Integration of Remote-Sensing Techniques for the Preventive Conservation of Paleolithic Cave Art in the Karst of the Altamira Cave

Round 1

Reviewer 1 Report

The paper presents a very interesting study involving the integration of  Geomatics remote sensing technologies (TLS and UAV photogrammetry) and Ground Penetrating Radar (GPR) applied to the Altamira Cave, a masterpiece recognized by UNESCO for the presence of prehistoric paintings, and subject to conservation issues.

Surely the integration of methods from different disciplines constitutes, in recent years, a significant and effective approach to the study of Heritage, so the topic is certainly of great interest.

Despite this, I believe that the paper has some shortcomings that, if they were filled, the paper could certainly be more suitable for publication in the journal Remote Sensing. These are some formal aspects of secondary importance, but others concern the methodological approach adopted by the authors, which in some sections has omitted a lot of information. (it is also partly true that the research has already been published in a conference proceeding (Spanish) and another journal (ref 15 and 17), but in my opinion, to be published, the paper needs the support of further information and considerations or comments not present now. I provide a list:

 

-        Introduction: the paper, in general, is rich in bibliographic references concerning geophysical investigations and, in particular, the GPR technique. The same cannot be said for the bibliographic references concerning geomatic techniques. In particular, at the beginning of the introduction, it is reported that these techniques have a high impact on improving the documentation derived from traditional techniques, and 9 bibliographic references of one or more authors of the paper are reported. This is considered not really appropriate, it is advisable to extend the bibliographic references on Geomatics techniques to other researches and authors in the international sphere.

-        Figure 1: I think one picture of Spain is enough.. (also because there are the same)

-        Figure 2 and all other maps (figures 11, 13, 14.. ): I suggest adding grids

-        The scheme of Figure 3 is not described.. but I don’t know if it is expected to communicate more than each technique foresees georeferenced data acquisition.

-        Paragraph 2.1.  The information provided in this paragraph is very poor.. (also considering that the paper’ goal is the integration of different techniques, based on georeferencing.. I know the authors cited a previously published work.. but I think some basic information about the approach, methods, and results in terms of data accuracy has to be provided (also because later, one important chance is the overlap between internal and external surface)

-        Paragraph 2.2: also this paragraph is very poor of information. (the same as the previous paragraph: even if authors published before (n. 17), this paper has to be well-founded over a rigorous and well-described approach or strategy. (accuracy of the traverses’ coordinates, the accuracy of the control points, which kind of alignment strategy for the LiDAR clouds has been used etc… final RMSE of the overall cloud etc.

-        Line 133: I don’t know what is the meaning of rigid solid transformations, In literature is well known the meaning of rigid transformation.. Can be explained, please?

-        Line 144: “high reliability in a shorter time” is not the only difference in using UAV photogrammetry in comparison with other techniques such as TTS or GNSS

-        Line 150 GSD has to be decodified

-        Line 152: UAV photogrammetry provides DSM (digital surface model), not DEM or DTM.

-        Line 154 what do the authors means for triangles of the mesh “textured with 8 textures of 8192x8192 pixels”.. the ortho-projection involve very many oriented images. Please, also here, can the authors declare the number of images, the accuracy of the bundle adjustment obtained, the use of makers, or another strategy? etc.?

-        Line 156: Do the authors intend to say they generated a multiscale model?

-        Line 171: please check the number of references

-        Line 183: Can the authors motivate better the choice of the grid spacing in relation to the antenna frequency and the expected size of the discontinuities and fractures, please?

-        Line 202, the same as line 183.

-        Line 229: here It’s not clear to me, sorry. If the authors say the GPR data acquisition was acquired during a week, in which way they decided the areas of deepening the investigation using different frequency antennas and a lower grid spacing?  Maybe using the underground LiDAR model?

-        Line 266: the authors say “the UAV terrain model was integrated with the 3DTLS model of the cave”, we know thanks to the georeferencing.. but they don’t say. (they neither say the final accuracy of this integration)

-        In 3.1 paragraph, there two figure 10

-        3.3 the title of the paragraph is Integration UAV-3DTLS-GPR but we saw in the previous pages so many overlapped maps of data derived from the different techniques. In this paragraph, in my opinion, an attempt at an integrated 3D visualization is presented.

-        Figure 17.19, the figures are so difficult to understand.. (we know that a video is helping). I think that the researchers from the international community have to improve the ability to represent such related surfaces. The authors can add some opinion about that?

-        Line 445. The authors say “Accurate geo-referencing is key for integrating remote sensing techniques in order to derive useful information of the cultural heritage,”.. I agree so much so why they didn’t describe anything about that? (see above the request to integrate the paragraphs concerning geomatic techniques.)

Author Response

Dear Reviewer 1,

Thank you very much for all your comments. They have been helpful and sometimes inspiring and have let us reflect on and improve the article. Thank you very much!

Please find attached the response to your comments.

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper presents an interesting research, and the results shown are of impact and can expand the scientific debate on the topic.

However, the paper lacks of correct development in the initial part, and few suggestions are listed below to adequate it to the expected scietinfic level of the journal.

The Introduction needs to be extended, clearly focusing the research statement of the paper and introducing the structure of the following sections. The description of the case study can be defined in a separated sub-paragraph. In the same way, references have to be extended in the introduction, providing a more complete state of the art regarding the field of application of the research.

In section 2. Materials and Methods, a critical consideration on the integration of different data is missing. "They are irregular in shape and variable in extent, so it is necessary to integrate different georeferenced remote sensing techniques to derive new cartographies and generate new information of the cultural heritage element" is not a sufficient statement to support the following workflow of documentation.

Author Response

Dear Reviewer 2,

Thank you very much for all your comments. They have been very helpful and sometimes inspiring and have let us reflect on and improve the article. Thank you very much!

Please find attached the response to your comments.

Author Response File: Author Response.pdf

Reviewer 3 Report

With respect to the amplitude time slice visualisations of the  GPR data shown in Figures 13-16 a colour bar key is required to indicate the amplitude of the reflection anomalies. Each figure currently uses a different false colour mapping and I wonder whether a common greyscale mapping would be more useful for all the data sets (cf Figure 16).

For Figure 16 it was unclear whether the linear anomalies attributed to the lapies groove system might also be data collection artefacts as they appear to run parallel to the orthogonal data acquisition grid shown for the 900MHz survey in Figure 7. It would be useful to discuss how the anomalies can be confidently interpreted as geological in origin - perhaps overlay the grid from Figure 7 on the data shown in Figure 16 perhaps?

Author Response

Dear Reviewer 3,

Thank you very much for all your comments. They have been very helpful and sometimes inspiring and have let us reflect on and improve the article. Thank you very much!

Please find attached the response to your comments.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Dear Authors,

I would like to thank you very much; the paper has been highly integrated and improved. I have very few minor revisions to suggest:

- lines 155-167 refer to general information about GNSS, highly known by Remote Sensing journal readers. I suggest eliminating them.

- in line 201, about the linear traverse closure, the Z is equal to 0, maybe an automatic correction about the decimal position occurred.

- in lines 207 and 210, a sentence is repeated.

Congratulation on your interesting paper!

Author Response

Dear reviewer,

Thank you very much for all your previous and current comments.

- lines 155-167 refer to general information about GNSS, highly known by Remote Sensing journal readers. I suggest eliminating them.

Thank you very much for your suggestion. We have eliminated it.

- in line 201, about the linear traverse closure, the Z is equal to 0, maybe an automatic correction about the decimal position occurred.

Thank you very much for your comment. It is correct, the closure error was 0.

- in lines 207 and 210, a sentence is repeated.

Thank you for the observation. It has been solved.

Regards,