At present, the determination of ZTD at GNSS stations
makes use of well-established methodologies. At the University
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 levels
of variability of the tropospheric delay and oceanic conditions
(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 correction
for coastal altimetry.