A linear model to derive melt pond depth on Arctic sea ice from hyperspectral data

König, Marcel; Oppelt, Natascha

doi:https://doi.org/10.5194/tc-14-2567-2020

Articles | Volume 14, issue 8

https://doi.org/10.5194/tc-14-2567-2020

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

https://doi.org/10.5194/tc-14-2567-2020

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

Articles | Volume 14, issue 8

Research article

|

12 Aug 2020

Research article |

| 12 Aug 2020

A linear model to derive melt pond depth on Arctic sea ice from hyperspectral data

Marcel König and Natascha Oppelt

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Final revised paper (published on 12 Aug 2020)
Preprint (discussion started on 09 Dec 2019)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review of tc-2019-261', Anonymous Referee #1, 07 Jan 2020
- AC1: 'Reply to RC1', Marcel König, 10 Jan 2020
RC2: 'Review of “A linear model to derive melt pond depths from hyperspectral data” by König and Oppelt', Anonymous Referee #2, 02 Mar 2020
- AC2: 'Reply to RC2', Marcel König, 13 Mar 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) (31 Mar 2020) by Stef Lhermitte

AR by Marcel König on behalf of the Authors (14 Apr 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (23 Apr 2020) by Stef Lhermitte

RR by Anonymous Referee #2 (09 May 2020)

Suggestions for revision or reasons for rejection

Review of “A linear model to derive melt pond depth on Arctic sea ice from hyperspectral data” by König and Oppelt

Note that my line numbers refer to the tracked changes version of the manuscript.

I am happy to find that the authors took onboard many of my comments. The additional text in the introduction provides much better justification for the study. The revised manuscript also contains a much more thorough review of previous literature, including some relevant research from the Greenland Ice Sheet. My one remaining concern is that the authors overstate the accuracy of their method. I would like to see some additional caveats included in the abstract and conclusions. For example, while it may be true that the errors are 2-3 cm (the uncalibrated error is 3.29 cm and the calibrated error is 2.81 cm) the ponds are extremely shallow. Looking at Figure 11, it appears that pond depths average around 16 cm which would equate to a 20% error. I encourage the authors to be upfront about their accuracies in the abstract (L14) and conclusions (L352) by presenting the errors as percentages as well as absolute values. I would also encourage the authors to add the word “shallow” in the abstract since the depths of melt ponds sampled were small (somewhere in L13-15). Below are some more specific comments.

L28: Suggest replacing “been put on” with “investigated”.

L33: “reckon” is informal, consider replacing.

L129: Typo, “the” instead of “he”

L303-311: The 3.05 cm error in dark ice melt ponds as shallow as 6 – 14 cm is still approximately 20-30%?

L307: How can the R2 be less than 0?

L314-315: Could the authors elaborate a bit more about solar zenith angles? How many days per year do solar zenith angles reach 58.9 and 61? Is it just July? Or a longer period?

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RR by Anonymous Referee #1 (10 May 2020)

Suggestions for revision or reasons for rejection

Review of manuscript titled “A linear model to derive melt pond depth on Arctic sea ice from hyperspectral data” by M. König and N. Oppelt
The questions and issues in my prior review have generally been addressed. The following are minor editorial comments that now should be addressed.
L 60: “acquired under and different illumination conditions” ??
L83: “with a spectral sampling rate < 1 nm and an spectral resolution of 3.0 nm”? It is not clear what this specification means. Is the light sampled with detectors spaced by 3.0 nm and then interpolated to 1 nm?
L154: ” We therefore defined a pure water column without absorbing or scattering water constituents and computed remote sensing reflectance in shallow water above the water surface…” so no absorption in the pond water?
L218: (and other instances): “solar” zenith angles, instead of “sun” zenith angles
L261: “Converting albedo to radiance is only possible when assuming a Lambertian scattering behaviour.” This sentence needs to be reworded. If I understand correctly, what the authors are trying to say is “It is only appropriate to derive an accurate radiance directly from the albedo of a Lambertian surface.”
L294: “The data set, however,origins from only three ponds, …” originates
L322: “separation of model calibration on simulated data” not sure what this phrase means. It needs to be rewritten.
L336: “We further assume that the additive signals of the water surface and the atmosphere on the spectrum measured at a remote sensor may complicate the retrieval of pond depth.” This sentence needs to be rewritten. Its meaning is not clear—of course the atmosphere will modulate the signal, but its not clear why the signal of the water surface is a potential problem.

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ED: Publish subject to minor revisions (review by editor) (27 May 2020) by Stef Lhermitte

AR by Marcel König on behalf of the Authors (28 May 2020) Author's response Manuscript

ED: Publish as is (01 Jul 2020) by Stef Lhermitte

Short summary

We used data that we collected on RV Polarstern cruise PS106 in summer 2017 to develop a model for the derivation of melt pond depth on Arctic sea ice from reflectance measurements. We simulated reflectances of melt ponds of varying color and water depth and used the sun zenith angle and the slope of the log-scaled reflectance at 710 nm to derive pond depth. We validated the model on the in situ melt pond data and found it to derive pond depth very accurately.