Station coordinates

The set of SLR marker coordinates used for the ERS-1 orbits are referred to as the LSC(DUT)93L05 coordinate solution [Noomen, 1993] which is based on 9.3 years of SLR observations of the LAGEOS I satellite during the period of January 1983 till December 1992. The epoch for this solution has been dated 1 January 1988. The effect of tectonic motion since that epoch has been accounted for using the solved-for station velocities incorporated in the coordinate set. These motions advance the coordinates to the epoch of the data arcs.

The a-priori coordinates of the various stations are not equally accurate, which may be caused by lack of tracking data contributing to the original solution or a higher system noise level of the laser system. As a consequence, the uncertainty of some station coordinates could affect the orbital solution negatively, and therefore these coordinates are estimated during the POD. For laser ranging sites that are not included in the LSC(DUT)93L05 coordinate set, initial coordinates will be derived either from the SSR&T LAGEOS Quick-Look analysis (if possible), or from previous ERS-1 orbit computations.