Review for: ‘Characterizing sea ice melt pond fraction and geometry in relation

to surface morphology’, by Lena G. Buth et al.

General comments

This manuscript describes the use of observations of sea ice and melt features  and examines the relationships between the presence of melt ponds, ice type, ridging and age.

This manuscript addresses a critical and persistently under-quantified component of Arctic sea ice evolution: the relationship between surface morphology, e.g. ridge fraction, ice age, and the geometric characteristics of melt ponds. The authors use a combination of high-resolution optical imagery and coincident airborne altimetry to assess melt pond distribution and shape across a 70 km² section of ice north of Greenland. The paper’s structure is clear and the results are well exposed and supported by the data analyzed.

I recommend the publication of this paper provided that the authors address a few points.

Specific comments

The introductions contains all the right concepts, but it is often presented in a very fragmented way with very short phrases and paragraphs not properly linked to each other. The authors could improve it by grouping some of the very short phrases (e.g. lines 20-25), and making the links between the concept presented more explicit.

The methodology (between paragraphs 2.3-2.6), could be moved to an appendix and more details could be added. A much shortened version describing it could be added in the main manuscript.

In particular, it would be nice to read about the choice of algorithm: here you use Fuchs (2023a). I am not questioning your choice, but  considering that several other algorithm used for sea ice, I believe that the reasoning behind this choice should be more explicit.

Another study (Buckley et al., 2020), uses pixel classification and seems to have less limitations when sea ice concentration is low.

My main concern is about the amount of data analysed: It would be nice to have a feel of the total number of images acquired and how many were used: how many images were discarded because of too low SIC for example? What is the threshold assumed to discard an image (it could be more explicit I line 92-93).

A more thorough description of the whole campaign would be useful (there is a map in figure A1, but there is no time described).

In line 113 you mention that there is no need to find references for the brightness temperature more than once per flight. Is this due to the length of the flight, to the weather (see also line 79).

In paragraph 3.4, Could you please add a comment on the reliability of the statistics: the area covered by the three flights (70km2), is not huge. Could you make a comment on how representative your conclusions are? When devising a new melt pond parameterization this would be an important information to consider.

Technical corrections

Line 4: "coincided laser altimeter data": correct to  “coincident laser altimeter data”

Line 44-46: too many interruptions for refs: please move them to the end of the phrase if the journal allows it.

Caption - figure 2: "examplary images": correct to “example of images”. Also in line 480.

The pink circles in this figure are either too big, too close or too many: they look like a line.

Line 68 – 70: subsections 2.2 on brightness correction and 2.3 on the removal of the tow cable introduce novel approaches and are therefore described in detail. Pls review punctuation for clarity.

Line 84: " by determining the modal value of the sum of the R, G, and B channel rightness per image (modal RGB sum), as..’: in the first part of the phrase pls write in full Red, Green and Blue.

Line 100: “...along each flight track” (if multiple are referred to) rather than “Along the flight track”.

Line 102: what is an expected modal RGB sum value?

Line 107: "histogramm stretch approach": correct to “histogram stretch approach”

Line 126: First rather than firstly

Line 146: the camera timestamps are precise only to 1 second": pls consider rephrasing to “...are only precise to one second”.

Line 188 and following: Could you please explain the 3.9% and 17.5% more clearly? Why these numbers?

Line 235: the colon is probably not appropriate. Pls also consider to have three subsections for the three chosen flights.

Line 244: fewer?

Line 338: Perhaps the ref to Horvat 2020 should come to the end of this phrase, since their study is based on the hypothesis that the distribution of pond is of fundamental importance for the distribution of light and energy under the ice.

Line 123, 374 and 419: Capitals after colons in a few instances. Please correct throughout

Others:

"preflight" and "postflight" not consistently hyphenated: pls correct in a uniform way of choice.

"behaviour" vs. "behavior”: please ensure consistency throughout.

This manuscript presents a study of the relationship between the surface morphology of sea ice (due to presence/absence of ridges) and two characteristics of melt ponding (areal pond fraction and individual melt pond circularity). The data, analysis, and results are described in a way that is comprehensive, clear, organized, and easy to read. I have only one minor suggestion (not a requirement) and a short list of very minor technical points. In my opinion, this manuscript can be published upon the authors’ attention to these points.

Suggestion (not required for publication!): In my opinion, a nice addition to this manuscript would be a figure containing a selection of images of ponds spanning a range of circularities. The description of pond circularity (how it is computed and what it represents) exists and is clear, so I don’t think this information is missing. It simply occurred to me while reading the manuscript that a menu of examples of ponds with different circularities would be a really nice addition.

Minor technical points:

4: coincident (also line 445)

107: histogram (only one m)

222: which on melt conditions (omit ‘on’)

244: fewer melt? How about ‘less melt’?

248: “…mix of ice types, including landfast first-year ice, secondyear ice, and multi-year ice.” Would be helpful to know how it was discerned that all these types existed?

250: ‘submerged ice’? Not sure exactly what this refers to? Rafted ice?

259: “coastal areas” which coasts?

261: “…slush-covered areas (example shown in Fig. 2g).” Am I supposed to be able to tell there is slush in the photo shown in Fig. 2g? If so, please help me know what to look for.

275: “was varied”, should just be “varied” (otherwise it sounds like it was manipulated)

283: orange? More like gold on my screen

292: “very variable”? how about “highly variable”?

391: “perimeter-area ratio” or perimeter:area ratio?

399: “previous subsection” how about “Section 3.3.1”?

423: “melt pond properties” how about stating it more specifically, as “melt pond geometry”? There are a lot of pond properties that are out of scope in this study.  Here, “pressure ridges” are referred to, whereas the title says “surface morphology”. I think maybe the title would be more fitting if it referred to “sea ice ridging”? Or even “ice surface morphology”?