A revised ocean glider concept to realize Stommel's vision and supplement Argo floats

Bruvik, Erik M.; Fer, Ilker; Våge, Kjetil; Haugan, Peter M.

doi:https://doi.org/10.5194/os-16-291-2020

Articles | Volume 16, issue 2

https://doi.org/10.5194/os-16-291-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/os-16-291-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 16, issue 2

Research article

|

06 Mar 2020

Research article |

| 06 Mar 2020

A revised ocean glider concept to realize Stommel's vision and supplement Argo floats

Erik M. Bruvik, Ilker Fer, Kjetil Våge, and Peter M. Haugan

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Final revised paper (published on 06 Mar 2020)
Preprint (discussion started on 02 May 2019)

Interactive discussion

Status: closed

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

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RC1: 'Note to the Editor', Anonymous Referee #1, 17 May 2019
- AC1: 'Short response to referee 1', Erik Magnus Bruvik, 24 May 2019
- AC3: 'Final response to review', Erik Magnus Bruvik, 04 Nov 2019
RC2: 'review', Anonymous Referee #2, 08 Oct 2019
- AC2: 'Final response to reviews and letter to the editor', Erik Magnus Bruvik, 04 Nov 2019

Peer-review completion

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

AR by Erik Magnus Bruvik on behalf of the Authors (25 Nov 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (10 Dec 2019) by Oliver Zielinski

RR by Lucas Merckelbach (06 Jan 2020)

Suggestions for revision or reasons for rejection

Dear Authors,

Thank you for providing thought-through responses to the issues I have raised. I generally don't feel qualified to make language suggestions, but when reading I thought it might be best to:

p.2/l.13) The use of "Only" gives this sentence an unnecessary negative sound. Perhaps you can consider an alternative (However, or replace only by though used later in the sentence).

and

reread the larger parts of inserted text in the revised manuscript, as I think they don't connect always so well with the context they are placed in. Reshuffle or provide a connecting sentence.

Also I would like to ask you to carefully check the references. I noticed that McMasters and Schmitz are not listed in the references. Perhaps others are missing too. I didn't check all of them.

p6 l29 Recently work by Merckelbach and coworkers was published building upon the gliderflight model you reference (Merckelbach 2010). In the recent publication the equations are correct and the model has been validated using data from a glider mounted Profiling Doppler Velocity Log, and a microrider mounted Electromagnetic current meter. You may refer to this paper instead (A Dynamic Flight Model for Slocum Gliders and Implications for Turbulence
Microstructure Measurements Merckelbach et al, Journal of Oceanic and Atmospheric Technology 2019, DOI: 10.1175/JTECH-D-18-0168.1)

p.10/l.8 You estimate that 1/16 W equals 5.4 kJ/day. That is expressing the same thing in different units. It is also a bit of a puzzle for the reader how to arrive at the numbers mentioned in this section.

You make a remark on using a free-flush CTD to save energy, and continue arguing that it is technically possibly to correct for errors in CTD readings due to thermal lag effects (p.9/l26). Then in Table 1 it is mentioned that 860 CTD samples are taken in about 11 hours, or 1 per minute. At this rate it is not possible to do any corrections at all. Even using the maximum sampling rate available on standard glider CTDs, namely 1 Hz, the correction is dubious when strong temperature gradients are present. Even if a 4x as efficient processor is used and all the energy is used to sample more frequent, then you would get at 1 sample every 5 seconds, which is not good enough for these corrections.

Table2: I find the break-down of costs not very convincing. More than once I heard from people in industry that the selling price of such instruments is normally about 10x the construction cost. Would you call that profit/recovering development costs? Your numbers for profit seem very modest. On the other hand. then numbers you quote for components seem rather expensive. So I wonder where those numbers come from. If they are (educated) guesses I would be reluctant to specify them, although I agree with you that a price of about 70k would seem realistic, in particular if scaling arguments apply.

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RR by Anonymous Referee #2 (08 Jan 2020)

Suggestions for revision or reasons for rejection

UPDATE FOR REVISED PAPER
All the above points have been addressed satisfactorily, the added text much improves the manuscript. The paper should be published. Specific comments below:

2.1 a quick comment on why the red and blue lines in Fig. 2 are different may be useful.
2.2 it seems a bit confusing to have a reference total velocity in Eq. 4 as 13 cm/s, but then use that regularly as a horizontal velocity. Is the effect simply too small to worry about in the power calculations?
2.4 any comment on the reasons for the difference between SG and SL in Fig. 3? Is it basically a larger volume of SG, hence more skin friction compared to SL? Why would this change at higher net buoyancy? (a curiosity question, may not be needed in text).
-what about the difficulties for 2000 m rated hulls? Won't this imply thicker Al walls and hence less room for internal electronics and batteries? Especially if a compressible design such as SG is used. Is 25-30L still a reasonable target? Larger hull mass also implies more displacement and overall volume needed.
2.6 Very useful example from a real mission. Thank you.
2.7 Table 2 is useful. However, a little confusing because Argo is mentioned in several places when in fact you are estimating the slow glider cost (with Argo as a guide, if I understand the text correctly). Also, maybe I missed it, but shouldn't the cost in Table 2 is for the first mission of the slow glider only. Wouldn't the 2nd, 3rd, and so on be significantly less? You could value the returned glider at higher value than the -10k cost, for example. This would quickly make a more competitive case with Argo. (also from environmental standpoint as you mention)

4.1 "eastward to Greenland" should be "westward" I think.

4.4 "targets to observing" is awkward...try "targets the observation of"
"highly needed and" should be removed

4.5 "launched off the coast..." replace with "launched and recovered near the coast"
5. Conclusions: reword "expectations to" as "expectations for"
New references much appreciated and useful.

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ED: Publish subject to technical corrections (23 Jan 2020) by Oliver Zielinski

AR by Erik Magnus Bruvik on behalf of the Authors (31 Jan 2020) Author's response Manuscript

Short summary

A concept of small and slow ocean gliders or profiling floats with wings is explored. These robots or drones measure the ocean temperature and currents. Even if the speed is very slow, only 13 cm s¹, it is possible to navigate the (simulated) ocean using a navigation method called Eulerian roaming. The slow speed and size conserve a lot of energy and enable scientific missions of years at sea.