Dear Dr. Caviezel and coauthors,

this paper is a really innovative and interesting contribution to the understanding of rockfall trajectories before and subsequent to impacts on the ground. The methodology combining a full four-dimensional trajectory reconstruction based on in-situ accelerometer, gyroscope data, videogrammetric and UAV mapping techniques provides unprecedented insight into rock rotations, ground penetration and translational scarring.

The relatively positive comments of both reviewers have been implemented carefully. I went through the entire new version of your paper and it is now very well structured and clearly presented including figures. A few minor technical issues that I would like to see improved prior to publication are listed hereafter:

(i) Introduction: In ESurf, there should also be a more prominent statement highlighting the scientific importance of such data next to the engineering practice. The reach of disc shaped particles with a better rotation of particles has been postulated since the pioneering work of Anders Rapp in the 1960s; many scientific papers have speculated on energy transformation of particles during the impact with the ground and scaled it with particle size, surface material, vegetation etc. and introduced an assumed constant "restitution coefficient". Your data provides very good evidence to reject the existence of such a constant restitution coefficient and you mention it in the conclusion. However, there should be a small paragraph in the Introduction better explaining the scientific debate mentioned above to prepare the wider ESurf readership to be able to follow your assumptions.

(ii) Starting from the state of the art of “restitution coefficients”, it would make sense to provide ratios of ingoing and outgoing kinetic and rotational energies at the impact rather than absolute values to underline the different types of impact. For example in Table 2, I would add a final column at the right with the ratio of E kin b / E kin e as well as E rot b / E rot e such as 0.39/1.03 (first line). These two ratios are the crucial outcome in terms of how much kinetic and rotational energy is proportionally lost (or even gained as in the case of rotational energy) and it is much better readable than the non-normalised absolute values. The ratios are a conciser and better normalised information and you also use them implicitly in the text to explain near-perfect elastical rebounds (p17 l2) and so on. I would also suggest using them in the conclusion/abstract to highlight the differences between the alternative types of ground contacts.
(iii) In the conclusion, rather than indicating that these experiments can be transferred to other settings (obviously), I suggest to include a sentence what type of information future experiments could add - other types of contact, greater variation of grain sizes, impact on structures...

(iv) In the attached pdf you find ca. 80 smaller remarks on spelling, readability, clarity etc.

Otherwise a very nice and innovative paper that provides unprecedented data and a novel methodology on rock-ground interaction. Subsequent to these technical revisions, I suggest to publish the paper.

All the best
Michael Krautblatter

Dear Andrin and colleagues,
Thank you for working with Assistant Editor Michael Krautblatter and his referees to bring your manuscript to publishable standard. Michael requests four revisions of the current version, none of which are invasive. Please address these four points, pyaing special attention to advice on the wider context and implications at the start and end of the paper. This will strongly improve the impact potential of the manuscript. After we receive the revised manuscript, it will not be sent out for review, but we may ask you to make further technical changes if we deem this necessary. Please try to make your corrections within three weeks from receipt of this message.
I very much look forward to working with you on the last steps towards publication of the manuscript.
Niels Hovius