GIOVE-A Precise Orbit Determination from Microwave and SLR Data - First Perspectives for the Scientific Use of Galileo
Schoenemann, E.¹; Dow, J.²; Springer, T.²; Otten, M.²; Becker, M.^1
1Institute of Physical Geodesy, Technische Universitaet Darmstadt; ²Navigation Support Office, European Space Operations Center

Since November 2006 the Galileo Experimental Sensor Station network provides microwave tracking data of the GIOVE-A satellite. In parallel SLR tracking data of GIOVE-A, provided by the International Laser Ranging Service (ILRS) network, are available.

Both observation types are analysed in detail focussing on a couple of main issues. One of our prime interests is to investigate how accurate we can determine the GIOVE-A orbit. Secondly, the amount and the stability of different possible observation biases like the receiver dependent bias between the GPS and GIOVE-A observations and biases between the different GIOVE-A observation types are analysed. Furthermore, the analysis of the microwave residuals are used to identify potential antenna phase centre variations of the GIOVE-A transmitter antenna, one of the (large?) unknowns in the GIOVE-A data processing. Finally the analyses of the code multipath behaviour for the different codes can give us a first hint of their performance and the accuracy level in comparison to GPS.

The results of different types of arc lengths and intra- as well as inter-technique residuals are shown. Radial and 3D residuals are used for an assessment of both internal and external orbit accuracy.

Although long time series are required for an identification of weaknesses in the orbit modelling, e.g., from residual radiation pressure model errors, the independent validation of microwave and SLR data may give first indications of range biases and other systematic effects. A further important point is the assessment of the orbit and clock prediction performance.

This analysis of the available GIOVE data is important because it allows for a preliminary assessment of the future contribution of the Galileo constellation to the improvement of the terrestrial reference frame and related aspects.