Signal Enhancement of Helicopter Rotor Aerodynamic Noise Based on Cyclic Wiener Filtering

Round 1

Reviewer 1 Report

The presented paper regards the acoustic of helicopter rotor. The authors study the noise and propose a function based on Cyclic Wiener Filter that enhances the detection range. The manuscript is well organized and the used methods are described properly. The results showed by the authors are interesting and can be useful for the readers. However there is some issues which should be revised prior to publication. Here are my comments:

1.       Based on the paper one can say that it presents use of an existing model for a specific application. Authors should clarify the novelty of this research.

2.       Figure 3 presents the spectrum – frequency data. Spectrum generally means range, I find it dubious to call the amplitude of certain frequency a spectrum.

3.       Description of used measurement equipment with uncertainty analysis would be appreciated.

4.       Page 9, 10, the Figures numbers are wrong

5.       The conclusions should give an insight into the achievements of the study, so far it is just an short abstract. It need to be revised.

Author Response

Dear Professor,

Firstly, thanks for your comments and precious advice which are really constructive. Responses to the comments are given below, and the amendments are highlighted in red in the revised manuscript.

Comment 1: Based on the paper one can say that it presents use of an existing model for a specific application. Authors should clarify the novelty of this research.

Response: We absolutely accept this comment and the advice. At the end of the introduction, the innovation of this paper has been added.

Comment 2: Figure 3 presents the spectrum – frequency data. Spectrum generally means range, I find it dubious to call the amplitude of certain frequency a spectrum.

Response: Thank you very much for your suggestion. The ordinate in figure 3 was changed to amplitude in the revised manuscript. Figure 3(a) was the spectrum diagram and figure 3(b) represented the envelope spectrum diagram. In addition, the ordinates of all envelope spectrum diagram in the revised manuscript were also changed to amplitude.

Comment 3: Description of used measurement equipment with uncertainty analysis would be appreciated.

Response: Thank you very much for your suggestion. A table has been added to the experimental section to complement the description of the experimental equipment. Moreover, the accuracy of some equipment is further explained. In addition, the uncertainty of the microphone is also provided, because the microphone is the most important device for collecting noise signals.

Comment 4: Page 9, 10, the Figures numbers are wrong

Response: We absolutely accept this comment and the advice. The Figures numbers has been corrected in the revised manuscript.

Comment 5: The conclusions should give an insight into the achievements of the study, so far it is just an short abstract. It need to be revised.

Response: Thank you very much for your suggestion. The conclusions section has been modified in the revised manuscript. In the conclusion part of the revised manuscript, the research results of this paper are better summarized. In addition, the application of cyclostationary analysis method to rotor aerodynamic noise and the application of acoustic detection method to helicopter are prospected.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript is generally well written. It is technically correct and the experimental results are convincing. I have only one concern, which is about the citation of previous works, which initiated the use of cyclic Wiener filtering for aeroacoustic signals. This is due to Antoni's team and dates backs before the publication of Ref. [13] -- which is itself based on Antoni's work. See for instance:

Boustany, R., and Antoni, J., “Blind Extraction of a Cyclostationary Signal Using Reduced-Rank Cyclic Regression—A Unifying Approach,” Mechanical Systems and Signal Processing, Vol. 22, No. 3, 2008, pp. 520–541.

In addition, recent work on a very similar application is:

Author Response

Dear Professor,

Thanks for your comments and precious advice which are really constructive. Responses to the comments are given below, and the amendments are highlighted in red in the revised manuscript.

Comment 1: I have only one concern, which is about the citation of previous works, which initiated the use of cyclic Wiener filtering for aeroacoustic signals.

Response: Thank you very much for your suggestion. Several references have been added to the revised manuscript. These papers describe Antoni's contributions to the field of cyclostationary signals, and discussed several methods of extracting cyclostationary signal. Furthermore, the advantages and disadvantages of cyclic wiener filtering and other cyclostationary analysis methods were compared. Therefore, the reason for using the cyclic wiener filter to enhance the helicopter rotor aerodynamic noise in the revised manuscript was explained.

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors applied a cyclic wiener filter to perform a signal enhancement of helicopter rotor aerodynamic Noise.

The article is well structured, however, the reviewer has some concerns.

1 – please improve the bibliography and highlight the contributions of the article.

2 – references should be added to “Spectral Coherence Theory”.

3 – In section 3 the authors need to introduce the concept of Hilbert Transform and the envelope before presenting h(t).

4 – Figures 7, 8, 9, and 10 b: we cannot see their peak values. 

5 – Please, provide more details about the instrumentation system.

6 – Please, improve the references and make a comparison of previously published articles in a table (if the authors agree).

Author Response

Dear Professor,

Thanks for your comments and precious advice which are really constructive. Responses to the comments are given below, and the amendments are highlighted in red in the revised manuscript.

Comment 1: Please improve the bibliography and highlight the contributions of the article.

Response: Thank you very much for your suggestion. Several references have been added to Introduction section in the revised manuscript. These papers describe Antoni's contributions to the field of cyclostationary signals, and discussed several methods of extracting cyclostationary signal.

Comment 2: References should be added to “Spectral Coherence Theory”.

Response: Thank you very much for your suggestion. In Section 2.1 of the revised manuscript, several papers using the cyclic spectral coherence theory are cited. In the previous manuscript, I forgot to quote relevant literatures here.

Comment 3: In section 3, the authors need to introduce the concept of Hilbert Transform and the envelope before presenting h(t).

Response: Thank you very much for your suggestion. Both the concept of the Hilbert transform and the definition of the envelope spectrum are supplemented in Section 3 of the revised manuscript.

Comment 4: Figures 7, 8, 9, and 10 b: we cannot see their peak values.

Response: Thank you very much for your suggestion. Due to the comments of the rest of the reviewers, the figure in the introduction of the revised manuscript was removed. Therefore, the serial number of the following figures has changed. In the revised manuscript, Figures 6, 7, and 8(b) have been redrawn, and the abscissa and ordinate of these peaks were marked. The abscissa of the detection function peak was the cyclic frequency a, and the ordinate is the value of the detection function T(a). Figure 9(b) was also redrawn, but the cyclic frequencies with a multiple relationship cannot be detected, which indicates that the cyclic frequencies of the helicopter rotor aerodynamic noise can no longer be detected. Therefore, there is no mark in this figure.

Comment 5: Please, provide more details about the instrumentation system.

Response: Thank you very much for your suggestion. A table has been added to the experimental section to complement the description of the experimental equipment. Moreover, the accuracy of some equipment is further explained.

Comment 6: Please, improve the references and make a comparison of previously published articles in a table (if the authors agree).

Response: Thank you very much for your suggestion. Several references have been added to the revised manuscript. These papers describe Antoni's contributions to the field of cyclostationary signals. And discussed several methods of extracting cyclostationary signal. Furthermore, the advantages and disadvantages of cyclic wiener filtering and other cyclostationary analysis methods were compared. Therefore, the reason for using the cyclic wiener filter to enhance the helicopter rotor aerodynamic noise in this paper was explained. The advantages of acoustic detection compared to radar detection of helicopters are also described, thereby clarifying why this paper uses rotor aerodynamic noise to detect helicopters. In addition, there are few literatures about the detection distance of helicopters, because the relevant research is sensitive and usually classified. This manuscript is not classified because the research object is a civil helicopter. Therefore, there is no way to add the comparison of detection distance to the revised manuscript.

Author Response File: Author Response.pdf

Reviewer 4 Report

The focus of the paper is wrong. The investigations are ok, but the direction driven by the authors is bad. Please focus on health effect of noise on citizens more than military purposes.

Errors occur in the text in the discussion and conclusions, which are missing or too shorts, references are poor, and unconventional editorial decisions are taken by the authors without following the journal’s guidelines.

Author Response

Dear Professor,

Thanks for your comments and precious advice which are really constructive. Responses to the comments are given below, and the amendments are highlighted in red in the revised manuscript.

Comment 1: The focus of the paper is wrong. The investigations are ok, but the direction driven by the authors is bad. Please focus on health effect of noise on citizens more than military purposes.

Response: Thank you very much for your suggestion. Your suggestions are very constructive. If some noise reduction method can be proposed, it can improve the quality of life of citizens. However, the main purpose of this paper is to use the rotor aerodynamic noise of the helicopter to realize the long-distance detection of the helicopter. And my technical means belongs to signal processing, which is to process the collected acoustic signals. If we want citizens to hear less noise, on the one hand, we must improve the source of the noise. On the other hand, we need a device to reduce the noise and then output it again, just like a noise reduction headset. However, this is not the subject of this manuscript.

Comment 2: Errors occur in the text in the discussion and conclusions, which are missing or too shorts, references are poor, and unconventional editorial decisions are taken by the authors without following the journal’s guidelines.

Response: Thank you very much for your suggestion. The conclusions section has been modified in the revised manuscript. In the conclusion part of the revised manuscript, the research results of this paper are better summarized. In addition, the application of cyclostationary analysis method to rotor aerodynamic noise and the application of acoustic detection method to helicopter are prospected. Furthermore, the research topic of this paper is acoustic signal processing, which falls within the scope of the Special Issue "Audio and Acoustic Signal Processing".

Author Response File: Author Response.pdf

Reviewer 5 Report

I personally do not like the “war” direction driven by the paper, especially in this historical period. Science journal should not encourage such type of writings. With this in mind, the paper is interesting and deserving attention, even without the interest for military operation. This means that the starting point of introduction should be reworked towards a civil direction, and eventually also just mentioning “military interest”.

Please provide more information and references about the generation mechanisms.

Please avoid figures in the introduction.

I can suggest to shift the work toward health noise reduction on citizens, that will boost significantly the work. In fact, in huge cities helicopters flies over houses and nearby country areas, even at low altitude producing noise. In this case, a period like the following can be added to enrich the work: “Exposure to noise should be reduced and prevented as is associated to many adverse effects on health such as sleep disorders with awakenings (Muzet A. Environmental noise, sleep and health. Sleep Med Rev 2007; 11: 135–42), learning impairment (Zacarías, F. F., Molina, R. H., Ancela, J. L. C., López, S. L., & Ojembarrena, A. A. (2013). Noise exposure in preterm infants treated with respiratory support using neonatal helmets. Acta Acustica united with Acustica, 99(4), 590-597; Minichilli, Fabrizio, et al. "Annoyance judgment and measurements of environmental noise: A focus on Italian secondary schools." International journal of environmental research and public health 15.2 (2018): 208; Erickson, Lucy C., and Rochelle S. Newman. "Influences of background noise on infants and children." Current Directions in Psychological Science 26.5 (2017): 451-457.), hypertension ischemic heart disease (Dratva, J., et al. (2012). “Transportation noise and blood pressure in a population‐based sample of adults.” Environmental Health Perspectives, 120(1): 50–55. Babisch, W., Beule, B., Schust, M., Kersten, N., Ising, H., ‘Traffic noise and risk of myocardial infarction’, Epidemiology, 16, 2005, pp. 33–40. ), diastolic blood pressure (Petri, D., Licitra, G., Vigotti, M. A. & Fredianelli, L. (2021). Effects of Exposure to Road, Railway, Airport and Recreational Noise on Blood Pressure and Hypertension. Int. J. Environ. Res. Public Health 2021, 18(17), 9145), reduction of working performance (Vukić, L., Fredianelli, L., & Plazibat, V. (2021). Seafarers’ Perception and Attitudes towards Noise Emission on Board Ships. International Journal of Environmental Research and Public Health, 18(12), 6671. Rossi, L., Prato, A., Lesina, L., & Schiavi, A. (2018). Effects of low-frequency noise on human cognitive performances in laboratory. Building Acoustics, 25(1), 17-33.), annoyance (Miedema HME, Oudshoorn CGM. Annoyance from transportation noise: relationships with exposure metrics DNL and DENL and their confidence intervals. Environ Health Perspect 2001; 109: 409–16; Licitra, G., Fredianelli, L., Petri, D., & Vigotti, M. A. (2016). Annoyance evaluation due to overall railway noise and vibration in Pisa urban areas. Science of the total environment, 568, 1315-1325.).”.

The conclusion should be improved and discussions are totally missing. Conclusions should better summarize the work done, also showing the importance of the work done, how it improves the knowledge and what the future perspectives will be. Discussions are a mandatory section where to compare results with others already know in literature. In this regards, a better research on background information is also needed and presented.

Author Response

Dear Professor,

Thanks for your comments and precious advice which are really constructive. Responses to the comments are given below, and the amendments are highlighted in red in the revised manuscript.

Comment 1: Please provide more information and references about the generation mechanisms.

Response: Thank you very much for your suggestion. Several references have been added to the Introduction section in the revised manuscript. These references describe the composition of helicopter rotor aerodynamic noise and clarify the generation mechanisms of these noises.

Comment 2: Please avoid figures in the introduction.

Response: Thank you very much for your suggestion. The figure in the introduction was deleted in the revised manuscript, and the serial numbers of all subsequent figures were adjusted accordingly.

Comment 3: I can suggest to shift the work toward health noise reduction on citizens, that will boost significantly the work.

Response: Thank you very much for your suggestion. Your suggestions are very constructive. If some noise reduction method can be proposed, it can improve the quality of life of citizens. However, the main purpose of this paper is to use the rotor aerodynamic noise of the helicopter to realize the long-distance detection of the helicopter. And my technical means belongs to signal processing, which is to process the collected acoustic signals. If we want citizens to hear less noise, on the one hand, we must improve the source of the noise. On the other hand, we need a device to reduce the noise and then output it again, just like a noise reduction headset. However, this is not the subject of this manuscript.

Comment 4: The conclusion should be improved and discussions are totally missing. Conclusions should better summarize the work done, also showing the importance of the work done, how it improves the knowledge and what the future perspectives will be. Discussions are a mandatory section where to compare results with others already know in literature. In this regards, a better research on background information is also needed and presented.

Response: Thank you very much for your suggestion. The conclusions section has been modified in the revised manuscript. In the conclusion part of the revised manuscript, the research results of this paper are better summarized. In addition, the application of cyclostationary analysis method to rotor aerodynamic noise and the application of acoustic detection method to helicopter are prospected. There are few literatures about the detection distance of helicopters, because the relevant research is sensitive and usually classified. This manuscript is not classified because the research object is a civil helicopter. Therefore, there is no way to add the comparison of detection distance to the revised manuscript. Furthermore, the advantages and disadvantages of cyclic wiener filtering and other cyclostationary analysis methods were compared in the Introduction of the revised manuscript. Therefore, the reason for using the cyclic wiener filter to enhance the helicopter rotor aerodynamic noise in this paper was explained. The advantages of acoustic detection compared to radar detection of helicopters are also described, thereby clarifying why this paper uses rotor aerodynamic noise to detect helicopters.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors' response is accepted, and the manuscript is revised.

Author Response

Dear Professor,

Firstly, thanks for your comments and precious advice which are really constructive. If you have any other comments, you can display them, I will revise and submit as soon as possible.

Reviewer 4 Report

Thanks to the authors for the kind explanations, but the references to war and military should be removed in my opinion. For the rest, the paper is good.

Author Response

Dear Professor,

Thanks for your comments and precious advice which are really constructive. Responses to the comments are given below, and the amendments are highlighted in red in the revised manuscript.

Comment 1: Thanks to the authors for the kind explanations, but the references to war and military should be removed in my opinion. For the rest, the paper is good.

Response: Thank you very much for your suggestion. In the Introduction section of the revised manuscript, the previously mentioned content about war and military has been revised.

Reviewer 5 Report

I agree that the work is interesting and is publishable, but all references to war and military focuses must be removed.

about health effects of noise,  a period like the following can be added and integrated by looking at specific helycopter noise works:

Exposure to noise should be reduced and prevented as is associated to many adverse effects on health such as sleep disorders with awakenings (Muzet A. Environmental noise, sleep and health. Sleep Med Rev 2007; 11: 135–42), learning impairment (Zacarías, F. F., Molina, R. H., Ancela, J. L. C., López, S. L., & Ojembarrena, A. A. (2013). Noise exposure in preterm infants treated with respiratory support using neonatal helmets. Acta Acustica united with Acustica, 99(4), 590-597; Minichilli, Fabrizio, et al. "Annoyance judgment and measurements of environmental noise: A focus on Italian secondary schools." International journal of environmental research and public health 15.2 (2018): 208; Erickson, Lucy C., and Rochelle S. Newman. "Influences of background noise on infants and children." Current Directions in Psychological Science 26.5 (2017): 451-457.), hypertension ischemic heart disease (Dratva, J., et al. (2012). “Transportation noise and blood pressure in a population‐based sample of adults.” Environmental Health Perspectives, 120(1): 50–55. Babisch, W., Beule, B., Schust, M., Kersten, N., Ising, H., ‘Traffic noise and risk of myocardial infarction’, Epidemiology, 16, 2005, pp. 33–40. ), diastolic blood pressure (Petri, D., Licitra, G., Vigotti, M. A. & Fredianelli, L. (2021). Effects of Exposure to Road, Railway, Airport and Recreational Noise on Blood Pressure and Hypertension. Int. J. Environ. Res. Public Health 2021, 18(17), 9145), reduction of working performance (Vukić, L., Fredianelli, L., & Plazibat, V. (2021). Seafarers’ Perception and Attitudes towards Noise Emission on Board Ships. International Journal of Environmental Research and Public Health, 18(12), 6671. Rossi, L., Prato, A., Lesina, L., & Schiavi, A. (2018). Effects of low-frequency noise on human cognitive performances in laboratory. Building Acoustics, 25(1), 17-33.), annoyance (Miedema HME, Oudshoorn CGM. Annoyance from transportation noise: relationships with exposure metrics DNL and DENL and their confidence intervals. Environ Health Perspect 2001; 109: 409–16; Licitra, G., Fredianelli, L., Petri, D., & Vigotti, M. A. (2016). Annoyance evaluation due to overall railway noise and vibration in Pisa urban areas. Science of the total environment, 568, 1315-1325.).”.

Author Response

Dear Professor,

Thanks for your comments and precious advice which are really constructive. Responses to the comments are given below, and the amendments are highlighted in red in the revised manuscript.

Comment 1: I agree that the work is interesting and is publishable, but all references to war and military focuses must be removed.

Response: Thank you very much for your suggestion. In the Introduction section of the revised manuscript, the previously mentioned content about war and military has been revised.

Comment 2: about health effects of noise, a period like the following can be added and integrated by looking at specific helicopter noise works:

Response: Thank you very much for your suggestion. In the Introduction section of the revised manuscript, some literature has been added to describe the impact of background noise on people's health, thereby clarifying the necessity of filtering the background noise.