A study on modeling the regional ionosphere using multi-constellation gnss observations for single-frequency PPP

Currently, the use of single-frequency Precise Point Positioning (PPP) technique for precise applications is limited by the effect of the ionospheric delay. For this purpose, a number of models have been developed for post processing and real-time applications. In addition, a number of international organizations have developed ionospheric correction products, including the International Global Navigation Satellite Systems (GNSS) Service (IGS). Unfortunately, however, those models and products have limited accuracy or spatiotemporal resolution, which may not be adequate for single-frequency PPP applications. To overcome this problem, this study introduces the development of regional ionospheric error correction models for single-frequency PPP users in Europe. A Regional Ionospheric Model (RIM) over Europe is firstly developed. The proposed model has a spatial and temporal resolutions of 1º×1º and 15 minutes, respectively. GNSS observations from a regional network consisting of 60 IGS and EUREF reference stations are processed using the Bernese 5.2 software to extract the Vertical Total Electron Content (VTEC) values. To validate the newly proposed RIM, the single-frequency PPP accuracy and convergence time for another set of stations are estimated and compared with those of the IGS Global Ionospheric Maps (IGS-GIM) counterparts in three different days. The ionosphere-free dual frequency PPP is used as reference. The findings reveal that the proposed RIM accelerates the convergence time and enhances the positioning accuracy by about 20%, 45% and 45% for the horizontal, height and 3D components, respectively, in comparison with the IGS-GIM model. In addition, a Real-Time Regional Ionospheric Model (RT-RIM) is developed using the IGS Real-Time Service (IGS-RTS) precise satellite orbit and clock products. The spatial and temporal resolutions of the proposed model are also 1º×1º and 15 minutes, respectively. In order to produce the real-time VTECs, Global Positioning System (GPS) observations from a regional network consisting of 60 IGS and EUREF reference stations are processed using the Bernese 5.2 software. The newly proposed RT-RIM is validated for PPP applications for another set of stations in three successive days. The PPP convergence time and positioning accuracy obtained through the RT-RIM is assessed and compared with those obtained through the IGS-GIM model. The ionosphere-free dual frequency PPP is used as reference. It is shown that the developed RT-RIM speeds up the convergence time. Moreover, the PPP accuracy is improved by about 40%, 55% and 40% for the 2D, height and 3D components, respectively, with respect to the IGS-GIM counterparts. To precisely model the ionosphere TEC, a Multi-constellation GNSS Receiver Differential Code Bias (MGR-DCB) estimation model is developed. The proposed model estimates the receiver DCBs for the GPS, Galileo and BeiDou signals using the ionosphere-corrected pseudoranges differences. A regional ionospheric model is developed in order to remove the ionospheric errors from the pseudorange differences. The proposed RIM has a spatial and temporal resolutions of 1º×1º and 15 minutes, respectively. To validate the developed MGR-DCB model, the receiver DCBs for three IGS Multi-GNSS Experiment (IGS-MGEX) stations are obtained for three different days. The estimated DCB values are compared with the published MGEX values. The results show that the agreement between the estimated DCBs and the MGEX is less than 1 ns for both of the mean difference and Root Mean Square Error (RMSE) values. Moreover, the VTEC values are computed from the combined GPS, Galileo and BeiDou measurements and compared with the IGS-GIM counterparts. It is shown that the computed VETC values have good agreement with the IGS-GIM counterparts with mean difference and RMSE values less than 1 Total Electron Content Unit (TECU).