Application of Optical Flow Technique and Photogrammetry for Rockfall Dynamics: A Case Study on a Field Test

Round 1

Reviewer 1 Report

This paper proposed an algorithm which is used for tracking the movement of objects based on optical flow technique and photogrammetry. The approach can estimate rockfall motion with high-accurate. The algorithm is applied to the field rockfall experimental data set in 2015, and the result of experiment show that the workflow proposed in this study can be applied to the time-varying rockfall event identification in the slope safety monitoring system.

The paper was a meaningful exploration, and some specific concerns about the contents of this paper are as follows:

1. Grammar is an issue throughout, this could be improved with a thorough read-through by someone with a good understanding of English.
2. At present, most of the papers cited by the author in the introduction are early literatures in the field, and relatively new articles in the last five years should be added to track the latest progress in the field. In addition, the logic between the paragraphs in the introduction is not tight enough and should be adjusted.
3. The research in the remote sensing should be problem-oriented, but the introduction does not describe the framework proposed in this paper to solve any existing problems in this field, so the author should be supplemented. In addition, please provide the generalization and innovation of your proposed method.
4. There are too many keywords in this paper, and the three keywords "computer vision; motion detection; object tracking" do not appear much in the paper, so please streamline them as appropriate.
5. Please further refine the diagram to ensure that its resolution is clear, that the elements are complete, and that the manuscript contains relevant descriptions.

(1) The colors of the subheadings in Figure 7 and Figure 10 are not consistent, please revise.

(2) Please standardize the format of Figure 6 and follow the format required by the journal to produce the figure.

6. In the methods section, the authors should expand and cite the literature to prove the theory, using more concise and easily understandable descriptions to elucidate it to interest the reader in reading. Also, it is recommended to include a well-thought-out technical roadmap.
7. This paper lacks a detailed description of the study area, such as the location of the study area, the geological background, and a discussion of other factors influencing rockfalls.
8. Line 99, “a variety of change detection algorithms have been developed to work best for purposes”, it is recommended that the author list these methods.
9. Section 3.2 is dataset evaluation and the authors list several factors that affect the quality of the dataset, but I do not see whether the quality of the dataset used in this paper is good or bad? Please explain this in the context of the dataset used in this paper.
10. As can be seen in Chapter 4, "Results and Discussion", the first part analyzes the monitoring results in terms of "image quality" and "optical flow", while the second part discusses the problems in the experiment. The second part discusses the problems in the experiment. I think it would be better to include "Discussion" as a separate chapter, please think about it and revise it as appropriate.
11. The conclusion section of this paper is not written concisely and clearly enough, and it is suggested that the language be reorganized and stated in separate clauses.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

The article “Application of Optical Flow Technique and Photogrammetry 2 for Rockfall Dynamics: A Case Study on a Field Test” by Kim and Gratchev provides an optical flow-based tracking algorithm that could be employed to extract the motion data from video records for slope monitoring. It also describes a workflow for a combined photogrammetry and optical flow technique to produce high-accurate estimations of rockfall motion. The article is well written and flows nicely. The data and techniques are sufficient and well suited to address the proposed objectives.

My main comment is related to the fact that the article lacks a detailed discussion on how changes in the object type, size, dimensions, bights value, state (fall, bounce, or slide) affect the object detectability.    

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Dear authors,

You manuscript entitled as "Application of Optical Flow Technique and Photogrammetry for Rockfall Dynamics: A Case Study on a Field Test" needs some refinements before being ready for publication. Please included a Discussion section and provide extended presentation of the outcomes and relate them with similar works. Some parts needs your attention in English language and syntax. You can find detailed comments and suggestions in the attached document.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors have addressed most of the previous comments, however, some comments have not addressed well.

 

Here are the comments:

1. The layout of this manuscript is too messy, so we suggest the author to provide a corrected and clear version, and just mark the changes. The author's response to the comments is too brief, and the specific changes could be listed in the response document to make it easier for reviewers to find them.
2. Many figures in this manuscript have no numbers and titles. Please add complete elements. Some figures are not standardized, use screenshots or have a messy layout; authors are requested to make corrections according to journal requirements.
3. The concise keywords do not accurately summarize the article and the author should revise them.
4. The sixth comment of the first review proposed that the author should present the overall technical flow chart, but the author did not modify it.

Author Response

Dear Reviewer

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

Please correct some minor misspelling and syntax errors. 

Author Response

Dear Reviewer

Please see the attachment.

Author Response File: Author Response.docx