  Altimetry data of two and a half years (June 2016-November 2018) of Sentinel
3A SRAL were validated at the sampling frequency of 80 Hz. The study areas are
three coastal sites in Spain: Huelva (HU) (Gulf of Cadiz), Barcelona (BA), and
Bilbao (BI). Two tracks were selected in each site: one ascending and one
descending. Data were validated using in situ tide gauge (TG) data provided by
the Spanish Puertos del Estado. In the 5 to 20 km segment, the results were 6-8
cm (rmse) and 0.7-0.8 (r) for all the tracks. The 0 to 5 km segment was also
analyzed in detail to study the land effect on the altimetry data quality. The
results showed that the track orientation, the angle of intersection with the
coast, and the land topography concur to determine the nearest distance to the
coast at which the data retain a similar level of accuracy than in the 5 to 20
km segment. This distance of good quality to shore reaches a minimum of 3 km
for the tracks at HU and the descending track at BA.
