. Further by downloading this data the user acknowledges that they agree with the NERC data policy (), and the following conditions:

1. To cite the data in any publication as follows:

Ferraccioli, F., Corr, H., Jordan, T., Forsberg, R., Matsuoka, K., Diez, A., Olesen, A., Ghidella, M., Zakrajsek, A., Robinson, C., & King, O. (2021). Processed airborne radio-echo sounding data from the ICEGRAV survey covering the Recovery Catchment and interior Dronning Maud Land, East Antarctica (2012/2013) (Version 1.0) [Data set]. NERC EDS UK Polar Data Centre. https://doi.org/10.5285/C6324118-94A2-4E03-8715-B24B82322A57

2. The user recognizes the limitations of data. Use of the data is at the users' own risk, and there is no warranty as to the quality or accuracy of any data, or the fitness of the data for your intended use. The data are not necessarily fully quality assured and cannot be expected to be free from measurement uncertainty, systematic biases, or errors of interpretation or analysis, and may include inaccuracies in error margins quoted with the data.

Methodology:

** Instrumentation and Processing:

Radar data were collected using the bistatic PASIN radar echo sounding system mounted on the BAS Twin Otter aircraft "VP-FBL" and operating with a centre frequency of 150 MHz and using a 4-microseconds, 10 MHz bandwidth linear chirp (deep sounding).

Chirp compression was applied using a Blackman window to minimise sidelobe levels, resulting in a processing gain of 10 dB. The chirp data was processed using an coherent averaging filter (commonly referred to as unfocused Synthetic Aperture Radar (SAR) processing) along a moving window of length 33. This data is best used to assess the bed and internals in deep ice conditions. Note that no pulse data is available for this survey.

The bed reflector was first automatically depicted on the chirp data using a semi-automatic picker in the PROMAX software package. All the picks were afterwards checked and corrected by hand if necessary. The picked travel time was then converted to depth using a radar wave speed of 168 m/microseconds and a constant firn correction of 10 m. Surface elevation is derived from radar altimeter for ground clearance < 750 m, and the PASIN system for higher altitudes.

** Coordinates and Positions:

The coordinates provided in the NetCDF for the surface and bed elevation for each radar trace are in longitude and latitude (WGS84, EPSG: 4326). The navigation attributes for the radar data in the NetCDF are in projected X and Y coordinates (Polar Stereographic, EPSG: 3031), as follows:

Latitude of natural origin: -71

Longitude of natural origin: 0

Scale factor at natural origin: 0.994

False easting: 0

False northing: 2082760.109

The coordinates in the SEGY data are also in projected X and Y coordinates (Polar Stereographic, EPSG: 3031), although note that these are in integer format due to the SEGY limitations (see section below).

Positions are calculated for the phase centre of the aircraft antenna. All positions (Longitude, Latitude and Height) are referred to the WGS1984 ellipsoid.

** Dataset:

Please note: Due to the unstable nature of SEGY-formatted data and its uncertain long-term future, as well as the issues documented below, we also provide the full radar data in NetCDF format. The dataset provided here consists of three parts: a NetCDF file per flightline, one SEGY files per flightline (chirp), and one quicklook PDF file per flightline. These are described in more details below.

- NetCDF: The NetCDF files contain the deep-sounding chirp-acquired data in its processed form, as well as the associated metadata, navigational information (in both EPSG: 3031 and WGS84 EPSG: 4326), and the associated radar-related information for each trace (e.g. surface/bed elevation and picks, ice thickness, aircraft altitude, range to surface, time of trace) which are provided as separate attributes in the NetCDF file. The navigational position of each trace comes from the surface files, and the processed GPS files when no surface information was provided in the surface files. Note that for these, interpolation of the navigational data might have been required to match closely the Coordinated Universal Time (UTC) of each trace in the surface files. No data is shown as "-9999" throughout the files.

NetCDF attributes:

- 'traces': Trace number for the radar data (x axis)

- 'fast_time': Two-way travel time (y axis) (units: microseconds)

- 'x_coordinates': Cartesian x-coordinates for the radar data (x axis) (units: meters in WGS84 EPSG:3031)

- 'y_coordinates': Cartesian y-coordinates for the radar data (x axis) (units: meters in WGS84 EPSG:3031)

- 'chirp_data': Radar data for the processed (coherent) chirp (units: power in dBm)

- 'longitude_layerData': Longitudinal position of the trace number (units: degree_east in WGS84 EPSG:4326)

- 'latitude_layerData': Latitudinal position of the trace ...(47)

Data collection:

** Instrument:

Radar data were collected using the bistatic PASIN (Polarimetric radar Airborne Science Instrument) radar echo sounding system mounted on the BAS Twin Otter aircraft "VP-FBL" and operating with a centre frequency of 150 MHz and using a 4-microseconds, 10 MHz bandwidth linear chirp (deep sounding). The Pulse Repetition Frequency was 15,635 Hz (pulse repetition interval: 64 microseconds).

** Antenna configuration:

8 folded dipole elements:

4 transmitters (port side)

4 receivers (starboard side)

Antenna gain: 11 dBi (with 4 elements)

Transmit power: 1 kW into each 4 antennae

Maximum transmit duty cycle: 10% at full power (4 x 1 kW)

** Radar receiver configuration:

Receiver vertical sampling frequency: 22 MHz (resulting in sampling interval of 45.4546 ns)

Receiver coherent stacking: 25

Receiver digital filtering: -50 dBc at Nyquist (11 MHz)

Effective PRF: 312.5 Hz (post-hardware stacking)

Sustained data rate: 10.56 Mbytes/second

Data quality:

- Average flying velocity: 65 m/s

- Along-track trace spacing: ~10 m

- Vertical resolution: ~8.4 m

- Radar centre frequency: 150 MHz

- Radar bandwidth: 10 MHz

- Radar Receiver vertical sampling frequency: 22 MHz

- Absolute GPS positional accuracy: ~0.1 m (relative accuracy is one order of magnitude better). Banking angle was limited to 10 degrees during aircraft turns to avoid phase issues between GPS receiver and transmitter.

The radar lines have a spacing of approximately 27 km. The majority of flights are at a constant elevation, required for coincident collection of gravity data.

Please note: The surface and bed pick information (surface and bed elevation, ice thickness, etc.) can also be found at: https://doi.org/10.5285/6549203d-da8b-4a22-924b-a9e1471ea7f1.The datasets found here have been considerably curated and improved, and thus can be considered the latest and full dataset.