Effects of Flight Heights and Nozzle Types on Spray Characteristics of Unmanned Aerial Vehicle (UAV) Sprayer in Common Field Crops

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this paper the authors investigate the effect of different flight heights and nozzle types on the spray volume of sprayers placed on UAVs.

The percentage coverage and the distribution of droplet size in cotton, soya and sugar cane plantations are analysed. 

Three different flight heights were compared in order to evaluate the characteristics of spraying. The results show that the lower flight heights lead to a significant improvement in volume, coverage and uniformity. Centrifugal nozzles provide better results in sugar cane.

The article is well-structured, and relevant to the purpose of the journal; some sections should necessarily be supplemented with better technical data, and in particular the methodology applied. Criteria for parameter selection, experimental conditions (wind speed and direction, relative humidity, phenological states...), flight characteristics and nozzle characteristics must be integrated.

It would be useful to include in the discussion a direct comparison with the results of other similar work published over the last 3 years.

The approach is original and innovative, but further details are needed on the replicability of the experimental method in other contexts.

Table 2 is too objective; it would be better to specify the average flight height (range) numerically.

The formatting of table 5 is wrong, "high" should not be underlined and bold.

The conclusions provide a comprehensive summary of the main findings but do not address the limitations of the study and suggestions for future research.

The manuscript is certainly relevant but needs revisions to improve methodological clarity, broaden critical discussion and correct some inaccuracies.

We also recommend that you review the bibliography and bring it into line with MDPI standards!

Author Response

In this paper, the authors investigate the effect of different flight heights and nozzle types on the spray volume of sprayers placed on UAVs.

The percentage coverage and the distribution of droplet size in cotton, soya and sugar cane plantations are analysed. 

Three different flight heights were compared in order to evaluate the characteristics of spraying. The results show that the lower flight heights lead to a significant improvement in volume, coverage and uniformity. Centrifugal nozzles provide better results in sugar cane.

The article is well-structured, and relevant to the purpose of the journal; some sections should necessarily be supplemented with better technical data, and in particular the methodology applied. Criteria for parameter selection, experimental conditions (wind speed and direction, relative humidity, phenological states...), flight characteristics and nozzle characteristics must be integrated.
Response:  The authors thank the reviewers for their constructive feedback. As recommended, we have made revisions to address the points raised. Specifically, additional sentences have been included in the second paragraph of the ‘Materials and Methods’ section to clarify the criteria for parameter selection. A new sentence has been added to explain the rationale behind selecting the specific nozzles, and the paragraph concludes with a justification for the overall drone settings used in the experiment. While it is challenging to provide detailed justifications for each individual drone setting, we consider the drone as an integrated tool for spraying, and most settings in sprayer drones are broadly similar across different models.

The impact of various environmental conditions is discussed in detail in the sixth paragraph, which discusses the effects of variability in wind, temperature, and humidity on the spraying process. The environmental conditions chosen for the experiment were selected to minimize their potential as random sources of variance while remaining practical and representative of real-world field conditions.

 

It would be useful to include in the discussion a direct comparison with the results of other similar work published over the last 3 years.
Response: The direct comparison with the results of other similar work published has been done in the sub-sections of the ‘Results’ section. The third paragraph in the 3.1 Flight heights section, 2^nd paragraph in the 3.2 Nozzle types section, and 3^rd paragraph in the 3.3 Canopy Penetration section mention different relevant research works related to our findings. We would appreciate it if you could suggest if any updates or revisions are needed.

 

The approach is original and innovative, but further details are needed on the replicability of the experimental method in other contexts.
- We did our best in the “Materials and Methods” section to provide all the details needed for the replicability of the experiment. A few minor editing was done in this section, but we truly think that the information provided in this section already has enough information for replicability. If the reviewers could specify a little about what information should be added, reviewed or removed to make it better, that would be really great.

 

Table 2 is too objective; it would be better to specify the average flight height (range) numerically.
- Table 2 has been revised. The ‘Flight Heights’ column has been updated with numerical values of the flight heights. This format is similar to the results table in Table 3.

 

The formatting of table 5 is wrong, "high" should not be underlined and bold.
- Corrected! The whole table has been rechecked and made sure everything is right.

 

The conclusions provide a comprehensive summary of the main findings but do not address the limitations of the study and suggestions for future research.
- The “Conclusion” section has been exhaustively revised, with more details on the limitations of the research and future research recommendations. The 3^rd paragraph addresses the different limitations and challenges faced in our experiments, and the 4^th paragraph talks about the prospects of future research.

 

The manuscript is certainly relevant but needs revisions to improve methodological clarity, broaden critical discussion and correct some inaccuracies.
- The whole manuscript has been revised, and edited to improve the details, and clarity. Inaccuracies and minor errors were corrected, and revisions were done in individual paragraphs. If the reviewers think more work is needed for the revision, we are open to revising our manuscript.

 

We also recommend that you review the bibliography and bring it into line with MDPI standards!
- All the citations and references have been updated to the MDPI standards.

 

Message to the reviewer:

We (the authors) heartfully thank the reviewer for providing their feedback and suggestions. We think we have addressed the comments as best as we could. If the reviewer thinks the submitted manuscript needs more revision, we are open to it too. We expect the reviewer to provide more specific information on where and how the revisions should be done. We appreciate the reviewers time.

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript investigates the effects of flight heights and nozzle types on spray characteristics of UAV sprayers across three field crops: cotton, soybean, and sugarcane. The study is well-structured, with clear objectives, methodology, and analysis. The results are presented systematically, showing significant findings related to spray volume, coverage, and droplet size distribution at different canopy levels. The discussion effectively connects the findings with existing literature, while the conclusion highlights practical applications in precision agriculture. However, the manuscript could benefit from improved clarity in explaining some statistical interactions and their practical implications. Additionally, while the methodology is robust, more discussion on the limitations, such as wind velocity variations and specific environmental factors, would strengthen the study. Overall, the manuscript contributes valuable insights to UAV spraying technology and is suitable for publication after addressing the minor revisions suggested below.

1.      Line 14: check “efficiency”

2.      Line 18: “impact” should be plural; replace ”spray volume” with “spray deposition” across the text, as this has been defined in ISO standard.

3.      The introduction effectively sets the context but could better emphasize the specific research gap in terms of UAV nozzle performance in different crops.

4.      Line 41: Please consider between “sprayer drones” or “drone sprayers” which is more suitable.

5.      Line 46: do authors think the uniformity of drone spraying is better than boom sprayer for field crops?

6.      Line 46-48: One of the most important problems in UAV spaying is high spray drift risk.

7.      Line 68: why not cite this paper?

8.      Line 75-81: authors didn’t give a good description of the research gap and the research significance of drone spraying in the US.

9.      The experimental setup is well-detailed, but some parameters, like environmental factors (e.g., wind velocity), were not fully accounted for. A brief note on how this might have influenced the results would add clarity.

10.   Line 91: check the full spelling of VMD and Fig. 3.

11.   The statistical interactions (e.g., flight heights × nozzle types) are presented in detail, but some results, such as why centrifugal nozzles produced larger droplets than expected, need further clarification or hypothesis.

12.   The discussion does a good job connecting findings to the literature, but it could expand on the practical implications for farmers regarding nozzle selection for specific crops.

13. The conclusion summarizes the key findings well, but a sentence highlighting future research directions (e.g., incorporating environmental variability or multi-season studies) would strengthen it.

Author Response

 

The manuscript investigates the effects of flight heights and nozzle types on the spray characteristics of UAV sprayers across three field crops: cotton, soybean, and sugarcane. The study is well-structured, with clear objectives, methodology, and analysis. The results are presented systematically, showing significant findings about spray volume, coverage, and droplet size distribution at different canopy levels. The discussion effectively connects the findings with existing literature, while the conclusion highlights practical applications in precision agriculture. However, the manuscript could benefit from improved clarity in explaining some statistical interactions and their practical implications. Additionally, while the methodology is robust, more discussion on the limitations, such as wind velocity variations and specific environmental factors, would strengthen the study. Overall, the manuscript contributes valuable insights to UAV spraying technology and is suitable for publication after addressing the minor revisions suggested below.

1. Line 14: check “efficiency”
   - Checked and spelling corrected!
2. Line 18: “impact” should be plural; replace ”spray volume” with “spray deposition” across the text, as this has been defined in ISO standard.
   - ‘impacts’ corrected! All the “spray volume” were replaced with “spray deposition”.
3. The introduction effectively sets the context but could better emphasize the specific research gap in terms of UAV nozzle performance in different crops.
4. Line 41: Please consider between “sprayer drones” or “drone sprayers” which is more suitable.
   - We think ‘sprayer drones’ is fine as this term is widely used in the US for any kind of UAV capable or used for spraying fields.
5. Line 46: do authors think the uniformity of drone spraying is better than boom sprayers for field crops?
   - Thank you for pointing this out. Since the uniformity of drone spraying is a topic of study, and is still debatable under the current information available, this phrase was taken out to avoid potentially false claims.
6. Line 46-48: One of the most important problems in UAV spaying is high spray drift risk.
   - Agreeing with the reviewer’s comment, the problem of high spray drift risk was added.
7. Line 68: why not cite this paper?
   - The paper is cited with the MDPI citation standard.
8. Line 75-81: authors didn’t give a good description of the research gap and the research significance of drone spraying in the US.
   - Addressing the comments of the reviewer, changes were made to the top half of the paragraph of lines 72 -81. Research gaps addressed by our experiment were specifically addressed with a better description, the objective of the study was properly mentioned, and the relevance/importance of the research findings was also stated.
9. The experimental setup is well-detailed, but some parameters, like environmental factors (e.g., wind velocity), were not fully accounted for. A brief note on how this might have influenced the results would add clarity.
   - This was addressed in line 137 – 143. Environmental factors and their influence were briefly mentioned with their potential impact on the experiment, and measures to avoid their effects were stated.
10. Line 91: check the full spelling of VMD and Fig. 3.
    - The full spelling of VMD was corrected to volume median diameter, and Fig. 3, was corrected to Table 1, where the information about the drone specifications was provided.
11. The statistical interactions (e.g., flight heights × nozzle types) are presented in detail, but some results, such as why centrifugal nozzles produced larger droplets than expected, need further clarification or hypothesis.
    - The results of centrifugal nozzles producing larger droplets than expected have already been clearly discussed with the possible explanations from lines 226 – 236. The authors don’t think they have any further clarification bases apart from the provided one. Other results, including the interactions, were also reviewed by the authors and had been lightly revised. The authors would also like to ask for some other specific sections should more discussion or clarification be needed.
12. The discussion does a good job connecting findings to the literature, but it could expand on the practical implications for farmers regarding nozzle selection for specific crops.
    - The practical implications have been discussed in the ‘Conclusion, Significance, and Future Outlook’ section, from lines 384 – 394. Details on the importance of the research’s findings are provided.
13. The conclusion summarizes the key findings well, but a sentence highlighting future research directions (e.g., incorporating environmental variability or multi-season studies) would strengthen it.
    - Future research directions have been exhaustively discussed from lines 404 – 412.

 

Message to the reviewer from the authors:

Thank you for your valuable comments and insights. Your feedback has certainly improved the quality of our manuscript. All the specific comments were properly addressed, and necessary changes were made accordingly. Updates in the manuscript include minor revisions on the grammar, citation errors, figures, and tables revisions. A few major revisions are also done, especially while describing the issue of centrifugal nozzles providing bigger droplets. The Conclusion section is updated with the limitations of our research, and future prospects. Please put forward your more constructive feedback that will help strengthen the quality of our article.

 

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

All revisions has been made. This manuscript can be accepted for publication.