Local Radio Telescope Ties from the Wettzell Precision Engineering Surveying Network

The Geodetic Observatory Wettzell is a fundamental station of Geodesy and a GGOS Core Site. This co-location site features all systems of the spacegeodetic techniques, i.e., three VLBI telescopes, two operational SLR telescopes, various GNSS receivers, a DORIS beacon, and a ring laser gyro for instantaneous measurement of the Earth rotation. The existence of a geodetic co-location site is justified by the need to synergistically combine the various techniques in order to derive all geodetic parameters of interest which are needed to realize the reference system. Although VLBI is the only technique capable of providing the full set of Earth orientation parameters, the determination of the geo-center (the origin of our coordinate system) is not possible at all, and SLR will be needed for this purpose. GNSS, in the end, provides easy access to the terrestrial reference frame. These synergies can only be exploited for Geodesy if precise geometric links between the reference points of the various systems are known, the so-called “local ties”. At Wettzell, these vectors are derived from a local precision engineering surveying network that is covering the entire observatory yielding a point precision around 0.2 to 0.4 mm for the majority of the points. This contribution will outline the methodology to derive the local tie vectors and to transform them into the ECEF system, present the latest results, and compare them with alternative methods like the direct local VLBI data analysis. 1. Geodetic Observatory Wettzell, Federal Agency for Cartography and Geodesy (BKG), Sackenrieder Str. 25, D-93444 Bad Kötzting, Germany 2. University of the Federal Armed Forces Munich, Faculty of Aerospace Engineering, Werner-Heisenberg-Weg 39, D-85577 Neubiberg, Germany