Galileo, and in general existing GNSS, are based on the broadcasting of electromagnetic ranging signals in the L frequency band. These satellite signals are subject to distortions when propagated through the Earth’s atmosphere. Earth’s atmosphere can be subdivided into the troposphere and the ionosphere, which is the ionised part of the atmosphere, inducing a dispersive group delay that is several orders of magnitude larger than the one from the troposphere.

Single frequency receivers will be able to counteract the errors introduced by the ionospheric propagation delay using the Galileo single-frequency ionospheric correction algorithms described below: