The paper presents a very promising application for snow measurement and SWE assessment in the near future that could be quite cheap and easy to retrieve. The topic is relevant for the journal and interesting for scientific and technological development, for hydrological aims, and for other applications (e.g. avalanche monitoring and safety).
At the same time, anyway this contribution is week in terms of comparative analysis and validation of its results.
Some comparisons should have been made against one of the already tested distributed techniques (e.g. laser scanner) to be more effective and relevant. Or, at least, against a validated physical based model or even using a much more dense set of manual measurements. This at least to have evidence of the expected effect of local topography and provide a validation of the method a little bit more reliable and significant.
To improve reliability and relevance of the measures and methods it is advisable to define and put in place some snow poles, properly and precisely located with GPS. These can be also used referencing images afterwards providing common points, and could give more information than probes, for time depletion curves, accumulation and melting processes. Finally, in any case I would add a great number of measure with snow probes in the peak accumulation survey as already suggested by other reviewers.
As the authors suggest, a more detailed and exhaustive comparison with existing techniques is advisable, and a greater number of points for snow probe measurement is required.
Deductions described in paragraph 4.3.2 appear not to be significantly innovative and quite week and not really straightforward. They sound to be not really convincing. Dataset is and remain quite poor and this statistics analysis is not giving a real plus, in my opinion.
The most informative analysis in this paragraph, in my opinion, is the part regarding standard deviation and CV (fig. 11). I would summarize or remove the other parts.
Paragraph 4.3.3 assumes without any validation that U.A.S. output for snow volume is the correct one. Even if the analysis then is correct and appropriate, a rigorous validation against a spatial already tested technique is missing and should be included to provide strengthens to the assertions.
Outlook section is essential to define the awareness for limitation of this research. In any case I would recommend to strengthen the sample data and/or the comparison with other distributed (remote sensing data or physical model) dataset.
Title: I would remove resolution info in title
l. 10: manual measurements: how? Where? Provide more details. As already said you should have collected more than 12 points
l. 17: add results of point values also in percentage
l. 21: include a short motivation about snow volume difference
l. 104: in my opinion the survey should has been made for two or three years to have more information
l. 109: include more details about 12 points measurements
l. 121: change "since it is an elevation that guarantees" with "since the elevation guarantees". I would stress more clearly that it is important that the study area has NO permanent snow.
l. 275: in order to better verify the quality of the surveyed data it would be better to compare the U.A.S. DSM with an already validated one, computing some statistics of the differences between the two DSM: please show results of the comparison you made.
l. 315: snow probe measurements should be more numerous and possibly located in flat zone, local maxima and local minima of the topography, in order to get the greatest variability
l. 340: "Basing on these results, a spatial resolution of 20 cm seems to be the trade-off between the number of pixels considered (i.e., computational time) and the description of the snow micro-topography for the considered area": this deduction is not straightforward. How do you evaluated 20 cm as the bets compromise? Rougher resolutions have not been investigated and an evaluation index is missing.
l. 345: "While the three maps considered in the previous section...": if you talk about these maps you should show them in figures
l. 349: "...the larger cell size, the lower degree of detail..." this assertion is quite obvious, please rephrase the sentence
l. 445: I would use "vehicle" or something similar instead of "support"
tab. 1: it seems that absolute and percentage (please add this information to the table) difference are greater for lower snow depth. This is reasonable but should be more in detail investigated and commented, and, also for this aim, much more measurements would be required.
tab. 2: negative values in Hmin? Explain the meaning or remove.
tab. 3: result clearly show that the snow probe sample size and location is not suitable to assess snow volume, assuming that U.A.S. value is reliable. Please consider to significantly improve the snow probe sample, and detail comment section about this.
fig. 3, 4, 5 and 7: make the upper layers a bit transparent in order to make visible the underlying map.
fig. 9: please consider to change the color map in order to better highlight where the difference is close to zero, where you have overestimation and where you have underestimation.
fig. 10 and 11: please consider to use different symbols instead of colors to allow black and white print and add the legend in the plots.
Grammar, typing, etc.: please check time of the verbs (past and present are used not in coherence) and improve readability of numbers (thousands, etc.)