Observing geometry effects on a Global Navigation Satellite System (GNSS)-based water vapor tomography solved by least squares and by compressive sensing

Heublein, Marion; Bradley, Patrick Erik; Hinz, Stefan

doi:https://doi.org/10.5194/angeo-38-179-2020

Articles | Volume 38, issue 1

https://doi.org/10.5194/angeo-38-179-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/angeo-38-179-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 38, issue 1

Regular paper

|

06 Feb 2020

Regular paper |

| 06 Feb 2020

Observing geometry effects on a Global Navigation Satellite System (GNSS)-based water vapor tomography solved by least squares and by compressive sensing

Marion Heublein, Patrick Erik Bradley, and Stefan Hinz

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Final revised paper (published on 06 Feb 2020)
Preprint (discussion started on 03 Jul 2019)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC1: 'comment', Anonymous Referee #1, 22 Aug 2019
- AC1: 'Answers to the referees' comments and revised manuscript', Marion Heublein, 26 Sep 2019
RC2: 'Observing geometry effects on a GNSS based water vapor tomography solved by Least Squares and by Compressive Sensing - review', Anonymous Referee #2, 28 Aug 2019
- AC2: 'Answers to the referees' comments and revised manuscript', Marion Heublein, 26 Sep 2019

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (further review by editor and referees) (01 Oct 2019) by Gunter Stober

AR by Marion Heublein on behalf of the Authors (05 Oct 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (07 Oct 2019) by Gunter Stober

RR by Anonymous Referee #1 (22 Oct 2019)

RR by Anonymous Referee #2 (03 Nov 2019)

Suggestions for revision or reasons for rejection

Dear authors,
thank you for accepting practically all of my minor comments and improving the manuscript in their regards. In case of major comments you unfortunatelly haven't repeated your processing using a vertical discretization with a higher number of layers as I recommended to you (i.e. at least with 10 vertical layers). I agree that your work is focused on evaluating the new methodology for GNSS tomography (CS), however the experiment still should be based on rational conditions under which the tomography can be providing some useful information about 3d water vapor field. I admit that in your revised version of the manuscript (namely in Section 5) you point out weaknesses of your study (including the discretization), however if you are really not able to repeat your processing using a more detailed vertical discretization (still based on sythetic slant delays and a single WRF simulation) I ask you to at least emphasize in the text the potential limitation of using only 5 vertical layers on the validity of the results. If this is done and my below given minor comments are solved, I can agree with the publication of your manuscript in Annales Geophysicae.

Minor comments (page and line numbering is based on the revised version of the manuscript):
- P1L18: I am not sure if "three dimensional (3d) atmospheric water vapor distribution is essential for climate research". I would say that climatologists are rather interested in spatio-temporal regional and global trends in water vapor 2D distribution and can live without the 3d information. Please reformulate the sentence accordingly or provide a reference for your statement.
- P1L20: Can you provide a reference for your statement that "a precise knowledge of the water vapor field e.g. is required for accurate deformation monitoring using InSAR."? Water vapor does not influence only microwave signals, it causes a problem also i.e. in optical remote sensing
- P8L3: I think you can shortly note in the text that numbers of signal directions you use as GPS-only or multi-GNSS are a bit pesimistic and in reality one can expect higher numbers. Usually at permanent GNSS stations (from which most of them have excellent visibility over the sky) you have 8-12 observations for GPS-only, 12-18 for GPS+GLONASS and we can expect around 25-35 satellites once Galileo and BeiDou are fully operational. Regarding the BeiDou - you answered my question that "there is no special reason." why you have ommited this system from your work, however I think you should inform the reader that there exists also this 4th GNSS which can be also used to increase the number of signal directions in tomography applications.
- P8: from L9 to L27 the text is repeated, I mean it is the same as text which you have from P7L24 to P8L9
- P8L28: in your section 3.4 you repeat some information which were already given and I think the rest of the information can (should) be provided within the section 3.3. Therefore I think sections 3.3 and 3.4 should be merged into one section to improve the readability of the manuscript.
- P10: what I see in figure 3 is: LSQ is everywhere except four boxes in the upper-left and lower-right corner providing better results than CS - although you summarize this in Section 5, I think you should mention it also here.
- P10L9: I recommend to replace "absolutely need to" from your sentence "... the chosen solution strategy as well as the effect of varying signal directions absolutely need to be taken into account." with "should be taken into account". Your statement with "absolutely" is too strong in my opininon considering the limited dataset you use.
- P11, figure3: please check figure for 5 signal directions/27 sites. It has some problem with plotting the caption for CS mean/std.
- P12: I am adressing my major comment for P8L13 from my previous review - in your reply you write: "We also analyzed differences among individual voxels but did not find any significant differences among the individual voxels. We also studied the distribution of the differences at various height levels. Yet, LSQ or CS did not systematically provide better / worse results either in the boundary layer or at the top of the troposphere." Please, add all this information to your manuscript to inform the reader about these results.
- P14L3: this is the first time in the manuscript you use term "ZWD", you should therefore provide its full meaning and ideally shortly desribe the relation between ZWD and SWD

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ED: Publish subject to minor revisions (review by editor) (06 Nov 2019) by Gunter Stober

AR by Marion Heublein on behalf of the Authors (23 Nov 2019) Author's response Manuscript

ED: Publish as is (27 Nov 2019) by Gunter Stober