Absolute Sea-level Monitoring and Altimeter Calibration Facility at Gavdos, Crete, Greece

We introduce the recently instrumented mean sea level (MSL) monitoring facility on western Crete and the isle of Gavdos. We will focus on the altimeter calibration aspect of the facility, in particular, its application to the JASON mission. The Eastern Mediterranean area is one of great interest for its intense tectonic activity as well as for its regional oceanography. Recent observations have convincingly demonstrated the importance of that area for the regional meteorological and climatologic changes. Tide-gauge monitoring with continuous GPS has gained importance lately since tectonics contaminate the inferred sea level variations, and a global network of tide-gauges with long historical records can be used as satellite altimeter calibration sites (e.g. TOPEX/POSEIDON, GFO, JASON-1, ENVISAT, etc.). This is at present a common IOC-GLOSS-IGS effort, already underway (TIGA), and our facility is part of it. Crete hosts two of the oldest tide-gauges in the regional network and our project will further expand it to the south with a new site on the isle of Gavdos, the southernmost European parcel of land. One component of our "GAVDOS" project is the repeated occupation of two already in existence tide-gauge sites at Souda Bay and Heraklion, and their tie to the new facility. We show here initial results from positioning of these sites and some of the available tidal records. Gavdos is situated under a ground-track crossing point of the original T/P and present JASON-1 orbits. It is an ideal calibration site if the tectonic motions are monitored precisely and continuously. The facility hosts in addition to the tide gauges: GPS and DORIS beacons for positioning, transponders for direct calibration, water vapor radiometers and solar spectrometers, GPS-loaded buoys, airborne surveys with gravimeters and laser profiling lidars, transportable laser ranging systems, etc., to ensure the best possible and most reliable results.