Validation of enhanced orbit determination for GPS satellites with LEO GPS data considering multi ground station networks

Abstract

Deriving the precise satellites orbits is a prerequisite condition for global navigation satellite system (GNSS) to provide the high precision positioning service. With GPS observations from low earth orbiters (LEOs) and terrestrial tracking stations, the orbit and clock parameters of GPS and LEO satellites can be estimated by a simultaneous least squares adjustment, called the combined precise orbit determination (CPOD) method. We select GPS data from three LEOs (GRACE, HY2A and Jason-2) and 150 terrestrial stations over half-month period to investigate the improved performance for GPS orbits when LEO GPS data are included in the process of POD. With the inclusion of LEO GPS data, the improved levels of GPS orbits are analyzed for different types of LEOs and different station networks. First the effect of LEO satellite with different orbital altitude and inclination on GPS orbits is analyzed under three ground station networks. Results show that the improved differences among different LEOs can achieve at millimeter and centimeter level for global and regional station networks, respectively. Then comparative experiments of POD with/without three LEOs are designed for global well-distributed (GW), global regional (GR), Asian-overseas regional (AOR) and Asian regional (AR) station networks, including fourteen station networks. The orbit accuracy of both GPS and LEO satellites and the improved level for GPS orbits are summarized. With the inclusion of three LEOs, contributions from LEO GPS data are comparative in GW and GR cases (more than 30 stations), 3D RMS for GPS orbits improving at mm level w.r.t. corresponding ground-only POD. With 20 stations, the improved levels are 4, 11 and 31 mm in the case of GW, AOR and AR, respectively; with 10 stations, the corresponding improved levels are 16, 24 and 87 mm. The improvements in GW and AOR cases are insignificant, within 3 cm level. In the AR case, the improved level can achieve at decimeter level, while the orbit accuracy with the inclusion of three LEOs is comparative to the inclusion of 5 ground stations evenly distributed in a non-regional area (i.e. AOR case). This study is helpful for deriving the final post-products or broadcast ephemerids for GNSS satellites when considering joining LEO data into the process of orbit determination.