Absolute positioning using Doris tracking of the SPOT‐2 satellite

The French DORIS doppler satellite tracking/positioning system has been operational on the SPOT-2 satellite since 1990. We have analyzed 80 days of data from 42 ground beacons and determined three dimensional site coordinates which agree with a set of SLR/VLBI positions at the 20–30 millimeter level in each coordinate after removal of common rotations, translations, and a scale difference. The accuracy of the vertical component is comparable to that of the horizontal components, indicating that residual troposphere error is not a limiting factor. The translation parameters indicate that the DORIS network realizes a geocentric frame to about 50 mm in each component. The considerable amount of data provided by the nearly global, all-weather DORIS network allowed this complex parameterization required to reduce the unmodelled forces acting on the low Earth satellite. The positioning results obtained from tracking using essentially the same ground network and the higher altitude TOPEX/POSEIDON spacecraft should be superior to those obtained for SPOT-2.