How Many Reindeer? UAV Surveys as an Alternative to Helicopter or Ground Surveys for Estimating Population Abundance in Open Landscapes

Round 1

Reviewer 1 Report

Nice work, thank you.

Author Response

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Reviewer 2 Report

The manuscript titled “How many reindeer? UAV Surveys as an Alternative to Helicopter or Ground Surveys for Estimating Population Abundance in Open Landscapes” presents a comparative study of UAV, helicopter, and ground surveys for estimating population abundance of reindeer communities in the Arctic Svalbard archipelago, Norway. The topic is interesting. However, there are many problems emerge. The biggest concern of mine about this study is that this study contributes less to remote sensing. I would expect to see some new algorithm that we can identify individual reindeer from UAV images automatically instead of that UAV produces the low precision results. The UAV survey conducted in this study more looks like an alternative to field sampling, which did not take advantage of the UAV. And the validation result was not presented in the manuscript, which hindered the understanding of which method could be used for reindeer population investigation. More details comments are seen below.

 

1. The experiment design is not appropriate enough. The present three methods are conducted in different spatial extents, which makes the survey results by each method incomparable in quantity. Moreover, in the present study, the UAV is more likely an alternative to a ground survey because it only collected the land surface information that is the same as the part of some ground survey transects, which could be the reason why the authors stated that the UAV survey showed low precision in population estimation although the validation of this study was not presented in the manuscript. Furthermore, in my opinion, the small quadcopter drone may be not suitable for species with sparse communities in a large area, since its advantage is providing quick and flexible images with high resolution and spatial continuity in a small area, for example, vegetation mapping in the study area. Therefore, the fixed-wing UAV could be the very method that should be used in this study.

 

2. The validation of the three presented methods was not shown in the manuscript. The accuracy of each method in the reindeer population estimation should be presented quantitatively to show which method produces the most accurate result. And, table 2 should also provide more quantitative information rather than its current data. We all know the qualitative assessment of these three methods in their economic cost, environmental impact, and animal disturbance. The current version looks like belongs to the introduction section. I suggest authors provide more quantitative results, for example, the accuracy assessment of these three methods and other factors, in table 2. In addition, more information is also needed to address the advantages and disadvantages of these methods in population abundance investigation, guiding future works in method selection. Such as, the flight height of the UAV is also needed to be evaluated for the best trade-off between reindeer detection and the spatial extent of the investigation, etc.

Author Response

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Reviewer 3 Report

Dear Authors,

The paper “How many reindeer? UAV surveys as an alternative to helicopter or ground surveys for estimating population abundance in open landscapes” presents a UAV-based count of reindeer in a Svalbard valley. The obtained results have been compared with results obtained from ground- and helicopter-based counting surveys.

 

GENERAL COMMENTS:

The topic is of interest but the manuscript is not easy to read.

The manuscript has too many sub-sections that should be numbered and in some cases merged. Figures and tables are often far from the point they are referred to into the text. Moreover, editing of English language is required.

The adopted method is not clearly explained in its entire steps (see also specific comments) and the workflow figure should be improved to help the understanding of the entire proposed methodology.

The comparison step between the three proposed approaches should be detailed more in deep helping the understanding of the presented results.

 

SPECIFIC COMMENTS:

- line 18: please define the acronym UAV because is the first time that it occurs in the abstract;

- line 39: please define the acronym UAV because is the first time that it occurs in the manuscript;

- lines 41-42: please use rounded brackets for the text and square brackets for the citations;

- line 50: please use just the acronym UAVs;

- lines 50-51: UAV, RPAS and drone indicate the same thing. Why did the Authors name all the three?

- line 73: please use rounded brackets for the text and square brackets for the citations;

- line 98: please number the sub-section as 2.1

- line 106: please number the sub-section as 2.2

- line 115: please number the sub-section as 2.3

- line 132: please use italic for the heading;

- line 146: please use italic for the heading;

- line 163: please use italic for the heading;

- line 173: please number the sub-section as 2.4

- lines 173-180: Why did the Authors add this sub-section? What is the effort in comparison of the three different methodologies adopted (i.e., ground- , UAV- , and helicopter-based survey)? According to the workflow figure, it seems that maxNDVI pixels have been used to count species, like a sort of truth, but this step it is not clear. According to the following sub-sections, it seems that maxNDVI pixels have been used to determine sub-areas to the count of the reindeers, but, again, it is not clear. Please clarify how and why the Authors used maxNDVI;

- line 181: please number the sub-section as 2.5

- line 186: please use italic for the heading;

- line 205: please use italic for the heading;

- lines 230-234: This step is not clear. Please rephrase to better explain this methodological step;

- line 245: please use italic for the heading;

- line 268: please number the sub-section as 2.6;

- line 283: please number the sub-section as 3.1;

- line 293: please number the sub-section as 3.2;

- line 306: please number the sub-section as 3.3;

- line 312: please number the sub-section as 3.4;

- line 325: please number the sub-section as 3.5;

- line 370: what did the Authors mean with “reasonable level”?

 

Author Response

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Round 2

Reviewer 2 Report

I am generally pleased with the revision. Most of my concerns are heeded though some of them may not be resolved in this study. Therefore, one more minor comments for the author is that the potential research could be conducted in future should be mentioned in the manuscript for guiding the further research on UAV investigation of the animal abundance.

Author Response

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Reviewer 3 Report

Dear Authors,

all my previous comments have been taken into account. Now the paper is stronger and with a more scientific sound. Thanks to the effort in this revision.

Author Response

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