An Automated Pipeline for Extracting Forest Structural Parameters by Integrating UAV and Ground-Based LiDAR Point Clouds
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsDear Autors and Editor,
I had the pleasure of reading the article “ An Automated Pipeline for Extracting Forest Structural Parameters by Integrating UAV and Ground-Based LiDAR Point Clouds”
Overall the article has the correct structure and is interesting to me. I’m impressed by the skill of the authors and the proposed methodology which in practice utilizes the tree segmentation from ULS and TLS. This is a big job and for sure this kind of research put the tree inventory techniques to a higher level. However, my privet opinion about the practical usage of such combination (TLS and ULS) is critical because I do not see the practical usage nowadays. First of all, it is costly, secondly, it has limited area coverage, thirdly the accuracy is too high for the biomass assessment (I completely disagree with the results expressed in millimeters for the tree!!!) and finally the real forests are much more complicated than the researched one. So I can strongly agree with the authors that “this setup led to idealized experimental outcomes”. I think the discussion section repeats the results chapter and there is not too much discussion there. Conclusions are too short according to the huge amount of results presented in this research.
Concluding this is really good research. I wish authors further succeed in publication.
Here are some small comments you can find below.
9-32
The abstract is too long and there are no single results expressed in digits.
67-75
I cannot agree that TLS is “commonly employed”. First of all, it is horribly expensive and the data processing is complicated and time-consuming. Additionally, you have used the FARO Focus3D which has one big issue – it cannot scan trees from one location for the sample plot because of the tree shadow. Check this texts:
Zasada, M.; Sterenczak, K.; Dudek, W.M.; Rybski, A. Horizon Visibility and Accuracy of Stocking Determination on Circular Sample Plots Using Automated Remote Measurement Techniques. For. Ecol. Manag. 2013, 302, 171–177
Sometimes such precision is not needed. You can easily make inventory by Apple products. Of course, it is not such accuracy – it is obvious – but you can easily use it for inventory and the errors are acceptable. Taking into account the efficiency and cost you could mention about such a solution
Mokroš, M.; Mikita, T.; Singh, A.; Tomaštík, J.; Chudá, J.; WË›e Ë™zyk, P.; Kuželka, K.; Surový, P.; Klimánek, M.; ZiË›eba-Kulawik, K.; et al. Novel Low-Cost Mobile Mapping Systems for Forest Inventories as Terrestrial Laser Scanning Alternatives. Int. J. Appl. Earth Obs. Geoinf. 2021, 104, 102512
Brach M., Tracz W., Krok G., GÄ…sior J. 2023. Feasibility of Low-Cost LiDAR Scanner Implementation in Forest Sampling Techniques. Forests 14(4) 706. 1-16.
Gollob, C.; Ritter, T.; Kraßnitzer, R.; Tockner, A.; Nothdurft, A. Measurement of Forest Inventory Parameters with Apple IPad Pro and Integrated LiDAR Technology. Remote Sens. 2021, 13, 3129.
78
It is optimistic and it is okay. Taking into account most above biomass model based on DBH is good enough. You can check that CCI index is a very good idea for DBH assessment
Krisanski, S.; Taskhiri, M.; Turner, P. Enhancing Methods for Under-Canopy Unmanned Aircraft System Based Photogrammetry in Complex Forests for Tree Diameter Measurement. Remote Sens. 2020, 12, 1652.
156
Such a value as 63 minutes does not exist. BTW please be more precise because the East value does not correspond to the description in figure 1.
166
I suggest reconstructing the figure completely. On the part "a" I really don’t know where it is in China (a small location map in the corner would be useful). In part "a" there is no visible location of the study area. The north symbol is not needed – all of us know that the map is orientated to the north. There is no visible scale bar – like 1 km or 500 meters. In part "b" the sample plots should be presented and the scale bar should be added.
171
How many battery packs?
177
Much more interesting would be a profile of the scan. Most of us know how the point cloud looks like. There is nothing new in figure 2.
190
Do not write such sentences: The locations of these sample plots are depicted in Figure 3
193
How many sample plots were established? Why some of them are rectangular and some circular?
196
What method was used to measure DBH in September 2022? It is important if you want to compare it to TLS results. Especially when you suggest that “It is optimistic” in line 78
215
I would change to crown width
598
Could you explain how the tree height was measured manually? The same to DBH.
Author Response
Dear Reviewer,
Thank you very much for your acknowledgement of our research work. We also appreciate your professional and meticulous review of our manuscript, which is of great significance for us to rigorously articulate the research work. We have carefully studied and addressed each of your suggestions, and the modifications have greatly improved the quality of our manuscript. We are grateful for your assistance and look forward to the opportunity to further interact and collaborate with you in this research field in the future. Below are the modifications made based on your comments.
（1）
Q:9-32
The abstract is too long and there are no single results expressed in digits.
A: The abstract has been rewrite. Simplified the textual description of the abstract and added a numerical description of the results
（2）
Q:67-75
I cannot agree that TLS is “commonly employed”. First of all, it is horribly expensive and the data processing is complicated and time-consuming. Additionally, you have used the FARO Focus3D which has one big issue – it cannot scan trees from one location for the sample plot because of the tree shadow. Check this texts:
Zasada, M.; Sterenczak, K.; Dudek, W.M.; Rybski, A. Horizon Visibility and Accuracy of Stocking Determination on Circular Sample Plots Using Automated Remote Measurement Techniques. For. Ecol. Manag. 2013, 302, 171–177
Sometimes such precision is not needed. You can easily make inventory by Apple products. Of course, it is not such accuracy – it is obvious – but you can easily use it for inventory and the errors are acceptable. Taking into account the efficiency and cost you could mention about such a solution
Mokroš, M.; Mikita, T.; Singh, A.; Tomaštík, J.; Chudá, J.; WË›e Ë™zyk, P.; Kuželka, K.; Surový, P.; Klimánek, M.; ZiË›eba-Kulawik, K.; et al. Novel Low-Cost Mobile Mapping Systems for Forest Inventories as Terrestrial Laser Scanning Alternatives. Int. J. Appl. Earth Obs. Geoinf. 2021, 104, 102512
Brach M., Tracz W., Krok G., GÄ…sior J. 2023. Feasibility of Low-Cost LiDAR Scanner Implementation in Forest Sampling Techniques. Forests 14(4) 706. 1-16.
Gollob, C.; Ritter, T.; Kraßnitzer, R.; Tockner, A.; Nothdurft, A. Measurement of Forest Inventory Parameters with Apple IPad Pro and Integrated LiDAR Technology. Remote Sens. 2021, 13, 3129.
A: We fully agree with your opinion. In fact, compared to expensive TLS methods, obtaining tree structure parameters through Apple products and other methods has more practical application value. The use of TLS data in our study is mainly due to its higher accuracy, which makes it easier to verify the performance of each step of the entire process in the study. We have re described this in the manuscript and cited it using the research paper you recommended.
（3）
Q: 78
It is optimistic and it is okay. Taking into account most above biomass model based on DBH is good enough. You can check that CCI index is a very good idea for DBH assessment
Krisanski, S.; Taskhiri, M.; Turner, P. Enhancing Methods for Under-Canopy Unmanned Aircraft System Based Photogrammetry in Complex Forests for Tree Diameter Measurement. Remote Sens. 2020, 12, 1652.
A:Thank you for your suggestion. We have conducted research on the literature you recommended and strongly agree with the statement 'CCI index is a very good idea for DBH assessment'. Therefore, we have cited it in the article.
（4）
Q:156
Such a value as 63 minutes does not exist. BTW please be more precise because the East value does not correspond to the description in figure 1.
A: Thank you very much for your detailed review. I apologize for our negligence, this mistake is very low-level. Based on your follow-up questions, we have rewritten the description of the research area and research data.
（5）
Q:166
I suggest reconstructing the figure completely. On the part "a" I really don’t know where it is in China (a small location map in the corner would be useful). In part "a" there is no visible location of the study area. The north symbol is not needed – all of us know that the map is orientated to the north. There is no visible scale bar – like 1 km or 500 meters. In part "b" the sample plots should be presented and the scale bar should be added.
A: Following your suggestion，the figure 1 and figure 2 were reconstructed completely.
（6）
Q:171
How many battery packs?
A: The imprecise wording here has been removed.
（7）
Q:177
Much more interesting would be a profile of the scan. Most of us know how the point cloud looks like. There is nothing new in figure 2.
A: Figure 2 has been deleted.
（8）
Q:190
Do not write such sentences: The locations of these sample plots are depicted in Figure 3
A: Figure 3 and inappropriate explanatory text has been removed.
（9）193
How many sample plots were established? Why some of them are rectangular and some circular?
A: Figure 3 and the explanatory text that may cause misunderstandings has been removed.
（10）
Q:196
What method was used to measure DBH in September 2022? It is important if you want to compare it to TLS results. Especially when you suggest that “It is optimistic” in line 78
A: The manual measurement method of Diameter at Breast Height (DBH) is indeed crucial to this study. In this research, the measurement of tree diameter is conducted as follows: the diameter at 1.3 meters above the ground surface is measured using a diameter tape. When the cross-sectional circularity is low, the average of the maximum and minimum values is taken. Compared to the precise measurement method of felling the trees, the accuracy of the data indeed impacts our research.
（11）
Q:215
I would change to crown width
A: Following your suggestion，it has been modified.
（12）
Q:598
Could you explain how the tree height was measured manually? The same to DBH.
A: The manual measurement method for tree height is indeed pivotal to this study. We employed a handheld forestry electronic altimeter, utilizing a three-point measurement approach for the tree height measurement. Compared to the precise measurement method of felling the trees, the accuracy of the data indeed bears implications for our research.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe manuscript is one that belongs to the current sphere of interest.
Congratulations to the authors! To contribute to the quality of the manuscript I bring some comments:
- line 45: starting from here I think references are put as exponenet;
- line 166: Figure 1 can be improved with map level location of the data collection site;
- line 637: charts can be improved, showing the same scale on the same axis;
- line 810: conclusions can be presented in points, in line with the results of the study.
Good luck!
Author Response
Dear Reviewer,
Thank you very much for your acknowledgement of our research work. We also appreciate your professional and meticulous review of our manuscript, which is of great significance for us to rigorously articulate the research work. We have carefully studied and addressed each of your suggestions, and the modifications have greatly improved the quality of our manuscript. We are grateful for your assistance and look forward to the opportunity to further interact and collaborate with you in this research field in the future. Below are the modifications made based on your comments.
(1) Q: line 45: starting from here I think references are put as exponenet;
A: Your suggestion is very relevant. Based on the opinions of other reviewers, we have adjusted the annotation position of the references.
(2)Q:line 166: Figure 1 can be improved with map level location of the data collection site;
A: Figures 1 to 3 have been replaced with new figures containing the map level location of the data collection site
(3)Q: line 637: charts can be improved, showing the same scale on the same axis;
A: Thank you for your suggestion. We have adjusted the second chart in the same scale on the same axis;
(4)Q:line 810: conclusions can be presented in points, in line with the results of the study.
A: Thank you for your suggestion. It has been presented in points, in line with the results of the study.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for Authors1. "Fig. 1a should include the study area."
2. "In line 167, is it 'DJI MTK R300' or 'DJI Matrice 300 RTK'?"
3. "The authors may also mention why TLS and ULS, or both, should be used for forestry."
"All sections have been well-prepared and contain innovative content. I recommend minor revisions."
Author Response
Dear Reviewer,
Thank you very much for your acknowledgement of our research work. We also appreciate your professional and meticulous review of our manuscript, which is of great significance for us to rigorously articulate the research work. We have carefully studied and addressed each of your suggestions, and the modifications have greatly improved the quality of our manuscript. We are grateful for your assistance and look forward to the opportunity to further interact and collaborate with you in this research field in the future. Below are the modifications made based on your comments.
- Q:"Fig. 1a should include the study area."
A: Figures 1 to 3 have been replaced with new figures containing the map level location of the data collection site
2.Q: "In line 167, is it 'DJI MTK R300' or 'DJI Matrice 300 RTK'?"
A: Thank you very much for your reminder. 'DJI Matrice 300 RTK' is a standard name given by the manufacturer. The text has been revised to 'DJI Matrix 300 RTK'
- Q:"The authors may also mention why TLS and ULS, or both, should be used for forestry."
A: In the third paragraph of the Introduction, we have added an explanation in this regard.
Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsLine 39 – „as well as positining” – these are two different things - locally, tree parameters are usually very good, but positioning depends on georeferencing, and georeferencing in forests can be poor - access to GNSS, GSM for RTK/RTN corrections, so please clearly define the goal and stick to it
Please use Terrestrial rather than Ground-based
I'm suprised that in the reference there are only one ref of Juha Hyyppa - expert in forest inventory from ALS datasets
it will be good to add some ref - for example: https://sciendo.com/pl/article/10.2478/apcrs-2019-0007
Line 64 - compromise - this is an exaggeration, unless they add 2-3 publications that say so, but in my opinion ULS is still ALS, only it is denser and the flight would have to be very low and with a wide angle, with leaf-off to catch the trunks
Please keep in mind information about quality of the ULS point cloud from L1 laser unit - especially footprint of laser beam:
https://doi.org/10.5194/isprs-archives-XLVIII-1-W3-2023-99-2023
What was the TLS registraiton method - with targets or cloud2cloud
What was the errors of ULS registration/adjustment – values, spatial distribution of errors, how mach flightlines?
There were any GCP or georeference directly from RTK M300
presented analyses use DEM - what algorithm was used to generate DEM, what was the error of DEM
what was the density of the ULS point clouds - this information is crucial for precise measure geometrical information of trees
Author Response
Dear Reviewer,
Thank you very much for your acknowledgement of our research work. We also appreciate your professional and meticulous review of our manuscript, which is of great significance for us to rigorously articulate the research work. We have carefully studied and addressed each of your suggestions, and the modifications have greatly improved the quality of our manuscript. We are grateful for your assistance and look forward to the opportunity to further interact and collaborate with you in this research field in the future. Below are the modifications made based on your comments.
（1）
Q: Line 39 – „as well as positining” – these are two different things - locally, tree parameters are usually very good, but positioning depends on georeferencing, and georeferencing in forests can be poor - access to GNSS, GSM for RTK/RTN corrections, so please clearly define the goal and stick to it
A: Thank you for your suggestions. The spatial positioning of the trunk and canopy is not the focus of this study. To avoid any misconceptions, we have revised the description accordingly.
（2）
Q:Please use Terrestrial rather than Ground-based
A:Thank you for your suggestions. It has been modified accordingly.
（3）
Q: I'm suprised that in the reference there are only one ref of Juha Hyyppa - expert in forest inventory from ALS datasets
it will be good to add some ref - for example:
https://sciendo.com/pl/article/10.2478/apcrs-2019-0007
Wężyk, P., HawryÅ‚o, P., Szostak, M., et al. Using LiDAR Point Clouds in Determination of the Scots Pine Stands Spatial Structure Meaning in the Conservation of Lichen Communities in “Bory Tucholskie” National Park. Archives of Photogrammetry, Cartography and Remote Sensing, 2019，31(1), 85-103.
A：Thank you very much for your valuable recommendation on reading classic literature concerning forest inventory from ALS datasets. This is crucial for a more comprehensive elucidation of our research status. Following your suggestion, we have adjusted our references accordingly and included several papers by Juha Hyyppa's team to support our discourse, such as Reference 1, Reference 3, etc.
（5）
Q:Line 64 - compromise - this is an exaggeration, unless they add 2-3 publications that say so, but in my opinion ULS is still ALS, only it is denser and the flight would have to be very low and with a wide angle, with leaf-off to catch the trunks
A:We agree with your perspective that ULS is still ALS. Relatively speaking, ULS has a higher point cloud density and exhibits a stronger capability in capturing trunk point clouds under deciduous conditions. In conjunction with feedback from other reviewers, we have removed the inaccurate statement you pointed out.
（6）
Q:Please keep in mind information about quality of the ULS point cloud from L1 laser unit - especially footprint of laser beam:
https://doi.org/10.5194/isprs-archives-XLVIII-1-W3-2023-99-2023
A:Thank you for bringing this to our attention. The relevant explanations have been added to the text, and following your suggestion, we have cited the paper “EVALUATION OF CONSUMER-GRADE AND SURVEY-GRADE UAV-LIDAR” for reference.
（7）
Q: What was the TLS registraiton method - with targets or cloud2cloud
A:The relevant description has been added. The scan registration, carried out using FARO SCENE 5.5.3.16 software, resulted in an average absolute error ranging from 4.1 mm to 6.7 mm, with a mean value of 5.4 mm.
Q: What was the errors of ULS registration/adjustment – values, spatial distribution of errors, how mach flightlines?
A:The relevant description has been supplemented. Registration was conducted in DJI Terra software with the errors of 5cm.
（8）
Q: There were any GCP or georeference directly from RTK M300
A：The georeference was conducted directly using RTK M300.
（9）
Q: presented analyses use DEM - what algorithm was used to generate DEM, what was the error of DEM
A:The method proposed by Cai et al. (Reference 41) was employed for generating the DEM. In our dataset, the maximum root mean square error (RMSE) for type I, type II, and total error on the ULS point cloud of Pinus tabulaeformis were 2.42%, 0.851%, and 0.49%, respectively. Similarly, the maximum root mean square error (RMSE) values for type I, type II, and total error on the Mongolian oak ULS point cloud are 2.11%, 0.751%, and 0.43%.
（10）
Q:what was the density of the ULS point clouds - this information is crucial for precise measure geometrical information of trees
A: The density of the ULS point clouds is 1772 points/m2
Author Response File: Author Response.pdf
