Geophysical Investigation of the Neolithic Calanais Landscape

Round 1

Reviewer 1 Report

This study confirms the well-accepted point that multi-instrument/technique remote sensing approaches are a productive means to understand challenging or poorly understood contexts. In particular, the authors have demonstrated the efficacy of a suite of techniques that will be productive in future investigations in this study area. I recommend acceptance with minor revisions suggested.

First, there are several places throughout the text where the authors should pay attention to readability. Complex and awkward sentence structures should be reworked for clarity, especially in sections 1, 2, 3, and 9.

Second, there are a couple issues in the presentation of the figures. In Figure 1, I would suggest highlighting the specific site featured in the article. Perhaps another color, size, or shape of the point for site XI could be used. In Figure 2, I believe the standing stone is incorrectly marked on the figure and this should be checked and potentially corrected.

Author Response

This study confirms the well-accepted point that multi-instrument/technique remote sensing approaches are a productive means to understand challenging or poorly understood contexts. In particular, the authors have demonstrated the efficacy of a suite of techniques that will be productive in future investigations in this study area. I recommend acceptance with minor revisions suggested.

 

First, there are several places throughout the text where the authors should pay attention to readability. Complex and awkward sentence structures should be reworked for clarity, especially in sections 1, 2, 3, and 9.

 

Rewording has been made for greater clarification

 

Second, there are a couple issues in the presentation of the figures. In Figure 1, I would suggest highlighting the specific site featured in the article. Perhaps another color, size, or shape of the point for site XI could be used. In Figure 2, I believe the standing stone is incorrectly marked on the figure and this should be checked and potentially corrected.

 

Figures re-drawn/Added to

Reviewer 2 Report

An interesting investigation into a landscape that, as the authors state, receives far less interest than the Northern Isles, and which will definitely benefit from more research of the type described here.

Strengths

The major strengths of the paper is the bathymetric remote sensing, and associated core analysis to ground-truth the results. This reviewer is not an expert in this type of remote sensing survey, but there are no obvious flaws, and this element of the study provides very interesting insights - even to the non-specialist.

Potential Improvements

There are minor typos throughout the document. Figure 1 is somewhat unclear as the caption refers to a 1b, which is either unlabelled or not present in the version of the paper I received for review. Figure 3 - the legend showing the conductivity values and colour ramp need to be much larger as they are illegible at A4 scale when printed. There is an overall lack of justification for the geophysical survey methodologies employed when one starts to consider the specifics. On page 6 discussing the design of the conductivity survey, the spatial resolution is actually 3m x 0.3m, but the potential impacts on the quality of the data, or the utility of the results is not discussed - this is particularly relevant given the fact that the survey aims to detect buried stone anomalies or stone sockets. I am not disputing the value of multi-modal survey or of undertaking the conductivity survey, but the potential effects of survey design do need evaluating in this paper. There is no display or discussion of the earth resistance results. If these were unsuccessful we need to see why, or if useful they need to be displayed and interpreted. What was the justification of a nominal depth of investigation of only 12cm - what is the likely depth of the peat? The magnetic gradiometer survey clearly provides the most fine-grained results of all the techniques, and correspondingly have the most value in the discussion section of the paper. These results do need displaying much more effectively though. Most at issue is the dipole anomalies that are described as being associated with the single extant standing stone. However, the reader cannot see the dipole associated with this stone properly because of the red dot marking its position, thus one cannot evaluate it in comparison with other anomalies. Furthermore, because the other 13 dipole anomalies are not indicated on figure 5, the reader has no means of identifying where they are on the plan, thus no means of interrogating the results or assessing the interpretation in a meaningful way. I can only identify 9, but crucially I don't know if I am looking at the right things because they are not marked. To a non-specialist in geophysics this would be even more problematic. Finally, I am not convinced that strong dipolar anomalies actually are indicative of fallen stones or stone sockets - strong dipoles are very often the result of iron-spikes in the overburden. To make this assertion, the authors need to provide references of other stone circle surveys where dipolar anomalies have been  revealed as such - otherwise the case is very weak, particularly when the circular arrangement of these anomalies is not presented i figure 5. I am unsure whether the results from the various modes of geophysical survey actually support the conclusions. Given the problems of point [6] above, I do not think it can be confidently asserted that there is definitely a stone circle present (not to say there isn't, but the method of presenting the results is problematic). Furthermore, the association of a stone circle as memorialising a lightning strike is enormously problematic. A) there is no chronological control indicating even vague contemporaenity, B) there is no actual necessity for there to have been a tree or stone as a target for such a strike - lightning can strike bare ground, C) there is no definitive evidence presented of a stone circle (at least in the current form of the paper).

Concluding Remarks

In summary, there are elements of this paper that deserve to be published unchanged. The bathymetric survey is appropriately ground-truthed and clearly represents an important contribution to knowledge (though note my limited experience in this area). The land-based geophysics though cannot be published in the present form, as the experimental design, its justification, the results, and the interpretation are not discussed in enough detail or appropriately substantiated.

Fundamentally, the most interesting thing may be that the paper demonstrates the problems of most geophysical survey methods over blanket peat - I fundamentally believe the negative results are just as important and worthy of publication as positive ones, as they inform future study. This paper could make a valuable contribution to the corpus if this was discussed in more detail, and the survey results explored from this angle. Indeed, perhaps marine survey is more useful in these landscapes.

Author Response

There are minor typos throughout the document.

 

Figure 1 is somewhat unclear as the caption refers to a 1b, which is either unlabelled or not present in the version of the paper I received for review. ]

 

 

New figure produced

 

 

Figure 3 - the legend showing the conductivity values and colour ramp need to be much larger as they are illegible at A4 scale when printed.

 

New figure produced and figures moved to supplementary information

 

There is an overall lack of justification for the geophysical survey methodologies employed when one starts to consider the specifics.

The techniques are in fact justified and mapped to specific objectives in the text and with table 1.  I believe that this was missing in the original manuscript.

 

On page 6 discussing the design of the conductivity survey, the spatial resolution is actually 3m x 0.3m, but the potential impacts on the quality of the data, or the utility of the results is not discussed - this is particularly relevant given the fact that the survey aims to detect buried stone anomalies or stone sockets. I am not disputing the value of multi-modal survey or of undertaking the conductivity survey, but the potential effects of survey design do need evaluating in this paper.

 

Actually the 3m spacing was only for the Explorer.  For the mini-explorer we used a spacing of less than 1m.  This was stated in the original text but has now also been made clearer.

 

There is no display or discussion of the earth resistance results. If these were unsuccessful we need to see why, or if useful they need to be displayed and interpreted. What was the justification of a nominal depth of investigation of only 12cm - what is the likely depth of the peat?

 

New figure added to show data and further discussed in text

 

The magnetic gradiometer survey clearly provides the most fine-grained results of all the techniques, and correspondingly have the most value in the discussion section of the paper. These results do need displaying much more effectively though. Most at issue is the dipole anomalies that are described as being associated with the single extant standing stone. However, the reader cannot see the dipole associated with this stone properly because of the red dot marking its position, thus one cannot evaluate it in comparison with other anomalies.

 

Red dot removed so that this can be now seen for comparison and the other anomalies are highlighted

 

Furthermore, because the other 13 dipole anomalies are not indicated on figure 5, the reader has no means of identifying where they are on the plan, thus no means of interrogating the results or assessing the interpretation in a meaningful way. I can only identify 9, but crucially I don't know if I am looking at the right things because they are not marked. To a non-specialist in geophysics this would be even more problematic.

 

Dealt with on a new combined figure

 

 Finally, I am not convinced that strong dipolar anomalies actually are indicative of fallen stones or stone sockets - strong dipoles are very often the result of iron-spikes in the overburden. To make this assertion, the authors need to provide references of other stone circle surveys where dipolar anomalies have been  revealed as such - otherwise the case is very weak, particularly when the circular arrangement of these anomalies is not presented i figure 5. I am unsure whether the results from the various modes of geophysical survey actually support the conclusions. Given the problems of point [6] above, I do not think it can be confidently asserted that there is definitely a stone circle present (not to say there isn't, but the method of presenting the results is problematic).

Issues dealt with by addition of figure.  Further a reference is now provided to substantiate the interpretation and a discussion follows to further justify the claims

 

Furthermore, the association of a stone circle as memorialising a lightning strike is enormously problematic. A) there is no chronological control indicating even vague contemporaenity, B) there is no actual necessity for there to have been a tree or stone as a target for such a strike - lightning can strike bare ground, C) there is no definitive evidence presented of a stone circle (at least in the current form of the paper).

A) We have made specific and explicit reference to the chronological control as far as can be done due to the nature of the lightning strikes and how they physically work. B)again , the physics of lightning strikes as we state makes it more likely that there were some upstanding object. however, we acknowledge that this might not of been the case in which case it makes the feature of even greater interest; C)we have used the figures to show our interpretation of results that we make for the presence of buried features that could be related to a stone circle. The only definitive way of proving this would be to excavate but this was not part of the remote sensing, geophysical exercise. With the correct permissions this might be something that would happen in the future based on this survey results.

Round 2

Reviewer 2 Report

Many thanks to the authors for their clear comments on my initial review, and the new figures they have provided. This is a marked improvement, and resolves my queries/suggestions. I think it should be published in its present form.