Ionospheric irregularities and potentialities of multifrequency correction in Global Navigation Satellite Systems

Measurements of propagation time or phase of a signal at two frequencies enable us to eliminate the first ionospheric correction and improve accuracy of the Global Navigation Satellite System (GNSS) from tens of meters to centimetres. This paper explores possibilities of eliminating higher-order ionospheric errors in going to measurements at more frequencies. It is shown that the second-order correction, associated with the geomagnetic field effect on the refractive index, may be taken into account already in dual-frequency measurements. Further improvement of accuracy in the triple-frequency GNSS in view of phase scintillations is complicated by diffraction effects.