The effects of conductivity on high-resolution impulse radar sounding, Ross Ice Shelf, Antarctica

A high-resolution impulse radar profiling system was evaluated for (1) detecting the existence of sea ice which coring has revealed to exist on the bottom of the Ross Ice Shelf at Site J-9; (2) detecting the preferred horizontal c-axis azimuthal direction of the sea ice crystals, using the voltage amplitude of the radar reflection from the sea ice bottom; and (3) determining the direction of the currents under an Antarctic ice shelf. A field program was conducted consisting of a surface radar survey on the Ross Ice Shelf at Site J-9 and surface and airborne radar profiling on the McMurdo ice Shelf. The CRREL impulse radar system, operating at a center frequency of either 80 MHz or 20 MHz, was unable to detect the shelf bottom at Site J-9, which drilling revealed to be 416 m below the snow surface. The radar system was used to profile the McMurdo ice Shelf both from the snow surface and from the air; a shelf thickness of about 275 m was easily detected. Theoretical considerations indicate that the bulk conductivity of the ice shelf at Site J-9 was higher than originally anticipated, and this limited the radar sounding depth to about 405 m when operating at a frequency of 20 MHz.