We can deduce the three-dimensional baseline vectors ref ering to the geocentric rectangular coordinate with GPS interferometry. We developed the free adjustment technique that make use of the observed three-dimensional baseline vectors in GPS network.
The free adjustment can be performed with aid of pseudo-inverse matrix N+ that is equivalent to solve the normal equation under the constraint equation Σ(ΔX_i)=o(i=1-k), where ΔX_i is the estimated correction values for the initial coordinates of GPS stations and k is the number of GPS stations. Then we can also estimate the confidence ellipsoid that indicates the errors of the coordinates at the GPS stations with the elements of variance-covariance matrix.
We apply the developed free adjustment to the results of GPS survey in the Boso Peninsula, Japan. This Boso GPS campaigns had been in operation during 25-28 October 1990 and the occupied stations were six points (Mito, Itako, Yayoi, Chiba, Chosi, Kominato). The observation scenario was divided into two sessions that are assigned asSession-1 (08:0010:00 UT) and the Session-2 (10:00-12:00 UT).
Standard deviations of the adjusted coordinates at the GPS stations range from 1.70 cm to 2.48 cm for the Boso GPS campaigns of the observation at the Session-1 in 27 October 1990, while at the Session-2 of the same day, standard deviations of the coordinates range from 8.73 cm to 10.49 cm. As compared the precision for the observation at the Session-1 with at the Session-2, it is clear that the precision for the observation at the Session-2 is inferior to the one at the Session-1. The cause of the difference of the precision mainly depends on the difference of the satellite configurations.
It is suggested that the direction of semimajor axis, the shape and the size of confidence ellipsoid are much affected by the GPS satellite configurations.