Multi-Sensor Analysis of Snow Seasonality and a Preliminary Assessment of SAR Backscatter Sensitivity to Arctic Vegetation: Limits and Capabilities

Round 1

Reviewer 1 Report

The authors present snow maps for Svalbard, derived from Sentinel-1 and Sentinel-2 data, as well as investigate the impact of soil water content and vegetation dynamics on NDVI and SAR backscatter. Most of the effort in this study is on producing and validating dry and wet snow maps, even though methods for detecting snow cover from passive optical and active microwave sensors have been widely addressed in previous literature. The snow map production can be included as a support analysis for the main research topic, but it cannot constitute the main theme of a research paper. The analysis of how vegetation properties and soil conditions affect the optical and SAR observations, stated as the novelty of this paper, is too narrow. No robust conclusions can be drawn based on the analysis performed here. Figure 11 and Tables 4 and 5 provide some information on these topics, but much deeper analysis is required to really understand the backscatter dependence on the soil and vegetation properties in the Arctic. Also, I don’t see how the snow map production contributes to the analysis of the vegetation and soil properties vs. backscatter during the snow free period. They seem like two separate aspects in this paper which are not very interrelated.

Author Response

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Reviewer 2 Report

Multi-sensor analysis of snow dynamics in relation to the sensitivity of the SAR signal to Arctic vegetation

Laura Stendardi, Stein Rune Karlsen, Eirik Malnes, Lennart Nilsen, Hans Tømmervik, Elisabeth J Cooper and Claudia Notarnicola

Submitted to Remote Sensing, reference 1635773

 

General comments

Normalized Difference Snow Index (NDSI)

soil water content (SWC)

 

This paper is concerned about observation of snow dynamics over Svalbard and how combined remote sensing and in situ observations can help to understand and monitor the vegetation.

Using combined microwave and optical spaceborne observations over the years 2017 and 2018, the authors clearly demonstrate and illustrate how the snow annual cycle differs between both years.

When addressing the effect of vegetation, matters become more complex and somewhat contradictory. Some plausible explanations are provided, and the possible influence of additional phenomena are pointed out.

In their introduction, the authors listed (L073-077) two objectives.  They are formulated carefully as improvements to the knowledge of snow and vegetation cycles in the Arctic, owing to the use of both optical and microwave spaceborne sensors, together with ground level measurements. The discussion and conclusion sections show that it was wise to set these limited objectives, and that they have been reasonably reached.

Concerning the form, the English is generally good. Some sentences, however, are unclear. In a few cases, the legend of the figures are not explicit enough.

 

Specific comments

 

01        L049: what do you mean by "normal"?

02        L064:  what is meant by "data layer"?

03        L067: You should mention that sigma_not is a notation for the backscatter cross section (unless I am mistaken…)

04        L090:  I do not know what the 99870 number in the brackets means; on the other hand, it might be useful to locate Adventdalen on the map on figure 1

05        L123:  On first sight of figure 3, one gets the feeling that the "SAR" title prevails overs the whole frame. You should try to introduce a clearer identification of the "optical/NDSI" part as distinct from the SAR part.

06        L142-144:       I find this reference puzzling. How to access this database? Surely the relevant information is only "eKlima"; but my browser tells me that from 2021 06 28 eKlima is no longer available…

07        L151   Actually I refer to table 2; Is not there something wrong with the "2017-03-06" line? Maybe the max and min air temperatures have been swapped?

08        L211:  While figure 7 is a nice figure, it seems to me that does not brings any additional information when compared to figure 6: the melting occurs earlier in year 2018.

09        L214;  typo on "grater"

10        L216:  I am a bit confused because the maps in figure 9 (and 10 as well) are only the top left part of the maps on the previous figure 7. It would be nice to point this out (and explain why?)

11        L310:  a "by" may be missing after "grubbing"

12        L325:  Do you mean by "considerable limits are derived…" that the ability to detect is limited? This sentence is unclear.

13        L327-328:       however, according to L234-238 and table 4, the findings seem somewhat contradictory.

 

Author Response

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Reviewer 3 Report

Dear authors,

I read with great interest your manuscript on the multi-sensor analysis of snow dynamics and the sensitivity of SAR applications to arctic flora on Spitsbergen. Their approach shows great promise in combining Sentinel-1 C-band SAR data and multispectral optical data from Sentinel-2 for better high-resolution detection of snow cover and its thawing, and then using both sensors for surface moisture and phenological evolution of different vegetation communities. I think the manuscript is already very well written and I suggest that it can be published after the following minor change requests:

Line 88: Remove space before comma "zone, the genus..."
Line 91: I'm sure you mean the air temperature, that should be mentioned.
Line 94: At what depth are soil temperature and moisture measured, you should mentioon that. DONE
Table 1: Name the UTM Zone. The taxa should be in italics.
Line 108: Since I know the inaccuracies in atmospheric correction at these high latitudes very well, I can understand that TOA reflectances were used, but perhaps that could be addressed in one sentence as to why atmospheric correction was also dispensed with.
Line 133: Which cloud detection methodes were used?
Line 142: Please also add the full URL of eKlima in the brackets, not only as link.
Line 145 & 147: Unit of temperature is missing.
Line 148: Add degree sign to lat and lon value.
Table 2: Place degree sign before 'C': '°C'.
Line 157: Insert thousands separator: 30,000.
Figure 4: Increase font size of the legend, labels and frame should be black.
Line 165: I recommend putting the reference to the equation before the equation: '[...], calculating their ration according to Equation 2. ... where RTS is [...]'
Line 168: see last comment
Line 168 & 169: Please use the unit µm instead of m.
Figure 7: The maps and legends are way too small. Please enlarge.
Figure 8: Here the x-axis is black, but the writing is gray, and both are gray on the y-axis. It would look much better if everything was black.
Figure 10: Same as for Figure 7, everything should be enlarged.
Line 232: Table 4 should be placed directly after this paragraph.

Wish you all the best!

Author Response

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