Influence of the Downwash Wind Field of Plant Protection UAV on Droplet Deposition Distribution Characteristics at Different Flight Heights

Round 1

Reviewer 1 Report

This manuscript requires serious editing before publication. The Authors have used the phrase “plant protection UAV” in several places in the manuscript. I think it is redundant and it is better to remove them. References to chemical pollution may be deleted and help shorten the manuscript.

I am going to highlight a few instances where better wording of the sentence would make the manuscript more readable. It is impossible for a Reviewer to edit the manuscript and it is not his job either.

Abstract:

Line 23: “reveal the influence mechanism of the downwash” sounds awkward. To understand the mechanism of downwash wind field, spray tests were conducted at different flight heights, using a DJI UAV.

Line 271: As shown in Figure 7, it showed: Reword as Figure 7 showed the droplet ---------.

Line 275: According to the evaluation method. This is another example of how sentence constructions in the manuscript are flawed and should be improved. Why not simply say, “The effective swath was ----- at different flight heights”?

 

Statistics: The authors say that the means were separated using the DMRT in Line 202. I have not seen in the manuscript that the authors have used this test.

Figure 8: I need to see more data on regression statistics including degrees of freedom, t-values.

Four different slopes are shown in the manuscript. Need to have regression statistics for each of the models tested. Homogeneity of regression coefficients: Did the slopes differ from each other? It seems that the sample size is 6. With N-2 degrees of freedom, the probability of making a Type 1 Error is highly likely. The data described in the manuscript were obtained under field conditions and are subject to vagaries of weather.  More data would make the conclusion realistic.    

Line 272: Previous studies References are needed.

The authors claim that in Table 4, the degrees of freedom was 79 in their rebuttal comments. But where is Table 4? 

Author Response

Dear reviewer,

 

Thank you for your review and insightful comments on our paper. The responds to your comments are as follow. According to your suggestion, the paper has been revised accordingly. Revised version and a copy that highlights the changes to the text in blue were attached in the attached file. Please let us know if you have any other ideas or suggestions. 

     Thanks for your support! 

 Respond

Line 23: “reveal the influence mechanism of the downwash” sounds awkward. To understand the mechanism of downwash wind field, spray tests were conducted at different flight heights, using a DJI UAV.

Response: Revised according to your suggestion.

Line 271: As shown in Figure 7, it showed: Reword as Figure 7 showed the droplet ---------.

Response: Revised according to your suggestion.

Line 275: According to the evaluation method. This is another example of how sentence constructions in the manuscript are flawed and should be improved. Why not simply say, “The effective swath was ----- at different flight heights”?

 Response: Revised according to your suggestion.

Statistics: The authors say that the means were separated using the DMRT in Line 202. I have not seen in the manuscript that the authors have used this test.

Response: Revised, as shown in Table 3.

Figure 8: I need to see more data on regression statistics including degrees of freedom, t-values.

Four different slopes are shown in the manuscript. Need to have regression statistics for each of the models tested. Homogeneity of regression coefficients: Did the slopes differ from each other? It seems that the sample size is 6. With N-2 degrees of freedom, the probability of making a Type 1 Error is highly likely. The data described in the manuscript were obtained under field conditions and are subject to vagaries of weather. More data would make the conclusion realistic. 

Response: Thanks for your comments. The sample size is 6, which may not be enough for statistical analysis. However, it is reasonable that these slopes were only used to reflect the change trend of droplets deposition with the wind field in Z-direction.  

In addition, a surrounding wall with a height of about 3 m was built around the site to block the external wind and eliminate the influence of external crosswind on the test. The data described in the manuscript are little affected by vagaries of weather.

Line 272: Previous studies References are needed.

Response: Revised according to your suggestion.

Author Response File: Author Response.docx

Reviewer 2 Report

Review comments on “Influence of the Downwash Wind Field of Plant Protection UAV on Droplet Distribution Characteristics at Different Flight Heights”

The study is needed in the area of UAV applications in agriculture. The concern of spray droplet drift or the spraying efficiency from UAVs are common and this research aims on identifying these issues. The experiment design was properly explained for the research objective. The results are interesting, and this research experiment has a novel approach. UAV propeller wind effect on spray droplets at different altitudes were properly represented and explained. The paper overall looks good but there are some minor changes needed as indicated below.

Line 49 – 50: The first sentence in the introduction is not clear, please revise the statement. Is chemical control an agricultural production technology? Or chemical application is an important agricultural production method of controlling plant disease, pests, and weeds?

Line 100 – 105: The final sentence is too long, can it be split or shortened?

Figure 2: Instead of upper computer and lower computer definition, could you explain what laptop is and what is transmission module either in the text or in the caption. Also, is this figure the working principle or system layout?

Line 147 – 175: Recommendation “UAV flight altitudes of 1 m, 1.5 m, 2 m, and 2.5 m were set during the experiments”.

Line 181: “… UAV was 5m away …”, here either keep space between value and the unit throughout the paper or remove the space.

Lines 192 - 196: I am not sure if the formula is necessary here. The description of CV seems good enough.

Lines 197 – 198: “Wireless wind speed sensor network system” it is too long, I think. I recommend using a single word for the entirety, may be call it “system” and provide description of it at the beginning of the materials and method section.

Figure 6: Could be moved to line 243, after the paragraph ending with “… droplets to drift horizontally.”

Figure 7: Change “Sampling location/(m)” to “Sampling location (m)”. Remove box around the legend if possible and bring it to the upper left corner below the edge to gain some empty space.

Line 295: Please indicate the four different heights. “… spray area was 58.3%, 62.0%, 56.6%, and 48.8% at altitudes 1 m, 1.5 m, 2 m, and 2.5 m”.

Table 2: Please double check CV values corresponding to the flight altitudes, especially the last two row.

 Lines 334 – 335: Please add a reference.

Lines 330 – 341: Please add references referring to problems of spraying with UAV at low altitudes if possible.

Lines 350 – 351: Please add reference indicating similar results if possible.

Conclusion: Please remove numbering and provide a full text with tailoring all the paragraphs.  

Comments for author File: Comments.pdf

Author Response

Dear reviewer,

Thank you for your review and insightful comments on our paper. The responds to your comments are as follow. According to your suggestion, the paper has been revised accordingly. Revised version and a copy that highlights the changes to the text in blue were attached in the attached file. Please let us know if you have any other ideas or suggestions. 

     Thanks for your support! 

 Respond

The study is needed in the area of UAV applications in agriculture. The concern of spray droplet drift or the spraying efficiency from UAVs are common and this research aims on identifying these issues. The experiment design was properly explained for the research objective. The results are interesting, and this research experiment has a novel approach. UAV propeller wind effect on spray droplets at different altitudes were properly represented and explained. The paper overall looks good but there are some minor changes needed as indicated below.

Line 49 – 50: The first sentence in the introduction is not clear, please revise the statement. Is chemical control an agricultural production technology? Or chemical application is an important agricultural production method of controlling plant disease, pests, and weeds?

Response : Revised. Chemical application is an important agricultural production method of controlling plant diseases, insect pests and weeds.

Line 100 – 105: The final sentence is too long, can it be split or shortened?

Response: Revised according to your suggestion.

Figure 2: Instead of upper computer and lower computer definition, could you explain what laptop is and what is transmission module either in the text or in the caption. Also, is this figure the working principle or system layout?

Response: Revised according to your suggestion.

Line 147 – 175: Recommendation “UAV flight altitudes of 1 m, 1.5 m, 2 m, and 2.5 m were set during the experiments”.

Response: Revised according to your suggestion.

Line 181: “… UAV was 5m away …”, here either keep space between value and the unit throughout the paper or remove the space.

Response: Revised according to your suggestion.

Lines 192 - 196: I am not sure if the formula is necessary here. The description of CV seems good enough.

Response: Revised according to your suggestion, the formula has been deleted.

Lines 197 – 198: “Wireless wind speed sensor network system” it is too long, I think. I recommend using a single word for the entirety, may be call it “system” and provide description of it at the beginning of the materials and method section.

Response: Revised according to your suggestion.

Figure 6: Could be moved to line 243, after the paragraph ending with “… droplets to drift horizontally.”

Response: Revised according to your suggestion.

Figure 7: Change “Sampling location/(m)” to “Sampling location (m)”. Remove box around the legend if possible and bring it to the upper left corner below the edge to gain some empty space.

Response: Revised according to your suggestion.

Line 295: Please indicate the four different heights. “… spray area was 58.3%, 62.0%, 56.6%, and 48.8% at altitudes 1 m, 1.5 m, 2 m, and 2.5 m”.

Response: Revised according to your suggestion.

Table 2: Please double check CV values corresponding to the flight altitudes, especially the last two row.

Response: Revised according to your suggestion.

 Lines 334 – 335: Please add a reference.

Response: Revised according to your suggestion.

Lines 330 – 341: Please add references referring to problems of spraying with UAV at low altitudes if possible.

Response: Revised according to your suggestion.

Lines 350 – 351: Please add reference indicating similar results if possible.

Response: Revised according to your suggestion.

Author Response File: Author Response.pdf

Reviewer 3 Report

It was interesting to see you have actually measured the wind field generated by the Hexrotors downwash, and the compare it to the spray distribution.

However I have some concerns about the significance of this paper, your conclusions seem sound, but I am not sure if the recommendations based on this paper warrant a publication. You have only used a single UAS type, would a flight height of 2m still be the best for a smaller or larger UAS, or perhaps one that have positioned there nozzles in different locations. Also while the downwash measurements seem to be unique this sort of work has been performed before.

There are a few grammatical errors throughout the paper, while nothing significant the sometimes make reading the paper a bit hard, I have highlighted some examples in the annotated copy of the paper I have attached.

Need a much better explanation of how you have obtained the spray volume distribution measurements. And how valid you think the method for converting droplet area to a volume is. For example I did a quick calculation but for your  run that generated an average application rate of 0.482 ul/cm^2 over a width of 6m flying at 5 m/s that would make the flow rate of about 1.2 l/min where as the spray UAS was spraying at 4.5 L/min which seems like a large difference.

Some additional comments are also included in the attached paper.

Comments for author File: Comments.pdf

Author Response

Dear reviewer,

Thank you for your review and insightful comments on our paper. The responds to your comments are as follow. According to your suggestion, the paper has been revised accordingly. Revised version and a copy that highlights the changes to the text in blue were attached in the attached file. Please let us know if you have any other ideas or suggestions. 

     Thanks for your support! 

Respond

It was interesting to see you have actually measured the wind field generated by the Hexrotors downwash, and the compare it to the spray distribution.

However I have some concerns about the significance of this paper, your conclusions seem sound, but I am not sure if the recommendations based on this paper warrant a publication. You have only used a single UAS type, would a flight height of 2m still be the best for a smaller or larger UAS, or perhaps one that have positioned there nozzles in different locations. Also while the downwash measurements seem to be unique this sort of work has been performed before.

Response: Thanks for your comments. The flight height of 2m may not be the best flight altitude for other types of aircraft, but for the DJI T16 plant protection UAV, the optimal flight height was 2.0m according to the results of this test. What’s more, the conclusion has guiding significance for practical operation of the DJI T16 UAV.

There are a few grammatical errors throughout the paper, while nothing significant the sometimes make reading the paper a bit hard, I have highlighted some examples in the annotated copy of the paper I have attached.

Response: Revised according to your suggestion about grammatical errors.

Need a much better explanation of how you have obtained the spray volume distribution measurements. And how valid you think the method for converting droplet area to a volume is. For example I did a quick calculation but for your  run that generated an average application rate of 0.482 ul/cm^2 over a width of 6m flying at 5 m/s that would make the flow rate of about 1.2 l/min where as the spray UAS was spraying at 4.5 L/min which seems like a large difference.

Response: Thanks for your comments. The method for converting droplet area to a volume was proposed and verified by the authors of reference [26], and was adopted by many researchers in the following years.

[26] Zhu Heping, Masoud Salyani, Robert D.Fox. A portable scanning system for evaluation of spray deposit distribution. Computers and Electronics in Agriculture, 2011, 76: 38-43.

Author Response File: Author Response.docx

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

This manuscript has many faulty sentences that requires serious editing before publication. It is beyond the scope of a reviewer to edit the manuscript. But I will point out one or two places where improved editing will help the paper. 

To begin with the Abstract: Lines 17 to 24: The aerial spraying of pesticides by unmanned vehicles is a process in which the spray droplet deposition on target sites occurs under the influence of down wash wind field. The down wash wind field is the most important factor affecting droplet deposition distribution characteristics in an aerial spray.  

Line 19: Although beginning a sentence with the conjunction And is probably acceptable, it is not common in scientific literature and it is preferable to avoid such a usage.

Line 97: Explain actual working test method.

Line 185: Nearly 30 seconds ------------, the sampling cards were collected and placed in properly labeled bags.

Line 189: Droplet deposition distribution is the title of the paper. There is no statement on spray droplet parameters measured in the study, importantly, D_v0.1, D_v0.5 and D_v0.9.

In the Introduction: Lines 46-57: The authors repeatedly state over application of pesticides (Lines 48 and 55). It is redundant and should be avoided.

Lines 62-64: Requires a reference. The authors state that an UAV causes high spraying efficiency, atomization effect and high pesticide utilization. What is atomization effect? Most UAVs are produced with factory-installed nozzles with varying droplet sizes.  

Line 66: remove the word “chemical”. Simply say, prevention and control.

Line 77: The reference cited is not Fritz et al. 2012.  In this citation, the authors were Huang, Y, Zhan, W., Fritz, B. K., and S. J . Thompson.  The authors did not report on UAVs in this study but reported on downward drift of aerial applied sprays by fixed-wing aircraft.

Lines 188-189: US USDA? Reference Needed. There are two commonly used software to study spray droplet spectra, namely, the DropletScan and the Accustain.

Whitney RW, Gardisser DR (2003) DropletScan Operators Manual. Stillwater, OK., WRK of Oklahoma and WRK of Arkansas.

AccuStain software (University of Illinois, Urbana-Champaign., Illinois) scanner-based system.

Lines 204-241: Many typo errors. Example, Line 208, give space between 1.0 and m.

Line 204-207: These sentences belong in the Methods and Materials Section.

Table 3: Provide t-values with degrees of freedom for the regression model. Need to see the regression equations with R² values.

Line 311: Both regression and ANOVA were used to analyze the data. The authors have provided only regression statistics.

Line 315: The sentence is redundant and that the 5% α is a commonly accepted value.

References: Lines 397 and 438 have two references in one citation.

Figure 8: What about the regression models for heights other than 2 m? Why have not these slope coefficients tested against one another for homogeneity?

The authors should consider changing the title of the paper: How about, “Influence of the Downwash -----------------of an UAV on Spray Droplet Deposition at Different Heights”. The word plant protection UAV is an anomaly.

Reviewer 2 Report

This article presents some interesting information but unfortunately cannot be acceptable in the present form. It has main issues with language, methodology and interpretation of the results.  Some aspects are discussed below and many other are commented on the pdf.

The document requires extensive proofreading of English language. This is obvious even from the first sentence “ The aerial spraying of plant protection unmanned aerial vehicles (UAV) is a process in 17 which…”  The authors are not quite familiar with English and should certainly ask for a help.

I stopped making comments on language on line 60. It makes no sense to continue neither it’s the reviewer’s position to proofread the text. I tried hardly though to continue reading in order to criticize the scientific methods and the soundness of the results. Even though it presents some valuable information, there are still many important issues to be solved. For instance, the description on the Material and Methods is insufficient and not concise in many points (please see also comments on the pdf). The specifications for example provided by the authors for the UAV are false. The company gives different information.

The methodology needs some clarification. Authors don’t mention measuring natural wind speed and direction. Even though they had built a wall around the testing area it is possible, small wind turbulences to have distort the results. Were there any measurements of wind before, during or after the flights? I would also suggest contacting some additional tests with different flying speeds. The effect of the UAV speed on the downwash flow field is very important and can alter the results. The authors doesn’t make even a single comment on the text for this important issue.

The document lacks completely discussion with references to findings from relative works in the Results and Discussion section. The authors claim for the originality of their research but in fact, dismiss to refer on other important work in the field like:

Zheng, Yongjun & Yang, Shenghui & Liu, Xingxing & Wang, Jie & Norton, Tomas & Chen, Jian & Tan, Yu. (2018). The computational fluid dynamic modeling of downwash flow field for a six-rotor UAV. Frontiers of Agricultural Science and Engineering. 5. 159-167. 10.15302/J-FASE-2018216.

Wu, Yalei & Qi, Lijun & Zhang, Hao & Musiu, Elizabeth & Yang, Zepeng & Wang, Pei. (2019). Design of UAV Downwash Airflow Field Detection System Based on Strain Effect Principle. Sensors. 19. 2630. 10.3390/s19112630.

The overall feeling by reading this text was that it was written hasty. Even though it includes some important information, it requires extensive review. Definitely, the poor English, didn’t helped the reviewing process and many points may been poorly understood or even been misunderstood.

Comments for author File: Comments.pdf