Differential code biases estimation from Sentinel-6A GPS and Galileo combined observations

Differential code bias (DCB) is the hardware delay in the ranging code of the global navigation satellite system (GNSS), which critically impacts ionospheric total electron content estimation, precise positioning and accurate timing. The GNSS receiver aboard the Sentinel-6A low Earth orbit satellite is a crucial payload for precise orbit determination and topside ionospheric studies, while the GNSS receiver DCB is one of the errors. In this paper, the DCB variations of both GNSS satellites and receivers are estimated and analyzed using dual-frequency observations from the Sentinel-6A GNSS receiver (GPS and Galileo) during different solar activity periods. The results show that DCB estimates from GPS and Galileo combined observations are significantly more accurate than those from single-system estimates. The combined estimate results show that the overall monthly mean differences between the DCB estimates of GPS and Galileo satellites and the reference values from the German Aerospace Center and the Chinese Academy of Sciences are stable at 0.31, 0.34, 0.15 and 0.19 ns, respectively. During the high solar activity, the mean difference between the combined estimation result and the reference value is 0.34 ns and 0.16 ns. The difference for the GNSS receiver DCB estimates between single-system and GPS + Galileo combined estimations is minimal, with mean differences within 0.11 ns. Using GPS + Galileo combined observations enhances the stability of the GNSS receiver DCB estimates by 7% and 32%, respectively when compared to single-system estimates. The GPS + Galileo combined observations provide a good DCB estimation for Sentinel-6A precise orbit determination and topside ionosphere modeling.