First Retrievals of Surface and Atmospheric Properties Using EnMAP Measurements over Antarctica

Round 1

Reviewer 1 Report

Summary statement:  This is good work that is suitable for publication. I have a few suggestions.

Comments:

(1) Page 2 lines 15-16. “we derive the snow grain size, snow specific surface area, spectral . . .”  Grain size and SSA have a 1:1 relationship. To indicate that you are not deriving them independently, you could say “we derive the snow grain size (alternatively, the specific surface area), . . .”

(2) Page 2 lines 15-17. “we derive the . . . snow bidirectional reflection distribution function (BRDF)”.  No results for BRDF are shown in this paper.

(3) Page 2 line18. “It is assumed that snow does not contain impurities”. This assumption can be supported by Figure 6 of Warren et al. (2006), which shows the black-carbon (BC) content of snow at Dome C. The BC values are small enough that their effect on albedo is probably below the measurement uncertainty.

(4) Page 4 line 14. “and BRDF (see Table 1).” Table 1 does not list BRDF.

(5) Page 4, Eq. 8. Explain how this “effective diameter” relates to the “effective radius” commonly used for radiative transfer in clouds and aerosols (eq. 2.53 of Hansen & Travis, 1974). In particular, just below Eq. 8 you say that V is the average volume and sigma is the average projected area. But these values should not be obtained as simple number-averages; they should be weighted averages, following Hansen & Travis. Or more directly, V could be the total volume of ice in a volume element of snowpack, and sigma could be the total projected area in a volume element.

(6) Figure 2. Show where the station is located. Is it at (0,0)?

(7) Figure 5. The validation data extend only to 1020 nm. You could extend the validation data out to 2400 nm (on Figure 4) using Figure 6 of Hudson et al. (2006). Hudson’s measurements at Dome C were not made on the same day as the satellite measurements, so you will still need Figure 5.

Spelling and punctuation:

Page 1, 3 lines from bottom.  Delete “he”.

Page 2 section 2 line 1. Change “has been” to “was”.

Page 3 line 4. Hyphenate “water-leaving”.

Page 3 section 3.1 line 5. Remove comma.

Page 9, two lines above Table 3. Change “boarders” to “borders”.

Page 17, 14 lines from bottom. Change “has been” to “was”.

Page 21, Ref. 44. Change “Plateu” to “Plateau”.

Page 22, Ref. 58. Change Mizuno to Mizuho.

References:

Hansen, J.E., and L.D. Travis, 1974: Light scattering in planetary atmospheres. Space Science Reviews, 16, 527-610.

Hudson, S.R., S.G. Warren, R.E. Brandt, T.C. Grenfell, and D. Six, 2006:  Spectral bidirectional reflectance of Antarctic snow:  Measurements and parameterization.  J. Geophys. Res., 111, D18106, doi:10.1029/2006JD007290.

Warren, S.G., R.E. Brandt, and T.C. Grenfell, 2006:  Visible and near-ultraviolet absorption spectrum of ice from transmission of solar radiation into snow.  Applied Optics, 45, 5320-5334.

English is adequate.

Author Response

The answer to Reviewer 1 is attached.

Author Response File: Author Response.docx

Reviewer 2 Report

Dear authors,

thank you very much for your manuscript. The article "First retrievals of surface and atmospheric properties using EnMAP measurements over Antarctica" shows the first attempt to determine spectral snow properties from a single EnMAP scene acquired on 29 october 2022 in Antarctica, more precisely at the Concordia Station in Dome C Plateau. They retrieved snow grain size using two SWIR wavelengths and susequently BOA snow reflectanca, snow specific surface area and broadband albedo. In addition, the most important (and variable) atmosphere parameters Preciptable Water Vapour (PWV) and Total Ozone Column (TOC) could be derived from the Enmap scene. All were in good agreement with ground measurements.

The introduction gives a good entry to the topic, the references and methods listed are complete, understandable and state-of-the-art. The article is very relevant because it shows the first attempt to derive these parameters from the new hyperspectral satellite Enmap, and the results achieved are very promising. The results are well reproducible due to the very detailed presentation of the calculations (27 equations).

The only weakness I see is the quality of most of the figures. It looks more as if these are put together from different sources, it would be more visually appealing if they were "from a single source". So a template with a uniform font, font size and also the axis labeling uniform. I will go into this in the following detailed descriptions. Another weak point concerns the layouting.

Another weak point concerns the layout. White spaces are often too many, or the font size (and type) in the continuous text is not appropriate. So the main text is PalatinoLinotype-Roman (size 10), URLs and e.g. the formula numbers are in TimesNewRomanPSMT (size 12). Also, the captions are inconsistent, they should be full and bold (e.g. Figure 8), but Figure 7 is labeled "Fig.7." abbreviated (not bold). In addition, the line spacing after the caption is missing here.

Subsequent Specific Comments:

Page 1, 1. Introduction: In my opinion, 300 m to 1 km is still "medium resolution", coarse resolution are e.g. passive microwave sensors like SSM/I or AMSR-E. Also, a "t" is missing in the sentence "In particular, he accurate information of specific snow features [...]".

Page 3, 2. EnMAP: Following the description of the processing levels: "The spectral ranges 1400-1450 nm and 1770-1930 nm are masked out", here it would make sense to mention why they are masked out. Further: "The results of measurements t these spectral intervals [...]" should be "in these spectral intervals", or maybe "within these spectral ranges".

In the next paragraph, it is written that EnMAP is capable to make the measurements over the polar regions, aren't the polar caps excluded from the coverage?

Page 4, 3.1. Retrieval of snow properties: Between equations 8 and 9: Correct "We sg=hall use the following value for the constant in Eq. (7)" with "shall".

Page 5: Table 1: Change "Abbreviation" to the "Abbreviation / Units".

Page 9: 4. Application of the retrieval algorithm to L1B top-of-atmosphere EnMAP radiance data: I wonder if it makes sense to show an RGB quick look of the scene (probably everything is white anyway), but it would help to use an overview map to understand the distance from Concordia Station to the coast, for example. A map (possibly just a DEM) would also make sense to give the readers an idea of the Dome C plateau.

Page 10: Figure 2 a-c: I would suggest revising figures 2 and 3. If the spatial resolution corresponds to 30 m (horizontally and vertically), I would expect a square image. It is also not immediately clear what the X and Y axes mean (here I would consider whether an orthographic projection would not be better, where the coordinates are given). In figure 2c I would adjust the range according to the values since BBA does not go beyond 0.835.

Page 11: Figure 3 a-b: See above.

Page 12: Figure 4: I suggest that the Figure related paragraph should be moved here from page 9-10.

Page 12: 5. The comparison with ground measurements: The reference "(Picard et al., 2016b)" does not correspond to the MDPI Style and should be linked either to refence [27] or [48].

Page 12: 5. The comparison with ground measurements (third paragraph): "EnMAP is less affected by such effects due to the larger footprint (30 m)" Do you really mean footprint or spatial resolution here? I only know the definition that the footprint corresponds to the entire width of the scanned earth's surface (30 km).

Page 14: Figure 6.a. I would change the caption to "Figure 6", and call the one below "Figure 7".

Page 15: Figure 6.b. See last comment. Also, please change the Y-Axis because there is no need to have an albedo range from -0.04 to 1.04. A range from 0.75 to 1.0 would fit better. Additionally, according to the caption, the numbering should not start at 270 because it means days since day 270 of the year 2007 if I understood that correctly.

Page 16: Figure 7: Please add a title. It is also not quite clear what "day" means, so I would either label the axis directly by "1st Oct 2022" or write "Day of October 2022" as X-label. In addition, there should be a blank line after the figure caption.

Page 16: 5. The comparison with ground measurements (The total ozone column (TOC)): "The root mean square (rms) of deviations [...]" RMS in upper case.

With best regards

Author Response

The answer to reviewer 2 is attached.

Author Response File: Author Response.docx