Before revision: A riometer (commonly relative ionospheric opacity meter, although originally: Relative Ionospheric Opacity Meter for Extra-terrestrial Emissions of Radio noise) is an instrument used to quantify the amount of electromagnetic-wave ionospheric absorption in the atmosphere.
After revision: A riometer (commonly relative ionospheric opacity meter, although originally: Relative Ionospheric Opacity Meter for Extra-Terrestrial Emissions of Radio noise) is an instrument used to quantify the amount of electromagnetic-wave ionospheric absorption in the atmosphere.