Measurement of Cracks in Concrete Bridges by Using Unmanned Aerial Vehicles and Image Registration
Round 1
Reviewer 1 Report
Regardless that this article does not present a novel research with a significant impact in the State of the Art focused to develop reliable methods to identify different types of damage in bridges in real time; the methodology proposed and the results provided can be useful as a contribution for improving some aspects of the methods based on UAV and image registration for detecting cracks in bridges. In general, the article is well written and organized. Therefore, I recommend this article to be published after a major revision:
* This article does not have numbers of lines and therefore it is difficult to indicate where the mistakes are.
* There are several typos/spelling mistakes that must be corrected, some of them are shown below. Please, recheck the entire article.
- There are 2 typos in page 1, second line of the Abstract: “inspections which” instead of “inspections, which” and “cars are” instead of “cars, are”.
- There is a typo in page 1, line 12 of the Introduction: “0.012 in.” instead of “0.012 in”.
- There is a typo in page 5, first line after equation (6): “yare” instead of “y are”.
- There is a typo in page 6, line 1 of Section 2.5.1.: “2004 which” instead of “2004, which”.
- There is a typo in page 7, line 2 of Section 2.5.2.: “image matching” instead of “image-matching”.
- There are 2 typos in page 7, lines 9-10 of that page: “D(x)in” and “D(x)is” instead of “D(x) in” and “D(x) is”, respectively.
- There is a typo in page 8, lines 2-3 of that page: “structures which” instead of “structures, which”.
- There is a typo in Figure 7: “Distance(mm)” instead of “Distance (mm)”.
- There is a typo in page 9, line 9 of that page: “fist” instead of “first”.
- There is a typo in page 9, line 14 of that page: “disadvantage which” instead of “disadvantage, which”.
- There are several typos in Tables 3-5: “ImageX” and “ImageY” instead of “Image X” and “Image Y”, respectively.
- There is a typo in page 10, line 5 of Section 3.2.: “0.1mm” instead of “0.1 mm”.
- The authors sometimes use “ortho-images” and others “ortho images”.
- There are 6 typos in page 12, Section 3.3, in each one of the 6 points: “images which” instead of “images, which”.
- A blank space between a value (number) and its measurement unit must be included. Re-check the entire article.
- There is a typo in page 12, last paragraph of that page: “This research measure crack sizes” instead of “This research measures crack sizes”.
* Which are the novel aspects/advantages of this research against other similar methods using UAV and image registration? The authors should highlight those advantages in the different Sections of the article (Abstract, last part of the Introduction, Results and Conclusions).
* How this technique can be applied for sudden ruptures of elements of bridges produced by internal cracks that are not visible on the surface?
* How this technique can be applied for very long bridges in real time and in a global/reliable manner, since at any tiny section of the bridge can exist a crack, which can lead to the collapse of the structure at any time?
* Which are the advantages of this technique against methods based on vibration signals post-processing?
* In the Section “Discussions”, the authors should include a comparative table where the proposed method is compared against other methods and indicating its advantages.
* If a critical crack appears at night in a scenario of darkness, the cameras/method can detect the damage?
* The cost of the equipments required is a disadvantage to apply this method at least in the most critical bridges?
* Laboratory experiments are required to validate the method in different scenarios of damage (types of cracks, positions, severity, width, depth, materials, etc.).
* The numbering of Tables is wrong, Table 1 is mentioned twice.
* Titles of Table 1 and 2 are very short, they must be more detailed, at least the authors must indicate that the info provided applies for Infrastructures or specify which type of structures/elements.
* The authors mention that their method is useful for detecting cracks in concrete, but what about other materials used for critical elements of a bridge; for example, anchoring elements made with steel used in cable-stayed bridges? I guess the method is useful for any material; however, the method won’t be able to take pictures in all the zones of the bridge.
* In Figure 2, some info is incomplete/cut (Image Orientation and Registra-).
* Be sure that all the variables mentioned in Equations and Figures are described (explanation of the meaning) and the format is uniform (do not use lower case for a variable and then upper case for the same variable, italics/normal, different letter fonts/sizes, etc.), since there are several inconsistencies.
* The description of the bridge used for the experiments is very short, it should be more detailed and a picture for a general view should be included, as well as a layout for showing general dimensions.
* The format of the different Sections of the article is not uniform.
* The meaning of the acronym DEM is not mentioned.
* The sensitivity and accuracy of the proposed method can be established?
* The manual work included in the proposed method is a limitation for applying this method in real-life structures in real time?
* In Tables 7-9 units were not included?
* In Figure 12, the legend for the X-axis was not included?
Minor editing of English language required.
Author Response
Dear Reviewer,
Thank you for the comments concerning our manuscript. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our research. We have studied comments carefully and have made corresponding revision that we hope meet with approval. The revised parts are marked with yellow background color.
Special thanks to your insightful and inspiring comments on our work, and helpful, instructive and guiding suggestions, which have improved the quality of our manuscript.
We have tried our best to improve the manuscript and made some changes accordingly in the manuscript. We appreciate Reviewer’s warm work earnestly, and hope that the corrections will meet with approval. Once again, thank you very much for your insightful comments and guiding suggestions.
Yours Sincerely,
Hsuan-Yi Li
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The article is very well written. The purpose of the work is explained. The article contains a clearly formulated research methodology. The results of the work were presented, a discussion was held, conclusions support the results of the work. The presented application of the UAV and high-resolution digital cameras by authors to measure (inspect) concrete bridge cracks is very useful, the topic is needed. Authors showed how images obtained from cameras and UAVs can become useful and convey information very important to the society. This is an interesting UAV application. The presented research and results are interesting. The article is worth publishing.
Minor editing of English language required.
Author Response
Dear Reviewer,
Thank you for the comments concerning our manuscript. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our research. We have studied comments carefully and have made corresponding revision that we hope meet with approval.
Yours Sincerely,
Hsuan-Yi Li
Author Response File: Author Response.pdf
Reviewer 3 Report
《Measurement of cracks in concrete bridges by using Unmanned Aerial Vehicles and image registration》
Major Revision
The article addresses the traditional bridge inspection method which is time-consuming and laborious. A solution is proposed to apply an unmanned aerial vehicle (UAV) and a high-resolution digital camera to measure cracks in concrete bridges. A pilot study was conducted on the concrete bridge over the Ai River in Yangmei District, Taoyuan City, Taiwan Province. The two types of images were aligned for crack size measurement. Finally, the crack size was determined by manual measurement method and inflection point method for comparison, which has some engineering practicality, and in general, the subject of this study is interesting and important. However, the article also has many shortcomings and some technical issues need to be fully clarified before it can be accepted for publication.
1. In the introduction part, the background information provided is not detailed enough and does not mention the relevant research in the last five years. If there is any suggestion, please add.
2. In subsection 2.5.2, can the use of automatic contact point generation consider some new methods to make the section more reasonable and comprehensive.
3. The UAV can only shoot the image information of the bridge surface, how to achieve the complex and changeable actual bridge condition shooting?
4. The article does not explain the results adequately, and the summary of the results is not sufficiently fleshed out and clear.
5. Some articles have very blurred pictures and are very unprofessional, as shown in Figure 11. Tables and figures are not clearly expressed. Please check the modification.
6. There are also typographical, punctuation, essay and grammatical errors in the manuscript. Please recheck the entire manuscript.
7. The reference format is confusing, please check carefully.
There are some grammatical and sentence errors in the language, which need to be improved.
Author Response
Dear Reviewer,
Thank you for the comments concerning our manuscript. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our research. We have studied comments carefully and have made corresponding revision that we hope meet with approval. The revised parts are marked with yellow background color.
Special thanks to your insightful and inspiring comments on our work, and helpful, instructive and guiding suggestions, which have improved the quality of our manuscript.
We have tried our best to improve the manuscript and made some changes accordingly in the manuscript. We appreciate Reviewer’s warm work earnestly, and hope that the corrections will meet with approval. Once again, thank you very much for your insightful comments and guiding suggestions.
Yours Sincerely,
Hsuan-Yi Li
Author Response File: Author Response.pdf
Reviewer 4 Report
Accept in present form
Author Response
Dear Reviewer,
Thank you very much for your kind comment.Yours Sincerely,
Hsuan-Yi Li
Round 2
Reviewer 1 Report
The authors provided adequate responses for each comment/suggestion and the corresponding changes were made in the article. Therefore, I recommend this article to be published in present form.
Reviewer 3 Report
The authors responded carefully to the review comments and provided comprehensive answers and improvements to the questions raised.
