On the resolutions of ocean altimetry maps

Ballarotta, Maxime; Ubelmann, Clément; Pujol, Marie-Isabelle; Taburet, Guillaume; Fournier, Florent; Legeais, Jean-François; Faugère, Yannice; Delepoulle, Antoine; Chelton, Dudley; Dibarboure, Gérald; Picot, Nicolas

doi:https://doi.org/10.5194/os-15-1091-2019

Articles | Volume 15, issue 4

https://doi.org/10.5194/os-15-1091-2019

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

Special issue:

The Copernicus Marine Environment Monitoring Service (CMEMS):...

https://doi.org/10.5194/os-15-1091-2019

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

Articles | Volume 15, issue 4

Research article

|

20 Aug 2019

Research article |

| 20 Aug 2019

On the resolutions of ocean altimetry maps

Maxime Ballarotta, Clément Ubelmann, Marie-Isabelle Pujol, Guillaume Taburet, Florent Fournier, Jean-François Legeais, Yannice Faugère, Antoine Delepoulle, Dudley Chelton, Gérald Dibarboure, and Nicolas Picot

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Final revised paper (published on 20 Aug 2019)
Preprint (discussion started on 07 Jan 2019)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'On the resolutions of ocean altimetry maps', Fu Lee Lueng, 28 Jan 2019
- AC1: 'Response to Lee Lueng Fu review', Maxime Ballarotta, 23 May 2019
RC2: 'Review comments on : "On the resolutions of ocean altimetry maps"', Anonymous Referee #2, 18 Feb 2019
- AC2: 'Response to anonymous review', Maxime Ballarotta, 23 May 2019
RC3: 'Review of paper submitted to Ocean Science: ``On the resolutions of ocean altimetry maps" by Ballarotta, Ubelmann, Pujol, Taburet, Fournier, Legais, Faugere, Chelton, Dibarboure, and Picot', Tom Farrar, 27 Mar 2019
- AC3: 'Response to Tom Farrar review', Maxime Ballarotta, 23 May 2019
  - AC4: 'Notebooks', Maxime Ballarotta, 23 May 2019

Peer-review completion

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

AR by Maxime Ballarotta on behalf of the Authors (23 May 2019) Manuscript

ED: Referee Nomination & Report Request started (11 Jun 2019) by Emil Stanev

RR by Anonymous Referee #2 (24 Jun 2019)

RR by Tom Farrar (26 Jun 2019)

Suggestions for revision or reasons for rejection

Review of "On the resolutions of ocean altimetry maps" by Ballarotta et al. (submitted to Ocean Science)

The authors have improved the manuscript dramatically in their revised version. I believe the new analysis method is sound, and the description of what was done is also much clearer. It seems like a substantially different paper than the previous version I reviewed, and I am happy to recommend publication after minor revisions. I would also like to thank the authors for their pleasant and constructive attitude in responding to my previous, critical review. (There were actually two versions of the previous review-- I made an updated one with more detail and gave it to the authors directly, but the OSD system would not allow me to upload that review because the online discussion period had ended. I am uploading that review now.)

My only substantial reservation about this version of the manuscript has to do with the approach and conclusion about the temporal resolution. Something does not add up, as described in the following paragraph. I suggest the authors investigate this a little more and either add this as a caveat and change the plot and conclusions accordingly, or adjust the analysis to have finer frequency resolution.

Page 4, lines 26+: There is another important consequence of choosing to analyze 100-day segments. This sets the coarseness of the resulting evaluation of temporal resolution, by setting the frequency resolution of the spectral analysis. For 100-day segments, the frequency resolution is 1/100 cycles per day (cpd) (actually, the frequency resolution is effectively somewhat less because of the taper window, but I think it is the frequency grid that matters here). If the record chunks are actually 100 days long as stated (instead of 100 data points long), the frequency bands will be centered at frequencies corresponding to periods of 101, 50.5, 33.67, 25.25, 20.20, 16.83, and 14.43 days. This means that the analysis should only be able to coarsely determine the temporal resolution (e.g., 50.5 days versus 33.67 days). It seems to me that the color scale chosen for displaying the results is thus misleading, or else, there has been some kind of interpolation of the spectral results to arrive at values between 34 and 50 days. It is not clear to me that such interpolation would be a valid approach.

Page 6, line 6: I do not think Figure 3 supports the claim that midlatitude temporal resolution is 14-28 days. I see lots of points in midlatitudes that are dark red (~45 days). Furthermore, as noted above, something seems inconsistent about the frequency resolution of the analysis and the higher frequency resolution at which the results are being stated.

Minor comment:
Figure B1c: What are the white areas?

Referee Report: PDF

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ED: Publish subject to minor revisions (review by editor) (05 Jul 2019) by Emil Stanev

AR by Maxime Ballarotta on behalf of the Authors (12 Jul 2019) Author's response Manuscript

ED: Publish as is (16 Jul 2019) by Emil Stanev

AR by Maxime Ballarotta on behalf of the Authors (19 Jul 2019) Manuscript

Short summary

This study investigates the resolving capabilities of the DUACS gridded products delivered through the CMEMS catalogue. Our method is based on the noise-to-signal ratio approach. While altimeter along-track data resolve scales on the order of a few tens of kilometers, we found that the merging of these along-track data into continuous maps in time and space leads to effective resolution ranging from ~ 800 km wavelength at the Equator to 100 km wavelength at high latitude.