Review Reports - Study of a Steady-State Landscape Using Remote Sensing and Topographic Analysis

Round 1

Reviewer 1 Report

The objective of this paper is to apply InSAR to determine a steady state landscape by rates of river incision and hillslope erosion using remote sensing and topographic analysis. In particular, it is analyzed the way that the active mountain landscapes of sub-threshold hillslopes evolve towards a dynamic equilibrium state, as well as the hillslope erosion pattern of landslide evolution and the spatial variation of landslide frequency.

This is an interesting and well-structured paper. All necessary sections (Introduction, Materials and Methods, Results, Discussion, Conclusions) have been considered. Moreover, the “Materials and Methods” and “Results” sections are divided into sub-sections, providing additional details. Furthermore, all Figures, Tables and Diagrams are consistent with the analysis provided in the manuscript. Regarding the mathematical part, predominantly included in the “Materials and Methods” section, it is valid and satisfactorily explained. However, some changes should be implemented, which will improve the paper. In particular:

Lines 34-35: The references are not provided in the correct form. Please, apply throughout the manuscript the reference style, provided by the paper template.

Lines 62-66: This is a significant part of the “Introduction” section. However, it is not supported with the corresponding references. Typical and recent papers, which include the relative information and can be optionally cited, are the following: 1. Kalantar, B., Ueda, N., Saeidi, V., Ahmadi, K., Halin, A. A., & Shabani, F. (2020). Landslide Susceptibility Mapping: Machine and Ensemble Learning Based on Remote Sensing Big Data. Remote Sensing, 12(11), 1737. https://doi.org/10.3390/rs12111737, 2. Karagianni, A., Lazos, I., & Chatzipetros, A. (2019). Remote Sensing Techniques in Disaster Management: Amynteon Mine Landslides, Greece. In Lecture Notes in Geoinformation and Cartography. https://doi.org/10.1007/978-3-030-05330-7_9, 3. Liu, P., Wei, Y., Wang, Q., Chen, Y., & Xie, J. (2020). Research on Post-Earthquake Landslide Extraction Algorithm Based on Improved U-Net Model. Remote Sensing, 12(5), 894. https://doi.org/10.3390/rs12050894. Please, update the bibliographic references.

Lines 89-90: Although the tectonic regime is described in detail, no analysis is provided about the major geological formations of the study area. Please, add a brief paragraph with their description, as well as a lithostratigraphic column, if applicable.

Line 130: Please, provide Figure 2 in a higher resolution. It contains several blur parts in its current form.

Line 316: The “Conclusions” section should be modified. In the current form, it resembles an abstract rather than conclusions. This section should be comprehensive, while the major findings of the paper should be highlighted. Maybe, numbering of the conclusion remarks could be performed. Please, apply.

The quality of English is satisfactory. Some minor linguistic corrections could be performed.

Author Response

Dear editor of RS and reviewers,

We greatly appreciate your kind encouragement and significant reviews. We cherish your trust and the chance to revise our manuscript. We absolutely accept all issues mentioned in the three reviewer's comments that are very helpful for our deeper thinking and study, and modified carefully the manuscript including adding more details about the methodology and rewriting some contents. We show the changes with mark in red color. Here we would like to show the detailed revision note and respond to all comments one-by-one.

Reviewer: 1

Comments to the Author

Thank you for spending your valuable time in giving us so many significant and helpful reviews and encouragement.

However, some changes should be implemented, which will improve the paper. In particular: Lines 34-35: The references are not provided in the correct form. Please, apply throughout the manuscript the reference style, provided by the paper template.

Thank you for your kind suggestion. We revised the reference style based on the paper template.

Thank you for your careful review. We added the important references in our new version in lines 53-56.

Thank you for your kind suggestion. We added a brief paragraph with description of major geological formations and lithology of the study area in lines 66-72.

Line 130: Please, provide Figure 2 in a higher resolution. It contains several blur parts in its current form.

Thank you for your careful review. We exported the photogrammetry with higher resolution obtained by UAV again and changed Figure 2 in the new version.

Thank you for your kind suggestion. Based on your suggestion, we rewrote the conclusions section by performing the conclusion remarks using three paragraphs in lines 324-336.

Author Response File: Author Response.docx

Reviewer 2 Report

The paper with the title 'A steady landscape determined by rates of river incision and hillslope erosion using sensing and topographic analysis' focuses on estimating both erosion rate and fluvial incision rate at Qilian Mountain at the Qingyang site by UAV and OSL methods. It shows that a state of dynamic equilibrium had likely existed during the past 117 ka. Well, the results based on the data collected in this paper show the new finding of a new balance between uplift and erosion. There are several questions should be considered during the revision process as follows.

1. The current fig.1a is smaller in scale, I suggest the co-authors should add a regional map which covering the whole Qilian Fault and nearby faults, which shows the previous rates by other scholars which can be compared to the result in detail, the current version just cite several result in text, and fig.1a is very small to showing the geological setting in general;

2. The L01-L05 are five landslides to be used as the hillslope erosion sites in this study, but from the reviewer's view, the whole landslides in Fig.4 are located at the left band of the river, its boundaries are not clear, especially to L01, I mean that can you explain more detail information about how to connecting the original land sliding between the terrace formation and hillslope erosion, the landslides may be the rock falls not the traditional landslides. So the process of sliding may relate to the rock weathering and movement from the source area;

3. to the calculation process in this paper, the estimated thickness of each landslide from the profile extracted from UAV DEM may be bigger than the real thickness, I mean we do not know the real feature before sliding at the deposit section, so the Dd is a coarse data, the co-authors should take it carefully for deciding the results in your paper, or co-authors should add some words in text to address this point;

4. minor points.

a) Qingyang Mountain(QYM) first appears in Line 71 in the text, and second appear in Line 112,line 115,, so it should be in the form of QYM, the same as UAV;

b)Fig.3b should add the camera direction and river flow direction;

c)Even the article in communication type, the reviewer suggests that the introduction section and discussion section should add some sentences to cite more rates by previous scholars in this region and argue the uncertainty of result;

d)line102, the volume should be in cube meters, i.e. 260×10³m³， correct it.

Author Response

Dear editor of RS and reviewers,

Reviewer: 2

Thank you for spending your valuable time in giving us so many significant and helpful reviews and encouragement.

The current fig.1a is smaller in scale, I suggest the co-authors should add a regional map which covering the whole Qilian Fault and nearby faults, which shows the previous rates by other scholars which can be compared to the result in detail, the current version just cite several result in text, and fig.1a is very small to showing the geological setting in general;

Thank you for your kind suggestion. Based on your suggestion, we changed Fig. 1 by a regional map which covering a larger range of Qilian Fault and nearby faults. We also show the previous rates by adding more data of rates as presented in Fig. 1 and lines 75-80.

The L01-L05 are five landslides to be used as the hillslope erosion sites in this study, but from the reviewer's view, the whole landslides in Fig.4 are located at the left band of the river, its boundaries are not clear, especially to L01, I mean that can you explain more detail information about how to connecting the original land sliding between the terrace formation and hillslope erosion, the landslides may be the rock falls not the traditional landslides. So the process of sliding may relate to the rock weathering and movement from the source area;

Thank you for your careful review. We changed the color of the boundaries to make them clear. Meanwhile, it is difficult to delineate the exact boundaries of historic landslides from the imagery. However, based on field investigation, we infer that some sections of the terrace in eastern QYM was destroyed by historic landslides and hence that colluvium identified in the field was deposited after the fluvial terrace formed. We calculate the ratio (α) of channel width (W) to channel depth (D) of the existing not destroyed strath terrace to estimate the initial width of the fluvial terrace that was subsequently eroded and covered by colluvium. As what you pointed out, the landslides may be the rock falls not the traditional landslides and the process of sliding may relate to the rock weathering and movement from the source area. We explained more detail information and statement in lines 186-193.

to the calculation process in this paper, the estimated thickness of each landslide from the profile extracted from UAV DEM may be bigger than the real thickness, I mean we do not know the real feature before sliding at the deposit section, so the Dd is a coarse data, the co-authors should take it carefully for deciding the results in your paper, or co-authors should add some words in text to address this point;

Thank you for your significant review. It is an important part in considering uncertainty as you mentioned. We acknowledge that there is much uncertainty in our estimates of volume of colluvium generated by hillslope erosion, especially in the values of average thickness (Dd). We also do not know the exact extent of the colluvial sediments when the strath terrace formed, although we can safely assume that most of the colluvium accumulated on the terrace after the strath was abandoned. We also do not know whether some sediment deposited on the terrace removed by erosion, thus limiting our estimates of after Dd. It is for these reasons, that we view our hillslope erosion rates in QYM as minimum values. We added the uncertainty analysis in lines 312-318.

minor points.
a) Qingyang Mountain(QYM) first appears in Line 71 in the text, and second appear in Line 112,line 115,, so it should be in the form of QYM, the same as UAV;

We change all of them in the new version.

b) Fig.3b should add the camera direction and river flow direction.

We added the camera direction in line 146 and river flow direction in Fig. 3b.

c) Even the article in communication type, the reviewer suggests that the introduction section and discussion section should add some sentences to cite more rates by previous scholars in this region and argue the uncertainty of result;

Thank you for your significant review. We searched more papers to find the date of rates around our study area as many as possible. We added more data in lines 75-80 now. Considering the important uncertainty of result, we added a specific paragraph in lines 312-322.

d) line102, the volume should be in cube meters, i.e. 260×103m3， correct it.

Thank you for your detailed review. We checked it in lines 96-97.

Author Response File: Author Response.docx

Reviewer 3 Report

The manuscript “A steady state landscape determined by rates of river incision and hillslope erosion using remote sensing and topographic analysis”, authors Xueliang Wang, Yanjie Zhang, John J. Clague, Songfeng Guo, Qisong Jiao, Junfei Wang, Juanjuan Sun, Wenxin Fang and Shengwen Qi, propose a procedure to estimate lower and upper bounding values of hillslope erosion rate, i.e. landslide and gulley erosion rates, by means of remote sensing and topographic analysis. The authors estimated topographic characteristics, hillslope erosion rate and river incision rate in Qingyang Mountain (Tibetan Plateau) by means of field observations, optical stimulated luminescence (OSL) ages on fluvial terraces and measurements of high-resolution DEM extracted using the Structure from Motion photogrammetric technique from images acquired by an Unmanned aerial vehicle (UAV). Finally, they estimated average river incision rates of 0.32±0.07 mm/yr and hillslope erosion rates of 0.17±0.04 mm/yr.

In my opinion, the authors present an interesting Communication for the readers of the Remote Sensing Journal: however, at present, some improvements are needed.

The description of the UAV photogrammetric survey and data processing is very poor; please, provide more information: type of used drone, relative flight altitude, images overlap, number of strips, etc. Is the UAV equipped with RTK-GNSS sensor? How many GCPs were measured and used in the data processing? Where are located? How were they measured? Using RTK-GNSS, total station… Were check points used to evaluate uncertainties? What is the chosen reference system? These information are very useful for the readers…

In the text, citations are not in the Journal style; in the References section, the references are not in the Journal style.

Some other remarks/suggestions in detail:

- Page 3, Figure 1: (b) In the caption, explain the legend of Figure 1b: JV… ksn… the intervals 1 – 5, 5 – 10 …;

- Page 4, line 132 and page 6, line 186: Are the "remote sensing images" acquired with the UAV the final orthophoto map resulting from data processing? Please clarify;

- Page 7, Figure 5: What do the values “0.11” (lower) and “0.15” (upper) in the legend mean? Why are there no upper values in landslides L01 and L02? Similarly, why are there no lower values in U03? Please provide explanations;

- Page 10, Table 3: Please improve the readability of the column headers in Table 3;

- Page 11, Figure 8: To better visualize the green, black and red lines it could be useful to enlarge the Figure.

Author Response

Dear editor of RS and reviewers,

Reviewer: 3

In my opinion, the authors present an interesting Communication for the readers of the Remote Sensing Journal: however, at present, some improvements are needed.

Thank you for spending your valuable time in giving us so many significant and helpful reviews and encouragement.

Thank you for your significant review and kind suggestions. Based on your suggestions, we added the information as follows: The UAV provides real-time, centimeter-scale positioning data (https://www.dji.com/ca/ phantom-4-rtk). A minimum of six ground control points (GCP) were used at each for geometrical positioning during the UAV survey. When applying the single base station measurement method, the points for GCPs are generally chosen as the intersection of linear objects with small elevation differences, as well as the centers of point-like objects. The reference coordinate system of WGS84 was chosen for measurements of GCPs. The instrument must be shut down and initialized before observation on site. The number of automatic observations per measurement should be no less than 30, and the average value is taken as the result. The accuracy threshold for each measuring point is H ≤ 2 cm in the horizontal plane and V ≤ 3 cm in the vertical direction. Flight height and velocity were calculated automatically. The lateral overlap of photographs is more than 65%, and heading overlap is more than 75%. The Structure-from-Motion algorithm was used to derive DEM data from aerial images and involved feature point extraction, image matching and bundle adjustments. We implemented a high accuracy, key point limit of 40,000, aggressive depth filtering, and arbitrary surface type in Photoscan. We added the description in lines 111-123, 125-127 and 130-131.

In the text, citations are not in the Journal style; in the References section, the references are not in the Journal style.

Thank you for your detailed review. We revised the reference style based on the paper template.

Some other remarks/suggestions in detail:

- Page 3, Figure 1: (b) In the caption, explain the legend of Figure 1b: JV… ksn… the intervals 1 – 5, 5 – 10 …;

It is our fault that we messed the legend. We deleted the unrelated legend in the new version.

- Page 4, line 132 and page 6, line 186: Are the "remote sensing images" acquired with the UAV the final orthophoto map resulting from data processing? Please clarify;

Thank you for your kind suggestion. The image used is the UAV-acquired orthophoto acquired with the UAV, we changed it in lines 136-137. We also clarify the sentences in lines 181-185.

Thank you for your detailed review. Lowe avg. erosion rates and upper avg. erosion rates are from Tables 2 and 3. We explained it in lines 200-201. Because there is no obvious colluvium in gully 03 (U03 in Fig. 5), we did not calculate the lower bounding value there. Similarly, because there are not no obvious gullies on the colluvial deposits in gullies 01 and 02 (L01 and L02 in Fig. 5), we did not calculate the upper bounding values there. We added the explanations in lines 281-284.

- Page 10, Table 3: Please improve the readability of the column headers in Table 3;

We simplified the columns in Table 3 to make it clear.

- Page 11, Figure 8: To better visualize the green, black and red lines it could be useful to enlarge the Figure.

We bolded green and red lines and enlarge the Figure 8.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Dear co-authors,

I'm appreciate that the new version of your manuscript had absorbed my comments and advice, there are minor questions should be checked during your final revision.

1. Fig.1 there are different name of the same Fault, Qilianbeiyuan Fault in 1a, but North Qilian Shan Fault in 1b, also in the text, so It should be corrected in the same type;

2. Also in Fig.1a, there is no the symbol of the type of movement for each fault in the fig, so you should add them, thrust or horizontal? It should be addressed or the author can know what is you target fault;

3. In Fig.1b, the current version some words in the figure covering the location of the targeted landslide boundaries and/or sampling location, it should be updated for see the content clearly, suggest to delete the 'study area' in the Fig.1b, it will be confused the readers which one is your study area compared to the Fig.1a.

Author Response

Fig.1 there are different name of the same Fault, Qilianbeiyuan Fault in 1a, but North Qilian Shan Fault in 1b, also in the text, so It should be corrected in the same type;

Thank you for your detailed review. We checked the name of “Changma-Ebo Fault” in Fig. 1b, and added the name in Fig.1a. We also checked the name of “The Haiyuan Fault” in the text in line 72.

Also in Fig.1a, there is no the symbol of the type of movement for each fault in the fig, so you should add them, thrust or horizontal? It should be addressed or the author can know what is you target fault;

Thank you for your kind suggestion. Based on your suggestion, we added the symbol of the type of movement for the faults that we could be sure about in Fig. 1a.

In Fig.1b, the current version some words in the figure covering the location of the targeted landslide boundaries and/or sampling location, it should be updated for see the content clearly, suggest to delete the 'study area' in the Fig.1b, it will be confused the readers which one is your study area compared to the Fig.1a.

Thank you for your careful review and kind suggestion. We changed the locations of the words and deleted the 'study area' in the Fig.1b.

Author Response File: Author Response.docx

Reviewer 3 Report

In this second version of the manuscript “Study of a steady-state landscape using remote sensing and topographic analysis”, the Authors have significantly improved the work addressing all my requests / comments / suggestions: I suggest publication in the present form.

Author Response

Thank you for your kind encouragement and helpful reviews.

Author Response File: Author Response.docx