Glacier movement measured with a radio echo technique

In the radio echo sounding method for measuring the thickness of polar ice masses, the sounder transmits regular pulses each containing several cycles of VHF radio waves into the ice. Usually the glacier bed is rough so the echo is a distorted version of the transmitted pulse: it is lengthened and the amplitude and phase of the carrier wave vary within its length (Fig. 1). The echoes also vary rapidly with horizontal displacement of the radio echo sounder1, and this variation is known as the spatial fading pattern