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)

• Main Authors: Nicholls, Keith, Robinson, Carl, Corr, Hugh, Jordan, Tom
• Format: Dataset
• Language: English
• Published: NERC EDS UK Polar Data Centre 2021
• Subjects: "EARTH SCIENCE","CRYOSPHERE","GLACIERS/ICE SHEETS","GLACIER ELEVATION/ICE SHEET ELEVATION"; "EARTH SCIENCE","CRYOSPHERE","GLACIERS/ICE SHEETS","GLACIER THICKNESS/ICE SHEET THICKNESS"; "EARTH SCIENCE","CRYOSPHERE","GLACIERS/ICE SHEETS","GLACIER TOPOGRAPHY/ICE SHEET TOPOGRAPHY"; "EARTH SCIENCE","CRYOSPHERE","GLACIERS/ICE SHEETS"; "EARTH SCIENCE","SPECTRAL/ENGINEERING","RADAR"; Antarctic; aerogeophysics; ice thickness; radar; surface elevation; Filchner Ice Shelf; Foundation Ice Stream; Antarc*; British Antarctic Survey; Ice Sheet; Ice Shelf
• Online Access: https://dx.doi.org/10.5285/144ceb0d-9d76-4a39-aa01-7b94ac80fac9; https://data.bas.ac.uk/full-record.php?id=GB/NERC/BAS/PDC/01572

This dataset contains bed and surface elevation picks derived from airborne radar collected in 2015/16 over Foundation Ice Stream and Filchner Ice Shelf as part of the 5-year Filchner Ice Shelf System (FISS) project funded by NERC (grant reference number: NE/L013770/1) and awarded to the British Antarctic Survey with contribution from the National Oceanography Centre, the Met Office Hadley Centre, University College London, the University of Exeter, Oxford University, and the Alfred Wenger Institute. The aim of this project was to investigate how the Filchner Ice Shelf might respond to a warmer world, and what the impact of sea-level rise could be by the middle of this century. This collaborative initiative collected ~7,000 line-km of new aerogeophysical data using the 150MHz PASIN radar echo sounding system (Corr et al., 2007) deployed on a British Antarctic Survey (BAS) Twin Otter. : 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'. : 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. : - 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.