The DTU25 mean sea surface: from and for SWOT

Abstract. We introduce a new Mean Sea Surface model (MSS) that incorporates the wide-swath altimetry obtained from the Surface Water and Ocean Topography (SWOT) satellite, along with long timeseries of conventional altimetry. The DTU25MSS constrains long wavelengths (> 20 km) from a suite of conventional altimeters while utilizing almost 2 years of SWOT observations to reduce the short wavelength noise and incorporate previously unmapped geodetic features into the MSS. Parametric long wavelength corrections of the SWOT data in order to compensate for the short time-scale is presented, and the resulting MSS model is compared with contemporary MSS models as well as data from the SWOT Cal/Val orbit. The MSS is available on http://doi.org/10.11583/DTU.29412275, and includes an experimental MSS which has the reference period moved to 2023 as opposed to 2003, to compensate for sea level rise. To extend the MSS into the coastal zone, the high-resolution 250 m SWOT data is used close to the coast (< 40 km), and resolves complex features previously not included. Using an updated MSS with better resolved short wavelength signals is seen to be a large benefit for interpreting the detailed SWOT observations with reduced leakage of geodetic features into the oceanographic signals, as well as ~30 % increase in spatial resolution. Due to incorporating complex novel features in the coastal zone that have been resolved by SWOT the full effect on other more coarse observations is a potential for further studies. The SWOT data and utilization of it is only expected to be improved with time and further development of methods for utilizing this new dataset will move it closer to its full potentials.