General comments

Dear authors, congratulations for this interesting and well-written article! It will serve the scientific community with a valuable dataset of high quality and a detailed description of the data. The presented dataset is both unique and useful and well comprises the existing data sets for the Col de Porte open site. Accuracies of the measurements are well provided. The text is well structured and of appropriate detail and length. The English is very good and there are only few minor language errors in the text.

The published dataset can be rated significant - in terms of uniqueness, usefulness and completeness. Both data and presentation qualtity are very good.

I only have the following minor specific comments and suggestions for technical improvement. All in all my recommendation is „minor revision“, but all this can be done with modest additional effort.

Specific comments and technical corrections

- 70: since the tree species are listed later (in Figure 3) it could be sufficient here to formulate it in a more general way and distinguish only between coniferous and deciduous trees

- 71: „The smallest one“ should probably better be „The smaller one“ (if there are only two?)

- Figure 1: (i) caption: the sentence „The sensors of the open meadow area appear on the left of the picture“ would better be something like „On the left is the meadow with part of the long-term instrumentation for the Col de Porte site“? (ii) legend: better move to one of the left corners of the picture so that it does not cover trees. Same for the scale bar and the N arrow. (iii) Rugged laserscan: is it possible to indicate the viewing direction and the scanned area of Figure 8 here (see also comment to Figure 8)?

- Figure 2: (i) can you adopt the extent of this map to exactly the same as the picture in Figure 1, or alternatively, provide a map inlet that shows the two map extents? (I consider the first solution the better one). This would support to identify the location of the devices which are shown in Figure 1 also in Figure 2. (ii) can you indicate the gaps here? Which one is where? (iii) add scale bar and N arrow

- Figures 1-4: provide corresponding date in the caption

- 122: „geometric information on“: can you formulate explicitely what can be processed and replace „information on“?

- 123: „a campaign covering 123.5 km2“: where is this area, does it fully integrate the Col de Porte site?

- 127: software packages „RiAnalyse“, „RiWorld“ and „Terrasolid“: can you provide version numbers and links?

- 128: „accuracy on elevation measurements“ should probably be „accuracy of elevation measurements“

- 129: „GNSS accuracy is around 2-3 cm“: horizontal or vertical?

- 130: „yielded to an altitudinal accuracy“: delete „to“

- 131: what is a „LAS 1.2“ file?

- 132: with a „200 m buffer“: what does this mean? Maybe that the point cloud covers an area 200 m wider than the site in the N, E, S and W direction?

- 133: „LAS file (v1.1 format 1)“: why different versions (see comment on 131)? Is the LAS version issue of any interest here? If yes, it could be explained here. If not, maybe this would be better formulated in the caption of table 2 or eventually even in a small appendix?

- 134: „The area located more than 30 m to the SE of the study area was not covered by the acquisition“: what should be expressed here, which area? Is there something missing? How does this correspond with the 200 m buffer? This should be made clear here.

- 166: „13 … pyranometers and 11 … pyrgeometers“: how does this match what is visible in Figure 1 (11 locations for SW and LW plus 4 locations for SW), shouldn’t it be 15 pyranometers? Comparison with the sensor_plan.pdf file (online with the data) suggests that the „SW2“ and „SW3“ devices in Figure 1 should be deleted?

- 196: maybe better „until“ instead of „through“?

- Figure 6: maybe better make two panels in this figure, one for (i) temperature and snow depth, and a second one for (ii) soil temperatures? Adding a legend with the different colors for the soil temperatures would probably also be a benefit. What about the data gaps in the snow depth time series, where is this explained at least briefly?

- 208, 211, 213: is the differentiation between „snow height“ and „snow depth“ based on a purpose and carried out consistently all through the text?

- 224: how was the mass of the precipitation tanks measured?

- 234: „azimuth angles varying from -90° to +90°“: are you sure, where is zero (usually N or S)? Maybe you can add the viewing field of the RLS into Figure 1 (see respective comment there)?

- 254: find a better formulation than „uncertainties on the sensors“ („of“?)

- 256: „reliable information on sensor accuracy“: can you formulate explicitely what the manufacturers generally provide, and replace/delete „information on“ (probably it is the accuracy itself which is provided)?

- 263: do you mean „relation to the canopy…“ instead of „relation with …“?

- 264: „In clear sky“: maybe better „In clear sky conditions“

- Figure 10: add a), b), c) and d) in the four panels

- 281: what is „0.2°CK“? (probably it is either degree Celsius, or Kelvin)

- Figure 11: colors in the left panel are orange, red and purple (on the screen), not red and blue as indicated in the text of the caption. Red seems to be the color resulting from the overlay of orange and purple. Printer output may again looks different than screen display. Can one improve this for the sake of clarity?

- 300: here would be an appropriate place to add 2-3 sentences about existing modelling studies (and some references) which show how the forest canopy processes mainly depend on LAI, exposition and amount of snow precipitation, amongst other effects. Readers might be interested in this

- Figure 12: add the explicit years to the panels a) and b), and also a complete legend; is it possible to mark the poles such that they can be identified in Figure 1?

- Figure 13: add the explicit years to the panels a) and b), and also a complete legend

- 311: can table 2 be moved to the end of the text (after „Data availability“)?

Very nice paper, well done! Thank you for considering me as a reviewer.

Snow accumulation and ablation measurements in a mid-latitude mountain coniferous forest (Col de Porte, France, 1325 m alt.): The Snow Under Forest field campaigns dataset

General comments:

The authors present a much-needed collection of datasets from extensive field measurements to help quantify snow in the canopy at the Col de Porte site. This work will progress our understanding of physical processes in the canopy and provide ground-truth data for future modeling studies that look to improve snow-canopy interactions. In general I though the paper was well written and had very clear methods. I do suggest however that Section 2 seems to encompass a lot of information, and perhaps looking to organize this a bit differently may improve the structure and readability. Also, the instrument uncertainties and the methodology are well documented, but I suggest that more could be stated on post-processing of the data. This includes adding more details on the thresholding approach used in classifying hemispherical photography, more details on leveling/covering correction on radiometer array data, and more details on how snow mass was estimated from the precipitation tanks. I include more details on these points, as well as other points that I believe can help strengthen the paper.  

Specific comments:

L23 : “This paper presents the field site, instrumentation, and collection methods”… And post-processing?

L24: Do you mean to say “an array of radiometers”?

L30: Consider re-working this sentence. You mention the scale of this issue which I feel is important, but I am a bit lost with how you are presenting Rutter et al., 2009 in this context, perhaps finding another reference here would be helpful. Additionally, correct me if I am wrong but this site is not technically classified as boreal forest, which could be misleading to some readers. Finally, is it canopy as a key control on snow cover? The way you have it written seems like you are getting at that snow cover under the canopy influences tree characteristics, and while this has implications for an ecohydrological study, I don’t know if it quite captures what you are going for and setting up in this paper.

L33: Consider removing “e.g.,” in your citations it is not needed. This is the same comment throughout

L33: Consider adding “For example,” before “The model inter-comparison project SNOWMIP2…”

L41: Consider removing “all of the effects of particularly”

L42: In this sentence you should include that detailed canopy measurements are required too?

L45-47: Consider changing to, “CDP meadow site has been operated by CEN-MeteoFrance, with daily measurements of snow depth, air temperature, and precipitation recorded since 1960 (Lejeune et al., 2019; Morin et al., 2012).”

L61: Same comment as above, consider rewriting to “array of radiatiomers”

L65: I feel as if “Site and forest description” does not quite capture all of the work you are doing in this section. Consider revising your sub headings throughout to include the various remote sensing products and snow datasets.

 L69: Consider rewriting to, “The stand is dominated by Norway spruce (Picea abies), with young silver firs (Abies alba) and various broadleaved trees along the western edge of the parcel.” …. Also, if you know the types of broadleaved trees it may be useful to include (e.g., x, y, z)..

L72: While I get how you are displaying the data, this may confuse some readers. Perhaps just write it out. While it is a bit verbose, it will help the reader I’m sure.

Figure 1: It would be nice to see a location map in the upper right hand corner of Figure 1 to know the approximate location in France. Also, when was the image taken? Perhaps could show time of image on the caption.

L87: I realize this may seem self-explanatory as why there were particular thresholds for tree heights and DBH, but perhaps one sentence on stating why you made this decision would be helpful for those that wish to use your canopy data in the future…. Circling back to this after reading ahead, you do this quite a bit, and so adding one sentence on these thresholds would I believe help clear up the next few paragraphs…. i.e., Are you considering trees over 1.3 m because this is the typical snow depth at CDP? Etc…

L91: Consider rewriting to “In total, 141 trees were inventoried, including 128 live trees, 3 dead trees and 10 stumps.”

L92: If there is a reference for this method, please include it here.

L104: It doesn’t make sense for the reader here to reference the airborne lidar data that has not been presented yet. I recommend changing Forest inventory to Section 2.2.2 and putting the airborne lidar section first. Then this will allow the reader to understand better in how you are arriving at canopy heights from forest inventory data. This would also allow Figure 2 to make more sense.

L107: Consider changing “southern fence are” to “southern fence included”

L113: Is this accuracy the resultant vector of distance and height, or are you just referring to ground surface distance error?

L122: Provide reference for use of ALS to quantify forest structure, which ever closest matches your method.

L134-135: This is unclear as to 1) where exactly this is, and 2) why you are mentioning here

Figure 4: This does not look like the entire 123.5 km2 acquisition, therefore, should specify as “a small subset” or “area of interest”. Also, a scale bar and legend for the colorization is needed.

L153: Maybe to be more concise because I will assume there was no snow on the ground either, you could just say that all sites were snow-free during the hemispherical photographs.

L155: An additional sentence on your brightness threshold methodology would be helpful to see here, as well as a reference if you are using an existing method. For example, ss Nobis et al. (2005) mentions there are issues especially in clear sky sun conditions in dense canopy. It would be helpful to see how your method solved for this or adapted to changing cloud cover.

Figure 5: Seems simple but should clearly state in the caption that white pixels are sky and black pixels are canopy if no legend is provided. Alternatively, creating a simple legend could be helpful.

L169: To what height above the snow were the radiometers typically adjusted to?

L175: Please consider expanding on how periods were identified where the sensor was potentially tilted.

L178: Quantify the dense canopy. If you have hemispherical photography near this site, I would use these to estimate canopy cover percentage. You could also discuss the CHM measurements at this site. “Rather dense” is a little too arbitrary.

L183: Check tense in the sentence? Should read “was used”

Table 1: Capitalize “variable”. Also, consider adding the 15 minute temporal resolution in the table caption. Also, lambda as wavelength is not defined.

L196-197: It is a little confusing to read that the temperature gradient of the soil was reversed. Are you saying the temperature gradient within the soil profile matrix reversed, where deeper soil was warmer? It is a little difficult to see that from this figure 6, but perhaps if you added a Figure 6b that enlarged the snowmelt region you could draw more attention to this.

Figure 6: Temperature axis should be black, as there are other temperatures being shown. Having blue axis was confusing at first for me to visualize the results. Also, there are several colors and a legend is needed. Additionally, your Dates September 2018 to June 2019 do not match up with what you present on Line 193.

L206: Please change to “were deployed”

L208: Please add “For each pole the snow height…”

L217: Please change to “the forest canopy” or just “the canopy”

L222: Define CEN

L223: Can shorten here to just “but additional studies are needed.”

L224: I’m not sure if I am catching them all but watch out for this where you are using “was” instead of “were”. Sentence should be changed to “precipitation tanks were measured…”

L224: Additionally, it is not clear how the “mass of snow” was collected? Are you making assumptions for density? Are the precipitation tanks measuring weight? Are there markers on the tanks to know the depth?

L236: You can shorten this down and just say that, “Data acquired during a given day by the laser meter is interpolated averaged on a regular 3-cm grid”.

L242: change “has” for “had”

Figure 8: Please be consistent with either snow height (as shown in the legend) or snow depth as shown in the caption throughout the text for clarity. Either are fine, but it would be clearer to stay with just one. Also, make sure to use past tense on your verbs throughout, “The measurement area encompassed three radiometers (I3, I4, and I5).”

L264: Sunflecks as one word

L265: Please remove the rest of the sentence after “,superimposed”. This does not need to be stated I believe.

L267: Are you referring to Figure 10 C or D here?

L268: Once again I feel like you are stating something that doesn’t need to be there. The added longwave radiation is from the forest and is well known. Additionally, please check grammar on this sentence. Colons should be followed by a list, not a statement.

Figure 10: Line color for sky view factor needs to be shown in a legend. Additonally, you need to have a, b,c, and d marked on the figure.

L280: Once again, check you are using the correct use of colons. Please consider changing to “Thus, average daily air temperatures are quite similar in the forest and meadow site (dT ~ 0.2°CK on average during the 2018 campaign) because warmer nights counterbalance cooler days in the forest relative to the meadow. “

L281: Celsius (C)?

Figure 11: Capitalize “Difference” and also please provide a legend for day time versus night time measurements. Also, please provide (A) and (B) on the figure itself.

L296-299: The ablation is a little more nuanced and for that I agree that more research needs to be done. However, I recommend reading Jessica Lundquist’s meta-analysis for looking at the ablation melt phase and how this varies across snow regimes and climate. I believe it would be a good idea to provide context on how your field data relates to this meta-analysis.

Lundquist, J. D., Dickerson‐Lange, S. E., Lutz, J. A., & Cristea, N. C. (2013). Lower forest density enhances snow retention in regions with warmer winters: A global framework developed from plot‐scale observations and modeling. Water Resources Research, 49(10), 6356-6370.

Table 2: Should this be listed instead in the code and data availability statement?