Ground Penetrating Radar (GPR)

Ground penetrating radar (GPR) measurements provide an image of the internal layering of a glacier and the topography of the ice-rock interface beneath. We applied low and high frequency radar pulses (35 MHz, 200MHz, and 400MHz) to map the bedrock interface and internal flow structures in the glacier. Those features are identified through reflectors that result from changes in physical and chemical properties, such as dust layers or aerosol and density variations and are thought to represent isochrones [Morse et al., 1998; Vaughan et al., 1999]. The choice of antenna frequency involves a trade-off between penetration depth and mapping resolution. The control units were mounted on a Nansen Slege, pulling transmitter and transceiver antennae. page 4 The sledge also carried high precision GPS antenna, which is tied to the temporary GPS base station deployed at the Evans Piedmont Glacier camp.

Fig.3: GPR/GPS set-up. A 400MHz antenna travels in front of the first skidoo. A second skidoo tails the set-up for crevasse safety.

Traverses totaling approximately 30km have been surveyed with GPR. The measurements show that the glacier thickness exceeds on average 150m (Fig.4) and is well over 200m deep at the identified drilling location. Excellent isochrone reflections are visible throughout the profile (Fig. 4), which will also be used to investigate geographical and chronological accumulation changes. Further post-processing will enhance the reflectors and will correct for surface topography.

Fig.4: Radar profile from Evans Piedmont Glacier showing bedrock topography, ice thickness and internal flow structures