Interpreting Sentinel-1 SAR Backscatter Signals of Snowpack Surface Melt/Freeze, Warming, and Ripening, through Field Measurements and Physically-Based SnowModel

Round 1

Reviewer 1 Report

This is a very good and interesting paper, I just have some issues. -> Abstract: I think the abstract is too long and it is not easy to catch key messages for this paper.  -> Introduction: I recommend that you can highlight your contributions of this paper in Section 1 and then shortly introduce your organization of this paper at the end of Introduction. -> Figure 1: I think the color should be reconsidered. For example, if the white points denote IOP measurement sites, the legend is grey points actually. Also, white points are easily confused with cloud, and green points and boxes are easily confused with forest/vegetation. -> Sec2.2.4 you use 30m land cover dataset, and what is the resolution of Sentinel? 10m or 30m or others? if they are not the same resolution, how do you deal with different resolution RS images and LC product? -> Some references could be considered to cite if you think they are suitable for your paper. Mei, L., Rozanov, V., Jiao, Z., & Burrows, J. P. (2022). A new snow bidirectional reflectance distribution function model in spectral regions from UV to SWIR: Model development and application to ground-based, aircraft and satellite observations. ISPRS Journal of Photogrammetry and Remote Sensing, 188, 269-285. Zheng, J., Fu, H., Li, W., Wu, W., Yu, L., Yuan, S., ... & Kanniah, K. D. (2021). Growing status observation for oil palm trees using Unmanned Aerial Vehicle (UAV) images. ISPRS Journal of Photogrammetry and Remote Sensing, 173, 95-121. Varade, D., Manickam, S., & Singh, G. (2021). Remote Sensing for Snowpack Monitoring and Its Implications. Geographic Information Science for Land Resource Management, 99-117.

Author Response

Thank you for your valuable feedback. Our response to your suggestions is in the attached file.

Author Response File: Author Response.docx

Reviewer 2 Report

This paper deploys in situ measurements and physical models to interprete SAR backscatter signals of snow pack.

 

My global impression is that the descriptions are often verbose so that it is difficult to get the main idea of the long text. Efforts to summarize and to highlight the important conclusions seem necessary. Moreover, the main contribution of the paper is not clear to me, please clarify.

 

Detailed comments :

 

1) What is the data assimilation method used ? How did you deal with model and data uncertainties ?

 

2) Authors mentioned on page 5, (l. 205 – 207) that in situ measurements and remotely sensed data were used to constrain the model output. But it seems that remote sensing data (S1 data) were not assimilated according to the descriptions thereafter. Please clarify.

 

3) The presentation of Fig.1 needs to be improved. The same for Fig.2(c) (gray color does not apprear in the figure, we see only white and black)

 

4) What is the main conclusion of Fig.7 ? Can we say that S1 observations are not consistent with in situ pit measurements ?

 

5) Fig. 9, please add ‘’bottom row’’ in the figure caption. What are the main conclusions of this figure ? Please make some syntheses instead of giving long (almost 1 page) detailed descriptions.

 

6) Fig. 10, can you explain more the observed difference between S1 and the physical model ? Which one is likely to be more reliable ? I suppose that when authors mentioned model, you mean the assimilation results, in other words, the combination of the model and in situ measurements ?

Author Response

Thank you for your valuable feedback. Our responses to your suggestions may be found in the attached file.

Author Response File: Author Response.docx

Reviewer 3 Report

The manuscript titled “Interpreting Sentinel-1 SAR backscatter signals of snowpack surface melt/freeze, warming, and ripening, through field measurements and physically based SnowModel” explore the use of Sentinel-1 SAR backscatter signal of snowpack to approach physical properties of the snow surface. As field-truth, the authors used 50 snow pit observations of temperature and wetness. In addition, they run physically based models, SnowModel, to estimate Snow Water Equivalent (SWE) and run off.  Snowpack phases of warming, ripening, and runoff were identified and corroborated by comparing field measurements with Snow Model outputs. S1 SAR backscatter seems to indicate sensitivity to significant Surface melt/freeze, as well as the status of the underlying snowpack, during snowpack ripening and runoff. I agree with the authors that integrating field measurement, remotely sensed data, and physically-based snow modelling modalities offers complementary perspectives on snow conditions and their potential drivers.

Although the results associated with the ability of the S1 SAR backscatter to identify the state of the snow are limited, combining these with field data and physically based models the usefulness of the method is undoubted. The authors have made a great effort to present their research and results. This effort has resulted in a work of great quality and aesthetic value. The workflows make the work reproducible by other cryosphere researchers who want to complement their studies with Sentinel-1 images. As is my case, I am working in albedo of the Antarctic glaciers with images (MODIS) and field data (radiometers and snow-pits) and I wanted to introduce the Sentinel-1 images for studies of surface roughness and structure of the snowpack.  Moreover, the work is well structured; the figures are of quality and very useful to be consulted in digital version. The data supports the conclusions and is well documented.

Author Response

Thank you for your valuable feedback.

Reviewer 4 Report

This is a nice work about phase transitions of snowpack. Indeed, I'm not so familiar with the topic, but through a careful read I'm sure there is something new and important about snow cover in cold regions. Thus, I think it can be considered for possible publication in RS. There are some small problems about the figures in the manuscript. For example, in Fig.3, labels of latitude and longitude need revision. In Fig.4, mean temperature (C?). In Fig. 8, I think it would be better to place the titles of axis along the axis.

Author Response

Thank you for your valuable feedback. Our responses to your suggestions may be found in the attached file.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors have addressed all my issues well. I recommend this article to publish in this journal