RADAR REFLECTIONS REVEAL A WET BED BENEATH STAGNANT ICE-STREAM-C AND A FROZEN BED BENEATH RIDGE BC, WEST ANTARCTICA

Digital airborne radar data were collected during the 1987-88 Antarcti c field season in nine gridded blocks covering the downstream portions of Ice Stream B (6 km spacing) and Ice Stream C (11 km spacing), toge ther with a portion of ridge BC between them. An automated processing procedure was used for picking onset times of the reflected radar puls es, converting travel times to distances, interpolating missing data, converting pressure transducer readings, correcting navigational drift , performing crossover analysis, and zeroing remanent crossover errors . Interpolation between flight-lines was carried out using the minimum curvature method. Maps of ice thickness (estimated accuracy 20 m) and basal-reflection strength (estimated accuracy 1 dB) were produced. Th e ice-thickness map confirms the characteristics of previous reconnais sance maps and reveals no new features. The reflection-strength map sh ows pronounced contrasts between the ice streams and ridge BC and betw een the two ice streams themselves. We interpret the reflection streng ths to mean that the bed of Ice Stream C, as well as that of Ice Strea m B, is unfrozen, that the bed of ridge BC is frozen and that the boun dary between the frozen bed of ridge BC and the unfrozen bed of Ice St ream C lies precisely below the former shear margin of the ice stream.