Local ionospheric modelling of GPS code and carrier phase observations

A limiting factor for successful ambiguity resolution in precise GPS positioning is the existence of un-modelled ionospheric errors in both the carrier phase and the pseudorange measurements. In this study, the ionospheric delay is modelled using a four-parameter polynomial utilizing dual frequency observations in the region of study in southern Iran. Thereafter, the corrected and non-corrected observations for ionospheric delay are compared with the ionospheric-free solution of the same observations. Two baselines (15 km and 72 km) are used for this comparison. An improvement of 0.22 ppm and 0.07 ppm is achieved, respectively, for the two baselines. Further, the ionospheric delay is modelled using two other methods, i.e. the Klobuchar and divergence models. The divergence model uses single frequency observations. The improvement of the results is restricted as the noise level in code observations is high. An improvement of 0.15 ppm for the 72 km baseline and no improvement for the 15 km baseline are observed using the divergence model. The Klobuchar model corrects 50%-60% of the ionospheric errors in this study