Ground-Based Deep-Penetrating Radar Studies Along The US-ITASE Traverse

In recent years airborne geophysical surveys have provided high-quality data over selected portions of the West Antarctic Ice Sheet (WAIS). Coupled with new information at visible and radar wavelengths from satellite sensors, these surveys have greatly enhanced our understanding of the dynamics of the WAIS. Until recently, ground-based radar studies have generally been limited to more localized areas and small-scale ice dynamics problems where they provide greater spatial resolution than airborne surveys, often with higher definition (S/N) of imaged features. During the past four years, the US-ITASE platform has provided an opportunity for ground-based deep radar profiling over several thousand kilometers of the WAIS and portions of the East Antarctic Ice Sheet, including more detailed studies of selected sites where ice cores have been drilled. These traverses have enabled us to produced high definition images of bedrock and internal stratigraphy on a continental scale, combining attributes of both airborne and ground-based surveys. We have developed a ruggedized impulse-based radar system to withstand the physical demands of a heavy vehicle traverse at speeds up to 15 Km/hr and also obtain data with high spatial resolution along-track and high definition of internal reflectors. Operating at a center frequency of 3 MHz this system utilizes a 14 bit A/D board at digitizing rates of 100 MHz and records stacked waveforms depicting bedrock and ice internal reflections approximately every 15 meters of surface travel. Surface coordinates are obtained from precision GPS measurements which together with the high data density enable us to migrate profile sections to correctly image steeply-dipping reflectors. We present here a sample of results from over 2000 km of profiles completed during the 2001-2003 field seasons, including routes from Byrd Station toward Siple Station and Byrd to South Pole. In addition to the bedrock record that identifies a number of new regions of high topographic relief, we have obtained radar profiles across several of the major ice divides that will enable us to investigate divide stability from model studies of the internal layers. We have a grid of profiles showing details of the bedrock and internal layer stratigraphy beneath Hercules Dome, a site of possible interest for a deep climate core just upflow from "The Bottleneck" where ice is funneled from the East to West Antarctic Ice Sheets. Our profiles also depict several unusual areas with disturbed internal stratigraphy that may result from bedrock topographic features with large (>50% of ice thickness) and abrupt (> few km) relief. Our interpretation of sub-ice reflectors is aided by information on surface features and ice flow from MODIS and RADARSAT imagery.