The Gavdos and Crete Cal/Val Permanent Facility for Altimetry Calibration has been operating and providing absolute biases for altimetry satellites for more than a decade. It was established in 2001 and has been on continuous operation as of 2004. It provides calibration/validation (Cal/Val) for all international altimetric missions (i.e., Sentinel-3, Sentinel-6, Jason series, HY-2, SARAL/AltiKa, CryoSat-2, etc.). It includes a major set of permanent facilities, prototype scientific equipment (transponder), while at the same time it collects archives, analyses, interprets and disseminates scientific data internationally. It has thus established an international reputation, and standing underpinned by consistency, accuracy and reliability in calibration results.

It is capable of calibrating ascending and descending orbits of the same altimeters in the open ocean around Crete. Ocean tides at this location are very small (a few cm), however the ocean circulation, and the reference models are well established.

The Gavdos and RDK1 Cal/Val facilities are to be used for sea-surface calibration of Sentinel-3A & -3B but also Jason satellites. Under the framework of the SeRAC project, a new sea-surface Cal/Val site called "SUG1", at the south west Crete has been established. This SUG1 Cal/Val site will calibrate S3A, S3B and Jason series satellites using the established sea-surface methodology.

At least two tide gauges, one GNSS and one meteorological station shall be continuously operating at each sea-surface Cal/Val site.