Multi-Sensor Analysis of a Weak and Long-Lasting Volcanic Plume Emission

Round 1

Reviewer 1 Report

The authors present detailed observations of the volcanic ash plume from a specific eruption of Mt Etna on 24 December 2018. The study combines observations from different sources. Unique measurements with a camera, a Sun photometer, and an aerosol lidar very close to the volcano are employed. Nevertheless, the scientific merit of the study does not exceed that of a purely descriptive report of the events.

The presentation could be improved by focussing on the relevant figures rather then presenting everything that has been collected. Specifically, Figures 2, 3, 5, 7, 8, and 9 could be omitted, combined, or moved to the supplement to facilitate a more straightforward storyline.

Specific comments:

• Figures 2 and 3 are not needed. The relevant information is quantified in a much better way in Figure 3. If those figures should make it into a supplement, there should also be a description of what is shown. I have no idea what the lines in Figure 2 are supposed to present.
• Is it possible to exchange Figure 5 with something more quantitative, such as area of the ash plume at different time steps. Right now, the authors leave it to the readers to see whatever they want.
• The information in Table 1 could easily be mentioned in a statement in the text. Also, what is meant with negative wind direction? This should be defined in the caption.
• Table 2 adds no value. It would be sufficient to provide daily mean values in the discussion of the AOD time series.
• Figure 6 should be combined to two panels, maybe even adding the profiles in Figure 10. Also, omit the point so that the lines are not fully blocked.
• Figure 7 should be omitted. It is not being discussed and there is no description of how PBL height was derived from the lidar measurement. Just give the values in the text.
• Figures 8 and 9b should be combined. Focus on AOD at 2 or 3 wavelength and one AE, maybe 440/870. Why do you show TPC when it's not discussed in the text?
• Figure 10 could be combined with Figure 6. In any case, get rid of the points.
• Figure 12 could combine all profiles in a single panel for easier comparison.

 

 

Author Response

Point 1: The authors present detailed observations of the volcanic ash plume from a specific eruption of Mt Etna on 24 December 2018. The study combines observations from different sources. Unique measurements with a camera, a Sun photometer, and an aerosol lidar very close to the volcano are employed. Nevertheless, the scientific merit of the study does not exceed that of a purely descriptive report of the events.

Response 1: We thanks the reviewer for the comments. The aim of the paper is to characterize the long-lasting and weak explosive activity similar to the Etna event of 28 December 2018 using several remote sensing systems. In this revised version we improved the correlation among the different instruments and we added a new sub-section on the thickness of the volcanic plume. Respect to the previous version, we also evaluated some new adding features as the speed of the volcanic plume dispersal.

Point 2: The presentation could be improved by focussing on the relevant figures rather then presenting everything that has been collected. Specifically, Figures 2, 3, 5, 7, 8, and 9 could be omitted, combined, or moved to the supplement to facilitate a more straightforward storyline.

Response 2: We followed the suggestions of the reviewer. Figure 2 and 3 were combined, Figure 5 was modified adding the area of both SO2 and Ash detected by satellite. Figure 7 was deleted. Figure 8 and 9 were combined. 

Point 3: Figures 2 and 3 are not needed. The relevant information is quantified in a much better way in Figure 3. If those figures should make it into a supplement, there should also be a description of what is shown. I have no idea what the lines in Figure 2 are supposed to present.

Response 3: Figure 2 and 3 were joined to explain the variation of the volcanic plume thickness that is now included into a new paragraph. Figure 4 is now Figure 1.

Point 4: Is it possible to exchange Figure 5 with something more quantitative, such as area of the ash plume at different time steps. Right now, the authors leave it to the readers to see whatever they want.

Response 4: Figure 5 was replaced with a new Figure 4 that shows only four satellite images at 00:00, 06:00, 12:00, and 18:00 UTC. Moreover, following the suggestion of the reviewer, the area covered by ash and SO2 has been added.

Point 5: The information in Table 1 could easily be mentioned in a statement in the text. Also, what is meant with negative wind direction? This should be defined in the caption.

Response 5: Following the suggestion of the reviewer, Table 1 was deleted and some new statements were only added the text to explain the variation of wind direction with the altitude.

Point 6: Table 2 adds no value. It would be sufficient to provide daily mean values in the discussion of the AOD time series.

Response 6: Table 2 was deleted and the mean values were added in the text.

Point 7: Figure 6 should be combined to two panels, maybe even adding the profiles in Figure 10. Also, omit the point so that the lines are not fully blocked.

Response 7: Following the suggestion of the reviewer, we modify Figure 6 combining it with Figure 10.

Point 8: Figure 7 should be omitted. It is not being discussed and there is no description of how PBL height was derived from the lidar measurement. Just give the values in the text.

Response 8: Following the suggestion of the reviewer, Figure 7 was deleted and results moved in the text.

Point 9: Figures 8 and 9b should be combined. Focus on AOD at 2 or 3 wavelength and one AE, maybe 440/870. Why do you show TPC when it's not discussed in the text?

Response 9: Following the suggestion of the reviewer, Figure 8 and Figure 9 were combined (now Figure 6).

Point 10: Figure 10 could be combined with Figure 6. In any case, get rid of the points.

Response 10: Done, see previous comment.

Point 11: Figure 12 could combine all profiles in a single panel for easier comparison.

Response 11: Done.

Reviewer 2 Report

General comments:

1. The structure and content of the abstract are improper. The first partof the abstract are background introductions, but only the last two sentences are the highlights. However, the author did not give specific support for the highlights. It is recommended to reorganize and explain clearly. For example, what important implication does the lidar observations have for the algorithm that analyze satellite data. And why “this work gives new insights on the main features of volcanic plumes produced during prolonged ash emission having low intensity”. In short, the authors should give a more direct description in the abstract, especially the quantitative result analysis.
2. It is not clear why the authors chose different times in different figures (Fig.6, Fig.7, Fig.10 and Fig.12). In other words, more words are needed to show how and why the authors selected these times in the analysis.
3. Most of the drawings in this paper have errors in detail and lack aesthetics, so it is recommended to check and redraw.
4. As there are some grammatical errors and rigorous language, it is necessary to check the English writing of this paper.
5. This paper is mostly a statement of data. For a case study, the author did not give a specific difference analysis between this one and other cases，there is a lack of correlation analysis between remote sensing data. Authors could enhance the understanding of the needs of the users in order to improve the application effect of volcanic ash emission remote sensing data.

 

Specific comments:

1. Line 24: Change “last years” to “the last year”.
2. Line 30: Change “on last day” to “on the last day”.
3. Line 33: Change “shows” to “show”.
4. Line 45: Check the space between the letters of “fractu res”.
5. Line 65: Delete “(3)”.
6. Line 211-213: A description of time should be added in Fig.6, and the figures can be merged and indicated by different colors.
7. Line 215-217: The time displayed in Fig.7 is inconsistent with the title of the figure.
8. Line 244-246: “TCM” in Fig.8 is inconsistent with “TCW” in the title of the figure.
9. Line 247-251: For Fig. 9, it is recommended to divide the left and right figures into pictures a and b. Besides, the resolution of the right one is too low. Moreover, the meaning of each line is not marked in Fig.9, and the meaning of the blue curve is not clearly explained in its title.
10. Line 263: add “of” before “~1-25”.
11. Line 268: “355 nm (blu)” should be changed to “355 nm (blue)” in thetitle of10.
12. Line 281: Change “3.4” to “3.3”.
13. Line 312: Move “using”, and change “different remote sensing systems” to “using different remote sensing systems”.
14. Line 322: Change “his” to “its”.

 

Author Response

Point 1: The structure and content of the abstract are improper. The first part of the abstract are background introductions, but only the last two sentences are the highlights. However, the author did not give specific support for the highlights. It is recommended to reorganize and explain clearly. For example, what important implication does the lidar observations have for the algorithm that analyze satellite data. And why “this work gives new insights on the main features of volcanic plumes produced during prolonged ash emission having low intensity”. In short, the authors should give a more direct description in the abstract, especially the quantitative result analysis.

Response 1: The structure and content of the abstract were improved following the suggestion of MDPI article template. As suggested by the reviewer, we added more quantitative results. The double stratification is important because satellite retrievals consider only one plume layer (often 1 km). The explanation was added in the text.

Point 2: It is not clear why the authors chose different times in different figures (Fig.6, Fig.7, Fig.10 and Fig.12). In other words, more words are needed to show how and why the authors selected these times in the analysis. Most of the drawings in this paper have errors in detail and lack aesthetics, so it is recommended to check and redraw.

Response 2: In Figure 6 we selected two measurements before and after 13:00 when there is a variation of explosive activity. Consequently we could consider representative of two different period. In Figure 10 we plot the Lidar measurements using also the Raman channels. Figure 7 was deleted. In Figure 10 we selected 4 different time step by 1 hour (two before 13.30 and two after 13:00). However, following the suggestion of the reviewer 1, the most of figures were combined, modified and improved. In this new version there is only one Figure which plot Lidar measurements. Furthermore, why we chose the Lidar measurements at different time was also added in the text.

Point 3: As there are some grammatical errors and rigorous language, it is necessary to check the English writing of this paper.

Response 3: The paper was now corrected by Steve Conwey, a native English mother tongue for our Institution that is strongly thanked.  

Point 4: This paper is mostly a statement of data. For a case study, the author did not give a specific difference analysis between this one and other cases.There is a lack of correlation analysis between remote sensing data. Authors could enhance the understanding of the needs of the users in order to improve the application effect of volcanic ash emission remote sensing data.

Response 4: We thanks the reviewer. We added the main differences among different instruments.  

Point 5: Line 24: Change “last years” to “the last year”.

Response 5: The sentence was modified.

Point 6: Line 30: Change “on last day” to “on the last day”.

Response 6: Done.

Point 7: Line 33: Change “shows” to “show”.

Response 7: Done.

Point 8: Line 45: Check the space between the letters of “fractu res”.

Response 8: Done.

Point 9: Line 65: Delete “(3)”.

Response 9: Done.

Point 10: Line 211-213: A description of time should be added in Fig.6, and the figures can be merged and indicated by different colors.

Response 10: Figure 6 was merged with Figure 10 and a description of time was added.

Point 11: Line 215-217: The time displayed in Fig.7 is inconsistent with the title of the figure.

Response 11: Following the reviewer 1/2, Figure 7 was deleted.

Point 12: Line 244-246: “TCM” in Fig.8 is inconsistent with “TCW” in the title of the figure.

Response 12: Following the reviewer 1/2, TCM was deleted.

Point 13: Line 247-251: For Fig. 9, it is recommended to divide the left and right figures into pictures a and b. Besides, the resolution of the right one is too low. Moreover, the meaning of each line is not marked in Fig.9, and the meaning of the blue curve is not clearly explained in its title.

Response 13: Following the reviewer 1, Figure 9 was combined with Figure 8 and the MODIS images was deleted. The meaning of the blue line is added in the text.

Point 14: Line 263: add “of” before “~1-25”.

Response 14: Done.

Point 15: Line 268: “355 nm (blu)” should be changed to “355 nm (blue)” in the title of10.

Response 15: Done.

Point 16: Line 281: Change “3.4” to “3.3”.

Response 16: Done.

Point 17: Line 312: Move “using”, and change “different remote sensing systems” to “using different remote sensing systems”.

Response 17: Done.

Point 18: Line 322: Change “his” to “its”.

Response 18: Done.

Reviewer 3 Report

Review of "Multi sensor analysis of volcanic ash emission" by Scollo et al., 2020. The submitted manuscript analyzes a volcanic eruption from Etna, Sicily in December 2018.

The topic  is relevant to the journal because the characterization of the ash layers is crucial, especially for aviation purposes.

For this reason, the manuscript needs some improvement before publication.  Most of the remote sensing techniques should be described in detail while now the interpretation is left to the reader.

This fact is especially true for the lidar retrievals. It is missing a table stating the lidar technical parameters. Moreover, it is not clear if AMPLE is a prototype developed at the university or if it is a commercial lidar.  A very delicate point is the mass concentration retrieval. In fact, are needed three wavelengths to have a reliable measurement. In the manuscript, it is not at all specified.

Retrievals at Figure 12 don't show any error bars and seem to be too good to be true.

The attached file shows some specific comments.

Comments for author File: Comments.pdf

Author Response

Point 1: Review of "Multi sensor analysis of volcanic ash emission" by Scollo et al., 2020. The submitted manuscript analyzes a volcanic eruption from Etna, Sicily in December 2018. The topic  is relevant to the journal because the characterization of the ash layers is crucial, especially for aviation purposes. For this reason, the manuscript needs some improvement before publication.  Most of the remote sensing techniques should be described in detail while now the interpretation is left to the reader.

Response 1: We thanks the reviewer. We followed his/her suggestion improving the method section mainly in the camera, Lidar and satellite sub-sections.

Point 2: This fact is especially true for the lidar retrievals. It is missing a table stating the lidar technical parameters. Moreover, it is not clear if AMPLE is a prototype developed at the university or if it is a commercial lidar. 

Response 2: AMPLE is a prototype and this statement was added in the text. Lidar technical parameters can be found in Boselli et al. (2018) that was widely cited in the paper. 

Point 3: A very delicate point is the mass concentration retrieval. In fact, are needed three wavelengths to have a reliable measurement. In the manuscript, it is not at all specified.

Response 3: The reviewer is right. In fact our analysis is an estimation of volcanic ash mass concentration using several approximations that were added in the text. Some considerations and the error analysis were added also in the discussion section. We hope in the next future to implement the Lidar in order to have three different wavelengths.

Point 4: Retrievals at Figure 12 don't show any error bars and seem to be too good to be true.

Response 4: The error was added in the caption.

Point 5: The attached file shows some specific comments.

Response 5: We followed all specific comments in the attached pdf.

Round 2

Reviewer 1 Report

The authors have considered all my concerns and I have no further objections to publishing this work.

Author Response

We thank the reviewer for his/her useful suggestions and comments that have greatly increased the quality of the paper.

Reviewer 3 Report

The authors improved the manuscript with respect to the past version resolving all the pending issues. Currently in the title a space is needed between "volcanic" and "plume"

Author Response

We thank the reviewer for his/her useful suggestions and comments that have greatly increased the quality of the paper. The space in the title was added.