An ionosonde is a swept-frequency vertical-incidence high frequency radar. It consists of a transmitter, a receiver, a controller and a data processor, as shown in the diagram below.

Ionosonde block diagram

The controller measures the time delay between transmitting a pulse and receiving its echo back from the ionosphere. This delay can be converted into a height.

The final output of the ionosonde is in the form of a graph termed an ionogram, which is a plot of ionospheric echoes as a function of height and frequency. An example is shown below.

(IPS Radio and Space Services)

An ionogram may then be used to compute a plot of the density of the plasma throughout the ionosphere. This type of plot is shown in the next image.

Electron density graph

An ionosonde is not only used in scientific research to measure and monitor the ionosphere. It is also used to support many applications that rely on or are affected by the ionosphere. These include shortwave broadcasting and high frequency communication, over the horizon radar systems and signal location (direction-finding), satellite communication and navigation, and radio astronomy.

Ionosonde at Perth Observatory
Exterior view of an ionosonde at Perth Observatory

ASAAustralian Space Academy