SWOT-Derived Geometric Marine Geoid Surface complements Gravimetric Geoid Modelling approaches

This research investigates the synergy of utilizing sea surface height (SSH) measurements from the non-dedicated Surface Water and Ocean Topography (SWOT) altimetry mission in conjunction with hydrodynamic models and in-situ measurements. The SSH and geoid are linked through dynamic topography (DT), which can be obtained from hydrodynamic models. The method considers satellite altimetry and modelled data to be reasonably accurate so that the static geometric marine geoid surface can be derived (i.e., geoid = SSH - DT). The application of this method not only enhances existing geometric geoid models but also has the potential to assist in deriving new ones in regions where current geoid models are inaccurate and of lower quality due to gravity data deficiencies. The proposed method is tested in the Baltic Sea, where accurate geoid models are available, as well as in areas near and inside the Russian sea border, where the lack of in-situ gravity measurements causes inaccuracies in gravimetric geoid modelling.A critical aspect of the proposed approach is in the validation phase, where the SWOT-derived geoidal heights are compared with (i) marine geoid models of the Baltic Sea (e.g., NKG2015, BSCD2000), (ii) geoidal heights obtained from precise airborne laser scanning, and (iii) shipborne GNSS measurements.The results demonstrate that by utilizing KaRIn data (L2_LR_SSH, Basic, 2×2 km grid), it is possible to identify and quantify errors in areas lacking gravity data, revealing discrepancies of a few decimeters in existing geoid models. In summary, SWOT-derived geometric geoid has the potential to compete with existing Baltic Sea marine geoid models that have an accuracy of around 3 cm. The results indicate that KaRIn altimeter data can help determine the marine geoid surface with sufficient accuracy of 5 cm or even better. The methodology explored with the synergy of datasets paves the way for novel opportunities for geometric geoid determination for other sea areas globally. This is especially useful for maritime activities, climate research, and navigation opportunities.