Research on Laser Dual-Mode Fusion Detection Method of Ship Wake Bubbles

Round 1

Reviewer 1 Report

Reviewer’s Recommendation

The manuscript needs above major revisions. Consequently, it should be rejected.

Summary

The candidate paper is relevant to the detection method of ship-wake bubble

General comments

The authors have made a considerable effort, but the final result is somehow chaotic and hard to follow. Furthermore, crucial validation of the experiment is missing, methods are unclear, and a reader cannot find out a method strategy even in an analytical manner. Consequently, authors should check the whole document and thus add important missed facts and details. Also, the expression and grammar should undergo an extensive check by a native speaker.

Suggested Improvements

In addition to the previously mentioned, please apply the following suggestions, and import your answers inside the revised paper for a future version:

1.      "Aiming at the application background of laser tracking of ship wake, the laser detection characteristics of ship wake are analyzed": Please revise the expression.

2.      The abstract is not correctly shaped by terms of expression nor by explaining seamlessly the purpose of this work. Please revise properly.

3.      Line 14: "Dual-mode": It is the 4th time of this expressed term till this point. Please fix it.

4.      Line 17: "Aiming at the problems": The same here. It is the 2nd time this expression follows the same beginning of the previous sentence. Please revise.

5.      "Using the Mie scattering effect of bubbles": Please explain.

6.      "The blue-green laser wake detection device can identify micron-sized bubbles in the wake of the ship": It is badly shaped. Please revise.

7.      "The detection system needs to meet the detection of far-field sparse, discrete bubbles and near-field turbulent disturbance dense bubbles": Too much info without explaining.

8.      "and detected the scattering signal of bubbles in the wake of a real ship within 11.5s": It is badly shaped. Please revise.

9.      "The blue-green laser is used to irradiate the wake region, and the adaptive gain adjustment APD and low-illumination CMOS are used to detect the wake bubble echo, respectively": Please revise the whole sentence.

10.  At the end of the introduction there is no paper structure. Please do so.

11.  "ship wake laser detection characteristics and analysis": Capitals are missing.

12.  Line 88" "ship wake": You keep on referring to ship wake which is the imminent result of a moving ship (more or less). You should have explained that in your own words to clarify the central idea of your work even if you think that various scientists know it which is not true. Please do so.

13.  Lines from 110 to 121 should be highlighted by using at the end a bullet-style format.

14.  Lines 150-153 -- "Through the analysis of the existing data, it can be concluded that the echo signal or 151 image has the following characteristics: 1.weak echo signal ( target feature ) ;2.random discrete distribution of echo signal ( target ) ;3.large environmental interference 4.large amount of target echo signal data [17-19]": Existing data? Is it yours? Please revise the expression.

15.  "According to the reference 22": Please revert to According to [22] or similar expression.

16.  Lines 204-206: Please revise expression.

17.  "Monte Carlo simulation model" gives minimal information about the procedure. Please elaborate properly.

18.  "The number of photons is set to 107, the output wavelength is 532 nm, and the water attenuation coefficient is 0.151 m-1." Please explain the used values.

19.  Figures are of low analysis. Please revise.

20.  "The change of laser backscattering when the thickness changes is analyzed": Meaning?

21.  You start presenting Figures 5 and 6 without giving before this relevant information of how they were acquired in detail.

22.  Figure 8 gives a lot of redundant information, please explain.

23.  Figure 10 schematic should be followed by appropriate proofs.

24.  The 4.2 section should be rewritten more carefully and simply.

25.  Figure 14 should be revised. There is too little analysis and not proper info in some cases.

26.  Figure 16 should be also commented on based on a true frequency and not only in a baseband mode.

27.  5.2 Image detection module results are not in a proper format. It is chaotic. Please make checkpoints thus bullet-style summaries.

28.  Figure 17 needs major revisions.

29.  The conclusion should be split into various paragraphs to properly referring to the appropriate results and thus future scopes.

30.  References need enrichment.

Manuscript Rating:

1.    This manuscript should be rejected.

Extensive editing of English language required

Author Response

Dear Reviewer,

Hello! I am truly grateful for your attention to this paper and for the valuable guidance and suggestions you have provided. Your feedback is extremely important to me, and I believe that with your insights, this paper will be significantly improved.

I appreciate the time you have taken to review my work and offer your expert opinion. I am committed to addressing each of your comments and suggestions to ensure that the paper is as robust and clear as possible.

Thank you again for your dedication and support. I look forward to incorporating your feedback into the revised version of this paper.

Best regards,

Zhang xin

Suggested Improvements

In addition to the previously mentioned, please apply the following suggestions, and import your answers inside the revised paper for a future version:

1. "Aiming at the application background of laser tracking of ship wake, the laser detection characteristics of ship wake are analyzed": Please revise the expression.

Modified to "Addressing the issues of weak echo signals and strong background interference in laser detection of ship wakes, an analysis of the laser backscatter detection characteristics of ship wakes has been conducted. "

2.The abstract is not correctly shaped by terms of expression nor by explaining seamlessly the purpose of this work. Please revise properly.

The abstract section has been revised to emphasize the research purpose and significance of this paper. Modified to "Addressing the issues of weak echo signals and strong background interference in laser detection of ship wakes, an analysis of the laser backscatter detection characteristics of ship wakes has been conducted. Based on the Monte Carlo method, a simulation model for dual-mode fusion detection of ship wake bubbles using laser technology was constructed under different target characteristics. A dual-mode fusion detection system for ship wakes was designed, and an indoor experimental platform for dual-mode fusion detection of ship wake bubbles using laser technology was established. To address problems such as a wide range of echo signal intensity changes, severe signal fluctuations, low resolution, poor image contrast, and blurred target edge information, an algorithm based on multi-time scale hierarchical fusion signal processing and temporal difference accumulation image processing was proposed.Verification experiments for ship wake detection were conducted, which revealed that the dual-mode fusion detection method for ship wake bubbles using laser technology can effectively enhance the detection signal-to-noise ratio and counter the maneuvering evasion of underwater weapons by ships. It achieved high sensitivity, large dynamic range, high resolution, and wide field of view detection and real-time signal processing of ship wake bubble targets of different magnitudes against a strong reverberation background. The effectiveness of the dual-mode fusion detection mode was validated, providing theoretical support for the overall system design and parameter settings. "

3. Line 14: "Dual-mode": It is the 4th time of this expressed term till this point. Please fix it.

The terminology has been unified, and "laser" has been deleted in line 14 section.

4. Line 17: "Aiming at the problems": The same here. It is the 2nd time this expression follows the same beginning of the previous sentence. Please revise.

Modified, this section has removed "Aiming at the problems". Modified to "To address problems such as a wide range of echo signal intensity changes, severe signal fluctuations, low resolution, poor image contrast, and blurred target edge information, an algorithm based on multi-time scale hierarchical fusion signal processing and temporal difference accumulation image processing was proposed. "

5. "Using the Mie scattering effect of bubbles": Please explain.

This section has been deleted, and most scholars are aware of it.

6. "The blue-green laser wake detection device can identify micron-sized bubbles in the wake of the ship": It is badly shaped. Please revise.

This section has been deleted due to excessive elaboration.

7. "The detection system needs to meet the detection of far-field sparse, discrete bubbles and near-field turbulent disturbance dense bubbles": Too much info without explaining.

The relevant information has been deleted and directly modified to " These systems must possess the ability to identify bubble size, number density, and thickness, thereby enhancing their engineering application capabilities under conditions of strong artificial interference."

8. "and detected the scattering signal of bubbles in the wake of a real ship within 11.5s": It is badly shaped. Please revise.

Modified to "Effective scattering signal detected for 11.5s of real ship wake bubbles".

9. "The blue-green laser is used to irradiate the wake region, and the adaptive gain adjustment APD and low-illumination CMOS are used to detect the wake bubble echo, respectively": Please revise the whole sentence.

This section has been deleted due to excessive elaboration.

10. At the end of the introduction there is no paper structure. Please do so.

Modified to" This paper primarily adopts a research approach that combines theory, simulation, system design, and experimental verification. The first section focuses on analyzing the laser detection characteristics of ship wakes. In the second section, based on Monte Carlo simulations, the laser dual-mode fusion detection characteristics of different bubbles are analyzed. In the third section, based on theoretical and simulation studies, system design and signal processing algorithms are investigated. Finally, in the fourth section, experimental verification tests are conducted using the system. "

11. "ship wake laser detection characteristics and analysis": Capitals are missing.

Modified to" Ship wake laser detection characteristics and analysis".

12. Line 88" "ship wake": You keep on referring to ship wake which is the imminent result of a moving ship (more or less). You should have explained that in your own words to clarify the central idea of your work even if you think that various scientists know it which is not true. Please do so.

This section is uniformly referred to as "ship bubble wake", which actually refers more to the bubbles in the ship's wake.

13. Lines from 110 to 121 should be highlighted by using at the end a bullet-style format.

Modified, added "●".

14. Lines 150-153 -- "Through the analysis of the existing data, it can be concluded that the echo signal or 151 image has the following characteristics: 1.weak echo signal ( target feature ) ;2.random discrete distribution of echo signal ( target ) ;3.large environmental interference 4.large amount of target echo signal data [17-19]": Existing data? Is it yours? Please revise the expression.

Modified to" According to [17-19], it can be concluded that the echo signal or image has the following characteristics:

• weak echo signal (target feature);
• random discrete distribution of echo signals (targets);
• large environmental interference ;
• large amount of target echo signal data. "

15. "According to the reference 22": Please revert to According to [22] or similar expression.

Modified to" According to [22] ":

16. Lines 204-206: Please revise expression.

Modified to"This section is based on Monte Carlo simulation to analyze the backscattering characteristics of ship wake bubbles and the imaging characteristics of laser illumination, verifying the effectiveness of the dual-mode fusion detection method. ".

17. "Monte Carlo simulation model" gives minimal information about the procedure. Please elaborate properly.

Monte Carlo method is a computer simulation based on the trajectory of photon motion. The statistics of photon motion reflect the propagation rules of photons in water. It can simulate the movement process of a large number of photons and record the state of photons without excessive approximation. It can simulate the absorption and scattering characteristics of water bodies under different attenuation coefficients. Many scholars have studied the backward scattering characteristics of bubbles through Monte Carlo method, which is known to most scholars, so it is not detailed here.

18. "The number of photons is set to 107, the output wavelength is 532 nm, and the water attenuation coefficient is 0.151 m-1." Please explain the used values.

Modified ,according to[23].

19. Figures are of low analysis. Please revise.

We have added.

20. "The change of laser backscattering when the thickness changes is analyzed": Meaning?

The bubble field in ship wake is a constantly changing process, and the echo characteristics of the bubble layer at different distances are different. Therefore, studying the thickness characteristics of ship wake bubbles is of great significance.

21. You start presenting Figures 5 and 6 without giving before this relevant information of how they were acquired in detail.

Figures 5 and 6 are consistent with Figure 4, all based on the relevant parameter conditions.

22. Figure 8 gives a lot of redundant information, please explain.

Figure 8 shows the imaging characteristics of bubbles under different thicknesses of bubble layers, which are complementary to the backscattered echo signals of bubbles. All the red dots in the figure represent the returned photons and there is no other redundant information.

23. Figure 10 schematic should be followed by appropriate proofs.

Added image.

24. The 4.2 section should be rewritten more carefully and simply.

Modified and deleted relevant content.

25. Figure 14 should be revised. There is too little analysis and not proper info in some cases.

Modified.

26. Figure 16 should be also commented on based on a true frequency and not only in a baseband mode.

The horizontal axis in Figure 16 should be the number of cycles, no longer the number of sampling points.

27. 5.2 Image detection module results are not in a proper format. It is chaotic. Please make checkpoints thus bullet-style summaries.

Modified, added "●".

28. Figure 17 needs major revisions.

Modified.

29. The conclusion should be split into various paragraphs to properly referring to the appropriate results and thus future scopes.

Modified to"This article focuses on the application background of laser guidance for ship wake bubbles. It studies the laser backscatter characteristics and illumination imaging characteristics of ship wake bubbles with different distances, scales, number densities, and thicknesses. The results indicate that as the target size of the bubbles, the thickness of the bubble layer, and the bubble number density gradually increase, the peak amplitude of the bubble echo signal gradually becomes stronger. However, when it increases to a certain extent, a broadening phenomenon occurs. Additionally, the photons within the receiving lens area of the bubbles become more concentrated, and the number of photons in the circumferential area increases. The position of these photons varies more randomly. The echo characteristics of ship wake bubbles differ between the two detection methods, each having its own advantages that can complement each other. Integrating these two detection modes can further enhance their benefits.

A dual-mode fusion detection experimental platform for laser detection of ship wake bubbles has been established. Methods based on multi-time scale hierarchical signal processing and algorithms based on time differential cumulative gating image processing have been proposed. Tests and verification analyses have been conducted on the bubbles. The results show that the detection signal-to-noise ratio under the laser adaptive detection mode can reach up to 3.26, but it cannot distinguish false wakes. The signal-to-noise ratio under the imaging mode can reach approximately 16, and when a false wake appears, the maximum detection signal-to-noise ratio can reach 31. The experiments demonstrate that the dual-mode fusion detection of ship wake bubbles using lasers can effectively enhance the detection SNR and effectively counter ship maneuver evasion methods to a certain extent. It achieves effective detection and real-time signal processing of ship wake bubble targets of different magnitudes with high sensitivity, large dynamics, high resolution, and large field of view against a strong reverberation background. This verifies the feasibility of the dual-mode fusion detection mode.

In future work, control experiments or simulations under different lighting conditions will be conducted to address issues related to image color degradation. "

30. References need enrichment.

We have added.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript requires an extensive English editing. The scientific methodology is not clear. The authors should explain the motivation for the proposed Monte Carlo simulation. The conclusions do not show any scientific research, unless the Enlgish used confuses the reader.

The main research question addressed by the authors is not clear. Although the laser dual-mode fusion method is analyzed in the context of ship wake tracking using a Monte Carlo simulation, the English issues make it very difficult to understand the ideas behind this.

It is not clear how the proposed algorithm based on time difference cumulative image processing solves the problem of underwater image color degradation. The methodology should include at least two block diagrams: one describing the problem and another describing the proposed solution. Also, the manuscript does not show proper motivation.

The part relevant to the field, LIDAR, is only the Monte Carlo Simulation with different target characteristics. However, there is no validation of the results with control experiments or simulations. Again, this could be solved after a major English revision.

The references are appropriate.

The conclusion is not appropriate, as it is the same abstract as the paper. In the conclusion sections, the findings, recommendations, results, or future work are not present.

For example, the authors could address the image color degradation issue by including a study in different light conditions with control experiments or simulations as well.

The manuscript requires an extensive English editing. The scientific methodology is not clear. The authors should explain the motivation for the proposed Monte Carlo simulation. The conclusions do not show any scientific research, unless the Enlgish used confuses the reader.

Author Response

Dear Reviewer,

Hello! I am truly grateful for your attention to this paper and for the valuable guidance and suggestions you have provided. Your feedback is extremely important to me, and I believe that with your insights, this paper will be significantly improved.

I appreciate the time you have taken to review my work and offer your expert opinion. I am committed to addressing each of your comments and suggestions to ensure that the paper is as robust and clear as possible.

Thank you again for your dedication and support. I look forward to incorporating your feedback into the revised version of this paper.

Best regards,

Zhang xin

Comments and Suggestions for Authors

1.The manuscript requires an extensive English editing. The scientific methodology is not clear. The authors should explain the motivation for the proposed Monte Carlo simulation. The conclusions do not show any scientific research, unless the Enlgish used confuses the reader.

The abstract section has been revised to emphasize the research purpose and significance of this paper. Modified to "Addressing the issues of weak echo signals and strong background interference in laser detection of ship wakes, an analysis of the laser backscatter detection characteristics of ship wakes has been conducted. Based on the Monte Carlo method, a simulation model for dual-mode fusion detection of ship wake bubbles using laser technology was constructed under different target characteristics. A dual-mode fusion detection system for ship wakes was designed, and an indoor experimental platform for dual-mode fusion detection of ship wake bubbles using laser technology was established. To address problems such as a wide range of echo signal intensity changes, severe signal fluctuations, low resolution, poor image contrast, and blurred target edge information, an algorithm based on multi-time scale hierarchical fusion signal processing and temporal difference accumulation image processing was proposed.Verification experiments for ship wake detection were conducted, which revealed that the dual-mode fusion detection method for ship wake bubbles using laser technology can effectively enhance the detection signal-to-noise ratio and counter the maneuvering evasion of underwater weapons by ships. It achieved high sensitivity, large dynamic range, high resolution, and wide field of view detection and real-time signal processing of ship wake bubble targets of different magnitudes against a strong reverberation background. The effectiveness of the dual-mode fusion detection mode was validated, providing theoretical support for the overall system design and parameter settings. "

Monte Carlo method is a computer simulation based on the trajectory of photon motion. The statistics of photon motion reflect the propagation rules of photons in water. It can simulate the movement process of a large number of photons and record the state of photons without excessive approximation. It can simulate the absorption and scattering characteristics of water bodies under different attenuation coefficients. Many scholars have studied the backward scattering characteristics of bubbles through Monte Carlo method, which is known to most scholars, so it is not detailed here.

     The conclusion has been revised, and the specific answer is elaborated in detail in question 6.

2.The main research question addressed by the authors is not clear. Although the laser dual-mode fusion method is analyzed in the context of ship wake tracking using a Monte Carlo simulation, the English issues make it very difficult to understand the ideas behind this.

The abstract section has been revised to emphasize the research purpose and significance of this paper. Modified to "Addressing the issues of weak echo signals and strong background interference in laser detection of ship wakes, an analysis of the laser backscatter detection characteristics of ship wakes has been conducted. Based on the Monte Carlo method, a simulation model for dual-mode fusion detection of ship wake bubbles using laser technology was constructed under different target characteristics. A dual-mode fusion detection system for ship wakes was designed, and an indoor experimental platform for dual-mode fusion detection of ship wake bubbles using laser technology was established. To address problems such as a wide range of echo signal intensity changes, severe signal fluctuations, low resolution, poor image contrast, and blurred target edge information, an algorithm based on multi-time scale hierarchical fusion signal processing and temporal difference accumulation image processing was proposed.Verification experiments for ship wake detection were conducted, which revealed that the dual-mode fusion detection method for ship wake bubbles using laser technology can effectively enhance the detection signal-to-noise ratio and counter the maneuvering evasion of underwater weapons by ships. It achieved high sensitivity, large dynamic range, high resolution, and wide field of view detection and real-time signal processing of ship wake bubble targets of different magnitudes against a strong reverberation background. The effectiveness of the dual-mode fusion detection mode was validated, providing theoretical support for the overall system design and parameter settings. "

3.It is not clear how the proposed algorithm based on time difference cumulative image processing solves the problem of underwater image color degradation. The methodology should include at least two block diagrams: one describing the problem and another describing the proposed solution. Also, the manuscript does not show proper motivation.

The color degradation part of the underwater image has been removed and the content in Figure 14 has been modified.

4.The part relevant to the field, LIDAR, is only the Monte Carlo Simulation with different target characteristics. However, there is no validation of the results with control experiments or simulations. Again, this could be solved after a major English revision.

This section has been elaborated in the text, and simulation can be mutually validated with experiments.

5.The references are appropriate.

We have added 4 references according to the opinion of another expert

6.The conclusion is not appropriate, as it is the same abstract as the paper. In the conclusion sections, the findings, recommendations, results, or future work are not present.

Modified to"This article focuses on the application background of laser guidance for ship wake bubbles. It studies the laser backscatter characteristics and illumination imaging characteristics of ship wake bubbles with different distances, scales, number densities, and thicknesses. The results indicate that as the target size of the bubbles, the thickness of the bubble layer, and the bubble number density gradually increase, the peak amplitude of the bubble echo signal gradually becomes stronger. However, when it increases to a certain extent, a broadening phenomenon occurs. Additionally, the photons within the receiving lens area of the bubbles become more concentrated, and the number of photons in the circumferential area increases. The position of these photons varies more randomly. The echo characteristics of ship wake bubbles differ between the two detection methods, each having its own advantages that can complement each other. Integrating these two detection modes can further enhance their benefits.

A dual-mode fusion detection experimental platform for laser detection of ship wake bubbles has been established. Methods based on multi-time scale hierarchical signal processing and algorithms based on time differential cumulative gating image processing have been proposed. Tests and verification analyses have been conducted on the bubbles. The results show that the detection signal-to-noise ratio under the laser adaptive detection mode can reach up to 3.26, but it cannot distinguish false wakes. The signal-to-noise ratio under the imaging mode can reach approximately 16, and when a false wake appears, the maximum detection signal-to-noise ratio can reach 31. The experiments demonstrate that the dual-mode fusion detection of ship wake bubbles using lasers can effectively enhance the detection SNR and effectively counter ship maneuver evasion methods to a certain extent. It achieves effective detection and real-time signal processing of ship wake bubble targets of different magnitudes with high sensitivity, large dynamics, high resolution, and large field of view against a strong reverberation background. This verifies the feasibility of the dual-mode fusion detection mode.

In future work, control experiments or simulations under different lighting conditions will be conducted to address issues related to image color degradation. "

7.For example, the authors could address the image color degradation issue by including a study in different light conditions with control experiments or simulations as well.

This section has been revised in the text. Thank you for your feedback and suggestions.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have made revisions. Nevertheless, in some cases these are superficial but even now I should have proposed rejection. Nevertheless, I hope that some superficial changes are only misunderstandings. So I am giving authors a final chance to help. Check and incorporate properly the revisions inside the manuscript. Also, next time all changes must be highlighted:

1)      In the first review and under general comments you have not made revisions about “Furthermore, crucial validation of the experiment is missing, methods are unclear, and a reader cannot find out a method strategy even in an analytical manner”. Please do so. I will give special emphasis on this. This is crucial.

2)      "Using the Mie scattering effect of bubbles": Please explain inside the manuscript’s position you had it earlier and do not erase.

3)      “Rao Jionghui, Xia Min et al.studied the laser backscattering characteristics of bubble curtain by Monte Carlo simulation method, and effective scattering signals from the wake bubbles of a real ship were de-56 tected at 11.5s [ 9 ].” [9] does not correspond to such Authors. Please revise also expression.

4)      Please do not erase “The blue-green laser is used to irradiate the wake region, and the adaptive gain adjustment APD and low-illumination CMOS are used to detect the wake bubble echo, respectively": Please revise the whole sentence. Why do you keep on declaring that it was erased “due to excessive elaboration”?

5)      In the previous line 88 and now 84: "ship wake": You keep on referring to ship wake which is the imminent result of a moving ship (more or less). You should have explained that in your own words to clarify the central idea of your work even if you think that various scientists know it which is not true. Please do so.

6)      "Monte Carlo simulation model" gives minimal information about the procedure. Please elaborate properly. Your answer is “Monte Carlo method is a computer simulation based on the trajectory of photon motion. The statistics of photon motion reflect the propagation rules of photons in water. It can simulate the movement process of a large number of photons and record the state of photons without excessive approximation. It can simulate the absorption and scattering characteristics of water bodies under different attenuation coefficients. Many scholars have studied the backward scattering characteristics of bubbles through Monte Carlo method, which is known to most scholars, so it is not detailed here.”
Please give information about Monte Carlo simulations. You cannot include it in your presentation without giving any details as others do. Please revise and elaborate otherwise it cannot be accepted.

7)      According to [23], the number of photons is set to 10^7, the output wavelength is 532 nm, and the water attenuation coefficient is 0.151 m^-1. Why? You use these values so please elaborate on them.
Comment on the first review: "The number of photons is set to 107, the output wavelength is 532 nm, and the water attenuation coefficient is 0.151 m-1." Please explain the used values.

8)      Figures are of low analysis. You answered, “We have added.” What do you mean?

9)      "The change of laser backscattering when the thickness changes is analyzed": Meaning? You gave this answer “The bubble field in ship wake is a constantly changing process, and the echo characteristics of the bubble layer at different distances are different. Therefore, studying the thickness characteristics of ship wake bubbles is of great significance.”. Where is it inside the manuscript?

10)   You start presenting Figures 5 and 6 without giving before this relevant information of how they were acquired in detail.
Your answer “Figures 5 and 6 are consistent with Figure 4, all based on the relevant parameter conditions.” You do not elaborate. No revisions were made.

11)   “The 4.2 section should be rewritten more carefully and simply.”
You answer “Modified and deleted relevant content.”. Where are the highlighted changes? Please report other time the most important changes if you cannot include them inside cover letter.

Moderate editing of the English language required.

Author Response

The modification description can be seen at the end of the document：

1) In the first review and under general comments you have not made revisions about “Furthermore, crucial validation of the experiment is missing, methods are unclear, and a reader cannot find out a method strategy even in an analytical manner”. Please do so. I will give special emphasis on this. This is crucial.

For the key verification of the experiment : the introduction is modified, and the God problem is more targeted. The introduction is as follows ; in this paper, the relevant principles and formulas of Monte Carlo are added ( question 6 ), which provides support for the relevant information in the following pictures ; add a comparison in the 4.2 part of the article ( question 11 ) ; and here in the explanation, the simulation provides a feasibility analysis for dual-mode fusion detection ; on this basis, a signal processing algorithm is proposed, and then the advantages of signal processing are verified by experiments.

Introduction Part One:The wake of the ship is a dynamic air curtain belt formed at the tail of the ship when the ship is sailing on the water surface due to the cavitation of the propeller, the breaking of the wave and the involvement of a large amount of air in the water line of the ship[1]. The laser detection method of ship wake is a new type of self-guided method[2-3]. The theoretical geometric optics of the scattering characteristics of bubbles in water is in good agreement with the Mie scattering theory. Using the Mie scattering effect of the ship wake bubbles on the laser, the detection of the ship wake can be real-ized, so as to invert the trajectory and velocity characteristics of the ship in the ocean[4-5].The underwater vehicle equipped with the laser detection system can realize the tracking and striking of the ship. However, laser detection of ship wake bubbles has the characteristics of large dynamic change range ( near and far field wake ), severe signal jitter ( bubble sparse and discrete ), low SBR ( weak bubble echo ) and so on[6-7]. At present, in the wake bubble detection method, the intensity detection based on laser forward scattering is mostly used, and the backward radar detection is mostly used. In the wake signal processing, the intensity modulation detection mode is mostly used. The experimental scene is mostly concentrated in the laboratory simulation environ-ment, without considering the environmental interference such as scattering and mul-ti-target occlusion. The model application scene is limited, and the signal processing method has low adaptability to the external field experiment. Therefore, there is an urgent need for a laser detection method that combines multiple detection modes to meet the adaptive performance of ship wake laser detection in different hydrological conditions, sea areas, seasons, hydrology and other external environments, and to achieve high sensitivity, strong anti-interference, large dynamic echo, high reliability of underwater weapon wake laser detection and tracking.

For the method : the relevant principles and formulas of Monte Carlo are added to the text ( question 6 ), and the part of 4.2 is modified in detail, and the method used ( question 11 ) is described in detail.

2) "Using the Mie scattering effect of bubbles": Please explain inside the manuscript’s position you had it earlier and do not erase.

We explain this sentence is”The theoretical geometric optics of the scattering characteristics of bubbles in water are in good agreement with the Mie scattering theory, so this paper also uses the Mie scattering theory of bubbles to study the bubbles in the wake of ships.” It is highlighted in line 35 to 37 in the text.

3) “Rao Jionghui, Xia Min et al.studied the laser backscattering characteristics of bubble curtain by Monte Carlo simulation method, and effective scattering signals from the wake bubbles of a real ship were de-56 tected at 11.5s [ 9 ].” [9] does not correspond to such Authors. Please revise also expression.

We modified it to:”9.Rao,J. H.; Yang, K. C; Zhang, X.H;Xu,D.S.;Xia,M.;Zheng,Y. Simulation of ship bubble wake using pulse laser detection.Optics and Optoelectronics Technology. 2007 ,05, 40-42.”

4) Please do not erase “The blue-green laser is used to irradiate the wake region, and the adaptive gain adjustment APD and low-illumination CMOS are used to detect the wake bubble echo, respectively": Please revise the whole sentence. Why do you keep on declaring that it was erased “due to excessive elaboration”?

We modify the whole sentence to ' The wake bubble area is illuminated by green light, and the light scattered back by the bubble is received by the APD receiving system and the imaging CMOS detection receiving system. It is highlighted in lines 71 to 73 in the text.

5) In the previous line 88 and now 84: "ship wake": You keep on referring to ship wake which is the imminent result of a moving ship (more or less). You should have explained that in your own words to clarify the central idea of your work even if you think that various scientists know it which is not true. Please do so.

In the introduction, the following is added : ' Ship wake is a dynamic air curtain belt formed at the tail of a ship when it is sailing on the surface of the water due to the cavitation of the propeller, the breaking of the waves and the involvement of a large amount of air in the water line of the ship. The relationship between ship wake and ship wake bubbles is explained. It is highlighted in line 30 to 32 in the text.

6) "Monte Carlo simulation model" gives minimal information about the procedure. Please elaborate properly. Your answer is “Monte Carlo method is a computer simulation based on the trajectory of photon motion. The statistics of photon motion reflect the propagation rules of photons in water. It can simulate the movement process of a large number of photons and record the state of photons without excessive approximation. It can simulate the absorption and scattering characteristics of water bodies under different attenuation coefficients. Many scholars have studied the backward scattering characteristics of bubbles through Monte Carlo method, which is known to most scholars, so it is not detailed here.”

Please give information about Monte Carlo simulations. You cannot include it in your presentation without giving any details as others do. Please revise and elaborate otherwise it cannot be accepted.

From line 217 to line 232, we add : ' In the study of the propagation of laser in water, water is regarded as a discrete scattering medium, and the laser beam is regarded as a photon beam composed of many photons. Therefore, the problem of laser propagation in water can be transformed into the problem of photon beam propagation in water. The distribution of particles in seawater is random. When photons propagate in water, they will randomly collide with the medium. The Monte Carlo method is based on the computer simulation of the photon motion trajectory. The basic process is that the photon enters the medium in a specific direction to determine the free path of the photon motion when the collision occurs. If scattering occurs, the corresponding scattering phase function can be selected. Determine the new direction of motion of the photon. If absorption occurs, the photon disappears. These processes are repeated randomly until the photon is received by the receiver. The statistics of photon motion reflect the propagation law of photons in water. Monte Carlo simulation is based on the statistical experimental method of computer, which can simulate the motion process of a large number of photons and record the state of photons. It does not need too much approximation, and can simulate the absorption and scattering characteristics of water body under different attenuation coefficients. '

7) According to [23], the number of photons is set to 10^7, the output wavelength is 532 nm, and the water attenuation coefficient is 0.151 m^-1. Why? You use these values so please elaborate on them.

Comment on the first review: "The number of photons is set to 107, the output wavelength is 532 nm, and the water attenuation coefficient is 0.151 m-1." Please explain the used values.

In this paper, we explain that the more the number of photons, the better the simulation effect. However, due to the performance limitation of the computer, when the number of photons is set to 10⁷, the simulation efficiency is high and the effect is good. The laser transmission distance of 532 nm is set to be far, and the water scattering is smaller than other wavelengths. Setting the water attenuation coefficient to 0.151 m^-1 can approximately simulate the offshore seawater quality. It is highlighted in lines 260 to 265 in the text.

8) Figures are of low analysis. You answered, “We have added.” What do you mean?

Add: The pulse width remains basically unchanged

Add:and its pulse width also varies greatly.

Add :The overall change is stronger than the change in bubble number density .

Add:But its variation is stronger than when the bubble number density changes, second only to when the bubble thickness changes. The overall peak change showed a trend of slow rise first and then rapid rise, and the pulse width showed obvious broadening. The backscattering signal of microbubbles changes little, and the backscattering signal of 275large-scale bubbles changes greatly.

In lines 300-303, it is modified as :From Figure 7, it can be found that as the bubble number density increases, the  number of photons received by the receiving lens gradually increases, and the overall change becomes stronger and stronger. In addition, the photons in the central region become more concentrated and brighter.

Add:It can also resist the ship from avoiding underwater weapons by judging the change of bubble number density characteristics.

Modify the content :From the perspective of imaging, it can also be concluded that bubbles with a large thickness have a greater impact on the detection system, resulting in higher detection sensitivity.

Modify the content :This change is more significant compared to variations  in bubble layer thickness.

It is highlighted in lines 278 to 390 in the text.

9) "The change of laser backscattering when the thickness changes is analyzed": Meaning? You gave this answer “The bubble field in ship wake is a constantly changing process, and the echo characteristics of the bubble layer at different distances are different. Therefore, studying the thickness characteristics of ship wake bubbles is of great significance.”. Where is it inside the manuscript?

Add this sentence to the document and highlight it in lines 283 to 285.

10) You start presenting Figures 5 and 6 without giving before this relevant information of how they were acquired in detail.

Your answer “Figures 5 and 6 are consistent with Figure 4, all based on the relevant parameter conditions.” You do not elaborate. No revisions were made.

The free path formula :

                    (1)

is the new beam propagation distance after m collisions ;  is the probability of collision of motion ; is the probability that the motion does not collide ; is the particle radius ; N is the logarithmic density about c ; is a random number between ( 0, 1 ).

After the mth collision, the emission direction of the photon is  relative to the previous coordinate system. After the m + 1th collision, the emission direction is  relative to the mth coordinate system. Among them :

             (2)

Fig.5 and Fig.6 are obtained by inputting the relevant bubble characteristic parameters from the above formula.

11) “The 4.2 section should be rewritten more carefully and simply.”

You answer “Modified and deleted relevant content.”. Where are the highlighted changes? Please report other time the most important changes if you cannot include them inside cover letter.

The following contents are added in 4.2.1 :

However, the highest SBR of these two methods is about 1.5 ,which is difficult to adapt to the laser echo detection of wake bubbles.

Signal-to-Background Ratio (SBR) is the ratio of the intensity of the target signal to that of the backscattered signal from the waters in a given time or space. That is:

                                  (3)

where  is the target echo signal amplitude and  is the water background signal amplitude. For wake detection, the farther the detection SBR is from 1, the greater the discrepancy between the wake signal and the background signal of the water, the better the detection performance. However, when detecting low-density, small-scale bubble groups, the laser echo signal is very weak, and its amplitude is often similar to the water background signal. In this case, the signal-to-background ratios of both amplitude and pulse width are close to 1, making it difficult to determine whether a wake is detected.

As shown in Fig. 12, in the coordinate system , the blue curve  is the simulated wake echo signal with amplitude  and pulse width  . The red curve  is the simulated water background signal with amplitude  and pulse width . The amplitude SBR of the two signals in Fig. 12 is:

                           (4)

Calculating the ratio of the pulse widths of the two signals in the same way, the SBR of the pulse widths is:

                           (5)

Approximating the two signals as sinusoids, the tail flow signal expression is:

                        (6)

The water background signal expression is:

                        (7)

Integrate the two signals separately in time:

               (8)

               (9)

The SBR of the integral values of the two signals is:

           (10)

          (11)

Therefore, the SBR of the integral value is larger than that of the amplitude and pulse width. The integration method improves the detection SBR, which can amplify the characteristics of the wake signal and make the target easier to be recognized.

Fig. 12. One-cycle echo curve of wake and water background.

Added more principle content.

The following contents are added in 4.2.2 :

In this paper, a ship wake detection device is constructed using a high-frequency laser. When the motion speed of the detection device matches the pulse period of the laser, the signals of consecutive  cycles can be approximated as the echoes of the same wake bubble. Therefore, the method first splits the signal into  intervals of length : . The signal amplitude corresponding to the endpoints of each interval is . The maximum value in each interval is , . The two endpoints and the maximum point within each interval are used to fit the envelope of the signal by employing cubic spline interpolation, which maximizes the retention of the echo signal characteristics of the wake. Cubic spline interpolation is a numerical analysis method that fits discrete points into smooth curves by means of cubic polynomials [13]. Let the cubic spline function in each interval be:

                  (10)

Then the cubic spline function satisfies three conditions:

(1) Interpolation condition, i.e. ;

(2) Equal values of the spline function at the common endpoints of adjacent intervals, i.e. ;

(3) The curve is smooth, i.e.  is continuous;

From these three conditions, the value of the cubic spline function coefficients  can be derived, which in turn fits the envelope of the original echo signal.

The amplitude distribution of the fitted envelope curve still has a large dispersion affected by the original signal amplitude jitter. In order to reduce the standard deviation of the signal envelope amplitude, a sliding mean filtering algorithm is used to further smooth it. It is a filtering algorithm that takes the average of  consecutive points instead of the rd point value .  is the size of the sliding window and must be an odd number. For example, if the value of a point is , after the sliding mean filter algorithm, the value is:

              (11)

The description is more detailed and the end of 4.2.2 is deleted.

Author Response File: Author Response.pdf

Round 3

Reviewer 1 Report

Research on laser dual-mode fusion detection method of ship wake bubble

In this manuscript, the authors undertake a comprehensive analysis of the laser backscatter detection characteristics associated with ship wakes. They meticulously construct a simulation model and design a detection system tailored for dual-mode fusion detection, bolstered by the establishment of an indoor experimental platform. To mitigate challenges such as wide-ranging echo signal intensity changes and severe signal fluctuations, they propose an innovative algorithm based on multi-time scale hierarchical fusion signal processing and temporal difference accumulation image processing. Through rigorous verification experiments, they demonstrate the efficacy of the dual-mode fusion detection method, showcasing its ability to significantly enhance the Signal-to-Background Ratio and counteract the maneuvering evasion of underwater weapons by ships. This research not only validates the effectiveness of the proposed detection mode but also provides invaluable theoretical insights for the overall system design and parameter settings.

This work is intriguing and presents an application of interest to a specific audience niche. However, I have noticed certain aspects that need to be promptly addressed by the authors before it can be accepted. These include:

1.      The authors commence their introduction with a direct approach to the presented topic. However, I believe that a clearer context should be added, addressing questions such as the importance of the studied market and its current functioning. Additionally, various aspects of laser technology should be presented clearly, including how it functions and why it is utilized in this type of application. I would suggest discussing LiDAR and laser technologies and their potential uses, such as airborne laser applications in mapping (Balsa-Barreiro et al., 2012), as well as in vehicle tracking and detection.

2.      In the introduction, the authors argue, “However, laser detection of ship wake bubbles has the characteristics of a large dynamic change range (near and far field wake), severe signal jitter (bubble sparse and discrete), low SBR (weak bubble echo), and so on [6-7].” -> Perhaps the authors could discuss bathymetric laser or similar devices, whose approach could be valuable here.

3.       Also in the introduction, they argue, “For example, Li Tenglong and He Junhua of Xi 'an Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, studied the bubble size distribution and bubble rising law in the bubble curtain of simulated ship wake by using high-speed photography technology in the laboratory environment. Yuan Junxing, Chen Liangyi et al. used holographic imaging technology to detect the wake, and studied the forward scattering characteristics of wake bubbles [8].” -> The manner of including references to other studies should be clearer, more stringent, and in accordance with the guidelines and style of the journal.

Author Response

1. The authors commence their introduction with a direct approach to the presented topic. However, I believe that a clearer context should be added, addressing questions such as the importance of the studied market and its current functioning. Additionally, various aspects of laser technology should be presented clearly, including how it functions and why it is utilized in this type of application. I would suggest discussing LiDAR and laser technologies and their potential uses, such as airborne laser applications in mapping (Balsa-Barreiro et al., 2012), as well as in vehicle tracking and detection.

From line 30 to line 35, we add : “Underwater laser detection is a technology that uses laser to search, track, detect, locate and identify underwater targets. It has the characteristics of high precision, high robustness and rapid response. It has great application value in marine remote sensing surveying and mapping, underwater target detection and tracking. Ship wake detection technology based on laser guidance is a typical application of underwater laser detection technology[1].” It is highlighted in line 30 to 35 in the text.

2.In the introduction, the authors argue, “However, laser detection of ship wake bubbles has the characteristics of a large dynamic change range (near and far field wake), severe signal jitter (bubble sparse and discrete), low SBR (weak bubble echo), and so on [6-7].” -> Perhaps the authors could discuss bathymetric laser or similar devices, whose approach could be valuable here.

We modify the whole sentence to“ However, the current laser detection system has problems and bottlenecks such as large dynamic changes in the received signal, poor stability of the received signal, and low SBR of the received signal. [6-7].” It is highlighted in line 43 to 45 in the text.

3.Also in the introduction, they argue, “For example, Li Tenglong and He Junhua of Xi 'an Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, studied the bubble size distribution and bubble rising law in the bubble curtain of simulated ship wake by using high-speed photography technology in the laboratory environment. Yuan Junxing, Chen Liangyi et al. used holographic imaging technology to detect the wake, and studied the forward scattering characteristics of wake bubbles [8].” -> The manner of including references to other studies should be clearer, more stringent, and in accordance with the guidelines and style of the journal.

We modify the whole sentence to“ For example, Li Tenglong et al. [ 8 ] studied the bubble size distribution and bubble rising law in the bubble curtain of simulated ship wake by using high-speed photog-raphy technology in the laboratory environment. Yuan Junxing et al.used holographic imaging technology to detect the wake, and studied the forward scattering characteris-tics of wake bubbles .” It is highlighted in line 60 to 65 in the text.

We modify the whole sentence to“ Rao Jionghui et al. [ 9 ]studied the laser backscattering characteristics of bubble curtain by Monte Carlo simulation method, and effective scattering signals from the wake bubbles of a real ship were detected at 11.5s.”It is highlighted in line 68 to 70 in the text.

Author Response File: Author Response.pdf