. 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:

Nicholls, K., Robinson, C., Corr, H., & Jordan, T. (2021). Processed airborne radio-echo sounding data from the FISS 2015 survey covering the Foundation Ice Stream, Bungenstock Ice Rise, and the Filchner Ice Shelf system, West Antarctica (2015/2016) (Version 1.0) [Data set]. NERC EDS UK Polar Data Centre. https://doi.org/10.5285/3507901F-D03E-45A6-8D9B-59CF98A03E1D

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 new bistatic PASIN-2 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, 13 MHz bandwidth linear chirp.

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 a coherent averaging filter (commonly referred to as unfocused Synthetic Aperture Radar (SAR) processing) with Doppler beam sharpening to enhance the signal to clutter ratio of the bed echo and improve visualisation. The received chirp of 4 microseconds, 13 MHz bandwidth data was compressed, filtered, and decimated from the original trace acquisition rate of 125 Hz to 5Hz, equivalent to ~11m in along-track spacing. The chirp data is best suited to assess the bed and internals in deep ice conditions. The coherent pulse-data (0.1-microseconds) was processed using a coherent averaging filter. This data is best used to assess the internal structure and bed in shallow ice conditions.

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. Where possible, the ice surface location within the radargrams was calculated using lidar measurements of surface elevation. In areas where lidar data was not available, the location of the surface reflection was picked directly from the radargram. The origin of the elevation measurement can be found in the 'surface_source_layerData' variable in this NetCDF, and is composed of either: 0 = LIDAR, 1 = interpolated LIDAR for gaps ~55 m, 2 = radar.

** 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, two SEGY files per flightline (one chirp and one pulse), and one quicklook PDF file per flightline. These are described in more details below.

- NetCDF: The NetCDF files contain the processed deep-sounding chirp and shallow-sounding pulse-acquired data in their 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 or when duplicates were found in the surface file (see Quality section above). Note that for these,...(60)

Data collection:

** Instrument:

Radar data were collected using the bistatic PASIN-2 (Polarimetric radar Airborne Science Instrument 2) 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 pulse-coded waveform at an effective acquisition rate of 312.5 Hz and a bandwidth of 13 MHz. The Pulse Repetition Frequency was 15,625 Hz (pulse repetition interval: 64 microseconds).

** Antenna configuration:

8 transmitters (4x port side and 4x starboard side)

12 receivers (8x wings and 4x belly)

Transmit power: 1 kW into each antennae

Maximum transmit duty cycle: 10% at full power

** Waveform details:

Five waveforms, 4uS Tukey port, 4uS Tukey starboard, 1uS Tukey port, 1uS Tukey starboard, 1 uS Tukey antenna 1 (port).

** 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: 125 Hz (post-hardware stacking)

Sustained data rate: 10.56 Mbytes/second

Data quality:

- Average spacing between radar traces: 11 m

- Radar centre frequency: 150 MHz

- Radar bandwidth: 13 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.