A new short-pulse digital profiling radar system that operates at lower frequencies than most ice radars used in polar regions to date has been designed and built by the U.S. Geological Survey. The transmitter is an avalanche transistor pulser which drives a resistively loaded dipole transmitting antenna. A similar, but separate antenna is connected to the receiver. The receiver has adjustable sensitivity time control (STC) of as much as 60 dB to compensate for attenuation and geometric spreading factors. A fiber-optic cable is used to transmit both control signals and data. The data-acquisition and display system incorporates very high-speed digitizing and signal averaging, real-time profile display, and data storage on standard computer nine-track magnetic tape.
The system was successfully used on Ice Stream B in West Antarctica at centre frequencies of 1, 2, 4, 8, and 12.5 MHz. Bottom-return signal-to-noise ratios of more than 40 dB were obtained at 2 MHz through 800 m of ice. Convoluted internal surfaces not related to present bottom topography were resolved within the ice streams and anomalous strong reflections or “bright spots” were identified near the base of the ice. At present, there is no satisfactory glaciological explanation for either of these observations.