The Topological Detection of Spatially Proximate Emitters in Spaceborne-Radio-Environment Maps: An ImprovedPersistent-Homology Approach

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript proposes an unsupervised emitter detection method, termed PH-AC, for spaceborne radio environment maps (REM). By combining Persistent Homology and Agglomerative Clustering, the proposed approach enables emitter detection without requiring annotated training data. The authors construct a simulated REM dataset containing isolated emitters, adjacent emitters, and complex distribution scenarios, and conduct extensive experiments for validation. The experimental results demonstrate that the proposed method achieves promising detection performance while maintaining relatively low computational complexity.

The study addresses a practical problem in the field of electromagnetic situational awareness and introduces topological data analysis into emitter detection, which provides a certain degree of novelty. The overall structure of the manuscript is well organized, and the experimental design is relatively comprehensive. However, the current version still contains several issues related to manuscript formatting, figure presentation, consistency, and reference formatting. The following comments are provided for the authors’ consideration:

1. The MDPI logo on the first page is displayed as a file path (e.g., “Definitions/logo-mdpi-eps-converted-to.pdf”) rather than a rendered image. This issue may be caused by PDF compilation or image embedding errors. The authors are advised to check the source files and regenerate the PDF to ensure that all logos and figures are displayed correctly.
2. The formatting of equation descriptions is inconsistent throughout the manuscript. The “where” statement following Equation (1) starts from the left margin, whereas the descriptions following Equations (2)–(5) are indented. The authors are encouraged to unify the formatting style of equation explanations throughout the manuscript to improve consistency and readability.
3. Figure 8 is displayed incorrectly. Several subfigures are replaced by image file paths (e.g., “Definitions/figs/fig8(c)Wavelet(1).png”), indicating that the corresponding images were not successfully embedded into the PDF file. The authors should carefully check the source files and compilation process to ensure that all subfigures are properly rendered.
4. The formatting of several references is incomplete or inconsistent. Some references are missing page numbers (or article numbers), and the author format in Reference 19 differs significantly from the other references. The authors are advised to thoroughly review the entire reference list and ensure that all references comply with the journal’s formatting requirements.
5. Figures 1 and 2 have identical captions, both titled “Schematic Diagram of Simulated Dataset Generation Based on Theoretical Model.” However, according to the manuscript description, Figure 2 presents the overall workflow of the proposed PH-AC method rather than the dataset generation process. Therefore, the caption of Figure 2 appears to be a copy-and-paste error and should be revised to accurately reflect the figure content.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Please, see the attached file.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The paper develops a detection method for spatially proximate emitters within spaceborne radio environment maps. Its main contributions are summarized as follows:
1.A simulated spaceborne REM dataset covering three types of emitter distribution patterns is established.
2.The persistent homology algorithm is introduced into the field of emitter detection based on REM data.
3.With the extracted multi-dimensional topological features, hierarchical agglomerative clustering using Ward linkage is adopted to implement unsupervised classification.

Revision suggestions:
1.Part of the content in Figure 8 is incomplete and missing relevant information.
2.Comparative experiments with existing approaches targeting the same task should be added, and corresponding references for all compared methods need to be provided.
3.The discrepancies between the self-developed simulated dataset and real practical scenarios should be discussed, along with a brief analysis of how these differences affect the practical application of the proposed method.
4.The conclusion section is excessively long. It is recommended to shorten this part to concisely conclude the paper’s work and briefly list potential future research directions.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have revised the manuscript according to my first-round review comments, and the overall quality of the paper has been improved. I suggest that the authors further check and correct the following formatting and wording details in the final version to improve the consistency and professionalism of the manuscript.

1. On the first page, there is no space between the third author’s name and the superscript, whereas spaces are used between the names and superscripts for the other authors. It is suggested to add the corresponding space to ensure consistent formatting of the author information.
2. In Table 6, the term “YOLOv13n” is used, while “YOLOv13” is mentioned in several places in the preceding text. The authors are suggested to clarify whether the model used in this paper is YOLOv13, YOLOv13n, or another specific scale of YOLOv13, and ensure consistent terminology throughout the manuscript.
3. In line 326 on page 10, the phrase “as illustrated in the figure” is used without specifying the exact figure number. It is suggested to revise it to a more explicit expression, such as “as illustrated in Fig. X”, so that readers can clearly identify the corresponding figure.
4. The manuscript uses both “YOLOv13_FreqFusion” and “YOLOv13-FreqFusion” in different places. The authors are suggested to carefully check the whole manuscript and unify the notation of this method name to avoid inconsistency and potential confusion.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The revised manuscript is clearly improved according to reviewer’s comments. Several changes have been added that enhance the manuscript. No further comments.

Author Response

We would like to express our sincere gratitude for your positive comments on our revised manuscript. We are very glad to learn that the changes we made, following your constructive suggestions, have improved the paper and that you have no further comments. Your insightful review has been invaluable in strengthening our work. We truly appreciate the time and effort you have dedicated to reviewing our manuscript.

Should you have any additional questions or suggestions, please do not hesitate to let us know. We remain open to further improvements.

Reviewer 3 Report

Comments and Suggestions for Authors

My comments have been addressed.

Author Response

We would like to express our sincere gratitude for your positive comments on our revised manuscript. We are very glad to learn that the changes we made, following your constructive suggestions, have improved the paper and that you have no further comments. Your insightful review has been invaluable in strengthening our work. We truly appreciate the time and effort you have dedicated to reviewing our manuscript.

Should you have any additional questions or suggestions, please do not hesitate to let us know. We remain open to further improvements.