DYNAMIC ORBIT DETERMINATION USING GPS MEASUREMENTS FROM TOPEX POSEIDON

The GPS data acquired by the TOPEX/POSEIDON (T/P) Demonstration Receiv er (DR) have been used in a dynamic orbit determination, which was bas ed on the description of the gravitational and nongravitational forces in the equations of motion. The GPS carrier phase data were processed in a double difference mode to remove clock errors, including the eff ects of Selective Availability. Simultaneous estimation of the T/P orb it and GPS orbits was performed using five 10-day cycles in the interv al between December (1992) and April (1993). The resulting T/P orbits have been compared with the orbits determined from Satellite Laser Ran ging, the French one-way Doppler tracking system, DORIS, and with the JPL reduced dynamic orbits obtained from the GPS/DR data. Using simila r dynamic orbit determination strategies and force models with the GPS /DR to those used with SLR/DORIS, the radial component of the T/P orbi t (based on JGM-2) was found to agree to better than 30 mm (rms) and 3 5 mm with the JPL reduced dynamic orbit. An experimental gravity tunin g was accomplished using four cycles of GPS/DR data. The resulting GPS /DR-orbits, determined by the dynamic technique with the experimental gravity field, are in better agreement with the JPL reduced dynamic or bits in both the radial component (21-25 mm) and altimeter crossover r esiduals than the JGM-2 orbits.