Precise orbit computations of LAGEOS for WEGENER-MEDLAS

The WEGENER-MEDLAS project was conceived to investigate crustal motions in the Eastern Mediterranean using highly accurate laser tracking of the LAGEOS satellite. The tracking data are processed to produce accurate point positions of the laser tracking systems. By repeating these position determinations at regular time intervals, changes in the relative positions may be observed, providing quantitative data on the crustal motions which are expected to be of the order of 1 – 5 cm/year. Initial tracking started in January 1986. This paper discusses some of the data analysis techniques applied by the Section Orbital Mechanics of Delft University of Technology. These techniques are based on one-week data arcs and on a data arc with a length of one year, and involve the accurate modeling of the trajectory of LAGEOS. The effects of various perturbations on the motion of this satellite are discussed including the earth's gravity field, solar radiation pressure and third-body perturbations. Recent improvements in the modeling of some of these effects are highlighted and results are given for the evolution of some parameters recovered from one-week data arcs. To demonstrate the overall accuracy of the orbit modeling for one-week data periods, some examples of the results obtained for the relative motions between various global stations are presented. They are compared with results derived from independent geophysical data.