Propellers Spin Rate Effect of a Spraying Drone on Quality of Liquid Deposition in a Crown of Young Spruce
, Gerhard Moitzi 2, Jiřà Dvořák 3, Anna Keutgen 4, Jan Najser 5, Jan Kielar 5, Tomáš Najser 5 and Marcel Mikeska 5Round 1
Reviewer 1 Report
Comments for author File: 
Comments.pdf
Author Response
Precision farming requires the latest and most accurate measurement techniques. For this purpose, various solutions are used. For this purpose, for example, variable dosage technology, i.e. VRA, is used.
Obtained results are important to obtain progress for further development of the use of drones in agricultural production.
- Introduction part requires a minor reconstruction.
- In the introduction and in the materials and methods, the authors refer only to the importance of diseases and the possibility of using drones in DSS.
- Information on research from the technological side is included.
- It is necessary for the authors to provide information about the multifunctionality of drones.
Reply from the authors
We thank the reviewer for his valuable comment. The authors have indeed focused in the manuscript on too narrow a topic concerning only the use of drones exclusively as unmanned aerial spraying systems, forgetting about their multifunctional use in agriculture. The "Introduction" chapter has been supplemented with an overview of other drone use technologies, enriching the subject matter studied. This new information has been inserted into the text and helped us to develop the intention of tested problems and stronger justify the choices. The new information is incorporated mainly on lines: 51-135.
- There is no information that no research has yet been carried out on the profitability of performing spraying treatments using drones.
- Using more concentrated agents in drones than in a traditional sprayer gives greater efficiency, but is associated with the risk of contact with the substance during handling. Therefore, it is necessary to introduce detailed provisions allowing spraying while maintaining the safety of the environment and the operator.
- Pointing out that they cannot be used in inhabited areas (as the author writes) – line 54, 111 – 112
Reply from the authors
This essential information was placed in the text of the improved manuscript, lines: 108-114 and 118-122.
2 Materials and Methods
Information in the lines 110 – 14 are a part of the introduction
What liquid was used and its viscosity
Reply from the authors
In all experiments, distilled water, stained with aqueous nigrosin dye at a concentration of 0.5%, was used, lines 317-319. Unfortunately, the viscosity of this liquid was not measured.
3 . There is a lack of Discussion
The author refers to the results without introducing information about research conducted by other teams, if there are no reports in the literature, it is important to emphasize the importance of this research
Reply from the authors
The authors thank the reviver for this critical comment. Since the authors supplemented the "Introduction" chapter with new information from studies that were thematically similar to their research, it was possible to discuss the results and supplement the "Discussion" chapter with selected literature items.
- Conclusions Lines 428 – 431 as a first conclusion, that drones may be used in DSS and the present study contributed to the development of this technology
Reply from the authors
The authors would like to thank you for drawing their attention to this essential piece of information arising from their research. The authors have changed the Conclusions and Abstract under the reviewer's comments.
The author refers to the results without introducing information carried out by other teams, if there are no reports in the literature, it is to emphasize the importance of his research
Thank you. It seems to us that this is.
Author Response File: Author Response.pdf
Reviewer 2 Report
General comment
This paper deals with a domain of intensive research while UAVs have the potential to limit operator exposure and tediousness in row crops. However, the capacity of spraying drones to be used in 3D crops is still a current domain of research while regulators ask for more data.
This study is well conducted, the paper is well written but some questions on the protocol and the analysis of results are raised.
Detailed comments
Line 133-139 : it might be interesting to indicate some droplet size values (VMD) at 2 bar, not only the classification. UASS manufacturers generally provide fine droplet atomizers (FF or rotary atomizers) arguing of a better coverage.
Line 152: The flying height of 0.6 above the tree crown was defined on which basis exactly ? do we have an idea about the spray swath of the UASS ?
Line 158: The “trunk” collector is not easy to see on Fig 2. A separate figure showing the tripod. Why is it necessary to assess deposition on the trunk? Are there some specific application son trunks?
Line 173-180 : this paragraph is quite dense and difficult to understand without drawing/figure. it is not clear whether the experiments were repeated : how many trees per modality (travel speed, rotor revolution speed) ?
Line 198 : these two flying speeds appear still correspond to low travel speeds (~2 and 3.4 km/h). Is it a limitation from the motorized cart? A typical flying speed is 5-6 km/h at minimum.
Line 223 : a reference indicating the experimental protocol with nigrosine dye would be appreciated. Is there a calibration of concentration and the response of photo colorimeter?
Line 246 : LAI. I don’t catch the point of including the deposition on the tree trunk and not on the branches (supporting the needle leaves)
Page 8 results. Fig 4a and 4b : A statistical analysis showing significant differences would probably help
These data are not really commented…
Line 324 : is this Table 2 necessary ? since there are no comments…
Fig 5 I am not sure this Fig is essential
Page 10 Fig 6a-Fig6b: these results on the air speed inside the vegetation are interesting but are not related to previous deposition data… Were they achieved in a static position of the UAV ? … These results on the air speed could been presented before the deposition in order to characterize the airstream conditions inside the trees ?
Author Response
Detailed comments
Line 133-139 : it might be interesting to indicate some droplet size values (VMD) at 2 bar, not only the classification. UASS manufacturers generally provide fine droplet atomizers (FF or rotary atomizers) arguing of a better coverage.
Reply from the authors
The fine droplets produced by pressure and rotary atomisers are highly susceptible to drift by air currents. Bearing in mind that air drift of pesticides during ornamental tree spraying could lead to environmental pollution in the vicinity of the drone's treatment sites, the fine droplet nozzle was abandoned for the tests, and an air-injector flat spray compact nozzle - IDK 90-015 was to the experiments. The droplet size values according to VMD were not given, as no such tests had been carried out. The classification used in the tests was that given in a table produced by the nozzle manufacturer Lechler under ISO 25358 norm (https://www.lechler.com/fileadmin/media/datenblaetter/agrar/EN/lechler_agrar_datenblatt_idk-idkn_en.pdf). It was considered that the data from the manufacturer's website was sufficient to represent the characteristics of the nozzle and the droplet pattern produced, as the same nozzle, in each experiment, always sprayed the same liquid at the same pressure. Relevant information is included in the text of the manuscript lines:213-215. The rationale for choosing the IDK atomiser is included in lines: 205-210
The authors thank the reviewer for the valid comment and will keep it in mind for future studies using more nozzles and higher liquid pressures.
Line 152: The flying height of 0.6 above the tree crown was defined on which basis exactly ? do we have an idea about the spray swath of the UASS ?
Reply from the authors
A detailed answer to this question is presented and justified in the text of the revised manuscript, lines: 123-135 and 227-236.
The authors were mainly driven by environmental aspects - a lower height of the raid means air drift smaller liquid away, a lower height of the raid also means greater precision in the execution of the treatment, and a lower height means a more significant impact of the air stream on the deposition of droplets into the tree crown.
There was no done evaluation of the spray swath of the UASS because only one nozzle was used, and the idea of this atomizer use is in lines: 215-218.
Line 158: The “trunk” collector is not easy to see on Fig 2. A separate figure showing the tripod. Why is it necessary to assess deposition on the trunk? Are there some specific application son trunks?
Reply from the authors
The contents of Figure 2 have been exchanged. The drawing now shows a spruce tree with a tripod mounted in the crown and, next to the tree, an identical tripod assembled specifically for experiments without the tree. The figure is shown and marked points where the 'trunk' and 'branch' samplers are attached to the tripod rods. Both types of samplers are samplers to measure liquid deposited on the branches of the tree. Trunk" samplers are mounted close to the trunk of the tree (0.06 m from the trunk axis, the zone of the tree, close to trunk) and "branch" samplers at a distance of 0.21 m from the trunk axis (the vertical zone of the tree, away to the trunk). The name 'trunk' next to the sampler only indicates the proximity of the sampler to the trunk. The liquid deposited on the tree trunk was not evaluated. The liquid deposited on the samplers located in close proximity to the trunk was evaluated.
The authors thank you for pointing out the inaccuracy of the explanation of the 'trunk' sampler designation in the text. The text has been corrected.
Line 173-180 : this paragraph is quite dense and difficult to understand without drawing/figure. it is not clear whether the experiments were repeated: how many trees per modality (travel speed, rotor revolution speed) ?
Reply from the authors
Description corrected, lines 259-269 and 290-292.
Line 198 : these two flying speeds appear still correspond to low travel speeds (~2 and 3.4 km/h). Is it a limitation from the motorized cart? A typical flying speed is 5-6 km/h at minimum.
Reply from the authors
Thank you for your question. The chapter "2.1. Test stands" is supplemented by relevant information that answers the question, lines 270-272,
Line 223 : a reference indicating the experimental protocol with nigrosine dye would be appreciated. Is there a calibration of concentration and the response of photo colorimeter?
Reply from the authors
Thank you for the question, but in this scientific paper, to not lose reader time on a whole data reading, we decided to provide only result data obtained from the instrument, in this case, from the spectrometer. However, if the reviewer is interested in such information as the calibration of the concentration and response of the photo colorimeter, we present below the calibration printout from the spectrometer.
Line 246 : LAI. I don’t catch the point of including the deposition on the tree trunk and not on the branches (supporting the needle leaves)
Reply from the authors
The amount of liquid deposited on the tree trunk was not measured. The measurement of the amount of liquid deposited on the branches of the tree only was estimated. The LAI formula also refers to the leaves on the branches. The word "trunk," in inverted commas, describes samplers placed on tripod rods close to the trunk but not on the trunk. The test was to see how the liquid settles on the tree's branches at locations in the central part of the tree. Additionally, we improved the diagrams in the Figures and pointed out "trunk" and "branch" samplers in quotation marks.
Page 8 results. Fig 4a and 4b : A statistical analysis showing significant differences would probably help
These data are not really commented…
Reply from the authors
Thank you for the comments, but we kindly ask the reviewer to read the chapter "3.1 Effect of propellers rotations on liquid deposition" more carefully. There you will find a comprehensive statistical analysis of the results presented in Figures 4a and 4b. In addition, the figures show, in the form of whiskers on the bars of the results, the values of standard deviations, which allow us to evaluate the differences in the values of the results or the lack of differences in the values of the results, if it is interested in the reader.
Line 324 : is this Table 2 necessary ? since there are no comments…
Reply from the authors
Thank you for your question, and we explain. Table 2 can be found in Chapter "3. Results" It shows the statistically elaborated values derived from dividing the results of liquid deposition tests on tree levels at lower drone speed by the results of liquid deposition tests on the same tree levels at higher drone speed. In contrast, a commentary on the results in Table 2 can be found in Chapter "4. Discussion" in text lines 506-516.
Fig 5 I am not sure this Fig is essential
Reply from the authors
Thank you for your comment. The authors believe that Figure 5 conveys information about the values of uniformity of liquid deposition at the levels of the tree crown. Since the influence of the studied parameters on the uniformity of performing tree spraying with a drone was one of the crucial points of the conducted research, the results should have been presented.
Page 10 Fig 6a-Fig6b: these results on the air speed inside the vegetation are interesting but are not related to previous deposition data…
Reply from the authors
Authors, thank you for reviver attention.
The authors believe that the results presented in Figures 6a and 6b have been linked to the results of the liquid deposition studies. It is presented in Chapter "4. Discussion" lines: 461 - 467, 476-482 and 518 - 534.
Were they achieved in a static position of the UAV ? …
The drone was stationary over the stands where the airflow was measured. A detailed description of the positioning of the stationary drone to the tree and tripod and how the airflow was measured can be found in the lines: 298-310.
These results on the air speed could been presented before the deposition in order to characterize the airstream conditions inside the trees ?
Thank you to the reviewer for a good point.
The authors recognized that the main topic of the manuscript and the main objective of the research was 'Propellers spin rate effect of a spraying drone on quality of liquid deposition in a crown of young spruce.' The evaluation of changes in airflow velocity through the crown of a spruce tree and the assessment of its LAI were used to attempt to analyse factors that could indirectly influence the liquid deposition results obtained, in addition to the drone operating parameters studied directly. However, the rotating propellers generated the airflow, but the direct measurement concerned the rotation speed of the propellers and not the airflow. The drone was stationary during the airstream measurements. It was moved at two different speeds during the liquid deposition tests. These were, therefore, different situations for taking measurements. Furthermore, the airflow measurements were only taken at the points where the liquid collection samplers were placed, only in one vertical plane of the tripod, so these results cannot be considered as overall results characterising the airflow produced by the drone's rotors. Therefore, the airflow velocity results can only be considered information, like the LAI results, characterising the test stand and the tree.
Author Response File: Author Response.pdf
Reviewer 3 Report
It is difficult to identify the contributions of this research. This would be a relavent report for a science expo project, or maybe an undergrad experiment to identify statistical analysis. It could even be an initial study to justify if there is value to pursue the research. This paper would be more appropriate for a conference paper than a journal paper.
The English grammar is acceptable, but there are a few minor edits that could be made.
Author Response
It is difficult to identify the contributions of this research. This would be a relavent report for a science expo project, or maybe an undergrad experiment to identify statistical analysis. It could even be an initial study to justify if there is value to pursue the research. This paper would be more appropriate for a conference paper than a journal paper.
Comments on the Quality of English Language
The English grammar is acceptable, but there are a few minor edits that could be made.
Reply of the authors of the manuscript to the reviewer's comments
The authors thank the reviewer for his legitimate comments.
The authors have made many corrections to the manuscript's text, clarifying both the scientific problem and the sense in which the described study was undertaken and the scientific interpretation of the results obtained.
The authors hope that the current version of the manuscript meets the requirements of research innovation in the topic undertaken and classifies the manuscript for publication in an excellent scientific journal such as Agriculture - MDPI Basel.
Author Response File: Author Response.pdf
Reviewer 4 Report
The research aims at the practical problems of forestry production and has certain application value. However, there are still some problems in the article. There are many researches on UAV plant protection, so the author should compare the latest research results, especially the introduction and discussion part, so as to propose the necessity of research and summarize the innovation and novelty of the article.
（1）Table 2，Figure4， 5 should be revised.
（2）Ref. 1, Wrong URL, missing "h".
Author Response
The research aims at the practical problems of forestry production and has certain application value. However, there are still some problems in the article. There are many researches on UAV plant protection, so the author should compare the latest research results, especially the introduction and discussion part, so as to propose the necessity of research and summarize the innovation and novelty of the article.
Reply from the authors
The authors thank the reviewer very much for their opinion and comments.
The authors again reviewed the world's scientific literature on the research topic presented in the manuscript and supplemented the list of references with new items. With these new scientific articles, it was possible to improve the text of the "Introduction" chapter and to make the scientific problems we investigated more specific and prominent. The authors believe that the text of the "Introduction" chapter, enriched by the new comments, better justified the purpose of the study and the intentions that guided the authors when they undertook the research. Mainly, it concerns the purpose: environmental protection and using drone in precision agriculture.
Thanks to supplementing the review in new literature positions, it was possible to improve the "Discussion" chapter and supplement it with references to scientific articles addressing a similar scientific topic to ours, as suggested by the reviewer.
We thank you, the reviver, again for your valuable opinion.
(1）Table 2，Figure4， 5 should be revised.
Reply from the authors
The authors thank you for the reviver, and they have reviewed Figures 4 and 5 and Table 2, indicated by the reviewer for amendment. Where they found defects made require significant corrections or changes.
(2）Ref. 1, Wrong URL, missing "h".
Reply from the authors
The error pointed out by the reviewer has been corrected.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The paper was qualitatively revised taking into consideration the remarks.
