A comparison of the annual cycle of sea level in coastal areas from gridded satellite altimetry and tide gauges

In this work we compare the annual component of sea level variations derived from 478 worldwide-distributed tide gauges with the annual component computed from a weekly gridded multi-mission altimeter product. Gridded altimetry data products allow for spatio-temporal analyses that are not possible based on along-track altimetry data. However, a precise validation is necessary in the coastal region before the gridded data can be used. Results of the comparisons show that root-mean-square differences (RMSD) between the two datasets are ≤2 cm for 76.4% of the sites. RMSD higher than 4 cm are caused by narrow coastal currents, nearby river outflows or other local phenomena. A methodology is proposed to assess the accuracy of the seasonal component of the gridded altimeter product in regions with a low density net of tide gauges. As a case study it is shown that the Southwestern Atlantic coast is a suitable region to study the spatio-temporal variability of the annual cycle of sea level since RMSD between annual altimetry data and in-situ data are lower than 2.1 cm.