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 bed elevation picks from airborne radar depth sounding from the FISS 2015 survey covering the Foundation Ice Stream and the Filchner Ice Shelf system (2015/2016) (Version 1.0) [Data set]. NERC EDS UK Polar Data Centre. https://doi.org/10.5285/144CEB0D-9D76-4A39-AA01-7B94AC80FAC9

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:

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. Data provided here includes picks and derived elevations of the ice sheet surface and bed.

The radar 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 156.25 Hz to 5Hz, equivalent to ~11m in along-track spacing.

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' header in the CSV, and is composed of either: 0 = LIDAR, 1 = interpolated LIDAR for gaps ~55 m, 2 = radar.

Positions are calculated for the phase centre of the aircraft antenna. All positions (Longitude, Latitude and Height) are referred to the WGS1984 ellipsoid. Longitude and Latitude are provided in WGS84 (EPSG 4326).

DATA FORMAT:

The dataset includes an intermediate processing product (in .csv), with attributes as follows:

Line_ID: Flight name e.g. FO3A

Trace: Radar segy file trace number

Longitude_decimal_degrees: Longitude in decimal degrees (WGS84 EPSG:4326)

Latitude_decimal_degrees: Latitude in decimal degrees (WGS84 EPSG:4326)

DateTime_YYYY-MM-DD_HH:MM:SS.SSS: Date (YYYY/MM/DD) and Time UTC (HH:MM:SS.SSS) of trace separated by 'T'

Surface_elevation_WGS84_m: Surface Elevation (m) relative to WGS84 Ellipsoid

Ice_thickness_m: Ice thickness (m) calculated for a radar velocity in ice of 168 microseconds and applying a 10-m firn

Bed_elevation_WGS84_m: Bedrock Elevation (m) relative to WGS84 Ellipsoid

PriNumber: Radar counter in segy header (arbitrary units)

Surface_pick: Location down trace of surface pick

Bed_pick: Location down trace of bed elevation pick

Surface_Source: Source of elevation measurements 0 = lidar, 1 = interpolated lidar for gaps ~ 55 m, 2 = from ice sounding radar

Aircraft_elevation_WGS84_m: Elevation (m) of aircraft IMU relative to WGS84 Ellipsoid

Campaign_name: Name of the campaign

Owner: Owner of the data

Funding: Funding provider and grant number

Note: missing data values where no surface/bed pick/elevation exist are reported as '-9999'.

Data collection:

Radar data were collected using the new bistatic PASIN-2 radar echo sounding system

operating with a centre frequency of 150 MHz and using a 4-microseconds, 13 MHz bandwidth linear chirp.

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.