Site survey at Skinner Saddle and Gawn Ice Piedmont

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 (8 MHz, 35 MHz, 200MHz, and 500MHz) 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 Sledge, pulling transmitter and transceiver antennae. The sledge also carried high precision GPS antenna, which is tied to the temporary GPS base station deployed at the SKS and GIP camps.

Traverses totaling 150km at Skinner Saddle and 35km at Gawn Ice Piedmont have been surveyed with GPR. Excellent isochrone reflections are visible from both the bedrock/glacier interface and in the top part of the profile, 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. 2 A) ASTER satellite image of Skinner Saddle and vicinity. See Figure 1 for overview. Image from 31 October 2005. Yellow flag indicates location of camp, red flag indicates proposed drilling location. B) Digital elevation model. X/Y/Z grid in UTM 58 map units. Red lines indicate location of ground penetrating radar survey lines

Fig. 3 A) ASTER satellite image of Gawn Ice Piedmont and vicinity. See Figure 1 for overview. Image from 08 January 2004. Yellow flag indicates location of camp, red flag indicates proposed drilling location. B) Digital elevation model. X/Y/Z grid in UTM 58 map units. Red lines indicate location of ground penetrating radar survey lines