The dynasonde sounds the ionosphere using radio waves to provide information on the vertical and
horizontal distribution of ionisation. The sounder transmits a series of radio pulses skywards at
successively higher frequencies. Each pulse is reflected from a different altitude between about 60km and
500km depending on the electron concentration. The echoes are received by an array of antennas on the
ground and the time delay between transmission and reception gives a measure of the distance to the
reflection point. The radio wave phase differences between antennas allow the horizontal distance and
line-of-sight velocity of each echoing region to be estimated. These parameters allow the location and
dynamics of large-scale ionospheric features to be studied.