GPS RELATIVE POSITIONING AT A PRECISION LEVEL OF ONE PART PER BILLION

Six days of data from the GIG'91 experiment have been analyzed with a fiducial strategy. The results obtained with our orbital software GEOS AT, show daily horizontal and length repeatabilities at the level of 1 part in 10(9) plus 2 mm for baseline.lengths up to 4000 km. A direct comparison with results from the GIPSY software shows, with some excep tions, mean differences at the sub-cm level. After transformation to I TRF'90 the rms of the coordinate differences is 14.8 mm. Studies of or bital predictions and comparisons with external high precision orbits indicate a mean orbit precision and accuracy of around 35 cm in each c artesian coordinate. Correlations between the GEOSAT and GIPSY solutio ns indicate some common model deficiencies.