Single-frequency precise point positioning (PPP) for retrieving ionospheric TEC from BDS B1 data

The customary approach to determine ionospheric total electron content (TEC) with BeiDou navigations satellite system (BDS) data normally requires dual-frequency (DF) data provided by geodetic-grade receivers. In this study, we present an analysis of the performance of a new TEC estimation procedure based on single-frequency (SF) BDS data. First, the ionospheric observable is retrieved from the SF BDS code and phase data using precise point positioning (PPP) instead of the carrier-to-code leveling (CCL) technique used in the customary DF method. Then, the absolute ionospheric slant TEC (STEC) values are isolated from the ionospheric observables by modeling the ionospheric observable with the adjusted spherical harmonic (ASH) expansion and constraining the satellite differential code bias (SDCB) to very precise values provided externally. The experimental data were taken from the multi-GNSS experiment (MGEX) network for high and low sunspot periods, covering the 2 months, i.e., December 2014 and September 2017. The TEC data obtained from the combined final global ionospheric map (GIM) provided by the international GNSS service (IGS), the JASON DF altimeter, and the BDS-measured differential STEC (dSTEC) are used as reference data to evaluate the performance of the TEC values estimated by the proposed method. The evaluation results indicate that compared to the reference TEC data, the ionospheric TEC estimated by the proposed method using BDS B1 data and the customary CCL-based DF method based on BDS B1 + B2 data, perform at roughly equal levels.