| 26 Aug 2025
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.
General comments
The manuscript proposed by Nilsson et al. aims providing a new Mean Sea Surface from satellite altimetry including features from recent observations of the wide-swath altimeter SWOT. Depending considered wavelengths, the use of SWOT altimetry allows improving Mean Sea Surface at intermediate and short wavelengths including coastal regions.
The manuscript is detailed, clearly explained and all limitations of the product are explicitly discussed. Even if the product will most probably evolve with improvements in SWOT processing and the increasing length of observed time series, the provided dataset is an important step in the Mean Sea Surface estimation.
Specific comments
Figures are particularly well designed. However, following ESSD publishing recommendations, it would be important to double check with provided tools to improve the accessibility of colour figures (https://www.earth-system-science-data.net/submission.html#figurestables) mainly for uncertainties.
Minor and technical corrections
Figure 4
As for figures 2 and 3, it would improve the readability to see the location where are show the coastal comparisons.
Figure 8
The chosen colormaps are not perceptually uniform. It could make sense for MSS to track large features but I would suggest to use a perceptually uniform colomap for uncertainties.
Figure 14
Please revise the figure caption to improve readability as several a,b,c appears on the figures and are not described in the caption.
p.6 / l. 127 – please replace “The parameters is” by “The parameter is”
p.14 / l. 276 – please corrct “latitudional” by “latitudinal” or “meridional”