Sentinel-3 radar altimetry for river monitoring –  a catchment-scale evaluation of satellite water  surface elevation from Sentinel-3A and Sentinel-3B

Kittel, Cecile M. M.; Jiang, Liguang; Tøttrup, Christian; Bauer-Gottwein, Peter

doi:https://doi.org/10.5194/hess-25-333-2021

Articles | Volume 25, issue 1

https://doi.org/10.5194/hess-25-333-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/hess-25-333-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 25, issue 1

Research article

|

21 Jan 2021

Research article |

| 21 Jan 2021

Sentinel-3 radar altimetry for river monitoring – a catchment-scale evaluation of satellite water surface elevation from Sentinel-3A and Sentinel-3B

Cecile M. M. Kittel, Liguang Jiang, Christian Tøttrup, and Peter Bauer-Gottwein

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Final revised paper (published on 21 Jan 2021)
Preprint (discussion started on 15 May 2020)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review of hess-2020-165 manuscript', Anonymous Referee #1, 11 Jun 2020
- AC1: 'Response to anonymous referee #1', Cécile Kittel, 03 Aug 2020
RC2: 'Review of Kittel et al., 2020', Anonymous Referee #2, 18 Jun 2020
- AC2: 'Response to anonymous referee #2', Cécile Kittel, 03 Aug 2020

Peer-review completion

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

ED: Reconsider after major revisions (further review by editor and referees) (03 Aug 2020) by Jan Seibert

AR by Cécile Kittel on behalf of the Authors (03 Sep 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (21 Sep 2020) by Jan Seibert

RR by Anonymous Referee #1 (30 Sep 2020)

Suggestions for revision or reasons for rejection

The reviewed version of the manuscript has been quite improved by the authors. I only have minor suggestions below (line number refers to the manuscript version with changes highlighted, at the end of the authors replies to reviewers’ comments).

Specific comments:

Line 1: “Sentinel-3 is the first satellite altimetry mission to operate in Synthetic Aperture Radar (SAR) mode and in open-loop tracking mode nearly globally”, maybe replace “and in open-loop” with “and one of the first to have open-loop”. Indeed, Jason-3 also has open-loop targets nearly globally...

In their reply to my main concern, the authors wrote (among other):
“The purpose is not the specific Zambezi-database (although that is an important product of the study) but rather to demonstrate that by using the publicly available processing platforms, such databases can be created for any catchment globally. We believe that a framework to extract catchment-scale monitoring networks to suit specific study areas has a wide range of applications in hydrology”.
It is a fair purpose. I think it would be worth to state it even more clearly in the abstract (put similar words than what you wrote in your reply to my comment), maybe around line 4 of the abstract. It would be more impactful than a sentence like “demonstrate the potential application of Sentinel-3 for monitoring river interactions with wetlands and floodplains”, because 1- it was expected that S3A/B will indeed bring valuable information on these interactions, like previous altimetry mission and 2- you did not demonstrate much these interactions in the study, to my point of view.

Line 18-20: “This was largely related to the open-loop tracking mode: while correct on board elevation information is crucial, steep changes in the receiving window position can have detrimental effects on the WSE observations if post-processing options are not adapted.” This sentence bothers me. Indeed, the issue is that “nominal” parameters for the post-processing have been defined for close-loop cases. Your study is just showing that parameters has to be changed for open-loop mode, which makes sense. However, the open-loop mode itself is not “detrimental” to WSE estimation. As written, the sentence could give a false idea to readers unfamiliar with close-loop/open-loop modes. Please rewrite to acknowledge that as implemented, GPOD parameters (i.e. receiving window size) needs to be adjusted for open-loop mode.

Line 25: I would remove “which holds important implications for future hydrology-oriented missions”, because it is speculative and honestly, I don’t see how S3A/B coverage could have important implications for SWOT (just to cite the mission you were referring to in the previous version of the manuscript).

Line 104: “Sentinel-3 could potentially provide a much denser VS network than Jason-2 while maintaining a relatively short return period” I agree that S3A/B have a much denser VS network than J2/3, but writing that “maintaining a relatively short return period” is somewhat excessive. S3A/B repeat period is 27 days (to be compared to 10 days for J2/3 and to less than an hour for some automatic gauges). 27 days means one measurement and rarely two measurements per month… not well adapted even to compute monthly mean. It is better than Envisat, but it could not be labelled as “short return period” (it is overselling S3A/B time sampling).

Figure 1, in legend, contemporary in situ gauge corresponds to orange large dots, whereas on the map there are only green large dots.

Line 170: replace “global ACE2 DEM” with “global DEM”, as I think ACE2 is not used at all in the last versions of the OLTC. The sentence will be therefore more general.

Line 216-220: “the standard fixed-size receiving window of 256 samples cannot
store the elevation of all the samples in the echogram prior to Level-1b processing (e.g. Figure 5 in Dinardo et al. (2018)” The new explanation of the receiving window is still not clear to me. I don’t really see how the “receiving window” is different from the “range window”.

Section 3.1 and especially Table 3 deals with the SV fulfilling criteria on L1b and L2 in the two datasets. Among the ~250 VS that do not fulfill these criteria, how many are in open-loop mode and in close-loop mode?

Hydroweb has Jason-3 and S3A/B virtual stations that are “operational” (for some validated VS, after a thorough quality control), meaning that there are automatically updated. Will it be the case for your database? Is it possible with SciHub and/or GPOD to do such automatic update? Whatever the answer is, it will be good to add it in section 4 (especially in section 4.1).

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RR by Anonymous Referee #2 (14 Oct 2020)

ED: Publish subject to minor revisions (review by editor) (17 Oct 2020) by Jan Seibert

AR by Cécile Kittel on behalf of the Authors (23 Oct 2020) Author's response Manuscript

ED: Publish subject to technical corrections (25 Nov 2020) by Jan Seibert

AR by Cécile Kittel on behalf of the Authors (01 Dec 2020) Author's response Manuscript

Short summary

In poorly instrumented catchments, satellite altimetry offers a unique possibility to obtain water level observations. Improvements in instrument design have increased the capabilities of altimeters to observe inland water bodies, including rivers. In this study, we demonstrate how a dense Sentinel-3 water surface elevation monitoring network can be established at catchment scale using publicly accessible processing platforms. The network can serve as a useful supplement to ground observations.