Referee’s comments on the manuscript “Rockfall monitoring with a Doppler radar on an active rock slide complex in Brienz/Brinzauls (Switzerland)”

This paper addresses the assessment of a complete rockfall inventory based on the Doppler radar technology resulting in an unprecedented temporal and spatial resolution. Thanks to the coupling with meteorological and InSAR measurements, the authors showed that the movement of (single compartments) of the rock slide complex is the main preparatory causal factor for the total of 5667 observed rockfall events (2018-2021). Rain and temperature play a minor, but not neglectable role in triggering rockfalls in the given study area Brienz/Brienzauls (Switzerland). Thanks to the rockfall inventory's high temporal resolution, the data's low daily correlation could have been compared to the hourly meteorological evolution. This thorough analysis showed that during the winter months, the daily maximum temperature and in the summer months, the rain intensity correlated with the rockfall activity.

While the data is worth publishing, this current manuscript needs a revision aiming for more consistent terminology (e.g., shadow zone, danger zone hazard zone) and concise writing with an enhanced reading flow (e.g., without “on the other hand”). As a non-native English speaker, I did not notice many linguistic errors. Instead, minor repetitions or the lack of an introduction (e.g., the activity parameter) should be tackled.

Specific comments:

l. 3 (and throughout the whole manuscript) :

Spaces must be included between number and unit, without italics: 1 m³, not 1m³ (https://www.natural-hazards-and-earth-system-sciences.net/submission.html#assets)

l. 17-20:

Although the reference is given to Evans and Hungr (1993), and the shadow zone of the rockfall process is described in detail with different wording, it might make sense to reference Figure 7, introducing a visual explanation of the shadow zone.

l. 47:

Consider using Geopraevent AG or Geopraevent Ltd. to clarify their requirements as a private sector company (see methods).

l. 49:

The reference is missing any DOI/internet address.

Figure 1:

The layout of Fig. 1 could be enhanced: The inset map of Switzerland has much-unused space, but the legend and the main figure are hardly readable (in original zoom size). The information content of the figure can be increased if the weather-stations of Tab. 1 are additionally shown (certainly those of Brienz in the main map, but also the others in a larger section of the map or a second inset map of the region/canton). Also, displaying the longitudinal profile of Fig. 7, including the APEX point and the (additional) compartment names, would increase the information content. The designation of the danger zone needs to be clarified: Does it refer to the shadow zone, or is it based on the danger map of the canton?

Figure 2:

Although this figure and its caption give a good overview of the study area, some details might be enhanced or clarified: 2.a) Consider including the Photo location in Fig. 1. Caption 2.b): In the text is also the road closing infrastructure mentioned (l. 74). The red light visible in Fig. 2.b) is thus worth mentioning. Additionally, Fig. 2.b, c) would benefit from an overlay with the geological formations and/or the landslide compartments. Fig. 2.e) Why is there a shift between the mapped rock outlines and the orthophoto? Fig. 2.f) Mark the dams better (The lowest, far western dam directly on the road is barely visible). Again, both terms are mentioned (which might be right): Shadow and danger zone. Make it more clear by mapping the shadow zone.

Table 1:

Only here you make use of parentheses. In the other figures’ labels, you use brackets around the units. To enhance consistency, I would use only parentheses (as in most NHESS publications) or adapt at least here the parentheses to brackets.

l. 74-76:

The observed velocity changes of the reflectors between the seasons belong (besides a good explanation) to the result section.

l. 80:

Again a new term: “hazard zone”. Its definition is also not concise. Instead, rephrase it: “We define this grassland including the cantonal road as a danger zone (Fig. 1), due to the increased damage potential (traffic).” This is necessary, as the grassland itself barely accounts for a higher damage potential.

l.81:

Source of the large volume events?

l.85:

“…and a/the local station…”

l. 89-90:

Which temperature sensor is used, and which accuracy according to the manufacturer? Is the housing ventilated? What is the ground material (indirect radiation)?

l. 91-95:

For clarity, I propose to rewrite the section. The most obvious choice to use the temperature data is the local station, as it is the closest one. So I would argue the other way around. E.g., “The proximity to the process area makes it suitable to use the temperature data set from the local station for further analysis. A high overall correlation (0.93) has been observed between the temperature of Savogingn and the local station (BRINZ). The slight differences might be due to topographic temperature effects, as the station in Savognin measures lower mean temperatures in winter (2 °C), but higher temperatures in summer (1 °C). ”

l. 96-100:

Please rewrite for clarity: The sentence “Secondly, freeze-thaw (FT) cycles can be divided into three phases.” has the potential for confusion. Consider rewriting: “Secondly, freeze-thaw (FT) cycles, which we divide into three phases”. Thanks to the proposed phrasing, it is clear, that only two metrics (l. 96) are meant and not three. Also, equations 6-8 could be moved directly after l. 100 to enhance clarity.

l 113.:

How is the temperature corrected?

l. 119:

Is the snow height also elevation-corrected?

l. 127-132:

Shorten the section: Slightly repetition within

l. 137:

Reconsider: “The device has a 90° horizontal field of view, from 302° - 32° azimuth.”

l.140-142:

Unclear relationship of the volume and distance: “Within a distance of 100 m the radar can detect moving masses larger than 0.1m³. Increasing the distance to 1km, a minimum volume of 1m³ is necessary for detection.”

l.142-143:

The minimal velocity is not mentioned in the source (Gassner et al., 2022)

Figure 4:

Consider writing “true positive wrong extent (TPWE)” instead of “TPWE”, as this abbreviation is not common and in the figure is (in the current typesetting) before the mention within the text

l. 146- 150:

Also, the signal-to-noise ratio is not explained in detail in the source (Gassner et al., 2022), However, such deeper insights are very welcome. Especially as the further “advanced algorithms” are described rather mysteriously. What do they do? And how? If these algorithms are developed by the company Geopraevent AG and are not meant to be disclosed, that should be mentioned clearly.

l. 155:

The Nr. of detected rockfalls belongs to the results section. However, another total amount of detected rockfalls (5667, l. 199) is given for a slightly different period. Clarify which period is more meaningful.

l. 156:

Activity maps: provided by whom?

l 178:

Specify how you include the caution in treating the eastern starting point or move this sentence to the discussion.

l 183:

Typo: “in the danger”?

l 192:

Which is the minimum rock size?

Figure 5:

Fig. 5.a and Fig. 5.d look very alike. Therefore, I propose that the subplot titles are descriptive and highlight the difference: “All rockfall event time series…” vs. “Days with high rockfall activity (>10 events d^-1)”.

l. 204,

To maintain a concise terminology, you might change grassland to shadow- or danger zones.

l. 209,

The Doppler radar only observed rare events released from colluvial deposits.

l. 211,

The small second peak in the N-S-histogram of Figure 6 may also result from the different orientations of the map and the radar/mountain exposition. Try to rotate the map such that the histograms get even more meaningful.

l. 212:

If the daily rockfall rate strongly fluctuates, besides the mean, the standard deviation would also be of interest.

l. 213, 231, 251:

“Significantly” in terms of a statistical test? Which one? Rephrase otherwise.

l. 219:

To reference all subplots separately, write ”..hereafter considered as days with high rockfall activity (Fig. 5d).”

l. 249:

Consistency: Grassland or shadow: If you use it as a synonym, clarify that earlier and use just one term here. Otherwise, focus on shadow.

l.285:

To prepare the reader that the division between summer and winter also resulted in different subplots, you might add the corresponding references: “…we divide the data set into summer (April to September, Fig 10.b-c) and winter (October to March, Fig. 10.d-e) months.”

Table2:

After looking at the data plotted in Fig. 10 b and d, I would assume a negative coefficient with mean hourly summer rain (highest rockfall activity during the night, while rainfall events have their peak in the afternoon) and a positive coefficient for mean winter temperature (rockfall and temperature have their peak in the afternoon). Explain in the table caption (and text) more proactive the differences compared to Fig. 10 (daily/hourly). Even better: integrate the hourly correlation coefficients as well into the table.

Figure 10:

Adapt the y-axis label of Fig.10.b and d with the corresponding season for clarity. Although the caption correctly describes the summer and winter months, the bar graphs (b, d) are confusing because they show different data, despite identical axis labels: E.g., “Tot. events summer (h^-1)”

l. 307-310.:

This topic has already been introduced in the methods section. Shorten this repetition.

l. 316-320:

hard-to-read, long introduction sentence, followed by two very short ones. Rephrase to avoid imbalance and enhance readability.

l. 344-345:

After an interesting thought and a good argumentation(342-344), mental agility is required by the reader to understand also the third sentence, which begins with a typical sentence intro (However, therefore, on the other hand). The wrong references (Fig.3 instead of 2 and Fig. 5 instead of 4?) and the prior missing link between the two figures are additionally unhelpful. Try to combine these figures into one and/or add the Pearson’s correlation coefficients in Tab. 2. Then, the results section will describe the missing linear correlation, and here, the reader would not be surprised. Additionally, a reference to Fig. 8 could underline the argumentation and the importance of InSAR observations.

“Therefore, local rock slope displacement and acceleration can be seen as major rockfall preparatory factors (Fig. 8). This insight is only possible thanks to the spatial InSAR observation, as the single, nearby monitoring points (Fig. 3 or new combined fig.) and rockfall frequency (Fig. 5 or new combined fig.) have no linear correlation. “

l. 346-349:

Elaborate the activity parameter A and its calculation base in more detail. Why is the assumption of a few m³ per event necessary, but appears not in the unit of A? What is the unit of A anyhow: per year per hour per square meter? As your findings are due to the observed high rate very relevant, they should be better introduced.  

l. 383-384:

Can this assumption (“is likely related”) be underlined with data? Different DEM over time?

l. 385-386:

Inconsistency in the terminology: Does your mapped “Danger zone” (Fig. 1) contain the here mentioned dam? Even if so, the second sentence does not make sense: reaching the dam would then mean: reaching the danger zone.

l. 387:

If a literature study is mentioned, it would be helpful to provide the sources.

l. 402-405:

Twice “the road is automatically reopened after a few minutes”. Rewrite for reading flow.

l. 400-410:

Own data? Otherwise: Sources?

l 420-430:

Mentioning the activity parameter and the dam filling in the conclusion stresses the importance of the comments l. 346-349 and l. 383-384.

l. 436:

Consider also including the limitations of the previously widely used monitoring system into the conclusion: “than weather data or single monitoring points.”

Dear Editor,

Please find below my review of the manuscript: egusphere-2023-555 entitled:

Rockfall monitoring with a Doppler radar on an active rock slide complex in Brienz/Brinzauls (Switzerland)

By

Marius Schneider, Nicolas Oestreicher, and Simon Loew

This paper presents an analysis of rockfall occurrences within an active landslide, utilizing both observational data and Doppler radar measurements. The study demonstrates the significance of climatic factors and landslide displacements in facilitating rockfall activity. While the title implies a focus on Doppler monitoring, the main objective of the research is to investigate rockfall triggering mechanisms and evaluate potential rock arrest locations using Doppler Radar.

This review provides general comments on the paper's content, suggests improvements, and highlights specific areas for clarification.

General Comments

The title could be refined to better reflect the focus on analyzing rockfall triggering and evaluating rock arrest locations using Doppler Radar. Additionally, the inclusion of a geological map would greatly enhance the understanding of the study, considering the frequent references to geological aspects throughout the text. Section 3.3 requires a clearer explanation, potentially aided by a flowchart to elucidate the selection process for the displayed source areas in Figure 4. Further clarification is needed regarding the manual mapping of 70% of the 971 events on pictures and the utilization of machine learning, particularly since only 10% are allocated as test sets. Additionally, the authors could consider utilizing cross-correlation analysis to examine the time delay between climate effects and rockfall triggering. Lastly, certain sections, such as lines 400 to 410, seem irrelevant to the paper's purpose.

In terms of references, while D'Amato et al. (2016) is cited for freezing and thawing, it is also relevant to rainfall effects.

The term "Cantonal Road" requires clarification, as it appears to be a Swiss classification that could be replaced with "main road" for better comprehension.

Exploring the influence of temperature alone could provide valuable insights, especially considering the south-facing slope indicated in Figure 10d, where the effect of freezing and thawing cycles appears immediate, though the feasibility of such an analysis may be challenging.

Specific Comments

• Line 37: Consider adding the following reference: Hungr, O., Evans, S.G., and Hazzard, J. 1999. The magnitude and frequency of rock falls and rockslides along the main transportation corridors of southwestern British Columbia. Canadian Geotechnical Journal, 36: 224–238. doi:10.1139/t98-106.
• Fig. 1: It is recommended to include a geological map alongside the existing figures.
• Figure 3: Clarify the meaning of "TPS."
• Lines 203 and 2008: Specify whether 60 m³ and 100 m³ refer to maximum block volume, and source volume respectively.
• Line 202: Provide information on the minimum and maximum per day values.
• Figure 6: Improve the legend's clarity by explaining the histogram and consider using lines instead of transparent histograms.
• Consider employing the term "shadow area" or "rockfall shadow" instead of "shadow zone," as previously used by Evans and Hungr.
• In conclusion, this scientific paper review acknowledges the research's contributions in analyzing rockfall triggering in an active landslide context