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Riometer is a radio receiver used for monitoring the intensity
of cosmic radio noise. Riometer is, in principle, a sensitive,
calibrated radio receiver which measures the signal strength of
the weak radio signals received from the sky.
The riometer technique for examining electron density
enhancements in the ionosphere is based on the absorption of
cosmic radio noise, the broadband RF energy radiated by stellar
sources in the galaxy.
Riometer record the noise coming to earth from the sky by using
narrow beam antennas, with beamwidths of 10 to 20 degrees, are
sensitive to smaller scale features of ionization, it rejects
noise coming in from sources on the ground and responds mostly
to signals coming from outside the ionosphere. The data from
several riometers operated at different frequencies, but
examining the same sky with broadbeam antennas, show effects
which have been interpreted as being due to small scale spatial
structure in the electron precipitation region, which does not
completely fill the antenna beam.
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