Altimeter Calibration Campaigns at Ibiza Island and Cape of Begur (Spain)
Juan Jose Martinez-Benjamin(1) , Marina Martinez-Garcia(2) , Miquel Angel Ortiz Castellon(3) , Gema Rodriguez Velasco(4) , Jose Martin Davila(5) , Jorge Garate Pasquin(5) , Pascal Bonnefond(6) , Yves Menard(7) , Begoña Perez(8) , and Cristina Garcia Silva(5)
Technical University of Catalonia,
Campus Nord B5,
(2) INAVE, Paseo Santa Madrona, 08034 Barcelona, Spain
(3) Cartographic Institute of Catalonia, Parc montjuic, 08038 Barcelona, Spain
(4) Universidad Complutense de Madrid, Facultad de Ciencias Matematicas, 28040 Madrid, Spain
(5) Real Instituto y Observatorio de la Armada, Cecilio Pujazon s/n, 11110 San Fernando (Cadiz9, Spain
(6) OCA/GEMINI, Av. Nicolas Copernic, 06130 Grasse, France
(7) CNES/LEGOS, Av. Edouard Belin 14, 31400 Toulouse, France
(8) Puertos del Estado, Av. Partenon 10, 28042 Madrid, Spain
Topex Side-B altimeter experiences have been developed at the Cape of Begur area in 1999, 2000 and for Jason-1 in 2002 using wave rider GPS buoys. M-GDR products (in 1999 and 2000) and I-GDR products (in 2002) have been used for the comparison between the GPS derived sea surface (computed from the buoys) and the respective altimeter measurements. The kinematic solution (differential kinematic positioning) for the buoy placed underneath the satellite ground track (187) has used precise GPS orbits and the estimates of the wet zenith tropospheric delay computed at a fiducial GPS station placed in the coast. Results of the point calibrations are in agreement with the official values obtained in single point experiments with buoys, which range several centimeters . For the Topex Side-B single calibration, the range bias was estimated in +6.5 cm with 32.1 cm of rms and + 3.7 cm with 32.6 cm of rms in 1999 (Selective availability still on) and in +3.43 cm with 7.9 cm of rms in 2000, and for Jason-1 in +10.52 cm with 10.52 cm with 10.35 cm of rms in 2002.
L’Estartit float tide gauge has been used in all three campaigns. Description of the long-term time series of sea level records and of the actual activities related to the installation of a high-quality geodetic GPS and a new radar tide gauge at l’Estartit location to become a CGPS Reference Station will be presented.
A Spanish campaign, with French support, (including the IBIZA2003 Team) was conducted on June 10-16, 2003. The main objective has been to map with a new designed, builded and calibrated GPS catamaran, the local marine geoid gradient in three areas around Ibiza island under the ascending (187) and descending (248) Jason-1ground tracks in order to allow a better extrapolation of the open-ocean altimetric data to on-shore tide gauge locations.
Five GPS reference stations were deployed on Ibiza island and two tide gauges at Ibiza (ESEAS) and San Antonio harbours were used. The geodetic activities (e.g., GPS, levelling) have permitted to build a very accurate (few mm) local network linked to the European one, with a reference frame compatible with ITRF2000.
It is presented the first results on Jason-1 altimeter calibration using the marine geoid derived from the data collected during the Ibiza 2003 campaign. The Jason-1 altimeter bias was estimated to be 120 ± 5 mm They agree relatively well with results obtained at Corsica, Harvest and Bass Strait calibration permanent sites. The main objective has been to test the value of Ibiza island as a permanent calibration site in the Mediterranean Sea complementary to the Corsica site. It is expected in the new campaigns to include ENVISAT ground tracks
These campaigns have been supported by the Spanish Government as Space Research R+D+I projects, CICYT ref: ESP97-1816-CO4-03 and ESP2001-4534-PE.