A Quantitative Graph-Based Approach to Monitoring Ice-Wedge Trough Dynamics in Polygonal Permafrost Landscapes

Round 1

Reviewer 1 Report

The ice-wedges, serving as typical permafrost geomorphology across the permafrost regions in the Arctic and Sub-Arctic, have been receiving increasing attention from the relevant stakeholders as they are good indicators of climate change on the fragile Arctic regions. Some of the past research correlated the dynamics of ice wedges to the evolution of permafrost hydrology in the aspects of their spatial distribution, height, and morphology on the basis of the field investigations and related in-situ observations of soil moisture content and temperatures, as well as the utilization optical remote sensing images. However, as far as I know, none of these studies were concerned about the permafrost hydrology and hydrological connectivity with the graph analysis theory after the processing of remote sensing images at present. Therefore, this study is generally innovative and may facilitate the application of theories of geographical information science (GIS) and remote sensing (RS) in permafrost, and accelerate the development of permafrost research. The authors provide a workflow for obtaining the morphology of ice wedges, including DTM detrending, binarization and denoising, Skeletonization, Transformation to graph, and Trough parameter extraction. This workflow may facilitate the automatic extraction of ice wedges in the Arctic and Sub-Arctic regions with computers and the Theory of computer graphics. I would like to recommend the acceptance of this paper with minor revision. In the following, there are some minor concerns about this paper:

1, The extraction of nodes and edges of the ice-wedge troughs should be verified with in-situ field investigations.

2, “python” should be changed into “Python” throughout this paper;

3, Line 134, add “to” after “Prior”;

4, Line 299-300, Line 305, “however” should not be put in the middle of this sentence.

Author Response

Dear reviewer,

thanks again for your time in this review process. Please see the attachment for our point-by-point response to your concerns.

We acknowledge that there are still some formatting issues in the compiled PDF. However, our editor Ms. Tina Jiang has ensured that these will be taken care of by MDPI's formatting offices.

With best regards,

Tabea Rettelbach on behalf of all authors

Author Response File: Author Response.pdf

Reviewer 2 Report

Overview and general recommendation:

This manuscript proposed a semi-automatic approach to mapping ice-wedges polygonal trough, a sensitive permafrost landscape in Arctic, based on graph-theoretic and high-resolution digital surface model derived from airborne LiDAR. This method efficiently extract the trough locations, depth, and width. These information is important for simulation of the thermokarst degradation processes at local scale. The method proposed undoubtedly is excellent, and minor revision just is needed before accepted to publish in Remote Sensing.

I just have one concern. What is the situation compared to the results derived from high resolution optical images? Which is a less cost of available data. The advantages and disadvantages of both should be discussed at least.

Author Response

Dear reviewer,

thanks again for your time in this review process. Please see the attachment for our point-by-point response to your concerns.

We acknowledge that there are still some formatting issues in the compiled PDF. However, our editor Ms. Tina Jiang has ensured that these will be taken care of by MDPI's formatting offices.

With best regards,

Tabea Rettelbach on behalf of all authors

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear editors, dear authors,

Thank you for the manuscript, which was a very interesting read and presents your research very well.

I do have a few, mostly minor, remarks:

The two ALS data-sets were acquired at different times of the year (beginning July vs. end of July). you then state in your conclusions that the number of throughs and their width has increased. I do not doubt this, but might the later acquisition date of the second dataset also influence the results since there has most likely been more thawing end of July vs. beginning of July?

I think some of the figures should be amended a little in order to make them more understandable/readable. In Fig.6, the scales are rather rough, especially considering that the the values are often located in a small range.

Fig. 8 is rather small and comes before fig.7 for some reason. 

Best regards

Author Response

Dear reviewer,

thanks again for your time in this review process. Please see the attachment for our point-by-point response to your concerns.

We acknowledge that there are still some formatting issues in the compiled PDF. However, our editor Ms. Tina Jiang has ensured that these will be taken care of by MDPI's formatting offices.

With best regards,

Tabea Rettelbach on behalf of all authors

Author Response File: Author Response.pdf

Reviewer 4 Report

Dear authors,

you have written excellent article. English language is OK and to my opinion doesn’t need any major improvements. You cited the literature correctly, and all the literature is cited in the text. Some improvements are needed regarding the design of the article, but nothing major. Something happened with the used template although irrelevant, line numbers are on the left not on the right as they are supposed to be.

The good points of the article are:

1. very interesting topic
2. explanation of used methods
3. presentation of the results

According to my opinion, the weak points of your article are:

1. design of the article
2. problems with the template

The improvement should be done in the following:

Ad 1.) Figure order 6-8-7-9?! The numeration of those figures is wrong, something happened. It should be changed under the figures and in the text as well.

The section 2.2. – Study area should be placed after the section 2. Materials and Methods and become section 2.1. Figure 2 should become figure 1 and be placed in new section 2.1 Study area. Figure 1 should become figure 2 and should be placed in new section 2 – Materials.

Ad 2.) Something happened with the template – line numbers are on the left, not on the right. Please used provided template under instructions for authors and check what happened.

 Suggestion by “lines”:

- line 122-126 – you explained the point density, spatial resolution, and vertical accuracy for first flight in 2009. Please provide this data also for the second flight from 2019, after line 127, since that flight was on a lower height 500 m vs. 1000 m. Also is this relevant for DTMs used for the analysis and final results.

- line 178 – please explain the term detrended DTM

- line 420 – please mark a, b, c on the figure 6

- line 454 – the figure 7 is not cited in the text

- line 482 - For the sake of… Please use another phrase or simply delete sake of.

Best regards.

Author Response

Dear reviewer,

thanks again for your time in this review process. Please see the attachment for our point-by-point response to your concerns.

We acknowledge that there are still some formatting issues in the compiled PDF. However, our editor Ms. Tina Jiang has ensured that these will be taken care of by MDPI's formatting offices.

With best regards,

Tabea Rettelbach on behalf of all authors

Author Response File: Author Response.pdf