Riometers

-what they do and how they work

Riometer = Relative Ionospheric Opacity meter

Riometers measure the absorption of radio-noise from the stars ('cosmic-noise') in the ionosphere. They usually operate at frequencies between 25Mhz and 50 Mhz where radio-waves are absorbed when there are significant numbers of free electrons in the height region from about 60-110 km.
They make continuous observations of the noise-level and observe deceases in noise relative to the quiet-day level, when high-energy electrons and protons precipitate and cause increased ionisation.

The absorption is calculated by the simple relation

A (dB)= 10 x log10 (Po / P)

where A is the cosmic noise absorption in dB

Po is the quiet-day noise power

P is the noise-power during the disturbance

The riometers used at IRF are manufactured by La Jolla Sciences, California, and operate at 30Mhz and 38Mhz. They are connected to simple antennas of the type shown below and data is recorded directly on a PC at the measurement site. A copy of the data is sent in real-time over a radio link to the IRF main building.