On Detection of Anomalous VHF Propagation over the Adriatic Sea Utilising a Software-Defined Automatic Identification System Receiver
Round 1
Reviewer 1 Report
The paper presents a study on the detection of Very High Frequency (VHF) anomalous propagation over the Adriatic Sea. The researchers employed a Software Defined Radio (SDR) Automatic Identification System (AIS) receiver to collect AIS data packets at a fixed location in the Northern Adriatic. The data were collected over a 24-hour period and provided information from 115 AIS targets, comprising 159,965 AIS packets with a 54.3% Packet Error Rate (PER).
The subsequent analysis and post-processing of the signals and decoded packets revealed instances where the SDR AIS receiver detected and decoded data packets from AIS targets located significantly farther than the VHF nominal ranges. To determine the propagation magnitude of radio waves, the researchers calculated the great circle distances between the receiver antenna and the decoded positions of AIS packets. The results showed propagation distances of hundreds of Nautical Miles (NM).
The paper discusses and evaluates possible reasons for these occurrences, including tropospheric scattering, diffraction, ionospheric sporadic E layer, and refraction.
In general, the paper seems to be in the initial state of research, and i cannot agree that this paper is ready for publication. In my opinion, the paper shows a basic approach without any details. What exactly is the novelty of your approach? Moreover, the authors describe data that could be made available and properly explained, including the possibilities of their use. The solution itself should be compared to similar analysis on publicly avaibled datasets. It would show a proper comparison with state of art etc. Moreover, the paper should not contain screenshots, but a properly evaluated data. The other issue is why the authors did not use a machine learning solution. The application of the solution is also not discussed in terms of IoT, vessels, etc. The conclusion section is also missing.
Author Response
Dear reviewer,
Thank you for your time, comments and suggestions.
Please find our responses to your comments and suggestions below.
"The paper presents a study on the detection of Very High Frequency (VHF) anomalous propagation over the Adriatic Sea. The researchers employed a Software Defined Radio (SDR) Automatic Identification System (AIS) receiver to collect AIS data packets at a fixed location in the Northern Adriatic. The data were collected over a 24-hour period and provided information from 115 AIS targets, comprising 159,965 AIS packets with a 54.3% Packet Error Rate (PER).
The subsequent analysis and post-processing of the signals and decoded packets revealed instances where the SDR AIS receiver detected and decoded data packets from AIS targets located significantly farther than the VHF nominal ranges. To determine the propagation magnitude of radio waves, the researchers calculated the great circle distances between the receiver antenna and the decoded positions of AIS packets. The results showed propagation distances of hundreds of Nautical Miles (NM).
The paper discusses and evaluates possible reasons for these occurrences, including tropospheric scattering, diffraction, ionospheric sporadic E layer, and refraction."
Thank you very much. We are glad that you have recognized our research.
"In general, the paper seems to be in the initial state of research, and i cannot agree that this paper is ready for publication. In my opinion, the paper shows a basic approach without any details."
We believe that the presented findings are significant, and that they explain the atmospheric phenomena which occurred over the Adriatic region at a specific time period, and which we were able to: detect with a novel approach using the SDR AIS receiver; present in detail; and ultimately confirm. These findings are preliminary results, which is the reason why we declared our manuscript as Communication, rather than usual, Research Article (MDPI: Communications are short articles that present groundbreaking preliminary results or significant findings that are part of a larger study over multiple years. They can also include cutting-edge methods or experiments, and the development of new technology or materials.). Once again, we believe that our findings are relatively new, and this is in accordance with thorough literature review we made and also presented.
"What exactly is the novelty of your approach? Moreover, the authors describe data that could be made available and properly explained, including the possibilities of their use. The solution itself should be compared to similar analysis on publicly avaibled datasets. It would show a proper comparison with state of art etc."
The aforementioned thorough literature review did not find an approach similar to the one presented in our manuscript. In other words, no one has used the SDR AIS receiver to detect anomalous propagations. Therefore, we cannot make any comparison. Regarding the previous facts, the novelty is that we have connected new technologies for receiving AIS data packets (SDR with Matlab) with the phenomenon of refractive propagation of VHF radio waves.
The one familiar with the AIS technology and the structure of the AIS data packets would not ask for the data to be properly explained. This data has been widely used on a daily basis for many years. Additionally, the one familiar with the Matlab program and its license would not request that data obtained with it be made publicly available. Additionally, this data is the same as the previously mentioned widely used AIS data, except that it was received by an SDR AIS receiver, not a commercial one.
Furthermore, the one familiar with the WMO radiosondes and the AREPS program, would know that the data obtained by these radiosondes are publicly available, which is also stated and referenced in the manuscript. By using these data and the AREPS program, which is not publicly available, the atmospheric profiles were created, which ultimately detected refractive phenomena. Again, in the detailed literature review, we did not find that for the observed time period (24 hours in February 2023) anyone made a similar analysis on the selected WMO stations.
Therefore, we made a comprehensive literature review and evaluation, and provided with published findings, and placed them in the context of our research. These findings are state-of-the art in the respective field. Perhaps, if the reviewer would provide with more details and specify his concrete request, we would be happy to answer him and act accordingly.
"Moreover, the paper should not contain screenshots, but a properly evaluated data."
The screenshots from the MarineTraffic Live Map, shown in Figures 2-5, were used to verify the collected and decoded AIS data, which is explained in detail and referenced in the Results Analysis and Discussion section. It is not unusual to find such screenshots in scientific publications, given that the MarineTraffic authorizes the reproduction of live map images for the digital and printed formats of academic publications. Again, one familiar with the AIS in general would know that the MarineTraffic Live Map graphically displays real AIS data collected from actual AIS receivers around the world.
"The other issue is why the authors did not use a machine learning solution. The application of the solution is also not discussed in terms of IoT, vessels, etc."
We are really sorry, but we find these remarks too general. A machine learning solution for what? IoT, the same? Application to ‘vessels’, at least in this, initial phase, is not feasible. We analysed the natural phenomena, and not their application.
Please bear in mind that the basis of our manuscript was to present our findings and observation of the propagation phenomenon, a usual form when Communication type of manuscript is provided. Again, if the reviewer could give concrete suggestion, i.e. on which specific detail he/she thought when writing these remarks, we will be happy to answer and act accordingly.
"The conclusion section is also missing."
As retrieved from JMSE Instructions referring to Conclusions: ‘’This section is not mandatory but can be added to the manuscript if the discussion is unusually long or complex.’’ Since we discussed the results and summarized the findings during the final section, we decided that the Conclusion section would be redundant. Again, if the reviewer insists, we can provide with Conclusion section.
Dear reviewer, we truly hope that we clarified your remarks. We would also like you to answer on our questions stated in these answers, so that we can act properly.
Once again, thank you for your effort and time.
Best regards.
Reviewer 2 Report
According to the authors, their research goal was to build a simple Automatic Identification System (AIS) receiver to analyze the received data to detect VHF signals of objects beyond the horizon.
The manuscript as it stands represents only a comprehensive report of experimental research, not a scientific paper.
In addition, the description of the project to build a simple Software Defined Radio (SDR) AIS receiver was omitted, which was the announced goal of the paper.
In order for the current manuscript to become a scientific and research work, it is necessary to supplement it with the following topics:
1. In the Introduction, the thesis of the work should be formulated, and then the goals of the work resulting from it, which become the titles of the following chapters.
2. Present what is the original achievement of the authors, not yet solved by other authors.
2. A new chapter should be developed, for example titled "Software Defined Radio (SDR) AIS Synthesis", containing in addition to a detailed description of the software, also its pseudocode.
3. In line 311, renumber Figure 3 to Figure 12.
4. Create a new chapter "Conclusions", in which you first present your original scientific achievement, and then a detailed and specific plan for further research on the paper.
Author Response
Dear reviewer,
Thank you for your time, comments and suggestions.
Please find our responses to your comments and suggestions below.
"According to the authors, their research goal was to build a simple Automatic Identification System (AIS) receiver to analyze the received data to detect VHF signals of objects beyond the horizon."
Partially correct. Our goal was to employ the software-defined radio AIS receiver to research, investigate and detect eventual anomalous radio waves’ propagation. We succeeded, and are really happy for that, since through the comprehensive literature review we did not find similar approach.
"The manuscript as it stands represents only a comprehensive report of experimental research, not a scientific paper."
Thank you. But given the nature of the research and our findings, we categorized our manuscript as Communication (as per MPDI Instructions for authors (https://www.mdpi.com/about/article_types): ‘’Communications are short articles that present ground breaking preliminary results or significant findings that are part of a larger study over multiple years. They can also include cutting-edge methods or experiments, and the development of new technology or materials. The structure is similar to an article and there is a suggested minimum word count of 2000 words.’’)
"In addition, the description of the project to build a simple Software Defined Radio (SDR) AIS receiver was omitted, which was the announced goal of the paper."
As stated before, our goal was the investigation rather than build-up. In these terms, an employment of such a receiver acts as a simple matter. In the Experimental setup and Methodology section, it is explained how the SDR AIS receiver was assembled (not build): the VHF antenna; the connection to the NESDR SMArt v5; the connection to the computer with Matlab’s built-in program Ship Tracking Using AIS Signals, etc. We do not know in what way was the description omitted?
"In order for the current manuscript to become a scientific and research work, it is necessary to supplement it with the following topics:
1. In the Introduction, the thesis of the work should be formulated, and then the goals of the work resulting from it, which become the titles of the following chapters."
Thank you for this remark. We have modified the Introduction section accordingly.
"2. Present what is the original achievement of the authors, not yet solved by other authors."
The detailed literature review did not find an approach similar to the one presented in our manuscript. In other words, no one has used the SDR AIS receiver to detect anomalous propagations. Therefore, the novelty is that we have connected new technologies for receiving AIS data packets (SDR with Matlab) with the phenomenon of refractive propagation of VHF radio waves. Moreover, by using data obtained by the WMO radiosondes and the AREPS program, the atmospheric profiles were created, which ultimately detected refractive phenomena. Again, in the detailed literature review, we did not find that for the observed time period (24 hours in February 2023) anyone made a similar analysis on the selected WMO stations.
All of the above is presented in the manuscript.
"2. A new chapter should be developed, for example titled "Software Defined Radio (SDR) AIS Synthesis", containing in addition to a detailed description of the software, also its pseudocode."
The one familiar with the Matlab program and its license would not request for its pseudocode to be described. Also, there is a corresponding reference for the mentioned software and its built-in program Ship Tracking Using AIS Signals in the manuscript. Please refer to it for its detailed pseudocode.
"3. In line 311, renumber Figure 3 to Figure 12."
Thank you for your remark. It has been renumbered accordingly.
"4. Create a new chapter "Conclusions", in which you first present your original scientific achievement, and then a detailed and specific plan for further research on the paper."
As retrieved from JMSE Instructions referring to Conclusions: ‘’This section is not mandatory but can be added to the manuscript if the discussion is unusually long or complex.’’ Since we discussed the results and summarized the findings during the final section, we decided that the Conclusion section would be redundant. Again, if the reviewer insists, we can provide with the Conclusion section.
Dear reviewer, we truly hope that we clarified your remarks. We would also like you to answer on our questions stated in these answers, so that we can act properly and modify our manuscript where needed.
Once again, thank you for your effort and time.
Best regards.
Round 2
Reviewer 1 Report
Thanks for answering my comments. However some minor questions:
1. Can you extend the introduction to a proper evaluation of references? It seems that each reference should be explained, not put many at once.
2. Is it possible to use your solution in the autonomous unmanned vessel? If yes, please add some small discussion and analysis of existing solutions in AUV mainly from 2023. It seems a practical application of your approach in latest solutions
Author Response
Dear reviewer,
Thank you once again for your time and review.
Please find our replies to your comments and suggestions below.
"1. Can you extend the introduction to a proper evaluation of references? It seems that each reference should be explained, not put many at once."
Thank you for this remark. We have modified the Introduction section by evaluating each individual reference.
"2. Is it possible to use your solution in the autonomous unmanned vessel? If yes, please add some small discussion and analysis of existing solutions in AUV mainly from 2023. It seems a practical application of your approach in latest solutions"
Thank you for this comment. We have added at the end of the Experimental setup and Methodology section our thoughts regarding AUVs and anomalous propagation of VHF radio waves. Although we have not found any similar existing solutions for AUVs in 2023, there is one potential data exchange system within the e-navigation concept that uses VHF radio waves.
We hope that we have been able to adopt all your comments and suggestions.
Best regards.
Reviewer 2 Report
I propose the publication of the manuscript.
Author Response
Dear reviewer,
Thank you for your proposal, time and effort.
Best regards.
