Examining the capabilities of SWOT to derive the tidal characteristics in the North Sea
Summary
The Surface Water and Ocean Topography (SWOT) satellite provides a promising new method to measure the global sea surface height (SSH). With the use of radar interferometry, it is possible to improve the spatial resolution by an order of magnitude compared to previous missions using radar altimetry. This development can help with the understanding of mesoscale and submesoscale oceanic processes. Additionally, tidal reconstruction based on observations in challenging environments, such as high latitude and coastal areas, can benefit. However, the accuracy of SWOT in challenging environments, such as the Dutch coastal zone has not yet been fully tested. Using in-situ measurements of tidal gauge stations of Rijkswaterstaat (RWS), the SSH measurements of the SWOT_L2_LR_SSH_EXPERT_2.0 dataset are validated. Here it is shown that the correlation between SWOT and tidal gauge data is good (R2 = 0.88, RMSE = 0.22m). However, the quality of the SWOT measurements decreases towards the coast (6.3% ‘good quality’ data points, compared to 48% further from the coast). In the Wadden Sea the correlation decreases to 0.79, with a RMSE of 0.34m and only 0.79% ‘good quality’ datapoints. Additionally, the possibility of using SWOT data to reconstruct the tidal signal over a large area has not yet been fully explored. In this paper a new approach to reconstruct the tidal signal using a representative tidal cycle based on SWOT data has been tested successfully. The M2 tidal constituent showed a good fit (high SNR). However, the M4 tidal constituent was less accurate, likely because the amplitude (0-0.3m) is in the same range as the error in SSH measurements. Although it lacks in the possibility to resolve low resolution tidal constituents, it is able to fit the dominant semidiurnal tidal component in the North Sea. The demonstrated approach can be useful for further studies that want to reconstruct the tidal signal with limited temporal data availability.