Impact of higher order ionospheric delay on continuous GPS coordinate time series

Based on the higher order ionospheric delay correction model, impact magnitude of different order ionospheric delay on GPS double frequency carrier signals with different frequencies has been determined. Then GPS data of 109 globally distributed IGS stations spanning from 1999 to 2003 have been reprocessed to quantify the contributions of higher order ionospheric delay to global GPS coordinate time series using GAMIT with state of the art models according to IERS Conventions 2010. Results show that higher order ionospheric delay correction would result in large velocity change. The vertical velocity of stations near the equator reaches up to about 1 mm a?1, which should not be neglected in high precision GPS data processing. Considering the impact of higher order ionospheric delay could also remarkably reduce the vertical WRMS of stations near the equator and the North WRMS of stations in South Asia, among which station LHAS in China exhibits the best improvement by about 10% in the North component. Moreover, it could effectively reduce the amplitudes of various periodical signals, therefore plays very important role in the geophysical explanations of the non-linear variations in the GPS coordinate time series. The annual amplitude in the Up component and the semi-annual amplitude in the East component of stations in middle latitudes, together with the vertical semi-annual amplitude of stations in low latitudes and the signal with periods as about 422 days in the East component of stations in high latitudes are effectively reduced after higher order ionospheric delay correction, thus we propose that the second and third order ionospheric delay is probably one of the main reasons that cause the vertical annual and East-West semi-annual motions of middle-latitude stations as well as the vertical semi-annual motion of low-latitude stations.