Radio-Echo Sounding Instrumentation

The Transmitter

There are numerous radio-echo sounding devices used by various researchers thorughout the world. The components described here are those used by researchers at the University of Wyoming, which is based on that designed by Barry Narod and Garry Clarke at the University of British Coloumbia (Narod & Clarke, J. of Glaciology, 1995). It has been designed for use on temperate glaciers.

The transmitter emits a 10 ns (nanosecond) long pulse at a frequency of 100 MHz. The details of the pulse-generation circuitry can be found in Narod & Clarke, 1995. The frequency of the pulse is modulated for use on temperate glaciers by attaching two 10 m antennas. The resulting 5 MHz frequency is ideal for temperate glacier radio-echo sounding. The transmitter is powered by a 12 V battery.

The transmitter and battery are housed in a small tackle box which is attached to a pair of old skis. The antennas extend out the front and back of the tackle box. The forward antenna is carried by the person pulling the transmitter sled's tow rope, while the rear antenna drags behind. There is no focusing of the transmitted signal, so it propagates in all directions into the ice and air. In order to reduce "ringing" of the signal along the antenna, resistors are embedded every meter along the antenna. The total resistance of each 10 m antenna is 11 ohms.

The Receiver

The receiver begins with an antenna identical to that of the transmitter. As each pulse is sent out of the transmitter, some of the transmitted energy travels through the air and some through the ice. The velocity of radio waves in air is almost twice that in ice, so the receiver first detects the "Direct Wave" transmitted through the air between the transmitter and receiver. This triggers the oscilloscope to begin recording the signal. For the next 10 µs, the oscilloscope records the voltage of the signals that have reflected off nearby surfaces. The scope averages 64 of the transmitter pulses and reflected waves to generate a single trace. By averaging the scope reduces niose due to signal scatter and instrument noise in order to obtain a better trace to be recorded on the laptop computer. The entire receiver is placed in a small sled which is pulled by a tow rope. A third researcher monitors the signals on the oscilloscope and records the information onto the laptop. Both the scope and the laptop are powered by a 12 V battery which can be charged by a solar panel for extended surveys.

Related Topics

• How it Works

• Radio-Echo Sounding in the Field

• Frequencies & Wavelengths

• References

Return to Main Radio-Echo Sounding Page

Updated: August 03, 2011
© 1998, Brian C. Welch, Univ. of Wyoming