Evaluation of Water Level in Flowing Channels Using Ultrasonic Sensors

Round 1

Reviewer 1 Report

The manuscript “Evaluation of Water Level in Flowing Channels Using Ultrasonic Sensors” by Rodrigues Pereira et al. is an overall well-written and well-presented manuscript that tests the feasibility of using low-cost ultrasonic sensors and a microcontroller to monitor water level changes. 

While not entirely innovative, the topic is vital and contributes to potential solutions to ongoing practical relevant issues in hydrological monitoring.

To achieve this, the authors installed ultrasonic sensors in an experimental channel under lab conditions and tested their accuracy in detecting water level changes within short events.  

However, the manuscript should be, from my point of view, considered as a technical note rather than a research article, due to the absence of in-depth scientific analysis or insights. Since sustainability does not support this type of manuscript, I leave it up to the Editor to decide and I will present my review and comments independently from this factor.

Please find below some comments, divided into general and specific remarks, which the authors might consider when revising their manuscript:

• Introduction: The authors might consider restructuring the introduction to indicate the purpose and the research question(s) of their study more clearly. In the beginning, the introduction is focused on discharge measurements and their associated difficulties. However, the solution the authors present is not related to discharge, but only to water level measurements. Particularly the link to the PIV mentioned by the authors remains unclear. Furthermore, I would suggest moving parts of the introduction (e.g., L66-83; 90-97) to the discussion. 
• Methods: While the authors put effort into selecting well-working sensors, including a bench test, I have major methodological objections regarding one point of the entire study. According to L241 the measurements are not temperature compensated. Even though the results are typically not highly prone to temperature changes, I would appreciate it if the authors would elaborate more in detail on why they do not compensate for this effect. The authors might include references stating the effect of temperature on the results and calculate and present the potential influence in their case of application.
• Results: The authors mention the use of an ADV to evaluate the accuracy of the measurements in different flow conditions. However, the results are not presented in the current version of the script. Besides, the added value of using an ADV is not obvious since velocity or discharge is not the concern of this study.  
• Discussion: The discussion is rather short. I am missing a link to the general contribution of this study to ongoing research questions. The discussion would also benefit from a broader discussion on how these results could be applied in the field. What is the benefit of using the sensors? What is still missing to investigate before applying the sensors? How stable will the sensors work in the long run? What should be addressed in future research? Do the authors plan to use their systems in future activities? 
• Data availability: I strongly encourage the authors to consider publishing all data generated along with this manuscript within a scientific repository like Zenodo.org or similar. This includes the raw results, but particularly the Arduino code developed. This would allow other groups of researchers or practitioners to further investigate or apply the framework the authors presented in this manuscript.  

Specific remarks: 

• L56,75, 90…: Check the citation style.
• L217: Please confirm the distance. Is 0,004m correct, or would 0,4m be right?
• L542: How does high brightness influence the results? Please expand and include proper references
• L413 – 430: The cost estimation is not very comparable or informative. Prices for which country are given here? Maybe consider using reference prices (e.g., from suppliers in the USA). With which systems are the prices compared? Which PIV (and again, why a PIV) is mentioned to be 0,10, or one hundred times more expensive? 

Overall, I am looking forward to seeing this study published after some concerns have been addressed. I encourage the authors to continue exploring the application of low-cost sensors to improve the hydrological data sets worldwide.

 

Author Response

"Please see the attachment."

Author Response File: Author Response.pdf

Reviewer 2 Report

L32: Check “in”, change to “is”

L42-43: Sentence is not clear. Please rephrase for the correct meaning.

L59-60: Authors are talking about the current study or previously used? If previous studies please give appropriate references.

L67: Remove the word “reference”

L75: Please double-check the reference format as specified by the journal. Modify all references throughout the manuscript to reflect this change.

L143: In Fig.3, hard to see where the sensors are located. Please provide a clear figure or location where the sensors are exactly.

L144: What is the useful length? What is total length and how much length is not useful and why?

L150: Please provide the total channel length

L159: Please provide a reference or weblink

L203: What criteria are used to determine which sensors are the best?

What are the advantages of using ultrasonic sensors to control the irrigation flow on a farmer's farm?

Author Response

"Please see the attachment."

Author Response File: Author Response.pdf

Reviewer 3 Report

The article is simple and clear. The problem is solved both by the claimed accuracy of the sensors and by their low cost. From a scientific point of view, it is interesting to look at the accuracy of the transition from laminar to turbulent flow with increasing turbulence. It is better to depict it graphically. I noticed one inaccuracy: in line 218, instead of 0.004 m, it is necessary to write 0.400 m.

Author Response

"Please see the attachment."

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Most of my major comments are addressed in the revised manuscript. 

However, I still don't agree with the connections the authors make to PIV systems, nor am I convinced by the cost estimates in the discussion.  PIV has a different target to measure than the ultrasonic water level (WL) systems developed by the authors. In the current version, the reader can still get the impression that the system developed by the authors should support discharge measurements. However, this is clearly not the case. Regarding the cost estimation, I am wondering where the prices are coming from (particularly 35k-USD for PIV) and, of course, comparing the prices from an Arduino for WL measurements to a full PIV-System that measures discharge doesn't make much sense to compare. 

Anyway, I would leave it up to the authors to include further changes here or to keep the manuscript in the current version. The main idea (measuring WL with low-cost ultrasonic sensors) is transported in the current version. 
Besides, I would like to honor that the authors have now published the source code in the Annex. 

*L44: "in" missing in front of "the study section". 

Author Response

"Please see the attachment."

Author Response File: Author Response.pdf