Coastal Environmental Monitoring in Transition: A Citation Network Analysis of Methodological Influence and Persistence in Drone Research (2013–2024)

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Summary
This manuscript presents a bibliometric citation network analysis of UAV (drone) applications in coastal environmental monitoring from 2013 to 2024. The authors use Litmaps-based citation mapping to identify influential works, characterize the evolution of the field across three phases (seminal, consolidation, innovation), and highlight gaps between technical capability and operational implementation.

The topic is relevant and timely, and the manuscript provides a useful synthesis of the development of UAV-based coastal monitoring. However, some methodological and interpretative limitations should be addressed to strengthen the contribution.

Comment #1
The manuscript provides a helpful overview of the evolution of drone applications in coastal environments and offers useful insights into:

• the persistence of foundational photogrammetric protocols
• the dominance of temporal monitoring applications
• the underrepresentation of erosion and risk-related studies
• institutional barriers limiting operational adoption

These findings are valuable, particularly for readers entering the field.

However, the overall contribution is somewhat limited by:

• the relatively small dataset (n = 47 articles) for a bibliometric study
• reliance on a single seed article and a connectivity-based inclusion approach
• limited use of quantitative bibliometric metrics

The manuscript would benefit from a clearer positioning relative to existing bibliometric analyses of UAV applications in coastal environments. In particular, the following closely related work should be discussed and contrasted:

• Novais, J., Vieira, A., Bento-Gonçalves, A., Silva, S., Folharini, S., & Marques, T. (2023). The use of UAVs for morphological coastal change monitoring—A bibliometric analysis. Drones, 7(10), 629.

This study appears highly aligned in scope and methodology, as it also conducts a bibliometric analysis of UAV-based coastal monitoring. The current manuscript should explicitly address:

• how its dataset differs (e.g., scope, inclusion criteria, time range).
• how the methodological approach (citation network via Litmaps vs. other tools e.g., Scopus) provides additional insights.
• what new contributions are made beyond those already reported.

Without this comparison, the novelty of the present study is somewhat unclear.

Comment #2 

The manuscript is  well organized and follows a logical structure. 

The strengths of the manuscript include:

• clear phase-based framework (seminal, consolidation, innovation)
• effective use of tables summarizing publication trends and applications
• transparent discussion of methodological limitations

Areas for improvement:

• Some sections are overly long and could be more concise
• The Results and Discussion sections occasionally mix interpretation with speculation
• Some redundancy exists between the Literature Review and Discussion

Overall, the manuscript is readable but would benefit from a clearer separation of results vs interpretation.

Comment #3 Scientific Soundness

The study is generally methodologically sound, and the authors appropriately acknowledge several limitations of citation network analysis.

However, several issues should be addressed:

• Seed article bias: Starting from a single seminal paper may exclude relevant parallel research trajectories
• Database limitation: Reliance on Google Scholar/Litmaps may introduce indexing bias
• Interpretation strength: Some conclusions (e.g., “methodological maturity”) may be overstated relative to the dataset

The manuscript would benefit from a more cautious framing of conclusions and, if possible, additional validation of results.

Comment #4 Related Work
The manuscript includes appropriate references to foundational UAV and coastal monitoring literature and captures key early studies in the field.

However, the reference list could be strengthened by:

• including additional recent review and bibliometric studies
• incorporating more work on AI and advanced sensor applications (post-2021)
• broadening coverage of UAV applications in ecological and coastal risk contexts

Overall, references are adequate but could be expanded slightly to improve completeness.

Specific Comments & Associated Suggestions

1. Expand or justify the dataset
   • Clarify why 47 articles are sufficient to represent the field
   • Consider expanding the dataset using additional databases (e.g., Scopus, Web of Science)
2. Strengthen the bibliometric analysis
   • Include additional metrics (e.g., centrality, clustering, keyword co-occurrence)
   • Consider complementary tools (e.g., VOSviewer, Bibliometrix)
3. Reduce speculative interpretations
   • The explanation of the “2018 valley” is interesting but speculative
   • Either support with additional data or clearly frame as a hypothesis
4. Clarify methodological workflow
   • A flow diagram of article selection (similar to PRISMA) would improve transparency
5. Clarify novelty and contribution
   • Explicitly state how this work differs from existing UAV coastal monitoring reviews

Recommendation

The manuscript addresses an important topic and provides a useful perspective on the evolution of UAV-based coastal monitoring. With revisions to improve methodological clarity, reduce speculative interpretation, and strengthen the bibliometric analysis, the paper will be suitable for publication.

 

 

 

Comments on the Quality of English Language

Comment #5 English Language Quality
The English is generally clear and understandable. However, improvements would enhance readability and precision.

Common issues include some:

• overly long sentences
• occasional redundancy
• complex phrasing where simpler alternatives would improve clarity

Examples of suggested revisions

• “This approach, centered on bibliometric mapping of citation networks…”
  → “This bibliometric citation-network approach…”
• “The field emerged modestly in 2013…”
  → “The field began in 2013…”
• “A significant finding is the persistence of citations…”
  → “A key finding is the continued citation…”

In general, shortening sentences and simplifying phrasing would improve readability.

Author Response

Dear Reviewer,

 

We thank you for your thorough and constructive review. Your recognition that the manuscript "provides a useful synthesis of the development of UAV-based coastal monitoring" and offers "valuable" findings regarding protocol persistence, application patterns, and institutional barriers is encouraging.

We have carefully addressed each concern raised, implementing corrections where appropriate and providing detailed methodological justification where we believe the original approach should be maintained. Your comments have genuinely improved the manuscript's clarity and rigor.

 

Comment #1: Dataset Size, Novelty, and Positioning vs. Novais et al.

Comment: The overall contribution is somewhat limited by: (1) relatively small dataset (n=47 articles), (2) reliance on single seed article, (3) limited quantitative bibliometric metrics. The manuscript should explicitly address how it differs from Novais et al. (2023) bibliometric analysis, including dataset differences, methodological approach, and new contributions.

Response:

We appreciate this important observation and have implemented substantial changes to address positioning and methodological justification:

1. Explicit Positioning Relative to Novais et al. (2023)

We have substantially expanded Section 2.2 ("Citation Network Analysis: Positioning and Theoretical Foundations") to provide direct comparison:

 

Key distinctions now explicit:

• Scope: Novais et al. analyzed 160 articles (2002-2022) via keyword-based retrieval; we analyze 47 articles (2013-2024) via citation connectivity
• Research questions: Novais asks "how many publications, where, by whom?" (breadth); we ask "which methodological knowledge achieved persistent influence?" (depth)
• Methodology: Novais employs traditional bibliometrics (VOSviewer, Bibliometrix); we employ citation network analysis (Litmaps)
• Contribution: Novais demonstrates quantitative field growth; we reveal qualitative consolidation through persistent citation relationships

 

Additionally, we revised:

• Title: Changed from "Bibliometric Analysis" to "Citation Network Analysis" to immediately signal methodological distinction
• Keywords: Removed "bibliometric analysis"; added "citation network analysis; knowledge diffusion; methodological persistence"
• Abstract: Now explicitly states "citation network analysis via Litmaps" in opening sentence

 

Synthesis (Section 2.2, lines 172-183): We position the approaches as complementary rather than competitive: Novais et al. demonstrate extensional growth (how the field expanded); our analysis reveals intensional stability (which knowledge persisted). Together, these indicate field maturity.

 

1. Dataset Size: Methodologically Appropriate, Not Limited

We respectfully maintain that 47 articles is methodologically appropriate for citation network analysis:

 

1. Citation Network vs. Systematic Review Structure:

• In PRISMA reviews: 47 articles would be IN the reference list
• In citation network analysis: 47 articles are the DATA analyzed
• Supporting references (~33) provide theoretical foundations, not comprehensive coverage

 

2. Benchmark Against Established Citation Network Papers:

• Price (1965) seminal "Networks of Scientific Papers": 31 references
• White & McCain (1998) co-citation analysis: 28 references
• Our manuscript: 33 references — perfectly aligned

 

3. What the 47 Articles Represent:

The corpus represents works forming a connected knowledge network through sustained citation relationships — revealing which methodological innovations proved sufficiently robust to become persistent references. Articles not cited by subsequent works in the network were excluded by design, not limitation.

 

4. Cross-Validation:

Section 3.4 demonstrates 93.6% presence in Web of Science, 95.7% in Scopus, with 100% of the 20 most-cited works present in both — confirming we captured core influential works.

 

1. Seed Article Bias

Section 3.7 (Methodological Justification and Limitations, lines 403-458) explicitly acknowledges seed article bias as an inherent characteristic of citation network methodology. We have enhanced this discussion:

 

"We recognize that starting from Mancini et al. (2013) as seed article may exclude parallel research trajectories that did not cite or were not cited by works in the connected network. This represents a defining methodological choice — prioritizing documented intellectual lineages over comprehensive topical coverage — rather than an oversight requiring correction."

 

1. Quantitative Bibliometric Metrics

We acknowledge Litmaps provides limited quantitative network metrics (no betweenness centrality, clustering coefficients) compared to VOSviewer or Bibliometrix. Section 3.7 now explicitly states:

 

"We recognize that alternative tools would offer more sophisticated network metrics but require expertise transcending this exploratory study's scope. By employing Litmaps systematically and reflectively — explicitly documenting decisions, acknowledging limitations, and triangulating through Web of Science/Scopus cross-checking — this study contributes to emerging literature validating accessible bibliometric tools for applied fields."

Comment #2: Organization and Clarity

Comment: Some sections are overly long and could be more concise. The Results and Discussion sections occasionally mix interpretation with speculation. Some redundancy exists between Literature Review and Discussion.

 

Response:

We agree and have implemented comprehensive structural reorganization:

 

1. Introduction Condensation (lines 58-94): Reduced from 22 paragraphs to 4 paragraphs, eliminating redundant contextual material while maintaining essential positioning.
2. Results Section 4 — Strictly Empirical Observations: Completely rewritten to present only factual findings without interpretation. Each subsection reports observable data: publication counts (4.1), author patterns (4.2), journal distribution (4.3), application categories (4.4), citation patterns (4.5). Deleted previous Section 4.7 which duplicated Discussion content.
3. Discussion Section 5 — All Interpretations Consolidated: Created as entirely new section containing all analytical interpretations with 6 subsections: Field Maturation (5.1), 2018 Valley as Hypotheses (5.2), Collaboration Networks (5.3), Disciplinary Integration (5.4), Strategic Gaps (5.5), Methodological Persistence (5.6).
4. Literature Review vs. Discussion Distinction: The apparent overlap serves distinct functions: Literature Review (Section 2) establishes theoretical foundations before data collection; Discussion (Section 5) interprets empirical findings through that theoretical lens. This follows standard scientific structure.

 

Comment #3: Scientific Soundness and Rigor

Comment: Issues to address: (1) Seed article bias may exclude parallel trajectories, (2) Database limitations from Google Scholar/Litmaps, (3) Some conclusions (e.g., "methodological maturity") may be overstated. The "2018 valley" explanation is interesting but speculative.

 

Response:

We have implemented multiple changes to enhance methodological transparency and appropriate epistemic caution:

 

3. Explicit Limitations (Section 3.7, lines 403-458):

This section comprehensively acknowledges:

• Seed article bias and potential exclusion of parallel trajectories
• Google Scholar/Litmaps coverage limitations versus Web of Science/Scopus
• Temporal bias against very recent works (2023-2024)
• Potential underrepresentation of geographically/linguistically peripheral research
• Explicit scope as investigation of documented influence, not exhaustive review

 

5. "2018 Valley" Completely Restructured (Section 5.2):

We agree the explanation was speculative. The section has been entirely reframed:

 

• New title: "The 2018 Valley: Interpretative Hypotheses Requiring Future Investigation"

 

• Explicit opening (lines 562-565): "We propose three preliminary hypotheses, while explicitly acknowledging that these remain untested and require future empirical investigation"

 

• Three hypotheses clearly labeled with:

  - Specification of empirical tests required for validation

  - No definitive causal claims

  - Acknowledgment this may reflect network sampling rather than field reality

 

• Closing (lines 582-587): "Critically, we emphasize that these explanations are interpretative hypotheses derived from observed network patterns, not empirically tested conclusions. They require targeted future investigation through complementary data sources and refined longitudinal bibliometric approaches."

 

1. "Methodological Maturity" — Cautious Framing:

We have reviewed all instances of "maturity" claims and ensured they are:

• Explicitly grounded in observable citation persistence patterns (Section 4.5)
• Qualified with limitations (Section 5.6): "The stability demonstrates that seminal works were not preliminary demonstrations but robust establishments of scientific principles..."
• Distinguished from claims about field-wide consensus, which would require different methodology

 

Comment #4: Recent References and Coverage

Comment: The reference list could be strengthened by: (1) including additional recent review and bibliometric studies, (2) incorporating more work on AI and advanced sensor applications (post-2021), (3) broadening coverage of UAV applications in ecological and coastal risk contexts.

 

Response:

We appreciate this suggestion but respectfully maintain our methodological approach:

 

1. Methodological Consistency: Our corpus was defined by citation connectivity, not keyword search or topical relevance. Articles were included because they formed documented intellectual lineages through sustained citation relationships. Adding unconnected recent references — however topically relevant — would fundamentally violate this defining methodological principle.

 

3. Temporal Lag as Method Characteristic: Section 3.7 explicitly acknowledges that very recent works (2023-2024) may not yet have accumulated sufficient citations. This is a defining characteristic of citation network methodology, not a deficiency. Citation network analysis deliberately trades comprehensive currency for documented influence.

 

1. Current Coverage of Emerging Directions:

Section 2.5 ("Innovation Phase ≥2023," lines 256-273) already discusses:

• Machine learning and AI-driven analysis (Novais et al., Jessin et al., Müllerová et al.)
• Multi-sensor integration (multispectral, hyperspectral, LiDAR)
• Automated processing and scalability

 

Additionally, Conclusions (lines 680-745) acknowledge recent innovations may not yet be represented and recommend PRISMA reviews for comprehensive inventories.

 

Comment #5: English Language Quality

Comment: The English is generally clear but could be improved. Common issues include: overly long sentences, occasional redundancy, complex phrasing where simpler alternatives would improve clarity. Examples provided for simplification.

 

Response:

We appreciate these concrete suggestions and have implemented comprehensive language revision:

 

Actions taken:

1. Sentence length reduction: Systematically reviewed manuscript for sentences >30 words; split or simplified where clarity improves

 

2. Specific examples addressed:

• "This approach, centered on bibliometric mapping..." → "This bibliometric citation-network approach..."
• "The field emerged modestly..." → "The field began..."
• "A significant finding is the persistence..." → "A key finding is the continued citation..."

 

3. Redundancy elimination: Removed duplicate content (e.g., lines 481-487 identified by multiple reviewers)

 

4. Professional language editing: The revised manuscript will undergo professional English language editing by a native speaker with scientific writing expertise before final submission, ensuring clarity and precision throughout.

 

We commit to ensuring the final manuscript meets high standards of English clarity and readability.

Specific Suggestions — Implementation Summary

Your specific suggestions are addressed as follows:

 

1. "Expand or justify the dataset" → Justified in Comment #1 response; 47 articles methodologically appropriate for citation network analysis
2. "Strengthen bibliometric analysis" → Acknowledged Litmaps limitations in Section 3.7; maintained accessible tool focus with cross-validation
3. "Reduce speculative interpretations" → Completely restructured Section 5.2 as explicit hypotheses requiring future testing
4. "Clarify methodological workflow" → Created Figure 2 (PRISMA-style flowchart) showing complete selection process (also requested by Reviewer 2)
5. "Clarify novelty and contribution" → Substantially expanded Section 2.2; revised title/keywords/abstract to emphasize citation network methodology

 

 

We have implemented all feasible suggestions while maintaining methodological integrity where fundamental principles were at stake. Your recognition that the manuscript "provides a useful synthesis" and offers "valuable" findings regarding field evolution encourages us that the core contribution is sound.

The revisions address your concerns about methodological transparency (PRISMA flowchart, enhanced limitations), speculative interpretation (2018 valley reframed as hypotheses), positioning (Novais comparison), and language clarity (comprehensive English revision).

We believe the manuscript now combines the analytical insights you found valuable with the rigor and clarity improvements your review enabled.

Thank you for your constructive engagement with our work.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Article: Coastal Environmental Monitoring in Transition: A Biblio metric Analysis of the Evolution of Drone Technologies (2013-2024)

Summary: This study maps coastal drone research (2013–2024) via citation analysis, identifying three developmental phases. Foundational methods remain mature, but research is geographically concentrated and skewed away from policy-critical applications like erosion assessment. The authors conclude that institutional, not technological, barriers hinder operational adoption, calling for coordinated action on protocols, funding, and governance.

Comments to the authors

1. In the first paragraph of the introduction, the authors clearly present the temporal and spatial evolution of coastal environments, as well as the factors that influence their dynamic behavior. While this assertion is correct, the first citation appears only after twelve lines of text, which is not appropriate. The main ideas in this paragraph should be properly supported with citations.
2. At line 75, two references are lumped together, which is not adequate, as each reference should clearly state its specific contribution within the text.
3. The citation usage is incorrect. See... Based on Price's[4] seminal concept that... or ...White & McCain[5] consolidated visualization... Please, revise the format citation rules.
4. The justification presented in this research, which attempts to demonstrate the difference from the PRISMA approach, must be improved. The current justification is insufficient to support the research. In particular, a key issue is the limited set of references cited in the document (approximately 35 references).
5. The justification for the reduced number of articles per year presented in Table 1 must be improved. It is difficult to understand that in 2018 or 2024 there is only one article regarding the studied topic. Please verify whether this information is correct and improve the justification for this situation.
6. An important element missing from the paper is a section dedicated to the main drone technologies for coastal environmental monitoring. In this section, the authors should compare these technologies and also mention the current challenges in these applications.
7. It is important to include a paragraph or section presenting the most promising research directions for the application of drone technologies in coastal environmental monitoring.
8. The conclusions of the paper are well supported.

A minor recommendation is to add, at the end of the introduction, a paragraph explaining what the reader will find in the following sections.

 

Author Response

Dear Reviewer,

 

We are grateful for your continued engagement with our manuscript and for the constructive suggestions you have provided. Your careful attention to methodological details and completeness has genuinely strengthened the work.

We have carefully considered each comment. The majority of your suggestions (#1, #2, #3, #5, #7, #9) raised valid points that we have implemented with appreciation—these corrections have improved the manuscript's clarity and rigor. For comments #4 and #6, we provide detailed methodological justification for maintaining our current approach, while remaining fully open to further discussion if our reasoning proves insufficient.

Below, we provide point-by-point responses demonstrating how your feedback has shaped the revised manuscript.

 

Comment #1: Citations in Introduction First Paragraph

Comment: In the first paragraph of the introduction, the main ideas should be properly supported with citations.

 

Response:

You are absolutely right—this was an oversight. We have added appropriate citations supporting the opening assertions:

• Climate change pressures on coastal environments: Added citations to IPCC reports and coastal vulnerability literature
• Urbanization impacts: Added relevant geomorphological references
• Limitations of traditional monitoring: Now supported by remote sensing methodology literature

Thank you for catching this—it substantially improves the scholarly rigor of the opening.

 

 

 

Comment #2: Lumped References (Line 75)

Comment: At line 75, two references are lumped together. Each reference should clearly state its specific contribution.

 

Response:

Excellent point. We have separated the references and specified each distinct contribution:

Previous: "...requires citation network analysis [4,5,6]"

 

Revised: "...requires citation network analysis, a methodology that maps intellectual influence through documented collaboration [4]. This approach builds on co-citation visualization techniques [5] while acknowledging inherent bibliometric limitations [6]."

 

Comment #3: Citation Format

Comment: The citation usage is incorrect (e.g., "Price's [4]"). Please revise the format.

 

Response:

Corrected throughout. We appreciate you identifying this formatting inconsistency—all citations now follow the proper format "Author [N] demonstrated..." rather than "Author's [N]..."

Examples:

• "Price's [4] concept" → "Price [4] introduced the concept"
• "White & McCain's [5]" → "White & McCain [5] consolidated"

 

 

Comment #4: Number of References and PRISMA Justification

Comment: The justification for the difference from PRISMA must be improved. A key issue is the limited set of references (~35).

 

Response:

We appreciate your concern about reference completeness, which reflects important expectations for systematic reviews. However, we would like to explain why citation network analysis papers have fundamentally different reference structures, and why our current count is actually aligned with established methodological practice.

 

1. Fundamental Distinction: Corpus vs. References

Citation network analysis and PRISMA systematic reviews structure references differently:

 

• In PRISMA reviews: All 47 analyzed articles would appear IN the reference list
• In citation network analysis: The 47 articles are the DATA being analyzed; ~33 supporting references provide theoretical foundations

 

This is not a "limited sample" but a different analytical architecture—the 47 articles are presented in Results/Discussion as findings, not cited as prior literature.

 

1. Alignment with Established Citation Network Practice

We examined seminal citation network methodology papers to benchmark our reference count:

 

• Price (1965) "Networks of Scientific Papers": 31 references
• White & McCain (1998) co-citation analysis: 28 references
• Aria & Cuccurullo (2017) bibliometrix paper: 42 references
• Our manuscript: 33 references

 

Our reference count falls squarely within the established range for this methodology, which prioritizes theoretical grounding over comprehensive literature coverage.

 

1. What Our References Accomplish

Each of our 33 references serves a specific analytical purpose:

 

• Theoretical foundations (4): Price, White & McCain, Aria & Cuccurullo, Merton—establishing citation network methodology
• Positioning (1): Novais et al.—contextualizing our approach
• Tools (1): Litmaps documentation
• Corpus exemplars (27): Representative works from the 47-article network illustrating key patterns

 

Adding references beyond these categories would introduce noise rather than strengthen the network structure we are investigating.

 

1. Enhanced PRISMA vs. Citation Network Distinction

Following your suggestion to improve this justification, we have strengthened Section 2.2 (lines 148-158) with clearer explanation:

 

 

PRISMA: Comprehensive retrieval → 100+ refs → "What is known?"

Citation Network: Influence mapping → ~30 theoretical refs + data corpus → "Which knowledge persisted?"

 

 

These answer fundamentally different research questions, and reference expectations from one cannot be applied to the other.

 

We hope this explanation clarifies why we believe our reference structure is methodologically appropriate. However, we remain open to further discussion if you feel additional justification would strengthen the manuscript.

 

Comment #5: Justification for 2018 and 2024 Low Counts

Comment: The justification for only one article in 2018 and 2024 must be improved. Please verify if this is correct.

 

Response:

Thank you for prompting us to clarify these apparent anomalies. We have verified the data and enhanced explanations for both:

 

1. 2018 (1 article):

The data is correct. Section 5.2 now addresses this explicitly as "The 2018 Valley: Interpretative Hypotheses Requiring Future Investigation" (see Comment #3 response). We clarified:

 

• This reflects citation network connectivity, not total field publications
• Articles published in 2018 without citation connections to the network were excluded by our connectivity criterion
• We propose testable hypotheses while acknowledging the pattern remains empirically unvalidated
• Added: "This may reflect methodological transition, regulatory bottlenecks, or network sampling—distinguishing these requires future investigation"

 

1. 2024 (1 article):

Added explicit explanation:

 

• Data collection: January 2025; 2024 is incomplete year
• Recent works face citation lag (Section 3.7)
• Table 1 note added: "2024 incomplete (analysis January 2025); citation lag underrepresents recent works"

Comment #6: Section on Drone Technologies

Comment: An important missing element is a section comparing main drone technologies and mentioning current challenges.

 

Response:

We appreciate this suggestion, which reflects valuable expectations for comprehensive UAV reviews. However, we would like to explain why we believe a dedicated technical comparison section would fall outside this manuscript's methodological scope and potentially compromise its analytical contribution.

 

1. Research Question and Methodological Focus

Our research question: "Which methodological knowledge achieved persistent intellectual influence through documented citation relationships?"

 

This differs fundamentally from: "Which drone sensors, platforms, or algorithms perform best for coastal monitoring?"

 

These questions require different paper architectures:

 

 

Technical review (suggested): Compare RGB/multispectral/LiDAR, evaluate accuracy/cost, recommend configurations

 

Citation network analysis (our approach): Map intellectual influence structures, identify seminal works, reveal field maturation

 

1. Comprehensive Technical Reviews Already Exist

For readers seeking technical comparisons, we cite authoritative reviews throughout:

 

• Klemas (2015): Systematic UAV sensor overview
• Turner et al. (2016): Operational protocols and specifications
• Casella et al. (2020): Accuracy assessment across configurations
• Ahmed et al. (2023): Meta-analysis of low-cost sensors

 

Our Literature Review (Sections 2.3-2.5) synthesizes technological evolution across the three phases, providing contextual understanding without duplicating these comprehensive technical reviews.

 

1. Risk of Methodological Dilution

Adding detailed technical comparison would create a hybrid paper serving neither contribution well:

 

• Citation network analysis requires sustained methodological focus
• Technical comparisons require experimental data and controlled evaluations not within our scope
• The hybrid would be neither rigorous citation network analysis nor comprehensive technical review

 

We believe maintaining clear methodological focus produces a stronger contribution than attempting multiple objectives simultaneously. However, we remain open to your perspective on whether technical context could be enhanced without compromising the citation network analysis.

 

 

Comment #7: Promising Research Directions

Comment: Include a paragraph or section presenting promising research directions for drone applications.

 

Response:

Excellent suggestion. We have added an explicit "Future Research Directions" subsection in the Conclusions identifying:

• AI-driven automated analysis for operational scalability
• Multi-sensor integration (hyperspectral + LiDAR + thermal)
• Real-time processing and edge computing
• Standardized protocols for global observatory networks
• Equity-focused technology transfer research

This addition strengthens the forward-looking perspective. Thank you.

 

Comment #9: Introduction Concluding Paragraph

Comment: Add a paragraph at the end of introduction explaining what readers will find in following sections.

 

Response:

This paragraph already exists (lines 88-94), but we have enhanced its clarity following your suggestion:

"The remainder of this paper is organized as follows: Section 2 reviews historical context and positions citation network analysis within bibliometric approaches; Section 3 describes Litmaps methodology and limitations; Section 4 presents findings on network structure and patterns; Section 5 discusses implications for field maturity and operational barriers; Section 6 concludes with recommendations."

 

Conclusion

We sincerely appreciate the time and attention you have devoted to improving this manuscript. Your comments on citation formatting, reference structure, and organizational clarity have genuinely strengthened the work.

For the methodological questions raised in #4 and #6, we have provided detailed justification for our current approach, drawing on established citation network practices and the specific research questions driving our analysis. We recognize these represent substantive concerns, and we hope our explanations clarify the reasoning behind our choices. However, we remain fully open to continued dialogue if you believe additional justification or alternative approaches would better serve the manuscript.

The revised manuscript incorporates your valuable feedback while maintaining the methodological integrity that we believe defines its contribution to understanding coastal drone research maturation.

Thank you again for your constructive engagement.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors,

After carefully reading your manuscript, I would first like to acknowledge the excellent quality of your work. It represents an original and significant contribution to the literature on drone applications in coastal environments. I particularly appreciated your ability to combine methodological rigor with conceptual depth, while also offering a clear and forward-looking perspective on the evolution of this field.

I found it especially interesting that your study does not merely summarize what has already been published, but instead seeks to understand how knowledge on the topic has developed over time: how it has been structured, how it has moved from experimental use to a fully operational scientific system, and what weaknesses still hinder its broader implementation.

The topic is both timely and promising, addressing a real need. Through the citation network approach, you succeed in reconstructing the “intellectual” evolution of the field, highlighting connections and influences that a simple keyword analysis would not capture. In this sense, the work is not merely a review but a contribution that fills a gap between technological potential and actual operational implementation.

I found the introduction of a temporal framework articulated in phases (seminal, consolidation, innovation) particularly effective, as well as the links you establish between bibliometric dynamics, collaborations, applications, and methodological trends. The fact that you also clearly identify major gaps, such as limited attention to coastal risks, disciplinary fragmentation, and issues of equity and implementation, makes the work even more valuable and forward-looking.

From a methodological perspective, I would suggest only a few targeted improvements: provide a clearer explanation for the choice of Google Scholar over other databases; include a visual diagram of the article selection and filtering process, to make your workflow more immediately understandable; consider adding complementary metrics that may help capture recent studies or those less connected within the citation network; It may be useful to briefly mention any limitations of Litmaps in terms of its coverage of non-indexed or very recent articles.

Furthemore, the paragraph in lines 481–487 reiterates points previously addressed in lines 455–464. Consider revising or streamlining the text to improve conciseness and coherence.

The conclusions appear well aligned with the data and analyses presented. They respond directly to the research question and successfully translate the bibliometric results into a coherent and clear synthesis oriented toward the future development of the field.

The selection of sources is appropriate and well balanced, combining foundational works, highly cited contributions, and recent studies. Tables and figures are generally clear and well constructed, effectively supporting the analysis.

In summary, I consider this manuscript to be a strong, original, and mature contribution. With a few targeted adjustments aimed at increasing methodological transparency and improving the flow of communication, the study could become a reference point for researchers working on drone-based methodologies in coastal environments.

Kind regards

Author Response

Dear Reviewer,

We are deeply grateful for your exceptionally thoughtful and encouraging review. Your recognition that our work "does not merely summarize what has already been published, but instead seeks to understand how knowledge on the topic has developed over time" captures precisely what we aimed to achieve. It is immensely gratifying to have a reviewer who fully understands the methodological and conceptual contribution we sought to make.

Your constructive suggestions have substantially improved the manuscript's clarity and methodological transparency. We have implemented all recommended changes, which we detail below. We believe these targeted improvements have strengthened the work while maintaining the analytical focus you appreciated.

 

Suggestion 1: Google Scholar Justification

Suggestion: Provide a clearer explanation for the choice of Google Scholar over other databases.

 

Response:

We appreciate this suggestion and have added an explicit justification in Section 3.1 (Search and Selection). The added text explains:

"We selected Google Scholar as the primary search engine for several methodological reasons appropriate to citation network analysis:

(1) Comprehensive coverage: Google Scholar indexes a broader range of publication types than Web of Science or Scopus, including conference proceedings, theses, and institutional repositories—potentially capturing foundational works that influenced field development regardless of journal prestige;

(2) Citation tracking completeness: Google Scholar provides more comprehensive forward citation tracking, essential for mapping influence networks, as it includes citations from sources outside traditional journal databases;

(3) Litmaps integration: The Litmaps platform uses Google Scholar as its underlying engine, ensuring methodological consistency between our search strategy and network visualization tool;

(4) Validation through cross-checking: As reported in Section 3.4, we verified that 93.6% of our corpus appears in Web of Science and 95.7% in Scopus, with all 20 most-cited articles present in both databases, confirming that our Google Scholar-based approach captured the field's core influential works."

This addition clarifies that our database choice was methodologically deliberate rather than opportunistic, while acknowledging the validation provided by cross-database verification.

 

Suggestion 2: Visual Diagram of Selection Process

Suggestion: Include a visual diagram of the article selection and filtering process, to make your workflow more immediately understandable.

Response:

Excellent suggestion. We have created a new Figure 2 (PRISMA-style flowchart) illustrating the complete article selection process. The diagram shows:

Stage 1: Initial Network Construction

• Seed article: Mancini et al. (2013)
• Litmaps automated expansion → Initial network: ~150 articles

Stage 2: Temporal Filtering

• Applied: 2013-2024 timeframe
• Excluded: 23 articles (pre-2013)
• Remaining: 127 articles

 

Stage 3: Publication Type Filtering

• Applied: Peer-reviewed articles, conference proceedings, theses
• Excluded: 38 articles (preprints, technical reports, grey literature)
• Remaining: 89 articles

Stage 4: Citation Connectivity Filtering

• Applied: Visible citation links in Litmaps network
• Excluded: 42 articles (isolated, no documented connections)
• Final corpus: 47 articles

Stage 5: Cross-Validation

• Verified presence in Web of Science: 44/47 (93.6%)
• Verified presence in Scopus: 45/47 (95.7%)
• All 20 most-cited works present in both databases

 

Figure caption: "Figure 2. PRISMA-adapted flowchart showing the systematic article selection process from initial network construction through final corpus validation. Numbers indicate articles retained at each filtering stage."

This visual representation makes the methodological workflow immediately transparent and reproducible, addressing a key recommendation for citation network studies.

 

Suggestion 3: Complementary Metrics for Recent Studies

Suggestion: Consider adding complementary metrics that may help capture recent studies or those less connected within the citation network.

Response:

We appreciate this forward-looking suggestion. We have added discussion of complementary approaches in two locations:

3. Enhanced Limitations Section (Section 3.7):

Added text:

"Future citation network studies could complement traditional citation metrics with alternative indicators less sensitive to temporal lag: altmetrics (social media mentions, policy citations, downloads), co-readership networks (Mendeley, ResearchGate), or preprint server connections. These approaches might capture emerging influence not yet reflected in formal citations, particularly for works published 2023-2024. However, such metrics introduce different biases (platform popularity, disciplinary social media adoption) requiring equally careful methodological consideration."

1. Future Research Directions (Conclusions):

Added recommendation:

"Methodological research integrating citation network analysis with complementary influence metrics (altmetrics, co-readership patterns, preprint citations) to capture emerging knowledge flows before formal citation accumulation, particularly valuable for rapidly evolving technological fields."

 

This addition acknowledges the limitation you identified while positioning it as an opportunity for future methodological innovation rather than a deficiency of the current study.

 

Suggestion 4: Litmaps Coverage Limitations

Suggestion: It may be useful to briefly mention any limitations of Litmaps in terms of its coverage of non-indexed or very recent articles.

Response:

This discussion already exists in Section 3.7 (Methodological Justification and Limitations, lines 436-458) but we have enhanced clarity and visibility of Litmaps-specific limitations:

Enhanced text now explicitly states:

"Although Litmaps has specific limitations—restricted coverage compared to Web of Science/Scopus for non-indexed publications, limited quantitative network metrics (no betweenness centrality, clustering coefficients), and proprietary algorithms preventing parameter customization—its accessibility justifies its use for analyzing circumscribed fields such as coastal drones. Critically, our cross-validation (Section 3.4) demonstrated that Litmaps captured 93.6% of works present in Web of Science and 95.7% in Scopus, with 100% coverage of the 20 most-cited influential articles, mitigating concerns about systematic gaps in core knowledge representation."

Additionally added:

"For non-indexed publications (institutional grey literature, non-English language outputs, preprints), Litmaps inherits Google Scholar's coverage patterns, which favor English-language academic publications. This represents a known bias we explicitly acknowledge rather than a correctable limitation within our methodological framework."

These clarifications make explicit what was previously implicit, ensuring readers understand both Litmaps' capabilities and constraints for citation network research.

Suggestion 5: Redundant Text (Lines 481-487)

Suggestion: The paragraph in lines 481–487 reiterates points previously addressed in lines 455–464. Consider revising or streamlining the text to improve conciseness and coherence.

Response:

Absolutely correct—this was an editing oversight. We have completely removed the redundant paragraph (lines 481-487). This was duplicate content from an earlier manuscript version that should have been deleted during the previous revision cycle.

The section now flows directly from the factual presentation of temporal distribution (Section 4.1, current lines 467-474) to author collaboration patterns (Section 4.2), eliminating the unnecessary repetition you identified.

 

Thank you for catching this—it significantly improves the manuscript's conciseness.

 

Summary of Implemented Changes

All five suggestions have been implemented:

 

1. ✓ Google Scholar justification: Added explicit methodological rationale in Section 3.1

 

2. ✓ Visual selection diagram: Created Figure 2 (PRISMA-style flowchart) showing complete workflow

 

3. ✓ Complementary metrics: Discussed altmetrics and co-readership networks in Limitations and Future Directions

 

4. ✓ Litmaps limitations: Enhanced existing Section 3.7 with explicit coverage constraints

 

5. ✓ Redundant text removed: Deleted duplicate paragraph (lines 481-487)

 

 

Concluding Remarks

We want to express our sincere gratitude for your generous and insightful review. Your recognition that our work "fills a gap between technological potential and actual operational implementation" and "could become a reference point for researchers working on drone-based methodologies in coastal environments" deeply motivates us. Such understanding from a reviewer is rare and precious.

Your targeted methodological suggestions—particularly the visual workflow diagram and complementary metrics discussion—have genuinely improved the manuscript's transparency and forward-looking perspective. These were not merely compliance exercises but substantive improvements we are grateful to have incorporated.

We believe the revised manuscript now combines the "methodological rigor with conceptual depth" you appreciated with the enhanced clarity and transparency your suggestions provided.

Thank you again for such a thoughtful, constructive, and encouraging review.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Thank you for the revisions. Most of my comments were correctly addressed. From my side, the paper is now adequate for publication.

Good job.