PRECISE ERS-1 ORBIT CALCULATION

This analysis was performed with the GEOSAT software developed at NDRE for high-precision analysis of satellite tracking and VLBI data for geodetic and geodynamic applications. For applications to ERS-1, a realistic surface force model is used together with the Jacchia 77 atmospheric model, semi-daily drag coefficients, a l-cpr sinusoidal along-track acceleration, and the GSFC JGM-2 gravity model. ERS-1 orbits have been derived for 5.5-day arcs of laser tracking data between July 6 and August 12, 1992. Results from overlapping orbits and comparison with precise D-PAF orbits indicate an orbital accuracy of 10-15 cm in the radial direction, similar to 60 cm in the along-track direction and similar to 15 cm in the cross-track direction.