Dear Authors,

I have now read your revised manuscript and yours responses to the referees. The three referees were generally positive about your study and I think you addressed satisfyingly most of their comments.

However, I still have myself some minor comments on your paper before it can be finally accepted for publication. You will find them below.

To facilitate and speed up the review process, please attach to your revised manuscript a cover letter including my original comments and detailing the changes you have made in response to them.

Best regards,

Etienne Berthier

PS: note that I will be away during the next three weeks, so take your time to make the final adjustments.

Editor’s comments:

3D Animation. No way to include a color bar?

The line numbers below refer to the track-change version of the MS

HS not needed in the abstract. Also Defined twice in the main text (L32 not needed).
L49. Check tense. Past needed here I think.
L98. End sentence after fulfil.
L99. “except you want to fly”. Improve wording.
L120. I concur with rev#3. You need to recall in the text the size of the surveyed area, the table is good but not sufficient. To complement the table (in km²), could you give the size on the text in length * length (i.e., 300 m * 400 m for example).
L133. “concluding” from “his own experience” is a bit too conclusive. Downplay, i.e. use other word than “conclude”
L192. Write also 2015 after the winter dates
L216. Interesting addition. However I do not think this is “noise” (noise is what you describe in the shadow of the church for example). What about “systematic error”?
L248 . Sentence: “A big advantage of a multicopter UAS is that they can be started and landed by hand, which is the appropriate starting/landing procedure we apply in alpine terrain”
Following rev#3, replace by
“A multicopter UAS can be started and landed by hand, which is a strong advantage in alpine terrain”
L258-259. Weird sentence with alpine terrain repeated twice. Could be improved
L260-271. About further applications (now listed in the discussion and not in the conclusion). Some of these applications are rather indirect such that much more details should be needed so that a reader clearly understands why UAS monitoring would be specifically helpful. Further, as underlined by the referees, these applications are not really specific to UAS. I think that they should be deleted from the MS. Right now, they really break the flow of the discussion.
L367. Improve the last sentence of the paper! Bad impression right in the end. “for mapping applications also high alpine terrain”

Bühler et al.,
Revised version, 25 April 2015

Dear Authors,
Thanks for the revision of your paper and for taking into account or answering to the last comments. I have the pleasure to accept your revised manuscript for publication in The Cryosphere.

Two more technical corrections (to take into account when proof-reading the MS):
L94 "The UAS has to be within light of sight and the pilot should be able to". seems better to me.
L186. 12 May 2015 (for consistency)

Thanks a lot for choosing The Cryosphere to publish your work,
Best regards,
Etienne Berthier