The Effects of Depth and Altitude on Image-Based Shark Size Measurements Using UAV Surveillance

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1.      Overview：

This article found that UAV measurements of underwater targets without correcting for flight height and target depth significantly underestimate the size. After correction, the measurement accuracy can be improved to less than 5%.

The article is very meaningful, but there are still shortcomings, I suggest that major revision.

2. Modification problems：

（1）I think the structure of the article is incomplete, normal articles should have a conclusion section, and this article does not. In addition, the discussion section has too much content and is recommended to be reduced.

（2）In the methodology section, the authors lack further discussion on how to choose a specific UAV flight altitude and target depth. The rationale for these choices and their impact on the experimental results should be explained in more detail.

（3）In the data processing section, the authors mention the use of local regression fitting splines to assess the variation in measurement error, but do not provide enough details to explain why this method is chosen or the rationale for the method.

（4）Authors are advised to more systematically compare existing similar studies, especially those using different methods to measure dimensions of organisms, to highlight the advantages of the method.

 

（5）The indentation on line 145 is wrong, please correct it.

Author Response

We thank the reviewer for their time and effort in reviewing and improving this manuscript. We have attached a point-by-point response to your comments and required modifications.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The paper is very well planned and its purpose is important, both from a scientific point of view (a proposal for the correct measurement of shark size) and for improving safety. I also like the idea. Of course, I have this doubt whether something that does not have a flexible shape can be used to measure size of animals. As previous studies using drones to measure the length of marine mammals have shown, this always suggests a great deal of caution, because in the end the animals in the wild are smaller than they actually are, for example, when they are bent. Then the measurement should be the sum of the lengths of the smaller sections. This would need to be clarified in the paper. Here I suggest to look at the two papers:

An accurate and adaptable photogrammetric approach for estimating the mass and body condition of pinnipeds using an unmanned aerial system DJ Krause, JT Hinke, WL Perryman, ME Goebel, DJ LeRoi PloS one 12 (11), e0187465

Breeding colony dynamics of southern elephant seals at Patelnia Point, King George Island, Antarctica K Fudala, RJ Bialik Remote Sensing 12 (18), 2964

Otherwise, the introduction and discussion are comprehensive. I like the discussion more. The introduction could be expanded, if only by the points mentioned above. I also think it would be worth mentioning that there are some restrictions on the use of drones, e.g. the height over mammals in water should not be less than 15 m.

Also, the description of Figure 1 could be clearer. I suggest that the captions (A) and (B) be clearly inserted, so that it is immediately clear what the drawing is about.

I hope the paper will be published. My comments are of an aesthetic nature and do not detract from the perception of this interesting work.

Author Response

We thank you very much for your time in reviewing our manuscript. We believe the modifications have made it a stronger paper. Please see the attached response to your reviews and required modifications.

Author Response File: Author Response.docx