First Evidence of Peat Domes in the Congo Basin using LiDAR from a Fixed-Wing Drone

Round 1

Reviewer 1 Report

This is a potentially interesting article and investigated topic. However, in this present form, it cannot be published in RS for the following reasons:

1) the work is site-specific; a generalization of the methodology presented and validation in other regions is missed;

2) field evidence, and field pictures; this seems missed in the study;

The two above points are not minor; they can mine the entire work on its basis, especially point #1. My suggestion is to enlarge the study area with other examples around the world in order to make the methodology presented more solid and novel for RS

Author Response

This is a potentially interesting article and investigated topic. However, in this present form, it cannot be published in RS for the following reasons:

1) the work is site-specific; a generalization of the methodology presented and validation in other regions is missed;

The logistics of deploying this system to remote locations precludes enlarging the study area, and would be the subject of a rather larger work. Ultimately the current study size was sufficient to answer a specific unknown question about these globally-significant peatlands (the largest in the tropics). The method and technique used was untested prior to this study, so obtaining funding for a larger, pantropical field campaign, was not possible before the publication of this paper: however we suspect after publication it may be possible for us or others to apply this technique more widely. We have added some discussion of the applicability of this technique to other study sites in section 2.1 as suggested by the editor.

2) field evidence, and field pictures; this seems missed in the study;

Field evidence of ground elevation could not be acquired in the forest because GNSS systems deployed at ground level could not lock on to satellite signals due to the high tree and palm cover. It is for this reason that the effort was made to bring a UAV LiDAR system to this remote part of the Congo, and develop these analysis methods. We have added a note in the manuscript to this effect. We have further added photographs of the field work and UAV launch.

The two above points are not minor; they can mine the entire work on its basis, especially point #1. My suggestion is to enlarge the study area with other examples around the world in order to make the methodology presented more solid and novel for RS

We appreciate your comment, and agree this would be ideal. However, for the reasons above, this is not possible without the prior publication of this study, as a proof of the utility of these data and methods in these systems.

Reviewer 2 Report

Title: First Evidence of Peat Domes in the Congo Basin using LiDAR from a fixed-wing drone

 

This technical note article use a laser altimeter mounted on an UAV to measure peat surface elevation along two transects at the edges of a peatland, in the northern Republic of Congo, to centimetre accuracy, and compare the results with satellite LiDAR data (ICESat and ICESat-2). This is an interesting article with drone and I believe that it adds knowledge to the remote sensing applications.

I did not get technical glitches in reporting. Research is framed nicely and necessary documentations on methods and materials are provided. Results is supported by the data and methods. References look relevant.

However, I did not find much differences between the section on Results and Discussion and the section on Conclusions. The conclusions are reported in numbers, citations as similar to the Results and Discussion section. Conclusion should be conclusion of the research reported on this article not the repetition of results and discussion. I recommend the authors must address this issue before it goes for publication.

Author Response

However, I did not find much differences between the section on Results and Discussion and the section on Conclusions. The conclusions are reported in numbers, citations as similar to the Results and Discussion section. Conclusion should be conclusion of the research reported on this article not the repetition of results and discussion. I recommend the authors must address this issue before it goes for publication.

While there is some restatement of results in Conclusions, the Instructions for Authors provided by Remote Sensing state that the Conclusions “must be self-contained, a reader should not have to read through the paper to understand it”. Thus, when following the guidelines, we believe some repetition is essential. The only figures from our work cited are the width and central elevation of the peatland, and this is important for comparison to other peat domes.

 

Reviewer 3 Report

Dear Authors,

this is an interesting and useful study of the peat swamp surface morphology.

To make the manuscript publishable you should address the following points:

1. Your experiment design is faulty because of the datasets have different vertical datums, i.e., ASTER is on EGM96 datum (orthometric heights roughly mean sea level); TanDEM-X is on WGS84 (geodetic or ellipsoidal elevations must add geoid undulation to convert); LiDAR is probably on a local datum close to orthometric elevations.
2. To convert geodetic (or GPS heights) to orthometric heights in your AOI you should add approx. 8 m.
3. You are using the TanDEM-X data (3") a free version, and not a commercial product which is WordDEM. TanDEM-X is roughly DSM and not DTM (see e.g., DOI: 10.3390/rs8110934)! Again these elevations must be converted to orthometric elevations (+8m)
4. The ICESat data are completely redundant here.
5. To the ASTER data, you should also apply a moving average filter.
6. Your discussion/conclusions would include observations based on the ASTER/TanDEM-X data. Otherwise, TanDEM-X and ASTER are redundant here.
7. Try to estimate the elevation bias or forest impenetrability (60-80%) and subtract the vegetation height to approximate the surface of the peat.

Regards,

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors provided a detailed reply to my comments; I'm now satisfied and convinced about their argumentation. The paper could be published.

Author Response

Thank you for your help in improving this article, it is much appreciated.

Reviewer 3 Report

Dear Authors,

You still got the vertical datum issue wrong!

To compare these DEMs you need to bring them to a common vertical datum. Except for TanDEM-X, the other DEMs are on the mean sea level datum. To use the TanDEM-X data you need to add approx. 8 m to every point along the transect. Don't add anything to the ASTER data!.

Attached is one of your figures showing the correct vertical position of the TanDEM-X transect.

My suggestion is to drop the ASTER altogether as it is not good enough and redundant for this study. See: my paper on this issue: https://ieeexplore.ieee.org/document/6651798

Other things are fine.

Best Regards,

KB

 

Comments for author File: Comments.docx

Author Response

Thank you for this correction; we have removed the ASTER GDEM data from this work and adjusted the TanDEM-X data between 8.6m and 9.9m upwards according to the difference between the EGM2008 and WGS1984 datums.