Review of "Airborne ultra-wideband radar sounding over the shear margins

and along flow lines at the onset region of the Northeast Greenland

Ice Stream" by Franke et al..

This manuscript describes a newly constructed airborne radar sounding dataset over the initiation zone of Greenlands largest outlet glacier, NEGIS. The survey area covers several hundread kilometers along strike, including the EastGRIP drill site, and with many transects perpendicular to ice flow. The authors describe the data collection and processing steps, resulting in the construction of numerous 'cleaned' radargram profiles for download by interested readers.

The authors have written a concise and well formated manuscript which achieves their goals of presenting and releasing a new radar dataset of NEGIS. This dataset covers a larger spatial extent than previous products, and has been robustly processed and archived, and hence is a valuable dataset for future work. I only have minor comments, as the paper is already of high quality, and is suitable for publication in ESSD.

Minor comments:

1). The paper could be strengthened by emphasazing with more precise examples what types of new insights, and scientific discoveries, this dataset may help address. In the `Relavance of the data set' section, they say "These observables constitute boundary conditions and elucidate properties and processes of NEGIS" (Lines, 268 - 269), which is true, but it is vauge. Perhaps the authors should identify the key things in glaciology that refined bed and ice column images could help reconcile: e.g., basal hyrdaulic processes, stick-slip processes, rheologic deformation laws (Podolskiy and Walter, 2016), etc. The connections of their data to the many previous studies at NEGIS could also be highlighted more; such as, are the main features of these data consistent with  Christianson et al., 2014, Villelonga et al., 2014, Riverman, 2019, etc?

2). In  Figure 3), caption, it's stated, "ice flow direction is out of page". However, the ice flow direction is actually "into the page", as can be seen since c1', c2', c3', are all on the right hand side of these transects, and in map view Fig. 1, the c1', c2', c3', are on the south-east side of the ice stream, and of course NEGIS flows north.

3). In discussing the flow perpendicular radargrams, they state " In the anticlines’ cores, we find strong englacial reflections, which have been misinterpreted before as bedrock (Franke et al., 2020)". (Lines 212 - 213). Can the authors clarify this point? What new lines of evidence are being used here, compared with the study Franke et al., 2020, to re-interpret these features? The remaining sentences of this paragraph, "We note that some of the englacial reflections appear to be attached to the basal reflection (Figure 3a). Figure 3b shows that the deformations patterns in the anticline cores are very complex" (Lines 213 - 214) could also be expanded to include more details.

4). In relation to SAR processing, it's stated that "We used a two-layered velocity model with constant permittivity values for air (r = 1) and ice (r = 3.15)" (Line 137).  Can the authors clarify that no problems are encountered by ignoring the uppermost ~50 - 100 m of firn in the ice? Clearly the ice column is not precisely a homogenous medium, so the authors should qualitatively (or quantitaively) justify the effects of this approximation.

This manuscript presents a high-resolution airborne radar data set (EGRIP-NOR-2018) for the onset region of NEGIS. We found that the authors have used this data set to produce and publish the gridded ice thickness and bed topography data as well as the TWTs of the ice thickness along the radar profiles in the onset region of NEGIS, which constitute important boundary conditions for numerical model. Even so, the data presented in this manuscript is of exciting importance. From it, we can also derive the characteristics of isochronous layer to reveal the historical properties and processes of the NEGIS, especially when combined with ice core data. There are, however, major issues with the manuscript that would be valuable to address.

First, the data set is not accessible via the given identifier in the paper (https://doi.pangaea.de/10.1594/PANGAEA.928569) may for it is still under review (it shows “The rights given by your login do not allow downloading of dataset #928569. Please login with another user name!”). As a result, I have not been able to assess whether the data set meets the requirements of the journal.

Second, “line 63” says “unique airborne radar data”. I think it is a needless over-assertion which weakens the credibility of the authors and manuscript. Does IceBridge have any observations in this area? If so, I think the authors should make a cross-comparison with IceBridge to validate the data set. If not, can use crossover analysis to validate the data set. In addition, can the authors give the calculation and accuracy of GPS and INS in this manuscript? From the manuscript, they have an important impact on the accuracy of the data set. In a word, I think the accuracy evaluation of the data set is not enough.

I made some specific comments and suggestions below, which I hope will help improve this paper.

L175: What does “ki” mean in equation 4?

L182: What does “kt” mean in equation 5?

Figure 3 “C1,2,3” should be “C1-C1’, C2-C2’, C3-C3’”, keep the same with Figure 1