Precise Orbit Determination of GPS Satellites using Carrier Phase Measurements Tomoji Takasu*, Shoji Kasai**

We have developed a software package to determine high precision GPS satellite orbit and clock, using undifferenced carrier phase measurements at ground stations. In the software, the GPS satellite orbit and clock are estimated by Extended Kalman Filter (EKF). This paper introduces algorithms for the precise determination GPS satellite and clock, including measurement models, precise correction models, satellite orbit models, and the parameter estimation filter. For evaluation, using world-wide 40 IGS (International GPS Service) station observation data, 29 GPS satellite orbits and clocks were determined. A priori satellite position and clock bias were obtained from broadcast ephemerides. Station positions were fixed to the previous week PPP (Precise Point Positioning) results. Compared with IGS Final Orbit and Clock, the estimated satellite position 3D RMS error was 5.2 cm and clock bias RMS error was 0.14 nsec