CoAuthors

Tilo Schöne (GFZ, Helmholtz-Centre Potsdam, Germany); Julia Illigner (GFZ, Helmholtz-Centre Potsdam, Germany); Robert Weiß (BfG, The German Federal Institute of Hydrology, Germany)

The precision of the total water level envelope (TWLE) from Jason-3 and Sentinel-3A is assessed at six tide gauge stations in the German Bight (SE North Sea) for the period 2016 to 2019 based on RMS errors and correlation coefficients. The comparison is done based on TWLE instead of sea surface heights since the tidal and barotropic dynamic is not known with sufficient accuracy in this area. The tide gauges are partly located at the open sea, partly at the coast close to mudflats. The tide gauge data is available every minute and is referenced by GPS. The 20 Hz level 2 altimetry data is interpolated to virtual stations at distances between 2 and 13 km to the tide gauges. The analysis is based on standard retrackers, the correction models are adjusted to coastal applications and exclude the corrections for ocean tides and dynamic atmosphere. To account for slight differences of the tidal dynamics between gauge and altimetry an optimal time shift and scale between each pair of locations is estimated and applied. This tidal correction improves the RMS errors by 15-75%. The correlation is excellent at all stations (>0.996). The resultant RMS error is 2.9-3.0 cm for Jason-3 at the open ocean and 7.4 cm very close to the coast. For Sentinel-3A the RMS errors range between 3.1-6.1 cm. There is no significant drift between Jason-3 and the investigated tide gauges. However, Sentinel-3A seems to drift relative to the tide gauges with values ranging between 6 and 13 mm/year depending on the location.