GGSP - Realisation and Maintenance of the Galileo Terrestrial Reference Frame
Gendt, G.¹; Soehne, W.²; Rothacher, M.^1
1GeoForschungsZentrum Potsdam; ²Bundesamt fuer Kartographie und Geodaesie

The realization and maintenance of a highly precise and stable Galileo Terrestrial Reference Frame (GTRF), the basis for all Galileo products and services, is the main function of the Galileo Geodetic Service Provider (GGSP). The GGSP is serving both the Galileo Core System as well as the Galileo User Segment. The project is funded by the European GNSS Supervisory Authority with funding from the Sixth Framework Programme of the European Community for research and technological development. Under the lead of GeoForschungsZentrum Potsdam (GFZ) a consortium of seven institutions has been established to set up a GGSP prototype and to develop a plan for the operational GGSP.

The GTRF shall be a realisation of the International Terrestrial Reference Frame (ITRF) on a position precision level of 3 cm (2 sigma). Since the GTRF will already be required by the time when the first Galileo signals are going to be emitted during the In-Orbit-Validation, an initial realisation of the GTRF has to be based on other station positioning data, notably GPS. It will be demonstrated by the GGSP Prototype that this GTRF can be maintained by including the Galileo Signal-in-Space (SIS) once Galileo reaches its operational stage.

Since the Galileo tracking stations, named Galileo Sensor Stations (GSS), will form a sparse global network, it is necessary to densify the network with additional IGS stations to get the highest possible precision and stability for the GTRF. The connection to the ITRF is realized and validated by IGS stations, which are part of the ITRF, and especially by local ties to other geodetic techniques like satellite laser ranging and VLBI.

In addition to the GTRF, the GGSP will establish a service with additional products and information, such as Earth Rotation Parameters, satellites orbits, clocks for satellites and stations, which will be offered to the Galileo user community to have most precise access to the GTRF and will be used to monitor the accuracy of the corresponding Galileo Mission Segment (GMS).

Although the schedule for Galileo has been delayed the prototype of the GGSP is going to be built up in time.

The presentation starts with an overview about the project facing the main topics and first steps. The strategy for the GTRF realisation following the 'state of the art' TRF implementation will be described. Results to be expected from the GGSP prototype and considerations for the future will be discussed.