Spatiotemporal Analysis of Sonar Detection Range in Luzon Strait

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

A brief summary 

The Authors used the Bellhop acoustic propagation model to estimate transmission loss, applied a detection probability integration approach to determine sonar detection range in the Luzon Strait.  They focused on the data from period 2019 – 2023, and results were subjected to statistical analysis. The article employs the methodology established by Ferla and Porter to determine the optimal receiving depth for the calculation of sonar detection range. This method initiates with the sonar equation and calculates the signal excess (SE) by utilizing the figure of merit (FOM) in conjunction with the transmission loss (TL). Obvious and simple conclusions about longer and shorter detection ranges are provided. These findings are commonly known, though the authors did a good job.

 

General concept comments

The manuscript is generally clear and relevant for the field and presented in a well-structured manner. There is no Discussion section and should be supplemented. Authors should discuss the results and how they can be interpreted in viewpoint of previous studies. The findings and their implications should be discussed as well as future scientific directions provided.

Authors cited only 4 references within the last 5 years and too many publications within 20 years. The list of publications is quite short and rather insufficient. The manuscript is not rather scientifically sound. Some figures (images) are of poor quality and should be replaced for higher resolution maps, images, diagrams (fig. 4, 5, 6, 7, 8). On the other hand, they are easy to interpret. The conclusions are clear and consistent, but commonly known. 

 Specific comments 

These are provided in the pdf file of the manuscript (yellow highlights).

 

 

Comments for author File: Comments.pdf

Author Response

Comment 1: The Authors used the Bellhop acoustic propagation model to estimate transmission loss, applied a detection probability integration approach to determine sonar detection range in the Luzon Strait.  They focused on the data from period 2019 – 2023, and results were subjected to statistical analysis. The article employs the methodology established by Ferla and Porter to determine the optimal receiving depth for the calculation of sonar detection range. This method initiates with the sonar equation and calculates the signal excess (SE) by utilizing the figure of merit (FOM) in conjunction with the transmission loss (TL). Obvious and simple conclusions about longer and shorter detection ranges are provided. These findings are commonly known, though the authors did a good job.

Response 1: Thank you for pointing this out. The understanding of the impact of the mixed layer and water depth on underwater acoustic propagation is relatively well-established. It seems you suggest that there is a perceived lack of innovation and scientific rigor in the paper. To address this, we have made several adjustments:

1. We have added content to the introduction to clarify the purpose of our research, which is to understand the changes in sonar detection range across the Luzon Strait. This understanding is intended to support anti-submarine warfare operations, such as the configuration of surface vessel sonar arrays and the planning of mission paths for various sonar platforms. With this goal in mind, our study conducts statistical analyses of the complex marine environment in the Luzon Strait to extract practical and applicable patterns, which is of significant importance.
2. In the Discussion section, we have highlighted the challenges of obtaining information for actual mission planning, such as the difficulty of access and the need for real-time data. We have analyzed the necessity of predicting DR using limited information.
3. In the Discussion section, we have demonstrated the use of an empirical formula fitted with two parameters, MLD and water depth, to predict DR. This further emphasizes the significance of our analysis of the spatiotemporal variation patterns of DR. It also provides a conceptual framework for predicting DR in support of underwater detection activities.

 

Comment 2: The manuscript is generally clear and relevant for the field and presented in a well-structured manner. There is no Discussion section and should be supplemented. Authors should discuss the results and how they can be interpreted in viewpoint of previous studies. The findings and their implications should be discussed as well as future scientific directions provided.

Response 2: Thank you for pointing this out. The article has been enhanced with a new Discussion section. In this section, we explore the general patterns of DR variations with the MLD and water depth in the study area. We then fit these patterns with an empirical formula, which allows for a rapid estimation method of the detection range. This addition strengthens the academic rigor and innovation of our paper. Furthermore, we contemplation of future applications of this research.

 

Comment 3: Authors cited only 4 references within the last 5 years and too many publications within 20 years. The list of publications is quite short and rather insufficient. The manuscript is not rather scientifically sound. Some figures (images) are of poor quality and should be replaced for higher resolution maps, images, diagrams (fig. 4, 5, 6, 7, 8). On the other hand, they are easy to interpret. The conclusions are clear and consistent, but commonly known. 

Response 3: Thank you for pointing this out. To enhance the clarity and relevance of our research objectives and significance, we have supplemented the reference section with additional citations of the latest studies. Moreover, we have redrafted some of the figures to improve their quality and clarity.

 

Comment 4: These are provided in the pdf file of the manuscript (yellow highlights).

Response 4: In response to the issues you identified in the PDF, we have made all the necessary revisions.

Reviewer 2 Report

Comments and Suggestions for Authors

The paper explores a methodology to determine the optimal receiving depth for calculating sonar detection range, particularly in the Luzon Strait area. The approach involves using the sonar equation to compute signal excess (SE) and figure of merit (FOM) along with transmission loss (TL) derived from an acoustic propagation model. The study utilizes data from the Hybrid Coordinate Ocean Model (HYCOM) and Mackenzie’s empirical formula to analyze sound propagation characteristics over a five-year period.

Comments:

1. The paper relies heavily on the acoustic propagation model without providing sufficient empirical validation or comparisons with other models.

2. The study uses a fixed spatial resolution of 0.5° and a temporal resolution of 10 days. This granularity may not capture finer-scale variations in the underwater environment, which could impact the accuracy of the sonar detection range calculations.
3. The methodology accounts for acoustic wave interference by integrating TL curves to avoid manual selection errors. However, the paper does not adequately address how this method handles complex interference patterns.

4. The analysis is based on historical data spanning five years. Given the dynamic nature of oceanographic conditions, the authors should discuss how the results would validate with time.

Author Response

Comment 1: The paper relies heavily on the acoustic propagation model without providing sufficient empirical validation or comparisons with other models.

Response 1: Thank you for pointing this out. In actuality, conducting acoustic detection experiments at sea is quite challenging, and the data obtained are often subject to strict confidentiality, precluding our access to a substantial amount of data necessary to validate our research. The Bellhop model, however, has gained widespread adoption due to its superior acoustic simulation capabilities. The computed sound fields by the Bellhop model exhibit a high degree of agreement with experimental data and theoretical models within the frequency range of 0.6~30 kHz. It has been designated as the standard model by the United States Navy for predicting acoustic propagation in the 10~100 kHz frequency band. Given the model's excellence and the practical difficulties in experimental validation, we have chosen to employ the Bellhop model in our study to elucidate the spatiotemporal variability of sonar detection ranges across the Luzon Strait, thereby providing a foundation for subsequent engineering applications. We have included a similar description in the manuscript to account for these considerations.

 

Comment 2: The study uses a fixed spatial resolution of 0.5° and a temporal resolution of 10 days. This granularity may not capture finer-scale variations in the underwater environment, which could impact the accuracy of the sonar detection range calculations.

Response 2: Thank you for pointing this out. We fully concur that enhancing the granularity of research is essential for investigating mechanisms in marine environments where conditions are characterized by complexity and variability. However, the decision to employ a coarser research granularity in the present study was primarily influenced by several considerations:

1. In the real ocean, sound propagation is greatly influenced by environmental factors. Our research aimed to offer concrete and intuitive support for practical applications, and a finer granularity might render the description of regularities more challenging, potentially leading to confusion among application personnel.
2. In practical applications, such as using detection ranges within a marine area for route and array positioning planning, an overly refined distribution of detection distances can impose unnecessary burdens on the planning process.
3. A spatial resolution of 0.5° is adequate to represent the variations in detection ranges with changes in bathymetry and mixed layer depth across the research area.

 

Comment 3: The methodology accounts for acoustic wave interference by integrating TL curves to avoid manual selection errors. However, the paper does not adequately address how this method handles complex interference patterns.

Response 3: Thank you for pointing this out. We will utilize graphics in the "Data and Methods" section of the article to illustrate the advantages of this method.

 

Comment 4: The analysis is based on historical data spanning five years. Given the dynamic nature of oceanographic conditions, the authors should discuss how the results would validate with time.

Response 4: Thank you for pointing this out. In section 3.2.2, we provide a supplementary explanation for the physical oceanographic reasons behind the temporal variation of the MLD based on previous research findings. Specifically, we clarify that the instability of surface water caused by buoyancy flux is the primary factor leading to the formation of a stronger mixed layer. This also offers an explanation for the temporal changes in DR, as MLD is a key factor influencing DR.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors responded to all my comments and suggestions. They made major improvements. They completed some sections, e.g. Discussions. The authors also referred to additional references that they included in the article. I believe that the paper in this form, after significant improvement, can be published.