the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 10 Feb 2026
Brief Communication: Bed mapping of southern Greenland outlet glaciers using helicopter-borne ground penetrating radar (AIRETH)
Abstract. We present the first southern Greenland deployment of the redesigned Airborne Ice Radar of ETH Zurich (AIRETH). We surveyed 348 km of flight lines over three outlet glaciers and identified bed reflections along 102 km (29 %). The 25 MHz configuration achieved an effective penetration depth of about 300 m and a maximum inferred ice thickness of about 340 m, while bed detectability decreased over thicker and/or heavily crevassed ice. These results define the current depth limitation of our system and show that terrain-following helicopter surveys can provide targeted constraints that complement existing datasets in complex topography.
Competing interests: At least one of the (co-)authors is a member of the editorial board of The Cryosphere.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-488', Emanuele Forte, 10 Mar 2026
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RC2: 'Comment on egusphere-2026-488', Thomas Teisberg, 26 Mar 2026
This paper introduces a helicopter-borne GPR survey carried out over several southern Greenland outlet glaciers. The radar survey was carried out with a low frequency impulse system carried at low ground speeds by helicopter close to the surface, all of which enable this survey to capture bed reflections in challenging conditions (temperature ice, steep valley walls). The survey produced new bed topography picks, which are compared against both other radar bed measurements (from NASA's Operation IceBridge flights) and the BedMachine basal topography data product.
Overall, the paper is a great contribution towards improving knowledge of Greenland outlet glacier topography and thinking about the best types of radar sounder instruments for particular locations. A few minor comments and suggestions are below:
1 - New radar data is most valuable when it is publicly released in useful formats. I would encourage the authors to release their original source radar data and processed radargrams. Particularly for the former, working with Open Polar Radar may be valuable as a publicly-accessible repository for such large datasets. Notably, those who generate bed topography data products may desire to use the bed picks from this data. In cases where this data differs from OIB surveys (as identified in Figure 3), creators of bed topography products must have access to both sets of radar data in order to make informed judgments.
2 - The migration of the radar data will produce an effective beam pattern that is narrower in the along-track direction as compared to the cross-track direction. This could account for places where only one of two crossing tracks has a detectable basal interface. It could also account for the cross-flow lines having better basal interface detection probability, as noted in the manuscript. Depending on how the processing was implemented, it is also likely that the different target flight speeds in across-flow and along-flow survey modes explains part of the difference in basal detection. It would be helpful to note the window over which migration was performed. These possible causes should be noted in the same section as the comment about better detection probability in the across-flow direction. If this is a subject of interest, a comparison of radargrams produced using only one of the two orthogonal antennas and/or without migration at a crossover point would be interesting.
3 - The comparison between newly collected bed measurements and OIB/BedMachine topography in Figure 3 is very interesting. In addition to the two radargrams showing comparisons against BedMachine, I would like to see what the comparison against OIB radargrams looks like for one of the large offset cases (such as the handful of points where OIB seems to have bed picks about 400 meter below the newly reported bed picks). Consider commenting on how you determine that the newly reported bed picks are not a cold-to-temperate transition (as the supplement suggests you have observed at least once). It would also be helpful to comment on the significance of the new bed picks seeming to diverge from BedMachine around 0 meters (which I interpreted to be 0 m WGS84).
4 - Related to the above, I would encourage the authors to remove the > 600 meter difference outlier criterion and include all offsets in the Figure 3 scatter plot. A difference in bed elevation in excess of 600 meters is potentially extremely important to modelling. Such an extreme difference likely results from an incorrect bed pick in some radar data source, which can only be reviewed and corrected if it is identified.
Overall, this paper and accompanying dataset are great contributions, and I look forward to seeing the manuscript published soon.
Citation: https://doi.org/10.5194/egusphere-2026-488-RC2
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The paper entitled Bed mapping of southern Greenland outlet glaciers using helicopter-borne ground penetrating radar (AIRETH) focuses on a new GPR dataset collected in March 2025 using a redesigned helicopter-borne radar. The manuscript is well written and organised. It contains interesting comparisons between the new ice thickness estimates and previous publicly available datasets from the same area. While the analysis is rigorous and meaningful, I suggest some possible improvements and clarifications:
- The text states that the effective penetration depth is approximately 300 m, reaching 340 m in around 5% of measurements. These values are reported multiple times throughout the manuscript, but they are somewhat confusing. I recommend marking the maximum penetration depth obtained, detailing that it is reduced under specific ice conditions.
- Figure 1 summarises the ice thicknesses were the AIRETH profiles provide an interpretable glacier bad. There are crossing point at which such an interface is detected only along one of the two crossing profiles. This peculiar situation should be commented on and discussed.
- Figure 2 shows examples of AIRETH-interpreted profiles. The authors state in the text that: " the basal return commonly manifests as a transition from low-amplitude, texture-like clutter to a zone of persistently higher backscatter", but this is not always the case, as is apparent from the examples themselves, as well as the supplementary material. The authors merely state that "in a few sectors (see Figure 2b–c), the bed forms a continuous, high-amplitude horizon." I recommend deepening the analysis by discussing the high radar signature variability in the text.
I recommend publishing the paper after the previous points have been addressed and a minor revision process has been completed.