Evaluating the Differenced Normalized Burn Ratio for Assessing Fire Severity Using Sentinel-2 Imagery in Northeast Siberian Larch Forests

Round 1

Reviewer 1 Report

In this study, the authors investigated the potential of the differenced Normalized Burn Ratio (dNBR), calculated from MSI/Sentinel-2 over two fire scars, to track fire severity in three forest types of Northeast Siberia. For this purpose, several regression relationships were evaluated between the dNBR and other field parameters representing fire severity (e.g., burn depth).

In general, this is a well-written manuscript. The objectives are clearly defined. In spite of the simplicity of the statistical data analysis (I am conscious of the fieldwork efforts), the manuscript deserves publication. As mentioned by the authors, this is the first study using MSI/Sentinel-2 data for the assessment of fire severity in Siberia. This is the main contribution of the work because most of the global boreal forests are located in this region.

I just have a few comments to be addressed in a revised version.

 

Major comments:

1. I do not see any reason to keep the class “Open forest (mixture LC and PS)” in the data analysis. This class distracts the readers. You have only 4 sample plots for this class. Consequently, it is not possible to establish any regression relationship for this forest type, as shown in figures and tables. If you remove the 4 sample plots from the analysis, the conclusions will not change. This modification will facilitate reading and comprehension.
2. There are serious problems with table indexing. The manuscripts indicates the presence of 9 tables, but Tables 2 and 3 are missing and are not cited in the manuscript. In reality, the text has 7 Tables, which is still an excessive number for publication
3. In relation to the previous point, the present Tables 4 to 9 are not really necessary for publication. You should migrate all the statistical information from these tables into the corresponding figures, using different colors for the text to match the fitting lines. This will facilitate a quick inspection of the results, especially if you remove the 4 sample plots [Open forest (mixture LC and PS)] from the graphs.
4. On each figure (regression relationships), please, insert the fitting equations, n, R2, RMSE and statistical significance (or p-value) (Figures 2; 6 to 10).
5. The conclusions sound to some extent as Discussion, especially the statements in the second and third paragraphs. Therefore, some statements should be moved to Discussion. It is not necessary to define the objectives again in Conclusions. Please, be clear in your conclusions.
6. The main objective of this study is to assess the potential of the dNBR as a proxy for fire severity, as mentioned in Introduction. Therefore, you should at least test the use of the best regression relationship with dNBR (all sample plots) to produce an image of the most correlated field parameter representing fire severity. Depending on the quality of the image and spite of the moderate correlation coefficients and data dispersion, this approach could strength the manuscript to some extent.

 

Minor comments:

- Figure 3: Please, insert a small space between photographs (b), (c) and (d).

- Line 201, Figure4: Please, insert a statement to describe how the canopy cover was determined.

- Line 203-205: Please, add more details about the procedure for strata definition.

- Line 219: “... Bottom-of-Atmosphere (BOA) reflectance (surface reflectance product).”

- Line 219 to 223: Please, clearly mention the atmospheric parameters and model used for atmospheric correction (type of aerosol, atmospheric model, and ozone).

- Line 225: insert a paragraph here.

- Line 273: Please, rephrase the truncated sentence (“…The GeoCBI for the four vegetation strata, the GeoCBI–dNBR relationship was slightly stronger…”).

- Table 4 is not necessary. You can easily migrate the statistical information to Figure 3 using the corresponding colors of the legend. You can mention in the caption the absence of statistically significant relationships for open forest (mixture LC and PS) due to the small number of plots. It is important to consider the possibility of removing the 4 sample plots from the entire manuscript. It is also important to indicate the statistical significance in the figure (at least p-values) and the number of samples (n) used to obtain the relationships (14 and 23).

-  Please, do the same for the remaining figures and tables (Tables 5 to 9). This will save space in the text and provide a quick view of the results, avoiding the presence of a great number of tables in the manuscript. Please, in all figures, insert also the statistical significance in the figure or p-values and the number of samples (n) (14 and 23).

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Evaluating the differenced Normalized Burn Ratio for assessing fire severity using Sentinel-2 imagery in Northeast Siberian larch forests

Combee et al. (2021) have evaluated the potential of NBR to assess fire severity in Northeast Siberian larch forests using orbital data. The orbital data-derived estimates were posteriorly compared to field data. This thematic is within the scope of Remote Sensing and would be interesting to the readers of the journal.

This is a very pleasant reading. The manuscript is very well written, the hypothesis of the work is clear, methods are satisfactorily detailed and results are clearly presented and discussed.

In my opinion the manuscript is ready for publication. I would like to congratulate the authors for the fine and methodological work that will greatly contribute to the understanding of fires in boreal forests.  

There are a few minor comments below that should be considered by the authors:

Line 44: Impact of fire in boreal forests.

Lines 63-65: What about anthropogenic fires? Are they a disturbance in your study area?

Lines 74-75: Please add a reference to this definition.

Line 99: In my opinion Figure 3(a) would be easily interpreted using percentual values instead of number of occurrence.

Line 201: Please add the GeoCBI equation in here.

Line 258: Show a clear

Line 408: What about the slope and other surface characteristics?

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

This paper describes about the differenced Normalized Burn Ratio for assessing fire severity using Sentinel-2 imagery in Northeast Siberian larch forests.
The authors used Sentinel-2 satellite imagery to test the potential for using the most common spectral index for assessing fire severity, the differenced Normalized Burn Ratio (dNBR).
In order to improve the completeness of this paper, the following items should be clearly stated and reviewed.
Since the main conclusions are based on 23 surveys for dense and young larch forest, the authors need to show how much error the biased analysis has.
In addition, to avoid misleading readers, the authors need to provide a various information like in the below:
1. Show (rough) percentage of the three different forest types (dense larch-dominated, open forest with a mixture of larch and pine, open larch-dominated forest) in the target areas of Yert fire scar and Batamay fire scar, and the western part of Yakutsk (61-65N, 125-130E). 
2. Describe about open pine forest is one of the unique forest types in Yakutsk area.
In addition, describe about alas (small pond) and their effect on analysis results.
3. Describe about surface fires. They are the main type of fire in the Yakutsk area.
4. Provide information on active layer in Yert fire scar and Batamay fire scar.
And show the effect of their water contents in active layer on analysis results.
5. Provide information on surface vegetation and their effect on fire and analysis results.
6. Perhaps most readers are unfamiliar with the adventitious root. 
Try to insert a photo or sketch of the adventitious root in Figure 2.
7. Provide information on dead root in the three different forest types.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

I checked the revised manuscript.
1. Soil organic layer (SOL) depth was measured but little information is given on the depth of defoliation on the forest floor.
Soil horizon in a few suitable sites are needed. 
Among them, depth of fallen leaves from larch will be one of important factors for burn depth. With the help of soil horizon (depth of fallen leaves), your analysis result may be better.
2. “mineral soil” in title for x axis in Figure 2 (b) is not suitable word and should be replaced by a word from the above soil horizon or just replaced by general term, “forest floor”.

Author Response

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Author Response File: Author Response.pdf