The Impact of the Number of Sensors on Stress Wave Velocity in 2D Acoustic Tomography of Araucaria cunninghamii Sweet

Round 1

Reviewer 1 Report (Previous Reviewer 1)

Comments and Suggestions for Authors

Dear Authors,

Congratulations on making pertinent corrections, including correcting the title, supplementing the description of the research material, and conducting a more extensive discussion with reference to many publications.
I have no comments regarding the content.
The text still requires editing, in particular the addition of discussion elements where there are duplicate references to literature: the author's name and year, as well as the number on the References list. Only the publication numbers from the list should remain. 

Yours sincerely
Reviewer

Author Response

Reviewer 1

Dear Authors,

Congratulations on making pertinent corrections, including correcting the title, supplementing the description of the research material, and conducting a more extensive discussion with reference to many publications.

I have no comments regarding the content.

The text still requires editing, in particular the addition of discussion elements where there are duplicate references to literature: the author's name and year, as well as the number on the References list. Only the publication numbers from the list should remain.

A.

Thank you very much for your valuable feedback.

Regarding the duplicate references in the discussion section, we apologize for this oversight. As we incorporated extensive content based on the valuable suggestions from all four reviewers, some citations were formatted redundantly.

We have now conducted a thorough review and revision of the entire manuscript. All duplicate literature citations have been corrected, and we have ensured that the citation format throughout the paper, including the reference numbers, fully complies with this journal's guidelines.

 

Author Response File: Author Response.pdf

Reviewer 2 Report (Previous Reviewer 4)

Comments and Suggestions for Authors

After the manuscript was revised, I recommend accepting this form.

Author Response

Reviewer 2

After the manuscript was revised, I recommend accepting this form.

A.

Thank you for your review and positive recommendation. We are very grateful for your valuable feedback, which has helped us significantly improve the quality of our manuscript.

 

Reviewer 3 Report (New Reviewer)

Comments and Suggestions for Authors

This manuscript explores the effect of sensor number (8, 12, 16, and 20) on stress wave velocity in 2D acoustic tomography of Hoop pine trees (Araucaria cunninghamii Sweet). It combines acoustic tomography with resistance drilling to validate findings, aiming to improve diagnostic accuracy for detecting decay and cavities in trees .

Here are six minor comments for improvement:

1. The description of study site and tree selection (DBH > 70 cm, 5 trees, Gongguan Campus) is repeated almost verbatim in sections 2.1 and 2.2; consider merging to avoid redundancy .

2. Figures (e.g., Figures 1–7) use different formats and legends; ensuring consistent scales, colors, and labeling would improve readability .

3. The introduction repeats the objectives twice (lines 55–61 and 87–92). Streamlining would make the narrative more concise and professional .

4. Results mention significance with ANOVA and Tukey tests, but p-values are sometimes given only as thresholds (e.g., p ≤ 0.05). Exact values or confidence intervals would strengthen the rigor .

5. Phrases such as “healthy trees exhibited more scattered acoustic velocity distributions” could be rewritten more precisely (e.g., “greater variability in acoustic velocity across radial directions”) .

6. The discussion notes limitations of acoustic tomography but does not sufficiently address sample size (only 5 trees, all of the same species and site). Highlighting this limitation explicitly would add transparency .

Author Response

Reviewer 3

This manuscript explores the effect of sensor number (8, 12, 16, and 20) on stress wave velocity in 2D acoustic tomography of Hoop pine trees (Araucaria cunninghamii Sweet). It combines acoustic tomography with resistance drilling to validate findings, aiming to improve diagnostic accuracy for detecting decay and cavities in trees .

A.

Thank you for your concise and accurate summary of our research. We are very grateful for your insightful review, which confirms that the core objectives of our study have been clearly communicated. We have revised the manuscript to better highlight these key points and to ensure our research's purpose is even more explicit to the reader.

 

Here are six minor comments for improvement:

1. The description of study site and tree selection (DBH > 70 cm, 5 trees, Gongguan Campus) is repeated almost verbatim in sections 2.1 and 2.2; consider merging to avoid redundancy.

A.

Thank you for your careful review. You are correct; the information regarding the study site and tree selection was unnecessarily repeated. We have now revised the manuscript by removing the redundant content and consolidating the details into a single, clear section to enhance readability.

 

1. Figures (e.g., Figures 1–7) use different formats and legends; ensuring consistent scales, colors, and labeling would improve readability .

A.

Thank you for your valuable feedback. We agree that consistency is crucial for readability. We have now revised Figures 1-7 to ensure a unified format, including consistent scales, colors, and labeling, to facilitate easier comparison and observation.

 

1. The introduction repeats the objectives twice (lines 55–61 and 87–92). Streamlining would make the narrative more concise and professional .

A.

Thank you for your careful review. We agree that the research objectives were stated twice in the introduction. We have now revised the manuscript to remove the redundant text and streamline the narrative, making it more concise.

 

1. Results mention significance with ANOVA and Tukey tests, but p-values are sometimes given only as thresholds (e.g., p ≤ 0.05). Exact values or confidence intervals would strengthen the rigor.

A.

We have revised Table 4 to include the exact p-values, providing a more precise presentation of the significance test results.

 

1. Phrases such as “healthy trees exhibited more scattered acoustic velocity distributions” could be rewritten more precisely (e.g., “greater variability in acoustic velocity across radial directions”) .

A.

Thank you for your valuable feedback. Your suggestion regarding the precision of our language is very important. We have revised the phrase "more scattered acoustic velocity distributions" to "greater variability in acoustic velocity across radial directions." We have also conducted a comprehensive review of the entire manuscript to ensure all similar descriptions are rephrased for greater accuracy and professionalism.

 

1. The discussion notes limitations of acoustic tomography but does not sufficiently address sample size (only 5 trees, all of the same species and site). Highlighting this limitation explicitly would add transparency .

 

A.

Thank you for your review and guidance.

Regarding the points you raised, we have added a new paragraph in Section 4.4 of the discussion to explicitly state the limitations of this study regarding sample size. This new section also explains the rationale behind our selection of a single tree species and location, as well as the directions for future research.

In discussing the application of acoustic tomography, this study must explicitly state that a major limitation is the sample size. As the focus of this research was to investigate the effect of different numbers of sensors on stress wave velocity detection, we selected five trees of the same species (Hoop pine, Araucaria cunninghamii Sweet) from a single location to ensure highly consistent experimental conditions. The small sample size and the single location and species do limit the generalizability of the findings, and the conclusions cannot be fully extrapolated to other tree species or different growing environments. Nevertheless, under these specific controlled conditions, this study successfully established the relationship between the number of sensors and the detection results. Future research will expand the sample size to include a wider range of tree species and growing environments to further validate and strengthen the findings of this study.

 

Author Response File: Author Response.pdf

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors,

It is an interesting and carefully prepared manuscript. However, before publishing the manuscript, a few corrections/additions should be made. I present my comments in accordance with the arrangement of chapters in the article. 

Substantive comments

Title: The title of the article should be precise and indicate which tree species was examined. Individual species differ significantly in anatomical structure, distinguishable heartwood and whitewood zones, and humidity of individual zones, which influences the results of acoustic tests. A method that works in the trunks of growing araucarias will not necessarily be as effective in the case of other species, e.g., deciduous ones. The current title is too general and therefore somewhat misleading, suggesting a more extensive cross-sectional study.

Keywoords: Keywords should be supplemented with the English or Latin name of the trees being examined: hoop pine or Araucaria cunninghamii

Materials and Methods
Experimental methods
The full name of the trees examined should be given at least once: hoop pine (Araucaria cunninghamii Aiton ex A.Cunn). In this type of study, the age of the trees should at least be estimated. It would be valuable to use a Presnel drill and determine this age based on visible annual growth. The time of year when the tree trunk examination was conducted should be given because it affects the moisture content of the wood in the tree.

Resistance Drilling Test
The drill geometry should be presented; providing only the diameters is not sufficient.

Discussion
It should be clearly emphasized in the discussion that the tests were conducted on five hoop pine trunks. There should also be a critical assessment of whether the results obtained can be applied to other tree species.

Conclusion
The conclusions also lack an indication of what species of trees were studied. This element should be supplemented. In their current wording, the conclusions also constitute an excessive and unjustified generalization, as does the title of the manuscript. 

Yours sincerely
Reviewer

Author Response

Dear Authors,

Q.

It is an interesting and carefully prepared manuscript. However, before publishing the manuscript, a few corrections/additions should be made. I present my comments in accordance with the arrangement of chapters in the article.

A.

Thanks.

Q.

Substantive comments

Title: The title of the article should be precise and indicate which tree species was examined. Individual species differ significantly in anatomical structure, distinguishable heartwood and whitewood zones, and humidity of individual zones, which influences the results of acoustic tests. A method that works in the trunks of growing araucarias will not necessarily be as effective in the case of other species, e.g., deciduous ones. The current title is too general and therefore somewhat misleading, suggesting a more extensive cross-sectional study.

A.

"I have revised the title to 'The Impact of the Number of Sensors on Stress Wave Velocity in 2D Acoustic Tomography of Araucaria cunninghamii Sweet'."

Q.

Keywoords: Keywords should be supplemented with the English or Latin name of the trees being examined: hoop pine or Araucaria cunninghamii

A.

"I have supplemented the keywords with the scientific name of the tree being examined. The updated keywords now include 'hoop pine (Araucaria cunninghamii Sweet).' Thank you for your suggestion."

Materials and Methods
Experimental methods
The full name of the trees examined should be given at least once: hoop pine (Araucaria cunninghamii Aiton ex A.Cunn). In this type of study, the age of the trees should at least be estimated. It would be valuable to use a Presnel drill and determine this age based on visible annual growth. The time of year when the tree trunk examination was conducted should be given because it affects the moisture content of the wood in the tree.

A.

"I have made the revisions based on your suggestions. The text now includes that the age of the sampled trees is estimated using an increment corer to extract core samples, and the examination was conducted during March 2025."

This study was conducted at the Gongguan Campus of National Taiwan Normal University, located in the Wenshan District of Taipei City, Taiwan. Hoop pine (Araucaria cunninghamii Sweet) trees were examined during the period of March 2025. Trees growing along the roadside were selected as the research subjects. To ensure effective detection of the internal condition of tree trunks, sample trees with a diameter at breast height (DBH) greater than 70 cm were chosen for analysis. The estimated age of the sampled trees, based on visible annual growth rings, is between 47 and 51 years, determined using an increment corer to extract core samples. A total of five qualified trees were selected for subsequent acoustic tomography and resistance drilling tests.

 

Q.

Resistance Drilling Test
The drill geometry should be presented; providing only the diameters is not sufficient.

A.

The drill bit specifications were as follows: a cylindrical drill bit with a tip diameter of 3.0 mm, a shaft diameter of 1.5 mm, and made of stainless steel with a special coating. The drill bit features a sharp conical tip designed for efficient penetration.

 

Q.

Discussion

It should be clearly emphasized in the discussion that the tests were conducted on five hoop pine trunks. There should also be a critical assessment of whether the results obtained can be applied to other tree species.

A.

We appreciate the valuable suggestions from the committee. We have incorporated the committee's feedback into the discussion section, adding explanations regarding the limitations of the study and the significant value of this research. Specifically, we emphasized the contributions of this study to tree health diagnosis and how the complementary advantages of acoustic tomography and resistance micro-drilling can enhance diagnostic accuracy and operational efficiency. Additionally, we discussed future research directions to expand the sample scope and integrate more techniques, further promoting the scientific assessment of urban tree risk.

This study does have limitations, influenced by various factors such as tree species, sample size, moisture content, wood grain, and decay, which may affect the test results. However, this does not diminish the value and importance of this research. As a conifer, the low wood density of the tropical cedar provides important testing methods and results that can serve as a basis for future applications of similar tree species or wood materials.

Future studies are recommended to expand the sample scope by including more tree species, different diameter classes, and diverse environmental conditions to establish a representative acoustic parameter database. Additionally, the integration of three-dimensional imaging technologies, machine learning algorithms, and various non-destructive testing tools should be explored to enhance diagnostic precision and support the development of intelligent systems. Special attention should be given to the relationship between acoustic velocity variability and different types of damage, in order to develop practical threshold values—either fixed or adaptive—as indicators for early decay detection, thereby promoting the scientific and standardized assessment of urban tree risk.

 

Q.

Conclusion

The conclusions also lack an indication of what species of trees were studied. This element should be supplemented. In their current wording, the conclusions also constitute an excessive and unjustified generalization, as does the title of the manuscript. 

A.

I have modified the content in the "Conclusion" section to include a description of the tree species.

 

Reviewer 2 Report

Comments and Suggestions for Authors

This is an interesting study carried out in forest site, which push the research one step forward to real forest management. There are some questions and suggestions to be discussed with authors:

 

1. The main content of this article is dealing with the Impact of the Number of Sensors on Stress Wave Velocity in Tree 2D Acoustic Tomography. It is obvious that the stress wave velocity in wood depends on the wood density and elastic modulus. There is a study focused on this field and please authors read this reference at Effects of Tangential Angles on Stress Wave Propagation Velocities in Log's Cross Sections Scientia Silvae Sinicae. 2011，（8）P139-142.

 

2. As the authors stated in the article that sensors number and distribution also have some effects on the measurement accuracy of stress propagating 2D tomography. This should be one of the key research objectives of study like this. There is an early close study showed some very interesting results. Please authors read it at Effects of Sensor Quantity and Planar Distribution on Testing Results of Log Defects Based on Stress Wave. Scientia Silvae Sinicae，2008（44）（5）.

 

3. Tress wave propagation is affected by measurement environment factors significantly. Those factors, such as sample tree species, moisture content and temperature, are also important for readers. So I suggest that authors should state more about the main parameters of these sample trees.

 

 

 

 

Comments for author File: Comments.pdf

Author Response

Reviewer B

This is an interesting study carried out in forest site, which push the research one step forward to real forest management. There are some questions and suggestions to be discussed with authors:

Q.

1. The main content of this article is dealing with the Impact of the Number of Sensors on Stress Wave Velocity in Tree 2D Acoustic Tomography. It is obvious that the stress wave velocity in wood depends on the wood density and elastic modulus. There is a study focused on this field and please authors read this reference at Effects of Tangential Angles on Stress Wave Propagation Velocities in Log's Cross Sections Scientia Silvae Sinicae. 2011，（8）P139-142.

1. I have already used them as references and discussed them in the 'Discussion' chapter.

 

Q.

1. As the authors stated in the article that sensors number and distribution also have some effects on the measurement accuracy of stress propagating 2D tomography. This should be one of the key research objectives of study like this. There is an early close study showed some very interesting results. Please authors read it at Effects of Sensor Quantity and Planar Distribution on Testing Results of Log Defects Based on Stress Wave. Scientia Silvae Sinicae，2008（44）（5）.

1. I have already used them as references and discussed them in the 'Discussion' chapter.

 

Q.

1. Tress wave propagation is affected by measurement environment factors significantly. Those factors, such as sample tree species, moisture content and temperature, are also important for readers. So I suggest that authors should state more about the main parameters of these sample trees.

1. I have already used them as references and discussed them in the 'Discussion' chapter.

 

Regarding the literature review on factors affecting the velocity of stress waves for wood detection, I have added the discussion content to the 'Discussion' chapter, including four articles such as Bucur 2023, Wang et al. 2008, and 2011, El-Hadad et al., 2018.

There are numerous factors influencing the velocity of stress waves for wood detection, including the physical properties, microstructure, and the angles of annual rings and fibers. The wood's physical characteristics, such as density, moisture content, grain angle, and modulus of elasticity, directly affect the propagation speed of mechanical waves. From a microscopic perspective, the arrangement of wood cells, the layered structure of annual rings, and the physical properties of cell walls all influence wave velocity. Specifically, studies have found a high negative correlation between annual ring width and longitudinal wave velocity, meaning that smaller and more regular annual rings result in higher stress wave velocities. Additionally, the microfibril angle is a critical factor, with a smaller microfibril angle typically corresponding to a higher ultrasonic velocity. As wood is an anisotropic material, its elastic constants differ in radial, tangential, and longitudinal directions, which leads to varying stress wave velocities in different directions (Bucur, 2023). The velocity of stress waves propagating across a log's cross-section is also affected by the tangential angle, following a cubic curve trend; moreover, different tree species have a significant impact on stress wave velocity (Wang et al., 2011). The factors mainly affecting the results of stress wave detection for logs are the number and planar distribution of sensors. A proper increase in the number of sensors can improve the image fitting degree and reduce the error rate, thereby enhancing the accuracy of stress wave detection for log defects (Wang et al., 2008). Besides, factors influencing the velocity of stress waves in wood include wood species, moisture content, input signal frequency, signal propagation distance, and the condition of the wood, such as the presence of cracks. The literature points out that as moisture content increases, the speed of sound waves decreases. Similarly, cracks or decay within the wood also cause a reduction in ultrasonic wave velocity, which in turn affects the accuracy of detection (El-Hadad et al., 2018).

 

 

Reviewer 3 Report

Comments and Suggestions for Authors

This paper investigates the application of two-dimensional acoustic tomography combined with resistance micro-drilling for identifying internal defects in trees and evaluates the effect of different sensor quantities on diagnostic outcomes. Overall, the research methods employed are rather conventional, and the experimental design is simplistic, relying solely on commercially available equipment ( Fakopp 3D Acoustic Tomograph and RESI PD500 Resistance Drill). The study lacks innovation in terms of sensor technology, algorithm improvements, or novel data-processing methods.

Major issues include:

• Lack of Innovation:

The equipment and methods utilized are existing commercial technologies without any modification or improvement. The paper provides no description or analysis of the algorithms employed by these products. Furthermore, it lacks theoretical exploration into sensor mechanisms, wave propagation patterns, or underlying causes of velocity variations. Important questions remain unanswered, such as: What are the inherent limitations of ultrasonic detection? Does ultrasound detection have specific limitations for shallow defects, and could visual sensing methods potentially compensate for these shortcomings? For instance, the ultrasonic images in Table 2 show red points at sensor positions near edges—why does this occur?

• Simplistic Experimental Design and Routine Data Analysis:

The sample size is limited (only 5 trees), thus weakening the representativeness of the data. Consideration of prior knowledge integration or employing machine learning methods could improve detection reliability. Moreover, how might early-stage diseases in trees be effectively identified?

Addressing any of these points would significantly enhance the innovation and depth of the study, moving it beyond merely superficial analysis using commercial sensors.

Minor suggestions:

• A schematic diagram clearly illustrating sensor placement, including ultrasonic signal generators and receivers, should be provided.
• Excessive blank space appears on page 3, requiring formatting improvements.
• If possible, employing tomography slice scans could enhance the credibility and robustness of the results.
• On page 14, the reference should correctly indicate "Table 4" instead of "Table 9."

In conclusion, the study's content, methods, and conclusions remain conventional and do not present notable innovations or substantial contributions in theory or methodology. Primarily, this research merely demonstrates standard applications of commercial detection equipment without deeper exploration or improvements in sensor technologies, methodologies, or underlying mechanisms.

Author Response

Reviewer C

Q.

This paper investigates the application of two-dimensional acoustic tomography combined with resistance micro-drilling for identifying internal defects in trees and evaluates the effect of different sensor quantities on diagnostic outcomes. Overall, the research methods employed are rather conventional, and the experimental design is simplistic, relying solely on commercially available equipment ( Fakopp 3D Acoustic Tomograph and RESI PD500 Resistance Drill). The study lacks innovation in terms of sensor technology, algorithm improvements, or novel data-processing methods.

A.

I have revised the text and incorporated it into the "Introduction" chapter, specifically in the third and sixth paragraphs.

This study aims to investigate the impact of sensor quantity on the distribution of stress wave velocity (V) in 2D acoustic tomography images. The specific objectives are to: (1) analyze image differences across various sensor quantities; (2) assess the spatial distribution and variability of V values; (3) examine correlations of V values between different sensor configurations; and (4) compare V values between healthy and damaged regions. The findings are expected to provide a valuable reference for interpreting acoustic tomography images and for assessing the extent of internal trunk damage in practical applications.

Therefore, this study aims to investigate the impact of sensor quantity on the distribution of stress wave velocity (V) in 2D acoustic tomography images. The specific objectives are to: (1) analyze image differences across various sensor quantities; (2) assess the spatial distribution and variability of V values; (3) examine correlations of V values between different sensor configurations; and (4) compare V values between healthy and damaged regions. The findings are expected to provide a valuable reference for interpreting acoustic tomography images and for assessing the extent of internal trunk damage in practical applications.

 

Q.

Major issues include:

• Lack of Innovation:

The equipment and methods utilized are existing commercial technologies without any modification or improvement. The paper provides no description or analysis of the algorithms employed by these products. Furthermore, it lacks theoretical exploration into sensor mechanisms, wave propagation patterns, or underlying causes of velocity variations. Important questions remain unanswered, such as: What are the inherent limitations of ultrasonic detection? Does ultrasound detection have specific limitations for shallow defects, and could visual sensing methods potentially compensate for these shortcomings? For instance, the ultrasonic images in Table 2 show red points at sensor positions near edges—why does this occur?

A.

Thank you for your valuable feedback regarding the innovation aspects of my report. I have carefully considered your comments and made the necessary adjustments to the discussion section to clarify the innovative elements of this study. Below is a summary of the added explanations and modifications, with changes highlighted in bold.

In the discussion, I elaborated on the integration of two-dimensional acoustic tomography and resistance micro-drilling as a novel approach for tree health diagnosis. The innovation of this study lies in the integration of these two techniques, forming a new method for tree health diagnosis, which is not commonly found in the existing literature. This unique combination enhances diagnostic accuracy and operational efficiency, providing a comprehensive assessment of internal decay and cavities within tree trunks.

Additionally, I addressed the impact of the number of sensors on image quality more systematically. Another innovation of this study is the systematic evaluation of the impact of sensor numbers on image quality, which is often described qualitatively in previous studies. I also highlighted the limitations of increasing sensor numbers, noting that the differences in measured velocities between various sensor configurations did not reach statistical significance (p ≥ 0.05), indicating that the benefits of increasing the number of sensors are limited within a certain range.

Furthermore, I emphasized the relationship between acoustic velocity and tree health, providing a new perspective on how acoustic measurements can be applied to monitor tree conditions. This finding provides a new perspective on understanding the relationship between acoustic velocity and tree health, highlighting the potential application of acoustic measurements in tree health monitoring.

Lastly, I acknowledged the limitations of acoustic tomography in depicting the shapes of decay or crack boundaries, reminding readers to interpret results cautiously. This limitation reminds us that, despite the potential of acoustic tomography, results should be interpreted cautiously in applications.

These revisions aim to clarify the innovative contributions of this research while addressing the concerns raised. I appreciate your guidance, which has significantly improved the clarity and depth of the discussion.

Thank you for your consideration.

 

Q.

• Simplistic Experimental Design and Routine Data Analysis:

The sample size is limited (only 5 trees), thus weakening the representativeness of the data. Consideration of prior knowledge integration or employing machine learning methods could improve detection reliability. Moreover, how might early-stage diseases in trees be effectively identified?

Addressing any of these points would significantly enhance the innovation and depth of the study, moving it beyond merely superficial analysis using commercial sensors.

A.

I have modified and added explanations within the discussion section 4.3 and included 16 additional references.

 

1.  

Minor suggestions:

• A schematic diagram clearly illustrating sensor placement, including ultrasonic signal generators and receivers, should be provided.
• Excessive blank space appears on page 3, requiring formatting improvements.
• If possible, employing tomography slice scans could enhance the credibility and robustness of the results.
• On page 14, the reference should correctly indicate "Table 4" instead of "Table 9."

A.

The following modifications have been made:

1. Changes have been made in Figure 1. 2. Formatting adjustments have been completed. 3. Explanations for the stress wave velocity tomography 2D maps have been added in Figures 3-7, as detailed in the last column of Table 2. 4 The Figure 4 has been finalized.

 

In conclusion, the study's content, methods, and conclusions remain conventional and do not present notable innovations or substantial contributions in theory or methodology. Primarily, this research merely demonstrates standard applications of commercial detection equipment without deeper exploration or improvements in sensor technologies, methodologies, or underlying mechanisms.

A.

I have modified and added explanations within the discussion section 4.3 and included 16 additional references.

 

Reviewer 4 Report

Comments and Suggestions for Authors

Forests-3710935

Comments and Suggestions for Authors,

As I reviewed the manuscript “The Impact of the Number of Sensors on Stress Wave Velocity in Tree 2D Acoustic Tomography”, the authors presented a good experiment on sustainable material. Overall, I found that the paper is well-organized, with moderate English, and some parts could be performed in an original article. However, some points need to be revised and clarified for the overall improvement of this manuscript. Therefore, my response is "minor revision".

Some requirements are needed, as seen in the comments.

1. The introduction needs to be improved, including more recent research that is related to the topic.
2. Why did the authors select sample trees with a diameter at breast height (DBH) greater than 70 cm? What is the reference?
3. Please explain what the author needs to demonstrate in 1^st paragraph of “3.2. Stress Wave Velocity 2D Tomographic Image Analysis”
4. In figures 3-7, the number of “Distance from bark (S, cm)” needs to be revised the scale because it is hard to separate the value.
5. The citation needs to follow the format of the journal.

Author Response

Reviewer D

Q.

Comments and Suggestions for Authors,

As I reviewed the manuscript “The Impact of the Number of Sensors on Stress Wave Velocity in Tree 2D Acoustic Tomography”, the authors presented a good experiment on sustainable material. Overall, I found that the paper is well-organized, with moderate English, and some parts could be performed in an original article. However, some points need to be revised and clarified for the overall improvement of this manuscript. Therefore, my response is "minor revision".

Some requirements are needed, as seen in the comments.

1. The introduction needs to be improved, including more recent research that is related to the topic.
2. Why did the authors select sample trees with a diameter at breast height (DBH) greater than 70 cm? What is the reference?
3. Please explain what the author needs to demonstrate in 1^st paragraph of “3.2. Stress Wave Velocity 2D Tomographic Image Analysis”
4. In figures 3-7, the number of “Distance from bark (S, cm)” needs to be revised the scale because it is hard to separate the value.
5. The citation needs to follow the format of the journal.

 

A.

Thank you for the committee's comments.

1. Based on the feedback from all reviewers, I have added numerous literature citations and summarized relevant information, which have been incorporated into the introduction and discussion sections. As a result, the report has undergone significant revisions.
2. Previous literature reports primarily used medium to small diameter samples, while this study employs trees with a diameter greater than 70 cm. In addition to the statistical analysis differences, the use of larger diameter trees adds innovation and uniqueness to the report.
3. I made an error in the content of the first paragraph, which has been deleted.
4. The font size of the X-axis labels has been changed for better visibility.
5. The formatting has been revised, but if there are still discrepancies in the future, I will continue to make adjustments to meet the journal's standards.