Performance evaluation of BDS-3 ionospheric delay correction models (BDSK and BDGIM): First year for full operational capability of global service

The BeiDou global navigation satellite system (BDS-3) has been providing full operational capability of global service since July 31, 2020. There are two kinds of broadcast ionospheric delay correction models for the BDS-3, i.e., the BDS Klobuchar model (BDSK) and the BeiDou global ionospheric delay correction model (BDGIM). We first assessed the performance of the BDS-3 ionospheric models during the first year from August 1, 2020, to July 31, 2021. The assessment was conducted in both the ionospheric total electron content (TEC) domain and the BDS single-frequency standard point positioning domain. A consistency experiment shows that the BDSK and BDGIM can correct the ionospheric delay by approximately 64% and 75%, respectively, when compared with the global ionospheric map (GIM) provided by the international global navigation satellite system service (IGS). The model precision and accuracy were also computed by comparing these models with the internal GPS-derived slant TEC (STEC) and the external Jason-3-derived vertical TEC (VTEC), respectively. A precision experiment shows that the root mean square (RMS) of the BDSK and the BDGIM are 5.0 and 3.0 total electron content unit (TECU), respectively, in the continental region. There exists systematic bias (6.4 TECU for the BDSK and 2.9 TECU for the BDGIM) between the global navigation satellite system (GNSS) VTEC and the Jason-3 VTEC. The standard deviation (STD) in the accuracy experiment for the BDSK and the BDGIM are 4.2 and 3.4 TECU, respectively, in the oceanic region. When applying the BDSK model or the BDGIM model in the BDS standard point positioning using B1I frequency pseudorange observations, the 3D RMS positioning error is better than 3 m for most stations under different solar activity conditions, and the positioning accuracy of the BDGIM outperforms that of the BDSK by approximately 10%. The GPS Klobuchar model and the Galileo NeQuickG model were also included for comparison. All the results in our experiment demonstrate that the newly designed BDGIM has the best performance among the GNSS broadcast ionospheric models.