Accuracy evaluation of ionospheric delay from multi-scale reference networks and its application for fast PPP ambiguity resolution

Abstract

The Precise Point Positioning (PPP) can achieve a fast ambiguity resolution (PPP-RTK) when augmented with precise ionospheric delays derived from regional GNSS networks. In this study, the accuracy of the ionospheric delay derived from multi-scale networks are assessed and used for the GPS and Galileo PPP-RTK demonstration. First, the convergence time of the GPS-only PPP are evaluated based on the GFZ final and CNES real-time products. Results indicated that an average convergence time of 30 min and 20 min is needed for the CNES and GFZ float solutions, respectively, in order to achieve a decimetre level horizontal position accuracy. After applying the ambiguity resolution method, 20% and 35% improvements are observed reaching 24min and 13min, respectively. Then, the accuracy of ionospheric delays derived from the ambiguity-fixed PPP and the CODE global products are assessed. A short-baseline comparison indicated that the mean bias and standard deviation of the derived multi-day ionospheric errors are within 0.15 TECU and 0.06 TECU, respectively, with a presence of a daily periodic term. The accuracy of the interpolated ionospheric delay from global models are more related to the location of the stations, ranging from 1 TECU to 3 TECU. Finally, precise ionospheric delays derived from the EUREF permanent network with the inter-station distance larger than 73 km are selected for ionospheric modelling at the user location. Results indicated that the PPP ambiguity resolution can be achieved within a minute. After enlarging the inter-station distance to 209 km, ambiguity resolution can be achieved within several epochs with improved fixing rate as well.