Sentinel-1 Response to Canopy Moisture in Mediterranean Forests before and after Fire Events
Round 1
Reviewer 1 Report
Manuscript ID: remotesensing-2120890
Title: Sentinel-1 Response to Canopy Moisture in Mediterranean Forests Before and After Fire Events
In this study, the authors have performed a study to investigate the sensibility of Sentinel-1 C-band backscatter values to moisture content of forest canopy. Authors have provided a nice introduction and the subject is worthy of investigation. Results are interesting and can be helpful for the investigation of fire weather danger. I have some comments before recommending the manuscript for publication:
1. At the end of the introduction, the authors have directly jumped to their study. The innovation of this article is not clear to the reader. It is better to explain the drawbacks and missing links in the previous literature and connect your study with those. Please discuss the main points and innovations of the current work in more detail.
2. The overall results from this analysis are comparable to previous studies. Then how do authors justify the importance of the current study and, please briefly discuss the different models used in the previous study and their advantages/disadvantages to justify the current work?
3. Please also discuss the future directions of the work.
4. Analysis seems reasonable and even the results seem reasonable and have been analyzed sensibly. However, my experience is that models are often deeply wrong, and sometimes even wrong to first order. Here, for the results in this paper to have any meaning at all, one must trust the climate models upon which they are based. We are not presented with any reason to trust them. Their output is basically treated like observed data. Please discuss
5. Authors could present some results regarding the fit of models to observations using past data. Were there trends in the errors that are noteworthy? Can we see some plots of the errors, or of the model forecasts next to actual observations, for comparison?
6. Reference style as per the MDPI Remote sensing.
Author Response
We thank the reviewer for her/his constructive comments. Below our response for each comment.
- At the end of the introduction, the authors have directly jumped to their study. The innovation of this article is not clear to the reader. It is better to explain the drawbacks and missing links in the previous literature and connect your study with those. Please discuss the main points and innovations of the current work in more detail.
+++ we have added the following paragraph at the end of the introduction, to give the reader a primer on the contents of the work.
The main points of interest of the current work are related to better understanding the behavior of backscatter of C-band SAR with respect to canopies in different moisture conditions, from drought to wet canopies, and what happens when fire events change the canopy structure. We discuss results that show that wet canopies consistently provide a stronger backscatter than dry canopies. We show that canopies after fire events lose this type of response, likely due to the fire changing the composition of the canopy in terms of the ratio between leaves, small and larger branches.
- The overall results from this analysis are comparable to previous studies. Then how do authors justify the importance of the current study and, please briefly discuss the different models used in the previous study and their advantages/disadvantages to justify the current work?
+++ In the discussion section, at the end of each paragraph, we have compared our results with previous studies, highlighting the importance of results with respect to other work.
- Please also discuss the future directions of the work.
+++ we have added several paragraphs to discussion and conclusion section on this topic.
- Analysis seems reasonable and even the results seem reasonable and have been analyzed sensibly. However, my experience is that models are often deeply wrong, and sometimes even wrong to first order. Here, for the results in this paper to have any meaning at all, one must trust the climate models upon which they are based. We are not presented with any reason to trust them. Their output is basically treated like observed data. Please discuss
+++ If by climate models the reviewer means drought code values, we agree that models intrinsically carry a standard error and different uncertainties. We consider DC values as trustful observations due to their use in official maps distributed by the Joint Research Center. Undoubtedly DC values calculated with climate sensors positioned at each cell node and at each burnt area would drastically increase reliability and, probably, also our results. It can be noted that the decrease of backscatter with increasing drought values is more marked when calculated at cell nodes, and less marked when interpolated with bilinear interpolation at fire areas. This can be considered an indicator that sensibility depends on the climate model, as it decreases when model data are interpolated. This has been added in the discussion section as it is a point worth discussing.
- Authors could present some results regarding the fit of models to observations using past data. Were there trends in the errors that are noteworthy? Can we see some plots of the errors, or of the model forecasts next to actual observations, for comparison?
+++ it is not easy to understand what is meant here. If the reviewer would like to see a map of predicted DC values using past data (e.g. an independent dataset), and then compare the predicted DC values with DC values interpolated from weather station, this would require some time as the DC values must be requested to JRC (Joint Research Center) and processing would take some time. We prefer to keep this work as is without further processing, and keep this for future work. We have added a last sentence on this in the conclusions section.
- Reference style as per the MDPI Remote sensing.
+++ we double checked and fixed reference style
Reviewer 2 Report
This article reports on how dose C-VH and C-VV backscatter values of Sentinel-1 response to forest canopy moisture before and after fire events. A large number of Sentinel-1 images were used to analyze the correlation between backscatter and canopy wetness. The subject is interesting and significant. There are, however, some issues to pay attention to and pleases see the attachment for details.
Comments for author File: 
Comments.pdf
Author Response
We thank the reviewer for her/his time and constructive comments. Below the answers to the posed questions.
pg 4 "what does Rd represent" - Rd represents daily rainfall values in mm.
Figure 3 - thank you for catching this, a draft of the graph was mistakenly used, we have updated the workflow
Fonts in figures were enlarged (all figures with boxplots have been improved).
Discussion section was improved and errors corrected.
Reviewer 3 Report
The article addresses a topic that is relevant and appropriate for the journal. However, the article needs significant improvements to be published. The description of the results and discussion is insufficient for understanding the article. In this context, I describe below my main suggestions.
Original research manuscripts must contain at least 18 pages following the Instructions for Authors (https://www.mdpi.com/journal/remotesensing/instructions), and the present article is only 16 pages
The abstract can have a concluding sentence at the end.
In the introduction, I suggest including a topic of related works, increasing the bibliographic review on the subject.
In the topic “Fire Maps,” the text could briefly describe the data and methodological procedures used in the European Forest Fire Information System (EFFIS).
The results could have a better description of the data.
In topic 3.1, the text needs to describe the results in detail, lacking information for the reader. Table 1 is not described, and the linear regressions represent the lack of correlation with R2 values lower than 0.4. In the text, the authors describe that Figure 6 demonstrates that the resulting corrected backscattering has no relationship with AIL. Figure 6 does not show this statement. Table 2, which was placed on this topic, needs to be described, but its description is in the discussion. The results of Figure 6 are also to be desired, being completed in the other topic.
Topic 3.2 also needs a detailed description of the results. Figures 8 and 9 have no references in the text. Authors should highlight the results and their importance in the study.
The discussion should focus on the theoretical and practical implications of the research, the relationship between the results and the literature, the limitations found, and future work. The text must indicate why the results are acceptable and their consistency considering the low correlations described and previously published knowledge.
The meanings of some acronyms, such as “VV,” “VH,” “NOAA-AVHRR,” and “WGS,” are missing.
There are two terms used with the same objective “tree loss” (figure 4) and “forest loss” (topic 2.6.3 and in the rest of the text. I suggest standardizing.
Minor corrections
P.1 “to moisture content” I suggest “to the moisture content”
P.1 “Confounding variables such as tree cover and incidence angle were accounted for.” The sentence is incomplete.
P.1 “canopy (e) the C-VH” I suggest “canopy; and (e) the C-VH”
P.2 “will be done only for” I suggest “will only be done for”
P.4 “we identifies fire areas” I suggest “we identified fire areas”
P.4 “a resolution of 30 m as it” I suggest “a resolution of 30 m, as it”
P.4 “allowed to map” I suggest “allowed us to map”
P.4 “For this study the GFC” I suggest “For this study, the GFC”
P.4 “rt is rainfall of” I suggest “rt is the rainfall of”
P.4 “DCt−1 i.e., the” I suggest “DCt−1, i.e., the”
P.5 “considered the areas having a” I suggest “considered areas with”
P.8 “DC values of very wet canopy scenarios (0.1-1) from the dry and very dry scenarios” Enter the values for dry and very dry scenarios “DC values of very wet canopy scenarios (0.1-1) from the dry (???) and very dry scenarios (???)
P. 13 “extremely dry condition (DC” I suggest “extremely dry conditions”
P. 13 “that backscatter average” I suggest “that backscatter the average”
P. 13 “Figure 8 show that” I suggest “Figure 8 shows that”
P. 13 “1.45 dB respectively for A” I suggest “1.45 dB, respectively, for A”
P. 13 “with the results in the work in [34] carried” I suggest “with the work [34] carried”
P. 13 “The analysis over the burnt areas show” I suggest “The analysis of the burnt areas shows”
P. 13 “scenarios the C-VH” I suggest inserting a comma “scenarios, the C-VH”
P. 13 “C-VH backscatter values … that was observed” I suggest “C-VH backscatter values … that were observed”
P. 13 “different dielectric property” I suggest putting it in the plural “different dielectric properties”
P. 13 “backscatter-DC relation return to” I suggest “backscatter-DC relation returned to”
P. 13 “After 360 days from the fire event the C-VH” I suggest inserting a comma “After 360 days from the fire event, the C-VH”
Author Response
We thank the reviewer for her/his time and constructive comments.
Original research manuscripts must contain at least 18 pages following the Instructions for Authors (https://www.mdpi.com/journal/remotesensing/instructions), and the present article is only 16 pages
++ more discussion and material was added and now the article surpasses the required length
The abstract can have a concluding sentence at the end.
++ We have changed the abstract to make it more direct and added a concluding sentence addressing the three main points of the article
In the introduction, I suggest including a topic of related works, increasing the bibliographic review on the subject.
++ we have added references to related work in introduction and also to discussion sections.
In the topic “Fire Maps,” the text could briefly describe the data and methodological procedures used in the European Forest Fire Information System (EFFIS).
++ Several lines were added regarding to this in the Fire Maps section
The results could have a better description of the data.
++ We have added more detailed description under multiple parts of results.
In topic 3.1, the text needs to describe the results in detail, lacking information for the reader. Table 1 is not described, and the linear regressions represent the lack of correlation with R2 values lower than 0.4.
++ correlation with LIA values are well established by theoretical and empirical observations, the low correlation is due to focusing on total forest cover, thus canopies, where the leaves lower this correlation. Nevertheless the backscatter must be normalized. This explanation was added to the results, to improve the description as pointed out in the previous point.
In the text, the authors describe that Figure 6 demonstrates that the resulting corrected backscattering has no relationship with AIL. Figure 6 does not show this statement.
++ we have added the corrected backscatter values plot at the bottom, to show the difference between before and after correction.
Table 2, which was placed on this topic, needs to be described, but its description is in the discussion. The results of Figure 6 are also to be desired, being completed in the other topic.
Topic 3.2 also needs a detailed description of the results. Figures 8 and 9 have no references in the text. Authors should highlight the results and their importance in the study.
++ We have further described results in discussion section
The discussion should focus on the theoretical and practical implications of the research, the relationship between the results and the literature, the limitations found, and future work. The text must indicate why the results are acceptable and their consistency considering the low correlations described and previously published knowledge.
++ We have added some parts and paragraphs citing existing research to improve this part.
The meanings of some acronyms, such as “VV,” “VH,” “NOAA-AVHRR,” and “WGS,” are missing.
++ acronyms have been defined in the new version
There are two terms used with the same objective “tree loss” (figure 4) and “forest loss” (topic 2.6.3 and in the rest of the text. I suggest standardizing.
++ “tree loss” changed to “forest loss”
Minor corrections
P.1 “to moisture content” I suggest “to the moisture content”
+++ changed
P.1 “Confounding variables such as tree cover and incidence angle were accounted for.” The sentence is incomplete.
+++ Changed to “Confounding variables such as tree cover and incidence angle were accounted for by masking using specific thresholds”
P.1 “canopy (e) the C-VH” I suggest “canopy; and (e) the C-VH”
+++ changed
P.2 “will be done only for” I suggest “will only be done for”
+++ changed
P.4 “we identifies fire areas” I suggest “we identified fire areas”
+++ changed
P.4 “a resolution of 30 m as it” I suggest “a resolution of 30 m, as it”
+++ changed
P.4 “allowed to map” I suggest “allowed us to map”
+++ changed
P.4 “For this study the GFC” I suggest “For this study, the GFC”
+++ changed
P.4 “rt is rainfall of” I suggest “rt is the rainfall of”
+++ changed
P.4 “DCt−1 i.e., the” I suggest “DCt−1, i.e., the”
+++ changed
P.5 “considered the areas having a” I suggest “considered areas with”
+++ changed
P.8 “DC values of very wet canopy scenarios (0.1-1) from the dry and very dry scenarios” Enter the values for dry and very dry scenarios “DC values of very wet canopy scenarios (0.1-1) from the dry (???) and very dry scenarios (???)
+++ DC classes corresponding to dry and very dry scenarios added
- 13 “extremely dry condition (DC” I suggest “extremely dry conditions”
+++ changed
- 13 “that backscatter average” I suggest “that backscatter the average”
+++ changed to “that the average backscatter”
- 13 “Figure 8 show that” I suggest “Figure 8 shows that”
+++ changed
- 13 “1.45 dB respectively for A” I suggest “1.45 dB, respectively, for A”
+++ changed
- 13 “with the results in the work in [34] carried” I suggest “with the work [34] carried”
+++ changed
- 13 “The analysis over the burnt areas show” I suggest “The analysis of the burnt areas shows”
+++ changed
- 13 “scenarios the C-VH” I suggest inserting a comma “scenarios, the C-VH”
+++ changed
- 13 “C-VH backscatter values … that was observed” I suggest “C-VH backscatter values … that were observed”
+++ changed
- 13 “different dielectric property” I suggest putting it in the plural “different dielectric properties”
+++ changed
- 13 “backscatter-DC relation return to” I suggest “backscatter-DC relation returned to”
+++ changed
- 13 “After 360 days from the fire event the C-VH” I suggest inserting a comma “After 360 days from the fire event, the C-VH”
+++ changed
Round 2
Reviewer 1 Report
Authors have answered all the comments. Recommended for publication.
Reviewer 3 Report
The authors have made all suggested corrections. I still have some minor corrections
P.2 “2/3 day” I suggest “2/3 days”
P.2 “over data acquired over mature” I suggest “over data acquired from mature”
P.9 “testing, i.e. wet/dry” I suggest inserting a comma “testing, i.e., wet/dry”
P. 20 “It must be noted though that the model is applicable to the same conditions used in our data, therefore a forest cover equal.” I suggest inserting commas “It must be noted, though, that the model is applicable to the same conditions used in our data; therefore, a forest cover equal to or greater than 90%.”
