Range-Based Reactive Deployment of a Flying Robot for Target Coverage

Round 1

Reviewer 1 Report

The manuscript presents a sliding mode control method to navigate a flying robot to track a group of moving targets. Using the distance information extracted from the wireless communications, this method does not require the knowledge of targets’ locations. The navigation law is easily implementable in real-time due to its simple form. 

 

Overall, the manuscript is well organized and easy to follow. However, there are some issues still requiring to be addressed. 

 

1. The problem statement section formulates the smallest circle problem (3). This formulation is a bit misleading as it is for stationary targets. However, the manuscript proposes to deal with both moving targets and stationary targets. So, the formulation should be amended to cover the dynamic scenarios.

 

2. The methodology section mainly focuses on presenting the horizontal navigation method, and the discussion of the vertical direction control is quite brief. It is suggested to elaborate more about the latter. For example, how to deal with the case that even at the highest altitude the camera cannot cover the smallest circle due to the sparse distribution of the targets.

 

3. An important assumption of this manuscript is that the targets move as a group. Without this assumption, a single flying robot may not be sufficient to simultaneously monitor multiple targets. So, it is necessary to clearly mention this assumption in both Abstract and Conclusion.

Author Response

We thank the comments from the reviewer and have already made a point-by-point response. Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

1. In line-386, why the performance is improved by changing the control law from 1 to 0.01? Please give more detail description.

2. In line-391, time consumed by the drone has decreased from 120s to 26s. I do not see this result. Please add necessary figures to show this conclusion.

Author Response

We thank the comments from the reviewer and have already made a point-by-point response. Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Please refer to the attached file.

Comments for author File: Comments.pdf

Author Response

We thank the comments from the reviewer and have already made a point-by-point response. Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

This paper presents an approach to monitor a set of targets by a UAV in a way all targets can be observed by an onboard camera facing down. The problem is formulated as the smallest circle problem assuming all target locations are known. However, the locations of the targets are estimated using the received signal strength. The problem is interesting, and it contains a nice literature review that covers a wide range of works where the main difference with other papers is that the coordinate location of the targets is not known. However, the contribution is not clear. 

I have the following comments to improve the paper:

* The argument related to saving energy by the fact that the UAV flies as low as possible is misleading.

* If the targets transmit an RF signal, would it not be better to transmit their location instead of calculating it from the signal strength?   

* The contribution must be explained better since what is presented is a combination of applying conventional solutions taken from the literature. First, the target location is done by a conventional signal strength calculation. Then, the navigation control law is also taken from the literature. Finally, the solution to the smallest circle problem is conventional. The contribution has to be clear in the abstract and the introduction. 

* Is it necessary to control the orientation of the UAV? A UAV is a holonomic robot, placing the camera in its geometric center would be enough and more efficient in terms of movements. 

* In order to complement the comparison of the proposed algorithm and the welzl algorithm include the execution time and algorithm complexity. 

* The paper needs proofreading; there are a number of typos and language issues in the document that needs to be corrected. The paper also mixes American English with British English, e.g., centre/optimize. Please check it thoroughly.

 

Author Response

We thank the comments from the reviewer and have already made a point-by-point response. Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have addressed all my concerns. The paper can be accepted for publication.

Reviewer 2 Report

The authors have answered my questions and added the descriptions in the paper. This article can be accepted in current version.

Reviewer 3 Report

The authors addressed correctly my issues, and their answers increased the scientific soundness of the paper. I would only suggest to indicate the angle phi (or phi/2) in Fig. 2. I would recommend publication of the paper in its present form.

Reviewer 4 Report

I am happy with the responses to my comments. However, this version has issues with references. Something is missing in the latex code that no references display correctly.

Author Response

We thank the reviewer point out the situation, it seems that the compiler incompatibility causes the missing reference. We have already uploaded the zip code file and the pdf file for reference. Thank you!

Round 3

Reviewer 4 Report

I have no more comments