GPS Differential Code Bias Estimation Using Swarm LEO Constellation Onboard Observations

  Objectives  The differential code biases(DCBs) have a great influence on the estimation of ionosphere with GPS observations, which should be precisely calibrated when obtaining ionospheric slant total electron content (STEC). With the increasing number of low-orbit satellites, DCB estimation of low earth orbit (LEO) receivers becomes particularly important for the topside ionosphere research.

  Methods  Based on the onboard observations of GPS satellites by the Swarm constellation, two different estimation schemes for three satellites in constellation are designed, including individually estimation and combined estimation.

  Results  Taking the DCB products provided by Chinese Academy of Sciences (CAS) and Deutsches Zentrum für Luft - und Raumfahrt (DLR) as reference values , we analyze the accuracy and stability of these two strategies . Compared with the individual estimation strategy, the combined estimation strategy achieves more stable satellite DCB with a stability improvement of 16.6% for GPS satellites, and the satellite DCB presents better consistency with the reference DCB provided by the two analysis centers.

  Conclusions  Both strategies can be used to estimate DCB and the combined estimation strategy results in better performance.