Here we present ultra-wideband radio-echo sounding data in northeast Greenland upstream of the northern catchment of the Nioghalvfjerdsbrae (79°North Glacier; 79NG). The radar data were acquired with AWI's multi-channel ultra-wideband (UWB) radar system in 2018. Most radar lines are located close to the ice divide; where ice flow velocity is almost zero and increases eastwards to as much as 15 meters per year. The survey was designed to closely investigate a set of folds. Twelve RES profiles were flown, at 7.5 km spacing, and oriented perpendicular to the 100° true North trend of the fold axes. The radar data has been used to decipher the regional ice-flow history of the northeastern Greenland Ice Sheet based on its internal stratigraphy. We applied a three-dimensional reconstruction of time-equivalent horizons to map folds deep below the surface that we then attribute to the deformation caused by now-extinct ice streams. We propose that locally this ancient ice flow regime was much more focused and reached much further inland than today's and was deactivated when the main drainage system was reconfigured and relocated southwards. The insight that major ice streams in Greenland might start, shift or abruptly disappear will affect future approaches to understanding and modeling the response of Earth's ice sheets to global warming.

We present two radar data products: CSARP_qlook (unfocused) and CSARP_standard (SAR focused). For both, the files contain the radar data in the .mat format as well as pdf files of each segment with flight tracks and a radargram for each frame. Furthermore, we include an excel spreadsheet (rds_param_2018_Greenland_Polar6_FINEGIS.xls, see Further details link) which contains all radar data processing parameters.--CSARP_qlook: This product uses unfocused synthetic aperture radar processing for each channel and assumes that all reflections arrive at the receiver from nadir. The data are coherently stacked in slow time, and no correction for propagation delay changes is applied. Here, no motion compensation is applied. Finally, the signals from all eight channels are averaged incoherently. The range resolution is the same as for all other products. The trace spacing is ∼ 27–30 m.--CSARP_standard: This data product uses focused synthetic aperture radar processing (fk migration) on each channel individually. The SAR processing requires a uniformly sampled linear trajectory along the extent of the SAR aperture. Motion compensation is applied using high-precision processed GPS and INS data from the aircraft. The direction of arrival is estimated by delay-and-sum beam forming to combine the channels. A Hanning window is applied in the frequency domain to suppress side lobes. This product is comparable to the CReSIS standard data product. The trace spacing is ∼ 15 m.Further Reading:https://data.cresis.ku.edu/#RDShttps://ops.cresis.ku.edu/wiki/index.php/Main_Page