Characteristics of Freeze–Thaw Cycles in an Endorheic Basin on the Qinghai-Tibet Plateau Based on SBAS-InSAR Technology

Round 1

Reviewer 1 Report

This paper makes a detailed study of the different cycles that the areas affected by permafrost suffer. In general, the paper is well structured and the different technical aspects are explained. In my case, I can focus on my area of ​​expertise in radar remote sensing, and I leave other more geotechnical aspects to other peer reviewers. From my side, the paper would be ready to publish with minor changes.

Below I detail my doubts or requests for change:

1. Why do you use a single orbit (descending) for Sentinel-1 data? Using the two orbits, ascending and descending, the vertical component of motion can be estimated without any approximation. The paper indicates that a vertical projection of the LOS (Line Of Sight) measurements is made, but this is an approximation, and if there is a horizontal component of motion, it can generate large errors in the measurements.

2. Grammar error at line 186: "Figure 2 shows...".

3. Atmospheric artifacts (APS) are calculated from a model (GACOS). Why are they not estimated using their statistical characteristics within the interferometric process? Models can be misleading, while statistical studies do not rely on external data and can efficiently separate motion and atmospheric artifacts.

4. At line 375 I don't quite understand why the SDA results can be different when using the various interferometric algorithms. Can you explain it better?

Author Response

Thank you very much for your professional questions. We tried our best to reply to your questions one by one in the revised manuscript.

Author Response File: Author Response.docx

Reviewer 2 Report

Line 213-216. It is necessary to specify what means the value of t formula 1.

Figure 6 shows the spatial distribution of deformations. The white colors correspond to the water surface (low coherence), as can be seen from Fig. 1. Apart from the water surface, does the rest of the surface have apparently high coherence values? Why is the coherence threshold not specified? Why is there no information on the size of the filtration window??
During such melting and freezing processes, as a rule, the coherence of more than 0.2 is discrete. In this case, have you chosen the filtering parameters such as to smooth out as much as possible?

Author Response

Thank you very much for your professional questions. We tried our best to reply to your questions one by one in the revised manuscript.

Author Response File: Author Response.docx

Reviewer 3 Report

 

 

The manuscript regards the characterization of freeze-thaw cycles in on the Qinghai-Tibet plateau in China. Different data, statistical tools and a simple analytical model are used together to Sentinel-1 data. Many previous studies have been cited to integrate the work and many analyses have been carried out to describe the characteristics of the area of interest.

 

A huge number of acronyms have been used. This is partially justified from the number of parameters investigated, although sometimes it makes not simple the reading. I recommend the use of a synoptic table for acronyms or their reduction, avoiding using them for terms mentioned only a few times in the work. The work follows a well-defined logical flow and single aspects are generally well described also with the help of bibliographic citations.  Some points have to be better described or clarified. Problems are still present in terms of formatting, figures, and little inaccuracies, therefore a carefully revision in this sense is necessary.

 

 Below, I list my suggestions and major and minor comments on the paper. The number indicates the rows of the manuscript.

 

22: DOY 193 in no leap years is July 12. It is strange because it is out of the interval between July 25th and September 21^st _. Possibly it is a mistake, because in the conclusion a different value is specified.

 

 25: It is written: “Although the SDA in the study area is mainly affected by the thermal state of permafrost, it still has the most apparent relationship with vegetation cover, the soil water content in AL, and active layer thickness”. This aspect cited at this point seems to be relevant (as it is), but in my opinion is not enough highlighted, described and justified in the later part of the paper when this must be done.

 

 166: Is there a precise motivation to select this relative orbit and not others (eventually a couple ascending + descending)?

216: “(2|A|)”. What do you mean?

 

269: This sentence is not sufficiently explained and connected to the immediately preceding considerations to which it seems linked in the text.

 

273: Describing fig. 6 it is written “In mountainous areas, the SDA is 0 ~ 20 mm with concentrated distribution, and its central value is about 12 mm, while in intermountain basins, the SDA is 20 ~ 60 mm with widely distributed, and its central value is about 32 mm” etc. It would be very useful to highlight these different areas in this or another figure

 

344 & 345: How is the soil moisture measured in the boreholes. The following point must be better explained: “In space, we use NDVI to indicate the soil water content data”. The relation between NDVI and soil moisture is not so obvious

 

359:  Can this difference depend on the presence of vegetation?

431: Since this point the number of the figure is wrong

 

474: It is written “al” instead of “AL”

I also have a question. Is there snow cover at some time of the year? If so, how does this affect the use of SBAS?

 

Author Response

Thank you very much for your professional questions. We tried our best to reply to your questions one by one in the revised manuscript.

Author Response File: Author Response.docx

Reviewer 4 Report

The well-written and clearly structured paper describes and discusses interesting characteristics of freeze-thaw cycles on the Qinghai-Tibet based on remote sensing analysis and field evidence. Data analyses and the statistical approach are carefully presented and reflected with due consideration of the available international knowledge in the field. The methodology is rigorous and consistent, integrating several complementing techniques, whereas data back the interpretations. The results support the findings. Therefore, I suggest acceptance of the manuscript after some minor revisions. These are outlined below:

1. One of the most important environmental controlling factors of ground freezing is snow. However, I couldn`t find any information regarding snow onset/duration/thickness in your study area. Please refer to snow as well when interpreting your findings.

2. Ground freezing/thawing indices are also usually considered in similar approaches. Do you think you can also calculate these indices and present them in your paper?

3. Are there similar approaches elsewhere, in which surface displacement determined by remote sensing is to be interpreted based on freezing/thawing characteristics of the active layer? Would be nice in the Discussion to compare it with similar findings in other permafrost regions if this is the case.

4. What is the elevation of the Wudaoliang meteo station? It is also difficult to see on the map (fig. 1) the symbol for the borehole at ZL05. The inset small map has no scale.

 

 

 

 

Author Response

Thank you very much for your professional questions. We tried our best to reply to your questions one by one in the revised manuscript.

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

Thank you for answering my questions and accepting my suggestions. I do not think any other changes are necessary for the publication of the paper.