GNSS Radio Occultation Advances the Monitoring of Volcanic Clouds: The Case of the 2008 Kasatochi Eruption

Round 1

Reviewer 1 Report

The authors present a study on the use of GNSS radio occultation to detect/monitor the height of volcanic clouds, which is an important issue not only for volcanologists but also for civil/military aviation. The injection height controls the plume dispersion in the  atmosphere, so there are links to global climate too. The article is well structured, the science is sound, the method is convincing, the topic is actual. I have minor concerns, that I express below. Therefore, I suggest the editor to publish this study after minor revisions.

My minor concerns:

the authors focus on the  2008 Kasatochi eruption. This happened more than ten years ago. I am sure that there is a specific reason why the authors concentrate their efforts on this specific past eruption (and not on a more recent one); I believe this particular reason should be mentioned clearly in the introduction. 

In the introduction, the authors state : "However, current  detection and monitoring techniques still suffer from resolution problems causing discrepancies between the different observation methods and dispersion models." In actual detection techniques, the authors do not mention recent advances in  photogrammetry based techniques, with improved spatial and vertical resolution. I suggest to mention :

de Michele M., Raucoules D., Arason Þ.,
Volcanic Plume Elevation Model and its velocity derived from Landsat 8, Remote Sensing of Environment, Volume 176, 2016, Pages 219-224, https://doi.org/10.1016/j.rse.2016.01.024.

Kahn, R.A., and J.A. Limbacher, 2012. Eyjafjalljökull Volcano Plume Particle-Type Characterization from Space-Based Multi-angle Imaging. Atmosph. Chem. Phys. 12, 9459–9477, doi:10.5194/acp-12-9459-2012.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Please find my review of the manuscript “GNSS radio occultation advances the monitoring of volcanic clouds: the case of the 2008 Kasatochi eruption” submitted to Remote sensing by Cigala et al.

This paper examines possibility in evaluation of volcanic cloud height by using GNSS RO BA profiles. The author dealt with the 2008 eruption at Kasatochi for the application, and compared with the results from GNSS RO with CALIOP which is satellite-based lidar system. The comparison shows that the evaluated height from GNSS RO have good agreement with that from CALIOP. As the GNSS network has been expanded worldwide and is low cost, the author suggests the GNSS RO methods can be used for automatic tracking of height of VCs.

This paper clearly shows the good agreement of the heights of volcanic cloud evaluated from GNSS RO and CALIOP. Thus, I agree with the author’s suggestion that GNSS RO have possibility to track the height of volcanic cloud with high accuracy. Therefore I recommend to publish this paper in Remote sensing after minor revisions. I summarized minor comments in the following.

Minor comments

L166. The author picked the peaks of GNSS RO after giving lower limit of altitude. However, it is difficult to give such the lower limit in advance in real-time monitoring. As Figure 1 shows, the vertical variation of BA anomaly have many peaks and it is difficult to pick appropriate peak without other constraint. I think it is crucial for automation of the VC altitude estimation for eruption monitoring. The explanation is needed.

L30. Can you show Figure for location of Kasatochi volcano? Figure 3 is too complex to identify the location.

L78. What’s the technique?

L82. 12km square?

L85-86. Can you add more explanations? For example, what is “a three-step approach”?

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

The paper entitled „ GNSS radio occultation advances the monitoring of volcanic clouds: the case of the 2008 Kasatochi eruption” is devoted to combined RO & imaging of the volcanic cloud evolution after the eruption as a tool for potential operational global cloud altitude monitoring

The paper is based on appropriate methods (to some extent), which are typically used for the integration of RO and lidar data for tracking natural phenomena. Thus it is a valuable contribution to the field of research on phenomena formed during a volcanic eruptions.

Article will be accepted after correction according to the below comments:

1. The authors claim that “present a novel cloud altitude detection methodology using the GNSS”. Before the publication authors should very clearly state in the text the novelty, especially against existing research, e.g.

a) Riccardo Biondi, Andrea K. Steiner, Gottfried Kirchengast, Hugues Brenot, Therese Rieckh, Supporting the detection and monitoring of volcanic clouds: A promising new application of Global Navigation Satellite System radio occultation, Advances in Space Research, Volume 60, Issue 12, 2017, Pages 2707-2722, https://doi.org/10.1016/j.asr.2017.06.039.

b) Biondi, R. and Steiner, A. and Kirchengast, G. and Brenot, H. and Rieckh, T., A novel technique including GPS radio occultation for detecting and monitoring volcanic clouds, Atmospheric Chemistry and Physics Discussions, 2016, pages 1--26, https://doi.org/10.5194/acp-2015-974

c) Cigala, Valeria & Biondi, Riccardo & Steiner, A.K. & Kirchengast, Gottfried & Brenot, Hugues, Detection and monitoring of the volcanic ash cloud top height applying the Global Navigation Satellite System Radio Occultation technique,

d) Biondi, Riccardo & Steiner, A.K. & Kirchengast, Gottfried & Brenot, Hugues & Rieckh, Therese. (2017). Supporting the detection and monitoring of volcanic clouds: A promising new application of Global Navigation Satellite System radio occultation. Advances in Space Research. https://doi.org/10.1016/j.asr.2017.06.039.

e) Wang, K.-Y., Lin, S.-C., and Lee, L.-C. ( 2009), Immediate impact of the Mt Chaiten eruption on atmosphere from FORMOSAT-3/COSMIC constellation, Geophys. Res. Lett., 36, L03808, https://doi.org/10.1029/2008GL036802

f) Ikuya Okazaki, Kosuke Heki, Atmospheric temperature changes by volcanic eruptions: GPS radio occultation observations in the 2010 Icelandic and 2011 Chilean cases, Journal of Volcanology and Geothermal Research, Volumes 245–246, 2012, Pages 123-127, https://doi.org/10.1016/j.jvolgeores.2012.08.018

and other publications from the field not mentioned above. Currently compared to existing research I don’t see the novelty.

2. Figure 1 is of very poor quality and should be changed and put into supplementary materials as a part of Figure S1.

3. Currently, GNSS systems are used more widely in the movements of Earth's crust caused by natural phenomena such as earthquakes or volcanic eruptions:

a) Lee, S.‐W., Yun, S.‐H., Kim, D. H., Lee, D., Lee, Y. J., and Schutz, B. E. ( 2015), Real‐time volcano monitoring using GNSS single‐frequency receivers, J. Geophys. Res. Solid Earth, 120, 8551– 8569, https://doi.org/10.1002/2014JB011648

b) Yu Chen, Dominique Remy, Jean-Luc Froger, Aline Peltier, Nicolas Villeneuve, José Darrozes, Hugo Perfettini, Sylvain Bonvalot, Long-term ground displacement observations using InSAR and GNSS at Piton de la Fournaise volcano between 2009 and 2014, Remote Sensing of Environment, Volume 194, 2017, Pages 230-247, https://doi.org/10.1016/j.rse.2017.03.038

c) Richter, E. Ivins, H. Lange, L. Mendoza, L. Schröder, J.L. Hormaechea, G. Casassa, E. Marderwald, M. Fritsche, R. Perdomo, M. Horwath, R. Dietrich, Crustal deformation across the Southern Patagonian Icefield observed by GNSS, Earth and Planetary Science Letters, Volume 452, 2016, Pages 206-215, https://doi.org/10.1016/j.epsl.2016.07.042

d) Tiryakioglu İ., Gulal E., Solak H.I., Ozkaymak C. (2018) Crustal Deformation Modelling by GNSS Measurements: Southwestern Anatolia, Turkey. In: Kallel A., Ksibi M., Ben Dhia H., Khélifi N. (eds) Recent Advances in Environmental Science from the Euro-Mediterranean and Surrounding Regions. EMCEI 2017. Advances in Science, Technology & Innovation (IEREK Interdisciplinary Series for Sustainable Development). Springer, Cham

whereas currently PPP is most common in use among other GNSS techniques, mainly due to the lack of errors of the reference stations:

a) İ. Şanlıoğlu, M. Zeybek, and C. Özer Yiğit, “Landslide Monitoring with GNSS-PPP on Steep-Slope and Forestry Area: Taşkent Landslide,” in ICENS International Conference on Engineering and Natural Science, 2016, pp. 1–7.

b) Maciuk, “GPS-only, GLONASS-only and Combined GPS+GLONASS Absolute Positioning under Different Sky View Conditions,” Teh. Vjesn. - Tech. Gaz., vol. 25, no. 3, Jun. 2018.

c) Szołucha, K. Kroszczyński, and D. Kiliszek, “Accuracy of Precise Point Positioning (PPP) with the use of different International GNSS Service (IGS) products and stochastic modelling,” Geod. Cartogr., vol. 67, no. 2, p. 207, 2018.

It would be a plus for this work if the authors wrote a few sentences about usage of GNSS techniques referring to the above  literature positions.

4. For a better interpretation of the readers please change data presented in Table 1 into a graph.

5. Figure 3 must be significantly enlarged and/or put into supplementary materials. In this form it is very illegible

6. For a better interpretation please change x-axis scale on all of the CALIOP backscatter images should be changed into equal geographical coordinates (e.g. Figure S2, latitude 35⁰, 40⁰,…, longitude -100⁰, -101⁰…

7.There are some typos and editorial lapse e.g. line 31 instead of ‘22:01UTC’ should be ’22:01 UTC’ and others

8. Tables A1 and A2 should be in supplementary materials.

Finally I recommend a publication of this paper in Remote Sensing after taking into account the above remarks.

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

Response 1. We added text in the Introduction (L61-66) that include now a comment on reference e) and f). Wang et al. (2009) and Okazaki et al. (2012) used for the first time GNSS RO to study the effect of volcanic eruptions on atmospheric temperature comparing RO profiles before and after the eruption. We extended the comment on reference a), indeed Biondi et al. 2017 made the very first attempt to use GNSS RO to detect VC altitude applying the same algorithm used in previous literature for the detection of convective clouds. In the current manuscript, we applied an algorithm based on the knowledge gained from Biondi et al. (2017) but specifically tuned to detect volcanic clouds.

We note that reference a) and c) correspond to the same paper, they have the same doi (Biondi et al., 2017, doi:10.1016/j.asr.2017.06.039). Reference b) is not an actual published paper; it was not accepted after revision as stated on the website. However, due to the journal policies of open discussion, the manuscript stays online with an assigned doi. Biondi et al. (2017) (reference a) above) is the actual published paper and the correct reference. Finally, reference c) is the abstract of a poster presented at the EGU’s General Assembly last April by the authors of the current manuscript and where we showed the preliminary results.

In this paper, at this stage I do not see anything new providing any kind of a novelty to already existing knowledge. A paper published in a journal indexed in JCR shall provide new methods or new results, and this article appears to be rather copy of existing publications and results. which already shows. Discussion and Conclusions sections are obvious and fully predictable, i.e. ‘Due to the nature of the refraction method, GNSS RO cannot differentiate between VCs and convective clouds’

Without very clearly statement of novelty comparing to other studies and the added value to the RO field I will not recommend this work for publication in RS.

Response 3. We agree with the Reviewer that ground-based GNSS systems are used for the monitoring of ground deformation and are indeed giving good results. However, in the present work, we focus on radio occultations resulting from satellite-based GNSS systems only. Thus, due to the very different nature of the techniques, we do not find it appropriate to add the above-mentioned references in the manuscript. We think they may lead to confusion for the readers.

I do not agree with the authors. I believe that showing other uses of GNSS systems in the field of Earth’s crust deformation is an added value, it will not lead to confusion for the readers. Please add a paragraph about other uses of GNSS systems in analyzed field based on the proposed positions.