Nominal Evaluation of Automatic Multi-Sections Control Potential in Comparison to a Simpler One- or Two-Sections Alternative with Predictive Spray Switching

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript presents a careful nominal evaluation of Automatic Section Control (ASC) compared to simpler 1 or 2 section alternatives with predictive spray switching. The work is technically solid, and the economic analysis is a valuable contribution. However, several aspects require clarification, restructuring, and additional discussion before the manuscript is ready for publication.

The sentence “Materials and methods, results, discussion and the conclusion are described in Sec. 2-5” could be improved by describing the content of each section.

Figure 7 is referenced before Figure 6 in the text. Please correct the order of references or figures to maintain logical flow.

Figures 13 to 18 need clearer captions and higher resolution.

While prior works are cited, the discussion could better compare this study to existing ASC evaluations. 

The statement that “most of the wasted volume is water, so the economic impact is much smaller” is misleading. Once mixed, the spray solution is homogeneous, and a percentage increase (or saving) in spray volume directly translates into the same percentage change in chemical product applied. For example, a 40% saving in spray volume is also a 40% saving in chemical use. The reduced economic impact arises because chemicals form a small percentage of the solution by volume, not because “mostly water” is wasted. Please rephrase the discussion accordingly to avoid confusion.

Maintenance and software upgrade costs for ASC are mentioned but not quantified.

The current analysis only considers uniform section widths. In practice, fine control is most beneficial at the ends, while central nozzles operate closer to the reference velocity. A cost-effective compromise would be to use smaller sections at the ends and larger sections in the middle.

Author Response

Comments and Suggestions for Authors

Reviewer 1:

The manuscript presents a careful nominal evaluation of Automatic Section Control (ASC) compared to simpler 1 or 2 section alternatives with predictive spray switching. The work is technically solid, and the economic analysis is a valuable contribution. However, several aspects require clarification, restructuring, and additional discussion before the manuscript is ready for publication.

The sentence “Materials and methods, results, discussion and the conclusion are described in Sec. 2-5” could be improved by describing the content of each section.
-->
. The sentence was rephrased (see p.3 the last paragraph of the Introduction): 
'The remaining paper is organised as follows: materials and methods, results, ...'

. This reformulated sentence is a common phrasing and is used in many publications as the last paragraph of the Introduction.

Figure 7 is referenced before Figure 6 in the text. Please correct the order of references or figures to maintain logical flow.
-->
. Thank you for this point. There was a bracket '(see Fig. 7)' in the 3rd line on p.7. This is now removed. Fig. 6 is now referenced before Fig. 7 in the text.

Figures 13 to 18 need clearer captions and higher resolution.
-->
. The captions of Fig. 13-18 have been adapted.

. Fig. 16 has been enlarged.

. Fig. 17 and 18 have previously been presented on one page. The figures have now been greatly enlarged and are presented on two separate pages.

While prior works are cited, the discussion could better compare this study to existing ASC evaluations. 
-->
. The paper presents an ASC-solution for comparison. This ASC-solution is quite efficient with its polygon-based approach to determine if an area has already been sprayed or not (see Fig. 14(d)).

. Other ASC-methods may also be efficient. However, they will always also approach the theoretical spray volume reference results, S_field^ref in Table 3. 

. All comparisons are reported with respect to this theoretical spray volume reference. Therefore, using a different ASC-solution would not change the interpretation results of the paper since results are reported with respect to the theoretcial spray volume references S_field^ref.

The statement that “most of the wasted volume is water, so the economic impact is much smaller” is misleading. Once mixed, the spray solution is homogeneous, and a percentage increase (or saving) in spray volume directly translates into the same percentage change in chemical product applied. For example, a 40% saving in spray volume is also a 40% saving in chemical use. The reduced economic impact arises because chemicals form a small percentage of the solution by volume, not because “mostly water” is wasted. Please rephrase the discussion accordingly to avoid confusion.
-->
. The phrase “most of the wasted volume is water, so the economic impact is much smaller” is not used in the paper. Also ctrl+f for 'waste' or 'wasted' did not yield any results.

. Yes, 40% saving in spray volume is also a 40% saving in chemical use. This is because cost scales linearly with spray volume. However, the cost contribution of water and chemical to the total cost is very different. The key equation is Eq. (7). This relates normalized chemicals and water cost, their weighting in the spray volume, and the spray volume differentce between, e.g., a 1-sections method and an ASC-method.

Maintenance and software upgrade costs for ASC are mentioned but not quantified.
-->
. These are not mentioned since they are difficult to quantify. However, it is explicitly stressed that all results and in particular also the economic cost discussion is *optimistic* with respect to ASC (see the 3rd last paragraph of Section 4.2). This is the main message of the paper and was the greatest surprise of the results. ASC is a very good idea theoretically, but economically it is actually often not worth it (especially for small farms). 

The current analysis only considers uniform section widths. In practice, fine control is most beneficial at the ends, while central nozzles operate closer to the reference velocity. A cost-effective compromise would be to use smaller sections at the ends and larger sections in the middle.
-->
. This might be a very good idea. However, the benefits are not entirely clear. Essentially all of the problems of Table 1 associated with ASC would also apply for this idea. 

. This idea would be something in between the 1-secions solution and the ASC-solution.

. To have a conclusive argumentation (a comparison of 1-section, 2-sections and ASC) it is preferred to not mention this in the Conclusion as a potential outlook.

------------------------
Reviewer 2:

Dear Author, Congratulations on this important research. I've made some considerations to make it even better. Sincerely,

-->
. Thank you very much for this encouraging comment and the detailed review !

1. 'It is crucial to note that this evaluation under 'nominal conditions' establishes a theoretical upper bound for ASC's performance. In the real world, performance will inevitably be affected and degraded by the multiple uncertainty factors detailed in Table 1, which may reduce the potential savings.'

-->
. The phrase has been incorporated into the paper.

2. 'The Alternative (M2) method for path planning, detailed in [27], differs from Boustrophedon by optimizing the sequence of lanes and turns to minimize total path length, often employing less conventional but more efficient field patterns for non-convex and obstructed areas. It aims to reduce maneuvers and travel time, even if this may imply a more complex nozzle switching logic to avoid overlaps.'

-->
. The phrase has been incorporated into the paper.

. The part 'It aims to reduce maneuvers and travel time, even if this may imply a more complex nozzle switching logic to avoid overlaps' is not included since Sec. 2.3 focuses on the path planning level (not yet on the nozzle switching level).

3. 'Enhance the color legend to clearly distinguish non-sprayed areas (white/very light gray), single-pass sprayed areas (light green), and double-pass/overlap areas (dark green). Add a numerical scale bar to each figure to facilitate the interpretation of dimensions and distances.'

-->
. I agree that the representation of the previous two Figures Fig. 17 and Fig. 18 was not ideal.

. Fig. 17 and 18 have now been greatly enlarged and are now shown on two separate pages. 

. Having all 6 subplots for 1 field on one page is important to visually spot the differences between (i) the 1-, 2-sections and ASC-solution, and (ii) the 2 different path plans M1 and M2. It is also the preferred solution for compactness.

. Fig. 17 and 18 let a reader understand the differences between the 1-, 2-sections and ASC-solution. In addition, the reader was already prepared via Fig. 15, where a zoom-in emphasised the differences between the 3 methods.

. The meaning of gray areas in figures are explained in the caption of Fig. 10 and in the paragraph above Eq. (4) ('smaller and larger s_volume^{actual,i} are differentiated by brighter and darker gray colors').

. Adding a color legend in view of the size of the figures and nuances in gray-colors is preferably avoided. Overlaps (darker areas) are clearly visible. Variations of spray volumes along the boom bar during turn maneuvers for the 1- and 2-secions solution are also clearly visible (brighter gray areas during the turn maneuvers).

4. 'By 'intermediate overlap', we refer to a level of overlap that, while greater than ASC's ideal, is considered an acceptable and economically viable trade-off compared to the implementation costs and complexity of ASC, especially for small farms. A more precise quantification or an expected range for this 'intermediate overlap' (e.g., X% - Y%) would be beneficial here or in the results section.'

-->
. Thank you for this comment. The term 'intermediate overlap' is indeed ambiguous. There were previously 3 occurrences of that term (Abstract, Sec. 4.1, Conclusion). The respective sentences are now all reformulated without that term.

5. 'Beyond spraying applications, the efficiency demonstrated by the M2 method in path planning suggests significant potential for applicability in other agricultural operations that rely on optimized area coverage, such as seeding, tillage, or harvesting. This adaptability reinforces the broader value of the presented methodology.'

-->
. Thank you very much for this good recommendation !

. The phrase is now incorporated into the paper (see the last paragraph of Sec. 4.1).

5. 'For greater clarity, 'sensor-free' refers to the absence of complex and expensive sensors like RTK-GPS. While it relies on visual cues (which a human operator uses as a 'sensor'), the implementation is 'low-cost' and 'free from advanced sensors'. However, it is important to acknowledge that reliance on visual cues can be susceptible to environmental conditions (fog, darkness) and variability in human perception, which could introduce a margin of error in application accuracy not captured under 'nominal conditions'.'

-->
. Thank you very much for this remarkably good recommendation !

. The phrase is now incorporated into the paper (see the last paragraph of Sec. 4.1).

6. 'I recommend that the authors include a sentence in the abstract and reiterate in the introduction that "nominal conditions" are used to establish a theoretical upper bound for ASC's performance, and that real-world performance will inevitably be degraded by the uncertainty factors listed in Table 1. This manages reader expectations from the outset regarding the immediate practical applicability of the presented savings values.'

-->
. There is a sentence in the Abstract ('The comparison is provided under nominal conditions').

. As recommend, the nominal conditions aspect is now further emphasized in the Introductioon ('It is
crucial to note that this evaluation under ’nominal conditions’ establishes a theoretical upper bound for ASC’s performance. In the real world, performance will inevitably be affected ...')

7. 'Additionally, although the alternative method is suitable for manual operation, the effectiveness in compensating for switching delays through 'human driving experience' (mentioned on line 430) can vary significantly among operators. The learning curve to achieve optimal precision may require training and practice, and variability in individual operator skill could introduce inconsistencies in application that need to be considered in a real-world scenario analysis.'

-->
. The phrase is now incorporated into the paper (see Sec. 4.3).

8. 'To advance the practical applicability of this promising alternative method, future research should focus on field validation under a variety of real-world conditions, quantifying the impact of factors such as wind and terrain variability. Furthermore, the development of low-cost support tools, such as mobile applications or simple visual displays that guide manual section switching based on the predictive logic, could mitigate reliance on exclusive operator experience and standardize application quality, thereby maximizing the economic benefits identified in this study.'

-->
. Thank you for this suggestion!

. The phrase is now added as the last paragraph of the Conclusion.

9. 'It would be valuable if the authors could define "intermediate overlap" more precisely (e.g., in terms of percentage or comparison to benchmarks) and justify its acceptability or advantage as a conscious trade-off against the economic and operational benefits of the alternative method.'

-->
. Thank you for this comment. The term 'intermediate overlap' is indeed ambiguous. There were previously 3 occurrences of that term (Abstract, Sec. 4.1, Conclusion). The respective sentences are now all reformulated without that term.

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Author, Congratulations on this important research. I've made some considerations to make it even better. Sincerely,

Comments for author File: Comments.pdf

Author Response

Comments and Suggestions for Authors

Reviewer 1:

The manuscript presents a careful nominal evaluation of Automatic Section Control (ASC) compared to simpler 1 or 2 section alternatives with predictive spray switching. The work is technically solid, and the economic analysis is a valuable contribution. However, several aspects require clarification, restructuring, and additional discussion before the manuscript is ready for publication.

The sentence “Materials and methods, results, discussion and the conclusion are described in Sec. 2-5” could be improved by describing the content of each section.
-->
. The sentence was rephrased (see p.3 the last paragraph of the Introduction): 
'The remaining paper is organised as follows: materials and methods, results, ...'

. This reformulated sentence is a common phrasing and is used in many publications as the last paragraph of the Introduction.

Figure 7 is referenced before Figure 6 in the text. Please correct the order of references or figures to maintain logical flow.
-->
. Thank you for this point. There was a bracket '(see Fig. 7)' in the 3rd line on p.7. This is now removed. Fig. 6 is now referenced before Fig. 7 in the text.

Figures 13 to 18 need clearer captions and higher resolution.
-->
. The captions of Fig. 13-18 have been adapted.

. Fig. 16 has been enlarged.

. Fig. 17 and 18 have previously been presented on one page. The figures have now been greatly enlarged and are presented on two separate pages.

While prior works are cited, the discussion could better compare this study to existing ASC evaluations. 
-->
. The paper presents an ASC-solution for comparison. This ASC-solution is quite efficient with its polygon-based approach to determine if an area has already been sprayed or not (see Fig. 14(d)).

. Other ASC-methods may also be efficient. However, they will always also approach the theoretical spray volume reference results, S_field^ref in Table 3. 

. All comparisons are reported with respect to this theoretical spray volume reference. Therefore, using a different ASC-solution would not change the interpretation results of the paper since results are reported with respect to the theoretcial spray volume references S_field^ref.

The statement that “most of the wasted volume is water, so the economic impact is much smaller” is misleading. Once mixed, the spray solution is homogeneous, and a percentage increase (or saving) in spray volume directly translates into the same percentage change in chemical product applied. For example, a 40% saving in spray volume is also a 40% saving in chemical use. The reduced economic impact arises because chemicals form a small percentage of the solution by volume, not because “mostly water” is wasted. Please rephrase the discussion accordingly to avoid confusion.
-->
. The phrase “most of the wasted volume is water, so the economic impact is much smaller” is not used in the paper. Also ctrl+f for 'waste' or 'wasted' did not yield any results.

. Yes, 40% saving in spray volume is also a 40% saving in chemical use. This is because cost scales linearly with spray volume. However, the cost contribution of water and chemical to the total cost is very different. The key equation is Eq. (7). This relates normalized chemicals and water cost, their weighting in the spray volume, and the spray volume differentce between, e.g., a 1-sections method and an ASC-method.

Maintenance and software upgrade costs for ASC are mentioned but not quantified.
-->
. These are not mentioned since they are difficult to quantify. However, it is explicitly stressed that all results and in particular also the economic cost discussion is *optimistic* with respect to ASC (see the 3rd last paragraph of Section 4.2). This is the main message of the paper and was the greatest surprise of the results. ASC is a very good idea theoretically, but economically it is actually often not worth it (especially for small farms). 

The current analysis only considers uniform section widths. In practice, fine control is most beneficial at the ends, while central nozzles operate closer to the reference velocity. A cost-effective compromise would be to use smaller sections at the ends and larger sections in the middle.
-->
. This might be a very good idea. However, the benefits are not entirely clear. Essentially all of the problems of Table 1 associated with ASC would also apply for this idea. 

. This idea would be something in between the 1-secions solution and the ASC-solution.

. To have a conclusive argumentation (a comparison of 1-section, 2-sections and ASC) it is preferred to not mention this in the Conclusion as a potential outlook.

------------------------
Reviewer 2:

Dear Author, Congratulations on this important research. I've made some considerations to make it even better. Sincerely,

-->
. Thank you very much for this encouraging comment and the detailed review !

1. 'It is crucial to note that this evaluation under 'nominal conditions' establishes a theoretical upper bound for ASC's performance. In the real world, performance will inevitably be affected and degraded by the multiple uncertainty factors detailed in Table 1, which may reduce the potential savings.'

-->
. The phrase has been incorporated into the paper.

2. 'The Alternative (M2) method for path planning, detailed in [27], differs from Boustrophedon by optimizing the sequence of lanes and turns to minimize total path length, often employing less conventional but more efficient field patterns for non-convex and obstructed areas. It aims to reduce maneuvers and travel time, even if this may imply a more complex nozzle switching logic to avoid overlaps.'

-->
. The phrase has been incorporated into the paper.

. The part 'It aims to reduce maneuvers and travel time, even if this may imply a more complex nozzle switching logic to avoid overlaps' is not included since Sec. 2.3 focuses on the path planning level (not yet on the nozzle switching level).

3. 'Enhance the color legend to clearly distinguish non-sprayed areas (white/very light gray), single-pass sprayed areas (light green), and double-pass/overlap areas (dark green). Add a numerical scale bar to each figure to facilitate the interpretation of dimensions and distances.'

-->
. I agree that the representation of the previous two Figures Fig. 17 and Fig. 18 was not ideal.

. Fig. 17 and 18 have now been greatly enlarged and are now shown on two separate pages. 

. Having all 6 subplots for 1 field on one page is important to visually spot the differences between (i) the 1-, 2-sections and ASC-solution, and (ii) the 2 different path plans M1 and M2. It is also the preferred solution for compactness.

. Fig. 17 and 18 let a reader understand the differences between the 1-, 2-sections and ASC-solution. In addition, the reader was already prepared via Fig. 15, where a zoom-in emphasised the differences between the 3 methods.

. The meaning of gray areas in figures are explained in the caption of Fig. 10 and in the paragraph above Eq. (4) ('smaller and larger s_volume^{actual,i} are differentiated by brighter and darker gray colors').

. Adding a color legend in view of the size of the figures and nuances in gray-colors is preferably avoided. Overlaps (darker areas) are clearly visible. Variations of spray volumes along the boom bar during turn maneuvers for the 1- and 2-secions solution are also clearly visible (brighter gray areas during the turn maneuvers).

4. 'By 'intermediate overlap', we refer to a level of overlap that, while greater than ASC's ideal, is considered an acceptable and economically viable trade-off compared to the implementation costs and complexity of ASC, especially for small farms. A more precise quantification or an expected range for this 'intermediate overlap' (e.g., X% - Y%) would be beneficial here or in the results section.'

-->
. Thank you for this comment. The term 'intermediate overlap' is indeed ambiguous. There were previously 3 occurrences of that term (Abstract, Sec. 4.1, Conclusion). The respective sentences are now all reformulated without that term.

5. 'Beyond spraying applications, the efficiency demonstrated by the M2 method in path planning suggests significant potential for applicability in other agricultural operations that rely on optimized area coverage, such as seeding, tillage, or harvesting. This adaptability reinforces the broader value of the presented methodology.'

-->
. Thank you very much for this good recommendation !

. The phrase is now incorporated into the paper (see the last paragraph of Sec. 4.1).

5. 'For greater clarity, 'sensor-free' refers to the absence of complex and expensive sensors like RTK-GPS. While it relies on visual cues (which a human operator uses as a 'sensor'), the implementation is 'low-cost' and 'free from advanced sensors'. However, it is important to acknowledge that reliance on visual cues can be susceptible to environmental conditions (fog, darkness) and variability in human perception, which could introduce a margin of error in application accuracy not captured under 'nominal conditions'.'

-->
. Thank you very much for this remarkably good recommendation !

. The phrase is now incorporated into the paper (see the last paragraph of Sec. 4.1).

6. 'I recommend that the authors include a sentence in the abstract and reiterate in the introduction that "nominal conditions" are used to establish a theoretical upper bound for ASC's performance, and that real-world performance will inevitably be degraded by the uncertainty factors listed in Table 1. This manages reader expectations from the outset regarding the immediate practical applicability of the presented savings values.'

-->
. There is a sentence in the Abstract ('The comparison is provided under nominal conditions').

. As recommend, the nominal conditions aspect is now further emphasized in the Introductioon ('It is
crucial to note that this evaluation under ’nominal conditions’ establishes a theoretical upper bound for ASC’s performance. In the real world, performance will inevitably be affected ...')

7. 'Additionally, although the alternative method is suitable for manual operation, the effectiveness in compensating for switching delays through 'human driving experience' (mentioned on line 430) can vary significantly among operators. The learning curve to achieve optimal precision may require training and practice, and variability in individual operator skill could introduce inconsistencies in application that need to be considered in a real-world scenario analysis.'

-->
. The phrase is now incorporated into the paper (see Sec. 4.3).

8. 'To advance the practical applicability of this promising alternative method, future research should focus on field validation under a variety of real-world conditions, quantifying the impact of factors such as wind and terrain variability. Furthermore, the development of low-cost support tools, such as mobile applications or simple visual displays that guide manual section switching based on the predictive logic, could mitigate reliance on exclusive operator experience and standardize application quality, thereby maximizing the economic benefits identified in this study.'

-->
. Thank you for this suggestion!

. The phrase is now added as the last paragraph of the Conclusion.

9. 'It would be valuable if the authors could define "intermediate overlap" more precisely (e.g., in terms of percentage or comparison to benchmarks) and justify its acceptability or advantage as a conscious trade-off against the economic and operational benefits of the alternative method.'

-->
. Thank you for this comment. The term 'intermediate overlap' is indeed ambiguous. There were previously 3 occurrences of that term (Abstract, Sec. 4.1, Conclusion). The respective sentences are now all reformulated without that term.

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Dear author,

Congratulations on the excellent work.

Sincerely,

Author Response

Editor:

"Problem 1" in the beginning of "Materials and Methods" should be changed into "Research questions" because you do not have "problem 2 or 3". Please move these "Research Questions" to right before line 82: "Thus, in total 6 different experimental setups are compared.". Then add your research objectives.  

-->
. Done as recommended. It is pointed out that to do this the file 'mdpi.cls' had to be changed.
  . (ctrl+f 'Research Questions' in mdpi.cls).

. Adapted: "To address aforementioned Research Questions the two area coverage path planning strategies.."

. Adapted: "This was done intentionally (as outlined in aforementioned Research Questions) to derive a best-case \emph{upper performance bound} for ASC. .."

"Last sentence of the INTRODUCTION" should be: "The remaining paper is organised as follows: materials and..."."

-->
. Done

"When reporting results, use past tense. Please read you manuscript through and change them."

-->
. All verbs in the Results-section (i.e. Sec. 3) were set into the past tense.

. 'Input data compromised' in caption of Fig. 16.
  'were compared with 3 different ' 
  'Thus, overall 6 different setups were compared.'
  'Parameters were used uniformly..'
  'Vehicle dynamics were..'
  'was assumed, which corresponds '
  'was assumed. For'
  'this resulted in a maximum'
  'The working width was..'
  'The working width was..'
  
  
. 'was between -3.9% and ..'  
  '24m wide boom bar approached the' 
  'was 2.1%
  'the percentage difference was higher'
  'were 21\% and..'
  'seemed' 
  
 
--------------- 
Comments and Suggestions for Authors

Dear author,

Congratulations on the excellent work.

Sincerely,

-->
. Thank you very much for the positive review !