Ionosondes are simple radars that use radio pulses to detect and range
density in the bottomside ionosphere.
The frequency of the vertically transmitted wave determines
the plasma density from which the pulse is relfected in the ionosphere.
The time delay between transmission
and reception of the reflected pulse on the ground is a measure of the
height of the
ionospheric layer from which the pulse was relfected. In this way the
height of a specific plasma density is obtained.
operates by stepping the frequency of the pulses from say 1 to 20 MHz,
thereby producing a map of the bottomside ionosphere. The data from
such a frequency sweep is presented as the time-of-flight (virtual
height) versus the transmitted frequency (the plasma frequency which is
related to the plasma density). The result is