The authors describe and discuss detailed measurements of surface snow SSA in East Antarctica. The methods are described in detail and reproducible.  This dataset may serve as ground truth validation for optical remote sensing. The sensor measures the surface (a few millimetres of the snowpack). The repeat measurements on the 1000 km traverses with very high spatial resolution illustrate the complexity of the snow surface in Antarctica. 

The surface reflectivity is certainly the most important factor in albedo calculations. However, the very small penetration depth of light at 1320 nm into snow is also a limitation in the albedo calculation, as the visible and short near-infrared wavelength backscattering also occurs deeper into the snowpack. This should be clarified in more detail in this paper and discussed. 

I was also missing measurements of any snow impurities. Known to be small, they may not be negligible, especially in the coastal region, and could contribute to an altered albedo. 

The manuscript is a very important contribution to a better understanding of the antarctic snowpack and its interaction with short-wave radiation.

For directional reflectance calculations, the snow particle shape is important. Robledano et al. 2023 demonstrate that snow grain shape is an important factor in BRDF-calculations, which are necessary for satellite albedo retrievals. Could the author also record the snow particle shape together with their instrumental observations?

The authors mention the potential of these measurements to be used for satellite remote sensing validation. However, there are no temporally coincident optical satellite passes mentioned, so will the large spatial and temporal variability of the surface snow SSA allow later for a direct comparison?

The authors nicely illustrate the observed trends and spatial variability in Fig. 7. In table 2, it would be interesting to see if the differences between the Regions are significant. 

There is always a temperature gradient in the snowpack in Antarctica, so isothermal metamorphism is not relevant. The reviewer suggests that more weight is put on temperature gradients and not absolute temperature.

Title: "Spatiotemporal" implicitly suggests that the measurements are during an entire year.  I suggest as title "Spatial variation ... during austral summer"

25: "enable the validation ..." this is not shown in greater detail in the paper

43 ff: The isothermal case does not exist in Antarctica, and can be deleted here (or then the newer papers by Kaempfer et al, Calonne et al must be cited and commented.

54: the sentence "In addition ..." is not relevant in the context of this paper

75: ASSSAP was mainly used in Antarctica: I suggest to delete "alpine"

176: "shares the same measurement principle ..." replace by " shares a similar measurement principle ..."

203: "... with the accurate ..." there is quite a large measurement uncertainty by the methane absorption method, give precision in text

249: You could mention here that the measurements are during austral summer, and not spring, autumn and winter

323: meteorological events are by definition short-term. Delete "short-term".

431: I think it's interesting that glazed surfaces do not always lead to a very high variability?

453: the magnitude and frequency of temperature gradients are much more important than absolute temperature

599: "under high pressure." there could also be clear days without high atmospheric pressure.

Robledano, A., Picard, G., Dumont, M., Flin, F., Arnaud, L., and Libois, Q.: Unraveling the optical shape of snow, Nat Commun, 14, 3955, https://doi.org/10.1038/s41467-023-39671-3, 2023.

The study describes a rich dataset of measurements of the specific surface area (SSA) of snow acquired during four traverses from the coast to the inland plateau of Antarctica and during a 13-day stay at Dome Fuji Station, on the plateau. The authors present the measurement locations, methods and auxiliary data in a reproducible way. The drivers of the variations of the SSA observed are then discussed. The article is clear, the results are well presented, and figures are effective. Overall, it nicely highlights the complexity of the surface processes impacting the snow optical and microstructural properties over the Antarctic ice sheet during summer.

However, some details about the measurement procedure should be cleared in the text. At line 193 the SSA is said to be measured “at 10 different surfaces, spaced 2 m apart along a transect perpendicular to the predominant wind direction”. First, a more detailed scheme of the measurement area could help improve both understanding of the text and potential for satellite product validation. Second, why the choice of the transect perpendicular to the predominant wind direction? Is it related to the presence of wind-induced bedforms? Third, how was the sampling carried out over rough surfaces (surfaces c. and d. in section 2.2.2), considering that erosion bedforms present different snow properties according to their exposition to the wind (Sommer et al. 2018)? Finally, it would be interesting to have more details about the measurement uncertainty and how it compares to the SSA variability observed along the transects.

Some minor comments:

Line 56 : clarify the difference between sublimation that decreases the snow SSA and that increases the snow SSA (line 58).

Line 60 : a brief description of snow bedforms that result from wind-induced redistribution could be introduced here, with the heterogeneous distribution.

Figure 3 : a horizontal grid could improve the clarity of the figure, as most variations of the SSA in time are small

Line 313 : the definition of erosion surfaces as “aged deposition surfaces” is confusing with respect to the definitions in section 2.2.2

Line 466 : the sentence “Also, the observed SSA  … air temperatures.” is not clear, please rephrase

References:

Sommer, C. G., Wever, N., Fierz, C., and Lehning, M.: Investigation of a wind-packing event in Queen Maud Land, Antarctica, The Cryosphere, 12, 2923–2939, https://doi.org/10.5194/tc-12-2923-2018, 2018.