Tectonic Motion Monitoring at the Altimeter Calibration Facility on Gavdos, Crete, Greece.

The intense tectonic activity of Eastern Mediterranean is of great interest for many decades. Recently, sea-level monitoring and climate change studies generated great interest as well as for its regional oceanography. A plethora of observations has convincingly demonstrated the importance of the area for regional meteorological and climatologic changes affecting Eurasia and North Africa. GPS monitors tectonics, while tide gauges record the variations in Mean Sea Level (MSL). Continuous monitoring of tide gauge locations with GPS removes the uncertainties introduced by local tectonics, that contaminate the observed sea level variations. Such a global tide gauge network with long historical records is already used to calibrate satellite altimeters (e.g. on TOPEX/POSEIDON, GFO, JASON-1, ENVISAT, etc.), at present, a common IOC-GLOSS-IGS effort --TIGA. Crete hosts two of the oldest tide gauges in the regional network, at Souda Bay and Heraklion. A third site, state-of-the-art MSL monitoring facility in southwestern Crete was established, on the isle of Gavdos, the southernmost European parcel of land, under a joint effort of the European Union, NASA, and the Swiss Federal Government. The site at Souda Bay is only 5 km away from the continuously operating GPS site at TUC, Chania, with a nearly seven year record of operation. The Gavdos facility is an ideal altimeter calibration site if the tectonic motions are monitored precisely and continuously. This presentation focuses on this aspect of the project, the local and regional tectonic motions relative to the "stable" part of the Eurasian plate. The facility hosts in addition to two tide gauges, multiple GPS receivers, a DORIS beacon for positioning and orbit control, and a transponder for direct calibration. During 2003, the French Transportable Laser Ranging System (FTLRS) completed a co-location campaign at Chania, Crete, for improved orbit control over the site, and to ensure the best possible and most reliable results in connecting the regional sites to ITRF2000.