Optimisation of quasi-3D electrical resistivity imaging – application and inversion for investigating heterogeneous mountain permafrost

Abstract

Abstract. This study aimed to optimise the application, efficiency and interpretability of quasi-3D resistivity imaging for investigating the heterogeneous permafrost distribution at mountain sites by a systematic forward modelling approach. A three dimensional geocryologic model, representative for most mountain permafrost settings, was developed. Based on this geocryologic model quasi-3D models were generated by collating synthetic orthogonal 2D arrays, demonstrating the effects of array types and electrode spacing on resolution and interpretability of the inversion results. The effects of minimising the number of 2D arrays per quasi-3D grid were tested by enlarging the spacing between adjacent lines and by reducing the number of perpendicular tie lines with regard to model resolution and loss of information value. Synthetic and measured quasi-3D models were investigated with regard to the lateral and vertical resolution, reliability of inverted resistivity values, the possibility of a quantitative interpretation of resistivities and the response of the inversion process on the validity of quasi-3D models. Results show that setups using orthogonal 2D arrays with electrode spacings of 2 m and 3 m are capable of delineating lateral heterogeneity with high accuracy and also deliver reliable data on active layer thickness. Detection of permafrost thickness, especially if the permafrost base is close to the penetration depth of the setups, and the reliability of absolute resistivity values emerged to be a weakness of the method. Quasi-3D imaging has proven to be a promising tool for investigating permafrost in mountain environments especially for delineating the often small-scale permafrost heterogeneity, and therefore provides an enhanced possibility for aligning permafrost distribution with site specific surface properties and morphological settings.

A systematic evaluation of electrical resistivity tomography for permafrost interface detection using forward modeling

“…ERT forward modeling is a tool that simulates field data for a given ERT survey and subsurface resistivity model 31 . In the permafrost literature, forward modeling has been used to test how well subsurface features can be resolved, 32,33 to explore the performance of different array types and/or survey geometries, 34,35 and to generate data in order to test novel inversion strategies 36 . Forward modeling can be undertaken with only a few inputs, including electrode locations, array type, boundary conditions, and a subsurface resistivity model that has been discretized appropriately.…”

“…ERT forward modeling is a tool that simulates field data for a given ERT survey and subsurface resistivity model. 31 In the permafrost literature, forward modeling has been used to test how well subsurface features can be resolved, 32,33 to explore the performance of different array types and/or survey geometries, 34,35 and to generate data in order to test novel inversion strategies. 36 package.…”

Frozen ground dynamics resolved by multi‐year and year‐round electrical resistivity monitoring at three alpine sites in the Swiss Alps

“…Day‐Lewis, Singha and Binley () affiliate the inaccuracy of resistivity values to limitations arising from the imperfect and variable tomographic resolution. On their approach to optimizing quasi‐3D ERT for permafrost‐related problems using synthetic modelling, Schwindt and Kneisel () have shown that inverted specific resistivity values vary strongly among the different setups as well as from the initial model for different electrode spacings and array types (Wenner and dipole‐dipole).…”

Multi-Scale Geophysical Methodologies Applied to Image Archaeological Ruins at Various Depths in Highly Terraneous Sites

“…The parameters were selected based on a trade-off between the area coverage and resolution. Second, ERT was executed in the form of a quasi-three-dimensional (3D) setup [15,[59][60][61], where five parallel lines heading south-north (Figure 3C) were acquired in a profile mode using the WB configuration because it has been used commonly in the imaging of different archaeological prospections [15,62] and characterized by a high signal-to-noise ratio [63]. Additionally, it provides a good vertical resolution, which means that the depth to the base of archaeological targets can be detected well.…”