LEO–BDS–GPS integrated precise orbit modeling using FengYun-3D, FengYun-3C onboard and ground observations

The new FengYun-3 (FY-3) meteorological satellite, FengYun-3D (FY-3D), carries an enhanced version of the GNSS Occultation Sounder (GNOS) instrument with increased BDS and GPS tracking channels. These high-quality onboard BDS observations together with FengYun-3C (FY-3C) data can serve as an effective supplement to overcome the weakness in BDS tracking geometry. To assess the scope of the low earth orbit (LEO)-induced improvements on the BDS satellite orbits, we processed the ground network and two FY-3 satellites (FY-3C and FY-3D) in a common least-squares adjustment. Three integrated precise orbit determination (POD) schemes with the individual LEO and a combination of two LEOs are designed to investigate the contribution of the new FY-3D satellite. The performance of FY-3D POD is discussed first. Due to the increase in observation redundancy, the FY-3D orbit presents smaller overlap differences than FY-3C. The corresponding precision improvement can reach 72% for the BDS-only POD, 13% for the GPS-only POD and 25% for the GPS and BDS POD. The overlap result of integrated POD indicates that FY-3D contributes a stronger enhancement to GPS and BDS orbits than FY-3C because of its noticeable increase in onboard observations. The most pronounced benefit can be observed in BDS GEO orbits, which is improved by 44% for the regional solution and 41% for the global solution compared to the FY-3C solution. As expected, a further reduction in the overlap differences can be noted when adding FY-3C to the FY-3D global solution. Compared with the FY-3D solution, the orbit precision of BDS GEO, IGSO and MEO for the 2-LEO solution is slightly improved by 3%, 3%, and 1%, respectively, which is mainly limited by the few observations contributed by FY-3C.