Comparative Analysis of Gully Morphology Extraction Suitability Using Unmanned Aerial Vehicle and Google Earth Imagery

Round 1

Reviewer 1 Report

This manuscript offered very useful information for the accuracy of gully morphology extraction based on field measurement and was written clearly. I believe this manuscript could be helpful for people who are working in the field of gully research and management. Nevertheless, several elements should be further improved before being accepted for Remote Sensing publication. 

(1)   Title: The title could be revised into “Comparative Analysis of Gully Morphology Extraction Accuracy using UAV and Google Earth Imagery”.

(2)   Abstract: The results in the abstract need to be revised to be more concise and highlight the key points. And the names for the two terrain regions are suggested to be mentioned.

(3)   Please provide the full expansion of acronyms upon their first occurrence, for example, in Line 15, UAV, and GE. Revise through the manuscript.

(4)   Introduction: The first two sentences need to be revised and make it more logical.

(5)   I understand the knowledge gap was stated in Line 89-95, while my suggestion is to make it more focused on the accuracy of UAV and GE images.

(6)   Suggest use international units throughout the text, for example, 1ft² in line 40.

(7)   Materials and Methods: Figure 1 needs to be revised. Suggested include the geographical coordinates using latitude and longitude when referring to the location within the borders of China.

(8)   Add a description of temperature and rainfall in both two watersheds.

(9)   Ensure tables and figures provide readers with sufficient information to understand them without ambiguity. Revise through the manuscript.

(10)           In section 2.4, I can not well understand the following sentence “The length of each tributary gully is calculated separately.” revise and make it clearer.

(11)           Results: It appears that Figure 4 has an outlier. Please confirm this and provide the results after removing the outlier.

(12)           Why are there 14 gully heads in the black soil gully in Table 2, I understand in methods, there are 7 gullies measured in this region.

(13)           Explain why the influence of gully morphology to accuracy based on UAV images was not analyzed.

(14)           Discussion: a clearer implication of this research is needed in this session

(15)           Conclusions: it should be more useful for readers, and a “take-home message” should be offered. Especially, the first conclusion in Line 456-460 should be more related to the topic and scientific questions.

(16)           Careful revision is needed to format the references one by one.

The language is clear and concise with good logic. 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Dear editor,

The manuscript "Gully morphology extraction accuracy: compared filed and remote sensing methods in two terrain regions" was submitted to remote sensing. It's a nice research about assessment of gully erosion using remote sensing, but I have some concerns and my decision is major revision. Finally I recommend to authors that improve the quality of this nice paper as following:

·     The results should be stated more accurately in the abstract. This will be of great help to the readers in the future and has an effective role in attracting the readers.

·     I can’t find any sentence in abstract about conclusion. Also you can complete it by applications of remote sensing in gully erosion.

·     In the introduction, it is recommended to state more evidence in the field of remote sensing.

·     The importance and necessity of research should be stated in more details in introduction.

·     Congratulations, the results are well stated.

·     One of the significant concerns is that the authors should carefully develop a discussion section to talk about the significance, shortages or advantages of the methods you proposed, the reliability and meaning of your results (compared to other related studies) etc.

·     Please speak about remote sensing in discussion.

·     The conclusion should be shorter and in one paragraph.

·      Please be sure that all the references cited in the manuscript are also included in the reference list and vice versa with matching spellings and dates.

·     Finally, I checked plagiarism detection of this research and the similarity is 17%, please checked attached file.

 

 

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

The manuscript “Gully morphology extraction accuracy: compared field and remote sensing methods in two terrain regions” gave helpful information on how the based images could influence gully extraction accuracy. And the images involved in this research are Google Earth submeter resolution images and UAV-sourced centimeter images. Both are now widely used in gully research and many other research fields. More remarkably, the authors compared this accuracy in different regions with varied gully geometries. This will give us a clearer, more comprehensive, and more rational understanding of the accuracy of extracting gullies based on different images. This topic is suitable for REMOTE SENSING. However, this manuscript needs major revisions, detailed comments as follows:

(1)   The differences of UAV and GE image in gully extraction includes different causes, such as the image resolution, the quality of images. Image resolution directly affect the extraction accuracy, which is validated by previous studies. For example, Dai 2019 (https://doi.org/10.1016/j.catena.2019.02.010) investigated the resolution effection on gully mapping from DEMs. On ther other hand, the effect of image quality, such as color fidelity, stability of the photography platform, image pre-processing, etc, is hard to be quatified. So, the topic of this paper is a complex issues and worth to be investigated. Indeed, this paper analyzed the synthesize effect of the two source of images. However, further deep analysis is expected. For example, could you resample the UAV image to a same resolution of GE image, and then compared their difference. This could except the effect of resolution, and reveal the effect of image quality. 

(2)   The title of this manuscript needs to be revised, as readers would be confused about what was compared. In my view, this research compared gully extraction accuracy based on two kinds of images.

(3)   The knowledge gap is not written clearly in the introduction. Revise to make it more clear. If possible, please offer your hypothesis.

(4)   Fig.1 is hard to read, especially for the locations. Grids are needed in this figure.

(5)   A more detailed description of gully geometry differences and two kinds of image quality is needed in the Materials and Methods.

(6)   Supplementing the morphology of all the gullies measured will offer precise information and help the readers understand and use the results of this work.

(7)   Most of the descriptions of the main findings in the results need to be more concise.

(8)   Previous related work, such as DEM resolution effect on gully mapping, should be cited and discussed. Moreover, the image based method only can get 2D parameter of gullies; while DEM-based method can get 3D parameters. The discussion of the two is needed. 

 

(9)   The manuscript needs careful English grammar checking and avoiding wrong spelling throughout.

need to be improved

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Dear editor, 

I'm agree with the revision for publishing in remote sensing. 

Regards

Author Response

Dear reviewer:

Thank you for your recognition of this study and for providing valuable feedback during the first round of the review process. Your suggestions have helped to enhance the structure and content of the article. We sincerely appreciate your efforts.

Best regards!

Author Response File: Author Response.docx

Reviewer 3 Report

This paper compared different images (GE and UAV) for gully morphology extraction. It is obviously improved from the last round. But many minor revisions are still required.

L15.  '-' should be ':'

L15-16.  GE (Google Earth) is unstable. The full name should be placed in the main text, and abbreviations should be enclosed in parentheses. Please check here and elsewhere.

L18. Unclear. What are the similar types of imagery?  

L122-123. 'in two regions characterized by significant terrain variations' should be 'in in two regions with different terrain characteristic'

L120-124. The author said "objective of the paper is to..." and then said " this study aims to....". it seems repeated although I know they are differnt. I suggest to summrise these into two point and revise the sentence into "objective of the paper is to: 1)....;2)...."

Fig.1. I think the China map should be deleted as it is not important for this study. Direct show of the study areas is OK. Do not place nation maps unless necessary.

The Response 1. As I know, the maximum flying height of DJI drones is generally 500m. But this could be different in different sources of drones. The  resolutions is determined by flying height and the camera pixels. The paper focuse on the centimeter-level UAV images. A detail describtion should be added in the Sec. introduction or Sec. methods. 

Minor editing of English language required

Author Response

Dear reviewer:

We have made the revisions to the manuscript as per your request. Please find our point-by-point responses in the attached document. Thank you for providing us with valuable feedback that has helped improve the manuscript's structure and content. In the uploaded revised manuscript, the Word document includes all the tracked changes from both rounds of revisions, while the PDF only contains the content modified in the second round. 

We sincerely appreciate your efforts.

Best regards!

Author Response File: Author Response.docx