Combining satellite observations to develop a global soil moisture product for near-real-time applications

Enenkel, Markus; Reimer, Christoph; Dorigo, Wouter; Wagner, Wolfgang; Pfeil, Isabella; Parinussa, Robert; De Jeu, Richard

doi:https://doi.org/10.5194/hess-20-4191-2016

Articles | Volume 20, issue 10

https://doi.org/10.5194/hess-20-4191-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/hess-20-4191-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 20, issue 10

Research article

|

17 Oct 2016

Research article |

| 17 Oct 2016

Combining satellite observations to develop a global soil moisture product for near-real-time applications

Markus Enenkel, Christoph Reimer, Wouter Dorigo, Wolfgang Wagner, Isabella Pfeil, Robert Parinussa, and Richard De Jeu

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Final revised paper (published on 17 Oct 2016)
Supplement to the final revised paper
Preprint (discussion started on 03 Nov 2015)

Interactive discussion

Status: closed

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

- Printer-friendly version

- Supplement

RC C5835: 'Interactive comment on "Combining satellite observations to develop a daily global soil moisture product for a wide range of applications" by Enenkel et al.', Anonymous Referee #1, 26 Dec 2015
- AC C6497: 'Reply to Reviewer #1', M.E. Enenkel, 01 Feb 2016
RC C6396: 'Review of "Combining satellite observations to develop a daily global soil moisture product for a wide range of applications"', Anonymous Referee #2, 27 Jan 2016
- AC C6500: 'Reply to Reviewer #2', M.E. Enenkel, 01 Feb 2016

Peer-review completion

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

ED: Reconsider after major revisions (17 Feb 2016) by Alexander Loew (deceased)

AR by Markus Enenkel on behalf of the Authors (10 Apr 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (20 Apr 2016) by Alexander Loew (deceased)

RR by Anonymous Referee #1 (02 May 2016)

RR by Anonymous Referee #2 (01 Jun 2016)

Suggestions for revision or reasons for rejection

This is a well-written manuscript that presents a comparison of retrospective versus NRT CCI soil moisture products generated during 2013. From an applications point of view, this paper provides a valuable assessment of the decline in quality expected in NRT soil moisture products (versus a retrospective benchmark). However, because of the weakness described below, the paper still lacks a clear methodological contribution. A number of these issues were raised in my original review and, unfortunately, were not adequately addressed in this round of revisions.

Therefore, I’d (still) recommend revision focusing on the following points:

1) The paper still offers no clear description of what specific methodological differences (e.g. calibration issues, screening difference and algorithm parameterizations) exist between the retrospective and NRT CCI soil moisture data sets and how these differences may potentially lead to retrospective versus NRT differences in SM products. Without a clear understanding of these source differences, it’s difficult for the reader to gain any real insight from the SM comparison results presented in the paper. Towards the beginning of the paper the author’s need to summarize these differences and present (at least) some cursory discussion of their expected impact. I understand that some of the differences might require a tedious level of detail/explanation…in these cases it would be fine to keep the discussion at a relatively high level.

2) While there is some attribution discussion in Section 5, it is presented in a cursory and unsatisfying manner. For instance, lines 381-382 say that “Since most of these regions are covered by AMSR2, the most likely error sources are the GLDAS-based rescaling parameters.”

There are two issues here. First, both AMSR2 and ASCAT soil moisture products are rescaled via by “GLDAS-based rescaling parameters”, so it’s unclear why the use of AMSR2 in these regions points to a re-scaling problem. Second, the “problems” being referred to are associated with poor temporal correlations. This is odd since correlations should be minimally impacted by rescaling (i.e., correlation is not impacted by any kind of linear scaling).

3) Along the same lines, in lines 392-394 it is unclear how a 2013 (retrospective versus NRT) bias can be attributed to a AMSR-E/AMSR2 cross-calibration issue given that AMSRE stopped functioning in 2010 and obviously played no direct role in the generation of any 2013 soil moisture product. I suspect that there is a subtle calibration/scaling issue at play here - whereby AMSRE does, in fact, end up impacting the calibration of the 2013 soil moisture results. However no explanation is given on exactly what this issue/connection is.

4) Same issue with line 396 – which mentions the potential benefits of a “dynamic snow map for ASCAT.” The sounds plausible but it’s also not clear how snow mapping errors may be affecting the observed retrospective versus NRT differences. Is snow masking applied differently in the two products? I couldn’t find any discussion on this issue. The same issue with the RFI masking mentioned later in the paragraph…how exactly does this issue lead to retrospective versus NRT differences (i.e. the core issue examined in the paper)?

5) In contrast, Lines 400-404 are very good…they clearly describe how ASCAT calibration issues may be driving retrospective versus NRT differences. I’d really like to see more of that in a revised version.

So, in summary, I’d still urge the authors to spend more time: 1) describing/listing the underlying sources of retrospective versus NRT soil moisture differences and 2) providing a better attribution discussion which clarifies the connection between these sources of differences with specific inter-comparison results presented in the paper (see above for specific advice on how to do this). I don’t think this would require a significant amount of re-writing…just a modest amount of additional text in Sections 1 and 5 or the revised manuscript.

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ED: Reconsider after major revisions (08 Jun 2016) by Alexander Loew (deceased)

AR by Markus Enenkel on behalf of the Authors (20 Jul 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (21 Jul 2016) by Alexander Loew (deceased)

RR by Anonymous Referee #1 (17 Aug 2016)

ED: Publish as is (15 Sep 2016) by Alexander Loew (deceased)

AR by Markus Enenkel on behalf of the Authors (19 Sep 2016) Manuscript

Short summary

Soil moisture is a crucial variable for a variety of applications, ranging from weather forecasting and agricultural production to the monitoring of floods and droughts. Satellite observations are particularly important in regions where no in situ measurements are available. Our study presents a method to integrate global near-real-time satellite observations from different sensors into one harmonized, daily data set. A first validation shows good results on a global scale.