A Compact Muon Tracker for Dynamic Tomography of Density Based on a Thin Time Projection Chamber with Micromegas Readout

Round 1

Reviewer 1 Report

This contribution is a kind of review of investigation that author presented recently at conferences (AGU Meeting, ect.) and papers (Ref. [15] J. Phys. Conf. Ser. 2019 …).  The paper details the design of such a TPC aiming at maximizing primary signal and minimizing track reconstruction artifacts. The results are important and needed for cosmic ray investigation, transdisciplinary research, geophysics, instrumentation, etc.

The paper is between review and report. It could have been longer and more informative. But even in this form it is acceptable. Only a few minor technical issues need to be fixed.

In the authors affiliation: No need for superscript in author affiliation. There is just one institution and author.

Text on axis and legends for almost all figures (Figs 2, 3, 4) need to be enlarged. Please correct if possible.

Line 116: “…(0,107mm/ns for …600V/cm…)” => “…(0,107 mm/ns for …600 V/cm…)”

-The sections: Author Contributions, Funding, Conflicts of Interest, are missing.

Maybe to write additional few words in “Sec. 4 Discussion: application and perspectives” about: improve angular resolution, also about transdisciplinary research i.e. possibility of combining Muography with classical geophysical techniques, etc. Additional discussion of the research would be helpful.

It would be good to expand the literature.

In refs. [7, 9, 12, 14, 18] author should provide the full list of the authors i.e.

“Giomataris, I. et al.,…” => “Giomataris, I., De Oliveira, R., Andriamonje, S., Aune, S., Charpak, G., Colas, P,…..”

If a source has more than 10 authors, list the first ten followed by “et al.”

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript describes the design of a compact muon tracker, based on a time projection chamber with a Micromegas readout plane, for muography applications. In particular, the imaging of a water reservoir is presented as case study. The paper is quite interesting and well written, but I believe it requires a major revision before publication. In the following I listed the points which need to be addressed, divided into three categories: major issues, minor issues and language and style. 

MAJOR ISSUES:

• It is not clear the novelty of this work with respect to previous publications as, for example, the exact same experimental results (section 3 of this work) were already published in 2019, by the same author, in the following conference proceeding: https://doi.org/10.1051/e3sconf/20198801003 and I did not find, here, any novelty or refinement with respect to that previous work. 
   
• I have a major concern about plot 5 and its interpretation. The author wants to investigate the water monitoring capabilities of the technique, by comparing the time evolution of the water level in the dam and the measured muon flux. Muon flux depends on several meteorological effects: barometric effect, temperature effect, humidity effect, and others (see Dorman). Specially the the barometric and temperature effects play a very important role in the variation of the muon flux and, apparently, data in figure 5 are not corrected for pressure and temperature. So, in short, meteorological effects on data are not properly assessed. Nevertheless, the author states that "it is possible to appreciate that the emptying trend of the dam is translated into a statistically significant augmentation of the muon flux [19]". This "statistically significant augmentation of the muon flux" is not clarified in the text, but sends the reader to a conference proceeding where the author used the p-value of a t-test between the first 45 h and second 45 h of data, to support this claim. This is not statically sound, and this is not the way we check the stationarity of a time series. A KPSS test seems more appropriate in this case, but, still, even if the null hypothesis is rejected, the correlation with the water level in the dam does not come as a consequence. For these reasons section 3.2 should be revised.

MINOR ISSUES:

• The paper is proposed as "Review article", while it should be "Article"
   
• A comment about the term "muography", whose use is not coherent across the paper. At line 69 the author refers to "scattering and transmission muography", so using the term muography to collectively name all imaging methods based on absorption or scattering, as some authors do (this is fine, though many others use the term to indicate muon radiography only). At line 46, though, we find "Muon tomography (or muography)..." as if muography were referred to muon tomography only. This should be fixed.
   
• Line 55: "Scattering is particularly useful to discriminate between materials of high, medium, and low atomic number in objects with a typical size of a few meters". This sentence sounds a bit reductive to me, as scattering tomography has also been applied to large structures, like blast furnaces, and many applications reached a performance well above the simple discrimination between high, medium and low atomic number objects (see https://www.sciencedirect.com/science/article/pii/S0146641020300156 for example). I suggest to rephrase.
   
• Line 197: "A good correlation between the image of measured muon flux and the apparent opacity simulation of the target volume due to the structures behind the dam is observed.". Here I suggest to elaborate a bit more as this "good correlation" is not that glaring and having produced figures 4c and 4d with different ranges on the zenith angle (and aspect ratios) does not help.
   
• Line 211: "The muon flux increase is consistent with the loss of opacity of the target volume, as seen in Figure 5b." How figure 5b has been produced? How is it "consistent" with the muon flux? The only text related to figure 5b is in the caption...
   
• References: the list of references is not very rich (and tidy) and has a quite high (self-citations) / (total citations) ratio, which does not seem to be very justified

LANGUAGE AND STYLE:

• Title: please remove the point at the end
• Please consider to use a proper math font for the equation 1 (and also in the text when referring to the variables in that equation)
• Line 125: 675ns --> 675 ns 
• Line 126: 427,85±78,22 ns --> 428 ± 78 ns
• Line 178: its height --> whose height 
• Line 182: please write formulas in a proper math environment and check the "deg" symbol
• Line 189: ~90h --> ~90 h
• Line 189: image to for --> image for
• Line 194: see comment at line 182 
• Line 202: Figure 5 --> Figure 5a
• Line 206: figure --> Figure (as in the rest of the paper)
   
   
   
    

Author Response

Please see the attachment

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The author provided a new version, which addresses most of the issues were reported previously.  The author improved the data analysis, by using a more reasonable test for stationarity of the time series, and softened the claim about the correlation between the variation of the water level and the flux of detected muons.

The original contribution of this article, with respect to previous publications, is still not very substantial, however, because of the new parts on the TPC and the changes to the analysis of data I believe this manuscript could be published, after few other fixes detailed below.

MAJOR:

• review article

Here I believe there is a misunderstanding of what review articles are meant for. The quoted sentence by the author, that is, they should provide "the latest progress made in a given area of research" means that a review article should inform about the latest major results from all people working in that area, and not just about the latest activities of the author. This manuscript cannot be considered as a review article and should be proposed as an article.

• figures 2

They are stretched and low quality. Axes labels are too small in all figures. If I compare (c) and (d), I clearly see that (c) is  stretched. Voltage scale is unreadable. This should be fixed. If space is a problem, the author could consider to remove some of those figures, for example (e) and (f), and make more room for the others. 

MINOR:

• figures 3

I would make (b) bigger, trying to match the height of (a), and I would consider to remove (c). 

• figures 4

It is very pity that (c) and (d) have a different styles and aspect ratio. Those are very important images for the present work. I would strongly consider to use a common style for both. I would also consider to keep (c) and (d) separated from (a) and (b), by creating a new figure for them.

• equation 1

Equation 1 has been written in a math environment, but its variables are still written as plain text when recalled in the text. For example:

• • primary ionization (N_T) 
  • signal strength (S)
  • R represents
  • A stands
  • and so on...

Author Response

Dear reviewer, thanks your your quick and detailed answer.

Please, find my answers next to your comments:

MAJOR:

• review article

Here I believe there is a misunderstanding of what review articles are meant for. The quoted sentence by the author, that is, they should provide "the latest progress made in a given area of research" means that a review article should inform about the latest major results from all people working in that area, and not just about the latest activities of the author. This manuscript cannot be considered as a review article and should be proposed as an article.

I have changed the contribution type to Article as explained.

• figures 2

They are stretched and low quality. Axes labels are too small in all figures. If I compare (c) and (d), I clearly see that (c) is  stretched. Voltage scale is unreadable. This should be fixed. If space is a problem, the author could consider to remove some of those figures, for example (e) and (f), and make more room for the others. 

The axis and labels of the figures a,b,c &d have been redone to ensure readability. The relative aspect ratio between similar figures is conserved.

MINOR:

• figures 3

I would make (b) bigger, trying to match the height of (a), and I would consider to remove (c). 

Done. The text relative to subfire C has been rephrased for consistency.

• figures 4

It is very pity that (c) and (d) have a different styles and aspect ratio. Those are very important images for the present work. I would strongly consider to use a common style for both. I would also consider to keep (c) and (d) separated from (a) and (b), by creating a new figure for them.

I have split the figures as proposed, unfortunately remaking the figure d  (renamed as 5b) would be too time consuming and non-viable given the delay and my current workload. I'd like to stress that horizontal axis are the same and in the past I've superimposed the two figures with same scales to see the structures alignement, but the figure is even harder to interpret without playing with the transparency (see picture from dropbox). https://www.dropbox.com/s/nwndkio6ib3qr37/Captura%20de%20pantalla%202021-06-21%20a%20las%2011.07.56.png?dl=0

• equation 1

Equation 1 has been written in a math environment, but its variables are still written as plain text when recalled in the text. For example:

• • primary ionization (N_T) 
  • signal strength (S)
  • R represents
  • A stands
  • and so on...

Text replaced for equation-like content