DOI: 10.5285/d55e87dd-a74d-4182-be99-93ab805103ab
title: Processed bed elevation picks from the POLARGAP radar survey across the Pensacola-Pole Basin (2015/2016)

description: This dataset contains bed and surface elevation picks derived from airborne radar collected during the POLARGAP 2015/16 project funded by the European Space Agency (ESA) and with in-kind contribution from the British Antarctic Survey, the Technical University of Denmark (DTU), the Norwegian Polar Institute (NPI) and the US National Science Foundation (NSF). This collaborative project collected ~38,000 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. The primary objective of the POLARGAP campaign was to carry out an airborne gravity survey covering the southern polar gap beyond the coverage of the GOCE orbit. This dataset covers the South Pole as well as parts of the Support Force, Foundation and Recovery Glaciers. The bed pick data acquired during the POLARGAP survey over the Recovery Lakes is archived at NPI: https://doi.org/10.21334/npolar.2019.ae99f750.
description: Radar data were collected using the 150-MHz PASIN radar echo sounding system operating in full polarimetric mode. Data provided here includes picks and derived elevations of the ice sheet surface and bed for the BAS-led part of this campaign, which includes the survey lines over the South Pole, as well as Support Force, Foundation and Recovery Glaciers. 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, 12 MHz bandwidth data was compressed, filtered, and decimated from the original trace acquisition rate of 156.25 Hz to 2Hz, equivalent to ~30m in along-track spacing. The bed reflector was picked in a semi-automated manner within the seismic processing package ProMax. An automatic first break picker was applied initially, with subsequent manual editing/removal of picks which appear unreasonable. 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 (principally due to terrain clearance, cloud or where the lidar was not used), the location of the surface reflection was picked directly from the radargram and a regression, local to the data gap, was used to fit the radar range to terrain clearance. Bed elevation was integrated with a high precision kinematic dual-frequency GPS position solution to provide the final point data set of ice thickness and bed elevation relative to WGS84. 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. P03.1 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 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 providers Note: missing data values where no surface/bed pick/elevation exist are reported as '-9999'.
description: Radar data were collected using the PASIN radar echo sounding system operating in full polarimetric mode with a centre frequency of 150 MHz and using a 4-microseconds, 12 MHz bandwidth linear chirp.
description: Crossover analysis of recovered bed elevation across the entire survey gives an error estimate for the PolarGAP survey of ~28 m.