Analysis of spatial–temporal characteristics for BDS-3 broadcast ionospheric models (BDS Klobuchar and BDGIM) in multi-GNSS real-time single-frequency precise point positioning

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With the full operation of BDS-3 broadcast ionospheric models, i.e., the BeiDou global ionospheric delay correction model (BDGIM) and the BDS Klobuchar model, its impact on the multi-GNSS real-time (RT) single-frequency (SF) precise point positioning (PPP) needs to be investigated for low-cost GNSS users. The GPS Klobuchar model as a reference is also considered in this study. Two types of SF-PPP models including the ionosphere-corrected (IC) and ionosphere-weighted (IW) strategies are adopted in the positioning domain. GPS + GLONASS + Galileo + BDS-3 observations from 40 multi-GNSS experiment (MGEX) stations distributed in different latitudes are selected for conducting RT SF-PPP during the ionospheric quiet and active periods. The experiment shows that the positioning accuracy of IC RT SF-PPP can be degraded with the increase of the ionospheric activity levels or the decrease of latitudes. Except for low-latitude regions during the ionospheric active period, the 3D positioning accuracy of the northern hemisphere can be improved by at least 15.2 % compared to the southern hemisphere in the IC model with the BDS Klobuchar. The BDGIM model has the best performance among all IC RT SF-PPP solutions, but its 3D positioning accuracy can reach the sub-meter level only in mid-latitude regions. With the adoption of ionospheric constraints, the convergence of the IW model is always superior to that of the group and phase ionospheric correction (GRAPHIC) model, and the improvement of convergence in mid-latitude regions is clearly better than that in low-latitude regions. Due to the quality limitation of the BDS Klobuchar model, it has the longest convergence time among all IW models regardless of ionospheric conditions or latitude regions. Compared to the GPS Klobuchar, the significant improvement of convergence for the BDGIM-constrained RT SF-PPP is mainly presented in low-latitude regions of the northern hemisphere. The horizontal positioning accuracy of the BDGIM-constrained model is always improved in comparison with the GRAPHIC model, but there is a degradation in the vertical component, and the improvement of 3D positioning accuracy is no more than 11.7 %. In summary, the BDGIM-constrained model has the best performance among all RT SF-PPP solutions, its 3D positioning accuracy has the ability to achieve 0.25 m at present.