Ground Risk Assessment for Unmanned Aircraft Focusing on Multiple Risk Sources in Urban Environments

Round 1

Reviewer 1 Report (Previous Reviewer 2)

Thank you for the opportunity to review a revised version of the manuscript. I believe the authors have addressed the issues raised in my original review report. However, there is still a significant quantum of grammatical errors and awkward sentences. For this reason, I suggest that the authors have the paper professionally copy-edited. In terms of content, I believe that the manuscript is now ready for publication.

Author Response

Dear reviewer:

    We sincerely thank you for your time and efforts in reviewing our revised manuscript! Following your positive and constructive suggestions, we revise our paper carefully. The responses to your comments are in the file 'ResponsesToReviewer1.pdf'. 

    we hope that the corrections will meet with approval. Once again, thank you very much for your time and efforts!

    Yours Sincerely

    Qiyang Li, Qinggang Wu, Haiyan Tu, Jianping Zhang, Xiang Zou and Shan Huang

 

Author Response File: Author Response.pdf

Reviewer 2 Report (Previous Reviewer 3)

The article has improved a lot since your last submission. 

Notes:

1 - Still missing a proper comparison with other state-of-the-art methods. This is essential in this article type;

2 - Missing a resume of the innovations/considerations that your method brings that make it superior to the others. E.g., A table comparing all the existing methods in the Related work section;

3 - Compare the results of the several methods in the Results section - On the same environment/study scenario;

4 - A simplified schematic in the introduction should help to understand your method better.

Author Response

Dear reviewer:
    We sincerely thank you for your time and efforts in reviewing our revised manuscript! Following your positive and constructive suggestions, we revise our paper carefully. The responses to your comments are in the file 'ResponsesToReviewer2.pdf'. 
    we hope that the corrections will meet with approval. Once again, thank you very much for your time and efforts!
    Yours Sincerely
    Qiyang Li, Qinggang Wu, Haiyan Tu, Jianping Zhang, Xiang Zou and Shan Huang

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report (Previous Reviewer 3)

The article has improved a lot.

- Instead of "This method" it is probably better to use "Our method"

- In "Comparison" justify why you compare your method with [34} and [18] and not with others e.g. best performance.

- Update the conclusions to reflect the new experimental results. Can you say that you have improved the current algorithm performance compared with other state-of-the-art methods? What was the improvement? 

 

Author Response

Dear reviewer:
    We sincerely thank you again for your time and efforts! We revise our paper carefully by following your positive and constructive comments. The responses to your comments are also in the file 'ResponsesToReviewer2.pdf'. 
    we hope that the corrections will meet with approval. Once again, thank you very much for your time and efforts!
    Yours Sincerely
    Qiyang Li, Qinggang Wu, Haiyan Tu, Jianping Zhang, Xiang Zou and Shan Huang

Author Response File: Author Response.pdf

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

In this article, the risk quantification for Unmanned Aircraft (UA) in urban environments, focusing on the safety of ground people is investigated. In this article, the whole subject is well explained, and the results are also well stated. But if more up-to-date sources are used, especially after 2021, it can help to improve the quality of the article. In addition, the shapes used in this article are not of good quality and can be improved.

Reviewer 2 Report

Thank you for the opportunity to review this manuscript. The topic area is an important one, and the authors have offered a useful contribution. That said, I think the contribution has potential to be improved or clarified. Below are some specific points that I hope the authors can use to improve the manuscript (presented in no particular order):

1. There are a few grammatical issues that need to be corrected with a thorough proofread, or perhaps use of a professional copyeditor.

2. Line 24 - they are not widely used in delivery yet - though they are growing in use for medical and emergency related deliveries

3. Line 27 - should be "...will continue to increase for the foreseeable future." - we cannot say when it will mature and growth will plateau

4. Lines 28-29 - can the authors explain what is meant by the first sentence of this paragraph?

5. Lines 33- 34 - perhaps also worth mentioning EVLOS (extended visual line of sight operations) - a common middle ground between true BVLOS and true VLOS

6. Line 42 - I don't think "strong limitations" is the right terminology - perhaps "to have robust regulations" or similar. Ultimately, not all urban environments are densely populated, and indeed many recreational UAV operations occur with minimal risk. If the model is specifically for densely populated urban environments then this need to be made clear and perhaps the title of the study changed. Ultimately, there will always be risk inherent in an aviation operation, it is just working out what are acceptable levels of risk, which relies upon robust risk measurements.

8. Section 1.2 could be expanded with further examples of studies looking at UAV ground risk, whether by developing quantitative models, or measuring risk more conceptually/qualitatively. Some examples below may be considered by the authors:

https://doi.org/10.2514/6.2017-3272

https://doi.org/10.3390/drones6020032

https://doi.org/10.1109/DASC.2006.313735

There are likely others too - the reference lists of the articles above may also highlight some useful sources.

I also think the JARUS SORA approach could also be explained in much greater detail given this is the basis for the work. The statement about this only applying to EASA is also untrue - there are now over 60 countries that are part of JARUS and most use the JARUS SORA process for assessing more complex operations (or expect applicants to submit one), even if they do not explicitly say so.

9. Lines 101-102 - no higher priority than avoiding collisions with other aircraft - for example, helicopters are often flying in urban environments - perhaps "key priority" would be better than "highest priority"

10. I find the use of "glide descent" a little strange for the Inspire 2 as it is a multicopter model and cannot glide - rather they fall out of the sky (though still move forward some time due to their momentum). Can different terms be used for the two types of craft, or perhaps a slightly different term used? Conceptually, it is fine, but for readability it is unusual.

11. Are automatic ballistic parachutes worth mentioning? They reduce the kinetic energy released upon impact, but only when released with sufficient altitude (usually around 250ft). For multicopter aircraft, this introduces an anomaly, where the safest failures occur either very close to the ground (as the authors mention) or above a minimum safe altitude (MSA). Professionally, I have worked on projects where parachutes and MSAs are the way of managing risks associated with transiting a multicopter UAV over an urban environment. Of course the effectiveness of this is conditional on the parachute system used. 

12. For the fixed-wing model, you are also assuming that control is lost at the same time as failure of the motor. With similar logic to point 11, you can fly a fixed-wing aircraft at an MSA, which would be calculated based upon its speed and glide slope, giving sufficient area for a controlled crash to occur. However, that relies on it being possible to control the aircraft when the motor fails, which is common on fixed-wing VTOL aircraft, but not so much on just fixed-wing aircraft. The same as point 11, automatic ballistic parachutes can also be applied to fixed-wing aircraft.

I think these issues should be easy enough to address. Points 11 and 12 may also be more appropriate to raise in a "limitations" section after the conclusion. With changes made, I think the paper can make a good contribution to the literature.

 

Reviewer 3 Report

The article analyzes the risk of using unmanned aircraft in urban environments.

The article's organization and content need to be improved. I didn't comment in detail on all the situations.

1) Introduction:

- The introduction is not well structured, missing a correct introduction to the subject, the innovation, and the introduction of the adopted method, among others

2)Related work:

- Missing a related work section, the introduction is confusing with the previous and current work

- Divide the related work by applications 

- What is the difference between using fixed-wing and quadcopters?

 3)Methodology:

- What is old and what is new? 

- Missing a comparison of your method with other state-of-the-art methods

- Why did you choose this framework?

4) Results:

- Why did you choose these aircraft?

- What is the difference between using fixed-wing and quadcopters?

- Explain the used performance metrics better and the used study environment

- Missing a comparison of your method with other state-of-the-art methods

5)Conclusions

- What innovation was comprised by your method? Comparison with state-of-the-art methods

- Improvement in the accuracy given by your method?