Three preliminary campaigns for TOPEX/POSEIDON (T/P) were made in March 1999 and July 2000 and for JASON-1 in August 2002, in the NW Mediterranean Sea at the Begur Cape area. Direct absolute altimeter calibration, and mapping of the sea surface, were made in these campaigns from direct overflights using GPS buoys with a toroidal design performed at the ICC based in the original design of the University of Colorado at Boulder and a estimation of the TOPEX Alt-B bias was made. A Spanish JASON-1 geoid gradient campaign with Fench support has been made in June 2003 at the Ibiza island in the NW Mediterranean Sea. The main objective has been to map with a new designed, builded and calibrated GPS catamaran, the local geoid gradient in three areas around Ibiza island under the ascending (187) and descending (248) Jason-1ground tracks. The catamaran equipped with two GPS antennas to perform continuous sea level measurements was towed by the Patrol Deva from the Spanish Navy. Five GPS reference stations were deployed on Ibiza island: one in Portinatx, two in San Antonio and two in Ibiza. The marine geoid has been used to relate the coastal tide gauge data from Ibiza and San Antonio harbours to offshore altimetric data. In the framework of the campaign, the levelling of the Ibiza and San Antonio tide gauges to the respective GPS markers was performed. We present synthesis of the results obtained from Topex/Poseidon and the first results on Jason-1 altimeter calibration using the direct measurements from GPS buoys and the derived marine geoid. The Ibiza results agree relatively well with results obtained at Corsica, Harvest and Bass Strait calibration permanent sites. Moreover, the geodetic activities (e.g., GPS, levelling) has permitted to build a very accurate (few mm) local network linked to the European one, with a reference frame compatible with the satellite altimetry missions (ITRF2000). The GPS kinematic data were processed using two different softwares allowing to check the consistency of the solutions. A perspective of a new Jason-1, including Envisat, Ibiza campaign to be made around 2007 will be presented. These campaigns were supporte by the Spanish Ministery of Science and Technology under projects of the National Space Program ref: ESP1997-1816-CO4- 03 and ESP2001-4534-PE.
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