Adaptable Underwater Networks: The Relation between Autonomy and Communications
, Paul Mitchell 3, Nils Morozs 3, Andrea Munafò 2,4 and Jeremy Sitbon 5
Round 1
Reviewer 1 Report
Review of “Adaptable Underwater Networks: the Relation between Autonomy and Communications” by Hamilton et al. submitted to Remote Sensing (manuscript #remotesensing-9388000)
The manuscript deals with the real problem of underwater acoustic communication between autonomous underwater vehicles, while providing two examples from military applications that academics and the public are not often exposed to. The authors provide a good background on the limitations of underwater acoustic communication. The authors discuss different approaches to transmission of data in the marine environment, their advantages and disadvantages and offer up their own innovative solution. The most intriguing development in my opinion is their attempt at integration between autonomy and communications. They do not propose to reinvent communication standards, but simplify how they are implemented. The authors are also well aware of the pitfalls in the communication architecture they propose and do not ignore them. Overall, the article is clear and well written. It can be understood by non-experts, which is a huge plus in such an article. It has been a while since I have come across an article that I do not have that much to comment on.
The only "big" issues I have with the manuscript are:
Affiliations – the authors’ affiliations are not complete. Missing city and country information
Abstract – the abstract is too short and does not fully present the aims, results and findings of the study.
Figure 5 must be improved. This is a main figure. As it stands now, it is small, faint and hard to read.
Please see annotated PDF file for more comments
Comments for author File: 
Comments.pdf
Author Response
We thank the Reviewers for their constructive comments, suggestions and indications. This new version of the manuscript has been thoroughly revised and re-structured following the Reviewers’ suggestions, in the manner indicated below.
To mark the differences with respect to the previous version we have highlighted in the text the main changes in red. We hope that these modifications meet the Reviewers requirements.
Reviewer 1
Comment: Affiliations – the authors’ affiliations are not complete. Missing city and country information
A: Done.
Comment: Abstract – the abstract is too short and does not fully present the aims, results and findings of the study.
A: The abstract has been re-written and rephrased to highlight the work objectives, and its main contributions and results.
Comment: Figure 5 must be improved. This is a main figure. As it stands now, it is small, faint and hard to read.
A: Figure 5 has been improved and made it easier to read.
Comment: Line 183, Introduce the concept of “UWA communication links via reflections off the seabed.”
A: The reference Caiti A., Munafò A., Petroccia R. (2020) Underwater Communication. In: Ang M., Khatib O., Siciliano B. (eds) Encyclopedia of Robotics. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-41610-1_14-1 has been added to point the reader to more details and more references on these concepts.
Comment: Line 210, How efficient is this in terms of memory usage, battery life, etc...?
A: This is a very good point and still an open question. We are aware of the work done by the MIT group to deploy acoustic modeling in real-time and we now point the reader to that work for additional clarifications. Reference “T. Schneider and H. Schmidt, "Model-Based Adaptive Behavior Framework for Optimal Acoustic Communication and Sensing by Marine Robots," in IEEE Journal of Oceanic Engineering, vol. 38, no. 3, pp. 522-533, July 2013, doi: 10.1109/JOE.2012.2232492.” has been added.
Comment: Line 331, reference [36] should be before the coma
A: Done
Comment: Line 375, "the robot" - which robot?
A: We agree with the reviewer and we have removed the word robot as the concept is more general.
Comment: Line 439-441, Please avoid one sentence paragraphs
A: Done
Comment: Line 460, You cannot mention Figure 10 before you mention Figure 9
A: Reference to Figure 10 has been removed from this line as there was no need to point the reader to a figure that is only discussed in later sections.
Comment: Line 474, Is the sounds speed assumed or measured by the node?
A: We have now clarified that the sound speed was only measured once and then assumed constant (lines 529-530).
Comment: Line 505, Were there any environmental changes encountered in the Loch Ness experiment that needed adjustment of navigation? If so, what were they and how were the paths adjusted?
A: The final part of Section 5.1 (now Section 6) has been re-written to clarify what navigational advantages the system brought to the mission and how the network was using one of the services provided to maintain its geometry (line 542-548).
Comment: Line 506, “would typically preclude AUV technology”: such as? Please provide examples.
A: The paper now includes the sentence: “Highly dynamic environments characterised by variable and/or strong currents, or deep waters where DVL bottom-lock is difficult to obtain” to provide examples (lines 546-548).
Comment: Line 607-608, “The layers communicate via a message bus, the socket interface (a wrapper system for IP communication), to pass data between processes.” This sentence is unclear
A: As suggested by the reviewers, the Interoperability section has now been removed, including this sentence.
Reviewer 2 Report
After comparing the current version with respect to the initial version, it seems that most of the reviewers' comments remain unsatisfied. You can easily observe it by checking the highlighted parts, that are actually for both reviewers. So, I believe that the authors didn't consider the most important comments in order to improve the readability of the paper. I believe that since the paper is worthwhile, it should be sent for revision again.
Author Response
We thank the Reviewers for their constructive comments, suggestions and indications. This new version of the manuscript has been thoroughly revised and re-structured following the Reviewers’ suggestions, in the manner indicated below.
To mark the differences with respect to the previous version we have highlighted in the text the main changes in red. We hope that these modifications meet the Reviewers requirements.
Reviewer 2
After comparing the current version with respect to the initial version, it seems that most of the reviewers' comments remain unsatisfied. You can easily observe it by checking the highlighted parts, that are actually for both reviewers. So, I believe that the authors didn't consider the most important comments in order to improve the readability of the paper. I believe that since the paper is worthwhile, it should be sent for revision again.
Comment: The abstract is unnecessarily too long. It has to be re-written (re-shaped) in order to be more compact and highlight the basic and important topic of the paper so as for readers to grasp the important information fast.
A: The abstract has been rewritten and shortened as suggested with respect to the original version of the manuscript. This new version highlights the objectives and the contribution of the paper as recommended.
Comment: It is not clear within the introduction section what is exactly the main contribution of this paper. More specifically, the authors claimed that in order to provide motivation for this work, the paper presents two uses cases. Are these use cases the main contribution of this work? In the reviewer opinion, the authors should explicitly state the main contribution (s) of this work in the introduction section and its relationship to the current state of the art at UWA.
A: This revised version explicitly includes a ‘Main contributions’ section to clarify the objectives of the paper (see Section 1.2 Main Contributions).
Comment: I suggest to authors to move the sections 3.1 and 5.1 into the introduction in order to emphasize the specific literature review and then clarify what is exactly the main contribution of this work in relation to this specific literature review. It seems that this paper presents a series of bibliographic reviews in various parts of the manuscript (see section 5, 3.1, etc). It would be great if authors collect all of them and move them into the introductory section in order to highlight efficiently the major article contribution. In addition, I highly recommend the authors to make a separate sub-section entitled "main contribution" in the introductory section (after a full discussion of the current state of the art) where the major contribution of the work is presented.
A: Section 5 has now been moved to the introduction and retitled as Section 1.1 Related Work. A new subsection titled Main contribution has also been added as Section 1.2. Section 3.1 is now Section 3.2. We decided to leave this part inside Section 3 on Acoustics and Underwater Networks as we believe that it provides motivations for the subsequent Section 3.3 on Network adaptation.
Comment: The literature review part regarding the (communication) limitation of underwater robotics is missing relevant papers in the field. Especially, regarding communication limitations in underwater (multi-agent) robotics (e.g. limited bandwidth, time delay etc). In this respect, the authors need to pay attention to the following recent and related papers which may benefit your vision and literature review (regarding potential limitation (e.g. communication) underwater robotics):
[A] “Cooperative Impedance Control for Multiple Underwater Vehicle Manipulator Systems Under Lean Communication," in IEEE Journal of Oceanic Engineering, 2020, doi: 10.1109/JOE.2020.2989603.” Link: https://ieeexplore.ieee.org/document/9118878
[B] E. Simetti and G. Casalino, “Manipulation and transportation with cooperative underwater vehicle manipulator systems,” IEEE Journal of Oceanic Engineering, 2016.
A: This new version of the introduction now includes references and discussions on communication limitations in underwater (multi-agent) robotics. The two suggested papers have been included.
More broadly, the paper has been thoroughly revised and all the highlighted typos and minor corrections have been included in this new version.
Reviewer 3 Report
In my opinion, the authors spared the effort of revising the paper adequately, thus failing to address minimally the issues raised by both reviewers. They limited themselves to perform minor text changes consisting of rephrasing and rewording and, at least in one case, just removing the controversial statement. Actually, they declined even to add relevant bibliographic references suggested by Reviewer1. Detailed illustrations of these issues are presented below in my final comments to authors.
In view of this reaction of the authors and the limited quality of this last version, I cannot recommend the paper for publication in the journal.
Author Response
We thank the Reviewers for their constructive comments, suggestions and indications. This new version of the manuscript has been thoroughly revised and re-structured following the Reviewers’ suggestions, in the manner indicated below.
To mark the differences with respect to the previous version we have highlighted in the text the main changes in red. We hope that these modifications meet the Reviewers requirements.
Overall comments and appreciation: The issues of underwater (UW) communications are well-known in underwater robotics and, in general, still constitute an open problem despite the important advances achieved in the last decades. As such, the main problem addressed in the manuscript - the robustness and efficiency of UW communications and in particular the problem of its integration with the guidance-navigation-and-control system of autonomous underwater vehicles taking into account mission objectives and constraints - is very relevant and deserves further research.
This manuscript is very well written, concepts are clearly presented in general and the illustrations are also very good, making the paper easy and pleasant to read despite some structural issues that will be mentioned later. The motivating use cases are also interesting and realistic. However, and despite this favorable appreciation, in my opinion a substantial part of the manuscript consists of mere conceptual proposals that lack proper demonstration of its applicability and efficacy (this comment is justified below). In my opinion the manuscript should not be published in its current form. In view of the work reported here, this paper already reveals a great amount of high-quality work and deserves to be improved. The authors and their research groups evidence to have the expertise and the technological resources to provide a more convincing document than current one, i.e., a manuscript describing more compelling results relatively to the main contribution of the work (Sections 4 and 5) and presenting improved formulations and experimental demonstrations of the novel methods proposed in the final part of the paper (Sec. 6).
Alternatively, I suggest the authors reformulate the paper in order to remove those parts that are not sufficiently mature and clarify their main contributions as commented below.
A: We thank the reviewer for the thorough assessment and the suggestions. We have reshaped the paper according to the comments and we agree with the reviewer that this new version reads better and highlights the main contribution of the work. We hope that this revised version meets the Reviewer’s requirements.
Comment: Manuscript structure and contents: The sequence of sections should be revised: introductory and state-of-art matters (Sec. 3, and part of Sec. 5) appear in the middle of technical sections of the paper in a way that does does articulate well.
A: The structure of the paper has been changed and it now reflects the suggested modifications. Section 5 has now been moved to the introduction and retitled as Section 1.1 Related Work. A new subsection titled Main contribution has also been added as Section 1.2. Section 3.1 is now Section 3.2. We decided to leave this part inside Section 3 on Acoustics and Underwater Networks as we believe that it provides motivations for the subsequent Section 3.3 on Network adaptation.
Comment: Subsection 5.1.1 does not seem appropriate as a sub-section of 5.1. Actually, given its importance, it should rather be promoted to a Section of Experiments or Practical Demonstrations.
A: Section 5.1.1 is now a Section that stands in its own right: Section 5 “A successful case study: the Low-Cost AUV Technology (LCAT) project”.
Comment: After having read the previous text, the first paragraph of 5.1 (lines 391...) contains some redundant statements describing the difficulties of UW communications and its consequences in terms of operation.
A: Section 5.1.1. (now Section 1.1 Related Work) has been modified to avoid the redundant statements.
Comment: The character of Sec. 4 is highly hypothetical; it describes and proposes an already known concept and does not provide any substantial contribution or supporting results.
A: We agree with the reviewer that the section is mostly reporting known concepts. However, it is of the authors opinion that this is not a well documented concept and we believe that the data mule concept can have an important role to address some of the main requirements of the discussed use cases. To acknowledge the limited scope of this section within the broader scope of the paper, this new version now describes the Data Mule concepts as a subsection of Section 3. A new paragraph has also been added to clarify its links with the use cases (Line 389-395)
Comment: In Sec. 5 (lines 372-389) the authors comment on relevant references [6] and [43]. However, it is not clear what are the advantages and additional contributions of the present work relatively to those prior works.
A: This paper builds on that previous work and aims at moving those concepts one step forward using the described use cases to provide context and motivations. In this respect, the key contribution of this work is that it proposes a service-based architecture where both autonomy and communications live and interact as peers. This was not part of the work described in neither [6], where the autonomy is not considered, nor in [43], that only focuses on acoustic modeling and point-to-point communications. The main contributions of the work have been clarified and highlighted in Section 1.2, Main Contributions.
Comment: The second paragraph of Sec. 6 refers to the JANUS protocol, which as is well-known constitutes an important advance in the sense of increased interoperability of UW communication technology. However, it is not clear how does the present paper positions itself relatively to other initiatives like JANUS. What are the relevant differences and (dis)advantages of each other? With regard to this, only a brief reference is made in the last paragraph of the Conclusions.
A: As suggested in other comments, Section 6 on Interoperability has now been removed and some of the discussed concepts moved under the new Section 6, Discussions. The original statement of JANUS is still reported but this new version makes it clear that a discussion on the interoperability and standardisation is not the objective of this work. We refer the reader to the recent paper by Costanzi R et al, ”Interoperability Among Unmanned Maritime Vehicles: Review and First In-field Experimentation”, Frontiers in Robotics and AI, vol 7, 2020 for more in depth discussions on these topics.
Comment: In Sec. 6 the authors claim to propose a “modular communication architecture”. However, the document only describes conceptually a series of hypothetical implementations that may reveal problematic (as recognized in the text, although without proposing the corresponding solutions; see, e.g. lines 621 and 627) and where is notorious the use of conditional expressions such as “would”, “should”, “could be”, etc. In summary, this section does not seem to be sufficiently mature to deserve its inclusion in the paper.
A: We agree with the reviewer that Section 6 was less mature than other proposed concepts. Following the reviewer’s suggestion this section has been removed.
Comment: What type of optical communications is proposed in 4.3 (line 278)?
A: The paper references to J. Li et al., "A Real-Time, Full-Duplex System for Underwater Wireless Optical Communication: Hardware Structure and Optical Link Model," in IEEE Access, vol. 8, pp. 109372-109387, 2020, doi: 10.1109/ACCESS.2020.3001213, and it explicitly mentions the Sonardyne BlueComm200.
Comment: The label “Vehicle position” in the diagram represented in Fig. 8 appears to be used twice for distinct types of data; one could possibly be “range (relative position) measurements” and the other “(relative) position estimates” or “filtered position”; please check.
A: The “Vehicle position” in the diagram does refer to the same data content being used in two separate places. To better highlight that is an estimated position we have updated the figure to mention “Estimated Vehicle Position”
Comment: As documented, the “localisation service” has not been exploited in the experiment with the AUVs, which means that the full proposed solution has not been tested. This fact should be mentioned in the final section, Conclusion & Discussion, possibly indicated as a topic of future work.
A: We apologise for the confusion that the previous version of the paper created on what was implemented for the experiments. We have added information in Section 5 to clarify what services have been implemented and tested and under what constraints. This has also been reflected in the conclusion section that now describes how the services have been used during the experiment. The addition of more complex services is briefly mentioned for future work.
Comment: Please describe fully the conditions of the experiment (including environmental conditions). For example, what “changes in the environment” are being considered in line 517? This is not a minor issue since dealing with changing underwater environmental conditions is one of the main claims of the proposed approach.
A: Section 5, A successful case study: the Low-Cost AUV Technology (LCAT) project now clarifies the main experimental conditions affecting the trial, with the presence of a moderate water current moving from NW to SE. The final part of the section has been re-written to clarify how the system allowed to augment the navigation performance and to tackle the presence of the water current.
Comment: Typos and other minor issues: Punctuation with semicolons is used in situations where it does not seem appropriate and a comma would be correct. Conversely, commas are often used where a semicolons would be appropriate. These and other minor issues, including typos, are annotated with color marks in the attached PDF.
A: Done. The paper has been thoroughly revised, typos and mistakes have been corrected throughout.
Round 2
Reviewer 2 Report
I would like to thank the authors for clarifying my concerns. I have no further comments and agree to accept this paper now.
Reviewer 3 Report
Given that this is already the third review of the article, my brief and final comment is as follows.
Although the article has not undergone significant changes in content and maintains some of the limitations described in previous reviews, the restructuring of some sections and the clarification of the topics that had been indicated as more ambiguous or incomplete, allowed to considerably improve its quality. In my opinion, it may be accepted for publication.
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
Review: Adaptable Underwater Networks: the Relation
between Autonomy and Communications
Two use cases considering underwater acoustic communication and by utilizing autonomous underwater systems are considered and presented in this work (mine counter measures and Anti-submarine warfare). More specifically, some results from UK project (LCAT) have been provided which concluded that various number of the vehicle (and hardware system) limitations could be overcome by employing a strong interaction between the autonomy and the communication system. A very strong discussion has been provided in order to show potential ways to overcome these limitations and to achieve standardization across the whole autonomy and communications protocol stacks.
The paper is well-written and coherent. However, some modifications are still needed in order to improve the flow and readability of the manuscript. The paper length is acceptable for the complicated concept under consideration. Please consider the following major comments for the resubmission of an improved journal version in order to be able to be published.
Major comments
1. The abstract is unnecessarily too long. It has to be re-written (re-shaped) in order to be more compact and highlight the basic and important topic of the paper so as for readers to grasp the important information fast.
2. It is not clear within the introduction section what is exactly the main contribution of this paper. More specifically, the authors claimed that in order to provide motivation for this work, the paper presents two uses cases. Are these use cases the main contribution of this work? In the reviewer opinion, the authors should explicitly state the main contribution (s) of this work in the introduction section and its relationship to the current state of the art at UWA.
3. I suggest to authors to move the sections 3.1 and 5.1 into the introduction in order to emphasize the specific literature review and then clarify what is exactly the main contribution of this work in relation to this specific literature review. It seems that this paper presents a series of bibliographic reviews in various parts of the manuscript (see section 5, 3.1, etc). It would be great if authors collect all of them and move them into the introductory section in order to highlight efficiently the major article contribution. In addition, I highly recommend the authors to make a separate sub-section entitled "main contribution" in the introductory section (after a full discussion of the current state of the art) where the major contribution of the work is presented.
4. The literature review part regarding the (communication) limitation of underwater robotics is missing relevant papers in the field. Especially, regarding communication limitations in underwater (multi-agent) robotics (e.g. limited bandwidth, time delay etc). In this respect, the authors need to pay attention to the following recent and related papers which may benefit your vision and literature review (regarding potential limitation (e.g. communication) underwater robotics):
[A] “Cooperative Impedance Control for Multiple Underwater Vehicle Manipulator Systems Under Lean Communication," in IEEE Journal of Oceanic Engineering, 2020, doi: 10.1109/JOE.2020.2989603.”
Link: https://ieeexplore.ieee.org/document/9118878
[B] E. Simetti and G. Casalino, “Manipulation and transportation with cooperative underwater vehicle manipulator systems,” IEEE Journal of Oceanic Engineering, 2016.
Reviewer 2 Report
Overall comments and appreciation:
The issues of underwater (UW) communications are well-known in the underwater robotics and, in general, still constitute an open problem despite the important advances achieved in the last decades. As such, the main problem addressed in the manuscript - the robustness and efficiency of UW communications and in particular the problem of its integration with the guidance-navigation-and-control system of autonomous underwater vehicles taking into account mission objectives and constraints - is very relevant and deserves further research.
This manuscript is very well written, concepts are clearly presented in general and the illustrations are also very good, making the paper easy and pleasant to read despite some structural issues that will be mentioned later. The motivating use cases are also interesting and realistic. However, and despite this favorable appreciation, in my opinion a substantial part of the manuscript consists of mere conceptual proposals that lack proper demonstration of its applicability and efficacy (this comment is justified below).
In my opinion the manuscript should not be published in its current form. In view of the work reported here, this paper already reveals a great amount of high-quality work and deserves to be improved. The authors and their research groups evidence to have the expertise and the technological resources to provide a more convincing document than current one, i.e., a manuscript describing more compelling results relatively to the main contribution of the work (Sections 4 and 5) and presenting improved formulations and experimental demonstrations of the novel methods proposed in the final part of the paper (Sec. 6).
Alternatively, I suggest the authors reformulate the paper in order to remove those parts that are not sufficiently mature and clarify their main contributions as commented below.
-------------------------------------------------------------------------------------------------
Main issues and technical comments:
1. Manuscript structure and contents
1.1. The sequence of sections should be revised: introductory and state-of-art matters (Sec. 3, and part of Sec. 5) appear in the middle of technical sections of the paper in a way that does does articulate well.
1.2. Subsection 5.1.1 does not seem appropriate as a sub-section of 5.1. Actually, given its importance, it should rather be promoted to a Section of Experiments or Practical Demonstrations.
1.3. After having read the previous text, the first paragraph of 5.1 (lines 391...) contains some redundant statements describing the difficulties of UW communications and its consequences in terms of operation.
-------------------------------------------------------------------------------------------------
2. Main contributions
2.1. The character of Sec. 4 is highly hypothetical; it describes and proposes an already known concept and does not provide any substantial contribution or supporting results.
2.2. In Sec. 5 (lines 372-389) the authors comment on relevant references [6] and [43]. However, it is not clear what are the advantages and additional contributions of the present work relatively to those prior works.
2.3. The second paragraph of Sec. 6 refers the JANUS protocol, which as is well-known constitutes an important advance in the sense of increased interoperability of UW communication technology. However, it is not clear how does the present paper positions itself relatively to other initiatives like JANUS. What are the relevant differences and (dis)advantages of each other? With regard to this, only a brief reference is made in the last paragraph of the Conclusions.
2.4. In Sec. 6 the authors claim to propose a “modular communication architecture”. However, the document only describes conceptually a series of hypothetical implementations that may reveal problematic (as recognized in the text, although without proposing the corresponding solutions; see, e.g. lines 621 and 627) and where is notorious the use of conditional expressions such as “would”, “should”, “could be”, etc. In summary, this section does not seem to be sufficiently mature to deserve its inclusion in the paper.
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3. Other technical issues
3.1. What type of optical communications is proposed in 4.3 (line 278)?
3.2. The label “Vehicle position” in the diagram represented in Fig. 8 appears to be used twice for distinct types of data; one could possibly be “range (relative position) measurements” and the other “(relative) position estimates” or “filtered position”; please check.
3.3. As documented, the “localisation service” has not been exploited in the experiment with the AUVs, which means that the full proposed solution as not been tested. This fact should be mentioned in the final section, Conclusion & Discussion, possibly indicated as a topic of future work.
3.4. Please describe fully the conditions of the experiment (including environmental conditions). For example, what “changes in the environment” are being considered in line 517? This is not a minor issue since dealing with changing underwater environmental conditions is one of the main claims of the proposed approach.
-------------------------------------------------------------------------------------------------
Typos and other minor issues:
Punctuation with semicolons is used in situations where it does not seem appropriate and a comma would be correct. Conversely, commas are often used where a semicolons would be appropriate. These and other minor issues, including typos, are annotated with color marks in the attached PDF.
Comments for author File: Comments.pdf
