Assessing the Performance of a Handheld Laser Scanning System for Individual Tree Mapping—A Mixed Forests Showcase in Spain

Round 1

Reviewer 1 Report

Dear authors, please find my main points in the Word document, and minor observation applied directly to the .pdf file as comments.

Overall I think you have a strong manuscript, with a very sound experimental design and detailed analysis of results. My main point of issue is with section 3.6. You mention the strong agreement between ALS/HLS heights multiple times, but this agreement is not apparent to me in most of the scatterplots presented (especially for Qp). This section is also a bit confusing because you present ALS vs. HLS in the plots, but you also talk about field-measured heights. So it’s not entirely clear which comparison is your focus: HLS vs. field, HLS vs. field or even ALS vs. field. Same issue in Discussions (lines 531-534): you mention Fig. 10 (which shows ALS vs. HLS heights), but talk about under-estimation from field-collected heights. So it’s not clear what you comparing your HLS-derived heights with.

You also have an interesting cluster of severely overestimated heights in plots b-c-d for Ad and plots a-b-c-d for Qp. This should be talked about, it’s very surprising to me that HSL would grossly overestimate heights, instead of underestimate (look at plot c column 1 for example, you have about 5 trees with ALS heights of a few metres with HLS heights of over 20 metres, could this be a case of misidentification of trees?). It would also be worth mentioning if these trees falling very far from the trendline are (for the most part) the same trees across the scatterplots and if they’re clustered spatially or randomly distributed over the test site.

Other issues:

Ø  It’s not clear to me if your GCPs were registered directly by GNSS (as described at lines 171), or using the total station (as described elsewhere). I think a short section describing the land surveying carried out is warranted (where are the GNSS points located – I assume outside the forested area -, what receiver was used, what accuracy you obtained). This is an important aspect because the positioning accuracy you obtained will have a direct impact on how meaningful validation with ALS data is.

Ø  For most of the paper, you use scientific notations for tree species and then in the Discussion section you start refering to them by their popular names (oak etc.). Since you are not aiming to publish in a forestry-oriented journal, please either add the popular names when you first mention the species or refer to the scientific names consistently so readers can follow your arguments.

Ø  Also note you use “None rigid” instead of “Non-rigid” across the whole manuscript.

Minor observations can be found directly on the manuscript’s PDF.

 

 

 

 

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

In chp. 2. Materials and Methods, Subchp. 2.3 Point cloud post-processing using Forest Structural Complexity Tool, pag. 6, rows 222-223: in the sentence “We have made the four HLS point clouds available (see 10.5281/zenodo.7308680).”; please explain what is 10.5281/zenodo.7308680.

 

In chp. 4. Discussion, pag.20, rows 535 – 540: “The study from [37] performed…”; please The study from [37] performed an enhanced segmentation of tree canopies to address 535 the tree height estimation problem, reducing error rates below 1.5 m for the whole experiment compared to height measurements measured with the same instrument we used – 537 assumed as reference. The approach is promising and followed in recent studies [54] and authors reported better results than us considering all species, so their method can improve our results on tree height.”; please comment shortly how the cited study can improve the results presented in this paper.

In chp. 4. Discussion, pag. 20, rows 552-555: “This is the case in Spain where the multi-temporal LiDAR PNOA project….”; please include a reference about the LiDAR PNOA project.

Author Response

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