Systems for measuring thickness of temperate and polar ice from the ground or from the air.
Equipment has been designed and tested for ground-based and airborne sounding of temperate glaciers. The transmitter is a free-running pulse generator that uses avalanche-mode transistor breakdown to create high-voltage pulses. The transmit and receive antennas are resistively loaded dipoles; for the airborne system, a twin-lead transmit element and a three-layer coaxial receive element are used on the inboard end of the respective antennas. The sounders are broadband systems; oscilloscopes are used for receivers. The oscilloscope trace is recorded photographically in the ground-based systems. A sampling oscilloscope is used in the airborne system—the sampling process strobes the waveform to audio frequencies so that it can be recorded on magnetic tape. Echoes have been obtained from ice depths of 550 m using the airborne system and about 1 000 m using the ground-based system.