Helicopter-borne and ground-towed radar surveys of the Fourcade Glacier on King George Island, Antarctica

Abstract. To determine subglacial topography and internal features of the Fourcade Glacier on King George Island in Antarctica, helicopter-borne and ground-towed ground-penetrating radar (GPR) data were recorded along four profiles in November 2006.Signaturedeconvolution, f-kmigrationvelocity analysis, andfinite-difference depthmigration applied to the mixed-phase, single-channel, ground-towed data, were effective in increasing vertical resolution, obtaining the velocity function, and yielding clear depth images, respectively. For the helicopter-borne GPR, migration velocities were obtained as root-mean-squared velocities in a two-layer model of air and ice. The radar sections show rugged subglacial topography, englacial sliding surfaces, and localised scattering noise. The maximum depth to the basement is over 79m in the subglacial valley adjacent to the south-eastern slope of the divide ridge between Fourcade and Moczydlowski Glaciers. In the ground-towedprofile,we interpret a complicatedconduit abovepossible basalwater andother isolated cavities,whichare a fewmetres wide. Near the terminus, the GPR profiles image sliding surfaces, fractures, and faults that will contribute to the tidewater calving mechanism forming icebergs in Potter Cove. Key words: Fourcade Glaciers, helicopter-borne and ground-towed GPR, internal features, subglacial topography