Review of "High-resolution subglacial topography around Dome Fuji, Antarctica, based on ground-based radar surveys conducted over 30 years" by Shun Tsutaki and coauthors.

Summary:  

This a report on a subset of ice thickness data that has been collected over Dome Fuji, which has seen increased activity over the last few years as part of the Oldest Ice Challenge.  This is a unique dataset, and I think the authors miss some opportunities to make it more relevant to the community  and to the search for old ice.  There is a significant focus on uncertainty analysis, but little quantitative justification for the significance of the uncertainties in the context of the old ice search. I recommend revisions that more fully utilize the available data.

Major issues:

Data:  I think at a minimum, given the main point of the paper is the quality of the new grid derived from point data, to validate those claims the point data really should be released as part of the paper (if not here, where?).  This will make this paper a lot more valuable for both future data intercomparion papers, but also research into interpolation methods, and comparison studies between old ice sites.

Data integration:  This does seem to be a missed opportunity to integrated both the Kansas-Alabama radar data from JARE59 and the AWI data, would make the conclusions stronger. The Rodriguez-Morales et al., 2020 paper cited for the Kansas-Alabama radar is a radar engineering paper, and does not deal with interpretation or presentation of the ice thickness data in the context of old ice at all.

Beam patterns:  Given the focus on the Yagi improvements over the years, having a figure plotting the beam patterns for the different systems would be beneficial, including any side lobes.  Given the anisotropy in the beam patterns, caution should be used using crossovers to account for intersystem bias - over rough terrain, bias for an anisotropic sensor may be a function of the intersection angle (see the Appendix on the Young et al., 2017 Dome C paper). It seems expanding Figure 2 to include JARE 33 and JARE 37 would be instructive.

Comparison with other ice thickness products (section 4.2): It is unclear what the goal of section 4.2 is, in particular Figure 6.  Comparing an interpolated DEM which includes recent radar along the line of comparison, with other that don't, does not seem to be a fair comparison.  It would be better to the different interpolations along lines that are not aligned with included radar profiles, or better yet, along a radar profile that was not included in any of the DEMs, including the JARE DEM.  For each of the DEM's compared with, maps of the datasets that were used in their generation should be included in the supplementary material, with the line of comparison plotted.

Importance of the uncertainty analysis:  A lot of effort is spent on ways to quantify the uncertainty in ice thickness both of the profile data and of the interpolated grid; however, it is not made clear quantitatively what science reduced uncertainty allows.  How does improved confidence in ice thickness allow for a better assessment of locations of old ice?  What are the horizontal and vertical resolution requirements for constraining these targets?  

Analysis beyond ice thickness: The authors don't really go beyond ice thickness in any quantitative fashion.  Bed reflectivity for water distribution with such heterogenous data could be a stretch, but some additional parameters, like bed interface roughness, bed rock slope, and ice driving stress could easily be calculated from these data and be informative of regions for follow up. 

Minor issues: 

"Conventional" and "modern" radar should explicitly defined in the introduction - I think you mean by "conventional' is "real aperture" or "incoherent" radar.

Line 238:  Bedmachine Antarctica does not use mass conservation in slow moving regions, but instead a streamline diffusion method (Morlighem et al., 2019).

Figure 2: what is the cause of the change of gain in the NDF end of the JARE59 radargram?  The authors should highlight the key 2500 m depth on these radargrams.  It is notable that in general the bed roughness and the brightness of the scattered bed return appear much brighter above that line, consistent with a frozen, immobile bed with very little englacial attenuation.

Figure 7: Using the final 2500 m ice thickness contour on these difference maps would help orient the reader as to where major differences are.

Figure 8: Hill shading the zoomed in region may help in visualizing the roughness better.

Review of “High-resolution subglacial topography around Dome Fuji, Antarctica, based on ground-based radar surveys conducted over 30 years” by M.J. Wolovick et al.

22 November 2021

Summary

This MS describes a new grid of ice thickness and subglacial topography in the vicinity of Dome Fuji in East Antarctica. The underlying data and their strengths and limitations are summarized, the details of the gridding are discussed an evaluation of the output is performed against existing datasets.

The MS is mostly what it claims to be, which is refreshing, although no significant geophysical insight is gained into the Dome Fuji region beyond the subglacial topography that is presented. This limits the long-term value and reach of the MS, but the MS is thorough in its analysis of these data and in the clear application of necessary corrections (e.g., firn). The authors make a convincing argument that multi-element ground-based Yagi antennas are a reasonable alternative to SAR focusing. Separately, MS is well structured and visualized, but contains within several presentation decisions that raise concerns, outlined below.

Comments

Data availability. It’s not clear to me if the raw radargrams or lat/lon/thickness data are already available. If not, they ought to be. Otherwise, it implies proprietary data used herein are simply remaining so, which is not a great look in 2021. Along the same lines, the draft grid ought to be available publicly upon submission for review. This may not be required by TCD, but it is increasingly recognized as good practice and is required by some Copernicus journals. In my view, the authors should, at a minimum, point to a public repository with *both* the JARE lat/lon/thickness data and the grid. Prior to publication.

What is NDF? It is never defined other than its location. I’d have assumed it meant “North Dome Fuji”, but that doesn’t make sense geographically based on its location. Further, it is inconsistently identified in the figures. Shows up in some, not others.

274-277: It’s not clear to me why deep ice in subglacial troughs is subject to “complex ice flow” but that it is not the case for to subglacial ridges? See, e.g., Bell et al. (2011, Science, https://www.science.org/doi/10.1126/science.1200109) on the Gamburtsev Mountains.

Figure 3a: Given the contour lines shown, why not also use a discrete color bar? Little is gained from the continuous color bar, as features are not distinguishable between e.g., 2800 and 2825 m thickness at this scale.

Figure 4: Was “H” defined prior to mention in this x-axis? I assume it denotes ice thickness, following convention, but it would be good to clarify if in fact it wasn’t defined.

15: Degrees/minutes/seconds are archaic. Please present station coordinates in decimal degrees instead.

17: How close to the pressure-melting point?

25: What is “it”?

33: not yet identified

47: What is “solid” smoothing?

75-77: The mean annual temperature and accumulation rate presented here and in Figure S2 do not appear to add much to the discussion in the MS.

106: thicker ice to be detected

165, 166: bounce -> reflect

237-239: BedMachine Antarctica’s supplement makes clear that streamline diffusion, not mass conservation, is used to interpolate data in the slow-flowing interior of Antarctica, including the Dome Fuji region.

Summary

The manuscript presents recent high-resolution radar surveys around Dome Fuji, Antarctica with the motivation to inform future selection of oldest ice core drilling locations. They extract high-resolution bed topography and make a convincing case of the advantages of using a radar system with a highly directive beam pattern to study this region. The authors also combine recent and earlier surveys to generate new gridded ice thickness data covering the Dome Fuji region which is useful for oldest-ice drilling projects. However, it is unclear how the authors combine data from multiple systems and there could be missed opportunities to integrate the JARE data further with AWI or University of Kansas/University of Alabama data that was also mentioned in the manuscript. The new high-resolution survey and gridded product provide new and useful details on bed topography. However, the authors miss opportunities to provide further radar analysis and interpretation of the subglacial environment which would better narrow down locations for potential oldest-ice drilling.

Major Issues:

1. Radar Processing: To create the gridded ice thickness data, the authors combine data from multiple systems, which could suffer many potential issues. The manuscript does not provide enough evidence for how potentially data-combination issues were measured, dismissed, or corrected for, which is needed for the reader to evaluate the findings clearly. This should be added to the relevant sections on the radar processing steps involved in developing the gridded product before discussing the uncertainties in ice thickness which is separate for potential issues involved in combining data from different radar systems. The authors also discuss data from AWI and the University of Kansas/University of Alabama, which seems could be added to the gridded ice thickness. Or if not added, this should be convincingly explained why not.
2. Radar Analysis: Regarding the analysis and interpretation of the subglacial environment, the radar analysis does not go further than plotting ice thickness and extracting bed topography. Hence, the analysis does not provide sufficient evidence to demonstrate that there is an improvement in knowledge of the subglacial environment needed for selecting ice core drilling locations. There is no updated analysis of the basal thermal state or the bed roughness. I suggest more analysis on quantifying the subglacial environment such as extracting bed power/radar reflectivity/roughness to demonstrate the improvements of this new radar dataset in constraining the subglacial conditions.

Minor Issues:

1. NDF is not defined anywhere
2. Figure 2: The values for the color range is not specified. It would be best to add colorbars or at least state the range in power that is plotted in these radargrams. Are the color ranges the same for a and b? Are the colors saturated?
3. Figure 3: Plot/label NDF for consistency and comparison to figure 1.
4. Figure 4: I suggest writing frequency on all the furthest left y-axes for clarity (instead of just the middle row). Same for delta H for the columns.
5. Figure 6: again colorbar for the background radargram power.
6. Figure 7: it would be helpful to have NDF labeled
7. In section 4.3, the authors suggest that even higher spatial resolution is needed to resolve the best candidate points for drilling. The authors should suggest what radar system design might be needed to achieve this spatial resolution.
8. Discussion around Line 275 should be tied back to the radargram figure along with more concrete discussion. For example, I would like to see a list or examples of what portions of the radar survey shows undisturbed layers just above the bed.