The Northeast Greenland Ice Stream (NEGIS) efficiently drains a large area of the Greenland Ice Sheet and is a crucial component of the ice sheet mass balance . It extends from the central ice divide over more than 600 km towards the northeastern coast, where it discharges ice through the three marine-terminating glaciers (79∘ North glacier, Zachariae Isbræ, and Storstrømmen glacier). The currently prevailing hypothesis is that an anomaly of elevated geothermal heat flux (GHF) leads to extensive basal melting and induces ice flow. The GHF at the onset of NEGIS is the most important and, at the same time, most uncertain parameter in the representation of basal melt and the subglacial hydrology in ice flow models . However, the large gap between observed and modeled basal melt rates inside the ice stream and in the broader surroundings of the NEGIS onset raises questions about the real thermal state at the bed. The exceptionally high GHF proposed by would be non-compatible with known geological processes . Therefore, raise the question of how fast flow at the NEGIS onset is possible without an extraordinarily high basal heat flux and melt rates.

Unlike other ice streams in Greenland, the NEGIS lacks an extensive overdeepened bed and thus lateral topographic constraints . The ice stream more or less symmetrically broadens along flow, as more ice is dragged through the shear margins . Subglacial water routing in combination with subglacial till deformation seems to be a further controlling mechanism of ice flow at the onset of the NEGIS . The outlet area is characterized by an overdeepened basin covered with unconsolidated sediments . Ice thinning as a consequence of increasing oceanic water temperatures around Greenland could thus potentially be transmitted far upstream , and changes in the hydropotential might have significant effects on the ice stream geometry. The high susceptibility of NEGIS to marine-triggered discharge and the expected increase in ocean water temperatures in the years to come raises questions about the future ice stream stability and its effect on the Greenland Ice Sheet mass balance.

Large-scale ice flow models are essential tools to predict the future behavior of glaciers and ice sheets and are necessary to estimate future sea-level rise. Until today, these models fail to successfully simulate the NEGIS due to insufficient understanding of the key processes responsible for ice flow dynamics , limiting the prediction accuracy. The East Greenland Ice-Core Project (EastGRIP; https://eastgrip.org, last access: 17 March 2021) aims to drill a deep ice core in the upstream area of the NEGIS, providing valuable insights into the climate record, basal properties, and ice flow history at the drill site. Ice cores provide in situ information on physical and chemical properties at high resolution but are limited as being a spatial point measurement. Hence, further geophysical techniques are required to extrapolate this information to obtain a complete picture of the ice dynamic properties.

Radio-echo sounding (RES) has long become a standard method in glaciology. The polar ice sheets as well as low-latitude glaciers and ice caps have extensively been covered by airborne e.g., or ground-based e.g., RES surveys. The transmitted electromagnetic waves are sensitive to changes in dielectric permittivity and electrical conductivity and get reflected, scattered, or refracted at interfaces of dielectric contrasts in the medium they propagate . The most common glaciological application is the sounding of ice thickness and bed topography e.g.,. Reflections within the ice column, or so-called internal reflection horizons (IRHs), are often caused by impurity layers of volcanic origin representing isochronous horizons . These provide valuable information on the ice flow regime and strain history and can be used to reconstruct past accumulation rates e.g.,, match ice cores from different locations e.g.,, and validate numerical ice flow models e.g.,. Further applications of RES include the detection of crevasses e.g.,, mapping of subglacial lakes and basal hydrology e.g.,, identifying thermal regimes e.g.,, determining snow and firn genesis e.g.,, and obtaining information on the crystal orientation fabric e.g.,.

We present airborne radar data of the onset region of NEGIS recorded in 2018 by a multichannel ultra-wideband radar system. The data set consists of profiles oriented parallel and perpendicular to the ice flow direction. The high along-track and range resolution allows consistent isochrone tracing, providing insights into the three-dimensional structure of the ice stream. In combination with the EastGRIP ice core, this data set contributes to a better understanding of ice flow dynamics of the NEGIS. In our paper, we introduce the study site and survey design. Furthermore, we describe the radar data processing and the respective data products. The data are freely available from the PANGAEA data publisher (https://doi.pangaea.de/10.1594/PANGAEA.928569; ).

In May 2018, we recorded radar data in the vicinity of the drill site of the EastGRIP ice core. An area of ∼24000 km2 was mapped, with 7494 km of radar profiles along flow lines and perpendicular to ice flow (Fig. 1). The survey region extends ∼150 km upstream and downstream of the EastGRIP drill site and ranges from the central part of the ice stream up to 50 km beyond the shear margins. In our survey region, the ice stream accelerates from ∼10 to more than 80 m a-1 and widens from ∼15 to ∼55 km. The radar data also cover the transition in the position of the shear margin as well as strongly folded internal stratigraphy outside of the ice stream (see Fig. 1). Figure 1b and c show the locations of radar profiles in relation to the ice surface velocity. Profiles extending perpendicular to ice flow have a spacing of 5 km in the region close to the drill site and 10 km further up- and downstream. Along-flow profiles either follow flow lines, which in some cases pass through the shear margins, or are constantly located inside the ice stream. Other profiles are oriented parallel to ice flow of the NEGIS but are located outside of the ice stream.

The ice thickness in our survey region ranges from 2059 to 3092 m and shows, on average, a gradual decrease in thickness from the upstream to the downstream part . An analysis of the bed topography, basal roughness, and bed return echoes by shows that our survey area can be divided into two different morphological regimes. The upstream part (upstream of EastGRIP) is characterized by a narrow ice stream width with accelerating ice flow velocity, a smooth bed with elongated flow-parallel subglacial landforms, and a soft till layer at the base . Downstream of EastGRIP, the ice stream widens, and we note an overall change to a rougher and more variable bed geomorphology. The ice stream widens up to 57 km, and ice flow velocity keeps constant and decreases locally .

In the 2012 summer field season, a scientific consortium collected ground-based geophysical data (RES and seismic survey) as well as a shallow ice core . examined the ice–bed interface by means of radar and seismic data analysis. They found high-porosity, water-saturated till, which lubricates the ice stream base and most likely facilitates ice streamflow. used the same radar data to analyze the internal radar stratigraphy and suggest that the basal hydrology controls the upstream portion of the NEGIS. By contrast, the downstream part is rather confined by the bed topography. and analyzed the shear margins in particular and observed an increased accumulation and enhanced firn densification in the upper ice column as well as wet elongated subglacial landforms at the bed. Furthermore use RES data to evaluate 3D thermomechanical models of the NEGIS. The authors highlight the complexity of the stagnant-to-streaming ice flow transition and provide insights into the englacial heat transport. Finally, a comprehensive chemical analysis of a 67 m deep firn core was conducted by . The results demonstrated that a deep ice core at this location has the potential to retrieve a reliable record of the Holocene and last glacial cycle.

The design of the EGRIP-NOR-2018 radar survey enables a detailed analysis of the bed and englacial stratigraphy: (i) along radar profiles which are parallel to the ice flow (Fig. c) and (ii) along radar profiles perpendicular to the ice flow, crossing the shear margins (Fig. b). In addition, several radar lines cover the location where the northern shear margin shifts its location (Fig. a) and an area southwest of EastGRIP where we observe patterns of strong internal ice deformation (location indicated in Fig. a).

In flow-parallel profiles, we observe three regimes showing different characteristics in the radar stratigraphy. Figure  shows a ∼200 km long flow-parallel radargram extending from the far upstream end outside of the NEGIS up to 30 km downstream of EastGRIP. The area outside of the ice stream at a distance of 0–60 km shows slightly folded internal layers, which have no connection to the local basal topography. Steeply dipping internal layers are characterized by a decrease in reflectivity with depth. The part of the profile which is crossing the shear zone (at 60–90 km distance) is characterized by tight folds in the internal layers, which extend almost up to the ice surface. The folds' apparent wavelength in profile direction depends on the intersection angle with respect to the shear margin orientation. Folds are tightest in profiles oriented ∼90∘ to the shear margin fold axis. We observe the best resolution of internal layers inside the ice stream, particularly in the lower part of the ice column. All distortions in the internal stratigraphy inside the ice stream seem to be related to the underlying bed.

Radar profiles oriented perpendicular to ice flow show a strong imprint of NEGIS' dynamics. The most striking features are tight folds in the area of the shear margins. Bright stripes characterize them in the radargrams (e.g., Fig. ), which represent a loss in return power due to steeply inclined internal reflectors . The onset of this kind of folding starts at the shear zone's outer boundary (marked by yellow triangles in Fig. c and d). Depending on the ice stream's location and width, these folds can be traced towards the ice stream center for up to tens of kilometers, also towards locations where no shearing at the ice surface is observed. This becomes evident by comparing the upstream and farther-downstream radargram in Fig. c and d.

At several locations in flow-perpendicular radargrams we observe a drawdown of the radar stratigraphy towards the shear zone's outer margin (see Fig. c). The drawdown could be explained by temperate ice at the base . Melting at the base at this location would be in agreement with subglacial hydrology modeling results by , who suggest that melt out of sediments within the ice column potentially creates the subglacial bedforms they identified. In general, the stratigraphy of internal layers northwest of the NEGIS differs from the stratigraphy southeast of the NEGIS. The northwest is much more undisturbed than the southeast. A distinct example is shown in Fig. a and b. The stratigraphy is marked by long-wavelength anticlines and synclines with elevation differences of almost half of the ice column. In the anticlines' cores, we find strong englacial reflections, which have been misinterpreted before as bedrock . We note that some of the englacial reflections appear to be attached to the basal reflection (Fig. a). This could be an indication that the strong englacial reflection could be due to basal material (e.g., soft sediments) that was transported upwards by the folding process. Figure b shows that the deformation patterns in the anticline cores are very complex. Some of the reflection patterns (e.g., in Fig. b) result in connected structures similar to the isochrones in the upper part of the ice column. In addition, we find isolated patches with high reflectivity, which, however, do not show a coherent pattern (highlighted in Fig. b).

This radar data set provides essential observations of internal and bed reflections to determine spatial distribution of ice thickness, internal layering, and reflectivity. These observables constitute boundary conditions and elucidate properties and processes of the NEGIS. The tightly spaced survey lines allow information on the past and present ice flow dynamics to be derived, revealing the paleo-processes of the NEGIS, in particular when combined with ice core data. Hereby it might be possible to address the question of how long the NEGIS has been active in its present form. The radar data furthermore allow a systematic analysis of the return power of internal layers and the bed and could potentially reveal information about the englacial temperature regimes and properties of the bed and basal hydrology e.g., as well as provide crucial boundary conditions for ice flow models . In addition our data hold the potential to map the crystal orientation fabric (COF) and especially the horizontal anisotropy from the birefringence effects , e.g., at the shear margins or at intersecting radar profiles of different polarization directions. Because ice stream regimes have a strong effect upon the COF , it is another important, but yet poorly constrained parameter in ice flow modeling.

The data comprise ∼7500 km high-resolution radar data for the scientific community to use. In contrast to previous surveys in this area, the data presented here were specifically recorded over a broad spatial extent to understand the history of the NEGIS and our general understanding about ice streams. The tightly spaced radar profiles perpendicular to ice flow allow a 3D interpretation of the ice-internal stratigraphic architecture. Because most radar lines are directly or indirectly spatially connected to the location of the drill site of the EastGRIP ice core, these data are significant for various objectives regarding the ice dynamic understanding of NEGIS as well as interpretation of the climate proxy record retrievable from the ice core. With this data set the scientific community will be able to upscale the findings of the EastGRIP project from the location of the ice core to the immediate surroundings of the upstream part of the NEGIS. The prospect that parts of the ice core can be rotated back into their correct geographic direction also allows a systematic analysis of ice crystal orientation fabric together with the radar data. Furthermore, the data presented here can be combined with the radar data acquired during Operation Ice Bridge (OIB) to extend the large-scale understanding of glaciological properties in the Greenland Ice Sheet.

The EGRIP-NOR-2018 radar data products are available from the PANGAEA data publisher (10.1594/PANGAEA.928569; ). The EGRIP-NOR-2018 bed topography is available under 10.1594/PANGAEA.907918. The CReSIS toolbox is available under https://github.com/CReSIS/ , and the main documentation can be found at https://ops.cresis.ku.edu/wiki/ . The MEaSUREs Greenland Ice Sheet velocity map from InSAR data, Version 2, from is available from 10.5067/OC7B04ZM9G6Q .

We present a high-resolution ice-penetrating radar data set at the onset region of the NEGIS. The EGRIP-NOR-2018 radar data reveal the internal stratigraphy and bed topography of the upstream part of the NEGIS in high vertical and horizontal resolution, given the dense coverage. Several survey lines intersect at the EastGRIP drill site location, enabling a combination of both data sets. Ultimately, this data set will improve our understanding of the NEGIS in its present form and also contributes to our understanding of its genesis and evolution. Radar and auxiliary data are provided as matfiles for the combined echograms as well as for the individual waveforms. The radar data products comprise unfocused data (qlook), SAR-focused data (SAR1), and SAR-focused data with a wider angular range (SAR2)