters. For each line, measurements were performed using a Dipole-Dipole (dd) and a Wenner-Schlumberger (ws) electrode configuration.

All ERT lines locations can be visualized in ERT_map_lines_2019-2021.jpg.

A result overview can be vizualized in ERT_allResults_3Doverview.png.

Data Structure

Two Juypter Notebook files are provided and can be used to reproduce all inversion analyses.

1_createInput_prosys_to_pygimli.ipynb : Transforms the raw data from Syscal Pro (exported with ProsysII software as .csv) to a processed .dat file formated for inversion using the pyGIMLi library.

2_ERT_inversion.ipynb : Reads the processed .dat file and performs a 2D robust inversion for a set of regularization parameters for the selected line.

In ERT_data.zip, 3 folders with similar structure contain all data for year 2019, 2020 and 2021. Each folder contains :

GPS : folder with electrodes coordinates for each ERT line

inputGiMLi

prosys_csv: contains the raw field measurements (downloaded from the Syscal device using ProsysII)

input_ERT : stores the processed .dat file. (created from notebook 1)

results_lambda : contains a .png image with the inversion results using different values of the regularization parameter lambda used to assess the sensitivity of the inversion results (over/underfitting). Analysis is performed for each line and each electrode configuration (dd or ws). (created from notebook 2)

results_final : contains a .png image with the final inversion results for each line and electrode configuration (dd or ws) using the optimal lambda parameter only (all arrays are shown from East to West). (created from notebook 2)

vtk : contains a .vtk file for each final results for 3D vizualization in the Paraview software.

ERT_line_description_yyyy.csv : a file describing the ERT arrays characteristics (read in notebook 1 and 2)

The results folder contains :

ERT_3Dview_paraview folder : contains Paraview state files (.pvsm) for 3D vizualization of all results, as well as image files.

ERT_results_all.pdf : A summary of all final results for all years (similar content as ERT/inputGiMLi/results_final folders)

ERT_results_bedrock.pdf : Contains the vizualization of specific ERT profiles in the outwash plain and their field location . The separation between a surface layer of water-saturated sediments (resistivity <2500 Ωm) and the underlying bedrock is delimited. The likely presence of buried ice blocks (isolated blocks with resistivity >5000-10000 Ωm) is also highlighted.

ERT_timelapse_salt_tracer.gif : results of a time-lapse ERT measurement performed on 9 August 2019 to track the movement of a salt plume injected at 06 am, 9.38 meters upslope (see paper by Müller et al., 2022 for detailed analysis). The tracer starts to appear at 12:45 at a distance of 30m on the array. Minimum resistivity is reached at between 16:45 and 17:45.