LOCAL GEODESY BY SATELLITE LASER RANGING - A EUROPEAN SOLUTION

Errors in the modelling the satellite orbit have so far limited the ac curacy in the processing of Satellite Laser Ranging (SLR) data. ii new method is proposed to achieve a residual size consistent with the obs ervational errors, and a stability of the geodetic network coordinates at the same level. The orbit of the geodetic satellite LAGEOS is deco mposed into very short arcs (less than half orbital period); if an are is observed by at least 3 SLR stations, its initial conditions can be determined. By combining hundreds of arcs, the position of the observ ing stations, forming a local geodetic network, can be solved for. Oth er new features of the algorithm are: formation of normal points and r ejection of outliers totally independent from the orbit model; use of a body fixed reference frame; processing only of the data from the sta tions to be solved for. As a test, solutions are computed for European networks of 5-6 stations using ly of data. These solutions are proven to be robust with respect to dynamical modelling errors and truncatio ns, and the residuals for the normal points are 1-2 cm for third gener ation stations. The accuracy (as opposed to formal precision) of the s olved for local network is tested by comparing two solutions using dis joint data sets; the ly European network solutions are stable to 1 cm rms in station coordinates, 1.5 cm rms in baseline lengths. The main l imitation to the accuracy comes from systematic errors in the observat ion process, e.g. in the calibration of the SLR stations; even better accuracies could be achieved if enough data of the best quality were a vailable. The new method is used, with 7 y of LAGEOS data, to compute a local solution for 6 fixed European stations, including positions/ba selines and station velocities/baseline rates. The results are consist ent with zero relative motion for all stations in the local network, i ncluding Matera; the accuracy, as estimated by the disjoint data sets method, is 3.5 mm/y for the baseline rates. Matera is more likely to b e on the European plate, but a few more years of data are needed to ac hieve a high confidence level on this statement.