Methodology:

The ground based DELORES (DEep LOoking Radio Echo Sounder), system transmits a broadband impulse signal through a 20 m dipole antenna and receives reflections from the ice sheet base and internal reflecting horizons via a second 20 m dipole antenna. Signal/noise ratio is improved by moving the radar system slowly along the survey line with a high pulse repetition frequency, and 1024x onboard pulse stacking. Scattering losses are avoided by directly coupling the dipole transmit and receive antennae to the surface, orientated along-track. The ground based nature of the survey allowed for very tight line spacing to be achieved (generally 250 m or 500 m between lines); however, the total area of Little Dome C coverage was limited compared to the earlier airborne surveys.

Data collection:

The DELORES radar system raw data events file processed to a format suitable for import to a seismic processing package (ReflexW, version 7.5, Sandmeier Geophysical Research, 2017). Positional data for each shot is interpolated from the processed L1/L2 GPS position data recorded mid-way between the transmit and receive antennas and taken to be the nadir position of the basal radar reflection. Several filters are applied, in the time and depth domains, to increase the signal/noise ratio of the internal reflecting horizons and bedrock return, including suppression of the direct air wave, bandpass filtering, a gain function to correct for spherical spreading loss and migration to collapse diffractions to their source points. The original sampling period of 4 ns is averaged to 12 ns (expressed as 12000 ps) in the post-processed data. Because the collection of ground-based radar data is dependent on the speed of the vehicle, which varies due to the terrain roughness during collection, the radar data are interpolated onto a 5 m regular horizontal spacing during the post-processing.

Data quality:

Position data recorded by L1/L2 geodetic GPS, mounted along-track mid-way between the centres of the transmit and received dipole antennas. Rinex position data is recorded at 10 second intervals, and the Rinex files post-processed to account for satellite vehicle ephemeris, and atmospheric effects, using the Canadian Spatial Reference System - Precise Point Positioning available at Geodetic tools and data (nrcan.gc.ca).

Note that the SEG-Y standard specifies that the Sample Interval in the Binary File Header should be expressed as microseconds for time data, and must be an integer. To overcome these limitations, the vertical sampling interval is expressed as 12000 picoseconds.