The Mawson station in Antarctica has a riometer since 08 December 1989.

Ionosondes are ground-based swept-frequency vertical radars that are used to determine the electron density of the ionosphere. They provide information about the E and F layers in the altitude range of about 100 to 500 km. However, most of the absorption that occurs when a radio wave transits the ionosphere occurs in the D-region from about 70 to 100 km in height.

The riometer (relative ionospheric opacity meter) is one of the few instruments that can be used to determine ionospheric absorption. The first riometers were single beam units and operated at or near a frequency of 30 MHz. The principle of operation is to compare the currently received cosmic radio noise with a calibration curve (called a quiet day curve or QDC). The difference between the two is the current ionospheric absorption over the region monitored by the antenna at the time.

Most of the cosmic noise monitored by a riometer comes from our own galaxy, and varies over the sky. It has a maximum when looking at the galactic centre (in the direction of Sagittarius) and a minimum at right angles to this direction. To minimize contamination with terrestrial RFI, riometers either employ a wide bandwidth (eg 500 kHz) to dilute the interference and/or sweep rapidly in frequency over several 100 kHz and use the minimum signal detected in this range.

Riometers are most often employed at high latitude and polar regions where they are used to detect polar cap absorption. This provides a measure of solar-generated high energy protons. The absorption is caused by the particles precipitating down to D-region altitudes. Riometers can also be deployed at lower latitudes, and although natural absorption is much less here, they have been used to monitor atmospheric nuclear explosions.

Australian Bureau of Meteorology's Space Weather Services (SWS) operates several riometers in Antarctica and the data is available in real-time on the SWS web site at Riometer Data.