Multisensor validation of tidewater glacier flow fields derived from synthetic aperture radar (SAR) intensity tracking

Rohner, Christoph; Small, David; Beutel, Jan; Henke, Daniel; Lüthi, Martin P.; Vieli, Andreas

doi:https://doi.org/10.5194/tc-13-2953-2019

Articles | Volume 13, issue 11

https://doi.org/10.5194/tc-13-2953-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/tc-13-2953-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 13, issue 11

Research article

|

13 Nov 2019

Research article |

| 13 Nov 2019

Multisensor validation of tidewater glacier flow fields derived from synthetic aperture radar (SAR) intensity tracking

Christoph Rohner, David Small, Jan Beutel, Daniel Henke, Martin P. Lüthi, and Andreas Vieli

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Final revised paper (published on 13 Nov 2019)
Preprint (discussion started on 21 Jan 2019)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review of: Multisensor validation of tidewater glacier flow fields derived from SAR intensity tracking, by: Rohner et al. for The Cryosphere (tc-2018-278)', Anonymous Referee #1, 20 Feb 2019
- AC1: 'Response to reviewers', Christoph Rohner, 31 May 2019
RC2: 'Comments of “Multisensor validation of tidewater glacier flow fields derived from SAR intensity tracking” by Rohner et al.', Anonymous Referee #2, 12 Apr 2019
- AC1: 'Response to reviewers', Christoph Rohner, 31 May 2019

Peer-review completion

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

ED: Reconsider after major revisions (27 Jun 2019) by Stef Lhermitte

AR by Christoph Rohner on behalf of the Authors (04 Jul 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (09 Jul 2019) by Stef Lhermitte

RR by Anonymous Referee #1 (16 Aug 2019)

Suggestions for revision or reasons for rejection

2nd Review of: Multisensor validation of tidewater glacier flow fields derived from SAR intensity tracking
By: Rohner et al. for The Cryosphere (Ms. Ref. No tc-2018-278)

General comments

The comments here concern the revised version of the manuscript by Rohner et al. on multisensor validation of tidewater glacier flow fields derived from SAR intensity tracking. The paper has improved, and the authors addressed most of my earlier comments sufficiently. The revisions include recalculations, clarifications, corrections, additional references, as well as an added section and adjusted and new figures. The additional scrutiny appears to have led to changes in some of the reported numbers.

I appreciate the efforts by the authors to clarify their adopted approach, but I do not think that the issue regarding the sampling interval is adequately solved by simply down-sampling the strongly overlapping template patches in a final step. Nor do I believe that it makes much sense to use a 2-pixel sampling step to ‘improve the representation of velocity gradients’ near the calving front as stated now in the newly added paragraph 4.1. For this, the sampling step is not so much of relevance but rather the patch size. What you end up with now is, for the example stated (2 px. versus 40 px. in x and y direction), a 400(!) times higher computational cost for measurements that are more than 98% the same, i.e. for each correlation window 98% of the measurement is basically the same as the previous one (you gain less than 2% new information). Finally down-sampling the strongly auto-correlated measurements seems to me a waste of computational resources (‘higher computational cost’ (see 4.1) is rather an understatement in this respect). Maybe for some particular cases it could make sense, I am not sure, but certainly not on an operational basis at the ice sheet scale, as the last paragraph in the conclusions and abstract seem to suggest. These conclusions seem to me not justified but I leave it up to the editor to decide on this. That said, at least the methods are now better documented and some sections have been improved considerably. A few additional minor comments for consideration:

Pg 2 ln 10: remote sensing systems -> remote sensing data
Pg 2. Ln 17: with a relatively -> with relativel
Pg2. Ln 18: remove ‘as well as’

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RR by Anonymous Referee #2 (28 Aug 2019)

ED: Publish subject to minor revisions (review by editor) (30 Aug 2019) by Stef Lhermitte

AR by Christoph Rohner on behalf of the Authors (12 Sep 2019) Author's response Manuscript

ED: Publish as is (27 Sep 2019) by Stef Lhermitte

Short summary

The recent increase in ice flow and calving rates of ocean–terminating glaciers contributes substantially to the mass loss of the Greenland Ice Sheet. Using in situ reference observations, we validate the satellite–based method of iterative offset tracking of Sentinel–1A data for deriving flow speeds. Our investigations highlight the importance of spatial resolution near the fast–flowing calving front, resulting in significantly higher ice velocities compared to large–scale operational products.