Mining Exploration with UAV, Low-Cost Thermal Cameras and GIS Tools—Application to the Specific Case of the Complex Sulfides Hosted in Carbonates of Udías (Cantabria, Spain)

Round 1

Reviewer 1 Report

The manuscript research aim is relevant, although the writing and structure must be strongly improved. The materials and methods is a mixture of the adopted methodologies, possible alternative solutions and problematics, leading to a very confusive section for the reader. The results section includes parts that belong to the methodology. (i.e: sensors specifications). The experimental results should be exposed better, providing clear representations of the analysis (i.e: provide a geological map of the area of interest as you present the study area). Discussion section has to be expanded and take into account the possible uncertainties deriving from the application of thermal sensors in heterogeneous landscapes. The manuscript conclusion is good. Overall, additional references should be included 

In my opinion, the methodology resulted successful in distinguishing limestone and dolostone thanks to the prior knowledge of the lithological contact position. The method could be efficient taking into account other variables as exposure, vegetation, aspect of the lithologies. 

Comments for author File: Comments.pdf

Author Response

“The manuscript research aim is relevant, although the writing and structure must be strongly improved. The materials and methods is a mixture of the adopted methodologies, possible alternative solutions and problematics, leading to a very confusive section for the reader. The results section includes parts that belong to the methodology. (i.e: sensors specifications). The experimental results should be exposed better, providing clear representations of the analysis (i.e: provide a geological map of the area of interest as you present the study area). Discussion section has to be expanded and take into account the possible uncertainties deriving from the application of thermal sensors in heterogeneous landscapes. The manuscript conclusion is good. Overall, additional references should be included

In my opinion, the methodology resulted successful in distinguishing limestone and dolostone thanks to the prior knowledge of the lithological contact position. The method could be efficient taking into account other variables as exposure, vegetation, aspect of the lithologies.”

Dear Reviewer,

First of all we would like thank your time and assessment. Your comments have been very useful to improve the comprehensibility of our work. In the following lines we provide a list of all the changes that we have made in the manuscript that are related to your suggestions.

“Page 3, Line 107. Suggest to divide the issues affecting each topic of paragraph 2.1 and 2.2”

Given that the length of these sections is not very extensive, we have considered that subdividing them into subsections could excessively compartmentalise the article. [Page 3, Line 109].

“Line 158: On what basis the 5 cm/px GSD is assessed? I would recommend to further expand this suggestion adding the specifications of the thermal sensor you used and thus adding value to your suggestion”

An explanation has been included in the manuscript. “Conventionally, current photogrammetric flights with UAVs using RGB sensors reach accuracies in the order of 1 or 2 cm. In the particular case of the use of thermal sensors, the intrinsic characteristics of the latter condition a worse resolution, so it is normal to obtain results with lower accuracies, which are associated with higher GSD values. For example, flying with a dual sensor such as the Zenmuse XT with an infrared resolution of 600x512 px for a focal length of 19 mm, at a flight altitude of 50 m, as proposed in this work, a GSD of 5 cm/px is obtained. However, the RGB sensor of the device reaches values of 1.3 cm/px for the same flight height.” [Page 4, Lines 163-171].

“Line 246-248: Have you taken in account how the different exposure of rock affects the thermal behaviour and therefore the temperature limit you are adopting?”

The exposure of the entire surface of the study area is not homogeneous, due to the height of the sun, the irregularity of the terrain or the vegetation. However, regardless of these factors, the second iteration of the transformation is performed to define the temperature based on the measurement of the surface temperature of the check points with the hand-held sensor. This provides a correction of the entire resulting orthomosaic or map.

“Line 262: Please adopt a different explanation more easy to follow”.

The explanation has been modified: “In this way, a new map will be obtained, through a reclassification operation that will re-assign a new value to the pixels of temperature lower than or equal to the limit. This value will be different to the one assigned to pixels whose temperature is higher” [Page 7,  Lines 278-283].

“Line 295-304: create a separate paragraph for study area”

A line break has been included to separate the explanation of the study area in a new paragraph. [Page 8, line 315].

“Section 3.1 should be included in materials and methods”.

A description of the methodological proposal was made in the section on Methodology and Materials. In the "Results" section, the results associated with the application of the methodology, of general character, to the particular case of the dolostone and limestones of Udías are included. For this reason, the structure has been maintained as it was initially conceived.

“Line 335-335: State at the beginning that the rock samples have been exposed to sunlight”

It is mentioned in page 8, line 338.

“Line 346 - 349: I would suggest to extrapolate this limitation to a new section titled boundary conditions, where also”

To avoid further compartmentalization, it has been decided to avoid the creation of a new subsection, but it has been included in a new paragraph [Page 9, Line 370].

“ Line 365: what is a medium sized platform?”

The reference to "middle size" has been eliminated. [Page 10, Line 389].

“Line 395: place an enter to separate the two sections”

It has been included [Page 12, Line 421]

“Line 407-408: Maybe with digital level you mean digital number?”

The sentence has been rephrased: “. Having made a projection of the thermographic information on the RGB model, both of them are geometrically the same, except that in the case of the RGB one for every point the value of the RGB band of each colour is obtained, while for the thermal model the value is correlated with the temperature de-termined for each point from the thermal images.”

“Line 425-426: simplify, declare immediately the reason why you acquired the thermal images”

The sentence has been modified: “These images were obtained to verify the measurements made by the airborne sensor.” [Page 12, Lines 453-454].

“Line 436- 438: what do you base yourself on to make this statement? I'd suggest to support this affirmation with either the data for both lithologies acquired with the camera and the uav; or recall the table showing the contrast in temperatures for the two lithologies.”

To justify this affirmation, a new column has been included in Table 5 in order to show the rock type that was present in each check point. In the text, the average differences between dolostones and limestones for the data captured with both technologies have been included “Despite this, the thermal difference between the points taken in the two lithologies is nota-bly higher for both sensors (4.2 °C in the case of the camera, and 3.8 for the airbone sensor) , allowing the identification of the contacts.” [Page 13, lines 464-465].

“Figure 7: add where the lithological contact is  based on field surveys for a better comprehension of the results. I'd suggest to do the same with the first RGB image of the study area”

We believe that superimposing the more accurate technique of contrasting results that has been applied with the thermal image itself in this figure may be hasty and misleading.

“Line 611: The amount of references used could be improoved, especially focussing on thermal rock and soil variability. I would suggest these references as a starting point.

Smith, B. J., Srinivasan, S., Gomez-Heras, M., Basheer, P. A. M., & Viles, H. A. (2011). Near-surface temperature cycling of stone and its implications for scales of surface deterioration. Geomorphology, 130(1-2), 76-82.

Frodella, W., Lazzeri, G., Moretti, S., Keizer, J., & Verheijen, F. G. (2020). Applying infrared thermography to soil surface temperature monitoring: Case study of a high-resolution 48 h survey in a vineyard (Anadia, Portugal). Sensors, 20(9), 2444.

30 years of thermal weathering research: From Yatsu' s "The Nature of Weathering" to ir thermal imaging M. Gomez-Heras ISSN: 0389-1755 地形 [[チケイ]] , 2019, Vol.40(3), p.243-257

Grab, S. (2007). Near-surface rockwall temperatures in high Drakensberg basalt: spatio-temporal differences and possible implications for weathering. Zeitschrift für Geomorphologie, Supplementary Issues, 103-113.”

The references provided have been included [30-33]. 12 new references have been added.

We hope that our response meet your criteria. Once again, thank you for your contribution to improve the quality of the paper.

Kind regards,

The Corresponding Author.

Reviewer 2 Report

Unmanned Air Vehicles (UAVs) are becoming more and more important in our lives. UAV technology which is developed for military purposes is slowly moving toward engineering applications.In this study , the use of UAVs is proposed for the gproduction of maps and analysed by means of GIS tools. This is very important using area of UAV. I would like to advice some articles to add your introduction section.

Gis and three-dimensional modeling for cultural heritages (https://doi.org/10.26833/ijeg.378257 )

Accuracy assessment of digital surface models from unmanned aerial vehicles’ imagery on archaeological sites  (https://doi.org/10.26833/ijeg.696001 ) 

Investigation of three-dimensional modelling availability taken photograph of the unmanned aerial vehicle; sample of kanlidivane churc (https://doi.org/10.26833/ijeg.285216 )

Author Response

“Unmanned Air Vehicles (UAVs) are becoming more and more important in our lives. UAV technology which is developed for military purposes is slowly moving toward engineering applications.In this study , the use of UAVs is proposed for the gproduction of maps and analysed by means of GIS tools. This is very important using area of UAV. I would like to advice some articles to add your introduction section.

Gis and three-dimensional modeling for cultural heritages (https://doi.org/10.26833/ijeg.378257 )

Accuracy assessment of digital surface models from unmanned aerial vehicles’ imagery on archaeological sites  (https://doi.org/10.26833/ijeg.696001 )

Investigation of three-dimensional modelling availability taken photograph of the unmanned aerial vehicle; sample of kanlidivane churc (https://doi.org/10.26833/ijeg.285216 )”

Dear Reviewer,

Thank you for your comments and for providing those useful references to improve the approach provided about the current state of these technologies. They have been included [References 23-25].

We hope that the new version of our work meet your criteria.

Once again, thank you for your time.

Kind regards,

The Corresponding Author.

Reviewer 3 Report

Congrats Rubén and colleagues! I enjoyed reading your paper and think it will be useful to other researchers in the field.

There are two main things that I recommend changing:

1) Please cite references to laser fluorescence remote sensing done in caves and from UAVs. This would greatly strengthen your introduction section by showing your awareness of the complete landscape in the field. The 3 references are given in the mark up.

2) Please add a little more detail to the captions so that each caption tells you all the key information the reader needs to orientate themselves. Most of the captions are too short.

Both suggestions are simple and easy to implement so I hope you can make them.

I look forward to seeing your paper published in Minerals very soon.

Comments for author File: Comments.pdf

Author Response

“There are two main things that I recommend changing:

1) Please cite references to laser fluorescence remote sensing done in caves and from UAVs. This would greatly strengthen your introduction section by showing your awareness of the complete landscape in the field. The 3 references are given in the mark up.

2) Please add a little more detail to the captions so that each caption tells you all the key information the reader needs to orientate themselves. Most of the captions are too short.

Both suggestions are simple and easy to implement so I hope you can make them.

I look forward to seeing your paper published in Minerals very soon.”

Dear Reviewer,

Our team wish to thank your comments and suggestion. In the following lines we provide an response to your comments.

“This portion of the introduction is missing recent remote sensing advancements using laser fluorescence imaging in both caves and from UAVs.

Please cite these three important and directly relevant papers to give the reader a better overview of current work in this area:

Kaye TG, Garcia J, Pittman M. Cavern imaging using Laser-Stimulated Fluorescence. CREG Journal. 2019;105:21-4. [cave-based remote sensing]

Kaye TG, Garcia J. Laser stimulated imaging of large scale fluorescence in caves. National Speleological Society News. 2017:11-5. [cave-based remote sensing]

Kaye TG, Pittman M. 2020. Fluorescence-based detection of field targets using an autonomous unmanned aerial vehicle system. Methods in Ecology and Evolution. 2020. 11(8): 890-898.

https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/2041-210X.13402 [paper specifically mentions potential for mining operations]”

These references have been included to improve the introduction [18-20].

“Degree sign is underlined? Not sure if this is a typo or the journal's style. Please check other uses if it is a typo.”

It has been corrected through the text.

Line 161:” Extra space?”

It has been removed.

Figure 1: “I recommend putting a green solid border around each of the boxes relating to RGC image processing and deleting the large green dashed box which is  confusing as it crosses several arrows. The 'RGC image processing' label can just be in green above the boxes.” “Thermal image processing is fine (no need for 's')” “I recommend putting a red solid border around each of the boxes relating to thermal image processing and deleting the large red dashed box which is confusing as it crosses several arrows. The 'Thermal image processing' label can just be in red above the boxes.” “Image alignment” “It would be very helpful to the reader if you can briefly summarise the workflow in one or two sentences in the caption. For example: The workflow starts with flight planning followed by RGC and thermal image acquisition with the dual sensor and then image processing the leads to contact delimitation in the outcrop.”

All the suggestions made have been included in the image and its caption.

Figure 2”Please add some observational data to better orientate the reader. For example: The dolostone sample shows a considerably higher surface temperature than the limestone samples.”.

The caption has been improved according to your suggestion.

Line 322: “thermographic”

It has been corrected.

Figure 3: “It is probably more accurate to say: Surface Temperature” “Graph needs a x-axis label. Time of Day at Field Site?” “Please add a little more detail to the caption to better orientate the reader. For example: Thermal behaviour of the lithologies at the study site during the day. Note that the dolostone always has a higher surface temperature than the limestone.”

All the suggestions made have been included in the image and its caption.

Table 2: “small p to be consistent with other table entries.”

It has been corrected.

Figure 6: “This is very brief. Please give a little more detail e.g., add an extra sentence about the drone's capabilities that the general reader can relate to.”

It has been stated that the device is adequate for this kind of applications. Since the features appear in the following paragraph, we wished to avoid redundance.  

Figure 5 “This is too brief. Caption should stand alone. For example: Ground Control Point (GCP) distribution over the study area. GCPs in red.”

The caption has been expanded according to your kind suggestion.

Figure 6: “How are these different from GCPs? This is unclear from the caption and was a bit confusing. Please explain this in the caption. The point labels are very hard to read. I recommend placing a shadow behind the text labels.”

The term used has been modified (Check Points) in the text and in the caption itself. The figure has been improved adding the shadow behind the labels.

Figure 7: “Too brief.  'Thermal image of the study site' would be better. When was this image taken. On one day at one time? Or an average from different fly pasts? Please put this information in the caption.”

The caption has been modified (“Thermal orthomosaicimage of the study area. The flight duration was 92 minutes.”)

Figure 8: “Please give this temperature limit info in the caption. 30.63 degrees C?”

It has been included.

Figures 9-11-12-13: “Please label 'limestone' and 'dolostone' on the map to help the reader.” (In Table 6): “You can use 'West Limestone' and 'East Limestone' in the figures to be consistent with this table.”

The figures been modified according to the designation applied in Table 6.

Figure 9: “best to reference workflow in Figure 1: proposed method and workflow (Figure 1)”

It has been changed.

Figure 10: “Which one is which? Please add (grey) and (orange) behind the respective rock type to help the reader. Please give an approximate scale e.g. field of view is X cm.”

Both suggestion have been followed.

Figure 12: “Is this a common term? Maybe 'using photo interpretation' is better?”

Photo interpretation has been applied through the text instead of “photogeology”. Figure 13: Typographic mistakes have been corrected according to your suggestions. The caption has been modified, too. (“'between the limestone and dolostone' would be more helpful to the reader.”- “change to: the three methodologies applied (detail geological mapping, RGB photo interpretation and quasi-automatic thermal processing.”)

Figure 6: “You use 'mapping' and 'cartography' in the paper. Please use just one to avoid confusion. I suggest using 'mapping'”

Mapping has been applied through the text.

“I'd greatly appreciate a formal thanks for my review at the end of the final paper.”

An Acknowledgement section has been included to recognize the reviewers’ valuable contribution.

We hope that this new version of our work meets your criteria. Once again, thank you for your contribution.

Kind regards,

The Corresponding Author.

Reviewer 4 Report

Dear authors, 

Thank you for submitting an interesting manuscript to this journal. 

I reviewed your manuscript and recommend publication after minor revisions. 

1) Title & Objective:  Your manuscript presents a case study for initial geological mapping using UAV and low-cost thermal camera. Although these results could be used for mining exploration, the current results are not sufficient to show the possibility. Therefore, it is necessary to revise the title to reflect the scope of the actual research results.

2) Method & Result interpretation: In this study, the analysis results of RGB image and thermal image are interpreted separately. However, since the two data can be acquired together from the UAV, it is possible to analyze them together through digital image processing. I wonder how the accuracy of geological boundary mapping changes when analyzed together.

3) I found several typo errors from the text. Please check the whole manuscript and revise them. 

Thank you. 

Author Response

“Dear Authors,

Thank you for submitting an interesting manuscript to this journal.

I reviewed your manuscript and recommend publication after minor revisions.”

Dear Reviewer,

Thank you for your assessment. In the following line we will provide an answer to your comments, which have contributed to improve the quality of the work.

“1) Title & Objective:  Your manuscript presents a case study for initial geological mapping using UAV and low-cost thermal camera. Although these results could be used for mining exploration, the current results are not sufficient to show the possibility. Therefore, it is necessary to revise the title to reflect the scope of the actual research results.”

Following your suggestion, we have indicated that this methodology has been applie to the “Specific Case of the Complex Sulfides Hosted in Carbonates of Udias”. Other lithologies could provide different results.

“2) Method & Result interpretation: In this study, the analysis results of RGB image and thermal image are interpreted separately. However, since the two data can be acquired together from the UAV, it is possible to analyze them together through digital image processing. I wonder how the accuracy of geological boundary mapping changes when analyzed together.”

The thermal model is based on the geometry of the RGB model, so the geometric accuracy is that of the latter. The technique for obtaining the boundary is different (manual for the delimitation based on the RGB) and through GIS analysis (for the contact determined according thermal information). The proposal you indicate is interesting and would undoubtedly be of interest for future lines of work, not being the object of analysis in the present investigation.

“3) I found several typo errors from the text. Please check the whole manuscript and revise them.”

The text has been reviewed to solve this issue.

We hope that these changes meet your criteria. Once again, thank you for your contribution.

Kind regards,

The Corresponding Author.

Round 2

Reviewer 1 Report

I appreciate your effort in applying the suggested corrections.