Drone-Based Ground-Penetrating Radar with Manual Transects for Improved Field Surveys of Buried Ice

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript showcases the use of an airborne GPR to assess the internal structure of a debris-covered glacier. This subject clearly falls within the scope of the journal, and the manuscript discusses the use of drone-based instruments in what is generally considered a ground-based technique, the GPR survey. It is correct that direct GPR profiling over rugged terrain is often complicated, thus airborne solutions are of particular interest. Emerging (relatively) low-cost instruments promise certain advances in this research field, but the associated uncertainties are still to be evaluated. In this scope the present manuscript provides the direct comparison and uncertainty assessment of drone-based and manual GPR techniques. The manuscript is concise and well-written, and there are only minor typos to correct. The authors are explicit in explaining that such a comparison lacks direct ground trothing from debris pits and ice body drilling, which is the major shortcoming of the research plan (and the manuscript). Therefore, the manuscript results support the potential use of airborne GPR systems in rock glaciers and on debris-covered slopes, notably for the buried ice detection, but gives only a vague idea of the technique’s accuracy and precision. Eventually, I can not insist on addressing the issue because it will require a full-scale field campaign, which is too restrictive and beyond the scope of the review. Despite this shortcoming I would recommend the manuscript for publication if the handling editor finds it appropriate.

I would however suggest that the authors discuss two points that refer to their results. First, is there any effect of debris/boulder size on signal-to-noise ratio at any of the antenna frequencies? Second, how able the drone-based solution might be in detecting buried ice in finer sediment? Third, can this technique be applied to study river ice thickness, or look for ground ice buried in river channel deposits (as was done by Delaney et al., 1990)? I propose to include the dedicated sub-section 4.3 in the Discussion section reflecting on the use of drone-based GPR solutions in research fields outside mountain permafrost studies.

Author Response

Comment 1: First, is there any effect of debris/boulder size on signal-to-noise ratio at any of the antenna frequencies? 

Response 1: Thank you for the comment. Related to the later points to be addressed, I have added discussion of debris size and interpretation of the data in the newly added section 4.3 on lines 365-369. We did not produce any quantitative assessment of SNR through our analysis to compare between antennas since the GPR interpretation is achieved by judging the layered traces in the radargram, so there is no straightforward way to measure SNR directly. Thus, we were only able to make a general recommendation based on the results of the drone-based GPR and the physics of GPR. 

Comment 2: Second, how able the drone-based solution might be in detecting buried ice in finer sediment?

Response 2:  Please see the additions noted above. We made recommendations related to this point.

Comment 3:  Third, can this technique be applied to study river ice thickness, or look for ground ice buried in river channel deposits (as was done by Delaney et al., 1990)? I propose to include the dedicated sub-section 4.3 in the Discussion section reflecting on the use of drone-based GPR solutions in research fields outside mountain permafrost studies.

Response 3: Please see the added section 4.3 as suggested. This comment is addressed more generally for methodological recommendations that can be made for applying drone-based GPR in geophysical investigations. No specific recommendations can be reasonably made for use in specific sub-fields such as river ice studies since the use would depend on field conditions, as described in this section.

 

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript “Drone-based ground-penetrating radar with manual transects for improved field surveys of buried ice” by Tjoelker et al. compared two surveyed modes (drone-based and manual) to survey buried ice. This work is significance to develop drone-based GPR. This manuscript is well written and organized. However, I have to point out that the difference between drone-based and manual GPR.  In other words, I do not get the point what is the difficulty or effect factors of drone-based GPR though authors compared the results of the two surveyed modes. Anyway, I would suggest it should be minor revised.

Line 102 Drone-based GPR this section is no enough.

Is the air layer the only thing that affects the measurements due to drone flight height besides  a little bit different path?

Line 172 Done-based radargrams

This section is too little compared with section 3.2

Author Response

Comment 1: Line 102 Drone-based GPR this section is no enough. Is the air layer the only thing that affects the measurements due to drone flight height besides  a little bit different path?

Response 1: The section "Drone-based GPR" is kept concise to allow for more detailed discussion of the impacts of different sources of uncertainty on the data in section 4.2.1 and 4.2.2. The air layer separating the drone from the surface and the path taken are only two of many sources of uncertainty in the data. 

Comment 2: Line 172 Done-based radargrams This section is too little compared with section 3.2

Response 2: This section is kept concise and shorter than 3.2, since 3.2 covers the comparison of the two methods while 3.1 just introduces the results from the drone. Figure 3 displays these results in full detail on the following page.