An Optimized Workflow for Digital Surface Model Series Generation Based on Historical Aerial Images: Testing and Quality Assessment in the Beach-Dune System of Sa Ràpita-Es Trenc (Mallorca, Spain)
Round 1
Reviewer 1 Report
I am recommending minor revision. I felt this was a very well crafted paper, that was easy to understand and read, with a clearly defined "point". There are no line numbers in my review draft (!), but my suggested revisions are as follows:
1) While the special issue focuses on "4D" analyses, and the term is included in the paper title, it is not mentioned anywhere in the text. I have interpreted (perhaps incorrectly) that the term 4D as used with SfM references a particular analysis technique, which you all didn't used. I suggest considering a revision to the title to reflect what you mean when you say 4D there.
2) In the introduction, first paragraph, you mention "high- and ultra-high-resolution" Can you please include some scaling so I can understand what you mean with those terms?
3) There are locations (town names, "basin of Campos", etc.) referenced in section 2, first paragraph, and it would be VERY helpful if I could use Figure 1 to geographically place those locations...but Figure 1 includes no annotation or labelling.
4) Also in section 2.1 you talk about "the presence of the sea" as a limitation - can you clarify what you mean? I think what you are getting at is that its difficult to analyze a water surface with SfM techniques, please GCPs, etc.?
5) This is a small one, but I found it difficult to track the various references to ALS - you mention LIDAR ALS, ALS-LIDAR, DSM-ALS and so on, which I think are all referencing either aerial lidar data OR the DSMs created from aerial lidar. It may be simpler just to use a term like "aerial lidar" OR ALS consistently throughout?
6) Figure 3 - fonts in the figure are tiny, and almost invisible.
7) Figure 4 is great, but you've got a bunch of symbology in there that appears to have meaning - white, blue and grey lines, blue arrows, black arrows, and dashed lines, blue and black text, a little computer symbol, etc.. Maybe include some additional information in the caption that helps a reader to understand your full intent?
8) I might have missed it, but I don't think you ever spelled out and defined MAE
9) Figure 6 - consider revising color and symbology to improve readability
10) On page 14 you talk about DSM quality "look good and coherent". I think fleshing that out a bit to describe a bit more what you mean by "look good" would be useful
11) the last sentence of the second paragraph of the discussion was confusing to me...'which affected and prompted generation of the 1945 and 1979 DSMs'? The whole point of the study seemed to be about testing whether you could generate DSMs from those older imagery...how did you study area prompt their generation?
Author Response
Please find attached our answers to the reviewer's comments and suggestions.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This is a good manuscript, ready to be published in my opinion.
Please indicate the percentage of overlap within the text. In addition, in Fig S1: what unit is the number in the the color scale?
Author Response
Please find attached our answers to the reviewer's comments and suggestions.
Author Response File: 
Author Response.docx
Reviewer 3 Report
The authors have done a commendable work in developing hDSM methods and presenting the workflow in a transparent approach. The study has been carried out extensively and the manuscript is near to the perfection. There are some minor improvements needed to enhance the quality of the following,
Figure 3 can be improved. Legends and symbols on the map are not clearly visible.
Figure can be improved. Makes difficult to interpret due to light color.
Fusion process of 2014 and 2019 with 63 scenes should be rechecked once again. Both are having different resolutions.
Few more information can be added to support the 4th dimension in DSM
The manuscript can be processed for publication after fine tuning with above mentioned.
Author Response
Please find attached our answers to the reviewer's comments and suggestions.
Author Response File: Author Response.pdf
