Altimetric signal and three-dimensional structure of the sea in the Channel of Sicily

The 1996 Altimeter/Synoptic Mesoscale Plancton Experiment (ALT/SYMPLEX) was specifically designed to perform in situ measurements simultaneous with th e passage of TOPEX/POSEIDON (TIP) and ERS 2 over selected tracks in the cen tral and eastern Sicily Channel. This experiment made it possible to have, for the first time, a validation of altimetry with in situ data over the Me diterranean, where weak dynamics results in a modest sea elevation, rarefy exceeding 10 cm. Historical infrared and altimetric satellite data were fir st analyzed in order to study the variability of the circulation in the are a. The comparative and integrative analysis of simultaneous satellite data and in situ measurements permitted investigation of the relation between th e altimeter-derived surface topography and the three-dimensional structure of the sea. The Pearson correlation coefficients between altimeter data and dynamic heights along track resulted to be 0.72-0.89 (T/P) and 0.88 (ERS 2 ) when using conventional repeat track analysis. For TIP, a correlation val ue of 0.87 was found for time differences computed basing on a collinear an alysis technique. This analysis also led to the identification of a strong barotropic component of the velocity field located near the Sicilian contin ental shelf, where it is responsible for approximately 60% of the signal.