the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 19 Feb 2025
Brief communication: Use of lightweight and low-cost steel net electrodes for electrical resistivity tomography (ERT) surveys performed on coarse-blocky surface environments
Abstract. ERT is a widely used geophysical technique for characterizing various mountainous environments where land surfaces consist of coarse blocks and debris, such as landslide deposits or rock glaciers. In this situation, installing the common steel spike electrodes is both challenging and time-consuming, and achieving galvanic contact between the electrodes and the surface is difficult. In this work, we have successfully tested an alternative electrode that is tougher, lighter and cheaper than the recently proposed conductive textile electrode. A thin stainless-steel net and sponges are used to create small bags that can be easily inserted between the blocks, and then removed.
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RC1: 'Comment on egusphere-2025-405', Anonymous Referee #1, 11 May 2025
Reviewer Recommendation and Comments for Manuscript egusphere-2025-405
Brief communication: Use of lightweight and low-cost steel net electrodes for electrical resistivity tomography (ERT) surveys performed on coarse-blocky surface environments
Summary
The manuscript presents a study on a newly developed electrode design, i.e., stainless steel-net electrodes, which the authors propose for electrical resistivity tomography (ERT) measurements in coarse blocky environments. The electrodes facilitate and accelerate ERT surveys and are cheaper and lighter compared to conventional stainless-steel spike electrodes. The authors demonstrate that contact resistances and reciprocal errors are lower when using stainless-steel net electrodes compared to conventional stainless-steel spike electrodes. Correlations of apparent resistivity values between the two electrode types are high for an exemplary landslide deposit and an Italian rock glacier and slightly lower for a Swiss rock glacier. The inversion results are similar for both electrode types and successfully reconstruct the known internal structure of the landforms. The results are clearly presented and highlight the relevance of lightweight, easily deployable equipment in harsh alpine terrain with limited accessibility.
However, upon closer examination, the manuscript offers limited novelty and primarily reiterates concepts and methodologies previously presented, particularly in the study by Bast et al. (2024). One of the main concerns lies in the similarity between the figures of the two articles. The representations and analysis of the data are almost identical, with no substantial additions, enhancements or new interpretations. For instance, the authors could have included additional pseudosections to visualize the spatial consistency in the apparent resistivity readings as well as the position of the removed quadrupoles for the different electrode types. In my opinion, the results related to the application of stainless-steel net and textile electrodes could have been presented together in one publication, as the study sites are identical and the data analysis and structure is very similar.
To strengthen the manuscript, I recommend that the authors explore the usability of such stainless-steel net electrodes for induced polarization measurements, as suggested in the Discussion section. Such an investigation would offer a clear advancement over previous research. Another benefit highlighted by the authors consists in the increased durability of stainless-steel net electrodes compared to textile electrodes, which tend to oxidize more rapidly. Showing time lapse ERT data of e.g., hourly measurements could further underline advantages of the stainless-steel net electrodes and enhance the relevance of the article. Clearly, this would require considerable additional effort. Nonetheless, without any further developments compared to Bast et al. (2024) the study lacks substantial new data or insights that would justify its publication as an independent contribution to the field. Additionally, I would include a comparative analysis between net and textile electrodes to clearly demonstrate the advantages of the new design over both textile and traditional spike electrodes. I also suggest revising the Discussion section; vague terms such as “good contact resistances” should be replaced and the discussion points need to be better supported with relevant literature.
Taking these concerns along with a number of specific comments and technical corrections listed within the attached PDF into account, I recommend accepting this manuscript after major revisions.
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AC1: 'Reply on RC1', Mirko Pavoni, 23 May 2025
We would like to thank the anonymous reviewer for his/her comments. While we carefully considered his/her suggestions, we disagree with the assertion that there is a lack of novelty compared to previous papers. Our work Bast et al. (2024) was, in fact, substantially different: to verify the reliability of the conductive textile electrodes proposed by Buckel et al. (2023). This work, which is limited in scope as it is a BRIEF communication, proposes a new approach to electrodes that provides an improved solution for performing ERT surveys in coarse, blocky environments.
While we agree that the presented study shows a similar analysis to that in our previous work (Bast et al., 2024), this BRIEF communication has a completely different aim. Rather than proposing a comparative analysis of different electrode approaches, this work aims to propose a new type of electrode with significant improvements compared to the recently tested conductive textile electrodes (Buckel et al., 2023). As highlighted in Bast et al. (2024), conductive textile electrodes are a reliable tool for facilitating the acquisition of ERT measurements on coarse-blocky surfaces such as rock glaciers and landslide deposits. Textile electrodes can be easily inserted and removed between the blocks without the need for steel spikes to be hammered in, which significantly speeds up the preparation of ERT arrays. Nevertheless, in our discussion in Bast et al. (2024), we identified several important problems related to the application of these conductive textile electrodes that this work intends to overcome: i) The same weight of steel spike electrodes (50 steel spike electrodes or 50 conductive textile electrodes weigh about 15 kg in total); ii) The oxidation problem related to the conductive metals used to make the textile (copper and nickel), which will drastically reduce the performance of the electrodes after few surveys; iii) The cost of making (or replacing damaged ones) the textile electrodes (15 euros each, mainly due to the cost of the conductive textile, i.e. 750 euros for a set of 50 electrodes);iv) the conductive textile is fragile and prone to be cut by rough surfaces.
As we highlighted in the submitted BRIEF communication, the proposed steel-net electrodes clearly overcome all these problems: i) each electrode is just 50 g (50 electrodes, which can easily fit in a traditional medium size mountain bag as the textile electrodes, are about 2.5 kg), ii) the net is realized with stainless steel, therefore we don’t face any oxidation problem, and this means that the high performance of the electrodes is guaranteed in future surveys; iii) producing the steel-net electrodes is also much more advantageous from an economic point of view, the net can be easily found in hardware stores, and the cost to produce an electrode is around 2 euros, about 100 euro for 50 electrodes; iv) finally, the mechanical resistance of the electrodes is improved, these new steel-net electrodes do not break and last a long time.
Taking all this into account, we believe that the proposed electrodes offer some significant advantages: i) The low weight of the electrodes is a valuable improvement for researchers working in high mountain environments who are accustomed to carrying all the ERT equipment without the support of vehicles (e.g. helicopters); ii) once the electrodes have been made, there is no need to replace them due to oxidation (or to spend time drying the textile at the end of each survey to reduce oxidation) or breakage; iii) even if they need to be replaced, the cost of the net electrode is low and the material is easily available. Therefore, our new solution is a significant improvement on textile electrodes: we have all the advantages presented by Buckel et al. (2023), while overcoming the issues identified by Bast et al. (2024).
While we agree that the analysis is similar to that of Bast et al. (2024), also here we have considered and compared the relevant parameters in an ERT survey, namely contact resistances, the quality of the measured datasets (via reciprocal error) and the results (i.e. the inverted resistivity model). We could add the pseudo-sections, but we have already plotted the linear regression of the measured apparent resistivities to demonstrate the consistency between the datasets obtained using different electrodes. However, Cs BRIEF Communications are limited to 3 figures, so we must make a precise and concise selection of what to show readers. In our opinion, the structure of the figures is not exactly the same as that shown by Bast et al. (2024). While it is true that we present and compare the same parameters, this is unavoidable for an ERT survey performance evaluation. Regarding the choice of test sites, the work is not finalised to characterise the subsurface structure/composition, which is already well known, but rather to verify the reliability of the proposed electrodes for acquiring ERT surveys in these environments.
This analysis could not be included in Bast et al.'s (2024) previous work since the steel-net electrodes were developed after the manuscript had been submitted. As the reviewer correctly stated, the performance of textile and stainless-steel net electrodes is substantially the same, as verified at the same study sites. Therefore, we preferred to compare our new electrodes with the commonly used steel spikes coupled with sponges (soaked in salt water), the traditional approach to acquiring ERT datasets in rock glacier environments, and consequently a more representative way to confirm the reliability of the new electrodes.
In each test-site we performed both ERT and time-domain IP measurements. However, the IP data error (considering reciprocal errors and fitting of the curve relaxation) was too large with both the electrode types, and hindered a relevant and significant IP analysis, in our opinion.
The Syscal acquisition parameters were configured for the IP to the best of our knowledge, with a 2-second injection-measurement period and 20 custom sampling intervals increasing from 20 ms to 200 ms. A specific dipole-dipole sequence was used to avoid the use of polarized electrodes as potential electrodes. A 10-minute break between direct and reciprocal measurements was allowed to provide sufficient time for the depolarization of the electrodes. Hence, our understanding is that the very high IP errors were related to the arrangement of the ERT cables. In fact, multicore cables were used without separating current and potential arrays, as extensively discussed by Maierhofer et al., (2022). The IP errors we estimated are in line with this study (see for example the number of discharged measurements in their figure 2), confirming that IP surveys in such rocky and challenging environments likely require separating current and potential cables. Note that, in our study, the choice of not separating the cables reflected the focus on ERT data quality and kept our tests comparable with the vast majority of similar studies and applications.
As an example, from the Marocche test site, the following figure (see attached pdf) summarizes the IP error analysis. The figure shows how both spike and net electrodes have extremely high reciprocal errors for the chargeability (y axis), also relative to the resistance reciprocal errors (x axis). The scattering highlights how resistance and IP errors are not correlated. The colours represent the error estimated from the fitting of the IP decay curve analysis, following the algorithm suggested by Orozco et al., (2018), which is also not clearly related to the reciprocal errors in this case. We also tried to ignore early and late decay curve samples, but this did not have significant effects.
In conclusion, our understanding is that these IP errors are 1) too large to support a relevant IP analysis, 2) very complex, with no clear relationships between the resistance and IP reciprocal errors, nor between decay curve analysis and reciprocal errors, nor between spike and net electrodes; and 3) in line with previous studies using non-separated cables in such environments, which also limits the possible novelty.
Therefore, as the Reviewer can clearly understand, we decided to not insert the comparison between the collected IP measurements, but we will run new tests in future using different cables for injecting electrodes and potential electrodes, to improve the quality of the IP measurements.Regarding the oxidation problem of the textile electrodes, we agree that it could be measured using a time-lapse configuration, but only with very long-time monitoring. We doubt in fact that we could verify a performance drop using hourly measurements, given that we have used them with excellent results in several campaigns during the 2023 summer season. The degradation process is much slower, becoming apparent after several weeks of continuous use of the textile electrodes. Anyway, the aim of this work was not to verify the 'lifetime' of textile electrodes, but rather to propose a new type of electrode that does not oxidise.
Taking all this into account, while we respect the opinion of the anonymous Reviewer but we believe that this BRIEF communication explores significant advantages for permafrost ERT community, since the proposed steel-net electrodes represent a clear cheap and effective improvement.
The reply to the specific comments are in the attached pdf.
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AC3: 'Reply on AC1', Mirko Pavoni, 14 Jun 2025
Following Reviewer #2’s suggestion, we believe it would be valuable to include in the submitted Brief Communication some results demonstrating the high mechanical resistance and oxidation resistance of the net electrodes, and thus the long-term reliability of their performance. In June 2024, a permanent ERT monitoring line was installed on the Sadole rock glacier using 48 net electrodes (the first 24 electrodes correspond to those used in the test presented in this study). Over the past year, several datasets have been acquired to investigate the seasonal variations of permafrost in this study area. Therefore, Figure 2 of the manuscript can be updated to include a comparison of contact resistances, injected electrical currents, and reciprocal error from the datasets acquired in June 2024 and June 2025. As shown in panels (j), (k), and (l), after one year, the performance remained essentially unchanged, despite the electrodes having remained in situ. Achieving the same result would not have been possible with textile electrodes (Buckel et al., 2023), as oxidation issues would have inevitably compromised data acquisition. Therefore, similar to traditional stainless-steel spikes, net electrodes can also be employed in permanent ERT monitoring lines on rock glaciers.
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AC3: 'Reply on AC1', Mirko Pavoni, 14 Jun 2025
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AC1: 'Reply on RC1', Mirko Pavoni, 23 May 2025
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RC2: 'Comment on egusphere-2025-405', Anonymous Referee #2, 26 May 2025
The manuscript describes and evaluates the performance of a modified electrode design that aims to optimize the process of acquiring resistivity measurements in blocky, rocky terrain. The manuscript, submitted in the form of a brief communication, focuses on i) describing the construction and practical advantages of the modified electrode design, and on ii) confirming the reliability of the proposed electrode design in comparison to more established electrode types (stainless steel spikes).
The principle of the proposed electrode design - sachets made of a conductive material filled with a porous matter that holds moisture and allows the sachet to mould to its surroundings - was, as the authors state, inspired by a cited study (Buckel et al. (2023)). The modifications in the present manuscript propose replacing the conductive textile with more robust and cheaper stainless-steel nets, and the fill of fine sand with lighter carwash sponges. These modifications resulted in three main improvements: the proposed stainless steel mesh electrodes are reported to be cheaper, lighter and more durable than the conductive textile electrodes proposed by Buckel et al. (2023) - all being important considerations when preparing for a resistivity survey.
The manuscript delivers on its two main objectives: in terms of description of the proposed electrode design, it is well described and its practical advantages are clearly stated. In terms of evaluating the performance and reliability of the proposed electrodes, the manuscript reports on a number of well-presented and well-established, and thus easily inter-comparable metrics, including ‘contact’ resistances, reciprocal errors, and comparison of the apparent and inverted resistivities acquired with the proposed electrodes vs. well-established steel spike electrodes. These tests show that the proposed electrodes yield results equivalent to those achieved with spike electrodes in terms of the quality of the measured resistivity datasets. The proposed electrodes do not appear to significantly and consistently improve the electrode ‘contact’ resistances (which was, however, not stated among the goals of the experiment).
I commend the authors for pursuing practical improvements to electrode design, especially for ever-challenging mountain environments, as well as for carefully evaluating the performance of the new electrode design prior to basing any interpretations on it. As the focus of the manuscript is practical innovation, I would suggest exploring opportunities to compensate for the somewhat limited novelty (the key design principles are largely inspired by a previously published study) and increase the impact (the electrodes’ grounding qualities match though do not significantly outperform the more established electrode types) of the experiment by expanding the types of applications for which the proposed electrodes are validated. In this context, and especially as the brief communication was submitted for a special issue on 'Emerging geophysical methods for permafrost investigations: recent advances in permafrost detecting, characterizing, and monitoring' it would be relevant to quantify the performance of the proposed electrodes in repeated measurements. This could be as simple as measuring the same profile with the proposed electrodes at the same location right after installation (wetted with saline solution, ideal conditions), after drying out (poor measurement conditions), and after re-wetting naturally e.g. by a rain event (good though less-than-ideal conditions as salts may be progressively washed out of the sponges). I reckon a summary of such an experiment would be relevant for the target audience of the special issue, and could be reported in one paragraph.
Line 81: What is the protocol for measuring the ‘contact’ resistances by Syscal-Pro? (type of the electrode test)
I would suggest the authors to consider the advantages of using the term 'grounding resistance' instead of 'contact resistance'. Use of 'grounding' resistance communicates that what’s measured during the electrode test is not only the resistance at the contact between the electrode and the embedding medium, but also the effect of geometry of the electrode and properties of the embedding medium, including any alteration zone in the immediate vicinity of the electrode (the saltwater soaked sponges).
Citation: https://doi.org/10.5194/egusphere-2025-405-RC2 -
AC2: 'Reply on RC2', Mirko Pavoni, 14 Jun 2025
We thank Reviewer #2 for reviewing our manuscript and providing valuable suggestions to improve the quality of our manuscript. The reviewer clearly understood our aims and intentions, and we are aligned with the critical comments raised by the reviewer.
1. Reviewer #2: The manuscript describes and evaluates the performance of a modified electrode design that aims to optimize the process of acquiring resistivity measurements in blocky, rocky terrain. The manuscript, submitted in the form of a brief communication, focuses on i) describing the construction and practical advantages of the modified electrode design, and on ii) confirming the reliability of the proposed electrode design in comparison to more established electrode types (stainless steel spikes).
Authors' reply: The reviewer has clearly grasped the aim of the submitted Brief Communication, which is to propose novel electrodes that facilitate and optimize ERT measurements in high-mountain environments with debris-block surfaces, compared to traditional steel rods and textile bags (Buckel et al., 2023).2. Reviewer #2: The principle of the proposed electrode design - sachets made of a conductive material filled with a porous matter that holds moisture and allows the sachet to mould to its surroundings - was, as the authors state, inspired by a cited study (Buckel et al. (2023)). The modifications in the present manuscript propose replacing the conductive textile with more robust and cheaper stainless-steel nets, and the fill of fine sand with lighter carwash sponges. These modifications resulted in three main improvements: the proposed stainless steel mesh electrodes are reported to be cheaper, lighter and more durable than the conductive textile electrodes proposed by Buckel et al. (2023) - all being important considerations when preparing for a resistivity survey.
Authors’ reply: Our proposed steel net electrodes provide all the advantages of the textile electrodes introduced by Buckel et al. (2023), whilst addressing the limitations highlighted in the comparative tests presented by Bast et al. (2024), namely the high costs of the conductive fabric, the issue of oxidation affecting the copper-nickel textile, and the considerable weight of the bags (250–300 g each, comparable to traditional steel rods). The new electrodes are made from inexpensive stainless-steel mesh, which reduces production costs and eliminates oxidation concerns. Furthermore, their weight is significantly lower (approximately 50 g each; 50 electrodes = 2.5 kg), making them much easier to transport, for example, in a medium-sized mountain backpack, with substantially less physical effort. In our opinion, this represents a major advantage for researchers conducting ERT measurements in challenging and remote environments such as rock glaciers.3. Reviewer #2: The manuscript delivers on its two main objectives: in terms of description of the proposed electrode design, it is well described and its practical advantages are clearly stated. In terms of evaluating the performance and reliability of the proposed electrodes, the manuscript reports on a number of well-presented and well-established, and thus easily inter-comparable metrics, including ‘contact’ resistances, reciprocal errors, and comparison of the apparent and inverted resistivities acquired with the proposed electrodes vs. well-established steel spike electrodes. These tests show that the proposed electrodes yield results equivalent to those achieved with spike electrodes in terms of the quality of the measured resistivity datasets. The proposed electrodes do not appear to significantly and consistently improve the electrode ‘contact’ resistances (which was, however, not stated among the goals of the experiment).
Authors’ Reply: As correctly noted, the aim of this work is not to propose new electrodes that improve contact resistance, an inherently challenging parameter in such study environments, but rather to provide a cost-effective and durable alternative to the recently introduced textile electrodes by Buckel et al. (2023). Through our tests and comparison of key parameters in ERT acquisition (contact resistance, injected current, measured apparent resistivity, data quality assessed via reciprocal error, and the inverted resistivity models), we have demonstrated the reliability of net electrodes for surveys in debris-block surface environments such as rock glaciers. Net electrodes combine the advantages of both traditional steel rods and textile electrodes: they allow for quick and easy installation and removal of ERT transects in blocky terrains (as textile electrodes do), while also offering high mechanical strength, resistance to oxidation, and relatively low cost. Moreover, net electrodes present a significant additional advantage over both traditional and textile electrodes: their remarkably low weight. As previously highlighted, each net electrode weighs only 50 g, significantly reducing the physical effort required to transport them in challenging high-mountain environments.4. Reviewer #2: I commend the authors for pursuing practical improvements to electrode design, especially for ever-challenging mountain environments, as well as for carefully evaluating the performance of the new electrode design prior to basing any interpretations on it. As the focus of the manuscript is practical innovation, I would suggest exploring opportunities to compensate for the somewhat limited novelty (the key design principles are largely inspired by a previously published study) and increase the impact (the electrodes’ grounding qualities match though do not significantly outperform the more established electrode types) of the experiment by expanding the types of applications for which the proposed electrodes are validated. In this context, and especially as the brief communication was submitted for a special issue on 'Emerging geophysical methods for permafrost investigations: recent advances in permafrost detecting, characterizing, and monitoring' it would be relevant to quantify the performance of the proposed electrodes in repeated measurements. This could be as simple as measuring the same profile with the proposed electrodes at the same location right after installation (wetted with saline solution, ideal conditions), after drying out (poor measurement conditions), and after re-wetting naturally e.g. by a rain event (good though less-than-ideal conditions as salts may be progressively washed out of the sponges). I reckon a summary of such an experiment would be relevant for the target audience of the special issue, and could be reported in one paragraph.
Authors’ reply: We have already published a study in which we explored the effect of performing ERT measurements in debris-block surface environments, both with and without wetting the electrodes with saltwater (Pavoni et al., 2022). In that work, we clearly showed that conducting measurements without adding saltwater results in extremely high contact resistance values (several hundred kOhm), which clearly prevent the acquisition of reliable ERT datasets (Pavoni et al., 2022; data quality was assessed through reciprocal error). Furthermore, in Bast et al. (2024), we investigated the effect of using freshwater instead of saltwater for wetting the electrodes. In that study, the site where both traditional and textile electrodes were wetted with freshwater showed significantly higher contact resistance values compared to the two test sites where saltwater was used.
In accordance with Reviewer #2’s suggestion, we believe it would be valuable to include in the submitted Brief Communication some results demonstrating the high mechanical resistance and oxidation resistance of the net electrodes, and thus the long-term reliability of their performance. In June 2024, a permanent ERT monitoring line was installed on the Sadole rock glacier (North Italy) using 48 net electrodes (the first 24 electrodes correspond to those used in the test presented in this study). Over the past year, several datasets have been acquired to investigate the seasonal variations of permafrost in this study area. Figure 2 of the manuscript can be updated to include a comparison of contact resistances, injected electrical currents, and reciprocal error from the datasets acquired in June 2024 and June 2025 (refer to the attached PDF). As shown in panels (j), (k), and (l), after one year, the performance remained essentially unchanged, despite the electrodes having remained in situ. Achieving the same result would not have been possible with textile electrodes (Buckel et al., 2023), as oxidation issues would have inevitably compromised data acquisition. Therefore, we demonstrated that, similar to traditional stainless-steel spikes, net electrodes can also be employed in permanent ERT monitoring lines on rock glaciers.5. Reviewer #2: Line 81: What is the protocol for measuring the ‘contact’ resistances by Syscal-Pro? (type of the electrode test).
Authors’ reply: We agree, and we will provide a more detailed description of the procedure used by the Syscal Pro instrument to measure contact resistance in the modified manuscript.6. Reviewer #2: I would suggest the authors to consider the advantages of using the term 'grounding resistance' instead of 'contact resistance'. Use of 'grounding' resistance communicates that what’s measured during the electrode test is not only the resistance at the contact between the electrode and the embedding medium, but also the effect of geometry of the electrode and properties of the embedding medium, including any alteration zone in the immediate vicinity of the electrode (the saltwater soaked sponges).
Authors reply: We agree, and we will replace the term contact resistance with grounding resistance in the revised manuscript.
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AC2: 'Reply on RC2', Mirko Pavoni, 14 Jun 2025
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