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”

• The study has modeled a MSS in different frequency bands, including long wave (>20km), intermedium wave (4-20km), and short wave (<40 km from coasts). How to define the long wave (>20km), intermedium wave (4-20km), and short wave (<40 km from coasts) of MSS? The scale around 20km in oceanography should be sub-mesoscale.
• Multiple sources of satellite altimeter data were used in the manuscript. Detailed information on all satellite altimetry data used should be provided. How to unify the spatiotemporal datum of different altimetry data?
• Is the MSS model constructed using 20 years of satellite altimeter data?
• The MSS in Eq. (1) corresponds to t0. But t0 is 2003, why? t0 should be the middle time of the data period.
• There are a large number of data gaps in the SWOT/KaRin altimetry data for one cycle. How to handle these data gaps?
• The signal-to-noise ratio of the 250m SWOT/KaRin altimetry data is very low. How to improve the quality of these data?
• The SWOT/KaRin altimetry data has a relatively short time. What corrections have been made to the short-term SWOT/KaRin altimeter data in order to obtain data that is consistent with the observation time required for MSS modeling?
• How to determine the weights in Eq. (13)?
• Why is the PSD of DTM25 the smallest in the high-frequency part in Figure 7 (c)?
• How are the data gaps handled in Figure 8?
• What corrections are made to Sentinel-3 altimeterry data in Table 1? How to define short wavelength?
• Why is the PSD of DTM25 the smallest in the high-frequency part in Figure 15?