Use of modified carrier-to-code leveling to analyze temperature dependence of multi-GNSS receiver DCB and to retrieve ionospheric TEC

Deriving the ionospheric total electron content (TEC) from the global navigation satellite systems (GNSS) measurements typically assumes the receiver differential code biases (RDCBs) to remain unchanged within at least 1 day. However, the RDCBs sometimes can exhibit remarkable intraday variability, probably due to the ambient temperature fluctuation. The modified carrier-to-code leveling (MCCL) method enables one to eliminate the adverse impact of the short-term variations of RDCBs (called RDCB offsets) on the retrieval of ionospheric TECs. In this study, we extend the GPS-only MCCL method to the multi-GNSS case and further carry out a series of investigations. First, in terms of the Pearson correlation coefficient (PCC), the dependence of multi-GNSS RDCB offsets upon ambient temperature is verified. As suggested by the results, a strong linear correlation exists between the estimated RDCB offsets and measured temperature values. The percentages of the stations analyzed with the absolute PCC values above 0.5 are 76.5%, 94.1% and 64.2% for GPS, BDS and Galileo, respectively. Second, the global ionospheric map provided by the center for orbit determination in Europe (CODE), the JASON altimeter and the difference of slant TEC (dSTEC) are chosen as the references for evaluating the performance of MCCL-derived TECs. After removing the significant RDCB offsets, an improvement of 69.7%, 93.4% and 87.6% for GPS, BDS and Galileo has been achieved in the dSTEC validation, respectively.