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Calibration/Validation of GOCE Measured Mediterranean Sea level Using Satellite Altimetry and GRACE

Juan Jose Martinez-Benjamin(1), Alexander Braun(2), C.K. Shum(3), Chung-Yen Kuo(3), Shin-Chan Han(3), Yuchan Yi(3), Y. Tony Song(4), Marina Martinez-Garcia(1) and Gema Rodriguez-Velasco(5)

(1) Technical University of Catalonia, Campus South, bldg. P, 08028 Barcelona, Spain
(2) University of Calgary, 2500 University Drive NW, Calgary, Canada
(3) The Ohio State University, 2070 Neil Avenue, 43210-1275, Columbus, United States
(4) Jet Propulsion Laboratory, 4800 Oak Grove Drive, 91109 , Pasadena, United States
(5) Complutense University of Madrid, Avda. Complutense, s/n, 28040 Madrid, Spain

Abstract

European Space Agency (ESA)’s Gravity field and steady state Ocean Circulation Explorer (GOCE) mission is planned to launch in 2007 for a 20- month time period to primarily measure the Earth’s mean gravity field. In a sun-synchronous orbit and at an altitude of 250 km, the GOCE onboard space gravity gradiometer (SGG) will measure primarily 4 components (3 diagonals and 1 off-diagonal) of the gravity gradient tensor field of the Earth. One of GOCE’s primary high-level data products is the global gravity model with an anticipated geoid accuracy of 1 cm RMS and a spatial resolution of 130 km or longer. The Mediterranean Sea is a semi-enclosed ‘true’ ocean. Recent Mediterranean circulation and sea level studies using various observations (multi-mission altimetry, tide gauge, thermosteric sea level from WOA01, and to a lesser extent, GRACE) and ocean circulation models (e.g., JPL's ECCO and non-Boussinesq models) show good coherence and agreement. The satellite altimetry and tide gauge observed and model predicted sea level show good coherent with correlation coefficient of 0.6. The barotropic pressure response accounts for about 66% of the Mediterranean sea level rise (1948–2001). The estimated sea level trend (1.54±0.75 mm/yr) using decadal altimetry (1985–2001) after correcting the interannual/decadal signals reconstructed using tide gauge data, agrees well with the long term trend (1948–2001) estimated using tide gauges (1.43±0.09 mm/yr) in the Mediterranean Sea, and is in better agreement than before with the global long-term sea level trend (1.7–1.8 mm/yr). Finally, multiple altimetry sea level measurements are being calibrated in dedicated campaigns to quantify the error characteristics. This study makes use of all of the above knowledge in a simulation study to show that the GOCE data (gravity gradient tensors) and data product (GOCE geoid in the Mediterranean), after correcting for temporal variability (e.g., from GRACE to potentially account for hydrologic fluxes), could be validated in the Mediterranean Sea.

 

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry