Relationship between wind observation accuracy and the ascending node of the sun-synchronous orbit for the Aeolus-type spaceborne Doppler wind lidar

Zhang, Chuanliang; Sun, Xuejin; Lu, Wen; Shi, Yingni; Dou, Naiying; Li, Shaohui

doi:https://doi.org/10.5194/amt-14-4787-2021

Articles | Volume 14, issue 7

https://doi.org/10.5194/amt-14-4787-2021

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

Special issue:

Aeolus data and their application (AMT/ACP/WCD inter-journal...

https://doi.org/10.5194/amt-14-4787-2021

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

Articles | Volume 14, issue 7

Research article

|

07 Jul 2021

Research article |

| 07 Jul 2021

Relationship between wind observation accuracy and the ascending node of the sun-synchronous orbit for the Aeolus-type spaceborne Doppler wind lidar

Chuanliang Zhang, Xuejin Sun, Wen Lu, Yingni Shi, Naiying Dou, and Shaohui Li

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Final revised paper (published on 07 Jul 2021)
Preprint (discussion started on 29 Jun 2020)

Interactive discussion

Status: closed

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

- Printer-friendly version

- Supplement

RC1: 'Evaluation of optional orbits for an Aeolus follow-on mission', Gert-Jan Marseille, 13 Jul 2020
- AC1: 'Reply to RC1', Chuanliang Zhang, 15 Oct 2020
- AC2: 'Reply to RC2', Chuanliang Zhang, 15 Oct 2020
RC2: 'Comment on "On the relationship between wind observation accuracy and the ascending node of sun-synchronous orbit for the Aeolus-type spaceborne Doppler wind lidar"', Karsten Schmidt, 18 Aug 2020
- AC1: 'Reply to RC1', Chuanliang Zhang, 15 Oct 2020
- AC2: 'Reply to RC2', Chuanliang Zhang, 15 Oct 2020

Peer-review completion

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

AR by Chuanliang Zhang on behalf of the Authors (30 Jan 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (01 Feb 2021) by Ad Stoffelen

RR by Anonymous Referee #3 (15 Feb 2021)

Suggestions for revision or reasons for rejection

The authors provide suggestions for future Aeolus-type follow-on missions, with different local overpass times compared to 6/18 UTC (dawn-dusk) for Aeolus and taking into account increased solar background radiation in measured Aeolus signals, hence reduced data quality, as a consequence of selecting different sun-synchronous orbits.

I thank the authors for considering my earlier review and corresponding comments to improve the manuscript.

Some aspects are still not convincing enough in my view.

point 1
====
line 10: "For that the future spaceborne DWLs may not operate on sunsynchronous dawn-dusk orbits due to their observation purposes"

The "observation purposes" have not been mentioned in the text. The authors seem to suggest in lines 52-53 that being more flexible on orbit selection for an Aeolus follow-on (FO) mission, rather than fixed to dawn-dusk as in Marseille (2008), offers the possibility to sample the diurnal cycle with Aeolus.

The motivation or need for Aeolus-FO to sample the diurnal cycle is not given in the text. The authors could refer here to the WMO OSCAR database which provides a list of requirements for future observing systems to be beneficial for NWP, among others (http://www.wmo-sat.info/oscar/requirements, see Ids 311-313). Aeolus meets the observation cycle threshold requirement of 12 hours. The orbits suggested by the authors improve on this, approaching the "breakthrough" requirement.

Another motivation for flying other than dawn-dusk is experience from scatterometer use in global NWP. Scatterometers measure winds near the ocean surface. It has been demonstrated that scatterometers provide independent information to NWP for overpass times separated by only ~3 hours (Indian scatterometer OSCAT with ~12UTC local overpass time provides independent information relative to ASCAT with ~9:30 local overpass time). Some details are found in figure 24 of the pdf at
https://www.knmi.nl/kennis-en-datacentrum/publicatie/research-and-development-in-europe-on-global-application-of-the-oceansat-2-scatterometer-winds

point 2
====
I am not convinced that the simulations of SBR are representative for Aeolus. Figure 2c of the rebuttal shows values up to 5e+5 ACCD counts, while Figure 2b (also winter period) shows values a factor of 10 higher. How can the authors conclude that "the number of ACCD counts is consistent"?

Regarding Figure 4 of the rebuttal and figure 2 of the supplement. First the authors conclude: "The comparisons between Fig. 4 and Fig. 2 of the supplement show large difference." Can the authors explain this large difference?

"However, the uncertainties of wind observation are about 2∼3 m/s when the SBR is about 72.19 mW·m−2·sr−1·nm−1". The value of 72.19 corresponds to a "typical" SBR value, which is plotted as a red curve in Figure 4. I cannnot see uncertainly values of 2-3 m/s in this plot. Can the authors please explain?

========

In the rebuttal the authors state: "In the manuscript, Aeolus was assumed to be operated on best case scenario." Please add this to the abstract explicitly, to ensure that the context of the manuscript is very clear for all readers already at the beginning, also for those readers who are used to work with real Aeolus data, whose random error is substantially worse than the best case scenario presented in the manuscript.

Line 316: "The comparison illustrates that SBR caused the maximum increase in the averaged wind observation uncertainty of about 3.04-2.61=0.43 m/s for Aeolustype DWLs operating on the sun-synchronous orbits."
That is actually a marginal degradation, so that could be an argument to fly other than dawn dusk, in case of flying more than a single Aeolus type instrument at the same time. These random error values correspond to the right hand side of the last figure in the supplementary material, which shows an increase of 1.2 m/s random error between typical and worst case SBR scenario, so a factor of 3 larger increase than simulated by the authors. It seems that the simulated results of the authors are much more positive than what can be infered from real Aeolus data. Can the authors please comment?

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RR by Karsten Schmidt (16 Feb 2021)

ED: Reconsider after major revisions (18 Feb 2021) by Ad Stoffelen

AR by Chuanliang Zhang on behalf of the Authors (16 Apr 2021) Author's response Author's tracked changes Manuscript

ED: Publish subject to technical corrections (28 Apr 2021) by Ad Stoffelen

AR by Chuanliang Zhang on behalf of the Authors (09 May 2021) Author's response Manuscript

Short summary

The first spaceborne doppler wind lidar (DWL) Aeolus operates on sun-synchronous dawn–dusk orbit to lower the impact of solar background radiation (SBR) on wind observation accuracy. Increased SBR leads to an increment of averaged wind observation uncertainties from 0.19 to 0.27 m s^-1 comparing Aeolus and two added spaceborne DWLs operating on orbits with local ascending times of 15:00 and 12:00 LT. A quantitative design of laser pulse energy according to accuracy requirements is also proposed.