Objectives
The first objective of
GAVDOS is the establishment of an absolute sea level monitoring and altimeter
calibration facility on the isle of Gavdos, south of the island of Crete,
Greece. The purpose of such a permanent facility is:
- 1. To conduct comparative laser distance measurements between the
facility and satellite radar altimeters, such as TOPEX/Poseidon (T/P),
Jason-1, Envisat, etc;
- 2. To ensure the unbiased establishment of the Mean Sea Level, as
realised by the globally distributed altimeter measurements;
- 3. To monitor consistently and reliably any radar altimeter errors
by determining:
- a. The altimeter biases and drifts for these altimetry missions,
- b. The bias among different missions.
- c. To cross-calibrate different satellite altimeter missions and each one of them, on a common and long-term basis.
The second objective of GAVDOS is
to monitor deformations of the earth's surface at the tide gauges in
the area as a contribution to the European Sea-level Observing System
(EOSS) project. This objective will be achieved by:
- Monitoring horizontal and vertical land deformation at the calibration
site of Gavdos island using GPS permanent tracking stations at TUC
and at the tide gauge sites (Souda Bay, Gavdos, etc.) and elsewhere
on the island of Crete;
- Determining, independently of GPS, the local tectonics by operating
a DORIS (Doppler Orbitography by Radiopositioning Integrated on Satellite)
radio-positioning beacon;
- Providing absolute geodetic positions within the network of the International
GPS Service for Geodynamics (IGS);
- Monitoring local sea-level variations with a regional network of
tide gauges to be established at Gavdos, at Souda Bay and also with
auxiliary sensors (meteorological, oceanographic, and Sea Surface Topography)
at Gavdos site, and finally by;
- Providing reliable MSL data.
The third objective is the development
of a detailed regional geoid and Sea Surface Topography (SST) model.
These models are required for referencing the altimeter measurements
over the calibration facility and for studying the regional sea current
circulation. This objective will be achieved by:
- Carrying out a regional airborne campaigns using an appropriate aircraft
equipped with laser (for laser topography surveys), airborne gravimeter,
inertial unit, GPS, etc. (for airborne gravimetry);
- Creating the best-detailed gravimetric geoid of the region;
- Verifying radar altimeter measurements with GPS buoys receivers to
be placed under the satellite ground-tracks to provide in situ sea
surface topography data, and with the deployment of altimeter transponder(s)
measuring direct distances to the satellite with a ~5 mm precision;
- Operating an ultra mobile laser on site for precise Satellite Laser
Ranging (SLR) tracking of the over-flown satellites, after the end
of the validation period for Jason-1, (Calibration results at Gavdos
will be compared with those from the French Western Mediterranean site
at Corsica);
- Reducing radar altimeter distances to sea surface heights using spectral
algorithms, the airborne and shipborne gravity data, etc. and verifying
these models and results.
Finally, the fourth objective of
the GAVDOS project is to:
- Involve this regional array in other European and international programs
and in particular the European
Union Cluster on Operational Forecasting,
Euro-GLOSS (Global Sea Level Observing System), in the extension of
WEGENER (Working Group of European Scientists for the Establishment
of Networks for Earthquake Research) and in TIGA (International GPS
Service, GPS Tide Gauge benchmark Monitoring Pilot Project);
- And to integrate it with the global geodetic reference frame, maintained
by the International Earth Rotation Service (IERS), and the IGS activities
in this region.
