At present, the determination of ZTD at GNSS stations makes use of well-established methodologies. At the Uni-versity of Porto (U.Porto), ZTD have been calculated using the GAMIT software (Herring et al., 2006), hereafter referred as “U.Porto solutions”, for a set of 51 stations with global distribution, to cover regions with different lev-els of variability of the tropospheric delay and oceanic con-ditions (Fig. 1) covering the period from January 1, 2002 to December 31, 2009. From these stations, 46 are coastal ones, with a distance to the coast of less than 10 km, ideal for use in the computation of the wet tropospheric correc-tion for coastal altimetry.